how to filter a switching power supply?

space-cake · 5th March 2007, 06:50 AM

i made a power supply using a dc converter (TL499A) and i have some noise in the signal so i would like to filter it out. there are active and passive filters, which one should i take?

the problem i see with using an active filter is that my supply is from a 9V battery and the active filter will also need supply so maybe i need to take it's supply directly from the battery? if not, will it work with the converter's output? also i need to filter 18V and i could not find any OA that is able to take over 13V.

the second option is a passive PI filter, like on this page - http://www.pronine.ca/butlf1.htm
the problem here is that the caps and inductors will only be approx. the needed values and that i'm not sure how many parts are needed? 3, 4... more?

any help would be appreciated!

fku · 11th March 2007, 01:56 AM

most of the smps have feedbacks. using large capacitors there could introduce instabilities, as most application notes would advise against the use of such capacitors.

large capacitors are used in 50/60hz systems simply because the time between charging up the capacitors is too long at those frequencies.

smps operates at much higher frequencies and you don't need such large capacitors.

5th March 2007, 06:50 AM	#1
space-cake diyAudio Member Join Date: Apr 2006 Location: home	how to filter a switching power supply? i made a power supply using a dc converter (TL499A) and i have some noise in the signal so i would like to filter it out. there are active and passive filters, which one should i take? the problem i see with using an active filter is that my supply is from a 9V battery and the active filter will also need supply so maybe i need to take it's supply directly from the battery? if not, will it work with the converter's output? also i need to filter 18V and i could not find any OA that is able to take over 13V. the second option is a passive PI filter, like on this page - http://www.pronine.ca/butlf1.htm the problem here is that the caps and inductors will only be approx. the needed values and that i'm not sure how many parts are needed? 3, 4... more? any help would be appreciated!

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11th March 2007, 01:56 AM	#2
fku diyAudio Member Join Date: Mar 2007	most of the smps have feedbacks. using large capacitors there could introduce instabilities, as most application notes would advise against the use of such capacitors. large capacitors are used in 50/60hz systems simply because the time between charging up the capacitors is too long at those frequencies. smps operates at much higher frequencies and you don't need such large capacitors.

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