IRs2092 oscillating, any suggestions ? - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 26th November 2010, 02:34 AM   #1
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Default IRs2092 oscillating, any suggestions ?

Just got my latest revision of pcb through for my 2092 class d amplifier.

The previous version worked fine and ran off +/- 35 volts.

For the new version I have upped the voltage to +/- 45 volts and scaled the VB charge resistor accordingly. Also increased a bit the vaa and vss supply resistors, scaled them to match the 10mA supply requirement.

For some reason the new version has a low level 1KHz-ish oscilation. The audio plays fine it just has this extra tone on top of it. The tone is fairly low level, with oscillation i usually expect a high level but it isnt.

Clearly I am 99% of the way there with the chip running.
Just need a little help with this last hurdle.

Other than the mods mentioned above the components used are as per the datasheet. This new pcb layout is much tighter than the previous one with plenty of decoupling. Seems odd the older slack layout worked and the new tighter one doesnt.

Tried different inductors. Tried extra decoupling. A scope on some of the 2092 pins makes it better or worse.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 26th November 2010, 03:52 AM   #2
luka is online now luka  Slovenia
diyAudio Member
 
luka's Avatar
 
Join Date: Sep 2005
Location: in Slovenia :)
Send a message via Skype™ to luka
I "have" about the same problem, but in my case I think its more gnd problem, being connected to PC, no ground wire in my home,... if I disconnect input, it goes silent
Also RC LFP on input makes it less apparent
__________________
home page @ http://www.classdaudio.tk/ @ 24/7 all year long
I FEEL SLOVENIA
  Reply With Quote
Old 26th November 2010, 07:46 AM   #3
Pafi is offline Pafi  Hungary
diyAudio Member
 
Join Date: May 2004
Location: Budapest
It may be an interference. Does the audible freq. change if you modify switching freq.? Is there any other high freq. source nearby (other channel, PC, SMPS, unintentionally oscillating linear power supply or preamp)?
  Reply With Quote
Old 26th November 2010, 08:13 PM   #4
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by Pafi View Post
It may be an interference. Does the audible freq. change if you modify switching freq.? Is there any other high freq. source nearby (other channel, PC, SMPS, unintentionally oscillating linear power supply or preamp)?
There does seem to be a lot of noise around especially on the supplies.
Despite having very thick tracks the HF seems to get on the ground too.

If I put a scope probe on VAA it cancels out the tone.
Will look into it a bit more tonight.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 26th November 2010, 09:05 PM   #5
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Had a look tonight and the problem is lack of decoupling on the VCC rail.
Added another 47uF elect. and now the oscillation on the output has totally gone.

Oddly that is the same capacitor I had problems with on my first design taken from the datasheet. The datasheet says it should be 10uF, so I changed it to 47uF to stop glitches on the VCC rail.

I can only guess the cheap 12 volt regulator is not really doing its job very well despite having decoupling on the 12 volts out.


Click the image to open in full size.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk

Last edited by nigelwright7557; 26th November 2010 at 09:11 PM.
  Reply With Quote
Old 26th November 2010, 09:06 PM   #6
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by luka View Post
I "have" about the same problem, but in my case I think its more gnd problem, being connected to PC, no ground wire in my home,... if I disconnect input, it goes silent
Also RC LFP on input makes it less apparent
Add a bit more decoupling to the VCC rail, about 100uF should fix it.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 26th November 2010, 09:40 PM   #7
luka is online now luka  Slovenia
diyAudio Member
 
luka's Avatar
 
Join Date: Sep 2005
Location: in Slovenia :)
Send a message via Skype™ to luka
Quote:
Originally Posted by nigelwright7557 View Post
Add a bit more decoupling to the VCC rail, about 100uF should fix it.
amm... I already have 470u for lower and 47 for top...
__________________
home page @ http://www.classdaudio.tk/ @ 24/7 all year long
I FEEL SLOVENIA
  Reply With Quote
Old 26th November 2010, 09:55 PM   #8
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by luka View Post
amm... I already have 470u for lower and 47 for top...
For top ?

VCC is on its own.

Dont get confused with vaa, gnd and vss which are sperate supplies.

VCC to COM should be 100uf.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 26th November 2010, 10:39 PM   #9
luka is online now luka  Slovenia
diyAudio Member
 
luka's Avatar
 
Join Date: Sep 2005
Location: in Slovenia :)
Send a message via Skype™ to luka
top as in capacitor for opening top fet, goes from vcc(there is only one vcc) to diode and then to that cap... you don't have it on picture
So, 470uF from VCC to COM, and 47uF from VB to VS
__________________
home page @ http://www.classdaudio.tk/ @ 24/7 all year long
I FEEL SLOVENIA
  Reply With Quote
Old 26th November 2010, 10:45 PM   #10
diyAudio Member
 
nigelwright7557's Avatar
 
Join Date: Apr 2008
Location: Carlisle, England
Quote:
Originally Posted by luka View Post
top as in capacitor for opening top fet, goes from vcc(there is only one vcc) to diode and then to that cap... you don't have it on picture
So, 470uF from VCC to COM, and 47uF from VB to VS
You have to be careful with the upper voltage capacitor as it is charged from the VCC rail when VS goes low.
So the VCC capacitor has to be bigger to stop glitches on the vcc rail.

I guess what was happening with mine was the vcc undervoltage check was just on the border and causing a high frequency clicking on the output.
__________________
PCBCAD50 software. http://www.murtonpikesystems.co.uk
  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
Irs2092 luka Class D 50 15th July 2012 01:48 PM
Difference between self oscillating and non-self oscillating D-amp. sildex Class D 36 4th August 2010 03:30 PM
Self Oscillating (Oscillating Calculations) Help! Reactance Class D 7 12th March 2010 07:37 PM
IRS2092 help! yudi02 Class D 2 11th October 2009 03:30 AM


New To Site? Need Help?

All times are GMT. The time now is 08:04 AM.


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