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Laser driver to diode resistance.

Discussion in 'LEDs and Optoelectronics' started by EvilsConscience, Apr 2, 2016.

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  1. EvilsConscience

    EvilsConscience

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    Apr 2, 2016
    Hey! This is my first personal project where I'm adapting a design to my own ideas. I'm taking an infrared laser diode and making a handheld laser engraver with it. Since this is my first build, I want to double check with more experienced people that the resistance I calculated between the driver and the diode is correct.

    The driver info page said it had an output of 3.0-4.5V. I'm going to provide 3V.
    The page also said the constant current was 8mha, I assume a typo meaning 8mAh, so .8 amps, bring the R to 3.75Ω.

    The diode needs only 2.2V and 650mA.I calculated that I need an R of 3.38mA, but I don't see how the R O the diode could be lower than the output from the driver.

    I don't want to waste $50 of equipment. Could someone correct me where I went wrong?
     
  2. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Cc of 8ma is not 0.8amps :eek:

    2.2v 600ma sounds like what it is rated, 3-2.2/ 0.6

    0.6ohm resistor to drive it at max current using (at a push) a 1/2w resistor but i'd use a 1w

    If you do, be careful 1 splash of IR could do serious damage to eyes
     
    EvilsConscience likes this.
  3. cjdelphi

    cjdelphi

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    Oct 26, 2011
    But it sounds like you already have a driver?
     
  4. EvilsConscience

    EvilsConscience

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    Apr 2, 2016
    I have a driver that can reach my diode's frequency, but it's a 3V driver. Would that not destroy my 2.2 Diode?
     
  5. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Diodes work on current, it should not providing max current (650ma?) Is not reached, when the driver limits the current the voltage will drop to around the foward voltage it's supposed be, if current rises then the voltage across the diode will rise as well

    Take a normal LED and stick a 300ohm - 1k in series to the LED, supply 3 - 5v you'll see the voltage stay pretty constant unless you push it past it's current capability
     
  6. cjdelphi

    cjdelphi

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    Oct 26, 2011
    Screenshot_2016-04-02-16-19-14.png

    Notice how the voltage stays pretty constant? This is a poor mans way of a voltage regulator using an LED, the voltage is passed to a transistor and then regulates a component which requires that level of voltage
     
    EvilsConscience likes this.
  7. EvilsConscience

    EvilsConscience

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    Apr 2, 2016
    I see. So, as long as I have the driver set to the proper frequency of my IR laser diode, I won't need a resistor because the driver is already limiting the current.
     
  8. cjdelphi

    cjdelphi

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    Oct 26, 2011
    The ir diode could not care about frequency really only current, for example if it was on for 1ms off for 1ms in theory can drive it harder than it's rated current, pwm is merely a way of driving the diode

    To test it you could stick resistor on the end of the driver, but as long as the driver does not supply more current than the diode can handle you should be safe...

    But please hold out if you must, as others will have more experience than myself with lasers, after almost burning my retina out i decided to stay away from them lol
     
    EvilsConscience likes this.
  9. EvilsConscience

    EvilsConscience

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    Apr 2, 2016
    Thank you for your help! I'll hold out for a bit because I still have to buy goggles, but you've helped.
     
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