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Old 18th February 2007, 03:47 PM   #1
zilog is offline zilog  Sweden
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Default output rectifier choice for SMPS

I am having trouble finding suitable diodes for my smps, as the transformer is 3+3:16+16 turns, 16V input yields 170V peak reverse voltage for the diodes in a full bridge. The current rating should be 7A minimum. I would also like the diodes to have soft recovery characteristics, but that seems like yet a demand I cannot meet. Are there any diodes that meet these demands and dont waste too much energy due to reverse recovery at my fs of 2x55kHz? Am I forced to look for a synchronous rectifier solution to avoid this problem, and if I do that, are there any more or less suitable mosfets that dont cause EMI with the recovery process of their body diodes?
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Old 18th February 2007, 04:22 PM   #2
Eva is offline Eva  Spain
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Ultrafast 200V diodes (usually rated for Trr=50 to 75ns) would be fine as the leakage inductance is much higher as seen from the secondary side of the transformer (28 times for 3:16) and this helps a lot to limit dI/dt. To tame the abrupt impedance changes of the diodes use a suitable RC snubber in parallel with each one.
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Old 18th February 2007, 04:36 PM   #3
zilog is offline zilog  Sweden
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Quote:
Originally posted by Eva
Ultrafast 200V diodes (usually rated for Trr=50 to 75ns) would be fine as the leakage inductance is much higher as seen from the secondary side of the transformer (28 times for 3:16) and this helps a lot to limit dI/dt. To tame the abrupt impedance changes of the diodes use a suitable RC snubber in parallel with each one.
Are those ordinary switch diodes? I cant find any schottky rated for those voltages in the ordinary buying places. What is the difference except forward voltage drop between using switch- or schottk diodes for this application?

I have my eyes on MUR820, is this an appropriate choice? Are there any choices in this range that have soft enough recovery not to necessitate snubbing?
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Old 18th February 2007, 04:56 PM   #4
zilog is offline zilog  Sweden
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Whst about this one - http://www.elfa.se/pdf/70/07021793.pdf , has fairly soft recovery .. and is not that expensive.
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