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From: muller@sdcc7.ucsd.EDU (Keith Muller)
Newsgroups: sci.electronics
Subject: Re: Choosing Cap Size in Power Supply
Message-ID: <936@sdcc7.ucsd.EDU>
Date: Wed, 29-Jul-87 13:55:53 EDT
Article-I.D.: sdcc7.936
Posted: Wed Jul 29 13:55:53 1987
Date-Received: Fri, 31-Jul-87 05:52:59 EDT
References: <5705@ut-ngp.UUCP> <1884@kitty.UUCP> <935@sdcc7.ucsd.EDU> <1666@midas.TEK.COM>
Organization: University of California, San Diego
Lines: 23

In article <1666@midas.TEK.COM>, jeffw@midas.TEK.COM (Jeff Winslow) writes:
> In the cases I have worked with, the capacitors actually have much better
> response to dynamic load swings than the rectifier-transformer-60Hz line
> behind them. The problem is that they can only store so much energy, so
> eventually they can no longer cover up the shortcomings of these other
> components.
> 
> 						Jeff Winslow

On good quality supplies, the RAW supply (before the regulator) does have
large capacitors for what can very loosely be called an energy store. But
the actual performance of the supply is solely the function of the closed
loop feedback system that consists of the reference supply , difference
amps and the regulator. For example a typical low voltage small wattage
supply would have something like 1800 uf between the bridge and the
regulator. The output cap is on the order of 51 uf. The whole system 
follows simple control system theory in terms of performance
mesurements (which shows why the output cap has to be kept small).
Take a look at a good supply circuit diagram and you can see (lambda, ac/dc,
power designs, hp ...) what I mean.

	Keith Muller
	UCSD