| 摘要 |
PROBLEM TO BE SOLVED: To provide a power-supply unit which can reduce a voltage drop produced in a communication medium and permits communication using a long communication medium. SOLUTION: The power-supply unit 1, in normal times, outputs a voltage between the emitter and the ground of a transistor Q1 to between output terminals 10, 11 via a resistor R2 and feeds an output current IL to a load RL. If the output current IL increases and a voltage generated at the both ends of the resistor R2 reaches a voltage VBE between the base and the emitter of the transistor Q2, the transistor Q2 is turned on. Consequently, a voltage between the base and the emitter of the transistor Q1 is short-circuited with the transistor Q2, so that the transistor Q1 assumes a non-conducting state, an output voltage drops to 0 V and the increase of the output current IL is limited. COPYRIGHT: (C)2004,JPO
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