WO2014144349A1

WO2014144349A1 - System and method for learning dimmer characteristics

Info

Publication number: WO2014144349A1
Application number: PCT/US2014/028715
Authority: WO
Inventors: John L. Melanson; Eric King; Siddharth MARU
Original assignee: Cirrus Logic, Inc.
Priority date: 2013-03-15
Filing date: 2014-03-14
Publication date: 2014-09-18
Also published as: EP2974542A1; US20140265893A1; US9101010B2; US9282598B2; CN105309045B; US20140265933A1; CN105309045A

Abstract

Systems and methods for learning dimmer characteristics provide improved efficiency in operating lighting devices. In one embodiment, an apparatus includes a lamp controller that is configured to monitor voltage information associated with one or more lamps or a dimmer of a system, adjust one or more parameters of an attach current profile in conformity with the voltage information to arrive at a selected attach current profile, and apply within the system the selected attach current profile.

Description

SYSTEM AND METHOD FOR LEARNING DIMMER CHARACTERISTICS

FIELD OF THE INVENTION

[0001] This disclosure relates generally to lighting, lighting circuits, and lighting controllers. More particularly, the disclosure concerns systems and methods for learning dimmer

characteristics, particularly for operating LED lamps, although the disclosure is not so-limited.

BACKGROUND OF THE INVENTION

[0002] Lighting control circuits that are operated from thyristor-based dimmers are designed to provide proper operation of the dimmers, as well as the alternative lighting devices, i.e. light- emitting diodes.

[0003] It is desirable to provide improvements in efficiency, compatibility and other characteristics of lighting control circuits designed for operation from a dimmer as disclosed in further detail below.

DISCLOSURE OF THE INVENTION

[0004] Circuits and methods that learn characteristics of dimmers monitor voltage information associated with one or more lamps or a dimmer of a system, adjust one or more parameters of an attach current profile in conformity with the voltage information to arrive at a selected attach current profile, and apply the selected attach current profile within the system.

[0005] Several representative embodiments of the present disclosure are described below and in the appended claims. For example, the elements of the claims summarize components and/or method steps for various embodiments. Note that different embodiments may utilize those components or method steps in any combination, order, or the like. For example, any component or method step in a dependent claim may be utilized in a suitable independent claim. Components or steps described in a combination may be used individually, and those described individually may be used in any combination.

DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a diagram of lighting devices connected to a triac-based dimmer circuit.

[0007] Figure 2 is a pictorial diagram depicting a voltage waveform in the circuit of Figure 1.

[0008] Figure 3A is a simplified schematic diagram of an example lighting control circuit.

[0009] Figure 3B is a pictorial diagram of a voltage waveform in the example lighting control circuit of Figure 3 A.

[0010] Figure 4 is a block diagram illustrating features of an example lighting control circuit.

[0011] Figures 5A-5E are waveform diagrams showing voltages and currents within the circuit of Figure 4.

[0012] Figure 6 is a waveform diagram depicting details of waveforms within Figures 5A-5E. [0013] Figure 7 is a block diagram illustrating features of another example lighting control circuit.

[0014] Figure 8 is a schematic diagram illustrating details of the example lighting control circuit of Figure 7. [0015] Figure 9 is a waveform diagram depicting waveforms within the circuit of Figure 7.

[0016] Figure 10 is a block diagram depicting an exemplary lighting circuit.

[0017] Figure 11 is a block diagram depicting details of switching power converter circuit 12 of Figure 1.

[0018] Figure 12 is a signal waveform diagram illustrating various phases of operation of lighting circuits described herein.

[0019] Figure 13 is a signal waveform diagram illustrating details of the damping phase of the diagram of Figure 12 for different damping impedances of different attach current profiles.

[0020] Figure 14 is a signal waveform diagram illustrating details of the active and hold phases of the diagram of Figure 12 for different attach current profiles.

[0021] Figure 15 is a simplified schematic diagram of another exemplary lighting circuit.

[0022] Figure 16 is a signal waveform diagram illustrating application of different attach current profiles that may be applied in the circuits of Figures 10-11 and Figure 15.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] While existing dimmer compatibility techniques may be effective at providing a load that allows proper operation of many types of dimmers, room for improvement remains. For example, a need exists to better address differences between dimmers that may require, e.g., 50 mA holding current, while another may require, e.g., only 25 mA holding current. The holding current for a triac is defined as the current that must be conducted through the dimmer to maintain the triac within the dimmer in the on-state, once the triac is activated , and is generally determined by resistive losses in the triac. A lamp should draw sufficient current to keep the triac in conduction for a period of time, and the holding current may be conducted through one lamp, or through multiple lamps in parallel. The efficiency of a lighting system should similarly be optimized for a given configuration of dimmer and lamps. U.S. Patent Application Publication No. US 20120049752 and having a priory date of August 24, 2010, is incorporated herein by reference in its entirety and shows circuits for providing power to LED lighting circuits from an AC power line .

[0024] In the arrangement described above, if a required holding current is 50 mA, and it is known a priori that there will always be at least two lamps on a dimmer output, each lamp is only required to maintain a 25 mA (or less) current draw, which allows the lamps to be lower in cost and higher in efficiency. However, designing such a lamp sacrifices the ability to operate properly in a single lamp circuit.

[0025] In one embodiment, to achieve high efficiency and a larger range of compatibility, a lamp may be configured to adaptively learn, for example, a required hold current. The hold current drawn by the lamp may be reduced until the dimmer disconnects, and then increased to a "just adequate" level (e.g., at or slightly above a level that ensures attachment, satisfactory operation, and/or compatibility with that dimmer). This adjustment may be done automatically and may compensate for, e.g., dimmer hold current and lamp multiplicity. [0026] In some embodiments, the current drawn by the lamp can be reduced until the required current is drawn across an entire available part of a line cycle. This approach may minimize ripple current, decreasing flicker, and increasing the system power factor.

[0027] In some embodiments, one or more parameters of a more generalized attach current profile may be adjusted (e.g., in an iterative manner) within a lighting environment or lighting system, so that a hold current, or other parameter, associated with one or more lamps may be selected and applied. In a representative embodiment, an attach current profile may generally involve timing, amplitude, slope, or other parameters of a current waveform . An attach current profile may be associated with a leading edge of a dimmer. Representative, non-limiting parameters associated with the attach current profile may include information concerning: starting current, steady state hold current, timing (e.g., time duration between start of current and steady state hold current, each relative to a leading edge of a dimmer), etc. The additional parameters included in the profile are desirable because many dimmers require a current during the first several hundred microseconds after the leading edge (the time of triac start of conduction) that is greater than a current required later in the cycle. Additionally, positive and negative half line cycles may cause different behaviors in the triac, and different attach current profiles may be required for the positive and negative half line cycles.

[0028] In operation, once adjustment (e.g., iterative adjustment) of one or more parameters of an attach current profile leads to the selection of a suitable attach current profile (e.g., a current profile in which a hold current or other parameter may be adjusted to a "just adequate" level), the selected suitable profile can be applied to power one or more lamps. The selected attach current profile may take into account a number of factors, such as, but not limited to, whether parallel lamps are connected within the system. [0029] In one embodiment, a given lamp may sense the presence of other lamps in an environment or system by monitoring the behavior of, e.g., an input voltage after sufficient power is drawn from a line. If another lamp utilizes probe cycles to determine the location of a zero crossing, that effect can be observed by monitoring the line voltage. If an incandescent lamp, or similar load, is present, the input voltage will consistently track the input sine wave after attach, and nearly to the zero crossing without aid of a probe cycle. If a dimmer is a FET-type dimmer, there is no required minimum hold current, and only a glue current is required. This again may increase power factor and efficiency.

[0030] In some embodiments, more generally, voltage information may be used to determine whether, for example, parallel lamps are connected to a dimmer, and that information may in turn be used to adjust (e.g., iteratively) one or more parameters of an attach current profile until a suitable profile is selected and applied to the appropriate one or more lamps within the environment or system.

[0031] Typically, when a lamp is turned on, a system configuration will be identical or substantially identical to the prior operating state. The prior operating state can be remembered, and the proper operation immediately entered.

[0032] A typical dimmer circuit model is shown in Figure 1. An EMI capacitor L_E and a timing capacitor C_T reduce high-frequency emissions and allow for quieter operation. EMI capacitor L_E and timing capacitor C_T also store energy, requiring the energy to be damped by the load to avoid disconnecting the triac on initiation of a leading edge. [0033] Figure 2 shows ringing Vd_ng on the input voltage V_LIN_E at the dimmer. Significant current must be drawn by the lamp in order to damp the ringing if the values of EMI capacitor L_E and timing capacitor C_T are large. In other dimmers, there is little or no filtering. The ringing effect can be characterized for each lamp, and only sufficient current is drawn to damp the actual LC circuit formed by EMI capacitor L_E and timing capacitor C_T. The damping also requires less current if there are multiple lamps in parallel.

[0034] One or more of the parallel lamps may be constructed with a different style of dimmer compatibility circuit. In some installations, probe operation by one lamp may disrupt the operation of a lamp not designed for probing operation.

[0035] In one embodiment, disruption to a line voltage source may be minimized by

synthesizing the line voltage at the mains, and causing the same voltage to be replicated at the input to the lamp. The synthesizing maintains the voltage impressed across dimmer at a zero value until the next zero crossing of the line voltage, which may maximize dimmer compatibility, especially when a large number of lamps are interconnected. Figure 3A

illustrates a switching power supply circuit including an input bridge rectifier BRl connected to input line voltage LINE, a capacitor C3, a switching transistor Nl, a transformer Tl and a control circuit 100 that performs the above-described operation, which is also illustrated by Figure 3B, which from time ti until time t₂ shows the current drawn through input bridge rectifier BRl and from time t₂ until time t₃ shows the current drawn to emulate a sinusoidal waveform.

[0036] It is desirable to carry as much information as possible from one operation of a lamp to the next operation. For example, if a lamp is activated every evening, and turned off in the morning, preferably information is retained in the lamp, which can be accomplished in multiple ways.

[0037] In one embodiment, a lamp may contain non-volatile memory. The memory can be programmed on power-down.

[0038] A lamp, if on a smart dimmer that requires current in the off phase, may use a small amount of that current to maintain a random access memory (RAM) memory, or other type of memory, with the information.

[0039] In one embodiment, a lamp may be programmed for a configuration. For example, information may be carried on a power line to allow a lamp to be provided information related to a configuration. For example, four (4) rapid on/off cycles (or another indicator) may be used to signal a lamp that it will always be in a multi-lamp configuration. That configuration information may be stored in internal memory. Other power line communications protocols may be used, e.g. X10. Optical or radio communications may also be used.

[0040] In other embodiments, a dimming curve may be altered using dimmer and/or configuration information.

[0041] Some dimmers require a lamp to dissipate significantly more power than others. High holding current and large filter components are exemplary causes. In these lamps, the total light output may be reduced to simplify thermal management, while allowing full output in other cases. The shape of the dimming curve may also change; an example would be increasing the light output at a time corresponding to 90 degrees of phase-cut. Similarly, multiple parallel lamps, when the lamp determines that there is less dissipation required, may operate at a greater brightness.

[0042] Other embodiments involve two (2)-wire versus three (3)-wire dimmers. Many smart dimmers (those including a power supply for a micro-controller) may be wired as either 3 -wire or 2-wire. Figure 4 illustrates a circuit arrangement in which a smart control 102 returns current through circuit path 106 A to the input voltage source. In the 3 -wire configuration, the dimmer smart current is retumed through the direct neutral line. In the 2- wire configuration, all current is returned to neutral through the lamp as shown by circuit path 106B. In general, the 3-wire configuration is more stable, and does not require glue current (current during the "dimmer off ' part of the phase). This configuration may be determined by the lamp, and a 3-wire configuration may often result in higher lamp efficiency.

[0043] Other embodiments involve techniques for detecting system configuration. If the voltage at a lamp has a waveform as shown in Figure 5A, when the current profile of the lamp appears as shown in Figure 5B, the hold current may be safely reduced. An example acceptable current is shown in Figure 5E. If instead, when trying to draw current as shown by Figure 5B, the waveform collapses, as shown in Figure 5C, or the current cannot be reduced to the desired level (in the given example, 10 mA) as shown in Figure 5D.

[0044] The reduction of current may be made in slow steps, e.g., from 50ma, 45ma, 40ma, etc., until a minimum acceptable level is determined.

[0045] Other embodiments involve optimization of an attach or hold current. In a similar way to that described above, an attach current (e.g., a current drawn by a lamp to damp an LC dimmer circuit) may be reduced to minimize dissipation. This may be accomplished by measuring an undershoot of the ringing and adjusting appropriately.

[0046] Other embodiments involve optimization of damping dissipation. To optimize attach current dissipation, as illustrated in Figures 6A-6C, a control system such as that shown in Figure 7 may be used. Figure 6B shows an optimized voltage profile 60B, and Figure 6C shows the line current I_LINE- The control system of Figure 7 includes an input bridge rectifier BR2, a current source (sink) II, an EMI filter 110, an LED driver 112, a control circuit 114 and a memory 116. One technique for minimizing dissipation is to draw current from the line only when the lamp voltage (after the dimmer) is greater than the line voltage. In general, the line voltage is unknown until after the settling of the ringing.

[0047] Another embodiment involves calculating the line voltage at the time of attach from prior cycle information. That information may be simply storing the voltage at, for example, 250us after the attach, and using that voltage to determine when to draw current on the following cycle. Another method is to synthesize an estimate of the incoming waveform, using phase-lock techniques. This method may be advantageous when dynamic changes in the phase cut are expected to be regular. The learning of the input waveform helps optimization of the attach current profile; an exemplary profile would draw extra current only when an input voltage to the lamp is greater in magnitude than the input voltage to the dimmer from the mains.

[0048] In some embodiments, more generally, voltage information from one cycle to another cycle within a given environment or system may be utilized to adjust one or more parameters of an attach current profile to yield more efficient or satisfactory operation of one or more lamps within that environment or system.

[0049] Figure 8 shows a potential circuit for implementing current source/sink II of Figure 7. The depicted circuit includes a resistor R_s, a transistor N_s and a capacitor C_s that filters the source voltage of transistor Q2 to produce supply voltage VDD. In the depicted example, much of the current used is dumped into the power supply VDD for the control IC. By carefully timing the current drain, simplification of the auxiliary power supply may be accomplished.

[0050] The start of current drain may be set by a comparator, with the threshold set by a value calculated from the prior cycle, and the timing fixed. Alternately, a second voltage threshold may initiate the release.

[0051] Because of the delay caused by the EMI filter, the attach module can be configured before much or all of the EMI filter circuitry. This allows for a faster response time.

[0052] Figure 9 illustrates example parameters associated with an attach current profile. Illustrated are a starting current (current at to), peak current I_peak, steady state hold current Iss, and various timing information. For example, time to is the time of the starting current, and ti is the start of the time period that the current assumes the value of steady state hold current Iss- As illustrated, timing information may correspond to, or be relative to, a leading edge of a dimmer, shown generally in the voltage curve below the current curve. One having ordinary skill in the art will appreciate, with the benefit of this disclosure, that many parameters may make up, and be adjusted, for an attach current profile, such that performance of a lamp environment or system may be improved or optimized. [0053] It should be understood that various operations and techniques described here may be implemented by processing circuitry or other hardware components. The order in which each operation of a given method is performed may be changed, and various elements of systems illustrated herein may be added, reordered, combined, omitted, modified, etc. It is intended that this disclosure embrace all such modifications and changes and, accordingly, the above description should be regarded in an illustrative rather than a restrictive sense.

[0054] The present disclosure reveals circuits and methods for powering and controlling lighting devices. In particular embodiments, strings of light-emitting diodes (LEDs) are packaged to replace incandescent lamps, and the energy supplied to the LED strings is varied in accordance with a dimming value determined from operation of a thyristor-controlled dimmer supplying the replacement lighting device, so that dimmed operation is achieved. The devices disclosed herein obtain and store information about load conditions at the output of the thyristor-controlled dimmer and control operation of the devices in accordance with the stored information.

[0055] Referring now to Figure 10, an exemplary lighting circuit is shown. An AC power line source 6 provides an AC line voltage Vune to a replacement lighting device 10 through a triac-based dimmer 8 that is, for example, designed for operation with incandescent bulbs having a power consumption of 40W or greater. Replacement lighting device 10 uses LEDs LEDA, LEDB, to supply light, which may be strings of LEDs connected in series, as shown. LEDs LEDA, LEDB receive their operating currents from a string selector 14 that, in turn, receives the output of a switching power converter 12 that transfers energy from a capacitor CI that is charged from a bridge rectifier BR coupled to the input terminals of replacement lighting device 10, which are connected to the output terminals of triac-based dimmer 8. A smart controller 5 is also connected to the output terminals of triac-based dimmer 8 and may communicate with circuits in replacement lighting device 10 as described in further detail below.

[0056] Within the block depicting triac-based dimmer 8, a model equivalent circuit is shown that is useful for describing the operation of the triac and timing circuits within an actual triac-based dimmer. A switch g illustrates operation of the triac itself, which alternately conducts current Ii_n between AC power line source 6 and replacement lighting device 10. Initially, when switch g is open, EMI capacitor C_E and the timing circuit formed by a timing resistor Rp and timing capacitor C_T charge through the load applied at the output terminal of triac-based dimmer 8, which in ordinary operation is typically an incandescent bulb of 40W or greater power consumption. Once capacitor C_T is charged to a threshold voltage magnitude, switch g closes (i.e., the gate of the triac is triggered) and AC line voltage Vu_ne is provided to the output of triac-based dimmer through an inductor L_E, which is provided for EMI filtering and to reduce lamp buzz (acoustic noise in an incandescent filament). Once switch g is closed, switch g remains closed (i.e., the triac continues to conduct) until the magnitude of current I^ conducted through triac-based dimmer 8 falls below the hold current of the triac. However, if an insufficiently low-impedance load is connected to the output of the triac, the stored energy from capacitor C_E, which has been dumped into inductor L_E, will return to capacitor C_E as the parallel combination of capacitor C_E and inductor L_E begins to oscillate. When the current through inductor L_E falls below the hold current of the triac, the triac will rum off.

[0057] Since a 100W equivalent high-efficiency replacement bulb using LEDs consumes only 13W of power, the input current requirements of an LED replacement lamp will generally be less than 1/3 of that conducted through the minimum specified wattage incandescent bulb. As LED efficiency continues to improve, the input current may decrease to values low as 1/10th the current that would be required by the minimum specified wattage incandescent bulb. Therefore, the triac in triac-based dimmer 8 can prematurely open due to the reduced current conducted through the triac, unless one or more other lighting devices are installed, for example, in sockets SK connected to the outputs of triac-based dimmer 8, or unless replacement lighting device 10 is designed to draw sufficient current to cause triac-based dimmer 8 to operate properly. Also, the timing circuit that triggers the triac in triac-based dimmer 8 can turn on the triac at the wrong time unless the proper conditions are present at the output of triac-based dimmer 8 from the time of the zero-crossing of AC line voltage Vu_ne until the triac in triac-based dimmer 8 is triggered. If switching power converter 12, in combination with any other devices connected to the output of triac-based dimmer 8, does not draw sufficient current from the output of triac-based dimmer 8 during the entire active period while energy is being transferred, the triac in triac-based dimmer 8 will turn off and the timing circuit will also be disrupted. Further, if the operation of replacement lighting device 10, which contains a switching power converter 12, is not somehow coordinated with the cut sine wave of rectified dimmer output voltage Vdi_m, then switching power converter 12 may not receive all of the energy needed to supply LEDs LED A, LEDB for the cycle. Switching power converter 12 may also improperly re-trigger triac-based dimmer 8 if a low impedance is suddenly introduced at the output of triac-based dimmer 8 by starting another active cycle of switching power converter 12 after triac-based dimmer 8 has turned off for the current cycle.

[0058] In order to maintain proper operation of various phases of operation of replacement lighting device 10 that meet each of the above criteria for proper operation of triac-based dimmer 8 for all possible brightness settings, it is generally necessary under some conditions to dissipate some energy supplied by triac-based dimmer 8, rather than transferring all of the energy to LEDs LEDA, LEDB. The amount of current that must be drawn from the output of triac-based dimmer 8 for proper operation is dependent not only on the characteristics of triac-based dimmer 8 itself and the amount of energy needed to supply LEDs LEDA, LEDB, but also the number and energy consumption of other devices connected to the same circuit. In order to provide the most efficient operation, it is desirable to control the current drawn by replacement lighting device to minimize the energy supplied by triac-based dimmer 8 that is purposefully dissipated as heat. Therefore, in the instant disclosure, various techniques for determining and applying an attach current profile are implemented in switching power converter 12. The attach current profile may be a current waveshape that switching power converter 12 follows, or may be defined by one or more discrete values of input current ½ and/or times during a cycle that input current ½ assumes a particular value.

[0059] Referring now to Figure 11, details of switching power converter 12 are shown. In order to prevent the above-described mis-triggering and/or early termination of an active cycle, triac-based dimmer 8, replacement lighting device 10 includes an input current control circuit 16 that, upon detection of a rise in a rectified dimmer output voltage Vdi_m caused by a turn-on event of triac-based dimmer 8, applies an attach current profile for the cycle. Input current control circuit 16 controls both a switching control circuit 17 that controls the transfer of energy from an input capacitor CI to LEDs LEDA, LEDB according to a control signal active, and also a controllable load 15 according to a control signal load, when current must be drawn from the output of triac-based dimmer 8 but energy is not used for illuminating to LEDs LEDA, LEDB. A transistor Nl, a diode Dl and an inductor LI provide a boost switched-power converter stage that supplies energy to string selector circuit 14, which may include another switched-power stage. The output of switching power converter 12 may be. a boost converter in a non-isolated configuration as shown, a fiyback, buck or buck-boost converter state in a non-isolated configuration, or may be an isolated or non-isolated transformer-coupled output stage. The attach current profile may be entirely, or in part, determined by values stored in a storage circuit 13 that provide indications of one or more attach current characteristics that are used to control the current drawn by replacement lighting device 10 from the output terminals of triac-based dimmer 8 in the given half-cycle of AC line voltage Vune- Storage 13 may be a non-volatile storage so that the circuit configuration, once received or determined may be retained until the configuration changes. The attach current values may be determined from a measurement circuit 21 that observes the value of dimmer output voltage Vin (or alternatively rectified dimmer output voltage Vdi_m) as the amount of current drawn by switching power converter is varied during the various phases of operation. Or, alternatively or in combination, information may be received from smart controller 5 or other lighting devices via signaling over the power line circuit that connects replacement lighting device 10 to triac-based dimmer 8. The communication may be, for example, by rapid pulsing of the line voltage, or via a signal imposed on the power lines such as the signaling employed by XI 0 protocols. As another alternative, wireless

communications, such as optical, infrared or radio-frequency may be employed to communicate with replacement lighting device 10 independent of the electrical connections of replacement lighting device 10. For example, smart controller 5 may communicate the number and type of lighting devices connected to the output of triac-based dimmer 8 to a communication circuit 20 within switching power converter 12, which then determines a suitable attach current profile and stores information indicating the attach current profile in storage 13. The attach current profile might, for example, be selected from multiple predetermined attach current profiles corresponding to a number and type of lighting devices connected to the output of triac-based dimmer 8, and/or the attach current profile might vary between alternating half-cycles due to differences in the current requirements for each polarity of AC line voltage Vune-

[0060] Input current control circuit 16 performs management of the current drawn from the output terminals of triac-based dimmer 8 by replacement lighting device 10 according to the various phases of operation, as will be described with additional reference to Figure 12. When the leading edge of dimmer output voltage V_di_m is detected by a leading edge detector 18, a control signal dima is asserted, causing input current control circuit 16 to present a damping impedance level that is sufficient to prevent the re-triggering of the triac in triac-based dimmer 8 by damping the resonant circuit formed by capacitor C_E and inductor L_E. The impedance at the input of replacement lighting device 10 is generally maintained at or below the requisite damping impedance level until a predetermined time period has passed. The requisite damping impedance level varies with the particular triac design and with the external loading conditions due to other lamps connected to the circuit, but is generally between 100 ohms and 1 kOhm, corresponding to an input current between approximately 120mA and 1.2 A if no other device is connected, if for example, dimmer output voltage V_di_m is 120V when triac 8 turns on. If, for example, another device identical to replacement lighting device 10 is connected to the output of triac-based dimmer 8, the required damping impedance might be in the range of 200 Ohms to 2k Ohms for each device, and if an incandescent lamp were connected to the output of triac-based dimmer 8, no damping impedance and thus no minimum input current is needed. The required initial (starting) current level, the peak current level, or a direct indication of the minimum impedance imposed during damping may form part of the attach current profile stored in storage, and may be determined by information received by communication circuit 20 and/or by measurements made by measurement circuit 21. At least a portion of the damping impedance can be provided by operation of switching power converter 12 which operates during a time period t_acti_ve beginning just after a time t_on- In the depicted

embodiment, control signal active, which is provided to switching power converter 12 to indicate to switching power converter 12 both when to start an energy transfer cycle, and how long the cycle may potentially extend, i.e., the maximum duration of the active cycle is the duration of the high- state pulse of control signal active. After a predetermined time period t_dam_p has passed, replacement lighting device 10, along with any other connected devices, only needs to draw enough current to maintain the triac-based dimmer in a conducting state while energy needed to supply LEDs LEDA, LEDB for the cycle is being transferred. The predetermined time period may also be part of the attach current profile, as time period t_dam_p may be determined, for example, by measuring and optimizing ringing on voltage waveform of dimmer output voltage Vdi_m as the damping impedance level is decreased.

[0061] After active time period t_acti_ve time period has expired, which is when the energy transfer needed to supply LEDs LEDA, LEDB for the cycle is complete at a time t_xfrc, replacement lighting device 10 enters a high impedance state for idle time period ti_di_e. During idle time period ti_di_e, input current control circuit 16 disables controllable load 15 and disables switching power converter 12 so that a sudden change in input current due to activation of switching power converter 12 does not trigger triac-based dimmer 8. Otherwise triac-based dimmer 8 might re-triggered capacitor CT being re-charged to the trigger threshold during a remaining portion of the half-cycle of AC line voltage Viine for which the corresponding triac output cycle already been terminated. At time tz when the zero-crossing of AC line voltage Vu_ne is predicted or detected, a "glue" impedance required for proper timer operation as described above is applied across the input terminals of replacement lighting device 10 for a time period t_gi„_e. Then, the damping impedance is applied for a predetermined period t_dam_p commencing when the triac in triac-based dimmer 8 rums on. Finally, a current equal to or greater than the minimum hold current is drawn during the next active time period. The hold current is the minimum current required to maintain the conducting state of the triac in triac-based dimmer 8, which is generally between 25 and 70 milliamperes. However, as noted above for the damping impedance, if another replacement lighting device is connected to the output terminals of triac-based dimmer 8, the required hold current would be reduced

proportionately and if an incandescent bulb were connected, the hold current requirement could be ignored. The hold current value also may form part of the attach current profile(s) stored in storage 13. [0062] In order to maintain the triac in triac-based dimmer 8 in a conducting state, for the total duration of the active time period t_active, input current control circuit 16 ensures that the minimum hold current is drawn from the output terminals of triac-based dimmer 8 by the parallel combination of all of the devices connected to the output of triac-based dimmer 8. After active time period t_active is complete, input current control circuit 16 disables all sources of current drain through the input terminals of replacement lighting device 10. When the next zero-crossing of AC line voltage Vu_ne occurs at time t_z, in order to ensure that the next leading edge of the output of triac-based dimmer 8 occurs at the correct time, proper operation of the timer circuit formed by capacitor C_T and resistor R_T must be provided. As mentioned above, at time t_z the next zero-crossing of AC line voltage Vu_ne occurs, and from time t_z until triac-based dimmer 8 turns on again at a time t_ON2, a path for the input current 1^ that is charging timing capacitor C_T must be provided at the input of replacement lighting device, which is provided by supplying an impedance less than or equal to a maximum glue impedance across the output terminals of triac-based dimmer 8. The glue impedance must be low enough not to generate a voltage drop across the inputs of replacement lighting device 10 that would substantially affect the trigger point of the triac, e.g., the time at which switch g closes. In order to prevent the above-described mis-operation of triac-based dimmer 8, replacement lighting device 10 includes a zero-cross circuit 19 that predicts or detects a zero-cross time of AC line voltage Vune by observing dimmer output voltage V_di_m. Zero-cross circuit 19 provides a control signal zero that signals input current control circuit 16 to ensure that the sufficiently low "glue" impedance is presented at the input terminals of replacement lighting device 10 from the zero-cross time until the turn-on event is detected by leading edge detection circuit 18. The glue impedance needed to ensure proper timing is generally an impedance substantially equal to 100 ohms or less, which also may form part of an attach current profile stored in storage 13 and which, as with the other impedances mentioned above, can be increased for replacement lighting device 10 when other devices are connected to the output of triac-based dimmer 8. For example, a 100W incandescent bulb has an impedance of approximately 87 Ohms and so no additional glue impedance would need to be supplied b replacement lighting device 10 if such a bulb were connected to the output of triac-based dimmer 8.

[0063] Referring now to Figure 13, examples of optimizing the attach current profile to provide a sufficiently low damping impedance is illustrated. The output voltage Vdi_m of triac-based dimmer 8 will exhibit ringing when the damping current level is too low as illustrated by waveform 30, which can be detected by voltage measurement circuit 21. If the damping current level is unnecessarily high, then the leading edge of the output voltage Vdim may take on the waveshape illustrated by waveform 32. Waveform 31 illustrates a desirable critically-damped condition. Dimmer output voltage Vdim may be measured and the impedance level presented by replacement lighting device 10 during time period t_damp adjusted iteratively over several cycles in order to obtain the waveshape illustrated in waveform 31. Then the value of the damping current or impedance may be stored in storage 13 and used for subsequent operation of input current control circuit 16. Other values that may be measured and stored are a peak value I_peak of an input current Ii_n and a subsequent steady state value I_ss of input current 1^.

[0064] Referring now to Figure 14, examples of optimizing an attach current profile to provide the proper hold current for input current 1^ during time period t_active and We are shown. A waveform 33 shows a level of active current that may be higher than necessary, which would result in dissipating energy via controllable load 15 during the idle period between times and t_z. Also, the terminating step in input current Ii_n that occurs at the end of active time period t_active will result in a transient on the output terminals of triac-based dimmer 8 that can cause an undershoot in the total current supplied from triac-based dimmer 8 that falls below the minimum hold current, causing the triac in triac-based dimmer 8 to turn off. Therefore, it is desirable to extend the active time period tactive to the maximum duration that does not cause input current Ii_nto fall below the minimum hold current, while avoiding dissipation of excess energy in controllable load 15. An optimized attach current profile is shown in a waveform 35, in which input current Ii_n is constant, which may all be due to transfer by switching power converter 12 or by matching the value of controllable load 15 to the impedance presented by switching power converter 12 during transfer to provided a minimum hold current level. Another waveform 34 illustrates a condition under which it was not possible to reduce the hold current to the level illustrated by waveform 33, because the hold current does not meet the minimum requirements of triac-based dimmer 8 and the triac in triac-based dimmer 8 has turned off at time t_off. Another set of waveforms 36-38 for input current Ii_n is shown, in which current 1^ is progressively optimized to reduce a constant level of input current 1^ during time period t_active by increasing time period t_active. In general, time period t_active should be made as long as possible while maintaining input current Ii_{n >} I _oi_d and time tr_frc < zero-crossing time Waveform 36 of input current Ii_n has an active time period t_activei that is too short and can cause the above- mentioned transient, as does waveform 37 of input current I^, which has a longer active time period tactive2, but that can still cause the transient behavior. Waveform 38 has an active time period t_active3, that extends to the next zero-crossing time t_z while maintaining a current level of input current 1^ that is greater than minimum hold current I _oi_d and does not exhibit the transient behavior.

[0065] Referring now to Figure 15, another exemplary lighting circuit 50 is shown. The output of a dimmer is provided to a bridge rectifier 41 that generates a rectified dimmer output voltage V_di_m- A capacitor C_REC_T provides filtering of higher frequency switching components generated by a boost input stage implemented by an inductor L10, a switching transistor N10, a diode D10 and a capacitor C_LINK- A resistor Rl provides for current-sensing of the primary current provided through transistor N10. An integrated circuit 40 provides control of transistor N10 from a first stage controller 44A and further controls a flyback converter stage from a second stage controller 44B that switches a transistor Nil to provide current through a transformer Tl in response to feedback provided from a current sensing circuit 46. A second stage controller 44B provides information about energy requirements to input current control circuit 16, which provides control indication to first stage controller 44A to dynamically control the input current drawn from the output of bridge rectifier 41, thereby controlling the impedance presented to the output of triac-controller dimmer 8. Zero-cross predictor 19 and leading edge detector 18 operate as described above for the circuit of Figures 10-11. Current for operating LEDs LEDA, LEDB may be supplied through a secondary switching circuit 48 that alternates application of the secondary current between LED strings, which may be of different color in order to provide a color profile that varies with the dimming value dim or under other control input. First stage controller 44A is activated by control signal zero as described above with reference to Figures 10-11.

[0066] Referring now to Figure 16, application of selectable attached current profiles is shown. As mentioned above, storage 13 may store multiple attach current profiles, from which selections may be made according to operating conditions. As illustrated in waveforms 72A, 72B and 72C, the input current Ii_n during the damping phase should be higher for conditions in which no other device is connected to the output of triac-based dimmer 8, which is illustrated by waveform 72A. If for example, one other identical replacement lighting device 10 were connected to the output of triac- based dimmer 8, only half of the damping current level would be required from each device, as illustrated by waveform 72B, and if an incandescent bulb or other high-current load is connected to the output of triac-based dimmer 8, no damping current would be required, as illustrated by waveform 72C. The bottom waveform illustrates a condition under which damping is determined to be needed only during positive half-cycles of AC line voltage Vune, which could be due to the design of the dimmer or due to an asymmetrical load connected to the output of triac-based dimmer. A different attach current profile is selected for positive half-cycles of AC line voltage Vii_nethan for negative half-cycles, resulting in a different damping current in a waveform 74A of input current Ii_n than in a waveform 74B of input current Ii_n.

[0067] While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form, and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. An apparatus comprising a lamp controller configured to:

monitor voltage information associated with one or more lamps or a dimmer of a system;

adjust one or more parameters of an attach current profile based on the voltage information to arrive at a selected attach current profile; and

apply within the system the selected attach current profile.

2. The apparatus of claim 1, wherein the attach current profile is associated with a leading edge of the dimmer.

3. The apparatus of claim 1, wherein the one or more parameters of the attach current profile comprise one or more of: a starting current, a peak current, a steady state hold current, or timing associated with a current.

4. The apparatus of claim 3, wherein the timing is relative to a leading edge of the dimmer.

5. The apparatus of claim 4, wherein the timing is relative to the starting current, the peak current, or the steady state hold current.

6. The apparatus of claim 1, wherein the controller is configured to adjust the one or more parameters of the attach current profile iteratively.

7. The apparatus of claim 6, wherein the selected attach current profile is chosen from among two or more iteratively adjusted attach current profiles, based on a performance of the one or more lamps or dimmer of the system.

8. The apparatus of claim 1, wherein the selected attach current profile is chosen based at least in part on different behavior associated with positive and negative half line cycles associated with the system.

9. The apparatus of claim 1, wherein the controller is configured to adjust the one or more parameters of the attach current profile automatically.

10. The apparatus of claim 1, wherein the one or more lamps comprise one or more LED lamps.

11. The apparatus of claim 1, wherein the controller is further configured to determine whether parallel lamps are within the system based on the voltage information.

12. The apparatus of claim 11, wherein the selected attach current profile is different, depending on whether parallel lamps are determined to be within the system.

13. The apparatus of claim 1, wherein the controller is configured to monitor voltage information iteratively for one or more cycles of dimmer operation.

14. A method comprising:

monitoring voltage information associated with one or more lamps or a dimmer of a system;

adjusting one or more parameters of an attach current profile based on the voltage information to arrive at a selected attach current profile; and

applying within the system the selected attach current profile.

15. The method of claim 14, wherein the attach current profile is associated with a leading edge of the dimmer.

16. The method of claim 14, wherein the one or more parameters of the attach current profile comprise one or more of: a starting current, a peak current, a steady state hold current, or timing associated with a current.

17. The method of claim 16, wherein the timing is relative to a leading edge of the dimmer.

18. The method of claim 17, wherein the timing is relative to the starting current, the peak current, or the steady state hold current

19. The method of claim 14, wherein adjusting comprises adjusting the one or more parameters of the attach current profile iteratively.

20. The method of claim 19, wherein the selected attach current profile is chosen from among two or more iteratively adjusted attach current profiles, based on a performance of the one or more lamps or dimmer of the system.

21. The method of claim 14, wherein the selected attach current profile is chosen based at least in part on different behavior associated with positive and negative half line cycles associated with the system.

22. The method of claim 14, wherein the adjusting is performed automatically.

23. The method of claim 14, wherein the one or more lamps comprise one or more LED lamps.

24. The method of claim 14, further comprising determining whether parallel lamps are within the system based on the voltage information.

25. The method of claim 24, wherein the selected attach current profile is different, depending on whether parallel lamps are determined to be within the system.

26. The method of claim 14, wherein the monitoring comprises monitoring voltage information iteratively for one or more cycles of dimmer operation.

27. A lighting circuit for powering one or more lighting devices from an output of a thyristor- switched dimmer circuit, comprising:

input terminals for coupling the lighting circuit to the output of the thyristor-switched dimmer circuit, wherein the thyristor-switched dimmer circuit supplies an input voltage and an input current to the lighting circuit at the input terminals;

a power converter having an input coupled to the input terminals and at least one output for supplying energy to the one or more lighting devices, wherein the power converter transfers energy from the input terminals to the at least one output during an active time period;

an input current control circuit for controlling the input current at least during the active time period;

a sensing circuit for sensing the input voltage and determining at least one attach current characteristic indicative of a load at the input terminals including external loads coupled to the output of the thyristor-switched dimmer circuit ; and

a storage circuit for storing information indicative of the at least one attach current characteristic, and wherein the control circuit controls the input current in conformity with the stored at least one attach current characteristic.

28. The lighting circuit of Claim 27, wherein the at least one attach current characteristic comprises one or more of a starting value of the input current, a peak value of the input current, a steady-state hold value of the input current or at least one timing value indicating a time at which the input current was equal to a predetermined value.

29. The lighting circuit of Claim 28, wherein the at least one attach current characteristic comprises the at least one timing value, and wherein the at least one timing value is relative to a time of a leading edge of the input voltage.

30. The lighting circuit of Claim 29, wherein the at least one timing value includes a value at which the input current is equal to the starting value of the input current, the peak value of the input current or the steady-state hold value of the input current.

31. The lighting circuit of Claim 27, wherein the sensing circuit iteratively adjusts the at least one attach current characteristic in conformity with subsequent measurements of the input voltage.

32. The lighting circuit of Claim 27, wherein the control circuit selects between at least two attach current characteristics stored by the storage circuit and controls the input current in conformity with a selected attached current characteristic.

33. The lighting circuit of Claim 32, wherein the sensing circuit determines differing attach current characteristics for positive and negative half cycles of an AC line voltage supplied to the a thyristor- switched dimmer circuit, and wherein the control circuit selects between the differing attach current characteristics for alternating half cycles.

34. The lighting circuit of Claim 27, wherein the sensing circuit determines, from the input voltage, whether or not other lighting devices are connected to the output of the thyristor-switched dimmer circuit, and wherein the sensing circuit selects from among differing attach current characteristics in conformity with whether or not other lighting devices are connected to the output of the thyristor- switched dimmer circuit.

35. The lighting circuit of Claim 27, wherein the one or more lighting devices are light-emitting diode (LED) devices.

36. A method of powering one or more lighting devices from an output of a thyristor-switched dimmer circuit, comprising:

receiving the output of the thyristor-switched dimmer circuit at input terminals;

supplying energy to the one or more lighting devices by converting energy drawn from the input terminals during an active time period;

controlling an input current drawn by the receiving from the input terminals at least during the active time period;

sensing an input voltage across the input terminals and determining at least one attach current characteristic indicative of a load across the input terminals including external loads coupled to the output of the thyristor-switched dimmer circuit; and

storing information indicative of the at least one attach current characteristic, and wherein the controlling controls the input current in conformity with the stored at least one attach current characteristic.

37. The method of Claim 36, wherein the at least one attach current characteristic comprises one or more of a starting value of the input current, a peak value of the input current, a steady-state hold value of the input current or at least one timing value indicating a time at which the input current was equal to a predetermined value.

38. The method of Claim 37, wherein the at least one attach current characteristic comprises the at least one timing value, and wherein the at least one timing value is relative to a time of a leading edge of the input voltage.

39. The method of Claim 38, wherein the at least one timing value includes a value at which the input current is equal to the starting value of the input current, the peak value of the input current or the steady-state hold value of the input current.

40. The method of Claim 36, wherein the sensing comprises iteratively adjusting the at least one attach current characteristic in conformity with subsequent measurements of the input voltage.

41. The method of Claim 36, further comprising selecting between at least two attach current characteristics stored by the storage circuit, and wherein the controlling controls the input current in conformity with a selected attached current characteristic.

42. The method of Claim 41, wherein the sensing determines differing attach current characteristics for positive and negative half cycles of an AC line voltage supplied to the a thyristor-switched dimmer circuit, and wherein the controlling selects between the differing attach current characteristics for alternating half cycles.

43. The method of Claim 36, wherein the sensing determines, from the input voltage, whether or not other lighting devices are connected to the output of the thyristor-switched dimmer circuit, and wherein the sensing further selects from among differing attach current characteristics in conformity with whether or not other lighting devices are connected to the output of the thyristor- switched dimmer circuit.

44. The method of Claim 36, wherein the one or more lighting devices are light-emitting diode (LED) devices.

45. An integrated circuit for operating a circuit that powers one or more lighting devices from an output of a thyristor-switched dimmer circuit, comprising:

a power converter control circuit having an output for controlling a power converter for supplying current to the one or more lighting devices from the output of the thyristor-switched dimmer circuit, wherein the power converter transfers energy during an active time period; an input current control circuit for controlling the input current at least during the active time period;

46. The integrated circuit of Claim 45, wherein the at least one attach current characteristic comprises one or more of a starting value of the input current, a peak value of the input current, a steady-state hold value of the input current or at least one timing value indicating a time at which the input current was equal to a predetermined value.