mkb@rover.ri.cmu.edu (03/19/91)
I'm looking for a source of bare motor amplifiers. Nothing fancy, just
something that will switch its output between ground and +24VDC at 10-15 amps
(float would be nice, too). PWM will be produced up stream. I'd rather provide
my own heat sinking. I don't think such a thing should be too complicated, but
our home brew attempt (with a push/pull FET pair and some compensation for the
slower P-channel device) suffers a bad case of ringing induced, i believe, by
back EMF from the motor. Any pointers (or even your favorite design) would be
greatly appreciated!
Mike Blackwell mkb@rover.ri.cmu.edu
The Robotics Institute, Carnegie Mellon Universityjshapiro@mcs213a.cs.umr.edu (Jeff Shapiro) (03/19/91)
>I'm looking for a source of bare motor amplifiers. Nothing fancy, just >something that will switch its output between ground and +24VDC at 10-15 amps >(float would be nice, too). PWM will be produced up stream. I'd rather provide >my own heat sinking. I don't think such a thing should be too complicated, but >our home brew attempt (with a push/pull FET pair and some compensation for the >slower P-channel device) suffers a bad case of ringing induced, i believe, by >back EMF from the motor. Any pointers (or even your favorite design) would be >greatly appreciated! You might try a powerful audio amplifier. I know a person who used one for a superconducting motor and it worked pretty well. I don't know if it could float though :). Jeff Shapiro r103336@apollo.physics.umr.edu jshapiro@cs.umr.edu
gene@cooper.cooper.EDU (Gene (the Spook) ) (03/21/91)
in article <1991Mar18.193938.14805@cs.cmu.edu>, mkb@rover.ri.cmu.edu says: > I don't think such a thing should be too complicated, but > our home brew attempt (with a push/pull FET pair and some compensation for the > slower P-channel device) suffers a bad case of ringing induced, i believe, by > back EMF from the motor. The most likely cause of your ringing problem would be the series inductance of the driver fighting with the inherent capacitance of the FET's gate. If using a discrete gate driver (such as those from Micrel), try running the lead to the gate through a ferrite bead, if you can get your hands on a few. There are a few circuits in back issues of EDN, it you *really* want to go homebrew. Offhand, I'd recommend sticking with your original design and using the ferrite beads first, before you scrap your design. The only real thing you have to watch out for is to make sure that you never get both FETs turned on at the same time (such as in a transition, but you mentioned compensating for the P-channel device). I don't get here very often, so if you want to leave a reply, don't be offended if you don't get an immediate response. My access to this machine has kind of dropped off some. :^) As Confucius say: "Good ruck!"