JP5585408B2 - Switching power supply - Google Patents

Description

  The present invention has an operation mode in which the voltage input to the primary side is transformed and output from the secondary side, and an operation mode in which the voltage input to the secondary side is transformed and output from the primary side. The present invention relates to a switching power supply device capable of bidirectional operation.

  In recent years, various power storage devices have been developed against the background of advances in power electronics technology. The power storage device is used for, for example, a purpose of accumulating (charging) natural energy such as photovoltaic power generation, and discharging and using the accumulated energy when necessary. Such a power storage device is generally equipped with a converter (switching power supply device) that controls charging and discharging of power.

  Conventionally, such a converter is composed of two networks for charging and discharging, and has been used by switching between them. However, in recent years, converters (bidirectional converters) capable of realizing charging and discharging with one circuit network have been proposed due to demands for miniaturization and weight reduction. For example, Patent Document 1 proposes a switching power supply device configured by a full bridge circuit provided on the primary side and a push-pull circuit provided on the secondary side. In this switching power supply device, in the step-down operation mode (charging mode), the full bridge circuit converts the DC voltage input to the primary side into an AC voltage, the transformer steps down the AC voltage, and the push-pull circuit is a rectifier circuit. , The AC voltage is rectified, a smoothing circuit including an inductor smoothes the voltage to generate a DC voltage, and charges the battery connected to the secondary side. On the other hand, in the boost operation mode (discharge mode), the push-pull circuit converts the DC voltage input to the secondary side into an AC voltage, the transformer boosts the AC voltage, and the full bridge circuit functions as a rectifier circuit. Thus, the AC voltage is converted into a DC voltage, and the operation is performed to discharge to the primary side.

  By the way, various methods for discharging energy stored in an inductor have been disclosed. For example, Patent Document 2 discloses a switching power supply circuit in which a circuit network including a resistor, a capacitor, and a diode is connected in parallel to an inductor, and energy stored in the inductor is consumed. For example, in Patent Document 3, another inductor magnetically coupled to an inductor provided on the primary side is connected to an input power source (primary side) via a diode to regenerate energy stored in the inductor. A push-pull type converter is disclosed. Also, for example, in Patent Document 4, another inductor magnetically coupled to an inductor provided on the primary side is connected to the output voltage terminal (secondary side) via a diode to regenerate energy stored in the inductor. A push-pull type DC-DC converter is disclosed. For example, Patent Document 5 discloses a DC-DC converter that controls energy stored in an inductor by bringing a switching frequency close to a resonance frequency composed of an inductance and a capacitance. For example, Patent Document 6 discloses a charging device for an electric vehicle in which a switch is connected in parallel to an inductor.

JP 2007-209084 A Japanese Unexamined Patent Publication No. 1-311862 JP-A-62-68067 JP 2005-204463 A JP 2001-112253 A JP-A-8-65904

  By the way, in the switching power supply device disclosed in Patent Document 1, in the step-up operation mode (discharge mode), for example, immediately after startup, when the primary side voltage is not sufficiently high, 2 of the push-pull circuit. Two switches may be alternately turned on and off so as to have a period in which they are turned off at the same time. By doing so, for example, even when there is a large capacitive load on the primary side, it is possible to reliably accumulate charges and increase the voltage on the primary side.

  However, when such an operation is performed, a surge voltage due to the energy accumulated in the inductor of the smoothing circuit is generated during the period when both of these two switches are in the OFF state. This surge voltage exceeds the withstand voltage of these two switches and may destroy the switches.

  In such a switching power supply device, in order to reduce the surge voltage, when the methods disclosed in Patent Documents 2 to 5 are applied, although desired characteristics can be obtained in the boost operation mode (discharge mode), Various problems may occur in the step-down operation mode (charging mode). That is, the methods disclosed in Patent Documents 2 to 5 are not all intended to be applied to a bidirectional converter, and thus there is a possibility that bidirectional operation cannot be performed. For example, in the method disclosed in Patent Document 2, the current flows through the diode not only in the step-up operation mode (discharge mode) but also in the step-down operation mode (charge mode), so that the function as a smoothing circuit is sufficient. There is a risk that it will not be able to be fulfilled. Further, for example, in the methods disclosed in Patent Documents 3 and 4, current flows through the regeneration circuit not only in the step-up operation mode (discharge mode) but also in the step-down operation mode (charge mode). There is a possibility that the function as a circuit cannot be sufficiently performed.

  Further, when the method disclosed in Patent Document 6 is applied, even if the switch is turned on in the boosting operation mode (discharge mode), the on-resistance of the switch has a certain value that is not zero. However, current flows, energy is accumulated, and the switch may be destroyed by a surge voltage.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a switching power supply device capable of bidirectional operation capable of reducing a surge voltage caused by an inductor.

  The switching power supply according to the present invention includes a step-down operation mode in which the supplied first DC voltage is stepped down to generate a second DC voltage, and the supplied second DC voltage is stepped up to increase the first DC voltage. And includes a transformer, a primary side switching circuit, a secondary side switching circuit, an inductor, discharge means, and one or a plurality of discharge switches. The transformer has a primary winding and a secondary winding. The primary side switching circuit is connected to the primary side winding and converts the first DC voltage into an AC voltage by the switching operation in the step-down operation mode. The secondary side switching circuit is connected to the secondary side winding and converts the second DC voltage into an AC voltage by the switching operation in the step-up operation mode. The inductor is connected to the secondary winding and constitutes a smoothing circuit for generating the second DC voltage in the step-down operation mode. The discharging means discharges energy stored in the inductor. The discharge switch is for controlling the discharge operation of the discharge means.

  In the switching power supply device of the present invention, in the step-down operation mode, the primary side switching circuit converts the first DC voltage into an AC voltage, the transformer steps down the AC voltage, and based on the stepped-down AC voltage, A second DC voltage is generated by a smoothing circuit including an inductor. In the step-up operation mode, the secondary side switching circuit converts the second DC voltage into an AC voltage, the inductor and the transformer boost the AC voltage, and the first DC voltage is based on the boosted AC voltage. Is generated. At that time, the energy stored in the inductor is transmitted to the discharge means by turning on the discharge switch, and is discharged from the inductor.

  In the switching power supply device of the present invention, it is desirable that the discharging means is an energy consuming means, and the consuming means is preferably a resistance element, for example. In this case, the switching power supply device further includes, for example, a reset circuit connected between both ends of the inductor, and the reset circuit is configured by connecting a reset resistor and a reset capacitor in parallel, and further connecting a diode in series, The element and the emission switch may be connected in series and may be connected in parallel to the reset resistor and the reset capacitor. Further, for example, the discharge switch is a first and second discharge switch, and the first and second discharge switches and the resistor element are connected in series so that the first and second discharge switches sandwich the resistor element. And may be connected in parallel with the inductor.

  In addition, for example, the discharging unit may be a regenerating unit that regenerates energy to the first voltage or the second voltage.

  For example, the secondary winding includes first and second secondary windings, the secondary switching circuit includes first and second switching elements, and the first secondary winding One end and one end of the second secondary winding are connected to each other and to the inductor, and the other end of the first secondary winding is connected to the first switching element, and the second secondary winding The other end of the side winding may be connected to the second switching element.

  For example, the switching power supply device rectifies the AC voltage supplied from the primary winding by switching the primary side switching circuit in the step-up operation mode, and switches the secondary side switching circuit in the step-down operation mode. It is desirable to rectify the AC voltage supplied from the secondary winding by operating. In addition, for example, it is connected to the primary side winding, and in the step-up operation mode, it is connected to the primary side rectifier circuit that rectifies the AC voltage supplied from the primary side winding and the secondary side winding, and the step-down operation is performed. The mode may further include a secondary side rectifier circuit that rectifies an AC voltage supplied from the secondary side winding.

  For example, the switching power supply device further includes a primary side switching circuit, a secondary side switching circuit, and a control unit that controls on / off of the release switch, and the control unit has a first voltage higher than a predetermined voltage in the boost operation mode. When the first voltage is low, the first switching element and the second switching element are alternately turned on / off so that each of the first switching element and the second switching element are simultaneously turned off. When the first voltage is higher than a predetermined voltage, It is desirable to alternately turn on and off the first switching element and the second switching element so as to have a period in which the first switching element and the second switching element are simultaneously turned on. Further, for example, in the step-up operation mode, when the first voltage is lower than the predetermined voltage, the control unit gradually increases the period during which the first switching element and the second switching element are turned on. You may control to. In addition, for example, in the step-up operation mode, the control unit turns on the release switch when the first voltage is lower than the predetermined voltage, and turns off the release switch when the first voltage is higher than the predetermined voltage. It may be in a state.

  According to the switching power supply device of the present invention, since the discharge means and the discharge switch are provided, the bidirectional operation can be performed while reducing the surge voltage caused by the inductor.

It is a circuit diagram showing the example of 1 structure of the switching power supply device which concerns on embodiment of this invention. FIG. 2 is a timing waveform diagram illustrating an operation example in a step-down operation mode of the switching power supply device illustrated in FIG. 1. FIG. 2 is a circuit diagram illustrating one state of operation in a step-down operation mode of the switching power supply device illustrated in FIG. 1. FIG. 10 is a circuit diagram illustrating another state of operation in the step-down operation mode of the switching power supply device illustrated in FIG. 1. FIG. 2 is a timing waveform diagram illustrating an operation example in a step-up operation mode of the switching power supply device illustrated in FIG. 1. FIG. 2 is a circuit diagram illustrating one state of operation in a boosting operation mode of the switching power supply device illustrated in FIG. 1. FIG. 10 is a circuit diagram illustrating another state of operation in the boosting operation mode of the switching power supply device illustrated in FIG. 1. FIG. 10 is a circuit diagram illustrating another state of operation in the boosting operation mode of the switching power supply device illustrated in FIG. 1. FIG. 10 is a timing waveform diagram illustrating another operation example in the boosting operation mode of the switching power supply device illustrated in FIG. 1. FIG. 3 is a timing waveform diagram illustrating an operation example in a first activation period of the switching power supply device illustrated in FIG. 1. FIG. 2 is a circuit diagram illustrating a state of an operation in a first activation period of the switching power supply device illustrated in FIG. 1. It is a timing waveform diagram showing an example of an operation in the starting period of the switching power supply according to the comparative example of the embodiment. It is a circuit diagram showing the example of 1 structure of the switching power supply device which concerns on a modification. It is a timing waveform diagram showing an operation example in the step-up operation mode of the switching power supply according to the modification. It is a circuit diagram showing the one state of operation | movement in the pressure | voltage rise operation mode of the switching power supply device which concerns on a modification. It is a circuit diagram showing the other state of operation | movement in the pressure | voltage rise operation mode of the switching power supply device which concerns on a modification. It is a circuit diagram showing the other structural example of the switching power supply device which concerns on a modification. It is a circuit diagram showing the other structural example of the switching power supply device which concerns on a modification.

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

[Configuration example]
FIG. 1 shows a configuration example of a switching power supply device according to the first embodiment of the present invention. The switching power supply device 1 is a power supply device capable of bidirectional operation. That is, for example, when the DC voltage VH is input from an external power source connected to the terminals (input / output terminals) T1 and T2, the switching power supply device 1 generates the DC voltage VL by stepping down the voltage. The battery BL is supplied to the connected battery BL via terminals (input / output terminals) T3 and T4 (hereinafter referred to as a step-down operation mode or a charging mode). Further, for example, when supplying power to a load connected to the terminals T1 and T2, the switching power supply device 1 generates the DC voltage VH by boosting the DC voltage VL supplied from the battery BL, and the terminal The load is driven through T1 and T2 (hereinafter referred to as a boosting operation mode or a discharge mode). In this example, the DC voltage VH is a voltage of about 350V, and the DC voltage VL is a voltage of about 50V. However, the DC voltages VH and VL are not limited to these voltages, and may be any value as long as the DC voltage VH is higher than the DC voltage VL during a normal operation period described later.

  The switching power supply 1 includes a smoothing capacitor CH, switching circuits 10 and 20, a transformer 30, an inductor Lch, a smoothing capacitor CL, a reset circuit 50, a discharge circuit 60, a control unit 73, and a SW drive unit. 74.

  The smoothing capacitor CH is disposed between the primary high-voltage line L1H connected to the terminal T1 and the primary low-voltage line L1L connected to the terminal T2, and is input between the terminals T1 and T2 from the outside. This is for smoothing the voltage.

  The switching circuit 10 functions as a full-bridge switching circuit that converts an externally supplied DC voltage VH into an AC voltage in the step-down operation mode, and rectifies the AC voltage supplied from the transformer 30 in the step-up operation mode. It functions as a rectifier circuit. The switching circuit 10 includes switching elements SW11 to SW14 and capacitive elements Cr11 to Cr14.

  As the switching elements SW11 to SW14, for example, elements such as a MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor) can be used. In this example, the switching elements SW11 to SW14 are all configured by N-channel MOS-FETs. A SW control signal S11 is supplied to the gate of the switching element SW11, the source is connected to the drain of the switching element SW12, and the drain is connected to the primary side high-voltage line L1H. Further, the SW control signal S12 is supplied to the gate of the switching element SW12, the source is connected to the primary side low-voltage line L1L, and the drain is connected to the source of the switching element SW11. Further, the SW control signal S13 is supplied to the gate of the switching element SW13, the source is connected to the drain of the switching element SW14, and the drain is connected to the primary side high-voltage line L1H. Further, the SW control signal S14 is supplied to the gate of the switching element SW14, the source is connected to the primary side low-voltage line L1L, and the drain is connected to the source of the switching element SW13. The source of the switching element SW11 and the drain of the switching element SW12 are connected to one end of a primary winding 31 (described later) of a transformer 30 described later via a resonance inductor Lr described later. The source of the switching element SW13 and the drain of the switching element SW14 are connected to the other end of the primary side winding 31 (described later). In this example, the switching elements SW11 to SW14 have body diodes (diodes D11 to D14 described later), respectively. The body diode has an anode connected to the source of the switching element and a cathode connected to the drain of the switching element.

  Capacitance elements Cr11 to Cr14 are inserted between the drains and sources of the switching elements SW11 to SW14, respectively. Specifically, the capacitive element Cr11 is inserted between the drain and source of the switching element SW11, the capacitive element Cr12 is inserted between the drain and source of the switching element SW12, and the capacitive element Cr13 is inserted between the drain and source of the switching element SW13. The capacitive element Cr14 is inserted between the sources, and the capacitive element Cr14 is inserted between the drain and source of the switching element SW14. Capacitance elements Cr11 to Cr14 are for forming a partial resonance circuit with a resonance inductor Lr, which will be described later, and a leakage inductor of the transformer 30.

  With this configuration, in the switching circuit 10, in the step-down operation mode, the switching elements SW11 to SW14 are turned on and off in accordance with SW control signals S11 to S14 supplied from the SW drive unit 74 (described later), and supplied from the outside. DC voltage VH is converted to AC voltage. At this time, a so-called ZVS (Zero Volt Switching) operation can be realized by the partial resonance circuit including the capacitive elements Cr11 to Cr14, the resonance inductor Lr, and the leakage inductor of the transformer 30, and the efficiency is improved by reducing the switching loss. Can be achieved. In the step-up operation mode, the switching elements SW11 to SW14 are set in an off state, and the body diode is used as a rectifying element, so that the AC voltage supplied from the transformer 30 is rectified.

  A resonance inductor Lr is inserted between the switching circuit 10 and the transformer 30. The resonance inductor Lr is for configuring a predetermined LC resonance circuit together with the capacitive elements Cr11 to Cr14 and the leakage inductor of the transformer 30.

  The switching circuit 20 functions as a push-pull type switching circuit that converts the DC voltage VL supplied from the battery BL into an AC voltage in the step-up operation mode, and rectifies the AC voltage supplied from the transformer 30 in the step-down operation mode. It functions as a rectifier circuit. The switching circuit 20 includes switching elements SW21 and SW22.

  As the switching elements SW21 and SW22, for example, elements such as MOS-FETs and IGBTs can be used in the same manner as the switching elements SW11 to SW14 of the switching circuit 10. In this example, the switching elements SW21 and SW22 are configured by N-channel MOS-FETs. The SW control signal S21 is supplied to the gate of the switching element SW21, the source is connected to the secondary low-voltage line L2L, and the drain is connected to one end of the secondary winding 32B (described later) of the transformer 30. Further, the SW control signal S22 is supplied to the gate of the switching element SW22, the source is connected to the secondary low voltage line L2L, and the drain is connected to one end of the secondary winding 32A (described later) of the transformer 30. . In this example, the switching elements SW21 and SW22 each have a body diode (diodes D21 and D22 described later). The body diode has an anode connected to the source of the switching element and a cathode connected to the drain of the switching element.

  With this configuration, the switching circuit 20 is supplied from the battery BL in the step-up operation mode by performing on / off control of the switching elements SW21 and SW22 according to SW control signals S21 and S22 supplied from the SW drive unit 74 (described later). The direct current voltage VL is converted into an alternating voltage. In the step-down operation mode, the switching elements SW21 and SW22 are set to an off state, and the body diode is used as a rectifying element, so that the AC voltage supplied from the transformer 30 is rectified.

  The transformer 30 insulates the primary side and the secondary side in a DC manner and connects them in an AC manner, and includes a primary side winding 31 and secondary side windings 32A and 32B. It is a winding type transformer. The primary winding 31 is connected to the switching circuit 10 as described above. One end of the secondary winding 32A is connected to the drain of the switching element SW22 of the switching circuit 20, and one end of the secondary winding 32B is connected to the drain of the switching element SW21 of the switching circuit 20. The other ends of the secondary windings 32A and 32B are connected to each other by a center tap CT and further connected to the secondary high voltage line L2. Here, the number of turns of the primary winding 31 is n1 (n1 is an integer), and the number of turns of the secondary windings 32A and 32B is n2 (n2 is an integer). That is, the turns ratio between the primary winding 31 and the secondary winding 32A and the turns ratio between the primary winding 31 and the secondary winding 32B are n (= n1 / n2): 1, respectively. Set to In this example, n is 6, for example.

  With this configuration, in the step-down operation mode, the transformer 30 steps down the AC voltage supplied between both ends of the primary side winding 31 by 1 / n times and outputs it from the secondary side windings 32A and 32B. It has become. In the step-up operation mode, the transformer 30 boosts the AC voltage supplied to the secondary side windings 32 </ b> A and 32 </ b> B by about n times and outputs the boosted voltage from the primary side winding 31.

  The inductor Lch is inserted and disposed between the secondary high-voltage line L2 and the secondary high-voltage line L2H. One end of the inductor Lch is connected to the center tap CT of the transformer 30 and the other end is connected to the terminal T3. .

  The smoothing capacitor CL is disposed between the secondary high voltage line L2H connected to the terminal T3 and the secondary low voltage line L2L connected to the terminal T4.

  With this configuration, the inductor Lch and the smoothing capacitor CL function as a smoothing circuit (low-pass filter LPF) that smoothes the voltage supplied from the transformer 30 and the switching circuit 20 in the step-down operation mode. That is, the inductor Lch functions as a choke coil. On the other hand, in the step-up operation mode, the smoothing capacitor CL smoothes the voltage VL supplied from the battery BL between the terminals T3 and T4, and the inductor Lch accumulates energy based on the switching operation of the switching circuit 20, and the voltage The voltage VL is boosted and supplied to the secondary windings 32A and 32B of the transformer 30.

  The reset circuit 50 is an RCD snubber circuit for resetting energy stored in the parasitic inductor of the push-pull circuit including the switching circuit 20 and the transformer 30. The reset circuit 50 is connected in parallel to the inductor Lch.

  The reset circuit 50 includes a resistance element Rs, a capacitance element Cs, and a diode Ds. The resistive element Rs and the capacitive element Cs are connected in parallel to each other. One end of the resistor element Rs and the capacitor element Cs connected in parallel is connected to the cathode terminal of the diode Ds. The anode terminal of the diode Ds is connected to one end of the inductor Lch, and the other end of the resistor element Rs and the capacitive element Cs connected in parallel is connected to the other end of the inductor Lch.

  The impedances of the resistance element Rs and the capacitance element Cs are set to predetermined values that can reset the energy accumulated in the parasitic inductor of the push-pull circuit. That is, when the impedance is smaller than the predetermined value, in the boosting operation mode, the reset circuit 50 resets not only the parasitic inductor of the push-pull circuit but also the energy accumulated in the inductor Lch. There is a risk that the pressure cannot be increased sufficiently. Further, in the step-down operation mode, a current flows through the reset circuit 50, so that the voltage supplied from the transformer 30 and the switching circuit 20 may not be sufficiently smoothed. Therefore, the resistance value of the resistance element Rs and the capacitance value of the capacitance element Cs are set in consideration of these.

  The emission circuit 60 is a circuit for resetting the energy accumulated in the inductor Lch in the step-up operation mode. Specifically, as will be described later, the emission circuit 60 has a predetermined period (first activation period P1 described later) in the process of increasing the voltage between the terminals T1 and T2 to a desired value in the boosting operation mode. ), The energy stored in the inductor Lch is extracted and consumed. The emission circuit 60 is connected in parallel with the resistance element Rs and the capacitance element Cs of the reset circuit 50.

  The emission circuit 60 includes a resistance element Rp and a switching element SW23. As the resistance element Rp, for example, individually provided resistance components, connection wiring having a resistance component, or the like can be used. As the switching element SW23, for example, an element such as a MOS-FET or IGBT can be used in the same manner as the switching elements SW11 to SW14, SW21, and SW22 of the switching circuits 10 and 20. In this example, the switching element SW23 is configured by an N-channel MOS-FET. In the emission circuit 60, the SW control signal S23 is supplied to the gate of the switching element SW23, the source is connected to one end of the resistance element Rs and the capacitance element Cs of the reset circuit 50, and the drain is connected to one end of the resistance element Rp. Yes. The other end of the resistor element Rp is connected to the other end of the resistor element Rs and the capacitor element Cs of the reset circuit 50. That is, the resistance element Rp and the switching element SW23 are connected in series. In this example, the switching element SW23 has a body diode. The body diode has an anode connected to the source of the switching element SW23 and a cathode connected to the drain of the switching element SW23. The direction of the body diode is opposite to the direction of the diode Ds in the series circuit including the diode Ds, the resistance element Rp, and the switching element SW23 of the reset circuit 50. As a result, when the switching element SW23 is in the OFF state, no current flows through the resistance element Rp regardless of the voltage across the inductor Lch.

  With this configuration, as will be described later, in the first activation period P1 (described later) in the boosting operation mode, the emission circuit 60 sets the switching element SW23 according to the SW control signal S23 supplied from the SW drive unit 74 (described later). The energy stored in the inductor Lch is reset by turning it on. Further, in other periods in the step-up operation mode and in the step-down operation mode, the inductor Lch supplies energy by turning off the switching element SW23 according to the SW control signal S23 supplied from the SW drive unit 74 (described later). Accumulate and perform its original operation.

  The controller 73 keeps the voltage VL between the terminals T3 and T4 at a predetermined voltage in the step-down operation mode, and keeps the voltage VH between the terminals T1 and T2 at a predetermined voltage in the step-up operation mode. An instruction for controlling the switching elements SW11 to SW14, SW21, and SW22 is supplied to the SW drive unit 74. The control unit 73 also has a function of instructing the SW drive unit 74 to turn on the switching element SW23 of the emission circuit 60 in a first activation period P1 (described later) in the boost operation mode. Yes.

  The SW drive unit 74 generates SW control signals S11 to S14 based on an instruction from the control unit 73, supplies the SW control signals S11 to S14 to the switching elements SW11 to SW14, generates SW control signals S21 and S22, and switches the switching element SW21. , SW22, and a SW control signal S23 is generated and supplied to the switching element SW23, thereby driving them to be on / off controlled.

  In the switching power supply device 1, in order to detect the voltage VH between the terminals T1 and T2, a voltage detection circuit 71 is inserted between the primary high voltage line L1H and the primary low voltage line L1L. Further, in order to detect the voltage VL between the terminals T3 and T4, a voltage detection circuit 72 is inserted between the secondary high voltage line L2H and the secondary low voltage line L2L.

  With this configuration, the control unit 73 issues an instruction to the SW drive unit 74 based on the detection results in the voltage detection circuits 71 and 72, and the SW drive unit 74 performs switching elements SW <b> 11- SW14, SW21 to SW23 are driven.

  Here, the DC voltage VH corresponds to a specific example of “first DC voltage” in the present invention. The DC voltage VL corresponds to a specific example of “second DC voltage” in the present invention. The switching circuit 10 corresponds to a specific example of “primary side switching circuit” in the present invention. The switching circuit 20 corresponds to a specific example of “secondary side switching circuit” in the present invention. The resistance element Rp corresponds to a specific example of “emission means” in the present invention. The switching element SW23 corresponds to a specific example of “a release switch” in the invention. The resistance element Rs corresponds to a specific example of “reset resistance” in the present invention. The capacitive element Cs corresponds to a specific example of “reset capacitor” in the present invention. Secondary windings 32A and 32B correspond to a specific example of “first and second secondary windings” in the present invention. The switching elements SW21 and SW22 correspond to a specific example of “first and second switching elements” in the present invention.

[Operation and Action]
Next, the operation and action of the switching power supply device 1 of the present embodiment will be described.

(Steady operation in step-down operation mode)
First, the operation of the switching power supply device 1 in the step-down operation mode (charging mode) will be described with reference to FIG.

  In the step-down operation mode, the switching power supply 1 steps down the DC voltage VH supplied from the external power supply BH to the terminals T1 and T2, outputs the stepped down DC voltage VL from the terminals T3 and T4, and is connected to the connected battery BL. To charge.

  Specifically, the switching circuit 10 converts the DC voltage VH into an AC voltage by switching the switching elements SW <b> 11 to SW <b> 14 and supplies the AC voltage between both ends of the primary side winding 31 of the transformer 30. The transformer 30 transforms (steps down) the alternating voltage to 1 / n times, and outputs the transformed alternating voltage from the secondary windings 32A and 32B. The switching circuit 20 functions as a rectifier circuit in the step-down operation mode, and rectifies this AC voltage. Inductor Lch and smoothing capacitor CL function as a smoothing circuit in the step-down operation mode, and smoothes the rectified signal to generate DC voltage VL.

  FIG. 2 shows the operation of the switching power supply device 1 in the step-down operation mode. (A) to (D) show the waveforms of the SW control signals S11 to S14, respectively, and (E) shows the SW control signals S21 and S22. (F) shows the waveform of the SW control signal S23. In this example, the switching elements SW11 to SW14 and SW21 to SW23 are turned on when the SW control signals S11 to S14 and S21 to S23 applied to their gates are at a high level, and are turned off when they are at a low level. is there.

  In the step-down operation mode, the SW drive unit 74 generates periodic SW control signals S11 to S14 and supplies them to the switching elements SW11 to SW14, respectively (FIGS. 2A to 2D). In addition, the SW drive unit 74 generates SW control signals S21 to S23 fixed at a low level and supplies them to the switching elements SW21 to SW23, respectively (FIGS. 2E and 2F).

  As shown in FIG. 2, the SW drive unit 74 generates the SW control signals S11 and S12 so as not to be at a high level at the same time (FIGS. 2A and 2B). Therefore, the switching elements SW11 and SW12 are not turned on at the same time. Similarly, the SW drive unit 74 generates the SW control signals S13 and S14 so as not to be at a high level at the same time (FIGS. 2C and 2D). For this reason, the switching elements SW13 and SW14 are not simultaneously turned on. That is, in the switching power supply 1, the primary high voltage line L1H and the primary low voltage line L1L are not electrically short-circuited. Thus, the time interval taken to avoid the electrical short circuit between the primary high-voltage line L1H and the primary low-voltage line L1L is referred to as a dead time Td.

  Further, as shown in FIG. 2, the SW drive unit 74 generates the SW control signals S11 and S14 so as to have a period T11 that is at a high level at the same time (FIGS. 2A and 2D). Similarly, the SW drive unit 74 generates the SW control signals S12 and S13 so as to have a period T12 that is at a high level at the same time (FIGS. 2B and 2C).

  3 and 4 show the operation of the switching power supply device 1 in the step-down operation mode, FIG. 3 shows the operation in the period T11, and FIG. 4 shows the operation in the period T12. 3 and 4, diodes D11 to D14, D21, and D22 correspond to body diodes of the switching elements SW11 to SW14, SW21, and SW22, respectively. In these drawings, for convenience of explanation, the switching elements SW11 to SW14 and SW21 to SW23 are shown in the form of a switch representing the operation state (on state or off state). For convenience of explanation, circuit blocks and elements that are not directly necessary for the explanation are omitted as appropriate.

  In the period T11, as shown in FIGS. 2A to 2D, the switching elements SW11 and SW14 of the switching circuit 10 are turned on and the switching elements SW12 and SW13 are turned off. Thus, on the primary side of the switching power supply device 1, as shown in FIG. 3, the switching element SW11, the resonance inductor Lr, the primary winding 31 of the transformer 30, the switching element SW14, the external power supply BH, and the smoothing capacitor A primary loop current Ia11 flows through CH in order. On the other hand, on the secondary side, a secondary loop current Ia21 that passes through the diode D21, the secondary winding 32B of the transformer 30, the inductor Lch, the battery BL, and the smoothing capacitor CL in order flows.

  On the other hand, in the period T12, as shown in FIGS. 2A to 2D, the switching elements SW12 and SW13 of the switching circuit 10 are turned on and the switching elements SW11 and SW14 are turned off. As a result, on the primary side of the switching power supply 1, as shown in FIG. 4, the switching element SW13, the primary winding 31 of the transformer 30, the resonance inductor Lr, the switching element SW12, the external power supply BH, and the smoothing capacitor CH , The primary loop current Ia12 flows. On the other hand, on the secondary side, a secondary loop current Ia22 that passes through the diode D22, the secondary winding 32A of the transformer 30, the inductor Lch, the battery BL, and the smoothing capacitor CL in order flows.

  As described above, in the switching power supply device 1, the secondary loop currents Ia21 and Ia22 flow in the periods T11 and T12. As shown in FIG. 2, the lengths of the periods T11 and T12 are controlled by the phase difference φ between the SW control signals S11 and S14 and the phase difference φ between the SW control signals S12 and S13. That is, for example, when the phase difference φ decreases, the lengths of the periods T11 and T12 become longer and the time during which the secondary loop currents Ia21 and Ia22 flow becomes longer, so the voltage VL generated in this step-down operation mode becomes higher. Become. Based on the voltage VL detected by the voltage detection circuit 72, the control unit 73 controls the phase difference φ so that the voltage VL maintains a predetermined voltage.

(Steady operation in boost operation mode)
Next, the operation of the switching power supply device 1 in the step-up operation mode (discharge mode) will be described with reference to FIG.

  In the step-up operation mode, the switching power supply device 1 boosts the DC voltage VL supplied from the battery BL to the terminals T3 and T4, outputs the boosted DC voltage VH from the terminals T1 and T2, and connects the connected load L. To drive.

  Specifically, the switching circuit 20 converts the DC voltage VL into an AC voltage by switching the switching elements SW21 and SW22. At that time, the inductor Lch boosts this AC voltage and supplies it to the center tap CT of the secondary windings 32A and 32B of the transformer 30. The transformer 30 transforms (boosts) this alternating voltage n times, and outputs the transformed alternating voltage from the primary side winding 31. The switching circuit 10 functions as a rectifier circuit in the step-up operation mode, and rectifies this AC voltage. The smoothing capacitor CL smoothes the rectified signal and generates a DC voltage VH.

  FIG. 5 shows the operation of the switching power supply device 1 in the step-up operation mode. (A) and (B) show the waveforms of the SW control signals S21 and S22, respectively, and (C) shows the waveform of the SW control signal S23. (D) shows the waveforms of the SW control signals S11 to S14, (E) shows the waveform of the current Ich flowing through the inductor Lch, and (F) shows the voltages of the secondary windings 32A and 32B of the transformer 30. The waveform of V32B-V32A is shown, (G) shows the waveform of the voltage V31 of the primary side winding 31 of the transformer 30.

  In the step-up operation mode, the SW drive unit 74 generates periodic SW control signals S21 and S22 and supplies them to the switching elements SW21 and SW22, respectively (FIGS. 5A and 5B). In addition, the SW drive unit 74 generates SW control signals S23 and S11 to S14 fixed at a low level and supplies them to the switching elements SW23 and SW11 to SW14, respectively (FIGS. 5C and 5D).

  As shown in FIG. 5, the SW drive unit 74 generates the SW control signals S21 and S22 so as to be alternately at a high level. At that time, the SW drive unit 74 generates the SW control signals S21 and S22 so as to have a period of high level at the same time. Specifically, the SW drive unit 74 includes a period T21 in which the SW control signals S21 and S22 are simultaneously at a high level, a period T22 in which the SW control signal S21 is at a high level and the SW control signal S22 is at a low level, The SW control signals S21 and S22 are generated so that the period T21 and the period T23 in which the SW control signal S22 is at a low level and the SW control signal S22 is at a high level circulate.

  6 to 8 show the operation of the switching power supply device 1 in the boosting operation mode, FIG. 6 shows the operation in the period T21, FIG. 7 shows the operation in the period T22, and FIG. 8 shows the period T23. The operation in is shown. 6-8, the direction of each terminal voltage V31, V32A, V32B of the transformer 30 is shown by an arrow.

  In the period T21, as shown in FIGS. 5A and 5B, the switching elements SW21 and SW22 of the switching circuit 20 are simultaneously turned on. Thereby, on the secondary side of the switching power supply device 1, as shown in FIG. 6, the secondary passes through the inductor Lch, the secondary winding 32B of the transformer 30, the switching element SW21, the battery BL, and the smoothing capacitor CL in order. While the side loop current Ib21 flows, the secondary side loop current Ib22 flows through the inductor Lch, the secondary side winding 32A of the transformer 30, the switching element SW22, the battery BL, and the smoothing capacitor CL in order. At this time, in the secondary side windings 32A and 32B of the transformer 30, the magnetic field generated by the secondary side loop current Ib21 and the magnetic field generated by the secondary side loop current Ib22 cancel each other. No current is induced, and therefore the impedance (load) of the transformer 30 viewed from the inductor Lch is almost zero. In this way, in the period T21, the secondary loop currents Ib21 and Ib22 flow in the inductor Lch (FIG. 5E), and energy is accumulated based on these.

  In the period T22, as shown in FIGS. 5A and 5B, the switching element SW21 of the switching circuit 20 is turned on and the switching element SW22 is turned off. Thereby, on the secondary side of the switching power supply device 1, as shown in FIG. 7, the secondary passes through the inductor Lch, the secondary winding 32B of the transformer 30, the switching element SW21, the battery BL, and the smoothing capacitor CL in order. Side loop current Ib21 flows. At this time, the voltage V32B across the secondary winding 32B is obtained by adding the voltage ΔV based on the energy accumulated in the inductor Lch in the period T21 prior to the period T22 to the voltage VL of the battery BL (VL + ΔV). (FIG. 5F). On the other hand, on the primary side, as shown in FIG. 7, the primary side loop current that passes through the diode D14, the primary side winding 31 of the transformer 30, the resonance inductor Lr, the diode D11, the load L, and the smoothing capacitor CH in this order. Ib11 flows. At this time, the both-ends voltage V31 of the primary side winding 31 is n × (VL + ΔV) obtained by multiplying the both-ends voltage V32B (voltage VL + ΔV) of the secondary side winding 32B by the winding ratio of the transformer 30.

  In the period T23, as shown in FIGS. 5A and 5B, the switching element SW21 of the switching circuit 20 is turned off and the switching element SW22 is turned on. Thereby, on the secondary side of the switching power supply device 1, as shown in FIG. 8, the secondary passes through the inductor Lch, the secondary winding 32A of the transformer 30, the switching element SW22, the battery BL, and the smoothing capacitor CL in order. Side loop current Ib22 flows. At this time, the voltage V32A across the secondary winding 32A is obtained by adding the voltage ΔV based on the energy accumulated in the inductor Lch in the period T21 prior to the period T23 to the voltage VL of the battery BL (VL + ΔV). (FIG. 5F). On the other hand, on the primary side, as shown in FIG. 8, the primary side loop current that passes through the diode D12, the resonance inductor Lr, the primary side winding 31 of the transformer 30, the diode D13, the load L, and the smoothing capacitor CH in this order. Ib12 flows. At this time, the both-ends voltage V31 of the primary side winding 31 is n × (VL + ΔV) obtained by multiplying the both-ends voltage V32A (voltage VL + ΔV) of the secondary side winding 32A by the winding ratio of the transformer 30.

  As described above, in the step-up operation mode, in the steady operation state, the switching elements SW21 and SW22 operate so as to have the period T21 in which they are turned off at the same time. In the period T21, the inductor Lch accumulates energy. For example, in the period T22, the secondary winding 32B can be supplied with the voltage VL + ΔV that exceeds the voltage VL of the battery BL, and is higher than n × VL. Can be output as the voltage VH.

  In the switching power supply device 1, in the periods T22 and T23, a voltage of n × (VL + ΔV) appears at both ends of the primary side winding 31, and primary side loop currents Ib11 and Ib12 flow. By controlling the lengths of the periods T22 and T23, the voltage VH generated in this boosting operation mode can be controlled. Specifically, the voltage VH can be increased by increasing the proportion of the period T21 in the “one cycle period” including the periods T21, T22, T21, and T23. Based on the voltage VH detected by the voltage detection circuit 71, the control unit 73 sets the ratio of the time of the periods T22 and T23 and the time of the period T21 so that the voltage VH maintains a predetermined voltage (target voltage VT). Control.

(Detailed operation in step-up operation mode)
Next, detailed operation of the switching power supply device 1 in the boosting operation mode (discharge mode) will be described.

  FIG. 9 shows the start-up operation of the switching power supply device 1 in the step-up operation mode. (A) and (B) show the waveforms of the SW control signals S21 and S22, respectively. (C) shows the SW control signal S23. A waveform is shown, (D) shows the waveform of the voltage VH.

  The switching power supply device 1 performs the above-described steady operation (steady operation period P3) through the first activation period P1 and the second activation period P2 at the time of activation.

  In the first activation period P1, as shown in FIGS. 9A and 9B, the SW drive unit 74 generates the SW control signals S21 and S22 so as to be alternately at a high level. At that time, unlike the above-described steady operation, the SW drive unit 74 generates the SW control signals S21 and S22 so as to have a period of low level at the same time. Further, the SW drive unit 74 generates the SW control signals S21 and S22 so that their pulse widths gradually increase. In the first activation period P1, the voltage VH can be raised to a voltage (n × VL) obtained by multiplying the voltage VL by the winding ratio of the transformer 30. In other words, the switching power supply device 1 performs a step-down operation at the beginning of the first activation period P1, and thereafter gradually increases the voltage VH while performing a step-up operation.

  In the first activation period P1, as shown in FIG. 9C, the SW drive unit 74 generates a high level SW control signal S23. That is, in the first activation period P1, the switching element SW23 of the emission circuit 60 is turned on, and the resistance element Rp extracts and consumes the energy accumulated in the inductor Lch.

  The switching power supply device 1 monitors the voltage VH using the voltage detection circuit 71, and shifts to the second activation period P2 when the voltage VH reaches a predetermined voltage VT1. Here, the predetermined voltage VT1 can be, for example, a voltage (n × VL).

  In the second activation period P2, the SW drive unit 74 generates the SW control signals S21 and S22 so as to be alternately at a high level. At that time, as in the steady state (FIG. 5), the SW drive unit 74 generates the SW control signals S21 and S22 so as to have a period (period T21 in FIG. 5) that is simultaneously at a high level. Then, the voltage VH is further increased from the voltage VT1 toward the target voltage VT2 by gradually lengthening the period during which the ON state is simultaneously achieved.

  In the second activation period P2, as shown in FIG. 9C, the SW drive unit 74 generates a low level SW control signal S23. That is, in the second activation period P2, the switching element SW23 of the emission circuit 60 is turned off, and the inductor Lch accumulates energy based on the SW control signals S21 and S22.

  When the voltage VH reaches the target voltage VT2, the switching power supply device 1 operates so as to maintain the voltage (steady operation period P3).

  Next, detailed operation of the switching power supply device 1 in the first activation period P1 will be described.

  FIG. 10 shows an example of the operation of the switching power supply device 1 in the first activation period P1, (A) and (B) show the waveforms of the SW control signals S21 and S22, respectively, and (C) shows the SW control. The waveform of the signal S23 is shown, (D) shows the waveforms of the SW control signals S11 to S14, (E) shows the waveform of the current Ich flowing through the inductor Lch, and (F) shows the secondary side winding 32A of the transformer 30. , 32B shows the waveform of the voltage V32B-V32A, (G) shows the waveform of the voltage V21 of the switching element SW21, (H) shows the waveform of the voltage V22 of the switching element SW22, and (I) shows 1 of the transformer 30. The waveform of the voltage V31 of the secondary winding 31 is shown.

  In the first activation period P1, as shown in FIGS. 10A and 10B, the SW drive unit 74 generates the SW control signals S21 and S22 so as to be alternately at a high level. At that time, the SW drive unit 74 generates the SW control signals S21 and S22 so as to have a period of low level at the same time. Specifically, the SW drive unit 74 includes a period T31 in which the SW control signals S21 and S22 are simultaneously at a low level, a period T32 in which the SW control signal S21 is at a high level and the SW control signal S22 is at a low level, The SW control signals S21 and S22 are generated so that the period T31 and the period T33 in which the SW control signal S21 is at a low level and the SW control signal S22 is at a high level circulate.

  The SW drive unit 74 generates a SW control signal S23 fixed at a high level, supplies the SW control signal S23 to the switching element SW23, and generates SW control signals S11 to S14 fixed at a low level. Each is supplied to SW14 (FIGS. 10C and 10D).

  FIG. 11 illustrates the operation of the switching power supply device 1 in the period T31. In the period T31, as shown in FIGS. 10A and 10B, the switching elements SW21 and SW22 of the switching circuit 20 are simultaneously turned off. Thereby, on the secondary side of the switching power supply device 1, as shown in FIG. 11, no loop current flowing through the transformer 30 is generated, and therefore no loop current is induced on the primary side.

  At this time, the inductor Lch tries to maintain the current flowing through the inductor Lch in the periods T32 and T33 prior to the period T31 even in the period T31. That is, as will be described later, in the periods T32 and T33, a current flows through the inductor Lch from the battery BL toward the transformer 30, and therefore, in the period T31, the current tends to flow in that direction. At this time, the switching elements SW21 and SW22 of the switching circuit 20 are both in the off state, but the switching element SW23 of the emission circuit 60 is in the on state, so that the inductor Lch, the diode Ds, the resistance element Rp, and the switching element SW23 are connected. A loop current Ib3 that passes in sequence flows. In other words, the energy accumulated in the inductor Lch in the periods T32 and T33 is removed from the inductor Lch by the loop current Ib3 and is consumed in the resistance element Rp.

  In the period T32, as shown in FIGS. 10A and 10B, the switching element SW21 of the switching circuit 20 is turned on and the switching element SW22 is turned off. As a result, the secondary loop current Ib21 flows on the secondary side of the switching power supply device 1 as in the case of the steady operation state described above (FIG. 7). At this time, unlike the case of the steady operation state, the energy accumulated in the inductor Lch is removed in the period T31 prior to this period T32. Therefore, the voltage V32B across the secondary winding 32B is simply the voltage VL. Is supplied (FIG. 10F). On the other hand, on the primary side, the primary-side loop current Ib11 flows as in the case of the steady operation state (FIG. 7). At this time, the both-ends voltage V31 of the primary side winding 31 is n × VL obtained by multiplying the both-ends voltage V32B (voltage VL) of the secondary side winding 32B by the winding ratio of the transformer 30 (FIG. 10 ( I)). The DC output voltage VH is supplied to the load L by the primary loop current Ib11.

  In the period T33, as shown in FIGS. 10A and 10B, the switching element SW21 of the switching circuit 20 is turned off and the switching element SW22 is turned on. As a result, the secondary loop current Ib22 flows on the secondary side of the switching power supply 1 as in the case of the steady operation state described above (FIG. 8). At this time, unlike the case of the steady operation state, the energy accumulated in the inductor Lch is removed in the period T31 prior to this period T32. Therefore, the voltage V32B across the secondary winding 32B is simply the voltage VL. Is supplied (FIG. 10F). On the other hand, on the primary side, the primary loop current Ib12 flows as in the steady operation state (FIG. 8). At this time, the voltage V31 across the primary winding 31 is n × VL, which is obtained by multiplying the voltage V32A across the secondary winding 32A (voltage VL) by the winding ratio of the transformer 30 (FIG. 10 ( I)). The DC output voltage VH is supplied to the load L by the primary loop current Ib12.

  As described above, in the first activation period P1, the switching elements SW21 and SW22 operate so as to have the period T31 in which they are turned off simultaneously. Therefore, the energy accumulated by the current flowing through the inductor Lch in the periods T32 and T33 prior to the period T31 is not released via the switching elements SW21 and SW22 in the period T31, unlike the steady operation state. If there is no energy release path, as will be described below as a comparative example, a surge voltage resulting from this energy may be generated in the circuit, possibly destroying the switching element and the like. However, in the switching power supply device 1, since the switching element SW <b> 23 of the emission circuit 60 is turned on in the first activation period P <b> 1, the accumulated energy can be emitted by the emission circuit 60.

(Comparative example)
Next, a switching power supply device 1R according to a comparative example will be described. In this comparative example, the switching power supply device 1 (FIG. 1) does not have the emission circuit 60. Other configurations are the same as those of the present embodiment (FIG. 1).

  FIG. 12 shows the operation of the switching power supply device 1R according to the comparative example in the first activation period P1. (A) and (B) show the waveforms of the SW control signals S21 and S22, respectively. The waveforms of the SW control signals S11 to S14 are shown, (D) shows the waveform of the current Ich flowing through the inductor Lch, and (E) shows the waveforms of the voltages V32B-V32A of the secondary windings 32A and 32B of the transformer 30. , (F) shows the waveform of the voltage V21 of the switching element SW21, (G) shows the waveform of the voltage V22 of the switching element SW22, and (H) shows the waveform of the voltage V31 of the primary winding 31 of the transformer 30. Show.

  As shown in FIGS. 12F and 12G, the surge voltage VS appears in the switching element SW21 voltage V21 and the switching element SW22 voltage V22 at the moment of switching to the period T31. That is, the inductor Lch tries to maintain the current flowing through the inductor Lch in the periods T32 and T33 prior to the period T31 even in the period T31. However, in this comparative example, since the emission circuit 60 in the above embodiment is not provided, there is no path through which this current flows in the period T31. As a result, the drain potential of the switching elements SW21 and SW22 rises to generate a surge voltage VS. If the voltage rises beyond the breakdown voltage of the switching elements SW21 and SW22, the switching elements SW21 and SW22 may be destroyed. There is.

  As described above, in the switching power supply device 1R according to this comparative example, since there is no path for discharging the energy of the inductor Lch accumulated in the periods T32 and T33 in the period T31 following the periods T32 and T33, the surge voltage VS is generated in the circuit. May occur, and the switching element or the like may be destroyed.

  On the other hand, in the switching power supply device 1 according to the present embodiment, since the emission circuit 60 is provided and the switching element SW23 is turned on in the first activation period P1, the energy of the inductor Lch accumulated in the periods T32 and T33. Can be released in the period T31, the surge voltage VS due to the energy can be reduced, and the risk of destroying the switching element or the like can be reduced.

[effect]
As described above, in the present embodiment, since the emission circuit is provided, the energy accumulated in the inductor can be released and the surge voltage can be reduced.

  In this embodiment, since the switching element is provided in the emission circuit, the energy stored in the inductor can be released only when necessary.

  In this embodiment, since the switching element of the emission circuit is turned on only in a predetermined operation, the design of the emission circuit can be made suitable for the predetermined operation, and the design freedom can be achieved. The degree can be increased.

  In this embodiment, since the switching element of the emission circuit is turned on only during the first activation period in the step-up operation mode, the operation can be performed without being affected by the emission circuit in other periods. It becomes possible. Specifically, in the step-down operation mode, since the switching element SW23 is turned off, no current flows through the emission circuit 60 in this operation, so that the inductor Lch and the smoothing capacitor CL can function as a smoothing circuit. . In the step-up operation mode, since the switching element SW23 is turned off in the second activation period P2 and the steady operation period P3, no current flows through the emission circuit 60 in this operation. VL can be boosted.

  In the present embodiment, since a discharge circuit that consumes the energy is used as a means for discharging the energy accumulated in the inductor, it can be configured by a resistance element, and the circuit can be downsized.

[Modification 1]
In the above embodiment, the switching element SW32 is turned on during the first activation period P1, but the present invention is not limited to this. For example, the energy stored in the inductor Lch is used instead. You may be in an ON state only for the period which can be reset.

[Modification 2]
In the above embodiment, the emission circuit 60 including the resistance element Rp and the switching element SW23 is used. However, the present invention is not limited to this, and instead, for example, as shown in FIG. 13, the resistance element Rp Alternatively, an emission circuit 60B including two switching elements SW24 and SW25 may be used. The switching elements SW24 and SW25 are both turned on and off by the SW control signal S23. Here, the switching elements SW24 and SW25 correspond to a specific example of “first and second release switches” in the present invention. In this example, the switching elements SW24 and SW25 have body diodes. These body diodes face in opposite directions in a series circuit including the switching element SW24, the resistance element Rp, and the switching element SW25. Thus, when the switching elements SW24 and SW25 are in the off state, no current flows through the resistance element Rp regardless of the voltage across the inductor Lch. Even in such a configuration, similarly to the above-described embodiment, when operating in the step-up operation mode, the switching elements SW24 and SW25 are set to the ON state during the first activation period P1, thereby causing a surge caused by the inductor Lch. The voltage VS can be reduced.

  In this example, the reset circuit 50 in the above embodiment (FIG. 1 and the like) is omitted, but the reset circuit 50 may be included. In this case, the emission circuit 60B is connected in parallel to the resistance element Rs and the capacitance element Cs of the reset circuit 50, as in FIG.

[Modification 3]
In the above-described embodiment, the body diode is used as the rectifying element in the switching circuits 10 and 20, but the present invention is not limited to this. Instead, the switching elements SW11 to SW14 of the switching circuits 10 and 20 SW21 and SW22 may be on / off controlled to perform rectification by so-called synchronous rectification. Hereinafter, as an example, a steady operation when synchronous rectification is performed in the step-up operation mode will be described.

  FIG. 14 shows the steady operation of the switching power supply device 1 in the step-up operation mode. (A) and (B) show the waveforms of the SW control signals S21 and S22, respectively. (C) shows the SW control signal S23. The waveforms (D) to (G) indicate the waveforms of the SW control signals S11 to S14, respectively. Also in the switching power supply device according to this modification, the SW drive unit 74 performs the SW control signals S21 and S22 so that the period T21, the period T22, the period T21, and the period T23 circulate similarly to the case of the above embodiment. Is generated.

  15 and 16 show the steady operation of the switching power supply device 1 in the step-up operation mode. FIG. 15 shows the operation in the period T22, and FIG. 16 shows the operation in the period T23.

  In the period T22, as shown in FIG. 14, the switching element SW21 of the switching circuit 20 is turned on and the switching element SW22 is turned off (FIGS. 14A and 14B). In the switching circuit 10, the switching elements SW11 and SW14 are turned on, and the switching elements SW12 and SW13 are turned off (FIGS. 14D to 14G). As a result, the secondary loop current Ib21 flows on the secondary side of the switching power supply 1 as shown in FIG. On the other hand, on the primary side, a primary loop current Ib11 flows through the switching element SW14, the primary winding 31 of the transformer 30, the resonance inductor Lr, the switching element SW11, the load L, and the smoothing capacitor CH in order.

  In the period T23, as shown in FIG. 14, the switching element SW21 of the switching circuit 20 is turned off and the switching element SW22 is turned on (FIGS. 14A and 14B). In the switching circuit 10, the switching elements SW11 and SW14 are turned off and the switching elements SW12 and SW13 are turned on (FIGS. 14D to 14G). As a result, the secondary loop current Ib22 flows on the secondary side of the switching power supply 1 as shown in FIG. On the other hand, on the primary side, a primary loop current Ib12 that passes through the switching element SW12, the resonance inductor Lr, the primary winding 31 of the transformer 30, the switching element SW13, the load L, and the smoothing capacitor CH flows in this order.

  Even when synchronous rectification is performed in this manner, in the case of operating in the boosting operation mode, the switching element SW23 is set to the on state during the first activation period P1, so that the inductor Lch is turned on. The resulting surge voltage VS can be reduced.

[Modification 4]
In the above-described embodiment and the like, the emission circuit 60 that extracts and consumes energy from the inductor Lch is used. However, the present invention is not limited to this, and instead, for example, as shown in FIGS. A regenerative circuit that extracts energy from the transformer 81 (corresponding to the inductor Lch in the above embodiment) and regenerates it to a power source or the like may be used. 17 includes a regeneration circuit 80B having a transformer 81, a diode D82, and a switching element SW83. When the switching element SW83 is turned on, energy stored in the transformer 81 is transferred to the primary side. Regenerative power. Here, the transformer 81 and the diode D82 correspond to a specific example of “regeneration means” in the present invention, and the switching element SW83 corresponds to a specific example of “release switch” in the present invention. 18 includes a regenerative circuit 80C having a transformer 81, a diode D84, and a switching element SW85. When the switching element SW85 is turned on, the switching power supply device 1C shown in FIG. Regenerates to BL. Here, the transformer 81 and the diode D84 correspond to a specific example of “regeneration means” in the present invention, and the switching element SW85 corresponds to a specific example of “release switch” in the present invention.

  Although the present invention has been described with reference to the embodiments and the modifications, the present invention is not limited to these embodiments and the like, and various modifications can be made.

  For example, in the above-described embodiment, the primary side switching circuit 10 has a full-bridge type circuit configuration, but is not limited thereto, and instead, for example, a half-bridge type or push-pull type Circuit configurations can be used.

  Further, for example, in the above-described embodiment, the switching element SW23 is an N-channel MOS-FET. However, the switching element SW23 is not limited to this, and any switching element may be used as long as it functions as a switch. Also good. For example, it may be a P-channel MOS-FET, or may be a mechanical switch such as a relay as well as the above-described semiconductor switch such as a MOS-FET or IGBT.

  Further, for example, in the above-described embodiment and the like, the switching power supply device 1 is a bidirectional DC / DC converter that inputs a DC voltage and outputs a DC voltage. However, the present invention is not limited to this. Any switching power supply device such as a DC converter may be used.

  DESCRIPTION OF SYMBOLS 1,1B, 1C ... Switch-on power supply device 10, 20 ... Switching circuit, 30 ... Transformer, 31 ... Primary side winding, 32 ... Secondary side winding, 50 ... Reset circuit, 60, 60B ... Release circuit, 71, 72 ... voltage detection circuit, 73 ... control unit, 74 ... SW drive unit, 80B, 80C ... regeneration circuit, 81 ... transformer, BL ... battery, CH, CL ... smoothing capacitor, Cr11-Cr14, Cs ... capacitive element, Ds, D82, D84 ... Diode, Ia11, Ia12, Ib11, Ib12 ... Primary loop current, Ia21, Ia22, Ib21, Ib22 ... Secondary loop current, Ib3 ... Loop current, L1H ... Primary high voltage line, L1L ... primary side low voltage line, L2, L2H ... secondary side high voltage line, L2L ... secondary side low voltage line, Lch ... inductor, Lr ... resonance inductor, DESCRIPTION OF SYMBOLS 1 ... 1st starting period, P2 ... 2nd starting period, P3 ... Steady operation period, Rp, Rs ... Resistance element, S11-S14, S21-S23 ... SW control signal, SW11-SW14, SW21-SW23, SW83, SW85 ... switching elements, T1 to T4 ... terminals, VH, VL, VT1 ... voltage, VS ... surge voltage, VT2 ... target voltage.

Claims (4)

A step-down operation mode in which the supplied first DC voltage is stepped down to generate a second DC voltage, and a step-up operation mode in which the supplied second DC voltage is stepped up to generate the first DC voltage. A switching power supply device comprising:
A transformer having a primary winding and a secondary winding;
A primary side switching circuit that is connected to the primary side winding and converts the first DC voltage into an AC voltage by a switching operation in the step-down operation mode;
A secondary side switching circuit that is connected to the secondary side winding and converts the second DC voltage into an AC voltage by a switching operation in the step-up operation mode;
An inductor connected to the secondary winding and constituting a smoothing circuit for generating the second DC voltage in the step-down operation mode;
A resistance element for consuming energy stored in the inductor;
And a first and second release switches for controlling energy consumption in the resistive element,
One end of the resistance element is connected to one end of the inductor via the first release switch,
The switching power supply device, wherein the other end of the resistance element is connected to the other end of the inductor via the second release switch . The secondary winding includes first and second secondary windings,
The secondary side switching circuit includes first and second switching elements,
One end of the first secondary winding and one end of the second secondary winding are connected to each other and to the inductor,
The other end of the first secondary winding is connected to the first switching element,
The switching power supply according to claim 1, wherein the other end of the second secondary winding is connected to the second switching element. A control unit for controlling on / off of the primary side switching circuit, the secondary side switching circuit, and the first and second release switches;
The control unit, in the boost operation mode,
When the first voltage is lower than a predetermined voltage, the first switching element and the second switching element are alternately turned on and off so as to have a period in which each of the first voltage and the second switching element is simultaneously turned off.
When the first voltage is higher than the predetermined voltage, the first switching element and the second switching element are alternately turned on and off so as to have a period in which the first switching element and the second switching element are simultaneously turned on. 3. The switching power supply device according to 2. The control unit, in the boost operation mode,
If the first voltage is lower than the predetermined voltage, turn on the first and second release switches;
The switching power supply according to claim 3 , wherein when the first voltage is higher than the predetermined voltage, the first and second release switches are turned off.

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