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Thread: Data sheets

  1. #1
    Join Date
    Nov 2021
    Posts
    4

    Default Data sheets

    Complete newbie, but I was given a few Lasers with drivers. Seems fine but I have no idea what to do next. On one it says it’s an 808nm 5V 500mW.
    So connecting this to a DC power supply I know it’s 5V input but how do I discover the Amps in ?
    Someone told me “Oh there are Data sheets available everywhere” but I can’t find them.
    If I don’t know the manufacturers name or the shop where it was purchased, is there a formula to work out the Amps in please ?
    Thanks guys.

  2. #2
    Join Date
    Nov 2007
    Location
    Sydney, Australia
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    602

    Default

    Hey Brett

    Laser diodes, just like LEDs, are constant current devices, so you really need to know the current rating to avoid destroying them.

    The other thing to watch is that that diode is an 808nm laser and therefore not visible, so watch your eyes.
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  3. #3
    Join Date
    Jan 2006
    Location
    Charleston, SC
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    2,147,489,292

    Default

    You said that you received a few lasers "with drivers". If they have a driver, then Loopee's warning above regarding constant-current is not applicable; that's what the driver is for.

    All you need to do is ensure that your 5 volt DC power supply can provide enough current to the driver. The driver will reduce the 5 volts on the input down to around 2 volts to power the diode, and it should maintain a constant current through the diode.

    In practice, an 808 nm IR laser diode running at 500 mw is unlikely to need more than 1 amp of current, so as long as your 5 volt DC power supply can deliver at least 1 amp, you should be just fine. (A brief Google search suggests that the maximum current for an 808 nm 500 mw diode is in fact around 700 mA.)

    Unfortunately, there's no easy way to calculate the maximum current rating for a given laser diode. You can make some general assumptions based on the type of diode and the power rating, but you need the manufacturer's datasheet to be exact. Fortunately, the maximum current rating is only needed when you are setting up the driver. If the laser already has a calibrated driver attached, then you just need to be sure your power supply can source enough current. If it can't, then the output voltage will sag, and the laser may not come on at full intensity, or in extreme cases it may not lase at all. But using a power supply that is too small should not harm the diode or the driver.

    It's important to note that using a much larger power supply is also not an issue. ("Larger" in terms of maximum output current; obviously you still need to stick with a 5 volt supply.) This is because it's the driver that controls the current flow through the diode, not the power supply. Thus, a 5 volt DC power supply rated at 10 amps will work just as well as one rated for 1 amp in this application

    In fact, you could easily make the argument that using a larger power supply is desirable, since it will be less likely to overheat and fail if it is not running near it's maximum current output all of the time. Even so, a 10 amp supply is overkill. But something in the 2-5 amp range would be ideal for the diode you mentioned.

    Having said all that, once you get the laser working I have a feeling you're going to be very disappointed. 808 nm is near infrared and well below the threshold for human vision. This means you won't be able to see the beam. Admittedly, most people can perceive 808 nm as a very dull red color when looking right at the emitter, but obviously for safety reasons this is a terrible thing to do. 500 mw is more than enough energy to cause permanent eye injury! What's worse is that because the retina is so insensitive to IR, you won't have any blink, pain, or aversion responses. So you could just stare into the beam as your vision fades to black, forever. (shudder!) Hell of a way to go blind...

    Despite the eye injury hazard, 500 mw of IR is not enough to be able to easily burn things, unless you can focus the beam down to a very tiny spot. So there's not much you can do with this diode, unless you're planning to experiment with DPSS laser designs. (808 nm IR is often used to pump Vanadate or YAG; the most common lasing wavelength for both of those materials is 1064 nm, which can be frequency-doubled with a KTP crystal to get 532 nm green.)

    Adam

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