LEVEL SHIFT CIRCUIT, LEVEL DECISION DEVICE, AND LEVEL DECISION METHOD

Abstract

To provide a level shift circuit, a level determination device, and a level determination method, which realize low cost and space saving.SOLUTION: A level shift circuit 11 is provided that converts an input voltage to be output. The circuit includes: an input terminal 111; a first resistor R1, one end of which is connected to the input terminal 111; a second resistor R2, one end of which is connected to the other end of the first resistor R1; and a third resistance R3, one end of which is connected to the other end of the second resistor R2 and the other end of which is grounded. Further included are: a semiconductor switching element 113, a first terminal of which is grounded and a control terminal of which is connected to a connecting point between the second resistor R2 and the third resistance R3; a fourth resistance R4 connected between a connecting point between the first resistor R1 and the second resistor R2 and the second terminal of the semiconductor switching element 113; and an output terminal 112 connected to a connecting point between the first resistor R1 and the second resistor R2. In this circuit, a voltage characteristic line indicating an output voltage Vout with respect to an input voltage Vin has a linear region and a nonlinear region.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a level shift circuit, a level determining device, and a level determining method. [Background technology]

[0002] In vehicle low-current systems, interface circuits are used that use lead batteries or other devices with fluctuating voltages as signal sources. Meanwhile, the detection voltage of a microcomputer (MCU) that reads signals from the interface circuit has threshold values ​​(upper and lower limits). Since the voltage fluctuation range of the signal source and the detection voltage range of the MCU do not usually match, an interface that converts (level shifts) the voltage of the signal source into the detection voltage range of the MCU is required to read signals from the signal source with the MCU.

[0003] Patent Document 1 discloses an interface circuit that uses an integrated circuit (IC) to level-shift an input signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 61-81228 Summary of the Invention [Problem to be solved by the invention]

[0005] The interface circuit described in Patent Document 1 has problems in that it requires a large number of components, is large in size, and is expensive.

[0006] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a level shift circuit, a level determination device, and a level determination method that realize low cost and space saving. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a level shift circuit that converts an input voltage and outputs it. This circuit has an input terminal, a first resistor having one end connected to the input terminal, a second resistor having one end connected to the other end of the first resistor, and a third resistor having one end connected to the other end of the second resistor and the other end grounded. The circuit also has a semiconductor switching element having a first terminal grounded and a control terminal connected to a connection point between the second resistor and the third resistor, a fourth resistor connected between the connection point between the first resistor and the second resistor and a second terminal of the semiconductor switching element, and an output terminal connected to the connection point between the first resistor and the second resistor. In this circuit, a voltage characteristic line showing the output voltage with respect to the input voltage has a linear region and a nonlinear region. Effect of the Invention

[0008] According to the present invention, the level shift circuit is composed only of a semiconductor switching element and a plurality of resistors, which reduces the number of parts, thereby realizing low cost and space saving. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a low-current system including a level determining device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing voltage characteristic lines of the level shift circuit. [Diagram 3] FIG. 3 is a diagram showing voltage characteristic lines of a level shift circuit according to a comparative example. [Figure 4] FIG. 4 is a diagram showing voltage characteristic curves of the level shift circuit according to the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (First embodiment) FIG. 1 is a schematic diagram of a low-current system 100 including a level determining device 10 according to a first embodiment of the present invention.

[0012] The low-voltage system 100 includes a battery 1, a switch 2, a level determination device 10, etc. The low-voltage system 100 is mounted on a vehicle or the like, and the level determination device 10 determines whether the switch 2 is on or off, etc.

[0013] The battery 1 is a low-power battery for use in a vehicle, for example a lead battery with a voltage of 12 V. The battery 1 is connected to a level determination device 10 via a switch 2.

[0014] The switch 2 is, for example, an ignition switch of a vehicle. When the switch 2 is turned on manually or automatically, a signal (low-current) voltage is input from the battery 1 to the level determination device 10. That is, the switch 2 uses the battery 1, which is an in-vehicle low-current battery, as a supply source of signal power, and configures an electronic unit together with the battery 1.

[0015] In addition, when starting (restarting) the vehicle, a large amount of current is required, and therefore the voltage of the battery 1 may drop due to a voltage drop, while the voltage of the battery 1 may rise due to a surge or the like. That is, the voltage of the battery 1 fluctuates within a certain range. For example, the 12V lead battery in this embodiment may fluctuate from 6V to 24V, albeit momentarily.

[0016] The level determining device 10 is an electronic control unit (ECU) including a level shift circuit 11 serving as an interface circuit and a microcomputer 12.

[0017] The level shift circuit 11 shifts the input voltage V into a voltage within the range of the detection voltage of the microcomputer 12 and outputs it to the microcomputer 12. For example, when the range (threshold) of the detection voltage of the microcomputer 12 for a voltage of 5V is from 2.4V to 5V, the level shift circuit 11 converts the input voltage (which varies, for example, from 6V to 24V) input from the battery 1 via the switch 2 to a voltage within the range of 2.4V to 5V and outputs it. The operation of the level shift circuit 11 will be described in detail later.

[0018] The microcomputer 12 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM) and an input / output interface (I / O interface), and reads the signal input from the level shift circuit 11 and determines the level of the input signal. The microcomputer 12 determines, for example, whether the level of the signal input from the switch 2 via the level shift circuit 11 is High (on) or Low (off).

[0019] As described above, the low-voltage system 100 uses the interface circuit (level shift circuit) 11 that uses the battery 1, whose voltage fluctuates, as a signal source, but the detection voltage of the microcomputer 12 that reads the signal from the interface circuit 11 has threshold values ​​(upper and lower limits). Since the voltage fluctuation range of the signal source (battery) 1 and the detection voltage range of the microcomputer 12 do not match, the level shift circuit 11 converts (level shifts) the voltage of the signal source (battery) 1 into the detection voltage range of the microcomputer 12.

[0020] However, if an interface circuit for converting the voltage of a signal source into the range of the detection voltage of a microcomputer is configured using an expensive integrated circuit (IC) with a large number of parts, the size becomes large and the cost becomes high. In contrast, the level shift circuit 11 of this embodiment is configured only with a semiconductor switching element (transistor) 113 and multiple resistors R1 to R4 as described later, thereby realizing low cost and space saving.

[0021] The configuration and operation of the level shift circuit 11 will be described below with reference to FIGS.

[0022] As shown in FIG. 1, the level shift circuit 11 includes an input terminal 111, an output terminal 112, a semiconductor switching element 113, and first to fourth resistors R1 to R4.

[0023] One end of the input terminal 111 is connected to the switch 2, and the other end is connected to the first resistor R1. One end of the first resistor R1 is connected to the input terminal 111, and the other end is connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to one end of the third resistor R3. The other end of the third resistor R is grounded. In addition, the connection point between the first resistor R1 and the second resistor R2 is connected to one end of the fourth resistor R4 and the output terminal 112.

[0024] The semiconductor switching element 113 is a bipolar transistor (hereinafter referred to as a transistor) with a first terminal (emitter) grounded, a control terminal (base) connected to the connection point between the second resistor R2 and the third resistor R3, and a second terminal (collector) connected to a fourth resistor R4. The fourth resistor R4 is connected between the connection point between the first resistor R1 and the second resistor R2 and the second terminal (collector) of the transistor 113.

[0025] FIG. 2 shows the input voltage V of the level shift circuit 11. in Output voltage V out 2 is a diagram showing voltage characteristic lines (hereinafter referred to as voltage characteristic lines) indicating that the transistor 113 is in an off state, the transistor 113 is in a half-on state, and the transistor 113 is in an on state.

[0026] The output voltage V of the level shift circuit 11 out is a predetermined first threshold V outth1 In a region A1 where V is less than V, the transistor 113 is in an off state. When the transistor 113 is in an off state, the output voltage V out is a voltage division value between the first resistor R1 and the second and third resistors R2 and R3. Since the resistance values ​​of the first to third resistors R1 to R3 are constant, when the transistor 113 is in the off state, the voltage characteristic line is linear, as shown in area A1 of FIG.

[0027] The output voltage V of the level shift circuit 11 out is the first threshold V outth1 or more and a predetermined second threshold value V outth2 In a region A2 where V is less than 1 V, the transistor 113 is in a half-on state. When the transistor 113 is in a half-on state, the output voltage V out is the divided voltage value between the first resistor R1, the second resistor R2, the third resistor R3, the second resistor R2 and the base-emitter voltage Vbe of the transistor 113, and the fourth resistor R4 and the collector-emitter voltage Vce of the transistor 113, whichever has the smaller impedance.

[0028] When the transistor 113 is in a half-on state, the first to fourth resistors R1 to R4 are adjusted according to the physical properties of the transistor 113, so that the voltage characteristic line becomes a nonlinear curve as shown in region A2 of Fig. 2. For example, by setting the first resistor R1 to about 30 kΩ, the second resistor R2 to about 20 kΩ, the third resistor R3 to about 5 kΩ, and the fourth resistor R4 to about 10 kΩ according to the physical properties of the transistor 113, a voltage characteristic line having a nonlinear region as shown in Fig. 2 can be obtained. As shown in Fig. 2, in region A2, the slope of the voltage characteristic line curve is gentler than in the linear region.

[0029] The output voltage V of the level shift circuit 11 out is the second threshold V outth2 In the region A3, the transistor 113 is in the on state. When the transistor 113 is in the on state, the output voltage V out is a voltage division value between the first resistor R1 and the fourth resistor R4. Since the resistance values ​​of the first and fourth resistors R1 and R4 are constant, when the transistor 113 is in the on state, the voltage characteristic line is linear, as shown in area A3 in FIG.

[0030] As described above, the input voltage V of the level shift circuit 11 in Output voltage V outThe voltage characteristic line showing the voltage difference is a linear curve when the transistor 113 is in the on or off state, and a nonlinear curve when the transistor 113 is in the half-on state. That is, in this embodiment, the voltage characteristic line has a linear region and a nonlinear region.

[0031] In addition, in the level shift circuit 11, the input voltage V in The resistance values ​​of the resistors R1 to R4 and the operation of the transistor 113 are set so that the input voltage V from the switch 2 (i.e., the voltage of the battery 1) is converted into a range of the detection voltage of the microcomputer 12. As shown in FIG. in The minimum value of V inmin Output voltage V out is the lower limit of the detection voltage of the microcomputer 12 (hereinafter referred to as the lower limit of the microcomputer 12) V outmin On the other hand, the input voltage V in Maximum value of V inmax Output voltage V out is the upper limit of the detection voltage of the microcomputer 12 (hereinafter referred to as the upper limit of the microcomputer 12) V outmax or upper limit V outmax The voltage from switch 2 to the level shift circuit 11 is set to the following value. inmin From V inmax When a voltage in the range of V in V outmin From V outmax The voltage is converted to a range of V and output to the microcomputer 12. outmin From V outmax When a voltage within the range of V, i.e., the range of the detection voltage of the microcomputer 12, is input, the microcomputer 12 determines that the level of the input signal is High (i.e., the switch 2 is on). outmin If the voltage is not equal to or greater than this, the microcomputer 12 determines that the level of the input signal is Low (that is, the switch 2 is off).

[0032] The signal voltage input from switch 2, which is the ignition switch, is V inmin Below that, the microcomputer 12 is V outminWhen the signal voltage above this level is no longer input, the microcomputer 12 ends its operation, and the low-power system 100 enters a termination sequence. On the other hand, when the signal voltage input from the switch 2, which is an ignition switch, is V inmax When the voltage exceeds a certain upper limit, the microcomputer 12 detects outmax When a signal voltage exceeding this value is input, the microcomputer 12 determines that a high voltage abnormality has occurred.

[0033] Here, the input voltage V in is the minimum value V inmin In this case, if the voltage characteristic line is in a region where the nonlinear curve is gentle (the slope of the voltage characteristic line is gentle), the input voltage V in is the minimum value V inmin When the input voltage V in is the minimum value V inmin When the output voltage V out is almost the lower limit of microcomputer 12 V outmin The input voltage V in The minimum value of V inmin is the branch point where the microcontroller 12 judges the signal level as High or Low, so the input voltage V in The minimum value of V inmin If the input voltage V is in a nonlinear region where the slope of the voltage characteristic line is gentle, it becomes difficult to distinguish between High and Low signal levels. Therefore, it becomes difficult to determine whether the switch 2 is on or off, which may result in an erroneous determination. In contrast, in the level shift circuit 11 of this embodiment, in is the minimum value V inmin The operation of the transistor 113 is set so that the voltage characteristic line is in a linear region in the case of . Specifically, the first threshold V outth1 However, the lower limit V of the microcomputer 12 outmin This sets the input voltage V in is the minimum value V inmin In the case of output voltage V outmin is the first threshold V outth1 Therefore, the transistor 113 is always in an off state. in is the minimum value V inminIn this case, the voltage characteristic line is in the linear region. This makes it clear that the signal from switch 2 is divided into high and low levels, making it easy to determine whether switch 2 is on or off. This prevents erroneous determination.

[0034] In addition, when an operational amplifier or the like is used as an interface circuit (level shift circuit) for converting the voltage of the signal source into the range of the detection voltage of the microcontroller 12, the input voltage V in Output voltage V out The voltage characteristic line showing the input voltage V in Output voltage V for fluctuations in out Therefore, the fluctuation range of the input voltage V in If the fluctuation range of is large, the input voltage V in Output voltage V out is the upper limit of the detection voltage of the microcontroller, V outmax That is, the input voltage V in For example, in Figure 3, the input voltage V in is the maximum value V inmax In the case of output voltage V out is the upper limit of the detection voltage of the microcontroller, V outmax In contrast, in this embodiment, the voltage characteristic line has a nonlinear region with a gentle slope, so the input voltage V in Output voltage V for fluctuations in out Therefore, the fluctuation range of the input voltage V in Even when the input voltage V in to the desired range of output voltage V out In this embodiment, the input voltage V in is the maximum value V inmax Even if the output voltage V out is the upper limit of the detection voltage of the microcontroller 12, V outmaxA second threshold V outth2 This sets the input voltage V in Even if the input voltage V in is converted into a detection voltage range of the microcomputer 12, and it is possible to determine whether the switch 2 is on or off.

[0035] According to the level shift circuit 11, the level determining device 10, and the level determining method of the first embodiment described above, the following effects can be obtained.

[0036] The level shift circuit 11 includes an input terminal 111, a first resistor R1 having one end connected to the input terminal 111, a second resistor R2 having one end connected to the other end of the first resistor R1, and a third resistor R3 having one end connected to the other end of the second resistor R2 and the other end grounded. The level shift circuit 11 also includes a transistor (semiconductor switching element) 113 having a first terminal grounded and a control terminal connected to a connection point between the second resistor R2 and the third resistor R3, a fourth resistor R4 connected between the connection point between the first resistor R1 and the second resistor R2 and a second terminal of the transistor (semiconductor switching element) 113, and an output terminal 112 connected to the connection point between the first resistor R1 and the second resistor R2. The level shift circuit 11 outputs an input voltage V in and output it, while also converting the input voltage V in Output voltage V out The voltage characteristic line showing the input voltage V in The level shift circuit 11, which converts and outputs the signal, is composed of only a transistor (semiconductor switching element) 113 and a plurality of resistors R1 to R4. This reduces the number of components, thereby achieving low costs and space savings.

[0037] In addition, since the voltage characteristic line of the level shift circuit 11 has a nonlinear region, the input voltage V in Output voltage V for fluctuations in out The fluctuation range of is smaller than when the voltage characteristic line has only a linear region. This allows the fluctuation of the input voltage V incan be converted to a voltage in the desired range and output.

[0038] According to the level determination method using the level shift circuit 11, the input terminal 111 is connected to the switch 2, and the output voltage V out is within a predetermined range, it is determined that switch 2 is on. In addition, the voltage characteristic line of level shift circuit 11 has a linear region and a nonlinear region. Therefore, by adjusting the branch point of the voltage characteristic line for determining whether switch 2 is High (on) or Low (off) to be in the linear region, the division between High and Low of the signal from switch 2 becomes clear, making it easier to determine whether switch 2 is on or off. In other words, erroneous determination can be prevented.

[0039] In addition, since the voltage characteristic line of the level shift circuit 11 has a nonlinear region, the input voltage V in Output voltage V for fluctuation range out The fluctuation range of the input voltage V can be made smaller than when the voltage characteristic line has only a linear region. in Even if the fluctuation of V out That is, the input voltage V in Even if the fluctuation in the output voltage is large, it is possible to determine whether the switch 2 is on or off.

[0040] The level determination device 10 includes a microcomputer 12 that determines whether the switch 2 is on or off, and performs level determination of the signal of the switch 2 using a level shift circuit 11. The level shift circuit 11 converts the input voltage V in The microcomputer 12 converts the output voltage V outis within the range of the detection voltage of the microcomputer 12, it is determined to be on. Since the voltage characteristic line of the level shift circuit 11 has a linear region and a nonlinear region, the branch point of the voltage characteristic line for determining whether the input signal is high or low can be adjusted so that it is in the linear region of the voltage characteristic line, thereby making it possible to clearly distinguish between high and low input signals. This makes it easier for the microcomputer 12 to determine whether the switch 2 is on (high) or off (low), and makes it possible to prevent erroneous determinations.

[0041] In addition, since the level judgment device 10 uses the level shift circuit 11 whose voltage characteristic curve has a nonlinear region, the input voltage V in Output voltage V for fluctuations in out Therefore, the fluctuation range of the input voltage V from switch 2 can be reduced. in Even if the fluctuation of the output voltage V out is the upper limit V of the detection voltage of the microcomputer 12. outmax Therefore, the level shift circuit 11 can be adjusted so that the input voltage V from the switch 2 does not exceed in Even when the fluctuation in the output voltage is large, it is possible to determine whether the switch 2 is on or off.

[0042] In the level determination device 10, the level shift circuit 11 includes a transistor 113. The transistor 113 is connected to the output voltage V out is a predetermined first threshold V outth1 OFF state when less than the first threshold V outth1 or more and a predetermined second threshold value V outth2 When the second threshold V outth2 In the above cases, the output voltage V out is the lower limit V of the detection voltage of the microcomputer 12 outmin In other words, the transistor 113 is in an off state when the first threshold V outth1 But, V outminOn the other hand, the output voltage V out is the upper limit V of the detection voltage of the microcomputer 12. outmax In this case, the transistor 113 is in an on state. out V outmin When the input signal is turned on, the transistor 113 is adjusted to be in the off state, so that the branch point for determining whether the input signal is high or low on the voltage characteristic line is in a linear region. This makes it clearer to distinguish between high and low signals from the switch 2, making it easier for the microcomputer 12 to determine whether the switch 2 is on or off. This makes it possible to prevent erroneous determination.

[0043] Also, the output voltage V out is the first threshold V outth1 or more and a predetermined second threshold value V outth2 Since the transistor 113 is in a half-on state when the input voltage V in Output voltage V for fluctuations in out Therefore, the fluctuation range of the second threshold V outth2 By appropriately setting and adjusting the half-off region, the input voltage V in is the maximum value V inmax Even if the output voltage V out is the upper limit of the detection voltage of the microcontroller 12, V outmax Therefore, the input voltage V from switch 2 can be prevented from exceeding in Even if the fluctuation of the output voltage V out can be converted into the range of the detection voltage of the microcomputer 12, so that the on / off state of the switch 2 can be reliably determined.

[0044] In this embodiment, the switch 2 is an ignition switch, but the switch 2 is not limited to this. However, it is preferable that the switch 2 be a switch that is not frequently switched on and off, such as an air conditioner switch.

[0045] In addition, in the present embodiment, the low-current system 100 including the level determining device 10 is mounted on a vehicle, but this is not necessarily limited to this, and the level determining device 10 does not necessarily have to be mounted on a vehicle.

[0046] Furthermore, in this embodiment, the battery 1 is a 12V lead battery, but the type of battery 1 is not limited to this.

[0047] In this embodiment, the first resistor R1 is about 30 kΩ, the second resistor R2 is about 20 kΩ, the third resistor R3 is about 5 kΩ, and the fourth resistor R4 is about 10 kΩ, but the resistance values ​​of the resistors R1 to R4 are not limited to these. The resistance values ​​of the resistors R1 to R4 are determined so that the voltage characteristic line of the level shift circuit 11 has a linear region and a nonlinear region, and the output voltage V out is set so as to fall within the range of the voltage detected by the microcomputer 12, and may be any value within the range that satisfies this condition.

[0048] (Modification of the first embodiment) A level determination device 10 according to a modified example of the first embodiment will be described with reference to Fig. 4. Note that the same elements as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted.

[0049] 4 is a diagram showing voltage characteristic curves of the level shift circuit 11 according to a modification of the first embodiment. This modification is different from the first embodiment in that the branch point for determining whether the input signal is High or Low on the voltage characteristic curve is in the region A2 where the transistor 113 is in the half-on state.

[0050] As shown in FIG. 1 and FIG. 4, the input voltage V in Output voltage V outThe voltage characteristic line showing the output voltage V has a linear characteristic in the regions A1 and A3 where the transistor 113 is in the off or on state, and has a non-linear characteristic in the region A2 where the transistor 113 is in the half-on state. However, even in the region A2 where the transistor 113 is in the half-on state, the voltage characteristic line has an almost linear characteristic in a portion close to the region A1 where the transistor 113 is in the off state. out is a first threshold V outth1 Even if the voltage characteristic curve is larger than 10 V, the voltage characteristic curve has a nearly linear characteristic up to a certain point.

[0051] In this modification, the level shift circuit 11 is adjusted so that the branch point of the voltage characteristic line for determining whether the input signal is high or low is in a substantially linear region within the region A2 of the half-on state of the transistor 113. In this way, even if the branch point for determining whether the input signal is high or low is in the region A2 of the half-on state of the transistor 113, the signal from the switch 2 is clearly separated into high and low as long as the voltage characteristic line is in a substantially linear portion. Therefore, the microcomputer 12 can easily determine whether the input signal is on or off, and erroneous determination is prevented.

[0052] In each embodiment, the level shift circuit 11 uses a bipolar transistor as the semiconductor switching element 113, but this is not necessarily limited to this. In other words, the level shift circuit 11 may be constructed using other semiconductor switching elements as long as the voltage characteristic line can be set to have a linear region and a nonlinear region. For example, the semiconductor switching element 113 may be a MOSFET, an IGBT, or the like.

[0053] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments.

[0054] Although the above-described embodiments have been described as separate embodiments, they may be combined as appropriate. [Explanation of symbols]

[0055] 1, battery, 2, switch, 10, level determination device, 11, level shift circuit, 12, microcomputer, 111, input terminal, 112, output terminal, 113, transistor (semiconductor switching element), 100, low-current system

Claims

1. A level shift circuit that converts an input voltage and outputs the converted voltage, An input terminal; A first resistor having one end connected to the input terminal; a second resistor having one end connected to the other end of the first resistor; a third resistor, one end of which is connected to the other end of the second resistor and the other end of which is grounded; a semiconductor switching element having a first terminal grounded and a control terminal connected to a connection point between the second resistor and the third resistor; a fourth resistor connected between a connection point between the first resistor and the second resistor and a second terminal of the semiconductor switching element; an output terminal connected to a connection point between the first resistor and the second resistor, A voltage characteristic line showing an output voltage relative to an input voltage has a linear region and a nonlinear region. Level shift circuit.

2. A level determination device using the level shift circuit according to claim 1, A microcomputer is provided to determine whether the switch is on or off, the level shift circuit, the input terminal of which is connected to the switch, converts an input voltage from the switch and outputs the converted voltage to the microcomputer; the microcomputer determines that the level shift circuit is on when the output voltage from the level shift circuit is within a range of a detection voltage of the microcomputer; Level determination device.

3. 3. The level determination device according to claim 2, the semiconductor switching element is a transistor, the transistor is in an off state when the output voltage of the level shift circuit is less than a predetermined first threshold, in a half-on state when the output voltage is equal to or greater than the first threshold and less than a predetermined second threshold, and in an on state when the output voltage is equal to or greater than the second threshold, When the output voltage is equal to a lower limit of a detection voltage of the microcomputer, the transistor is in an off state or a half-on state; When the output voltage is equal to an upper limit value of a detection voltage of the microcomputer, the transistor is in an on state. Level determination device.

4. 4. The level determination device according to claim 2, The switch uses an on-board low-power battery as a power supply source, and constitutes an electronic unit together with the on-board low-power battery. Level determination device.

5. 5. A level determination device according to claim 2, further comprising: The switch is an ignition switch. Level determination device.

6. 6. The level determination device according to claim 5, When the ignition switch is turned on, a signal voltage is input to the level shift circuit. Level determination device.

7. 7. The level determination device according to claim 5, When the signal voltage of the ignition switch falls below a predetermined lower limit, the microcomputer ends its operation. When the signal voltage of the ignition switch exceeds a predetermined upper limit value, the microcomputer determines that a high voltage abnormality has occurred. Level determination device.

8. A level judgment method in which a microcomputer performs judgment using the level shift circuit according to claim 1, The input terminal is connected to a switch, The microcomputer determines that the switch is on when the output voltage from the output terminal is within a predetermined range. How to determine the level.

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