Diode Rectifier

[Alf]

Really you're supposed to use "avalanche rated" diodes

Sorry for my ignorance but what exactly are they ??

What types are there to be used in the power supply instead of the 1N4007 ?

[Steve Conner]

Modern best practice would be to use a single high voltage diode like the SF1600 or GP10Y from Vishay, rather than stringing lower voltage ones in series. The SF1600 is avalanche rated anyway.

[Alf]

So , if I understand correctly you could use them in front of the regular bridge rectifer which I always use ?

[Steve Conner]

No, why on earth would you want to do that? The diodes in a bridge rectifier only see a PIV of 1x the DC output voltage, so for typical guitar amp voltages, even 1000V diodes are fine. There is no need to go shopping for 1600V ones or stringing them in series.

Avalanche rated diodes are theoretically more rugged and resistant to being zapped by spikes from the mains. If you made your bridge rectifier out of SF1600s, it would be a pretty tough cookie. But their main advantage is that they automatically share voltage when connected in series. Any diode that finds itself taking more than its share of the voltage will just avalanche harmlessly.

Ordinary diodes do exactly the same, the difference is that the maker gives no warranty that the avalanche breakdown won't damage them.

[R.G.]

Steve is absolutely correct. Use a modern, avalanche rated diode rated for the full voltage or more.

"Avalanche" is the term used for when a diode breaks over backwards due to a reverse voltage bigger than it can handle. "Avalanche rated" means that the diode and the packaging it's in have been designed to withstand this without damage within the specified avalanche limits.

The old wisdom - which is what I learned and hide behind at every opportunity - is to not ever break them over. Avalanche rated diodes are tougher in those circumstances and let you do some breakover within limits without worrying that you'll kill them.

[Alf]

Thanks , Steve and R.G for your very enlightening explanation.

[Tom Phillips]

For those who would like to read a little more about applications using avalanche diodes there is an interesting white paper posted at High voltage avalanche diodes .

The paper also includes links to additional related information.

Cheers,
Tom