How to choose a snubber diode?

[cznie]

Please help! My questions are : 1.If the coil's working voltage is 12V DC, what breakdown voltage should the anti kickback diode have? If the coil draws 200mA what the currect rating should the diode have? Thanks! cz 3/31/2011

 

[enjunear]

For your situation, the diode can be just about anything, so long as you don't exceed the reverse breakdown. If your coil voltage is 12V, then find one around 15V or better. A little 1N4148 will handle 100V in reverse, and can handle 450 mA of peak fwd current (200 mA continuous). Since you are using the diode to let the current in the coil slowly drop (rather than stop instantly), the diode will initially see your steady-state current of 200 mA. However, that will only last for a short time before the magnetic field in the coil collapses, and the current beings to drop to zero.

 

[Orson Cart]

If you want the relay to open at a similar rate to its closing speed then a zener diode of 2 x the driving voltage across the driving device (e.g. the transistor energising the relay) will give a much faster opening rate of the contacts than a simple diode across the relay coil, Regards, Orson Cart.

 

[cznie]

For your situation, the diode can be just about anything, so long as you don't exceed the reverse breakdown. If your coil voltage is 12V, then find one around 15V or better. A little 1N4148 will handle 100V in reverse, and can handle 450 mA of peak fwd current (200 mA continuous). Since you are using the diode to let the current in the coil slowly drop (rather than stop instantly), the diode will initially see your steady-state current of 200 mA. However, that will only last for a short time before the magnetic field in the coil collapses, and the current beings to drop to zero.

Thank you so much! This was a question from a test. The answer was 10 times, and I do not believe it was correct. Thank you for your quick reply which comfirmed my understanding how the snubber works. I will not site your answer to question the tester. Just for my own better understanding. Best regards!

 

[Kral]

enjunear is correct regarding the peak diode current. The test answer, as you suspect, is wrong. Orson Cart's suggestion is recommended because if a relay contact opens slowly, excessive arcing can occur, reducing the life of the relay contacts.

 

[cznie]

enjunear is correct regarding the peak diode current. The test answer, as you suspect, is wrong. Orson Cart's suggestion is recommended because if a relay contact opens slowly, excessive arcing can occur, reducing the life of the relay contacts.

Dear Carl: Thank you very much! I did not expect getting help from so many people in such a short time for my little questions. Thank you again! Best wishes! cz 4/3/2011

---------- Post added at 00:14 ---------- Previous post was at 00:11 ----------

If you want the relay to open at a similar rate to its closing speed then a zener diode of 2 x the driving voltage across the driving device (e.g. the transistor energising the relay) will give a much faster opening rate of the contacts than a simple diode across the relay coil, Regards, Orson Cart.

Dear Orson Cart: Thank you very much for your help. I am a new comer, and I sure appreciate all the help that I am getting here. Best wishes! cz 4/3/2011