| 摘要 |
PURPOSE:To obtain a fixed and stable threshold by setting the threshold of a photocoupler by means of resistances and bypassing a current flowing in a light-emitting element when a transmission signal is larger than the threshold by means of a bypass transistor between both ends of the light-emitting element of a second photocoupler. CONSTITUTION:An input signal is inputted between the input terminals 7 and 8 of a transmission circuit 1A and is photoelectrically converted by the first photocoupler 6. The output of the first photocoupler 6 controls an output transistor 5 and transmits a transmission signal S2 to a bidirectional signal line 40. An output signal S4 photoelectrically converts the transmission signal S2 based on a threshold TL2 decided by the resistances 30 and 31, and it is outputted from an output terminal 24. Namely, when the level of the transmission signal S2 is larger than a threshold TK2, the bypass transistor 29 is conducted, and the output signal S4 of a low level is outputted from the output terminal 24. Thus, the fixed and stable threshold can be obtained. |
