EP3231255A1

EP3231255A1 - Driving circuitry for a lighting arrangement

Info

Publication number: EP3231255A1
Application number: EP15867454.9A
Authority: EP
Inventors: Mikael Pettersson; Iman HABIB; Gustav Josefsson
Original assignee: Switchtech An
Current assignee: Vadsbo Transformatorer AB
Priority date: 2014-12-12
Filing date: 2015-12-11
Publication date: 2017-10-18
Anticipated expiration: 2035-12-11
Also published as: EP3231255A4; EP3231255B1; WO2016093767A1

Abstract

The present invention generally relates to a driving circuitry for a lighting arrangement comprising at least one light emitting diode (LED). The invention also relates to a lighting arrangement comprising such a driving circuitry.

Description

DRIVING CIRCUITRY FOR A LIGHTING ARRANGEMENT

TECHNICAL FIELD

BACKGROUND OF THE INVENTION

Light emitting diodes, LEDs, are employed in a wide range of lighting applications. As LEDs have the advantage of providing controllable light in a very efficient way, it is becoming increasingly attractive to use LEDs as an alternative light source instead of traditional incandescent and fluorescence light sources. Furthermore, LEDs are

advantageous since they may allow for simple control in respect to e.g. dimming.

Known electrical circuits for driving LEDs include on one hand linear mode driving circuits. Such linear mode driving circuits are known to the skilled person and may be implemented in many different ways. A linear current driver comprises an amplification element (such as, for example, an operational amplifier, a transistor, MOSFET or other comparable component) and a current sensing means for sensing a current through the driver and controlling the amplification element to achieve an analogue control with feedback. Linear current drivers can be designed to have the advantage of simple implementation, but are known to introduce high losses.

Another known type of driving circuit is a switching-mode power supply (SMPS). Such a driving circuitry comprises at least one switching element and an energy storage element (such as an inductance or capacitance, or both). An output voltage is generated by sequential switching operations of the switching element. By controlling the duty cycle, the output may be controlled. Switching converters are known for high efficiency, but to introduce unwanted disturbances, e.g. propagating to an AC mains grid supplying electrical energy to the driving circuitry.

To fulfill AC mains power factor requirements, the SMPS can include active Power-Factor-Correction (PFC) circuitry that controls the input current so that the input current waveform is in phase with the waveform of the AC input voltage (e.g., a sine wave). For a high power factor, the input current waveform will have approximately the same shape and phase as the AC input voltage waveform, but will vary in amplitude or Root Mean Square (RMS) value. Conventional SMPS driving circuits for LED drivers having PFC circuitry typically require large electrolytic capacitors, which are bulky, unreliable and can shorten the life of the SMPS system and therefore the overall lighting arrangement.

There is thus a desire to provide further enhancements in relation to a driving circuitry for a lighting arrangement, typically adapted for driving/controlling a lighting arrangement comprising at least one LED. Specifically, it is desirable to provide

enhancements in relation to operational lifetime and size of the driving circuitry, as well as in relation to improved energy efficiency, low stand-by power and by introducing a minimal amount of interference.

Further attention is drawn to US2011080110, disclosing a light-emitting diode (LED) driver implemented using a linear regulator and analog circuitry arranged at a primary side of a thereto comprised flyback transformer.

In addition, in US2011241569 there is disclosed a method for operation of an actively clocked PFC circuit with a connected load circuit at the output of the PFC circuit, wherein the load circuit has a lighting means, in particular one or more LEDs.

SUMMARY OF THE INVENTION

According to an aspect of the invention, the above is at least partly alleviated by a driving circuitry for a lighting arrangement comprising at least one light emitting diode (LED), the driving circuitry comprising a primary side galvanically separated from a secondary side, wherein the driving circuitry further comprises a primary side switched power converter comprising a transformer having a primary and a secondary winding, wherein the primary side power converter is configured to receive an alternating voltage (AC) input and to provide a rippled (time varying) direct current (DC) output, a first control unit having computational capability, the first control unit connected to and configured to control the operation of the primary side switched power converter, a secondary side switched power converter configured to receive the rippled DC output from the primary side power converter and to provide a ripple reduced DC output to the lighting arrangement, a second control unit having computational capability, the second control unit connected to and configured to control the operation of the secondary side switched power converter, a bulk capacitor connected to the input of the secondary side switched power converter, and a digital communication interface configured to allow a galvanically separated bi-directional data communication between the first and the second control unit, wherein the second control unit is further configured to adjust a secondary switching frequency for the secondary side switched power converter according to a secondary side switching pattern, to receive a representation of a sampled voltage level across the bulk capacitor and to transmit the sampled voltage level to the first control unit, and wherein the first control unit is further configured to control a current level at the primary side switched power converter based on the sampled voltage level of the bulk capacitor received from the second control unit, and to control a primary switching frequency of the primary side switched power converter based on the primary side switching pattern.

By means of the invention, an advantageous control of the different component and their individual operation is achieved in a distributed manner by separating the control functionality between the primary and secondary side using a first and a second control unit. Because the control functionality is separated between the primary and secondary side, a bidirectional interface is provided for allowing at least some control functionality to be synchronized, e.g. by bidirectional transmission of data between the first and the second control unit. Within the context of the invention, the control unit is preferably a micro processor or any other type of computing device having some form computational capability. The control unit could possibly be implemented as an ASIC.

In addition, by the hardware implementation as is suggested in accordance with the invention, it is possible to arrange the bulk capacitor on the secondary side, thereby minimizing the stress forced upon the bulk capacitor. This is made possible as the voltage level applied to the bulk capacitor is lower as compared to the peak values at the alternating input. Thus, also the size of the bulk capacitor may be reduced as compared to when in accordance with prior art, the bulk capacitor is arranged at the primary side.

Within the context of the invention, the expression "ripple reduced DC output", which is the DC output being provided to the lighting arrangement, this expression should throughout the description be understood to mean an essentially constant power flicker free DC signal used for operating the lighting arrangement. In addition, it should be understood that the ripple reduced DC output provided as an output from the secondary side power converter comprises less ripple as compared to what is received at an input to the secondary side power converter.

In a preferred embodiment of the invention, the second control unit is further configured to receive a representation of a current operational point of the lighting arrangement and to transmit the representation of the current operational point to the first control unit, and wherein the first control unit is further configured to control the current level at the primary side switched power converter based on the current operational point. In a possible embodiment, the first control unit is further configured to receive a representation of a sampled voltage level of the alternating input and to control the current level at the primary side switched power converter based on the sampled input voltage level.

It may in one embodiment be preferred to further control the current level at the primary side switched power converter by modulating a power level transferred from the primary side switched power converter to the secondary side switched power converter to be in linear proportion to the alternating input. It is preferred to modulate the power level in phase with the alternating input. The expression "in phase" would however be interpreted broadly, i.e. not necessarily being in exact phase of the alternating input but rather having a close relation (linear approximation) to the alternating input. Other advantages generally following with the invention include less component count as compared to separate dedicated hardware implemented PFC stages where the AC input energy is stored in a bulk capacitor (and inductor) on the primary side and then further transformed using a galvanically separated converter. By including the PFC switching behavior in the galvanically isolated converter the size and complexity of the overall solution may be minimized. This is made possible by digital control and communication between the primary and secondary side control units for the primary and secondary side converters respectively. The regulation and transient response in change of load conditions is made possible by transmission of a representation of measured values rather than simple over voltage indications across the galvanically isolated bi-directional interface.

Within the context of the invention, it is preferred to configure the second control unit to transmit the secondary switching frequency to the first control unit, and the first control unit is further configured to base the primary switching frequency on the secondary switching frequency received from the second control unit. This feature will allow for a synchronized switching of the driving circuitry, possibly allowing the primary and secondary side to be switched in such a manner that the frequency response of the switching is "spread out", thereby allowing for an overall reduction of unwanted disturbances back to the AC mains. This feature will allow for the possibility to set the switching frequency of the second converter in respect to the primary side converter and vice versa. The switching frequencies could be chosen so that the primary side and secondary side switch at frequencies that does not generate overtones close to each other at each moment. In another algorithm the switching frequency could be chosen so that the primary side and secondary side follows the same switching pattern so that the frequency content of a base tone and or overtones are in phase or at a defined phase shift in relation to each other. These and similar algorithms will typically allow for the possibility to comply with relevant electromagnetic interference (EMI) specifications.

It should be noted that within the scope of the invention it may be possible to dynamically adjust at least one of the primary side and the secondary side switching patterns based on at least one of the sampled voltage level across the bulk capacitor and the power level. Preferably, at least one of the primary side and the secondary side switching pattern is dynamically adjustable based on at least one of the sampled voltage level across the bulk capacitor and the power level. The dynamic adjustability allows for the possibility of reducing the number of and size of electromagnetic compatibility (EMC) components necessary in the design in order to fulfill the AC mains current harmonic standards (i.e.

comply with current regulations). This may in accordance with the invention be achieved by allowing the control units to be "aware" of the EMI characteristics of the hardware at the specific operating point in order to optimize the shape and timing of switching patterns for both primary and secondary side converters. Within the context of the invention, the expression "aware" should be interpreted broadly and will for example include a present operating point for the load (point of load), for example based on previously determined voltage and current levels for the load. The determined point of operation may subsequently be used as a pointer to e.g. a look-up-table holding information as to previously determined (previously measured or previously modeled) EMI characteristics for the hardware comprised with the driving circuitry. The EMI characteristics may be determined using e.g. a spectrum analyzers.

In a possible embodiment of the invention, the first control unit is further configured to receive data requesting a change in output level ("dimming") of the lighting arrangement and to transmit data corresponding to the requested change to the second control unit, and the second control unit is configured to adjust the ripple reduced DC output provided to the lighting arrangement based on the change request received from the first control unit. This feature will allow primary side reception of control data to easily be relayed to the secondary side. For example, the driving circuitry may be configured to receive Digital Addressable Lighting Interface (DALI) control data at the primary side for provision to the secondary side where the second control unit adapts the operation of the secondary side switched power converter based on the DALI control data. The e.g. DALI control data may be received by a first input interface connected to the first control unit. Furthermore this will allow for other types of user input modes including phase pulse switching and phase cut dimming including triac and transistor dimming of the mains input power, consequently the alternating input may be used for controlling the output level of the lighting arrangement. The invention allows for such input change to be transmitted using the digital interface to the secondary side without need for separate galvanic separated communication interfaces. In addition, this will allow for a high power factor even without a proper sinusoidal shape of the incoming voltage.

It may also, for example additionally, be possible to include a second input interface connected to the second control unit, and the second input interface is configured for receiving the data requesting a change in output level of the lighting arrangement and to adjust said output level accordingly. The input interface connected to the second control unit may for example be configured to be connected to wireless transceiver arranged at the secondary side. The wireless transceiver may for example be one of a Bluetooth, Zigbee, a WiFi transceiver, or any other ISM band technology (present or future).

In a possible embodiment of the invention the wireless transceiver in combination with e.g. the second control unit may be configured for allowing remote Internet based control of the driving circuitry. For example, based on the suggested implementation the driving circuitry could be given e.g. an IP address, allowing the driving circuitry to download updated control algorithms to be executed by the first and/or second control unit. Furthermore, the driving circuitry according to the invention could also be adapted for new lighting arrangements being placed on the market, i.e. at a later point in time as compared to when the driving circuitry was first put in operation. Still further, the driving circuitry could in one embodiment be configured to a broadcast a URL for the driving circuitry allowing easy access to the driving circuitry, e.g. implemented within the context of "The Physical Web". Alternatively, or also, the driving circuitry may be implemented as an uniquely identifiable device within the context of "Internet of Things", allowing simple connection to the driving circuitry

In a preferred implementation of the invention, the first control unit is further configured to determine a requested output level of the lighting arrangement based on information coded within the alternating input and to transmit data to the second control unit, where the second control unit is configured to adjust the ripple reduced DC output provided to the lighting arrangement based on the request received from the first control unit. In this embodiment the first control unit may be configured to "decode' the voltage waveform of the alternating input. When using e.g. a tyristor or transistor dimmer, the phase angle is adjusted. The first control unit determines the present state of the alternating input and computes a related output level of the lighting arrangement. Data corresponding to the requested output level is transmitted from the first control unit to the second control unit. The second control unit will subsequently adjust the operation of the secondary side switched power converter such that the lighting arrangement operates at the requested output level.

Preferably, the operational control functionality provided by the control units allow for the possibility of changing control parameters in real time, for example depending on operating conditions of the lighting arrangement, and hence the behavior of the driving circuitry from a control point of view. This is in accordance with the invention achieved by allowing the control units to be "aware" of the dynamic behavior of the components constituting the different converter stages. In addition, the operational control functionality provided by the control units also allow for the possibility of seamless stepping (or "mixing") between current control dimming and pulse width modulation (PWM) mode depending on selected power level that enable high color accuracy of the LEDs while at the same time taking advantage of high efficiency from current dimming. In a similar manner as discussed above, in accordance with the invention, the control parameters may be allowed to be dependent on previously determined (previously measured or previously modeled) dynamic behavior for the components constituting the different converter stages. That is, when dynamically adjusting the control parameters it may in accordance with the invention be possible to achieve e.g. optimum transient response when having prior knowledge of how the components will function/respond to different driving conditions. In regard to a mixed current control and PWM dimming scenario, this may e.g. be realized by the selection of a minimum current level and the frequency selected in relation to PWM. Within the context of the invention it may also be possible to "match" a dimming level (not necessarily being a combined current control and PWM dimming scenario) with the EMI characteristic of the driving circuitry.

In a possible embodiment of the invention the driving circuitry further comprises a programmable user interface, such as e.g. a dip-switch, connected to the second control unit for allowing reprogramming of the second control unit. For example, different constant voltage and constant current modes selectable by a user may be defined as a binary- bit pattern decoded by the control units allowing the maximum number of perturbations and also allowing arbitrary values for the settings. The binary-bit pattern may be provided as an input to the second control unit using the above mentioned dip-switch. In a possible scenario, some of the possible predefined binary-bit patterns may be provided for controlling different operating points for the driving circuitry, e.g. in relation to a power level for the load. It may also be possible to use some binary-bit pattern for debugging, development, etc. For electrically powering the first control unit, there may be possible to arrange the transformer to also include an auxiliary primary winding connected to a further primary side switched power converter connected to a first low-dropout regulator (LDO) configured to power the first control unit, the further primary side switched power converter and the first LDO comprised with the driving circuitry. The further primary side switched power converter is preferably operated by the first control unit. It may in accordance with the invention be possible to provide a similar implementation for the second control unit, i.e. by providing an auxiliary secondary winding connected to a further secondary side switched power converter connected to a second LDO configured to power the second control unit. In a similar manner as above, the further secondary side switched power converter is preferably operated by the second control unit.

The suggested implementation with a first and/or a second LDO allow for further optimization in relation to energy efficiency of the inventive driving circuitry. The synergistic effect of allowing the respective further switched power converter to be controlled by the respective control unit further shows the advantages with distributed control and operation for the driving circuitry. Advantages following the use of LDO technology is simple and inexpensive implementation/operation as well as low stand-by power

consumption.

The driving circuitry as discussed above preferably forms part of a lighting arrangement further comprising at least one light emitting diode (LED). The lighting arrangement may in such an embodiment be seen as a luminaire, typically further comprising means for out coupling of light emitted by the at least one LED during operation.

The components forming the driving circuitry are typically arranges on a printed circuit board (PCB), e.g. having an input port for receiving power from the AC mains and having at least one output for providing power to the lighting arrangement. In addition, a first and a second input interface port may be provided at the PCB for receiving data requesting the change in output level of the lighting arrangement. The first and a second input interface may typically be low voltage input ports, such as e.g. DALI, 0 - 10 V, etc. as will be understood by the person skilled in the art.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled addressee realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawing, in which:

Fig. 1 illustrates a driving circuitry in accordance with a currently preferred embodiment of the invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

Referring now to Fig. 1, there is illustrated a driving circuitry 100 for controlling the operation of a load, such as a lighting arrangement 102 comprising at least one light emitting diode (LED). The driving circuitry 100 comprises a primary side switched power converter 104 and a secondary side switched power converter 106. A transformer 108 is comprised with the primary side switched power converter 104, where the transformer 108 efficiently provides a galvanic separation between a primary and a secondary side of the driving circuitry 100 (in Fig. 1 illustrated as an isolation barrier).

The transformer 108 comprises a primary and a secondary winding, where the primary and secondary winding typically are selected based on the type of switching technology used for, at least, the primary side switched power converter 104. For example, in an embodiment of the invention the primary side switched power converter 104 may be configured as a flyback converter, the transformer 108 may be selected as an inductor- transformer, thus having a somewhat different construction as compared to a "normal" transformer. Specifically, the primary side switched power converter 104 is preferably arranged as a single stage PFC converter. Alternatively, the primary side switched power converter 104 may be implemented as a forward switched power converter or a push-pull forward switched power converter. In the illustrated embodiment, the driving circuitry 100 further comprises an input filter 110, typically connected to a power line 112. The input filter 110 has provided for preventing electromagnetic interference, generated by the primary side switched power converter 104 from reaching the power line 112, for interfering with the components of the driving circuitry 100, and affecting other equipment. A rectifier bridge 114 is provided between the input filter 110 and the primary side switched power converter 104.

In addition, in accordance with the invention a first control unit 116 and a second control unit 118 are comprised with the driving circuitry 100. The first control unit 116 is connected to and configured to control the operation of the primary side switched power converter 104, whereas the second control unit 118 is connected to and configured to control the operation of the secondary side switched power converter 106. A communication interface 120 is also comprised with the driving circuitry 100 and configured to allow galvanically separated bi-directional data communication between the first 116 and the second 118 control unit. The communication interface 120 may for example be implemented using opto-coupling technology. Alternatively, it may be possible to use capacitive or inductive (e.g. an air-core transformer) high frequency technology for the same purpose. The first 116 and the second 118 control units are preferably implemented as digital

microprocessors, typically each comprising a plurality of analog-to-digital input stages for measuring e.g. voltage/current levels at different "positions" of the driving circuitry. Various information may be transmitted via the communication interface 120, such as measured values, states and/or control signals, etc. The information may be transmitted

asynchronously. The information transmitted between the first 116 and the second 118 control unit via the communication interface 120 is preferably digital. It should be noted that is in accordance with the invention may be possible to include more than one control unit on the primary side and more than one control unit on the secondary side. The number of control units used on either of the primary/secondary side may depend on the selected

implementation strategy and the computational demand of the driving circuitry 100.

Furthermore, the inventive driving circuitry 100 comprises a first capacitor 122, for example arranged on the primary side between the rectifier bridge 114 and the primary side switched power converter 104. The driving circuitry 100 also comprises a bulk capacitor 124 arranged on the secondary side and connected to the input of the secondary side switched power converter 106. The bulk capacitor 124 is typically an electrolytic capacitor having a larger capacitance as compared to the first capacitor 122. The first capacitor 122 is preferably not an electrolytic capacitor. In a possible implementation of the invention, the bulk capacitor 124 is configured to operate in a voltage range of 70 - 100 V, allowing the rippled DC output received from the primary side switched power converter 104 to ripple within this range. It may of course be possible to implement the driving circuitry 100 in a different manner, i.e. where the voltage range is selected to be higher or lower.

During operation of the driving circuitry 100, the power line 112 is electrified by an alternating voltage (AC) input, for example being in the range from 85 - 264 VAC. The alternating input will be received by the rectifier bridge 114, which will provide a time varying input to the primary side switched power converter 104. A first switching element 126 comprised with the primary side switched power converter 104 will be operated by the first control unit 116, based on a desired output level, V3, to be provided to the secondary side power converter 106. The first switching element 126 will be operated at a primary switching frequency, the primary switching frequency being based on a primary side switching pattern.

The primary side switched power converter 104 will in turn generate a rippled

(also referred to as time varying) direct current (DC) output to be provided to the secondary side switched power converter 106, the secondary side switched power converter 106 for example being implemented as a buck converter. It could also in an alternative embodiment be implemented as a zero voltage/current switching buck-boost converter. A (or a plurality of) second switching element(s) (not shown) of the secondary side switched power converter 106 will in turn be operated at a secondary switching frequency, the secondary switching frequency being based on a secondary side switching pattern, and provide the desired output level, V3, to the lighting arrangement 102.

In addition, the second control unit 118 will during operation of the driving circuitry 100 sample, e.g. using an analog-to-digital input channel, a voltage level across the bulk capacitor 124, V2, and transmit the sampled voltage level via the communication interface 120 to the first control unit 116. The first control unit 116 will in a similar manner sample a voltage level, VI, at the first capacitor 122. The sampled voltage level across the bulk capacitor 124, V2, and the sampled voltage level, VI, at the first capacitor 122 will be used by the first control unit 116 for controlling the current through a sensing resistor connected in series with the first switching element 126.

In addition to the above, e.g. the second control unit 118 may be configured to sample a plurality of additional voltage/current levels at the secondary side of the driving circuitry 100, use these sampled values for controlling the operation of the secondary side switched power converter 106, and for communicating the sampled,

compiled/computed/derived values to the first control unit 116. Such additional sampled values may for example include the current operational point of the lighting arrangement 102. It is preferred to allow the current operational point of the lighting arrangement 102 to be communicated (using the digital communication interface 120) to the first control unit 116, where the first control unit 116 includes the current operational point of the lighting arrangement 102 with its computation of the value of the current level at the primary side switched power converter. The current operational point may typically be a current power level for the lighting arrangement 102, e.g. relating to a dimming level for the lighting arrangement 102. The dimming level may be provided as an instruction to the driving circuitry 100 as is elaborated above and below.

The first control unit 116 is typically configured in a similar manner, i.e. to sample a plurality of different voltage/current levels at the primary side of the driving circuitry 100, use these sampled values for controlling the operation of the primary side switched power converter 104, and for communicating the sampled values to the second control unit 118.

As is indicated above, the driving circuitry 100 according to the invention is adapted to be controlled for optimized energy efficiency and operated to minimize

radiated/conducted electromagnetic interference. This is in accordance with the invention achieved by controlling the power transmitted from the primary side switched power converter 104 by modulating a power level transferred from the primary side switched power converter 104 to the secondary side switched power converter 106 to be in linear proportion to the alternating input, and preferably modulated in phase with the alternating input, VI, and/or preferably to maximize efficiency of the driving circuitry 100.

In addition, for reducing the interference generated by the driving circuitry

100, the inventive implementation comprising the first 116 and the second 118 control unit will allow for an individual control of the switching frequency of the primary 104 and the secondary 106 side switched power converter. Specifically, during operation of the driving circuitry 100, it may for example be possible to control the secondary switching frequency based on the (current) operational point of the lighting arrangement 102, e.g. the sampled voltage/current/power level at the lighting arrangement 102. The secondary switching frequency may thus be selected based on different operational conditions of the driving circuitry 100, where different secondary switching frequencies for operating the secondary side switched power converter 106 may be stored in a memory section comprised with the second control unit 118. The second control unit 118 may, based on sampled voltage/current levels, look-up (e.g. retrieve from a predetermined table memory) and/or calculate a preferred secondary switching frequency. In such an embodiment, data representing the secondary switching frequency is transferred to the first control unit 116, and used in selecting a primary switching frequency for operating the primary side switched power converter 104.

Accordingly, similar look-up functionality may be implemented in the first control unit 116. In a preferred embodiment, a plurality of operational conditions for the driving circuitry 100 may be "pre-identified", e.g. during testing of the driving circuitry 100. As such, it may for example be possible to perform EMC testing for a selected plurality of operational conditions, where the first and the second switching frequencies are individually adjusted for minimizing any interference generated by the driving circuitry 100. It may also be possible to take into account different operational temperatures for the driving circuitry 100, i.e. in optimizing the operation of the driving circuitry 100. In such an embodiment a temperature sensor may be comprised with the driving circuitry 100 and connected to the first 116 and/or the second 118 control unit.

It should be understood that any determinations/calculations done based on any measured value may be performed by either of the control units 116, 118. That is, data transferred between the control units 116, 118 may be any of representations and/or

"measurements values". Accordingly, the determinations/calculations performed in accordance with the invention may by means of the presented hardware configuration be truly distributed between the control units 116, 118 and thus performed where it fits best. Therefore, for example look-up functionality and similar may be stored at either of the control units 1 16, 1 18.

In the illustrated embodiment the driving circuitry 100 is provided with a first 128 and a second 130 input interface, typically for controlling a light output level of the lighting arrangement 102.

In summary, the present invention relates to a driving circuitry for a lighting arrangement comprising at least one light emitting diode (LED), the driving circuitry comprising a primary side galvanically separated from a secondary side, wherein the driving circuitry further comprises a primary side switched power converter comprising a

transformer having a primary and a secondary winding, wherein the primary side power converter is configured to receive an alternating voltage (AC) input and to provide a rippled (time varying) direct current (DC) output, a first control unit connected to and configured to control the operation of the primary side switched power converter, a secondary side switched power converter configured to receive the rippled DC output from the primary side power converter and to provide a ripple reduced DC output to the lighting arrangement, a second control unit connected to and configured to control the operation of the secondary side switched power converter, a bulk capacitor connected to the input of the secondary side switched power converter, and a communication interface configured to allow a galvanically separated bi-directional data communication between the first and the second control unit, wherein the second control unit is further configured to adjust a secondary switching frequency for the secondary side switched power converter according to a secondary side switching pattern, to receive a representation of an sampled voltage level across the bulk capacitor and to transmit the sampled voltage level to the first control unit, and wherein the first control unit is further configured to receive a representation of an sampled voltage level of the alternating input, to control a current level at the primary side switched power converter based on the sampled input voltage level and the sampled voltage level of the bulk capacitor received from the second control unit, and to control a primary switching frequency of the primary side switched power converter based on the primary side switching pattern.

Advantages with the invention include individual and distributed operation by separating the control functionality between the primary and secondary side using a first and a second control unit. In addition, by the hardware implementation as is suggested in accordance with the invention, it is possible to arrange the bulk capacitor on the secondary side, thereby minimizing the stress forced upon the bulk capacitor. This is made possible as the voltage level applied to the bulk capacitor is lower as compared to the peak values at the alternating input. Thus, also the size of the bulk capacitor may be reduced as compared to when in accordance with prior art, the bulk capacitor is arranged on at the primary side.

In addition, the control functionality of the present disclosure may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium.

Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

Although the figures may show a sequence the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. Additionally, even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art.

Further, a single unit may perform the functions of several means recited in the claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The person skilled in the art realizes that the present invention is not limited to the preferred embodiments.

Claims

1. A driving circuitry for a lighting arrangement comprising at least one light emitting diode (LED), the driving circuitry comprising a primary side galvanically separated from a secondary side, wherein the driving circuitry further comprises:

- a primary side switched power converter comprising a transformer having a primary and a secondary winding, wherein the primary side power converter is configured to receive an alternating voltage (AC) input and to provide a rippled direct current (DC) output;

- a first control unit having computational capability, the first control unit connected to and configured to control the operation of the primary side switched power converter;

- a secondary side switched power converter configured to receive the rippled

DC output from the primary side power converter and to provide a ripple reduced DC output to the lighting arrangement;

- a second control unit having computational capability, the second control unit connected to and configured to control the operation of the secondary side switched power converter;

- a bulk capacitor connected to the input of the secondary side switched power converter; and

- a digital communication interface configured to allow a galvanically separated bi-directional data communication between the first and the second control unit, wherein the second control unit is further configured to adjust a secondary switching frequency for the secondary side switched power converter according to a secondary side switching pattern, to receive a representation of a sampled voltage level across the bulk capacitor and to transmit the sampled voltage level to the first control unit, and

wherein the first control unit is further configured to control a current level at the primary side switched power converter based on the sampled voltage level of the bulk capacitor received from the second control unit, and to control a primary switching frequency of the primary side switched power converter based on the primary side switching pattern.

2. The driving circuitry according to claim 1 , wherein the second control unit is further configured to receive a representation of a current operational point of the lighting arrangement and to transmit the representation of the current operational point to the first control unit, and wherein the first control unit is further configured to control the current level at the primary side switched power converter based on the current operational point.

3. The driving circuitry according to any one of claims 1 and 2, wherein the first control unit is further configured to receive a representation of a sampled voltage level of the alternating input and to control the current level at the primary side switched power converter based on the sampled input voltage level.

4. The driving circuitry according to any one of the preceding claims, wherein the current level at the primary side switched power converter is further controlled by modulating a power level transferred from the primary side switched power converter to the secondary side switched power converter to be in linear proportion to the alternating input.

5. The driving circuitry according to claim 4, wherein the power level is modulated in phase with the alternating input.

6. The driving circuitry according any one of the preceding claims, wherein the second control unit is configured to transmit the secondary switching frequency to the first control unit, and the first control unit is further configured to base the primary switching frequency on the secondary switching frequency received from the second control unit.

7. The driving circuitry according to claim 6, wherein first and the second control unit are configured to synchronize the switching of the primary and secondary side switched power converter.

8. The driving circuitry according to any one of claims 4 - 6, wherein at least one of the primary side and the secondary side switching pattern is dynamically adjusted based on at least one of a power level at an input of the driving circuitry, a power level at an output of the driving circuitry or a voltage level at the output of the driving circuitry.

The driving circuitry according to any one of the preceding claims, wherein at of the primary side and the secondary side switching pattern is selected based on a predetermined electromagnetic interference (EMI) characteristic of the components of the driving circuitry.

10. The driving circuitry according any one of the preceding claims, wherein the first control unit is further configured to receive data requesting a change in output level of the lighting arrangement and to transmit data corresponding to the requested change to the second control unit, and the second control unit is configured to adjust the ripple reduced DC output provided to the lighting arrangement based on the change request received from the first control unit.

1 1. The driving circuitry according to claim 10, wherein the driving circuitry further comprises a first input interface connected to the first control unit, and the first input interface is configured for receiving the data requesting the change in output level of the lighting arrangement.

12. The driving circuitry according any one of the preceding claims, wherein the driving circuitry further comprises a second input interface connected to the second control unit, and the second input interface is configured for receiving the data requesting a change in output level of the lighting arrangement and to adjust said output level accordingly.

13. The driving circuitry according any one of the preceding claims, wherein the driving circuitry further comprises a programmable user interface connected to the second control unit for allowing programming of settings for the second control unit.

14. The driving circuitry according any one of the preceding claims, wherein the first control unit is further configured to determine a requested output level of the lighting arrangement based on information coded within the alternating input, to transmit data corresponding to the request to the second control unit, and the second control unit is configured to adjust the ripple reduced DC output provided to the lighting arrangement based on the change request received from the first control unit.

15. The driving circuitry according to any one of the preceding claims, wherein the primary side switched power converter comprising the transformer together with the first control unit forms a single stage PFC power converter.

16. The driving circuitry according to any one of the preceding claims, wherein the transformer further comprises an auxiliary primary winding connected to a further primary side switched power converter connected to a first low-dropout regulator (LDO) configured to power the first control unit, the further primary side switched power converter and the first LDO comprised with the driving circuitry.

17. The driving circuitry according to claim 16, wherein the further primary side switched power converter is operated by the first control unit.

18. The driving circuitry according to any one of the preceding claims, wherein the transformer further comprises an auxiliary secondary winding connected to a further secondary side switched power converter connected to a second LDO configured to power the second control unit, the further secondary side switched power converter and the second LDO comprised with the driving circuitry.

19. The driving circuitry according to claim 18, wherein the further secondary side switched power converter is operated by the second control unit.

20. Lighting arrangement, comprising:

- at least one light emitting diode (LED), and

- a driving circuitry according to any one of the preceding claims for powering the at least one LED.