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Thread: is my 300 mw blue labby DOA?

  1. #61
    Join Date
    May 2007
    Location
    Sydney, Australia
    Posts
    81

    Default

    Ok , so the sense resistor is 0.05 ohms , and with 300mv across it, means that there's 6 amps of current flowing through the pump diode( 50mv per amp). Still less than the 8 amps that the 5v supply is feeding into the circuit.

    For an idea of how this part of the circuit works, look at:
    http://www.repairfaq.org/sam/glpdrv1.gif
    Much smaller scale, but the output stage compares. R9 & R10 are the current sense resistors, one end attached to the neg rail, the anode (+) of the pump diode attached to "ground", the opamp (u1A) turns on the drive transistor(Q1) to allow current to flow through the diode. The opamp U1B scales the voltage read across the sense resistors, opamp U1A then compares this value with a reference voltage (pin 3) in order to control the amount of "on-ness" of the transistor. Your driver is a lot more complex, but that's the principal of it.

    I think that now you've worked out that the power supply is OK, and you're feeding it a good modulation signal, If it's still not working, then it's time to talk to the manufacturer , because I'm running out of ideas.
    B.

  2. #62
    Join Date
    Aug 2008
    Location
    Michigan-USA
    Posts
    132

    Default

    Fuzcub:

    Yes, I see how that is 2 power resistors in parallel. No wonder it looks like a short. I can't measure that low. The resistance in the probe wires is higher than .05 ohms.

    Thank you for all your help. I have learned about rail supplies and primary and secondary grounds.

    Also I want to thank everyone else on the forum that has contributed to trying to figure out how this thing should be hooked up and what is wrong.

    I am going to move on to other projects like some more DIY handhelds, finishing my 3 mirror spiro, and more work on my RGB projector.

    I won't be able to make Orlando in a few weeks, but you can count on me in August of 2009.

    John

  3. #63
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,805

    Smile

    Quote Originally Posted by Docjohn View Post
    I won't be able to make Orlando in a few weeks, but you can count on me in August of 2009.
    John
    I heard that! It's a date. I'm going to hold you to it! (You'll have a blast - trust me.)

    Adam

  4. #64
    Join Date
    Jul 2005
    Location
    Flying over a town near you
    Posts
    1,404

    Default

    So whats with the laser now? Is it for sale or???
    You are the only one that can make your dreams come true....and the only one that can stop them...A.M. Dietrich

  5. #65
    Join Date
    Aug 2008
    Location
    Michigan-USA
    Posts
    132

    Smile

    Kyle, I sent you a PM.

    Buffo, I will be there. Thanks

    John

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