JP2013172529A - Charger and charging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a charging circuit from generating heat due to increased power consumption of the charging circuit when a secondary battery is charged.SOLUTION: A charger 1 which charges a secondary battery 4 charged to a predetermined preliminary charging voltage by preliminary charging for charging with a small current suppressed within a predetermined range, detects the voltage of the secondary battery 4 by a voltage conversion circuit 3 and outputs the voltage corresponding to the detected voltage, and charges the secondary battery 4 by the current corresponding to the voltage outputted by the voltage conversion circuit 3, with a charging circuit 2. Then the charging circuit 2 supplies a current to the secondary battery 4 so as to increase monotonously according to the voltage outputted by the voltage conversion circuit 3 so that the power consumption of the charging circuit 2 indicated by a product of the differential voltage indicating the difference between the external voltage supplied from the outside and the voltage of the secondary battery 4 detected by the voltage conversion circuit 3, and the current with which the charging circuit 2 charges the secondary battery 4 does not exceed a predetermined power.

Description

  The present invention relates to a charging device and a charging method, and relates to a charging device and a charging method for charging a secondary battery.

  In recent years, with the progress of downsizing and weight reduction of electronic devices, portable devices have been popularized. With the spread of these portable devices, demand for secondary batteries such as rechargeable lithium-ion batteries that serve as power sources for portable devices is increasing. Secondary batteries such as lithium-ion batteries are normally charged (preliminary charge) to a predetermined voltage (preliminary charge voltage) with a small current with the charging current kept within a predetermined range, and then the charge current is reserved. Charge with a larger current than when charging (main charge or fast charge).

  Patent Document 1 discloses a charge control circuit that precharges a lithium ion battery and then rapidly charges the lithium ion battery. The charging control circuit disclosed in Patent Document 1 performs initial charging of a lithium ion battery with a current limited within a predetermined range by a preliminary charging circuit, and when the lithium ion battery is charged to a predetermined voltage, the charging circuit needs to be charged. The battery is quickly charged with a large constant current until the voltage is reached. And after a lithium ion battery becomes a required charge voltage, it switches to a constant voltage charge so that the voltage of a lithium ion battery may not rise more than a required charge voltage. As described above, the charge control circuit disclosed in Patent Document 1 quickly charges a lithium ion battery after preliminary charging with a large constant current at a stretch, and sets the voltage of the lithium ion battery to a necessary charging voltage.

  Patent Document 2 describes a technique for rapidly charging a lithium ion battery after preliminary charging. As shown in FIG. 10, the secondary battery charging device described in Patent Document 2 includes a charging current supply circuit 21, a charging current detection unit 22, a battery voltage detection unit 23, and a charge control unit 24. The charging current supply circuit 21 supplies a charging current for charging the secondary battery. The charging current detection means 22 detects the value of the charging current. The battery voltage detection means 23 detects the battery voltage of the secondary battery. Based on the voltage value of the secondary battery, the charging control unit 24 controls the charging current supply circuit 21 to adjust the charging current value. And the charge control part 24 starts this charge with a 1st charging current value with respect to the secondary battery after preliminary charging. Then, the charging control unit 24 uses a reference voltage whose secondary battery voltage is the same as or lower than the full charge voltage (indicating the voltage of the secondary battery when the secondary battery is fully charged). , The charging current value is switched to the second charging current value smaller than the first charging current value, and charging is continued. Thereafter, when the voltage of the secondary battery is lower than the reference voltage, the charging control unit 24 reduces the second charging current to be smaller than the first charging current value until the voltage of the secondary battery recovers the reference voltage. Charging is performed with a charging current value larger than the value. When the voltage of the secondary battery reaches the reference voltage, the charging current value is switched to the second charging current value. That is, the charging device 20 of the secondary battery described in Patent Document 2 starts main charging with the first charging current value with respect to the secondary battery, and the voltage of the secondary battery is the same as the full charge voltage or is fully charged. When a reference voltage lower than the voltage is reached, charging is performed by switching the charging current value to a second charging current value smaller than the first charging current value. As described above, the secondary battery charging device 20 described in Patent Document 2 has the first charging larger than the second charging current value until the voltage of the secondary battery becomes close to the full charge voltage after the preliminary charging. The battery is charged at a stretch depending on the current value.

Japanese Patent No. 3427341 JP 2011-211846 A

  The charge control circuit disclosed in Patent Document 1 described above makes the voltage of the lithium ion battery the required charge voltage by rapidly charging the lithium ion battery after the preliminary charging at a stretch with a large constant current. Further, the secondary battery charging device disclosed in Patent Document 2 described above has a first charging current larger than the second charging current value until the voltage of the secondary battery becomes close to the full charge voltage after preliminary charging. Charging at a stretch depending on the value. However, charging a secondary battery at once using a large charging current up to a necessary charging voltage or a full charging voltage has a problem that the power consumption of the charging circuit increases and the charging circuit may generate heat. Further, when the charging circuit generates heat, there is a problem that the user may be burned when removing the secondary battery from the charging device after charging.

  An object of the present invention is to solve the above-described problems and provide a charging device and a charging method in which the charging circuit does not increase power consumption and the charging circuit does not generate heat.

  The charging device of the present invention is a charging device for charging a secondary battery charged to a predetermined preliminary charging voltage by preliminary charging for charging with a small current suppressed within a predetermined range. A voltage conversion circuit that detects a voltage and outputs a voltage corresponding to the detected voltage; and a charging circuit that charges the secondary battery with a current corresponding to the voltage output by the voltage conversion circuit, and the charging The circuit is represented by a product of a difference voltage indicating a difference between an external voltage supplied from the outside and a voltage of the secondary battery detected by the voltage conversion circuit, and a current at which the charging circuit charges the secondary battery. In order to prevent the power consumption of the charging circuit from exceeding a predetermined power, a current is supplied to the secondary battery so as to increase monotonously according to the voltage output from the voltage conversion circuit.

  The charging method of the present invention is a charging method in which a secondary battery charged to a predetermined preliminary charging voltage by preliminary charging charged with a small current suppressed within a predetermined range is charged by a charging circuit. A voltage of the secondary battery is detected, a voltage corresponding to the detected voltage is output, the secondary battery is charged with a current corresponding to the output voltage by the charging circuit, and the charging circuit is supplied from the outside Power consumption of the charging circuit indicated by a product of a difference voltage indicating a difference between the detected external voltage and the detected voltage of the secondary battery and a current for charging the secondary battery by the charging circuit is predetermined. In order not to exceed the generated power, a current is supplied to the secondary battery so as to increase monotonously according to the output voltage.

  Thus, according to the present invention, the power consumption of the charging circuit does not increase and the charging circuit does not generate heat.

It is a figure which shows an example of the charging device which concerns on the 1st Embodiment of this invention. It is a figure which shows an example of the charging device which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the input-output voltage characteristic of the voltage converter circuit of the charging device which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the input-output characteristic of the constant current circuit of the charging device which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the charge characteristic of the charging device which concerns on the 2nd Embodiment of this invention. It is a figure which shows an example of the charging device which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example of the input-output voltage characteristic of the reciprocal calculation circuit of the charging device which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example of the input-output characteristic of the constant current circuit of the charging device which concerns on the 3rd Embodiment of this invention. It is a figure which shows an example of the charge characteristic of the charging device which concerns on the 3rd Embodiment of this invention. It is a figure which shows the charging device of a secondary battery in related technology.

Next, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram showing an example of a charging apparatus according to the first embodiment of the present invention.

  FIG. 1 also shows an external power supply 5 (for example, an AC (Alternating Current) adapter) that supplies a voltage to the charging circuit 2 and a secondary battery 4 (for example, a lithium ion battery) that is charged by the charging circuit 2. . The external power supply 5 supplies a predetermined voltage (external voltage: for example, 5 V (Volt)) to the charging circuit 2. The secondary battery 4 is charged to a predetermined preliminary charging voltage (for example, 3 V) by preliminary charging with a small current (for example, 100 mA (milliampere)) suppressed within a predetermined range.

  The charging device 1 according to the present embodiment includes a charging circuit 2 and a voltage conversion circuit 3.

  The voltage conversion circuit 3 detects the voltage of the secondary battery 4 and outputs a voltage corresponding to the detected voltage. The charging circuit 2 charges the secondary battery 4 by flowing the current so as to increase monotonously according to the voltage output from the voltage conversion circuit 3. The power consumption of the charging circuit 2 is the product of the difference voltage indicating the difference between the external voltage supplied to the charging circuit 2 and the voltage of the secondary battery 4 and the current at which the charging circuit 2 charges the secondary battery 4. Indicated. The charging circuit 2 allows the current to flow through the secondary battery 4 in a monotonous manner according to the voltage output from the voltage conversion circuit 3 so that the power consumption does not exceed a predetermined power. The predetermined power is power (for example, 1 W (Watt)) that does not cause the charging circuit 2 to generate heat. This power is not limited to 1 W (Watt), and may be any power as long as the charging circuit 2 does not generate heat.

As described above, according to the embodiment of the present invention, the charging circuit monotonously increases the current according to the voltage output from the voltage conversion circuit so that the power consumption of the charging circuit does not exceed the predetermined power. And charge the secondary battery. For this reason, when the charging circuit charges the secondary battery, the power consumption of the charging circuit does not exceed a predetermined power, so that the power consumption of the charging circuit does not increase and there is no possibility that the charging circuit generates heat.
(Second Embodiment)
FIG. 2 is a diagram illustrating an example of a charging apparatus according to the second embodiment of the present invention.

  FIG. 2 also shows an external power supply 5 (for example, an AC adapter) that supplies a voltage to the charging circuit 2 and a secondary battery 4 (for example, a lithium ion battery) that is charged by the charging circuit 2. The external power supply 5 supplies a predetermined voltage (external voltage: for example, 5 V (Volt)) to the charging circuit 2. The secondary battery 4 is charged to a predetermined preliminary charging voltage (for example, 3 V) by preliminary charging with a small current (for example, 100 mA (milliampere)) suppressed within a predetermined range.

  The charging device 1 according to the present embodiment includes a charging circuit 2 and a voltage conversion circuit 3. The charging circuit 2 includes a constant current circuit 6 and a constant voltage circuit 7. The voltage conversion circuit 3 detects the voltage of the secondary battery 4 and outputs a voltage corresponding to the detected voltage. The constant current circuit 6 of the charging circuit 2 is configured so that the secondary battery 4 charged to the precharge voltage is charged at a full charge voltage (2 to 0.5 A to 0.75 A) with a current proportional to the output voltage of the voltage conversion circuit 3 (for example, 0.5 A to 0.75 A). The secondary battery 4 is charged up to a voltage of, for example, 4.2 V when the secondary battery 4 is fully charged. This charging is called main charging or rapid charging. The constant voltage circuit 7 of the charging circuit 2 charges the secondary battery 4 by passing a current so that the voltage of the secondary battery 4 maintains a fully charged voltage. The power consumption of the charging circuit 2 is the product of the difference voltage indicating the difference between the external voltage supplied to the charging circuit 2 and the voltage of the secondary battery 4 and the current at which the charging circuit 2 charges the secondary battery 4. Indicated. The charging circuit 2 allows the current to flow through the secondary battery 4 in a monotonous manner according to the voltage output from the voltage conversion circuit 3 so that the power consumption does not exceed a predetermined power. The predetermined power is power (for example, 1 W (Watt)) that does not cause the charging circuit 2 to generate heat. This power is not limited to 1 W (Watt), and may be any power as long as the charging circuit 2 does not generate heat.

  As described above, according to the embodiment of the present invention, the charging circuit monotonously increases the current according to the voltage output from the voltage conversion circuit so that the power consumption of the charging circuit does not exceed the predetermined power. And charge the secondary battery. For this reason, when the charging circuit charges the secondary battery, the power consumption of the charging circuit does not exceed a predetermined power, so that the power consumption of the charging circuit does not increase and there is no possibility that the charging circuit generates heat.

  Next, the operation of the second exemplary embodiment of the present invention will be described in detail with reference to FIGS.

  FIG. 3 is a diagram illustrating an example of input / output voltage characteristics of the voltage conversion circuit of the charging device according to the second embodiment of the present invention. The horizontal axis represents the input voltage of the voltage conversion circuit 3 (voltage of the secondary battery 4), and the vertical axis represents the output voltage of the voltage conversion circuit 3. The voltage conversion circuit 3 detects the voltage of the secondary battery 4, and if this voltage is equal to or lower than a threshold voltage (eg, 3.7 V) that is a middle voltage between the full charge voltage and the precharge voltage, the first voltage (For example, 2V) is output. When the detected voltage exceeds the threshold voltage, a second voltage higher than the first voltage (for example, 3 V) is output.

  FIG. 4 is a diagram illustrating an example of input / output characteristics of the constant current circuit of the charging device according to the second embodiment of the present invention. The horizontal axis indicates the input voltage of the constant current circuit 6 (output voltage of the voltage conversion circuit 3), the vertical axis indicates the output current of the constant current circuit 6 (charging current of the secondary battery 4), and the input voltage is 2V and 3V. It shows that the output current is 0.5A and 0.75A.

FIG. 5 is a diagram illustrating an example of the charging characteristics of the charging device according to the second embodiment of the present invention.
(A) shows an example of the time change of the charging current of the charging circuit 2 when the secondary battery 4 is charged. (B) shows an example of the time change of the power consumption of the charging circuit 2 at the time of charge of the secondary battery 4. FIG. (C) shows an example of the time change of the voltage (battery voltage) of the secondary battery 4 at the time of charge.

  Here, when the secondary battery 4 charged in advance to the preliminary charging voltage (3 V) is connected to the charging device 1 to which the external power supply 5 is connected, the voltage conversion circuit 3 detects the voltage of the secondary battery 4. As shown in FIG. 3, the voltage conversion circuit 3 is configured such that the detected voltage of the secondary battery 4 is a middle threshold voltage between a full charge voltage (for example, 4.2 V) and a precharge voltage (for example, 3 V). It is checked whether or not (for example, 3.7 V) or less. When the result of the examination is equal to or lower than the threshold voltage, a first voltage (for example, 2V) is output. When the result of the examination exceeds the threshold voltage, a second voltage (for example, 3 V) higher than the first voltage is output. Then, the constant current circuit 6 of the charging circuit 2 is proportional to the first voltage and the second voltage output from the voltage conversion circuit 3, respectively, and is a first current (for example, a larger current than that during the preliminary charging) (for example, , 0.5 A) and a second current (for example, 0.75 A) are output, and the secondary battery 4 is rapidly charged to the full charge voltage.

  The above operation will be described with reference to FIG.

  When the battery voltage of the secondary battery 4 detected by the voltage conversion circuit 3 is between the precharge voltage and the threshold voltage, the voltage conversion circuit 3 outputs the first voltage (2V) as shown in FIG. Then, based on this voltage, the constant current circuit 6 uses the first current (0.5 A), which is a larger current than that during the preliminary charging, as shown in FIG. 4 and FIG. 4 is charged. Then, the battery voltage of the secondary battery 4 rises from 3V to 3.7V as shown in FIG. Next, when the battery voltage of the secondary battery 4 detected by the voltage conversion circuit 3 exceeds the threshold voltage (3.7 V), the voltage conversion circuit 3 has a second voltage higher than the first voltage as shown in FIG. (3V) is output. Based on this voltage, the constant current circuit 6 generates a secondary battery with a second current (0.75 A) that is larger than the first current, as shown in FIG. 4 and FIG. 4 is charged. Then, the battery voltage of the secondary battery 4 increases from 3.7V to 4.2V as shown in FIG. When the battery voltage of the secondary battery 4 detected by the voltage conversion circuit 3 reaches the full charge voltage (4.2 V), the voltage conversion circuit 3 outputs a full charge signal. When receiving the full charge signal from the voltage conversion circuit 3, the charging circuit 2 switches the circuit for charging the secondary battery 4 from the constant current circuit 6 to the constant voltage circuit 7. And this constant voltage circuit 7 charges the secondary battery 4 with the electric current shown to (a) of FIG. 5 so that the voltage of the secondary battery 4 may maintain a full charge voltage.

  Here, the power consumption of the charging circuit 2 when charging the secondary battery 4 from the preliminary charging voltage to the full charging voltage will be described. The power consumption of the charging circuit 2 is the product of the voltage applied to the charging circuit 2 and the current flowing through the charging circuit 2. The voltage applied to the charging circuit 2 is a value obtained by subtracting the battery voltage of the secondary battery 4 shown in FIG. 5C from the voltage (5 V) supplied from the external power supply 5 to the charging circuit 2. The current flowing through the charging circuit 2 is a charging current for charging the secondary battery 4 shown in FIG. Therefore, as shown in FIG. 5B, when the battery voltage of the secondary battery 4 is between the preliminary charging voltage and the threshold voltage, the power consumption of the charging circuit 2 is (5- 3) When V × 0.5A = 1W (Watt) gradually decreases to (5-3.7) V × 0.5A = 0.65W, and the battery voltage of the secondary battery 4 becomes the threshold voltage. The power consumption of the charging circuit 2 is (5-3.7) V × 0.75A = 0.975W. When the battery voltage of the secondary battery 4 is between the threshold voltage and the full charge voltage, the power consumption of the charging circuit 2 is changed from 0.975 W to (5-4.2) V × 0.75 A = 0.6 W. Decrease gradually. Thus, the power consumption of the charging circuit 2 can be charged from the precharge voltage to the full charge voltage without exceeding 1 W. By the way, when charging only from a precharge voltage to a threshold voltage with a large current (0.75 A), the power consumption of the charging circuit 2 is (5-3) V × 0.75 A = 1.5 W (Watt) From (5-3.7) V × 0.75A = 0.97W, it will gradually decrease, and well over 1W. For this reason, in this case, the charging circuit may generate heat.

As described above, according to the embodiment of the present invention, when the secondary battery is rapidly charged after the preliminary charging, the secondary battery is charged with a relatively small current (0.5 A) when the voltage is lower than the threshold voltage, and exceeds the threshold voltage. In this case, charging is performed with a large current (0.75 A). Therefore, the charging circuit charges the secondary battery 4 by flowing the current to the secondary battery in a monotonous manner according to the voltage output from the voltage conversion circuit so that the power consumption does not exceed the predetermined power. I am doing so. For this reason, when the charging circuit charges the secondary battery, the power consumption of the charging circuit does not exceed a predetermined power, so that the power consumption of the charging circuit does not increase and there is no possibility that the charging circuit generates heat.
(Third embodiment)
FIG. 6 is a diagram illustrating an example of a charging apparatus according to the third embodiment of the present invention.

  FIG. 6 also shows an external power supply 5 (for example, an AC (Alternating Current) adapter) that supplies a voltage to the charging circuit 11 and a secondary battery 4 (for example, a lithium ion battery) that is charged by the charging circuit 11. . The external power supply 5 supplies a predetermined voltage (for example, 5 V (Volt)) to the charging circuit 11. The secondary battery 4 is charged to a predetermined preliminary charging voltage (for example, 3 V) by preliminary charging with a small current (for example, 100 mA (milliampere)) suppressed within a predetermined range.

  The charging device 10 according to the present embodiment includes a charging circuit 11 and a voltage conversion circuit 16. The charging circuit 11 includes a constant current circuit 6 and a constant voltage circuit 7. The voltage conversion circuit 16 includes a subtraction circuit 12 and an inverse calculation circuit 13. The subtraction circuit 12 outputs a difference voltage Vd between the voltage of the external power supply 5 supplied to the charging circuit 11 and the voltage (battery voltage) of the secondary battery 4 charged by the charging circuit 11. The reciprocal calculation circuit 13 outputs a reciprocal voltage (1 / Vd) indicating a reciprocal voltage of the difference voltage Vd output from the subtraction circuit 12. The constant current circuit 6 of the charging circuit 11 receives a reciprocal voltage output from the reciprocal calculation circuit 13 and is in proportion to this voltage, for example, a current larger than a current (for example, 100 mA) at the time of preliminary charging (for example, 0.5 A to 1 The secondary battery 4 is charged to a full charge voltage (for example, 4.2 V) by .25A). This charging is called main charging or rapid charging. The constant voltage circuit 7 of the charging circuit 11 charges the secondary battery 4 by passing a current so that the voltage of the secondary battery 4 is kept at the full charge voltage.

  The power consumption of the charging circuit 11 is the product of the difference voltage indicating the difference between the external voltage supplied to the charging circuit 11 and the voltage of the secondary battery 4 and the current at which the charging circuit 11 charges the secondary battery 4. Indicated. The charging circuit 11 allows the current to flow through the secondary battery 4 so as to increase monotonously in accordance with the voltage output from the voltage conversion circuit 16 so that the power consumption does not exceed a predetermined power. The predetermined power is power (eg, 1 W (Watt)) that does not cause the charging circuit 11 to generate heat. This power is not limited to 1 W (Watt), and may be any power that does not cause the charging circuit 11 to generate heat.

  Here, operation | movement of the charging device 10 which concerns on this Embodiment is demonstrated.

  The secondary battery 4 charged in advance to the preliminary charging voltage (3 V) is connected to the charging device 10 to which the external power source 5 is connected. The subtraction circuit 12 outputs a difference voltage Vd between the voltage (5 V) of the external power supply 5 supplied to the charging circuit 11 and the voltage (battery voltage) of the secondary battery 4 charged by the charging circuit 11. Initially, 5V-3V = 2V. The reciprocal calculation circuit 13 outputs a reciprocal voltage (1 / Vd) of the difference voltage output from the subtraction circuit 12. The initial voltage is 1 / 2V (0.5V). The charging circuit 11 receives the reciprocal voltage output from the reciprocal calculation circuit 13 and charges the secondary battery 4 with a current that is proportional to the voltage and is larger than the current at the time of preliminary charging. Assuming that the proportionality constant is 1, the reciprocal voltage is 0.5V at the beginning, so the charging circuit 11 rapidly charges the secondary battery 4 at 0.5A. The charging circuit 11 continues charging with a current proportional to the voltage while receiving the reciprocal voltage output from the reciprocal calculation circuit 13. Then, when the charging circuit 11 is charged, the battery voltage of the secondary battery 4 gradually increases, and when the secondary battery 4 is charged up to the full charge voltage (4.2 V), the battery voltage of the secondary battery 4 at this time is 4 Since it is 0.2 V, the subtraction circuit 12 outputs 5V-4.2V = 0.8V. Further, the reciprocal calculation circuit 13 outputs 1 / 0.8V = 1.25V. Therefore, at this time, the charging circuit 11 rapidly charges the secondary battery 4 at 1.25 A.

  Here, the power consumption of the charging circuit 11 when charging the secondary battery 4 from the preliminary charging voltage to the full charging voltage will be described. The power consumption of the charging circuit 11 is the product of the voltage applied to the charging circuit 11 and the current flowing through the charging circuit 11. The voltage applied by the charging circuit 11 is a value obtained by subtracting the battery voltage of the secondary battery 4 from the voltage (5 V) supplied from the external power supply 5 to the charging circuit 11, and this is the difference voltage Vd output from the subtraction circuit 12. . Further, the current flowing through the charging circuit 11 is Ac = K × (1 / Vd) (where K is a proportional multiplier), and the current proportional to the output (1 / Vd) of the reciprocal calculation circuit 13 is 1. Then, the current flowing through the charging circuit 11 is Ac = 1 / Vd. Therefore, the power consumption of the charging circuit 11 when charging the secondary battery 4 from the precharge voltage to the full charge voltage is Ac × Vd = 1 W, which is a constant low power consumption. Incidentally, in the case of charging only with a large current (0.75 A) from the precharge voltage (3 V) to the full charge voltage (4.2 V), the power consumption of the charging circuit 11 is (5-3) V × 0. .75A = 1.5W (Watt) is gradually reduced from (5-4.2) V × 0.75A = 0.6W, and there is a period well exceeding 1W. For this reason, in this case, the charging circuit may generate heat.

  As described above, according to the embodiment of the present invention, the difference voltage between the voltage (5V) of the external power source supplied to the charging circuit and the voltage of the secondary battery (battery voltage) charged by the charging circuit by the subtracting circuit. Vd is output, and the reciprocal voltage (1 / Vd) of the difference voltage is output by the reciprocal calculation circuit. The charging circuit charges the secondary battery with a current Ac = 1 / Vd (proportional constant is 1) proportional to the reciprocal voltage. For this reason, the power consumption of the charging circuit when charging the secondary battery 4 from the preliminary charging voltage to the full charging voltage is Ac × Vd = 1 W, which is a constant low power consumption. There is no risk that the charging circuit will generate heat.

  Next, the operation of the third embodiment of the present invention will be described in detail with reference to FIGS.

  FIG. 7 is a diagram illustrating an example of input / output voltage characteristics of the reciprocal calculation circuit of the charging device according to the third embodiment of the present invention. The input voltage is the difference voltage Vd output from the subtraction circuit 12. The difference voltage Vd is a difference between the voltage of the external power supply 5 supplied to the charging circuit 11 and the battery voltage of the secondary battery 4 charged by the charging circuit 11. The output voltage is a reciprocal 1 / Vd of the differential voltage Vd.

  FIG. 8 is a diagram illustrating an example of input / output characteristics of the constant current circuit of the charging device according to the third embodiment of the present invention. The horizontal axis represents the input voltage of the constant current circuit 14 (output voltage (1 / Vd) of the reciprocal calculation circuit 13), and the vertical axis represents the output current of the constant current circuit 14 (charging current of the secondary battery 4).

  FIG. 9 is a diagram illustrating an example of the charging characteristics of the charging device according to the third embodiment of the present invention. (A) shows an example of the time change of the charging current of the charging circuit 11 when the secondary battery 4 is charged. (B) shows an example of the time change of the power consumption of the charging circuit 11 at the time of charge of the secondary battery 4. FIG. (C) shows an example of the time change of the voltage (battery voltage) of the secondary battery 4 at the time of charge.

  Here, when the secondary battery 4 charged in advance to the preliminary charging voltage (3 V) is connected to the charging device 10 to which the external power supply 5 is connected, the subtraction circuit 12 is supplied with the voltage of the external power supply 5 supplied to the charging circuit 11. A difference voltage Vd between (5 V) and the voltage (battery voltage) of the secondary battery 4 charged by the charging circuit 11 is output. Then, as shown in FIG. 7, the reciprocal calculation circuit 13 outputs a reciprocal voltage (1 / Vd) of the difference voltage output from the subtraction circuit 12. Next, as shown in FIG. 8, the constant current circuit 14 of the charging circuit 11 receives the reciprocal voltage output from the reciprocal calculation circuit 13 and is proportional to this voltage. The current Ac = K is larger than the current at the time of precharging. The secondary battery 4 is charged by × (1 / Vd) (where K is a proportional multiplier). When the proportionality constant is 1, the charging current is Ac = 1 / Vd. The constant current circuit 14 charges the secondary battery 4 from the precharge voltage (3V) to the full charge voltage (4.2V) by this charging current.

  The above operation will be described with reference to FIG.

  As shown in FIG. 9 (c), the battery voltage of the secondary battery 4 is gradually increased and charged by the constant current circuit 14 from the precharge voltage (3V) to the full charge voltage (4.2V). The At this time, since the voltage of the external power supply 5 is 5V, the difference voltage Vd that is the output of the subtraction circuit 12 varies from (5-3) = 2V to (5-4.2) = 0.8V. The reciprocal voltage (1 / Vd) that is the output of the reciprocal calculation circuit 13 varies from 1/2 = 0.5V to 1 / 0.8 = 1.25V. For this reason, since the output of the constant current circuit 14 of the charging circuit 11 is Ac = 1 / Vd, it varies from 0.5 A to 1.25 A as shown in FIG. With this current, the secondary battery 4 is charged until it reaches a full charge voltage (4.2 V). Then, the subtraction circuit 12 outputs a full charge signal when the battery voltage of the secondary battery 4 reaches the full charge voltage. When receiving the full charge signal from the subtraction circuit 12, the charging circuit 11 switches the circuit for charging the secondary battery 4 from the constant current circuit 14 to the constant voltage circuit 15. And this constant voltage circuit 15 charges the secondary battery 4 with the electric current shown to (a) of FIG. 9 so that the voltage of the secondary battery 4 may maintain a full charge voltage.

  Here, the power consumption of the charging circuit 11 when charging the secondary battery 4 from the preliminary charging voltage to the full charging voltage will be described. The power consumption of the charging circuit 11 is the product of the voltage applied to the charging circuit 11 and the current flowing through the charging circuit 11. The voltage applied to the charging circuit 11 is a value obtained by subtracting the battery voltage of the secondary battery 4 shown in FIG. 9C from the voltage (5 V) supplied from the external power source 5 to the charging circuit 11. Output voltage Vd. Further, the current flowing through the charging circuit 11 is a current Ac = K × (1 / Vd) (where K is a proportional multiplier) proportional to the output (1 / Vd) of the reciprocal calculation circuit 13, where K is 1. The current flowing through the charging circuit 11 is Ac = 1 / Vd. Therefore, as shown in FIG. 9B, the power consumption of the charging circuit 11 when charging the secondary battery 4 from the precharge voltage to the full charge voltage is Ac × Vd = 1 W, which is a constant low power consumption. Become. Incidentally, in the case of charging only with a large current (0.75 A) from the precharge voltage (3 V) to the full charge voltage (4.2 V), the power consumption of the charging circuit 11 is (5-3) V × 0. It gradually decreases from .75A = 1.5W to (5-4.2) V × 0.75A = 0.6W, and there is a period well exceeding 1W. For this reason, in this case, the charging circuit may generate heat. Here, in the above description, the proportional multiplier K is set to 1. However, the value may be appropriately determined within a range in which the power consumption of the charging circuit is low without being particular about this value.

  As described above, according to the embodiment of the present invention, the subtraction circuit outputs the difference voltage Vd between the voltage of the external power source supplied to the charging circuit and the voltage of the secondary battery (battery voltage) charged by the charging circuit. Then, the reciprocal calculation circuit outputs the reciprocal voltage (1 / Vd) of the differential voltage. The charging circuit charges the secondary battery with a current Ac = 1 / Vd (proportional constant is 1) proportional to the reciprocal voltage. For this reason, the power consumption of the charging circuit when charging the secondary battery from the precharge voltage to the full charge voltage is Ac × Vd = 1 W, which is a constant low power consumption, so the power consumption of the charging circuit does not increase. There is no risk that the charging circuit will generate heat.

  Thus, according to the present invention, the charging circuit allows the current to flow monotonously according to the voltage output from the voltage conversion circuit so that the power consumption of the charging circuit does not exceed the predetermined power. Charge the secondary battery. For this reason, when the charging circuit charges the secondary battery, the power consumption of the charging circuit does not exceed a predetermined power, so that the power consumption of the charging circuit does not increase and there is no possibility that the charging circuit generates heat.

Part or all of the above-described embodiments can be described as in the following supplementary notes, but is not limited thereto.
(Appendix 1)
A charging device for charging a secondary battery charged to a pre-charge voltage set in advance by pre-charging with a small current suppressed within a predetermined range,
A voltage conversion circuit that detects a voltage of the secondary battery and outputs a voltage corresponding to the detected voltage;
A charging circuit that charges the secondary battery with a current corresponding to the voltage output by the voltage conversion circuit;
The charging circuit is a product of a difference voltage indicating a difference between an external voltage supplied from the outside and a voltage of the secondary battery detected by the voltage conversion circuit, and a current at which the charging circuit charges the secondary battery. In order to prevent the power consumption of the charging circuit shown in FIG. 2 from exceeding a predetermined power, a current is supplied to the secondary battery in a monotonically increasing manner according to the voltage output from the voltage conversion circuit. Charging device.
(Appendix 2)
The voltage conversion circuit includes:
The voltage of the secondary battery is equal to or lower than a predetermined threshold voltage which is a middle voltage between a full charge voltage indicating the voltage of the secondary battery when the charge of the secondary battery is satisfied and the precharge voltage. In this case, a predetermined first voltage is output, and when the voltage of the secondary battery exceeds the threshold voltage, a predetermined second voltage higher than the first voltage is output,
The charging circuit is proportional to the first voltage and the second voltage output from the voltage conversion circuit, respectively, and has a first current and a second current that are larger than those during the preliminary charging. To charge the secondary battery,
The charging device according to claim 1, which is configured as described above.
(Appendix 3)
When the voltage of the secondary battery reaches the full charge voltage, the voltage conversion circuit outputs a full charge signal,
The charging circuit receives the full charge signal from the voltage conversion circuit, and charges the secondary battery so that the voltage of the secondary battery maintains the full charge voltage after receiving the full charge signal.
The charging device according to claim 1 or 2, wherein
(Appendix 4)
The charging circuit is a constant current that charges the secondary battery with the first current and the second current that are proportional to the first voltage and the second voltage output from the voltage conversion circuit, respectively. Circuit,
A constant voltage circuit for charging the secondary battery so that the voltage of the secondary battery maintains the full charge voltage;
The charging device according to claim 3, further comprising:
(Appendix 5)
The voltage conversion circuit includes:
A subtracting circuit for outputting the difference voltage indicating a difference between an external voltage supplied from the outside to the charging circuit and the detected voltage of the secondary battery;
A reciprocal calculation circuit that outputs a reciprocal voltage indicating a reciprocal voltage of the difference voltage output by the subtraction circuit, and
The charging circuit receives the reciprocal voltage output from the reciprocal calculation circuit and charges the secondary battery with a larger current than in the preliminary charging in proportion to the voltage.
The charging device according to claim 1.
(Appendix 6)
The subtracting circuit outputs a full charge signal when the voltage of the secondary battery becomes a full charge voltage indicating a voltage when the charge of the secondary battery is satisfied,
The charging circuit receives the full charge signal from the subtraction circuit, and charges the secondary battery so that the voltage of the secondary battery maintains the full charge voltage after receiving the full charge signal.
The charging device according to claim 5.
(Appendix 7)
The charging circuit is
A constant current circuit for receiving the inverse voltage output from the inverse calculation circuit and charging the secondary battery with a current proportional to the voltage;
The charging device according to claim 6, further comprising: a constant voltage circuit that charges the secondary battery so that a voltage of the secondary battery maintains the full charge voltage.
(Appendix 8)
A charging method for charging a secondary battery charged to a predetermined precharge voltage by a precharge with a small current suppressed within a predetermined range by a charging circuit,
Detecting the voltage of the secondary battery and outputting a voltage according to the detected voltage;
The charging circuit charges the secondary battery with a current corresponding to the output voltage,
The charging circuit is represented by a product of a difference voltage indicating a difference between an external voltage supplied from the outside and the detected voltage of the secondary battery, and a current at which the charging circuit charges the secondary battery. A charging method, wherein a current is supplied to the secondary battery so as to increase monotonously according to the output voltage so that power consumption of the charging circuit does not exceed a predetermined power.
(Appendix 9)
The voltage of the secondary battery is equal to or lower than a predetermined threshold voltage which is a middle voltage between the full charge voltage indicating the voltage of the secondary battery when the charge of the secondary battery is satisfied and the precharge voltage. Whether or not
When the examined result indicates a threshold voltage or less, the secondary battery is charged with a first current that is larger than that during the preliminary charging,
If the result of the examination does not indicate a threshold voltage or less, the secondary battery is charged with a second current that is greater than that during the preliminary charge and that is greater than the first current;
The charging method according to claim 8.
(Appendix 10)
Create a differential voltage between the external voltage supplied from the outside to the charging circuit and the voltage of the secondary battery,
Create a reciprocal voltage indicating the reciprocal voltage of the created differential voltage,
Charging the secondary battery with a larger current than that during the preliminary charging in proportion to the created reciprocal voltage;
The charging method according to claim 8.
(Appendix 11)
The charging method according to appendix 9, wherein when the voltage of the secondary battery reaches the full charge voltage, the secondary battery is charged so that the voltage of the secondary battery maintains the full charge voltage. .
(Appendix 12)
When the voltage of the secondary battery becomes a full charge voltage indicating a voltage when the charge of the secondary battery is satisfied, the secondary battery is set so that the voltage of the secondary battery maintains the full charge voltage. The charging method according to appendix 10, wherein charging is performed.

DESCRIPTION OF SYMBOLS 1 Charging device 2 Charging circuit 3 Voltage conversion circuit 4 Secondary battery 5 External power supply 6 Constant current circuit 7 Constant voltage circuit 10 Charging device 11 Charging circuit 12 Subtraction circuit 13 Reciprocal calculation circuit 14 Constant current circuit 15 Constant voltage circuit 16 Voltage conversion circuit DESCRIPTION OF SYMBOLS 20 Charging apparatus 21 Charging current supply circuit 22 Charging current detection means 23 Battery voltage detection means 24 Charge control part

Claims (10)

A charging device for charging a secondary battery charged to a pre-charge voltage set in advance by pre-charging with a small current suppressed within a predetermined range,
A voltage conversion circuit that detects a voltage of the secondary battery and outputs a voltage corresponding to the detected voltage;
A charging circuit that charges the secondary battery with a current corresponding to the voltage output by the voltage conversion circuit;
The charging circuit is a product of a difference voltage indicating a difference between an external voltage supplied from the outside and a voltage of the secondary battery detected by the voltage conversion circuit, and a current at which the charging circuit charges the secondary battery. In order to prevent the power consumption of the charging circuit shown in FIG. 2 from exceeding a predetermined power, a current is supplied to the secondary battery in a monotonically increasing manner according to the voltage output from the voltage conversion circuit. Charging device. The voltage conversion circuit includes:
The voltage of the secondary battery is equal to or lower than a predetermined threshold voltage which is a middle voltage between a full charge voltage indicating the voltage of the secondary battery when the charge of the secondary battery is satisfied and the precharge voltage. In this case, a predetermined first voltage is output, and when the voltage of the secondary battery exceeds the threshold voltage, a predetermined second voltage higher than the first voltage is output,
The charging circuit is proportional to the first voltage and the second voltage output from the voltage conversion circuit, respectively, and has a first current and a second current that are larger than those during the preliminary charging. To charge the secondary battery,
The charging device according to claim 1, which is configured as described above. When the voltage of the secondary battery reaches the full charge voltage, the voltage conversion circuit outputs a full charge signal,
The charging circuit receives the full charge signal from the voltage conversion circuit, and charges the secondary battery so that the voltage of the secondary battery maintains the full charge voltage after receiving the full charge signal.
The charging device according to claim 1 or 2, wherein The charging circuit is a constant current that charges the secondary battery with the first current and the second current that are proportional to the first voltage and the second voltage output from the voltage conversion circuit, respectively. Circuit,
A constant voltage circuit for charging the secondary battery so that the voltage of the secondary battery maintains the full charge voltage;
The charging device according to claim 3, further comprising: The voltage conversion circuit includes:
A subtracting circuit for outputting the difference voltage indicating a difference between an external voltage supplied from the outside to the charging circuit and the detected voltage of the secondary battery;
A reciprocal calculation circuit that outputs a reciprocal voltage indicating a reciprocal voltage of the difference voltage output by the subtraction circuit, and
The charging circuit receives the reciprocal voltage output from the reciprocal calculation circuit and charges the secondary battery with a larger current than in the preliminary charging in proportion to the voltage.
The charging device according to claim 1. The subtracting circuit outputs a full charge signal when the voltage of the secondary battery becomes a full charge voltage indicating a voltage when the charge of the secondary battery is satisfied,
The charging circuit receives the full charge signal from the subtraction circuit, and charges the secondary battery so that the voltage of the secondary battery maintains the full charge voltage after receiving the full charge signal.
The charging device according to claim 5. The charging circuit is
A constant current circuit for receiving the inverse voltage output from the inverse calculation circuit and charging the secondary battery with a current proportional to the voltage;
The charging device according to claim 6, further comprising: a constant voltage circuit that charges the secondary battery so that a voltage of the secondary battery maintains the full charge voltage. A charging method for charging a secondary battery charged to a predetermined precharge voltage by a precharge with a small current suppressed within a predetermined range by a charging circuit,
Detecting the voltage of the secondary battery and outputting a voltage according to the detected voltage;
The charging circuit charges the secondary battery with a current corresponding to the output voltage,
The charging circuit is represented by a product of a difference voltage indicating a difference between an external voltage supplied from the outside and the detected voltage of the secondary battery, and a current at which the charging circuit charges the secondary battery. A charging method, wherein a current is supplied to the secondary battery so as to increase monotonously according to the output voltage so that power consumption of the charging circuit does not exceed a predetermined power. The voltage of the secondary battery is equal to or lower than a predetermined threshold voltage which is a middle voltage between the full charge voltage indicating the voltage of the secondary battery when the charge of the secondary battery is satisfied and the precharge voltage. Whether or not
When the examined result indicates a threshold voltage or less, the secondary battery is charged with a first current that is larger than that during the preliminary charging,
If the result of the examination does not indicate a threshold voltage or less, the secondary battery is charged with a second current that is greater than that during the preliminary charge and that is greater than the first current;
The charging method according to claim 8. Create a differential voltage between the external voltage supplied from the outside to the charging circuit and the voltage of the secondary battery,
Create a reciprocal voltage indicating the reciprocal voltage of the created differential voltage,
Charging the secondary battery with a larger current than that during the preliminary charging in proportion to the created reciprocal voltage;
The charging method according to claim 8.

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