Adjustable Voltage Regulator

Adjustable/Variable Voltage Regulator using LM 117 IC

A circuit that regulates the output voltage within a desired range and can be adjustable within that range is called an Adjustable Voltage Regulator. Depending on the range of voltage to be adjusted, there are many types of adjustable voltage regulators. Two of the most commonly used IC’s are the LM317 and LM117.

Given below is the diagram of a 1.2 V to 25 Volts adjustable voltage regulator circuit using LM117 IC. The LM117 series of adjustable 3-terminal positive voltage regulators are able to provide in excess of 0.5A over a 1.2V to 37V output range. They are very easy to handle and require only two external resistors to set the output voltage.

This power supply is able to deliver a maximum of 0.5 A current. The circuit is easy to assemble and provides great results. Resistances R1 and R2 are used for voltage adjustment.Vary pot R2 to get the required voltage. If exact value components are not available try components with the nearest values. Parts list is given with the circuit diagram.

Notes:

1. For getting a 1.2 A output current replace LM117 with LM317. All connections are same.
2. To reduce min output voltage from 1.2 volt to 0V connect two IN4007 diodes in series to the output ( 1.2  – (0.7+0.7) = -0.2 V  ie ; 0 V approx).
3. To protect the IC from thermal overload, fit the IC with a suitable heat sink.
4. You can use as less as 5V DC as input voltage. No problem but remember the maximum regulated output voltage will also decrease almost by the same fraction. Here a minimum 28V   2A DC input is needed for the IC. The capacitor C1 is used to reduce the sensitivity to input line impedance. C2 is used to reduce unnecessary ringing. Please go through the circuit diagram shown in the figure below.

Adjustable Voltage Regulator Circuit Diagram

Note: Potentiometer R2 is 5K (R2 is the pot connected between ADJ and Ground)

LM 117 Pin Out Diagrams