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Re: HV supply regulation

Tesla List wrote:
> 
> Original Poster: "rwall" <rwall-at-gateway-dot-net>
> 
> 1/10/99
> 
> Greg,
> 
> Would you go more into detail on high voltage DC active regulation?  I am
> building a 7 kV 1.0 A DC power supply with a bridge made of four 872A
> rectifier tubes.  I am going to use big chokes and big filter caps for
> regulation.  How can this power supply be actively regulated to say 1%?
> 
> RWW
> ----------
> 
> > Avoid the big DC filter cap if at all possible.
> > If you really need 1% stability, active regulation
> > is far simpler, and more accurate.
> > --
> >
> >
> > -GL
> > www.lod-dot-org
> >

Richard,

You could consider a hard tube shunt regulator scheme exactly like they
used in the old color TV sets.  Here they employed a 6BK4 HV triode. 
The cathode was basically tied to supply ground (neg)with a series
resistor to establish cathode bias and the plate went directly to the HV
positive load terminal.  A dropping resistor was either employed between
the load(CRT ultor)/shunt regulator and the supply, or the supply was of
sufficiently high impedance that they didn't bother (you will definitely
have to employ one).  A restive divider stack sampled the high voltage
and a low end tap (actually a voltage set pot in series with the bottom
of the divider) drove the control grid of the shunt regulator triode. 
If the high voltage across the load went more positive, the shunt
regulator grid would be driven more positive (or less negative
referenced the cathode) and the tube would conduct more heavily, putting
more drag on the HV supply and lowering the voltage.

I think you could do a big version of this using a transmitting triode
tube like perhaps a 3CX10000D, or a tetrode like the 4CX10000D.  These
tubes will handle up to 3 amps on the plate at up to 7500 volts.  

I would expect the tetrode might be better because the control grid has
much higher gain (you want a sharp cutoff tube).  You might best supply
the screen from a resistive divider to ground from the tube's plate
terminal.

What you would in effect be doing is achieving regulation by employing a
"smart load".

Robert W. Stephens
Who likes big toobz