| 摘要 |
PURPOSE:To make preliminary preheating, lighting-up control, and dimming control of a discharge lamp with a series of control signals by performing the changeover control of the preliminary preheating, lighting-up, and light-up preheating of the filament of discharge lamp in conformity to the control signals of a plurality of voltage levels, i.e., the bottom level, high level, and middle level. CONSTITUTION:In the preliminary preheating mode until a lighting-up command is given after the power is put on, a switch SW1 in a control signal producing circuit 10 is turned on, and a control signal Sin of the bottom level voltage obtained by dividing the voltage Vd by resistances R2, RC3 is given. If a transistor Q1 is in Off condition when a lighting-up command and the switch SW1 is put off, a signal of high level voltage which is the signal voltage Vd as it is, emitted as the control signal Sin. When the dimming mode is entered and a variable resistor VR is adjusted, a pulse signal of a duty ratio (d) corresponding to the voltage is given by a PWM controller 12, and therewith emission of the control signal Sin is made with which changing- over is made so that the high level voltage is attained at Off time with turn-on of the transistor Q1 and the middle level voltage presccribed by a Zenor diode ZD is attained at On time. |
