smps problem (strange waveforms) - 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 18th November 2007, 10:43 PM   #1
PM650 is offline PM650  United States
diyAudio Member
 
Join Date: Jul 2005
Location: Tennessee
Default smps problem (strange waveforms)

I have an smps with a bit of a problem. It works, but the gate drive and primary waveforms look quite nasty. Also, the transformer makes a noise that is unaffected by any amount of physical manipulation. The supply is tl494 based with regulation, and does provide the correct dc outputs.

Gate drive:
http://www.mustangmods.com/ims/u/1363/4389/207366.jpg
http://www.mustangmods.com/ims/u/1363/4389/207367.jpg
Primary:
http://www.mustangmods.com/ims/u/1363/4389/207368.jpg

Any ideas?
  Reply With Quote
Old 19th November 2007, 05:47 AM   #2
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Well, you could use a faster shutter speed, and turn down the scope's intensity. :-)

From what I can see, there is some evidence that you might need a snubber or two.

There is a good paper about snubber design on the Cornell Dubilier website, at http://www.cde.com , in the technical papers section:

http://www.cornell-dubilier.com/design.pdf

There are some other good ones on line, too:

http://www.hagtech.com/pdf/snubber.pdf

http://www.ridleyengineering.com/snubber.htm

http://www.maxim-ic.com/appnotes.cfm...te_number/3835

http://archive.chipcenter.com/circui.../c1100rp58.htm

- Tom Gootee

http://www.fullnet.com/~tomg/index.html
  Reply With Quote
Old 19th November 2007, 06:50 AM   #3
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
Looks like you need a better trigger source to look at your waveform. If you're using delayed or expanded sweep... that could be a problem.

What you are seeing is "jitter"...

Your signals really don't look that bad... they are just not getting on the screen very well.

Getting a good look at gate drives is usually difficult on good day!

Also, what topolgy of SMPS are we talking about here?

A schematic would help a bit.

  Reply With Quote
Old 19th November 2007, 06:37 PM   #4
PM650 is offline PM650  United States
diyAudio Member
 
Join Date: Jul 2005
Location: Tennessee
The supply already has snubbers on the primary and gate drive as far as I know - I won't be able to look at it until i get home tomorrow. I guess those will be the first thing I check.

The supply is a standard half brigde with regulation; both +/- outputs on common mode inductor. I suppose it's worth noting that this is from a fairly reputable commercial manufacturer, not a diy. I can't remmember off-hand what settings I used on my scope, but I did use it earlier to test a smps and it provided no strange waveforms.
  Reply With Quote
Old 19th November 2007, 06:41 PM   #5
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
PM,

It is not about your scope... it's more about how you are triggering the waveform...

How are you doing that?

  Reply With Quote
Old 19th November 2007, 07:11 PM   #6
PM650 is offline PM650  United States
diyAudio Member
 
Join Date: Jul 2005
Location: Tennessee
Quote:
Originally posted by poobah
PM,

It is not about your scope... it's more about how you are triggering the waveform...

How are you doing that?


Yes I understood your point from the first post. The point I attempted to make was that I used the scope with the same trigger setting on another smps and everything seemed fine. I believe it's set to auto/int, whichever this scope has (I don't have it in front of me).

I'm afraid I don't have a schematic available to me; it would probably take a few hours to draw one up and I really don't want to take this thing appart again if I can avoid it.
  Reply With Quote
Old 19th November 2007, 07:32 PM   #7
poobah is offline poobah  United States
diyAudio Member
 
poobah's Avatar
 
Join Date: Nov 2005
I got ya...

The trick with gat drive waveforms, because of the constantly changing duty cycle, is to trigger off the same edge you wish to view. Try taking "auto off" and setting the trig level manually.

From what I could see your gate drive looked pretty good... any time you can get a good clear view of the MILLER step... you're doing prtty good.

  Reply With Quote
Old 21st November 2007, 04:55 AM   #8
PM650 is offline PM650  United States
diyAudio Member
 
Join Date: Jul 2005
Location: Tennessee
Ok, the settings I had before were not auto/int but now they are; this allowed manual adjustment and I got more or less the same gate drive waveform. The transformer primary waveform came out to be:
Click the image to open in full size.

I seriously don't think everything is right with this thing. The transformer didn't make noise before and I'm not quite sure what to think.
  Reply With Quote
Old 21st November 2007, 04:13 PM   #9
luka is offline luka  Slovenia
diyAudio Member
 
luka's Avatar
 
Join Date: Sep 2005
Location: in Slovenia :)
Send a message via Skype™ to luka
Hi

I think if you will load trafo a bit, that sinus will go away... try that
__________________
home page @ http://www.classdaudio.tk/ @ 24/7 all year long
I FEEL SLOVENIA
  Reply With Quote
Old 22nd November 2007, 10:27 PM   #10
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
The sinus is normal behaviour at low duty cycles, it's produced by transformer magnetizing inductance resonating with the capacitance or whatever stuff is connected to the windings.
__________________
I use to feel like the small child in The Emperor's New Clothes tale
  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
SMPS 2KW full bridge strange signal Orcino Power Supplies 3 30th July 2009 12:27 AM
strange waveforms at CD player oscillator capslock Digital Source 6 21st June 2007 07:28 AM
strange amp problem!!! moonchild Solid State 23 14th January 2006 01:05 PM
Strange little problem (or maybe not so) elizard Chip Amps 8 4th January 2004 07:25 AM
Aleph simulation- strange waveforms SteveG Pass Labs 40 31st July 2002 10:40 PM


New To Site? Need Help?

All times are GMT. The time now is 02:27 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