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Old 03-28-2008, 07:26 AM   #1
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Default dvd burner laser, what voltage?

i've just bought an 20x dvd burner for a home made laser.
i want to put the diode in an nice flashlight i have but the flashlight works on 4.5 volts
is it possible to connect the diode to this flashlight on 4.5 volts? or wil it burn out?
otherwise i will buy another flashlight that works on 2 AA batteries, does this work without a driver?
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Old 03-28-2008, 08:00 AM   #2
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Default Re: dvd burner laser, what voltage?

Dont use it without a driver. For 2xAA it will work but its not guranteed. A driver provides clean constant and sufficient power for the laser. Your best bet is to build the driver(read forums) and use a 3ohm resistor to get a nice current for the 20x open can diode.

You will need at least 6 volts to run the driver. If you were to run your diode straight off 4.5 there is a high chance it will die. If you run it off 2xAA(3v) it MAY not die but because it is open can, it will be severly under powered(id say around 70mW)
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Old 03-28-2008, 02:24 PM   #3
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Default Re: dvd burner laser, what voltage?

Running a laser diode straight off of batteries is never a good idea. The current will not be controlled, and even if the typical current is not too much (which it probably will be anyway), the current can spike when it the laser is switched on. This spike can easily be prevented, and the current can easily be limited, with a simple driver that you can build with parts from your local RadioShack. The driver will be much less expensive than the diode, and even more so when you have to buy the 2nd diode because the first one burned out due to a lack of control. There are ample topics on here about building your own driver, or you can get a driver prebuilt and ready to drop into your host.

Also, one thing you didn't say is if the flashlight is an LED light or if it has a bulb. Lights that use LEDs already have a protection circuit, so you only have to add a couple of components to them, whereas lights that use bulbs need to have an entire circuit added. Again, there are topics on this available all over the forum.

Good luck, and enjoy your laser hobby
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Old 03-28-2008, 11:41 PM   #4
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Default Re: dvd burner laser, what voltage?

Like everybody said above, you need a driver if you are modding a flashlight.

Also, it isn't the batteries voltage the kills the laser diode when you don't use a diode, it is the current that kills it. Running these things over 3 volts is fine as long as you keep the current regulated. I have a DIY red running at 5 volts that I made for an experiment, and it is still working fine after a couple of months.
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Old 03-29-2008, 02:04 PM   #5
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Default Re: dvd burner laser, what voltage?

so it will run at 4.5v but the current can kill the diode, but if i use a resistor to limit the current? if that works, what resistor will work?
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Old 03-29-2008, 02:45 PM   #6
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Default Re: dvd burner laser, what voltage?

You can use this formula to determine what resistors you need:
(voltage of batteries - voltage drop of laser diode) / desired current in amps = proper resistor in ohms. The voltage drop of a DVD burner laser diode is around 2.5 volts. So if you want to power your laser with 4.5 volts, you plug those numbers into the formula:
4.5(battery voltage) - 2.5(Voltage drop of laser diode) / .200 (200ma, good current for a DVD burner laser diode) = 10 (resistor value in ohms). So you would need a 10 ohm resistor in your flashlight. But if you aren't using a driver, at least also put a small capacitor in parallel with the laser diode to eat voltage spikes from the batteries.
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Old 03-29-2008, 06:07 PM   #7
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Default Re: dvd burner laser, what voltage?

Take a look at this thread for building a laser diode driver and this video walkthrough.
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