Thanks to the kind and patient help of people in this list, plus RTFM-ing and sacrifices to the Google Gods, I now have the answer for you.  So be ye not afraid.

A diode blocks AC and allows DC to pass.  By using the correct combination of diodes you can convert an AC current into a DC current.  (Pages 45-46 of The Art of Electronics, 2nd Ed., Page 47 of Forrest Mimms' Getting Started in Electronics.)  This diode circuit is called a full-wave rectifier.  The output of this looks like a bunch of speed bumps next to each other.  Forrest calls this a "pulsating voltage" (page 36) while Horowitz & Hill call it a "ripple" (Page 46).  

How to fix this?  This gets confusing.  Forrest Mimms shows on page 36 that a capacitor connected to + and - will smooth out (filter) the output voltage.  But on page 45 of The Art, Figure 1.72, they show a resistor on the + side with the capacitor crossing + and -.  However on page 37, Mimms calls this particular RC circuit an Integrator which would turn a square wave into a sawtooth wave.

Hope this helps!  (-:


-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of kenasw@btinternet.com
Sent: Thursday, May 12, 2005 15:56
To: Microcontroller discussion list - Public.
Subject: Re: [EE] Will phone charger work as a 5v DC power supply?

Linsey,
If you want to know what ripple is, why don't you open an electronics
general purpose text book, they normally have whole chapters on
power supplies?



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