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What is Switched Mode Power Supply?

by Team Goseeko

The Switched mode power supply is abbreviated as SMPS. It is used for converting the regulated DC output voltage from unregulated DC or AC voltage.

Block Diagram

The block diagram shows the working of Switched Mode Power Supply as shown below.

Input Unit

The rectifiers and filters are having supply of 50Hz as its input supply. The capacitance value of the capacitor should be high as there can be fluctuations in the output. We do not need any transformer for input supply. Since the rectifier and filter circuit combinations are present.

Switching Section

Since, there are many fluctuations at the output of the input unit Power transistors. Hence, we use MOSFETs for fast switching. They can be turned ON or OFF as per the need and the output from here is fed to the transformer present in this section.

Output Unit

The desired DC output is obtained by again passing the output from the switching section to the rectifier and filter unit. The regulated output voltage obtained from here is again fed as input to the control unit through a feedback circuit.

Control Unit

The control unit consists of many other small units functioning together as represented below.

The input to the control unit is fed to the sensor. If we control chopping frequency final output voltage can be controlled. This helps to maintain the final voltage level. This is reached by comparing the error amplifier inputs. The input to the error amplifier is the signal from the sensor and one reference signal. The reference signal is nothing but the required output signal. The error amplifier compares the mentioned two signals and generates the required output voltage level accordingly. The PWM oscillator produces a standard PWM wave fixed frequency.

Types of Switched Mode Power Supply

The four main types of SMPS listed below

  • DC to DC Converter
  • AC to DC Converter
  • Fly back Converter
  • Forward Converter


There are many applications of SMPS. We can find SMPS in the motherboard of computers, mobile phone chargers, HVDC measurements. We can also find them in battery chargers, central power distribution and motor vehicles. In consumer electronics, laptops and security systems also SMPS can be employed.

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