Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

CCFL inverter question?

  1. Sep 11, 2011 #1
    1. When the CCFL tube lights up does it become a short circuit?

    2. Are all CCFL inverters short circuit current limited?


    Thanks for the help!
     
  2. jcsd
  3. Sep 11, 2011 #2
    They aren't a short circuit but the resistance certainly goes down when lit (they're practically an open circuit when dark). How much the resistance drops depends on the geometry of the light, gases used, ambient temperature, and drive voltage and duty cycle. Some CCFL driver circuits that drive small (low power) devices are not necessarily designed for efficiency, but modern circuits that drive higher power CCFL lights can be quite efficient, like the circuit that drives the backlight on a modern LCD computer screen. I doubt there are many that have good short circuit protection since many CCFL lights are unlikely to short. I wouldn't rely on it!
     
  4. Sep 13, 2011 #3
    The ccfl tube typically requires a fairly high voltage, i.e. a thousand volts, to become ionized. Afterwards, it operates at some few hundreds of volts.
    To acheive this operation efficiently, the inverters are designed to have an open circuit voltage sufficient to "fire" the tube. Then, a series impedance, typically a small, high voltage capacitor, limits the operating current.
    Since the capacitor is a reactive load (not a resistor), it doesn't consume much power in serving it's function, and the circuit remains efficient.

    Mike
     
  5. Sep 14, 2011 #4

    berkeman

    User Avatar

    Staff: Mentor

    Hi hobbs,

    What is the context of the question?
     
  6. Sep 15, 2011 #5
    I am wanting to use a ccfl inverter for something other than a ccfl which has a constant resistance of about 50 ohms. I'm not sure if the ccfl inverter will work with such a low impedance load. I know the inverter puts out a higher voltage at first then it drops. I'm just not sure if the inverter will work when it starts out with a low impedance load?
     
    Last edited: Sep 15, 2011
  7. Sep 16, 2011 #6

    berkeman

    User Avatar

    Staff: Mentor

    What is the load? What voltage do you want to put across the load? Why do you want to use a CCFL inverter?
     
  8. Sep 16, 2011 #7
    The load is a resistive load, no reactance, 50 ohms. I want a high voltage across it of at least 500v.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: CCFL inverter question?
  1. Inverter Question (Replies: 2)

Loading...