How do brushless DC motors work? The need for a drive circuit explained

DC motors are electric motors that are powered by direct current. Features include the ability to rotate at high speeds, and high starting torque. They are used in a wide range of situations, being a type of motor that is commonly found in numerous familiar applications. DC motors can be broadly divided into two groups: brushed DC motors and brushless DC motors.

This page goes into detail about how brushless DC motors work.

Electric motors can be divided into a number of different types according to their characteristics, such as AC motors, stepper motors, and DC motors. Compared to the other types, DC motors benefit from high starting torque and the ability to rotate at high speeds. They do not suffer from the issues of slip or loss of synchronization.

DC motors can be further divided into brushed DC motors and brushless DC motors, depending on whether they have brushes (electrodes).

Making an electric motor rotate requires that the direction of current flow through the motor windings (coils) is alternated in order to generate a rotating magnetic field. In the case of brushed DC motors, this is achieved through the mechanical action of brushes and commutator. Then how do brushless DC motors, which don’t have these parts, generate the rotating magnetic field and turn?

Instead of a commutator and brushes, brushless DC motors use semiconductor switches. Brushless DC motors generally have three coils, with semiconductor switches connected to each of these. Turning the semiconductor switches on and off in the correct sequence alternates the current flow, which generates the rotating magnetic field that causes the motor to turn. Accordingly, the motors require a drive circuit to perform this sequencing. Furthermore, the semiconductor switches are switched by detecting the orientation of the permanent magnet rotor, using a magnetic sensor (typically a hall sensor).

Excitation sequence of brushless DC motor

The following link provides more details about the mechanism and control of brushless DC motors.

Do brushless DC motors require a drive circuit? - Controlling brushless DC motors

Brushless DC motors can be broadly divided into outer-rotor and inner-rotor motors.

Brushless DC motors are further divided into SPM and IPM motors depending on how the permanent magnets are attached to the rotor.

Brushless DC motors are electric motors that do not require the consumable brushes and commutator. They benefit from quiet operation together with long life and low maintenance.

Instead of brushes and a commutator, driving a brushless DC motor is done electronically using a drive circuit. The drive circuit is needed to turn semiconductor switches on and off in the correct sequence to generate the rotating magnetic field that causes the motor to turn.

We hope that the information provided here will prove useful to you.

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