Thanks Guys, I know that you all appreciate that the "current hogging" problem doesn't happen for "SiC" diodes in parallel, because they have a "Positive temperature coefficient". -They automatically share the current equally between each other when paralleled.
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What duty cycle are you running.
For the design in the top post the duty cycle over 85-265VAC is 0.3 to 0.1
-it was deliberately made to be this so as to reduce secondary rms and peak current.
However thankyou for the above 200V single schottky suggestion, if using this then I would change the flyback txfmr turns ratio so as to allow less reflected voltage to the secondary diode, so I will look into that.
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That is a great idea to use just one standard 200V schottky.
Some of the high current, 200V schottkys have superbly low Vf’s, and initially appear great to use, but then you notice they actually have a significant reverse recovery time, or a really high junction capacitance. –So you then try and get round this by just using DCM, but then you notice that the high current 200V schottkys have a really high reverse leakage current, which really increases losses. So we can’t use the really high current , low Vf, 200V schottkys at all without a heatsink…..
Therefore, I then went for a VT5202 200V, 5A Schottky in TO220. This appears to have no reverse recovery time, so I actually opted to use it in CCM..-but then I changed my mind and thought what the heck I’ll use it in DCM anyway because that gets rid of the RHPZ.
So I reckon the VT5202 200V Schottky would dissipate 0.65V*1.3A = 0.845W
To be honest, 0.845W is a bit too much power for a TO220 with no heatsink.
The 52 degC per Watt referred to in the VT5202 datasheet refers to “Free Air”, and of course, the air inside an enclosed case isn’t “Free Air”.
Therefore, I reckon that the multiple paralleled SiC Schottky diodes is the only way to actually avoid the need for a heatsink in this Flyback SMPS.