JP2008054429A - Charge circuit and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a temperature rise within a case body during charging a secondary battery mounted on small-sized electronic equipment such as a mobile phone. <P>SOLUTION: A charge control signal cct outputted from a charge control unit 52a in a charge circuit is supplied to respective base electrodes of transistors 53a, 53b as base current, a resistance value between an emitter electrode and a collector electrode is controlled, and the charge electrode is dispersed to be supplied to the secondary battery 55. Accordingly, a heating source is dispersed, and heat generation amount per heating source becomes half to prevent a temperature on the case body surface from rising. This can eliminate design for software of charge control for restraining a temperature rise, thus eliminating the use of components, such as a temperature sensor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging circuit and an electronic device, and more particularly to a charging circuit and an electronic device suitable for use in a small portable electronic device such as a mobile phone, a PDA (Personal Digital Assistants), and a portable music player. About.

  In a portable electronic device such as a mobile phone, a predetermined operation is performed using the attached secondary battery as a power source. When the power is turned on, the remaining capacity of the secondary battery is automatically displayed on the display unit. It has come to be. When the user recognizes that there is no or little remaining capacity, the user recharges the secondary battery by attaching a charging device (external power supply device) to the electronic device.

  For example, as shown in FIG. 8, this type of electronic apparatus is a mobile phone 1, which includes an upper unit 10 and a lower unit 20, and the lower unit 20 is a hinge portion with respect to the upper unit 10. 11 through 11. The upper unit 10 is provided with an antenna 12, and a display unit 13 and a receiver unit 14 are provided on the front side in contact with the lower unit 20 when folded so as to be in contact with the lower unit 20. . When the lower unit 20 is folded so as to be in contact with the upper unit 10, an operation unit 21 including a plurality of button switches and a transmission unit (microphone) 22 are provided on the front surface in contact with the upper unit 10. When the secondary battery for power supply is discharged, the battery is mounted and mounted on the stand 30 of the dedicated charging device. The charging device table 30 inputs the power supply voltage supplied from the AC adapter 31 to a charging power input terminal (not shown) of the lower unit 20. The AC adapter 31 converts an AC power source (for example, a commercial power source) obtained from the AC outlet 32 into a DC power source having a predetermined voltage.

FIG. 9 is a block diagram showing an electrical configuration of a main part in the mobile phone 1 in FIG.
As shown in FIG. 9, the cellular phone 1 includes a power input terminal 41, a power management IC (integrated circuit) 42, a transistor 43, a current detector 44, a secondary battery 45, and a CPU (central processing unit). Device) 46. The power management IC 42 converts the DC power supplied from the AC adapter 31 via the power input terminal 41 into a voltage used inside the mobile phone 1 and outputs it to each unit. When shifting to, output to each unit is stopped. Further, the power management IC 42 has a charge control unit 42 a for charging the secondary battery 45.

  The charging control unit 42a charges the secondary battery 45 based on a command from the CPU 46, and stops charging when the secondary battery 45 reaches full charge. In this case, the charging control unit 42a detects the voltage of the secondary battery 45, detects the charging current by the current detection unit 44, and corresponds the charging current to the secondary battery 45 based on the detection results. A charge control signal cct for controlling to a predetermined current value is generated. The transistor 43 is formed of a pnp type bipolar transistor, and the charge control signal cct output from the charge control unit 42a is supplied to the base electrode to control the resistance value between the emitter electrode and the collector electrode, thereby controlling the charging current. Do. The current detection unit 44 is configured by, for example, a resistor, and sends a voltage corresponding to the charging current to the charging control unit 42a as a charging current detection value. The secondary battery 45 is composed of, for example, a lithium ion battery. The power management IC 42, the transistor 43, the current detection unit 44, and the CPU 46 are mounted on a printed board (not shown).

  In the cellular phone 1, the charging control unit 42a performs constant current charging corresponding to the capacity of the secondary battery 45 at the start of charging, and the voltage of the secondary battery 45 exceeds a predetermined reference value. The constant voltage charging is performed until the full charge voltage is reached, and when the voltage of the secondary battery 45 reaches the full charge voltage, the charging is stopped.

In addition to the above-described cellular phone, there is a conventional technique of this type described in, for example, Patent Document 1.
In the power amplifier described in Patent Document 1, a plurality of final stage transistors connected in parallel are divided into a plurality of final stage output blocks, and the same number of temperature compensation circuits as these final stage output blocks are provided. The output block and each temperature compensation circuit are thermally coupled to each other.

  In the charger described in Patent Document 2, charging currents are respectively supplied to a plurality of charging terminal portions by an emitter follower circuit of a plurality of charging transistors having the same characteristics, and only from the emitter of one charging transistor. By applying feedback to the constant voltage circuit, fluctuations in the emitter voltage due to changes in temperature around other charging transistors of the same type connected in the same way are corrected, and the charging current to each rechargeable battery is highly accurate. Controlled.

Further, in the voltage-current conversion circuit described in Patent Document 3, at least one of the transistors T1 to T6 constituting the cross-connected low distortion voltage-current conversion circuit has two or more transistors connected in parallel. Configured. By arbitrarily setting the number of parallel connections of the transistors T1 to T6, the current distribution of the circuit is optimized while maintaining the conventional low distortion operation.
Utility Model Registration No. 3061553 (abstract, Fig. 1) JP 2004-364487 A (Abstract, FIG. 1) JP 2006-129416 A (Abstract, FIG. 1)

However, the above conventional mobile phone has the following problems.
That is, in the mobile phone 1 of FIG. 9, the charging control unit 42a controls the charging current and charging voltage for the secondary battery 45 through the transistor 43. At this time, [(output voltage of AC adapter 31−charging The power calculated by (Voltage) × Charging current] is released from the transistor 43 as heat. This heat is conducted through the printed circuit board on which the transistor 43 is mounted, and the temperature of the surface of the casing of the mobile phone 1 rises. In this case, the temperature of the surface of the housing is lower than the temperature of the surface of the transistor 43, but if the user touches the housing for a long time, anxiety may be felt, and deterioration of each internal component may occur. There is a problem that the progress of the is faster.

  In order to solve these problems, a temperature sensor is provided inside the mobile phone 1, and when a certain temperature is exceeded, a mechanism such as stopping charging or reducing the charging current is provided to increase the temperature. It is possible to suppress it. However, in this case, there are problems that the number of man-hours for designing software related to charge control for suppressing the temperature rise and the number of parts such as a temperature sensor increase.

  In the power amplifier described in Patent Document 1, a plurality of final stage transistors are connected in parallel and divided into a plurality of final stage output blocks, and a temperature compensation circuit is provided for each final stage output block. However, the fundamental reason for connecting a plurality of final stage transistors in parallel is to obtain a high output and a low output impedance, not to dissipate heat and suppress a temperature rise. In the present invention, no temperature compensation circuit is provided. Therefore, the object and configuration are different from the present invention.

  The charger described in Patent Document 2 has a configuration in which each charging transistor is individually connected to each battery, and is not connected in parallel. Moreover, since the temperature rise of each charging transistor is not suppressed, the object and the configuration are different from the present invention.

  In the voltage-current conversion circuit described in Patent Document 3, the current distribution of the circuit is adjusted according to the set number of parallel connections of the transistors T1 to T6, and does not improve the above problem.

  The present invention has been made in view of the above circumstances, and without providing a temperature control mechanism or the like by software and a temperature sensor, a charging circuit with a small temperature rise, and the same charging even during charging of a secondary battery It is an object to provide an electronic device provided with a circuit.

  In order to solve the above-described problem, the invention according to claim 1 is provided in an electronic device that performs a predetermined operation using a mounted secondary battery as a power source, and the power source supplied from an external power source is the secondary power source. A charge control unit for generating a charge control signal for controlling the charge current to a predetermined current value, the charge control unit for converting the charge current into a charge current for the battery, and connected in parallel to each other, the charge based on the charge control signal; And a plurality of transistors that supply current to the secondary battery in a distributed manner, and the plurality of transistors are distributed and arranged at predetermined sites inside the electronic device.

  A second aspect of the present invention relates to the charging circuit according to the first aspect, wherein each of the transistors is attached so as to be connected to a predetermined portion inside a casing of the electronic device.

  A third aspect of the present invention relates to the charging circuit according to the first or second aspect, wherein each of the transistors is a bipolar transistor, and the charging control unit includes a current detecting unit that detects the charging current, A base current for controlling the charging current to the predetermined current value is supplied to the base electrode of each bipolar transistor as the charging control signal based on a detection result by the current detection unit. It is said.

  The invention according to claim 4 relates to the charging circuit according to claim 1 or 2, wherein each of the transistors is formed of a MOS transistor, and the charging control unit includes a current detecting unit that detects the charging current, A control voltage for controlling the charging current to the predetermined current value based on a detection result by the current detection unit is applied to the gate electrode of each MOS transistor as the charging control signal. It is said.

  The invention according to claim 5 relates to an electronic device that performs a predetermined operation using the mounted secondary battery as a power source, and includes a charging circuit that converts power supplied from an external power supply device into a charging current for the secondary battery. The charging circuit is connected in parallel to a charging control unit that generates a charging control signal for controlling the charging current to a predetermined current value, and distributes the charging current based on the charging control signal. A plurality of transistors to be supplied to the secondary battery, and the plurality of transistors are distributed and arranged in a predetermined portion inside the electronic device.

  A sixth aspect of the present invention relates to the electronic device according to the fifth aspect, wherein each of the transistors is attached so as to be connected to a predetermined portion inside the casing of the electronic device.

  Invention of Claim 7 is related with the electronic device of Claim 5 or 6, Each said transistor is comprised with a bipolar transistor, The said charge control part has a current detection part which detects the said charge current, A base current for controlling the charging current to the predetermined current value is supplied to the base electrode of each bipolar transistor as the charging control signal based on a detection result by the current detection unit. It is said.

  The invention according to claim 8 relates to the electronic apparatus according to claim 5 or 6, wherein each of the transistors is configured by a MOS transistor, and the charge control unit includes a current detection unit that detects the charge current, A control voltage for controlling the charging current to the predetermined current value based on a detection result by the current detection unit is applied to the gate electrode of each MOS transistor as the charging control signal. It is said.

  According to the configuration of the present invention, the charging control unit generates a charging control signal for controlling the charging current to a predetermined current value, and the same charging is performed by a plurality of transistors connected in parallel with each other. Since the charging current is distributed based on the control signal and supplied to the secondary battery, the amount of heat generated per transistor is reduced, and the temperature of the surface of the casing of the electronic device is hardly increased. As a result, it is possible to eliminate the need to design software related to charge control for suppressing temperature rise, and to eliminate the need for components such as a temperature sensor. Further, when each transistor is composed of a MOS transistor, the base current as a charge control signal does not flow as compared with the case where it is composed of a bipolar transistor, so that current consumption can be reduced.

  Disclosed are a charging circuit that disperses heat generated during charging of a mounted secondary battery at two or more locations and suppresses a rise in temperature that appears outside a housing, and an electronic device provided with the charging circuit.

FIG. 1 is a block diagram showing an electrical configuration of a main part of an electronic apparatus provided with a charging circuit according to a first embodiment of the present invention.
As shown in the figure, the electronic apparatus of this example is a mobile phone 50, which includes a power input terminal 51, a power management IC 52, transistors 53a and 53b, a current detection unit 54, a secondary battery 55, and a CPU 56. In the same manner as in FIG. 6, it is connected to an AC outlet 32 through an AC adapter 31. The power management IC 52 converts the DC power supplied from the AC adapter 31 via the power input terminal 51 into a voltage used inside the mobile phone 1 and outputs it to each part. When shifting to, output to each unit is stopped. Further, the power management IC 52 has a charge control unit 52 a for charging the secondary battery 55.

  The charging control unit 52a charges the secondary battery 55 based on a command from the CPU 56, and stops charging when the secondary battery 55 reaches full charge. In this case, the charging control unit 52a detects the voltage of the secondary battery 55, detects the charging current by the current detection unit 54, and corresponds the charging current to the secondary battery 55 based on the detection results. A charge control signal cct for controlling to a predetermined current value is generated. The transistors 53a and 53b are composed of pnp bipolar transistors with uniform characteristics and are connected in parallel to each other. The charge control signal cct output from the charge control unit 52a is supplied to each base electrode as a base current to be an emitter electrode. The resistance value between the collector electrodes is controlled, and the charging current is distributed and supplied to the secondary battery 55. A base resistor (not shown) is connected between each base electrode of the transistors 53a and 53b and the charge control unit 52a, and an emitter resistor (not shown) is connected between each emitter electrode and the charge control unit 52a. Yes. These base resistance and emitter resistance absorb variations in characteristics of the transistors 53a and 53b. The current detection unit 54 is configured by a resistor, for example, and sends a voltage corresponding to the charging current to the charging control unit 52a as a charging current detection value. Secondary battery 55 is formed of, for example, a lithium ion battery. The power management IC 52, the current detection unit 44, and the CPU 46 are mounted on a printed circuit board (not shown), and the transistors 53a and 53b are attached so as to be connected to predetermined portions inside the casing of the mobile phone 50. ing.

2 and 3 are external views showing an open state when the casing of the mobile phone 50 in FIG. 1 is configured to be foldable. FIG. 2 is a front view, and FIG. 3 is a rear view. It is.
As shown in FIG. 2, the mobile phone 50 includes a unit 61, a unit 62, and a hinge part 63. The unit 61 is provided with an antenna 64, and includes a receiver 65, an LCD 66, and a sub camera 67 on the front surface. The unit 62 includes an operation key 68 and a microphone 69 on the front surface, and includes a power management IC 52, transistors 53a and 53b, a current detection unit 54, a secondary battery 55, and a CPU 56 in FIG. Further, as shown in FIG. 3, the unit 62 has a main camera 70 incorporated in the back surface, and transistors 53a and 53b are connected to predetermined internal parts and attached in a distributed manner. Then, the unit 61 and the unit 62 are configured to be folded via a hinge portion 63 in such a manner that the front surface of the unit 61 and the front surface of the unit 62 face each other.

4 is a cross-sectional view taken along line AA in FIG.
As shown in FIG. 4, transistors 53 a and 53 b and other circuit components 72 in FIG. 1 are mounted on a circuit board 71. The circuit board 71 is connected to the metal frame 75 via the ground contacts 73 and 74, and the metal frame 75 is connected to the unit 62. Further, each operation key 68 in FIG. 2 is mounted on the key board 76 via each spring 68a.

FIG. 5 is a schematic diagram showing the diffusion of heat of the transistors 53a and 53b, and FIG. 6 is a diagram for explaining an example of the operation of the charging control unit 52a. The vertical axis indicates the voltage level, and the horizontal axis indicates the charging time. It has been taken.
With reference to these drawings, the operation of the mobile phone 50 of this example will be described.
As shown in FIG. 6, the mobile phone 50 is charged with a constant current by CC (Constant Current) constant charging at the start of charging. After that, when the battery voltage exceeds about 4.1 V, it is automatically switched to CV (Constant Voltage, constant voltage) charging, and charging is performed at a constant voltage. The battery voltage gradually approaches the full charge voltage of 4.2V. Under the control of the charging control unit 52a, the voltage 4.2V is applied to the secondary battery 55, and the current required by the secondary battery 55 flows, so that the current gradually decreases until the charging is completed at time te. To go.

  That is, when DC power is supplied from the AC adapter 31 to the power management IC 52 via the power input terminal 51, an operation of charging the secondary battery 55 by the power management IC 52 is started based on an instruction from the CPU 56. Then, a charge control signal cct is supplied as a base current from the charge control unit 52a to the base electrodes of the transistors 53a and 53b, and the charge current flowing into the secondary battery 55 from the collector electrodes of the transistors 53a and 53b is controlled. In this case, if the capacity of the secondary battery 55 is, for example, 800 mAh, it is generally desirable to perform constant current charging of 800 mA during CC charging. Therefore, by supplying a current of 400 mA to the transistor 53a and a current of 400 mA to the transistor 54b, a total current of 800 mA is supplied to charge the secondary battery 55. At this time, in the transistors 53a and 53b, the power calculated by [(output voltage of the AC adapter 31−charge voltage) × charge current] is released as heat, but the amount of heat generated per transistor is It becomes 1/2 with respect to the structure of the prior art which uses only one transistor. Since these two transistors 53a and 53b are dispersedly mounted inside the mobile phone 50, heat is transmitted to the surface of the housing (unit 62) with the heat source dispersed. In this case, as shown in FIG. 5, the heat of the transistors 53a and 53b propagates to the unit 62 along the propagation paths h and j, and also propagates to the unit 62 via the internal spaces u and v.

  As described above, in the first embodiment, the charge control signal cct output from the charge control unit 52a is supplied as the base current to the base electrodes of the transistors 53a and 53b, whereby the emitter electrode and the collector electrode are connected. Is controlled, and the charging current is dispersed and supplied to the secondary battery 55. For this reason, the heat sources are dispersed and the amount of heat generated per one heat source is halved, which makes it difficult for the temperature of the housing surface to rise. This eliminates the need for software design related to charge control for suppressing temperature rise, and eliminates the need for components such as a temperature sensor.

FIG. 7 is a block diagram showing an electrical configuration of a main part of a mobile phone provided with a charging circuit according to a second embodiment of the present invention, and is common to the elements in FIG. 1 showing the first embodiment. These elements are denoted by common reference numerals.
In the cellular phone 50A of this example, as shown in FIG. 7, in place of the transistors 53a and 53b in FIG. 1, resistors 57a and 57b and p-channel MOS transistors with uniform characteristics (hereinafter referred to as “pMOS”) are used. 58a and 58b are provided. The pMOSs 58a and 58b are connected in parallel to each other, and the charge control signal cct output from the charge control unit 52a is applied to each gate electrode as a control voltage via the resistors 57a and 57b, and the resistance value between the source electrode and the drain electrode is increased. The charging current is distributed and supplied to the secondary battery 55 under control. The other configuration is the same as that shown in FIG.

  In the cellular phone 50A of this example, the charge control signal cct output from the charge control unit 52a is applied as a control voltage to the gate electrodes of the pMOSs 58a and 58b, whereby the resistance value between the source electrode and the drain electrode is controlled. The charging current is dispersed and supplied to the secondary battery 55. Therefore, in addition to the same advantages as the first embodiment, since the pMOS 58a and 58b are voltage control elements, the base current does not flow like the transistors 53a and 53b in FIG. Become.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the embodiment, and even if there is a design change without departing from the gist of the present invention, Included in the invention.
For example, the pMOS 58a and 58b in FIG. 7 may be, for example, an IGBT (Insulated Gate Bipolar Transistor). Further, the number of the two transistors 53a and 53b in FIG. 1 may be increased to three or more. Similarly, the pMOSs 58a and 58b in FIG. 7 may be increased to three or more. The operation of the charging control unit 52a shown in FIG. 6 corresponds to the case where the secondary battery 55 is a lithium ion battery, but the type of the secondary battery 55 (for example, a nickel cadmium battery, a nickel hydrogen battery, or the like). Will be changed accordingly.

  The present invention is applicable to all portable electronic devices such as mobile phones, PDAs, and portable music playback devices (MD players, hard disk players, etc.) that have a miniaturized housing and incorporate a secondary battery charging circuit. it can.

It is a block diagram which shows the electrical constitution of the principal part of the electronic device provided with the charging circuit which is 1st Example of this invention. It is an external view of the mobile phone 50 in FIG. It is an external view of the mobile phone 50 in FIG. It is the sectional view on the AA line of FIG. It is a schematic diagram which shows the thermal diffusion of the transistors 53a and 53b. It is a figure explaining an example of operation of charge control part 52a. It is a block diagram which shows the electric constitution of the principal part of the mobile telephone provided with the charging circuit which is 2nd Example of this invention. It is a figure which shows the state in which the secondary battery of the electronic device provided with the conventional charge control circuit is charged. It is a block diagram which shows the electric constitution of the principal part in the mobile telephone 1 in FIG.

Explanation of symbols

50, 50A mobile phone (electronic equipment)
51 Power input terminal (part of electronic equipment)
52 Power management IC (part of charging circuit)
52a Charge control unit (part of the charging circuit)
53a, 53b Bipolar transistor (part of charging circuit)
54 Current detector (part of charging circuit)
55 Secondary battery 56 CPU (Central processing unit, part of charging circuit)
57a, 57b Resistance (part of charging circuit)
58a, 58b p-channel MOS transistor (part of charging circuit)

Claims (8)

A charging circuit that is provided inside an electronic device that performs a predetermined operation using a mounted secondary battery as a power source, and converts power supplied from an external power supply device into a charging current for the secondary battery,
A charge control unit that generates a charge control signal for controlling the charge current to a predetermined current value;
A plurality of transistors connected in parallel to each other and distributed to the secondary battery by distributing the charging current based on the charging control signal; and
The plurality of transistors are:
A charging circuit, wherein the charging circuit is distributed in a predetermined portion inside the electronic device. Each of the transistors is
The charging circuit according to claim 1, wherein the charging circuit is attached so as to be connected to a predetermined portion inside the casing of the electronic device. Each of the transistors is a bipolar transistor,
The charge controller is
A current detection unit for detecting the charging current, and a base current for controlling the charging current to the predetermined current value based on a detection result by the current detection unit as the charge control signal; The charging circuit according to claim 1, wherein the charging circuit is configured to be supplied to the base electrode. Each of the transistors is a MOS transistor,
The charge controller is
A current detection unit for detecting the charging current, and a control voltage for controlling the charging current to the predetermined current value based on a detection result by the current detection unit as the charge control signal; 3. The charging circuit according to claim 1, wherein the charging circuit is configured to be applied to the gate electrode. An electronic device that performs a predetermined operation using a mounted secondary battery as a power source,
A charging circuit for converting power supplied from an external power supply device into a charging current for the secondary battery is provided,
The charging circuit is
A charge control unit that generates a charge control signal for controlling the charge current to a predetermined current value;
A plurality of transistors connected in parallel to each other and distributed to the secondary battery by distributing the charging current based on the charging control signal; and
The plurality of transistors are:
An electronic device, wherein the electronic device is distributed and arranged in a predetermined part inside the electronic device. Each of the transistors is
6. The electronic device according to claim 5, wherein the electronic device is attached so as to be connected to a predetermined portion inside the casing of the electronic device. Each of the transistors is a bipolar transistor,
The charge controller is
A current detection unit for detecting the charging current, and a base current for controlling the charging current to the predetermined current value based on a detection result by the current detection unit as the charge control signal; The electronic apparatus according to claim 5, wherein the electronic apparatus is configured to be supplied to a base electrode. Each of the transistors is a MOS transistor,
The charge controller is
A current detection unit for detecting the charging current, and a control voltage for controlling the charging current to the predetermined current value based on a detection result by the current detection unit as the charge control signal; The electronic apparatus according to claim 5, wherein the electronic apparatus is configured to be applied to the gate electrode.

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