Discharge device and semiconductor device

Abstract

A discharge device that is connected in parallel to a capacitive element and discharges, as discharge current, charge that is accumulated in the capacitive element, the discharge device comprising a plurality of constant current circuits that conduct constant discharge current, wherein the plurality of constant current circuits are connected in series.

Description

Discharge device and semiconductor device

[0001] The present invention relates to a discharge device and a semiconductor device.

[0002] For example, Patent Document 1 discloses a discharge device that can be miniaturized. This discharge device is for discharging the charge of a smoothing capacitor provided in a drive device of a motor that rotates the wheels of a vehicle, and includes a discharge circuit component connected in parallel with the smoothing capacitor and a current adjustment circuit component that adjusts the current of the discharge circuit component, with the discharge circuit component and the current adjustment circuit component configured as a set, and multiple sets connected in series.

[0003] JP 2018-160954 A

[0004] The discharge device disclosed in Patent Document 1 has multiple discharge circuit components connected in series and multiple current adjustment circuit components connected in series. That is, the discharge device disclosed in Patent Document 1 includes a row in which multiple discharge circuit components are connected in series and a row in which multiple current adjustment circuit components are connected in series. Furthermore, each row has multiple resistors connected in series. In Patent Document 1, if the lowest resistor shorts out, for example, the discharge current cannot be adjusted, which could result in an excessively large discharge current and increased heat generation.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to prevent the discharge current from becoming excessive in a discharge device.

[0006] The present invention employs the following configuration as a means for solving the above problems.

[0007] A first aspect of the present invention is a discharge device that is connected in parallel to a capacitance element and discharges the charge accumulated in the capacitance element as a discharge current, and is configured to include a plurality of constant current circuits that conduct a constant discharge current, and the plurality of constant current circuits are connected in series.

[0008] A second aspect of the present invention is a semiconductor device comprising: a capacitor unit including a capacitance element; a power module connected to the capacitor unit and having a plurality of semiconductor power devices; and a control board that controls the power module and on which the discharge device of the first aspect is formed, wherein the control board has a printed wiring board disposed opposite to the power module, a discharge semiconductor switch is mounted on the surface of the printed wiring board opposite to the surface facing the power module, and a heat dissipation pad that receives heat from the discharge semiconductor switch is formed on the surface of the printed wiring board facing the power module.

[0009] According to the present invention, multiple constant current circuits are connected in series, so that even if one of the constant current circuits fails, the remaining non-failed constant current circuits can prevent the discharge current from becoming excessively large.

[0010] Fig. 1 is a schematic configuration diagram of a vehicle equipped with a discharge device according to a first embodiment of the present invention. Fig. 2 is a circuit diagram of the discharge device according to the first embodiment of the present invention. Fig. 3 is an exploded perspective view showing a schematic structural configuration of a power conversion device equipped with the discharge device according to the first embodiment of the present invention. Fig. 4 is a schematic diagram showing the upper surface of a part of a gate driver substrate on which a discharge device according to the first embodiment of the present invention is formed. Fig. 5 is a circuit diagram of a discharge device according to a second embodiment of the present invention. Fig. 6 is a schematic diagram showing the upper surface of a part of a gate driver substrate on which a discharge device according to a third embodiment of the present invention is formed.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a discharge device and a semiconductor device according to the present invention will be described below with reference to the drawings.

[0012] 1 is a schematic diagram of a vehicle 100 equipped with a discharge device 5 according to the present embodiment. The vehicle 100 is, for example, an electric vehicle or a hybrid vehicle. As shown in FIG. 1 , the vehicle 100 includes, for example, a high-voltage battery HB, a low-voltage battery LB, a motor M, and a power conversion device 1.

[0013] The high-voltage battery HB is a secondary battery such as a lithium-ion battery, and outputs relatively high-voltage DC power of, for example, several hundred volts. This high-voltage battery HB is a battery that outputs drive power to be supplied to the motor M, and is a so-called drive battery. The low-voltage battery LB is a secondary battery such as a lead-acid battery, and outputs relatively low-voltage DC power of, for example, about 12 V. This low-voltage battery LB is a battery that outputs auxiliary power to be supplied to auxiliary devices (not shown), and is a so-called auxiliary device battery.

[0014] The motor M generates rotational power by receiving drive power from the high-voltage battery HB via the power conversion device 1. The rotational power generated by the motor M is transmitted to the drive wheels of the vehicle 100 via a transmission mechanism (not shown).

[0015] The power conversion device 1 is a device that performs power conversion. For example, the power conversion device 1 converts DC power to AC power, AC power to DC power, and voltage. Specifically, the power conversion device 1 boosts and converts drive power output from a high-voltage battery HB to AC power and supplies the power to a motor M. The power conversion device 1 also converts regenerative power output from the motor M to DC power, reduces the voltage, and supplies the power to the high-voltage battery HB. Furthermore, the power conversion device 1 reduces the voltage of the drive power output from the high-voltage battery HB to generate power for auxiliary devices and supply the power to a low-voltage battery LB.

[0016] 1, the power conversion device 1 includes a step-up / step-down converter 2, an inverter 3, a smoothing capacitor 4, a discharge device 5, and a DC-DC converter 6. The step-up / step-down converter 2, the inverter 3, and the DC-DC converter 6 constitute a power conversion circuit H that performs power conversion.

[0017] The buck-boost converter 2 is a circuit including a reactor and a capacitor, and performs a step-up or step-down of power. Specifically, the buck-boost converter 2 has a pair of primary-side input / output terminals and a pair of secondary-side input / output terminals, and selectively performs a step-up process in which the battery power at the primary-side input / output terminals is boosted and output to the secondary-side input / output terminals, or a step-down process in which the regenerative power at the secondary-side input / output terminals is reduced and output to the primary-side input / output terminals. In other words, the buck-boost converter 2 boosts the drive power supplied from the high-voltage battery HB and outputs it to the inverter 3. The buck-boost converter 2 also reduces the regenerative power supplied from the inverter 3 and outputs it to the high-voltage battery HB.

[0018] The inverter 3 converts DC power to AC power or AC power to DC power. For example, the inverter 3 converts DC driving power supplied from the step-up / step-down converter 2 into three-phase AC power and outputs it to the motor M. The inverter 3 also converts regenerative AC power supplied from the motor M into DC power and outputs it to the high-voltage battery HB.

[0019] The step-up / step-down converter 2 and the inverter 3 each include a plurality of semiconductor power devices. Each of the semiconductor power devices includes a power transistor. These semiconductor power transistors include semiconductor elements and are mounted on an insulated circuit board. For example, one semiconductor power device includes two power transistors. However, a semiconductor power device having a single power transistor may also be included. For example, each power transistor includes a plurality of semiconductor elements formed of, for example, SiC (silicon carbide). Note that the power transistor may also include semiconductor elements formed of other materials such as Si (silicon) or GaN (gallium nitride).

[0020] 1 , the smoothing capacitor 4 is a capacitance element provided between the buck-boost converter 2 and the inverter 3. That is, one end of the smoothing capacitor 4 is connected to one of the secondary-side input / output terminals of the buck-boost converter 2, and the other end is connected to the other of the secondary-side input / output terminals of the buck-boost converter 2. In this embodiment, one end of the smoothing capacitor 4 is connected to the high-voltage end, which is one of the secondary-side input / output terminals of the buck-boost converter 2. The other end of the smoothing capacitor 4 is connected to the high-voltage end, which is the other of the secondary-side input / output terminals of the buck-boost converter 2.

[0021] Such a smoothing capacitor 4 smoothes ripples in the boost power output from the secondary-side input / output terminals of the boost / buck converter 2. Furthermore, this smoothing capacitor 4 charges or discharges an electric charge so that one end has a higher potential than the other end, using the boost power output from the secondary-side input / output terminals of the boost / buck converter 2 or the regenerative power input from the inverter 3. Note that it is also possible to adopt a configuration in which the smoothing capacitor 4 is provided but the boost / buck converter 2 is not provided.

[0022] The discharge device 5 is provided between the step-up / step-down converter 2 and the inverter 3 in a state connected in parallel to the smoothing capacitor 4. This discharge device 5 is a discharge circuit that forcibly discharges the smoothing capacitor 4 that has accumulated charge using the boosted power of the step-up / step-down converter 2 or the regenerative power of the inverter 3. In other words, the discharge device 5 discharges the charge accumulated in the smoothing capacitor 4 as a discharge current.

[0023] The voltage across the smoothing capacitor 4 is applied to the discharge device 5 as a discharge voltage. The discharge device 5 generates a discharge current that corresponds to the discharge voltage and its own internal resistance (discharge resistance). The discharge device 5 constantly discharges the power stored in the smoothing capacitor 4, and when the power supply from the high-voltage battery HB is stopped by a contactor (not shown), the discharge device 5 reduces the voltage of the smoothing capacitor 4. The discharge device 5 will be described in detail later.

[0024] The DC-DC converter 6 converts the drive power output from the high-voltage battery HB into DC power for the auxiliary devices by stepping down the voltage of the drive power.

[0025] Next, the discharge device 5 will be described in detail. FIG. 2 is a circuit diagram of the discharge device 5. As shown in FIG. 2, the discharge device 5 includes two constant current circuits 5a and a midpoint connection line 5b. The two constant current circuits 5a are connected in series via the midpoint connection line 5b. These constant current circuits 5a are connected in series between one end and the other end of the smoothing capacitor 4. Each constant current circuit 5a is a circuit that flows a constant, predetermined current regardless of fluctuations in the voltage between the terminals of the smoothing capacitor 4. In other words, each constant current circuit 5a conducts a constant discharge current.

[0026] In this embodiment, as described above, two constant current circuits 5a are connected in series. Of these two constant current circuits 5a, the constant current circuit 5a on one end side of the smoothing capacitor 4 (the high-voltage end side of the step-up / step-down converter 2) will be referred to as a first constant current circuit 5a1 as necessary. Also, of these two constant current circuits 5a, the constant current circuit 5a on the other end side of the smoothing capacitor 4 (the low-voltage end side of the step-up / step-down converter 2) will be referred to as a second constant current circuit 5a2 as necessary.

[0027] Each constant current circuit 5a includes a discharge unit 5c and a current adjustment unit 5d. The discharge unit 5c is a circuit that conducts a discharge current. The current adjustment unit 5d is a circuit that adjusts the current conducted by the discharge unit 5c so that the discharge current flowing through the constant current circuit 5a is constant. In other words, the current adjustment unit 5d adjusts the discharge unit 5c based on the magnitude of the discharge current conducted to the discharge unit so that the discharge current flowing through the constant current circuit 5a is constant. Note that a portion of the discharge current flows through the current adjustment unit 5d.

[0028] The discharge unit 5c includes a discharge semiconductor switch 5c1, a discharge resistor 5c2, and a current adjustment semiconductor switch connection line 5c3. The discharge semiconductor switch 5c1 and the discharge resistor 5c2 are connected in series. In this embodiment, the discharge semiconductor switch 5c1 is a metal oxide semiconductor field effect transistor (MOSFET), which has higher voltage resistance than a bipolar transistor. However, the discharge semiconductor switch 5c1 is not limited to a metal oxide semiconductor field effect transistor.

[0029] The drain terminal of the discharge semiconductor switch 5c1, which is an input terminal for the discharge current, is connected to one end of the smoothing capacitor 4. The drain terminal of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 is connected to one end of the smoothing capacitor 4 via the first constant current circuit 5a1. The source terminal of the discharge semiconductor switch 5c1, which is an output terminal for the discharge current, is connected to the other end of the smoothing capacitor 4. The source terminal of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 is connected to the other end of the smoothing capacitor 4 via the discharge resistor 5c2 of the first constant current circuit 5a1 and the second constant current circuit 5a2.

[0030] The gate terminal, which is the control end of the discharge semiconductor switch 5c1, is connected to a discharge semiconductor switch control line 5d3, which will be described later. When a discharge current is supplied to the discharge semiconductor switch control line 5d3 and a voltage is applied to the gate terminal, the discharge semiconductor switch 5c1 is brought into a conductive state in which a discharge current flows from the drain terminal to the source terminal. Note that the discharge semiconductor switch 5c1 is brought into a non-conductive state when no voltage is applied to the gate terminal.

[0031] One end of the discharge resistor 5c2 is connected to the source terminal (output terminal) of the discharge semiconductor switch 5c1. The other end of the discharge resistor 5c2 is connected to the other end of the smoothing capacitor 4. The other end of the discharge resistor 5c2 of the first constant current circuit 5a1 is connected to the drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2. The discharge resistor 5c2 of the first constant current circuit 5a1 is connected to the other end of the smoothing capacitor 4 via the second constant current circuit 5a2.

[0032] 2, the discharge section 5c of the first constant current circuit 5a1 and the discharge section 5c of the second constant current circuit 5a2 are connected in series. From one end of the smoothing capacitor 4 to the other, the discharge semiconductor switch 5c1 of the first constant current circuit 5a1, the discharge resistor 5c2 of the first constant current circuit 5a1, the discharge semiconductor switch 5c1 of the second constant current circuit 5a2, and the discharge resistor 5c2 of the second constant current circuit 5a2 are arranged in this order.

[0033] The drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 is connected to one end of the smoothing capacitor 4. The source terminal (output terminal) of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 is connected to one end of the discharge resistor 5c2 of the first constant current circuit 5a1. The other end of the discharge resistor 5c2 of the first constant current circuit 5a1 is connected to the drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2. The source terminal (output terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 is connected to one end of the discharge resistor 5c2 of the second constant current circuit 5a2. The other end of the discharge resistor 5c2 of the second constant current circuit 5a2 is connected to the other end of the smoothing capacitor 4.

[0034] One end of the current adjustment semiconductor switch connection line 5c3 is connected to the midpoint between the discharge semiconductor switch 5c1 and the discharge resistor 5c2. That is, one end of the current adjustment semiconductor switch connection line 5c3 is connected to the source terminal of the discharge semiconductor switch 5c1 and one end of the discharge resistor 5c2. The other end of the current adjustment semiconductor switch connection line 5c3 is connected to the base terminal, which is the control terminal, of the current adjustment semiconductor switch 5d2.

[0035] Therefore, when a discharge current flows through the discharge semiconductor switch 5c1, a current is supplied to the base terminal of the current adjustment semiconductor switch 5d2 via the current adjustment semiconductor switch connection line 5c3, and the current adjustment semiconductor switch 5d2 becomes conductive. In other words, the current adjustment semiconductor switch 5d2 becomes conductive when the discharge semiconductor switch 5c1 becomes conductive.

[0036] The current adjustment unit 5d includes a current adjustment resistor 5d1, a current adjustment semiconductor switch 5d2, and a discharge semiconductor switch control line 5d3. The current adjustment resistor 5d1 and the current adjustment semiconductor switch 5d2 are connected in series. In this embodiment, the current adjustment semiconductor switch 5d2 is an NPN bipolar transistor. However, the current adjustment semiconductor switch 5d2 is not limited to a bipolar transistor.

[0037] One end of the current adjustment resistor 5d1 is connected to one end of the smoothing capacitor 4. The other end of the current adjustment resistor 5d1 is connected to the collector terminal (input end) of the current adjustment semiconductor switch 5d2. One end of the current adjustment resistor 5d1 of the second constant current circuit 5a2 is connected to one end of the smoothing capacitor 4 via the first constant current circuit 5a1.

[0038] The current adjustment semiconductor switch 5d2 has a collector terminal, which is an input terminal for the discharge current, connected to one end of the smoothing capacitor 4. The current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 has a collector terminal, which is connected to one end of the smoothing capacitor 4 via the current adjustment resistor 5d1 of the second constant current circuit 5a2 and the first constant current circuit 5a1. The current adjustment semiconductor switch 5d2 has an emitter terminal, which is an output terminal for the discharge current, connected to the other end of the smoothing capacitor 4. The current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 has an emitter terminal, which is connected to the other end of the smoothing capacitor 4 via the second constant current circuit 5a2.

[0039] The base terminal, which is the control end of the current adjustment semiconductor switch 5d2, is connected to the discharge semiconductor switch control line 5d3. When a discharge current is supplied to the discharge semiconductor switch control line 5d3 and a voltage is applied to the base terminal, the current adjustment semiconductor switch 5d2 enters a conductive state in which a discharge current flows from the collector terminal to the emitter terminal. Note that the current adjustment semiconductor switch 5d2 enters a non-conductive state when no voltage is applied to the base terminal.

[0040] 2, the current adjustment unit 5d of the first constant current circuit 5a1 and the current adjustment unit 5d of the second constant current circuit 5a2 are connected in series. From one end of the smoothing capacitor 4 to the other end, the current adjustment resistor 5d1 of the first constant current circuit 5a1, the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1, the current adjustment resistor 5d1 of the second constant current circuit 5a2, and the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 are arranged in this order.

[0041] One end of the current adjustment resistor 5d1 of the first constant current circuit 5a1 is connected to one end of the smoothing capacitor 4. The other end of the current adjustment resistor 5d1 of the first constant current circuit 5a1 is connected to the collector terminal (input terminal) of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1. The emitter terminal (output terminal) of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 is connected to one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2. The other end of the current adjustment resistor 5d1 of the second constant current circuit 5a2 is connected to the other end of the smoothing capacitor 4.

[0042] One end of the discharge semiconductor switch control line 5d3 is connected to the midpoint between the current adjustment resistor 5d1 and the current adjustment semiconductor switch 5d2. That is, one end of the discharge semiconductor switch control line 5d3 is connected to the other end of the current adjustment resistor 5d1 and the collector terminal of the current adjustment semiconductor switch 5d2. One end of the discharge semiconductor switch control line 5d3 is connected to the gate terminal, which is the control end, of the discharge semiconductor switch 5c1.

[0043] One end of the midpoint connection line 5b is connected to the midpoint between the emitter terminal (output terminal) of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 and one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2. In other words, one end of the midpoint connection line 5b is connected to the emitter terminal (output terminal) of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 and one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2.

[0044] The other end of the midpoint connection line 5b is connected to the midpoint between the other end of the discharge resistor 5c2 of the first constant current circuit 5a1 and the drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2. In other words, the other end of the midpoint connection line 5b is connected to the other end of the discharge resistor 5c2 of the first constant current circuit 5a1 and the drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2.

[0045] In this embodiment, the first constant current circuit 5a1 and the second constant current circuit 5a2 are connected using a midpoint connection line 5b. However, the present invention is not limited to this circuit configuration. For example, the other end of the discharge resistor 5c2 of the first constant current circuit 5a1 is connected to the emitter terminal (output terminal) of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1, forming the output terminal of the first constant current circuit 5a1. Furthermore, one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2 is connected to the drain terminal (input terminal) of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2, forming the input terminal of the second constant current circuit 5a2. The first constant current circuit 5a1 and the second constant current circuit 5a2 may be connected in series by connecting the output terminal of the first constant current circuit 5a1 to the input terminal of the second constant current circuit 5a2.

[0046] In the discharge device 5 of this embodiment, a portion of the power stored in the smoothing capacitor 4 is supplied as a discharge current. When the discharge semiconductor switch 5c1 and the current adjustment semiconductor switch 5d2 are both in a non-conductive state, charge is stored in the smoothing capacitor 4 and the voltage between its terminals increases, causing the voltage applied to the gate terminal of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 to increase. When the voltage applied to the gate terminal of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 increases, the discharge semiconductor switch 5c1 becomes conductive and a discharge current flows through the discharge semiconductor switch 5c1 of the first constant current circuit 5a1.

[0047] When the discharge current flows through the discharge semiconductor switch 5c1 of the first constant current circuit 5a1, the discharge resistor 5c2 of the first constant current circuit 5a1 is also energized, causing a voltage drop across the discharge resistor 5c2 of the first constant current circuit 5a1, resulting in a voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1.

[0048] A voltage drop across the discharge resistor 5c2 of the first constant current circuit 5a1 causes a voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1, causing the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 to become conductive.

[0049] When the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 is turned on, the voltage applied to the gate terminal of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 decreases, reducing the discharge current flowing through the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 and the discharge current flowing through the discharge resistor 5c2 of the first constant current circuit 5a1. In other words, the discharge current flowing through the discharge unit 5c of the first constant current circuit 5a1 decreases.

[0050] On the other hand, when the discharge current flowing through the discharge part 5c of the first constant current circuit 5a1 decreases, the voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 decreases, so the discharge current flowing through the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 decreases, the gate voltage of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 increases, and the discharge current flowing through the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 increases.

[0051] The discharge current flowing through the first constant current circuit 5a1 is kept constant by repeating the operations of the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 and the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 in this manner. As a result, the first constant current circuit 5a1 conducts a constant discharge current regardless of the voltage of the smoothing capacitor 4.

[0052] The second constant current circuit 5a2 is connected in series with the first constant current circuit 5a1 via the midpoint connection line 5b, so that the discharge current output from the first constant current circuit 5a1 is supplied to both the discharge section 5c and the current adjustment section 5d of the second constant current circuit 5a2.

[0053] When the discharge current flows through the discharge semiconductor switch 5c1 of the second constant current circuit 5a2, the discharge resistor 5c2 of the second constant current circuit 5a2 is also energized, causing a voltage drop across the discharge resistor 5c2 of the second constant current circuit 5a2, resulting in a voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2.

[0054] A voltage drop across the discharge resistor 5c2 of the second constant current circuit 5a2 causes a voltage difference between the base and emitter terminals of the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2, causing the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 to become conductive.

[0055] When the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 is turned on, the voltage applied to the gate terminal of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 decreases, reducing the discharge current flowing through the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 and the discharge current flowing through the discharge resistor 5c2 of the second constant current circuit 5a2. In other words, the discharge current flowing through the discharge unit 5c of the second constant current circuit 5a2 decreases.

[0056] On the other hand, when the discharge current flowing through the discharge part 5c of the second constant current circuit 5a2 decreases, the voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 decreases, the discharge current flowing through the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 decreases, the gate voltage of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 increases, and the discharge current flowing through the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 increases.

[0057] The discharge current flowing through the second constant current circuit 5a2 is kept constant by repeating the operations of the discharge semiconductor switch 5c1 and the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 in this manner. As a result, the second constant current circuit 5a2 conducts a constant discharge current regardless of the voltage of the smoothing capacitor 4.

[0058] For example, suppose the discharge resistor 5c2 of the first constant current circuit 5a1 is shorted. This causes no voltage difference between the base terminal and the emitter terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1, and the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 is constantly in a non-conducting state. As a result, the first constant current circuit 5a1 is no longer able to adjust the discharge current, and an excessive discharge current may flow through the first constant current circuit 5a1. However, in the discharge device 5 of this embodiment, even if an excessive discharge current flows through the first constant current circuit 5a1, the second constant current circuit 5a2 adjusts the discharge current so that the discharge current passing through the discharge device 5 remains constant.

[0059] Furthermore, suppose that the discharge resistor 5c2 of the second constant current circuit 5a2 is shorted. Even in such a case, the first constant current circuit 5a1 can adjust the discharge current to a constant value. Therefore, the discharge current passing through the discharge device 5 is adjusted to be constant.

[0060] In this way, in the discharge device 5 of this embodiment, even if one of the first constant current circuit 5a1 and the second constant current circuit 5a2 experiences a short circuit failure for some reason, the other of the first constant current circuit 5a1 and the second constant current circuit 5a2, which is not experiencing a failure, can adjust the discharge current so that the discharge current passing through the discharge device 5 remains constant.

[0061] Next, the structure of the power conversion device 1 including the discharge device 5 of this embodiment will be described with reference to FIGS.

[0062] Fig. 3 is an exploded perspective view showing a schematic structural configuration of the power conversion device 1. As shown in Fig. 3, the power conversion device 1 includes an intelligent power module 10 (semiconductor device), a main body case 11, a capacitor unit 12, a reactor unit 13, a DC-DC converter unit 14, a connector unit 15, and a motor connection bus bar 16.

[0063] In the following description, for convenience of explanation, the direction in which the DCDC converter unit 14 and the like are located relative to a partition wall 31a of a center plate 31 (described later) of the main body case 11 is referred to as "upward," and the direction in which the intelligent power module 10 is located relative to a partition wall 31a of a center plate 31 (described later) of the main body case 11 is referred to as "downward." However, the installation posture of the power conversion device 1 is not particularly limited.

[0064] The intelligent power module 10 includes a power module 20, a gate driver board 21, an ECU board 22, etc. The power module 20 includes a plurality of semiconductor power devices having semiconductor elements, a resin power module case that houses these semiconductor power devices, etc.

[0065] The gate driver board 21 is a board on which gate drivers that generate drive signals for the step-up / step-down converter 2 and inverter 3, which are formed by semiconductor power devices, are provided. Such gate driver board 21 is stacked on the power module 20. The ECU board 22 is a board on which an ECU (Electronic Control Unit) that controls the gate driver board 21 is provided. This ECU board 22 is stacked on the gate driver board 21.

[0066] In this embodiment, the gate driver board 21 and the ECU board 22 constitute a control board 23. That is, in this embodiment, the control board 23 has two boards. The gate driver board 21 and the ECU board 22 may also be integrated. In such a case, the control board 23 consists of a single board.

[0067] In this embodiment, the above-mentioned constant current circuit 5a is formed on the gate driver substrate 21. Fig. 4 is a schematic diagram showing the upper surface of a portion of the gate driver substrate 21. As shown in this figure, the gate driver substrate 21 has a printed wiring board 21a. In this embodiment, the gate driver substrate 21 is located below the power module 20. Therefore, an upper surface 21a1 of the printed wiring board 21a is the surface facing the power module 20. In addition, a lower surface 21a2 of the printed wiring board 21a is the surface opposite to the surface facing the power module 20.

[0068] 4, the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 and the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 are mounted on the upper surface 21a1 of the printed wiring board 21a, and the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 and the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 are mounted on the lower surface 21a2 of the printed wiring board 21a.

[0069] 4, the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 is referred to as a first discharge semiconductor switch 5c11, and the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 is referred to as a second discharge semiconductor switch 5c12. Furthermore, the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 is referred to as a first current adjustment semiconductor switch 5d21, and the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 is referred to as a second current adjustment semiconductor switch 5d22.

[0070] 4, heat dissipation pads 21b are formed on the upper surface 21a1 of printed wiring board 21a so as to overlap with discharge semiconductor switch 5c1. Specifically, first heat dissipation pad 21b1 is formed so as to overlap with first discharge semiconductor switch 5c11 mounted on the lower surface 21a2, and second heat dissipation pad 21b2 is formed so as to overlap with second discharge semiconductor switch 5c12 mounted on the lower surface 21a2.

[0071] Heat dissipation pad 21b is thermally connected to discharge semiconductor switch 5c1 through thermal vias (not shown) and receives heat from discharge semiconductor switch 5c1. For example, first heat dissipation pad 21b1 receives heat from first discharge semiconductor switch 5c11. Second heat dissipation pad 21b2 receives heat from second discharge semiconductor switch 5c12.

[0072] The heat dissipation pad 21b is formed on the upper surface 21a1, which faces the power module 20, which is cooled by a cooling jacket described below. The upper surface 21a1 is disposed opposite the power module 20 with a certain clearance between them. Heat transferred from the discharge semiconductor switch 5c1 to the heat dissipation pad 21b is dissipated into the space between the upper surface 21a1 and the power module 20, and is prevented from being transferred to the power module 20. In other words, it is possible to prevent heat from being transferred between the printed wiring board 21a and the power module 20.

[0073] 4, first current adjustment semiconductor switch 5d21 is arranged closer to first discharge semiconductor switch 5c11 than to second discharge semiconductor switch 5c12. That is, first current adjustment semiconductor switch 5d21 is arranged closer to first heat dissipation pad 21b1 than to second heat dissipation pad 21b2. Also, second current adjustment semiconductor switch 5d22 is arranged closer to second discharge semiconductor switch 5c12 than to first discharge semiconductor switch 5c11. That is, second current adjustment semiconductor switch 5d22 is arranged closer to second heat dissipation pad 21b2 than to first heat dissipation pad 21b1.

[0074] The distance from the first current adjustment semiconductor switch 5d21 to the first heat dissipation pad 21b1 is the same as the distance from the second current adjustment semiconductor switch 5d22 to the second heat dissipation pad 21b2. Furthermore, the positional relationship between the first discharge semiconductor switch 5c11 and the first heat dissipation pad 21b1 is the same as the positional relationship between the second discharge semiconductor switch 5c12 and the second heat dissipation pad 21b2. Therefore, the distance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 is the same as the distance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12. The distance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 and the distance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12 do not necessarily have to be the same. Depending on factors such as layout to ensure insulation of elements, the distance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 and the distance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12 may differ.

[0075] Since the distance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 is the same as the distance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12, in this embodiment, the thermal resistance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 is the same as the thermal resistance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12.

[0076] Bipolar transistors have a characteristic that the current they conduct varies with heat. For example, when a bipolar transistor becomes hot, the current it conducts decreases, and when a bipolar transistor becomes cold, the current it conducts increases. Therefore, in this embodiment, the current adjustment semiconductor switch 5d2 has a characteristic that the current it conducts varies with heat. When the discharge semiconductor switch 5c1 is energized, the discharge semiconductor switch 5c1 generates heat, heating the current adjustment semiconductor switch 5d2. By making the distance from the first current adjustment semiconductor switch 5d21 to the first discharge semiconductor switch 5c11 the same as the distance from the second current adjustment semiconductor switch 5d22 to the second discharge semiconductor switch 5c12, the thermal influence on the first current adjustment semiconductor switch 5d21 from the first discharge semiconductor switch 5c11 and the thermal influence on the second current adjustment semiconductor switch 5d22 from the second discharge semiconductor switch 5c12 can be made similar. Therefore, the thermal characteristics of the first constant current circuit 5a1 and the second constant current circuit 5a2 can be made similar.

[0077] 3 , the main body case 11 is a case that houses the intelligent power module 10, the capacitor unit 12, the reactor unit 13, the DCDC converter unit 14, the connector unit 15, the motor connection bus bar 16, etc. This main body case 11 includes an upper cover 30, a center plate 31, and a lower cover 32. The upper cover 30, the center plate 31, and the lower cover 32 are formed so as to be separable in the vertical direction.

[0078] The upper cover 30 is a portion that covers from above the DCDC converter unit 14 and the reactor unit 13, which are fixed from above to the center plate 31. In other words, the upper cover 30 is fastened to the center plate 31 via bolts or the like (not shown).

[0079] The central plate 31 is a support plate located between the upper cover 30 and the lower cover 32. The central plate 31 includes a flat partition wall portion 31a and a surrounding wall portion 31b that is provided so as to surround the partition wall portion 31a from the side.

[0080] The partition wall 31a is disposed with one surface facing upward and the other surface facing downward, and supports, for example, the intelligent power module 10, the capacitor unit 12, the reactor unit 13, and the DCDC converter unit 14.

[0081] In this embodiment, the reactor unit 13 and the DCDC converter unit 14 are disposed above the partition wall 31a. Also, in this embodiment, the intelligent power module 10 is disposed below the partition wall 31a. Also, in this embodiment, a portion of the capacitor unit 12 is provided so as to penetrate the partition wall 31a in the vertical direction. Therefore, the partition wall 31a is provided with an insertion opening 31c through which the capacitor unit 12 is inserted.

[0082] The intelligent power module 10, the capacitor unit 12, the reactor unit 13, the DCDC converter unit 14, and the connector unit 15 are fastened to bosses or the like provided on the partition wall portion 31a by bolts or the like (not shown).

[0083] A flow path for guiding a coolant is provided inside the partition wall 31 a. By flowing the coolant through this flow path, the partition wall 31 a functions as a cooling jacket, and the intelligent power module 10, the capacitor unit 12, the reactor unit 13, the DCDC converter unit 14, and the connector unit 15 are cooled.

[0084] The surrounding wall portion 31b is provided so as to surround the intelligent power module 10, the capacitor unit 12, the reactor unit 13, and the DCDC converter unit 14 from the sides. The surrounding wall portion 31b is connected to the edge of the partition wall portion 31a and is provided so as to protrude upward and downward from the partition wall portion 31a. The upper end of the surrounding wall portion 31b is abutted by the upper cover 30. The lower end of the surrounding wall portion 31b is abutted by the lower cover 32.

[0085] The lower cover 32 is a part that covers from below the intelligent power module 10 that is fixed from below to the central plate 31. The lower cover 32 also covers from below the capacitor unit 12 and the motor connection bus bar 16. The lower cover 32 is fastened to the central plate 31 via bolts or the like (not shown). The lower cover 32 is provided with a connector opening 32a that exposes the connector unit 15.

[0086] The capacitor unit 12 is connected to the intelligent power module 10 and is disposed to the side of the power module 20. The capacitor unit 12 is a unit that includes the capacitors provided in the step-up / step-down converter 2 and the smoothing capacitor 4. The capacitor unit 12 includes elements that form the smoothing capacitor 4 and the like, and a housing that covers these elements.

[0087] The reactor unit 13 is fixed to the center plate 31. The reactor unit 13 is connected to the intelligent power module 10 via a bus bar (not shown), and in this embodiment, is disposed above the center plate 31. The reactor unit 13 is a unit including a reactor provided in the step-up / step-down converter 2.

[0088] The DCDC converter unit 14 is fixed to the center plate 31. The DCDC converter unit 14 is connected to the intelligent power module 10 via a bus bar (not shown), and in this embodiment, is disposed above the center plate 31. The DCDC converter unit 14 is a unit that forms the DCDC converter 6 shown in FIG.

[0089] The connector unit 15 is a unit that connects the power module 20 and the motor unit. In this embodiment, the connector unit 15 is disposed below the partition wall portion 31a of the center plate 31. The connector unit 15 is also disposed further below the intelligent power module 10.

[0090] The discharge device 5 of this embodiment as described above is connected in parallel to the smoothing capacitor 4 and discharges the charge accumulated in the smoothing capacitor 4 as a discharge current. A plurality of discharge devices 5 of this embodiment are provided, each conducting a constant discharge current. In the discharge device 5 of this embodiment, the plurality of constant current circuits 5a are connected in series.

[0091] In the discharge device 5 of this embodiment, since the multiple constant current circuits 5 a are connected in series, even if one of the constant current circuits 5 a fails, the remaining non-failed constant current circuits 5 a can prevent the discharge current from becoming excessive. If the discharge current becomes excessive, the amount of heat generated increases, resulting in large energy loss. However, the discharge device 5 of this embodiment can prevent the discharge current from becoming excessive, so that even if a failure occurs, excessive energy loss can be prevented.

[0092] Furthermore, the discharge device 5 using such a constant current circuit 5a can generate a discharge current similar to that when the voltage of the smoothing capacitor 4 is high, even when the voltage of the smoothing capacitor 4 is low. Therefore, even when the voltage of the smoothing capacitor 4 is low, it is possible to reduce the voltage of the smoothing capacitor 4 in a short time.

[0093] In the discharge device 5 of this embodiment, each constant current circuit 5a includes a discharge unit 5c and a current adjustment unit 5d. The discharge unit 5c conducts a discharge current. The current adjustment unit 5d adjusts the discharge unit 5c based on the magnitude of the discharge current conducted to the discharge unit 5c so that the discharge current flowing through the constant current circuit 5a is constant.

[0094] In the discharge device 5 of this embodiment, the constant current circuit 5 a is a feedback constant current circuit. With this discharge device 5, the discharge current can be adjusted to a constant value even if the voltage between the terminals of the smoothing capacitor 4 changes.

[0095] In the discharge device 5 of this embodiment, the discharge unit 5c includes a discharge semiconductor switch 5c1 and a discharge resistor 5c2. The discharge semiconductor switch 5c1 has an input terminal connected to one end of the smoothing capacitor 4. The discharge resistor 5c2 has one end connected to the output terminal of the discharge semiconductor switch 5c1. The current adjustment unit 5d includes a current adjustment semiconductor switch 5d2, a current adjustment resistor 5d1, and a discharge semiconductor switch control line 5d3. The current adjustment semiconductor switch 5d2 is turned on when the discharge semiconductor switch 5c1 is turned on. The current adjustment resistor 5d1 has one end connected to one end of the smoothing capacitor 4 and the other end connected to the input terminal of the current adjustment semiconductor switch 5d2. The discharge semiconductor switch control line 5d3 connects the other end of the current adjustment resistor 5d1 to the control terminal of the discharge semiconductor switch 5c1.

[0096] According to the discharge device 5 of this embodiment, the constant current circuit 5a has a circuit configuration using semiconductor switches such as the discharge semiconductor switch 5c1 and the current adjustment semiconductor switch 5d2, etc. Therefore, according to the discharge device 5 of this embodiment, the constant current circuit 5a can have a simple circuit configuration.

[0097] Furthermore, in the discharge device 5 of this embodiment, the discharge semiconductor switch 5c1 is a metal oxide semiconductor field effect transistor. Metal oxide semiconductor field effect transistors have a higher withstand voltage than bipolar transistors. Using such a metal oxide semiconductor field effect transistor as the discharge semiconductor switch installed in the discharge section 5c through which the discharge current mainly flows can improve the withstand voltage performance of the constant current circuit 5a. As a result, the number of constant current circuits 5a connected in series can be reduced compared to when the discharge semiconductor switch 5c1 of the constant current circuit 5a is formed of a bipolar transistor. This also reduces the number of components included in the discharge device 5.

[0098] The discharge device 5 of this embodiment also includes a constant current circuit 5a, which is a first constant current circuit 5a1 and a second constant current circuit 5a2 connected in series. The output terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 is connected to one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2. The other end of the discharge resistor 5c2 of the first constant current circuit 5a1 is connected to the input terminal of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2. The discharge device 5 of this embodiment also includes a midpoint connection line 5b. The midpoint connection line 5b connects the midpoint between the output terminal of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 and one end of the current adjustment resistor 5d1 of the second constant current circuit 5a2, and the midpoint between the other end of the discharge resistor 5c2 of the first constant current circuit 5a1 and the input terminal of the discharge semiconductor switch 5c1 of the second constant current circuit 5a2.

[0099] In the discharge device 5 of this embodiment, by using the midpoint connection line 5b, the discharge section 5c of the first constant current circuit 5a1 and the discharge section 5c of the second constant current circuit 5a2 are arranged in series, and the current adjustment section 5d of the first constant current circuit 5a1 and the current adjustment section 5d of the second constant current circuit 5a2 are arranged in series, and the first constant current circuit 5a1 and the second constant current circuit 5a2 can be connected in series.

[0100] In the discharge device 5 of this embodiment, the constant current circuit 5a is formed on the printed wiring board 21a. On the printed wiring board 21a, the distance between the discharge semiconductor switch 5c1 and the current adjustment semiconductor switch 5d2 included in the same constant current circuit 5a is the same as the distance between the discharge semiconductor switch 5c1 and the current adjustment semiconductor switch 5d2 included in another constant current circuit 5a.

[0101] According to the discharge device 5 of this embodiment, the thermal influence that the first current adjustment semiconductor switch 5d21 receives from the first discharge semiconductor switch 5c11 can be made similar to the thermal influence that the second current adjustment semiconductor switch 5d22 receives from the second discharge semiconductor switch 5c12. Therefore, the thermal characteristics of the first constant current circuit 5a1 and the second constant current circuit 5a2 can be made similar to each other.

[0102] The intelligent power module 10 of this embodiment also includes a power module 20 and a control board 23. The power module 20 is connected to a capacitor unit 12 including a smoothing capacitor 4 and has a plurality of semiconductor power devices. The control board 23 controls the power module 20 and has a discharge device 5 formed thereon. The control board 23 also has a printed wiring board 21a disposed opposite to the power module 20. A discharge semiconductor switch 5c1 is mounted on the surface of the printed wiring board 21a opposite to the surface facing the power module 20. A heat dissipation pad 21b that receives heat from the discharge semiconductor switch 5c1 is formed on the surface of the printed wiring board 21a facing the power module 20. A space is provided between the opposing surface of the printed wiring board 21a and the power module 20.

[0103] According to the discharge device 5 of this embodiment, it is possible to prevent heat from being transferred between the printed wiring board 21 a and the power module 20 .

[0104] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 5. In the description of this embodiment, the description of the same parts as those in the first embodiment will be omitted or simplified.

[0105] 5 is a circuit diagram of a discharge device 5A according to this embodiment. As shown in this figure, in the discharge device 5A according to this embodiment, each of the current adjustment units 5d of the constant current circuit 5a includes a Zener diode 5d4. The cathode terminal of each Zener diode 5d4 is connected to the emitter terminal (output terminal) of the current adjustment semiconductor switch 5d2. The anode terminal of the Zener diode 5d4 is connected to the other end of the smoothing capacitor 4. The anode terminal of the Zener diode 5d4 of the first constant current circuit 5a1 is connected to the collector terminal of the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2. In other words, the anode terminal of the Zener diode 5d4 of the first constant current circuit 5a1 is connected to the other end of the smoothing capacitor 4 via the current adjustment unit 5d of the second constant current circuit 5a2.

[0106] Such Zener diode 5d4 has the opposite temperature characteristics to that of current adjustment semiconductor switch 5d2. That is, Zener diode 5d4 has the characteristic that the current it conducts increases as the temperature increases and decreases as the temperature decreases. Therefore, by providing such Zener diode 5d4, it is possible to offset the temperature characteristics of current adjustment semiconductor switch 5d2 and suppress performance changes due to temperature of constant current circuit 5a.

[0107] Third Embodiment Next, a third embodiment of the present invention will be described with reference to Fig. 6. In the description of this embodiment, the description of the same parts as those in the first embodiment will be omitted or simplified.

[0108] 6 is a schematic diagram showing the top surface of a portion of the gate driver substrate 21 according to this embodiment. As shown in this figure, in this embodiment, the second current adjustment semiconductor switch 5d22 is mounted in the same position as the first current adjustment semiconductor switch 5d21 in the first embodiment. In other words, the second current adjustment semiconductor switch 5d22 is disposed closer to the first discharge semiconductor switch 5c11 than the second discharge semiconductor switch 5c12. Therefore, the second current adjustment semiconductor switch 5d22 is disposed closer to the first heat dissipation pad 21b1 than the second heat dissipation pad 21b2.

[0109] In this embodiment, the first current adjustment semiconductor switch 5d21 is mounted in the same position as the second current adjustment semiconductor switch 5d22 in the first embodiment. That is, the first current adjustment semiconductor switch 5d21 is disposed closer to the second discharge semiconductor switch 5c12 than to the first discharge semiconductor switch 5c11. Therefore, the first current adjustment semiconductor switch 5d21 is disposed closer to the second heat dissipation pad 21b2 than to the first heat dissipation pad 21b1.

[0110] As described above, in this embodiment, the current adjustment semiconductor switch 5d2 is arranged closer to the discharge semiconductor switch 5c1 included in another constant current circuit 5a than to the discharge semiconductor switch 5c1 included in the same constant current circuit 5a. In this embodiment, for example, when the discharge semiconductor switch 5c1 of the first constant current circuit 5a1 generates heat, the temperature of the current adjustment semiconductor switch 5d2 of the second constant current circuit 5a2 increases, reducing the current flow, thereby preventing a temperature rise in the second constant current circuit 5a2. On the other hand, when the discharge semiconductor switch 5c1 of the second constant current circuit 5a2 generates heat, the temperature of the current adjustment semiconductor switch 5d2 of the first constant current circuit 5a1 increases, reducing the current flow, thereby preventing a temperature rise in the first constant current circuit 5a1.

[0111] Therefore, according to this embodiment, the temperature rise of the two constant current circuits 5a (the first constant current circuit 5a1 and the second constant current circuit 5a2) is suppressed. Furthermore, according to this embodiment, the temperatures of the two constant current circuits 5a (the first constant current circuit 5a1 and the second constant current circuit 5a2) can be made uniform.

[0112] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to the above-described embodiments. The shapes and combinations of the components shown in the above-described embodiments are merely examples, and various modifications can be made based on design requirements, etc., without departing from the spirit of the present invention.

[0113] For example, in the above embodiment, the discharge device 5 is described as having two constant current circuits 5 a. However, the present invention is not limited to this. For example, it is also possible to adopt a configuration including three or more constant current circuits 5 a.

[0114] In the above embodiment, the constant current circuit 5 a has been described as having a feedback circuit configuration. However, the present invention is not limited to this, and constant current circuits having other circuit configurations may be provided.

[0115] The above embodiment can also be described as follows, for example:

[0116] (Appendix 1) A discharge device that is connected in parallel to a capacitance element and discharges electric charges accumulated in the capacitance element as a discharge current, the discharge device comprising a plurality of constant current circuits that conduct the constant discharge current, and the plurality of constant current circuits are connected in series.

[0117] (Appendix 2) The discharge device according to appendix 1, characterized in that each of the constant current circuits comprises: a discharge unit that conducts the discharge current; and a current adjustment unit that adjusts the discharge unit based on the magnitude of the discharge current conducted to the discharge unit so that the discharge current flowing through the constant current circuit is constant.

[0118] (Supplementary Note 3) The discharge device according to Supplementary Note 2, characterized in that the discharge unit comprises: a discharge semiconductor switch having an input terminal connected to one end of the capacitance element; and a discharge resistor having one end connected to the output terminal of the discharge semiconductor switch; and the current adjustment unit comprises: a current adjustment semiconductor switch that is turned on when the discharge semiconductor switch is turned on; a current adjustment resistor having one end connected to one end of the capacitance element and the other end connected to the input terminal of the current adjustment semiconductor switch; and a discharge semiconductor switch control line that connects the other end of the current adjustment resistor to the control terminal of the discharge semiconductor switch.

[0119] (Supplementary Note 4) The discharge device according to Supplementary Note 3, wherein the discharge semiconductor switch is a metal oxide semiconductor field effect transistor.

[0120] (Supplementary Note 5) The discharge device according to Supplementary Note 3 or 4, characterized in that the constant current circuits comprise a first constant current circuit and a second constant current circuit connected in series, the output terminal of the current adjustment semiconductor switch of the first constant current circuit is connected to one end of the current adjustment resistor of the second constant current circuit, the other end of the discharge resistor of the first constant current circuit is connected to an input terminal of the discharge semiconductor switch of the second constant current circuit, and a midpoint connection line is provided connecting a midpoint between the output terminal of the current adjustment semiconductor switch of the first constant current circuit and one end of the current adjustment resistor of the second constant current circuit, and a midpoint between the other end of the discharge resistor of the first constant current circuit and the input terminal of the discharge semiconductor switch of the second constant current circuit.

[0121] (Supplementary Note 6) The discharge device according to any one of Supplementary Notes 3 to 5, wherein the current adjustment unit includes a constant voltage diode having a cathode terminal connected to the output terminal of the current adjustment semiconductor switch.

[0122] (Appendix 7) The discharge device according to any one of Appendices 3 to 6, wherein the constant current circuit is formed on a printed wiring board, and on the printed wiring board, the distance between the discharge semiconductor switch and the current adjustment semiconductor switch included in the same constant current circuit is the same as the distance between the discharge semiconductor switch and the current adjustment semiconductor switch included in another constant current circuit.

[0123] (Appendix 8) The discharge device according to any one of Appendices 3 to 6, characterized in that the constant current circuit is formed on a printed wiring board, and the current adjustment semiconductor switch is arranged closer to the discharge semiconductor switch included in another constant current circuit than to the discharge semiconductor switch included in the same constant current circuit.

[0124] (Supplementary Note 9) A semiconductor device comprising: a power module connected to a capacitor unit including the capacitance element, and having a plurality of semiconductor power devices; and a control board that controls the power module and on which the discharge device according to Supplementary Note 7 or 8 is formed; wherein the control board has the printed wiring board disposed opposite to the power module, the discharge semiconductor switch is mounted on a surface of the printed wiring board opposite to a surface facing the power module, a heat dissipation pad that receives heat from the discharge semiconductor switch is formed on the surface of the printed wiring board facing the power module, and a space is provided between the facing surface of the printed wiring board and the power module.

[0125] REFERENCE SIGNS LIST 1 Power conversion device 2 Step-up / down converter 3 Inverter 4 Smoothing capacitor (capacitive element) 5 Discharge device 5a Constant current circuit 5A Discharge device 5a1 First constant current circuit 5a2 Second constant current circuit 5b Midpoint connection line 5c Discharge section 5c1 Discharge semiconductor switch 5c11 First discharge semiconductor switch 5c12 Second discharge semiconductor switch 5c2 Discharge resistor 5c3 Current adjustment semiconductor switch connection line 5d Current adjustment section 5d1 Current adjustment resistor 5d2 Current adjustment semiconductor switch 5d21 First current adjustment semiconductor switch 5d22 Second current adjustment semiconductor switch 5d3 Discharge semiconductor switch control line 5d4 Zener diode (voltage regulation diode) 6 DCDC converter 10 Intelligent power module (semiconductor device) 11 Main body case 12 Capacitor unit 13 Reactor unit 14 DCDC converter unit 15 Connector unit 16 Motor connection bus bar 20 Power module 21 Gate driver board 21a Printed wiring board 21a1 Upper surface 21a2 Lower surface 21b Heat dissipation pad 21b1 First heat dissipation pad 21b2 Second heat dissipation pad 22 ECU board 23 Control board 30 Upper cover 31 Center plate 31a Partition wall portion 31b Surrounding wall portion 31c Insertion opening 32 Lower cover 100 Vehicle

Claims

1. A discharge device connected in parallel with a capacitive element and discharging the charge stored in the capacitive element as a discharge current, comprising a plurality of constant current circuits that conduct a constant discharge current, and the plurality of constant current circuits being connected in series. A discharge device characterized by that.

2. Each of the constant current circuits includes a discharge unit that conducts the discharge current, and a current adjustment unit that adjusts the discharge unit so that the discharge current flowing through the constant current circuit becomes constant based on the magnitude of the discharge current conducted to the discharge unit. The discharge device according to claim 1, characterized by that.

3. The discharge unit includes a discharge semiconductor switch having an input end connected to one end of the capacitive element, and a discharge resistor having one end connected to the output end of the discharge semiconductor switch. The current adjustment unit includes a current adjustment semiconductor switch that becomes conductive when the discharge semiconductor switch becomes conductive, a current adjustment resistor having one end connected to one end of the capacitive element and the other end connected to the input end of the current adjustment semiconductor switch, and a discharge semiconductor switch control line connecting the other end of the current adjustment resistor and the control end of the discharge semiconductor switch. The discharge device according to claim 2, characterized by that.

4. The discharge semiconductor switch is a metal oxide semiconductor field effect transistor. The discharge device according to claim 3, characterized by that.

5. As the constant current circuit, a first constant current circuit and a second constant current circuit connected in series with each other are provided. The output end of the current adjustment semiconductor switch of the first constant current circuit and one end of the current adjustment resistor of the second constant current circuit are connected. The other end of the discharge resistor of the first constant current circuit and the input end of the discharge semiconductor switch of the second constant current circuit are connected. A midpoint connection line connecting the midpoint between the output end of the current adjustment semiconductor switch of the first constant current circuit and one end of the current adjustment resistor of the second constant current circuit, and the midpoint between the other end of the discharge resistor of the first constant current circuit and the input end of the discharge semiconductor switch of the second constant current circuit is provided. The discharge device according to claim 3 or 4, characterized by that.

6. The current adjustment unit includes a constant voltage diode having a cathode terminal connected to the output end of the current adjustment semiconductor switch. The discharge device according to claim 3 or 4, characterized by that.

7. The constant current circuit is formed on the printed wiring board, and on the printed wiring board, the distance between the discharge semiconductor switch and the current adjustment semiconductor switch included in the same constant current circuit is the same as the distance between the discharge semiconductor switch and the current adjustment semiconductor switch included in another constant current circuit. The discharge device according to claim 3 or 4, characterized in that.

8. The constant current circuit is formed on the printed wiring board, and the current adjustment semiconductor switch is arranged closer to the discharge semiconductor switch included in another constant current circuit than the discharge semiconductor switch included in the same constant current circuit. The discharge device according to claim 3 or 4, characterized in that.

9. A power module having a plurality of semiconductor power devices, connected to a capacitor unit including the capacitive element, and a control board on which the discharge device according to claim 7 is formed while controlling the power module. The control board has a printed wiring board arranged to face the power module, and the discharge semiconductor switch is mounted on a surface of the printed wiring board opposite to the surface facing the power module. A heat dissipation pad that receives heat from the discharge semiconductor switch is formed on the surface of the printed wiring board facing the power module, and a space is provided between the facing surface of the printed wiring board and the power module. A semiconductor device, characterized in that.

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