Weird Question About Inverter Transformer:

[RayRay1132]

I am just a beginner when it comes to high frequency high voltage ac so this question may or may not sound stupid. I have a ccfl inverter that takes 12 volts dc and turns it into 900 volts ac at around 25khz, when I plugged a neon indicator bulb into one of 2 outputs it glowed like normal, but I accidently disconnected one of the leads going to the bulb, and to my amazement, it was still glowing, albeit a lot dimmer. How can this light work with only one end attached to a power source? Thanks in advance -Ray.

 

[JimB]

Because of the relatively high frequency, (25kHz), there is sufficient capacitance in the neon lamp and the unconnected wire for a small current to flow through the neon lamp and excite the gas.

JimB

 

[ronsimpson]

Try adding a length of wire to the not connected neon lamp's leg. (turn off the power first!)
Or you could just set a tool on the leg. (turn off the power first! don't get killed)

 

[unclejed613]

it's the stray capacitance of the open electrode with the air around it that provides a path for what amounts to leakage current... when i was young, and working my first summer job in a TV shop, we would use a neon bulb (not wired to anything at all) to verify that the Horizontal Output tube and the flyback transformer were actually working... the working frequency was 15.75khz... later on with solid state TVs, a neon bulb held near the flyback transformer was still useful.

 

[RayRay1132]

Thanks, now I understand.

 

[Reloadron]

You also may want to understand that when ypu power a neon lamp and the gas ionizes it becomes, for all purposes a short. This is why Neon bulbe always have a series resistor. The lamp has a breakdown or ionization voltage at which point the gas breaks down and the lamp glows. Once this happens the voltage across the lamp can be reduced and the bulb will continue to glow, this is maintaining voltage. At 900 volts you are effectively shorting your supply at the neon lamps breakdown voltage. A typical NE2 lamp will have a breakdown voltage of about 60 ~ 90 VDC and the DC current is about 300 uA. You can find the specifications for Neon lamps here.

Ron