[Laser] Mod Power to several lasers?

Sat, 30 Aug 2003 19:28:38 EDT

In a message dated 8/30/03 5:37:59 PM GMT Daylight Time, 
[email protected] writes:

> I wonder if anyone has an idea how to run six 5mw lasers from a circuit 
> similar to K3PGP's Tx modulator. I can get one diode running fine but then as 
> you add more diodes the current is shared unequaly between the diodes  (they 
> take what they need)and then they blow!!!!!
> I could build a seperate K3PGP's Tx modulator for each diode and run them in 
> parallel, but driven from common mod source, but that  seems over 
> complicated.
> Has anyone any ideas or circuits they could point me to please.
> 
> 

No problem.......

How about taking seperate dropper resistors from the main supply to each of 
the laser diodes. These resistors can be individually selected to match the 
laser diode it feeds. It's the dropper resistor that is really critical in the 
K3PGP circuit.  The shunt modulator FET or darlington can then be wired across 
each of the lasers with a normal 1N4001 etc in series with each one to prevent 
coupling. The silicon diodes will not have any serious effect on performance 
because although they will have 0.7V across each one, this is  well below the 
lasing threshold of the laser diodes.

73

David  G0MRF

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