SWITCH (SWITCHING) MODE POWER SUPPLY

Generally a power supply used to produce required output voltage for different circuits.  In starting transformers used for making lower supplies, output voltage changes according to input AC volts, it means when input AC voltage increase output DC voltage also increases and if input AC voltage decrease output DC volts also decrease and this type of power supply called unregulated power supply. But when we use integrated circuit for making electronics equipments, this is necessary to use regulated supply. First of all transistor are used as a series regulator, problem of regulation not ended, because of working efficiency up to 25% to 40%. For example if we use 100watt as a input then we get only 25 watt to 40 watt as a output and rest of energy lost in power supply. So we can say there is high loss of energy in this type of power supply and use of heavy transformer in circuit is difficult. After few year we use SCR, which also loss energy, because of this we can’t use SCR power supply in high rating, so there is a necessary to use power supply having high working efficiency about to 80% with less price. By using switch mode power supply we can achieve this.

SMPS stands for Switch-Mode-Power-Supply. In a modern computer, there is a SMPS that takes rectified AC input from the wall, performs power factor correction and then converts the output into one or more lower voltage DC outputs.  In a laptop this is generally about 19Vdc.  In a desktop, this is usually +12Vdc.  More SMPS's convert that voltage into other voltages (+5Vdc, +3.3Vdc, -12Vdc, 1.2Vdc, etc).  The computer runs off of these voltages. 

Advantages of switched-mode power supplies:

• Higher efficiency of 68% to 90%

• Regulated and reliable outputs regardless of variations in input supply voltage

• Small size and lighter

• Flexible technology

• High power density

Disadvantages:

• Generates electromagnetic interference

• Complex circuit design

• Expensive compared to linear supplies

Switched-mode power supplies are used to power a wide variety of equipment such as computers, sensitive electronics, battery-operated devices and other equipment requiring high efficiency.