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From: Winfield Hill
Newsgroups: sci.electronics.design
Subject: Re: LM317 or 7808 is better performance for 9V output ?
Date: 11 Dec 2002 09:00:16 -0800
Organization: Rowland Institute
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Fred wrote...
>
> It is an approximation to the better known boostrap regulator.
> Rsu is required for start-up among other things:
>
> +---------------+
> | 7805 |
> --------| IN OUT |-------+----------+----+->> 9V
> | | | | |
> | | | / |
> ---+ | GND | | 5R ---
> | +---------------+ | / ---
> | | | \ 10u
> | | | / | | |
> | | |/ +|------+ |
> | | / | | |
> | +-----+-----+-- LM358 | |
> | | | | \ | / |
> | / | | |\ -|-+ 4R |
> | Rsu --- | | \ | | / |
> | / --- | | | \ |
> | \ | +---------+ | |
> | | | | | |
> +------------+-----+---------+----------+----+->> GND
A small capacitor on the controlled node is often helpful with
these circuits, improving the regulator's transient response by
counteracting the rising Zout of the opamp at high frequencies.
Thanks,
- Win
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