Switching power supply

Abstract

To provide a switching power supply device complying with an electric shock protection class 2 that is able to effectively prevent noise current flowing in a ground resistor.SOLUTION: A voltage generated in a primary-side main winding 24 (1) becomes a noise source, resulting in generation of a noise current Icom (1) that flows out to a ground line 32 through unstable-potential stray capacitors Cf1 to Cf3 and a noise current Icom (2) that flows out to the ground line 32 through a secondary-side stray capacitor Cy2. An insulating transformer 22 has a secondary-side auxiliary winding 40(2) one end of which is connected to a secondary-side stable potential line 14; and a capacitance forming region 42c of a wiring pattern 42 connected to the other end of the secondary-side auxiliary winding 40(2) and a capacitor forming region 44c of a primary-side stable potential line 12 are disposed opposite to each other to form a wiring-pattern stray capacitor Ch. When a predetermined level of current flows through the wiring-pattern stray capacitor Ch, a magnitude of the current obtained by combining the noise currents Icom (1) and Icom (2) can be restricted to a reference value or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an isolated switching power supply device in which a primary circuit and a secondary circuit are connected via an isolation transformer.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1 for example, in order to cancel the influence of common mode noise current flowing from the primary winding to the secondary winding of a transformer, a noise compensation winding that generates a voltage with the same level and opposite polarity as the common mode noise voltage is provided on the secondary side of the transformer, and there has been a switching regulator in which a capacitor element is connected between one end of the noise compensation winding where the voltage with the opposite polarity is generated and the line of the input power supply. According to this configuration, a canceling current with the same level as the common mode noise current can be generated and made to flow backward to the primary side through the capacitor element, so that the influence of the common mode noise current can be canceled.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The conventional switching power supply device 10 shown in FIG. 16 is a device classified into the electric shock protection class 2 defined by IEC standards, JIS standards, etc. First, the configuration of the internal circuit of the switching power supply device 10 will be described. The switching power supply device 10 converts the input voltage Vi input between a primary power supply line 12a and a primary ground line 12b formed by a pair of wiring patterns into a predetermined output voltage Vo and generates it between a secondary power supply line 14a and a secondary ground line 14b formed by a pair of wiring patterns.

[0005] A primary phase-to-phase capacitor element 16 is connected between the primary power line 12a and the primary ground line 12b. The two lines 12a and 12b are substantially short-circuited by the primary phase-to-phase capacitor element 16 in a frequency band above the switching frequency Fsw, forming a potentialally stable primary stable potential line 12. Similarly, a secondary phase-to-phase capacitor element 18 is connected between the secondary power line 14a and the secondary ground line 14b. The two lines 14a and 14b are substantially short-circuited by the secondary phase-to-phase capacitor element 18 in a frequency band above the switching frequency Fsw, forming a potentialally stable secondary stable potential line 14.

[0006] An inverter circuit 20 is connected to the primary power line 12a and the primary ground line 12b. The inverter circuit 20 has an isolation transformer 22 (primary main winding 24(1), secondary main winding 24(2)) and a switching element 26. The primary main winding 24(1) and the switching element 26 are connected in series, and the switching element 26 switches at a switching frequency Fsw, thereby generating a voltage across the primary main winding 24(1) that is an intermittent input voltage Vi.

[0007] A rectifier circuit 28 is connected to the secondary main winding 24(2) of the isolation transformer 22 to rectify the voltage generated on the secondary main winding 24(2) and generate a rectified voltage. Furthermore, a smoothing circuit 30 is connected to the output terminal of the rectifier circuit 28 to smooth the rectified voltage and generate an output voltage Vo. The switching power supply 10 is a so-called flyback converter, and the rectifier circuit 28 is composed of one diode 28a, and the smoothing circuit 30 is composed of a secondary interphase capacitor element 18, with the output voltage Vo generated across the secondary interphase capacitor element 18.

[0008] In terms of actual use, the switching power supply 10 is connected to an input power supply 34 which is grounded to an earth line 32 via an earth resistor Rs, and the input voltage Vi is input to the primary side stable potential line 12 (12a, 12b). In addition, an external load 36 is connected to the secondary side stable potential line 14 (14a, 14b), and the output voltage Vo is output toward the external load 36.

[0009] At this time, the primary side stable potential line 12 and the ground line 32 are connected by the primary side stray capacitance Cy1, and the secondary side stable potential line 14 and the ground line 32 are connected by the secondary side stray capacitance Cy2. In addition, an inter-winding stray capacitance Ct is formed between the primary side main winding 24(1) and the secondary side main winding 24(2).

[0010] Furthermore, the wiring patterns at multiple points in the inverter circuit 20, rectifier circuit 28, and smoothing circuit 30 where pulse voltages oscillating at the switching frequency Fsw are generated are connected to the ground line 32 by unstable potential stray capacitance. Specifically, the connection point between the primary main winding 24(1) and the switching element 26 is connected to the ground line 32 by unstable potential stray capacitance Cf1, and the connection point between the secondary main winding 24(2) and the rectifier circuit 28(28a) is connected to the ground line 32 by unstable potential stray capacitance Cf2.

[0011] The capacitance values ​​of the above-mentioned stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2 are typically small, less than a few tens of pF, and should be considered as stray capacitances that are the main paths through which switching noise flows. In addition, numerous other stray capacitances exist between the switching power supply 10 and the ground line 32. However, since the voltage across these stray capacitances other than Cy1, Cy2, Ct, Cf1, and Cf2 does not change AC-wise (or changes very little), they can be ignored in relation to the input feedback noise problem described later.

[0012] Next, I will explain the problems with the switching power supply 10. Since the switching power supply 10 is Class 2 in terms of electric shock protection, in actual use, numerous stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2 are formed between the internal circuit and the ground line 32. The voltage generated in the primary main winding 24(1) becomes a noise source, causing noise currents to flow from each stray capacitance to the ground line 32, resulting in a problem of increased input feedback noise. Input feedback noise is the noise that flows out from the switching power supply 10 towards the input power supply 34.

[0013] Generally, the common-mode component of input feedback noise is evaluated by the magnitude of the noise current Icom flowing through the ground resistance Rs. For example, the noise terminal voltage, one of the evaluation items in EMI standards, is evaluated by inserting a LISN (Low-Intensity Network System) containing a fixed resistor of several tens of ohms that simulates the ground resistance Rs between the input power supply, the input terminal of the power supply unit, and the ground line, and then evaluating the frequency characteristics (150kHz to 30MHz) of the voltage generated across the fixed resistor.

[0014] In the switching power supply unit 10, in order to suppress the common-mode component of input feedback noise, it is important to design it so that the noise current Icom flowing through the grounding resistance Rs is small under actual operating conditions. However, since it is a device compliant with Class 2 electric shock protection and there are many stray capacitances Cy1, Cy2, Ct, Cf1, and Cf2, it is not easy to appropriately control and keep the noise current Icom small.

[0015] For example, the technology described in Patent Document 1 cancels out the current flowing through the stray capacitance Ct between the primary and secondary main windings of an isolation transformer, and can be said to be a technology that substantially reduces the capacitance value of the stray capacitance Ct to a negligible degree. However, even if this technology is applied to the switching power supply device 10, only one of the many stray capacitances Cy1, Cy2, Ct, Cf1, Cf2 (stray capacitance Ct) is reduced, and the noise current Icom cannot be effectively reduced.

[0016] The present invention has been made in view of the above-mentioned background art, and aims to provide a switching power supply device compliant with electric shock protection class 2 that can effectively suppress noise current flowing through the grounding resistor. [Means for solving the problem]

[0017] The present invention is a device formed by mounting circuit components on a printed wiring board having multiple wiring layers, which converts an input voltage input between a primary power line and a primary ground line consisting of a pair of wiring patterns into a predetermined output voltage and generates it between a secondary power line and a secondary ground line consisting of a pair of wiring patterns. A primary-side interphase capacitor element is connected between the primary-side power supply line and the primary-side ground line, substantially short-circuits the primary-side power supply line and the primary-side ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable primary-side stable potential line. A secondary phase interphase capacitor element is connected between the secondary power line and the secondary ground line, substantially short-circuits the secondary power line and the secondary ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable secondary stable potential line. An inverter circuit comprising an isolation transformer and a switching element, wherein the primary main winding of the isolation transformer and the switching element are connected in series, and the switching element switches at the switching frequency to generate an intermittent voltage across the primary main winding of the primary main winding, A rectifier circuit connected to the secondary main winding of the isolation transformer, which rectifies the voltage generated in the secondary main winding to generate a rectified voltage, The system includes the secondary phase-phase capacitor element, smooths the rectified voltage to generate the output voltage, and generates the output voltage across the secondary phase-phase capacitor element, In actual use, the input voltage is supplied from an input power supply grounded to the ground line via a grounding resistor, the primary stable potential line and the ground line are connected by primary stray capacitance, the secondary stable potential line and the ground line are connected by secondary stray capacitance, interwinding stray capacitance is formed between the primary main winding and the secondary main winding, and the wiring patterns of the locations in the inverter circuit, the rectifier circuit and the smoothing circuit where pulse voltages oscillating at the switching frequency are generated are connected to the ground line by unstable potential stray capacitance. This switching power supply device generates a first noise current that flows out to the ground line through the unstable potential stray capacitance and a second noise current that flows out to the ground line through the secondary side stray capacitance, with the voltage generated in the primary side main winding acting as a noise source.

[0018] In the invention described in claim 1, the isolation transformer has a secondary auxiliary winding, one end of which is connected to the secondary side stable potential line; a wiring pattern connected to the other end of the secondary side auxiliary winding has a second main body region and a second capacitance-forming region continuous therewith; the primary side stable potential line has a first main body region and a first capacitance-forming region continuous therewith; a wiring pattern stray capacitance is formed by the first and second capacitance-forming regions facing each other; the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the opposing area of ​​the first and second capacitance-forming regions; and in the actual operating state, a current corresponding to the capacitance value flows through the wiring pattern stray capacitance, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less. In this case, the secondary side main winding and the secondary side auxiliary winding may be configured to be partially or entirely shared with each other (invention described in claim 2).

[0019] In the invention described in claim 3, the isolation transformer has a primary auxiliary winding, one end of which is connected to the primary side stable potential line; a wiring pattern connected to the other end of the primary side auxiliary winding has a first main body region and a first capacitance-forming region continuous therewith; the secondary side stable potential line has a second main body region and a second capacitance-forming region continuous therewith; a wiring pattern stray capacitance is formed by the first and second capacitance-forming regions facing each other; the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the opposing area of ​​the first and second capacitance-forming regions; and in the actual operating state, a current corresponding to the capacitance value flows through the wiring pattern stray capacitance, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less. In this case, the primary side main winding and the primary side auxiliary winding may be configured to be partially or entirely shared by each other (invention described in claim 4).

[0020] Furthermore, the configuration may include a coupling capacitor element connected between the primary side stable potential line and the secondary side stable potential line, which substantially short-circuits the primary side stable potential line and the secondary side stable potential line in a frequency band above the switching frequency (invention described in claim 5). First A Q-damping resistor element may be inserted in series at least one of the boundary between the main body region and the first capacitance-forming region, and the boundary between the second main body region and the second capacitance-forming region, such that the sharpness of the resonance that appears in a frequency band higher than the switching frequency of the resonant system formed by the inter-winding stray capacitance, the wiring pattern stray capacitance, and the parasitic inductance components present in their vicinity is suppressed by the Q-damping resistor element (invention described in claim 6). [Effects of the Invention]

[0021] The switching power supply device of the present invention forms a wiring pattern capacitance by opposing the wiring patterns of different wiring layers of a printed wiring board, and can freely set the magnitude and direction of the current flowing through the wiring pattern stray capacitance with the opposing area of the wiring pattern, the number of turns and polarity of the auxiliary winding. Therefore, it is possible to effectively suppress the noise current flowing through the ground resistance in the actual use state, and it is possible to easily obtain a Class 2 touch protection switching power supply device with small input feedback noise.

[0022] Also, in the switching regulator of Patent Document 1, a capacitor element is connected between the noise compensation winding and the input power supply line. However, since this capacitor element is an element spanning between the primary and secondary, a large-sized high withstand voltage product must be selected. However, in the case of the switching power supply device of the present invention, since the capacitor spanning between the primary and secondary is a stray capacitance (wiring pattern stray capacitance) formed by the wiring pattern of the printed wiring board, it can be configured very compactly.

[0023] Further, the present invention is a very highly versatile technology, and the types of applicable inverter circuits are not particularly limited. For example, it can be applied to various isolated inverter circuits such as flyback method, single-ended forward method, half-bridge method, full-bridge method, etc.

Brief Description of Drawings

[0024] [Figure 1] It is a circuit diagram showing a first embodiment [flyback method / step-down type] of the switching power supply device of the present invention. [Figure 2] It is a longitudinal sectional view schematically showing the structure of an isolation transformer, a wiring pattern stray capacitance, and its peripheral part of the switching power supply device [flyback method / step-down type] of the first embodiment. [Figure 3] It is a common mode equivalent circuit (a) showing an example of the operation of the switching power supply device [flyback method / step-down type] of the first embodiment, and a common mode equivalent circuit (b) showing the operation of a comparative example without a wiring pattern stray capacitance and a secondary side auxiliary winding. [Figure 4] (a) is the measured noise field strength of the switching power supply [flyback type / step-down type] of the first embodiment, and (b) is the measured data of a comparative example in which the Q damping resistor is short-circuited. [Figure 5] (a) shows the measured resonant characteristics of the resonant system formed by the isolation transformer, wiring pattern stray capacitance and surrounding area of ​​the switching power supply device [flyback type / step-down type] of the first embodiment, and (b) shows a circuit diagram illustrating the method for measuring the resonant characteristics. [Figure 6] (a) is a common-mode equivalent circuit showing an example of operation of a modified example [flyback type / boost type] of the switching power supply of the first embodiment, and (b) is a common-mode equivalent circuit showing the operation of a comparative example without wiring pattern stray capacitance and secondary auxiliary winding. [Figure 7] This is a circuit diagram showing a second embodiment [flyback type / step-down type] of the switching power supply device of the present invention. [Figure 8] This is a schematic longitudinal cross-sectional view showing the structure of the isolation transformer, wiring pattern stray capacitance, and surrounding parts of the switching power supply device [flyback type / step-down type] of the second embodiment. [Figure 9] (a) is a common-mode equivalent circuit showing an example of the operation of the switching power supply [flyback type / step-down type] of the second embodiment, and (b) is a common-mode equivalent circuit showing the operation of a comparative example without wiring pattern stray capacitance and primary-side auxiliary winding. [Figure 10] (a) is a common-mode equivalent circuit showing the operation of a modified example [flyback type / boost type] of the switching power supply of the second embodiment, and (b) is a common-mode equivalent circuit of a comparative example without wiring pattern stray capacitance and primary-side auxiliary winding. [Figure 11] This is a circuit diagram showing a third embodiment [single-ended forward type / step-down type] of the switching power supply device of the present invention. [Figure 12](a) is a common-mode equivalent circuit showing an example of the operation of a switching power supply [single-ended forward type / step-down type] of the third embodiment, and (b) is a common-mode equivalent circuit showing the operation of a comparative example without wiring pattern stray capacitance and secondary auxiliary winding. [Figure 13] This is a circuit diagram showing a fourth embodiment [single-ended forward type / step-down type] of the switching power supply device of the present invention. [Figure 14] This is a circuit diagram showing another modification of the switching power supply of the first embodiment [a modification of the secondary auxiliary winding structure]. [Figure 15] This is a circuit diagram showing another modification of the switching power supply device of the first embodiment [with the addition of a coupling capacitor element]. [Figure 16] This is a circuit diagram showing a conventional switching power supply. [Modes for carrying out the invention]

[0025] <<<Switching power supply device of the first embodiment and its modified form>>> The following describes a first embodiment of the switching power supply device of the present invention and its modified examples. Here, components similar to those in the conventional switching power supply device 10 are denoted by the same reference numerals and their description is omitted. <<Switching power supply unit 38>> First, a switching power supply device 38, which is a first embodiment of the switching power supply device of the present invention, will be described with reference to Figures 1 to 5. <Configuration of switching power supply unit 38> The switching power supply unit 38 is a flyback converter similar to the conventional switching power supply unit 10, and is a step-down converter in which the output voltage Vo is lower than the input voltage Vi. Therefore, the primary main winding 24(1) has more turns than the secondary main winding 24(2). The switching power supply unit 38 is a switching power supply unit 10 with several additional components (essential parts of the invention) added, so here we will mainly explain the components added to the switching power supply unit 10.

[0026] As shown in Figure 1, the switching power supply 38 has a third winding, a secondary auxiliary winding 40(2), added to the isolation transformer 22, with one end connected to the secondary stable potential line 14(14b). The wiring pattern 42 connected to the other end of the secondary auxiliary winding 40(2) consists of a second main region 42h and a second capacitance-forming region 42c that is continuous therewith, and a Q-damp resistor element Rh is inserted in series at the boundary between the two regions 42h and 42c.

[0027] The primary side stable potential line 12(12b) has a first main body region 44h and a first capacitance-forming region 44c that is continuous therewith, and the first capacitance-forming region 44c and the second capacitance-forming region 42c face each other, forming a wiring pattern stray capacitance Ch.

[0028] The structure of the isolation transformer 22 and its surrounding parts will be briefly explained using Figure 2. The switching power supply unit 38 is assembled by mounting circuit components on a printed circuit board 46 which has multiple wiring layers inside a base material 46a. The isolation transformer 22 has a structure in which three windings 24(1), 24(2), and 40(2) are formed by the wiring patterns of each wiring layer, and a magnetic core 48 is mounted around them.

[0029] The wiring pattern 42 connected to one end of the secondary auxiliary winding 40(2) has a second main body region 42h located near the magnetic core 48 and a second capacitance-forming region 42c located further away, with a Q-dampping resistor Rh inserted in series at the boundary. The second capacitance-forming region 42c faces a first capacitance-forming region 44c located on another wiring layer, and a wiring pattern stray capacitance Ch is formed between them.

[0030] The wiring pattern stray capacitance Ch is set to a predetermined capacitance value by adjusting the opposing area of ​​the two capacitance-forming regions 42c and 44c. The specific capacitance value to be set will be explained in detail later. It is preferable to position the capacitance-forming regions 42c and 44c in locations where leakage flux from the magnetic core 48 is unlikely to link. This is because if leakage flux links, eddy currents will flow in the capacitance-forming regions 42c and 44c, resulting in unnecessary losses.

[0031] The stray capacitance to be considered in the actual operating state of the switching power supply 38 is as shown in the circuit diagram of Figure 1. The difference from the switching power supply 10 shown in Figure 16 is that an unstable potential stray capacitance Cf3 is added connecting the wiring pattern 42 (42h, 42c) at the other end of the secondary auxiliary winding 40(2) to the ground line 32, and a wiring pattern stray capacitance Ch is added between the first capacitance formation region 44c and the second capacitance formation region 42c.

[0032] <Operation of the switching power supply unit 38> Next, the operation of the switching power supply 38 will be explained using the common-mode equivalent circuit shown in Figure 3(a). This common-mode equivalent circuit is a simplified equivalent circuit that shows operation in a frequency band of approximately Fsw ~ 10 × Fsw. The Q-damp resistor Rh contributes almost nothing to the operation in this frequency band, so it has been excluded (short-circuit removed) from the common-mode equivalent circuit. Here, the current obtained by combining the currents flowing out to the ground line 32 through the unstable potential stray capacitances Cf1, Cf2, ... is defined as the first noise current Icom(1), and the current flowing out to the ground line 32 through the secondary side stray capacitance Cy2 is defined as the second noise current Icom(2). In other words, the noise current Icom that returns to the switching power supply 38 through the ground resistance Rs and the primary side stray capacitance Cy1, which is the main cause of input feedback noise, is given by Icom = Icom(1) + Icom(2).

[0033] Before explaining the operation of the switching power supply 38, we will first explain the operation of comparative example 50a, which lacks wiring pattern stray capacitance Ch and secondary auxiliary winding 40(2), based on Figure 3(b). In the common-mode equivalent circuit of Figure 3(b), the voltage source labeled "Vp" is a voltage source that outputs the voltage Vp generated across the primary main winding 24(1) when the switching element 26 switches, and the sinusoidal voltages of various frequencies contained in the pulsed voltage Vp become noise sources. The voltage source labeled "Ks·Vp" is a voltage source that outputs the voltage Ks·Vp generated on the secondary main winding 24(2), where Ks is the value obtained by dividing the number of turns of the secondary main winding 24(2) by the number of turns of the primary main winding 24(1) (turns ratio). Since the switching power supply 38 (and comparative example 50a) is a step-down flyback converter, the turns ratio Ks is less than 1. Furthermore, the "+" and "-" signs attached to each voltage source indicate polarity, and the dots attached to the two windings 24(1) and 24(2) in the circuit diagram of Figure 1 correspond to "+".

[0034] The solid arrows in Figure 3(b) indicate the direction of the noise current flowing through each part. The current values ​​are numerical examples for the sake of clarity, and represent the noise current values ​​flowing through each part when the noise current flowing through the unstable potential stray capacitance Cf1 is assumed to be 100 μA. In comparative example 50a, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is 20 μA, and the noise current Icom, which is the main cause of input feedback noise, is 130 μA.

[0035] In contrast, the switching power supply 38 has a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) added to reduce the noise current Icom = 130 μA of Comparative Example 50a. Therefore, the common-mode equivalent circuit is modified as shown in Figure 3(a) by adding a wiring pattern stray capacitance Ch, an unstable potential stray capacitance Cf3, and a voltage source labeled "Kh2·Vp".

[0036] The voltage source labeled "Kh2·Vp" is a voltage source that outputs the voltage Kh2·Vp generated in the secondary auxiliary winding 40(2), where Kh2 is the value obtained by dividing the number of turns of the secondary auxiliary winding 40(2) by the number of turns of the primary main winding 24(1) (turns ratio). The "+" and "-" signs labeled with this voltage source indicate polarity, and the dots on the secondary auxiliary winding 40(2) in the circuit diagram in Figure 1 correspond to "+".

[0037] In the switching power supply unit 38, in addition to the current indicated by the solid arrow in Figure 3(b), the current indicated by the dashed arrow is also generated. As a result, the first noise current Icom(1) is 120 μA and the second noise current Icom(2) is -120 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0038] As can be seen in Figure 3(a), the current flowing through the voltage source labeled "Kh2·Vp" and the stray capacitance Ch of the wiring pattern, as indicated by the dashed arrow, is a cancellation current that suppresses the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the stray capacitance Ch of the wiring pattern and the number of turns of the secondary auxiliary winding 40(2). By setting the noise current Icom to be below the reference value, the input feedback noise can be suppressed to a minimum. For example, the noise terminal voltage (150k~30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0039] In the switching power supply unit 38, one end of the secondary auxiliary winding 40(2) is connected to the secondary ground line 14b, but the same effect can be obtained by connecting it to the secondary power line 14a. Also, in the switching power supply unit 38, the first main body region 44h and the first capacitance forming region 44c are provided on the primary ground line 12b, but the same effect can be obtained by providing them on the primary power line 12a.

[0040] Next, the function of the Q-dampping resistor Rh will be explained based on Figures 4 and 5. The Q-dampping resistor Rh is effective in suppressing noise electric field strength (30 MHz to 1 GHz), which is one of the evaluation items for radiated interference waves.

[0041] Figure 4(a) shows the measured noise field strength data for the switching power supply unit 38, and Figure 4(b) shows the measured data for comparative example 50b, in which the Q-damp resistor element Rh is short-circuited. Comparing the two sets of measured data, the level at 35 MHz to 65 MHz is relatively high when the Q-damp resistor element Rh is absent, whereas when the Q-damp resistor element RH is provided, the level at 35 MHz to 65 MHz drops by several dB. This can be explained based on the data in Figure 5.

[0042] Figure 5(a) shows the measured frequency characteristics of the combined stray capacitance (combined stray capacitance) which is the sum of the inter-winding stray capacitance Ct and the wiring pattern stray capacitance Ch. The combined stray capacitance is calculated by assembling the measurement circuit shown in Figure 5(b), measuring the voltage V applied by the oscillator OSC and the current I flowing through it, calculating Z = V / I, and then converting this to a capacitance value by considering it as the impedance of a pure capacitor.

[0043] When the Q-damping resistor Rh was absent, a resonance point occurred at approximately 60 MHz, and the combined stray capacitance in the 20-70 MHz range increased significantly. However, when the Q-damping resistor Rh (47 Ω) was added, although the resonance point remained at approximately 60 MHz, the increase in the combined stray capacitance in the 20-70 MHz range was significantly reduced. This suggests that by adding the Q-damping resistor Rh (47 Ω in this example), the sharpness of the resonance that appears in a frequency band sufficiently higher than the switching frequency Fsw (approximately 60 MHz in this example) of the resonant system formed by the inter-winding stray capacitance Ct, the wiring pattern stray capacitance Ch, and the parasitic inductance components present in their vicinity was greatly suppressed.

[0044] Generally, this type of resonance phenomenon is known to be likely to cause an increase in the radiated interference waves from the switching power supply device. However, even if an unintended resonance system is formed in the insulation transformer 22 and its surrounding parts as in the switching power supply device 38, by connecting the Q-damping resistor element Rh in series near the wiring pattern stray capacitance Ch, unnecessary radiated interference waves can be effectively suppressed.

[0045] In the switching power supply device 38, the Q-damping resistor element Rh is provided at the boundary between the second main body region 42h and the second capacitance forming region 42c, but it may also be provided at the boundary between the first main body region 44h and the first capacitance forming region 44c, and substantially the same effect can be obtained.

[0046] <<Modified Switching Power Supply Device 38x>> Next, a modified example of the switching power supply device 38, the switching power supply device 38x, will be described based on FIG. 6.​​​​​​​​​​​​​Next, the operation of the switching power supply 38x will be explained using the common-mode equivalent circuit shown in Figure 6(a). This common-mode equivalent circuit is also a simplified equivalent circuit that shows operation in a frequency band of approximately Fsw ~ 10 × Fsw with respect to the switching frequency Fsw. Before explaining the operation of the switching power supply unit 38x, we will first explain the operation of comparative example 50b, which lacks the wiring pattern stray capacitance Ch and the secondary auxiliary winding 40(2), based on Figure 6(b). The current values ​​shown in Figure 6(b) are numerical examples to make the explanation easier to understand, and represent the noise current values ​​flowing through each part when the noise current flowing through the unstable potential stray capacitance Cf1 is assumed to be 10 μA. In comparative example 50b, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is -130 μA, and the noise current Icom, which is the main cause of input feedback noise, is -20 μA. Since comparative example 50b has Ks > 1, there are differences compared to the case where Ks < 1 (Figure 3(b)), such as the direction of the current flowing through the inter-winding stray capacitance Ct being reversed.

[0049] In contrast, the switching power supply 38x has a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) added to reduce the noise current Icom = -20μA in comparative example 50b. Therefore, the common-mode equivalent circuit is modified as shown in Figure 6(a) by adding a wiring pattern stray capacitance Ch, an unstable potential stray capacitance Cf3, and a voltage source labeled "Kh2·Vp".

[0050] The voltage source labeled "Kh2·Vp" is a voltage source that outputs the voltage Kh2·Vp generated in the secondary auxiliary winding 40(2). However, the switching power supply 38x has the polarity of the secondary auxiliary winding 40(2) reversed, so the positions of "+" and "-" are reversed compared to the switching power supply 30 (Figure 3(a)).

[0051] In the switching power supply unit 38x, in addition to the currents indicated by the solid arrows in Figure 6(b), the currents indicated by the dashed arrows are also generated. As a result, the first noise current Icom(1) is 100 μA and the second noise current Icom(2) is -100 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0052] As can be seen in Figure 6(a), the current flowing through the voltage source labeled "Kh2·Vp" and the stray capacitance Ch of the wiring pattern, as indicated by the dashed arrow, is a cancellation current used to suppress the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the stray capacitance Ch of the wiring pattern and the number of turns of the secondary auxiliary winding 40(2). By setting the noise current Icom to be below the reference value, the input feedback noise can be kept low.

[0053] Thus, the boost-type switching power supply 38x operates in a similar manner to the buck-type switching power supply 38, and the same effect can be obtained. <<Summary of Switching Power Supply Units 38 and 38x>> The switching power supplies 38 and 38x form a wiring pattern stray capacitance Ch by facing the wiring patterns of different wiring layers on the printed circuit board 46, and the magnitude and direction of the current flowing through the wiring pattern stray capacitance Ch can be freely set by the facing area of ​​the wiring patterns and the number of turns and polarity of the secondary auxiliary winding 40(2). Therefore, the noise current Icom flowing through the ground resistance Rs in actual use can be effectively suppressed, and a switching power supply with low input feedback noise and electric shock protection class 2 can be obtained.

[0054] Furthermore, in the switching regulator described in Patent Document 1, a capacitor element is connected between the noise compensation winding and the input power supply line. However, since this capacitor element spans between the primary and secondary windings, a large, high-voltage component must be selected. In contrast, in the case of switching power supply devices 38 and 38x, the capacitor spanning between the primary and secondary windings is a stray capacitance (wiring pattern stray capacitance Ch) formed by the wiring pattern of the printed circuit board, allowing for a very compact configuration.

[0055] <<<Switching power supply device of the second embodiment and its modified form>>> Next, a second embodiment of the switching power supply device of the present invention and a modified example thereof will be described. Here, components similar to those in the conventional switching power supply device 10 are denoted by the same reference numerals and their description is omitted. <<Switching power supply unit 52>> First, the switching power supply device 52 of the second embodiment will be described with reference to Figures 7 to 9. <Configuration of switching power supply unit 52> The switching power supply unit 52 is a flyback converter, similar to the conventional switching power supply unit 10, and is a step-down converter in which the output voltage Vo is lower than the input voltage Vi. Therefore, the primary main winding 24(1) has more turns than the secondary main winding 24(2). The switching power supply unit 52 is a switching power supply unit 10 with several additional components (essential parts of the invention) added, and this explanation will focus on the components added to the switching power supply unit 10.

[0056] As shown in Figure 7, the switching power supply 52 has a third winding, a primary auxiliary winding 40(1), added to the isolation transformer 22, with one end connected to the primary stable potential line 12(12a). The wiring pattern 54 connected to the other end of the primary auxiliary winding 40(1) consists of a first main body region 54h and a first capacitance forming region 54c that is continuous therewith, and a Q-damp resistor element Rh is inserted in series at the boundary between the two regions 54h and 54c.

[0057] The secondary side stable potential line 14(14b) has a second main body region 56h and a second capacitance-forming region 56c that is continuous therewith, and the first capacitance-forming region 54c and the second capacitance-forming region 56c face each other, forming a wiring pattern stray capacitance Ch.

[0058] The structure of the isolation transformer 22 and its surrounding parts will be briefly explained with reference to Figure 8. The switching power supply 52 is assembled by mounting circuit components on a printed circuit board 46 which has multiple wiring layers inside a base material 46a. The isolation transformer 22 has a structure in which three windings 24(1), 24(2), and 40(1) are formed by the wiring patterns of each wiring layer, and a magnetic core 48 is mounted around them.

[0059] The wiring pattern 54 connected to one end of the primary auxiliary winding 40(1) has a first main body region 54h located near the magnetic core 48 and a first capacitance-forming region 54c located further away, with a Q-dampping resistor Rh inserted in series at the boundary. The first capacitance-forming region 54c faces a second capacitance-forming region 56c located on another wiring layer, and a wiring pattern stray capacitance Ch is formed between them.

[0060] The wiring pattern stray capacitance Ch is set to a predetermined capacitance value by adjusting the opposing area of ​​the two capacitance-forming regions 54c and 56c. The specific capacitance value to be set will be explained in detail later. It is preferable to position the capacitance-forming regions 54c and 56c in locations where leakage flux from the magnetic core 48 is unlikely to link. This is because if leakage flux links, eddy currents will flow in the capacitance-forming regions 54c and 56c, resulting in unnecessary losses.

[0061] The stray capacitance to be considered in the actual operating state of the switching power supply 52 is as shown in the circuit diagram of Figure 7. The difference from the switching power supply 10 shown in Figure 16 is the addition of an unstable potential stray capacitance Cf4 connecting the wiring pattern 54 (54h, 54c) at the other end of the primary auxiliary winding 40(1) to the ground line 32, and the addition of a wiring pattern stray capacitance Ch between the first capacitance formation region 54c and the second capacitance formation region 56c.

[0062] <Operation of switching power supply 52> Next, the operation of the switching power supply 52 will be explained using the common-mode equivalent circuit shown in Figure 9(a). This common-mode equivalent circuit is also a simplified equivalent circuit that shows operation in a frequency band of approximately Fsw ~ 10 × Fsw. The Q-damp resistor Rh contributes almost nothing to the operation in this frequency band, so it has been excluded (short-circuit removed) from the common-mode equivalent circuit. Furthermore, the meanings of the first noise current Icom(1), the second noise current Icom(2), and the noise current Icom that appear in this explanation are the same as described above.

[0063] Before explaining the operation of the switching power supply 52, we will first explain the operation of Comparative Example 50c, which lacks the wiring pattern stray capacitance Ch and the primary-side auxiliary winding 40(1), based on Figure 9(b). The common-mode equivalent circuit of this Comparative Example 50c has the same configuration as the common-mode equivalent circuit of Comparative Example 50a (Figure 3(b)) described above. The current values ​​are also numerical examples to make the explanation easier to understand, and they show the noise current values ​​flowing through each part when the noise current flowing through the unstable potential stray capacitance Cf1 is assumed to be 100 μA. In the case of Comparative Example 50c, the first noise current Icom(1) is 110 μA, the second noise current Icom(2) is 20 μA, and the noise current Icom, which is the main cause of input feedback noise, is 130 μA.

[0064] In contrast, the switching power supply 52 has a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) added to reduce the noise current Icom = 130 μA of comparative example 50c. Therefore, the common-mode equivalent circuit is modified as shown in Figure 9(a) by adding a wiring pattern stray capacitance Ch, an unstable potential stray capacitance Cf4, and a voltage source labeled "Kh1·Vp".

[0065] The voltage source labeled "Kh1·Vp" is a voltage source that outputs the voltage Kh1·Vp generated in the primary auxiliary winding 40(1), where Kh1 is the value obtained by dividing the number of turns of the primary auxiliary winding 40(1) by the number of turns of the primary main winding 24(1) (turns ratio). The "+" and "-" signs labeled with this voltage source indicate polarity, and the dots on the primary auxiliary winding 40(1) in the circuit diagram in Figure 7 correspond to "+".

[0066] In the switching power supply 52, in addition to the current indicated by the solid arrow in Figure 9(b), the current indicated by the dashed arrow is also generated. As a result, the first noise current Icom(1) is 100 μA and the second noise current Icom(2) is -100 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0067] As can be seen in Figure 9(a), the current flowing through the voltage source labeled "Kh1·Vp" and the stray capacitance Ch of the wiring pattern, as indicated by the dashed arrow, is a cancellation current that suppresses the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the stray capacitance Ch of the wiring pattern and the number of turns of the primary auxiliary winding 40(1). By setting the noise current Icom to be below the reference value, the input feedback noise can be suppressed to a minimum. For example, the noise terminal voltage (150k~30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0068] In the switching power supply unit 52, one end of the primary auxiliary winding 40(1) is connected to the primary power line 12a, but the same effect can be obtained by connecting it to the primary ground line 12b. Also, in the switching power supply unit 52, the second main body region 56h and the second capacitance forming region 56c are provided on the secondary ground line 14b, but the same effect can be obtained by providing them on the secondary power line 14a.

[0069] The function of the Q-dump resistor element Rh is the same as that of the Q-dump resistor element Rh of the switching power supply device 38 described above. It suppresses the sharpness of resonance that appears in a frequency band sufficiently higher than the switching frequency Fsw of a resonance system formed by the inter-turn stray capacitance Ct, the wiring pattern stray capacitance Ch, and the parasitic inductance components existing in the vicinity thereof. As a result, unnecessary radiation interference waves can be effectively suppressed.

[0070] In the switching power supply device 52, the Q-dump resistor element Rh is provided at the boundary between the first main body region 54h and the first capacitance forming region 54c. However, it may be provided at the boundary between the second main body region 56h and the second capacitance forming region 56c, and substantially the same effect can be obtained.

[0071] <<Switching power supply device 52x of the modification example>> Next, a switching power supply device 52x, which is a modification example of the switching power supply device 52, will be described based on FIG. 10. <Configuration of the switching power supply device 52x> Since the above-described switching power supply device 52 is a step-down converter [Vi>Vo], the value (turns ratio Ks) obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) is less than 1. Also, since it is a step-down converter, one end of the primary-side auxiliary winding 40(1) with a dot is connected to the primary-side stable potential line 12.

[0072] In contrast, the switching power supply device 52x of the modification example is a step-up converter [Vi<Vo], and the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1. There is a difference in that one end of the primary-side auxiliary winding 40(1) without a dot is connected to the primary-side stable potential line 12. Other configurations are the same. <Operation of the switching power supply device 52x> Next, the operation of the switching power supply device 52x will be described using the common-mode equivalent circuit shown in FIG. 6(a). This common-mode equivalent circuit is also a simplified equivalent circuit showing the operation in a frequency band of about Fsw to 10×Fsw with respect to the switching frequency Fsw.

[0073] Before explaining the operation of the switching power supply 52x, we will first explain the operation of Comparative Example 50d, which lacks the wiring pattern stray capacitance Ch and the primary auxiliary winding 40(1), based on Figure 10(b). The common-mode equivalent circuit of this Comparative Example 50d is the same as the common-mode equivalent circuit of Comparative Example 50b (Figure 6(b)) described above, and the current values ​​are numerical examples for the sake of clarity, showing the noise current values ​​flowing through each part when the noise current flowing through the unstable potential stray capacitance Cf1 is assumed to be 10μA. Therefore, in Comparative Example 50d, the first noise current Icom(1) is 110μA, the second noise current Icom(2) is -130μA, and the noise current Icom, which is the main cause of input feedback noise, is -20μA. Since Ks>1 in Comparative Example 50d, there are differences compared to the case where Ks<1 (Figure 9(b)), such as the direction of the current flowing through the inter-winding stray capacitance Ct being reversed.

[0074] In contrast, the switching power supply 52x has a wiring pattern stray capacitance Ch and a primary-side auxiliary winding 40(1) added to reduce the noise current Icom = -20μA of comparative example 50d. Therefore, the common-mode equivalent circuit is modified as shown in Figure 10(a) by adding a wiring pattern stray capacitance Ch, an unstable potential stray capacitance Cf3, and a voltage source labeled "Kh1·Vp".

[0075] The voltage source labeled "Kh1·Vp" is a voltage source that outputs the voltage Kh1·Vp generated in the primary auxiliary winding 40(1). However, the switching power supply 52x has the polarity of the primary auxiliary winding 40(1) reversed, so compared to the switching power supply 52 (Figure 9(a)), the positions of the "+" and "-" labels on this voltage source are reversed.

[0076] In the switching power supply unit 52x, in addition to the current indicated by the solid arrow in Figure 10(b), the current indicated by the dashed arrow is also generated. As a result, the first noise current Icom(1) is 120 μA and the second noise current Icom(2) is -120 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0077] As can be seen in Figure 10(a), the current flowing through the voltage source labeled "Kh1·Vp" and the stray capacitance Ch of the wiring pattern, as indicated by the dashed arrow, is a cancellation current used to suppress the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the stray capacitance Ch of the wiring pattern and the number of turns of the primary auxiliary winding 40(1). By setting the noise current Icom to be below the reference value, the input feedback noise can be kept low.

[0078] Thus, the boost-type switching power supply 52x operates similarly to the buck-type switching power supply 52, and the same effect can be obtained.

[0079] <<Summary of Switching Power Supplies 52 and 52x>> The switching power supplies 52 and 52x form a wiring pattern stray capacitance Ch by facing the wiring patterns of different wiring layers on the printed circuit board 46, and the magnitude and direction of the current flowing through the wiring pattern stray capacitance Ch can be freely set by the facing area of ​​the wiring patterns and the number of turns and polarity of the primary auxiliary winding 40(1). Therefore, the noise current Icom flowing through the ground resistance Rs in actual use can be effectively suppressed, and a switching power supply with low input feedback noise and electric shock protection class 2 can be obtained. Furthermore, similar to the switching power supply devices 38 and 38x described above, it can be configured more compactly than the switching regulator described in Patent Document 1.

[0080] <<<Switching power supply device of the third embodiment and its modified form>>> Next, a third embodiment of the switching power supply device of the present invention and a modified example thereof will be described. Here, components similar to those in the conventional switching power supply device 10 are denoted by the same reference numerals and their description is omitted. <<Switching power supply unit 58>> First, the switching power supply unit 58 of the third embodiment will be described with reference to Figures 11 and 12. Here, components similar to those in the conventional switching power supply unit 10 are denoted by the same reference numerals and their description is omitted. <Configuration of Switching Power Supply Unit 58> While the conventional switching power supply 10 is a flyback converter, the switching power supply 58 is a single-ended forward converter, with the rectifier circuit 28 consisting of two diodes 28b and 28c, and the smoothing circuit 30 consisting of an inductor 30a and an output phase-phase capacitor element 18. Furthermore, several components that constitute the core of the present invention have been added. In addition, since the switching power supply 58 is a step-down converter where the output voltage Vo is lower than the input voltage Vi, the primary main winding 24(1) has more turns than the secondary main winding 24(2). The configuration of the switching power supply 58 will be described below, focusing on the added components (the core of the invention).

[0081] As shown in Figure 11, the switching power supply 58 has a third winding, a secondary auxiliary winding 40(2), added to the isolation transformer 22, with one end connected to the secondary stable potential line 14(14b). The wiring pattern 42 connected to the other end of the secondary auxiliary winding 40(2) consists of a second main region 42h and a second capacitance-forming region 42c that is continuous therewith, and a Q-damp resistor Rh is inserted in series at the boundary between the two regions 42h and 42c.

[0082] The primary side stable potential line 12(12b) has a first main body region 44h and a first capacitance-forming region 44c that is continuous therewith, and the first capacitance-forming region 44c and the second capacitance-forming region 42c face each other, forming a wiring pattern stray capacitance Ch.

[0083] The stray capacitances to be considered in the actual operating state of the switching power supply 58 are, as shown in the circuit diagram of Figure 11, the primary side stray capacitance Cy1 connecting the primary side stable potential line 12 and the ground line 32, the secondary side stray capacitance Cy2 connecting the secondary side stable potential line 14 and the ground line 32, the inter-winding stray capacitance Ct formed between the primary side main winding 24(1) and the secondary side main winding 24(2), and the wiring pattern stray capacitance Ch formed between the first capacitance formation region 44c and the second capacitance formation region 42c.

[0084] Furthermore, the unstable stray capacitances to be considered include: an unstable potential stray capacitance Cf1 connecting the connection point of the primary main winding 24(1) and the switching element 26 to the ground line 32; an unstable potential stray capacitance Cf2 connecting the connection point of the secondary main winding 24(2) and the rectifier circuit 28(28a) to the ground line 32; an unstable potential stray capacitance Cf3 connecting the wiring pattern 42(42h,42c) to the ground line 32; and an unstable potential stray capacitance Cf5 connecting the diode 28a and the inductor 30 to the connection point 60 and the ground line 32.

[0085] <Operation of switching power supply unit 58> Next, the operation of the switching power supply 58 will be explained using the common-mode equivalent circuit shown in Figure 12(a). This common-mode equivalent circuit is also a simplified equivalent circuit that shows operation in a frequency band of approximately Fsw ~ 10 × Fsw. The Q-damp resistor Rh contributes almost nothing to the operation in this frequency band, so it has been excluded (short-circuit removed) from the common-mode equivalent circuit. Furthermore, the meanings of the first noise current Icom(1), the second noise current Icom(2), and the noise current Icom that appear in this explanation are the same as described above.

[0086] Before explaining the operation of the switching power supply 58, we will first explain the operation of comparative example 50e, which lacks the wiring pattern stray capacitance Ch and the secondary auxiliary winding 40(2), based on Figure 12(b). In the common-mode equivalent circuit of Figure 12(b), the voltage source labeled "Vp" is a voltage source that generates the voltage Vp that occurs across the primary main winding 24(1) when the switching element 26 switches, and the sinusoidal voltages of various frequencies contained in the pulsed voltage Vp become noise sources. The voltage source labeled "Ks·Vp" is a voltage source that outputs the voltage Ks·Vp generated in the secondary main winding 24(2), where Ks is the value obtained by dividing the number of turns of the secondary main winding 24(2) by the number of turns of the primary main winding 24(1) (turns ratio). The voltage source labeled "Kc·Vp" is a voltage source that outputs the voltage Kc·Vp generated in the inductor 30a, where Kc is a coefficient indicating the amplitude ratio with voltage Vp. Furthermore, the "+" and "-" signs attached to each voltage source indicate polarity, and in the circuit diagram in Figure 11, the dots attached to the two windings 24(1) and 24(2) and the inductor 30 correspond to "+".

[0087] The current values ​​shown in Figure 12(b) are numerical examples for the purpose of making the explanation easier to understand, and represent the noise current values ​​flowing through each part when the noise current flowing through the astable potential stray capacitance Cf1 is assumed to be 100 μA. In comparative example 50e, the first noise current Icom(1) is 115 μA, the second noise current Icom(2) is 15 μA, and the noise current Icom, which is the main cause of input feedback noise, is 130 μA.

[0088] In contrast, the switching power supply 58 has a wiring pattern stray capacitance Ch and a secondary auxiliary winding 40(2) added to reduce the noise current Icom = 130 μA of comparative example 50e. Therefore, the common-mode equivalent circuit is modified as shown in Figure 12(a), with the addition of a wiring pattern stray capacitance Ch, an unstable potential stray capacitance Cf3, and a voltage source labeled "Kh2·Vp".

[0089] The voltage source labeled "Kh2·Vp" is a voltage source that outputs the voltage Kh2·Vp generated in the secondary auxiliary winding 40(2), where Kh2 is the value obtained by dividing the number of turns of the secondary auxiliary winding 40(2) by the number of turns of the primary main winding 24(1) (turns ratio). The "+" and "-" signs labeled with this voltage source indicate polarity, and the dots on the secondary auxiliary winding 40(2) in the circuit diagram in Figure 11 correspond to "+".

[0090] In the switching power supply 58, in addition to the current indicated by the solid arrow in Figure 12(b), the current indicated by the dashed arrow is also generated. As a result, the first noise current Icom(1) is 125 μA and the second noise current Icom(2) is -125 μA, and the noise current Icom, which is the main cause of input feedback noise, is suppressed to almost zero μA.

[0091] As can be seen in Figure 12(a), the current flowing through the voltage source labeled "Kh2·Vp" and the stray capacitance Ch of the wiring pattern, as indicated by the dashed arrow, is a cancellation current used to suppress the noise current Icom. The magnitude of this cancellation current can be changed by adjusting the capacitance value of the stray capacitance Ch of the wiring pattern and the number of turns of the secondary auxiliary winding 40(2). By setting the noise current Icom to be below the reference value, input feedback noise can be suppressed. For example, the noise terminal voltage (150k~30MHz), which is one of the evaluation items of the EMI standard, can be easily cleared.

[0092] In the switching power supply unit 58, one end of the secondary auxiliary winding 40(2) is connected to the secondary ground line 14b, but the same effect can be obtained by connecting it to the secondary power line 14a. Also, in the switching power supply unit 58, the first main body region 44h and the first capacitance forming region 44c are provided on the primary ground line 12b, but the same effect can be obtained by providing them on the primary power line 12a.

[0093] The function of the Q-dump resistor element Rh is the same as that of the Q-dump resistor element Rh of the switching power supply device 38 described above. It suppresses the sharpness of resonance that appears in a frequency band sufficiently higher than the switching frequency Fsw of a resonance system formed by the inter-turn parasitic capacitance Ct, the wiring pattern parasitic capacitance Ch, and the parasitic inductance components existing in the vicinity thereof. As a result, unnecessary radiation interference waves can be effectively suppressed.

[0094] In the switching power supply device 58, the Q-dump resistor element Rh is provided at the boundary between the second main body region 42h and the second capacitance forming region 42c. However, it may be provided at the boundary between the first main body region 44h and the first capacitance forming region 44c, and substantially the same effect can be obtained.

[0095] <<Switching power supply device 58x of the modification example>> Next, a switching power supply device 58x, which is a modification example of the switching power supply device 58, will be described.

[0096] Since the above-described switching power supply device 58 is a step-down converter [Vi>Vo], the value (turns ratio Ks) obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) is less than 1. Also, since it is a step-down converter, one end of the secondary-side auxiliary winding 40(2) without a dot is connected to the secondary-side stable potential line 14.

[0097] In contrast, the switching power supply device 58x of the modification example is a step-up converter [Vi<Vo], and the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1. There is a difference in that one end of the secondary-side auxiliary winding 40(2) with a dot is connected to the secondary-side stable potential line 14. Other configurations are the same.

[0098] The description of the operation of the switching power supply device 58x is omitted. Even in the step-up switching power supply device 58x, operations similar to those of the step-down switching power supply device 58 are performed, and the same effects can be obtained.

[0099] <<Summary of Switching Power Supply Units 58 and 58x>> As described above, the switching power supply units 58 and 58x (single-ended forward converters) operate in a similar manner to the switching power supply units 38 and 38x (flyback converters), and similar effects can be obtained.

[0100] <<<Switching power supply device of the fourth embodiment and its modified form>>> Next, a fourth embodiment of the switching power supply device of the present invention and a modified example thereof will be described. Here, components similar to those in the conventional switching power supply device 10 are denoted by the same reference numerals and their description is omitted. <<Switching power supply 62>> First, the switching power supply 62 of the fourth embodiment will be described with reference to Figure 13. <Configuration of switching power supply unit 62> Conventional switching power supply units 10 are flyback converters, but switching power supply units 62 are single-ended forward converters, with the rectifier circuit 28 consisting of two diodes 28b and 28c, and the smoothing circuit 30 consisting of an inductor 30a and an output phase-to-phase capacitor element 18. Furthermore, several components that constitute the core of the present invention have been added. In addition, since switching power supply units 62 are step-down converters where the output voltage Vo is lower than the input voltage Vi, the primary main winding 24(1) has more turns than the secondary main winding 24(2). The configuration of switching power supply units 62 will be described below, focusing on the added components (the core of the invention).

[0101] As shown in Figure 13, the switching power supply 62 has a third winding, a primary auxiliary winding 40(1), added to the isolation transformer 22, with one end connected to the primary stable potential line 12(12a). The wiring pattern 54 connected to the other end of the primary auxiliary winding 40(1) consists of a first main body region 54h and a first capacitance forming region 54c that is continuous therewith, and a Q-damp resistor element Rh is inserted in series at the boundary between the two regions 54h and 54c.

[0102] The secondary side stable potential line 14(14a) has a second main body region 56h and a second capacitance-forming region 56c that is continuous therewith, and the first capacitance-forming region 54c and the second capacitance-forming region 56c face each other, forming a wiring pattern stray capacitance Ch.

[0103] The stray capacitances to be considered in the actual operating state of the switching power supply 62 are, as shown in the circuit diagram of Figure 13, the primary side stray capacitance Cy1 connecting the primary side stable potential line 12 and the ground line 32, the secondary side stray capacitance Cy2 connecting the secondary side stable potential line 14 and the ground line 32, the inter-winding stray capacitance Ct formed between the primary side main winding 24(1) and the secondary side main winding 24(2), and the wiring pattern stray capacitance Ch formed between the first capacitance formation region 54c and the second capacitance formation region 56c.

[0104] Furthermore, the unstable stray capacitances to be considered include: an unstable potential stray capacitance Cf1 connecting the connection point of the primary main winding 24(1) and the switching element 26 to the ground line 32; an unstable potential stray capacitance Cf2 connecting the connection point of the secondary main winding 24(2) and the rectifier circuit 28(28a) to the ground line 32; an unstable potential stray capacitance Cf4 connecting the wiring pattern 54(54h,54c) to the ground line 32; and an unstable potential stray capacitance Cf5 connecting the diode 28a and the inductor 30 to the connection point 60 and the ground line 32.

[0105] <Operation of the switching power supply 62> The operation of the switching power supply 62 is omitted. The switching power supply 62 (single-ended forward converter) operates in a similar manner to the switching power supply 52 (flyback converter) and the switching power supply 58 (single-ended forward converter) described above, and the same effects are obtained.

[0106] <<Modified Switching Power Supply 62x>> Next, we will describe a modified example of the switching power supply 62, namely the switching power supply 62x. Since the switching power supply device 62 described above is a step-down converter [Vi>Vo], the value obtained by dividing the number of turns of the secondary-side main winding 24(2) by the number of turns of the primary-side main winding 24(1) (turns ratio Ks) is less than 1. Also, since it is a step-down converter, one end of the primary-side auxiliary winding 40(1) with a dot is connected to the primary-side stable potential line 14.

[0107] In contrast, the switching power supply device 62x of the modified example is a step-up converter [Vi<Vo], and the turns ratio Ks between the primary-side main winding 24(1) and the secondary-side main winding 24(2) is greater than 1. The difference is that one end of the primary-side auxiliary winding 40(1) without a dot is connected to the primary-side stable potential line 12. Other configurations are the same.

[0108] Although the description of the operation of the switching power supply device 62x is omitted, in the step-up switching power supply device 62x as well, an operation similar to that of the step-down switching power supply device 62 is performed, and the same effects are obtained.

[0109] <<Summary of Switching Power Supply Devices 62 and 62x>> As described above, in the switching power supply devices 62 and 62x (single-ended forward converters) as well, an operation similar to that of the switching power supply devices 52 and 52x (flyback converters) is performed, and the same effects are obtained.

[0110] <<<Other Embodiments, Modified Examples, etc.>>> The switching power supply device of the present invention is not limited to the above embodiments and modifications. For example, in the switching power supply device 38 of Figure 1, the secondary main winding 24(2) and the secondary auxiliary winding 40(2) can be partially or entirely interchangeable. Since the switching power supply device 38 is a step-down type, as shown in the switching power supply device 38y of Figure 14, an additional winding 66(2) can be connected in series to one end of the secondary main winding 24(2), and the entire secondary main winding 24(2) and the additional winding (2) can be made into the secondary auxiliary winding 40(2). Even with this modification, the same operation as the above switching power supply device 38 can be performed and the same effects can be obtained. Furthermore, in the case of a switching power supply device 52x which is a step-up type of the switching power supply device 52 of Figure 7, the primary main winding 24(1) and the primary auxiliary winding 40(1) can be partially or entirely interchangeable. The statement that "if the conditions are met, the auxiliary winding and the main winding can be partially or completely interchangeable" also applies to converters other than flyback converters and single-ended forward converters.

[0111] Furthermore, as shown in Figure 15, a coupling capacitor element 66 may be connected between the primary side stable potential line 12 and the secondary side stable potential line 14, as shown in the switching power supply unit 38z (a modified example of the switching power supply unit 38). This coupling capacitor element 66 substantially shorts the primary side stable potential line 12 and the secondary side stable potential line 14 in a frequency band of Fsw or higher. By providing the coupling capacitor element 66, the noise current that would otherwise flow out toward the external load 36 is recovered to the primary side through the coupling capacitor element 66. The phrase "a coupling capacitor element may be provided" also applies to converters other than flyback converters and single-ended forward converters.

[0112] Furthermore, while the switching power supply devices of the above embodiments and modifications are all DC-DC converters of electric shock protection class 2, the present invention is also applicable to AC-DC converters of electric shock protection class 2. An AC-DC converter of electric shock protection class 2 can be constructed by providing a rectifier and smoothing circuit (a circuit that rectifies and smooths the AC voltage e output by the input power supply to generate an input voltage Vi) before the input interphase capacitor element 16 of the above DC-DC converter, and similar effects can be obtained.

[0113] It should be noted that the common-mode equivalent circuits used in the above embodiments and modified examples are merely simplified equivalent circuits and do not accurately represent actual operation. Therefore, it is practical to conduct experiments with prototypes and simple calculations using the common-mode equivalent circuits in parallel, and then derive the optimal values ​​for the number of turns of the auxiliary windings and the stray capacitance of the wiring pattern based on the results, before proceeding with the printed circuit board pattern design (new design, improved design). [Explanation of symbols]

[0114] 10, 38, 38x, 38y, 38z, 52, 52x, 58, 62 Switching Power Supply 12 Primary side stable potential line 12a Primary power line 12b Primary Ground Line 14. Secondary side stable potential line 14a Secondary power line 16 Primary-side inter-phase capacitor element 18 Secondary phase-to-phase capacitor element 20 Inverter Circuit 22 Isolation transformer 24(1) Primary main winding 24(2) Secondary main winding 26 Switching elements 28 Rectifier circuit 30 Smoothing circuit 32 Grounding line 34 Input Power 36 External load 40(2) Secondary auxiliary winding 42 Wiring Patterns 42h Second main area 42c Second volume-forming region 44h First main unit area (primary side stable potential line) 44c First capacitance-forming region (primary side stable potential line) 46 Printed circuit boards 46a Base material 48 Magnetic Cores 50a~50e Comparative Example Switching Power Supply 54 Wiring Patterns 54h First main area 54c First volume-forming region 56h Second main region (secondary side stable potential line) 56c Second capacitance formation region (secondary side stable potential line) 60 connection points 64(2) Additional winding 66 Coupling Capacitor Elements Cf1~Cf5 Unstable potential stray capacitance Ch Wiring Pattern Stray Capacitance Ct Inter-winding stray capacitance Cy1 Primary side stray capacity Cy2 secondary stray capacity Rh Q-damped resistor element Rs Earth resistance Vi Input Voltage Vo Output Voltage

Claims

1. A device formed by mounting circuit components on a printed circuit board having multiple wiring layers, which converts an input voltage input between a primary power line and a primary ground line consisting of a pair of wiring patterns into a predetermined output voltage and generates it between a secondary power line and a secondary ground line consisting of a pair of wiring patterns, A primary-side interphase capacitor element is connected between the primary-side power supply line and the primary-side ground line, substantially short-circuits the primary-side power supply line and the primary-side ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable primary-side stable potential line. A secondary phase interphase capacitor element is connected between the secondary power line and the secondary ground line, substantially short-circuits the secondary power line and the secondary ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable secondary stable potential line. An inverter circuit comprising an isolation transformer and a switching element, wherein the primary main winding of the isolation transformer and the switching element are connected in series, and the switching element switches at the switching frequency to generate an intermittent voltage across the primary main winding of the primary main winding, A rectifier circuit connected to the secondary main winding of the isolation transformer, which rectifies the voltage generated in the secondary main winding to generate a rectified voltage, The system includes the secondary phase-phase capacitor element, smooths the rectified voltage to generate the output voltage, and generates the output voltage across the secondary phase-phase capacitor element, In actual use, the input voltage is supplied from an input power supply grounded to the ground line via a grounding resistor, the primary stable potential line and the ground line are connected by primary stray capacitance, the secondary stable potential line and the ground line are connected by secondary stray capacitance, interwinding stray capacitance is formed between the primary main winding and the secondary main winding, and the wiring patterns of the locations in the inverter circuit, the rectifier circuit and the smoothing circuit where pulse voltages oscillating at the switching frequency are generated are connected to the ground line by unstable potential stray capacitance. In a switching power supply device in which a voltage generated in the primary main winding acts as a noise source, generating a first noise current that flows out to the ground line through the unstable potential stray capacitance and a second noise current that flows out to the ground line through the secondary stray capacitance, The isolation transformer has a secondary auxiliary winding, one end of which is connected to the secondary side stable potential line; a wiring pattern connected to the other end of the secondary side auxiliary winding has a second main body region and a second capacitance-forming region continuous therewith; the primary side stable potential line has a first main body region and a first capacitance-forming region continuous therewith; a wiring pattern stray capacitance is formed by the first and second capacitance-forming regions facing each other; and the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the opposing area of ​​the first and second capacitance-forming regions. A switching power supply device characterized in that, in the actual operating conditions, a current corresponding to the capacitance value flows through the stray capacitance of the wiring pattern, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less.

2. The switching power supply device according to claim 1, wherein the secondary main winding and the secondary auxiliary winding are partially or entirely shared with each other.

3. A device formed by mounting circuit components on a printed circuit board having multiple wiring layers, which converts an input voltage input between a primary power line and a primary ground line consisting of a pair of wiring patterns into a predetermined output voltage and generates it between a secondary power line and a secondary ground line consisting of a pair of wiring patterns, A primary-side interphase capacitor element is connected between the primary-side power supply line and the primary-side ground line, substantially short-circuits the primary-side power supply line and the primary-side ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable primary-side stable potential line. A secondary phase interphase capacitor element is connected between the secondary power line and the secondary ground line, substantially short-circuits the secondary power line and the secondary ground line in a frequency band above the switching frequency, and makes the two lines a potentialally stable secondary stable potential line. An inverter circuit comprising an isolation transformer and a switching element, wherein the primary main winding of the isolation transformer and the switching element are connected in series, and the switching element switches at the switching frequency to generate an intermittent voltage across the primary main winding of the primary main winding, A rectifier circuit connected to the secondary main winding of the isolation transformer, which rectifies the voltage generated in the secondary main winding to generate a rectified voltage, The system includes the secondary phase-phase capacitor element, smooths the rectified voltage to generate the output voltage, and generates the output voltage across the secondary phase-phase capacitor element, In actual use, the input voltage is supplied from an input power supply grounded to the ground line via a grounding resistor, the primary stable potential line and the ground line are connected by primary stray capacitance, the secondary stable potential line and the ground line are connected by secondary stray capacitance, interwinding stray capacitance is formed between the primary main winding and the secondary main winding, and the wiring patterns of the locations in the inverter circuit, the rectifier circuit and the smoothing circuit where pulse voltages oscillating at the switching frequency are generated are connected to the ground line by unstable potential stray capacitance. In a switching power supply device in which a voltage generated in the primary main winding acts as a noise source, generating a first noise current that flows out to the ground line through the unstable potential stray capacitance and a second noise current that flows out to the ground line through the secondary stray capacitance, The isolation transformer has a primary auxiliary winding, one end of which is connected to the primary side stable potential line; a wiring pattern connected to the other end of the primary side auxiliary winding has a first main body region and a first capacitance-forming region continuous therewith; the secondary side stable potential line has a second main body region and a second capacitance-forming region continuous therewith; a wiring pattern stray capacitance is formed by the first and second capacitance-forming regions facing each other; and the wiring pattern stray capacitance is set to a predetermined capacitance value by adjusting the opposing area of ​​the first and second capacitance-forming regions. A switching power supply device characterized in that, in the actual operating conditions, a current corresponding to the capacitance value flows through the stray capacitance of the wiring pattern, thereby suppressing the magnitude of the combined current of the first noise current and the second noise current to a reference value or less.

4. The switching power supply device according to claim 3, wherein the primary main winding and the primary auxiliary winding are partially or entirely shared with each other.

5. A switching power supply device according to any one of claims 1 to 4, comprising a coupling capacitor element connected between the primary side stable potential line and the secondary side stable potential line, which substantially short-circuits the primary side stable potential line and the secondary side stable potential line in a frequency band equal to or greater than the switching frequency.

6. A Q-damp resistor element is inserted in series at at least one of the boundary between the first main body region and the first capacitance forming region, and the boundary between the second main body region and the second capacitance forming region. The switching power supply device according to any one of claims 1 to 4, wherein the sharpness of the resonance that appears in a frequency band higher than the switching frequency of the resonant system formed by the interwinding stray capacitance, the wiring pattern stray capacitance, and the parasitic inductance components present in the vicinity thereof is suppressed by the Q-damping resistor element.

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