PSU oscillating - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st June 2005, 10:44 AM   #1
diyAudio Member
 
Join Date: Jan 2004
Location: rouen
Send a message via ICQ to apolon34
Default PSU oscillating

Hi,

I've designed a PSU for the 5v part of my philips cd-pro2.

you can find schematic and layout there:
http://belinfabien.free.fr/cd/cd%20d...lim%20meca.htm

I use ad797 for op-amp and all caps are os-con SG series.
From the schematic, I replaced R9 by a wire. With R9, I got some spikes at low freq with cd-pro2 plugged. Without, it oscillates at several Mhz

I also removed C12 (100nf) and the oscillation ampliftude decreased to about 0.3vpp

unregulated psu is around 9.5v, output is at 5v.
  Reply With Quote
Old 23rd June 2005, 08:30 PM   #2
diyAudio Member
 
Join Date: Jan 2004
Location: rouen
Send a message via ICQ to apolon34
hi,

it seems that adding a 1k/100uF filter on the opamp psu nearly solved the problem. I still have some 20mVpp of oscillation. The opamp psu seems to be clean so there probably is another thing, but I don't know what.
  Reply With Quote
Old 23rd June 2005, 08:51 PM   #3
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: Behind you
According to the NE5534 datasheet it's only compensated for a minimum gain of 3, but in that circuit it has a gain of 1, plus it has extra transistors inside the feedback loop. So try adding an extra compensation capacitor between pins 1 and 8 of maybe 22pF or so.

EIT: Oops, I see you're using AD797. The datasheet for that one looks like you need to take even more care with compensation.
__________________
https://mrevil.asvachin.eu/
  Reply With Quote
Old 24th June 2005, 02:20 PM   #4
diyAudio Member
 
Join Date: Jan 2004
Location: rouen
Send a message via ICQ to apolon34
Today i went to the electronic lab of my job to test the PSU. It seems that my trick to add a rc filter on opamp PSU solved the problem. I don't know why I was seeing oscillation with my scope. I'll look again this evening but I hope the problem's gone.

If not, i'll try to add a serial RC on opamp output

thanks mr evil
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
please help with an oscillating amp ballai.tibi Solid State 101 19th June 2010 09:19 AM
6j4 oscillating? Klimon Tubes / Valves 2 18th January 2008 09:32 PM
oscillating...always oscillating WoulYaShassu Solid State 30 9th April 2004 05:31 PM


New To Site? Need Help?

All times are GMT. The time now is 05:25 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2