Dont think my DVD burner laser is as bright as it should...

[Angelofhevn]

Well i have extracted my DVD laser diode from a old IDE drive and its a 16x diode.
i bought a Aixiz Laser Housing of Aixiz Lasers on Ebay for 5$. (the 5mw one)
got the old out and pressed the DVD laser into it. went flawlessly and it works with this Driver i built ( i didnt have a 100Ohm potentiometer so i used a 50ohm 20turn potentiometer instead)

but theres one problem... i see videos on youtube lighting matches at 25cm away from the laser with a bright small beam but i can only do that if i focus the lens at around 4-5cm from the laser and when i focus it to a point at we say 5m i dont get any heat whatsoever like on youtube...
what i was wondering if im undervolting the diode when i have a 50ohm potentiometer instead of the 100ohm that was required for the driver? cause i heard that the diodes max is around 250mW and it feels like its only like a 100mW...
Anyone help?

 

[Eudaimonium]

First, the schematic is wrong, and was always wrong.

The problem are 2x 10 ohms in parallel. This is equal to 1x 5 ohm.

With potentiometer set to zero, that's still 5 ohms on the Vref line of the chip, which results in 250 mA of current output, according to Ohm's Law:

I = V / R

In future, use this schematic.



Quick hint: You want 3.3 ohms on the Vref line, IF the diode is long-can type.

Long diodes have their "can" (the gray metal part) about 3.5 - 4 mm long, while short diodes have 2mm (or a hair less).

EDIT,
PS - so yeah, you are actually almost dead on - the diode should give some 100-150mW of output at lower current like that, instead of it's full power at some 400 mA.

 

[Angelofhevn]

so you mean that i should get rid of the 2 resistors and use a 3.3Ohm resistor instead and leave out the potentiometer?
or how do i get the laser to run at around 250mW and have it variable? im still learning and i got a ton of components at home in my partsbin
Cause im new to the resistor calculating for the Laser circuits
Thanks for the Good explanation u had there! realy made much clear for me!
this is the diode im using and i assume its the long can version

 

[oahu99]

If you short the potentiometer across the volt out and adjust pins on the lm317 you can adjust the current by turning the pot. Hook the diode+ to the adjust pin and the - to the negative of the battery. Just use a multimeter to see what resistance the pot is at and plug that into ohms law with 1.25 as the voltage to find your current.

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[Angelofhevn]

so now i made the New driver as listed ontop without the diodes and the resistors...
soo did you mean that i can make the same schematic as above without any resistor(s) and just use the potentiometer? :thinking:

And 1 question when the LM regulator gets 0 ohm it gives the max power output and the more resistanse i give the less power it puts trugh? am i right?
so i could leave out the resistors and only use a potentiometer?

 

[oahu99]

You can replace the resistor with the potentiometer.
Yes the lower the resistance the higher the current.

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[cheech226]

so you mean that i should get rid of the 2 resistors and use a 3.3Ohm resistor instead and leave out the potentiometer?
or how do i get the laser to run at around 250mW and have it variable? im still learning and i got a ton of components at home in my partsbin
Cause im new to the resistor calculating for the Laser circuits
Thanks for the Good explanation u had there! realy made much clear for me!
this is the diode im using and i assume its the long can version

read the thread wrong, oops sorry

 

[Angelofhevn]

Thank You oahu99!
gonna try out my new driver! :3

 

[oahu99]

No problem, have fun and stay safe!
Post again here if you have any problems and I'll try to help.

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[Angelofhevn]

hmm now i built the driver again and having the potentiometer between the adjust and output leads and i draw the lasers power from the adjust lead and i cannot adjust it... it lights up bright and i even tried to place instead of the pot a 340k ohm resistor to see if it works (with 340k ohm no light) but it was as bright as before + when i removed the pot/resistor completely (no connections from output to adjust) it still lights up :O
what do i have done wrong? :/
nevermind!!!! <----
found the problem

 

[oahu99]

Good job finding the problem.
Have fun with your new laser!

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