| 摘要 |
PURPOSE:To prevent an excess current from being conducted to a Zener diode in a power supply circuit by providing an overcurrent detection circuit and a current bypass resistor. CONSTITUTION:The overcurrent detection transistor (TR) 9, a resistor 8 to conduct the TR 9 and a resistor 10 limiting a bypass current are provided. The feeding current received from a communication signal input terminal 1 and a communication signal are separated by a power separation circuit 2, amplified by an amplifier 3 and fed to a power separation circuit 4. If an overcurrent takes place, the overcurrent is conducted to the resistor 8, the overcurrent detection TR 9 is conductive by the voltage drop. Thus, the supplied overcurrent is branched into a circuit from the resistor 8 to the Zener diode 7 and a circuit from the TR 9 to the current limit resistor 10 and then fed to the power separation circuit 4. Thus, the overcurrent conducting to the Zener diode 7 is prevented.
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