EP3038433B1 - Led light module, signal light with such a light module and method for operating such a light module - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to an LED light module, a signal light with such a light module, in particular for rail, water, air or road traffic, and a method for operating such a light module.

BACKGROUND OF THE INVENTION

Due to their properties such as low power consumption and long service life, light-emitting diodes (LEDs) are increasingly being used as a replacement for classic light sources, including in safety-relevant lights such as traffic signals, side lights and vehicle lights, including lights for all types of land, water and and aircraft are understood.

For many lights, automated monitoring of correct functioning is desired or even mandatory. While it is usually easy to monitor the correct functioning of classic light sources (it is usually sufficient to monitor whether current is flowing through the light source or not; if no current is flowing through the light source despite the voltage being applied, it can be assumed that that the lamp is defective and needs to be replaced), monitoring the function of LEDs is not trivial for various reasons. For example, an LED may not light up even though current is flowing through it.

Total failure of an LED can be detected by combined current-voltage monitoring. However, this type of monitoring does not allow a change in the luminous flux (degradation) caused, for example, by aging of the LEDs to be detected.

It is known to provide LED light modules, i.e. arrangements with usually several LEDs and other elements such as ballast units for operating the LEDs, with an operating time counter that records the actual operating time of the LEDs. When a certain service life is reached, the LEDs are replaced, regardless of whether the light they emit is still sufficient to meet the requirements that may have been stipulated or not. This procedure means that LEDs that are still working correctly are regularly replaced.

It has been shown that the aging of LEDs depends not only on their actual operating time, but also on other factors, in particular the operating current and the operating temperature.

An obvious solution to the problem of detecting an aging-related reduction in light output is direct monitoring of the light emitted during operation of an LED using appropriate sensors. To this the DE 197 54 222 proposes a monitoring unit for an LED, in which the light emitted by an LED is measured using a photo sensor. If the brightness of the light falls below a certain limit value, a warning signal is generated which indicates to an operator of the LED that the LED should be replaced.

The ones from the DE 197 54 222 The well-known type of monitoring, especially in the case of so-called route signals for rail traffic, can be associated with very high material costs, because the monitoring unit is supplied with its own operating voltage, with the corresponding cables often being a few hundred, sometimes even a thousand or more meters from a corresponding one Connection point must be performed to the monitoring unit.

the U.S. 6,078,148 describes a control for a transformer with primary and secondary windings with a large number of turns and taps for changing the number of effective turns and thus an LED string light output. In this case, the taps are controlled as a function of an operating parameter of the LEDs for maintaining the light output LEDs above a predetermined level based on a combination of measurements of voltages and currents on the LEDs.

the EP 0 974 947 A1 shows a traffic signal system with at least one signal transmitter, the light source of which is formed by LEDs arranged in the form of a matrix, and with a monitoring device for checking the light-emitting diodes for their error-free operating status, which has a light sensor arranged in the beam path of the LEDs and an evaluation device connected to it for comparing a having a light sensor signal generated by the light sensor with a predetermined desired value, which corresponds to a normal operating state of the light-emitting diodes.

the DE 10 2005 032 719 A1 shows a traffic signal system with at least one signal transmitter having light-emitting diodes for emitting a light signal, with a control unit for actuating, evaluating and monitoring the signal transmitter, with lines for power supply and lines for data transmission between the control unit and the signal transmitter, and with a switching device for controlling the signal transmitter, as well as a switching device for each signal transmitter arranged in its immediate vicinity, the signal transmitters being connected to the control unit via a line section having the energy supply lines and the data transmission lines.

According to the DE 10 2010 026 012 A1 a signaling device for generating different colored points of light with RGB LEDs has an optical sensor for reliable signaling monitoring of the color location and the light intensity of the signaling device.

To operate a fan shows DE 10 2010 013 310 A1 an output circuit connected to an output of a ballast for supplying a lighting module with electrical energy, both the fan and a control circuit for supplying electrical energy being connected to the output circuit.

the WO 2014/179379 A1 and the WO 2009/116854 A2 each show an LED light module according to the preamble of claim 1. The US 8,159,146 B1 shows an LED driver with pulse width modulation.

DISCLOSURE OF THE INVENTION

The invention is based on the object of specifying an LED light module with a monitoring unit and a signal lamp equipped therewith, in which the monitoring unit can be made ready for operation with a minimum of material expenditure and therefore particularly cost-effectively.

The invention is also based on the object of specifying a method for operating an LED light module that can be implemented in a cost-saving manner while at the same time ensuring a high level of operational reliability.

The objects are achieved by an LED light module having the features of claim 1, a signal light having the features of claim 4 and a method having the features of claim 3.

The LED light module according to the invention does not require a separate power supply for the monitoring unit, but this can use the current supplied to the light module with pulse width modulation in order to monitor the emitted luminous flux and thereby dispense with the time-consuming calculation of scattered light components that are also recorded by conventional monitoring units . These and other advantages result from the following, purely exemplary and non-limiting description of exemplary embodiments in connection with the drawing, which consists of two drawing figures.

BRIEF DESCRIPTION OF THE DRAWING

1

shows a highly schematic block diagram for a basic understanding of the mode of operation of the invention.

2

shows an exemplary embodiment of a light module according to the invention in a highly schematic manner.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the 1 shows the basic idea of the invention in a highly schematic manner, according to which a string 10 of series-connected LEDs of a corresponding LED light module, in particular a light module for signal lights in road and rail traffic, is supplied with a current with a specific voltage in a manner known per se via a line 12 supplied and then part of the supplied current is used via a parallel to at least some of the LEDs of the strand circuit for operating a monitoring unit 14. The monitoring unit 14 can record certain operating parameters of the light module, such as the current flowing through the strand during operation, the voltage drop across the strand, the temperature in the vicinity of the strand and the luminous flux generated by the strand, and transmit values characteristic of these operating parameters to a higher-level system Output evaluation unit 16.

The monitoring unit 14 can be fed completely via the power supply of the LED string, so that a separate power supply is advantageously dispensed with and, in particular when the light module is used in signal lights for rail traffic, considerable amounts of cable can sometimes be saved. Means such as voltmeters for the LED forward voltage can be provided connected in parallel to one or more LEDs 18 of the string 10 . During operation of the light module, these means can be supplied with power via the power supply 20 of the LEDs.

The higher-level evaluation unit 16 is supplied via the power supply of the LED string, thus avoiding detection of scattered light when the LED string is switched off in pulses. The modern components required for this, such as temperature or photo sensors and microcontrollers, have such a low current consumption that there is no noticeable effect on the luminous flux of the LED string if part of the current to supply units 14 and 16 is branched off.

Typically, an LED string 10 of the type in question, for example, eight series-connected LEDs with a current consumption of 350 mA, while a Photo sensor as a means for detecting another operating parameter and a corresponding microcontroller for evaluating the signal of the photo sensor have a current consumption in the range of about 1 to 2 mA. It has been shown that a circuit according to the invention works particularly well when the current consumption of the units 14 and 16 is more than 20 times smaller than the current consumption of the LED string, preferably about 50 to 100 times smaller.

In the 2 an exemplary embodiment of the invention is shown, two operating parameters being recorded here and used to monitor and control the LED string in the manner according to the invention. The units of 1 corresponding units were also in 1 provided reference symbols used.

In this exemplary embodiment, the light module shown forms a unit that is installed in particular in a signal light and can be externally supplied with power via a line 12 . The LED string is formed by a number of series-connected LEDs 18, only a few of which are shown here, with the supply voltage and current being controlled by a ballast unit 20. In this exemplary embodiment, the ballast unit 20, like the evaluation unit 16, is part of the light module, but, like the evaluation unit 16, can also be arranged outside of the actual light module. Evaluation unit 16 and upstream unit can be part of a single control unit.

As indicated by the line 22, a monitoring unit 14 is supplied with current at a first point via a circuit parallel to the series connection of the LEDs 18, the various square-wave signals symbolically illustrated in the figure being intended to indicate that the current is pulse-width modulated.

As indicated by the corresponding circuit diagram, the monitoring unit 14 in this exemplary embodiment comprises a photo sensor 24 which is arranged in the light module and detects a value which is proportional to the luminous flux which is generated during operation of the LEDs. In light modules of the type in question, the LEDs are typically arranged rotationally symmetrically, and the light module is provided with an attachment or diffusing screen, as a result of which part of the emitted light is reflected back, which can then be detected by the photo sensor 24 .

In this exemplary embodiment, the monitoring unit 14 also includes two voltmeters 26 which, together with corresponding shunt resistors 28 and lines 30, enable an indirect current measurement of the current flowing through the LED string during operation.

Not shown, but provided in a preferred embodiment, is a voltmeter that measures the entire voltage drop across the LED string, which can be particularly advantageous in light modules for use in signal lights for rail traffic. The advantages of combined current-voltage monitoring when monitoring LED strings are well known and can be found, for example, in EP 1 992 524 A2 , the content of which is hereby incorporated by reference. In one embodiment variant of the invention, means provided for detecting the current and/or the voltage can be supplied with current in a pulsed manner via the power supply of the LEDs.

The values that are representative of the actual current, i.e. the current actually flowing through the LED string, from the voltmeters 26 and a value measured by the photo sensor 24 that is proportional to the luminous flux emitted during operation of the LEDs are fed to the evaluation unit 16, which is Embodiment includes a microcontroller 32 and a controller 34, which is designed to output a control value to the upstream unit 20. It should be noted that the evaluation unit 16 does not have its own power supply, as in previously known light modules, but is advantageously fed by the current supplied to the LEDs 18 in the same way as the monitoring unit 14 . If the photo sensor now detects that the luminous flux emitted during operation is decreasing, for example due to degradation of the LEDs 18, the evaluation unit 16 can generate a corresponding control signal, by means of which the ballast unit 20 is prompted to increase the current supplied to the LEDs so that the desired luminous flux. With the above boundary condition that the power consumption of the monitoring unit 14 and Evaluation unit 16 is significantly smaller than the power consumption of the LEDs, the reduction in the brightness of the LEDs due to the current diversion can be neglected, especially since such a detection by the photo sensor 24 anyway and led to a readjustment of the current.

The evaluation unit 16 is designed to control the current supplied to the LED string directly or indirectly as a function of the so-called “additional operating parameters”, i.e. here the luminous flux, i.e. either to influence the current directly as part of a more complex control circuit or to communicate with a separate unit, here the ballast unit 20, and to transmit this information that is the basis for controlling the current, and thus to control the current indirectly.

At the in 2 In the exemplary embodiment shown, the actual current detection has two channels and is therefore redundant, so that incorrect measurements are practically ruled out because the microcontroller 32 can be designed in such a way that it can generate a corresponding error message if there are deviations between the two signals that are representative of the actual current can then be transmitted in a manner known per se to a higher authority, for example a maintenance center.

In addition to the already mentioned guarantee of a stable color locus, the pulse width modulated operation provided in a preferred embodiment of the invention has two further significant advantages. In those cases, in which the means for detecting at least one further operating parameter has a photo sensor as in 2 include a complex calculation of the stray light component, since the sensor is only in operation due to the inventive supply via the LED current when the LEDs are switched on, in which case stray light components can be neglected. Light that falls on the sensor when the LEDs are switched off between two current pulses is not included in the usual summation by the sensor, so that advantageously inexpensive standard photo sensors, which sum light over a certain period of time to output a measured value, are used can become.

Another advantage of pulse width modulated operation is that evaluation unit 16 can check whether photo sensor 24 or voltmeter 26 is supplying signals during the time between two current pulses, from which a malfunction of the photo sensor and/or the voltmeter can be concluded and in a manner known per se way a corresponding error message can be generated. The evaluation unit 16 thus has a function for testing the means for detecting the at least one additional operating parameter. It is therefore checked whether the signals output by the ammeter and/or the photo sensor show a profile that corresponds to the profile of the pulse width modulated current.

Numerous modifications and developments are possible within the scope of the inventive idea, which relate in particular to the type and number of means for detecting operating parameters of the LEDs. Thus, in a preferred embodiment of the invention, the temperature in the vicinity of the LEDs of the strand is recorded, with this value then being able to be used to switch on a fan, for example, via the evaluation unit. Such a fan can also advantageously be supplied with power via the operating current of the LEDs, since the fan only needs to have a low power in typical applications.

The invention allows in a particularly simple and cost-effective manner for the first time the implementation of a particularly reliable monitoring of the correct functioning of an LED light module, since three different monitoring methods - monitoring the voltage drop across the LED strand, monitoring the current flowing through the strand and detecting a delivered Luminous flux of proportional value - can be combined.

REFERENCE LIST

10

LED strand

12

Management

14

monitoring unit

16

evaluation unit

18

LEDs

20

ballast unit

22

Management

24

photo sensor

26

tension meter

28

shunt resistors

30

cables

32

microcontroller

34

regulation

Claims (4)

1. An LED light module, in particular for signal lights of road and rail traffic, comprising

   - at least one string (10) of series-connected LEDs (18),

   - means for monitoring (26, 28, 30) the current flowing through the string during operation of the string and/or the voltage dropping across the string,

   - a current supply (20) of the LEDs,

   - a monitoring unit (14), comprising means for sensing at least one further operating parameter of the LEDs, which comprise a sensor (24) for sensing a value proportional to a luminous flux emitted during operation of the light module and for outputting a signal on the basis of the value, and

   - an evaluation unit (16), which is configured to control the current supply (20) of the LEDs for a current supplied to the LED string by pulse-width modulation as a function of the signal,
   characterised in that
   during operation of the light module, the monitoring unit (14) is likewise supplied with current via the current supply (20) of the LEDs (18) according to the pulse-width modulation.
2. The LED light module according to claim 1, characterised in that the evaluation unit (16) has a function for testing the means for sensing the at least one further operating parameter.
3. A method for operating an LED light module, in particular for signal lights of road and rail traffic, wherein

   - the light module has a string (10) of series-connected LEDs,

   - the current flowing through the string during operation and/or the voltage dropping across the string are monitored,

   - a value proportional to a luminous flux emitted during operation of the light module is sensed and a signal on the basis of the value is output to a higher-level evaluation unit (16) using a sensor (24) of a monitoring unit (14), and

   - the current supplied to the string during operation is controlled by pulse-width modulation of the current supply of the LEDs as a function of the value,
   characterised in that
   during operation of the light module, the monitoring unit (14) is likewise supplied with current via the current supply of the LEDs according to the pulse-width modulation.
4. A signal light, in particular for road and rail traffic, characterised in that it comprises an LED light module according to claim 1 or 2.

Images