JP3350464B2 - Noise protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise protection circuit for protecting a power supply line from external noise that enters the power supply line when the power supply line is used as a communication line in an electronic device such as a vehicle.

[0002]

2. Description of the Related Art Conventionally, in an air bag system mounted on a vehicle, a main control device and a sub control device are arranged at different positions of a vehicle, and wiring for supplying power from the main control device to the sub control device is provided. The information is transmitted from the sub control device to the main control device. Such prior art is disclosed, for example, in Japanese Patent Application Laid-Open No. 9-295551.

[0003] In an airbag system, a plurality of electronic control units (hereinafter abbreviated as "ECUs") are used.
Communication is performed by superimposing a signal on a power supply line between a main module which is a main ECU and a side module which is a sub ECU.

FIG. 2 shows an electrical configuration for power supply and communication to the side module 1 in a conventional airbag system. The side module 1 includes a microcomputer (hereinafter abbreviated as “microcomputer”) 2 and a G sensor 3 for detecting impact acceleration, and a voltage regulated to 5V supplied from a 5V power supply circuit 4. Work by. The microcomputer 2 in the side module 1 uses the output transistor 5 to change the supplied power supply current and communicate information to the main module that supplies power. That is, when the output transistor 5 is turned on, the current supplied to the side module 1 changes to a state equivalent to the state where the resistors 6 and 7 are added as loads. When the output transistor 5 is turned off, the resistors 6,
The current flowing through 7 is almost zero. Therefore, if the microcomputer 2 intermittently controls the switching of the output transistor 5, the intermittent change in the power supply current causes the side module 1 side to supply the operating power to the side module 1 via the power supply line 10. Side can transmit information and data.

The power supply line 10 has diodes 11, 1
2, the power stored in the battery 15 is supplied from the Acc line 13 and the IG line 14. A
The cc line 13 is operated by a key switch of the vehicle,
When the accessory switch is turned on, the battery 15
Connected to. When the key switch turns on the ignition switch, the IG line 14
Connected to.

FIG. 3 shows another embodiment for transmitting information via the power supply line 10. In this embodiment, portions corresponding to those in the embodiment of FIG. 2 are denoted by the same reference numerals, and redundant description will be omitted. The DC-DC converter 16 is used for converting the voltage of the power supply line 10 to be higher than the output voltage of the battery 15. By making the voltage of the power supply line 10 higher than the output voltage of the battery 15 of about 13 V, a margin for voltage fluctuation of the power supply line 10 can be increased, and the influence of a signal superimposed on the power supply line 10 can be reduced.

[0007]

In the side module 1 as shown in FIGS. 2 and 3, the power supply line 10 is used for both power supply and signal transmission. In particular, in the case of in-vehicle electronic devices, it is important to reduce the number of signal lines constituting a wire harness in order to reduce the weight. This,
The power supply line 10 also serves as a signal transmission line. However, the battery 15 of the vehicle is a power source for supplying power to various parts of the vehicle and is connected to many wirings, so that it is easy to pick up ignition noise and the like generated by the own vehicle and other vehicles, and external noise is easily mixed. . The side module 1 prevents the microcomputer 2 from running out of control by performing a reset operation when the high-voltage external noise is mixed into the power supply line 10 to avoid malfunction due to noise. Reset of the microcomputer 2 of the side module 1
This is performed by the power-on reset function of the V power supply circuit 4. When the microcomputer 2 enters the reset state, the preset program is restarted from the initial setting.

Once the program is started, if a reset is applied by the 5V power supply circuit 4 due to a high-voltage external noise, the operation of the side module 1 is stopped halfway, and the operation from the initial setting is performed again. Be started.
On the main module side, the side module 1 changes to the reset state at an unexpected timing, which may hinder reception of signals via the power supply line 10.
Even if the side module is reset, in order to continue signal transmission smoothly, it is necessary to set in advance a procedure for smooth signal transmission processing when restarting from the reset state by a program. is there. In addition, since it takes time from the reset state of the side module 1 to the restart of the normal operation, a predetermined function cannot be performed during that time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise protection circuit which does not easily shift to a reset state even when high-voltage external noise enters a power supply line.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a first module of an airbag system for performing communication with a second module of an airbag system by superimposing a signal on a power supply line supplied with power from a power supply. A power supply circuit having a reset function for resetting the microcomputer of the first module when a high-voltage external noise enters, having a noise absorption voltage characteristic that is higher than the power supply voltage, In the noise protection circuit of the airbag system, provided with a noise reduction element for reducing high-voltage external noise on the power supply line side, a constant voltage circuit is connected between the noise reduction element and the power supply circuit, The signal is superimposed on a power supply line between the constant voltage circuit and the power supply circuit to perform communication, and power is supplied to the power supply circuit. Is a noise protection circuit to be.

According to the present invention, the first module of the airbag system communicates with the second module by superimposing a signal on a power supply line supplied with power from a power supply.
The electronic device is provided with a power supply circuit that shifts to a reset state for resetting the microcomputer of the first module when high-voltage external noise enters from the power supply line.
The power supply line has a noise absorption voltage characteristic that is higher than the power supply voltage and is provided with a noise reduction element that reduces external noise of a high voltage equal to or higher than the noise absorption voltage. It is possible to prevent the power supply circuit from transitioning to the reset state with the high-voltage external noise in the range. Since the power supply circuit shifts to the reset state with respect to high-voltage external noise that cannot be sufficiently reduced even by the noise reduction element, it is possible to reliably protect the first module from external noise.

[0012]

The supply of power to the first module and the communication of signals from the first module to the second module are performed using the output line of the constant voltage circuit connected to the power supply line. Even if external noise is superimposed on the power supply line on the input side of the constant voltage circuit, the voltage change on the output side can be reduced by the constant voltage circuit, and a high voltage such that the power supply circuit of the first module causes a reset operation. The possibility that external noise leaks to the output line of the constant voltage circuit can be extremely reduced.

In the present invention, the output line of the constant voltage circuit is provided with an overvoltage protection element for protecting a power supply circuit provided in the first module from an overvoltage caused by external noise.

According to the present invention, the output line of the constant voltage circuit is provided with an overvoltage protection element for protecting the power supply circuit provided in the first module of the airbag system from overvoltage caused by external noise. Thus, even if external noise is superimposed on the output line of the constant voltage circuit, the influence of the noise can be eliminated by the overvoltage protection element, and the power supply circuit can be protected from overvoltage.

[0016]

FIG. 1 shows a schematic electrical configuration of an embodiment of the present invention. In this embodiment, a side module 21 constituting an airbag system mounted on a vehicle includes a microcomputer 22 and a G sensor 23 therein, and is a 5V power supply circuit 2 which is integrated into an IC and has a reset function.
While operating with the power supply voltage of 5 V output from
A series circuit of an N-type output transistor 25 and resistors 26 and 27 is connected together with a Zener diode 28 to perform communication based on a change in current based on power supplied from a power supply line 30. However, in this embodiment, the power supply line 3
Between 0 and the side module 21, a circuit to be described later is provided.

The power supply line 30 includes diodes 31 and 3
Acc line 33 and IG line 34 into which 2 is inserted
Is supplied from the battery 35 via the. Battery 35 serving as a power supply has a power supply voltage of, for example, 12 to 13V. 5V power supply circuit 24 in side module 21
Converts the power supply voltage supplied from the power supply line 30 to 5 V, stabilizes the power supply voltage, and supplies it to each unit in the side module 21. When the voltage of the power supply line 30 decreases, the voltage between the input and output of the 5V power supply circuit 24 decreases, the operation margin decreases, it becomes difficult to make the output voltage constant, and malfunctions due to voltage fluctuations easily occur. When noise higher in voltage than a predetermined power supply voltage supplied from the power supply line 30 enters, the 5V power supply circuit 24 generates a reset signal for controlling the microcomputer 22 to a reset state.

In an airbag system for a vehicle or the like, external noise is most likely to invade from the A from the battery 35.
Since they are the cc line 33 and the IG line 34, a Zener diode 37 as a noise reduction element is commonly connected to the cathodes of the diodes 31 and 32. The Zener voltage of Zener diode 37 is set to, for example, 35V. When a high-voltage external noise exceeding a zener voltage of 35 V enters the Acc line 33 or the IG line 34, the Zener diode 37 has a low impedance with respect to a noise portion exceeding the zener voltage, and reduces high-voltage noise. Perform the absorbing operation. That is, in this case, it has a noise absorption voltage characteristic of 35V.

In this embodiment, the Zener diode 37
The voltage from the battery 35 whose high-voltage noise has been reduced is boosted by the DC-DC converter 36 and is converted to a constant voltage by the constant voltage circuit 40. The power for the operation of the side module 21 and the power for communication Supply.

The constant voltage circuit 40 includes an NPN type bipolar output transistor 41, a Zener diode 42,
And a resistor 43. The collector of the output transistor 41 and one end of the resistor 43 are connected to the output side of the DC-DC converter 36. The other end of the resistor 43 is connected to the base of the output transistor 41. The base of the output transistor 41 is also connected to the cathode side of the Zener diode 42. The anode side of the Zener diode 42 is grounded. The emitter of the output transistor 41 is connected to the output line 44. The output line 44 is a communication IC 45
Is connected to the side module 21 via the.

The base of the output transistor 41 is maintained at a constant voltage of 13 V, which is the Zener voltage of the Zener diode 42. Accordingly, the output of the emitter of the output transistor 41 is lower than the base voltage by about 0.7 V which is the forward junction voltage between the base and the emitter, ie, 12.3 V
Voltage is output. Since the emitter voltage of the output transistor 41 is determined by the base voltage, the influence of the fluctuation of the input voltage on the collector side hardly appears.

The communication IC 45 detects a change in current on the output line 44 of the constant voltage circuit 40 and separates it as a communication output to a microcomputer included in a main module or the like. Communication to the communication IC 45 is performed by ON / OFF control of the NPN output transistor 25 of the side module 21.
The voltage fluctuation caused by the current change of the output line 44 is 5 V
A power supply voltage absorbed by the power supply circuit 24 and stabilized at 5 V is supplied to the side module 21. Since the Zener diode 28 is also connected as an overvoltage protection element in the side module 21 connected to the output line 44, external noise of a high voltage exceeding, for example, 30 V, which is the Zener voltage of the Zener diode 28, is generated by the Zener diode 28. As a result, the 5V power supply circuit 24 is not affected by the overvoltage. The constant voltage characteristic of the Zener diode 28 can eliminate the possibility that the 5V power supply circuit 24 will shift to the reset state due to high-voltage external noise or the like.

In the present embodiment, a Zener diode 37 for reducing high-voltage external noise that enters the power supply line 30 from the battery 35 shown in FIG. 3 and a high-voltage noise by inserting a constant voltage circuit 40 shown in FIG. In addition, a countermeasure against reset due to an overvoltage by inserting the Zener diode 28 into the side module 21 shown in FIG. In other words, the Zener diodes 28 and 37 and the constant voltage circuit 40 reduce the external noise, respectively, but when all of them are combined, the protection against the external noise can be surely performed. In addition, Zener diode 2
Instead of 8, 37, a surge absorber element can be used. However, since external noise is likely to enter on the battery 35 side, the reset operation of the 5V power supply circuit 24 due to high-voltage external noise can be prevented even with a configuration in which only the zener diode 37 is provided. It is. Further, if the constant voltage circuit 40 is provided, the influence of external noise can be further reduced. The constant voltage circuit 40 can contribute not only to protection from external noise but also to stable use of power supply and current communication via the output line 44. In addition, the 5V power supply circuit 24 resets the microcomputer 22 with respect to strong noise that remains even if absorbed, thereby preventing malfunction.

[0024]

[0025]

As described above, according to the present invention, a power supply line to which power is supplied from a power supply has a noise absorption voltage characteristic of a voltage higher than the power supply voltage, and has a high voltage higher than the noise absorption voltage. A power supply that is connected to a power supply line to generate power for operating the first module of the airbag system because it has a noise reduction element that absorbs external noise, and that enters a reset state when high-voltage external noise enters the power supply line The circuit can be protected from being easily shifted to the reset state. As the noise reduction element, for example, a Zener diode, a surge absorber, or the like can be used, and communication using a highly reliable power supply line can be performed with a simple configuration.

Also, the power supplied from the power supply is supplied to the first module via the constant voltage circuit, and the output line of the constant voltage circuit is used for both power supply and communication with the second module. Even if external noise enters the power line that supplies power from the first module, the effect of the external noise can be reduced by the constant voltage circuit, and the power supply circuit of the first module can be protected from shifting to the reset state.

According to the present invention, the first module of the airbag system is supplied with electric power, and the first module is connected to the output line of the constant voltage circuit used for communication between the first module and the second module. The power supply circuit has an overvoltage protection element that protects against overvoltage due to external noise so that it is not reset by external noise of high voltage.For example, using a Zener diode as an overvoltage protection element,
The power supply circuit can be protected from being reset by an overvoltage due to external noise.

[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 for communication using a conventional power supply line.

FIG. 3 is a block diagram showing another electrical configuration for communication using a conventional power supply line.

[Explanation of symbols]

 Reference Signs List 21 side module 22 microcomputer 23 G sensor 24 5V power supply circuit 25 output transistor 28, 37, 42 zener diode 30 power supply line 35 battery 36 DC-DC converter 40 constant voltage circuit 44 output line 45 communication IC

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-8791 (JP, A) JP-A-10-224984 (JP, A) JP-A-9-295551 (JP, A) JP-A-10-1998 35407 (JP, A) JP-A-63-135185 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J 1/00 H02H 3/22 B60R 21/32 B60R 16/00- 16/08

Claims (2)

(57) [Claims] 1. A high-voltage external noise is generated in a first module of an airbag system that performs communication with a second module of the airbag system by superimposing a signal on a power supply line supplied with power from a power supply. Provide a power supply circuit with a reset function that resets the microcomputer of the first module when invading, has a noise absorption voltage characteristic that is higher than the power supply voltage, and reduces external noise of high voltage higher than the noise absorption voltage A noise protection circuit for an airbag system, comprising a noise reduction element to be provided on the power supply line side, wherein a constant voltage circuit is connected between the noise reduction element and the power supply circuit, and the constant voltage circuit, the power supply circuit, A noise protection circuit characterized in that the signal is superimposed on a power supply line between them to perform communication, and power is supplied to the power supply circuit. 2. The noise protection circuit according to claim 1, wherein an output line of the constant voltage circuit includes an overvoltage protection element for protecting a power supply circuit provided in the first module from an overvoltage caused by external noise. .