| 摘要 |
PURPOSE:To hold the effective voltage of a load at a constant value, by turning on an AC switch when saw tooth voltage and error voltage have been incoincidence between zero crossing points, in a lamp regulator of an exposure lamp of a copying machine. CONSTITUTION:A transistor TR1 inputs saw tooth voltage VT which has synchronized with voltage VAC of an AC power source 3, to a comparator 11 from a saw tooth voltage generating circuit 4, by a zero crossing pulse P2 which is outputted from a zero-cross detecting circuit 1. On the other hand, AC voltage V out of a lamp load 5 is outputted through a transformer 6, is rectified 7, is full-wave-rectified by a squaring circuit 8, is averaged 9 through the squaring circuit 8, its output is compared with reference voltage VREF by a differential amplifier 10, error voltage VER is compared with the voltage VT. When both signal voltage hss been in coincidence between zero crossing points, a trigger pulse is generated 12 in ordr to turn on an triode AC switch 14 which has been inserted between the load 5 and the electric power source 3. In this way, effective voltage of the load 5 is held at a constant value. |
