P-Channel Mosfets getting very hot

Hi Guys,

I'm having some problems with my design, before i finalize it I have decided to do a quick hook up with wires to check if everything is working fine, basically I have and external source of the PWM signal ( just focus only to the first channel for now) it has a resistor divider each of 1K and a 10K in series, then feeded to the MC33926 which is actually a H-Bridge, Brushed DC Motor Driver, but i actually using it as a gate driver for my others mosfets P-Channel from Vishay, each channel should cope with more than 30A. However I feed my PWM signal and have to the output a nice inverted PWM signal ready to drive my Mosfets, and the first test I just tried a small load max 3.3A and the control was working fine and the mosfet was not getting hot at all, but when i switched load and not even too big a 5/6A the mosfet gets very very hot! and I cannot understand why? please find attached my schematic.

Any help would be really appreciated,

thanks

Your schematic shows NO supply voltages and also does not show the PWM frequency.

A 25kΩ gate resistor will slow the turn-on and turn-off of the MOSFETs due to their gate capacitance, which causes high switching losses.
Why is that resistor such a high value?

Audioguru said:

Your schematic shows NO supply voltages and also does not show the PWM frequency.

Click to expand...

Hi sorry you are right! Vin is 12V and pwm frequency is around 12.5KHz. But i sorted out, there was a problem with my connection, I connected the Vin of the MC33926 to the output of the mosfet instead to Vin..:bang: I should have checked the connections first.

I wanted to add to the motor control an overcurrent protection any suggestion? I was thinking a resettable fuse to each output or a circuit breaker, but i have some concerns about the time reaction of those two. would it be better considering to add a micro with some current sensing to each output and if is drawing more than it should turn off the mosfets?

thanks

- - - Updated - - -

crutschow said:

A 25kΩ gate resistor will slow the turn-on and turn-off of the MOSFETs due to their gate capacitance, which causes high switching losses.
Why is that resistor such a high value?

Click to expand...

Hi actually is only 25 Ohm..! thanks for your for message.

Don't forget that a DC motor draws a HUGE current when it is stalled. It is stalled when it starts running and when something stops it when it is running.

Audioguru said:

Don't forget that a DC motor draws a HUGE current when it is stalled. It is stalled when it starts running and when something stops it when it is running.

Click to expand...

What are you suggesting? any advise for over-current protection?

thx

Allow for the very high starting current and the very high stalled current if you limit the current. Maybe make a timer to allow the very high current before the current limiting works.