| 摘要 |
PURPOSE:To prevent a sound signal from being leaked and lost regardlessly of the presence of rower feeding by connecting a Zener diode to the base of a transistor(TR) in order to prevent the TR from energizing by the sound signal. CONSTITUTION:A PNP TR Tr1 to constitute a feeder circuit 30 is connected to a signal line 12a at its collector, and the emitter is grounded. The cathode of the Zener diode DZ2 is connected to the base of Tr1, and a resistor R2 for bias is connected between the collector of Tr1 and the anode of DZ2. Besides, the cathode of the diode DZ3 is connected to the emitter of Tr1, and the anode of DZ2 is connected to the anode of DZ3. Then, at the time of the close of relay switches 15a, 15b, the inter-base-emitter voltage of Tr1 is made about 12V by the Zener voltage of DZ3 and DZ2, and Tr1 becomes conductive, and a constant current is fed. At the time of non-feeding, since Tr1 is not energized, the sound signal transmitted through the signal line 12a can be prevented from being leaked and lost from the feeder circuit 30. |
