JPH0619099Y2 - Open collector signal transmission line disconnection detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an open collector signal transmission for transmitting a signal via a transmission line for controlling from a remote location or measuring at a remote location. The present invention relates to an open collector signal transmission line disconnection detection circuit for automatically detecting a disconnection of a transmission line in a signal transmission system using lines.

[Prior Art] A conventional circuit in a signal transmission system for transmitting a signal via a transmission line and controlling or measuring at a remote location will be described with reference to FIG.

In FIG. 2, 1 is a base resistance of a signal transmission transistor provided on the transmission side, 2 is a signal transmission transistor, 3 is a connector connected between the collector of the signal transmission transistor and a transmission line, 4 is a transmission line, 5 is a connector connected between the transmission line and the device on the receiving side, 6 is a load resistor connected to the receiving side for the collector on the transmitting side, 7 is an amplifying circuit on the receiving side, and 8 is a transistor via the resistor 6. 2 is a power supply bus bar for supplying voltage to 2. The signal sent from the previous stage on the transmitting side is input to the base of the open collector transistor 2 which is the output stage, and is input from the collector to the amplifying circuit 7 on the receiving side via the transmission line. In the figure, the left side of the connector 3 is a transmitting side device of the signal transmission line, the right side of the connector 5 is a receiving side device, and the transmission line is between the connectors 4 and 5.

[Problems to be Solved by the Invention] In the above circuit, when the transmission line 4 is broken, the voltage of the power supply bus 8 and the resistance 6 keep the voltage on the receiving side of the transmission line high, but the transistor 2 It was not possible for the receiving side to judge whether the cutoff was caused by the original proper operation, and thus it became higher or the disconnection made it higher.

[Means for Solving the Problems] The present invention is intended to provide means for solving the above-mentioned problems and detecting the presence or absence of disconnection of a transmission line at the receiving side, and an output stage at the transmitting side. In a signal transmission system in which an open-collector transistor is provided in the second collector, the collector and the emitter of the second transistor are connected in parallel to the collector and the emitter of the first transistor of the open collector, and the base input of the second transistor is connected. It is characterized in that the open side of the open collector signal transmission line is detected by transmitting a control signal from the receiving side of the signal transmission system.

[Operation] According to the above configuration, when the base voltage of the second transistor is kept at a low level, the second transistor is cut off, so that even if the transistors are connected in parallel, the signal transmission is not affected. Absent. By increasing the base voltage of the second transistor when the voltage level on the receiving side of the transmission line is high, the second transistor lowers the voltage level on the receiving side of the transmission line to absorb current through the transmission line. Let However, if the voltage level on the receiving side of the transmission line is high because the transmission line is broken, even if an attempt is made to raise the base voltage of the second transistor to pass a current, a current is passed through the collector circuit. The voltage on the receiving side of the transmission line does not drop because it cannot. In this way, it can be judged on the receiving side that the transmission line is broken. Also,
Normally, a large number of open collector transmission lines are laid in parallel, but the transmission line for controlling the voltage of the base for controlling the second transistor to be added and the switch circuit are complete and common to multiple signal transmission lines. Should be used for. In this case, since a plurality of lines are diagnosed by one control switch circuit, if all lines do not respond in the same way when diagnosing by switch operation, it can be judged that the diagnostic switch circuit is defective. .

[Embodiment] An embodiment of the present invention will be described with reference to FIG. 1. In the drawing, 1 is a base resistance of a signal transmission transistor provided on the transmission side, 2 is a first transistor for signal transmission, and 3 is signal transmission. Connector connected between the collector circuit of the transistor for transmission and the transmission line, 4 is a transmission line, 5 is a connector connected between the transmission line and a device on the receiving side, and 6 is a load for the collector of the transistor on the transmitting side. A resistor, 7 is an amplifier circuit on the receiving side, and 8 is a power bus for supplying a voltage to the transistor 2 via the resistor 6. Reference numeral 9 is a second transistor connected in parallel to the first transistor 2, 10 is a resistor connected to the base of the second transistor 9, and 11 is another transmission arranged in parallel with the base of the second transistor 9 and the transmission line 4. Connector connected between line 12 and 13
Is a connector connected between the transmission line 12 and the circuit on the receiving side, 14 is a switch circuit for sending a signal voltage to the base of the transistor 9, and 15 is a resistor for determining the base current of the transistor 9, one of which is The terminal of is connected to the bus bar 16 having a predetermined voltage. A voltage measuring circuit 17 measures the voltage level of the transmission line. The second transistor 9 is always the first transistor 2
The second transistor 9 has a base of a resistor 1 because the switch 14 is normally open.
It is grounded by 0 and the second transistor 9 is cut off. Therefore, the transmission line 4 does not affect the signal transmission regardless of the presence of the transistor 9 and performs the original signal transmission.

In this circuit, when the switch 14 is closed when the measured value of the receiving circuit, for example, the voltage measuring circuit 17 becomes high and the transmission line 4 may be disconnected, the voltage of the power bus 16 passes through the resistor 15 and is transmitted. The transistor 9 which is supplied to the base of the transistor 9 by the line 12 and has a high base voltage becomes conductive.

If the transmission line 4 is not broken, there is a voltage drop due to the resistor 6 to absorb the current due to the conduction of the transistor 9, and the voltage of the transmission line 4 which has been at a high level is lowered to a low level, but the transmission line is broken. When the transistor 9 is turned on, the voltage level cannot be lowered because no current flows through the transmission line 4 even when the transistor 9 is turned on. As described above, the presence or absence of disconnection of the transmission line can be easily known by operating the switch 14.

Although only one line is shown for the first transistor and the transmission line in the figure, many output transistors and many transmission lines are provided in parallel because it is necessary to send many signals for information processing in an actual system. Has been. Therefore, the number of the second transistors is also required, but the control transmission line 12 and the switch circuit 14 may be used as a set and commonly used for a plurality of signal transmission lines. In that case, if the transmission line 12 for controlling the second transistor
Is disconnected, the voltage of all the transmission lines to which the transistor 9 is connected does not change even if the switch 14 is operated, so that the disconnection of the transmission line 12 can be known.

In this circuit, the switch circuit 14 may be an ordinary switch, but the switch may be configured by a gate element of an IC and controlled by a control circuit on the receiving side, or may be included in the control circuit.

The voltage measuring circuit 17 does not need to be constantly connected to all circuits, and can be folded into the function of the control device by the receiving side, for example, a computer.

[Advantage of the Invention] As described above, in the present invention, the second transistor is connected in parallel to the first signal transmitting transistor and the base voltage thereof is controlled from the receiving side. Therefore, the second
When the base voltage of the transistor is set to a low level, the second transistor is cut off, so that even if the transistors are connected in parallel, the signal transmission is not affected. By increasing the base voltage of the second transistor when the voltage level on the receiving side of the transmission line is high, the second transistor lowers the voltage level on the receiving side of the transmission line to absorb current through the transmission line. Let However, if the voltage level on the receiving side of the transmission line is high because the transmission line is broken, even if an attempt is made to raise the base voltage of the second transistor to pass a current, a current is passed through the collector circuit. The voltage on the receiving side of the transmission line does not drop because it cannot. In this way, it can be judged on the receiving side that the transmission line is broken. In general, a large number of open collector transmission lines are laid in parallel, but the transmission line and the switch circuit for controlling the voltage of the base for controlling the second transistor to be added are complete, and a plurality of signal transmissions are performed. It can be used for all lines. In this case, since a plurality of lines are diagnosed by one control switch circuit, if all lines do not respond in the same way when diagnosing by switch operation, it can be judged that the diagnostic switch circuit is defective. .

[Brief description of drawings]

FIG. 1 is a transmission circuit diagram by an open collector according to the present invention. FIG. 2 is a conventional open collector transmission circuit diagram. 1 ... resistance 2 ... transistor 3 ... connector 4 ... transmission line 5 ... connector 6 ... load resistance 7 ... amplifier circuit 8 ... power supply bus 9 ... transistor 10 ... resistor 11 ... connector 12 ... … Transmission line 13 …… Connector 14 …… Switch circuit 15 …… Resistance 16 …… Power supply bus 17 …… Voltage measuring circuit

Claims (1)

[Scope of utility model registration request] 1. In a signal transmission system in which an open collector transistor is provided in an output stage on the transmission side, another transistor is additionally connected in parallel with the open collector transistor, and the control signal of the transistor additionally connected in parallel is used as the signal. A disconnection detection circuit for an open collector signal transmission line, which is configured to detect the disconnection of the open collector signal transmission line by transmitting from the receiving side of the transmission system.