EP1659831B1 - Automobil lighting device incorporating LEDs - Google Patents

Automobil lighting device incorporating LEDs Download PDF

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Publication number
EP1659831B1
EP1659831B1 EP05024986A EP05024986A EP1659831B1 EP 1659831 B1 EP1659831 B1 EP 1659831B1 EP 05024986 A EP05024986 A EP 05024986A EP 05024986 A EP05024986 A EP 05024986A EP 1659831 B1 EP1659831 B1 EP 1659831B1
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European Patent Office
Prior art keywords
led
current
temperature
lighting device
leds
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EP05024986A
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German (de)
French (fr)
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EP1659831A1 (en
Inventor
Martin Pfeil
Christoph Kenn
Christian Spreitzer
Stephan Berlitz
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Audi AG
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Audi AG
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/10—Controlling the intensity of the light
    • H05B45/18—Controlling the intensity of the light using temperature feedback
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/50—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits
    • H05B45/56—Circuit arrangements for operating light-emitting diodes [LED] responsive to malfunctions or undesirable behaviour of LEDs; responsive to LED life; Protective circuits involving measures to prevent abnormal temperature of the LEDs
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/20—Controlling the colour of the light
    • H05B45/28—Controlling the colour of the light using temperature feedback

Definitions

  • the invention relates to a lighting device for a motor vehicle comprising one or more LEDs, at least one temperature sensor for detecting the temperature of at least one LED, a power supply of the LEDs serving switching power supply and the LED operation steuemdes control unit that communicates with the switching power supply and the temperature sensor.
  • LEDs In modern motor vehicles, lighting devices comprising one or more LEDs are increasingly being used, for example for better illumination of curves to be traveled in the form of a curve or cornering light.
  • the use as low beam is intended.
  • the problem with using individual LEDs or multiple discrete LED's exhibiting modules is that the LEDs must not exceed a certain limit temperature, otherwise they are irreversibly destroyed.
  • a temperature sensor To detect the LED temperature, a temperature sensor is provided in the prior art, which communicates with the control unit. If the temperature reaches a critical range, then in the prior art, the power supply is abruptly reduced, which in the following leads to a reduction in temperature, but equally also to a considerable reduction in brightness. However, such is not desirable.
  • the invention is therefore based on the problem to provide a lighting device that allows within certain limits, a temperature-sensitive LED control without serious loss of brightness.
  • a lighting device is provided with the features of claim 1.
  • a current interval is defined within which the output current of the switching power supply, which is given to the LEDs, can be varied depending on the temperature, the LED limit current is dimensioned so that given due to the current reduction decrease in brightness also in a tight limited interval between the maximum brightness at rated LED current and the brightness decreases when the LED limit current is applied.
  • the current regulation now takes place as a function of the detected temperature.
  • the lower limit of the current is just the LED limit current.
  • the predetermined value by which the brightness can be reduced without being recognized by the viewer's eye is according to the invention a maximum of 10%.
  • any other predetermined value, with respect to which the LED limit current is defined can be selected.
  • the LED limit current can be used approx. 60% of the rated LED current. This means that it is possible to lower the output current to 60% of the rated LED current, and then still move within the permitted brightness interval. A further current regulation would lead to an exceeding of the predetermined brightness value, which would then result in a noticeable reduction in brightness.
  • a maximum current reduction of 40% means that the heat development also decreases by a good third.
  • the actual value by which the brightness or the current can be reduced depends on the manufacturer or type of LED.
  • the control is carried out as described in dependence on the measured actual temperature. Basically, the LED is operated with the rated current. As the heat builds up, the temperature rises. From a certain temperature, the Stromabregelung begins, with the continuously measured LED temperature serves as a controlled variable.
  • the manipulated variable, ie the output current is changed so that a lower temperature level is adjusted, if this is possible by a current change in the specified current interval.
  • the control unit is expediently designed for automatically switching off the LEDs in order to prevent their destruction.
  • the current limit or Stromabregelung can be done in different ways.
  • a plurality of different resistances can be provided for this purpose in the switched-mode power supply, which are connected via the control unit as a function of the measured temperature for varying the output current depending on the required current limitation.
  • the resistors are designed so that a stepwise current reduction is possible, preferably to e.g. maximum 60% of the rated current.
  • the switching power supply can also be provided with a control element, in particular a transistor, which can be activated via the control device and which can be correspondingly activated in dependence on the measured temperature for varying the output current.
  • a control element in particular a transistor
  • This stepless control is possible via the transistor, the output current of the switching power supply, which corresponds to the LED current, are easily controlled to a desired value.
  • Fig. 1 shows in the form of a schematic representation of a lighting device 1 according to the invention, comprising a plurality of light sources in the form of three LED's 2a, 2b and 2c, each of which a control electronics 3a, 3b and 3c is assigned. These communicate with a control unit 4, which controls the control electronics via pulse width modulation signals.
  • a switching power supply 5 comprising a voltage converter 6, via which the vehicle electrical system voltage of 12 V DC voltage can be increased to the LED supply voltage of 20 V.
  • the output current of the switching power supply 5 and the voltage converter 6 can be set, that is, the output current given to the LEDs 2a-c can be varied here.
  • a temperature sensor 7 in the form of a PTC thermocouple is provided in the example shown, the output signal of which is given to the control unit 4. This now controls, for example, on the basis of a corresponding characteristic or the like as a function of the given temperature signal the switching power supply 5 to vary the output current depending on the given temperature.
  • ohmic resistances can be provided in the switched-mode power supply 5 or in the voltage converter 6, which are switched on depending on the signal from the control unit 4 and via which a stepwise adjustment of the output current is possible. It is also conceivable, however, for a control element in the form of a transistor to be provided in the switched-mode power supply 5 or in the voltage converter 6, which can be set in its on-state behavior via the output signal of the control device 4, which then causes the output current to change as a function of the temperature.
  • a maximum current reduction is starting from a maximum LED current, namely, the nominal current I nom of 100%, on a pre-defined limit LED current I limit permitted.
  • Fig. 2 Fig. 12 is a graph showing the ratio of the LED brightness in percent to the LED current in percentage.
  • the LEDs are lit at maximum brightness of 100%.
  • Such a decrease in brightness is hardly noticeable to the eye of the beholder. That is, with a considerable current reduction by 40% is an extremely low brightness reduction to a predetermined brightness value, here, for example, 5% (ie 95% brightness) accompanied.
  • a stronger current reduction then clearly leads to a significantly greater decrease in brightness than in the specified interval.
  • the current supplied to the LEDs via the control unit 4 can be measured in the interval between the rated current I rated limit current I limit can be varied to regulate to a temperature level at which the LEDs will not be damaged, without any noticeable loss of brightness would be associated with it. Nevertheless, a considerable reduction of the heat development can be achieved within this interval, so that for most applications, the current variation in the specified interval as a function of the temperature can be used to avoid exceeding the critical temperature range. Nevertheless, should the control limit I limit be lower than the actual temperature in order to be able to control a given temperature development, the switching off of the LEDs or of the entire module takes place via the control unit 4 expediently.
  • Fig. 1 shows as an example the construction of a lighting device, which serves to give a cornering or cornering light, to which the three LEDs, 2a - c are directed in different directions to the vehicle side.
  • a time-shifted switching operation of the LED's 2a - c is provided as a function of the actual steering angle, it is expedient, via the temperature sensor 7, only the temperature of that LED, which is turned on as the first and switched off when last as the last to detect, since the temperature the other LED's is at most equal to this LED, but usually below it.
  • the detection of the temperature of only one LED is representative of all others.

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  • Lighting Device Outwards From Vehicle And Optical Signal (AREA)
  • Circuit Arrangement For Electric Light Sources In General (AREA)

Description

Die Erfindung betrifft eine Leuchteinrichtung für ein Kraftfahrzeug umfassend eine oder mehrere LED's, wenigstens einen Temperatursensor zum Erfassen der Temperatur wenigstens einer LED, ein der Stromversorgung der LED's dienendes Schaltnetzteil und ein den LED-Betrieb steuemdes Steuergerät, das mit dem Schaltnetzteil und dem Temperatursensor kommuniziert.The invention relates to a lighting device for a motor vehicle comprising one or more LEDs, at least one temperature sensor for detecting the temperature of at least one LED, a power supply of the LEDs serving switching power supply and the LED operation steuemdes control unit that communicates with the switching power supply and the temperature sensor.

In modernen Kraftfahrzeugen werden zunehmend Leuchteinrichtungen umfassend ein oder mehrere LED's eingesetzt, beispielsweise zum besseren Ausleuchten von zu befahrenden Kurven in Form eines Kurven- oder Abbiegelichts. Auch der Einsatz als Abblendlicht ist beabsichtigt. Problematisch bei Verwendung einzelner LED's oder mehrere diskrete LED's aufweisender Module ist, dass die LED's eine bestimmte Grenztemperatur nicht überschreiten dürfen, da sie ansonsten irreversibel zerstört werden. Um die LED-Temperatur zu erfassen, ist im Stand der Technik ein Temperatursensor vorgesehen, der mit dem Steuergerät kommuniziert. Erreicht die Temperatur einen kritischen Bereich, so wird im Stand der Technik die Stromzufuhr abrupt reduziert, was zwar nachfolgend zu einer Temperaturemiedrigung führt, gleichermaßen aber auch zu einer beachtlichen Helligkeitsabnahme. Eine solche ist jedoch nicht wünschenswert.In modern motor vehicles, lighting devices comprising one or more LEDs are increasingly being used, for example for better illumination of curves to be traveled in the form of a curve or cornering light. The use as low beam is intended. The problem with using individual LEDs or multiple discrete LED's exhibiting modules is that the LEDs must not exceed a certain limit temperature, otherwise they are irreversibly destroyed. To detect the LED temperature, a temperature sensor is provided in the prior art, which communicates with the control unit. If the temperature reaches a critical range, then in the prior art, the power supply is abruptly reduced, which in the following leads to a reduction in temperature, but equally also to a considerable reduction in brightness. However, such is not desirable.

Der Erfindung liegt damit das Problem zugrunde, eine Leuchteinrichtung anzugeben, die in gewissen Grenzen eine temperatursensitive LED-Steuerung ohne gravierende Helligkeitseinbußen ermöglicht.The invention is therefore based on the problem to provide a lighting device that allows within certain limits, a temperature-sensitive LED control without serious loss of brightness.

Zur Lösung dieses Problems ist eine Leuchteinrichtung mit den Merkmalen des Patentanspruchs 1 vorgesehen.To solve this problem, a lighting device is provided with the features of claim 1.

Bei der erfindungsgemäßen Leuchteinrichtung ist ein Stromintervall definiert, innerhalb welchem der Ausgangsstrom des Schaltnetzteils, der den LED's gegeben wird, in Abhängigkeit der Temperatur variiert werden kann, wobei der LED-Grenzwertstrom so bemessen ist, dass die aufgrund der Stromabsenkung gegebenen Helligkeitsabnahme ebenfalls in einem eng begrenzten Intervall zwischen der maximalen Helligkeit bei LED-Nennstrom und der Helligkeit bei Anliegen des LED-Grenzwertstroms abnimmt. Dem liegt die Erkenntnis zugrunde, dass der Ausgangsstrom und damit der LED-Strom ausgehend vom Nennstrom um ein gewisses Maß reduziert werden kann, ohne dass es überhaupt zu einer für den Betrachter wahrnehmbaren Helligkeitseinbuße kommt, wenngleich die Helligkeit messbar etwas abnimmt. Dies ist darauf zurückzuführen, dass die bei Kraftfahrzeugen eingesetzten LED's beim Nennstrom extrem helles Licht emittieren, das für den Betrachter nicht erkennbar etwas abgedimmt werden kann.In the lighting device according to the invention, a current interval is defined within which the output current of the switching power supply, which is given to the LEDs, can be varied depending on the temperature, the LED limit current is dimensioned so that given due to the current reduction decrease in brightness also in a tight limited interval between the maximum brightness at rated LED current and the brightness decreases when the LED limit current is applied. This is based on the finding that the output current and thus the LED current, starting from the rated current, can be reduced to a certain extent without there being any perceptible brightness loss for the observer, even though the brightness decreases measurably somewhat. This is due to the fact that the LEDs used in motor vehicles emit extremely bright light at the rated current, which can not be dimmed noticeably for the observer.

Erfindungsgemäß erfolgt nun die Stromregelung in Abhängigkeit der erfassten Temperatur. Je höher die erfasste Temperatur ist, desto stärker wird der Strom abgeregelt, wobei die Stromuntergrenze eben der LED-Grenzwertstrom ist. Nachdem dieser aber in Bezug auf eine zulässige Helligkeitsabnahme definiert wurde, ergibt sich für den Betrachter kein gravierender erfassbarer Helligkeitsunterschied, wenngleich durch die Stromerniedrigung die LED-Temperatur in beachtlichem Maß reduziert werden kann.According to the invention, the current regulation now takes place as a function of the detected temperature. The higher the detected temperature, the stronger the current is regulated, the lower limit of the current is just the LED limit current. However, after this has been defined in terms of a permissible decrease in brightness, there is no significant detectable difference in brightness for the observer, although the lowering of the current can considerably reduce the LED temperature.

Der vorbestimmte Wert, um den die Helligkeit reduziert werden kann, ohne dass sie vom Betrachterauge erkannt wird, beträgt erfindungsgemäß maximal 10 %. Innerhalb dieses Intervalls kann natürlich auch jeder andere vorbestimmte Wert, bezüglich welchem der LED-Grenzwertstrom definiert ist, gewählt werden. Für übliche im Kraftfahrzeugbereich verwendete LED-Module, beispielsweise solche der Firma Osram, kann dabei der LED-Grenzwertstrom ca. 60 % des LED-Nennstroms betragen. Das heißt, eine Erniedrigung des Ausgangsstroms auf 60 % des LED-Nennstroms ist möglich, man bewegt sich dann immer noch im zulässigen Helligkeitsintervall. Eine weitere Stromabregelung würde zu einer Überschreitung des vorbestimmten Helligkeitswerts führen, die dann in einer erkennbaren Helligkeitsabnahme resultieren würde. Für die Wärmeentwicklung der LED's bedeutet eine maximale Stromabsenkung um 40 %, dass auch die Wärmeentwicklung um gut ein Drittel abnimmt. Der konkrete Wert, um den die Helligkeit beziehungsweise der Strom reduziert werden kann, hängt vom Hersteller beziehungsweise Typ der LED ab. Die Regelung erfolgt wie ausgeführt in Abhängigkeit der gemessenen Ist-Temperatur. Grundsätzlich wird die LED mit dem Nennstrom betrieben. Mit zunehmender Wärmeentwicklung steigt die Temperatur. Ab einer gewissen Temperatur beginnt die Stromabregelung, wobei als Regelgröße die kontinuierlich gemessene LED-Temperatur dient. Die Stellgröße, also der Ausgangsstrom, wird so verändert, dass ein niedrigeres Temperaturniveau eingeregelt wird, sofern dies durch eine Stromveränderung im angegebenen Stromintervall möglich ist. Für den Fall, dass sich eine Temperaturreduzierung durch diese Regelungsmaßnahme nicht erzielen lässt, ist das Steuergerät zweckmäßigerweise zum automatischen Abschalten der LED's ausgebildet, um eine Zerstörung derselben zu verhindern.The predetermined value by which the brightness can be reduced without being recognized by the viewer's eye is according to the invention a maximum of 10%. Within this interval, of course, any other predetermined value, with respect to which the LED limit current is defined, can be selected. For customary LED modules used in the motor vehicle sector, for example those from Osram, the LED limit current can be used approx. 60% of the rated LED current. This means that it is possible to lower the output current to 60% of the rated LED current, and then still move within the permitted brightness interval. A further current regulation would lead to an exceeding of the predetermined brightness value, which would then result in a noticeable reduction in brightness. For the heat development of the LEDs, a maximum current reduction of 40% means that the heat development also decreases by a good third. The actual value by which the brightness or the current can be reduced depends on the manufacturer or type of LED. The control is carried out as described in dependence on the measured actual temperature. Basically, the LED is operated with the rated current. As the heat builds up, the temperature rises. From a certain temperature, the Stromabregelung begins, with the continuously measured LED temperature serves as a controlled variable. The manipulated variable, ie the output current, is changed so that a lower temperature level is adjusted, if this is possible by a current change in the specified current interval. In the event that a temperature reduction can not be achieved by this control measure, the control unit is expediently designed for automatically switching off the LEDs in order to prevent their destruction.

Die Strombegrenzung oder Stromabregelung kann auf unterschiedliche Weise erfolgen. Nach einer ersten Erfindungsausgestaltung können hierzu im Schaltnetzteil mehrere unterschiedliche Widerstände vorgesehen sein, die über das Steuergerät in Abhängigkeit der gemessenen Temperatur zur Varüerung des Ausgangsstroms je nach der erforderlichen Strombegrenzung zugeschaltet werden. Die Widerstände sind dabei so ausgelegt, dass eine stufenweise Stromreduzierung möglich ist, bis bevorzugt auf z.B. maximal 60 % des Nennstroms.The current limit or Stromabregelung can be done in different ways. According to a first embodiment of the invention, a plurality of different resistances can be provided for this purpose in the switched-mode power supply, which are connected via the control unit as a function of the measured temperature for varying the output current depending on the required current limitation. The resistors are designed so that a stepwise current reduction is possible, preferably to e.g. maximum 60% of the rated current.

Alternativ zur Verwendung diskreter zuzuschaltender Widerstände kann im Schaltnetzteil auch ein über das Steuergerät ansteuerbares Regelglied, insbesondere ein Transistor vorgesehen sein, das in Abhängigkeit der gemessenen Temperatur zur Variierung des Ausgangsstroms entsprechend ansteuerbar ist.As an alternative to the use of discrete switches to be switched on, the switching power supply can also be provided with a control element, in particular a transistor, which can be activated via the control device and which can be correspondingly activated in dependence on the measured temperature for varying the output current.

Hierüber ist eine stufenlose Ansteuerung möglich, über den Transistor kann der Ausgangsstrom des Schaltnetzteils, der dem LED-Strom entspricht, ohne weiteres auf einen Soll-Wert geregelt werden.This stepless control is possible via the transistor, the output current of the switching power supply, which corresponds to the LED current, are easily controlled to a desired value.

Weitere Vorteile, Merkmale und Einzelheiten der Erfindung ergeben sich aus dem im folgenden beschriebenen Ausführungsbeispiel sowie anhand der Zeichnungen. Dabei zeigen:

Fig. 1
eine Prinzipdarstellung einer erfindungsgemäßen Leuchteinrichtung, und
Fig. 2
ein Diagramm zur Darstellung der Helligkeit des von einer LED abgestrahlten Licht gegenüber dem LED-Strom.
Further advantages, features and details of the invention will become apparent from the embodiment described below and with reference to the drawings. Showing:
Fig. 1
a schematic diagram of a lighting device according to the invention, and
Fig. 2
a diagram illustrating the brightness of the light emitted by an LED light against the LED current.

Fig. 1 zeigt in Form einer Prinzipsdarstellung eine erfindungsgemäße Leuchteinrichtung 1, umfassend mehrere Lichtquellen in Form dreier LED's 2a, 2b und 2c, denen jeweils eine Ansteuerelektronik 3a, 3b und 3c zugeordnet ist. Diese kommunizieren mit einem Steuergerät 4, das die Ansteuerelektroniken über Pulsweitenmodulationssignale steuert. Fig. 1 shows in the form of a schematic representation of a lighting device 1 according to the invention, comprising a plurality of light sources in the form of three LED's 2a, 2b and 2c, each of which a control electronics 3a, 3b and 3c is assigned. These communicate with a control unit 4, which controls the control electronics via pulse width modulation signals.

Vorgesehen ist ferner ein Schaltnetzteil 5 umfassend einen Spannungswandler 6, über den die Bordnetzspannung von 12 V Gleichspannung auf die LED-Versorgungsspannung von 20 V angehoben werden kann. Über einen entsprechenden Pin am Steuergerät 4, das beispielsweise als Microcontroller oder Schaltregler-IC ausgeführt ist, kann der Ausgangsstrom des Schaltnetzteils 5 bzw. des Spannungswandlers 6 eingestellt werden, das heißt, der den LED's 2a - c gegebene Ausgangsstrom kann hierüber variiert werden.Also provided is a switching power supply 5 comprising a voltage converter 6, via which the vehicle electrical system voltage of 12 V DC voltage can be increased to the LED supply voltage of 20 V. Via a corresponding pin on the control unit 4, which is designed for example as a microcontroller or switching regulator IC, the output current of the switching power supply 5 and the voltage converter 6 can be set, that is, the output current given to the LEDs 2a-c can be varied here.

Um eine temperaturabhängige Stromregelung zu ermitteln, ist im gezeigten Beispiel ein Temperatursensor 7 in Form eines PTC-Thermoelements vorgesehen, dessen Ausgangssignal dem Steuergerät 4 gegeben wird. Dieses steuert nun beispielsweise unter Zugrundelegung einer entsprechenden Kennlinie oder dergleichen in Abhängigkeit des gegebenen Temperatursignals das Schaltnetzteil 5, um je nach gegebener Temperatur den Ausgangsstrom zu variieren.In order to determine a temperature-dependent current control, a temperature sensor 7 in the form of a PTC thermocouple is provided in the example shown, the output signal of which is given to the control unit 4. This now controls, for example, on the basis of a corresponding characteristic or the like as a function of the given temperature signal the switching power supply 5 to vary the output current depending on the given temperature.

Zu diesem Zweck können im Schaltnetzteil 5 bzw. im Spannungswandler 6 mehrere unterschiedliche ohm'sche Widerstände vorgesehen sein, die je nach Signal vom Steuergerät 4 zugeschalten werden und über die eine stufenweise Einstellung des Ausgangsstrom möglich ist. Denkbar ist es aber auch, dass im Schaltnetzteil 5 oder im Spannungswandler 6 ein Regelglied in Form eines Transistors vorhanden ist, der in seinem Durchlassverhalten über das Ausgangssignal des Steuergeräts 4 eingestellt werden kann, worüber dann die Veränderung des Ausgangsstroms in Abhängigkeit der Temperatur erfolgt.For this purpose, several different ohmic resistances can be provided in the switched-mode power supply 5 or in the voltage converter 6, which are switched on depending on the signal from the control unit 4 and via which a stepwise adjustment of the output current is possible. It is also conceivable, however, for a control element in the form of a transistor to be provided in the switched-mode power supply 5 or in the voltage converter 6, which can be set in its on-state behavior via the output signal of the control device 4, which then causes the output current to change as a function of the temperature.

Im Rahmen der temperaturabhängigen Stromregelung ist eine maximale Stromabsenkung ausgehend von einem maximalen LED-Strom, nämlich dem Nennstrom INenn von 100 %, auf einen vorab definierten LED-Grenzwertstrom IGrenz zulässig.As part of the temperature dependent current scheme, a maximum current reduction is starting from a maximum LED current, namely, the nominal current I nom of 100%, on a pre-defined limit LED current I limit permitted.

Fig. 2 zeigt ein Diagramm zur Darstellung des Verhältnisses der LED-Helligkeit in Prozent gegenüber dem LED-Strom in Prozent. Bei 100 % LED-Strom INenn leuchten die LED's mit maximaler Helligkeit von 100 %. Wie aus Fig. 2 ersichtlich ist, nimmt die Helligkeit im LED-Stromintervall von 100 % - 60 % nur unwesentlich ab, die prozentuale Helligkeitsänderung ΔH beträgt im gezeigten Beispiel rund 5 %. Das heißt, die Reduzierung des LED-Stroms auf 60 % führt zu einer Helligkeitsabnahme von ca. 5 %. Eine solche Helligkeitsabnahme ist für das Auge des Betrachters kaum bemerkbar. Das heißt, mit einer beachtlichen Stromabsenkung um 40 % geht eine äußerst geringe Helligkeitsreduzierung auf einen vorbestimmten Helligkeitswert, hier beispielsweise 5 % (also 95 % Helligkeit) einher. Eine stärkere Stromabsenkung führt dann ersichtlich zu einer deutlich stärkeren Helligkeitsabnahme als im angegebenen Intervall. Fig. 2 Fig. 12 is a graph showing the ratio of the LED brightness in percent to the LED current in percentage. At 100% LED current I nominal , the LEDs are lit at maximum brightness of 100%. How out Fig. 2 can be seen, the brightness in the LED power interval of 100% - 60% decreases only insignificantly, the percentage brightness change ΔH in the example shown around 5%. This means that the reduction of the LED current to 60% leads to a decrease in brightness of approx. 5%. Such a decrease in brightness is hardly noticeable to the eye of the beholder. That is, with a considerable current reduction by 40% is an extremely low brightness reduction to a predetermined brightness value, here, for example, 5% (ie 95% brightness) accompanied. A stronger current reduction then clearly leads to a significantly greater decrease in brightness than in the specified interval.

Erfasst nun der Temperatursensor 7 kontinuierlich die Temperatur, so kann über das Steuergerät 4 der den LED's gegebene Strom, ausgehend von ursprünglich 100 % Nennstrom INenn, im Intervall zwischen dem Nennstrom INenn-Grenzwertstrom IGrenz variiert werden, um auf ein Temperaturniveau einzuregeln, bei dem die LED's keinen Schaden nehmen, ohne dass in irgendeiner Weise bemerkbare Helligkeitseinbußen damit verbunden wären. Gleichwohl kann innerhalb dieses Intervalls eine beachtliche Reduzierung der Wärmeentwicklung erreicht werden, so dass für die meisten Anwendungsfälle durch die Stromvariation im angegebenen Intervall in Abhängigkeit der Temperatur ein Überschreiten des kritischen Temperaturbereichs vermieden werden kann. Sollte dennoch die Regelgrenze IGrenz im Hinblick auf die Ist-Temperatur zu unterschreiten sein, um eine gegebene Temperaturentwicklung beherrschen zu können, erfolgt über das Steuergerät 4 zweckmäßigerweise die Abschaltung der LED's bzw. des gesamten Moduls.If the temperature sensor 7 now continuously detects the temperature, the current supplied to the LEDs via the control unit 4, starting from the originally 100% rated current I nominal , can be measured in the interval between the rated current I rated limit current I limit can be varied to regulate to a temperature level at which the LEDs will not be damaged, without any noticeable loss of brightness would be associated with it. Nevertheless, a considerable reduction of the heat development can be achieved within this interval, so that for most applications, the current variation in the specified interval as a function of the temperature can be used to avoid exceeding the critical temperature range. Nevertheless, should the control limit I limit be lower than the actual temperature in order to be able to control a given temperature development, the switching off of the LEDs or of the entire module takes place via the control unit 4 expediently.

Fig. 1 zeigt als Beispiel den Aufbau einer Leuchteinrichtung, die zur Gabe eines Kurven- oder Abbiegelichts dient, wozu die drei LED's, 2a - c in unterschiedliche Richtungen zur Fahrzeugseite hin gerichtet sind. Dem Steuergerät 4 wird, wie durch den Pfeil 8 dargestellt ist, zusätzlich der Lenkwinkel gegeben, in dessen Abhängigkeit die Zuschaltung der LED's über das Steuergerät 4 gesteuert wird. Sofern ein zeitversetzter Zuschaltbetrieb der LED's 2a - c in Abhängigkeit des Ist-Lenkwinkels vorgesehen ist, ist es zweckmäßig, über den Temperatursensor 7 lediglich die Temperatur derjenigen LED, die als erste eingeschaltet und beim Zurücklegen als letzte ausgeschaltet wird, zu erfassen, da die Temperatur der anderen LED's maximal gleich dieser LED ist, in der Regel aber darunter liegt. Für Module, bei denen alle LED's simultan zu- und abgeschaltet werden, ist ebenfalls die Erfassung der Temperatur nur einer LED stellvertretend für alle anderen ausreichend. Fig. 1 shows as an example the construction of a lighting device, which serves to give a cornering or cornering light, to which the three LEDs, 2a - c are directed in different directions to the vehicle side. The control unit 4, as shown by the arrow 8, additionally given the steering angle, in whose dependence the connection of the LED's is controlled by the control unit 4. If a time-shifted switching operation of the LED's 2a - c is provided as a function of the actual steering angle, it is expedient, via the temperature sensor 7, only the temperature of that LED, which is turned on as the first and switched off when last as the last to detect, since the temperature the other LED's is at most equal to this LED, but usually below it. For modules in which all LEDs are switched on and off simultaneously, the detection of the temperature of only one LED is representative of all others.

Claims (6)

  1. Lighting device for a motor vehicle comprising one or more LEDs, at least one temperature sensor for detecting the temperature of at least one LED, a switched mode power supply for supplying power to the LEDs and a control device controlling the LED operation, said control device communicating with the switched mode power supply and the temperature sensor, characterized in that, via the control device (4) and depending on the detected temperature of the at least one LED (2a), the output current of the switched mode power supply (5) is variable within an interval between the LED rated current (Irated) and a lower LED limit value current (Ilimit), up to which the brightness decreases by a predetermined value (AH) in comparison with the brightness when the LED rated current (Irated) is present, the predetermined value (ΔH) being at most 10%.
  2. Lighting device according to Claim 1, characterized in that the LED limit value current (Ilimit) is 60% of the LED rated current (Irated).
  3. Lighting device according to Claim 1 or 2, characterized in that a plurality of different resistances are provided in the switched mode power supply (5), it being possible for said resistances to be connected via the control device (4), depending on the measured temperature, so as to vary the output current.
  4. Lighting device according to Claim 1 or 2, characterized in that a control element which can be driven by the control device (4), in particular a transistor, is provided in the switched mode power supply (5), it being possible for said control element to be driven, depending on the measured temperature, so as to vary the output current.
  5. Lighting device according to one of the preceding claims, characterized in that the control device (4) is designed to automatically switch off the LEDs (2a, 2b, 2c) at a determined temperature, which requires a reduction in the output current to below the LED limit value current (Ilimit).
  6. Lighting device according to one of the preceding claims, characterized in that the LEDs (2a, 2b, 2c) serve to produce a turn-off light or cornering light.
EP05024986A 2004-11-19 2005-11-16 Automobil lighting device incorporating LEDs Active EP1659831B1 (en)

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