JP2014138514A - Device for charging secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging device that reduces power on standby, power during charging and power after charging.SOLUTION: A charging circuit 10 for supplying power to a battery pack 30 and a control circuit 20 for controlling charging of the battery pack are connected to a secondary side of a transformer T. The charging circuit 10 has first and second constant voltage setting sections for holding a voltage of the charging circuit at preset constant values. The first constant voltage setting section D3 has the setting of a voltage capable of charging the battery pack to be charged to any battery voltage, and the second constant voltage setting section D2 has the setting of a voltage lower than the first charging voltage and higher than a voltage necessary to drive the control circuit 20. The control circuit 20 includes a battery state discrimination circuit 22 for detecting a charge state of the battery pack, and a charge control section 21 for switching between the first and second constant voltage setting sections in response to the detection result of the battery state discrimination circuit, and when no battery pack is mounted or when a charge is complete, causes a current of the lower voltage set by the second constant voltage setting section D2 to flow from the charging circuit 10 to the control circuit 20.

Description

  The present invention relates to a charging device for a secondary battery, and in particular, as a secondary winding of a transformer for stepping down a power supply voltage, a main winding connected to a charging circuit and a sub winding connected to a control circuit The present invention relates to a charging device having

  Conventionally, as a secondary battery charging device, for example, as shown in Patent Document 1 to Patent Document 3, a switching power supply in which a transformer and a switching element for generating AC are combined is generally used. In this switching power supply, a commercial power supply is connected to the primary side of the transformer, a secondary battery charging circuit and its control circuit are connected to the secondary side, and switching elements such as transistors and FETs are arranged on the primary side of the transformer. ing. Electric power required in the charging circuit is detected by the control circuit on the secondary side, and this is fed back to the primary side to turn on / off the switching element.

  In this type of prior art charging circuit, the driving power of the control circuit is ensured at the time of standby when the battery pack is not attached to the charging device or when the battery pack is fully charged, or the switching element A bleeder resistor is provided to stabilize the operation.

  That is, since a large voltage is required for the charging circuit while the battery pack is being charged, a large amount of power is supplied to the secondary side by the continuous switching operation of the switching element, so that the driving power of the control circuit can be sufficiently provided. However, when the battery pack is not charged and the load is light, the secondary side does not require a large amount of power, so the oscillation frequency of the switching element also decreases, and the power supplied to the secondary side decreases. As a result, the drive power of the control circuit will be insufficient, so by inserting a bleeder resistor in the charging circuit, the power consumed by the bleeder resistor is supplied to the secondary side, and the power supply required for the control circuit is supplied. Is made.

JP 2004-357420 A JP 2006-20437 A Japanese Patent No. 3661472

  In recent years, energy savings related to home appliances have been promoted for the purpose of reducing CO2 emissions, and the standardization of energy consumption has progressed in each country, and standby power and power supply efficiency have to be below the standard values. Similarly, in battery chargers, total energy regulations during standby, during charging, and after charging are being standardized.

  However, in such a conventional technique, the power consumption of the bleeder resistor at the time of standby or completion of charging has hindered the reduction of energy consumption. That is, this type of charging device controls the switching element in accordance with the load of the charging circuit, but the switching element is lightly loaded at a light load such as when a battery pack is not inserted in such a circuit. In order to reduce time loss, the oscillation frequency is lowered or intermittent oscillation called burst mode is performed.

  On the other hand, even when the charging circuit is lightly loaded, the control circuit connected to the sub-winding needs to maintain a voltage above a certain value necessary for the operation of the control circuit. It is not preferable to reduce the power supplied to the secondary side by reducing the frequency to a certain level or intermittently oscillating. Therefore, in the prior art, by providing a bleeder resistor in the charging circuit, a load corresponding to the bleeder resistor remains in the charging circuit even at a light load, thereby stabilizing the switching element and reducing the driving power of the control circuit. I was trying to secure it. However, the presence of such a bleeder resistance has nothing to do with charging performance and user convenience, and simply consumes power, which is not preferable in terms of effective use of power. It was.

  In particular, the control circuit is generally provided with a series regulator so that a constant voltage necessary for the control circuit can be obtained. At light load, if the oscillation is in burst mode in order to reduce the power consumption of the primary side control unit, the rectification unit on the control circuit side also configures the rectifier circuit by the burst cycle according to the load on the charging side The capacitor is being charged. However, by consuming power on the control circuit side during the burst period, the charge stored in the capacitor on the control circuit side is consumed, which is below the minimum input voltage that guarantees stable operation of the series regulator. Stable operation may not be possible.

  The present invention has been proposed to solve such problems of the prior art. An object of the present invention is to provide a charging device for a secondary battery that eliminates the need for a bleeder resistor and enables power reduction at light loads.

The secondary battery charging device of the present invention is characterized by having the following configuration.
(1) A power supply circuit is connected to a primary winding of a transformer, a first switching element for turning on and off a voltage applied to the transformer of the power supply circuit, and a primary side control unit for performing on / off control thereof Is connected.
(2) The main winding and sub-winding are connected to the secondary side of the transformer, the main winding has a charging circuit that supplies power to the battery pack to be charged, and the sub-winding is the status of the battery pack. A control circuit for controlling charging of the battery pack is connected in accordance with the control.
(3) The charging circuit is provided with first and second constant voltage setting units that hold the voltage of the charging circuit at a preset constant value.
(4) In the first constant voltage setting unit, a voltage that can be charged with any battery voltage of the battery pack to be charged is set, and in the second constant voltage setting unit, the voltage is lower than the first voltage, A voltage higher than the voltage required for driving is set.
(5) The control circuit includes a battery state determination circuit that detects a charge state of the battery pack, and a charge control unit that switches between the first and second constant voltage setting units according to the detection result of the battery state determination circuit, When the battery pack is not mounted or when charging is completed, a current necessary for the control circuit is supplied from the low voltage set by the second constant voltage setting unit to the control circuit.

  In the present invention, the first and second constant voltage setting units can be constituted by Zener diodes. In addition, the charging circuit can be provided with a first rectifier circuit for charging the battery pack and a second rectifier circuit for driving the control circuit when the voltage of the battery pack is low.

  According to the present invention, by eliminating the need for the bleeder resistance, it is possible to reduce the power for the bleeder resistance and to ensure the driving power of the control circuit at the time of light load.

1 is a circuit diagram showing a first embodiment of the present invention. The circuit diagram which shows 2nd Embodiment of this invention.

[1. First Embodiment]
[1-1. Constitution]
(1) Primary side circuit Hereinafter, a first embodiment of the present invention will be described in detail with reference to FIG. In the present embodiment, the AC power supply 2 is connected to one end of the primary winding 1a of the transformer T via the rectifier circuit unit 3, and the switching element Q1 is connected to the other end of the primary winding 1a. The switching element Q1 is provided with a primary side control unit 5 for controlling on / off thereof.

  The primary-side control unit 5 is connected to the receiving unit of the photocoupler PHC, and this receiving unit receives the control signal of the switching element Q1 transmitted from the control circuit 20. The transmitter of the photocoupler PHC is provided in the charging circuit 10 connected to the secondary side of the transformer T. Thereby, the primary side control part 5 receives the signal from the feedback element of the secondary side via the photocoupler PHC, and controls on / off of the switching element Q1. The primary-side control unit 5 sets the switching element Q1 to an intermittent oscillation state such as a burst mode in order to reduce power consumption when the battery pack is not attached or at a light load such as when charging is completed.

  The switching element Q <b> 1 is controlled to be turned on / off by the primary side control unit 5 based on a control signal from the control circuit 20, and outputs a charging output to the secondary side via the transformer T. On the secondary side of the transformer T, two main and sub windings 1b and 1c are provided. A charging circuit 10 is connected to the main winding 1b, and a control circuit 20 is connected to the sub winding 1c.

(2) Charging circuit 10
A battery pack 30 to be charged is connected to the charging circuit 10, and a voltage necessary for charging the battery pack 30 is supplied from the main winding 1b. The battery pack 30 includes a secondary battery connected in series and a battery pack internal circuit 31 such as a temperature and a protection element inside the battery in one package.

  The charging circuit 10 is provided with a rectifying diode D1 and a capacitor C1 connected to the main winding 1b, and a charging switch 11 for starting or stopping charging the battery pack 30. In this embodiment, the charge switch 11 includes a switching element Q3 that is turned on / off by a signal from the control circuit 20, and a backflow prevention diode D4 that is inserted on the battery pack 30 side.

(3) Control circuit 20
The control circuit 20 controls the voltage and power of the charging circuit 10 according to the charging / discharging state of the battery pack 30, and the driving power is supplied from the sub winding 1c. The control circuit 20 includes a rectifying diode D5 and a capacitor C2 connected to the sub winding 1c, and a series regulator 23. The diode D5 and the capacitor C2 constitute a rectification unit for the control circuit 20, and rectify the secondary side output (control side) of the transformer T. The series regulator 23 converts the voltage of the rectifying unit for the control circuit 20 that changes depending on the state of the load on the charging side into a constant stable voltage.

  The control circuit 20 includes a charge control unit 21 connected to the charging switch 11 of the charging circuit 10 and a battery state determination circuit 22 connected to the battery pack internal circuit 31 in order to determine the state of the battery pack 30. . The charge control unit 21 is connected to the battery state determination circuit 22 and turns on / off the charge switch 11 according to the charge / discharge state of the battery pack 30 and the temperature of the battery detected by the battery state determination circuit 22.

  The charging control unit 21 is connected to the current control unit 12 provided in the charging circuit 10. The current control unit 12 is a circuit unit that controls the current flowing through the battery pack 30. A current detection resistor R5 is connected between the current control unit 12 and one end of the battery pack 30, and a Zener diode D3 is connected between the current control unit 12 and the other end of the battery pack 30. The transmission unit of the photocoupler PHC is connected to the current control unit 12 via the resistor R4.

  The current detection resistor R5 detects the current flowing through the battery pack 30 as the voltage at both ends thereof, and quantifies the amount of current flowing through the charging circuit 10. The Zener diode D3 has a Zener voltage that is equal to or higher than the maximum battery voltage, and a reference voltage (Zener voltage) is set so as not to exceed a certain voltage when the charging switch 11 is OFF.

(4) Voltage switching circuit 40
In the present embodiment, the reference voltage to be fed back to the switching element Q1 on the primary side is switched between charging the battery pack 30 by the charging circuit 10 and a light load such as when the battery pack is not installed or when charging is completed. The voltage switching circuit 40 is provided. The voltage switching circuit 40 includes a switching element Q4 such as a transistor connected between the charging circuit 10 and the control circuit 20 via resistors R2 and R3.

  The switching element Q4 is for reducing the voltage of the control circuit 20 when the charging circuit 10 is lightly loaded, that is, when the charging switch 11 is off. Therefore, when the charge control unit 21 is connected to the base terminal of the switching element Q4 and the voltage of the control circuit 20 is lowered, the charge control unit 21 outputs a signal for turning on the switching element Q4.

  The charging circuit 10 is provided with a switching element Q2 for voltage switching in parallel with the Zener diode D3. An FET or a transistor can be used as the switching element Q2. The gate terminal of the switching element Q2 is connected to the switching element Q4 connected to the charge control unit 21 at the connection point between the resistors R2 and R3. One terminal of the switching element Q2 is connected to the main winding 1b of the charging circuit 10, and the other terminal is connected to the current control unit 12 via the Zener diode D2. Therefore, when the switching element Q4 connected to the charging control unit 21 is turned on, a current flows through the resistors R2 and R3, and the switching element Q2 is turned on.

  Zener diode D2 becomes conductive when switching element Q4 is turned on, and a current flows through secondary side photocoupler PHC. Therefore, the voltage that has been fed back and controlled by the Zener voltage of the Zener diode D3 to the primary side until now is controlled by the Zener voltage of the Zener diode D2. At this time, the Zener voltages of the Zener diodes D2 and D3 have the following relationship.

Zener voltage of D3> Zener voltage of D2> Minimum operating voltage of series regulator 23

  Between the rectifying diode D1 connected to the main winding 1b and the series regulator 23 of the control circuit 20, a diode D6 that allows current to flow from the charging circuit 10 toward the control circuit 20 is provided. The diode D6 supplies a current to the control circuit 20 side when the voltage of the control circuit 20 is lower than the voltage of the charging circuit 10.

[1-2. Action]
(1) When charging the battery pack In this embodiment, when the battery pack 30 to be charged is connected to the charging circuit 10, the charge control unit 21 of the control circuit 20 detects the battery state determination circuit 22 from the battery pack internal circuit 31. Whether or not charging is necessary is determined according to the state of the battery pack 30, and when it is determined that the battery pack 30 needs to be charged, the charging switch 11 is turned on. At the same time, the charging control unit 21 turns off the switching element Q4 connected thereto, which is in a charging state, and outputs a control start command for the switching element Q1 on the primary side to the current control unit 12 of the charging circuit 10. .

  The current control unit 12 monitors the voltage of the current detection resistor R5, and controls the ON / OFF of the switching element Q1 on the primary side to the transmission unit of the photocoupler PHC via the resistor R4 when the voltage exceeds a set voltage value. A current that is a signal for the operation is supplied. As a result, a signal for controlling the current and voltage on the secondary side is fed back to the primary side using the photocoupler PHC.

  The primary side control unit 5 that has received the signal from the secondary side via the photocoupler PHC performs on / off control of the switching element Q1, and supplies the necessary power to the primary side of the transformer T accordingly. . On the secondary side of the transformer T, after the main winding 1b steps down the voltage controlled by the switching element Q1 to generate a voltage required by the charging circuit 10, the voltage is rectified by the diode D1 and the capacitor C1 that are rectifying elements. The battery pack 30 is charged. In this case, since the voltage necessary for charging the battery pack 30 is supplied to the secondary side of the transformer T, the voltage sufficient to stably operate the series regulator 23 of the control circuit 20 also in the sub winding 1c. Is supplied.

(2) When the battery pack is not attached and when the charging is completed When the battery state determination circuit 22 of the control circuit 20 detects the completion of charging of the battery pack 30, the charging control unit 21 turns off the charging switch 11 and stops charging. The switching element Q4 is turned on. Then, a voltage is applied from the resistors R2 and R3 to the gate terminal of the voltage switching switching element Q2, and the switching element Q2 is turned on.

  In the Zener diodes D3 and D2 connected to the current control unit 12, the set Zener voltage is set lower for D2, so that the voltage value set by the Zener voltage of the Zener diode D2 is set. A current serving as a signal for controlling on / off of the switching element Q1 on the primary side is supplied from D2 to the transmission unit of the photocoupler PHC via the resistor R4. As a result, the switching element Q1 on the primary side is on / off controlled at such a timing that a voltage lower than that at the time of charging is generated in the charging circuit 10.

  The low voltage current generated by the charging circuit 10 flows from the charging circuit 10 toward the control circuit 20 via the diode D6, and drives the series regulator 23. In this case, since the Zener voltage of the Zener diode D2 is set higher than the minimum operating voltage of the series regulator 23, the series regulator 23 operates stably and each part of the control circuit 10 is also driven appropriately.

[1-3. effect]
According to the present embodiment, the voltage of the charging circuit 10 is reduced to the minimum voltage required by the series regulator 23 by the voltage switching circuit 40, and the power supplied from the sub winding 1c to the control circuit 20 at the time of light load is insufficient. Can be supplemented by the electric power on the charging circuit 10 side via the diode D6. As a result, the stable operation of the control circuit 20 at the time of light load of the charging circuit 10 can be realized by appropriately selecting the Zener voltage set in the Zener diodes D2 and D3 without providing a bleeder resistor in the charging circuit 10. Power loss due to bleeder resistance can be avoided, and power consumption during standby and after completion of charging can be reduced.

  In particular, in the circuit having such a configuration, the charging switch 11 has a parasitic diode inside, and when the voltage of the battery pack 30 is higher than the voltage of the charging circuit 10, a current flows from the battery pack 30 to the charging circuit 30 and is charged. The battery pack 30 is discharged. In this embodiment, since the backflow prevention diode D4 is inserted in order to prevent this, such inconvenience is prevented. In the circuit having such a configuration, when the charging switch 11 is the transistor Q3, the transistor Q3 is turned on when the voltage of the battery pack 30 and the voltage of the charging circuit 10 have a voltage difference greater than the breakdown voltage between the emitter and the base. In this embodiment, conduction is blocked by the backflow prevention diode D4.

[2. Second Embodiment]
[2-1. Constitution]
A second embodiment of the present invention will be described with reference to FIG. In addition, about the structure similar to earth embodiment, the same part number is attached | subjected and description is abbreviate | omitted.

  In the present embodiment, the charging circuit 10 has two systems in the charging circuit 10 by providing the second rectifying diode D7 and the capacitor C3 in parallel with the rectifying diode D1 and the capacitor C1 provided in FIG. The rectifier circuit is formed. The second rectifier circuit including the diode D7 and the capacitor C3 is a first rectifier circuit including the diode D1 and the capacitor C1 when the battery pack 30 is not inserted or when the transistor Q4 is off during charging. And almost the same potential.

  The voltage switching circuit 40 is provided with a switching element Q5 made of FET, and a switching element Q4 connected to the charge control unit 21 is connected to the gate terminal thereof. The drain-side terminal of the switching element Q5 is connected to the switching element Q4 on the charge control unit 21 side via resistors R2 and R3. A source-side terminal of the switching element Q5 is connected to the current control unit 12 via a Zener diode D2. In this case, the Zener voltages of the Zener diodes D2 and D3 have the following relationship.

Zener voltage of D3> Zener voltage of D2> Minimum operating voltage of series regulator 23

The terminal on the source side of the switching element Q5 is further connected to the input side of the series regulator 23 via the diode D6. The diode D6 supplies a current to the control circuit 20 side when the voltage of the control circuit 20 is lower than the voltage of the charging circuit 10.
[2-2. Action]
(1) At the time of charging the battery pack In the present embodiment, when the battery pack 30 is charged, the switching element Q4 is turned off by a command from the charge control unit 21, so that no current flows through the switching element Q5. Therefore, the current control unit 12 monitors the voltage of the current detection resistor R5, and when the voltage value exceeds the set voltage value, the primary switching element Q1 is turned on / off to the transmission unit of the photocoupler PHC via the resistor R4. A current is supplied as a signal for controlling the current. As a result, a signal for controlling the secondary side current using the photocoupler PHC is fed back to the primary side.

(2) When the battery pack is not attached and when the charging is completed When the battery state determination circuit 22 of the control circuit 20 detects the completion of charging of the battery pack 30, the charging control unit 21 turns off the charging switch 11 and stops charging. The switching element Q4 is turned on. Then, the voltage switching switching element Q5 is turned on from the resistors R2 and R3.

  When the switching element Q5 is turned on, the Zener diode D2 becomes conductive, and a current flows through the secondary photocoupler PHC. Therefore, the voltage that has been fed back and controlled by the Zener voltage of the Zener diode D3 to the primary side until now is controlled by the Zener voltage of the Zener diode D2. As a result, the switching element Q1 on the primary side is on / off controlled at such a timing that a voltage lower than that at the time of charging is generated in the charging circuit 10.

  The diode D6 has a low voltage generated by the charging circuit 10 because the switching element Q5 is on and a current flows through the control circuit 20 when “the voltage of the control circuit 20 <the charging circuit 10”. Current flows from the charging circuit 10 toward the control circuit 20 via the switching element Q5 and the diode D6 from the second rectifier circuit side, and drives the series regulator 23. In this case, since the Zener voltage of the Zener diode D2 is set higher than the minimum operating voltage of the series regulator 23, the series regulator 23 operates stably and each part of the control circuit 20 is also driven appropriately.

[2-3. effect]
In the present embodiment, the rectifier circuit portion provided in the charging circuit 10 is divided into two, and a signal for turning on the switching element Q4 is issued from the charging control unit 21 during standby and when charging is completed, and the voltage switching circuit unit 40 is operated. Then, the voltage of the charging circuit 10 is lowered to a voltage at which the series regulator 23 can operate at a minimum, and power is supplied to the control circuit 20. Therefore, according to the present embodiment, a bleeder resistor is not required, the power consumption at light load can be greatly reduced, and a voltage at which the series regulator 23 operates at a minimum can be secured by the Zener voltage of the Zener diode D2. A stable operation of the circuit 20 can also be secured.

  In the present embodiment, when the charging of the battery pack 30 is completed and the switching element Q4 is turned on, the charging circuit 10 becomes the voltage of the battery pack 30, but the current from the battery pack 30 because of the diode D1. Does not flow to the diode D6. In the first embodiment, there is a problem that the current from the battery pack 30 after the charging is completed flows to the control circuit 20, but in this embodiment, the rectifying diode D1 blocks the current from the battery pack 30, The backflow prevention diode D4 of the first embodiment is not necessary, and no loss is caused by the backflow prevention diode D4 during charging. Further, during charging, the switching element Q4 is turned off, so that almost no loss occurs in this portion.

  In the present embodiment, the charging switch 11 is configured when “battery voltage after completion of charging> voltage of charging circuit 10 after switching after completion of charging (voltage at which series regulator 23 operates at a minimum)”. Even without the switching element Q3, the charging switch 11 can be deleted because the charging current does not flow to the battery pack 30 side. That is, when there is no battery pack 30, the charging circuit 10 and the control circuit 20 have substantially the same potential, and even if there is a battery pack 30 having a voltage higher than the voltage of the charging circuit 10, Charging current does not flow. In this case, the power during charging can also be reduced.

[3. Other Embodiments]
The present invention is not limited to the illustrated embodiment, and includes other embodiments as follows.
(1) In the illustrated embodiment, the Zener diodes D2 and D3 are used as the constant voltage setting unit for charging and light load provided in the voltage switching circuit 40, but other constant voltage setting is used instead of the Zener diode. Members and circuits can also be used.
(2) In order to supply electric power from the charging circuit 10 to the control circuit 20 side at a light load, a member other than the diode D6 connected to the position shown in the figure is used, and the series regulator 23 is connected from other places. The current after rectification can flow in the previous stage. For example, the switching element Q5 as in the second embodiment is used, and power can be supplied directly from the charging-side rectifier circuit by the diode D6 as in the first embodiment.
(3) The means for transmitting secondary side charging circuit information to the primary side control unit 5 is not limited to the photocoupler PHC, and signal transmission means using other electrical circuits can be used. .

T: Transformers D1, D5, D7 ... Rectifying diodes C1, C2, C3 ... Rectifying capacitors D2, D3 ... Zener diode D4 ... Backflow prevention diode D6 ... Diodes R2-R5 ... Resistors Q1-Q5 ... Switching element PHC ... Photo Coupler 1a ... primary winding 1b ... main winding 1c ... sub winding 2 ... AC power supply 3 ... rectifier circuit unit 4 ... switching element 5 ... primary side control unit 10 ... charging circuit 11 ... charging switch 12 ... current control unit 20 ... Control circuit 21 ... Charge control unit 22 ... Battery state determination circuit 23 ... Series regulator 30 ... Battery pack 31 ... Battery pack internal circuit 40 ... Voltage switching circuit
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Claims (7)

A power supply circuit is connected to the primary winding of the transformer, a first switching element that turns on and off a voltage applied to the transformer of the power supply circuit, and a primary-side control unit that performs on / off control thereof are connected,
A main winding and a sub-winding are connected to the secondary side of the transformer, a charging circuit that supplies power to the battery pack to be charged is connected to the main winding, and a sub-winding according to the state of the battery pack A control circuit that controls the charging of the battery pack is connected,
The charging circuit is provided with first and second constant voltage setting units for holding the voltage of the charging circuit at a predetermined constant value,
The first constant voltage setting unit is set to a voltage that can be charged with any battery voltage of the battery pack to be charged, and the second constant voltage setting unit is lower than the first voltage and is necessary for driving the control circuit. Voltage higher than the correct voltage,
The control circuit includes a battery state determination circuit that detects a charge state of the battery pack, and a charge control unit that switches between the first and second constant voltage setting units according to the detection result of the battery state determination circuit. Charging of a secondary battery characterized in that, when not installed or when charging is completed, a current necessary for the control circuit is caused to flow from the low voltage set by the second constant voltage setting unit to the control circuit from the charging circuit. apparatus.   A second switching element that is turned on when the battery pack is not attached or when charging is completed is connected to the charge control unit. When the second switching element is turned on, the first constant voltage setting unit is set to the second constant voltage setting unit. The secondary battery charging device according to claim 1, wherein the secondary battery charging device is switched to a voltage setting unit.   A first and a second constant voltage setting unit are connected in parallel to the charging circuit, the second switching element is connected to a second constant voltage setting unit, and the second switching element is turned on. The secondary battery charging device according to claim 2, wherein a second constant voltage setting unit is inserted.   The charging circuit includes two rectification units, a rectification unit for charging and a rectification unit for light load, and the first constant voltage setting unit is connected to the rectification unit for charging. The voltage setting unit is connected to a rectification unit for light load, the second switching element is connected to a second constant voltage setting unit, and the second constant voltage setting unit is turned on by turning on the second switching element. The secondary battery charging device according to claim 2, wherein the charging device is charged.   The secondary battery according to claim 2, wherein the charging circuit and the control circuit are connected via a diode provided between a rectifying unit provided in the charging circuit and the control circuit. Charging device.   5. The charging device for a secondary battery according to claim 4, wherein the charging circuit and the control circuit are connected via a diode provided between the rectifier for the light load and the control circuit. 6. . The secondary battery charging device according to claim 1, wherein the first and second constant voltage setting units are configured by Zener diodes.
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