JP4544130B2 - Charging circuit, electronic device, and current control method for charging circuit - Google Patents

Description

  The present invention relates to a constant current charging type charging circuit, an electronic device, and a current control method for the charging circuit that are supplied with constant voltage from an external power source.

  As a conventional technique, a configuration example of a constant current charging type charging circuit that is supplied with a constant voltage from an external power supply is shown in FIG. 5 and will be described below.

  In FIG. 5, a constant voltage current is supplied from the outside to the terminal 1. This current is supplied to a charging current control unit (Field Effect Transistor / hereinafter referred to as a charging current control FET) 3 through a diode 2. Hereinafter, the charge current control FET 3 will be described as an n-channel type.

  The control unit 7 detects a charging current based on a signal from the current detector 4. The control unit 7 detects a current value flowing between the source and the drain, that is, a signal from the current detector 4, and charges the detected signal so that the current flowing between the source and the drain becomes a predetermined constant current value. The gate voltage of the current control FET 3 is changed and adjusted. That is, this is a constant current charge type operation. Further, the current detector 4 is configured such that there is no potential difference between both ends of the detector.

  The constant-voltage current fed from the outside to the terminal 1 is divided into a current IL flowing into the load side and a current IB flowing into the battery side, and the current IB is used for charging the battery 6. The battery 6 is charged by the current IB, and the battery voltage b rises.

  In the case of such a conventional charging circuit configuration, the total current of the current IL and the current IB is made constant by the charging current control FET 3, so that when the load current IL is large, the battery charging current is relatively large. IB decreases. That is, the battery voltage b gradually increases, and the potential difference a between the drain and source of the charging current control FET 3 gradually decreases as indicated by A in FIG.

  At this time, as shown in FIG. 2, since the potential difference a between both ends of the charging current control FET 3 is large, the heat generation of the FET 3 is large and the temperature rises rapidly as shown in FIG. Therefore, the charging circuit portion becomes high temperature, and the surface of the casing of the electronic device equipped with this charging circuit is likely to become high temperature, which causes a problem that the user of the device is uncomfortable and uneasy.

As an example of the prior art, there is a “battery control device” that performs optimal charging control for a plurality of operation modes and can prevent a voltage drop by charging with a small current or stopping charging when the capacity of the AC adapter is exceeded. Yes (for example, see Patent Document 1). Also, as another prior art example, a “battery movable electronic device and its charge control method” that can optimally charge a plurality of built-in batteries without increasing the size of an external power source and deteriorating the usability of the device. (See, for example, Patent Document 2).
Japanese Unexamined Patent Publication No. 07-2441047 Japanese Patent No. 2777872

However, the invention described in Patent Document 1 is for secondary detection of the current flowing through the load due to voltage drop, and in general, the user himself may use an AC adapter purchased in the market. Since adapters vary widely from one adapter to another, the accuracy of load current detection is low when measuring voltage drop values, and heat generation cannot be suppressed accurately.
On the other hand, since the invention described in Patent Document 2 does not have a function of switching the battery capacity by detecting the load current, for example, when two batteries are connected in parallel, one battery is not charged, There is a problem that user convenience is low.

  From the above, there is a demand for a charging circuit that can accurately suppress heat generation by accurately detecting the absolute value of the load current and switching the battery capacity appropriately.

  The present invention has been made in view of the above circumstances, and in a charging circuit in which a plurality of batteries are connected in parallel, by appropriately switching the battery capacity according to the absolute value of the detected load current IL, the charging current is It is an object of the present invention to provide a charging circuit capable of accurately suppressing heat generation of a control FET and, in turn, accurately suppressing heat generation of the device itself, an electronic device including the charging circuit, and a current control method for the charging circuit. To do.

In order to achieve such an object, as a first aspect, the charging circuit of the present invention is a charging circuit in which a plurality of batteries are connected in parallel, and charging is performed by constant voltage power supply from an external power source. The absolute value is detected, and the absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries are disconnected from the charging circuit, and at least one battery is removed. Control is performed so as to remain in the charging circuit .

The charging circuit of the present invention is a charging circuit in which a plurality of batteries are connected in parallel and charged by constant voltage power supply from an external power source, as a second aspect, and a switch means provided corresponding to the battery; The load current detecting means for detecting the absolute value of the load current is compared with the predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries are charged among the plurality of batteries. And control means for controlling the switch means so as to be separated from the circuit and leave at least one battery in the charging circuit .

In the charging circuit of the present invention, when the absolute value is less than the threshold value as a result of the comparison, control is performed such that a plurality of batteries are left in the charging circuit.

The electronic device of the present invention includes the charging circuit of the present invention .

A current control method for a charging circuit according to the present invention is, as a first aspect, a current control method for a charging circuit in which a plurality of batteries are connected in parallel and charged by constant voltage power supply from an external power source, The absolute value is detected, and the absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries are disconnected from the charging circuit, and at least one battery is removed. Control is performed so as to remain in the charging circuit .

A second aspect of the current control method for a charging circuit according to the present invention is a current control method for a charging circuit in which a plurality of batteries are connected in parallel and charged by constant voltage power supply from an external power source. A load current detection step for detecting an absolute value, and comparing the absolute value with a predetermined threshold value.If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries are disconnected from the charging circuit among the plurality of batteries. And a control step of controlling switch means provided corresponding to the battery so as to leave at least one battery in the charging circuit .

The current control method for a charging circuit according to the present invention is characterized in that, in the control step, when the absolute value is less than a threshold value as a result of comparison, control is performed such that a plurality of batteries are left in the charging circuit.

  According to the present invention, it is possible to accurately suppress the heat generation of the charging current control FET, and thus to accurately suppress the heat generation of the device itself.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

  The present invention is a charging circuit used in an electronic device such as a portable terminal. Further, the present invention is a constant current type charging circuit in which a plurality of batteries are connected in parallel and supplied with a constant voltage from an external power source, and either one of the batteries or a battery depending on a predetermined load current IL. The battery capacity can be changed by connecting and charging only a part of the battery capacity. With this configuration, it is possible to reduce the temperature rise of the charging current control FET 3 even during charging, and as a result, it is possible to suppress an increase in the housing surface temperature of the device itself.

  In FIG. 1, the switch 8 controlled by the control unit 7 disconnects some of the batteries 6-2 among a plurality of batteries configured in parallel from the charging circuit, and reduces the battery capacity to be charged. If the battery capacity can be reduced in accordance with the load capacity in this way, the potential difference a between both ends of the charging current control FET 3 decreases rapidly, and the amount of heat generated by the charging current control FET 3, that is, the temperature rise can be suppressed. it can.

  According to the present invention, since the battery capacity to be charged is reduced by the load current, the battery voltage rises relatively quickly, and the potential difference a between the drain and source of the charging current control FET 3 rapidly decreases. It is possible to suppress the heat generation of the charging current control FET 3 and to accurately suppress the heat generation of the device itself.

  FIG. 1 is a diagram showing a configuration of a charging circuit according to an embodiment of the present invention. In this embodiment, an electronic device including the charging circuit shown in FIG. 1 is a mobile terminal device such as a mobile phone. Note that each configuration has already been described above with reference to FIG. 5 of the conventional configuration, and the description is omitted in FIG. In FIG. 1, only the parts different from FIG. 5 of the conventional configuration will be described.

  In FIG. 1, two batteries, a battery 6-1 and a battery 6-2, are connected in parallel. The total battery capacity of the battery 6-1 and the battery 6-2 is equivalent to the battery capacity required for the mobile terminal. That is, as compared with the conventional configuration, the combined battery capacity of the battery 6-1 and the battery 6-2 is the same battery capacity as the battery 6 of FIG.

  The current IB is divided into a current IB-1 and a current IB-2, respectively. Further, the battery 6-2 is provided with a switch 8 so that the current IB-2 does not flow into the battery 6-2. That is, the battery 6-2 can be disconnected from the charging circuit by the operation of the switch 8. The switch 8 can be connected / disconnected (hereinafter referred to as ON / OFF) under the control of the control unit 7.

  The load current IL flowing into the load 5 is detected by the load current detector 9. The load current detector 9 accurately detects the absolute value of the load current IL. This is a secondary detection method based on voltage drop as in the prior art (for example, Patent Document 1), the detection accuracy is low, there is a risk of heat generation, and there is a problem of Product Liability (PL). It can be. In this embodiment, since the load current detector 9 can accurately detect the absolute value of the load current IL, the battery capacity can be switched accurately and heat generation can be suppressed accurately.

  After receiving the absolute value of the load current IL flowing into the load 5 from the load current detector 9, the control unit 7 compares this absolute value with a predetermined threshold value Ith. When it is determined as a result of the comparison that the absolute value of the load current IL is less than the predetermined threshold value Ith, the control unit 7 turns on the switch 8 and controls the battery 6-2 to be charged. That is, the total battery capacity is equivalent to the conventional configuration described in FIG. On the other hand, when it is determined that the absolute value of the load current IL is larger than the predetermined threshold value Ith, the control unit 7 turns off the switch 8 so that no current flows through the battery 6-2 (so as not to be charged). Control.

Here, the operation when the load current IL is larger than the predetermined threshold value Ith and the switch 8 is turned off will be described in detail.
The charging current IB does not flow to the battery 6-2 but flows all into the battery 6-1, and the battery voltage b rises rapidly. Therefore, in FIG. 2, as shown by B, the potential difference a between the drain and the source of the charging current control FET 3 is rapidly reduced as compared with A in the conventional configuration. That is, since a constant voltage is supplied to the terminal 1 from the outside, the drain side of the charging current control FET 3 is a constant voltage, while the source side is equivalent to the battery voltage b, so the potential difference a rapidly decreases.

  The heat generation of the charging current control FET 3 is proportional to both the current flowing between the drain and the source and the potential difference a between the drain and the source. This embodiment is intended for a constant current type charging circuit. In the constant current type charging circuit, the current between the drain and the source is constant regardless of the battery capacity and the load current IL. Therefore, it is the potential difference a between the drain and the source that affects the heat generation of the FET 3. Accordingly, since the potential difference a rapidly decreases, an effect that the heat generation amount of the FET 3 shown in FIG. 3 is lower than that of A of the conventional configuration as shown in B can be obtained.

On the other hand, a case where the load current IL is lower than a predetermined threshold value Ith will be described.
The current supplied to the terminal 1 is almost supplied to the battery charging current IB because the load current IL is small. Here, it is necessary to charge the total battery capacity of the battery 6-1 and the battery 6-2. However, since the charging current IB is large, the battery voltage b is no longer increased, and the potential difference a of the FET is rapidly decreased to generate heat. The amount is small. Therefore, when the load current IL is lower than the predetermined threshold value Ith, there is no problem because the amount of heat generated is small even if the switch 8 is turned on. In addition, by setting the switch 8 to ON, both the battery 6-1 and the battery 6-2 can be sufficiently charged, so that there is an advantage that convenience is high.

Next, the operation of the charging circuit of this embodiment will be described with reference to the flowchart of FIG.
First, the threshold value Ith of the load current IL is stored in advance in a storage unit (not shown) of the control unit 7 so that it can be read out in a timely manner (step S1). The control unit 7 receives the absolute value of the load current IL from the signal of the signal line 10 from the load current detector 9 (step S2), reads the threshold Ith of the predetermined load current IL from the storage unit, and calculates the absolute value of the load current IL. (Step S3). As a result of the comparison, when the absolute value of the load current IL is larger than the threshold value Ith (step S3 / YES), the control unit 7 controls the switch 8 to be OFF (step S4). On the other hand, when the absolute value of the load current IL is less than the threshold value Ith (step S3 / NO), the switch 8 is controlled to be ON (step S5). Thereafter, in order to compare the relationship between the change in the load current IL and the threshold value Ith, the detection of the load current IL in step S2 is repeated after step S4 and step S5.

  As described above, according to the charging circuit of this embodiment, the absolute value of the load current is detected, and the battery capacity to be charged is reduced based on the comparison result with the threshold value. Since the potential difference a between the drain and source of the charging current control FET 3 rapidly increases and rapidly decreases, the heat generation of the FET 3 can be suppressed. In addition, it is possible to suppress the heat generation of the mobile terminal device itself.

  In the first embodiment, when the load current IL is larger than the predetermined threshold value Ith in FIG. 1, the control unit 7 controls the switch 8 to be turned off to disconnect the battery 6-2 from the charging circuit. As another example, in FIG. 1, a switch is also provided in 6-1 and OFF control is performed similarly to the control for the switch 8, so that all the batteries (6-1 and 6-2 in FIG. 1) are disconnected. May be. Note that a mobile phone, which is an example of a mobile terminal, has a wireless unit that performs a burst operation on the load, and the battery is supplied to the charging circuit, that is, the wireless unit even with a small capacity in order to prevent deterioration of wireless characteristics due to sudden load fluctuations. Usually connected to a circuit. Therefore, in such a case, it is better to use the control of the first embodiment.

  As mentioned above, although the Example of this invention was described, it is not limited to the said Example, A various deformation | transformation is possible in the range which does not deviate from the summary.

  The present invention can be applied to all constant current type charging circuits supplied with constant power from the outside and to all electronic devices including the charging circuit.

It is a figure which shows the structure of the charging circuit which is an Example of this invention. It is a graph which shows the relationship between time and an electric potential difference. It is a graph which shows the relationship between time and the emitted-heat amount. It is a flowchart which shows operation | movement of the charging circuit which is an Example of this invention. It is a figure which shows the structure of the conventional charging circuit.

Explanation of symbols

1 terminal 2 diode 3 charge current control FET
4 Current detector 5 Load 6, 6-1, 6-2 Battery 7 Control unit 8 Switch 9 Load current detector IL, IB Current

Claims (7)

A charging circuit in which a plurality of batteries are connected in parallel and is charged by constant voltage power supply from an external power source,
An absolute value of the load current is detected, and the absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries among the plurality of batteries are charged. A charging circuit, wherein the charging circuit is controlled so as to be separated from the circuit and leave at least one battery in the charging circuit. A charging circuit in which a plurality of batteries are connected in parallel and is charged by constant voltage power supply from an external power source,
Switch means provided corresponding to the battery;
Load current detection means for detecting the absolute value of the load current;
The absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries among the plurality of batteries are disconnected from the charging circuit, and at least one battery is removed. Control means for controlling the switch means to remain in the charging circuit ;
A charging circuit comprising: 3. The charging circuit according to claim 1, wherein when the absolute value is less than the threshold value as a result of the comparison, control is performed so that the plurality of batteries are left in the charging circuit. 4.   An electronic device comprising the charging circuit according to claim 1. A current control method for a charging circuit in which a plurality of batteries are connected in parallel and charged by constant voltage power supply from an external power source,
An absolute value of the load current is detected, and the absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries among the plurality of batteries are charged. A method for controlling a current of a charging circuit, wherein the current is controlled so as to be separated from the circuit and leave at least one battery in the charging circuit . A current control method for a charging circuit in which a plurality of batteries are connected in parallel and charged by constant voltage power supply from an external power source,
A load current detection step for detecting an absolute value of the load current;
The absolute value is compared with a predetermined threshold value. If the absolute value is larger than the threshold value as a result of the comparison , a predetermined number of batteries among the plurality of batteries are disconnected from the charging circuit, and at least one battery is removed. A control step of controlling switch means provided corresponding to the battery so as to remain in the charging circuit ;
A current control method for a charging circuit, comprising: 7. The charging circuit according to claim 5, wherein, in the control step, when the absolute value is less than the threshold value as a result of the comparison, the charging circuit is controlled to leave the plurality of batteries in the charging circuit. 8. Current control method.

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