Simple Adjustable Power Supply Circuit with IC LM317

Voltage regulators are super important in power supply circuits because they keep the voltage steady even when the input voltage changes or the load varies.

One popular type of regulator is the IC LM317 which lets you pick an output voltage between 1.25V and 37V depending on the resistors you choose.

This post is about the Simple Adjustable Power Supply Circuit using the LM317 will explore how it works, how to build it, and the formulas with calculations for better understanding to design a circuit with this adjustable voltage regulator.

Circuit Working:

Parts List:

The IC LM317 is a handy little device that helps keep the voltage steady and reliable.

It has three important parts and works with two resistors VR1 and R1 which help set the exact voltage we want.

Input Voltage (Vin) can take in a voltage of up to 28V DC making it useful for many different projects

Adjustment Terminal (Adj) voltage helps us change the output voltage by using the values of VR1 and R1 to make fine tuned adjustments.

Output Voltage (Vout) can find the steady output voltage at pin 2 of the LM317.

Capacitors C1 helps the circuit respond quickly while C2 keeps the output voltage stable.

When the LM317 gets power it automatically adjusts its parts to keep the voltage steady based on the settings from the VR1 and R1 resistors.

Formulas with Calculations:

The formulas with calculations for Simple Adjustable Power Supply Circuit with IC LM317 is mentioned below:

The output voltage of the LM317 regulator is given by the formula:

Vout = 1.25V (1 + R1/VR1) + (Iadj × R1)

where,

• Vout is the output voltage
• 1.25V is the internal reference voltage
• VR1 and R1 are the resistors in the voltage divider
• Iadj is the adjustment pin current usually negligible at 50µA

Here,

VR1 is 5k
R1 is 240Ω

Substituting the values:

Vout = 1.25V (1 + 240/5000)

Vout = 1.25V (1 + 0.048)

Vout = 1.25V × 1.048

Vout = 1.31V

By varying VR1 or R1 different output voltages can be obtained.

How to Build:

To build a Simple Adjustable Power Supply Circuit with IC LM317 follow the below mentioned steps:

• Gather all the components as mentioned in the above circuit diagram
• Connect ADJ pin 1 of ICI LM317 to the junctions of resistor VR1 and resistor R1
• Connect OUPUT pin 2 of IC1 to one terminal of resistor R1 and other terminal of R1 connect between ADJ pin and one terminal of VR1 pot and other terminal of VR1 connect to GND
• Connect the INPUT pin 3 of IC1 to one terminal of capacitor C1 and other terminal of C1 connect to GND.
• Connect capacitor C2 one terminal to pin 2 of IC1 and other terminal of C2 connect to GND
• Connect INPUT pin 3 of IC1 to Vin power supply of the circuit
• Connect the OUTPUT pin 2 of IC1 to Vout supply of the circuit.

Conclusion:

The Simple Adjustable Power Supply Circuit with IC LM317 is a handy and dependable part for creating power supplies that you can adjust.

By choosing the right resistor values you can get different output voltages.

This easy to use circuit can be applied in many ways like in battery chargers, power supplies for microcontrollers and adjustable DC sources.

References:

LM317 3-Terminal Adjustable Regulator