| 摘要 |
PURPOSE:To facilitate handling as the signal source of a control system by comparing a phase digitally so as to detect that the phase order is switched with the use of two photocouplers after two-phase alternation waveforms are converted into a binary signal. CONSTITUTION:A phase detecting circuit is provided with a D-type FF 18 acted by the drive outputs of two sets of photocouplers 16 and 17 between input terminals 11 and 12 and output terminals 14 and 15 to a control circuit. With the terminal 12 as a common terminal, light emitting diodes 16a and 17a of the photocouplers 16 and 17 are installed between the terminals 11 and 12 and those 12 and 13 so that their normal directions can be different. Moreover Zener diodes 19 and 20 are serially connected to said diodes 16a and 17a so that the diodes 16a and 17a can execute the constant voltage action at the positive iteration period of the voltage waveform of a load drive system. With this constitution the photocouplers 16 and 17 carrying out a constant voltage drive by the Zener diodes 19 and 20, convert the two-phase alternation waveform into the binary signal, and the D-type FF 18 executes the synchronous detection, whereby switching of the phase order of three-phase AC, that is, a subject to be detected, is detected.
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