Indirect lightning protection circuit and device selection method thereof

Abstract

The application belongs to the technical field of indirect lightning protection between cable ports of avionics, and particularly relates to an indirect lightning protection circuit and a device selection method thereof, wherein the indirect lightning protection circuit comprises: a gas discharge tube (GDT); a transient voltage suppression diode (TVS) connected in parallel with the GDT; and a pulse resistor (R) connected between a line in which the GDT and the TVS are located, for voltage division.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of indirect lightning protection between cable ports of avionics, and particularly relates to an indirect lightning protection circuit and a device selection method thereof. BACKGROUND

[0002] Lightning is an important natural factor affecting the flight safety of an aircraft. The avionics existing in the cabin of the aircraft do not need to be directly protected from lightning, but need to be designed for indirect lightning protection. The RTCA / DO-160G Chapter 22 is the main source of the indirect lightning protection requirements for avionics, which specifies different indirect lightning protection waveforms and levels to match the indirect lightning protection requirements of the avionics in different cabin sections of the aircraft.

[0003] The indirect lightning protection of the avionics mainly sets a special indirect lightning protection circuit at the port of the equipment. The protection circuit adopts different protection devices to construct a first lightning protection circuit, a second lightning protection circuit, a third lightning protection circuit, etc. according to the protection waveform and level.

[0004] In the patent document with the application number CN201911238087.5, a high-level lightning protection circuit and a design method are disclosed, in which a protection circuit based on a TVS tube is introduced. The protection circuit can only meet the 4th protection requirement, and the estimated pulse power of the TVS tube obtained by the method is the calculation result under the conditions of waveform 3 (5us and 500ns damped sinusoidal waveform) and waveform 4 (6.4 / 69us double exponential waveform). The nominal power of the TVS tube is the pulse power under the condition of 10 / T=1000us double exponential waveform. The error is large when the TVS tube is selected directly according to the calculation results of the two waveforms.

[0005] The present application is proposed in view of the existence of the above technical defects.

[0006] It should be noted that the disclosure of the above background art is only used to assist in understanding the inventive concept and technical solutions of the present application, and it does not necessarily belong to the prior art of the present patent application. In the absence of explicit evidence that the above content has been disclosed on the filing date of the present application, the above background art should not be used to evaluate the novelty and inventiveness of the present application. SUMMARY

[0007] The purpose of the present application is to provide an indirect lightning protection circuit and a device selection method thereof to overcome or alleviate at least one aspect of the known technical defects.

[0008] The technical solution of the present application is:

[0009] In one aspect, an indirect lightning protection circuit is provided, comprising:

[0010] Gas Discharge Tube (GDT);

[0011] Transient voltage suppressor diode (TVS) is connected in parallel with gas discharge tube (GDT).

[0012] The pulse resistor R is connected between the gas discharge tube (GDT) and the transient voltage suppressor diode (TVS) to perform voltage division. The pulse resistor R can be composed of multiple resistors connected in series.

[0013] On the other hand, a method for selecting indirect lightning protection circuit devices is provided, including:

[0014] Determine the maximum withstand voltage V based on the signal characteristics of the subsequent circuit. clamp-max and the maximum series resistance R max ;

[0015] Pre-select the transient voltage suppression diode TVS clamping voltage V clamp Required to be less than V clamp-max ;

[0016] Pre-select the pulse resistor R value R0, which must be less than or equal to R max ;

[0017] Pre-select the gas discharge tube GDT model and determine its breakdown voltage V. GDT-impulse Based on the breakdown voltages V1 and V2 with rising slopes of 100V / us and 1000V / us given in the GDT device datasheet, select its breakdown voltage V. GDT-impulse = (V1+V2) / 2, determine its clamping voltage V clamp-GDT It is required that it is less than V. clamp-max ;

[0018] Determine the open-circuit voltage V of waveform 4 or waveform 5 according to the requirements of the indirect lightning test. OC Short-circuit current I SC and internal resistance R S The internal resistance R S =V OC / I SC Determine the waveform 4 function expression Waveform 5A function expression

[0019] Calculate the conduction time ΔT1 of the transient voltage suppressor diode TVS, corresponding to waveform 4, where V WF4 (△T1)=V clamp Corresponding to waveform 5A is V WF5A (△T1)=V clamp ;

[0020] Calculate the conduction time ΔT2 of the gas discharge tube (GDT), corresponding to waveform 4. Corresponding to waveform 5A has

[0021] Calculate the pulse resistance R equivalent rectangular pulse maximum transient power value P MAX-R And pulse width T R Corresponding to waveform 4 has Corresponding to waveform 5A has

[0022] According to the pulse resistance R resistance R0, the maximum transient power value P MAX-R And pulse width T R , select the pulse resistance R type, such as resistance R0, the requirement pulse width T R , the pulse power is greater than the maximum transient power value P MAX-R ;

[0023] Calculate the transient voltage suppression diode TVS equivalent 10 / 20us double exponential waveform maximum transient power value P MAX-TVS And pulse width T TVS Corresponding to waveform 4 has Corresponding to waveform 5A has

[0024] Calculate the equivalent pulse width T of transient voltage suppression diode TVS TVS Corresponding to waveform 4 has Corresponding to waveform 5A has

[0025] Wherein, a is the waveform attenuation coefficient, b is the waveform rising coefficient;

[0026] According to the clamping voltage V clamp , the maximum transient power value P MAX-TVS And the equivalent pulse width T TVS Select the transient voltage suppression diode TVS type, such as clamping voltage V clamp , the requirement pulse width T TVS , the pulse power is greater than the maximum transient power value P MAX-TVS ;

[0027] Calculate the gas discharge tube GDT equivalent 8 / 20us double exponential waveform maximum current I MAX-GDT Corresponding to waveform 4 has I MAX-GDT = I 8×20 ×(e -120000×0.000008 -e -140000×0.000008 )、 Corresponding to waveform 5A has I MAX-GDT = I 8×20 ×(e -120000×0.000008 -e -140000×0.000008 )、 Wherein, I 8×20 is the current amplitude proportional coefficient;

[0028] Determine whether the pre-selected gas discharge tube GDT model meets the requirements, such as the maximum current I MAX-GDT Less than its maximum withstand current, then it meets the requirements. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the schematic diagram of the indirect lightning protection circuit provided by the embodiment of the present application;

[0030] Figure 2 is the pulse power curve diagram of SG732B-W3A series resistor provided by the embodiment of the present application;

[0031] Figure 3 is the pulse power curve diagram of SMJA series TVS provided by the embodiment of the present application;

[0032] Figure 4 is the schematic diagram of voltage waveform 5A provided by the embodiment of the present application;

[0033] Figure 5 is the schematic diagram of voltage waveform 4 provided by the embodiment of the present application.

[0034] In order to better illustrate the embodiments, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size, in addition, the drawings are only used for illustrative description, and cannot be understood as a limitation of the patent. DETAILED DESCRIPTION

[0035] In order to make the technical scheme of the present application and its advantages clearer, the technical scheme of the present application will be further described in detail below with reference to the drawings, it can be understood that the specific embodiments described herein are only part of the embodiments of the present application, and are only used to explain the present application, but not limited to the present application. It should be noted that, in order to facilitate description, only part of the present application is shown in the drawings, other related parts can refer to the usual design, in the case of no conflict, the embodiments in the present application and the technical features in the embodiments can be combined to obtain new embodiments.

[0036] In addition, unless otherwise defined, technical terms or scientific terms used in the description of the application shall be understood as the common meaning understood by one of ordinary skill in the art to which the application belongs. The words "upper", "lower", "left", "right", "center", "vertical", "horizontal", "inner", "outer" and the like used in the description of the application only indicate relative directions or positional relationships, and do not imply that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and the relative positional relationship may also change accordingly when the absolute position of the described object changes, therefore it cannot be understood as a limitation to the application. The "first", "second", "third" and the like used in the description of the application are only for the purpose of description, to distinguish different components, and cannot be understood as indicating or implying relative importance. The "one", "a" or "the" and the like used in the description of the application should not be understood as an absolute limitation on the number, but should be understood as the presence of at least one. The "including" or "containing" and the like used in the description of the application means that the elements or objects appearing before the word are encompassed by the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0037] In addition, it should be further pointed out that, unless otherwise explicitly specified and limited, the "installation", "connection", "connection" and the like used in the description of the application should be understood broadly, for example, the connection can be fixed connection, or detachable connection, or integral connection; can be mechanical connection, or electrical connection; can be directly connected, or indirectly connected through intermediate medium, or the internal communication of two elements, and those skilled in the art can understand the specific meaning of the application according to the specific circumstances.

[0038] The following will be described in conjunction with the accompanying drawings Figures 1 to 5 The application will be further described in detail.

[0039] An indirect lightning protection circuit, see Figure 1The circuit uses a gas discharge tube GDT, a pulse resistor R (which can also be multiple pulse resistors in series), a transient voltage suppression diode TVS tube, and in accordance with the indirect lightning signal flow, GDT is connected in parallel, R is connected in series, and TVS is connected in parallel. The response time of TVS is less than the response time of GDT. When indirect lightning is applied, TVS in the circuit is first turned on to clamp the ns-level overvoltage. As the transient voltage continues to rise, the voltage across the pulse resistor continues to rise. When the sum of the voltages across the pulse resistor R and the TVS is greater than the breakdown voltage of the GDT, the GDT will be turned on (short-circuit) to withstand most of the energy of the remaining indirect lightning test waveform. At this time, the TVS will be closed and in an open circuit state to avoid overloading and burning out, and can protect the RTCA / DO-160G "Airborne Equipment Environmental Test Conditions" Chapter 22 highest level 5 level requirements.

[0040] The main performance parameters of GDT include DC breakdown voltage, impulse breakdown voltage, maximum withstand current under 8 / 20us double exponential waveform, and clamping voltage. In addition, its response time is greater than 500ns;

[0041] The main performance parameters of TVS include breakdown voltage, maximum withstand power curve under 10 / Tus double exponential waveform, and clamping voltage. The response time is in the ns level.

[0042] In the indirect lightning test, waveform 3 is tested with waveform 4 or waveform 5A. The pulse width of waveform 3 is 5us, which is much smaller than the pulse width of waveform 4 (69us) and waveform 5A (120us). The source impedance internal resistance of waveform 3 (25Ω) is greater than the waveform internal resistance (4Ω) and the waveform 5A internal resistance (1Ω), so that the energy coupled to the device end of waveform 3 is smaller, i.e. it meets the requirements of waveform 4 or waveform 5A, and is considered to meet the requirements of waveform 3, so there is no need to calculate waveform 3. A device selection method for indirect lightning protection circuit is provided, which is as follows:

[0043] According to the signal characteristics of the rear circuit of the avionics equipment, the maximum withstand voltage V clamp-max and the maximum series resistance R max are determined;

[0044] The clamping voltage V clamp of the TVS is preselected and required to be less than V clamp-max ;

[0045] The pulse resistor R value R0 is preselected and required to be less than or equal to R max ;

[0046] The GDT model is preselected to determine its breakdown voltage V GDT-impulse . The 100V / us and 1000V / us rising slope breakdown voltages V1 and V2 given in the GDT device manual are selected, and the breakdown voltage V GDT-impulse= (V1+V2) / 2, while determining its clamping voltage V clamp-GDT , which is required to be less than V clamp-max ;

[0047] According to the requirements of the indirect lightning test, the open circuit voltage V OC , short circuit current I SC and internal resistance R S of waveform 4 or waveform 5A are determined, where R S = V OC / I SC , and its waveform function expression is determined, as shown in formulas (1)-(2), V WF4 (t) is the function expression of waveform 4, and V WF5A (t) is the function expression of waveform 5A.

[0048]

[0049]

[0050] The on-time △T1 of the TVS is calculated, and the calculation formula is shown in formulas (3)-(4).

[0051] V WF4 (△T1) = V clamp ……(3)

[0052] V WF5A (△T1) = V clamp ……(4)

[0053] The on-time △T2 of the GDT is calculated, and the calculation formula is shown in formulas (5)-(6).

[0054]

[0055]

[0056] The maximum transient power value P MAX-R and pulse width T R of the equivalent rectangular pulse of the pulse resistor R are calculated, and the calculation formula is shown in formulas (7)-(8). For waveform 4, the formulas are shown in formulas (7)-(8). For waveform 5A, the formulas are shown in formulas (7)-(8).

[0057]

[0058]

[0059] According to the pulse resistor value R0, the maximum transient power value P MAX-R and the pulse width T R , the pulse resistor model is selected. For example, the resistor value is selected as R0, and the SG73 2B-W3A series resistor is selected. Its pulse power curve is as followsFigure 2 As shown, the required pulse width is T. R At that time, the pulse power is greater than the maximum transient power value P. MAX-R At this point, the selected pulse resistor meets the requirements for indirect lightning protection.

[0060] Calculate the maximum transient power value P of the TVS equivalent 10 / T us double exponential waveform. MAX-TVS and pulse width T TVS P MAX-TVS For the calculation formula, please refer to formula (9). For the formula corresponding to waveform 4 and waveform 5A, please refer to formula (9):

[0061]

[0062] Pulse width T TVS The parameters of the double exponential waveform function differ depending on the value of , and the expression of the double exponential waveform function for TVS performance testing 10 / T us is formula (10):

[0063] I TVS (t)=I 0-TVS ×(e -at -e -bt )……(10)

[0064] Among them, I TVS (t) represents the test current, I 0-TVS Let be the current amplitude proportionality coefficient, a be the waveform attenuation coefficient, and b be the waveform rise coefficient. Taking their derivatives, we get formula (11):

[0065]

[0066] The derivative of the double exponential waveform function is 0 at 10µs, yielding formula (12):

[0067]

[0068] With T TVS Using half-peak time and 10µs as the maximum peak time, substituting into formula (10) yields formula (13):

[0069]

[0070] When the energy of the test waveform applied to the TVS is the same as the energy of the waveform during the TVS performance test, formula (14) can be obtained. For waveform 4 and waveform 5A, refer to formula (14):

[0071]

[0072] When T TVSWhen a certain value is taken, formula (13)-(14) can be established at the same time, at which T TVS will be the equivalent pulse width of TVS, etc.

[0073] According to the clamping voltage V clamp , the maximum transient power value P MAX-TVS , and the pulse width T TVS , the TVS model is selected, for example, the clamping voltage V clamp is selected, and the SMJA series TVS has a pulse power curve as shown in Figure 3 , and when the pulse width T TVS is required, the pulse power is greater than the maximum transient power value P MAX-TVS , at which time the selected TVS meets the indirect lightning protection requirements.

[0074] The maximum current I MAX-GDT of the GDT equivalent 8 / 20us double exponential waveform is calculated, and the 8 / 20us double exponential current waveform function can be expressed by formula (15), I GDT (t) is the test current, I 8×20 is the current amplitude ratio coefficient, which can be expressed by formula (16), I MAX-GDT can be expressed by formula (17), and the corresponding formula under the conditions of waveform 4 and waveform 5A is referred to formula (16).

[0075] I GDT (t)=I 8×20 ×(e -120000t -e -140000t )……(15)

[0076]

[0077] I MAX-GDT =I 8×20 ×(e -120000×0.000008 -e -140000×0.000008 )……(17)

[0078] Determine whether the pre-selected GDT model meets the requirements, for example, the pre-selected model is UN2E8-75MSMD, and the maximum withstand current is 10kA, and when I MAX-GDT is less than 10kA, the selected GDT meets the indirect lightning protection requirements.

[0079] The indirect lightning protection circuit device selection method converts the RTCA / DO-160G chapter 22 indirect lightning waveforms 4 and 5A into 8 / 20us double exponential waveform, 10 / Tus double exponential waveform and rectangular pulse waveform equivalent performance indicators, so as to directly correspond to the performance indicators given in the device manual, has high calculation precision, can accurately obtain the performance requirements of GDT, TVS and pulse resistor devices, prevents the selection of devices with insufficient performance, and prevents the selection of devices with excessive performance, and causes resource waste.

[0080] In one specific embodiment, certain avionics equipment needs to be protected by B5K5M5 indirect lightning, according to RTCA\DO-160G chapter 22, the pin injection test waveform information of this level is as follows:

[0081]

[0082] The indirect lightning protection circuit provided in the present application is used for port protection, the TVS breakdown voltage is small, and the response time is fast, which will be earlier than the GDT conduction, and will clamp the voltage to a low voltage, thereby playing a role in early overvoltage protection. With the rise of the voltage across the pulse resistor, the GDT is turned on, and at this time the voltage across the TVS is lower than the breakdown voltage, and the TVS stops working.

[0083] The devices in the indirect lightning protection circuit are selected, and the specific process is as follows:

[0084] The maximum withstand voltage V of the 5V discrete signal of the avionics equipment is 70V, and the maximum allowed series resistance R is 20Ω. clamp-max max The maximum allowed series resistance R is 20Ω.

[0085] The TVS clamping voltage V is preselected to be 45.4V. clamp The TVS clamping voltage V is preselected to be 45.4V.

[0086] Two pulse resistor values R0 are preselected to be 10Ω.

[0087] The GDT model is preselected to be UN2E8-75MSMD, the 100V / us, 1000V / us rise slope breakdown voltage V1 of the GDT device manual is 500V and V2 is 600V, the breakdown voltage V is 550V, and the clamping voltage V is 15V. GDT-impulse The breakdown voltage V is 550V, and the clamping voltage V is 15V. clamp-GDT The breakdown voltage V is 550V, and the clamping voltage V is 15V.

[0088] According to the open circuit voltage V of the indirect lightning test waveform 5A, the short circuit current I is 1600A, and the waveform is as shown in OC SC According to the open circuit voltage V of the indirect lightning test waveform 5A, the short circuit current I is 1600A, and the waveform is as shown in Figure 4 Figure 5 ​​​), where the transient signal source internal resistance R S =V OC / I SC For a current of 1Ω, its waveform function expression V WF5A (t) See formula (18) for details;

[0089]

[0090] Calculate the TVS conduction time ΔT1. The calculation formula is detailed in formula (19). The result is ΔT1 = 0.397 μs.

[0091] V WF5A (△T1)=V clamp ……(19)

[0092] The GDT conduction time ΔT2 is calculated. The calculation formula is detailed in formula (20). The result is ΔT2 = 5.858 μs.

[0093]

[0094] Calculate the maximum transient power P of the equivalent rectangular pulse with pulse resistance R. MAX-R and pulse width T R The calculation formulas are detailed in formulas (21)-(22), from which the maximum transient power value P is obtained. MAX-R The pulse width T is 6336.1W. R It is 1.97us;

[0095]

[0096]

[0097] The selected pulse resistor is SG73 2B-T-TD-100-K, with a resistance R0 of 10Ω. The pulse power curve of this resistor is shown below. Figure 2 As shown, in pulse width T R At a pulse duration of 1.97µs, the pulse power is approximately 11000W, which is greater than the maximum transient power value P. MAX-R Therefore, the selected pulse resistor meets the requirements for indirect lightning protection;

[0098] Calculate the maximum transient power value P of the TVS equivalent 10 / T us double exponential waveform. MAX-TVS and pulse width T TVS P MAX-TVS For the calculation formula, please refer to formula (23);

[0099]

[0100] Pulse width T TVSThe TVS performance detection 10 / 20 us double exponential waveform function expression is formula (24), I TVS (t) is the test current, I 0-TVS is the current amplitude ratio coefficient, a is the waveform attenuation coefficient, b is the waveform rising coefficient, and is the derivative of formula (25). The test double exponential waveform function is 10 us and T TVS , and its expressions are formulas (26)-(27), respectively.

[0101] I TVS (t) = I 0-TVS ×(e -at -e -bt )……(24)

[0102]

[0103]

[0104]

[0105] When the energy of the test waveform applied to the TVS is the same as the waveform energy when the TVS performance is tested, formula (28) can be obtained. When T TVS takes a certain value, formulas (27)-(28) can be established at the same time, and T TVS will be the equivalent pulse width of the TVS, and the maximum transient power value P MAX-TVS is 1326.7 W and the pulse width T TVS is 30 us.

[0106]

[0107] Select SMAJ28CA-HR type TVS, the clamping voltage V clamp is 45.4 V, and the pulse power curve is shown in Figure 3 . When the pulse width T TVS is 30 us, the pulse power is about 2600 W, which is greater than the maximum transient power value P MAX-TVS . At this time, the selected TVS meets the indirect lightning protection requirements.

[0108] Calculate the equivalent 8 / 20 us double exponential waveform maximum current I MAX-GDT of the GDT; the 8 / 20 us double exponential current waveform function can be expressed by formula (29); I GDT (t) is the current, I 8×20 is the current amplitude ratio coefficient, which can be expressed by formula (30), I MAX-GDT can be expressed by formula (31), and I MAX-GDT is 9188.6 A.

[0109] I GDT (t) = I 8×20 × (e -120000t - e -140000t ) … … (29)

[0110]

[0111] I MAX-GDT = I 8×20 × (e -120000×0.000008 - e -140000×0.000008 ) … … (31)

[0112] The GDT model is UN2E8-75MSMD, and the maximum withstand current is 10kA, and I MAX-GDT is less than 10kA, at this time, the UN2E8-75MSMD model GDT selected satisfies the indirect lightning protection requirements.

[0113] So far, the technical scheme of the present application has been described in combination with the preferred embodiments shown in the drawings, and those skilled in the art should understand that the protection scope of the present application is obviously not limited to these specific embodiments, and those skilled in the art can make equivalent changes or replacements to the related technical features without deviating from the principles of the present application, and the technical scheme after the changes or replacements will fall within the protection scope of the present application.

Claims

1. A method for selecting components in an indirect lightning protection circuit, the indirect lightning protection circuit comprising: a gas discharge tube (GDT); a transient voltage suppression (TVS) diode connected in parallel with the GDT; and a pulse resistor (R) connected between the GDT and the TVS for voltage division, the method comprising: selecting a component in the indirect lightning protection circuit based on a voltage across the GDT and the TVS, a voltage across the R, and a voltage across the component. ​ ​ ​ ​ Determination of maximum withstand voltage according to signal characteristics of a downstream circuit , and maximum series resistance ; Preselecting transient voltage suppression diode (TVS) clamping voltage , less than ; Pre-select the pulse resistance R value , request less than or equal to ; Pre-select the gas discharge tube GDT model, determine its breakdown voltage , according to the gas discharge tube GDT device manual given 100V / us, 1000V / us rising slope breakdown voltage , , select its breakdown voltage , determine its clamping voltage , require less than ; open circuit voltage according to indirect lightning test requirements , short circuit current and internal resistance , wherein the internal resistance , the function expression of the waveform 4 , the function expression of the waveform 5A ; Computing the turn-on time of a transient voltage suppression diode, TVS For waveform 4 there is For waveform 5A there is ; Computing gas discharge tube (GDT) turn-on time For waveform 4 there is For waveform 5A there is ; Calculating the pulse resistance R equivalent rectangular pulse maximum transient power value and pulse width corresponding to waveform 4 has , corresponding to waveform 5A has , ; According to the pulse resistance R value , the maximum transient power value , and the pulse width , the pulse resistance R model is selected, such as selecting the resistance value of , requiring the pulse width of , and the pulse power is greater than the maximum transient power value ; Computing the maximum transient power value of a transient voltage suppression diode, TVS, equivalent 10 / μs bi-exponential waveform and pulse width corresponding to waveform 4 has corresponding to waveform 5A has ; Computing the equivalent pulse width of a transient voltage suppression diode (TVS) For waveform 4, there is , , For waveform 5A, there is , , where a is a waveform decay coefficient and b is a waveform rise coefficient. According to the clamping voltage , the maximum transient power value , and the equivalent pulse width , a transient voltage suppression diode TVS model is selected, such as selecting a clamping voltage , and requiring a pulse width of , the pulse power is greater than the maximum transient power value ; Calculate the maximum current of the equivalent 8 / 20 µs double exponential waveform in the gas discharge tube (GDT). Corresponding to waveform 4 , Corresponding to waveform 5A , ,in, This is the current amplitude proportionality coefficient; determining whether a preselected gas discharge tube GDT model meets the requirements, such as the gas discharge tube GDT maximum current for an 8 / 20 us double exponential waveform less than its maximum withstand current, then the requirements are met.

Images