| 摘要 |
PURPOSE:To execute a phase control exactly at a low cost by detecting a zero crossing point of an AC power source at a non-operating point of a triar AC switch, and driving a timer for determining a trigger timing. CONSTITUTION:A halogen lamp HA of a copying machine, etc. and a triar AC switch RA are connected to an AC power source AC, and a phase control is executed by a control part CPU consisting of a peak value detecting circuit PD of power supply voltage and a microcomputer. The detection of a zero crossing point for this phase control is executed by detecting an electric conduction end point of the triar AC switch RA, by a photocoupler PC2 provided in parallel to the triar AC switch RA. Subsequently, a detecting signal of this electric conduction end point is inputted to the control part CPU, and by using it as a reference point, a timer time counting operation in the CPU is started, and at the end time point of the timer, a trigger pulse TP is generated. In this state, the triar AC switch RA is triggered through a photocoupler PC1, and the lamp HA is brought to a phase control. |
