A power supply is used to energize and control the electronic system. The power supply converts AC voltage into revaluated DC voltage according to the requirement of particular system. Since the rectifier also performs this operation but the DC output will not be ripple less hence the filter circuit is used to obtain ripple less DC voltage. The filter circuit makes the rectifier inefficient and weighty because physically the filter circuit is quite large. Therefore a switched mode power supply is used to convert AC into very high fleered DC. SMPS is based on the principle of chopper.
Chopper is a device which converts a fixed dc voltage to a variable de voltage. Chopper provides smooth acceleration control fast response regeneration and high efficiency choppers are used in subway cars trolley buses marine hoists forklift trucks and mine haulers.