Need lased diode driver schematic for 500mW IR diode

Hi everyone, this is my first post here, so pleaseforgive me if this question has been asked a billion times already, I've poked around on this site, but have not been able to find exactly what I'm looking for so far.

I am actually an electronics tech, but need some suggestions about which driver is the best, simplest, and most stable and reliable to build to drive a c-mount 500mW infra red 808nM laser diode.

I have seen ALOT of different drivers out there, some complex, and some as simple as an LM317 voltage regulator and a couple capacitors, so I'm wondering what it actually "recommended" to drive a diode such as this, in CW mode, nothing fancy, just a driver that will give it the current it needs, at the specified voltage.

One issue however is that I don't have the diodes yet, they are in shipping somewhere, so I'm not sure about the specs, such as how much current and voltage is supposed to be applied, the datasheet and hook-up instructions are included, but I' don't have them yet.

I was kinda thinking that there is a "standard" driver circuit that will drive a diode such as this, a one driver fits all kinda thing, hope I'm right about that.

I also am getting some 680nM red diodes, 500mW c-mount as well in my order, so I'm hoping again that one driver will work for both diodes.

Thanks in advance for your help and suggestions!

Chris

Search the forum for "DDL" driver. It is a constant current driver which uses an LM317 regulator. The circuit is very simple and it can be set up to provide up to 1.5A of current, which is more than enough for a 500mW diode.

Hi, thanks for that suggestion, I'll do that!

So basically, if you have an unidentified diode, how do you know how to test it, without frying it? How do you know how much current it is designed to take?

I have a red diode, an industrial one, which connects to it's supplied 120V powered supply, that has a TTL input.

I was told by the seller of this laser assembly that when I applied a 5V voltage signal to the TTL input, between 1-15khz, it would "wake up" the laser, and it's full output power would be activated, and I wont get the full 100-150mW of power output. I'm really not sure what kind of output it is giving, only that if I focus the beam tightly and bring it up close to an object, i can burn it, like black tape, or burning my initials into my wooden table.

I measured the current to the diode, it was taking 165ma of current, and when I added the TTl voltage as specified from my digital pulse supply, it did not "boost" anything. The current consumption was the same, nothing any different in the intensity, the only difference was that "now" I could "modulate" the frequency of the laser, pulsing it on and off at different rates.

Is this what the TTL input is for? Simply to "flash" the laser at a desired frequency?

If so, what purpose does this serve, for what kind of application?

Thanks!
Chris

TTL inputs are for exactly that: pulsing the laser on and off. The primary use is in laser show projectors. In order to draw an image, some connecting points must be "blanked" so that you don't see them. Otherwise, things like letters and images would have a lot of connecting lines between them. It's almost like painting parts of a neon sign black for spaces between letters, etc.

Testing unidentified diodes is risky every time, since you might push the diode too far while trying to determine how much power it can take. There is no easy way to do it other than to guess.

Thanks again for answering that!

Hope you don't mind these questions in a rather unorganized fashion in one non-specific post.

What about collimation of a c-mount diode?? I've never actually even used one before, only the small TO-18 cans or whatever they are. How can one collimate the beam that comes out of a c-mount diode? Fromn what I see in the pictures of them running, there is a rectangular beam with a very wide divergance, what is the best way to collimate a beam like that into a round point? I've seen c-mount collimation lense assemblies for sale, but I was wondering if I can manage to build something myself if possible.

Also, if I were to take a 5mW green laser pointer apart, and simply replace the whimpy IR diode in it with a more powerful one, how powerful can I replace the diode with, without burning out or damaging that green crystal that it pumps through to produce a green light?

This last thing you said is a really bad idea. Normally the pointers fail to deliver their power because of the crystals. If all was a matter of the IR diodes you would see much more power full pointers around

Even if you don't fry the crystals you won't get more power since they are alredy saturated (and I also don't think it's a good idea to modify the green pointers drivers xD)

I've seen the crystals advertised, pre-glued on a brass peice that fits into the collimating lense housing.

Like this one:

Nd:yvo4+ Ktp Glued Laser Crystal- 500mw LD Pumped! on eBay.ca (item 130344312777 end time 13-Dec-09 08:36:48 EST)

I guess what your saying is that you need to purchase a crystal that is specifically made for the power of the IR diode your going to pump it with?

What about if I pointed my 808nm 1/2 watt laser beam through this crystal, this would give me a powerful green output right?

Is that all there really is to it? Just focusing an IR beam onto one of these types of crystals to produce a green coloured beam?

2%Nd:YVO4 Laser crystal!!!!!!!!!!!!!! on eBay.ca (item 140359606821 end time 13-Dec-09 08:36:48 EST)

You can go over the crystals ratings by a fair bit, but the most power you'll be able to pump the crystals in a 5mW laser with is around 400-500mW of 808.

So the crystal that is in a 5mw laser pointer can be pumped with a more powerful IR diode to get up to 400-500mW?

What is the highest power IR laser diode you can use to do this that will give you 400-500mW? Your saying that as I mentioned in the first place, that a more powerful IR laser diode can replace the laser diode currently in the pointer?

Chris

I meant that the original 200mW pump diode inside the 5mW greenie could be upgrade to a 400-500mW pump diode and not ruin the crystals in most cases, but not always.. Any time you overdrive something you run the risk of failure. 500mW of incident pump energy will possibly get you around 50-75mW of green with those crystals, but the beam quality will suffer a bit.

ElektroFreak said:

I meant that the original 200mW pump diode inside the 5mW greenie could be upgrade to a 400-500mW pump diode and not ruin the crystals in most cases, but not always.. Any time you overdrive something you run the risk of failure. 500mW of incident pump energy will possibly get you around 50-75mW of green with those crystals, but the beam quality will suffer a bit.

Click to expand...

Thanks for that info, I appreciate it.

Clearly there is "something" I'm missing though, because I've taken many green laser pointers apart, to see what makes them tick, and pretty much destroyed a couple in the process, because they're put together with glue and stuff, so you pretty much can't open one without wrecking it, at least the cheap Chinese ones anyhow. So I've got lots of spare parts to play with.

So, I've taken an IR laser from a DVD burner, extracted it, and can clearly see it lasing, meaning I can "barely" see a red glow at the element (no, I'm not dumb enough to look directly into the beam...lol) and can tell IR is coming out of it, but when I insert that diode into the spot where the old diode was in the green laser pointer, noting happens, no output at all.
So, what am i missing?

I have a crystal mounted in a peice of brass with a lense glued into it, out of a green laser pointer, and if I put the output of the laser diode direclty to the in side of that crystal assembly, still nothing happens. Again, what am I missing?

Try rotating the crystals. Proper alignment is very important if you want to get max efficiency/power.

The laser used to pump crystals in a green laser must be 808nm. DVD burner IR diodes are 780nm. If you take an 808nm diode and use a lens to focus it on those crystals you'll likely see a little green. Get some good IR goggles if you don't have some already. Hundreds of mW of IR is quite dangerous.

ElektroFreak said:

The laser used to pump crystals in a green laser must be 808nm. DVD burner IR diodes are 780nm. If you take an 808nm diode and use a lens to focus it on those crystals you'll likely see a little green. Get some good IR goggles if you don't have some already. Hundreds of mW of IR is quite dangerous.

Click to expand...

That's the weird thing, I'm pretty sure some of the IR diodes I've inserted into the green laser pointer assembly were ones that originally "came" from those very pointers that were cannibilized, so it seems weird that I can't get any beam output no matter what diode I try.

Oh well, I'll try out the high power c-mount ones when they arrive and see what happens.

Is there any way to couple a c-mount laser diode to a standard TO18 can laser diode assembly, like the ones found in a laser pointer, meaning I've removed the diode only, and am now wanting to connect the new higher power c-mount diode to where i removed the TO18 laser diode from the laser pointer assembly.

Oh, BTW, I'm viewing the IR beam via a night vision camcorder, NOT looking at the beam at all, and I DO actually already have protective goggles that I wear when messing with anything over 5mW.

The beam needs to be focused to a point just inside the rear face of the crystal. When using hybrid crystals (like from pointers) the rear face will have a prominent green coating on it. Both sides of the crystal will appear greenish but the front will have less green and more pink to it.

Also, give this section of Sam's Laser FAQ a read: Sam's Laser FAQ - Solid State Lasers

It will really help you understand DPSS and how it works. It's comparatively easy to understand and by the time you finish you should have the knowledge to try building a hybrid DIY DPSS without much difficulty.

I'm a bit confused. I think I just fried my 5mw green laser pointer.

I took it apart, because the beam was fluctuating, and then turned the little potentiometer on the driver board, at first it straightened out the problem, then the beam died all together.

I was watching the current, it was about 150mA or so when it croaked.

The weird thing is that I can still see the element glowing red when I view the output of the crystal, as if there is still an infra red beam being emitted from it, but no green.

I tried a different driver board on the same laser diode assembly (unsoldered the one that came with the pointer and soldered on another one) and it still does the same thing.

If it was totally dead, then "why" is it still glowing red in the element of the laser diode?

All the other laser diodes I've recovered from dead cd rom drives also seem to look just like this diode, they glow red, but there is no green beam emitted if I insert these dioded into an assembly from a green laser pointer in which the diode has been removed.

Any ideas on what I'm doing wrong??