JP2835162B2 - RAM backup power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a RAM backup power supply device used for various electronic devices having a microprocessor and other RAMs, and particularly to other components. The present invention relates to a RAM backup power supply that can surely destroy the contents of RAM without affecting the RAM.

(Conventional technology) A conventional RAM backup power supply device is provided with a DC power supply that converts commercial power to a predetermined DC voltage and outputs the converted DC voltage and a secondary battery for backup. During normal operation, the output voltage of the DC power supply is stored in RAM. While supplying, the secondary battery is charged via the charging resistor. When the commercial power supply is cut off, the voltage of the backup secondary battery is supplied to the RAM.

By the way, in various electronic devices having a RAM, it is necessary to confirm the operation of the RAM after the completion of the device manufacturing. In such a case, after initializing the RAM area, writing / writing data to / from the RAM. By performing the reading, it is confirmed whether or not the operation of the RAM is normal. Here, the initialization is to set a value suitable for software processing, and is generally a process of setting all areas to “0”.

If the operation of the RAM is confirmed to be normal in this way, the contents of the RAM are initialized by software processing, and then R
Destroy data in all areas of AM and return to manufacturing completed state.
Here, to destroy the contents of the RAM means not to initialize it to a fixed value of "1" or "0" but to make it an undefined value. Normally, RAM initialization and data write / read processing are performed when checking the operation of the RAM.
Important data such as keywords, setting data required for operation, operation history at the time of the first operation startup, etc. are written in the RAM status area, etc., but the data in this area is not initialized, Specifically, it is an area that cannot be initialized by the initialization processing. For this reason, at the time of shipment after the completion of device
There is a problem that the keyword, the operation history, and the like must be given to the user in a state of being left in the RAM.

Therefore, at the time of shipment after the completion of device manufacture, the keyword once initialized at the time of normal operation confirmation of RAM, operation history, etc.
It is necessary to destroy the contents of RAM before shipping. User is RAM
For example, even if the data of the keyword or the operation history area is read after the contents are destroyed, the data is indefinite. Therefore, the keyword and the operation history cannot be read, and the intention of destroying the RAM contents can be achieved.

In addition, there are many requests by the user himself to destroy the contents of the RAM, construct new keywords, operation histories, and the like, and use the RAM.

Therefore, conventionally, when the contents of RAM are destroyed due to the above necessity, there is a means to remove the secondary battery during backup and a means to cut off the backup power using a switch. RAM
Means of destruction of contents are adopted. With this switch
Means for providing a push button switch between the DC power supply, the secondary battery and the RAM, that is, a power supply line, and disconnecting the power supply to the RAM by opening the push button switch even when the contents of the RAM are destroyed; There is a means for providing a push button switch in parallel with a closed circuit comprising a secondary battery and a RAM, and discharging the secondary battery by closing the push button switch.

(Problems to be Solved by the Invention) Among the means for destroying the contents of RAM using switches as described above, the means provided with a push button switch on the power supply line destroys the contents of the RAM by opening the push button switch. Although possible, the switches often cause poor contact. In this case, there is a problem that the RAM is opened without operating the switch and the contents of the RAM are destroyed.

On the other hand, a switch is provided in parallel with a closed circuit composed of the secondary battery and the contents of the RAM, and in the RAM contents destruction means for discharging the secondary battery by closing the switch, the switch is closed only when the switch is operated, and always Since the switch is open, there is no problem that the contents of the RAM will be destroyed even if the contact is poor.However, since the discharge of the secondary battery takes time, the contents of the RAM cannot be destroyed quickly, and the contents of the RAM cannot be destroyed. When the battery is destroyed, the secondary battery is completely discharged, so it is necessary to recharge it when backing up again.

Further, it is conceivable to reduce the charging resistance in order to speed up the charging, but there is a problem that an overcurrent flows when the secondary battery is erroneously connected or the like, and the charging resistance is damaged.

The present invention has been made in view of the above circumstances, and the content of the RAM is not destroyed even if there is a contact failure of the switch for destroying the content of the RAM, and the discharge amount of the secondary battery is small when the content of the RAM is destroyed. It is an object of the present invention to provide a RAM backup power supply device in which overcurrent does not occur even if the secondary battery is erroneously connected or the like.

[Means for Solving the Problems] In order to solve the above problems, the present invention monitors a DC power supply voltage and a battery power supply voltage, and controls a normal operation control signal according to the magnitude relationship between the two voltages. Or, a voltage monitoring means for outputting a control signal at the time of interruption, and provided between the DC power supply and the RAM,
Upon receiving the normal operation control signal output from the voltage monitoring means, the DC power supply and the RAM are electrically connected, and
DC power supply shut-off means for receiving the control signal at the time of cut-off and disconnecting the RAM from the DC power supply, and receiving DC power supply and outputting a predetermined constant current to charge the battery power supply during normal operation and controlling the power supply at the time of cut-off from the voltage monitoring means. A first constant current circuit for interrupting a constant current path when receiving a signal;
M to receive a control signal during normal operation from the voltage monitoring means and cut off the constant current path, and receive the control signal at cutoff to electrically connect the battery power supply and the RAM. 2 constant current circuit and always off, RAM
When a turn-on operation is performed to destroy the contents of the above, a closed circuit is formed between the battery power supply and the second constant current circuit and between the battery power supply and the RAM, respectively. FIG. 2 is a configuration diagram including a push button switch that destroys the contents of the RAM with a small amount of discharge.

(Operation) Therefore, according to the present invention, by taking the above means, when the voltage monitoring means determines that the DC power supply voltage is higher than the battery power supply voltage, a normal operation control signal is transmitted from the voltage monitoring means, In response to this, the DC power supply cutoff means and the first constant current circuit are turned on, and the second constant current circuit cuts off the constant current path, so that the DC power supply supplies power to the RAM and the battery power supply. Constant current charging. Further, since the second constant current circuit is in the cutoff state, even if the push button switch is operated, the contents of the RAM are not destroyed. On the other hand, when the voltage monitoring means determines that the battery power supply voltage is higher than the DC power supply voltage, the voltage monitoring means sends a shut-off control signal, and receives the DC power cut-off means and the first constant current circuit. Is cut off and the second
Is in a normal state, power is supplied from the battery power source to the RAM, and the secondary battery is not charged. At this time, when the push button switch is operated, a closed circuit is formed between the RAM and the push button switch in addition to the closed circuit including the battery power supply, the second constant current circuit, and the push button switch, and the contents of the RAM are securely confirmed. In addition, the battery power supply when the contents of the RAM are destroyed is a constant current discharge by the second constant current circuit, so that the discharge amount can be extremely reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. First
FIG. 1 is a configuration diagram showing one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a DC power supply that converts a commercial power supply voltage into a predetermined DC voltage and supplies the DC voltage to the microcomputer 2 and the RAM 3. The microcomputer 2 exchanges data with the RAM 3 for saving and reading data, and the RAM 3 sends out data in response to instructions for saving and reading the sent data.

On the other hand, a secondary battery 4 is provided in parallel with the DC power supply 1, and a current is supplied to the RAM 3 by the secondary battery 4 when the DC power supply 1 is cut off. Reference numeral 5 compares the respective voltages of the DC power supply 1 and the secondary battery 4, and sends a control signal during normal operation when the DC power supply voltage is high, and sends a control signal during shut down when the voltage of the secondary battery is high. The voltage monitoring means is introduced into a transistor switch 6, a first constant current circuit 7, and a second constant current circuit 8, which will be described later. The transistor switch 6 is provided between the DC power supply 1 and the RAM 3 and has a DC power supply cutoff function of electrically connecting or disconnecting the DC power supply 1 and the RAM 3 in response to a control signal from the voltage monitoring means 5. The first constant current circuit 7 is provided so as to form a closed circuit together with the DC power supply 1 and the secondary battery 4, and receives a control signal from the voltage monitoring means 5 to charge the secondary battery 4 with a constant current. The constant current is supplied or cut off. The second constant current circuit 8 is provided between the RAM 3 and the secondary battery 4, and receives a control signal from the voltage monitoring means 5 in the same manner as the first constant current circuit 7 to receive the RAM 3 and the secondary battery 4. Is electrically connected or cut off, and furthermore, has a function of discharging a constant current when the contents of the RAM described later are destroyed. 9 is provided to form a closed circuit between the secondary battery 4 and the second constant current circuit 8 and between the RAM 3 and the second constant current circuit 8, respectively, and is normally open, A push button switch for performing a pressing operation when the contents of the RAM 3 are destroyed.

Next, the operation of the device configured as described above will be described. Normally, the voltage monitoring means 5 compares the DC power supply voltage with the voltage of the rechargeable battery 4. When the DC power supply voltage is higher than the voltage of the rechargeable battery 4, it is determined that the normal operation is performed. When the time control signal is the transistor switch 6, the first
To the second constant current circuit 7 and the second constant current circuit 8. Upon receiving the normal operation signal, the transistor switch 6 is turned on, and the power of the DC power supply 1 is supplied to the RAM 3.
The first constant current circuit 7 supplies a constant current to charge the secondary battery 4 with a constant current, and the second constant current circuit 8 enters a cutoff state to electrically cut off the secondary battery 4 and the RAM 3. I do. As a result, power is supplied from only the DC power supply 1 to the RAM, and the secondary battery 4 is charged at a constant current. In this normal operation, even if the push button switch 9 is operated, the DC power from the DC power supply 1 is supplied to a part of the second constant current circuit 8 and the RAM 3, and the RAM 3 is supplied to the RAM 3. Since a constant voltage is applied, the contents of RAM3 are not destroyed.

Next, when the commercial power supply is cut off, since the voltage of the secondary battery 4 is higher than the voltage of the DC power supply 1,
Then, based on this, a control signal at the time of shutoff is sent to the transistor switch 6, the first constant current circuit 7, and the second constant current circuit 8. As a result, the transistor switch 6 is turned off, the DC power supply 1 and the RAM 3 are electrically cut off, the first constant current circuit 7 is turned off, the secondary battery 4 is not charged, and the second constant current circuit Reference numeral 8 electrically connects the RAM 3 and the secondary battery 4, and supplies power to the RAM 3 from the secondary battery 4. As a result, power is supplied only from the secondary battery 4 to the RAM 3, and the secondary battery is not charged.

Next, when the contents of the RAM 3 are destroyed when the DC power supply is cut off, the push button switch 9 is operated. At this time, the voltage of the secondary battery 4 is discharged at a constant current by the second constant current circuit 8, while the contents of the RAM 3 are discharged. Is discharged, and the contents of the RAM 3 are destroyed. The amount of discharge of the secondary battery 4 in the destruction of the RAM contents is extremely small due to the constant current as described above.

FIG. 2 is a circuit diagram showing the components of FIG. 1 in more detail. That is, in this circuit configuration, the voltage dividing resistors _R51 and _R52 are connected between the output terminals of the DC power supply 1, and
Both resistance between the voltage determination element IC ₅₁ provided to operate the transistor TR _51, TR ₅₂ by applying a current to the determined resistance R ₅₃ to the voltage of the DC power source 1 is turned, for example, 2.5V or more. Here, when the transistors TR ₅₁ and TR ₅₂ operate, the DC power supply voltage and the rechargeable battery 4 are controlled by the transistors TR ₅₁ and TR ₅₂ .
And the magnitude of the voltage.

In this case, when the DC power source voltage is larger than the secondary battery voltage, the transistor TR ₅₂ is turned on, the voltage determination element IC _52,
Low voltage is output from the IC _53. As a result, the voltage judgment element
Current flows through the resistor R ₆₁ of the IC ₅₂ output, transistor TR ₆₁ is turned on, electric power is supplied from the DC power source 1 to the RAM 3.
Also, conducting the diode D ₇₁ in the output of the voltage determination element IC _53, the transistor TR _71, TR ₇₂ a current flows through the resistor R ₇₁ is turned on, yet the resistor R _72, R ₇₃ and transistors TR _71, TR ₇₂ a constant current flows through the resistor R ₇₁ since it constitutes a Karentomira by such secondary battery 4
The charging current to is also constant. Also, since the diode D ₈₁ conducts and current flows through the resistors R ₈₁ , R ₈₄ and R ₈₅ , F
ET ₈₁ turns off. Therefore, the RAM 3 is disconnected from the secondary battery 4, and no current is supplied from the secondary current 4 to the RAM 3.
At this time, even if the push button switch 9 is pressed, a current flows from the DC power supply 1 to the resistors R ₈₁ , R ₈₄ , and R ₈₅ , and the current is limited, so that the voltage applied to the RAM 3 does not decrease.
The contents of RAM3 are not destroyed.

Then, when the secondary power supply voltage is the voltage monitoring means 5 greater than the DC supply voltage, the transistor TR ₅₂ is turned off, a high voltage from the voltage determination element IC ₅₁ is output. As a result, no current flows through the resistor R _61, the transistor TR ₆₁ is turned off, a DC power source 1 to be disconnected RAM 3. Further, the diodes D ₇₁ and D ₇₂ are turned off, and the resistance R ₇₁
, The transistors TR ₇₁ and TR ₇₂ are turned off, the diode D ₈₁ is turned off, the gate voltage of the FET ₈₁ is increased and turned on, and power is supplied from the secondary battery 4 to the RAM 3. In this case, when pressed the push button switch 9, the resistor diode D ₈₁ a current flows through the R ₈₂ is turned off, the lower the gate voltage of the FET _81, and the resistor R by the voltage applied to the RAM3 _When current flows through ₈₁ , the contents of RAM3 are destroyed when the RAM voltage falls below 0.3V. Then, a predetermined discharge current flows from the secondary battery 4 by the FET ₈₁ and the resistors R ₈₁ , R ₈₂ , R ₈₄ , and R ₈₅ .

Therefore, according to the configuration of the above embodiment, when switching between the DC power supply 1 and the secondary battery 4 using the voltage monitoring means 5, the voltage of the DC power supply 1 and the voltage of the secondary battery 4 are set at the same timing. , The power supply fluctuation of RAM3 does not become transient. As a result, the contents of the RAM are not destroyed due to sudden voltage fluctuation. When the contents of the RAM are destroyed, the second constant current circuit 8 is used to discharge the battery, so that the discharge of the secondary battery 4 is extremely small, and the recharge is not required or the recharge time is short. Further, the second constant current circuit 8 has a low drop voltage and thus has a high power supply efficiency, and has no mechanical contact, so that a contact failure does not occur and the reliability is high. Further, at the time of normal operation, the second constant current circuit 8 is in a cut-off state.
The contents of the RAM are not destroyed, and the contents of the RAM can be protected against inadvertent operations. Further, by the constant current charging by the first constant current circuit 7, even when the secondary battery 4 is erroneously connected, an overcurrent does not flow and damage to the secondary battery 4 and its related devices can be avoided.

In the above embodiment, the rechargeable battery 4 is charged with a constant current until the rechargeable battery 4 reaches a specific voltage, and is charged with a small current when the voltage exceeds the specific voltage. In this case, overcharging of the secondary battery can be easily prevented.

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, the RAM contents are not destroyed due to a contact failure of the switch for destroying the RAM contents. It is possible to provide a RAM backup power supply device that requires an extremely small amount and does not generate an overcurrent even if a secondary battery is erroneously connected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.
The figure is a circuit configuration diagram that embodies the components of FIG. 1. DC power supply 2. Microcomputer 3.
RAM, 4 ... secondary battery, 5 ... voltage monitoring means, 6 ... transistor switch, 7 ... first constant current circuit, 8 ...
2nd constant current circuit, 9 ... push button switch.

Claims (1)

(57) [Claims] A DC power supply for converting a commercial power supply to DC power and a battery power supply as a backup power supply are connected in parallel, and when the commercial power supply is energized (hereinafter referred to as energizing operation), the DC power of the DC power supply is supplied. In the RAM backup power supply that supplies battery power to the RAM when the commercial power is cut off, the DC power supply voltage and the battery power supply voltage are monitored. A voltage monitoring unit that outputs a normal operation control signal or a shutoff control signal according to the magnitude relation; and a normal operation control signal that is provided between the DC power supply and the RAM and that is output from the voltage monitoring unit. DC power supply disconnecting means for electrically connecting the DC power supply to the RAM and receiving the control signal at the time of disconnection and disconnecting the RAM from the DC power supply; A first constant current circuit that outputs a constant current to charge a battery power supply, and that interrupts a constant current path when receiving a shutoff control signal from the voltage monitoring means; and a first constant current circuit that is provided between the battery power supply and the RAM. Receiving a control signal during normal operation from the voltage monitoring means to cut off a constant current path, and receiving a control signal during cutoff to receive a battery power supply and a RAM.
And a second constant current circuit for electrically connecting the battery power supply and the second constant current circuit, which is normally in an off state and is turned on to destroy the contents of the RAM. And a push button switch for forming a closed circuit between the RAM and the RAM to destroy the contents of the RAM with a small amount of discharge of the battery power by the second constant current circuit. apparatus.