how to protect FET against overtemperature?

[hul]

I'm going to build this charge guard:
http://mujweb.cz/www/coro/Detaily.htm
but would like to add overtemperature protection for the FET (FET needs to turn off if its temperature is high).

What's the easiest way to do this?

Thanks, Hans

[Acetronics]

:) Hi, Hul

simply use TempFets from Infineon ...

refs are BTS 100 to 240 ...

Alain

[hul]

thanks, didn't know such a thing existed...

Just out of interest, how would I do it with external components?

Hans

[Acetronics]

Hi, Hul

See here for details ... very simple, indeed !

http://www.infineon.com//upload/Document/cmc_upload/migrated_files/document_files/Application_Notes/anps040e.pdf

Alain

[hul]

Thanks again, Alain. I will use a temperature protected FET for that circuit in post #1. Bought a VPN35N07 today (can't get the TempFETs off the shelf here) thanks to your tip.

But what would I do if I wanted to protect a conventional (unprotected) FET? This would be necessary if higher voltage capability were needed.

Hans

[Acetronics]

;)

very convenient devices are the RXE or RUE Polyswitches from RAYCHEM ... or equivalents

for Tempfets ... one paralled to other Fet's is sufficient. just have a thermal coupling !!!

Alain

[hul]

one paralled to other Fet's is sufficient. just have a thermal coupling
I was worried about that. The TempFet trips at 150degC; the load carrying FET would be hotter. Possibly too hot?

NTC or PTC resistor aren't used for this?

Hans

[coro]

I was worried about that. The TempFet trips at 150degC; the load carrying FET would be hotter. Possibly too hot?

NTC or PTC resistor aren't used for this?

Hans
As I hope I did understand Alain and the TempFet datasheet, it will short its gate with source when thermal activates, which will stop also all other paralleled fets. Only need to be sure that TempFet will have similar temperature as others.
There can be problem with current limit, the accidentaly destroyed fet will mostly remain shorted.

[Acetronics]

Hi, coro

I'm really sorry, but I don't have the Fet shouting " Heeeeelp" or "papa, mamma " :D

:rolleyes: next century, maybe ?

Alain

[coro]

:) ... I've got one... just with with piezo alarm paraleled on it.
In this module it's screaming something about charger setup or quality..?,
but I really can't say exact words. :)))