Patent ID: 6211623
Filing Date: 2001-04-03
Classification: H05B

Abstract:
An integrated circuit for driving first and second MOS gated power transistors which are connected in a half bridge arrangement for supplying an oscillating current to power a fluorescent lamp through a lamp resonant circuit, the integrated circuit comprising circuitry for automatically switching between at least the following plurality of modes of operation in accordance with a state diagram in which the mode of operation is determined based upon the status of various inputs to the integrated circuit indicating the integrated circuit supply voltage, driver frequency, lamp fault or lamp exchange condition, DC bus voltage, and integrated circuit temperature, the plurality of modes of operation including:1) an under voltage lockout mode;2) a preheat mode;3) an ignition ramp mode;4) a run mode; and5) a fault mode,wherein the integrated circuit switches sequentially after power on from the under voltage lockout mode to the preheat mode, then to the ignition ramp mode, and then to the run mode under normal operating conditions; andwherein the integrated circuit switches from the preheat mode, the ignition ramp mode, or the run mode to the under voltage lockout mode in the presence of a fault condition selected from the group consisting of insufficient integrated circuit supply voltage, insufficient DC bus voltage, and absence of a lamp; andwherein the integrated circuit switches:from the preheat mode to the fault mode when the temperature of the integrated circuit exceeds an over temperature condition;from the ignition ramp mode to the fault mode when the temperature of the integrated circuit exceeds an over temperature condition, the lamp fails to strike or hard switching of the first and second MOS gated power transistors occurs; andfrom the run mode to the fault mode when the temperature of the integrated circuit exceeds an over temperature condition, the lamp fails to strike or hard switching of the first and second MOS sated power transistors occurs, when the resonance frequency of the lamp resonant circuit is below a preset minimum, or a no load condition is present.