Osram PLPVQ-940A driver question

[DrMario]

Hey all.

I got my hands on an interesting VCSEL diode (Osram PLPVQ-940A) from Digikey website for almost $10 for the DIY Infrared illuminator for some of my digital camera so I can use it for certain night shoots without disturbing anything in the dark. It's powerful for such a tiny laser - almost 500mW CW if I am not mistaken. Its intended usage was for smartphone face / irises biometric identification. Like some of my lasers, it will be in Convoy S2+ host, however this time no drilling involved since this laser diode is a DFN-2 surface mount device (obviously designed for phones).

However, I am a bit curious, will two AMC7135 altogether for 700mA do fine with this and the usual Gallium-Arsenide laser diodes or am I playing with the fires? From the datasheet, 750mA continuous and 1,200mA pulsed (surge) current and 2.2 - 2.5 Volts ratings for this Infrared VCSEL diode. I hope I am playing it safe (and yes, I will solder it on a LED MCPCB designed for Cree XP LEDs, that way I keep it cool enough for longer than 10 minutes without overheating the laser).

Of course, 940 nanometers Infrared laser light is no joke, so I am using a 60 degrees "fly eyes" TIR optics to spread it all out. I won't even attempt to look directly at this VCSEL, it's too powerful - especially in CW mode.

* EDITED: I added the night vision illuminator into my to do list in my signature - if the "infrared" texts are too hard to read for you guys, just let me know, I will just put in 670 - 620 nanometer red equivalent color so it is readable.

 

[DrMario]

Another update - I ordered SJ9000 generic GoPro rip-off specifically for the all-spectrum imaging so it will be handy for viewing in the Infrared if my other cameras won't see it well. It's cheap enough to perform the hardware mod - removing the Infrared filter from the lens assembly.

 

[DrMario]

I decided I will just gamble - I am going to use the modified Nanjg AK-47A LED driver with one AMC7135 LED driver LDO regulator deleted. It has soft-modded firmware for 15 - 50 - 100% modes (just so I can control how much Infrared light I will need for the digital camera night vision). The Infrared and red (Gallium Arsenide or Indium : Gallium Phosphide) VCSELs are supposed to be stupidly tough - I used to have 850nm VCSELs but lost them a decade back. Gallium Nitride ones are apparently even more fragile, to the point AMC7135 is simply unsuitable.

Why did I ask if AMC7135 is okay with the beefy GaAs laser diodes including this VCSEL diode? That's so I feel better having double-checked as some lasers aren't cheap. I may have gotten away with that with the blue laser diode - that's because the laser diode have very high Vf, and it kinda sounded like to me off the datasheet that it was designed for the Gallium Nitride LEDs. Apparently the general census showed that it is usable with Gallium Arsenide LEDs. Guess I am safe.

And as for the attached image of the SMD component, I took a picture of this 940nm Infrared VCSEL that I ordered from Digikey to show my friend what I was talking about, so you guys would know what it looks like if you are curious. I am amazed that a laser that powerful could be made very small - the VCSEL diode die is estimated to be about 1mm or smaller, while edge-emitting laser diode could be a bit larger.

 

[paul1598419]

Interesting find. I would be careful using LED drivers for LDs as the noise level for LEDs is much higher than it is for a laser diode. If you just have to use one of these drivers, I would try to set the current low so that any spikes might be under the threshold of failure for the diode.

 

[DrMario]

This is true, and I totally agree, which is why I wanted to double- or triple-check to be sure. VCSEL diodes are supposed to be more resistant to COD (Catastrophic Optical Damage) owing to the more wide laser cavity face, meaning the heat is simply spread out. In my experience, VCSEL is kinda hard to kill compared to the Jelly Bean favored laser diodes (I basically have driven one of my VCSEL like a LED), but the damage can still occur if you really try, like zapping it with static electricity.

To be on safe side, I will solder 1 or 10 uF MLCC (multi-layered ceramic capacitor) to dampen the spikes a bit - I used 1uF capacitor with the AMC7135 driver in the blue laser, zero problem with it.

 

[paul1598419]

Glad to hear you have not had problems. It isn't difficult to blow a laser diode, even a surface layered one, so I just thought I'd tell you just in case....

 

[DrMario]

Yep. Laser diodes are naturally sensitive to everything including ESD and spikes (funny enough, some lower power Gallium Nitride LEDs can be murdered this way too), I killed a VCSEL due to spikes from cobbled-together laser driver when I was younger - I didn't know better back then. However, now that I have access to some laser diode driver options, that kind of save me some headaches here.

I have been taking serious care regarding ESD, as I am paranoid of killing some pricey parts - I don't use line-powered soldering iron much anymore - I have TS100 soldering iron, even though it's line-powered, it can be grounded, and sometimes for some LED soldering job, I use a portable blowtorch to solder it on the MCPCB. (I first keep them both apart to ramp up to soldering temperature slowly with torch pointing up on the bottom of MCPCB as hot air rises up, then closely to finish off soldering process. I have successfully soldered a few Nichia NVSU233A-U365 LEDs this way before, no problem with those LEDs. I have a Convoy S2 flashlight with this LED, it's one powerful portable blacklight.) All to try and keep ESD exposure low.

I am a bit anxious to see how it come together once I get some parts from Mountain Electronics in the mail.

 

[Cyparagon]

Why would you use a laser instead of an LED (for example) ? Although an LED would be slightly less efficient, it would be much higher output, more robust, easier to drive, easier to heat sink, easier to collimate, and cheaper.

 

[DrMario]

Why do I want to use laser? Better optical quality especially for Infrared lights. But you do have few good point though.

Following the datasheet, VCSEL is already heatsunk (Cathode tab on the DFN-2 package is where I'd solder the VCSEL on the LED MCPCB heatsink pad along with Cathode pad - the Convoy S2+ will have its body connected to the Cathode (-) end of the Lithium-ion battery so it's no problem, I only need to worry about Anode connection as it result in short circuit). Of course, that's true that LED is easily driven and cheap. But collimation - not so much (but hey, it's not a laser diode), but if you want diffused output it will work too.

In the end, it's just a brighter Infrared illuminator, and I can switch out the pill if I need to, now that I have an extra pill to use, and I am already looking at Osram 940nm Infrared LED, more specifically the OSLON 4725S LED which should have similar electrical and optical specification as the PLPVQ-940A VCSEL (same manufacturer that I bought the 500mW VCSEL from), if I need some eye safety in the close range.

Nevertheless, I will take picture of the completed Infrared VCSEL pill (and when my action camera arrives and gets modified, I will do night vision picture too).