DIY Homemade laser diode driver

[Comidt]

Okay, now If I put one of these circuits in my light which takes 2 lithium batts (7.2v total), how would I reduce this to run a LD from it?
Resistors or what?
Does the LM317 regulate voltage and current or just current?
Thanks
JOnno

 

[yuip]

I reread Daedal's post, and it sounds like the capacitor is used to regulate the voltage. If the laser diode becomes disconnected from the capacitor, for even half a second, the capacitor will take on a nearly 6 volt charge. In your case, it would be nearly 7.2 volts. If you connected that too the laser diode without cutting the power to the circuit and discharging the cap, the LD would blow. So you don't really want to loose the connection.

I am making an assumption that the capacitor only feeds the LD the voltage that it needs. :-/

Gazoo also said that the way the circuit is designed, the most you will see out of it would be 3 volts when you used 6 volts in.

 

[pseudonomen137]

I reread Daedal's post, and it sounds like the capacitor is used to regulate the voltage. If the laser diode becomes disconnected from the capacitor, for even half a second, the capacitor will take on a nearly 6 volt charge. In your case, it would be nearly 7.2 volts. If you connected that too the laser diode without cutting the power to the circuit and discharging the cap, the LD would blow. So you don't really want to loose the connection.

I am making an assumption that the capacitor only feeds the LD the voltage that it needs.  :-/

Gazoo also said that the way the circuit is designed, the most you will see out of it would be 3 volts when you used 6 volts in.

The capacitor is like a buffer. If there's a quick change in voltage, the capacitor will absorb the brunt of it so that the diode isn't harmed. The cap itself has no effect on the voltage though, its just a store of energy that can either absorb or release some to filter the circuit.

As I think I understand it now, the problem with the cap charging to 6V was if the diode disconnects and the circuit is directly hooked up to the cap.

 

[Gazoo]

So, if i got this: http://cgi.ebay.com/LM317M-SMT-Volt...2582019QQihZ017QQcategoryZ36331QQcmdZViewItem
ANd I put it together, it would be really small?
But, can it only take 100mA?
What is it mounted on?
Thanks

Hello Comidt,
This kit also comes with a SMT MJD31C 3 AMP transistor and it is the same size as the SMT LM317M.....very small. It would need to be soldered in the circuit to provide more that 100ma of current. Also the kit does not come with any schematic diagrams or instructions. But the spec sheet for the LM317 does, and you can find schematic diagrams all over the Internet. The SMT devices are very tiny and I don't recommend working with them unless you nave a very fine tip soldering iron, magnifying glasses, tweezers, and very steady hands. The other problem is since the devices are so small they are bound to generate more heat. So figuring out a way to heat sink the SMT MJD31C transistor could be a problem. I am by no means saying it can't be done, but I am trying to explain what you are getting yourself into.

I would stick to the standard kit for now, work with it since it is very easy, and fool proof using Daedal's circuit. My main reason for posting the link to it is because it ends up being a heck of a lot cheaper than running back and forth to Radio Shack. Remember Daedal did say the LM317T doesn't even feel warm to the touch. And if you solder the components close enough to each other, you can end up with a nice small circuit that might fit into the head of a flashlight. The circuit board can be cut down in size. There might be a way to get the whole thing to fit especially if using the the smaller Aixiz module. We just all need to be creative, and help each other out...lol.

 

[Gazoo]

Okay, now If I put one of these circuits in my light which takes 2 lithium batts (7.2v total), how would I reduce this to run a LD from it?
Resistors or what?
Does the LM317 regulate voltage and current or just current?
Thanks
JOnno

It is regulating both. The more voltage you apply to the diode, the more current you are applying. By using Daedal's circuit, you use the trimpot to adjust the output voltage.

7.2 volts would work well with his circuit, but as soon as the voltage of the batteries reaches 5.5 volts, the LM317 would begin to loose voltage to it's output. This is assuming you are driving the diode with 3 volts. Speaking of all of this, it would be a good idea to test the circuit with something before one hooks the laser diode up to it. And don't use lithium batteries to test it. I am sure you know the dangers of using lithium batteries.

I plan to test mine with a meter and put a load on the output that resembles the diode, like a regular light bulb.

 

[Daedal]

I can see that too much confusion is being had at this circuit. Let me try and clarify a couple of things as I see them:

First of all, the LM317T has a 3V drop across it. Meaning, if you feed it 6V you would see 3V on the other side. BluRay diodes need 4.5 volts, to get that much across you'd need 7.5V on the input side. Do you see how that works now?

Second, the LM317 IS NOT regulating voltage. That doesn't mean it is not capable of doing it, in fact it is very well capable of regulating the voltage, but it is here being used to regulate the CURRENT ONLY. I can design a new circuit that uses TWO LM317's and have one regulating the voltage and the other regulating the current. But then again this is something that is easy to figure out if you read the data sheet available at the link I provided earlier in my guide.

Third, the capacitor is charged to what the circuit is providing. The capacitor is being charged UP TO 3V and while it is connected to the LD, it is dissipating 3V. This is because the LM317 is BEFORE the capacitor, so it will only charge to what the LM317 is supplying. When there is a spike, all this does is take the first little jolt by charging up in a split second and not getting the full jolt from the battery spike to the LD immediately, as would be the case WITHOUT a capacitor. Therefore, and let me take it slowly here, LM317 is putting out a total voltage of (Battery - 3V), if the battery spikes up, the voltage is being dropped by 3V by the LM317, then the capacitor is a selfish SOB and will suck up all the current before it lets it pass to the LD. Once the capacitor is fully charged, then the LD starts seeing some current and starts lighting up.

LOL @ SOB.

Now, some of you might come up and tell me that after analyzing the data here, with a 6V supply and a 60V max jolt, the LM317 taking it down to 57V, the capacitor is not going to hold that much and the battery will pretty much fry everything. Ok, let me say this. The LM317 also limits the voltage to 37V, as far as I know. So, the rest of this jolt will be shut off, a max of 34-37V will pass through and the capacitor with a 35V rating would easily suck it up. Also note that the cap I am using is a 10V and it has not failed me yet, but I wouldn't put it past it that my last DVD-burner diode diode probably died because of the lower rating on the Cap. Again, this circuit was made to be as generic and as safe as possible, having your way with it here and there is something that is your own choice. LD's die, taking this whole thing to the next step does not guarantee the life of the LD. There is no such guarantee with LD's. They are just simply uber sensitive and we can't do anything about it! We can try to line their beds with velvet and silk, but if someone so much as burps in the other room they might plop and die! No way around it... :-[

Fourth, the 1N4001 is being used for two reasons. One is to stop the diode from overkilling itself when you connect the battery the wrong way around by passing all the current through the 1N4001 and not through the LD. Second, when the battery is connected properly, there is a drop of 0.7V across the 1N4001. Therefore, 6V - 3V = 3V to the diode. With most cases I have tried this I got a little past 3V and closer to 3.5V to the LD. The diodes we are getting from the SenKat group buy, and that is what this circuit is designed for, and most other laser diodes even, require between 2.5 and 3V to lase. With a 0.7V drop off the 3-3.5V supply form the LM317, you have a margin of 2.3-2.8V going into the diode. Which is perfect! You can take it out if you want, again, this is a personal choice.

There are other regulators out there that are more suited for regulation and would probably be more efficient for such an application, but the LM317 is a great chip available from RS and is very easy to work with.

Gl all and please keep the questions coming to help me tailor this circuit more towards the needs of those who need it;
DDL

 

[Daedal]

Gazoo... no offense... but you are seriously confusing everyone here... :-?

The LM317 is NOT regulating voltage. I said this many times already. Perhaps I did not iterate it enough! Gazoo, if you have a better circuit in mind, please go ahead and build it and let us know how your results are. I would be very pleased to have such a post to replace mine since mine is generating so much confusion.

--DDL

 

[Gazoo]

Daedal,
Yes, your circuit is regulating current. I apologize as I kept looking at your circuit as regulating voltage. I feel like a dummy. I need to get my one good eye checked ;D

I will build your circuit, and built another circuit as a voltage regulator. For everyone else I apologize to you all too. The kits I posted the links to have everything you need to build both circuits.


I am going to stay out of this thread until after I have built the circuits.

 

[paper183]

what power source do you use for 6v ? 2x cr123 3v ? or is there something else we can use ? apart from 4x AAAs...

 

[Daedal]

Hehe... 4 x AA/AAA or 2 x CR123A, or any of the other 3V batteries, and there are some tiny ones. You can also get creative and use one of the batteries intended for R/C cars...

It all depends on where you're going to put it and how much you're going to use it

GL, and let us know what you decide to go with;
DDL

 

[falchionsmight]

Great driver circuit Daedal! I've got some questions though. Is there a way to use an LED in place of the 1N4001, or some other place so that I could be sure the driver is sending current through the LED (in case this were to be used on an IR laser, I'd want to know the laser is indeed on )

Next question, is there a way to make a driver that is designed like this one is, where someone who isn't well versed in electronics could make it, with it running off of 3V or 2.4 V? Using the 4 AA/AAA is going to make me have a very large laser!

Thanks for the driver design, it's exactly what I was hoping someone would post somewhere! I guess tomorrow I'll be visiting Rat Shack.... Thanks Daedal.

 

[Daedal]

You know... I had a reply all typed up and everything... and now I'm not so sure anymore...

Let me look into it and I'll let you know. Must be the lack of sleep again... :-[

I'm sure if we figure out a way to use a 2-3V LED in there it would be alright to use a 9V battery. Thus minimizing space and number of batteries... lol ;D

--DDL

 

[Comidt]

OK, Well, I will see what driver circuit my light is, then will check if I need it at all.
Thanks
i understand now.
Jonno

 

[paper183]

I think I'll use 2x cr123a if i try to put it in a flashlight, or i might find some cellphones/rc car 6v battery that i can recharge.

 

[Xenodius]

Hey, I have a stupid question-- Why bother with a 4 ohm resistor when you have a 100 ohm pot? Why not just adjust the pot less? :-? >.>

 

[rog8811]

@ DDL I have built the power supply to your design...except that my VR is 200ohm and the series res is 4.4ohm.

When I power it with 6 volts it lights an led, at lowest setting, with a measured output of 4.63v @ 6.5ma
turning the pot to other end of scale... the led doesn't appear to get brighter and I measure 5.84v @ 36ma

Does any of that look right?

Regards rog8811

Just thought I am using a 1n4148 diode, but that should only effect things on reverse polarity.