Step-down converter

Abstract

The purpose of the present invention is to achieve downsizing while suppressing common mode noise. This step-down converter (100) comprises a first capacitor (1), a second capacitor (2), a first inductor (11), a second inductor (12), a first switching element (Q1), a second switching element (Q2), a third inductor (13), a fourth inductor (14), a third capacitor (3), a fourth capacitor (4), a fifth capacitor (5), a ground conductor part (10), a sixth capacitor (6), a seventh capacitor (7), a fifth inductor (15), an eighth capacitor (8), and a resistor (31). The fifth inductor (15) is connected between a fifth node (N5) and the first capacitor (1). The eighth capacitor (8) is connected in series to the fifth inductor (15) between the fifth node (N5) and the first capacitor (1). The resistor (31) is connected in series to the fifth inductor (15) between the fifth node (N5) and the first capacitor (1).

Description

Buck Converter

[0001] The present disclosure relates to a buck converter, and more particularly to a buck converter including a switching element.

[0002] In recent years, the switching frequencies of switching elements have been increasing in order to reduce the size of passive components included in switching power supply circuits. However, increasing the switching frequency can lead to increased electromagnetic noise. In particular, common-mode noise is dominant in the frequency band of 1 MHz to 300 MHz (hereinafter also referred to as the MHz band) in switching power supply circuits. Therefore, reducing common-mode noise is important in order to accommodate higher switching frequencies.

[0003] Japanese Patent Application Laid-Open No. 2003-144222 discloses a power supply circuit capable of reducing common-mode noise.

[0004] The power supply circuit disclosed in Patent Document 1 includes a DC-DC converter and a choke coil. The DC-DC converter has a switching element that switches a DC input voltage input from a DC power supply, and supplies a DC output voltage to a load according to the on / off duty ratio of the switching element. The DC-DC converter includes an input-side capacitor, a transistor (switching element), a diode, a coil, an output-side capacitor, etc.

[0005] The choke coil has a pair of windings wound in opposite directions, and this pair of windings is connected between a DC power supply and a DC-DC converter. The power supply circuit disclosed in Patent Document 1 uses the choke coil to reduce noise generated between the DC power supply and the load.

[0006] In the power supply circuit disclosed in Patent Document 1, as the switching frequency becomes higher, the impedance of the choke coil that constitutes the noise filter needs to be increased, which may result in the choke coil becoming larger and hinder the miniaturization of the power supply circuit.

[0007] International Publication No. 2017 / 002550

[0008] An object of the present disclosure is to provide a step-down converter that can be miniaturized while suppressing common-mode noise.

[0009] A step-down converter according to one aspect of the present disclosure includes a positive input terminal and a negative input terminal, a positive output terminal and a negative output terminal, a first positive wiring section, a first negative wiring section, a second positive wiring section, a second negative wiring section, a first capacitor, a second capacitor, a first inductor, a second inductor, a first switching element, a second switching element, a third inductor, a fourth inductor, a third capacitor, a fourth capacitor, a fifth capacitor, a ground conductor section, a sixth capacitor, a seventh capacitor, a fifth inductor, an eighth capacitor, and a resistor. The first positive wiring section is connected to the positive input terminal. The first negative wiring section is connected to the negative input terminal. The second positive wiring section is connected to the positive output terminal. The second negative wiring section is connected to the negative output terminal. The first capacitor is connected between a first node of the first positive wiring section and a second node of the first negative wiring section. The second capacitor is connected between a third node of the first positive side wiring portion and a fourth node of the first negative side wiring portion. The first inductor is provided between the first node and the third node. The second inductor is provided between the second node and the fourth node. The first switching element is connected to the first positive side wiring portion. The second switching element is connected between the first switching element and the first negative side wiring portion. The third inductor is connected between a fifth node between the first switching element and the second switching element and the second positive side wiring portion. The fourth inductor is connected between a sixth node which is a connection point between the first negative side wiring portion and the second switching element and the second negative side wiring portion. The third capacitor is connected in parallel with the third inductor. The fourth capacitor is connected in parallel with the fourth inductor. The fifth capacitor is connected between a seventh node of the second positive side wiring portion and an eighth node of the second negative side wiring portion. The sixth capacitor is connected between the ground conductor and a ninth node between the seventh node and the positive output terminal in the second positive wiring portion.The seventh capacitor is connected between the ground conductor and a tenth node between the eighth node and the negative output terminal in the second negative wiring portion. The fifth inductor is connected between the fifth node and the first capacitor. The eighth capacitor is connected in series with the fifth inductor between the fifth node and the first capacitor. The resistor is connected in series with the fifth inductor between the fifth node and the first capacitor.

[0010] FIG. 1 is a schematic circuit diagram of a step-down converter according to a first embodiment. FIG. 2 is a circuit diagram of the step-down converter according to the first embodiment. FIG. 3 is a circuit diagram showing an equivalent circuit in the MHz band of the step-down converter according to the first embodiment. FIG. 4 is a frequency characteristic diagram of the synthetic impedance of the main parts of the step-down converter circuit according to the first embodiment. FIG. 5 is a circuit diagram used in simulating noise generated in the step-down converter according to the first embodiment. FIG. 6 is a graph showing the frequency characteristics of common-mode noise generated in the step-down converter according to the first embodiment and the step-down converter according to the comparative example. FIG. 7 is a graph showing the frequency characteristics of normal-mode noise generated in the step-down converter according to the first embodiment and the step-down converter according to the comparative example. FIG. 8 is a waveform diagram of ringing generated in the step-down converter according to the first embodiment and the step-down converter according to the comparative example. FIG. 9 is a schematic circuit diagram of a step-down converter according to a second embodiment. FIG. 10 is a schematic circuit diagram of a step-down converter according to a third embodiment. FIG. 11 is a circuit diagram showing an equivalent circuit in the MHz band of the step-down converter according to the first embodiment. FIG. 12 is a schematic circuit diagram of a step-down converter circuit according to a fourth embodiment. Fig. 13 is a circuit diagram showing an equivalent circuit in the MHz band of the above step-down converter Fig. 14 is a schematic circuit diagram of a step-down converter circuit according to a fifth embodiment.

[0011] First Embodiment A step-down converter 100 according to a first embodiment will be described below with reference to FIGS.

[0012] 1 and 2, the step-down converter 100 includes a positive input terminal T1, a negative input terminal T2, a positive output terminal T3, and a negative output terminal T4. The step-down converter 100 converts a first voltage input between the positive input terminal T1 and the negative input terminal T2 into a second voltage smaller than the first voltage and outputs the second voltage between the positive output terminal T3 and the negative output terminal T4. In the step-down converter 100, for example, a DC power supply is connected between the positive input terminal T1 and the negative input terminal T2, and a load is connected between the positive output terminal T3 and the negative output terminal T4.

[0013] (2) Details As shown in Fig. 1 , the step-down converter 100 includes a positive input terminal T1, a negative input terminal T2, a positive output terminal T3, a negative output terminal T4, a first positive wiring section W11, a first negative wiring section W12, a second positive wiring section W21, and a second negative wiring section W22. The step-down converter 100 also includes a first capacitor 1, a second capacitor 2, a first inductor 11, a second inductor 12, a first switching element Q1, a second switching element Q2, a third inductor 13, a fourth inductor 14, a third capacitor 3, a fourth capacitor 4, a fifth capacitor 5, a ground conductor 10, a sixth capacitor 6, a seventh capacitor 7, a fifth inductor 15, an eighth capacitor 8, and a resistor 31. The step-down converter 100 also includes a control device 20.

[0014] The positive input terminal T1 is connected to, for example, a high-potential output terminal (positive electrode) of a DC power supply E1 (see FIG. 5). The DC power supply E1 may include, for example, a battery, but is not limited to this, and may also include a DC-DC converter or an AC-DC converter.

[0015] The negative input terminal T2 is connected to, for example, the low potential side output terminal (negative electrode) of the DC power supply E1 (see FIG. 5).

[0016] A load R12 (see FIG. 5), for example, is connected between the positive output terminal T3 and the negative output terminal T4. In the step-down converter 100, instead of the load R12, for example, a DC-AC converter may be connected between the positive output terminal T3 and the negative output terminal T4.

[0017] The first positive side wiring section W11 is connected to the positive input terminal T1. That is, the first positive side wiring section W11 is a wiring section connected to the positive input terminal T1 in the step-down converter 100. More specifically, the first positive side wiring section W11 is a wiring section between the positive input terminal T1 and the first switching element Q1. In other words, the first positive side wiring section W11 is an input positive bus.

[0018] The first negative side wiring section W12 is connected to the negative input terminal T2. That is, the first negative side wiring section W12 is a wiring section connected to the negative input terminal T2 in the step-down converter 100. The first negative side wiring section W12 has a first end and a second end. The negative input terminal T2 is connected to the first end of the first negative side wiring section W12, and the second switching element Q2 is connected to the second end of the first negative side wiring section W12. Therefore, a series circuit of the first switching element Q1 and the second switching element Q2 is connected between the first positive side wiring section W11 and the first negative side wiring section W12. The first negative side wiring section W12 is an input negative bus.

[0019] The second positive side wiring section W21 is connected to the positive output terminal T3. That is, the second positive side wiring section W21 is a wiring section connected to the positive output terminal T3 in the step-down converter 100. The second positive side wiring section W21 is a wiring section between a fifth node N5 and the positive output terminal T3. The fifth node N5 is a node on the path between the first switching element Q1 and the second switching element Q2. The second positive side wiring section W21 is an output positive bus.

[0020] The second negative wiring section W22 is connected to the negative output terminal T4. That is, the second negative wiring section W22 is a wiring section connected to the negative output terminal T4 in the step-down converter 100. The second negative wiring section W22 has a first end and a second end, and the first end of the second negative wiring section W22 is connected to the second switching element Q2 and the second end of the first negative wiring section W12, and the second end of the second negative wiring section W22 is connected to the negative output terminal T4. The second negative wiring section W22 is an output negative bus.

[0021] The first capacitor 1 is connected between a first node N1 of the first positive wiring portion W11 and a second node N2 of the first negative wiring portion W12. In other words, the first capacitor 1 is connected between the positive input terminal T1 and the negative input terminal T2. The first capacitor 1 has a first end and a second end. The first end of the first capacitor 1 is connected to the first node N1 of the first positive wiring portion W11, and the second end of the first capacitor 1 is connected to the second node N2 of the first negative wiring portion W12. The first capacitor 1 functions as a smoothing capacitor. The first capacitor 1 is, for example, an electrolytic capacitor. The capacitance of the first capacitor 1 is, for example, 200 nF or more and 600 μF or less.

[0022] The second capacitor 2 is connected between a third node N3 of the first positive wiring portion W11 and a fourth node N4 of the first negative wiring portion W12. In other words, the second capacitor 2 is connected between the positive input terminal T1 and the negative input terminal T2. The second capacitor 2 functions as a smoothing capacitor. The second capacitor 2 is, for example, an electrolytic capacitor. The capacitance of the second capacitor 2 is, for example, 200 nF or more and 600 μF or less.

[0023] The first inductor 11 is disposed between the first node N1 and the third node N3. The inductance of the first inductor 11 is smaller than the inductance of the third inductor 13. The inductance of the first inductor 11 is, for example, 2 nH or more and 30 nH or less. The first inductor 11 is formed, for example, by a part of the first positive side wiring portion W11. In other words, the first inductor 11 is formed, for example, by a parasitic inductance component of a portion of the first positive side wiring portion W11 between the first node N1 and the third node N3. In this case, the inductance of the first inductor 11 can be calculated, for example, by three-dimensional electromagnetic field analysis or impedance measurement as the parasitic inductance component of a portion of the first positive side wiring portion W11 formed on a circuit board between the first node N1 and the third node N3. The first inductor 11 may be a mounted component (for example, a chip inductor).

[0024] The second inductor 12 is disposed between the second node N2 and the fourth node N4. The inductance of the second inductor 12 is smaller than the inductance of the third inductor 13. The inductance of the second inductor 12 is, for example, 2 nH or more and 30 nH or less. The second inductor 12 is configured, for example, by a part of the first negative side wiring portion W12. In other words, the second inductor 12 is formed, for example, by a parasitic inductance component of a portion of the first negative side wiring portion W12 between the second node N2 and the fourth node N4. In this case, the inductance of the second inductor 12 can be calculated, for example, by three-dimensional electromagnetic field analysis or impedance measurement as the parasitic inductance component of a portion of the first negative side wiring portion W12 formed on a circuit board between the second node N2 and the fourth node N4. The second inductor 12 may be a mounted component (for example, a chip inductor).

[0025] The first switching element Q1 is connected to the first positive side wiring portion W11. The second switching element Q2 is connected between the first switching element Q1 and the first negative side wiring portion W12.

[0026] Each of the first switching element Q1 and the second switching element Q2 is, for example, a normally-off n-channel metal-oxide-semiconductor field effect transistor (MOSFET), as shown in Fig. 2. In Fig. 2, the first diode D1 connected in anti-parallel to the first switching element Q1 is a parasitic diode of the n-channel MOSFET constituting the first switching element Q1, but is not limited to this and may be an external diode. Furthermore, the second diode D2 connected in anti-parallel to the second switching element Q2 is a parasitic diode of the n-channel MOSFET constituting the second switching element Q2, but is not limited to this and may be an external diode.

[0027] In the example of Fig. 2, each of the first switching element Q1 and the second switching element Q2 has a first main terminal (drain terminal), a second main terminal (source terminal), and a control terminal (gate terminal). In the example of Fig. 2, the first main terminal of the first switching element Q1 is connected to the first positive side wiring section W11, the second main terminal of the first switching element Q1 is connected to the first main terminal of the second switching element Q2, and the second main terminal of the second switching element Q2 is connected to the first negative side wiring section W12. In the first diode D1, the anode of the first diode D1 is connected to the second main terminal (source terminal) of the first switching element Q1, and the cathode of the first diode D1 is connected to the first main terminal (drain terminal) of the first switching element Q1. In the second diode D2, the anode of the second diode D2 is connected to the second main terminal (source terminal) of the second switching element Q2, and the cathode of the second diode D2 is connected to the first main terminal (drain terminal) of the second switching element Q2.

[0028] In the step-down converter 100, the first switching element Q1 and the second switching element Q2 are controlled by the control device 20. In the step-down converter 100, the first switching element Q1 and the second switching element Q2 are alternately turned on and off. The switching frequency of the first switching element Q1 and the second switching element Q2 is, for example, 1 kHz or more and 1 MHz or less.

[0029] The third inductor 13 is connected between a fifth node N5 between the first switching element Q1 and the second switching element Q2 and the second positive side wiring portion W21. The fifth node N5 is provided in the wiring portion between the first switching element Q1 and the second switching element Q2. In terms of the circuit, the fifth node N5 is the connection point between the first switching element Q1 and the second switching element Q2. The third inductor 13 is, for example, a choke coil (first choke coil). The inductance of the third inductor 13 is, for example, not less than 200 nH and not more than 30 μH.

[0030] The fourth inductor 14 is connected between the second negative side wiring section W22 and a sixth node N6, which is a connection point between the first negative side wiring section W12 and the second switching element Q2. The fourth inductor 14 is, for example, a choke coil (second choke coil) different from the first choke coil. The inductance of the fourth inductor 14 is, for example, 200 nH or more and 30 μH or less. The inductance of the fourth inductor 14 is the same as the inductance of the third inductor 13, but may be different from the inductance of the third inductor 13.

[0031] The third capacitor 3 is connected in parallel with the third inductor 13. The capacitance of the third capacitor 3 is smaller than the capacitances of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5. The third capacitor 3 is formed, for example, by the line capacitance of the third inductor 13. In this case, the capacitance of the third capacitor 3 can be calculated as the line capacitance of the third inductor 13, which is a choke coil, by three-dimensional electromagnetic field analysis or impedance measurement. Therefore, the capacitance of the third capacitor 3 is uniquely determined by the winding structure of the third inductor 13, which is the first choke coil. The capacitance of the third capacitor 3 is, for example, 1 pF or more and 100 nF or less. The third capacitor 3 may also be a mounted component (chip capacitor).

[0032] The fourth capacitor 4 is connected in parallel to the fourth inductor 14. The capacitance of the fourth capacitor 4 is smaller than the capacitances of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5. The fourth capacitor 4 is formed, for example, by the line capacitance of the fourth inductor 14. In this case, the capacitance of the fourth capacitor 4 can be calculated by three-dimensional electromagnetic field analysis or impedance measurement as the line capacitance of the fourth inductor 14, which is the second choke coil. Therefore, the capacitance of the fourth capacitor 4 is uniquely determined by the winding structure of the fourth inductor 14, which is the second choke coil. The capacitance of the fourth capacitor 4 is, for example, 1 pF or more and 100 nF or less. The fourth capacitor 4 may also be a mounted component (chip capacitor).

[0033] The fifth capacitor 5 is connected between a seventh node N7 of the second positive side wiring portion W21 and an eighth node N8 of the second negative side wiring portion W22. The fifth capacitor 5 has a first end and a second end. The first end of the fifth capacitor 5 is connected to the seventh node N7 of the second positive side wiring portion W21, and the second end of the fifth capacitor 5 is connected to the eighth node N8 of the second negative side wiring portion W22. The fifth capacitor 5 functions as a smoothing capacitor. The fifth capacitor 5 is, for example, an electrolytic capacitor. The capacitance of the fifth capacitor 5 is, for example, 200 nF or more and 600 μF or less.

[0034] The ground conductor 10 is formed, for example, by a housing provided in the step-down converter 100. The housing accommodates a circuit module of the step-down converter 100. The circuit module includes a circuit board (e.g., a printed wiring board) and a plurality of circuit elements arranged on the circuit board. The plurality of circuit elements include the first capacitor 1, the second capacitor 2, the first switching element Q1, the second switching element Q2, the third inductor 13, the fourth inductor 14, and the fifth capacitor 5 described above. The housing is conductive. The housing is made of, for example, a metal or an alloy. The housing has a function of shielding a leakage magnetic field generated in the step-down converter 100. The ground conductor 10 may be a ground conductor provided on the circuit board.

[0035] The sixth capacitor 6 is connected between the ground conductor 10 and a ninth node N9, which is located between the seventh node N7 and the positive output terminal T3 in the second positive wiring portion W21. The ninth node N9 is located between the seventh node N7 and the positive output terminal T3 in the second positive wiring portion W21. The capacitance of the sixth capacitor 6 is smaller than the capacitances of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5. The capacitance of the sixth capacitor 6 is, for example, not less than 2 nF and not more than 30 nF. The sixth capacitor 6 may be formed, for example, by parasitic capacitance generated between the second positive wiring portion W21 and the ground conductor 10.

[0036] The seventh capacitor 7 is connected between the ground conductor 10 and a tenth node N10, which is located between the eighth node N8 and the negative output terminal T4 in the second negative wiring portion W22. The seventh capacitor 7 is connected between the ground conductor 10 and the tenth node N10 in the second negative wiring portion W22. The tenth node N10 is located between the eighth node N8 and the negative output terminal T4 in the second negative wiring portion W22. The capacitance of the seventh capacitor 7 is smaller than the capacitances of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5. The seventh capacitor 7 may be formed, for example, by parasitic capacitance generated between the second negative wiring portion W22 and the ground conductor 10.

[0037] The fifth inductor 15 is connected between the fifth node N5 and the first capacitor 1.

[0038] The eighth capacitor 8 is connected in series to the fifth inductor 15 between the fifth node N5 and the first capacitor 1.

[0039] The resistor 31 is connected in series with the fifth inductor 15 between the fifth node N5 and the first capacitor 1.

[0040] The control device 20 controls the first switching element Q1 and the second switching element Q2. The execution entity of the control device 20 includes a computer system. The computer system has one or more computers. The computer system is mainly composed of a processor and memory as hardware. The processor executes a program recorded in the memory of the computer system, thereby realizing the function of the control device 20 as the execution entity in the present disclosure. The program may be pre-recorded in the memory of the computer system, provided via a telecommunications line, or recorded and provided on a non-transitory recording medium such as a memory card, optical disk, or hard disk drive (magnetic disk) readable by the computer system. The processor of the computer system is composed of one or more electronic circuits including a semiconductor integrated circuit (IC) or a large-scale integrated circuit (LSI). The multiple electronic circuits may be integrated into a single chip or distributed across multiple chips. The multiple chips may be integrated into a single device or distributed across multiple devices.

[0041] The control device 20 outputs a first control signal that controls the on / off of the first switching element Q1 and a second control signal that controls the on / off of the second switching element Q2. Each of the first control signal and the second control signal is, for example, a PWM (Pulse Width Modulation) signal whose potential level changes between a first potential level (hereinafter also referred to as a low level) and a second potential level (hereinafter also referred to as a high level) that is higher than the first potential level. The first switching element Q1 is turned on when the first control signal is at a high level and turned off when the first control signal is at a low level. The second switching element Q2 is turned on when the second control signal is at a high level and turned off when the second control signal is at a low level. The control device 20 sets a dead time period between the high-level period of the first control signal and the high-level period of the second control signal so that the on-period of the first switching element Q1 and the on-period of the second switching element Q2 do not overlap.

[0042] In this specification, the circuit constants of the components are defined as follows.

[0043] In this specification, the capacitance of the first capacitor 1 is designated C1, the capacitance of the second capacitor 2 is designated C2, the capacitance of the third capacitor 3 is designated C3, and the capacitance of the fourth capacitor 4 is designated C4. Also in this specification, the capacitance of the fifth capacitor 5 is designated C5, the capacitance of the sixth capacitor 6 is designated C6, the capacitance of the seventh capacitor 7 is designated C7, and the capacitance of the eighth capacitor 8 is designated C8.

[0044] Furthermore, in this specification, the inductance of the first inductor 11 is L1, the inductance of the second inductor 12 is L2, the inductance of the third inductor 13 is L3, the inductance of the fourth inductor 14 is L4, and the inductance of the fifth inductor 15 is L5.

[0045] Fig. 3 is a circuit diagram showing an equivalent circuit in the MHz band of the step-down converter 100 of Fig. 1. In Fig. 3, the inductor 41 is an inductor having a parallel combined inductance of the first inductor 11 and the second inductor 12 = (L1 × L2) / (L1 + L2). Also in Fig. 3, the capacitor 67 is a capacitor having a parallel combined capacitance of the sixth capacitor 6 and the seventh capacitor 7 = (C6 + C7).

[0046] Each of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5 is a smoothing capacitor having a relatively large capacitance, for example, greater than or equal to 200 nF and less than or equal to 600 μF. In the step-down converter 100, the impedance of each of the first capacitor 1, the second capacitor 2, and the fifth capacitor 5 in the MHz band is negligibly small compared to the impedance of each of the first inductor 11, the second inductor 12, the third capacitor 3, and the fourth capacitor 4 in the MHz band. Therefore, in an equivalent circuit of the step-down converter 100 in the MHz band, the first node N1 and the second node N2 are considered to be short-circuited, and the first node N1 and the second node N2 can be considered to be the same node. Furthermore, in an equivalent circuit of the step-down converter 100 in the MHz band, the third node N3 and the fourth node N4 are considered to be short-circuited, and the third node N3 and the fourth node N4 can be considered to be the same node. In addition, in the equivalent circuit of the step-down converter 100 in the MHz band, the seventh node N7 and the eighth node N8 can be considered to be short-circuited, and the seventh node N7 and the eighth node N8 can be considered to be the same node.

[0047] The third inductor 13 is a choke coil and has an inductance of, for example, 200 nH or more and 30 μH or less. In the step-down converter 100, the impedance of the third inductor 13 in the MHz band is much larger than the impedance of the third capacitor 3 in the MHz band. Therefore, in the equivalent circuit of the step-down converter 100 in the MHz band, the portion of the third inductor 13 can be considered to be in an open state.

[0048] The fourth inductor 14 is a choke coil and has an inductance of, for example, 200 nH or more and 30 μH or less. In the step-down converter 100, the impedance of the fourth inductor 14 in the MHz band is much larger than the impedance of the fourth capacitor 4 in the MHz band. Therefore, in the equivalent circuit of the step-down converter 100 in the MHz band, the portion of the fourth inductor 14 can be considered to be in an open state.

[0049] The switching circuit unit including the first switching element Q1 and the second switching element Q2 is connected as a noise source between the fifth node N5 and the third and fourth nodes N3 and N4 in the MHz band equivalent circuit diagram of the step-down converter 100. The noise source generates a voltage Vsw between the fifth node N5 and the third node N3 (or the fourth node N4) due to the operation of the first switching element Q1 and the second switching element Q2.

[0050] Furthermore, in the step-down converter 100, the circuit constants of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 are set so that the impedance of the fifth inductor 15 is dominant (inductive) in the composite impedance characteristics of the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 in the MHz band. In other words, in the equivalent circuit of the step-down converter 100 in the MHz band, the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 can be regarded as consisting of only the fifth inductor 15.

[0051] If mode conversion outside the circuit of the step-down converter 100 is ignored, the common mode noise of the step-down converter 100 in the MHz band originates from the potential V1 (common mode voltage V1) of the first node N1 (or the second node N2) relative to the ground conductor 10, or the current I1 (hereinafter also referred to as the common mode current I1) flowing through the ground conductor 10.

[0052] The equivalent circuit shown in Fig. 3 has a Wheatstone bridge circuit configuration. Therefore, in the equivalent circuit shown in Fig. 3, when the ratio of the "impedance of the fifth inductor 15" to the "parallel combined impedance of the first inductor 11 and the second inductor 12" is equal to the ratio of the "impedance of the third capacitor 3" to the "impedance of the fourth capacitor 4," the voltage transfer coefficient (= V1 / Vsw) from the switching circuit unit to the positive input terminal T1 and the negative input terminal T2 becomes zero. In other words, when the condition of the following equation (1) is satisfied, the voltage transfer coefficient is ideally zero.

[0053]

[0054] where ω is the angular frequency.

[0055] Equation (1) can be transformed into the following equation (2).

[0056]

[0057] In the step-down converter 100, by designing each circuit constant (L1, L2, L5, C3, C4) so ​​as to satisfy the condition of equation (2) (hereinafter also referred to as the impedance balance condition), it is possible to suppress the generation of common-mode noise due to the operation of the first switching element Q1 and the second switching element Q2, regardless of frequencies in the MHz band.

[0058] Equation (2) can be transformed into the following equation (3).

[0059]

[0060] Therefore, in the step-down converter 100, by designing each circuit constant (L1, L2, L5, C3, C4) so ​​as to satisfy the condition of equation (3), it is possible to suppress the generation of common-mode noise due to the operation of the first switching element Q1 and the second switching element Q2, regardless of the frequency in the MHz band.

[0061] In terms of suppressing the occurrence of common-mode noise compared to when there is no series circuit connected between the fifth node N5 and the first capacitor 1, including the fifth inductor 15, the seventh capacitor 7, and the resistor 31, the inductance L5 of the fifth inductor 15 is not limited to a value that satisfies the impedance balance condition. For example, the inductance L5 of the fifth inductor 15 may be a value that is 0.5 to 2 times the value that satisfies the impedance balance condition. In other words, the inductance L5 of the fifth inductor 15 may be a value that satisfies the following equation (4).

[0062]

[0063] Even if the impedance balance condition is not satisfied, the step-down converter 100 can reduce common-mode noise compared to a configuration that does not include a series circuit that is connected between the fifth node N5 and the first capacitor 1 and includes the fifth inductor 15, the seventh capacitor 7, and the resistor 31, as long as the inductance L5 of the fifth inductor 15 is between 0.5 and 2 times the value that satisfies the impedance balance condition.

[0064] (3) Characteristics The characteristics of Examples 1 to 5 of the step-down converter 100 according to the first embodiment will be described below.

[0065] In Example 1, the circuit constants of the components were set to the values ​​shown in Table 1 so as to satisfy the impedance balance conditions. Furthermore, the ESR (Equivalent Series Resistance) and ESL (Equivalent Series Inductance) were taken into consideration for each of the first capacitor 1, the second capacitor 2, the fourth capacitor 4, the fifth capacitor 5, and the sixth capacitor 6.

[0066]

[0067] In the first embodiment, the composite impedance characteristic of the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 has the frequency characteristic shown in FIG. 4 . As can be seen from FIG. 4 , the composite impedance of the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 has a frequency characteristic in which the composite impedance increases as the frequency increases in a frequency band of 10 MHz or higher. In other words, the impedance of the fifth inductor 15 is dominant in the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 in a frequency band of 10 MHz or higher. Therefore, in the equivalent circuit of the step-down converter 100 of the first embodiment in a frequency band of 10 MHz or higher, the series circuit of the fifth inductor 15, the seventh capacitor 7, and the resistor 31 connected between the fifth node N5 and the first capacitor N1 can be regarded as consisting of only the fifth inductor 15.

[0068] When the step-down converter 100 according to the first embodiment is operated in a state where the DC power supply E1 and the load R12 are connected as shown in Fig. 5, the frequency characteristics of the common mode noise generated therein have the characteristic A1 in Fig. 6. When the step-down converter 100 according to the first embodiment is operated in a state where the DC power supply E1 and the load R12 are connected as shown in Fig. 5, the frequency characteristics of the normal mode noise generated therein have the characteristic A1 in Fig. 7.

[0069] In the circuit shown in Fig. 5, a DC power supply E1 is connected between a positive input terminal T1 and a negative input terminal T2 of a step-down converter 100 via a pseudo power supply network 19. In the example of Fig. 5, the pseudo power supply network 19 is a circuit network for stabilizing the power supply impedance when the DC power supply E1 is viewed from the step-down converter 100. In the example of Fig. 5, the pseudo power supply network 19 includes two inductors 190 and 195, four capacitors 191, 192, 196, and 197, and four resistors 193, 194, 198, and 199. Also, in the example of Fig. 5, a load R12 is a load resistor.

[0070] The common mode noise indicated by A1 in Fig. 6 is a value calculated by Vcm = (V1 + V2) / 2, where Vcm (see Fig. 3) is the common mode noise, V1 is the voltage across resistor 194 of pseudo power supply network 19 in the circuit shown in Fig. 5 (corresponding to the potential of positive input terminal T1 with reference to the junction point between resistor 194 and resistor 199), and V2 is the voltage across resistor 199 (corresponding to the potential of negative input terminal T2 with reference to the junction point between resistor 194 and resistor 199). The frequency characteristics of the common mode noise of Example 1 indicated by A1 in Fig. 6 are the characteristics when the output voltage of DC power supply E1 is 24 V, the switching frequencies of each of first switching element Q1 and second switching element Q2 are 100 kHz, and the output power of step-down converter 100 is 144 W. Furthermore, the normal mode noise indicated by A1 in FIG. 7 is calculated as Vnm = (V1 - V2) / 2, where Vnm is the normal mode noise. The frequency characteristics of the normal mode noise of Example 1 indicated by A1 in FIG. 7 are obtained when the output voltage of the DC power supply E1 is 24 V, the switching frequencies of the first switching element Q1 and the second switching element Q2 are 100 kHz, and the output power of the step-down converter 100 is 144 W. Furthermore, B1 in FIG. 6 shows the frequency characteristics of the common mode noise of the step-down converter according to the comparative example. The step-down converter according to the comparative example does not include the series circuit of the fifth inductor, the eighth capacitor 8, and the resistor 31 of the step-down converter 100 according to the first embodiment. The frequency characteristics of the common mode noise of the comparative example indicated by B1 in FIG. 6 are obtained under the same conditions as those of Example 1. Furthermore, B1 in FIG. 7 shows the frequency characteristics of the normal mode noise of the step-down converter according to the comparative example.

[0071] 6, Example 1 can reduce common mode noise in a frequency band of 10 MHz or more compared to the comparative example. In Fig. 6, the maximum value of the common mode noise in Example 1 is 87.5 dBμV, while the maximum value of the common mode noise in the comparative example is 97.7 dBμV.

[0072] 7, Example 1 can reduce normal mode noise in a frequency band of 10 MHz or more compared to the comparative example. In Fig. 7, the maximum value of the normal mode noise in Example 1 is 77.8 dBμV, while the maximum value of the normal mode noise in the comparative example is 79.4 dBμV.

[0073] Also, A1 in Fig. 8 shows the ringing waveform of Example 1. More specifically, A1 in Fig. 8 shows the waveform of the voltage Vds across the second switching element Q2. The voltage Vds across the second switching element Q2 is the drain-source voltage of the MOSFET that constitutes the second switching element Q2, and corresponds to the voltage between the fifth node N5 and the fourth node N4. B1 in Fig. 8 shows the ringing waveform of the comparative example.

[0074] From FIG. 8, it can be seen that Example 1 can attenuate ringing in a shorter time than the comparative example.

[0075] 8 is generated due to a resonant current flowing in a current loop including the second switching element Q2, the resistor 31, the eighth capacitor 8, the fifth inductor 15, and the second inductor 12. From the viewpoint of suppressing ringing, it is preferable that the resistance value of the resistor 31 of the step-down converter 100 of the first embodiment is large, but from the viewpoint of reducing common-mode noise, it is preferable that the resistance value in the MHz band is sufficiently smaller than the impedance of the fifth inductor 15.

[0076] The characteristics of common mode noise, normal mode noise, etc. in Example 1 described above are the results of simulations performed using circuit constants designed to satisfy the impedance balance condition. However, in reality, variations in the circuit constants occur for each component. Therefore, Table 2 shows the results of simulations performed when the circuit constants other than the inductance L5 of the fifth inductor 15 were set to the same values ​​as in Table 1 and the inductance L5 of the fifth inductor 15 was variously changed. In Example 1, the impedance balance condition was satisfied only when the inductance L5 of the fifth inductor 15 was 100 nH. Note that the common mode noise values ​​in Table 2 are maximum values ​​of common mode noise in a frequency band of 10 MHz or higher.

[0077]

[0078] It can be seen from Table 2 that common-mode noise is minimized when the inductance L5 of the fifth inductor 15 satisfies the impedance balance condition (i.e., when L5 = 100 nH). Also, even when the inductance L5 of the fifth inductor 15 is set to a value that does not satisfy the impedance balance condition, it is still possible to reduce common-mode noise more than in the comparative example as long as the inductance L5 of the fifth inductor 15 is 0.5 to 2 times the value that satisfies the impedance balance condition.

[0079] (4) Advantages The step-down converter 100 according to the first embodiment includes a positive input terminal T1 and a negative input terminal T2, a positive output terminal T3 and a negative output terminal T4, a first positive wiring portion W11, a first negative wiring portion W12, a second positive wiring portion W21, a second negative wiring portion W22, a first capacitor 1, a second capacitor 2, a first inductor 11, a second inductor 12, a first switching element Q1, a second switching element Q2, a third inductor 13, a fourth inductor 14, a third capacitor 3, a fourth capacitor 4, a fifth capacitor 5, a ground conductor 10, a sixth capacitor 6, a seventh capacitor 7, a fifth inductor 15, an eighth capacitor 8, and a resistor 31. The fifth inductor 15 is connected between a fifth node N5 and the first capacitor 1. The eighth capacitor 8 is connected in series to the fifth inductor 15 between the fifth node N5 and the first capacitor 1. The resistor 31 is connected in series to the fifth inductor 15 between the fifth node N5 and the first capacitor 1.

[0080] The above configuration enables miniaturization while suppressing common-mode noise. More specifically, the step-down converter 100 according to the first embodiment includes the first inductor 11, the second inductor 12, the third capacitor 3, the fourth capacitor 4, and the fifth inductor 15, and thus its equivalent circuit in the MHz band has a Wheatstone bridge circuit configuration. As a result, the step-down converter 100 according to the first embodiment can suppress common-mode noise without using a common-mode choke coil, thereby enabling miniaturization while suppressing common-mode noise. Furthermore, the step-down converter 100 according to the first embodiment includes the resistor 31, which can suppress ringing caused by a resonant current flowing through a current loop including the fifth inductor 15 and the eighth capacitor 8, thereby reducing normal-mode noise.

[0081] Furthermore, in the step-down converter 100 according to the first embodiment, when the inductance L5 of the fifth inductor 15 is a value that satisfies the above-mentioned formula (3), it is possible to further reduce common-mode noise.

[0082] Furthermore, in the step-down converter 100 according to the first embodiment, when the inductance L5 of the fifth inductor 15 satisfies the above-mentioned formula (4), a capacitor with a larger tolerance for the inductance L5 can be used as the fifth inductor 15, and the cost of the step-down converter 100 can be reduced by reducing the cost of the fifth inductor 15.

[0083] (5) Modification of First Embodiment In the step-down converter 100, the second switching element Q2 may be configured as a diode. In this case, the diode configuring the second switching element Q2 has an anode connected to the first negative-side wiring section W12 and a cathode connected to the first switching element Q1. In addition, the control device 20 controls the on / off of the first switching element Q1.

[0084] Second Embodiment A step-down converter 101 according to a second embodiment will be described with reference to Fig. 9. Regarding the step-down converter 101 according to the second embodiment, the same components as those of the step-down converter 100 according to the first embodiment (see Figs. 1 and 2) are denoted by the same reference numerals, and description thereof will be omitted.

[0085] The step-down converter 101 according to the second embodiment differs from the step-down converter 100 according to the first embodiment in that the series circuit including the fifth inductor 15, the eighth capacitor 8, and the resistor 31 is connected between the first node N1 and the fifth node N5, rather than between the second node N2 and the fifth node N5.

[0086] In the step-down converter 101 according to the second embodiment, the first node N1 and the second node N2 can be regarded as the same node in the MHz band, similar to the step-down converter 100 according to the first embodiment. Therefore, the equivalent circuit of the step-down converter 101 according to the second embodiment in the MHz band is the same as that shown in Fig. 3. Therefore, similar to the step-down converter 100 according to the first embodiment, the step-down converter 101 according to the second embodiment can be miniaturized while suppressing common-mode noise.

[0087] Furthermore, in the step-down converter 100 according to the first embodiment, the wiring portion between the fifth node N5 and the resistor 31 intersects with the first negative side wiring portion W12 in a plan view in the thickness direction of the circuit board, and therefore, for example, a multilayer printed wiring board may be used as the circuit board, and part of the wiring portion between the fifth node N5 and the resistor 31 may be routed via a via conductor or the like to a layer of the circuit board different from the layer on which the first negative side wiring portion W12 is formed. In contrast, in the step-down converter 101 according to the second embodiment, the wiring portion between the fifth node N5 and the resistor 31 does not intersect with other wiring portions (including the first positive side wiring portion W11 and the first negative side wiring portion W12), and therefore it is possible to suppress the generation of unnecessary parasitic inductance components in the wiring portion between the fifth node N5 and the resistor 31. Furthermore, in the step-down converter 101 according to the second embodiment, the wiring section between the fifth node N5 and the resistor 31, the first positive side wiring section W11, and the first negative side wiring section W12 can be routed on the same layer, thereby improving the degree of freedom in the wiring design of the circuit board.

[0088] Third Embodiment A step-down converter 102 according to a third embodiment will be described with reference to Figures 10 and 11. With respect to the step-down converter 102 according to the third embodiment, the same components as those of the step-down converter 101 according to the second embodiment (see Figure 9) are denoted by the same reference numerals, and description thereof will be omitted.

[0089] (1) Configuration The step-down converter 102 according to the third embodiment differs from the step-down converter 101 according to the second embodiment in that it further includes a sixth inductor 16, a ninth capacitor 9, and a second resistor 32 that is different from the first resistor 31.

[0090] The sixth inductor 16 is connected between the fifth node N5 and the second node N2. The ninth capacitor 9 is connected in series with the sixth inductor 16 between the fifth node N5 and the second node N2. The second resistor 32 is connected in series with the sixth inductor 16 between the fifth node N5 and the second node N2. Therefore, the step-down converter 102 according to the second embodiment includes the fifth inductor 15 connected to the first end of the first capacitor 1 via the first node N1, and the sixth inductor 16 connected to the second end of the first capacitor 1 via the second node N2.

[0091] Fig. 11 is a circuit diagram showing an equivalent circuit in the MHz band of the step-down converter 102 of Fig. 10. In Fig. 11, the inductor 41 is an inductor having a parallel combined inductance of the first inductor 11 and the second inductor 12 = (L1 × L2) / (L1 + L2). Furthermore, if the inductance of the sixth inductor 16 is L6, in Fig. 11 the inductor 42 is an inductor having a parallel combined inductance of the fifth inductor 15 and the sixth inductor 16 = (L5 × L6) / (L5 + L6).

[0092] The equivalent circuit in the MHz band of the step-down converter 102 according to the third embodiment has a Wheatstone bridge circuit configuration, similar to that of the first embodiment. The impedance balance condition in the third embodiment is expressed by the following equation (5).

[0093]

[0094] In the step-down converter 102, by designing each circuit constant (L1, L2, L5, L6, C3, C4) so ​​as to satisfy the impedance balance condition of equation (5), it is possible to suppress the generation of common-mode noise due to the operation of the first switching element Q1 and the second switching element Q2, regardless of the frequency in the MHz band.

[0095] Here, equation (5) can be transformed into the following equation (6).

[0096]

[0097] Therefore, in the step-down converter 103, by designing each circuit constant (L1, L2, L5, L6, C3, C4) so ​​as to satisfy the condition of equation (6), it is possible to further suppress the generation of common-mode noise due to the operation of the first switching element Q1 and the second switching element Q2, regardless of the frequency in the MHz band.

[0098] Furthermore, from the viewpoint of suppressing the occurrence of common-mode noise compared to a comparative example that does not include either a series circuit including the fifth inductor 15, the eighth capacitor 8, and the first resistor 31, or a series circuit including the sixth inductor 16, the ninth capacitor 9, and the second resistor 32, the parallel combined inductance of the fifth inductor 15 and the sixth inductor 16 is not limited to a value that satisfies the impedance balance condition, but may be, for example, a value that is 0.5 to 2 times the value that satisfies the impedance balance condition. In other words, the parallel combined inductance of the fifth inductor 15 and the sixth inductor 16 may be a value that satisfies the following equation (7).

[0099]

[0100] In other words, even if the impedance balance condition is not satisfied, the step-down converter 102 can reduce common-mode noise compared to the comparative example, as long as the parallel combined inductance of the fifth inductor 15 and the sixth inductor 16 is 0.5 to 2 times the value that satisfies the impedance balance condition.

[0101] (2) Advantages The step-down converter 102 according to the third embodiment includes a positive input terminal T1 and a negative input terminal T2, a positive output terminal T3 and a negative output terminal T4, a first positive side wiring portion W11, a first negative side wiring portion W12, a second positive side wiring portion W21, a second negative side wiring portion W22, a first capacitor 1, a second capacitor 2, a first inductor 11, a second inductor 12, a first switching element Q1, a second switching element Q2, a third inductor 13, a fourth inductor 14, a third capacitor 3, a fourth capacitor 4, a fifth capacitor 5, a ground conductor portion 10, a sixth capacitor 6, a seventh capacitor 7, a fifth inductor 15, an eighth capacitor 8, and a resistor 31. The fifth inductor 15 is connected between a fifth node N5 and the first node N1. The eighth capacitor 8 is connected in series to the fifth inductor 15 between the fifth node N5 and the first node N1. The first resistor 31 is connected in series to the fifth inductor 15 between the fifth node N5 and the first node N1. The sixth inductor 16 is connected between the fifth node N5 and the second node N2. The ninth capacitor 9 is connected in series to the sixth inductor 16 between the fifth node N5 and the second node N2. The second resistor 32 is connected in series to the sixth inductor 16 between the fifth node N5 and the second node N2.

[0102] The above configuration enables miniaturization while suppressing common-mode noise. More specifically, the step-down converter 102 according to the third embodiment includes the first inductor 11, the second inductor 12, the third capacitor 3, the fourth capacitor 4, the fifth inductor 15, and the sixth inductor 16, so that its equivalent circuit in the MHz band has a Wheatstone bridge circuit configuration. This allows the step-down converter 102 according to the third embodiment to suppress common-mode noise without using a common-mode choke coil, thereby enabling miniaturization while suppressing common-mode noise. Furthermore, the step-down converter 102 according to the third embodiment includes the first resistor 31, so that ringing caused by a resonant current flowing through a current loop including the fifth inductor 15 and the eighth capacitor 8 can be suppressed, thereby reducing normal-mode noise. Furthermore, the step-down converter 102 according to the third embodiment includes the second resistor 32, so that ringing caused by a resonant current flowing through a current loop including the sixth inductor 16 and the ninth capacitor 9 can be suppressed, thereby reducing normal-mode noise.

[0103] Furthermore, in the step-down converter 102 according to the third embodiment, when (L5×L6) / (L5+L6) is a value that satisfies the above-mentioned formula (6), it is possible to further reduce common-mode noise.

[0104] Furthermore, in the step-down converter 102 according to the third embodiment, when (L5×L6) / (L5+L6) is a value that satisfies the above-mentioned equation (7), inductors with larger inductance tolerances can be used as the fifth inductor 15 and the sixth inductor 16, and the cost of the step-down converter 102 can be reduced by reducing the cost of the fifth inductor 15 and the sixth inductor 16.

[0105] Fourth Embodiment A step-down converter 103 according to a fourth embodiment will be described with reference to Figures 12 and 13. With respect to the step-down converter 103 according to the fourth embodiment, the same components as those of the step-down converter 100 according to the first embodiment (see Figures 1 and 2) are denoted by the same reference numerals, and description thereof will be omitted.

[0106] (1) Configuration The step-down converter 103 according to the fourth embodiment differs from the step-down converter 100 according to the first embodiment in that it further includes a series inductor 17 connected in series to the fifth inductor 15 between the fifth node N5 and the first capacitor 1. That is, in the step-down converter 103, the series circuit connected between the fifth node N5 and the first capacitor 1 is an RCLL circuit including the resistor 31, the eighth capacitor 8, the fifth inductor 15, and the series inductor 17. In the step-down converter 103, the series inductor 17 is connected between the fifth inductor 15 and the second node N2.

[0107] Fig. 13 is a circuit diagram showing an equivalent circuit in the MHz band of the step-down converter 103 of Fig. 12. In Fig. 13, the inductor 41 is an inductor having a parallel combined inductance of the first inductor 11 and the second inductor 12 = (L1 × L2) / (L1 + L2). Furthermore, when the inductance of the fifth inductor 15 is L51 and the inductance of the series inductor 17 is L52, the inductor 45 is an inductor having a series combined inductance of the fifth inductor 15 and the series inductor 17 = L51 + L52.

[0108] The step-down converter 103 satisfies the impedance balance condition of the following equation (8) when the capacitance of the third capacitor 3 is C3, the capacitance of the fourth capacitor 4 is C4, the inductance of the first inductor 11 is L1, the inductance of the second inductor 12 is L2, the inductance of the fifth inductor 15 is L51, and the inductance of the series inductor 17 is L52.

[0109]

[0110] From the viewpoint of suppressing the occurrence of common-mode noise compared to when there is no RCLL circuit connected between the fifth node N5 and the first capacitor 1, the series combined inductance of the inductance L51 of the fifth inductor 15 and the inductance L52 of the series inductor 17 is not limited to a value that satisfies the impedance balance condition. For example, L51+L52 may be a value that is 0.5 to 2 times the value that satisfies the impedance balance condition. In other words, L51+L52 may be a value that satisfies the following equation (9).

[0111]

[0112] Even if the impedance balance condition is not satisfied, the step-down converter 103 can reduce common-mode noise compared to a configuration that does not include a series circuit that is connected between the fifth node N5 and the first capacitor 1 and includes the fifth inductor 15, the series inductor 17, the eighth capacitor 8, and the resistor 31, as long as L51+L52 is a value that is 0.5 to 2 times the value that satisfies the impedance balance condition.

[0113] (2) Advantages Like the step-down converter 100 according to the first embodiment, the step-down converter 103 according to the fourth embodiment can be miniaturized while suppressing common-mode noise.

[0114] Furthermore, the step-down converter 103 according to the fourth embodiment includes the resistor 31 connected in series with the fifth inductor 15 between the fifth node N5 and the second node N2. This makes it possible to suppress ringing when the second switching element Q2 changes from an off state to an on state, thereby further suppressing normal noise.

[0115] Moreover, the step-down converter 103 according to the fourth embodiment further includes a series inductor 17 connected in series to the fifth inductor 15 between the fifth node N5 and the first capacitor 1.

[0116] The above configuration increases the degree of freedom in the circuit constants of the fifth inductor 15 and the sixth inductor 16. This increases the degree of freedom in component selection, as it is sufficient to set the inductance L5 of the fifth inductor 15 and the inductance L6 of the sixth inductor 16 so as to satisfy the impedance balance condition of equation (9).

[0117] Fifth Embodiment A step-down converter 104 according to a fifth embodiment will be described with reference to Fig. 14. With respect to the step-down converter 104 according to the fifth embodiment, the same components as those of the step-down converter 100 according to the first embodiment (see Figs. 1 and 2) are denoted by the same reference numerals, and description thereof will be omitted.

[0118] (1) Configuration In the step-down converter 104 according to the fifth embodiment, the third inductor 13 and the fourth inductor 14 are magnetically coupled with opposite polarities.

[0119] (2) Effects The step-down converter 104 according to the fifth embodiment includes the fifth inductor 15, the eighth capacitor 8, and the resistor 31, similar to the step-down converter 100 according to the first embodiment, and therefore can reduce common-mode noise and normal-mode noise.

[0120] In the step-down converter 104 according to the fifth embodiment, the third inductor 13 and the fourth inductor 14 are magnetically coupled with opposite polarities.

[0121] According to the above configuration, the mutual conductance between the third inductor 13 and the fourth inductor 14 can be utilized, the inductance of each of the third inductor 13 and the fourth inductor 14 can be reduced, and the size of each of the third inductor 13 and the fourth inductor 14 can be reduced.

[0122] (Other Modifications) The above-described first to fifth embodiments are merely examples of various embodiments of the present disclosure. The above-described first to fifth embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved.

[0123] Furthermore, each of the first switching element Q1 and the second switching element Q2 in the step-down converter 100 according to the first embodiment is not limited to an n-channel MOSFET, but may be a p-channel MOSFET. Although each of the first switching element Q1 and the second switching element Q2 is a Si-based MOSFET, the present invention is not limited thereto and may be, for example, a SiC-based MOSFET. Each of the first switching element Q1 and the second switching element Q2 may be, for example, a bipolar transistor, an IGBT (Insulated Gate Bipolar Transistor), or a GaN-based GIT (Gate Injection Transistor).

[0124] Furthermore, the series inductor 17 of the fourth embodiment may be applied to, for example, the second, third, and fifth embodiments. Furthermore, the configuration of the third inductor 13 and the fourth inductor 14 of the fifth embodiment may be applied to the other second to fourth embodiments.

[0125] (Aspects) The following aspects are disclosed in this specification.

[0126] A step-down converter (100; 101; 102; 103; 104) according to a first aspect includes a positive input terminal (T1) and a negative input terminal (T2), a positive output terminal (T3) and a negative output terminal (T4), a first positive side wiring portion (W11), a first negative side wiring portion (W12), a second positive side wiring portion (W21), a second negative side wiring portion (W22), a first capacitor (1), a second capacitor (2), a first inductor (11), and a The power supply includes a second inductor (12), a first switching element (Q1), a second switching element (Q2), a third inductor (13), a fourth inductor (14), a third capacitor (3), a fourth capacitor (4), a fifth capacitor (5), a ground conductor portion (10), a sixth capacitor (6), a seventh capacitor (7), a fifth inductor (15), an eighth capacitor (8), and a resistor (31). The first positive side wiring portion (W11) is connected to the positive input terminal (T1). The first negative side wiring portion (W12) is connected to the negative input terminal (T2). The second positive side wiring portion (W21) is connected to the positive output terminal (T3). The second negative side wiring portion (W22) is connected to the negative output terminal (T4). The first capacitor (1) is connected between a first node (N1) of the first positive side wiring portion (W11) and a second node (N2) of the first negative side wiring portion (W12). The second capacitor (2) is connected between a third node (N3) of the first positive side wiring portion (W11) and a fourth node (N4) of the first negative side wiring portion (W12). The first inductor (11) is provided between the first node (N1) and the third node (N3). The second inductor (12) is provided between the second node (N2) and the fourth node (N4). The first switching element (Q1) is connected to the first positive side wiring portion (W11). The second switching element (Q2) is connected between the first switching element (Q1) and the first negative side wiring portion (W12). The third inductor (13) is connected between a fifth node (N5) between the first switching element (Q1) and the second switching element (Q2) and the second positive side wiring portion (W21). The fourth inductor (14) is connected between a sixth node (N6) which is a connection point between the first negative side wiring portion (W12) and the second switching element (Q2) and the second negative side wiring portion (W22).The third capacitor (3) is connected in parallel to the third inductor (13). The fourth capacitor (4) is connected in parallel to the fourth inductor (14). The fifth capacitor (5) is connected between the seventh node (N7) of the second positive side wiring portion (W21) and the eighth node (N8) of the second negative side wiring portion (W22). The sixth capacitor (6) is connected between the ground conductor portion (10) and a ninth node (N9) between the seventh node (N7) of the second positive side wiring portion (W21) and the positive output terminal (T3). The seventh capacitor (7) is connected between the ground conductor portion (10) and a tenth node (N10) between the eighth node (N8) of the second negative side wiring portion (W22) and the negative output terminal (T4). The fifth inductor (15) is connected between the fifth node (N5) and the first capacitor (1). The eighth capacitor (8) is connected in series with the fifth inductor (15) between the fifth node (N5) and the first capacitor (1). The resistor (31) is connected in series with the fifth inductor (15) between the fifth node (N5) and the first capacitor (1).

[0127] According to this aspect, it is possible to achieve miniaturization while suppressing common mode noise.

[0128] In the step-down converter (101; 102) according to the second aspect, in the first aspect, the fifth inductor (15) is connected between the fifth node (N5) and the first node (N1).

[0129] According to this aspect, it is possible to suppress the occurrence of unnecessary parasitic inductance components between the fifth node (N5) and the resistor (31), the fifth inductor (15), or the eighth capacitor (8).

[0130] A step-down converter (100; 101; 102; 104) according to a third aspect is a step-down converter according to the first or second aspect, in which, when the capacitance of the third capacitor (3) is C3, the capacitance of the fourth capacitor (4) is C4, the inductance of the first inductor (11) is L1, the inductance of the second inductor (12) is L2, and the inductance of the fifth inductor (15) is L5,

[0131] Satisfy.

[0132] According to this aspect, it is possible to further reduce common mode noise.

[0133] The step-down converter (102) according to a fourth aspect is the second aspect, and further includes a sixth inductor (16), a ninth capacitor (9), and a second resistor (32) different from the first resistor (31). The sixth inductor (16) is connected between a fifth node (N5) and a second node (N2). The ninth capacitor (9) is connected in series with the sixth inductor (16) between the fifth node (N5) and the second node (N2). The second resistor (32) is connected in series with the sixth inductor (16) between the fifth node (N5) and the second node (N2).

[0134] According to this aspect, by providing the first resistor (31), ringing occurring in the voltage across the first switching element (Q1) can be suppressed, and by providing the second resistor (32), ringing occurring in the voltage across the second switching element (Q2) can be suppressed.

[0135] A step-down converter (102) according to a fifth aspect is the step-down converter (102) of the fourth aspect, in which, when the capacitance of the third capacitor (3) is C3, the capacitance of the fourth capacitor (4) is C4, the inductance of the first inductor (11) is L1, the inductance of the second inductor (12) is L2, the inductance of the fifth inductor (15) is L5, and the inductance of the sixth inductor (16) is L6,

[0136] Satisfy.

[0137] According to this aspect, it is possible to further reduce common mode noise.

[0138] The step-down converter (103) according to the sixth aspect is the step-down converter (103) according to the first aspect, further comprising a series inductor (17) connected in series with the fifth inductor (15) between the fifth node (N5) and the first capacitor (1).

[0139] According to this aspect, the degree of freedom in the circuit constant of the fifth inductor (15) is increased.

[0140] A step-down converter (103) according to a seventh aspect is the sixth aspect, in which, when the capacitance of the third capacitor (3) is C3, the capacitance of the fourth capacitor (4) is C4, the inductance of the first inductor (11) is L1, the inductance of the second inductor (12) is L2, the inductance of the fifth inductor (15) is L51, and the inductance of the series inductor (17) is L52,

[0141] Satisfy.

[0142] According to this aspect, it is possible to further reduce common mode noise.

[0143] In the step-down converter (104) according to an eighth aspect, in any one of the first to seventh aspects, the third inductor (13) and the fourth inductor (14) are magnetically coupled with each other in opposite polarity.

[0144] According to this aspect, the mutual conductance between the third inductor (13) and the fourth inductor (14) can be utilized, the inductance of each of the third inductor (13) and the fourth inductor (14) can be reduced, and the size of each of the third inductor (13) and the fourth inductor (14) can be reduced.

[0145] In a step-down converter (100; 101; 102; 103; 104) according to a ninth aspect, in any one of the first to eighth aspects, the first inductor (11) is configured from a part of the first positive side wiring portion (W11), and the second inductor (12) is configured from a part of the first negative side wiring portion (W12).

[0146] According to this aspect, the number of parts can be reduced, and it is possible to achieve miniaturization and cost reduction.

[0147] A step-down converter (100; 101; 102; 103; 104) according to a tenth aspect is any one of the first to ninth aspects, in which the third inductor (13) is the first choke coil, the fourth inductor (14) is the second choke coil, the third capacitor (3) is the line capacitance of the first choke coil, and the fourth capacitor (4) is the line capacitance of the second choke coil.

[0148] According to this aspect, the number of parts can be reduced, and it is possible to achieve size reduction and cost reduction.

[0149] REFERENCE SIGNS LIST 1 First capacitor 2 Second capacitor 3 Third capacitor 4 Fourth capacitor 5 Fifth capacitor 6 Sixth capacitor 7 Seventh capacitor 8 Eighth capacitor 9 Ninth capacitor 10 Ground conductor section 20 Control device 11 First inductor 12 Second inductor 13 Third inductor 14 Fourth inductor 15 Fifth inductor 16 Sixth inductor 17 Series inductor 31 Resistor (first resistor) 32 Second resistor 100, 101, 102, 103, 104 Step-down converter Q1 First switching element Q2 Second switching element T1 Positive input terminal T2 Negative input terminal T3 Positive output terminal T4 Negative output terminal W11 First positive side wiring section W12 First negative side wiring section W21 Second positive side wiring section W22 Second negative side wiring section

Claims

1. A step-down converter comprising: a positive input terminal and a negative input terminal; a positive output terminal and a negative output terminal; a first positive-side wiring portion connected to the positive input terminal; a first negative-side wiring portion connected to the negative input terminal; a second positive-side wiring portion connected to the positive output terminal; a second negative-side wiring portion connected to the negative output terminal; a first capacitor connected between a first node of the first positive-side wiring portion and a second node of the first negative-side wiring portion; a second capacitor connected between a third node of the first positive-side wiring portion and a fourth node of the first negative-side wiring portion; a first inductor provided between the first node and the third node; a second inductor provided between the second node and the fourth node; a first switching element connected to the first positive-side wiring portion; a second switching element connected between the first switching element and the first negative-side wiring portion; a third inductor connected between a fifth node between the first switching element and the second switching element and the second positive-side wiring portion; a fourth inductor connected between a sixth node, which is a connection point between the first negative-side wiring portion and the second switching element, and the second negative-side wiring portion; a third capacitor connected in parallel with the third inductor; a fourth capacitor connected in parallel with the fourth inductor; a fifth capacitor connected between a seventh node of the second positive-side wiring portion and an eighth node of the second negative-side wiring portion; a ground conductor portion; a sixth capacitor connected between a ninth node between the seventh node in the second positive-side wiring portion and the positive output terminal and the ground conductor portion; a seventh capacitor connected between a tenth node between the eighth node in the second negative-side wiring portion and the negative output terminal and the ground conductor portion; a fifth inductor connected between the fifth node and the first capacitor; an eighth capacitor connected in series with the fifth inductor between the fifth node and the first capacitor; and a resistor connected in series with the fifth inductor between the fifth node and the first capacitor.

2. The step-down converter according to claim 1, wherein the fifth inductor is connected between the fifth node and the first node.

3. When the capacitance of the third capacitor is C3, the capacitance of the fourth capacitor is C4, the inductance of the first inductor is L1, the inductance of the second inductor is L2, and the inductance of the fifth inductor is L5, The step-down converter according to claim 1 or 2, which satisfies 4. A sixth inductor connected between the fifth node and the second node, a ninth capacitor connected in series with the sixth inductor between the fifth node and the second node, and a second resistor different from the first resistor and connected in series with the sixth inductor between the fifth node and the second node. The step-down converter according to claim 2, further comprising:

5. When the capacitance of the third capacitor is C3, the capacitance of the fourth capacitor is C4, the inductance of the first inductor is L1, the inductance of the second inductor is L2, the inductance of the fifth inductor is L5, and the inductance of the sixth inductor is L6, The step-down converter according to claim 4, which satisfies.

6. The step-down converter according to claim 1, further comprising a series inductor connected in series with the fifth inductor between the fifth node and the first capacitor.

7. When the capacitance of the third capacitor is C3, the capacitance of the fourth capacitor is C4, the inductance of the first inductor is L1, the inductance of the second inductor is L2, the inductance of the fifth inductor is L51, and the inductance of the series inductor is L52, The step-down converter according to claim 6, which satisfies.

8. The step-down converter according to any one of claims 1 to 7, wherein the third inductor and the fourth inductor are magnetically coupled with opposite polarities.

9. The step-down converter according to any one of claims 1 to 8, wherein the first inductor is constituted by a part of the first positive-side wiring portion, and the second inductor is constituted by a part of the first negative-side wiring portion.

10. The step-down converter according to any one of claims 1 to 9, wherein the third inductor is a first choke coil, the fourth inductor is a second choke coil, the third capacitor is the inter-turn capacitance of the first choke coil, and the fourth capacitor is the inter-turn capacitance of the second choke coil.

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