Newsgroups: comp.robotics
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From: ted@nmsu.edu (Classic Ted)
Subject: Re: motor driver for large current loads
In-Reply-To: fredm@media.mit.edu's message of Tue, 20 Oct 1992 16:53:01 GMT
Message-ID: <TED.92Oct26194130@lole.nmsu.edu>
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Organization: Computing Research Lab
References: <1992Oct19.214046.267@news.dfrf.nasa.gov>
	<1992Oct20.162818.9394@news.media.mit.edu>
	<1992Oct20.165301.9903@news.media.mit.edu>
Date: Tue, 27 Oct 1992 02:41:30 GMT
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In article <1992Oct20.165301.9903@news.media.mit.edu> fredm@media.mit.edu (Fred G Martin) writes:

   Whoops, I missed the keyword "PWM" from your description of
   motor-driving requirements on my first quick read and reply.

   Well obviously, relays won't do.  Or will they?  Here's a control idea
   I first saw in an article by Karl Lunt.  It's ideal for controlling
   large motors using PWM, when you don't want to break the bank paying
   for the H-bridge electronics required for all that current.

   The concept is to use a single MOSFET (or HEXFET, or whatever) to do
   the PWM, and a DPDT relay to flip the polarity when you want to drive
   your motor backward.


it should be noted that when reversing motor direction using this
circuit, the current through the relay should be near zero to avoid
arcing and subsequent short life.

this can be done in software.
