Abstract:
A light-emitting diode (LED) module includes a body assembly, a printed circuit board assembly (PCBA) having LEDs, and a power conditioning board having a controller. The PCBA and power conditioning board are encapsulated by the body assembly. The power conditioning board is driverless, i.e., characterized by an absence of a switching power supply, and includes a rectifier and reducer. The reducer detects an AC waveform zero-crossing and phase angle of AC line power, reduces the rectified voltage, and selectively turns the LEDs on or off using corresponding signals. The controller receives the reduced peak-to-peak rectified voltage from the reducer, adjusts operating parameters of the reducer in response to the phase angle and zero-crossing to illuminate or extinguish some/all of the LEDs and increase the power factor of the LED module, and adjusts the limiter to provide a constant power level to the LEDs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/498,730 filed on Jun. 20, 2011, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a light-emitting diode (LED)-based lighting module and a control method for powering the same. 
     BACKGROUND 
     Businesses and consumers have begun considering the benefits of alternative forms of lighting as a consequence of rising energy costs. Inefficient incandescent bulbs have been largely replaced with standard T8-sized fluorescent lamp tubes in ceiling light fixtures. Likewise, compact fluorescent (CFC) bulbs in various sizes have emerged as cost-effective replacements for incandescent bulbs. However, CFC and other fluorescent bulbs contain trace levels of mercury, and thus breakage or replacement of such bulbs typically requires special disposal and handling procedures. 
     The unique properties of light-emitting diodes (LEDs) has led to the development of LED bulbs as viable replacements for existing fluorescent and incandescent bulbs. The operating life of an LED bulb vastly exceeds that of a typical fluorescent bulb. Additionally, unlike fluorescent bulbs, the life of an LED bulb is not severely degraded by frequent on/off cycling. This makes LED bulbs an ideal choice for various applications, e.g., closet, garage, or storage room lighting. 
     The long relative working life of an LED bulb coupled with the high efficiencies provided by emerging LED technology has spawned a rapidly growing but still nascent industry in LED replacement bulbs. The relatively high initial cost of an LED retrofit bulb will continue to decrease as market share increases. However, the cost of a conventional LED replacement bulb may remain less than optimal relative to fluorescent designs due in large part to the substantial costs associated with LED power supply switching and conversion methods. 
     SUMMARY 
     A light-emitting diode (LED) module is disclosed herein. The LED module is driven using an existing AC line voltage source that is external to any lamp or other fixture using the LED module. The present design and control approach is therefore referred to hereinafter as “driverless”. The present driverless approach may achieve greater than 90 percent efficiencies with a power factor in excess of 90 percent, along with other potential benefits as set forth herein. 
     In particular, the LED module includes a body assembly, a printed circuit board assembly (PCBA) having a plurality of light emitting diodes (LEDs), and a power conditioning board. The PCBA and power conditioning board are encapsulated by the body assembly. The power conditioning board is characterized by an absence of a switching power supply. The power conditioning board includes a full-wave voltage rectifier, a reducer, and a limiter. 
     In an associated control method, the rectifier outputs a peak-to-peak rectified voltage as a function of AC line power. The reducer detects the peak-to-peak rectified voltage, phase angle, and AC waveform zero-crossing of the AC line power, reduces the rectified voltage to provide a reduced voltage, and selectively sends a signal to turn on/illuminate or turn off/extinguish the LEDs as needed. 
     The controller, which is arranged in a closed control loop with the LEDs via the reducer and the limiter, receives the reduced peak-to-peak rectified voltage and AC waveform zero-crossing from the reducer. The controller automatically adjusts operating parameters of the reducer in response to the detected phase angle and zero-crossing to thereby selectively illuminate or extinguish some/all of the LEDs and thereby increase the power factor of the LED module. The controller also selectively adjusts a characteristic of the limiter to provide a substantially constant power level to the LEDs. 
     In another embodiment, the LED module includes a two-piece body assembly having a plastic lens portion, i.e., a translucent, clear, or frosted portion, and an aluminum shell portion. The aluminum shell portion is thermally conductive, and defines a first set of axial grooves positioned adjacent to the lens portion and a second set of axial grooves positioned between the first axial groove and the shell portion. The PCBA in this embodiment is supported along its edges by the first set of axial grooves. The power conditioning board is likewise supported along its edges by the second set of axial grooves. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view illustration of an example LED module as disclosed herein. 
         FIG. 2  is a schematic exploded view illustration of a portion of the LED module shown in  FIG. 1 . 
         FIG. 3  is a schematic end view illustration of the LED module of  FIG. 1  with a removed end cap. 
         FIG. 4  is a schematic block diagram describing elements of the power conditioning circuit used within the module of  FIG. 1 . 
         FIG. 5  is a flow chart describing an example method for controlling the LED module of  FIGS. 1-3  using the circuit shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to the same or similar components throughout the several views, an example light emitting diode (LED) module  10  is shown in  FIG. 1 . The LED module  10  may be configured as a conventional cylindrical retrofit bulb, e.g., a T8 bulb in the example embodiment shown in  FIG. 1 . However, while the T8 tube is a common tube size for use in fluorescent ceiling lamp fixtures, those of ordinary skill in the art will recognize that the present design may be readily scaled for use in other fixtures. 
     Conventional approaches for powering LED bulbs using multi-phase/alternating current (AC) power typically generate a relatively low direct current (DC) voltage level using a switching power supply. By way of contrast, the driverless approach set forth herein instead directly energizes a string of LEDs arranged on one or more printed circuit board assemblies (PCBAs). This approach eliminates the need for relatively inefficient and costly switching power supplies. As is well understood in the art, conventional switching power supplies are only about 70 to 85 percent efficient. As a result, a substantial amount of power may be lost as heat during the power switching process. Moreover, the cost of implementing conventional switching power supplies may continue to increase in conjunction with rising power supply efficiencies. The LED module  10  disclosed herein thus provides an alternative cost-effective approach to conventional LED bulb designs. 
     The present LED module  10  includes a cylindrical body assembly  12 . Each end  14  of the LED module  10  is enclosed by an end cap  16 . The different shading patterns used in  FIG. 1  represent an optional two-piece clamshell design in which light (arrows  11 ) is emitted through a lens portion  112 . The remainder of the body assembly  12  is constructed of an opaque shell portion  212 . Electrical contact pins  18  extend axially outward from each of the end caps  16 . In different embodiments, one or both electrical contact pins  18  at a given end  14  of the LED module  10  may be connected to neutral/ground, while one or both of the contact pins  18  at the other end  14  may be connected to multi-phase/alternating current (AC) line power, for instance the source  46  shown in  FIG. 4 . 
     An electrical ballast of the type used to limit voltage to a conventional fluorescent fixture is not required when using the present LED module  10 . If the LED module  10  is to be used as a retrofit bulb, the ballast of the existing light fixture may be simply removed or bypassed. Incoming AC power is then tied directly to either side of the light fixture. Polarity is not important in the present design. Thus, any incoming wire can be connected to either side of the light fixture, and thus to either side of the LED module  10  of  FIG. 1 . New light fixtures may be designed without an electrical ballast. 
     Referring to  FIG. 2 , the lens portion  112  and the opaque shell portion  212  may connect to each other to form a clamshell as noted above. The respective diffuser and opaque shell portions  112  and  212  may be approximately equal in size, and may be positioned with respect to each other to form a generally cylindrical whole. The portions  112  and  212  may include an optional edge feature  21  that enables a snap-fit or tongue-and-groove connection. In one embodiment, the diffuser portion  212  may be constructed of shatter-resistant plastic configured to pass emitted light (arrows  11  of  FIG. 1 ) with a desired level of diffusion and/or filtering, e.g., ultraviolet or infrared filtering. The shell portion  212  is thermally conductive and may be constructed of aluminum or another material providing sufficient voltage isolation. 
     An electrical contact plate  17 , e.g., a copper bar, is connected within each end cap  16 , only one of which is shown in  FIG. 2  for simplicity. The contact plate  17  may define holes  19  through which the electrical contact pins  18  extend. Fasteners  22  may be used in a particular embodiment to further secure each end cap  16  to the remainder of the LED module  10 . The fasteners  22  may be self-tapping sheet metal screws in one possible embodiment. In such an embodiment, the fasteners  22  align with axial grooves  126  of the shell portion  212  as indicated by arrow  41 , and then engage and cut threads into the shell portion  212 , e.g., in a slot  126  as shown in  FIG. 3  and explained below. 
     A printed circuit board assembly (PCBA)  20  having respective first and second sides  25  and  27  and a plurality of light-emitting diodes (LEDs)  24  may be inserted into an axial groove  26  defined by the shell portion  212 . The LEDs  24  may be arranged in electrical series in any desired pattern on the first side  25  of the PCBA  20  and oriented toward the lens portion  112 . The second side  27  of the PCBA  20  is oriented toward the shell portion  212 . While only one PCBA board  20  is shown in  FIG. 1 , those of ordinary skill in the art will recognize that multiple PCBA boards  20  may be connected in series as shown in  FIG. 4  to extend the LED module  10 . In such an approach, a relatively long PCBA may be constructed from a plurality of PCBAs  20 , thereby simplifying manufacturing. 
     The LED module  10  of  FIG. 1  also includes a power conditioning board  30 . The power conditioning board  30  is received within the axial groove  126 . The axial groove  126  may be defined by the shell portion  212 , and may be parallel to the axial groove  26  as shown. The cross-sectional profile of the axial groove  126  may be circular to better facilitate use of the fasteners  22  when the fasteners  22  are self-tapping screws. Together, the axial grooves  26 ,  126  form shelves within the shell portion  212  that receive and retain the edges of the respective PCBA  20  and power conditioning board  30 , as best shown in  FIG. 3 . 
     The power conditioning board  30  of  FIG. 2  is electrically connected to the PCBA(s)  20  via one or more electrical connector  32 , e.g., a typical surface mounted multi-pin power connector block(s). The power conditioning board  30  also includes a contact block  34  having a plurality of conductive pads  36 . When the LED module  10  of  FIGS. 1 and 2  is fully assembled, the conductive pads  36  are brought into direct physical contact with the contact plate  17 . Electrical energy can then flow from an AC power source, through the contact pins  18 , into the power conditioning board  30 , and ultimately into the PCBA(s)  20  to illuminate the LEDs  24  arranged thereon. 
     Referring to  FIG. 3 , the LED module  10  of  FIGS. 1 and 2  is shown in a schematic end view with the end caps  16  of  FIG. 2  removed for illustrative clarity. The PCBA  20  is positioned within the axial grooves  26  and supported thereby, i.e., with the edges of the PCBA  20  supported by the axial grooves  26 . The LEDs  24  are oriented toward the lens portion  112  as noted above. The power conditioning board  30 , which is positioned between the PCBA  20  and the shell portion  212 , is likewise positioned within the axial grooves  126  between the PCBA(s)  20  and the shell portion  212 . The contact block  34  and the conductive pads  36  are aligned such that the conductive pads  36  come into direct physical contact with the contact plate  17  of  FIG. 2  when the end caps  16  of the same Figure are installed. 
     Referring to  FIG. 4 , the power conditioning board  30  may be a separate circuit board from the PCBA(s)  20  as noted above. In another embodiment, the components of the power conditioning board  30  may be surface mounted on the second surface  27  of the PCBA  20  (see  FIG. 2 ). However, the use of separate boards may be advantageous for optimal thermal management and control. 
     The power conditioning board  30  may include a surge protector  40 , a rectifier  42 , a limiter  44 , a reducer  48 , and a controller  50 . The rectifier  42  is electrically connected to the reducer  48  and the LEDs  24  of the PCBAs  20  via a first circuit path  58 . The reducer  48  is electrically connected to the LEDs  24  via a second circuit path  60 . The limiter  44  is electrically connected to the LEDS  24  via a third circuit path  62 . 
     Additionally, the controller  50  is in communication with the reducer  48  and the limiter  44  over respective first and second control channels  63  and  65 , e.g., wireless or hard wired communications busses. The controller  50  is configured to control the LEDS  24  of the PCBA(s)  20  via a method  100 , an example of which is described below with reference to  FIG. 5 . The controller  50  receives LED calibration data (arrow  52 ) describing the particular type(s) and personality or behavior of LEDs  24  used with the one or more PCBA(s)  20  of the LED module  10  of  FIG. 1 . Such LED personality data (arrow  52 ) may be received from an external LED data source  54 , for instance via uploading or manual data entry from a manufacturer data sheet. 
     AC line power is delivered from an AC power source  46 , such as a wall socket or a main circuit panel, to the LED module  10  via the electrical contact pins  18  shown in  FIGS. 1 and 2 . The surge protector  40  is configured to protect the remaining components of the PCBA(s)  20  and power conditioning board  30  from power surges or short circuit conditions. The surge protector  40  may be embodied as a metal oxide varistor or other suitable component capable of diverting excess voltage to ground during a transient power spike, as is well understood in the art. 
     The rectifier  42  of  FIG. 4  is configured to rectify the AC line voltage from the AC power source  46  into a calibrated DC peak-to-peak sine wave, for example a sine wave measuring 1.414 times the AC line voltage. Thus, a 277 VAC root mean square (RMS) line voltage in this particular example could be rectified to a 392 VDC peak-to-peak signal at the output of the rectifier  42 . The output of the rectifier  42  feeds into the PCBA  20  through a first circuit path (arrow  58 ), with the PCBA  20  shown in  FIG. 4  as an example series of multiple serially-connected PCBAs  20 . As shown in  FIG. 1 , however, any number of PCBAs  20  may be used within the scope of the present invention. Alternatively, the output of the rectifier  42  feeds into the reducer  48  through a fourth circuit path (arrow  59 ). The controller  50  determines which of the two mutually exclusive circuit paths (arrows  58  and  59 ) to use as set forth below. 
     The output of the PCBA(s)  20  feeds into the limiter  44 . The limiter  44  may use field effect transistors (FETs) and other circuit components to perform its required tasks, which is to selectively limit electrical current delivered to the LEDs  24  as explained below. Such a device may be useful in case of brown outs or other electrical faults induced by the power grid where a re-initialization of the controller  50  may be required. Use of the limiter  44  may therefore help ensure that the LED module  10  remains operational during such a fault condition. 
     Conventionally, the output voltage of the LEDs  24  would be presented to a magnetic core or a transformer through a power switching circuit. Such components are eliminated from the present design, along with their inherent inefficiencies. That is, conventionally a current in a transformer is switched on and off at a rate required to obtain a desired output voltage, with the current determined by transformer selection and wire winding ratio. Electrical and magnetic noise caused by the switching frequency of the power switching circuit generates electromagnetic interference or EMI. Such noise can travel along any wires connected to a lamp using such a conventional design. 
     The present approach instead feeds the output of the rectifier  42  to the LEDs  24  directly, at times directly and at other times via the reducer  48 . Again, the output of rectifier  42  may be a DC peak-to-peak sine wave measuring 1.414 times the AC line voltage. The reducer  48  detects the peak of the AC voltage waveform and AC phase angle from the rectifier  42 , and presents this and other variables to the controller  50  for processing. 
     The controller  50  may be embodied as a microprocessor and any necessary supporting circuitry that collectively controls the LEDs  24  in a real-time and in a closed-loop. The controller  50  enables the LEDs  24  to turn on or off at specific times and for a specific duration. The controller  50  synchronizes this on/off sequence to the phase of the AC line power from source  46 . The resulting power factor increase allows for efficient AC line power transfer from the source  46  to the LED module  10 . 
     As is understood in the art, the LEDs  24 , as with all LEDs, have a forward voltage drop, i.e., a V(f) drop, as an electrical atomic structural manifestation in light generation. When connected in electrical series, the forward voltage drop of the LEDs  24  add together to create a gradual voltage drop from a high-voltage source, e.g., the output of the reducer  48 , to a low-voltage level. The natural forward voltage drop of the LEDs  24  is utilized by the controller  50  to limit the drive power provided to the LEDs  24 . The closer the overall voltage drop is to the input line voltage from the rectifier  42 , the lower the non-light emitting heat loss within the LED module  10 , thus increasing power conversion efficiency. 
     The controller  50  closely monitors and varies the system parameters to the reducer  48  and limiter  44  in real time to stabilize the LED drive power to the LEDs  24 , and other functions described herein. Such software and hardware-driven parameter adjustments via the controller  50  results in a substantially constant power level as presented to the LEDs  24  irrespective of AC line voltage fluctuations. The above feature is considered a significant advantage as compared to conventional approaches. 
     Because LED parameters tend to change with technology improvements and vary across LED manufacturers, the controller  50  of  FIG. 4  can also receive LED calibration data (arrow  52 ) from the LED data source  54  as noted above. This may occur prior to test and delivery of the LED module  10 . In this manner, the behavior of the LEDs  24  can be captured in the calibration data (arrow  52 ) to fine tune the behavior or personality of the LED module  10 . Additionally, because line power can be selectively dimmed using a conventional rheostat, the LEDs  24  of the present LED module  10  can also be dimmed, unlike conventional AC/DC designs. 
     Referring to  FIG. 5  in conjunction with the structure shown in  FIG. 4 , an example method  100  of controlling the LED module  10  of  FIG. 1  begins with step  102 , wherein AC power is provided from the source  46  to the LED module  10 . For instance, a wall switch (not shown) may be turned on. As is understood in the art, AC power may be represented as a sine wave, and may be provided by two or more AC power lines, e.g., 277 VAC RMS with a 60 Hz frequency. 
     At step  104 , the rectifier  42  converts the waveform, which is first passed through the surge protector  40 , into a full wave, e.g., 392 VDC peak, at twice the frequency, for instance 120 Hz in keeping with the 60 Hz example of step  102 . In this embodiment, the time between zero-crossings of the AC sine wave is 0.00833 seconds. 
     At step  106 , the reducer  48  detects the zero-crossing of the sine wave and communicates the detected zero-crossing to the controller  50  over the first control channel  63 . All LEDs  24  are extinguished at this point. 
     At step  108 , some LEDS  24  are turned on as the controller  50  synchronizes its internal firmware timers to the zero-crossing, and then commands the reducer  48  to turn on one or more of the LEDS  24  at a specific time from the zero-crossing, and for a calibrated duration. The specific number/duration may be selected based on the personality data for the LED type used in the PCBAs  20 . This number/duration information is communicated to the LEDs  24  over the second circuit path (arrow  60 ). 
     At step  110 , at a specific time from the zero-crossing, but before the sine wave midpoint, the controller  50  commands the reducer  48  to turn off/extinguish the LEDs  24  it previously illuminated at step  108 . 
     At step  112 , when the rectifier voltage exceeds the combined LED forward voltage V(f), the LEDS  24  will start conducting current, thereby illuminating all of the LEDs  24 . Conduction occurs at a period after the reducer  48  is commanded to turn off, but before the sine wave peaks at the sine wave midpoint. 
     At step  114 , current flows from the rectifier  42  through the LEDS  24  over the first circuit path (arrow  58 ), then through the limiter  44  to ground. The limiter  44  detects the ground current and communicates the value to the controller  50  via the second control channel  65 . All LEDS  24  remain on. 
     At step  116 , the controller  50 , using embedded firmware, commands the limiter  44  over channel  65  to increase or decrease resistance to ground in order to limit the LED forward current to an operational window. The operation window is determined by LED calibration data (arrow  52 ) for the types of LEDS  24  used on the PCBA(s)  20 . Constant power is thus maintained to the LEDs  24  during conduction by adjusting the forward current for the varying AC line voltage levels. 
     At step  118 , the LEDS  24  are extinguished when the sine wave from the rectifier  42  falls below the combined LED forward voltage drop V(f). The limiter  44  detects when the forward current is zero and communicates this event to the controller  50  over the second control channel  65 . All LEDs  24  are off at the completion of step  118 . 
     At step  120 , the controller  50  commands the reducer  48  over channel  63  to turn on one or more LEDs  24  at a time after the current drop equals zero, doing so according to the LED calibration data (arrow  52 ). The LEDS  24  are illuminated for a period that may extend up to the next sine wave zero-crossing. At the next zero-crossing, the firmware timers of the controller  50  are reset and the reducer  48  is commanded to turn off all of the LEDs  24  over the second circuit path (arrow  60 ). 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.