Re: Analysis Of Pulse Width Modulator With Motor Control

On Mon, 05 May 2008 07:39:35 -0700, seryuz wrote:

http://img255.imageshack.us/img255/2396/pwmmotorcontrolcr7.jpg



how to analyse the Pulse Width Modulator with Motor control?

How can we make an analysis for this circuit. Can we make something
mathematical? it says:

Designing a PWM Circuit
The concept of PWM inherently requires timing. Two 555 timer ICs and
some potentiometers can be used to generate a PWM signal, and since PWM
provides a digital, on/off signal, it is also easy to use a PC or
micro-controller to create the signal; however this is beyond the scope
of this article.
The circuit in figure 2 uses two 555 ICs and is actually a combination
of two types of circuit. The first is a free running multivibrator
(astable) with an adjustable frequency around 30Hz. The output of this
circuit then triggers a pulse shaping (monostable) circuit which adjusts
the width of the pulse. The circuit produces a duty cycle in the range
of approximately 0.3% to 97%.

The speed of the motor is controlled with a single potentiometer
(variable resistor). It is possible to run a Meccano M5 motor to test
the circuit, and it will run from dead still to full speed using the
potentiometer speed control and a 6V battery as the sole power source.
If you have a 12V motor, you can of course use a 12V power source. The
motor is switched on and off via a TIP31C transistor (shown in figure 3)
which can handle motors rated up to 3A at 100V, or a total power of 40W.
If you are using a high power motor, make sure there is a heatsink
bolted to the transistor.

What do you want to find out?

If you have SPICE with a model for a 555 you can model this whole
circuit. For any given constant motor speed, model the motor as a
voltage source proportional to the speed with a series resistor. This
will give you some basic idea of how the circuit will work.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
.

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