Power supply

Lore & Background

Power supplies are categorized in various ways, including by functional features. A regulated power supply maintains constant output voltage or current despite variations in load current or input voltage, while an unregulated supply's output can change significantly. Adjustable power supplies allow output to be programmed by mechanical controls or a control input. An isolated power supply has a power output electrically independent of its power input. Power supplies are packaged differently: bench power supplies are stand-alone desktop units; open frame supplies have only a partial enclosure; rack mount supplies fit into standard equipment racks; integrated supplies share a circuit board with their load; and external supplies (AC adapters or wall warts) are located in the load's AC power cord. Power supplies can be broadly divided into linear and switching types. Linear converters process input power directly with components in linear operating regions, while switching converters convert input power to AC or DC pulses using components in non-linear modes. Switching converters are usually more efficient because their components spend less time in linear operating regions, where power is lost as heat.

Reader's Guide

Power supplies are fundamental to nearly all electronic devices, converting raw electrical power from sources like the electric power grid, batteries, or generators into the precise voltage, current, and frequency required by a load. Their significance lies in enabling safe and reliable operation of equipment ranging from desktop computers to consumer electronics. The distinction between linear and switched-mode power supplies is critical: linear supplies offer simplicity and low noise but are less efficient, while switched-mode supplies are smaller, lighter, and more efficient but can introduce line interference and require careful design for safety. The development of switched-mode power supplies has allowed miniaturization of electronics and improved energy efficiency. Power supplies also perform essential protective functions such as current limiting, fault shutdown, power conditioning, and power-factor correction. Their legacy is evident in every device that plugs into a wall outlet or runs on batteries, as they ensure that the power delivered is safe, stable, and appropriate for the load.

Did You Know?

• Power supplies are sometimes referred to as electric power converters.
• Some power supplies employ wireless energy transfer to power loads without wired connections.
• In a switched-mode power supply, switching occurs at a very high frequency (typically 10 kHz — 1 MHz), enabling smaller and lighter transformers and capacitors.
• A capacitive power supply uses the reactance of a capacitor to reduce mains voltage to a smaller AC voltage.