Testing Diode with Multimeter

Discussion in 'The Projects Forum' started by skqureshi, May 12, 2010.

  1. skqureshi

    Thread Starter New Member

    May 12, 2010
    I wanted to check a diode using a digital multimeter. I had the meter set on resistance mode. The problem is for different settings the value of resistance offered is different. Why does it happen so.
    The next thing i did was to test the applied voltage by the multimeter for different ranges of resistance testing. I found that for different ranges the applied voltage is different.Why is it so.
  2. Markd77

    Senior Member

    Sep 7, 2009
    If your meter doesn't have a diode check, try putting the led in series with a 1k resistor and a 5V supply and measure the voltage across the diode. This should tell you the Vf of the diode with it connected one way and you should get 5V the other way if it is working correctly.
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  3. SgtWookie


    Jul 17, 2007
    Diodes have a non-linear resistance. Actually, it's called "conductance".

    Many DMM's have a "diode test" function. The diode test function supplies a constant current from the test probes, and the DMM measures the voltage drop between the test probes. If there is no connection between the probes (or if the voltage drop is too high) you will get an out-of-range indication on the DMM.

    The diode test function is very useful for checking not only diodes, but transistors as well.
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  4. yasir_66

    Active Member

    Jun 25, 2009
    For more precise result set your multimeter to diode function.It will beep then check diode.Only on one way it will conduct & show resistance on other way it will show infinite resistance such that diode is called uni directional.
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  5. retched

    AAC Fanatic!

    Dec 5, 2009
    Not on my meter. And not on countless other meters that have no sound or no diode check.

    OP, if the diode is in the circuit, you must pull one end to test it. The traces on the PCB can cause false positives. Also, make sure there is no power on the board when testing.
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  6. hgmjr


    Jan 28, 2005
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