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 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.
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.
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.
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.
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.