JPH0646373B2 - Memory backup circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Use of the Present Invention> The present invention relates to storage of memory by supplying power to the memory of the device instead of the device power when the power supply from the device power is stopped. The present invention relates to a memory backup circuit for holding contents, and more particularly to a memory backup circuit including a mechanical contact type switch for volatilizing stored contents of a memory.

<Prior Art and Problems> (FIGS. 7 to 8) In an apparatus that performs various controls based on programs and data stored in a memory, stored contents are controlled by a switch to prevent leakage of the programs and data. There is a case where a memory (for example, RAM) that can volatilize the memory is used. In such a device, a backup circuit for holding the stored contents of the memory is required when the device power is turned off or a power failure occurs.

FIG. 7 is a diagram showing an example of a backup circuit of a memory having such a volatilizing switch.

In the figure, a power supply terminal 1a of a readable / writable memory 1 (hereinafter referred to as a RAM) in which programs and data for controlling the device are stored is connected to a device power supply A through a diode 2 connected in series in the forward direction. Are connected.

The RAM 1 is a memory in which the stored contents are volatilized when the voltage supplied to the power supply terminal 1a becomes a specified value (for example, 2 volts) or less.

Further, in the backup circuit 3, a diode 5 is connected in series in the forward direction on the positive electrode side of the backup battery 4, and between the diode 5 and the power supply terminal 1 a of the RAM 1, a RAM is connected.
A mechanical contact type switch 6 for volatilizing the stored contents of No. 1 is provided. The switch 6 opens and closes between the contacts 6a and 6b by interlocking with a door (not shown) of the apparatus.

The volatilization switch 6 is connected through the connector 7, and the contacts 6a and 6b are in a closed state during normal operation of the device.

Here, for example, assume that the voltage of the device power supply A is 5.6 volts, the voltage of the backup battery 4 is 3.6 volts, and the voltage drops of the diodes 2 and 5 are 0.6 volts and 0.3 volts, respectively. Assuming that the operating current at the time of reading and writing of the RAM1 is about several tens of milliamperes, the voltage of the power supply terminal 1a of the RAM1 becomes about 5 volts and the diode 5 when the device power A is supplied.
Is reverse-biased, and RAM1 is driven only by the device power supply A.

When the device power supply A is turned off or a power failure occurs, the voltage supplied from the device power supply A to the power supply terminal 1a of the RAM 1 drops from about 5 V, and when the voltage reaches about 3.3 V, the diode 5 Is turned on, and the power source terminal 1a of the RAM 1 is switched from the backup battery 4 via the switch 6.
Is supplied with power, and the programs and data stored in the RAM 1 are retained.

At this time, the diode 2 is reverse biased, and the current from the backup battery 4 to the device power supply A side is cut off.

Further, when the door is opened by an improper operation while the memory is being held, the contacts of the switch 6 are opened, the power supply to the RAM 1 is cut off, and the stored contents of the RAM 1 are volatilized and the programs and data are leaked. Is prevented.

However, in this way RAM1 is placed between the contacts of the switch.
In a circuit for stably supplying a memory holding current, that is, a minute current of about several microamperes, for a long period of time, the stored contents are volatilized due to contact failure between contacts unless a switch with gold plating is used for each contact. Therefore, there is a problem that an extremely expensive switch is required.

In order to solve this, as shown in FIG. 9, a backup is performed in which the memory contents of the RAM 1 are held in a state where the contacts of the switch 6 are opened and the memory contents of the RAM 1 are volatilized when the contacts of the switch 6 are closed. It is also conceivable to use the circuit 3 '. In this circuit, the resistor 8 is inserted in series between the backup battery 4 and the diode 5, one end of the resistor 9 is connected to the connecting portion between the resistor 8 and the diode 5, and the other end side is connected to the switch 6. , When the switch 6 is open, the RAM 1 is supplied with a power source having a voltage equal to or higher than a specified voltage via the resistor 8 to hold the stored content, and when the switch 6 is closed, the specified value is determined by the resistors 8 and 8. A voltage lower than the voltage is supplied to the RAM 1 to volatilize its stored contents.

However, in such a circuit, the switch 6 is opened because the resistance value of the resistor 8 cannot be increased (for example, about several kilo-ohms) because the voltage drop due to the resistor 8 at the time of storage is required to be small. During this period, a very large current (for example, 7 to 800 microamperes) constantly flows from the backup battery 4 to the resistors 8 and 9 and the switch 6, which causes a problem that the backup battery 4 is significantly consumed.

<Objects of the Present Invention> The present invention has been made to solve the above problems, and enables stable memory retention and reliable volatilization without using a particularly expensive switch, and also consumes a backup battery. It is an object of the present invention to provide a memory backup circuit that can be made small.

<Means of the Present Invention> In order to achieve the above object, a backup circuit for a memory of the present invention includes: a backup battery for holding the stored content of the memory instead of the power source of the device; and a volatilized storage content of the memory. A switch of a mechanical contact type, and a resistor and a capacitor connected in series, connected between the positive and negative electrodes of the backup battery via the contact of the switch, and when the contact between the switches is closed, the contact Whether or not the current flowing between the contacts of the switch, which is provided between the backup battery and the power supply terminal of the memory, is provided between the CR series circuit for transiently flowing a current of a predetermined value or more for a predetermined time or more Is detected by the voltage at the connection point of the resistor and capacitor of the CR series circuit, and the back-up voltage is stored in the memory while the current between the contacts is smaller than the predetermined value. Powers of up battery, the current between the contacts is provided between the predetermined value or more, and a semiconductor switching circuit for stopping the power supply of the backup battery to the memory.

<Operation> With this configuration, in the memory backup circuit of the present invention, the current flowing between the contacts of the switch is equal to or less than the predetermined value while the switch is open and during the predetermined time after the switch is closed. Then, the power of the backup battery is supplied to the memory via the semiconductor switching circuit. In addition, a predetermined amount of current or more flows between the contacts of the switch until the predetermined time elapses after the switch is closed, during which the supply of power to the memory is stopped.

<One Embodiment of the Present Invention> (FIG. 1) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, and is a diagram showing an example in which a C-MOS type OR circuit is used as a switching circuit.

In the figure, 10 is a RAM in which the stored contents are volatilized when the supply voltage to the power supply terminal 10a becomes equal to or lower than a specified voltage (for example, 2 volts), and 11 is a program stored in the RAM 10 that controls the device according to the data. It is a CPU.

The voltage of the device power supply A is set to, for example, 5.6 volts, and the RAM 10, the CPU 11, and other circuits (not shown) are connected from the device power supply A through the diodes 12 and 13.
Is supplied with a voltage of about 5 volts.

The C-MOS type OR circuit 16 of the memory backup circuit 15 constitutes the semiconductor switching circuit of this embodiment, and the output terminal thereof is the power supply terminal 1 of the RAM 10.
0a.

The voltage of the device power supply A is divided by the resistors 17 and 18 so that an input voltage slightly lower than the power supply voltage of the OR circuit 16 is applied to one input terminal 16a of the OR circuit 16, and the logic level "H" is set. Corresponding voltage (eg 4.5V)
Has been entered.

The other input terminal 16b of the OR circuit 16 is connected to the CR series circuit 19.

The CR series circuit 19 is composed of a resistor 20 and a capacitor 21 which are connected in series, and the input terminal 16b of the OR circuit 16 is connected to the connection portion of the resistor 20 and the capacitor 21.

On the other end side of the capacitor 21, through the connector 22,
One contact 23a of the mechanical contact type volatilization switch 23
Are connected. The other contact 23 of the switch 23 is grounded.

The switch 23 communicates with a door (not shown) of this device to open and close the contacts, closes the contacts when the door is opened by an improper means, and opens the contacts during normal operation. ing.

The other end of the resistor 20 of the CR series circuit 19 has a backup battery (for example, a battery whose output voltage is 3.6 V) 2
5 is connected to the positive electrode side through a backflow preventing diode 26.

The resistance value of the resistor 20 and the capacity of the capacitor 21 of the CR series circuit 19 are set in the switch 23 until the predetermined time elapses after the switch 23 is closed while receiving the power from the backup battery 25. It is predetermined to transiently pass sufficient current between the contacts. Further, as the diode 26, a Schottky type diode having a small forward voltage drop (for example, 0.3 V) is used.

The output side of the diode 26 is connected to the output side of the diode 27 which is connected in series with the device power supply A in the forward direction,
The power supply terminal of the OR circuit 16 is connected to this connection portion.

<Operation of the Embodiment> (FIGS. 2-3) Next, the operation of the embodiment will be described.

When the device power supply A is being supplied (that is, when the device is operating), a voltage of about 5 V is supplied to the power supply terminal 10a of the RAM 10 via the diode 12.

At this time, a voltage of about 5 V is also supplied from the device power supply A to the power supply terminal of the OR circuit 16 via the diode 27, and one of the input terminals 16a becomes "H" level, so that the output of the OR circuit 16 is output. Is "H" level (about 5 volts)
Therefore, the RAM 10 is driven by the device power supply A and the output of the OR circuit.

The other input terminal 16b of the OR circuit 16 has a CR
The "H" level voltage is supplied through the resistor 20 of the series circuit 19, and when the contacts of the switch 23 are closed in this state, a second voltage is applied between the contacts of the CR series circuit 19 and the switch 23. As shown in the figure, a current i whose maximum value is determined by the resistance 20 and the voltage of the device power supply A transiently flows.
Therefore, the voltage Vc across the terminals of the capacitor 21 instantaneously becomes zero volt, as shown in FIG. 2, and rises from zero volt to about 5 V with a predetermined time constant determined by the resistance value of the resistor 20 and the capacitance of the capacitor 21. .

Therefore, from the time when the contacts of the switch 23 are closed until the terminal voltage Vc of the capacitor 21 reaches the voltage corresponding to the logic level "H", T is "L" at the other input terminal 16b of the OR circuit 16. However, the output of the OR circuit 16 does not change because one input terminal remains at the “H” level.

Further, the output from the diode 27 is the diode 26
Since a reverse bias voltage is applied to the diode 26, the diode 26 does not turn on and no current flows from the backup battery 25.

Next, when the device power supply A is turned off while the switch 23 is open, the voltage of the device power supply A gradually drops from 5.6 volts, and when the voltage drops to about 3.9 volts or less, the diode 26 becomes conductive. Then, the backup battery 25 supplies the CR series circuit 19 and the OR circuit circuit 16 with a power of about 3.3 volts.

Therefore, the "H" level voltage is input to the other input terminal 16b of the OR circuit 16 via the resistor 20 of the CR series circuit 19, and the output of the OR circuit 16 is at the "H" level (about 3.3). Voltage), and the power supply terminal 1 of the RAM 10
Since 0a is supplied with a voltage of about 3.3 volts, R
The program and data of the AM 10 are stored and held.

At this time, the diodes 12, 13, and 27 are in a reverse bias state, and the backup battery 25 side causes the device power supply A
The current to the side is cut off.

The current consumption of the backup battery 25 during storage is
It becomes the total value (for example, 5 microamperes) of the current supplied to the OR circuit 16, that is, the drive current of the OR circuit 16 and the output current of the OR circuit 16 (both several microamperes).

When the door of the device is opened and the contact between the switches 23 is closed, the CR series circuit 19 and the switch 2 are closed.
As shown in FIG. 3, a current i whose maximum value is determined by the resistance 20 and the voltage of the backup battery 25 transiently flows between the contacts of No. 3. Therefore, the terminal voltage Vc of the capacitor 21 of the CR series circuit 19 instantaneously becomes zero volt,
As shown in FIG. 3, the voltage rises from zero volt to about 3.3 volt with a predetermined time constant.

Therefore, until the terminal voltage Vc of the capacitor 21 reaches the logic level "H" from zero volt, the input voltage of the other input terminal 16b of the OR circuit 16 becomes "L" level during T'and the input voltage of the one input terminal 16a is increased. Input voltage is also device power supply A
Is not supplied and is at "L" level, the output of the OR circuit 16 becomes "L" level (about zero volt). Therefore, the voltage supplied to the power supply terminal of the RAM 10 becomes equal to or lower than the specified voltage for a predetermined time, and during this time, the RAM 10
The programs and data stored in are volatilized.

During this volatilization period (T '), the backup battery 16 to C
The current flowing through the contacts of the R series circuit 19 and the switch 23 changes the resistance value of the resistor 20 of the CR series circuit 19 from 4 to 4, for example.
If it is 50 kilohms, the maximum is about 70 microamperes, and the minimum is about half of it, which is sufficiently large compared to the minute current at the time of memory retention. Therefore, even if it is not an expensive switch, the connection state between the contacts of the switch 23 is stably maintained. Is
The contents stored in the RAM 10 can be surely volatilized. Moreover, since the current after the lapse of a predetermined time from the closing of the switch 23 decreases to zero, the switch 23
Even when the battery is closed, the consumption of the backup battery 25 other than this volatilization period is the same as that at the time of storing the memory, and is small.

When the volatilized program or data is re-stored in the RAM 10, the program or data is input from the outside of the device via the CPU 11 or the volatilized RAM is used.
10 and the backup circuit 15 of the memory connected to the RAM 10 are replaced with those in which the program is stored in advance.

<Other Embodiments of the Present Invention> (FIGS. 4 to 6) In the above embodiment, the switching between the device power supply A and the backup battery 25 was performed by a diode switch. For example, this switching is performed by an analog switch. A voltage comparator may be used.

That is, as shown in FIG. 4, the device power supply A and the device power supply A
The comparator 31 compares the voltage with the reference power source 30 having a lower voltage, and when the voltage of the device power source A becomes lower than the voltage of the reference power source 30, the analog switch 32 is turned on to supply power from the backup battery 33. be able to. In this case, the backup battery 33 may also be used as the reference power source 30.

Further, in the above-described embodiment, the CMOS type OR circuit 16 is used as the semiconductor switching circuit, but this is not limited to the OR circuit. For example, as in the semiconductor switching circuit 40 of FIG. Inverter 4
You may comprise by connecting 1 and 42 in series.

In FIG. 5, the diode 43 inserted on the output side of the inverter 42 blocks the current flowing from the device power supply A side to the output side of the inverter 42 by turning on the switch 23 when the device power supply A is supplied. To do.

Further, as in the CR series circuit 50 of FIG. 6, the resistor 20 and the capacitor 21 are exchanged to form a differentiating circuit, and the switch 23 is connected to the power source side, so that the semiconductor switching circuit 60 is composed of one inverter 61 and diode 62.
Can also be configured.

Further, in the above embodiment, the switch 23 is activated when the device is in operation.
Although it is configured so that does not work, the CPU 11 detects that the switch 23 is turned on when the device is operating, and the CP
It is also possible to volatilize the storage content of the RAM 10 via U11.

<Effects of the Present Invention> As described above, in the backup circuit of the memory of the present invention, the CR series circuit composed of the resistor and the capacitor is connected between both electrodes of the backup battery via the mechanical contact type switch, Allow a current greater than a predetermined value to transiently flow between the contacts for a predetermined time after the contacts are closed, and stop the power supply to the memory by the semiconductor switching circuit while the current more than the predetermined value flows. Is configured to.

Therefore, memory storage and volatilization can be stably and reliably performed without using an expensive switch. In addition, the current after a lapse of a predetermined time after the switch is closed transiently decreases from the predetermined current to zero, so that even if the switch remains closed, the backup battery does not have to be greatly consumed. effective.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2, and FIG.
FIG. 7 is a diagram showing changes in voltage and current for explaining the operation of one embodiment, and FIGS. 4, 5, and 6 are circuit diagrams showing another embodiment of the essential part of the present invention. 7 and 8 are circuit diagrams showing a conventional memory backup circuit. 10 ... RAM, 11 ... CPU, 15 ... Memory backup circuit, 16 ... OR circuit, 19 ... CR series circuit, 23 ... Switch, 23a, 23b ... Contact, 2
5 ... Backup battery.

Front page continuation (72) Inventor Morifumi Okugawa 1-2356 Takeshi, Yokosuka City, Kanagawa Prefectural Telegraph and Telephone Corporation, NTT Corporation (72) Inventor Tatsujiro Kawakita 1-2356 Takeshi, Yokosuka City, Kanagawa Nippon Telegraph and Telephone Corporation (56) Reference Japanese Patent Laid-Open No. Sho 60-129858 (JP, A) Actually Open Sho 61-120957 (JP, U)

Claims (1)

[Claims] 1. A backup battery for holding the stored contents of the memory instead of the power source of the apparatus, a mechanical contact type switch for volatilizing the stored contents of the memory, and a resistor and a capacitor connected in series. And a CR series circuit connected between the positive and negative electrodes of the backup battery via the contacts of the switch, and when the contacts of the switch are closed, a current of a predetermined value or more is transiently flowed between the contacts for a predetermined time. Provided between the backup battery and the power supply terminal of the memory, and detects whether or not the current flowing between the contacts of the switch is equal to or more than the predetermined value by the voltage at the connection point of the resistor and the capacitor of the CR series circuit. Then, while the current between the contacts is smaller than the predetermined value, the power of the backup battery is supplied to the memory, and when the current between the contacts is equal to or more than the predetermined value, Backup circuit of memory; and a semiconductor switching circuit for stopping the power supply of said backup battery for Li.