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Three SiC diodes in parallel for Full Bridge SMPS output rectifier?

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cupoftea

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Hi,
We are doing a 300W Full Bridge. 10-36vin, 32vout, 300wout. 125kHz.
Not synchronous.
Transformer = split sec. (Ns/Np = 4.5:1)
LTspice and jpeg attached.

The dv/dt on the output diodes, and the voltage peak on them (when at 36vin), means its too risky to do synchronous rectifiers. In fact, the best way, appears to be to put three D2PAK , FFSB1265A, SiC diodes in parallel for each rectifier.
Doing synchronous rectifiers in this case would require quite a swathe of "mothering" circuitry here, and appears not worth it, would you agree?

FFSB1265A (D2PAK) (£2.20 per 1000)
https://www.onsemi.com/pdf/datasheet/ffsb1265a-d.pdf

The Vf through these, at 175degc, goes as (If + 8.42) / 10.5.
As such, there will be a maximum of 2.5W in each D2PAK diode. We can thermal via them down to the 1cm thick Alu baseplate that this PCB sits on.

Would you agree we make a judicious choice here?

The other option is to do a single TO220, layed flat to the PCB, and a PCB cutout done so that its tab can be screwed to the Alu Baseplate. Or a hole drilled through the baseplate, and a screw poked through to screw the tab to the baseplate like that.....which means we dont mean to tap the "unfortunately-cheese-like" aluminium with threads.

So, are you a "triple D2PAK'er", or a "TO220'er" in this case?...or do you say that both methods are bad?
 

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  • 300W fullBridge _SplitSec _230116.jpg
    300W fullBridge _SplitSec _230116.jpg
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  • fullBridge300w_SS_FASTRUN.zip
    2.8 KB · Views: 79

I'd be concerned about current sharing and if two won't do,
be suspicious about three if the third either fails or is out-of-family
high Vf@If.

"Goes as" being something other than a guarantee across large
population and long time.
 
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