IRF's Hexfred or Schottky?

[Ouroboros]

It's all to do with how fast the voltage on the 'input' side to the diode drops when the diode gets reverse biased. on 50 or 60Hz full-wave rectified mains, the rate-of-change of the voltage is obviously defined by the fact that the signal is a FW rectified sine wave.

The real problem is with continuous-conduction boost power-factor-correction stages for SMPSUs like I have to design (for my paid work) at times.

Standard 50Hz bridge rectifiers diodes will not have controlled recovery characteristics. You can slug the reverse recovery by putting capacitors across each diode. This increases the reverse conduction time, but slows down the recovery time, so it reduces the unwanted RF noise caused by the fast di/dt turn-off.

[richie00boy]

Cheers, that's cleared it up. The question now though is whether to slug each diode or just across AC and DC on the rectifier (2 snubbers in total).

[eeka chu]

Originally posted by richie00boy
Cheers, that's cleared it up. The question now though is whether to slug each diode or just across AC and DC on the rectifier (2 snubbers in total).

I'd also like to ask that question.

I'm wondering if it's fussing for the need of fussing. Theoretically, it makes sense, and you could probably measure some change on a scope. But if you were to click the snubbers in and out of place, would you actually hear a worth while difference with modern diodes like Hexfreds?

Would ceramics be suitable for snubbers?

[Ouroboros]

If you are using diodes designed for SMPSU high-frequency use (like the HexFREDs) then you are unlikely to gain any benefit from the capacitors.

The only time I've had a serious HF noise problem with a transformer/bridge rectifier on normal 50Hz mains was using a bridge made of 1N4004 diodes in a low-current 18V supply.

[tubee]

Sorry for kickin' this old thread, but rather interesting facts where discussed here.

What i have done a while ago is swapping the standard two (for dual mono) 35A diode bridges to a diy diode bridge with four HFA08TB60 hexfred diodes mounted isolated on an aluminium L profile. The new bridges are for the current section of a diy hybrid amplifier with E88CC srpp voltage stage and a old pair of hitachi K135/J50 powerfets to the speaker.

The sound compared to the standard diode bridge was more "backward', and maybe some more detailed in treble. But the bass is worsened imo, less control, more boomy, it sounds like a higher Q factor speaker, and i only swapped the diodes!
Tried a snubber on it also, but removed it, didn't help much

Anyone the same sort of sound experiences?