Discharge lamp lighting device and projector

#1. Technical Field

#The present invention relates to a high pressure discharge lamp lighting device and a projector including the same, and more specifically, to a technique for preventing flicker.

#2. Related Art

#The invention will be described with reference to the accompanying drawings, wherein like numbers refer like elements.

#FIG. 1 is a block diagram illustrating the structure of a high pressure discharge lamp lighting device according to a first embodiment of the invention.

#FIGS. 2A-F are timing charts illustrating signal waveforms for generating a lamp current shown in FIG. 1.

#FIG. 1 is a block diagram illustrating the structure of a high pressure discharge lamp lighting device according to a first embodiment of the invention. The high pressure discharge lamp lighting device shown in FIG. 1 includes a down chopper 11, an inverter 12, an igniter 13, a DC/DC converter 14, and a control circuit 15. A lamp 20 is connected to output terminals of the igniter 13. The down chopper 11 corresponds to a DC power supply circuit according to the embodiment of the invention and adjusts an input DC voltage to supply a predetermined constant power to the lamp 20. In this embodiment, the down chopper 11 performs a chopper process on an input voltage to drop the input voltage and performs current control to supply a predetermined constant power to the lamp 20. A current output from the down chopper 11 is input to the inverter 12. Resistors R1 and R2 are connected in parallel to output terminals of the down chopper 11, and the potential of a node between the resistors R1 and R2 is supplied to the control circuit 15 as an output voltage of the down chopper 11. A resistor R3 is connected in series to a negative potential side of the down chopper 11. A current flowing through the resistor R3 is detected as a lamp current (driving current) and is supplied to the control circuit 15.

#The inverter 12 is composed of, for example, four switching elements connected to one another in a full bridge manner. The inverter 12 alternately switches the four switching elements to convert an input DC voltage to an AC voltage, and the converted AC voltage is output to the igniter 13. The igniter 13 includes, for example, an igniter transformer and a circuit for driving the igniter transformer, and generates a high voltage when turning on the lamp 20 and applies the high voltage to the lamp 20. The DC/DC converter 14 generates a driving voltage for the control circuit 15. The DC/DC converter 14 drops an input voltage and supplies the dropped voltage to the control circuit 15. The control circuit 15 is composed of, for example, a microprocessor, and controls the down chopper 11, the inverter 12, and the igniter 13. The control circuit 15 is supplied with an output voltage and current from the down chopper 11 and controls an output current of the down chopper 11 such that constant power is supplied to the lamp 20. In addition, the control circuit 15 appropriately controls an output frequency of the inverter 12 and controls the igniter 13 to generate a high voltage when turning on the lamp 20. An external control IF 15a for receiving control signals from the outside and a variable resistor VR are connected to the control circuit 15. The variable resistor VR corresponds to a frequency regulator used in the invention, and the variable resistor VR is adjusted to regulate the frequency of current pulses (which will be described later) superposed on the lamp current. The lamp 20 is, for example, a reflective light source device. In the lamp 20, a light-emitting tube 21 is fixed to the center of a reflecting mirror 22 with a heat-resistant cement interposed therebetween.

#Next, the operation of the high pressure discharge lamp lighting device shown in FIG. 1 will be described below. The down chopper 11 performs a chopper process on an input DC voltage to drop the input DC voltage and outputs a current corresponding to the dropped DC voltage to the inverter 12. The inverter 12 converts the input DC current into an AC current having a predetermined frequency and outputs the AC current to the igniter 13. The igniter 13 generates a high voltage when the lamp 20 starts to be turned on and supplies the high voltage to the lamp 20. When the lamp 20 is turned on, the output voltage of the inverter 12 is applied to the lamp 20, which causes the lamp to be maintained in the on state. In this case, the control circuit 15 is supplied with the output voltage and output current of the down chopper 11 and controls the down chopper 11 such that constant power is supplied to the lamp 20. However, in this embodiment, in order to stabilize a discharge arc occurring in the lamp 20, the control circuit 15 controls the down chopper 11 such that a current pulse is superposed on a lamp current supplied to the lamp 20. A detailed description thereof will be made with reference to FIG. 2.