H-bridge blowing up in my face...

Thread Starter

cmartinez

Joined Jan 17, 2007
7,510
Dissipating heat is not a real problem in this particular case. The valve will be activated only about once or twice a day, and the duration of the activation pulse is in the range of 150 to 200 ms, so not enough heat will accumulate for it to become a menace.

I've just looked up the ptc fuse you've suggested, it's a very interesting alternative of which I was unaware of. I'm going to give it some consideration.

Many thanks!
 

picn00b

Joined Feb 6, 2020
5
As for "keep your face out of circuits when powering",
as things like that sometimes happen with some delay, and it's hard to keep the face away when inspecting stuff:

A pair of ballistic glasses is what I use ;) And I'm not kidding. I also tend to use them when soldering, to not get biting fumes or little flying balls of flux and stuff into the eyes - but holding a slipping away soldering iron at bay for at least a short impact is also not something I'd complain about.
 

Johnfoxwell

Joined May 23, 2021
4
From your data sheet. Gate-Source maximum is +/-8v and Drain-Source is 12V. You are running the circuits from a 16V volt supply. I would use a larger margin of safety and choose a FET that has the maximums significantly above 16V.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,510
From your data sheet. Gate-Source maximum is +/-8v and Drain-Source is 12V. You are running the circuits from a 16V volt supply. I would use a larger margin of safety and choose a FET that has the maximums significantly above 16V.
Good catch, thanks for that. I actually built the original circuit using DMG2302U-7 nFets on the bridge's low side, which have a 20V rating drain to source. Somehow I forgot to update that detail in my sim.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,510
I actually worked with an engineer that would lift the soldering iron to his nose and sniff it to see if it was hot. Saw him with a blister on his nose once or twice.
:oops: ... well, I guess that's fine as long as he never used someone else's nose for that ... :rolleyes:
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,510
For the record. I decided to build the circuit in post #26. Maybe later on I'll build the super-simplified version of it, but right now I have to make sure I'm on the safe side of things.

The circuit is working as expected, and the transistors are not even warming up at all.
 
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