Re: gEDA-user: Laser diode operation?

[Mike Jarabek <mjarabek@xxxxxxxxx>]

Robert Butts wrote:
>
> Below is the link to the datasheet of a laser diode in using.  It's 
> not clear how I would wire this.  Any suggestions on how to wire these?
>
> Digikey link: 
> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=67-1500-ND 
>
> Datasheet link: http://www.lumex.com/pdf/OED-LDP65001E.pdf
>
> <http://www.lumex.com/pdf/OED-LDP65001E.pdfTG%20keenly>
These devices usually have a laser diode and a PIN diode facing the back 
facet of the main diode.  The PIN diode is to sense the power output of 
the main diode, and can be used in a control loop to servo it.  The data 
sheet shows the current through the PIN diode when the laser is 
operating at 5mW, this information can be used to design a control circuit.

The terminals you are interested in for the main diode are the ones 
labled LD+ and LD-.  The PIN diode is connected across the terminals 
labled PD+ and PD-.  (The + is probably the anode and the - is the cathode.)

The typical circuit to drive one of these things is a constant current 
source,  I have seen circuits that have an op-amp that controls a FET 
with a series resistance on the ground side to measure the current, and 
feed it back to be compared to a reference control voltage.  If you can 
get your hands on a dollar store laser pointer, you will probably find a 
simple circuit with a single transistor to limit the current, this will 
probably work fine but won't protect against the thing 
self-destructing.  Either the sense resistor or the current from the PIN 
diode (or both) can be fed back to control the output power.

You do have to be a bit careful with the voltage and current on one of 
these things, if the power gets to high they run away and self 
destruct.  Don't exceed the operating voltage or current with your 
current source. Don't hook it up backwards, as this will also wreck it.

You will also need some optics as the beam coming out of this device 
won't be colimated.  Note too that the beam is quite oval shaped, 9 
degrees in the horizontal and 35 degrees in the vertical.

Hope this helps.


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