What is an H-bridge and how does it enable bidirectional DC motor control?

• A. An H-bridge uses two switches to apply polarity to the motor.
• B. An H-bridge uses four switches to apply either polarity to the motor; PWM on the control lines sets speed; enabling forward/reverse rotation.
• C. An H-bridge converts DC to AC.
• D. An H-bridge uses a single switch to reverse the current.

Answer: (B)

An H-bridge is a four-switch arrangement that lets you reverse the voltage across a DC motor, which is how you flip its rotation direction. By turning on one diagonal pair of switches, the motor terminals are connected so that one terminal is driven high and the other low, making the motor spin in one direction. Switching to the opposite diagonal reverses the polarity across the motor and makes it spin the other way. PWM on the control signals modulates the average voltage applied to the motor, so you can control speed while keeping the direction chosen by which diagonal is energized. The four-switch layout also safely isolates the supply and provides a path for the inductive current when the motor’s current is interrupted or reversed. This setup, often implemented with transistors or MOSFETs and included diodes for flyback protection, is what enables reliable bidirectional DC motor control.