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I am wondering what the effects are of putting diodes in parallel or putting them in series. (like current capabilities, voltage capabilities etc.) Let's say I have a datasheet of a diode. What characteristics would change ? My estimation is that putting parallel would increase the current capabilities, but may have a negative effect in reverse leakage. I have no idea if I am right or how to test it, so any info on diodes in parallel or series would be great.

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4 Answers 4

up vote 2 down vote accepted

Connecting diodes in series (AK-AK --|<--|<--) will increase the forward voltage of the resultant diode.

Connecting diodes in series (AK-KA --|<-->|--) will cause an open circuit until peak inverse voltage (smallest diode) is applied on total resultant.

Connecting diodes in parallel (AK/AK --|<-- + --|<--) will increase the current carrying capacity of the diode.

Connecting diodes in parallel (AK/KA --|<-- + -->|--) will not get you a resultant diode conduction in both sides.

I hope my illustrations are understandable :-)

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I am affraid you cannot increase current capability so easily. At least some small resistors in series would be handy in that parallel combination of diodes. – Al Kepp Jan 7 '13 at 6:16
This answer is very misleading at point 3. Connecting diodes in Parallel does not increase the carrying current of the diodes. An good explanation of what happens when you connect diodes in parallel can be found here – AK_ Aug 28 '14 at 13:55

Putting diodes in series will add the diode drops together. Reverse leakage (and capacitance) should reduce in this configuration.

In parallel, the drop will stay the same (reverse leakage and capacitance will add), but the current capability may not be much higher, due to the possibility of thermal runaway (since as a diode gets hotter it's Vf drops, then it draws more current relative to the rest, gets hotter still, and so on). You can avoid this somewhat by placing the diodes in thermal contact with each other, and/or using a small resistor in series with each.

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The same applies to diodes in series; you cannot rely on increasing the voltage rating unless you add a HIGH value resistance across each diode - rated to conduct say 10x the worst-case reverse leakage current across the volt/temperature range. Otherwise one diode leaks, and the other breaks down... – Brian Drummond Jan 7 '13 at 11:45
@BrianDrummond - Yes, good point, you're right - the figures cannot be accurately predicted. – Oli Glaser Jan 7 '13 at 13:09
What about paralleling 2 diodes that are in the same package? They have the same temperature and same characteristics, so the current is shared roughly equally? I see this often in power supply rectifiers, from people who ostensibly know what they are doing. – endolith May 12 '14 at 14:30
I would mark this answer as correct. The previous one is very misleading – AK_ Aug 28 '14 at 13:56

Diodes in series with the same polarity each behave no differently than a single diode. The voltage drop and current capabilities of each diode remains the same. The overall voltage drop of the series combination of the diodes will be equal to the total of all of the diode voltage drops. The current capability of the diodes does not change.

Diodes in parallel with the same polarity each behave no differently than a single diode. However, due to the fact that the current into each diode is lower because of the current divider rule, each diode will have less current flowing through it, and therefore its voltage drop will be lower, as this is a characteristic of diodes. Therefore, assuming the diodes are all identical, the overall voltage drop of the parallel combination of diodes will be lower than it would be for a single diode. Although each individual diode's current capability does not change, the parallel combination of diodes can handle more current overall, once again because of the current divider rule.

Great illustration here:

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What you say is partially true, but putting two 600v diodes in series does not result in an effective 1200v working, unless you put current balancing resistors across each diode.

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