| 摘要 |
PROBLEM TO BE SOLVED: To operate a switch without using a zero voltage switching circuit in the same way as in the case where zero voltage switching is used out, thereby simplifying the circuit structure, reducing the number of used parts, and decreasing the costs. SOLUTION: To a commercial AC power 1, a lighting load 3 is connected through a bi-directional triode thyristor 2, and a filter capacitor 5 is connected through a diode 4. The filter capacitor is connected in parallel to a charge and discharge capacitor 7 through a resistor 6, a DIAC 8 is connected between the connecting point of the resistor with the capacitor 5, and the gate of the thyristor, thereby forming a saw-tooth oscillating circuit for generating saw-tooth oscillation at a high frequency. A photoelectric element 9 for reducing an internal resistance in proportion to an illumination level of the exterior light is connected in parallel to the charging and discharging capacitor. At night, when the internal resistance in the photoelectric element increases, the saw-tooth oscillating circuit oscillates at a high frequency, and the thyristor performs conduction and non-conduction operation equal to those at the zero voltage switching, so that the lighting load is turned on. |
