-----Original Message-----
From: Tom Rauch <w8ji@contesting.com>
To: amps@contesting.com <amps@contesting.com>; Steve Thompson
<g8gsq@qsl.net>
To: <amps@contesting.com>
Date: 13 April 2001 01:16
Subject: Re: [AMPS] Zener screen supplies
snip
>> One advantage of an 'electronic' screen supply is that you can build
>> in a current sink limit and make the VDRs work for a living.
>
>.....and you can win the lotto by buying only one ticket!
>
>Think about the problem a little bit.
>
>The screen has to rise to probably a thousand volts or more to give
>any transient protection time and voltage to act.
As I understand it, VDRs act all but instantaneously. Conduction will start
at about 375V at a few mA, but they are not hard clamps (like Tranzorbs or
gas tubes).
>
>You better be very careful what you are doing, and not be foolish
>enough to assume current limiting will protect anything.
>
>On the other hand, you could also protect a zener supply just as
>easily. It is not an advantage at all to use a more complex circuit.
My idea for a solution was to feed the screen through series diodes to
prevent any arc getting back into the regulator, with a bleed resistor to
cope with normal current requirements, and take the feedback for the
regulator from the screen side of the diodes.
I'm a great fan of simplicity - what's the trick for protecting the zener
based supply?
Thanks, Steve
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