>-----Original Message-----
>From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]
>On Behalf Of Lindy Mayfield


>How can something be both AC and DC at the same time?

Look at it this way... It doesn't have DC in it, but can be made into DC...
You can look at it as a pure AC signal, and the low pass filter simply
averages the AC signal over a long time constant to get a DC signal. This
isn't exactly correct, but it's close enough to conceptualize AC/DC
relationships in PWM. For instance, the DC component of standard 110V line
voltage is 0 volts. If you put a low-pass filter (with a high time constant)
on the electricity coming out of your wall, it would average out the
positive peaks and negative peaks of the electricity to come up with 0 VDC.

Good luck!


- Robert

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