JP2007274847A - Charge control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit, capable of controlling discharge by positively detecting discrimination between primary and secondary batteries, and the presence or the absence of overdischarging of the secondary battery. <P>SOLUTION: A microcomputer 16 of a digital camera 1 discriminates a first battery 10 (primary battery) from a second battery (secondary battery) 12, as a built-in battery. When a dedicated charger is connected to the digital camera, the microcomputer 16 turns on a transistor switch 18 to detect a terminal voltage of the secondary battery 12; and if the voltage has a finite value, it is discriminated that the secondary battery 12 is incorporated. If the terminal voltage is substantially zero, the microcomputer 16 turns on a transistor switch 20 to apply a predetermined voltage. If a voltage drop occurs due to a resistor 22, it is discriminated that the second battery 12 is in an overdischarged state. When the second battery 12 is incorporated, charging of the second battery 12 using a charging line 200 is permitted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charge control circuit, and more particularly, to a circuit for discriminating between a primary battery and a secondary battery and controlling the availability of charging.

  2. Description of the Related Art Conventionally, a technique for discriminating the type of battery and performing charging according to the type of battery is known. For example, the following documents describe that an external battery is connected by a mechanical mechanism or electrically detected via a connection detection terminal, and is provided in advance on the battery side. It is described that the type of external battery connected to the device is determined by reading the obtained resistance value and impedance value and using the value as an ID signal. In addition, it is described that an electric pulse signal is exchanged between the detection unit and the battery pack using a microprocessor or the like to determine the type of battery connected to the device.

  Reference 2 also calculates the amount of voltage change between the voltage at the battery terminal when a voltage is applied from the outside and the voltage at the battery terminal when no voltage is applied from the outside, according to the amount of voltage change. Discrimination between types of primary batteries and secondary batteries is described.

JP 2002-10508 A JP 2001-54243 A

  However, it is preferable not to use a mechanical mechanism but to more easily discriminate the type of battery. Moreover, when determining the type of battery using the terminal voltage, it is preferable that not only the primary battery and the secondary battery but also the overdischarge state of the secondary battery can be determined. That is, when the terminal voltage of the secondary battery is substantially zero, in addition to the case where the secondary battery is not present, there are cases where the secondary battery is present but is simply in an overdischarged state. This is because if the secondary battery is mistakenly determined not to exist even though the secondary battery is in an overdischarged state, the secondary battery that is originally required may not be charged.

  It is an object of the present invention to provide a circuit that can control charging by reliably discriminating between a primary battery and a secondary battery, and reliably detecting the presence or absence of overdischarge of the secondary battery.

  The present invention relates to a charge control circuit for charging a secondary battery of a device capable of storing a primary battery and a secondary battery as a built-in battery with an external charging device, and detecting means for detecting a voltage of a terminal for the secondary battery; Determining means for discriminating a state where no secondary battery is present and an overdischarged state of the secondary battery by applying a predetermined voltage to the secondary battery terminal when no voltage is detected by the detecting means; It is characterized by that.

  Further, the present invention is a charge control circuit for charging a secondary battery of a device capable of storing a primary battery and a secondary battery as a built-in battery by an external charging device, wherein the terminal voltage for the secondary battery of the built-in battery is set. A first terminal voltage detection circuit that detects that the built-in battery is a secondary battery when a predetermined terminal voltage is detected, and a case where the predetermined terminal voltage is not detected by the first terminal voltage detection circuit. A second terminal voltage detection circuit that detects that the built-in battery is an overdischarged secondary battery when a predetermined voltage is applied to the secondary battery terminal of the built-in battery and a voltage drop is detected; And a control circuit that allows charging of the internal battery by the charging device when the internal battery is detected as a secondary battery by the first terminal voltage detection circuit and the second terminal voltage detection circuit. And

  According to the present invention, it is possible to control charging by reliably discriminating between a primary battery and a secondary battery, and reliably detecting whether or not the secondary battery is overdischarged.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of a charge control circuit in the present embodiment. The charge control circuit 1 is mounted on a digital camera, for example. In a digital camera, a primary battery and a secondary battery can be used as a built-in battery. Examples of primary batteries that cannot be charged include alkaline dry batteries and lithium batteries (AA, CR-V3). On the other hand, as a rechargeable secondary battery, there are a lithium ion battery and a nickel metal hydride battery (AA size or square). In this embodiment, CR-V3 (hereinafter referred to as a first battery) as a primary battery, and a unique lithium ion battery (hereinafter referred to as an output terminal position different from that of CR-V3 as a secondary battery). In the digital camera using the second battery, a circuit configuration for identifying the first battery and the second battery and identifying the insertion state and the overdischarge state of the second battery is shown. FIGS. 3A to 3C show the appearances of the AA type primary battery 100, the CR-V3 battery 200, and the dedicated lithium ion battery 300, respectively. The CR-V3 battery 200 has a terminal 200 and a flat surface portion 200a on the side surface. The dedicated secondary battery 300 has a terminal 300 at a position different from that of the CR-V3 battery 200, and a flat surface portion 300a is formed on the side surface. A recess 304 is further formed in the flat surface portion 300a of the dedicated secondary battery 300. This is for mechanically distinguishing between the CR-V3 battery 200 and the dedicated secondary battery 300, and in this embodiment, the recess is formed. 304 is not necessary.

  As shown in FIG. 1, the digital camera is driven by a built-in battery, and is also connected to a DC-Jack (DC jack) or a dedicated charger and driven by receiving power from an external power source. The DC-Jack or dedicated charger is connected to the power supply line 100, and power is supplied to each part of the digital camera. A first battery 10 and a second battery 12 are connected to the power line 100 via switches SW1 and SW2, respectively. The DC-Jack and the dedicated charger are separately connected to SW1 and SW2, and when either one is connected to the digital camera, both SW1 and SW2 are turned off by the transistor circuit. When connection of DC-Jack or a dedicated charger is detected by a command from the microcomputer 16, SW1 and SW2 may be turned off. The first battery 10 and the second battery 12 are alternatively built in the digital camera, and the first battery 10 and the second battery 12 have terminals at different positions as shown in FIGS. 3A to 3C. SW 1 is connected to the terminal of the first battery 10, and SW 2 is connected to the terminal of the second battery 12. When the digital camera is connected to DC-Jack or a dedicated charger, SW1 and SW2 are turned off, so that only power from the external power supply is supplied to the power supply line 100 and not from the built-in battery.

  When the digital camera is connected to the dedicated charger, the charging line 200 that connects the charging circuit of the dedicated charger and the charging circuit of the digital camera is enabled, and the second battery 12 is charged by supplying power from the dedicated charger. Is done. Specifically, when the microcomputer 16 detects that the digital camera is connected to the dedicated charger, and detects that the second battery 12 is incorporated instead of the first battery 10, the second battery The detection signal is transmitted to the microcomputer on the dedicated charger side. The microcomputer on the side of the dedicated charger receives the detection signal from the microcomputer 16 on the side of the digital camera and controls the SW in the dedicated charger to be turned on to enable the charging line 200. When the built-in battery is the first battery 10, the SW inside the dedicated charger remains in the OFF state. When the digital camera is disconnected from the DC-Jack or from the dedicated charger, SW1 and SW2 are turned on to connect the built-in battery to the power supply line 100. Digital cameras operate with power supplied from the built-in battery.

  One terminal of the second battery 12 is connected to the power supply line 100 via SW2 as described above, but the determination signal line 300 is connected at a point P between SW2 and the terminal of the second battery 12. The discrimination signal line 300 includes transistor switches 18 and 20, and the transistor switches 18 and 20 are ON / OFF controlled by control signals CHK1 and CHK2 from the microcomputer 16, respectively. The transistor switch 20 is connected to a point Q of the determination signal line 300, that is, a point between the point P and the input terminal of the transistor switch 18 via the resistor 22, and a predetermined voltage (for example, 4) is connected to the other terminal of the transistor switch 20. .2V) is applied. The voltage signal BC output to the output terminal of the transistor switch 18 is supplied to the microcomputer 16 as a determination result.

  The microcomputer 16 detects the terminal voltage of the second battery 12 by turning on the transistor switch 18. When the voltage signal BC shows a finite value, it can be detected that the second battery 12 is incorporated instead of the first battery 10. On the other hand, when the voltage signal BC is substantially zero (when it is not a finite value), it may be estimated that the battery is not inserted or the first battery 10 is incorporated instead of the second battery 12. it can. However, when the overcharged second battery 12 is incorporated instead of the first battery 10, the voltage signal BC may be substantially zero in the same manner, and it is necessary to determine both. In such a case, the microcomputer 16 turns on the transistor switch 20 in addition to the transistor switch 18 and applies a predetermined voltage to the terminal of the second battery 12. When the battery is not inserted or the first battery 10 is incorporated instead of the second battery 12, the voltage signal BC substantially indicates a predetermined voltage (4.2V). On the other hand, when the overcharged second battery 12 is built in, if a predetermined voltage is applied, a voltage drop corresponding to the resistance 22 occurs, so that the voltage signal BC is substantially smaller than the predetermined voltage 4.2V. Therefore, the microcomputer 16 compares the voltage signal BC when the transistor switches 18 and 20 are turned on with a predetermined threshold value, so that the second battery 12 is not built in or is in the overdischarged second state. Whether or not the battery 12 is built in can be determined.

  FIG. 2 shows a processing flowchart of the present embodiment. First, the microcomputer 16 determines whether or not the digital camera is connected to a DC-Jack (DC jack) (S101). When not connected to DC-Jack, it is further determined whether or not it is connected to a dedicated charger (dock) (S102). The power source of the DC-Jack and the dedicated charger is connected to the microcomputer 16 via a circuit (not shown), and the microcomputer 16 determines whether or not the external power source is connected and the type of the external power source using this circuit. When neither the DC-Jack nor the dedicated charger is connected to the digital camera, it is either whether or not a battery is built in, and when the battery is built in, the voltage is detected on the power line 100. . When a voltage is detected on the power supply line 100 with no external power supply connected, the microcomputer 16 turns on the CHK0 signal and turns off SW2 (S103), whether the built-in battery is the first battery 10 or the second battery 12. Is discriminated (S104). That is, when the voltage is detected on the power supply line 100 even when SW2 is turned off, it is determined that the built-in battery is the first battery, and when the voltage is not detected, the built-in battery is the second battery 12. By performing this determination, it is possible to distinguish and detect the remaining amounts of the first battery and the second battery having different voltages, and it is possible to display an appropriate remaining amount for the user (S105). On the other hand, when either DC-Jack or a dedicated charger is connected to the digital camera, both SW1 and SW2 are turned off as described above. When DC-Jack is connected (YES in S101), charging is not performed, and thus battery determination processing is not performed.

  When the dedicated charger is connected (YES in S102), the process proceeds to battery discrimination processing. That is, the microcomputer 16 turns on the CHK1 signal (S106). As a result, the transistor switch 18 is turned on, and the voltage signal BC is supplied to the microcomputer 16. The microcomputer 16 determines whether or not the voltage signal BC is a finite value (S107). If the voltage signal BC is not a finite value (NO in S107), the second battery 12 is not built in, or the second battery 12 is built in, but the terminal voltage is abnormally low, that is, in an overdischarged state. Either. Therefore, next, the CHK2 signal is turned ON (S108), the transistor switch 20 is turned ON, and a predetermined voltage is applied to the terminal of the second battery 12. When the second battery 12 is present, a current flows to the second battery 12 side, a voltage drop occurs due to the resistor 22, and the voltage signal BC becomes smaller than the predetermined voltage by the voltage drop. Therefore, the voltage signal BC is compared with a predetermined voltage 4.2V-α (α is a voltage drop caused by the resistor 22) (S109). If the voltage signal BC is smaller than 4.2-α (YES in S109). Since the second battery 12 is built in and is in an overdischarged state, charging from the dedicated charger is permitted (S111). That is, the second battery detection signal is transmitted to the dedicated charger side, and the charging line 200 is validated. On the other hand, when the voltage signal BC is not smaller than 4.2 V−α (NO in S109), the second battery 12 is not built in, and thus charging from the dedicated charger is not permitted (S110). That is, the second battery detection signal is not transmitted to the dedicated charger side, and the charging line 200 is invalidated.

  If the voltage signal BC indicates a finite value (YES in S107), the second battery 12 is built in, and charging from the dedicated charger is permitted (S111).

  As described above, in the present embodiment, it is possible to easily determine the primary battery, the secondary battery, and the overdischarge state of the secondary battery, whereby the secondary battery can be reliably charged.

It is a circuit block diagram of an embodiment. It is a processing flowchart of an embodiment. It is a perspective view of a primary battery (AA type). It is a perspective view of a CR-V3 battery. It is a perspective view of a dedicated secondary battery.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Charge control circuit, 10 1st battery, 12 2nd battery, 16 microcomputer, 18, 20 Transistor switch.

Claims (2)

A charge control circuit for charging the secondary battery of an apparatus capable of storing a primary battery and a secondary battery as an internal battery by an external charging device,
Detection means for detecting the voltage of the terminal for the secondary battery;
A discriminating means for discriminating a state where no secondary battery exists and an overdischarged state of the secondary battery by applying a predetermined voltage to the secondary battery terminal when no voltage is detected by the detecting means;
A charge control circuit comprising: A charge control circuit for charging the secondary battery of an apparatus capable of storing a primary battery and a secondary battery as an internal battery by an external charging device,
A first terminal voltage detection circuit that detects a terminal voltage for the secondary battery of the internal battery and detects that the internal battery is a secondary battery when a predetermined terminal voltage is detected;
When the predetermined terminal voltage is not detected by the first terminal voltage detection circuit, the internal battery is overdischarged when a predetermined voltage is applied to the secondary battery terminal of the internal battery and a voltage drop is detected. A second terminal voltage detection circuit for detecting that the secondary battery is in a state;
A control circuit that allows charging of the internal battery by the charging device when the internal battery is detected as a secondary battery by the first terminal voltage detection circuit and the second terminal voltage detection circuit;
A charge control circuit comprising:

Images