Author Topic: Overvolt input protection  (Read 724 times)

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Offline JustMeHereTopic starter

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Overvolt input protection
« on: February 25, 2020, 02:53:07 am »
So I just hit the wrong button on my bench power supply and switched from 5v to 30v. (Don't ask how because there is a safety to prevent this.)  Needless to say I made the magic smoke.

What's a good and cheap way to protect my circuit?   I found an IC, but I was wondering what is best.  Simple MOV? TVS diode?  I'm looking for opinions with pros and cons.
 

Offline digsys

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Re: Overvolt input protection
« Reply #1 on: February 25, 2020, 03:36:33 am »
I've always just used a polyfuse and pretty much any of the above, depending on how accurate a voltage you want to allow. All have some sort of temp / current / time variation. IF you want it exact and instant, then a VRef device and SCR (plus the poly) is by far the best option.
Hello <tap> <tap> .. is this thing on?
 

Online Ian.M

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Re: Overvolt input protection
« Reply #2 on: February 25, 2020, 05:02:22 am »
IF you want it exact and instant, then a VRef device and SCR (plus the poly) is by far the best option.
A classic 'crowbar' circuit.  See fig. 22 in  the T.I. TL431 shunt regulator datasheet.   N.B. The TL431 crowbar is not well suited to operation at low supply voltages as the TL431 tends to have an on-state Vak of 2V or higher depending on the current, so there isn't much headroom to reliably trigger a SCR on a 3.3V rail.   If you can tolerate a 3.6V trip threshold it should be workable, but if you need to crowbar lower voltage rails than 3,3V look elsewhere.
« Last Edit: February 25, 2020, 05:04:01 am by Ian.M »
 


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