WO2013092455A1

WO2013092455A1 - Led converter with pwm pulses with stabilised amplitude

Info

Publication number: WO2013092455A1
Application number: PCT/EP2012/075704
Authority: WO
Inventors: Thomas KÜNG; Ueli Keller
Original assignee: Tridonic Gmbh & Co Kg
Priority date: 2011-12-19
Filing date: 2012-12-17
Publication date: 2013-06-27
Also published as: EP2795997A1; DE102011088977A1

Abstract

In a first aspect, the invention provides an LED converter for the control of at least two LED channels, wherein the LED converter supplies the LED channels with a cyclically increasing and then decreasing LED current by means of high-frequency switching processes, and wherein the LED converter is designed to perform the high-frequency switching processes during a switch-on duration of comparatively low-frequency pulses, particularly PWM pulses, to detect the temporal mean value of the LED current or a parameter reflecting same in an LED channel at least at certain times during the switch-on duration of a pulse, and to lengthen a rising edge of the LED current of the LED channel in a later, preferably immediately subsequent pulse, if the detected temporal mean value has deviated from a specified setpoint mean value, preferably by more than a specified threshold differential value.

Description

LED CONVERTER WITH PWM PULSE WITH STABILIZED AMPLITUDE

The present invention generally relates to the operation of light-emitting diodes (LEDs), light-emitting diodes being understood to mean inorganic light-emitting diodes, but also organic light-emitting diodes (OLEDs). In the following the term LED is used as an example. Light-emitting diodes or semiconductor light sources have become increasingly interesting for lighting applications in recent years. The reason for this is u.a. Significant progress has been made in both the brightness and light efficiency of the LEDs. The comparatively long life of the LEDs compared to conventional light sources, such as incandescent or gas discharge lamps, is also advantageous.

It is known that the light emission of an LED correlates with the current flow through the LED. to

Therefore, for brightness control (dimming) LEDs are preferably operated in a mode in which the current flow is controlled by an LED. To control this example, high-frequency clocked switching regulator, eg buck converter (step-down or buck converter) are used, which are for example part of an LED converter. A control unit controls, for example, a high-frequency clocked switch, for example a power transistor, in which LED converter on. In the switched-on state of the switch, current flows through at least one LED and a coil, whereby the coil is charged thereby. The cached energy of the coil discharges in the off state of the high-frequency clocked switch via the LED. When the switch is switched on, the current through the LED shows a rising edge for the LED current; when the switch is switched off, this results in a falling edge. The time average of the LED current represents the RMS current through the LED and is a measure of the brightness of the LED. By appropriate timing of the high-frequency clocked switch so the average effective current can be controlled. By controlling the high-frequency clocked switch therefore a desired average current flow through the LED, due to the high frequency switching on and off of the switch (typically in the range above 10 kHz, for example. 100kHz), and the temporal fluctuation of the current set.

In order to keep the emitted light spectrum as constant as possible during operation, it is further known not to vary the current amplitude for a brightness control (dimming) of LEDs, but to use a pulse width modulation method (PWM). For this purpose, the LED converter of a control gear in comparison to the above-mentioned timing low-frequency pulses (typically having a frequency in the range of 100 to 1000 heart) supplied with a variable duty cycle, which thus low-frequency modulate the high-frequency clocking, so the LED converter performs the above-described RF timing only during the turn-on period of the PWM pulses.

In Fig. 1 is an example of a basic circuit according to the invention an LED converter 1 with a buck converter for the operation of at least two LEDs, preferably three LEDs shown. Of course, instead of a buck converter, another clocked converter with or without electrical isolation, eg a flyback converter, can be used to generate the high-frequency switching operations. About at least two LED channels 3, 4, preferably three LED channels 3, 4, 5, the LEDs (or more series-connected LEDs) of the LED converter 1 with LED currents I _{LE D} I, I _{LE D} 2, or supplied with LED currents I _{LE D} I, I _{LE D} 2, I _{LE D} 3.

A provided for generating the low-frequency pulses operating device 10 is also shown in Fig. 1. For example, a dimming value and / or a color value can be supplied to the operating device 10 as input values which can represent desired values for the light to be set by the LEDs, which then internally converts the operating device into PWM pulses with a variable duty cycle. In particular, the operating device 10 may change the low-frequency PWM pulses, or a t_on_nf and a t_off_nf time for these pulses, e.g. to set a dimming value and / or a color value. Additionally or alternatively, the operating device 10 can also transmit amplitude information to the LED converter 1, if instead of or in addition to the pulse width modulation

Pulse amplitude modulation is to be used. The LED current within a low-frequency pulse, ie the LED current during the switch-on of an LED channel 3, 4, 5, is superimposed by high-frequency pulses (ripple), which are generated by the high-frequency switching operations.

This is shown schematically in FIG. A brightness of the LEDs can now be controlled by the frequency of the low-frequency pulses and the LEDs can be dimmed, for example, by changing the time interval between the low-frequency pulses, a ratio between the duty cycle t_on_nf and a switch-off duration t_off_nf, or shortening the duty cycle t_on_nf becomes. 2 shows by way of example the course of a current I _D through an LED. A low frequency pulse turns on the LED current I _D for the LED during a period F _D for a duty cycle t_on_nf and off for a turn off time t_off_nf, while a high frequency PWM switching signal varies the AI _D by the desired time average for the LED current generated by the LED.

The operating method described so far or the circuit used therefor can also be maintained within the scope of the invention.

The present invention now relates to the LED converter 1, with a plurality of LED channels 3, 4, 5, which are used in particular for driving different colored LEDs (eg RGB LEDs or RPB LEDs, where R is a red, G for a green, B for a blue and P for a blue LED may be provided, the latter being provided with a color conversion layer, eg a phosphor layer). In particular, the LED channels 3, 4, 5 are thus LED color channels.

When using the LED converter 1 with multiple LED channels 3, 4, 5, however, the problem arises that the LED channels 3, 4, 5 influence each other unintentionally. If, for example, during the switch-on of a first LED channel 3, a second second LED channel 4 is turned on, so driving two LEDs, each with a low-frequency pulse via one of the LED channels 3, 4, takes place, the amplitude of the remains LED current, which was generated by the respective low-frequency pulse on eg the second LED channel is not constant as desired, but changes temporarily and breaks in particular. This type of disturbance is also referred to below as "crosstalk".

This effect is disadvantageous in particular because it causes the emitted light spectrum to fluctuate during operation. It is therefore an object of the invention to overcome this disadvantage.

This object is achieved by an LED converter, a method and an integrated circuit according to the independent claims. The dependent claims further advantageously form the central idea of the invention. The invention therefore provides, in a first aspect, an LED converter for driving at least two LED channels, wherein the LED converter supplies the LED channels with high-frequency switching operations with a cyclically rising and then falling LED current, and wherein the LED Converter is designed to perform the high-frequency switching operations during a duty cycle of comparatively low-frequency pulses, in particular PWM pulses, in an LED channel at least temporarily during the duty cycle of a pulse the time average of the LED current or a parameter reproducing this and to extend a rising edge of the LED current of the LED channel in a later, preferably the immediately following pulse, when the detected time average, preferably more than a predetermined threshold difference value has deviated from a predetermined desired mean value.

The LED converter can have a control unit which is set up to detect the time average of the LED current or the parameter representing it on an LED channel during the switch-on period of a low-frequency pulse.

The control unit can be set up to detect a deviation of the detected time average of the LED current or of the parameter representing this from the desired mean value. Switch-on times and / or the duty cycle of the low-frequency pulses on the LED channels can be known to the control unit and / or transmitted to the control unit.

The control unit may be configured to sample the LED current on the LED channel based on the switch-on times and / or the switch-on duration of the low-frequency pulses on a different LED channel and / or the time average of the LED current or the parameter representing it on the LED channel.

The control unit may be configured to detect an amplitude dip of the LED current on the LED channel.

The control unit may be configured to change the duty cycle of the high-frequency switching operations as a function of the detected mean value.

The control unit may be configured to continuously sample the low-frequency pulses.

The control unit may be an integrated circuit and in particular a microcontroller.

Further, in another aspect, the invention provides a method of driving at least two LED channels through an LED converter, wherein the LED converter transmits the LED channels by high frequency switching with a cyclically rising and then decreasing LED current supplied, and wherein the LED converter performs the high-frequency switching operations during a duty cycle of comparatively low-frequency pulses, in particular PWM pulses, in an LED channel, at least temporarily during the ON period of a pulse, the time average of the LED current or this detects the reproducing parameter, and extends the rising edge of the LED current of the LED channel in a later, preferably the immediately following pulse, when the detected time average, preferably more than a predetermined threshold difference value has deviated from a predetermined desired average.

Finally, the invention provides an integrated circuit, in particular a microcontroller, which is designed and / or programmed to carry out a method as described above.

The invention will be described in more detail below with reference to the drawings.

Show it:

Fig. 1 shows schematically an arrangement with an LED converter according to the invention.

Fig. 2 shows schematically a LED current during the

Duty cycle, i. during the low-frequency

Pulse, by Dchfreque switching operations increases cyclically and then drops. Fig. 3 a) schematically shows a pulse transmitted on a first LED channel; b) schematically a pulse transmitted on a second LED channel, wherein the amplitude of the LED current is influenced by the pulse on the first LED channel; c) schematically a pulse transmitted on a third LED channel, wherein the amplitude of the LED current is influenced by the pulses on the first and second LED channel.

Fig. 4 shows schematically the pulses of Fig. 3 a) -c) with superimposed ripple.

Fig. 5 shows schematically the pulses of Fig. 3 a) -c) with

Measuring points, or measuring times, for recording a time average.

Fig. 6 shows schematically the pulses of Fig. 3 a) -c) with superimposed ripple, wherein in b) and c) respectively rising flanks of the high-frequency

Switching operations generated LED current, are shown extended.

Fig. 7 schematically corrected pulses on the LED channels.

As already described above, FIG. 1 shows an LED converter 1 according to the invention which supplies at least two LED channels 3, 4 each with one LED current I _{LE D} I, I _{LE D} 2, but in particular three LED channels 3, 4 , 5 with LED currents I LEDl _/ IL 2 _/ IL CONTINUED. In one embodiment, the LED converter 1 has a first control unit 20 and a second control unit 2. The first control unit 20 clocks a switch in a converter 21, which is fed from a mains voltage or a DC voltage. If necessary, the converter 21 feeds via an electrical isolation 25 (eg, a transformer) an electrical energy store 22 which has one switching regulator stage or preferably a plurality of parallel switching regulator stages 23a, 23b, 23c, each for one of the plurality of LED channels.

The second control unit 2 is in particular adapted to the two LED currents I _{LE D} I _/ I _{LE D} 2 and the three LED currents I _{LE D} I _/ I _{LE D} 2, I _{LE D} 3 on the two LED channels 3, 4 or the three LED channels 3, 4, 5 temporarily, that is to be detected in a time division, possibly with even more tasks. Thus, for reasons of the available resources of the control unit (preferably a microcontroller), it is not the current amplitude of several LED channels that is detected simultaneously, but always only one amplitude section of a single channel at any given time. The LED converter 1 can for controlling the LED channels 3, 4, 5 only have a common switching regulator stages or as shown also separate switching regulator stages 23a, 23b, 23c, each one switching regulator can feed an LED channel. The switching regulator can, for example, by a

Buck converter (step-down or buck converter) are formed. The individual LED channels are thus preferably each driven by a switching regulator stage, and this switching regulator stage is clocked to adjust the LED current of the associated channel accordingly by the second control unit 2. Each switching regulator stage 23a, 23b, 23c typically has at least one switch 24a, 24b, 24c which is actively activated, ie actuated by the second control unit 2, and a buffer (not shown), for example an inductance, which is triggered by the timing of the switch 24a, 24b , 24c is specifically loaded and unloaded. These individual parallel-connected switching regulator stages 23a, 23b, 23c are preferably fed from the common electrical energy store 25 (for example, capacitor). The common energy store can in turn preferably be connected by a converter stage 21, which is thus common for all LED channels 3, 4, 5. This upstream converter stage 21 can be:

an AC-DC converter such as an actively clocked PFC circuit such as a flyback converter, or

- a DC-DC converter like a series resonant

Half-bridge converter with potential separation.

The problem solved by the invention arises from the said parallel connection of several switching regulator stages for the independent feeding of several LED channels 3, 4, 5, namely, when the switches 24a, 24b, 24c of the switching regulator stages 23a, 23b, 23c are activated for different lengths, and For example, the detection of the control loop of the LED current through the second control unit 2 is relatively slow or else only a sampling of the LED currents by the second control unit 2 at certain times takes place (eg when using a microcontroller as the second control unit 2). By switching on at least one additional switch of a parallel switching regulator stage, the energy store, which has only a limited capacity and, for example, is recharged by the upstream converter due to a limited fast control loop, not immediately provide the required energy, but it can cause a drop in the current one or more LED channels come. To prevent this, according to the invention, the duty cycle or the turn-on time of the switches is adapted to parallel switching regulator stages.

It is to be understood that the method can also be used for only two LED channels or for more than three LED channels.

Based on detected LED current samples ("samples") for the LED currents I _{LE D} I _/ I _{LE D} 2, I _{LE D} 3 on the LED channels 3, 4, 5, the control unit 2 is adapted to a switching behavior of the In this way, for example, the rising edge of one or more of the LED currents I _LED i, I _{LE D} 2 _/ I _{LE D} 3 _/ caused by the high-frequency pulses can be influenced by a high-frequency switching operation in a subsequent PWM switch-on pulse of the respective LED channel can be generated on the LED channels 3, 4, 5 are extended.

As already mentioned, the control unit 2 of the LED converter 1 detects, at least at times during the switch-on period of the low-frequency PWM pulses, samples Ml ', M2', M3 ', M3''of the LED currents I _{LE D} I, I _{LE D} 2, I _{LE D} 3 on the LED channels 3, 4, 5 (or these reproducing parameters), but at least on at least two LED channels 3, 4. The samples directly or indirectly represent the time average of the respective LED current.

On the basis of the detected time averages Ml ', M2', M3 ', M3' ', the control unit 2 changes the high-frequency switching operations in a respectively following PWM cycle ("cycle-to-cycle") so that a rising edge of at least one LED Current I LEDI, I LED2, I LED3 on at least one of the two / three LED channels 3, 4, 5 is changed.

The influencing of the high-frequency switching operations by the control unit 2 for generating the extended rising edge of the at least one LED current I _{LE D} I _/ I _{LE D2} , I _{LE D} 3 is performed in particular by the LED converter 1, if one of the for the respective LED current I _LED i, I _{LE D} 2 _/ I _LE deviates _D 3 detected time averages Ml ', M2', M3 ', M3''is preferably more than a predetermined Schwelldifferenzwert from a predefined target average Ml, M2, M3 ,

In particular, it is provided that the control unit 2 only then averages Ml ', M2', M3 ', M3''of the LED currents I _LED i, I _{LE D} 2 _/ I _{LE D} 3 on the LED channels 3, 4, 5 determined when a low-frequency pulse is switched on at least two LED channels, as in particular then a crosstalk of an LED channel can be done on another LED channel. For this purpose, the control unit 2 is aware of or is supplied with the switch-on times of the low-frequency pulses for each LED channel 3, 4, 5. Crosstalk from the first LED channel 3 to the second LED channel 4 is shown by way of example in FIG. In Fig. 3 low-frequency pulses for the three LED channels 3, 4, 5 are shown. In this case, a low-frequency pulse on the first LED channel 3 (FIG. 3 a)) influences a low-frequency pulse on the second LED channel 4. This influencing results, for example, in an amplitude dip or some other disturbance on the second LED channel 4, as it does by way of example in FIG. 3b). The pulses on the first and second LED channel 3, 4 then continue to act on a pulse on the third LED channel 5 and affect this as well. This leads, as shown schematically in FIG. 3 c, to at least one amplitude dip on the third LED channel 5.

The aim of the invention is therefore to compensate for the interference caused by crosstalk. In particular, the invention proposes each one

High-frequency pulse, ie a turn-on time t_on_hf the high-frequency switching operations, to extend or shorten and thus counteract the interference that occurs periodically. The control unit 2, which can be implemented as an integrated circuit, in particular as a microcontroller or ASIC, and which influences the high-frequency switching operations and thus the switch-on time t_on_hf, can exploit the fact that the faults always occur occur with the same periodicity, namely when switching on the low-frequency pulses.

This is particularly advantageous because a single pulse control (peak control) for each

High-frequency pulse can not be done by the control unit 2, since the resolution behavior of the control unit 2, and their performance is limited. In particular, continuous monitoring of the currents on the individual LED channels 3, 4, 5 by the control unit 2 is not possible. However, since the control unit 2 is able to control the current values, i. To periodically check the amplitudes of the low-frequency pulses, a disturbance on an LED channel 3, 4, 5 can be compensated on the basis of the determined measured values of a plurality of low-frequency pulses.

In order to achieve the desired time average for the respective LED current I _{LE D} I _/ I _{LE D} 2, I _{LE D} 3 by the respective LED, therefore, the individual low-frequency pulses for which a disturbance due to crosstalk, eg an amplitude dip, was detected by the control unit 2 (eg by periodic averaging), compensated by a targeted (individual) change of individual high-frequency pulses generated by the high-frequency switching operations.

In this case, the calculation of the compensation can be performed as a control loop and due to the control of the other LED channels 3, 4, 5, in particular without Feedback, done. It is also possible to use algorithms from adaptive filter technology (eg an LMS algorithm) for the calculation. Consequently, to compensate for the temporary break in an amplitude of the respective LED current I LEDI, I LED2, I LED3 generated during the switch-on time t_on_nf of a low-frequency pulse, the switch-on time t_on_hf of the high-frequency pulses is changed, in particular increased.

FIG. 4 shows, for example, that when the amplitude on the second LED channel 4 drops, as shown in FIG. 4b), the desired average value M2 can not be achieved, but only the mean value M2 'for the LED current I _{LE D} 2 is reached (there is no crosstalk on the first LED channel 3, the detected mean time Ml 'therefore corresponds to the desired time average Ml for the LED current I _{LE D} I _/ see FIG. Accordingly, the desired mean value M3 for the LED current I _{LE D} 3 is not reached on the third LED channel 5, as shown in FIG. 4c), but only the mean value M3 'or the mean value M3 ". By controlling individual high-frequency pulses, the rising edge of the respective LED current I _{LE D} I, I _{LE D} 2, I _{LE D} 3 thus be extended in a subsequent low-frequency pulse when the detected time average deviates from a desired time average. For this purpose, a threshold value can be specified, upon reaching which the change or extension of the rising edge of the current on the LED channel 3, 4, 5 takes place.

Thus, in the sense of an iteration and in succession for each of the LED channels 3, 4, 5, an adaptation of the rising edges of the respective LED current I _{LE D} I, I _{LE D} 2, I _{LE D} 3 made. That is, in a first step, the effect of crosstalk on a different LED channel is evaluated. After knowing this evaluation, the duty cycle t_on_hf of the high-frequency pulses is correspondingly increased in the next step. This process is then preferably carried out for each LED channel 3, 4, 5 until a deviation from the respective desired average value Ml, M2, M3 on the LED channels 3, 4, 5 is below a predetermined threshold value. If this is achieved, the readjustment or compensation ends. The achievement, or the exceeding / falling below the threshold value can thus represent a termination criterion. Typically, about ten iteration steps are performed to achieve sufficient compensation for crosstalk interference. Of course, it is also possible for a control unit 2 to require more or fewer iteration steps, depending on its performance. If, for example, the control unit 2 is more powerful and therefore more accurate information about the LED current profile on the LED channels 3, 4, 5 can be determined in a shorter time, it is possible to achieve a faster compensation by the control unit 2 reacting faster and the high-frequency pulses are adjusted accordingly. Thus, the invention only requires that the effects of the amplitude collapse can be detected. Of course, this is possible by a "continuous" sampling of the current waveform of the LED currents I _{LE D} I, I _{LE D} 2, I _{LE D} 3 over the respective total duty cycle t_on_nf by the control unit 2.

Since the control unit 2 generally knows the switch-on times t_on_nf for the low-frequency pulses on the LED channels 3, 4, 5, it is possible in a further embodiment of the invention to determine the number of sampling points or the measuring points necessary for detecting a time average , or measuring times, to reduce the LED current waveforms. Thus, the control unit 2 must check a current amplitude on one of the LED channels 3, 4, 5 only during the switch-on time t_on_nf of a low-frequency pulse on another LED channel 3, 4, 5.

This is shown schematically in FIG. 5. In the presence of a low-frequency pulse on the first LED channel 3, as shown in Fig. 5a), a change in the amplitude of the LED current I _{LE D} 2 on the second LED channel 4 (see Fig. 5b)) only to the time at which the low-frequency pulse on the first LED channel 3 is active. Therefore, for example, an LED current value IM2 for the LED current I _{LE D} 2 must be determined only during the switch-on time t_on_nf of the low-frequency pulse on the first LED channel 3 in the second LED channel 4. Analogously, it is sufficient to determine a measured value for the LED current I _{LE D} 3 during the time on the third LED channel 5, as shown in FIG. 5 c, during the time on at least one other LED channel 3, 4 low-frequency pulse is present. Thus, for example, it is sufficient to have a measured value I _M 3, I for the LED current I _{LE D} 3 on the third LED channel 5 and / or a second measured value I _M 3, 2 for the LED current I _{LE D} 3 the third LED channel 5 to detect a time average, or to detect the effects of crosstalk. The measurements must then take place in each period only at these measuring points, or at the respective, periodically repeating, measuring times in order to detect a fault. It is also sufficient if the measuring points lie within an interval that is predetermined by the switch-on duration t_on_nf on another LED channel 3, 4, 5 (indicated schematically by dashed lines in FIG. 5). Thus, the invention makes use of the fact that caused by the crosstalk interference in an LED channel 3, 4, 5 occurs periodically.

From measured values I _M1 , I _M2 , I _M 3, I, I _M 3, 2 determined in this way, the disturbance in an LED channel 3, 4, 5 can be estimated and the turn-on duration t_on_hf of the high-frequency switching operations can be increased accordingly.

Fig. 6 shows schematically such an increase in the high-frequency switching operations or such a change in the high-frequency pulses. This is carried out in order, for example, on the second LED channel 4 (FIG. 6b)) to obtain the desired mean value M2 for the LED current I _{LE D} 2 CLOSE reach, or on the third LED channel 5 (Fig. 6c) to set the desired mean value M3 for the LED current I LED3. It should be noted that the problem underlying the invention would not occur if the current waveform could be monitored during each low frequency pulse. However, as already mentioned, there is the problem that the control unit 2, especially when executed as a microcontroller, does not provide enough resources to allow continuous monitoring of the current flow during each low-frequency pulse. Rather, only one LED channel 3, 4, 5 can be monitored temporarily. Thus, there will always come to a variety of low-frequency pulses that occur unsupervised.

The inventive approach to compensate for a disturbance caused by crosstalk on the LED channels 3, 4, 5, takes place advantageously when switching on the power supply or at periodic intervals. It is also possible that the compensation is continuous, i. is continuously performed during operation of the LED converter by the control unit 2.

Thus, constant changes in the effects of crosstalk, for example, by

Temperature changes, to be compensated. In addition, it can also be provided that changes not only the duty cycle of the low-frequency pulses in a change of a Dimmwertvorgabe, but that Alternatively or additionally, the amplitude of the low-frequency pulses changes, or caused by the crosstalk negative influence on the LED currents I LEDI _/ I LED2, I LED3 - Through a continuously performed by the control unit 2 compensation process such influences can also be compensated ,

Claims

claims

LED converter (1) for controlling at least two LED channels (3, 4),

wherein the LED converter (1) comprises:

- for each LED channel a high frequency of one

Control unit (2) clocked switching regulator stage has

(23a, 23b, 23c), wherein the switching regulator stages (23a, 23b 23c), starting from a common Eenergiespeicher

(22) are supplied and each one of the plurality of LED channels (3, 4) supplied by high-frequency switching operations with a cyclically rising and then falling LED current (ILEDI, ILED2),

- At least one unit (10) which superimposes a high-frequency pulse modulation on the high-frequency clocking of the switching regulator stages, and

wherein the LED converter (1) is adapted to the high-frequency switching operations during a

Duty cycle (t_on_nf) of the compared

low-frequency pulses, in particular PWM pulses to execute,

- In an LED channel (4) at least temporarily during the turn-on (t_on_nf) of a pulse to capture the time average (Μ2 ^Λ ) of the LED current (I _LED2 ) or a parameter reproducing this, and

- A rising edge of the LED current (I _LED2 ) of the LED channel (4) in a later, preferably the

to increase the immediately following pulse, if the detected time average (Μ2 ^Λ ) preferably more than a predetermined threshold difference value of a deviated predetermined mean value (M2).

LED converter (1) according to claim 1, wherein the LED converter (1) has a control unit (2), which is adapted, during the on-time (t_on_nf) of a low-frequency pulse, the temporal

Average value (Μ2 ^Λ ) of the LED current (I _{LE D} 2) or the parameter representing this on an LED channel (4).

LED converter (1) according to claim 1 or 2, wherein the control unit (2) is adapted to a deviation of the detected time average (Μ2 ^Λ ) of the LED current (I _{LE D} 2) or of the latter reproducing parameter of the target Average value (M2).

LED converter (1) according to one of the preceding

Claims, wherein turn-on and / or the

Duty cycle (t_on_nf) of the low-frequency pulses on the LED channels (3, 4) of the control unit (2) are known and / or transmitted to the control unit (2).

LED converter (1) according to one of the preceding

Claims, wherein the control unit (2) is set up, based on the switch-on times and / or the switch-on duration (t_on_nf) of the low-frequency pulses on another LED channel (3), the LED current (I _{LE D} 2) on the LED Channel (4) and / or the time average (Μ2 ^Λ ) of the LED current (I _{LE D} 2) or the latter determine the reproducing parameters on the LED channel (4).

6. LED converter (1) according to one of the preceding

Claims, wherein the control unit (2) is adapted to detect an amplitude dip of the LED current (I _L ED2) on the LED channel (4).

7. LED converter (1) according to one of the preceding

Claims, wherein the control unit (2) is adapted to change the duty cycle (t_on_hf) of the high-frequency switching operations depending on the detected time average (Μ2 ^Λ ). 8. LED converter (1) according to one of the preceding

Claims, wherein the control unit (2) is adapted to the low-frequency pulses continuously

to scan. 9. LED converter (1) according to one of the preceding

Claims, wherein the control unit (2) is an integrated circuit and in particular a microcontroller.

10. A method for controlling at least two LED channels (3, 4) by an LED converter (1),

- Wherein the LED converter (1) each of the LED channels (3, 4) by each independent of the other channel high-frequency switching operations with a cyclic

rising and then falling LED current (ILED1, ILED2) supplied, starting from one for at least two LED channels common energy storage (22) is generated

- where the high-frequency switching operations

be superimposed low-frequency pulses, wherein

preferably whose duty cycle is changed to achieve a dimming,

- wherein the LED converter (1) the high-frequency

Switching operations during a switch-on period (t_on_nf) which in comparison to low-frequency pulses, in particular PWM pulses executes,

- detects in a LED channel (4) at least temporarily during the switch-on (t_on_nf) of a pulse, the time average (M2 ^Λ ) of the LED current (ILED2) or a parameter reproducing this, and

- The rising edge of the LED current (ILED2) of the LED channel (4) in a later, preferably the

extended immediately following pulse when the detected time average (Μ2 ^Λ ) preferably more than a predetermined threshold difference value of a predetermined desired average value (M2) has deviated.

11. The method of claim 10, wherein the LED converter

(1) has a control unit (2) which detects the time average (Μ2 ^Λ ) of the LED current (I _L ED2) or of the parameter representing this on an LED channel (4) during the switch-on time (t_on_nf) of a low-frequency pulse ,

12. The method according to claim 10 or 11, wherein the

Control unit (2) a deviation of the detected time average (Μ2 ^Λ ) of the LED current (I _{LE D} 2) or the parameter representing this from the desired average (M2).

13. The method according to any one of the preceding claims, wherein switch-on and / or the duty cycle

(t_on_nf) of the low-frequency pulses on the LED channels (3, 4) of the control unit (2) are known and / or transmitted to the control unit (2).

14. The method according to any one of the preceding claims, wherein the control unit (2) based on the

Switching times and / or the duty cycle (t_on_nf) of the low-frequency pulses on another LED channel (3) the LED current (I _LED2 ) on the LED channel (4) scans and / or the time average (Μ2 ^Λ ) of the LED -stream

(I _{LE D} 2) or the parameter representing this on the LED channel (4).

15. The method according to any one of the preceding claims, wherein the control unit (2) detects an amplitude dip of the LED current (I _{LE D} 2) on the LED channel (4).

16. The method according to any one of the preceding claims, wherein the control unit (2) changes the duty cycle (t_on_hf) of the high-frequency switching operations depending on the detected time average (Μ2 ^Λ ).

17. The method according to any one of the preceding claims, wherein the control unit (2) continuously samples the low-frequency pulses.

18. The method according to any one of the preceding claims, wherein the control unit (2) is an integrated circuit and in particular a microcontroller.

19. Integrated circuit, in particular

A microcontroller designed and / or programmed to perform a method according to any of claims 9 to 16.