Diodes in parallel

akis · 24th November 2010, 03:05 PM

Can I place silicon diodes in parallel so as to achieve higher continuous forward currents than it would be possible with just one?

Any gotchas?

AndrewT · 24th November 2010, 04:49 PM

unlikely to work efficiently.
The one with lower Vf will hog a bit of extra current.
It will then heat more and hog a higher proportion of the current.

It will do this positive feedback trick unless you can introduce negative feedback.

akis · 24th November 2010, 09:08 PM

oh, like we put a tiny resistance to parallel transistors to prevent thermal runway...

Hmm, it seems hard to find 6A + rectifier diodes, non-schottky. Currently aiming at this:

IXYS SEMICONDUCTOR|DPG10I400PA|DIODE, FAST, TO-247AC | Farnell United Kingdom

akis · 24th November 2010, 09:14 PM

how about using a suitable transistor with base wired to collector?

sawreyrw · 24th November 2010, 11:12 PM

Putting diodes in parallel is not a great idea, but adding series resistors to help balance them will help. I would recommend using a single diode
that can handle thge required current.

Connecting a transistor with base to collector will act like a diode, but the reverse voltage rating will be only about 6.8 volts. The 6.8 volts is a generalization, but that is typical of the base emitter junction.

akis · 25th November 2010, 06:42 AM

How about putting a high voltage, low amps diode in series with the base pin, will that help the base-emitter junction? Will it also cause the transistor now to act as a diode but with 1.2V drop instead of the nominal 0.6V (at low currents) ? I am not at home to try this on the simulation just now.

Enzo · 25th November 2010, 08:20 AM

You want over 6A, but don;t want schottky. Do you still want fast recovery as your example part has?

Since this seems to be a power supply application, have you considered a bridge? They commonly are available in substantial currents. Is the TO package a requirement, or can they be shaped otherwise?

akis · 25th November 2010, 08:25 AM

I want something better than the 1N5401 series, those are 3A. I have nothing in my drawers for say 5A or 6A, except as you said bridges.

I was told to stay away from Schottky because of leakage currents and other stuff

metalsculptor · 25th November 2010, 09:05 AM

I do not know why you are having a hard time finding diodes greater than 6A, go to the phone book and look up a company like semikron or westcode, There are 3 westcode 1800A 1600V diodes on top of my fridge.

For smaller stuff the MUR8xx and RUR15XX TO220 package diodes are common getting larger the stud mount DO packages start at 10A and go around 400A Unfortunately they get expensive

Bridges in 25 35 and 50 amp are common and cheap 100A are available but assembling from 2 diode modules is popular in this current range.

Diodes are used in parallel and they share current if matched, that is how rectifiers are built to handle 10's of kA.

tangmonster · 26th November 2010, 10:58 AM

24th November 2010, 03:05 PM	#1
akis diyAudio Member Join Date: Jul 2008	Diodes in parallel Can I place silicon diodes in parallel so as to achieve higher continuous forward currents than it would be possible with just one? Any gotchas?

24th November 2010, 04:49 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	unlikely to work efficiently. The one with lower Vf will hog a bit of extra current. It will then heat more and hog a higher proportion of the current. It will do this positive feedback trick unless you can introduce negative feedback. __________________ regards Andrew T.

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24th November 2010, 09:08 PM	#3
akis diyAudio Member Join Date: Jul 2008	oh, like we put a tiny resistance to parallel transistors to prevent thermal runway... Hmm, it seems hard to find 6A + rectifier diodes, non-schottky. Currently aiming at this: IXYS SEMICONDUCTOR\|DPG10I400PA\|DIODE, FAST, TO-247AC \| Farnell United Kingdom

24th November 2010, 09:14 PM	#4
akis diyAudio Member Join Date: Jul 2008	how about using a suitable transistor with base wired to collector?

24th November 2010, 11:12 PM	#5
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	Putting diodes in parallel is not a great idea, but adding series resistors to help balance them will help. I would recommend using a single diode that can handle thge required current. Connecting a transistor with base to collector will act like a diode, but the reverse voltage rating will be only about 6.8 volts. The 6.8 volts is a generalization, but that is typical of the base emitter junction.

25th November 2010, 06:42 AM	#6
akis diyAudio Member Join Date: Jul 2008	How about putting a high voltage, low amps diode in series with the base pin, will that help the base-emitter junction? Will it also cause the transistor now to act as a diode but with 1.2V drop instead of the nominal 0.6V (at low currents) ? I am not at home to try this on the simulation just now.

25th November 2010, 08:20 AM	#7
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	You want over 6A, but don;t want schottky. Do you still want fast recovery as your example part has? Since this seems to be a power supply application, have you considered a bridge? They commonly are available in substantial currents. Is the TO package a requirement, or can they be shaped otherwise?

25th November 2010, 08:25 AM	#8
akis diyAudio Member Join Date: Jul 2008	I want something better than the 1N5401 series, those are 3A. I have nothing in my drawers for say 5A or 6A, except as you said bridges. I was told to stay away from Schottky because of leakage currents and other stuff

25th November 2010, 09:05 AM	#9
metalsculptor diyAudio Member Join Date: Sep 2010 Location: Melbourne	I do not know why you are having a hard time finding diodes greater than 6A, go to the phone book and look up a company like semikron or westcode, There are 3 westcode 1800A 1600V diodes on top of my fridge. For smaller stuff the MUR8xx and RUR15XX TO220 package diodes are common getting larger the stud mount DO packages start at 10A and go around 400A Unfortunately they get expensive Bridges in 25 35 and 50 amp are common and cheap 100A are available but assembling from 2 diode modules is popular in this current range. Diodes are used in parallel and they share current if matched, that is how rectifiers are built to handle 10's of kA.

26th November 2010, 10:58 AM	#10
tangmonster diyAudio Member Join Date: Jul 2007 Location: Cape Town	6A10 http://www.diodes.com/datasheets/ds28009.pdf Here is different options from UK Rs components. a local electronics store should be cheaper. I paid ZAR 1.00 for per 6a10 for one of my projects. Taiwan Semiconductor \| Semiconductors \| Discretes \| Rectifier \| Diodes - Rectifiers \|SF63 Fairchild Semiconductor \| Semiconductors \| Discretes \| Rectifier \| Diodes - Rectifiers \|RURD660

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