Patent ID: 6420838
Filing Date: 2002-07-16
Classification: H05B,Y02B

Abstract:
A gas discharge lamp ballast with protection against significant rectification of lamp voltage, comprising:a) a resonant load circuit for at least one lamp, including a DC blocking capacitor connected between a reference node and the at least one lamp; b) a switching arrangement including first and second switches serially connected between a rail node at a DC potential and the reference node, for supplying AC current to the load via a midpoint node between the first and second switches; c) an integrated circuit including: i) a driver for the switching arrangement; ii) a shut-down pin associated with an internal shut-down latch for shutting down the driver in response to a shut-down signal that exceeds a threshold level; and d) a protection circuit for comparing a first voltage representing an average voltage on the midpoint node with a second voltage representing the voltage of the DC blocking capacitor, and for sending a shut-down signal to the shut-down pin when one of the first and second voltages exceeds the other by respective predetermined amounts.