[Laser] laser diode data sheets ?

[TWOSIG at aol.com]

I hope you can find the data sheets that you are looking for.  If not,  here 
are some things that I have done with a few that I have that may be  similar:
 
I have gotten two types of the units that use three 1.5 volt watch  
batteries, so they are intended to be use with no more than 4.5 volts.   Some have a 
yellow plastic screw cap, with a 3mm hole for the beam to  exit, that holds the 
collimating lens in place.  Unless you intend to  change the collimation, best 
to leave that alone.  I assume these are the  really cheap units, as the 
other type have a brass collimating screw cap.
 
The designers of these units are pushing for minimum cost, not good  
performance, so they have selected a series resistor to limit the current so  that it 
will not destroy the laser diode with fresh batteries.  (The design  
philosophy of minimum cost has LED flashlight makers to use the internal  resistance of 
batteries to limit current.  That the laser pointer has to  have an added 
resistor should warn you how fragile laser diodes are.)  What  I did with my 
units was to measure the current with a hard 4.5 volt source  (three fresh D cells 
will do) and use that value (or a few percent more if  I am willing to fry 
the diode if I am wrong - and I bought several just so that  I could risk a 
few).  I have not fried any yet, but I do not try to push  for better performance.
 
The other thing that I do is to drive them with a current limited  circuit.  
I run the diode from the plus power supply to the collector of a  2N2222, 
whose emitter is connected to a resistor to the ground return.  The  signal that 
switches the transistor on usually comes from a 555 timer so it is  close to 
the positive supply rail when on.  I run that signal through a  resistor 
(typically 1K) to voltage limiting device such as a zener  diode, but often it is 
1N4148 diode and an LED that has a voltage drop of about  1.6 volts, which limits 
the voltage to about 2.2 volts.  By connecting the  base of the 2N2222 to 
this switched, regulated voltage, I can use the resistance  of the emitter 
resistor to control the collector current.  I start by  assuming that the base 
emitter drop will equal the 1N4148 diode drop.  
 
For a target current of 30 ma with a voltage from emitter to ground of 1.6  
volts, I use a standard resistance above the calculated value.  For this  
example, the calculation say 53.33 ohms, and I would use 100.  Then WITHOUT  the 
laser diode in the circuit, I test it.  Sometimes I use a beefy LED to  simulate 
the load, but the Idea is to measure what the current driver is  doing.  I 
also check the voltages at the emitter and base to make sure  I am getting what 
I expect.  Then I recalculate the amount of resistance to  add in parallel to 
the emitter resistor to increase the current  through  the circuit.  I add the 
resistor, then retest.  If I really want tight  control on the circuit, I may 
use four resistors to adjust it.
 
One side benefit of this circuit is that if I use an LED for the voltage  
reference, then I can see when the unit should be on.  The only drawback of  the 
system that I see, other than it is a build and adjust for each project, is  
that the laser diode is "HOT" and even a momentary touch to ground could fry 
the  laser diode.  Fortunately, the case is the + lead and I am more likely to  
short the power to ground than kill the bug.
 
Happy tinkering.
 
 
James
N5GUI
 
 
 
>I've picked up a few cheap laser pointers (CDN$1.95!)
>and am  wondering about proper drive for the diodes. 
>There is no driver  circuitry in the pointers, just a
>68 ohm series resistor in series with  the 3 LR44 1.5V
>cells and draw in the vicinity of 30 mA.  The  label
>indicates that the output is less than 1 mW at  630-680
>nm.  
>
>Does anyone know where I can find a  data sheet for a
>diode or diode module of this type so I can  better
>understand what I should be doing with these diodes ? 
>I've  spend some time searching the web and can't find
>any data sheets for  diodes at this power level.

Steve VE3SMA