# LM317 Voltage Regulator Circuit

The LM317 IC is an Adjustable three terminal Positive Voltage Regulator and gives Regulated Output voltage range from 1.25V to 37V with output Current up to 1.5A. LM317 IC can be used as fixed output voltage Regulator. IC LM317 Requires only two external Resistors to set the output voltage. This Regulator IC includes current limiting, Internal overload protection and Thermal overload protection.

5V DC Power supply circuit using LM317 designed to work as Standalone power source. This circuit gives constant 5V DC Power Supply from 230V AC supply.

## Construction & Working

This Circuit designed to convert 230V AC to 5V DC, As we know in order to obtain low voltage from high voltage AC we need to use Stepdown transformer. Here 230V AC to 6V AC output Stepdown transformer used. 6V AC supply from secondary winding of stepdown transformer is directly applied to the Bridge Rectifier module, you can use either bridge rectifier module or four 1N4007 diodes in bridge rectifier form.

Here the 6V AC Converted into 6V DC supply then this unfiltered DC applied to the filter capacitor C1 and then filtered DC applied to the Regulator IC LM317 (Package To-220) this IC has three terminals, terminal 1 (Adjust) and terminal 2 (output) are connected with feedback Resistor R1 and R2, by Varying these two Resistors value we can get our desired output voltage from 1.25V to 37V (if we apply enough input voltage to the terminal 3) and output current up to 1.5 Amps.

We Can Calculate Output Voltage of LM317 as,

For this Circuit,

Vout = 1.25(1+ (1000/330))

Vout = 5.0V

After filter Capacitor C2, We can get Constant Regulated 5.0V DC supply as output. For Standalone Circuits, you can use LED indicator to know the Input voltage and Output voltage Status.

## 6V, 9V, 12V DC Power Supply Circuit using LM317

Construction and operation of this circuit is same as the previous circuit. To obtain desired level of voltage we change the Value of R2 Resistor as per the following output voltage formula.

For 6V output, R1 = 470Ω, R2 = 1.8KΩ , Vout = 1.25(1+ (1800/470)), Vout = 6.0V

For 9V output, R1 = 240Ω, R2 = 1.5KΩ, Vout = 1.25(1+ (1500/240)), Vout = 9.0V

For 12V output, R1 = 370Ω, R2 = 3.3KΩ, Vout = 1.25(1+ (3300/370)), Vout = 12.3V

## LM317

LM317 is a three terminal Adjustable Voltage Regulator Capable of Supplying up to 1.5 Amps output current and 1.25 to 37 Output voltage.

## Pin Configuration of LM317

Most Interesting thing about this Regulator is we just need two external Resistors to Adjust the output voltage. This Regulator gives good voltage Regulation and current limiting and also thermal overload protection.

Datasheet of LM317.