Low power voilet LD driver circuit

[dbyrnes47]

Hi Everyone,

First time at this forum. I've done a bunch of research and I'm trying to build an EXTREMELY small (as small as I possibly can!) circuit board with the Sanyo voilet Laser diode DL-4146-101S including the driver circuit (I've attached the schematic). I've also attached a picture of what the PCB would look like. I found a DBGA LM317 that is 1mm x 1mm in the upper right corner. Could I get some feedback on what you guys think? Does the circuit look OK? Could there be issues with packing the circuitry so tight?

The reference voltage on the LM317 is 1.25V so the 37.4ohm resistor should force the current to be about 33.4mA at 25C which is a little below typical operating voltage, but above the threshold.

The PCB is 8 x 6.5 mm

Sanyo LD Data sheet link
http://www.thorlabs.us/Thorcat/22000/DL4146-101S-MFGSpec.pdf

Thanks guys!

Devyn

 

[Wolfman29]

You won't be able to run a 405nm laser with an LM317 and only 8.4V input is my guess.

 

[dbyrnes47]

Really? Why not? Operating voltage range for the 20mW DL-4146-101S is 4.8V - 5.6V and the LM317 should be plenty fine for keeping the current within it's operable range above the threshold current of 26 mA. Through all the research I did, everyone seems to suggest the LM317 for these low power lasers. I admit that the 9V supply is riding pretty close to the line though. Still should work, though.

Please let me know if I'm wrong about any of this! Thanks for replying.

Devyn

 

[Wolfman29]

Oh, 9V should be enough. 8.4V isn't.

 

[dbyrnes47]

Cool, thanks for your input Wolfman.

Anyone else want to critique the build? Please post! Much appreciated!

Devyn

 

[Addonex]

A board that small would be pretty slick if it works, would love to see it if you get it built.

 

[lasersbee]

Your Schematic looks fine... and your input is more
than enough to drive your LD through the LM317.

Just be careful to test your circuit on a Test Load and
to discharge your 1uF capacitor on the output BEFORE
you connect your LD.

Don't forget to show us the finished project...:beer:

Jerry