ELECTRONIC SYSTEM PROTECTION AGAINST SURGES

Abstract

Overvoltage protection circuit (2) for an electronic device, comprising two connection terminals (21, 22) for connection to the electronic device to be protected, and comprising between said connection terminals: - a first branch comprising a controlled switch (25) having a control terminal (250), - a second branch comprising at least one Zener diode (26, 27), the second branch being connected to the control terminal (250) of the controlled switch (25), - a third branch comprising two input terminals (23, 24) for connection to a test circuit (3), the third branch also being connected to the control terminal (250) of the controlled switch (25), the test circuit being capable of closing the controlled switch via the control terminal. Figure for the abbreviation: Figure 2

Description

Title of the invention: ELECTRONIC SYSTEM PROTECTION AGAINST SURGES technical field

[0001] The present invention relates to the protection of electronic systems against overvoltages. It relates more particularly to an overvoltage protection circuit, for example in the event of a lightning strike, which can be substituted for a transient voltage suppression diode known as a TVS diode (from the English "Transient Voltage Suppression").

[0002] The overvoltage protection circuit can be applied to many types of electronic systems, particularly in aeronautical environments, or in other varied technical fields such as, for example: automotive, defense, medical, nuclear. Prior state of the art

[0003] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft and to those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations.

[0004] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development, in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts.

[0005] This sustained research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, in particular through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aviation biofuels.

[0006] In this context, the trend is towards an increase in electrical voltage levels in aircraft networks. It is known to use a TVS diode (from the Anglo-Saxon terminology "Transient Voltage Suppression") to protect an electronic system against overvoltages. Under normal operating conditions, the TVS diode presents a high impedance to the protected circuit, but when When the safe operating voltage of the protected circuit is exceeded, the TVS diode operates in "avalanche" mode, diverting the transient current to ground or a low-impedance electrical ground. A TVS diode absorbs the excess current during an overvoltage to clip the voltage and dissipates the energy.

[0007] TVS diodes have advantages such as good level of protection, long service life, very low response time.

[0008] However, there are situations in which TVS diodes are not accessible after installation in the electronic system. For example, in the context of lightning protection for equipment such as a backup control module (BCM) of an aircraft flight control system, it is not possible to test the TVS diodes once integrated into the backup control module without having to disassemble and therefore replace them.

[0009] Indeed, in this context, TVS diodes with a high voltage limit, for example on the order of 90 V, are used. However, the electrical architecture has a floating ground and is also single-board. There is no access point for easily performing a test. It is not possible to reach the TVS diode's voltage limit without making the area disconnectable. There is therefore a risk of damaging the related components whose supply levels are lower than the voltage limit. Description of the invention

[0010] The invention aims to solve the problems of the prior art by providing a protection circuit for an electronic device against overvoltages, comprising two connection terminals intended to be connected to the electronic device to be protected and comprising between said connection terminals:

[0011] - a first branch comprising a controlled switch comprising a terminal order,

[0012] - a second branch comprising at least one Zener diode, the second branch being connected to the control terminal of the controlled switch,

[0013] - a third branch comprising two input terminals intended to be connected to a test circuit, the third branch also being connected to the control terminal of the controlled switch, the test circuit being capable of controlling the closing of the controlled switch via the control terminal.

[0014] The invention proposes an alternative surge protection solution to the use of TVS diodes by implementing components having protection properties similar to a TVS diode, while being able to be tested directly on the board without risk of damaging the surrounding components. It is possible to test the surge protection function both during manufacturing and repair without dismantling components.

[0015] Thus, the invention proposes a surge protection solution, which is equivalent to a T VS diode and which can be monitored throughout the equipment's operational life. This solution is highly advantageous for protecting aircraft electrical equipment in a floating, single-board architecture, such as a backup control module (BCM).

[0016] According to a preferred characteristic, the controlled switch is bidirectional.

[0017] According to a preferred feature, the controlled switch comprises an element chosen from a TRIAC, a MOSFET or an IGBT.

[0018] According to a preferred feature, the second branch comprises two Zener diodes connected in a back-to-back configuration.

[0019] According to a preferred feature, the test circuit is integrated into the protection circuit.

[0020] According to a preferred feature, the test circuit comprises a primary part capable of receiving a first control current and a secondary part galvanically isolated from the primary part, the secondary part being connected between the input terminals of the third branch and providing a second control current capable of controlling the closing of the controlled switch when the primary part receives the first control current.

[0021] The invention also relates to an electronic device comprising at least one overvoltage protection circuit as previously described.

[0022] The invention also relates to an aircraft comprising at least one electronic device as previously described.

[0023] The electronic device and the aircraft have advantages similar to those previously presented. Brief description of the drawings

[0024] Other features and advantages will become apparent from the following description of a preferred embodiment given by way of non-limiting example, described with reference to the figures in which:

[0025] [Fig.1] illustrates an electronic device to be protected against overvoltages, equipped with a protection circuit, according to an embodiment of the invention.

[0026] [Fig.2] illustrates a protection circuit and a test circuit, according to a mode of realization of the invention.

[0027] Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the transition from one figure to another.

[0028] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0029] The different possibilities (variants and embodiments) should be understood as not being mutually exclusive and can be combined with each other.

[0030] Detailed explanation of specific implementation methods

[0031] According to a preferred embodiment shown in [Fig. 1], an electronic device to be protected against overvoltages comprises a backup control module 1 of an aircraft flight control system. In particular, the module 1 is to be protected against lightning.

[0032] To this end, a surge protection circuit 2 has two connection terminals 21 and 22 intended to be connected to two terminals 11 and 12 of module 1. For the sake of understanding the invention, a protection circuit 2 separate from module 1 has been shown; however, in practice, the protection circuit 2 is generally integrated into module 1. The protection circuit 2 protects against surges the internal electronic part of module 1 which is connected to terminals 11 and 12.

[0033] The protection circuit 2 also includes two input terminals 23 and 24 intended to be connected to two terminals 31 and 32 of a test circuit 3. The test circuit 3 includes two test input terminals 33 and 34.

[0034] According to a first variant, the test circuit 3 is integrated into the protection circuit 2. In this case, only the test input terminals 33 and 34 are directly accessible to perform a test of the protection circuit.

[0035] According to another embodiment, the test circuit 3 is not integrated into the protection circuit 2 and must be connected to it to perform a test. In this case, the input terminals 23 and 24 of the protection circuit 2 are accessible, and the terminals 31 and 32 of the test circuit must be connected to the input terminals 23 and 24 of the protection circuit 2. The test terminals 33 and 34 are also accessible for testing the protection circuit.

[0036] To simplify the presentation, a single protection circuit 2 equipping module 1 has been represented. Of course, the same electronic device 1 to be protected can be equipped with several protection circuits 2.

[0037] Fig. 2 represents an embodiment of a protection circuit 2 and a test circuit 3.

[0038] The protection circuit 2 includes, between the two connection terminals 21 and 22 intended to be connected to the electronic device to be protected 1, a first branch comprising a controlled switch 25. This is, for example, a TRIAC which has two terminals, generally called anodes, connected to the connection terminals 21 and 22. The controlled switch may also include another type of component, for example, a transistor, such as a MOSFET or an IGBT.

[0039] In the present example, the TRIAC also includes a control gate, or terminal, 250. As will be seen, the TRIAC allows the connection terminals 21 and 22 to be short-circuited in the event of an overvoltage between these terminals in order to protect the device 1. The voltage seen by the device 1 between its terminals 11 and 12 connected to the connection terminals 21 and 22 is limited to an acceptable predefined value.

[0040] The controlled switch is preferably a bidirectional component, such as the TRIAC shown here. Alternatively, a unidirectional controlled switch may be used.

[0041] The protection circuit 2 also includes, between the two connection terminals 21 and 22 intended to be connected to the electronic device to be protected, a second branch comprising at least one Zener diode, preferably two Zener diodes 26 and 27 connected in reverse, the two Zener diodes also being connected to the control gate 250 of the TRIAC 25.

[0042] Zener diodes 26 and 27 have a predetermined avalanche voltage that is chosen according to the voltage level that the module to be protected 1 can withstand. The use of two Zener diodes 26 and 27 makes it possible to obtain a bidirectional avalanche voltage. Zener diodes 26 and 27 make it possible to obtain a voltage similar to the limiting voltage of a T VS diode.

[0043] The Zener diodes 26 and 27 are also connected in series with a resistor 28. The resistor 28 is connected on the one hand to a midpoint between the Zener diode 26 and the control gate 250 of the TRIAC 25 and on the other hand to the connection terminal 22.

[0044] In the case of a unidirectional controlled switch, a single Zener diode would be sufficient.

[0045] The protection circuit 2 further includes a third branch in parallel with the Zener diodes, this third branch having input terminals 23 and 24 intended to be connected to terminals 31 and 32 of the test circuit 3. The test circuit 3 allows the TRIAC 25 to be closed for testing purposes. The third branch is also connected to the control gate 250 of the TRIAC 25.

[0046] As mentioned above, the test circuit 3 is integrated into the protection circuit 2 or is an independent circuit that can be connected to the protection circuit 2.

[0047] In both cases, the test circuit 3 includes a primary section capable of receiving a first control current at the test input terminals 33 and 34. The test circuit 3 also includes a secondary section galvanically isolated from the primary section. The secondary section includes a transistor 35 whose output is connected between terminals 31 and 32. The first control current in the primary section generates a second control current in the secondary section so as to control the closing of the TRIAC 25.

[0048] An example of a protection circuit operating method is as follows. The operating method is implemented, for example, by protection circuit 2.

[0049] The protection circuit 2 protects module 1 against overvoltages. Three situations are distinguished: absence of overvoltage, presence of overvoltage, and testing of the protection circuit 2.

[0050] In the absence of an overvoltage between terminals 11 and 12 of module 1, i.e., under nominal conditions, no current flows through Zener diodes 26 and 27, the test circuit is not used, and no voltage is applied to the control gate 250 of the TRIAC 25. Consequently, the TRIAC 25 is open. Module 1 operates without the protection circuit 2 intervening.

[0051] In the event of an overvoltage between terminals 11 and 12 of module 1, the voltage exceeds the avalanche voltage of Zener diodes 26 and 27. The Zener diodes then conduct current, which is applied to the control gate 250 of the TRIAC 25. Consequently, the TRIAC 25 conducts and absorbs the additional current due to the overvoltage. The voltage between terminals 11 and 12 of module 1 is limited to the avalanche voltage of the Zener diodes, thus protecting module 1.

[0052] In the event of a test of the protection circuit 2, a first control current is applied to the test input terminals 33 and 34 of the primary part of the test circuit 3.

[0053] The first control current in the primary section generates a second control current in the secondary section of the test circuit 3. This second control current is applied to the control gate 250 of the TRIAC 25. As a result, the TRIAC 25 becomes conductive. To verify the proper operation of the TRIAC 25, it is necessary to check that the TRIAC 25 becomes conductive following the activation of the test circuit 3. This can be done by measuring the impedance or voltage between the connection terminals 21 and 22. If the measured voltage is close to zero or if the impedance is low, then the TRIAC 25 is functioning normally and the protection circuit is fulfilling its function.

[0054] Furthermore, components 26, 27 and 28 can be tested by standard testing methods directly on the board (for example in-situ testing or Takaya type testing) without risk of degradation of the rest of the components.

Claims

Demands

1. Overvoltage protection circuit (2) for an electronic device (1), comprising two connection terminals (21, 22) for connection to the electronic device to be protected and comprising between said connection terminals: - a first branch comprising a controlled switch (25) having a control terminal (250), the controlled switch (25) comprising an element selected from a TRIAC, a MOSFET or an IGBT, - a second branch comprising at least one Zener diode (26, 27), the second branch being connected to the control terminal (250) of the controlled switch (25), - a third branch comprising two input terminals (23, 24) connected to a test circuit (3), the third branch also being connected to the control terminal (250) of the controlled switch (25),the test circuit being capable of controlling the closing of the controlled switch via the control terminal and comprising a primary part capable of receiving a first control current and a secondary part galvanically isolated from the primary part, the secondary part being connected between the input terminals (23, 24) of the third branch and providing a second control current capable of controlling the closing of the controlled switch (25) when the primary part receives the first control current.

2. Overvoltage protection circuit of an electronic device according to claim 1, wherein the controlled switch (25) is bidirectional.

3. Overvoltage protection circuit for an electronic device according to claim 2, wherein the second branch comprises two Zener diodes (26, 27) connected in back-to-back.

4. Electronic device (1) comprising at least one overvoltage protection circuit (2) according to any one of claims 1 to 3.

5. Electronic device according to claim 4, characterized in that it forms at least a part of a backup control module of an aircraft flight control system.

6. Aircraft comprising at least one electronic device according to any one of claims 4 or 5.

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