Abstract:
A connected light node (CLN) induction light ballast module for powering an induction lamp includes a printed circuit board having components mounted thereon and an earth ground region electrically isolated from a PCB ground region. A heat sink is disposed on a lower layer of the printed circuit board and electrically connected to the earth ground region, wherein a parasitic capacitance occurs between the printed circuit board ground region and the heat sink. A capacitive shield sandwiched by a lower insulating pad and an upper insulating pad is electrically isolated from the heat sink supporting the shield. A damping network electrically connects the capacitive shield to the PCB ground region. Switch-mode power converters are mounted above the upper insulating pad and the shield. The damping network suppresses noise by a parasitic capacitance between the PCB ground region and the heat sink during high frequency power converter operation.

Description:
RELATED APPLICATIONS 
       [0001]    The present application claims priority to U.S. Prov. 61/968,786, filed Mar. 21, 2014, the entire content of which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to electromagnetic compatibility of switch-mode power converters of a connected light node induction light ballast module. 
         [0003]    Federal Communications Commission (FCC) rules and regulations contained in Title 47 mandates standards that require any electronic system with a switching device operating in excess of 9 kHz, for intentional and unintentional RF transmitters, switching power systems, to comply with FCC following requirements: 
         [0004]    (A) Conducted Emission: FCC Part 15 (150 kHz-30 MHz, Average and Quasi Peak Limits). Industrial applications are classified as Class A requirements. 
         [0005]    (B) Conducted Emission: FCC Part 18 (450 kHz-30 MHz, for Wireless Light Modules). Industrial applications are classified as Class A requirements. 
         [0006]    (C) Radiated Emission FCC Part 15 (30 MHz-1000 MHz, Quasi Peak Limits). Industrial applications are classified as Class A requirements. 
         [0007]    The invention is directed to resolving and mitigating EMI non-conformance with respect to Conducted Emission and Radiated Emission requirements per FCC. Class A part 15 and part 18 specifications for a connected light node induction light ballast module providing power to an induction lamp. 
         [0008]    Providing a capacitive plate shunt element is a concept that has been considered as a mitigation technique for conducted emission failure by Electromagnetic Compatibility (EMC) experts. However, the inclusion of a capacitive shunt plate increases radiated emission profile and results in radio frequency (RF) noise energy (spectral shift of RF energy content to higher frequencies). More critically, addition of a capacitive plate shunt element may create structural resonances, which will contribute to radiated emission non-compliance. As a result of this, the capacitive plate shunt concept has been avoided. 
         [0009]    Creation of any unintended structural radiating antennas, i.e., as a result of a capacitive shield or from a metallic enclosure that alters or modifies the magnitude and direction of common mode RF currents are issues with regard to EMI non-conformance. Thus, such factors must be compensated for to obtain Conducted Emission and Radiated Emission field Compliance. 
         [0010]    A mitigation device must be adaptable for application to a large variety of high frequency switching circuits and correlate well with full FCC measurements and standards. The mitigation device and components must employ an arrangement to limit the level of RF currents on external cables of an induction light ballast module to ensure full EMI compliance as per FCC requirements delineated earlier. 
       SUMMARY 
       [0011]    One embodiment of the invention resolves and mitigates for a connected light node (CLN) induction light ballast module, the presence of EMI non-conformance with respect to Conducted Emission and Radiated Emission requirements per FCC Class A part 15 and part 18 specifications. The arrangement is adapted for RF switching power circuits, wherein the change of current di/dt and charge of voltage dv/dt is sudden, for example changing at a frequency of greater than 200 KHz. More specifically, such RF switching power circuits are the source of high frequency energy, and with a parasitic capacitance formed between a printed circuit board (PCB) ground region and an earth ground, which provides an RF current return path for switching frequencies and its entire harmonics. In some embodiments, the PCB ground region contains high frequency switching current and voltage waveforms, such as 210 KHz, and harmonics as high as 200 MHz. A parasitic capacitance of, for instance, 600 pF with one plate at PCB ground and a second plate at AC earth ground is, unfortunately an ideal RF current path for circulation currents. Therefore, all AC input power wires, more specifically an AC Ground wire, behaves as unintentional antenna (Antenna Mode) with high Common Mode RF currents (210 kHz and its higher harmonics up to 200 MHz). The Magnitude of Common Mode Currents would easily exceed 10 micro amps and at higher frequencies is a potential compliance concern for Conducted RF Emission (150 kHz-30 MHz) and Radiated Emission (30 MHz-1000 MHz) per FCC Class. A requirements. Further, output wires from an induction light ballast module are capable of performing as unintentional antennas. 
         [0012]    The invention ensures that the level of RF current on CLN induction light ballast module cables (AC input, lamp and all additional cables) is at an RF measured current level (I m )&lt;10 micro amps to ensure full EMI compliance as per FCC requirements delineated. earlier. By maintaining such a low current value FCC requirements are met. In addition, creation of any unintended structural radiating antennas, i.e., as a result of a capacitive shield or from a metallic enclosure that alters or modifies the magnitude and direction of common mode RF currents are accounted for, thus providing Conducted Emission and Radiated Emission field Compliance. 
         [0013]    In one embodiment, the invention provides an induction light ballast module for powering an induction lamp comprising: a printed circuit board including an upper layer partitioned into an earth ground region and a printed circuit board ground region, wherein the earth ground region is electrically isolated from the printed circuit board ground region; a heat sink disposed on an opposing lower layer of the printed circuit board and electrically connected to the earth ground region of the printed circuit board, the heat sink dimensioned to extend beyond at least one outer edge of the printed circuit board, and wherein a parasitic capacitance occurs between the printed circuit board ground region and the heat sink; an alternating current receiving connector and an EMT filter disposed on the earth ground region of the printed circuit board; an elongate capacitive shield sandwiched by a lower insulating pad and an upper insulating pad provided on the outwardly opposing faces of the capacitive shield, wherein the capacitive shield and the upper and lower insulating pads are disposed across a length of the heat sink adjacent to at least one edge of the printed circuit board, Wherein the capacitive shield is electrically isolated from the heat sink by the lower insulating pad; a damping network electrically connecting the capacitive shield to the printed circuit board ground region; a rectifier connected to the EMI filter, wherein the rectifier is disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink; a power factor correction circuit connected to the rectifier and disposed on the printed circuit board ground region, and including switch-mode power converters disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink; and an output power inverter circuit connected to the switch-mode power converter, the output power inverter circuit being disposed on the printed circuit board ground region and including switch-mode power converters disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink, wherein a parasitic capacitance occurs between the printed circuit board ground region and the heat sink, and Wherein the capacitive shield and the damping network provide common mode noise suppression. 
         [0014]    In another embodiment, the invention provides an induction light ballast module, wherein the output from the output power inverter circuit operates at an RF frequency and the damping network comprises at least one of a resistor and a ferrite that dampens resonance and harmonics to minimize incidental RF broadcast by external cables corrected to the induction light ballast module. 
         [0015]    In another embodiment, the induction light ballast module includes a zigbee circuit for wireless communication with other devices; a flyback circuit for providing, power supply voltages to the power factor correction circuit, the output power inverter circuit and the zigbee circuit; and a controller for operating, the circuits and for enabling remote wireless control of the induction light ballast module via the zigbee circuit. 
         [0016]    In another embodiment, the induction light ballast module provides an output power of between approximately 300 watts and approximately 500 watts for driving a lamp and the upper layer and the lower layer comprise two of four layers of the printed circuit board. 
         [0017]    In another embodiment, the rectifier comprises a bridge rectifier, and the power factor correction circuit comprises four switch-mode power converters, wherein the switch-mode power converters comprise two output power diodes and two field effect transistors. The damping network and the capacitive shield minimize resonant frequencies incidentally output by the switch-mode power converters. 
         [0018]    In one embodiment, the induction light ballast module includes thermally conducting fasteners securing the power converters and the printed circuit board to the heat sink, the fasteners enabling thermal conduction from the power converters to the heat sink. Further, the induction light ballast module includes grounding fasteners securing the printed circuit board to the heat sink and electrically connecting the earth ground region of the printed circuit board to the heat sink. 
         [0019]    In one embodiment, the switch-mode power converters of the power factor correction circuit comprise two output power diodes and two power factor correction field effect transistors. 
         [0020]    In another embodiment, the induction light ballast module includes a temperature sensor for sensing temperature and a controller for controlling operation of the induction light ballast module in response to sensed temperature and the induction light ballast module comprises a connected light node induction light ballast module 
         [0021]    In one embodiment, the invention provides a connected light node induction light ballast system comprising: a housing; a connected light node induction light ballast module disposed in the housing, the connected light node induction light ballast module comprising: a printed circuit board including an upper layer partitioned into an earth ground region and a printed circuit board ground region, wherein the earth ground region is electrically isolated from the printed circuit board ground region; a heat sink disposed on an opposing lower layer of the printed circuit board and electrically connected to the earth ground region of the printed circuit board, the heat sink dimensioned to extend beyond at least one outer edge of the printed circuit board, and wherein a parasitic capacitance occurs between the printed circuit board ground region and the heat sink; an alternating current receiving connector and an EMI filter disposed on the earth ground region of the printed circuit board; an elongate capacitive shield sandwiched by a lower insulating pad and an upper insulating pad provided on the outwardly opposing faces of the capacitive shield, wherein the capacitive shield and the upper and lower insulating pads are disposed across a length of the heat sink adjacent at least one edge of the printed circuit board, wherein the capacitive shield is electrically isolated from the heat sink by the lower insulating pad; a damping network electrically connecting the capacitive shield to the printed circuit board ground region; a rectifier connected to the EMI filter, wherein the rectifier is disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink; a power factor correction circuit connected to the rectifier and disposed on the printed circuit board ground region, and including switch-mode power converters disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink; and an output power inverter circuit connected to the switch-mode power converter, the output power inverter circuit being disposed on the printed circuit board ground region and including switch-mode power converters disposed on the upper insulating pad adjacent to the capacitive shield and electrically isolated from the capacitive shield and the heat sink. The connected light node induction light ballast system also includes an induction lamp secured to a bottom of the housing and controlled by the connected light node induction light ballast module, wherein a parasitic capacitance occurs between the printed circuit board ground region and the heat sink, and wherein the capacitive shield and the damping network provide common mode noise suppression. 
         [0022]    In another embodiment, the output from the output power inverter circuit of the induction light ballast system operates at an RF frequency of greater than 200 KHz for powering the induction lamp. 
         [0023]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a top view of a printed circuit board and components of a connected light node induction light ballast module. 
           [0025]      FIG. 2  is a perspective view of the printed circuit board disassembled from a heat sink and a capacitive shield. 
           [0026]      FIG. 3  is a bottom view of the capacitive shield. 
           [0027]      FIG. 4  is a perspective partial view of the printed circuit board with components and the heat sink. 
           [0028]      FIG. 5  is a top partial view of the printed circuit board and a damping network. 
           [0029]      FIG. 6  is a block diagram and flowchart for the connected light node induction light ballast module. 
           [0030]      FIG. 7  is a block diagram of a processor connected to associated circuits of the induction light ballast module. 
           [0031]      FIG. 8  is a block diagram of the connected light node induction light ballast module and devices connected thereto. 
           [0032]      FIG. 9  shows a perspective view of connected light node induction light ballast system. 
           [0033]      FIG. 10  shows another perspective view of connected light node induction light ballast system. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0035]      FIG. 1  shows major components of a CLN induction light ballast module  20  that, in some embodiments, acts as a switching power device operating at 210 KHz switching frequency. The arrangement shown in  FIG. 1  includes a printed circuit board  22  divided into an earth ground region  24  and a printed circuit board (PCB) ground region  26 . In one embodiment, the printed circuit board is a four layer board including an upper layer receiving the components as illustrated in  FIG. 1 . A printed circuit board lower layer (not shown) is a solid copper providing, a return plane in one embodiment. The inner layers (not shown) are dedicated to signal and power nets for best EMI practices to reduce crosstalk and provide optimum signal integrity. 
         [0036]    As shown in  FIG. 1 , the printed circuit board  22  includes a front edge  28  and a rear edge  30 . Further, the printed circuit board  22  includes earth ground region apertures  32 ,  34  and PCB ground region apertures  36 ,  38 ,  40 . 
         [0037]    The induction light ballast module  20  of  FIG. 1  includes a plurality of components mounted onto the top layer of the printed circuit board  22 . The components include an AC power supply connector  50  for receiving a mains power supply cable including an AC voltage wire and an AC neutral wire from an AC mains power supply (not shown). Further, an AC ground wire connector  52  is disposed on the printed circuit board  22  for receiving a ground wire of the AC mains power supply. 
         [0038]    The induction light ballast module  20  includes an electromagnetic interference (EMI) filter  60  labeled in broken line as a box containing a plurality of components including capacitors and inductors. The EMI filter is mounted to the. earth ground region  24  of the printed circuit board  22  and operates in a known manner. 
         [0039]    The induction light ballast module  20  includes an active power factor correction (PFC) circuit  70  mounted to the PCB ground region  26  of the printed circuit board  22 . The power factor correction circuit  70  includes capacitors and various components and operates in a known manner. 
         [0040]    The induction light ballast module  20  includes a lower power flyback circuit  80  mounted to the PCB ground region  26  of the printed circuit board  22 . The flyback circuit SO provides a power supply voltage to the PFC circuit  70 , an output power inverter circuit  90  and a zigbee circuit  100 . The flyback circuit  80  includes various electrical components and operates in a known manner. 
         [0041]    The output power inverter circuit  90  of the induction light ballast module  20  is mounted to the PCB ground region  26  of the printed circuit board  22 . The output power inverter circuit  90  includes various electrical components and operates in a known manner to provide an output voltage to a lamp. 
         [0042]    A 2.4 GHz Zigbee circuit  100  of the induction light ballast module  20  is mounted to the PCB ground region  26  of the printed circuit board  22 . The Zigbee circuit  100  includes a printed circuit  102  that provides for wireless communication with other devices. Further, a microprocessor (not shown in  FIG. 1 ) is disposed in or near the broken line box  100  defining the Zigbee circuit. The microprocessor controls the operation of the induction light ballast module  20 . 
         [0043]    The induction light ballast module  20  includes a plurality of power converters, including switch-mode power converters. The power converters include a bridge rectifier  110 . The power factor correction circuit  70  includes or is associated with a pair of converters comprising PFC field effect transistors (FETs)  112 ,  114  and a pair of PFC power diodes  116 ,  118 . Further, the output power inverter circuit  90  includes or is associated with a pair of output power inverter field effect transistors (FETs)  120 ,  122 . Other types of transistors and power converters are contemplated. 
         [0044]      FIG. 2  shows the CLN induction light ballast module  20  including a heat sink  130 . The heat sink  130  includes fastener receiving, elements  132 ,  134  and a heat sink rear region  136  extending outwardly and rearwardly beyond the rear edge  30  of the printed circuit board  22 . For safety, the heat sink  130  is electrically bonded to chassis ground, an AC ground wire joined to the AC ground wire connector  52 . The electrical bonding is essential for the prevention of electrical shock. 
         [0045]      FIG. 2  shows an upper SIL pad  140  and a lower SIL pad  142  that act as insulating pads surrounding or enclosing an elongate capacitive shield  150 . The capacitive shield  150  includes a mounting aperture  152  and an electrical connector element  154  projecting outwardly. The electrical connector element  154  is also defined by with parallel opposing slots  156 ,  158  extending into the capacitive shield  150  as shown in  FIG. 3 . The capacitive shield  150  is a thin conductive metal plate made from copper or other conductive materials. 
         [0046]      FIG. 4  shows a tool  159  lifting upwardly a portion of the upper SIL pad  140  to show the capacitive shield  150  disposed on the lower SIL pad  142 . Thus,  FIG. 4  shows the lower SIL pad  142  is in surface-to-surface contact with the heat sink rear region  136 .  FIG. 4  also shows how the capacitive shield  150  is disposed with a first surface contacting the opposing surface of the lower SIL pad  142  and a second opposing surface contacting a surface of the upper SIL pad  140 . While the heat sink rear region  136  in  FIG. 4  is shown as a metal plate secured to a portion of the heat sink  130 , in some embodiments, the heat sink and the heat sink rear region  136  are a monolithic structure.  FIG. 4  also shows the output inverter FETs  120 ,  122  secured to the upper SIL pad  140 , and thus insulated from the capacitive shield  150 . 
         [0047]    As shown in  FIGS. 1 and 2 , the rectifier  11  and the power converters  112 ,  114 ,  116 ,  118 ,  120 ,  122  are mounted to the upper SIL pad  140 . 
         [0048]      FIG. 5  is an expanded view of the left top corner of  FIG. 1  illustrating a damping network  160  that includes a resistor  162  electrically connected to the electrical connector element  154  and a wire  164  electrically connected to the PCB ground region  26  of the printed circuit board  22 . The network  160  includes a ferrite or other elements in different embodiments. The resistor  162  has a value of about 10 ohms in some embodiments. 
         [0049]    Returning to  FIG. 2 , fasteners  172 ,  174  provide an electrical and a thermal connection between the AC ground wire connector  52  via a printed circuit within the printed circuit board  22 . Thus, an AC earth ground wire of an AC power supply to the induction light ballast module  20  provides an earth ground to the earth ground region  24  of the printed circuit board  22  and to the heat sink  130  supporting the printed circuit board. 
         [0050]      FIG. 2  shows a pair of fasteners  176 ,  178  that secure the printed circuit board  22  to the heat sink  130 . While the fasteners  176 ,  178  provide a thermal connection, there is no electrical ground connection between the printed circuit board  22  and the heat sink  130 . 
         [0051]      FIGS. 2 and 3  show a plurality of fasteners  180  and plates  182  that secure the SIL pads  140 ,  142 , the capacitive shield  150 , the bridge rectifier  110 , and the power converters  112 ,  114 ,  116 ,  118 ,  120 ,  122  to the heat sink  130  through receiving elements (not shown) provided therein. The fasteners  180  provide a thermal connection between the power converters and the heat sink  130 . No electrical ground connection is provided between any of the power converters, the capacitive shield  150 , the SIL pads with each other or with the heat sink  130 . Thus, the PCB ground region  22  acts as a reference plane for the active PFC circuit  70 , the output power inverter circuit  90 , the flyback circuit  80  and the 2.4 GHz Zigbee circuit  100 . The earth ground region  24  is electrically isolated from PCB ground region  22 . 
         [0052]      FIG. 6  illustrates the block diagram of the operation of the CLN induction light ballast module  20 . The arrangement is based on the integration of capacitive shield  150  with the damping, network  160  in active power factor correction.  FIG. 6  shows a single phase AC building mains power supply  188  that supplies AC power to the EMI filter circuit  60 . The EMI filter circuit  60  provides the power to the full-wave bridge rectifier  110 . The full-wave bridge rectifier  110  provides DC voltage to the active PFC circuit  70 . The PFC circuit  70  provides power to the flyback circuit  80  and to the power inverter circuit  90 . The flyback circuit  80  provides power to a controller and auxiliary loads  190 . The power inverter circuit  90  provides a high frequency AC power at 200-400 KHz to an induction lamp  200 . 
         [0053]      FIG. 7  shows a processor  210  for the CLN induction light ballast module  20 . ASIC, microprocessors and other types of controllers are also contemplated. The processor  210  is in two way wireless communication with other wireless lamps and other devices via the Zigbee antenna  102 . Further, the processor  210  receives power from the flyback circuit  80  and controls operation of the PFC circuit  70  and the power inverter circuit  90 . The processor  210  receives inputs from a temperature sensor  216  and an ambient light sensor  220  and an isolated dimmer circuit  224 . Further, in some embodiments the processor  210  controls an auxiliary heater  230  of the induction lamp  200  and communicates with auxiliary sensors  234 . Thus, the processor  210  controls the power output by the induction light ballast module  20  in view of many factors.  FIG. 8  shows the inputs and outputs of the induction light ballast module  20  and a detailed explanation is not necessary. The resistor load represents the auxiliary heater  234  shown in  FIG. 7  for heating the induction lamp  200  to enable proper operation thereof. 
       Determining the Damping Network 
       [0054]    In operation, the power converters  112 ,  114 ,  116 ,  118 ,  120 ,  122  of the CLN induction light ballast module  20  strongly influence and generate RF energy, including various high frequency signals and thermal energy. In some embodiments, the output power requirements range from 300 Watts to 500 Watts with efficiency in excess of 90%. The high frequency signals, and harmonics of signals processed by the power converters, must not incidentally broadcast via the A/C input wires providing power to the CLN induction light ballast module  20  due to the A/C input wires acting as an antenna. Further, similar high frequency voltage signals must not incidentally broadcast via the output power wires  236 ,  238  of the CLN induction light ballast module  20  illustrated in  FIG. 4 . The output power wires  236 ,  238  connect to the induction lamp  200 . Additional wires (not shown) provide power to an auxiliary heater must not broadcast RF signals. 
         [0055]    The operation includes providing the capacitive shield  150  to the induction light ballast module  20  in combination with a specific damping network  160 . Measuring the impedance of the capacitive shield  150  with respect to the PCB Ground  26  and the earth ground region  24  corresponding to the heat sink  130  enables determination of resonance(s) of the impedance of the capacitive shield to assist in determining/calculating of a damping network “resistive” and/or, a frequency dependent device, i.e., “ferrite” for damping the RF energy. Thus, for example, the damping network mounted on the PCB ground region may comprise a 0603 SMD resistor, 0603 Ferrite (MuRata BLM series ferrite), or a resistor-ferrite combination placed in series between the capacitive shield  150  and the PCB ground region  26 . 
         [0056]    In regard to thermal management, the fasteners  180  and the plates  182  allow the transfer of thermal energy from the high power, power converters to the heat sink  130  grounded to the earth ground region  24 . Other high temperature components are also thermally connected to the heat sink  130 . 
         [0057]      FIG. 9  shows an induction light ballast system  240  including an induction light ballast module housing  240  that contains the CLN induction light ballast module  20 . An induction lamp  200  is secured to the lower edge of the housing  240 . The induction lamp  200  transmits light downwardly and away from the housing  240 .  FIG. 10  better illustrates the induction lamp  200 , which in some embodiments, contains a donut-shaped fluorescent bulb. 
         [0058]    The invention provides, among other things, a capacitive shield and damping network for common mode noise suppression for switch-mode power converters operating at an RF frequency. Various features and advantages of the invention are set forth in the following claims.