Diode Vf testing

Discussion in 'General Electronics Chat' started by RodneyB, Sep 3, 2013.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    I have bought some blue LED's from our local supplier. They do not have a datasheet and I need to know what the Vf. Imax is.

    Is there a way of testing this.

    I need to put 20 Blue LED's in an array. The first one I built was very bright, this one not bright at all. I did ask for super bright and used the same specifications but there is a distinct difference.

    Many thanks

  2. #12


    Nov 30, 2010
    Make a circuit that can deliver a constant current, run that current through the LED, and measure the voltage. That will find a voltage. If you don't know the maximum current, that is a problem I can't fix.
    Last edited: Sep 3, 2013
  3. WBahn


    Mar 31, 2012
    One thing that might get you a wag at the max current would be to look at datasheets for other LEDs and see what they give as their nominal forward voltage at some reference current. Then increase the current in yours until you get that same voltage (and try to keep the LED at the same temperature that is in the data sheet) and see what the current is. That should be approximately the same fraction of the max current ad the reference current was for the LEDs in the spec sheets. I don't know if this method is valid or not or, even if it is, if it is too twitchy in the realy world to yield useful numbers.
  4. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    Thank you very much. For all the information. I will report back my results based on the above advice.