Re: gEDA-user: Laser diode operation?

[Mike Jarabek <mjarabek@xxxxxxxxx>]

Robert Butts wrote:
>
> Woe...
>
> I'm using ten of these and parallel.  I WAS going to just use a 1 amp 
> 5 vdc power supply with a 2.8 V zener diode to adjust the voltage to 
> 2.2 V.  I take it this is too simple.
>
I didn't mean to scare you.  You can probably get away with putting a 
bunch of simple current limiter circuits on the diodes, like the ones in 
the dollar store pointers.  The circuit looks pretty simple, but I never 
traced it out.  The main advantage to a current control circuit is that 
it will allow you to control the brightness as the diodes age, 
especially if you use the PIN diode for power feedback.

I have even seen people drive these like an LED with a series ballast 
resistor, but this does not protect the diodes from destruction as they 
age, or protect them from over current.

> On Fri, Aug 29, 2008 at 10:46 PM, Mike Jarabek <mjarabek@xxxxxxxxx 
> <mailto:mjarabek@xxxxxxxxx>> wrote:
>
>     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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