Step 5: Step 3: Driver

Picture of Step 3: Driver
test load01.jpg
What's this?
This is used to regulate the current flowing through the diode.

Do I need this?
YES! You must NEVER connect the LD directly to the power supply because it WILL die!

Can I just use a resistor?
Theoretically yes, but the current will not stay constant as the components heat up and the battery voltage decreases and this can shorten the diode's life.

But kipkay didn't use any driver...
Why do you think we have to deal with n00bs crying about their dead Laser Burning Flashlight Hack? (Just read the text above...)

A lot of people ask me about the diode's forward voltage stuff. This is a constant current driver. That means, it will adjust it's output voltage in order to keep the optput current fixed. So, it doesn't matter if you connect a red (2.2V), IR (2V), 405nm or a 445nm (>4V), as long as your power supply's voltage is above the diode's voltage + 1.5V, your laser will be running fine at the set current.
Also, the answer to question: "What voltage is diode XY?" can't be answered directly. Every diode's forward voltage (Vf) depends on her type and on the current. For example, a LPC-815 has Vf from 1.8V up to about 3.2V, as the current increases. Every diode has a PIV plot, which describes it's dependancy between the current, optical power and voltage. Google your diode's PIV plot, such as "LPC-815 PIV" or "22x red PIV" and so on.
Since we're building a red laser here (based on LPC-815), here's the PIV plot for LPC-815: http://www.diy-lasers.com/images/LEC_LPC-815-red.png

You can either buy one or build one (if you can)
the most common commercially sold drivers are:
http://laserpointerforums.com/f64/lava-micro-flexdrive-driver-lavadrive2-fits-pens-22502.html (usage instructions: http://hacylon.case.edu/ebay/laser_diode/MicroFlexDrive_V5_manual.pdf)

The most common DIY driver is called DDL driver and it uses LM317 as current regulator.

you will also need a thing called TEST LOAD, which consists of 4 1N4007 diodes and 1 1ohm resistor wired in series (check the pics). To use it, connect the output terminals of driver to test load (+ on the diode's anode, - to the resistor) and measure the voltage across the resistor. With 1ohm resistor, 1mV of voltage equals to 1mA flowing through the setup. Now rotate the small potentiometer, until the DMM reading matches your desired current.

recommended currens for various diodes:
gul.m.rafiq6 months ago

hello sir ,
i am working on same project

i used dvd rw laser for my project. I follow the circuit diagram given above but laser is not upto the mark not focus and not burning paper or any other things. Is this problem is due to lens that i havent used yet or any other thing ?

plz help

3zuli (author)  gul.m.rafiq6 months ago
You need to use a focusing lens in order for the laser to burn stuff. Otherwise you just get a wide beam which is very weak.
john1a made it!1 year ago

I Made it! Actually I made all this laser using a NDV 4542 405nm diode at 120mA using this driver. I also made gerbers (PCB schematic) for this driver and uploaded it in this comment.

You can see my build (CNC Laser Engraver) in my profile.

cas24063 years ago
hi there

i did every thing as you did but i can't get the laser to burn, could you please help me? i used the same parts (laser diode, parts for the driver).

3zuli (author)  cas24063 years ago
1. what PSU are you using?
2. is the laser focused?
cas2406 3zuli3 years ago
I am using a dell PS-5161-1D PSU
Output: at 5V, max 11A, 85W max
at 12V, 9A max, 160W max.
i have tested at both voltage. and the beam is focused
Electorials4 years ago
"But kipkay didn't use any driver...
Why do you think we have to deal with n00bs crying about their dead Laser Burning Flashlight Hack?"

lol that was funny :D

There's something I don't really understand:

In these examples, it means that the diode will run at
U=P/I = 200mW/250mA = 0.80V
U=P/I = 300mW/400mA = 0.75V

Isn't that voltage Really low?
Datasheets say that a dvd burner diode runs at +- 4V ?!

Also, the power (e.g. 200mW) is that electrical or optical power?
3zuli (author)  Electorials4 years ago
the power I'm talking about is the optical output from laser diode. the electrical power is greater.

And what is the average efficiency value of a DVD burner diode?
(Output power / Input power)
3zuli (author)  Electorials4 years ago
I don't remember the exact efficiency, each type of diode is a bit different. for example, this graph is for lpc815 (22x) burner diode
Ok, Thank you ;)
can i connect a 3v power supply to my diode without anything else mabey a diode?
Sorry, but I have one more question. When measuring the voltage to adjust my driver's pot, should the power supply be on? I imagine it should, but I just want to make sure since the power supply comes in the step after you adjust your driver. Maybe I worry too much, but I don't want to fry my diode. :)
3zuli (author)  instructanator4 years ago
of course, the power supply has to be powered on while adjusting the current
Yea, that was a little stupid of me. Just making sure.
I have been looking for a resistor for the test load.  I found over a hundred 1 ohm resistors on digikey, and I'm kinda confused.  Could you give me some more info on which to use, or does it not matter for this application as long as it is 1 ohm?
3zuli (author)  instructanator4 years ago
you should use a resistor that is rated for at least 1W of power. the common 1/4 or 1/2W resistors can't handle bigger currents. so get a 1ohm 1W (or any higher wattage)
Thank you!