Well I just quickly put together a red laser pointer from a DVD recorder (Cyber Home CH-DVD Recorder With Progressive Scan Playback). It's bright as hell and I can easily see the beam outside at night. The thing is I don't know if I'm overdriving it. How can you tell? Can you? I'm using two AA's in series to focus the lens. Seems to be typical for all the laser hacks. I'm going to install it in a small box with some circuitry to help with any voltage spikes and a Pot for some control. Any help would be greatly appreciated.
DVD laser question
- Thread starter Thanatos
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You're doing what now? Two AAs in series to focus the lens? What does that mean?
Anyway, it's not very healthy, to drive a laser directly from the batteries. You asked how you can tell if you're overdriving it. That's how.
Your laser can probably do 300mA at slightly less than 3V so at 3V you are seriously overdriving it.
If you like your laser, and don't want it to die, you should really look into a driver circuit. They're not that hard to build. The LM317 is perfect for this, and allows you to set the current exactly, and the current won't change, as the laser heats up, or the batterie's voltage goes down.
The only problem with this, is that you need more than 6V to power the LM317 driver. Four AAs (6V) won't be enough, because the driver needs at least 3V more, than the laser. If you were to use 4 AAs, the power would start dropping as soon as their voltage would drop under 5.8V.
So you would either need 5AAs or AAAs to get 7.5V or six Ni-Mh rechargables, to get 7.2V.
Or you could go for rechargable Li-Pos, like the CR123 (3.6V each) and use two of those. They are very small and perfect for a driver.
This would give you 8.4V when they were full, and 6V when they were empty. The current to the laser would be constant over this entire voltage range.
Again: Many people think, that the driver circuit needs 6V, so they use batteries that add up to 6V. As their batteries discharge, their voltage drops, and so does the current.
In reality it needs 6V or more, for the output to be stable. You could even feed it 12V or 24V and the output would still be stable, but the 317 would be overheating.
So you have to use batteries, that will give you the best preformance over their entire capacity, as they are discharging. 2x 3.6V Li-Pos are best for this, because they have 8.4V when full and 6V when empty.
Good luck!
If you don't want to make a driver circuit, the very least you would need would be a capacitor directly soldered to the laser diode, to protect it from spikes at power ON/OFF, and a resistor to limit the current.
But you would have to test what the best resistance is, to give you a safe current, and you would have to set the current quite a bit lower than you could with a driver.
This is because when the LD heats up, it's internal resistance drops, so even more current starts flowing through it. In the worst case, this can result in a thermal runaway, where the heat increases the current, the current increases the heat and so on, untill the laser is dead.
With a proper driver circuit, you can squeeze out more power, and still be safe, because when the LD's resistance drops, the regulator drops the voltage a little, to keep the current the same.
But you would have to test what the best resistance is, to give you a safe current, and you would have to set the current quite a bit lower than you could with a driver.
This is because when the LD heats up, it's internal resistance drops, so even more current starts flowing through it. In the worst case, this can result in a thermal runaway, where the heat increases the current, the current increases the heat and so on, untill the laser is dead.
With a proper driver circuit, you can squeeze out more power, and still be safe, because when the LD's resistance drops, the regulator drops the voltage a little, to keep the current the same.
Sure, even i could make it for you.
I work with electronics and our company builds pretty much anything anyone wants.
PM me, if you want one.
You just need to tell me how small and how powerfull you want it.
You would still have to solder a capacitor and the leads from the circuit to the laser diode yourself tho... I can't sell any of those.
BTW: There are three different drivers available:
- small LM317 up to 200mA
- slightly larger LM317, up to 1000mA
- and a completelly new step up converter, that can make either 3.3 or 5V from a single AA or AAA Ni-Mh cell. (allows for the smallest possible enclosure and still a powerfull laser) This one is perfect for a Blue Ray, and i'm working on turning it into a current source, so it's gonna be even better with DVD burner LDs..
It can even be mounted in an enclosure together with battery compartments. Almost plug and play.
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