A switched-mode power supply (SMPS) regulates electrical power by rapidly switching semiconductor devices and controlling energy transfer. Its exact parts depend on the topology: a small DC-DC converter and an isolated AC-DC adapter do not use identical circuits.

Power flow at a glance

In a DC-DC converter, a controlled switch works with an inductor or other energy-transfer network; a diode or synchronous switch and output capacitors smooth the delivered power. A feedback controller senses the output and adjusts switching to keep the voltage within its design range.

An offline AC-DC supply commonly adds an input rectifier and bulk capacitor. Isolated designs transfer energy across a high-frequency transformer; non-isolated designs use a different power path. A transformer is not present in every SMPS, and isolation must be confirmed from the actual design.

Common components

• Input stage: connector, fuse, filtering and, for many AC supplies, rectification and energy storage.
• Switch and controller: semiconductor switch plus control circuitry that sets switching behavior and responds to feedback.
• Magnetics: an inductor, transformer or coupled components selected for the chosen topology.
• Output stage: rectifier or synchronous switch, output capacitors and any additional filtering.
• Protection and thermal parts: current, voltage and temperature protection; heatsinking where the design requires it.

Why topology matters

Component roles change between buck, boost, flyback and other converter designs. Read the schematic as a complete power path instead of assigning one universal function to every diode, inductor or transformer. For a clear introduction to DC-DC switching behavior, see Analog Devices' SMPS basics guide.

Safety

Mains-powered supplies can expose hazardous voltages, and input capacitors may remain charged after unplugging. This overview is for understanding component roles; do not probe or repair an offline supply unless you are trained to work safely with high-voltage equipment.