richard_jay
Newbie level 3
Hi,
I'm designing an unregulated DC power supply operating from a 208 VAC / 60 Hz power source. I'm concerned that the use of a solely capacitive smoothing filter at the output of the bridge rectifier will result in high frequency current harmonics being generated when the capacitor charges. I would like to limit the rate of change of the current drawn from the power source in order to limit the frequency content of the current drawn form the supply. This is a EMI design consideration.
I'm considering using a LC filter at the output of the bridge rectifier. I've set the cut-off frequency to approximately 35 Hz in order to reject the 120 Hz ripple. I’ve employed a 10mH inductor and 2200uF capacitor. The inductor is specified to handle the full DC current drawn by the load. Simulations show that the current waveform drawn from the load is much improved from a harmonic perspective.
Other filter designs I've seen tend to use very large values of inductance (1 - 10 H) and much smaller capacitors. I'm concerned that resonance may be in issue in the circuit that I'm proposing. Any comments on the design of this filter would be much appreciated.
Thanks, Rich
I'm designing an unregulated DC power supply operating from a 208 VAC / 60 Hz power source. I'm concerned that the use of a solely capacitive smoothing filter at the output of the bridge rectifier will result in high frequency current harmonics being generated when the capacitor charges. I would like to limit the rate of change of the current drawn from the power source in order to limit the frequency content of the current drawn form the supply. This is a EMI design consideration.
I'm considering using a LC filter at the output of the bridge rectifier. I've set the cut-off frequency to approximately 35 Hz in order to reject the 120 Hz ripple. I’ve employed a 10mH inductor and 2200uF capacitor. The inductor is specified to handle the full DC current drawn by the load. Simulations show that the current waveform drawn from the load is much improved from a harmonic perspective.
Other filter designs I've seen tend to use very large values of inductance (1 - 10 H) and much smaller capacitors. I'm concerned that resonance may be in issue in the circuit that I'm proposing. Any comments on the design of this filter would be much appreciated.
Thanks, Rich