Patent ID: 6127786
Filing Date: 2000-10-03
Classification: H05B,Y10S

Abstract:
A ballast circuit for energizing a lamp, comprising:a resonant inverter including a resonant inductive element coupled to a first switching element for providing an AC signal to the lamp;a first control circuit coupled to the first switching element for controlling a conduction state of the first switching element, the first control circuit including an inductive bias element that is inductively coupled to the resonant inductive element for alternately biasing the first switching element to conductive and non-conductive states;a second switching element coupled to the first switching element, the second switching element having a first state which causes the first switching element to transition to a non-conductive state and second state which allows the first switching element to transition to a conductive state, anda third switching element coupled to the second switching element for controlling a duty cycle of the second switching element; andan end of life circuit coupled to the bias element for limiting a voltage level applied to the lamp when it fails to light, the end of life circuit including a first threshold circuit coupled to the third switching element.