Patent ID: 6541925
Filing Date: 2003-04-01
Classification: H02M,H05B,Y02B

Abstract:
A method of operation of a resonant converter which is adapted for use as a ballast circuit for controlling operation of a gas discharge lamp connected thereto, the converter being in a form of a full or half-bridge circuit having at least first and second power switches which are respectively actuated by first and second cyclic gating signals of substantially the same frequency, the gating signal frequency being above a resonant frequency of said converter, the first and second gating signals being substantially square waves having complementary duty ratios; said method comprising:effecting a change in operating state of said converter by increasing the duty ratio of the first gating signal by a selected proportion and decreasing the duty ratio of the second gating signal by the same selected proportion; and the change in the duty ratio of each of said gating signals being ramped so as to occur incrementally over a plurality of cycles thereof, the incremental change per cycle being the same for both gating signals; the ramped change in duty ratios producing said change in operating state of said converter with substantial suppression of transient high voltages and currents which would occur with a step-wise change in said duty ratios.