L-section filters

Joined Jan 19, 2004
220
hi
what is the purpose of the bleeder resistance in the L-section filter..my books says its for better voltage regulation at low currents but i cant seem to figure that out.
Also if someone can let me know on how to decide the value of a bleeder resistance while designeing a rectifier with a L-section filter.

thank you

n9xv

Joined Jan 18, 2005
329
Another reason for bleeder resistance is to "bleed" off the voltage stored in the filter caps so the supply will not be "live" after being turned off. Bleeder resistors are generally designed to bleed 3 to 10-% of full load current. Just for numbers, lets say you have a supply of 600-VDC @ .5-AMPS. Choosing 5-% bleeders - that would be 5-% of .5 which is .025 or 25-mA of bleeder current. Now apply Ohm's law - 600-VDC supply voltage / 25-mA bleeder current = 24,000-Ohms of bleeder resistance. The I^2 * R wattage is calculated to be 15-Watts. So, I would use 1.5 to 2 times that value or 25 to 30 Watt resistors.