What Is a Motor Driver?
A motor driver is a power interface circuit that raises an MCU's low-power control signal to the high current that will actually turn a motor.
Why Is It Needed?
MCU pins can give only a few milliamps; a motor draws hundreds of mA to amperes. Connecting the motor directly to the MCU burns the pin. The driver bridges this power gap and separates the control from the load.
H-Bridge
The heart of most DC motor drivers is the H-bridge: this structure of four switches (usually MOSFETs) provides forward/reverse rotation and braking by changing the direction of the current going to the motor.
| Function | Explanation |
|---|---|
| Power amplification | Turns the signal into motor current |
| Direction (H-bridge) | Forward / reverse |
| Speed | PWM input |
Speed Control
The PWM signal given to the driver sets the speed by adjusting the average voltage applied to the motor. The direction pins select which diagonal of the H-bridge conducts.
Driver Types
There are H-bridge ICs for DC motors, special stepper drivers for stepper motors, and three-phase ESC drivers for BLDC. Each motor type wants its own driver.
Where Is It Used?
Robots, 3D printers, CNC, toys and all systems where a motor is controlled by an MCU.
Common Mistakes
- Current limit: the driver's current capacity must not be below the motor current.
- Heat: at high current the driver needs a heat sink/heat management.
- Common ground: if the MCU and motor power ground aren't joined, the control won't work.
Frequently Asked Questions
What is an H-bridge for?+
Is the same driver fine for every motor?+
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