Is it a no-no to parallel power rectifier diodes?

Question

I need a reverse battery voltage scheme for a 60A max automotive circuit design. Nominal current is 50A.

My first idea was just to throw a Schottky diode in series with the battery feed like I do in every other circuit. However, 60A diodes in a reasonably sized package are hard to come by.

I found a single diode in a TO-220 package that can carry 30A. The problem being I would need to place two diodes in parallel to carry a maximum of 60A. My concern is whether or not the devices will share current evenly. If power dissipation is slightly higher on one than the other, won't it self heat more and create an even higher non-distribution of current (Vf drop decreases as the device heats).

Both diodes will be bolted next to each other on a liquid cooled aluminum heat sink.

Thanks,

George

Homer J Simpson · Accepted Answer

Wire to one diode only then bridge to the second. Reverse this for the output. It'll help some.-- +++++++++++++++++++++++++++++++++++++++++++++++++++++ Required crap appended to avoid restrictions imposed by brain   ++ damaged idiots. ++ Server Response: '441 Posting Failed (Rejected by POST filter)', ++ Port: 119, Secure(SSL): No, Server Error: 441, ++ Error Number: 0x800CCCA9 +++++++++++++++++++++++++++++++++++++++++++++++++++++

Lares · Answer

Placing a low value high wattage resistor in series with each of the diodes will distribute load evenly. I have seen this done with Diodes before, but not Schottky, so there may be issues related to that.

-Lares

Ge0rge Marutz · Answer

Thank you for the hints gentlemen.Ge0rge

Ge0rge Marutz · Answer

How about something like a 0.001ohm precision current shunt?  Thiswould work for prototype purposes but not volume production.Ge0rge

PhattyMo · Answer

Perhaps make your own resistors..Maybe something like a foot or two of #16 wire,just enough resistance to help balance the current.

Baron · Answer

At those current levels the connecting wires will probably be enoughresistance !-- Baron:

default · Answer

check the datasheet for the diodes and see what 60 millivolts represents in terms of heating - that may be a clue.

"Volume production?" That's one of those times it just doesn't pay to make a mistake - consult the diode manufacturer.

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john jardine · Answer

Shottkys do work well in parallel if in the same package. Something like  should be the kind of thing. Farnells stock arange of them.john-- Posted via a free Usenet account from

Homer J Simpson · Answer

Per the suggestion I made above, in effect the bridging wires become theseries resistors. You could even make them longer if you need morestability.-- +++++++++++++++++++++++++++++++++++++++++++++++++++++ Required crap appended to avoid restrictions imposed by brain   ++ damaged idiots. ++ Server Response: '441 Posting Failed (Rejected by POST filter)', ++ Port: 119, Secure(SSL): No, Server Error: 441, ++ Error Number: 0x800CCCA9 +++++++++++++++++++++++++++++++++++++++++++++++++++++

jasen · Answer

I've seen 60A diodes in a package the size (and approximate shape)of a LR44 button cell... try an automitive electrical place - they use themin the recitifiers of the altenators.Bye.   Jasen

Blake · Answer

A sixty amp diode shouldn't be any larger than two thirty amp ones. Consider this 60 amp diode in a TO-220 package, for example.

Is it a no-no to parallel power rectifier diodes?

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