Electrical Engineering Stack Exchange
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1500 questions
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1 answer

Unusual chemical reaction on PCB (SMPS circuit)

I have a PCB with smps circuit on it 220V to 5V (using Viper22a). Here is the schematic: And here is the board layout: In the yellow circle region, I am seeing some sort of white deposition in a few PCBs(bottom layer). Please see the images…
Whiskeyjack
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2 answers

Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors

The Raspberry Pi B+ models have a protection circuit between the USB connector and the 5V net on the board. They recommend putting a similar protection circuity on a Pi HAT before 'backpowering' the pi through its GPIO header along with a polyfuse.…
Mark Walker
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2 answers

Resistance Vs Impedance?

What is the difference between the Resistance and Impedance? When we will say it is an Impedance and when we will say it as an Resistance? Can you explain it with diagram (If possible) and real time example. And how the reactances will form in…
Gouse Shaik
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28
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6 answers

Ferrite bead vs common mode choke

simulate this circuit – Schematic created using CircuitLab I inherited the top circuit from a previous designer on my robotics team. The circuit uses two ferrite beads, a zener, a TVS and a capacitor to filter incoming power. The incoming power…
vini_i
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3 answers

Spectrum of a LED

As I understand it a LED emits a photon when an excited electron falls back to a lower orbit, and this is always the same energy (read: wavelength). So then why is the spectrum of a LED a bell-shaped curve instead of just a line (maybe a couple of…
Peter Galleyn
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28
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3 answers

Is MOSFET gate threshold voltage a limit or minimal "Full-on" switching voltage?

I've been shopping for some mosfet transistors, for a starter kit, and noticed listings that state a mosfet is suitable for 5v logic, but the data sheets says Gate Threshold is 1-2v. 4v gated mosfets, which are closer to 5v, by the same seller are…
Zero
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28
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5 answers

Standard PCB Layout Book

Are there any good references on advanced PCB design/layout/routing? There seems to be a large wealth of circuit design books, books about RF PCB design, and books dealing with high-speed digital design. None of these books are what I'm talking…
Joel B
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How does a NOT gate generate power?

I know that a NOT gate always inverts its input. When the input is "ON" I can imagine the gate stopping the flow of current. But how does the gate generates flow of current when the input is OFF? Please could you explain how this happens as simply…
The King
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4 answers

How can I rename a Sheet in Altium Designer?

I'm trying to rename a schematic sheet file inside Altium Designer 14 (in Project Panel). The only way I can do it is renaming the sheet file in Windows Explorer and relink the file to the project. This is very time consuming and unproductive. I…
RHaguiuda
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4 answers

Very long distance Ethernet connection for internet and other data (2000 feet)

I am building a house. It's located about 2000 feet away from the nearest internet cable. I had to run our electrical service underground the whole way, and have already installed a conduit for internet/phone cables from end to end with pull points…
Ryan Griggs
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1 answer

How does a ball mouse know the direction?

Foreach axis on a mechanical (ball) mouse there is an IR transmitter and receiver pair with a wheel that looks like having only simple slits. How is the direction calculated?
zaf
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28
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6 answers

Why exactly do chips start malfunctioning once they overheat?

Once a chip overheats it can start malfunctioning - for example many programs may start failing once some or all parts in a computer overheat. What exactly happens that makes chips malfunction when they overheat?
sharptooth
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3 answers

Mounting hole on a PCB

Here is a picture of 3 mounting holes on three different PCBs. The red one is what I prepared on Eagle CAD and used "hole" button on the left side menu , something like this: Do I need to use "via" in order to have the same style mounting hole…
Angs
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4 answers

Do "blown" fluorescent lights still use electricity?

When a fluorescent light fixture goes out, it often flickers and then after a while stops shining altogether. When this happens and when it finally dies is the circuit broken and does it still use electricity? I don't understand too much what…
PressingOnAlways
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8 answers

How do USB charging and "smart" charging ports (e.g. Anker's PowerIQ) work?

Software engineer with a hobbyist understanding of EE here. I've noticed lately lots of claims from producers of USB battery packs that their ports are "smart" and "identify the device" to "deliver the maximum current for the device." A cursory look…
Kevin Wood
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