electronic circuits

Abstract

The electronic circuit (7) includes a common mode choke coil (8), a first capacitor (9) and a second capacitor (10) as a set of line bypass capacitors, and a DC / DC converter (11) connected to a power line (A) and a ground line (B) connected to a ground line (5A) of a substrate (5). The first capacitor (9) is connected to the power line (A) between the CMCC (8) and the DC / DC converter (11). The first capacitor (9) is connected between the power line (A) and the metal housing (2). The second capacitor (10) is connected to the ground line (B) between the CMCC (8) and the DC / DC converter (11). The second capacitor (10) is connected between the ground line (B) and the metal housing (2).

Description

Technical Field

[0001] The present disclosure relates to an electronic circuit used in an in-vehicle device including a non-insulated DC / DC converter. Background Art

[0002] In electronic circuits used for noise suppression in in-vehicle equipment using a substrate and a metal casing, a configuration is known in which the substrate ground line is short-circuited to the metal casing (Non-Patent Document 1). In the electronic circuit described in Non-Patent Document 1, a common-mode choke coil is placed between the power line and the ground line to suppress conducted emissions.

[0003] Non-Patent Document 1: Maeno and Iida, "Circuit Board Design and Grounding for Automotive Electronic Devices Aiming at Noise Immunity," Proceedings of the 26th Spring Conference of the Japan Society of Electronics Installation Engineers, Japan Society of Electronics Installation Engineers, 8A-08, March 2012

[0004] Furthermore, in the electronic circuit described in Non-Patent Document 1, the substrate ground is short-circuited to the metal housing's DC ground. In this case, the substrate ground is connected to the vehicle body, which serves as a reference potential, through the metal housing, thus stabilizing the substrate ground potential. However, as a noise countermeasure, a line bypass capacitor (Y capacitor) cannot be connected to the substrate ground. Therefore, common-mode noise is reduced solely by using a common-mode choke coil.

[0005] However, if the common mode noise is high, it may not be sufficiently reduced. Furthermore, if current or size constraints dictate the use of only low-inductance common mode choke coils, countermeasures against common mode noise may be insufficient. Summary of the Invention

[0006] An object of one embodiment of the present invention is to provide an electronic circuit capable of enhancing the effect of reducing common mode noise.

[0007] One embodiment of the present invention is an electronic circuit for use in an in-vehicle device including a substrate, a metal housing, and a non-insulated DC / DC converter. The metal housing is connected to a reference ground line, the substrate's ground line is not directly connected to the metal housing, the non-insulated DC / DC converter is connected to a power line and to a ground line connected to the substrate's ground line, a first capacitor is connected between the power line and the metal housing, and a second capacitor is connected between the ground line and the metal housing.

[0008] According to one embodiment of the present invention, the effect of reducing common mode noise can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1This is a schematic diagram showing an in-vehicle device to which the electronic circuit according to the first embodiment is applied.

[0010] Figure 2 Yes Figure 1 Electronic circuit, circuit diagram of non-insulated DC / DC converter.

[0011] Figure 3 It is a schematic diagram showing the noise reduction effect of the first embodiment.

[0012] Figure 4 It means that the measurement is applied Figure 1 Block diagram of the conducted emission measurement system for an electronic circuit.

[0013] Figure 5 : is a characteristic line diagram showing the frequency characteristics of the noise level of the comparative example.

[0014] Figure 6 : is a characteristic line diagram showing the frequency characteristics of the noise level in the first embodiment.

[0015] Figure 7 This is a schematic diagram showing an in-vehicle device to which the electronic circuit according to the second embodiment is applied.

[0016] Figure 8 This is a schematic diagram showing an in-vehicle device to which the electronic circuit according to the third embodiment is applied. DETAILED DESCRIPTION

[0017] Hereinafter, an electronic circuit according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the embodiments described below, "connection" means electrical connection.

[0018] Figures 1 to 6 FIG. 7 shows an electronic circuit 7 according to a first embodiment of the present invention. The overall structure of the vehicle-mounted device 1 to which the electronic circuit 7 is applied is as follows: Figure 1 As shown. The vehicle-mounted device 1 constitutes, for example, a car navigation system. Figure 1 As shown, in-vehicle equipment 1 is provided with an electronic circuit 7 for reducing common-mode noise (noise) generated between a DC power supply 6 serving as the input side of the electronic circuit 7 and a load 16 serving as the output side of the electronic circuit 7. Specifically, in-vehicle equipment 1 includes a metal housing 2, a substrate 5, a DC power supply 6, the electronic circuit 7, a DC / DC converter 11 constituting a non-insulated DC / DC converter, and a load 16.

[0019] The metal housing 2 is formed into a box shape, for example, from a conductive metal material. The metal housing 2 is connected to, for example, the body of a vehicle, which serves as a reference ground 3. The metal housing 2 and the reference ground 3 are electrically connected via a wire 4. Alternatively, the metal housing 2 and the reference ground 3 may be directly connected using bolts or the like. This provides the metal housing 2 with a ground potential. A substrate 5 on which electronic circuitry 7 and other components are mounted is housed within the metal housing 2.

[0020] The substrate 5 is, for example, a flexible substrate (flexible printed circuit substrate) formed into a planar shape by an insulating material such as a resin material. The substrate 5 is fixed to the metal shell 2 in a state where the metal shell 2 and the ground wire 5A (ground electrode) of the substrate 5 are not directly connected. In addition, the substrate 5 can be a single-layer substrate formed by a single insulating layer or a multi-layer substrate stacked with multiple insulating layers. The substrate 5 is not limited to a flexible substrate and can also be a rigid substrate. The substrate 5 is not limited to a resin material and can also be formed by, for example, a ceramic material, a glass substrate, or a liquid crystal polymer. The ground wire 5A is, for example, provided on the first main surface or the second main surface of the substrate 5. In the case where the substrate 5 is composed of a multi-layer substrate, the ground wire 5A can also be formed in the middle layer of the substrate 5, for example.

[0021] Electronic circuit 7, DC / DC converter 11, and load 16 are provided on substrate 5. DC / DC converter 11 and load 16 are arranged, for example, on the first main surface of substrate 5. A DC power supply 6 supplies a DC input voltage to DC / DC converter 11 via input-side power supply line A1 and input-side ground line B1. DC / DC converter 11 outputs a DC output voltage, for example, by stepping down the DC input voltage, and supplies this DC output voltage to load 16. Load 16 is driven based on the DC output voltage from DC / DC converter 11. Load 16 is connected to DC / DC converter 11 via output-side power supply line A2 and output-side ground line B2.

[0022] In this case, the input power line A1 and the input ground line B1 are formed, for example, by wires of a wiring harness connecting the DC power supply 6 and the vehicle-mounted device 1. The output power line A2 and the output ground line B2 are formed, for example, by a conductor pattern provided on the first main surface of the substrate 5.

[0023] A DC power supply 6 is disposed outside the metal housing 2. This power supply 6 is, for example, a vehicle battery, and supplies a predetermined, constant DC input voltage. The positive terminal of the DC power supply 6 is connected to the power line A of the substrate 5 via an input-side power line A1. The negative terminal of the DC power supply 6 is connected to the ground line B of the substrate 5 via an input-side ground line B1.

[0024] The electronic circuit 7 is connected to a power supply line A and a ground line B of the substrate 5 . Here, the power supply line A and the ground line B are formed by a conductor pattern provided on the first main surface of the substrate 5 , for example.

[0025] In addition, if Figure 2 As shown, electronic circuit 7 includes a common-mode choke coil 8 (hereinafter referred to as CMCC 8) as a noise countermeasure component, and a pair of line bypass capacitors (Y capacitors), namely a first capacitor 9 and a second capacitor 10, as noise countermeasure components. A DC power supply 6 is connected to the input side of electronic circuit 7. A DC / DC converter 11 is connected to the output side of electronic circuit 7. Electronic circuit 7 suppresses common-mode noise generated between DC power supply 6 and DC / DC converter 11 using CMCC 8, first capacitor 9, and second capacitor 10.

[0026] Specifically, CMCC 8 is installed between DC power supply 6 and DC / DC converter 11. CMCC 8 is placed midway between power supply line A and ground line B to reduce common-mode noise propagating through these lines. CMCC 8 is located closer to the input side (i.e., the DC power supply 6 side) than first capacitor 9 and second capacitor 10. CMCC 8 includes a first choke coil 8A connected to power supply line A and a second choke coil 8B connected to ground line B. The inductance of CMCC 8 is set to approximately 2 μH, for example.

[0027] like Figure 3 As shown, the CMCC 8 reflects common mode noise or converts it into heat by utilizing the difference between the impedance of the CMCC 8 (common mode impedance) and the common mode characteristic impedance of the power supply line A and the ground line B, that is, the characteristic impedance of the wiring. Thus, the CMCC 8 reduces common mode noise.

[0028] More specifically, CMCC 8 does not operate as an inductor in the differential mode (normal mode) in which currents flow in different directions through power line A and ground line B. Therefore, the impedance of CMCC 8 in the differential mode (normal mode impedance) is low.

[0029] In contrast, in the common mode, where currents flow in the same direction on power line A and ground line B, the CMCC 8 acts as an inductor. Therefore, the impedance of the CMCC 8 increases in the common mode. This reduces common mode noise.

[0030] First capacitor 9 is connected to power line A between CMCC 8 and DC / DC converter 11. First capacitor 9 is connected (shunt-connected) between power line A and metal housing 2. First capacitor 9 is connected to reference ground 3 via metal housing 2. First capacitor 9 reduces common-mode noise propagating through power line A. First capacitor 9 causes common-mode noise propagating through power line A to flow back to reference ground 3.

[0031] Second capacitor 10 is connected to ground line B between CMCC 8 and DC / DC converter 11. Second capacitor 10 is connected (shunt-connected) between ground line B and metal housing 2. Second capacitor 10 is connected to reference ground line 3 via metal housing 2. Second capacitor 10 reduces common-mode noise propagating through ground line B. Second capacitor 10 causes common-mode noise propagating through ground line B to flow back to reference ground line 3. Alternatively, second capacitor 10 may be connected between ground line 5A of substrate 5 and metal housing 2.

[0032] Here, the capacitance C1 of the first capacitor 9 and the capacitance C2 of the second capacitor 10 are equal (C1=C2). The capacitance C1 of the first capacitor 9 and the capacitance C2 of the second capacitor 10 are set to, for example, approximately 1000 pF (approximately 10000 pF to 100 pF). Alternatively, the capacitance C1 of the first capacitor 9 and the capacitance C2 of the second capacitor 10 may be different (C1≠C2).

[0033] The DC / DC converter 11 is, for example, a DC / DC converter installed in an in-vehicle device 1 such as a car navigation system and connected to a 12V battery. In this case, the DC / DC converter 11 steps down the power supply voltage (12V) of the DC power supply 6 to a drive voltage (e.g., 5V, 3.3V, etc.) for use by a load 16 such as a controller. Furthermore, the DC / DC converter 11 is not limited to a step-down DC / DC converter connected to a 12V battery; for example, it may be a 48V-to-12V step-up / step-down DC / DC converter installed in a 48V mild hybrid electric vehicle (48V-Mild-HEV).

[0034] The DC / DC converter 11 is connected to the power line A and the ground line B. The ground line B is connected to the ground line 5A of the substrate 5. The DC / DC converter 11 is arranged midway between the power line A and the ground line B. The DC / DC converter 11 is arranged between the CMCC 8 and the load 16. The DC / DC converter 11 steps down the DC input voltage input from the DC power supply 6 into a DC output voltage according to the duty ratio of the on and off of the first switching element 13A and the second switching element 13B. The DC / DC converter 11 supplies the DC output voltage to the load 16 as a driving voltage for the load 16. More specifically, as Figure 2 As shown, the DC / DC converter 11 includes an input-side capacitor 12 , a first switching element 13A and a second switching element 13B, a coil 14 , and an output-side capacitor 15 .

[0035] The input side capacitor 12 is connected in parallel with the DC power supply 6. Specifically, a first end of the input side capacitor 12 is connected to the power supply line A. A second end of the input side capacitor 12 is connected to the ground line B.

[0036] The first switching element 13A and the second switching element 13B are formed of, for example, field effect transistors (FETs). The first switching element 13A and the second switching element 13B may be, for example, bipolar transistors.

[0037] The first switching element 13A is connected to the power supply line A between the first choke coil 8A of the CMCC 8 and the coil 14. The drain of the first switching element 13A is connected to the first choke coil 8A of the CMCC 8. The source of the first switching element 13A is connected to the first end of the coil 14. The second switching element 13B is connected between the connection point between the first choke coil 8A and the coil 14 and the ground line B. The drain of the second switching element 13B is connected to the source of the first switching element 13A and to the first end of the coil 14. The source of the second switching element 13B is connected to the ground line B. A diode may be used in place of the second switching element 13B.

[0038] The gates of the first switching element 13A and the second switching element 13B are connected to a control circuit (not shown) that controls the duty ratios of the first switching element 13A and the second switching element 13B. The control circuit steps down the DC input voltage input from the DC power supply 6 to a DC output voltage according to the duty ratios.

[0039] The first end of coil 14 is connected to the connection point between the source of first switching element 13A and the drain of second switching element 13B. The second end of coil 14 is connected to load 16. Thus, a DC output voltage is supplied to load 16 via coil 14. At this time, the DC output voltage is smoothed by output-side capacitor 15 and supplied to load 16. The first end of output-side capacitor 15 is connected to power line A. The second end of output-side capacitor 15 is connected to ground line B.

[0040] The electronic circuit 7 of this embodiment has the above-described configuration, and its operation will be described below.

[0041] The input side of electronic circuit 7 is connected to DC power supply 6. The output side of electronic circuit 7 is connected to DC / DC converter 11. At this time, DC power supply 6 supplies a DC input voltage to DC / DC converter 11 via electronic circuit 7. DC / DC converter 11 steps down the DC input voltage to a DC output voltage based on the on / off duty ratio of first switching element 13A and second switching element 13B. This DC output voltage is smoothed by output-side capacitor 15 and supplied to load 16.

[0042] Here, the first switching element 13A and the second switching element 13B of the DC / DC converter 11 perform switching operations. Consequently, high-frequency noise signals may be introduced into the power supply line A and the ground line B. In this case, the noise signal consists of a common mode, where signals propagate in the same direction through the power supply line A and the ground line B, and a normal mode (differential mode), where signals propagate in opposite directions through the power supply line A and the ground line B. Specifically, in the common mode, currents flow in the same direction through the first and second choke coils 8A and 8B, while in the normal mode, currents flow in different directions through the first and second choke coils 8A and 8B.

[0043] On the other hand, the electronic circuit 7 includes a CMCC 8, a first capacitor 9, and a second capacitor 10. Figure 3 As shown, first capacitor 9 and second capacitor 10 reflect or reflux common-mode noise generated between DC power supply 6 and load 16. More specifically, first capacitor 9 and second capacitor 10 are arranged between CMCC 8 and DC / DC converter 11, primarily reducing common-mode noise generated by DC / DC converter 11. Furthermore, the provision of first capacitor 9 and second capacitor 10 reduces the characteristic impedance of the wiring (power line A and ground line B). The lower the characteristic impedance of the wiring, the greater the noise reduction effect of CMCC 8. Therefore, the impedance difference between CMCC 8 and the wiring with respect to common-mode noise can be increased, resulting in a synergistic effect whereby CMCC 8 facilitates common-mode noise reduction. In other words, the provision of both CMCC 8 and first capacitor 9 and second capacitor 10 enhances the common-mode noise reduction effect.

[0044] Japanese Utility Model Application Laid-Open No. 61-205290 discloses a power supply circuit including an isolated DC / DC converter. This isolated DC / DC converter does not share a common ground line on both the input and output sides. Therefore, a filter (noise filter) including a line bypass capacitor (Y capacitor) is connected to either the input or output side of the isolated DC / DC converter.

[0045] In contrast, the vehicle-mounted device 1 of the first embodiment includes a DC / DC converter 11 composed of a non-insulated DC / DC converter. Such a non-insulated DC / DC converter uses a common ground wire on both the input and output sides. Therefore, generally, the ground wire B is directly connected to the metal casing. However, if the ground wire B is connected to the metal casing, the metal casing and the reference ground wire are short-circuited even at high frequencies, and a Y capacitor cannot be used (there is no connection destination for the Y capacitor). Therefore, only using CMCC 8 to reduce common-mode noise may not be sufficient to counteract common-mode noise. Therefore, the electronic circuit 7 of the first embodiment includes a first capacitor 9 and a second capacitor 10 in addition to CMCC 8. This electronic circuit 7 reduces common-mode noise (noise) by using CMCC 8, the first capacitor 9, and the second capacitor 10.

[0046] Next, to confirm the noise reduction effect of the CMCC 8 and the first and second capacitors 9 and 10, conducted emissions were measured using the electronic circuit 7 of the first embodiment and the electronic circuit of the comparative example. The electronic circuit of the comparative example omitted the first and second capacitors 9 and 10 from the electronic circuit 7 of the first embodiment, and short-circuited the metal housing 2 and the ground line 5A of the substrate 5, as described in Non-Patent Document 1.

[0047] Specifically, the conducted emission was measured using the voltage method of CISPR25 on a demonstration board of a 48V-12V DC / DC converter assuming a 48V mild hybrid (48V-Mild-HEV). Figure 4 The inductance of the CMCC 8 used in this measurement system is set to approximately 2 μH, and the capacitance C1 of the first capacitor 9 and the capacitance C2 of the second capacitor 10 are set to approximately 100 pF.

[0048] like Figure 4 As shown, in order to measure the conducted emission, first to fourth pseudo power supply circuit networks 17A to 17D are provided ( Figure 4 In other words, the first to fourth pseudo power supply circuit networks 17A to 17D and the EMI receiver 18 are added to the vehicle-mounted device 1 that uses the electronic circuit 7 connected to the DC power supply 6, the DC / DC converter 11, and the load 16.

[0049] Specifically, a first pseudo power supply network 17A is installed midway between the DC power supply 6 and the substrate 5, on the input-side power supply line A1. An EMI receiver 18 is connected to the first pseudo power supply network 17A. The EMI receiver 18 detects noise waves from the first pseudo power supply network 17A and measures conducted emissions. A second pseudo power supply network 17B is installed midway between the DC power supply 6 and the substrate 5, on the input-side ground line B1. A third pseudo power supply network 17C is installed midway between the substrate 5 and the load 16, on the output-side power supply line A2. A fourth pseudo power supply network 17D is installed midway between the substrate 5 and the load 16, on the output-side ground line B2. To ensure space for the third and fourth pseudo power supply networks 17C and 17D, conducted emissions are measured with the load 16 positioned away from the substrate 5.

[0050] Next, for the comparative example and the first embodiment, Figure 4 The results of conducting emission measurements using the measurement system are shown as the frequency characteristics of the noise level. Figure 5 as well as Figure 6 .

[0051] Figure 5 For comparative examples, use Figure 4 The result obtained by measuring the conducted emission with the measurement system is used as the frequency characteristic of the noise level. Figure 5 As shown, in the comparative example, the noise level is approximately 30 dBμV in a frequency band of 100 MHz (for example, FM radio band).

[0052] Furthermore, with the 30 MHz frequency band as the boundary, the characteristics differ depending on the difference in detection bandwidth. For example, in the frequency band below 30 MHz, the bandwidth is approximately 9 kHz. In contrast, in the frequency band above 30 MHz, the bandwidth is approximately 100 kHz.

[0053] Figure 6 The first embodiment shows the use of Figure 4 The result obtained by measuring the conducted emission with the measurement system is used as the frequency characteristic of the noise level. Figure 6 As shown, in the first embodiment, the noise level is 20 dBμV or less in a frequency band of 100 MHz, for example.

[0054] like Figure 5 as well as Figure 6 As shown, the electronic circuit 7 of the first embodiment suppresses the noise level by 10 dBμV or more in the 100 MHz frequency band compared to the comparative example. Thus, the use of the electronic circuit 7 can reduce the common mode noise (noise) generated between the DC power supply 6 and the load 16.

[0055] In other words, in the comparative example using only CMCC8 for common-mode noise reduction, only the difference between the characteristic impedance of the existing wiring and the impedance of the CMCC8 contributes to noise reduction. On the other hand, in the first embodiment, in addition to the noise reduction effect of the CMCC8, the common-mode noise reduction effect of the first capacitor 9 and the second capacitor 10 is also achieved. Furthermore, the provision of the first capacitor 9 and the second capacitor 10 reduces the characteristic impedance of the wiring, creating a synergistic effect that enhances the noise reduction effect of the CMCC8.

[0056] Furthermore, in the electronic circuit 7 of the first embodiment, the metal housing 2 is connected to the reference ground line 3, and the ground line 5A of the substrate 5 is not directly connected to the metal housing 2. The DC / DC converter 11 is connected to the power line A and to the ground line B to which the ground line 5A of the substrate 5 is connected. A first capacitor 9 is connected between the power line A and the metal housing 2. A second capacitor 10 is connected between the ground line B and the metal housing 2.

[0057] With this configuration, first capacitor 9 can reflux or reflect common-mode noise propagating through power line A. Second capacitor 10 can reflux or reflect common-mode noise propagating through ground line B. Consequently, in vehicle-mounted equipment 1 including DC / DC converter 11, the effect of reducing common-mode noise can be enhanced compared to conventional systems.

[0058] Furthermore, CMCC 8 is placed midway between power line A and ground line B. This configuration increases the common-mode impedance of CMCC 8, thereby reducing common-mode noise. Furthermore, the presence of first capacitor 9 and second capacitor 10 lowers the characteristic impedance of the wiring. This creates a synergistic effect, facilitating the reduction of common-mode noise with CMCC 8. This significantly improves the common-mode noise reduction effect compared to conventional designs.

[0059] Furthermore, first capacitor 9 is connected to power line A between CMCC 8 and DC / DC converter 11, and second capacitor 10 is connected to ground line B between CMCC 8 and DC / DC converter 11. With this configuration, first capacitor 9 and second capacitor 10 can primarily reduce common-mode noise generated in DC / DC converter 11. This improves the common-mode noise reduction effect compared to conventional designs.

[0060] Furthermore, the capacitance C1 of the first capacitor 9 is equal to the capacitance C2 of the second capacitor 10. This configuration allows the common-mode noise propagating through the first capacitor 9 and the second capacitor 10 to be of equal magnitude. Therefore, the effect of reducing common-mode noise can be enhanced compared to a configuration in which the capacitance C1 of the first capacitor 9 and the capacitance C2 of the second capacitor 10 are different.

[0061] Next, Figure 7 The following illustrates an in-vehicle device employing an electronic circuit according to a second embodiment of the present invention. The second embodiment is characterized in that the positional relationship between the common mode choke coil and the two line bypass capacitors that constitute the electronic circuit of the first embodiment is reversed. In the second embodiment, components identical to those of the first embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0062] In the first embodiment described above, the first capacitor 9 and the second capacitor 10 are connected to the output side (DC / DC converter 11 side) of the CMCC 8. Specifically, the first capacitor 9 is connected to the power supply line A between the CMCC 8 and the DC / DC converter 11. Furthermore, the second capacitor 10 is connected to the ground line B between the CMCC 8 and the DC / DC converter 11.

[0063] In contrast, in the second embodiment, the first capacitor 9 and the second capacitor 10 are connected to the input side (DC power supply 6 side) of the CMCC 8. Therefore, the positional relationship between the CMCC 8 and the first capacitor 9 and the second capacitor 10 is reversed in the first and second embodiments.

[0064] Specifically, in the electronic circuit 21 of the second embodiment, the first capacitor 9 is connected to the power line A between the DC power supply 6 and the CMCC 8. In addition, the second capacitor 10 is connected to the ground line B between the DC power supply 6 and the CMCC 8. The CMCC 8 is arranged closer to the output side (i.e., the load 16 side) than the first capacitor 9 and the second capacitor 10. At this time, in the electronic circuit 21, the first capacitor 9 and the second capacitor 10 mainly reduce the common mode noise generated by the DC power supply 6. In addition, in the second embodiment, the first capacitor 9 can also be connected to the power line A via the input-side power line A1 of the electric wires as the wiring harness. Similarly, in the second embodiment, the second capacitor 10 can also be connected to the ground line B via the input-side ground line B1 of the electric wires as the wiring harness.

[0065] Furthermore, in the second embodiment as well, similarly to the first embodiment, the effect of reducing common mode noise can be enhanced.

[0066] Next, Figure 8 A vehicle-mounted device employing an electronic circuit according to a third embodiment is shown. The third embodiment is characterized in that the common mode choke coil is omitted from the electronic circuit according to the first embodiment. In the third embodiment, components identical to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted.

[0067] The first embodiment described above is configured such that the electronic circuit 7 includes the CMCC 8. However, the third embodiment is configured such that the CMCC 8 is omitted from the electronic circuit 7 of the first embodiment.

[0068] Specifically, in the electronic circuit 31 of the third embodiment, the first capacitor 9 is connected to the power supply line A between the DC power supply 6 and the DC / DC converter 11. Furthermore, the second capacitor 10 is connected to the ground line B between the DC power supply 6 and the DC / DC converter 11. Thus, even in a configuration without the CMCC 8, the first capacitor 9 and the second capacitor 10 can reduce common mode noise.

[0069] Furthermore, in the third embodiment as well, similarly to the first embodiment, the effect of reducing common mode noise can be enhanced.

[0070] Furthermore, in the first and second embodiments described above, the configuration was described using the first capacitor 9 and the second capacitor 10 as a pair of line bypass capacitors. The present invention is not limited to this configuration; for example, two sets of line bypass capacitors (a first capacitor and a second capacitor) may be used. Specifically, a configuration may be made such that the common-mode choke is sandwiched between these two sets of line bypass capacitors. That is, one set of line bypass capacitors may be connected closer to the input side of the common-mode choke (more specifically, between the DC power supply and the common-mode choke), and another set of line bypass capacitors may be connected closer to the output side of the common-mode choke (more specifically, between the common-mode choke and the non-insulated DC / DC converter).

[0071] Furthermore, the higher the characteristic impedance of the wiring, the greater the noise reduction effect of installing a line bypass capacitor. Therefore, connecting a line bypass capacitor to the input or output side with the higher characteristic impedance improves the noise reduction effect. The characteristic impedance of the wiring varies depending on the device status, noise standards, and other factors.

[0072] The specific numerical values ​​described in the first embodiment are merely examples, and the present invention is not limited to the exemplified values.

[0073] The above-described embodiments are merely examples, and it is naturally possible to replace or combine the components shown in different embodiments.

[0074] Next, as an electronic circuit included in the above-mentioned embodiment, for example, an electronic circuit of the following form is considered.

[0075] A first embodiment provides an electronic circuit for use in an in-vehicle device including a substrate, a metal housing, and a non-insulated DC / DC converter. The metal housing is connected to a reference ground, the substrate's ground is not directly connected to the metal housing, the non-insulated DC / DC converter is connected to a power supply line and to a ground line connected to the substrate's ground, a first capacitor is connected between the power supply line and the metal housing, and a second capacitor is connected between the ground line and the metal housing.

[0076] According to the first embodiment, the first capacitor can reflux or reflect common-mode noise propagating through the power line. The second capacitor can reflux or reflect common-mode noise propagating through the ground line. This improves the common-mode noise reduction effect compared to conventional systems in vehicle-mounted equipment equipped with a non-insulated DC / DC converter.

[0077] As a second aspect, in the first aspect, a common-mode choke is provided midway between the power line and the ground line. According to the second aspect, the provision of the common-mode choke increases the impedance of the common-mode choke. This reduces common-mode noise. Furthermore, the provision of the first and second capacitors reduces the characteristic impedance of the wiring. This creates a synergistic effect, where the common-mode choke facilitates the reduction of common-mode noise. This improves the common-mode noise reduction effect compared to conventional methods.

[0078] As a third aspect, in the second aspect, the first capacitor is connected to the power line between the common-mode choke coil and the non-isolated DC / DC converter, and the second capacitor is connected to the ground line between the common-mode choke coil and the non-isolated DC / DC converter. According to the third aspect, the first and second capacitors can primarily reduce common-mode noise generated by the non-isolated DC / DC converter. This improves the common-mode noise reduction effect compared to conventional designs.

[0079] As a fourth aspect, in any of the first to third aspects, the capacitance of the first capacitor is equal to the capacitance of the second capacitor. According to the fourth aspect, the common-mode noise propagating through the first capacitor 9 and the second capacitor 10 can be made equal. Therefore, the common-mode noise reduction effect can be enhanced compared to a configuration in which the capacitance of the first capacitor is different from that of the second capacitor.

[0080] Explanation of the reference numerals: 1…on-vehicle equipment, 2…metal casing, 3…reference ground wire, 5…substrate, 5A…ground wire, 7, 21, 31…electronic circuit, 8…CMCC (common mode choke), 9…first capacitor, 10…second capacitor, 11…DC / DC converter (non-insulated DC / DC converter), A…power line, B…ground wire, C1, C2…capacitors.

Claims

1. An electronic circuit used in an in-vehicle device comprising a substrate, a metal housing, and a DC / DC converter, characterized in that: The metal shell is connected to the reference ground wire. The ground wire of the substrate is not directly connected to the metal shell. The DC / DC converter is connected to a ground line and a power line from a DC power source. The grounding wire is connected to the grounding wire of the substrate. A common mode choke coil is provided midway between the power line and the ground line. A first capacitor is connected between the power line and the metal shell. The first capacitor is connected to the power line between the common mode choke coil and the DC / DC converter. A second capacitor is connected between the grounding wire and the metal shell. The second capacitor is connected to the ground line between the common mode choke coil and the DC / DC converter.

2. The electronic circuit according to claim 1, wherein: The capacitance of the first capacitor is the same as the capacitance of the second capacitor.

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