PI Filter (CLC)

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Hari jakkam

Joined May 31, 2006
can any one help me out in finding the values of the L & C values in a PI-Filter (CLC).
i am desining a power supply ckt from a 240VAC/50Hz(input) to a 24VDC(output).
and i want to use a pi filter to regulate the voltage as well as to filter out the ripples present in the AC supply.


Joined May 16, 2005
First pick an inductor. The inductor must be rated to handle as much current as you expect to draw from your power supply. I strongly suggest that your inductor be rated for current at least 20% higher than what you expect to draw. Inductance value (henries) should be "as much as you can afford."

Once you've got the inductor, you can determine the cap size needed. Divide your expected maximum output current by your maximum permited ripple voltage. (Division by zero is meaningless, so pick something other than zero for your ripple voltage.) Divide the result by your input frequency. Divide by two. From this result, subtract your inductor value. Divide again by two. This is the minimum value of capacitor you should use for both caps.

Please note that the above is "rule of thumb" and not a precise formula.

Voltage ratings of the caps should be at least twice the output voltage of the supply. You will want caps rated for fifty volts or more.

Note: a filter will do nothing to regulate the voltage. Only a voltage regulator will do that.