Patent ID: 7368878

Claim:
A ballast circuit, comprising: a resonant circuit, formed by a series connection of an inductor and a capacitor to operate a lamp; a first switch, coupled to said resonant circuit for supplying a first voltage to said resonant circuit, wherein said first switch is controlled by a first switching signal; a second switch, coupled to said resonant circuit for supplying a second voltage to said resonant circuit, wherein said second switch is controlled by a second switching signal; a first resistor, connected in series with said first switch for generating a first control signal in response to a switching current of said first switch; a second resistor, connected in series with said second switch for generating a second control signal in response to a switching current of said second switch; a first control circuit, for generating said first switching signal to control said first switch in response to said first control signal; and a second control circuit, for generating said second switching signal to control said second switch in response to said second control signal.