JP2001327101A - Backup circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backup circuit in which capacitance can be reduced and further a capacitor can be miniaturized by increasing a backup time a little. SOLUTION: In a backup circuit for charging a backup capacitor of a system power source circuit, the backup time of the backup capacitor 12 in the case of discharge is elongated by increasing a supply time of an operation voltage to the system power source circuit 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a backup circuit, and more particularly to a backup circuit for charging a backup capacitor.

[0002]

2. Description of the Related Art Conventionally, a backup circuit for charging a backup capacitor has been known. The backup circuit has a booster circuit that raises the voltage of the battery to a predetermined voltage, and the output voltage of the booster circuit charges the backup capacitor via a charging circuit.

With this backup capacitor, a voltage can be supplied to the system power supply for a certain period of time when the supply of voltage from the battery is stopped. Therefore, a large-capacity capacitor is used as the backup capacitor in order to back up the system operation after the supply of the voltage from the battery is stopped.

[0004]

However, since this backup capacitor has a large capacity, it is unavoidable that the component size becomes large, and it is necessary to reduce the capacity even a little. In such a state, specifications have been increased in order to provide various added values, and corresponding CPUs (central processing units) have been added.
(nit) The speeding up of the process has resulted in an increase in current consumption.

An object of the present invention is to provide a backup circuit capable of reducing the capacity and further reducing the size of the capacitor by slightly increasing the backup time.

[0006]

In order to achieve the above object, a backup circuit according to the present invention is a backup circuit for charging a backup capacitor of an operation power supply circuit, wherein the operation circuit supplies an operation voltage to the operation power supply circuit. It is characterized in that the supply time is lengthened and the backup time when the backup capacitor is discharged is lengthened.

With the above configuration, in the backup circuit for charging the backup capacitor of the operation power supply circuit, the supply time of the operation voltage to the operation power supply circuit becomes longer, and accordingly, the backup capacitor is discharged. The backup time is also longer. Therefore, by slightly increasing the backup time, it is possible to reduce the capacity and further reduce the size of the capacitor.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a backup circuit according to an embodiment of the present invention. As shown in FIG. 1, the backup circuit 10 raises the battery voltage by a booster circuit and charges a capacitor (backup capacitor) that backs up the system operation. The backup circuit 10 includes a booster circuit 11, a backup capacitor 12, a switch 13, and It has a control circuit 14.

The booster circuit 11 is connected to the battery 15, and raises the output voltage of the battery 15 to a predetermined voltage V1 and outputs it. The backup capacitor 12 is connected to the booster circuit 11 via the charging circuit 16, and is charged by the output voltage of the booster circuit 11 via the charging circuit 16. When the voltage supply from the battery 15 to the system power supply circuit (operation power supply circuit) 17 is stopped, the voltage is supplied to the system power supply circuit 17 for a certain period of time or more.

The switch 13 connects the backup capacitor 12 to the booster circuit 11 by ON operation, and supplies a voltage from the backup capacitor 12 to the booster circuit 11 via the switch 13.

When the voltage supply from the battery 15 is cut off and the terminal voltage of the backup capacitor 12 approaches the target voltage V2, the control circuit 14 sends a control signal a for turning on the switch 13 to the switch 13 Output to The control circuit 14 includes a CPU (centra)
l processing unit), and A /
It has the functions of a D converter, a comparator, etc., and performs boost control in accordance with a threshold change.

By the backup circuit 10, when the voltage supply from the battery 15 is stopped, the operation of the unit can be backed up by discharging from the backup capacitor 12, and the backup time can be extended.

That is, a voltage is supplied from the backup capacitor 12 to the booster circuit 11 during the backup operation.
An energizing path with a switch is provided, and during the backup operation, the switch of the energizing path is turned on before the voltage of the backup capacitor 12 drops below the system minimum operating voltage.

Therefore, the boosting circuit 11 after the supply of the voltage performs the boosting operation as long as the voltage is supplied from the backup capacitor 12, and even if the terminal voltage of the backup capacitor 12 is lower than the minimum operating voltage of the system, the boosted voltage is increased. Is supplied to the system power supply circuit 17 which is a power supply for CPU operation, so that the energy stored in the electrolytic capacitor can be used efficiently.

FIG. 2 is a circuit diagram showing a specific example of the backup circuit of FIG. As shown in FIG. 2, the backup circuit 10 is provided between the battery 15 and the system power supply circuit 17.

The battery 15 is connected to an input terminal of the booster circuit 11 via a diode 18. Booster circuit 11
Are connected to the system power supply circuit 17 via the diode 19 and to the backup capacitor 12 via the diode 19, the resistor 20 and the diode 21, respectively. This resistor 20 and diode 21
Has a function as a charging circuit.

The backup capacitor 12 is a P-channel FET (Field Effect Transistor).
tor) 22 and booster circuit 11 via diode 23
Are connected to a CPU (control circuit) 14 via an input circuit 24, respectively. The P-channel FET 22 may be a transistor, and the input circuit 24
Performs waveform processing at the stage before input of the CPU 14.

The gate of the P-channel FET 22 is connected to the comparator of the CPU 14 via the transistor 25. The boosted output (boost target voltage value, for example, 21V → 8V) from the CPU 14 is input to the booster circuit 11. I do.

FIG. 3 is a timing chart for explaining the operation of the backup circuit of FIG. As shown in FIG. 3, after the voltage supply to the battery 15 is cut off (off), the backup circuit 12
Is switched from the system power supply circuit 17 to the booster circuit 11.

At this time, the booster circuit 11 lowers the boost target voltage to a voltage V2 (for example, 8 V) which is higher than the system minimum operating voltage, instead of the normal voltage V1 (for example, 21 V). This is to prevent wasteful use of the energy of the backup capacitor 12 that is low. This backup capacitor 12 always has 20.
It is charged to 3V.

The control circuit 14 turns on the switch 13 just before the voltage supply of the battery 15 is cut off and the terminal voltage of the backup capacitor 12 approaches the boosting target voltage V2, and the voltage supply to the boosting circuit 11 is performed. To start. The step-up circuit 1 that has been stopped when the voltage supply from the battery 15 is cut off due to the start of the voltage supply
1 resumes operation, and the voltage is supplied to the system power supply circuit 17.

That is, when the voltage supplied to the system power supply circuit 17 is equal to the ON determination threshold of the switch 13 (for example, 6.
7V), the voltage is increased (for example, 7.3V),
Thereafter, when the minimum operating voltage of the system power supply circuit 17 is reached, the system is reset (operation stopped).

Therefore, when the voltage supplied to the system power supply circuit 17 is boosted, the voltage is directly reduced without being boosted to reach the minimum operating voltage of the system power supply circuit 17 (corresponding to the conventional case, as indicated by the dotted line in the figure). (Shown), it is possible to extend the time b until the system is reset after the boosting. As a result, the system operating voltage can be supplied to the system power supply circuit 17 for a longer time.

As described above, according to the present invention, the system operating voltage can be supplied to the system power supply circuit 17 for a longer time, and the backup time can be increased even slightly, so that the backup capacitor 12 is required. The capacity can be reduced.

Since the components required for the switch 13 are not so large, the capacity of the capacitor can be reduced, the size of the capacitor can be reduced, and further effects can be obtained.

In the present invention, the system operation voltage is supplied for a longer time by restarting the operation of the booster circuit 11 which has been stopped for the purpose of increasing the backup time at the time of discharging. The capacitor 12 is always charged with the voltage raised to a high potential. Switching by the switch 13 is performed in a state where the backup time of the backup capacitor 12 is also guaranteed.

The backup circuit 10 having such a purpose and configuration is desirably used, for example, for a backup capacitor used in an airbag device for an automobile. That is, in the safety system of an automobile, the reliability is the most important, and therefore the backup circuit 10 according to the present invention, in which the backup capacitor is always charged, is more suitable.

[0029]

As described above, according to the present invention, in the backup circuit for charging the backup capacitor of the operating power supply circuit, the supply time of the operating voltage to the operating power supply circuit is lengthened. Accordingly, the backup time at the time of discharging the backup capacitor becomes longer. Therefore, by slightly increasing the backup time, it is possible to reduce the capacity and further reduce the size of the capacitor.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a backup circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific example of the backup circuit of FIG. 1;

FIG. 3 is a timing chart illustrating the operation of the backup circuit of FIG. 1;

[Explanation of symbols]

 Reference Signs List 10 backup circuit 11 booster circuit 12 backup capacitor 13 switch 14 control circuit 15 battery 16 charging circuit 17 system power supply circuit 18, 19, 21, 23 diode 20 resistor 22 P-channel FET 24 input circuit 25 transistor a control signal

Claims (6)

[Claims] 1. A backup circuit for charging a backup capacitor of an operation power supply circuit, comprising: extending a supply time of an operation voltage to the operation power supply circuit;
A backup circuit for extending a backup time when discharging the backup capacitor. 2. The method according to claim 1, wherein the voltage supplied to the operation power supply circuit is boosted, and the voltage supplied to the operation power supply circuit is reduced without being boosted to reach the minimum operation voltage of the operation power supply circuit.
2. The backup circuit according to claim 1, wherein a time required until the minimum operation voltage of the operation power supply circuit is reached after boosting is extended. 3. The backup circuit according to claim 1, wherein the backup capacitor is always charged with a voltage boosted to a high potential. 4. A booster circuit connected to a battery for increasing the output voltage of the battery to a predetermined voltage and outputting the boosted voltage; the backup capacitor charged by an output voltage from the booster circuit; A switch for connecting a backup capacitor to the booster circuit and supplying a voltage from the backup capacitor to the booster circuit; and a state before the voltage supply from the battery is cut off and the terminal voltage of the backup capacitor approaches the target voltage. At the time
4. The backup circuit according to claim 1, further comprising a control circuit that outputs a control signal for turning on the switch. 5. The power supply circuit according to claim 4, wherein the backup capacitor supplies a voltage to the operation power supply circuit for a predetermined time or more when the supply of voltage from the battery to the operation power supply circuit is stopped. Backup circuit. 6. The backup circuit according to claim 1, wherein said backup capacitor is a backup capacitor used in an airbag device for a vehicle.