Protection device and hygrothermograph

Abstract

The utility model discloses a protection device and a hygrothermograph, the protection device comprises a first switch circuit, a second switch circuit and a third switch circuit, the first end of the first switch circuit is connected with the first end of the third switch circuit, and the second end of the first switch circuit is connected with a battery and the first end of the second switch circuit; the second end of the second switching circuit is connected with the second end of the third switching circuit, the third end of the second switching circuit is connected with the third end of the third switching circuit, and the third end of the second switching circuit is the output end of the protection device; the first switching circuit is used for controlling the second switching circuit to be in a turn-off state and controlling the third switching circuit to be in a turn-on state under the condition that the battery is powered down; and the second switching circuit is used for being in a turn-off state under the condition that the battery is reversely connected. According to the embodiment of the invention, the current can be prevented from flowing back to the battery, and the load can be protected under the condition that the battery is reversely connected.

Description

Technical Field

[0001] The present application relates to the technical field of electronic circuits, and in particular to a protection device and a thermometer and hygrometer. Background Art

[0002] With the continuous development of electronic technology, the application range of batteries is becoming increasingly broad. When using batteries, users may encounter situations such as reverse battery connection or sudden battery power loss. Reverse battery connection can cause irreversible damage to the load. In the event of a sudden battery power loss, current may flow back into the battery, causing damage. Therefore, preventing current backflow and protecting the load from reverse battery connection have become urgent technical issues when using batteries. Utility Model Content

[0003] The embodiments of the present application disclose a protection device and a thermometer and hygrometer, which are used to protect the load in the event of a sudden battery power failure and prevent current from flowing back into the battery in the event of reverse connection of the battery.

[0004] In a first aspect, an embodiment of the present application discloses a protection device, including a first switch circuit, a second switch circuit, and a third switch circuit, wherein:

[0005] The first end of the first switch circuit is connected to the first end of the third switch circuit, the second end of the first switch circuit is connected to the battery and the first end of the second switch circuit respectively, the second end of the second switch circuit is connected to the second end of the third switch circuit, the third end of the second switch circuit is connected to the third end of the third switch circuit, and the third end of the second switch circuit is the output end of the protection device;

[0006] The first switch circuit is used to control the second switch circuit to be in an off state and control the third switch circuit to be in an on state when the battery loses power;

[0007] The second switch circuit is configured to be in an off state when the battery is reversely connected.

[0008] In one embodiment, the first switching circuit includes a first switching device and a first resistor, wherein:

[0009] The first end of the first switching device is respectively connected to the third end of the first switching device, one end of the first resistor and the first end of the third switching circuit, the second end of the first switching device is respectively connected to the first end of the battery and the second switching circuit, and the other end of the first resistor is grounded.

[0010] In one embodiment, the second switching circuit includes a second switching device, wherein:

[0011] The first end of the second switching device is connected to the second end of the first switching circuit, the second end of the second switching device is connected to the second end of the third switching circuit, and the third end of the second switching device is connected to the third end of the third switching circuit.

[0012] In one embodiment, the third switching circuit includes a third switching device and a second resistor, wherein:

[0013] The first end of the third switching device is connected to the first end of the first switching circuit, the second end of the third switching device is connected to the third end of the second switching circuit, the third end of the third switching device is respectively connected to one end of the second resistor and the second end of the second switching circuit, and the other end of the second resistor is grounded.

[0014] In one embodiment, the protection device further comprises a filtering circuit, wherein:

[0015] The filter circuit is connected to the third end of the second switch circuit and the third end of the third switch circuit respectively.

[0016] In one embodiment, the filtering circuit includes a first capacitor and a second capacitor, wherein:

[0017] One end of the first capacitor and one end of the second capacitor are connected to the third end of the second switch circuit and the third end of the third switch circuit respectively, and the other end of the first capacitor and the other end of the second capacitor are grounded respectively.

[0018] In one embodiment, the first switching device is a PNP transistor.

[0019] In one embodiment, the second switching device is a PMOS transistor.

[0020] In one embodiment, the second switching device is a PNP transistor.

[0021] In a second aspect, an embodiment of the present application discloses a thermometer and hygrometer, comprising the protection device disclosed in the first aspect.

[0022] In an embodiment of the present application, a protection device includes a first switch circuit, a second switch circuit, and a third switch circuit; a first end of the first switch circuit is connected to a first end of the third switch circuit, a second end of the first switch circuit is connected to a battery and a first end of the second switch circuit, a second end of the second switch circuit is connected to a second end of the third switch circuit, and a third end of the second switch circuit is connected to a third end of the third switch circuit; the third end of the second switch circuit is an output end of the protection device; the first switch circuit is configured to control the second switch circuit to be in an off state and the third switch circuit to be in an on state when the battery loses power; and the second switch circuit is configured to be in an off state when the battery is reversely connected. It can be seen that in the event of a sudden battery power loss, the first switch circuit can control the second switch circuit to be in an off state and the third switch circuit to be in an on state, so that the reverse current can be discharged through the third switch circuit without flowing back into the battery through the second switch circuit, thereby preventing the current from flowing back into the battery and thus avoiding damage to the battery; in the event of a reverse battery connection, the second switch circuit is turned off, thereby preventing the current from flowing to the load and thus avoiding damage to the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 This is a schematic structural diagram of a protection device disclosed in an embodiment of the present application;

[0025] Figure 2 is a structural diagram of a first switch circuit disclosed in an embodiment of the present application;

[0026] Figure 3 It is a structural schematic diagram of another protection device disclosed in an embodiment of the present application;

[0027] Figure 4 This is a schematic structural diagram of another protection device disclosed in an embodiment of the present application;

[0028] Figure 5 This is a schematic structural diagram of another protection device disclosed in an embodiment of the present application;

[0029] Figure 6 This is a structural diagram of another protection device disclosed in an embodiment of the present application. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0031] The present application discloses a protection device and a thermo-hygrometer, which are used to protect the load in the event of a sudden battery power loss and to prevent current from flowing back into the battery in the event of reverse battery connection.

[0032] In order to better understand the embodiments of the present application, the relevant technologies of the embodiments of the present application are described below.

[0033] With the continuous development of electronic technology, the application range of batteries is becoming increasingly wider. When users use batteries, there may be situations such as the battery being connected in reverse or the battery suddenly losing power. In the prior art, a P-type metal oxide semiconductor (MOS) tube, namely a PMOS tube, can be used to prevent the battery polarity from being reversed. The source of the PMOS tube is connected to the positive electrode of the battery, the drain of the PMOS tube is connected to the load, and the gate of the PMOS tube is connected to the negative electrode of the battery. The conduction of the PMOS tube can be controlled by the voltage between the positive electrode and the gate of the battery. When the battery is connected correctly, the voltage between the gate and the source is lower than the threshold voltage, the PMOS tube is turned on, and current can flow from the battery to the load; when the battery polarity is reversed, the voltage between the gate and the source is higher than the threshold voltage, the PMOS tube is turned off, and the current can be prevented from flowing to the load, thereby protecting the load from damage. However, in the event of a sudden power loss or disconnection of the battery, if the load is capacitive or inductive, the energy stored in these components can continue to maintain the voltage in the circuit after the battery is disconnected. The voltage maintained by the load may continue to keep the PMOS tube in the on state, causing the voltage and current on the load side to flow back to the battery through the PMOS tube, causing damage to the battery.

[0034] In order to solve the above problems, the present application designs a protection device and a thermometer and hygrometer, which can protect the load in the event of a sudden battery power failure and prevent the current from flowing back into the battery in the event of reverse connection of the battery.

[0035] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a protection device disclosed in the embodiment of this application. Figure 1 As shown, the protection device may include a first switching circuit, a second switching circuit and a third switching circuit.

[0036] The first end of the first switch circuit is connected to the first end of the third switch circuit, the second end of the first switch circuit is respectively connected to the battery and the first end of the second switch circuit, the second end of the second switch circuit is connected to the second end of the third switch circuit, the third end of the second switch circuit is connected to the third end of the third switch circuit, and the third end of the second switch circuit is the output end of the protection device.

[0037] The first end of the first switch circuit is the input end of the protection device, which can receive the first DC signal provided by the battery. When the battery loses power, the first switch circuit can control the second switch circuit to be in the off state, thereby blocking the current flowing to the load; and control the third switch circuit to be in the on state, so that the third switch circuit is connected to the ground. When the battery loses power, the current flowing back from the load can flow to the ground, which can quickly eliminate the residual voltage in the load, thereby preventing the current from flowing back to the battery from the output end.

[0038] Reverse battery connection occurs when the battery's positive and negative poles are opposite to those of the load. Without proper protection, this can immediately damage sensitive components in the circuit. The second switch circuit is designed to be off in this situation, preventing current from flowing through the loop between the battery and the load, thereby preventing current from flowing to the load and protecting it.

[0039] It should be understood that the connection in this application may be an electrical connection.

[0040] exist Figure 1 The described protection device includes a first switch circuit, a second switch circuit, and a third switch circuit, wherein: the first end of the first switch circuit is connected to the first end of the third switch circuit, the second end of the first switch circuit is connected to the battery and the first end of the second switch circuit respectively, the second end of the second switch circuit is connected to the second end of the third switch circuit, and the third end of the second switch circuit is connected to the third end of the third switch circuit, and the third end of the second switch circuit is the output end of the protection device; the first switch circuit is used to control the second switch circuit to be in an off state and the third switch circuit to be in an on state when the battery loses power; the second switch circuit is used to be in an off state when the battery is reversely connected. It can be seen that in the event of a sudden battery power loss, the first switch circuit can control the second switch circuit to be in an off state and the third switch circuit to be in an on state, so that the reverse current can be discharged through the third switch circuit instead of flowing back into the battery through the second switch circuit, thereby preventing the current from flowing back into the battery and thus avoiding damage to the battery; in the event of reverse battery connection, the second switch circuit is turned off, preventing the current from flowing to the load and thus avoiding damage to the load.

[0041] See also Figure 2 , Figure 2This is a schematic diagram of the structure of a first switch circuit disclosed in an embodiment of the present application. Figure 2 As shown, the first switching circuit may include a first switching device Q1 and a first resistor R1.

[0042] A first end of the first switching device Q1 is respectively connected to the third end of the first switching device Q1, one end of the first resistor R1 and the first end of the third switching circuit; a second end of the first switching device Q1 is respectively connected to the first end of the battery and the second switching circuit; and the other end of the first resistor R1 is grounded.

[0043] The first switch device Q1 can be a transistor, or other devices used to control circuit switching. Specifically, the first switch device Q1 can be a PNP transistor. Figure 2 The description is made by taking the first switch device Q1 as a PNP transistor as an example.

[0044] When the first switching device Q1 is a PNP transistor, the base of the PNP transistor is the first end of the first switching device Q1, the emitter of the PNP transistor is the second end of the first switching device Q1, and the collector of the PNP transistor is the third end of the first switching device Q1.

[0045] The first resistor R1 serves as a current-limiting resistor, which can increase the resistance in the loop where the first switching device Q1 is located, and can reduce the current flowing through the collector of the first switching device Q1 when the first switching device Q1 is turned on, thereby preventing the first switching device Q1 from being damaged due to overcurrent.

[0046] When the battery is properly connected, current flows from the battery to the emitter (E) of the first switching device Q1. Since the collector (C) and base (B) of the first switching device Q1 are connected to ground via the first resistor R1, the voltage Vbe between the base and emitter of the first switching device Q1 = 0V - the battery voltage Vin < the threshold voltage Vbe(sat) between the base and emitter of the first switching device Q1. Therefore, the first switching device Q1 is turned on and in a saturated state. The third switching circuit is in the off state, and the second switching circuit is in the on state. The battery can power the load through the second switching circuit. The current flows from the battery to the second switching circuit, then through the load to ground. The circuit is conductive, and the battery can normally power the subsequent load.

[0047] See also Figure 3 , Figure 3 This is a schematic diagram of the structure of another protection device disclosed in the embodiment of this application. Figure 3 The protective device shown consists of Figure 1 The protective devices shown and Figure 2 The first switching circuit shown is optimized. Figure 3As shown, the second switching circuit may include a second switching device Q2.

[0048] A first terminal of the second switching device Q2 is connected to the second terminal of the first switching circuit, a second terminal of the second switching device Q2 is connected to the second terminal of the third switching circuit, and a third terminal of the second switching device Q2 is connected to the third terminal of the third switching circuit.

[0049] The second switch device Q2 may be a metal oxide semiconductor (MOS) transistor, or other devices with equivalent functions. Specifically, the second switch device Q2 may be a PMOS transistor.

[0050] When the second switch device Q2 is a PMOS tube, the drain of the PMOS tube is the first end of the second switch device Q2, the gate of the PMOS tube is the second end of the second switch device Q2, and the source of the PMOS tube is the third end of the second switch device Q2.

[0051] When the battery is properly connected, current flows from the battery to the emitter (E) of the first switching device Q1. Since the collector (C) and base (B) of the first switching device Q1 are connected to ground via the first resistor R1, the voltage Vbe between the base and emitter of the first switching device Q1 = 0V - the battery voltage Vin < the threshold voltage Vbe(sat) between the base and emitter of the first switching device Q1. Therefore, the first switching device Q1 is turned on and in saturation. Since the conduction speed of a transistor is faster than that of a MOS transistor, the second switching device Q2 is turned off, and the output voltage Vout is 0V. The source (S) of the second switching device Q2 is connected to the third terminal of the third switching circuit, and the first terminal of the third switching circuit is connected to the base (B) of the first switching device Q1, so the third switching circuit is in the off state. Since there is a body diode inside the second switching device Q2, the positive electrode of the battery first passes through the body diode and then through the subsequent load to the ground, the internal diode of the second switching device Q2 will be turned on. At this time, the source (S pole) voltage of the second switching device Q2 is the conduction voltage of the body diode, which is approximately 0.7V; at the same time, the gate (G pole) of the second switching device Q2 is directly grounded through the third switching circuit, so the voltage between the gate and the source of the second switching device Vgs = 0V-0.7V < the conduction requirement of the second switching device Q2, the second switching device Q2 is turned on, and after the second switching device Q2 is turned on, the conduction voltage drop is approximately 0V. At this time, the source (S pole) voltage of the second switching device Q2 is approximately equal to the battery voltage, the second switching device Q2 remains in the on state, the circuit is conductive, and the battery can normally supply power to the subsequent load.

[0052] In the event of reverse battery connection, the gate (G) of the second switching device Q2 is connected to the positive terminal of the battery through the third switching circuit, and the source (S) of the second switching device Q2 is connected to the positive terminal of the battery through the load. Therefore, Vgs = 0V > the conduction requirement of the second switching device Q2, and the second switching device Q2 is in the off state. At this time, the drain (D) of the second switching device Q2 is the negative terminal (GND) of the battery, and the source (S) of the second switching device Q2 is the positive terminal of the battery. The body diode of the second switching device Q2 is reverse biased and will not conduct, so no current can flow through the second switching device Q2. In other words, the battery is disconnected from the downstream load, preventing reverse connection.

[0053] In summary, when the battery is connected in reverse, the second switching device Q2 is turned off and the subsequent circuit is disconnected; when the battery is connected correctly, the second switching device Q2 is turned on and the subsequent circuit works normally, so that it can automatically shut down when the battery is reversed, preventing current from flowing to the load, thereby avoiding damage to the load.

[0054] See also Figure 4 , Figure 4 This is a schematic diagram of the structure of another protection device disclosed in the embodiment of this application. Figure 4 The protective device shown consists of Figure 3 The protection device shown is optimized. Figure 4 As shown, the third switching circuit may include a third switching device Q3 and a second resistor R2.

[0055] A first end of the third switching device Q3 is connected to the first end of the first switching circuit, a second end of the third switching device Q3 is connected to the third end of the second switching circuit, a third end of the third switching device Q3 is respectively connected to one end of the second resistor R2 and the second end of the second switching circuit, and the other end of the second resistor R2 is grounded.

[0056] The third switch device Q3 may be a transistor, or other devices for controlling circuit switching. Specifically, the third switch device Q3 may be a PNP transistor. Figure 4 The description is given by taking the third switch device Q3 as a transistor as an example.

[0057] When the third switching device Q3 is a PNP transistor, the base of the PNP transistor is the first end of the third switching device Q3, the emitter of the PNP transistor is the second end of the third switching device Q3, and the collector of the PNP transistor is the third end of the third switching device Q3.

[0058] The second resistor R2 serves as a current-limiting resistor, which can increase the resistance in the loop where the third switching device Q3 is located, and can reduce the current flowing through the third switching device Q3 when the third switching device Q3 is turned on, thereby preventing the third switching device Q3 from being damaged due to overcurrent.

[0059] When the battery is correctly connected, the current flows from the battery to the emitter (E pole) of the first switching device Q1. Since the collector (C pole) of the first switching device Q1 and the base (B pole) of the first switching device Q1 are connected to the ground through the first resistor R1, the voltage Vbe between the base and the emitter of the first switching device Q1 = 0V - the battery voltage Vin < the threshold voltage Vbe (sat) between the base and the emitter of the first switching device Q1. Therefore, the first switching device Q1 is turned on and is in a saturation state. Since the conduction speed of the triode is faster than that of the MOS tube, at this time, the second switching device Q2 is turned off, the output voltage Vout is 0V, the source (S pole) of the second switching device is connected to the emitter (E pole) of the third switching device Q3, and the base (B pole) of the third switching device Q3 is connected to the base (B pole) of the first switching device Q1. Therefore, the voltage between the base and the emitter of the third switching device Q3 Vbe=0V-0V>the threshold voltage Vbe(sat) between the base and the emitter of the third switching device Q1, and the third switching device Q3 is turned off. Since there is a body diode inside the second switching device Q2, the positive electrode of the battery first passes through the body diode and then through the subsequent load to the ground, the internal diode of the second switching device Q2 will be turned on. At this time, the source (S pole) voltage of the second switching device Q2 is the conduction voltage of the body diode, which is approximately 0.7V; at the same time, the gate (G pole) of the second switching device Q2 is directly grounded through the second resistor R2, so the voltage between the gate and the source of the second switching device Vgs = 0V-0.7V < the conduction requirement of the second switching device Q2, the second switching device Q2 is turned on, and after the second switching device Q2 is turned on, the conduction voltage drop is approximately 0V. At this time, the source (S pole) voltage of the second switching device Q2 is approximately equal to the external battery voltage, the second switching device Q2 remains in the on state, the circuit is conductive, and the battery can normally supply power to the subsequent load.

[0060] In the event of reverse battery connection, the gate (G) of the second switching device Q2 is connected to the positive terminal of the battery via the second resistor R2, and the source (S) of the second switching device Q2 is connected to the positive terminal of the battery via the load. Therefore, Vgs = 0V > the conduction requirement of the second switching device Q2, and the second switching device Q2 is in the off state. At this time, the drain (D) of the second switching device Q2 is the negative terminal (GND) of the battery, and the source (S) of the second switching device Q2 is the positive terminal of the battery. The body diode of the second switching device Q2 is reverse biased and will not conduct, so no current can flow through the second switching device Q2. In other words, the battery is disconnected from the downstream load, preventing reverse connection.

[0061] In the event of a sudden battery disconnection or power failure, due to the presence of load capacitance, the output voltage Vout of the protection device exceeds the input Vin. At this time, the emitter (E) voltage of the third switching device Q3 is equal to the output voltage Vout, the base (B) voltage of the third switching device Q3 is 0V, and Vbe of the third switching device Q3 is less than 0V - the output voltage Vout < the saturation conduction voltage Vbe(sat) of the third switching device Q3. Therefore, the third switching device Q3 will be saturated and turned on. After the third switching device Q3 is saturated and turned on, the collector (C) voltage of the third switching device Q3 is equal to the emitter (E) voltage of the third switching device Q3, causing the gate (G) voltage of the second switching device Q2 to be pulled up to the source (S) voltage of the second switching device Q2. At this time, Vgs = 0V > the conduction requirement of the second switching device Q2, and the second switching device Q2 is turned off, thereby preventing the carrier current from flowing back into the battery through the second switching device Q2, thereby preventing current backflow.

[0062] See also Figure 5 , Figure 5 This is a schematic diagram of the structure of another protection device disclosed in the embodiment of this application. Figure 5 The protective device shown consists of Figure 1 The protection device shown is optimized. Figure 5 As shown, the protection device may further include a filter circuit connected to the third terminal of the second switch circuit and the third terminal of the third switch circuit respectively.

[0063] The filter circuit can eliminate noise and interference in the first DC signal, thereby providing a stable voltage for the load and avoiding the influence of battery voltage ripple and excessive noise on the load.

[0064] See also Figure 6 , Figure 6 This is a schematic diagram of the structure of another protection device disclosed in the embodiment of this application. Figure 6 The protective device shown consists of Figure 1 The protective devices shown and Figure 5 The protection device shown is optimized. Figure 6 As shown, the filtering circuit may include a first capacitor C1 and a second capacitor C2.

[0065] One end of the first capacitor C1 and one end of the second capacitor C2 are connected to the third end of the second switch circuit and the third end of the third switch circuit respectively, and the other end of the first capacitor C1 and the other end of the second capacitor C2 are grounded respectively.

[0066] The first capacitor C1 and the second capacitor C2 have different capacitance values.

[0067] Among them, the first capacitor C1 can be a capacitor with a capacitance value range of microfarad level, which can filter out low-frequency noise, smooth the lower frequency components in the voltage ripple, and provide a large energy storage for the circuit, thereby maintaining voltage stability during instantaneous load changes.

[0068] The second capacitor C2 may be a capacitor with a capacitance value in the nanofarad range, which can filter out high-frequency noise, process higher-frequency spikes, and quickly respond to high-frequency changes.

[0069] It should be understood that the first capacitor C1 may include one capacitor or multiple capacitors. In the case where the first capacitor C1 includes multiple capacitors, the first capacitor C1 may be formed by connecting these multiple capacitors in parallel. The second capacitor C2 may include one capacitor or multiple capacitors. In the case where the second capacitor C2 includes multiple capacitors, the second capacitor C2 may be formed by connecting these multiple capacitors in parallel.

[0070] An embodiment of the present application discloses a thermometer and hygrometer, which may include the above-mentioned protection device.

[0071] For a detailed description of the protection device, reference may be made to the above description.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A protective device, characterized in that: It includes a first switch circuit, a second switch circuit and a third switch circuit, wherein: The first end of the first switch circuit is connected to the first end of the third switch circuit, the second end of the first switch circuit is connected to the battery and the first end of the second switch circuit respectively, the second end of the second switch circuit is connected to the second end of the third switch circuit, the third end of the second switch circuit is connected to the third end of the third switch circuit, and the third end of the second switch circuit is the output end of the protection device; The first switch circuit is configured to control the second switch circuit to be in an off state and control the third switch circuit to be in an on state when the battery loses power; The second switch circuit is configured to be in an off state when the battery is reversely connected.

2. The protection device according to claim 1, characterized in that The first switching circuit includes a first switching device and a first resistor, wherein: The first end of the first switching device is respectively connected to the third end of the first switching device, one end of the first resistor and the first end of the third switching circuit, the second end of the first switching device is respectively connected to the battery and the first end of the second switching circuit, and the other end of the first resistor is grounded.

3. The protection device according to claim 1, characterized in that: The second switching circuit includes a second switching device, wherein: The first end of the second switching device is connected to the second end of the first switching circuit, the second end of the second switching device is connected to the second end of the third switching circuit, and the third end of the second switching device is connected to the third end of the third switching circuit.

4. The protection device according to claim 1, characterized in that The third switch circuit includes a third switch device and a second resistor, wherein: The first end of the third switching device is connected to the first end of the first switching circuit, the second end of the third switching device is connected to the third end of the second switching circuit, the third end of the third switching device is respectively connected to one end of the second resistor and the second end of the second switching circuit, and the other end of the second resistor is grounded.

5. The protection device according to any one of claims 1 to 4, characterized in that: The protection device further includes a filter circuit, wherein: The filter circuit is connected to the third end of the second switch circuit and the third end of the third switch circuit respectively; The filtering circuit is used to eliminate noise and interference.

6. The protection device according to claim 5, characterized in that: The filtering circuit includes a first capacitor and a second capacitor, wherein: One end of the first capacitor and one end of the second capacitor are connected to the third end of the second switch circuit and the third end of the third switch circuit respectively, and the other end of the first capacitor and the other end of the second capacitor are grounded respectively.

7. The protection device according to claim 2, characterized in that: The first switching device is a PNP transistor.

8. The protection device according to claim 3, characterized in that: The second switching device is a PMOS tube.

9. The protection device according to claim 3, characterized in that: The second switching device is a PNP transistor.

10. A thermometer and hygrometer, characterized in that: The protective device comprises the protective device according to any one of claims 1 to 9.

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