WO2017021272A1 - Method for identifying a short-circuit of an organic light-emitting diode of a light-emitting diode string, and light-emitting diode arrangement - Google Patents

Abstract

Various embodiments provide a method for identifying a short-circuit of an organic light-emitting diode (12, 14, 16, 18) of a light-emitting diode string (20). In said method, an alternating voltage is applied to the light-emitting diode string (20), the amplitude of said voltage being at least partially lower than the sum of the threshold voltages of all organic light-emitting diodes (12, 14, 16, 18) of the light-emitting diode string (20). At least one operating value of an electrical operating variable of the light-emitting diode string (20) is detected. The presence of a short-circuit is identified if the detected operating value lies outside a pre-defined threshold value.

Description

 METHOD FOR DETECTING A SHORT-CIRCUIT OF AN ORGANIC LUMINAIRE DIODE OF AN LUMINAIRE DIODE STRAND AND LUMINOUS DIODE ASSEMBLY DESCRIPTION

The invention relates to a method for detecting a

Short circuit of an organic light emitting diode of a

Light-emitting diode string and a light-emitting diode array.

A conventional light-emitting diode arrangement has at least one light-emitting diode string with one, two or more

organic light emitting diodes (OLED), which are electrically connected in series, and a control device and a voltage source for operating the organic light emitting diodes on.

Despite elaborate quality controls of organic

Light-emitting diodes, it can not be completely ruled out that the organic light emitting diodes in the application spontaneously fail. For example, in the case of an OLED, a typical fault pattern for a spontaneous failure is a short circuit

 (English: Short) between the electrodes of the corresponding light emitting diode element. Such a short circuit is usually small area. Therefore, much of the total current is concentrated in the small area short-cut point. Consequently, the current density is clearly excessive in the short-circuit point, with the result that this short-circuit point can strongly heat up depending on its areal extent. This can cause melting of the electrodes, dark spots in the

Illuminating the OLED, lead to a completely dark OLED and / or to a hot spot on the OLED.

To a potential danger from overheating

(Burn hazard, fire, bursting, etc.) to prevent such a short circuit should be detected by a driver electronics of the light emitting diode array and a suitable protection reaction initiated (shutdown of the OLED or the LED array, redirecting the supply current to the shorted OLED, output of a warning signal, etc.). For example, in the automotive sector is required that defective OLEDs, for example in taillights, electronically detected and reported at least on-board system.

A common interconnection of light-emitting diode elements,

For example, OLEDs, a light emitting diode array in the application is for technical reasons and for cost reasons, the series connection of the organic light-emitting diodes.

For example, a plurality of organic light-emitting diodes in the form of light emitting diode elements and / or light emitting diode segments of a light emitting diode array formed on a substrate and electrically connected in series and / or it can be formed on a plurality of organic light emitting diodes corresponding to a plurality of substrates and electrically connected in series. In many applications,

For example, in the automotive sector or in the field of

General lighting, therefore, become more organic

Light-emitting diodes electrically connected in series. If individual defective organic light-emitting diodes are to be recognized in a series connection with simple methods, this represents a particular challenge.

From US 2011 204 792 AI, WO 2010 060 458 AI and

WO 2012 004 720 A2 discloses methods for determining

 Short circuits of individual OLEDs are known in which an overvoltage or undervoltage at the corresponding OLED is used as a criterion for a defect. The upper or

Under-voltages are detected during normal operation of the OLEDs. On the detection of the short circuit is reacted with a redirecting of the driving current (Bypaseing) and / or with an error signal generation.

With a measurement of the forward voltage in accordance with

Conventional methods for determining the short circuit may result in the following problems: a

Short circuit resistance is, for example in an OLED, in a wide range, for example between 10 ohms and several kOhms. With one input of the light-emitting diode string and one output of the light-emitting diode string, only one total voltage can be detected across all the light-emitting diode elements during nominal operation. The total voltage thus corresponds to the same organic light emitting diodes in the LED strand one

 Quadruple corresponding individual voltages of the organic light emitting diodes. If you set the detection threshold for the

Short circuit in one of the organic light-emitting diodes to a value similar to the sum of the corresponding individual voltages, the measured total voltage in the event of a fault can be very close to or even below the detection threshold, which does not provide sufficient detection reliability in reality. For example, a corresponding short circuit can be higher impedance than the organic shorted OLED. The individual voltage of the corresponding OLED is thus determined mainly by the organic and not by the short circuit. Nevertheless, the current density at the

Short-circuit point increases, which leads to the temperature increase, which is why should respond to the short circuit.

The reduction of the total voltage by a short circuit goes in several organic light emitting diodes in one

Luminous diode strand below percent, especially at long strand lengths, or is partially offset by the voltage drop across the short circuit and is so

tolerance vulnerable. A total voltage signature of the short circuit is difficult or impossible

recognizable. Thus, the problems arise that in a short circuit, the single voltage on the short-circuited organic

LED does not necessarily significantly decrease due to the voltage drop at the short circuit in nominal operation compared with an organic light emitting diode without short circuit and that in principle can not be detected whether the

 Total voltage normal or due to a short circuit

lower than normal. Therefore, it is known to provide only one organic light emitting diode per driver circuit, so none

Series connection, or on each organic light emitting diode is mounted its own detection electronics or it must be at each OLED connection point voltage measurement lines for

 Driver control electronics are performed, which means an increased wiring costs. These approaches are expensive and expensive. To measure the individual forward voltages, a measuring system must therefore be connected either to each OLED, which requires a large amount of wiring and a high number of

 Requires measuring systems and thus causes high costs, or a single measurement system must be switched through each of the individual OLEDs, for example by means of multiplexing, which, however, also requires a high wiring complexity and complexity for multiplexing and thus causes high costs.

An object of the invention is a method for detecting a short circuit of an organic light emitting diode of a

To provide a light emitting diode string that allows: the short circuit of a single organic light emitting diode of the

LED strand to reliably detect the short circuit of the organic light emitting diode in a series circuit of

identify organic light-emitting diodes in the light-emitting diode strand, the detection of the short circuit with only one input and one output of a control unit and / or minimizing a disturbance influence of aging and / or temperature on the detection of the short circuit. An object of the invention is to provide a light-emitting diode array with a light-emitting diode strand, which makes it possible: to reliably detect a short circuit of a single organic light-emitting diode of the light-emitting diode string, the short circuit of the organic light-emitting diode in a series circuit of

identify organic light emitting diodes in the light emitting diode strand, the detection of the short circuit with only one input and one output of a control unit and / or a Minimization of disturbance influence of aging and / or temperature on the detection of the short circuit.

An object is achieved according to one aspect of the invention by a method for detecting a short circuit of an organic light emitting diode of a light emitting diode strand, in which an alternating voltage is applied to the light emitting diode whose amplitude is at least temporarily smaller than a sum of the threshold voltages of all organic light emitting diodes of the light emitting diode strand; at least one operating value of an electrical operating variable of the light-emitting diode string is detected; and the short circuit is detected as present when the detected operating value is beyond a predetermined one

Threshold is.

The light-emitting diode string has at least one organic light-emitting diode (OLED). The light-emitting diode string can also have one, two or more further organic light-emitting diodes (OLEDs), which are connected to the one organic light-emitting diode

are electrically connected in series. The operating variable may be, for example, an operating current or a phase shift between the applied AC voltage and the Betriebsström. The operating value of the operating variable may be, for example, a current value of the operating current or a phase value of the phase shift. The operating value can be recorded one, two or more times in succession or continuously, so that, for example, a progression of operating values,

For example, a course of the operating current, can be determined.

If one applies to the light-emitting diode string, so the one OLED or the OLED series circuit, the AC voltage whose

Amplitude initially as less than the sum of the

Threshold voltages of the OLED is assumed, the organic light-emitting diodes are always in nichtleitendend state and do not light up. However, because of each of the OLEDs

Electrodes in the non-conductive state a significant

Capacity parallel to the organics, yet flows Operating current, in particular an alternating current through which

Series. If one chooses a suitable operating frequency, then the operating current is significantly dependent on the

AC impedance and thus of the capacity and the Betriebsfreguenz the AC voltage. At an appropriately selected AC operating point has at a

intact OLED, the AC a certain RMS current value, in particular a corresponding amplitude of the operating current, a corresponding maximum current value of the operating current and an associated phase shift to the applied AC voltage. Arises in the OLED

Significant short circuit, so this shows up as the

Capacitance of parallel-connected low-impedance electrical resistance. This causes the maximum current value of the operating current and the amplitude of the operating current to increase while the AC voltage remains the same. This can be detected by a current measurement, in particular a measurement of the maximum current value and / or the amplitude of the operating current. Likewise, the reduced

Phase shift between the operating current and the

AC voltage due to the added impedance of the

Short circuit resistance. This can also be detected by a measurement, for example by measuring the

Time difference of the zero crossing of a course of the

Operating current and a course of the AC voltage.

Even if the amplitude of the AC voltage temporarily greater than the sum of the threshold voltages of the organic

Light-emitting diodes in the light-emitting diode string, the effects described above can still be recognized from the measurements, whereby the detection of the short circuit is still possible even then.

The applied AC voltage can be regular or

irregular, for example, changing or constant. That the recorded operating values beyond the

Threshold may mean that if the

Operating value is chosen so that it without short circuit is less than the threshold, the operating value is greater than the predetermined threshold, or that, if the operating value is selected to be greater than the threshold without a short circuit, the operating value is less than the predetermined threshold.

Depending on the type, number and / or size of the organic light emitting diodes in the light emitting diode string and / or depending on a range of resistance values of the short circuit to be detected, different frequencies and / or maximum amplitudes of the alternating voltage may be ideal to detect the corresponding short circuit. The ideal frequency or ideal maximum amplitude for the desired detection of the short circuit can be determined simply by simulation and / or empirically based on the actually used

 Light-emitting diode strand can be determined. In particular, the frequency or the maximum amplitude are chosen so that the used for the LED string and for

Detecting range of resistance values, the operating value significantly changed.

In a further development, the electrical operating variable is an electric current that flows via the light-emitting diode string, the operating value is a current value of the operating current, the predetermined threshold value is a predetermined one

 Current threshold. This can help the

Accurately detect operating value and / or detect the short circuit. In most cases, the short circuit will be detected as present if the current value is greater than the current value

is predetermined threshold. Alternatively, the

Frequency and / or the maximum amplitude of the AC voltage can be selected such that in the presence of the

Short circuit the current value compared to the error-free case is lower, in which case the threshold must be selected so that the short circuit is detected as present when the current value is smaller than the predetermined threshold. In a further development, the electrical operating variable is a phase shift between the applied

AC voltage and a Betriebsström over the

LED string flows, the operating value is on

Phase value of the phase shift, the predetermined

 Threshold is a given phase threshold. This makes it possible to detect the operating value by means of a current measuring device. In most cases, the short circuit will be detected as present if the phase value is less than the predetermined threshold. Alternatively, the

Frequency and / or the maximum amplitude of the AC voltage are chosen such that in the presence of the

Short circuit the phase value compared to the error-free case is greater, in which case the threshold must be selected so that the short circuit is detected as present when the phase value is greater than the predetermined threshold.

In a further development is the predetermined

Phase threshold in a range between 70 ° and 90 °, for example 80 ° to 90 °, i. that the current leads by 70 ° to 90 ° degrees of the voltage and the phase shift behaves capacitively. This contributes to the fact that

Short circuit can be detected safely. In a refinement, to detect the phase value, zero crossings of a profile of the applied alternating voltage and a profile of the operating current are detected and compared with one another. This can help to provide the phase value in a simple and / or very precise manner

to capture.

In a further development, a rising edge of a profile of the operating current is used to detect the phase value. This can help to provide the phase value in a simple and / or very precise manner

to capture. In particular, when the amplitude of the

AC voltage is at least temporarily greater than the sum the threshold voltages of the organic light emitting diodes of the light emitting diode strand.

In a development, a fast Fourier transformation is performed to detect the phase value. This can help to capture the phase value in a simple manner and / or with particular precision.

In a further development, the current value of

Operating current and the phase value of the phase shift detected and the presence of the short circuit is detected when the detected current value is greater than or equal to the predetermined current threshold value and / or if the detected phase value is smaller than the predetermined

Phase threshold is.

In a further development, the amplitude of the alternating voltage is always smaller than the voice of the threshold voltages of the organic light-emitting diodes of the light-emitting diode string. This causes, during testing, whether the short circuit

is present, the organic light emitting diodes do not shine.

In a further development, the light-emitting diode strand

at least one further organic light emitting diode. The organic light emitting diodes of the light emitting diode strand are

electrically connected in series. The presence of the

Short circuit of at least one of the organic light-emitting diodes of the light-emitting diode string is detected if the operating value is greater than the predetermined threshold value.

In a further development, the applied AC voltage is sinusoidal. This can contribute to the fact that the operating value, in particular the current value and / or the phase value, can be determined particularly precisely.

In a development, the applied alternating voltage has a predetermined offset value which is not equal to zero. Thus, the AC voltage does not fluctuate around the zero value, but a non-zero mean. Of the

Mean value can be, for example, greater or lesser than zero. In other words, the AC voltage has one

DC voltage component on. This can contribute to the fact that the operating value can be detected in a particularly simple manner and / or particularly precisely. For example, a negative dc component may contribute to the maximum current value being particularly high because the

AC voltage amplitude can be increased without the threshold voltage is exceeded. Due to the particularly high maximum current value, the recognizability of the

Short circuit can be improved. On the other hand, a positive DC component can help to avoid negative voltage components of the applied AC voltage, which can contribute to making a control device for performing the method technically simpler and / or less expensive. In general, increasing the AC amplitude by means of the DC component can contribute to a particularly good detectability of the operating value and / or a particularly good signal-to-noise ratio, as a result of which the short circuit can be identified particularly well and reliably.

An object is achieved according to an aspect of the invention by a light-emitting diode arrangement comprising: the

 Light-emitting diode strand, the at least one organic

Having light emitting diode; a voltage source associated with the

Light-emitting diode is electrically coupled and which is adapted to the AC voltage to the

Apply LED string, the AC voltage at least temporarily smaller than the sum of

Threshold voltages of all organic light emitting diodes of the

Light-emitting diode string is; a meter that works with the

Light-emitting diode strand is electrically coupled and which is adapted to at least the one operating value of

To detect the operating variable of the light-emitting diode string; and a controller electrically coupled to the voltage source and the meter and configured to Detecting the presence of the short circuit of the at least one organic light emitting diode of the Leucntdiodenatrange, if the erfaaste operating value beyond the predetermined

Threshold is. The previously explained

Further developments of the method for detecting the short circuit can be readily transferred to the Leuchtdiodenanoxdnung, in particular to the control unit, the

may be configured to perform the method steps explained above.

In a further development, at least one organic light-emitting diode of the light-emitting diode string is a capacitor

electrically connected in parallel. In a further development, one capacitor is electrically connected to each organic light-emitting diode of the light-emitting diode string

connected in parallel.

The capacitor (s) may help to make detection of the short circuit easier and / or more accurate. For example, by means of the capacitor (s) another frequency of the

AC voltage can be selected, for example a

lower frequency than without the capacitor (s). This can contribute to making the control unit technically simpler and / or less expensive.

Embodiments of the invention are illustrated in the figures and are explained in more detail below.

Bs show:

Figure 1 is a block diagram of an embodiment

 a light emitting diode array;

Figure 2 is a block diagram of an embodiment

a luminous dynasty order; an equivalent circuit diagram of an embodiment of a light emitting diode array; a block diagram of an embodiment of a light emitting diode array; a flowchart of an embodiment of a method for detecting a short circuit of an organic light emitting diode of a light emitting diode strand; an example of a frequency-current diagram; an example of a time-current / voltage diagram; an example of a time-current / voltage diagram.

In the following detailed description, reference is made to the accompanying drawings, which form a part of this specification, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. Because components of

Embodiments in a number of different

Orientations can be positioned, the serves

Directional terminology for illustration and is in no way limiting. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from

To deviate scope of the present invention. It is understood that the features of the various embodiments described herein may be combined with each other unless specifically stated otherwise. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. In the figures are identical or similar

Elements provided with identical reference numerals, as appropriate. 1 shows a block diagram of an exemplary embodiment of a light-emitting diode arrangement 10. The light-emitting diode arrangement 10 has a light-emitting diode string 20 with at least one organic light-emitting diode 12. The light-emitting diode arrangement 10 has a voltage source 22, a measuring device 24 and a

Control unit 26 on. The light-emitting diode strand 20, the

Voltage source 22 and meter 24 are electrically connected in series. Alternatively, the meter 24 may also be electrically connected in parallel with the light emitting diode string 20.

The organic light emitting diode 12, which may also be referred to as OLED, emits light during operation. The light can be light in the visible wavelength range, infrared light or UV light. The component strand 20 has an input and an output, via which the organic light-emitting diode 12 is electrically coupled to the voltage source 22, the measuring device 24 and the control unit 26. The voltage source 22 is adapted to detect a short circuit of the organic light emitting diode 12 a

Apply alternating voltage to the light-emitting diode strand 20. The voltage source 22 can also be set up to apply a DC voltage to the light-emitting diode string 20 for the normal operation of the organic light-emitting diode 12, that is to say for the lighting operation.

The measuring device 24 is configured to provide an operating value of an operating variable of the organic light emitting diode 12

to capture. The operating size, for example, a

 Betriebsetrom, which flows over the LED strand 20, in which case the operating value is a current value.

Alternatively, the operating size a

Phase shift between the applied AC voltage and the operating current and the operating value can be

Be phase value. The phase value can be detected, for example, by means of the measuring device 24, in that the measuring device 24 has a zero crossing, in particular in the case of an ascending Edge detected a course of the operating current and in which the controller 26, the time of the zero crossing of the

History of the operating current with a time of

Zero crossing of a curve of the applied AC voltage compares.

The control unit 26 is set up to specify and / or determine the AC voltage and to process the detected measured value. The control unit 26 is set up to compare the detected measured value with a predetermined threshold value and, depending on the comparison, to detect the presence of a short circuit in the organic light-emitting diodes 12. The control unit 26 may be configured to detect the presence of the short circuit, the organic light emitting diode 12, the light emitting diode strand 20 and / or the

 Turn off light emitting diode array 10. The control unit 26 may be adapted to the light-emitting diode string 20, in particular the organic light-emitting diode 12, in the normal

To operate lighting operation. The controller 26 may

For example, be a driver or a device driver and / or be designed as a microchip and / or integrated circuit.

Optionally, the light emitting diode array 10 one, two or more other organic light-emitting diodes 12 in the

 Light-emitting diode strand 20 and / or one, two or more further light-emitting diode strands 20 have. Furthermore, the

Light-emitting diode arrangement 10 for normal operation,

In particular, the lighting operation, the organic light emitting diode 12 and the light emitting diode strand 20 is a separate

 Power source, for example, a separate power source or a separate power source, have.

FIG. 2 shows a block diagram of an exemplary embodiment of a light-emitting diode arrangement 10, which for example can largely correspond to the light-emitting diode arrangement 10 shown in FIG. The light-emitting diode arrangement 10 has, in addition to the organic light-emitting diode 12, in this context Also, as the first organic light-emitting diode 12 may be referred to, three other organic light emitting diodes, in particular a second organic light emitting diode 14, a third organic light emitting diode 16 and a fourth organic light emitting diode 18. The organic light-emitting diodes 12, 14, 16, 18 emit light in normal operation. The organic light emitting diodes 12, 14, 16, 18 may be the same or different. The organic light emitting diodes 12, 14, 16, 18 may be formed on a respective substrate, wherein the organic functional layer structures and electrodes are separated from each other. Alternatively, the organic

Light emitting diodes 12, 14, 16, 18 on the same substrate

be formed, wherein at least two of the organic light-emitting diodes 12, 14, 16, 18 share the same organic functional layer structure and / or one of its electrodes. In other words, the organic light-emitting diodes 12, 14, 16, 18 can be light-emitting diode segments of a segmented light-emitting diode. FIG. 3 shows an equivalent circuit diagram of an exemplary embodiment of a light-emitting diode arrangement 10 which, for example, largely corresponds to one of the preceding ones

Light emitting diode arrangements 10 may correspond. The

Light-emitting diode arrangement 10 has three organic light-emitting diodes 12, 14, 16, which are electrically connected in series in the light-emitting diode string 20. At each of the organic

Light emitting diodes 12, 14, 16 acts as an organic functional layer structure, the organics of the corresponding

formed organic light-emitting diode 12, 14, 16 and in which the light is generated in normal operation, as a diode and is shown in Figure 3 as a diode symbol. In addition to the organic, each of the organic light-emitting diodes 12, 14, 16 each have two electrodes, between which the corresponding organics

and other elements, such as a substrate or encapsulant, of which intrinsic resistive and intrinsic capacitances are formed. In particular, each of the organic light emitting diodes 12, 14, 16 has an intrinsic capacitance intrinsic ohmic resistor electrically connected in parallel with the intrinsic capacitance, and another intrinsic ohmic resistor connected to the intrinsic capacitance and the ohmic resistor electrical series connected in parallel therewith.

Thus, the organic light-emitting diodes 12, 14, 16, on account of their intrinsic properties, have capacitances and resistances which, in addition to the diode symbols, are shown in FIG

independent electronic components are located. The intrinsic capacities are shown in FIG. 3 as

Capacitors 34, 44, 54 shown. The with the

intrinsic capacitances electrically connected in series ohmic resistances are shown in Figure 3 as

Electrode resistors 32, 42, 52 shown. The ohmic resistances electrically connected in parallel with the intrinsic capacitances are shown in FIG. 3 as bulk resistors 36, 46, 56. The bulk resistors 36, 46, 56 may also be referred to as leakage resistors.

In particular, the first organic light emitting diode 12, a first electrode resistor 32, a first capacitor 34 and a first bulk resistor 36. The second organic light-emitting diode 14 has a second electrode resistor 42, in the second capacitor 44 and a second bulk resistor 46. The third organic light emitting diode 16 has a third electrode resistor 52, a third capacitor 54, and a third bulk resistor 56. The electrode resistors 32, 42, 52 are each of

ohmic resistances of at least one of the electrodes (not shown) of the corresponding organic light emitting diodes 12, 14, 16 are formed. However, it can also ohmic

Resistors of both electrodes of the organic

LEDs 12, 14, 16 by the corresponding

 Electrode resistance 32, 42, 52 symbolizes his. The

Capacitors 34, 44, 54 are each of two electrodes the corresponding organic light-emitting diodes 12, 14, 16 are formed.

If there is no short circuit and a voltage applied to one of the organic light emitting diodes 12, 14, 16, which is greater than a threshold voltage of the corresponding organic

Light emitting diode 12, 14, 16, so flows a Betriebsström on the corresponding electrode resistance 32, 42, 52 and the corresponding organics. If you compare by means of

Control unit 26 the Betriebsström, which can be detected by means of the measuring device 24, with the applied AC voltage, which is known due to the control of the voltage source 22, it is found that no or at least

approximately no phase shift between the

Operating current and the applied AC voltage is present.

If there is no short circuit and a voltage applied to one of the organic light emitting diodes 12, 14, 16 is smaller than a threshold voltage of the corresponding organic light emitting diode 12, 14, 16, then no operating current flows through the organic light of the corresponding organic light emitting diode 12, 14, 16. However, if the applied voltage is a

Is alternating voltage, so flows due to the corresponding capacitor 34, 44, 54 also in the case that the voltage is smaller than the threshold voltage of the corresponding

organic light emitting diode 12, 14, 16, an operating current through the corresponding organic light emitting diode 12, 14, 16, in particular an alternating current. If one compares then the

Operating current with the applied AC voltage, it is found that between the operating current and the

AC voltage is a phase shift.

If there is no short circuit and the organic

Light-emitting diodes 12, 14, 16 are identical, then falls on each of the organic light-emitting diodes 12, 14, 16, a third of the voltage applied to the light-emitting diode 20 voltage. Thus, an operating current then flows across the electrode resistors 32, 42, 52 and the organic functional layer structure when the voltage applied to the light-emitting diode string 20 is equal to or greater than a sum of the threshold voltages of the organic light-emitting diodes 12, 14, 16 and the organic light-emitting diodes 12, 14, 16 light up. Again, there is no phase shift between the applied AC voltage and the Betriebsström.

If there is no short circuit, the organic light-emitting diodes 12, 14, 16 are identical, the voltage applied to the light-emitting diode 20 voltage less than the sum of

 Threshold voltage of the organic light emitting diodes 12, 14, 16 and the applied voltage is an AC voltage, so no electric current flows through the organic

functional layer structures, which is why the organic light-emitting diodes 12, 14, 16 do not shine, however, the operating current flows, in particular the alternating current over the

Light-emitting diode strand 20. This is again the

Phase shift between the applied AC voltage and the operating current before.

If one of the organic light-emitting diodes 12, 14, 16 has a short circuit, for example due to damage in one of the organic functional layer structures, then this short circuit acts like another ohmic

Resistor which is electrically connected in parallel with the corresponding capacitor 34, 44, 54. This further ohmic resistance is referred to below as short-circuit resistance. The short-circuit resistance causes, even if the voltage is lower than the threshold voltage, above the corresponding organic functional

Layer structure, in particular on the short circuit itself, an electric current flows. This causes the operating current and, if the phase shift is present, the phase value to change. In particular, this causes in most cases that the operating current increases and the phase value is smaller. However, the organic light emitting diodes 12, 14, 16 may be formed and / or a frequency and / or amplitude of the applied AC voltage may be selected so that the operating current becomes smaller and / or the phase shift increases. Which type of change in the specific case, ie the specific types of organic light-emitting diodes 12, 14, 16 used and / or the specific number of organic light emitting diodes 12, 14, 16 in the

 Light-emitting diode 20, present can be easily determined by simulation and / or empirically. In addition, a recognition accuracy can be optimized by the frequency and / or the amplitude of the applied AC voltage can be varied in this case by simulation or empirical experiments.

The above explained with reference to Figure 3

Operation of the light emitting diode array 10 can without

Further to that shown in Figure 1, 2 or 4

Light emitting diode arrangements 10 or any other

Light emitting diode array 10, in particular with any number of organic light-emitting diodes 12, 14, 16 in the

Light-emitting diode 20, are transmitted.

FIG. 4 shows a block diagram of an exemplary embodiment of a light-emitting diode arrangement 10, which for example largely corresponds to one of the above

 Light emitting diode arrangements 10 may correspond to each of the organic light-emitting diodes 12, 14, 16 is an additional capacitor 60, 62, 64 connected in parallel. The additional capacitors 60, 62, 64 can contribute to the presence of a

Short circuit a change of the operating current or the

Phase shift is greater than without

Additional capacitors 60, 62, 64. Thus, using the

 Additional capacitors 60, 62, 64 a recognition accuracy for detecting the presence of the short circuit can be improved.

5 shows a flow diagram of a method for detecting a short circuit of an organic light-emitting diode of a

Light-emitting diode strand, for example one of the organic light-emitting diodes 12, 14, 16, 18 of the light-emitting diode strand 20 of one of the light-emitting diode arrangements 10 explained above. In a step S2, an AC voltage is applied to the

Light-emitting diode strand 20 applied. The AC voltage can, for example, by means of the voltage source 22 to the

Light-emitting diode strand 20 are created. The alternating voltage is chosen such that a maximum amplitude of the

AC voltage less than a sum of the

Threshold voltages of all organic light emitting diodes 12, 14, 16, 18 of the light emitting diode strand 20 is. Alternatively, the AC voltage can be selected such that the maximum amplitude of the AC voltage at least briefly,

for example, during a period less than one

Quarter period of oscillation of the AC voltage, equal to or greater than the sum of the threshold voltages. Further, the AC voltage may be selected to oscillate about a zero potential or about a non-zero positive or negative voltage value. In other words, in addition to the AC voltage, a

DC voltage to the LED strand 20 are applied. The alternating voltage can be applied so that it runs sinusoidally. The application of the alternating voltage by means of the voltage source 22 can, for example by means of the

Control unit 26 controlled and / or regulated. In step S4, an operating value of an operating variable is detected. The operating value can be detected, for example, by means of the measuring device 24. For example, the

Current value of the operating current and / or the phase value of the phase shift detected. The operating value can be recorded several times in succession, for example continuously, so that a course of operating values and thus a course of the operating variable can be detected over a certain period of time. The operating value can be detected, for example, at a time at which a profile of the operating variable has a zero crossing and / or a rising edge. The phase value can be detected, for example, by first determining the operating value and the phase value depending on the detected operating value is determined. For example, the history of the

Operating current can be detected and depending on the course of the operating current and the course of the AC voltage, the phase value is determined.

In a step S6, it is checked whether the operating value

is beyond a predetermined threshold.

For example, depending on the choice of the operating value, it can be checked whether the operating value is greater than that

predetermined threshold value, which is shown in Figure 5 in step S6, or less than the predetermined

Threshold is what is not shown in Figure 5 in step S6 for reasons of clarity. For example, it can be checked if the current value is greater than one

predetermined current threshold is. Alternatively, it can be checked if the phase value is less than one

is predetermined phase threshold. If the course of the operating variable is detected, then, for example, a maximum operating value of the profile of the operating variable can be determined and this maximum operating value can then be compared with the predetermined threshold value. If the condition of step 36 is satisfied, the

Processing continued in a step S8. if the

Condition is not satisfied in the step S6, the processing is continued in a step S10.

In step S8, the presence of the short circuit in one of the organic light-emitting diodes 12, 14, 16, 18 is detected. Optionally, in step S8 a warning signal can be generated, for example by means of the control unit 26, and / or the light-emitting diode string 20 and / or the light-emitting diode arrangement 10 can be switched off as a precautionary measure.

Optionally, the warning signal can be sent, for example, to a higher-level arithmetic unit. If

for example, the corresponding light-emitting diode array 10 is arranged in a motor vehicle, the warning signal can be sent to a board computer of the motor vehicle, and / or, for example, if the board computer Control unit 26 includes, the warning signal can from the

Board computer can be optically and / or acoustically output.

In step S10, it is recognized that none of

organic light-emitting diodes 12, 14, 16, 18 is a short circuit.

The procedure can after switching on the

Light-emitting diode arrangement 10 before the normal lighting operation, in pauses of the normal lighting operation and / or after completion of the normal lighting operation and before switching off the

LED array 10 are processed once, twice or more times in a row. FIG. 6 shows an example of a frequency-current diagram in which a frequency f of the applied voltage is applied to the X-axis

Alternating voltage in kHz is plotted and on the Y-axis operating values of the operating current in mA are plotted. The frequency-current diagram shows a first trace 70 of the operating current for a case where there is a short circuit with a resistance of 1000Ω, a second trace 72 of the operating current for a case where there is a short circuit with a resistance of 100Ω , and a third history 74 of the operating current for a case where there is a short circuit having a resistance of 50 Ω. In the event of short circuits with resistance values greater than 1000 Ω, the recorded (not individually shown) runs of the operating current are almost complete

However, short circuits with such high resistance values can often be classified as non-critical. In other words, an organism having such a high resistance value can be classified as having no short circuit. The second curve 72 lies above the first curve 70 and the third curve 74 lies above the second curve 72. Thus, the lower the resistance value of the short circuit, the higher the current value of the operating current. In the light-emitting diode arrangement 10, by means of which the frequency-current diagram shown in FIG. 6 has been recorded, the optimum frequency for the AC voltage for detecting the short circuit can now be determined by determining at which frequency the current value is at most from the current value in the faultless Case deviates, for example, the first curve 70 may be representative of a course in error-free case. The optimal determined in this way

Frequency is 1.0 kHz in the case shown in Fig. 6, which is shown by the dashed lines.

FIG. 7 shows a time-current / voltage diagram in which the time in .mu.O and on the Y-axis are generated on the X-axis

Operating current I and the applied AC voltage U

are offered. The time-current / voltage diagram shows a first curve 80 of the AC voltage, a first curve 82 of the operating current, a second curve 84 of the

BetriebsStroms and a third course 86 of the

Operating current.

The curves 82, 84, 86 of the operating current were all recorded at the same frequency of the alternating voltage, in particular at 10 kHz, the applied alternating voltage being the same for all measurements and being represented by the first curve 80 of the alternating voltage. Furthermore, the courses 80, 82, 84, 86 were recorded by means of a light-emitting diode arrangement which corresponds to one of the light-emitting diode arrangements 10 explained above, the maximum amplitude of the alternating voltage being smaller than the sum of the alternating voltages of all the organic ones at any time

LEDs 12, 14, 16, 18 in the corresponding

Light emitting diode strand 20. Therefore, the curves 82, 84, 86 of the operating current always have a phase shift with respect to the first curve 80 of the applied AC voltage.

The first curve 82 of the operating current was at a

Short circuit with a short circuit resistance of 100 Ω

detected. The second course 84 of the operating current was at detected a short circuit with a short-circuit resistance of 10 Ω. The third curve 86 of the operating current was detected in the event of a short circuit with a short-circuit resistance of 5 Ω. At the applied AC voltage with the

predetermined frequency is the zero crossing of the curves 82, 84, 86, the sooner, the greater the short circuit resistance. In the case of the applied AC voltage, one of the zero crossings of the second curve 84 of the operating current takes place, for example, at a first time T 1 and one of the zero crossings of the first curve 80 of the AC voltage takes place, for example, at a second time T 2. The time interval between the first time Tl and the second time T2 defines the phase value DT of

Phase shift. The earlier the zero crossing of the curves 82, 84, 86 of the operating currents, the greater the phase value of the corresponding phase shift with respect to the applied AC voltage.

Thus, in the fault-free case, in which there is no short circuit and in which the short circuit resistance is maximum, for example, greater than 1 kQ, the phase shift maximum, in particular approximately 90 °, and the

Light-emitting diode strand 20 and in particular the organic

Light-emitting diodes 12, 14, 16, 18 show a strong capacitive behavior with the phase shifts shown.

When the short circuit occurs increases with increasing

Heavy short circuit whose short circuit resistance, whereby the phase shift is lower, so that the light emitting diode strand 20 and in particular the affected

organic light emitting diode 12, 14, 16, 18 more and more shows an ohmic behavior in which between the applied AC voltage and the detected operating current no

Phase shift is present.

Furthermore, the time-current / voltage diagram according to Figure 7 can also be seen that with decreasing

Short circuit resistance, ie with increasing severity of the Short circuit, the maximum operating value of the operating current increases.

FIG. 8 shows a time-current / voltage diagram in which the time in ps and on the y-axis is generated on the x-axis

Betriebsström I and the applied AC voltage U

are offered. The time-current / voltage diagram shows a second curve 90 of the AC voltage and a fourth curve 92 of the operating current. In addition, the time-current / voltage diagram shows a third time T3, a fourth time T4, a fifth time T5, and a sixth time T6.

The fourth curve 92 of the operating current was recorded at a different frequency of the alternating voltage and at a different short-circuit resistance than that in FIG. 7

shown curves 82, 84, 86 of the operating current. Of

Furthermore, the curves were 90, 92 by means of a

Light-emitting diode arrangement recorded, which is one of the

Previously explained light-emitting diode arrangements 10

corresponds, wherein the amplitude of the AC voltage between the third time T3 and the fourth time T4 and after the sixth time T6 is greater than the sum of the threshold voltages of all the organic light emitting diodes 12, 14, 16, 18 in the corresponding LED strand 20. Therefore, the fourth History 92 of the operating current only outside these time ranges, a phase shift with respect to the second curve 90 of the applied AC voltage and within these time ranges no phase shift with respect to the second curve 90 of the applied AC voltage.

The falling edge of the fourth curve 92 of the

Operating current immediately after the fourth time T4 is still primarily influenced by the forward current, the up to the fourth time T4 on the luminous organic light-emitting diodes 12, 14, 16, 18 was flowing, which is why the

Zero crossing of the fourth curve 92 of the operating current at its falling edge is not for detecting the phase value the phase shift is suitable. The zero crossing of the fourth curve 92 of the operating current, however, can readily on the rising edge of the fourth curve 92 of

Operating current, in particular at the fifth time T5, are detected. Thus, the method explained above for detecting the short circuit is also suitable in the case in which the amplitude of the alternating voltage exceeds the sum of the threshold voltages of the organic light-emitting diodes 12, 14, 16, 18.

Claims

claims 1. A method for detecting a short circuit of a organic light emitting diode (12, 14, 16, 18) of a Light-emitting diode string (20), in which  an alternating voltage is applied to the light-emitting diode string (20) whose amplitude is at least temporarily smaller than a sum of the threshold voltages of all organic light-emitting diodes (12, 14, 16, 18) of the light-emitting diode string (20), at least one operating value of an electrical current  Operating size of the light emitting diode string (20) is detected, and the short circuit is detected as present when the detected operating value beyond a predetermined Threshold is. 2. The method of claim 1, wherein the electrical Operating size is an electric current that exceeds the Light emitting diode string (20) flows, wherein the operating value is a current value (II, 12) of the operating current and in which the predetermined threshold value is a predetermined current threshold. 3. The method of claim 1, wherein the electrical Operational variable is a phase shift between the applied AC voltage and an operating current, which exceeds the LED strand (20) flows in which the operating value is a phase value (DT) of the phase shift and wherein the predetermined threshold is a predetermined Phase threshold is. 4. The method of claim 3, wherein the predetermined Phase threshold in a range is between 70 ° and 90 °. 5. The method according to any one of claims 3 or 4, wherein for detecting the phase value (DT) zero crossings of a curve (80, 90) of the applied AC voltage and a course (82, 84, 86, 92) of the operating current are detected and compared with each other. 6. The method according to any one of claims 3 to 5, wherein for detecting the phase value (DT) a rising edge of a History (82, 84, 86, 92) of the operating current is used. 7. The method according to any one of claims 3 to 6, wherein for detecting the phase value (DT) a fast Fourier transformation is performed. 8. The method according to claim 2 and one of claims 3 to 7, wherein the current value (II, 12) of the operating current and the phase value (DT) of the phase shift are detected and in which the presence of the short circuit is detected when the detected current value ( II, 12) is greater than or equal to the predetermined current threshold and / or if the detected phase value (DT) is less than the predetermined one Phase threshold is. 9. The method according to any one of the preceding claims, wherein the amplitude of the AC voltage is always smaller than the sum of the threshold voltages of the organic light-emitting diodes (12, 14, 16, 18) of the light-emitting diode string (20). 10. The method according to any one of the preceding claims, wherein the light-emitting diode string (20) at least one further organic light-emitting diode (12, 14, 16, 18), wherein the organic light emitting diodes (12, 14, 16, 18) of the Light emitting diode string (20) are electrically connected in series, and  the presence of the short circuit of at least one of the organic light emitting diodes (12, 14, 16, 18) of the Light-emitting diode string (20) is detected if the operating value is beyond the predetermined threshold value. A method according to any one of the preceding claims, wherein the applied AC voltage is sinusoidal. A method according to any one of the preceding claims, wherein the applied AC voltage has a predetermined offset value other than zero. 13. Light emitting diode arrangement (10), comprising  a light-emitting diode string (20) which has at least one organic light-emitting diode (12, 14, 16, 18),  a voltage source (22) connected to the Light-emitting diode string (20) is electrically coupled and which is adapted to an AC voltage to the Light emitting diode strand (20) create, the AC voltage at least temporarily smaller than a sum of Threshold voltages of all organic light-emitting diodes (12, 14, 16, 18) of the light-emitting diode string (20),  a measuring device (24), which is electrically coupled to the light emitting diode string (20) and which is adapted to at least one operating value of an operating variable of the To detect light emitting diode string (20), and  a controller (26) electrically coupled to the voltage source (22) and the meter (24) and configured to detect the presence of a short circuit at least one organic light-emitting diode (12, 14, 16, 18) of the light-emitting diode string (20) to detect if the detected operating value is beyond a predetermined threshold. 14. Light-emitting diode arrangement (10) according to claim 13, wherein at least one organic light-emitting diode (12, 14, 16, 18) of the light-emitting diode string (20), a capacitor (60, 62, 64) is electrically connected in parallel. 15. Light emitting diode arrangement (10) according to claim 14, wherein to each organic light emitting diode (12, 14, 16, 18) of the Light-emitting diode string (20) each have a capacitor (60, 62, 64) is electrically connected in parallel.