Common Cathode Diodes: Safe to Use in Parallel?

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Discussion Overview

The discussion centers around the safety and practicality of using common cathode diodes in parallel configurations. Participants explore the implications of this design choice, particularly in the context of current sharing and thermal management.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that using diodes in parallel is generally poor design practice due to the risk of unequal current distribution if the diodes are not perfectly matched.
  • One participant questions the necessity of using two diodes in parallel, suggesting that a single diode rated for higher current would be more appropriate for design purposes.
  • Another participant proposes that diodes on a common integrated circuit (IC) can be assumed to be well matched, which could mitigate the risk of run-away current.
  • Concerns are raised about the thermal performance of the diodes, with one participant noting that the device's ratings may be overly optimistic and warning about potential overheating issues.

Areas of Agreement / Disagreement

Participants express differing views on the safety and practicality of using common cathode diodes in parallel. While some suggest it may be acceptable under certain conditions, others emphasize the risks and recommend alternative approaches.

Contextual Notes

Participants highlight the importance of matching diodes and the potential for thermal issues, but do not resolve the debate on the overall safety of the configuration.

DragonPetter
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I know that using diodes in parallel is generally a bad design practice since you will have run away current in one of the diodes since they are not necessarily matched exactly.

But is it safe to use diodes in parallel if they're designed as a common cathode part?

this is an example:
http://www.onsemi.com/pub_link/Collateral/MBRD620CT-D.PDF

So is it safe for me to use the 2 diodes in the package in parallel?

Thank you
 
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Why would you want to use two diodes in parallel? If you need 6A current use something like this:

http://www.vishay.com/docs/94252/94252.pdf

If you just happen to have some of the product you mentioned on hand and want to use them for a prototype it will likely work fine, but if you are designing something, use a single diode.

Fish
 
Why would you want to use two diodes in parallel? If you need 6A current use something like this:

http://www.vishay.com/docs/94252/94252.pdf

If you just happen to have some of the product you mentioned on hand and want to use them for a prototype it will likely work fine, but if you are designing something, use a single diode.

Fish
 
DragonPetter said:
I know that using diodes in parallel is generally a bad design practice since you will have run away current in one of the diodes since they are not necessarily matched exactly.

But is it safe to use diodes in parallel if they're designed as a common cathode part?

this is an example:
http://www.onsemi.com/pub_link/Collateral/MBRD620CT-D.PDF

So is it safe for me to use the 2 diodes in the package in parallel?

Thank you

Diodes on a common IC can be assumed to be very well matched, so you could put them in parallel.

There won't be any "run-away current" anyway. the problem would be that the diodes would not share the current equally if they were mismatched.

The ratings for this device look optimistic, though.
It is about 0.25 inches square and drops 0.9 volts at 6 amps. That is 5.4 watts.

It is going to get very hot. Hot enough to burn a 0.25 inch square in your fingertip if you touch it.
 

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