Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!milton!whit
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Power supply construction
Summary: Big ones are always switchers
Message-ID: <1991Jun27.004728.7909@milton.u.washington.edu>
Date: 27 Jun 91 00:47:28 GMT
References: <1991Jun25.010640.22405@com50.c2s.mn.org>
Organization: University of Washington, Seattle
Lines: 30

In article <1991Jun25.010640.22405@com50.c2s.mn.org> jwhite@com50.c2s.mn.org (Jeffrey J. White) writes:

>   I need to build or aquire a rather odd power supply.  I need a 24VDC
>15-20 amp power supply for an older (early '70s) ham radio. 

>   After scoping out the National Semi linear data books and application book,
>I have considered building a power supply to meet my needs. 
> ... However none of the application notes
>really comes close to the high power I need.

	Linear devices would have to dissipate a fair fraction of the
total rated power (which is about 500W).  It is axiomatic, therefore,
that linear applications do NOT include this kind of power.  What
you will want to consider is a switching power supply.  

	Unfortunately, build-it-yourself switchers are difficult 
(because the high-frequency high-current inductor is tricky to
design/build).  ACDC model RS24N13 is 24V, 13A; Powertec model
9K24-32-372-FG-3 will deliver 24V at 32A.  Both these are ASTEC
brands ('cuz that's the catalog I have handy); phone (619) 439-4243
to find out about local distributors or ordering.

	Expensive though it may be, the switcher might be your
only real option, because large power transformers (which would
be needed for the linear version) are becoming hard to find (and
if you CAN find one, it'll be so expensive that maybe it's not
worth it).  The only cheap alternative is to put two car batteries
in series and trickle-charge 'em after an hour or so of transmission.

	John Whitmore