Power supply apparatus for discharge lamp and control method for the same

Abstract

An apparatus supplies power to at least one discharge lamp. The apparatus includes a buck converter for regulating power supplied to at least one discharge lamp having a switching element driven by PWM pulses, and a control unit for supplying PWM pulses to the buck converter. The control unit includes a function for controlling an output power of the buck converter so as to be constant using PWM pulses of a first frequency; and a function for controlling an output voltage of the buck converter so as to be maximum using PWM pulses of a second frequency that is lower than the first frequency. The buck converter is capable of operating in discontinuous mode based on the PWM pulses of the second frequency.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a circuit diagram showing the configuration an apparatus;

FIG. 2 is a graph showing a transition from glow discharge to arc discharge for a discharge lamp;

FIG. 3 is a flowchart showing the operation of an apparatus at a start of illumination; and

FIG. 4 includes graphs showing characteristics of the output voltage and the output current at the start of illumination.

Claims

1. A method of controlling an apparatus, the apparatus including a buck converter for regulating power supplied to at least one discharge lamp, the buck converter including a switching element driven by PWM pulses, the method comprising:regulating an output power of the buck converter so as to be constant using PWM pulses of a first frequency; andregulating, prior to the regulating the output power, an output voltage of the buck converter so as to be a target voltage using PWM pulses of a second frequency that is lower than the first frequency and operating the buck converter in discontinuous mode.

2. The method according to claim 1, further comprising: regulating, in between the regulating the output voltage and the regulating the output power, using PWM pulses of the second frequency, the output power of the buck converter so as to be constant.

3. A method of controlling an apparatus, the apparatus including a buck converter for regulating power supplied to at least one discharge lamp, the buck converter including a switching element driven by PWM pulses, the method comprising:regulating an output power of the buck converter so as to be constant using PWM pulses of a first frequency; andregulating, prior to the regulating the output power, an output voltage of the buck convert so as to be maximum using PWM pulses of a second frequency that is lower than the first frequency and operating the buck converter in discontinuous mode.

4. The method according to claim 3, further comprising: regulating, in between the regulating the output voltage and the regulating the output power, using PWM pulses of the second frequency, the output power of the buck converter so as to be constant.

5. An apparatus comprising: a buck converter for regulating power supplied to at least one discharge lamp, the buck converter including a switching element driven by PWM pulses; anda control unit for supplying PWM pulses to the buck converter, the control unit including:a function for controlling an output power of the buck converter so as to be constant using PWM pulses of a first frequency; anda function for controlling an output voltage of the buck converter so as to be maximum using PWM pulses of a second frequency that is lower than the first frequency, the buck converter being capable of operating in discontinuous mode based on the PWM pulses of the second frequency.

6. The apparatus according to claim 5, wherein the control unit further including: a function for controlling, using the PWM pulses of the second frequency, the output power of the buck converter so as to be constant.

7. The apparatus according to claim 5 being a power supply unit for supplying power to the at least one discharge lamp.

8. The apparatus according to claim 5 being a lighting system and further including the at least one discharge lamp.

9. The apparatus according to claim 5 being a projector and further including the at least one discharge lamp.

10. A program product for controlling an apparatus, the apparatus including: a buck converter with a switching element driven by PWM pulses for regulating power supplied to at least one discharge lamp; and a control unit for supplying PWM pulses to the buck converter, the program product comprising:regulating, by the control unit, an output power of the buck converter so as to be constant using PWM pulses of a first frequency; andregulating, prior to the regulating the output power, by the control unit, an output voltage of the buck converter so as to be maximum using PWM pulses of a second frequency that is lower than the first frequency and operating the buck converter in discontinuous mode.