[Episode 3] All of Sudden, a Rival Appears for Ichinose Manabu!?

2025.07.22

table of contents

Up until the last time, I had been talking about the principles of motor rotation and the construction of brushless motors. From here on, I will be explaining the driver circuits that are used to drive brushless motors.

Fundamentals of Brushless Motor Driving

In order to understand the principles behind brushless motor driving, you first need to understand the circuits that are used to pass currents through the windings in a motor. The timing with which these currents flow is indicated by timing charts, which are a kind of waveform diagram. A timing chart indicates the specifications needed for a motor driver to drive a motor, and so shows the relationship between the rotor position and the current waveforms.

As the fundamentals of brushless motor driving, I will be discussing the following three topics.

Contents of Episode 3:

Driving Circuits for Brushless Motors

A brushless motor is provided with transistors, which are electrical switches, and a controller that controls the switching operations of the transistors (see “Construction of Brushless Motors”). In addition to the controller, in some cases support components are required to drive a brushless motor; here, however, I will explain driving circuits using the circuit shown below, which is widely used.

Circuit board

■Control IC (controller)

  • ・Receives rotor position signals and generates switching signals for power transistors.
  • ・Receives external instructions and controls the voltage to be applied to the windings.
  • ・May also perform more sophisticated control, such as adjusting the motor revolution rate.

■Level shifter (gate driver)

  • ・Converts signals from the controller into signals to operate the power transistors (adjusts voltage levels and polarities).

■Power transistors

  • ・Form the circuit that supplies electric power to the motor windings.
  • ・In a three-phase brushless motor, six transistors are used. The side connected to the positive side of the power source is called the high (or Hi) side; the side connected to the negative side (ground) of the power supply is called the low (or Lo) side. Example: The three high-side transistors are all turned off.

■Position detectors (Hall elements)

  • ・Detect the rotor position. In addition to Hall elements, other devices such as encoders and resolvers may be used for position detection.
  • ・There are also sensorless driving designs in which the rotor position is inferred from winding voltages and currents, without using position detectors.

Actual motor boards may also have ICs that incorporate both the controller IC and the level-shifting functions, as well as devices which include multiple power transistors in a single package. Hall elements are located at positions where they can easily detect magnetic flux from a permanent magnet, and boards also have externally mounted components such as resistors and capacitors. These components may not appear on simplified circuit diagrams. Circuit diagrams that include peripheral components are provided for application circuits that include specifications.

Next time, I will explain how brushless motors are made to rotate, by talking about the signals output by the driver circuit and the magnetic fields that are created by windings acting as electromagnets.

Key points of this article

・In order to drive a brushless motor, the motor driving circuitry and timing chart must be understood.

・Driving circuitry for a brushless motor includes a controller IC, a level shifter, power transistors, position detectors, and other devices and components.

・Hall elements are used as position detectors.

・On the circuit boards of actual motors, often there are ICs which incorporate the functions of controller ICs and level shifters, as well as devices in which a number of power transistors are present in a single package.

Next page: Timing Charts for Brushless Motor Driving Circuits

    Teacher Sugiken’s Motor Library

    Teacher Sugiken’s Motor Driver Dojo

    An Introduction to Motors

    Brushless Mortor Driver

    Motor Q&A

    THIS WEBSITE USES COOKIES.
    By continuing to browse this website without changing your web-browser cookie settings, you are agreeing to our use of cookies.
    Privacy Policy
    OK