Electronic fuse circuit and current limiting circuit

Abstract

The utility model discloses an electronic fuse circuit and a current limiting circuit, the fuse circuit comprises a switch control module, a pre-charging starting circuit module and a current limiting output module which are built by discrete components, the input end of the switch control module is used for inputting a switch control signal; the output end of the switch control module is connected with the control end of the current-limiting output module; the output end of the pre-charging starting circuit module is connected with the input end of the switch control module; the input end of the current-limiting output module is connected with a power supply, the output end of the current-limiting output module is connected with a load through the pressure-bearing switch, and the control end of the current-limiting output module is used for controlling the pressure-bearing switch to work in an amplification area and limiting the output current within a current-limiting output threshold value when the power supply current of the power supply is greater than the preset current-limiting output threshold value. According to the utility model, the electronic fuse circuit is constructed by discrete devices, so that the circuit cost is reduced, the current-limiting output function of the circuit is realized, and the overcurrent problem of the circuit is avoided.

Description

Technical Field

[0001] The utility model relates to the field of power distribution control, in particular to an electronic fuse circuit and a current limiting circuit. Background Art

[0002] The existing electronic fuse circuits all have functions such as current detection and voltage detection. However, the main body of the circuit uses a chip as the main component of the circuit design, and then is combined with an external circuit for matching design. Therefore, the cost of the electronic fuse circuit implemented by such an integrated chip is relatively high, and there are problems such as overcurrent and large power consumption during circuit sleep. Summary of the Invention

[0003] Embodiments of the utility model provide an electronic fuse circuit and a current limiting circuit to solve the problems of relatively high cost and overcurrent of the electronic fuse circuit.

[0004] In a first aspect, an electronic fuse circuit is provided, and the electronic fuse circuit includes:

[0005] A switch control module 10, a precharge start circuit module 20, and a current limiting output module 30 built with discrete components. Among them, the input end of the switch control module 10 is used to input a switch control signal, and the output end of the switch control module 10 is connected to the control end of the current limiting output module 30; the input end of the precharge start circuit module 20 is used to input a load power distribution signal, and the output end of the precharge start circuit module 20 is connected to the input end of the switch control module 10;

[0006] The input end of the current limiting output module 30 is connected to a power supply, the output end of the current limiting output module 30 is connected to a load through a pressure-bearing switch Q2, and the control end of the current limiting output module 30 is used to control the pressure-bearing switch Q2 to work in the amplification region when the supply current of the power supply is greater than a preset current limiting output threshold, so as to limit the output current within the current limiting output threshold.

[0007] Optionally, the current limiting output module 30 includes:

[0008] A first resistor R1, a second resistor R2, a third resistor R3, and a first switch Q1. The input end of the first resistor R1 is connected to the power supply, and the output end of the first resistor R1 is used to connect to the input end of the pressure-bearing switch Q2;

[0009] The input end of the second resistor R2 is connected to the input end of the first resistor R1. The second resistor R2 is in series with the third resistor R3, and the output end of the third resistor R3 is connected to the output end of the first resistor R1;

[0010] The input end of the first switch Q1 is connected to the input end of the first resistor R1, the output end of the first switch Q1 is connected to the control end of the pressure-bearing switch Q2, and the control end of the first switch Q1 is used to connect the output end of the second resistor R2 and the output end of the switch control module 10.

[0011] Optionally, the current-limiting output module 30 further includes:

[0012] A fourth resistor R6, the input end of the fourth resistor R6 is connected to the control end of the first switch Q1, and the output end of the fourth resistor R6 is connected to the output end of the switch control module 10.

[0013] Optionally, the formula for the current-limiting output threshold limited by the current-limiting output module 30 is as follows:

[0014]

[0015] Where, I th is the current-limiting output threshold, V be is the voltage between the input end and the control end of the first switch Q1, R1 is the resistance value of the first resistor R1, R2 is the resistance value of the second resistor R2, and R3 is the resistance value of the third resistor R3.

[0016] Optionally, the switch control module 10 includes:

[0017] A second switch Q3, a fifth resistor R10, a sixth resistor R11, a first diode D3, a seventh resistor R2. Among them, the input end of the second switch Q3 is used to connect the control end of the current-limiting output module 30, the output end of the second switch Q3 is connected to the ground, the control end of the second switch Q3 is respectively connected to the input end of the fifth resistor R10 and the input end of the sixth resistor R11, the output end of the fifth resistor R10 serves as the input end of the switch control module 10, and the output end of the sixth resistor R11 is connected to the ground; the output end of the fifth resistor R10 is connected to the first diode D3, and the first diode D3 is connected in series with the seventh resistor R2.

[0018] Optionally, the pre-charge enabling circuit module 20 includes:

[0019] A third switch Q5, an eighth resistor R13, a ninth resistor R14. Among them, the control end of the third switch Q5 is respectively connected to the output end of the eighth resistor R13 and the input end of the ninth resistor R14, the input end of the eighth resistor R13 is used to input a load power distribution signal, and the output end of the ninth resistor R14 is connected to the ground; the input end of the third switch Q5 is connected to the ground, and the output end of the third switch Q5 is connected to the input end of the switch control module 10.

[0020] Optionally, the electronic fuse circuit further includes:

[0021] A short - circuit - to - ground protection module 40 built with discrete components, the input end of the short - circuit - to - ground protection module 40 is connected to the output end of the pressure - bearing switch Q2, the output end of the short - circuit - to - ground protection module 40 is connected to the input end of the switch control module 10, and the short - circuit - to - ground protection module 40 is used to output a short - circuit - to - ground protection signal to the switch control module 10 when detecting a short - circuit - to - ground fault, and control the pressure - bearing switch Q2 to disconnect through the switch control module 10 and the current - limiting output module 30.

[0022] Optionally, the short - circuit - to - ground protection module 40 includes:

[0023] A fourth switch Q4, a tenth resistor R7, an eleventh resistor R8, a twelfth resistor R9, and a second diode D1. Among them, the input end of the fourth switch Q4 is connected to the power supply through the twelfth resistor R9, the output end of the fourth switch Q4 is connected to the input end of the switch control module 10, the control end of the fourth switch Q4 is sequentially connected to the output end of the pressure - bearing switch Q2 through the tenth resistor R7 and the second diode D1, one end of the eleventh resistor R8 is connected to the control end of the fourth switch Q4, and the other end of the eleventh resistor R8 is connected to the input end of the fourth switch Q4.

[0024] Optionally, the electronic fuse circuit further includes:

[0025] A current detection module 50, a voltage detection module 60, and a wake - up module 70 built with discrete components. Among them, the first detection end of the current detection module 50 is connected to the output end of the current - limiting output module 30, the second detection end of the current detection module 50 is connected to the input end of the pressure - bearing switch Q2, and the detection output end of the current detection module 50 is used to output a sampled current signal;

[0026] The input end of the voltage detection module 60 is connected to the output end of the pressure - bearing switch Q2, the control end of the voltage detection module 60 is used to input a voltage sampling control signal, and the output end of the voltage detection module 60 is used to output a sampled voltage signal;

[0027] The input end of the wake - up module 70 is connected to the detection output end of the current detection module, and the wake - up module 70 is used to compare the sampled current signal with a preset wake - up signal current threshold and output a wake - up control signal.

[0028] In a second aspect, a current - limiting circuit is provided. The current - limiting circuit includes:

[0029] A current-limiting output module 30 and a pressure-bearing switch Q2. The input end of the current-limiting output module 30 is connected to a power supply, the output end of the current-limiting output module 30 is connected to a load through the pressure-bearing switch Q2, and the control end of the current-limiting output module 30 is used to control the pressure-bearing switch Q2 to operate in the amplification region when the supply current of the power supply is greater than a preset current-limiting output threshold, so as to limit the output current within the current-limiting output threshold.

[0030] Optionally, the current-limiting output module 30 includes:

[0031] A first resistor R1, a second resistor R2, a third resistor R3, and a first switch Q1. The input end of the first resistor R1 is connected to the power supply, and the output end of the first resistor R1 is used to connect to the input end of the pressure-bearing switch Q2;

[0032] The input end of the second resistor R2 is connected to the input end of the first resistor R1. The second resistor R2 is connected in series with the third resistor R3, and the output end of the third resistor R3 is connected to the output end of the first resistor R1;

[0033] The input end of the first switch Q1 is connected to the input end of the first resistor R1, the output end of the first switch Q1 is connected to the control end of the pressure-bearing switch Q2, and the control end of the first switch Q1 is used to connect to the output end of the second resistor R2.

[0034] Optionally, the formula for the current-limiting output threshold limited by the current-limiting output module 30 is as follows:

[0035]

[0036] Where, I th is the current-limiting output threshold, V be is the voltage between the input end and the control end of the first switch Q1, R1 is the resistance value of the first resistor R1, R2 is the resistance value of the second resistor R2, and R3 is the resistance value of the third resistor R3.

[0037] The above electronic fuse circuit is realized by a switch control module 10, a pre-charge start circuit module 20, and a current-limiting output module 30 built by discrete devices. It does not need to use any chip as the main body and is all realized by discrete devices, which reduces the circuit cost. Moreover, it realizes the current-limiting output function of the circuit and avoids the over-current problem of the circuit. Description of the Drawings

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 is a circuit schematic diagram of an electronic fuse circuit in an embodiment of the present invention;

[0040] Figure 2 is a timing waveform diagram of the control signal output by the non-capacitive load turn-on processor MCU in an embodiment of the present invention;

[0041] Figure 3 is a timing waveform diagram of the control signal output by the capacitive load turn-on processor MCU in an embodiment of the present invention;

[0042] Figure 4 is a schematic diagram of the connection relationship of the functional modules of the electronic fuse circuit in an embodiment of the present invention;

[0043] The label descriptions are as follows:

[0044] 10. Switch control module; 20. Pre-charge turn-on circuit module; 30. Current-limiting output module; 40. Short-circuit-to-ground protection module; 50. Current detection module; 60. Voltage detection module; 70. Wake-up module. Specific embodiments

[0045] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0046] It should be understood that the present invention can be implemented in different forms and should not be construed as limited to the embodiments presented here. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated. The same reference numerals represent the same elements throughout the drawings.

[0047] It should be understood that when an element or layer is referred to as "on", "adjacent to", "connected to" or "coupled to" another element or layer, it can be directly on, adjacent to, connected or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as "directly on", "directly adjacent to", "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Thus, without departing from the teachings of the present utility model, the first element, component, region, layer or part discussed below may be denoted as the second element, component, region, layer or part.

[0048] Spatial relationship terms such as "under", "below", "beneath", "underneath", "above", "over", etc. are used herein for convenience in describing the relationship of one element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, then an element or feature described as "under" or "beneath" or "underneath" another element or feature will be oriented "above" the other element or feature. Thus, the exemplary terms "under" and "beneath" can include both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are to be interpreted accordingly.

[0049] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present utility model. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0050] To thoroughly understand the present utility model, detailed structures and steps will be presented in the following description to illustrate the technical solutions proposed by the present utility model. The preferred embodiments of the present utility model are described in detail below. However, in addition to these detailed descriptions, the present utility model may also have other embodiments.

[0051] In one embodiment, asFigure 1 As shown, an electronic fuse circuit is provided. The electronic fuse circuit includes:

[0052] A switch control module 10, a pre-charge enable circuit module 20, and a current-limiting output module 30 built with discrete components. Among them, the input end of the switch control module 10 is used to input a switch control signal, and the output end of the switch control module 10 is connected to the control end of the current-limiting output module 30; the input end of the pre-charge enable circuit module 20 is used to input a load power distribution signal, and the output end of the pre-charge enable circuit module 20 is connected to the input end of the switch control module 10;

[0053] The input end of the current-limiting output module 30 is connected to the power supply, the output end of the current-limiting output module 30 is connected to the load through a pressure-bearing switch Q2, and the control end of the current-limiting output module 30 is used to control the pressure-bearing switch Q2 to work in the amplification region when the supply current of the power supply is greater than a preset current-limiting output threshold, so as to limit the output current within the current-limiting output threshold.

[0054] Among them, the working principle of the current-limiting output module 30 is:

[0055] When the switch control signal input by the switch control module 10 is at a low level and the load power distribution signal input by the pre-charge enable circuit module 20 is at a low level, the control end of the current-limiting output module 30 is used to achieve an equivalent floating state according to the switch control signal input from the switch control module 10 and the load power distribution signal input from the pre-charge enable circuit module 20.

[0056] When the supply current from the power supply flows through the current-limiting output module 30, when the supply current of the current-limiting output module 30 is greater than a preset current-limiting output threshold, it controls the pressure-bearing switch Q2 to work in the amplification region, and the pressure-bearing switch Q2 bears most of the voltage, so that the circuit is in a dynamic balance of power supply, so as to keep the current output within the current-limiting output threshold.

[0057] In this embodiment, the pressure-bearing switch Q2 is preferably a P-type switch tube. For example, a PMOS tube can be used to implement it. The source electrode of the PMOS tube is connected to the output end of the current-limiting output module 30, the drain electrode of the PMOS tube is used as the voltage output end to connect to the load, and the gate electrode of the PMOS tube is used as the controlled end to receive the control of the current-limiting output module 30.

[0058] The electronic fuse circuit of this embodiment is implemented by a switch control module 10, a pre-charge enable circuit module 20, and a current-limiting output module 30 built with discrete devices. It does not need to use any chip as the main body and is all implemented with discrete devices, which reduces the circuit cost. Moreover, the current-limiting output function of the circuit is realized, and the over-current problem of the circuit is avoided.

[0059] In one embodiment, such asFigure 1 As shown, the current-limiting output module 30 includes:

[0060] A first resistor R1, a second resistor R2, a third resistor R3, and a first switch Q1. The input end of the first resistor R1 is connected to the power supply, and the output end of the first resistor R1 is used to connect to the input end of the pressure-bearing switch Q2;

[0061] The input end of the second resistor R2 is connected to the input end of the first resistor R1. The second resistor R2 is in series with the third resistor R3, and the output end of the third resistor R3 is connected to the output end of the first resistor R1;

[0062] The input end of the first switch Q1 is connected to the input end of the first resistor R1, the output end of the first switch Q1 is connected to the control end of the pressure-bearing switch Q2, and the control end of the first switch Q1 is used to connect to the output end of the second resistor R2 and the output end of the switch control module 10.

[0063] In this embodiment, the input end of the first resistor R1 serves as the input end of the current-limiting output module 30, the output end of the first resistor R1 serves as the output end of the current-limiting output module 30, and the control end of the first switch Q1 serves as the control end of the current-limiting output module 30.

[0064] The working principle of the above current-limiting output module 30 is as follows:

[0065] After the initial power-on, when power supply VBAT is required for power supply, at this time, the switch control signal input to the input end of the switch control module 10 is set to a low level, and the load power distribution signal input to the input end of the pre-charge enable circuit module 20 is set to a low level; the output end of the switch control module 10 is not conducting, so the control end of the first switch Q1 (which can be a PNP triode) is not affected by the switch tube in the switch control module 10, and is equivalent to the output end of the switch control module 10 being floating.

[0066] When the supply current of the power supply flows through the first resistor R1, and when this supply current reaches the current-limiting output threshold, the voltage drop across the second resistor R2 is greater than the reference voltage that can make the first switch Q1 conduct. Therefore, the first switch Q1 conducts, and the output end (i.e., the c pole) of the first switch Q1 is approximately the voltage of the power supply VBAT, so that the voltage between the control end and the input end of the pressure-bearing switch Q2 (i.e., the GS pole voltage) will change, but will not become 0V. Furthermore, the pressure-bearing switch Q2 operates in the amplification region, and most of the voltage begins to be borne by the pressure-bearing switch Q2, making the circuit in a dynamic balance of power supply, so as to maintain current output within the current-limiting output threshold.

[0067] In one embodiment, as Figure 1Under the circuit structure of the current-limiting output module 30 shown, the formula for the current-limiting output threshold limited by the current-limiting output module 30 is as follows:

[0068]

[0069] Wherein, I th is the current-limiting output threshold, V be is the reference voltage between the input terminal and the control terminal of the first switch Q1, R1 is the resistance value of the first resistor R1, R2 is the resistance value of the second resistor R2, and R3 is the resistance value of the third resistor R3.

[0070] The current-limiting output module 30 of this embodiment can set the current-limiting output threshold according to the parameters of the first resistor R1, the second resistor R2, the third resistor R3, and the first switch Q1. Among them, the first switch Q1 can be a PNP triode, and the BE-pole voltage when the device is turned on is Vbe.

[0071] According to the circuit design structure of the current-limiting output module 30, when the supply current reaches the current-limiting output threshold I th , since the voltage drop across the second resistor R2 is greater than the reference voltage that can turn on the first switch Q1, the first switch Q1 is turned on, causing the voltage between the control terminal (i.e., the G pole) and the input terminal (i.e., the S pole) of the pressure-bearing switch Q2 to change immediately. The pressure-bearing switch Q2 will be in the amplification region to achieve switch dynamic balance.

[0072] In one embodiment, as Figure 1 shown, the current-limiting output module 30 further includes:

[0073] A fourth resistor R6, the input terminal of the fourth resistor R6 is connected to the control terminal of the first switch Q1, and the output terminal of the fourth resistor R6 is connected to the output terminal of the switch control module 10.

[0074] Among them, since the fourth resistor R6 is connected between the control terminal of the first switch Q1 and the output terminal of the switch control module 10, when the switch control module 10 is not turned on, the output terminal of the switch control module 10 is connected to the control terminal of the first switch Q1 through the resistor R6. Then, the control terminal of the first switch Q1 is not affected by the switch of the switch control module 10, which is equivalent to leaving the fourth resistor R6 and the output terminal of the switch control module 10 floating.

[0075] In one embodiment, as Figure 1 shown, the switch control module 10 includes:

[0076] The second switch Q3, the fifth resistor R10, the sixth resistor R11, the first diode D3, the seventh resistor R12, wherein the input end of the second switch Q3 is used to connect the control end of the current limiting output module 30, the output end of the second switch Q3 is connected to the ground, the control end of the second switch Q3 is respectively connected to the input end of the fifth resistor R10 and the input end of the sixth resistor R11, the output end of the fifth resistor R10 serves as the input end of the switch control module 10, and the output end of the sixth resistor R11 is connected to the ground; the output end of the fifth resistor R10 is connected to the first diode D3, and the first diode D3 is connected in series with the seventh resistor R12.

[0077] Wherein, the second switch Q3 can be an NPN transistor; the output end of the fifth resistor R10 can be used as the control end of the switch control module 10, and the switch control signal of the switch control module 10 is input through the output end of the fifth resistor R10, or the original switch control signal MCU_Control_1 can also be input from one side of the seventh resistor R12, and after the signal conditioning of the first diode D3 and the seventh resistor R12, the switch control signal is output.

[0078] As Figure 1 shown, the pre-charge enable circuit module 20 includes:

[0079] The third switch Q5, the eighth resistor R13, the ninth resistor R14, wherein the control end of the third switch Q5 is respectively connected to the output end of the eighth resistor R13 and the input end of the ninth resistor R14, the input end of the eighth resistor R13 is used to input the load power distribution signal, and the output end of the ninth resistor R14 is connected to the ground; the input end of the third switch Q5 is connected to the ground, and the output end of the third switch Q5 is connected to the input end of the switch control module 10.

[0080] Wherein, the third switch Q5 can be an NPN transistor, and the input end of the eighth resistor R13 is used to input the load power distribution signal MCU_Control_2 sent from the MCU.

[0081] When the non-capacitive load connected to the pressure-bearing switch Q2 is turned on, the power distribution turn-on process of the electronic fuse circuit is as follows:

[0082] When power is applied, the power supply VBAT starts to supply power, the switch control signal MCU_Control_1 is set to low level and the load power distribution signal MCU_Control_2 is set to high level, and the waveform is as Figure 2As shown; at this time, since the control terminal of the third switch Q5 is at a high level, the third switch Q5 is turned on; since the control terminal of the second switch Q3 is at a low level, the second switch Q3 is not turned on; the input terminal (collector) of the second switch Q3 is connected to the control terminal (base) of the first switch Q1 through the resistor R6, then the control terminal of the first switch Q1 transistor is not affected by the second switch Q3, and the part of the resistor R6 and the second switch Q3 is equivalently suspended.

[0083] When the supply current flows through the resistors R1, R2, R3, R4, R5 to the ground, and the supply current is less than the current limit output threshold, the first switch Q1 is not conducting, and the voltage at the output terminal (i.e., the collector) of the first switch Q1 depends on the voltage division between the resistors R4 and R5 connected to the output terminal of the first switch Q1. Therefore, the voltage at the input terminal (source) of the voltage-bearing switch Q2 is less than the voltage at the control terminal (gate), and the voltage-bearing switch Q2 conducts, forming a supply loop.

[0084] When the capacitive load connected to the voltage-bearing switch Q2 is turned on, the power distribution startup process of this electronic fuse circuit is as follows:

[0085] For the case where the external load is a capacitive load, the switch control signal MCU_Control_1 is set to a low level and the load power distribution signal MCU_Control_2 is set to PWM control; the waveform is as Figure 3 shown.

[0086] When the switch control signal MCU_Control_1 is set to a low level and the load power distribution signal MCU_Control_2 is at the high level of the PWM; since the third switch Q5 is turned on, the control terminal (base) of the second switch Q3 is grounded; the second switch Q3 is not turned on; the input terminal (collector) of the second switch Q3 is connected to the control terminal (base) of the first switch Q1 through the resistor R6, then the control terminal of the first switch Q1 is not affected by the second switch Q3, and the part of the resistor R6 and the second switch Q3 is equivalently suspended; so in the case of no overcurrent, the voltage-bearing switch Q2 is in the conducting state.

[0087] When the switch control signal MCU_Control_1 is set to a low level and the load power distribution signal MCU_Control_2 is at the low level of the PWM; since the third switch Q5 is turned off, the control terminal (base) of the second switch Q3 is at a high level; the second switch Q3 is turned on; the input terminal (collector) of the second switch Q3 is connected to the control terminal (base) of the first switch Q1 through the resistor R6, then the first switch Q1 conducts, and the voltage-bearing switch Q2 is in the off state.

[0088] Therefore, by controlling the conduction and turn-off of the voltage-bearing switch Q2 to form the output of the PWM, it is possible to achieve the charging and power-on of the capacitive load without overcurrent protection.

[0089] When the capacitive load connected to the pressure-bearing switch Q2 is turned off, the power distribution off control process of this electronic fuse circuit is as follows:

[0090] When the power supply is on, the switch control signal MCU_Control_1 is set to high level, and the load power distribution signal MCU_Control_2 is set to low level; the control terminal (b-pole) of the third switch Q5 is at low level, the third switch Q5 is turned off, the control terminal (b-pole) of the second switch Q3 is at high level, and the second switch Q3 is turned on; then the control terminal (b-pole) of the first switch Q1 is connected to the ground, the first switch Q1 conducts, and the output terminal (c-pole) of the first switch Q1 is approximately the voltage of the power supply VBAT. The voltage at the input terminal (S-pole) of the pressure-bearing switch Q2 is approximately equal to the voltage at the control terminal (G-pole), and the pressure-bearing switch Q2 is turned off, realizing the shutdown of the power supply circuit.

[0091] The electronic fuse circuit of this embodiment can be applied to the power supply / distribution circuit in the automotive domain controller to complete the intelligent and reliable power supply to the external load. Through two control signals, the switching components in the circuit are controlled to turn on or off, thereby controlling the power-on of the external load. Through the PWM switching control of the circuit, the charging power distribution of the capacitive load by this electronic fuse circuit is realized. At the same time, combined with the circuit design, the current limiting output of the circuit can be carried out. After reaching a certain current threshold, the circuit is limited to output at the current limiting threshold without external signal intervention.

[0092] It should be noted that for power distribution control (capacitive load charging start), since the current conditions of the load are different during the initial power distribution of capacitive and non-capacitive loads. There is a large current when the capacitive load is powered on for the first time, and at the same time, the electronic fuse circuit has an overcurrent protection function. Directly performing switch power distribution will cause the circuit to trigger overcurrent protection, so that the external capacitive load cannot be powered on normally. Therefore, by designing the switch of the control circuit and performing PWM control, a soft start is formed when powering on the capacitive load, and the voltage of the external load is increased step by step, and the normal power distribution function of the capacitive load can be realized. For non-capacitive loads, direct switch power distribution can be used to realize the power distribution of the external load.

[0093] In the case of a short circuit to the ground, when it is detected that the voltage of the external output circuit drops, the output of the circuit can also be automatically turned off to quickly respond to the protection of the external circuit.

[0094] In one embodiment, as Figure 1 shown, the electronic fuse circuit further includes:

[0095] The short - circuit - to - ground protection module 40 built with discrete components, the input end of the short - circuit - to - ground protection module 40 is connected to the output end of the pressure - bearing switch Q2, the output end of the short - circuit - to - ground protection module 40 is connected to the input end of the switch control module 10, and the short - circuit - to - ground protection module 40 is used to output a short - circuit - to - ground protection signal to the switch control module 10 when detecting a short - circuit - to - ground fault, and control the pressure - bearing switch Q2 to disconnect through the switch control module 10 and the current - limiting output module 30.

[0096] In this embodiment, after the switch control module 10 receives the short - circuit - to - ground protection signal, it sends a control signal to the current - limiting output module 30 through the second switch Q3 of the switch control module 10, and the current - limiting output module 30 controls the pressure - bearing switch Q2 to disconnect, realizing short - circuit - to - ground protection.

[0097] In one embodiment, as Figure 1 shown, the short - circuit - to - ground protection module 40 includes:

[0098] The fourth switch Q4, the tenth resistor R7, the eleventh resistor R8, the twelfth resistor R9, and the second diode D1. Among them, the input end of the fourth switch Q4 is connected to the power supply through the twelfth resistor R9, the output end of the fourth switch Q4 is connected to the input end of the switch control module 10, the control end of the fourth switch Q4 is sequentially connected to the output end of the pressure - bearing switch Q2 through the tenth resistor R7 and the second diode D1, one end of the eleventh resistor R8 is connected to the control end of the fourth switch Q4, and the other end of the eleventh resistor R8 is connected to the input end of the fourth switch Q4.

[0099] Among them, the working principle of the short - circuit - to - ground protection module 40 is as follows:

[0100] After the initial power - on is completed, when the voltage is supplied, at this time, the switch control signal MCU_Control_1 is set to low level and the load power - distribution signal MCU_Control_2 is set to low level; the b - pole of the second switch Q3 is at low level, and the second switch Q3 does not open; the c - pole of the second switch Q3 is connected to the b - pole of the first switch Q1 through the resistor R6, then the b - pole of the first switch Q1 is not affected by the second switch Q3, and this part of the resistor R6 and the second switch Q3 is equivalent to being suspended.

[0101] At the initial power - on, the voltage at the output end VOUT of the pressure - bearing switch Q2 is 0, then there is a current loop of the twelfth resistor R9, the eleventh resistor R8, the tenth resistor R7, and the second diode D1, and the fourth switch Q4 (which can be a PNP triode) is turned on. Due to the opening of the third switch Q5, the output end (c - pole) of the fourth switch Q4 is at low level.

[0102] When the output port VOUT of the pressure-bearing switch Q2 is shorted to ground, the voltage at the output end VOUT of the pressure-bearing switch Q2 is 0. The resistors R9, R8, R7 and the diode D1 form a loop. The voltage drop across R8 is equal to the eb voltage drop across the fourth switch Q4, and the fourth switch Q4 conducts; the resistors R9, the triode Q4, the resistors R10, and R11 form a current loop, and the second switch Q3 conducts; then the base of the first switch Q1 is connected to ground, and the first switch Q1 conducts. Then the collector of the first switch Q1 is approximately at the voltage of VBAT. The voltage at the S pole of the pressure-bearing switch Q2 is approximately equal to the voltage at the G pole, and the pressure-bearing switch Q2 is turned off, realizing the shutdown of the power supply circuit.

[0103] In one embodiment, as Figure 1 shown and Figure 4 shown, the electronic fuse circuit further includes:

[0104] A current detection module 50, a voltage detection module 60 and a wake-up module 70 built with discrete components. Among them, the first detection end of the current detection module 50 is connected to the output end of the current limiting output module 30, the second detection end of the current detection module 50 is connected to the input end of the pressure-bearing switch Q2, and the detection output end of the current detection module 50 is used to output a sampled current signal;

[0105] The input end of the voltage detection module 60 is connected to the output end of the pressure-bearing switch Q2. The control end of the voltage detection module 60 is used to input a voltage sampling control signal, and the output end of the voltage detection module 60 is used to output a sampled voltage signal;

[0106] The input end of the wake-up module 70 is connected to the detection output end of the current detection module. The wake-up module 70 is used to compare the sampled current signal with a preset wake-up signal current threshold and output a wake-up control signal.

[0107] The electronic fuse circuit of this embodiment combines the functions of current sampling and voltage sampling, and reports the fault information to the processor in time, so that the processor can make control instructions; it realizes the dual protection of both hardware self-protection and software-assisted protection of the circuit, greatly improving the reliability of the circuit. When the system is in the sleep state, if there is a wake-up situation in the external load and the working current increases, if the circuit of the processor supports ADC sampling wake-up, it can be woken up by directly reading the value of the current sampling. If the processor does not support ADC sampling wake-up, it can directly read the high and low level output information of this circuit to wake up the control unit.

[0108] In one embodiment, as Figure 1 shown, the current detection module 50 includes:

[0109] Current sensing resistor (sampling resistor) Rsense, current limiting resistors R21, R22, R23, R24, R25, and operational amplifier U1, filter capacitor C4. Among them, the non-inverting input terminal of operational amplifier U1 is connected to the input terminal of current sensing resistor Rsense through resistor R22, and the inverting input terminal of operational amplifier U1 is connected to the output terminal of current sensing resistor Rsense through resistor R23. The input terminal of current sensing resistor Rsense is connected to the output terminal of current limiting output module 30, and the output terminal of current sensing resistor Rsense is connected to the input terminal of pressure-bearing switch Q2; the output terminal of operational amplifier U1 is connected to one end of resistor R25, and the other end of resistor R25 serves as the detection output terminal of current detection module 50 to output detection signal Current_ADC, and this detection output terminal is used to connect to the processor. One end of resistor R24 is connected to the inverting input terminal of operational amplifier U1, and the other end of resistor R24 is connected to the output terminal of operational amplifier U1; one end of resistor R21 is connected to the non-inverting input terminal of operational amplifier U1, and the other end of resistor R21 is connected to bias power supply VDD.

[0110] Among them, the input terminal of this resistor Rsense serves as the first detection terminal of current detection module 50, and the output terminal of current sensing resistor Rsense serves as the second detection terminal of current detection module 50.

[0111] The resistors Rsense, R21, R22, R23, R24, R25 and operational amplifier U1 in the above current detection module 50 form an operational amplifier circuit. Preferably, the resistance values of resistor R21 and resistor R24 are equal, and the resistance values of resistor R22 and resistor R23 are equal. Then this operational amplifier circuit can reduce the influence of the common-mode voltage and facilitate the calculation of the gain of the operational amplifier. Specifically, the current detection operation formula of the current sampling detection module is as follows:

[0112]

[0113] In the formula, Iout is the circuit supply current, Vcurrent_ADC is the output voltage of operational amplifier U1, which can be read by the main control unit (processor); VDD is the bias voltage of operational amplifier U1; Rsense is the current sensing resistor.

[0114] The working principle of the above current detection module 50 is as follows:

[0115] When the supply current flows through the current-sensing resistor Rsense, the operational amplifier U1 samples the voltage across the current-sensing resistor Rsense, amplifies the voltage across the resistor Rsense by a gain A, and the processor MCU reads the output voltage of the operational amplifier U1; the current is converted according to the above current detection operation formula. The current detection data is sent to the processor MCU through the feedback detection signal Current_ADC, and the circuit supply current Iout is calculated in the processor MCU, so that the processor MCU controls the output switch control signal MCU_Control_1 to be at a high level and the load power distribution signal MCU_Control_2 to be at a low level, realizing the processor MCU to control the shutdown of the electronic fuse circuit and increasing the reliability of circuit protection.

[0116] Among them, the voltage detection module 60 includes:

[0117] Resistors R15, R16, R17, R18, R19, R20, PNP transistor Q6, NPN transistor Q7, and filter capacitor C3. Among them, the control terminal of the NPN transistor Q7 is connected to the processor MCU through the resistor R17 for receiving the voltage sampling control signal MCU_Control_3. The input terminal of the NPN transistor Q7 is connected to the control terminal of the PNP transistor Q6 through the resistor R16. The output terminal of the NPN transistor Q7 is connected to the ground. One end of the resistor R18 is connected to the control terminal of the NPN transistor Q7, and the other end of the resistor R18 is connected to the output terminal of the NPN transistor Q7.

[0118] The input terminal of the PNP transistor Q6 is connected to the output terminal of the pressure-bearing switch Q2. The output terminal of the PNP transistor Q6 is connected to the processor MCU through the resistor R19 for outputting a sampled voltage signal Voltage_ADC from the output terminal of the resistor R19. One end of the resistor R15 is connected to the control terminal of the PNP transistor Q6, and the other end of the resistor R15 is connected to the input terminal of the PNP transistor Q6. One end of the resistor R20 is connected to the resistor R19, and the other end is connected to the ground. The filter capacitor C3 is connected in parallel with the resistor R20.

[0119] With the voltage detection module 60 having the above structure, when the voltage sampling control signal MCU_Control_3 outputs a high level, the NPN transistor Q7 conducts, the PNP transistor Q6 conducts, and the output port voltage flows through the resistors R19 and R20 for voltage division. The voltage obtained by voltage division is read by the processor MCU. Then, the voltage detection formula of the voltage detection circuit is:

[0120]

[0121] In the formula, Vout is the circuit supply voltage to be calculated, and Vvoltage_ADC is the voltage read by the processor MCU.

[0122] The working principle of the above voltage detection module 60 is as follows:

[0123] By setting the voltage sampling control signal MCU_Control_3 to a high level, the NPN transistor Q7 conducts, and then a ground loop is formed by resistors R15 and R16. The voltage drop across R15 is equal to the voltage between the emitter and base of transistor Q6, and the PNP transistor Q6 conducts. The voltage at the VOUT output port is divided by resistors R19 and R20, and the processor MCU reads the voltage drop across resistor R20 and calculates the output voltage conversion with reference to the above voltage detection formula. The sampled voltage signal Voltage_ADC detected is fed back to the processor MCU through the output terminal of resistor R19, which enables the processor MCU to control the switch control signal MCU_Control_1 to be at a high level and the load power distribution signal MCU_Control_2 to be at a low level, so as to realize the processor MCU to control the closing of the electronic fuse circuit and increase the reliability of circuit protection.

[0124] When the voltage sampling control signal MCU_Control_3 is set to a low level, the voltage detection function of the electronic fuse circuit can be turned off.

[0125] Among them, as Figure 1 shown, the wake-up module 70 includes:

[0126] Resistors R25, R26, R27, R28, R29, comparator U2 and filter capacitor C5. Among them, the first input terminal 2IN+ of comparator U2 is connected to the output terminal of the current detection module 50 through resistor R26. The second input terminal 2IN- of comparator U2 is connected to the power supply VCC through resistor R27 and connected to the ground through resistor R28. The output terminal of comparator U2 is connected to one end of resistor R29, and the other end of resistor R29 is connected to filter capacitor C5 and the processor MCU. The other end of resistor R29 serves as the output terminal of the wake-up module 70, outputting the wake-up control unit signal WAKEUP_SIG.

[0127] According to the circuit structure of the above wake-up module 70, the current threshold calculation formula of the wake-up control unit signal WAKEUP_SIG is:

[0128]

[0129] In the formula, I WAKE_TH is the current threshold, R sense is the resistance value of the current detection resistor, VCC is the supply voltage of operational amplifier U1, and VDD is the bias voltage of operational amplifier U1.

[0130] The working principle of the above wake-up module 70 is as follows:

[0131] When the external load is in the working state and the working current increases, if the MCU control unit circuit supports ADC sampling wake-up, it can be woken up by directly reading the detection signal Current_ADC value sampled by the current detection module 50.

[0132] If the control unit does not support wake-up by ADC sampling, directly read the wake-up control unit signal WAKEUP_SIG. According to the above current threshold calculation formula, when the working current is greater than the current threshold I WAKE_TH , the wake-up control unit signal WAKEUP_SIG is at a high level, and when the working current is less than the current threshold I WAKE_TH , the wake-up control unit signal WAKEUP_SIG is at a low level; then the high-level rising edge that appears due to the increase in the working current can be read to wake up the processor MCU.

[0133] The electronic fuse circuit of this embodiment has the following advantages:

[0134] First, all modules are designed with discrete components, and the overall cost is low, which is convenient for production and procurement;

[0135] Second, the logic of the circuit is simple, and there are few control signals, which can realize the distribution control of the electronic fuse, such as the charging on and off of capacitive / non-capacitive loads, current limiting output, overcurrent (short circuit) protection, current sampling, voltage sampling, control unit wake-up, and low-power maintenance power supply for system sleep.

[0136] Third, it can cooperate with the processor MCU for logic control to realize functions such as current limiting output and short circuit protection; in addition to the hard protection function of the hardware design, it can also combine with the processor MCU for data feedback to increase the reliability of protection.

[0137] In one embodiment, as Figure 1 shown, a current limiting circuit is provided, and the current limiting circuit includes:

[0138] A current limiting output module 30 and a pressure-bearing switch Q2. The input end of the current limiting output module 30 is connected to the power supply, the output end of the current limiting output module 30 is connected to the load through the pressure-bearing switch Q2, and the control end of the current limiting output module 30 is used to control the pressure-bearing switch Q2 to work in the amplification region when the supply current of the power supply is greater than the preset current limiting output threshold, so as to limit the output current within the current limiting output threshold.

[0139] Among them, when the supply current from the power supply flows through the current-limiting output module 30, when the supply current of the current-limiting output module 30 is greater than the preset current-limiting output threshold, the pressure-bearing switch Q2 is controlled to work in the amplification region, and the pressure-bearing switch Q2 bears most of the voltage, so that the circuit is in a dynamic balance of power supply, so as to maintain the current output within the current-limiting output threshold.

[0140] In one embodiment, as Figure 1 shown, the current-limiting output module 30 includes:

[0141] A first resistor R1, a second resistor R2, a third resistor R3 and a first switch Q1. The input end of the first resistor R1 is connected to the power supply, and the output end of the first resistor R1 is used to connect the input end of the pressure-bearing switch Q2;

[0142] The input end of the second resistor R2 is connected to the input end of the first resistor R1. The second resistor R2 is connected in series with the third resistor R3, and the output end of the third resistor R3 is connected to the output end of the first resistor R1;

[0143] The input end of the first switch Q1 is connected to the input end of the first resistor R1. The output end of the first switch Q1 is connected to the control end of the pressure-bearing switch Q2, and the control end of the first switch Q1 is used to connect the output end of the second resistor R2.

[0144] Among them, when the supply current of the power supply flows through the first resistor R1 and reaches the current-limiting output threshold, the voltage drop across the second resistor R2 is greater than the reference voltage that can turn on the first switch Q1. Therefore, the first switch Q1 is turned on, and the output end (i.e., the c pole) of the first switch Q1 is approximately the voltage of the power supply VBAT, so that the voltage between the control end and the input end of the pressure-bearing switch Q2 (i.e., the GS pole voltage) will change, but will not become 0V. Furthermore, the pressure-bearing switch Q2 works in the amplification region, and most of the voltage begins to be borne by the pressure-bearing switch Q2, so that the circuit is in a dynamic balance of power supply, so as to maintain the current output within the current-limiting output threshold.

[0145] In other application scenarios, Figure 1 the current-limiting output module 30 in

[0146] can also be applied to other power distribution and supply circuits. One end of the power supply circuit is the power supply, and the other end of the power supply circuit is connected to the load. The current-limiting output from the power supply to the load is realized through the current-limiting output module and the pressure-bearing switch connected in series in the power supply circuit.

[0147]

[0148] Among them, I th is the current limiting output threshold, V be is the voltage between the input terminal and the control terminal of the first switch Q1, R1 is the resistance value of the first resistor R1, R2 is the resistance value of the second resistor R2, and R3 is the resistance value of the third resistor R3.

[0149] Among them, the current limiting output threshold can be set according to the parameters of the first resistor R1, the second resistor R2, the third resistor R3, and the first switch Q1.

[0150] The above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and 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 invention, and should all be included in the protection scope of the present invention.

Claims

1. An electronic fuse circuit, characterized in that, The electronic fuse circuit includes: A switch control module (10), a pre-charge enable circuit module (20), and a current-limiting output module (30) built with discrete components. Among them, the input end of the switch control module (10) is used to input a switch control signal, and the output end of the switch control module (10) is connected to the control end of the current-limiting output module (30); the input end of the pre-charge enable circuit module (20) is used to input a load power distribution signal, and the output end of the pre-charge enable circuit module (20) is connected to the input end of the switch control module (10); The input end of the current-limiting output module (30) is connected to the power supply, the output end of the current-limiting output module (30) is connected to the load through a pressure-bearing switch (Q2), and the control end of the current-limiting output module (30) is used to control the pressure-bearing switch (Q2) to operate in the amplification region when the supply current of the power supply is greater than a preset current-limiting output threshold, so as to limit the output current within the current-limiting output threshold.

2. The electronic fuse circuit according to claim 1, wherein The current-limiting output module (30) includes: A first resistor (R1), a second resistor (R2), a third resistor (R3), and a first switch (Q1). The input end of the first resistor (R1) is connected to the power supply, and the output end of the first resistor (R1) is used to connect to the input end of the pressure-bearing switch (Q2); The input end of the second resistor (R2) is connected to the input end of the first resistor (R1). The second resistor (R2) is in series with the third resistor (R3), and the output end of the third resistor (R3) is connected to the output end of the first resistor (R1); The input end of the first switch (Q1) is connected to the input end of the first resistor (R1), the output end of the first switch (Q1) is connected to the control end of the pressure-bearing switch (Q2), and the control end of the first switch (Q1) is used to connect to the output end of the second resistor (R2) and the output end of the switch control module (10).

3. The electronic fuse circuit according to claim 2, characterized in that, The formula for the current-limiting output threshold limited by the current-limiting output module (30) is as follows: Among them, I th is the current limiting output threshold, V be is the voltage between the input terminal and the control terminal of the first switch (Q1), R1 is the resistance value of the first resistor (R1), R2 is the resistance value of the second resistor (R2), and R3 is the resistance value of the third resistor (R3).

4. The electronic fuse circuit according to claim 2, characterized in that, The current-limiting output module (30) further includes: A fourth resistor (R6). The input end of the fourth resistor (R6) is connected to the control end of the first switch (Q1), and the output end of the fourth resistor (R6) is connected to the output end of the switch control module (10).

5. The electronic fuse circuit according to claim 1, characterized in that, The switch control module (10) includes: A second switch (Q3), a fifth resistor (R10), a sixth resistor (R11), a first diode (D3), and a seventh resistor (R2). The input terminal of the second switch (Q3) is used to connect to the control terminal of the current-limiting output module (30). The output terminal of the second switch (Q3) is connected to ground. The control terminal of the second switch (Q3) is respectively connected to the input terminals of the fifth resistor (R10) and the sixth resistor (R11). The output terminal of the fifth resistor (R10) serves as the input terminal of the switch control module (10). The output terminal of the sixth resistor (R11) is connected to ground. The output terminal of the fifth resistor (R10) is connected to the first diode (D3), and the first diode (D3) is connected in series with the seventh resistor (R2).

6. The electronic fuse circuit according to claim 1, wherein The precharge enabling circuit module (20) includes: A third switch (Q5), an eighth resistor (R13), and a ninth resistor (R14). The control terminal of the third switch (Q5) is respectively connected to the output terminal of the eighth resistor (R13) and the input terminal of the ninth resistor (R14). The input terminal of the eighth resistor (R13) is used to input a load power distribution signal. The output terminal of the ninth resistor (R14) is connected to ground. The input terminal of the third switch (Q5) is connected to ground, and the output terminal of the third switch (Q5) is connected to the input terminal of the switch control module (10).

7. The electronic fuse circuit according to claim 1, wherein The electronic fuse circuit further includes: A short-circuit-to-ground protection module (40) built with discrete components. The input terminal of the short-circuit-to-ground protection module (40) is connected to the output terminal of the pressure-bearing switch (Q2). The output terminal of the short-circuit-to-ground protection module (40) is connected to the input terminal of the switch control module (10). The short-circuit-to-ground protection module (40) is used to output a short-circuit-to-ground protection signal to the switch control module (10) when a short-circuit-to-ground fault is detected, and controls the pressure-bearing switch (Q2) to turn off through the switch control module (10) and the current-limiting output module (30).

8. The electronic fuse circuit according to claim 7, wherein The short-circuit-to-ground protection module (40) includes: A fourth switch (Q4), a tenth resistor (R7), an eleventh resistor (R8), a twelfth resistor (R9), and a second diode D1. The input terminal of the fourth switch (Q4) is connected to the power supply through the twelfth resistor (R9). The output terminal of the fourth switch (Q4) is connected to the input terminal of the switch control module (10). The control terminal of the fourth switch (Q4) is sequentially connected to the output terminal of the pressure-bearing switch (Q2) through the tenth resistor (R7) and the second diode D1. One end of the eleventh resistor (R8) is connected to the control terminal of the fourth switch (Q4), and the other end of the eleventh resistor (R8) is connected to the input terminal of the fourth switch (Q4).

9. The electronic fuse circuit according to claim 1, wherein, The electronic fuse circuit further includes: A current detection module (50), a voltage detection module (60) and a wake-up module (70) built with discrete components, wherein a first detection end of the current detection module (50) is connected to an output end of the current limiting output module (30), a second detection end of the current detection module (50) is connected to an input end of the pressure-bearing switch (Q2), and a detection output end of the current detection module (50) is used for outputting a sampled current signal; An input end of the voltage detection module (60) is connected to an output end of the pressure-bearing switch (Q2), a control end of the voltage detection module (60) is used for inputting a voltage sampling control signal, and an output end of the voltage detection module (60) is used for outputting a sampled voltage signal; An input end of the wake-up module (70) is connected to a detection output end of the current detection module, and the wake-up module (70) is used for comparing the sampled current signal with a preset wake-up signal current threshold and outputting a wake-up control signal.

10. A current limiting circuit, characterized in that, The current limiting circuit includes: A current limiting output module (30) and a pressure-bearing switch (Q2), an input end of the current limiting output module (30) is connected to a power supply, an output end of the current limiting output module (30) is connected to a load through the pressure-bearing switch (Q2), and a control end of the current limiting output module (30) is used for controlling the pressure-bearing switch (Q2) to work in an amplification region when a supply current of the power supply is greater than a preset current limiting output threshold, so as to limit the output current within the current limiting output threshold.

11. The current limiting circuit according to claim 10, wherein The current limiting output module (30) includes: A first resistor (R1), a second resistor (R2), a third resistor (R3) and a first switch (Q1), an input end of the first resistor (R1) is connected to the power supply, and an output end of the first resistor (R1) is used for connecting to an input end of the pressure-bearing switch (Q2); An input end of the second resistor (R2) is connected to the input end of the first resistor (R1), the second resistor (R2) is in series with the third resistor (R3), and an output end of the third resistor (R3) is connected to the output end of the first resistor (R1); An input end of the first switch (Q1) is connected to the input end of the first resistor (R1), an output end of the first switch (Q1) is connected to a control end of the pressure-bearing switch (Q2), and a control end of the first switch (Q1) is used for connecting to an output end of the second resistor (R2).

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