Re: Whining PWM motor control
- From: Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 19 Aug 2005 00:24:22 GMT
Hello Robert,
As Jim already said a fixed frequency is better. What I usually do if it has to be cheap (or in your case the parts should already be flying around in your garage): Take a Schmitt trigger such as the 74HC14 or CD40106, build an oscillator and then quench that with a FET or transistor that is controlled from the feedback point. IOW if the motor current wants to exceed your limit it throttles the oscillator's "on" period but not its frequency too much. Actually the frequency changes a bit but not a lot.
If you want absolutly constant frequency you can build that oscillator and follow with a one-shot that can also be made from a Schmitt gate. Then quench that one-shot instead. There are six in a chip so you have plenty.
Regards, Joerg
http://www.analogconsultants.com .
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