Path: utzoo!attcan!uunet!zephyr!midas!jeffw
From: jeffw@midas.STS.TEK.COM (Jeff Winslow)
Newsgroups: sci.electronics
Subject: Re: Substituting Caps oin Logic Supplies
Message-ID: <4453@midas.STS.TEK.COM>
Date: 26 May 89 19:30:14 GMT
References: <484@dalek.UUCP> <1989May24.154332.29113@utzoo.uucp> <814@rex.cs.tulane.edu>
Reply-To: jeffw@midas.STS.TEK.COM (Jeff Winslow)
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 20

In article <814@rex.cs.tulane.edu> hoang@rex.UUCP (Dzung Hoang) writes:

>    Uh, high internal resistance is desirable in capacitors.  I really doubt
>that much AC current will flow through the capacitor if it is used as a power
>supply filter.

The first statement is true for parallel resistance, which is virtually
irrelevant in power supplies. What Henry was talking about, and he is 
absolutely right, is internal series resistance, which is most definitely
UNdesirable in a capacitor. (Unless you are relying on the ESR of the
capacitor to stabilize your regulator feedback loop or damp your decoupling
circuit - but those are subtleties.)

As for your second statement, I implore you to become a believer. If there's
not much AC current flowing through a power supply filter capacitor, somebody
wasted a capacitor. The whole point of such capacitors is to prevent AC
currents from affecting the power supply voltage. And internal series
resistance will of course conflict with that purpose.

						Jeff Winslow