Need help on building a filter for power supply Last Post 10 Jan 2013 09:11 AM by jwd217. 3 Replies.
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einstein2nd

New Member
Posts:3

 05 Jan 2013 05:59 PM I am building a power supply from scratch and need help on selecting the right size inductor and capacitor for an LC filter. The power supply consists of: transformer, full wave rectifiers, filters, and regulators. Transformer specs: Input: 110 VAC 60 Hz rated @ 15 amps; Output: 15 VAC 60 Hz rated @ 30 amps; Full Wave Rectifier specs: bridge rectifiers rated @ 40 amps; LC Filter specs: Input: 15 Volt Pulsating DC rated @ 40 amps; Regulator specs are currently unknown. I have avionics background but a little rusty on LC filter circuits. I am trying to flatten out the ripple as much as possible before sending it to the regulator. I am hoping someone can help me.
einstein2nd

New Member
Posts:3

 05 Jan 2013 06:50 PM Transformer specs: Input: 110 VAC 60 Hz rated @ 15 amps; Output: 15 VAC 60 Hz rated @ 30 amps; When I built the transformer as an 8:1 I didn't realize that when rectified the output voltage would be cut in half. So I will have to redesign the transformer to currect the output voltage. I will test the outputs of the transformer soon to see if my realization is correct then make changes accordingly.
jwd217

New Member
Posts:35

 10 Jan 2013 09:10 AM An LC filter is not normally used in a power supply. Normally the transformer output is connected to a bridge rectifier and then a relatively large capacitor is used to filter the pulsing DC to fairly smooth DC. The “L” inductor is not needed. Also when the output of a transformer is connected to a bridge rectifier, the DC voltage output increases about 30 to 40% more than the AC input, instead of being cut in half. After the capacitor you would then have any regulation circuitry needed. Something like this. Trans Rectifier -- ------- AC )( _/\___________ DC Output )( | \/ _|_ ) ------- _ _ Cap -- |_________|____ Common
jwd217

New Member
Posts:35

 10 Jan 2013 09:11 AM When my previous reply was posted it got reformated so the text based drawing I did got messed up. Sorry.