Startup and shutdown circuit

Abstract

The utility model discloses a startup and shutdown circuit which comprises a switch S1, a first voltage dividing unit, an energy storage unit, a first switch assembly, a second switch assembly, an MOS tube Q1, an MOS tube Q2, a second voltage dividing unit and a control chip MCU. The first switch assembly is provided with a first connecting end to a third connecting end, and the second switch assembly is provided with a fourth connecting end to a sixth connecting end; one end of the first voltage dividing unit is connected with a power supply VBAT + and a source electrode of the MOS tube Q1, the other end of the first voltage dividing unit is connected with the switch S1 and the energy storage unit, the other end of the switch S1 is grounded, the other end of the energy storage unit is connected with the first connecting end, a grid electrode of the MOS tube Q1 is electrically connected with the first voltage dividing unit, and the second connecting end is connected with a drain electrode of the MOS tube Q1, a source electrode of the MOS tube Q2 and the second voltage dividing unit. The third connecting end is connected with the fourth connecting end and the IO pin of the control chip MCU, the fifth connecting end is grounded, the sixth connecting end is connected with the other end of the second voltage dividing unit, the grid electrode of the MOS tube Q2 is connected with the second voltage dividing unit, and the drain electrode of the MOS tube Q2 is connected with the VCC pin of the control chip MCU.

Description

Technical Field

[0001] This utility model relates to the field of power on / off circuit technology, specifically, to a power on / off circuit. Background Technology

[0002] A power switch circuit is a circuit structure in electronic devices used to control the on / off state of power. Current smart home products typically use hardware switches to directly control the physical connection of the lithium battery, achieving direct battery disconnection and connection through the switch's own on / off action. Although the control circuit design of a hardware switch is relatively simple, the rapid voltage or current changes when the switch is turned on or off create a violent switching action, which can easily cause arcing and damage to circuit components. Furthermore, with a hardware switch control scheme, if the switch remains closed even when the product's control system malfunctions, the lithium battery continues to power the system, potentially leading to circuit damage. Utility Model Content

[0003] To address the shortcomings of existing technologies, a power-on / off circuit is provided.

[0004] To achieve the above objectives, this utility model provides a power-on / off circuit, including a switch S1, a first voltage divider unit, an energy storage unit, a first switch assembly, a second switch assembly, MOSFETs Q1 and Q2, a second voltage divider unit, and a control chip MCU. The first switch assembly has a first connection terminal, a second connection terminal, and a third connection terminal, and the second switch assembly has a fourth connection terminal, a fifth connection terminal, and a sixth connection terminal. One end of the first voltage divider unit is connected to the power supply VBAT+ and the source of MOSFET Q1, and the other end is connected to one end of the switch S1 and one end of the energy storage unit. The other end of the switch S1 is grounded, and the other end of the energy storage unit is connected to the first connection terminal. The gate of MOSFET Q1 is electrically connected to the first voltage divider unit. The second connection terminal is connected to the drain of MOSFET Q1, the source of MOSFET Q2, and one end of the second voltage divider unit. The third connection terminal is connected to the fourth connection terminal and the IO pin of the control chip MCU. The fifth connection terminal is grounded, and the sixth connection terminal is connected to the other end of the second voltage divider unit. The gate of MOSFET Q2 is connected to the second voltage divider unit, and the drain of MOSFET Q2 is connected to the VCC pin of the control chip MCU.

[0005] According to one embodiment of the present invention, the first switching assembly includes a resistor R6, a resistor R4, and a transistor Q3. One end of the resistor R6 is connected to the energy storage unit, and the other end is connected to the base of the resistor R4 and the transistor Q3. The other end of the resistor R4 is connected to the emitter of the transistor Q3, the drain of the MOSFET Q1, the source of the MOSFET Q2, and the second voltage divider unit. The collector of the transistor Q3 is connected to the fourth connection terminal and the IO pin of the control chip MCU.

[0006] According to one embodiment of the present invention, the second switching assembly includes a resistor R7, a resistor R8, and a transistor Q4. One end of the resistor R7 is connected to the third connection terminal and the IO pin of the control chip MCU. One end of the resistor R8 is connected to the base of the resistor R7 and the transistor Q4, and its other end is connected to ground along with the emitter of the transistor Q4. The collector of the transistor Q4 is connected to the second voltage divider unit.

[0007] According to one embodiment of the present invention, it further includes a voltage regulator component, the input terminal of which is connected to the drain of the MOS transistor Q2, and its output terminal is connected to the VCC pin of the control chip MCU.

[0008] According to one embodiment of the present invention, the voltage regulator component includes a first filter unit, a voltage regulator chip U1, and a second filter unit. One end of the first filter unit is connected to the drain of the MOS transistor Q2, and the other end is connected to the input terminal of the voltage regulator chip U1. The output terminal of the voltage regulator chip U1 is connected to one end of the second filter unit, and the other end of the second filter unit is connected to the VCC pin of the control chip MCU.

[0009] According to one embodiment of the present invention, it further includes a diode DD1B, the anode of which is connected to the drain of the MOSFET Q2, and the cathode of which is connected to the VCC pin of the control chip MCU.

[0010] According to one embodiment of the present invention, it further includes a diode D1, the negative terminal of which is connected to the third connection terminal and the fourth connection terminal respectively, and the positive terminal of which is connected to the IO pin of the control chip MCU.

[0011] According to one embodiment of the present invention, the first voltage divider unit includes resistor R1 and resistor R3. One end of resistor R1 is connected to the power supply VBAT+ and the source of MOSFET Q1, respectively. The other end of resistor R1 is connected to the gate of MOSFET Q1 and resistor R3, respectively. The other end of resistor R3 is connected to switch S1 and energy storage unit, respectively.

[0012] According to one embodiment of the present invention, the second voltage divider unit includes resistor R2 and resistor R5. One end of resistor R2 is connected to the drain of MOSFET Q1, the source of MOSFET Q2 and the second connection terminal, respectively. The other end of resistor R2 is connected to the gate of MOSFET Q2 and resistor R5, respectively. The other end of resistor R5 is connected to the sixth connection terminal.

[0013] The beneficial effects of this invention are as follows: Power is supplied to the control chip MCU by sequentially turning on MOSFET Q1, the first switching assembly, the second switching assembly, and MOSFET Q2. The energy storage characteristics of the energy storage unit are utilized to control the on / off state of the first switching assembly, thereby controlling the switching of subsequent circuits. This avoids directly disconnecting and connecting the battery using a physical switch, preventing arcing and effectively protecting the components in the circuit. Furthermore, even if switch S1 is closed in the event of a circuit malfunction, the control chip MCU can detect the malfunction. When the circuit malfunctions, the MCU's I / O pins maintain a low-level signal, preventing continuous power supply to the circuit and thus protecting it. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0015] Figure 1 This is a power-on / off circuit diagram from an embodiment.

[0016] Reference numerals

[0017] 1. First voltage divider unit; 2. Energy storage unit 2; 3. First switching assembly; 31. First connection terminal; 32. Second connection terminal; 33. Third connection terminal; 4. Second switching assembly; 41. Fourth connection terminal; 42. Fifth connection terminal; 43. Sixth connection terminal; 5. Second voltage divider unit; 6. Voltage regulator assembly; 61. First filter unit; 62. Second filter unit. Detailed Implementation

[0018] The following drawings will disclose several embodiments of this utility model. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details should not be used to limit this utility model. That is, in some embodiments of this utility model, these practical details are not essential. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0019] Furthermore, in this utility model, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the utility model. They are merely used to distinguish components or operations described with the same technical terms and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0020] Please refer to Figure 1 , Figure 1 Figure 1 This embodiment provides a power-on / off circuit diagram, including a switch S1, a first voltage divider unit 1, an energy storage unit 2, a first switching assembly 3, a second switching assembly 4, MOSFETs Q1 and Q2, a second voltage divider unit 5, a voltage regulator assembly 6, and a control chip MCU. The first switching assembly 3 has a first connection terminal 31, a second connection terminal 32, and a third connection terminal 33. The second switching assembly 4 has a fourth connection terminal 41, a fifth connection terminal 42, and a sixth connection terminal 43. During connection, one end of the first voltage divider unit 1 is connected to the power supply VBAT+ and the source of MOSFET Q1. The other end of the first voltage divider unit 1 is connected to the switch S1 and the energy storage unit 2, and the other end of the switch S1 is grounded. The other end of the energy storage unit 2 is connected to the first connection terminal 31 of the first switching assembly 3. The gate of MOSFET Q1 is electrically connected to the first voltage divider unit 1, and the second connection terminal 32 of the first switching assembly 3 is connected to the drain of MOSFET Q1, the source of MOSFET Q2, and one end of the second voltage divider unit 5. The third connection terminal 33 of the first switching component 3 is connected to the fourth connection terminal 41 of the second switching component 4 and the IO interface of the control chip MCU. The fifth connection terminal 42 of the second switching component 4 is grounded, and the sixth connection terminal 43 of the second switching component 4 is connected to the other end of the second voltage divider unit 5. The gate of MOSFET Q2 is connected to the second voltage divider unit 5, and the drain of MOSFET Q2 is connected to the VCC pin of the control chip MCU. In this example, both MOSFETs Q1 and Q2 are PMOS transistors, and the energy storage unit 2 is capacitor C5.

[0021] Specifically, in actual use, in the initial state, switch S1 is open, and the entire circuit is in a powered-off state. When the circuit needs to be turned on, the user manually closes switch S1, and the power supply VBAT+ supplies power to MOSFET Q1 after being divided by the first voltage divider unit 1. In this example, the power supply VBAT+ is provided by an externally connected lithium battery. At this time, after being divided by the first voltage divider unit 1, the source voltage of MOSFET Q1 is higher than its gate voltage, causing MOSFET Q1 to conduct. The electrical signal output by the power supply VBAT+ flows sequentially through MOSFET Q1, the second connection terminal 32 of the first switching assembly 3, and the first connection terminal 31 to charge the energy storage unit 2. During the charging process of energy storage unit 2, the voltage of energy storage unit 2 gradually rises. Since energy storage unit 2 is connected in series with the first connection terminal 31 of the first switching unit, as the voltage of energy storage unit 2 rises, the voltage of the first connection terminal 31 of the first switching unit gradually decreases, and the first connection terminal 31 of the first switching unit becomes low-level, causing the first connection terminal 31 of the first switching assembly 3 to conduct with the third connection terminal 33. At this time, the fourth connection terminal 41 of the second switching component 4 is at a high level, causing the second switching component 4 to conduct. After the second switching component 4 is turned on, the gate level of the MOSFET Q4 is pulled low by the sixth connection terminal 43 of the second component, causing the MOSFET Q2 to conduct. After the MOSFET Q2 is turned on, the power supply signal VBAT+ supplies power to the control chip MCU through the MOSFET Q2, enabling the control chip MCU to work normally.

[0022] When the MCU (Microcontroller Unit) starts working, it determines if the circuit is malfunctioning. If the MCU determines the circuit is functioning normally, it sends a high-level signal to its I / O pins, keeping the fourth connection terminal 41 of the second switch assembly 4 high to maintain the second switch assembly 4's conduction and ensure continuous power supply to the circuit, thus completing the power-on process. If the MCU determines the circuit is malfunctioning, it outputs a low-level signal from its I / O pins. At this time, after the energy storage unit 2 is fully charged, the first connection terminal 31 of the first switch assembly 3 returns to a high level, causing both the first connection terminal 31 and the third connection terminal 33 of the first switch assembly 3 to stop conducting. Consequently, there is no voltage at the fourth connection terminal 41 of the second switch assembly 4, causing the second switch assembly 4 to turn off. This causes the gate of the MOSFET Q2 to return to a high level, and the MOSFET Q2 turns off. At this point, the voltage regulator assembly 6 and the MCU cannot receive power, and the circuit returns to the power-off state.

[0023] When the circuit is powered on, there are two ways to power it off. One is a hardware shutdown: the user manually disconnects switch S1, turning off MOSFET Q1 and preventing the circuit from conducting. The other is a soft shutdown: switch S1 remains closed, and the MCU's I / O pin generates a low level, causing the fourth connection terminal 41 of the second switch assembly 4 to go low, turning off the second switch assembly 4 and consequently, turning off MOSFET Q2. This prevents the circuit from conducting, thus completing a soft shutdown. It should be noted that if a soft shutdown is used, the circuit must be turned on again by disconnecting and then closing switch S1.

[0024] Thus, by sequentially turning on MOSFET Q1, the first switching assembly 3, the second switching assembly 4, and MOSFET Q2, power is supplied to the control chip MCU. The energy storage characteristics of the energy storage unit 2 are used to control the on / off state of the first switching assembly 3, thereby controlling the switching of subsequent circuits. This avoids directly disconnecting and connecting the battery using a physical switch, preventing arcing and effectively protecting the components in the circuit. Furthermore, even if a circuit malfunction occurs and switch S1 is closed, the control chip MCU can detect the malfunction. When a circuit malfunction occurs, the MCU's I / O pins maintain a low-level signal, preventing continuous power supply to the circuit and thus protecting it.

[0025] Furthermore, the first switching assembly 3 includes resistors R6 and R4, and transistor Q3. One end of resistor R6 is connected to the energy storage unit 2, and the other end of resistor R6 is connected to resistor R4 and the base of transistor Q3. The other end of resistor R4 is connected to the emitter of transistor Q3, the drain of MOSFET Q1, the source of MOSFET Q2, and the second voltage divider unit 5. Resistors R6 and R4 are used for voltage division. The collector of transistor Q3 is connected to the fourth connection terminal 41 of the second switching assembly 4 and the I / O pin of the control chip MCU. In this example, transistor Q3 is a PNP transistor.

[0026] It should be noted that the end of resistor R6 connected to energy storage unit 2 is the first connection terminal 31 of the first switching assembly 3, the end of resistor R4 connected to the emitter of transistor Q3 is the second connection terminal 32 of the first switching assembly 3, and the collector of transistor Q3 is the third connection terminal 33 of the first switching assembly 3.

[0027] The second switching assembly 4 includes resistors R7 and R8, and transistor Q4. One end of resistor R7 is connected to the third connection terminal 33 of the first switching assembly 3 and the I / O pin of the control chip MCU. The other end of resistor R7 is connected to resistor R8 and the base of transistor Q4. The other end of resistor R8 and the emitter of transistor Q4 are connected to ground. The collector of transistor Q4 is connected to the second voltage divider unit 5. The end of resistor R7 connected to the third connection terminal 33 of the first switching assembly 3 is the fourth connection terminal 41 of the second switching assembly 4; the end of resistor R8 connected to the emitter of transistor Q4 is the fifth connection terminal 42 of the second switching assembly 4; and the collector of transistor Q4 is the sixth connection terminal 43 of the second switching assembly 4.

[0028] In this example, transistor Q4 is an NPN transistor. One end of resistor R7 is connected to the collector of transistor Q3 and the I / O pin of the control chip MCU. One end of resistor R8 is connected to resistor R7 and transistor Q4, and the other end of resistor R8 is connected to ground along with the emitter of transistor Q4. The collector of transistor Q4 is connected to the second voltage divider unit 5.

[0029] In actual operation, after switch S1 is turned off, the voltage of the power supply VBAT+ is supplied to the gate of MOSFET Q1 through the first voltage divider unit 1, causing MOSFET Q1 to conduct. The power supply VBAT+ then passes through MOSFET Q1, and after being divided by resistors R2 and R4, charges energy storage unit 2, causing the voltage of energy storage unit 2 to gradually increase. This pulls down the base level of transistor Q3, causing transistor Q3 to conduct. After transistor Q3 conducts, its collector is at a high level, causing the base of transistor Q4 to be at a high level, thus turning on transistor Q4. The collector current of transistor Q4 is divided by the second voltage divider unit 5 and input to the gate of MOSFET Q2. Since the collector of transistor Q4 is at a low level, the gate of MOSFET Q2 is at a low level, causing MOSFET Q2 to conduct, and the power supply VBAT+ supplies power to the control chip MCU.

[0030] In this embodiment, the first voltage divider unit 1 includes resistor R1 and resistor R3. One end of resistor R1 is connected to the power supply VBAT+ and the source of MOSFET Q1, respectively. The other end of resistor R1 is connected to the gate of MOSFET Q1 and resistor R3, respectively. The other end of resistor R3 is connected to switch S1 and energy storage unit 2, respectively.

[0031] The second voltage divider unit 5 includes resistors R2 and R5. One end of resistor R2 is connected to the drain of MOSFET Q1, the source of MOSFET Q2 and the second connection terminal 32 of the first switching component 3, respectively. The other end of resistor R2 is connected to the gate of MOSFET Q3 and one end of resistor R5, respectively. The other end of resistor R5 is connected to the sixth connection terminal 43 of the second switching component 4.

[0032] Furthermore, the power-on / off circuit also includes a voltage regulator component 6. The input terminal of the voltage regulator component 6 is connected to the drain of the MOSFET Q2, and the output terminal of the voltage regulator component 6 is connected to the VCC pin of the control chip MCU. The voltage regulator component 6 is used to regulate the electrical signal output by the MOSFET Q2, and then outputs the regulated electrical signal to the control chip MCU to ensure that the input electrical signal of the control chip remains stable.

[0033] Furthermore, the voltage regulator component 6 includes a first filter unit 61, a voltage regulator chip U1, and a second filter unit 62. One end of the first filter unit 61 is connected to the drain of the MOSFET Q2, and the other end of the first filter unit 61 is connected to the input terminal of the voltage regulator chip U1. The output terminal of the voltage regulator chip U1 is connected to one end of the second filter unit 62, and the other end of the second filter unit 62 is connected to the VCC pin of the control chip MCU.

[0034] In practical use, the electrical signal output from the drain of MOSFET Q2 is filtered by the first filter unit 61 and then input to the voltage regulator chip U1. The voltage regulator chip U1 receives the electrical signal output from the first filter unit 61 and converts it into a stable 3.3V voltage output. The electrical signal output from the voltage regulator chip U1 is then filtered by the second filter unit 62 and output to the VCC pin of the control chip MCU to power the control chip MCU.

[0035] In this example, the first filter unit 61 includes capacitors C3 and C4, and the second filter unit 62 includes capacitors C1 and C2. One end of capacitor C3 is connected to the drain of MOSFET Q2 and the input terminal of voltage regulator chip U1, and the other end is grounded. Capacitor C4 is connected in parallel with capacitor C3. One end of capacitor C2 is connected to the output terminal of voltage regulator chip U1 and the VCC pin of control chip MCU, and the other end is grounded. Capacitors C1 and C2 are connected in parallel.

[0036] In addition, the power-on / off circuit in this example also includes diode DD1B. The anode of diode DD1B is connected to the drain of MOSFET Q2, and the cathode of diode DD1B is connected to the input terminal of voltage regulator component 6. The electrical signal output from the drain of MOSFET Q2 is input to voltage regulator component 6 after passing through diode DD1B. Diode DD1B is used for voltage regulation and also prevents reverse current flow in the circuit.

[0037] In another embodiment, the power-on / off circuit further includes a diode DD1A, the cathode of which is connected to the drain of MOSFET Q2 and the input terminal of the control chip MCU. In practical circuit applications, when the power supply VBAT+ has no output (lithium battery is dead), the MCU is continuously powered by directly connecting 5V to the anode of diode DD1A.

[0038] The power-on / off circuit also includes diode D1. The cathode of diode D1 is connected to the I / O pin of the control chip MCU, and the anode of diode D1 is connected to the third connection terminal 33 of the first switch assembly 3 and the fourth connection terminal 41 of the second switch assembly 4. In the actual circuit connection, the anode of diode D1 is connected to the collector of transistor Q3 and one end of resistor R7. Diode D1 is used to prevent the electrical signal from flowing in the opposite direction. The signal output by the control chip MCU is sent to the collector of transistor Q3 and resistor R7 after passing through diode D1.

[0039] The above description is merely an embodiment of this utility model and is not intended to limit the scope of this utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this utility model should be included within the scope of the claims of this utility model.

Claims

1. A power on / off circuit, characterized in that, include: The system comprises a switch S1, a first voltage divider unit (1), an energy storage unit (2), a first switch assembly (3), a second switch assembly (4), MOSFETs Q1 and Q2, a second voltage divider unit (5), and a control chip MCU. The first switch assembly (3) has a first connection terminal (31), a second connection terminal (32), and a third connection terminal (33). The second switch assembly (4) has a fourth connection terminal (41), a fifth connection terminal (42), and a sixth connection terminal (43). One end of the first voltage divider unit (1) is connected to the power supply VBAT+ and the source of the MOSFET Q1, and the other end is connected to one end of the switch S1 and one end of the energy storage unit (2). The other end of the switch S1 is grounded. The other end of the energy storage unit (2) is connected to the first connection terminal (31). The gate of the MOS transistor Q1 is electrically connected to the first voltage divider unit (1). The second connection terminal (32) is connected to the drain of the MOS transistor Q1, the source of the MOS transistor Q2 and one end of the second voltage divider unit (5). The third connection terminal (33) is connected to the fourth connection terminal (41) and the IO pin of the control chip MCU. The fifth connection terminal (42) is grounded. The sixth connection terminal (43) is connected to the other end of the second voltage divider unit (5). The gate of the MOS transistor Q2 is connected to the second voltage divider unit (5). The drain of the MOS transistor Q2 is connected to the VCC pin of the control chip MCU.

2. The power on / off circuit according to claim 1, characterized in that, The first switching assembly (3) includes a resistor R6, a resistor R4 and a transistor Q3. One end of the resistor R6 is connected to the energy storage unit (2), and the other end is connected to the base of the resistor R4 and the transistor Q3. The other end of the resistor R4 is connected to the emitter of the transistor Q3, the drain of the MOS transistor Q1, the source of the MOS transistor Q2 and the second voltage divider unit (5). The collector of the transistor Q3 is connected to the fourth connection terminal (41) and the IO pin of the control chip MCU.

3. The power on / off circuit according to claim 1, characterized in that, The second switching assembly (4) includes resistor R7, resistor R8 and transistor Q4. One end of resistor R7 is connected to the third connection terminal (33) and the IO pin of the control chip MCU. One end of resistor R8 is connected to resistor R7 and the base of transistor Q4. Its other end is connected to ground along with the emitter of transistor Q4. The collector of transistor Q4 is connected to the second voltage divider unit (5).

4. The power on / off circuit according to claim 1, characterized in that, It also includes a voltage regulator component (6), the input of which is connected to the drain of the MOS transistor Q2, and its output is connected to the VCC pin of the control chip MCU.

5. The power on / off circuit according to claim 4, characterized in that, The voltage regulator component (6) includes a first filter unit (61), a voltage regulator chip U1 and a second filter unit (62). One end of the first filter unit (61) is connected to the drain of the MOS transistor Q2, and the other end is connected to the input terminal of the voltage regulator chip U1. The output terminal of the voltage regulator chip U1 is connected to one end of the second filter unit (62), and the other end of the second filter unit (62) is connected to the VCC pin of the control chip MCU.

6. The power on / off circuit according to claim 1, characterized in that, It also includes a diode DD1B, the anode of which is connected to the drain of the MOSFET Q2, and the cathode of which is connected to the VCC pin of the control chip MCU.

7. The power-on / off circuit according to claim 1, characterized in that, It also includes a diode D1, the negative terminal of which is connected to the third connection terminal (33) and the fourth connection terminal (41) respectively, and the positive terminal of which is connected to the IO pin of the control chip MCU.

8. The power on / off circuit according to claim 1, characterized in that, The first voltage divider unit (1) includes resistors R1 and R3. One end of resistor R1 is connected to the power supply VBAT+ and the source of the MOS transistor Q1, respectively. The other end of resistor R1 is connected to the gate of the MOS transistor Q1 and the resistor R3, respectively. The other end of resistor R3 is connected to the switch S1 and the energy storage unit (2), respectively.

9. The power on / off circuit according to claim 1, characterized in that, The second voltage divider unit (5) includes resistor R2 and resistor R5. One end of resistor R2 is connected to the drain of MOS transistor Q1, the source of MOS transistor Q2 and the second connection terminal (32), respectively. The other end of resistor R2 is connected to the gate of MOS transistor Q2 and resistor R5, respectively. The other end of resistor R5 is connected to the sixth connection terminal (43).

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