Constant Current DC Power Supply Circuit

Some sensitive Electronic components and Integrated Circuits requires constant current source power supply hence we designed simple and easy to construct constant current DC power supply circuit using Three terminal adjustable regulator IC LM317.

This circuit will provide different voltage output according to the input voltage and constant current output depends on the value of Reference Resistor R1.

Circuit Diagram

Components Required

  1. Step down transformer (0-9 V AC output)
  2. Diode 1N4007 = 4
  3. IC LM317
  4. Capacitor 100μF/16V, 0.1μF each one
  5. Resistor (Choose depends on your Requirement and calculate using Iout)

Construction & Working

To construct constant current DC power supply circuit first we need to build Rectifier circuit by implementing step down transformer and Bridge Rectifier. Here 230V input primary, 0-9V AC secondary step down transformer used and 1N4007 diode used to form Bridge Rectifier. Filter capacitors are C1, C2 placed to remove AC ripples from DC supply, then IC LM317 added to Regulate the current output.

IC LM317

IC LM317 from texas instruments is a three terminal adjustable regulator and it can handle output current up to 1.5A and it has internal short circuit current limiting options, Thermal overload protection circuit.

The Adjust terminal of LM317 is connected with output load after R1 (reference) Resistor and it acts as a current feedback.

Iout = Vref/R1

Vref = 1.25V for LM317

Use this formula to calculate R1 resistor value depends on your current output requirements.

In the prototype circuit, we have used 10Ω / 5W resistor and obtained 125mA constant current output DC power supply.

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