What is an SMPS and how is it different from a linear power supply?

A Switched-Mode Power Supply (SMPS) is a type of power supply that uses a high-frequency switching regulator to efficiently convert electrical power from a source (like the AC mains) to a different voltage and current level (like the DC voltages needed by electronic components).

The core principle involves switching a power transistor (like a MOSFET) on and off very rapidly—thousands or even millions of times per second. This process creates a high-frequency AC waveform that can be passed through a very small and lightweight transformer before being converted back to a stable DC output. A feedback circuit constantly monitors the output and adjusts the switching rate to keep the voltage precisely regulated.

A Linear Power Supply works on a much simpler, but less efficient, principle. It uses a large, heavy transformer to step down the AC voltage, which is then converted to DC. To regulate the voltage, it uses a pass transistor that acts like a variable resistor, continuously dissipating any excess energy as heat to maintain a constant output.

Think of it this way:

• A linear supply is like controlling water flow with a faucet that's always partially open, letting the excess pressure escape as wasted water (heat).
• An SMPS is like turning a tap on and off very quickly to get the exact average flow you need—a much more efficient method that wastes very little.

Here’s a direct comparison: