Fast startup circuit and method for driver circuits

Abstract

The invention relates to a fast startup circuit and method for self-supplied single-stage drivers with large energy storage buffer capacitance. An auxiliary winding for supplying a controller on the primary side of a transformer may comprise a tapped winding and a selector for choosing a proper winding for supplying the controller. During an initial charging phase of an output capacitor in the startup phase, a voltage supply capacitor of the controller is connected to an enlarged auxiliary winding, thus applying a higher voltage to the voltage supply capacitor. Once the supply voltage has reached a maximum level, the selector switches to a tap to thereby reduce the connected voltage.

Description

[0001] Fast startup circuit and method for driver circuits

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of power supplies for lighting systems, such as - but not limited to - solid-state lighting systems or other loads, for use in various different applications for home, office, retail, hospitality and industry.

[0004] BACKGROUND OF THE INVENTION

[0005] A luminaire can be any type of lighting unit or lighting fixture which comprises one or more light sources (e.g., visible or non-visible (infrared (IR) or ultraviolet (UV)) light sources) for illumination and / or communication purposes and optionally other internal and / or external parts necessary for proper operation of the lighting, e.g., to distribute the light, to position and protect the light sources and ballast (where applicable), and to connect the luminaires to a power supply.

[0006] Solid-state lighting (SSL) is a type of lighting that uses semiconductor lightemitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gas. Solid state electroluminescence is used in SSL, as opposed to incandescent bulbs (which use thermal radiation) or fluorescent tubes. Compared to incandescent lighting, SSL creates visible light with reduced heat generation and less energy dissipation.

[0007] A driver is required to deliver a highly stable constant current to the luminaire(s) irrespective of variations in the luminaire characteristics or the supply voltage while complying with increasingly stringent regulations covering power factor and harmonic distortion.

[0008] Basic elements of a two-stage luminaire driver may be a power factor correction (PFC) stage followed by a constant current (CC) driver (e.g., a flyback converter). Each stage in the driver introduces losses. If the two functions of PFC and CC drive were to be combined into a single stage, many fewer components would be required and efficiency could be increased. With only one switching stage, the single-stage driver can significantly increase efficiency whilst dramatically reducing component cost. Therefore, single-stage drivers for luminaires are low cost and energy efficient. They are widely used in massproduction lighting products.

[0009] However, single-stage drivers suffer from high ripple current and thus a high stroboscopic visibility measure (SVM). SVM is a measure of the probability of a stroboscopic effect. The threshold of visibility of a stroboscopic effect is the value of SVM equal to or greater than 1. If the value is less than 1, the stroboscopic effect will not be visible for the observer. It is known to apply ripple removers to reduce SVM, however at the cost of energy efficiency. Energy efficiency has become a hot topic in recent years. New Class A light sources have to achieve 210 Im / W efficacy. Driver loss is one of the major factors for Class A.

[0010] To reduce the ripple, one may consider adding more storage capacitors to the switching stage. A consequence of adding large electrolytic capacitors is the long startup time since the capacitor bank has to be charged to a sufficient voltage level exceeding the luminaire threshold voltage. During this process the energy stored in the voltage supply capacitor at the primary side depletes to a low level and may trigger an undervoltage lockout (UVLO) protection of the controller. This results in multiple driver startup attempts and delayed light generation and / or light flashing during startup. Thereby, driver components can be overstressed during the startup phase.

[0011] SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide reduced startup time of single-stage drivers with large storage capacitance of the switching stage.

[0013] This object is achieved by an apparatus as claimed in claim 1, by a driver device as claimed in claim 3, by a lighting system as claimed in claim 8, by a method as claimed in claim 9, and by a computer program product as claimed in claim 10.

[0014] According to a first aspect, an apparatus (e.g., an electronic circuit or a (programmable) integrated circuit (such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) or a programmable controller) for controlling a driver device having one or more output storage capacitors for suppling power to a load device is provided, the apparatus being configured to monitor a level of a supply voltage at an voltage supply capacitor of the driver device, and to control a selector to apply a first charging current to the voltage supply capacitor when a startup level of the supply voltage has been reached and to switch to a lower second charging current in response to a detection that the level of the supply voltage has reached a predetermined maximum level.

[0015] Furthermore, according to a second aspect, a driver device is provided that comprises an apparatus of the first aspect and a transformer for supplying power to the one or more output storage capacitors, wherein the selector is configured to select the first and second charging currents from different terminals of at least one auxiliary winding of the transformer.

[0016] Furthermore, according to a third aspect, a lighting system comprising a plurality of driver devices of the second aspect connected to respective luminaires is provided.

[0017] Additionally, according to a fourth aspect, a method of controlling a driver device having an output storage capacity for supplying power to a load device is provided, the method comprising monitoring a level of a supply voltage at an voltage supply capacitor of the driver device, applying a first charging current to the voltage supply capacitor when a startup level of the supply voltage has been reached, and switching to a lower second charging current in response to a detection that the level of the supply voltage has reached a predetermined maximum level.

[0018] Moreover, according to a fifth aspect, a computer program product is provided, which comprises code means for producing the steps of the above method of the fourth aspect when run on a controller device.

[0019] Accordingly, a fast startup circuit and method for various types of driver devices (such as self-supplied single-stage drivers) with large energy storage buffer capacitance is provided. During the initial charging phase of the output capacitor in the startup phase, the voltage supply capacitor of the driver device (e.g., at the Vcc input of the controller) is supplied with an enlarged charging current (e.g., from an enlarged auxiliary winding), thus applying a higher voltage to the voltage supply capacitor. Once the supply voltage has reached a maximum value, the charging current is reduced (e.g., the selector switches to a tap of the auxiliary winding or another (portion of the) auxiliary winding). The auxiliary winding(s) for supplying the voltage supply capacitor on the primary side may comprise a tapped winding. A selector (switch) may be used for selecting the proper winding (portion) for supplying the voltage supply capacitor.

[0020] Thus, a fast startup can be achieved. As a further benefit, the tapped auxiliary winding may also allow for a wider output voltage window. According to a first option of any of the first to fifth aspects, a voltage detector may be provided (e.g., in or at the apparatus) for measuring the supply voltage and for controlling the selector to apply the first charging current to the voltage supply capacitor when the startup level of the supply voltage has been reached and to switch to the lower second charging current when the measured level of the input voltage has reached the predetermined maximum level.

[0021] According to a second option of any of the first to fifth aspects, which may be combined with the first option, the transformer may comprise at least two auxiliary windings for generating the first and second charging currents, and wherein the selector is configured to select one of the auxiliary windings to apply the lower second charging current and to select at least two of the auxiliary windings to apply the first charging current .

[0022] According to a third option of any of the first to fifth aspects, which may be combined with the first or second option, the at least two auxiliary windings may comprise a tapped winding.

[0023] According to a fourth option of any of the first to fifth aspects, which may be combined with any one of the first to third options, the selector may comprise a controllable switch for switching between terminals of the one of the auxiliary windings and the at least two of the auxiliary windings.

[0024] According to a fifth option of any of the first to fifth aspects, which may be combined with any one of the first to fourth options, the driver circuit may be a single-stage flyback LED driver.

[0025] It is noted that the above apparatus may be implemented based on discrete hardware circuitries with discrete hardware components, integrated chips, or arrangements of chip modules, or based on signal processing devices or chips controlled by software routines or programs stored in memories, written on a computer readable media, or downloaded from a network, such as the Internet.

[0026] It shall be understood that the apparatus of claim 1, the driver circuit of claim 3, the lighting system of claim 8, the method of claim 9, and the computer program product of claim 10 may have similar and / or identical preferred embodiments, in particular, as defined in the dependent claims.

[0027] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or above embodiments with the respective independent claim. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the following drawings:

[0030] Fig. 1 shows schematically a block diagram of a luminaire driver with fast startup circuit control according to various embodiments;

[0031] Fig. 2 shows schematically a waveform diagram of a Vcc startup voltage of a luminaire driver with large storage capacitor;

[0032] Fig. 3 shows schematically a circuit diagram of an example of an enhanced single-stage flyback LED driver with fast startup circuit according to an embodiment;

[0033] Fig. 4 shows schematically a waveform diagram of a Vcc startup voltage of the enhanced single-stage flyback LED driver with fast startup circuit shown in Fig. 3; and

[0034] Fig. 5 shows a flow diagram of a fast driver startup procedure according to various embodiments.

[0035] DETAILED DESCRIPTION OF EMBODIMENTS

[0036] Various embodiments of the present invention are now described, which are applicable to luminaires of a solid-state lighting system, such as semiconductor LEDs, semiconductor lasers, vertical-cavity surface emitting lasers (VCSELs), organic lightemitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination or light sources in visible or non-visible light spectra.

[0037] More specifically, the following embodiments are directed to LED luminaires. They can be implemented in connection with any type of LED module or board and are applicable to various kinds of LED drivers or converters of luminaires.

[0038] Fig. 1 shows schematically a block diagram of a luminaire driver with fast startup circuit control according to various embodiments.

[0039] It is noted that - throughout the present disclosure - the structure and / or function of blocks or circuit components with identical reference numbers that have been described before are not described again, unless an additional specific functionality is involved. Moreover, only those structural elements and functions are shown, which are useful to understand the embodiments. Other structural elements and functions are omitted for brevity reasons. A power supply AC voltage VAC (e.g., a power grid voltage of 110 or 220V at a mains frequency of 50 or 60Hz) is supplied to an electromagnetic interference (EMI) filter 10 which is an electronic device that attenuates electromagnetic interference from the power system to limit the noise in the system and lower a risk of malfunctioning of the luminaire driver.

[0040] The filtered AC voltage is then supplied to a rectifier stage (RECT) 20 which is an electronic device that converts the transformed AC voltage into a DC voltage by using one or more rectifying elements (e.g., diodes or other valve elements) that allow current to flow in a single direction only. In an example, the rectifier stage may be a full-bridge rectifier stage.

[0041] The rectified DC voltage is supplied to a high-voltage startup (HVSU) circuit 30 that is configured to supply a sufficient level of current to a supply voltage (Vcc) terminal of a switching stage (SW CTRL) 40 at switch-on, enabling a Vcc supply capacitor to charge rapidly and allowing the driver system to start up. This avoids the need for startup resistors that waste power and introduce noticeable delay on startup at low line voltages. The high- voltage startup circuit 30 may be an integrated part of the switching stage 40.

[0042] A converter stage of the luminaire driver may be configured as an isolating power converter and may comprise a switching part, magnetics (inductor / transformer), a converter output part (rectifying part) (CONV) 60 and a controller (not shown in Fig. 1) of the switching stage 40.

[0043] The switching stage 40 is configured to control the converter output part 60 of the converter stage via an electronic transformer (TRA) 50 to supply a desired power level to an LED luminaire 70. The converter stage may be a flyback converter, a forward converter, a resonant converter or the like.

[0044] When the terminal of the supply voltage Vcc at the terminal of the switching stage 40 reaches a predetermined start level (e.g., 15V), all internal functions of the switching stage 40 start to run to provide a driving pulse for the converter output part 60. At this time, a (tapped) auxiliary winding on the primary side of the transformer 50 may provide a required working voltage for the switching stage 40 via a selector (SEL) 80.

[0045] The selector 80 may be implemented as a controllable semiconductor switching circuit. In an example, the selector 80 may be a simple switching element for selecting one of at least two terminals of the (tapped) auxiliary winding for controlling / adjusting the level of the working voltage supplied to the Vcc terminal of the switching stage 40. The selection process of the selector 80 is controlled by a voltage detector (V-DET) 90 that is configured to measure the supply voltage at the Vcc terminal of the switching stage 40 and to control the selector 80 in response to the detected level of the supply voltage. The measurement or detection operation of the voltage detector 90 may be based on a resistive voltage divider and / or a comparator function that generates a control signal for the selector 80 if one or more predetermined levels of the supply voltage have been reached.

[0046] As mentioned above, the switching stage 40, the transformer 50 and the converter output part 60 are configured to operate as an electrical power converting device (power converter) that regulates the power to the LED luminaire 70 and that may respond to changing needs of the LED luminaire 70 by supplying a constant amount of power to the LED luminaire 70 as its electrical properties change e.g. with temperature. Thereby, the LED luminaire 70 can be provided with a very specific electrical power in order to operate properly. If the voltage supplied to the LED luminaire 70 is lower than required, very little current runs through the LED junction, resulting in low light and poor performance. On the other hand, if the voltage is too high, too much current flows through the LED junction and it can overheat and be severely damaged or fail completely (thermal runaway). This certainly applies to other kinds of luminaires or other load devices as well.

[0047] Fig. 2 shows schematically a waveform diagram of a Vcc startup voltage of a conventional luminaire driver with large storage capacitor (e.g., at the converter stage) without voltage detector 80 and selector 90 of Fig. 1.

[0048] As shown in Fig. 2, during startup, the Vcc capacitor at the voltage supply terminal of the switching stage is first charged through the high-voltage startup circuit. This may be a high-voltage junction field effect transistor (JFET) startup circuit (which may be integrated in a controller of the switching stage itself). When the voltage reaches a startup level Vccs (e.g., 20V), the controller of the switching stage starts operating and draws current from the Vcc capacitor. As a result, the Vcc supply voltage will drop since the current consumed by the controller is much higher than the high-voltage startup current (typically a few mA). At that time, the output voltage at the luminaire is still at very low level and not able to charge the Vcc capacitor through the auxiliary winding of the transformer. Thus, Vcc will continue to drop until it reaches the UVLO level (e.g., 6V), and the controller is disabled for a certain amount of time. Then, the Vcc capacitor is charged via the high-voltage startup circuit again and the cycle repeats. It can take several startup attempts, depending on the size of the storage capacitor of the converter stage, to reach a stable operation. The startup delay at a lower mains voltage (e.g., 120V) is longer, because the startup current of the high- voltage startup circuit is lower.

[0049] Thus, the Vcc startup voltage of a luminaire driver with large storage capacitors shows multiple startup attempts, which delays the luminaire startup process.

[0050] According to various embodiments, the combination of the tapped auxiliary winding of the primary side of the transformer 50 together with the voltage detector 90 and the selector 80 provides a quick startup circuit for the LED driver of Fig. 1. During the initial charging phase of the storage capacitor of the converter output part 60 in the startup phase, the Vcc capacitor of the switching stage 40 can be supplied via the selector 80 with an output volage at the entire or a larger portion (Tn) of the auxiliary winding, thus giving the highest possible voltage to the Vcc capacitor for fast charging. Once the Vcc voltage detected by the voltage detector 90 has reached a maximum or predetermined upper value, the selector 80 switches to a tap or a smaller portion of the auxiliary winding, giving a lower voltage. Thereby, a fast startup can be achieved without reaching the UVLO level. Moreover, the variable auxiliary winding allows for a very wide output voltage window.

[0051] Fig. 3 shows schematically a more detailed circuit diagram of an example of an enhanced single-stage flyback LED driver with fast startup circuit according to an embodiment. Thereby, a high-efficiency LED driver with fast startup circuit can be obtained for large energy storage at the secondary side.

[0052] As shown in Fig. 3, the exemplary single-stage driver is based on a flyback topology with high power factor. The circuit, to which the mains voltage VAC is supplied, comprises an EMI filter circuit 10 with an inductor LI and two capacitors C2 and C3 at the input, a rectifier stage bridge with four diodes DI to D4, a transformer with multiple windings Tl-1, Tl-2, Tl-3 and Tl-4, a switching stage with a power metal oxide semiconductor FET (MOSFET) Ml and a controller (CTRL) 42. The output converter circuit (flyback circuit) that generates the output voltage Vo for an LED luminaire D8 comprises a diode D5 and a (large) capacitor bank 62 with parallel-connected (electrolytic) capacitors C4, C6, C7, etc.

[0053] Optionally, a ripple remover (RR) circuit 22 may be provided, which may be configured to reduce the peak-to-peak amplitude of the converter output current by using a linear post regulator to remove the output ripple, thereby minimizing the LED current ripple. A simple circuit solution may be a self-biasing emitter follower circuit. A Darlington configuration may be used to keep the impedance of the base resistor relatively high, so that a small capacitor can be used to filter the ripple frequency (e.g., 100Hz). The circuit can be placed at the output voltage terminal using NPN transistors, or at the ground terminal using PNP transistors. Loss in the ripple remover depends on the energy storage buffer capacitor size. Thus, efficiency of the ripple remover circuit 22 can be improved by adding more capacitors to the capacitor bank 62.

[0054] For energy efficiency and easy layout for creepage distances (i.e., shortest distances along the surface of a solid insulating material between two conductive parts), a self-supplied Vcc circuit is beneficial. As shown in Fig. 3, the Vcc supply voltage is selfsupplied via auxiliary windings Tl-3 and Tl-4 on the main transformer itself. An auxiliary voltage supply via a standalone switched-mode power supply (SMPS) would cause extra losses and require extra space to meet creepage distances, e.g., as defined in standard IEC 61347-1.

[0055] Because of low frequency ripple and mains voltage variation, high power factor (PF) topologies typically use a diode conduction phase to supply the Vcc capacitor C5 at the primary side of the transformer thanks to the stable voltage at the output.

[0056] As shown in Fig. 3, when diode D5 of the flyback circuit at the output conducts (i.e., MOSFET Ml is off), the output voltage is reflected / coupled to the auxiliary windings Tl-3 and Tl-4 with a fixed turn ratio of the transformer (i.e., number of winding turns on the input (primary side) versus number of winding turns on the output (secondary side) of the transformer). Thus, the voltage supplied to the Vcc capacitor C5 is directly related to the output voltage Vo across the storage capacitors (i.e., capacitor bank 62).

[0057] The proposed tapped auxiliary winding with windings Tl-3 and Tl-4 and tap T allows a very wide output voltage window, since now the Vcc supply be connected to a voltage from one or both auxiliary windings Tl-3 and Tl-4 via respective decoupling diodes D6 and D7 at terminals Tn and TL and a selector 80 that is controlled by a voltage detector 90. The selector 80 may be configured as a selection switch SI that either connects to a higher voltage terminal Tn (both auxiliary windings Tl-3 and Tl-4) or a lower voltage terminal TL (auxiliary winding Tl-3 only) in response to a control signal supplied by the voltage detector 90.

[0058] In an exemplary design with equal number of turns for the auxiliary windings Tl-3 and Tl-4, the driver output voltage window can be extended by a factor of two. Fig. 4 shows schematically a waveform diagram of a startup attempt of a startup voltage of the enhanced single-stage flyback LED driver with fast startup circuit shown in Fig. 3.

[0059] In the embodiment of Fig. 3, the Vcc capacitor C5 is first charged with a voltage of both auxiliary windings Tl-3 and Tl-4, which gives much higher voltage for charging the Vcc capacitor C5, e.g., double the voltage if the auxiliary windings Tl-3 and T- 4 are configured with equal number of turns. Thereby, Vcc supply voltage drops to UVLO level and triggered protection measures can be avoided. Because of the higher reflected selfsupplied feedback voltage from both auxiliary windings Tl-3 and Tl-4, the Vcc capacitor C5, which has initially been charged via the high-voltage startup circuit 20, will now be charged by a higher reflected voltage from the secondary side of the transformer, achieving a smooth startup.

[0060] As shown in Fig. 4, the Vcc capacitor C5 is initially charged via the output current of the high-voltage startup circuit 20 until the startup voltage level Vccs is reached and the controller 42 is activated. In response, the controller 42 is activated and the Vcc capacitor C5 is discharged by the input current of the controller 42 and concurrently charging via the increased self-supplied reflected voltage at the higher voltage terminal Tn connected to both auxiliary windings Tl-3 and Tl-4. The reflected voltage increases with increased output voltage Vo during charging of the capacitor bank 62, so that the UVLO level is not reached due to the higher reflected portion of the output voltage Vo.

[0061] The voltage detector 90 monitors the Vcc supply voltage level at the Vcc capacitor C5 and once it reaches a predetermined maximum level Vcc max, the switch SI of the selector 80 switches over from default position 1 (terminal Tn) to position 2 (terminal TL), supplying the Vcc capacitor C5 with the lower voltage at the auxiliary winding Tl-3 in the steady state. As a result, the waveform of Fig. 4 drops until it reaches a steady state below the maximum level Vcc_max. This avoids over-voltage at the Vcc capacitor C5 and the Vcc input of the controller 42. The initial higher reflected voltage from both auxiliary windings would be too high for the steady state operation.

[0062] As an alternative option, instead of the auxiliary windings Tl-3 and Tl-4, a voltage doubler circuit or other voltage increasing circuit may be controlled (e.g., enabled, disabled) by the selector 80. The voltage doubler may be configured to provide a double charging current when the Vcc capacitor C5 is charged up to a first level (i.e., Vccs of Fig. 3), and may be deactivated by the selector 80 under control of the voltage detector 90. Thus, the selector 80 may then be arranged to control (e.g., enable, disable) the voltage divider.

[0063] Fig. 5 shows a flow diagram of a fast driver startup procedure for a luminaire driver according to various embodiments. The procedure may be implemented through a software routine stored in a memory of a controller (e.g., the controller 42 of Fig. 3 or a controller of the switching stage 40 of Fig. 1) and comprising instructions for controlling the controller to trigger and / or perform the steps of Fig. 5. When the voltage level Vccs has been reached at the Vcc terminal of the controller (e.g., via a high-voltage startup circuit), step S300 of the procedure is triggered and the Vcc capacitor at the Vcc input of the controller is initially charged with an increased charging current. This can be achieved by controlling a selector or switch (e.g., the selector 80 of Fig. 1 or 3) to connect to an increased self-supplied reflected voltage (e.g., a larger or two or more auxiliary windings (e.g., Tl-3 and Tl-4 in Fig. 3) of a transformer of the luminaire driver) or an increased external voltage. Because of the higher charging current, the Vcc capacitor will be charged faster to achieving a smooth driver startup.

[0064] In step S301, the level of the Vcc supply voltage is monitored via a voltage detection function of the controller or via a read-out process of an external voltage detector. Then in step S302, the detected or read Vcc voltage level is compared to a predetermined maximum level (e.g., Vcc max in Fig. 4) and it is checked whether the detected or read voltage level has reached the predetermined maximum level.

[0065] In the affirmative case (i.e., maximum level reached), the procedure continues with step S303 and the selector or switch is controlled to reduce the charging current of the Vcc capacitor by switching to a smaller or single or less auxiliary winding(s) or to a smaller externally supplied charging current to avoid over-voltage at the Vcc terminal of the controller.

[0066] Otherwise (i.e., maximum level not yet reached), the procedure jumps back to step S301 and continues monitoring the detected or read Vcc voltage level until the maximum level has been reached.

[0067] To summarize, a fast startup circuit and method for self-supplied single-stage drivers with large energy storage buffer capacitance have been described. An auxiliary winding for supplying a controller on the primary side of a transformer may comprise a tapped winding and a selector for choosing a proper winding for supplying the controller. During an initial charging phase of an output capacitor in the startup phase, a voltage supply capacitor of the controller is connected to an enlarged auxiliary winding, thus applying a higher voltage to the voltage supply capacitor. Once the supply voltage has reached a maximum level, the selector switches to a tap to thereby reduce the connected voltage.

[0068] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments concerning solid-state luminaires (e.g., LED luminaires). The proposed feed-forward balance control can be applied in connection with any type of load that is sensible to output ripple. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. 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. A single processor or other unit may fulfil the functions of several items recited in the claims. 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 foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in the text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated.

[0069] A single unit or device may fulfill the functions of several items recited in the claims. 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.

[0070] The described procedures like the one indicated in Fig. 5 can be implemented as program code means of a computer program and / or as dedicated hardware of the receiver devices or transceiver devices, respectively. The computer program may be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Claims

CLAIMS:

1. A driver device comprising an apparatus (40; 42) for controlling a driver device having one or more output storage capacitors (62) for suppling power to a load device (70), the apparatus being configured to monitor a level of a supply voltage at a voltage supply capacitor (C5) of the driver device, and to control a selector (80) to apply a first charging current to the voltage supply capacitor (C5) when a startup level (Vccs) of the supply voltage has been reached and to switch to a lower second charging current in response to a detection that the level of the supply voltage has reached a predetermined maximum level (Vcc max), the driver device comprising a transformer (50) for supplying power to the one or more output storage capacitors (62), wherein the selector (80) is configured to select the first and second charging currents from different terminals of at least one auxiliary winding (Tl-3, Tl-4) of the transformer (50), wherein the transformer (50) comprises at least two auxiliary windings (Tl-3, Tl-4) for generating the first and second charging currents, and wherein the selector (80) is configured to select one (Tl-3) of the auxiliary windings (Tl-3, Tl-4) to apply the lower second charging current and to select at least two of the auxiliary windings (Tl-3, Tl-4) to apply the first charging current.

2. The driver device of claim 1, wherein the apparatus comprises a voltage detector (90) for measuring the supply voltage and for controlling the selector (80) to apply the first charging current to the voltage supply capacitor (C5) when the startup level (Vccs) of the supply voltage has been reached and to switch to the lower second charging current when the measured level of the input voltage has reached the predetermined maximum level (Vcc_max).

3. The driver device of claim 1, wherein the at least two auxiliary windings (Tl-3, Tl-4) comprise a tapped winding.

4. The driver device of any one of the preceding claims, wherein the selector (80) comprises a controllable switch (SI) for switching between terminals (Tn, TL) of the one (Tl-3) of the auxiliary windings (Tl-3, Tl-4) and the at least two of the auxiliary windings (Tl-3, Tl-4).

5. The driver device of any one of the preceding claims, wherein the driver device is a single-stage flyback LED driver.

6. A lighting system comprising a plurality of driver devices of claim 5 connected to respective luminaires (70).

7. A method of controlling a driver device having an output storage capacity (62) for suppling power to a load device (70), the method comprising: monitoring a level of a supply voltage at an voltage supply capacitor of the driver device; applying a first charging current to the voltage supply capacitor when a startup level of the supply voltage has been reached; and switching to a lower second charging current in response to a detection that the level of the supply voltage has reached a predetermined maximum level.

8. A computer program product comprising code means for producing the steps of claim 7 when run on a controller device (42).

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