JP2765502B2 - Backup power supply 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 backup power supply circuit for supplying backup power to a memory or a microcomputer using a battery, and more particularly to a backup power supply circuit for a device having a clock function.

[0002]

2. Description of the Related Art Conventionally, in various devices having a clock function, backup power supply is performed to operate the clock function even when the power is turned off. However, during backup power supply, data in the memory may be destroyed due to a battery failure or the like. Therefore, after turning on the power,
A technique of checking data in a memory and initializing the memory when it is determined that the data has been destroyed and notifying the user is described in, for example, Japanese Patent Application Laid-Open No. 5-298195. By using this technique, the user can determine whether or not data in the memory has been destroyed after turning on the power. Further, in this technique, if data in a memory is not destroyed, data before a battery failure occurs is used as data at power-on.

On the other hand, in a wireless device such as a mobile phone, the operating voltage has been reduced, the difference between the power supply voltage and the operating voltage of a microcomputer or the like has been reduced, and the voltage of the backup battery and the microcomputer or memory (for example, SRAM) have been reduced. The difference from the operating voltage is also reduced. Therefore, the power supply voltage from the backup battery to the microcomputer processing the clock data and the like is likely to be lower than the minimum operating voltage of the microcomputer. For example, the battery voltage may be temporarily lower than the operating voltage of the microcomputer when the wireless device is inserted into or removed from the charger, or in the case of an in-vehicle wireless telephone, when the ignition key of a car is turned.

In the case where the battery voltage is lowered due to such disturbances or the like, if the above-described conventional technique is used, it is determined whether the contents of the memory are to be used as they are or to be in an initial state, depending on whether or not data in the memory is destroyed. There is no problem.

[0005]

However, in the case where the state in which the power supply battery is disconnected is maintained for a long time, the capacity of the backup battery is reduced, and the backup battery voltage becomes lower than the operating voltage of the microcomputer, the above-described conventional technique does not work. Since the memory retains the state before the backup battery voltage drops even after the power is turned on, there is a problem that the display time and the like become inaccurate. This is due to the difference in the minimum voltage between the operating voltage of the microcomputer and the holding voltage of the memory.

In a portable wireless device, generally, a minimum holding voltage of a memory is lower than an operating voltage of a microcomputer. Therefore, when the backup battery voltage actually decreases due to the fact that the backup battery continues to supply power and the battery capacity decreases, the microcomputer first reaches the minimum operating voltage. At this time,
In order to prevent malfunction of the microcomputer, the microcomputer is forcibly stopped. When the operation of the microcomputer is stopped, the current consumption is extremely reduced, so that the backup battery voltage hardly decreases. Therefore, if the backup battery voltage does not reach the minimum holding voltage of the memory, the memory normally stores data and the like.

That is, in the time period when the backup battery voltage is lower than the operating voltage of the microcomputer and higher than the minimum holding voltage of the memory, the data in the memory is not destroyed.
No abnormality can be detected after the power is turned on, and the data in the memory is retained. Then, even if the microcomputer is stopped for a long time, the time displayed after the power is turned on is the data held in the memory, that is, the time when the backup battery voltage is less than or equal to the operating voltage of the microcomputer. Will shift. However, since no abnormality is reported, the user cannot determine whether or not the correct time is displayed.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a backup power supply circuit for erasing the contents of a memory when a battery voltage drops due to a decrease in battery capacity.

Another object of the present invention is to provide a backup power supply circuit that can distinguish between a battery voltage drop due to disturbance or the like and a battery voltage drop due to a battery capacity drop.

[0010]

In order to achieve the above-mentioned object, a backup power supply circuit according to the present invention comprises a power supply battery, a backup battery, and a voltage of the power supply battery or a voltage of the backup battery . The load supplied and the
Forcibly discharge the voltage of the backup battery, and
Discharge means for lowering the voltage to the power supply battery,
Or, the voltage of the backup battery falls below the first voltage.
When the battery voltage drops, the backup battery is
And discharge the voltage of the backup battery to the
The voltage is reduced to a second voltage lower than the first voltage .

The load is a watch to which the voltage is supplied.
Microcomputer with built-in memory
1 is the minimum operating voltage of the microcomputer,
2 is the lowest holding voltage of the memory.
New In addition, the discharging means includes the backup battery.
Is desirably discharged over a predetermined time. Further
According to the present invention, when the microcomputer is restarted,
When it is detected that the pressure has fallen below the second voltage,
Preferably, the memory is initialized.

[0012]

With the above configuration, the backup power supply circuit according to the present invention can reduce the backup battery voltage to the minimum memory holding voltage by controlling the discharge of the backup battery when the battery voltage is within a predetermined voltage range. As a result, data in the memory can be erased. As a result, there is no need to restart using old data in the memory when the power is turned on again.

Also, the microcomputer can be controlled by distinguishing the battery voltage drop due to the battery capacity drop from the voltage drop due to other factors.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of a backup power supply circuit showing one embodiment of the present invention. The backup power supply circuit includes a power supply battery 1, a charging circuit 2, a backup battery 3,
It comprises a power supply battery voltage detection circuit 4, a backup battery voltage detection circuit 5, diodes 6 and 11, a discharge determination circuit 7, a microcomputer 8, a switch 9, and a discharge circuit 10.

The battery voltage of the battery 1, for example, 4.5 to 5.0
V is a diode 1 to the microcomputer 8 for controlling the clock function and the like.
1. The microcomputer 8 is formed of, for example, a one-chip microcomputer, and has a memory (for example, an SRAM) for storing time information and the like therein. This microcomputer 8
Is connected to a clock (not shown). The minimum operating voltage of the microcomputer 8 is, for example, about 2.0 V, and the minimum holding voltage of the internal memory is, for example, about 1.8 V. Further, the battery voltage is also supplied to the backup battery 3 via the charging circuit 2 composed of, for example, a resistor. This is to prevent the battery current from the battery 1 from suddenly flowing to the backup battery 3 and destroying the battery 3. However, the charging circuit 2 is not always necessary, and the battery voltage from the battery 1 does not have to be supplied to the backup battery 3.

The battery voltage detecting circuit 4 detects whether or not the battery voltage of the battery 1 or the backup battery 3 is higher than the minimum operating voltage (2.0 V) of the microcomputer. It is supplied to the reset terminal. When the detected battery voltage is lower than the minimum operating voltage of the microcomputer, the microcomputer is reset.

The backup battery voltage detection circuit 5 detects whether the backup battery voltage is equal to or higher than the minimum holding voltage (1.8 V) of the memory, and the detected voltage is supplied to the discharge determination circuit 7.

The discharge determination circuit 7 determines whether to discharge the backup battery 3 based on the outputs of the battery voltage detection circuit 4 and the backup battery voltage detection circuit 5.
N / OFF is controlled. When the battery voltage is higher than the minimum operating voltage of the microcomputer or lower than the minimum holding voltage of the memory, the switch 9 is turned off. When the battery voltage is lower than the minimum operating voltage of the microcomputer and higher than the minimum holding voltage of the memory, the switch 9 is turned on. Become. When the switch 9 is ON, the backup battery 3 is connected to the discharge circuit 10 and thus starts discharging, and the battery voltage supplied to the microcomputer 8 decreases. The discharge circuit 10 is formed of a resistor, and one end of the discharge circuit is grounded.

When the switch 9 is OFF, the battery voltage of the backup battery 3 is supplied to the microcomputer 8 via the diode 6. In other words, when the battery voltage is equal to or higher than the minimum operating voltage of the microcomputer, the microcomputer operates normally, so that the backup battery 3 does not need to be discharged. When the battery voltage is equal to or lower than the minimum holding voltage (1.8 V) of the memory, the contents of the memory are erased, and it is not necessary to discharge the backup battery any more. On the other hand, when the battery voltage is equal to or lower than the minimum operating voltage of the microcomputer and equal to or higher than the minimum holding voltage of the memory, the backup battery 3 is discharged so that the backup battery voltage falls below the minimum holding voltage of the memory. At this time, the contents of the memory are destroyed.

When the supplied battery voltage is lower than the minimum operating voltage of the microcomputer, the microcomputer 8 is reset to prevent malfunction. When the supplied battery voltage becomes equal to or higher than the minimum operating voltage of the microcomputer, the stored contents of the memory are checked. If the battery voltage is destroyed, the contents of the memory are erased and an initial start is performed. On the other hand, if the contents of the memory are not destroyed, the contents of the memory are not erased, and restart from the stored contents. As a check of the memory content of the memory in the microcomputer 8, for example, as shown in the above-mentioned prior art, predetermined data is stored in the memory in advance, and it is checked whether or not this data is destroyed. May be used.

Here, when the battery voltage supplied to the microcomputer 8 becomes lower than the minimum holding voltage of the memory, the contents of the memory are destroyed. Therefore, according to the present invention, when the battery voltage supplied to the microcomputer falls below the minimum operating voltage of the microcomputer, the backup battery 3 is discharged and the battery voltage is forcibly reduced to the minimum holding voltage of the memory. As a result, the contents of the memory are destroyed, and an initial start is performed when the microcomputer is restarted. On the other hand, if the voltage drops momentarily due to disturbance or the like, the backup battery is discharged. However, the battery voltage recovers immediately and exceeds the minimum operating voltage of the microcomputer, so that the discharge is stopped and the contents of the memory are not destroyed.

The diode 6 is provided to prevent the current supplied from the battery 1 to the microcomputer 8 from flowing back to the backup battery 3. Also, the diode 11
Is provided to prevent the current from the backup battery 3 from flowing back to the battery 1.

FIG. 2 is a diagram showing a change in the backup battery voltage. In FIG. 2, a solid line indicates a change in the backup battery voltage in the related art, and a dashed line indicates a change in the backup battery voltage in the present invention. The two-dot chain line indicates a temporary change in the backup battery voltage due to disturbance or the like.

When the backup battery voltage becomes equal to or lower than the microcomputer minimum operating voltage at the time T1 when the power battery is not connected, the operation of the microcomputer is stopped. Therefore, the backup battery voltage does not drop to the memory minimum holding voltage (see the solid line), and the data in the memory is held. When the power battery is connected at time T2, in the related art,
Since the data in the memory is not destroyed, (T2-T
In spite of the lapse of the time between 1), the time display is restarted at the time T2 based on the information of the time T1.

On the other hand, in the present invention, the discharge determination circuit 7 turns on the switch 9 at the time T1 when the backup battery voltage falls below the minimum operating voltage of the microcomputer, as indicated by the one-dot chain line. Discharging to the minimum holding voltage destroys the contents of the memory. Therefore, when the battery is connected at time T2, the microcomputer 8
Erases the contents of the memory by the function of checking the contents of the memory after turning on the power and performs an initial start.

When the power supply battery 1 is connected to a charger, or when a temporary voltage drop (see a chain double-dashed line) occurs due to disturbance such as when an ignition key of a car is turned, the backup battery is discharged for a short time. However, since the backup voltage is recovered immediately before falling below the memory minimum holding voltage, it exceeds the microcomputer minimum operating voltage. Therefore, the switch 9 is turned off, and the microcomputer checks the contents of the memory. Since the contents are not destroyed, the microcomputer restarts from the state held before the voltage drop.

As described above, the resistance value of the discharge circuit 10 is set so that the backup battery voltage does not fall below the minimum memory holding voltage in a short time so that it can be distinguished from the voltage drop due to disturbance.

In the embodiment described above, two independent battery voltage detection circuits are provided, but one battery voltage detection circuit may be used to compare the minimum operating voltage of the microcomputer and the minimum holding voltage of the memory. In this case, the one battery voltage detection circuit 4 or 5 in FIG. 1 becomes unnecessary.

[0030]

As described above, the backup power supply circuit according to the present invention uses the backup battery when the battery voltage supplied to the microcomputer is lower than the minimum operating voltage of the microcomputer and higher than the minimum holding voltage of the memory. By discharging to the following and erasing the stored contents of the memory, the microcomputer starts the memory from the initial state after the connection of the power supply battery.

Further, the microcomputer can be controlled by distinguishing the battery voltage drop due to the backup battery capacity drop from the voltage drop due to other factors based on the discharge characteristics. The microcomputer does not malfunction due to a temporary voltage drop due to disturbance.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a change in a backup battery voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Charging circuit 3 ... Backup battery 4 ... Battery voltage detection circuit 5 ... Battery voltage detection circuit 6 ... Diode 7 ... Discharge determination circuit 8 ... Microcomputer 9 ... switch 10 ... discharge circuit 11 ... diode

Claims (7)

(57) [Claims] 1. A backup power supply circuit, comprising: a power supply battery; a backup battery; and a voltage of the power supply battery.OrThe backup batteryVoltage
And the load that is supplied Forcibly discharging the voltage of the backup battery,
Discharge means for reducing the voltage to the load, When the voltage of the power supply battery or the backup battery is the first
When the voltage drops below the voltage of
Discharge the backup battery voltage, and
The voltage is reduced below a second voltage lower than the first voltage.
Let A backup power supply circuit, characterized in that: 2. The load according to claim 1, wherein the load is a microcomputer having a built-in memory having a clock function or the like to which the voltage is supplied , and a minimum holding voltage of the memory is different from a minimum operating voltage of the microcomputer. Item 2. The backup power supply circuit according to Item 1. 3. The backup power supply circuit according to claim 2, wherein the first voltage is a minimum operating voltage of the microcomputer, and the second voltage is a minimum holding voltage of the memory. 4. The microcomputer according to claim 1, wherein said first voltage is a minimum operating voltage of said microcomputer.
Operating voltage, wherein the second voltage is a minimum holding voltage of the memory.
And the content of the memory when the voltage is equal to or less than the second voltage.
3. A back-up according to claim 2, wherein
Power supply circuit. 5. When the microcomputer is restarted, the voltage becomes
When detecting that the voltage has become equal to or lower than the second voltage, the message
5. The battery according to claim 4, wherein the memory is initialized.
Power supply circuit. 6. The discharge means for discharging the backup battery over a predetermined time.
2. The backup power supply circuit according to 1 . 7. The backup power supply circuit according to claim 1, wherein the backup battery is charged from the power battery.