Friday, February 1, 2019




This article talks about SWITCH MODE POWER SUPPLY (SMPS ) , I cover the basic SMPS Working Process and SMPS block diagram and their  functioning .  The article also talks about the Advantages or Disadvantages  of SMPS and many more.


-> SMPS stands for switching mode power supply . also known as a power supply unit. It is an electronic device or module that used to convert a particular DC voltage to another DC or AC voltage level . SMPS is  a combination of semiconductor devices like diodes and mosfet  and inductors, capacitors  etc. SMPS are used in a variety of sensitive electronic equipment , such as computer , Mobile , almost all home electronic equipments , CCTV , etc .

Advantages  of SMPS :-

  • Regulated and reliable output voltage regardless of variations in input supply voltage.
  • Small size and lighter.
  • High power density.
  • varieties of high voltage damage protection .

Disadvantages of SMPS :-

  • Electro Magnetic Interface (EMI ) is a product of “ON-OFF” switching of the switching circuit . this interference can be conducted to the load . ( resulting in high output ripple and noise ) it can be conducted back to the AC line and it can be created a interference into surrounding atmosphere. 
  • The rapid switching of the chopping current  generates strong bad signal in the circuit.
  • Strong EMI  interference generated by the SMPS , without proper shielding can cause computer and other devices to generate intermitted problem .   

The Common Section Of The SMPS power supply :-


  • EMI (Electromagnetic Interference ) filter section.
  • Input rectifier and filter section.
  • Switching section.
  • Transformer section.
  • Output rectifier and filter section.
  • Feedback and control circuit section.

Block description of SMPS/ SMPS working process :- 

In a SMPS (Switching Mode Power Supplythe Main AC (220 vac )supply is first send to a EMI (Electromagnetic Interference ) filter section . which filter the AC voltage .

Then filter AC voltage send to a input rectifier and filter section ,which converts the AC supply into a very high value DC voltage and filter it.

The high voltage DC supply in given to a switching circuit. Switching circuits consist by switching Transistor . This switching transistor circuit switched ON/OFF at a  very high speed by a control  circuit. Which generates very high frequency square wave pulse .

This switching transistor circuit switch the given high voltage DC ON/OFF at same high frequency, gives  square wave plus at the   output. This square wave pulse  then given to the primary winding of SM transformer . this pulses induced a voltage, at the primary winding of the transformer which will generated voltage at the secondary winding .

This voltage  at the secondary winding is send to a output rectifier and filter section to produce the required output voltage.

The regulated output voltage send back to the switching section . this voltage is first send to a scanner Amplifier which compares it with  a reference voltage and generates and error voltage.  And the control circuit gives Three major voltage , like :- 
  • PS ON voltage
  • SB voltage .
  • PG voltage

This error voltage is such that :-
  •  when there is an increase in the out voltage . the error voltage reduce the “ON” time of the switching transistor, which reduce the output voltage.

  • when there is a reduction in the output voltage. The error voltage increases the “ON” time switching transistor, which increase the output voltage.

Other then this the basic operation most of the SMPS have facility to protect them self from overload and short circuit output section.  

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