EP2795999B1 - Operating circuit for light emitting diodes and method for operating light emitting diodes - Google Patents

Description

The present invention relates to a circuit and method for operating one or more light emitting diodes (LEDs) by means of switching regulators to provide an operating current for the LEDs.

For the operation of LEDs, it is basically already known to use an operating circuit with switching regulators. For example, switching regulators such as buck converters or buck converters, boost converters or boost converters, flyback converters, etc. can be used to drive LEDs. In this case, a control unit controls a clocked semiconductor power switch, by means of which in the on state, an inductance is magnetized, wherein the inductance in the off state of the switch then, for example, via the LEDs discharges or demagnetizes.

The control of the switch can be done by the control unit via pulse width modulation (PWM). In particular, it is known to provide for the PWM control signal a constant high frequency on the order of e.g. 100 kHz to use. By selecting a corresponding duty cycle of the PWM control signal then a dimming of the LEDs can be made possible.

Furthermore, the use of operating circuits is known for a controlled operation of LEDs, the regulation For example, support the power supplied to the LEDs or the current supplied to the LEDs. Such a regulation requires a recirculated measured variable which can directly or indirectly reproduce, for example, the voltage drop across the LEDs and / or the current flowing through the LEDs.

When controlling the LED current, a regulator tries to keep the current constant through the LEDs. An operating circuit with such a regulation should also be usable for different LED loads.

However, the problem with such a control is the fact that e.g. Depending on the LED load and depending on the dimming value, the control behavior may change. The disadvantage here is, for example, the varying behavior of the controller in terms of stability and temporal response.

From the DE 10 2008 057 333 A1 is an adaptive PFC for a lamp load circuit, in particular a load circuit with LED known. In this case, the control parameters of a PFC control for the output voltage of the clocked PFC can be set as a function of a control signal or a measurement signal. The clocked PFC feeds a driver circuit which in turn powers the bulbs.

The US 2012/0119669 A1 shows a phase dimmer trailing edge dimmer). This supplies a converter for a light source. A current control module of the converter is supplied with a signal which predicts a time-phased-edge prediction.

The US 2008/167734 A1 discloses a method and apparatus for digitally controlling a lighting device that enables a desired operative setpoint of the lighting device to be achieved in a rapid manner while substantially reducing overshoot and oscillation about the desired operational setpoint of the lighting device. In particular, in US 2008/167734 A1 a PID controller is configured to vary the PID controller parameters based on the desired operational setpoint of the lighting device and / or on the present operating point of the lighting device.

It is therefore an object of the present invention to provide an operating circuit for at least one light-emitting diode and a method for operating at least one light-emitting diode, which improves the regulation of the current, voltage or electrical power supplied to the LED, even if different LED loads can be connected.

This object is achieved by the features of the independent claims. The dependent claims further form the central idea of the invention in a particularly advantageous manner.

According to a first aspect of the present invention, a method is provided for operating at least one light-emitting diode by means of an actively clocked switching regulator circuit designed as a step-down converter, to which an input voltage is supplied, and an output voltage for supplying the at least one light-emitting diode by means of at least one switch clocked by a control unit provides. The switching regulator circuit is a current (or its time average) by the LED (s), the voltage via the LED (s) or the LED (s) supplied electrical power directly or indirectly reproducing actual value signal fed back, which with a current, voltage or power setpoint is compared. Thus, a control loop is formed whose control variable is the timing of the switch. The properties of the control loop are dependent on the operating mode of the switching regulator circuit. Typically, the control is a hysteresis control in which, in the case of current regulation, the LED current fluctuates cyclically between two values.

The control algorithm can be implemented analog or digital. Particularly in the case of digital implementation, the change in the properties of the control loop preferably takes place by changing the parameter of the digitally implemented control. Meanwhile, the change of the characteristics can also be carried out elsewhere in the control loop, for example by selective switching of a bandpass filter, for example, in the feedback branch of the actual value signal.

According to a further aspect of the invention, an operating circuit is provided for at least one light-emitting diode, comprising a switching regulator circuit, which is supplied with an input voltage and which provides an output voltage (current) for supplying the at least one light-emitting diode by means of at least one switch clocked by a control unit. The control parameters are for the regulation of the output current, the output voltage or the electrical power output dependent on the operating mode of the switching regulator circuit.

Advantageously, in a transition from one operating mode of the switching regulator circuit to another operating mode, the control parameters can be changed.

Advantageously, the operating mode of the switching regulator circuit can be detected. Depending on this, the control parameters can be adjusted.

Different control parameter sets may advantageously be provided for different operating modes.

Advantageously, the switching regulator circuit can be operated in a continuous and / or in a discontinuous mode. For each of these operating modes, a respective control parameter set can be provided.

The discontinuous operating mode can be detected by detecting a reversal or rising of the output voltage of the switch when the switch is switched off. Alternatively, the discontinuous mode of operation be recognized that when the switch is off, a reversal or rising of the voltage dropping at a diode downstream of the switch is determined. Alternatively, the discontinuous operating mode can be detected by detecting, when the switch is switched off, a reversal or rising of the voltage drop across an energy store of the switching regulator circuit.

The discontinuous mode of operation may be further recognized by the fact that, when the switch is turned on, the output voltage of the switch or the voltage dropping across a diode connected to the switch or the voltage dropping across an energy store of the switching regulator circuit is greater than a predefined value, e.g. Zero, is or is within a certain range of values.

Preferably, an operating mode or a transition between two operating modes can be determined by means of a flip-flop circuit.

The flip-flop circuit can advantageously be designed in the form of a D flip-flop circuit. The clock input of the D flip-flop circuit can be fed with the control signal generated by the control unit for the switch. The D input of the D flip-flop circuit may be supplied with a signal representing an electrical parameter of the switching regulator circuit. The output of the D flip-flop circuit may be connected to an input of the control unit.

Preferably, the signal at the D input of the D flip-flop circuit can represent the output voltage of the switch of the switched-mode switching regulator circuit formed as a down converter.

The control signal for the switch at the clock input can be delayed in such a way that the propagation times of the switch drive are compensated.

Advantageously, a comparator can be connected to the D input for detecting the operating mode.

The adaptation of the control parameters may preferably be made dependent on the static amplification being greater in a continuous operating mode of the switching regulator circuit than in a discontinuous operating mode.

The switch can preferably be clocked by means of a pulse width modulation control by the control unit.

According to a further aspect of the invention, an integrated circuit is provided, preferably in the form of a microcontroller, an application specific integrated circuit (ASIC) or a digital signal processor. The integrated circuit is designed to carry out the method.

According to a further aspect of the invention, a luminaire is provided. The luminaire has the integrated circuit or the operating circuit.

In accordance with one aspect of the invention, the controller is adaptive in the sense that it has two different sets of control parameters for the continuous conduction mode on the one hand and the borderline / discontinuous conduction mode on the other hand.

Control parameters are adjusted based on the operating mode to compensate for the various static gains of the buck converter or the controlled system.

To be able to carry out the conversion of the control parameters, it is preferably determined in which state the switching regulator circuit or the converter is currently located. This can be done, for example, by determining the current through the inductance or through the LEDs or an electrical quantity dependent thereon at the switch-on time of the switch of the buck converter. In the continuous mode of operation, an LED current flows at the switch-on time of the switch. This is of course not the case in the critical operating mode or in the discontinuous operating mode.

Advantage of the invention is that the different slopes of the line characteristic of the LED load are taken into account in the scheme. On the one hand, the regulation in the range of high slope of the line characteristic curve can be very stable. On the other hand, the control can also be fast enough for the region of the flat line characteristic.

Fig. 1

eine Betriebsschalung für Leuchtdioden gemäß einem Ausführungsbeispiel der vorliegenden Erfindung,

Fig. 2

den geregelten Stromverlauf durch eine Leuchtdiodenstrecke in Abhängigkeit von einem gewünschten Dimmwert,

Fig. 3

eine detaillierte Ansicht bezüglich des Stromverlaufs durch die Leuchtdiodenstrecke in einem ersten Betriebsmodus der Betriebsschaltung,

Fig. 4

eine detaillierte Ansicht bezüglich des Stromverlaufs durch die Leuchtdiodenstrecke in einem zweiten Betriebsmodus der Betriebsschaltung,

Fig. 5

eine Betriebsschalung für Leuchtdioden gemäß einem weiteren Ausführungsbeispiel der vorliegenden Erfindung,

Fig. 6

eine Betriebsschalung für Leuchtdioden gemäß einem noch weiteren Ausführungsbeispiel der vorliegenden Erfindung, und

Fig. 7

ein Beleuchtungssystem gemäß der vorliegenden Erfindung.

Further features, advantages and features of the present invention will now be described with reference to FIGS the accompanying drawings and the detailed description of embodiments will be explained. This shows

Fig. 1

an operating form for light emitting diodes according to an embodiment of the present invention,

Fig. 2

the regulated current flow through a light-emitting diode path as a function of a desired dimming value,

Fig. 3

a detailed view with respect to the current flow through the light-emitting diode path in a first operating mode of the operating circuit,

Fig. 4

a detailed view with respect to the current flow through the light-emitting diode path in a second operating mode of the operating circuit,

Fig. 5

an operating form for light-emitting diodes according to a further exemplary embodiment of the present invention,

Fig. 6

an operating form for light emitting diodes according to a still further embodiment of the present invention, and

Fig. 7

an illumination system according to the present invention.

Note: Although the invention will be explained below with reference to a current regulation, it should be understood that the invention may equally be applied to voltage regulation or power regulation.

In a voltage regulation, at least one parameter representing the LED voltage is fed back and compared with a setpoint value. Accordingly, in the case of an LED power control, one or preferably a plurality of, preferably combinatorially, that is to say by reference to a plurality of parameters, the parameters representing the LED power are fed back and then compared with a desired value.

In Fig. 1 schematically an embodiment of an operating formwork 21 according to the invention for LEDs 5, 6 is shown.

An operating form according to the present invention comprises a converter for providing an output voltage and an output current for the LEDs 5, 6. The converter can also be referred to as a switching regulator, in which the power supply of the LEDs by means of a periodically operating electronic switch and at least one energy storage, the power supply the light-emitting diodes is ensured.

In the Fig. 1 Operating circuit 21 shown comprises a switching regulator in the form of a down converter 20. The down converter 20 consists of a switch 1, a diode or rectifier diode 2, an inductor 3 and a capacitor or smoothing capacitor 15. For the operation of at least one light emitting diode 5, 6, the down converter 20, an input voltage VDC is supplied. This input voltage VDC is preferably a DC voltage, but may alternatively be an AC voltage or a rectified AC voltage.

The input voltage VDC feeds a first input of the switch 1, which may be configured, for example, as a field-effect transistor (FET) or semiconductor power switch, in particular MOSFET. The switch 1 is switched on or off via a control input, preferably by means of a PWM signal VG. The output of the switch 1 is connected to the cathode of the diode 2. The diode 2 is connected to ground on the anode side. At the connection point from the output of the switch 1 and from the cathode of the diode 2, the inductance 3 is connected. The capacitor 15 is connected between ground or shunt resistor and the other terminal of the inductor 3.

The role of the aforementioned energy storage takes over the inductance 3, in which the switch 1 in the on state generates an output voltage VM, which is greater than the output voltage VOUT of the down converter 20. During the switch-on phase of the switch 1 thus the current through the inductance third ,

During a subsequent freewheeling phase or blocking phase, the switch is switched off. This causes the output voltage VM of the switch to drop. At the inductance 3 is now a negative Voltage so that the current through this inductance 3 linearly drops again and the stored electrical energy is passed to the LEDs 5, 6.

At the output of the down converter 20 is a series circuit of an inductor 4 and at least one light emitting diode 5, 6 is provided. The series circuit of inductance 4 and light-emitting diodes 5, 6 is connected in parallel with the capacitor 15. The inductor 4 forms an output filter together with the capacitor 15.

In the embodiment of Fig. 1 is a plurality of light emitting diodes 5, 6 connected in series. Alternatively, the operating circuit 21 can be used for only one light-emitting diode. Alternatively, the LEDs can also be connected in parallel. Preferably, the light-emitting diodes can also be arranged according to a serial and parallel connection. The light-emitting diodes can be OLEDs. Furthermore, it may be, for example, monochromatic light-emitting diodes, dye-converted white light-emitting diodes and / or RGB light-emitting diode modules. In the case of the latter, it is particularly advantageous if each luminous color is arranged in a separate light-emitting diode path ("light-emitting diode channel").

As an alternative to the down converter 20, an operating circuit according to the invention may, for example, also comprise an up-converter (not shown). The buck converter generates at its output a lower output voltage VOUT with respect to the DC input voltage VDC. By contrast, a boost converter generates a higher output voltage VOUT.

At the connection point between the capacitor 15 and the light-emitting diodes 5, 6, a shunt resistor or measuring resistor 13 is connected. The other connection point of the shunt resistor 13 is connected to ground. The voltage dropping across the shunt resistor 13 is a measure of the total current flowing through the light emitting diodes.

The shunt resistor 13 is preferably followed by a low-pass filter. According to the embodiment of the Fig. 1 the low-pass filter is formed in the form of an RC filter consisting of a resistor 12 and a capacitor 11. Because of the low-pass characteristic of the RC filter, the series connection of the measuring resistor 13 and the RC filter causes the mean value of the voltage drop across the measuring resistor 13 to be formed at the output of the RC filter. The output of the RC filter is supplied to a measuring input 17 of the control unit 10, so that the control unit 10 is an actual value for the current through the light emitting diodes available.

Preferably, the control unit 10 is returned an average value of the current through the LEDs 5, 6. Alternatively, the signal at the measuring input 17 can also reproduce the instantaneous value of the current through the light-emitting diodes 5, 6. In this case, the control unit 10 may preferably internally cause the averaging of the light-emitting diode current.

The control unit 10 is designed to control the timing of the switch 1, for example in the form of PWM-modulated as a control variable of the control of the light-emitting diode power or pulse width modulated signals at the output 19 pretend.

As feedback signal to which is regulated (and which, for example, is compared with a setpoint value), at least the current flowing through the light-emitting diode path 5, 6 is measured. This measurement takes place at the input 17. This light-emitting diode current can be measured at any point in the light-emitting diode current path. As in Fig. 1 shown, the light-emitting diode current can be measured in particular with the measuring resistor 13 and then preferably averaged.

If a plurality of parallel light-emitting diode paths are arranged (not shown), it is advantageous if each light-emitting diode path is controlled via its own feedback signal, which reproduces, for example, the current flowing in the light-emitting diode path.

As a setpoint for the control, a dimming value supplied externally via the input 22 of the control unit 10 can be used. It may, for example, be an analogue dimming via amplitude change. Alternatively, a digital dimming value can be taken into account, which, for example, via a digital data bus (s. Fig. 7 ) is transmitted.

The operating circuit according to the invention is an adjustable current source, for example from 1% to 100% for various light-emitting diode loads, for example from 14V to 44V. The down converter 20 is preferably controlled via a designed as a microcontroller control unit 10 by means of PWM. Preferably, a constant RF-PWM frequency of, for example, 100 kHz is selected, so that the output filter can be optimally dimensioned to reduce the current ripple. This has the consequence that the down converter 20 operates in continuous, in the critical or in the discontinuous operating mode, depending on the operating point.

The light-emitting diode current is preferably kept constant with a digital PI controller in the control unit 10 or in the microcontroller at a desired current level. Up to about 10% light-emitting diode current is preferably dimmed continuously analog. Thereafter, the light-emitting diode current is reduced to 1% with a NF-PWM of e.g. 312Hz to keep the effective LED current at a minimum of 10%. Thus, larger Farbortverschiebungen can be avoided and occur to 10% LED current no disturbing stroboscopic effects.

The regulated current flow through the light-emitting diode path is in Fig. 2 shown. In Fig. 2 For this purpose, the dimming value or the pulse duty factor of the PWM signal is shown along the X axis and the light-emitting diode current along the Y axis. Shown is the current plotted over the switch-on period of the switch 1 of the buck converter 20. The different characteristics K1, K2, K3, K4, K5, K6 refer to different loads.

It is shown that, depending on the degree of dimming, which is determined, for example, in the case of an analogue dimming via an amplitude change, and the load, the characteristic curve of the load has, in particular, two sections with different slopes.

For example, in the characteristic K4 two areas with different slopes are visible. In a first Area B1 is the slope shallower than in a second area B2. The duty cycle is greater in the second region B2 than in the first region B1. In particular, these two sections with different slopes reflect that depending on the degree of dimming and the LED load, the converter may be in Continuous Conduction Mode or in Borderline Conductive Mode. The frequency of the control of the switch 1 preferably remains constant in the high-frequency range.

With regard to the control characteristics, in particular the time constant of the control, the controller can be improved so that it has different control parameter sets depending on the state of the converter. The control parameter sets are particularly adapted to these respective very different track characteristics. Different control parameter sets are provided for different operating modes of the converter.

The adjustment of the control parameters can be carried out in a known manner depending on the static gain ks. The static gain ks corresponds to the slope of in Fig. 2 shown characteristics.

As in Fig. 2 As can be seen, the static gain ks increases extremely with higher light-emitting diode currents. Before this climb, there is even a very flat spot with extremely small gain. This behavior is caused by the transition from the continuous mode of operation in the discontinuous mode of operation and is technically disadvantageous.

The inventive solution, depending on the operating state of the switching regulator circuit to adjust the control parameters, ensures that the controller can still work stably on the one hand in the continuous mode at the largest static gains and in particular at a duty cycle in the vicinity of 100%. On the other hand, the control parameters can also be adjusted separately in the discontinuous mode, so that the control is no longer sluggish. On the contrary, this adaptation means that even in the discontinuous operating mode and at lower currents, rapid adjustment to the desired value takes place. Another advantage is that the ripple of the characteristic curves is no longer visible in the lower current range.

By adapting the control parameters depending on the operating mode a very stable control in the range of high slope of the route characteristic and on the other hand a fast control for the range of flat running line characteristic are possible.

The adaptive controller according to the invention will adjust its parameters depending on the operating point. For this purpose, it should be recognized when the transition between the discontinuous and the continuous mode of operation is present, since in this transition, a large change in the static gain ks has been recognized. However, this point is very different depending on the light-emitting diode load and component tolerances and makes a switching of the controller, for example by means of current measurement and / or duty cycle rather inaccurate.

Fig. 3 shows a detailed view of the current waveform through the light emitting diode path in the continuous mode of operation of the operating circuit. The course of the control signal VG for the switch 1 and the voltage VM at the output of the switch 1 are also shown. In the switch-on phase E of the switch 1 defined by the control signal VG, the voltage VM assumes a positive value and the current through the inductance IL rises linear. If the control signal VG assumes the value zero, the voltage VM drops approximately to the value -0.7 V. During this freewheeling phase F or blocking phase, the current through the inductance 3 decreases linearly, but does not return to zero. When the switch 1 is subsequently switched on, the voltage VM assumes the positive value in pulses.

Fig. 4 shows the current profile through the light-emitting diode path in the discontinuous operating mode of the operating circuit. In the freewheeling phase F, the current through the inductance 3 decreases to zero. At the moment when the current through the inductance becomes zero, the voltage VM jumps to the value VOUT. It forms a resonant circuit, which is excited by the voltage jump on the diode 2. The voltage VM evolves according to a decaying vibration by a positive value.

With the control signal VG and the voltage VM, the operating mode is detected according to the invention. For this purpose, a D flip-flop circuit 9 is provided, which is clocked with the positive drive edge of the control signal VG. As in Fig. 1 1, the clock input of the flip-flop circuit is connected to the control signal VG generated by the control unit 10 for the switch 1.

The data or D input of the D flip-flop formwork 9 is connected via a voltage divider 7, 8 to the center VM of the buck converter. The output of the D flip-flop formwork 9 is connected to an input 18 of the control unit 10.

In this embodiment, the detection of the operation mode is implemented by means of the D flip-flop 9, which is clocked in synchronism with the timing of the down-converter switch 1. The D input of the D flip-flop is supplied with a signal representing the bridge voltage VM.

Optionally, a diode 16 may be provided at the D input of the D flip-flop form 9. The anode of the diode is connected to the center of the consisting of two resistors 7, 8 voltage divider. The anode of the diode 16 is connected to the D input of the D flip-flop formwork 9. The cathode of the diode 16 is connected to a positive voltage VCC. At the output of the flip-flop 9, the current operating mode is always output.

The detection of the operating mode by means of the D-flip-flop 9. With a positive drive edge of the control signal VG and in continuous operation, the voltage VM has the value zero or -0.7 V. The output of the flip-flop circuit 9 thus assumes the logic state 0 which is detected by the control unit 10. This in turn closes to the continuous mode of operation and takes into account for the light-emitting diode control according to the invention provided for this operation corresponding control parameters. These control parameters are adapted to the high static amplification of the continuous operating mode.

In the discontinuous operating mode, however, the voltage VM when driving the switch 1 is no longer at about -0.7 V. This voltage VM is much greater than the required 1 level voltage of the D input at startup. The output of the flip-flop thus outputs the logic state 1. The control unit thus concludes with a discontinuous operating mode and adjusts the control parameters accordingly.

Based on the output signal of the flip-flop 9, the control unit 10 can now adjust the parameters of the controller, so as to compensate for the various static gains of the controlled system.

Advantageously, a delay (e.g., RC) may be incorporated at the clock input of the flip-flop circuit 9 (not shown) to compensate for the drive times of the switch driver.

In Fig. 5 is a section of a variation of the in Fig. 1 shown circuit shown. The only difference to the circuit of Fig. 1 is a comparator 50, which is connected in front of the D input of the flip-flop 9. By setting a reference value VREF, which is compared with the signal from the voltage divider 7, 8, thus the detection of the one or the other operating mode by the control unit 10 can be determined more accurately. The comparator can be advantageous in particular for a lower switching level or if the voltage gradient of the voltage VM is too small.

The Fig. 6 shows a further embodiment of an operating circuit 51 according to the present invention. Components with on Fig. 1 shown components are identical, are provided with identical reference numerals, so that can be dispensed with a repetition of the description of these components.

The down converter 54 corresponds to the in Fig. 1 shown down converter 20, with the difference that now a secondary winding 52 is provided. This secondary winding 52 is magnetically coupled to the inductor 3 of the buck converter 20. The voltage at the secondary winding 52 is supplied to an input 53 of the control unit 10.

The voltage applied to the secondary winding 52 and measured by the control unit 10 is proportional to the voltage VM-VOUT of the inductance 3, the voltage VOUT preferably being constant. Namely, the voltages at the secondary winding 52 and at the inductance 3 behave as each other as the number of turns of the two electrical components.

Optionally, this voltage applied to the inductance according to Fig. 1 a D flip-flop circuit 9 are supplied, wherein the output of the D flip-flop circuit 9, the operating state of the down converter 20 reproduces.

In Fig. 7 For example, an illumination system 60 according to the present invention is shown. The illumination system 60 preferably comprises an operating circuit 64 for light-emitting diodes 5, 6. The operating circuit 64 has a down-converter 20 according to FIG Fig. 1 shown first Embodiment on. Alternatively, for example, a down converter 54 may be used after the in Fig. 6 be shown further embodiment.

The down converter 20 is connected downstream of an AC-DC converter 61, which converts an AC voltage VIN provided by a power network 62 into a rectified voltage or into a DC voltage. Alternatively, the buck converter 20 may also be powered by an AC voltage.

The control unit 10 can be transmitted via the input 22 dimming. These dimming values may be transmitted over a data bus 63 e.g. from a central unit (not shown). Preferably, the control unit 10 via the data bus 63 itself also data, e.g. Regarding the scheme send back to the central unit.

For control purposes, feedback variables from the area of the operating circuit 64 are made available to the control unit. Depending on the mode of operation of the buck converter 20, the control unit 10 adjusts the control parameters as described above. The various control parameter sets can be transmitted to the control unit 10, for example via the data bus.

The control algorithm can be implemented analog or digital. Particularly in the case of digital implementation, the change in the properties of the control loop preferably takes place by changing the parameter of the digitally implemented control. However, the change of properties can also be found elsewhere For example, by selective switching of an example. Bandpass filter in the feedback branch of the actual value signal. It is also possible to switch the control loop or parts of the control loop.

List of reference characters

1

switch

2

diode

3

inductance

4

inductance

5

led

6

led

7

resistance

8th

resistance

9

Flipflopschalung

10

control unit

11

capacitor

12

resistance

13

Measuring resistor

15

capacitor

16

diode

17

Input of the control unit

18

Input of the control unit

19

Output of the control unit

20

down converter

21

operating circuit

22

Input of the control unit for dimming values

50

comparator

51

operating circuit

52

secondary winding

53

Input of the control unit

54

down converter

60

lighting system

61

AC-DC converter

62

power grid

63

Data bus

64

operating circuit

Claims (17)

1. Method for operating at least one light-emitting diode (5, 6) by means of a switching regulator circuit (20), preferably configured as buck converter, to which an input voltage (VDC) is supplied, and that provides, by means of at least one switch (1) clocked by a control unit (10), an output voltage (VOUT) for supplying the at least one light-emitting diode (5, 6) with LED current, LED voltage or electrical LED power, continuously controlled at least in the time average, wherein the desired value for the LED current, the LED voltage or the LED power is adjustable for dimming, characterized in that the control parameters of the control loop for the LED current, the LED voltage or the LED power are changed depending on the operating mode of the switching regulator circuit (20).
2. Method for operating at least one light-emitting diode (5, 6) by means of a switching regulator circuit (20), preferably configured as buck converter, to which an input voltage (VDC) is supplied, and that provides, by means of at least one switch (1) clocked by a control unit (10), an output voltage (VOUT) for supplying the at least one light-emitting diode (5, 6) with LED current, LED voltage or LED power, continuously controlled at least in the time average, wherein the desired value for the LED current, the LED voltage or the LED power is adjustable for dimming, characterized in that the control parameters of the control loop for the LED current, the LED voltage or the LED power are changed depending on the LED load and/or on the desired value of the LED current, the LED voltage or the LED power.
3. Method according to claim 1 or 2, wherein the control parameters are changed when switching from one operating mode of the switching regulator circuit (20) to another operating mode.
4. Method according to one of the preceding claims, wherein the operating mode of the switching regulator circuit (20) is recognized and the control parameters are adapted depending on that.
5. Method according to one of the preceding claims, wherein different sets of control parameters are provided for different operating modes.
6. Method according to one of the preceding claims, wherein the switching regulator circuit (20) can be operated in a continuous and in a discontinuous mode, and a set of control parameters is provided respectively for each of these operating modes.
7. Method according to claim 6, wherein the discontinuous operating mode is thus recognized that, when the switch (1) is switched off, a reverse of the output voltage (VM) of the switch (1) or a reverse of the voltage (VM) falling on a diode (2) downstream from the switch (1) or a reverse of the voltage falling on an energy store (3) of the switching regulator circuit (20) is detected.
8. Method according to claim 6, wherein the discontinuous operating mode is thus recognized that, when the switch (1) is switched on, the output voltage (VM) of the switch (1) or the voltage (VM) falling on a diode (2) downstream from the switch (1) or the voltage falling on an energy store (3) of the switching regulator circuit (20) is greater than a pre-defined value, e.g. zero, or is in a specific value range.
9. Method according to one of the preceding claims and in particular according to claim 8, wherein an operating mode or a transition between two operating modes is detected by means of a flip-flop circuit (9).
10. Method according to claim 9, wherein the flip-flop circuit is designed in form of a D flip-flop circuit (9), wherein:

    - the clock input thereof is supplied with the control signal for the switch (1) generated by the control unit (10),

    - the D input thereof is supplied with a signal that represents an electric parameter of the switching regulator circuit, and

    - the output thereof is connected with an input (18) of the control unit (10).
11. Method according to claim 10, wherein the signal on the D input of the flip-flop circuit (9) reproduces the output voltage (VM) of the switch (1) of the switching regulator circuit configured as buck converter.
12. Method according to one of the claims 10 or 11, wherein the control signal for the switch (1) is delayed at the clock input in such a way that the running times of the switch activation is compensated.
13. Method according to one of the claims 10 to 12, wherein a comparator (50) is connected at the D input for recognizing the operating mode.
14. Method according to one of the preceding claims, wherein the adapting of the control parameters is made dependent on that the steady-state gain (ks1, ks2) is greater in a continuous operating mode of the switching regulator circuit than in a discontinuous operating mode.
15. Integrated circuit, preferably in form of a microcontroller, an application-specific integrated circuit (ASIC) or a digital signal processor, for carrying out a method according to one of the preceding claims.
16. Operating circuit for at least one light-emitting diode (5, 6), having a switching regulator circuit (20), preferably configured as buck converter, to which an input voltage (VDC) is supplied, and that provides, by means of at least one switch (1) clocked by a control unit (10), an output voltage (VOUT) for supplying the at least one light-emitting diode (5, 6) with current, voltage or power, continuously controlled at least in the time average, wherein the desired value for the LED current, the LED voltage or the LED power is adjustable for dimming, characterized in that the control parameters of the control loop for the LED current, the LED voltage or the LED power are changeable depending on the operating mode of the switching regulator circuit (20).
17. LED luminaire, or retrofit LED luminaire, having an integrated circuit according to claim 15 or an operating circuit according to claim 16.

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