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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Iamsmooth, do you have a copy of Switching Power Supply Design, A. Pressman, published by McGraw-Hill? If not, you should. I just got hold of a PDF copy (not saying how :X ) and it's excellent. There's pretty much a whole chapter on diode recovery problems in boost converters.
Pressman's Tip Of The Day: Use the lowest voltage diode you can. Higher voltage ones have worse recovery behaviour.
And as Patrick pointed out, terrible PCB layout won't help either. (I haven't looked at your layout, so I can't comment on whether it is in fact terrible.)
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Steve McConner wrote ...
Iamsmooth, do you have a copy of Switching Power Supply Design, A. Pressman, published by McGraw-Hill? If not, you should. I just got hold of a PDF copy (not saying how :X ) and it's excellent. There's pretty much a whole chapter on diode recovery problems in boost converters.
Pressman's Tip Of The Day: Use the lowest voltage diode you can. Higher voltage ones have worse recovery behaviour.
And as Patrick pointed out, terrible PCB layout won't help either. (I haven't looked at your layout, so I can't comment on whether it is in fact terrible.)
Yes I have a copy. I've started reading it a few days ago.
The PCB layout around the IGBT is in the beginning of the thread. I have not posted the PCB layout of the buck converter, but it is the same as on Wikipedia, figure 3
If the diode is going to see the full voltage, how does one use the "lowest voltage possible"? For me, the input voltage is 750DC.
I might try using an IGBT as a second switch instead of the diode if the faster diode or the high voltage schottky does not work, althought this will make the circuit more complex: adding another driver and checking that there is no shoot-through.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Steve, what page talks about the diode? I found something in section 1.3.5.
It states that recovery times of 35-50ns are preferable (page 17). Right now my diode is 85ns in order to achieve the voltage that I need. I'm going to try a 65ns diode. We'll see what happens when I get zero recovery time schottkys.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
IamSmooth wrote ...
We'll see what happens when I get zero recovery time schottkys.
when the corps' say this do they really mean "zero time" or are schottkys speed in the single nS to hundreds of pS time periods, so they just say zero meaning real close?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
They really mean zero.
But schottkys also have a capacitance that causes the same problems as recovery charge. I remember Richie analyzing a high-voltage boost converter with a SiC schottky and he concluded that it actually performed no better than an ordinary one. But that was several years ago, and I think the technology must have got better since.
No, I am not telling you which page. You need to read the whole book before starting any more threads here It's somewhere in the section on current-fed inverters.
"Very short recovery time Extremely low switching losses Soft recovery behaviour"
I plan to get a few of this too....even if I find it hard to believe the data-sheet about it being able to conduct 100A continuous, I don't see how it could with the TO247 package.
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Help with cleaning up gate drive to IGBT buck converter
It's somewhere in the section on current-fed inverters.
