Abstract:
A three phase rectifier rectifies received three phase a.c. power to generate a ripple d.e. voltage. A power distribution bus conveys distribution power comprising the ripple d.c. voltage or an a.c. voltage derived therefrom to a location of an LED based lamp that is distal from the three phase rectifier. Additional circuitry disposed with the LED based lamp drives the LED based lamp using the distribution power.

Description:
BACKGROUND 
     The following relates to the illumination arts, lighting arts, electrical power arts, and related arts. 
     Light emitting diode (LED)-based lamps are employed in diverse outdoor lighting and illumination systems, such as traffic lighting, overhead (e.g., post-mounted) lamps, billboard and other commercial illuminated signage, and so forth. These lighting or illumination systems are sometimes in the context of commercial or industrial applications, such as commercial signage, parking lot illumination for retail centers, malls, supermarkets, and the like, or so forth. 
     In commercial and industrial settings, the available electrical power is typically three-phase a.c. power, such as 120/208 V or 277/480 V three-phase power as is typical in commercial or industrial settings in the United States, or 220/380 V three phase power in China, or so forth. The three-phase power is typically high voltage (for example, over 100 volts per phase). For high operating efficiency, the powered load should be balanced amongst the three phases. 
     LED-based lamps, on the other hand, are typically driven by d.c. power, since the diodes have polarity and do not operate under “negative” bias. Light emitting diodes also typically operate at relatively low voltage (a few volts across the p/n junction) and at relatively high current (of order a few hundred milliamperes to a few amperes current flow through each diode). Thus, LED-based lamps are generally not well-matched to three-phase a.c. power. 
     In a known approach for driving an LED-based lamp using three-phase a.c. power, the lamp is driven by one phase of a Y-connected three-phase a.c. power source (i.e., between the phase and ground), or is driven across two phases of a Y- or Δ-connected a.c. power source. To balance the load, a plural number of such LED-based lamps are distributed in balanced fashion amongst the phases of the power source. The generally sinusoidal a.c. phase-to-ground or phase-to-phase voltage is converted to d.c. using a costly electrolytic capacitor as a filter. Still further, for efficient power usage a power factor (PF) correction circuit is employed to ensure the LED-based lamp is driven at a PF close to unity. 
     These approaches employ complex and costly circuitry. Additionally, these are nonstandard approaches for drawing power off the three-phase a.c. distribution bus. As a result, the electrical connection of an LED-based lamp typically requires performing substantial electrical work at the three-phase a.c. power distribution panel, such as installing one or more dedicated phase-to-ground or phase-to-phase power taps. Such extensive electrical work at the distribution panel is undesirable and can introduce substantial safety concerns. 
     Another consideration is the location of the power conversion system. In commercial or industrial settings, LED-based lamps are sometimes mounted in locations that are remote or difficult to access. Examples include post-mounted lamps, illuminated channel letter signage mounted on an elevated billboard or building wall, or so forth. Typically, underground conduits supply the a.c. power at ground level. In one approach, the power conversion circuitry is mounted proximate to the elevated lamp. This approach adversely impacts maintenance. If the power circuitry fails or needs repair, a crew of typically three persons (an electrician, an lift operator, and a third “safety spotter”) are required to perform the maintenance at the location of the elevated lamp. In another approach, the power conversion circuitry is located at ground level. However, this approach has the disadvantage of requiring low voltage, high current d.c. electrical power to be conducted from ground level to the elevated location of the lamp, which increases “I 2 R” resistive power losses. Additionally, this approach may entail adding a dedicated weatherproof housing at ground level to house the specialized power conversion circuitry for the LED-based lamp. 
     BRIEF SUMMARY 
     In some embodiments disclosed herein as illustrative examples, an apparatus comprises: a three phase rectifier configured to rectify received three phase a.c. power to generate a ripple d.c. voltage; and a d.c.-to-d.c. converter configured to convert the ripple d.c. voltage to a regulated d.c power. 
     In some embodiments disclosed herein as illustrative examples, a method comprises: at a first location, performing three phase rectification of received three phase a.c. power to generate a ripple d.c. voltage; and, at a second location, performing d.c.-to-d.c. conversion to generate regulated d.c power from the ripple d.c. voltage. 
     In some embodiments disclosed herein as illustrative examples, an apparatus comprises: a three phase rectifier configured to rectify received three phase a.c. power to generate a ripple d.c. voltage; a power distribution bus configured to convey distribution power comprising the ripple d.c. voltage or an a.c. voltage derived therefrom to a location of an LED based lamp that is distal from the three phase rectifier; and additional circuitry disposed with the LED based lamp and configured to drive the LED based lamp using the distribution power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
         FIG. 1  diagrammatically illustrates an apparatus including an LED-based lamp and a power supply apparatus for converting three-phase a.c. power to drive the LED-based lamp. 
         FIG. 2  diagrammatically shows the power supply apparatus in additional detail including illustrative examples of suitable electrical circuitry. 
         FIG. 3  diagrammatically shows an illustrative quantitative example of the power supply apparatus of  FIG. 1 . 
         FIG. 4  plots the ripple d.c. voltage output by the three-phase full wave rectifier of the power supply apparatus of  FIGS. 1 and 2 . 
         FIG. 5  diagrammatically illustrates an embodiment of the three-phase full wave rectifier of the power supply apparatus of  FIGS. 1 and 2  in which the three-phase full wave rectifier is disposed in or on a terminal block configured for mounting in a three phase power distribution panel. 
         FIG. 6  diagrammatically illustrates an apparatus including a post-mounted LED-based lamp and a power supply fixture for driving the post-mounted LED-based lamp. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIGS. 1-5 , an apparatus includes a three-phase full-wave rectifier  10  which in the illustrated embodiment of  FIG. 1  is disposed in a three-phase power distribution panel  12 . The three-phase full-wave rectifier  10  receives three-phase a.c. power including phases V P1 , V P2 , V P3  and outputs a ripple d.c. voltage V RDC . The phases V P1 , V P2 , V P3  may, for example, be phase-to-neutral or phase-to-phase a.c. voltages of a wye (“Y”) connected three-phase power configuration or of a delta (“Δ”) connected three-phase power configuration. As shown in  FIG. 5 , the three phases V P1 , V P2 , V P3  are input via corresponding three terminals T P1 , T P2 , T P3  of a terminal block  14  configured for installation in the three-phase a.c. power distribution panel  12 , while the ripple d.c. voltage V RDC  is output across terminals T o   + , T o   − . The illustrated terminal block  14  also includes an optional neutral path having an input terminal T N  connected with the electrical neutral or ground of the three-phase a.c. power feeding directly to an output terminal T NO . This provides an electrical neutral or ground at the output if needed to comply with electrical safety considerations. The terminal block  14  advantageously can be configured as a conventional terminal block that is conventionally used in the three-phase a.c. power distribution panel  12 , so that no special wiring or other configuration is needed to install the three-phase full-wave rectifier  10 . With continuing reference to  FIG. 5  (and as also shown in  FIG. 2 ), the three-phase full-wave rectifier  10  is suitably embodied by three sets of power diode pairs. One power diode pair provides a first-polarity connection between the phase V P1  and the first or positive terminal T o   +  and a second-(opposite) polarity connection between the phase V P1  and the second or negative terminal T o   − . One power diode pair provides a first-polarity connection between the phase V P2  and the positive terminal T o   +  and an opposite polarity connection between the phase V P2  and the negative terminal T o   − . One power diode pair provides a first-polarity connection between the phase V P3  and the positive terminal T o   +  and an opposite polarity connection between the phase V P3  and the negative terminal T o   − .  FIG. 4  shows the resulting ripple d.c. voltage V RDC  across the terminals T o   + , T o   − . Each power diode pair performs full-wave rectification of the connected phase. The three full-wave rectified phase voltages are shown by dotted lines in  FIG. 4 , with the three full-wave rectified phase voltages superimposed across the terminals T o   + , T o   −  defining the ripple d.c. voltage V RDC  across the terminals T o   + , T o   − . The ripple d.c. voltage V RDC  typically has a ripple of about 10% of the average d.c. value, although the precise ripple depends on various factors such as harmonic distortion of the phases. The ripple d.c. voltage V RDC  is a high-voltage signal. For example,  FIG. 3  provides illustrative quantitative values for input three-phase a.c. power of 480 volts, “Y” connected at 60 Hz, such as is typical of some commercial and industrial three-phase a.c. power in the United States. The output of the three-phase full wave rectifier  10  for this input (neglecting harmonic distortion or the like) is a ripple d.c. voltage of about 648 volts, with a ripple of typically a few tens of volts. 
     With continuing reference to  FIGS. 1-5 , in some embodiments the ripple d.c. voltage V RDC  is suitably distributed via a power distribution bus  16  (shown diagrammatically in phantom) to power LED-based lamps. In  FIG. 1 , an illustrative LED lamp fixture  20  driven by the ripple d.c. voltage V RDC  is illustrated with some components diagrammatically illustrated, while additional LED lamp fixtures  22  are diagrammatically indicated in phantom. The fixture  20  includes components suitable to convert the ripple d.c. voltage V RDC  to a regulated lower-voltage d.c. power suitable to operate an LED-based lamp  30 , which in the embodiment shown in  FIG. 1  is a portion of illuminated signage which in this illustrated example is a channel letter  32  having the shape of the letter “E” of the Latin alphabet illuminated by LEDs  34 . Some illustrative examples of channel letter signage illuminated by LEDs are described, for example, in International Publication WO 02/097770 A2 published 5 Dec. 2002. 
     More generally, as used herein the term “LED-based lamp” and similar phraseology is intended to encompass any light source that employs one or more light emitting diodes (LEDs) for a lighting purpose such as general illumination, architectural accent illumination, illuminated signage, or so forth. The term “light emitting diode” or “LED” or similar phraseology as used herein denotes a compact solid-state light emitting device that generates illumination responsive to input d.c. power of relatively low voltage (e.g., a few volts) and relatively high current per LED device. The term “light emitting diode” or “LED” as used herein encompasses semiconductor-based LEDs (optionally including integral phosphor), organic LEDs (sometimes represented in the art by the acronym OLED), semiconductor laser diodes, or so forth. The terms “light emitting diode” or “LED” as used herein does not encompass devices such as incandescent light bulbs, fluorescent light tubes or compact fluorescent lamp (CFL) devices, halogen bulbs, or so forth that incorporate an evacuated volume or a fluid (that is, gaseous or liquid) component or that operate at high voltage per device, e.g. tens or hundreds of volts per device in the case of incandescent or fluorescent devices. 
     With continuing reference to  FIGS. 1-3 , the illustrative LED lamp fixture  20  includes a d.c.-to-a.c. converter  40  that converts the ripple d.c. voltage V RDC  to an a.c. voltage V HAC . In the illustrative example of  FIG. 2 , the d.c.-to-a.c. converter  40  is embodied by a half bridge converter defined by power diodes switched by control transistors driven by a suitable oscillator or the like (not shown). In some embodiments, the switching frequency of the half bridge converter is around 20-50 kHz, although higher or lower switching frequencies are also contemplated. The illustrative half bridge converter chops the ripple d.c. voltage V RDC  into a square wave voltage that defines the a.c. voltage V HAC  in this illustrative embodiment. An optional high-frequency step-down transformer  42  transforms the a.c. voltage V HAC  to a.c. voltage V LAC  at a lower voltage. In the illustrative quantitative example of  FIG. 3 , the d.c.-to-a.c. converter  40  is a half bridge converter that chops the 648 V (RMS) ripple d.c. voltage V RDC  to a.c. voltage V HAC  in the form of a square wave voltage having amplitude 678 V (bipolar, that is, switching between +678 V and −678 V as the square wave voltage switches between positive and negative polarities) and a frequency in the range 20-50 kHz. This square wave voltage is then reduced to the a.c. voltage V LAC.  at a lower voltage of 36 V in the quantitative example of  FIG. 3 , by the optional high-frequency step-down transformer  42 . 
     With continuing reference to  FIGS. 1-3 , the illustrative LED lamp fixture  20  further includes a regulated power supply  44  that is driven by the a.c. voltage V HAC  output by the d.c.-to-a.c. converter  40  or that is driven by the lower voltage a.c. voltage V LAC  output by the optional high-frequency step-down transformer  42 . In the illustrative example of  FIG. 2 , the regulated power supply  44  is a switched-mode power supply; however, other regulated power supply topologies such as a linear regulator topology are also contemplated. The regulated power supply  44  outputs a regulated d.c. power V R  suitable for driving the LED-based lamp  30 . The illustrative switched-mode power supply shown in  FIG. 2  includes a full-wave rectifier defined by a four-diode combination that generates full-wave rectified voltage that is smoothed by reactive filtering components and drives an operational amplifier (op-amp) or hysteresis based current-regulating switching circuit. The regulated d.c. power V R  output by the switched-mode power supply of  FIG. 2  is regulated with respect to current—in other words, the power regulation is constant current regulation which ensures that the output power is at a selected constant current level (within tolerances of the power regulation design). The selected constant current level for the regulated d.c. power V R  is selected to provide suitable current to operate the LED-based lamp  30 . Alternatively, employing a regulated power supply outputting a regulated voltage is also contemplated, in which case the regulation ensures that the output voltage is at a selected constant voltage level (again, within tolerances of the power regulation design). 
     The detailed circuitry of  FIG. 2  is provided as an illustrative example. It is to be understood that the various components such as the d.c.-to-a.c. converter  40  and the regulated power supply  44  can be implemented in other ways, such as using various switched-mode or linear power regulation topologies for the regulated power supply  44 , various chopping circuits for the d.c.-to-a.c. converter  40 , or so forth. The a.c. voltage V HAC  can have a waveform other than the illustrative bipolar square wave generated by the illustrative d.c.-to-a.c. converter  40 , such as a sinusoidal or triangle wave form. It is also contemplated to include filtering components to reduce the ripple of the ripple d.c. voltage V RDC . 
     The circuitry can also be viewed in a different way. As indicated in  FIG. 2 , the d.c.-to-a.c. converter  40 , the high frequency step-down transformer  42 , and the rectifier bridge component  46  of the regulated power supply  44  can be collectively considered as a d.c.-to-d.c. converter  48 . The illustrated d.c.-to-d.c. converter  48  employs the d.c.-to-a.c. converter  40  which is embodied in the illustrated embodiment as a half bridge converter. However, other d.c.-to-d.c. converter topologies are also contemplated, such as a forward d.c.-to-d.c. converter topology, a flyback d.c.-to-d.c. converter topology, or so forth. In the forward and flyback topologies, there is no d.c.-to-a.c. converter component. Regardless of the d.c.-to-d.c. converter topology that is chosen, the purpose of the d.c.-to-d.c. converter  48  is to take the ripple d.c. voltage V RDC  from the three-phase full-wave rectifier  10  and generate a lower-voltage rectified d.c. voltage. The portion of the regulated power supply  44  electrically downstream of the rectifier bridge component  46  provides smoothing or other conditioning of the converted d.c. voltage to generate the regulated d.c. power V R  suitable for driving the LED-based lamp  30 . 
     In some preferred embodiments, however, the apparatus does not include an electrolytic filter capacitor configured to perform or contribute to performing an a.c.-to-d.c. conversion. This preferred omission reduces manufacturing cost and weight of the power conversion apparatus, and improves the reliability of the system. It is contemplated, however, to use electrolytic capacitors elsewhere in the power conversion apparatus. For example, the one, some, or all of the capacitors of the circuitry shown in  FIG. 2  can be embodied by electrolytic capacitors. 
     An advantage of the system of  FIG. 1  is that the load imposed by the LED-based lamp  30  is inherently balanced, since the three-phase full wave rectifier  10  operates symmetrically and equally on the three phases V P1 , V P2 , V P3  in generating the ripple d.c. voltage V RDC . The system of  FIG. 1  also advantageously does not employ a power factor (PF) correction circuit, but nonetheless provides a load that has a approximately unity power factor. The illustrated three-phase rectifier  10  is a full wave rectifier. It is contemplated to substitute a three-phase half wave rectifier for the illustrated three phase full wave rectifier  10 . A three-phase half wave rectifier also provides the advantage of an inherently balanced load. 
     Another advantage of the system of  FIG. 1  is that the three-phase a.c. power distribution panel  12  can be of a conventional configuration, and tapping off of the three-phase a.c. power distribution panel  12  to power the LED-based lamp  30  entails installation of the terminal block  14  which, as illustrated in.  FIG. 5 , can be configured for installation in a conventional three-phase a.c. power distribution panel. The arrangement of  FIG. 1  includes the power distribution bus  16  which distributes the ripple d.c. voltage V RDC . For some applications, it may be preferable to instead distribute the high voltage a.c. power V HAC  that is output by the d.c.-to-a.c. converter  40 , since this facilitates the use of transformer action for electrical isolation or other purposes while still providing a high voltage so as to reduce “I 2 R” resistive power losses over long transmission lines. 
     With reference to  FIG. 6 , another illustrative application is shown which employs transmission of the high voltage a.c. power V HAC.  The application of  FIG. 6  is overhead lighting such as is typically used for illuminating parking lots, roadways, walkways, or so forth. In this application, a post  100  is held generally upright by a base  102  and includes an upper housing or assembly  104  that supports or integrally includes an LED-based lamp  130  held in an elevated position respective to ground level by the post  100 . The post  100 , base  102 , and upper housing or assembly  104  collectively define a lamppost assembly  100 ,  102 ,  104 . The illustrative elevated LED-based lamp  130  is configured as a downlight in which LEDs  134  are mounted on a substrate  140  in an arrangement that provides illumination in a generally downward direction. Although the illustrated post  100  is held precisely vertical, some cant or tilt of the post  100  is contemplated, for example to cause the lamp to overhang the roadway or other illuminated area. Optionally, the LED-based lamp  130  may include suitably configured reflectors, reflective baffles, or the like (not shown) in order to optimize the downward illumination pattern. Some examples of such arrangements are described, for example, in International Publication WO 2009/012314 A1 published 22 Jan. 2009. The illustrative LED-based lamp  130  also includes a heat sink  142  for dissipating heat generated by the LEDs  134 , and may optionally include other operative components such as an ambient light sensor (not shown) for controlling operation of the lamp  130 . 
     In the arrangement shown in  FIG. 6 , the three-phase full wave rectifier  10  is disposed in the base  102  of the lamppost assembly  100 ,  102 ,  104 . The ripple d.c. voltage V RDC  output by the d.c.-to-a.c. converter  40  is conducted up the post  100  by a cable  150  passing through a hollow conduit or interior of the post  100  to the d.c.-to-d.c. converter  48  (see  FIG. 2 ) which in the illustrated embodiment includes the d.c.-to-a.c. converter  40 , the high frequency step-down transformer  42 , and the regulated power supply  44  all of which are located at the elevated position in the upper housing or assembly  104  that supports or integrally includes an LED-based lamp  130 . Since the three-phase full wave rectifier  10  is disposed in the base  102  which is at ground level, repair or maintenance of this component  10  is simplified since a repair or maintenance person can access the three-phase full wave rectifier  10  without the use of a lift truck or the like. The three-phase full wave rectifier  10  is typically the most likely component to fail or require maintenance, since it operates at high a.c. voltage. On the other hand, the d.c.-to-d.c. converter in the elevated upper housing  104  is less prone to failure, and may in some embodiments be replaceable as a single modular unit. Accordingly, the arrangement of  FIG. 6  advantageously balances equipment accessibility against operational efficiency and power transmission efficiency. 
     Moreover, as already noted with reference to  FIGS. 1 and 5 , the three-phase full wave rectifier  10  is optionally mounted in the three-phase a.c. power distribution panel, for example embodied as the terminal block  14  shown in  FIG. 5 , rather than in the lamp base  102  as shown in  FIG. 6 . In such an arrangement, a single terminal block  14  mounted in the three-phase a.c. power distribution panel can be used to generate the ripple d.c. voltage V RDC  which is then distributed to the bases of a plurality of post-mounted lamps to drive the lamps. 
     Other divisions of components are also contemplated for use in various applications. For example, in the distribution system of  FIG. 1 , the d.c.-to-a.c. converter  40  is optionally integrated or included with the terminal block  14  shown in  FIG. 5 . In this alternative arrangement, the output terminals T o   + , T o   −  carry the high voltage a.c. power V HAC  for power distribution, which in turn advantageously enables optional incorporation of transformer-based couplings into the power distribution bus  16 . In some such embodiments it is contemplated to employ the high frequency step-down transformer  42  both for voltage step-down and also for tapping off of the power distribution bus  16 . If the embodiment of  FIG. 6  is modified in this way, then the high voltage a.c. power V HAC  is conducted up the cable  150  passing through the post  100  to the post-mounted assembly including the electrical fixture and the post-mounted LED-based lamp  130 . In such embodiments, the high voltage a.c. power V HAC  is suitably distributed to the bases of a plurality of post-mounted lamps to drive the lamps. 
     The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.