I have designed a laser diode driver circuit with LM317. I powered with a 9V battery. I am getting Vout as 4.6V and 37mA. But the actual specification of the diode is 1.7V and 40mA. How to reduce the voltage without changing the current.?

I used R1 = 330Ohm and R2 = 100Ohm.
Please suggest

 

I'm pretty sure that if you add a potentiometer or a resistor of the right value (using basic Ohm's Law), you can drop the voltage to 1.7V and keep the current constant.

Remember, current stays constant in series!

*That's if you're only going to exclusively add a laser diode at the output of your Vout

 

hi vis,
Your resistor values are incorrect, look at this image.

E

Try this Tool,
http://www.electro-tech-online.com/tools/LM317V2.php

 

hi vis,
Your resistor values are incorrect, look at this image.

E

Try this Tool,
http://www.electro-tech-online.com/tools/LM317V2.php

Thanks!.
I tried with the values in the link and got 1.6V
But how to know the value of current ?

 

hi vis,
Your resistor values are incorrect, look at this image.

E

Try this Tool,
http://www.electro-tech-online.com/tools/LM317V2.php

I am using a 9V Battery and measured 95mA current

 

hi vis,
Do you have a datasheet for the laser diode, you could post.?
E

 

hi vis,
Do you have a datasheet for the laser diode, you could post.?
E

Yes,
http://www.qphotonics.com/Single-mode-laser-diode-10mW-760nm.html

 

hi vis,
The spec data says Vfwd is 2.4V, 55mA typical. 760nm
Why are you driving at 1.7V.
E

 

Thanks!.
I tried with the values in the link and got 1.6V
But how to know the value of current ?

I assume that laser diodes are driven with constant current ?
Remove R2 and choose R1 = 1.25 / current.

 

hi vis,
The circuit you have posted is for a voltage regulator.
Look at the datasheet for the LM317, it shows a constant current source circuit.
E

 

hi vis,
The spec data says Vfwd is 2.4V, 55mA typical. 760nm
Why are you driving at 1.7V.
E

Sorry. The datasheet I received from the company for the laser shows Fwd Voltage: 1.7V and operating current 47mA.

 

The current is about 1.25/R1

how to measure this with multimeter?

 

how to measure this with multimeter?

Calculate R1=1.25/ operating current.
Check the current with multimeter ( in current measuring mode) connected between LM317 output and laser diode anode.

 

Calculate R1=1.25/ operating current.
Check the current with multimeter ( in current measuring mode) connected between LM317 output and laser diode anode.

With this Laser diode is not working. And current is read as 0 A with multimeter

 

hi vis,
The circuit you have posted is for a voltage regulator.
Look at the datasheet for the LM317, it shows a constant current source circuit.
E

I have a doubt. I tried with LM317 constant voltage source circuit. How should I power the circuit with the battery? I mean what should be the minimum voltage and current ratings of the battery to obtain 1.7V and 0.47mA as output ..?

 

See

 

I have a doubt. I tried with LM317 constant voltage source circuit. How should I power the circuit with the battery? I mean what should be the minimum voltage and current ratings of the battery to obtain 1.7V and 0.47mA as output ..?

Did you use the circuit in msg#10
You have specified three different operating currents.
In msg#1 40mA, in the datasheet in msg#7 72mA and msg#11 47 mA.
Do you know which is correct and what are the minimum and maximum currents?
With R1 = 27 ohm, the current is 46.5mA.
LM 317 needs at least 5V input voltage to get 1.7V
With the constant current circuit you don't have to worry about the laser diode voltage.

 

I am using a 9V Battery and measured 95mA current

This is too much, you have probably burned the laser.

 

Did you use the circuit in msg#10
You have specified three different operating currents.
In msg#1 40mA, in the datasheet in msg#7 72mA and msg#11 47 mA.
Do you know which is correct and what are the minimum and maximum currents?
With R1 = 27 ohm, the current is 46.5mA.
LM 317 needs at least 5V input voltage to get 1.7V
With the constant current circuit you don't have to worry about the laser diode voltage.

I gave the link by mistake. But actual specification shows, threshold current - 37mA and operating current 47mA and maximum current as 55mA with operating voltage = 1.7V. So I chose the current value in between threshold and operating current value.

 

This is too much, you have probably burned the laser.

I did not connect laser. I just verified the voltage drop and current value using multimeter