Electronics 113: Motor Drivers & H-Bridges Explained
A clear, engineering-focused guide to driving DC motors, stepper motors, and actuators safely: why microcontroller pins are never enough, how H-bridges actually work, and how to choose the correct motor driver without smoke, resets, or mysterious failures.
1) Why motors need drivers
Motors draw far more current than a microcontroller pin can supply. They also generate electrical noise and voltage spikes.
2) Common motor types
| Motor Type | Control Complexity | Typical Use |
|---|---|---|
| Brushed DC | Low | Robots, wheels, fans |
| Stepper | Medium–High | 3D printers, CNC |
| Servo | Low (external driver) | Position control |
3) DC motor electrical behavior
A DC motor is an inductive load with a very high startup (stall) current.
4) What is an H-bridge?
An H-bridge uses four switches to control motor direction. By changing which switches are on, current flows through the motor in either direction.
5) Direction & speed control
- Direction: Select which half of the H-bridge is active
- Speed: Use PWM to control average motor voltage
- Braking: Short motor terminals (dynamic braking)
6) Motor driver architectures
| Architecture | Description | Notes |
|---|---|---|
| BJT-based | Older, inefficient | High heat |
| MOSFET-based | Modern standard | High efficiency |
| Integrated IC | All-in-one driver | Easiest to use |
7) Common driver modules compared
| Driver | Type | Pros | Cons |
|---|---|---|---|
| L298N | BJT H-bridge | Cheap, common | Very inefficient, hot |
| TB6612FNG | MOSFET H-bridge | Efficient, compact | Lower current |
| BTS7960 | High-power MOSFET | High current | Large, needs care |
| A4988 / DRV8825 | Stepper driver | Microstepping | Setup critical |
8) Current sensing & protection
Better drivers include:
- Over-current shutdown
- Thermal shutdown
- Current limiting
9) Power supply & grounding rules
- Separate motor supply from logic where possible
- Common ground is required for control signals
- Use bulk capacitors near the driver
- Keep motor wires short and twisted
10) Thermal limits & heatsinking
Motor drivers dissipate power proportional to current and resistance.
11) Selection guide
- Small robots: TB6612FNG
- High current DC motors: BTS7960 or discrete MOSFETs
- 3D printers: DRV8825 / TMC drivers
- Learning projects: Avoid L298N if possible
12) Common mistakes & failures
- Undersized driver current rating
- No bulk capacitance
- Poor grounding
- Ignoring stall current
- Over-trusting marketing specs
