Mixing different rated LEDs on the same circuit

Discussion in 'General Electronics Chat' started by Barry M, Mar 19, 2009.

  1. Barry M

    Thread Starter Active Member

    Feb 11, 2009
    I read that mixing different LEDs in series will mean that only one/the same will come on, tried it and no surprises only 1 came on.

    On a breadboard I have 3 UV LEDs in series on one side and 3 white in series on the other, they are powered by a single 9V battery.

    I thought I had 2 series circuits in paralell with this configuration and neither side would affect the other in a majorly negative way, seeing how both should get 9V and the rails carry the power. But when the white are on the UV go a lot dimmer. I could wire them all paralell with resistors but I want to test how long they will last as is, well see if they can go for a good day or so without burning out and how much heat they produce like that.

    Can someone please tell me what I missed.
  2. bertus


    Apr 5, 2008

    Does each string of leds have its own resistor to limit the current ?
    For three white leds in series the 9 volts may be to low.
    A white led has a forward voltage drop between 3.5 and 4 volts.

  3. Barry M

    Thread Starter Active Member

    Feb 11, 2009
    Theres no resistors. When its only white or UV on they are very bright. What I dont get is how the 2 in parallel are not. I thought the only difference would be the battery draining quicker.
  4. beenthere

    Retired Moderator

    Apr 20, 2004