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

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

Reply to
Ge0rge Marutz
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Wire to one diode only then bridge to the second. Reverse this for the output. It'll help some.

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Reply to
Homer J Simpson

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

Reply to
Lares

Thank you for the hints gentlemen.

Ge0rge

Reply to
Ge0rge Marutz

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

Ge0rge

Reply to
Ge0rge Marutz

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

Reply to
PhattyMo

At those current levels the connecting wires will probably be enough resistance !

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Reply to
Baron

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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Reply to
default

Shottkys do work well in parallel if in the same package. Something like

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should be the kind of thing. Farnells stock a range of them. john

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Reply to
john jardine

Per the suggestion I made above, in effect the bridging wires become the series resistors. You could even make them longer if you need more stability.

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Reply to
Homer J Simpson

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 them in the recitifiers of the altenators.

Bye. Jasen

Reply to
jasen

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.

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Reply to
Blake

They won't. The diode with the lower forward voltage rating will take he whole load, release its magic-smoke, go open circuit, then the second diode will do the same.

In theory, you could put resistors in series with each diode to equalise the current, but it'd be cheaper, easier, tidier & more reliable to simply use a single diode that's rated for the maximum possible load (plus a safety factor!).

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Reply to
Lionel

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