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From: Ken Smith
Subject: Re: An interesting little prob.
Date: Wed, 30 Oct 2002 17:58:18 +0000 (UTC)
Organization: a2i network
NNTP-Posting-Date: Wed, 30 Oct 2002 17:58:18 +0000 (UTC)
In article <firstname.lastname@example.org>,
Tony Williams wrote:
> Unregulated dc+>---[ V-controlled ]--|>|-+-----+---->
> [Current-Source] | |
> /|\ | |
> | [V-controlled] |
> [12-bit]--------+ [ Shunt-reg ] | Iout
> [ DAC ] /|\ | _|_
> | | /_\
> [12-bit]--------------------+ | |
> [ DAC ] | |
Is there any good reason that the Unregulated input can't be the
(-) suppy? NPN and N channel devices are easier to get.
I built basically what you describe here many years ago as a bench supply
for home use. I used PNP transistors for both pass elements. The nice
thing about the PNP for the shunt regulator is that the base voltage
doesn't have to move very far to go from no conduction to full
conduction. The bad thing about the PNP is that you need a diode in the
emitter leg because of the low breakdown voltage.
In the one I made, I had to put a choke in the collector of the current
source and use a fast rectifier on the shunt regulator before the current
spike on a sudden short was small enough.
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