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I'm trying to design a circuit for a relay similar to the following (except using SMT components):

enter image description here

When I went to Mouser to try to find a suitable SMT diode to use in place of the 1N4001, I noticed there are four main categories:

TVS Diodes (21,395)
Rectifiers (9,872)      
Schottky Diodes & Rectifiers (8,259)    
Zener Diodes (15,726)

I'm pretty sure Zener & Schottky diodes are not supposed to be used as flyback diodes, which leaves TVS Diodes and Rectifiers.

Looking on Wikipedia, a TVS diode is shown as:

enter image description here

I did a little searching online and it seems some designs use a Rectifier like the 1N4001, while others use TVS diodes. I couldn't find a clear answer as to which is better.

Is there any advantage to using a TVS diode over a Rectifier diode for flyback applications such as a relay circuit?

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Schottkys are perfectly suitable and commonly used as flyback diodes. –  Matt Young May 18 at 0:16
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2 Answers 2

up vote 2 down vote accepted

Why the drama. Just use this: -

enter image description here

If you want a SMD version of the 1N400x series use the above and not a TVS. TVS diodes conduct in both directions and are not suitable for flyback diodes.

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Thanks! Two quick questions: 1) How did you find the SMD equivalent of the 1N400x? Did you just know of a device from experience, or is there a method you used to find it? 2) Are you sure TVS diodes can't be used as flyback diodes? I saw them being suggested on several websites. –  Nate May 17 at 23:07
1  
I knew there was one so I used google to find it. You can use a TVS providing it's single ended but efficiency might be lower. –  Andy aka May 18 at 10:02
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The TVS diode (bipolar type only) will give you maximum relay life, at the cost of a much more expensive part (sub 1 cent for an LL4148) and working the drive transistor harder (I suggest an MMBT4401).

Without getting pathological, the rectifier diode is about as bad as you can get for slowing the opening of the relay contacts, and thus maximizing the arcing.

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