To smoothly start a field bus signal transmission system by restricting the inrush current which flows into an apparatus.
A transistor T2 for controlling the base current of a transistor T1 for regulating the power receiving/feeding amount is connected to the base of the transistor T1 and the base current of this transistor T2 is controlled to regulate the DC current amount to receive/feed from a field bus. One terminal of a resistor R4 is connected to the input side of the transistor T1, a Zener diode ZD1 is connected between the base of the transistor T1 and the other terminal of the resistor R4 to connect the base of the transistor T1 and an anode side, and the maximum value of the sum of a voltage drop of the resistor R4 and a base-emitter voltage VBE of the transistor T1 is restricted. When the sum exceeds the breakdown voltage of the Zener diode ZD1, the DC current flows through the Zener diode ZD1 to the side of the transistor T2, thereby restricting the current amount pulled in by the transistor T1.
COPYRIGHT: (C)2005,JPO&NCIPI
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Yoshiaki Naito
Cui Shu Tetsu