27 votes

Suicidal ASUS power brick?

That's the power factor correction circuitry. The FET Q1 will be switching at high frequency so it won't short rectifed 300V to 0V as there are inductors in the path, most likely L4 is the boost ...
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24 votes
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What would it take to make a PS/2 keyboard interface hot-swap?

Somehow, un-plugging or plugging in a keyboard can cause a surge. I don't recall having these issues with serial ports (RS-232, Appletalk, etc), parallel ports, VGA, etc. These don't power the ...
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  • 57.5k
24 votes
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Suicidal ASUS power brick?

As the other answer points out this looks like active power factor correction. Power factor is the ratio of real power (short-term average rate of net energy transfer) divided by apparent power (RMS ...
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  • 19.2k
23 votes
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Varistor? Purpose and principle

This is an NTC current limiting resistor. When plugging in the circuit, the NTC is cold and a bad conductor - this is limiting the charge current to the input capacitor. When the NTC is hot from the ...
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  • 8,613
22 votes

Can lightning strike into the phone line damage electronics in the house through the ADSL modem?

There are many 'entry points' to your house for electrical disturbances, once lightning has struck close by, and the most important of these is the mains. A nearby strike will lift the ground ...
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  • 140k
19 votes

Varistor? Purpose and principle

It’s likely a negative temperature coefficient device used to limit inrush current into the bulk storage capacitor and prevent fuses blowing or breakers tripping. It’s quite a common thing to ...
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  • 379k
18 votes

Zener Diode for overvoltage protection

You could consider a Transient Voltage Suppressor (TVS). They are basically diode arrangements that are intended to protect circuits like yours from over/under voltages. Since they are designed to ...
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  • 624
15 votes
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Is it Safe to Plug an Extension Cord Into a Power Strip?

To be honest, I do it all the time. However, there are some things to keep in mind: Never exceed the maximum power, current and voltage. Voltage will normally not be a problem since this is (more ...
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12 votes
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Is there a reason for the shape surge arrests have?

It is to increase the length of the surface path from one side to another. The surface is more conductive and has lower spark voltage than the middle of a material (because it can be coated with dust ...
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  • 6,460
11 votes
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Difference between ESD and TVS diode?

A TVS diode is typically capable of much higher power than ESD diodes. TVS - "Transient Voltage Suppression" can, if rated accordingly, be capable of suppressing surge pulses - these are ...
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  • 1,640
10 votes
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Polarity of gas discharge tubes

Photo attribution:By Ceinturion 17:47, 19 August 2007 (UTC) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2587926 Small dot indicates "gas-filled". Likely at sub-...
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  • 18k
10 votes
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Discharge risk of an LED fade-in circuit

There is no danger to the LED from removing the voltage source V1 or shorting it to ground. The LED itself limits the voltage across the capacitor, i.e. if it was safe while the voltage source was ...
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9 votes

Can all surge protectors wear out, and how would you know if this is the case with the surge protector you have?

It truly depends whether your surge protector contains MOVs or not. The wear mechanism for a MOV is that the clamping voltage DECREASES slightly every time the MOV is required to clamp a transient. ...
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9 votes

Is this TV power supply board damaged?

Those two main filter caps definitely look bad, as though the electrolyte has boiled away. I'd try replacing them next.
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9 votes
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Surge protector helped me discover bad wiring at home -- neutral and line swapped; should I be concerned?

Yes, you should care. The electric code is generally designed so that it takes two independent failures before you get shocked. In you're apartment, one is already used up by the line and neutral ...
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9 votes

Connecting TVS before or behind Ethernet transformer?

Interesting question. In reality it probably does not matter much which side you put them on, however there are pros and cons to both. Connector Side PRO: As a general rule of thumb you want ...
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7 votes
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Why does the power light on surge protectors flicker

What you took from the discussion is roughly correct. Neon lamps wear out. The brighter you make them (the lower the value of series resistor) the shorter their lifetime. For example, the ubiquitous ...
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7 votes
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Lightning surge protection

Most surge protectors are made to handle 'transient events' caused by other devices in a power distribution system, such as an un-controlled voltage spike from an improperly switched inductive load (...
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7 votes

Is it Safe to Plug an Extension Cord Into a Power Strip?

If you only plug low current devices into the extension cord there should be no problem. In any case, you need to keep the total current requirements of everthing plugged into the surge protector and ...
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7 votes

Is it Safe to Plug an Extension Cord Into a Power Strip?

I'll add some information to what Michael and Peter wrote in their good answers. You are right about lots of warnings being written everywhere on the subject. This is some sort of scarecrow tactic ...
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7 votes

Can lightning strike into the phone line damage electronics in the house through the ADSL modem?

Back in my hardware days, I was a technician repairing modems for a modem manufacturer. I repaired many modems hit by lightning strikes. They all had a couple large resistors connected to the phone ...
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  • 71
6 votes

Why is daisy-chaining surge protectors not recommended?

Re a few of the responses, supposedly from knowledgeable engineers . . . . Daisy chaining surge suppressors (running them in series) would not increase or decrease their current interrupting ...
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6 votes
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Preventing Arduino from getting lightning strikes and protecting it

By the fact you're using an Arduino I suspect your project is not done in a professional framework, but it is some hobby or research project, i.e. something with relatively low budget. Please, correct ...
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6 votes
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Zener Diode for overvoltage protection

For over-voltage protection of signal lines a zener diode is generally a poor choice. You haven't given enough details of your application for me to give many specific reasons, but you should consider ...
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  • 5,185
6 votes

Short life of LED parallel to Solenoid as indicator

The LED may already have a series resistor, the OP states that it is "rated" for 12V. I suspect so because without current limiting an LED wouldn't last a second with 12V across it. In that case it ...
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  • 19.5k
6 votes
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How much surge protection do external power supplies provide?

There are two kinds of surges, differential-mode and common-mode. A differential-mode surge means that the voltage difference between line and neutral rises to an abnormal value. This type of surge ...
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  • 164k
6 votes
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On a wire designated as '3x14AWG' what does the '3x' part mean?

'3x' = 3 of. It is specifying a 3-core cable with 14 AWG conductors. These will be L, N and E or live, neutral and earth.
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  • 159k
6 votes

Should I buy a diode with higher maximum ratings if it costs the same?

Yes, you can substitute a higher spec part for a lower spec one for a case like this. The second question, however, is a bit trickier. The data sheet you referenced has this graph: So as you can see,...
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