H-Bridge DC Motor: Working Principle, Selection, and Applications

Introduction

An H-Bridge is an electrical circuit designed to change the polarity of voltage applied to a load. This configuration enables DC motors to move both forward and backward, making it an essential component in robotics, motor controllers, and power electronics.

The name “H-Bridge” originates from its schematic representation, which resembles the letter “H.” In the diagram, the load (motor) is connected as the crossbar, and the four switching elements form the sides of the “H.”

H-Bridges are widely used in DC-to-AC converters (power inverters), AC/AC converters, isolated DC-to-DC converters, push-pull converters, and various types of motor drivers. In particular, a motor controller with two H Bridges is often used to drive a bipolar stepper motor.

How Does an H-Bridge Work?

A small DC motor typically has two terminals — “A” and “B.” When terminal A is connected to the positive supply (+V) and terminal B to ground (-V), the current flows from A to B, causing the motor to rotate in one direction (clockwise or forward).

If the connections are reversed — terminal A to ground and terminal B to +V — the current direction also reverses (from B to A), and the motor rotates in the opposite direction (counterclockwise or reverse).

Working Principle of an H-Bridge Circuit

An H-Bridge consists of four switching elements, commonly MOSFETs, arranged in a bridge configuration. These switches control the direction and speed of the motor by altering the path of current flow. A simple MOSFET based H-Bridge schematic is illustrated below: When a PWM (Pulse Width Modulation) signal is applied to input In1 and a logic HIGH to In4, a current path from the supply voltage (Vs) to ground (GND) is established through the motor, causing it to rotate forward. The motor speed can be controlled by varying the PWM duty cycle at In1.

Similarly, applying the PWM signal to In3 and a logic HIGH to In2 reverses the current direction, causing the motor to rotate in the opposite direction. In both cases, the PWM technique effectively turns the motor on and off at a controlled rate, regulating its speed. The flyback diodes in the H-Bridge play a vital role in protecting the MOSFETs. When the motor switches off, these diodes provide a path for the back electromotive force (EMF) generated by the rotating motor, preventing voltage spikes that could damage the circuit.

Selecting the Right H-Bridge

When selecting an H-Bridge for your project, it’s crucial to know the maximum current your DC motor will draw, particularly during startup (stall current). The chosen H-Bridge must handle this current safely; otherwise, the circuit may overheat or fail.

For example, the Pololu High Power Motor Driver supports a motor voltage range between 5.5V and 30V and can continuously handle up to 15A without a heat sink. This makes it ideal for most robotics and automation projects. On the other hand, the STMicroelectronics H-Bridge can handle up to 30A continuously, making it suitable for automotive applications or heavy-duty DC motors. For typical 12V–24V motors drawing up to 10A, the Pololu motor driver is an excellent and cost-effective choice.

Advantages of an H-Bridge Circuit

• High efficiency: Delivers excellent power conversion with minimal losses.
• Compact design: Can be easily integrated into small or portable systems.
• Low heat generation: Reduces energy waste and the need for complex cooling systems.

Applications of H-Bridge Circuits

Due to the availability of several integrated circuit (IC) solutions, constructing an H-Bridge from discrete components is often unnecessary. Popular H-Bridge ICs include L293D, L298N, TA7257P, and SN754410. These modules simplify control — connect the motor and power source, and then apply control signals to manage motor direction and speed.

Among these, the L298N motor driver module is especially popular among beginners for its ease of use, affordable cost, and straightforward wiring. It can control two DC motors simultaneously and supports bidirectional rotation and PWM-based speed control.

Conclusion

The H-Bridge DC Motor Circuit is a fundamental element in motion control and power electronics. Its ability to precisely control motor direction and speed makes it indispensable in robotics, automation, and electric vehicles. With various ready-made IC modules available, implementing H-Bridge control is now easier and more efficient than ever before.-