OK to mix different Vf LED in series?

Discussion in 'The Projects Forum' started by StupidPig, Jul 17, 2009.

  1. StupidPig

    Thread Starter Member

    Jun 5, 2009
    12
    0
    Is it ok to mix LED with different Vf connected in series? For example, can I connect white 3W LED (3.5 Vf, 700ma) and amber 3W LED (2.2 Vf, 700ma) in series and power by one 700ma driver?

    Thanks for any help.
     
  2. millwood

    Guest

    it depends.

    if the leds are driven via a linear driver where the current going through the leds vary with their forward voltage, the current *may* be off spec.

    if the leds are driven via a constant current source, the answer is *generally* yes, assuming that the voltage going through the diodes are sufficient.
     
  3. millwood

    Guest

    the above applies to diodes in serial.

    if you are running the diodes in parallel, the answer is generally "no".
     
  4. StupidPig

    Thread Starter Member

    Jun 5, 2009
    12
    0
    Sounds like it will be ok since I'm planning to use the buckpuck to drive, which provide constant current. Thanks.
     
  5. millwood

    Guest

    buckpuck uses a step-down topology. so replacing an LED of higher Vf with a LED of lower Vf will always work.

    most LED drivers use a step-up topology. there, replacing an LED with another one of lower Vf may not work. but replacing an LED with one of higher Vf will always work, within reason.
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Current is the big thing with LEDs. If you overdrive an LED it shortens the life, but many LEDs can be very different and have similar current specs.

    Have you read this?

    LEDs, 555s, Flashers, and Light Chasers
     
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