The difference is what happens in the inactive phase of the PWM

[G+_Jeff Gros]

The difference is what happens in the inactive phase of the PWM. "Forward" would be the active phase, and "Brake/coast" would be the inactive phase.

 

Refer to your manufacturer datasheet for details as they can use different terminology.

 

Fast decay vs slow decay can make a big difference in your application.

 

For example, I was driving a proportional valve using the DRV8833 (its a dual output part, but we just used both sides for twice the oomph). The valve was normally closed and needed to be energized to open it.

 

Originally, I PWMed in the Forward/Fast decay configuration without really thinking about the consequences. I found that with a given voltage the duty cycle required to crack the valve was much higher than expected. What was happening was that the magnetic field was collapsing during the inactive phase of the PWM so the valve went back to its normally closed position and wouldn't stay open.

 

Switching to Forward/Slow Decay kept the field alive and allowed the valve to crack at much lower duty cycle.

 

Originally shared by Mike Meyer

 

Got a question about H-bridge motor drivers. The data sheet for some of them talk about "forward/coast", "forward/brake", "reverse/coast" and "reverse/brake" operating modes. The tutorials I've found just talk about forward, reverse, coast and brake, and I think I understand those. Except that given that understanding, the other four don't make any sense.

 

Any care to either explain them or provide a pointer to a tutorial that covers them?