A protection circuit and a protection method for a weak current power supply port

Abstract

The present invention discloses a protection circuit for a weak current power supply port and a protection method therefor. The protection circuit includes a high-voltage protection sub-circuit, a filtering and delaying sub-circuit, a residual voltage absorption sub-circuit, and a damping sub-circuit that are connected in sequence. One end of the high-voltage protection sub-circuit is connected to the weak current power supply port, and the other end is connected to the filtering and delaying sub-circuit, which is used for high-voltage protection of the weak current power supply port. The filtering and delaying sub-circuit uses its own generated delay effect to enable the high-voltage protection sub-circuit to respond prior to the residual voltage absorption sub-circuit. The residual voltage absorption sub-circuit is used for absorbing the residual voltage that is not completely discharged after the varistor in the high-voltage protection sub-circuit is broken down. The damping sub-circuit is used for increasing the inductive reactance of the inductance coil, generating a damping effect, and suppressing the common-mode interference current. By adopting the present invention, multi-stage protection and filtering can be performed through the protection circuit to eliminate common-mode interference and differential-mode interference, and achieve protection against EFT and Surge.

Description

Technical Field

[0001] The present invention relates to the protection technology of power supply ports, and particularly to an electrical fast transient (EFT), surge protection circuit and its protection method for weak current power supply ports. Background Art

[0002] Most of the protection circuits for traditional weak current power supply ports adopt safety standard X / Y capacitors and filter out differential mode / common mode interference through filtering. However, the anti-interference ability of such protection circuits is very limited, and there is a risk of capacitor breakdown due to excessive transient voltage. Thus, it is obviously insufficient in the protection against EFT and Surge. Therefore, based on the requirements of electromagnetic compatibility (EMC) performance and circuit reliability, there is an urgent need to develop a new protection technology for weak current power supply ports.

[0003] The existing metal oxide varistor (MOV), as a commonly used EFT and surge absorption device, will be broken down when the voltage in the circuit changes suddenly. Its resistance value will decrease sharply, shunting and discharging the current in the circuit. And the transient voltage suppressor (TVS) has a faster response speed to spike voltages. The TVS tube can absorb instantaneous large pulse power between its two poles and clamp the voltage to a predetermined level, and can respond to transient overvoltage phenomena quickly and efficiently.

[0004] Therefore, on the basis of traditional safety standard capacitors and common mode inductance protection, when developing a new protection technology for weak current power supply ports, it can be considered to add a metal oxide varistor and a TVS tube to be used in combination to further improve the protection performance of weak current power supply ports. Summary of the Invention

[0005] In view of this, the main purpose of the present invention is to provide a protection circuit and its protection method for weak current power supply ports, aiming to perform multi-stage protection and filtering through this protection circuit to eliminate common mode interference and differential mode interference, realize the protection against EFT and Surge; and further improve the protection effect of the protection circuit.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A protection circuit for a weak current power supply port includes a high-voltage protection sub-circuit, a filtering and delaying sub-circuit, a residual voltage absorption sub-circuit and a damping sub-circuit connected in sequence;

[0008] One end of the high-voltage protection sub-circuit is connected to the weak current power supply port, and the other end is connected to the filtering and delaying sub-circuit, and is used for performing high-voltage protection on the weak current power supply port;

[0009] The filtering delay sub-circuit, by utilizing the delay effect generated by itself, enables the high-voltage protection sub-circuit to generate a response prior to the residual voltage absorption sub-circuit;

[0010] The residual voltage absorption sub-circuit is used to absorb the residual voltage that has not been completely discharged after the varistor in the high-voltage protection sub-circuit is broken down;

[0011] The damping sub-circuit is used to increase the inductive reactance of the inductance coil, generate a damping effect, and suppress the common-mode interference current.

[0012] Wherein: after the damping sub-circuit, there further includes:

[0013] The common-mode filtering sub-circuit is used to consume and filter the common-mode interference current through a filtering effect.

[0014] The connection mode of the high-voltage protection sub-circuit to the weak-current power supply port is:

[0015] One end of the varistor Z1 is connected to the positive pole of the DC power supply, and the other end is grounded to PE; one end of the varistor Z2 is connected to the positive pole of the DC power supply, and the other end is connected to the 0V ground; one end of the varistor Z3 is connected to the 0V ground, and the other end is grounded to PE.

[0016] The connection mode of the filtering delay sub-circuit to the high-voltage protection sub-circuit is: the capacitor C1 is connected across the two ends of the subsequent stage of the varistor Z2, the input pin of the inductor L1 is connected to one end of the capacitor C1, and the input pin of the inductor L2 is connected to the other end of the capacitor C1.

[0017] The connection mode of the residual voltage absorption sub-circuit to the filtering delay sub-circuit is:

[0018] The two poles of the TVS tube D3 are connected across the two output pins of the inductors L1 and L2, and the TVS tube D1 and the TVS tube D2 are respectively led out from the two pins of the TVS tube D3 and connected to the ground PE, and the two poles of the capacitor C2 are connected to the two ends of the subsequent stage of the TVS tube D3.

[0019] The connection mode of the damping sub-circuit to the filtering delay sub-circuit is:

[0020] Connect the two poles of the capacitor C2 to the two input pins of a common-mode inductor L3.

[0021] The connection mode of the common-mode filtering sub-circuit to the damping sub-circuit is:

[0022] Lead out from the two output pins of the common-mode inductor L3, and connect the capacitors C3 and C4 in series, and the middle of the capacitors C3 and C4 is grounded to PE.

[0023] A lightning protection device applying a weak-current power supply port protection circuit.

[0024] An electronic device applying a protection circuit for a weak-current power supply port.

[0025] A protection method for a weak-current power supply port, comprising the following steps:

[0026] A. Connect one end of the weak-current power supply port to be protected to a high-voltage protection sub-circuit, and connect the other end of the high-voltage protection sub-circuit to the filter delay sub-circuit;

[0027] B. By using the delay effect generated by the filter delay sub-circuit, make the high-voltage protection sub-circuit generate a response prior to the residual voltage absorption sub-circuit;

[0028] C. Absorb the residual voltage that has not been completely discharged after the varistor in the high-voltage protection sub-circuit is broken down through the residual voltage absorption sub-circuit;

[0029] D. Use the damping sub-circuit to increase the inductive reactance of the inductance coil, generate a damping effect, and suppress the common-mode interference current;

[0030] Preferably, after the step D, it further includes:

[0031] E. Use the common-mode filtering sub-circuit to consume and filter the common-mode interference current through filtering.

[0032] The protection circuit and the protection method for the weak-current power supply port according to the embodiments of the present invention have the following beneficial effects:

[0033] 1) The protection circuit of the present invention adopts multi-stage protection and multi-layer filtering processing, and has a good suppression effect on the transient current and transient high voltage generated by differential-mode interference and common-mode interference. Among them, the varistors Z1 and Z3 are first broken down, and the residual voltage formed after the breakdown is clamped and protected by the subsequent-stage TVS tubes. The common-mode inductance L3 and Y capacitors C3 / C4 also play a role in suppressing the common mode, thereby realizing the filtering of common-mode interference; the varistor Z2 is first broken down, and the residual voltage formed after the breakdown is clamped and protected by the TVS tube D3. The capacitors C1 and C2 cooperate with the inductors L1 and L2 to also play a role in differential-mode low-pass filtering, thereby realizing the filtering of differential-mode interference.

[0034] 2) The protection circuit provided in the embodiments of the present invention is applicable to providing protection for weak-current power supply circuits applied in various scenarios, especially for the protection of EFT and Surge, and significantly improves the electromagnetic compatibility performance. Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the multi-stage protection architecture of the protection circuit for the weak-current power supply port according to the embodiment of the present invention;

[0036] Figure 2 It is a schematic diagram of the principle of the protection circuit for the weak-current power supply port according to the embodiment of the present invention. Detailed implementation manners

[0037] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments of the present invention.

[0038] Figure 1 It is a schematic diagram of the multi - level protection architecture of the weak - current power supply port protection circuit in the embodiment of the present invention.

[0039] As Figure 1 shown, the multi - level protection architecture of the weak - current power supply port protection circuit mainly includes a plurality of sub - circuits connected in sequence, namely a high - voltage protection sub - circuit, a filtering and delaying sub - circuit, a residual voltage absorption sub - circuit, a damping sub - circuit, and a common - mode filtering sub - circuit.

[0040] Figure 2 It is a schematic diagram of the principle of the protection circuit of the weak - current power supply port in the embodiment of the present invention.

[0041] Referring to Figure 2 , the protection circuit of the weak - current power supply port specifically includes:

[0042] The first - level protection, that is, the high - voltage protection sub - circuit, mainly includes varistors Z1, Z2, and Z3;

[0043] The π - type filtering, that is, the filtering and delaying sub - circuit, mainly includes inductors L1, L2, capacitors C1, and C2;

[0044] The second - level protection, that is, the residual voltage absorption sub - circuit, mainly includes TVS diodes D1, D2, and D3;

[0045] The third - level protection, that is, the damping sub - circuit, mainly includes inductor L3;

[0046] The fourth - level protection, that is, the common - mode filtering sub - circuit, mainly includes capacitors C3 and C4.

[0047] Among the above - mentioned circuit elements: Z1, Z2, and Z3 are varistors; C1 and C2 are X - capacitors; D1, D2, and D3 are TVS diodes; L1 and L2 are differential - mode inductors; L3 is a common - mode inductor; C3 and C4 are Y - capacitors.

[0048] Referring to Figure 2 , the protection circuit of the weak - current power supply port in the embodiment of the present invention aims at the deficiency of the EMC performance of the existing protection circuit, especially to achieve and improve the protection against EFT and Surge.

[0049] In this embodiment, taking the weak - current power supply port (DC 24V power supply) to be protected as an example, as described above, the protection circuit mainly includes the following components: varistors, safety capacitors, differential - mode inductors, TVS diodes, and common - mode inductors. Through the circuit composed of the above - mentioned components, multi - level protection is achieved to ensure that the subsequent circuit is not damaged by EFT and Surge.

[0050] The protection circuit structure and its working principle of this low-voltage power supply port are as follows:

[0051] The protection circuit of the embodiment of the present invention includes four levels of protection sub-circuits and one level of π-type filter sub-circuit, where:

[0052] The first level of protection, that is, the high-voltage protection sub-circuit, is mainly composed of varistors Z1, Z2, and Z3. One end of varistor Z1 is connected to the positive pole of DC 24V, and the other end is grounded to PE; one end of varistor Z2 is connected to the positive pole of DC 24V, and the other end is connected to 0V ground; one end of varistor Z3 is connected to 0V ground, and the other end is grounded to PE. In practical applications, the high-voltage protection sub-circuit is mainly used to prevent strong electricity such as lightning, high voltage, and ultra-high voltage AC power transmission and transformation from being connected in series to the low-voltage power supply circuit to burn the power supply and the electronic devices connected thereto.

[0053] The π-type filter circuit, that is, the filter delay sub-circuit, is mainly composed of inductors L1, L2, capacitors C1, and C2. The X capacitor C1 is connected across the two ends of the subsequent stage of varistor Z2. The input pin of inductor L1 is connected to one end of capacitor C1, and the input pin of inductor L2 is connected to the other end of capacitor C1.

[0054] The second level of protection, that is, the residual voltage absorption sub-circuit, is mainly composed of TVS tubes D1, D2, and D3. The two poles of TVS tube D3 are connected across the two output pins of inductors L1 and L2, and TVS tubes D1 and D2 are respectively led out from both ends of TVD tube D3 and grounded to PE. The two poles of capacitor C2 are connected in parallel across both ends of TVS tube D3.

[0055] Here, in the second level of protection, the position of the TVS tube can be perfectly combined with the π-type filter sub-circuit. TVS tubes D1, D2, and D3 must be placed after inductors L1 and L2 and before capacitor C2 and inductor L3 of the third level of protection circuit. The reason for this design is that the response time of the TVS tube is much faster than that of the varistor. In this way, using the characteristic that the current of inductors L1 and L2 cannot change suddenly, a delay effect is achieved, so that the high-voltage protection sub-circuit responds before the residual voltage absorption sub-circuit. Therefore, it can well avoid the problem that the varistor of the first level of protection does not respond while the TVS tube of the subsequent stage responds first.

[0056] The reason for placing capacitor C2 and inductor L3 in the subsequent stage (damping sub-circuit) is that their functions in the circuit are to suppress and filter out interference signals in the form of filtering. Because for high-power interference, the filtering devices placed too far forward may be damaged, losing their functions and affecting the overall circuit operation at the same time. Similarly, capacitors C3 and C4 applicable to the fourth level of protection circuit (common-mode filtering sub-circuit) are placed at the end of the circuit, and the filtering devices are arranged as far back as possible, so as to make the protection effect of the protection circuit and the common-mode / differential-mode interference suppression effect the best.

[0057] The third-level protection, i.e., the damping sub-circuit, is mainly composed of L3. Two input pins of a common-mode inductor L3 are connected to two poles of a capacitor C2.

[0058] The fourth-level protection, i.e., the common-mode filtering sub-circuit, is mainly composed of capacitors C3 and C4. It is led out from two output pins of the common-mode inductor L3, and two Y capacitors C3 and C4 are connected in series. The middle of the capacitors C3 and C4 is grounded to PE. Through the protection and filtering of the entire protection circuit, most of the EFT and Surge interferences can be consumed or filtered out, playing a very reliable protection role for the subsequent working circuit.

[0059] In the selection of components in the embodiments of the present invention, considering that the voltage of the weak-current power supply port is 24V DC, in order to maintain a certain design margin, a derating design is carried out, and varistors Z1, Z2, and Z3 with a withstand voltage of 47V are selected. Considering the harmfulness of the leakage current to users, according to the national requirements for safety capacitors, the peak value of the leakage current cannot exceed 0.7mA, so the maximum value of the capacitor cannot exceed 4.7nF.

[0060] In the embodiments of the present invention, capacitors C1, C2, C3, and C4 are selected as 2.2nF, and the withstand voltage is selected as 1000V.

[0061] In the embodiments of the present invention, the clamping voltages of the selected TVS tubes D1, D2, and D3 shall not be lower than the upper limit value of the normal range of the input power supply and shall not be higher than the maximum tolerance limit of the subsequent components. In the embodiments of the present invention, the maximum reverse peak current of the selected TVS tubes is 30A, and the maximum clamping voltage is 49.9V.

[0062] In the embodiments of the present invention, the selected inductors L1 and L2 are differential-mode inductors with an inductance of 22uH and a rated current of 1.7A. The inductor L3 is a common-mode inductor. A common-mode inductor with a low differential-mode impedance shall be selected, with a rated working voltage of 80V, a rated current of 5A, and a DC resistance of only 10mΩ, which can meet the design requirements.

[0063] In the implementation of the present invention, it plays a protective role against common-mode interference, which is mainly achieved by varistors Z1, Z3, TVS diodes D1, D2, inductor L3, and capacitors C3, C4. When common-mode interference enters the circuit through the power supply port, it first enters the first-level protection of the circuit. The transient high voltage of the interference will cause the varistors Z1 / Z3 to be broken down first. At this time, the impedance of the varistors Z1, Z3 is very low, and most of the overvoltage will be discharged to the ground PE. However, it is very likely that the first-level protection is not sufficient to discharge all the interference to the ground. Therefore, two TVS diodes D1, D2 are added in the second-level protection to absorb the residual voltage that is not completely discharged after the varistors Z1, Z3 are broken down. On the basis of the first two levels of protection, a common-mode inductor L3 is added in the third-level protection. Due to the co-directionality of the current of common-mode interference, a co-directional magnetic field will be generated in the coil of the inductor, increasing the inductive reactance of the coil. The coil shows a high impedance and has a strong damping effect to suppress the common-mode interference current, thereby achieving the purpose of filtering.

[0064] Finally, by using the fourth-level protection, that is, the two Y capacitors C3, C4 of the common-mode filtering sub-circuit filter the common-mode interference to the ground PE through filtering. After the protection of the above multi-level circuits, the common-mode interference can be well consumed and filtered, ensuring that the subsequent working circuit will not be affected.

[0065] In the embodiment of the present invention, the protective effect against differential-mode interference is mainly achieved by a circuit composed of varistor Z2, capacitor C1, inductors L1, L2, TVS diode D3, capacitor C2, and inductor L3. When differential-mode interference enters the power supply port, it first passes through the varistor Z2 of the first-level protection. The transient high voltage of the interference will directly break down the varistor Z2. At this time, the impedance of Z2 drops suddenly, and the current flowing through itself rises sharply. The energy of the differential-mode interference is consumed by the internal resistance of the varistor Z2 in the form of a large current. Then, through π-type filtering, where capacitors C1, C2 are used as X capacitors, cooperating with two differential-mode inductors L1, L2, the differential-mode interference is filtered out in the form of filtering. In addition, the TVS diode D3 in the second-level protection can also be instantaneously turned on when common-mode interference comes, clamping the voltage at a predetermined position to absorb the residual voltage of the previous level. Finally, the leakage inductance of the common-mode inductor L3 also has a very effective effect on suppressing differential-mode interference.

[0066] In traditional circuits, varistors and TVS diodes are not used in combination. Since the response speed of TVS diodes is much faster than that of varistors, in most cases, common-mode / differential-mode interference is clamped by TVS diodes, and varistors cannot play their due absorption role. In response to this situation, the circuit design of the present invention solves this problem well. First of all, the TVS diodes D1, D2, and D3 must be placed at the rear stage of the differential-mode inductors L1 and L2. Since the current in the differential-mode inductors L1 and L2 cannot change suddenly, it can delay the time for interference to reach the TVS diodes. Especially for transient high voltages, the response speed of TVS diodes is faster than that of varistors. If there are no inductors L1 and L2 designed in front of the TVS diodes, when the transient high voltage of the interference enters the circuit, before the varistor in the first-stage protection can respond, the TVS diodes in the rear stage will conduct first, and at this time, the first-stage protection will lose its function and cannot achieve the protection effect. At the same time, two differential-mode inductors are combined with two X capacitors to form a π-type filter circuit, which not only ensures that both the varistor and the TVS diode can respond normally, but also can smooth the circuit current and make the clamping of the TVS diode more accurate.

[0067] The position of the TVS diode D3 should be placed as far as possible before the capacitor C2. Because in the rules of circuit protection and filtering, it is necessary to perform protection first and then filtering. Otherwise, if filtering is performed first without proper protection, once the rear-stage circuit is damaged by common-mode / differential-mode interference, the previous-stage filtering will lose its meaning and is likely to damage the filtering components, failing to achieve the protection effect, and thus not meeting the design intention of the protection circuit.

[0068] The protection circuit of the weak-current power supply port in the embodiment of the present invention can be applied in lightning protection devices or in various electronic devices using a secondary power supply as a backup power supply. The electronic devices include, but are not limited to, wireless communication base stations, microwave communication ground stations, and satellite communication ground stations, etc.

[0069] For EFT and Surge protection of the weak-current power supply port, without departing from the protection circuit design concept of the present application, various protection circuits can be evolved, and the same technical effects as those of this embodiment can be achieved, and all should be regarded as falling within the scope of patent protection of the protection circuit of the present invention.

[0070] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention.

Claims

1. A protection circuit for a weak current power supply port, characterized in that, it includes a high-voltage protection sub-circuit, a filtering and delaying sub-circuit, a residual voltage absorption sub-circuit, and a damping sub-circuit connected in sequence; One end of the high-voltage protection sub-circuit is connected to the weak current power supply port, and the other end is connected to the filtering and delaying sub-circuit, which is used for high-voltage protection of the weak current power supply port; The filtering and delaying sub-circuit uses its own generated delay effect to make the high-voltage protection sub-circuit respond before the residual voltage absorption sub-circuit; The residual voltage absorption sub-circuit is used to absorb the residual voltage that is not completely discharged after the varistor in the high-voltage protection sub-circuit is broken down; The damping sub-circuit is used to increase the inductive reactance of the inductor coil, generate a damping effect, and suppress the common-mode interference current.

2. The protection circuit for a weak current power supply port according to claim 1, characterized in that, after the damping sub-circuit, it further includes: A common-mode filtering sub-circuit, which is used to consume and filter the common-mode interference current through filtering.

3. The protection circuit for a weak current power supply port according to claim 1, characterized in that, The connection method of the high-voltage protection sub-circuit and the weak current power supply port is: One end of the varistor Z1 is connected to the positive pole of the DC power supply, and the other end is grounded to PE; one end of the varistor Z2 is connected to the positive pole of the DC power supply, and the other end is connected to the 0V ground; one end of the varistor Z3 is connected to the 0V ground, and the other end is grounded to PE.

4. The protection circuit for a weak current power supply port according to claim 1 or 3, characterized in that, The protection circuit further includes a varistor Z2; The connection method of the filtering and delaying sub-circuit and the high-voltage protection sub-circuit is: The capacitor C1 is connected across the two ends of the latter stage of the varistor Z2, the input pin of the inductor L1 is connected to one end of the capacitor C1, and the input pin of the inductor L2 is connected to the other end of the capacitor C1.

5. The protection circuit for a weak current power supply port according to claim 1, characterized in that, The connection method of the residual voltage absorption sub-circuit and the filtering and delaying sub-circuit is: The two poles of the TVS tube D3 are connected across the two output pins of the inductors L1 and L2, and the TVS tube D1 and the TVS tube D2 are respectively led out from the two ends of the TVS tube D3 and grounded to PE, and the two poles of the capacitor C2 are connected in parallel across the two ends of the TVS tube D3.

6. The protection circuit for a weak current power supply port according to claim 1, characterized in that, The protection circuit further includes a capacitor C2, and the connection method of the damping sub-circuit and the filtering and delaying sub-circuit is: Connect the two poles of the capacitor C2 to the two input pins of a common-mode inductor L3.

7. The protection circuit for a weak current power supply port according to claim 2, characterized in that, The connection method of the common-mode filtering sub-circuit and the damping sub-circuit is: Lead out from the two output pins of the common-mode inductor L3, and connect the capacitors C3 and C4 in series, and the middle of the capacitors C3 and C4 is grounded to PE.

8. A lightning protection device applying the protection circuit for a weak current power supply port according to any one of claims 1 to 7.

9. An electronic device applying the protection circuit for a weak current power supply port according to any one of claims 1 to 7.

10. A protection method for a protection circuit of a weak-current power supply port according to any one of claims 1-7, characterized in that, it includes the following steps: A. Connect one end of the weak-current power supply port to be protected to the high-voltage protection sub-circuit, and connect the other end of the high-voltage protection sub-circuit to the filter delay sub-circuit; B. Utilize the delay effect generated by the filter delay sub-circuit to make the high-voltage protection sub-circuit respond prior to the residual voltage absorption sub-circuit; C. Absorb the residual voltage that has not been completely discharged after the varistor in the high-voltage protection sub-circuit is broken down through the residual voltage absorption sub-circuit; D. Utilize the damping sub-circuit to increase the inductive reactance of the inductor coil and generate a damping effect to suppress the common-mode interference current.

11. The protection method for a weak-current power supply port according to claim 10, characterized in that, after step D, it further includes: E. Utilize the common-mode filtering sub-circuit to consume and filter the common-mode interference current through filtering.

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