Koninklijke Philips Corporation N.v.

Oledworks Gmbh

Lumileds LLC

Philips Lighting Holding B.v.

Christian Kalkschmidt

Dirk Hente

Joseph Hendrik Anna Maria Jacobs

Céline Catherine Sarah Nicole

Etienne Nicolaas Kathalijntje Paulus Marie Eberson

Udo Karbowski

Jan-Rene Luetz

Alexander Rudolf Albrecht Isphording

Harold Josef Gunther Radermacher

A lighting unit includes a power supply that provides a maximum voltage and multiple LED lighting circuits. Each of the LED lighting circuits includes an LED string, multiple switches, a switching sequencer and a switch controller. The LED string includes multiple series-connected emitters having a total forward voltage that exceeds the maximum voltage of the power supply. Each of the switches is coupled in parallel with a respective LED of the LED string. The switching sequencer provides a sequence of switching patterns such that a total forward voltage of simultaneously active LEDs in each switching pattern does not exceed the maximum voltage of the power supply. The switch controller actuates switches according to each of the switching patterns in the sequence. The LED string of each of the plurality of LED lighting circuits is arranged in a two-dimensional array.

Operating an LED matrix where power supply voltage is less than total forward voltage of LEDs

An LED driver implements a first constant-current drive scheme for a first range of sensed voltages up to a threshold voltage. After this, a second drive scheme is implemented with a current lower than the constant current of the first drive scheme.

LED driver, lighting system and driving method with prolonged lifetime of luminous output

An electrical circuit is described for detection of an electrical hazard condition of a load, in particular of an OLED lighting element comprising driving terminals A, C. An electrical hazard condition, such as an overvoltage or short circuit is to be detected between terminalsof the circuit. A disabling elementis connected to one of the terminalsto disable the load. A monitoring circuit is connected to monitor a voltage V or current magnitude at at least one of the terminals. The monitoring circuit comprises a maximum or minimum value detectorto deliver a maximum or minimum value Vof the voltage or current magnitude over time. The monitoring circuit is disposed to monitor the maximum or minimum value Vto detect the electrical hazard condition. A monitoring circuit is connected to activate the disabling elementif an electrical hazard condition is detected. The electrical circuit, a lighting arrangement including an LED or OLED lighting element and the electrical circuit, and a detection method allows to operate a load with different types of power supply, in particular also by PWM.

Detection of a hazard condition of a load

A short detection circuit is provided for detecting a short circuit condition of an LED. A voltage threshold is set which is dependent on the LED operating current, such that there are at least two different voltage thresholds at two different LED operating currents. This means false detections can be reduced and the LED current operating range can be increased over which the short detection functions.

Short detection circuit for an LED driver and short detection method

The invention relates to a current determination apparatus for determining an operational driving current for driving a light source of a group of light sources. A same color shift function defining a light color shift depending on a driving current can be provided for all light sources of the group. An operational driving current is determined based on the color shift function such that the light color () of the light source of the group of light sources is shifted from a nominal color, which may be specific for each light source, to a light color () within a target color window (). Since for the different light sources the same color shift function can be used, a determination of individual operational driving currents such that the light sources of the group emit light having substantially the same color can be simplified.

Current determination apparatus

The present invention relates to a method for adjusting a color point () of light emitted () from an organic light emitting diode OLED () by using current () with a modulated waveform for driving the OLED (), wherein the waveform is characterized by at least three different parameters, and wherein the color point () is located in a color space, the method comprising: &#x2014;defining a color point target (); &#x2014;adjusting simultaneously the at least three parameters to tune the waveform such that the resulting light output of the OLED () is lying within a predefined area around the color point target and for which the brightness of the OLED () remains at a predefined level; and &#x2014;employing the tuned waveform to provide the current () with the modulated waveform to the OLED ().

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Aachen, Germany

Christian Kalkschmidt