LED MATCHER

Discussion in 'Homebrew and Kit Projects' started by K7ELP, Jan 15, 2019.

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  1. K7ELP

    K7ELP Premium Subscriber QRZ Page

    For a number of years I have been connecting LED's in parallel, with great results. About six months ago I decided to improve this process by building a LED matcher. This device allows the user to select the voltage or current desired. Then monitor the other reading. For example if the Vf is selected then the current can be monitored for each LED plugged into the matcher box. If the If is selected then the Vf can be monitored for each LED plugged into the matcher box.

    If there are individuals interested in this device I will be glad to post pictures and a schematic.
    Ned
     
  2. K6BSU

    K6BSU Ham Member QRZ Page

    Hard to imagine needing one of these. The LEDs nowadays are very efficient, making good output with just a couple mA, whereas the older ones needed 10-15 mA.

    It takes just a minute to test an LED with a power supply and resistor decade box. Select the series resistor based on how bright you want.
     
  3. K7ELP

    K7ELP Premium Subscriber QRZ Page

    I think you misunderstand the need for the device. Have you ever connected many LED's directly in parallel ?
     
  4. KF5FEI

    KF5FEI Ham Member QRZ Page

    Ever see some cheap Chinese multi-LED device (crappy LED tail light assemblies) that has LEDs that wink on and off -- this is because they did not match the LEDs and those with a higher turn-on voltage go on and off.
     
  5. VK6YSF

    VK6YSF Ham Member QRZ Page

    Please post circuit and photos.

    Cheers
     
  6. K7ELP

    K7ELP Premium Subscriber QRZ Page

    Sorry for the delay in posting the pictures and the schematic, I needed to take some new pictures.
    CURRENT.jpg
    FORWARD VOLTAGE.jpg LED MATCHER B.jpg
    In the schematic the LM317LZ is a current limiter, and the adjustment current is adjustable from about 1mA to about 10mA. SW1 is a normally closed pushbutton switch. It is a safety feature to ensure that the Vf is not present when the test LED is put in the socket (white in photo's). Once a LED is inserted SW1 is depressed to measure Vf and If. The forward voltage is a direct reading across the LED. The forward current is the voltage measurement across R2(100 ohm) with the calibration with the LM358N. The extra tip jacks for Vf and If were added to check the readings of the installed DVM
     

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