JP2000139037A - Charge switching circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching circuit which can make charging possible while electricity is turned on without shifting between precharge and regular charge repeatedly. SOLUTION: A charge switching circuit 60 is provided with a first terminal 68 connected to both terminals of a battery, a second terminal 69 connected to a charging terminal of a charging circuit, a first switch 61 connected between the first terminal 68 and the second terminal 69 and opened/closed by control of a CPU 18, a second switch 62 connected between the first terminal 68 and the second terminal 69 and opened/closed by control of a precharge control circuit 64, a third switch 63 with one end connected to the first terminal 68 through a voltage division circuit 66 and the other end connected to the negative pole terminal of the battery and so controlled as to be closed when the precharge control circuit 64 is operating and opened when the precharge control circuit 64 stops, and a voltage detection circuit 65 which detects the voltage at a voltage division point 70 of the voltage division circuit 66 and outputs a control signal 67 which stops the operation of the CPU 18 when the detected voltage is a threshold voltage (3 V) or below and causes the CPU 18 to start regular charging when the detected voltage is threshold voltage or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charge switching circuit, and more particularly to a charge switching circuit used for charging a lithium ion secondary battery used in a portable terminal.

[0002]

2. Description of the Related Art In recent years, for example, the demand for portable electronic devices has increased, and secondary batteries used therein have been required to be small, light and high in performance. From such a background, a lithium ion secondary battery has been used in many recent portable electronic devices instead of a nickel cadmium secondary battery or the like.

This is because lithium ion secondary batteries are lightweight and have excellent characteristics such as high energy density, high voltage storage characteristics, and cycle life. In particular, a graphite-based lithium ion secondary battery has excellent discharge characteristics that maintain a flat voltage level without a change in the battery due to battery consumption. As a charging device for charging such a lithium ion secondary battery, a dedicated charging device suitable for the properties of the lithium ion secondary battery is used. That is, since a lithium ion secondary battery has almost no resistance, it is necessary to charge it with a low voltage and low current circuit.

In addition, unlike a nickel-cadmium secondary battery, the voltage of a lithium-ion secondary battery does not stop rising even when overcharged, and when the dry battery voltage exceeds 4.5 V, gas is generated due to decomposition of an electric field region and the inside of the battery is discharged. Has the property of increasing pressure. Therefore, the charging device must have a function of stopping charging when the dry cell voltage of the lithium ion secondary battery reaches, for example, 4.2 V.

[0005] Therefore, in general, a lithium ion secondary battery is charged by control by a CPU (hereinafter, referred to as normal charging) when the battery voltage is about 3 V or more, and is precharged by a timer IC or the like when the battery voltage is 3 V or less. Charging is performed by control by a circuit (hereinafter, referred to as preliminary charging). In particular, when charging a battery with a lithium ion secondary battery installed in a portable terminal, the battery voltage is detected by a voltage detection circuit such as a voltage detection IC, and the output signal (control signal) is detected by C.
The signal is transmitted to the PU, and it is determined whether the charging is performed by the normal charging or the preliminary charging. As described above, when charging the lithium ion secondary battery, when the voltage is 3 V or less, preliminary charging is performed first, the threshold voltage of the voltage detection circuit is set to 3 V, and when the increased battery voltage exceeds this threshold voltage, the CPU is charged.
Was switched to the normal charging.

[0006]

However, if the normal charging is performed while the portable terminal is in the operating state, the battery voltage of the lithium ion secondary battery being charged becomes lower than the threshold voltage of the voltage detecting circuit due to the current consumed by the operation of the portable terminal. May drop.

FIG. 4 is a diagram showing charging characteristics of a conventional charging switching circuit. It is assumed that the threshold voltage of the voltage detection circuit is 3V. If the battery voltage drops to 3 V or less due to discharging, charging is started with the portable terminal equipped with the battery set in the charger. When charging is started (charging ON), the battery voltage gradually increases due to charging from the charging terminal under the control of the pre-charging control circuit. When the battery voltage reaches the threshold voltage 3V of the voltage detection circuit, switching to normal charging under the control of the CPU occurs according to a control signal from the voltage detection circuit.

The period shown in FIG. 4 is a precharge period,
The periods indicated by indicate normal charging periods, respectively.
If the battery voltage is slightly lower than the threshold voltage of 3 V due to the current consumption while the mobile terminal is operating, the process returns to the precharge again. This operation is repeated several times, and the conventional charging switching circuit has a problem that it takes a long time to charge the battery.

FIG. 2 is a diagram showing a battery pack protection circuit for preventing overcharging and overdischarging of a battery. In the case of a lithium ion secondary battery, when the cell voltage of the battery drops below a certain voltage in order to prevent performance deterioration and ensure safety, the protection IC 51 in the battery pack turns off the discharge control FET Q1 and stops the output. Circuit.

The battery pack protection circuit 50 includes terminals 54 and 55
The battery cell 52, the temperature protection circuit (PTC) 53, and the control FET Q1 are connected in series. A protection diode D1 is connected in parallel to the control FET Q1. The protection IC 51 is connected between the terminals 54 and 56, and outputs a control signal F when the voltage of the battery cell 52 becomes lower than a predetermined voltage.
Output to ETQ1 to turn off FETQ1.

PTC (Positive Temper)
When the temperature inside the battery pack rises due to an overcurrent, the attraction circuit 53 turns off and stops charging. Normal charging is performed by supplying charging power from a charging supply circuit (not shown) to terminals 54 and 55 via a charging switching circuit. When charging a lithium ion secondary battery in which such a protection circuit is operating, it is necessary to first perform preliminary charging and then perform normal charging after the battery voltage of the battery cell 52 becomes equal to or higher than the protection circuit release voltage.

However, since the lithium ion secondary battery in which the protection circuit operates is charged via the protection diode D1, the protection circuit release voltage is higher than the cell voltage by the forward voltage (VF) of the diode D1. Become. Therefore, if the threshold voltage of the voltage detection circuit is set to the protection circuit release voltage, it becomes higher than the minimum operating voltage of the portable terminal. For this reason, when a battery having a voltage of about 3 V is set in the charger with the power of the portable terminal turned on and charging is started, the mode is switched to the pre-charging operation, and the operation of the CPU is performed by the output signal (control signal) of the voltage detection circuit. Stops. Therefore,
There has been a problem that the threshold voltage of the voltage detection circuit must be set to be equal to or lower than the protection circuit release voltage.

The present invention solves the above-mentioned problems of the prior art, and does not repeat the transition operation between the preliminary charging and the normal charging. It is an object of the present invention to provide a charge switching circuit that enables charging without stopping the operation of the charging.

[0014]

According to the present invention, there is provided a charging device which performs normal charging under the control of the CPU when the battery voltage is higher than a predetermined threshold voltage, and performs preliminary charging under the control of a preliminary charging control circuit when the battery voltage is lower than the threshold voltage. In a switching circuit, a first terminal connected to an anode terminal of a battery, a second terminal connected to a charging terminal of a charging supply circuit, and a connection between the first terminal and the second terminal. A first switch that is opened and closed under the control of the CPU, a second switch that is connected between the first terminal and the second terminal, and that is opened and closed under the control of the precharge control circuit; One end is connected to the first terminal via a voltage dividing circuit, the other end is grounded together with the cathode terminal of the battery, and is controlled to be closed during operation of the precharge control circuit and open during stoppage of the precharge control circuit. Third switch Detecting the voltage of the voltage dividing point of the voltage dividing circuit, stopping the operation of the CPU when the detected voltage of the voltage dividing point is equal to or lower than the threshold voltage, and stopping the operation of the CPU when the detected voltage is equal to or higher than the threshold voltage. A voltage detection circuit that outputs a control signal to start normal charging.

The present invention also provides a charge switching circuit that performs normal charging under the control of the CPU when the battery voltage is equal to or higher than a predetermined threshold voltage, and performs preliminary charging under the control of the preliminary charging control circuit when the battery voltage is equal to or lower than the threshold voltage. When the voltage is equal to or lower than the threshold voltage, the operation of the CPU is stopped, and when the voltage is equal to or higher than the threshold voltage, a voltage detection circuit that outputs a control signal to cause the CPU to start normal charging is provided. This is a difference between during pre-charging and during CPU operation.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a charge switching circuit according to an embodiment of the present invention; FIG. 1 is a block diagram showing a charge switching circuit for a portable terminal according to the present invention. The charge switching circuit 60 is connected to the terminal 6
Two switches 6 openably and closably connected between 8, 69
1, 62, a precharge control circuit 64, a switch 63 connected between a terminal 68 and a ground terminal via a voltage dividing circuit 66, and a voltage dividing point 70 of the voltage dividing circuit 66 and the CPU 18. And a voltage detection circuit 65 connected thereto.
The switch (SW1) 61 is opened and closed under the control of the CPU 18 and operates during normal charging. In addition, a switch (SW
2) 62 operates under the control of the pre-charge control circuit 64 and operates during pre-charge.

As described above, the normal charging is performed by the CPU 18 in the SW1 mode.
Is ON / OFF controlled to perform charging control. For pre-charging, the pre-charging control circuit 64 performs ON / OFF control of SW2 to perform charging control. SW3 is closed during preliminary charging (O
N), and operates to open (OFF) during normal charging. In order to charge the battery pack having the battery pack protection circuit as shown in FIG. 2, the terminal 68 and the terminal 54 are connected, the terminal 69 is connected to the charging terminal of a charging supply circuit (not shown), and the terminal 55 of the battery pack is connected. This is done by grounding.

FIG. 3 is a functional block diagram showing the configuration of a PHS portable telephone 10 equipped with the charge switching circuit 60 according to the present invention. The antenna 12 radiates or receives radio waves to exchange data with a public base station (not shown) corresponding to the standby zone. This antenna 12
Are connected to the RF unit 14. The RF unit 14 amplifies and frequency-converts a signal received by the antenna 12 and outputs a demodulation signal to the baseband unit 16, and amplifies and frequency-converts a voice-modulated signal from the baseband unit 16. And a transmission circuit for outputting to the antenna 12. The baseband unit 16 is connected to a CPU 18 and a codec 28, and under the control of the CPU 18, demodulates an RF signal received from the antenna 12 including a voice signal and a caller number. The baseband unit 16 also notifies the CPU 18 of the ID, which is the identification number of the public base station, received by the RF unit 14 and the received electric field strength when the power unit is on standby.

The codec 28 is a converter for converting a digital signal into an analog signal and converting an analog signal into a digital signal. That is, the codec 28 is
8, the digital audio signal input from the baseband unit 16 or the CPU 18 is converted into an analog signal and output to the speaker (SP) 26, and the microphone (MI)
C) The analog audio signal input from 24 is converted into a digital audio signal and output to the baseband unit 16. The codec 28 is also connected to the DTMF receiver 30, converts a digital signal input from the baseband unit 16 into an analog signal, and outputs the analog signal to the DTMF receiver 30. DT
When the signal input from the codec 28 is a DTMF signal, the MF receiver 30 outputs the content to the CPU 18.

The CPU 18 is a control unit for controlling the entire mobile communication terminal, and includes a ROM 18a, which is a nonvolatile memory in which programs and the like are written, and a RAM 18a.
18b. The RAM 18b temporarily stores various information including information on the base station selected as the base station at the time of standby. The CPU 18 has a display unit 20 for displaying a telephone number and the like and a received electric field strength of the base station.
And an input key for inputting phone numbers and characters, a power key,
A key input unit 22 composed of various keys such as a call key for performing a call process is connected.

A charge switching circuit 60 shown in FIG. 1 is coupled to the CPU 18 and responds to an output signal (control signal) 67 from the voltage detection circuit 65 by turning on the switch 61.
It instructs the N / OFF control and precharge control circuit 64 to stop the control operation. By incorporating the charge switching circuit 60 in the mobile phone 10 as described above, the battery cell 52 housed in the battery pack protection circuit 50 can be charged in an operating state.

Next, the charging operation of the charging switching circuit shown in FIG. 1 will be described in detail with reference to the charging characteristic diagram shown in FIG.
The period shown in FIG. 5 indicates the preliminary charging period, and the period shown in FIG. 5 indicates the normal charging period. It is assumed that the threshold voltage of the voltage detection circuit 65 is 3V. That is, the detection voltage of the input terminal (IN) of the voltage detection circuit 65 is 3
When the voltage is equal to or higher than V, the signal level of the control signal 67 output from the output terminal (OUT) becomes HIGH. When the voltage of the battery cell is 3 V or less, the preliminary charging operation is started simultaneously with the start of charging (charging ON).

In FIG. 1, the switch 63 is turned on and the switch 61 is turned off. When the switch 63 is turned on, a current flows between the terminal 68 and the ground terminal via the voltage dividing circuit 66 during the pre-charging. Therefore, the voltage at the voltage dividing point 70 of the two resistors R1 and R2 is lower than the voltage appearing at the terminal 68.

As shown in FIG. 5, when the pre-charging is started and the pre-charging of the battery cell is performed via the switch 62 and the terminal voltage of the battery cell increases, the voltage of the terminal 68 also increases. The voltage at point 70 also increases. Thus, hysteresis is provided by the voltage dividing circuit. When the voltage at the branch point 70 reaches 3 V, which is the threshold voltage of the voltage detection circuit 65, the control signal 67 of the voltage detection circuit 65 becomes HIGH.
In response to this control signal, the CPU stops the operation of the pre-charge control circuit 64.

Further, the CPU 18 starts normal charging by controlling the switch 61. With the stop of the pre-charging, the switch 63 is turned off, and the current flowing through the voltage dividing circuit 66 stops. Accordingly, the voltage at the voltage dividing point 70 rises and becomes equal to the voltage level of the terminal 68. That is, the voltage applied to the input terminal of the voltage detection circuit 65 becomes higher than 3V. Therefore, as shown in FIG. 5, the voltage applied to the input terminal of the voltage detection circuit 65 is equal to the voltage level of the terminal 68 even when the precharge period ends and the battery voltage drops after switching to the normal charge period. Since they are the same, the voltage is much higher than the threshold voltage 3V.

That is, if the voltage division ratio of the resistors R1 and R2 is appropriately determined, for example, if the voltage of the voltage dividing point 70 is 3V, the voltage of the terminal 68 is set to 3.7V. Even if the battery voltage drops to about 3.5 V after switching from the normal charging to the normal charging, the voltage detection circuit 6
Since the voltage applied to the input terminal of No. 5 is equal to or higher than the threshold voltage of 3 V, the signal level of the control signal 67 is still at the HIGH level, and the precharge circuit 64 does not operate again.

By setting the voltage divided by the resistors R1 and R2 to be equal to or higher than the threshold voltage of the voltage detection circuit 65, when the battery voltage is equal to or lower than the protection circuit release voltage, the precharge control is performed and the protection circuit release is performed. When the voltage is higher than the voltage, normal charge control by the CPU 18 can be performed. Note that the voltage detection circuit 65 can be easily configured using a comparison circuit (comparator). Further, the voltage dividing circuit 66 can be configured by connecting the resistors R1 and R2 in series as shown in FIG. 1, but other configurations can be employed.

[0028]

As described in detail above, in the present invention,
Since the applied voltage applied to the input terminal of the non-voltage circuit for determining the charge control is changed between during the pre-charging and during the normal charging, the mode is switched from the pre-charging to the normal charging, and then the pre-charging is resumed. Will not be repeated. Further, even if the battery whose voltage is near the threshold voltage of the voltage detection circuit is charged in the power-on state, the CPU does not stop. Therefore, it is possible to charge the battery while operating the mobile phone.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a charge switching circuit of the present invention.

FIG. 2 is a diagram showing a configuration of a battery pack protection circuit.

FIG. 3 is a functional block diagram showing a configuration of a PHS mobile phone in which the charge switching circuit of the present invention is mounted.

FIG. 4 is a diagram showing charging characteristics of a conventional charge switching circuit.

FIG. 5 is a diagram showing charging characteristics of the charging switching circuit of the present invention.

[Explanation of symbols]

 18 CPU 60 Charge switching circuit 61 Switch (SW1) 62 Switch (SW2) 63 Switch (SW3) 64 Precharge control circuit 65 Voltage detection circuit 66 Voltage divider circuit 67 Control signal 68, 69 terminal

Claims (5)

[Claims] 1. A charge switching circuit for performing normal charging under the control of a CPU when the battery voltage is equal to or higher than a predetermined threshold voltage, and performing preliminary charging under the control of a preliminary charging control circuit when the battery voltage is equal to or lower than the threshold voltage. And a second terminal connected to a charging terminal of a charging supply circuit; and a switching terminal connected between the first terminal and the second terminal and controlled by the CPU. A first switch connected between the first terminal and the second terminal, and a second switch that is opened and closed under the control of the pre-charge control circuit; A third switch that is connected to the first terminal, the other end is grounded together with the cathode terminal of the battery, is closed during operation of the precharge control circuit, and is controlled to be open during stoppage; Dividing voltage of the voltage dividing circuit Detecting a voltage, when the voltage of the detected voltage dividing point is equal to or less than the threshold voltage stops the operation of the CPU, when the a threshold voltage or higher, the CP
A charge switching circuit comprising: a voltage detection circuit that outputs a control signal to cause U to start normal charging. 2. The charge switching circuit according to claim 1, wherein the voltage dividing circuit is composed of two resistors connected in series, one end of which is connected to the first terminal and the other end of which is connected to the third switch. A charge switching circuit, wherein a connection point is connected to a ground terminal and an input terminal of the voltage detection circuit. 3. A charge switching circuit that performs normal charging under the control of a CPU when the battery voltage is equal to or higher than a predetermined threshold voltage, and performs preliminary charging under the control of a preliminary charging control circuit when the battery voltage is equal to or lower than the threshold voltage. At the time of, the operation of the CPU is stopped, and when the voltage is equal to or higher than the threshold voltage, a voltage detection circuit that outputs a control signal to the CPU to start normal charging is provided. A charge switching circuit characterized in that the charge switching circuit is different from that during a CPU operation. 4. The charge switching circuit according to claim 3, further comprising switch means controlled to be closed during operation of the pre-charge control circuit and to be opened during stop of the preliminary charge control circuit, wherein the different threshold voltage has one end. Is connected to the anode terminal of the battery via a voltage dividing circuit, and the other end is obtained by the voltage dividing point of the voltage dividing circuit grounded together with the cathode terminal of the battery via the switch means. Switching circuit. 5. The charge switching circuit according to claim 1, wherein the charge switching circuit is applied to charge a lithium ion battery.