JPH09327133A - Power-supply circuit mounted on vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the malfunction of a microcomputer or the like without causing the destruction or the like of a current-limiting resistance for surge absorption and to miniaturize a circuit. SOLUTION: A power-supply circuit is provided with a surge absorption means 4 which is provided with a current-limiting resistor 30 one end of which is connected to a power-supply line 2 connected to a battery 15 mounted on a vehicle and the other end of which is connected to constant-voltage supply means 5, 6 which supply prescribed constant voltages to a microcomputer 46 and the like, with a first bidirectional surge absorption element 31 which is inserted in parallel with the resistance and with a second surge absorption element 32 which is inserted across the other end of the current-limiting resistor 30 and a ground. A voltage across both ends of the current-limiting resistor 30 is suppressed by the first surge absorption element 31 so as to reduce its resistance value and its rating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle-mounted power supply circuit.

[0002]

In a vehicle-mounted power supply circuit which receives a power supply voltage from a vehicle-mounted battery and supplies a predetermined constant voltage to a low voltage load such as a microcomputer,
If the power supply terminal of the vehicle-mounted battery comes off or the alternator fails for some reason while traveling, surge may enter from the vehicle-mounted battery and damage the vehicle-mounted power supply circuit. In particular, in a large vehicle such as a bus equipped with a 24V battery and using a large amount of electric power in the passenger compartment, an extremely large surge occurs. As means for absorbing such a large surge, as shown in FIG. 3, a current limiting resistor 100 having one end connected to a vehicle-mounted battery and the other end connected to a constant voltage circuit, and the other end of the current limiting resistor 100. Surge absorbing element 200 inserted between the ground and
It is conceivable to provide a surge absorption circuit consisting of
In this case, from the viewpoint of improving the surge withstand voltage, it is desired to increase the resistance value of the current limiting resistor 100. However, when the resistance value of the current limiting resistor 100 is increased, the voltage drop in the current limiting resistor 100 is large. Therefore, the constant voltage circuit may not be able to maintain a predetermined constant voltage depending on the state of the battery voltage, and a microcomputer or the like supplied with power from the constant voltage circuit may malfunction. On the contrary, if the resistance value of the current limiting resistor 100 is reduced, it is possible to prevent the malfunction of the microcomputer or the like, but the current limiting resistor 100 is destroyed when a large surge occurs. Therefore, in such a vehicle-mounted power supply circuit, it is desired to prevent malfunction of a microcomputer or the like and prevent the current limiting resistance from being destroyed by a large surge. . Further, if a resistor having a large rating is used as the current limiting resistor 100, the current limiting resistor becomes large and the size of the vehicle-mounted power supply circuit becomes large. Therefore, it is desirable to use a resistor having a small rating. Be done.

Further, in such a vehicle-mounted power supply circuit, a power supply backup means may be provided for data protection of a microcomputer, but in such a case, reduction of circuit components and simplification of the power supply circuit. From the viewpoint of achieving the above, it is desired that the backup power supply and the normal power supply share the surge absorbing circuit and the constant voltage circuit.

The present invention has been made based on the above viewpoint, and an object thereof is to make it possible to reduce the resistance value and rating of a current limiting resistor for absorbing surge, and to cause destruction of the current limiting resistor. Another object of the present invention is to provide a vehicle-mounted power supply circuit capable of preventing malfunction of a microcomputer or the like and downsizing the circuit.

Another object of the present invention is to mount a surge absorbing circuit and a constant voltage circuit between a backup power source and a normal power source to reduce the number of parts and simplify the circuit structure. It is to provide a power supply circuit.

[0006]

According to the present invention, a power supply line connected to an on-vehicle battery via at least one operation switch, a current limiting resistor having one end connected to the power supply line, and the current limiting resistor. Surge absorbing means having a bidirectional first surge absorbing element inserted in parallel with the current limiting resistor and a second surge absorbing element inserted between the other end of the current limiting resistor and the ground; The above-described object is achieved by a vehicle-mounted power supply circuit having a constant voltage supply unit that is connected to the other end of the current limiting resistor of the absorption unit and that supplies a predetermined constant voltage to a low voltage load including a microcomputer. According to such a configuration, the voltage across the current limiting resistor is suppressed by the first surge absorbing element, and the resistance value of the current limiting resistor can be reduced,
Further, the current flowing through the current limiting resistor is small, that is, the power consumption in the current limiting resistor is small, and the rating can be reduced.

Further, in the present invention, a power supply line connected to the on-vehicle battery via at least one operation switch, a backup power supply line connected to the on-vehicle battery via a backup switch, and one end of the power supply Between the current limiting resistor connected to the line and the backup power supply line, the bidirectional first surge absorbing element inserted in parallel with the current limiting resistor, and the other end of the current limiting resistor and the ground. Second inserted in
The surge absorbing means having the surge absorbing element and the method for going from the vehicle-mounted battery to the surge absorbing means are inserted in the power supply line in a forward direction, and the battery voltage from the backup power supply line to the power supply line is inserted. A constant voltage supply means for supplying a predetermined constant voltage to a low voltage load including a microcomputer, which is connected to the other end of the current limiting resistor of the surge absorbing means, At least one constant voltage supply terminal for supplying the predetermined constant voltage in response to turning on of a switch, and a backup supply terminal for supplying the predetermined constant voltage in response to turning on of the operation switch and / or the backup switch. The above object is achieved by a vehicle-mounted power supply circuit having the constant voltage supply means having With such a configuration, the resistance value and rating of the current limiting resistor can be reduced as described above, and a surge is generated between the backup power supply provided by the backup power supply line and the normal power supply provided by the power supply line. The absorption circuit and the constant voltage circuit can be shared.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an example of an embodiment of the present invention, in which 1 is a vehicle-mounted power supply circuit, a power supply line 2, a backup power supply line 3, a surge absorption circuit 4, and a 15V constant voltage. It has a voltage circuit 5 and a 5V constant voltage circuit 6.

The power supply line 2 is connected to the first, second and third power supply input terminals 9, 10, 11 via a reverse connection preventing diode 7 and a diode OR circuit 8. The first to third power input terminals 9 to 11 are adapted to be connected to the on-vehicle battery 15 via the first, second and third operation switches 12, 13 and 14, respectively, and at least the first to third The battery voltage is supplied to the power supply line 2 by closing any of the third operation switches 12 to 14. First to third power input terminals 9
10 to 10 are also connected to the first, second and third switch information output terminals 16, 17 and 18, and the operation switches 1 to 1 are connected from the first to third switch information output terminals 16 to 18.
2-14 on / off information is provided. The power supply line 2 is also connected to the surge absorbing circuit 4 via the blocking diode 19 and supplies the battery voltage to the base of the first switching transistor 20 and the voltage conversion circuit 21. The blocking diode 19 is inserted in the power supply line 2 so that the direction from the vehicle-mounted battery 15 to the surge absorbing circuit 4 is the forward direction. The first switching transistor 20 has a base connected to the power supply line 2 via a resistor 22, an emitter grounded and a resistor 23 connected to the base, and a collector connected to a second switching transistor 24 described later. It is connected to the base of the third switching transistor 25, and is turned on when the battery voltage is supplied to the power supply line 2 by closing at least one of the first to third operation switches 12 to 13. The second and third switching transistors 24 and 25 are turned on. The voltage conversion circuit 21 supplies the battery voltage supplied to the power supply line 2 to the battery voltage information output terminal 26 as battery voltage information.

The backup power supply line 3 is connected to the backup power supply input terminal 27 and also connected to the surge absorbing circuit 4 via a reverse connection prevention diode 28. The backup power supply input terminal 27 is connected to the on-vehicle battery 15 via the backup switch 29, and the battery voltage is supplied to the backup power supply line 3 by closing the backup switch 29. The backup switch 29 is set in advance to a closed state or an open state depending on the necessity / unnecessity of backing up the power source.

One end of the surge absorbing circuit 4 is the power supply line 2
And a current limiting resistor 30 connected to the backup power supply line 3, a bidirectional first surge absorbing element 31 inserted in parallel with the current limiting resistor 30, and a current limiting resistor 3
It has a second surge absorbing element 32 inserted between the other end of 0 and the ground. In this example, the first surge absorbing element 31 is a varistor, and the second surge absorbing element 32 is composed of two Zener diodes connected in series from the viewpoint of improving the response to a surge. Current limiting resistor 3
Since the first surge absorbing element 31 is inserted in parallel with 0, the voltage across the current limiting resistor 30 can be suppressed by the first surge absorbing element 31, and the resistance value of the current limiting resistor 30 can be reduced. In addition, the current flowing through the current limiting resistor 30 is small, that is, the power consumption in the current limiting resistor 30 is small, and the rating can be reduced.

FIGS. 2A and 2B show both ends of the current limiting resistance when the same surge is applied when the first surge absorbing element is not inserted in parallel with the current limiting resistance and when it is inserted. In the experimental example of measuring the voltage, (a) is the first
2B shows the case where the surge absorbing element is not inserted, and (b) shows the case where the first surge absorbing element is inserted in parallel as shown in FIG. 2 (a) and (b)
As is clear from the above, the peak voltage becomes −120 V when the first surge absorbing element is not inserted in parallel, whereas it becomes −80 V when the first surge absorbing element is inserted in parallel, and the voltage across the current limiting resistor becomes You can see that it can be suppressed.

The 15V constant voltage circuit 5 is connected to the other end of the current limiting resistor 30 of the surge absorbing circuit 4 via a noise removing capacitor circuit 33 inserted between the 15V constant voltage circuit and the ground. The output side of the 15V constant voltage circuit 5 has a noise removing capacitor circuit 34 inserted between it and the ground.
Is connected to the 5V constant voltage circuit 6 via
It is connected to the emitter of the second switching transistor 24. The collector of the second switching transistor 24 is connected to the first constant voltage supply terminal 35, the base is connected to the emitter via the resistor 36, and the first switching transistor 20 is connected via the resistor 37 and the diode 38. Connected to the collector.
With this configuration, when the first switching transistor 20 is turned on and the second switching transistor 24 is turned on, the 15V constant voltage of the 15V constant voltage circuit 5 is supplied to the first constant voltage supply terminal 35. It is like this.

The 5V constant voltage circuit 6 is connected to the 15V constant voltage circuit 5 on the input side via a noise removing capacitor 39 inserted between the input side and the ground, and on the output side via a noise removing capacitor circuit 40. It is connected to the backup power supply terminal 41 and also to the emitter of the third switching transistor 25. The collector of the third switching transistor 25 is connected to the second constant voltage supply terminal 42, the base is connected to the emitter via the resistor 42, and the first switching transistor 20 is connected via the resistor 43 and the diode 44. Connected to the collector. With such a configuration, the 5V constant voltage is supplied to the backup power supply terminal 41 by closing the backup switch 29 and / or at least one of the operation switches 12 to 13, and the first switching is performed. When the transistor 20 is turned on and the third switching transistor 25 is turned on, the 5V constant voltage of the 5V constant voltage circuit 6 is supplied to the second constant voltage supply terminal 42.

The first constant voltage supply terminal 35 for supplying a constant voltage of 15V is used as a power source for a 15V system load 45 such as an operational amplifier, and the backup power supply terminal 41 for supplying a constant voltage of 5V is used as a power source for the microcomputer 46. The second constant voltage supply terminal 42 which is used and supplies a constant voltage of 5V is used as a power source of a 5V system load 47 such as a logic circuit. The switch information output terminals 16 to 18 are connected to the microcomputer 46 via the interfaces 48, 49 and 50 so that the ON / OFF information of each operation switch 12 to 14 is given to the microcomputer 46. The microcomputer 46 executes a predetermined control operation according to the switch information. The battery voltage information output terminal 26 is connected to the microcomputer 46, and the battery voltage information from the voltage conversion circuit 21 is sent to the microcomputer 46 as information for determining whether or not all the operation switches 12 to 14 are turned off. To be given. As a result, the microcomputer 46 determines whether all the operation switches 12 to 14 are turned off based on the battery voltage information of the voltage conversion circuit 21, in other words, whether the supply of the battery voltage to the power supply line 2 is cut off. By determining whether or not all the operation switches 12 to 14 are off, it is possible to quickly shift to the standby mode, and all the operation switches 12 to 14 caused by delay elements such as the capacitor circuits 33 and 34. The malfunction of the microcomputer 46 when the switch is turned off is prevented.

In such a configuration, if the backup switch 29 is closed, even if all the first to third operation switches 12 to 13 are off, the backup power supply line 3 to the surge absorbing circuit 4, A 5V constant voltage is supplied to the backup power supply terminal 41 through the 15V constant voltage circuit 5 and the 5V constant voltage circuit 6. The battery voltage of the backup power supply line 3 is not supplied to the power supply line 2 by the blocking diode 19, so that the first switching transistor 20 is turned off and the constant voltage is supplied to the first and second constant voltage supply terminals 35 and 42. Not done. When at least one of the first to third operation switches 12 to 13 is turned on in this state, the battery voltage is supplied to the power supply line 2 via the diode OR circuit 8 and the first switching transistor 20 is turned on. The second and third switching transistors 24 and 25 are turned on to turn on the first constant voltage supply terminal 35 and the second constant voltage supply terminal 4.
A constant voltage of 15V and a constant voltage of 5V are also supplied to 2, respectively. On the other hand, if the backup switch 29 is opened, the battery voltage is supplied to the power supply line 2 by turning on at least one of the first to third operation switches 12 to 14, and the blocking diode 19, the surge absorbing circuit 4, 15V. The constant voltage is supplied to the first constant voltage supply terminal 35, the second constant voltage supply terminal 42 and the backup power supply terminal 41 through the 5V constant voltage circuits 5 and 6, respectively, as described above. As described above, since the surge absorbing circuit 4, the constant voltage circuits 5 and 6 are shared by the backup power source and the normal power source, the number of parts can be reduced and the circuit configuration can be simplified.

Further, as described above, the voltage across the current limiting resistor 30 is suppressed by the first surge absorbing element 31, the resistance value of the current limiting resistor 30 can be reduced, and the current limiting resistor 30 can be reduced. The current flowing through the device is small, that is, the power consumption of the current limiting resistor 30 is small, and the rating can be reduced. Therefore, the current limiting resistor 3
The voltage drop at 0 can be made small, and even if the power supply voltage of the on-vehicle battery 15 drops in winter, etc.
The V constant voltage circuit 5 and the 5V constant voltage circuit 6 can maintain a predetermined constant voltage, and it is possible to prevent malfunction of the microcomputer 46 and the like that are supplied with power from the constant voltage circuits 5 and 6. Further, even if a large surge occurs due to the disconnection of the power supply terminal of the on-vehicle battery 15, the voltage across the current limiting resistor 31 is suppressed by the first surge absorbing element 31, so that the current limiting resistor 30 is destroyed. There is no such thing. Further, since the rating of the current limiting resistor 30 can be reduced, the current limiting resistor 30 can be downsized, and hence the vehicle-mounted power supply circuit can be downsized. In addition, although such a vehicle-mounted power supply circuit tends to spread positive and negative surges caused by on / off of the peripheral inductive load, the first surge absorbing element 31 inserted in parallel with the current limiting resistor 30.
Has a bidirectionality, it effectively functions not only for positive surges but also for negative surges.

In the example described above, two Zener diodes connected in series are used as the second surge absorbing element 32 of the surge absorbing circuit 4, but a varistor can be used like the first surge absorbing element 31, According to this, the number of types of components can be reduced.

[0019]

As described above, according to the present invention, one end is connected to the power supply line connected to the vehicle battery,
A current limiting resistor, the other end of which is connected to a constant voltage supply means for supplying a predetermined constant voltage to a low voltage load including a microcomputer, and a bidirectional first surge absorber inserted in parallel with the current limiting resistor. Since the surge absorbing means having the element and the second surge absorbing element inserted between the other end of the current limiting resistor and the ground is provided, both ends of the current limiting resistor are provided by the first surge absorbing element. Is suppressed, the resistance value of the current limiting resistor can be reduced, and the current flowing through the current limiting resistor is small, that is, the power consumption in the current limiting resistor is small, and the rating can be reduced. Therefore, the current limiting resistor is not destroyed by a large surge, and the predetermined constant voltage can be maintained even when the power supply voltage of the vehicle-mounted battery drops in winter, etc., and the malfunction of the microcomputer etc. can be prevented. Further, it is possible to reduce the size of the current limiting resistor and thus the size of the vehicle-mounted power supply circuit. Furthermore,
Since the first surge absorbing element has bidirectionality, it functions effectively not only for positive surges but also for negative surges, and positive and negative surges caused by on / off of inductive loads in the surroundings. Can be absorbed.

Further, since the surge absorbing means and the constant voltage supplying means are shared with the backup power source provided by the backup power source line and the normal power source provided by the power source line, the number of parts is reduced and the circuit configuration is reduced. It can be simplified.

In the surge absorbing means, the first surge absorbing element may be a varistor and the second surge absorbing element may be two Zener diodes connected in series, whereby improvement in response to surge can be expected. Further, by using both the first and second surge absorbing elements as varistors, the types of constituent parts can be further reduced.

Further, by providing a voltage conversion circuit for inputting the battery voltage supplied to the power supply line and giving it to the microcomputer as battery voltage information, the microcomputer can promptly operate when the power supply to the power supply line is cut off. In addition, it is possible to shift to the standby mode, and it is possible to prevent the malfunction of the microcomputer due to the delay element in the circuit when the power supply to the power supply line is cut off.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of an embodiment of the present invention.

FIG. 2 is an experimental example in which the voltage across the current limiting resistor is measured when the same surge is applied with and without the first surge absorbing element inserted in parallel with the current limiting resistor. , (A) shows the case where the first surge absorbing element is not inserted in the current limiting resistor, and (b) shows the case where the first surge absorbing element is inserted in parallel in the current limiting resistor as shown in FIG. Indicate the case.

FIG. 3 is an example of a surge absorbing circuit of a vehicle-mounted power supply circuit, which is considered from a known technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 In-vehicle power supply circuit 2 Power supply line 3 Backup power supply line 4 Surge absorption circuit 5,6 Constant voltage circuit 12-14 First to fourth actuation switch 15 In-vehicle battery 19 Blocking diode 20 First switching transistor 21 Voltage conversion circuit 24 Second Switching Transistor 25 Third Switching Transistor 29 Backup Switch 30 Current Limiting Resistor 31 First Surge Absorbing Element 32 Second Surge Absorbing Element 35 First Constant Voltage Supply Terminal 41 Backup Power Supply Terminal 42 Second Constant voltage supply terminal 46 Microcomputer

Claims (8)

[Claims] 1. A power supply line connected to a vehicle-mounted battery via at least one operation switch, a current limiting resistor having one end connected to the power supply line, and a bidirectionality inserted in parallel with the current limiting resistor. A surge absorbing means having a first surge absorbing element and a second surge absorbing element inserted between the other end of the current limiting resistor and the ground, and the current limiting resistor of the surge absorbing means. A vehicle-mounted power supply circuit having a constant voltage supply unit connected to an end and supplying a predetermined constant voltage to a low-voltage load including a microcomputer. 2. The on-vehicle power supply circuit according to claim 1, wherein the first surge absorbing element is a varistor, and the second surge absorbing element is two Zener diodes connected in series. 3. The in-vehicle power supply circuit according to claim 1, wherein both the first and second surge absorbing elements are varistor. 4. A power supply line connected to the vehicle-mounted battery via at least one operation switch, a backup power supply line connected to the vehicle-mounted battery via a backup switch, and one end of the power supply line and the backup A current limiting resistor connected to the power supply line, and a bidirectional first surge absorbing element inserted in parallel with the current limiting resistor;
The surge absorbing means having a second surge absorbing element inserted between the other end of the current limiting resistor and the ground, and the power source so that the method from the vehicle-mounted battery to the surge absorbing means is forward. A low-voltage load that is connected to the other end of the current limiting resistor of the surge absorbing means and that is inserted into the line and that blocks the supply of the battery voltage from the backup power line to the power line; Constant voltage supply means for supplying a predetermined constant voltage to at least one constant voltage supply terminal for supplying the predetermined constant voltage in response to turning on of the operation switch, and the operation switch and / or the backup. The constant voltage having a backup power supply terminal that supplies the predetermined constant voltage in response to turning on of a switch Automotive power supply circuit and a supply unit. 5. The vehicle-mounted power supply circuit according to claim 4, wherein the first surge absorbing element is a varistor, and the second surge absorbing element is two Zener diodes connected in series. 6. The on-vehicle power supply circuit according to claim 4, wherein both the first and second surge absorbing elements are varistor. 7. The constant voltage supply means inputs first battery voltage of the vehicle-mounted battery to provide a first predetermined constant voltage, and the first predetermined constant voltage is input, Second lower than this
Second constant voltage means for applying a predetermined constant voltage to the backup power supply terminal, first switching means connected to the power supply line and turned on when the operation switch is turned on, and the first constant voltage means While the switching means is on, the second switching means that is in the ON state and applies the first predetermined constant voltage of the first constant voltage means to the first constant voltage supply terminal; and the first switching means The on-vehicle power supply according to claim 4, further comprising: a third switching means that is in an on state while being on and that applies the second predetermined constant voltage of the second constant voltage means to a second constant voltage supply terminal. circuit. 8. The vehicle-mounted power supply circuit according to claim 1, further comprising a voltage conversion circuit that inputs a battery voltage supplied to the power supply line and applies the voltage as battery voltage information to the microcomputer.