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CCFL inverters

Discussion in 'Electronic Design' started by [email protected], Dec 20, 2006.

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  1. Guest

    Hi,

    I am quite new in this subject but I have a question about a CCFL
    inverter which I've tested. The inverter's current was measured to be
    14 to 20 mA and the rms voltage was 520V. From most app. notes on CCFL
    especially the Maxim note, the current stated usually in the region of
    3mA to 8mA. What are the advantages and disadvantages of running the
    inverter at 14 to 20 mA?

    Cheers
    Geoff
     
  2. On 19 Dec 2006 21:41:12 -0800,
    How did you measure the RMS current and voltage? What does the user's
    manual of the thing that you used to measure current and voltage have
    to say about frequencies and waveforms?

    robert
     
  3. You need to look at the bulb specifications, not (just) the inverter.

    If run over-current, the bulb lifetime will be much shorter.
     
  4. PeteS

    PeteS Guest

    Most CCFL backlights operate at about 5-6mA, but there could well be
    some that operate much higher.

    Did you look at the waveform with a scope? Most CCFL devices require a
    (fairly good) sinusoid, but your measurement may have distorted the
    waveform (and therefore changed the crest factor so you got an invalid
    measurement). [I know this was already mentioned :)]

    Make sure it's already started before looking with even a HV probe - the
    startup voltages required for CCFL backlights can be as much as 3x the
    run voltage.

    Cheers

    PeteS
     
  5. Guest

    Hi,

    The sine wave looks fine when measured by the voltage and current
    probe. I have carried out the measurement using a Tektronix and Agilent
    scope and both gave similar results. I believe the tube brightness was
    measured to be 25000 nits but I can verify it when I start work next
    year. The tubes used were straight and used in a 12 inch LCD panel. I
    have another inverter which is used to drive another 12 inch panel but
    when I increase the current by adjusting the PWM, the sine wave becomes
    jagged instead of curved. Could this be caused by the inductance from
    the transformer? Can someone direct me to link that describes about
    this sine wave issue?

    Cheers
    Geoff


     
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