JP2003204631A - Charging control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging control circuit, capable of minimizing the heat loss due to a charging control transistor and further reducing the heat loss, without reducing the charging current. <P>SOLUTION: The charging control circuit 6 is used to charge a battery 5 from a power supply terminal 1. The charging control circuit 6 is provided between a power supply and the charging control transistor 3 with a constant- voltage circuit 9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge control circuit used when charging a battery attached to a mobile phone, a mobile information terminal or the like.

[0002]

2. Description of the Related Art A conventional charge control circuit will be described below with reference to the drawings. FIG. 4 is a circuit diagram showing an example of a conventional charge control circuit, and FIG. 5 is a graph showing charge voltage and charge current waveforms in a lithium ion battery.

In FIG. 4, a power supply terminal 1 is used as an output circuit of a charge control circuit 6 and serves as a charge control transistor. A P channel type MOS transistor (hereinafter referred to as Pch-MOS)
3) is connected to one end (source) of Pch-MO
The other end (drain) of S3 is connected to one end of the charging current detection resistor 4, the other end of the charging current detection resistor 4 is connected to the positive voltage terminal of the battery 5, and the negative voltage terminal of the battery 5 is connected to the ground terminal 2. Has been done. The charging control circuit 6 is supplied with power from the power supply terminal 1, detects a voltage corresponding to the charging current from both ends of the charging current detection resistor 4, applies it to the gate of the Pch-MOS 3, and controls the charging current flowing through the Pch-MOS 3. Is configured to.

[0004]

However, in such a structure, the set board is being reduced in size in response to the miniaturization of the set in the mobile phone and the portable information terminal, and the set when the battery is charged is being set. Heat loss is a problem. That is, in this circuit configuration, the power supply terminal 1
The voltage is always constant regardless of the battery voltage and the charging current. For example, when the constant current / constant voltage control shown in FIG. 5 is performed, the heat loss in the Pch-MOS 3 changes the voltage of the power supply terminal 1 to 5. If it is set to 4 V (always constant regardless of the charging current), it can be calculated as follows. (1) Heat loss when battery voltage is 2.0 V or less P1 P1 = 50 mA × (5.4 V−V1) V1: Battery average voltage until battery voltage reaches 2.0 V Here, V1 = 1.5 V Then, P1 = 170 mW (2) Heat loss when battery voltage is 2.0 V or more and 3.2 V or less P2 P2 = 100 mA × (5.4 V−V2) V2: From battery voltage reaching 2.0 V to 3.2 V Battery average voltage Here, assuming that V1 = 3.0V, P2 = 240 mW (3) Heat loss P3 when battery voltage is 3.2 V or more (at maximum charging current) P3 P3 = 700 mA × (5.4 V−V3) V3: Battery average voltage when battery voltage is 3.2 V or higher and charging current is maximum Here, when V3 = 3.6 V, P3 = 1260 mW (4) Heat loss P4 when battery voltage is 3.2 V or higher (charging current decreases) P4 = I4 × (5.4V-V4) I4: Average charging current until the end of charging V4: Average voltage of the battery when the battery voltage is 3.2 V or higher and the charging current is decreased. Here, when V4 = 4.15 V and I4 = 70 mA, P
4 = 87.5 mW From the above result, the total heat loss amount P in the Pch-MOS 3 at the time of charging is represented by P = P1 + P2 + P3 + P4, and from the above result, P = 1757.5 mW.

The heat loss of the charge control transistor needs to be reduced because it involves the risk of battery damage, liquid leakage, etc. However, if it is attempted to reduce the charge current, the charging time becomes long. .

The present invention solves the above-mentioned conventional problems and provides a charge control circuit capable of minimizing the heat loss due to the charge control transistor and reducing the heat loss without reducing the charging current. The purpose is to provide.

[0007]

A charge control circuit according to the present invention is a charge control circuit used when a battery is charged from a power supply, in which a constant voltage circuit is provided between the power supply and a charge control transistor. Is.

According to the present invention, the heat loss due to the charge control transistor can be minimized.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. The same parts as those of the conventional one are designated by the same reference numerals.

FIG. 1 is a circuit diagram showing a basic configuration of an embodiment of a charge control circuit of the present invention, FIG. 2 is a circuit diagram showing a concrete configuration of an embodiment of a charge control circuit of the present invention, and FIG. FIG. 6 is a circuit diagram showing a specific example of a constant voltage circuit used in an embodiment of a charge control circuit of the present invention.

First, the basic structure of the circuit shown in FIG. 1 will be described. The power supply terminal 1 has a constant voltage circuit 9 and a charge control circuit 6
Is connected to one end (source) of the Pch-MOS 3 serving as a charge control transistor of the charge control circuit 6, and the other end (drain) of the Pch-MOS 3 is connected to one end of the charging current detection resistor 4 for charging. The other end of the current detection resistor 4 is connected to the positive voltage terminal of the battery 5, and the negative voltage terminal of the battery 5 is connected to the ground terminal 2.

Here, the charging control circuit 6 detects a voltage corresponding to the charging current from both ends of the charging current detecting resistor 4 and detects Pch-
The constant voltage circuit 9 is configured to control the gate of the MOS 3 and detects the voltage of the battery 5 with the battery detection voltage 7 to obtain an output voltage according to the voltage of the battery 5 and to obtain the voltage of the constant voltage output terminal 8. Works to stabilize.

Due to the operation of the constant voltage circuit 9, the heat loss due to the charge control transistor can be minimized, and the heat loss at the charge control transistor can be reduced, so that the charging current can be increased, so that the charging time can be shortened. However, it will be described in more detail with reference to the specific circuit of FIG. The description of the parts common to those of the circuit shown in FIG. 1 will be omitted.

The circuit shown in FIG. 2 more specifically shows the circuit inside the broken line frame in FIG. 1, in which the power supply terminal 1 is connected to one end (source) of the Pch-MOS 11 for detecting the charging current.
The other end (drain) of Pch-MOS 11 is Pch-MO.
The output voltage negative feedback 12 is connected to the constant voltage circuit 9 while being connected to one end (source) of S3. Pch-M
The gate 10 of the OS 11 is connected to the constant voltage circuit 9, and the constant voltage output terminal 8 is connected to the Schottky diode 13 and the output stabilizing capacitor 14 with respect to the ground terminal 2, and other circuits are shown in FIG. It is equivalent to the circuit shown in.

With such a configuration, the constant voltage circuit 9 detects the voltage of the battery 5 by the battery detection voltage 7, and at the same time obtains the output voltage according to the voltage of the battery 5 by the output voltage negative feedback 12, and Pch- The gate 10 of the MOS 11 is controlled to stabilize the voltage of the constant voltage output terminal 8. With the voltage of the constant voltage output terminal 8 stabilized in this manner, a gate-source voltage and a source-drain voltage are secured between the battery 5 and the constant voltage output terminal 8 so that the Pch-MOS 3 can flow the charging current. Then, by setting the source / drain voltage to the minimum, the loss due to the Pch-MOS 3 can be minimized.

Further, details of the contents of the constant voltage circuit will be described in more detail with reference to FIG. The circuit shown in FIG. 3 more specifically shows the circuit of the constant voltage circuit 9 in the broken line frame of FIG. 2, and the constant voltage circuit 9 is a DC-DC converter and is detected by the battery detection voltage 7. The voltage of the battery 5 and the voltage preset by the voltage setting resistor 19 and the constant current source 20 are compared by the voltage comparator 21, and the voltage of the variable reference voltage 23 is controlled. The voltage of the output voltage negative feedback 12 is divided by the negative feedback resistor 24 and the negative feedback resistor 25 and input to the error amplifier 22. The error amplifier 22 compares the variable reference voltage 23 variably controlled by the battery voltage with the divided voltage value of the output voltage negative feedback 12, amplifies it by the integrating capacitor 17 and the integrating resistor 18, and outputs it to the pulse width modulation circuit 16. The pulse width modulation circuit 16 compares the triangular wave formed by the triangular wave oscillator 15 with the output voltage of the error amplifier 22 and outputs it to the drive buffer 26 of the Pch-MOS 11. The drive buffer 26 power-amplifies the output pulse of the pulse width modulation circuit 16 and controls ON / OFF of the Pch-MOS 11.

Depending on the voltage of the battery 5, the Pch-MOS 11
By controlling the pulse width of the gate terminal 10 of, the constant voltage output terminal 8 is stabilized to a voltage corresponding to the battery voltage. By setting the gate-source voltage and the source-drain voltage sufficient to allow the charging current to flow through the Pch-MOS 3 between the battery 5 and the constant voltage output terminal 8 and setting the source-drain voltage to the minimum, the Pch- It is possible to minimize the loss due to the MOS3 and maximize the charging current.

In FIG. 3, the difference between the battery voltage and the output voltage value of the constant voltage circuit is represented by (Equation 1) by the voltage setting resistor 19 and the constant current source 20.

[0019]

## EQU1 ## (constant voltage output voltage-battery voltage) = voltage setting resistance × constant current source current value Here, when the constant voltage output voltage control and the charging control as shown in FIG. Each loss is calculated as follows. (1) Heat loss when battery voltage is 2.0V or less P1 P1 = 50mA × (2.5V-V1) V1: Battery average voltage until battery voltage reaches 2.0V Here, V1 = 1.5V Then, P1 = 50 mW (2) Heat loss when battery voltage is 2.0 V or more and 3.2 V or less P2 P2 = 100 mA × (3.6 V−V2) V2: From battery voltage reaching 2.0 V to 3.2 V Battery average voltage Here, assuming V1 = 3.0V, P2 = 60 mW (3) Heat loss P3 when battery voltage is 3.2 V or higher (at maximum charging current) P3 P3 = 700 mA × (4.2 V−V3) V3: Battery average voltage when battery voltage is 3.2 V or higher and charging current is maximum Here, when V3 = 3.6 V, P3 = 420 mW (4) Heat loss P4 when battery voltage is 3.2 V or higher (when charging current decreases) P4 = I4 * (4.4V-V4) I4: Average charging current V4 until the end of charging: Battery average voltage when the battery voltage is 3.2 V or higher and the charging current decreases Here, when V4 = 4.15 V and I4 = 70 mA, P
4 = 17.5 mW From the above result, the total loss amount P in the Pch-MOS3 at the time of charging is represented by P = P1 + P2 + P3 + P4, and from the above result, P = 547.5 mW. This is an improvement of about 68.8% with respect to the calculation result P = 1757.5 mW in the conventional circuit configuration.

As described above, according to the present embodiment, the heat loss due to the charge control transistor can be minimized, and the heat loss at the charge control transistor can be reduced, so that the charging current can be increased. It is possible to shorten the time.

Although the P-channel MOS transistor is used as the charge control output transistor illustrated in this embodiment, a PNP transistor or a charge control circuit using an N-channel MOS transistor or an NPN transistor depending on the circuit configuration is used. The same effect can be obtained in. Further, in FIG. 2, the constant voltage circuit 9 is a DC power supply-DC power supply converter in consideration of the efficiency of the circuit, but the same result can be obtained with other circuit configurations as long as it is a constant voltage output.

[0022]

As described above, according to the present invention, the heat loss due to the charge control transistor can be minimized, and the heat loss at the charge control transistor can be reduced to increase the charging current. It is possible to obtain the advantageous effect that it becomes possible to shorten.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration in an embodiment of a charge control circuit of the present invention.

FIG. 2 is a circuit diagram showing a specific example of an embodiment of a charge control circuit of the present invention.

FIG. 3 is a circuit diagram showing a specific example of a constant voltage circuit used in an embodiment of a charge control circuit of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional charge control circuit.

FIG. 5 is a graph showing charge voltage and charge current waveforms in a lithium-ion battery.

[Explanation of symbols]

1 power supply terminal 2 Ground terminal 3,11 P-channel MOS transistor 4 Charging current detection resistor 5 batteries 6 Charge control circuit 7 Battery detection voltage 8 constant voltage output terminal 9 constant voltage circuit 10 P-channel MOS transistor gate 12 Output voltage negative feedback 13 Schottky diode 14 Output stabilization capacity 15 Triangle wave oscillator 16 pulse width modulation circuit 17 Integral capacity 18 Integral resistance 19 Voltage setting resistor 20 constant current source 21 Voltage comparator 22 Error amplification circuit 23 Variable reference voltage 24 Voltage setting resistor A 25 Voltage setting resistor B 26 Drive buffer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5G003 AA01 BA01 CA12 CC02 GA01                       GB03                 5H030 AA03 AS14 BB01 FF43                 5H430 BB01 BB09 BB11 BB12 EE06                       EE12 FF01 FF08 FF11 GG17                       HH03 LA10                 5H730 AA14 AS01 AS02 AS17 BB13                       BB86 CC25 DD04 DD26 EE07                       FD03 FD33 FF02 FG05 FG25

Claims (2)

[Claims] 1. A charge control circuit used when charging a battery from a power supply, wherein a constant voltage circuit is provided between the power supply and the charge control transistor. 2. The charge control circuit according to claim 1, wherein the output voltage of the constant voltage circuit is set according to the battery voltage to be charged.