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Short note: SMPS

Short answer

An SMPS regulates output by high-frequency switching and PWM control. It rectifies AC input, chops it via a MOSFET, passes through a small HF transformer, then rectifies and filters. Advantages: high efficiency (70 – 95 %), small size; disadvantages: switching noise, complexity.

Write a short note on SMPS (switched mode power supply).

A Switched Mode Power Supply (SMPS) is a power supply that converts AC or DC input into a regulated DC output by switching a power transistor ON and OFF at high frequency (20 kHz – 1 MHz) and controlling the duty cycle with PWM.

AC->[RECTIFIER]->[HF SWITCH]->[HF  ]->[RECTIFIER]->DC
    [+ FILTER ]  [ (MOSFET)]  [TRAN]  [+ FILTER ]  out
                      ^                    |
                      |                    |
                 [PWM CONTROL]<-[ISOLATION]<+
                                [+ERROR AMP]

Working:

  1. AC mains is rectified and filtered to unregulated DC.
  2. A MOSFET chops this DC at high frequency.
  3. A small high-frequency transformer steps the voltage up/down and gives isolation.
  4. The secondary is rectified and filtered to DC.
  5. The output is compared with a reference; the PWM controller adjusts the duty cycle to keep the output constant (feedback through an opto-coupler).

Common topologies: flyback, forward, push-pull, half-bridge, full-bridge (and non-isolated buck, boost, buck-boost).

Advantages: high efficiency (70–95 %), small size and weight (high-frequency transformer), wide input range.

Disadvantages: complex circuit, switching noise/EMI, output ripple, needs careful design.

Uses: computers, TV, mobile chargers, LED drivers, telecom equipment.

✓ Answer checked by Claude Opus 5.5 (high effort)

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