Pages: [1]   Go Down
Author Topic: Filter before, or after regulation?  (Read 228 times)
0 Members and 1 Guest are viewing this topic.
UK
Offline Offline
God Member
*****
Karma: 1
Posts: 530
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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?
Logged

Offline Offline
Edison Member
*
Karma: 20
Posts: 2112
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

UK
Offline Offline
God Member
*****
Karma: 1
Posts: 530
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 439
Posts: 23748
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

UK
Offline Offline
God Member
*****
Karma: 1
Posts: 530
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 439
Posts: 23748
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't generally use inductors - I don't a supply on hand, have to be concerned about current & saturating magnetic fields, etc.
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Victoria, Australia
Online Online
God Member
*****
Karma: 24
Posts: 988
Electronics Engineer/Industrial Control
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

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.
Logged

Everything runs on smoke, let the smoke out, it stops running......VK3DMK

Pages: [1]   Go Up
Jump to: