JP2013027227A - Charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charger capable of charging various kinds of secondary batteries.SOLUTION: A charger 1 comprises a charging switch element Q1 having a body diode BD1, a charging switch element Q2 having a body diode BD2, resistors R1 and R2, control switch elements SW1 and SW2, and a constant voltage source VDD. The charger 1 controls whether to charge the secondary battery BT by controlling the control switch element SW1 and prevents the backflow of current from the secondary battery BT to a DC power supply DC by controlling the control switch element SW2.

Description

  The present invention relates to a charging device.

  Conventionally, a charging device for charging a secondary battery has been proposed (see, for example, Patent Document 1).

  FIG. 3 is a circuit diagram of a charging apparatus 100 according to a conventional example. The charging device 100 controls whether or not the secondary battery BT is charged. The charging device 100 includes a charge switch element Q formed of a P-channel MOSFET, resistors Ra and Rb, a control switch element SW, and a diode D.

  A positive electrode of a DC power source DC is connected to the source of the charge switch element Q, and an anode of the diode D is connected to the drain of the charge switch element Q. The positive electrode of the secondary battery BT is connected to the cathode of the diode D.

  A resistor Ra, a resistor Rb, and a control switch element SW are connected in series between the positive electrode and the negative electrode of the DC power source DC, and a charging switch element is provided at a connection point between the resistor Ra and the resistor Rb. The gate of Q is connected. Specifically, one end of the resistor Ra is connected to the positive electrode of the DC power source DC, and one end of the resistor Rb and the gate of the charge switch element Q are connected to the other end of the resistor Ra. The other end of the resistor Rb is connected to the negative electrode of the DC power source DC via the control switch element SW. The negative electrode of the secondary battery BT is also connected to the negative electrode of the DC power source DC.

  The charging device 100 having the above configuration controls whether to charge the secondary battery BT by switching the charge switch element Q by controlling the control switch element SW.

Japanese Patent Laid-Open No. 10-14127

  In the charging device 100 shown in FIG. 3, if the control switch element SW is turned on so that the charge switch element Q is turned on, the voltage of the positive electrode of the secondary battery BT is applied to the gate of the charge switch element Q. That is, a voltage obtained by dividing the charging voltage of the secondary battery BT by the resistance Ra and the resistance Rb is applied.

For example, assuming that the charging voltage of the secondary battery BT is V _BT , the resistance value of the resistor Ra is RA, and the resistance value of the resistor Rb is RB, the charging switch element Q and the control switch element SW are both in the on state. The potential VG of the gate of the element Q is expressed by the following formula (1), and the potential VS of the source of the charge switch element Q is expressed by the following formula (2).

  For this reason, the gate-source voltage VGS of the charge switch element Q is expressed by the following equation (3) from the equations (1) and (2).

  As described above, in the charging device 100, the gate-source voltage of the charging switch element Q depends on the charging voltage of the secondary battery BT. For this reason, when the secondary battery BT having a high charging voltage is connected to the charging device 100, the withstand voltage of the charging switch element Q may be exceeded. Therefore, charging of various types of secondary batteries cannot be supported, and there are restrictions on secondary batteries that can be charged by the charging device 100, and the charging device 100 lacked versatility.

  In view of the above-described problems, an object of the present invention is to provide a charging device that can handle charging of various types of secondary batteries.

The present invention proposes the following items in order to solve the above-described problems.
(1) The present invention is a charging device (for example, equivalent to the charging device 1 in FIG. 1) for charging a secondary battery (for example, equivalent to the secondary battery BT in FIG. 1), and is a positive electrode of the secondary battery. And a first charge switch element (for example, equivalent to the charge switch element Q1 in FIG. 1) that intermittently connects the positive electrode of the DC power supply (for example, equivalent to the DC power supply DC in FIG. 1), and the first charge switch element A first control switch element (for example, FIG. 1) that intermittently connects a first terminal (for example, equivalent to the source of the charge switch element Q1 in FIG. 1) and a control terminal (for example, equivalent to the gate of the charge switch element Q1 in FIG. 1). A constant voltage source (e.g., corresponding to one control switch element SW1) and a positive terminal connected to the control terminal of the first charge switch element and a negative electrode connected to the first terminal of the first charge switch element (for example, Equivalent to the constant voltage source VDD in FIG. 1), A positive terminal of the secondary battery is connected to a first terminal of the first charge switch element, and a second terminal of the first charge switch element (for example, a drain of the charge switch element Q1 in FIG. 1). Is connected to the positive electrode of the DC power source, and in the first charging switch element, when the potential of the control terminal is higher than the potential of the first terminal by the power source voltage of the constant voltage source, A charging device is proposed in which the first terminal and the second terminal are electrically connected.

  According to this invention, the charging device for charging the secondary battery is provided with the first charging switch element, the first control switch element, and the constant voltage source. The positive terminal of the secondary battery is connected to the first terminal of the first charge switch element, and the positive terminal of the DC power source is connected to the second terminal of the first charge switch element. The positive electrode of the secondary battery and the positive electrode of the DC power source were intermittently connected by the switch element. In addition, the first terminal of the first charge switch element and the control terminal are intermittently connected by the first control switch element. The control terminal of the first charge switch element was connected to the positive electrode of the constant voltage source, and the first terminal of the first charge switch element was connected to the negative electrode of the constant voltage source. Further, in the first charge switch element, when the potential of the control terminal is higher than the potential of the first terminal by the power supply voltage of the constant voltage source, the first terminal and the second terminal are conducted.

  For this reason, when the first control switch element is in the OFF state, the potential of the control terminal of the first charge switch element is a constant voltage source as compared with the potential of the first terminal of the first charge switch element. Increases by the amount of power supply voltage. Therefore, the first terminal and the second terminal of the first charge switch element are brought into conduction, and the first charge switch element is turned on.

  On the other hand, when the first control switch element is in the ON state, the potential of the control terminal of the first charge switch element is equal to the potential of the first terminal of the first charge switch element. For this reason, the 1st terminal and 2nd terminal of a 1st charge switch element will be in an insulation state, and the 1st charge switch element will be in an OFF state.

  According to the above, in a state where the charging voltage of the secondary battery is equal to or lower than the power supply voltage of the DC power supply, the first control switch element is turned off to turn on the first charging switch element, and the DC power supply The secondary battery can be charged by passing a current from the positive electrode toward the positive electrode of the secondary battery. Further, in a state where the charging voltage of the secondary battery is equal to or lower than the power supply voltage of the DC power supply, the first control switch element is turned on to turn off the first charging switch element, and from the positive electrode of the DC power supply. The charging of the secondary battery can be stopped by preventing the current from flowing toward the positive electrode of the secondary battery.

  The control terminal of the first charge switch element is connected to the first terminal of the first charge switch element via the first control switch element, and the first charge switch via the constant voltage source. The first terminal of the element is connected. For this reason, in the first charge switch element, the potential of the control terminal is equal to the potential of the first terminal or higher than the potential of the first terminal by the power supply voltage of the constant voltage source. Therefore, the potential difference between the first terminal and the control terminal of the first charging switch element depends on the power supply voltage of the constant voltage source, but does not depend on the charging voltage of the secondary battery. For this reason, even when the charging voltage of the secondary battery is high, since the secondary battery can be connected to the charging device, it is possible to handle charging of various types of secondary batteries.

  Further, in the first charge switch element, when the potential of the control terminal becomes higher than the potential of the first terminal by the power supply voltage of the constant voltage source, the first terminal and the second terminal become conductive. For this reason, the first charge switch element can be constituted by, for example, an N-channel MOSFET. Here, the charging apparatus 100 according to the conventional example shown in FIG. 3 corresponds to the charging switch element Q between the positive electrode of the secondary battery BT and the positive electrode of the DC power source DC, that is, the first charging switch element of the present invention. The switch element to be configured is composed of a P-channel MOSFET. The on-resistance of the N-channel MOSFET is smaller than the on-resistance of the P-channel MOSFET. During charging of the secondary battery, a current flows through the switch element between the positive electrode of the secondary battery and the positive electrode of the DC power source. For this reason, compared with the charging device 100, the loss during charging of the secondary battery can be reduced.

  (2) The present invention includes a backflow prevention means (e.g., equivalent to the charge switch element Q2 in FIG. 1 or a diode) for flowing a current from one end to the other end of the charging device of (1), and the backflow prevention. A charging device is proposed in which a first terminal of the first charging switch element is connected to one end of the means, and a positive electrode of the secondary battery is connected to the other end of the backflow preventing means. doing.

  Here, in the charging device of (1), when the first charging switch element is turned on while the charging voltage of the secondary battery is higher than the power supply voltage of the DC power supply, the positive electrode of the DC power supply is changed from the positive electrode of the secondary battery. There is a risk that the current will flow backward.

  Therefore, according to the present invention, in the charging device of (1), the backflow prevention means for flowing a current from one end to the other end is provided, and the first terminal of the first charge switch element is provided at one end of the backflow prevention means. The positive electrode of the secondary battery was connected to the other end of the backflow prevention means.

  For this reason, it is possible to prevent the current from flowing backward from the positive electrode of the secondary battery toward the positive electrode of the DC power supply by the backflow prevention means.

  (3) The present invention relates to the charging device of (2), wherein the backflow prevention unit is configured to connect a first terminal of the first charge switch element and a positive electrode of the secondary battery. For example, it corresponds to the charge switch element Q2 in FIG. 1 and a second control switch element that intermittently connects the first terminal and the control terminal of the second charge switch element (for example, equivalent to the control switch element SW2 in FIG. 1). And a positive terminal of the secondary battery is connected to a first terminal of the first charge switch element via the second charge switch element, and a second terminal of the second charge switch element One terminal (for example, corresponding to the source of the charge switch element Q2 in FIG. 1) is connected to the first terminal of the first charge switch element and the negative electrode of the constant voltage source, and the second charge switch element. Second terminal (for example, the charge of FIG. The positive electrode of the secondary battery is connected to the switch element Q2 and the control terminal of the second charge switch element (for example, the gate of the charge switch element Q2 in FIG. 1). When the positive electrode of the constant voltage source is connected and the potential of the control terminal in the second charge switch element is higher than the potential of the first terminal by the power supply voltage of the constant voltage source, A charging device is proposed that is electrically connected to a terminal.

  According to the present invention, in the charging device of (2), the second charge switch element and the second control switch element are provided in the backflow preventing means. Then, the first terminal of the first charge switch element is connected to the positive electrode of the secondary battery via the second charge switch element, and the second charge switch element is used to connect the first charge switch element to the first charge switch element. The one terminal and the positive electrode of the secondary battery were intermittently connected. Specifically, the first terminal of the second charge switch element is connected to the first terminal of the first charge switch element and the negative electrode of the constant voltage source, and is connected to the second terminal of the second charge switch element. Connected the positive electrode of the secondary battery, and connected the positive electrode of the constant voltage source to the control terminal of the second charge switch element. Further, the first control switch element is intermittently connected to the first terminal and the control terminal of the second charge switch element. Further, in the second charge switch element, when the potential of the control terminal is higher than the potential of the first terminal by the power supply voltage of the constant voltage source, the first terminal and the second terminal are conducted.

  Therefore, when the second control switch element is in the OFF state, the potential of the control terminal of the second charge switch element is a constant voltage source compared to the potential of the first terminal of the second charge switch element. Increases by the amount of power supply voltage. Accordingly, the first terminal and the second terminal of the second charge switch element are brought into conduction, and the second charge switch element is turned on.

  On the other hand, when the second control switch element is in the ON state, the potential of the control terminal of the second charge switch element becomes equal to the potential of the first terminal of the second charge switch element. For this reason, the 1st terminal and 2nd terminal of a 2nd charge switch element will be in an insulation state, and the 2nd charge switch element will be in an OFF state.

  According to the above, when the charging voltage of the secondary battery is higher than the power supply voltage of the DC power supply, the first control switch element is turned on regardless of the state of the first control switch element, so that the first Regardless of the state of the charge switch element, it is possible to prevent the current from flowing backward from the secondary battery toward the DC power supply by turning off the second charge switch element.

  Moreover, even if the backflow prevention means in the charging device of (2) is configured with a diode as in the diode D in FIG. 3, the current flows back from the secondary battery toward the DC power source as described above. Can be prevented. However, the on-resistance of the second charge switch element is smaller than the on-resistance of the diode. During charging of the secondary battery, a current flows through the second charge switch element or a diode provided instead of the second charge switch element. For this reason, compared with the case where a diode is provided instead of the second charge switch element, loss during charging of the secondary battery can be reduced.

  (4) In the charging device of (3), the present invention turns off the first control switch element after turning off the second control switch element when charging the secondary battery is started. The charging device characterized by making it into a state is proposed.

  Here, a case where the second control switch element is turned off after the first control switch element is turned off when charging of the secondary battery is started will be considered. In this case, the second charge switch element is turned on after the first charge switch element is turned on. For this reason, since the second charge switch element is in the OFF state at the timing when the first charge switch element is turned on, the first terminal of the first charge switch element and the positive electrode of the secondary battery are in an insulated state. It is. According to this, at the timing when the first charge switch element is turned on, the impedance of the load as viewed from the DC power supply becomes small, and therefore, a large current may be output from the DC power supply.

  Therefore, according to the present invention, when charging the secondary battery in the charging device of (3), the first control switch element is turned off after the second control switch element is turned off. I decided to make it. For this reason, when charging of the secondary battery is started, the first charge switch element is turned on after the second charge switch element is turned on. Therefore, at the timing when the first charge switch element is turned on, since the second charge switch element is already turned on, the first terminal of the switch element and the positive electrode of the secondary battery are in a conductive state. According to this, since the secondary battery is already connected as a load to the DC power supply at the timing when the first charge switch element is turned on, a large current is output from the DC power supply. Can be prevented.

  (5) In the charging device of (3) or (4), the present invention provides the second control after turning on the first control switch element when the charging of the secondary battery is finished. A charging device characterized by turning on a switching element is proposed.

  Here, the case where the first control switch element is turned on after the second control switch element is turned on when the charging of the secondary battery is finished will be considered. In this case, the first charge switch element is turned off after the second charge switch element is turned off. Since the unidirectional element such as a body diode is built in the second charge switch element, the first charge switch element and the second charge switch element even if the second charge switch element is turned off. Current flows from the positive electrode of the DC power source to the positive electrode of the secondary battery via the unidirectional element incorporated in the battery. For this reason, a loss increases when a current flows through the unidirectional element incorporated in the second charge switch element.

  Therefore, according to the present invention, in the charging device of (3) or (4), when the charging of the secondary battery is finished, the second control switch is turned on after the first control switch element is turned on. The element was turned on. For this reason, when the charging of the secondary battery is finished, the second charge switch element is turned off after the first charge switch element is turned off. Therefore, no current flows from the positive electrode of the DC power source toward the positive electrode of the secondary battery at the timing when the first charge switch element is turned off. Therefore, current can be prevented from flowing through the unidirectional element built in the second charge switching element, and loss can be suppressed.

  According to the present invention, by controlling the first control switch element, the switching of the first charge switch element can be controlled to control the charging of the secondary battery. In addition, the potential of the control terminal of the first charge switch element depends on the power supply voltage of the constant voltage source, but does not depend on the charge voltage of the secondary battery, so that the charge voltage of the secondary battery is high. However, the secondary battery can be connected to the charging device, and can be charged for various types of secondary batteries. Moreover, compared with the charging apparatus 100 according to the conventional example shown in FIG. 3, the loss during charging of the secondary battery can be reduced.

It is a circuit diagram of a charging system provided with the charging device which concerns on one Embodiment of this invention. It is a timing chart of the said charging device. It is a circuit diagram of the charging device which concerns on a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the constituent elements in the following embodiments can be appropriately replaced with existing constituent elements, and various variations including combinations with other existing constituent elements are possible. Accordingly, the description of the following embodiments does not limit the contents of the invention described in the claims.

  FIG. 1 is a circuit diagram of a charging system AA including a charging device 1 according to an embodiment of the present invention. Charging system AA includes DC power supply DC and secondary battery BT in addition to charging device 1. The charging device 1 controls whether or not the secondary battery BT is charged and prevents a current from flowing backward from the secondary battery BT toward the DC power source DC.

[Configuration of Charging Device 1]
The charging device 1 includes charge switch elements Q1 and Q2 configured by N-channel MOSFETs, control switch elements SW1 and SW2 configured by phototransistors, resistors R1 and R2, and a constant voltage source VDD.

  The charge switch element Q1 includes a body diode BD1, and the source of the charge switch element Q1 is connected to the anode of the body diode BD1, and the positive electrode of the secondary battery BT is connected via the charge switch element Q2 described later. Connected. The drain of the charge switch element Q1 is connected to the cathode of the body diode BD1 and the positive electrode of the DC power source DC.

  Control switch element SW1 is provided between the source and gate of charge switch element Q1. Specifically, the source of the charge switch element Q1 is connected to one end of the control switch element SW1, and the gate of the charge switch element Q1 is connected to the other end of the control switch element SW1. The control switch element SW1 intermittently connects the source and gate of the charge switch element Q1 depending on whether light is emitted from a photodiode (not shown) provided in a pair with the control switch element SW1.

  A device in which a constant voltage source VDD and a resistor R1 are connected in series is also provided between the source and gate of the charge switch element Q1. Specifically, the negative electrode of the constant voltage source VDD is connected to the source of the charge switch element Q1, and the gate of the charge switch element Q1 is connected to the positive electrode of the constant voltage source VDD via the resistor R1.

  The charge switch element Q2 includes a body diode BD2, and the source of the charge switch element Q2 is connected to the anode of the body diode BD2 and the source of the charge switch element Q1. The drain of the charge switch element Q2 is connected to the cathode of the body diode BD2 and the positive electrode of the secondary battery BT.

  Control switch element SW2 is provided between the source and gate of charge switch element Q2. Specifically, the source of the charge switch element Q2 is connected to one end of the control switch element SW2, and the gate of the charge switch element Q2 is connected to the other end of the control switch element SW2. The control switch element SW2 intermittently connects the source and gate of the charge switch element Q2 depending on whether light is emitted from a photodiode (not shown) provided in a pair with the control switch element SW2.

  A device in which a constant voltage source VDD and a resistor R2 are connected in series is also provided between the source and gate of the charge switch element Q2. Specifically, the negative electrode of the constant voltage source VDD is connected to the source of the charge switch element Q2, and the gate of the charge switch element Q2 is connected to the positive electrode of the constant voltage source VDD via a resistor R2.

  The negative electrode of DC power supply DC and the negative electrode of secondary battery BT are connected to each other.

[Operation of Charging Device 1]
The charging device 1 having the above configuration controls whether or not the secondary battery BT is charged by controlling the control switch element SW1, and controls the control switch element SW2 to make direct current from the secondary battery BT. This prevents the current from flowing backward toward the power source DC.

FIG. 2 is a timing chart of the charging device 1. In FIG. 2, _VDC represents the positive voltage of the DC power supply DC, that is, the power supply voltage of the DC power supply DC. ST _SW1 indicates the state of the control switch element SW1, and ST _SW2 indicates the state of the control switch element SW2. ST _Q1 indicates the state of the charge switch element Q1, and ST _Q2 indicates the state of the charge switch element Q2.

  Here, it is assumed that the DC power source DC is stopped and the control switch elements SW1 and SW2 are both in the on state in a period before time t1. For this reason, the control switch element SW1 in the on state causes the source and gate of the charge switch element Q1 to conduct, and the voltage between the gate and the source of the charge switch element Q1 is zero. Therefore, the charge switch element Q1 is in the off state. is there. Further, the source and gate of the charge switch element Q2 are brought into conduction by the control switch element SW2 in the on state, and the voltage between the gate and the source of the charge switch element Q2 is zero, so that the charge switch element Q2 is in the off state. . Accordingly, since no current flows from the positive electrode of the DC power source DC toward the positive electrode of the secondary battery BT, the secondary battery BT is not charged.

At time t1, the DC power source DC is activated. According to this, the power supply voltage V _DC of the _DC power supply DC rises to V1. However, since the control switch element SW1 remains on, the charge switch element Q1 remains off. For this reason, charging of the secondary battery BT is not started.

  At time t2, the control switch element SW2 is turned off. According to this, the gate-source voltage of the charging switch element Q2 becomes equal to the positive voltage of the constant voltage source VDD, that is, the power supply voltage of the constant voltage source VDD. In the present embodiment, it is assumed that the power supply voltage of the constant voltage source VDD is equal to or higher than the threshold voltage of the charging switch element Q2. For this reason, the charge switch element Q2 is turned on. However, since the control switch element SW1 remains on, the charge switch element Q1 remains off. Therefore, charging of the secondary battery BT is not started.

At time t3, the control switch element SW1 is turned off. According to this, the gate-source voltage of the charging switch element Q1 becomes equal to the power supply voltage of the constant voltage source VDD. In the present embodiment, it is assumed that the power supply voltage of the constant voltage source VDD is equal to or higher than the threshold voltage of the charging switch element Q1. For this reason, the charge switch element Q1 is turned on. Then, current flows from the positive electrode of the DC power source DC toward the positive electrode of the secondary battery BT via the charge switch elements Q1 and Q2, and charging of the secondary battery BT is started. Therefore, the power supply voltage V _DC of the _DC power supply _DC is substantially equal to the voltage of the positive electrode of the secondary battery BT, that is, the charging voltage V _BT of the secondary battery BT.

At time t4, the control switch element SW1 is turned on. According to this, the source and gate of the charging switch element Q1 are conducted, and the voltage between the gate and the source of the charging switch element Q1 becomes zero, so that the charging switch element Q1 is turned off. Then, since no current flows from the positive electrode of the DC power source DC toward the positive electrode of the secondary battery BT, the charging of the secondary battery BT ends. For this reason, since the DC power supply DC is in a no-load state, the power supply voltage V _DC of the _DC power supply DC returns to V1.

  At time t5, the control switch element SW2 is turned on. According to this, the source and gate of the charge switch element Q2 are conducted, and the voltage between the gate and the source of the charge switch element Q2 becomes zero, so that the charge switch element Q2 is turned off.

At time t6, the DC power source DC is stopped. According to this, the power supply voltage V _DC of the _DC power supply DC decreases to zero.

  According to the above charging device 1, the following effects can be produced.

The charging device 1, in a state charged voltage _{V BT} is less than the power supply voltage _{V DC} of the DC power source DC secondary battery BT, to turn off the control switch element SW1. Then, the charge switch element Q1 is turned on. Here, if the control switch element SW2 is in an off state, the charge switch element Q2 is in an on state, and therefore, from the positive electrode of the DC power source DC to the positive electrode of the secondary battery BT via the charge switch elements Q1 and Q2. Current flows and the secondary battery BT is charged. On the other hand, if the control switch element SW2 is in the on state, the charge switch element Q2 is in the off state, but it goes from the positive electrode of the DC power source DC to the positive electrode of the secondary battery BT via the charge switch element Q1 and the body diode BD2. Current flows, and the secondary battery BT is charged. According to the above, in the state charging voltage V _BT is less than the power supply voltage V _DC of the DC power source DC secondary battery BT, a control switch element SW1 by the OFF state, the charging of the secondary battery BT Can do.

The charging device 1, in a state charged voltage _{V BT} is less than the power supply voltage _{V DC} of the DC power source DC secondary battery BT, the control switch element SW1 in the ON state. Then, the charge switch element Q1 is turned off. Therefore, regardless of whether the control switch element SW2 is in the on state or the off state, that is, whether the charge switch element Q2 is in the off state or the on state, the secondary power supply from the positive electrode of the DC power source DC is Since no current flows toward the positive electrode of the battery BT, the secondary battery BT is not charged. According to the above, in the state charging voltage V _BT is less than the power supply voltage V _DC of the DC power source DC secondary battery BT, a control switch element SW1 by the ON state, to stop charging the secondary battery BT be able to.

In addition, the charging device 1 connects the gate of the charging switch element Q1 to the source of the charging switch element Q1 via the control switching element SW1, and also connects the gate of the charging switch element Q1 via the resistor R1 and the constant voltage source VDD. Connected. For this reason, the gate-source voltage of the charging switch element Q1 becomes zero when the control switch element SW1 is in the on state, and becomes the power supply voltage of the constant voltage source VDD when the control switch element SW1 is in the off state. Almost equal. Therefore, the gate of the charging switch elements Q1 - source voltage is dependent on the supply voltage of the constant voltage source VDD, the charging voltage V _BT of the secondary battery BT is independent. Therefore, even when the charging voltage of the secondary battery is high, the secondary battery can be connected to the charging device 1, so that various types of secondary batteries can be charged.

  In addition, the switching device between the positive electrode of the secondary battery BT and the positive electrode of the DC power supply DC is configured by a P-channel MOSFET in the charging device 100 according to the conventional example shown in FIG. The charging device 1 according to the embodiment of the present invention shown in FIG. 1 is composed of an N-channel MOSFET. The on-resistance of the N-channel MOSFET is smaller than the on-resistance of the P-channel MOSFET. During charging of the secondary battery BT, a current flows through the switch element between the positive electrode of the secondary battery BT and the positive electrode of the DC power source DC. For this reason, compared with the charging device 100, the loss during charging of the secondary battery BT can be reduced.

The charging device 1, the charging voltage _{V BT} of the secondary battery BT is in the higher state than the power supply voltage _{V DC} of the DC power source DC, the control switch element SW2 is turned on. Then, the charge switch element Q2 is turned off. For this reason, regardless of whether the control switch element SW1 is in the on state or in the off state, that is, regardless of whether the charge switch element Q1 is in the off state or the on state, a direct current is applied from the positive electrode of the secondary battery BT. No current flows toward the positive electrode of the power supply DC. According to the above, in higher than the power supply voltage V _DC charging voltage V _BT DC power supply DC secondary battery BT, a control switch element SW2 by turning on state, the DC from the positive electrode of the secondary battery BT power DC It is possible to prevent the current from flowing backward toward the positive electrode.

  Further, as described above, the charging device 1 prevents the current from flowing backward from the positive electrode of the secondary battery BT toward the positive electrode of the DC power supply DC by turning off the charging switch element Q2. Here, even if a diode is provided instead of the charge switch element Q2 as in the diode D of FIG. 3, it is possible to prevent the current from flowing backward from the positive electrode of the secondary battery BT toward the positive electrode of the DC power source DC. . However, since the charge switch element Q2 is composed of an N-channel MOSFET, the on-resistance of the charge switch element Q2 is smaller than the on-resistance of the diode. During charging of the secondary battery BT, a current flows through the charge switch element Q2 or a diode provided instead of the charge switch element Q2. For this reason, compared with the case where a diode is provided instead of the charge switch element Q2, loss during charging of the secondary battery BT can be reduced.

  Here, the case where the control switch element SW2 is turned off after the control switch element SW1 is turned off when the charging of the secondary battery BT is started will be considered. In this case, after the charge switch element Q1 is turned on, the charge switch element Q2 is turned on. For this reason, at the timing when the charge switch element Q1 is turned on, the charge switch element Q2 is in the off state, so that the source of the charge switch element Q1 and the positive electrode of the secondary battery BT are in an insulated state. According to this, at the timing when the charging switch element Q1 is turned on, the impedance of the load as viewed from the DC power source DC becomes small, so that a large current may be output from the DC power source DC.

  However, when the charging device 1 starts charging the secondary battery BT, the control switch element SW1 is turned off after the control switch element SW2 is turned off as shown at time t2 and time t3 in FIG. By setting the state, the charge switch element Q1 is turned on after the charge switch element Q2 is turned on. For this reason, at the timing when the charge switch element Q1 is turned on, since the charge switch element Q2 is already turned on, the source of the charge switch element Q1 and the positive electrode of the secondary battery BT are in a conductive state. According to this, since the secondary battery BT is already connected as a load to the DC power source DC at the timing when the charging switch element Q1 is turned on, a large current is output from the DC power source DC. Can be prevented.

  Here, the case where the control switch element SW1 is turned on after the control switch element SW2 is turned on when the charging of the secondary battery BT is finished will be considered. In this case, after the charge switch element Q2 is turned off, the charge switch element Q1 is turned off. Since the charge switch element Q2 incorporates the body diode BD2, even when the charge switch element Q2 is turned off, the secondary battery BT is connected from the positive electrode of the DC power source DC via the charge switch element Q1 and the body diode BD2. Current flows toward the positive electrode. For this reason, the loss increases due to the current flowing through the body diode BD2.

  However, when the charging device 1 finishes charging the secondary battery BT, the charging switch element Q1 is turned off by turning on the control switch element SW2 after turning on the control switch element SW1. After that, the charging switch element Q2 is turned off. For this reason, current stops flowing from the positive electrode of the DC power source DC toward the positive electrode of the secondary battery BT at the timing when the charging switch element Q1 is turned off. Therefore, it is possible to prevent a current from flowing through the body diode BD2, and to suppress loss.

  The present invention is not limited to the above-described embodiment, and various modifications and applications can be made without departing from the gist of the present invention.

  For example, in the above-described embodiment, the control switch elements SW1 and SW2 are configured by phototransistors. However, the present invention is not limited to this. It may be configured.

  In the above-described embodiment, the charging switch element Q2 is used as the backflow prevention means for preventing the current from flowing back from the positive electrode of the secondary battery BT toward the positive electrode of the DC power supply DC. Alternatively, an element or a circuit that allows current to flow from one end to the other end may be used. For example, a diode can be used in place of the charging switch element Q2 as the backflow prevention means. When a diode is used, the cathode of the diode may be connected to the positive electrode of the secondary battery BT, and the anode of the diode may be connected to the source of the charge switch element Q1.

DESCRIPTION OF SYMBOLS 1,100; Charging apparatus AA; Charging system BD1, BD2; Body diode BT; Secondary battery D; Diode DC; DC power supply Q, Q1, Q2; Charge switch element Ra, Rb, R1, R2; Resistor SW, SW1, SW2; control switch element VDD; constant voltage source

Claims (5)

A charging device for charging a secondary battery,
A first charge switch element for intermittently connecting a positive electrode of the secondary battery and a positive electrode of a DC power source;
A first control switch element for intermittently connecting a first terminal and a control terminal of the first charge switch element;
A constant voltage source having a positive electrode connected to the control terminal of the first charge switch element and a negative electrode connected to the first terminal of the first charge switch element;
The first terminal of the first charge switch element is connected to the positive electrode of the secondary battery, the second terminal of the first charge switch element is connected to the positive electrode of the DC power source,
In the first charge switch element, when the potential of the control terminal is higher than the potential of the first terminal by the power supply voltage of the constant voltage source, the first terminal and the second terminal are conductive. Charging device. Comprising backflow prevention means for flowing current from one end to the other end;
The first terminal of the first charge switch element is connected to one end of the backflow prevention means, and the positive electrode of the secondary battery is connected to the other end of the backflow prevention means. Item 2. The charging device according to Item 1. The backflow prevention means includes
A second charge switch element for intermittently connecting a first terminal of the first charge switch element and a positive electrode of the secondary battery;
A second control switch element for intermittently connecting a first terminal and a control terminal of the second charge switch element;
The positive terminal of the secondary battery is connected to the first terminal of the first charge switch element via the second charge switch element,
The first terminal of the second charge switch element is connected to the first terminal of the first charge switch element and the negative terminal of the constant voltage source, and the second terminal of the second charge switch element is connected to the second terminal of the second charge switch element. , The positive electrode of the secondary battery is connected, the control terminal of the second charge switch element is connected to the positive electrode of the constant voltage source,
In the second charge switch element, when the potential of the control terminal becomes higher than the potential of the first terminal by the power supply voltage of the constant voltage source, the first terminal and the second terminal become conductive. The charging device according to claim 2. When starting to charge the secondary battery,
The charging device according to claim 3, wherein the first control switch element is turned off after the second control switch element is turned off. When finishing the charging of the secondary battery,
The charging device according to claim 3 or 4, wherein the second control switch element is turned on after the first control switch element is turned on.

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