texts: Short circuit protecting a class AB amplifier

texts:
I am designing a little class AB amplifier for a small circuit. This circuit is biased such that it has low crossover distortion. Below is a schematic:

As you can see, I have inserted 68 ohm resistors in series with the power supply lines.  This is such that when the output is shorted, the current is limited to about +/-200mA. In this demo, I have inserted such a short; a 10m resistor. However, in operation the resistors dissipate 1.5W each and in short circuit conditions about 2.5W, which means I have to use two big and expensive 5W resistors to remain within safe operating boundaries, and it also might cause problems for the power supply.

So I'm looking for some way to limit output current to about +/-100mA before the amplifier begins clipping (which the current solution manages), but without the "hack" of using resistors on the power supply lines. I was considering a comparator measuring the output current across a shunt resistor, but I wasn't sure how to achieve this for short circuits of both polarities. Also, I need the circuit to ideally work up to around 5 MHz, which limits the choice of components.

Edit: Thanks to russ_hensel and opencircuits.com, I devised the following current limiter (including amplifier), which actually works really well (it clips the output and doesn't make it sag or invert, like some limiting circuits.)


texts: Is "process" statement concurrent or sequential in nature?

texts:
So i have looked around this exchange and other places too, but it has only increased the confusion..:(
Below are two links out of many which contribute to the confusion:
1.) csee.umbc-states that process is a concurrent stmt
2.)states process stmt as a sequential stmt
I am super confused as to how this could be reconciled.....
One theory i have is that VHDL is inherently concurrent and that process could be a way to make stmts sequential but they themselves are executed concurrently, but i don't get how two University guides could say entirely contradictory things...


texts: If a PEC surface completely reflects an EM wave, why doesn't an ungrounded shield work?

texts:
I was thinking about shielding and its effectiveness.
An ungrounded shield doesn't work well for either inductive or capacitive coupling.

However, if you think about plane wave theory, a PEC surface completely reflects the EM wave (reflection coefficient is -1), so you don't have any power density at the other side of the PEC surface. That seems to be the ideal shield for any EM wave/interference. This should lead to the conclusion that if I wrap around a cable with a PEC shield, no EM waves will be able to either go out or into the shield, be it grounded or ungrounded. Therefore, it should be immune to any interference or coupling.

But it seems not to be the case, why?

I suppose it has to do with the fact that coupling is a near field phenomenon, while plane wave theory usually considers the far field. But how exactly it is different, that I don't know.


texts:
I have a Serial-ATA Controller design working on almost any kind of Xilinx 7-series devices, except for the Artix-7 device, which gives me headaches...

The pure design (SATA 6.0Gb/s, 150 MHz design clock) can be implemented on my Artix-7 200T. If I add ILA cores (formerly known as ChipScope), the timing is not met.

What did I do the relax the situation:
- added 2 pipeline stages in each ILA core
- added 1 pipeline stage between GTP transceiver and the logic
- used retiming, remap and wide placement as alternative implementation strategy

This images show the normal design flow. The ILA cores are far away from the SATAController (SATAC) and the 8-bit CPU (SoFPGA), but the controller still has failing paths (that's the only region with failing paths).

It feels like the Artix-7 is out of routing resources in some areas. How can I get a report indicating such a suspicion?

I also tried retiming, remap and wider placement strategies. The result is this:

The timing failure is almost the same...

P.S. The design uses only 178 of >300 BlockRAMs. I used Xilinx ISE to use almost every BlockRAM in other designs, but I never encountered such a behavior.

Edit:

Here is a heat map of all negative slack values per Slice (colored in red)


texts:
For a darlington configuration: $$h_{ie}=1k,h_{fe}=\beta=50,h_{oe}=25 \times 10^{-6},h_{re}=0 \quad for \quad both \quad transistors,R_L=3k.$$  how can we find the current and voltage gain?
My Approach:

simulate this circuit – Schematic created using CircuitLab
$$Current \quad Gain= I_{R_L}/I_{b1} \quad and \quad Voltage \quad gain = V_{R_L}/V_{input}  $$
now how will i proceed....any hints or suggestions please...?
UPDATE:
What will be \$A_I \$ and \$ A_V \$ if there is a resistor \$ R_{C2} =1k \Omega \$ between \$ V_{CC} \$ and \$ v_o\$?

simulate this circuit


texts: Is it safe to use "uninsulated crimp" crimpers on insulated crimps?

texts: Besides needing a bigger size, will it work to use crimpers meant for uninsulated crimps on insulated? Will it crack the insulation or cause other significant problems?


texts: Do Cable Connectors/Terminal Blocks impact power requirements?

texts:
I am planning on using a bunch of spare ego-T parts to build some mods and was thinking of hooking some AA battery block via some Cable Connectors/Terminal Blocks to an LED, Button and 510 Threaded head.

I know that the 510 will be taking a 1.8 Ohm cartomizer and needs to run at roughly 3.7 volts and just less than 2Amps at the head and I want to be sitting pretty at arround 6 to 8 watts in the cart. Will I be adding any significant resistance that I need to take into account by using Cable Connector Blocks?

I plan to use the blocks just because I can make and remake my set up until I have something I am happy with and also because I really do suck at soldering.


texts:
TLDR: Please share your experience on how much shading can affect electric current produced by a solar panel.
I got some time to spend with my parents, due to this Corona situation. So, I went to our farm house and setup a solar panel system there. I used 380Wp Mono crystalline PERC panels and the voltage, current I am getting from each one of those panels are satisfactory. Now, I moved back to my place in a city and I live on 13th floor of an old 20 storey apartment. I decided to setup some solar panels for myself too.
I used the same panels that I used in the farm house. The difference is, since its an apartment, I dont have access to roof top. I can put my solar panels outside the window over the ledge, which I did. There is a grill outside the window which casts a shadow. I believe that may be the reason for which I am not getting a decent current output. Can you please take a look at the picture and let me know how much of an impediment is that shadow, from your experience?
This is a 380Wp Mono PERC panel. I have observed it to produce close to 330W under decent sunlight in the farm house where the array is roof top mounted, even though it is a little cloudy at this time of the year. The highest I got from the same panel in my apartment, with those grill shadows is 236W.

Update. As per my coordinates, I should be facing 90 degree to south. I was a little off. Besides, the elevation was not right. Look what I am getting once I fixed that.I got a maximum of 379W out of a panel rated for 380W under STC, hovering somewhere around 350-370W. The temperature at the time of taking the reading is 31 celsius. STC is 25 celsius. These seem to be good quality panels.


texts: Opto-coupled EIA-422 receiver (understanding suggested circuits)

texts:
I am looking at a standard for communication of marine electronics (NMEA). The standard is electrically essentially EIA-422 but it prescribes opto-coupled differential receiver pins without connection to ground.

The differential receiver must:

tolerate 15V differential voltage including reverse polarity
not draw more than 2mA at 2V differential voltage
not draw more than 3.25mA at 10V differential voltage
work at 38 400 baud

The standard suggests two circuits that "offer overvoltage, reverse voltage and power dissipation protection for the optoisolator and serve to limit current drawn from the line":

simulate this circuit – Schematic created using CircuitLab

I understand how circuit 2 is supposed to work:

R3 is limits the current
D3 offers reverse polarity protection for the optocoupler and Q4
R4 is a current sense resistor
which allows Q4 to act current limiter for the optocoupler by providing a bypass when the current through D4 exceeds a threshold

Questions:

Why would a separate current limiting for D4 be desirable? Since the total current drawn from the line must not exceed 3.24mA this seems superfluous. The optocouplers I am familiar with usually operate at 20mA.
How is circuit 1 supposed to work?

I cannot make sense of it:

D1 provides reverse polarity protection
J1 seems to limit current through the optocoupler for "correct polarity"
in reverse polarity J1 presents no resistance however. Thus R1 is required to limit current in reverse polarity
but since R1 must be fairly large for this, the current through the optocoupler for "correct polarity" becomes incredibly small. To my understanding too small to be useful: In the 10s to 100s of µA.

I am clearly missing something essential here.


texts:
We all know the Double Dabble algorithm, it works great for Binary to BCD conversion, but what about a BCD to binary algorithm or decoder? I am trying to make a calculating machine but I could not come up or find algorithms for BCD to binary conversion, I need one as soon as possible. Help is very appreciated.

Edit: I am sorry, I did not do a very good job at specifying the details of this question. I will keep this in mind the next time I ask. Thank you all for your answers :)!


texts: Is it important to consider GBP of transimpedance amplifier while choosing feedback resistor?

texts: I have designed a circuit which uses AD8630 transimpadance amplifier to amplify incoming current to voltage. The GBP of this amplifier is 2.5 MHz and I'm thinking using 5 mega ohm or 10 mega ohm as a feedback resistor instead of 1 mega ohm so that I can further increase the amplification. Is it feasible to use 5 or 10 mega ohm resistor? will it have any consequence on the performance of the circuit. Kindly share your thoughts. I have attached the circuit below.


texts: Why does voltage not appear in the battery life calculation?

texts:
I have a PCB with a few radio modules on it. In its various states it currently uses anywhere between 100 µA and 100 mA. I can calculate how much time it spends in each of its states over a given year.

The radio modules on my PCB all have a wide acceptable input voltage range. My main processor and Bluetooth Low Energy module, for example, accepts anything from 1.8V to 3.6V. Right now I'm running it at 3.0V, using a step down DC-DC converter.

The battery is a 18650 lithium-ion (datasheet).

When fully charged, it provides about 4.3V. I'll step it down to 3.0V. The battery has a capacity of 3400 mAh.

Assuming the average current I'm drawing from it is 400 µA. My calculation for battery life is simply:

  time (h) = capacity (Ah) / current (A)

  3.4 Ah / 400 µA = about one year

Now, I know that in order to reduce my power consumption, I should run my circuit at the lowest possible voltage, so I'm considering changing my DC-DC converter and running my main processor and BLE module at 1.8V instead of 3.0V.

My question is: why isn't the voltage featured anywhere in my battery life calculation?


texts:
If a carrier (\$f_c\$) is FM modulated by a single sine wave (\$f_m\$), its spectrum is composed of frequencies at \$f_c + kf_m\$ (\$k \in \mathbb{Z}\$) whose amplitudes are weighted by \$J_n(\beta)\$, the \$k\$-order Bessel function of modulation index \$\beta\$. We could get such spectra :

Now, what would be the spectrum of the carrier if it was modulated by a more complex signal like speech or music ? What would happen in the simple example of a 2 tones modulating signal ?
Short term Fourier transform of the modulating signals would be :

Harmonic (e.g. : vowel in speech, or a violin note)
Non harmonic (e.g. : some consonants in speech, some percussive instrument)

In both case, modulating signal will have a more richer frequency content than a single sinusoid.
Will these rich spectra just repeat regularly around \$f_c\$ as in the case of a single tone modulating signal ? Why ?
If a carrier is AM modulated by complex signal like speech, we find the spectrum of modulating signal shifted around the carrier (as seen in the spectrogram below) : what would happen with FM modulation ?


texts:
I am struggling with solving this question.

The problem is that i cannot understand why the same current "i" can flow allover the circuit starting from ground to 4R resistor on V0+ wire through 4R,3R,R,2R,R,3R,4R.

Assume that it can flows, it is ideal, operating in linear region so, V2+=V2- and V1+=V2- and we get i=(V2-V1)/2R.

To find Vo, the equation is written as V0-i(4R+3R+R+2R+R+3R+4R)=0, V0=-18R*i

But i don't get the idea of why we adding last 4R resistors voltage to the equation because it is connected to ground. I think it should be as:
V0-i(4R+3R+R+2R+R+3R)=0. Can you please help me about these thoughts ?

I asked these questions because it is solved when the circuit is like this;

How can current "i" flow from v2+ to v2- also same on from v1- to v1+?

There is no voltage change between v1-,v1+ and v2+,v2- but a current flows through them.

Also, 4R resistor is connected to ground but current i is drawen. I just don't get the idea. Can someone explain ?


texts: I am using a lug crimper which has two rotating dies that come together to form a hex crimp. Design similar to the Greenlee  K05-1GL. From a long term performance and safety perspective, How important is the alignment of the two halves in such applications (apart from cosmetics)? The attached photo shows two halves of a 35 square mm crimp that are not well-aligned by default. (There is some play in the dies so if really required I can align them with my hand before crimping.)


texts:
Trying to refresh my knowledge I was design and construct a fixed unregulated power supply 12V/5A using parts that I have around. Parts are 150VA/12V toroid, an 25A rectifier bridge in
KBPC case and 20 electrolytic capacitors 1000μF/35V each.
Trying to calculate a plate  heatsink for the rectifier, I test my construction with an ohmic load (a tungsten lamp rated 55W/12V) and monitoring the rectifier case temperature

I find the temperature rise abnormal and  I cut the power around 100oC, then I remove the capacitor bank, and get temperature again

This is the graph

I can not explain the reason of this difference in temperature rise. I used another rectifier but no deference even using a 35A one.
The maximum current during charging period is calculated about 33A but it lasts just 1,8ms and with a duty cycle 0.22 the total dissipation is about 6.6W in total.
In no load condition, there is no consumption  by the capacitors.


texts: Understand this filter and biasing circuit

texts:
Hello

I don't have much experience with electronics and I am trying to understand how this circuit works and its effect on AC input signals.

My understanding so far is that the circuit acts as a high pass filter. But I am not sure of the effect of changing the resistor values (different for both resistors).

Thank you


texts: Do all PHY Ethernet chips have a hard-coded MAC address?

texts:
For example, this TI PHY chip DP83630 has two MAC addresses that can be used as destination and source MAC addresses for PHY control frames. (page 72 and 94)

Does this means all PHY chips will have the same MAC or am I missing something?


texts: RFID (RC522) scans very slowly second time

texts:
I am using raspberry pi 3a+ to get the scanned result from the RFID module. The scanning works very fast the first time when the program initiates but my program requires performing a second scan after a press of a button. I have attached a callback function with that button and the code to scan the RFID card again is written in that function but when done this way the scanning is done very slowly.
I have a total of 5 buttons thus 5 callback functions. I tried starting only one button callback to confirm if this is a CPU load issue but still it did a very slow scanning (10-15 seconds).
I am stuck with this. RFID module is perfect, pi is perfect but I guess I am missing a concept. Kindly help!


texts: What is the advantage of concatenating two nMOSFETs M1,M2 with Source of M1 connected to Gate of M2?

texts:
I am trying to understand the circuit in the figure here :

I hope I analyzed correctly its gain (for small AC signal). My small-AC-signal-circuit is attached in the bottom of this post). However, I don't understand its purpose. What is the advantage of concatenating two mosfets this way? i.e.

    Does it allow us to raise (or attenuate) the gain without effecting Rin and Rout?
    Does it allow us to reduce (or raise) VDD without effecting the resistances or currents or gain?
    Does it allow us to change the values of Rs1, Rs2?
    Also, I hope I get correct Rin and Rout. Can I say that Rin=(R1||R2) and Rout=(r_ds2||R2)?

I tried to run these scenarios in my head but I didnt manage to come with any satisfying explanation to any of the scenarios.

Thanks!


texts: Decode an infrared signal with an IR demodulator inside a microphone jack

texts:
I was looking at this tutorial about how to decode an infrared signal.
One of the posts says

  For the scoped challenged (like me), a PC microphone jack works great
  for reverse engineering IR protocol.  It even has power (5V through a
  200-ohm resister, I think) to drive the IR transistor.  To see the
  signal, use any audio recorder that lets you zoom in on the waveform
  (like Audacity).

So I am just wondering if I can plug an IR demodulator (say, this one here) into my microphone jack, record the output, and decode the signal binary from the sound waves?


texts: When is voltage level shifting needed/unneeded?

texts:
I know the question sounds simple, but I am facing an edge case here. I have a microcontroller with 3.3V on the GPIO's. I want to use it with this LCD panel. Adafruit creates their own breakout board, but I would like better speed/color depth so I am making my own board to support the 8080 MCU 18-bit parallel interface.

The LCD has the following stats for voltage:

VCC
    Recommended - Min: 2.5 Typ: 2.8V Max: 3.3V
    Absolute Max - 4.6V
Backlight
    Recommended - Min: - Typ: 3.2V Max: 3.4V

Now I know i can use 3.3V on the backlight, but I am a little worried about using 3.3V directly on the VCC pins. Do you think I need a level shifter? Explain your reasoning.


texts: Raspberry Pi and USB modem - can I connect it like this?

texts:
As some of you know - Raspberry Pi model B has only 100mA available on USB ports.
I want to connect USB modem (that takes > 500mA sometimes) to my Raspberry without powered USB hub.

I have:

Raspberry Pi with USB ports that can deliver 100mA (recommended)
USB modem with high power demands (theoretically: 500mA, tested: sometimes 650mA)
2A USB power supply with 2 USB ports (it's 2A total or 2x 1A, doesn't matter)
USB extension wire

I want to:

carefully remove some sheath (outer "insulation") from USB extension wire
cut +5V wire
connect modem +5V directly to my power supply
leave +5V wire from Raspberry not connected

Like on picture pictore below:

Question:

Can I connect power to USB device from source other than USB port, where device is connected?


texts: Why is vivado so wasteful with its D-flipflop placement?

texts:
I have an implemented project in vivado, and I'm looking at the resultant layout between 8 slices:

As you can see, all 8 slices except one only have a single D-flipflop. This seems awfully wasteful. Why not put all of these flip-flops on two slices?


texts: Using TVS at the circuit input with or without a resistor

texts:
I'm new in the subject and cannot figure out how to use TVS for a particular reason.

Here is what I commonly see TVS at the input of a circuit:

Here another circuit has TVS again at the input, but this time with a resistor before:

So should the topology be: Input signal -->TVS or Input signal-->Resistor-->TVS ?

EDIT:

Please see the difference? Which one is appropriate? I found the diagrams from this question.

With resistor:

Without resistor:

Edit 2:

What should be the rule of thumb when sizing TVS? Let me ask with an example:

For example I don't want voltage transients to the input of an opamp exceed 12V. And if I use this TVS, would it be proper?

Below are the specs for the TVS:

Regarding the specs and my 12V limitation which condition should be satisfied:

Maximum Breakdown Voltage > 12V ?

Minimum Clamping Voltage > 12V ?


texts: High definition video on a composite cable

texts: Does anyone know if there exists an electrical/electronic standard for high definition video on a single wire, like composite TV which integrates luma, chroma and sync? I'm still interested in this long distance high bandwidth project, and maybe transmitting analog HD is the answer. 720p would be good, 1080p would be fantastic. And a way to convert between component and composite would need to be figured out by me, but I figure a very fast DSP or even FPGA ought to be the solution.


texts: How to design a feed line for a single wire antenna

texts:
I am trying to design a PCB for a wireless Thermometer using the RFM69CW Radio Module and the ATMega328p as an MCU. I placed the MCU and the RFM69CW back-to-back on my PCB and routed all the connections, however I am unsure what to do with the antenna line.

While prototyping the setup on a breadboard i simply soldered a 1/4 wavelength (865 MHz) monopole wire antenna to the antenna pad of the RFM69CW modules and everything worked fine.

However now I read a lot about RF Design and I am completely unsure what I should or shouldn't do.

I originally intended to simply route a standard trace from the ANT pad of the module to a plated trough hole and then solder my wire antenna to the hole. However, I read in several places, that i have to match the impedance of the trace to 50 Ohm and that i also have to put a ground plane next to or under(?) the trace.

What is the best way to add a simple wire antenna to my PCB design? I already saw designs like the Aaduino or the Moteino from LowPowerLabs that just connected a plated trough hole some millimeters away from the ANT pad of the RFM69CW and put a ground plane on the other side of the PCB. Is it that simple or are there certain calculations behind these designs?

Attached is my design, the trough hole on the top left is my current attempt for mounting the wire antenna.


texts: How can I attenuate any signal to 5V peak-peak?

texts:
How can I attenuate any signal to 5V peak to peak?

I tried the following design  :

While I limited the output to 5V peak-peak, the circuit clipped the output to 5V instead of attenuating it.

My main problem is that I don't know the input signal's amplitude. I don't know how to make a circuit that will attenuate the input by a variable amount to achieve an output signal that is always 5V peak-peak. What are circuit designs that will allow me to vary the gain or attenuation to produce a constant amplitude signal?


texts:
I have a 3D printer that has a "dumb" 12V DC fan on the extruder. It is always on and starts with printer; but unless the (12V DC) heater is turned on, it is useless and just makes noises.

I can't attach manual switch to it - if I'd forget to turn it on, heater will burn if turned on. I can't simply wire fan relay to heater - fan needs to cool heater down for few minutes after heater goes off.

I need to add a switch that will turn the fan on as soon as heater turns on, BUT this switch must be "sticky" - it must stay on onward, until 3D printer is powered off. I know how to add MOSFET switch, but can't figure out how to make control input "sticky".


texts: Does it exist a non-powered electrical switch that switches electrically?

texts:
I know that a relay can remain in closed circuit under current and open without current (or the other way around, depending on the relay), but is there any sort of relay that just requires any power to be applied to be switched, then remains under that state (closed or open) without any power applied? Even better if one can suggest one that is manufactured in solid state (opposed to relays that have moving parts).

Wall switches do not fit this description since those need to be switched mechanically and I'm looking for one that switches electrically.


texts: What is the difference between MOSFETs and BJTs

texts:
After reading this page :

http://learn.adafruit.com/rgb-led-strips/usage

I was wondering what is the difference between N-channel MOFSET and a TIP120 transistor. More specifically, why does he add 100-220 ohm resistors at the base when using the TIP120?


texts: Is Dark Silicon a good thing or a bad thing?

texts:
Recently in my computer architecture lecture my professor just mentioned the topic of Dark Silicon for a minute or less. But I found that topic interesting and searched the internet. What I found out from wiki is that

In the electronics industry, dark silicon is the amount of circuitry
of an integrated circuit that cannot be powered-on at the nominal
operating voltage for a given thermal design power (TDP) constraint.

But I was not able to get is it a good thing or a bad thing? Say if my rest of the circuitry is switched off when other part is working doesn't it lead to power utilization? And which is in turn a good thing. Or does it affect parallel computing?


texts: Can anybody guide me how to protect an IC from air arcing at high voltage test?

texts:
I want to check the isolation voltage of an IC by applying high AC voltage up to 10kV across the primary and secondary sides of the IC. During this process, I am facing a problem of air arcing above 5kV maybe through creepage or clearance.
Can anybody guide me on how to resolve this issue?


texts:
I have a RS232 device that sends data following the modbus protocol. I have problems communicating with it and I think my wiring is wrong. Since most modbus devices work over RS485 it is hard to find information about this.

This is the cable from the sensor:

I have an USB to RS232 converter and an RS232 cable.
I stripped one side of the RS232 cable and attached the RXD, TXD and GND wires to corresponding wires of the sensor. following the this diagram:

The sensor is powered by an external 5v power supply. I don't get any communication going to the sensor. I have tried this by reversing the RXD and TXD and also on an raspberry pi with power for the sensor coming from the pi.

I have also tried using an RS485 to USB converter, I do get data this way but they don't make any sense following the modbus protocol, they seem random.
I have used the minimalmodbus python module and serial test tools.
The sensor is an Calex PyroCube S, according to the datasheet it uses a bout rate of 9600, Parity none and 2 stopbits. I think that the slave number is 1?


texts: Proper way to recover 18650 cells from laptop batteries

texts:
I'm looking for a tutorial on how to recover 18650 cells from laptop battery packs. Like what should I do, and what should I not do, how to test them to see their condition.

The way I'm doing it now is break the battery case with a screwdriver and pliers, then take out the batteries and remove the wiring, then put them on a charger to see the voltage. If the charger doesn't show anything I assume the cell is dead, if it shows below 2.5V I throw it away and if it shows above 2.5V I charge it to 4.20V at 500 mA. Then I discharge it at 1000 mA and the charger shows me the amount of current discharged in mA. I assume that's the available capacity. If it has above 1800 mA I keep it and charge it again, otherwise I throw it away.


texts: I am attempting to create a displayPort source signal from scratch.  I just read through the 1.1 Specification (which is outdated and free on the displayPort website) and it gave a decent overview.  What I am lacking is an "implementation guide".  Specifically I want to know the sequence of events that I must do electrically to effectively send the pixel data.  For example when I plug in and power up, first I must send or receive "x" (or whatever).  Then I must do "y" over the "z" pin...etc...etc.  I attempted to sign up with displayPort to get free additional documentation, but that costs $5000.  If someone can point me to a book, guide, or website that gives more specific implementation data, it would be greatly appreciated.


texts: Why the diode has higher impact on dc characteristics than ac?

texts:
Consider this circuit which consists of a DC bias and an AC source connected with a diode and resistor:

Source: Boylestad and Nashley book 11th ed.

Using superposition theorem the circuit was solved.

In the book,the DC resistance across the diode can be found to be around 150 Ohms, whereas the AC resistance (dynamic resistance) is only 8 Ohms which was found using the formula:

$$r=\frac{26\mathrm{mV}}{i_d}$$

where \$i_d\$ is the current through the diode.

Similarly, the DC voltage across the diode was assumed to be 0.7 volts which is the barrier potential, while the AC voltage across the diode was only 0.01 volts!!

What is the reason behind this weird behaviour? If the DC voltage across the diode is 0.7V, then to my thought it appears that AC voltage must also be around 0.7V.

Questions

Why is the DC resistance high in the circuit whereas the AC resistance is low?
Why does the diode have such a low (0.01 volts) AC voltage across it? or why does the diode have higher impact on DC voltage while lower impact on AC voltage?

I also say that the above behavior is almost true in all the p-n junction diode circuits which I've seen.


texts: How to switch on/off RFID using piezo sensor?

texts:
I need to connect a piezo sensor to a RFID tag such that when someone presses on the piezo, the voltage generated activates the tag. A nearby RFID reader continuously looks for the tag. The tag remains off/undetectable while the piezo sensor is not touched.

Can I achieve this by removing the antenna on a RFID tag and connecting the terminals to a piezo sensor? The voltage spike can from my piezo sensor can be up to 10 volts. Should I try to limit it before connecting it to the RFID chip.

Also I need this in low latency i.e. small time gap between touch/un-touching piezo and that activating/deactivating tag.

Thanks.


texts: Bypass capacitor pad in series or in parallel with load?

texts:
I have been skimming through various good bypass cap layouts and cannot tell if this makes any difference:

On the first case, I would have a load and the bypass cap's VCC pad connected from different traces starting from the power lines, so technically there is no current on the trace leading to the bypass cap

On the second case, I would have the load and the bypass cap's VCC pad connected with a single trace on the PCB.
Is there any preferred layout? (Is it something to avoid to have current running through a bypass cap's pad?)


texts:
I have what should be a simple misunderstanding of a piece of text from "RF Circuit Design" by Lugwig.  I am not in a class, just self-teaching. This book has been quite helpful, and I have not found anything inaccurate in it (yet).

This is a large model for a BJT.

Here is a page:

It all is quite clear, except equations 7.10 and 7.11 seem opposite to me.

The Ie equation makes sense if we are dealing with electron flow, but the Ic equation makes sense if we are dealing with hole flow.
(because the Ir and Ic arrows are opposing, so the If and Ie flows must be opposing as well, per the equations).

Any brief comments helping me to understand these two relations would be appreciated.


texts: Calculation of current generated by generator when no load is connected

texts:
I just started 3-phase circuits and in my book it written that "for a delta connected coils of generator, in a balanced system the resultant emf in the closed circuit will be zero and hence there will be no circulating current in the mesh if no load is connected to the lines".
But I actually didn't understand how current is zero so I draw a picture of coils and connected it in delta connection(shown in image) and after that intuitively it feels  after looking at picture that it should be zero but I cannot able to prove it mathematically using Faraday's law(or kirchoff's law) , so
1.is there any mistakes in my coils arrangements or in diagram for ?
2.how to prove that net current in loop will be zero using Faraday's law (or kirchoff's  law)  when switch  'k' (in image)  is closed.
3.what changes occur  if we open the switch 'k'


texts: Value of resistor and the current in branch with the capacitor

texts:
I am trying to learn electronics basics.  I have a question asking for the current in the capacitor branch and the value of the resistor that is before the ground

I have used a circuit simulation software to find out that the value of the resistor is 4.2ish and this circuit is at time = 0.

I have added the original question below.

Can anyone explain to me how the current and the resistance value is found out?


texts: Building an LED matrix to plot mathematical curves

texts:
I've decided of building an LED matrix(10x10) to plot mathematical curves such as line, parabola, etc. I'm a total beginner so I just wanted to ask how to proceed about this.

At first, I thought of just joining the specific LED's to give the desired curve. But that would have been too naive , wouldn't it ?

So please help.


texts: Is using SPI communication for 3 meters length still tolerable?

texts:
I'm trying to communicate my master board to slave, with SPI port.
Our mechanical team says that it will be 3 meters long.
Is it still tolerable? how about its noise?
Thanks


texts: \$\mu\$ Symbol on a Relay Module's Nameplate

texts:
One of our customers gave us a sample product for inspection. It has a relay output for 220V loads (e.g. fan, bulb, etc.)

Just out of curiosity, what is the meaning of the \$\mu\$ symbol here?


texts: Can I switch an L78L05 with a transistor?

texts:
I need some help. I have the following circuit.

simulate this circuit – Schematic created using CircuitLab

The highlighted area is what I am having trouble with. I understand that I cannot use the component (transistor) in the that area as it shows on the diagram but I hope you can push me in the right direction. Here is what I am trying to do. When the button (Switch) is pushed the whole circuit is powered. The MIC5219's enable pin activates the chip which is powering the ATMEGA. That way, when not needed I can power the whole chip/circuit down and preserve power. Once the chip starts up first thing I pull pin D8 high which keeps the MIC5219 powered. Then I can run my program and move the servo.

My issue:
The 7805 uses about 2mA in standby mode even when nothing happens. I need to shut the power flow off somehow and was thinking using a transistor. The connection between the 7805 and the battery has to be cut off in order to save these 2mA but of course the transistor does not work that way. How can I design that part of the circuit to have a "switch" that I can control with pin D8 and activate the power flowing through the 7805 and provide the power to the servo?

Just in case you wonder why I want to do this? The MIC5219 does not provide enough current to the circuit and the voltage drop when the servo starts up causes the whole circuit to reset and start over. Not the desired behavior. That's why I want to provide the servo with its own voltage regulation.

Thank you very much for your help.

EDIT:

@justme @vtolentino could you guys please have another look at the updated circuit and advise if I got that right?
Really appreciate your feedback.


texts:
Does anyone know why AC coupling caps should be implemented in USB3 interface while it's not required in USB1/2?

Anything to do with transmition speed, encode method?


texts:
First of all I need to say that I have almost no experience with programming microcontrollers (aside for some Arduino stuff). I have worked with C (and x86 ASM) on some low level projects (think of kernel stuff, embedded systems) so I think the software part should not be an issue.
Since I'm trying to learn something about microcontrollers I figured the best way to do it is to take a pet project. I made up my mind and I want to implement Spacewar! on a microcontroller. If it was able to run on a PDP1 in the 60's should run on a microcontroller (I think).
So here's my question, could you recommend any particular development board that would have a VGA port for me to display (just black/white) the game. I am planning to use a usb keyboard for the controls.
Would the VGA displaying (i need only b/w, 640x480 would be more than enough, I would go for even less) be out of the reach for a cheap board (<=100$)?
Any recommendations for the board? Any other issues you think I might encounter?
Thank you!


texts: How series resistors influence clearance-creepage requirements?

texts:
simulate this circuit – Schematic created using CircuitLab

I'm designing a circuit which should leak some amount of current from AC line to PE. The question is regarding clearance-creepage calculation for this specific case.

The part (triac optocoupler) is rated for 600V peak on TRIAC terminals, but the pin spacing is below minimum required by safety standard (2mm instead of 3mm required from line to PE).

The question is if I can count clearance-creepage added by each resistor leads spacing?

For example: If I have 4 resistors of 1206 size it will give me ~4x1.5mm=6mm donated by resistors + 2mm pin spacing of triac optocoupler.

The most intuitive answer will be yes, but in case triac is not conducting we will have line voltage at its terminals and it can probably arc the leads.

Thank you in advance.


texts:
I have a Daikin BRP069A61, which is a heatpump accessory that allows the heatpump te smartgrid controlled. In simple terms: It will turn on when PV-power is available and will limit power to whatever is available from the grid using a pulse meter.
I want to drive the pulse meter input from this BRP069A61 using a NodeMCU. I have the NodeMCU part working in the sense that I have a PWM output which I can control. So eg when there is 1 kW of PV-output it should pulse 1000 times per hour of 0.27 times a second with a max. of 17 kW, which would mean 4,7 pulses/sec
The BRP069A61 has a 5V DC Pulse detection.
I assume I can't just connect the 3.3V PWM output of the NodeMCU to the 5V Pulse detector input of the Daikin device. So I thought I need an optocoupler. Is that correct?
If so, I need to drive an optocoupler that works with 3.3V input. I was thinking of using an PC817 which has a 1.2V forward voltage with a maximum of 6V. To 3.3V is fits in the middle.
My questions are:

Should my idea work? Using PWM output to drive an optocoupler? and drive a pulse detection system?
An optocoupler reverses output. Input high is output low and vice versa. How can I swap this another time around?

My schematic would be very simple.
Input side: [NodeMCU D1] -> [R1] -> [PC817] -> GND
Output side: [Daikin 5V V+] -> [R2] -> [PC817] -> GND
Would this work?


texts: Cause of diode failure in step-down switching mode power supply

texts:
In a basic switching step-down LM2675 voltage regulator design (as shown in the picture from the datasheet below), what could possibly be the main cause of a short-circuited diode failure (D1 in the picture)?

A little background:

The company I am working for designed a special power supply as part of a larger product a few years back, that accepts 24V as input and uses an LM2675 to produce 5V output.
The type of the diode is MBRS340 (Shottky, 3A, 40V).

Some devices (with these power supply units) have been returned by the customer and all units have the same fault: All Shottky diodes are short-circuited.

Additional to the circuit in the picture there is also a poly fuse to limit the output current to 0.9A, so a secondary short-circuit should not destroy the diode. Usually the output load is less than 100 mA.

The strange thing is that the rest of the circuit (on the 5V part) does not get damaged, so it remains working after replacing the faulty diodes.

The waveform across working diodes looks like this while the input voltage is 24V, so no unusual high voltage spikes visible.

Waveform:

Original image source

Waveform zoomed in:

Original image source

Do you have any experience with these kind of faults?


texts: Tolerating Logic Inputs in Excess of Vcc

texts:
Referencing this TI inverter as an example part: http://www.ti.com/lit/ds/symlink/sn74ac14.pdf

Specifically, the table at the bottom of page 2 (I would put a picture but I do not know where to upload it).  It lists the max Vcc as 6V.  It also says the voltage input range is -0.5V to Vcc+0.5V.  There is also a note 1 which says "The input and output voltage ratings may be exceeded if the input and output current ratings are observed."

I want to use a Vcc of 3.3V, but I have one input that would be 5V.  TI has other inverters that allow 5V inputs with 3.3V Vcc, but their input leakage current is too high for my other inputs.  Therefore I am interested in exploring this note.

What does it mean when it says "if the input current rating is observed"?  Would this be the input clamp current, Iik (+/- 20 mA)?  If so, does that mean I need to put a series resistor in front of the input, so that e.g. 5V - 3.3V = 1.7V (EDIT: and subtract diode drop 0.5V = 1.2V) dropped over the series resistor induces Iik < 20 mA?  Should I be concerned about this series resistor being too large, such that the induced current would be less than the input current Ii = +/- 1 uA max?

This question is slightly related to another question on this stackexchange ( Why is it important not to exceed Vcc at the input to a logic gate? ), where one answer off-handedly mentions using resistors to limit input currents, but I would like more detail using a concrete example, especially since this datasheet implies that it's possible to do safely.


texts: Burned the voltage regulator of a DC motor driver,

texts:
While I check the specs and thought the driver could handle it, after about an hour of discontinuous use, the driver stopped working...
I used the following :
Motor
Specs:
24V 250w,
rated current 13.4 Amps,
No load current <2.2 Amps,
Gear reduction 9.78:1
With this driver
Dual channel,
5-25 volts
10 amp max continuous in each channel
30 amp max (upto 10 seconds)
While I ran the setup at no load, I checked the temperature of voltage regulator ic 7812 (on the driver board) after 45 mins or so, it was piping hot and the board had stopped conducting.
Also, the operation involved a pwm input from a potentiometer, which would gradually change the speed of motor from 0-300 rpm and had an emergency stop which would immediately turn the pwm to 0.
The motor would start slightly humming even at 0 pwm and would stop with a jerk when used emergency stop.
Please help...


texts: Is there any compact relay (or any high current) chip for Raspberry PI?

texts:
I am fascinated how L293D makes it easy to control a DC motor.

I wonder if there is any similar popular chip that controls a set of relays, so I don't have to use a bunch of transistors?

PS. I am aware that I can buy a relay pack. With this post, I like to learn if there is any relay controller chip.

Update:
ULN2803A suggested by @Ghanima is the answer. This chip can be very useful for Raspberry PI or Arduino projects. Not sure why this question is moved here?
I am  updating the title and body of the question and including keywords "Raspberry PI", to help others when they search for this info.


texts: Why would a time signal receiving watch have an airplane mode?

texts:
I've been looking at radio controlled watches online. I noticed that some radio controlled Casio watches have an 'airplane mode', which disables GPS and terrestrial time signal reception:

Now, why would signal reception be restricted? The watch in question does not have a Bluetooth module or similar.


texts: How to use the newest version of VHDL in Vivado?

texts:
The below code gives me an error hat i cant read from out object Q
Im sure newer version of VHDL supports it, how do i enable in Vivado does anyone know?
Before i used GHDL compiler with a flag option --use ieee=08
Or something similar to this
library IEEE;
use IEEE.Std_logic_1164.all;

--Non-gated SR latch, general configuration 2NORS
--Only works when using the new VHDL version

--Declare SR_Latch entity
entity SRLatch is
    port(
        clk: in std_logic;
        set : in std_logic:='0';
        reset : in std_logic:= '0';
        Q : out std_logic:='0';
        Q_n : out std_logic:='1'
    );
end SRLatch;

architecture behavioural of SRLatch is

begin
    process(clk) begin
            Q <= reset NOR Q_n;
            Q_n <= set NOR Q;
    end process;
end behavioural;

```


texts:
I don't know much electronics (I'm a software engineer). I want to build or buy a remote power control, controlling over SMS or IP.
I don't care if I need to implement my own API or do my own electronics.

Where can I find some resources for that? I found:

iBoot: too expensive
X10: I don't understand the difference between 3 pin appliance to the wall switch and i dont know if they are the cheapest solution.


texts: Analyze a circuit with two diodes and two voltage rails

texts:
I want to find \$I\$, \$I_{D2}\$ and \$V\$ in this circuit. The diodes are made of Silicium. I'm a beginner and normally I would assume the Diode bias and then apply KVL to see if it is true. However, I've only encountered circuits where the wire forms a loop.

How am I supposed to apply KVL in this case?
If voltage is the difference in potential between two points, how can I find the voltage of V if one point is outside of the circuit, therefore, outside of KVL application?


texts: I read that an LED (primarily emits light) can also be used as a photodiode (primarily detects light). Is this true in reverse? I mean, can a photodiode also emit light?


texts: TTL logic level , how NOT gate checks logic level ?

texts:
This is a TTL logic level checker circuit , highlighted blue area is a checker pin. Voltage at checker pin is 0.65V so this must be logic 0 , LOW LED will on.

But in input of first 7404 NOT gate in first row is 1.3V and 2nd 7404output is LOW , logic 0.

Why first NOT gate in first row thinks 1.3V is a logic 0 , (LOW)

isn't TTL voltage range in 0.8-2V is a unvilad area ?


texts: how to interpret the RTL report after synthesis in Xilinx?

texts:
I did verilog code of a circuit. It was simulating well and giving output correct after Simulation. Now i did synthesis, the RTL schematic after synthesis showing some green and red box. Is it indicating any kind of error?
Please give any comment to clear this confusion.
Thank you.

Asking about the red and green boxes which i highlight using white color lines.


texts: What are the specifics of PoE ethernet magnetics

texts:
I have a PoE powered design, and it is currently equipped with magnetics not labelled as PoE, HX1188NL. There is also a transformer with a similar topology, HX2019NL.

However, the only difference I can see is the provided isolation.

The non PoE one can stand 1650 V for 6 seconds.
The PoE one can stand 1500 V for 60 seconds.

Apart from different isolation characteristics, what are the differences between non PoE and PoE transformers ?


texts:
let's consider a generic differentiator circuit, i.e. a circuit whose transfer function is \$\text{constant}\cdot j\omega\$. For instance, you may consider this circuit with Op-Amp:

I was reading this paragraph about it ("Pulse And Digital Circuits", Prakash Rao):

Which is the precise reason for its unstability? In general, I know that a linear system is stable if and only if its transfer function has only poles with negative real part. In this case I do not see any poles, and so?

Moreover, I have seen that usually negative feedback (as that present in this circuit) improves the stability: is, despite this fact, this circuit unstable?


texts:
I do a fair bit of soldering (lead-free). Is breathing in solder/flux/paste fumes actually going to harm me?

Are cheap fume extractors worth buying?


texts: How to estimate/compute for disconnected neutral potential rise?

texts:
This is a different question, I want to know what could be the minimum distances between poles before the ungrounded neutral in one pole can create different potential from the other neutrals in other poles. If they are close like 30 meters apart, maybe the neutral with removed ground rod is as good as fully grounded??

As illustration. Supposed you have 3 distribution poles (from 13,000 volts primary to 120/240v secondary single split phase supplying American houses).

And one of the poles lost the connection of its centertap neutral to the ground by the pole grounding wire disconnected from the ground rod accidentally  (note I'm describing the US power system). What would be the potential of that floating neutral when all the other poles neutral are connected together (With other poles centertap still connected to their corresponding ground rods)?


texts: What are these long gold plated SMD components on the NVidia Tesla A100?

texts:
This photo shows a NVIDIA Tesla A100 board. Please note the 4 SMD components on each side of the chip. Looks like gold plated ceramics. I have never seen components like this. Can someone identify this components?

Link to full story:
https://www.guru3d.com/news-story/nvidia-tesla-a100-with-ga100-ampere-gpu-spotted.html


texts: Reducing the clamping voltage of a TVS diode

texts:
Followup to my previous question.

I'm designing a product powered from a 5V supply that feeds it into a TLV1117LV33 LDO. Typical current draw for the project is less than 500mA, but the regulator is cheap and stable with ceramic output caps so I like it so far. Anyway, I was advised in the previous question to put some ESD and transient protection on the Vin line, which makes sense to me, so the solution I'm thinking of is a PTC polyfuse in series, followed by a standard unidirectional TVS diode to ground.

However, all the diodes I've looked at (eg Littelfuse SP1003, Vishay GSOT05C) have quite a high clamping voltage. I understand that this is standard, ie that the maximum clamp voltage of a TVS diode will be a lot higher than its max reverse standoff. I'm also aware that lower clamping voltage and lower dynamic resistance is considered a figure of merit for TVS diodes.

However, my regulator's safe operating input range is up to 5.5V (6V absolute max). These diodes have 5V reverse standoff and typically ~7V clamping voltage at 1A (~12V at 30A). That's gonna fry my regulator easily! I've seen devices with lower clamping voltages, but when I say "lower", I mean 10V as opposed to 12V (at 30A). How do I reduce the clamping voltage so that, if an inductive transient appears on my 5V rail (or something similar), my regulator will survive?

Devices like MOVs seem to have even higher clamping voltages, so as far as I can tell, that's not a superior solution. I've also heard a bit about multi-stage ESD protection, but no advice on how to do it. Am I overthinking things?


texts: Using High Endurance Flash Memory on PIC processor

texts:
I am designing with a PIC10F322 ( http://ww1.microchip.com/downloads/en/DeviceDoc/40001585D.pdf ).  I want to use the "high endurance flash memory" and the document states that the high endurance memory refers to the "lower byte last 128 addresses" and that the "self-timed write cycle time" is 2.5 ms max.  I am running the CCS compiler if it makes any difference.  The data sheet also says to refer to “PIC10(L)F320/322 Flash Memory Programming
Specification” (DS41572) which seems to be mainly concerned with ICSP.

I have a couple of questions if anyone has experience with these things:

There is no specific instruction set to write to "high endurance" flash memory.  If I write to it the same way I would write to program flash memory (14 -bit words, unlock sequence, etc.), I am guessing I only write and read the lower 8 bits?  Are the upper 6  bits returned from the read sequence not "high endurance" and therefore unreliable?  Must they be masked off during a read?

Thanks in advance.


texts: How to tell if a switching element is operating linearly?

texts: For example, a p-mosfet in a buck or buck boost topology converter. Is it working optimally or inefficiently?


texts: atmega328p GPIO with 3.3V regulator reads 2.5V at pin when High

texts: I am driving the enable on a boost regulator and the boost is not turning on. When I checked the voltage on the enable, it was 2.5V. The boost worked on an identical set of boards I tried before this (I didn't measure it then). Is this likely a cold solder joint? I used flux.


texts: Simplest circuit to briefly (100ms) power a 1W LED?

texts: I am very new to electronics. My project calls for an array (20) of addressable high power LEDs. Each LED needs to be on for at most 100ms. Only one of 20 LEDs is going to be on at any given time(running lights kind of arrangement). I am considering driving those LEDs off single MOSFET per LED with aruduino's digital pin gating the MOSFET. I realize LEDs like constant current but hand-soldering 20 constant current circuits for every LED feels like overkill. What do you think? On a scale of 1 to 10, how sloppy is this approach? Should i also include a beefy current limiting resistor or there is no need given the short duration of pulse?


texts: Why the audio subcarrier is never transmitted with baseband analogue video signal?

texts:
In the era of analogue video, when you needed to connect a local video source (STB, VCR, game console, DVD player, etc.), the most ubiquitous way to do so, next to using an RF modulator, would be to use a composite video connection. But it only carried a video signal - for audio you needed a second RCA cable. And as the audio is often in stereo, it became common to see triple RCA cables with colour-coded white, red and yellow plugs on both ends.

There are of course combination cables like SCART or D-Terminal, but let's put that aside for now.

Now the question is - why not just carry the audio signal, modulated in the same manner as in a broadcast channel, within the baseband video cable? It should not significantly affect the quality of either video (as the audio subcarrier is outside the video bandwidth) or audio (as the audio carrier frequency of, depending on region, 4.5-6.5 MHz - and its bandwidth - are high enough to encode all audible frequencies). Stereo could also be carried the usual broadcast way (MTS, A2 or NICAM).

I don't know what is the practical bandwidth for a typical composite video cable, but in PAL regions, the baseband signal already carries the 4.43 MHz chroma carrier - around the same frequency that NTSC (and PAL-M/N) audio is on (4.5 MHz), so I guess that suffices as a proof of feasibility at least in NTSC regions.

Analogue video devices used to commonly include an RF modulator anyway - so all the logic necessary for modulating that FM (or AM in France) audio signal was usually already there - so it shouldn't significantly affect the price of the device.

Such arrangement would allow to connect a baseband video source with a single cable - which seems like a pretty good convenience and selling point - connecting a bunch of identical plugs can be error-prone, especially with the less technology-savvy customers.

In addition, composite video cables can get much thinner, longer, more robust and cheaper than e.g. the afore-mentioned SCART cables - I can see many people willing to accept the sacrifice in quality (compared to S-Video or RGB offered by SCART - and many people wouldn't even see the difference) for the greater flexibility in cable arrangement gained this way.

So... why was it never done that way?


texts: Does PCIe 100ms boot-up time requirement including the entire FPGA device?

texts:
we know most of the FPGA vendor have way to ensure the entire FPGA device can be configured within the 100ms time. However, since most of the PCIe solution is a harden block (dedicated circuitry) sitting inside the same FPGA device. I supposed the entire link training should be totally independent from the FPGA core.

In this case, I assume partial configuration just need to be done earlier to wake up the PCIe circuitry and ensure the LTSSM operation happen to fulfill the 100ms boot-up time requirement.

However, why it looks like the 100ms boot time requirement also apply to the entire FPGA device especially on the core fabric (This means the FPGA core also has to be ready within 100ms)? Is this really necessary? If there a hidden reason in behind?


texts: What happened when I join two different materials?

texts: It is noob question cause I am noob, but if I have two different materials with different amount of electrons and I join them (just in hand if you know what I mean), why there is no electric current? They should try to balance the electrical potential or?


texts:
I really can't determine what my professor meant by this. He wanted me to calculate parameters of BJT differential amplifier that will have -100 amplification for signals difference and -1 for their sum. What is confusing me is this -1 for sum of the signals. Is this meant for common mode signal? But common mode is (s1 - signal 1, s2 - signal 2) (s1+s2)/2. Should I took -1/2 for common mode amplification? I'm confused also because BJT amplifiers attenuate common mode signals and I can't take 1, because amplification is typically below 1.

Thank you very much in advance.


texts: I just programmed my Atmega328p with an Arduino as ISP. I am making a permanent circuit on a piece of perf-board. I need to connect the Nokia 5110s Vcc pin to 3.3V on the Atmega328p. Which pin is 3.3V because there are two positive pins and I'm not sure which one gives 3.3V and I'm not sure if they are both input (I need output). Can someone please tell me which pin is 3.3V output on the Atmega328p?


texts:
I have been learning about electronics as a hobby. And I'm still confused about current and voltage. I've read many sites and watched many videos. But still have questions.

Here is what I learned so far.

Voltage is how much force the electrons are being pushed. Current is how many are flowing.
So If I increase the voltage, means I increase the pressure and current will increase too. There are different kind of power supplies, those supply different currents in same voltage. They reduce current using resistance and increase using transistors. Right ?

Now the confusion part, what I think is that how much current will be pulled from power supply is depend on the device that need the electricity. And if device pulls more current than power supply can push, power supply will heat up and blow.

Now lets say, I have an air conditioner, I think it takes around 10A. While a normal fan takes 1A. That seems to prove, it depends on device how much current it will take.
So if I put 100 air conditioner which will take 1000A, it will blow up the power supply. Means power supply was unable to push that much of current.

Now lets take a phone, that comes with a charge that supplies 200mA and good for phone. But if I use a phone charger than can output 1500mA, why my phone will charge fast ? It is suppose to only use 200mA(or enough) only, not 1500mA. And it might blow up the phone charging circuit or battery.

My actual question is, can we force an electronic device to use more current if more current is being pushed from power supply ? If yes, then how come a fan only takes 1A while air conditioner takes 10A on same power supply. Why fan is not blowing up ?

Please if possible, try to explain in simple words. Thank you :)


texts:
I need to create a lot of BRAM blocks in my (Altera) design. Each one has unique memory contents, determined a priori using an algorithm.

Before, I was setting a parameter for each BRAM cell to read from a .MIF, but this caused my compilation time to take forever.

Another approach I concocted was to allow "dynamic" population of the memory; the host controller would be able to send symbols to the FPGA to populate its BRAM blocks with. This is a little more complicated than I would like.

I was hoping there was a way to initialize BRAMs with a literal. Each block is only 1 bit x 256, so the resulting HDL code wouldn't even look that ghastly.

Does anyone know how to do this with Altera's BRAM IP, or perhaps even Xilinx's?

UPDATE 8/31/2016:

Hey guys, I actually found a very easy almost "turn key" solution to BRAM initialization on Altera. In Quartus, there are built-in VHDL and Verilog templates which can automatically infer BRAM. These templates have memory initialization utilities built-in which the user can modify to populate with whatever data they want (such as a bit vector from a generic). See this Quartus help page.


texts: Digitally measure current on very high voltage line

texts:
I would like to measure current to a standard CO2 lasertube, which is already possible with a battery-powered digital or analog ampere meter available for cheap, but these do not allow me to read this value into e.g. a microcontroller.

I have already seen some designs based on a shunt and an isolation amplifier (http://www.ti.com/lit/ug/slau521/slau521.pdf?ts=1588611452800), but this is only rated up to 2kV, whereas my system can reach up to 25kV.

Is there another way to measure the current / voltage across a shunt resistor and isolating it?


texts: 12V to Arduino ground. Did this destroy my arduino uno?

texts:
simulate this circuit – Schematic created using CircuitLab

Due to some bad late-night wiring, I ended up with the above circuit. Pins 4 and 5 are digital pins configured as inputs. I can confirm that zener d2 is blown.

The arduino seems to be working relatively fine, accepting new sketches, blinking the internal LED according to the programming logic etc. One exception is that external signals as low as 1.8V are consistently being registered as HIGH by the arduino. I tested this on digital pins 7 and 8 as well.

I would like to ask what the probable damage is, and if replacing the atmega chip would be advised?

EDIT: One thing I forgot to mention is that the arduino was being powered by a seperate 7.2V source through the power jack.


texts: Low power ESP8266 LDO or switching regulator

texts:
I'm going to use 1S Li-po, 3.7V. ESP8266 needs 3.3V and it takes 350mA peak on startup. When running it needs about 70mA.

The ESP task is to wake up, measure, connect to wifi and post data to server. It will wake up every 2 hours. I'm wondering which regulator is better for low power modules, LDO or switching. I know that LDO efficiency is a lot less efficient but they have lower quiescent current. On the other hand the switching offers better efficiency. Which one I should use?


texts: Why is this oscillator's output gets distorted?

texts:
The following oscillator is outputting distorted sine waves during the end of negative swings:

What could be the reason? How to fix this issue? I tried to play with some parameters like C1, C2, L and Vs or even R1 and R2, but I couldn't succeed anything.


texts: wiring electric motor to run CW without name plate or diagram information, other than my diagram of it running CCW

texts:
Motor does not have name plate or diagram. It is running CCW rotation now.
From my wiring diagram is it possible to re-wire to run CW?
Thanks for your help.


texts: I am working with the FET335xS-II OBC developed by Forlinx for a school project. On the data sheet, There is no indication of pins pertaining to MOSI and MISO but instead "data 0" and "data 1". I am a little confused by this as I cannot find any documentation regarding this. Any help would be appreciated. I can upload and share more photos if needed.


texts: Determine the current through a voltage source for nodal analysis

texts:
I'm struggling with a problem our professor gave us, which states:

"In the following circuit, find the value of the resistor R_x so that the power consumed by the resistor R1 is the maximum."

simulate this circuit – Schematic created using CircuitLab

I'm trying to solve this with the nodal method as follows:

KCL for node A: $$-I_{AC}+I_{GND-A}+I_{AB} = 0$$
KCL for node B: $$-I_{AB}-I_{GND-B}+I_{CB} = 0$$
KCL for node C: $$-I_{GND-C}+I_{AC}+I_{CB} = 0$$

I've expressed the currents as follows:
$$I_{GND-A}=\frac{E_A}{2} A$$
$$I_{AB}=1 A$$
$$I_{GND-B}=E_B$$
$$I_{AC}=-\frac{E_A-E_C}{3}$$
$$I_{CB}=\frac{E_C-E_B}{x}$$

The problem is that I can't find a way to express the current $$I_{GND-C}$$ as a function of the unknown node voltages. Any ideas?

Thanks in advance.


texts: Question on spark gap transmitter circuit

texts:
I am trying to understand how basic electromagnetic communication works.
From what I understand, spark-gap transmitters were the first wireless devices made by man. A couple of circuits I found online involve high voltage devices that create a spark across a small gap (electro boom.)
However, I came across videos from two gentlemen with similar circuits that do not use high voltage. Adding a link here for reference.
Basically, it involves an electromagnet that disconnects a circuit when powered, and then when power gets reestablished circuit reconnects, and the cycle repeats. Is this feasible for creating EM wave? Is this a spark gap or something else.
Reference: https://www.youtube.com/watch?v=izCV1WrPFds


texts: How would I apply this type of dupont wire to a 0.64mm SMD pin?

texts:
While browsing for more robust solutions to those plastic dupont jumper wires, I came across these wires:

The datasheet didn't really provide any information and I haven't come across these wires yet. I was wondering how are these applied to pins. I have 0.64mm square / SMD pins on my board. Do you just slide them over for easy reversibility or do they have to be pinched with pliers or perhaps heated?


texts: How to use the "Switching characteristics" parameters in the BJT's datasheet

texts:
In Fairchild's MMBT4401's datasheet (Note: This is not the newest one from official site, but it seems it contain more information than the newest one, so I use it as an alternative), there are some parameter tables and diagrams relative to "switching characteristics".

All them are tested under certain conditions, such as Vcc = 30V, Ic = 150mA, etc. I wonder how can I use them to get the parameters in my own circuit configurations, such as Vcc = 5V, Ic = xx mA. Is there some simple math equations, or estimations to get them from the given ones at given conditions?


texts: Series variable resistance with NPN transistor

texts:
i'm trying to build a symple voltage controlled low pass filter and in the design they ask for a transconductance amplifier (which works as a series resistance in the R C pair for the passive low pass).
But the order i made for my parts came out wrong and i got a triac instead of the transconductance ampplifier...
so i was wondering if i could use a NPN transistor as the variable resistance kinda like what i did in my voltage controlled oscilator design

so i tried to use that NPN in place of the series resistor of the low pass filter and it didn't work...
i imagine it's because the emitter is not tied to ground or something like that.
so there are two solutions to my problem: one is to find a low pass topology with the resistor that controls the cutoff point tied to ground and the other one is to find a way of making an NPN transistor work as a series resistance.
i also tried the first solution by using the active low pass topology and replacing the feedback resistor like so:

also didn't work
maybe i'll try to replace the feedforward resistor with the transistor as well
but it might be some error in the assembly of the circuit
so now i'm kinda stuck
any ideas?


texts:
I'm getting another error in OrCAD when I try to create the netlist. When I try to create the netlist I get this warning:

  ERROR(ORCAP-36022): Pin number missing from Pin "DRIVE" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.
  ERROR(ORCAP-36022): Pin number missing from Pin "BAT" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.
  ERROR(ORCAP-36022): Pin number missing from Pin "SENSE" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.
  ERROR(ORCAP-36022): Pin number missing from Pin "TIMER" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.
  ERROR(ORCAP-36022): Pin number missing from Pin "!SHDN" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.
  ERROR(ORCAP-36022): Pin number missing from Pin "PAUSE" of Package 100301_7 , U10A: SCHEMATIC1, PAGE1 (6.37, 0.95). All pins should be
  numbered.

There is a total of 35 instances of this error. I don't understand the error though. If I go into edit part for U10A, all the pins are already numbered. So I don't see where else these pins should be numbered?


texts: Value of loop gain for steady state oscillations

texts:
I was reading on a book (High-Frequency Oscillator Design for Integrated Transceivers, J. van der Tang, Dieter Kasperkovitz, Arthur H.M. van Roermund) this paragraph about the start-up condition for an oscillator:

Let's consider for instance a common base Colpitts Oscillator (biasing network for the base is not shown):

Now, I may do a small signal analysis of this circuit at open loop, find the expression of the loop gain, and size the components in order to make its absolute value greater than one. But, which is the mechanism that will reduce it once the oscillator has started? Is it automatic? How can I size the components in order to make it exactly equal to 1?


texts: In order to increase the duty cycle span of a 555 timer above 50%, I should connect a diode. The equation of duty cycle without diode is $$D = \frac{R_1+R_2}{R_1+2R_2}$$ but when I add the diode what is the exact equation of the duty cycle?


texts: I am designing a printed circuit board with Sigfox IC ATA8520 from Microchip. The max frequency I have worked with is 20 MHz for PIC microcontrollers. I have been searching for design considerations while layout the board so that I do not have a lot of noise on the board. I am using Altium Designer 19 for this. Any suggestions?


texts: Transimpedance Amplifier: Silly question that's killing me

texts:
I'm having huge trouble with this problem, I've probably done it 10 times already and there must be something that's slipping my attention.

The givens are:
\$I_{PMT}\$ = 150.0 pA, R1 = 73.0 MΩ, R2 = 2.0 kΩ and R3 = 200.0 kΩ.
What my calculations have been:

V+ = 0 so V- (at U1) is also zero. The equation at the node entering V- :

\$\frac{(0-V_O)}{R_1} + I_{PMT} = 0\$

which gives:
\$V_o = -I_{PMT} * R_1 = -73*150*10^{(-12+6)}\$
in the other input node entering V- of U2:

\$\frac{(0- V_O)}{R_2} + (0 - V_{out})/R3\$

which gives:
\$V_{out} = 73*-150*10^{(-4)} = -1095 mV\$

Someone help!!!

Thank you :)

edit1: by V_o I mean the voltage at node after R1 and before R2- the node output for the first op-amp


texts: Series and parallel Lipo question (20,000mAh capacity)

texts:
I got a battery bank from China and it says in the back that the rated capacity is 20,000mAh (3.7V). After some use (charging my laptop) I decided to open the thing and I noticed four cells of 5000mAh connected in series at 14.8V. The battery bank offers two ports: 1 USB port of 5V,2A(max) and one DC output of 19V/4A(max). I contacted the people and they said that the configuration of 4x5000mAh in series (achieving 14.8V) is the same as the 20,000mAh at 3.7V (4x5000mAh in parallel), because the power is the same.

How can that be? are they flat out lying? shouldn't a parallel connection give you more capacity than the series connection? even if the power at any given instant is the same, the capacity should be 5000mAh and not 20,000mAh, wouldn't it? or is it that the DC-DC converter design requirements inside the product make the two configurations equivalent?

I think inside there is this configuration: 14.8V stepped down to 5V@2A and 14.8 stepped up to 19V@4A. Since stepping up from 3.7V to 19V and still give 4A(max) would ideally require more current from the 20,000mAh battery than from the 5000mAh battery (since the voltage step would be from 14.8 to 19, not so big), is it then that the two configurations (series and parallel) are similar/equal and the reason they are marketing their product as 20,000mAh?

I would really hope you guys could help me with this puzzle and point any mistakes I've made. Thanks in advance!


texts: Double Integration with the BNO055 for position data

texts:
I am trying to get position data(x, y, z) from the BNO055 IMU from adafruit. I have been given a library in java, so I can communicate with the IMU. I have been able to get heading, yaw, pitch to +/- 0.1 degrees and so I think I can do the same with positional data. My current code, measures a time elapsed in samples and then adds the new sample multiplied by the change in time. The problem with this is that the error is time^4 because i have to integrate twice. My goal is to get the position accuracy of +/- a half an inch. How can I change my code to get better accuracy.

I've heard things about sensor fusion, I don't exactly understand how it applies to my case, but I do have access to encoders on all of the wheels of my drive train.


texts: How does the blocking FET Q1 exactly work in this case?

texts: This is a wireless power controller chip. Means it is a controller that switches between a wired (5 V) USB supply and a wireless power supply based on availability and also based on priority. In the page no. 35 of its datasheet bq51013b, it is mentioned that the blocking FET Q1 is used in the configuration. So the power controller is not being used at all when the wired supply is detected? Somebody please break down this P-MOSFET combination.


texts: Can a display landline phone instrument be made to work without a separate electrical connection

texts:
Since phone lines can supply power, there are landline phone instruments which work without a separate electrical connection. Typically these have no display etc.

There are also those instruments which require an electrical connection. I imagine that it would be possible to design these instruments in such a way that when they are connected to the phone line but not to an electrical line separately, they should atleast work like a basic phone instrument without the display and other features which require the additional power. However none of them seem to do so.

Anyway, my question is about this particular model from AT&T - model 1187 - http://www.manualslib.com/manual/10649/AtAndt-1187.html#manual

Is there a way to modify the phone such that it can work without an electrical connection all the time. I am not interested in the display or speaker phone or any other features. Is there any simple change I can do to the instrument easily to make it work without the power cord being connected?


texts: Loop of Icbo for this NPN common emitter biasing circuit

texts:
From what I understand, for an NPN transistor the reverse saturation current Icbo flow can be shown as in the red current loop:

My conclusion was that for an NPN transistor the Icbo does not add up to the base current.

But if we look at to the following common emitter circuit:

In the above case(when the transistor in active forward region) does the Icbo adds up to the base current Ib?
Can you draw/indicate the current path for the Icbo in this case?


texts: Why does CNY70 output peak at a distance only?

texts:
I am using the CNY70 sensor similar as in Understanding the CNY70 Reflective Optical Sensor (FTR: V=3.3V (instead of 5V) R=1k (instead of 200Ω) and X=10k putting the output voltage in the range of 0–0.9V in my measurements):

If I read the datasheet correctly, I would assume that collector current (and thus voltage across the resistor X) peaks when a reflective surface is at 0mm distance:

However in my experiments this is not the case. Voltage peaks at a distance of ~3mm and then sharply declines.
I couldn’t find an explanation for this (other than not using the Kodak paper). I tried this with different surfaces and it reproduces consistently. Any ideas?

x axis: distance to plain white paper (left: 10cm, right: 0mm, not a linear scale)
y axis: measured voltage


texts: How much resistance does the capacitor itself contribute to an RC circuit?

texts: Are the effects of the internal resistance of a capacitor in a non-repetitive RC circuit with an RC time constant of less than a nanosecond significant? I have only been able to find equivalent series resistance ratings for capacitors, which are usually measured at 100 kHz.


texts: Commonmode voltage and measurement with voltmeter and an instrumentation amplifier

texts:
I'm trying to compare a voltmeter and instrumentation amplifier which both measures voltage. Below in Figure 1, Figure 2 and Figure 3 I made these diagrams to ask my question. Basically a device(on the left side in diagrams) has two output terminals A and B. It also has its own ground called SGND. Voltage at terminal A with respect to SGND is 1000.5V and voltage at terminal B with respect to SGND is 995.5V. So the voltage difference between A and B is 1V. So we have a device which has 1V differential and 1000V common mode voltage:

simulate this circuit – Schematic created using CircuitLab

At Figure 1 this device is coupled to an instrumentation amplifier which has its own ground called AGND. Now because SGND and AGND are connected by a wire(I explicitly connected these grounds with a blue wire), then the instrumentation amplifier will see that huge common mode voltages at node A and B as 1000.5V and 999.5V, which will damage it.

At Figure 2 the device is coupled to a voltmeter terminals. But now the voltmeter's COM/ground is not connected to SGND of the device. This means the voltmeter will not see the common mode voltage but only will measure the differential voltage.

Finally at Figure 3 the same device is coupled to the same instrumentation amplifier just in the same way as the voltmeter. Which means at Figure 3 the terminals A and B are coupled to the instrumentation amplifier inputs but AGND and SGND are not connected as in the voltmeter case. I deliberately gave different colors to these disconnected grounds at Figure 3.

Here is my question:

1-) It seems the voltmeter already rejects the 1000V common mode voltage plus it doesn't blow up. But in Figure 2 the amplifier is in danger because of the common mode voltage. So why is an instrumentation amplifier not built in the same way as a voltmeter is? I don't know the inner workings of a voltmeter, so what makes it inferior to an instrumentation amplifier even though it rejected the common mode voltage in Figure 2?

2-) At Figure 3, I cut the connection between SGND and AGND and I read this causes bias currents not to return to the source and the instrumentation amplifier will not work correct. But why doesn't this issue appear in voltmeter's case even though it also has the same way of 2-wire connection.


texts: Implementing Carry look ahead Unit in logism

texts:
I'm quite new to logism and circuits and I have an assignment about implementing a carry look ahead unit. I Just want some help in regards to clearing some of my confusions to carry look ahead units. So from what I understand, A CLA has 3 main parts to it, a Carry input, a Propagator and a Generator. Carry input can be calculated via the following formula:

\$C_{i+1} = G_i + P_iC_i\$

And \$G_i =\$ A XOR B, \$P_i=AB\$

And the what I really need to find out the rest of the carry inputs is just \$C_0\$

Now, as I am implementing my CLA unit in Logism, am I supposed to make different circuits for each carry input? Like for example, for \$C_1\$ I would implement the circuit of \$G_0 + P_0C_0\$ and then another for \$C_2\$, I would implement the circuit \$G_1 + P_1C_1\$, and then concatenate them via a splitter. I ask this because I tried just plugging every variable up to \$C_4\$ and implementing the long expression, only to get things wrong. Any helpful hints is appreciated. Please don't outright give a picture of the CLA implementation as I want to actually do this myself :)

edit: I managed to figure it out. I did indeed have to calculate each carry in and make a circuit for each expression.


texts: Why is this optocoupling circuit useless?

texts:
Could someone explain me why I can't use the same ground when optocoupling?

How can the uC get damaged if there is a short circuit in the phototransistor side?


texts:
Good day,
If you look on google for ARF446/447 in the datasheet you won't find the channel length (in micrometers). I need it to calculate the unity gain cutoff frequency.
Also in the case of IRFP360 it's the same, it doesn't appear in the datasheet and other transistors as well. Is there a catalogue for this?
https://nptel.ac.in/courses/Webcourse-contents/IIT-Delhi/Semiconductor%20Devices/LMB2A/5h.htm


texts: Can I use a plug rated for a DC circuit in a low voltage AC circuit?

texts:
I have an spare 2-conductor plug rated for 12VDC at 5A from an old project.  I’m now working on a Class II low voltage (24VAC) projet for which I need just such a plug.  Is the plug rated for the DC circuit suitable for this, or do I need to look for a plug rated for an AC circuit?

(Since I was asked for a picture, here’s a link to the plug in question: https://www.radioshack.com/products/enercell-2-conductor-accessory-cables)


texts: What are all the reasons that transformers are considered safer?

texts:
I am making a circuit for measuring AC mains voltage and current and I want to avoid using a transformer because it introduces distortions. But everyone says that the circuit will be considered unsafe (without explaining why).

I know one of the reasons for this is that using a transformer separates the neutral and it is harder to complete a short circuit. But this isn't a big downside for safety in a case enclosed circuit (or at least that's what I think).

What are the other reasons? How is using a transformer different than using a voltage divider (apart from the neutral separation)? Is it because of possible malfunction of a resistor causing it to short?


texts: LTC3115 Buck-Boost Converter isn`t able to provide specified current

texts:
Currently I am designing a regulator circuit based on an LTC3115-1 Buck-Boost regulator which should be able to supply a current of 1.5 A for charging a NiMH battery pack with 18 cells (18...28 V).
As a power source there will be a MeanWell GST120A which provides 5A @24V.
Since I am new to the LTC3115 I first built an eval board with the following circuitry to test the LTCs performance. The circuit is a slightly modified application example from the datasheet p. 34.
The frequency is set to 550 kHz and the inductor L1 is 22 µH (Vishay).

Now the problem is that I do not get an output current higher than 800...900 mA. Over this limit the output voltage drops to 0 V likely because the LTC stops regulating.
Yes it says 500 mA output but in the load current diagram on the same page of the datasheet it states > 1.5 A for input voltages > 22 V.
As a load I use a Hameg HM8143 in electronic load mode (current sink).
I also tried the following modifications but without success:

different frequencies (750 kHz, 1 MHz)
different inductors (Bourns 22µH, CTC 33µH)
electrolytic caps at PVin and PVout (Panasonic)
output voltage set to 5 V (Rbot = 240k)
completely new board
different setup as on p. 36 in the datasheet

When the output current is increased to high the behavior is as follows:
(yellow: PVout, blue: FB)

Here you can see the eval circuitry (not necessarily the same config as in the schematic):

I know that it is not easy to find a solution by just interpreting some rough explanations.
It would be super helpful for me to get some ideas of you guys what could possibly be wrong in my setup.
Thanks in advance for any comments, hints or ideas :-)


texts:
When a motor is already rotating, the rotor's mass and velocity carries a momentum and will continue to rotate in one or the other direction to align to the stator's magnetic field as the polarity of coil switches periodically.
Let's consider the simplest brush motor with only one pole as shown in the picture. If the rotor initially sits at rest in perpendicular to stator's magnetic field before current is applied, then once current is applied the rotor can either rotate clockwise or counter-clockwise to align to stator's magnetic field. The initial direction should be indeterministic (or 50% equivalent chance of rotating either clockwise or counter-clockwise).
How are those small DC motors always rotate in one direction unless we reverse supply's polarity?

[EDIT]
Most results I found on Google and videos on Youtube are self-contradictory or straight out erroneous.
Here I provide the diagram for Fleming's left hand rule for motor and the cross section of a 3-pole brush DC motor, where the green arrow indicates the close path of the magnetic field, and right arrow indicates direction of a conventional current.  The coil wrapped around the pole (circled in red) is subject to higher current than other two poles (hence the bias). The magnetic field generated by the coil (circled in red) opposes that from the stator (dark vs. light green arrow). Rotor has to rotate then - but to which direction?

If I apply the Fleming's rule, the force induced by the front section of the coil will get canceled out by that part of the coil that goes behind that pole. Coil on the right will have a force pushing to the left (CCW), canceling out the force pointing right (CW) from the left coil. It's easier to visualize it through the diagram along with description given for F, B, R and L  - all induced Lorentz forces get cancelled in that coil that wraps around the directly energized pole!!

The only explanation I can see for why the rotor has to "move away" from its current position is because the magnetic field generated by the coil (lighter green) goes in opposite direction to that of the stator's magnet. But to which direction the rotor rotates away should be indeterministic. In other words, if I tab the rotor CCW with my finger right before current is applied, the motor will rotate CCW (because I give it that initial momentum), or vice versa for CW rotation.


texts: RC Calculation With Charge Already On Capacitor

texts: Is there a formula for charging/discharging a capacitor which is already charged to a certain voltage?  For example, if I charge a capacitor to 3v, then switch to a 1v power source, how can V(t) be found?


texts: MOSFET Differential Amplifier voltages via PSpice and by hand

texts:
I want to do an analysis on a differential pair and there is  a problem when the pair is in common-mode, at least that's what PSpice says. I find that \$V_{DS}\$ of both MOSFETs is 1.1V and PSpice agrees. However \$V_{GS}\$ is different than my calculations. Here is my circuit:

We have W/L = 10 and my model is the following:

.model nch nmos LEVEL=1 TOX=25 VTO=0.5 KP=140.0e-6 LAMBDA=0.1 PHI=0.6

Am I using the right transistors for this? I calculate \$V_{GS}\$ = 0.594 V. Also since it's an identical pair, shouldn't the voltage at the common-node at the source be 0 and not 98.51mV?


texts: If I want to use a 2-stage opamp for the current to voltage converter application, How should I check for the stability of the circuit? Will it need any kind of stability correction? An uncompensated 2- stage opamp is unstable as voltage amplifier with feedback.


texts:
How could I, a cheapskate hobbyist, generate large currents around 8–10 Amps to run through a short circuit? That is, the objective is to stress test a very low-resistance circuit going through relays, wires, and connectors, all rated for 10 A / 250 V or more.

For example, would it be feasible to build a high-current, low-voltage switch-mode supply?

The load circuit's total resistance will be less than 1 Ω — hopefully a lot less, since at 10 A that would still consume 100 Watts.

I know that people have rewound transformers for huge currents and tiny voltages to melt metallic objects, but that seems hard to do and to control (though I suppose a dimmer on the primary side would do it).

I realised that I could just power a toaster, hot air gun, etc. from mains through the circuit. I would first measure a suitable combination using a power meter, so that the load is e.g. 2300 W when I want 10 A (at 230 V). But this will make noise and heat up my home, so the testing would have to be relatively short-lived. I'd still be interested in a more elegant, laboratory-style solution :-)


texts: How to extract data from an NAND chip with an NAND reader from iphone 6?

texts:
I am not an electrical engineer and I cannot take phones apart.

I had an iphone 6 that suffered no water damage, no smashed screens, no dust... but suddenly it got an NAND memory issue. The phone boot loops and I cannot get my data out.
I am mostly concerned with the photos. I have already sent it to 2 repair places to see if they can get the phone to turn on (this was before we found out the problem), and 2 data retrieval places, of which the last said it was an NAND memory issue. (first one just said it was a memory chip issue).

I really need the photos back. I read about NAND chip readers - my question is, are they worth it, do they work, and how do I go about getting my data back with an NAND reader when I can't do it myself? (Found readers online but I can't open the case myself, nor are my soldering skills good).

Does anyone have any tips?
(PS I live in Australia and yes I have been to Apple support. They were ironically the least helpful and least nice)


texts: Can you split an AC power cord into a 'y' to feed two AC loads?

texts:
I usually work with low voltage DC stuff, like little Arduino circuits and things. I've had no problem powering multiple things from a single power source that need roughly the same voltage (or using buck converters to step things down, or whatever).
However, I recently had a need to have two AC loads plugged into a single outlet. The positioning of the thing sort of necessitated a 'y' shaped power cable, something like this:

I tried to take a couple of extension cords and splice them together like this, but failed in a way that involved blowing a breaker and a lot of smoke. Obviously I was doing something wrong.
I am curious if cords like this are simply just heftier wire and maybe a different solder than I'm used to... or if there's something else going on inside that "splice block" you see there in the middle. Can you just split an AC cord into a 'y' like this or is there something else going on?
I've tried searching for other questions and Googling for the answer, but I don't think I even know the right terms to search for. I come up with a lot of discussion about doing this for DC power, but nothing about AC.

Note: terminology corrected to "AC loads" that I'm connecting to the cable rather than "AC power sources" - however, even though that's not the right term, not knowing that and being able to search under the wrong term is helpful so other beginners like me might find the answer and learn the right term - as noted, I didn't even know what to Google - so... this little "AC power source" explanation block is here for searchability.


texts: In a single-phase transformer output, which-wire would be phase, and which-one would be neutral?

texts:
In a single-phase transformer input, one wire getting entry as live, another as neutral. But what would be in case of its output? In output, which-wire would be phase, and which-one would be neutral?
Is it a possibility that both the output would be "live" (of opposite type) (according to the drawing)? or one will act as phase and the other neutral?
The stepdown transformers I buy from market, for small gadgets, (are not like  those diagrams (as I drawn));  contain a center-tap. I guess, the center tap is used to resemble the neutral wire. is it so? or there is some-other cause behind using that center tap? does same mechanism (center taps) used in high-voltage transformers also?


texts: How to replace TTL PROMs in a design operating at 20MHz

texts:
I am attempting to come up with a reasonable way of implementing a design that was intended for cheap computer applications in the 1980s and which was originally designed to use a pair of TTL PROMs (a 28S42 and a 24S10) to control a state machine and decode state to outputs.  The usual recommendation I see for these devices (which are still available, but at ludicrously high price -- the cheapest I see from a distributor is in excess of £30 per chip) is to replace them with a parallel EPROM, but the fastest EPROM I can find has 45ns access time which is cutting it very fine for the 50ns cycle time I'm working to.  I'd really like to find a replacement part that can match the 35ns access time of the original parts.

What kind of options do I have available?  I've considered switching to an FPGA, but (1) this is a much more expensive solution than I'd ideally like and (2) FPGAs seem to only be available in surface-mount packages with narrow pin spacing, and I'm not really comfortable soldering those.  I've looked at CPLDs, but I can't really tell whether they are suitable for this application: how would I encode the transition table of the state machine, for example?  Are there parallel EPROMs or a similar technology out there that can match the access times of these old PROMs?  Are there other possible solutions to this kind of problem that I'm missing?


texts: How to Calculate UPS Batteries DC to AC Efficiency?

texts:
For simplicity's sake, we will use this APC UPS for example: https://www.apc.com/shop/id/en/products/APC-Power-Saving-Back-UPS-Pro-550/P-BR550GI. It has 330W rating, loaded with 66 Watt-Hour (Volt-Amp-Hour in their site), and 91.7% efficiency when using 20% load (can be accessed from their Efficiency Graph).
Theoretically, the battery can supply 66 Watt for 1 hour. But their Runtime Graph showed that we can only get around 39 minutes with 66 Watt load. It is supposed to have 91.7% efficiency, but we just get about ~65% (39/60 minutes).
Can someone enlighten me where's those remaining efficiency gone to? We have about ~26.7% difference in efficiency here.
Edit #1:
I've supplement material: https://www.apc.com/shop/id/en/tools/ups_selector/home/load/recommendations?power=50&powerUnit=w&operatingVoltage=230&voltageScheme=singlePhase&runtime=120&powerMargin=0&pageNumber=1&sortOption=RUNTIME_ASC
If I need 50 Watt and 2 hour runtime, I can get 5 hour 40 minutes from BR1500GI + External batteries with total Watt 187 + 372 = 559 Watt-Hour. BR1500GI rating is 865 Watt. With total power draw 50 Watt translate to 5.7% load, efficiency ~86%. Rough estimate how much hour we can get from the batteries is 559/50 = ~11.2 hour, but as we can see in the link, they calculate it can only supply power for 5 hour 40 minutes. That about ~51% (340/672) efficiency.


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I have another question regarding output voltage and current of the driver as continuation of my question @ Inductance overheating
Voltage measured on the input of the piezo has a square wave shape on the positive part and sine wave form on the negative side. But the current shows very strange shape and frequency about 160 kHz instead of 80 kHz. Please, I need your help to understand the current shape reasons and to calculate the output power of the driver. It is very important for me. Thanks in advance.

!The blue one is a voltage, and yellow is a current1
Thanks @ Tony Stewart, next week I will receive inductances from Coilcraft with composite cores and can try them out.


texts: Does the databus size matter for determining the range of the memory addresses?

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If you have byte addressable memory, does it matter if you have a 32 bit or 64 bit databus for the range of the memory addresses for the words of the memory?

E.g.
: Assume a 32-bit word. If you have a processor connected to a byte addressable \$2^{32}\$ byte memory,

Would the address of the lowest word be 0 and the address of the highest word simply be \$2^{32}-4\$  (0xFFFFFFFC) regardless of whether your databus size is 32 bit or 64 bit?

What difference would it make when you assume a 64-bit word or a 16-bit word?


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Naive perhaps, but

Why is high input impedance a good thing?
Is high input impedance always a good thing?


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edit: I also found out that with a LM741, that problem does not occur.

edit: First of all, this is not a "should I use LM324 as a comparator or not" question. Besides that, I just wonder the reason for this behaviour. I will paste one of my comments also here, since I think it describes the part I don't understand better.

  However, I don't understand why it is related to opAmp's capability of resposing fast. The output goes 0 as soon as V+ goes below V-. So it looks like it does not have a problem with catching up. Rather, it, not understandably(to me, at least), goes high again while no change occurs in the state of V- to V+.

Why does not output stay at 0 but rises again high? I am talking about the yellow rectangle portion. The signal at the non-inverting input is higher than Vref on the inverting input for that duration. I would expect it to stay at GND as long as V- > V+.

I am using LM324 model from Texas Instruments Website.

Update : For all who might be having difficulties in such applications, I figured out this will be a better solution, after the answer of Marcus Müller.