| 摘要 |
PROBLEM TO BE SOLVED: To provide a two-wire system signal transmitter which can prevent the flow of an overcurrent that is caused by erroneous connections of a measurement device, can protect a circuit for improving its reliability and also can prevent the generation of heat due to the overcurrent to improve the safety, by setting the current flowing through the resistance that is put in series into the emitter of a 1st TR(transistor) at a level almost equal to that of an output current. SOLUTION: The emitter of a TR Q1 is connected to an output terminal T3 via a resistance Rc. A TR Qc has its emitter and base connected in parallel to both ends of the Rc and its collector connected to the collector of a TR Q2 . The emitter current of the TR Qc is limited by a resistance R1 , and is therefore sufficiently small as compared with an output current Io. Thereby, the current is limited to Io×Rc≈VBE (≈0.6 V) since Ic≈Io which is to be satisfied. VBE of the TR Qc is reduced as the temperature rises. As a result, the limited current level is lowered as the temperature rises.
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