ELECTRONIC DEVICE FOR CONTROLLING KNX BUSES OR SIMILAR, WITH PROTECTION OF THE ELECTRONIC COMPONENT

Description

[0001] The present invention relates to the field of electrical safety, more particularly electrical safety in home automation and relates to an electronic device for managing a KNX bus or the like, with electronic component protection. It also relates to a method for protecting an electronic component in an electronic device for managing a KNX bus or the like.

[0002] In the electrical field, we know that marketed products must guarantee the safety of property and people and, in this context, comply with current safety standards.

[0003] For electronic products, the standards specify that all electronic components, except for a few certified safety components, must be considered as being capable of failing in a short circuit or open circuit. Therefore, tests are required to ensure that products do not present a hazard in the event of a short circuit or open circuit of electronic components. More specifically, in the event of failure of an electronic component, when the temperature exceeds a high temperature for a certain period of time, for example 300°C on a printed circuit board (PCB) for a period of more than 30 seconds, it is considered that there may be a harmful fire, unless a fire-resistant enclosure, such as a cabinet or box, meeting all the standard criteria, is used to protect the product.

[0004] However, it is permissible to test only electronic components deemed critical, i.e. electronic components for which it is estimated that, in the event of a fault, they may present a risk.

[0005] While risks are generally assessed in circuits directly connected to the electricity distribution network, they are also assessed in very low voltage circuits such as safety extra low voltage circuits (SELVs).

[0006] As part of the risk assessment in these very low voltage circuits, the following are concerned: field buses, as opposed to computer buses. Among the field buses, a well-known bus is the KNX bus, which connects the controllers to the components in a home automation system. The KNX bus is a two-wire bus on which a direct current power supply, generally 29 or 30V, is superimposed, decoupled by inductors with data that is transmitted in a pulsed manner, at a specific frequency, via a resistance, generally between 27 and 68 ohms, called the transmission resistance.

[0007] The KNX bus is particularly suitable for home automation, particularly building control, by allowing numerous components or devices, from the same or different manufacturers, installed and connected in these buildings, to communicate with each other. The KNX bus therefore makes it possible to control different home automation applications with a single system.

[0008] The management of the KNX bus or similar is carried out by a pulsed current electronic circuit comprising a connection point to said bus for transmitting data to the latter, a transmission resistor and an electronic data transmission circuit comprising a transmission output, called the TXO output, and being capable and intended to deliver to said transmission output a pulsed data transmission signal. The TXO output is connected to said connection point via the aforementioned transmission resistor. The data transmission signal is subsequently called the TXO signal. Such an electronic data transmission circuit, based on a microprocessor or microcontroller, is, for example, marketed under the reference NCN5121.

[0009] In normal operation of such an electronic data transmission circuit:

[0010] - when the TXO signal is not transmitted, the TXO output is opened / disconnected in said control circuit by a transistor-type means, until the next transmission pulse, i.e. for a period called the OFF period. No current then flows in this TXO output, nor in the transmission resistor,

[0011] - when the TXO signal is transmitted, the TXO output is short-circuited to ground in the electronic transmission circuit for the duration of the transmission pulse, called the ON duration.

[0012] Thus the transmit resistor connected to the TXO output only conducts electric current during the ON duration of the transmit pulses. However, these transmit pulses are very short, i.e. the ON duration is much less than the OFF duration, so the duty cycle, i.e. the ratio of the ON duration to the OFF duration, is very low. Consequently, the average power dissipated in the transmit resistor is very low since it only conducts current during each pulse and the duration of each pulse is short.

[0013] The emission resistor is therefore chosen by manufacturers taking this operation into account. In the example of the NCN5121 circuit mentioned above, the corresponding document provided by the manufacturer recommends an emission resistor of 27 ohms for a maximum power not to exceed 1W. Other manufacturers use SMD (surface mount component) type resistors with a maximum power not to exceed 1 or 2W. These values ​​are largely sufficient to guarantee, in normal operation, the reliability and proper functioning of the emission resistor.

[0014] However, in the event that operation is no longer normal, i.e. in the event of a failure of the electronic transmission circuit, with the TXO output permanently short-circuited to ground, the power dissipated in the transmission resistor can reach values ​​of up to 13 to 33 W permanently. The power dissipated in this case also depends on the power supply used on the KNX bus and the other products or devices connected to said bus. Such powers can generate fires and pose real safety problems. Indeed, at such powers, the temperature in the transmission resistor can reach values ​​between 300 and 600°C. The French NF standard, for example, used in a large number of home automation products integrating actuators, considers that there can be a fire hazard from 0.5W of power dissipated during a failure.

[0015] Furthermore, current safety standards, such as European standards EN60669, EN60730, EN60950, etc., require manufacturers to validate the absence of safety risks, including excessive overheating, for all components.

[0016] To overcome these drawbacks, several solutions can be considered to respond to the case where the TXO signal is permanently short-circuited following a failure:

[0017] A first solution would be to provide a much larger emission resistor so that it can remain within reasonable temperatures without causing excessive overheating that could cause fires. However, a large resistor size would go against the miniaturization objectives that manufacturers want to achieve today and would be incompatible with the size of the electronic boards currently in use.

[0018] A second solution would be to use a fusible resistor that would open quickly in the event of excessive overheating. However, this solution would be almost impossible because such a resistor should not deteriorate during power peaks during data transmission pulses, while being able to open for the same applied power for a longer time in the event of a circuit failure. The reliability of the product with such a fusible resistor would thus be called into question.

[0019] A third solution would be to size a fuse mounted in the circuit in series with the transmission resistor so that it opens in the event of excessive current, but this solution would not work because the fault current is the same as the current peaks during the transmission of a KNX communication. The difference would only be in the duration of the current maintenance.

[0020] A fourth solution would be to use a thermal fuse to protect the resistor and the circuit in the event of excessive overheating. However, while this solution improves circuit safety, it poses problems with the thermal inertia of the thermal fuse and imposes significant thermal coupling constraints between the emission resistor and the thermal fuse. In addition, this protection would only be triggered when the temperature becomes critical in the circuit. Reproducibility when reusing from one product to another would not be guaranteed, as this solution may require a different development phase for each product in which it is to be integrated.

[0021] The Internet document “Stmicroelectronics: “Miniature KNX transceiver with voltage regulators and microcontroller support” dated February 8, 2012, concerns a miniature KNX transmitter comprising a transmitter, a connection branch to a KNX bus comprising a transmitter output, a current limiting resistor RTX and a connection point to said bus (Cathode of the diode).

[0022] However, this transmitter does not provide protection for the RTX current limiting resistor by preventing potentially dangerous excessive overheating of the latter when the transmission output is permanently shorted to ground during a failure of the data transmission electronic circuit.

[0023] The present invention aims to overcome these drawbacks by proposing an electronic device for managing a KNX bus or similar, with electronic component protection making it possible to avoid any excessive, potentially dangerous, overheating of the emission resistor or any other similar current limiting element.

[0024] For this purpose, the electronic device, according to the present invention, for managing a KNX bus or the like, with electronic component protection, said device comprising a main electronic circuit with pulsed current capable and intended to manage the transmission of data in a KNX bus or the like in which a continuous power supply is superimposed with said data, said main electronic circuit comprising, on the one hand, an electronic circuit for transmitting data comprising a transmission output and being capable and intended to deliver to said transmission output a pulsed data transmission signal and, on the other hand, a connection point to said bus for the transmission of said data to the latter and a transmission resistor, or other similar current limiting element, through which said signal passes, said transmission output being transiently set, at each pulse,in a short-circuit state by being short-circuited to ground in said electronic data transmission circuit and, between two pulses, in an open-circuit state, is essentially characterized in that it further comprises an electronic protection circuit configured and connected to said main electronic circuit so as to monitor the state of said transmission output to detect a state of the latter, called a permanent short-circuit state, where it is short-circuited to ground permanently, that is to say with a duration at least greater than that of a pulse or a train of pulses, following a possible failure of the electronic data transmission circuit and to instantly trigger, following said detection, an opening in a branch of said main electronic circuit, between said transmission output and the connection point,having the effect of instantly interrupting the flow of electric current in said emission resistance.,

[0025] The present invention also relates to a method for protecting an electronic component in an electronic device for managing a KNX bus or the like, said device comprising a main pulsed current electronic circuit capable and intended to manage the transmission of data in a KNX bus or the like in which a continuous power supply is superimposed with said data, said main electronic circuit comprising, on the one hand, an electronic data transmission circuit comprising a transmission output and being capable and intended to deliver to said transmission output a pulsed data transmission signal and, on the other hand, a connection point to said bus for the transmission of said data to the latter and a transmission resistor, or other similar current limiting element, through which said signal passes, said transmission output being transiently set, at each pulse,in a short-circuited state by being short-circuited to ground in said electronic data transmission circuit and, between two pulses, in an open-circuited state, characterized essentially in that it consists of monitoring the state of said transmission output to detect a state of the transmission output, called a permanent short-circuited state, where it is permanently short-circuited to ground, i.e. with a duration at least greater than that of a pulse or a train of pulses, following a possible failure of the electronic data transmission circuit and to instantly trigger, following said detection, an opening in a branch of said main electronic circuit, between said transmission output and the connection point, having the effect of instantly interrupting the flow of electric current in said transmission resistor.,

[0026] The invention will be better understood from the following description, which relates to a preferred embodiment, given as a non-limiting example, and explained with reference to the appended schematic drawings, in which: [ Fig. 1 ] is a functional or synoptic representation of the electronic device, according to the present invention, for managing a KNX bus or the like, [ Fig. 2 ] shows the electronic diagram of the device shown in the figure 1 , in a preferred embodiment of the electronic protection circuit diagram.

[0027] The attached figures show an electronic device, according to the present invention, for managing a KNX bus or the like, with electronic component protection, said device comprising a main electronic circuit 1 with pulsed current capable and intended to manage the transmission of data in a KNX bus or the like in which a continuous power supply is superimposed with said data. The main electronic circuit 1 comprises, on the one hand, an electronic circuit for transmitting data 1a comprising an output, called the transmit output 10a, and being capable and intended to deliver to said transmit output 10a a pulsed data transmit signal and, on the other hand, a connection point to said bus for the transmission of said data to the latter and a resistor R1, called the transmit resistor R1, or other similar current limiting element, through which (or which) said data transmit signal passes.

[0028] A bus analogous to a KNX bus is a bus that uses the electronic operating principle of the KNX bus. On the other hand, it is well known as a current limiting element analogous to such an emission resistor R1, for example, a transistor current limiter.

[0029] The electronic data transmission circuit 1a can be an integrated or discrete circuit.

[0030] The emission output is transiently (or temporarily): at each pulse, in a short-circuit state by being short-circuited to ground in said electronic data transmission circuit, and, between two pulses, in an open-circuit state.

[0031] According to the present invention, such a management device further comprises an electronic protection circuit 3, 4 configured and connected to said main electronic circuit 1 so that: to monitor the state of said transmission output 10a to detect a state of the latter, called permanent short-circuit state, where it is short-circuited to ground M in a permanent (or prolonged) manner, that is to say with a duration at least greater than that of a pulse or a train of pulses, following a possible failure of the electronic data transmission circuit 1a, and to instantly trigger, following said detection, an opening in a branch 1c of said main electronic circuit 1, between said transmission output 10a and the connection point 1b, having the effect of instantly interrupting the flow of electric current in said transmission resistor R1.

[0032] In a known manner, to achieve the transient short circuit to ground M in the electronic data transmission circuit 1a, the transmission output 10a is connected in said transmission electronics 1a to an electronic switch 10b connected to ground M ( figure 1 ) and controlled in closing to transiently short-circuit, at each pulse, said emission output 10a and in opening to transiently disconnect, between two pulses, said emission output 10a.

[0033] Such an electronic data transmission circuit 1a, based on a microprocessor or microcontroller, may be a known circuit marketed, for example, by the company “ON SEMI” under the reference “NCN5121” or any other equivalent circuit.

[0034] In a preferred embodiment, the protection circuit 3, 4 comprises, on the one hand, an electronic detection and control circuit 3 and, on the other hand, an electronic protection switch 4 connected in said branch 1c and configured to be controlled in a closed state allowing the current to flow in said branch 1c and in an open state triggering the opening of said branch 1c. The detection and control circuit 3 is configured so as to detect the permanent short-circuit state and, following said detection, to instantly control the electronic protection switch 4 to put it in the open state and to maintain it in the closed state when said emission output 10a is transiently put in the short-circuit state.

[0035] Preferably, the electronic protection switch 4 is connected in the branch 1c between the emission resistor R1 and the connection point 1c. The electronic protection switch 4 can then be connected in series with the resistor R between the latter and the connection point 1c.

[0036] The electronic protection switch 4 is preferably a semiconductor device T1 from the transistor family such as an insulated gate field effect transistor T1, more commonly called MOSFET (according to the English acronym for Metal Oxide Semiconductor Field Effect Transistor) as shown in the figure 2 or, not shown in the attached figures, a bipolar transistor or any other electronic switch technology capable of operating in switching mode. The insulated gate field effect transistor T1 may be enhancement or depletion and N or P channel.

[0037] In a first embodiment, the detection and control circuit 3 is an electronic circuit essentially based on semiconductor device(s) T2 from the transistor family, resistor(s) R2, R3, R4, R5, R6, R7, R8, capacitor(s) C1, C2, C3 and, possibly, diode(s) D1.

[0038] Furthermore, the detection and control circuit 3 can be configured so that the capacitor(s) C1: when detecting the permanent short-circuit state, charges until the voltage across its terminals reaches a voltage, called the control voltage, having the effect of putting the electronic protection switch 4 in the open state, when the emission output 10a is transiently put in the short-circuit state, charges, at each pulse, without the voltage across its terminals having time to reach said control voltage so that the electronic protection switch 4 is maintained or put in the closed state. It can then be considered that the protection circuit is in this case "transparent", when said emission output 10a is transiently, between two pulses, put in an open circuit state, discharges so that the electronic protection switch 4 is maintained or put in the closed state.

[0039] The semiconductor device T2 may be an insulated gate field effect transistor T2 as shown in the figure 2 or, not shown in the attached figures, a bipolar transistor or any other electronic switch technology capable of operating in switching mode. The insulated gate field effect transistor T2 may be enhancement or depletion and N or P channel.

[0040] As can be seen on the figure 2 , in a preferred embodiment, the transistor T2 of the detection and control circuit 3 is an N-channel enrichment insulated gate field effect transistor T2 and the transistor T1 forming the electronic protection switch 4 is a P-channel enrichment insulated gate field effect transistor.

[0041] Thus, in the preferred embodiment of the electronic diagram of the protection circuit 3, 4 shown in the figure 2, the operation of the electronic device, according to the present invention, depending on whether the operation is normal (without failure of the electronic data transmission circuit 1a leading to a permanent short circuit of the transmission output 10a) or abnormal (failure of the electronic data transmission circuit 1a leading to the state of permanent short circuit of the transmission output 10a) is as follows, taking into consideration the supply voltage Vin:

[0042] In normal operation: without pulse emission: the emission output 10a of the electronic data emission circuit 1a is disconnected, i.e. in an open state. No current flows in said emission output 10a and no data emission signal is delivered to this output. Diode D1 is reverse biased and transistor T2 is biased to conduct. Capacitor C1 is then discharged and the potential difference across resistor R2 and the gate-source junction of transistor T1 is high enough so that transistor T1 is on. In this case, the emission resistor R1 is connected to voltage Vin across transistor T1, in emission: the emission output 10a is transiently connected to ground M in the electronic data emission circuit 1a at each pulse emitted. The ON duration of a pulse is much less than the OFF duration between two pulses, so that the ON / OFF duty cycle is very low.As a result, the average power dissipated in the emission resistor R1 is also very low and does not cause excessive overheating of said emission resistor R1 which could pose a safety problem. During the emission pulses, the diode D1 conducts briefly with each pulse, but the capacitor C1 does not have time to charge sufficiently to put the transistor T1 in the off state, the latter then remaining conducting. The emission resistor R1 is thus connected directly to the voltage Vin during the emission pulses.

[0043] In abnormal operation: The emission output 10a is in the permanent short-circuit state and the diode D1 conducts permanently, which has the effect of putting the transistor T2 in the blocked state. The capacitor C1 charges, the voltage across the resistor R2 decreases and the gate voltage of the transistor T1 rises relative to ground, which has the effect of reducing the gate-source voltage of the transistor T1 whose source is connected to Vin and putting the latter in the blocked state. Due to the blocked state of the transistor T1, that is to say the open state of the electronic protection switch 4, formed here by the transistor T1, the emission resistor R1 is thus disconnected from Vin, avoiding any risk of overheating of said emission resistor R1.

[0044] It is understood, even taking into account of course the connection times of the various electronic components present and the charging time of the capacitor C1, that a permanent short circuit to ground of the emission output 10a is immediately detected by the detection and control circuit 3 and that the electronic protection switch 4 is controlled instantly, that is to say almost instantly, to open upon said detection and well before the resistor R1 has time to overheat excessively, that is to say causing its deterioration, or even the start of a fire. The protection of the device by the protection circuit 3, 4 according to the present invention is then ensured. Such a protection circuit 3, 4 thus guarantees the operation and reliability of the device and eliminates any risk of possible fire starting caused by excessive overheating of the emission resistor R1.

[0045] In a second embodiment, not shown in the attached figures, the detection and control circuit 3 comprises an electronic duration (or time delay) measuring device capable of measuring the duration of the short-circuit state of the emission output 10a. Furthermore, the detection and control circuit 3 is configured to process said measured duration by comparing it to the duration of a pulse or a train of pulses and, when this measured duration is greater than said duration of a pulse or a train of pulses, to instantly control the electronic protection switch 4 in order to put it in the open state.

[0046] Still in this second embodiment, preferably, the detection and control circuit 3 may comprise a microcontroller or any other similar integrated circuit used for duration measurement or timing such as, for example, an integrated circuit known as NE555 and commonly called 555 or an ASIC (acronym for "application-specific integrated circuit"). The microcontroller, or the similar integrated circuit, includes the duration measurement device. The microcontroller, or the similar integrated circuit, may then be configured to process said duration measured by the duration measurement device by comparing it to the duration of a pulse or a train of pulses and, when this duration is at least greater than said duration of a pulse or a train of pulses, to instantly control the electronic protection switch 4 in order to put the latter in the open state.

[0047] The present invention also relates to a method for protecting an electronic component in an electronic device for managing a KNX bus or the like, said device comprising the main electronic circuit 1 with pulsed current described previously.

[0048] According to the present invention, such a method consists of: to monitor the state of the transmission output 10a to detect a state of the transmission output 10a, called a permanent short-circuit state, where it is permanently short-circuited to ground M following a possible failure of the electronic data transmission circuit 1a, and to instantly trigger, following said detection, an opening in a branch 1c of said main electronic circuit 1, between said transmission output 10a and the connection point 1b, having the effect of instantly interrupting the flow of electric current in said transmission resistor R1. It is understood that before said opening, said branch 1c is previously in a closed state, or put in a closed state, allowing the flow of electric current in said transmission resistor R1.

[0049] In a first embodiment, the method may consist of measuring the duration of the short-circuit state of the emission output 10a and in that said detection and control circuit 3 is configured to process said measured duration by comparing it to the duration of a pulse or a train of pulses and, when this measured duration is greater than said duration of a pulse or a train of pulses, to instantly control the electronic protection switch 4 in order to put it in the open state.

[0050] In a second embodiment, the method may consist of: during the permanent short-circuit state, to charge a capacitor C1 until the voltage across its terminals reaches a voltage, called the control voltage, having the effect of triggering the opening of said branch 1c to instantly interrupt the flow of electric current in said emission resistor R1, when said emission output 10a is transiently put in the short-circuit state, to charge, at each pulse, said capacitor C1, without the voltage across its terminals having time to reach the control voltage so as not to trigger the opening of said emission branch 1c to allow or maintain the flow of electric current in said emission resistor R1, when said emission output 10a is transiently, between two pulses, put in an open-circuit state, to discharge said capacitor C1 so as to allow or maintain the flow of electric current in said emission resistor R1.

[0051] The electronic management device, according to the present invention, for managing a KNX bus or the like, is suitable for or allows the implementation of such a method.

[0052] Such a device or method, according to the present invention, which allows the immediate detection and instantaneous opening of the circuit in the branch comprising the emission resistor R1 following the detection of the permanent short-circuiting of the emission output 10a is much more efficient than a solution using a thermal fuse whose thermal inertia is very slow or a method, using for example such a fuse, opening the circuit when the electric current in it reaches or exceeds a given intensity value for a certain time. With a thermal fuse the risk can be reduced but not eliminated unlike the device according to the present invention.

Claims

1. Electronic device for managing a KNX bus or the like, with electronic component protection, said device comprising a pulsed-current main electronic circuit (1) able and intended to manage the transmission of data in a KNX bus or the like in which a DC power supply is superposed with said data, said main electronic circuit (1) comprising, on the one hand, an electronic data-transmission circuit (1a) comprising a transmission output (10a) and being able and intended to deliver a pulsed data-transmission signal to said transmission output (10a), and, on the other hand, a connection point (1b) to said bus for transmitting said data thereto, and a transmission resistor (R1), or other similar current-limiting element, through which said signal passes, said transmission output (10a) being transiently put, at each pulse, into a short-circuit state by being short-circuited to ground (M) in said electronic data-transmission circuit (1a) and, between two pulses, into an open-circuit state, characterized in that it further comprises an electronic protection circuit (3, 4) configured and connected to said main electronic circuit (1) so as to monitor the state of said transmission output (10a) to detect a state thereof, referred to as a permanent short-circuit state, where said output is short-circuited to ground (M) permanently, that is to say for a duration of at least greater than that of a pulse or a pulse train, following a possible failure of the electronic data-transmission circuit (1a) and to instantaneously trigger, following said detection, an opening in a branch (1c) of said main electronic circuit (1), between said transmission output (10a) and the connection point (1b), having the effect of instantaneously interrupting the flow of the electric current through said transmission resistor (R1).

2. Electronic device according to Claim 1, characterized in that the protection circuit (3, 4) comprises, on the one hand, an electronic detection and control circuit (3) and, on the other hand, an electronic protection switch (4) connected in said branch (1c) and configured to be controlled into a closed state allowing the current to flow through said branch (1c) and into an open state triggering the opening of said branch (1c), said detection and control circuit (3) being configured so as to detect the permanent short-circuit state and, following said detection, to instantaneously control the electronic protection switch (4) to put it in the open state and to keep it in the closed state when said transmission output (10a) is transiently put in the short-circuit state.

3. Electronic device according to Claim 2, characterized in that the electronic protection switch (4) is connected in the branch (1c) between the transmission resistor (R1) and the connection point (1b).

4. Electronic device according to Claim 2 or 3, characterized in that the electronic protection switch (4) is a semiconductor device of the family of transistors such as an insulated-gate field-effect transistor (T1) or a bipolar transistor.

5. Electronic device according to any one of Claims 2 to 4, characterized in that the detection and control circuit (3) comprises an electronic duration-measuring device able to measure the duration of the short-circuit state of the transmission output (10a) and in that said detection and control circuit (3) is configured to process said measured duration by comparing it with the duration of a pulse or a pulse train and, when this measured duration is greater than said duration of a pulse or a pulse train, to instantaneously control the electronic protection switch (4) in order to put it in the open state.

6. Electronic device according to Claim 5, characterized in that the detection and control circuit (3) comprises a microcontroller or any other similar integrated circuit used for measuring duration and in that said microcontroller, or similar integrated circuit, includes said duration-measuring device.

7. Electronic device according to any one of Claims 2 to 4, characterized in that the detection and control circuit (3) is an electronic circuit essentially based on one or more semiconductor devices (T2) of the family of transistors, one or more resistors (R2, R3, R4, R5, R6, R7, R8) and one or more capacitors (C1, C2, C3) and in that the detection and control circuit (3) is configured such that the or one of the capacitors (C1): - upon detection of the permanent short-circuit state, is charged until the voltage across its terminals reaches a voltage, called the control voltage, which has the effect of putting the electronic protection switch (4) in the open state, - when the transmission output (10a) is transiently put in the short-circuit state, is charged, at each pulse, without the voltage across its terminals having the time to reach said control voltage such that the electronic protection switch (4) is kept or put in the closed state, - when said transmission output (10a) is transiently, between two pulses, put in an open-circuit state, is discharged such that the electronic protection switch (4) is kept or put in the closed state.

8. Method for protecting an electronic component in an electronic device for managing a KNX bus or the like, said device comprising a pulsed-current main electronic circuit (1) able and intended to manage the transmission of data in a KNX bus or the like in which a DC power supply is superposed with said data, said main electronic circuit (1) comprising, on the one hand, an electronic data-transmission circuit (1a) comprising a transmission output (10a) and being able and intended to deliver a pulsed data-transmission signal to said transmission output (10a), and, on the other hand, a connection point (1b) to said bus for transmitting said data thereto, and a transmission resistor (R1), or other similar current-limiting element, through which said signal passes, said transmission output (10a) being transiently put, at each pulse, into a short-circuit state by being short-circuited to ground (M) in said electronic data-transmission circuit (1a) and, between two pulses, into an open-circuit state, characterized in that it consists in monitoring the state of said transmission output (10a) to detect a state of the transmission output (10a), referred to as a permanent short-circuit state, where said output is short-circuited to ground (M) permanently, that is to say for a duration of at least greater than that of a pulse or a pulse train, following a possible failure of the electronic data-transmission circuit (1a) and to instantaneously trigger, following said detection, an opening in a branch (1c) of said main electronic circuit (1), between said transmission output (10a) and the connection point (1b), having the effect of instantaneously interrupting the flow of the electric current through said transmission resistor (R1).

9. Method according to Claim 8, characterized in that it consists in measuring the duration of the short-circuit state of the transmission output (10a), in processing said measured duration by comparing it with the duration of a pulse or a pulse train and, when this measured duration is greater than said duration of a pulse or a pulse train, in instantaneously triggering the opening in said branch 1c in order to instantaneously interrupt the flow of the electric current through said transmission resistor (R1).

10. Method according to Claim 8, characterized in that it consists: - during the permanent short-circuit state, in charging a capacitor (C1) until the voltage across its terminals reaches a voltage, called the control voltage, which has the effect of triggering the opening of said branch (1c) in order to instantaneously interrupt the flow of the electric current through said transmission resistor (R1), - when said transmission output (10a) is transiently put in the short-circuit state, in charging, at each pulse, said capacitor (C1) without the voltage across its terminals having the time to reach the control voltage so as not to trigger the opening of said transmission branch (1c) to allow or keep the flow of the electric current through said transmission resistor (R1), - when said transmission output (10a) is transiently, between two pulses, put in an open-circuit state, in discharging said capacitor (C1) so as to allow or keep the flow of the electric current through said transmission resistor (R1).