LIGHT DIMMING CONTROL METHOD, LIGHT DIMMING CONTROL APPARATUS AND AUTOMATIC LIGHT DIMMING CONTROL APPARATUS

摘要

PURPOSE: To lessen the light dimming coefficient difference depending on frequency even if the light dimming coefficient is small by controlling the brightness by sending out a triger signal after a prescribed time corresponding to a prescribed light dimming level while the center of a semicycle of an a.c. electric power source being used as a standard. CONSTITUTION: A zero-cross point of an a.c. electric power source is detected by a cycle signal generating means 2. During a synchronous signal which exceeds the point, a clock signal with high frequency is counted by a first counter 31 and a clock signal with a half of the frequency of the former is counted by a second counter 32. A computing circuit 4 adds a value corresponding to a previously set light modulation level to the counted value of the counter 32 and stored in a memory means 5. Comparison of the computed result of the semicycle stored immediate before with the counted value of the counter 31 is carried out by a comparator 6 and a triger signal is sent to a Triac TRC from a triger output circuit 7. Voltage supplied to an incandescent lamp LP can be controlled by that phase control and the light dimming degree at 50Hz and 60Hz electric power frequency thus becomes low and an apparatus can be economical.