NL2030193B1

NL2030193B1 - LED driver

Info

Publication number: NL2030193B1
Application number: NL2030193A
Authority: NL
Inventors: De Brouwer Bert; Jansen Eddy
Original assignee: Eldolab Holding Bv
Priority date: 2021-12-20
Filing date: 2021-12-20
Publication date: 2023-06-28
Also published as: WO2023118137A1

Abstract

An LED driver for powering an LED fixture is described, the LED driver comprising: - an input terminal configured to receive a rectified AC voltage; - a flyback converter having: o a primary winding coupled to the input terminal; o a switch coupled to the primary winding and configured to control a current of the primary winding based on a drive signal; o a secondary winding configured to provide a supply voltage Vsup for 1 powering the LED fixture; - a feedback circuit configured to generate a feedback signal, the feedback circuit being configured to: - receive a first signal representing the supply voltage as provided by the secondary winding; - receive a second signal representing the rectified AC voltage; - process the second signal to obtain a processed signal representing a time-derivative of an inversion of the second signal; - determine the feedback signal by combining the ﬁrst signal and the processed signal; - outputting the feedback signal. - a control unit configured to receive the feedback signal and determine the drive signal for controlling the switch based on the feedback signal.

Description

TITLE: LED driver

The present invention relates to an LED driver for powering an LED fixture, in particular an LED driver comprising a flyback converter.

LED based lighting applications are more and more applied. As such, they represent an important load of the electrical grid or mains. In order to efficiently operate such an electrical grid or mains supply, it is desirable to keep a power factor (PF) of a load close to one, and a total harmonic distortion (THD) of a load as low as possible.

It would be desirable that an LED driver enables such characteristics in various load conditions.

SUMMARY

It is therefore an object of the present invention to provide an LED driver with an improved PF or THD characteristic.

According to an aspect of the invention, there is provided an LED driver according to claim 1.

The invention is about controlling a power factor (PF) and/or total harmonic distortion (THD) of an LED driver powering an LED fixture.

It is desirable that an LED driver acts as a load with a high power factor when powering an LED fixture. It is further desirable that a THD of the LED driver is as low as possible.

The present invention describes an effective manner to control an LED driver such that a PF and/or THD is improved.

It can be observed that at present it is desirable to apply an LED driver in various circumstances, e.g. at a wide range of mains voltage and/or a wide range of output power.

Typically, an LED driver is powered from a rectified AC mains supply or comprises a mains rectifier unit as a mains input section. Such an LED driver or mains rectifier unit will in general comprise a filter capacitance which represents a capacitive load which will generate a mains current that is 90 degrees out of phase, independent of the required output power of the LED driver.

When the LED driver only requires a comparatively small output power, the capacitive load formed by the filter capacitance becomes more present and will cause the PF to drop.

In accordance with the present invention, a control of an LED driver is realised such that the

LED driver slightly reacts as an inductive load.

The LED driver according to the present invention comprises a flyback converter, whereby a switch connected to a primary winding of the flyback converter is controlled by a drive signal generated by a control unit of the LED driver.

The control unit of the LED driver is configured to determine the drive signal based on a feedback signal.

In a typical LED driver, a low bandwidth feedback is applied. The control unit can e.g. receive a signal representing the supply voltage available at the secondary side of the flyback converter.

Typically, the control unit will control a switching of the switch at the primary side so as to maintain the supply voltage at the secondary side at a predetermined desired level.

The signal representing the supply voltage as available at the secondary side of the flyback converter may e.g. be provided to the control unit via an optical coupling or an opto-coupler.

The presence of the buffer cap or filter cap results in the mains input current to remain zero for a while near the mains input voltage zero crossings. As a result, the PF decreases and the

THD increases.

In accordance with the present invention, the feedback signal as received by the control unit is adjusted, based on the actual rectified mains supply voltage. In particular, a signal is added to the feedback signal which can be described as a time-derivative of the inverted full-wave rectified mains supply voltage.

In accordance with the present invention, the LED driver comprises a feedback circuit configured to generate the adjusted feedback signal.

In accordance with the present invention, the feedback circuit is configured to:

» receive a first signal representing the supply voltage as provided by the secondary winding for powering an LED fixture; * receive a second signal representing an inverted rectified AC voltage of the rectified AC voltage; ‚ generate a time-derivative of the second signal; » determine the feedback signal by combining the first signal and the time derivative of the second signal, » outputting the feedback signal.

In according with the present invention, the first signal as received by the feedback circuit represents the supply voltage Vsup as generated on the secondary side of the flyback converter and which is used, during use, for powering the LED fixture. The first signal may thus be a signal proportional to the substantially DC voltage Vsup generated at the secondary side.

In a typical operation, such a signal can be used as feedback to control a switch of the primary winding, thereby controlling the power supplied to the secondary side. In case the voltage Vsup is too low, a power transfer to the secondary side needs to be increased. The first signal, when used as a feedback signal to the control unit of the flyback converter can thus be considered a request for power or power request, or can be used to derive a power request, e.g. by comparing the signal with a required or desired supply voltage at the secondary side.

In accordance with the present invention, said feedback signal, or power request signal, is adjusted based on a time-derivative of a signal representing an inverted signal of the rectified

AC supply voltage of the LED driver

As will be illustrated in more detail below, this results in time-dependent modification or adjustment of the power request. In particular, the combination of the power request signal with the time-derivative of a signal representing an inverted rectified AC supply voltage causes a reduction of the power request during an increase of the mains supply voltage and causes an increase of the power request during a decrease of the mains supply voltage.

At each zero-crossing of the mains supply voltage, the adjustment is reset.

In an embodiment, the second signal can e.g. be obtained from an auxiliary winding arranged on the primary side of the flyback converter.

Such a winding can e.g. be wound in such manner that the voltage across the winding represents the inverted rectified AC voltage.

Alternatively, the second signal representing an inverted rectified AC voltage may also be derived from the primary circuit of the flyback converter, said primary circuit e.g. comprising an input terminal for receiving a rectified AC voltage, a filter or buffer capacitor, the primary winding of the flyback converter and the switch in series with the primary winding.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically depicts an LED driver according to an embodiment of the present invention.

Figures 2a-2d schematically show signals / voltages illustrating the modulation of the feedback circuit as applied in the present invention.

Figure 3 schematically shows another embodiment of an LED driver according to the present invention.

Figure 4a schematically shows a processing circuit which can be applied in an LED driver according to the invention.

Figures 4b-4e schematically show signals / voltages illustrating the modulation of the feedback circuit as applied in the present invention

DETAILED DESCRIPTION

Figure 1 schematically shows an LED driver 100 according to an embodiment of the present invention. In the embodiment as shown, the LED driver 100 comprises an input terminal 110 which is configured to receive a rectified AC supply voltage. Such a rectified AC supply voltage can e.g. be provided by a rectifier, e.g. a full bridge or half bridge rectifier that is configured to receive an AC supply voltage, e.g. a 230 V, 50 Hz supply voltage and output a rectified AC supply voltage. In the embodiment as shown, the LED driver according to the present invention further comprises a flyback converter 120. In the embodiment as shown, the fly back converter 120 comprises a primary side or circuit comprising a primary winding 120.1 that is coupled to the input terminal 110, e.g. to receive the rectified AC supply voltage provided at the input terminal 110.

The flyback converter 120 further comprises secondary side or circuit comprising a secondary winding 120.2 which is configured to provide, together with rectifying diode 120.3 and capacitance 120.4, a DC supply voltage Vsup, which can be used to power an LED assembly.

The flyback converter further comprises a switch 120.5 coupled to the primary winding 120.1 and configured to control a current of the primary winding 120.1, based on a drive signal 130.1.

In the embodiment as shown, the drive signal 130.1 is provided by a control unit 130.

In the embodiment as shown, the LED driver 100 further comprises a buffer capacitor 160.

The LED driver 100 according to the invention further comprises a feedback circuit 150 that is configured to provide a feedback signal 150.3 to the control unit 130.

In accordance with the present invention, the feedback circuit 150 is configured to receive a first signal 150.1, representing the supply voltage Vsup as generated on the secondary side, and a second signal 150.2 that is derived from the rectified AC supply voltage or represents the rectified AC supply voltage as provided at the input terminal 110 of the LED driver. In an embodiment, the feedback circuit 150 is configured to process the second signal 150.2 and combine the signal 150.2 with the processed signal so as to generate the output signal 150.3.

In an embodiment, the processed signal of the signal 150.2 may be a time-derivative of an inversion of the rectified AC supply voltage, e.g. the voltage applied to input terminal 110 of the

LED driver 100. As will be understood, the processed signal of the second signal 150.2 may also be an inversion of a time-derivative of the rectified AC supply voltage. In such embodiment, the second signal 150.2 as provided to the feedback circuit 150 may thus be a signal representing the rectified AC supply voltage or may be a signal representing an inversion of the rectified AC supply voltage.

In an embodiment, the feedback circuit may then be configured to process the second signal 150.2 by determine a time-derivative of said signal and optionally inverting said signal, so as to arrive at a processed signal which can be considered a time-derivative of an inversion of the rectified AC supply voltage which is supplied to the LED driver.

It has been found by the inventors that combining the first signal 150.1, representing the supply voltage as generated at the secondary side of the flyback converter, with the processed second signal as described, can provide an improvement of the PF and/or THD of the power as drawn from the mains supply.

In this respect, it can be pointed out that in a typical known LED driver, a signal representing the supply voltage as generated at the secondary side of the flyback converter, is fed back to a control unit controlling the switch of the flyback converter at the primary side. The feedback signal representing the supply voltage on the secondary side may also be referred to as a power request; it is a feedback signal provided to the control unit to indicate the available Vsup on the secondary side. When the Vsup-value is too low, which can be assessed by the control unit 130 by comparing the feedback signal to a desired value of the supply voltage, the switch

120.3 can be controlled so as to increase the power to the secondary side, thus increasing the voltage Vsup.

By the addition of the processed signal, i.e. the signal derived from the second signal 150.2, the power request, as represented by the first signal 150.1, is modulated. The processed signal which is combined with the power request, is a periodic signal which causes, as will be detailed below, that the power request is decreased during a rise of the mains voltage and is increased during a decrease of the mains voltage.

Without the addition of the processed signal, in particular when a comparatively low output power is requested, a current step would occur near a zero-crossing of the mains supply voltage. The aforementioned modulation of the feedback signal helps to prevent or mitigate such a current step, thus improving PF and/or THD.

Using the processed signal as derived from the second signal 150.2, the feedback signal can be considered to be manipulated in such manner that the momentary power as supplied by the mains supply to the LED driver is somewhat modulated, within each half period of the mains supply voltage.

Note that this is done without affecting the low bandwidth output voltage regulation.

So the processed signal is a periodic signal that is superimposed on the low-bandwidth voltage feedback signal, i.e. the first signal 150.1.

Figure 2a schematically shows a rectified mains supply voltage 200 as e.g. can be used as an input voltage for a flyback converter such as converter 100 shown in Figure 1. Such a rectified mains supply voltage 200 can e.g. be supplied to terminal 110 of the converter 100 shown in

Figure 1.

Figure 2b schematically shows an inverted waveform 210 representing the rectified mains supply voltage 200 of Figure 2a. Within the meaning of the present invention, an inverted voltage or signal refers to a reversed voltage or signal. Inverting a voltage or signal V thus results in a voltage or signal -V.

Figure 2c schematically shows a time-derivative 220 of the inverted waveform 210 of Figure 2b, together with the inverted waveform 210, indicated in dotted line 230.

In accordance with the present invention, such a time-derivative 220 of the inverted rectified mains supply voltage 210 is combined with a low-bandwidth voltage feedback signal, i.e. a signal representing the supply voltage as generated at the secondary side of the flyback converter. Such a low-bandwidth voltage feedback signal, which may also be referred to as a power request, is typically proportional to the available supply voltage at the secondary side of the flyback converter.

Figure 2d schematically shows the rectified mains supply waveform 200 of Figure 2a, a substantially constant feedback signal 240 representing the supply voltage as available on the secondary side of the flyback converter, and a signal 250 combining the feedback signal 240 with a time-derivative of the inverted rectified mains supply signal. Signal 250 thus comprises the feedback signal 240 combined with a time-derivative signal similar to signal 220 shown in

Figure 2c. In accordance with the present invention, such a signal 250 is thus provided to a control unit, e.g. control unit 130 of the flyback converter 100 of Figure 1, to control the switch on the primary side of the flyback converter, e.g. switch 120.5 of the flyback converter 100 of

Figure 1. As can be seen, the addition of the time-derivative signal causes a modulation of the feedback signal 240.

In particular, the feedback signal 240, or power request, is modulated with the time-derivative of the momentary input voltage of the flyback converter, i.e. the rectified mains supply voltage. As a result of the addition of the time-derivative, the power request is reduced, graph 250 is below graph 240, during a rise of the rectified mains supply voltage, i.e. during periods T1, and is increased, graph 250 is above graph 240, during a fall of the rectified mains supply voltage, i.e. during periods T2. At each mains-zero crossing the sequence is reset.

It can also be pointed out that the applied modulation, i.e. the addition of a signal representing or proportional to the time-derivative of the momentary input voltage of the flyback converter, increases with the amplitude of the applied AC mains voltage, and the frequency of the applied

AC mains voltage.

The applied modulation to the feedback signal, e.g. signal 150.1 shown in Figure 1 and representing the supply voltage as generated at the secondary side of the flyback converter, causes a modulation or change of the input current of the LED driver, i.e. the current as retrieved from the mains supply.

In particular, it has been observed that, without the applied modulation, the input current of the

LED driver remains low, or near zero, for a particular duration or period, at or near the zero crossing instants of the rectified AC mains voltage. This duration or period that the input current of the LED driver remains low, or near zero, will increase when the required output power of the LED driver decreases.

So, phrased differently, at comparatively low output power, an LED driver input current, i.e. an input current drawn from the AC mains supply, will suffer from having a duration or period during which the current is low, or near zero, said period being located near the zero crossing of the mains supply voltage.

The occurrence of the such a low, or near zero, current period, also referred to as death time, has been found to adversely affect the power factor (PF) and the total harmonic distortion (THD) of the power drawn from the mains supply. In particular at low output power levels, the mains input voltage needs to increase above the remaining voltage at the input of the flyback converter, before the mains input current can increase with a step. Using the invention, the death time at mains zero crossings is somewhat shortened due to the application of the adapted feedback signal, i.e. the addition of a signal representing a time-derivative of an inversion of the rectified AC supply signal.

As a result of the adapted feedback signal, the momentary power of the flyback converter is slightly suppressed in the rising part of the mains period (0-90° and 180-270°) and slightly boosted in the decreasing part of mains period(90-180° and 270-360°). near the mains zero crossings, the compensation or modification resets.

The lower the output power the higher the sudden mains input current step.

The application of the modulation as described, has been found to result in a prevention or reduction of the sudden mains input current step at low power levels. Instead, a gradual increase of the mains input current is obtained. As a result, the THD - and PF performance of the LED driver are improved for lower output power levels.

In the LED driver according to the invention, the control unit feedback is thus manipulated, using a voltage/ signal derived from the AC mains input voltage. This AC mains input voltage is rectified and AC coupled into the feedback signal, e.g. signal 150.1 shown in Figure 1 and representing the supply voltage as generated at the secondary side of the flyback converter, of the control unit of the LED driver.

The effect is a compensation on the momentary power of the LED driver, within each half period of the mains supply voltage. It can further be pointed out that the proposed manipulation or modulation does not or hardly affect the low bandwidth output voltage regulation, i.e. the regulation of the supply voltage as generated at the secondary side of the flyback converter.

The mains input current waveform is slightly changed, resulting in an increased PF, in particular at higher input voltages.

In an embodiment of the present invention, the flyback converter as applied further comprises an auxiliary winding. In such an embodiment, the voltage across said auxiliary winding can be used to generate the required processed signal according to the invention. In particular, the voltage across the auxiliary winding can also be considered a signal such as the second signal 150.2 shown in Figure 1 that represents the rectified AC supply voltage as provided at the input terminal 110 of the LED driver.

Figure 3 schematically shows another embodiment of an LED driver 300 according to the present invention which comprises a flyback converter having an auxiliary winding.

Figure 3 schematically shows an LED driver 300 comprising a flyback converter 320. In the embodiment as shown, the LED driver 300 comprises an input terminal 310 which is configured to receive a rectified AC supply voltage. Such a rectified AC supply voltage can e.g. be provided by a rectifier 302, e.g. a full bridge or half bridge rectifier that is configured to receive an AC supply voltage 304, e.g. a 230 V, 50 Hz supply voltage and output a rectified AC supply voltage. In the embodiment as shown, feature 306 represents a mains input filter. The LED driver 300 according to an embodiment of the present invention further comprises a flyback converter 320. In the embodiment as shown, the fly back converter 320 comprises a primary side or circuit comprising a primary winding 320.1 that is coupled to the input terminal 310, e.g. to receive the rectified AC supply voltage provided at the input terminal 310. Feature 308 in

Figure 3 represents a buffer capacitor of the LED driver 300.

The flyback converter 320 further comprises secondary side or circuit comprising a secondary winding 320.2 which is configured to provide, together with rectifying diode 320.3 and capacitance 320.4, a DC supply voltage Vsup, which can be used to power an LED assembly.

The flyback converter further comprises a switch 320.5 coupled to the primary winding 320.1 and configured to control a current of the primary winding 320.1, based on a drive signal 330.1.

In the embodiment as shown, the drive signal 330.1 is provided by a control unit 330.

In the embodiment as shown, the primary side of the LED driver 300 further comprises an auxiliary winding 320.6. In the embodiment as shown, the voltage Vaux of the auxiliary winding 320.6 can e.g. be used to power the control unit 330 of the LED driver. In the embodiment as shown, the voltage Vaux of the auxiliary winding 320.6 is further used as input for a feedback circuit 350 of the LED driver.

The LED driver 300 according to the invention further comprises a feedback circuit 350 that is configured to provide a feedback signal 350.3 to the control unit 330.

In accordance with the present invention, the feedback circuit 350 is configured to receive a first signal 350.1, representing the supply voltage Vsup as generated on the secondary side of the flyback converter 320. In the embodiment as shown, the flyback converter comprises a

Vsup regulator 380 that is configured to receive a signal Vsup representing the supply voltage.

Typically, the regulator is used to regulate the required Vsup with a controlled bandwidth far below mains input frequency. The Vsup regulator 380 further controls the optocoupler 390, in order to provide the signal 350.1 on the primary side of the flyback converter 320. In the embodiment as shown, the feedback circuit 350 further comprises a second signal 350.2 that represents the rectified AC supply voltage as provided at the input terminal 310 of the LED driver. In particular, in the embodiment as shown, the second signal 350.2 corresponds to the voltage Vaux across the auxiliary winding 320.6. Because the auxiliary winding 320.6 and the primary winding 320.1 are magnetically coupled, the voltage across the auxiliary winding 320.6 can be considered to represent the voltage across the primary winding 320.1, i.e. the rectified

AC voltage as available at the input terminal 310 as well. In the embodiment as shown, the feedback circuit 350 is configured to process the second signal 350.2, by means of the processing circuit 390, in a similar manner as discussed above and combine the signal 350.1 with the processed signal 350.4 so as to generate the output signal 350.3. In an embodiment, the processed signal 350.4 of the signal 350.2 may be or represent a time-derivative of an inversion of the rectified AC supply voltage, e.g. the voltage applied to input terminal 310 of the

LED driver 300. Depending on the winding characteristics of the auxiliary winding, the voltage

Vaux may already be a representation of an inversion of the rectified AC supply voltage.

As such, in an embodiment, the feedback circuit 350 may be configured to process the second signal 350.2 by determine a time-derivative of said signal and optionally inverting said signal, so as to arrive at a processed signal 350.4 which can be considered a time-derivative of an inversion of the rectified AC supply voltage which is supplied to the LED driver 300.

As a result of the combination of the signal 350.1 with the processed signal 350.4, the feedback signal 350.3 as provided to the control unit 330 is modified, in a similar manner as signal 150.3 is a modification of signal 150.1, as discussed with reference to Figure 1.

The modification as applied to the signal 350.1, i.e. the combination with the processed signal 350.4 can result in a similar improvement of the PF or THD as discussed above.

Figure 4a schematically shows a processing circuit 400 which can be used to generate the processed signal 350.4, with the voltage at the auxiliary winding Vaux as input.

In the embodiment as shown, the processing circuit 400 has a terminal 400.1 to which the voltage of the auxiliary winding Vaux can be connected. The circuit as shown comprises a rectifying diode 401 that is configured to rectify the forward stroke of the voltage Vaux of the auxiliary winding.

Within the meaning of the present invention, the forward stroke refers to the operating state whereby the switch of the flyback converter, e.g. switch 120.5 or switch 320.5, is closed. In said state, the voltage across the primary winding of the flyback converter corresponds to the voltage across the buffer capacitor, e.g. capacitor 160, of the flyback converter of the LED driver. It can further be pointed out that the voltage across the auxiliary winding has a similar waveform.

The rectifying diode 401 thus filters out the forward stroke voltage across the auxiliary winding.

Resistor 402 enables a discharging of the rectified forward stroke voltage, whereas capacitor 403 enables a buffering of the rectified forward stroke voltage.

Capacitor 404 and resistor 405 form a high pass filter towards the output terminal 400.2 of the processing circuit 400. Due to the high pass filter 404, 405, the voltage Vout at the output terminal 400.2 can be considered the time-derivative of the filtered rectified forward stroke voltage.

In the above processing circuit, it is assumed that the auxiliary winding is wound in opposite direction as the primary winding. When the swich 320.5 of the flyback converter 300 would be continuously closed, the voltage at the input terminal 310 would have a shape as e.g. shown in

Figure 2a, whereas the voltage Vaux at the terminal of the auxiliary winding 320.6 may have a shape as e.g. shown in Figure 2b, i.e. an inverted rectified AC voltage.

Due to the switching of the switch 320.5, the actual voltage across the auxiliary winding also comprises a high frequency component. The application of the diode 401 in the processing circuit 400 however enables that only the forward stroke parts of the auxiliary winding voltage pass. As such, the voltage at node 400.3 can be like the voltage shown in Figure2b.

Figure 4b schematically shows the waveform of the voltage as can be observed at the terminal 400.1, i.e. the voltage across the auxiliary winding of the flyback converter. Portions FS of the voltage waveform as shown correspond to the forward stroke voltage across the auxiliary winding.

Figure 4c schematically shows the rectified forward stroke voltage Vr, i.e. the voltage at the node 400.3 of the processing circuit 400. Note that the time-scale of Figure 4c is different from the time-scale of Figure 4b. In Figure 4c, T denotes the period of the mains supply voltage, whereas Ts in Figure 4b denotes the switching period of the switch of the flyback converter.

Figure 4d schematically shows the high pass filtered voltage Vif, i.e. the voltage at the node between capacitor 404 and resistor 405. This signal is injected via resistor 405 into the low ohmic output terminal 400.2 and can be considered to corresponds to signal 350.4 shown in

Figure 3. As shown in Figure 3, said signal 350.4 is then combined or coupled with the signal 350.1, representing the supply voltage Vsup as generated on the secondary side of the flyback converter 320. Said combination is realised by means of capacitor 350.5 shown in Figure 3.

The voltage across the capacitor 350.5 is then applied by the control unit 330 to control the switch 320.5 of the flyback converter 30. Figure 4e schematically shows the control signal CS, which corresponds to signal 350.3 in Figure 3, and which is applied to the control unit 330. Said control signal CS is thus a superposition of the signal 350.4 as generated by the processing circuit 400 and the signal 350.1, i.e. the Vsup feedback signal obtained from the optocoupler 390.

Because of the modulation of the signal 350.1 by the signal 350.3, the PF and/or the THD of the LED driver can be improved, as discussed above.

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the invention.

The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.

A single processor or other unit may fulfill the functions of several items recited in the claims.

Claims

CONCLUSIONS

An LED driver for powering an LED fixture, the LED driver comprising: an input terminal configured to receive a rectified AC voltage; - a flyback converter with: - a primary winding coupled to the input terminal; - a switch coupled to the primary winding and configured to drive a current from the primary winding based on a control signal; - a secondary winding configured to provide a supply voltage Vsup for powering the LED luminaire; - a feedback circuit configured to generate a feedback signal, the feedback circuit configured to: - receive a first signal representing the supply voltage as supplied by the secondary winding; - receive a second signal representing the rectified alternating voltage; - process the second signal to obtain a processed signal representing a time derivative of an inversion of the second signal; - determine the feedback signal by combining the first signal and the processed signal; - output the feedback signal. - a control unit configured to receive the feedback signal and determine the control signal for controlling the switch based on the feedback signal.

The LED driver of claim 1, wherein the flyback converter includes an auxiliary winding magnetically coupled to the primary winding.

The LED driver according to claim 2, wherein the feedback circuit is configured to: - receive as a second signal a voltage signal from the auxiliary winding of the flyback converter; - apply a low-pass filtering of the voltage signal; - coupling the low-pass filtered signal via a capacitor to the first signal, thereby adding the time derivative of the low-pass filtered signal to the first signal.

4. LED driver according to claim 1 or 2, wherein the first signal is obtained via an optocoupler.

The LED driver of any of the preceding claims, further comprising a capacitance coupled to the input terminal.

6. In which the capacity is a buffer capacity.

7. LED driver according to one of the preceding claims, further comprising a rectifying diode connected to the secondary winding.

8. LED driver as claimed in claim 7, further comprising a capacitance coupled to the rectifying diode for supplying the supply voltage.