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?
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?
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/appnote_number/3835
http://archive.chipcenter.com/circuitcellar/november00/c1100rp58.htm
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
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/appnote_number/3835
http://archive.chipcenter.com/circuitcellar/november00/c1100rp58.htm
- Tom Gootee
http://www.fullnet.com/~tomg/index.html
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.
😉
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.
😉
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.
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.
PM,
It is not about your scope... it's more about how you are triggering the waveform...
How are you doing that?
😉
It is not about your scope... it's more about how you are triggering the waveform...
How are you doing that?
😉
poobah said:
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.
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.
😉
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.
😉
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:
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.
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.
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.
Alright I tested it with a load and the noise almost completely goes away as duty cycle approaches 50% (the waveform looks fairly normal at this point as well). Does anyone think the transformer noise is a problem or is this normal?
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