Power electronics and power control

Power control is the part of electronics concerned with switching and converting electrical power efficiently, rather than processing small information signals. Its devices handle significant currents and voltages, so they are designed to act as switches that are either fully on or fully off, minimising the power wasted as heat. This switching approach is the foundation of motor drives, power supplies and many control systems where energy must be delivered in controlled amounts.

A central technique is pulse-width modulation (PWM), in which a switch is turned on and off rapidly and the proportion of on-time, the duty cycle, sets the average power delivered. By adjusting the duty cycle, a circuit can smoothly vary the speed of a motor or the output of a converter without dissipating the excess as a linear regulator would. Because the switching is fast, a simple filter or the load's own inertia smooths the pulses into a steady effect.

To drive a load in both directions, power circuits often use an H-bridge, an arrangement of four switches that can connect a load such as a DC motor to the supply in either polarity. Closing one diagonal pair drives current one way; the other pair reverses it, allowing forward and reverse operation, and combined with PWM, full speed control. The same switching principles appear in converters that step voltage up or down and in inverters that produce AC from DC.

Frequently asked questions

Why is switching more efficient than linear control?

A switch that is fully on or fully off dissipates little power, whereas a linear regulator drops the excess voltage as heat. Switching therefore wastes far less energy when controlling large loads.

What does an H-bridge do?

An H-bridge uses four switches to connect a load to the supply in either polarity, allowing a DC motor to run forward or in reverse.

How does PWM control power?

PWM switches the supply on and off rapidly; the fraction of time it is on, the duty cycle, sets the average power delivered, so varying the duty cycle controls speed or output.