Smoothing capacitor discharge circuit and smoothing capacitor discharge program

Abstract

To reduce an amount of heat generation of a resistance element by positively heating a transistor in a discharge circuit of a smoothing capacitor.SOLUTION: A discharge circuit (40) causes a smoothing capacitor (31) for smoothing a DC voltage to discharge. The discharge circuit includes: a resistance element (41) connected in parallel to the smoothing capacitor; a transistor (42) connected in series to the resistance element; and adjustment circuits (44, 45, 46) that adjust a voltage applied to a gate terminal of the transistor to make the transistor half-on for a predetermined time and then fully on when causing the smoothing capacitor to discharge through the resistance element and the transistor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a discharge circuit that discharges a smoothing capacitor that smooths a DC voltage. [Background technology]

[0002] Conventionally, this type of discharge circuit includes a transistor connected in series to a resistive element, and controls the gate voltage of the transistor so that the discharge current flowing through the resistive element is constant when discharging a smoothing capacitor through the resistive element (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-192868 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the discharge circuit described in Patent Document 1, even if the power capacity of the resistance element is reduced, the temperature of the resistance element is kept below its heat resistance temperature by keeping the discharge current constant. However, Patent Document 1 does not include the idea of reducing the amount of heat generated by the resistance element by actively causing the transistor to generate heat.

[0005] The present invention has been made to solve the above-mentioned problems, and its main object is to reduce the amount of heat generated by a resistor element in a discharge circuit of a smoothing capacitor by actively causing a transistor to generate heat. [Means for solving the problem]

[0006] The first means for solving the above problem is: A discharge circuit (40) for discharging a smoothing capacitor (31) for smoothing a DC voltage, a resistance element (41) connected in parallel to the smoothing capacitor; a transistor (42) connected in series with the resistive element; an adjustment circuit (44, 45, 46) that adjusts a voltage applied to a gate terminal of the transistor when discharging the smoothing capacitor through the resistor element and the transistor, to turn the transistor half-on for a predetermined time and then fully on; Equipped with.

[0007] According to the above configuration, the discharge circuit discharges a smoothing capacitor that smoothes a DC voltage. The discharge circuit includes a resistive element connected in parallel to the smoothing capacitor and a transistor connected in series to the resistive element. Therefore, by discharging the smoothing capacitor through the resistive element and the transistor, the voltage of the smoothing capacitor can be reduced.

[0008] When discharging the smoothing capacitor through the resistor and the transistor, the adjustment circuit adjusts the voltage applied to the gate terminal of the transistor to turn the transistor half-on for a predetermined period of time and then fully on. Therefore, by turning the transistor half-on for a predetermined period of time, the transistor can be actively heated, reducing the amount of heat generated by the resistor. After a certain amount of electrical energy has been consumed in the smoothing capacitor, the transistor is turned fully on, and the remaining electrical energy in the smoothing capacitor is consumed by the resistor. As a result, the smoothing capacitor can be discharged in a shorter time, and the temperature of the resistor can be more easily maintained below its heat-resistant temperature.

[0009] The amount of heat generated by the transistor increases when it is half-on and decreases when it is fully on. On the other hand, the amount of heat generated by the resistor element increases until the discharge current decreases.

[0010] In contrast, in the second aspect, when the smoothing capacitor is discharged through the resistor element and the transistor, the instantaneous heat generation amount of the transistor increases faster than the instantaneous heat generation amount of the resistor element. With this configuration, the transistor generates heat first, thereby reducing the heat generation amount of the resistor element. Therefore, the maximum temperature of the resistor element can be reduced, making it easier to maintain the temperature of the resistor element below its heat-resistant temperature.

[0011] In a third aspect, when the smoothing capacitor is discharged through the resistor element and the transistor, the peak instantaneous heat generation of the transistor occurs before the peak instantaneous heat generation of the resistor element. This configuration allows the time when the amount of heat generated by the transistor increases to occur before the time when the amount of heat generated by the resistor element increases. This reduces the maximum temperature of the resistor element, making it easier to maintain the temperature of the resistor element below its heat-resistant temperature.

[0012] Specifically, as in the fourth aspect, the transistor may be a depression-type transistor, and the adjustment circuit may include a voltage application unit that applies a negative voltage to the gate terminal of the transistor and a passive element connected in parallel between the gate terminal and source terminal of the transistor. With this configuration, when the application of the negative voltage to the gate terminal of the transistor by the voltage application unit is stopped, the voltage applied to the gate terminal of the transistor is adjusted by a passive element (e.g., a resistor and a capacitor), and the transistor can be turned on half-on for a predetermined time and then turned on fully. Furthermore, the same effect can be achieved even when the application of the negative voltage to the gate terminal of the transistor by the voltage application unit is unintentionally stopped.

[0013] The fifth means includes an acceleration sensor (38, 39) that detects acceleration, and a control unit (37) that stops the application of the negative voltage by the voltage application unit when the acceleration detected by the acceleration sensor is greater than a predetermined acceleration.

[0014] According to the above configuration, if the acceleration detected by the acceleration sensor is greater than a predetermined acceleration, for example, if a vehicle equipped with the discharge circuit is involved in a collision, the control unit stops the application of the negative voltage by the voltage application unit, so that the voltage applied to the gate terminal of the transistor is adjusted by the resistor element and the capacitor, and the transistor can be turned on fully after being turned on halfway for a predetermined period of time.

[0015] Specifically, as in the sixth aspect, the transistor may be a depletion-type transistor, and the adjustment circuit may include a voltage adjustment unit that adjusts a negative voltage applied to the gate terminal of the transistor. With this configuration, the negative voltage applied to the gate terminal of the transistor is adjusted by the voltage adjustment unit, so that the transistor can be turned half-on for a predetermined time and then turned fully on.

[0016] In a seventh aspect, the resistor element is mounted on a substrate and sealed with resin to be integrated with the substrate. With this configuration, heat generated by the resistor element can be conducted to the resin, and further conducted from the resin to the substrate. Therefore, it is possible to suppress a rise in the temperature of the resistor element.

[0017] In an eighth aspect, the resin has a flat surface formed thereon, and a cooling member having a temperature lower than that of the resin is in contact with the flat surface. With this configuration, the resin sealing the resistance element can be cooled by the cooling member, and the temperature rise of the resistance element can be further suppressed.

[0018] In a ninth aspect, the resin is provided on both sides of the substrate, and the thickness of the resin on the cooling member side of the substrate is thinner than the thickness of the resin on the opposite side of the substrate from the cooling member. With this configuration, heat can be efficiently conducted from the resistance element to the cooling member via the thin resin on the cooling member side of the substrate. Furthermore, the thick resin on the opposite side of the substrate from the cooling member can increase the heat capacity of the resin, thereby suppressing a rise in the temperature of the resistance element.

[0019] The thermal conductivity of typical epoxy resin is about 0.3 W / mK.

[0020] In this regard, in the tenth aspect, the thermal conductivity of the resin is 0.6 [W / mK] or more. With this configuration, it is possible to promote the heat conduction from the resistance element to the resin, and further suppress the temperature rise of the resistance element.

[0021] In an eleventh aspect, wiring connected to both ends of the smoothing capacitor and wiring controlling the current flow to the resistance element extend from the substrate to the outside of the resin. With this configuration, in a configuration in which the resistance element is sealed with resin and integrated into the substrate, it becomes easy to connect wiring to a discharge circuit from the outside.

[0022] The twelfth measure is: A program applied to a discharge circuit (40) including a resistor element (41) connected in parallel to a smoothing capacitor (31) that smooths a DC voltage, and a transistor (42) connected in series to the resistor element, When the smoothing capacitor is discharged through the resistive element and the transistor, the computer executes a process of adjusting the voltage applied to the gate terminal of the transistor to turn the transistor half-on for a predetermined time and then fully on.

[0023] According to the above configuration, in the program that causes a computer to execute the process, it is possible to achieve the same effects as the first means.

[0024] In a thirteenth means, the transistor is a depletion-type transistor, and the computer is caused to execute a process of adjusting a negative voltage applied to a gate terminal of the transistor.

[0025] According to the above configuration, in the program that causes a computer to execute the process, it is possible to achieve the same effects as those of the sixth aspect. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 2 is a circuit diagram of a control system for a rotating electric machine. [Figure 2] FIG. 4 is a circuit diagram showing a control system for a rotating electric machine after a vehicle collision. [Figure 3] FIG. [Figure 4] FIG. [Figure 5] FIG. [Figure 6] FIG. 10 is a side view of the discharge circuit and the cooler after being sealed with resin. [Figure 7] FIG. 10 is a perspective view of the discharge circuit after being sealed with resin. [Figure 8] 6 is a graph showing the amount of heat generated by each element and the target voltage of a smoothing capacitor over time. [Figure 9] 4 is a flowchart showing a procedure for discharge control. [Figure 10] 10 is a graph showing the amount of heat generated by a resistance element at each position with respect to time. [Figure 11] 4 is a graph showing the relationship between the resistance value of an adjustment resistor element and the gate voltage of a MOSFET. [Figure 12] 4 is a graph showing the on-resistance of a MOSFET, the amount of heat generated by a resistor and a MOSFET, and the voltage of a smoothing capacitor over time. [Figure 13] 6 is a graph showing the temperature of the discharge resistance element with the highest temperature in the present embodiment. [Figure 14] 6 is a graph showing the temperature of a MOSFET 42 in the present embodiment. [Figure 15]10 is a graph showing the temperature of the discharge resistance element with the highest temperature in the first modified example. [Figure 16] 10 is a graph showing the temperature of the discharge resistance element with the highest temperature in the second modified example. [Figure 17] 10 is a graph showing the temperature of the discharge resistance element with the highest temperature in the third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment embodied in a control system for a rotating electrical machine mounted on an electric vehicle or the like will be described with reference to the drawings.

[0028] As shown in FIG. 1, a vehicle 10 is provided with a rotating electric machine 20 in a wheel housing. The rotating electric machine 20 is an in-wheel motor integrally provided with a wheel of the vehicle 10. The rotating electric machine 20 is a three-phase synchronous machine and is provided with star-connected stator windings 21 for each phase. The stator windings 21 for each phase are arranged with an offset of 120° in electrical angle. The rotating electric machine 20 of this embodiment is a permanent magnet synchronous machine in which a rotor 22 is provided with permanent magnets as field poles.

[0029] The rotating electric machine 20 is an in-vehicle main engine, and its rotor 22 rotates integrally with the drive wheels of the vehicle 10. The torque generated by the rotating electric machine 20 functioning as an electric motor (in power running) and as a generator (in regeneration) is transmitted from the rotor 22 to the drive wheels. The drive wheels are rotationally driven by the torque generated by the rotating electric machine 20 in power running.

[0030] The vehicle 10 includes, within its body, an inverter 30, a low-voltage power supply +B, and a storage battery 12, which is a DC power supply. The inverter 30 (drive circuit) includes three phases of series-connected upper-arm switches SWH (upper-side switching elements) and lower-arm switches SWL (lower-side switching elements). In this embodiment, each switch SWH, SWL is a voltage-controlled semiconductor switching element, specifically an IGBT. Therefore, the high-potential side terminal of each switch SWH, SWL is the collector, and the low-potential side terminal is the emitter. Freewheel diodes DH, DL are connected in antiparallel to each switch SWH, SWL.

[0031] In each phase, a first end of the stator winding 21 is connected to the emitter of the upper arm switch SWH and the collector of the lower arm switch SWL via a wire 24. Second ends of the stator windings 21 of each phase are connected to each other at a neutral point. In this embodiment, the stator windings 21 of each phase are set to have the same number of turns.

[0032] The collectors of the upper-arm switches SWH of each phase are connected to the positive terminal of the storage battery 12 via a positive bus Lp. The emitters of the lower-arm switches SWL of each phase are connected to the negative terminal of the storage battery 12 via a negative bus Ln. The positive bus Lp and the negative bus Ln are connected via a smoothing capacitor 31. The smoothing capacitor 31 smoothes the DC voltage applied from the storage battery 12 to the switches SWH and SWL. A permanent discharge resistor 32 is connected in parallel to the smoothing capacitor 31. When the smoothing capacitor 31 needs to be discharged, if the charge stored in the smoothing capacitor 31 is discharged only through the discharge resistor 32, it takes several minutes for the voltage of the smoothing capacitor 31 to drop below 60 V. The smoothing capacitor 31 may be built into the inverter 30 or provided externally to the inverter 30.

[0033] A system main relay SMR is provided between the storage battery 12 and the inverter 30. The collector of the upper arm switch SWH of each phase, the positive electrode of the smoothing capacitor 31, and the discharge resistor 32 are connected to the positive side system main relay SMR via a wiring 25. The emitter of the lower arm switch SWL of each phase, the negative electrode of the smoothing capacitor 31, and the discharge resistor 32 are connected to the negative side system main relay SMR via a wiring 26.

[0034] The storage battery 12 is, for example, a battery pack, and the terminal voltage of the storage battery 12 is, for example, several hundred V. The storage battery 12 is, for example, a secondary battery such as a lithium ion battery or a nickel-metal hydride battery.

[0035] The inverter 30 (vehicle 10) includes an ECU 37. The ECU 37 (control unit) is mainly configured with a microcomputer including a CPU, ROM, RAM, an input / output interface, etc. Power is supplied to the ECU 37 from a low-voltage power supply +B. The low-voltage power supply +B and the ECU 37 are connected via a wiring 27. The ECU 37 receives a command torque Trq* from, for example, a higher-level ECU (Electronic Control Unit). The command torque Trq* is a positive value when the rotating electric machine 20 is powering, and is a negative value when the rotating electric machine 20 is regenerating (generating electricity). The ECU 37 controls the switching of each switch SWH, SWL that configures the inverter 30 to control the torque of the rotating electric machine 20 to the command torque Trq*.

[0036] A first acceleration sensor 38 is provided within the ECU 37. A second acceleration sensor 39 is provided at the front of the vehicle. The acceleration sensors 38 and 39 each detect acceleration. The detection results of the acceleration sensors 38 and 39 are input to the CPU of the ECU 37 via an input interface.

[0037] For example, when the user parks the vehicle, the ECU 37 discharges the smoothing capacitor 31. In this case, the ECU 37 controls the switches SWH and SWL of the inverter 30 with the system main relay SMR open (disconnected) to pass a d-axis current Id (reactive current) through the stator winding 21 of the rotating electric machine 20. As a result, the electrical energy stored in the smoothing capacitor 31 is consumed as heat in the rotating electric machine 20, for example, in 0.5 to 1.0 seconds.

[0038] When a vehicle collides with an obstacle, as shown in FIG. 2, wires 24, 25, 27, etc. may break. Wire 24, which connects inverter 30 to rotating electric machine 20 located in a wheel well, is particularly susceptible to breakage. If wire 24 breaks, d-axis current Id cannot flow through stator winding 21 of rotating electric machine 20. If wire 27 breaks, power is no longer supplied from low-voltage power supply +B to ECU 37, rendering ECU 37 inoperable. This prevents control of switches SWH and SWL of inverter 30, preventing d-axis current Id from flowing through stator winding 21 of rotating electric machine 20. Therefore, the smoothing capacitor 31 cannot be quickly discharged by flowing d-axis current Id through stator winding 21 of rotating electric machine 20. Furthermore, if the drive wheels, which rotate integrally with rotor 22 of rotating electric machine 20, begin to spin, an induced voltage of up to 600 V may be generated.

[0039] Therefore, the inverter 30 is provided with a discharge circuit 40 that rapidly discharges the smoothing capacitor 31. The wiring connecting the smoothing capacitor 31 and the discharge circuit 40 is shorter than the wiring connecting the smoothing capacitor 31 and the rotating electric machine 20, and preferably shorter than the wiring connecting the smoothing capacitor 31 and the switches SWH and SWL, so as to be less likely to break in the event of a vehicle collision.

[0040] The discharge circuit 40 includes a plurality of resistance elements 41, a MOSFET 42, a diode 43, a capacitor 44, an adjustment resistance element 45, and a negative power supply 46. The discharge circuit 40 discharges the smoothing capacitor 31 through the plurality of resistance elements 41 and the MOSFET 42.

[0041] The plurality of resistor elements 41 are connected in series with each other by wiring. The MOSFET 42 is connected in series with the resistor elements 41.

[0042] The MOSFET 42 (transistor, switching element) is a depression-type N-channel transistor, and its drain current is maximum when no voltage is applied between the gate and source, and decreases to zero as a negative voltage is applied to the gate terminal. The drain current of the MOSFET 42 becomes zero when a voltage of −5 V or less is applied to the gate terminal. A diode 43 is connected in antiparallel to the MOSFET 42. The heat-resistant temperature of the MOSFET 42 is, for example, 150° C. Note that instead of the depression-type N-channel MOSFET 42, another normally-on switching element may be used.

[0043] A capacitor 44 (passive element) and an adjustable resistor element 45 (passive element) are connected in parallel between the gate terminal and the source terminal of the MOSFET 42. The capacitance of the capacitor 44 and the resistance value of the adjustable resistor element 45 will be described later.

[0044] The negative power supply 46 (voltage application unit) applies a voltage of −15 V to the gate terminal of the MOSFET 42. When the negative power supply 46 applies a voltage of −15 V to the gate terminal of the MOSFET 42, the drain current of the MOSFET 42 becomes zero. The negative power supply 46 is controlled by the ECU 37, and is switched between a state in which −15 V is applied and a state in which application of −15 V is stopped. If the ECU 37 becomes inoperable, the negative power supply 46 stops applying −15 V. The capacitor 44, the adjustment resistor element 45, and the negative power supply 46 form an adjustment circuit.

[0045] 3 and 4, the discharge circuit 40 includes a rectangular plate-shaped substrate 50. A plurality of resistive elements 41 (11 to 45) are mounted on a front side surface 50a (first surface) of the substrate 50. The plurality of resistive elements 41 (11 to 45) are rectangular plate-shaped chip resistors, and each have electrodes 41a, 41b at both ends in the longitudinal direction, spanning the entire length in the lateral direction.

[0046] Resistance elements 41(11), 41(12), 41(13), 41(14), and 41(15) are connected in series by wiring 47(11), 47(12), 47(13), and 47(14), respectively. Electrodes 41b and 41a of adjacent resistance elements 41 are connected by wiring 47. For example, electrode 41b of resistance element 41(11) and electrode 41a of resistance element 41(12) are connected by wiring 47(11). Resistance elements 41(11), 41(12), 41(13), 41(14), and 41(15) and wiring 47(11), 47(12), 47(13), and 47(14) form a first series-connected body.

[0047] Similarly, the resistor elements 41(21), 41(22), 41(23), 41(24), 41(25) and the wirings 47(21), 47(22), 47(23), 47(24) form a second series-connected body. The resistor elements 41(31), 41(32), 41(33), 41(34), 41(35) and the wirings 47(31), 47(32), 47(33), 47(34) form a third series-connected body. The resistor elements 41(41), 41(42), 41(43), 41(44), 41(45) and the wirings 47(41), 47(42), 47(43), 47(44) form a fourth series-connected body.

[0048] The first series-connected body and the second series-connected body are connected in series by a wiring 48(2). The second series-connected body and the third series-connected body are connected in series by a wiring 48(3). The third series-connected body and the fourth series-connected body are connected in series by a wiring 48(4). The wiring 48(1) is connected to the positive bus Lp.

[0049] Because the resistor elements 41 are connected in series by the wiring 47, heat generated by the resistor elements 41 is conducted between them via the wiring 47. Therefore, if a large amount of heat is conducted between them via the wiring 47, the resistor elements 41 have difficulty dissipating heat, and the temperature of the resistor elements 41 is likely to rise. In particular, the resistor elements 41 are chip resistors. Chip resistors have smaller volumes and heat capacities than typical resistor elements, and therefore their temperature is likely to rise due to heat generation. Furthermore, the resistor element 41 has electrodes 41a and 41b at both ends in the first direction X1 and extending over the entire length in the second direction X2. Therefore, heat generated by the resistor elements 41 is likely to be conducted between the electrodes 41a and 41b extending over the entire length in the second direction X2 via the wiring 47.

[0050] Therefore, the resistive elements 41(11), 41(12), 41(13), 41(14), and 41(15) are arranged at intervals in a first direction X1 parallel to the short side of the substrate 50. The resistive elements 41 included in the series-connected body that are adjacent to each other in the first direction X1 are shifted in position from each other in a second direction X2 (a direction parallel to the long side of the substrate 50) that is perpendicular to the first direction X1. That is, the resistive elements 41 included in the series-connected body that are adjacent to each other in the first direction X1 have different positions in the second direction X2. More specifically, there is no range in which the resistive elements 41 included in the series-connected body that are adjacent to each other in the first direction X1 overlap in the second direction X2 (less than half the total length of the resistive elements 41 in the second direction X2). For example, there is no range in which the resistive elements 41(11) and 41(12) overlap in the second direction X2.

[0051] Furthermore, there is no range where the electrodes 41a, 41b of the resistor elements 41 adjacent to each other in the first direction X1 in the series-connected body overlap in the second direction X2 (less than half the total length of the resistor elements 41 in the second direction X2). For example, there is no range where the electrode 41b of the resistor element 41(11) and the electrode 41a of the resistor element 41(12), which are connected to each other by the wiring 47(11), overlap in the second direction X2.

[0052] Of the resistance elements 41 (11 to 15) included in the series-connected body, the first, third, and fifth resistance elements 41 (11, 13, 15) are positioned at the same position in the second direction X2, the position of the second resistance element 41 (12) is shifted in the second direction X2, and the position of the fourth resistance element 41 (14) is shifted in the opposite direction to the second direction X2 (-X2 direction). That is, throughout the entire series-connected body, the positions of the resistance elements 41 in the second direction X2 are shifted in a sinusoidal pattern. Note that, although the above description has been given using the first series-connected body as an example, the same applies to the second to fourth series-connected bodies.

[0053] When multiple resistor elements 41 connected in series by wiring 47 are arranged in the first direction X1, heat tends to concentrate and dissipate more slowly toward the center of the resistor elements 41 in the first direction X1. Therefore, the resistance values of the resistor elements 41 included in the series-connected body are such that the first and fifth resistor elements 41 (11, 15) have a high resistance, the third resistor element 41 (13) has a low resistance, and the second and fourth resistor elements 41 (12, 14) have a resistance intermediate between the resistance values of the first and fifth resistor elements 41 (11, 15) and the third resistor element 41 (13). In other words, the resistance values of the resistor elements 41 included in the series-connected body decrease toward the center of the resistor elements 41 in the first direction X1. While the first series-connected body has been described above as an example, the same applies to the second to fourth series-connected bodies.

[0054] 5, a plurality of resistive elements 41 are also mounted on the rear surface 50b (second surface) of the substrate 50. Similar to the first to fourth series-connected bodies, a plurality of series-connected bodies extending in the first direction X1 are arranged side by side in the second direction X2 on the rear surface 50b of the substrate 50. On the rear surface 50b of the substrate 50, the plurality of series-connected bodies are connected in series to one another by wiring.

[0055] 3 and 4 is connected to the first series-connected unit on the backside 50b of the substrate 50 through a via hole (conduction hole) provided in the substrate 50. The last series-connected unit on the backside 50b of the substrate 50 is connected to the drain terminal of the MOSFET 42 mounted on the frontside 50a of the substrate 50 through a via hole (conduction hole) provided in the substrate 50 and a wiring 48(6). The source terminal of the MOSFET 42 is connected to the negative bus Ln through a wiring 48(7).

[0056] In the projection onto the front side surface 50a, the resistive element 41 mounted on the front side surface 50a and the resistive element 41 mounted on the back side surface 50b do not overlap at all. That is, in the projection onto the front side surface 50a, the area of the overlapping portion between the resistive element 41 mounted on the front side surface 50a and the resistive element 41 mounted on the back side surface 50b is 0 (less than half the area of the resistive element 41).

[0057] As shown in FIG. 6, the discharge circuit 40 is sealed with resin 51. That is, the resistive element 41 and the MOSFET 42 are sealed with the resin 51 and integrated with the substrate 50. The thermal conductivity of the resin 51 is 0.6 [W / mK] (0.6 [W / mK] or more). The thermal conductivity of general epoxy resin is 0.3 [W / mK], and the thermal conductivity of air is 0.026 [W / mK]. The overall shape of the resin 51 is a rectangular parallelepiped (plate-like). The resin 51 has a flat surface portion 51a formed thereon.

[0058] A cooler 53 is attached to (in contact with) a flat surface 51a of the resin 51. The cooler 53 (cooling member) is made of metal or the like, and has a cooling water flow path formed therein. The cooler 53 cools the resin 51, and therefore the substrate 50, the resistance element 41, and the MOSFET 42, by circulating cooling water therein. A thickness Z1 of the resin 51 on the cooler 53 side relative to the substrate 50 is thinner than a thickness Z2 of the resin 51 on the opposite side of the substrate 50 from the cooler 53.

[0059] As shown in FIG. 7 , bus bars 54, 55 and a lead frame 56 extend from the discharge circuit 40 sealed with resin 51 to the outside of the resin 51. The bus bars 54, 55 are formed into a plate shape from a copper alloy or the like. The lead frame 56 is formed into a rod shape from a copper alloy or the like. One end of the bus bar 54 (wiring) is connected to the wiring 48(1) of the discharge circuit 40 inside the resin 51, and the other end is connected to the positive bus bar Lp (positive electrode of the smoothing capacitor 31) outside the resin 51. One end of the bus bar 55 (wiring) is connected to the wiring 48(7) of the discharge circuit 40 inside the resin 51, and the other end is connected to the negative bus bar Ln (negative electrode of the smoothing capacitor 31) outside the resin 51. The lead frame 56 (wiring that controls the current supply to the resistance element 41) has one end connected to the negative power supply 46 of the discharge circuit 40 inside the resin 51 and the other end connected to the ECU 37 outside the resin 51.

[0060] FIG. 8 is a graph showing the amount of heat generated by each element and the target voltage of the smoothing capacitor 31 over time.

[0061] As shown in Fig. 8(a), in this embodiment, the target is to reduce the voltage of the smoothing capacitor 31 to 60 V or less within 2 seconds from the start of discharge. At that time, it is necessary to maintain the temperature of the resistance element 41 at or below its heat resistance temperature. The heat resistance temperature of the resistance element 41 varies depending on whether or not the resistance element 41 itself is generating heat, but is, for example, 145°C.

[0062] Therefore, in order to reduce the amount of heat generated by the resistance element 41, the MOSFET 42 is turned half-on (high on-resistance) at the beginning of the discharge of the smoothing capacitor 31, and the electrical energy of the smoothing capacitor 31 is consumed by the MOSFET 42. As a result, as shown in FIG. 8(b), when the voltage of the smoothing capacitor 31 is still high and the amount of heat generated by the discharge is large, the MOSFET 42 is made to share part of the amount of heat generated. As a result, the amount of heat generated by the resistance element 41 is reduced, and the temperature rise of the resistance element 41 is suppressed.

[0063] 9 is a flowchart showing the procedure of discharge control. This series of processes is repeatedly executed by the ECU 37 at predetermined intervals.

[0064] First, the first acceleration sensor 38 detects acceleration (S11). The second acceleration sensor 39 detects acceleration (S12). Note that the order of the processing of S11 and S12 may be reversed.

[0065] Next, it is determined whether or not an impact has been detected by both the first acceleration sensor 38 and the second acceleration sensor 39 (S13). More specifically, it is determined whether or not the accelerations detected by the first acceleration sensor 38 and the second acceleration sensor 39 are both greater than a predetermined acceleration A. The predetermined acceleration A is an acceleration at which it can be determined that the vehicle has collided with an obstacle or the like.

[0066] If it is determined in S13 that an impact has been detected by both the first acceleration sensor 38 and the second acceleration sensor 39 (S13: YES), the negative power supply 46 (gate voltage source) is turned OFF (S14). This stops the application of a voltage of -15 [V] to the gate terminal of the MOSFET 42 by the negative power supply 46. As a result, the charge in the capacitor 44 is gradually discharged through the adjustment resistance element 45, and the gate voltage of the MOSFET 42 gradually increases (the voltage applied to the gate terminal of the MOSFET 42 is adjusted). Therefore, the MOSFET 42 is turned half-on for a predetermined time and then fully on, and the smoothing capacitor 31 is discharged through the multiple resistance elements 41 and MOSFET 42 connected in series. In other words, high-speed discharge is performed by the discharge circuit 40. Thereafter, this series of processes is temporarily terminated (END). On the other hand, if it is determined in step S13 that no impact has been detected by at least one of the first acceleration sensor 38 and the second acceleration sensor 39 (S13: NO), this series of processes is temporarily ended (END). In other words, high-speed discharge by the discharge circuit 40 is not performed.

[0067] 10 is a graph showing the amount of heat generated by the resistor element 41 at each position over time during high-speed discharge by the discharge circuit 40. The resistance value of the resistor element 41 decreases toward the center and increases toward the outer edge. Therefore, the resistor element 41 in the center generates the least amount of heat, the resistor element 41 in the outer edge generates the most, and the resistor element 41 in the middle generates the most heat.

[0068] FIG. 11 is a graph showing the relationship between the resistance value of the adjustment resistor element 45 and the gate voltage of the MOSFET 42. Varying the resistance value of the adjustment resistor element 45 changes the rate of increase in the gate voltage when the application of a negative voltage from the negative power supply 46 to the gate terminal of the MOSFET 42 is stopped. Simulations and other tests have confirmed that the amount of heat generated by the MOSFET 42 increases when the gate voltage of the MOSFET 42 is between −4.25 and −2.75 V (heat generation region). When the resistance value of the adjustment resistor element 45 is 10 MΩ, the time during which the gate voltage falls within the heat generation region is longest, and the gate voltage becomes approximately zero within 2 seconds. Therefore, in this embodiment, the resistance value of the adjustment resistor element 45 is set to 10 MΩ. The capacitance of the capacitor 44 is set to a predetermined value depending on the characteristics of the MOSFET 42 and the resistance value of the adjustment resistor element 45.

[0069] FIG. 12 is a graph showing the on-resistance of the MOSFET 42, the heat generation amount of the resistor element 41 and the MOSFET 42, and the voltage of the smoothing capacitor 31 over time during high-speed discharge by the discharge circuit 40. In FIG. 11, in the heat generation region where the gate voltage of the MOSFET 42 is −4.25 to −2.75 V, the on-resistance of the MOSFET 42 is 20 kΩ to 400 Ω. As shown in FIG. 12(b), the heat generation region includes a peak in the heat generation amount of the MOSFET 42. When the smoothing capacitor 31 is discharged through the resistor element 41 and the MOSFET 42, the instantaneous heat generation amount of the MOSFET 42 increases faster than the instantaneous heat generation amount of the resistor element 41. This allows the MOSFET 42 to share some of the heat generation amount when the voltage of the smoothing capacitor 31 is still high and the amount of heat generated by the discharge is large. Furthermore, when the smoothing capacitor 31 is discharged through the resistor element 41 and the MOSFET 42, the instantaneous heat generation amount peaks before the instantaneous heat generation amount peaks. The shape of the graph of the heat generation amount of the resistance element 41 and the MOSFET 42 can be changed by adjusting the heat capacity of the resistance element 41 and the MOSFET 42.

[0070] 13 is a graph showing the temperature of the highest temperature resistance element 41 in this embodiment. In this embodiment, the fourth resistance element 41 (34) in the third series-connected body has the highest temperature. The peak temperature of the resistance element 41 (34) is approximately 132°C, which is below the heat-resistant temperature of 145°C.

[0071] Fig. 14 is a graph showing the temperature of the MOSFET 42 in this embodiment. The temperature peak of the MOSFET 42 occurs earlier than the temperature peak of the resistance element 41 (34) in Fig. 13. The temperature peak of the MOSFET 42 is about 88°C, which is below the heat-resistant temperature of 150°C.

[0072] 15 is a graph showing the temperature of the highest temperature resistance element 41 in the first modified example. The first modified example differs from this embodiment only in that the resistance values of the resistance elements 41 are uniform and are not smaller toward the center in the first direction X1. In the first modified example, the temperature of the third resistance element 41 (33) in the third series-connected body is the highest. The peak temperature of the resistance element 41 (33) is approximately 136°C, which is below the heat-resistant temperature of 145°C.

[0073] 16 is a graph showing the temperature of the highest temperature resistor element 41 in the second modified example. The second modified example differs from the present embodiment in that the resistance value of the resistor element 41 is uniform and is not smaller toward the center in the first direction X1, and in that the MOSFET 42 is not turned half-on but is immediately turned fully on. In the second modified example, the temperature of the third resistor element 41 (33) in the third series-connected body is the highest. The peak temperature of the resistor element 41 (33) is approximately 144°C, which is below the heat-resistant temperature of 145°C.

[0074] 17 is a graph showing the temperature of the highest temperature resistor element 41 in the third modified example. The third modified example differs from the present embodiment in that the resistance value of resistor element 41 is uniform and is not smaller toward the center in the first direction X1, that MOSFET 42 is not half-on but is immediately turned fully on, that resistor element 41 is not sealed with resin 51, and that cooler 53 is omitted. In the third modified example, the temperature of resistor element 41 located at the center of rear surface 50b of substrate 50 is the highest. The peak temperature of resistor element 41 is approximately 280°C, exceeding the heat-resistant temperature of 145°C.

[0075] The present embodiment described above in detail has the following advantages.

[0076] The discharge circuit 40 includes a series-connected body in which at least three resistive elements 41 are arranged at intervals in the first direction X1 and connected in series by wiring 47. When the plurality of resistive elements 41 connected in series by wiring 47 are arranged in the first direction X1, the resistive elements 41 closer to the center in the first direction X1 tend to concentrate heat and are less able to dissipate it. In this regard, the resistance values of the resistive elements 41 included in the series-connected body are smaller as the resistive elements 41 closer to the center in the first direction X1 become smaller. Therefore, the amount of heat generated can be reduced for the resistive elements 41 closer to the center, which are less able to dissipate heat, and the temperature of the resistive elements 41 that are less able to dissipate heat can be prevented from exceeding their heat resistance temperature.

[0077] Because the resistor elements 41 are connected in series by the wiring 47, heat generated by the resistor elements 41 is transferred between them via the wiring 47. Therefore, if a large amount of heat is transferred between them via the wiring 47, the resistor elements 41 have difficulty dissipating heat, and the temperature of the resistor elements 41 is likely to rise. In this regard, the range over which the positions of the resistor elements 41 adjacent to each other in the first direction X1 included in the series-connected element overlap in the second direction X2 perpendicular to the first direction X1 is less than half the total length of the resistor elements 41 in the second direction X2. Therefore, the wiring 47 connecting the resistor elements 41 adjacent to each other in the first direction X1 can be lengthened, and the heat generated by the resistor elements 41 can be prevented from being transferred between them via the wiring 47. Therefore, the resistor elements 41 are able to easily dissipate heat, and the temperature of the resistor elements 41 can be prevented from rising.

[0078] The above two effects make it possible to discharge the smoothing capacitor 31 in a shorter time and to easily maintain the temperature of the resistance element 41 at or below its heat-resistant temperature.

[0079] The resistive element 41 is a chip resistor. Chip resistors have smaller volumes and heat capacities than typical resistive elements 41, and therefore their temperature is more likely to rise due to heat generation. Furthermore, the resistive element 41 includes electrodes 41a and 41b at both ends in the first direction X1, extending over the entire length in the second direction X2. Therefore, heat generated in the resistive element 41 is easily conducted between the electrodes 41a and 41b, which extend over the entire length in the second direction X2, via the wiring 47. In this regard, the overlapping range in the second direction X2 between the electrodes 41a and 41b of the resistive elements 41 adjacent to each other in the first direction X1 included in the series-connected element is less than half the entire length of the resistive element 41 in the second direction X2. Therefore, the wiring 47 connecting the electrodes 41a and 41b of the resistive elements 41 adjacent to each other in the first direction X1 can be lengthened, thereby preventing heat generated in the resistive elements 41 from being conducted between the electrodes 41a and 41b via the wiring 47.

[0080] There is no range in which the positions of the resistor elements 41 adjacent to each other in the first direction X1 included in the series-connected body overlap in the second direction X2. With this configuration, the wiring 47 connecting the resistor elements 41 adjacent to each other in the first direction X1 can be made longer, and the heat generated in the resistor elements 41 can be further prevented from being conducted to each other via the wiring 47. That is, in the discharge circuit 40, which is required to efficiently arrange the multiple resistor elements 41, the heat dissipation properties of the resistor elements 41 can be improved by intentionally making the wiring 47 connecting the resistor elements 41 adjacent to each other in the first direction X1 longer.

[0081] The multiple resistive elements 41 are mounted on both surfaces of the substrate 50, that is, the front surface 50a and the back surface 50b, and in a projection onto the front surface 50a, the overlapping area between the resistive elements 41 mounted on the front surface 50a and the resistive elements 41 mounted on the back surface 50b is less than half the area of the resistive elements 41. With this configuration, in the discharge circuit 40 in which the multiple resistive elements 41 are mounted on both surfaces of the substrate 50, that is, the front surface 50a and the back surface 50b, the overlapping area between the resistive elements 41 can be reduced in a projection onto the front surface 50a. Therefore, the heat conducted between the resistive elements 41 mounted on the front surface 50a and the resistive elements 41 mounted on the back surface 50b can be reduced, and the heat dissipation of each resistive element 41 can be improved.

[0082] The resistor element 41 is sealed with resin 51 and integrated with the substrate 50. With this configuration, heat generated in the resistor element 41 can be conducted to the resin 51, and further conducted from the resin 51 to the substrate 50. Therefore, it is possible to suppress a rise in the temperature of the resistor element 41.

[0083] A flat surface 51a is formed in the resin 51, and a cooler 53 having a temperature lower than that of the resin 51 is in contact with the flat surface 51a. With this configuration, the resin 51 sealing the resistance element 41 can be cooled by the cooler 53, and the temperature rise of the resistance element 41 can be further suppressed.

[0084] The resin 51 is provided on both sides of the substrate 50, and a thickness Z1 of the resin 51 on the cooler 53 side of the substrate 50 is thinner than a thickness Z2 of the resin 51 on the opposite side of the substrate 50 from the cooler 53. With this configuration, heat can be efficiently conducted from the resistance element 41 to the cooler 53 via the thin resin 51 on the cooler 53 side of the substrate 50. Furthermore, the thick resin 51 on the opposite side of the substrate 50 from the cooler 53 can increase the heat capacity of the resin 51, thereby suppressing a rise in temperature of the resistance element 41.

[0085] The thermal conductivity of the resin 51 is 0.6 W / mK or more. This configuration can promote heat conduction from the resistance element 41 to the resin 51, and can further suppress the temperature rise of the resistance element 41.

[0086] Bus bars 54, 55 connected to both ends of the smoothing capacitor 31, respectively, and a lead frame 56 that controls the flow of current to the resistive element 41 extend from the substrate 50 to the outside of the resin 51. With this configuration, in a configuration in which the resistive element 41 is sealed with the resin 51 and integrated into the substrate 50, it becomes easy to connect the wiring 47 to the discharge circuit 40 from the outside.

[0087] When discharging the smoothing capacitor 31 through the resistor element 41 and the MOSFET 42, the adjustment circuit adjusts the voltage applied to the gate terminal of the MOSFET 42 to keep the MOSFET 42 half-on for a predetermined time and then fully-on. Therefore, by keeping the MOSFET 42 half-on for the predetermined time, the MOSFET 42 can actively generate heat, reducing the amount of heat generated by the resistor element 41. Then, after a certain amount of electrical energy has been consumed in the smoothing capacitor 31, the MOSFET 42 is turned fully-on, and the remaining electrical energy of the smoothing capacitor 31 is consumed by the resistor element 41. As a result, the smoothing capacitor 31 can be discharged in a shorter time, and the temperature of the resistor element 41 can be more easily maintained below its heat-resistant temperature.

[0088] When the smoothing capacitor 31 is discharged through the resistance element 41 and the MOSFET 42, the instantaneous amount of heat generated by the MOSFET 42 increases faster than the instantaneous amount of heat generated by the resistance element 41. With this configuration, the MOSFET 42 generates heat first, thereby reducing the amount of heat generated by the resistance element 41. This reduces the maximum temperature of the resistance element 41, making it easier to maintain the temperature of the resistance element 41 at or below its heat-resistant temperature.

[0089] When the smoothing capacitor 31 is discharged through the resistance element 41 and the MOSFET 42, the instantaneous peak of heat generation in the MOSFET 42 occurs before the instantaneous peak of heat generation in the resistance element 41. With this configuration, the time when the amount of heat generated by the MOSFET 42 increases can be made earlier than the time when the amount of heat generated by the resistance element 41 increases. This makes it possible to reduce the maximum temperature of the resistance element 41, making it easier to maintain the temperature of the resistance element 41 at or below its heat-resistant temperature.

[0090] The MOSFET 42 is a depletion-mode transistor, and the adjustment circuit includes a negative power supply 46 that applies a negative voltage to the gate terminal of the MOSFET 42, and an adjustment resistor element 45 (passive element) and a capacitor 44 (passive element) connected in parallel between the gate and source terminals of the MOSFET 42. With this configuration, when the application of the negative voltage to the gate terminal of the MOSFET 42 from the negative power supply 46 is stopped, the voltage applied to the gate terminal of the MOSFET 42 is adjusted by the adjustment resistor element 45 and the capacitor 44, and the MOSFET 42 can be turned fully on after being half-on for a predetermined period of time. Furthermore, the same effect can be achieved even when the application of the negative voltage to the gate terminal of the MOSFET 42 from the negative power supply 46 is unintentionally stopped.

[0091] If the acceleration detected by the acceleration sensors 38, 39 is greater than a predetermined acceleration A, for example, if a vehicle equipped with the discharge circuit 40 collides, the ECU 37 stops the application of the negative voltage from the negative power supply 46. As a result, the voltage applied to the gate terminal of the MOSFET 42 is adjusted by the adjustment resistor element 45 and the capacitor 44, and the MOSFET 42 can be turned fully on after being half-on for a predetermined period of time.

[0092] The above embodiment can be modified as follows: The same parts as those in the above embodiment are denoted by the same reference numerals and the description thereof will be omitted.

[0093] The thickness Z1 of the resin 51 on the cooler 53 side of the substrate 50 may be equal to the thickness Z2 of the resin 51 on the opposite side of the substrate 50 from the cooler 53 .

[0094] The resin 51 may be a general epoxy resin or the like.

[0095] The resin 51 may not seal the entire substrate 50, but may seal only the resistor element 41, or only the resistor element 41 and the MOSFET 42. The resin 51 may also be omitted. The cooler 53 may also be omitted.

[0096] A coil may be included as a passive element connected in parallel between the gate terminal and the source terminal of the MOSFET 42.

[0097] When the smoothing capacitor 31 is discharged through the resistance element 41 and the MOSFET 42, the peak instantaneous amount of heat generated by the MOSFET 42 and the peak instantaneous amount of heat generated by the resistance element 41 may occur simultaneously.

[0098] When the smoothing capacitor 31 is discharged through the resistive element 41 and the MOSFET 42, the instantaneous amount of heat generated by the MOSFET 42 and the instantaneous amount of heat generated by the resistive element 41 may increase simultaneously.

[0099] Of the resistive elements 41 (11 to 15) included in the series-connected body, the first, third, and fifth resistive elements 41 (11, 13, 15) may be positioned at the same position in the second direction X2, and the second and fourth resistive elements 41 (12, 14) may be positioned at different positions in the second direction X2. That is, throughout the entire series-connected body, the resistive elements 41 may be positioned at different positions in the second direction X2 in a half-wave (staggered) pattern.

[0100] The larger the resistive element 41, the larger the portion that comes into contact with the wiring 47 and the substrate 50, making it easier to dissipate heat from the resistive element 41 to the wiring 47 and the substrate 50. Therefore, the size of the resistive elements 41 included in the series-connected body may be larger for the resistive elements 41 closer to the center in the first direction X1. With this configuration, heat can be more easily dissipated from the resistive elements 41 closer to the center, which have difficulty dissipating heat, to the wiring 47 and the substrate 50, and the temperature of the resistive elements 41 closer to the center can be prevented from exceeding their heat resistance temperature. Instead of chip resistors, general resistive elements can also be used as the resistive elements 41.

[0101] In a projection onto the front side surface 50a, the area of the overlapping portion between the resistive element 41 mounted on the front side surface 50a and the resistive element 41 mounted on the back side surface 50b may be half or more of the area of the resistive element 41. The resistive element 41 may be mounted only on the front side surface 50a of the substrate 50. The discharge circuit 40 may be divided into multiple substrates and integrated with the resin 51.

[0102] The resistive elements 41 may be disposed only on the outer edge of the front surface 50a of the substrate 50, rather than over the entire surface of the front surface 50a of the substrate 50. When the series-connected bodies extend from the outside to the inside of the substrate 50 at the outer edge of the front surface 50a of the substrate 50, the resistance values of the resistive elements 41 included in the series-connected bodies may be made smaller as the resistive elements 41 are closer to the center of the series-connected bodies extending from the outside to the inside. When the series-connected bodies extend along the outer edge of the front surface 50a of the substrate 50, the resistance values of the resistive elements 41 included in the series-connected bodies may be made smaller as the resistive elements 41 are closer to the center of the series-connected bodies extending along the outer edge of the substrate 50.

[0103] Whether the vehicle has collided with an obstacle or the like can be determined based on the detection results of a yaw rate sensor or the like mounted on the vehicle body or wheel instead of the acceleration sensors 38, 39. The acceleration sensors 38, 39 may be omitted, and the ECU 37 may not execute discharge control. Even in this case, if the vehicle collides with an obstacle or the like and the negative power supply 46 is turned off, high-speed discharge by the discharge circuit 40 is automatically executed.

[0104] The adjustment circuit may include a voltage adjustment unit (variable setting unit) that adjusts (variably sets) the negative voltage applied to the gate terminal of the MOSFET 42, instead of the adjustment resistor element 45, the capacitor 44, and the negative power supply 46. With this configuration, the negative voltage applied to the gate terminal of the MOSFET 42 is adjusted by the voltage adjustment unit, so that the MOSFET 42 can be turned fully on after being half-on for a predetermined period of time. Also, instead of the depletion-mode N-channel MOSFET 42, a depletion-mode P-channel MOSFET, an enhancement-mode N-channel MOSFET, an enhancement-mode P-channel MOSFET, or the like may be used.

[0105] The discharge circuit 40 and the method described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions (instructions) embodied in a computer program. Alternatively, the discharge circuit 40 and the method described herein may be implemented by a special-purpose computer configured with a processor configured with one or more dedicated hardware logic circuits. Alternatively, the discharge circuit 40 and the method described herein may be implemented by one or more special-purpose computers configured with a processor and memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by a computer on a computer-readable non-transitory storage medium. [Explanation of symbols]

[0106] 31...smoothing capacitor, 40...discharge circuit, 41...resistance element, 42...MOSFET, 44...capacitor, 45...adjustable resistance element, 46...negative power supply, 47...wiring, 50...circuit board.

Claims

1. A discharge circuit (40) for discharging a smoothing capacitor (31) for smoothing a DC voltage, a resistor element (41) connected in parallel to the smoothing capacitor; a transistor (42) connected in series with the resistive element; an adjustment circuit (44, 45, 46) that adjusts a voltage applied to a gate terminal of the transistor when discharging the smoothing capacitor through the resistor element and the transistor, to turn the transistor half-on for a predetermined time and then fully on; A smoothing capacitor discharge circuit comprising:

2. 2. The smoothing capacitor discharge circuit according to claim 1, wherein when the smoothing capacitor is discharged through the resistor element and the transistor, the instantaneous amount of heat generated by the transistor increases faster than the instantaneous amount of heat generated by the resistor element.

3. 3. The smoothing capacitor discharge circuit according to claim 1, wherein when the smoothing capacitor is discharged through the resistor element and the transistor, a peak instantaneous amount of heat generated by the transistor occurs before a peak instantaneous amount of heat generated by the resistor element.

4. the transistor is a depletion-mode transistor, The smoothing capacitor discharge circuit according to any one of claims 1 to 3, wherein the adjustment circuit comprises a voltage application unit (46) that applies a negative voltage to the gate terminal of the transistor, and a passive element (44, 45) connected in parallel between the gate terminal and the source terminal of the transistor.

5. acceleration sensors (38, 39) for detecting acceleration; a control unit (37) that stops the application of the negative voltage by the voltage application unit when the acceleration detected by the acceleration sensor is greater than a predetermined acceleration; The smoothing capacitor discharge circuit according to claim 4 , comprising:

6. the transistor is a depletion-mode transistor, 4. The smoothing capacitor discharge circuit according to claim 1, wherein the adjustment circuit includes a voltage adjustment unit that adjusts the negative voltage applied to the gate terminal of the transistor.

7. 7. The smoothing capacitor discharge circuit according to claim 1, wherein the resistance element is mounted on a substrate (50), sealed with resin (51), and integrated with the substrate.

8. The resin has a flat surface (51a) formed thereon, 8. The smoothing capacitor discharge circuit according to claim 7, wherein a cooling member (53) having a temperature lower than that of the resin is in contact with the flat portion.

9. the resin is provided on both sides of the substrate, 9. The smoothing capacitor discharge circuit according to claim 8, wherein a thickness (Z1) of the resin on the cooling member side of the substrate is thinner than a thickness (Z2) of the resin on the opposite side of the substrate from the cooling member.

10. 10. The smoothing capacitor discharge circuit according to claim 7, wherein the resin has a thermal conductivity of 0.6 [W / mK] or more.

11. The smoothing capacitor discharge circuit according to any one of claims 7 to 10, wherein wiring (54, 55) connected to both ends of the smoothing capacitor and wiring (56) for controlling the flow of current to the resistance element extend from the substrate to the outside of the resin.

12. A program applied to a discharge circuit (40) including a resistor element (41) connected in parallel to a smoothing capacitor (31) that smooths a DC voltage, and a transistor (42) connected in series to the resistor element, A smoothing capacitor discharge program that causes a computer to execute a process of adjusting the voltage applied to the gate terminal of the transistor to turn the transistor half-on for a predetermined period of time and then fully on when discharging the smoothing capacitor through the resistance element and the transistor.

13. the transistor is a depletion-mode transistor, The smoothing capacitor discharging program according to claim 12 , which causes the computer to execute a process of adjusting a negative voltage applied to a gate terminal of the transistor.

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