Abstract:
A controller may be configured to: (i) predict based on an electronic transformer secondary signal an estimated occurrence of a high-resistance state of a trailing-edge dimmer coupled to a primary winding of an electronic transformer, wherein the high-resistance state occurs when the trailing-edge dimmer begins phase-cutting an alternating current voltage signal; (ii) operate a power converter in a trailing-edge exposure mode for a first period of time immediately prior to the estimated occurrence of the high-resistance state, such that the power converter is enabled to transfer energy from the secondary winding to the load during the trailing-edge exposure mode; and (iii) operate the power converter in a power mode for a second period of time prior to and non-contiguous with the first period of time, such that the power converter is enabled to transfer energy from the secondary winding to the load during the power mode.

Description:
RELATED APPLICATIONS 
       [0001]    The present disclosure claims priority as a continuation-in-part to U.S. patent application Ser. No. 13/798,926 filed Mar. 13, 2013, which claims priority to U.S. Provisional Patent Application Ser. No. 61/667,685, filed Jul. 3, 2012, and U.S. Provisional Patent Application Ser. No. 61/673,111, filed Jul. 18, 2012, all of which are incorporated by reference herein in their entirety. 
         [0002]    The present disclosure also claims priority to U.S. Provisional Patent Application Ser. No. 61/826,250, filed May 22, 2013, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF DISCLOSURE 
       [0003]    The present disclosure relates in general to the field of electronics, and more specifically to systems and methods for ensuring compatibility between one or more low-power lamps and the power infrastructure to which they are coupled. 
       BACKGROUND 
       [0004]    Many electronic systems include circuits, such as switching power converters or transformers that interface with a dimmer The interfacing circuits deliver power to a load in accordance with the dimming level set by the dimmer For example, in a lighting system, dimmers provide an input signal to a lighting system. The input signal represents a dimming level that causes the lighting system to adjust power delivered to a lamp, and, thus, depending on the dimming level, increase or decrease the brightness of the lamp. Many different types of dimmers exist. In general, dimmers generate an output signal in which a portion of an alternating current (“AC”) input signal is removed or zeroed out. For example, some analog-based dimmers utilize a triode for alternating current (“triac”) device to modulate a phase angle of each cycle of an alternating current supply voltage. This modulation of the phase angle of the supply voltage is also commonly referred to as “phase cutting” the supply voltage. Phase cutting the supply voltage reduces the average power supplied to a load, such as a lighting system, and thereby controls the energy provided to the load. A particular type of phase-cutting dimmer is known as a trailing-edge dimmer A trailing-edge dimmer phase cuts from the end of an AC cycle, such that during the phase-cut angle, the dimmer is “off” and supplies no output voltage to its load, but is “on” before the phase-cut angle and in an ideal case passes a waveform proportional to its input voltage to its load. 
         [0005]      FIG. 1  depicts a lighting system  100  that includes a trailing-edge, phase-cut dimmer  102  and a lamp  142 .  FIG. 2  depicts example voltage and current graphs associated with lighting system  100 . Referring to  FIGS. 1 and 2 , lighting system  100  receives an AC supply voltage V SUPPLY  from voltage supply  104 . The supply voltage V SUPPLY , indicated by voltage waveform  200 , is, for example, a nominally 60 Hz/110 V line voltage in the United States of America or a nominally 50 Hz/220 V line voltage in Europe. Trailing edge dimmer  102  phase cuts trailing edges, such as trailing edges  202  and  204 , of each half cycle of supply voltage V SUPPLY . Since each half cycle of supply voltage V SUPPLY  is 180 degrees of the supply voltage V SUPPLY , the trailing edge dimmer  102  phase cuts the supply voltage V SUPPLY  at an angle greater than 0 degrees and less than 180 degrees. The phase cut, input voltage V Φ     —     DIM  to lamp  142  represents a dimming level that causes the lighting system  100  to adjust power delivered to lamp  142 , and, thus, depending on the dimming level, increase or decrease the brightness of lamp  142 . 
         [0006]    Dimmer  102  includes a timer controller  110  that generates dimmer control signal DCS to control a duty cycle of switch  112 . The duty cycle of switch  112  is a pulse width (e.g., times t 1 −t 0 ) divided by a period of the dimmer control signal (e.g., times t 3 −t 0 ) for each cycle of the dimmer control signal DCS. Timer controller  110  converts a desired dimming level into the duty cycle for switch  112 . The duty cycle of the dimmer control signal DCS is decreased for lower dimming levels (i.e., higher brightness for lamp  142 ) and increased for higher dimming levels. During a pulse (e.g., pulse  206  and pulse  208 ) of the dimmer control signal DCS, switch  112  conducts (i.e., is “on”), and dimmer  102  enters a low resistance state. In the low resistance state of dimmer  102 , the resistance of switch  112  is, for example, less than or equal to 10 ohms. During the low resistance state of switch  112 , the phase cut, input voltage V Φ     —     DIM  tracks the input supply voltage V SUPPLY  and dimmer  102  transfers a dimmer current i DIM  to lamp  142 . 
         [0007]    When timer controller  110  causes the pulse  206  of dimmer control signal DCS to end, dimmer control signal DCS turns switch  112  off, which causes dimmer  102  to enter a high resistance state (i.e., turns off). In the high resistance state of dimmer  102 , the resistance of switch  112  is, for example, greater than 1 kiloohm. Dimmer  102  includes a capacitor  114 , which charges to the supply voltage V SUPPLY  during each pulse of the dimmer control signal DCS. In both the high and low resistance states of dimmer  102 , the capacitor  114  remains connected across switch  112 . When switch  112  is off and dimmer  102  enters the high resistance state, the voltage V C  across capacitor  114  increases (e.g., between times t 1  and t 2  and between times t 4  and t 5 ). The rate of increase is a function of the amount of capacitance C of capacitor  114  and the input impedance of lamp  142 . If effective input resistance of lamp  142  is low enough, it permits a high enough value of the dimmer current i DIM  to allow the phase cut, input voltage V Φ     —     DIM  to decay to a zero crossing (e.g., at times t 2  and t 5 ) before the next pulse of the dimmer control signal DCS. 
         [0008]    Dimming a light source with dimmers saves energy when operating a light source and also allows a user to adjust the intensity of the light source to a desired level. However, conventional dimmers, such as a trailing-edge dimmer, that are designed for use with resistive loads, such as incandescent light bulbs, often do not perform well when supplying a raw, phase modulated signal to a reactive load such as a power converter or transformer, as is discussed in greater detail below. 
         [0009]      FIG. 3  depicts a lighting system  100  that includes a trailing-edge, phase-cut dimmer  102 , an electronic transformer  122 , and a lamp  142 . Such a system may be used, for example, to transform a high voltage (e.g., 110V, 220 V) to a low voltage (e.g., 12 V) for use with a halogen lamp (e.g., an MR16 halogen lamp).  FIG. 4  depicts example voltage graphs associated with lighting system  101 . 
         [0010]    As is known in the art, electronic transformers operate on a principle of self-resonant circuitry. Referring to  FIGS. 3 and 4 , when dimmer  102  is used in connection with transformer  122  and a low-power lamp  142 , the low current draw of lamp  142  may be insufficient to allow electronic transformer  122  to reliably self-oscillate. 
         [0011]    To further illustrate, electronic transformer  122  may receive the dimmer output voltage V Φ     —     DIM  at its input where it is rectified by a full-bridge rectifier formed by diodes  124 . As voltage V Φ     —     DIM  increases in magnitude, voltage on capacitor  126  may increase to a point where diac  128  will turn on, thus also turning on transistor  129 . Once transistor  129  is on, capacitor  126  may be discharged and oscillation will start due to the self-resonance of switching transformer  130 , which includes a primary winding (T 2a ) and two secondary windings (T 2b  and T 2c ). Accordingly, as depicted in  FIG. 4 , an oscillating output voltage V s    400  will be formed on the secondary winding of transformer  132  and delivered to lamp  142  while dimmer  102  is on, bounded by an AC voltage level proportional to V Φ     —     DIM . 
         [0012]    However, as mentioned above, many electronic transformers will not function properly with low-current loads. With a light load, there may be insufficient current through the primary winding of switching transformer  130  to sustain oscillation. For legacy applications, such as where lamp  142  is a 35-watt halogen bulb, lamp  142  may draw sufficient current to allow transformer  122  to sustain oscillation. However, should a lower-power lamp be used, such as a six-watt light-emitting diode (LED) bulb, the current drawn by lamp  142  may be insufficient to sustain oscillation in transformer  122 , which may lead to unreliable effects, such as visible flicker and a reduction in total light output below the level indicated by the dimmer. 
         [0013]    In addition, traditional approaches do not effectively detect or sense a type of transformer to which a lamp is coupled, further rendering it difficult to ensure compatibility between low-power (e.g., less than twelve watts) lamps and the power infrastructure to which they are applied. 
       SUMMARY 
       [0014]    In accordance with the teachings of the present disclosure, certain disadvantages and problems associated with ensuring compatibility of a low-power lamp with a dimmer and a transformer may be reduced or eliminated. 
         [0015]    In accordance with embodiments of the present disclosure, an apparatus may include a controller to provide compatibility between a load and a secondary winding of an electronic transformer. The controller may be configured to: (i) predict based on an electronic transformer secondary signal an estimated occurrence of a high-resistance state of a trailing-edge dimmer coupled to a primary winding of the electronic transformer, wherein the high-resistance state occurs when the trailing-edge dimmer begins phase-cutting an alternating current voltage signal; (ii) operate a power converter in a trailing-edge exposure mode for a first period of time immediately prior to the estimated occurrence of the high-resistance state, such that the power converter is enabled to transfer energy from the secondary winding to the load during the trailing-edge exposure mode; and (iii) operate the power converter in a power mode for a second period of time prior to and non-contiguous with the first period of time, such that the power converter is enabled to transfer energy from the secondary winding to the load during the power mode. 
         [0016]    In accordance with these and other embodiments of the present disclosure, a method for providing compatibility between a load and a secondary winding of an electronic transformer may include: (i) predicting based on an electronic transformer secondary signal an estimated occurrence of a high-resistance state of a trailing-edge dimmer coupled to a primary winding of the electronic transformer, wherein the high-resistance state occurs when the trailing-edge dimmer begins phase-cutting an alternating current voltage signal; (ii) operating a power converter in a trailing-edge exposure mode for a first period of time immediately prior to the estimated occurrence of the high-resistance state, such that the power converter is enabled to transfer energy from the secondary winding to the load during the trailing-edge exposure mode; and (iii) operating the power converter in a power mode for a second period of time prior to and non-contiguous with the first period of time, such that the power converter is enabled to transfer energy from the secondary winding to the load during the power mode. 
         [0017]    Technical advantages of the present disclosure may be readily apparent to one of ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. 
         [0018]    It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
           [0020]      FIG. 1  illustrates a lighting system that includes a phase-cut trailing-edge dimmer, as is known in the art; 
           [0021]      FIG. 2  illustrates example voltage and current graphs associated with the lighting system depicted in  FIG. 1 , as is known in the art; 
           [0022]      FIG. 3  illustrates a lighting system that includes a phase-cut trailing-edge dimmer and an electronic transformer, as is known in the art; 
           [0023]      FIG. 4  illustrates example voltage and current graphs associated with the lighting system depicted in  FIG. 3 , as is known in the art; 
           [0024]      FIG. 5  illustrates an example lighting system including a controller for providing compatibility between a low-power lamp and an electronic transformer driven by a trailing-edge dimmer, in accordance with embodiments of the present disclosure; 
           [0025]      FIG. 6  depicts example voltage and current graphs associated with particular embodiments of the lighting system depicted in  FIG. 5 , in accordance with embodiments of the present disclosure; and 
           [0026]      FIG. 7  depicts example voltage and current graphs associated with other particular embodiments of the lighting system depicted in  FIG. 5 , in accordance with embodiments of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 5  illustrates an example lighting system  500  including a controller  512  for providing compatibility between a low-power lamp  542  and other elements of a lighting system, in accordance with embodiments of the present disclosure.  FIG. 6  depicts example voltage and current graphs associated with lighting system  500  depicted in  FIG. 5 , in accordance with embodiments of the present disclosure. As shown in  FIG. 5 , lightning system  500  may include a voltage supply  504 , a dimmer  502 , a transformer  522 , a lamp  542 , and a controller  512 . Voltage supply  504  may generate a supply voltage V SUPPLY  that is, for example, a nominally 60 Hz/110 V line voltage in the United States of America or a nominally 50 Hz/220 V line voltage in Europe. 
         [0028]    Dimmer  502  may comprise any system, device, or apparatus for generating a dimming signal to other elements of lighting system  500 , the dimming signal representing a dimming level that causes lighting system  500  to adjust power delivered to a lamp, and, thus, depending on the dimming level, increase or decrease the brightness of lamp  542 . Thus, dimmer  502  may include a trailing-edge dimmer similar to that depicted in  FIGS. 1 and 3 , or any other suitable dimmer 
         [0029]    Transformer  522  may comprise any system, device, or apparatus for transferring energy by inductive coupling between winding circuits of transformer  522 . Thus, transformer  522  may include an electronic transformer similar to that depicted in  FIG. 3 , or any other suitable transformer. 
         [0030]    Lamp assembly  542  may comprise any system, device, or apparatus for converting electrical energy (e.g., delivered by electronic transformer  522 ) into photonic energy (e.g., at LEDs  532 ). In some embodiments, lamp assembly  542  may comprise a multifaceted reflector form factor (e.g., an MR16 form factor). In these and other embodiments, lamp assembly  542  may comprise an LED lamp. As shown in  FIG. 5 , lamp assembly  542  may include a bridge rectifier  534 , a boost converter stage  536 , a link capacitor  552 , a buck converter stage  538 , a load capacitor  554 , and a controller  512 . 
         [0031]    Bridge rectifier  534  may comprise any suitable electrical or electronic device as is known in the art for converting the whole of alternating current voltage signal v s  into a rectified voltage signal v REC  having only one polarity. 
         [0032]    Boost converter stage  536  may comprise any system, device, or apparatus configured to convert an input voltage (e.g., v REC ) to a higher output voltage (e.g., v LINK ) wherein the conversion is based on a control signal (e.g., a pulse-width modulated control signal communicated from controller  512 ). Similarly, buck converter stage  538  may comprise any system, device, or apparatus configured to convert an input voltage (e.g., v LINK ) to a lower output voltage (e.g., v OUT ) wherein the conversion is based on another control signal (e.g., a pulse-width modulated control signal communicated from controller  512 ). 
         [0033]    Each of link capacitor  552  and output capacitor  554  may comprise any system, device, or apparatus to store energy in an electric field. Link capacitor  552  may be configured such that it stores energy generated by boost converter stage  536  in the form of the voltage v LINK . Output capacitor  554  may be configured such that it stores energy generated by buck converter stage  538  in the form of the voltage v OUT . 
         [0034]    LEDs  532  may comprise one or more light-emitting diodes configured to emit photonic energy in an amount based on the voltage V OUT  across the LEDs  532 . 
         [0035]    Controller  512  may comprise any system, device, or apparatus configured to, as described in greater detail elsewhere in this disclosure, determine one or more characteristics of voltage v REC  present at the input of boost converter stage  536  and control an amount of current i REC  drawn by the boost converter stage  536  based on such one or more characteristics of voltage v REC . Operation of controller  512  may be described by reference to  FIG. 6 . 
         [0036]    As previously described in reference to  FIG. 4  in the Background section, an oscillating voltage V S  of the secondary winding of electronic transformer  522  may be delivered to lamp assembly  542 , wherein the oscillating voltage is bounded by the waveform V Φ     —     DIM  of the output of dimmer  502  depicted in  FIG. 6 , the trailing edge of dimmer  502  occurring at times t 4  shown in  FIG. 6 . Bridge rectifier  534  may in turn rectify transformer secondary voltage V S , generating an oscillating rectified voltage V REC  delivered to boost stage  536 , wherein the oscillating voltage is bounded by the waveform |V REC | depicted in  FIG. 6 . 
         [0037]    In operation, controller  512  may receive and analyze the rectified V REC  to determine one or more characteristics of the rectified voltage V REC . For example, controller  512  may be configured to detect an estimated occurrence of a positive edge of the V REC  waveform occurring at time t 1  during each half-line cycle when electronic transformer  522  begins oscillating. Such positive edge may occur after the beginning (occurring at time t 0 ) of the half line cycle of the supply voltage V SUPPLY  when the voltage V Φ     —     DIM  is large enough for electronic transformer  522  to charge its timer capacitor. As another example, controller  512  may be configured to detect an estimated occurrence of a negative edge of the V REC  waveform occurring at time t 3  during each half-line cycle corresponding to the trailing edge of dimmer  502  output signal V Φ     —     DIM  (e.g., the estimated occurrence of the high-resistance state of dimmer  502 ). The estimated occurrence of the trailing edge/high-resistance state of dimmer  502  may be predicted in any suitable manner, for example, using systems and methods disclosed in U.S. patent application Ser. No. 13/298,002 filed Nov. 16, 2011 and entitled “Trailing Edge Dimmer Compatibility with Dimmer High Resistance Prediction,” which is incorporated in its entirety herein for all purposes. 
         [0038]    From such determination of the estimated occurrences of the positive edge and the negative edge, controller  512  may determine the estimated half-line cycle of supply voltage V SUPPLY  (e.g., based on the difference between successive estimated occurrences of the positive edge), the estimated phase angle of dimmer  502  (e.g., based on the difference between an estimated occurrence of the positive edge and an estimated occurrence of a subsequent negative edge), and/or other characteristics of the rectified voltage V REC . Thus, during each half-line cycle, controller  512  may use characteristics determined during the previous half-line cycle to control operation of map assembly  542 . 
         [0039]    Based on one or more of the characteristics of the rectified voltage V REC  described above, controller  512  may sequentially operate boost stage  536  in a plurality of modes. For example, from approximately the estimated occurrence of the positive edge at time t 1  to a subsequent time t 2 , controller  512  may operate in a high-current power mode in which it enables boost converter stage  536 , allowing boost converter stage  536  to draw a substantially non-zero current I REC  such that energy is transferred from electronic transformer  522  to link capacitor  552 . The duration T on  (T on =t 2 −t 1 ) of the power mode may be based on the estimated phase angle of dimmer  502  determined by controller  512 . 
         [0040]    Following the power mode, controller  512  may enter a low-current idle mode from time t 2  to time t 3  in which it disables boost converter stage  536  such that substantially no energy is delivered from electronic transformer  522  to link capacitor  552 . Accordingly, during the idle mode, a small amount of ripple is present on link voltage V LINK  and link capacitor  552  discharges to buck converter stage  538 . 
         [0041]    Following the idle mode, controller  512  may enter a high-current trailing-edge exposure mode in which it enables boost converter stage  536  from time t 3  to time t 4  to allow controller  512  to detect the negative edge. The time t 3  may occur at a period of time before a predicted occurrence of the negative edge (based on the determination of the estimated occurrence of the negative edge from the previous half-line cycle) and time t 4  may occur at the detection of the estimated occurrence of the negative edge. In some embodiments, the duration of time between t 3  and the predicted occurrence of the negative edge may remain constant, irrespective of the phase angle of dimmer  502 . During the trailing-edge exposure mode, boost converter stage  536  may draw a substantially non-zero current I REC  such that energy is transferred from electronic transformer  522  to link capacitor  552 . Accordingly, controller  512  may control the cumulative durations of the power mode and the trailing-edge exposure mode such that the power delivered from electronic transformer  552  to lamp assembly  542  in each half-line cycle is commensurate with the control setting and phase-cut angle of dimmer  502 . 
         [0042]    Following the trailing-edge exposure mode, from time t 4  to the beginning of the subsequent power mode at time t 1  (e.g., at the estimated occurrence of the subsequent positive edge), controller  512  may enter a low-impedance glue mode in which it continues to enable boost converter stage  536 , but substantially zero current I REC  is delivered to boost converter stage  536 , on account of the phase cut of dimmer  502  and a substantially zero voltage V REC . The glue mode applies a low impedance to the secondary winding of electronic transformer  522 , thus allowing discharge of any residual energy stored in the capacitors of dimmer  502  and/or electronic dimmer  522 . After the trailing-edge exposure mode, controller  512  may again enter the power mode. 
         [0043]    Although the foregoing discussion contemplates that controller  512  determines one of more characteristics of rectified voltage signal V REC  in order to control operation of boost converter stage  536 , in some embodiments controller  512  may control operation of boost converter stage  536  by receiving and analyzing the unrectified electronic transformer voltage V S . 
         [0044]    Although  FIG. 6  and its accompanying discussion contemplate the existence of a single power mode per half-line cycle, in some embodiments controller  512  may employ a plurality of power modes per half-line cycle, as shown in  FIG. 7  and described below. As shown in  FIG. 7 , from approximately the estimated occurrence of the positive edge at time t 1  to a subsequent time t A , controller  512  may operate in a first power mode in which it enables boost converter stage  536 , allowing boost converter stage  536  to draw a substantially non-zero current I REC  such that energy is transferred from electronic transformer  522  to link capacitor  552 . Following the first power mode, controller  512  may enter a first idle mode from time t A  to time t B  in which it disables boost converter stage  536  such that substantially no energy is delivered from electronic transformer  522  to link capacitor  552 . After the first idle mode, from approximately time t B  to a subsequent time t 2 , controller  512  may operate in an additional power mode in which it enables boost converter stage  536 , allowing boost converter stage  536  to draw a substantially non-zero current I REC  such that energy is transferred from electronic transformer  522  to link capacitor  552 . Following the additional power mode, controller  512  may enter an additional idle mode from time t 2  to time t 3  in which it disables boost converter stage  536  such that substantially no energy is delivered from electronic transformer  522  to link capacitor  552 . Following the additional idle mode, controller  512  may enter a trailing-edge exposure mode in which is enables boost converter stage  536  from time t 3  to time t 4  to allow controller  512  to detect the negative edge. After the trailing-edge exposure mode, from time t 4  to the beginning of the subsequent power mode at time t 1  (e.g., at the estimated occurrence of the subsequent positive edge), controller  512  may enter a glue mode in which it continues to enable boost converter stage  536 , but substantially zero current I REC  is delivered to boost converter stage  536 , on account of the phase cut of dimmer  502  and a substantially zero voltage V REC . 
         [0045]    Although  FIG. 7  represents embodiments in which controller  512  enters two power modes during a single half-line cycle, in these and other embodiments controller  512  may have any positive number of power modes. In a half-line cycle with two or more power modes, the cumulative durations of the power modes in the half-line cycle may be based on the estimated phase angle of dimmer  502  determined by controller  512 , such that cumulative durations of the power modes and the trailing-edge exposure mode are such that the power delivered from electronic transformer  552  to lamp assembly  542  in each half-line cycle is commensurate with the control setting and phase-cut angle of dimmer  502 . 
         [0046]    As used herein, when two or more elements are referred to as “coupled” to one another, such term indicates that such two or more elements are in electronic communication whether connected indirectly or directly, without or without intervening elements. 
         [0047]    This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. 
         [0048]    All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.