Brushless DC motor drive circuit

The power stage drive circuit of BLDC usually consists of 6 N-channel power MOS tubes to form a three-phase full bridge. These 6 MOS tubes are divided into two groups, three high-side MOS tubes are connected to the positive pole of the power supply (VBus), and three low-side MOS tubes are connected to the negative pole of the power supply. By controlling the on and off of the MOS tubes, the current is distributed in the motor windings to drive the motor to operate.

When a single NMOS is turned on, it needs to provide current instantly to charge the internal parasitic capacitor. The gate-source voltage (VGS) reaches the threshold and the MOS tube is turned on. After the MOS tube is turned on, VGS needs to be maintained in the on state so that the current can provide power to the motor.

The source (S) of the low-side MOS tube is connected to the negative pole of the power supply, the gate-source voltage is easy to meet, and the driving is simple. The source of the high-side MOS tube is connected to the motor phase line, and its voltage is always in dynamic change, with many uncertain factors. If the high-side MOS tube is to be turned on, it is necessary to use a bootstrap circuit to provide a suitable gate voltage. This process involves complex circuit design and signal processing, and is difficult to drive.

 Generally, the on-resistance of MOS tubes decreases as VGS increases. When VGS is 10-15V, MOS tubes can reach the minimum on-resistance (RDSON). At this time, the energy loss when the current is transmitted in the circuit is greatly reduced, thereby improving the efficiency of the entire drive circuit.

The controller controls the on and off of 6 MOS tubes to achieve BLDC commutation and adjust the motor speed and direction to meet different application requirements, such as acceleration and deceleration and energy recovery of electric vehicles. If the motor is blocked during operation and causes overcurrent, the MOS drive circuit can detect and cut off the circuit to protect the controller and motor and ensure system operation.