From: "Frank Bemelman"
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: Sat, 18 Jan 2003 20:30:42 +0100
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Organization: EuroNet Internet
NNTP-Posting-Date: 18 Jan 2003 19:33:27 GMT
"Winfield Hill" schreef in bericht
> Winfield wrote...
> > Thomas wrote...
> >> Winfield Hill wrote:
> >>>. see below
> >>> ... As a design quiz, tell us what the problem is, and
> >>> find a solution that doesn't significantly affect any
> >>> of the circuit's functionality. ...
> >> If the switch is flipped, and the pot is in zero position, the
> >> 1.5 K resistor gets to see 300 volts, maybe even 470+ volts if
> >> the switch is open for a moment.
> >> That's 60 watts, and nearly half a joule. Probably too much
> >> for whatever little R is there.
> > Actually, the 1500-ohm resistor has never minded the short power
> > surge. Amazingly, neither did the '5600. However a 5.1V zener
> > was placed across this resistor in a design refinement; I should
> > have shown it.
> >> And the 200 mA will be too much for the pot...
> > BINGO, that's part of the answer. If the pot is turned down
> > when the switch is thrown, a small part of the pot's resistance
> > path has to absorb all the 10uF capacitor's energy. Bamm!
> > OK, what's the solution?
> Frank and Gibbo both suggested a capacitor to ground at the
> ADJ pin, as shown below.
I actually meant to place the cap across the pot, at the
*other* side of the switch. The cap is discharged before the
switch is moved to the pot.
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