JP3840319B2 - Current communication circuit using power line - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a current communication circuit using a power line that performs data communication while supplying power between a plurality of electronic control units.
[0002]
[Prior art]
Conventionally, prior art about signal transmission using a power line is disclosed in Japanese Utility Model Application Laid-Open No. 5-48488, for example. In this prior art, a plurality of electronic control devices mounted on a vehicle are distributed and a signal is transmitted together with electric power from the main control device to one or a plurality of load devices to reduce the wire harness. Yes. In an in-vehicle electronic control device, for example, an electronic control device for airbag control, an electronic control device is disposed along with an impact sensor on a door of a vehicle body, and power is supplied from the electronic control device that controls inflation of the airbag. It is necessary to transmit the signal in the reverse direction.
[0003]
FIG. 5 shows a schematic configuration of a current communication circuit using a power line as a basic technique of the present invention. The current communication circuit performs signal transmission in a direction opposite to the supply of electric power between a plurality of electronic control units (hereinafter, abbreviated as “ECU”) constituting the airbag system. The sub ECU 1 disposed in the vehicle door or the like is supplied with electric power from the main ECU 2 via the communication line 3 and the ground line 4 and sends a signal by current communication. In the sub ECU 1, a microcomputer 6, which is a microcomputer that operates with the power supply voltage Vcc stabilized by the 5 V regulator 5 and 5 V regulator 5 that stabilizes the voltage of the operating power supplied via the communication line 3 to 5 V. A communication circuit 7 that performs current communication on data transmitted from the microcomputer 6 to the main ECU 2, a capacitor 8 that removes noise superimposed on the communication line 3, and the like are included. The output of the 5V regulator 5 is used not only as the power supply voltage Vcc of the microcomputer 6, but also as an operation power supply voltage for an internal circuit in the sub ECU 1, for example, for an impact sensor. The ground voltage Vss of the microcomputer 6 is connected to the ground line 4.
[0004]
In the communication circuit 7, a current limiting resistor 9 and a protective resistor 10 are inserted in series between the emitter and the ground, and between the collector and the communication line 3, respectively, and the base of the NPN transistor 11 is provided. A PNP transistor 12 driven by a collector is included. An input resistor 13 is connected between the base of the NPN transistor 11 and the collector of the PNP transistor 12. An output resistor 14 is connected between the collector of the PNP transistor 12 and the ground. A bias resistor 15 is connected between the emitter and base of the PNP transistor 12, and a drive resistor 16 is connected between the base of the PNP transistor 12 and the output OUT terminal of the microcomputer 6.
[0005]
In the main ECU 2, a power supply 17 that supplies a DC voltage + B supplied from a battery, a generator, or the like stabilized to 10 V, for example, and a sensing resistor 18 connected between the output of the power supply 17 and the communication line 3 are provided. A / A having a function of amplifying the voltage across the sensing resistor 18 and an analog / digital conversion (hereinafter abbreviated as “A / D”) by inputting the output voltage of the differential amplifier 19. A microcomputer 20 having a D port, a comparator 21 and a reference voltage source 22 for monitoring the output of the differential amplifier 19 so as not to become abnormal values are included. The microcomputer 20 operates with a power supply voltage Vcc of 5V and a ground voltage Vss.
[0006]
In the sub ECU 1, the microcomputer 6 and the internal circuit are operated by the power supply voltage stabilized to 5 V from the 5 V regulator 5, and a signal is transmitted from the communication circuit 7 to the main ECU 2 through the communication line 3 as necessary. For signal transmission, the transistors 12 and 11 are driven at the output OUT terminal of the microcomputer 6 of the sub ECU 1. When the transistor 11 is turned on, the current supplied from the power source 17 of the main ECU 2 via the communication line 3 flows from the protective resistor 10 between the collector and the emitter of the transistor 11 and flows to the ground via the current limiting resistor 9. When the transistor 11 is cut off, this current is also cut off, and the current supplied via the communication line 3 is only the current supplied from the 5V regulator 5 to the microcomputer 6 and the internal circuit. The current limiting resistor 9 is, for example, 150Ω, and the protective resistor is 47Ω. The sensing resistor 18 is 10Ω. When the transistor 11 is turned on, a current of about 29 mA flows as a standard, and the potential difference between both ends of the sensing resistor 18 increases by 29 × 10 = 290 mV. This change in current is converted into a change in voltage by the differential amplifier 19 and amplified.
[0007]
[Problems to be solved by the invention]
In the prior art of Japanese Utility Model Laid-Open No. 5-48488, a signal is transmitted by changing a power supply voltage when power is supplied from a main control device to a load device. The power supply direction and the signal transmission direction are the same, and signal transmission in the opposite direction cannot be performed. Further, since the signal is transmitted by changing the power supply voltage, it is easily affected by noise and the like.
[0008]
With the configuration as shown in FIG. 5, signal transmission can be performed from the sub ECU 1 side to the main ECU 2 in the direction opposite to the current. The voltage change due to the current communication is about 0.3 V as described above, and is smaller than the forward voltage drop of the switching diode of Japanese Utility Model Laid-Open No. 5-48488. In addition, since data communication is performed with a constant increase / decrease in current, it is less susceptible to noise and the like.
[0009]
However, the configuration of FIG. 5 has a problem that the variation in communication current increases. Although the 5V regulator 5 of the sub ECU 1 is a semiconductor integrated circuit as a so-called three-terminal regulator and is standardized, the accuracy of the output voltage is ± 10%. The communication current is almost determined by this output and the variation with respect to the temperature change of the base-emitter voltage Vbe of the output transistor 11 for current communication and the accuracy ± 5% of the current limiting resistor 9, and TYP = 29 mA which is a standard value. In contrast, a variation of about ± 6 mA occurs. That is, a deviation of ± 20% may occur. When the variation is large in this way, it becomes difficult to set a threshold value for reading at the A / D port of the microcomputer 20 and the reference voltage source 22 for the comparator 21 to detect an abnormality in the communication line 3.
[0010]
Although the capacitor 8 is provided to suppress noise generated from the communication line 3, if the capacity of the capacitor 8 is increased, the communication waveform transmitted from the sub ECU 1 to the main ECU 2 via the communication line 3 is distorted, resulting in high speed. Therefore, the capacity of the capacitor 8 cannot be increased so much that sufficient noise removal cannot be performed.
[0011]
The communication circuit 7 includes a driving transistor 12 driven by the output of the microcomputer 6 and an output transistor 11 driven by the transistor 12 and connected to the communication line 3 to which the power supply voltage from the main ECU 2 is supplied. Including. For this reason, the input resistor 13, the output resistor 14 or the protective resistor 10 is required, and the number of components increases, resulting in an increase in cost.
[0012]
An object of the present invention is to provide a current communication circuit using a power line that can reduce the components of the communication circuit and improve the accuracy of the communication current.
[0021]
[Means for Solving the Problems]
The present invention is a circuit that supplies power from a power source side to a load side via a power line, and performs current communication from the load side to the power source side via the power line,
A constant voltage circuit that is provided on the load side and converts the voltage supplied from the power supply side to a constant voltage;
Provided with a current change circuit that is provided on the load side and performs current communication by changing the load current of the constant voltage circuit;
The current change circuit is configured to communicate a load current to be changed when communicating a signal whose load current change cycle is shorter than a predetermined cycle, and to transmit a signal whose load current change cycle is longer than a predetermined cycle. A current communication circuit using a power line, wherein the current communication circuit increases the load current .
[0022]
According to the present invention, when a signal whose load current change cycle is shorter than a predetermined cycle is communicated, the load current is changed so as to increase. Therefore, the amount of current change increases, and the waveform is rounded by a capacitor or the like. However, important and urgent signals can be reliably transmitted by increasing the load current.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a schematic electrical configuration of an embodiment of the present invention. This embodiment is based on the technique shown in FIG. 5 and is improved to solve the problem. The sub ECU 31 is connected to the main ECU 32 via a communication line 33 and a ground line 34. The one or more sub ECUs 31 and the main ECU 32 constitute an airbag system mounted on the automobile. The sub ECU 31 includes an impact sensor and its signal processing circuit as an internal circuit, and the power supply voltage is stabilized and supplied by the 5V regulator 35. The power supply voltage 5V is a standard power supply voltage for digital circuits, and the 5V regulator 35 is commercially available from various companies as a standard three-terminal IC regulator. The microcomputer 36 uses the output voltage of the 5V regulator 35 as the power supply voltage Vcc, and derives an output for communication from the output OUT terminal to the main ECU 32.
[0024]
In the present embodiment, the communication circuit 37 operates with a voltage of 5V on the output side of the 5V regulator 35. A noise reducing capacitor 38 is connected to the input side of the 5V regulator 35. On the output side of the 5V regulator 35, the output of the 5V regulator 35 is given to the collector of the output NPN transistor 41 via the current limiting resistor 39. The emitter of the transistor 41 is grounded, and the output voltage of the 5V regulator 35 is led to the base via the bias resistor 45. The base of the transistor 41 is further connected to the output OUT of the microcomputer 36 via the drive resistor 46. In this way, the communication circuit 37 is connected to the 5V power source of the sub ECU 31, the transistor 41 is driven by the microcomputer 36, and the current of the communication line 33 is controlled. The resistance value of the current limiting resistor 39 is 150Ω.
[0025]
The main ECU 32 includes a power supply 47 that stabilizes 10V supplied to the sub ECU 31, and a power supply current is supplied to the communication line 33 via a sensing resistor 48 for signal current detection. This power supply current corresponds to the current consumed by the internal circuit of the sub ECU 31 and the microcomputer 36 when the transistor 41 is cut off, and the current flowing between the current limiting resistor 39 and the collector and emitter of the transistor 41 when the transistor 41 is turned on. Join. The voltage change across the sensing resistor 48 is amplified by the differential amplifier 49 and applied to the A / D port of the microcomputer 50 included in the main ECU 32. The output voltage of the differential amplifier 49 is further compared with the output voltage of the reference voltage source 52 by the comparator 51. When an abnormality occurs such that the output voltage of the differential amplifier 49 exceeds the voltage of the reference voltage source 52, the input terminal of the microcomputer 50 An interrupt signal or the like is given to IN, and processing for voltage abnormality or the like is performed. The resistance value of the sensing resistor 48 is 10Ω.
[0026]
In this embodiment, the communication circuit 37 performs switching control so that the load current is increased by the output voltage of the 5V regulator 35. However, as a result of the experiment, the voltage fluctuation of the output voltage line of the 5V regulator is It is confirmed that the operation is suppressed by the feedback control and does not affect the operation in the sub ECU 31. As can be easily understood by comparing the communication circuit 7 of FIG. 5 and the communication circuit 37 of the present embodiment, the communication circuit 37 of the present embodiment operates with the output of the 5V regulator 35. Can be utilized, the configuration of the current communication circuit 37 is simplified, and the number of components used is reduced.
[0027]
FIG. 2 shows a schematic configuration of a sub ECU 55 according to another embodiment of the present invention. In this embodiment, parts corresponding to those in the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. A part of the communication circuit 57 is also built in the microcomputer 56. As a result, the communication circuit 57 includes only the current limiting resistors 59 and 60. The microcomputer 56 includes output MOS FETs 61 and 62, and the respective outputs OUT 1 and OUT 2 are connected to the output of the 5V regulator 35 through current limiting resistors 59 and 60. In the present embodiment, the output MOS FETs 61 and 62 are simultaneously controlled in the microcomputer 56, and the current is simultaneously supplied to the current limiting resistors 59 and 60 to perform constant current communication. In this embodiment, although the switching element is divided into the two output MOS FETs 61 and 62, more output MOS FETs can be used according to the current value. In the case of two divisions, the resistance value of the current limiting resistors 59 and 60 is 300Ω, which is twice that of the current limiting resistor 39 of FIG. Since the communication circuit 57 outside the microcomputer 56 includes only the current limiting resistors 59 and 60 as in the present embodiment, the parts used in the communication circuit 57 are reduced, and the current limiting resistors 59 and 60 Since the current limiting resistor can be manufactured with higher accuracy than when the current limiting resistor is formed in the microcomputer 56, the accuracy of the load current for performing current communication can be increased.
[0028]
FIG. 3 shows a configuration of a sub ECU 65 according to still another embodiment of the present invention. The microcomputer 66 of this embodiment includes three switching elements, and the communication circuit 67 includes three current limiting resistors 69, 70, and 71. The three current limiting resistors 69, 70, 71 are all 300Ω and are connected to the output of the 5V regulator 35 and can be changed in two stages of load current. The base communication is performed by simultaneously turning on / off the outputs OUT1a and OUT1b, and the extended communication is performed by further turning on / off the output OUT2. For this reason, it is expected that the change in the load current on the output side of the 5V regulator 35 will increase, and the output of the 5V regulator 35 is supplied to the internal circuit of the sub ECU 65 and the microcomputer 66 via the rectifier diode 72. Since this supply voltage decreases from the output voltage of the 5V regulator 35 by the forward voltage drop of the rectifier diode 72, the reference voltage of the 5V regulator 35 is increased by the voltage adjustment diode 73. The forward voltage drop between the rectifier diode 72 and the voltage adjustment diode 73 is, for example, about 0.6 to 0.7 V for a silicon diode, and the output voltage of the 5V regulator 35 is increased by the voltage drop due to the rectifier diode 72. Thus, 5V can be supplied to the internal circuit and the microcomputer 66. A smoothing capacitor 74 is also provided for smoothing the supply voltage.
[0029]
FIG. 4 shows a change in communication current when performing current communication in the embodiment of FIG. Since the extended communication is performed by operating OUT1a, 1b and OUT2 in parallel, the current value becomes large, and even a signal having a shorter cycle than the communication by the base OUT1a, 1b can be reliably transmitted. Further, since the levels of communication currents are different, two systems of communication can be divided and communicated by changing the threshold value of the input voltage at the A / D port of the microcomputer 50 on the main ECU 32 side in FIG. In this embodiment, if the number of current limiting resistors 69, 70, 71 included in the communication circuit 67 is increased and the number of switching circuits in the microcomputer 66 is increased, more types of current communication can be performed simultaneously. Become.
[0030]
In each embodiment described above, the configuration on the main ECU 32 side is common. The A / D port of the microcomputer 50 can perform A / D every 7 μsec, for example. Therefore, the microcomputer 50 can efficiently confirm the input of the A / D port by creating an operation program so as to check the input of the A / D port, for example, every 20 μsec. Since low-level base communication as shown in FIG. 4 is performed with a period of about several tens of milliseconds, for example, if the A / D port is checked every 20 μsec, one signal can be checked many times. . For extended communication in a short time, for example, by setting a period of several tens of microseconds, it is possible to perform detection once or twice in an A / D port input confirmation every 20 microseconds. Can communicate.
[0031]
In addition, although each embodiment is also configured to constitute an airbag system mounted on an automobile, generally, a plurality of electronic control units are arranged in a distributed manner, and the satellite 1 is changed from the main electronic control unit to 1 or The present invention can also be applied to applications in which power is supplied to a plurality of electronic control units and signals are transmitted in the reverse direction using the power lines.
[0032]
【The invention's effect】
As described above, according to the present invention, current communication is performed by changing the load current of the constant voltage circuit that makes the power supply voltage supplied from the power supply side to the load side constant, thereby reducing the components of the communication circuit. Can be simplified.
[0036]
In addition , since a signal having a short change cycle has a large current change value, signal transmission can be reliably performed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic electrical configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing a schematic electrical configuration of a sub ECU 55 according to another embodiment of the present invention.
FIG. 3 is a block diagram showing a schematic electrical configuration of a sub ECU 65 according to still another embodiment of the present invention.
4 is a waveform diagram of the output and communication current of the embodiment of FIG.
FIG. 5 is a schematic block diagram showing a configuration as a basis of the present invention.
[Explanation of symbols]
31, 55, 65 Sub ECU
32 Main ECU
33 communication line 34 ground line 35 5V regulator 36, 56, 66 microcomputer 37, 57, 67 communication circuit 38 capacitor 39, 59, 60, 69, 70, 71 current limiting resistor 41 transistor 47 power supply 48 sensing resistor 49 differential amplifier 51 Comparator 61, 62 Output MOS FET
72 Rectifier diode 73 Voltage adjustment diode 74 Smoothing capacitor

Claims (1)

A circuit that supplies power from the power source side to the load side via the power line and performs current communication from the load side to the power source side via the power line,
A constant voltage circuit that is provided on the load side and converts the voltage supplied from the power supply side to a constant voltage;
Provided with a current changing circuit that is provided on the load side and performs load communication by changing the load current of the constant voltage circuit;
The current change circuit is used to communicate a load current to be changed when communicating a signal whose load current change cycle is shorter than a predetermined cycle. A current communication circuit using a power line, characterized by increasing the load current .

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