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From: John Larkin
Subject: Re: A protection problem
Date: Tue, 07 Jan 2003 14:29:06 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On Tue, 7 Jan 2003 18:17:39 +0000 (UTC), email@example.com (Ken
>I'm currently working on a voltage regulator with a major protection
>problem. The specs are:
>Input voltage 23 to 28V. This is easy enough.
>Output voltage DAC controled 0 to 25V (doesn't need to boost make 25V when
>input is too low). This isn't too hard.
>Output current limited at 100mA. This isn't too hard.
>Some moron may hook a (+) or (-) 600V supply to the output. This 600V
>supply can supply a zillion amps so MOVs aren't the answer. PTC devices
>don't seem to be able to handle this case either.
>I'm tinkering with various active circuits but they all seem to end up
>with quite a few parts in them. Does anyone have an idea?
How about a nice transzorb zener at the regulator output followed by
an active/foldback current limiter? For the current limiter, I'm
thinking an 800 volt power fet and a simple one-transistor
limiter/foldback control thing. Floating battery power is appealing
here, or maube a photovoltaic. You'll need a diode for the reverse
No, I can't think of a *simple* way to do this.
You might look into depletion-mode power fets... Supertex?
Do any of the DC solid-state relays include overload protection?
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