A power supply is an electrical device that supplies electric power to an electrical load. The primary function of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power.
Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power (uninterruptible power supply).
12V Power supply: Use a 12 V power supply, the supply should be a portable one like a battery.
7805 Ic: 7805 IC is a DC-DC voltage regulator which regulates the voltage to +5V.
7905 IC:7905 IC is a DC-DC-DC voltage regulator which regulates the voltage to -5V.
Potentiometers: Use potentiometers to vary the power supply, as you increase the resistance the voltage decreases.
12V to 9V DC-DC voltage regulator: This regulates from 12V to 9V.
The main power supply is 12V batery, connect this to all the ICs and the regulators.
Connect the potentiometers at the output end of all the regulators.
Fix everything in a portable small box so that it is easy to carry.
Project Brief:The project lets you use all the DC-DC voltage regulators and vary the voltage with the elp of the pots.
Kit required to develop Portable variable voltage supply: