Patent ID: 7034471
Filing Date: 2006-04-25
Classification: H05B

Abstract:
1. A cold cathode tube lighting apparatus comprising: a rectangular wave voltage generating circuit to generate a positive-negative-symmetrical rectangular wave voltage from a direct current input voltage; a series resonance circuit having a resonance inductance connected in series with a parallel connection of a first resonance capacitor and a cold cathode tube, to convert the rectangular wave voltage into a sinusoidal wave voltage, a constant of the series resonance circuit being set to make a maximum output voltage for a predetermined cold cathode tube current value exceed a tube voltage of the cold cathode tube at the start of lighting the cold cathode tube and in an operating load range of the cold cathode tube of negative resistance characteristic; a cold cathode tube voltage sensing circuit to detect a tube voltage of the cold cathode tube and output a voltage detected signal; a cold cathode tube current sensing circuit to detect a tube current of the cold cathode tube and output a current detected signal; and a control circuit controlling the duty of the rectangular wave voltage, the control circuit including: the drive signal being outputted to the rectangular wave voltage generating circuit while the cold cathode tube is in a lit state so that a cold cathode tube current has a predetermined current according to the current detected signal from the cold cathode tube current sensing circuit, the drive signal being outputted to the rectangular wave voltage generating circuit until the cold cathode tube is lit at the time of black start of the cold cathode tube so that a tube voltage of the cold cathode tube is set to be greater than a lighting start voltage and smaller than an open protective voltage according to the voltage detected signal from the cold cathode tube voltage sensing circuit, and the drive signal being output to the rectangular wave voltage generating circuit when the cold cathode tube is detached so that a tube voltage of the cold cathode tube is set to be greater than the lighting start voltage and lower than the open protective voltage according to the voltage detected signal from the cold cathode tube voltage sensing circuit, and the drive signal to the rectangular wave voltage generating circuit being stopped after the delay period.