DIY Homemade laser diode driver

I'm working at a lab during the summer, and the electronics dept. are really good, and I've got them making things for me in the past (SMD). As they've got all the kit, (huge TC microscope, some special soldering iron, solder pads etc.) 2 of the guys are qualified to assemble circuits and solder components for space rockets, the spec they have to follow that they've shown is actually insane!
BUT, I'm only there for another 2 weeks, so I don't mean to push you, but if you could get me the dual voltage/current circuit driver in the next few days. I can then mill the PCB myself (as I've got a CNC) and get the electronics guys at work to make them for me
BTW: I've had a go with SMD and they are crazy!

Thanks,


Dan

Boy, that sure sounds like fun. Ok, so... let me get this then... you want to have BOTH voltage AND current regulation? Using 2 pots?

It seems easy enough with a 9V battery supply and 2 LM317's, one in current regulation mode, the other in voltage regulation mode, both of which can be controlled through a pot. I'm sure this wouldn't be the best solution, but it's worth a shot if you wanna give it a go. You'd have to use a capacitor across the battery terminals and silicon diode on there would help eliminate reverse polarity issues. Although, 9V batteries can only be plugged in the right way if you use the designated clamp.

If you want a more sophisticated circuit, one that requires only 3V input and such, you;d have to give me some time and I honestly don't have the time for that right now as I'm busy with a few other things right now. I could probably find a suitable regulator with a low dropout, but 3V input to a 2.5-3V output is a VERY tiny margin. Most 1.5V batteries will deplete to .9V by the end of their life. the LDO will need MINIMUM .1V through it. with 2 regulators, you're looking at least .3V dropout in ideal situations. When you put in 2 lithiums, you'll get 2.4V out of them, which is not good enough to drive the LD without a boost circuit to bump up the voltage... thus you need a third chip... the madness keeps going. I wouldn't plan on this being a very powerful circuit unless it can be powered by, say, a 3.6V CR123A battery. That gives you a better V-drop margin.

On the other hand, if you haven't checked it out yet, I'd say take a look at Sam's FAQ. He's got some very nice circuit over there that can be of much help to you.

Link here: http://www.repairfaq.org/sam/laserfaq.htm

GL;
DDL

If you want the ability to regulate both I think the L200c would be the ideal IC

http://eu.st.com/stonline/books/pdf/docs/1318.pdf

I personally have never used one but from the data sheet it looks promising. if you want to avoid using 2 lm317's however i think ther is a design for using a lm317 for both current and voltage regulating simultaneously

possibaly even a mic5219 but it maxes out at 500ma

Cheers, I see what you mean....

I don't really care what the volatge is, as long as I can ultimatley stuff it in a Mini Maglite. But I want to first use the circuit as a "bench test". I've done some rough dimension calcs with the maglite and batteries, and the best solution so far, is: 2x AA (101mm in length 14.5 dia) but if I swap them out with 2x CR123A's (35mm length 17mm dia) so I'd have 31mm to play with to condense the circuit down to??? But more importantly, it gives us 6V. Is this enough to play with 2x LM317's?

Appriciate you help loads

Dan

You will not be able to get a CR123 to fit in a mini mag.

Why not? It's only 3 mm bigger, and I'm quite happy to drill/ream the hole bigger.

SMD isn't too bad if you already know how to solder and apply heat correctly. I use a small 25 watt temp controlled iron and I have 0.010 and 0.005" solder for the purpose. It also helps to be very near sighted like me !!

Mike

danielbriggs said:

Why not? It's only 3 mm bigger, and I'm quite happy to drill/ream the hole bigger.

Click to expand...

You would end up with less than 1mm thickness since the outside diameter of a mini mag is 18.03 mm's. Plus you need to allow a bit of room for play so you can get the battery in. How would you improvise so you could screw the end cap on, since the threads that are currently there would be lost?

Oh, 1mm's a bit thin....
BTW: 17mm is the max, the min is 16mm according to Energiser Datasheet. I could peel of the plastic cover to get an extra 0.1mm

Threads are not a problem; tap and dies (Taps in this case!)
I can sort out the mechanics of it, it's the electronics I cant do!!

On another note: You know the Maglite accessory that replaces the botton cap, with a 5 press click thing. I think it's 100%, 75%, 50%, Slow Pulse, Fast Pulse.
Would that be OK to use? i.e. the lasers can take fast a slow pulses, along with varying power.


Lastly, if I get the 5mw aixiz module that's reccomended for the DVD Maglite, does that have all the electronics on it? i.e. ready to plug in straight to 3v batteries (2x AA)?

Well it will be interesting if you can get a mini mag to accept the cells. Please keep us updated if you decide to try it.

I believe you are referring to the nite ize thing...I have wondered too. It should work since it comes with their 1 watt LED upgrade as an option. However, from what I have read about it that switch, some current is lost due to the circuitry. Nevertheless, I have been meaning to try one with a laser

The 5mw aixiz module comes with a driver and wires soldered to it. The problem is the driver will not handle the power of our DIY laser diodes.

Sorry I can help you with the circuitry. I do think you would be fine just regulating current. You really don't need to regulate voltage and current.

Ok thanks, I'll do that then.

Again off topic: So how do all those people that have ripped 250mw diodes from DVD-RW drives and stuck them in a 5mw Aizix housing get them to burn things? If the power is limited to 5mw???

Again off topic: So how do all those people that have ripped 250mw diodes from DVD-RW drives and stuck them in a 5mw Aizix housing get them to burn things? If the power is limited to 5mw???

Click to expand...

The aixiz module is just a convenient means of holding and focusing the LD, there would still be some circuitry to go with it I would guess.

Regards rog8811

The power is not limited by the Aixiz module. We do not use the drivers or diodes that come with them. All of that is removed, then we mount our DVD diodes and connect our own circuitry.

WOW, Gazoo... Way to keep up with the replies man. Thank you

As Gazoo said, and as the guide says, there is no need to regulate the voltage of a DV battery. It already is regulated. If you are using this circuit to drive the LD from a battery, then slap a capacitor in there and forget about regulating the voltage.

The LM317 can, regulate both, but I haven't personally tried it as I have not needed it yet, and as such I will not comment on its efficiency/ability.

The AixiZ module is simply a smaller drive circuit like this one with a nominal voltage of about 0.7V, but I have had that drop to about 0.3-0.4V. It's a nice little driver with wonderful results and a very small footprint. The only drawback is that it will not capable of driving the LD's we are using here. Not enough heat sinking first of all, and I haven't even tried to look at the circuit to see if it is moddable.

Placing 2 X CR123A batts in a minimag... lol... sorry, I'm holding both right now... Even if you used the most accurate lathe to drill it out... have you thought about it first?

On the bottom side of the minimag you have an internal thread for the battery cap. If you were to drill this thing out to the size of the 123 batts, which I don't know if the tube would survive, the thickness of the tube would not be enough for the threads to go on there. :-/

--DDL

Ive been toying with a few different current regulated power supplies for the DVD diodes. One thing I've run into is the "overhead" voltage needed by the LM317 - I can't get above 225mA, regardless of resistor values when using 4 NiMH cells (4.8V). I believe this is due to the voltage drop in the LM317. Are you guys using Alkalines (6V) ? Or has anyone had success with 4 NiMH cells?
Thanks,
Rob

Daedal said:

As Gazoo said, and as the guide says, there is no need to regulate the voltage of a DV battery. It already is regulated. If you are using this circuit to drive the LD from a battery, then slap a capacitor in there and forget about regulating the voltage.
--DDL

Click to expand...

hey Daedal; first of all thank you so much for all your expertise with lasers. your helping all of us newbies out and im sure i speak for everyone when i say thanks!!

so; as you said quoted above,

does that mean that since i am doing the dorcy mini mod, i can scrap the regulated circuit board included *IN* the dorcy, and just put a capacitor (47uF 16v) in line between the cr123 batt and the diode? obviously its possible; but, will *JUST* a capacitor maximize the laser diodes life and power output (PW aside) and be as sufficient enough in its job that your "DIY Homemade laser diode driver" does ????

mabye a 47uF + a resistor inline?

thanks!
eric b