Power converter

Abstract

To provide a power conversion device capable of detecting connection failure of a switching element.SOLUTION: A power conversion device according to one embodiment of the present invention includes: a power input terminal; a power output terminal; a switching circuit including a first switching element including a first terminal, a second terminal, a third terminal connected electrically to the second terminal, and a first control terminal; a substrate having the first switching element mounted thereon and including a first electrode and a second electrode; a first solder bonding part for bonding the second terminal of the first switching element to the first electrode of the substrate; a second solder bonding part for bonding the third terminal of the first switching element to the second electrode of the substrate; a control circuit capable of controlling the operation of the switching circuit; and a diagnosis circuit capable of diagnosing a connection state between the first switching element and the substrate by detecting the impedance of a first route connecting the first electrode and the second electrode through the first switching element.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power conversion device for converting power.

Background Art

[0002] In an electronic circuit, connection failures may occur for various reasons. For example, Patent Document 1 discloses a circuit for detecting connection failures.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an electronic circuit, for example, due to aging deterioration, a bonding wire may peel off from a pad of a semiconductor chip, or a crack may occur in a solder joint, resulting in a connection failure. For example, in a power conversion device, such a connection failure is likely to occur in a switching element that can operate at high power. Therefore, it is desirable to detect a connection failure of a switching element in a power conversion device.

[0005] It is desirable to provide a power conversion device capable of detecting a connection failure of a switching element.

Means for Solving the Problems

[0006] A first power converter according to one embodiment of the present invention comprises a power input terminal, a power output terminal, a switching circuit, a substrate, a first solder joint, a second solder joint, a control circuit, and a diagnostic circuit. The switching circuit includes a first switching element. The first switching element has a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, and is capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal. The first switching element is mounted on the substrate, which has a first electrode and a second electrode. The first solder joint connects the second terminal of the first switching element to the first electrode of the substrate. The second solder joint connects the third terminal of the first switching element to the second electrode of the substrate. The control circuit is capable of controlling the operation of the switching circuit. The diagnostic circuit can diagnose the connection state between the first switching element and the substrate by detecting the impedance of the first path connecting the first electrode and the second electrode via the first switching element. The first electrode of the substrate is connected to the first reference power supply node. The second electrode of the substrate is connected to the second reference power supply node. The control circuit has a first drive unit connected to the first power supply node and the second reference power supply node, which is capable of driving the first switching element. A second power converter according to one embodiment of the present invention comprises a power input terminal, a power output terminal, a switching circuit, a substrate, a first solder joint, a second solder joint, a third solder joint, a fourth solder joint, a fifth solder joint, a control circuit, and a diagnostic circuit. The switching circuit includes a first switching element. The first switching element has a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, and is capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal. The first switching element is mounted on the substrate, and the substrate has a first electrode and a second electrode. The first solder joint connects the second terminal of the first switching element to the first electrode of the substrate. The second solder joint connects the third terminal of the first switching element to the second electrode of the substrate. The control circuit is capable of controlling the operation of the switching circuit. The diagnostic circuit is capable of diagnosing the connection state between the first switching element and the substrate by detecting the impedance of the first path connecting the first electrode and the second electrode via the first switching element. The switching circuit further includes a second switching element having a fourth terminal, a fifth terminal, a sixth terminal electrically connected to the fifth terminal, and a second control terminal, and capable of controlling the conduction state between the fourth terminal and the fifth terminal based on a signal from the second control terminal. The second switching element is mounted on the substrate. The substrate further has a third electrode, a fourth electrode connected to the third electrode, and a fifth electrode. A third solder joint connects the first terminal of the first switching element to the third electrode of the substrate. A fourth solder joint connects the fifth terminal of the second switching element to the fourth electrode of the substrate. The fifth solder joint connects the sixth terminal of the second switching element to the fifth electrode of the substrate. The diagnostic circuit can further diagnose the connection status between the first and second switching elements and the substrate by detecting the impedance of the second path connecting the first electrode and the fifth electrode via the first and second switching elements.

[0007] According to one embodiment of the present invention ThirdThe power converter comprises a power input terminal, a power output terminal, a switching circuit, a circuit board, a first solder joint, a third solder joint, a fourth solder joint, a fifth solder joint, a control circuit, and a diagnostic circuit. The switching circuit includes a first switching element and a second switching element. The first switching element has a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, and is capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal. The second switching element has a fourth terminal, a fifth terminal, a sixth terminal electrically connected to the fifth terminal, and a second control terminal, and is capable of controlling the conduction state between the fourth terminal and the fifth terminal based on a signal from the second control terminal. A first switching element and a second switching element are mounted on the substrate, and the substrate has a first electrode, a third electrode, a fourth electrode connected to the third electrode, and a fifth electrode. The first solder joint connects the second terminal of the first switching element to the first electrode of the substrate. The third solder joint connects the first terminal of the first switching element to the third electrode of the substrate. The fourth solder joint connects the fifth terminal of the second switching element to the fourth electrode of the substrate. The sixth solder joint connects the sixth terminal of the second switching element to the fifth electrode of the substrate. The control circuit is capable of controlling the operation of the switching circuit. The diagnostic circuit is capable of diagnosing the connection state between the first and second switching elements and the substrate by detecting the impedance of the second path connecting the first electrode and the fifth electrode via the first and second switching elements. [Effects of the Invention]

[0008] First power converter according to one embodiment of the present invention 、 Second power converter , and a third power converter According to this method, connection failures in switching elements can be detected. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram showing one example configuration of a power conversion device according to the first embodiment of the present invention. [Figure 2] Figure 1 is a circuit diagram showing a specific example of a transistor, control circuit, and diagnostic circuit. [Figure 3] This is an explanatory diagram illustrating an example of surface mounting. [Figure 4] This is an explanatory diagram showing an example of a diagnostic operation according to the first embodiment. [Figure 5] Figure 4 is a circuit diagram showing an example of an equivalent circuit for the diagnostic operation circuit. [Figure 6] This is a circuit diagram showing a specific example of a transistor, control circuit, and diagnostic circuit according to a modification of the first embodiment. [Figure 7] This is a circuit diagram showing an example configuration of a power conversion device according to another modification of the first embodiment. [Figure 8] Figure 7 is a circuit diagram showing a specific example of a transistor, control circuit, and diagnostic circuit. [Figure 9] This is a circuit diagram showing an example configuration of a power conversion device according to the second embodiment. [Figure 10] Figure 9 is a circuit diagram showing a specific example of a circuit consisting of two transistors, a control circuit, and a diagnostic circuit. [Figure 11] This is an explanatory diagram illustrating an example of the first diagnostic operation according to the second embodiment. [Figure 12] Figure 11 is a circuit diagram showing an example of an equivalent circuit for the circuit portion related to the first diagnostic operation. [Figure 13] This is an explanatory diagram illustrating an example of a second diagnostic operation according to the second embodiment. [Figure 14] Figure 13 is a circuit diagram showing an example of an equivalent circuit for the circuit portion related to the second diagnostic operation. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The description will be made in the following order. 1. First Embodiment 2. Second Embodiment

[0011] <1. First Embodiment> [Configuration Example] FIG. 1 shows a configuration example of a power conversion device (power conversion device 1) according to a first embodiment of the present invention. This power conversion device 1 is a DC / DC conversion circuit configured to convert DC power supplied from a DC power source PDC and supply the converted DC power to a load LD.

[0012] The power conversion device 1 includes power terminals T11, T12, an inductor 11, a switching circuit 12, a diode 13, a capacitor 14, a voltage sensor 15, an auxiliary power supply circuit 16, a control circuit 20, a diagnostic circuit 30, and power terminals T21, T22. The inductor 11, the switching circuit 12, the diode 13, the capacitor 14, the voltage sensor 15, the auxiliary power supply circuit 16, the control circuit 20, and the diagnostic circuit 30 are mounted on a printed circuit board.

[0013] The power terminals T11, T12 are power input terminals for the power conversion device 1. The power terminal T11 is connected to one end of the DC power source PDC, and the power terminal T12 is connected to the other end of the DC power source PDC. The DC power source PDC may be, for example, a power supply circuit that generates DC power or a battery. The power terminal T12 is connected to a reference voltage line L2 inside the power conversion device 1. This reference voltage line L2 is led to the power terminal T22 and connected to a reference power node of the power supply voltage PGND.

[0014] One end of the inductor 11 is connected to the power terminal T11, and the other end is connected to the anodes of the switching circuit 12 and the diode 13.

[0015] The switching circuit 12 has a transistor SW1. In this example, transistor SW1 is an N-type field-effect transistor (FET) and is configured to perform switching operations based on a gate signal G1. Figure 1 also shows the body diode of transistor SW1. Transistor SW1 is a discrete component, and its package is provided with a gate terminal G, a drain terminal D, a source terminal S, and a Kelvin terminal K. The Kelvin terminal K and the source terminal S are connected to each other inside the package of transistor SW1. The gate signal G1 is supplied to the gate terminal G of transistor SW1, the drain terminal D is connected to the other end of inductor 11 and the anode of diode 13, the source terminal S is connected to the reference voltage line L2, and the Kelvin terminal K is connected to the reference power supply node of the power supply voltage SGND.

[0016] In this example, a field-effect transistor was used to construct transistor SW1, but this is not the only option, and various switching elements can be used. For example, an insulated-gate bipolar transistor (IGBT) may be used to construct transistor SW1. In this case, transistor SW1 has a gate terminal, a collector terminal, an emitter terminal, and a Kelvin terminal. The Kelvin terminal and the emitter terminal are connected to each other inside the package of transistor SW1.

[0017] The anode of diode 13 is connected to the other end of inductor 11 and the drain of transistor SW1, while the cathode is connected to voltage line L1, which is led to power terminal T21.

[0018] Capacitor 14 is constructed using, for example, an electrolytic capacitor, with one end connected to voltage line L1 and the other end connected to reference voltage line L2.

[0019] The voltage sensor 15 is configured to detect the output voltage Vout of the power converter 1. One end of the voltage sensor 15 is connected to the voltage line L1, and the other end is connected to the reference voltage line L2. The voltage sensor 15 detects the voltage of the voltage line L1, with the voltage of the reference voltage line L2 as the reference, as the output voltage Vout. The voltage sensor 15 then supplies the detection result of the output voltage Vout to the control circuit 20.

[0020] The auxiliary power supply circuit 16 is configured to generate the power supply voltage VCC supplied to the control circuit 20 and the diagnostic circuit 30. The auxiliary power supply circuit 16 is connected to the power supply node of the power supply voltage VCC and the reference power supply node of the power supply voltage SGND. The auxiliary power supply circuit 16 is configured to generate the power supply voltage VCC based, for example, on power supplied from a DC power supply PDC.

[0021] The control circuit 20 is configured to control the operation of the power converter 1.

[0022] The diagnostic circuit 30 is configured to perform a diagnostic operation to diagnose the connection status between transistor SW1 and the printed circuit board on which transistor SW1 is mounted. For example, the diagnostic circuit 30 diagnoses the connection status between transistor SW1 and the printed circuit board based on the voltage difference between the power supply voltage SGND and the power supply voltage SGND during the period after the DC power supply PDC is connected to the power converter 1 and before the power converter 1 performs power conversion operation.

[0023] Power terminals T21 and T22 are output terminals for the power converted by the power converter 1. Power terminal T21 is connected to one end of the load LD, and power terminal T22 is connected to the other end of the load LD.

[0024] Figure 2 shows a more specific example of the configuration of transistor SW1, control circuit 20, and diagnostic circuit 30.

[0025] The semiconductor chip of transistor SW1 is housed in a package. The gate of the main body of transistor SW1 on the semiconductor chip is connected to the gate terminal G of the package via a bonding wire. In Figure 2, the resistance component of this bonding wire is shown as resistance component RGB. The drain of the main body of transistor SW1 is connected to the drain terminal D of the package via a bonding wire. In Figure 2, the resistance component of this bonding wire is shown as resistance component RDB. The source of the main body of transistor SW1 is connected to the source terminal S of the package via a bonding wire, and also to the Kelvin terminal K of the package via another bonding wire. In Figure 2, the resistance component of the bonding wire between the source of the main body of transistor SW1 and the source terminal S of the package is shown as resistance component RSB, and the resistance component of the bonding wire between the source of the main body of transistor SW1 and the Kelvin terminal K of the package is shown as resistance component RKB. Note that while a bonding wire is used in this example, it is not limited to this, and various bonding methods such as bumps and clips can be used.

[0026] The package of transistor SW1 is mounted on a printed circuit board. The printed circuit board has four electrodes EG, ED, ES, and EK. These four electrodes EG, ED, ES, and EK are located at positions corresponding to the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the package, respectively. The package of transistor SW1 is then mounted on this printed circuit board using solder. In this way, the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the package are soldered to the four electrodes EG, ED, ES, and EK on the printed circuit board, respectively. In Figure 2, the resistance components of the solder joints between the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the transistor SW2 package and the electrodes EG, ED, ES, and EK on the printed circuit board are shown as resistance components RGS, RDS, RSS, and RKS, respectively.

[0027] The transistor SW1 package can be mounted on the printed circuit board in any way, for example, by surface mounting or through-hole mounting.

[0028] Figure 3 shows an example of surface mounting. In this example, the package 100 is mounted on the surface of the printed circuit board 110. The package 100 is provided with terminals 101, and the printed circuit board 110 is provided with electrodes 111. These terminals 101 correspond to the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K shown in Figure 2, and the electrodes 111 correspond to electrodes EG, ED, ES, and EK shown in Figure 2. In this example, electrodes 111 are pad electrodes. Electrodes 111 and terminals 101 are joined by soldering. Note that this example describes the surface mounting case, but in the case of through-hole mounting, for example, terminal 101 is a lead terminal and electrode 111 is a through-hole.

[0029] As shown in Figure 2, a gate signal G1 is supplied to electrode EG on the printed circuit board. Electrode ED on the printed circuit board is connected to the other end of inductor 11 (Figure 1) and the anode of diode 13 (Figure 1). Electrode ES on the printed circuit board is connected to the reference power node of power supply voltage PGND. Electrode EK on the printed circuit board is connected to the reference power node of power supply voltage SGND.

[0030] The control circuit 20 includes a power conversion control unit 21, a drive unit 22, and a diagnostic control unit 23. The power conversion control unit 21 and the diagnostic control unit 23 are configured using, for example, a microcontroller.

[0031] The power conversion control unit 21 is configured to control the power converter 1 to perform power conversion operations by controlling the switching operation in the switching circuit 12. During power conversion operations, the power conversion control unit 21 generates a control signal corresponding to the gate signal G1 based on the detection result of the voltage sensor 15. As a result, the power conversion control unit 21 controls the operation of the power converter 1 so that the output voltage Vout of the power converter 1 becomes a predetermined voltage.

[0032] The drive unit 22 is configured to generate a gate signal G1 based on a control signal supplied from the power conversion control unit 21 and to drive the transistor SW1 using this gate signal G1. The drive unit 22 is connected to a power supply node of power supply voltage VCC and a reference power supply node of power supply voltage SGND, and generates the gate signal G1 based on the power supply voltages VCC and SGND. This reference power supply node of power supply voltage SGND is connected to the Kelvin terminal K of the transistor SW1 via electrode EK1. As a result, the transistor SW1 is supplied with a gate signal G1 of an appropriate voltage level, referenced to the source voltage of the body of the transistor SW1.

[0033] The diagnostic control unit 23 is configured to control the diagnostic operation of the diagnostic circuit 30. Specifically, for example, after the DC power supply PDC is connected to the power converter 1 but before the power converter 1 performs power conversion, the diagnostic control unit 23 activates the voltage of the control signal TEST to an active level, thereby causing the diagnostic circuit 30 to perform a diagnostic operation. The diagnostic control unit 23 then checks whether the connection between transistor SW1 and the printed circuit board is normal based on the detection signal DET supplied from the diagnostic circuit 30. If the connection between transistor SW1 and the printed circuit board is normal, the diagnostic control unit 23 supplies a control signal to the power converter control unit 21 to control the power converter 1 to start power conversion operation. If the connection between transistor SW1 and the printed circuit board is not normal, the diagnostic control unit 23 controls the power converter 1 not to start power conversion operation. The diagnostic control unit 23 then uses the control signal CTL to supply information to an external device of the power converter 1 indicating, for example, that the connection between transistor SW1 and the printed circuit board is not normal.

[0034] The diagnostic circuit 30 includes an amplification circuit 31, a comparison circuit 32, and a transistor 33.

[0035] The amplifier circuit 31 is configured to amplify the voltage difference between the power supply voltage SGND and the power supply voltage PGND. The positive input terminal of the amplifier circuit 31 is connected to the reference power supply node of the power supply voltage SGND, the negative input terminal is connected to the reference power supply node of the power supply voltage PGND, and the output terminal is connected to the positive input terminal of the comparator circuit 32. The gain of the amplifier circuit 31 is "-α", that is, the gain is negative. The output voltage of the amplifier circuit 31 is "-α × (SGND - PGND)". The output voltage of the amplifier circuit 31 is configured to increase as the power supply voltage SGND becomes lower than the power supply voltage PGND.

[0036] The comparison circuit 32 is configured to generate a detection signal DET by comparing the output voltage of the amplifier circuit 31 with a reference voltage REF. The positive input terminal of the comparison circuit 32 is connected to the output terminal of the amplifier circuit 31, and the reference voltage REF is supplied to the negative input terminal. The comparison circuit 32 raises the detection signal DET to a high level when the output voltage of the amplifier circuit 31 is higher than the reference voltage REF, and lowers the detection signal DET to a low level when the output voltage of the amplifier circuit 31 is lower than the reference voltage REF. The comparison circuit 32 then supplies this detection signal DET to the diagnostic control unit 23.

[0037] In this example, transistor 33 is an N-type field-effect transistor, with its drain connected to the power supply node VCC, the gate supplied with the control signal TEST, and its source connected to the reference power supply node PGND. Transistor 33 can be, for example, a JFET (Junction Field Effect Transistor). Transistor 33 turns on when the voltage of the control signal TEST is at an active level (e.g., high level) and functions as a constant current element, allowing current to flow from the power supply node VCC to the reference power supply node PGND. Transistor 33 is also configured to turn off when the voltage of the control signal TEST is at an inactive level (e.g., low level).

[0038] In the diagnostic circuit 30, during diagnostic operation, transistor 33 is turned on, and current flows from the power supply node VCC to the reference power supply node PGND. This current flows through a path (P1, described later) connecting electrode ES, source terminal S, Kelvin terminal K, and electrode EK in that order. As a result, a voltage difference is generated between the two ends of this path P1, corresponding to the impedance of the bonding wires and solder joints. The diagnostic circuit 30 diagnoses the connection status between transistor SW1 and the printed circuit board based on this voltage difference between the two ends of path P1.

[0039] Here, power terminals T11 and T12 correspond to a specific example of a "power input terminal" in this disclosure. Power terminals T21 and T22 correspond to a specific example of a "power output terminal" in this disclosure. Switching circuit 12 corresponds to a specific example of a "switching circuit" in this disclosure. Transistor SW1 corresponds to a specific example of a "first switching element" in this disclosure. Drain terminal D corresponds to a specific example of a "first terminal" in this disclosure. Source terminal S corresponds to a specific example of a "second terminal" in this disclosure. Kelvin terminal K corresponds to a specific example of a "third terminal" in this disclosure. Gate terminal G corresponds to a specific example of a "first control terminal" in this disclosure. Printed circuit board 110 corresponds to a specific example of a "substrate" in this disclosure. Solder joint corresponding to the resistive component RSS corresponds to a specific example of a "first solder joint" in this disclosure. Electrode ES corresponds to a specific example of a "first electrode" in this disclosure. The solder joint corresponding to the resistive component RKS corresponds to a specific example of the "second solder joint" in this disclosure. Electrode EK corresponds to a specific example of the "second electrode" in this disclosure. Control circuit 20 corresponds to a specific example of the "control circuit" in this disclosure. Diagnostic circuit 30 corresponds to a specific example of the "diagnostic circuit" in this disclosure. The reference power node for power supply voltage PGND corresponds to a specific example of the "first reference power node" in this disclosure. The reference power node for power supply voltage SGND corresponds to a specific example of the "second reference power node" in this disclosure. The power node for power supply voltage VCC corresponds to a specific example of the "first power node" in this disclosure. Drive unit 22 corresponds to a specific example of the "first drive unit" in this disclosure. Transistor 33 corresponds to a specific example of the "constant current element" in this disclosure.

[0040] [Action and function] Next, the operation and function of the power converter 1 of this embodiment will be described.

[0041] (Overview of overall operation) First, the overall operation of the power converter 1 will be explained with reference to Figures 1 and 2. The voltage sensor 15 detects the output voltage Vout of the power converter 1. The power conversion control unit 21 of the control circuit 20 controls the switching operation in the switching circuit 12 to control the power converter 1 to perform power conversion operations. The drive unit 22 generates a gate signal G1 based on the gate signal supplied from the power conversion control unit 21 and drives the transistor SW1 using this gate signal G1. The diagnostic control unit 23 controls the diagnostic operation of the diagnostic circuit 30. The diagnostic circuit 30 generates a detection signal DET by diagnosing the connection state between the transistor SW1 and the printed circuit board on which the transistor SW1 is mounted, based on the voltage difference between the power supply voltage SGND and the power supply voltage SGND. Based on this detection signal DET, the diagnostic control unit 23 checks whether the connection state between the transistor SW1 and the printed circuit board is normal.

[0042] (Detailed operation) The diagnostic control unit 23, for example, causes the diagnostic circuit 30 to perform diagnostic operations during the period after the DC power supply PDC is connected to the power converter 1 but before the power converter 1 performs power conversion operations. These diagnostic operations will be described in detail below.

[0043] Figure 4 shows an example of the operation of transistor SW1, control circuit 20, and diagnostic circuit 30 during a diagnostic operation. Figure 5 shows the equivalent circuit of the circuit portion involved in the diagnostic operation.

[0044] During the diagnostic operation, the power conversion control unit 21 controls transistor SW1 to the OFF state. The diagnostic control unit 23 sets the voltage of the control signal TEST to an active level (e.g., a high level). As a result, transistor 33 in the diagnostic circuit 30 turns ON, and transistor 33 functions as a constant current element. Transistor 33 flows current I1 from the power supply node VCC of the power supply voltage to the reference power supply node PGND of the power supply voltage.

[0045] As shown in Figures 4 and 5, this current I1 flows through a path P1 connecting electrode ES, source terminal S, Kelvin terminal K, and electrode EK of the printed circuit board in that order. This creates a voltage difference across both ends of this path P1, corresponding to the impedance of the bonding wires and solder joints related to transistor SW1. In this way, a voltage difference is created between the power supply voltage PGND and the power supply voltage SGND. Here, path P1 corresponds to one specific example of the "first path" in this disclosure.

[0046] For example, if a crack occurs in the solder joint connecting the source terminal S of the package and the electrode ES of the printed circuit board, the resistance value of the resistive component RSS shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. Also, for example, if the bonding wire connecting the body and source of transistor SW1 on the semiconductor chip to the source terminal S of the package is detached, the resistance value of the resistive component RSB shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. Also, for example, if the bonding wire connecting the source of the body of transistor SW1 on the semiconductor chip to the Kelvin terminal K of the package is detached, the resistance value of the resistive component RKB shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. Also, for example, if a crack occurs in the solder joint connecting the Kelvin terminal K of the package to the electrode EK of the printed circuit board, the resistance value of the resistive component RKS shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. In this way, when the impedance of path P1 is high, the power supply voltage SGND becomes lower than the power supply voltage PGND in proportion to the increase in impedance in path P1.

[0047] The amplifier circuit 31 amplifies the voltage difference between the power supply voltage SGND and the power supply voltage PGND. The lower the power supply voltage SGND is compared to the power supply voltage PGND, the higher the output voltage of the amplifier circuit 31. Therefore, the output voltage of the amplifier circuit 31 is higher by an amount corresponding to the increase in impedance in path P1. In other words, the output voltage of the amplifier circuit 31 is low when the impedance in path P1 is low, and high when the impedance in path P1 is high.

[0048] The comparison circuit 32 generates a detection signal DET by comparing the output voltage of the amplifier circuit 31 with the reference voltage REF. For example, if the impedance in path P1 is sufficiently small, the output voltage of the amplifier circuit 31 is lower than the reference voltage REF, so the detection signal DET is at a low level. Conversely, for example, if the impedance in path P1 is large and the output voltage of the amplifier circuit 31 is higher than the reference voltage REF, the detection signal DET is at a high level.

[0049] The diagnostic control unit 23 checks whether the connection between transistor SW1 and the printed circuit board is normal based on the detection signal DET. For example, if the detection signal DET is at a low level, the diagnostic control unit 23 determines that the connection is normal, and if the detection signal DET is at a high level, it determines that the connection is not normal.

[0050] The diagnostic control unit 23 controls the power converter 1 to start power conversion operation by supplying a control signal to the power conversion control unit 21 when the connection between transistor SW1 and the printed circuit board is normal. Conversely, the diagnostic control unit 23 controls the power converter 1 not to start power conversion operation when the connection between transistor SW1 and the printed circuit board is not normal. The diagnostic control unit 23 then uses the control signal CTL to supply information to an external device of the power converter 1, for example, indicating that the connection between transistor SW1 and the printed circuit board is not normal.

[0051] Thus, the power converter 1 includes a switching circuit 12 that includes a transistor SW1 having a drain terminal D, a source terminal S, a Kelvin terminal K electrically connected to the source terminal S, and a gate terminal G, and which controls the conduction state between the drain terminal D and the source terminal S based on the signal from the gate terminal G; a printed circuit board on which the transistor SW1 is mounted and which has electrodes ES and EK; a first solder joint (for example, a part corresponding to the resistance component RSS) that connects the source terminal S of the transistor SW1 to the electrode ES of the printed circuit board; a second solder joint (for example, a part corresponding to the resistance component RKS) that connects the Kelvin terminal K of the transistor SW1 to the electrode EK of the printed circuit board; a control circuit 20 that controls the operation of the switching circuit 12; and a diagnostic circuit 30 that diagnoses the connection state between the transistor SW1 and the printed circuit board by detecting the impedance of the path P1 connecting the electrode ES and the electrode EK via the transistor SW1. As a result, the power converter 1 can detect connection problems with the transistor SW1. Specifically, for example, if the bonding wire connecting the source of transistor SW1 in the semiconductor chip to the source terminal S of the package is detached, the resistance value of the resistive component RSB shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. Therefore, the diagnostic circuit 30 can detect this connection failure. Also, for example, if a crack occurs in the solder joint connecting the source terminal S of the package to the electrode ES of the printed circuit board, the resistance value of the resistive component RSS shown in Figures 4 and 5 is large, resulting in a high impedance in path P1. Therefore, the diagnostic circuit 30 can detect this connection failure. In this way, the power converter 1 can effectively detect connection failures of transistor SW1 by utilizing the Kelvin terminal K.

[0052] In particular, the power converter 1 detects the impedance of the path P1 connecting electrodes ES and EK on the printed circuit board via transistor SW1. This allows the power converter 1 to improve the diagnostic accuracy of diagnosing the connection state between transistor SW1 and the printed circuit board. That is, for example, when detecting the impedance of the path connecting electrodes ED and ES on the printed circuit board via transistor SW1, it is necessary to turn on transistor SW1 included in this path, and the detected impedance includes the on-resistance component of transistor SW1. The on-resistance of transistor SW1 can change, for example, with temperature. Therefore, the diagnostic accuracy of diagnosing the connection state between transistor SW1 and the printed circuit board based on the detected impedance may decrease. On the other hand, since the power converter 1 detects the impedance of the path P1 connecting electrodes ES and EK on the printed circuit board via transistor SW1, the detected impedance is not affected by the characteristics of transistor SW1. Therefore, the power converter 1 can improve the diagnostic accuracy.

[0053] Furthermore, in the power converter 1, the switching circuit 12 performs a switching operation during the first period, the control circuit 20 turns off the transistor SW1 during the second period which is different from the first period, and the diagnostic circuit 30 diagnoses the connection state between the transistor SW1 and the printed circuit board by detecting the impedance of the path P1 during the second period. As a result, the power converter 1 can diagnose the connection state between the transistor SW1 and the printed circuit board during the second period which is different from the first period in which the power conversion operation is performed, thereby improving the accuracy of the diagnosis. In addition, the power converter 1 can enhance safety by, for example, diagnosing the connection state between the transistor SW1 and the printed circuit board during the period before the power converter 1 performs the power conversion operation. That is, in this case, for example, the diagnostic circuit 30 can control the power converter 1 so as not to start the power conversion operation if the connection state between the transistor SW1 and the printed circuit board is not normal. In this case, the power converter 1 can be prevented from performing power conversion operations when the connection state is not normal, thereby enabling the power converter 1 to operate normally and enhancing safety.

[0054] [effect] As described above, this embodiment includes a switching circuit including a transistor having a drain terminal, a source terminal, a Kelvin terminal electrically connected to the source terminal, and a gate terminal, and controlling the conduction state between the drain terminal and the source terminal based on the signal from the gate terminal; a printed circuit board on which the transistor is mounted and which has electrodes ES and EK; a first solder joint connecting the source terminal of the transistor to electrode ES of the printed circuit board; a second solder joint connecting the Kelvin terminal of the transistor to electrode EK of the printed circuit board; a control circuit for controlling the operation of the switching circuit; and a diagnostic circuit for diagnosing the connection state between the transistor and the printed circuit board by detecting the impedance of the path connecting electrode ES and electrode EK via the transistor. As a result, a faulty connection of the transistor can be detected.

[0055] In this embodiment, the impedance of the path connecting electrode ES and electrode EK of the printed circuit board is detected via a transistor, thereby improving diagnostic accuracy.

[0056] In this embodiment, during the first period, the switching circuit performs a power conversion operation by switching, the control circuit turns off the transistor during the second period which is different from the first period, and the diagnostic circuit diagnoses the connection state between the transistor and the printed circuit board by detecting the impedance of the path during the second period. As a result, the power conversion device can be operated normally, and safety can be enhanced.

[0057] [Variation 1-1] In the above embodiment, the positive input terminal of the amplification circuit 31 of the diagnostic circuit 30 is connected to a reference power supply node of power supply voltage SGND, and the negative input terminal is connected to a reference power supply node of power supply voltage PGND, but it is not limited to this. Alternatively, for example, a bias circuit may be connected to the positive input terminal and negative input terminal of the amplification circuit 31, as in the diagnostic circuit 30A shown in Figure 6. The diagnostic circuit 30A has resistor elements RS1, RS2, RP1, and RP2. The resistor elements RS1, RS2, RP1, and RP2 constitute a bias circuit. A voltage VREF is supplied to one end of resistor element RS1, and the other end is connected to one end of resistor element RS2 and the positive input terminal of the amplification circuit 31. One end of resistor element RS2 is connected to the other end of resistor element RS1 and the positive input terminal of the amplification circuit 31, and the other end is connected to a reference power supply node of power supply voltage SGND. A voltage VREF is supplied to one end of resistor element RP1, and the other end is connected to one end of resistor element RP2 and the negative input terminal of the amplification circuit 31. One end of resistor RP2 is connected to the other end of resistor RP1 and the negative input terminal of amplifier circuit 31, while the other end is connected to the reference power supply node of the power supply voltage PGND. For example, the resistance values ​​of resistor RS1 and resistor RP1 are set to the same value, and the resistance values ​​of resistor RS2 and resistor RP2 are set to the same value. Amplifier circuit 31 amplifies the voltage difference between the voltage divided by resistors RS1 and RS2 and the voltage divided by resistors RP1 and RP2. This bias circuit allows adjustment of the voltages at the positive and negative input terminals of amplifier circuit 31.

[0058] [Variation 1-2] In the above embodiment, the diagnostic circuit 30 is configured to perform diagnostic operations before the power converter 1 performs power conversion operations. However, it is not limited to this configuration, and for example, it may also perform diagnostic operations during the period when the power converter 1 performs power conversion operations. This modified example will be described in detail below.

[0059] Figure 7 shows an example configuration of the power converter 1B according to this modified example. The power converter 1B includes a control circuit 20B and a diagnostic circuit 30B. Figure 8 shows an example configuration of the control circuit 20B and the diagnostic circuit 30B.

[0060] The control circuit 20B includes a diagnostic control unit 23B. Similar to the diagnostic control unit 23 in the above embodiment, the diagnostic control unit 23B causes the diagnostic circuit 30B to perform a diagnostic operation by setting the voltage of the control signal TEST to an active level during the period after the DC power supply PDC is connected to the power converter 1B but before the power converter 1B performs a power conversion operation. The diagnostic control unit 23B then checks whether the connection state between transistor SW1 and the printed circuit board is normal based on the detection signal DET supplied from the diagnostic circuit 30B. The diagnostic control unit 23B also has a function to check whether the connection state between transistor SW1 and the printed circuit board is normal based on the detection signal DETB supplied from the diagnostic circuit 30B during the period when the power converter 1B performs a power conversion operation.

[0061] The diagnostic circuit 30B includes resistive elements RS3, RS4, RP3, and RP4, and a comparator circuit 34B.

[0062] Resistor elements RS3, RS4, RP3, and RP4 constitute a bias circuit. A voltage VREF is supplied to one end of resistor element RS3, and the other end is connected to one end of resistor element RS4 and the positive input terminal of comparator circuit 34B. One end of resistor element RS4 is connected to the other end of resistor element RS3 and the positive input terminal of comparator circuit 34B, and the other end is connected to the reference power supply node of the power supply voltage SGND. A voltage VREF is supplied to one end of resistor element RP3, and the other end is connected to one end of resistor element RP4 and the negative input terminal of comparator circuit 34B. One end of resistor element RP4 is connected to the other end of resistor element RP3 and the negative input terminal of comparator circuit 34B, and the other end is connected to the reference power supply node of the power supply voltage PGND.

[0063] The comparison circuit 34B is configured to generate a detection signal DETB by comparing the voltage divided by resistors RS3 and RS4 with the voltage divided by resistors RP3 and RP4. The positive input terminal of the comparison circuit 34B is connected to the other end of resistor RS3 and one end of resistor RS4, and the negative input terminal is connected to the other end of resistor RP3 and one end of resistor RP4. The comparison circuit 34B raises the detection signal DETB to a high level when the voltage divided by resistors RS3 and RS4 is higher than the voltage divided by resistors RP3 and RP4, and lowers the detection signal DETB to a low level when the voltage divided by resistors RS3 and RS4 is lower than the voltage divided by resistors RP3 and RP4. The comparison circuit 34B then supplies this detection signal DETB to the diagnostic control unit 23B.

[0064] In the period before performing the power conversion operation, the power converter 1B diagnoses the connection status between the transistor SW1 and the printed circuit board, similar to the embodiment described above. Furthermore, during the period when the power conversion operation is performed, the power converter 1B also diagnoses the connection status between the transistor SW1 and the printed circuit board, as shown below.

[0065] During the period when the power converter 1B is performing power conversion, the transistor SW1 performs switching operations based on the gate signal G1. For example, during the period when transistor SW1 is ON, current flows in the order of DC power supply PDC, inductor 11, transistor SW1, and DC power supply PDC in Figure 7. Therefore, current flows from the drain terminal D to the source terminal S in transistor SW1. Thus, during this period, the power supply voltage SGND is higher than the power supply voltage PGND.

[0066] For example, if the bonding wire connecting the source of transistor SW1 on a semiconductor chip to the source terminal S of the package is detached, the resistance value of the resistive component RSB shown in Figure 8 is large, resulting in a high impedance in the partial path of path P1 connecting the source of the main body of transistor SW1 to the electrode ES. Also, for example, if a crack occurs in the solder joint connecting the source terminal S of the package to the electrode ES of the printed circuit board, the resistance value of the resistive component RSS shown in Figure 8 is large, resulting in a high impedance in the partial path of path P1 connecting the source of the main body of transistor SW1 to the electrode ES. When the impedance in this partial path is high in this way, the power supply voltage SGND is even higher than the power supply voltage PGND, and the voltage at the positive input terminal of the comparator circuit 34B is higher than the voltage at the negative input terminal. As a result, the detection signal DETB is at a high level. On the other hand, if there is no detachment of the bonding wire or crack in the solder joint, the impedance in this partial path is small, so the voltage at the positive input terminal of the comparator circuit 34B is lower than the voltage at the negative input terminal. As a result, the detection signal DETB is at a low level.

[0067] On the other hand, when transistor SW1 is in the off state, no current flows through transistor SW1. Therefore, during this period, the power supply voltage SGND is approximately the same as the power supply voltage PGND, and the voltage at the positive input terminal of the comparator circuit 34B is lower than the voltage at the negative input terminal. As a result, the detection signal DETB is at a low level.

[0068] Thus, if the impedance in a portion of the path P1 is sufficiently small, the detection signal DETB is maintained at a low level. Conversely, if the impedance in this portion of the path is large, the detection signal DETB is at a high level when transistor SW1 is ON and at a low level when transistor SW1 is OFF. During the period when the power converter 1B is performing power conversion operations, the diagnostic control unit 23B checks whether the connection between transistor SW1 and the printed circuit board is normal based on this detection signal DETB. For example, if the detection signal DETB is maintained at a low level, the diagnostic control unit 23B determines that the connection is normal, and if the detection signal DETB is intermittently at a high level, the diagnostic control unit 23B determines that the connection is not normal.

[0069] The diagnostic control unit 23B controls the power converter 1B to continue power conversion operation if the connection between transistor SW1 and the printed circuit board is normal. The diagnostic control unit 23B controls the power converter 1B to stop power conversion operation if the connection between transistor SW1 and the printed circuit board is not normal. The diagnostic control unit 23B then uses the control signal CTL to supply information, for example, that the connection between transistor SW1 and the printed circuit board is not normal, to an external device of the power converter 1B.

[0070] [Modification 1-3] In the above embodiment, the technology was applied to a non-isolated power converter without a transformer, but it is not limited to this, and instead, for example, it may be applied to an isolated power converter with a transformer.

[0071] [Other variations] Furthermore, two or more of these variations may be combined.

[0072] <2. Second Embodiment> Next, a power converter 2 according to a second embodiment will be described. In this embodiment, the circuit configuration of the power converter differs from that of the first embodiment described above. Components that are substantially the same as those in the power converter 1 according to the first embodiment are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0073] Figure 9 shows an example configuration of the power converter 2. The power converter 2 includes power terminals T11, T12, a switching circuit 41, an inductor 42, a transformer TR, a capacitor 43, diodes 44-47, a capacitor 14, a voltage sensor 15, an auxiliary power supply circuit 16, a control circuit 50, a diagnostic circuit 60, and power terminals T21, T22. The switching circuit 41, inductor 42, transformer TR, capacitor 43, diodes 44-47, capacitor 14, voltage sensor 15, auxiliary power supply circuit 16, control circuit 50, and diagnostic circuit 60 are mounted on a printed circuit board.

[0074] Power terminals T11 and T12 are power input terminals for the power converter 2. Power terminal T11 is connected to voltage line L11 inside the power converter 2. Power terminal T12 is connected to reference voltage line L12 inside the power converter 2. This reference voltage line L12 is connected to the reference power node of the power supply voltage PGND.

[0075] The switching circuit 41 has transistors SW1 and SW2. In this example, transistors SW1 and SW2 are N-type field-effect transistors, and transistor SW1 is configured to perform switching operations based on a gate signal G1, and transistor SW2 is configured to perform switching operations based on a gate signal G2. The gate terminal G of transistor SW1 is supplied with a gate signal G1, its drain terminal D is connected to the source terminal S of transistor SW2 and one end of inductor 42, the source terminal S is connected to a reference voltage line L12, and its Kelvin terminal K is connected to a reference power supply node of power supply voltage SGND. The gate terminal G2 of transistor SW2 is supplied with a gate signal G2, its drain terminal D is connected to a voltage line L11, its source terminal S is connected to the drain terminal D of transistor SW1 and one end of inductor 42, and its Kelvin terminal K is connected to a reference power supply node of power supply voltage SGNDH.

[0076] One end of inductor 42 is connected to the drain terminal D of transistor SW1 and the source terminal S of transistor SW2, and the other end is connected to transformer TR.

[0077] The transformer TR has windings 91 and 92. One end of winding 91 is connected to the other end of inductor 42, and the other end is connected to capacitor 43. One end of winding 92 is connected to the anode of diode 44 and the cathode of diode 45, and the other end is connected to the anode of diode 46 and the cathode of diode 47.

[0078] One end of capacitor 43 is connected to the reference voltage line L12, and the other end is connected to the other end of the winding 91 of transformer TR.

[0079] The anode of diode 44 is connected to one end of winding 92 and the cathode of diode 45, and the cathode is connected to voltage line L21 led to power terminal T21. The anode of diode 45 is connected to reference voltage line L22 led to power terminal T22, and the cathode is connected to one end of winding 92 and the anode of diode 44. The anode of diode 46 is connected to the other end of winding 92 and the cathode of diode 47, and the cathode is connected to voltage line L21. The anode of diode 47 is connected to reference voltage line L22, and the cathode is connected to the other end of winding 92 and the anode of diode 46.

[0080] One end of the capacitor 14 is connected to the voltage line L21, and the other end is connected to the reference voltage line L22. One end of the voltage sensor 15 is connected to the voltage line L21, and the other end is connected to the reference voltage line L22.

[0081] The control circuit 50 is configured to control the operation of the power converter 2, similar to the control circuit 20 in the first embodiment described above.

[0082] The diagnostic circuit 60 is configured to perform a diagnostic operation to diagnose the connection status between transistors SW1 and SW2 and the printed circuit board on which transistors SW1 and SW2 are mounted, similar to the diagnostic circuit 30 according to the first embodiment described above.

[0083] Figure 10 shows a more specific example of the configuration of transistors SW1 and SW2, control circuit 50, and diagnostic circuit 60.

[0084] The semiconductor chip of transistor SW1 is housed in a package, as in the first embodiment described above. In Figure 10, the resistance component of the bonding wire between the gate of the transistor SW1 body and the gate terminal G of the package is shown as resistance component RGB1. The resistance component of the bonding wire between the drain of the transistor SW1 body and the drain terminal D of the package is shown as resistance component RDB1. The resistance component of the bonding wire between the source of the transistor SW1 body and the source terminal S of the package is shown as resistance component RSB1. The resistance component of the bonding wire between the source of the transistor SW1 body and the Kelvin terminal K of the package is shown as resistance component RKB1.

[0085] Similarly, the semiconductor chip of transistor SW2 is housed in a package. In Figure 10, the resistive component of the bonding wire between the gate of the transistor SW2 body and the gate terminal G of the package is shown as resistive component RGB2. The resistive component of the bonding wire between the drain of the transistor SW2 body and the drain terminal D of the package is shown as resistive component RDB2. The resistive component of the bonding wire between the source of the transistor SW2 body and the source terminal S of the package is shown as resistive component RSB2. The resistive component of the bonding wire between the source of the transistor SW2 body and the Kelvin terminal K of the package is shown as resistive component RKB2.

[0086] The package of transistor SW1 is mounted on a printed circuit board. Similarly, the package of transistor SW2 is mounted on a printed circuit board. The printed circuit board has electrodes EG1, ED1, ES1, EK1, EG2, ED2, ES2, and EK2.

[0087] The gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the transistor SW1 package are soldered to four electrodes EG1, ED1, ES1, and EK1 on the printed circuit board, respectively. In Figure 10, the resistive components of the solder joints between the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the transistor SW1 package and the electrodes EG1, ED1, ES1, and EK1 on the printed circuit board are shown as resistive components RGS1, RDS1, RSS1, and RKS1, respectively.

[0088] The gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the transistor SW2 package are soldered to four electrodes EG2, ED2, ES2, and EK2 on the printed circuit board, respectively. In Figure 10, the resistive components of the solder joints between the gate terminal G, drain terminal D, source terminal S, and Kelvin terminal K of the transistor SW2 package and the electrodes EG2, ED2, ES2, and EK2 on the printed circuit board are shown as resistive components RGS2, RDS2, RSS2, and RKS2, respectively.

[0089] On the printed circuit board, electrode EG1 is supplied with gate signal G1. Electrode ED1 is connected to electrode ES2. Electrode ES1 is connected to the reference power supply node of power supply voltage PGND. Electrode EK1 is connected to the reference power supply node of power supply voltage SGND. Electrode EG2 is supplied with gate signal G2. Electrode ED2 is connected to voltage line L11 (Figure 9). Electrode ES2 is connected to electrode ED1. Electrode EK2 is connected to the reference power supply node of power supply voltage SGNDH.

[0090] The control circuit 50 includes a power conversion control unit 51, drive units 54 and 55, and a diagnostic control unit 53.

[0091] The power conversion control unit 51 is configured to control the power converter 2 to perform power conversion operations by controlling the switching operation in the switching circuit 41. During power conversion operations, the power conversion control unit 51 generates control signals corresponding to gate signal G1 and gate signal G2 based on the detection result of the voltage sensor 15. As a result, the power conversion control unit 51 controls the operation of the power converter 2 so that the output voltage Vout of the power converter 2 becomes a predetermined voltage.

[0092] The drive unit 54 is configured to generate a gate signal G1 based on a control signal supplied from the power conversion control unit 51 and to drive the transistor SW1 using this gate signal G1. The drive unit 54 is connected to a power supply node of power supply voltage VCC and a reference power supply node of power supply voltage SGND, and generates the gate signal G1 based on the power supply voltages VCC and SGND. This reference power supply node of power supply voltage SGND is connected to the Kelvin terminal K of the transistor SW1 via electrode EK1. As a result, the transistor SW1 is supplied with a gate signal G1 of an appropriate voltage level, referenced to the source voltage of the body of the transistor SW1.

[0093] The drive unit 55 is configured to generate a gate signal G2 based on a control signal supplied from the power conversion control unit 51, and to drive the transistor SW2 using this gate signal G2. The drive unit 55 is connected to the power supply node of the power supply voltage Vboot and the reference power supply node of the power supply voltage SGNDH, and generates the gate signal G2 based on the power supply voltages Vboot and SGNDH. During periods when the power converter 2 is not performing power conversion operations, the power supply voltages Vboot and SGNDH are set, for example, based on the power supply voltages VCC and SGND. During periods when the power converter 2 is performing power conversion operations, the power supply voltages Vboot and SGNDH are set, for example, by a bootstrap circuit (not shown). Specifically, for example, during the period when the transistor SW1 is ON, the power supply voltage SGNDH is set to a voltage corresponding to the power supply voltage PGND, and the power supply voltage Vboot is set to a voltage corresponding to the power supply voltage VCC. Then, for example, during the period when the transistor SW1 is OFF, the power supply voltages Vboot and SGNDH are increased by a bootstrap operation while maintaining the voltage difference between the power supply voltages Vboot and SGNDH. The reference power node for power supply voltage SGNDH is connected to the Kelvin terminal K of transistor SW2 via electrode EK2. This ensures that transistor SW2 is supplied with a gate signal G2 of an appropriate voltage level, referenced to the source voltage of the transistor SW2's body.

[0094] The diagnostic control unit 53 is configured to control the diagnostic operation of the diagnostic circuit 60. Specifically, for example, after the DC power supply PDC is connected to the power converter 2 but before the power converter 2 performs power conversion, the diagnostic control unit 53 activates the voltage of the control signal TEST, thereby causing the diagnostic circuit 60 to perform a diagnostic operation. The diagnostic control unit 53 controls the diagnostic operation of the diagnostic circuit 60 using control signals SEL1 and SEL2. The diagnostic control unit 53 then checks whether the connection status between transistors SW1 and SW2 and the printed circuit board is normal based on the detection signal DET supplied from the diagnostic circuit 60.

[0095] The diagnostic circuit 60 includes a switch 61, an amplification circuit 31, a comparator circuit 32, a transistor 33, and a switch 64.

[0096] Switch 61 is configured to select one of the power supply voltages SGND and SGNDH based on the control signal SEL1, and to supply the selected power supply voltage to the positive input terminal of the amplifier circuit 31. As a result, the amplifier circuit 31 amplifies the voltage difference between the power supply voltage supplied from switch 61 and the power supply voltage PGND, and the comparison circuit 32 generates a detection signal DET by comparing the output voltage of the amplifier circuit 31 with the reference voltage REF.

[0097] Switch 64 is configured to select one of the power supply voltages VCC and Vboot based on the control signal SEL2, and to supply the selected power supply voltage to the drain of transistor 33. As a result, transistor 33 turns on when the voltage of the control signal TEST is at an active level (e.g., high level), and causes current to flow from the power supply node connected by switch 64 to the reference power supply node of power supply voltage PGND.

[0098] Here, switching circuit 41 corresponds to a specific example of the “switching circuit” in this disclosure. Transistor SW1 corresponds to a specific example of the “first switching element” in this disclosure. Drain terminal D of transistor SW1 corresponds to a specific example of the “first terminal” in this disclosure. Source terminal S of transistor SW1 corresponds to a specific example of the “second terminal” in this disclosure. Kelvin terminal K of transistor SW1 corresponds to a specific example of the “third terminal” in this disclosure. Gate terminal G of transistor SW1 corresponds to a specific example of the “first control terminal” in this disclosure. Transistor SW2 corresponds to a specific example of the “second switching element” in this disclosure. Drain terminal D of transistor SW2 corresponds to a specific example of the “fourth terminal” in this disclosure. Source terminal S of transistor SW2 corresponds to a specific example of the “fifth terminal” in this disclosure. Kelvin terminal K of transistor SW2 corresponds to a specific example of the “sixth terminal” in this disclosure. Gate terminal G of transistor SW2 corresponds to a specific example of the “second control terminal” in this disclosure. The solder joint corresponding to the resistive component RSS1 corresponds to a specific example of the "first solder joint" in this disclosure. Electrode ES1 corresponds to a specific example of the "first electrode" in this disclosure. The solder joint corresponding to the resistive component RKS1 corresponds to a specific example of the "second solder joint" in this disclosure. Electrode EK1 corresponds to a specific example of the "second electrode" in this disclosure. The solder joint corresponding to the resistive component RDS1 corresponds to a specific example of the "third solder joint" in this disclosure. Electrode ED1 corresponds to a specific example of the "third electrode" in this disclosure. The solder joint corresponding to the resistive component RSS2 corresponds to a specific example of the "fourth solder joint" in this disclosure. Electrode ES2 corresponds to a specific example of the "fourth electrode" in this disclosure. The solder joint corresponding to the resistive component RKS2 corresponds to a specific example of the "fifth solder joint" in this disclosure. Electrode EK2 corresponds to a specific example of the "fifth electrode" in this disclosure. The control circuit 50 corresponds to one specific example of the “control circuit” in this disclosure. The diagnostic circuit 60 corresponds to one specific example of the “diagnostic circuit” in this disclosure. The reference power supply node for power supply voltage SGNDH corresponds to one specific example of the “third reference power supply node” in this disclosure.The power supply node with power supply voltage Vboot corresponds to one specific example of the “second power supply node” in this disclosure. The drive unit 54 corresponds to one specific example of the “first drive unit” in this disclosure. The drive unit 55 corresponds to one specific example of the “second drive unit” in this disclosure.

[0099] The diagnostic control unit 53, for example, causes the diagnostic circuit 60 to perform diagnostic operations during the period after the DC power supply PDC is connected to the power converter 2 but before the power converter 2 performs power conversion operations. In this example, the diagnostic circuit 60 first diagnoses the connection between transistor SW1 and the printed circuit board by performing a first diagnostic operation, and then diagnoses the connection between transistors SW1 and SW2 and the printed circuit board by performing a second diagnostic operation. The first and second diagnostic operations will be described in detail below.

[0100] Figure 11 shows an example of the operation of transistors SW1 and SW2, control circuit 50, and diagnostic circuit 60 in the first diagnostic operation. Figure 12 shows the equivalent circuit of the circuit portion related to the first diagnostic operation.

[0101] In the first diagnostic operation, the power conversion control unit 51 controls transistors SW1 and SW2 to the OFF state. The diagnostic control unit 53 generates a control signal SEL1 so that switch 61 selects the power supply voltage SGND, and generates a control signal SEL2 so that switch 64 selects the power supply voltage VCC. The diagnostic control unit 53 sets the voltage of the control signal TEST to an active level (e.g., a high level). As a result, transistor 33 in the diagnostic circuit 60 turns ON, and transistor 33 functions as a constant current element. Transistor 33 flows current I1 from the power supply node of power supply voltage VCC to the reference power supply node of power supply voltage PGND.

[0102] As shown in Figures 11 and 12, this current I1 flows through a path P1 connecting electrode ES1, source terminal S, Kelvin terminal K, and electrode EK on the printed circuit board in that order. As a result, similar to the first embodiment described above, a voltage difference is generated between the ends of this path P1, corresponding to the impedance of the bonding wires and solder joints related to transistor SW1. In this way, a voltage difference is generated between the power supply voltage PGND and the power supply voltage SGND.

[0103] The amplifier circuit 31 amplifies the voltage difference between the power supply voltage SGND and the power supply voltage PGND. The lower the power supply voltage SGND is compared to the power supply voltage PGND, the higher the output voltage of the amplifier circuit 31. Therefore, the output voltage of the amplifier circuit 31 is higher by an amount corresponding to the increase in impedance in path P1. In other words, the output voltage of the amplifier circuit 31 is low when the impedance in path P1 is low, and high when the impedance in path P1 is high.

[0104] The comparison circuit 32 generates a detection signal DET by comparing the output voltage of the amplifier circuit 31 with the reference voltage REF. For example, if the impedance in path P1 is sufficiently small, the output voltage of the amplifier circuit 31 is lower than the reference voltage REF, so the detection signal DET is at a low level. Conversely, for example, if the impedance in path P1 is large and the output voltage of the amplifier circuit 31 is higher than the reference voltage REF, the detection signal DET is at a high level.

[0105] In the first diagnostic operation, the diagnostic control unit 53 checks whether the connection between transistor SW1 and the printed circuit board is normal based on the detection signal DET. For example, if the detection signal DET is at a low level, the diagnostic control unit 53 determines that the connection is normal, and if the detection signal DET is at a high level, it determines that the connection is not normal.

[0106] Figure 13 shows an example of the operation of transistors SW1 and SW2, control circuit 50, and diagnostic circuit 60 in the second diagnostic operation. Figure 14 shows the equivalent circuit of the circuit portion related to the second diagnostic operation.

[0107] In the second diagnostic operation, the power conversion control unit 51 controls transistor SW1 to be turned on and transistor SW2 to be turned off. The diagnostic control unit 53 generates a control signal SEL1 so that switch 61 selects the power supply voltage SGNDH, and generates a control signal SEL2 so that switch 64 selects the power supply voltage Vboot. The diagnostic control unit 53 sets the voltage of the control signal TEST to an active level (e.g., a high level). As a result, transistor 33 in the diagnostic circuit 60 is turned on, and transistor 33 functions as a constant current element. Transistor 33 flows current I2 from the power supply node of power supply voltage Vboot to the reference power supply node of power supply voltage PGND.

[0108] As shown in Figures 13 and 14, this current I2 flows through a path P2 connecting electrode ES1 of the printed circuit board, source terminal S of transistor SW1, body of transistor SW1, drain terminal D of transistor SW1, electrode ED1, electrode ES2, source terminal S of transistor SW2, Kelvin terminal K of transistor SW2, and electrode EK2 in that order. This creates a voltage difference across both ends of this path P2, corresponding to the impedance of the bonding wires and solder joints related to transistors SW1 and SW2. In this way, a voltage difference is created between the power supply voltage PGND and the power supply voltage SGNDH. Here, path P2 corresponds to one specific example of the "second path" in this disclosure.

[0109] For example, if a crack occurs in the solder joint connecting the source terminal S of the transistor SW1 package and the electrode ES1 of the printed circuit board, the resistance value of the resistive component RSS1 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if the bonding wire connecting the source of the transistor SW1 body on the semiconductor chip and the source terminal S of the package is detached, the resistance value of the resistive component RSB1 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if the bonding wire connecting the drain of the transistor SW1 body on the semiconductor chip and the drain terminal D of the package is detached, the resistance value of the resistive component RDB1 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if a crack occurs in the solder joint connecting the drain terminal D of the transistor SW1 package and the electrode ED1 of the printed circuit board, the resistance value of the resistive component RDS1 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Furthermore, for example, if a crack occurs in the solder joint connecting the source terminal S of the transistor SW2 package and the electrode ES2 of the printed circuit board, the resistance value of the resistive component RSS2 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if the bonding wire connecting the source of the transistor SW2 body on the semiconductor chip and the source terminal S of the package is detached, the resistance value of the resistive component RSB2 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if the bonding wire connecting the source of the transistor SW2 body on the semiconductor chip and the Kelvin terminal K of the package is detached, the resistance value of the resistive component RKB2 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2. Also, for example, if a crack occurs in the solder joint connecting the Kelvin terminal K of the transistor SW2 package and the electrode EK2 of the printed circuit board, the resistance value of the resistive component RKS2 shown in Figures 13 and 14 is large, resulting in a large impedance in path P2.When the impedance of path P2 is large, the power supply voltage SGNDH becomes lower than the power supply voltage PGND, in proportion to the increase in impedance in path P2.

[0110] The amplifier circuit 31 amplifies the voltage difference between the power supply voltage SGNDH and the power supply voltage PGND. The lower the power supply voltage SGNDH is compared to the power supply voltage PGND, the higher the output voltage of the amplifier circuit 31. Therefore, the output voltage of the amplifier circuit 31 is higher by an amount corresponding to the increase in impedance in path P2. In other words, the output voltage of the amplifier circuit 31 is low when the impedance in path P2 is low, and high when the impedance in path P2 is high.

[0111] The comparison circuit 32 generates a detection signal DET by comparing the output voltage of the amplifier circuit 31 with the reference voltage REF. For example, if the impedance in path P2 is sufficiently small, the output voltage of the amplifier circuit 31 is lower than the reference voltage REF, so the detection signal DET is at a low level. Conversely, for example, if the impedance in path P2 is large and the output voltage of the amplifier circuit 31 is higher than the reference voltage REF, the detection signal DET is at a high level.

[0112] In the second diagnostic operation, the diagnostic control unit 53 checks whether the connection between transistors SW1 and SW2 and the printed circuit board is normal based on the detection signal DET. For example, if the detection signal DET is at a low level, the diagnostic control unit 53 determines that the connection is normal, and if the detection signal DET is at a high level, it determines that the connection is not normal.

[0113] In the first and second diagnostic operations, the diagnostic control unit 53 controls the power converter 2 to start power conversion operation by supplying a control signal to the power conversion control unit 51 if the connection state between transistors SW1 and SW2 and the printed circuit board is normal. Conversely, the diagnostic control unit 53 controls the power converter 2 not to start power conversion operation if the connection state between transistors SW1 and SW2 and the printed circuit board is not normal. The diagnostic control unit 53 then uses the control signal CTL to supply information to an external device of the power converter 2 indicating, for example, that the connection state between transistors SW1 and SW2 and the printed circuit board is not normal.

[0114] Thus, the power converter 2 includes a switching circuit 41 that includes a transistor SW1 having a drain terminal D, a source terminal S, a Kelvin terminal K electrically connected to the source terminal S, and a gate terminal G, and which controls the conduction state between the drain terminal D and the source terminal S based on the signal of the gate terminal G; a printed circuit board on which the transistor SW1 is mounted and which has electrodes ES1 and EK1; a first solder joint (for example, a part corresponding to the resistance component RSS1) that connects the source terminal S of the transistor SW1 to the electrode ES1 of the printed circuit board; a second solder joint (for example, a part corresponding to the resistance component RKS1) that connects the Kelvin terminal K of the transistor SW1 to the electrode EK1 of the printed circuit board; a control circuit 50 that controls the operation of the switching circuit 41; and a diagnostic circuit 60 that diagnoses the connection state between the transistor SW1 and the printed circuit board by detecting the impedance of the path P1 connecting the electrode ES1 and the electrode EK1 via the transistor SW1. As a result, the power converter 2 can effectively detect connection problems with transistor SW1 by utilizing the Kelvin terminal K of transistor SW1, as shown in the first diagnostic operation.

[0115] Furthermore, the power converter 2 is provided with a third solder joint (for example, a portion corresponding to the resistive component RDS1), a fourth solder joint (for example, a portion corresponding to the resistive component RSS2), and a fifth solder joint (for example, a portion corresponding to the resistive component RKS2). The switching circuit 41 further includes a transistor SW2 having a drain terminal D, a source terminal S, a Kelvin terminal K electrically connected to the source terminal S, and a gate terminal G, which controls the conduction state between the drain terminal D and the source terminal S based on the signal from the gate terminal G. The transistor SW2 is mounted on a printed circuit board, which has an electrode ED1, an electrode ES2 connected to electrode ED1, and an electrode EK2. The third solder joint connects the drain terminal D of transistor SW1 to electrode ED1 of the printed circuit board. The fourth solder joint connects the source terminal S of transistor SW2 to electrode ES2 of the printed circuit board. The fifth solder joint connects the Kelvin terminal K of transistor SW2 to electrode EK2 on the printed circuit board. The diagnostic circuit 60 further diagnoses the connection status between transistors SW1, SW2 and the printed circuit board by detecting the impedance of the path P2 connecting electrode ES1 and electrode EK2 via transistors SW1, SW2. As a result, the power converter 2 can effectively detect connection problems between transistors SW1, SW2 by utilizing the Kelvin terminal K of transistor SW2, as shown in the second diagnostic operation.

[0116] [effect] As described above, this embodiment includes a switching circuit including a transistor SW1 having a drain terminal, a source terminal, a Kelvin terminal electrically connected to the source terminal, and a gate terminal, and controlling the conduction state between the drain terminal and the source terminal based on the signal from the gate terminal; a printed circuit board on which the transistor is mounted and which has electrodes ES1 and EK1; a first solder joint connecting the source terminal of the transistor to electrode ES1 of the printed circuit board; a second solder joint connecting the Kelvin terminal of the transistor to electrode EK1 of the printed circuit board; a control circuit for controlling the operation of the switching circuit; and a diagnostic circuit for diagnosing the connection state between the transistor SW1 and the printed circuit board by detecting the impedance of the path P1 connecting electrode ES1 and electrode EK1 via the transistor SW1. This makes it possible to detect connection problems with the transistor SW1.

[0117] In this embodiment, the switching circuit further includes a transistor SW2 having a drain terminal, a source terminal, a Kelvin terminal electrically connected to the source terminal, and a gate terminal, which controls the conduction state between the drain terminal and the source terminal based on the signal from the gate terminal. The transistor SW2 is mounted on a printed circuit board, which has an electrode ED1, an electrode ES2 connected to electrode ED1, and an electrode EK2. A third solder joint connects the drain terminal of transistor SW1 to electrode ED1 of the printed circuit board. A fourth solder joint connects the source terminal of transistor SW2 to electrode ES2 of the printed circuit board. A fifth solder joint connects the Kelvin terminal of transistor SW2 to electrode EK2 of the printed circuit board. The diagnostic circuit further diagnoses the connection state between transistors SW1, SW2 and the printed circuit board by detecting the impedance of the path P2 connecting electrode ES1 and electrode EK2 via transistors SW1, SW2. This makes it possible to effectively detect connection problems of transistors SW1, SW2.

[0118] Other effects are the same as in the first embodiment described above.

[0119] [Variation 2-1] In the above embodiment, both the first and second diagnostic operations are performed, but the invention is not limited to this. For example, only the first diagnostic operation may be performed, or only the second diagnostic operation may be performed. When only the first diagnostic operation is performed, for example, switches 61 and 64 can be omitted from the diagnostic circuit 60, the power supply voltage SGND can be supplied to the positive input terminal of the amplifier circuit 31, and the power supply voltage VCC can be supplied to the drain of the transistor 33. When only the second diagnostic operation is performed, for example, switches 61 and 64 can be omitted from the diagnostic circuit 60, the power supply voltage SGNDH can be supplied to the positive input terminal of the amplifier circuit 31, and the power supply voltage Vboot can be supplied to the drain of the transistor 33.

[0120] [Modification 2-2] In the above embodiment, the technology was applied to an isolated power converter having a transformer, but it is not limited to this, and instead, for example, it may be applied to a non-isolated power converter without a transformer.

[0121] [Modification 2-3] Modifications 1-1 and 1-2 of the first embodiment may be applied to the power converter 2 according to the above embodiment.

[0122] [Other variations] Furthermore, two or more of these variations may be combined.

[0123] Although the present invention has been described above with reference to embodiments and modifications, the present invention is not limited to these embodiments and various modifications are possible.

[0124] For example, in the above embodiments, current is passed through paths P1 and P2, and the connection state is diagnosed based on the voltage difference between the ends of the paths, but the invention is not limited to this. Alternatively, for example, a voltage may be applied between the ends of paths P1 and P2, and the connection state may be diagnosed based on the current flowing through the paths.

[0125] For example, in the embodiments described above, the present technology was applied to a power converter having the circuit configuration shown in Figures 1 and 7, but it is not limited to this, and the present technology can be applied to power converters having various circuit configurations to which it can be applied.

[0126] For example, in the above embodiment, the technology was applied to a DC / DC conversion circuit that converts DC power to DC power, but it is not limited to this. Instead, for example, the technology may be applied to an AC / DC conversion circuit, a DC / AC conversion circuit, or an AC / AC conversion circuit. [Explanation of symbols]

[0127] 1,1B,2…Power converter, 11…Inductor, 12,41…Switching circuit, 13…Diode, 14…Capacitor, 15…Voltage sensor, 16…Auxiliary power supply circuit, 20,20B,50…Control circuit, 21,51…Power conversion control unit, 22,54,55…Drive unit, 23,23B,53…Diagnostic control unit, 30,30A,30B,60…Diagnostic circuit, 31…Amplifier circuit, 32…Comparator circuit, 33…Transistor, 34B…Comparator circuit, 42…Inductor, 43…Capacitor, 44~47…Diode, 61,64…Switch, 91,92…Winding, 100…Package, 101…Terminal, 110…Printed circuit board, 111…Electrode, CTL,TEST…Control signal, D…Drain terminal, DET,DETB…Detection signal, ED,EG,EK ES, ED1, EG1, EK1, ES1, ED2, EG2, EK2, ES2... electrodes, G... gate terminal, G1, G2... gate signal, K... Kelvin terminal, PDC... DC power supply, PGND, SGND, Vboot, VCC... power supply voltage, RDB, RGB, RKB, RSB, RDB1, RGB1, RKB1, RSB1, RDB2, RGB2, RKB2, RSB2... resistive components, RDS, RGS, RKS, RSS, RDS1, RGS1, RKS1, RSS1, RDS2, RGS2, RKS2, RSS2... resistive components, RP1~RP4, RS1~RS4... resistive elements, S... source terminal, SEL1, SEL2... control signals, SW1, SW2... transistors, LD... load, TR... transformer, T11, T12, T21, T22... power terminals.

Claims

1. Power input terminal and Power output terminal and A switching circuit including a first switching element having a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, and capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal, The first switching element is mounted on a substrate having a first electrode and a second electrode, A first solder joint is provided for joining the second terminal of the first switching element to the first electrode of the substrate, A second solder joint is provided for joining the third terminal of the first switching element to the second electrode of the substrate, A control circuit capable of controlling the operation of the switching circuit, A diagnostic circuit capable of diagnosing the connection state between the first switching element and the substrate by detecting the impedance of the first path connecting the first electrode and the second electrode via the first switching element. Equipped with, The first electrode of the substrate is connected to the first reference power supply node. The second electrode of the substrate is connected to a second reference power supply node. The control circuit is connected to the first power supply node and the second reference power supply node and has a first drive unit capable of driving the first switching element. Power converter.

2. The power conversion device is capable of converting power supplied via the power input terminal by the switching operation of the switching circuit during a first period, and is capable of outputting the converted power via the power output terminal. The control circuit can turn off the first switching element during a second period different from the first period. The diagnostic circuit can diagnose the connection state between the first switching element and the substrate by detecting the impedance of the first path during the second period. The power conversion device according to claim 1.

3. The constant current element has one end connected to the first power supply node and the other end connected to the first reference power supply node, and is capable of passing current along the first path from the first electrode to the second electrode during the second period. The diagnostic circuit can detect the impedance of the first path based on the voltage difference between the voltage at the first reference power supply node and the voltage at the second reference power supply node. The power conversion device according to claim 2.

4. The diagnostic circuit can further diagnose the connection state between the first switching element and the substrate by detecting the impedance of a portion of the first path based on the voltage difference between the voltage at the first reference power supply node and the voltage at the second reference power supply node during the first period. The power conversion device according to claim 2.

5. Power input terminal and Power output terminal and A switching circuit including a first switching element having a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, and capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal, The first switching element is mounted on a substrate having a first electrode and a second electrode, A first solder joint is provided for joining the second terminal of the first switching element to the first electrode of the substrate, A second solder joint is provided for joining the third terminal of the first switching element to the second electrode of the substrate, The third solder joint, The fourth solder joint and The fifth solder joint, A control circuit capable of controlling the operation of the switching circuit, A diagnostic circuit capable of diagnosing the connection state between the first switching element and the substrate by detecting the impedance of the first path connecting the first electrode and the second electrode via the first switching element. Equipped with, The switching circuit further includes a second switching element having a fourth terminal, a fifth terminal, a sixth terminal electrically connected to the fifth terminal, and a second control terminal, and capable of controlling the conduction state between the fourth terminal and the fifth terminal based on a signal from the second control terminal. The second switching element is mounted on the substrate. The substrate further comprises a third electrode, a fourth electrode connected to the third electrode, and a fifth electrode. The third solder joint connects the first terminal of the first switching element to the third electrode of the substrate. The fourth solder joint connects the fifth terminal of the second switching element to the fourth electrode of the substrate. The fifth solder joint connects the sixth terminal of the second switching element to the fifth electrode of the substrate. The diagnostic circuit can further diagnose the connection state between the first switching element, the second switching element and the substrate by detecting the impedance of the second path connecting the first electrode and the fifth electrode via the first switching element and the second switching element. Power converter.

6. The first electrode of the substrate is connected to the first reference power supply node. The second electrode of the substrate is connected to a second reference power supply node. The fifth electrode of the substrate is connected to a third reference power supply node. The control circuit is connected to the second power supply node and the third reference power supply node and has a second drive unit capable of driving the second switching element. The power conversion device according to claim 5.

7. The power conversion device is capable of converting power supplied via the power input terminal by the switching operation of the switching circuit during a first period, and is capable of outputting the converted power via the power output terminal. The control circuit is capable of turning on the first switching element and turning off the second switching element during a second period different from the first period. The diagnostic circuit can diagnose the connection state between the first switching element and the second switching element and the substrate by detecting the impedance of the second path during the second period. The power conversion device according to claim 6.

8. The constant current element has one end connected to the second power supply node and the other end connected to the first reference power supply node, and is capable of passing current along the second path from the first electrode to the fifth electrode during the second period. The diagnostic circuit can detect the impedance of the second path based on the voltage difference between the voltage at the first reference power supply node and the voltage at the third reference power supply node. The power conversion device according to claim 7.

9. Power input terminal and Power output terminal and A switching circuit comprising: a first switching element having a first terminal, a second terminal, a third terminal electrically connected to the second terminal, and a first control terminal, capable of controlling the conduction state between the first terminal and the second terminal based on a signal from the first control terminal; and a second switching element having a fourth terminal, a fifth terminal, a sixth terminal electrically connected to the fifth terminal, and a second control terminal, capable of controlling the conduction state between the fourth terminal and the fifth terminal based on a signal from the second control terminal; A substrate on which the first switching element and the second switching element are mounted, having a first electrode, a third electrode, a fourth electrode connected to the third electrode, and a fifth electrode, A first solder joint connects the second terminal of the first switching element to the first electrode of the substrate, A third solder joint connects the first terminal of the first switching element to the third electrode of the substrate, A fourth solder joint connects the fifth terminal of the second switching element to the fourth electrode of the substrate, A fifth solder joint connects the sixth terminal of the second switching element to the fifth electrode of the substrate, A control circuit capable of controlling the operation of the switching circuit, A diagnostic circuit capable of diagnosing the connection state between the first switching element, the second switching element and the substrate by detecting the impedance of the second path connecting the first electrode and the fifth electrode via the first switching element and the second switching element. A power conversion device equipped with this device.

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