Author Topic: High side LVD mod?  (Read 1933 times)

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Offline MadScientist267

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High side LVD mod?
« on: April 18, 2012, 08:11:18 PM »
Ghurd... Buddy, pal... LOL Ok enough with the formalities...

What I need is something that works as well as the original controller, but switches the high side instead of ground.

I've had a few ideas as to how to go about this, but wanted to run it past you since you have these things dialed in to a science.

What comes to brain about this concept? :)

Steve
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Offline Janne

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Re: High side LVD mod?
« Reply #1 on: April 19, 2012, 06:06:38 AM »
A relay? P-channel FET? SSR?
Just throwing some ideas to the mix... I think it largely depends of the load you want to disconnect.
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Offline ghurd

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Re: High side LVD mod?
« Reply #2 on: April 19, 2012, 06:47:43 AM »
Janne is correct.

There are a couple things out there with high side switching.

Standard controller, except a few tweaks so the power fets are P channel.
If it would help, I can make up a sketch in the next few days.

Good power P-fets are hard to find, and expensive.
G-

Offline MadScientist267

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Re: High side LVD mod?
« Reply #3 on: April 19, 2012, 10:25:56 AM »
Agreed, but luckily for me, they don't need to carry a whole lot of current. Any tranny that can handle 5A (to be safe) will work just fine.

I'm looking at a few possibilities, and yours is definitely one of them. Another is a LM339 based design, since I actually have 4 separate points that need to be monitored. Easy to set up the brain on a relatively small perf board with the threshold/hysteresis pots, and farm out the trannies to another board or boards.

The big thing is that they have almost no "operating" current. Efficient as possible is the primary concern. So that rules out things like standard relays. SSR maybe, but voltage drop is a concern on a couple of these. The P channel MOSFET is also the best method I've come up with so far as well, since I can also easily "slave" them to control more than one point in the system from a single LVD controller.

Any ideas/thoughts/caveats that anybody has are of course greatly appreciated.

Steve
Wanted: Schrödinger's cat, dead and alive.

Offline ghurd

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Re: High side LVD mod?
« Reply #4 on: April 22, 2012, 09:28:07 AM »

and farm out the trannies to another board or boards.

Any ideas/thoughts/caveats that anybody has are of course greatly appreciated.


Gate balast resistors.
If you get anything funky going on somehow, they can help save the fets... I think.
G-