Significant efficiency reduction when powering LEDs?

Discussion in 'General Electronics Chat' started by Obanion, Mar 17, 2010.

  1. Obanion

    Thread Starter New Member

    Nov 26, 2009
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    0
    I ran into a very interesting scenario today. After doing some tests with a DC-DC converter using a constant current DC electronic load, my efficiency was able to hit 99%. When I connected the converter to a series of high power LEDs using the same current, my efficiency dropped to 80%. The input voltage remained constant for the entire operation.

    Any ideas why this would have happened? I'm a bit baffled.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Show us a rough draft of your layouts. Right now all we can do is guess.
     
  3. Obanion

    Thread Starter New Member

    Nov 26, 2009
    24
    0
    Essentially, my DC-DC convert is one I build from scratch and pretty much looks like the one here:

    [​IMG]

    It's okay, I don't want to trouble anyone by going into too much. It's nothing critical or very important, however I was just kind of curious if there was an immediate reason or consequence of powering LEDs.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Please post the circuit that limits the current for the LEDs.

    Maybe the Mosfet has poor conductance.
    Maybe the inductor's core saturates when the curcuit is overloaded by the LEDs.
     
  5. Obanion

    Thread Starter New Member

    Nov 26, 2009
    24
    0
    Here is my schematic, and below is a photo of the actual circuit. I am controlling the MOSFET via PWM from an FPGA.

    Schematic:

    [​IMG]



    [​IMG]

    I am using the following components:

    MOSFET: IPP50CN10NG
    470uH Inductors: 542-2320-V-RC
    Schottky Diode: STPS40M100CT
    Ceramic caps: CKG57NX5R1H226M

    Thanks
     
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