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

 

These diodes at a frequency of 2 kHz allow 30 A of impulse current (see datasheet)

 

These diodes at a frequency of 2 kHz allow 30 A of impulse current (see datasheet)

Great. I did see that section, but was hoping for confirmation in general about their use. Thank you for that.

 

The intrinsic MOSFET substrate diodes are likely sufficient to provide protection for the current spikes of your inductive load.

 

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.

 

The intrinsic MOSFET substrate diodes are likely sufficient to provide protection for the current spikes of your inductive load.

Hi Crutschow. Helpful as ever. Thank you.

 

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

 

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.