Flyback diode selection

[SR19]

Hi,

I need to drive 10A stepper motor. Im planning to use A4989 Driver with IRLR024N. Kindly suggest me a spec for selecting Flyback diode across MOSFET.

Thank you

 

[FvM]

A H-bridge doesn't use flyback diodes.

 

[SR19]

In most of the H bridge circuit there is a diode across Mosfet ...what is that?

 

[FvM]

You didn't read the schematics exactly. The diode is the substrate diode inside the MOSFET.

In a few cases (MOSFETs with slow substrate diode, asynchronous switching scheme), connecting external schottky diodes might slightly improve the performance. It's meaningless with A4989 that implements synchronous switching.

 

[SR19]

Hi,
Thanks for your reply.i read some docs regarding synchronous rectification, it says that mosfets are used instead of diode..which means A4989 has inbuilt mosfets??

 

[FvM]

Thanks for your reply.i read some docs regarding synchronous rectification, it says that mosfets are used instead of diode..which means A4989 has inbuilt mosfets??

No synchronous rectification means that the MOSFET are switched alternatingly (with a short deadtime), so output current is switched between high-side and low-side FET instead of FET and diode.

 

[SR19]

Thanks for your explanation..