how to calculate / select flyback diode?

I plan to use a flyback diode to absorb the current from a12V/38.8A/10mH DC motor when disconnecting the motor. The circuit can be similar circuit in below link: or figure 4 in below link:

How to calculate / select flyback diode? for example, how to decide IFSM(Non-Repetitive Peak Forward Surge Current 8.3ms, Single Half Sine-Wave Superimposed on Rated Load), IF(Maximum average forward rectified current), etc. You can recommend an article to help me. Thank you.

by wangwg88
September 05, 2019
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1 Answer

Answer by Foxx

I was up against this problem many times when I worked for a living and the answer is really quite simple. Just understand that when the supply current is cut off the inductance of the motor (or other inductive device) becomes a current source generating the same current and current direction as existed immediately before the cutoff. When a flywheel (not flyback) diode is used this current flows through the diode and dies away on the L/R time constant of the inductive device. In the case of a dc motor this will probably be in the range of say 20 ms to 200 ms. You can shorten the time constant by adding a resistor in series with the flywheel diode but keep in mind that this will raise the voltage across the terminals of the inductive device.

+1 vote
by Foxx
September 07, 2019
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