DIY Homemade laser diode driver

[wooooooolazer]

Oops i meant voltage, the regulator will never work right, it will always be dropped out because the batteries cant give 6v since ni-mh have a normal 1.2v charge while alkalines have a normal 1.5v

...lazer... ;D ;D ;D

 

[flogged]

Oops i meant voltage, the regulator will never work right, it will always be dropped out because the batteries cant give 6v since ni-mh have a normal 1.2v charge while alkalines have a normal 1.5v

The regulator works fine, the diode just sees a little less voltage is all. I've got a working laser running off 4 AA nimh batteries that says you're wrong. It pops balloons to over 40 feet with a current draw of 225mA.

 

[Gazoo]

[quote author=wooooooolazer link=1185701612/690#702 date=1199485647]Thats not a good idea, it wont give nearly enough current, 4aa ni-mh wont even be 6v when fully charged, just use 6 of them and measure the current when you adjust it.

...lazer.... ;D ;D ;D

What are you talking about. AA nimh batteries have no trouble supplying 250mA (or more) of current. I did measure the current when I completed my pointer (to 225mA). 4 nimh batteries will not effect the current draw, the diode will just see less voltage than when using 6. If it works using 4 (and not 6) this is probably preferable.


[/quote]

No it is not preferable...the reason being is because your regulator is dropping out and not maintaining a constant current to the diode. If for some reason you use alkaline or lithium batteries, your current going to the diode will spike and possibly kill the diode. If you measure your voltage between the output and adjust it should always be 1.25 volts. If it is lower then your regulator is dropping out.

It is much better to run more voltage to the regulator and have it set at whatever current you want to drive your diode with, than to have the regulator dropping out. So for example if you want to drive your diode with ~160ma's, you would put an 8 ohm resistor between the output and adjust. The current going to the diode would stay the same no matter what your voltage going to the regulator is....as long as it is 6 volts or more. This is what is meant by constant current regulation.

Doing it your way will not harm the diode unless you use something other than nimh batteries. But it still isn't the right way to do it. For new members reading these posts it is best to explain the proper way of using such and such...with such and such.. ;D

 

[wooooooolazer]

Heh that reminds me of a digital camera that i set to use ni-mh batteries and i had just used up all the charge so while i was charging them i put in alkalines and i heard it pop and like sizzle. Luckly i hit it kinda hard and put ni-mh back in it and it worked... phew...

...lazer... ;D ;D ;D

 

[flogged]

No it is not preferable...the reason being is because your regulator is dropping out and not maintaining a constant current to the diode. If for some reason you use alkaline or lithium batteries, your current going to the diode will spike and possibly kill the diode. If you measure your voltage between the output and adjust it should always be 1.25 volts. If it is lower then your regulator is dropping out.

It is much better to run more voltage to the regulator and have it set at whatever current you want to drive your diode with, than to have the regulator dropping out. So for example if you want to drive your diode with ~160ma's, you would put an 8 ohm resistor between the output and adjust. The current going to the diode would stay the same no matter what your voltage going to the regulator is....as long as it is 6 volts or more. This is what is meant by constant current regulation.

Rubbish. The regulator works fine off 4.8 volts, about the lowest 4 AA nimh is going to go. You're aware that alkaline batteries drop voltage as they age, as well as while under load.. so the ddl circuit will be seeing LESS voltage with used alks than it will see using nimh. Look, I metered the current for some time and it's rock solid using 4 AA nimh. If the current regulation was not working properly I'd have a toasted diode by now.

See this thread for pictures of the pointer. I'm making another using the same setup.
http://www.laserpointerforums.com/forums/YaBB.pl?num=1198896548

You are correct about having to recalibrate the current draw if I were to switch to higher voltage batteries. However I'm only going to be using nimh so it's not a problem. I think it's stoopid not to use rechargeable batteries in these high drain devices, but to each their own. 4 aa nimh works fine, just be aware once tuned for them other batteries may be unsafe to use.

 

[Gazoo]

I am not going to argue with you.... I do agree using nimh batteries are the way to go. But please don't go telling me my posts are rubbish. Yes...I do know alkaline batteries sag quickly. The point I was making is if you have your regulator adjusted using fully charged nimh batteries, and you switch to alkalines, you would be applying at least a half volt more to the circuit. This half volt may not last very long but it could be enough to kill your diode.

Anyway, you go ahead and continue to do it your way. And I will continue to do it my way. And my way is what I will keep recommending, so members don't get confused and wonder why the regulator isn't working like it was designed to work because they tried it with 4 nimh batteries, or 2 CR123's for that matter.

 

[flogged]

(from page 4 of this long thread)

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:

(...)

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.

(...)

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.

Above can be used to calculate how much voltage the LD sees.

The regulator only needs 3V, which it will always get. So assuming 5 volts from a 4 AA nimh pack, that would put the voltage range between 1.3-1.8. So how much voltage do these Sony DVD diodes really need? The datasheet lists 2.5 volts. Apparently they can lase down to less than 2 volts however.

Now that I look at this I'm starting to wonder if I got lucky and used a diode that lases at an unusually low voltage. I suppose if I took the 1N4001 diode out that would raise the voltage range to 2-2.5, which is better... however I want the diodes protection.

I suppose you're right.. more than four nimh should be used.

 

[Gazoo]

The formula that works with the 317 should be used to calculate the resistor needed...1.25/I = R Or you can do it this way....1.25/R=I Always think in terms of current when working with LED's or LD's.

But yup, six nimh should really be perfect. All you need to do is measure the voltage between the adjust and output and you can tell if your regulator is working properly. Or just use the calculations for the resistor needed between the output and adjust, and make sure you have at least 6 volts running to it. The formulas really do work.

When I first got into this hobby I got into a heated argument with Daedal about the regulator...lol. I kept visualizing it as being used as a voltage regulator. After several PM's back and forth with Daedal I finally got it through my thick skull how and why it was being used as a current regulator...and it all has been crystal clear from that point on. I always think current, and measure the voltage across the diode only if I am curious.

 

[Abray]

hey, I'm back...

just 2 questiong this time though, you solder the silicon diode in "backwards" right? so that if the batteries were placed in the wrong way, it would be correct for the silicon diode?

and also. blu-rays need ~40 miliAmps, and GB diodes need ~250 (or something like that). would you just use different resistors and keep everything else in the circuit the same to make that change? or do you just need to adjust the pot?

 

[Gazoo]

hey, I'm back...

just 2 questiong this time though, you solder the silicon diode in "backwards" right? so that if the batteries were placed in the wrong way, it would be correct for the silicon diode?

and also. blu-rays need ~40 miliAmps, and GB diodes need ~250 (or something like that). would you just use different resistors and keep everything else in the circuit the same to make that change? or do you just need to adjust the pot?

You want to put the silicon diode in so that current flows through the circuit. Just search google for that one..

For the blu-ray, using a 33 ohm resistor between the output and adjust of the 317, will supply ~38ma's to the diode....check the formula's I just posted. The difference is the regulator requires at least 8 volts to work properly because the blu-rays require more voltage...about 5 volts.

So yes you could use the same circuit to power both diodes as long as you have a 50 ohm pot. But I would use separate circuits for them.

Some of us are using a 7805 voltage regulator for our blu's. It works well and you could do that too...for more info. take a look at this thread.

http://www.laserpointerforums.com/forums/YaBB.pl?num=1198710347/13#13

 

[Abray]

yes I am planning on doing that, I was just wondering what the differences are in the circuits.

So I'm guessing that for the blu-ray, you would need the 50 ohm pot, what would you need for the GB diode?

 

[Gazoo]

You don't need a pot. But if you use one you will want to put a resistor in series with it as is shown in Daedal's circuit. This way your current is limited to the value of the resistor. So if you use a 5 ohm resistor in series with the pot, your current will never exceed 250ma's. The radio shack 3 watt 25 ohm rheostat is an ideal pot to use to get started quickly with the reds. It is big and all...but it works. But if you are trying to keep your circuit small, then forget the pot..

The same applies to the blu....with the 317 you could put the next lower value resistor RS has in series with the pot...this would be a 22 ohm resistor. Then the regulator would supply a max of 57ma's. So you could get buy with a 10 ohm pot in series with it but your pot would always be turned to the most resistance which would equal a total of 32 ohms resistance. These are just examples...

 

[Abray]

so basically, if I don't use a pot then it would just be a fixed current circuit. Is the LM317 adjustable? I've also seen that it needs heatsinking...
and that post you told me to read explained about the 317, but it never said how much current it allows through, or how much it resists.

also, you said the reference voltage was only 1.25 for the LM317. I thought that the LM317 only took 3v from what the battery was supplying, or are we talking about 2 different things?

 

[Da_Dude]

So for blu-Ray, you could use a 9volt batt?
If you wernt going to use a pot for a blu-ray, what value Restor would you use?

 

[wooooooolazer]

yes, 9v batteries are perfect for blu-rays since they dont need much current but high voltage.

...lazer... ;D ;D ;D

 

[Da_Dude]

What about the resistor?
And the lack of a potinomeeter?