EP3125648A1 - Light emitting diode control circuit for a signal generator - Google Patents

Abstract

A light-emitting diode control circuit (27) with a voltage monitoring circuit (19, 29) for a light-emitting diode arrangement (1) of a signal generator of a traffic signal system is described. The voltage monitoring circuit (19, 29) has a reference voltage source (2) with an input and a first output (2a) and a second output (2b). In addition, the voltage monitoring circuit (19, 29) has a comparator circuit (3, 31) with a first input (3a), a second input (3b, 31b) and a signal output (3c, 31c). The first output (2a) of the reference voltage source (2) has a first reference potential (U ref) defined by the reference voltage source (2) and is electrically connected to the first input (3a, 31a) of the comparator circuit (3, 31). The second input (3b, 31b) of the comparator circuit (3, 31) is electrically connected to a terminal (1a) of the light-emitting diode arrangement (1) of the signal generator. The light-emitting diode control circuit further comprises a light-emitting diode interface and a fuse circuit (28) which is electrically connected to the output (3c, 32c) of the voltage monitoring circuit (19, 29), wherein the fuse circuit (28) by a turn-off signal at the output of the voltage monitoring circuit (28). 29) is displaceable in an off state in which the light-emitting diode array (1) is turned off. Furthermore, a signal generator (20, 30) of a traffic signal system is described. In addition, the use of a voltage monitoring circuit (19, 29) for monitoring an electrical voltage (U D) applied to a light-emitting diode arrangement (1) of a signal generator of a traffic signal system is described. Moreover, a method for monitoring a light-emitting diode arrangement (1) of a light-emitting diode voltage (U D) of a signal generator (20, 30) of a traffic signal system is described.

Description

The invention relates to a light-emitting diode control circuit. Furthermore, the invention relates to a signal generator for a traffic signal system. Moreover, the invention relates to the use of a light-emitting diode control circuit for monitoring a light emitting diode array. Moreover, the invention relates to a method for monitoring a light-emitting diode voltage of a light-emitting diode arrangement of a signal generator of a traffic signal system.

Traffic light systems, also referred to as a traffic light system, are used to control road traffic. They assign a certain behavior to road users by emitting controlled light signals. These different in shape and color traffic signs each have a different meaning and radiate only against the direction of traffic to be regulated. The use of traffic lights has different reasons, for example, to improve the flow of traffic and to defuse dangerous or dangerous traffic situations. In road traffic, these are in particular junctions and bottlenecks, for example at construction sites or bridges.

Nowadays LEDs are used for signaling as light sources, also called LED for short. These consume significantly less energy than conventional bulbs. LED signaling devices have a monitoring circuit with which defective LEDs can be detected and, in the event of a defect in an LED arrangement, a forced shutdown of the LED signal generator can be initiated. Such a monitoring circuit measures the voltage which is applied between the input and the output of an LED or an LED arrangement of a plurality of LEDs connected in series. If a voltage value is measured which lies outside a defined range, then it is concluded that the LED arrangement is defective, and the LED buzzer is switched off permanently. The shutdown can be achieved, for example, by blowing a fuse. An overvoltage on the LED array can be measured, for example, when no current flows due to breakage of an LED in the LED array. For example, undervoltage on the LED array may be measured if a short circuit occurs within an LED of the LED array. Conventionally, such voltage values are measured by means of a base-emitter circuit with a bipolar transistor.

A disadvantage in the voltage measurement by means of bipolar transistors with an emitter circuit is the dependence of the base-emitter switching voltage on production parameters and the ambient temperature. Due to this dependence, the switching voltage of bipolar transistors when used in LED signal generators can fluctuate up to a factor of 3. This results in a tolerance of approx. + -50% for the measurement of the LED voltages. Thus, a failure of an LED can only be determined very imprecisely based on a voltage measurement. Due to this inaccuracy, it may happen that a still functioning LED is erroneously detected as defective or a defective LED is not recognized.

It is therefore an object of the present invention to develop a light-emitting diode control circuit for a light-emitting diode arrangement of a signal generator of a traffic signal system, which monitors the functionality of the light-emitting diode arrangement of the signal generator with increased accuracy.

This object is achieved by a light-emitting diode control circuit according to claim 1, by a signal generator according to claim 11, the use of a light-emitting diode control circuit for monitoring a light emitting diode array according to claim 12 and a monitoring method according to claim 13.

The light-emitting diode control circuit according to the invention has a voltage monitoring circuit for a light-emitting diode arrangement of a signal generator of a traffic signal system, which has a reference voltage source with an input and a first output and a second output. For example, a supply voltage can be present at the input of the reference voltage source. The voltage monitoring circuit also includes a comparator circuit having a first input, a second input, and a signal output. The first output of the reference voltage source has a reference potential defined by the reference voltage source and is electrically connected to the first input of the comparator circuit. The second input of the comparator circuit is electrically connected to a terminal of the light emitting diode arrangement of the signal generator. The reference voltage source provides the comparator with a predetermined reference potential which the comparator uses as a reference for comparison with a voltage drop across the LED array.

A reference voltage source may be formed, for example, as a voltage divider circuit with a Zener diode. A reference voltage source can also be based on the bandgap frequency of semiconductor-based devices, wherein a temperature resistance of the reference voltage source can be achieved by skillful combination of devices with materials having opposite temperature coefficients. There is achieved an improved precision of the voltage monitoring circuit according to the invention in comparison with conventional, based on individual bipolar transistors monitoring circuits, in particular in the occurrence of temperature fluctuations and production-related fluctuations in the electronic properties of individual components. As a light emitting diode arrangement to be understood in the following both a single light emitting diode and a plurality of light emitting diodes connected in series. If a light-emitting diode group is used, then the second input of the comparator is with a terminal of one of the light emitting diodes of the light emitting diode group electrically connected. A comparator circuit or a comparator is understood to mean an electronic circuit which compares two electrical voltages or potentials present at their inputs. The output indicates in binary / digital form which of the two input voltages has the higher voltage value. Such a comparator has, for example, a positive, non-inverting input and a negative, inverting input. Furthermore, a negative and a positive supply voltage or alternatively a positive or negative supply voltage and ground are applied to the comparator. If the input voltage at the positive, non-inverting input is higher than the voltage at the negative, inverting input, the output voltage approaches the positive supply voltage. If a lower electrical voltage is present at the positive, non-inverting input than at the negative, inverting input, then the output voltage approaches the negative supply voltage or ground.

The light-emitting diode control circuit according to the invention also comprises a light-emitting diode interface and a fuse circuit, which is electrically connected to the output of the voltage monitoring circuit. The fuse circuit can be set to a switch-off state by a switch-off signal at the output of the voltage monitoring circuit. For the off state, the light emitting diode array is turned off by means of the fuse circuit. The light-emitting diode interface can, for example, comprise a diode base with which the light-emitting diodes of the light-emitting diode arrangement are mechanically and electrically connected. The diode base is electrically connected to a connector with the voltage monitoring circuit and the fuse circuit, so that a control and monitoring of the LEDs is possible.

The signal generator according to the invention for a traffic signal system has a light-emitting diode and a light-emitting diode control circuit according to the invention on. As already mentioned, the light-emitting diode control circuit according to the invention also comprises a voltage monitoring circuit and a fuse circuit with which a light emitting diode or a light emitting diode array can be switched off in the event of a defect occurring.

In the use according to the invention, a light-emitting diode control circuit according to the invention is used for monitoring an electrical voltage applied to a light-emitting diode arrangement of a signal generator of a traffic signal system. By using the light-emitting diode control circuit according to the invention in a signal generator circuit, it is possible to achieve a more precise and reliable functional monitoring of the light-emitting diode arrangement of the signal transmitter circuit.

In the method according to the invention for monitoring a light-emitting diode voltage of a light-emitting diode arrangement of a signal generator of a traffic signal system, an electrical voltage applied to a light-emitting diode arrangement of the signal generator is detected. Subsequently, the detected electrical voltage value is compared with a reference voltage and output a switch-off signal for the case that in the comparison, a deviation of the electrical voltage value from the reference voltage has exceeded a predetermined maximum value or has fallen below a predetermined minimum value. Exceeding a maximum value can, for example, be associated with a diode break in which no current flows through the light-emitting diode arrangement. A shortfall of a minimum value can occur, for example, when a short circuit occurs in a light emitting diode of a light emitting diode arrangement, so that only a small electrical voltage drops across the light emitting diode.

The dependent claims and the following description each contain particularly advantageous embodiments and further developments of the invention. In particular, the claims of a claim category can also be analogous to the dependent ones Be further developed claims of another claim category. In addition, in the context of the invention, the various features of different embodiments and claims can be combined to form new embodiments.

In a preferred refinement of the light-emitting diode control circuit according to the invention, the second output of the reference voltage source and the connection of the light-emitting diode arrangement are electrically connected to a common fixed second reference potential. This common fixed reference potential is preferably a ground potential or a ground potential. The common fixed reference potential is preferably subject to any temperature or time-related fluctuations, so that it can serve at least indirectly as a fixed reference for measuring the voltage applied to a light emitting diode array voltage. Between the light emitting diode array and the fixed reference potential, a current measuring resistor, also called a shunt resistor, may additionally be connected, at which a comparatively low electrical voltage drops.

In a preferred embodiment of the light-emitting diode control circuit according to the invention, the first terminal of the light-emitting diode arrangement is an anode terminal. The second terminal of the light-emitting diode arrangement is thus a cathode terminal and the defined first reference potential at the output of the reference voltage source is a positive potential. In this preferred embodiment, an electrical current flows from the first terminal to the second terminal of the light emitting diode array through the light emitting diode arrangement. At the second input of the comparator, which is electrically connected to the first terminal of the light-emitting diode array, in this embodiment is a positive potential. Thus, as a reference potential, which is applied to the first output of the reference voltage source, and a positive electrical potential is selected, which also at the first input the comparator is applied and which is compared with the potential at the anode of the light emitting diode array.

Alternatively, the light-emitting diode control circuit according to the invention may also be designed such that the first terminal of the light-emitting diode array is a cathode terminal, the second terminal of the light-emitting diode array is an anode terminal and the defined first reference potential at the first output of the reference voltage source is a negative potential. In this alternative embodiment, an electrical current flows from the second terminal to the first terminal of the light-emitting diode arrangement through the light-emitting diode arrangement. At the second input of the comparator, which is electrically connected to the first terminal of the light-emitting diode array, in this embodiment, there is a negative potential. Thus, as the reference potential at the first output of the reference voltage source, a negative electrical potential is selected, which is applied to the first input of the comparator and compared with the negative potential at the first terminal of the light emitting diode.

In a special embodiment of the light-emitting diode control circuit according to the invention, one of the two inputs of the comparator circuit is an inverting input (usually marked "-") and the other of the two inputs of the comparator circuit is a non-inverting input (usually labeled "+"). As already mentioned, the comparator circuit operates such that when the input voltage at the positive, non-inverting input is higher than the voltage at the negative, inverting input, the output voltage approaches the positive supply voltage. If a lower electrical voltage is present at the positive, non-inverting input than at the negative, inverting input, then the output voltage approaches the negative supply voltage of the comparator circuit. The voltage applied to the inverting input voltage is thus inverted in both cases in a voltage of opposite sign.

In a particularly practical variant of the light-emitting diode control circuit according to the invention, the voltage monitoring circuit has a first voltage divider which is connected in parallel to the light-emitting diode arrangement and has a first ohmic resistance and a second ohmic resistance which are connected in series with one another. The second input of the comparator circuit is connected between the first ohmic resistor and the second ohmic resistor of the first voltage divider. A voltage divider allows the adaptation of the voltage drop across the light-emitting diode arrangement to an input voltage which is favorable for the comparator.

The voltage monitoring circuit of the light-emitting diode control circuit according to the invention preferably has a second comparator circuit having a first input, a second input and a signal output whose first input is connected in parallel with the first input of the first comparator circuit and whose second input is electrically connected to the input of the light-emitting diode arrangement , Thus, a second comparator is used, wherein the inputs of the second comparator preferably have a function opposite to that of the first comparator. For example, if the first input of the first comparator circuit is a non-inverting input, the second input of the first comparator circuit is an inverting input, the first input of the second comparator circuit is an inverting input and the second input of the second comparator circuit is a non-inverting input.

The signals applied to the outputs of the two comparator circuits are evaluated as logical signals with an OR logic. This means that if an L signal (a signal with a low level) is present at one of the two outputs, this is interpreted as information in that the monitored LED is defective. This way a comparison can be made the voltage dropping across the light emitting diode array is carried out both with a predetermined maximum value and with a minimum value of the electrical voltage. Exceeding the maximum value can be interpreted as breaking a light-emitting diode, for example, while falling short of the minimum value can be interpreted as a short-circuit in the light-emitting diode arrangement. In this embodiment, therefore, a permitted range of values of the measured electrical voltage at the light-emitting diode arrangement is defined, which is brought into connection with a correctly functioning light-emitting diode arrangement. This range of values is used to compare a measured electrical light-emitting diode voltage. If the measurement voltage lies in the permitted range, then it is concluded that the light-emitting diode arrangement is in order, but if the measured voltage value is outside the permitted range, then a defect is suspected and automatic deactivation of the light-emitting diode arrangement is undertaken.

In a particularly preferred embodiment of the light-emitting diode control circuit according to the invention, the voltage monitoring circuit has a second voltage divider which is connected in parallel with the first voltage divider and comprises a third ohmic resistor and a fourth ohmic resistor which are connected in series with one another, the second input of the second comparator circuit is connected between the third ohmic resistor and the fourth ohmic resistor of the second voltage divider. The second voltage divider allows the adaptation of the voltage drop across the light-emitting diode arrangement to a voltage which is favorable for the second comparator.

In a particularly effective variant of the light-emitting diode control circuit according to the invention, the voltage monitoring circuit additionally has a third comparator circuit with a first, preferably non-inverting input, a second preferably inverting input and a Exit on. The first input of the third comparator circuit is electrically connected to an output of the reference voltage source and the second input of the third comparator circuit is electrically connected to the output of the first comparator circuit and / or the second comparator circuit. The third comparator preferably functions as an inverter which inverts the logic signal applied to its second, preferably inverting input. Advantageously, the first and second comparators output an L signal in the event of a defect of the LED which is then inverted by the third comparator circuit to an H (high level) signal. If an L signal is used as the output signal of the first and the second comparator for the occurrence of a defect, this has the advantage that this L signal has an H signal applied to the output of the respective other comparator when the outputs of the outputs are connected in parallel Both comparators can easily exaggerate. This means that the L signal prevails against the H signal when the two outputs are interconnected. In this way, an otherwise necessary additional logical OR circuit for logically combining the output signals of the first comparator and the second comparator can be omitted, whereby the monitoring circuit is simplified and thus cheaper. Such a circuit arrangement, which requires no additional logic components, and nevertheless acts as a logic gate, is also referred to as a wired OR logic circuit or wired OR circuit.

In a preferred variant of the light-emitting diode control circuit according to the invention, the voltage monitoring circuit according to the invention has a signal matching circuit which is connected between the output of the third comparator circuit and the output of the voltage monitoring circuit. The signal matching circuit adjusts the level of the output signal of the monitoring circuit to a level range of an input of a downstream unit.

The outputs of the first comparator circuit and the second comparator circuit of the voltage monitoring circuit may be designed as open collector outputs. As a circuit with an open collector output (open-collector output) should be understood an output circuit in which the emitter is connected to the ground and the collector is brought to the output unconnected. An H signal at an output of a comparator circuit is pulled up to a high level by means of a so-called pull-up resistor. In the case of an L signal at the output of a comparator circuit, a ground level is present at its output. Due to the uncoupled collector, it may not happen at a concern of different levels at the two outputs of the two comparator circuits that one of the respective output circuits is damaged by a short circuit. Thus, the two outputs of the two comparator circuits can be easily connected together to form an OR logic. Advantageously, no additional logic circuit must be used for the logical connection of the output signals.

In a variant of the light-emitting diode control circuit according to the invention, the safety circuit has a transistor, preferably a field-effect transistor, and a fuse resistor connected in series with the transistor. The use of a field-effect transistor as a switching transistor has the advantage, in comparison to the use of a bipolar transistor, that a field-effect transistor has a relatively low source-drain resistance in comparison with a collector-emitter resistor of a bipolar transistor. Thus, the field effect transistor can be dimensioned significantly smaller, which is space-saving and inexpensive.

Preferably, the fuse resistor is electrically connected at its end remote from the transistor to an input voltage. Furthermore, the inventive fuse circuit preferably comprises a supply voltage tap between the fuse resistor and the transistor. which is electrically connected via the already mentioned interface with the light-emitting diode arrangement and the light-emitting diode provides a supply voltage.

If the transistor is a field effect transistor, the gate of the field effect transistor in this embodiment is electrically connected to the output of the voltage monitoring circuit. If the field-effect transistor is designed, for example, as an n-channel field-effect transistor, the field-effect transistor switches at its gate at an H level, so that a strong current flows through the fuse resistor. As a result, the fuse resistor is set in a non-conductive state, so that a ground potential or no potential is applied to the supply voltage tap and thus the LED array is no longer supplied with electrical energy.

In one embodiment of the method according to the invention for monitoring a light-emitting diode voltage of a signal generator of a traffic signal system, a comparator circuit is used for the comparison step. As already mentioned, the use of a comparator circuit in combination with a reference voltage source allows a more precise voltage measurement that has been freed from precision fluctuations.

FIG 1

ein Schaltbild einer herkömmlichen Überwachungsschaltung einer Leuchtdiode eines Signalgebers einer Lichtsignalanlage,

FIG 2

ein Schaltbild einer Signalgeberschaltung mit einer Überwachungsschaltung gemäß einem Ausführungsbeispiel der Erfindung,

FIG 3

ein Schaltbild einer Signalgeberschaltung mit einer Überwachungsschaltung gemäß einem alternativen Ausführungsbeispiel der Erfindung,

FIG 4

ein Flussdiagramm, welches ein Verfahren zur Spannungsüberwachung einer Leuchtdiode eines Signalgebers einer Lichtsignalanlage gemäß einem Ausführungsbeispiel der Erfindung veranschaulicht.

The invention will be explained in more detail below with reference to the accompanying figures with reference to embodiments. Show it:

FIG. 1

a circuit diagram of a conventional monitoring circuit of a light emitting diode of a signal generator of a traffic signal system,

FIG. 2

1 is a circuit diagram of a signal generator circuit with a monitoring circuit according to an embodiment of the invention,

FIG. 3

2 is a circuit diagram of a signaling circuit with a monitoring circuit according to an alternative embodiment of the invention,

FIG. 4

a flowchart illustrating a method for voltage monitoring of a light emitting diode of a signal transmitter of a traffic signal system according to an embodiment of the invention.

In FIG. 1 a circuit diagram of a circuit 10 of a signal transmitter of a traffic signal system is shown. The circuit arrangement 10 comprises a light-emitting diode arrangement, in this embodiment a light-emitting diode 1 with an anode 1a and a cathode 1b, and a conventional monitoring circuit 9. The monitoring circuit 9 monitors an electrical voltage U _D applied to the diode 1. In detail, the monitoring circuit 9 comprises a voltage divider 11, which is connected in parallel with the light-emitting diode 1. The voltage divider 11 has a first ohmic resistance R ₁ and a second ohmic resistance R ₂ connected in series with the first ohmic resistance R ₁ . Between the two resistors R ₁ , R ₂ , the base 14 b of a bipolar transistor 14 is connected. The emitter 14a of the bipolar transistor 14 is electrically connected to ground M and the collector 14c of the bipolar transistor 14 forms the output of the monitoring circuit 9 and serves to control a fuse circuit (not shown), with a shutdown of the light emitting diode 1 can be made.

The operation of in FIG. 1 If, for example, due to a diode break, a high electrical voltage between the base 14b and the emitter 14a of the bipolar transistor 14, the transistor 14 turns on and leads the output of the circuit 9 to a potential with a low value , If the potential or a signal AS at the output of the circuit 9 falls below a predetermined value, this is interpreted as a signal for a defect due to a breakage of the light-emitting diode 1 and it is a shutdown of the diode 1, for example via a fuse circuit (not shown) made. On the other hand, if the electrical voltage applied to the light-emitting diode 1 is too low because the diode has a short circuit, for example, a very low base-emitter voltage is also present between the base 14b and the emitter 14a of the bipolar transistor 14. The low base-emitter voltage causes a significantly increased voltage drop between emitter and collector, so that in this case at the output of the circuit 9, a signal with a high level is applied, which exceeds a predetermined maximum value. Exceeding the maximum value of the potential at the output of the circuit 9 is interpreted as an indication of a short circuit in the light emitting diode 1 and there is also a shutdown of the light emitting diode due to a detected defect.

As already mentioned, the height of the base-emitter switching voltage of a bipolar transistor depends on fluctuating parameters of the manufacturing processes as well as on the temperature, so that very high measurement tolerances result.

In FIG. 2 a circuit diagram of a signaling device circuit 20 is shown with a monitoring circuit 19 of a light-emitting diode 1 according to an embodiment of the invention. The light-emitting diode comprises an anode 1a and a cathode 1b. The monitoring circuit 19 is connected in parallel to the light-emitting diode 1 and comprises a reference voltage source 2 whose first output 2a provides a predetermined reference potential U _ref and whose second input 2b is electrically connected to a ground potential M of the circuit arrangement 20. The value of the reference potential U _ref may, for example, correspond to a voltage value of an electrical voltage which is applied to the light-emitting diode 1, if this is not defective. Furthermore, the monitoring circuit 19 comprises a comparator 3. A first input 3a of the comparator 3 is electrically connected to the first output 2a of the reference voltage source 2, so that a reference voltage U _ref is applied to the first input 3a of the comparator 3. With his second input 3b, the comparator 3 is electrically connected to the input or the anode 1a of the light-emitting diode 1. The comparator 3 can switch at its output 3c between two signal values, depending on whether at its first input 3a, a higher potential is applied or at its second input 3b. In the in FIG. 2 In the embodiment shown, the first input 3a is designed as an inverting input (marked "-"), and the second input 3b of the comparator 3 is designed as a non-inverting input (marked "+").

The value of the reference voltage U _ref can, for example, be chosen such that it corresponds significantly above the value of the voltage U _D dropping across a correctly functioning light-emitting diode 1. Thus, at the second input 3b of the comparator during normal operation, a lower potential than at the first input 3a of the comparator 3. Thus results as the output signal AS of the comparator 3, a signal having a negative level, since the non-inverting input 3b lower potential than at the inverting input 3a. If a defect occurs due to breakage of the light-emitting diode 1, then the potential applied to the second input 3b increases significantly above the reference voltage U _{ref of} the reference voltage source applied to the first input, so that an output signal at the output 3c of the comparator 3 high potential applied, since now the voltage applied to the non-inverting input 3b potential is higher than the voltage applied to the inverting input 3a potential.

Such a change in potential of the output signal of the comparator 3 can be interpreted as an indication of the occurrence of a defect of the light emitting diode 1 due to a breakage of the light emitting diode 1. Since a reference potential U _ref is applied to one of the inputs of the comparator 3, the comparator 3 operates largely without production-related or fluctuations caused by temperature changes. In this way, a significantly improved measurement accuracy is achieved, resulting in a higher precision in the detection of defects in the LEDs 1 of a signal generator leads. Instead of a single light emitting diode, a signal generator usually has series connections of a plurality of light emitting diodes. In such a case, for example, a single monitoring circuit may be connected in parallel with a series of light-emitting diodes.

In FIG. 3 a circuit diagram is shown, which shows a signal generator circuit 30 with a light emitting diode 1 and a light-emitting diode control circuit 27 connected in parallel with a monitoring circuit 29 and a fuse circuit 28 according to an embodiment of the invention in detail. The fuse circuit 28, which is controlled by the monitoring circuit 29, serves to switch off the light-emitting diode 1 in the event of a defect of the light-emitting diode 1.

The monitoring circuit 29 is set up to determine whether the value of a voltage drop across the light-emitting diode 1 U _D lies in a predetermined value interval, which is associated with a correctly functioning light-emitting diode. If it is ascertained that the value of the electrical voltage U _D dropping across the light-emitting diode 1 is not within the predetermined value interval, then a control signal AS is output to the safety circuit 28, so that a fuse integrated in the safety circuit 28 can switch the relevant light-emitting diode 1 from an electrical Input voltage U _E disconnects and the LED 1 turns off.

The monitoring circuit 29 comprises a first voltage divider 11a. The first voltage divider 11a has a first ohmic resistor R1 and a second ohmic resistor R2, which are connected in series with one another. Between the first ohmic resistor R1 and the second ohmic resistor R2 is a tap for a first comparator circuit 3. The first comparator circuit 3 is with its first input 3a, a non-inverting input (which is identified by "+"), electrically connected to a first output 2a of a reference voltage source 2, so that a reference voltage U _ref defined by the reference voltage source 2 is applied to the non-inverting input 3a. The second input 3b of the first comparator circuit, an inverting input (denoted by "-"), forms the tap of the comparator circuit 3 between the first ohmic resistor R1 and the second ohmic resistor R2 of the first voltage divider 11a. At the second input 3b, a first measurement signal MS1 is present, which comprises a voltage value which corresponds to the voltage drop across the second resistor R2.

A second voltage divider 11b is connected in parallel with the first voltage divider 11a and also in parallel with the light-emitting diode 1. The second voltage divider 11b has a third ohmic resistor R3 and a fourth ohmic resistor R4, which are connected in series with one another. Between the third ohmic resistor R3 and the fourth ohmic resistor R4 is a tap for a second comparator circuit 31. The second comparator circuit 31 is connected to its first input 31a, an inverting input 31a (which is marked "-") with the first output 2a of the reference voltage source 2 is electrically connected, so that at the inverting input 31a is applied a defined by the reference voltage source 2 reference voltage U _ref . The second input 31b of the second comparator circuit 31, a non-inverting input (indicated by "+"), forms a tap of the second comparator circuit 31 between the third ohmic resistor R3 and the fourth ohmic resistor R4 of the second voltage divider 11b. At the second input 31b, a measurement signal MS2 is present, the voltage value of which corresponds to the voltage dropping across the fourth ohmic resistor R4.

The two outputs 3c, 31c of the two comparators 3, 31 are combined on a signal line SL. That at the Signal line SL applied signal LS is pulled in the event that at both outputs 3c, 31c, a signal AS1, AS2 with a high level (H signal), pulled by a so-called pull-up resistor R _p to an increased level the comparators 3 and 31 have an open collector output. The two comparators 3, 31 are connected so that in the event of a defect of the light emitting diode 1 at an output 3c, 31c of one of the two comparators, a low signal (also L signal), ie a signal AS1, AS2 with a low level is applied. This always occurs when a potential with a higher value is applied to one of the inverting inputs 3b, 31a of the two comparators 3, 31 than to the respective non-inverting input 3a, 31b. By forming an output of the comparators connected to a defect of the light emitting diode 1 as an L (low level) signal, an OR circuit of the two outputs 3c, 31c of the two comparators 3, 31 can be easily obtained by connecting the outputs 3c, 31c the two comparators are formed. For in such a configuration, an L signal represents a strong level that prevails over an H signal that can be considered a weak level because the H level is raised by "pulling up" with the aid of the pull-up resistor R _p comes about. In contrast, with an L signal at an output 3c, 31c of one of the two comparators 3, 31, an output of one of the two comparators is connected to ground or another fixed reference potential. Thus, an L signal at the output 3c, 31c of one of the two comparators 3, 31 always prevails against an H signal at the output of the other comparator 3, 31.

The two comparators 3, 31 are preferably formed with a so-called open collector output 3c, 31c (open collector output). The formation of the outputs 3c, 31c of the comparators 3, 31 with an open collector has the advantage that the two outputs 3c, 31c can be switched to a common signal line SL, without forming a short-circuit current at different output levels, the switching elements of the Damage comparators 3, 31 could. Thus, the outputs 3c, 31c of the two comparator circuits 3, 31 can be switched together as a so-called wired-OR circuit and an otherwise necessary additional OR gate can be saved.

The monitoring circuit 29 also comprises a third comparator 32, which functions as an inverter, ie inverts a signal LS applied to its inverting input 32b. A first input 32a of the third comparator 32, which is a non-inverting input (marked "+"), is connected to a third output 2c of the reference voltage source 2 so that at the first input 32a of the third comparator 32 one from the reference voltage source 2 defined reference voltage U _ref is present. As a reference voltage may be applied to the third comparator 32, the same electrical voltage as at the first and the second comparator 3, 31. That is, the reference voltage at the first output 2a can be used directly. However, it is also generally possible for a different reference voltage to be applied to the third comparator 32 than to the first and the second comparator 3, 31. The second input 32b of the third comparator 32 is connected to a signal line SL which combines the two output signals AS1, AS2 of the two first and second comparators 3, 31 into a signal LS. If, at the second input 32b, which is an inverting input (denoted by "-"), for example a signal LS with an H level, it is inverted by the third comparator 32, so that at the output 32c of the third comparator 32, an output signal AS3 is applied to an L level. An output signal AS3 with an L level corresponds to the information that the light-emitting diode 1 is functioning correctly. If, on the other hand, a signal LS with an L level is present at the second input 32b of the third comparator 32, then this signal is inverted by the third comparator 32 into a signal with an H level, so that at the output 32c of the third comparator Signal AS3 is at an H level. Such a signal AS3 corresponds to the information that the light-emitting diode 1 has a defect. The monitoring circuit 29 also includes a signal matching circuit 4 which is electrically connected to the output 32c of the third comparator 32 and adjusts the level of the output signal AS3 of the third comparator 32 to a voltage level which is compatible with an allowable input voltage of the fuse circuit 28 connected to the monitoring circuit 29.

The output signal AS output from the signal matching circuit 4 is sent to the fuse circuit 28. The fuse circuit 28 includes a switching transistor 5, in this embodiment, a field effect transistor, more specifically an N-FET whose gate G is electrically connected to the output of the monitoring circuit 29. The source S (source) of the switching transistor 5 is connected via the signal matching circuit 4 and therein specifically via a Zener diode 41 to the ground potential M and the drain D (drain) of the switching transistor is electrically connected to a fuse resistor R _s , in turn, a Input voltage U _E is present. Between the fuse resistor R _s and the switching transistor 5, a supply voltage U _{v is} tapped, from the other not listed here circuit elements (such as a switching converter), the LED _driving voltage U _{D is} generated.

The fuse circuit 28 operates as follows: If an H signal is present at the input of the fuse circuit 28, which corresponds to a damage event, the switching transistor 5 is conductive. This has the consequence that the fuse resistor R _s is short-circuited to ground M and a very strong current flows through the fuse resistor R _s , which can blow through the fuse resistor R _s , so that the supply voltage U _V falls to zero. This is for the drive circuit (not shown) of the light emitting diode 1 and thus to the light emitting diode 1 no electrical voltage, so that the light emitting diode 1 is turned off.

If an L signal is present at the input of the fuse circuit 28, which corresponds to a regular operating state, then it blocks the switching transistor 5. This has the result that the fuse resistance R _s is separated from mass M and a supply voltage U _v, that the input voltage U _E corresponds with a small fuse resistance R _s, is present at the output of the fuse circuit 28th This is applied to the drive circuit (not shown) of the light emitting diode 1 to a non-zero electrical voltage and it is generated a non-zero electrical voltage U _D , so that the light-emitting diode 1 is turned on, which corresponds to the regular operation. By using comparators instead of bipolar transistors for measuring the diode voltage U _D , the accuracy of the measurement of the diode voltage U _{D can be} considerably increased. At the same safety standard, this leads to a significantly improved accuracy compared to conventional monitoring circuits, since the safety tolerances must be designed significantly lower, ie the risk of incorrect shutdown still functioning LED signalers decreases and it is achieved with the same effectiveness, a significantly improved level of security the probability that defective LEDs are not recognized, is significantly reduced.

In FIG. 4 a flowchart 400 is shown which illustrates a method for monitoring a light-emitting diode voltage of a signal generator. In step 4.I, an electrical voltage U _D applied to a light-emitting diode is first measured. In step 4.II, the measured electrical voltage value U _{D is} compared with a reference voltage U _ref . If it is determined in the comparison that the difference of the two electrical voltages U _D -U _ref exceeds a maximum value max, which is in FIG. 4 is marked with "j", then a switch-off signal is output in step 4.III. In the event that the difference of the two electrical voltages U _D -U _ref does not exceed a maximum value max, which is in FIG. 4 is marked with "n", then it goes back to the step 4.I and the monitoring of the LED continues. The comparison in step 4.II can analogously also with the examination of the difference U _D -U _ref < min or the difference U _ref -DU> max or U _ref -U _D <min, where "min" corresponds to a predetermined minimum value and "max" represents the maximum value already introduced.

It is finally pointed out again that the above-described methods and devices are merely preferred embodiments of the invention and that the invention can be varied by a person skilled in the art without departing from the scope of the invention, as far as it is specified by the claims. In particular, the voltage monitoring circuit according to the invention can be used not only to monitor individual LEDs, but also for the monitoring of a plurality of serially connected light-emitting diodes. For the sake of completeness, it is also pointed out that the use of indefinite articles does not exclude "one" or "one", that the characteristics in question can also be present multiple times. Similarly, the term "unit" does not exclude that it consists of several components, which may also be spatially distributed.

Claims (14)

A light-emitting diode control circuit (27), comprising: a voltage monitoring circuit (19, 29) for a light-emitting diode arrangement (1) of a signal generator of a traffic signal system, comprising: a reference voltage source (2) having an input and at least one first output (2a) and a second output (2b), a comparator circuit (3, 31) having a first input (3a), a second input (3b, 31b) and a signal output (3c, 31c),
in which - The first output (2a) of the reference voltage source (2) by the reference voltage source (2) defined reference potential (U _ref ) and with the first input (3a, 31a) of the comparator circuit (3, 31) is electrically connected and the second input (3b, 31b) of the comparator circuit (3, 31) is electrically connected to a terminal (1a) of a light-emitting diode arrangement (1) of the signal generator, a light emitting diode interface, - a fuse circuit (28) which is electrically connected to the output (3c, 32c) of the voltage monitoring circuit (19, 29), wherein the fuse circuit (28) by a turn-off signal at the output of the voltage monitoring circuit (29) is set to an off state, in which the light-emitting diode arrangement (1) is switched off. Light-emitting diode control circuit (27), wherein the second output (2b) of the reference voltage source (2) and a second terminal (1b) of the light emitting diode array (1) are preferably electrically connected to a common fixed second reference potential (M). Light-emitting diode control circuit (27), wherein the first terminal (1a) of the light emitting diode array (1) is an anode terminal, the second terminal (1b) of the light emitting diode (1) is a cathode terminal and the defined first reference potential (U _ref ) is a positive potential or the first terminal (1a) of the light-emitting diode (1) is a cathode terminal, the second terminal (1b) of the light-emitting diode arrangement (1) is an anode terminal and the defined first reference potential (U _ref ) is a negative potential. A light-emitting diode control circuit (27) according to claim 1 or 2, wherein the voltage monitoring circuit comprises a first voltage divider (11a) connected in parallel with the light-emitting diode array (1) and having a first ohmic resistance (R1) and a second ohmic resistance (R2) which are connected in series with each other, wherein the second input (3b) of the comparator circuit (3) is connected between the first ohmic resistor (R1) and the second ohmic resistor (R2). A light-emitting diode control circuit (27) according to claim 4, wherein the voltage monitoring circuit comprises a second comparator circuit (31) having a first input (31a), a second input (31b) and a signal output (31c), the first input (31a) of the second Comparator circuit (31b) with the first input (3a) of the first comparator circuit (31) is connected in parallel and wherein the second input (31b) of the second comparator circuit (31) to the first terminal (1a) of the light emitting diode array (1) is electrically connected. A light-emitting diode control circuit (27) according to claim 5, wherein the first input (3a) of the first comparator circuit (3) is a non-inverting input, the second input (3b) of the first comparator circuit (3) is an inverting input, the first input (31a) of the second comparator circuit (31) is an inverting input and the second input (31b) of the second comparator circuit (31) is a non-inverting input. A light-emitting diode control circuit (27) according to claim 5 or 6, wherein said voltage monitoring circuit comprises a second voltage divider (11b) connected in parallel with said first voltage divider (11a) and having a third ohmic resistor (R3) and a fourth ohmic resistor (R4). includes, which are connected in series with each other, wherein the second input (31b) of the second comparator circuit (31) between the third ohmic resistor (R3) and the fourth ohmic resistor (R4) of the second voltage divider (11b) is connected. A light-emitting diode control circuit (27) according to any one of claims 5 to 7, wherein the voltage monitoring circuit comprises a third comparator circuit (32) having a first, preferably non-inverting input (32a), a second, preferably inverting input (32b) and an output (32c ), wherein the first input (32a) of the third comparator circuit (32) is electrically connected to an output (2a, 2c) of the reference voltage source (2) and the second input (32b) of the third comparator circuit (32) is connected to the output (3c ) of the first comparator circuit (3) and / or the output (31c) of the second comparator circuit (31c) is electrically connected. A light-emitting diode control circuit (27) according to any one of claims 5 to 8, wherein the outputs (3c, 31c) of the first comparator circuit (3) and the second comparator circuit (31) are designed as open collector outputs. The light-emitting diode control circuit (27) according to any one of claims 1 to 9, wherein the fuse circuit (28) comprises a transistor, preferably a field effect transistor (5) and a fuse resistor (R _s ) connected in series with the transistor (5), preferably gate (5b) of the transistor (5) is electrically connected to the output of the voltage monitoring circuit (29). Signal transmitter (20, 30) for a traffic signal system, comprising: a light-emitting diode arrangement (1), - A light-emitting diode control circuit (27) according to one of claims 1 to 10. Use of a light-emitting diode control circuit according to one of Claims 1 to 10 for monitoring an electrical voltage (U _D ) applied to a light-emitting diode arrangement (1) of a signal generator of a traffic signal system. Method for monitoring a light-emitting diode voltage (U _D ) of a light-emitting diode arrangement (1) of a signal generator of a traffic signal system, comprising the steps: Detecting an electrical voltage (U _D ) applied to the light-emitting diode arrangement (1), Comparing the detected electrical voltage value (U _D ) with a reference voltage (U _ref ), - Outputting a switch-off signal for the case that in the comparison, a deviation of the electrical voltage value (U _D ) from the reference voltage (U _ref ) has exceeded a predetermined maximum value (max) or has fallen below a predetermined minimum value (min). A method according to claim 13, wherein a comparator circuit (3, 31) is used for the comparing step.

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