Simple Laser Diode Driver Circuit using IC LM317

One way to supply a steady current to a laser diode is by constructing a basic circuit that uses the IC LM317 integrated circuit.

This has significance as laser diodes are highly susceptible to current and can sustain damage if the improper current is applied to drive them.

Instead of delivering voltage in this application, the well known adjustable voltage regulator integrated circuit LM317 is used to give a constant current.

Circuit Working:

Category	Item	Quantity	Power Rating
Resistors	330Ω	1	1/4 watt
Potentiometer	10k	1	–
Capacitors	Ceramic 0.1μF	1	–
	Electrolytic 1μF 25V	1	–
Semiconductors	IC LM317	1	–
	Laser diode 650nm, 5mW	1	–
Components	9V Battery	1	–

In this article IC LM317 circuit is a simple way to drive a laser diode.

The first thing the current encounters when electricity is delivered from the battery is a ceramic capacitor 0.1uF.

This capacitor filters out undesired noise from the DC source by operating as a high frequency filter.

The LM317 voltage regulator ICs pin 3 Vin is then given the filtered DC voltage.

The 10k potentiometer and fixed resistor that make up the voltage divider circuit are connected to pin 1 Adj of the IC LM317 and ground.

The output current is controlled by varying the reference voltage at pin 1 through adjustments to the potentiometer.

In essence, the laser diodes current limit is set by this setup.

Pin 2 Vout is where the LM317s controlled current exits.

A second capacitor 1uF is added to the output in order to further reduce any remaining oscillations.

By acting as a bypass capacitor, this capacitor reduces any brief voltage ripples or spikes.

You can efficiently manage the reference voltage at pin 1 of the IC LM317 by altering the potentiometer in the voltage divider circuit.

Changes in the output current result from variations in the reference voltage, which in turn regulates the laser lights intensity.

For extra safety to the laser diode you can put an additional IC LM317 based current limiting circuit as shown below:

Here is the formula for calculating the current limiting resistor (Rx):

Rx = (V_ref – 1.25V) / I_laser

where:

Rx: The current limiting resistors ohms Ω value
V_ref: The reference voltage in volts V at the LM317s ADJ pin, which is normally set by the voltage divider circuit
1.25V: The LM317s internal reference voltage, expressed in volts V.
I_laser: The intended operating current expressed in amps A for your particular laser diode

To build a Simple Laser Diode Driver Circuit using IC LM317 follow the below mentioned steps:

Gather all the components as mentioned in the circuit diagram above.
Connect pin 1 Adj of IC LM317 to upper leg of VR1 pot
Connect regulated output from IC LM317 Vout pin to the positive of laser diode and other end to ground.
Connect resistor R1 from positive supply of Vout pin to center leg of VR1 pot.
Connect pin 3 of IC LM317 Vin to positive supply of 9V battery through C1 capacitor and ground.
Connect capacitor C2 from Vout pin to ground.

The most important safety precaution is to wear laser safety glasses.
Wear laser safety glasses that are rated according to the optical density (OD) for the particular wavelength of your laser diode at all times.
The degree of blocking of the laser light is indicated by the OD rating.
Never, even for a brief period, gaze directly at the laser beam or its reflection.
You can reduce the dangers involved with working with laser diode driver circuits by adhering to these safety precautions.
Recall that if appropriate safety measures are not followed, even seemingly low powered lasers can result in significant eye injury.

A simple laser diode driver circuit that utilizes the LM317 IC to drive a laser diode may supply a steady current to the diode.

The laser diodes lifespan and correct operation depend on this controlled current.

It is best to get advice from someone with knowledge of electronics and laser safety procedures if you are new to dealing with lasers.