| 摘要 |
PURPOSE:To exert no influence of noise on other circuits in a simple constitution by counting the zero cross point where the AC voltage traverses at zero level and by switching on the TRIAC at this zero cross point at the rate of one (1) to N. CONSTITUTION:The zero cross point of the voltage of a commercial AC power source 138 is detected by a zero cross detection circuit 140 and the zero cross signal is sent out to the clear terminal of an up-counter 142. This up-counter 142 counts the clock signal, and when its counted value reaches e.g. 11, the output of AND gate 144 goes to H level, where the non-maskable interrupt signal and reset signal are outputted. The zero cross signal from the zero cross detection circuit 140 is counted by a counter 160 and when the counted value of the negative pulse of the zero cross signal reaches e.g. 15, the gate pulse signal is sent out at its zero cross point to the TRIAC 158, which is ignited.
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