Hi,

I may be wrong on this, but I believe that the 110 volt 60 hertz line 
voltage is converted to a frequency of from 20 to 100 kilohertz which is 
then sent through a very small  transformer to deliver the output voltage 
that is then rectified, filtered and regulated.  The higher switching 
frequency allows for a very small transformer with very few turns of wire. 
The old TV flyback transformers used to work in the same way except they 
stepped up the voltage to over 20000 volts which was then applied to the 
annode of the picture tube.

Bob Tinney, K8LR, [log in to unmask]
Skype, bobtinn
Life is full of challenges, that's what makes it interesting!

----- Original Message ----- 
From: "Howard Kaufman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, November 14, 2008 8:28 AM
Subject: Re: switching supplies cause interference


Basically as I understand it, switching supplies use circuitry to step down
the 110 VAC to a workable voltage, before it is converted to DC.  This
elliminates the need for the traditional heavy power transformer.