Amplifier circuit and lighting device

Abstract

Provided is an amplifier circuit or the like excellent in radiation resistance and capable of handling large power with a simple configuration. This amplifier circuit (10) comprises: an operational amplifier (1) having a MOSFET composed of a semiconductor having a wider band gap than an Si semiconductor; a bipolar transistor (2) electrically connected to the output side of the operational amplifier (1) and composed of an Si semiconductor; and a resistance element (4) for detecting one of a collector current and an emitter current of the bipolar transistor (2). A voltage of the resistance element (4) is applied to an inverting input terminal (1b) of the operational amplifier (1), and a prescribed direct-current voltage is applied to a non-inverting input terminal (1a) of the operational amplifier (1). The bipolar transistor (2) is electrically connected to an output unit (20) such that the other of the collector current and the emitter current flows to the output unit (20). The voltage across the collector and the emitter of the bipolar transistor (2) is lower than the sum of the voltage of the output unit (20) and the voltage of the resistance element (4).

Description

Amplification circuit and lighting device

[0001] The present disclosure relates to an amplifier circuit and the like.

[0002] Regarding electrical circuits of devices used in radiation environments such as nuclear power plants, for example, a technique described in Patent Document 1 is known. That is, Patent Document 1 describes providing an "operational amplifier made of a semiconductor having a band gap larger than that of silicon."

[0003] Japanese Patent Application Laid-Open No. 2023-048495

[0004] The technology described in Patent Document 1 cites silicon carbide (SiC) as an example of a semiconductor with a wider bandgap than silicon. Also, the technology described in Patent Document 1 aims to stabilize the power supply voltage while ensuring radiation resistance by providing a Si bipolar transistor on the output side of a SiC operational amplifier.

[0005] However, the technology described in Patent Document 1 is primarily targeted at low-voltage circuits, and does not particularly take into consideration the handling of high power. For example, experiments by the inventors have revealed that in high-voltage circuits where the voltage applied to the load exceeds 100 V, the peripheral circuits also need to be designed for stable operation.

[0006] Therefore, an object of the present disclosure is to provide an amplifier circuit or the like that has excellent radiation resistance and is capable of handling large power with a simple configuration.

[0007] In order to solve the above-mentioned problems, the amplifier circuit according to the present disclosure comprises an operational amplifier having a lateral MOSFET made of a semiconductor having a bandgap wider than that of a Si semiconductor, a bipolar transistor made of a Si semiconductor and electrically connected to the output side of the operational amplifier, and a resistive element that detects one of the collector current and the emitter current of the bipolar transistor, wherein the voltage of the resistive element is applied to the inverting input terminal of the operational amplifier and a predetermined DC voltage is applied to the non-inverting input terminal of the operational amplifier, the bipolar transistor is electrically connected to a load so that the other of the collector current and the emitter current flows to the load, and the collector-emitter voltage of the bipolar transistor is lower than the sum of the voltage of the load and the voltage of the resistive element.

[0008] According to the present disclosure, it is possible to provide an amplifier circuit or the like that has excellent radiation resistance and is capable of handling large power with a simple configuration.

[0009] FIG. 1 is a circuit diagram including an amplifier circuit according to a first embodiment; FIG. 2 is an explanatory diagram showing a breakdown of ON resistance in vertical-structure MOSFETs made of Si and SiC, and in a lateral-structure MOSFET; FIG. 3 is a cross-sectional view of a vertical-structure MOSFET as a comparative example; FIG. 4 is a cross-sectional view of a lateral-structure MOSFET provided in the amplifier circuit according to the first embodiment; FIG. 5 is an explanatory diagram showing characteristics of a bipolar transistor in the amplifier circuit according to the first embodiment; FIG. 6 is a circuit diagram including an amplifier circuit according to a second embodiment; FIG. 7 is a circuit diagram including an amplifier circuit according to a third embodiment; FIG. 8 is a circuit diagram of a lighting device including an amplifier circuit according to a fourth embodiment; and FIG. 9 is a circuit diagram including an amplifier circuit according to a modified example.

[0010] First Embodiment Configuration of Amplifier Circuit Fig. 1 is a circuit diagram including an amplifier circuit 10 according to a first embodiment. The amplifier circuit 10 shown in Fig. 1 is a circuit that amplifies current and voltage, and is used in a radiation environment such as a nuclear power plant. As shown in Fig. 1, the amplifier circuit 10 includes an operational amplifier 1, a bipolar transistor 2, a resistor element 3 for adjusting current, a resistor element 4 for detecting current, a DC power supply 5, and a resistor element 6 for dividing voltage.

[0011] The operational amplifier 1 is a circuit that amplifies the voltage between the non-inverting input terminal 1a and the inverting input terminal 1b with a predetermined gain. In the example of FIG. 1, the circuit including the operational amplifier 1 is configured as a so-called non-inverting amplifier circuit. Specifically, the voltage of the resistor element 4 is applied to the inverting input terminal 1b of the operational amplifier 1 via the wiring K4. By applying negative feedback in this manner, the gain when the operational amplifier 1 amplifies the voltage can be stabilized.

[0012] The operational amplifier 1 shown in FIG. 1 has a lateral-structure MOSFET 40 (Metal Oxide Semiconductor Field Effect Transistor: see FIG. 3B ) made of a semiconductor having a wider bandgap than a Si semiconductor (silicon). In the first embodiment, a case will be described in which SiC (silicon carbide) is used as the semiconductor having a wider bandgap than a Si semiconductor, but the present invention is not limited to this. The lateral-structure MOSFET 40 (see FIG. 3B ) will be described later.

[0013] In the following description, when an element such as a MOSFET is mainly made of Si, the term "made of Si" is used, and when an element such as a MOSFET is mainly made of SiC, the term "made of SiC" is used.

[0014] As shown in Fig. 1, the operational amplifier 1 has a non-inverting input terminal 1a, an inverting input terminal 1b, and an output terminal 1c. The operational amplifier 1 also has a pair of power supply terminals (reference numerals are not shown). One of the pair of power supply terminals is connected to a positive DC voltage V ＤＤ is applied to one end, and a negative DC voltage V ＳＳ is applied.

[0015] A predetermined DC voltage is applied to the non-inverting input terminal 1a of the operational amplifier 1 from a DC power supply 5. Furthermore, the voltage across the resistor element 4 is applied to the inverting input terminal 1b of the operational amplifier 1. The voltage between the non-inverting input terminal 1a and the inverting input terminal 1b is amplified with a predetermined gain in the operational amplifier 1. The voltage at the output terminal 1c of the operational amplifier 1 is applied between the base and emitter of the bipolar transistor 2 in the subsequent stage.

[0016] Generally, semiconductor elements are subject to degradation due to ionization caused by radiation. Ionization is a phenomenon in which electron-hole pairs are generated when radiation energy is applied to a substance, resulting in the accumulation of electric charges and other degradation of the characteristics of semiconductor elements. Until now, MOSFETs made of silicon have been the primary material used in operational amplifiers used in radiation environments.

[0017] In contrast, SiC has a wider range of bandgap energy (the energy required to move an electron from the valence band to the conductor) than Si, and therefore has excellent radiation resistance. Therefore, in the first embodiment, SiC is used as a constituent material of the MOSFET 40 (see FIG. 3B ) of the operational amplifier 1, thereby improving the radiation resistance of the operational amplifier 1. Note that the inventors have confirmed that, while an operational amplifier having a Si MOSFET breaks down when an absorbed radiation dose is on the order of several kGy (gray), an operational amplifier having a SiC MOSFET can normally perform its amplification function even when an absorbed radiation dose is on the order of MGy.

[0018] However, operational amplifiers having SiC MOSFETs tend to have lower maximum gains than those made of Si. Furthermore, the inventors' experiments have revealed the following: The inventors have found that the SiC lateral-structure MOSFET 40 (see FIG. 3B ) has lower channel mobility (i.e., higher channel resistance), and therefore has a higher ON resistance than that of a Si MOSFET.

[0019] Therefore, in the first embodiment, a Si bipolar transistor 2 is connected downstream of the operational amplifier 1 having a SiC MOSFET. As described above, the SiC lateral structure MOSFET 40 (see FIG. 3B) has a relatively large ON resistance, so the magnitude of the current is moderately suppressed in the operational amplifier 1, and the current is amplified by the downstream bipolar transistor 2. This makes it possible to handle large power while ensuring radiation resistance.

[0020] The bipolar transistor 2 shown in Fig. 1 is an element that amplifies current in response to the output from the operational amplifier 1. The bipolar transistor 2 is made of a Si semiconductor and is electrically connected to the output side of the operational amplifier 1. By configuring the bipolar transistor 2 from a Si semiconductor in this way, radiation resistance is ensured. As shown in Fig. 1, the output terminal 1c of the operational amplifier 1 is connected to the base of the bipolar transistor 2 via a wiring K1. A resistive element 3 for adjusting the current is provided on this wiring K1.

[0021] Then, a predetermined voltage is applied between the base and emitter of the bipolar transistor 2 from the operational amplifier 1, thereby amplifying the current. Specifically, in the bipolar transistor 2, the base current is amplified by a predetermined current amplification factor h ＦＥ A collector current having a magnitude obtained by multiplying the amplified current by the bipolar transistor 2 flows. The current amplified by the bipolar transistor 2 (i.e., the collector current) is supplied to the output section 20. The output section 20 is a "load" electrically connected to the amplifier circuit 10.

[0022] The bipolar transistor 2 is electrically connected to the output section 20 (load) so that a collector current flows to the output section 20. Specifically, the collector of the bipolar transistor 2 is connected to one terminal 20a of the output section 20 via a wiring K2. The emitter of the bipolar transistor 2 is connected to the negative electrode of the DC power supply 5 via a wiring K3, and is also connected to the inverting input terminal 1b of the operational amplifier 1 via a wiring K3 (part of) and a wiring K4 in that order. Note that, although an NPN type bipolar transistor is used as the bipolar transistor 2 in the example of FIG. 1, a PNP type may also be used.

[0023] 1, a resistor element 4 is provided on the wiring K3 closer to the DC power supply 5 than the connection point with the wiring K4. This resistor element 4 is an element for detecting the emitter current of the bipolar transistor 2. The voltage of the resistor element 4 is applied to the inverting input terminal 1b of the operational amplifier 1.

[0024] 1 is a power supply for applying a predetermined DC voltage to the non-inverting input terminal 1a of the operational amplifier 1. The positive electrode of the DC power supply 5 is connected to another wire K6 via wire K5, and is also connected to the non-inverting input terminal 1a of the operational amplifier 1 via wire K5 (part) and wire K7 in sequence. The negative electrode of the DC power supply 5 is connected to the inverting input terminal 1b of the operational amplifier 1 in sequence via wire K3 (part) and wire K4 in sequence.

[0025] As shown in Fig. 1, the potential of the negative electrode of the DC power supply 5 is set to the ground potential (GND: reference potential). A wire K6 is connected to the other terminal 20b of the output section 20. A predetermined DC voltage V is applied from the outside between the wire K6 and the wire K3 at the ground potential. ＤＣ The resistor element 6 shown in FIG. ＤＣ Specifically, the resistance element 6 is provided on the wiring K5 closer to the wiring K6 (the output unit 20 side) than the connection point with another wiring K7.

[0026] Figure 2 is an explanatory diagram showing the breakdown of ON resistance in vertical-structure MOSFETs made of Si and SiC, and in a lateral-structure MOSFET. The vertical axis in Figure 2 represents the ON resistance of each semiconductor element. Here, "ON resistance" refers to the resistance value between the drain and source when the MOSFET is in the ON state. The smaller the ON resistance, the smaller the loss during operation of the semiconductor element.

[0027] Fig. 2 shows four bar graphs arranged horizontally. These four bar graphs, from left to right on the page, show the breakdown of the ON resistance of a Si MOSFET with a vertical structure, a SiC MOSFET with a vertical structure, a Si MOSFET with a lateral structure, and a SiC MOSFET with a lateral structure. As shown in the dashed frame in Fig. 2, in the first embodiment, a SiC MOSFET with a lateral structure is used as the semiconductor element of the operational amplifier 1 (see Fig. 1). The three bar graphs other than those shown in the dashed frame in Fig. 2 are shown as comparative examples.

[0028] The ON resistance includes five types of resistance: specifically, from top to bottom in each bar graph in Figure 2, the resistance of the wire or lead frame from the source electrode to the source terminal, the channel resistance (shown by dots), the drift resistance (shown by hatching), the substrate resistance, and the resistance from the backside of the MOSFET chip to the solder or lead frame.

[0029] 2 is often used as a high-voltage power semiconductor device. In a vertical MOSFET, SiC MOSFETs have similar channel resistances, but the drift resistance of SiC MOSFETs is smaller, resulting in a smaller overall ON resistance.

[0030] The lateral structure MOSFET (made of Si or SiC) shown in FIG. 2 is often used as a low-voltage device such as an operational amplifier. The inventors have also discovered that a lateral structure MOSFET made of SiC has a higher ON resistance than a lateral structure MOSFET made of Si. This is because a lateral structure MOSFET made of SiC has low channel mobility, which increases the channel resistance (dotted area), resulting in a higher ON resistance. Incidentally, SiC is generally considered to have a low ON resistance because it is primarily used as a power semiconductor (high voltage).

[0031] As described above, a SiC lateral structure MOSFET has a large ON resistance, resulting in a large loss when a large current flows through it. Therefore, in the first embodiment, a Si bipolar transistor 2 (see FIG. 1) is provided in the subsequent stage of an operational amplifier 1 (see FIG. 1) including a SiC lateral structure MOSFET. This allows the bipolar transistor 2 to amplify the current, making it possible to handle large power while ensuring radiation resistance. Note that the Si bipolar transistor 2 (see FIG. 1) has high radiation resistance, as described above.

[0032] <Vertical and Lateral Structure MOSFETs> Fig. 3A is a cross-sectional view of a vertical structure MOSFET 30 as a comparative example. Note that the example of Fig. 3A shows an n-channel (n-type) vertical structure MOSFET 30. The following description will be given for a case where the MOSFET 30 is made of SiC, but the same applies to a case where the MOSFET 30 is made of Si. Also, while Fig. 3A shows a so-called planar type MOSFET 30, a trench type MOSFET also exists as a vertical structure.

[0033] 3A, in a vertical MOSFET 30, an n-type semiconductor substrate 32 and an n-type epitaxial layer 33 are sequentially formed on a metal layer 31 connected to a drain electrode. The semiconductor substrate 32 and the epitaxial layer 33 are formed of a compound semiconductor such as SiC.

[0034] One p-type well region 34a, 34b is provided on each of the n-type epitaxial layers 33. The aforementioned n-type epitaxial layer 33 exists between the p-type well regions 34a, 34b. An n-type high-concentration impurity region 35a is formed inside one well region 34a (similarly on the inside of the other well region 34b). A gate insulating film 36 is provided on the epitaxial layer 33, parts of the well regions 34a, 34b, and parts of the high-concentration impurity regions 35a, 35b. A gate electrode 37 is provided on the gate insulating film 36.

[0035] When a predetermined voltage is applied to the gate electrode 37, the p-type well regions 34a and 34b located directly below the gate electrode 37 are inverted to n-type, and a channel Ch1 is formed across the high-concentration impurity regions 35a and 35b. As a result, current flows vertically from the drain electrode connected to the metal layer 31 to the source electrodes 38a and 38b. As described above, the vertical MOSFET 30 is suitable for high voltage resistance and is often used when handling large amounts of power.

[0036] 3B is a cross-sectional view of a lateral MOSFET 40 included in the amplifier circuit according to the first embodiment. The example of FIG. 3B shows an n-channel (n-type) lateral MOSFET 40. The following description will be given of the case where the MOSFET 40 is made of SiC, but the same applies to the case where the MOSFET 40 is made of Si.

[0037] 3B , in a lateral MOSFET 40, n-type high-concentration impurity regions 42a and 42b are provided on a p-type well layer 41 connected to a body such as a semiconductor substrate. A source electrode 45 is provided on one of the high-concentration impurity regions 42a. A drain electrode 46 is provided on the other high-concentration impurity region 42b. The well layer 41 described above is provided between the high-concentration impurity regions 42a and 42b. A gate insulating film 43 is provided on the well layer 41 and (parts of) the high-concentration impurity regions 42a and 42b. A gate electrode 44 is provided on the gate insulating film 43.

[0038] When a predetermined voltage is applied to the gate electrode 44, the p-type well layer 41 located directly below the gate electrode 44 is inverted to n-type, and a channel Ch2 is formed across the high-concentration impurity regions 42 a and 42 b. As a result, a current flows laterally from the drain electrode 46 to the source electrode 45. Note that the configuration in FIG. 3B is merely an example, and the configuration of a lateral MOSFET is not limited to this.

[0039] In general, operational amplifiers including lateral MOSFETs are often used in low-voltage circuits, but in the first embodiment, a bipolar transistor 2 (see FIG. 1) is provided in the subsequent stage of an operational amplifier 1 (see FIG. 1) to achieve high power.

[0040] <Characteristics of Bipolar Transistor> Fig. 4 is an explanatory diagram showing the characteristics of a bipolar transistor (see also Fig. 1 as appropriate). The horizontal axis of Fig. 4 represents the voltage applied to the bipolar transistor 2. The vertical axis of Fig. 4 represents the current amplification factor h of the bipolar transistor 2 when irradiated with radiation. ＦＥ The multiple circles in FIG. 4 represent the degree of deterioration of the current amplification factor h when voltages of different magnitudes are applied to the bipolar transistor 2 in a situation where the bipolar transistor 2 is irradiated with radiation of a predetermined intensity. ＦＥ This shows the degree of deterioration.

[0041] As a result of repeated experiments by the inventors, it was found that the higher the voltage applied to the bipolar transistor 2, the greater the current amplification factor h ＦＥ In other words, the Si bipolar transistor 2 has a relatively high radiation resistance, but the higher the applied voltage, the lower the current amplification factor h ＦＥ It was found that the degree of degradation of the material increases (the radiation resistance decreases).

[0042] Therefore, in the first embodiment, the collector-emitter voltage V ＣＥis set to be lower than the sum of the voltage of the output section 20 (load) and the voltage of the resistance element 4. In the configuration of Fig. 1, the voltage of the output section 20 means the voltage between the terminals 20a and 20b of the output section 20. Furthermore, the voltage of the resistance element 4 means the voltage of one terminal of the resistance element 4 (the terminal to which the wiring K4 is connected) when the ground potential (GND) is used as a reference.

[0043] As mentioned above, the voltage V of the bipolar transistor 2 ＣＥ is lower than the sum of the voltage of the output section 20 and the voltage of the resistance element 4, ＣＥ This reduces the current amplification factor h ＦＥ As a result, even if the radiation absorbed dose is several tens of kGy, the amplifier circuit 10 can function normally and a large current can flow through the output section 20.

[0044] <Effects> According to the first embodiment, the Si bipolar transistor 2 is connected in a subsequent stage to the operational amplifier 1 having the SiC MOSFET 40. This makes it possible to stably supply large amounts of power to the output section 20 using the operational amplifier 1 and the bipolar transistor 2 even in a high radiation environment.

[0045] Furthermore, according to the first embodiment, the collector-emitter voltage V of the bipolar transistor 2 ＣＥ is set to be lower than the sum of the voltage of the output section 20 and the voltage of the resistor element 4. Therefore, the current amplification factor h ＦＥ The amplifier circuit 10 having such a configuration has excellent radiation resistance and operational stability, and can function normally even in a harsh radiation environment.

[0046] Furthermore, the amplifier circuit 10 has a simple configuration, which reduces the effort and cost required to manufacture the amplifier circuit 10. As described above, according to the first embodiment, it is possible to provide an amplifier circuit 10 that has excellent radiation resistance and is capable of handling large power with a simple configuration.

[0047] Second Embodiment The second embodiment differs from the first embodiment in that a Zener diode 7 (see FIG. 5) is used instead of the DC power supply 5 (see FIG. 1) described in the first embodiment. Note that the other points are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0048] 5 is a circuit diagram including an amplifier circuit 10A according to a second embodiment. As shown in Fig. 5, the amplifier circuit 10A includes an operational amplifier 1, a bipolar transistor 2, a current adjusting resistor 3, a current detecting resistor 4, a voltage dividing resistor 6, and a Zener diode 7.

[0049] The Zener diode 7 is an element in which, when a predetermined Zener voltage (reverse voltage) is applied, the voltage across both ends remains substantially constant regardless of changes in current. The anode of the Zener diode 7 is connected to the wiring K3 at ground potential. The cathode of the Zener diode 7 is connected to another wiring K6 via wiring K5, and is also connected to the non-inverting input terminal 1a of the operational amplifier 1 via wiring K5 (part of wiring K5) and wiring K7 in this order. A predetermined DC voltage is applied to the non-inverting input terminal 1a of the operational amplifier 1 via the Zener diode 7.

[0050] <Effects> According to the second embodiment, the amplifier circuit 10A includes the Zener diode 7, so that the DC voltage V ＤＣ Even if the voltage fluctuates, the potential of the non-inverting input terminal 1 a of the operational amplifier 1 can be kept substantially constant. Furthermore, since there is no particular need to separately provide the DC power supply 5 (see FIG. 1 ) as described in the first embodiment, the manufacturing cost of the amplifier circuit 10A can be reduced.

[0051] Third Embodiment The third embodiment differs from the first embodiment in that a resistive element 8 (see FIG. 6) is used instead of the DC power supply 5 (see FIG. 1) described in the first embodiment. Note that the other points are the same as those of the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0052] 6 is a circuit diagram including an amplifier circuit 10B according to a third embodiment. As shown in Fig. 6, the amplifier circuit 10B includes an operational amplifier 1, a bipolar transistor 2, a current adjusting resistor element 3, a current detecting resistor element 4, and voltage dividing resistor elements 6 and 8.

[0053] The two resistor elements 6 and 8 are connected in series by a wiring K5. A predetermined DC voltage V ＤＣ The resistor element 8 is connected to the other resistor element 6 via a DC voltage V ＤＣ at a predetermined voltage division ratio (ratio of resistance values). One end of the resistance element 8 is connected to the other resistance element 6 via a wiring K5 (part), and the other end is connected to the wiring K3 of the ground potential via a wiring K5 (part).

[0054] Furthermore, one end of another wire K7 is connected to the wire K5 between the resistor elements 6 and 8. The other end of the wire K7 is connected to the non-inverting input terminal 1a of the operational amplifier 1. A predetermined DC voltage is applied to the non-inverting input terminal 1a of the operational amplifier 1 via the resistor element 8 (voltage dividing resistor).

[0055] <Effects> According to the third embodiment, the input DC voltage V ＤＣ is divided by two resistor elements 6 and 8, and the voltage across resistor element 8 is applied to the non-inverting input terminal 1a of the operational amplifier 1. This eliminates the need to separately provide the DC power supply 5 (see FIG. 1) as described in the first embodiment, thereby reducing the manufacturing cost of the amplifier circuit 10B. Furthermore, since the voltage division ratio can be changed by appropriately changing the resistance values ​​of the resistor elements 6 and 8, the voltage applied to the non-inverting input terminal 1a of the operational amplifier 1 can be easily changed.

[0056] Fourth Embodiment In the fourth embodiment, a lighting device 100 (see FIG. 7) including a light-emitting unit 20C (see FIG. 7) as the output unit 20 (see FIG. 1) described in the first embodiment will be described. The configuration of the amplifier circuit 10 is the same as in the first embodiment. Therefore, only the parts that are different from the first embodiment will be described, and a description of the overlapping parts will be omitted.

[0057] FIG. 7 is a circuit diagram of a lighting device 100 including an amplifier circuit according to a fourth embodiment. The lighting device 100 shown in FIG. 7 is a device that illuminates its surroundings and includes an amplifier circuit 10 and a light-emitting unit 20C. The light-emitting unit 20C is a "load" that emits light when power is supplied. For example, a light-emitting diode (LED) is used as the light-emitting unit 20C. The amplifier circuit 10 is electrically connected to the light-emitting unit 20C (load). The collector current of the bipolar transistor 2 flows through the light-emitting unit 20C, causing the light-emitting unit 20C to emit a predetermined amount of light.

[0058] Although the light-emitting diode used as the light-emitting unit 20C typically consumes more power than sensors used in nuclear power plants, the amplifier circuit 10 shown in Fig. 1 includes an operational amplifier 1 having a SiC MOSFET and a Si bipolar transistor 2. Therefore, a large amount of power can be stably supplied to the light-emitting unit 20C even in a radiation environment.

[0059] <Effects> According to the fourth embodiment, a large amount of power can be stably supplied from the amplifier circuit 10 to the light-emitting unit 20C even in a radiation environment. Therefore, for example, by using the lighting device 100 in a nuclear power plant, workers can easily conduct investigations and inspections. Furthermore, because the lighting device 100 is less likely to malfunction due to the effects of radiation, the frequency of replacing malfunctioning parts can be reduced, and thus the radiation exposure dose of workers can be reduced.

[0060] <<Modifications>> Although the amplifier circuit 10 and the lighting device 100 according to the present disclosure have been described in the above embodiments, they are not limited to these descriptions and various modifications can be made.

[0061] FIG. 8 is a circuit diagram including an amplifier circuit 10D according to a modified example. As shown in FIG. 8, the amplifier circuit 10D may include multiple bipolar transistors 21 to 23. These bipolar transistors 21 to 23 are all made of Si semiconductors. In the example of FIG. 8, the bipolar transistors 21 and 22 are NPN type, and the bipolar transistor 23 is a PNP type.

[0062] 8, the bipolar transistors 21 and 22 are connected in a Darlington configuration. Specifically, the base of the bipolar transistor 21 is connected to the output terminal 1c of the operational amplifier 1 via a wiring K1. The collector of the bipolar transistor 21 is connected to the collector of the bipolar transistor 22 in the subsequent stage via a wiring K8 and a part of a wiring K9 in this order. The emitter of the bipolar transistor 21 is connected to the base of the bipolar transistor 22 in the subsequent stage.

[0063] The collector of the bipolar transistor 22 is connected to the base of the subsequent bipolar transistor 23 via wiring K9. The emitter of the bipolar transistor 22 is connected to wiring K3 at ground potential via wiring K10. By connecting the two bipolar transistors 21 and 22 in a Darlington configuration in this way, the current amplification factor is significantly increased. A resistor element 9a for adjusting the current is provided on wiring K10. A bypass capacitor 9b is connected in parallel to the resistor element 9a.

[0064] 8 is an element that amplifies its base current (collector current of the preceding bipolar transistor 22). As described above, the base of the bipolar transistor 23 is connected to the collector of the preceding bipolar transistor 22 via the wiring K9.

[0065] The emitter of the bipolar transistor 23 is connected to the output section 20 via a wiring K2. That is, the bipolar transistor 23 is electrically connected to the output section 20 so that its emitter current flows to the output section 20 (load). The collector of the bipolar transistor 23 is connected to a wiring K3. A resistive element 4 for current detection is provided on this wiring K3. The collector current of the bipolar transistor 22 on the preceding stage is amplified by the bipolar transistor 23 on the subsequent stage. By using three bipolar transistors 21 to 23 in this way, the current amplification factor of the entire circuit can be significantly increased compared to the first embodiment.

[0066] The resistor element 4 shown in FIG. 8 is an element that detects the collector current of the bipolar transistor 23. The voltage of the resistor element 4 is applied to the inverting input terminal 1b of the operational amplifier 1. Explaining both the circuit configurations of the modified example of FIG. 8 and the first embodiment (see FIG. 1), the resistor element 4 functions as an element that detects one of the collector current and the emitter current of a "bipolar transistor" (the bipolar transistor 2 in FIG. 1 or the bipolar transistor 23 in FIG. 8). The "bipolar transistor" is electrically connected to the output section 20 (load) so that the other of the collector current and the emitter current flows to the output section 20.

[0067] 8, the bipolar transistor 23 may be omitted. In this case, the collector current of the rear-stage bipolar transistor 22 of the two Darlington-connected bipolar transistors 21 and 22 may be made to flow to the output section 20.

[0068] In addition, although the embodiments have been described with reference to the case where SiC is used as a semiconductor having a wider band gap than a Si semiconductor, this is not limiting. That is, diamond or gallium nitride (GaN) may also be used as a semiconductor having a wider band gap than a Si semiconductor.

[0069] In the first embodiment, an n-channel configuration has been described as an example of the lateral MOSFET 40 (see FIG. 3B) included in the operational amplifier 1 (see FIG. 1), but this is not limiting. That is, a p-channel MOSFET may be used as the lateral MOSFET included in the operational amplifier 1 (see FIG. 1). Furthermore, the multiple lateral MOSFETs included in the operational amplifier 1 (see FIG. 1) may be a mixture of n-channel and p-channel MOSFETs.

[0070] Furthermore, in each embodiment, the operational amplifier 1 (see FIG. 1) is configured as a non-inverting amplifier circuit, but this is not limiting. For example, the operational amplifier 1 may be configured as an inverting amplifier circuit. Furthermore, the method of applying negative feedback in the operational amplifier 1 of the first embodiment is merely an example, and various well-known circuit configurations are applicable. The same can be said for the second to fourth embodiments and the modified example (see FIG. 8).

[0071] Furthermore, in the fourth embodiment, the illumination device 100 (see FIG. 7 ) including the light-emitting unit 20C (see FIG. 7 ) has been described, but the present invention is not limited to this. For example, the fourth embodiment can also be applied to other equipment used for inspection and measurement of nuclear power plants. As the above-mentioned equipment, a sensor that detects physical quantities such as pressure and temperature, mass, flow rate, illuminance, luminous intensity, sound volume, viscosity, current, and voltage may be used. Furthermore, as the above-mentioned equipment, a flaw detection probe or the like may be used.

[0072] The amplifier circuit 10 and the output unit 20 can also be applied to facilities used in the space field (including rockets carrying artificial satellites, space probes, etc.) and predetermined radiation utilization facilities. Furthermore, the amplifier circuit 10 and the output unit 20 do not particularly need to be installed in a location exposed to severe radiation (a radiation controlled area), and may be installed in other predetermined facilities.

[0073] Furthermore, each embodiment has been described in detail to clearly explain the present disclosure, and is not necessarily limited to having all of the described configurations. Furthermore, some of the configurations of each embodiment can be added to, deleted from, or replaced with other configurations.

[0074] Furthermore, the above-described configurations, functions, processing units, processing means, etc. may be partially or entirely realized in hardware, for example, by designing them as integrated circuits. Furthermore, the mechanisms and configurations shown are those considered necessary for the explanation, and do not necessarily represent all mechanisms and configurations in the product. Furthermore, the control lines and information lines shown are those considered necessary for the explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected.

[0075] REFERENCE SIGNS LIST 1 operational amplifier 1a non-inverting input terminal 1b inverting input terminal 1c output terminal 2, 21, 22, 23 bipolar transistor 4 resistive element 5 DC power supply 7 Zener diode 8 resistive element (voltage dividing resistor) 10, 10A, 10B, 10D amplifier circuit 100 lighting device

Claims

1. An amplifier circuit comprising: an operational amplifier having a lateral MOSFET made of a semiconductor with a wider bandgap than a silicon semiconductor; a bipolar transistor made of a silicon semiconductor and electrically connected to the output side of the operational amplifier; and a resistive element that detects one of the collector current and the emitter current of the bipolar transistor, wherein the voltage of the resistive element is applied to the inverting input terminal of the operational amplifier, and a predetermined DC voltage is applied to the non-inverting input terminal of the operational amplifier, the bipolar transistor is electrically connected to a load so that the other of the collector current and the emitter current flows to the load, and the collector-emitter voltage of the bipolar transistor is lower than the sum of the voltage of the load and the voltage of the resistive element.

2. The amplifier circuit according to claim 1, wherein the semiconductor having a band gap wider than that of a Si semiconductor is SiC, diamond, or GaN.

3. The amplifier circuit according to claim 1, wherein the predetermined DC voltage is applied to the non-inverting input terminal from a DC power supply, or is applied to the non-inverting input terminal via a Zener diode or a voltage dividing resistor.

4. A lighting device comprising: a load that emits light when power is supplied; and an amplifier circuit electrically connected to the load, wherein the amplifier circuit comprises: an operational amplifier having a lateral MOSFET made of a semiconductor with a bandgap wider than that of a Si semiconductor; a bipolar transistor made of a Si semiconductor and electrically connected to the output side of the operational amplifier; and a resistive element that detects one of the collector current and the emitter current of the bipolar transistor, wherein the voltage of the resistive element is applied to the inverting input terminal of the operational amplifier; and a predetermined DC voltage is applied to the non-inverting input terminal of the operational amplifier; the bipolar transistor is electrically connected to the load so that the other of the collector current and the emitter current flows to the load; and the collector-emitter voltage of the bipolar transistor is lower than the sum of the voltage of the load and the voltage of the resistive element.

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