| 摘要 |
PURPOSE:To attain low cost by obtaining a reference voltage from a voltage dividing circuit so as to switch is thereby obtaining an optional voltage. CONSTITUTION:An AC power 2 is subjected to phase control by a triac 11 and applied to an exposure lamp 1. A lamp voltage V2 is converted into an effective voltage V4 via a transformer T1, a full wave rectifier circuit 3 and an effective value detecting circuit 4. The voltage V4 is compared with a reference voltage Vr from a reference voltage generating circuit 12 at a differential amplifier circuit 5 and its output V5 and a sawtooth wave voltage V8 by a zero cross pulse V7 from a zero cross detecting circuit 8 control the triac 11 via a phase shift circuit 6 or the like. In this case, the reference voltage generating circuit 12 consists of a constant voltage power supply circuit, a voltage division circuit, and a switch element forming the voltage division control means. A prescribed voltage dividing ratio is changed by means of the on/off state of the switch element so as to change the output reference voltage Vr. |
