What do you think a filter capacitor does? Just sit there in the circuit to look good? =-) They absorb energy and feed it to the circuit during the low portion of the AC cycle. If you have a lot of ripple or it's a single phase AC mains supply there's quiet a bit of current going through the filter caps.
yeah i knew that... but where is the current actually lost? the capactior stores charge during the low part of the AC then feeds it back during the high part...
also, smanches, i had a look at pwm using a 555 and i understand it somewhat... but its hard to see exactly how it is varried in the curcuit... something to do with the op-amp?