CCFL inverter question?

[hobbs125]

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!

[fleem]

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!

[Mike_In_Plano]

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

[berkeman]

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!

Hi hobbs,

What is the context of the question?

[hobbs125]

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?

[berkeman]

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?

What is the load? What voltage do you want to put across the load? Why do you want to use a CCFL inverter?

[hobbs125]

The load is a resistive load, no reactance, 50 ohms. I want a high voltage across it of at least 500v.