I am just getting into electronics and my first project is a 555 timer PWM (0-100) and an H-bridge to drive a motor for my brewing equipment (500 mA max. rating).
Here is the setup:
I have a 12 V circuit, a mechanical switch to set the direction (powers up either "left side" or "right side" MOSFETs of the H-bridge). As I was afraid of shoot-through I added an extra P-channel MOSFET that is driven by the PWM and supplies the load.
The problem: Occasionally one of the MOSFETs (low-side) just burns after a while (gets hot/ smells and drain and source are shorted now), the motor stops and only has short flickers of movement.
Observations: I have the feeling that the pot position is connected to the problem. I think that it happens when the motor is insufficiently supplied with voltage and stops moving. If I stay in the 50% range or full load range, I have the feeling it works well, but still only a feeling.
I experienced that this happens much faster if the pot is 100 kΩ and not 10 kΩ, but I have no clue why.
Now that one of the MOSFETs has burned, I tried checking if the PWM is flawed and surprisingly it only does not work if the switch is supplying the side of the broken MOSFET (I disconnected the out pin from the circuit for checking that). The other way round the PWM is fine.
Can you tell me where I messed up?