This circuit is a simple circuit to obtain a 5V and 12V DC power supply using one circuit.The two ICs which are using in this circuit are IC1(7812) and IC2(7805) for obtaining the required voltages. The transformer which is used in this circuit is step down transformer T1 which is rectified by Bridge B1 and filtered by capacitor C1 is used for reduce the ripple and get a smooth DC voltage.The IC1 regulates this voltage to obtain a steady 12V DC. The output of the IC1 will be regulated by the IC2 to obtain a steady 5V DC at its output. In this way both 12V and 5V DC are obtained.This power supply is very useful in when we need to DC voltage for the operation of a circuit..If we used 7806 instead of IC2 we will get 6V instead of 5V.Same if we used 7809 instead of IC1 we get 9V instead of 12V.
* The transformer T1 can be a 230V primary, 15V secondary, 1A step-down transformer.
* The switch S1 can be a SPST ON/OFF switch.
* The fuse F1 can be of 1A.
* The LED D1 acts as a power ON indicator.
* If 1A bridge B1 is not available, make one using four 1N4007 diodes.
* 78XX series ICs can deliver only up to 1A output current.