From: "Frank Bemelman"
Subject: Re: Simple adjustable 0 - 400V regulator, with flaw
Date: Sat, 18 Jan 2003 19:24:30 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Organization: EuroNet Internet
NNTP-Posting-Date: 18 Jan 2003 18:24:45 GMT
"Winfield Hill" schreef in bericht
> Thomas wrote...
> > Winfield Hill wrote:
> >>. +480V ___ HIP5600
> >>. ---| |---+---+-----------(O) HV out
> >>. |___| | |
> >>. | | 1.5k
> >>. | | | adjust, 0 - 400V
> >>. '---- | --+----o->o--------,
> >>. | o--, |
> >>. 10uF === 300V | 500k
> >>. 450V | fixed | pot
> >>. | 380k |
> >>. ______|______________|_____|____
> >>. gnd
> >> ... 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?
A cap across the pot? BTW, how many pot (hehe) did you smoke before
you found out ?
(remove 'x' & .invalid when sending email)