Re: PWM

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1 total messages Started by Lalitesh Katragadda Fri, 08 Jan 1993 21:42

#1750

Author: Lalitesh Katragadda
Date: Fri, 08 Jan 1993 21:42

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PWM or Pulse Width Modulation is a method of controlling DC motor speed.
This is done by switching the motor on for a specified period of time over
a given interval. For example if the motor is switched on for 8 ms out of 
every 10 ms it will run slower than before. The dynamics of the motor prevent
it from stopping and going. Smooth motion can be achieved by experimenting
with period. If digital control is used (say a 68HC11), the period also 
determines the resolution of control. 

Benefits:
          Controlling speed using DC motors and a constant voltage source. 
Rough calculation can be done by the following formula. V = P*Vo/T
V : effective voltage, Vo : Applied voltage, T : time period, P : On period.


Cons:

   Have to be careful about transient spikes in voltage, could restrict it using
zeners.

   Could be ineffecient depending on circuitery in terms of power consumed and
the torque that can be squeezed out of the motor.

cheers,
lalit@ri.cmu.edu

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