SCR power supply (fwd)

From: 	Scott Stephens[SMTP:stephens-at-enteract-dot-com]
Sent: 	Monday, January 19, 1998 2:38 AM
To: 	Tesla List
Subject: 	Re: SCR power supply (fwd)

At 08:37 PM 1/18/98 -0700, you wrote:

>> A while back I ran across a book on induction furnaces. In the book was a
>> short discussion on using SCR's in a circut like a multivibrator  to
>> provide power for an induction furnace. The book was vague about the
>> circuitry involved but it did allude to a circuit that (1) provided back
>> EMF to shut off the SCR and (2) provide a trigger pulse to fire the SCR
>> the oppsite polarity. 
>My GE Xray machine power supply uses a pair of high power SCR's to make a
>500 Hz inverter at 100 Amps, 100 V.  It's pretty simple. The center tap of
>the transformer primary is connected to one side of the power. The SCR's
>switch the alternate sides of the transformer to the other side of the
>power. A capacitor across the whole winding provides energy for
>commutation. I am grossly oversimplifying here. If you email me your fax #
>or snail mail address, I'll send you the schematic.

I will add that the cap and triggered SCR short out the opposing SCR (which
is currently ON). You need a flip-flop, or comlementary driver to trigger
the SCR's.

> don't know what the upper frequency limit for tis
>> type of circut is, 
>limited by the commutation speed of the SCRs and the magnetics of the
>circuit, i.e. low (a few kHz at most)

Maybe 10's of KHz, if you wan't the SCR's hot, and have magnetics and low
ESR caps.

>but I'm thinking that it may be a way of generating
>> power at high enough frequency to make it cost effictive for us coilers
>> a budget. If any of you have run across this application, any information
>> would be helpful.....Thanx               Al Syme   KG0QJ

I thought the circuit would be a clever way to turn 60Hz transformers into
600Hz transformers, but from what I've heard about transformer fragility,
probably a very bad idea. Only usefull if you wrap your own, custom transformer.

Of course, SCR's can handle BIG power! :)