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Driving 505 35 mW diode correctly

MattBlix

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Hey everyone

I'm attempting to get a 505 diode working (sharp GH05030C2LM) correctly. I haven't found any specific info for this purpose so I thought I'd ask more experienced members.

I'm working on multispectral laser imaging techniques, and this wavelength is one among many that I have set up and already imaged with.

I have the actual diode (replacement), but not the original driver it came with (Lazeerer nano buck/boost) as we had a mishap with a supply.

However, I have on hand a Blackbuck 8M as well as can salvage a SXD v3.

I don't need this diode to last very long, just a day or two for imaging. However, I need it for yesterday.

Other means would be to image with what I've got (sequentially), and steal a nano buck/boost from one of my other diodes to get the 505 wavelength image.

Thoughts?

Thanks
MB
 

paul1598419

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That diode has a high forward voltage. That is the reason for a boost driver. It can't take much more than 350 mA, so the drivers you have will cause it to fail immediately if you supply them with enough voltage to overcome the Vf of the diode. The Nano Boost/Buck driver supplies 275 mA at ~6.3 volts. This should give you over 100 mW of optical power with most lenses. The only other option I can think of is to build a linear driver for it. You can do this with an LM317. You'll need to supply the driver with ~9 VDC and use the current sense resistor to adjust the output current. Make sure you use the control pin as the output so it will become a constant current source instead of a constant voltage source.
 

MattBlix

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Hi Paul

thanks for the information. While we had to proceed without the 505 due to time constraints, I will look into the option you suggested (diy driver) and stock up on driver and diode parts in the future. I will surely have to become (with or without my consent) a laser diode expert to go through my PhD.

I'll be sure to check here when I have questions. Thanks for the quick reply.

MB
 

MattBlix

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Hi Paul,

Finally had some time to look at assembling the LM317 linear driver you spoke of.

I also used some of the info on this site concerning using a dummy load to adjust the current (read in mV at the 1ohm resistor). In building it with the circuit schematic I found, I initially was using a pot that was not allowing adequate adjustment (super fine adjustment at first, then wham, max current!). Therefore I've used a fixed resistor to adjust the current.

Before trying the homemade driver, I thought the 505 diode I had received was non functional as it did not work using other test methods (besides using a suitable driver). More info on the 505 from this site lead me to think I had a case positive diode - it was. I was used to seeing the 505 in a case negative version, but testing for the continuity between leads (thought it was dead anyway) showed the pins were not arranged the way I thought they were (neg). So I was testing the diode with the wrong pins. This may have protected it from being destroyed using non ideal testing methods.

So anyhow, great lesson learned, and nothing broken. And it works!

Besides this, how stable use should I expect the LM317 driver to be, assuming I am giving the proper constant current (not max for the diode) and that electronic components in the driver itself seem to stay warm but not hot to the touch? I've added 2 capacitors in the circuit, and am considering putting a resistor to drain them so as not to accumulate and possibly discharge.

Regards!
Matt
 

paul1598419

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Hi, Matt. Yeah, most of the Sharp 505nm diodes are case positive. As long as you are not exceeding 350 mA it should be fine. I would heat sink both the LM317 and the laser diode as at currents approaching 250 mA they will get hot. I'm glad it all worked out for you.
 




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