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From: dje@datacube.UUCP
Newsgroups: sci.electronics
Subject: Driving Inductive Loads
Message-ID: <100500010@datacube>
Date: Tue, 26-May-87 07:46:00 EDT
Article-I.D.: datacube.100500010
Posted: Tue May 26 07:46:00 1987
Date-Received: Fri, 29-May-87 00:45:18 EDT
Lines: 31
Nf-ID: #N:datacube:100500010:000:1406
Nf-From: datacube.UUCP!dje    May 26 07:46:00 1987


Does anyone have experience with amplifiers  driving inductive loads?
I am building a small syncho system  that needs  to run  off +12V DC.
It  currently  uses  a  400  Hz  sine  wave  oscillator (Wien Bridge)
followed by an automotive type amplifier  chip (LM383)  followed by a
1:4 step up transformer to get enough voltage to drive the synchros.

Here's the problem.  A synchros presents an  inductive load.   When a
class  A  or  AB amplifier  drives an  inductive load  the current is
maximum  when load  voltage is  lowest (zero).   This  causes lots of
power dissipation in the amplifier.  This kills the batteries quickly
and gets the amp *hot*.  The synchros run cool as cukes.

A high efficiency (switching) amplifier would be better.  It only has
to  have reasonable  performance at  400 Hz.   But  that sounds over-
complicated.  Know any simple circuits?  

How about a capacitor  in series  to create  a resonant  circuit?  It
would have to be fairly large and stable.  Any drift in the  L, C, or
F would throw off resonance though.

Any ideas?  Theoretically driving an  inductive load  draws no power.
I'll settle for less power.  
 				Dave Erickson
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