LM317 1.5-30 Volt Adjustable Power Supply

Using an LM317, 3-terminal regulator in a TO-220 we can design various power supply circuits that can provide various output voltages , for different electronic projects .

This power supply electronic project will provide a wide output voltage range from 1.5V up to 30V by selecting two resistances. By using a potentiometer, R2, as one of the resistors you can dial up the output voltage wanted. Either AC  or DC input can be supplied to the Kit via a socket or terminal block.

the input DC voltage to the regulator must be at least 2.5V above the required output voltage ( if you want to obtain an output voltage of 30 volts you must to use at input voltage at least  of 32.5 volts).

To be safe for continuous operation the maximun input DC voltage to the regulator should not be over 33V.

You can draw up to 1.5A from the LM317 , but if you need a higher current you can use an LM338T rated to 5A.
When external capacitors are used with any IC regulator it is good practice to add protection diodes to prevent the  capacitors discharging back into the regulator in the event of abnormal operating conditions, like a sudden short  circuit on the input or the output, or a back emf from an inductive load (D1 and D2).

Source :http://www.electroniq.net/