[AMPS] Shunt regulated high voltage psu

[Steve Thompson]

-----Original Message-----
From: Tom Rauch <w8ji@contesting.com>
To: amps@contesting.com <amps@contesting.com>; Ian White, G3SEK
<g3sek@ifwtech.com>
Date: 29 January 2002 11:15
Subject: Re: [AMPS] Shunt regulated high voltage psu


>
>> However, it does show that the more you think about screen supplies,
>> the more potential failure modes you see, and the more complex the
>> design becomes to defend against them. Marv's is complex; Acom's is
>> complex; Alpha's is complex; and G4JZQ's and mine is complex. We all
>> did it differently, but we all agree that a handful of cheap zeners
>> won't cut it.
A couple of thoughts. MOVs are widely used to clamp screens in the event of
a flashover. At 10s amps, the clamping voltage will be in the regions of
600V for a 375V MOV. Many designs survive this ok, but I wonder how many
times it's luck rather than design. There can be hidden side effects - for
example, if the supply has a series element using a Nchannel FET, there's a
big parasitic diode which will carry the 600V from source to drain.
Similarly, a bipolar series element will suffer reverse emitter base
breakdown and make 590ishV available at the base.

Steve


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