JPH04222427A - Battery backup circuit - Google Patents

Abstract

PURPOSE:To hold the state of a CPU or the data in a memory as long as possible by prolonging the duration of effective voltage region for a load circuit when a battery is removed or consumed in a battery drive appliance. CONSTITUTION:A power supply circuit 14 having output voltage, which can be switched between high and low levels, is connected with a battery 10 and a parallel circuit of a high resistor 18 and a switching element 16 is connected in series with an electric double layer capacitor 20, and the series circuit is connected in parallel with the battery on the output side of the power supply circuit. Prior to exchange of the battery, the power supply circuit is switched to high voltage output and the switching element is conducted thus charging the electric double layer capacitor quickly and when the battery is removed, power is fed through a rectifying diode 22 to a load circuit.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery backup circuit for battery operated equipment. More specifically, this is a battery backup circuit that applies high voltage to quickly charge a power storage device such as an electric double layer capacitor before battery replacement, thereby extending the duration of the effective voltage range to the load circuit when the battery is removed. It is related to.

0002

2. Description of the Related Art Electronic devices are becoming increasingly smaller, as seen in notebook or palmtop computers, small word processors, and the like. Along with this trend, power consumption has also become micro-power, and devices that can operate for long periods on batteries are now on the market. In devices using such batteries, problems arise with the state of the CPU and data retention in the memory immediately before battery replacement.

[0003] Secondary batteries and electric double layer capacitors are used for backup when replacing batteries. In other words, a secondary battery or electric double layer capacitor is connected in parallel with the battery, and the current from the battery charges the battery during normal operation.When the battery is exhausted or removed, data is transferred from the secondary battery or electric double layer capacitor to the load circuit. This is a method that supplies enough power to prevent the etc. from disappearing. Figure 3 shows the discharge curve of a typical battery. The terminal voltage of the battery is monitored by a voltage detection circuit, and when it drops to the battery replacement voltage lower limit level, an alarm signal is generated to prompt battery replacement. Therefore, in the circuit of the above system, the charging voltage of the secondary battery or electric double layer capacitor immediately before battery replacement is required is equivalent to the battery replacement voltage lower limit level.

By the way, in connection with power saving during normal operation, there is a device in which a power supply circuit capable of switching high and low output voltage is connected to a battery to switch between a normal mode and a sleep mode (standby mode). Notebook computers and the like do not operate at full capacity all the time, and most of the time is spent when the CPU is not executing useful programs, such as when waiting for key input. Focusing on this point, the power supply voltage is lowered when most of the functions are asleep (sleep mode). With such power saving devices,
If an electric double layer capacitor is installed at the output of the power supply circuit for battery backup, the system will enter sleep mode (low voltage operation) when the battery terminal voltage drops to the battery replacement voltage lower limit level and an alarm signal is generated. The charging voltage of an electric double layer capacitor immediately before battery replacement is low.

[0005]

[Problems to be Solved by the Invention] As mentioned above, in conventional circuits, the charging voltage of a secondary battery or electric double layer capacitor is equivalent to the lower limit level of battery replacement voltage, and since discharging starts from this state, the capacity The duration of the effective voltage range due to the limited power storage device is short, which causes users to feel uneasy.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to make it possible to switch high and low output voltages for power saving, and to maintain the effective voltage range for the load circuit when the battery is removed. It is an object of the present invention to provide a battery backup circuit that can extend the operating time.

[0007]

[Means for Solving the Problems] The present invention is basically a battery backup circuit of a type in which a power storage body is connected in parallel with a battery and power is supplied from the power storage body to a load circuit when the battery is removed. In order to achieve the above object, the present invention connects a power supply circuit that can switch the output voltage high or low to the battery, and connects a parallel circuit of a high resistance and a switch element in series with the power storage body to connect the battery to the output side of the power supply circuit. Place it in parallel with the battery. Then, before battery replacement, the power supply circuit is switched to high voltage output and the switch element is controlled to be conductive, and when the battery is removed, power is supplied from the power storage body to the load circuit via the rectifier diode.

[0008] As the electricity storage body, an electric double layer capacitor is preferable. In addition, a voltage detection circuit is provided in parallel with the battery to generate an alarm signal when the battery terminal voltage drops to the battery replacement voltage lower limit level, and a switch is provided that is linked to the opening/closing of the battery case lid to generate the lid opening signal. A configuration in which a power supply circuit and a switch element are controlled is preferable.

[0009]

[Operation] Under normal conditions, the battery output is made into a constant voltage by the power supply circuit and supplied to the load circuit. At the same time, the power storage device is also charged via the high resistance. When the output voltage of the power supply circuit increases, the terminal voltage of the power storage body is charged so as to gradually increase, and when the output voltage decreases, the terminal voltage of the power storage body gradually decreases, and the power storage body is charged at that low voltage. In other words, the terminal voltage of the power storage body slowly fluctuates up and down depending on the output voltage of the power supply circuit.

[0010] When the battery is replaced or when the battery output drops to the battery replacement voltage lower limit level, the output voltage of the power supply circuit increases regardless of the operating state. Then, the switch element becomes conductive. As a result, the power storage body is rapidly charged at a high voltage. Thereafter, the output of the power supply circuit disappears due to battery consumption or removal of the battery, and discharge from the power storage body to the load circuit begins. Data etc. are saved by this power supply. Since the power storage body is once rapidly charged at a high voltage, the duration of the effective voltage range to the load circuit becomes longer when the battery is removed or when the battery is exhausted.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an embodiment of a battery backup circuit according to the present invention. This circuit includes a battery 10,
It includes a voltage detection circuit 12 connected in parallel thereto, and a power supply circuit 14 that controls the output of the battery 10 at a constant voltage. The voltage detection circuit 12 monitors the terminal voltage of the battery 10 and outputs an alarm signal VDS when the terminal voltage falls to the battery replacement voltage lower limit level (operating voltage lower limit level). The power supply circuit 14 boosts the voltage (for example, +5V) for a normal mode, or steps it down (for example, +3V) for a sleep mode (standby mode) such as waiting for a key input, and supplies it to a load circuit (not shown).
This is a circuit that supplies power with the operating voltage VCC1. In other words, this power supply circuit 14 is a circuit that can switch the output voltage to high or low. The high/low switching control is performed by the power supply control signal PWS.

In the present invention, the high resistance 18 and the switching element 1
A parallel circuit with 6 is connected to an electric double layer capacitor 20 serving as a power storage body and placed in parallel with the battery 10 on the output side of the power supply circuit 14. For example, the high resistance 18 is 100kΩ.
Use one with a certain resistance value. The switch element 16 may be a transistor switch, and its conduction (on) and non-conduction (off) are controlled by a switch control signal SWS. In addition, a rectifier diode 22 is connected to the positive electrode side of the electric double layer capacitor 20.
Connect the anode of and connect the cathode to the load circuit,
Hold voltage V in the load circuit when the battery is exhausted or when the battery is removed
Apply CC2.

[0013] When normal operation is performed with the battery 10 having sufficient energy remaining, the power supply circuit 14 is in operation. In normal mode, high voltage (+5V) is output. When in sleep mode (standby mode) such as waiting for a key input, the power control signal PWS switches to low voltage (+3V) output to suppress power consumption in the load circuit. Also, during this time, the switch element 16 is in a non-conductive state, and the output of the power supply circuit 14 charges the electric double layer capacitor 20 through the high resistance 18. Therefore, depending on the output voltage of the power supply circuit 14, the terminal voltage of the electric double layer capacitor 20 gradually approaches +5V when outputting a high voltage, and gradually approaches +3V when switching to a low voltage output. Terminal voltage changes. In other words, this +5~3
Charging and discharging are repeated within the V range according to the operating mode.

As the battery 10 becomes exhausted, the terminal voltage decreases as shown in FIG. When the battery replacement voltage lower limit level is reached, an alarm signal VDS is generated from the voltage detection circuit 12 to prompt battery replacement. This alarm signal VDS causes the display on the liquid crystal display to disappear. Further, the output voltage of the power supply circuit 14 is forcibly switched to a high voltage output by the power supply control signal PWS. The switch element 16 is then rendered conductive by the switch control signal SWS. Then, the electric double layer capacitor 20 is rapidly charged (in about a few seconds) with a high voltage from the power supply circuit 16 through the switch element 16. The operation is shown in FIG. The terminal voltage of the electric double layer capacitor 20 rises rapidly from a level near +3V to near +5V, as shown by the broken line. Eventually, the output from the power supply circuit 14 disappears, but after that, the electric double layer capacitor 20 naturally switches to supplying power to the load circuit.

Note that this operation is automatically performed when replacing the battery even when the terminal voltage of the battery 10 has not reached the battery replacement voltage lower limit level. A mechanical switch (not shown) is built into the battery case lid to turn it on and off by opening and closing the lid. When the battery case lid is opened to replace the battery, the switch detects this and generates a lid open signal. Then, similarly to the above, the output voltage of the power supply circuit 14 is forcibly switched to a high voltage (+5V) output by the power supply control signal PWS, and then the switch element 16 is made conductive by the switch control signal SWS, and the electric double layer capacitor 20 is made conductive. Charges quickly with high voltage.

When the charge charged in the electric double layer capacitor 20 is Q, the amount of charge is expressed by the following equation. Q (coulomb) = C・V…(1)
Here, C is the capacitance (farad) of the electric double layer capacitor, and V is the terminal voltage (charging voltage) of the electric double layer capacitor.
This is the potential difference (in volts) obtained by subtracting the lower limit voltage at which the load circuit can maintain operation. In the present invention, the voltage is increased to increase the amount of charge. The time that can be discharged from an electric double layer capacitor can be expressed by the following formula. T (time) = Q/I...(
2) Here, I is the average discharge current (ampere), Q is the amount of charge stored in the electric double layer capacitor, and the above (1)
Expressed by the formula. To summarize the above, the time that power can be supplied from an electric double layer capacitor is T=(C・V)/I...(
3).

In the present invention, even in the sleep mode (+3V), the output voltage increases as shown by the broken line in FIG. 2, and the electric double layer capacitor 20 is charged to a high voltage of approximately +5V when the battery is removed. . Therefore, it takes a relatively long time (the voltage holding time according to the present invention is indicated by the symbol TL) to reach the discharge end point TP (the point at which the load circuit's sleep operation voltage lower limit level VL is reached), and there is sufficient time for battery replacement. . On the other hand, in the conventional technology, since the terminal voltage of the electric double layer capacitor is at the battery replacement voltage lower limit level or the sleep mode voltage (+3V), the time until the discharge end point (the voltage holding time in the conventional circuit is indicated by the symbol TN) ) is quite short, leaving little time for battery replacement.

[0018]

[Effects of the Invention] As described above, the present invention is configured to apply a high voltage to rapidly charge the power storage device before replacing the battery, thereby reducing the effective voltage range for the load circuit when the battery is exhausted or when replacing the battery. The duration can be extended. As a result, there is ample time, so even if there is no battery at hand, there is less risk of data loss. Even when replacing batteries, the user can work slowly and with peace of mind. Furthermore, the present invention is suitable for devices incorporating a power supply circuit that switches the output voltage high and low for power saving, and is highly effective in effectively utilizing small portable devices and improving reliability.

[Brief explanation of the drawing]

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

FIG. 2 is an explanatory diagram of discharge curves of electric double layer capacitors in the circuit of the present invention and the conventional circuit.

FIG. 3 is an explanatory diagram of a battery discharge curve.

[Explanation of symbols]

10 Battery 12 Voltage detection circuit 14 Power supply circuit 16 Switch element 18 High resistance 20 Electric double layer capacitor 22 Rectifier diode

Claims (2)

[Claims] Claim 1: In a battery backup circuit that connects a power storage body in parallel with a battery and supplies power from the power storage body to a load circuit when the battery is removed, a power supply circuit that can switch the output voltage high or low is connected to the battery, A parallel circuit consisting of a resistor and a switch element is connected in series with the power storage body and placed in parallel with the battery on the output side of the power supply circuit, so that the power supply circuit is switched to a high voltage output and the switch element is made conductive before the battery is replaced. A battery backup circuit is characterized in that it controls the battery and supplies power to a load circuit from a power storage body through a rectifier diode when the battery is removed. 2. The battery backup circuit according to claim 1, wherein the electricity storage body is an electric double layer capacitor.