[sdiy] power-question

[Don Tillman]

I had a feeling Harry was going to jump in on this one.  :-)

   Date: Mon, 04 Jun 2001 23:39:27 -0400
   From: Happy Hairy Harry <harrybissell at prodigy.net>

   ulrich kehrer wrote:
   > i have a 2x18V/2.22A tansformer and after the bridge rectifier i
   > get +/- 28V thus my +/-15V regulators get really hot (i know that
   > the input of the regulator should only be 3V higher than its
   > output) i suppose the 28V are not normal, are they?

   The regulator MUST have at LEAST three volts to work right.

...even under worst-case case conditions. 

So with the line voltage low by, say, 20% and the transformer off
spec by, say, 10%, and maybe a volt of ripple on the filter cap under
full load...  If you do the math you'll see that there really is no
voltage to spare.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com