we all know--->Power electronics is the applications of solid-state electronics for the control and conversion of electric power.
Power electronic converters - to modify the form of electrical energy (voltage, current or frequency).
Now my question is ---> Do we require external power sources while in process of controlling & converting(processing) electric power like we do in CE BJT to work as Amplifier ?
As law of conversation of energy says "Energy can not be generated or destroyed -it can only be converted from one form into other form"
well, yes, you always have some power being used by the control circuit, so eg in an offline SMPS typically its gets started up by a linear regulator, and then when up and running, some power is often derived from a bias winding on the transformer, for the purpose of powering the control circuit, but its not really like a class a audio amp which consumes a lot of bias power and is very inefficient.