Switching Power Supply Unit

Abstract

This switching power supply device is provided with: a first switch having a first end configured to connect to an input voltage application end and a second end configured to connect to a first end of an inductor; a second switch having a first end configured to connect to the first end of the inductor and a second end configured to connect to an application end of a voltage lower than the input voltage; a third switch having a first end configured to connect to the first end of the inductor and a second end configured to connect to a second end of the inductor; a detection unit which detects an occurrence of an output voltage overshoot or a predictor thereof; and a control unit which controls on / off of the first switch, the second switch, and the third switch. The control unit provides a control state in which the first switch and the second switch are placed in off-state and the third switch is placed in on-state in a period after an occurrence of the output voltage overshoot or a predictor thereof is detected by the detection unit and before the output voltage overshoot converges.

Description

[Technical field]

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

[0002] In a step-down switching power supply device that steps down an input voltage to an output voltage, an overshoot generally occurs in the output voltage when the output current decreases sharply. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 6,271,651 (column 5, lines 2-45) Summary of the Invention [Problem to be solved by the invention]

[0004] By increasing the capacitance of the output capacitor, it is possible to suppress the overshoot of the output voltage. However, increasing the capacitance of the output capacitor leads to an increase in the size and cost of the device. For this reason, a method is desired that can suppress the overshoot of the output voltage without increasing the capacitance of the output capacitor.

[0005] In the switching power supply device disclosed in Patent Document 1, undershoot and overshoot of the output voltage are suppressed by repeatedly switching on and off the short-circuit switch connected in parallel to the inductor, or by changing the on-resistance of the short-circuit switch connected in parallel to the inductor.

[0006] However, the switching power supply disclosed in Patent Document 1 has a problem in that, when suppressing an overshoot of the output voltage, both the short-circuit switch and the rectifier switch are turned on, causing a current to flow from the load to ground via the short-circuit switch and the rectifier switch, resulting in large losses.

[0007] Furthermore, a method that does not fluctuate the switching frequency is desirable as a method for suppressing output voltage overshoot without increasing the capacitance of the output capacitor, because fluctuations in the switching frequency also cause fluctuations in the noise frequency, which can reduce the effectiveness of noise suppression means (such as a filter circuit) that suppresses fixed-frequency noise. [Means for solving the problem]

[0008] The switching power supply device disclosed in this specification is a switching power supply device that steps down an input voltage to an output voltage, and includes: a first switch having a first end configured to be connectable to an application end of the input voltage and a second end configured to be connectable to a first end of an inductor; a second switch having a first end configured to be connectable to the first end of the inductor and a second end of the first switch and a second end configured to be connectable to an application end of a voltage lower than the input voltage; a third switch having a first end configured to be connectable to the first end of the inductor, the second end of the first switch, and the first end of the second switch and a second end configured to be connectable to the second end of the inductor; a detection unit that detects an occurrence or a sign of an overshoot of the output voltage; and a control unit that controls on / off of the first switch, the second switch, and the third switch, wherein the control unit is configured to provide a control state (first configuration) in which the first switch and the second switch are turned off and the third switch is turned on during the period from when the detection unit detects an occurrence or a sign of an overshoot of the output voltage to when the overshoot of the output voltage is converged.

[0009] In the switching power supply device of the above first configuration, the control unit may be configured (second configuration) to turn off the first switch and the second switch and turn on the third switch when the detection unit detects the occurrence of an overshoot or a sign of an overshoot in the output voltage.

[0010] In the switching power supply device of the above-mentioned second configuration, the detection unit may also detect the convergence of an overshoot of the output voltage, and the control unit may turn off the third switch when the detection unit detects the convergence of the overshoot of the output voltage (third configuration).

[0011] In the switching power supply device of the above first configuration, the detection unit may also detect the convergence of an overshoot of the output voltage, and the control unit may set the first switch to an off state when at least the third switch is in an on state during a period from when the detection unit detects the occurrence of an overshoot of the output voltage or a sign of an overshoot to when the detection unit detects the convergence of the overshoot of the output voltage, and set the second switch to an off state when at least the third switch is in an on state, thereby switching between the on state and the off state of the third switch at a fixed cycle (fourth configuration).

[0012] In the switching power supply device of the above fourth configuration, the off state period of the third switch may be a fixed period from when the detection unit detects the occurrence or sign of an overshoot in the output voltage until the detection unit detects the convergence of the overshoot in the output voltage (fifth configuration).

[0013] In the switching power supply device of the fifth configuration described above, a sixth configuration may be adopted in which the off state period of the third switch is equal to or less than 1 / 10 of the fixed period during a period from when the detection unit detects the occurrence of an overshoot or a sign of an overshoot in the output voltage until the detection unit detects the convergence of the overshoot in the output voltage.

[0014] In the switching power supply device having any of the above fourth to sixth configurations, a configuration (seventh configuration) may be used in which a voltage of 1.8 MHz or more and 2.1 MHz or less is generated at a connection node between the first switch and the second switch.

[0015] In the switching power supply device having any of the fourth to seventh configurations described above, the third switch may be configured (eighth configuration) to include a first switch element and a second switch element connected in series to each other.

[0016] In the switching power supply device of the eighth configuration described above, a configuration (ninth configuration) may be used in which, during an on-state period of the third switch, the first switch element and the second switch element are in an on-state, and, during an off-state period of the third switch, the first switch element is in an off-state and the second switch element is in an on-state.

[0017] The switching power supply device of the eighth or ninth configuration may further include a clamp section that clamps the voltage of a connection node between the first switch element and the second switch element within a predetermined range (tenth configuration).

[0018] The switch control device disclosed in the present specification is a switch control device that controls on / off of a first switch, the first end of which is configured to be connectable to an application end of an input voltage and the second end of which is configured to be connectable to a first end of an inductor, on / off 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 and the second end of which is configured to be connectable to an application end of a voltage lower than the input voltage, and on / off of a third switch, the first end of which is configured to be connectable to the first end of the inductor, the second end of the first switch, and the first end of the second switch and the second end of which is connectable to the second end of the inductor. an acquisition unit that acquires a detection result from a detection unit that detects an occurrence or a sign of an overshoot in the output voltage, and a suppression unit that controls on / off of the first switch, the second switch, and the third switch based on the detection result acquired by the acquisition unit, and sets a control state in which the first switch and the second switch are in an off state and the third switch is in an on state to suppress the overshoot in the output voltage during the period from when the detection unit detects an occurrence or a sign of an overshoot in the output voltage to when the overshoot in the output voltage converges (an eleventh configuration).

[0019] In the switch control device of the above 11th configuration, the suppression unit may be configured (12th configuration) to, when the detection unit detects the occurrence of an overshoot in the output voltage or a sign of such an overshoot, turn off the first switch and the second switch and turn on the third switch to suppress the overshoot in the output voltage.

[0020] In the switch control device of the twelfth configuration described above, the detection unit may also detect the convergence of an overshoot of the output voltage, and the suppression unit may be configured to turn off the third switch when the detection unit detects the convergence of the overshoot of the output voltage (thirteenth configuration).

[0021] In the switch control device of the 11th configuration, the detection unit may also detect the convergence of an overshoot of the output voltage, and the suppression unit may be configured to turn off the first switch when at least the third switch is in an on state and turn off the second switch when at least the third switch is in an on state during a period from when the detection unit detects the occurrence of an overshoot of the output voltage or a sign of an overshoot to when the detection unit detects the convergence of the overshoot of the output voltage, thereby switching between the on state and the off state of the third switch at a fixed cycle to suppress the overshoot of the output voltage (14th configuration).

[0022] In the switch control device of the above-mentioned 14th configuration, the off state period of the third switch may be a fixed period from when the detection unit detects the occurrence or sign of an overshoot in the output voltage to when the detection unit detects the convergence of the overshoot in the output voltage (15th configuration).

[0023] In the switch control device of the above-mentioned 15th configuration, the off state period of the third switch may be less than 1 / 10 of the fixed period during the period from when the detection unit detects the occurrence or sign of an overshoot in the output voltage to when the detection unit detects the convergence of the overshoot in the output voltage (16th configuration).

[0024] In the switch control device of any one of the fourteenth to sixteenth configurations, a configuration (seventeenth configuration) may be used in which a voltage of 1.8 MHz or more and 2.1 MHz or less is generated at a connection node between the first switch and the second switch.

[0025] In the switch control device of any one of the fourteenth to seventeenth configurations, the third switch may be configured to include a first switch element and a second switch element connected in series to each other (eighteenth configuration).

[0026] In the switch control device of the 18th configuration, the first switch element and the second switch element may be in an on state during an on state period of the third switch, and the first switch element is in an off state and the second switch element is in an on state during an off state period of the third switch (19th configuration).

[0027] The in-vehicle device disclosed in this specification has a configuration (20th configuration) including the switching power supply device having any one of the first to tenth configurations above or the switch control device having any one of the eleventh to nineteenth configurations above.

[0028] The vehicle disclosed in this specification has a configuration (21st configuration) including the on-vehicle device of the 20th configuration and a battery that supplies power to the on-vehicle device. Effect of the Invention

[0029] According to the invention disclosed in this specification, it is possible to suppress overshoot of the output voltage of a switching power supply device. [Brief description of the drawings]

[0030] [Figure 1A] FIG. 1 is a diagram showing a first configuration example of an asynchronous rectification type switching power supply device. [Figure 1B] FIG. 1 is a diagram showing a first configuration example of a synchronous rectification type switching power supply device. [Figure 1C] A diagram showing an example of the configuration of a third switch [Figure 1D] FIG. 13 shows another example of the configuration of the third switch. [Diagram 2] 1 is a timing chart showing a first operation example of a switching power supply device according to a first configuration example when an overshoot occurs in an output voltage; [Diagram 3] Diagram showing the state in which the inductor current is regenerated [Figure 4] Load current time chart [Diagram 5]10 is a timing chart showing a second operation example of the switching power supply device according to the first configuration example when an overshoot occurs in the output voltage; [Figure 6] Diagram showing the state in which the inductor current is regenerated [Figure 7] The diagram shows the inductor current flowing from ground through the body diode of the second switch to the inductor. [Figure 8] Output voltage and switch voltage waveforms [Figure 9] Diagram showing the state in which the inductor current is regenerated [Figure 10] A diagram showing the state in which the inductor current flows from the inductor through the body diode of the first switch toward the input voltage application terminal. [Figure 11] Output voltage and switch voltage waveforms [Figure 12A] FIG. 2 is a diagram showing a second configuration example of an asynchronous rectification type switching power supply device. [Figure 12B] FIG. 1 shows a second configuration example of a synchronous rectification type switching power supply device. [Figure 13] 11 is a timing chart showing an example of the operation of a switching power supply device according to a second configuration example when an overshoot occurs in the output voltage; [Figure 14] A diagram showing the state in which the inductor current is regenerated (first control pattern) [Figure 15] A diagram showing the state in which the inductor current flows from ground to the inductor via the body diode of the second switch (first control pattern). [Figure 16] Output voltage and switch voltage waveforms (first control pattern) [Figure 17] A diagram showing the state in which the inductor current is regenerated (first control pattern) [Figure 18] A diagram showing a state in which the inductor current flows from the inductor through the body diode of the first switch toward the input voltage application terminal (first control pattern). [Figure 19] Output voltage and switch voltage waveforms (first control pattern) [Figure 20]A diagram showing the state in which the inductor current is regenerated (second control pattern) [Figure 21] A diagram showing the state in which the inductor current flows from ground to the inductor via the body diode of the second switch (second control pattern). [Figure 22] Output voltage and switch voltage waveforms (second control pattern) [Figure 23] A diagram showing the state in which the inductor current is regenerated (second control pattern) [Figure 24] This diagram shows the state in which the inductor current flows from the inductor through the body diode of the first switch toward the input voltage application terminal (second control pattern). [Diagram 25] Output voltage and switch voltage waveforms (second control pattern) [Figure 26] A diagram showing the state in which the inductor current is regenerated (third control pattern) [Figure 27] A diagram showing the state in which the inductor current flows from ground to the inductor via the body diode of the second switch (third control pattern). [Figure 28] Output voltage and switch voltage waveforms (third control pattern) [Figure 29] A diagram showing the state in which the inductor current is regenerated (third control pattern) [Diagram 30] This diagram shows the state in which the inductor current flows from the inductor through the body diode of the first switch toward the input voltage application terminal (third control pattern). [Diagram 31] Output voltage and switch voltage waveforms (third control pattern) [Diagram 32] FIG. 1 is an external view showing an example of a vehicle configuration. [Diagram 33] FIG. 13 is a diagram showing a modification of the synchronous rectification type switching power supply device according to the second configuration example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] In this specification, a constant voltage means a voltage that is constant under ideal conditions, but in reality, it is a voltage that may fluctuate slightly due to temperature changes and the like.

[0032] In this specification, a MOS transistor refers to a field effect transistor whose gate structure is composed of at least three layers: "a layer made of a conductor or a semiconductor such as polysilicon with a low resistance value," "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 a metal, an oxide, and a semiconductor.

[0033] <First Configuration Example of Switching Power Supply> 1A and 1B are diagrams showing an example of the configuration of a switching power supply device. The switching power supply device 1 shown in Fig. 1A and 1B is a switching power supply device that steps down an input voltage VIN to an output voltage VOUT, and includes a control unit CNT1, first to third switches SW1 to SW3, an inductor L1, an output capacitor C1, an output feedback unit FB1, and a detection unit DET1.

[0034] The control unit CNT1 controls the on / off of the first to third switches SW1 to SW3 based on the outputs of the output feedback unit FB1 and the detection unit DET1. In other words, the control unit CNT1 is a switch control device that controls the on / off of the first to third switches SW1 to SW3. The control unit CNT1 controls the on / off of the first to third switches SW1 to SW3 based on the detection result of the detection unit DET1 acquired by the acquisition unit 2, and the first switch SW1, the second switch SW2, and the third switch SW3 based on the detection result of the detection unit DET1 acquired by the acquisition unit 2. 3 and a suppression unit 3 that controls the on / off of the output voltage VOUT to suppress overshoot.

[0035] For example, when the detection unit DET1 detects an occurrence of an overshoot in the output voltage VOUT, the suppression unit 3 turns the first switch SW1 and the second switch SW2 to an OFF state and turns the third switch SW3 to an ON state to suppress an overshoot in the output voltage VOUT. As another example, the suppression unit 3 turns the first switch SW1 and the second switch SW2 to an OFF state and switches the third switch SW3 between an ON state and an OFF state in a fixed cycle during a period from when the detection unit DET1 detects an occurrence of an overshoot in the output voltage VOUT to when the detection unit DET1 detects the convergence of the overshoot in the output voltage VOUT.

[0036] The acquisition unit 2 and the suppression unit 3 may each be realized by software, by a hardware circuit, or by a combination of software and hardware.

[0037] The first switch SW1 has a first terminal connectable to an application terminal of the input voltage VIN, and a second terminal connectable to a first terminal of the inductor L1. The first switch SW1 conducts / cuts off a current path from the application terminal of the input voltage VIN to the inductor L1. For example, a P-channel MOS transistor, an N-channel MOS transistor, or the like can be used as the first switch SW1. For example, when an N-channel MOS transistor is used as the first switch SW1, a bootstrap circuit or the like may be provided in the switching power supply device 1 to generate a voltage higher than the input voltage VIN. The on state of the first switch SW1 means that a current can flow from the first terminal to the second terminal of the first switch SW1 and also from the second terminal to the first terminal of the first switch SW1. The off state of the first switch SW1 means that a current cannot flow from the first terminal to the second terminal of the first switch SW1.

[0038] The second switch SW2 has a first end connectable to the first end of the inductor L1 and the second end of the first switch SW1, and a second end connectable to an application end of the ground potential. The second switch SW2 conducts / cuts off a current path from the application end of the ground potential to the inductor L1. Unlike this configuration example, the second switch SW2 may have a second end connectable to an application end of a voltage lower than the input voltage VIN and other than the ground potential. For example, a diode, an N-channel MOS transistor, or the like can be used as the second switch SW2. The on state of the second switch SW2 means that a current can flow from the first terminal to the second terminal of the second switch SW2 and also from the second terminal to the first terminal of the second switch SW2. The off state of the second switch SW2 means that a current cannot flow from the first terminal to the second terminal of the second switch SW2.

[0039] For example, when a diode is used for the second switch SW2, the switching power supply device 1 becomes the asynchronous rectification type switching power supply device shown in FIG. 1A.

[0040] When the switching power supply device 1 is an asynchronous rectification type switching power supply device, the control unit CNT1 controls the bias voltage applied to the switch SW2 (diode) by controlling the on / off of the switch SW1. Since the on / off of the switch SW2 (diode) is determined by the bias voltage applied to the switch SW2 (diode), the control unit CNT1 indirectly controls the on / off of the switch SW2 (diode).

[0041] For example, when an N-channel MOS transistor is used for the second switch SW2, the switching power supply device 1 becomes a synchronous rectification type switching power supply device as shown in Fig. 1B. When the switching power supply device 1 is a synchronous rectification type switching power supply device, the switching power supply device 1 may be configured to operate in a continuous current mode under light load, or may have a reverse current prevention function and operate in a discontinuous current mode under light load.

[0042] By switching the first switch SW1 and the second switch SW2, a pulsed switch voltage VSW is generated at the connection node between the first switch SW1 and the second switch SW2. The inductor L1 and the output capacitor C1 smooth the pulsed switch voltage VSW to generate an output voltage VOUT, and the output voltage VOUT is supplied to the application terminal of the output voltage VOUT. A load LD1 is connected to the application terminal of the output voltage VOUT, and the output voltage VOUT is supplied to the load LD1.

[0043] The third switch SW3 has a first end connectable to the first end of the inductor L1, the second end of the first switch SW1, and the first end of the second switch SW2, and a second end connectable to the second end of the inductor L1. In other words, the third switch SW3 is connected in parallel to the inductor L1. As the third switch SW3, for example, an N-channel MOS transistor or the like can be used. The third switch SW3 may be composed of a plurality of elements. As the third switch SW3 composed of a plurality of elements, for example, the third switch SW3 having two N-channel MOS transistors Q1 and Q2 with back gates commonly connected as shown in FIG. 1C, and the third switch having three N-channel MOS transistors Q3 to Q5 with back gates commonly connected as shown in FIG. 1D can be given. The on state of the third switch SW3 means that a current can flow from the first terminal to the second terminal of the third switch SW3 and also from the second terminal to the first terminal of the third switch SW3. The off state of the third switch SW3 means that at least one of the current cannot flow from the first terminal to the second terminal of the third switch SW3 and the current cannot flow from the second terminal to the first terminal of the third switch SW3.

[0044] The output feedback section FB1 generates and outputs a feedback signal corresponding to the output voltage VOUT. For example, a resistive voltage divider circuit that resistively divides the output voltage VOUT to generate a feedback signal can be used as the output feedback section FB1. For example, the output feedback section FB1 may be configured to obtain the output voltage VOUT and output the output voltage VOUT itself as a feedback signal. Note that the output feedback section FB1 may be configured to generate and output a feedback signal corresponding to a current flowing through the inductor L1 (hereinafter referred to as "inductor current IL") in addition to the feedback signal corresponding to the output voltage VOUT. Current mode control becomes possible when the output feedback section FB1 generates a feedback signal corresponding to the inductor current IL.

[0045] The detection unit DET1 detects the occurrence and convergence of an overshoot of the output voltage VOUT. As the detection unit DET1, for example, a comparator that inputs the output voltage VOUT to a non-inverting input terminal and inputs a constant voltage (a voltage larger than a target value of the output voltage VOUT) to an inverting input terminal can be used. When an overshoot of the output voltage VOUT occurs, the comparator switches the output signal from a low level to a high level. When the overshoot of the output voltage VOUT converges, the comparator switches the output signal from a high level to a low level. This exemplary output signal is illustrated in FIG. 2, which will be described later.

[0046] It is also possible to input a divided voltage of the output voltage VOUT to the non-inverting input terminal of the comparator instead of the output voltage VOUT, and to input a divided voltage of the constant voltage to the inverting input terminal of the comparator instead of the constant voltage.

[0047] In addition, by using a hysteresis comparator as the comparator or by providing a separate comparator for detecting the occurrence of an overshoot and a comparator for detecting the convergence of an overshoot, the value of the output voltage VOUT at the time when the occurrence of an overshoot is detected and the value of the output voltage VOUT at the time when the convergence of the overshoot is detected can be made different from each other.

[0048] In addition, the detection unit DET1 does not necessarily have to detect the convergence of the overshoot of the output voltage VOUT. For example, a counter may be provided in the control unit CNT1, and the control unit CNT1 may determine that the overshoot of the output voltage VOUT has converged when a certain time measured by the counter has elapsed since the detection unit DET1 detected the occurrence of an overshoot of the output voltage VOUT.

[0049] Unlike this configuration example, the detection unit DET1 may detect signs of an overshoot in the output voltage VOUT, and when the detection unit DET1 detects signs of an overshoot in the output voltage VOUT, the above-mentioned suppression unit 3 may turn off the first switch SW1 and the second switch SW2 and turn on the third switch SW3 to suppress the overshoot in the output voltage VOUT.

[0050] Also, unlike this configuration example, the detection unit DET1 may detect signs of an overshoot in the output voltage VOUT, and when the detection unit DET1 detects signs of an overshoot in the output voltage VOUT, the above-mentioned suppression unit 3 may turn off the first switch SW1 and the second switch SW2 and switch the third switch SW3 between the on and off states at a fixed period to suppress the overshoot in the output voltage VOUT.

[0051] As a method for detecting signs of an overshoot in the output voltage VOUT, for example, when the load LD1 is a load that fluctuates regularly and abruptly becomes a light load after a certain specific fluctuation pattern, it is sufficient to detect a fluctuation pattern of the load current that corresponds to the certain specific fluctuation pattern.

[0052] <First operation example of a switching power supply device when an overshoot occurs in the output voltage> FIG. 2 is a time chart showing a first operation example of the switching power supply device 1 when an overshoot occurs in the output voltage VOUT.

[0053] When the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT, the switching power supply device 1 is controlled to enter the second state STATE2 by the control of the control unit CNT1. Voltage V1 is a time chart in which the occurrence of an overshoot in the output voltage VOUT is detected by the detection unit DET1 during an on-duty period of SW, the output of the detection unit DET1 is switched from a low level to a high level, and the state of the switching power supply device 1 transitions from a first state STATE1 to a second state STATE2. In the first state STATE1, under the control of the control unit CNT1, the first switch SW1 is in the ON state, the second switch SW2 is in the OFF state, and the third switch SW3 is in the OFF state.

[0054] In the second state STATE2, the first switch SW1 is in the OFF state, the second switch SW2 is in the OFF state, and the third switch SW3 is in the ON state under the control of the control unit CNT1. When an overshoot occurs in the output voltage VOUT and the state of the switching power supply device 1 becomes the second state STATE2, the inductor current IL is regenerated in a closed circuit including the inductor L1 and the third switch SW3 as shown in FIG. 3. This makes it possible to cut off the current supply to the load LD1 side. In addition, in the second state STATE2, since the first switch SW1 and the second switch SW2 are in the OFF state, the output voltage VOUT can be clamped almost to the level at which the overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 to the OFF state and turning the third switch SW3 to the ON state when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further, and to suppress the overshoot of the output voltage VOUT.

[0055] Furthermore, for example, when the load current (the output current of the switching power supply device 1) sharply decreases and then sharply increases as shown in FIG. 4, the regenerative energy stored in the closed circuit including the inductor L1 and the third switch SW3 when the load current sharply increases can be released to the load LD1 side, thereby suppressing undershoot of the output voltage VOUT when the load current sharply increases.

[0056] In this operation example, the state of the switching power supply device 1 is maintained in the second state STATE2 until the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1. While the second state STATE2 is maintained, the inductor current IL gradually decreases due to the on-resistance of the third switch SW3. In FIG. 2, when the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1 and the output of the detection unit DET1 is switched from a high level to a low level, the state of the switching power supply device 1 transitions from the second state STATE2 to the first state STATE1, but this transition is merely an example. In other words, after the second state STATE2 ends, the state may transition to a state other than the first state STATE1.

[0057] In this operation example, the second state STATE2 is maintained without interruption from the occurrence of an overshoot of the output voltage VOUT to its convergence. However, unlike this operation example, if the overshoot of the output voltage VOUT can be suppressed, the second state STATE2 may be temporarily interrupted from the occurrence of an overshoot of the output voltage VOUT to its convergence, and the second state STATE2 may be terminated without waiting for the convergence of the overshoot of the output voltage VOUT.

[0058] <Second Operation Example of a Switching Power Supply Device When an Output Voltage Overshoot Occurs> FIG. 5 is a time chart showing a second operation example of the switching power supply device 1 when an overshoot occurs in the output voltage VOUT.

[0059] When the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT, the control unit CNT1 controls the switching power supply device 1 to enter the second state STATE 2. Fig. 5 is a time chart when the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT in the middle of the first state STATE1 (in the middle of the on-duty period of the switch voltage VSW), the output of the detection unit DET1 switches from a low level to a high level, and the state of the switching power supply device 1 transitions from the first state STATE1 to a second state STATE2.

[0060] In the first state STATE1, under the control of the control unit CNT1, the first switch SW1 and the second switch SW2 switch between the on state and the off state in a complementary manner at a fixed period Tfix based on the periodic signal S1, and the third switch SW3 is in the off state. The periodic signal S1 is a signal that generates a pulse at a fixed period Tfix. The periodic signal S1 may be a signal generated inside the control unit CNT1, or may be a signal generated outside the control unit CNT1 and acquired by the control unit CNT1. Note that, in switching between the on state and the off state of the first switch SW1 and the second switch SW2 in a complementary manner, it is desirable to provide a dead time period during which both the first switch SW1 and the second switch SW2 are in the off state.

[0061] In the second state STATE2, under the control of the control unit CNT1, the first switch SW1 is turned off, the second switch SW2 is turned off, and the third switch SW3 is switched between on and off at a fixed period Tfix. In the second state STATE2, the control unit CNT1 switches the third switch SW3 between on and off based on the periodic signal S1.

[0062] In the second state STATE2, two states, STATE2-1 and STATE2-2, are repeated at a fixed cycle Tfix. STATE2-1 is a period during which the third switch SW3 is in the ON state, and STATE2-2 is a period during which the third switch SW3 is in the OFF state.

[0063] In this operation example, the state of the switching power supply device 1 is maintained in the second state STATE2 until the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1. While the second state STATE2 is maintained, the inductor current IL gradually decreases due to the on-resistance of the third switch SW3. In FIG. 5, when the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1 and the output of the detection unit DET1 switches from a high level to a low level, the state of the switching power supply device 1 transitions from the second state STATE2 to a third state STATE3. In the third state STATE3, the first to third switches SW1 to SW3 are turned off under the control of the control unit CNT1.

[0064] When a pulse occurs in the periodic signal S1 in the third state STATE3, a transition occurs from the third state STATE3 to the first state STATE1.

[0065] The details of STATE2-1 and STATE2-2 will be described below by taking as an example a case where N-channel MOS transistors are used for the first to third switches SW1 to SW3. Note that, unlike this example, for example, bipolar transistors may be used for the first to third switches SW1 to SW3, and a "reverse-connected diode" may be connected in parallel to each bipolar transistor. The direction in which current flows in the "reverse-connected diode" (the direction from the anode to the cathode of the "reverse-connected diode") is opposite to the direction in which current flows in the bipolar transistor connected in parallel to the "reverse-connected diode".

[0066] First, the case where the inductor current IL flows in the positive direction will be described.

[0067] In state STATE2-1, as shown in FIG. 6, since the third switch SW3 is in the ON state, the inductor current IL is regenerated in a closed circuit including the inductor L1 and the third switch SW3, and the switch voltage VSW and the output voltage VOUT become substantially equal.

[0068] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 to the OFF state and turning the third switch SW3 to the ON state when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot in the output voltage VOUT.

[0069] In state STATE2-2, as shown in Figure 7, Since the N-channel MOS transistor Q1 is in the off state, the inductor current IL is regenerated in a closed circuit including the inductor L1 and the body diode of the third switch SW3. Therefore, the switch voltage VSW is VOUT-Vf SW3 In addition, Vf SW3 is the forward voltage of the body diode of the third switch SW3.

[0070] In this operation example, the period of each state STATE2-2 is a fixed period. Specifically, the period of each state STATE2-2 is a fixed period corresponding to the pulse width of the periodic signal S1. It is desirable that the period of each state STATE2-2 is 1 / 10 or less of the fixed period Tfix. This is because if the period of each state STATE2-2 is longer than 1 / 10 of the fixed period Tfix, the time required for the overshoot of the output voltage VOUT to converge exceeds the allowable range.

[0071] When the inductor current IL is positive, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 8. Note that, in terms of the vertical scale of the paper of FIG. 8, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 8, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not fluctuate, the frequency of the noise caused by the switching frequency does not fluctuate either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0072] Next, a case where the inductor current IL flows in the negative direction will be described.

[0073] In state STATE2-1, as shown in FIG. 9, since the third switch SW3 is in the ON state, the inductor current IL is regenerated in a closed circuit including the inductor L1 and the third switch SW3, and the switch voltage VSW and the output voltage VOUT become substantially equal.

[0074] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 to the OFF state and turning the third switch SW3 to the ON state when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot in the output voltage VOUT.

[0075] In state STATE2-2, as shown in FIG. 10, since the third switch SW3 is in the off state, the inductor current IL flows from the inductor L1 through the body diode of the first switch SW1 toward the application terminal of the input voltage VIN. Therefore, the switch voltage VSW is VIN+Vf SW1 In addition, Vf SW1 is the forward voltage of the body diode of the first switch SW1.

[0076] When the inductor current IL is negative, the second state STATE 2The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 11. Note that, in terms of the vertical scale of the paper of FIG. 11, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 11, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not fluctuate, the frequency of the noise caused by the switching frequency does not fluctuate either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0077] <Second Configuration Example of Switching Power Supply> 12A and 12B are diagrams showing a second configuration example of a switching power supply device. In addition, in FIG. 12A and FIG. 12B, the description of the same parts as in FIG. 1A and FIG. 1B is omitted as appropriate. The switching power supply device 11 shown in FIG. 12A and FIG. 12B is a switching power supply device that steps down an input voltage VIN to an output voltage VOUT, and includes a control unit CNT1, first to third switches SW1 to SW3, an inductor L1, an output capacitor C1, an output feedback unit FB1, and a detection unit DET1. In addition, the diodes in FIG. 12A and FIG. 12B are body diodes of MOS transistors. Similarly, the diodes in FIG. 14, FIG. 15, FIG. 17, FIG. 18, FIG. 20, FIG. 21, FIG. 23, FIG. 24, FIG. 26, FIG. 27, FIG. 29, FIG. 30, and FIG. 33 described later are also body diodes of MOS transistors.

[0078] In this configuration example, the suppression unit 3 controls the on / off of the first switch SW1, the second switch SW2, and the third switch SW based on the detection result of the detection unit DET1 acquired by the acquisition unit 2, and keeps the first switch SW1 and the second switch SW2 in the off state during the period from when the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT to when the detection unit DET1 detects the convergence of the overshoot in the output voltage VOUT, and switches the third switch SW3 between the on state and the off state at a fixed cycle to suppress the overshoot in the output voltage VOUT.

[0079] For example, when a diode is used for the second switch SW2, the switching power supply device 11 becomes an asynchronous rectification type switching power supply device shown in FIG. 12A.

[0080] When the switching power supply device 11 is an asynchronous rectification type switching power supply device, the control unit CNT1 controls the bias voltage applied to the switch SW2 (diode) by controlling the on / off of the switch SW1. Since the on / off of the switch SW2 (diode) is determined by the bias voltage applied to the switch SW2 (diode), the control unit CNT1 indirectly controls the on / off of the switch SW2 (diode).

[0081] For example, when an N-channel MOS transistor is used for the second switch SW2, the switching power supply device 11 becomes a synchronous rectification type switching power supply device as shown in Fig. 12B. When the switching power supply device 11 is a synchronous rectification type switching power supply device, the switching power supply device 11 may be configured to operate in a continuous current mode under light load, or may be configured to have a reverse current prevention function and operate in a discontinuous current mode under light load.

[0082] The third switch SW3 may be, for example, an N-channel MOS transistor, etc. The third switch SW3 includes a first switch element and a second switch element that are connected in series to each other. The on state of the first switch element is a state in which a current can flow from the first switch element to the second switch element, and a current can also flow from the second switch element to the first switch element. The off state of the first switch element is a state in which a current cannot flow from the first switch element to the second switch element. The on state of the second switch element is a state in which a current can flow from the first switch element to the second switch element, and a current can also flow from the second switch element to the first switch element. The off state of the second switch element is a state in which a current cannot flow from the second switch element to the first switch element.In the configuration example shown in FIG. 1A and FIG. 1B, two N-channel MOS transistors Q1 and Q2 are used as the first switch element and the second switch element. The drain of the N-channel MOS transistor Q1 is connected to the connection node between the first switch SW1 and the second switch SW2. The source and back gate of the N-channel MOS transistor Q1 are connected to the source and back gate of the N-channel MOS transistor Q2. The drain of the N-channel MOS transistor Q2 is connected to the connection node between the inductor L1 and the output capacitor C1. Since the N-channel MOS transistor Q1 is provided on the input side and the N-channel MOS transistor Q2 is provided on the output side, it is preferable that the N-channel MOS transistor Q1 is a transistor with a higher withstand voltage than the N-channel MOS transistor Q2.

[0083] The detection unit DET1 detects the occurrence and convergence of an overshoot of the output voltage VOUT. As the detection unit DET1, for example, a comparator that inputs the output voltage VOUT to a non-inverting input terminal and inputs a constant voltage (a voltage larger than a target value of the output voltage VOUT) to an inverting input terminal can be used. When an overshoot of the output voltage VOUT occurs, the comparator switches the output signal from a low level to a high level. When the overshoot of the output voltage VOUT converges, the comparator switches the output signal from a high level to a low level. This exemplary output signal is illustrated in FIG. 13 described later.

[0084] It is also possible to input a divided voltage of the output voltage VOUT to the non-inverting input terminal of the comparator instead of the output voltage VOUT, and to input a divided voltage of the constant voltage to the inverting input terminal of the comparator instead of the constant voltage.

[0085] In addition, by using a hysteresis comparator as the comparator or by providing a separate comparator for detecting the occurrence of an overshoot and a comparator for detecting the convergence of an overshoot, the value of the output voltage VOUT at the time when the occurrence of an overshoot is detected and the value of the output voltage VOUT at the time when the convergence of the overshoot is detected can be made different from each other.

[0086] Unlike this configuration example, the detection unit DET1 may detect signs of an overshoot in the output voltage VOUT, and when the detection unit DET1 detects signs of an overshoot in the output voltage VOUT, the above-mentioned suppression unit 3 may turn off the first switch SW1 and the second switch SW2 and switch the third switch SW3 between the on and off states at a fixed period to suppress the overshoot in the output voltage VOUT.

[0087] As a method for detecting signs of an overshoot in the output voltage VOUT, for example, when the load LD1 is a load that fluctuates regularly and abruptly becomes a light load after a certain specific fluctuation pattern, it is sufficient to detect a fluctuation pattern of the load current that corresponds to the certain specific fluctuation pattern.

[0088] <Example of switching power supply operation when output voltage overshoot occurs> FIG. 13 is a time chart showing the operation of the switching power supply device 11 when an overshoot occurs in the output voltage VOUT.

[0089] When the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT, the control unit CNT1 controls the switching power supply device 11 to enter the second state STATE 2. Fig. 13 is a time chart when the detection unit DET1 detects the occurrence of an overshoot in the output voltage VOUT in the middle of the first state STATE1 (in the middle of the on-duty period of the switch voltage VSW), the output of the detection unit DET1 switches from a low level to a high level, and the state of the switching power supply device 11 transitions from the first state STATE1 to the second state STATE2.

[0090] In the first state STATE1, under the control of the control unit CNT1, the first switch SW1 and the second switch SW2 switch between the on state and the off state in a complementary manner at a fixed period Tfix based on the periodic signal S1, and the third switch SW3 is in the off state. The periodic signal S1 is a signal that generates a pulse at a fixed period Tfix. The periodic signal S1 may be a signal generated inside the control unit CNT1, or may be a signal generated outside the control unit CNT1 and acquired by the control unit CNT1. Note that, in switching between the on state and the off state of the first switch SW1 and the second switch SW2 in a complementary manner, it is desirable to provide a dead time period during which both the first switch SW1 and the second switch SW2 are in the off state.

[0091] In the second state STATE2, under the control of the control unit CNT1, the first switch SW1 is turned off, the second switch SW2 is turned off, and the third switch SW3 is switched between on and off at a fixed period Tfix. In the second state STATE2, the control unit CNT1 switches the third switch SW3 between on and off based on the periodic signal S1.

[0092] In the second state STATE2, two states, STATE2-1 and STATE2-2, are repeated at a fixed cycle Tfix. STATE2-1 is a period during which the third switch SW3 is in the ON state, and STATE2-2 is a period during which the third switch SW3 is in the OFF state.

[0093] In this operation example, the state of the switching power supply device 11 is maintained in the second state STATE2 until the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1. While the second state STATE2 is maintained, the inductor current IL gradually decreases due to the on-resistance of the third switch SW3. In FIG. 13, when the convergence of the overshoot of the output voltage VOUT is detected by the detection unit DET1 and the output of the detection unit DET1 is switched from a high level to a low level, the state of the switching power supply device 11 transitions from the second state STATE2 to a third state STATE3. In the third state STATE3, the first to third switches SW1 to SW3 are turned off under the control of the control unit CNT1.

[0094] When a pulse occurs in the periodic signal S1 in the third state STATE3, a transition occurs from the third state STATE3 to the first state STATE1.

[0095] Below, the details of states STATE2-1 and STATE2-2 will be explained for three control patterns, taking as an example a case where N-channel MOS transistors are used for the first switch SW1 and the second switch SW2. Note that, unlike this example, for example, bipolar transistors may be used for the first switch SW1 and the second switch SW2, and a "reverse-connected diode" may be connected in parallel to each bipolar transistor. The direction in which the current flows in the "reverse-connected diode" (the direction from the anode to the cathode of the "reverse-connected diode") is opposite to the direction in which the current flows in the bipolar transistor connected in parallel to the "reverse-connected diode". Similarly, bipolar transistors may be used instead of the N-channel MOS transistors Q1 and Q2, and a "reverse-connected diode" may be connected in parallel to each bipolar transistor.

[0096] <First control pattern> First, the case where the inductor current IL flows in the positive direction will be described.

[0097] In state STATE2-1, as shown in FIG. 14, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0098] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0099] In state STATE2-2, as shown in FIG. 15, since the N-channel MOS transistor Q1 is in the off state, the inductor current IL is regenerated in a closed circuit including the inductor L1, the body diode of the N-channel MOS transistor Q1, and the N-channel MOS transistor Q2. Therefore, the switch voltage VSW is VOUT-Vf Q1 In addition, Vf Q1 is the forward voltage of the body diode of N-channel MOS transistor Q1.

[0100] In this operation example, the period of each state STATE2-2 is a fixed period. Specifically, the period of each state STATE2-2 is a fixed period corresponding to the pulse width of the periodic signal S1. It is desirable that the period of each state STATE2-2 is 1 / 10 or less of the fixed period Tfix. This is because if the period of each state STATE2-2 is longer than 1 / 10 of the fixed period Tfix, the time required for the overshoot of the output voltage VOUT to converge exceeds the allowable range.

[0101] When the inductor current IL is positive, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 16. Note that, in terms of the vertical scale of the paper of FIG. 16, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 16, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not fluctuate, the frequency of the noise caused by the switching frequency does not fluctuate either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0102] Next, a case where the inductor current IL flows in the negative direction will be described.

[0103] In state STATE2-1, as shown in FIG. 17, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0104] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0105] In state STATE2-2, as shown in FIG. 18, since the N-channel MOS transistor Q1 is in the off state, the inductor current IL flows from the inductor L1 to the application terminal of the input voltage VIN via the body diode of the first switch SW1. Therefore, the switch voltage VSW is VIN+Vf SW1 In addition, Vf SW1 is the forward voltage of the body diode of the first switch SW1.

[0106] When the inductor current IL is negative, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 19. Note that, in terms of the vertical scale of the paper of FIG. 19, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 19, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not fluctuate, the frequency of the noise caused by the switching frequency does not fluctuate either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0107] <Second control pattern> First, the case where the inductor current IL flows in the positive direction will be described.

[0108] In state STATE2-1, as shown in FIG. 20, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0109] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0110] In state STATE2-2, as shown in FIG. 21, since the N-channel MOS transistor Q2 is in the off state, the inductor current IL flows from the ground to the inductor L1 via the body diode of the second switch SW2. Therefore, the switch voltage VSW is −Vf SW2 In addition, Vf SW2 is the forward voltage of the body diode of the second switch SW2.

[0111] When the inductor current IL is positive, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 22. Note that, in terms of the vertical scale of the paper of FIG. 22, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 22, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not vary, the frequency of the noise caused by the switching frequency does not vary either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0112] Next, a case where the inductor current IL flows in the negative direction will be described.

[0113] In state STATE2-1, as shown in FIG. 23, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0114] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0115] In state STATE2-2, as shown in FIG. 24, since the N-channel MOS transistor Q2 is in the off state, the inductor current IL is regenerated in a closed circuit including the inductor L1, the N-channel MOS transistor Q1, and the body diode of the N-channel MOS transistor Q2. Therefore, the switch voltage VSW is VOUT+Vf Q2 In addition, Vf Q2 is the forward voltage of the body diode of N-channel MOS transistor Q2.

[0116] When the inductor current IL is negative, the second state STATE 2The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 25. Note that, in terms of the vertical scale of the paper of FIG. 25, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 25, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not vary, the frequency of the noise caused by the switching frequency does not vary either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0117] <Third control pattern> First, the case where the inductor current IL flows in the positive direction will be described.

[0118] In state STATE2-1, as shown in FIG. 26, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0119] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0120] In state STATE2-2, as shown in FIG. 27, since the N-channel MOS transistors Q1 and Q2 are in the off state, the inductor current IL flows from the ground to the inductor L1 via the body diode of the second switch SW2. Therefore, the switch voltage VSW is −VfSW2 become.

[0121] When the inductor current IL is positive, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 28. Note that, in terms of the vertical scale of the paper of FIG. 28, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 28, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not vary, the frequency of the noise caused by the switching frequency does not vary either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0122] Next, a case where the inductor current IL flows in the negative direction will be described.

[0123] In state STATE2-1, as shown in FIG. 29, the N-channel MOS transistors Q1 and Q2 are in the ON state, so that the inductor current IL is regenerated in a closed circuit including the inductor L1 and the N-channel MOS transistors Q1 and Q2, and the switch voltage VSW and the output voltage VOUT become approximately equal.

[0124] In state STATE2-1, the current supply to the load LD1 can be cut off. In state STATE2-1, the first switch SW1 and the second switch SW2 are in the OFF state, so that the output voltage VOUT can be clamped approximately to the level at which an overshoot occurs. That is, by turning the first switch SW1 and the second switch SW2 off and turning the N-channel MOS transistors Q1 and Q2 on when an overshoot occurs in the output voltage VOUT, it is possible to prevent the output voltage VOUT from increasing further and suppress the overshoot of the output voltage VOUT.

[0125] In state STATE2-2, as shown in FIG. 30, since the N-channel MOS transistors Q1 and Q2 are in the off state, the inductor current IL flows from the inductor L1 to the application terminal of the input voltage VIN via the body diode of the first switch SW1. Therefore, the switch voltage VSW is VIN+Vf SW1 become.

[0126] When the inductor current IL is negative, the second state STATE 2 The output voltage VOUT and switch voltage VSW at this time are as shown in FIG. 31. Note that, in terms of the vertical scale of the paper of FIG. 31, the output voltage VOUT is enlarged relative to the switch voltage VSW. As can be seen from FIG. 31, the period of the switch voltage VSW is a fixed period Tfix. In other words, since the frequency (switching frequency) of the switch voltage VSW does not vary, the frequency of the noise caused by the switching frequency does not vary either. Therefore, there is no risk of reducing the effect of the noise suppression means (e.g., a filter circuit) that suppresses fixed-frequency noise.

[0127] <Application> Next, a description will be given of examples of applications of the switching power supply devices 1 and 11 described above. Fig. 32 is an external view showing one configuration example of a vehicle equipped with on-board devices. The vehicle X of this configuration example is equipped with on-board devices X11 to X17 and a battery (not shown) that supplies power to these on-board devices X11 to X17.

[0128] The in-vehicle device X11 is an engine control unit that performs engine-related controls (such as injection control, electronic throttle control, idling control, oxygen sensor heater control, and auto-cruise control).

[0129] The in-vehicle device X12 is a lamp control unit that controls the turning on and off of HIDs (high intensity discharged lamps) and DRLs (daytime running lamps).

[0130] The in-vehicle device X13 is a transmission control unit that performs control related to the transmission.

[0131] The in-vehicle device X14 is a body control unit that performs control related to the motion of the vehicle X (ABS [anti-lock brake system] control, EPS [electric power steering] control, electronic suspension control, etc.).

[0132] The in-vehicle device X15 is a security control unit that controls the driving of door locks, burglar alarms, etc.

[0133] The in-vehicle devices X16 are electronic devices that are installed in the vehicle X at the factory as standard equipment or manufacturer options, such as wipers, power door mirrors, power windows, power sunroof, power seats, and air conditioners.

[0134] The in-vehicle device X17 is an electronic device that is installed in the vehicle X at the user's discretion, such as an in-vehicle A / V (audio / visual) device, a car navigation system, and an ETC (Electronic Toll Collection System).

[0135] It should be noted that any of the switching power supply devices 1 and 11 described above can be incorporated into any of the in-vehicle devices X11 to X17.

[0136] <Points to note> In addition to the above-described embodiment, the configuration of the present invention can be modified in various ways without departing from the spirit of the invention. The above-described embodiment is illustrative in all respects and should be considered as not limiting, and the technical scope of the present invention is indicated by the claims, not the description of the above-described embodiment, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0137] In the second operation example described above, for example, when the inductor current IL is positive, the control unit CNT1 may turn on the second switch SW2 in state STATE2-2. Also, for example, when the inductor current IL is negative, the control unit CNT1 may turn on the first switch SW1 in state STATE2-2.

[0138] In the second operation example described above, for example, the set value of the fixed period Tfix may be changeable. The set value of the fixed period Tfix can be changed by changing the period of the periodic signal S1.

[0139] In the above-described operation example of the switching power supply device 11, for example, when the inductor current IL is positive in the second control pattern or the third control pattern, the control unit CNT1 may turn on the second switch SW2 in state STATE2-2. Also, for example, when the inductor current IL is negative in the first control pattern or the third control pattern, the control unit CNT1 may turn on the first switch SW1 in state STATE2-2.

[0140] In the above-described exemplary operation of the switching power supply device 11, for example, the set value of the fixed period Tfix may be changeable. The set value of the fixed period Tfix can be changed by changing the period of the periodic signal S1.

[0141] In the above-mentioned switching power supply device 11, it is desirable to provide a clamping section that clamps the voltage of the connection node between the above-mentioned first switch element and the above-mentioned second switch element within a predetermined range. For example, in the modification shown in FIG. 33, the body diode of the N-channel MOS transistor Q3 is used as the above-mentioned clamping section. The drain of the N-channel MOS transistor Q3 is connected to the connection node between the N-channel MOS transistor Q1 used as the first switch element and the N-channel MOS transistor Q2 used as the second switch element. The gate and source of the N-channel MOS transistor Q3 are connected to the ground potential. In the modification shown in FIG. 33, the lower limit of the voltage of the connection node between the N-channel MOS transistor Q1 and the N-channel MOS transistor Q2 is the value obtained by subtracting the forward voltage of the body diode of the N-channel MOS transistor Q3 from the ground potential. Also, in the modification shown in FIG. 33, the upper limit of the voltage of the connection node between the N-channel MOS transistor Q1 and the N-channel MOS transistor Q2 is the avalanche breakdown voltage of the body diode of the N-channel MOS transistor Q3 from the ground potential. [Industrial Applicability]

[0142] The present invention can be applied to step-down switching power supply devices used in a variety of fields (such as home appliances, automobiles, and industrial machinery). [Explanation of symbols]

[0143] 1, 11 Switching power supply 2 Acquisition part 3 Suppression part C1 Output capacitor CNT1 control unit DET1 Detector FB1 Output feedback section L1 Inductor LD1 load Q1~Q5 N-channel MOS transistors SW1~SW3 1st~3rd switches X Vehicle In-vehicle devices X11 to X17

Claims

1. A switching power supply device that steps down an input voltage to an output voltage, a first switch having a first terminal connectable to an application terminal of the input voltage and a second terminal connectable to a first terminal of an inductor; a second switch having a first end connectable to the first end of the inductor and a second end of the first switch, and a second end connectable to an application end of a voltage lower than the input voltage; a third switch having a first end connected to the first end of the inductor, the second end of the first switch, and the first end of the second switch, and a second end connected to the second end of the inductor; a detection unit that detects occurrence or a sign of an overshoot in the output voltage and convergence of the overshoot in the output voltage; A control unit that controls on / off of the first switch, the second switch, and the third switch; Equipped with The control unit is during a period from when the detection unit detects occurrence of an overshoot or a sign thereof in the output voltage until the detection unit detects convergence of the overshoot in the output voltage, the first switch is turned off when the third switch is in an on state, and the second switch is turned off when the third switch is in an on state, thereby switching between the on state and the off state of the third switch at a fixed cycle; The on state of the first switch means a state in which a current can flow from a first terminal to a second terminal of the first switch and a current can also flow from the second terminal to the first terminal of the first switch, The off state of the first switch is a state in which a current cannot flow from a first terminal to a second terminal of the first switch, The on state of the second switch means a state in which a current can flow from a first terminal to a second terminal of the second switch and also a state in which a current can flow from the second terminal to the first terminal of the second switch, The off state of the second switch is a state in which a current cannot flow from a first terminal to a second terminal of the second switch, The on state of the third switch means a state in which a current can flow from a first terminal to a second terminal of the third switch and a current can also flow from the second terminal to the first terminal of the third switch, A switching power supply device in which the off state of the third switch is a state in which at least one of a current flow from the first terminal to the second terminal of the third switch and a current flow from the second terminal to the first terminal of the third switch is impossible.

2. 2. The switching power supply device according to claim 1, wherein a period during which the third switch is in an off state is a fixed period from when the detection unit detects an occurrence or a sign of an overshoot in the output voltage until the detection unit detects a convergence of the overshoot in the output voltage.

3. 3. The switching power supply device according to claim 2, wherein a period during which the third switch is in an off state from when the detection unit detects an occurrence of an overshoot or a sign thereof in the output voltage to when the detection unit detects convergence of the overshoot in the output voltage, is equal to or shorter than 1 / 10 of the fixed period.

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

5. 4. The switching power supply device according to claim 1, wherein the third switch includes a first switch element and a second switch element connected in series to each other.

6. During an on-state period of the third switch, the first switch element and the second switch element are in an on-state, During an off-state period of the third switch, the first switch element is in an off-state and the second switch element is in an on-state; The on state of the first switch element is a state in which a current can flow from the first switch element to the second switch element and a current can also flow from the second switch element to the first switch element, The off state of the first switch element is a state in which a current cannot flow from the first switch element to the second switch element, The on state of the second switch element is a state in which a current can flow from the first switch element to the second switch element and a current can also flow from the second switch element to the first switch element, 6. The switching power supply device according to claim 5, wherein the off state of the second switch element is a state in which a current cannot flow from the second switch element to the first switch element.

7. 7. The switching power supply device according to claim 5, further comprising a clamping section that clamps a voltage at a connection node between said first switch element and said second switch element within a predetermined range.

8. 1. A switch control device that controls on / off of a first switch, the first end of which is configured to be connectable to an application end of an input voltage and the second end of which is configured to be connectable to a first end of an inductor, on / off 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, and the second end of which is configured to be connectable to an application end of a voltage lower than the input voltage, and on / off of a third switch, the first end of which is configured to be connectable to the first end of the inductor, the second end of the first switch, and the first end of the second switch, and the second end of which is connectable to the second end of the inductor, an acquisition unit that acquires a detection result of a detection unit that detects occurrence or a sign of an overshoot in the output voltage output from a switching power supply device that includes the first switch, the second switch, the third switch, and the switch control device and that steps down the input voltage to an output voltage, and convergence of the overshoot in the output voltage; a suppression unit that controls on / off of the first switch, the second switch, and the third switch based on the detection result acquired by the acquisition unit, and suppresses the overshoot of the output voltage by switching between the on state and the off state of the third switch in a fixed cycle, by turning off the first switch when the third switch is in an on state and turning off the second switch when the third switch is in an on state, during a period from when the detection unit detects an occurrence or a sign of an overshoot of the output voltage to when the detection unit detects convergence of the overshoot of the output voltage; Equipped with The on state of the first switch means a state in which a current can flow from a first terminal to a second terminal of the first switch and a current can also flow from the second terminal to the first terminal of the first switch, The off state of the first switch is a state in which a current cannot flow from a first terminal to a second terminal of the first switch, The on state of the second switch means a state in which a current can flow from a first terminal to a second terminal of the second switch and also a state in which a current can flow from the second terminal to the first terminal of the second switch, The off state of the second switch is a state in which a current cannot flow from a first terminal to a second terminal of the second switch, The on state of the third switch means a state in which a current can flow from a first terminal to a second terminal of the third switch and a current can also flow from the second terminal to the first terminal of the third switch, A switch control device, wherein the off state of the third switch is a state in which at least one of a current flow from the first terminal to the second terminal of the third switch and a current flow from the second terminal to the first terminal of the third switch is impossible.

9. 9. The switch control device according to claim 8, wherein a period during which the third switch is in an off state is a fixed period from when the detection unit detects an occurrence or a sign of an overshoot in the output voltage to when the detection unit detects a convergence of the overshoot in the output voltage.

10. 10. The switch control device according to claim 9, wherein during a period from when the detection unit detects an occurrence or a sign of an overshoot in the output voltage to when the detection unit detects convergence of the overshoot in the output voltage, an off state period of the third switch is equal to or less than 1 / 10 of the fixed period.

11. The switch control device according to any one of claims 8 to 10, wherein a voltage of 1.8 MHz to 2.1 MHz is generated at a connection node between the first switch and the second switch.

12. The switch control device according to any one of claims 8 to 10, wherein the third switch includes a first switch element and a second switch element connected in series with each other.

13. During an on-state period of the third switch, the first switch element and the second switch element are in an on-state, During an off-state period of the third switch, the first switch element is in an off-state and the second switch element is in an on-state; The on state of the first switch element is a state in which a current can flow from the first switch element to the second switch element and a current can also flow from the second switch element to the first switch element, The off state of the first switch element is a state in which a current cannot flow from the first switch element to the second switch element, The on state of the second switch element is a state in which a current can flow from the first switch element to the second switch element and a current can also flow from the second switch element to the first switch element, The switch control device according to claim 12 , wherein the off state of the second switch element is a state in which a current cannot flow from the second switch element to the first switch element.

14. An in-vehicle device comprising the switching power supply device according to any one of claims 1 to 7 or the switch control device according to any one of claims 8 to 13.

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

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