EP0955619A1 - Management method of a traffic light source - Google Patents

Abstract

The road signal light source has several electroluminescent diodes (11-18) connected to a number of parallel current supply branches. The operation of the diodes is individually controlled and the current supply (3,4) is controlled so as to maintain constant the luminous flux of the source. At the diode terminals (51-58) the voltage is compared with that of an adjacent diode so as to localize a faulty diode (11-18).

Description

Road signs use luminous signaling equipment when it is a question of being able to modify the signs or when they are likely to be invisible at night. This is the case of signaling lights or even indicator panels in the form of a box comprising a transparent front plate bearing an indication and lit by a source housed in the box.

As a source, an incandescent or halogen bulb can be used, which has the advantage of having a high optical power. In order to avoid a total failure, unacceptable in the application to a traffic control red light, two bulbs are mounted in parallel. As the failure of one bulb results in its breaking, there is therefore no short circuit and the other bulb remains powered.

However, the light source then lost half of its power and is then outside the set specifications. In addition, any new failure would be fatal.

When the required light power is relatively limited, for a signage display board or for the repeater, of small size, of three-color lights located halfway up a bracket of traffic lights, a plurality of light sources is used. low voltage, each consisting of a light emitting diode. The large number of such diodes aims to overcome any total failure of the light source.

Each diode, operating under a very low voltage, of a few volts, requires a determined electrical energy, that is to say in practice a determined current.

However, it is not possible to connect all the diodes in series and supply them, at medium voltage, with the same current because any interruption of one would interrupt the common current.

A known solution consists in mounting in parallel several branches made up of diodes in series. In this way, any failure, by cutting a diode in a branch, only results in a drop in power all the more limited the higher the number of branches, or redundancy rate. However, the multiplication of diodes all the more increases the probabilities of failures in this plurality of diodes and the deactivation of as many branches.

It is therefore necessary to be able to locate in each branch any defective diode which has become ineffective which, moreover, will disturb the other diodes of the branch: cut it puts them out of service, while, in short-circuit, it risks excessively increasing the current.

In the case of breaking, a simple measurement of the current of the branches, or of the total optical power, makes it possible to detect a fault, but without locating the faulty diode. In the case of a short circuit, the fault is difficult to detect.

To ensure a compromise between the frequency of maintenance operations and the risk of excessive drop in optical power, it is therefore necessary, on the one hand, to automatically locate the defective diodes and mask the effect of this failure and, on the other hand, detect that a certain number of failures have occurred and that the risk of no longer being able to hide new failures becomes significant.

The present invention aims to solve the problem of locating defective diodes.

To this end, the invention relates to a method for managing a light source comprising light elements connected according to a plurality of branches supplied with current in parallel and each formed from several light elements in series, characterized in that the correct operation of each element is controlled individually and the power supply is controlled to keep the light flux from the source constant.

The invention will be better understood using the following description of a preferred embodiment of the method of the invention, with reference to the single figure, which schematically represents a light-emitting diode card of a traffic signal light.

There is shown a printed circuit board 1, integrated, in this example, with a traffic signal repeater light mounted on the pole of a light pole. The card 1 has in practice a circular shape the size of the repeater and carries a plurality of low-voltage light elements, here light-emitting diodes 11 to 18, substantially evenly distributed on the card 1 and lighting in a direction perpendicular thereto. The representation which is made here of the card 1 illustrates only the electric diagram. Similarly, for clarity of the drawing, only a very limited number of light-emitting diodes have been shown, which may in fact exceed one hundred.

The plurality of light-emitting diodes is ordered into B branches of S diodes in series, with here B = 2 and S = 4. S could however be variable from one branch to another. As mentioned above, B and S can reach one or more tens.

The branches are supplied by a continuous supply 2 and, in this example, each is supplied through an adjustable generator, 3, 4 of constant current, controlled by an integrated circuit 5 with microprocessor, connected to ground just like the cathodes of the downstream diodes 14 and 18 of the two branches.

The integrated circuit 5 is supplied with DC voltage by another source or by the source 2, possibly through a level reducer.

The integrated circuit 5 comprises in particular test interface pins 51 to 58, in a number corresponding to the number of diodes 11 to 18. Each pin 51 to 58 is connected to a diode 11 to 18 which is specific to it and, more precisely , the pins 51 to 58 are all connected to homologous electrode terminals, here the anodes, of the diodes 11 to 18.

A microprocessor test circuit 50 of circuit 5 is connected at the input, not shown, to pins 51 to 58 and it commands the writing of a memory 60 comprising data from an electronic card representing and identifying the diodes 11 to 18 and indicating their possible failure, by short circuit or cut.

The memory card 60 controls itself, by a bundle of links 69, B branches of S dipoles 61 to 68, therefore having an electrical arrangement which is the image of that of the diodes 11 to 18.

Each dipole 61 to 68 connects two pins 51 to 58, neighboring in a branch, which are specific to it. Each dipole 61 to 68 can have two electrical conduction states: a blocked state, in which no current flows through it, and a conductive state, in which it lets at least one supply current from the diodes 11 to 18. It s is an all-or-nothing switch here.

A circuit 70 is here provided for emitting an alarm, under the control of circuit 50.

The operation of the above components will now be explained in more detail.

The microprocessor circuit 50 individually controls the proper functioning of each diode 11-18 and the loss of optical power, or luminous flux, due to a defective diode 11-18 is compensated, at least partially, by the circuit 50 or, automatically and independently, from one of the sources 3, 4.

Here, the microprocessor circuit 50 scans the voltages of the various pins 51 to 58 to compare the voltage of each diode terminal 11 to 18 with that of a terminal of an adjacent diode, in order to locate a diode 11 to 18 defective.

More precisely, in this example, it is a cyclic scanning of pairs of adjacent terminals. Thus, the voltages of pins 51 and 52 are compared to verify that they differ by a value within a specified range, for example from two to four volts.

In the event of a diode, such as 12, of a branch being cut off, this diode 12 forms a switch and has, between its terminals, a voltage exceeding the values of the range provided, while all the other diodes in the branch having a zero voltage, lack of supply current. An internal short circuit cannot therefore be detected in this cycle.

The circuit 50, after scanning of all the defective branch, determines that the diode 12 is cut (voltage greater than the upper limit of the range) and it writes this information in the card 60. The switch 62, in parallel on the diode 12, is then closed to short-circuit the latter and thus ensure the electrical continuity of the branch in question.

If one of the other diodes 11, 13, 14 of the branch was or becomes defective by short circuit, the absence of voltage across its terminals will, during the next branch test cycle, be detected and considered as a fault since the branch is now supplied. The card 60 is updated with the corresponding information, without however the need to close the corresponding switch.

The detection of another cut diode is also possible, as explained for the previous cycle.

The fault type information of the diodes 11-18 accumulated in the card 60 allow the circuit 50, according to the various electrical positions of the diodes 11 to 18 defective in the branches, to compensate for the variations in optical power, or light flux, due to one or more defective diodes. Indeed, a diode 11 to 18 cut and short-circuited by the associated switch 61 to 68 causes a loss of the total optical power since a constant current supply 3, 4 is provided here.

The circuit 50 controls in such a case an increase in the current in at least one of the branches and, for example, that comprising the diode 11 to 18 cut and externally short-circuited (61 to 68). In the latter case, it is possible to have an automatic correction at the level of the current generators 3, 4 by providing that they have a limited and regulated output impedance, so that any internal or external short circuit to a diode 11 to 14 or 15 to 18 causes a slight increase in current increasing the optical power of the other diodes 11 to 14 or 15 to 18 of the branch, to such an extent that the loss of optical power of the defective diode 11 to 18 is compensated for. In this case, it is therefore the branch, representing the electric charge of the generator 3, 4, which, by the voltage which it presents, controls the current supplied by the generator 3, 4.

In addition, the circuit 50 estimates, from the card 60, the consequences, in optical power, of the possible occurrence of a new diode failure 11 to 18 and it generates an alarm if an unacceptable risk threshold is then exceeded. .

The alarm can be a signal sent, by circuit 70, to a remote monitoring receiver, by wire or by radio. A short cyclical flashing of the diodes can also be provided, as long as it does not risk inducing users in error.

In a variant, the voltages of electrically adjacent diode terminals 11-18 are compared, such as for example the anodes of diodes 13 and 17, that is to say located at the same potential level, with the dispersions near the fall characteristics. of the various diodes 11 - 18.

In short, two diodes 11-18 can be electrically adjacent "vertically", in a branch, or, as here, "horizontally" from one branch to another.

If the diode 13 is cut, its anode potential and that of the diodes 11 and 12 upstream is too high and reaches the supply voltage while the downstream diode 14 has a zero anode voltage, therefore too low.

If the diode 13 is in internal short circuit, the anode voltages in the branch are too low compared to those of the other branch. In the case of a non-fixed current supply, for example at constant voltage, the diodes 11, 12, 14 having an increased voltage between their terminals: the anode of diode 12 is then at too low voltage and that of diode 14 is too high voltage.

As, in practice, the number B of branches clearly exceeds the value 2, the branches without defective diode provide, by majority vote on all the branches, a voltage reference value for each "voltage plane" of the homologous anodes, likewise level, various branches.

In either variant, the detection of the failure of a diode 11-18 can also be carried out in a different way than that indicated above.

For example, a diode cut 11-18 will cause the output of the generator 3 or 4 to pass, supplying it with a maximum voltage, tending to maintain the expected current. A detection of this maximum voltage therefore indicates a break in the branch considered. Conversely, an internal diode short circuit 11-18 causes a drop in voltage of the generator 3, 4, which can be detected. It is thus possible to start a control cycle only upon detection of a fault. A current or absence of current detector can likewise be provided. In the event of a break, activation of the switches 61 - 64 or 65 - 68 associated with the branch makes it possible to short-circuit the diodes 11 - 18, one by one to detect the position of the switch 61 - 68 which restores a current. In the event of failure, if several diodes are cut (11 and 13 for example), the switches 61, 62 are successively closed and they are kept closed until the current is restored, which occurs when a last switch is closed ( 63). The maintenance of the current is then tested during the opening of the other switches 61 and 62 and thus determines that the switch 61 must also remain closed.

The operating order of switches 61 - 64 of a branch can be arbitrary.

The individual control of the diodes 11-18 can also be carried out by a plurality of B x S optical sensors each associated with a particular diode 11-18. The indication of the failure of the diode 11 - 18 considered is thus obtained directly, failure the nature of which, internal short-circuit or break, is determined by the state, of operation or of apparent failure, of the other diodes of the branch . Closing the appropriate switch 61 - 68 restores their operation in such a case.

Claims (9)

Method for managing a light source comprising light elements (11 - 18) connected according to a plurality of branches supplied with current in parallel and each formed from several light elements (11 - 18) in series, characterized in that the proper functioning of each element (11 - 18) is controlled individually and that the current supply (3, 4) is controlled to keep the light flux from the source constant. Method according to claim 1, in which a set of homologous terminals (51 - 58) of the light elements (11 - 18) is accessed and the voltage of each terminal is compared to that of a terminal of an electrically adjacent light element to locate a faulty light element (11 - 18). Method according to claim 2, in which the terminal voltages of the light elements (11 - 18) of different branches are compared to locate the defective light element (11-18). Method according to one of claims 1 to 3, in which it is determined whether the localized light element (11 - 18) is defective by interruption and it is then short-circuited by a conductive element (61 - 68). Method according to one of claims 1 to 4, in which a lack of optical power due to a defective light element (11 - 18) is compensated for by an increase in current in at least one of the branches. Method according to claim 5, in which the current is increased in the branch comprising the defective light element (11 - 18). Method according to one of claims 1 to 6, in which an electronic card (60) of the positions of the defective light elements (11 - 18) is stored. Method according to Claim 7, in which the consequences, based on the map (60), are estimated, in optical power, of a possible new failure of the light element (11 - 18) and an alarm is generated if a threshold unacceptable risk is then exceeded. Method according to Claim 8, in which the alarm (70) is sent to a remote monitoring receiver.

Images