Pulse Width Modulation Explained - Relevant Links Included

[abs_vicky]

Actually i m new to electrical sciences, can anyone please explain me the working principle of a PWM?? and its applications , please provide any relevant links concerning it. Thanks in advance

 

[Bob S]

Here is a simple pulse width modulation (PWM) control of a mosfet switch:

http://www.solorb.com/elect/pwm/pwm2/

In both circuits, one LM324 provides a voltage reference, two LM324's produce a triangular waveform, and the fourth LM324 is used as a variable threshold comparator to produce a constant frequency, variable width PWM signal to the output switch. This circuit can be used for both resistive loads (lights) and inductive loads (electric motors).

LM324 datasheet:

http://www.national.com/profile/snip.cgi/openDS=LM324

Bob S

 

[berkeman]

Actually i m new to electrical sciences, can anyone please explain me the working principle of a PWM?? and its applications , please provide any relevant links concerning it. Thanks in advance

One key concept in the application of PWM is that while the voltage is ON, you are delivering full power to the load (generally). This is useful for modulating the speed of DC motors, for example. You do not vary the speed of a DC motor by lowering the drive voltage, because you sacrafice torque if you do that. But if you use PWM to lower the speed (by using lower and lower ON times per drive period), your torque holds up much better.

http://en.wikipedia.org/wiki/Pulse-width_modulation

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[UR_Correct]

A PWM signal has a frequency and a duty cycle. The frequency is related to how long the period is. The duty cycle is usually a percentage related to the percentage of the period that the signal is on. For instance, a 1kHz, 50% duty cycle, 5V peak to peak (0-5VDC) signal looks like a square wave with it being on (5V) for 0.5ms (50% * (1/1kHz)) and off (0V) for the other 0.5ms, repeat. This allows for what I think is called an apparent voltage, which is calculated by multiplying the duty cycle by the peak to peak voltage, or in this case, 2.5 V (50% * 5V). This is helpful in controlling motors, because the RPM of a motor is related to how much power you supply it. So, if you want a lower RPM, you use a PWM signal with a low duty cycle, and vice versa. I believe it's called proportional control. Arduino makes simply controllers (duemilanove and Uno) that center around PWM outputs. You'll obviously need an actuator to drive the motors, because you traditionally don't power motors from a microcontroller.

 

[Zelimir K.]

Please check domain "www.PWM-Theory.com". Please read "Introduction to PWM Control Systems. Zelimir