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How to choose the right Freewheel diode

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Jony130

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How I can choose the correct freewheeling diode for PWM control 25A DC Motor.
How do you choose the current rating of a diode.
 

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How I can choose the correct freewheeling diode for PWM control 25A DC Motor.
How do you choose the current rating of a diode.

If you are switching the motor On/Off, the current flowing in the motor at the moment you switch OFF will be the required Diode current peak rating.

For a 25A motor current, you use a diode with a peak 25A rating.
 
Do you mean this peak current form dataset Peak forward surge current, 8.3ms single
half sine-wave superimposed on rated load
?
 
I would select a diode with a 25A average rated load current.
 
You really need to know more about it than your spec.. Is 25 amps maximum motor current? Motor inductance. For example a motor with a few microhenries will be different than one with millihenries. Then PWM frequency.
 
look at Silicon Carbide diodes. they have ZERO reverse recovery time, so the PWM frequency isn't a big factor.

there's a selection chart here: **broken link removed**
 
Another type of fast switching diode is a Schottky and they are likely cheaper than Silicon Carbide devices.
 
that's only a 5A device. i thought you were looking for a 25A device.
 
that's a SINGLE PULSE rating, not a repetitive rating. that's like saying a speaker has the capability of two feet of cone excursion, ONCE.... use the right tool for the right job. if the diode fails, you will be driving a direct short with the transistor, and it won't last more than a few milliseconds either.
 
How about somewhere in the middle? Say 10 amps with a heatsink.
 

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i guess that really depends on the mosfet used..... the lower the Rds-on, the higher the diode current.
 
I think the maximum diode current occurs at a 50% duty cycle and high motor inductance. So a 25 amp motor will store 12.5 amps. Since the diode will see the same current during fly-back it will see 12.5 amps but only for 50% of the time or 6.25 amps average. Higher duty cycle will produce diode peak currents up to 25 amps but for only a very short part of the PWM cycle. There may be some reverse recovery time currents but with a schottky diode they can probably be ignored for this discussion.
 
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