Re: SCR power supply (fwd)

To: tesla-at-pupman-dot-com
Subject: Re: SCR power supply (fwd)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Mon, 19 Jan 1998 09:53:08 -0700 (MST)
Approved: mod1-at-pupman-dot-com


---------- Forwarded message ----------
Date: Mon, 19 Jan 1998 08:52:18 -0800
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: SCR power supply (fwd)


> 
> ---------- Forwarded message ----------
> Date: Mon, 19 Jan 1998 01:38:18 -0700
> From: Scott Stephens <stephens-at-enteract-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: SCR power supply (fwd)
> 
> At 08:37 PM 1/18/98 -0700, you wrote:
> 
> 
> 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.
Not really short out the SCR, just put a reverse bias on it long enough to
drop the current to zero to turn it off. And yes, there is a UJT oscillator
driving a flip flop to generate the trigger pulses in complementary
fashion. There are is also a lot of circuitry to create the proper trigger
pulse for this application (big spike at beginning, then a long back
porch). Hey, if it were simple, everyone would do it.

> 
> 
> Maybe 10's of KHz, if you wan't the SCR's hot, and have magnetics and low
> ESR caps.
Haven't built or designed one of these, so never went into the precise
timing analysis, but my gut feel was that, particularly at high powers (>
10 kW), an SCR just won't switch fast enough..
> 
> 
> 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.

Well, sure, you save a bunch on core metal, which is why the Xray machine
does it. It makes a 3000 pound machine into a 300 pound machine. It would
also make the output filter easier (not an issue for the Xray PS). I
suspect that cooling of the windings begins to be more of an issue without
all that iron to soak up the I2R heat.
> 
> Of course, SCR's can handle BIG power! :)
> 
no kidding... REALLY BIG power. kA at kV in one relatively inexpensive
device.