Patent ID: 6954038

Claim:
An electronic ballast for a discharge lamp comprising: a DC voltage regulator providing a DC voltage that varies with a voltage command being fed to said DC voltage regulator, an inverter converting said DC voltage into a high frequency AC power which is applied through a resonance circuit to said discharge lamp, said high frequency AC power being regulated to vary with a frequency command which designates a frequency at which said inverter is driven to oscillate; a dimming processor including a dimming unit that provides a dimming signal designating a varying dimming level for varying a light output of said discharge lamp in accordance with an external dimmer demand, wherein said dimming processor includes a command processing unit which, in response to the dimming signal, generates said voltage command and said frequency command, said frequency command designating a first frequency and a second frequency which is a function of said first frequency and gives a resulting lamp voltage higher than that obtained at said first frequency, said command processing unit driving said inverter at said first and second frequencies alternately with respect to time to thereby regulate said high frequency AC power of said inverter, said command processing unit including a memory for storing a first table that determines a predetermined relation between the dimming signal and voltage command as well as said frequency command, said command processing unit deriving from said memory said voltage command as well as said frequency command that matches with the dimming signal, and operating said DC voltage regulator and said inverter in accordance with said voltage command and said frequency command, respectively.