Protection Circuit and Switch Control Device

Abstract

To provide a protection circuit capable of preventing overheating with simple circuit structure.SOLUTION: A protection circuit 30 includes input / output terminals (I1, I2, O1) of which at least either input or output is made plural, first resistor circuits 31a, 32a connected to either of the plurality of input / output terminals (I1, I2, O1) having a first resistance temperature coefficient, and a second resistor circuits 31b, 32b connected to the other of the plurality of input / output terminals (I1, I2, O1) having a second resistance temperature coefficient having different temperature characteristic from the first resistance temperature coefficient. The protection circuit 30 is electrically connected to the control terminal (gate terminal) of a main switch Q27, and cuts off passage current of the main switch Q27 if the temperature of the main switch Q27 is a predetermined temperature (current cut off temperature) or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a protection circuit for protecting a semiconductor switch and a switch control device.

Background Art

[0002] Conventionally, a PTAT-based thermal shutdown circuit proposed for high-voltage GaN power HEMTs (High Electron Mobility Transistors) is known (for example, Non-Patent Document 1). For example, the thermal shutdown circuit described in Non-Patent Document 1 senses the temperature of a GaN power HEMT, generates and outputs a voltage that reflects the temperature. The voltage corresponding to the temperature generated by the GaN power HEMT is input to a comparator, compared with a fixed reference voltage, and a flag is set when a predetermined temperature condition is reached to shut off the GaN power HEMT.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the above thermal shutdown circuit is mounted on a substrate, there are problems that the circuit structure is complex and the dedicated area of the thermal shutdown circuit on the substrate is large.

[0005] The problem to be solved by the present invention is to provide a protection circuit that can prevent overheating with a simple circuit configuration.

Means for Solving the Problem

[0006] [1] The Switching control device according to the present invention includes a protection circuit for protecting a semiconductor switch, A switching control device comprising a voltage selection circuit for selecting a threshold voltage for switching on and off the semiconductor switch, wherein the protection circuit input / output terminals with at least one of the input and output being plural, has a first level shifter circuit and a second level shifter circuit. The first level shifter circuit and the second level shifter circuit each have a parallel circuit in which a first resistor circuit and a second resistor circuit are connected in parallel. They are connected to the control terminal of the semiconductor switch via the voltage selection circuit. The first resistor circuit has a first load resistor, a current source having a switching element and a first current source resistor connected in series. The second resistor circuit has a second load resistor, a current source having a switching element and a second current source resistor connected in series. The connection point between the first load resistor and the current source included in the first resistor circuit of the first level shifter circuit is connected to the gate terminal of the switching element included in the first resistor circuit of the second level shifter circuit. The connection point between the second load resistor and the current source included in the second resistor circuit of the first level shifter circuit is connected to the gate terminal of the switching element included in the second resistor circuit of the second level shifter circuit. Among the first load resistor, the first current source resistor, the second load resistor, and the second current source resistor, the resistance temperature coefficient of one resistor is different from that of the other resistor. The switching elements included in the first resistor circuit and the second resistor circuit are formed of a compound semiconductor. One of the one resistor and the other resistor is formed of a nitride material. The temperature of the protection circuit has a correlation with the temperature of the semiconductor switch. The voltage difference between the output voltage of the first resistor circuit and the output voltage of the second resistor circuit changes according to the temperature of the semiconductor switch. When the temperature of the semiconductor switch is equal to or higher than a predetermined temperature, the adjustment function of the threshold voltage by the voltage selection circuit acts due to the voltage difference between the output voltage of the first resistor circuit and the output voltage of the second resistor circuit, and the semiconductor switch turns off . [2] In the above invention, the Switch control device is the one resistor has the resistance temperature coefficient and the other resistor has the characteristics of the resistance temperature coefficient are the characteristics of the resistance with respect to temperature, and can be any of positive, negative, and flat characteristics, and are different from each other. [3] In the switch control device according to the present invention, when the temperature of the semiconductor switch is equal to or higher than the predetermined temperature, the voltage selection circuit sets the threshold voltage so that the semiconductor switch turns off regardless of the magnitude of the input voltage of the switch control device. [4] In the above invention, the switch control device has a variable resistor for adjusting the predetermined temperature.

Advantages of the Invention

[0007] According to the present invention, the protection circuit includes input / output terminals with at least one of the input and output being plural, a first resistance circuit connected to one of the plural input / output terminals and including a resistor having a first resistance temperature coefficient, and a second resistance circuit connected to the other of the plural input / output terminals and including a resistor having a second resistance temperature coefficient different in temperature characteristic from the first resistance temperature coefficient. The protection circuit is electrically connected to the control terminal of the semiconductor switch and cuts off the current passing through the semiconductor switch when the temperature of the semiconductor switch is equal to or higher than the predetermined temperature. Thereby, overheating of the semiconductor switch can be prevented with a simple circuit configuration.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0010] The switch control device 10 according to this embodiment will be described with reference to Figure 1. Figure 1 is a circuit diagram of the switch control device 10 according to this embodiment. Note that the circuit configuration and connection form of the input signal amplification circuit 20 and the like included in the switch control device 10 shown in Figure 1 are merely examples, and other circuit configurations may also be used. Also, the resistance values, voltage values, and current values shown in Figure 1 are merely examples.

[0011] The switch control device 10 is a control circuit for switching on and off the main switch Q27 based on an input signal. The input signal is a switching signal input from the outside, and the waveform of the input signal is an on-off waveform of a high level (on voltage) and a low level (off voltage). The switch control device 10 amplifies the voltage of the input signal and shifts the voltage level (converts the voltage level) in order to switch on and off the main switch Q27 with the voltage difference of the input signal. The voltage difference of the input signal corresponds to the difference between the high-level voltage indicating the on state and the low-level voltage indicating the off state.

[0012] The main switch Q27 is a GaN semiconductor switch. When an input voltage equal to or higher than the gate voltage selected by the gate voltage selection circuit 40 is input to the switch control device 10, the main switch Q27 turns on, and a current flows between the drain and source of the main switch Q27.

[0013] The switch control device 10 includes an input signal amplification circuit 20, a protection circuit 30, a gate voltage selection circuit 40, a tracking circuit 50, and a current source 60. The switching elements (switching transistors) included in each circuit are formed of a compound semiconductor such as a GaN semiconductor, for example.

[0014] Here, the element characteristics of the compound semiconductor will be described while comparing them with the element characteristics of the silicon process. The compound semiconductor has excellent characteristics such as breakdown strength, thermal conductivity, and operability at high temperatures, and has many advantages in terms of physical properties as a material. On the other hand, for example, a GaN-based process (manufacturing process, general availability in the market) as a compound semiconductor is not as mature as an Si-based process, so there is a large variation in elements, and there is also a problem that the element size of the compound semiconductor is larger than that of the Si-based process. Furthermore, the compound semiconductor also has problems in that it is difficult to easily obtain voltage references and temperature characteristics. Therefore, conventionally, when a circuit for protecting against overheating is configured with a compound semiconductor, the circuit configuration tends to be complex, and due to the complexity of the circuit configuration and the size of the compound semiconductor element itself, it is difficult to achieve a simple circuit configuration and area reduction.

[0015] The switch control device 10 according to the present embodiment is a monolithic control circuit (IC circuit) including a compound semiconductor for switching the main switch on and off, and by adopting a circuit configuration as shown in FIG. 1, it is possible to suppress thermal runaway and overcurrent associated with overheating with a simple circuit configuration / small area while using a compound semiconductor with large variations. Note that the circuit configuration shown in FIG. 1 is only an example, and the power supply voltage, resistance, or connection form of each circuit element may be changed according to the voltage range of the input signal or the operating voltage range of the main switch.

[0016] As shown in FIG. 1, an input signal amplification circuit 20 is provided on the input side of the switch control device 10. The input signal amplification circuit 20 includes a single-ended input differential circuit and amplifies the difference with respect to the input signal. The input signal amplification circuit 20 includes a gate resistor, a voltage dividing resistor, etc. in addition to the single-ended input differential circuit. The input signal (V in ) is a switching signal with 0V as the low level and +3.3V as the high level. The single-ended input differential circuit has a plurality of symmetrically connected switching elements Q10, Q11, and resistors R40 to R41. The drain terminal of the switching element Q10 is connected to the reference power supply via the resistor R40, and the drain terminal of the switching element Q11 is connected to the power supply via the resistor R41. The gate terminal of the switching element Q10 is connected to the input terminal via the gate resistor R19, and the gate terminal of the switching element Q11 is connected to the reference power supply via the voltage dividing resistor R20. The characteristics of the switching element Q10 and the characteristics of the switching element Q11 are the same. An input signal is input to the gate terminal (control terminal) of the switching element Q10, and a reference voltage is input to the gate terminal of the switching element Q11. The source terminals of the switching element Q10 and the switching element Q11 are commonly connected to one current source.

[0017] As shown in FIG. 1, the input signal amplification circuit 20 includes a differential amplification circuit, a voltage dividing resistor, etc. in addition to the single-ended input differential circuit. The output line of the input signal amplification circuit 20 is connected to the source terminal of the switching element Q19 included in the gate voltage selection circuit 40. Also, in the single-ended input differential circuit and the differential amplification circuit of the input signal amplification circuit 20, the paired switching elements Q10, Q11 and the switching elements Q16, Q17 are commonly connected to one current source respectively.

[0018] The protection circuit 30 is electrically connected to the gate terminal of the main switch Q27 via the gate voltage selection circuit 40. The protection circuit 30 is a circuit that cuts off the passing current of the main switch Q27 when the temperature of the main switch Q27 is equal to or higher than a predetermined temperature (current cutoff temperature). The protection circuit 30 is connected to the gate terminal of the switching element Q19 included in the gate voltage selection circuit 40.

[0019] FIG. 2 is a circuit diagram of the protection circuit 30. The protection circuit 30 shown in FIG. 2 is connected to the dotted line portion of FIG. 1. The protection circuit 30 has a first level shifter circuit 31, a second level shifter circuit 32, a current source 33, input terminals I1, I2, and an output terminal O1. The protection circuit 30 has input / output terminals (I1, I2, O1) where at least one of the input and output is plural. In the example of FIG. 2, the input terminals (I1, I2) are plural terminals. In the example of FIG. 2, the output terminal O1 is a common terminal. Note that the input / output terminals of the protection circuit 30 are not limited to the example of FIG. 2, and the output terminals may be plural.

[0020] The first level shifter circuit 31 has a first resistor circuit 31a in which a load resistor R31 and a current source are connected in series, and a second resistor circuit 31b in which a load resistor R34 and a current source are connected in series. The connection point between the load resistor R31 and the current source corresponds to the input terminal I1, and the connection point between the load resistor R34 and the current source corresponds to the input terminal I2. The current source included in the first resistor circuit 31a has a switching element Q31 and resistors (current source resistors) R32, R33. The resistor R32 is connected between the gate and source of the switching element Q31. The resistor R33 is connected in parallel with the resistor R32 and is connected to the source terminal of the switching element Q31. The current source included in the second resistor circuit 31b has a switching element Q32 and resistors (current source resistors) R35, R36. The connection form of the current source included in the second resistor circuit 31b is the same as the connection form of the current source included in the first resistor circuit 31a.

[0021] The connection point between the load resistor R31 included in the first resistance circuit 31a and the current source is connected to the gate terminal of the switching element Q33. The connection point between the load resistor R34 included in the second resistance circuit 31b and the current source is connected to the gate terminal of the switching element Q34.

[0022] The second level shifter circuit 32 has a first resistance circuit 32a in which the load resistors R37, R38 and the switching element Q33 are connected in series, and a second resistance circuit 32b in which the load resistors R39, R40 and the switching element Q34 are connected in series. The input terminals of the second level shifter circuit 32 are the gate terminals of the switching elements Q33, Q34, corresponding to the input terminals I1, I2. The drain terminal of the switching element Q33 is connected to the load resistor R37, and the source terminal of the switching element Q33 is connected to the load resistor R38. Also, the drain terminal of the switching element Q34 is connected to the load resistor R39, and the source terminal of the switching element Q34 is connected to the load resistor R40. The low voltage side terminals of the resistors R38 and R40 are connected to the output terminal (O1).

[0023] The current source 33 is connected to the low current side of the second level shifter circuit 32, and serves as a current source for flowing a constant current through the second level shifter circuit 32. The current source 33 has the switching element Q35 and the resistors R41, R42. The resistor R41 is connected between the gate and source of the switching element Q35. The resistor R42 is connected in parallel with the resistor R41 and is connected to the source terminal of the switching element Q35.

[0024] As shown in FIG. 1, the gate voltage selection circuit 40 is connected between the protection circuit 30 and the main switch Q27. The gate voltage selection circuit 40 is a circuit that selects a threshold voltage (gate threshold voltage) for turning on the main switch Q27. The main switch Q27 switches on and off based on the high and low of the input voltage based on the input signal (V in ) with the voltage selected by the gate voltage selection circuit 40 as a base.

[0025] The gate voltage selection circuit 40 includes switching elements Q19, Q20 and resistors R28, R29, R53. The drain terminal of the switching element Q19 is connected to the resistors R29, R53. The gate terminal of the switching element Q19 is connected to the output terminal (O1) of the protection circuit 30 via the resistor R28. The source terminal of the switching element Q19 is connected to the current source 60. The resistor R29 is connected between the gate and source of the switching element Q20. The resistor R53 is connected in parallel with the resistor R29 and is connected to the source terminal of the switching element Q20. The drain terminal of the switching element Q19 is connected to the resistors R29, R53. The drain terminal of the switching element Q19 is connected to the gate terminal of the main switch Q27.

[0026] The tracking circuit 50 is a circuit for stabilizing the gate voltage by causing the input voltage to follow the gate voltage. The circuit elements and circuit configuration included in the tracking circuit 50 are as shown in FIG. 1.

[0027] The current source 60 includes a plurality of constant current circuits. The plurality of constant current circuits are respectively connected to the low current sides of the input signal amplification circuit 20 and the tracking circuit 50, and serve as current sources for flowing a constant current through each circuit. The circuit elements and circuit configuration of each constant current circuit are as shown in FIG. 1.

[0028] Next, the resistors used in the protection circuit 30 and the combination of the resistor circuits included in the protection circuit 30 will be described.

[0029] The first resistor circuit 31a and the second resistor circuit 31b are level shifter circuits using two types of resistors. The first resistor circuit 31a and the second resistor circuit 31b include resistors with different resistor temperature coefficients among the load resistor R31, the resistors R32 and R33 used as current sources, the load resistor R34, and the resistors R35 and R36 used as current sources. In other words, among the load resistor R31, the resistors R32 and R33 used as current sources, the load resistor R34, and the resistors R35 and R36 used as current sources included in the first resistor circuit 31a and the second resistor circuit 31b, the resistor temperature coefficient of at least one resistor is different from that of the other resistors.

[0030] FIG. 3 shows the temperature characteristics of a general resistor and a resistor using a nitride material. In FIG. 3, graph a shows the characteristics of a general resistor, and graph b shows the characteristics of a resistor using a nitride material. The general resistor is a resistor (Epi-R) that utilizes the sheet resistance of a GaN-on-SiC epitaxial substrate. The resistor using a nitride material is a resistor (ZrN-R) that utilizes a zirconium nitride thin film. The nitride material may be titanium nitride (TiN), zirconium nitride (ZrN), tantalum nitride (TaN), or hafnium nitride (HfN) in addition to zirconium nitride.

[0031] As shown in FIG. 3, the temperature characteristic of a general resistor has a positive slope with respect to temperature. On the other hand, the temperature characteristic of a resistor using a nitride material (hereinafter also referred to as a nitride resistor) has a negative slope with respect to temperature. That is, a general resistor and a nitride resistor have different resistor temperature coefficients. In this embodiment, two types of resistors are used for the resistors included in the first level shifter circuit 31. Among the resistors included in the first level shifter circuit 31, one resistor is either a general resistor or a nitride resistor, and the other resistor is either the other of the general resistor and the nitride resistor. The two types of resistors may be different types among the plurality of resistors included in the first resistor circuit 31a, or may be different types between the resistors included in the first resistor circuit 31a and the resistors included in the second resistor circuit 31b.

[0032] FIG. 4 is a circuit diagram for explaining a combination of level shifter circuits using two types of resistors. General resistors are used in the dotted frame, and nitride resistors are used in the solid frame. As shown in FIG. 4(a), in the resistor circuit of Case1, a general resistor is used for the load resistor, and a nitride resistor is used for the resistor included in the current source. As shown in FIG. 4(b), in the resistor circuit of Case2, a general resistor is used for the load resistor, and a general resistor is used for the resistor included in the current source. As shown in FIG. 4(c), in the resistor circuit of Case3, a nitride resistor is used for the load resistor, and a nitride resistor is used for the resistor included in the current source. As shown in FIG. 4(d), in the resistor circuit of Case4, a nitride resistor is used for the load resistor, and a general resistor is used for the resistor included in the current source.

[0033] In Case1 and Case4, since different types of resistors are used in one resistor circuit, the temperature-resistance coefficient characteristics of each resistor are characteristics of the resistance with respect to temperature, which can be any of positive, negative, and flat characteristics, and are different from each other. For example, in the first resistor circuit 31a of Case1, the temperature-resistance coefficient of the resistor R31 has a positive characteristic, and the temperature-resistance coefficients of the resistors R32 and R33 have negative or flat characteristics. Note that the flat characteristic is a characteristic in which the resistance coefficient is substantially constant in a predetermined temperature range.

[0034] FIG. 5 is a graph showing the output voltage temperature characteristics of Case1 to Case4 shown in FIGS. 4(a) to (d). As shown in FIG. 5, the output voltage temperature characteristics of the resistor circuit included in the level shifter circuit differ depending on the type of resistor used. In this embodiment, a level shifter circuit is configured by combining Case1 to Case4, and a circuit is realized that uses the difference in output voltage to cut off the passing current when the temperature of the main switch Q27 becomes equal to or higher than a predetermined set temperature (current cutoff temperature).

[0035] Specifically, for example, the circuit of Case 1 is used for the first resistance circuit 31a, and the circuit of Case 4 is used for the second resistance circuit 31b. When the level shifter circuit is configured with the combination of Case 1 and Case 4, with the temperature around 25°C as the boundary, the difference in the output voltage of the resistance circuit becomes larger as the temperature increases. That is, the difference in the output voltage of the resistance circuit changes according to the temperature. When the set temperature for cutting off the passing current is 100 degrees, as shown in FIG. 5, the output voltage of the resistance circuit of Case 1 becomes approximately -10V, and the output voltage of the resistance circuit of Case 4 becomes approximately -22V. And when there is a difference in the output voltage at the set temperature (100 degrees), the voltage output from the protection circuit 30 to the gate voltage selection circuit 40 causes the adjustment function of the gate threshold voltage by the gate voltage selection circuit 40 to act, so that the main switch Q27 turns off regardless of the magnitude of the input voltage (Vi) of the input signal. Also, the temperature of the switching element Q27 and the temperature of the protection circuit 30 have a correlation. When the temperature of the main switch Q27 rises, the temperature of the resistor included in the protection circuit 30 rises in the same way as the temperature of the main switch Q27. When the temperature of the resistor included in the protection circuit 30 becomes equal to or higher than the set temperature (100 degrees) due to the temperature rise of the switching element Q27, the circuit parameters included in the protection circuit 30 and the gate voltage selection circuit 40 are set so that the main switch Q27 is forcibly turned off.

[0036] FIG. 6 is a graph showing the temperature characteristics of the switch control device in the present embodiment. (a) shows the voltage-temperature characteristics of the on-resistance of the main switch Q27, and (b) shows the passing current-temperature characteristics of the main switch Q27. As shown in FIG. 6(a), when the temperature becomes 100 degrees or higher, the on-resistance of the main switch Q27 rises steeply. Also, when the temperature becomes 100 degrees or higher, the passing current drops steeply to zero amperes. Thereby, when the temperature of the switching element Q27 becomes 100 degrees or higher, the main switch Q27 turns off regardless of the magnitude of the input voltage of the input signal, and the passing current is cut off.

[0037] In the present embodiment, the second resistor circuits 32a and 32b included in the second level shifter circuit 32 may be circuits using two types of resistors. For example, among the resistors R37 to 40, one resistor may be a general resistor and the other resistor may be a nitride resistor. Also, two types of resistors may be used between the load resistor included in the second resistor circuit 32a and the resistor used in the current source 33. Two types of resistors may be used between the load resistor included in the second resistor circuit 32b and the resistor used in the current source 33.

[0038] As described above, the protection circuit 30 according to the present embodiment includes input / output terminals (I1, I2, O1) with at least one of the input and output being plural, and first resistor circuits 31a, 32a that are connected to any one of the plural input / output terminals (I1, I2, O1) and include resistors having a first resistance temperature coefficient, and second resistor circuits 31b, 32b that are connected to any other one of the plural input / output terminals (I1, I2, O1) and include resistors having a second resistance temperature coefficient different from the first resistance temperature coefficient and temperature characteristics. The protection circuit 30 is electrically connected to the control terminal (gate terminal) of the main switch Q27, and when the temperature of the main switch Q27 is equal to or higher than a predetermined temperature (current cutoff temperature), cuts off the passing current of the main switch Q27. Thereby, overheating can be prevented with a simple circuit configuration. Also, a fail-safe function (overheat protection, overcurrent protection) can be realized with a reduced area. Also, a circuit for preventing overheating can be realized with a plurality of types of resistors having different resistance temperature coefficients.

[0039] Also, in the protection circuit 30 according to the present embodiment, the characteristics of the first resistance temperature coefficient and the second resistance temperature coefficient are characteristics of the resistance with respect to temperature, and are any of positive, negative, and flat characteristics, and are different from each other. Thereby, a circuit for preventing overheating can be realized with a plurality of types of resistors having different resistance temperature coefficients.

[0040] Also, in the protection circuit 30 according to the present embodiment, the first resistance circuits 31a and 32a include resistors R31 and R37 (corresponding to the "load resistance" of the present invention) and resistors R32, R33, R41, and R42 (corresponding to the "current source resistors" of the present invention), and the second resistance circuits 31b and 32b include resistors R34 and R39 (corresponding to the "load resistance" of the present invention) and resistors R35, R36, R41, and R42 (corresponding to the "current source resistors" of the present invention). Among the resistors R31, R37, resistors R32, R33, R41, R42, resistors R34, R39, and resistors R35, R36, R41, R42, the resistance temperature coefficient of one resistor is different from that of the other resistors. Thereby, a circuit for preventing overheating can be realized with a plurality of types of resistors having different resistance temperature coefficients. In the present embodiment, the resistance circuit including the first resistance circuit 32a and the current source 33 corresponds to the "first resistance circuit" of the present invention, and the resistance circuit including the second resistance circuit 32b and the current source 33 corresponds to the "second resistance circuit" of the present invention.

[0041] Also, in the protection circuit 30 according to the present embodiment, the switching elements included in the first resistance circuits 31a and 32a and the second resistance circuits 31b and 32b are formed of compound semiconductors, and either one of the one resistor and the other resistor is formed of a nitride material. Thereby, a circuit for preventing overheating can be realized with a plurality of types of resistors having different resistance temperature coefficients.

[0042] Also, in the protection circuit 30 according to the present embodiment, the voltage difference between the output voltage of the first resistance circuits 31a and 32a and the output voltage of the second resistance circuits 31b and 32b changes according to temperature. Thereby, since the current cutoff temperature can be arbitrarily set, the expandability of the circuit can be ensured.

[0043] Also, the switch control device 10 according to the present embodiment includes a gate voltage selection circuit 40 that selects a threshold voltage for switching on and off the main switch Q27. The protection circuit 30 is connected to the gate voltage selection circuit 40. When the temperature of the main switch Q27 is equal to or higher than a predetermined temperature, the gate voltage selection circuit 40 sets the threshold voltage so that the main switch Q27 turns off regardless of the magnitude of the input voltage of the switch control device 10. Thereby, overheating can be prevented with a simple circuit configuration. Also, a fail-safe function (overheat protection, overcurrent protection) can be realized with a reduced area.

[0044] As a modification of the present embodiment, the resistor R70 included in the input signal amplification circuit 20 may be a variable resistor, and the resistance value of the resistor R70 may be changed to arbitrarily set the temperature at which the passing current is cut off. FIG. 7 shows the passing current temperature characteristics of the main switch Q27 when the resistance value of the resistor R70 is changed. As shown in FIG. 7, when the resistance value of the resistor R70 is increased (for example, 220 kΩ), the passing current becomes zero when the current cutoff temperature of the main switch Q27 is about 120 degrees. As the resistance value of the resistor R70 decreases, the current cutoff temperature increases. When the resistance value of the resistor R70 is set to 180 (kΩ), the current cutoff temperature of the main switch Q27 becomes about 165 degrees. Thus, by changing the circuit parameters of the resistor R70, the current cutoff temperature of the main switch Q27 can be set to an arbitrary value. The switch control device 10 according to the modification has a variable resistor for adjusting the current cutoff temperature. Thereby, the current cutoff temperature can be arbitrarily set by changing the circuit parameters. Note that the resistor for adjusting the current cutoff temperature is not limited to the resistor R70, and other resistors included in the switch control device 10 may be used.

[0045] Note that the embodiments described above are described to facilitate the understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Description of Reference Numerals

[0046] 10 Switch control device 20 Input signal amplification circuit 30 Protection circuit 31 First-level shifter circuit 31а First resistance circuit 31b Second resistance circuit 32 Second-level shifter circuit 32а First resistance circuit 32b Second resistance circuit 33 Current source 40 Gate voltage selection circuit 50 Tracking circuit 60 Current source

Claims

1. A protection circuit for protecting a semiconductor switch, and A switching control device comprising a voltage selection circuit for selecting a threshold voltage for switching on and off the semiconductor switch, wherein The protection circuit includes Input and output terminals with at least one of input and output being plural, A first level shifter circuit, and A second level shifter circuit, The first level shifter circuit and the second level shifter circuit each have a parallel circuit in which a first resistance circuit and a second resistance circuit are connected in parallel, and are connected to a control terminal of the semiconductor switch via the voltage selection circuit, The first resistance circuit has a first load resistance, a current source having a switching element and a first current source resistance connected in series, The second resistance circuit has a second load resistance, a current source having a switching element and a second current source resistance connected in series, A connection point between the first load resistance and the current source included in the first resistance circuit of the first level shifter circuit is connected to a gate terminal of the switching element included in the first resistance circuit of the second level shifter circuit, A connection point between the second load resistance and the current source included in the second resistance circuit of the first level shifter circuit is connected to a gate terminal of the switching element included in the second resistance circuit of the second level shifter circuit, Among the first load resistance, the first current source resistance, the second load resistance, and the second current source resistance, the resistance temperature coefficient of one resistance is different from that of the other resistance, The switching elements included in the first resistance circuit and the second resistance circuit are formed of a compound semiconductor, One of the one resistance and the other resistance is formed of a nitride material, The temperature of the protection circuit has a correlation with the temperature of the semiconductor switch, A voltage difference between the output voltage of the first resistance circuit and the output voltage of the second resistance circuit changes according to the temperature of the semiconductor switch, When the temperature of the semiconductor switch is equal to or higher than a predetermined temperature, the adjustment function of the threshold voltage by the voltage selection circuit acts due to the voltage difference between the output voltage of the first resistance circuit and the output voltage of the second resistance circuit, and the semiconductor switch is turned off. A switching control device.

2. The switching control device according to claim 1, wherein The characteristics of the temperature coefficient of resistance of the one resistor and the temperature coefficient of resistance of the other resistor are characteristics of the resistance with respect to temperature, and are any of positive, negative, and flat characteristics, and are characteristics different from each other. A switch control device.

3. The switch control device according to claim 1 or 2, wherein When the temperature of the semiconductor switch is equal to or higher than the predetermined temperature, the voltage selection circuit sets the threshold voltage so that the semiconductor switch is turned off regardless of the magnitude of the input voltage of the switch control device. Switch control device.

4. The switch control device according to any one of claims 1 to 3, wherein A switch control device having a variable resistor for adjusting the predetermined temperature.

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