rkosiorek wrote:so just so i understand this.
1. the body diode of a FET actually make a terrible diode.
2. these diodes are supposed to help with the shoot thru problem, but because the body diode is so crappy it may actually contribute to it at part throttle.
the best solution would be to carefully tune the dead time between the high side and low side fet on times. but as a bandaid brushed controllers add a separate schottky in parallel with the fets.
the question being asked is whether or not this same bandaid can be used to help brushless controllers.
i have tried understanding the discussion, but i'm shy on a lot of the theory. i cannot determine if the question was ever answered. also why would not commercial controller designs include such diodes if it does work?
would it be work adding such diodes? or would the answer depend on knowing more specific information about the controller design and motor being used?
You almost have it. So in a brushed controller they dont always use an H bridge the simple controllers methy and I are talking about are for series wound motors and reversing the output of the controller will not reverse the motor it self so all the fets inside are parallel, and parallel to the fets there is some schottky diodes to help keep the stress off the fets them selfs.
Now I think I understand this correctly in a H bridge on a brushless controller you can turn on the opposite set of fets during the off times in PWM to save the diodes some stress. Example If you have the Hi side fets driving the motor with PWM the low side in the same H bridge can turn on when the hi side turns off. If you don't do this then the diodes in the low side fets will flow the current through the fets so its better to turn on the fet it self.