Switching power supplies, switch control devices, in-vehicle equipment, and vehicles

Abstract

A control unit of this switching power supply device includes a first state in which a first switch is turned on and a second switch is turned off, a second state in which the first switch is turned off and the second switch is turned on, a third state in which the first and second switches are turned off and a fourth state in which the voltage of a connection node of the first and second switches is lower than in the third state. The control unit repeats the first, second, third, and fourth states according to a periodic signal, and masks the periodic signal until the zero cross of the current flowing through the inductor is detected.

Description

Technical Field

[0006] ,

[0001] The invention disclosed in this specification relates to a switching power supply device, a switch control device, an in-vehicle device, and a vehicle that step down an input voltage to an output voltage.

Background Art

[0002] Conventionally, as a switching power supply device with high efficiency during light load, a switching power supply device with a fixed on-time control method is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A switching power supply device with a fixed on-time control method has a feature that the switching frequency varies according to the load state. When the switching frequency fluctuates, the frequency of the noise also fluctuates, so the effect of noise suppression means (such as a filter circuit) for suppressing noise with a fixed frequency may decrease. Therefore, it is desirable that the switching frequency of the switching power supply device used in an environment where noise is a problem be fixed as much as possible.

[0005] Also, when the load can be in a state within the normal range and a state heavier than within the normal range, normal switching control is required not only when the load is in a state within the normal range but also when the load is in a state heavier than within the normal range.

Means for Solving the Problems

[0006] The switching power supply disclosed herein is a switching power supply configured to step down an input voltage to an output voltage. The switching power supply comprises a first switch whose first end is connected to an input voltage application terminal and whose second end is connected to a first end of an inductor; a second switch whose first end is connected to a first end of the inductor and a second end of the first switch and whose second end is connected to an application terminal of a low voltage lower than the input voltage; and a control unit configured to control the on / off state of the first switch and the second switch. The control unit has a first state in which the first switch is turned on and the second switch is turned off; a second state in which the first switch is turned off and the second switch is turned on; a third state in which both the first and second switches are turned off; and a fourth state in which the voltage at the connection node between the first switch and the second switch is lower than in the third state. The control unit repeatedly cycles through the first, second, third, and fourth states based on the periodic signal, and masks the periodic signal until it detects a zero-crossing of the current flowing through the inductor.

[0007] A switch control device according to one embodiment disclosed herein controls the on / off switching of a first switch, the first end of which is configured to be connectable to an input voltage application terminal and the second end of which is configured to be connectable to a first end of an inductor, and the on / off switching of a second switch, the first end of which is configured to be connectable to a first end of the inductor and the second end of the first switch, and the second end of which is configured to be connectable to an application terminal of a low voltage lower than the input voltage. The switch control device has a first state in which the first switch is turned on and the second switch is turned off; a second state in which the first switch is turned off and the second switch is turned on; a third state in which both the first and second switches are turned off; and a fourth state in which the voltage at the connection node between the first switch and the second switch is lower than in the third state. The switch control device repeats the first, second, third, and fourth states based on a periodic signal and masks the periodic signal until it detects a zero-crossing of the current flowing through the inductor.

[0008] An in-vehicle device according to one embodiment disclosed herein comprises a switching power supply or a switch control device having the above configuration.

[0009] A vehicle according to one embodiment disclosed herein comprises the above-described in-vehicle equipment and a battery that supplies power to the in-vehicle equipment. [Effects of the Invention]

[0010] According to one embodiment of the invention disclosed herein, normal switching control is easily achieved and efficiency can be increased even when the load is heavier than the normal range. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the configuration of a switching power supply according to the first embodiment. [Figure 2]Figure 2 is a timing chart showing the operation of the switching power supply according to the first embodiment. [Figure 3] Figure 3 shows the configuration of a switching power supply according to the second embodiment. [Figure 4] Figure 4 is a time chart showing the operation of the switching power supply according to the second embodiment. [Figure 5] Figure 5 shows the configuration of a switching power supply according to the third embodiment. [Figure 6] Figure 6 is a timing chart showing the operation of the switching power supply according to the third embodiment. [Figure 7] Figure 7 shows the configuration of the switching power supply according to the fourth embodiment. [Figure 8] Figure 8 is a timing chart showing the operation of the switching power supply according to the fourth embodiment. [Figure 9] Figure 9 shows a first configuration example of the control unit according to the fifth embodiment. [Figure 10] Figure 10 is a timing chart showing the operation of the control unit shown in Figure 9. [Figure 11] Figure 11 shows a second configuration example of the control unit according to the fifth embodiment. [Figure 12] Figure 12 is a timing chart showing the operation of the control unit shown in Figure 11. [Figure 13] Figure 13 shows a third configuration example of the control unit according to the fifth embodiment. [Figure 14] Figure 14 is a timing chart showing the operation of the control unit shown in Figure 13. [Figure 15] Figure 15 shows a first configuration example of the control unit according to the sixth embodiment. [Figure 16] Figure 16 is a timing chart showing the operation of the control unit shown in Figure 15. [Figure 17] Figure 17 shows 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. 17. [Figure 19] FIG. 19 is a diagram showing a first configuration example of the 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. 19. [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. 21. [Figure 23] FIG. 23 is a diagram showing a first configuration example of the 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. 23. [Figure 25] FIG. 25 is a diagram showing 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. 25. [Figure 27] FIG. 27 is a diagram showing 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. 27. [[ID=…]] [Figure 29] FIG. 29 is a diagram showing a first configuration example of the 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. 29. [Figure 31] FIG. 31 is a diagram showing 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. 31. [Figure 33] FIG. 33 is a diagram showing 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. 33. [Figure 35]Figure 35 is an external view showing one example of the vehicle's configuration. [Modes for carrying out the invention]

[0012] In this specification, a MOS transistor refers to a transistor whose gate structure consists of at least three layers: a layer made of a conductor or a semiconductor such as polysilicon with 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 refers to a voltage that is constant under ideal conditions, and in reality, it is a voltage that may fluctuate slightly due to temperature changes, etc.

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

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

[0016] <First Embodiment> Figure 1 shows the configuration of a switching power supply according to the 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 the input voltage VIN to the output voltage VOUT, and comprises 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 conditions, or it may be configured to have a reverse current prevention function and operate in a discontinuous current mode under light load conditions.

[0017] The control unit CNT1 controls the on / off state 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 state of the first switch SW1 and the second switch SW2.

[0018] The first switch SW1 is configured such that its first terminal can be connected to the input voltage VIN application terminal, and its second terminal can be connected to the first terminal of inductor L1. The first switch SW1 conducts / blocks the current path from the input voltage VIN application terminal to inductor L1. For example, a P-channel MOS transistor or an N-channel MOS transistor can be used as the first switch SW1. For example, if an N-channel MOS transistor is used for the first switch SW1, a bootstrap circuit or the like should be provided in the switching power supply 1A to generate a voltage greater than the input voltage VIN.

[0019] The second switch SW2 is configured such that its first terminal can be connected to the first terminal of inductor L1 and the second terminal of the first switch SW1, and its second terminal can be connected to the terminal to which the ground potential is applied. The second switch SW2 conducts / blocks the current path from the terminal to which the ground potential is applied to inductor L1. For example, an N-channel MOS transistor can be used as the second switch SW2.

[0020] Switching between the first switch SW1 and the second switch SW2 generates a pulsed switch voltage VSW at the connection node between the first switch SW1 and the second switch SW2. Inductor L1 and output capacitor C1 smooth the pulsed switch voltage VSW to generate an output voltage VOUT, and supply this output voltage VOUT 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 unit FB1 generates and outputs a feedback signal corresponding to the output voltage VOUT. For example, the output feedback unit FB1 can be a resistive voltage divider circuit that generates a feedback signal by resistively dividing the output voltage VOUT. Alternatively, the output feedback unit FB1 may acquire the output voltage VOUT and output the output voltage VOUT itself as the feedback signal. Furthermore, the output feedback unit FB1 may also 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. By generating a feedback signal corresponding to the inductor current IL, current mode control becomes possible.

[0022] Figure 2 is a timing chart showing the operation of the switching power supply unit 1A. The control unit CNT1 sets the length of the first state ST1 according to 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 the input voltage VIN plus the forward voltage of the body diode of the first switch SW1, and then becomes approximately the same value as 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 is approximately the same as 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 terminates the second state ST2 and switches the control state from the second state ST2 to the third state ST3. A determination unit (not shown) that determines whether or not the inductor current IL has decreased to a predetermined value may be provided separately from the control unit CNT1 or may be built into the control unit CNT1. In this embodiment, the above 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 becomes high impedance, and the switch voltage VSW becomes approximately the same value as the output voltage VOUT. 3 Status ST 3 In this case, the inductor current IL becomes zero.

[0028] The periodic signal S1 is a signal that generates pulses with a fixed period Tfix. The periodic signal S1 may be a signal generated inside the control unit CNT1, or 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 terminates 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 off the first switch SW1 and turns on the second switch SW2. In the fourth state ST4, the switch voltage VSW is approximately the same as the ground potential GND. In the fourth state ST4, the inductor current IL flows from the application terminal of the output voltage VOUT toward 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 is regenerated. The regenerated energy of the inductor current IL is released when the system switches from the fourth state ST4 to the first state ST1, causing the switch voltage VSW to rise sharply when the system switches from the fourth state ST4 to the first state ST1.

[0031] When the pulse of the periodic signal S1 falls, the control unit CNT1 exits 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, second state ST2, third state ST3, and fourth state ST4 with a fixed period Tfix. It is desirable to include a dead time period between the first state ST1 and the second state ST2, and between the fourth state ST4 and the first state ST1, during which both the first switch SW1 and the second switch SW2 are in the off state. If a dead time period is included 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 will be equal to the sum of the dead time periods for the first state ST1, the dead time period between the first state ST1 and the second state ST2, the second state ST2, the third state ST3, the fourth state ST4, and the dead time period between the fourth state ST4 and the first state ST1.

[0033] Since the switching power supply 1A operates with a fixed period Tfix and has a configuration that does not cause losses in the third state ST3, it is possible to achieve high efficiency without changing the switching frequency. When the load LD1 is a light load, the length of the first state ST1 is shortened and the length of the third state ST3 is lengthened, so the switching power supply 1A can significantly improve its efficiency when the load LD1 is a light load.

[0034] As a variation of this embodiment, the second switch SW2 may be configured so that its second terminal is connected to a low voltage application terminal other than the input voltage VIN and the ground potential.

[0035] <Second Embodiment> In the second embodiment, the same configuration and operation as in the first embodiment will not be described. Figure 3 is a diagram showing the configuration of the switching power supply according to the second embodiment. The switching power supply 1B according to the second embodiment (hereinafter referred to as "switching power supply 1B") has a configuration in which a switch SW3 is added to the switching power supply 1A.

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

[0037] Switch SW3 has at least one of the following values ​​less on-resistance (resistance between the first and second terminals when in the ON state) and capacitance (parasitic capacitance between the first and second terminals) than switch SW2.

[0038] Figure 4 is a timing chart showing the operation of switching power supply unit 1B. The operation of switching power supply unit 1B differs from that of switching power supply unit 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, since switch SW3 has a smaller on-resistance and capacitance than switch SW2, the switching power supply 1B can reduce losses in the fourth state ST4 compared to the switching power supply 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 the third switch SW3 to the OFF state.

[0041] Since the switching power supply unit 1B operates with a fixed period Tfix and has a configuration that does not cause losses in the third state ST3, it is possible to achieve high efficiency without changing the switching frequency. When the load LD1 is a light load, the length of the first state ST1 is shortened and the length of the third state ST3 is lengthened, so the switching power supply unit 1B can significantly improve its efficiency when the load LD1 is a light load.

[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 variation 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 with a low voltage lower than the input voltage VIN and other than ground potential.

[0044] <Third Embodiment> In the third embodiment, the same configuration and operation as in the second embodiment will not be described. Figure 5 is a diagram showing the configuration of the switching power supply according to the third embodiment. The switching power supply 1C according to the third embodiment (hereinafter referred to as "switching power supply 1C") has a configuration in which a switch SW3, a capacitor C2, and a switch SW4 are added to the switching power supply 1A.

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

[0046] Switch SW3 has at least one of the on-resistance (resistance between the first and second terminals in the ON state) and capacitance (parasitic capacitance between the first and second terminals) that is smaller than that of switch SW2. However, unlike in this embodiment, switch SW3 may have the same on-resistance and capacitance as switch SW2.

[0047] Switch SW4 is a switch for discharging capacitor C2. When switch SW4 is turned ON, the terminals of capacitor C2 are short-circuited, causing capacitor C2 to discharge.

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

[0049] In switching power supply unit 1C, in the fourth state ST4, the switch voltage V SW divides the input voltage VIN by the parasitic capacitance between the first and second terminals of the first switch SW1, the parasitic capacitance between the first and second terminals of the third switch SW3, and capacitance C2. As a result, the switch voltage in the fourth state ST4 is determined by the capacitance value of capacitance C2. V The value of SW can be adjusted. In other words, the rise time of the switch voltage VSW when switching from the fourth state ST4 to the first state ST1 can be adjusted by the capacitance value of capacitor C2.

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

[0051] Since the switching power supply 1C operates with a fixed period Tfix and has a configuration that does not cause losses in the third state ST3, it is possible to achieve high efficiency without changing the switching frequency. When the load LD1 is a light load, the length of the first state ST1 is shortened and the length of the third state ST3 is lengthened, so the switching power supply 1C can significantly improve its efficiency when the load LD1 is a light load.

[0052] As a variation 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 with a low voltage lower than the input voltage VIN and other than ground potential.

[0053] <Fourth Embodiment> In the fourth embodiment, the same configuration and operation as in the third embodiment will not be described. Figure 7 is a diagram showing the configuration of the switching power supply according to the fourth embodiment. The switching power supply 1D according to the fourth embodiment (hereinafter referred to as "switching power supply 1D") has a configuration in which a capacity C2 is added to the switching power supply 1A.

[0054] The first terminal of 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 terminal of 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 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 voltage VA value in the fourth state ST4, it is possible to adjust the rise time of the switch voltage VSW when switching from the fourth state ST4 to the first state ST1.

[0056] Since the switching power supply 1D operates with a fixed period Tfix and has a configuration that does not cause losses in the third state ST3, it is possible to achieve high efficiency without changing the switching frequency. When the load LD1 is a light load, the length of the first state ST1 is shortened and the length of the third state ST3 is lengthened, so the switching power supply 1D can significantly improve its efficiency when the load LD1 is a light load.

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

[0058] <Fifth Embodiment> In the switching power supply devices according to the first to fourth embodiments described above, each control unit CNT1 shortens the length of the first state ST1 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 difficult to generate the control signal.

[0059] The switching power supply according to the fifth embodiment is a switching power supply that can solve the above-mentioned problems of the switching power supply 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. Therefore, in the fifth embodiment, the same configuration and operation as in the first embodiment will not be described.

[0061] In the fifth embodiment, the control unit CNT1 repeats the first state ST1, second state ST2, third state ST3, and 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 in the fifth embodiment can fix the switching frequency when the load LD1 is in the first range.

[0062] In the fifth embodiment, the control unit CNT1 repeats the first state ST1, second state ST2, third state ST3, and fourth state ST4 with a longer period as the load LD1 becomes lighter when it is in the second range (light load state), which is lighter than the first range. Therefore, the switching power supply device in the fifth embodiment suppresses the narrowing of the pulse width of the control signal for controlling the switch SW1 when the load LD1 is in the second range. In other words, in the switching power supply device in the fifth embodiment, normal switching control becomes easier 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, which turns off the first switch SW1 and the second switch SW2. 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 in the components. As a result, the switching power supply according to the fifth embodiment can reduce losses when the first switch SW1 is turned on, and thus achieve even higher efficiency.

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

[0065] The control unit CNT1 shown in Figure 9 comprises 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 Figure 9, an RS flip-flop is used as an example of latch circuit 4, and a D flip-flop is used as an example of latch circuit 10. Therefore, in the following description, latch circuit 4 will be described as RS flip-flop 4, and latch circuit 10 will be described as D flip-flop 10.

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

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

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

[0069] RS flip-flop 4 delays the signal supplied to the set terminal (S terminal) internally to generate a delay signal LON2DLY. RS flip-flop 4 then generates and outputs an on-time setting voltage VON, which is set by the delay signal LON2DLY and reset by the reset signal RST.

[0070] 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 that corresponds 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 VPFMOUT signal when the output voltage VOUT falls below a certain value.

[0072] Selector 7 selects either the periodic signal S1 or the signal VPFMOUT and supplies it to the set terminal (S terminal) of RS flip-flop 4. Selector 7 selects the periodic signal S1 when the light-load mode signal LCMMODE is at a low level. 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 delayed signal ONDLY by delaying the on-time setting voltage VON by a first predetermined time. The delay circuit 8 also generates a delayed 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 point 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 becomes high level when the inductor current IL decreases from positive to 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 Figure 9 determines that the load LD1 is in a light load state when the time from the start of the first state ST1 until the zero-crossing point of the inductor current IL is less than a certain value (second predetermined time).

[0077] The control unit CNT1 shown in Figure 9 uses the delay signal ONDLY to set the minimum time (first predetermined time) of 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 normal switching control even easier.

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

[0079] The control unit CNT1 shown in Figure 11 comprises an error amplifier 1, a PWM comparator 2, an RS flip-flop 4, a driver 5, a PFM comparator 6, and a selector 7.

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

[0081] Selector 7 selects the periodic signal S1 when the signal VPFMOUT is at a low level. Selector 7 selects the signal VPFMOUT when the signal VPFMOUT is at a high level.

[0082] The control unit CNT1 shown in Figure 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 the Control Unit According to the Fifth Embodiment>> Figure 13 shows a third configuration example of the control unit according to the fifth embodiment. Figure 14 is a timing chart showing the operation of the control unit shown in Figure 13. In this configuration example, explanations of parts that are the same as in the second configuration example will be omitted as appropriate.

[0084] The control unit CNT1 shown in Figure 13 has an AND gate 3 and a delay circuit 8 added to the control unit CNT1 shown in Figure 11.

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

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

[0087] The control unit CNT1 shown in Figure 13 uses the delay signal ONDLY to set the minimum time (first predetermined time) of 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 normal switching control even easier.

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

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

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

[0091] The switching power supply according to the sixth embodiment is an improved version of the switching power supply according to the first embodiment. Therefore, in the sixth embodiment, the same configuration and operation as in the first embodiment will not be described.

[0092] The control unit CNT1 according to the sixth embodiment repeats the first state ST1, second state ST2, third state ST3, and 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] In the sixth embodiment, the control unit CNT1 masks the periodic signal S1 until it detects the zero-crossing point of the inductor current IL. Therefore, the control unit CNT1 in the sixth embodiment operates independently of the periodic signal S1 when the load LD1 is in a heavy load state, which is heavier than the normal load state. As a result, in the switching power supply device of the sixth embodiment, normal switching control is easily achieved 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, which turns off the first switch SW1 and the second switch SW2. 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 in the components. As a result, the switching power supply according to the sixth embodiment can reduce losses when the first switch SW1 is turned on, and thus achieve even higher efficiency.

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

[0096] The control unit CNT1 shown in Figure 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 Figure 15, an RS flip-flop is used as an example of latch circuit 24, and D flip-flops are used as examples of latch circuits 26 and 30, respectively. Therefore, in the following description, latch circuit 24 will be described as an RS flip-flop 24, latch circuit 26 as a D flip-flop 26, and latch circuit 30 as a D flip-flop 30.

[0097] The error amplifier 21 outputs an error signal VERR corresponding 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, which is the result of comparing the error signal VERR with the ramp voltage VRAMP.

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

[0100] RS flip-flop 24 outputs the signal supplied to the set terminal (S terminal) to the RS flip-flop. 2 The delay signal LON2DLY is generated by delaying it internally in step 4. RS flip-flop 2 4 generates and outputs an on-time setting voltage VON, which is set by the delay 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] The D flip-flop 26 holds the voltage VCC supplied to its D terminal in synchronization with the periodic signal S1. The value of the voltage VCC supplied to the D terminal of the D flip-flop 26 is set to a value that is processed as a high-level signal in the AND gate 27. The D flip-flop 26 is cleared by the logic inversion signal of the on-time setting voltage VON output from the NOT gate 31.

[0103] The AND gate 27 supplies the logical AND 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 delayed 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 point 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 becomes high level when the inductor current IL decreases from positive to zero-crossing point.

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

[0107] The NOT gate 31 supplies a logic inversion signal of the on-time setting voltage VON to the clear terminals of the D flip-flops 26 and 30.

[0108] The control unit CNT1 shown in Figure 15 starts the fourth state ST1 when the zero-crossing point of the inductor current IL is detected after the pulse generation of the periodic signal S1. This allows the switching frequency to be changed according to the magnitude of the load when the zero-crossing point of the inductor current IL is detected after the pulse generation of the periodic signal S1, i.e., under heavy load conditions. In other words, it is possible to improve the load response under heavy load conditions.

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

[0110] The control unit CNT1 shown in Figure 17 has the same configuration as the control unit CNT1 shown in Figure 15, but with the D flip-flop 26 removed. In the control unit CNT1 shown in Figure 17, the AND gate 27 supplies the logical AND 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] The control unit CNT1 shown in Figure 17 starts the fourth state ST4 at the next pulse generation of the periodic signal S1, after the point at which the zero-crossing point of the inductor current IL is detected, if the zero-crossing point of the inductor current IL is detected after the pulse generation of the periodic signal S1. This allows the switching frequency to be varied in multiples of the frequency of the periodic signal S1, i.e., under heavy load conditions, when the zero-crossing point of the inductor current IL is detected after the pulse generation of the periodic signal S1. In other words, the switching frequency can be made discrete and limited.

[0112] <<Modification of the 6th Embodiment>> The switching power supply according to the sixth embodiment is an improved version of the switching power supply according to the first embodiment, as described above. However, similar improvements can also be made to the switching power supply according to the second to fifth embodiments. Furthermore, the switching power supply according to the sixth embodiment can be modified in the same way as the modified examples 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 the 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 according to the seventh embodiment is a switching power supply that can solve the above-mentioned problems of the switching power supply 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, the same configuration and operation as in the first embodiment will not be described.

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

[0117] In the seventh embodiment, the control unit CNT1 increases the length of the fourth state ST4 as the input voltage VIN increases. This prevents the switch voltage VSW from becoming larger than the input voltage VIN at the end of the dead time period DT (described later), thus preventing current from flowing from the inductor L1 through the parasitic diode of the first switch SW1 to the input voltage VIN application terminal. Therefore, the switching power supply device 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, which keeps the first switch SW1 and the second switch SW2 in the off state. 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 variation in the components, and also sets the length of the fourth state ST4 when the input voltage VIN is a constant value to a fixed value. As a result, the switching power supply according to the seventh embodiment can reduce losses when the first switch SW1 is turned on, and thus achieve even higher efficiency.

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

[0120] A first configuration example of the control unit CNT1 according to the seventh embodiment includes the setting circuit shown in Figure 19. The setting circuit shown in Figure 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] Capacitor 42 is charged by the current source 41. During the charging of capacitor 42, the charging voltage VCAP of capacitor 42 rises with a slope inversely proportional to the input voltage VIN.

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

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

[0125] The comparator 45 outputs a voltage VST4, which is the 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 defined as the fourth state.

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

[0127] A second configuration example of the control unit CNT1 according to the seventh embodiment includes the setting circuit shown in Figure 21. The setting circuit shown in Figure 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] Capacitor 42 is charged by the current source 41. During the charging of capacitor 42, the charging voltage VCAP of capacitor 42 rises at a constant rate.

[0130] The short-circuit switch 43 turns on when the charging voltage VCAP of capacitor 42 exceeds the variable voltage VV, short-circuiting the terminals of capacitor 42 and discharging 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, which is the 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 defined as the fourth state.

[0133] <<Modification of the 7th Embodiment>> The switching power supply according to the seventh embodiment is an improved version of the switching power supply according to the first embodiment, as described above. However, similar improvements can also be made to the switching power supply according to the second to sixth embodiments. Furthermore, the switching power supply according to the seventh embodiment can be modified in the same way as the modified examples described in the first to sixth embodiments.

[0134] <Eighth Embodiment> The 5th to 5th mentioned above 7 Each control unit CNT1 of the switching power supply according to the embodiment sets the length of the dead time period DT to a fixed value. In the switching power supply according to the 5th to 7th embodiments, variations in components may cause the length of the dead time period DT to deviate from an appropriate length, potentially leading to increased losses when the switch SW1 is turned on and a decrease in efficiency.

[0135] The switching power supply according to the eighth embodiment is a switching power supply that can solve the above-mentioned problems of the switching power supply 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 configuration and operation as in the first embodiment will not be described.

[0137] The control unit CNT1 according to the eighth embodiment repeats the first state ST1, second state ST2, third state ST3, and fourth state ST4 at a fixed period. Therefore, 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. As a result, the switching power supply according to the eighth embodiment can reduce losses when the first switch SW1 is turned on, even when there are variations in the characteristics of the components. Therefore, the switching power supply according to the eighth embodiment can achieve even higher efficiency even when there are variations in the characteristics of the components.

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

[0140] The control unit CNT1 shown in Figure 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 Figure 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 an RS flip-flop 51, and the latch circuit 56 will be described as a D flip-flop 56.

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

[0142] The delay circuit 52 generates a delayed signal LON2DLY, which delays the rising edge of signal LON2 by a predetermined time and does not delay the falling edge of signal LON2. The predetermined time is equal to the length of the fourth state ST4.

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

[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 point 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 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 low level, the D flip-flop 56 is cleared, and when the delay signal LON2DLY is 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 high at the rising edge of the on-time setting voltage VON, and increments the count value by one if the signal ZCSCAL is low at the rising edge of the on-time setting voltage VON.

[0148] The control unit CNT1 shown in Figure 23 lengthens 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 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 Figure 23 can bring the timing of the first switch SW1 turning on closer to the zero-crossing point of the inductor current IL.

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

[0150] The control unit CNT1 shown in Figure 25 is configured by removing the zero-crossing point detection circuit 55 from the control unit CNT1 shown in Figure 23, adding a voltage source 58 and a comparator 59, and setting the signal ZCSCAL as the zero-crossing point detection signal ZX held by the D flip-flop 56. In the control unit CNT1 shown in Figure 25, the comparator 59 supplies the result of comparing the switch voltage VSW with the reference voltage VREF0 output from the voltage source 58 to the D terminal of the D flip-flop 56.

[0151] The control unit CNT1 shown in Figure 25 lengthens the next dead time period DT if the switch voltage VSW is less than the reference voltage VREF0 at the end of the dead time period DT, and shortens the next dead time period DT if the switch voltage VSW is greater than the reference voltage VREF0 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in Figure 25 can bring the timing of the first switch SW1 turning on closer to the zero-crossing point of the inductor current IL.

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

[0153] The control unit CNT1 shown in Figure 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 Figure 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 an RS flip-flop 51, and the latch circuit 62 will be described as a D flip-flop 62.

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

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

[0156] The zero-crossing point detection circuit 60 detects the zero-crossing point 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 becomes high level when the inductor current IL is negative and low level 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 the 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 AND 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 Figure 27 starts the first state ST1 at the zero-crossing point of the inductor current IL. Therefore, the control unit CNT1 shown in Figure 27 can make the timing of the first switch SW1 turning on approximately coincide with the zero-crossing point of the inductor current IL.

[0161] <<Modification of the 8th Embodiment>> The switching power supply according to the eighth embodiment is an improved version of the switching power supply according to the first embodiment, as described above. However, similar improvements can also be made to the switching power supply according to the second to seventh embodiments. Furthermore, the switching power supply according to the eighth embodiment can be modified in the same way as the modified examples described in the first to seventh embodiments.

[0162] <Ninth Embodiment> In the switching power supply devices of the fifth, sixth, and eighth embodiments described above, each control unit CNT1 sets the length of the fourth state ST4 to a fixed value. In addition, in the switching power supply device of the seventh embodiment described above, each control unit CNT1 maintains a constant length of the fourth state ST4 unless the input voltage VIN fluctuates. Therefore, in the switching power supply devices of the fifth to eighth embodiments, variations in components may cause the length of the fourth state ST4 to deviate from the appropriate length, potentially leading to increased losses when the switch SW1 is turned on and a decrease in 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 will become 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, current flows from the inductor L1 through the parasitic diode of the first switch SW1 to the input voltage VIN application terminal, reducing efficiency.

[0163] The switching power supply according to the ninth embodiment is a switching power supply that can solve the above-mentioned problems of the switching power supply 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, the same configuration and operation as in the first embodiment will not be described.

[0165] The control unit CNT1 according to the ninth embodiment repeats the first state ST1, second state ST2, third state ST3, and fourth state ST4 at a fixed period. Therefore, 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 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 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. As a result, the switching power supply according to the ninth embodiment can reduce losses when the first switch SW1 is turned on, even when there are variations in the characteristics of the components. Therefore, the switching power supply according to the ninth embodiment can achieve even higher efficiency even when there are variations in the characteristics of the components.

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

[0168] The control unit CNT1 shown in Figure 29 comprises 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 Figure 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, which is set by the set signal SET supplied to the set terminal (S terminal) and reset by the reset signal RST supplied to the reset terminal (R terminal). In this configuration example, the periodic signal S1 is used as the set signal SET, and the PWM signal VPWM, generated by the same method as in the example shown in Figure 9, is used as the reset signal RST.

[0170] The delay circuit 72 generates a delayed signal LON2DLY by delaying the signal LON2 for a variable time. The variable time is equal to the length of the fourth state ST4. The variable time becomes longer as the count value of the up / down counter 78 increases.

[0171] The zero-current switch delay circuit 73 generates an on-time setting voltage VON by delaying the delay signal LON2DLY for a predetermined time. The predetermined time 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] Voltage source 75 outputs a reference voltage VREF1.

[0174] Comparator 76 supplies the comparison result between the switch voltage VSW and the reference voltage VREF1 to the D terminal of 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 held comparison result of the comparator 76. The comparison result of the comparator 76 held by the D flip-flop 77 is the signal TchCAL. The delay signal LON2DLY is supplied to the clear terminal of the D flip-flop 77. When the delay signal LON2DLY is low level, the D flip-flop 77 is cleared, and when the delay signal LON2DLY is 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 high at the rising edge of the on-time setting voltage VON, and increments the count value by one if the signal TchCAL is low at the rising edge of the on-time setting voltage VON.

[0177] The control unit CNT1 shown in Figure 29 lengthens the duration of the fourth state ST4 if the switch voltage VSW is less than the reference voltage VREF1 at the end of the dead time period DT, and shortens the duration of the fourth state ST4 if the switch voltage VSW is greater than the reference voltage VREF1 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in Figure 29 can bring the switch voltage VSW at the timing when the first switch turns on closer to the reference voltage VREF1.

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

[0179] The control unit CNT1 shown in Figure 31 has the same configuration as the control unit CNT1 shown in Figure 29, but with the addition of a zero-crossing point detection circuit 79 and a NOT gate 80.

[0180] The zero-crossing point detection circuit 79 detects the zero-crossing point 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 high level when the inductor current IL is negative and 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 held comparison result of the comparator 76.

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

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

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

[0185] The control unit CNT1 shown in Figure 33 is configured by adding a voltage source 81, a comparator 82, a latch circuit 83, an EXOR gate 84, and an AND gate 85 to the control unit CNT1 shown in Figure 31. In the configuration shown in Figure 33, a D flip-flop is used as an example of the latch circuit 83. Therefore, in the following description, the latch circuit 83 will be described as a D flip-flop 83.

[0186] Voltage source 81 outputs a reference voltage VREF2. Reference voltage VREF2 is greater than reference voltage VREF1.

[0187] Comparator 82 supplies the comparison result between the switch voltage VSW and the reference voltage VREF2 to the D terminal of 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 held comparison result of 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 low level, the D flip-flop 83 is cleared, and when the delay signal LON2DLY is high level, the D flip-flop 83 is not cleared.

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

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

[0191] The up / down counter 78 does not count when the signal ACTIVE is at a low level. Furthermore, the up / down counter 78 decrements the count value by one at the rising edge of the on-time setting voltage VON when both the signal ACTIVE and the signal DOWN are at a high level. Also, the up / down counter 78 increments the count value by one at the rising edge of the on-time setting voltage VON when both the signal ACTIVE and the signal DOWN are at a low level. Note that in Figure 34, at the timing when the up / down counter 78 increments the count value by one, it might appear that the signal DOWN is at a high level. However, since 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, at the timing when the up / down counter 78 increments the count value by one in Figure 34, the switch voltage VSW is still below the reference voltage VREF1, and the signal DOWN is at a low level.

[0192] The control unit CNT1 shown in Figure 33 lengthens the duration of the fourth state ST4 if the switch voltage VSW is less than the reference voltage VREF1 at the end of the dead time period DT, and shortens the duration of the fourth state ST4 if the switch voltage VSW is greater than the reference voltage VREF2 at the end of the dead time period DT. Therefore, the control unit CNT1 shown in Figure 33 can bring the switch voltage VSW at the timing when the first switch turns on closer to the range of reference voltage VREF1 or greater and reference voltage VREF2 or less.

[0193] <<Modification of the 9th Embodiment>> The switching power supply according to the ninth embodiment is an improved version of the switching power supply according to the first embodiment, as described above. However, similar improvements can also be made to the switching power supply according to the second to eighth embodiments. Furthermore, the switching power supply according to the ninth embodiment can be modified in the same way as the modified examples described in the first to eighth embodiments.

[0194] <Application> Next, we will describe some examples of applications for the switching power supply unit 1 described earlier. Figure 35 is an external view showing one example configuration of a vehicle equipped with in-vehicle equipment. In this example, vehicle X is equipped with in-vehicle equipment X11 to X17 and a battery (not shown) that supplies power to these in-vehicle equipment X11 to X17.

[0195] When any of the switching power supply devices described in the first to ninth categories above are installed in vehicle X, it is necessary to suppress radiated noise in the AM band so as not to adversely affect the reception of AM radio broadcasts. Therefore, it is desirable that the switching control circuit 1 generates a voltage of 1.8 MHz to 2.1 MHz 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 to 2.1 MHz. This is because if the switching frequency is less than 1.8 MHz, radiated noise in the AM band increases, and if the switching frequency is greater than 2.1 MHz, the switching loss exceeds the acceptable range.

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

[0197] The in-vehicle device X12 is a lamp control unit that controls the on / off state of lights such as HID (high-intensity discharged lamps) and DRL (daytime running lamps).

[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 motion of the vehicle X (such as ABS [anti-lock brake system] control, EPS [electric power steering] control, and electronic suspension control).

[0200] The X15 in-vehicle device is a security control unit that controls functions such as door locks and anti-theft alarms.

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

[0202] In-vehicle equipment X17 consists of electronic devices that are installed in vehicle X at the user's discretion, such as in-vehicle A / V (audio / visual) equipment, car navigation systems, and ETC (Electronic Toll Collection System).

[0203] Furthermore, each of the switching power supply devices described above (1st to 9th) can be incorporated into any of the in-vehicle devices X11 to X17.

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

[0205] For example, the fixed-period Tfix setting value may be changeable. The fixed-period Tfix setting value can be changed by changing the period of the periodic signal S1.

[0206] The switching power supply device (1A~1D) according to one embodiment described above is a switching power supply device configured to step down an input voltage to an output voltage, comprising: a first switch (SW1) whose first end is configured to be connectable to the input voltage application terminal and whose second end is configured to be connectable to the first end of an inductor (L1); a second switch (SW2) whose first end is configured to be connectable to the first end of the inductor and the second end of the first switch and whose second end is configured to be connectable to a low voltage application terminal lower than the input voltage; and a control unit (CNT1) configured to control the on / off state of the first switch and the second switch. The control unit comprises a first state in which the first switch is turned on and the second switch is turned off, a second state in which the first switch is turned off and the second switch is turned on, a third state in which both the first and second switches are turned off, and a fourth state in which the voltage at the connection node between the first and second switches is lower than in the third state. The control unit repeats the first, second, third, and fourth states based on a periodic signal and masks the periodic signal until it detects a zero-crossing point of the current flowing through the inductor. (First configuration)

[0207] The switching power supply device with the first configuration described above allows for easy and normal switching control even under heavy load conditions, and can achieve high efficiency.

[0208] In the switching power supply device having the first configuration described above, the control unit may be configured 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 (second configuration).

[0209] The switching power supply unit, which is the second configuration described above, can reduce losses when the first switch is turned on.

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

[0211] The switching power supply, which is the third configuration described above, can suppress fluctuations in the switching frequency.

[0212] In a switching power supply device having any of the first to third configurations described above, the control unit may be configured to start the fourth state (fourth configuration) when the zero-crossing point of the current flowing through the inductor is detected after the pulse generation of the periodic signal.

[0213] The switching power supply device, which is the fourth configuration described above, can change the switching frequency according to the magnitude of the load when the zero-crossing point of the current flowing through the inductor is detected after the generation of the pulse of the periodic signal, i.e., in the case of a heavy load.

[0214] In a switching power supply device having any of the first to third configurations described above, the control unit may be configured to start the fourth state (fifth configuration) at the time of the next pulse generation of the periodic signal, which is after the time of detection of the zero-crossing point of the current flowing through the inductor, if the zero-crossing point of the current flowing through the inductor is detected after the pulse generation of the periodic signal.

[0215] The fifth configuration described above, a switching power supply, can change the switching frequency by a multiple of the periodic signal frequency when the zero-crossing point of the current flowing through the inductor is detected after the pulse generation of the periodic signal, i.e., under heavy load conditions.

[0216] In a switching power supply device having any of the above configurations 1 to 5, the control unit may have a dead time period between the fourth state and the first state in which the first switch and the second switch are turned off, and may start the first state at the zero-crossing point of the current flowing through the inductor (sixth configuration).

[0217] The switching power supply unit, which is the sixth configuration described above, can reduce losses when the first switch is turned on, and thus can achieve even greater efficiency.

[0218] In a switching power supply device having any of the above configurations 1 to 6, the control unit may be configured to turn off the first switch and turn on the second switch in the fourth state (the seventh configuration).

[0219] The switching power supply, which is the seventh configuration described above, can achieve the fourth state with simple control.

[0220] In a switching power supply having any of the above configurations 1 to 7, a third switch (SW3) is provided which is configured to be connected in parallel to the second switch and which has at least one of the on-resistance and capacitance smaller than that of the second switch, the control unit is configured to control the on / off state of the third switch, and the control unit may be configured to turn the first switch to the off state and the third switch to the on state in the fourth state (the eighth configuration).

[0221] The eighth configuration of the switching power supply described above can reduce losses in the fourth state.

[0222] In a switching power supply device having any of the above configurations 1 to 6, the device includes a third switch (SW3) whose first terminal is configured to be connectable to the first terminal of the inductor and the second terminal of the first switch, and a capacitor (C2) whose first terminal is connected to the second terminal of the third switch and whose second terminal is connected to the low voltage application terminal, wherein the control unit is configured to control the on / off state 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 (the ninth configuration).

[0223] The switching power supply, which is the ninth configuration described above, can adjust the rise time of the connection node voltage between the first switch and the second switch immediately after the fourth state ends by adjusting the capacitance value of the capacity.

[0224] In the switching power supply device having the ninth configuration described above, a fourth switch (SW4) is provided that can be connected in parallel with the capacity, the control unit is configured to control the on / off state of the fourth switch, and the control unit may be configured to complementaryly control the on / off state of the third switch and the on / off state of the fourth switch (the tenth configuration).

[0225] The above 10 A switching power supply with this configuration can properly discharge its capacity.

[0226] In a switching power supply device having any of the above configurations 1 to 6, the device may include a capacitor (C2) whose first terminal is configured to be connectable to the first terminal of the inductor and the second terminal of the first switch, and whose second terminal is configured to be connectable to the terminal to which a variable voltage is applied, the control unit is configured to control the variable voltage, and the control unit may be configured to turn off the first switch in the fourth state and generate a potential difference between the first terminal and the second terminal of the capacitor by controlling the variable voltage (11th configuration).

[0227] The switching power supply in the 11th configuration described above can adjust the rise time of the connection node voltage between the first and second switches immediately after the fourth state ends by adjusting the value of the variable voltage in the fourth state.

[0228] In a switching power supply having any of the above configurations 1 to 11, a configuration (12th configuration) may be used in which a voltage of 1.8 MHz or more and 2.1 MHz or less is generated at the connection node between the first switch and the second switch.

[0229] The switching power supply with the 12th configuration described above can suppress radiated noise in the AM band. Furthermore, the switching power supply with the 12th configuration described above can keep switching losses within an acceptable range.

[0230] The switch control device (CNT1) according to one embodiment described above controls the on / off switching of a first switch (SW1), the first end of which is configured to be connectable to the input voltage application terminal and the second end of which is configured to be connectable to the first end of an inductor (L1), and the on / off switching of a second switch (SW2), the first end of which is configured to be connectable to the first end of the inductor and the second end of the first switch, and the second end of which is configured to be connectable to the application terminal of a low voltage lower than the input voltage, and has a first state in which the first switch is turned on and the second switch is turned off, a second state in which the first switch is turned off and the second switch is turned on, a third state in which both the first and second switches are turned off, and a fourth state in which the voltage at the connection node between the first switch and the second switch is lower than in the third state, and repeats the first, second, third, and fourth states based on a periodic signal, and masks the periodic signal until a zero-crossing point of the current flowing through the inductor is detected (13th configuration).

[0231] The switch control device, which has the 13th configuration described above, can easily perform normal switching control even under heavy load conditions, and can achieve high efficiency.

[0232] The in-vehicle equipment (X11 to X17) according to one embodiment described above is configured to include a switching power supply device with any of the 1st to 12th configurations described above, or a switch control device with the 13th configuration described above (14th configuration).

[0233] The switching power supply or switch control device installed in the in-vehicle equipment, as described in the 14th configuration above, allows for easy and efficient switching control even under heavy load conditions.

[0234] The vehicle (X) according to the above-described embodiment has a configuration (configuration 15) comprising the in-vehicle equipment of the configuration 14 described above and a battery that supplies power to the in-vehicle equipment.

[0235] The switching power supply or switch control device installed in the vehicle having the above-described configuration 15 allows for easy and efficient switching control even under heavy load conditions. [Explanation of Symbols]

[0236] 1.21 Error Amplifier 2.22 PWM Comparator 3, 23, 27, 63, 82, 85 AND gate 4, 24, 51, 71 Latch circuits 5, 25, 54, 74 drivers 6 PFM Comparator 7 Selector 8, 28, 52, 72 Delay Circuits 9, 29, 55, 60, 79 Zero-crossing point detection circuit 10, 26, 30, 56, 62, 77, 83 Latch circuits 31, 61, 80 NOT Gates 41 Current source 42 Capacitors 43 Short-circuit switch 44, 58, 75, 80, 81 Voltage sources 45, 59, 76, 82 Comparators 53, 73 Zero-current switch delay circuit 57, 78 Up / Down Counter 84 EXOR Gates 1A~1D Switching power supply according to the first to fourth embodiments C1 output capacitor C2 capacity CNT1 Control Unit FB1 Output Feedback Section L1 Inductor LD1 load SW1-SW4: Switches 1-4 X Vehicle X11~X17 In-vehicle equipment

Claims

1. A switching power supply device configured to step down the input voltage to an output voltage, A first switch, the first end of which is configured to be connectable to the input voltage application terminal and the second end of which is configured to be connectable to the first end of an inductor, A second switch whose first end is configured to be connectable to the first end of the inductor and the second end of the first switch, and whose second end is configured to be connectable to a low voltage application terminal lower than the input voltage, A control unit configured to control the on / off state of the first switch and the second switch, Equipped with, The control unit, A first state in which the first switch is turned ON and the second switch is turned OFF, A second state in which the first switch is in the OFF state and the second switch is in the ON state, A third state in which the first switch and the second switch are in the OFF state, A fourth state in which the voltage at the connection node between the first switch and the second switch is lower than that of the third state, It has, Based on the periodic signal, the first state, the second state, the third state, and the fourth state are repeated. A switching power supply device that masks the periodic signal until it detects the zero-crossing point of the current flowing through the inductor.

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

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 period based on the periodic signal.

4. The switching power supply device according to claim 1, wherein the control unit starts the fourth state when the zero-crossing point of the current flowing through the inductor is detected after the pulse generation of the periodic signal.

5. The switching power supply device according to claim 1, wherein the control unit, when it detects a zero-crossing point of the current flowing through the inductor after the generation of a pulse of the periodic signal, starts the fourth state at the time of the next pulse generation of the periodic signal, which is after the time of detection of the zero-crossing point of the current flowing through the inductor.

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

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

8. A third switch is provided, which is configured to be connected in parallel to the second switch and has at least one of its on-resistance and capacitance smaller than that of the second switch. The control unit is configured to control the on / off state of the third switch, The switching power supply device according to claim 1, wherein the control unit turns the first switch to the OFF state and the third switch to the ON state in the fourth state.

9. A third switch whose first end is configured to be connectable to the first end of the inductor and the second end of the first switch, A capacitor whose first end is connected to the second end of the third switch, and whose second end is configured to be connectable to the low voltage application terminal, Equipped with, The control unit is configured to control the on / off state of the third switch, The switching power supply device according to claim 1, wherein the control unit turns the first switch to the OFF state and the third switch to the ON state in the fourth state.

10. A fourth switch is provided that is configured to be connected in parallel to the aforementioned capacity, The control unit is configured to control the on / off state of the fourth switch, The switching power supply device according to claim 9, wherein the control unit complementarily controls the on / off state of the third switch and the on / off state of the fourth switch.

11. The capacitor has a first end that is configured to be connectable to the first end of the inductor and the second end of the first switch, and a second end that is configured to be connectable to the variable voltage application terminal. The control unit is configured to control the variable voltage, 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 and second ends of the capacitor by controlling the variable voltage.

12. The switching power supply device according to claim 1, wherein when the zero-crossing point of the current flowing through the inductor is detected before the pulse generation of the periodic signal, a voltage of 1.8 MHz or more and 2.1 MHz or less is generated at the connection node between the first switch and the second switch.

13. A switch control device for controlling the on / off state of a first switch, the first end of which is configured to be connectable to the input voltage application terminal and the second end of which is configured to be connectable to the first end of an inductor, and the on / off state of a second switch, the first end of which is configured to be connectable to the first end of the inductor and the second end of the first switch, the second end of which is configured to be connectable to the low voltage application terminal lower than the input voltage, A first state in which the first switch is turned ON and the second switch is turned OFF, A second state in which the first switch is in the OFF state and the second switch is in the ON state, A third state in which the first switch and the second switch are in the OFF state, A fourth state in which the voltage at the connection node between the first switch and the second switch is lower than that of the third state, It has, Based on the periodic signal, the first state, the second state, the third state, and the fourth state are repeated. A switch control device that masks the periodic signal until it detects the zero-crossing point of the current flowing through the inductor.

14. An in-vehicle device comprising a switching power supply device according to claim 1 or a switch control device according to claim 13.

15. The in-vehicle equipment described in claim 14, A battery that supplies power to the aforementioned in-vehicle equipment, A vehicle equipped with the following features.

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