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LED Tester

Discussion in 'Electronic Design' started by Myauk, Aug 22, 2008.

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  1. Myauk

    Myauk Guest

    Dear All,

    I am now working on design of a PCBA Tester. The PCBA I am going to
    test has a few LEDs. After assembly process, we will design a test
    station where the LED in PCBA will be checked for open/short/reverse
    The basic concept of the design include pumping in the current into
    LED via USB connector power supply (hope I could use up to 500 mA).The
    idea is to use USB connector from PC as a power supply to pump in the
    into the LEDs. There, I will add a 50 ohm resistor between the cathode
    of the LED and the 5 V USB Gnd. The voltage will be read from the LED
    to determine its condition.
    Practically testing it, if the LED is worngly mounted in reverse
    polarity, at least 50 mA is sinking into the PCBA. I wish to know
    whether this amount would do any harm to the PCBAs.
    Can anybody give me some advice on this?
    please help. I am also looking for alternative ways.

  2. neon


    Oct 21, 2006
    THAT IS GREAT IDEA USE A $1000 PC to tests $0.10 leds. if you get 500ma into a LED you probably have no more led to speak of. I am stupid i use a plain battery and a series diode and a resistor.
  3. Myauk

    Myauk Guest

    Thanks for your kind respond.

    What would you like to mean by grabbing 500 mA is not compilant with
    USB specs?

    I know that it limits the current up to 500 mA. We are using just a
    few mA round about 100 mA maximum. This won't create any problem,
    will it?
  4. Myauk

    Myauk Guest

    Thank you so much for your kind explanation joel and michel.

    I am thinking of testing LEDs installed DUT with automated test

    I will pump current into the LEDs and read out the voltage. If it is
    not shorted, open circuited or reversely installed, it will give
    readings in acceptable range and it will pass the test.

    I think it is a feasible solution for it. What i am worried is that at
    least 16 mA will be sinking into the DUT circuit.

    I hope 16 mA sink current into the PCBA when there is no power
    supplied won't damage the PCBA nor degrade any component in the PCBA
    because of this test.

    Any suggestions?

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