Dimmable operating unit and lighting system for increasing the life expectancy of leds and oleds

Abstract

The invention relates to an operating unit (1) for operating at least one LED (9). Said unit has an electronic control system (2) for adapting a supply current to the operating characteristics of the LED or LEDs and a control unit (3) for controlling the LED operation. The invention is characterised in that the operating unit limits the maximum output of the LED or LEDs in a first operating phase to a predetermined level and the operating unit converts an external dim command in an appropriate manner.

Description

[0001] The present invention relates to a control device for operating an LED or an OLED and to a lighting system with such a control device.

[0002] For an LED to be controlled correctly, the supply current, for example supplied from the mains, must be adjusted so that it corresponds to the operating characteristics of the LED.

[0003] In most cases, an AC / DC converter is required. Furthermore, the current and / or voltage must be limited so that both correspond to the LED's optimal operating point. This operating point is chosen to maximize light emission, while remaining within an acceptable range.

[0004] It is known that the light output of an LED decreases over time. With a constant power supply, the intensity, in the simplest case, drops exponentially over time.

[0005] Depending on the manufacturer, the steepness of this decline varies, and with some manufacturers, a superposition of two different decline curves can also be observed.

[0006] However, from a qualitative perspective, it always results in an exponential decline. Because of this, the decline is particularly pronounced during the initial operating phase, for example, in the first 20 to 200 hours.

[0007] This also has the disadvantage that, in the long term, a constant brightness cannot be guaranteed when using LED lighting.

[0008] The lifespan of light-emitting diodes – especially those with organic components (OLEDs) – is currently quite limited and must be ensured through expensive encapsulation and complex production processes. It would therefore be highly desirable to increase the lifespan of these components without resorting to even more expensive production or encapsulation methods.

[0009] US 7138 970 B2 discloses a method for operating an LED illumination system within a line scan camera, comprising an LED and a light sensor. The LED is operated at a pulse-width modulation (PWM) frequency of less than 100% to reduce LED aging and thus extend its lifespan. The light sensor is set to a higher sensitivity for this purpose. As the LED brightness decreases during operation, the PWM frequency is gradually increased to 100%.

[0010] US 6236 331 B1 discloses an electronic control unit for an LED traffic light. The control circuit ensures a constant light intensity that complies with legal regulations and remains below the maximum possible brightness of the LEDs. This constant brightness is maintained by a light sensor that measures the brightness of a separate LED. The control unit adjusts the brightness as needed. This increases the lifespan of the LEDs and allows the traffic light to comply with legal standards for a longer period. In a special version, the light is set to maximum brightness and reduced during dusk and nighttime. Ambient light is detected by a separate light sensor.

[0011] The problem is that while maintaining a constant light intensity of an LED throughout its lifespan is desirable, active control of the light intensity is also required. This is particularly crucial if the lighting is to have a dimming function.

[0012] The invention addresses this problem and provides a solution for making the operating characteristics of LEDs more constant and adaptable.

[0013] This problem is solved according to the invention by the features of the independent claims. The dependent claims further develop the central idea of ​​the invention in a particularly advantageous way.

[0014] According to the invention, the use of a suitable control system in a first operating phase of the LED or OLED is therefore proposed.

[0015] For this purpose, a control gear is designed to operate at least one LED or OLED. It includes control electronics to adapt the supply current to the operating characteristics of the at least one LED. In an initial operating phase, the control gear limits the maximum power of the at least one LED or OLED to a predetermined level. The control gear either ignores an incoming external dimming command or, for example, reduces it by scaling, ensuring that the LED or OLED power does not exceed the predetermined level in the initial operating phase.

[0016] For OLEDs, it can be advantageous to burn them in with a predefined current during the first few hours of operation. This means, for example, that incoming dimming commands are ignored during this period, and the OLED is operated with a predefined current or a current within a predefined current range. Within this range, incoming dimming commands can optionally be implemented.

[0017] The predetermined level is below the maximum permissible power input of the at least one LED. This ensures that the maximum possible light intensity of the LED is deliberately prevented during initial operation.

[0018] The invention further provides that the predetermined level changes over the operating time in the first operating phase of the at least one LED in such a way that it approaches the maximum permissible power input.

[0019] The first operating phase ends when the predetermined level has reached the maximum permissible power input.

[0020] The predetermined level changes over the operating time of the first operating phase of the at least one LED in such a way that the light intensity of the at least one LED remains constant.

[0021] In one embodiment, the predetermined level can increase linearly over the operating time.

[0022] In another embodiment, the predetermined level can increase logarithmically over the operating time.

[0023] Alternatively, the predetermined level can also increase over the operating time following any other non-linear curve.

[0024] The invention relates to an operating hours counter by means of which the change of the predetermined level is controlled as a function of the operating time.

[0025] The invention further relates to a memory, for example a One Time Programmable Memory, which specifies the temporal change of the predetermined level.

[0026] Furthermore, the invention can include a measuring device, preferably a light sensor, which detects the light intensity of the at least one LED when operating at the power of the predetermined level and supplies the measured values ​​to the control unit.

[0027] The control unit can adjust the predetermined level using supplied measured values ​​so that the light intensity of at least one LED remains constant when operating at the power of the predetermined level.

[0028] An interface allows for an externally received dimming command to be sent to adjust the light intensity.

[0029] The invention further provides that, in the case of an externally received dimming command of the light intensity, the dimming value actually set at the at least one LED depends on the predetermined level.

[0030] This means that the actual dimming of at least one LED is scaled down according to the current value of the predetermined level.

[0031] It is conceivable that an externally received dimming command could be implemented via user input.

[0032] It is also possible that an incoming dimming command from the outside can be carried out by means of adaptive adjustment to external conditions, such as daylight.

[0033] Furthermore, an incoming dimming command can be made via an input from another system, for example an external sensor device or a central control unit.

[0034] The brightness of at least one LED can be adjusted via a power control with a limited value, for example via pulse width modulation.

[0035] Alternatively, adjusting the brightness of at least one LED via current control is conceivable.

[0036] It is also intended that instead of at least one LED, at least one OLED or a combination of LEDs and OLEDs can be used.

[0037] Finally, the invention provides a system comprising a central control unit, a bus, and at least two operating devices connected to the bus for operating at least one LED each. Each operating device includes control electronics for adapting a bus supply current to the operating characteristics of the at least one LED. In a first operating phase, the maximum power of each LED is limited to a predetermined level below the maximum permissible power input.

[0038] The invention further relates to an operating device for operating at least one LED or OLED, comprising an interface for supplying external dimming commands from a central control unit or a sensor, and control electronics for controlling or regulating a supply current to the operating characteristics of the at least one LED or OLED depending on incoming dimming commands, wherein the operating device regulates or sets the supplied power or current of the at least one LED to a predetermined level in a first operating phase, and the operating device ignores an external dimming command or implements it in such a way, in particular by scaling it down, that the LED or OLED power does not exceed or fall below the predetermined level in the first operating phase.

[0039] Furthermore, an incoming dimming command from an external source is implemented in a suitable manner.

[0040] During the first operating phase, the predetermined level approaches the value of the maximum permissible power input.

[0041] The central control unit also has an interface through which an externally received dimming command for the light intensity can be sent.

[0042] An incoming dimming command can be ignored by the corresponding control gear during the first operating phase of an LED.

[0043] Alternatively, an incoming dimming command can be rescaled so that the actual dimming of each LED depends on the predetermined level.

[0044] Further features, advantages and properties of the present invention will now be explained in more detail with reference to the figures in the accompanying drawings and the detailed explanation of an exemplary embodiment. Fig. 1 qualitatively shows the temporal progression of the intensity decrease during conventional and in the operation of an LED according to the invention, Fig. 2 schematically shows an embodiment of an operating device according to the invention, Fig. 3 shows an exemplary method of how a dimming command can be scaled depending on the predetermined level, and Fig. 4 schematically shows an embodiment of an embodiment of a system according to the invention with two operating devices.

[0045] Fig. 1 This graph qualitatively shows the temporal progression of the intensity decrease in LEDs. Light intensity is plotted vertically and time horizontally, both with arbitrary units.

[0046] Row 1 represents the intensity decay of an LED operating at constant, normal parameters. It is clearly visible that the intensity initially drops very sharply, and then gradually levels off. This roughly corresponds to an exponential curve.

[0047] Series 2, on the other hand, depicts the intensity drop of an LED during operation according to the invention. It is evident that the LED is operated at a power level below its maximum permissible power during the initial operating phase, i.e., the start-up phase. This maximum permissible power is intended to correspond to the LED's normal operating parameters. The duration of this initial operating phase depends on the design and geometry of the components used (LED / OLED) and typically lasts between 20 and 200 hours. In the simplest case, a suitable control method could be implemented by maintaining the OLED's light intensity at, for example, 80% of its initially possible maximum luminous intensity.

[0048] Since the light intensity decreases continuously due to natural aging, constant adjustments are necessary to maintain a constant light intensity.

[0049] The first operating phase ends when the LED is operated at its maximum permissible power. Fig. 1 The end of the start phase is therefore reached at approximately time 12.

[0050] Following the initial operating phase, the control parameters are kept constant, as would be the case during normal operation. As a result, the light intensity will now gradually decrease.

[0051] However, it is evident that the intensity decreases more slowly even now than if the light-emitting diode (LED / OLED) had been controlled normally during the first operating phase.

[0052] In Fig. 2 Figure 1 shows a schematic embodiment of the operating device 1 for operating at least one LED and / or OLED 9.

[0053] The operating device essentially consists of a control electronics unit 2 and a control unit 3. The control electronics unit 2 and the control unit 3 communicate via an interface 7. Optionally, the operating device can also have a memory 4 and / or an operating hours counter 11.

[0054] The control electronics 2 adjust the supply current 5 so that it has suitable operating parameters for powering at least one LED and / or at least one OLED 9. The control electronics can include an AC-DC converter and an electronic circuit for current and voltage adjustment or limiting.

[0055] In contrast, control unit 3 is responsible for the intelligent control of the control electronics. Control unit 3 regulates the control unit according to the principle of the invention, as described in the description. Fig. 1This has already been explained. Furthermore, it is responsible for other inputs, such as user-initiated inputs, and the corresponding control of the control electronics. It is also possible for it to adaptively control the control electronics. The control unit, therefore, generally represents an intelligent controller capable of performing mathematical calculations or electronic data processing.

[0056] It should be emphasized that this arrangement is to be considered purely logical and functional. It does not represent a hardware configuration. This means that the hardware implementation may differ from this. For example, it is conceivable that the control unit is implemented as an integrated circuit. However, it is possible that part of the control electronics is implemented in the same integrated circuit. It is also possible that the memory and / or the operating hours counter are located in the same integrated circuit or on the same substrate.

[0057] In one embodiment, the control unit includes an operating hours counter 11. This is used to count the operating hours and thus successively increase the power supplied to the at least one LED during operation. In the simplest case, a linear increase in power would be conceivable. Preferably, however, the increase is logarithmic in order to optimally compensate for the exponentially decreasing light intensity of the at least one LED with operating time. Alternatively, the power curve over time can follow any other non-linear curve.

[0058] Furthermore, the time course can not only consist of a continuous curve, but can also exhibit individual discrete values.

[0059] In another embodiment, no measurement is performed, including no counting of operating hours. Instead, a memory 4 exhibits a predetermined time profile of the predetermined level. For this purpose, it can be provided that a starting value below 100% of the current value (for example, 80%) is selected for the time profile, which is increased to 100% of the current value over a defined period according to a predefined curve. This increase can be linear, as described above, or preferably logarithmic or exponential, in order to compensate for an exponential decrease in intensity.

[0060] One possible implementation is using so-called OTPs (One Time Programmable Memory). The programmed curve is traversed at 100% current during the first operating phase. Afterwards, at least one LED is operated at 100% current upon subsequent power-ups.

[0061] This information about the time course can be fed to the control unit 3, which in turn regulates the LED operation by means of the control electronics.

[0062] In a third embodiment, the intensity drop of the at least one LED is compensated for by a measuring device 12. This device is connected to the control unit via an interface 8. It should be noted, however, that the measuring device can be either external or integrated into the control unit, for example, located on the same substrate or in the same integrated circuit.

[0063] The measuring device is preferably a light sensor.

[0064] This sensor measures the intensity of the light emitted by the at least one LED. This value is transmitted to the control unit, which can then calculate the discrepancy between the actual light intensity and the target value. The target value used for this calculation is the light intensity set at the beginning of the first operating phase. The control unit then adjusts the activation of the at least one LED to compensate for the discrepancy between the actual and target values. In this way, the at least one LED always shines with the same brightness during the first operating phase.

[0065] It is also planned that the brightness of at least one LED can be adjusted externally. This means that externally forced dimming is possible.

[0066] This can be done via user input as a dimming command. Alternatively, it's conceivable that this can be done adaptively. In the latter case, the lighting provided by at least one LED can be adjusted to the ambient light. For this, it's advisable to use an additional sensor, such as a daylight sensor, to measure the ambient light.

[0067] Furthermore, it is conceivable that a dimming command is initiated by another system, for example, a central control unit. In particular, it is possible that the operating device is connected to a bus via an interface 12. The resulting advantageous features are described in the section on Fig. 4 explained in more detail.

[0068] It is now necessary for the control unit to calculate the control parameters of at least one LED, depending on the incoming dimming command and the discrepancy between the actual and target values, or the time course of the predetermined level.

[0069] Fig. 3 This example illustrates how the calculation can be performed. In this example, it is assumed that the level adjustment is carried out using a light sensor.

[0070] When the LED is first switched on in step S101, an initial initialization is triggered. During this process, in step S102, the LED's light output is set to a predetermined level, for example, 80% of the maximum permissible power. The light intensity I ACTUAL, MAX is then measured. In step S103, this value is assigned to the variable I SET, MAX. This value serves as a reference for further adjustments to the predetermined level during the initial operating phase. Naturally, this initial initialization from steps S101 to S103 only occurs once, during the first commissioning of the LED.

[0071] In S104, the actual light intensity I IST is measured again. This is compared with the target value in S105. If a discrepancy occurs between the two, the predetermined level is adjusted so that the actual and target values ​​are equal.

[0072] As already mentioned, it is conceivable to use an operating hours counter and / or a memory to adjust the predetermined level.

[0073] In this case, the initialization from S101 to S103 becomes unnecessary.

[0074] In this case, the predetermined level in S104 and S105 can be adjusted directly. This means that no measurement of the light intensity and no calculation of the level to be used is necessary. Instead, the level can be increased directly during operation, successively following a predefined curve.

[0075] In S106, an external dimming command D is measured, which, for example, has been set via a user interface. The actual light intensity I IST is then calculated based on the preset level P and the dimming value D.

[0076] In the simplest case, this involves multiplying the two values, as shown by formula (1). I IST = P × D

[0077] For example, if the currently valid level were 90% of the maximum permissible power and the dimming value 50%, then the actual light intensity (I IST) would be 45%. It should be noted that the preset level also changes linearly or non-linearly over the operating time. Furthermore, it is possible that the actual light intensity (I IST) to be set is calculated using a non-linear formula. This means that the actual light intensity (I IST) to be set is scaled down non-linearly.

[0078] In another implementation, the determination of the actual light intensity I IST could also be done using a look-up table. This table could, for example, be stored in memory 4. The table can assign an actual light intensity I IST to each combination of a dimming value and a preset level.

[0079] However, any other form of calculation is also possible. The crucial point is that, on the one hand, the aging of the LED is compensated for, and on the other hand, the actual light intensity, especially its properties as perceived by the viewer, corresponds to the set value. Therefore, compensation of the set dimming value must always be dynamic over time during the initial operating phase, i.e., it must correspond to the currently valid preset level.

[0080] The intensity value determined in S107 is converted by the control unit into corresponding operating parameters for the LED. These are then fed to the control electronics so that the LED illuminates in the desired manner. Pulse width modulation or current control, for example, can be used for this purpose.

[0081] Circuit S108 determines whether the LED is still in its first operating phase. This can preferably be determined via the current level. If this is lower than the maximum permissible power, the LED is still in its first operating phase.

[0082] When using an operating hour counter, a predetermined operating time can also be defined as the first operating phase.

[0083] In the case of traversing a predetermined curve, it can be defined that the first operating phase is over when the curve has been completely traversed.

[0084] If the first operating phase is not yet over, the system returns to S104. Optionally, a time t can be waited before the level is adjusted again in S104.

[0085] If the first operating phase is already over, the level is no longer changed. In this case, the program jumps directly to S106. Optionally, another time t can be waited.

[0086] It can also be added that there are two different ways to adjust the predetermined level in S104 and S105.

[0087] In the first iteration, the light intensity is briefly set to the predetermined level, i.e., the maximum light intensity permitted by the control gear, and a comparison between the actual and target values ​​is performed. The target value used is the one specified in S103.

[0088] In a second embodiment, the light intensity set by dimming is maintained. The dimming value is factored into the measured light intensity in such a way that the actual value when the LED is operated at the predetermined level can be calculated.

[0089] In this way, a comparison can again be made with the target value that has been defined in S103.

[0090] Since the first method may potentially lead to a kind of flickering, method 2 is preferable as long as error-free compensation of the dimming value is possible. Therefore, it is also conceivable to use this procedure in S102 and S103 to determine I SOLL, MAX.

[0091] In Fig. 4 The features according to the invention are advantageously applied to a system.

[0092] The system 16 consists of a central bus unit 17 and three operating devices 15, only the first operating device is shown in detail.

[0093] The central bus unit is connected to an electrical power supply 10. It also has an interface 8 through which a dimming command can be received. This command can be initiated by a user. An input device, such as a rotary knob, can be located on the central bus unit or externally. A display device, such as a screen, is also conceivable, for example, to show the preset level per LED / LED module or the set dimming value. Furthermore, the dimming command can be initiated by a measuring device 12. This could be a light sensor and / or a motion sensor. It is also conceivable that such a sensor is located as a device 13 on the central bus unit. Finally, the dimming command can be initiated by an external system.

[0094] For communication with the operating devices and for their power supply, a bus 14 exists, connecting the central bus unit and the operating devices. However, it is conceivable that the communication bus (or address bus) and the power supply bus are two separate devices. For example, communication could take place via a wireless interface and power supply via a cable.

[0095] Each operating device has its own "intelligence" in the form of a central control unit 3 and optionally a memory 4 and / or an operating hours counter 11. It also includes control electronics 2 and a connection 6 for connecting at least one LED 9. Instead of at least one LED, any combination of LEDs and OLEDs can again be used. It is also conceivable to connect an LED module or an LED chain consisting of any combination of LEDs and OLEDs.

[0096] Each LED or LED module is initially operated at a predetermined level below the maximum permissible power input during the first operating phase. This level is then increased during this initial phase as described above. The predetermined level is regulated individually by each control gear for the connected LED or LED module. This is particularly advantageous when a single LED or LED module is replaced and is therefore at the beginning of the first operating phase.

[0097] This could also be achieved by having the central bus unit calculate a predetermined level for each control device (or for the connected LEDs). This level could then be assigned to the control device using a unique address.

[0098] A dimming command received by the central bus unit, or a dimming command set by the central bus unit, can be forwarded to each control gear. This is then preferably processed locally in each control gear. In this process, the light intensity is again adjusted to the dimming command, depending on the predetermined level.

[0099] In another version, dimming commands from any control gear whose LEDs are still in the first operating phase are ignored. This way, the LEDs always shine at the same brightness during the first operating phase. Reference symbol list:

[0100] 1. Operating device 2. Control electronics 3. Control unit 4. Memory 5. Mains power supply 6. LED power supply 7. Interface between control electronics and operating device 8. Interface for setting the operating mode 9. LED or OLED 10. Mains power 11. Operating hours counter 12. Measuring device 13. Sensors 14. Bus 15. Operating device 16. System 17. Central bus unit

Claims

1. Operating device for operating at least one LED (9) or OLED, comprising: - an interface for supplying external dimming commands from a central control unit or a sensor - control electronics (2) to control or regulate a supply current to the operating characteristics of the at least one LED or OLED as a function of incoming dimming commands, characterized in that - in a first operating phase, the operating device is limiting the maximum power of at least one LED or OLED to a predetermined level below the maximum permissible power supply of the at least one LED or OLED, wherein the first operating phase is triggered with the first activation of the LED, - the operating device ignores or downscales an external dimming command in the first operating phase so that the maximum power of the at least one LED does not exceed the predetermined level in the first operating phase, - the operating device detects the end of the first operating phase and the level of the maximum power supply no longer changes when the end of the first operating phase is determined, - and the predetermined level changes over the operating time in the first operating phase of the at least one LED or OLED in such a way that it approaches the maximum permissible power supply.

2. Operating device (1) according to claim 1, characterized in that the operating device regulates or determines the supplied power or the supplied current of the at least one LED in the first operating phase.

3. Operating device according to one of the preceding claims, characterized in that the first operating phase is then ended when the predetermined level has reached the maximum permissible power supply.

4. Operating device according to one of the preceding claims, characterized in that the predetermined level so changes over the operating time of the first operating phase of the at least one LED that the light intensity of the at least one LED remains constant.

5. Operating device according to one of the preceding claims, characterized in that - the predetermined level increases linearly over the operating time, or - the predetermined level increases logarithmically over the operating time, or - the predetermined level increases non-linearly over the operating time.

6. Operating device according to one of the preceding claims, characterized in that the operating device comprises an operating hour counter (11) by means of which the change of the predetermined level is regulated as a function of the operating time.

7. Operating device according to one of the preceding claims, characterized in that the operating device has a memory (4), for example a one-time programmable memory, which gives the temporal change of the predetermined level.

8. Operating device according to one of the preceding claims, characterized in that the operating device comprises a measuring device (12), preferably a light sensor, wherein the measuring device determines the light intensity of the at least one LED during operation at the power of the predetermined level and supplies the measured values to the control unit .

9. Operating device according to one of the preceding claims, characterized in that the control unit (3) so adapts the predetermined level by means of the measured values supplied, that the light intensity of the at least one LED remains constant during operation with the power at the predetermined level.

10. Operating device according to one of the preceding claims, characterized in that the operating device has an interface (8) via which an incoming dimming command of the light intensity may be received.

11. Operating device according to one of the preceding claims, characterized in that in the case of a dimming command from the outside, the light intensity of the dimming value actually set at the at least one LED as a function of the predetermined level.

12. Operating device according to one of the preceding claims, characterized in that in the case of a dimming command coming from the outside, the actual value set at the at least one LED is down-scaled according to the current value of the predetermined level.

13. Operating device according to one of the preceding claims, characterized in that - a dimming command coming from the outside is ignored during the first operating phase, and / or - a dimming command coming from the outside may be made by means of adaptation to external conditions, for example daylight, and / or - a dimming command coming from the outside may be made by means of an input from another system, for example an external sensor device or a central circuit.

14. Operating device according to one of the preceding claims, characterized in that the brightness of the at least one LED is adjusted via power control with a limited value, preferably via pulse-width modulation.

15. Operating device according to one of the preceding claims, characterized in that the brightness of the at least one LED is adjusted via a current control.

16. Operating device according to one of the preceding claims, characterized in that at least one OLED or a combination of LEDs and OLEDs may also be operated in place of the at least one LED (9).

17. System (16), comprising a central control unit (13), a bus (14), and at least one operating device (15) according to one of the preceding claims connected to the bus by means of an interface.

18. Method for the optimized operation of at least one LED by means of an operating device according to one of the claims 1 to 16 with the following method steps: - supplying an external dimming command coming from a central control unit or a sensor by means of an interface of the operating device; - controlling or regulating a supply current to the operating characteristics of the at least one LED as a function of the incoming dimming command by means of the control electronics of the operating device, characterized in that - the maximum power of the at least one LED in a first operating phase is limited to a predetermined level under the maximum permissible power supply of the at least one LED by means of the operating device, wherein the predetermined level approaches the value of the maximum permissible power supply within a first operating phase, wherein the first operating phase is triggered with the first switching on of the LED, and, wherein in the first operating phase, an external dimming command is ignored or downscaled so that the at least one LED does not exceed the predetermined level in the first operating phase, - the operating device determines the end of the first operating phase of the LED, and - when the end of the first operating phase is determined, the level of the maximum power is no longer changed, and - and the predetermined level changes over the operating time in the first operating phase of the at least one LED or OLED in such a way that it approaches the maximum permissible power supply.

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