Re: Making square wave AC from DC? (inverting)

So you plan to connect 10 transistors in parallel to drive one leg of your output waveform? There may well be a problem with thermal runaway. No two physical devices are actually 100% identical. If you have two transistors fully "on" then one's conductance from collector to emitter will be slightly different from the other. In other words, one transistor will conduct slightly more current than the other. All solid state devices will change conductivity as they heat up -- some will become more conductive, some less. If your devices become more conductive as they heat up, then the one that starts out carrying an infinitesimal amount more current can wind up trying to carry it all, and blowing, and then they can all fail zipper-fashion. Google on "thermal runaway".

That's the only thing I can think of. You will have to be a little careful of your triggering circuit.

GWE (once an electronics engineer)

Ignoramus11916 wrote:

Let's say that I have a source of high current 300A 40V DC. Let's say
that I want to make square wave AC from it. I am thinking about
building a device on the cheap that could do it.

I could buy 40 power transistors like these:

http://cgi.ebay.com/2N5302-Power-Transistor-30A-60V-NPN-Qty-10_W0QQitemZ7543195186QQcategoryZ4666QQrdZ1QQcmdZViewItem

Item 7543195186

Say I have DC inputs A and B. Say I want square wave AC on outputs C
and D. All I need is connect A to C through 10 transistors, A to D
through 10 transistors, B to C through 10 transistors, and B to D
through 10 transistors.

I would then make appropriate AC input to signal input of transistors
so that A to C and B to D are turned on when AC signal input is
positive, and A to D and B to C are turned on when AC signal input is
the opposite.

That would generate a square wave AC between C and D.

The cost of this project, not counting time expense, would be around
$60 or so. 

Are there any fatal flaws with it?

Would this be sufficient to use it in welding applications?

i

.

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