Patent ID: 7692391
Filing Date: 2010-04-06
Classification: H05B

Abstract:
1. A discharge lamp ballast, comprising: a voltage step down converter connected to a DC power source with a positive terminal and a negative terminal; a converter control means that controls the voltage step down converter; a first capacitor that applies DC voltage across a discharge lamp through DC power from the voltage step down converter, said lamp having a first end and a second end; and a starting means that applies starting voltage across the discharge lamp in case of a starting mode, wherein said voltage step down converter is constructed with: a diode having a cathode and an anode, said anode being connected to the negative terminal of the DC power source and a negative voltage side of the first capacitor; a first switching element connected between the cathode of the diode and the positive terminal of the DC power source; and a first inductor connected between the cathode of the diode and a positive voltage side of the first capacitor, wherein said converter control means turns the first switching element on and off at a high frequency so as to supply DC power for steady operating to the discharge lamp via the first capacitor in case of a steady operating mode after the starting mode, wherein said starting means comprises: a second inductor, one end of the second inductor being connected to the first end of the discharge lamp, the other end of the second inductor being directly connected to the positive voltage side of the first capacitor; a second capacitor that is connected in parallel with the discharge lamp and forms a resonance circuit together with the second inductor; a second switching element, one end of the second switching element being directly connected to the positive terminal of the DC power source, the other end of the second switching element being connected to the second end of the discharge lamp; a third switching element connected between the second end of the discharge lamp and the negative voltage side of the first capacitor; and a starting control means that controls the second switching element and the third switching element, and wherein said starting control means is configured: to alternately turn the second switching element and the third switching element on and off so as to contribute resonance voltage of the resonance circuit for starting of the discharge lamp in case of the starting mode; and to operate so as to include an on period of the third switching element while keeping the second switching element turned off in case of the steady operating mode.