| 摘要 |
PROBLEM TO BE SOLVED: To optimally drive a heater in consideration for power supply status and to reduce an unwanted rush power generated at the time of turning on the heater, by making a zero cross signal generating circuit composed of plural zero cross signal generating circuits. SOLUTION: An AC voltage inputted from a commercial power source AC is rectified in full wave by a diode bridge DB with a time constant circuit consisting of resistors R1 -R5 and a capacitor C and added to the base of a transistor Tr through a photocoupler PC. Then, the transistor Tr is turned on in the vicinity of the zero cross point of the AC voltage and a zero cross signal is outputted from an output terminal (B part) connected to the collector of the transistor Tr. In the zero cross signal from the B part, when the voltage value of the commercial power source AC is changed, the signal width of the zero cross signal is changed. Therefore, the signal width of the zero cross signal is reduced by the drop of the voltage of the commercial power source AC. At this time, as the zero cross signal generating circuit, the plural zero cross signal generating circuits consisting of different constants are used. |
