Multiplexed feedback for driver circuits

Abstract

The invention relates to an apparatus and method for providing a multiplexed feedback path from an auxiliary winding of a transformer of a driver circuit to achieve a wide output range. The multiplexed feedback path can be switched for either sensing an output voltage of the driver circuit during a discharging phase of a transformer inductance (e.g., fly-back switch closed) or providing a supply voltage for a switching controller of the driver circuit during a charging phase of the transformer inductance (e.g., fly-back switch opened). A voltage doubler or charge pump may be used to increase the voltage at the auxiliary winding and thereby increase a charge-up speed of the supply voltage.

Description

[0001] Multiplexed feedback 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] Efficiency of electric lighting has improved to such an extent that efficiency of the driver (e.g., LED driver) has become a major aspect. In two-stage LED drivers, a boost- PFC (power factor correction) stage is followed by a constant current driver (e.g., a fly-back converter). For efficiency improvement of the driver, the second stage of the driver may be replaced by a mini converter or a linear current source. However, this poses additional challenges on the first stage for power supply and sensing of the controller. Another way to improve driver efficiency is to mitigate power losses in the second stage by eliminating the need of the second stage.

[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. However, as mentioned above, energy efficiency of light sources has increased in recent years. New Class A light sources need 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 output of the power factor stage. For isolated drivers, the consequence of adding large electrolytic capacitors to the output is the long startup time at power up since the capacitor bank needs to be charged to a sufficient voltage level such that the reflected output voltage of the transformer that feeds the controller is sufficient to supply the controller. During initial start, the supply capacitor of the controller is charged through a resistive divider and the internal current limiting circuit of the controller. Once the controller starts with switching the power to the transformer, the supply volage starts to drop until an auxiliary winding is able to supply the controller capacitor. Between the interval of start switching and replenishing supply via the auxiliary winding, 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 improve efficiency of single- stage drivers with large storage capacitance of the switching stage.

[0013] This object is achieved by a multiplexing circuit as claimed in claim 1, by a driver device as claimed in claim 8, by a luminaire as claimed in claim 11, by a lighting system as claimed in claim 12, by a method as claimed in claim 13, and by a computer program product as claimed in claim 15.

[0014] According to a first aspect, an multiplexing circuit (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 that supplies power to a load (e.g., luminaire or other light source) is provided, the multiplexing circuit comprising: a detector for detecting an operating phase of a transformer of a switched converter of the driver device; and a switching circuit for switching in response to the detected operating phase between a first path, through which a voltage at an auxiliary winding of the transformer is applied to a voltage supply input of a switching controller of the switched converter, and a second path, through which the voltage at the auxiliary winding of the transformer is applied to an output voltage measurement input of the switching controller of the switched converter.

[0015] Furthermore, according to a second aspect, a driver device comprising a switched converter with a switching controller, a transformer and the multiplexing circuit of the first aspect is provided.

[0016] Additionally, according to a third aspect, a luminaire comprising the driver device of the second aspect is provided.

[0017] Moreover, according to a fourth aspect, a lighting system comprising a plurality of driver devices of the second aspect connected to respective luminaires is provided.

[0018] Further, according to a fifth aspect, a method of controlling a driver device is provided, the method comprising: determining a charging or relaxation state of an inductance of a transformer of a switched converter of the driver device; forwarding a voltage at an auxiliary winding of the transformer to a power supply input of a switching controller of the switched converter during a charging phase of the inductance of the transformer; and forwarding the voltage at the auxiliary winding of the transformer to a measurement input of the switching controller of the switched converter during a relaxation phase of the inductance of the transformer.

[0019] Further, according to a sixth aspect, a computer program product is provided, which comprises code means for producing the steps of the method of the fifth aspect when run on a controller of a driver device.

[0020] Accordingly, an auxiliary supply winding can advantageously be used in two ways, i.e., one way to power the controller circuit by reflecting the forward voltage, and the other way by reflecting the output voltage to sense the output voltage. This can be achieved providing e.g. the proposed multiplexing circuit, which can be implemented by adding low- cost semiconductor devices or circuits to the existing driver circuit or integrating the proposed multiplexing functionality into an existing controller to supply the controller with the reflected input voltage and to measure the reflected output voltage. Thereby, efficiency can be improved, while the multiplexed auxiliary winding also allows for a wider output voltage window.

[0021] According to a first option of any of the first to sixth aspects, the detector may be configured to detect a polarity of the voltage at the auxiliary winding of the transformer and to control the switching circuit to switch to the first path at a first polarity of the voltage at the auxiliary winding in order to connect a reflected forward voltage of the switched converter to the voltage supply input of the switching controller, and to switch to the second path at a second polarity of the voltage at the auxiliary winding in order to connect a reflected output voltage to the output voltage measurement input of the switching controller.

[0022] According to a second option of any of the first to sixth aspects, which may be combined with the first option, another detector may be provided for detecting a level of the voltage at the auxiliary winding and for controlling the switching circuit to bypass a voltage multiplier or charge pump included in the first path in response to the detected level of the voltage at the auxiliary winding.

[0023] According to a third option of any of the first to sixth aspects, which may be combined with the first or second option, a timer or pulse former may be provided for controlling the timing of switching between the first path and the second path by the switching circuit.

[0024] According to a fourth option of any of the first to sixth aspects, which may be combined with the third option, the switching circuit may comprise a switching element that is set by the detector to a conducting state or to a non-conducting state in dependence on a detected polarity of the voltage at the auxiliary winding, wherein the detector may comprise the timer or pulse former, and wherein the timer or pulse former may be triggered by an edge of the voltage of the auxiliary winding.

[0025] According to a fifth option of any of the first to sixth aspects, which may be combined with any one of the first to fourth options, a holding capacitor may be provided at an output of the second path to reduce a voltage drop within a complete switching cycle of the switching converter.

[0026] According to a sixth option of any of the first to sixth aspects, which may be combined with any one of the first to fifth options, the switching circuit may be configured to reference the voltage at the auxiliary winding to a reference potential of the switching controller.

[0027] According to a seventh option of any of the first to sixth aspects, which may be combined with any one of the first to sixth options, the switching controller may be configured to turn off a power supply path when a power supply input voltage has reached a threshold value.

[0028] According to an eighth option of any of the first to sixth aspects, which may be combined with any one of the first to seventh options, the switched converter may be a fly-back converter.

[0029] According to a ninth option of any of the first to sixth aspects, which may be combined with any one of the first to eighth options, the charging or relaxation state of the inductance of the transformer may be determined by detecting a polarity of the voltage at the auxiliary winding.

[0030] It is noted that the above apparatus may be implemented based on discrete hardware circuitries with discrete hardware components, integrated circuits, or arrangements of integrated modules, or based on signal processing devices or integrated circuits controlled by software routines or programs stored in memories, written on a computer readable media, or downloaded from a network, such as the Internet.

[0031] It shall be understood that the multiplexing circuit of claim 1, the driver circuit of claim 8, the luminaire of claim 11, the lighting system of claim 12, the method of claim 13, and the computer program product of claim 15 may have similar and / or identical preferred embodiments, in particular, as defined in the dependent claims.

[0032] 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.

[0033] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In the following drawings:

[0036] Fig. 1 shows schematically a block diagram of a luminaire driver with multiplexed auxiliary winding feedback according to various embodiments;

[0037] Fig. 2 shows schematically a circuit diagram of an example of an enhanced single-stage fly-back LED driver with multiplexing circuit according to an embodiment; Fig. 3 shows schematically a circuit diagram of an example of the multiplexing circuit of Fig. 2 according to an embodiment;

[0038] Fig. 4 shows schematically a waveform diagram with waveforms of a voltage doubler enable signal and a Vcc supply voltage, as obtained by the multiplexing circuit of Fig. 3; and

[0039] Fig. 5 shows a flow diagram of a feedback multiplexing procedure according to various embodiments.

[0040] DETAILED DESCRIPTION OF EMBODIMENTS

[0041] 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.

[0042] 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.

[0043] Fig. 1 shows schematically a block diagram of a luminaire driver with enhanced efficiency and wide output voltage range according to various embodiments.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 (not shown in Fig. 1) 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. Additionally, a controller (e.g., a fly-back controller (integrated) circuit (IC), not shown in Fig. 1) is comprised in the switching stage 40 and configured to control the switching operation of the switching stage 40.

[0048] Furthermore, a switched converter of the luminaire driver may be configured as an isolating power converter and may comprise a switching part, magnetics (inductor / transformer), and a converter output part (rectifying part) (CONV) 60.

[0049] The switching stage 40 may be configured to control the converter output part 60 of the converter stage via an electronic transformer (TRA) 206 to supply a desired power level to an LED luminaire 70. The switched converter may be a fly-back converter, a forward converter or the like.

[0050] When the terminal of the supply voltage Vcc at the terminal of the switching stage 40 reaches a predetermined start level (e.g., 15 V), 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, an auxiliary winding on the primary side of the transformer 206 may provide an auxiliary winding voltage VAW voltage for the controller of the switching stage 40 via a multiplexing circuit (MUX) 212.

[0051] The multiplexing circuit 212 may be implemented as a switching circuit or a software-controlled processor circuit that is configured to provide a multiplexed feedback path which supplies the auxiliary winding voltage either as a supply voltage Vs to a supply input (e.g., the Vcc input) of the controller of the switching stage 40 or as a measured output voltage Vo to a measurement input of the controller of the switching stage, depending on the state / phase of the transformer 206.

[0052] Thus, the multiplexing circuit 212 allows to use the voltage at the auxiliary winding in a multiplexed manner as a supply voltage (e.g., reflected forward voltage during a charging phase of the transformer inductance, e.g., when the fly-back switch is closed) for the controller of the switching stage 40 while also enabling monitoring / sensing of the driver output voltage (e.g., reflected output voltage during a relaxation phase of the transformer inductance, e.g., when the fly-back switch is opened) by the controller of the switching stage 40. The additional multiplexing circuit 212 may be implemented as an external circuit or may be embedded with the controller of the switching stage 40 to save cost and space.

[0053] Thereby, the proposed multiplexing circuit 212 advantageously allows additional cost and space savings by excluding additional windings (e.g., tapped or two windings) at the transformer 206, which would otherwise be required for measuring the output voltage, and by reducing the number of interconnections required between the controller of the switching stage 40 and other external components (e.g., interconnections to additional (auxiliary) windings).

[0054] In an example, the multiplexing circuit 212 may comprise a first detection circuit for measuring the auxiliary winding voltage VAW (when used as supply voltage for the controller) to decide about using a voltage multiplier (e.g., doubler) for increasing the supply voltage, a switchable output voltage measurement circuit for referencing the received reflected output voltage to a common reference (e.g., ground potential), a second detection circuit for measuring the polarity of the voltage at the auxiliary winding, and a comparator for controlling the timing of power transfer (e.g., via the voltage multiplier or directly) to the supply voltage (Vcc) input of the controller at a single polarity.

[0055] 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 or current 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. Moreover, the control loop could be designed to control the output current such that the current / power variation due to the output voltage variation becomes negligible.

[0056] Fig. 2 shows schematically a more detailed circuit diagram of an example of an enhanced single-stage fly-back LED driver with multiplexing circuit 212 according to an embodiment. The single-stage fly-back LED driver should preferably be able to output a wide operating voltage window to support a wide range of LED loads. For isolated LED drivers with power levels equal to or less than 150W, the fly-back converter provides a favorable topology from size and cost point of view. In the circuit diagram of Fig. 2, a flyback controller 203 of the fly-back converter is supplied by an auxiliary winding 2003 of a fly-back transformer 206, that outputs a reflected forward voltage from the secondary side of the transformer 206. In addition, a reflected output voltage at the auxiliary winding 2003 is used to measure the output voltage, e.g., for protection purposes.

[0057] As shown in Fig. 2, an input power of the fly-back converter is supplied via the input terminals 101 and 102 and an input capacitor (e.g., smoothing capacitor) 201 for removing high-frequency noise and interference components, wherein the lower input terminal 102 is connected to ground potential (or another reference potential). Initially, at power up, the fly-back controller 203 is supplied with power via a current limiting resistor 202 (or an internal current limiting circuit within the controller 203) and a VCC capacitor 207 at the supply input (VCC) of the fly-back controller 203. A charge is built up across the VCC capacitor 207 until it has reached a threshold to start up the fly-back converter. Under control of the fly-back controller 203, a current thought the primary winding 2001 of the flyback transformer 206 is chopped (e.g., pulse-width modulated) by a metal oxide semiconductor (MOS) transistor 208. The MOS transistor 208 is controlled by the fly-back controller 203 via a respective control output connected to the gate terminal of the MOS transistor 208 via a control line 107 and a resistor 210. The chopped or switched current that flows via a connection line 104 through the MOS transistor 208 and the primary winding 2001 of the fly-back transformer 206 is measured through a current sensing resistor 209.

[0058] The switching cycle of the fly-back converter (as controlled by the fly-back controller 203) has at least two, but may contain three intervals, namely, a charging phase of the primary winding 2001, a relaxation phase of the secondary winding 2002, and potentially an idle phase where no current (or a little ringing current) is flowing through the transformer windings 2001 to 2003. During the charging phase, i.e., relaxation phase of the fly-back transformer 206, an output capacitor 402 of the fly-back converter connected between an output line 302 and a reference line 303 (connected to an output reference potential) is charged via a fly-back diode 401 connected to the secondary winding 2002 via a connection link 301. The output voltage of the fly-back converter is generated across the output capacitor 402. After the initial startup, power for supplying the fly-back controller 203 is supplied from the auxiliary winding 2003 to improve power conversion efficiency of the flyback converter. In operation, the path of supplying current though the current limiting resistor 202 is turned off (to a non-conductive state) e.g. via a switching element integrated in the flyback controller 203, e.g., in response to an enable / disable signal that is switched (e.g., by the fly-back controller 203) to the disable state when the input voltage threshold has been reached.

[0059] In the embodiment of Fig. 2, the fly-back converter uses the reflected input voltage at the auxiliary winding 2003 to supply the fly-back controller 203 by making use of the multiplexing circuit 212 as an electronic auxiliary supply and output voltage measurement circuit that is configured to either output an auxiliary supply voltage via a supply connection 105 to an auxiliary supply input of the fly-back controller 203, or to output a measured output voltage via an output line 108 and a voltage divider (resistors 205 and 211) to a measurement input connection 106 of the fly-back controller 203. To achieve this, the multiplexing circuit 212 is connected to terminals 103 and 108 of the auxiliary winding 2003.

[0060] The multiplexing circuit 212 may further comprise an electronic circuit which is configured to output the reflected output voltage received from the auxiliary winding 2003 of the fly-back transformer 206 with the same reference potential as the VCC supply voltage of the fly-back controller 203.

[0061] Thereby, an LED driver with high efficiency and fast start-up can be obtained for large energy storage at the secondary side.

[0062] Fig. 3 shows schematically a circuit diagram of an example of the multiplexing circuit 212 of Fig. 2 according to an embodiment.

[0063] The terminals 103 and 108 of the auxiliary winding 2003 are connected to the multiplexing circuit input which is connected to a switchable voltage doubler which comprises a series capacitor 214, a diode 217, a doubler enabler / disabler switch (MOS transistor) 216, a diode 215 and an output capacitor 219.

[0064] The multiplexing circuit 212 is configured to selectively output the input voltage as received via terminals 103, 108, or a double input voltage generated by the voltage doubler, in response to a result of detection of the input voltage though a first detection circuit 221 which may be implemented as a comparator with hysteresis. For example, in case of a lower input voltage of e.g. 1 lOVac, the voltage doubling function can be applied to double the reflected input voltage from the auxiliary winding 2003 in order to supply the flyback controller 203 with a higher voltage level to thereby increase the charging speed at the VCC capacitor 207. Otherwise, if a higher input voltage (e.g., 230Vac) is detected, the voltage doubler can be disabled by setting the doubler enabler / disabler switch 216 into a non- conductive state and using a bypass diode 213 to output the input voltage via the connection 105 to supply power to the flyback controller 203.

[0065] The control of the doubler enabler / disabler switch 216 can be realized by measuring the output voltage of the voltage doubler though a voltage divider consisting of resistors 223 and 224 and connected via a connection line 112 to the detection circuit 221, and by comparing the measured and divided output voltage with a reference level 222 (generated by any type of reference voltage source). The hysteresis prevents instable output states when the measured and divided output voltage is at or close to the reference level 222. To obtain a proper control voltage at the gate of the MOS transistor 216, a level shifter 220 may be connected via connection line 111 to the output of the detection circuit 221. The level shifter 220 may be implemented by a simple voltage divider or a differential cascade voltage switch (DC VS) structure or current mirror (CM) structure or any other suitable circuit. The output voltage of the level shifter 220 is connected via a connection line 110 to the gate terminal of the MOS transistor that forms the doubler enabler / disabler switch 216.

[0066] Furthermore, either the output voltage of the voltage doubler or the directly bypassed voltage of the auxiliary winding 2003 is applied across the capacitor 219 and needs to be transferred to the common reference level 102 of the fly-back controller 203. This is achieved by a second MOS transistor 227 (connected between an output line 228 and an input line 109) and a free-wheeling diode 229. The second MOS transistor 227 is set to a conducting state each time the polarity of the auxiliary winding terminal 103 is positive with respect to the auxiliary winding terminal 108 and is set to a non-conducting state each time the polarity of the auxiliary winding terminal 108 is positive compared to the auxiliary winding terminal 103, respectively. The second MOS transistor 227 is controlled at its gate terminal via an output terminal 231 of a pulse forming or timer circuit 230 (e.g., a mono-flop circuit or other kind of pulse (kind of one-shot) circuit or capacitor circuit, that detects a rising edge of a polarity and applies a constant or variable pulse width) that is triggered with a rising edge (i.e., change to positive polarity of the auxiliary winding terminal 103) at its control input terminal 113. The control input is derived from the auxiliary winding terminal 103 via a resistor 233 and a diode 226. Thus, the second MOS transistor 227 is switched to the conducting state for a predetermined duration determined by the pulse forming or timer circuit 230, during which either the output voltage of the voltage doubler or the directly bypassed voltage of the auxiliary winding 2003 is transferred to the common reference level 102 of the fly-back controller 203.

[0067] The reflected output voltage at the auxiliary winding 2003 is measured during the relaxation phase of the transformer. At this phase, the reflected output voltage across the terminals 103 and 108 is connected through a diode 218 and via the resistive voltage divider consisting of the resistors 205 and 211 to the measurement input connection 106 of the flyback controller 203, and through a further diode 225 back to the auxiliary winding terminal 103, wherein the voltage divider resistor 211 has a parallel holding capacitor 232 for holding the measured output voltage. A charge that is build up across the holding capacitor 232 is substantially such that the voltage drop within a complete switching cycle of the fly-back converter is negligible for accurate measurement of the reflected output voltage.

[0068] Fig. 4 shows schematically a waveform diagram with waveforms of an enable / disable control E / D of the voltage doubler control signal 110 and two cases of a supply voltage across at the VCC capacitor 207 of the fly-back controller 203.

[0069] The upper waveform represents the enable / disable control signal E / A of the voltage doubler and the lower waveforms represent two cases of the supply voltage across the VCC capacitor 207 of the fly-back controller 203. The first case (solid line) represents the supply voltage VCC of the controller 203 when the higher supply voltage (e.g., 230V mains) is applied. The second case (dashed line) represents the supply voltage VCC of the controller 203 when the lower supply voltage (e.g., 110V mains) is applied.

[0070] As can be gathered from Fig. 4, initially, as long as the voltage doubling is enabled (E / A signal on high level), the VCC capacitor is charged with a higher current. Thereafter, when the VCC supply voltage has reached its threshold, the voltage doubler is disengaged. Then, the voltage across the VCC capacitor increases with every switching cycle of the fly-back converter.

[0071] The dashed curve of the lower diagram indicates a lower initial charging speed due to the lower power supply voltage of 110V. However, the upper solid curve relates to the case where the higher power supply voltage of 230V is applied and the voltage doubler is engaged until VCC has reached its threshold value. This charging is much faster due to enabling of the voltage doubler and the higher input voltage.

[0072] Thus, the comparator 221 detects the VCC threshold level (e.g., 15 V). If this voltage is too high, the volage doubler is disengaged. Thus, when a higher input volage is applied, charging will be done faster towards the threshold level. Then, the voltage doubler is disengaged. Alternatively, at lower input voltage (e.g., 110V), the voltage doubler may remain engaged.

[0073] Fig. 5 shows a flow diagram of a supply / measurement multiplexing procedure according to various embodiments. The procedure may be implemented through a software routine stored in a memory of a controller (e.g., a controller of the multiplexing circuit 212 of Fig. 1) and comprising instructions for controlling the controller to trigger and / or perform the steps of Fig. 5.

[0074] When the threshold level has been reached at the VCC input of the fly-back controller 203, initiation step S300 of the procedure of Fig. 5 is triggered, e.g., via a control signal such as the E / A signal supplied from the fly-back controller 203 to the controller of the multiplexing circuit 212.

[0075] In step S301, the state or phase of the inductance of the transformer 206 is determined, e.g., by measuring the polarity of the voltage at the auxiliary winding 2003.

[0076] Then, in step S302, it is checked whether or not the transformer inductance is in the charging phase, e.g., whether the voltage at the auxiliary winding 2003 has a predetermined polarity (e.g., a positive polarity).

[0077] If so, the procedure branches to step S303 where the voltage Vs at the auxiliary winding 2003 is forwarded to the VCC input of the fly-back controller 203. Optionally, if the voltage at the auxiliary winding 2003 is determined to be below a predetermined threshold, a voltage doubling or multiplying step is added in step S303.

[0078] Otherwise, if it is determined in step S302 that the transformer inductance is not in the charging phase (e.g., the voltage at the auxiliary winding 2003 does not have the predetermined polarity), the procedure branches to step S304 and the voltage Vo at the auxiliary winding 2003 is forwarded to the measurement input 106 of the fly-back controller 203.

[0079] To summarize, an apparatus and method for providing a multiplexed feedback path from an auxiliary winding of a transformer of a driver circuit to achieve a wide output range. The multiplexed feedback path can be switched for either sensing an output voltage of the driver circuit during a relaxation phase of a transformer inductance (e.g., fly-back switch is in a non-conducting state) or providing a supply voltage for a switching controller of the driver circuit during a charging phase of the transformer inductance (e.g., fly-back switch is in conducting state). A voltage doubler or charge pump may be used to increase the voltage at the auxiliary winding and thereby increase a charge-up speed of the supply voltage. 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 multiplexed feedback from the auxiliary winding can be applied in connection with any type of load. Moreover, the function of multiplexing between supply of the switching controller (e.g., fly-back controller), measuring the reflected input voltage and measuring the reflected output voltage with a single winding with a common reference can be implemented in various different ways.

[0080] 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.

[0081] 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.

[0082] 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 multiplexing circuit (212) for controlling a driver device that supplies power to a load (70), the multiplexing circuit comprising: a detector (230) adapted to detect an operating phase of a transformer (206) of a switched converter of the driver device; and a switching circuit adapted to switch in response to the detected operating phase between a first path, through which a voltage at an auxiliary winding (2003) of the transformer (206) is applied to a voltage supply input of a switching controller (203) of the switched converter, and a second path, through which the voltage at the auxiliary winding (2003) of the transformer (206) is applied to an output voltage measurement input of the switching controller (203) of the switched converter, wherein the detector (230) is configured to detect a polarity of the voltage at the auxiliary winding (2003) of the transformer (206) and to control the switching circuit to switch to the first path at a first polarity of the voltage at the auxiliary winding (2003) in order to connect a reflected forward voltage of the switched converter to the voltage supply input of the switching controller (203), and to switch to the second path at a second polarity of the voltage at the auxiliary winding (2003) in order to connect a reflected output voltage to the output voltage measurement input of the switching controller (203).

2. The multiplexing circuit (212) of claim 1, further comprising another detector (221) adapted to detect a level of the voltage at the auxiliary winding (2003) and adapted to control the switching circuit to bypass a voltage multiplier or charge pump included in the first path in response to the detected level of the voltage at the auxiliary winding (2003).

3. The multiplexing circuit (212) of any one of the preceding claims, further comprising a timer or pulse former circuit (230) adapted to control the timing of switching between the first path and the second path by the switching circuit.

4. The multiplexing circuit (212) of claim 3, wherein the switching circuit comprises a switching element (227) that is set by the detector (230) to a conducting state orto a non-conducting state in dependence on a detected polarity of the voltage at the auxiliary winding (2003), wherein the detector comprises the timer or pulse former circuit (230) and wherein the timer or pulse former circuit (230) is triggered by an edge of the voltage of the auxiliary winding (2003).

5. The multiplexing circuit (212) of any one of the preceding claims, further comprising a holding capacitor (232) at an output of the second path to reduce a voltage drop within a complete switching cycle of the switching converter.

6. The multiplexing circuit (212) of any one of the preceding claims, wherein the switching circuit is configured to reference the voltage at the auxiliary winding (2003) to a reference potential of the switching controller (203).

7. A driver device comprising a switched converter with a switching controller (203), a transformer (206) and the multiplexing circuit (212) of any one of the preceding claims.

8. The driver device of claim 7, wherein the switching controller (203) is configured to turn off a power supply path when a power supply input voltage has reached a threshold value.

9. The driver device of claim 7 or 8, wherein the switched converter is a fly-back converter.

10. A luminaire comprising the driver device of any one of claims 7 to 9.

11. A lighting system comprising one or more driver devices of claim 9 connected to respective luminaires.

12. A method of controlling a driver device, the method comprising: determining a charging or relaxation state of an inductance of a transformerforwarding a voltage at an auxiliary winding (2003) of the transformer (206) to a power supply input of a switching controller (203) of the switched converter during a charging phase of the inductance of the transformer (206); and forwarding the voltage at the auxiliary winding (2003) of the transformer (206) to a measurement input of the switching controller (203) of the switched converter during a discharging phase of the inductance of the transformer (206), wherein the state of the inductance of the transformer (206) is determined by detecting a polarity of the voltage at the auxiliary winding (2003).

13. A computer program product comprising code means for producing the steps of claim 12 when run on a controller (206) of a driver device.

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