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Power Supply Filter Calculations

Posted: Sun May 25, 2008 11:28 pm
by mediatechnology
We often get the question "how large of a filter cap do I need?"

Here's a way to calculate it:


The load resistance term, Rl, can be estimated from the average voltage (at a hypothetical regulator input) divided by the maximum expected current. Fr is the ripple frequency. Using full-wave rectification Fr would be either 100 or 120 Hz. As a practical matter, use 100 Hz.

The full text where I obtained the equation is from Hemes: ... _Temes.pdf

And the National Semiconductor Audio Handbook: ... Design.pdf

Construction information for the Pico PSU board using the LM317/LM337 is here: ... uments.htm