Introduction: What is SMPS?

SMPS full form

The full form of SMPS is Switched Mode Power Supply. It is an electronic power supply system that uses a switching regulator to transfer electrical power efficiently. It is the power supply unit (PSU) which is normally used in computer systems to change the voltage of the computers to appropriate acceptable range.  SMPS circuit which is designed for obtaining the regulated DC output voltage from an unregulated DC or AC voltage.

SMPS is one of the most important part of the computer system required for the functioning of motherboards or PCBs (Printed Circuit Boards).

Working Principle: How does SMPS works?

The primary function of the SMPS is to supply the computer acceptable regulated DC  Voltage from an unregulated AC or DC voltage.
The switching regulators are used in SMPS device that switches the load current on and off in order to regulate and stabilize the output voltage. The average voltage between the off and on produces the appropriate power for a device. Unlike the linear power supply, the pass transistor of SMPS switches between low dissipation, full-on and full-off mode, and spends very less time in the high-dissipation cycles, which minimizes wasted energy.

The following figure shows the functional block diagram of SMPS:

Block diagram of smps
fig. Functional Block Diagram of SMPS

The working of SMPS can be understood by this functional block diagram. The above figure consists of various stages, let us try to understand what happens in each stage of the SMPS circuit. 

1. Input Rectifier and Filter : The unregulated AC Supply input signal of 50Hz is directly given to the first stage of SMPS i.e; Input Rectifier and Filter circuit without using any transformer. Input rectifier rectifies the AC signal to generate the DC signal. The rectified form of DC signal is fed to filter circuit to remove the AC ripple content (High frequency noise component), this gives pure form of DC Signal.

2. High Frequency Converter Switch : The SMPS requires higher frequencies for its operation, so a high frequency converter switch processes the DC signal that generates high frequency pulsating DC signals.The frequency switching operation is done by power MOSFET amplifier. 

3. Power Transformer : The high frequency DC Signals are step down to a appropriate level of DC signal by using power transformer.

4. Output Rectifier and Filter :  The output signal from the power transformer again rectified and filtered to achieve a steady constant DC output signal.

5. Control Circuit : The output voltage is controlled by a control circuit consist of comparator along with a pulse width modulator (PWM). It is like feedback circuit which always monitors the output voltage and adjusts the high frequency controller switch to ensure the continuous supply of desired output voltage.  

 Advantages of SMPS:

  1. SMPS are smaller in size and light-weighted.
  2. SMPS has better power efficiency of around 60 to 70 percent.
  3. Powerful anti-interference.
  4. Wide range of output.
  5. Produces less heat.

Disadvantages of SMPS:

  1. Design of SMPS is highly complex.
  2. High ripple content in output voltage and thus regulation is not satisfactory.
  3. SMPS only be limited for using as a step down regulator.
  4. SMPS has high frequency electrical noise.

Applications of SMPS:

  1. It is used in personal computers,servers and power stations .
  2. It is used for charging batteries in vehicles.
  3. It is used in Railways and security systems.
  4. It is used industries and factories for power systems.
  5. It is also used in consumer electronics and space stations.
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