JPH0496116A - Ram backup power source unit - Google Patents

Abstract

PURPOSE:To minimize the electric discharge quantity of a secondary battery in the case a RAM is broken down by providing a second constant-current circuit for receiving an operation time control signal and interrupting a constant-current line, receiving an interruption time control signal and connecting a battery power source and the RAM, and a specific push-button switch. CONSTITUTION:This unit is provided with a DC power source interrupting means for receiving an interruption time control signal and detaching a RAM 3 from a DC power source 1, and a first constant-current circuit 7 for interrupting a constant-current line at the time when the interruption time control signal is received from a voltage monitoring means 5. Also, this unit is provided with a second constant-current circuit 8 for receiving an operation time control signal and interrupting the constant-current line, and also, receiving the interruption time control signal and connecting electrically the battery power source 1 and the RAM 3. In such a state, when the push-button switch 9 is operated, a closed circuit is formed between a battery power source 4, a second constant-current circuit 8 and the push-button switch 9, or between the RAM 3 and the push-button switch 9, the RAM 3 can be broken down surely, and also, the discharge of the battery power source 4 at the time of the breakdown of the RAM becomes constant-current discharge by a second constant-current circuit 8. In such a manner, at the time of the breakdown of the RAM, the small discharge quantity of the secondary battery 4 is enough.

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 in various electronic devices including microprocessors and other RAM, and particularly relates to a RAM backup power supply device used in various electronic devices having a RAM. Reliably RA without any impact
The present invention relates to a RAM backup power supply device that can initialize M.

(Prior art) In addition to a DC power supply that converts commercial power to a predetermined DC voltage and outputs it, a conventional RAM backup power supply device is equipped with a secondary battery for backup, and during normal operation, the output voltage of the DC power supply is In addition to being supplied to the RAM, the secondary battery is charged via a charging resistor. Further, when the commercial power supply is cut off, the voltage of a secondary battery for backup is supplied to the RAM.

On the other hand, when initializing the RAM contents, that is, destroying the RAM, there are methods such as removing the secondary battery during backup or using a switch to cut off the backup power supply. Destructive measures are being taken.

Even when destroying the RAM using this switch, a push button switch is provided between the DC power supply, the secondary battery and the RAM, that is, on the power line, and the power to the RAM is disconnected by opening the push button switch. Means, secondary battery and R
A push button switch is provided in parallel to the closed circuit consisting of AM,
There is a means for discharging the secondary battery by closing this push button switch.

(Problem to be solved by the invention) Among the RAM destruction means using a switch as described above,
In the case where a push button switch is provided on the power supply line, the RA Fvl can be destroyed by opening the push button switch, but the switch often causes poor contact. In this case, there is a problem in that the switch becomes open even if the switch is not operated and the RAM is destroyed.

On the other hand, in the RAM destruction method, a switch is installed in parallel in a closed circuit consisting of a secondary battery and RAM, and the secondary battery is discharged by closing the switch.The switch is closed only when the switch is operated, and the switch is normally open. Therefore, even if there is a poor contact, there is no problem of destroying the RAM.
Since it takes time for the secondary battery to discharge, the RAM cannot be destroyed quickly, and when the RAM is destroyed, the secondary battery is completely discharged and must be recharged when backing up again.

Furthermore, in order to speed up charging, it is conceivable to reduce the charging resistor, but there is a problem in that when there is an erroneous connection of the secondary battery, an overcurrent flows and damages the charging resistor.

The present invention has been made in view of the above-mentioned circumstances, and the RAM contents will not be destroyed even if there is a contact failure of the RAM destruction switch, and the amount of discharge of the secondary battery will be small when the RAM is destroyed. It is an object of the present invention to provide a RAM backup power supply device that does not generate an overcurrent even if a secondary battery is incorrectly connected.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention monitors the DC power supply voltage and the battery power supply voltage, and generates a control signal during normal operation according to the magnitude relationship between the two voltages. or provided between a voltage monitoring means that outputs a control signal at the time of interruption, and the DC power supply and the RAM,
DC power supply cutoff means for electrically connecting the DC power supply and the RAM in response to a normal operation control signal output from the voltage monitoring means, and for disconnecting the RAM from the DC power supply in response to the cutoff control signal; During normal operation, it receives DC power and outputs a predetermined constant current to charge the battery power supply.
A first constant current circuit that cuts off a constant current path when receiving a cutoff control signal from the voltage monitoring means, and a first constant current circuit that is provided between the battery power source and the RAM and receives a control signal during normal operation from the voltage monitoring means. a second constant current circuit that receives the cut-off control signal and electrically connects the battery power source and the RAM; When there is a turn-on operation on the battery, a closed circuit is formed between the battery power source and the second constant current circuit and between the RAM, so that the RAM is activated with a small discharge amount of the battery power source by the second constant current circuit. It is equipped with a push button switch that destroys the

(Function) Therefore, by taking the above measures, the voltage monitoring means sends out a normal operation control signal when the voltage monitoring means determines that the DC power supply voltage is higher than the battery power supply voltage. In response to this, the DC power supply cutoff means and the first
Since the constant current circuit becomes energized and the second constant current circuit cuts off the constant current path, power can be supplied to the DC power source or the RAM, and the battery power source can be charged with constant current. Further, since the second constant current circuit is in a cut-off state, the RAM will not be destroyed even if the push button switch is operated. 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 cut-off control signal, and the DC power supply cut-off means receives this signal and the first constant current Since the circuit is cut off and the second constant current circuit is in the normal state, R is removed from the battery power source.
Power is supplied to AM, and the secondary battery is not charged.

At this time, when the push-button switch is operated, a closed circuit is formed between the battery power source, the second constant current circuit, and the push-button switch, as well as a closed circuit between the RAM and the push-button switch, ensuring that the RAM is destroyed. In addition, since the discharge of the battery power supply when the RAM is destroyed is a constant current discharge by the second constant current circuit, the amount of discharge can be extremely reduced.

(Example) Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a DC power supply that converts a commercial power supply voltage into a predetermined DC voltage and supplies it to the microcomputer 2 and RAM 3. This microcomputer 2 sends and receives data to and from the RAM 3 for data storage and reading.
3 sends out data in response to received data storage and read commands.

On the other hand, a secondary battery 4 is provided in parallel with the DC power source 1, and the secondary battery 4 supplies power to the RAM 3 when the DC power source 1 is cut off. 5 compares the respective voltages of the DC power supply 1 and the secondary battery 4, and when the DC power supply voltage is high, it sends out a normal operation control signal, and conversely, when the secondary battery voltage is high, it sends out a cut-off control signal. However, a transistor switch 6, a first constant current circuit 7 and a second
This is a voltage monitoring means introduced into the constant current circuit 8. This transistor switch 6 is provided between the DC power supply 1 and the RAM 3, and has a DC power 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. First constant current circuit 7
is provided to form a closed circuit together with the DC power source 1 and the secondary battery 4, and receives a control signal from the voltage monitoring means 5 to turn on or cut off constant current for constant current charging of the secondary battery 4. It is something to do. The second constant current circuit 8 is
It is provided between the RAM 3 and the secondary battery 4, and, like the first constant current circuit 7, receives a control signal from the voltage monitoring means 5 to electrically connect or disconnect the RAM 3 and the secondary battery 4, Furthermore, it has a function of performing constant current discharge when the RAM is destroyed, which will be described later. 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, and is normally in an open state; It is a push button switch that is pressed when destroying the RAM3.

Next, the operation of the apparatus configured as above will be explained.

Normally, the voltage monitoring means 5 compares the DC power supply voltage with the voltage of the secondary battery 4, and when the DC power supply voltage is higher than the voltage of the secondary battery 4, it is determined that normal operation is being performed. A control signal is sent to the transistor switch 6, the first constant current circuit 7, and the second constant current circuit 8. Upon receiving this normal operation signal, the transistor switch 6 turns on and supplies power from the DC power supply 1 to the RAM 3.
The first constant current circuit 7 is in a constant current state to charge the secondary battery 4 with a constant current, and the second constant current circuit 8 is in a cutoff state to electrically cut off the secondary battery 4 and RAM 3. do. As a result, power is supplied to the RAM only from the DC power supply 1, and the secondary battery 4 is charged with a constant current. Note that during this normal operation, even if the push button switch 9 is operated, the DC power supply 1 is not connected to a part of the second constant current circuit 8 and the RAM 3.
Since DC power is supplied from the RAM 3 and a constant voltage is applied to the RAM 3, the RAM 3 is 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, the voltage monitoring means 5 transmits a cut-off control signal based on the voltage to the transistor switch 6 and the first constant current circuit. 7. Send to second constant current circuit 8. As a result, the transistor switch 6 is turned off, and the DC power supply 1 and the RAM 3 are electrically cut off.
The first constant current circuit 7 is cut off and the secondary battery 4 is not charged, and the second constant current circuit 8 electrically connects the RAM 3 and the secondary battery 4 to supply power from the secondary battery 4 to the RAM 3. supply. As a result, power is supplied to the RAM 3 only from the secondary battery 4, and the secondary battery is not charged.

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

Next, FIG. 2 is a circuit configuration diagram showing the components of FIG. 1 in further detail. That is, in this circuit configuration, voltage dividing resistors R51 and R62 are connected between the output terminals of the DC power supply 1, and a voltage determining element IC51 is provided between the two resistors, so that the voltage of the DC power supply 1 is, for example, 2.5 V or higher. When it is determined that the current has become
, activate TR52. , where the transistor TR
6,, when TR52 is activated, these transistors T
The magnitude of the DC power supply voltage and the voltage of the secondary battery 4 is compared using R51 and T Rs2.

At this time, when the DC power supply voltage is higher than the secondary battery voltage, the transistor TR,2 is turned on and the voltage determination element I
A low voltage is output from C52 and IC6.

As a result, a current flows through the resistor R61 output from the voltage determining element IC52, turning on the transistor TR6□, and power is supplied from the DC power supply 1 to the RAM3. Also, the diode D71 at the output of the voltage determining element IC6 becomes conductive, and current flows through the resistor R71, causing the transistors TR71, TR,
□ is in the on state, and since the resistors R, 2, R73, transistors TR, □, TR7□, etc. constitute a current mirror, a constant current flows through the resistor R7, and the charging current to the secondary battery 4 also flows. It becomes constant. Also, diode D8+ becomes conductive, and resistors R80, R82,
Since current flows through R83, FET8. is turned off. Therefore, RAM 3 is separated from secondary battery 4,
No power is supplied from the secondary battery 4 to the RAM 3. At this time, even if the push button switch 9 is pressed, the DC power supply 1
A current flows through the resistors R81, R8°, and R8, and since the current is limited there, the voltage applied to the RAM3 does not drop, and the contents of the RAM3 are not destroyed.

Next, when the secondary power supply voltage is higher than the DC power supply voltage in the voltage monitoring means 5, the transistor TR62 is turned off, and the voltage determination element IC! A high voltage is output from +. As a result, no current flows through the resistor R6, the transistor TR6 is turned off, and the RAM 3 is disconnected from the DC power supply 1.

Also, the diodes D71 and D72 are turned off, and the resistance R
No current flows through transistor T R71.
, TR7□ turns off, and diode I)s+ turns off, and the gate voltage of FETa+ increases and turns on.
Power is supplied from the secondary battery 4 to the RAM 3. At this time, when the pushbutton switch 9 is pressed, a current flows through the resistor R8□, turning off the diode I)s+ and turning off the FET.
The gate voltage of 5+ becomes low, and current flows through resistor RS+ due to the voltage applied to RAM3, so that R
When the AM voltage drops below 0.3V, the contents of RAM3 are destroyed. Then, FET5+ and resistors R80 and R8
2, R84, and R8, a predetermined discharge current flows from the secondary battery 4.

Therefore, according to the configuration of the embodiment described above, 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 kept the same. Since the switching is done at the right timing, power fluctuations in the RAM 3 do not become transient. Therefore, destruction of the RAM contents due to sudden voltage fluctuations does not occur. Further, when the RAM is destroyed, by discharging it using the second constant current circuit 8, the amount of discharge of the secondary battery 4 is extremely small, and there is no need for recharging, but the recharging time can be shortened. Further, the second constant current circuit 8 has a low voltage drop, so it has good power supply efficiency, and since it has no mechanical contacts, it is highly reliable, with no contact failure occurring. Furthermore, during normal operation, the second constant current circuit 8 is cut off, and even if the push button switch 9 is operated at this time, the contents of the RAM will not be destroyed, and the RAM will be protected from accidental operation.
M contents can be protected. Further, due to the constant current charging by the first constant current circuit 7, even if the secondary battery 4 is connected incorrectly, no overcurrent will flow, and damage to the secondary battery 4 and related equipment can be avoided.

In addition, in the above embodiment, the secondary battery 4 is charged with a constant current until the secondary battery 4 reaches a specific voltage, and when the voltage reaches the specific voltage or higher, the secondary battery 4 is charged with a small current. For example, overcharging of the secondary battery can be easily prevented.

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

[Effects of the Invention] As explained above, according to the present invention, the RAM contents are not destroyed due to poor contact of the switch for destroying the RAM contents, and when the RAM is destroyed, the amount of discharge of the secondary battery is reduced. It is possible to provide a RAM backup power supply device that requires very little power and that does not generate overcurrent even if there is an erroneous connection of a secondary battery.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a circuit configuration diagram embodying the components shown in FIG. 1. 1...DC power supply, 2...Microcomputer, 3
... RAM, 4... Secondary battery, 5... Voltage monitoring means, 6... Transistor switch, 7... First constant current circuit, 8... Second constant current circuit, 9...Push button switch. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A DC power source that converts commercial power to DC power and a battery power source as a backup power source are connected in parallel, and when the commercial power is energized (hereinafter referred to as normal operation), the DC power of the DC power is Power is supplied to the RAM and the battery power source is charged, and when the commercial power source is cut off, the battery power source is transferred to the RAM.
A RAM backup power supply device for supplying power to the battery, comprising: voltage monitoring means for monitoring the DC power supply voltage and the battery power supply voltage and outputting a normal operation control signal or a cutoff control signal depending on the magnitude relationship between the two voltages; is provided between the DC power supply and the RAM, and receives the normal operation control signal output from the voltage monitoring means to control the DC power supply and the RAM.
a DC power supply cutoff means that electrically connects the RAM to the DC power supply and disconnects the RAM from the DC power supply upon receiving the cutoff control signal; and during normal operation, receives the DC power supply and outputs a predetermined constant current to charge the battery power supply; a first constant current circuit that cuts off a constant current path when receiving a cutoff control signal from the voltage monitoring means, and a normal operation control signal from the voltage monitoring means, which is provided between the battery power source and the RAM; a second constant current circuit that receives the cutoff control signal to cut off the constant current path, and receives the cutoff control signal to electrically connect the battery power source and the RAM;
It is normally in an off state, but when an on operation is performed to destroy the RAM, a closed circuit is formed between the battery power source and the second constant current circuit and between the RAM and the second constant current circuit. A RAM backup power supply device comprising a push button switch that destroys the RAM with a small amount of discharge from a battery power supply using a constant current circuit.