resonant filtering

[Kevin Weddle]

Are power supplies designed at resonant frequency? I've used many that weren't and I've never seen the circuits that show it.

[audioguru]

An ordinary power supply is not resonant. It rectifies the 50Hz or 60Hz from the transformer and filters out the low frequency ripple.

A high frequency switching power supply is resonant so it can efficiently stepup the voltage or efficiently stepdown the voltage with an inductor.

[Hero999]

Traditionally most low to medium power high frequency power supplies (<1kW) are not resonant and use PWM to adjust the amount of power i.e. regulate the output current or voltage.

More modern and higher powered SMPes, typically are resonant. The employ a technique known is zero voltage switching where the transistors are only turned on when the voltage across them is zero. Here's a link with more information.

http://www.powerdesignindia.co.in/STATIC/PDF/200901/PDIOL_2009JAN21_PMNG_TA_01.pdf?SOURCES=DOWNLOAD

[Kevin Weddle]

So the filtering of a 120vac power supply doesn't benefit by resonant filtering?

[Hero999]

If you're talking about EMC filtering then no, resonant filtering is no beneficial, it's harmful because tuned circuits can be excited leading amplification of certain frequencies.

Resonant filtering is only used for tuning a circuit to a particular frequency, for example in a tuned radio receiver a capacitor is placed in parallel with an inductor to form a tuned circuit.