However, in circuit design explained here, enables the output from the IC 7805 to be adjusted roughly between 5 V and 15 V (although, as mentioned, 15 volts. In general the majority of the circuits working with a 7805 regulators apply them for generating a fixed 5 volts. The remaining capacitors, C2 and C3, behave like bypass capacitors which further condition the voltage delivered to the IC 1 which is a 7805 voltage regulator. The capacitor C1 is employed to clean up and smooth the 100 Hz ripple generated by the bridge rectifier, and the charge stored in C1 is delivered to the voltage regulator. This transformer steps down the voltage around 18 VAC, which is subsequently full-wave rectified through a bridge-rectifier BR1. As soon as power button S1 is switched on, the mains AC is applied to the transformer T1. How the Circuit WorksДЄs indicated in the diagram, the output voltage is ranged between 5 V and 15 V DC. The circuit can also generate up to 1 amp output current which is a much bigger than most small AC adapters are rated to produce. The simple design provides you a range of voltages (which can be adjusted as desired by the user). The following figure shows the circuit diagram of the variable IC 7805 power supply.

Ic-7800 power supply schematic