As mentioned above, instead of mechanical control, electronic control is required to drive the brushless DC motor. The reason can be explained by how the generation of the rotating magnetic field in the brushless DC motor is different from other motors.
In order to make the motor rotate, you need to change the direction of current flowing through the motor windings and generate a rotating magnetic field. Although induction motors and other motors driven by AC power can use AC power voltage for this purpose, motors driven by DC power require some form of switching to change the direction of current in the motor, thereby generating a rotating magnetic field.
For brushed DC motors, this can be achieved by using brushes and commutators. However, for brushless DC motors, instead of using short-life brushes, semiconductor switches (such as bipolar transistors or FETs) are used to achieve current alternation and the resulting rotating magnetic field. Life is not the main issue.
The configuration of the brushless DC motor drive circuit
The drive circuit is composed of the following main components.
Rotation position sensor
Hall sensor is used to detect the N pole and S pole of the rotor magnet.
Position detection circuit
A circuit that converts the signal of the Hall sensor into a digital logic signal.
Based on the signal from the rotor position detection sensor, the circuit outputs a sequence that controls the direction of current flowing through each coil.
A circuit that converts a sequence signal into a signal used to open and close a semiconductor switch.
Generally, six semiconductor switches are used. It is turned on and off according to the sequence signal to allow current to flow through the coils required to rotate the motor.
Motor drive power
A power source is required to provide current flowing through the motor coils and to power logic and sensor circuits.