Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!decwrl!shelby!eos!jbm
From: jbm@eos.UUCP (Jeffrey Mulligan)
Newsgroups: sci.electronics
Subject: Re: Stepper Motor
Message-ID: <3933@eos.UUCP>
Date: 9 Jun 89 19:26:11 GMT
References: <21000031@m.cs.uiuc.edu>
Organization: NASA Ames Research Center, California
Lines: 27


From article <21000031@m.cs.uiuc.edu>, by irwin@m.cs.uiuc.edu:

> If the current required is known, and the voltage, I would think that
> power transistors in the T-036 case style could be found to drive it.
> A fudge factor could be added to the total wattage so that the transistor
> selected was not working at 100% of its power rating. Clamp diodes would
> be required across the driver transistors so that "punch through" did
> not kill the drivers as the transistor turned off and a reverse voltage
> spike got generated by the collapse of the field.

I have worked with a number of stepper drivers including commercial
ones, and one common feature is the presence of large wire wound
hi power resistors, presumably to prevent the drive transistor from
taking the voltage drop.  I don't remember the package designations,
but the (old) commercial units used those flat round metal packages about
the size of a quarter with two little ears for mounting,
while some replacement units designed and constructed by our department
technician used drive transistors in smaller rectangular plastic packages
(like 8 x 10 mm) with a metal tab for heat sinking (which was not
necessary).

-- 

	Jeff Mulligan (jbm@aurora.arc.nasa.gov)
	NASA/Ames Research Ctr., Mail Stop 239-3, Moffet Field CA, 94035
	(415) 694-6290