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Topic: Filter before, or after regulation? (Read 369 times) previous topic - next topic

jtw11

So, I've been trying to get some answers to this - but can't seem to find one...

Say for example you have a power supply with quite a degree of ripple, would one seek to filter this ripple using an LC filter or other technique, before, or after a voltage regulator? I've never really thought about this before, but surely there must be some difference.

Logic would say before the regulator, so the regulator dosen't have to work as hard to keep the output, well - in regulation.

What are you thoughts?

cjdelphi

Both is the answer.


What kind of power supply you using? (dc > dc? or ac > dc?)   filtering DC is simple as using a couple of capacitors on both the input to the regulator and the output of the regulator.

more info por favor.

jtw11

DC to DC, transient filtering is done upstream - but any ripple will still come through to the regulator. No design i've done in the past has had more than capacitors on the input and output of the regulator, but I'm looking for a little more finesse in this design.

CrossRoads

If you had a regulator that needed Vin to be >= Vout + 1V, and the incoming  had ripple that did not bring Vin below that level, say you had 250mV of ripple on a 7V Vin and Vout was 5V, then caps would be all that is needed.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

jtw11

Thanks Crossroads - your answers are always very helpful, I was thinking this - but I thought, so as to work the caps less hard - use an LC filter, but then the caps in the LC filter would be worked just as hard.

CrossRoads

I don't generally use inductors - I don't a supply on hand, have to be concerned about current & saturating magnetic fields, etc.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

TomGeorge

Hi, concentrate on getting rid of the ripple before the regulator, that way you can guarantee proper output regulation.
Inductors these days are used to minimize ripple/noise in high frequency switch mode designs.
Tom.
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

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