parallel rectifiers

[danielnaveen]

Hello,

I have two GBU802 rectifiers can i parallel them? how do i do that?

Thank you for your answers

Daniel

[janneman]

Originally posted by danielnaveen
Hello,

I have two GBU802 rectifiers can i parallel them? how do i do that?

Thank you for your answers

Daniel

You can parallel them, but it wouldn't be advantageous. Because the diodes will have small different forward thresholds, one will take the majority of the current. You can't parallel two 5A diodes and expect to be able to run 10A through the combo.

BTW Why do you ask?

Jan Didden

[Bobken]

Hi Daniel,

Many years ago I read that Kostas Metaxas (of Metaxas Amplifiers) advocated the use of multiple parallel low-current diodes in his PS bridges. Some sonic improvements were claimed, although it was so long ago that I don't now recall precisely what the theory behind this was.

Accordingly, as an experiment I made up a discrete diode bridge for a power amp with about 8 or 10 - 1N400* diodes in parallel, and used 4 of these parallel diode arrangements for each of the sides of this bridge.

This was an improvement sonically over the 'standard' encapsulated diode bridge which was replaced by this discrete arrangement, and I used it in a 100W amp for probably 2+ yrs without any problems. In fact I only replaced it later when I found that some fast/soft-recovery types (and Schottkys) provided a further sonic improvement over the suggestion made by Metaxas.

I still come across these discrete bridges from time to time when I go through my 'reclaimed parts' box as (so far) I have not broken them down again to use in other locations.
Possibly an Internet search will reveal Metaxas' reasoning behind his suggestion from long ago, but it must have made some sense to me at the time, or I wouldn't have wasted my time in trying it out for myself.

Regards,

[danielnaveen]

Thanks for the replies, and janneman i wanna use them in parallel to increase the current rating to use it in my LM3886 chip amp. I wanna use 26800 ufd of capacitance on each rail so i'm not sure if the 8amp rating of a single rectifier will be enough.

[Bobken]

Hi Daniel,

From my experiences before, there appeared to be no problems with current-sharing, but this is not to say that all diodes will behave in the same manner. This was in a 100W RMS per channel Class AB amp, which I used to drive hard without any problems, but I didn't ever measure the current drawn during heavy use. However, it must have been many times greater than a single 1N400* diode is rated for.

I certainly cannot believe that there will be so much variation in their electrical parameters that adding a pair of your suggested diodes together will not provide you with something getting close to twice the current-rating of a single diode, though, and it should be able to cope with greater currents than a solitary diode of the same type.

As you suggest, the initial surge at switch-on with large smoothing-caps is the most vulnerable time for any such diodes. It is this parameter which you should ideally check out on the data-sheet for these devices.

Good luck if you try this out, anyway.

Regards,

[danielnaveen]

Hi Bobken, well i just finished and tested both the channels of my LM3886 based amp on a stripboard its late now so i'll build the powersupply tomorrow and will see what happens. Hopefully it wont be a ball of fire

[AndrewT]

Hi,
Sugden use 1n5402 diode bridges to charge up 9400uF to +-72Vdc.
I have increased this to 19700uF on the same diodes and had no problems. These are rated at 3A continuous.

[danielnaveen]

Andrew do you think i'll be fine a single 8A rated rectifier with 26800Ufd on each rail?

[danielnaveen]

thats a total of 53600ufd's of capacitance.

[Bobken]

Hi Daniel,

It is not easy to precisely predict the switch-on surges in cases like this, and depending on the mains supply, they can vary, anyway.

However when not being absolutely confident during any new trial, it is sensible to take care, and not risk anything unnecessarily. The same goes even for a known situation, as not all components behave as they should, and things can still go wrong in spite of everything being according to specs etc.

Apart from Transzorbs (a totally different type of dode) in my own experiences, all other diode failures I have seen have failed with the diode going open-circuit, which is better/safer than shorting out.
They can burst apart, though, like a mini-explosion, so it would be sensible to wear some eye protection for the first few trials, just in case, and don't stand over anything during any such experiments. The internal parts of diodes are 'dry' so there is no acid or anything to worry about being thrown over yourself or your room, and my guess is that the worst you will experience if there is a failure is a small bang, a bit of smoke, and the failed device going open-circuit.

Regards,