Plz Help, Red burning Laser problem

Hi, I would first like to introduce myself.
I have been reading this forum for a few weeks and I found that this forum is great and therefore I have registered an account.
I am a undergraduate E.E student in NY and I am current playing with laser diodes.

I would like to construct a simple burning laser by providing a constant current to a SONY SLD1236VL laser diode.

However, I have applied 250mA current and 5V voltage to the laser diode and it does not light up a match ( black).

I have been trying higher voltage and not dare to try higher current yet ;(

The spec. sheet said that it will give out 130mW to 150mW @ 200mA.

The circuit is attached to this topic.

Can anyone plz tell me what I have done wrong? Thank you.

sniperpikachu said:

Hi, I would first like to introduce myself.
I have been reading this forum for a few weeks and I found that this forum is great and therefore I have registered an account.
I am a undergraduate E.E student in NY and I am current playing with laser diodes.
I would like to construct a simple burning laser by providing a constant current to a SONY SLD1236VL laser diode.
However, I have applied 250mA current and 5V voltage to the laser diode and it does not light up a match ( black).
I have been trying higher voltage and not dare to try higher current yet ;(
The spec. sheet said that it will give out 130mW to 150mW @ 200mA.
The circuit is attached to this topic.
Can anyone plz tell me what I have done wrong? Thank you.  

Click to expand...

Have you actually measured the current?
Have you measured the output of the laser?
Do you have goggles?
What module/optics are you using?
Are you getting it focused down to a very small dot?
Are you holding the laser in your hand?

Peace,
dave

The laser diode needs 3v, the regulator needs 3v, we reccomend a minimum input voltage of 7.2v for this combination.

Regards rog8811

Have you actually measured the current?
Well...actually the DMM I have can measure up to 200mA only.
I have a reading over 200mA and I assume it is 250mA.
I am planning to get a better DMM soon.

Have you measured the output of the laser?
I do not have anything that can measure the radiation power of the laser.
I only know the current regulator circuit gives 5V to the laser.
When the laser diode was turned on, I have measured 2.61V across the laser diode.

Do you have goggles?
I dont have googles but I didnt look into the laser.

What module/optics are you using?
I got the module from ebay.
I cant post link since I don have 10 post. I will attach the pohto.

Are you getting it focused down to a very small dot?
yes I did, and it suppose to be all the energy focused on the very small dot.

Are you holding the laser in your hand?
Well, I have tried holding and not holding it.
When I was not holding it, I put it on a heat sink I got from my old computer.


>>rog8811
I just measured, when input voltage is 9V battery, voltage across the laser diode is 2.4V.
when the input voltage is 5.3V, the voltage across the diode is 2.6V

I think I will try incressing the R in the regulator, then put a paralle resistor( according to Ohms Law it will get more the 3V, and divide the current to bias the diode is around 150mA)
I am going to find the resistor values and try it.

Thanks guys.

I just measured, when input voltage is 9V battery, voltage across the laser diode is 2.4V.

Click to expand...

The important thing is the ma, the drive circuit is designed to give constant current, the voltage takes care of itself. if your meter only goes up to 200ma put a 1ohm resistor in series with the LD and measure the voltage drop across it, mv = ma with 1ohm.

Regards rog8811

With the driver you are using, you can measure the current directly between the battery and the driver instead of between the driver and the diode. This is a MUCH safer way to do it, and the reading will be the same either way. This will only work on linear drivers like the "DDL" LM317 circuit you are using.