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DE19848925A1 - Light-emitting diode control method e.g. for display device, provides initial brightness reduction by reduction of current with further reduction of brightness by current pulsing - Google Patents

Light-emitting diode control method e.g. for display device, provides initial brightness reduction by reduction of current with further reduction of brightness by current pulsing

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Publication number
DE19848925A1
DE19848925A1 DE19848925A DE19848925A DE19848925A1 DE 19848925 A1 DE19848925 A1 DE 19848925A1 DE 19848925 A DE19848925 A DE 19848925A DE 19848925 A DE19848925 A DE 19848925A DE 19848925 A1 DE19848925 A1 DE 19848925A1
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DE
Germany
Prior art keywords
brightness
current
reduction
light
display device
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
DE19848925A
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German (de)
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DE19848925B4 (en
Inventor
Rolf Aengenendt
Torsten Berth
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lumino Licht Elektronik GmbH
Original Assignee
Lumino Licht Elektronik GmbH
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Application filed by Lumino Licht Elektronik GmbH filed Critical Lumino Licht Elektronik GmbH
Priority to DE19848925A priority Critical patent/DE19848925B4/en
Publication of DE19848925A1 publication Critical patent/DE19848925A1/en
Application granted granted Critical
Publication of DE19848925B4 publication Critical patent/DE19848925B4/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/04Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions
    • G09G3/06Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions using controlled light sources
    • G09G3/12Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions using controlled light sources using electroluminescent elements
    • G09G3/14Semiconductor devices, e.g. diodes
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/30Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
    • G09G3/32Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B45/00Circuit arrangements for operating light-emitting diodes [LED]
    • H05B45/10Controlling the intensity of the light
    • H05B45/14Controlling the intensity of the light using electrical feedback from LEDs or from LED modules
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2011Display of intermediate tones by amplitude modulation
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2014Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2077Display of intermediate tones by a combination of two or more gradation control methods
    • G09G3/2081Display of intermediate tones by a combination of two or more gradation control methods with combination of amplitude modulation and time modulation

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Control Of El Displays (AREA)

Abstract

The control method for a light-emitting diode reduces the brightness level by corresponding reduction of the supplied diode current, until a given threshold limit is reached, with further reduction of the brightness below this level effected by pulsation of the supplied current at a clock frequency which is above 60 Hz. An Independent claim for a control circuit for a light-emitting diode is also included.

Description

Die vorliegende Erfindung betrifft ein Verfahren zur Ansteuerung von Leuchtdioden (LED's) nach dem Oberbegriff von Patentanspruch 1 sowie eine Schaltungsanordnung zur Durchführung dieses Verfahrens nach dem Oberbegriff von Patentanspruch 4. LED's werden häufig für Anzeigevorrichtungen, wie Displays oder dergleichen, eingesetzt. Eine solche, mit LED's bestückte Anzeigevorrichtung sollte eine möglichst homogene und gleichmäßige Helligkeit aufweisen, um die anzuzeigende Information für einen Betrachter gut lesbar zu machen. Hierbei geht man davon aus, daß das menschliche Auge Helligkeits- bzw. Intensitätsunterschiede erst dann wahrnimmt, wenn die zu vergleichenden Intensitäten oder Lichtstärken (gemessen in candelar [cd]) um mehr als 100% differieren, d. h. wenn das Verhältnis der Intensitäten größer als 1 : 2 ist.The present invention relates to a method for controlling light-emitting diodes (LEDs) according to the preamble of claim 1 and a circuit arrangement for performing this method according to the preamble of claim 4. LEDs are often used for display devices, such as displays or the like, used. Such a display device equipped with LEDs should be one if possible have homogeneous and uniform brightness in order to display the information for to make a viewer easy to read. Here it is assumed that the human eye only perceives differences in brightness or intensity when the intensities or light intensities to be compared (measured in candelar [cd]) differ more than 100%, d. H. if the ratio of intensities is greater than 1: 2.

Aus diesem Grunde werden die auf Anzeigevorrichtungen eingesetzten LED's in der Regel als selektierte Ware in bestimmten, sogenannten Helligkeitsklassen angeboten bzw. bezogen. Diese Helligkeitsklassen sind dadurch definiert, daß der maximale Intensitätsunterschied der LED's in einer solchen Klasse bei einem festgelegten Flußstrom, beispielsweise einem konstanten Gleichstrom I = 20 mA, höchstens 2 : 1 beträgt. Die Bestückung einer Anzeigefläche mit LED's aus einer Helligkeitsklasse führt also zu dem gewünschten Ergebnis, bei einem festgelegten Flußstrom eine homogene Helligkeitsverteilung auf der Anzeigevorrichtung zu erzielen.For this reason, the LEDs used on display devices in the Usually offered as a selected product in certain so-called brightness classes or related. These brightness classes are defined in that the maximum Difference in intensity of the LEDs in such a class at a fixed Flux current, for example a constant direct current I = 20 mA, at most 2: 1 is. Equipping a display area with LEDs from a brightness class thus leads to the desired result, at a fixed flow current to achieve homogeneous brightness distribution on the display device.

Ein Nachteil dieses Selektionsverfahrens tritt dann auf, wenn die Helligkeit der Anzeigevorrichtung den Umgebungsbedingungen angepaßt werden muß. Beispielsweise muß eine außenseitig installierte Anzeigevorrichtung, wie zum Beispiel ein DFI- Anzeiger für Fahrgastinformationen, bei direkter Sonneneinstrahlung auf ihre größt­ mögliche Helligkeit eingestellt werden, um erkennbar und ablesbar zu bleiben. Bei Dunkelheit hingegen muß die Helligkeit der Anzeigevorrichtung verringert werden, da die LED's ansonsten derart überstrahlen, daß die dargestellte Information nicht mehr für den Betrachter erkennbar ist.A disadvantage of this selection process occurs when the brightness of the Display device must be adapted to the ambient conditions. For example a display device installed on the outside, such as a DFI Indicator for passenger information, in direct sunlight on their largest possible brightness can be set to remain recognizable and legible. At Darkness, on the other hand, must reduce the brightness of the display device because otherwise the LEDs shine in such a way that the information displayed no longer is recognizable to the viewer.

Die Anpassung der Helligkeit der LED's wird herkömmlicherweise über eine Änderung des Flußstromes durch die LED's vorgenommen. Die Helligkeit der LED's wird dabei über eine vom jeweiligen Halbleitermaterial abhängende Beziehung der emittierten Intensität vom Flußstrom bestimmt. Ein typischer Arbeitsbereich einer Anzeige­ vorrichtung liegt beispielsweise zwischen 1 mA (geringste Helligkeit) und 15 mA (höchste Helligkeit). Heutige Hochleistungsleuchtdioden sind dermaßen intensitätsstark, daß sie bei einer Ansteuerung mit dem genannten Flußstrom auch unter Extrem­ bedingungen, wie direkter Sonneneinstrahlung, eine gut lesbare Informationsanzeige gewährleisten.The adjustment of the brightness of the LED's is traditionally done via a change of the flow current through the LED's. The brightness of the LEDs is thereby via a relationship of the emitted that depends on the respective semiconductor material Intensity determined by the river current. A typical work area of an ad  device is, for example, between 1 mA (lowest brightness) and 15 mA (highest brightness). Today's high-performance LEDs are so intense, that when driven with the flow current mentioned, even under extreme conditions conditions, such as direct sunlight, an easily readable information display guarantee.

Allerdings ist das obige Selektionsverfahren nur bei einem diskreten Flußstrom bzw. in einem bestimmten eingeschränkten Bereich des Flußstromes gültig. Dies hat zur Folge, daß die Intensitäten der LED's bei einer Ansteuerung der LED's mit geringeren Flußströmen zum Zwecke einer Helligkeitsreduzierung je nach Halbleitermaterial auseinander driften. Dies bedeutet, daß der bei dem festgelegten Fließstrom maximale Intensitätsunterschied zwischen den einzelnen LED's innerhalb einer Helligkeitsklasse bei geringeren Flußströmen den Wert von 2 : 1 übersteigt. Dieser bei geringeren Flußströmen auftretende Intensitätsunterschied ist wiederum vom menschlichen Auge erkennbar und die auf der Anzeigevorrichtung dargestellte Information wird mit abnehmender Helligkeit zunehmend fleckiger und schwerer lesbar.However, the above selection process is only for a discrete flow current or in a certain restricted area of the river current. As a consequence, that the intensities of the LEDs when driving the LEDs with lower Flux currents for the purpose of reducing the brightness depending on the semiconductor material Drifting apart. This means that the maximum at the specified flow rate Difference in intensity between the individual LEDs within a brightness class at lower flow currents the value exceeds 2: 1. This at lower The difference in intensity of flux currents is again from the human eye recognizable and the information displayed on the display device becomes with decreasing brightness increasingly blotchy and more difficult to read.

Würde man das Intensitätsverhalten der LED's andererseits über weitere Bereiche des Flußstromes berücksichtigen wollen, so würde dies zu einer Unmenge von Helligkeits­ klassen führen. Diese Lösung ist sowohl aus herstellungstechnischen als auch aus wirtschaftlichen Gründen nicht anzustreben.Would the intensity behavior of the LED's on the other hand be spread over other areas of the Want to take into account the flow current, this would result in an enormous amount of brightness leading classes. This solution is both from manufacturing technology as well not to strive for economic reasons.

Weiterhin ist ein Verfahren bekannt, bei dem die Helligkeit der LED's ausschließlich über eine Modulation der Pulsweite der AN/AUS-Ansteuerung der LED's eingestellt wird. Dieses Verfahren hat den Nachteil, daß sehr hohe Ströme, die dem Maximalstrom der LED's entsprechen können, geschaltet werden.Furthermore, a method is known in which the brightness of the LEDs is exclusively via a modulation of the pulse width of the ON / OFF control of the LEDs becomes. This method has the disadvantage that very high currents, the maximum current of the LEDs can be switched.

Ausgehend von diesem Stand der Technik ist es eine Aufgabe der Erfindung ein Verfahren zur Ansteuerung von Leuchtdioden bereitzustellen, das die oben beim Stand der Technik beschriebenen Nachteile vermeidet und insbesondere über einen weiten Helligkeitsbereich eine homogene, gleichmäßige Helligkeitsverteilung der Leuchtdioden gewährleistet.Starting from this prior art, it is an object of the invention To provide a method for controlling light emitting diodes, which the above in the state avoids the disadvantages described in the art and in particular over a wide range Brightness area a homogeneous, uniform brightness distribution of the LEDs guaranteed.

Diese Aufgabe wird durch ein Verfahren mit den Merkmalen des Patentanspruches 1 gelöst.This object is achieved by a method having the features of patent claim 1 solved.

Dadurch daß der Betrag des Flußstromes durch die Leuchtdioden auch zur Reduzierung der Helligkeit nicht unter einen vorbestimmten unteren Grenzwert abfällt, bei dem zweckmäßigerweise der maximale Intensitätsunterschied der Leuchtdioden noch inner­ halb einer Helligkeitsklasse liegt, wird eine für das menschliche Auge homogene Helligkeitsverteilung der Anzeige gewährleistet. Um aber dennoch eine weitere Reduzierung der Helligkeit der Anzeige zu erreichen, wird der Flußstrom getaktet, wobei der Betrag des Flußstromes gleich oder größer als der untere Grenzwert ist.Because the amount of flux through the LEDs also for reduction the brightness does not fall below a predetermined lower limit at which Expediently, the maximum difference in intensity of the LEDs is still inside  is half a brightness class, it becomes homogeneous for the human eye Guaranteed brightness distribution of the display. But still another To reduce the brightness of the display, the flux current is clocked, the magnitude of the flow current being equal to or greater than the lower limit.

Die resultierende Helligkeit der Anzeige wird in diesem Arbeitsbereich somit durch das Verhältnis zwischen den Zeitdauern von eingeschaltetem und ausgeschaltetem Fluß­ strom bestimmt. Mittels dieses Verfahrens ist es möglich, kleinste Helligkeiten bei einer absolut homogenen und gleichmäßig hellen Anzeige zu erzielen.The resulting brightness of the display is thus in this work area by the Relationship between the times of on and off flow current determined. Using this method, it is possible to use the smallest brightness at a to achieve absolutely homogeneous and evenly bright display.

Vorzugsweise ist die Taktfrequenz des Flußstromes in diesem Arbeitsbereich größer als 60 Hz, so daß die tatsächlichen AN/AUS-Phasen der Leuchtdioden vom menschlichen Auge nicht wahrnehmbar sind und vom Betrachter nur als effektive Verminderung der Helligkeit erkannt werden.The clock frequency of the flow current is preferably greater than in this working range 60 Hz, so that the actual ON / OFF phases of the LEDs from the human Are imperceptible to the eye and only effective reduction of the viewer Brightness can be detected.

Weiter ist es eine Aufgabe der vorliegenden Erfindung, eine Schaltungsanordnung zur Ansteuerung von Leuchtdioden bereitzustellen, die zur Durchführung des erfindungs­ gemäßen Verfahrens geeignet ist.It is a further object of the present invention to provide a circuit arrangement for Provide control of light emitting diodes to implement the Invention according to the method is suitable.

Diese Aufgabe wird durch ein Verfahren mit den Merkmalen des Patentanspruches 4 gelöst.This object is achieved by a method with the features of claim 4 solved.

Die Schaltungsanordnung weist neben einer Regeleinrichtung zum Regeln des Betrages des Flußstromes durch die Leuchtdioden noch ein Schaltmittel zum Takten des Flußstromes auf, welches vorzugsweise mit einer Taktfrequenz größer als 100 Hz ansteuerbar ist.In addition to a control device for regulating the amount, the circuit arrangement has of the flow current through the light emitting diodes is a switching means for clocking the Flux current on, which preferably with a clock frequency greater than 100 Hz is controllable.

Weitere Ausgestaltungen und Weiterbildungen der Erfindung sind Gegenstand weiterer Unteransprüche.Further refinements and developments of the invention are the subject of further Subclaims.

Die vorliegende Erfindung wird im folgenden anhand eines bevorzugten Ausführungs­ beispieles mit Bezugnahme auf die beiliegende Zeichnung näher beschrieben. Darin zeigt die einzige Fig. 1 ein Blockschaltbild der Schaltungsanordnung gemäß der vorliegenden Erfindung.The present invention is described below with reference to a preferred embodiment example with reference to the accompanying drawings. It shows the single FIG. 1 is a block diagram of the circuit arrangement according to the present invention.

Fig. 1 zeigt schematisch eine Schaltungsanordnung zur Ansteuerung von Leuchtdioden 1. Die einzelnen Leuchtdioden 1 einer Anzeigevorrichtung werden üblicherweise separat angesteuert, d. h. sie sind in Fig. 1 nicht parallel zueinander geschaltet. Die Schaltungsanordnung 9 ist beispielsweise in Form eines IC's oder ASIC's realisierbar. Fig. 1 shows schematically a circuit arrangement for controlling light-emitting diodes 1. The individual light-emitting diodes 1 of a display device are usually controlled separately, ie they are not connected in parallel to one another in FIG. 1. The circuit arrangement 9 can be implemented, for example, in the form of an IC or ASIC.

Mit einer derartigen Schaltungsanordnung 9 können beispielsweise 32 LED's angesteuert werden, wobei eine Anzeigevorrichtung üblicherweise eine Vielzahl solcher Schaltungsanordnungen 9 aufweist.With such a circuit arrangement 9 , for example, 32 LEDs can be controlled, a display device usually having a large number of such circuit arrangements 9 .

Die Schaltungsanordnung 9 steuert den Flußstrom I durch die LED 1. Ob eine LED 1 der Anzeigevorrichtung für die gewünschte Anzeigeinformation überhaupt Licht emittieren soll oder nicht, wird über ein erstes Schaltmittel 2 gesteuert. Die Ansteuerung des ersten Schaltmittels 2 erfolgt mittels eines Registers 3, welches die Informationen über die gewünschte Anzeige enthält. Auf diese Weise können mit einer Anzeigevorrichtung verschiedene Anzeigeinformationen erzeugt bzw. angezeigt werden, wobei die Anzeige prinzipiell auch in Form einer bewegten Anzeige, wie beispielsweise einer Laufschrift, erfolgen kann.The circuit arrangement 9 controls the flow current I through the LED 1 . A first switching means 2 controls whether an LED 1 of the display device should emit light at all for the desired display information. The first switching means 2 is controlled by means of a register 3 which contains the information about the desired display. In this way, different display information can be generated or displayed with a display device, wherein the display can in principle also take the form of a moving display, such as a moving text.

Zur Regelung des Betrages des Flußstromes I, d. h. des konstanten Gleichstromes, durch die LED 1 ist eine Regeleinrichtung 4 vorgesehen, die im bevorzugten Ausführungs­ beispiel von Fig. 1 als regelbare Stromquelle ausgebildet ist, welche mit der LED 1 in Reihe geschaltet ist. Grundsätzlich sind auch andere Arten von Regeleinrichtungen 4 einsetzbar, wie beispielsweise regelbare Widerstände. Die Regeleinrichtung 4 muß dabei in der Lage sein, einen konstanten Flußstrom durch die LED 1 zu erzeugen, was jedoch im Falle der Verwendung eines regelbaren Widerstandes als Regeleinrichtung 4 aufgrund des unterschiedlichen Spannungsabfalles am Widerstand in Abhängigkeit von der Art der LED 1 nicht problemlos sichergestellt ist.To regulate the amount of the flow current I, ie the constant direct current, through the LED 1 , a control device 4 is provided, which in the preferred embodiment of FIG. 1 is designed as a controllable current source which is connected in series with the LED 1 . In principle, other types of control devices 4 can also be used, such as controllable resistors. The control device 4 must be able to generate a constant flux through the LED 1 , but this is not easily ensured when using a controllable resistor as a control device 4 due to the different voltage drop across the resistor depending on the type of LED 1 .

Die regelbare Stromquelle 4 wird von einem D/A-Wandler 5 angesteuert. Die Ansteuerung der regelbaren Stromquelle 4 durch den D/A-Wandler 5 erfolgt dabei gemäß einem digitalen Steuersignal BRT1, welches dem D/A-Wandler zugeführt wird.The controllable current source 4 is controlled by a D / A converter 5 . The controllable current source 4 is controlled by the D / A converter 5 in accordance with a digital control signal BRT1, which is fed to the D / A converter.

Der Betrag des von der regelbaren Stromquelle 4 erzeugten Flußstromes I bestimmt in Abhängigkeit vom jeweiligen Halbleitermaterial der LED 1 die Intensität der von der LED 1 emittierten Strahlung, d. h. die Helligkeit der LED 1. Im Arbeitsbereich A höherer Intensitäten wird die Helligkeit der LED 1 und damit die Helligkeit der Anzeigeinformation einer Anzeigevorrichtung durch Verringerung des Flußstromes I durch die LED 1 mittels der regelbaren Stromquelle 4 reduziert. In diesem oberen Arbeitsbereich A beträgt der maximale Intensitätsunterschied zwischen den eingesetzten Leuchtdioden 1 höchstens 2 : 1, d. h. die Strahlungsemissionen der LED's 1 sind innerhalb einer Helligkeitsklasse. Wie in der Beschreibungseinleitung erläutert, wird hierdurch eine homogene und gleichmäßige Helligkeitsverteilung der Anzeige­ information erzielt, die für einen Betrachter gut lesbar ist. The amount of the flow stream I generated by the variable current source 4 is determined depending on the particular semiconductor material of the LED 1, the intensity of the radiation emitted by the LED 1, that is, the brightness of the LED. 1 In the work area A of higher intensities, the brightness of the LED 1 and thus the brightness of the display information of a display device is reduced by reducing the flow current I through the LED 1 by means of the controllable current source 4 . In this upper working area A, the maximum difference in intensity between the light-emitting diodes 1 used is at most 2: 1, ie the radiation emissions from the LEDs 1 are within a brightness class. As explained in the introduction to the description, this achieves a homogeneous and uniform distribution of brightness of the display information, which is easy for a viewer to read.

Der Flußstrom I wird allerdings nur bis zu einem unteren Grenzwert reduziert, bei dem die Strahlungsemissionen der LED's noch innerhalb einer Helligkeitsklasse liegen. Um die Helligkeit der Anzeigeinformation dennoch weiter zu reduzieren und gleichzeitig eine homogene und gleichmäßige Helligkeitsverteilung der Anzeigeinformation auch im unteren Arbeitsbereich B sicherzustellen, erfolgt die Ansteuerung der LED's 1 im Arbeitsbereich B niedrigerer LED-Intensitäten wie nachfolgend beschrieben.However, the flux current I is only reduced to a lower limit at which the radiation emissions from the LEDs are still within a brightness class. In order to further reduce the brightness of the display information and at the same time to ensure a homogeneous and uniform brightness distribution of the display information even in the lower working area B, the LEDs 1 in the working area B of lower LED intensities are controlled as described below.

Im Arbeitsbereich B wird die regelbare Stromquelle 4 derart angesteuert, daß sie einen konstanten Flußstrom I liefert, dessen Betrag mit dem vorbestimmten unteren Grenzwert übereinstimmt. Gleichzeitig wird der Flußstrom I mittels eines zweiten Schaltmittels 8 getaktet, welches in Reihe mit der LED 1 und der regelbaren Stromquelle 4 geschaltet ist.In the working area B, the controllable current source 4 is activated in such a way that it supplies a constant flux current I, the amount of which corresponds to the predetermined lower limit value. At the same time, the flow current I is clocked by means of a second switching means 8 , which is connected in series with the LED 1 and the controllable current source 4 .

Das Takten des Flußstromes I erfolgt derart, daß das Schaltmittel 8 periodisch für eine erste Zeitdauer t1 geschlossen und anschließend für eine zweite Zeitdauer t2 geöffnet ist. Im oberen Arbeitsbereich A größerer Helligkeiten wird das zweite Schaltmittel 8 vorzugsweise ständig geschlossen angesteuert, d. h. t2 = 0. Die Frequenz f des Taktens des Flußstromes I im Arbeitsbereich B beträgt f = 1/T = 1/(t1 + t2) und ist bevorzugt größer als 60 Hz, besonders bevorzugt größer als 100 Hz.The current I is clocked in such a way that the switching means 8 is periodically closed for a first period t1 and then open for a second period t2. In the upper working area A of higher brightnesses, the second switching means 8 is preferably controlled continuously closed, ie t2 = 0. The frequency f of the clocking of the flux current I in the working area B is f = 1 / T = 1 / (t1 + t2) and is preferably larger than 60 Hz, particularly preferably greater than 100 Hz.

Eine derartige Ansteuerung der LED's 1 ergibt auch im Arbeitsbereich B niedrigerer Intensitäten eine homogene und gleichmäßige Helligkeitsverteilung der Anzeige auf der Anzeigevorrichtung. Dies deshalb, da der Betrag des Flußstromes I in einem Bereich gehalten wird, in dem die eingesetzten LED's ihre Strahlung innerhalb einer Helligkeitsklasse emittieren. Die resultierende, verringerte Helligkeit der Anzeige wird über das Verhältnis von t1/t2 bestimmt, da das menschliche Auge bei einer Frequenz oberhalb 60 Hz die AN/AUS-Phasen der LED's 1 nicht mehr auflösen kann und nur eine Schwächung der LED-Intensitäten wahrnimmt.Controlling the LEDs 1 in this way also results in a homogeneous and uniform brightness distribution of the display on the display device in the work area B of lower intensities. This is because the amount of the flux current I is kept in a range in which the LEDs used emit their radiation within a brightness class. The resulting reduced brightness of the display is determined via the ratio of t1 / t2, since the human eye at a frequency above 60 Hz can no longer resolve the ON / OFF phases of the LEDs 1 and only perceives a weakening of the LED intensities.

Um das zweite Schaltmittel 8 und die regelbare Stromquelle 4 wie oben beschrieben in beiden Arbeitsbereichen A und B ansteuern zu können, wird der Schaltungsanordnung 9 ein Steuersignal BRT zugeführt, welches Informationen über den einzustellenden Betrag des Flußstromes I und über die Taktung des Flußstromes I enthält. Dieses Steuersignal BRT wird von einer zentralen Steuerung (nicht dargestellt) der Anzeigevorrichtung übertragen, welche sämtliche LED's bzw. Schaltungsanordnungen 9 der Anzeige­ vorrichtung ansteuert. Die zentrale Steuerung berücksichtigt dabei insbesondere auch die erforderliche Helligkeit der Anzeige in Abhängigkeit von den Umgebungsbedingungen sowie den unteren Grenzwert des Flußstromes I zur Einhaltung der Helligkeitsklasse. Beispielsweise ist die zentrale Steuerung mit einem oder mehreren Helligkeitssensoren verbunden, die die Lichtverhältnisse in der Umgebung der Anzeigevorrichtung erfassen. Der untere Grenzwert des Flußstromes wird im allgemeinen experimentell bestimmt.In order to be able to control the second switching means 8 and the controllable current source 4 in both work areas A and B as described above, the circuit arrangement 9 is supplied with a control signal BRT which contains information about the amount of the flow current I to be set and about the timing of the flow current I. This control signal BRT is transmitted by a central controller (not shown) of the display device, which controls all LEDs or circuit arrangements 9 of the display device. The central controller takes into account in particular the required brightness of the display as a function of the ambient conditions and the lower limit value of the flux current I in order to maintain the brightness class. For example, the central controller is connected to one or more brightness sensors which detect the lighting conditions in the vicinity of the display device. The lower limit of the flux current is generally determined experimentally.

Das Steuersignal BRT wird einem Register 6, insbesondere einem seriellen Empfangsregister, zugeführt. Dieses Register 6 spaltet das Steuersignal BRT bzw. die darin enthaltenen Informationen in ein erstes Steuersignal BRT1 von in Bit Länge und ein zweites Steuersignal BRT2 von n Bit Länge auf. Das erste Steuersignal BRT1 enthält die Informationen über den einzustellenden Betrag des Flußstromes I und wird dem D/A-Wandler 5 zugeführt, der seinerseits die regelbare Stromquelle 4 entsprechend dem ersten Steuersignal BRT1 ansteuert. Das zweite Steuersignal BRT2 enthält die Informationen über das Takten bzw. die Taktfrequenz des Flußstromes I und wird einer Pulsweitenmodulations(PWM)-Steuereinrichtung 7 zugeführt, welche ihrerseits das zweite Schaltmittel 8 entsprechend dem zweiten Steuersignal BRT2 ansteuert.The control signal BRT is fed to a register 6 , in particular a serial receive register. This register 6 splits the control signal BRT or the information contained therein into a first control signal BRT1 of bit length and a second control signal BRT2 of n bit length. The first control signal BRT1 contains the information about the amount of the flow current I to be set and is fed to the D / A converter 5 , which in turn controls the controllable current source 4 in accordance with the first control signal BRT1. The second control signal BRT2 contains the information about the clocking or the clock frequency of the flux current I and is fed to a pulse width modulation (PWM) control device 7 , which in turn controls the second switching means 8 in accordance with the second control signal BRT2.

Zur Pulsweitenmodulation (PWM) benötigt die PWM-Steuereinrichtung 7 zusätzlich zu dem Steuersignal BRT2 ein Taktsignal Clk, welches der PWM-Steuereinrichtung 7 von der zentralen Steuerung der Anzeigevorrichtung zugeführt wird, in an sich bekannter Weise als Referenztakt. Die PWM kann beispielsweise auf zwei verschiedene Arten erfolgen. Zum einen ist es möglich, die Frequenz f, d. h. also t1 + t2 festzuhalten und die Pulsweite t1 für den eingeschalteten Flußstrom und die Pulsweite t2 für den ausgeschalteten Flußstrom zu variieren, um über das Verhältnis von t1/t2 die Helligkeit der LED 1 zu verändern. Ebenso kann zu diesem Zweck auch die Frequenz f bei fester Pulsweite t1 für den eingeschalteten Flußstrom I, d. h. also nur die Pulsweite t2 variiert werden. Um im oberen Arbeitsbereich A die Helligkeit der LED 1 nur über den Betrag des Flußstromes I einstellen zu können, sollte die PWM-Steuereinrichtung vorzugsweise das zweite Schaltmittel 8 auch derart ansteuern können, daß es ständig geschlossen ist.For pulse width modulation (PWM), the PWM control device 7 requires, in addition to the control signal BRT2, a clock signal Clk, which is fed to the PWM control device 7 from the central control of the display device, as a reference clock in a manner known per se. For example, the PWM can be done in two different ways. On the one hand, it is possible to record the frequency f, ie t1 + t2, and to vary the pulse width t1 for the switched-on flow current and the pulse width t2 for the switched-off flow current in order to change the brightness of the LED 1 via the ratio of t1 / t2 . Likewise, the frequency f with a fixed pulse width t1 for the switched-on flux current I, that is to say only the pulse width t2, can also be varied for this purpose. In order to be able to adjust the brightness of the LED 1 in the upper working area A only by the amount of the flux current I, the PWM control device should preferably also be able to control the second switching means 8 in such a way that it is constantly closed.

In diesem Zusammenhang ist es auch von Vorteil, aus schaltungstechnischen Gründen in jedem IC oder ASIC nur ein serielles Empfangsregister 6 vorzusehen, welches das empfangene Steuersignale BRT in die ersten und zweiten Steuersignale BRT1 und BRT2 der mehreren Schaltungsanordnungen 9 in dem IC oder ASIC aufspaltet, so daß nur ein Eingang des IC oder ASIC für den Empfang des Steuersignales BRT belegt werden muß.In this context, it is also advantageous for circuitry reasons to provide only one serial receive register 6 in each IC or ASIC, which splits the received control signals BRT into the first and second control signals BRT1 and BRT2 of the plurality of circuit arrangements 9 in the IC or ASIC, so that only one input of the IC or ASIC has to be assigned for the reception of the control signal BRT.

Claims (7)

1. Verfahren zur Ansteuerung von Leuchtdioden, bei dem der Flußstrom durch die Leuchtdioden zur Reduzierung der Helligkeit einer Anzeigevorrichtung verringert wird, dadurch gekennzeichnet, daß der Betrag des Flußstromes (I) durch die Leuchtdioden (1) nur bis zu einem vorbestimmten unteren Grenzwert verringert wird, und daß zur weiteren Reduzierung der Helligkeit der Flußstrom (I) getaktet wird, wobei der Betrag des Flußstromes gleich oder größer als der untere Grenzwert ist.1. A method for controlling light-emitting diodes, in which the flux current through the light-emitting diodes is reduced to reduce the brightness of a display device, characterized in that the amount of the flux current (I) through the light-emitting diodes ( 1 ) is only reduced to a predetermined lower limit value , and that the flux current (I) is clocked to further reduce the brightness, the magnitude of the flux current being equal to or greater than the lower limit value. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Taktfrequenz (f) des Flußstromes (I) größer als 60 Hz ist.2. The method according to claim 1, characterized, that the clock frequency (f) of the flux current (I) is greater than 60 Hz. 3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Takten des Flußstromes (I) pulsweitenmoduliert erfolgt.3. The method according to claim 1 or 2, characterized, that the clocking of the flow current (I) is pulse width modulated. 4. Schaltungsanordnung zur Ansteuerung von Leuchtdioden, mit einer Regel­ einrichtung (4) zum Regeln des Betrages des Flußstromes (I) durch die Leucht­ dioden (1) zur Regelung der Helligkeit einer Anzeigevorrichtung, gekennzeichnet durch ein Schaltmittel (8) zum Takten des Flußstromes (I).4. Circuit arrangement for controlling light-emitting diodes, with a control device ( 4 ) for regulating the amount of the flux current (I) through the light-emitting diodes ( 1 ) for regulating the brightness of a display device, characterized by a switching means ( 8 ) for clocking the flux current ( I). 5, Schaltungsanordnung nach Anspruch 4, dadurch gekennzeichnet, daß das Schaltmittel (8) mit einer Taktfrequenz (f) größer als 60 Hz ansteuerbar ist.5, circuit arrangement according to claim 4, characterized in that the switching means ( 8 ) with a clock frequency (f) greater than 60 Hz can be controlled. 6. Schaltungsanordnung nach Anspruch 4 oder 5, dadurch gekennzeichnet, daß zur Ansteuerung des Schaltmittels (8) eine Pulsweitenmodulations-Steuer­ einrichtung (7) vorgesehen ist. 6. Circuit arrangement according to claim 4 or 5, characterized in that a pulse width modulation control device ( 7 ) is provided for controlling the switching means ( 8 ). 7. Schaltungsanordnung nach einem der Ansprüche 4 bis 6, dadurch gekennzeichnet, daß die Regeleinrichtung (4) zum Regeln des Betrages des Flußstromes (I) eine regelbare Stromquelle ist.7. Circuit arrangement according to one of claims 4 to 6, characterized in that the control device ( 4 ) for controlling the amount of the flux current (I) is a controllable current source.
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