Short-circuit protection circuit, semiconductor device, and short-circuit protection method

Abstract

To protect a semiconductor switching element from short-circuit currents at an appropriate timing, without increasing the number of semiconductor switching elements.SOLUTION: A short-circuit protection circuit comprises: a divider circuit that divides the power supply voltage supplied from a power supply connected at an end; a semiconductor rectifier element one end of which is connected between resistive elements of the divider circuit and the other end of which is connected to a path of a conductor connected to a current flow-in side terminal of the semiconductor switching element to be protected, so that the direction from the one end to the other end forms the direction of rectification; an RC parallel circuit that connects to the other end of the divider circuit; and a drive unit that turns the semiconductor switching element off when, while the semiconductor switching element is on, a short-circuit current flowing to the conductor is detected, on the basis of the capacitor element voltage of the RC parallel circuit. The stray capacitance of the semiconductor rectifier element satisfies a condition that the voltage at one end of the capacitor element that connects to the divider circuit is higher than the voltage at the other end of the capacitor element of the RC parallel circuit when the short-circuit current is caused to flow to the conductor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a short-circuit protection circuit, a semiconductor device, and a short-circuit protection method. [Background technology]

[0002] Patent Document 1 discloses a protection circuit that uses a detection resistor (overcurrent detection resistor 7 in FIG. 1 of Patent Document 1) to detect an overcurrent in an IGBT (Insulated Gate Bipolar Transistor), which is a power semiconductor, to protect the power semiconductor from an overcurrent. However, even if the protection circuit is used to protect against a short-circuit current with a large current value, there is a problem in that the detection resistor cannot withstand a short-circuit current with a large current value. Therefore, the protection circuit disclosed in Patent Document 1 cannot be used to protect, for example, a high-output power converter or the like from a short circuit.

[0003] In contrast to this, a short-circuit protection circuit that can provide short-circuit protection even when a large short-circuit current occurs is, for example, a DESAT (Desaturation fault detection) short-circuit protection circuit shown in Figure 5-11(b) on page 42 of Non-Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-297695 [Non-patent literature]

[0005] [Non-Patent Document 1] “SiC Power Device Module Application Note Rev.003”, [Online], August 2020, ROHM Co., Ltd., [Retrieved June 24, 2022], Internet<https: / / fscdn.rohm.com / jp / products / databook / applinote / discrete / sic / common / sic_appli-j.pdf> Summary of the Invention [Problem to be solved by the invention]

[0006] Fig. 9 is a circuit diagram showing a general DESAT type short-circuit protection circuit. In Fig. 9, an N-channel enhancement type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is shown as an example of a semiconductor switch element 101 to be protected. For example, if a circuit element such as another semiconductor switch element (not shown) connected to the conductor 108 is in a fault state, and the semiconductor switch element 101 is turned on, a large short-circuit current I D will flow through the conductor 108.

[0007] Figure 10 shows the short-circuit current I D The short-circuit current I in the transient state when D and a graph 201 showing the change in the drain-source voltage V of the semiconductor switch element 101. ds (Hereinafter, the voltage between DS V ds Graph 202 shows the change in the DESAT voltage V, which is the voltage at DESAT terminal 111 of drive unit 107 (a gate drive circuit incorporating a DESAT type short circuit protection circuit). DESAT10 shows graph 201 and graph 202 showing changes in current. In FIG. 10, the horizontal axis is the time axis showing elapsed time, and the unit is [μsec]. The vertical axis on the left side, when graph 201 is the subject, is the axis showing the magnitude of current, and in this case, the unit is "A". Furthermore, when graph 202 is the subject, the vertical axis on the left side is the axis showing the magnitude of voltage, and in this case, the unit is "V". The vertical axis on the right side is the axis showing the magnitude of voltage for graph 203, and the unit is "V".

[0008] The semiconductor switch element 101 is turned on, and the short-circuit current I D begins to flow in the conductor 108, as shown in graph 201, D begins to increase. The short circuit current I D begins to increase, the parasitic inductance component L present in the conductor 108 causes L·dI D Therefore, as shown in the graph 202, a voltage drop of / dt occurs between the D-S voltage V ds This voltage V between the D and C terminals decreases. ds As a result of the decrease in the DESAT voltage V DESAT After that, when the current supplied from the power supply 109 via the resistors 102 and 103 accumulates and charges the blanking capacitor 105 (capacitor element) that is an external component of the DESAT circuit, the DESAT voltage V DESAT When the voltage detected at the DESAT terminal 111 reaches the threshold level indicated by the dashed line 213, the driving unit 107 turns the semiconductor switch element 101 to the OFF state. As a result, as shown in the graph 201, the short-circuit current I D decreases to 0 [A], and the semiconductor switch element 101 is turned on by the short-circuit current I D can be protected from

[0009] Voltage between DS V ds Due to the decrease in the DESAT voltage V DESATThe phenomenon of the decrease in the DESAT voltage V is observed, for example, when a high-speed switching power semiconductor made of SiC (Silicon Carbide) is used as the semiconductor switch element 101 and the capacitance of the blanking capacitor 105 is reduced to accommodate high-speed switching. DESAT The change in the short-circuit current I D Even if a current flows, the DESAT voltage V DESAT The change is such that the DESAT voltage V DESAT If the DESAT voltage V DESAT The time it takes for the DESAT voltage V to reach the threshold is also shortened. DESAT The time difference until the voltage Vcc reaches the threshold is about several tens of nanoseconds, as shown by reference numeral 214.

[0010] However, due to this time difference of about several tens of nanoseconds, the driving unit 107 is unable to start short circuit protection at the timing when it should be able to start short circuit protection, and the short circuit current I D In order to solve this problem, for example, a countermeasure of connecting the semiconductor switch elements 101 in parallel may be adopted. However, when this countermeasure is adopted, the number of semiconductor switch elements 101 increases, which leads to higher costs, and further, there are problems such as a decrease in power density due to an increase in the area of ​​the substrate and a decrease in output power.

[0011] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a short-circuit protection circuit, a semiconductor device, and a short-circuit protection method that can protect a semiconductor switch element from a short-circuit current at an appropriate timing without increasing the number of semiconductor switch elements. [Means for solving the problem]

[0012] In order to solve the above problem, the short-circuit protection circuit according to the present disclosure comprises: a voltage divider circuit that divides a power supply voltage supplied from a power supply connected at one end thereof; a semiconductor rectifier element that has one end connected between resistive elements of the voltage divider circuit and the other end connected on a path of a conductor that connects to a current-inflow terminal of a semiconductor switch element to be protected, the semiconductor rectifier element being connected so that the direction from the one end to the other end is a rectification direction; an RC parallel circuit connected to the other end of the voltage divider circuit; and a drive unit that, when the semiconductor switch element is in an ON state, detects that a short-circuit current is flowing in the conductor based on the voltage of a capacitor element provided in the RC parallel circuit, and switches the semiconductor switch element to an OFF state, wherein the stray capacitance of the semiconductor rectifier element is a stray capacitance that satisfies the condition that, when the short-circuit current flows in the conductor, the voltage of one end of the capacitor element of the RC parallel circuit that is connected to the voltage divider circuit becomes higher than the voltage of the other end of the capacitor element.

[0013] A semiconductor device according to the present disclosure comprises a semiconductor switch element, a voltage divider circuit that divides a power supply voltage supplied from a power supply connected at one end thereof, a semiconductor rectifier element having one end connected between resistive elements of the voltage divider circuit and the other end connected on a path of a conductor that connects to a terminal on the current inflow side of the semiconductor switch element, the semiconductor rectifier element being connected so that the direction from the one end to the other end is the rectification direction, an RC parallel circuit connected to the other end of the voltage divider circuit, and a drive unit that, when the semiconductor switch element is in an ON state, detects that a short-circuit current is flowing in the conductor based on the voltage of a capacitor element provided in the RC parallel circuit, and switches the semiconductor switch element to an OFF state, wherein the stray capacitance of the semiconductor rectifier element is a stray capacitance that satisfies the condition that, when the short-circuit current flows in the conductor, the voltage of one end of the capacitor element of the RC parallel circuit that is connected to the voltage divider circuit becomes higher than the voltage of the other end of the capacitor element.

[0014] In a short-circuit protection method according to the present disclosure, a voltage divider circuit divides a power supply voltage supplied from a power supply connected at one end thereof, and an RC parallel circuit connected to the other end of the voltage divider circuit includes a capacitor element that is charged based on a supplied current, and the semiconductor rectifying element has a rectifying direction from one end to the other end, and the one end is connected between resistive elements of the voltage divider circuit and the other end is connected to a conductor path that connects to a current-input terminal of a semiconductor switch element to be protected, and the semiconductor rectifying element has a stray capacitance that satisfies the condition that, when a short-circuit current flows through the conductor, the voltage of one end of the capacitor element of the RC parallel circuit that connects to the voltage divider circuit becomes higher than the voltage of the other end of the capacitor element, and the semiconductor rectifying element conducts a current in the rectifying direction when the voltage of the one end is higher than the voltage of the other end, and a drive unit detects that the short-circuit current is flowing through the conductor based on the voltage of the capacitor element of the RC parallel circuit when the semiconductor switch element is in an ON state, and switches the semiconductor switch element to an OFF state. [Effects of the Invention]

[0015] According to the short-circuit protection circuit, semiconductor device, and short-circuit protection method of the present disclosure, it is possible to protect semiconductor switch elements from short-circuit current at appropriate timing without increasing the number of semiconductor switch elements. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a circuit diagram illustrating a configuration example of a semiconductor device according to an embodiment of the present disclosure. [Figure 2] 1 is a diagram (part 1) illustrating an example of operation of a semiconductor device in a normal state according to an embodiment of the present disclosure. [Figure 3] FIG. 10 is a diagram (part 2) illustrating an example of operation of the semiconductor device in a normal state according to the embodiment of the present disclosure. [Figure 4] 10A and 10B are diagrams illustrating an example of operation of a semiconductor device according to an embodiment of the present disclosure when a short-circuit current flows. [Figure 5] 10A and 10B are diagrams illustrating an example of operation of a semiconductor device according to an embodiment of the present disclosure during a transient period when a short-circuit current flows. [Figure 6] FIG. 10 is a diagram showing changes in DESAT voltage for different stray capacitances calculated by computer simulation according to an embodiment of the present disclosure. [Figure 7] 10A and 10B are diagrams illustrating paths of currents generated due to capacitor elements during a transient period of a semiconductor device when a short-circuit current flows according to an embodiment of the present disclosure. [Figure 8] FIG. 1 is a diagram illustrating stray capacitance in a typical semiconductor diode. [Figure 9] FIG. 1 is a diagram for explaining short-circuit protection using the DESAT method. [Figure 10] FIG. 10 is a diagram showing changes in short-circuit current, DESAT voltage, and DS voltage when short-circuit protection is performed using the DESAT method. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Configuration example of semiconductor device) Hereinafter, a short-circuit protection circuit, a semiconductor device, and a short-circuit protection method according to embodiments of the present disclosure will be described with reference to FIGS. 1 to 8. FIG. 1 is a circuit diagram illustrating an example configuration of a semiconductor device according to an embodiment of the present disclosure. FIGS. 2 and 3 are diagrams illustrating an example operation of a semiconductor device in a normal state according to an embodiment of the present disclosure. FIG. 4 is a diagram illustrating an example operation of a semiconductor device according to an embodiment of the present disclosure when a short-circuit current flows. FIG. 5 is a diagram illustrating an example operation of a semiconductor device according to an embodiment of the present disclosure during a transient period when a short-circuit current flows. FIG. 6 is a diagram illustrating changes in DESAT voltage for different stray capacitances calculated by computer simulation according to an embodiment of the present disclosure. FIG. 7 is a diagram illustrating a current path caused by a capacitor element during a transient period when a short-circuit current flows in a semiconductor device according to an embodiment of the present disclosure. FIG. 8 is a diagram illustrating stray capacitance in a general semiconductor diode. Note that the same or corresponding components in each drawing are designated by the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0018] 1 is a circuit diagram showing an example configuration of a semiconductor device 1 according to an embodiment of the present disclosure. The semiconductor device 1 is a device that is applied to, for example, a power converter or an inverter, and when applied to an inverter, a semiconductor switch element 11 provided in the semiconductor device 1 corresponds to one arm of the inverter. The semiconductor device 1 includes the semiconductor switch element 11, a voltage divider circuit 12, a power supply 13, a semiconductor rectifier element 14, an RC (Resister Capacitor) parallel circuit 15, a driver 16, and a resistor element 17.

[0019] The semiconductor switch element 11 is a circuit element to be protected from short-circuit current, and is, for example, a high-speed switching power semiconductor such as SiC. FIG. 1 shows an N-channel enhancement-type MOSFET as an example. In the semiconductor switch element 11, the drain terminal is a current-inflow terminal and is connected to a conductor 61. The source terminal is a current-outflow terminal and is connected to a conductor 62. The gate terminal is a terminal to which a voltage is applied to turn the semiconductor switch element 11 into an ON state, and is connected to an OUT terminal 54 of the driver 16 via a resistor 17, which is a so-called gate resistor.

[0020] The voltage divider circuit 12 includes a resistor element 21 and a resistor element 22 connected in series. One end of the voltage divider circuit 12, more specifically, one end of the resistor element 21, is connected to the power supply 13. The voltage divider circuit 12 divides V CC Hereinafter, the resistance value of the resistive element 21 will be represented by R1, and the resistance value of the resistive element 22 will be represented by R2.

[0021] The semiconductor rectifying element 14 is, for example, a semiconductor diode, and its anode side is connected to a connection point 66 between the resistive elements 21 and 22 of the voltage divider circuit 12, and its cathode side is connected to the conductor 61 at a connection point 65 located on the path of the conductor 61.

[0022] The RC parallel circuit 15 includes a capacitor element 31 and a resistor element 32 connected in parallel. Here, the capacitor element 31 is, for example, a blanking capacitor that is an external component of the DESAT circuit. One end of the RC parallel circuit 15, more specifically, one end of the capacitor element 31 and the resistor element 32, is connected to the resistor element 22, which is the other end of the voltage divider circuit 12, and to the DESAT terminal 52 of the driver 16. The other end of the RC parallel circuit 15, more specifically, the other ends of the capacitor element 31 and the resistor element 32, is connected to a conductor 62. Hereinafter, the capacitance of the capacitor element 31 is denoted by C1, and the resistance of the resistor element 32 is denoted by R3.

[0023] The drive unit 16 is, for example, a gate drive circuit incorporating a DESAT type short-circuit protection circuit, and includes a drive processing unit 41, semiconductor diodes 42 and 43, a switch 44, an IN terminal 51, a DESAT terminal 52, a GND terminal 53, and an OUT terminal 54. The anode side of the semiconductor diode 42 is connected to the DESAT terminal 52, and the cathode side is connected to the IN terminal 51. The anode side of the semiconductor diode 43 is connected to the GND terminal 53, and the cathode side is connected to the DESAT terminal 52. The switch 44 is connected to the DESAT terminal 52 and the GND terminal 53. The IN terminal 51 is connected to the power supply 13. The GND terminal 53 is connected to a conductor 62. The conductor 62 is connected to the GND of the power supply 13.

[0024] The drive processing unit 41 is, for example, a gate driver IC (Integrated Circuit). When the drive processing unit 41 applies a voltage to the OUT terminal 54, the voltage is applied to the gate terminal of the semiconductor switch element 11 via the resistor element 17. When a voltage is applied to the gate terminal, the semiconductor switch element 11 is turned on, and electrical continuity is established between the drain terminal and the source terminal. In contrast, when the drive processing unit 41 stops applying a voltage to the OUT terminal 54, the semiconductor switch element 11 is turned off, and electrical continuity between the drain terminal and the source terminal is interrupted. When the drive processing unit 41 does not apply a voltage to the OUT terminal 54, it closes the switch 44. In this case, the DESAT terminal 52 and the GND terminal 53 are short-circuited via the switch 44. When the drive processing unit 41 applies a voltage to the OUT terminal 54, it closes the switch 44. In this case, the DESAT terminal 52 and the GND terminal 53 are not short-circuited via the switch 44.

[0025] When the voltage detected at the DESAT terminal 52 exceeds a predetermined threshold, the drive processing unit 41 stops applying voltage to the OUT terminal 54 and performs short-circuit protection processing to turn the semiconductor switch element 11 to the OFF state.

[0026] (Example of operation of semiconductor device in normal state) 2 and 3, the operation of the semiconductor device 1 in a normal state will be described. Here, the normal state refers to a state in which the current value flowing through the conductor 61 satisfies the rated current value. FIG. 2 illustrates a state in which the drive processing unit 41 of the drive unit 16 does not apply a voltage to the OUT terminal 54, and the semiconductor switch element 11 is in an OFF state. When the drive processing unit 41 does not apply a voltage to the OUT terminal 54, the switch 44 is connected, so that the DESAT terminal 52 and the GND terminal 53 are short-circuited via the switch 44. In this case, the current supplied from the power supply 13 via the voltage-dividing circuit 12 flows through the DESAT terminal 52, the switch 44, and the GND terminal 53 to the conductor 62 connected to the GND of the power supply 13. Therefore, the capacitor element 31 of the RC parallel circuit 15 is not charged, and the voltage of the DESAT terminal 52 is 0 V. Therefore, the drive processing unit 41 does not perform short-circuit protection.

[0027] 3 shows a state in which the drive processing unit 41 of the drive unit 16 applies a voltage to the OUT terminal 54, and the semiconductor switch element 11 is in the ON state. When the drive processing unit 41 applies a voltage to the OUT terminal 54, it opens the switch 44, so that the DESAT terminal 52 and the GND terminal 53 are not short-circuited via the switch 44. When the semiconductor switch element 11 is in the ON state, a current I d is supplied to the conductor 61. The current I d flows between the drain and source terminals of the semiconductor switch element 11, and a D-S voltage V of less than a few volts is generated at the node 65. ds The resistance value R1 of the resistor element 21 and the resistance value R2 of the resistor element 22 of the voltage dividing circuit 12 are determined by the power supply voltage V CC The voltage at node 66, which is generated by dividing the current I d The voltage V between the D and S terminals occurs when ds Therefore, the current I supplied from the power supply 13 is A flows to the semiconductor switch element 11 via the semiconductor rectifying element 14 and the conductor 61.

[0028] When a voltage is applied to the gate terminal of the semiconductor switch element 11, a current I d does not flow, but a current I flows between the drain and source terminals. d There is a transitional period from when current starts to flow until the state shown in FIG. 3 is reached. During this transitional period, switch 44 is open, and the voltage at node 65 becomes higher than the voltage at node 66. Therefore, current is supplied from power supply 13 via voltage-divider circuit 12 to capacitor element 31, causing it to be charged. However, the resistance values ​​R1 of resistor element 21, R2 of resistor element 22, R3 of resistor element 32, and capacitance C1 of capacitor element 31 are designed in advance so that the voltage at DESAT terminal 52 will be less than the threshold value even if capacitor element 31 is charged during this transitional period. Therefore, during normal operation, including the transitional period, drive processing unit 41 does not perform short-circuit protection processing.

[0029] (Example of semiconductor device operation when short-circuit current flows) 4 and 5, the operation of the semiconductor device 1 when a short-circuit current flows will be described, and the DESAT voltage V DESAT The mechanism by which the voltage drops in the section indicated by reference numeral 212 will be described.

[0030] For example, suppose that the semiconductor switch element 11 of the semiconductor device 1 is used as the lower arm of an inverter. Also, suppose that a semiconductor switch element of an upper arm (not shown) is connected to the conductor 61, and that this semiconductor switch element is in a fault state, causing a short circuit between the drain terminal and the source terminal. In this case, when the drive processing unit 41 applies a voltage to the OUT terminal 54, the semiconductor switch element 11 is turned on, and a short-circuit current I D begins to flow in the conductor 61.

[0031] Short-circuit current I D The magnitude of the current I that flows through the conductor 61 under normal conditions dThe voltage V between the D and S terminals of the semiconductor switch element 11 is several times or even ten times as large as the voltage V between the D and S terminals of the semiconductor switch element 11. ds increases as the current value of the current flowing between the drain terminal and the source terminal increases. Therefore, the DS voltage V of the semiconductor switch element 11 ds The voltage at is the short circuit current I D flows through the conductor 61, the current I d is larger than when it flows through the conductor 61. D The voltage divider circuit 12 and the RC parallel circuit 15 are designed in advance so that when a short-circuit current I flows through the conductor 61, the voltage at the node 65 is higher than the voltage at the node 66. D flows through the conductor 61, the current I supplied from the power supply 13 through the resistance element 21 A does not flow to the semiconductor rectifying element 14, but flows to the RC parallel circuit 15 via the resistive element 22.

[0032] The current I supplied to the RC parallel circuit 15 A is supplied to the capacitor element 31, the capacitor element 31 is charged, and the voltage at the DESAT terminal 52 increases. When the voltage at the DESAT terminal 52 becomes equal to or higher than the threshold, the drive processing unit 41 stops applying voltage to the OUT terminal 54 and turns the semiconductor switch element 11 to the OFF state. As a result, the semiconductor switch element 11 D will be protected from

[0033] FIG. 5 shows the state in which the semiconductor switch element 11 is turned on and a short-circuit current I flows through the conductor 61. D 5 is a diagram showing the state of the semiconductor device 1 in a transitional period from when the short-circuit current I starts to flow until the state shown in FIG. 4 is reached. Even when the semiconductor switch element 11 is turned on, a short-circuit current I D Therefore, the voltage V between the D and C of the semiconductor switch element 11 ds is the voltage V between DS when the semiconductor switch element 11 is in the OFF state. ds , i.e., DC voltage. Short circuit current I DAs the value of dI increases, the parasitic inductance L present in the conductor 61 between the connection point 65 and the drain terminal of the semiconductor switch element 11 decreases. D A voltage drop of / dt occurs between the DS voltage V ds As shown in the graph 202 of FIG. 10, decreases in the section indicated by the reference numeral 211.

[0034] Voltage between DS V ds When dV decreases, the voltage between the connection points 65 and 66, i.e., the voltage across the semiconductor rectifier element 14, also changes. This voltage change is called dV ds In this case, the stray capacitance C of the semiconductor rectifying element 14 is d1 According to C d1 dV ds In this case, a current with a value of / dt flows from the anode side to the cathode side. In FIG. 5, the direction of the current flow is indicated by the dashed arrow, and is the current I B where the current I B The current value of dV ds Since the current generated in the capacitor element 31 in response to the voltage change of / dt is included, the current value of the current generated in the semiconductor rectifying element 14, C d1 dV ds Does not match / dt.

[0035] Therefore, as shown in FIG. 5, the capacitor element 31 receives a current I A and the current I A The current I flows in the opposite direction to B Here, the current I A The current value of I A and the current I B The current value of I B When expressed as I A B , the terminal of the capacitor element 31 connected to the conductor 62 becomes positive and is charged. As a result, a phenomenon occurs in which the voltage at the DESAT terminal 52 drops in the section indicated by reference numeral 212 in FIG. 10. ​

[0036] (stray capacitance C of semiconductor rectifier element d1 (Conditions) In order to prevent the phenomenon of the voltage at the DESAT terminal 52 dropping in the section indicated by the reference numeral 212 in FIG. 10 from occurring, the short-circuit current I D During the transitional period from when the current begins to flow until the state shown in Figure 4 is reached, I A >I B It must be in the following state.

[0037] Figure 6 shows five types of stray capacitance C d1 Each of the semiconductor rectifying elements 14 is applied to the semiconductor device 1, and a short-circuit current I D DESAT voltage V when DESAT The graph is generated by computer simulation of the change in V. CC =17V, R1=4.7kΩ, R2=130kΩ, C1=10pF, dV ds The condition is / dt=400V / μsec.

[0038] In FIG. 6, the horizontal axis is the time axis showing the elapsed time in units of [μsec], and the vertical axis is the DESAT voltage V DESAT The axis indicates the magnitude of the stray capacitance C d1 The DESAT voltage V when a semiconductor rectifier element 14 with a capacitance of 0.1 pF is applied DESAT Graph 82 shows the change in stray capacitance C d1 The DESAT voltage V when a semiconductor rectifier element 14 with a capacitance of 5.1 pF is applied DESAT Graph 83 shows the change in stray capacitance C d1 The DESAT voltage V when a semiconductor rectifier element 14 with a capacitance of 10.1 pF is applied DESAT Graph 84 shows the change in stray capacitance C d1 The DESAT voltage V when a semiconductor rectifier element 14 with a capacitance of 20.1 pF is applied DESAT 10 is a graph showing the change in

[0039] Graph 85 shows the stray capacitance C d1 The DESAT voltage V when the semiconductor rectifier 14 is applied with a value sufficiently larger than "20.1 pF" DESAT In this case, the DESAT voltage V DESAT is clamped by the forward voltage of the semiconductor diode 43 of the driver 16. That is, the DESAT voltage V DESAT does not become lower than the forward voltage of the semiconductor diode 43, and maintains a value equal to the forward voltage of the semiconductor diode 43 in the range of about 0.75 to 1.25 μsec. As can be seen from the graph of FIG. 6, the stray capacitance C d1 For example, by setting the value between "0.1pF" and "5.1pF", the short-circuit current I D flows through the conductor 61, the DESAT voltage V DESAT does not become 0V or less, and I A >I B It can be seen that the state can be maintained.

[0040] (stray capacitance C d1 (Conditions) Referring to Figure 7, the short-circuit current I D Even if it flows, I A >I B The floating capacitance C of the semiconductor rectifying element 14 that maintains the state d1 Here, in order to specify the condition, the current I A and current I B 7, a path to ground the power supply 13 is added to the circuit configuration of the semiconductor device 1 based on the principle of superposition in an electric circuit, and thus the power supply 13 can be considered to be connected to the conductor 62. In FIG. 7, the current I B , the current I involved in charging the capacitor element 31 is BC1 and a path through which a current I flows that is not involved in charging the capacitor element 31. BR1 The current I BC1 flows through the paths indicated by the dashed and dotted arrows, and the current IBR1 will flow through the path shown by the dashed and dotted arrows. In other words, the path shown by the dotted arrows is BC1 and the current I BR1 In addition, Fig. 7 shows the path where the current I A and current I B This is a diagram showing the state where the current value of current I A and current I B The state in which the current value of I is at its maximum value means that the current supplied to the RC parallel circuit 15 does not flow through the resistance element 32, but is entirely used to charge the capacitor element 31. Therefore, in FIG. 7, the current I B It does not show the route.

[0041] <Current I A About > The current I that charges the capacitor element 31 with a positive voltage A The maximum value of I Amax is expressed by the following equation (1).

[0042]

number

[0043] Here, charging the capacitor element 31 with a positive voltage means charging the capacitor element 31 in a state where the voltage of the terminal of the capacitor element 31 connected to the DESAT terminal 52 is higher than the voltage of the terminal of the capacitor element 31 connected to the GND terminal 53. In contrast, charging the capacitor element 31 with a negative voltage means charging the capacitor element 31 in a state where the voltage of the terminal of the capacitor element 31 connected to the DESAT terminal 52 is lower than the voltage of the terminal of the capacitor element 31 connected to the GND terminal 53.

[0044] For example, if we substitute the numerical values ​​of the simulation conditions above into equation (1), we get I Amax ≒126μA.

[0045] <Current I B About > Voltage between DS Vds change in, i.e., dV ds The current I that charges the capacitor element 31 to a negative voltage by / dt B The maximum value of I Bmax can be calculated as follows: d1 and the capacitance C1 of the capacitor element 31. c is expressed by the following equation (2).

[0046]

number

[0047] Therefore, dV ds Current I generated by voltage change / dt B The maximum value of I Bmax is expressed by the following equation (3).

[0048]

number

[0049] The current I involved in charging the capacitor element 31 is BC1 The maximum value of I BC1max and a current I that is not involved in charging the capacitor element 31. BR1 The maximum value of I BR1max and the current I B The maximum value of I Bmax can be expressed as the following equations (4) and (5), respectively.

[0050]

number

[0051]

number

[0052] Substitute the numerical values ​​of the simulation conditions described above into equation (4), and then, Cd1 Substituting =20pF, I BC1max is about 90μA. d1 Substituting =4pF, I BC1max becomes about 40μA, and C d1 Substituting =5.1pF, I BC1max As explained with reference to Figure 6, by setting the value between "0.1 pF" and "5.1 pF", the short-circuit current I D flows through the conductor 61, the DESAT voltage V DESAT does not become equal to or lower than 0V, and the capacitor element 31 is charged with a positive voltage.

[0053] As mentioned above, the current I calculated by substituting the numerical values ​​of the simulation conditions into equation (1) is A The maximum value of I Amax is approximately 126 μA. 126 μA is C d1 = 4 pF BC1max This is 3.2 times the value of 40 μA, and C d1 = 5.1 pF BC1max Therefore, from the results of the simulation, the current I supplied to the capacitor element 31 is 2.7 times the value of 47 μA. A The maximum value of I Amax But the current I A The current I supplied to the capacitor element 31 in the opposite direction to BC1 The maximum value of I BC1max If the capacitance is about three times as large as the capacitance of the capacitor element 31, it is estimated that the capacitor element 31 will be charged with a positive voltage.

[0054] So, I Amax ×1 / 3>I BC1max By defining the above conditional expression and applying the expressions (1), (3), and (4) to the conditional expression, the following expression (6) is obtained.

[0055]

number

[0056] Since R1+R2>0, equation (6) can be transformed into the following equation (7).

[0057]

number

[0058] dV ds / dt is the D-S voltage V in the section indicated by reference numeral 211 in FIG. ds Since the slope is negative, the sign is negative. Amax ×1 / 3>I BC1max As can be seen from the conditional expression, the direction of the current is not taken into consideration, but only the magnitude of the current is taken into consideration. ds / dt can be thought of as an absolute value. Therefore, dV ds Since / dt>0 and R1>0, equation (7) can be transformed into the following equation (8) based on equation (2).

[0059]

number

[0060] C1>0, C d1 >0, so (1 / C1+1 / C d1 )>0, equation (8) can be transformed into the following equation (9).

[0061]

number

[0062] In equation (9), by transferring 1 / C1 to the right-hand side, the following equation (10) is obtained.

[0063]

number

[0064] When the right side of equation (10) is positive, equation (10) can be transformed into the following equation (11).

[0065]

number

[0066] For example, if we substitute the numerical values ​​of the simulation conditions into equation (11), we get C d1 <4.313pF. C d1 <4.313 pF indicates a condition smaller than 5.1 pF, and it can be seen that this matches the computer simulation shown in FIG.

[0067] Therefore, by using the semiconductor device 1 designed to satisfy the formula (11), the short-circuit current I D flows through conductor 61, I A >I B In other words, the condition that the voltage at one end of the capacitor element 31 connected to the voltage dividing circuit 12 is higher than the voltage at the other end of the capacitor element 31 connected to the conductor 62 can be satisfied. D flows in the conductor 61, the DESAT voltage V DESAT 10. This allows the semiconductor switch elements 11 to be turned on at an appropriate timing without increasing the number of semiconductor switch elements 11. D This will allow protection from

[0068] In addition, in equation (11), dV ds / dt does not directly indicate the value of the circuit element, but dV ds As described above, / dt is the short-circuit current I D The voltage drop due to the parasitic inductance component L caused by the flow of D / dt. dV ds The change in / dt is a value that can be approximated by a straight line, as shown by the change in graph 202 in the section indicated by reference numeral 221 in FIG. 10, and this value can be calculated in advance by simulation or manual calculation.

[0069] The parasitic inductance component L of the conductor 61 is a value calculated based on the length and diameter of the conductor 61 between the connection point 65 and the drain terminal of the semiconductor switch element 11, and is a value that depends on the circuit configuration, so it is not a value that can be determined arbitrarily. D dI is the rate of change of D / dt is also not a value that can be determined arbitrarily. ds / dt cannot be arbitrarily determined in the circuit design, but must be selected from several candidate values. CC is a value for which a rated value is generally used. Furthermore, when a high-speed switching power semiconductor made of SiC is applied as the semiconductor switch element 11, the capacitance C1 of the capacitor element 31 must be a capacitance that corresponds to high-speed switching, and therefore is not a value that can be determined arbitrarily. Therefore, in equation (11), the only things that can be determined arbitrarily are the resistance value R1 of the resistor element 21 and the stray capacitance C of the semiconductor rectifier element 14. d1 It has two values:

[0070] (Circuit design method for semiconductor device that satisfies formula (11)) The following two circuit design methods for designing the circuit of the semiconductor device 1 so as to satisfy the formula (11) are conceivable. The first circuit design method is a method in which values ​​other than the resistance value R1 of the resistive element 21 included in the formula (11) are determined in advance, and then the resistance value R1 of the resistive element 21 is adjusted to select a resistance value R1 that satisfies the formula (11). As can be seen from the formula (11), for example, when the resistance value R1 is reduced, the denominator of the left side of the formula (11) also becomes smaller, and therefore the value of the left side of the formula (11) becomes larger. Therefore, C d1 This widens the allowable range of the value of , and the range of options for the semiconductor rectifying element 14 becomes wider.

[0071] That is, the first circuit design method is a method of selecting a resistor element 21 having a resistance value R1 that satisfies the formula (11), and is a method of only replacing the resistor element 21, not adding a new component. Therefore, according to the first circuit design method, the short-circuit current I D Even if the short-circuit current I flows through the conductor 61, the semiconductor switch element 11 is turned on at an appropriate timing without delay. D However, if the resistance value R1 is reduced, the current I A increases, the power consumption of the resistor elements 21, 22, and 32 increases. Therefore, in the first circuit design method, it is necessary to increase the size of the circuit elements in order to ensure the rated power. Increasing the size of the circuit elements requires that the substrate of the semiconductor device 1 also be increased, which has the disadvantage of increasing the size of the semiconductor device 1 and reducing the output density.

[0072] The second circuit design method is to use the stray capacitance C of the semiconductor rectifying element 14 included in the equation (11) as d1 The values ​​other than are determined in advance, and the stray capacitance C d1 Adjust the stray capacitance C to satisfy equation (11). d1 This is a method to select the stray capacitance C d1 There are two ways to adjust the stray capacitance C d1 The first means for adjusting is a means for adjusting the area of ​​the PN junction surface of the semiconductor diode when a semiconductor diode is used as the semiconductor rectifying element 14. As shown in FIG. 8(a), when a P-type semiconductor 91 and an N-type semiconductor 92 are joined, a depletion layer 93 is generated between the P-type semiconductor 91 and the N-type semiconductor 92. As shown in FIG. 8(b), the depletion layer 93 can be regarded as a capacitor sandwiched between a junction surface 94 of the P-type semiconductor 91 and a junction surface of the N-type semiconductor 92, and the capacitance of the capacitor is expressed as a stray capacitance C d1 Therefore, the stray capacitance C d1 is a value calculated based on the following equation (12).

[0073]

number

[0074] In equation (12), ε is the dielectric constant of the depletion layer 93, and d is the length between the junction surfaces 94 and 95. S is the area of ​​the junction surfaces 94 and 95, i.e., the so-called chip area. Therefore, for example, to satisfy equation (11), the stray capacitance C d1 To reduce this, the chip area S of the bonding surfaces 94 and 95 should be reduced.

[0075] That is, the first means of the second circuit design method is to find a stray capacitance C that satisfies equation (11). d1 This is a method of selecting a semiconductor rectifying element 14 having the above-mentioned characteristic, and is not a method of adding new components but merely replacing the semiconductor rectifying element 14. Therefore, according to the first means of the second circuit design method, it is possible to reduce the short-circuit current I without adding new components and without the disadvantages of the first circuit design method such as an increase in the size of the semiconductor device 1 and a decrease in output density. D Even if the short-circuit current I flows through the conductor 61, the semiconductor switch element 11 is turned on at an appropriate timing without delay. D However, in the case of a typical semiconductor diode, when the chip area S is reduced, the size of the semiconductor diode also becomes smaller, which shortens the distance between the anode and cathode terminals. As a result, the insulation distance cannot be secured, which has the disadvantage of reducing the withstand voltage of the semiconductor diode.

[0076] Stray capacitance C d1 The second means for adjusting the capacitance C is to configure the semiconductor rectifying element 14 with a plurality of semiconductor diodes connected in series, and to adjust the number of semiconductor diodes connected in series. For example, by connecting n semiconductor diodes having the same stray capacitance in series, the size of the stray capacitance can be reduced to 1 / n compared to when using one semiconductor diode. In this way, when the semiconductor rectifying element 14 is made up of a plurality of semiconductor diodes connected in series, the stray capacitance C can be reduced while maintaining the withstand voltage of the semiconductor diodes. d1 It becomes possible to reduce

[0077] That is, according to the second means of the second circuit design method, the short-circuit current I D Even if the short-circuit current I flows through the conductor 61, the semiconductor switch element 11 is turned on at an appropriate timing without delay. D However, since the semiconductor rectifying element 14 is made up of a plurality of semiconductor diodes connected in series, there is a disadvantage in that the number of components increases.

[0078] (Other supplementary configuration examples) In the above embodiment, the semiconductor switch element 11 is, for example, an N-channel enhancement-type MOSFET. However, an N-channel depletion-type MOSFET may also be used as the semiconductor switch element 11. Furthermore, a P-channel enhancement-type MOSFET or a P-channel depletion-type MOSFET may also be used as the semiconductor switch element 11. Furthermore, a bipolar transistor such as an IGBT may also be used as the semiconductor switch element 11 instead of a MOSFET. Note that the terminals corresponding to the above-mentioned "current input terminal" and "current output terminal" vary depending on the type of circuit element used as the semiconductor switch element 11. For example, when a P-channel enhancement-type or depletion-type MOSFET is used as the semiconductor switch element 11, the terminal indicated by the "current input terminal" is a source terminal, and the terminal indicated by the "current output terminal" is a drain terminal.

[0079] In the above embodiment, the voltage-dividing circuit 12 includes two resistive elements, namely, resistive element 21 and resistive element 22. However, the voltage-dividing circuit 12 may include three or more resistive elements. When the voltage-dividing circuit 12 includes three or more resistive elements, the connection point 66 connecting to the semiconductor rectifying element 14 is located somewhere between the multiple resistive elements included in the voltage-dividing circuit 12. In this case, when multiple resistive elements exist between the power supply 13 and the connection point 66, the combined resistance value of the multiple resistive elements becomes resistance value R1, and the combined resistance value of the remaining resistive elements becomes resistance value R2.

[0080] In the above embodiment, the conductor 62 of the semiconductor device 1 is connected to the GND of the power supply 13. In contrast, for example, when the semiconductor switch element 11 of the semiconductor device 1 is applied to the upper arm of an inverter, a constant voltage is applied to the conductor 62, and the power supply voltage V CC The voltage at the semiconductor device 1 also increases by the fixed voltage, and the operating voltage of the semiconductor device 1 also increases by the fixed voltage.

[0081] In the above embodiment, the semiconductor switch element 11 is connected to the short-circuit current I D Although the short-circuit protection circuit for protecting the semiconductor device 1 from the short-circuit current I is not explicitly shown, for example, when the semiconductor device 1 is applied to a power converter or an inverter, the following portion corresponds to the short-circuit protection circuit. That is, the portion of the semiconductor device 1 excluding the configuration for processing the power converter or inverter from the drive processing unit 41, and further excluding the semiconductor switch element 11 and the resistor element 17 from the semiconductor device 1, is the portion that protects the semiconductor switch element 11 from the short-circuit current I D This corresponds to a short-circuit protection circuit that protects against

[0082] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0083] <Additional Notes> The short-circuit protection circuit included in the semiconductor device 1 according to each embodiment can be understood, for example, as follows.

[0084] (1) The short-circuit protection circuit according to the first aspect is a circuit that receives a power supply voltage V supplied from a power supply 13 connected at one end. CC a semiconductor rectifying element 14 having one end connected between resistor elements 21 and 22 of the voltage dividing circuit 12 and the other end connected to a path of a conductor 61 connected to a terminal on the current inflow side of a semiconductor switch element 11 to be protected, the semiconductor rectifying element 14 being connected so that the direction from the one end to the other end is the rectification direction; an RC parallel circuit 15 connected to the other end of the voltage dividing circuit 12; and a capacitor element 31 provided in the RC parallel circuit 15 that supplies a short-circuit current I to the conductor 61 when the semiconductor switch element 11 is in an ON state. D a drive unit 16 that turns the semiconductor switch element 11 to an OFF state when it detects that a current is flowing; and d1 is the short circuit current I D flows through the conductor 61, the voltage at one end of the capacitor element 31 of the RC parallel circuit 15 connected to the voltage divider circuit 12 becomes higher than the voltage at the other end of the capacitor element 31. d1 According to this aspect and the following aspects, the semiconductor switch element 11 can be turned on at an appropriate timing without increasing the number of semiconductor switch elements 11. D can protect against

[0085] (2) A short-circuit protection circuit according to a second aspect is the short-circuit protection circuit of (1), wherein the voltage dividing circuit 12 includes a resistive element 21 having one end directly connected to the power supply 13, the one end of the semiconductor rectifying element 14 is connected to the other end of the resistive element 21, the resistance value of the resistive element 21 is R1, and the voltage value of the power supply voltage 13 is V CC The capacitance of the capacitor element 31 of the RC parallel circuit 15 is C1, and the voltage change between the current inflow terminal of the semiconductor switch element 11 and the current outflow terminal of the semiconductor switch element 11 is dV ds / dt, and the stray capacitance of the semiconductor rectifying element 14 is C d1 In this case, the above Cd1 is 1 / {(3×dV ds / dt×R1) / V CC -1 / C1}>C d1 The condition expression is satisfied.

[0086] (3) A short-circuit protection circuit according to a third aspect is the short-circuit protection circuit of (2), in which variables other than R1 in the conditional expression are set to predetermined fixed values, and R1 is adjusted to select R1 that satisfies the conditional expression.

[0087] (4) A short-circuit protection circuit according to a fourth aspect is the short-circuit protection circuit of (2), in which the semiconductor rectifying element 14 is a semiconductor diode, and in the conditional formula, d1 The variables other than the above are set to predetermined fixed values, and the area of ​​the PN junction surface of the semiconductor diode is adjusted to obtain the C d1 Select .

[0088] (5) A short-circuit protection circuit according to a fifth aspect is the short-circuit protection circuit of (2), wherein the semiconductor rectifying element 14 is composed of a plurality of semiconductor diodes connected in series, and the C d1 The variables other than are set to predetermined fixed values, and the number of semiconductor diodes connected in series is adjusted to obtain the C d1 Select . [Explanation of symbols]

[0089] 1. Semiconductor device 11 Semiconductor switching element 12 Voltage divider circuit 13 Power supply 14 Semiconductor rectifier 15 RC parallel circuit 16 Drive unit 17, 21, 22, 32 Resistive elements 31 Capacitor element 41 Drive processing unit 42,43 Semiconductor diodes 44 Switch 51 IN terminal 52 DESAT terminal 53 GND terminal 54 OUT terminal 61,62 Conductor 65,66 connection points

Claims

1. a voltage divider circuit that divides a power supply voltage supplied from a power supply connected at one end; a semiconductor rectifying element having one end connected between the resistor elements of the voltage dividing circuit and the other end connected to a path of a conductor connected to a terminal on a current inflow side of the semiconductor switch element to be protected, the semiconductor rectifying element being connected so that the direction from the one end to the other end is the rectifying direction; an RC parallel circuit connected to the other end of the voltage divider circuit; a drive unit that, when the semiconductor switch element is in an ON state, detects that a short-circuit current is flowing through the conductor based on a voltage of a capacitor element provided in the RC parallel circuit, turns the semiconductor switch element to an OFF state; the voltage divider circuit includes a resistive element connected directly to the power supply at one end; the one end of the semiconductor rectifying element is connected to the other end of the resistive element, When the resistance value of the resistor element is R1, the voltage value of the power supply voltage is VCC, the capacitance of the capacitor element of the RC parallel circuit is C1, the voltage change between the current inflow terminal of the semiconductor switch element and the current outflow terminal of the semiconductor switch element is dVds / dt, and the stray capacitance in parallel to the semiconductor rectifier element is Cd1, The Cd1 is 1 / {(3×dVds / dt×R1) / VCC-1 / C1}>Cd1 Satisfy the condition Short circuit protection circuit.

2. In the conditional expression, variables other than R1 are set to predetermined fixed values, and R1 is adjusted to select R1 that satisfies the conditional expression.

2. The short circuit protection circuit of claim 1.

3. the semiconductor rectifying element is a semiconductor diode, In the conditional expression, variables other than Cd1 are set to predetermined fixed values, and the area of ​​the PN junction surface of the semiconductor diode is adjusted to select Cd1 that satisfies the conditional expression.

2. The short circuit protection circuit of claim 1.

4. the semiconductor rectifying element is composed of a plurality of semiconductor diodes connected in series, and variables other than the Cd1 in the conditional expression are set to predetermined fixed values, and the Cd1 that satisfies the conditional expression is selected by adjusting the number of the semiconductor diodes connected in series.

2. The short circuit protection circuit of claim 1.

5. a semiconductor switch element; a voltage divider circuit that divides a power supply voltage supplied from a power supply connected at one end; a semiconductor rectifying element having one end connected between the resistor elements of the voltage dividing circuit and the other end connected to a path of a conductor connected to a terminal on a current inflow side of the semiconductor switch element, the semiconductor rectifying element being connected so that a direction from the one end to the other end is a rectifying direction; an RC parallel circuit connected to the other end of the voltage divider circuit; a drive unit that, when the semiconductor switch element is in an ON state, detects that a short-circuit current is flowing through the conductor based on a voltage of a capacitor element provided in the RC parallel circuit, turns the semiconductor switch element to an OFF state; the voltage divider circuit includes a resistive element connected directly to the power supply at one end; the one end of the semiconductor rectifying element is connected to the other end of the resistive element, When the resistance value of the resistor element is R1, the voltage value of the power supply voltage is VCC, the capacitance of the capacitor element of the RC parallel circuit is C1, the voltage change between the current inflow terminal of the semiconductor switch element and the current outflow terminal of the semiconductor switch element is dVds / dt, and the stray capacitance in parallel to the semiconductor rectifier element is Cd1, The Cd1 is 1 / {(3×dVds / dt×R1) / VCC-1 / C1}>Cd1 Satisfy the condition Semiconductor device.

6. a voltage divider circuit for dividing a power supply voltage supplied from a power supply connected at one end thereof; a capacitor element provided in an RC parallel circuit connected to the other end of the voltage dividing circuit is charged based on the supplied current; a semiconductor rectifying element having a rectifying direction from one end to the other end, the one end of which is connected between the resistive elements of the voltage divider circuit, and the other end of which is connected to a conductor path that is connected to a terminal on the current inflow side of the semiconductor switch element to be protected, conducts a current in the rectifying direction when the voltage of the one end of the semiconductor rectifying element is higher than the voltage of the other end of the semiconductor rectifying element, a drive unit that, when the semiconductor switch element is in an ON state, detects that a short-circuit current is flowing through the conductor based on a voltage of the capacitor element of the RC parallel circuit, turns the semiconductor switch element to an OFF state; the voltage divider circuit includes a resistive element connected directly to the power supply at one end; the one end of the semiconductor rectifying element is connected to the other end of the resistive element, When the resistance value of the resistor element is R1, the voltage value of the power supply voltage is VCC, the capacitance of the capacitor element of the RC parallel circuit is C1, the voltage change between the current inflow terminal of the semiconductor switch element and the current outflow terminal of the semiconductor switch element is dVds / dt, and the stray capacitance in parallel to the semiconductor rectifier element is Cd1, The Cd1 is 1 / {(3×dVds / dt×R1) / VCC-1 / C1}>Cd1 Satisfy the condition Short circuit protection method.

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