Patent ID: 6369526
Filing Date: 2002-04-09
Classification: H05B

Abstract:
A method for operating electronic ballasts for High Intensity Discharge (HID) lamps, said electronic ballasts having a driver, two power switches connected in a half-bridge arrangement, an LC series circuit, a driver controller for controlling the operation of the driver, a current sensor in the lamp circuit, and a power sensor in the power switch circuit, said method comprising:(a) generating pulses of frequency f1 for a duration of time t1 being equal to n/f1, where n is a positive number, and f1 equals the resonance frequency of the ballast's LC series circuit; (b) monitoring the existence of current in the lamp circuit after the duration of time t1 has elapsed, and in the event that there is no current in the lamp circuit, proceeding to step (h); (c) monitoring the current in the lamp circuit, and proceeding to step (h) upon determining that the current in the lamp circuit has ceased to flow; (d) continuing the generation of said pulses of frequency f1 for a predetermined duration of time t2 counting from the start of the generation of said pulses according to step (a); (e) switching the frequency f1 of said pulses to an operating frequency f2, at which a set power for the lamp is reached; (f) monitoring the power on the lamp and stabilizing this power at the level of the power set for the lamp, by gradually modifying the frequency f2, and proceeding to step (h) in the event that the power in the lamp circuit exceeds the power set for the lamp by a given margin; (g) monitoring the current in, and power of, the lamp circuit according to steps (c) and (f); (h) inhibiting the generation of said pulses for a predetermined duration of time approximately equal to t2/k, where k is a positive number; (i) proceeding to step (a) until said predetermined duration of time t2, counting from the start of the generation of pulses according to step (a), has elapsed; and (j) inhibiting the generation of said pulses until the power to the ballast is first switched off and then on.