| 摘要 |
PURPOSE:To enable illuminance to be controlled over a wide range, and stable lighting state to be provided by generating a pulse having such width as corresponding to the preset illuminance and power on the basis of an electrical signal from an illuminance detecting device and a power detecting device, and then feeding back the pulse to a DC/AC converter. CONSTITUTION:An illuminance detecting device 7 converts the light of a discharge lamp into an illuminance signal S6 through a photoelectric conversion circuit 7b via an optical fiber 7a. A power detecting device 8 inputs signal from a power supply device 5 to a current and voltage detecting circuit 8b, and outputs AC/voltage signals S7 and S8. Feedback signal polarity selector circuits 8c and 8d reverse the negative polarity of the signals S7 and S8, and feed DC/voltage signals S3 and S4 to a multiplier 9a2. In this case, when a signal S5 is larger than reference voltage V01 to set illuminance, the output V1 of an operational amplifier 9a1 becomes positive and forward in line with the output V2 of the multiplier 9a2. Thus, an operation signal A outputted from an operational amplifier 9a3 drops. As a result, the width of the output pulse of a pulse width modulation section 9b is reduced and the illuminance is thereby lowered. |
