JPH08249585A - Signal transmission circuit - Google Patents

Abstract

PURPOSE: To provide a signal transmission circuit with which the grounding defect or power feeding defect of a signal input circuit part can be detected on the side of a signal output circuit part. CONSTITUTION: A signal output circuit part 1 is provided with a switching element 15 for output and a resistor 17 mutually parallelly connected between a ground line 12 and a signal line 2, and the signal output circuit part 1 transmits signals through the signal transmission line 2 to a signal input circuit part 3 under the control of the switching element 15 for output. The signal input circuit part 3 is provided with a switching element 33 for load and resistors 34 and 35 connected between a power source line 31 and the signal line 2 and supplies a load current to the signal transmission line 2. The signal input circuit part 3 is provided with a voltage dividing circuit composed of voltage dividing resistors 36 and 37 serially connected and arranged between the power source line 31 and a ground line 32 and this voltage dividing circuit stops power supply from the switching element 33 for load to the signal transmission line 2 by cutting off the switching element 33 for load when the ground line 32 is disconnected. As the result, even when the switching element 15 for output is turned off, the signal transmission line 2 is turned to a low level by the resistor 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission circuit for transmitting a signal from at least a signal output circuit section to a signal input circuit section. The signal transmission circuit of the present invention can transmit a grounding failure alarm signal from the signal input circuit section to the signal output circuit section, and the load current supplied to the signal transmission line when grounding failure occurs on the signal input circuit section side. It is possible to cut off the power to realize power saving.

[0002]

2. Description of the Related Art Japanese Utility Model Laid-Open No. 5-92736 discloses that when a signal is transmitted from a signal output circuit section to a signal input circuit section through a pair of signal transmission lines, a signal on the low potential side of the signal transmission line pair is input. Ground on the circuit side through a resistor. With this configuration, when at least one of the pair of signal transmission lines is broken, the voltage drop of this resistance becomes 0, so that the disconnection of the signal transmission line can be detected.

Japanese Unexamined Patent Publication No. 5-294167 discloses a signal transmission line, a signal output circuit section which is arranged between a power line and a ground line, and outputs a signal through the signal transmission line, and a power line. And a signal input circuit section that receives a signal through a signal transmission line while being disposed between the ground line and
The signal output circuit unit has an output switching element and a resistance element connected in parallel to each other between the ground line and the signal line, and the signal input circuit unit is connected between the power supply line and the signal line. A signal transmission circuit having a resistance element is disclosed. According to this circuit, when the signal transmission line is broken, the output end (signal transmission line connection end) of the signal output circuit section becomes a low potential despite the interruption of the output switching element. Can be detected.

[0004]

As described above, the disconnection (defective conduction) of the signal transmission line can be satisfactorily detected by the conventional technique. However, in the above-mentioned conventional technique, the signal output circuit unit side cannot detect the ground line continuity defect on the signal input circuit unit side, that is, the ground fault of the signal input circuit unit.

In addition, even in such an abnormal state, useless current flows through the signal transmission line to fix the potential of the signal transmission line, resulting in wasted power consumption. The present invention has been made in view of the above problems, and an object thereof is to provide a signal transmission circuit capable of detecting a grounding failure or a power feeding failure of a signal input circuit unit on the signal output circuit unit side.

Another object of the present invention is to provide a signal transmission circuit capable of saving wasteful power consumption in the case where the signal input circuit section has a ground failure or a power supply failure.

[0007]

The first structure of the present invention is as follows.
A signal transmission line, a signal output circuit unit that is provided between the power supply line and the ground line and outputs a signal through the signal transmission line, and is provided between the power supply line and the ground line. A signal input circuit section for receiving the signal through the signal transmission line, wherein the signal output circuit section is connected in parallel between one of the power supply line and the ground line and the signal line. A load current feeding circuit section including a switching element and a resistance element, wherein the signal input circuit section includes a load switching element connected between the other of the power supply line and the ground line and the signal line; A signal transmission circuit, comprising: a load switching element cutoff circuit section that cuts off the load switching element when one of the power supply line and the ground line on the signal input circuit section side fails in conduction. A.

The power supply line may have different power supply potentials on the signal input circuit section side and the signal output circuit section side. The ground potential of the ground line does not have to be the ground potential in this specification, and may be a potential lower than the power supply potential. According to a second configuration of the present invention, in addition to the first configuration, the signal output circuit section further includes a potential detection circuit section that detects a potential of the signal transmission line, and the signal detected by the potential detection circuit section. It is characterized in that grounding fault detection means for detecting a grounding fault on the side of the signal input circuit section based on the potential of the transmission line is provided.

A third structure of the present invention is the above-mentioned second structure, wherein the ground fault detecting means further comprises: when the potential of the signal transmission line is at a low level when the output switching element is cut off. The feature is that it is determined that a signal transmission failure state including a grounding failure and a power supply failure of the signal input circuit unit occurs. A fourth configuration of the present invention is the configuration according to any one of the first to third configurations, wherein the load switching element blocking circuit section further includes a first voltage dividing resistor having one end connected to the power supply line and one end. And a voltage dividing circuit including a second voltage dividing resistor connected to the ground line, the other ends of the two voltage dividing resistors being connected to the control terminal of the load switching element, and the load switching element. Is composed of a grounded-emitter or source-grounded transistor that conducts when a potential lower than the potential of the power supply line is applied to the control terminal from the other ends of the voltage dividing resistors.

A fifth structure of the present invention is the above first to third structures.
In any one of the above configurations, the load switching element cutoff circuit unit further has a base current regulation in which one end is connected to the ground line and the other end is connected to a control terminal of the load switching element including a bipolar pnp transistor. It is characterized by having a resistor. According to a sixth aspect of the present invention, in the configuration according to any one of the first to third aspects, the load current feeding circuit section further includes the load switching element and a resistance element connected in series with the load switching element. It is characterized by having and.

[0011]

In the first configuration of the present invention, the signal output circuit section includes the output switching element and the resistance element connected in parallel with each other between one of the power line and the ground line and the signal line. The signal output circuit unit transmits a signal to the signal input circuit unit through the signal transmission line under the control of the output switching element. The signal input circuit unit has a load current feeding circuit unit including a load switching element connected between the other of the power supply line and the ground line and the signal line, and the load current feeding circuit unit is a load of the output switching element. A load current is supplied to the signal transmission line as an element. In addition, the signal input circuit unit,
The load switching element cutoff circuit section includes a load switching element cutoff circuit section, which cuts off the load switching element when one of the power supply line and the ground line on the signal input circuit section side is defective in conduction.

Therefore, according to this structure, the grounding failure or power supply failure alarm signal of the signal input circuit section can be transmitted to the signal output circuit section, and the signal transmission line is generated when the above-mentioned failure occurs on the signal input circuit section side. It is possible to save power by cutting off the load current of the load current feeding circuit section that is fed to the. In the second configuration of the present invention, in addition to the first configuration, the signal output circuit section detects the grounding failure (or the power supply failure) on the signal input circuit section side based on the potential of the signal transmission line. Since the means is provided, it is possible to take measures against these defects.

In a third configuration of the present invention, in the second configuration, the ground fault detecting means further includes a signal input circuit section when the potential of the signal transmission line is at a low level when the output switching element is cut off. Since it is determined that the signal transmission failure state including the grounding failure and the power feeding failure has occurred, it is possible to easily realize the second configuration. According to a fourth configuration of the present invention, in any one of the first to third configurations described above,
The load switching element cutoff circuit section applies the voltage division of the voltage dividing circuit arranged between the power supply line and the ground line to the control terminal of the load switching element which is formed of a transistor with a grounded emitter or a source. With this configuration, since the load switching element is shut off when the signal input circuit section is grounded poorly, the function and effect of the first configuration can be easily achieved.

In a fifth structure of the present invention, in addition to any one of the first to third structures, the load switching element interruption circuit section has one end connected to the ground line and the other end connected to a bipolar pnp transistor. Is connected to the control terminal of the load switching element
The emitter of the p-transistor is connected to the power supply line. With this configuration, since the load switching element is shut off when the signal input circuit section is grounded poorly, the function and effect of the first configuration can be easily achieved.

According to a sixth aspect of the present invention, in any one of the first to third aspects, the load current feeding circuit section further includes a load switching element and a resistance element connected in series with the load switching element. Therefore, the optimum load current for the resistance value of the resistance element on the signal output circuit side and the on resistance of the output switching element can be easily supplied to the signal transmission line.

[0016]

[Embodiment 1] An embodiment of a signal transmission circuit according to the present invention will be described below with reference to FIG. This signal transmission circuit comprises a signal output circuit unit 1, a signal transmission line 2 and a signal input circuit unit 3, and the signal transmission line 2 includes a signal output terminal 10 of the signal output circuit unit 1 and a signal input circuit unit 3. It is connected to the signal input terminal 30.

The signal output circuit unit 1 is supplied with a power supply voltage from the power supply + B through the high-side power supply line 11 on the output side and is grounded through the grounding line 12 on the output side. To high-level power line 31 on the input side
A power supply voltage is supplied via the grounding line 32 on the input side. The signal output circuit unit 1 is C
It includes a PU 13, a signal line potential detection circuit unit 14, an output switching element 15, a current limiting resistor 16, and a bypass resistor 17. The output switching element 15 is an open collector type npn bipolar transistor whose base is C through a base current limiting resistor rb.
It is controlled by the PU 13, its emitter is connected to the ground line 12 on the output side, and its collector is connected to the signal output terminal 10. The bypass resistor 17 connects the signal output terminal 10 and the output side ground line 12.

The signal line potential detection circuit section 14 is composed of an operational amplifier amplifier circuit for amplifying the voltage of the signal output terminal 10 by a predetermined factor and inputting it to the CPU 33. The signal input circuit unit 3 includes a load switching element 33 having a pnp bipolar transistor whose emitter is connected to the power supply line 31 on the input side and whose collector is connected to the signal input terminal 30 through the current limiting resistors 34 and 35. The base of the load switching element 33 is connected to the input side power supply line 31 through the base current limiting resistor rb and the voltage dividing resistor 36, and is connected to the input side grounding line 32 through the base current limiting resistor rb and the voltage dividing resistor 37. Has been done. Here, the load switching element 33 and the resistor 34 form a load current feeding circuit section according to the present invention, and the resistors 36 and 37 form a load switching element cutoff circuit section according to the present invention.

The connection point Ip between the current limiting resistors 34 and 35 sends the above signal to an actuator circuit section (not shown) of the signal input circuit section 3 through the internal signal line 39. Further, this actuator circuit section has a built-in alarm circuit (not shown), and this alarm circuit has a function of driving and controlling the alarm transistor 38 to change the signal line potential and transmitting an alarm to the signal output circuit section 1. ing. More specifically, the alarm transistor 38 is an open collector type npn bipolar transistor, the emitter of which is connected to the ground line 32 on the input side and the collector of which is connected to the connection point Ip. Since the operation of the alarm transistor 38 is far from the gist of the present invention, further description will be omitted.

Next, the operation of this signal transmission circuit will be described below. During normal operation, the load switching element 33 is turned on and power is supplied from the power supply line 31 on the input side to the signal transmission line 2. The CPU 13 outputs a predetermined PWM (pulse width modulation) signal voltage to the output switching element 15, and when the output switching element 15 is turned on, the potential of the signal transmission line 2 becomes a predetermined low level and the output switching element 15 is turned off. Then, the potential of the signal transmission line 2 becomes a predetermined high-level potential defined by the voltage drop of the bypass resistor 17, and these potentials are transmitted to the signal input circuit unit 3.

Now, when the grounding line 32 on the input side has a poor continuity or a poor contact between the grounding line 32 and the signal input circuit section 3, the potential at the connection point of the voltage dividing resistors 36 and 37 rises, and the load switching element 33 is activated. As a result, the signal transmission line 2 is brought to the ground potential due to the discharge from the bypass resistor 17. This ground potential is detected by the signal line potential detection circuit unit 14 and input to the CPU 13.

Next, the signal input circuit section 3 by the CPU 13
The abnormality determination operation will be described with reference to the flowchart of FIG. First, it is determined whether the output switching element 15 is off based on the potential of the control voltage output from the CPU 13 to the output switching element 15 (10
0), if it is on, it waits or returns to the main routine, and if it is off, after waiting for a predetermined time (102), it is determined whether the potential of the signal transmission line 2 is low (below a predetermined potential). The determination is made based on the input voltage from the detection circuit unit 14 (104). If it is low, it is determined that the signal transmission line 2 is broken or that the signal input circuit unit 3 is not properly fed or grounded, and an alarm is output.

The above-mentioned power supply failure means the following cases. That is, when the contact between the signal input circuit unit 3 and the power supply line 31 on the input side is defective or the power supply line 31 on the input side is broken, the power supply through the load switching element 33 is stopped, and thus the above-described grounding failure occurs. The signal output circuit unit 1 can detect the same principle. The current limiting resistors 35 and 16 may be omitted. (Embodiment 2) Another embodiment will be described with reference to FIG.

In this embodiment, the voltage dividing resistor 3 is used in the first embodiment.
6 and base current limiting resistance r of switching element for load
b is omitted. Even in this case, the same effect as that of the first embodiment can be obtained. (Embodiment 3) Another embodiment will be described with reference to FIG.

This embodiment differs from the first embodiment in that the conductivity type of the transistors constituting the load switching element 33 and the output switching element 15 is changed, and the load switching element 33 is grounded on the signal transmission line 2 and the input side. It is connected between the line 32 and the output switching element 15
Is connected between the signal transmission line 2 and the power supply line 11 on the output side. In this case as well, the same operation and effect as those of the first embodiment can be obtained (conduction failure of the power supply line on the input side or it and the signal input circuit). It is possible to detect a poor contact with the portion 3).

[Brief description of drawings]

FIG. 1 is a circuit diagram of a signal transmission circuit according to a first embodiment,

FIG. 2 is a circuit diagram of a signal transmission circuit according to a second embodiment,

FIG. 3 is a circuit diagram of a signal transmission circuit according to a third embodiment,

FIG. 4 is a flowchart showing an abnormality detecting operation of the CPU 13.

[Explanation of symbols]

1 is a signal output circuit unit, 2 is a signal transmission line, 3 is a signal input circuit unit, 11 is an output side power supply line, 12 is an output side ground line,
13 is a CPU (ground fault detection means), 14 is a potential detection circuit section, 15 is an output switching element, 17 is a bypass resistance (resistive element), 33 is a load switching element (a part of the load current feeding circuit section), Reference numeral 34 is a resistor (the rest of the load current feeding circuit portion), and 36 and 37 are voltage dividing resistors (load switching element cutoff circuit portion).

Claims (6)

[Claims] 1. A signal transmission circuit, a signal output circuit section that is arranged between a power supply line and a ground line and outputs a signal through the signal transmission line, and between the power supply line and the ground line. And a signal input circuit unit that receives the signal through the signal transmission line, and the signal output circuit unit is in parallel with each other between the signal line and one of the power supply line and the ground line. A load current feed including a switching element for load connected between the signal line and the other of the power supply line and the ground line; A circuit section and a load switching element cutoff circuit section that cuts off the load switching element when one of the power supply line and the ground line on the signal input circuit side is defective in conduction. Signal transmission circuit. 2. The signal output circuit section detects the potential of the signal transmission line, and the signal input circuit section based on the potential of the signal transmission line detected by the potential detection circuit section. The signal transmission circuit according to claim 1, further comprising grounding failure detection means for detecting grounding failure on the side. 3. The ground fault detecting means includes a fault in signal transmission including a fault in grounding and a fault in power feeding of the signal input circuit section when the potential of the signal transmission line is at a low level when the switching element for output is cut off. The signal transmission circuit according to claim 2, which determines that a state has occurred. 4. The load switching element cutoff circuit section has a voltage dividing resistor including a first voltage dividing resistor having one end connected to the power supply line and a second voltage dividing resistor having one end connected to the ground line. A circuit, the other ends of the two voltage dividing resistors are connected to the control terminal of the load switching element, the load switching element has a potential lower than the potential of the power supply line, the other end of the two voltage dividing resistors. 4. The signal transmission circuit according to claim 1, comprising a grounded-emitter or source-grounded transistor that conducts when applied to the control terminal. 5. The load switching element cutoff circuit section has one end connected to the ground line and the other end connected to a bipolar p-type.
4. The signal transmission circuit according to claim 1, further comprising a base current regulating resistor connected to a control terminal of the load switching element formed of an np transistor. 6. The signal transmission circuit according to claim 1, wherein the load current feeding circuit section includes the load switching element and a resistance element connected in series with the load switching element.