General Flyback Diode Question

Thread Starter

Archaeus

Joined Sep 10, 2016
34
Hi,

I've been reading as much as I can about diode calculations for pwm in a mosfet h bridge. I have a new working soldered dual motor driver board tested with small hobby motors. No issues. No heat. Im about to ramp it to a 12v+, 10amp test, so I would like to have the protection aspects covered.

I have a standard configuration with two p channel (irf9540) and two n channel fets (irfz44) driven by a tc428 driver IC at 2Khz from a raspberry pi. I understand schottky diodes are preffered for emf kickback protection, however my local store has limited options. Will four 1n5820/21 schottky diodes work at 2k frequency? 3amp diodes are the largest they have and the data sheet indicates a recovery time of approx 500ns. I'm hoping they will have a fast enough capability to shunt around 10a of pulsed current safely. Any recommemdations would be appreciated.

Diode data: https://www.digikey.ca/product-detail/en/on-semiconductor/1N5821/1N5821FSCT-ND/4314811
 

Thread Starter

Archaeus

Joined Sep 10, 2016
34
A follow up question. These are only rated for 20-30v. Would emf spikes blow past that rating causing trouble? I just watched a video of someone scoping 700v momentary spikes from a low voltage relay.
 

BobTPH

Joined Jun 5, 2013
2,745
The back EMF forward biases the diode and is therefore clamped at the forward voltage of the diode. The reverse voltage on the diode is only the voltage used to drive the motor.

Bob
 

Thread Starter

Archaeus

Joined Sep 10, 2016
34
The back EMF forward biases the diode and is therefore clamped at the forward voltage of the diode. The reverse voltage on the diode is only the voltage used to drive the motor.

Bob
That really cleared up the working of that system. Perfect. Thanks for replying.
 
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