EP2365734A2 - Method for operating an LED assembly - Google Patents

Abstract

The method involves supplying LEDs (I) with constant and pre-determined power via a power source (D). The LEDs are connected with the power source via switching elements (E) e.g. MOSFETs, in a switching condition. The LEDs are separated from the power source during a switch-off condition. The switching elements are switched on and off by a control circuit (F), which is operated with clock frequency larger than 100 Hertz such that only a portion of the LEDs is already switched-on and the other LEDs are switched on in two switching conditions successive to each other.

Description

The invention relates to a method for operating an LED arrangement for illumination, backlighting, irradiation or signaling, which comprises at least one light-emitting diode which is operated with switched direct current.

Light emitting diodes, commonly referred to as LED, have been manufactured for some time now, justifying their lighting parameters to be used for lighting purposes as well. The progressive improvement of the parameters of these components has meant that with the use of these components significant improvements in terms of energy consumption and the luminous efficacy of such arrangements and lighting units with integrated arrangements compared to the use of incandescent and fluorescent lamps as illuminants result.

Light-emitting diodes as a component are offered in various designs. In the classical sense, they include the pn diode with its connection pair. Increasingly, a plurality of pn-type semiconductor diodes are integrated in a compact module with housing, wherein the diodes of the module have either a common or a number of separate terminal pairs. The LEDs contemplated herein include various configurations including one or more pn-type semiconductor diodes, but only one pair of terminals. However, it remains unavoidable to group together several such LEDs, ie to connect them in parallel or in series, so that they work like an LED. Similarly, it is incidental whether and in what way the LED is housed.

At present, the operating power of such LEDs is mainly provided by power supplies which convert the mains voltage to a DC voltage conducive to LEDs, or other DC power sources, e.g. Batteries. Since LEDs are current controlled devices, they must be operated via a current limiting element, a power source, to avoid destruction by excessive current in the event of too low internal resistance of the power supply or battery. For the purpose of this current limitation by increasing the internal resistance of the voltage source, resistors or power sources based on semiconductors are used.

For the operation of LED arrays in lighting units circuits are currently used which include a series and / or parallel connection of the LEDs. Dimming the arrangement is possible by means of control by means of pulse width modulation, the dimming being understood as the modification of the illumination intensity of the LED by changing the pulse / pause ratio of the voltage pulses or their chronological sequence. As is known, the manufacturers usually specify the operating parameters for two different modes of operation, the continuous current for the operating current and for pulse mode the pulse operating current, which is slightly higher than the operating current.

As is known, in the case of pulse width modulation, the duty cycle, ie the ratio of the widths of the two voltage states changing in one cycle, is modified at a constant clock frequency, so that linearly stepless brightness values can be set. A flicker is avoided by setting such a fundamental frequency at which the human eye no longer perceives the individual switching states. This technique is used in particular for the backlighting of displays, eg in mobile phones or cockpit displays, in which a high illuminance is not required and not desired.

In the DE 20 2009 001 708 U1 Dimming of LED arrays is described, which serve the ambient lighting. In order to enable dimming, the LED is driven by voltage pulses, whereby the pulses are modified in particular in their chronological sequence in order to vary the illuminance of the LED. This is done, for example, by means of a pulse width control for generating pulse trains with at least 100 Hz, which allows the individual emitted from the LED light pulses are not perceived as individual flashes, but as a uniform light. It should be noted that the value of the illuminance also includes the brightness sensitivity of the human eye and thus represents not only a photometric but also a physiological size. The illuminance is thus also a measure of the perceived by humans brightness of the arrangement.

In general, illuminance is a key factor in lighting technology and is used as a verification criterion in the computer-aided planning of indoor and outdoor lighting systems. This check of whether a luminaire or a luminaire also reaches the planned values in a specific environment is measured by means of a lux meter. Lux meters contain optical and electronic filters as well as components which suppress the change of the measured values in short time intervals in order to obtain stable measured values, which can also be displayed and also read. Such filters are used for. B. to adjust the detection range of the Luxmeters on certain light sources or only to hide certain frequency ranges of sunlight. Other filters are for certain color temperature ranges used or even to simulate the sensitivity of the human eye for certain spectral colors.

A luxmeter is used to measure the illuminance that describes the amount of luminous flux of a light source that strikes a surface: $$\mathrm{illuminance}\ddot{\mathrm{a}}\mathrm{strength\; E}\left(\mathrm{lx}\right)\mathrm{=}\mathrm{Luminous\; flux\; \Phi }\left(\mathrm{lm}\right)\mathrm{/}\mathrm{Fl}\ddot{\mathrm{a}}\mathrm{<figure-callout\; id="2"\; label="A\; m"\; filenames="imgf0004.png"\; state="\{\{state\}\}">A\; </figure-callout>}\left({\mathrm{m}}^{}\right)\left({\mathrm{}}^{\mathrm{2}}\right)$$

The luminous flux describes the amount of light emitted by a light source in a spherical space surrounding the light source as a whole without consideration of the emission angle. The beam angle, however, has an influence on the surface. The luminous flux in lumens is specified by the LED manufacturers in the data sheet.

By using LEDs that contain a plurality of LED chips with different luminous color in a housing, it is also possible, with appropriate individual control of these chips, the resulting mixed luminous color of the LEDs to adapt to the requirements.

In the operation of LED arrays for illuminating the environment of closed and open spaces, it is generally assumed that for normal operation, ie operation without dimming or color mixing, the highest energy efficiency is achieved in continuous operation of the LEDs based on the operating parameters guaranteed by the manufacturer and gives the highest light output for this arrangement. However, this is contrary to the general demand for reducing the required operating energy of the arrangement. Although dimming causes a reduction in power consumption, but this is always associated with a reduced light output, this method is not considered for many applications to increase energy efficiency.

The invention is therefore based on the object to provide a method for operating an LED array for lighting and also for backlighting, irradiation and signaling or other comparable applications available, which allows a reduction in power consumption of the LED array with undiminished brightness as possible.

In order to achieve the object, a method is described for operating an LED arrangement in which the LEDs of the LED arrangement, via a switching element associated with each LED, have a current source which serves to supply each LED with the constant current predetermined for it during a switch-on state connected and disconnected during a subsequent off state. By means of a control circuit, a clock frequency of an on and off state is set greater than 100 Hz, wherein in the case of two or more LEDs in the LED array whose switching elements are controlled by a control circuit with a uniform clock frequency of an on and off state greater than 100 Hz such in that only a part of the LEDs is always switched on and other LEDs are switched on in two successive switch-on states.

In the case of an LED in the LED arrangement, for which the method according to the invention with correspondingly adapted switching criteria is analogously applicable, and in one embodiment of the method for LED arrangements for more than one LED, such a clock frequency of an A is by means of a control circuit - and off state greater than 100 Hz set that the illuminance in the clocked operation of that in the untimed operation, ie in continuous operation with the predetermined for the LED characteristic operating current, with the predetermined for the LED characteristic operating current by at most 5% deviates. Preferably, the deviation should be at most 2%, most preferably at most 1%.

The operation of an LED array with one or more LEDs with the method according to the invention applicable for different purposes achieves in particular an increase in energy efficiency, lifetime and reliability of the LED array with the same or at least almost the same perceived illuminance compared to the continuous operation of a same Number of LEDs of the same type and with the same operating parameters.

Since only a part of the LED arrangement, at best an LED or LED group or the one LED of the LED arrangement is only temporarily in the on state and yet due to the inertia of the human eye or other physical and physiological effects, the perceived Illuminance of the LED array of the invention corresponds to a conventional LED array in continuous operation, the energy efficiency is significantly increased as set out below.

Due to the mode of operation according to the invention, the individual LEDs or LED groups of the LED arrangement are only in the on state for a short time, so that, in addition, a longer service life of the individual LEDs results. Because as you know, the life of an LED depends on the time in which it is in operation. The theoretical life of the LED array thus results from the multiplication of the lifetime of the individual LEDs, depending on the number of simultaneously operated LEDs.

Another effect of the method according to the invention is the increase in the reliability of the LED arrangement. Since each LED or possibly each LED group are operated via a separate switching element, the LED arrangement continues to operate in the event of a failure of only one LED. A short over The failed LED, which can also lead to a failure of the power source is prevented by the regular shutdown of the defective LED by the switching element. Thus, the assignment of switching elements to the individual LEDs improves the reliability of the LED array. Failures of LEDs, switching elements or circuit parts of the LED array lead due to their lack in the course of the clock only to a more or less noticeable reduction in the illuminance, not the total failure of the LED assembly. A failure of the LED array occurs only if the power source or the control circuit fails. In order to ensure the reliability even with multiple errors, ie the simultaneous failure of an LED and its associated switching element, such higher reliability components can be used or constructed redundantly, which serve the power supply or as a flow control of the LEDs via the switching elements.

Reliability also affects the heat balance of the LED array. The inventive type of driving of the LEDs and the resulting operation with the parameters specified by the LED manufacturer results in a very low heating of the arrangement, since the lower self-heating can be dissipated in any case to the environment. The reduced temperature load also reduces aging processes and a concomitant lowering of the light output of the LEDs.

The method according to the invention is suitable for LED arrangements in various applications. It allows, for example, to illuminate the environment for people in closed and open, eg street spaces, so that an increase in the luminous efficacy as a ratio of the luminous flux received by the LED array electrical power, in particular as a result Reduction of power consumption is possible. Due to the significantly lower energy requirement of the LED arrangement resulting from the constantly recurring switch-off states, a significantly higher light yield results, and this at almost the same illuminance compared to the prior art. The luminous efficacy of a light source is the ratio of the luminous flux to the recorded electrical power (1m / W). It is a measure of the energy efficiency of the light source.

In the method according to the invention, the one or more LEDs of the LED array are operated discontinuously, whereby the conditions of the human eye and the brain are exploited with regard to the perceived illuminance, in order to increase the luminous efficacy and, associated therewith, the energy efficiency, in order to reduce this To achieve power consumption through the LED arrangement.

On the one hand, use is made of the method according to the invention that the human eye is sluggish in its perception of brightness differences. This means that brightness differences are no longer perceived when they occur with a correspondingly high repetition frequency. On the other hand, abrupt transitions between off and on state in the eye produce a significantly higher brightness impression. The latter is known as the flash effect. If the clocked operation with steep pulse edges, such as in flash applications, the brightness impression can be increased by the abrupt brightness changes. The LEDs provide light sources that allow such operation due to their ability to be quickly turned on and off.

In view of the above-mentioned effects on human perception, it is for the impression of brightness and thus irrelevant to the illuminance, whether the light source is continuously switched on or switched on and off with a high repetition frequency. For the energy efficiency of a light source on the other hand, such operation is of great importance, since no operating power is recorded in the off states. Thus, even if the illuminance level is the same or at least 95%, preferably at least 98%, most preferably at least 99%, the illumination intensity will be halved by an LED if the turn-off states are at least as long as the turn-on states.

• Flimmerfreiheit der Anordnung
• Maximale wahrgenommene Beleuchtungsstärke ist nahezu gleich der Beleuchtungstärke der Anordnung bei Dauerbetrieb
• Geringster Verbrauch an Betriebsenergie

und ist leicht durch Versuche für die jeweilige LED-Anordnung zu ermitteln.The timing of the switching operations takes place with a clock frequency which is chosen so high that, depending on the number of successively switched on and off LEDs no flicker of the LED array as a whole results. In addition, it is possible that the perceived illuminance does not drop below a value that is close to at least 95%, preferably at least 98%, most preferably at least 99%, of that illuminance of this LED array in non-pulsed operation. The clock frequency to be set results from the following three optimization criteria:

• Flicker-free arrangement
• Maximum perceived illuminance is nearly equal to the illuminance of the assembly in continuous operation
• Lowest consumption of operating energy

and is easily determined by experiments for each LED array.

The lower limit of the frequency range of about 100 Hz is the one from which the human eye the discontinuous operation no longer perceives as such, ie no flicker is detected. The light flash effect can be used to increase the brightness impression. The upper limit of the frequency range is given by the avoidance of electromagnetic interference by alternating fields, known as EMC.

Thus, it is possible to operate an LED array so that it is practically sufficient, only one of the LEDs of the arrangement or, if the LED array includes only one LED, these only temporarily turn on and still achieve the desired level of illumination than all LEDs would be switched on simultaneously or one LED would be switched on continuously. But since only a few, in the optimal case only one LED per clock is turned on, only the power consumption of this effect. The energy efficiency increases accordingly with the ratio of the total number of LEDs of the LED array to the number of simultaneously switched LEDs. The luminous efficacy increases with the number of LEDs of the LED array as an addition of the luminous efficiencies of the individual LEDs. Limits in the execution of this mode of operation of the LED array with regard to the maximum number of LEDs to be controlled are, inter alia, the dissipation of the heat loss of the respective LED array and the switching times of the LEDs used and other components of the LED array.

According to one embodiment of the method, the LED arrangement can also be operated with pulse operating current. In this case, an operating current which is higher than the characteristic continuous operating current specified by the manufacturer can be fed in via the current source. Therefore, for example, the pulse current guaranteed by the manufacturer can be used for this embodiment variant. The prerequisite for this is that the dynamic power loss of the LEDs and other components is not exceeded. In these Dynamic power dissipation includes, for example, the on-off ratio and the environmental parameters as well as the parameters of the component housing used with regard to the thermal behavior.

This mode of operation leads to a further increase in the brightness due to the higher operating current and also to a brighter flash of light when switching on, whereby the above-described physiological flash effect is enhanced and a higher light output can be achieved.

It is known that the manufacturers usually specify the operating parameters for two different modes of operation, the operating current for continuous operation and the pulse operating current for pulsed operation, which is slightly higher than the operating current. That The operating parameters specified by the manufacturer of LEDs, in particular the operating current, are specified for pulse operation and continuous operation. The life of an LED depends due to the depletion of the semiconductor material, the aging of the diode chip and the phosphor white LEDs, as well as due to material migration processes in the LED structure, significantly on the duty cycle of the LED, the amount of operating currents and thus indicated heating of the semiconductor material as well as the environmental conditions during operation, both mainly determines the operating temperature.

An important parameter for increasing the LED life is the operating current per time. Thus, the method of the present invention, which is applicable to both intermittent and pulsed operation of an LED, has a positive effect on the life expectancy of the LEDs of the LED array. Thus, the reduced duty cycle of the light source in the operation of the invention leads to a lower heating of the LED. In addition, the heat can be released in the off states to the environment. With good heat dissipation can therefore also be used with an increased operating current and thus with improved utilization of the effects mentioned with a higher light output.

As is known, a white LED, comparable but also a colored LED, by utilizing the additive color mixture and using at least one colored or UV LED in conjunction with a photoluminescent material as a phosphor, usually phosphor realized. In addition to the physiological effects mentioned, the afterglow duration and the decay behavior of the excited phosphor also play a role in the brightness impression of the LED arrangement. Thus, it is possible to increase the impression of brightness even by this effect, since at a corresponding selected clock frequency of the off state is bridged by the afterglow of the phosphor, so that the use of this effect increases the positive balance in the light output and energy efficiency. When using LEDs with phosphorescent phosphors, e.g. With persistence times of 10 to 20 ms, this effect can be even more pronounced compared to the usual persistence times of currently 1 to 2 ms.

The energy-related control of LEDs is usually done by power supplies that convert the mains voltage to a positive for LEDs in their height DC voltage. Since LEDs are current controlled devices, they must be powered by a power source to avoid destruction by excessive current flow, such as may occur with a voltage source such as by reducing the internal resistance of the power supply or battery.

The implementation of the clocked operation according to the invention is carried out with a switching element, which is associated with the LED and by short switching times with a control steep pulse edges allowed. This can on the one hand realized a high clock frequency and on the other hand, the switching losses are kept low.

The LED arrangement in one embodiment comprises a control unit which adapts internal parameters to external parameters or vice versa. For example, For example, integrated brightness sensors may enable or disable the LED array depending on the ambient brightness and reduce the operating current provided by the power source. Although the described method initially serves for an LED arrangement in normal operation, it also allows the combination with the dimming of the LED arrangement by means of the control unit in accordance with a method embodiment. In this case, the power source for the LEDs is controlled so that the removable current is changed and the brightness of the LEDs is reduced. In addition, the pulse width modulation or the reduction of the clock frequency can be used for dimming.

Furthermore, a motion detector or presence detector can be integrated, which causes an automatic shutdown of an unneeded LED arrangement when no person is in the immediate vicinity or a reduction in the brightness in the event that the LED assembly is integrated into an emergency lighting system , which is operated by means of a backup battery. In addition, for example, when changing the temperature of the LED array by changing the ambient temperature or self-heating, a system for temperature, ie setting a preferred temperature by water cooling, ventilation or possibly also heating can be activated. For LEDs, it is generally the case that an increase in the LED temperature causes a reduction in the luminous efficacy, if the lower guaranteed operating temperature of the components is not undershot becomes.

In addition, in a further embodiment of the method, the LEDs can be influenced as light sources of the LED arrangement via this control unit. For example, For example, the control unit may include a radio interface for on / off operation or continuous control of the LEDs with regard to brightness or switching times or other additional functionalities. In addition, a programming of the power source with respect to the parameters of the individual LEDs to be controlled so that a reduction in the depth of selection of the LEDs used in the manufacturer of the LEDs is possible without sacrificing the functionality of the LED array, in particular the uniform light emission from the LED Having to accept the order.

The method described above is described for individual or via switching elements in parallel LEDs. Alternatively, instead of one, several or all LEDs per branch, an LED group of a plurality of LEDs connected in series or in parallel can also be used. In this case, the above explanations are analogously applicable to LED groups.

Fig. 1

ein Blockschaltbild einer LED-Anordnung mit mehreren LEDs, die über ihre Schaltelemente einzeln angesteuert werden,

Fig. 2

ein Blockschaltbild einer LED-Anordnung mit mehreren LEDs, die zu Blöcken zusammengefasst angesteuert werden,

Fig. 3

ein Blockschaltbild einer LED-Anordnung mit Fig. 4 mehreren LEDs, die zu Blöcken zusammenfassbar über einen Mikrocontroller angesteuert werden, einen Schaltplan für die Ausführung und den Betrieb eines Schieberegisters,

Fig. 5

einen beispielhaften Signalverlauf für die Ausführungsform, in welcher von einer Mehrzahl von LEDs immer nur eine je Takt eingeschaltet ist, bei dem vom LED Hersteller spezifizierten Betriebsstrom und

Fig. 6

einen beispielhaften Signalverlauf für eine Ausführungsform, in welcher von einer Mehrzahl von LEDs immer nur eine je Takt eingeschaltet ist und die LEDs mit Impulsbetriebsstrom betrieben werden.

The invention will be explained in more detail with reference to embodiments. The accompanying drawings show in

Fig. 1

a block diagram of an LED array with multiple LEDs, which are individually controlled via their switching elements,

Fig. 2

a block diagram of an LED array with multiple LEDs, which are controlled to form blocks,

Fig. 3

a block diagram of an LED array with Fig. 4 a plurality of LEDs, which are controlled to blocks collectively via a microcontroller, a circuit diagram for the execution and operation of a shift register,

Fig. 5

an exemplary waveform for the embodiment in which of a plurality of LEDs is always ON only one per clock is turned on, at the LED manufacturer specified operating current and

Fig. 6

an exemplary waveform for an embodiment in which of a plurality of LEDs always only one per clock is turned on and the LEDs are operated with pulse operating current.

The embodiment of the control of the LEDs of Fig. 1 to Fig. 3 represent only exemplary solutions that differ in their complexity of the respective LED arrangement with regard to the number of controllable LEDs and the integrable control or additional functionalities. All are based on the same operating principle that a certain number of LEDs are powered by a power source configured to provide the manufacturer-specific operating current for the type of LED being used, depending on the application, or one corresponding to the application.

As stated above, LED arrays are known to be operated with a voltage in the low voltage range, according to their characteristic diode characteristics and the manufacturer's specifications in the range of a few volts DC. It follows that the usual mains voltage of eg 110 V or 230 V AC must be converted to the voltage required for the LED arrangement. Suitable for this purpose Methods and devices are well known and are not the subject of the invention.

The LED arrangement according to the block diagram in Fig. 1 includes several LEDs I, which are connected in parallel in the illustrated embodiment via the switching elements E, together with the necessary complementary and not shown in the block diagram components, the three points between the last two LEDs I indicate that more than the LEDs shown I can be included in the circuit.

Alternatively, as mentioned above, with a correspondingly adapted current source D instead of a single LED I connected to a switching element E, an LED group I consisting of a plurality of LEDs I connected in series and / or in parallel can also be used, so that a switching element E is assigned to one LED group I each. In the presentation of the Fig. 1 to Fig. 3 Consequently, an LED symbol would alternatively also be able to stand for a plurality of LEDs I connected in series and / or in parallel, so that the same reference number is assigned to an LED group I as well. When subsequently speaking of an LED, the statements should consequently also refer to such an LED group I. For the sake of clarity, the description is given below by way of example with reference to an LED I per switching element E.

Since LEDs I are current-controlled components, they are operated via a current source D, which is connected to a suitable power supply A. The power supply A serves to supply all the components of the LED array. The power source D supplies a constant current, which is set for each LED I according to the manufacturer's specifications and the application. For the purpose of limiting the current, current sources D are semiconductor-based or, in the simplest case, series resistors are connected in series Voltage source used.

Each LED I is assigned a switching element E, which supports short switching times and a quick change of switching states. In particular, electronic switching elements, e.g. fast thyristors, transistors or MOSFETs. The switching elements are controlled so that in the simplest case only one LED I is in the ON state and with the subsequent switching operation, this LED I off and another LED I is turned on. Alternatively, several of the LEDs I can be switched on at the same time, these being switched off in the subsequent switching operation and other LEDs I being switched on.

The control of the switching elements E by means of a control circuit F, which can be realized in various ways, e.g. by means of a shift register or a runtime generator. With a shift register, which may be formed in the simplest case as a flip-flop, both the off state for only one LED I and any combination of several LEDs I can be realized. In any case, with the use of a shift register with each switching operation, the currently activated LED I changes so that, consecutively or in any order, each of the LEDs I was switched on and the remaining time is switched off. In addition, a shift register and incidentally, a runtime generator is easy and inexpensive to implement.

The timing of the switching operations by means of a clock generator G as a clock whose clock frequency is chosen so high that, depending on the number of successively switched LEDs I no flicker of the LED array as a whole results and the illuminance, as with the wavelength-dependent Hellempfindlichkeitsfunktion of the human eye and with the spectral radiant flux evaluated at the maximum of the photometric radiation equivalent, does not fall below a value which corresponds almost to the illuminance of this LED array in the non-pulsed mode.

The LED device according to the embodiment further comprises a control unit B which adapts internal parameters to external parameters, e.g. the ambient brightness via the activation or deactivation of the LED array or the reduction of the operating current, which is provided by the power source D. In addition, a programming of the current source D with respect to the parameters of the individual LEDs to be controlled I take place. Other functionalities, such as motion detectors or presence detectors or systems for controlling the temperature of the LED array can also be integrated.

Likewise, it is possible via the control unit B to influence the LEDs I as light sources of the LED arrangement. For example, For example, the control unit B may comprise a radio interface for the on / off operation or the continuous control of the LEDs I with regard to brightness or switching times or other additional functionalities. A combination of the method according to the invention with the known pulse width modulation of the clock generator G for dimming the LED arrangement is possible via the control unit B.

Conversely, parameters for operating the LED array that do not directly relate to the LEDs I and their arrangement with one another and are referred to herein as external parameters may be determined by the internal, i.e., the external, parameters. be influenced by the LEDs I parameters determined by the control unit B. Thus, e.g. a programming of the current source D with respect to the parameters of the individual LEDs to be controlled I done.

Based Fig. 1 For the example of six LEDs I, the energy efficiency achievable with the method according to the invention should be achieved the LED array compared to the continuous operation can be determined.

• Lichtstrom 100 lm
• Betriebsstrom 350 mA
• Spannung 3,4V

A type of LEDs I with the following operating parameters is used as a basis:

• Luminous flux 100 lm
• Operating current 350 mA
• Voltage 3,4V

• Aufgenommene Betriebsleistung: 6 * 350 mA * 3,4 V = 7,4 W $$\mathrm{Energieeffizienz}=\mathrm{Lichtstrom}/\mathrm{Betriebsleistung}$$
  
  $$\mathrm{Energieeffizienz}\mathrm{=}\mathrm{6}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}\mathrm{7}\mathrm{,}\mathrm{4}\mathrm{W}\mathrm{=}\mathrm{81}\mathrm{lm}\mathrm{/}\mathrm{W}$$
  

In continuous operation, the following energy efficiency results:

• Recorded operating power: 6 * 350 mA * 3.4 V = 7.4 W $$\mathrm{energy\; efficiency}=\mathrm{Luminous\; flux}/\mathrm{operating\; power}$$
  
  $$\mathrm{energy\; efficiency}\mathrm{=}\mathrm{6}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}\mathrm{7}\mathrm{.}\mathrm{4}\mathrm{W}\mathrm{=}\mathrm{81}\mathrm{lm}\mathrm{/}\mathrm{W}$$
  

• Aufgenommene Betriebsleistung: 350 mA * 3,4 V = 1,19 W $$\mathrm{Energieeffizienz}\mathrm{=}\mathrm{6}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}\mathrm{1}\mathrm{,}\mathrm{19}\mathrm{W}\mathrm{=}\mathrm{504}\mathrm{,}\mathrm{2}\mathrm{lm}\mathrm{/}\mathrm{W}$$
  

According to the inventive method with only one LED in the on state per clock results in the following energy efficiency:

• Recorded operating power: 350 mA * 3.4 V = 1.19 W $$\mathrm{energy\; efficiency}\mathrm{=}\mathrm{6}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}\mathrm{1}\mathrm{.}\mathrm{19}\mathrm{W}\mathrm{=}\mathrm{504}\mathrm{.}\mathrm{2}\mathrm{lm}\mathrm{/}\mathrm{W}$$
  

• Aufgenommene Betriebsleistung: 16 * 350 mA * 3,4V = 19,04W $$\mathrm{Energieeffizienz}\mathrm{=}\mathrm{16}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}7\mathrm{,}4\mathrm{W}\mathrm{=}\mathrm{84}\mathrm{lm}/\mathrm{W}$$
  
  
  und nach erfindungsgemäßem Verfahren:
• Aufgenommene Betriebsleistung: 350 mA * 3,4 V = 1,19 W $$\mathrm{Energieeffizienz}\mathrm{=}\mathrm{16}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}1\mathrm{,}19\mathrm{W}\mathrm{=}1.344,5\mathrm{lm}/\mathrm{W}$$
  

For LED mounting with 16 white LEDs, the following values result in continuous operation:

• Recorded operating power: 16 * 350 mA * 3.4V = 19.04W $$\mathrm{energy\; efficiency}\mathrm{=}\mathrm{16}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}7\mathrm{.}4\mathrm{W}\mathrm{=}\mathrm{84}\mathrm{lm}/\mathrm{W}$$
  
  
  and according to the method of the invention:
• Recorded operating power: 350 mA * 3.4 V = 1.19 W $$\mathrm{energy\; efficiency}\mathrm{=}\mathrm{16}\mathrm{*}\mathrm{100}\mathrm{lm}\mathrm{/}1\mathrm{.}19\mathrm{W}\mathrm{=}1344.5\mathrm{lm}/\mathrm{W}$$
  

With increasing LED number of the LED arrangement results in the operation of the invention thus a significant increase in Efficiency compared to a continuous operation of the LEDs.

In Fig. 2 an alternative embodiment is shown, in which the operation of an LED array is shown, which comprises a large number of LEDs I. In this case, in each case a plurality of LEDs I connected in parallel, each having a switching element E, are combined into a block and the blocks are comparable to the individual LEDs I in the exemplary embodiment Fig. 1 by means of the control circuit F, also a shift register controlled. In order nevertheless to be able to individually control the switching elements E and thus the LEDs I, a decoder K is interposed for each block. This converts the switching signal of the register position of the shift register F assigned to the respective decoder K into individual signals for each switching element E of the block.

Fig. 3 shows a single control of the LEDs I by means of microcontroller H. The microcontroller H takes over various functions, such as the functions of the clock generator G, the decoder K, and other important for the operation tasks, such as the control of a bus decoder and / or the individual setting of the power source D corresponding to the respective individual LEDs I or group of LEDs I. Also, a variation of the operating current of individual LEDs within the manufacturer parameters is possible. Thus, the individual switching elements E or a large number of LEDs I via bus decoder L can be controlled separately, so that any change of the on and off states between the individual LEDs I, but with the characteristic for the LED array clock frequency can be done and this parameter as well as others can also be stored and varied.

By means of microcontroller but also with other embodiments of the control circuit can according to an embodiment of the method on their operating current and / or the number of their turn-on states are controlled such that when using LEDs of different colors in the LED array and driving the corresponding color LEDs, a defined mixed color is set. By way of the different number of switch-on states of the different LEDs, ie their number of clock cycles in which the individual LEDs are switched on, in comparison with one another, a mixed color can be selectively adjusted by measurement or calculation. Additionally or alternatively, the brightness of the individual LEDs and thus their proportion of the mixed color over the operating current are still variable, so that as a result, the resulting mixed color special requirements (eg high daylight similarity according to CRI color rendering index) is customizable.

The programmability of the drive in this embodiment of the method also makes it possible that a main LED array can be extended by using the bus decoder L with spatially separated remote sub-assemblies. These are then operated as an extension of the shift register in the main LED array and further improve the energy efficiency of the device.

By using a microcontroller H in the LED array, certain types of failures in the LED array can also be detected, e.g. B. increasing the current flow in a branch of the arrangement, which consists of LED I and switching element E and it can, if present, redundant branches of the LED array take over their function.

In Fig. 4 is a simple design of the control circuit F in the form of a shift register and its connection with the LEDs I via the switching elements E and the power source D and the clock generator G shown. Other components of the LED arrangement are for better clarity because of Fig. 4 not shown.

The shift register F is made up of the individual, in Fig. 4 separately represented register locations SR1, SR2, etc. to SRN together, where n is the number of parallel to be controlled in succession LEDs I. The output of each register location SR1, SR2... SRN is connected to a switching element E, eg a MOS-FET, which switches the respectively assigned LED I on and off. By means of the current source D, the LEDs I are supplied with the respective constant current specified by the manufacturer. The timing of the switching operations is performed by a suitable clock generator G.

As is known from a shift register, the individual register locations are connected in series and their outputs are decoded such that the signal of a register location SR1, SR2... SRN, which implements the on or off state for the associated LED I, is applied to each clock moves the adjacent register location SR1, SR2 ... SRN in one direction. The embodiment according to Fig. 4 provides the possibility of measuring the output signal of each switching element E at the measuring points A1, A2, ... An, which is the input signal of the associated LED I.

Fig. 5 sets the resulting waveform according to the supply voltage U as a function of time at different points of the circuit according to Fig. 4 The signal course U _G (t) indicates the clocking superordinate from the clock generator G with a constant signal duration for the on state t _i and a very short off state t _p of about 1-2% of t _i and continuous change of this state, during the signal duration of the switch-off state tp always switch off all the switching elements E the LEDs I and the transition from one LED to the next takes place.

The register locations SR1, SR2... SRN of the memory register are assigned such that at a defined time a first LED I is connected to the current source D and all other LEDs I are separated, as shown by way of example in the signal curves U _SR1 (t), U _SR2 (t) and U _SR3 (t) and confirmed at the associated measuring points A1, A2 and A3. During the off state, the switching state of the first register location SR1 is transferred to the next register location SR2 and the content of the register location SR1 is set to zero. As a result, exactly one LED I is always switched on alternately and all others are switched off, then another is switched on and all the others are switched off again. This process is repeated continuously until each of the LEDs I was turned on once and the process starts again.

Fig. 6 provides a waveform analogous to that in Fig. 5 but applied to the pulsed operation of the LEDs I of the LED array. Accordingly, the LED array is fed with a pulse operating current specified by the LED manufacturer that is higher than the operating current (in Fig. 6 not shown).

To set the ratio of the on and off state of the higher clock of the clock generator G is also set with a constant signal duration for the on state t _i and the off state t _p , in which case the on state t _{i is} significantly shorter than the off state t _p . The higher clock of the clock generator is adapted to the requirements of the pulse mode (not shown). Accordingly, the illustrated waveform U _G (t) and the other signal waveforms shown. From these, in turn, the switching states, as above to Fig. 5 described, but with shorter switching times.

Due to the shorter switch-on times of the LEDs (I) compared to the representation in Fig. 5 it is possible to operate the LEDs I with pulse operating current without exceeding the dynamic power dissipation of the LEDs I and the other components, but still a higher perceived Illuminance of the LED array to achieve, as if it is operated with the manufacturer-specific operating current of the LEDs. Alternatively, as described above, more than one LED I can be switched on at the same time.

Fig. 5 and 6 It can be seen that the individual LEDs I are operated only with very short turn-on, followed by long turn-off states, which serve for recovery of the components involved and also for heat dissipation, It can be seen that the length of these turn-off states directly with the number of in the Arrangement used LEDs I related. Ie. in an LED arrangement with six LEDs I and a switched-on LED I, each of the LEDs I is only switched on again after all the remaining five LEDs I have also passed through their on and off states.

LIST OF REFERENCE NUMBERS

A

power supply

B

control unit

D

power source

e

switching element

F

Control circuit, shift register, runtime generator

G

clock generator

H

microcontroller

I

LED, LED, LED group

K

decoder

L

Busdekoder

SR1 ... SRn

Register location 1 ... n

A1 ... An

Measuring point at the output of the switching element 1 ... n

t _i

Signal duration of the switch-on state

t _p

Signal duration of the switch-off state

t _mos

Signal duration of the signal measured at a measuring point

Claims (12)

Method for operating an LED arrangement for illumination, backlighting, irradiation or signaling, which comprises at least two light emitting diodes, hereinafter referred to as LEDs (I), which by means of a current source (D) supplied with the constant current for the LEDs (I) and be operated with clocked control signals, characterized in that the LEDs (I) of the LED array via each one LED (I) associated switching element (E) connected to the power source (D) during a power-on state and during a subsequent off state again from the current source (D) are separated, wherein the switching elements (E) by means of a control circuit (F), which is operated with a uniform clock frequency greater than 100 Hz, switched off and on, that always only a part of the LEDs (I) turned on is and in two successive switch states each other LEDs (I) are turned on. Method for operating an LED arrangement according to claim 1, characterized in that the control circuit (F) comprises at least one shift register or a delay generator for controlling the switching elements (E). Method for operating an LED arrangement according to one of claims 1 or 2, characterized in that a plurality of parallel and / or in series LEDs (I) are combined into a block whose control is done separately and independently of the control of the remaining LEDs (I). Method for operating an LED arrangement according to one of Claims 1 to 3, characterized in that the LED arrangement comprises LEDs (I) of different color and such LEDs (I) are controlled by their operating current and / or the number of their turn-on states such that that a defined mixed color is set. Method for operating an LED arrangement according to one of claims 1 to 3, characterized in that in each ON state only one LED (I) is turned on. Method for operating an LED arrangement according to one of the preceding claims, characterized in that such a clock frequency of an on and off state is set greater than 100 Hz, that the illuminance in the clocked operation of that in the untimed operation with that for the LEDs (I) given characteristic operating current deviates by more than 5%. Method for operating an LED arrangement for illumination, backlighting, irradiation or signaling, which comprises at least one light emitting diode, hereinafter referred to as LED (I), which by means of a current source (D) supplied with the constant current for the LED (I) and is operated with clocked control signals, characterized in that the LED (I) of the LED array via at least one of the LED (I) associated switching element (E) to the power source (D) connected during a power-on state and separated again during a subsequent off state is, by means of a control circuit (F), such a clock frequency of an on and off state greater than 100 Hz is adjusted so that the illuminance in the clocked operation of that in the un-clocked operation with the specified for the LED (I) characteristic operating current deviates by more than 5%. Method for operating an LED arrangement according to one of the preceding claims, characterized in that the control circuit (F) comprises a microcontroller (H) for controlling the switching element (E) or the switching elements (E) or the current source (B). Method for operating an LED arrangement according to one of the preceding claims, characterized in that the LED arrangement is operated with pulsed operating current which is greater than the characteristic for the LED (I) or LEDs (I) operating current. Method for operating an LED arrangement according to one of the preceding claims, characterized in that by means of a control unit (B) the control of all switching elements (E), the power source (D) or the control circuit (F) or more of these components for each switching element ( E) is changed together or separately due to external or internal parameters. Method for operating an LED arrangement according to Claim 10, characterized in that the operating current provided by the current source (D) is modified by means of a control unit (B). Method for operating an LED arrangement according to one of the preceding claims, characterized in that an LED (I) is replaced by an LED group of a plurality of LEDs connected in series or in parallel (I).

Images