JP2001352686A - Low-voltage detection circuit for portable telephone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-voltage detection circuit for a portable telephone which can extend long-term storage period of a battery pack with simple circuit constitution, concerning a low-voltage detecting circuit for a portable telephone. SOLUTION: This is a circuit for detecting the low voltage of a portable telephone 10, which operates the circuit using a secondary battery 11. Only is a battery pack 20 provided with a protective circuit 13 against overdischarging, and the operating voltage of a signal generating circuit for alarm of low voltage within that protective circuit against overdischarging is varied according to the operation state of the portable telephone 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low voltage detection circuit for a portable telephone, and more particularly to a battery protection circuit for a portable telephone.

[0002]

2. Description of the Related Art Conventionally, when a power supply voltage of a portable telephone is lowered, the voltage of the device becomes unstable. For this reason, the operation is forcibly stopped at a certain voltage or lower to prevent the device from malfunctioning. In addition, lithium-ion batteries are mainly used for batteries used in mobile phones. Since a lithium ion battery is deteriorated by overdischarge, an overdischarge protection circuit is provided in a battery pack to protect the battery. The overdischarge protection circuit usually monitors the battery voltage and shuts off the battery output at a certain voltage or less.

FIG. 5 is a block diagram showing a conventional constant voltage protection circuit. In the figure, reference numeral 10 denotes a mobile phone. 1
For example, a DC voltage from an AC adapter is supplied to terminals 21 and 22.
, A charging circuit for charging the battery, D is a diode connected to the output of the charging circuit 1, and the output of the diode D is supplied to the charging battery 11 to perform charging. 2 is a mobile phone circuit necessary for the operation of the mobile phone,
Reference numeral 3 denotes a low-voltage protection circuit that is connected to the mobile phone circuit 2 and protects the circuit.

[0004] Reference numeral 20 denotes a battery pack. The battery pack 2
At 0, 11 is a secondary battery (hereinafter simply referred to as a battery),
Reference numeral 12 denotes an overdischarge protection circuit for protecting the battery 11 from overdischarge. The operation of the circuit thus configured will be described as follows.

A DC voltage, which is an AC adapter output, is applied to the charging circuit 1 from terminals 21 and 22. The output of the charging circuit 1 is output via the diode D and charges the battery 11. The output of the diode D also enters the mobile phone circuit 2 to operate the circuit. In this case, if the mobile phone circuit 2 is operated without charging, the battery 11
Voltage decreases.

Here, the low-voltage protection circuit 3 monitors the operating voltage of the mobile phone circuit 2, and stops applying the operating voltage to the mobile phone circuit 2 when the operating voltage drops below a predetermined value. In addition, malfunction of the mobile phone circuit 2 is prevented. The overdischarge protection circuit 12 of the battery pack 20 disconnects the battery 11 from the circuit when the battery voltage further decreases and affects the performance of the battery, thereby preventing the battery voltage from further lowering. are doing.

FIG. 6 is a diagram showing a relationship between a battery voltage of a portable telephone and an event. In the figure, A is a power restoration voltage, B is an alert sounding voltage, C is a low voltage protection voltage,
D indicates the overdischarge voltage of the battery pack.

The low voltage detection circuit in the low voltage protection circuit 3 provided in the mobile phone changes the detection voltage depending on the state of the mobile phone because the battery voltage and the remaining capacity do not match due to charging and discharging of the battery. . The detection voltage is about 3.1 V in the talking mode, and about 3.3 V in the standby mode.

At the above voltage, the portable telephone 10 sounds a battery exhaustion alert, alerts the user, and when the portable telephone 10 is continuously used, the operation of the telephone is stopped at a power supply voltage of about 2.7 V. In this state, the battery load is reduced by stopping the operation of the telephone, so that the battery terminal voltage increases. However, the mobile phone is not turned on again until the battery voltage recovers to about 3.5 V, and thus keeps the operation stopped.

If the mobile phone is left untouched, the battery capacity is consumed due to the operation of the protection circuit of the battery pack 20 and the current consumption when the mobile phone is cut off, and the power supply voltage is gradually reduced. When the battery voltage drops to about 2.3 V, the overdischarge protection circuit 12 inside the battery pack operates to cut off the battery output.

Although the current consumption of the telephone is eliminated by shutting off the battery output, the battery voltage continues to decrease gradually due to the current consumption of the protection circuit 12 of the battery pack 20 and the self-discharge of the battery. If the battery voltage becomes less than 1 V when left in this state,
Copper (Cu) as a current collector material of the lithium ion battery negative electrode starts to elute into the electrolytic solution, and remarkable deterioration of secondary battery performance starts. There are differences depending on the storage environment, battery type, etc.
The remarkable deterioration of the secondary battery performance starts from one to two years after the overdischarge protection circuit 12 is activated.

FIG. 7 is a diagram showing battery storage characteristics. The vertical axis represents the battery voltage (V), and the horizontal axis represents the number of storage days (DAY).
This figure shows the characteristics of the battery terminal voltage (cell voltage) when the battery pack is left unattached to the mobile phone. Initially, a voltage of about 3.8 V is maintained at 3.5 V or more until 400 days, but after 400 days,
It begins to decrease sharply, becomes 1 V or less after 800 days, and cannot be recovered. In the figure, Vh indicates the operating voltage of the overdischarge protection circuit 12. That is, Vh is set to about 2.3V.

[0013]

As shown in FIG. 5, the conventional low voltage protection circuit has a double circuit for detecting a drop in the battery voltage and stopping the operation. There is much wear. In addition, even if the battery is provided with the overdischarge protection circuit 12, the battery continues to discharge slightly due to power consumption of the protection circuit and self-discharge of the battery, and if left unattended for a long period of time, the battery will not recover as shown in FIG. There was a problem.

The present invention has been made in view of the above problems, and provides a low-voltage detection circuit for a portable telephone which has a simple circuit configuration and can extend a long-term storage period of a battery pack. It is intended to be.

[0015]

(1) FIG. 1 is a block diagram showing the principle of the present invention. The same components as those in FIG. 5 are denoted by the same reference numerals. In the figure, 10 is a mobile phone, and 20 is a battery pack. Reference numeral 1 denotes a charging circuit that receives a voltage from an AC adapter to charge a battery, D denotes a diode, and 2 denotes a mobile phone circuit that operates on the voltage supplied from the battery 11. Reference numeral 11 denotes the battery described above, and reference numeral 13 denotes an overdischarge protection circuit that detects that the battery voltage has dropped and shuts off the power supply circuit. In the overdischarge protection circuit 13, a low voltage alarm signal generation circuit (not shown) is provided. The operating voltage of the low voltage alarm signal generation circuit is changed according to the operating state of the mobile phone 10.

As described above, according to the present invention, the low voltage detection / protection circuit is provided only on the battery pack 20 side to simplify the circuit configuration, and the overdischarge protection operation voltage is set to the low voltage protection operation voltage of the conventional portable telephone. By doing so, it is possible to increase the overdischarge protection operating voltage and extend the period of time during which the battery performance of the battery pack deteriorates. Further, in the present invention, by changing the operating voltage of the low voltage alarm signal generation circuit according to the operating state of the mobile phone 10, the battery pack can be protected according to the load state.

(2) The invention according to claim 2 is characterized in that the overdischarge detection voltage is set to be 2.5 V or more and less than 3.1 V. With this configuration, by using the overdischarge detection voltage of 2.5 V or more and less than 3.1, it is possible to detect a voltage drop of the battery before the battery pack is deteriorated, and to extend the life of the battery. be able to.

(3) The invention according to claim 3 is characterized in that the voltage for restoring to a steady state after the protection operation is set to be higher than 2.5 V and lower than 3.1 V. With this configuration, it is possible to reliably restore the battery to a steady state.

(4) According to the fourth aspect of the present invention, when the protection operation is restored, a signal is transmitted to the portable telephone circuit to discriminate that the power supply voltage is within the normal range and that the protection operation is being performed. It is characterized by the following.

With this configuration, the restoration voltage can be reliably supplied to the mobile phone circuit. (5) According to a fifth aspect of the present invention, when the overdischarge protection is not activated, a signal indicating a power supply voltage normal range between the protection voltage according to the second aspect and the recovery voltage according to the third aspect is transmitted. It is characterized by doing.

With this configuration, the cellular phone circuit can
It is possible to operate in the above voltage range.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a diagram illustrating a configuration example of the overdischarge protection circuit 12. 1 are denoted by the same reference numerals. As shown in the figure, the overdischarge protection circuit 12 mainly includes a low voltage detection circuit 30. The voltage from the battery 11 is connected to the terminal via the resistor R1. The common potential of the battery 11 is connected to a terminal. A capacitor C1 is connected between one end of the resistor R1 and the common potential, and a capacitor C2 is connected between one end of the capacitor C1 and the terminal. The capacitors C1 and C2 are capacitors for removing noise.

Reference numerals 31 and 32 denote output terminals of the battery 11.
31 is a positive terminal and 32 is a negative terminal. Battery 11
A switching field effect transistor (FET) Q1 is connected between the common potential of
The gate G of the FET Q1 is connected to a terminal of the low voltage detection circuit 30. In the FET Q1, D is a drain and S is a source. The terminal is a detection signal output terminal output to the mobile phone circuit 2, and the terminal is a status signal input terminal input from the mobile phone circuit 2.

In the circuit thus constructed, during normal operation (when the battery voltage is at a normal value), the FET Q1 is turned on by a control signal from the terminal, and the mobile phone circuit 2 is turned on.
When the battery voltage becomes low, a control signal is output from the terminal to turn off the power supply to the mobile phone circuit 2 and cut off the power supply to the mobile phone circuit.

FIG. 3 is a diagram showing a specific configuration example of the low voltage detection circuit 30. The same components as those in FIG. 2 are denoted by the same reference numerals. In the figure, R2 and R3 are voltage dividing resistors, and the divided voltage is input to the negative input of the first comparator CMP1. 33 is a constant current source for outputting a constant current, and R4 and R5 are current / voltage conversion resistors connected to the constant current source 33 for generating a reference voltage. The voltage at one end of the resistor R4 is input as a reference voltage to the positive input of the first comparator CMP1.

Q2 has a collector / emitter whose current /
A transistor connected to both ends of the voltage conversion resistor R5,
A state signal from the mobile phone circuit 2 is input to the base of the transistor Q2. The output of the comparator CMP1 is a field effect transistor (FET) Q
3 is input to the gate.

R8 is a resistor to which a positive voltage of the battery voltage is applied at one end, and a drain D of the FET Q3 at the other end.
Is connected. The drain D of the FET Q3 is connected to the terminal and outputs a low-voltage warning signal. FE
The source of TQ3 is connected to a common potential. The constant current source 33, the resistors R2 to R5, the transistor Q2, and the comparator CMP1 constitute a low voltage alarm signal generation circuit 40. R6 and R7 are voltage dividing resistors, and the divided voltage is input to the positive input of the second comparator CMP2. The reference voltage VREF is input to the negative input of the comparator CMP2. The output of the comparator CMP2 is connected to the gate G of the switching FET Q1 (see FIG. 2). R9 is a resistor that receives a status signal input from the mobile phone circuit 2, and the status signal input from the terminal is connected to the base of the transistor Q2 via a resistor R9. The operation of the circuit thus configured will be described as follows.

First, according to the present invention, the circuit configuration is simplified by providing the low voltage detection / protection circuit only on the battery pack 20 side. When the operating voltage of the battery 11 is normal, the positive input voltage (reference voltage VREF) of the comparator CMP2 is higher than the negative input voltage, and the output is at the “H” level. Therefore, the switching FET Q1 is turned on, and the terminals 31,
32 supplies power to the mobile phone circuit 2. At this time,
The state signal from the mobile phone circuit 2 input from the terminal is "H", the transistor Q2 is turned on, and the resistance R
5 is short-circuited. As a result, the reference voltage of the comparator CMP1 is only the voltage applied across the resistor R4, the positive input voltage of the comparator CMP1 of the low voltage alarm signal generation circuit 40 is lower than the negative input voltage, and the output is “L”. Becomes

The FET Q3 receiving the "L" output of the comparator CMP1 is turned off, and its drain voltage becomes "H".
And outputs a signal to the effect that the signal is normal from the terminal to the mobile phone circuit 2. The mobile phone circuit 2 maintains the operating state.

Here, it is assumed that the operating voltage of the battery 11 has dropped. An "L" level signal is applied from the state signal input terminal and applied to the base of transistor Q2. As a result, the transistor Q2 is turned off, and the voltage applied to the resistors R4 and R5 is applied to the positive input of the comparator CMP1 as a reference voltage. Here, as the reference voltage, for example, about 2.5 V or more and less than 3.1 V is used. According to this, the battery voltage drop can be detected before the battery pack 20 is deteriorated, and the life of the battery can be extended.

As a result, the positive input voltage of the comparator CMP1 becomes higher than the negative input voltage,
1 becomes "H" level. As a result, the transistor Q3 is turned on, and the drain voltage thereof becomes "L" level. This “L” level signal is provided to the mobile phone circuit 2 as an abnormal voltage detection signal. The mobile phone circuit 2
Upon receiving the "L" signal, the circuit operation is stopped. Thus, malfunction of the circuit can be prevented.

According to this embodiment, the over-discharge protection operation voltage is set to the low-voltage protection operation voltage of the conventional portable telephone, so that the over-discharge protection operation voltage is raised, which leads to deterioration of the battery performance of the battery pack. The period can be extended. Further, in this embodiment, the operating voltage of the alarm signal generation circuit 40 is changed according to the operating state of the mobile phone (communication mode, standby mode, data transfer mode, etc.), and accordingly, according to the load state. Battery pack 2
0 can be protected.

In the present invention, as described above, the operating voltage (reference voltage) of the low-voltage warning signal generation circuit 40 is changed according to the load condition. This is because, even when the same voltage is generated, since the remaining flow rate of the battery is different, the alarm voltage is detected at the same remaining capacity of the battery.

FIG. 4 is a diagram showing an example of the characteristics of the battery voltage.
The horizontal axis shows the battery capacity, and the vertical axis shows the battery voltage. f1 indicates a characteristic under a light load, and f2 indicates a characteristic under a heavy load.
Even when the detection voltage Vth is the same, the remaining capacity of the battery is different as shown in the figure. Therefore, the reference voltage of the comparator CMP1 is changed so as to have the same remaining capacity under both light and heavy loads.

Next, the operation of the comparator CMP2 will be described. The comparator CMP2 detects an overvoltage, and when the battery voltage rises excessively, the comparator CMP2
The output of MP2 becomes “L” level, turning off the FET Q1 (see FIG. 2) inserted into the power supply circuit, shutting off the power supply, and protecting the circuit.

In the embodiment of FIG. 3, the operating voltage can be provided with a hysteresis characteristic. For example, when the reference voltage of the low-voltage alarm signal generation circuit 40 is set to be 2.5 V or more and less than 3.1 V, the battery is returned to a steady state by setting the recovery voltage higher than the voltage range. It can be performed reliably.

According to the embodiment of the present invention, a signal for distinguishing that the power supply voltage is within the normal range and that the protection operation is being performed is generated from the terminal to the portable telephone circuit 2 at the time of restoration. You can do so. This allows
The mobile phone circuit 2 can apply an operating voltage to the circuit and reliably supply a recovery voltage to the mobile phone circuit 2.

Further, according to the embodiment of the present invention, the reference voltage of the low voltage alarm signal generation circuit 40 is not less than 2.5 V and less than 3.1 V and not more than the restoration voltage, and the normal range of the power supply voltage is set. An indication signal may be transmitted. According to this, the configuration example telephone circuit 2 can operate in the above voltage range.

[0039]

As described above, according to the present invention, the following effects can be obtained. (1) According to the first aspect of the present invention, the low voltage detection / protection circuit is provided only on the battery pack side to simplify the circuit configuration.
By setting the over-discharge protection operation voltage to the low-voltage protection operation voltage of the conventional mobile phone, it is possible to increase the over-discharge protection operation voltage and extend the period of time during which the battery performance of the battery pack deteriorates. Also, in the present invention, the battery pack can be protected according to the load state by changing the operating voltage of the low voltage alarm signal generation circuit according to the operating state of the mobile phone.

(2) According to the second aspect of the invention, by using an overdischarge detection voltage of 2.5 V or more and less than 3.1, it is possible to detect a voltage drop of the battery before the battery pack is deteriorated. It is possible to extend the life of the battery.

(3) According to the third aspect of the invention, the battery can be reliably restored to a steady state. (4) According to the fourth aspect of the present invention, the restoration voltage can be reliably supplied to the mobile phone circuit.

(5) According to the fifth aspect of the invention, the portable telephone circuit can operate in the above voltage range. Thus, according to the present invention, the circuit configuration is simple,
A low-voltage detection circuit for a mobile phone that can extend the long-term storage period of a battery pack can be provided.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a diagram illustrating a configuration example of an overdischarge protection circuit.

FIG. 3 is a diagram illustrating a specific configuration example of a low-voltage detection circuit.

FIG. 4 is a diagram showing a characteristic example of a battery voltage.

FIG. 5 is a block diagram showing a conventional low-voltage protection circuit.

FIG. 6 is a diagram illustrating a relationship between a battery voltage of a mobile phone and an event.

FIG. 7 is a diagram showing battery storage characteristics.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 charging circuit 2 mobile phone circuit 10 mobile phone 11 battery 13 overdischarge protection circuit 20 battery pack D diode

Claims (5)

[Claims] 1. A low-voltage detection circuit for a mobile phone that operates a circuit using a secondary battery, wherein an over-discharge protection circuit is provided only in a battery pack, and a low-voltage alarm signal is generated in the over-discharge protection circuit. A low-voltage detection circuit for a mobile phone, wherein the operation voltage of the circuit is changed according to the operation state of the mobile phone. 2. The low voltage detection circuit for a mobile phone according to claim 1, wherein the overdischarge detection voltage is set to be 2.5 V or more and less than 3.1 V. 3. The low-voltage detection circuit for a mobile phone according to claim 1, wherein a voltage for restoring to a steady state after the protection operation is higher than 2.5 V and lower than 3.1 V. 4. A signal for distinguishing that a power supply voltage is within a normal range and that a protection operation is being performed is transmitted to a mobile phone circuit when the protection operation is restored. 4. The low-voltage detection circuit for a mobile phone according to any one of 3. 5. When the overdischarge protection is not activated, a signal indicating a power supply voltage normal range between the protection voltage according to claim 2 and the recovery voltage according to claim 3 is transmitted. A low-voltage detection circuit for a mobile phone according to claim 4.