Electronic Regulator

Manishankar asked:

how an electronic circuit works as a regulator?

In an ordinary regulator, the current in the circuit is controlled by increasing or decreasing the resistance.

But in an electronic regulator, the control is taken over by electronic circuits. There are different forms of electronic regulators available. Some use transistors, some use operational amplifiers etc. In electronic regulators, the voltage output is changes by electronic means (as in a transistor amplifier). Visit http://en.wikipedia.org/wiki/Voltage_regulator#Electronic_voltage_regulators for more details