Laser Diode Driver - How to increase current

Discussion in 'The Projects Forum' started by viswapravin, May 18, 2016.

1. viswapravin Thread Starter New Member

Mar 16, 2016
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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.

2. Chardi New Member

Oct 3, 2015
28
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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

Jan 29, 2010
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Mar 16, 2016
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Mar 16, 2016
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6. ericgibbs AAC Fanatic!

Jan 29, 2010
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hi vis,
Do you have a datasheet for the laser diode, you could post.?
E

Mar 16, 2016
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8. ericgibbs AAC Fanatic!

Jan 29, 2010
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hi vis,
The spec data says Vfwd is 2.4V, 55mA typical. 760nm
Why are you driving at 1.7V.
E

9. jjw Member

Dec 24, 2013
174
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I assume that laser diodes are driven with constant current ?
Remove R2 and choose R1 = 1.25 / current.

Last edited: May 18, 2016
10. ericgibbs AAC Fanatic!

Jan 29, 2010
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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

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11. viswapravin Thread Starter New Member

Mar 16, 2016
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Sorry. The datasheet I received from the company for the laser shows Fwd Voltage: 1.7V and operating current 47mA.

12. viswapravin Thread Starter New Member

Mar 16, 2016
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how to measure this with multimeter?

13. jjw Member

Dec 24, 2013
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Calculate R1=1.25/ operating current.
Check the current with multimeter ( in current measuring mode) connected between LM317 output and laser diode anode.

14. viswapravin Thread Starter New Member

Mar 16, 2016
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With this Laser diode is not working. And current is read as 0 A with multimeter

15. viswapravin Thread Starter New Member

Mar 16, 2016
21
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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 ..?

May 20, 2015
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See

17. jjw Member

Dec 24, 2013
174
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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.

18. jjw Member

Dec 24, 2013
174
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This is too much, you have probably burned the laser.

19. viswapravin Thread Starter New Member

Mar 16, 2016
21
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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.

20. viswapravin Thread Starter New Member

Mar 16, 2016
21
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I did not connect laser. I just verified the voltage drop and current value using multimeter