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Re: [Amps] HV Switch Mode Power Supplies

Subject: Re: [Amps] HV Switch Mode Power Supplies
From: Ian White GM3SEK <>
Reply-to: Ian White GM3SEK <>
Date: Sun, 26 Jun 2005 23:35:46 +0100
List-post: <>
Will Matney wrote:
>I would think it would be easy as some of the large commercial switch 
>mode supplies work with feedback regulation. It would be just a form of 
>a voltage regulation circuit like used on everything else I would 
>think. Adding a bleeder resistor to drag it down would be prett 
>wasteful after I looked into it. A 4000 ohm 250 watt resistor would do 
>it to get 250 mA.. Only thing is this wastes power just to get it down 
>some. Here the problem is that by viewing the curve, at 250 mA, there's 
>a 500 Vdc swing. For say a 300 volt swing equivelant to about 13% 
>transformer regulation, there would need to be a 400 mA draw from a 
>bleeder. That's a bunch! I'm not sure how accurate this curve they have 
>published is though.
The point K5AND was making is that you don't needed a bleeder, so no 
power is wasted.

When the amp is on (TX), the standing current in the PA tube brings the 
voltage down to the level where the regulation is quite good. When the 
amp is off (RX), the HV supply is switched off completely. On 
switch-over, the supply comes up in milliseconds so it's part of the 
normal RX-TX sequencing.

73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
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