DC chopper

A chopper is a static device that convert fixed dc input voltage to a variable dc output voltage directly.

A chopper may be thought of as dc equivalent of an ac transformer so that they behave in an identical manner. As chopper involve that one stage conversion, these are more efficient for circuit.

Chopper are now being all over for rapid transits systems. A chopper systems offer smooth control,  fast response, high efficiency, and regeneration.

The power semiconductor devices used for a chopper circuit can be force commutative thyristor, power BJT, IGBT, power MOSFET. 

As sated above, a chopper is dc equivalent to an ac transformer having continuously variable turn ratio. 

A  transformer, a chopper can be used to step up or step down for the fixed dc input voltage. As step down dc chopper are more common, the term dc chopper or chopper would mean a step down dc chopper.