JP2015006104A - Charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for appropriately charging a battery when a battery voltage becomes less than an overdischarge voltage value inhibiting discharge.SOLUTION: A battery in which a battery voltage Vb becomes less than a first discharge voltage value (about 1.6 V/cell) is charged with a constant current and a constant voltage at a first current value and a first output voltage value Vs (about 1.9 V/cell). When the battery voltage becomes equal to or higher than the first discharge voltage value, the battery is charged by the constant current at the first current value. When the battery voltage becomes equal to or higher than a second discharge voltage value (about 2.9 V/cell) larger than the first discharge voltage value, the battery is charged by the constant current and the constant voltage regulated to a maximum current value and a maximum output voltage value (about 4.2 V/cell).

Description

  The present invention relates to a charging method.

    The following patent documents disclose a charger for charging a lithium ion battery (a charger having a charging power source and a charging circuit unit). As disclosed in FIGS. 4 and 5 of this publication, a rectifier circuit 8 that converts alternating current into direct current, a switching unit 9 that converts direct current of the rectifier circuit 8 into a high-frequency pulse wave, and converts the pulse wave into a predetermined voltage Conversion transformer 11, PWM control circuit 13 that controls switching unit 9 to control a DC output, and photocoupler 17 that inputs a control signal to PWM control circuit 13.

    Then, when the constant current charging circuit 6 is used and the charging current exceeds a predetermined value, the photocoupler 17 is turned off, and this is used as a control signal, and the PWM control circuit 13 controls the transistor 10 to reduce the output. Control to reduce battery charging current. Therefore, the constant current charging circuit 6 prevents the battery charging current from becoming larger than the set value I1, and performs constant current charging.

  When the constant voltage charging circuit 5 is used and the charging voltage exceeds a predetermined value, the photocoupler 17 is turned off, and this is used as a control signal, and the PWM control circuit 13 controls the transistor 10 to reduce the output. Control to reduce battery charging voltage.

    JP-A-8-205418

    In addition, when the battery voltage of the lithium ion battery becomes less than the overdischarge voltage value that prohibits discharge, it is necessary to charge such a battery with a small current (trickle charge). .

  An object of this invention is to provide the method of charging appropriately, when a battery voltage becomes less than the overdischarge voltage value which prohibits discharge.

  In the charging method of the present invention, a battery whose battery voltage Vb is less than the first overdischarge voltage value (about 1.6 V / cell) is used as the first current value and the first output voltage value Vs (about 1.. 9V / cell) at a constant current and a constant voltage. When the battery voltage becomes equal to or higher than the first overdischarge voltage value, the battery voltage is constant at the first current value. When the second overdischarge voltage value (approximately 2.9 V / cell) is greater than the first overdischarge voltage value, the maximum current value and the maximum output voltage value (approximately 4.2 V / cell) are regulated. Charge at the constant current and constant voltage.

In the charging method of the present invention, less than the second overdischarge voltage value (in the case of two series cells, about 5.8 V (about 2.9 V / cell), for example, a battery voltage prohibiting discharge to an electronic device). In a certain overdischarge mode, the battery voltage Vb and the first output voltage value VS (when charging two series cells, from the power supply circuit 1 of about 3.8V (about 1.9V / cell) Output voltage) is small, and the amount of heat generation (loss power) can be suppressed.

1 is a circuit block diagram according to an embodiment of the present invention. It is a voltage and current graph concerning one Example of this invention. It is a voltage and electric current graph of a comparative example.

  A circuit block diagram which can be used in the embodiment of the present invention is shown in FIG. The battery 3 is charged via the charge control circuit 20 from the power supply circuit 1 that outputs the output voltage Vcc to be charged and the output current to be charged. The battery 3 is composed of a lithium ion battery, and two unit cells are connected in series.

  When the battery 1 is a lithium ion battery, the maximum current value and the maximum voltage value are regulated by a constant current (MAX current 0.5 to 1C) and (output) constant voltage (MAX4.2V / cell) charge (Charge mode) ).

  The charge control circuit 20 detects the battery voltage (1) by taking in the battery voltage Vs, and the current is determined by the charge control unit 21 to be controlled and the constant current value switching signal (3) from the charge control unit 21. A constant current control circuit 26 for sending a constant current constant voltage control feedback signal (5) to a control signal input section of the power supply circuit 1 to be described later, and a constant voltage value from the charge control section 21 so that the current value becomes constant. A constant voltage control circuit that sends a constant current / constant voltage control feedback signal (5) to a control signal input section of the power supply circuit 1 to be described later so that the output voltage Vcc becomes constant at a predetermined voltage value by the switching signal (4). 25, and a switching element 22 that is turned on and off by a charge switching element ON / OFF switching signal (2) from the charge control unit 21 based on the value of the battery voltage Vs.

  The charge control circuit 20 can also be used as an IC. Further, the current detection unit 27 connected in series with the switching element 22 detects the charging current, sends a signal corresponding to the current value to the charging control unit 21, and the charging control unit 21 controls the charging current, This is transmitted (feedback) to the constant current control circuit 26. The switching element 22 is also turned off when overcurrent is detected after completion of overcharging and charging.

  As the power supply circuit 1, a circuit as disclosed in the background art described above can be used. For example, a power supply circuit (not shown) having the following configuration can be used. Rectifier circuit that converts alternating current into direct current, switching unit that converts direct current of the rectifier circuit into high-frequency pulse wave, conversion transformer that converts pulse wave into predetermined voltage, and PWM control that controls the direct current output by controlling the switching unit The circuit includes a control signal input unit that inputs a control signal to the PWM control circuit 13. When the charging current exceeds a predetermined value, the constant current control circuit 26 is used to output a constant current / constant voltage control feedback signal (5), and the PWM control circuit controls the transistor via the control signal input unit. Then, the output is controlled to be low and the charging current of the battery is reduced. Therefore, the constant current control circuit 26 prevents the charging current of the battery from becoming larger than a predetermined value and performs constant current charging.

  When the charging voltage exceeds a predetermined value, the constant voltage control circuit 25 is used to output a constant current constant voltage control feedback signal (5), and the PWM control circuit controls the transistor via the control signal input unit. The output is controlled to be low, and the charging voltage of the battery is reduced. Therefore, the constant voltage control circuit 25 prevents the charging voltage of the battery from becoming higher than a predetermined value and performs constant voltage charging.

  In this embodiment, the above-described circuit is used to charge the battery as shown in the voltage / current graph of FIG.

A battery whose battery voltage Vb is less than the first overdischarge voltage value (about 3.2 V (about 1.6 V / cell if two series cells)) is used as the first current value (Trickle charging current), Charged at a constant current and a constant voltage at an output voltage value of 1 (output voltage from the power supply circuit 1 of about 3.8 V (about 1.9 V / cell) if 2 series cells are charged)
When the battery voltage becomes equal to or higher than the first overdischarge voltage value, a constant current is generated at the first current value (Trickle charging current). At this time, the output voltage Vcc of the power supply circuit 1 and the battery voltage Vb Rises as charging progresses.

  A second overdischarge voltage value that is greater than the first overdischarge voltage value (about 5.8 V (about 2.9 V / cell if two series cells), a battery voltage that inhibits discharge to an electronic device; Power supply circuit 1 having a maximum current value (Charging current) and a maximum output voltage value (about 8.4 V (about 4.2 V / cell) if charging two series cells) In this case, the output voltage Vcc and the battery voltage Vb of the power supply circuit 1 rise as charging progresses, and the output voltage Vcc is increased. The maximum output voltage value is reached first, the charging current value decreases from the maximum current value (Charging current), and the battery voltage Vb gradually approaches the maximum output voltage value.

  Furthermore, when charging progresses and the charging current value becomes a predetermined value or less, charging is stopped as full charging.

  Here, in the switching element 22 and the charging path in the charging control circuit 20, it is necessary to withstand the heat generation amount by (VS (output voltage value) −Vb (battery voltage)) × Ichg (charging current).

  In the above embodiment, the second overdischarge voltage value is less than about the second overdischarge voltage value (about 6.9 V (about 3.45 V / cell in the case of two series cells), for example, a battery voltage prohibiting discharge to an electronic device). In a certain overdischarge mode, when the battery voltage Vb is up to the first overdischarge voltage value (about 3.2 V (about 1.6 V / cell in the case of two series cells)), the first current value ( Trickle charging current), the first output voltage value (if charging two series cells, it will be charged at about 3.8V (about 1.9V / cell) from the power supply circuit 1). The difference between the voltage Vb and the first output voltage value VS (the output voltage from the power supply circuit 1 of about 3.8 V (about 1.9 V / cell) if two series cells are charged) is small, and heat is generated. The amount (power loss) can be reduced.

Further, a comparative example with the above-described embodiment will be described using the voltage and current graph of FIG. In the figure, the battery voltage Vb is less than the second overdischarge voltage value (in the case of two series cells, the battery voltage prohibiting discharge to an electronic device of about 5.8 V (about 2.9 V / cell)). Output voltage larger than this voltage value until the second overdischarge voltage value (if the two series cells are charged, the output voltage from the power supply circuit 1 of about 6.9 V (about 3.45 V / cell)) Thus, charging is performed at the same first current value (Trickle charging current) as in FIG. At this time, the difference between the battery voltage Vb and the output voltage is large, and the heat generation amount is large. In order for the charge control circuit 20 to withstand such a calorific value, the following measures can be considered, but each has the following problems.
Countermeasure (1) Lower the first current value (Trickle charging current). There is a problem that the charging time becomes long.
Countermeasure (2) The charge control circuit 20 is configured to withstand the heat generation amount. There is a problem that the circuit (IC package) becomes large and the product cannot be downsized.

  On the other hand, in the above embodiment, the difference between the battery voltage Vb and the first output voltage value VS is small, and the heat generation amount can be suppressed.

  For example, when the battery voltage of a battery in an overdischarged state is 0 V, the amount of heat generation (loss power) is calculated as follows with the first current value (Trickle charging current) as 0.1 A as the charging current.

Example (3.8V-0V) × 0.1A = 0.38W
Comparative Example (6.9V-0V) × 0.1A = 0.69W
0.38W ÷ 0.69W = 0.55, and compared with the comparative example, this embodiment can suppress the heat generation amount to 55%.

1 Power supply circuit 20 Charge control circuit 3 Battery

Claims (2)

A battery whose battery voltage is less than the first overdischarge voltage value is charged with a constant current and a constant voltage at a first current value and a first output voltage value,
When the battery voltage is equal to or higher than the first overdischarge voltage value, a constant current is applied at the first current value,
A charging method for charging with a constant current and a constant voltage regulated to a maximum current value and a maximum output voltage value when the battery voltage is equal to or greater than a second overdischarge voltage value greater than the first overdischarge voltage value. The charging method according to claim 1, wherein the battery is a lithium ion battery.