op amp to mosfet output destroyed

g2c · Sunday at 7:21 PM

danadak said:
This may have been the casue of failure :

View attachment 148071

View attachment 148072

If the Inv input was taken below its supply rail,. with no current limit, would have fried
the input structure thru the forward biased Zener acting as a simple diode when v+ goes
more negative than a diode drop.....Fix would be a series R to Inv input, say 1K ohm from
junction 12K and zener anode.

Sorry, my V+ and V- are misleading. Should have written non_inverting < inverting, when the battery becomes full

g2c · Sunday at 8:09 PM

the whole 'home' system with 20AH battery. This here with the 'lo_v disconnect' original version.

Nigel Goodwin · Sunday at 11:59 PM

g2c said:
I didn't think I needed any as it essentially a dc thing with slow ~.5Hz 'pompings ' by the maintainer. Only ac fluctuation when it disrupts / re-establishs power and i didn't see any changes with decoupling of the amp supply

All electronic circuits require them, the entire premise of electronics is that the supply rails are at the same AC potential, and that's what the decoupling capacitors do - leaving them out will affect operation, and could cause potentially damage as well. It's not something you can just leave out.

Tony Stewart · Monday at 1:56 PM

I hope you understand that this configuration as a switch loses 3V from the supply and heats up the FET by switching V+ rather than switching from the drain to V- of the load.

ZipZapOuch · Monday at 2:30 PM

Tony Stewart said:
I hope you understand that this configuration as a switch loses 3V from the supply and heats up the FET by switching V+ rather than switching from the drain to V- of the load.

3V? How are you calculating that? I see an 800mA load and 20mOhms of R(on), so only 16mV. Now you show yours.

g2c · Tuesday at 2:09 AM

Nigel Goodwin said:
All electronic circuits require them, the entire premise of electronics is that the supply rails are at the same AC potential, and that's what the decoupling capacitors do - leaving them out will affect operation, and could cause potentially damage as well. It's not something you can just leave out.

did as your recommend
The whole ups with the lov_disconnect improved by electro-tech-online

danadak · Tuesday at 2:26 AM

The electrolytic you added seems to have a bulging top, although
pic not well focused. Thats a sign of cap failure.

Regards, Dana.

Nigel Goodwin · Tuesday at 2:43 AM

danadak said:
The electrolytic you added seems to have a bulging top, although
pic not well focused. Thats a sign of cap failure.

It's only a sign of a 'possible' failing capacitor, many electrolytics are manufactured with a slightly bulging top, not all are flat.

danadak · Tuesday at 3:37 AM

many electrolytics are manufactured with a slightly bulging top

Curious, how many and what vendors are accepting / passing these as
good for sale ? Who do you know thats doing this ? I wonder what
tolerance / deviation from mechanical plane, manufacturers have.

Tony Stewart · Tuesday at 7:14 AM

ZipZapOuch said:
3V? How are you calculating that? I see an 800mA load and 20mOhms of R(on), so only 16mV. Now you show yours.

FET 101 laws apply. Both Drain and Op Amp R2R to 12V. Click the switch then reply. https://tinyurl.com/2bnjqn6w

Tony Stewart · Tuesday at 7:22 AM

Slightly domed lids are a sign of gas pressure events. This starts to evaporate C then oxidation causes a rapid rise in ESR which terminates usefulness.

ZipZapOuch · Tuesday at 8:45 AM

Tony Stewart said:
FET 101 laws apply. Both Drain and Op Amp R2R to 12V. Click the switch then reply. https://tinyurl.com/2bnjqn6w

https://tinyurl.com/2bnjqn6w
FET 101 laws? I'm not sure you need to go that far to fix your error.
It's possible you need to look at an earlier, more basic "Law". Like, "Reading Schematics 101 Law", or, "Garbage in, Garbage out" Law. Or, my favorite, "The person who yells loudest or has the flashiest graphics is rarely right" law.

Take another Peek at the OP's circuit. You may Pee yourself once you notice your error and aPologize for your Poor reading skills and/or incorrect assumPtions.

Tony Stewart · Tuesday at 9:25 AM

my bad

ZipZapOuch · Tuesday at 9:43 AM

Tony Stewart said:
High side Nch FET drivers need a boost voltage to act as low dropout switches,.

That's why the OP didn't use a Nch Mosfet

Edit: I'm really amazed that this hint wasn't assumed to be a hint.

ZipZapOuch said:
Take another Peek at the OP's circuit. You may Pee yourself once you notice your error and aPologize for your Poor reading skills and/or incorrect assumPtions.

Tony Stewart · Tuesday at 11:57 AM

g2c · 2024-12-18T13:09:46-0800

danadak said:
The electrolytic you added seems to have a bulging top, although
pic not well focused. Thats a sign of cap failure.

picture deleted

Regards, Dana.

Thanks, Below an in site picture with flash. Indeed a bit more convex than his friends. All are of brand samxon, marked 100uF. This one showed 60uf on a dvm. The other 3 I still have all measure ~90uF. Should I replace it?

danadak · 2024-12-18T13:36:24-0800

I would replace.... Looks like a crack in aluminum back triangle point area.

Nigel Goodwin · 2024-12-18T15:05:52-0800

g2c said:
Thanks, Below an in site picture with flash. Indeed a bit more convex than his friends. All are of brand samxon, marked 100uF. This one showed 60uf on a dvm. The other 3 I still have all measure ~90uF. Should I replace it?

If it reads low on a capacitance meter, then it's seriously duff, 60uF is well past it.

The actual failure mode is usually high ESR (this is by FAR the most common failure in electronics over the last 20+ years), and the cap is usually completely gone while it still reads within it's correct capacitance value. For this reason a capacitance meter is of little use, and an ESR meter is essential for repairs.

Presumably you used a capacitor taken out of something else, you should NEVER use electrolytics taken out of old equipment.

g2c · 2024-12-19T09:18:35-0800

danadak said:
I would replace.... Looks like a crack in aluminum back triangle point area.

I replaced it.
I must note your extraordinary sense of observation for having seen the concavity on that off focus picture. Also, thanks for the tip on identifying electrolytic defective caps!

g2c · 2024-12-19T09:24:36-0800

Nigel Goodwin said:
Presumably you used a capacitor taken out of something else, you should NEVER use electrolytics taken out of old equipment.

Not cannibalized cap. These was bought from futurlec.com, my preferred online passive- components store. They are of the brand samxon

op amp to mosfet output destroyed

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