| 摘要 |
PROBLEM TO BE SOLVED: To provide an excitation circuit of an electromagnetic flow meter, which can switch an excitation power supply voltage by an N-type switching element having comparatively high compatibility.SOLUTION: A power supply switching circuit PSW is provided with a diode D1 in which an anode terminal is connected to a low voltage VexL and a cathode terminal is connected to a power supply output terminal N0 and an N-type switching element Q1 in which an input terminal is connected to a high voltage VexH, an output terminal is connected to the power supply output terminal N0 and an output terminal of a photocoupler PC1 to be turned off in a high voltage period and turned on in a low voltage period and a voltage holding circuit VS for holding and outputting a driving voltage charged by the high voltage VexH are connected in parallel, between a control terminal and the output terminal. When the switching element Q1 is to be turned on in accordance with the high voltage period, the switching element Q1 is operated by the driving voltage outputted from the voltage holding circuit. |
