LED Tester

Discussion in 'General Electronics Chat' started by RodneyB, Feb 2, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    With all the new LED's available with forward voltages of 3 volts or more the diode tester on a multi meter is no longer suitable for testing these components.

    Can someone suggest a suitable circuit for testing these or a method.

    Many thanks Rodney
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    A 9V battery and a 1kΩ series resistor or
    two 1.5V batteries and a 220Ω series resistor.
     
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  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
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    A lab power supply with adjustable voltage and current, digitally metered outputs of same, RS232 input for computer control of V & I with data logging capability.
     
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  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
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    Best to use the higher V, 9 V or 12 V, with 470 to 1 k ohms in series with LED; add 2 red LED in series across test terminals. With no LED in test or a reversed LED, red LED's will be on. With correct polarity , test LED will light, reds off. With reversed test LED V will be limited to about 5 V which is usually safe for LED.
     
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  5. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    The simplest circuit for a functional test would be as Mr. Chips suggested except I would use three 1.5V batteries in series with a 220Ω instead of two, to insure there is sufficient voltage for the higher voltage LEDs.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    As the ranges of VF's and current ratings between LEDs are vastly different than they were a few years ago stating a supply voltage level and resistance is mostly pointless here..
    3 x 1.5V or 1 x 9V or 1 x 12V batteries ain't gonna do squat if the LED's Vf is greater than that.
    Ideally the "tester" would have a voltage exceeding the Vf of the LED (could be 9V..could be 12V... could be 30V,etc...) and sufficient current to allow a visual level of illumination.
     
  7. #12

    Expert

    Nov 30, 2010
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    I believe we did this a few days ago. Same TS, same question.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Déjà vu all over again?
     
  9. bertus

    Administrator

    Apr 5, 2008
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  10. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    783
    Some people favour the "joule thief" blocking oscillator/inverter - if you don't like winding coils, you can cross-connect the parallel inductors in a common mode choke from a small SMPSU such as in a scrap set top box.

    Another favourite is the well known astable oscillator with a 470uH choke as one of the collector loads.

    Both options run on a single 1.5V cell and rely entirely on inductor back emf to make the LED Vf.
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Get a different multimeter. My free Harbor Freight meters work fine for LED testing. They glow dimly - probably 1mA or so.
     
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