Over-voltage protection

[Demon]

... in practice :- just after every semiconductor device is destroyed SCR shorts out Fuse

What destroys ICs downstream after the SCR shorts to VSS?

Is it a current surge?

Or reverse voltage?


Robert



EDIT: Added NTC for current surge protection at output, and extra TVS up front (we get a lot of power surges here, hydro lines are not the most stable with so many trees).

EDIT SOME MORE: In keeping with Tim The Toolman's philosophy of "cause we can", I added a Varistor on output.

[richard]

Crowbar protection can be ineffective due to the time taken for it to activate. Everything of value is damaged in the milliseconds before comes in.

[Demon]

What about Zener/Mosfet design?

https://theorycircuit.com/over-volta...ction-circuit/

Darn, not that one either. It protects against reverse polarity.

I saw some earlier, but can't find them now.

[richard]

you could try


but i feel its a no gain process, a good switch-mode supply is cheaper and smaller

[Demon]

you could try ... but i feel its a no gain process ...

I'd really like to learn "something" in this exercise.


The majority of the over-voltage links on the web either point to the naked zener, or zener-SCR and zener-FET. And a LOT of those threads get taken apart in the comments. It's like amateurs acting like they're gurus now.


So I resorted to looking at the corporate sites; they usually know what they're doing, but I ignore them in the past cause it's often so much more complicated than my skill level.


And then I fall on this one from TI:



Technical specs here:
https://www.ti.com/lit/an/snoaa20/sn...FCIRCUIT060079

- 1 IC
- 4 Resistors
- 2 Zeners
- 1 MOSFET

And it includes all the math to convert for 5V (I think).


But I'm faced with the same question, will this design have a delay that won't really save anything sensitive downstream?


Richard, that circuit you buy, doesn't that also have some delay to a certain degree?


I'd be very interested in this IC, only downside, requires 7V in (without knowing more about it yet).
https://www.ti.com/lit/ds/symlink/tl714.pdf
NEVER MIND, 7-12mA.

Robert