Surge protection circuit

Abstract

The utility model provides a surge protection circuit which solves the problems that when an existing mass flow meter is used, a product is often placed outdoors and is extremely prone to being damaged by induction lightning stroke, conduction is conducted from a main line to a branch line or from the branch line to a bus, and the like, and according to the main scheme, the surge protection circuit comprises an access end, a gas discharge tube, a self-recovery fuse, a bidirectional TVS diode and a common mode inductor, one end of each gas discharge tube is grounded, the other end of each gas discharge tube is connected with the resettable fuse in series, one end of each bidirectional TVS diode is connected with the resettable fuse in series, the other end of each bidirectional TVS diode is connected with the common mode inductor in series, and the positive electrode and the negative electrode of the access end are electrically connected with the positive electrode and the negative electrode of the common mode inductor respectively.

Description

Technical Field

[0001] This utility model relates to the field of instrumentation technology, and in particular to a surge protection circuit. Background Technology

[0002] Mass flow meters directly measure the mass flow rate of the medium passing through them, and can also measure the density and indirectly the temperature of the medium. Because the transmitter is an intelligent instrument based on a microcontroller, it can derive more than a dozen parameters from the three basic quantities mentioned above for user application. Mass flow meters offer flexible configuration, powerful functions, and a high performance-price ratio, making them a new generation of flow meters.

[0003] Existing mass flow meters are often placed outdoors, making them highly susceptible to damage from induced lightning strikes. This damage can travel from the main line to branch lines or vice versa. Commonly used surge protection devices include discharge tubes, surge suppression inductors, varistors, X capacitors, Y capacitors, common-mode inductors, and TVS diodes. The common practice is to place slow-responding devices that withstand high current and voltage at the input of the circuit, and devices with the fastest response but low voltage and current tolerance at the end, or at the input of devices easily damaged by surges. Therefore, we propose a surge protection circuit to address these issues. Utility Model Content

[0004] The technical problem to be solved by this utility model is to overcome the defects of the existing technology. This utility model proposes a surge protection circuit. When a surge current or voltage suddenly occurs in an electrical circuit or communication line due to external interference, the surge protection circuit can conduct and divert the current in a very short time, thereby avoiding damage to the equipment caused by the surge.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is: a surge protection circuit, characterized in that it includes: an input terminal, a gas discharge tube, a resettable fuse, a bidirectional TVS diode, and a common-mode inductor. The gas discharge tube may include multiple tubes, one end of which is grounded and the other end is connected in series with the resettable fuse. The bidirectional TVS diode includes multiple tubes, one end of which is connected in series with the resettable fuse and the other end of which is connected in series with the common-mode inductor. The positive and negative terminals of the input terminal are respectively electrically connected to the positive and negative terminals of the common-mode inductor.

[0006] Furthermore, the access terminal includes RS485, current loop / Hart, and pulse terminal.

[0007] Furthermore, the surge protection circuit corresponding to RS485 includes two gas discharge tubes, two resettable fuses, three bidirectional TVS diodes, and one common-mode inductor. The two gas discharge tubes are connected in series, the two resettable fuses are connected in series at the positive and negative terminals of the circuit, and the three bidirectional TVS diodes are connected in parallel in pairs.

[0008] Furthermore, the surge protection circuit corresponding to the current loop / Hart includes one gas discharge tube, two resettable fuses, three bidirectional TVS diodes, and one common-mode inductor. The two resettable fuses are connected in series at the positive and negative terminals of the circuit, respectively, and the three bidirectional TVS diodes are connected in parallel in pairs.

[0009] Furthermore, the surge protection circuit corresponding to the pulse terminal includes two resettable fuses, one bidirectional TVS diode, and one common-mode inductor. The two resettable fuses are connected in series at the positive and negative terminals of the circuit, respectively, and the bidirectional TVS diode is connected in parallel with the common-mode inductor.

[0010] Compared with existing technologies, the beneficial effects of this invention include: by adopting the above circuit structure, when a surge occurs, the TVS diode reacts first, clamping the voltage to a predetermined low value and simultaneously entering a low-resistance state, providing a low-impedance conduction path for the instantaneous current. Approximately one microsecond later, the gas discharge tube begins to operate, triggering discharge and guiding the current to ground. If the current continues to rise and exceeds the protection range of the resettable fuse, the resettable fuse will instantly enter a high-resistance state, rapidly reducing the current in the circuit, thereby limiting and protecting the circuit. Attached Figure Description

[0011] The disclosure of this utility model is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this utility model. In the drawings, the same reference numerals are used to refer to the same parts. Wherein:

[0012] Figure 1 The schematic diagram shows a surge protection circuit structure according to one embodiment of the present invention.

[0013] Figure 2 The schematic diagram illustrates the working principle of a bidirectional TVS diode according to one embodiment of the present invention.

[0014] Figure 3 The diagram schematically shows a VI curve corresponding to a bidirectional TVS diode according to one embodiment of the present invention. Detailed Implementation

[0015] It is readily understood that, based on the technical solution of this utility model, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of this utility model. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative descriptions of the technical solution of this utility model and should not be considered as the entirety of this utility model or as limitations or restrictions on the technical solution of this utility model.

[0016] According to one embodiment of the present invention, in conjunction with Figure 1 As shown.

[0017] like Figure 1 As shown, for the overall circuit structure, a surge protection circuit includes: an RS485 circuit, a HART communication circuit, and a pulse circuit. When a spike current or voltage is suddenly generated in the electrical circuit or communication line due to external interference, the surge protection circuit can conduct and shunt the current in a very short time, thereby avoiding damage to the equipment caused by the surge.

[0018] The circuit mainly includes a first-stage protection unit for first-stage leakage of input voltage; a second-stage protection unit for preventing the failure to timely leakage of excessive current surges, thereby acting as a fuse system to protect the circuit; a third-stage protection unit for second-stage leakage of residual voltage after the first-stage leakage; and a fourth-stage unit for suppressing common-mode interference.

[0019] The first-level unit is a gas discharge tube, whose main function is to protect electronic equipment from overvoltage damage. When the external voltage exceeds a certain threshold, the gas discharge tube will trigger a discharge, introducing the overvoltage to the ground wire, thereby protecting the electronic equipment connected in parallel with the discharge tube.

[0020] The second-level unit is a resettable fuse. When the circuit encounters a large current surge, the system cannot discharge the current in time. The resettable fuse will quickly form a high-resistance state, and the operating current will decrease rapidly, thereby limiting and protecting the circuit. When the surge ends, the resettable fuse will automatically return to a low-resistance state, and the circuit will work normally.

[0021] The third-stage unit is a bidirectional TVS (Transient Voltage Suppressor) diode. When the circuit is operating normally, the TVS diode is in the off state and does not affect normal circuit operation. When an abnormal overvoltage occurs and reaches the TVS diode's breakdown voltage, the TVS diode rapidly changes from a high-resistance state to a low-resistance state, discharging the transient overcurrent caused by the overvoltage to ground, while simultaneously clamping the abnormal overvoltage to a lower level, thus protecting the subsequent circuits from damage caused by the abnormal overvoltage. When the abnormal overvoltage disappears, the TVS diode's resistance returns to the high-resistance state.

[0022] The fourth level unit is the common-mode inductor. Common-mode inductors are mainly used to limit the current during common-mode noise and surge power flow, and to protect other components from damage by controlling the current in the circuit. Their principle is to limit the change in current on two conductors and the potential difference between them through magnetic coupling.

[0023] TVS diodes and gas discharge tubes are commonly used devices in surge protection circuits. TVS diodes have a fast response and can clamp the voltage to a predetermined value, but they can only carry a small current. Gas discharge tubes can carry a large current, but their response speed is slow. Therefore, gas discharge tubes are used as the first level of protection, undertaking the task of greater energy consumption and grounding discharge. TVS diodes are used to protect communication lines and data transmission lines.

[0024] The circuit structure will be further explained below in conjunction with three application scenarios.

[0025] Example 1

[0026] The surge protection circuit corresponding to RS485 uses differential signal negative logic. Logic "1" is represented by a voltage difference of +(2~6)V between the two lines; logic "0" is represented by a voltage difference of -(2~6)V between the two lines. The maximum data transmission rate of RS-485 is 10Mbps.

[0027] The circuit includes two gas discharge tubes, two resettable fuses, three bidirectional TVS diodes, and one common-mode inductor. The two gas discharge tubes are connected in series, the two resettable fuses are connected in series at the positive and negative terminals of the circuit, and the three bidirectional TVS diodes are connected in parallel in pairs.

[0028] Example 2

[0029] Corresponding to the surge protection circuit of the current loop / Hart, HART communication refers to a half-duplex communication method. Its characteristic is that it realizes digital signal communication on existing analog signal transmission lines. It is a transitional product in the transition from analog to digital systems, and therefore has strong market competitiveness and has developed rapidly during the current transition period. HART communication uses a 0.5mA amplitude audio digital signal superimposed on a low-frequency 4-20mA analog signal for bidirectional digital communication, with a data transmission rate of 1.2kbit / s.

[0030] The circuit specifically includes one gas discharge tube, two resettable fuses, three bidirectional TVS diodes, and one common-mode inductor. The two resettable fuses are connected in series at the positive and negative terminals of the circuit, respectively, and the three bidirectional TVS diodes are connected in parallel in pairs.

[0031] Example 3

[0032] In contrast to surge protection circuits corresponding to pulse terminals, pulse output refers to the output of voltage or current signals in a discrete pulse manner in the electronics and communications fields, achieved through the control of switch states. Pulse output is widely used in digital circuits, timers, sensors, communication systems, and other fields, enabling precise time control and data transmission.

[0033] The circuit specifically includes two resettable fuses, one bidirectional TVS diode, and one common-mode inductor. The two resettable fuses are connected in series across the positive and negative terminals of the circuit, respectively, and the bidirectional TVS diode is connected in parallel with the common-mode inductor.

[0034] Taking the RS485 circuit in Example 1 as an example, when a surge occurs, the TVS (DA1, DA2, DA3) reacts first, clamping the voltage to a predetermined low value and simultaneously entering a low-impedance state, providing a low-impedance conduction path for the instantaneous current. Approximately one microsecond later, the gas discharge tube begins to operate, triggering GA2 to discharge and directing the current to ground. At this time, the TVS (DA1, DA3) also directs current to the gas discharge tube GA1, triggering GA1 to discharge and directing the current to ground. If the current continues to rise and exceeds the protection range of the resettable fuses (FA1, FA2), FA1 and FA2 will instantly enter a high-impedance state, rapidly reducing the current in the circuit, thereby limiting and protecting the circuit.

[0035] The technical scope of this utility model is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this utility model, and all such modifications and variations should fall within the protection scope of this utility model.

Claims

1. A surge protection circuit, characterized in that, include: The device includes an access terminal, a gas discharge tube, a resettable fuse, a bidirectional TVS diode, and a common-mode inductor. The gas discharge tube may include multiple tubes, one end of which is grounded and the other end is connected in series with the resettable fuse. The bidirectional TVS diode may include multiple tubes, one end of which is connected in series with the resettable fuse and the other end of which is connected in series with the common-mode inductor. The positive and negative terminals of the access terminal are respectively electrically connected to the positive and negative terminals of the common-mode inductor.

2. The surge protection circuit according to claim 1, characterized in that: The access point includes RS485, current loop / Hart, and pulse terminal.

3. A surge protection circuit according to claim 2, characterized in that: The surge protection circuit corresponding to RS485 includes two gas discharge tubes, two resettable fuses, three bidirectional TVS diodes, and one common-mode inductor. The two gas discharge tubes are connected in series, the two resettable fuses are connected in series at the positive and negative terminals of the circuit, and the three bidirectional TVS diodes are connected in parallel in pairs.

4. A surge protection circuit according to claim 2, characterized in that: The surge protection circuit corresponding to the current loop / Hart includes one gas discharge tube, two resettable fuses, three bidirectional TVS diodes and one common-mode inductor. The two resettable fuses are connected in series at the positive and negative terminals of the circuit, respectively, and the three bidirectional TVS diodes are connected in parallel in pairs.

5. A surge protection circuit according to claim 2, characterized in that: The surge protection circuit corresponding to the pulse terminal includes two resettable fuses, one bidirectional TVS diode, and one common-mode inductor. The two resettable fuses are connected in series at the positive and negative terminals of the circuit, respectively, and the bidirectional TVS diode is connected in parallel with the common-mode inductor.

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