| 摘要 |
PURPOSE:To obtain an accurate zero cross signal even from an AC input including noise by using the output of the 1st photocoupler to strobe the output from the 2nd photocoupler, extracting the output timing to output the zero cross signal. CONSTITUTION:An AC input A is rectified and converted into a DC voltage B. The voltage B is fed to photocouplers 4, 5 respectively via a resistor 9 or 10 and a Zener diode 2 or 3. A photodetector 4' of the coupler 4 is turned off when the voltage B is a Zener voltage of the diode 2 or velow and turned on when the voltage is over the Zener voltage. Thus, a signal fed to terminals D and CLR of a D FF 8 via an amplifier 6 is pulse signal C. The photodetector 5' is acted similarly and a signal fed to a terminal CK of an FF 8 via an amplifier 7 is a pulse signal D. Thus, a signal having a high level from the leading of the signal D until the trailing of the signal C, that is, the zero cross signal E is outputted from a terminal Q of the FF 8. |
