[Amps] Screen voltage regulation

[Radio WC6W]

On Wed, 12 May 2004 20:34:48 +0200 "Thomas Hoeppe"
<thomas.hoeppe at asamnet.de> writes:
> Hello guys,
> 
> I am new on this reflector, so may be I am asking a question whitch 
> has been discussed before.
> I am looking for a simple design for the regulation of a screen 
> supply. I need 800V and about 50 mA. I will have to take care of 
> some negative current, so the supply has to be able to do that or I 
> will use a 100mA supply and allow 50 mA of current through a 
> resistor to ground. My anode voltage is 5 KV, so I don't want to get 
> the G2 voltage from the anode voltage. 
> 
> I am looking for easy and rugged solutions. (KISS.......keep it 
> simple and stupid!) 
> 
> Any ideas?
> 
> Thanks in advance.......
> 
> Tom, DJ5RE (DL0AO crew)

Hi Tom,
   This is probably not the answer you seek but, I'm considering a
bidirectional Cuk converter for that spot in a project here.

   I already have a switching supply for heaters, grid bias & control
power so, I can source the converter from the available 300 volts on the
switcher primary.

  Running at 100 KHz, it only takes a small transformer, and a couple
each small chokes, capacitors, small FET's (IRF820's) plus a PWM control
IC (3525) to implement this scheme.

  I'm using a 1:1 transformer in my application for a 375V Screen.   A
2.5:1 part would better serve your 800 volt needs.  You would also need
to use a 1KV FET on the Screen side of the converter.

  The output is adjustable & regulated.   The output FET of the converter
will have an additional gate R to clamp the Screen V to ground in the
event the PWM drive fails.   I also have a separate SCR crowbar circuit
to protect the Screen... just in case. 

  This approach runs with 90% or so efficiency, requires no heatsinks on
the FET's, nor any bleed current.

73 & Good morning,
   Marv  WC6W








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