PWM

[Jnadke]

Originally posted by Katie Reynolds
This should probably be moved to the Q/A forum ... just a thought

No, not really.




Pulse Width Modulation is a neat little method of turning a digital signal into, effectively, an analog one. It alters the average voltage in a signal by varying the length of time it is on, versus the length of the time it is off, without varying the period.

Why? It's cheaper to produce than to recreate a varying analog signal. To recreate an analog signal would require dozens of inductors and capacitors, whereas this does it effectively, without really doing it. Effectiveness is all that matters.

If you want mathematical stuff... say if you turned a 12V signal on for half the period, and off for the other half... you would have an average voltage of:
1/2 * 12 + 1/2 * 0 = 6V
Now, if you turned it on for 25% of the period, and off for the other 75%, you would have:
1/4 * 12 + 3/4 * 0 = 3V
It works the other way too:
3/4 * 12 + 1/4 * 0 = 9V


Here's a picture that might help you a little. See how the period in the signals is the same. The the amount of time the voltage is applied is varied.