This is a DC motor drive circuit. The driving method is relatively easy, but a problem occurs during use: an abnormality occurs inside the motor, and the MCU or MOS tube is burned out after a while.

After inspection, it was found that the circuit abnormality was caused by a poor soldering of one end of the freewheeling diode connected in parallel next to the motor . After soldering it intact, the motor was able to work normally.

why is that?

We can see that this circuit uses PWM+MOS to drive the circuit . There is a coil inside the motor. During power failure, the coil will release electrical energy and affect the surrounding circuits.

We first use PWM to drive the transistor, and then drive the MOS tube. We use the MOS tube to drive the DC brushed motor to work. We need to use a freewheeling diode to protect the motor and the entire circuit.

This is because the motor is an inductive load and needs to be discharged.

If there is no discharge, the current of the motor will not be able to flow in one direction, and eventually burn out the MCU or MOS tube.