| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain a stable AC zero-cross signal that is not affected by a supply voltage. <P>SOLUTION: In an AC voltage zero-cross detection circuit 10, a zero-cross signal waveform of an AC signal is obtained by a current of a photocoupler 5. A transistor 4, which controls a current flowing in the input-side current carrying path of the photocoupler, is connected to the photocoupler 5, while a Zener diode 6 is connected to the transistor. A current is branched by the Zener diode, so that a current made to flow in the photocoupler by the transistor is limited to a certain value or lower. In a voltage range where the zero-cross signal is obtained, the transistor exerts large amplification factor, so that an AC zero-cross signal hardly depending on a supply voltage can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT |
