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Switching Mode Power Supply (SMPS)

A regulated linear power supply provides a constant voltage by varying their resistance to cope with input voltage changes or load current demand changes. The regulated linear power supply is an inefficient design. In order to improve the efficient, designers tried to rectify the circuit design. Therefore Switching Mode Power Supply (SMPS) is developed to improve efficiency.
Block diagram of a mains operated SMPS with output voltage regulation


Types of SMPS
Most commonly used types of SMPS are
  • Buck or forward converter
  • Boost or flyback converter
  • Bbuck-boost converter
  • Cuk converter
  • Push-pull converter
  • Resonant converter
  • Half-bridge and full-bridge converters


Table : Comparison Between Linear Regulated Power Supply and SMPS


Linear Regulated Power Supply


Size and weight


Heatsinks are used in linear regulated power supply. Due to large size of heatsinks, size and weight of linear regulated power supply increases. Transformers, if used, are large due to low operating frequency, i.e., 50 Hz.

Smaller transformer are used in SMPS due to higher operating frequency, i.e., 50 kHz – 1 MHz. Size and weight of adequate RF shielding may be significant.

Output voltage

When transformer used in linear regulated power supply, any voltages available at output. If unregulated, voltage varies significantly with load.

Any voltages available at output, but the output voltage is limited only by transistor breakdown voltages in circuits. The output voltage varies little with load.


Efficiency largely depends on voltage difference between input and output. Since output voltage is regulated by dissipating excess power as heat resulting in a typical efficiency of 30–40%.

Output voltage of SMPS is regulated using duty cycle control. As the transistors are switched fully on or fully off, there will be very little resistive losses between input and the load. Hence, the efficiency of SMPS is very high compared to linear regulated power supply.


Usually Liner regulated power supply is a simpler circuit than switched-mode circuits. than switched-mode circuits.

Since SMPS consists of a controller IC, one or several power transistors and diodes, inductors, and filter capacitors, SMPS is a complex circuit than Linear regulated power supply.

Radio Frequency Interference

Mild  high-frequency interference may be generated by AC rectifier diodes under heavy current loading.

EMI/RFI produced due to the current being switched on and off sharply. Therefore, EMI filters and RF shielding are needed to reduce the disruptive interference.

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