How to Make a Constant Current Source using LM317

Hi friends, today we will see how to make a constant current source using an LM317 regulator and a single DC supply. You can vary the magnitude of current using the formula given below.

Circuit diagram

The following figure shows the circuit diagram of constant current generator mini project.

Constant current source
Constant current source

Components required

  • LM317 voltage regulator
  • 12V DC power supply (9V can also be used)
  • Resistor (depends on your requirement)

Working principle of constant current source circuit

As shown in the figure, constant current source produces a 20mA current across its output. The voltage across output is lower than DC supply voltage by 3V. In this case, we have used 12V DC supply, therefore, we will get 20mA current with 9V across its output. If you use 9V DC supply you will get 6V across its output terminals.

LM317-pinout-diagram
LM317-pinout-diagram

LM317 is a linear voltage regulator IC having following specifications:

Attribute Value
Vout range 1.25 V – 37 V
Operation ambient temperature 0 °C – 125 °C
Vin – Vout difference 3 V – 40 V
Minimum Load Current 3.5 mA typical, 12 mA maximum
Output Imax 1.5 A (with proper heat sinking)

LM317 can be used as a current regulator by replacing its low side resistor of the divider with the load itself. In our case, suppose we are using DC motor as a load. We will get 20mA current flowing through DC motor. The formula for output current is given by,

I = Vref / R = 1.25 /62 = 20mA

1.25V is the reference voltage of the LM317 regulator.

You can download LM317 datasheets from the following links:

  • LM317 Texas Instruments
  • LM317 ON Semiconductor
  • LM317 STMicroelectronics

You may also like

If you like this article, please share it with your friends and like or facebook page for future updates. Subscribe to our newsletter to get notifications about our updates via email. If you have any queries, feel free to ask in the comments section below. Have a nice day!