Switching Power Supply

Abstract

To provide a switching power supply device capable of achieving high efficiency regardless of the value of an input voltage.SOLUTION: A control unit (CNT1) of a switching power supply device (1A) has a first state in which a first switch (SW1) is switched on and a second switch (SW2) is switched off, a second state in which the first switch is off and the second switch is on, a third state in which the first and second switches are off, and a fourth state in which a voltage at a connection node of the first and second switches is lower than in the third state. The control unit repeats the first state, the second state, the third state, and the fourth state, with the length of the fourth state increasing as an input voltage is greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The invention disclosed in this specification relates to a switching power supply device that steps down an input voltage to an output voltage. [Background technology]

[0002] BACKGROUND ART Conventionally, fixed on-time control switching power supply devices are known as switching power supply devices that are highly efficient under light loads (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-35316 Summary of the Invention [Problem to be solved by the invention]

[0004] Fixed-on-time control switching power supplies have the feature that the switching frequency can be varied depending on the load state. When the switching frequency fluctuates, the noise frequency also fluctuates, which can reduce the effectiveness of noise suppression means (such as a filter circuit) that suppress fixed-frequency noise. Therefore, it is desirable to keep the switching frequency of a switching power supply used in an environment where noise is a problem as fixed as possible.

[0005] It is also desirable that the switching power supply device be able to maintain high efficiency even when the input voltage value changes. [Means for solving the problem]

[0006] The switching power supply disclosed in this specification is configured to step down an input voltage to an output voltage. The switching power supply includes: a first switch having a first terminal connectable to an end to which the input voltage is applied and a second terminal connectable to a first terminal of an inductor; a second switch having a first terminal connectable to the first terminal of the inductor and a second terminal of the first switch and a second terminal connectable to an end to which a low voltage lower than the input voltage is applied; and a control unit configured to control the on / off of the first switch and the second switch. The control unit has a first state in which the first switch is in an on state and the second switch is in an off state; a second state in which the first switch is in an off state and the second switch is in an on state; a third state in which the first switch and the second switch are in an off state; and a fourth state in which the voltage at a connection node between the first switch and the second switch is lower than in the third state. The control unit repeats the first state, the second state, the third state, and the fourth state, and increases the duration of the fourth state as the input voltage increases.

[0007] A switch control device according to one aspect disclosed in the present specification controls the on / off of a first switch, the first terminal of which is configured to be connectable to an end to which an input voltage is applied and the second terminal of which is configured to be connectable to a first terminal of an inductor, and the on / off of a second switch, the first terminal of which is configured to be connectable to the first terminal of the inductor and the second terminal of the first switch, and the second terminal of which is configured to be connectable to an end to which a low voltage lower than the input voltage is applied. The switch control device has a first state in which the first switch is in an on state and the second switch is in an off state, a second state in which the first switch is in an off state and the second switch is in an on state, a third state in which the first switch and the second switch are in an off state, and a fourth state in which a voltage at a connection node between the first switch and the second switch is lower than in the third state. The switch control device repeats the first state, the second state, the third state, and the fourth state, and increases the duration of the fourth state as the input voltage increases.

[0008] An in-vehicle device according to one aspect disclosed in this specification includes the switching power supply device having the above-described configuration or the switch control device having the above-described configuration.

[0009] A vehicle according to one aspect disclosed in this specification includes an on-board device having the above-described configuration and a battery that supplies power to the on-board device. [Effects of the Invention]

[0010] According to one aspect of the invention disclosed in this specification, high efficiency can be achieved regardless of the value of the input voltage. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of a switching power supply device according to the first embodiment. [Figure 2] FIG. 2 is a timing chart showing the operation of the switching power supply device according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the configuration of a switching power supply device according to the second embodiment. [Figure 4] FIG. 4 is a time chart showing the operation of the switching power supply device according to the second embodiment. [Figure 5] FIG. 5 is a diagram showing the configuration of a switching power supply device according to the third embodiment. [Figure 6] FIG. 6 is a timing chart showing the operation of the switching power supply device according to the third embodiment. [Figure 7] FIG. 7 is a diagram showing the configuration of a switching power supply device according to the fourth embodiment. [Figure 8] FIG. 8 is a timing chart showing the operation of the switching power supply device according to the fourth embodiment. [Figure 9] FIG. 9 is a diagram illustrating a first configuration example of a control unit according to the fifth embodiment. [Figure 10] FIG. 10 is a timing chart showing the operation of the control unit shown in FIG. [Figure 11] FIG. 11 is a diagram illustrating a second configuration example of the control unit according to the fifth embodiment. [Figure 12] FIG. 12 is a timing chart showing the operation of the control unit shown in FIG. [Figure 13] FIG. 13 is a diagram illustrating a third configuration example of the control unit according to the fifth embodiment. [Figure 14] FIG. 14 is a timing chart showing the operation of the control unit shown in FIG. [Figure 15] FIG. 15 is a diagram illustrating a first configuration example of a control unit according to the sixth embodiment. [Figure 16] FIG. 16 is a timing chart showing the operation of the control unit shown in FIG. [Figure 17] FIG. 17 is a diagram illustrating a second configuration example of the control unit according to the sixth embodiment. [Figure 18] FIG. 18 is a timing chart showing the operation of the control unit shown in FIG. [Figure 19] FIG. 19 is a diagram showing a first configuration example of a setting circuit according to the seventh embodiment. [Figure 20] FIG. 20 is a timing chart showing the operation of the setting circuit shown in FIG. [Figure 21] FIG. 21 is a diagram showing a second configuration example of the setting circuit according to the seventh embodiment. [Figure 22] FIG. 22 is a timing chart showing the operation of the setting circuit shown in FIG. [Figure 23] FIG. 23 is a diagram illustrating a first configuration example of a control unit according to the eighth embodiment. [Figure 24] FIG. 24 is a timing chart showing the operation of the control unit shown in FIG. [Figure 25] FIG. 25 is a diagram illustrating a second configuration example of the control unit according to the eighth embodiment. [Figure 26] FIG. 26 is a timing chart showing the operation of the control unit shown in FIG. [Figure 27] FIG. 27 is a diagram illustrating a third configuration example of the control unit according to the eighth embodiment. [Figure 28]FIG. 28 is a timing chart showing the operation of the control unit shown in FIG. [Figure 29] FIG. 29 is a diagram illustrating a first configuration example of a control unit according to the ninth embodiment. [Figure 30] FIG. 30 is a timing chart showing the operation of the control unit shown in FIG. [Figure 31] FIG. 31 is a diagram illustrating a second configuration example of the control unit according to the ninth embodiment. [Figure 32] FIG. 32 is a timing chart showing the operation of the control unit shown in FIG. [Figure 33] FIG. 33 is a diagram illustrating a third configuration example of the control unit according to the ninth embodiment. [Figure 34] FIG. 34 is a timing chart showing the operation of the control unit shown in FIG. [Figure 35] FIG. 35 is an external view showing an example of the configuration of a vehicle. DETAILED DESCRIPTION OF THE INVENTION

[0012] In this specification, a MOS transistor refers to a transistor whose gate structure is composed of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with a low resistance, an insulating layer, and a P-type, N-type, or intrinsic semiconductor layer. In other words, the gate structure of a MOS transistor is not limited to a three-layer structure of metal, oxide, and semiconductor.

[0013] In this specification, the reference voltage means a voltage that is constant under ideal conditions, but in reality it is a voltage that may fluctuate slightly due to temperature changes and the like.

[0014] In this specification, a constant voltage means a voltage that is constant under ideal conditions, but in reality it is a voltage that may fluctuate slightly due to temperature changes and the like.

[0015] In this specification, a constant current means a current that is constant under ideal conditions, but in reality it is a current that may fluctuate slightly due to temperature changes and the like.

[0016] First Embodiment 1 is a diagram showing the configuration of a switching power supply according to a first embodiment. The switching power supply 1A according to the first embodiment (hereinafter referred to as "switching power supply 1A") is a switching power supply that steps down an input voltage VIN to an output voltage VOUT, and includes a control unit CNT1, a first switch SW1, a second switch SW2, an inductor L1, an output capacitor C1, and an output feedback unit FB1. The switching power supply 1A may be configured to operate in a continuous current mode under light load, or may be configured to have a reverse current prevention function and operate in a discontinuous current mode under light load.

[0017] The control unit CNT1 controls the on / off of the first switch SW1 and the second switch SW2 based on the output of the output feedback unit FB1. In other words, the control unit CNT1 is a switch control device that controls the on / off of the first switch SW1 and the second switch SW2.

[0018] The first switch SW1 has a first terminal connectable to the terminal to which the input voltage VIN is applied, and a second terminal connectable to the first terminal of the inductor L1. The first switch SW1 conducts / cuts off a current path from the terminal to which the input voltage VIN is applied to the inductor L1. For example, a P-channel MOS transistor, an N-channel MOS transistor, or the like can be used as the first switch SW1. For example, if an N-channel MOS transistor is used as the first switch SW1, a bootstrap circuit or the like can be provided in the switching power supply device 1A to generate a voltage higher than the input voltage VIN.

[0019] The second switch SW2 has a first end connectable to the first end of the inductor L1 and the second end of the first switch SW1, and a second end connectable to a ground potential application end. The second switch SW2 conducts / cuts off the current path from the ground potential application end to the inductor L1. For example, an N-channel MOS transistor or the like can be used as the second switch SW2.

[0020] By switching the first switch SW1 and the second switch SW2, a pulsed switch voltage VSW is generated at the connection node between the first switch SW1 and the second switch SW2. The inductor L1 and the output capacitor C1 smooth the pulsed switch voltage VSW to generate an output voltage VOUT, which is supplied to the application terminal of the output voltage VOUT. A load LD1 is connected to the application terminal of the output voltage VOUT, and the output voltage VOUT is supplied to the load LD1.

[0021] The output feedback section FB1 generates and outputs a feedback signal corresponding to the output voltage VOUT. The output feedback section FB1 can be, for example, a resistive voltage divider circuit that resistively divides the output voltage VOUT to generate a feedback signal. Alternatively, for example, the output feedback section FB1 may be configured to acquire the output voltage VOUT and output the output voltage VOUT itself as a feedback signal. Note that the output feedback section FB1 may also be configured to generate and output a feedback signal corresponding to the current flowing through the inductor L1 (hereinafter referred to as "inductor current IL") in addition to the feedback signal corresponding to the output voltage VOUT. Current mode control becomes possible when the output feedback section FB1 generates a feedback signal corresponding to the inductor current IL.

[0022] 2 is a timing chart showing the operation of the switching power supply device 1A. The control unit CNT1 sets the length of the first state ST1 in accordance with the feedback signal output from the output feedback unit FB1. The lighter the load LD1, the shorter the length of the first state ST1.

[0023] In the first state ST1, the control unit CNT1 turns on the first switch SW1 and turns off the second switch SW2. In the first state ST1, the switch voltage VSW becomes equal to the input voltage Vin plus the forward voltage of the body diode of the first switch SW1, and then becomes substantially equal to the input voltage Vin. In the first state ST1, the inductor current IL increases over time.

[0024] When the first state ST1 ends, the control unit CNT1 switches the control state from the first state ST1 to the second state ST2.

[0025] In the second state ST2, the control unit CNT1 turns off the first switch SW1 and turns on the second switch SW2. In the second state ST2, the switch voltage VSW becomes substantially equal to the ground potential GND. In the second state ST2, the inductor current IL decreases over time.

[0026] When the inductor current IL decreases to a predetermined value, the control unit CNT1 ends the second state ST2 and switches the control state from the second state ST2 to a third state ST3. A determination unit (not shown) that determines whether the inductor current IL has decreased to the predetermined value may be provided separately from the control unit CNT1 or may be built into the control unit CNT1. In this embodiment, the predetermined value is set to zero.

[0027] In the third state ST3, the control unit CNT1 turns off the first switch SW1 and the second switch SW2. In the third state ST3, the connection node between the first switch SW1 and the second switch SW2 is in a high impedance state, and the switch voltage VSW is substantially the same as the output voltage VOUT. In the second state ST2, the inductor current IL is zero.

[0028] The periodic signal S1 is a signal in which pulses are generated at a fixed period Tfix. The periodic signal S1 may be a signal generated inside the control unit CNT1, or may be a signal generated outside the control unit CNT1 and acquired by the control unit CNT1.

[0029] When the pulse of the periodic signal S1 rises, the control unit CNT1 ends the third state ST3 and switches the control state from the third state ST3 to the fourth state ST4.

[0030] In the fourth state ST4, the control unit CNT1 turns the first switch SW1 off and the second switch SW2 on. In the fourth state ST4, the switch voltage VSW becomes substantially equal to the ground potential GND. In the fourth state ST4, the inductor current IL flows from the application terminal of the output voltage VOUT to the connection node between the first switch SW1 and the second switch SW2, and the amount of current increases over time. In the fourth state ST4, the inductor current IL regenerates. The regenerative energy of the inductor current IL is released when switching from the fourth state ST4 to the first state ST1, so that the switch voltage VSW rises sharply when switching from the fourth state ST4 to the first state ST1.

[0031] When the pulse of the periodic signal S1 falls, the control unit CNT1 ends the fourth state ST4 and switches the control state from the fourth state ST4 to the first state ST1.

[0032] The control unit CNT1 repeats the first state ST1, the second state ST2, the third state ST3, and the fourth state ST4 at a fixed period Tfix. It is desirable to provide a dead time period during which both the first switch SW1 and the second switch SW2 are in the off state between the first state ST1 and the second state ST2 and between the fourth state ST4 and the first state ST1. When a dead time period is provided between the first state ST1 and the second state ST2 and between the fourth state ST4 and the first state ST1, the fixed period Tfix is ​​equal to the total period of the dead time periods provided in the first state ST1, between the first state ST1 and the second state ST2, the second state ST2, the third state ST3, the fourth state ST4, and between the fourth state ST4 and the first state ST1.

[0033] Since the switching power supply device 1A operates at a fixed cycle Tfix and is configured so that no loss occurs in the third state ST3, high efficiency can be achieved without varying the switching frequency. When the load LD1 is lightly loaded, the length of the first state ST1 is short and the length of the third state ST3 is long, so the switching power supply device 1A can significantly improve the efficiency when the load LD1 is lightly loaded.

[0034] As a modification of this embodiment, the second switch SW2 may be configured so that the second terminal thereof is connectable to an application terminal of a low voltage other than the ground potential that is lower than the input voltage VIN.

[0035] Second Embodiment In the second embodiment, the description of the same configuration and operation as in the first embodiment will be omitted. Fig. 3 is a diagram showing the configuration of a switching power supply device according to the second embodiment. A switching power supply device 1B according to the second embodiment (hereinafter referred to as "switching power supply device 1B") has a configuration in which a switch SW3 is added to the switching power supply device 1A.

[0036] The switch SW3 is connected in parallel to the switch SW2. That is, a first terminal of the switch SW3 is connected to a first terminal of the switch SW2, and a second terminal of the switch SW3 is connected to a second terminal of the switch SW2. The third switch SW3 may be, for example, an N-channel MOS transistor. The control unit CNT1 controls the on / off of the third switch SW3 in addition to the on / off of the first switch SW1 and the second switch SW2.

[0037] The switch SW3 has at least one of an on-resistance (resistance between the first terminal and the second terminal in the on state) and a capacitance (parasitic capacitance between the first terminal and the second terminal) smaller than that of the switch SW2.

[0038] 4 is a timing chart showing the operation of the switching power supply device 1B. The operation of the switching power supply device 1B differs from the operation of the switching power supply device 1A in that the control unit CNT1 turns off the second switch SW2 in the fourth state ST4.

[0039] In the fourth state ST4, the control unit CNT1 turns on the third switch SW3 instead of the second switch SW2. As described above, the switch SW3 has at least one of an on-resistance and a capacitance smaller than those of the switch SW2, and therefore the switching power supply device 1B can reduce the loss in the fourth state ST4 more than the switching power supply device 1A.

[0040] On the other hand, in the first state ST1, the second state ST2, and the third state ST3, the control unit CNT1 turns off the third switch SW3.

[0041] Since the switching power supply device 1B operates at a fixed cycle Tfix and is configured so that no loss occurs in the third state ST3, high efficiency can be achieved without varying the switching frequency. When the load LD1 is lightly loaded, the length of the first state ST1 is short and the length of the third state ST3 is long, so the switching power supply device 1B can significantly improve the efficiency when the load LD1 is lightly loaded.

[0042] As a modification of this embodiment, in the fourth state ST4, the control unit CNT1 may turn on both the second switch SW2 and the third switch SW3.

[0043] As a modification of this embodiment, the second terminal of the second switch SW2 and the second terminal of the third switch SW3 may be configured to be connectable to an application terminal of a low voltage that is lower than the input voltage VIN and other than the ground potential.

[0044] Third Embodiment In the third embodiment, the description of the same configuration and operation as in the second embodiment will be omitted. Fig. 5 is a diagram showing the configuration of a switching power supply device according to the third embodiment. A switching power supply device 1C according to the third embodiment (hereinafter referred to as "switching power supply device 1C") has a configuration in which a switch SW3, a capacitor C2, and a switch SW4 are added to the switching power supply device 1A.

[0045] A first terminal of the switch SW3 is connected to the connection node between the first switch SW1 and the second switch SW2. A second terminal of the switch SW3 is connected to a first terminal of the capacitor C2 and a first terminal of the fourth switch SW4. A second terminal of the capacitor C2 and a second terminal of the fourth switch SW4 are connected to the ground potential. The third switch SW3 may be, for example, an N-channel MOS transistor. The fourth switch SW4 may be, for example, an N-channel MOS transistor. The control unit CNT1 controls the on / off of the third switch SW3 and the fourth switch SW4 in addition to the on / off of the first switch SW1 and the second switch SW2.

[0046] The switch SW3 has at least one of an on-resistance (resistance between the first end and the second end in the on state) and a capacitance (parasitic capacitance between the first end and the second end) smaller than those of the switch SW2. Unlike this embodiment, the on-resistance and capacitance of the switch SW3 may be approximately the same as those of the switch SW2.

[0047] The switch SW4 is a switch for discharging the capacitor C2. When the switch SW4 is turned on, both ends of the capacitor C2 are short-circuited, causing the capacitor C2 to discharge.

[0048] FIG. 6 is a timing chart showing the operation of the switching power supply device 1C. The operation of the switching power supply device 1C is basically the same as that of the switching power supply device 1B. In the switching power supply device 1C, on / off control of the fourth switch SW4 by the control unit CNT1 is added. The control unit CNT1 controls the on / off of the third switch SW3 and the on / off of the fourth switch SW4 in a complementary manner. That is, the control unit CNT1 turns the fourth switch SW4 on in the first state ST1, the second state ST2, and the third state ST3, and turns the fourth switch SW4 off in the fourth state ST4.

[0049] In the switching power supply device 1C, in the fourth state ST4, the switch voltage SW is a voltage obtained by dividing the input voltage VIN by the parasitic capacitance between the first and second ends of the first switch SW1 and the parasitic capacitance between the first and second ends of the third switch SW3 and the capacitance C2. This makes it possible to adjust the value of the switch voltage SW in the fourth state ST4 by the capacitance value of the capacitance C2. In other words, it is possible to adjust the rise of the switch voltage VSW when switching from the fourth state ST4 to the first state ST1 by the capacitance value of the capacitance C2.

[0050] For example, by including the control unit CNT1 in a semiconductor integrated circuit device and making the capacitor C2 an external component of the semiconductor integrated circuit device, it becomes easier to adjust the value of the switch voltage SW in the fourth state ST4.

[0051] Since the switching power supply device 1C operates at a fixed cycle Tfix and is configured so that no loss occurs in the third state ST3, high efficiency can be achieved without varying the switching frequency. When the load LD1 is lightly loaded, the length of the first state ST1 is short and the length of the third state ST3 is long, so the switching power supply device 1C can significantly improve the efficiency when the load LD1 is lightly loaded.

[0052] As a modification of this embodiment, the second terminal of the second switch SW2, the second terminal of the capacitor C2, and the second terminal of the fourth switch SW4 may be configured to be connectable to an application terminal of a low voltage that is lower than the input voltage VIN and other than the ground potential.

[0053] <Fourth embodiment> In the fourth embodiment, the description of the same configuration and operation as in the third embodiment will be omitted. Fig. 7 is a diagram showing the configuration of a switching power supply device according to the fourth embodiment. A switching power supply device 1D according to the fourth embodiment (hereinafter referred to as "switching power supply device 1D") has a configuration in which a capacitance C2 is added to the switching power supply device 1A.

[0054] A first end of the capacitor C2 is connected to the connection node between the first switch SW1 and the second switch SW2. The control unit CNT1 controls the voltage VA applied to the second end of the switch SW3. For example, the control unit CNT1 sets the voltage VA to a HIGH level (e.g., the same value as the output voltage VOUT) in the third state ST3, and sets the voltage VA to a LOW level (e.g., ground potential GND) in the first state ST1, the second state ST2, and the fourth state ST4.

[0055] By adjusting the value of the voltage VA in the fourth state ST4, it is possible to adjust the rise of the switch voltage VSW when switching from the fourth state ST4 to the first state ST1.

[0056] Since the switching power supply device 1D operates at a fixed cycle Tfix and is configured so that no loss occurs in the third state ST3, high efficiency can be achieved without varying the switching frequency. When the load LD1 is lightly loaded, the length of the first state ST1 is short and the length of the third state ST3 is long, so the switching power supply device 1D can significantly improve the efficiency when the load LD1 is lightly loaded.

[0057] As a modification of this embodiment, the second terminal of the second switch SW2 may be configured to be connectable to an application terminal to which a low voltage other than the ground potential is applied and which is lower than the input voltage VIN.

[0058] Fifth Embodiment In each of the control units CNT1 of the switching power supply devices according to the first to fourth embodiments described above, the length of the first state ST1 is shortened as the load LD1 becomes lighter. In other words, in the switching power supply devices according to the first to fourth embodiments, the pulse width of the control signal for controlling the switch SW1 becomes narrower as the load LD1 becomes lighter, making it more difficult to generate the control signal.

[0059] The switching power supply device according to the fifth embodiment is a switching power supply device that can solve the above-mentioned problems of the switching power supply devices according to the first to fourth embodiments.

[0060] The switching power supply device according to the fifth embodiment is an improved version of the switching power supply device according to the first embodiment, so in the fifth embodiment, descriptions of the same configurations and operations as those in the first embodiment will be omitted.

[0061] The control unit CNT1 according to the fifth embodiment repeats a first state ST1, a second state ST2, a third state ST3, and a fourth state ST4 at a fixed cycle when the load LD1 is in the first range (normal load state). Therefore, the switching power supply device according to the fifth embodiment can fix the switching frequency when the load LD1 is in the first range.

[0062] When the load LD1 is in a second range (light load state) that is lighter than the first range, the control unit CNT1 according to the fifth embodiment repeats the first state ST1, the second state ST2, the third state ST3, and the fourth state ST4 with a longer period as the load LD1 becomes lighter. Therefore, the switching power supply device according to the fifth embodiment prevents the pulse width of the control signal for controlling the switch SW1 from becoming narrower when the load LD1 is in the second range. In other words, the switching power supply device according to the fifth embodiment facilitates normal switching control even when the load LD1 is in a light load state.

[0063] The control unit CNT1 according to the fifth embodiment provides a dead time period DT between the fourth state ST4 and the first state ST1, during which the first switch SW1 and the second switch SW2 are in the OFF state. The control unit CNT1 according to the fifth embodiment sets the length of the dead time period DT and the length of the fourth state ST4 to fixed values ​​so that the first state ST starts at the zero-crossing point of the inductor current IL when there is no variation between components. This allows the switching power supply device according to the fifth embodiment to reduce loss when the first switch SW1 is turned on, thereby achieving even higher efficiency.

[0064] <<First Configuration Example of Control Unit According to Fifth Embodiment>> Fig. 9 is a diagram showing a first configuration example of the control unit CNT1 according to the fifth embodiment. Fig. 10 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 9.

[0065] The control unit CNT1 shown in Fig. 9 includes an error amplifier 1, a PWM (Pulse Width Modulation) comparator 2, an AND gate 3, a latch circuit 4, a driver 5, a PFM (Pulse Frequency Modulation) comparator 6, a selector 7, a delay circuit 8, a zero-crossing point detection circuit 9, and a latch circuit 10. In the configuration shown in Fig. 9, an RS flip-flop is used as an example of the latch circuit 4, and a D flip-flop is used as an example of the latch circuit 10. Therefore, in the following description, the latch circuit 4 will be described as an RS flip-flop 4, and the latch circuit 10 will be described as a D flip-flop 10.

[0066] The error amplifier 1 outputs an error signal VERR according to the difference between the feedback signal VFB output from the output feedback section FB1 and the reference voltage VREF.

[0067] The PWM comparator 2 outputs a PWM signal VPWM which is the result of comparing the error signal VERR with the ramp voltage VRAMP.

[0068] The AND gate 3 outputs a reset signal RST, which is the logical product of the PWM signal VPWM and the delay signal ONDLY. The delay signal ONDLY will be described later.

[0069] The RS flip-flop 4 generates a delayed signal LON2DLY by delaying the signal supplied to the set terminal (S terminal) inside the RS flip-flop 4. The RS flip-flop 4 generates and outputs an on-time setting voltage VON that is set by the delayed signal LON2DLY and reset by the reset signal RST.

[0070] The driver 5 controls the first switch SW1 and the second switch SW2 based on the on-time setting voltage VON.

[0071] The PFM comparator 6 outputs a signal VPFMOUT corresponding to the difference between the feedback signal VFB output from the output feedback unit FB1 and the reference voltage VPFMREF. A pulse is generated in the signal VPFMOUT when the output voltage VOUT falls below a certain value.

[0072] The selector 7 selects either the periodic signal S1 or the signal VPFMOUT and supplies it to the set terminal (S terminal) of the RS flip-flop 4. The selector 7 selects the periodic signal S1 when the light load mode signal LCMMODE is at a low level. The selector 7 selects the signal VPFMOUT when the light load mode signal LCMMODE is at a high level. The light load mode signal LCMMODE will be described later.

[0073] The delay circuit 8 generates a delay signal ONDLY by delaying the on-time setting voltage VON by a first predetermined time. The delay circuit 8 generates a delay signal LCMDLY by delaying the on-time setting voltage VON by a second predetermined time. The second predetermined time is longer than the first predetermined time.

[0074] The zero-crossing point detection circuit 9 detects the zero-crossing points of the inductor current IL and outputs a zero-crossing point detection signal ZX. The zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 9 goes high when the inductor current IL decreases from a positive value and reaches a zero-crossing point.

[0075] The D flip-flop 10 holds the delay signal LCMDLY in synchronization with the zero-crossing point detection signal ZX and outputs an inverted signal of the held delay signal LCMDLY. The inverted signal of the delay signal LCMDLY held by the D flip-flop 10 is the light load mode signal LCMMODE described above.

[0076] The control unit CNT1 shown in FIG. 9 determines that the load LD1 is in a light load state when the time from the start of the first state ST1 to the detection of the zero cross point of the inductor current IL is less than a certain value (second predetermined time).

[0077] 9 uses the delay signal ONDLY to set the minimum time (first predetermined time) for the first state ST1 when the load LD1 is in a light load state. This prevents the length of the first state ST1 from becoming too short, making it easier to perform normal switching control.

[0078] <<Second Configuration Example of Control Unit According to Fifth Embodiment>> Fig. 11 is a diagram showing a second configuration example of a control unit according to the fifth embodiment. Fig. 12 is a timing chart showing the operation of the control unit shown in Fig. 11. Note that in this configuration example, descriptions of parts that are the same as those in the first configuration example will be omitted as appropriate.

[0079] The control unit CNT1 shown in FIG. 11 includes an error amplifier 1, a PWM comparator 2, an RS flip-flop 4, a driver 5, a PFM comparator 6, and a selector .

[0080] In this configuration example, the PWM signal VPWM serves as the reset signal RST.

[0081] The selector 7 selects the periodic signal S1 when the signal VPFMOUT is at a low level, and selects the signal VPFMOUT when the signal VPFMOUT is at a high level.

[0082] The control unit CNT1 shown in FIG. 11 determines that the load LD1 is in a light load state when the error signal VERR exceeds the reference voltage VPFMREF.

[0083] <<Third Configuration Example of Control Unit According to Fifth Embodiment>> Fig. 13 is a diagram showing a third configuration example of a control unit according to the fifth embodiment. Fig. 14 is a timing chart showing the operation of the control unit shown in Fig. 13. Note that in this configuration example, descriptions of parts that are the same as those in the second configuration example will be omitted as appropriate.

[0084] The control unit CNT1 shown in FIG. 13 is different from the control unit CNT1 shown in FIG. 11 in that an AND gate 3 and a delay circuit 8 are added.

[0085] The AND gate 3 and the delay circuit 8 are the same as those in the first configuration example, except that the delay circuit 8 generates only the delay signal ONDLY.

[0086] The control unit CNT1 shown in FIG. 13 determines that the load LD1 is in a light load state when the error signal VERR exceeds the reference voltage VPFMREF.

[0087] 13 uses the delay signal ONDLY to set the minimum time (first predetermined time) for the first state ST1 when the load LD1 is in a light load state. This prevents the length of the first state ST1 from becoming too short, making it easier to perform normal switching control.

[0088] <<Modification of the Fifth Embodiment>> As described above, the switching power supply device according to the fifth embodiment is an improved version of the switching power supply device according to the first embodiment. However, similar improvements can also be made to the switching power supply devices according to the second to fourth embodiments. Furthermore, the switching power supply device according to the fifth embodiment can also be modified in the same way as the modifications described in the first to fourth embodiments.

[0089] Sixth Embodiment In each of the control units CNT1 of the switching power supply devices according to the first to fifth embodiments described above, the length of the first state ST1 increases as the load LD1 becomes heavier. That is, in the switching power supply devices according to the first to fifth embodiments, the pulse width of the control signal for controlling the switch SW1 increases as the load LD1 becomes heavier, making it more difficult to control within the fixed period Tfix.

[0090] The switching power supply device according to the sixth embodiment is a switching power supply device that can solve the above-mentioned problems of the switching power supply devices according to the first to fifth embodiments.

[0091] The switching power supply device according to the sixth embodiment is an improved version of the switching power supply device according to the first embodiment, so in the sixth embodiment, descriptions of the same configurations and operations as those in the first embodiment will be omitted.

[0092] The control unit CNT1 according to the sixth embodiment repeats a first state ST1, a second state ST2, a third state ST3, and a fourth state ST4 at a fixed period based on the periodic signal S1. Therefore, the switching power supply device according to the sixth embodiment can fix the switching frequency in synchronization with the periodic signal S1.

[0093] The control unit CNT1 according to the sixth embodiment masks the periodic signal S1 until it detects a zero-cross point of the inductor current IL. Therefore, the control unit CNT1 according to the sixth embodiment operates out of synchronization with the periodic signal S1 when the load LD1 is in a heavy load state that is heavier than a normal load state. This makes it easy for the switching power supply device according to the sixth embodiment to perform normal switching control even when the load LD1 is in a heavy load state.

[0094] The control unit CNT1 according to the sixth embodiment provides a dead time period DT between the fourth state ST4 and the first state ST1, during which the first switch SW1 and the second switch SW2 are in the OFF state. The control unit CNT1 according to the sixth embodiment sets the length of the dead time period DT and the length of the fourth state ST4 to fixed values ​​so that the first state ST starts at the zero-crossing point of the inductor current IL when there is no variation between components. This allows the switching power supply device according to the sixth embodiment to reduce loss when the first switch SW1 is turned on, thereby achieving even higher efficiency.

[0095] <<First Configuration Example of Control Unit According to Sixth Embodiment>> Fig. 15 is a diagram showing a first configuration example of the control unit CNT1 according to the sixth embodiment. Fig. 16 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 15.

[0096] 15 includes an error amplifier 21, a PWM comparator 22, an AND gate 23, a latch circuit 24, a driver 25, a latch circuit 26, an AND gate 27, a delay circuit 28, a zero-crossing point detection circuit 29, a latch circuit 30, and a NOT gate 31. In the configuration shown in FIG. 15, an RS flip-flop is used as an example of the latch circuit 24, and D flip-flops are used as examples of each of the latch circuits 26 and 30. Therefore, in the following description, the latch circuit 24 will be described as the RS flip-flop 24, the latch circuit 26 will be described as the D flip-flop 26, and the latch circuit 30 will be described as the D flip-flop 30.

[0097] The error amplifier 21 outputs an error signal VERR according to the difference between the feedback signal VFB output from the output feedback section FB1 and the reference voltage VREF.

[0098] The PWM comparator 22 outputs a PWM signal VPWM that is the result of comparing the error signal VERR with the ramp voltage VRAMP.

[0099] The AND gate 23 outputs a reset signal RST, which is the logical product of the PWM signal VPWM and the delay signal ONDLY. The delay signal ONDLY will be described later.

[0100] The RS flip-flop 24 generates a delayed signal LON2DLY by delaying the signal supplied to the set terminal (S terminal) inside the RS flip-flop 4. The RS flip-flop 4 generates and outputs an on-time setting voltage VON that is set by the delayed signal LON2DLY and reset by the reset signal RST.

[0101] The driver 25 controls the first switch SW1 and the second switch SW2 based on the on-time setting voltage VON.

[0102] D flip-flop 26 holds voltage VCC supplied to its D terminal in synchronization with periodic signal S1. The value of voltage VCC supplied to the D terminal of D flip-flop 26 is set to a value that is processed as a high-level signal by AND gate 27. D flip-flop 26 is cleared by the logical inversion signal of on-time setting voltage VON output from NOT gate 31.

[0103] The AND gate 27 supplies the logical product of the output of the D flip-flop 26 and the output of the D flip-flop 30 to the set terminal (S terminal) of the RS flip-flop 24 .

[0104] The delay circuit 28 generates a delay signal ONDLY by delaying the on-time setting voltage VON by a predetermined time.

[0105] The zero-crossing point detection circuit 29 detects the zero-crossing points of the inductor current IL and outputs a zero-crossing point detection signal ZX. The zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 29 goes high when the inductor current IL decreases from a positive value and reaches a zero-crossing point.

[0106] D flip-flop 30 holds voltage VCC supplied to its D terminal in synchronization with zero-crossing point detection signal ZX. The value of voltage VCC supplied to the D terminal of D flip-flop 26 is set to a value that is processed as a high-level signal by AND gate 27. D flip-flop 30 is cleared by a logically inverted signal of on-time setting voltage VON output from NOT gate 31.

[0107] The NOT gate 31 supplies the logically inverted signal of the ON time setting voltage VON to the clear terminals of the D flip-flops 26 and 30 .

[0108] 15, when a zero-crossing point of the inductor current IL is detected after the pulse of the periodic signal S1, the control unit CNT1 enters the fourth state ST1 at the time of detection of the zero-crossing point of the inductor current IL. This allows the switching frequency to be changed according to the magnitude of the load when a zero-crossing point of the inductor current IL is detected after the pulse of the periodic signal S1, i.e., when the load is heavy. In other words, the load responsiveness under heavy loads can be improved.

[0109] <<Second Configuration Example of Control Unit According to Sixth Embodiment>> Fig. 17 is a diagram showing a second configuration example of a control unit according to the sixth embodiment. Fig. 18 is a timing chart showing the operation of the control unit shown in Fig. 17. Note that in this configuration example, descriptions of parts that are the same as those in the first configuration example will be omitted as appropriate.

[0110] The control unit CNT1 shown in Fig. 17 has a configuration in which the D flip-flop 26 is removed from the control unit CNT1 shown in Fig. 15. In the control unit CNT1 shown in Fig. 17, an AND gate 27 supplies the logical product of the periodic signal S1 and the output of the D flip-flop 30 to the set terminal (S terminal) of the RS flip-flop 24.

[0111] 17, when a zero-crossing point of the inductor current IL is detected after a pulse of the periodic signal S1, the control unit CNT1 enters the fourth state ST4 at the time when the next pulse of the periodic signal S1 occurs after the zero-crossing point of the inductor current IL is detected. This allows the switching frequency to be changed by a multiple of the frequency of the periodic signal S1 when the zero-crossing point of the inductor current IL is detected after the pulse of the periodic signal S1, i.e., in the case of a heavy load. In other words, the switching frequency can be made discrete and limited.

[0112] <<Modification of the Sixth Embodiment>> As described above, the switching power supply device according to the sixth embodiment is an improved version of the switching power supply device according to the first embodiment. However, similar improvements can also be made to the switching power supply devices according to the second to fifth embodiments. Furthermore, the switching power supply device according to the sixth embodiment can also be modified in the same way as the modifications described in the first to fifth embodiments.

[0113] Seventh Embodiment Each control unit CNT1 of the switching power supply devices according to the first to sixth embodiments described above keeps the length of the fourth state ST4 constant. Therefore, in the switching power supply devices according to the first to sixth embodiments, when the input voltage VIN fluctuates, the regenerative energy of the inductor current IL stored in the fourth state ST4 becomes insufficient for soft switching of the switch SW1. In other words, in the switching power supply devices according to the first to sixth embodiments, when the input voltage VIN fluctuates, the efficiency decreases.

[0114] The switching power supply device according to the seventh embodiment is a switching power supply device that can solve the above-mentioned problems of the switching power supply devices according to the first to sixth embodiments.

[0115] The switching power supply device according to the seventh embodiment is an improved version of the switching power supply device according to the first embodiment. Therefore, in the seventh embodiment, descriptions of the same configurations and operations as those in the first embodiment will be omitted.

[0116] The control unit CNT1 according to the seventh embodiment repeats the first state ST1, the second state ST2, the third state ST3, and the fourth state ST4 in a fixed cycle, so that the switching power supply device according to the seventh embodiment can fix the switching frequency.

[0117] The control unit CNT1 according to the seventh embodiment lengthens the length of the fourth state ST4 as the input voltage Vin increases. This prevents the switch voltage VSW from exceeding the input voltage Vin at the end of a dead time period DT, which will be described later, and prevents current from flowing from the inductor L1 to the terminal to which the input voltage Vin is applied via the parasitic diode of the first switch SW1. Therefore, the switching power supply according to the seventh embodiment can achieve high efficiency regardless of the value of the input voltage Vin.

[0118] The control unit CNT1 according to the seventh embodiment provides a dead time period DT between the fourth state ST4 and the first state ST1, during which the first switch SW1 and the second switch SW2 are turned off. The control unit CNT1 according to the seventh embodiment sets the length of the dead time period DT to a fixed value so that the first state ST starts at the zero-crossing point of the inductor current IL when there is no component variation, and also sets the length of the fourth state ST4 when the input voltage VIN is a constant value to a fixed value. This allows the switching power supply device according to the seventh embodiment to reduce losses when the first switch SW1 is turned on, thereby achieving even higher efficiency.

[0119] <<First Configuration Example of Control Unit According to Seventh Embodiment>> Fig. 19 is a diagram showing a first configuration example of a setting circuit according to the seventh embodiment, and Fig. 20 is a timing chart showing the operation of the setting circuit shown in Fig. 19.

[0120] A first configuration example of the control unit CNT1 according to the seventh embodiment includes a setting circuit shown in Fig. 19. The setting circuit shown in Fig. 19 includes a current source 41, a capacitor 42, a short-circuit switch 43, a voltage source 44, and a comparator 45.

[0121] The current source 41 outputs a current that is inversely proportional to the input voltage VIN.

[0122] The capacitor 42 is charged by the current source 41. While the capacitor 42 is charging, the charging voltage VCAP of the capacitor 42 increases at a slope inversely proportional to the input voltage VIN.

[0123] When the charging voltage VCAP of the capacitor 42 exceeds the constant voltage VC, the short-circuit switch 43 turns on, short-circuiting both ends of the capacitor 42 and discharging the capacitor 42.

[0124] The voltage source 44 outputs a constant voltage VC.

[0125] The comparator 45 outputs a voltage VST4 that is a result of comparing the capacitor charging voltage VCAP with the constant voltage VC. In the first configuration example of the control unit CNT1 according to the seventh embodiment, the period during which the voltage VST4 is at a high level is set to a fourth state.

[0126] <<Second Configuration Example of Control Unit According to Seventh Embodiment>> Fig. 21 is a diagram showing a second configuration example of the setting circuit according to the seventh embodiment, and Fig. 22 is a timing chart showing the operation of the setting circuit shown in Fig. 21.

[0127] A second configuration example of the control unit CNT1 according to the seventh embodiment includes a setting circuit shown in Fig. 21. The setting circuit shown in Fig. 21 includes a current source 41, a capacitor 42, a short-circuit switch 43, a voltage source 44, and a comparator 45.

[0128] The current source 41 outputs a constant current.

[0129] The capacitor 42 is charged by the current source 41. While the capacitor 42 is being charged, the charging voltage VCAP of the capacitor 42 increases at a constant slope.

[0130] When the charging voltage VCAP of the capacitor 42 exceeds the variable voltage VV, the short-circuit switch 43 turns on, short-circuiting both ends of the capacitor 42 and discharging the capacitor 42.

[0131] The voltage source 44 outputs a variable voltage VV that is proportional to the input voltage VIN.

[0132] The comparator 45 outputs a voltage VST4 that is a result of comparing the capacitor charging voltage VCAP with the variable voltage VV. In the second configuration example of the control unit CNT1 according to the seventh embodiment, the period during which the voltage VST4 is at a high level is set to a fourth state.

[0133] <<Modification of the Seventh Embodiment>> As described above, the switching power supply device according to the seventh embodiment is an improved version of the switching power supply device according to the first embodiment. However, similar improvements can also be made to the switching power supply devices according to the second to sixth embodiments. Furthermore, the switching power supply device according to the seventh embodiment can also be modified in the same way as the modifications described in the first to sixth embodiments.

[0134] Eighth Embodiment Each control unit CNT1 of the switching power supply devices according to the fifth to eighth embodiments described above sets the length of the dead time period DT to a fixed value. In the switching power supply devices according to the fifth to seventh embodiments, the length of the dead time period DT may deviate from the appropriate length due to variations in components, which may increase loss when the switch SW1 is turned on, resulting in reduced efficiency.

[0135] The switching power supply device according to the eighth embodiment is a switching power supply device that can solve the above-mentioned problems of the switching power supply devices according to the fifth to seventh embodiments.

[0136] The switching power supply device according to the eighth embodiment is an improved version of the switching power supply device according to the first embodiment. Therefore, in the eighth embodiment, the same configurations and operations as those in the first embodiment will not be described.

[0137] The control unit CNT1 according to the eighth embodiment repeats the first state ST1, the second state ST2, the third state ST3, and the fourth state ST4 in a fixed cycle, so that the switching power supply device according to the eighth embodiment can fix the switching frequency.

[0138] The control unit CNT1 according to the eighth embodiment provides a dead time period DT between the fourth state ST4 and the first state ST1, during which the first switch SW1 and the second switch SW2 are in the OFF state. The control unit CNT1 according to the eighth embodiment sets the length of the fourth state ST4 to a fixed value. The control unit CNT1 according to the eighth embodiment also adjusts the length of the dead time period. This allows the switching power supply device according to the eighth embodiment to reduce losses when the first switch SW1 is turned on even when there is variation in the characteristics of the components. Therefore, the switching power supply device according to the eighth embodiment can achieve even higher efficiency even when there is variation in the characteristics of the components.

[0139] <<First Configuration Example of Control Unit According to Eighth Embodiment>> Fig. 23 is a diagram showing a first configuration example of the control unit CNT1 according to the eighth embodiment. Fig. 24 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 23.

[0140] 23 includes a latch circuit 51, a delay circuit 52, a zero current switch delay circuit 53, a driver 54, a zero crossing point detection circuit 55, a latch circuit 56, and an up / down counter 57. In the configuration shown in FIG. 23, an RS flip-flop is used as an example of the latch circuit 51, and a D flip-flop is used as an example of the latch circuit 56. Therefore, in the following description, the latch circuit 51 will be described as the RS flip-flop 51, and the latch circuit 56 will be described as the D flip-flop 56.

[0141] The RS flip-flop 51 generates and outputs a signal LON2 that is set by a set signal SET supplied to a set terminal (S terminal) and reset by a reset signal RST supplied to a reset terminal (R terminal). In this configuration example, a periodic signal S1 is used as the set signal SET, and a PWM signal VPWM generated in the same manner as in the example shown in FIG. 9 is used as the reset signal RST.

[0142] The delay circuit 52 generates a delay signal LON2DLY that delays the rising edge of the signal LON2 by a predetermined time but does not delay the falling edge of the signal LON2. The predetermined time is the length of the fourth state ST4.

[0143] The zero-current switch delay circuit 53 generates the on-time setting voltage VON by delaying the delay signal LON2DLY by a variable time. The variable time is the length of the dead time period DT. The larger the count value of the up / down counter 57, the longer the variable time becomes.

[0144] The driver 54 controls the first switch SW1 and the second switch SW2 based on the on-time setting voltage VON.

[0145] The zero-crossing point detection circuit 55 detects the zero-crossing points of the inductor current IL and outputs a zero-crossing point detection signal ZX. The zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 55 becomes high level when the inductor current IL is negative, and becomes low level when the inductor current IL is not negative.

[0146] The D flip-flop 56 holds the zero-crossing point detection signal ZX in synchronization with the on-time setting voltage VON, and outputs an inverted signal of the held zero-crossing point detection signal ZX. The inverted signal of the zero-crossing point detection signal ZX held by the D flip-flop 56 is the signal ZCSCAL. A delay signal LON2DLY is supplied to the clear terminal of the D flip-flop 56. When the delay signal LON2DLY is at a low level, the D flip-flop 56 is cleared, and when the delay signal LON2DLY is at a high level, the D flip-flop 56 is not cleared.

[0147] The up / down counter 57 decrements the count value by one if the signal ZCSCAL is at a high level at the rising edge of the ON time setting voltage VON, and increments the count value by one if the signal ZCSCAL is at a low level at the rising edge of the ON time setting voltage VON.

[0148] The control unit CNT1 shown in Fig. 23 lengthens the length of the next dead time period DT if the inductor current IL is negative at the end of the dead time period DT, and shortens the length of the next dead time period DT if the inductor current IL is positive at the end of the dead time period DT. Therefore, the control unit CNT1 shown in Fig. 23 can bring the timing at which the first switch SW1 turns on closer to the zero-crossing point of the inductor current IL.

[0149] <<Second Configuration Example of Control Unit According to Eighth Embodiment>> Fig. 25 is a diagram showing a second configuration example of the control unit CNT1 according to the eighth embodiment. Fig. 26 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 25. Note that in this configuration example, descriptions of parts that are similar to those in the first configuration example will be omitted as appropriate.

[0150] 25 has a configuration in which the zero-crossing point detection circuit 55 is removed from the control unit CNT1 shown in Fig. 23, a voltage source 58 and a comparator 59 are added, and the signal ZCSCAL is replaced with a zero-crossing point detection signal ZX held by a D flip-flop 56. In the control unit CNT1 shown in Fig. 25, the comparator 59 compares the switch voltage VSW with the reference voltage VREF0 output from the voltage source 58 and supplies the result to the D terminal of the D flip-flop 56.

[0151] 25 increases the length of the next dead time period DT if the switch voltage VSW is smaller than the reference voltage VREF0 at the end of the dead time period DT, and decreases the length of the next dead time period DT if the switch voltage VSW is larger than the reference voltage VREF0 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in FIG. 25 can bring the timing at which the first switch SW1 turns on closer to the zero-crossing point of the inductor current IL.

[0152] <<Third Configuration Example of Control Unit According to Eighth Embodiment>> Fig. 27 is a diagram showing a third configuration example of the control unit CNT1 according to the eighth embodiment. Fig. 28 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 27.

[0153] 27 includes a latch circuit 51, a delay circuit 52, a driver 54, a zero-crossing point detection circuit 60, a NOT gate 61, a latch circuit 62, and an AND gate 63. In the configuration shown in FIG. 27, an RS flip-flop is used as an example of the latch circuit 51, and a D flip-flop is used as an example of the latch circuit 62. Therefore, in the following description, the latch circuit 51 will be described as the RS flip-flop 51, and the latch circuit 62 will be described as the D flip-flop 62.

[0154] The RS flip-flop 51 generates and outputs a signal LON2 that is set by a set signal SET supplied to a set terminal (S terminal) and reset by a reset signal RST supplied to a reset terminal (R terminal). In this configuration example, a periodic signal S1 is used as the set signal SET, and a PWM signal VPWM generated in the same manner as in the example shown in FIG. 9 is used as the reset signal RST.

[0155] The delay circuit 52 generates a delayed signal LON2DLY by delaying the signal LON2 by a predetermined time, which is the length of the fourth state ST4.

[0156] The zero-crossing point detection circuit 60 detects the zero-crossing points of the inductor current IL and outputs a zero-crossing point detection signal ZX. The zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 60 goes high when the inductor current IL is negative, and goes low when the inductor current IL is not negative.

[0157] The NOT gate 61 inverts the zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 60. The D flip-flop 62 holds the voltage VCC supplied to its D terminal in synchronization with the inverted signal of the zero-crossing point detection signal ZX, and outputs the held voltage VCC. The value of the voltage VCC supplied to the D terminal of the D flip-flop 62 is set to a value that is processed as a high-level signal by the AND gate 63.

[0158] The AND gate 63 generates an ON time setting voltage VON, which is the logical product of the delay signal LON2DLY and the output of the D flip-flop 62.

[0159] The driver 54 controls the first switch SW1 and the second switch SW2 based on the on-time setting voltage VON.

[0160] The control unit CNT1 shown in Fig. 27 starts the first state ST1 at the zero-cross point of the inductor current IL. Therefore, the control unit CNT1 shown in Fig. 27 can make the timing at which the first switch SW1 is turned on approximately coincide with the zero-cross point of the inductor current IL.

[0161] <<Modification of the Eighth Embodiment>> As described above, the switching power supply device according to the eighth embodiment is an improved version of the switching power supply device according to the first embodiment. However, similar improvements can also be made to the switching power supply devices according to the second to seventh embodiments. Furthermore, the switching power supply device according to the eighth embodiment can also be modified in the same way as the modifications described in the first to seventh embodiments.

[0162] Ninth Embodiment Each control unit CNT1 of the switching power supply devices according to the fifth, sixth, and eighth embodiments described above sets the length of the fourth state ST4 to a fixed value. Furthermore, in each control unit CNT1 of the switching power supply device according to the seventh embodiment described above, the length of the fourth state ST4 is constant unless the input voltage VIN fluctuates. Therefore, in the switching power supply devices according to the fifth to eighth embodiments, component variations can cause the length of the fourth state ST4 to deviate from the appropriate length, resulting in increased loss when the switch SW1 is turned on and reduced efficiency. In particular, if the length of the fourth state ST4 is too long and the regenerative energy stored in the inductor L1 in the fourth state ST4 becomes excessive, the switch voltage VSW at the end of the dead time period DT becomes greater than the input voltage VIN. When the switch voltage VSW at the end of the dead time period DT becomes greater than the input voltage VIN, a current flows from the inductor L1 to the terminal to which the input voltage VIN is applied via the parasitic diode of the first switch SW1, reducing efficiency.

[0163] The switching power supply device according to the ninth embodiment is a switching power supply device that can solve the above-mentioned problems of the switching power supply devices according to the fifth to eighth embodiments.

[0164] The switching power supply device according to the ninth embodiment is an improved version of the switching power supply device according to the first embodiment. Therefore, in the ninth embodiment, descriptions of the same configurations and operations as those in the first embodiment will be omitted.

[0165] The control unit CNT1 according to the ninth embodiment repeats the first state ST1, the second state ST2, the third state ST3, and the fourth state ST4 at a fixed cycle, so that the switching power supply device according to the ninth embodiment can fix the switching frequency.

[0166] The control unit CNT1 according to the ninth embodiment provides a dead time period DT, during which the first switch SW1 and the second switch SW2 are turned off, between the fourth state ST4 and the first state ST1. The control unit CNT1 according to the ninth embodiment sets the length of the dead time period DT to a fixed value. The control unit CNT1 according to the ninth embodiment also adjusts the length of the fourth state. This allows the switching power supply device according to the ninth embodiment to reduce losses when the first switch SW1 is turned on even when there is variation in the characteristics of the components. Therefore, the switching power supply device according to the ninth embodiment can achieve even higher efficiency even when there is variation in the characteristics of the components.

[0167] <<First Configuration Example of Control Unit According to Ninth Embodiment>> Fig. 29 is a diagram showing a first configuration example of the control unit CNT1 according to the 9th embodiment. Fig. 30 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 29.

[0168] 29 includes a latch circuit 71, a delay circuit 72, a zero current switch delay circuit 73, a driver 74, a voltage source 75, a comparator 76, a latch circuit 77, and an up / down counter 78. In the configuration shown in FIG. 29, an RS flip-flop is used as an example of the latch circuit 71, and a D flip-flop is used as an example of the latch circuit 77. Therefore, in the following description, the latch circuit 71 will be described as an RS flip-flop 71, and the latch circuit 77 will be described as a D flip-flop 77.

[0169] The RS flip-flop 71 generates and outputs a signal LON2 that is set by a set signal SET supplied to a set terminal (S terminal) and reset by a reset signal RST supplied to a reset terminal (R terminal). In this configuration example, a periodic signal S1 is used as the set signal SET, and a PWM signal VPWM generated in the same manner as in the example shown in FIG. 9 is used as the reset signal RST.

[0170] The delay circuit 72 generates a delayed signal LON2DLY by delaying the signal LON2 by a variable time. The variable time corresponds to the length of the fourth state ST4. The larger the count value of the up / down counter 78, the longer the variable time.

[0171] The zero current switch delay circuit 73 generates the on-time setting voltage VON by delaying the delay signal LON2DLY by a predetermined time, which is the length of the dead time period DT.

[0172] The driver 74 controls the first switch SW1 and the second switch SW2 based on the on-time setting voltage VON.

[0173] The voltage source 75 outputs a reference voltage VREF1.

[0174] The comparator 76 compares the switch voltage VSW with the reference voltage VREF1 and supplies the result to the D terminal of the D flip-flop 77.

[0175] The D flip-flop 77 holds the comparison result of the comparator 76 in synchronization with the on-time setting voltage VON, and outputs the comparison result of the comparator 76 that it has held. The comparison result of the comparator 76 that the D flip-flop 77 holds is the signal TchCAL. A delay signal LON2DLY is supplied to the clear terminal of the D flip-flop 77. When the delay signal LON2DLY is at a low level, the D flip-flop 77 is cleared, and when the delay signal LON2DLY is at a high level, the D flip-flop 77 is not cleared.

[0176] The up / down counter 78 decrements the count value by one if the signal TchCAL is at a high level at the rising edge of the ON time setting voltage VON, and increments the count value by one if the signal TchCAL is at a low level at the rising edge of the ON time setting voltage VON.

[0177] 29 increases the length of the fourth state ST4 if the switch voltage VSW is smaller than the reference voltage VREF1 at the end of the dead time period DT, and decreases the length of the fourth state ST4 if the switch voltage VSW is larger than the reference voltage VREF1 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in FIG. 29 can bring the switch voltage VSW closer to the reference voltage VREF1 at the timing when the first switch is turned on.

[0178] <<Second Configuration Example of Control Unit According to Ninth Embodiment>> Fig. 31 is a diagram showing a second configuration example of the control unit CNT1 according to the 9th embodiment. Fig. 32 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 31.

[0179] The control unit CNT1 shown in FIG. 31 has a configuration in which a zero-crossing point detection circuit 79 and a NOT gate 80 are added to the control unit CNT1 shown in FIG.

[0180] The zero-crossing point detection circuit 79 detects the zero-crossing points of the inductor current IL and outputs a zero-crossing point detection signal ZX. The zero-crossing point detection signal ZX output from the zero-crossing point detection circuit 79 is at a high level when the inductor current IL is negative, and is at a low level when the inductor current IL is not negative. The NOT gate 80 inverts the zero-crossing point detection signal ZX.

[0181] The D flip-flop 77 holds the comparison result of the comparator 76 in synchronization with the inversion of the zero-crossing point detection signal ZX, and outputs the comparison result of the comparator 76 that has been held.

[0182] The up / down counter 78 decrements the count value by one if the signal TchCAL is at a high level at the zero cross point of the inductor current IL, and increments the count value by one if the signal TchCAL is at a low level at the zero cross point of the inductor current IL.

[0183] The control unit CNT1 shown in Fig. 31 lengthens the length of the fourth state ST4 if the switch voltage VSW is smaller than the reference voltage VREF1 at the zero-crossing point of the inductor current IL, and shortens the length of the fourth state ST4 if the switch voltage VSW is larger than the reference voltage VREF1 at the zero-crossing point of the inductor current IL. Therefore, the control unit CNT1 shown in Fig. 31 can bring the switch voltage VSW closer to the reference voltage VREF1 at the timing when the first switch is turned on.

[0184] <<Third Configuration Example of Control Unit According to Ninth Embodiment>> Fig. 33 is a diagram showing a third configuration example of the control unit CNT1 according to the 9th embodiment. Fig. 34 is a timing chart showing the operation of the control unit CNT1 shown in Fig. 33.

[0185] The control unit CNT1 shown in Fig. 33 has a configuration in which a voltage source 81, a comparator 82, a latch circuit 83, an EXOR gate 84, and an AND gate 85 are added to the control unit CNT1 shown in Fig. 31. Note that in the configuration shown in Fig. 33, a D flip-flop is used as an example of the latch circuit 83. Therefore, in the following explanation, the latch circuit 83 will be explained as a D flip-flop 83.

[0186] The voltage source 81 outputs a reference voltage VREF2, which is greater than the reference voltage VREF1.

[0187] The comparator 82 compares the switch voltage VSW with the reference voltage VREF2 and supplies the result to the D terminal of the D flip-flop 83.

[0188] The D flip-flop 83 holds the comparison result of the comparator 82 in synchronization with the on-time setting voltage VON, and outputs the comparison result that has been held by the comparator 82. A delay signal LON2DLY is supplied to the clear terminal of the D flip-flop 83. When the delay signal LON2DLY is at a low level, the D flip-flop 83 is cleared, and when the delay signal LON2DLY is at a high level, the D flip-flop 83 is not cleared.

[0189] The EXOR gate 84 generates a signal ACTIVE, which is an inverted signal of the exclusive OR of the output of the D flip-flop 77 and the output of the D flip-flop 83 , and outputs the signal ACTIVE to the up / down counter 78 .

[0190] The AND gate 85 generates a signal DOWN, which is the logical product of the output of the D flip-flop 77 and the output of the D flip-flop 83 , and outputs the signal DOWN to the up-down counter 78 .

[0191] The up-down counter 78 does not count when the signal ACTIVE is low. The up-down counter 78 decrements its count by one when the signal ACTIVE is high and the signal DOWN is high at the rising edge of the on-time setting voltage VON. The up-down counter 78 increments its count by one when the signal ACTIVE is high and the signal DOWN is low at the rising edge of the on-time setting voltage VON. Note that in FIG. 34, when the up-down counter 78 increments its count by one, the signal DOWN appears to be high. However, because the first switch SW1 turns on slightly after the rising edge of the on-time setting voltage VON, the switch voltage VSW rises sharply slightly after the rising edge of the on-time setting voltage VON. Therefore, when the up-down counter 78 increments its count by one in FIG. 34, the switch voltage VSW is still less than the reference voltage VREF1, and the signal DOWN is low.

[0192] 33 increases the length of the fourth state ST4 if the switch voltage VSW is smaller than the reference voltage VREF1 at the end of the dead time period DT, and decreases the length of the fourth state ST4 if the switch voltage VSW is larger than the reference voltage VREF2 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in FIG. 33 can bring the switch voltage VSW at the timing when the first switch is turned on closer to the range of equal to or larger than the reference voltage VREF1 and equal to or smaller than the reference voltage VREF2.

[0193] <<Modification of the ninth embodiment>> As described above, the switching power supply device according to the ninth embodiment is an improved version of the switching power supply device according to the first embodiment. However, similar improvements can also be made to the switching power supply devices according to the second to eighth embodiments. Furthermore, the switching power supply device according to the ninth embodiment can also be modified in the same way as the modifications described in the first to eighth embodiments.

[0194] <Application> Next, we will explain an example of application of the previously explained switching power supply device 1. Fig. 35 is an external view showing an example of the configuration of a vehicle equipped with on-board devices. The vehicle X in this example is equipped with on-board devices X11 to X17 and a battery (not shown) that supplies power to these on-board devices X11 to X17.

[0195] When any of the switching power supply devices according to the first to ninth embodiments described above is mounted on a vehicle X, it is required to suppress radiation noise in the AM band so as not to adversely affect reception of AM radio broadcasts. Therefore, it is desirable that the switching control circuit 1 generates a voltage of 1.8 MHz or more and 2.1 MHz or less at the connection node between the first switch SW1 and the second switch SW2, at least when the load LD1 is in a normal load state. In other words, it is desirable that the switching control circuit 1 set the frequency of the switch voltage VSW (switching frequency) to 1.8 MHz or more and 2.1 MHz or less. This is because if the switching frequency is less than 1.8 MHz, radiation noise in the AM band increases, and if the switching frequency is greater than 2.1 MHz, switching loss exceeds the allowable range.

[0196] The in-vehicle device X11 is an engine control unit that performs engine-related controls (injection control, electronic throttle control, idling control, oxygen sensor heater control, auto-cruise control, etc.).

[0197] The in-vehicle device X12 is a lamp control unit that controls the turning on and off of HID (high intensity discharge lamp) and DRL (daytime running lamp).

[0198] The in-vehicle device X13 is a transmission control unit that performs control related to the transmission.

[0199] The in-vehicle device X14 is a body control unit that performs control related to the movement of the vehicle X (ABS [anti-lock brake system] control, EPS [electric power steering] control, electronic suspension control, etc.).

[0200] The in-vehicle device X15 is a security control unit that controls the operation of door locks, burglar alarms, etc.

[0201] The in-vehicle devices X16 are electronic devices that are installed in the vehicle X at the time of shipping from the factory as standard equipment or manufacturer options, such as wipers, power door mirrors, power windows, power sunroof, power seats, and air conditioners.

[0202] The in-vehicle device X17 is an electronic device that is installed in the vehicle X at the user's discretion, such as an in-vehicle A / V (audio / visual) device, a car navigation system, and an ETC (Electronic Toll Collection System).

[0203] Each of the switching power supply devices according to the first to ninth embodiments described above can be incorporated into any of the in-vehicle devices X11 to X17.

[0204] <Points to note> In addition to the above-described embodiments, various modifications can be made to the configuration of the present invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0205] For example, the set value of the fixed period Tfix may be changeable by changing the period of the periodic signal S1.

[0206] The switching power supply device (1A to 1D) according to one aspect described above is a switching power supply device configured to step down an input voltage to an output voltage, and includes a first switch (SW1) having a first end connectable to an application end of the input voltage and a second end connectable to a first end of an inductor (L1), a second switch (SW2) having a first end connectable to the first end of the inductor and a second end of the first switch and a second end connectable to an application end of a low voltage lower than the input voltage, and configured to control on / off of the first switch and the second switch. and a control unit (CNT1) that controls the input voltage, the control unit having a first state in which the first switch is in an on state and the second switch is in an off state, a second state in which the first switch is in an off state and the second switch is in an on state, a third state in which the first switch and the second switch are in an off state, and a fourth state in which a voltage at a connection node between the first switch and the second switch is lower than in the third state, the first state, the second state, the third state, and the fourth state are repeated, and the length of the fourth state is increased as the input voltage increases (first configuration).

[0207] The switching power supply device having the first configuration described above can achieve high efficiency regardless of the value of the input voltage.

[0208] In the switching power supply device having the above-mentioned first configuration, the control unit may be configured (second configuration) to repeat the first state, the second state, the third state, and the fourth state in the order of the first state, the second state, the third state, and the fourth state.

[0209] The switching power supply device having the second configuration can reduce the loss when the first switch is turned on.

[0210] In the switching power supply device having the above first or second configuration, the control unit may be configured to repeat the first state, the second state, the third state, and the fourth state at a fixed cycle (third configuration).

[0211] The switching power supply device having the third configuration can suppress fluctuations in the switching frequency.

[0212] In a switching power supply device having any of the above first to third configurations, the control unit may have a current source configured to output a current inversely proportional to the input voltage, and a capacitor configured to be charged by the current source, and may be configured (fourth configuration) to set the length of the fourth state based on the difference between the charging voltage of the capacitor and a constant voltage.

[0213] The switching power supply device having the fourth configuration described above can extend the length of the fourth state as the input voltage increases with a simple configuration.

[0214] In a switching power supply device having any of the above first to third configurations, the control unit may have a current source configured to output a constant current and a capacitor configured to be charged by the current source, and may be configured (fifth configuration) to set the length of the fourth state based on the difference between the charging voltage of the capacitor and a voltage proportional to the input voltage.

[0215] The switching power supply device having the fifth configuration described above can extend the length of the fourth state as the input voltage increases with a simple configuration.

[0216] In the switching power supply device having any of the above first to fifth configurations, the control unit may be configured (sixth configuration) to provide a dead time period between the fourth state and the first state, during which the first switch and the second switch are turned off, and to start the first state at a zero-cross point of the current flowing through the inductor.

[0217] The switching power supply device having the fourth configuration can reduce the loss when the first switch is turned on, thereby achieving even higher efficiency.

[0218] In the switching power supply device having any of the first to sixth configurations, the control unit may be configured to turn off the first switch and turn on the second switch in the fourth state (seventh configuration).

[0219] The switching power supply device having the seventh configuration can achieve the fourth state with simple control.

[0220] In a switching power supply device having any of the first to seventh configurations, the device may further include a third switch (SW3) that is configured to be connectable in parallel to the second switch and has at least one of an on-resistance and a capacitance smaller than that of the second switch, the control unit is configured to control the on / off of the third switch, and the control unit may be configured to turn the first switch off and the third switch on in the fourth state (eighth configuration).

[0221] The switching power supply device having the eighth configuration can reduce the loss in the fourth state.

[0222] A switching power supply device having any of the first to sixth configurations may further include a third switch (SW3) having a first end connectable to the first end of the inductor and the second end of the first switch, and a capacitance (C2) having a first end connected to the second end of the third switch and a second end connectable to the low voltage application end, wherein the control unit is configured to control the on / off of the third switch, and the control unit may be configured to turn the first switch off and the third switch on in the fourth state (ninth configuration).

[0223] The switching power supply device having the ninth configuration described above can adjust the rise of the voltage at the connection node between the first switch and the second switch immediately after the fourth state ends by adjusting the electrostatic capacitance value of the capacitor.

[0224] The switching power supply device of the ninth configuration may further include a fourth switch (SW4) that can be connected in parallel to the capacitance, the control unit configured to control the on / off of the fourth switch, and the control unit configured to control the on / off of the third switch and the on / off of the fourth switch complementarily (tenth configuration).

[0225] The switching power supply device having the tenth configuration can appropriately discharge the capacitance.

[0226] In a switching power supply device having any of the first to sixth configurations described above, the device may further include a capacitor (C2) having a first end connectable to a first end of the inductor and a second end of the first switch and a second end connectable to an application end of a variable voltage, the control unit configured to control the variable voltage, and the control unit turning off the first switch in the fourth state, and generating a potential difference between the first end and the second end of the capacitor by controlling the variable voltage (eleventh configuration).

[0227] The switching power supply device having the eleventh configuration described above can adjust the rise of the connection node voltage between the first switch and the second switch immediately after the fourth state ends by adjusting the value of the variable voltage in the fourth state.

[0228] The switching power supply device having any of the first to eleventh configurations may be configured (twelfth configuration) to generate a voltage of 1.8 MHz or more and 2.1 MHz or less at a connection node between the first switch and the second switch.

[0229] The switching power supply device having the twelfth configuration can suppress radiation noise in the AM band, and can keep switching loss within an allowable range.

[0230] The switch control device (CNT1) according to one aspect described above is a switch control device that controls the on / off of a first switch (SW1), which has a first terminal configured to be connectable to an application terminal of an input voltage and a second terminal configured to be connectable to a first terminal of an inductor (L1), and the on / off of a second switch (SW2), which has a first terminal configured to be connectable to a first terminal of the inductor and a second terminal of the first switch, and a second terminal configured to be connectable to an application terminal of a low voltage lower than the input voltage, and has a first state in which the first switch is in an on state and the second switch is in an off state, a second state in which the first switch is in an off state and the second switch is in an on state, a third state in which the first switch and the second switch are in an off state, and a fourth state in which the voltage of the connection node between the first switch and the second switch is lower than in the third state, and is configured to repeat the first state, the second state, the third state, and the fourth state, and the length of the fourth state is longer as the input voltage increases (thirteenth configuration).

[0231] The switch control device having the thirteenth configuration can achieve high efficiency regardless of the value of the input voltage.

[0232] The in-vehicle device (X11 to X17) according to one aspect described above has a configuration (fourteenth configuration) including the switching power supply device of any one of the first to twelfth configurations or the switch control device of the thirteenth configuration.

[0233] The switching power supply device or switch control device provided in the in-vehicle equipment having the fourteenth configuration can achieve high efficiency regardless of the value of the input voltage.

[0234] The vehicle (X) according to the above-described aspect has a configuration (15th configuration) including the on-vehicle device of the above-described 14th configuration and a battery that supplies power to the on-vehicle device.

[0235] The switching power supply device or switch control device provided in a vehicle having the fifteenth configuration can achieve high efficiency regardless of the value of the input voltage. [Explanation of symbols]

[0236] 1, 21 Error amplifier 2, 22 PWM comparator 3, 23, 27, 63, 82, 85 AND gates 4, 24, 51, 71 Latch circuit 5, 25, 54, 74 drivers 6 PFM Comparator 7 Selectors 8, 28, 52, 72 delay circuits 9, 29, 55, 60, 79 Zero cross point detection circuit 10, 26, 30, 56, 62, 77, 83 Latch circuit 31, 61, 80 NOT gates 41 Current source 42 Capacitor 43 Short-circuit switch 44, 58, 75, 80, 81 Voltage Source 45, 59, 76, 82 Comparators 53, 73 Zero current switch delay circuit 57, 78 Up / down counter 84 EXOR Gate 1A to 1D Switching power supply devices according to first to fourth embodiments C1 Output capacitor C2 capacity CNT1 control unit FB1 Output feedback section L1 inductor LD1 load SW1~SW4 1st to 4th switches X vehicle X11~X17 In-vehicle equipment

Claims

1. 1. A switching power supply configured to step down an input voltage to an output voltage, a first switch having a first end connectable to an application end of the input voltage and a second end connectable to a first end of an inductor; a second switch having a first end connectable to the first end of the inductor and the second end of the first switch, and a second end connectable to an application end of a low voltage lower than the input voltage; a control unit configured to control on / off of the first switch and the second switch; Equipped with The control unit a first state in which the first switch is in an on state and the second switch is in an off state; a second state in which the first switch is in an OFF state and the second switch is in an ON state; a third state in which the first switch and the second switch are turned off; a fourth state in which the voltage of the connection node between the first switch and the second switch is lower than that in the third state; and repeating the first state, the second state, the third state, and the fourth state; The switching power supply device is configured to increase the duration of the fourth state as the input voltage increases.

2. 2. The switching power supply device according to claim 1, wherein the control unit repeats the first state, the second state, the third state, and the fourth state in this order.

3. 3. The switching power supply device according to claim 1, wherein the control unit repeats the first state, the second state, the third state, and the fourth state at a fixed cycle.

4. The control unit a current source configured to output a current inversely proportional to the input voltage; a capacitor configured to be charged by the current source; and 4. The switching power supply device according to claim 1, wherein the length of the fourth state is set based on the difference between the charging voltage of the capacitor and a constant voltage.

5. The control unit a current source configured to output a constant current; a capacitor configured to be charged by the current source; and 4. The switching power supply device according to claim 1, wherein the length of the fourth state is set based on the difference between the charging voltage of the capacitor and the voltage proportional to the input voltage.

6. The control unit a dead time period during which the first switch and the second switch are in an OFF state is provided between the fourth state and the first state; 6. The switching power supply device according to claim 1, wherein the first state is initiated at a zero crossing point of a current flowing through the inductor.

7. 7. The switching power supply device according to claim 1, wherein the control unit, in the fourth state, turns the first switch off and turns the second switch on.

8. a third switch configured to be connectable in parallel to the second switch and having at least one of an on-resistance and a capacitance smaller than those of the second switch; the control unit is configured to control on / off of the third switch, 8. The switching power supply device according to claim 1, wherein the control unit, in the fourth state, turns the first switch off and turns the third switch on.

9. a third switch configured such that a first end thereof can be connected to the first end of the inductor and the second end of the first switch; a capacitor having a first terminal connected to the second terminal of the third switch and a second terminal connectable to the low voltage application terminal; Equipped with the control unit is configured to control on / off of the third switch, 7. The switching power supply device according to claim 1, wherein the control unit, in the fourth state, turns the first switch off and turns the third switch on.

10. a fourth switch configured to be connectable in parallel to the capacitor; the control unit is configured to control on / off of the fourth switch, 10. The switching power supply device according to claim 9, wherein the control unit controls the on / off of the third switch and the on / off of the fourth switch in a complementary manner.

11. a capacitor having a first end configured to be connectable to the first end of the inductor and the second end of the first switch, and a second end configured to be connectable to an application terminal of a variable voltage; the control unit is configured to control the variable voltage; 7. The switching power supply device according to claim 1, wherein the control unit turns off the first switch in the fourth state and generates a potential difference between the first end and the second end of the capacitance by controlling the variable voltage.

12. 12. The switching power supply device according to claim 1, wherein a voltage of 1.8 MHz or more and 2.1 MHz or less is generated at a connection node between the first switch and the second switch.

13. 1. A switch control device that controls on / off of a first switch, the first terminal of which is configured to be connectable to an application terminal of an input voltage and the second terminal of which is configured to be connectable to a first terminal of an inductor, and on / off of a second switch, the first terminal of which is configured to be connectable to the first terminal of the inductor and the second terminal of the first switch, and the second terminal of which is configured to be connectable to an application terminal of a low voltage lower than the input voltage, a first state in which the first switch is in an on state and the second switch is in an off state; a second state in which the first switch is in an OFF state and the second switch is in an ON state; a third state in which the first switch and the second switch are turned off; a fourth state in which the voltage of the connection node between the first switch and the second switch is lower than that in the third state; and repeating the first state, the second state, the third state, and the fourth state; The switch control device extends the period of the fourth state as the input voltage increases.

14. An in-vehicle device comprising the switching power supply device according to any one of claims 1 to 12 or the switch control device according to claim 13.

15. The in-vehicle device according to claim 14; a battery that supplies power to the in-vehicle device; A vehicle equipped with:

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