Abstract:
The present invention is directed to an intelligent dimmer that is capable of “learning” the type of load it is controlling, and adjusts its operating parameters accordingly. The present invention can adaptively drive electrical loads over a wide range of wattages. The intelligent dimmer of the present invention is configured to automatically calibrate itself based on the load current demands of a particular electrical load. The intelligent dimmer of the present invention also adaptively limits in-rush currents to extend the life expectancy of the solid state switching components used therein.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is application claims priority to U.S. Provisional Patent Application Ser. No. 61/635,600 filed on Apr. 19, 2012, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §119(e) is hereby claimed. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electrical wiring devices, and particularly to power control wiring devices such as dimmer and fan speed control devices. 
     2. Technical Background 
     In most residences, a simple ON/OFF switch may be the primary way people control the home&#39;s lighting fixtures or air-circulating fan fixtures. One obvious drawback to using simple ON/OFF switches to control these devices is experienced by the homeowner when he pays the electrical bill—a given light (or fan) is either ON or OFF—a simple switch is thus unable to vary the amount of light (and hence the amount of power consumed). Stated differently, by controlling light intensity or fan speed in accordance with needed or desired parameters, electricity usage is reduced, saving money and natural resources. In accordance with the present invention, therefore, a power control device refers to an electrical control device that may be employed to adjust the amount of current delivered to any variable electrical load, such as a light or a motor. 
     When the electric load is a lighting device, the power control device is commonly referred to as a dimmer. For example, when a light is dimmed 25%, a dimmer saves about 20% of the electricity required. When dimmed by 50%, it saves 40% of the electricity. Second, a dimmer greatly extends lamp life because it reduces strain on the filament. When dimmed 25%, a lamp lasts 4 times longer than it would at full power, and dimmed by 50%, it will last as much as 20 times longer. If the power control device is configured to control a motor, such as a fan motor, the power control device is referred to as a motor speed controller. Motor speed controllers are also used to control the speed of machinery such as power tools, electric drills, chair lifts, stationary machinery, and other such variable speed motor driven elements. 
     Power control devices are typically packaged in a wiring device form factor for installation in a wall outlet box. The wiring device may include one or more power control devices within the device housing. For example, wiring devices that are equipped with both fan motor control and lighting control features are ubiquitous. The exterior of the wiring device includes either screw terminals or wire terminals for subsequent connection between the AC power source and the load. The conventional wiring device form factor also provides a user accessible interface that includes one or more switch mechanisms such as buttons, levers, dials, slide switches, and other such input control mechanisms that permit a user to vary the power to a load or turn it ON/OFF. 
     Prior to device installation, wiring from the AC power source and wiring to the load(s) are disposed inside the outlet box. The outlet box is usually located proximate to the load being controlled. The device is installed by connecting the wiring inside the outlet box to the appropriate wiring device terminals disposed on the exterior of the wiring device. The power control wiring device is then inserted into the outlet box and attached to the outlet box using one or more fasteners. A cover plate is installed to complete the installation. One of the drawbacks associated with older conventional power control devices relates to the fact that many were often installed without a neutral wire being routed into the device box. What is needed therefore is a power control device that can be employed in any structure being retrofitted or remodeled. Stated differently, a power control device is needed that can work with existing wiring, i.e., whether the neutral is present or not present in the device box. 
     Often, a residence includes a three way lighting arrangement whereby one light fixture may be operated by two separate three-way switches. Often, one three-way switch is installed at an upstream location while a second three-way switch is installed at a downstream location. This allows a resident to conveniently turn the lights ON or OFF from two different locations. Unfortunately, this may lead to difficulties in when a structure or space is being retrofitted, since certain conventional dimmers may only be installed at one of the three way switch locations. This requires the homeowner to know how the existing wiring is disposed in the room (behind the plaster or sheet rock). What is needed therefore is a dimmer that can be installed at either three-way switch location. 
     Turning now to so-called “green” issues, the public has developed an increased awareness of the impact that energy generation has on the environment. Moreover, as the economies of countries such as Brazil, India, China, etc. improve and develop, their need for energy resources increases accordingly. As such, the global demand for energy has risen sharply, while the supply of planet earth&#39;s resources remains fixed. In light of the pressures of supply and demand, the cost of energy resources will only increase. There is thus a need to use limited energy resources more wisely and more efficiently. More efficient light sources and electrical fixtures have been developed to replace the conventional incandescent lighting devices in response to this need. For example, compact fluorescent lights (CFL) and light emitting diode (LED) devices are far more efficient than conventional incandescent lights and thus provide homeowners/tenants with an acceptable level of service while using less energy and incurring lower costs. 
     One of the drawbacks of conventional dimmer devices relates to the fact that incandescent lights, fluorescent lights, MLV lighting, ELV lighting, CFL devices and LED lighting may have different electrical operating characteristics. Dimmers have a solid state switching component that turns the lamp on during a user adjustable portion of each line frequency cycle and turns the lamp off during the remaining portion of the cycle. Dimmers whose switching components turn the load on at a zero crossing of the line frequency and then off at a user adjustable phase angle have been referred to as reverse phase dimmers. Those that turn the load on at the user adjustable phase angle and then off at the following zero cross have been referred to as forward phase dimmers. A particular type of lamp might be less susceptible to unwanted effects such as flickering using one type of dimmer or the other. Moreover, the life expectancy of the both the dimmer and the lighting may be adversely affected if the dimmer/lighting device are not properly matched. Of course, it is cumbersome to have to replace the dimmer simply whenever a lamp having different electrical operating characteristics is put in the light fixture. 
     Accordingly, a need exists for a power control device that can drive electrical loads over a wide range of wattages. An intelligent dimmer that is capable of “learning” the type of fixture it is controlling, and adjusts its operating parameters accordingly. For example, an intelligent dimmer is needed that can automatically calibrate the dimmer based on the load current demands of a particular electrical load. The intelligent dimmer should also be able to adaptively limit in-rush currents that are known to shorten the life expectancy of the solid state switching components used in dimmer products. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the needs described above by providing an intelligent dimmer that can be employed in any structure being retrofitted or remodeled. The present invention may be installed in existing wiring, i.e., whether the neutral is present or not present in the device box. The intelligent dimmer of the present invention may also be installed at either three-way switch location in a retrofit without regard to how the electrical wiring is disposed in the existing structure. The present invention is directed to an intelligent dimmer that is capable of “learning” the type of load it is controlling, and adjusts its operating parameters accordingly. The present invention can adaptively drive electrical loads over a wide range of wattages. The intelligent dimmer of the present invention is configured to automatically calibrate itself based on the load current demands of a particular electrical load. The intelligent dimmer of the present invention also adaptively limits in-rush currents to extend the life expectancy of the solid state switching components used therein. 
     One aspect of the present invention is directed to an electrical wiring device for use with an external three-way switch in a three-way switching arrangement. The device includes a housing assembly having a plurality of terminals at least partially disposed therein. The plurality of terminals includes a reversible terminal, a first traveler terminal and a second traveler terminal, the reversible terminal being configured to be coupled to an AC power source or an electrical load. A power regulation circuit is coupled to the plurality of terminals. The power regulation circuit is configured to provide at least one reference voltage derived from the AC power source and a zero cross signal substantially corresponding to a zero-crossing of an the AC power cycle of the AC power source. A switching mechanism includes a first throw coupled to the first traveler terminal, a second throw coupled to the second traveler terminal, and a common pole coupled to the reversible terminal. The switching mechanism is configured to connect the first traveler terminal to the common pole in a first switch state or the second traveler or the second traveler terminal to the common pole in a second switch state. An AC power routing circuit is coupled between the plurality of terminals and the power regulation circuit. The AC power routing circuit is configured to direct AC power to the power regulation circuit when the reversible terminal is connected to either the AC power source or the electrical load and when the switching mechanism and the external three-way switch are in any switch state. A regulation circuit is coupled to the power regulation circuit, the regulation circuit being configured to regulate an amount of power provided to the electrical load as a function of the zero-crossing signal. 
     In another aspect the present invention is directed to an electrical wiring device for use with an external three-way switch in a three-way switching arrangement. The device includes a housing assembly having a plurality of terminals at least partially disposed therein. The plurality of terminals includes a reversible terminal, a first traveler terminal and a second traveler terminal, the reversible terminal being configured to be coupled to an AC power source or an electrical load. A power regulation circuit includes a series pass element coupled to the reversible terminal. A switching mechanism is switchable between a first switch state where the series pass element is coupled to the first traveler terminal and a second switch state where the series pass element is coupled to the second traveler terminal. An AC power routing circuit is coupled to the reversible terminal, the first traveler terminal and the second traveler terminal. The AC power routing circuit has a return path coupled to the neutral terminal or the ground terminal, the AC power routing circuit being configured to direct AC power to the power regulation circuit whether the reversible terminal is connected to the AC power source or the electrical load and whether the switching mechanism is in the first switch state or the second switch state. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a general block diagram of a universal power control device in accordance with the present invention; 
         FIG. 2A-2B  are block diagrams of the universal power control device in accordance with the first embodiment,  FIG. 2A  is a block diagram of the AC power circuitry and  FIG. 2B  is a block diagram of the processing and logic circuitry; 
         FIG. 3  is a detailed circuit diagram of a microcontroller circuit in accordance with the first embodiment of the present invention; 
         FIG. 4  is a detailed circuit diagram of a user display circuit in accordance with an embodiment of the present invention; 
         FIG. 5  is a detailed circuit diagram of a power supply in accordance with the first embodiment of the present invention; 
         FIG. 6  is a detailed circuit diagram of a dimmer circuit in accordance with the first embodiment of the present invention; 
         FIG. 7  is a detailed circuit diagram of a switch relay circuit in accordance with an embodiment of the present invention; 
         FIG. 8  is a diagrammatic depiction of a load sensor in accordance with an embodiment of the present invention; 
         FIG. 9  is a detailed circuit diagram of a load sensor detector circuit in accordance with an embodiment of the present invention; 
         FIGS. 10A-10C  are diagrammatic depictions of a three-way switch arrangement in accordance with the present invention; 
         FIG. 11  is a block diagram of the AC power circuitry in accordance with a second embodiment of the present invention; 
         FIG. 12  is a detailed circuit diagram of a power supply in accordance with the second embodiment of the present invention; 
         FIG. 13  is a detailed circuit diagram of a dimmer circuit in accordance with the second embodiment of the present invention; 
         FIG. 14  is a detailed circuit diagram of a switch relay in accordance with the second embodiment of the present invention; 
         FIGS. 15A-15B  are diagrammatic depictions of another three-way switch arrangement in accordance with the present invention; 
         FIG. 16  is a flow chart diagram illustrating a software auto-calibration sequence in accordance with the present invention; 
         FIG. 17  is a flow chart diagram illustrating a software main program in accordance with the present invention; 
         FIG. 18  is a flow chart diagram illustrating a software zero cross interrupt routine in accordance with the present invention; 
         FIG. 19  is a flow chart diagram illustrating a software load timer interrupt routine in accordance with the present invention; 
         FIG. 20  is a front isometric view of a power control device in accordance with an embodiment of the present invention; 
         FIG. 21  is a rear isometric view of the power control device depicted in  FIG. 20 ; 
         FIG. 22  is a rear isometric view of the heat sink assembly of the power control device depicted in  FIG. 20 ; 
         FIG. 23  is a rear isometric view of the heat sink assembly and the power handling printed circuit board of the power control device depicted in  FIG. 20 ; 
         FIG. 24  is a front isometric view of  FIG. 20  with the ON/OFF actuator cover removed; 
         FIG. 25  is a front isometric view of  FIG. 20  with the ON/OFF actuator cover and the dimmer cover removed; 
         FIG. 26  is a front isometric view of the heat sink assembly of  FIG. 22  disposed within the back body member; 
         FIG. 27  is a front isometric view of the power handling printed circuit board of  FIG. 23  disposed within the back body member of the device of  FIG. 20 ; 
         FIG. 28  is an exploded view of the power control device depicted in  FIG. 20 ; 
         FIG. 29  is an isometric view of the ON/OFF actuator cover depicted in  FIG. 20 ; 
         FIGS. 30-31  are detailed isometric views of the dimmer actuator cover depicted in  FIG. 20 ; and 
         FIG. 32  is a cross-sectional view of the power control device depicted in  FIG. 20 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the universal power control device of the present invention is shown in  FIG. 1 , and is designated generally throughout by reference numeral  10 . 
     As embodied herein, and depicted in  FIG. 1 , a general block diagram of a universal power control device  10  in accordance with the present invention is disclosed. The device  10  includes a power handling printed circuit board (PCB)  10 - 1  and a processing or logic printed circuit board  10 - 2 . The power handling PCB  10 - 1  is coupled to the logic PCB  10 - 2  by an interface  10 - 3 . In another embodiment of the present invention, these circuits are disposed on a single printed circuit board (PCB). In yet another embodiment, for example, the power handling circuitry  10 - 1  is disposed on a printed circuit board adjacent a heat sink (not shown) whereas the logic circuitry  10 - 2  is disposed on a second PCB disposed adjacent to a cover portion. 
     The power handling circuit  10 - 1  is coupled to the AC power by way of the external AC terminals  12 . If the device is employed as a single pole single throw (SPST) switch, the power control device is coupled to the hot connector (black) and inserted between the AC power source and the load to provide the load with variable power (e.g., dimmed power in a lighting application). The power control device  10  may also be employed in three-way switching arrangements. In this case, the device  10  provides terminal connections for a hot (or load) wire, a first traveler wire and a second traveler wire. In many retrofits, the device box may not have a neutral wire whereas in newer construction, or in newer retrofits, the device box does include a neutral wire. The present invention can accommodate a neutral wire and may also include a ground wire in at least one embodiment. 
     The power supply  20  is configured to rectify the AC power derived from terminals  12  to provide a high voltage DC supply for the relay circuit  40  and a +5 VDC supply for use by the logic circuitry  10 - 2 . The power supply  20  further provides a zero-cross signal which is used by the processing circuitry  110  for timing purposes. The power handling circuit  10 - 1  also includes a load sensor  50  that is configured to provide the processing circuitry  110  with load current data. In one embodiment described below, the processing circuit  110  is configured to determine the type of lighting device that is installed by monitoring the load current data to determine whether the device  10  should operate using forward phase control or reverse phase control. Similarly, the processing circuit  110  also monitors the load current data to determine an optimal dimming voltage range for the specific lighting device type. In another embodiment described below (that has a neutral conductor or a ground conductor), the processor makes the dimming voltage range determination by monitoring the supply voltage. In another embodiment, this dimming range data is provided by the user via inputs  120  disposed in the logic circuitry portion  10 - 2  of the device  10 . 
     The user input circuitry  120  provides the processing circuitry  110  with information that includes, among other things, lighting device type, calibration commands, load ON/OFF commands, and dimmer setting inputs. The processing circuitry  110  is configured to actuate the relay circuit  40  to turn the load ON or OFF based on user commands. The processing circuit  110  also provides the dimmer circuit  30  with dimmer commands in accordance with the user inputs and the load sensor  50  input. The dimmer circuit, of course, provides a dimmed power signal to the load via the AC terminals  12 . As those skilled in the art will appreciate, dimming is accomplished in the reverse phase by switching the load current ON when the zero-crossing of the AC half-cycle is detected by the power detecting circuit  10 - 1  and turned OFF at a user adjustable phase angle. Conversely, in forward phase control, the load current is turned ON at the user adjustable phase angle and turned OFF when the next zero crossing is detected by the power detecting circuit. As those skilled in the art will appreciate, forward phase control is appropriate for conventional incandescent lighting, magnetic low voltage (MLV) lighting fixtures, conventional fluorescent lighting fixtures employing electronic ballasts (EFL), and halogen lighting. Reverse phase control is generally appropriate for electronic low voltage (ELV) lighting. Bulbs designed as higher efficiency 120V incandescent replacements, including LED bulbs and compact florescent lights (CFL) typically perform better with forward phase control. One of the universality features of the present invention is that the dimmer circuit may be employed in forward phase for certain optimized ELV, CFL and LED devices. 
     It will be apparent to those of ordinary skill in the pertinent art that modifications and variations can be made to the processing circuitry  110  of the present invention depending on the degree of processing sophistication provided in a given device. The processing circuitry  110  may employ random access memory (RAM), read only memory (ROM), I/O circuitry, and communication interface circuitry coupled together by a bus system. The buss typically provides data, address, and control lines between a processor and the other system components. Moreover, processor functions may be implemented using hardware, software, general purpose processors, signal processors, RISC computers, application specific integrated circuits (ASICs), field programmable gate array (FPGA) devices, customized integrated circuits and/or a combination thereof. Thus, embodiments of the present invention are not limited to any specific combination of hardware circuitry and/or software. Taken together, RAM and ROM may be referred to herein as “computer-readable media.” The term “computer-readable medium,” as used herein, refers to any medium that participates in providing data and/or instructions to the processor for execution. For example, the computer-readable media employed herein may include any suitable memory device including SRAM, DRAM, NVRWM, PROM, E 2 PROM, Flash memory, or any suitable type of memory. In one embodiment, data and instructions may be provided to device  10  via electromagnetic waves. The processing circuitry  110  provides dimmer status information to the output display  130  such as the dimmable setting, lamp type, or user instruction. 
     As embodied herein, and depicted in  FIG. 2A , a block diagram of the AC power handling circuitry  10 - 1  in accordance with an embodiment of the present invention is disclosed. The terminals include a hot/load terminal  12 - 1 , traveler terminal  12 - 2 , traveler terminal  12 - 3  and neutral terminal  12 - 4 . The neutral terminal  12 - 4  is employed as a means for referencing ground. In another embodiment of the invention (not shown), the terminals include a ground terminal to which the ground conductor of the electrical distribution system is connected. The ground terminal is also used, of course, to reference ground potential. In another embodiment both a ground terminal and a neutral terminal are provided and the ground reference is associated with either terminal depending on whether the neutral conductor or ground conductor is provided by the electrical distribution system. In each of these embodiments the device  10  also includes the traveler terminals ( 12 - 2 ,  12 - 3 ) for use in three-way switch arrangements. The hot/load terminal  12 - 1  may be connected to the hot terminal of the AC power source, or to the load. This capability is a feature of the power supply circuit  20  and the dimmer circuit  30  described below. 
     In one embodiment of the present invention, the interface device  10 - 3  is mounted on the power handling PCB  10 - 1  and is used to communicate power and logic signals between the PCB  10 - 1  and the PCB  10 - 2 . In addition, the power supply  20  provides +5 VDC and a reference ground connection via device  10 - 3 . The power supply  20  provides the processing circuitry  110  with the zero cross signal (ZC) and the load sensor  50  provides the processor circuitry with a sensor input (I sns) via an interface device  10 - 3 . The processing circuitry  110  provides the relay control signals (RC 1 , RC 2 ) and the dimmer control signal (PWM) via the interface  10 - 3 . 
     As embodied herein, and depicted in  FIG. 2B , a block diagram of the logic PCB  10 - 2  in accordance with one embodiment of the invention is disclosed. The logic PCB  10 - 2  includes interface pins  10 - 20  that mates with the interface device  10 - 3  ( FIG. 2A ) to complete the bi-directional communication path between the power PCB  10 - 1  and the logic PCB  10 - 2 . As noted above, power signals are conducted from the power handling circuit  10 - 1  to the logic circuit  10 - 2 , and the logic signals are conducted from logic circuit  10 - 2  to the power handling circuit  10 - 1  as appropriate. The load sensor detection circuit  112  employs the load sensor  50  signal (I Sns) to generate a sensor detection signal (I SNS AMP OUT) for use by the processor circuitry  110 . And as further shown in  FIG. 2B , the processor circuit  110  provides the relay commands (RC 1 , RC 2 ) and the dimmer command (PWM) to the power circuit  10 - 1  via the interface pins  10 - 20 . The processor circuit  110  also provides output data to the display circuit  130  which is also disposed on the logic PCB  10 - 2 . Although they are not shown in  FIG. 2B , the processor circuit  110  is also connected to user-accessible input devices that convert user commands into electronic commands. The user commands may be provided to the processor circuit by way of, but not limited to, switches, buttons, electromagnetic signals (e.g., RF or optical) that may originate from a keyboard, mouse, or by voice commands. 
     As embodied herein and depicted in  FIG. 3 , a detailed circuit diagram of a microcontroller circuit  110 - 1  in accordance with another embodiment of the present invention is disclosed. The processor circuit  110  is implemented using a microcomputer  110 - 1  which is selected based on a combination of characteristics including performance, cost, size and power consumption. In other words, the present invention contemplates a variety of models that provide the consumer with options that are closely suited to the consumers&#39; needs and desires. The term “microcomputer performance” refers to an optimal combination of processing speed, memory size, I/O pin capability, and peripheral set capabilities (e.g., A/D converter, comparators, timers, serial bus, etc). As those skilled in the art will appreciate, any suitable processing device may be employed. In one embodiment of the present invention, the microcomputer is implemented by a device known as the “ATtiny44a”, which is manufactured by the Atmel Corporation. In another embodiment that includes more features, the microcomputer is implemented using Atmel&#39;s “ATtiny84a” because the latter device offers more program memory than the former (i.e., 44a). Specifically, the ATtiny 84a includes 8 kB of program memory whereas the ATtiny 44a includes 4 kB of program memory. In one embodiment, the central processing unit (CPU) is operated at a clock frequency that is well below its rated frequency to thereby minimize power consumption. 
     It will be apparent to those of skilled in the pertinent art that modifications and variations can be made to the processor circuit  110  of the present invention depending on the amount and sophistication of features that are provided to the user. As noted previously, any suitable arrangement of hardware and/or software may be employed given the constraints of being disposed in an electrical wiring device. Thus, processor circuit  110  may be implemented using general purpose processors, signal processors, RISC computers, application specific integrated circuits (ASICs), field programmable gate array (FPGA) devices, customized integrated circuits and/or a combination thereof. With respect to the microcomputer  110 - 1  depicted in  FIG. 3 , any suitable microcomputer may be employed including, but not limited to those selected from the Microchip PIC12F family, the Freescale HCO8 family, the Texas Instruments MSP430 family, or the ST Micro STM8 family. 
     Turning now to  FIG. 3  in more detail, a description of the data signals used, and provided by, microcontroller  110 - 1  is provided to aid the reader&#39;s understanding of this embodiment of the present invention. The “nReset” signal is generated after power is removed from the device and subsequently reapplied. This signal causes the device to re-perform calibration before providing service. In this embodiment, the microcomputer is connected to three user-operated buttons (“ON/OFF” button  120 - 1 , “Down Button”  120 - 2 , and “UP Button”  120 - 3 ). As shown, each button circuit is pulled to a logic high (+5V) by a 100K pull-up resistor. When a user depresses a button, its corresponding switch (S 200 ,  5201 , S 202 ) is closed to ground the circuit such that the microcomputer reads a logic zero (0 V) to indicate that the user has made a command. With respect to the ON/OFF button  120 - 1 , if the current state of the wiring device is “OFF,” an actuation of the button  120 - 1  directs the microcontroller to send a signal via lines RC 1 , RC 2  such that the relay turns the load “ON.” When the user depresses the button  120 - 1  again, the same sequence plays out such that the relays turn the load “OFF.” The “down button” circuit  120 - 2  and the “up button” circuit  120 - 3  operate in the same identical way that the ON/OFF button operates. Obviously, the difference is in the way that the microcomputer  110 - 1  interprets the commands. An actuation of the up-button  120 - 3  is interpreted as a command to increase the power delivered to the load, and an actuation of the down-button  120 - 2  is just the opposite. 
     In particular, when the down-button  120 - 2  is depressed, the software in the microcontroller changes the PWM signal such that the dimmer circuit  30  causes the lighting load to be incrementally dimmed. (Of course, the circuit may be used to slow an electric motor, e.g., a fan motor). Conversely, when the up-button  120 - 3  is depressed, the software in the microcontroller changes the PWM signal such that the dimmer circuit  30  causes the lighting load to be incrementally raised. The programming header  120 - 4  allows a person having the appropriate skill level to reprogram and/or debug the microcomputer  110  when button  120 - 3  is depressed in a predetermined sequence. The sequence is an indication to the microcomputer  110 - 1  that a data input device (a host computer interface, RF interface, keyboard, etc.) is being connected to header  120 - 4  and a reprogramming sequence is being initiated. The microcontroller  110 - 1  is also connected to the display circuit (shown in  FIG. 4 ) by a serial clock signal (SCL) and a serial data signal (SDA) to provide a serial bit stream that corresponds to the appropriate device display settings (which are described below in conjunction with the circuit depicted in  FIG. 4 ). The display settings are transmitted to the display circuit  130  when the settings are changed by a user input command and refreshed periodically. In one embodiment of the present invention, the microcomputer refreshes the settings every 300 msec, or at a 3.3 Hz rate. Of course, any suitable refreshing rate may be selected depending on the processor load. 
     The zero cross signal (ZC) is provided by the power PCB  10 - 1  and is paired with the VREF FOR Z-Cross signal. These signals comprise a differential input that is provided to a differential comparator disposed inside the microcomputer  110 - 1 . The differential signal eliminates common-mode noise to prevent any false zero cross detections by the microcomputer  110 - 1 . Stated differently, the reference timing provided by the zero cross detector of the present invention is substantially immunized from common mode noise to thereby substantially eliminate spurious timing signals. The purpose and function of the remaining signals will become apparent when their corresponding circuits are described herein. 
     Referring to  FIG. 4 , a detailed circuit diagram of a user display circuit  130  in accordance with an embodiment of the present invention is disclosed. As alluded to above, the signals SCL and SDA are directed to the display circuit  130  which includes an I/O expander circuit  130 - 1 . The I/O expander  130 - 1  is configured to receive the serial bit stream from the microcomputer  110 - 1  and convert it into a parallel data output for use by the display LEDs  130 - 2 ,  130 - 3 ,  130 - 4  and  130 - 5 . In the embodiment of  FIG. 4 , seven (7) bar graph LEDs  130 - 2  are included to provide the user with an indication of the dimmer setting. For example, if one LED is ON and the other six LEDs are OFF, the bar graph indicates to the user that the light level setting is at its lowest setting. Conversely, if all seven (7) LEDs in the bar graph  130 - 2  are illuminated, the dimmer is at its highest setting. 
     The LEDs  130 - 3 ,  130 - 4 , and  130 - 5  work in conjunction with the transistor  130 - 6 . When the lighting load or the motor load is turned OFF by the relay circuit  40 , the microcomputer transmits an appropriate bit command such that transistor  130 - 6  is turned ON. This causes current to flow through the locator LED  130 - 5 . Once the lighting load is turned OFF, the LED  130 - 5  is turned ON to provide the user with a relatively small locator light that tells the user where to find the light switch in the darkened room. When current flows through LED  130 - 5 , however, current cannot flow through the (−) LED  130 - 3  and the (+) LED  130 - 4  because both of these LEDs are biased OFF. In other words, these LEDs are presented with the same voltage potential at their anodes and cathodes such that current cannot flow. The purpose of the (−) LED and the (+) LED displays is to direct the user to the down button  120 - 2  and the up button  120 - 3 , respectively. When the load is turned OFF, the dimming function is irrelevant and the −LED and the +LED are OFF to further indicate this fact. When these buttons are OFF, it is also a further indication that the load is OFF. 
     Referring to  FIG. 5 , a detailed circuit diagram of the power supply circuit in accordance with an embodiment of the present invention is disclosed. The power supply includes a half-wave rectifier circuit that is comprised of diodes  200 - 202 . The half-wave rectified DC signal is shown as HVDC. The half-wave rectified signal HVDC is employed by the regulator circuit  20 - 1  to further provide the power supply reference signals +5V and ground (GND) for the processor circuit  110 . 
     The diodes  200 - 202  are disposed in parallel with each other such that the AC power signal may be provided to the power supply via the hot/load pin or either of the traveler pins (T 1 , T 2 ). The utility of this parallel arrangement becomes more apparent in  FIGS. 10A-10C  and the description thereof. Needless to say, one of the features of the invention yields a universal dimmer that can be placed in either switch position of a retrofit three-way switch arrangement. Regardless of the switch position or which traveler pin the relay circuit  40  is connected, one of diodes  200 - 202  will furnish current to the power supply. Note also that diodes  204 - 206  (as a group) are placed in parallel with diodes  200 - 202  to provide the zero cross detector  20 - 2  with the half-wave rectified DC signal such that the zero cross detector  20 - 2  provides the zero cross (ZC) signal described above. Diodes  204 - 206  are also disposed in parallel with each other (like diodes  200 - 202 ) such that AC power signal may be provided to the zero-cross detection circuit  20 - 2  via the hot/load pin or either of the traveler pins (T 1 , T 2 ). Regardless of the switch position, or which traveler pin the relay circuit  40  is connected to, one of diodes  204 - 206  will furnish current to the zero-cross detection circuit. 
     Referring to  FIG. 6 , a detailed circuit diagram of the dimmer circuit in accordance with the present invention is disclosed. The microcomputer  110 - 1  controls the dimmer circuit  30  by way of the pulse width modulation (PWM) signal. The PWM signal propagates at logic levels (+5V, GND) and controls the operation of transistor  30 - 1 . The width of the PWM pulse is varied to control the amount of power provided to the load, whether a lamp load or a motor load. The PWM signal comprises at least one pulse in an AC line cycle. In one embodiment of the invention, the PWM signal may provide a plurality of pulses within an AC half cycle. By using pulse width modulation, the present invention may used as a universal dimmer device that can control any type of lighting load by varying the duty cycle of the pulse. In operation, when the PWM signal is high, the transistor  30 - 1  conducts through the opto-coupler  30 - 2  to turn transistors  30 - 3  and  30 - 40 N in accordance with the appropriate timing. Note that for the MOSFET implementation shown in  FIG. 6 , two transistors ( 30 - 3 ,  30 - 4 ) are required for operation. This is due to the internal body diode inherent in MOSFET technology; one MOSFET blocks a portion of the positive AC half cycle, and the other blocks a portion of the negative half-cycle to the load. The timing of the PWM pulse is of course controlled by the microcomputer and it is timed relative to the zero crossing of the AC cycle. As noted above, dimming is accomplished in the forward phase by switching the load current ON sometime after the zero-crossing of the AC half-cycle and turned OFF at the next zero-crossing of the AC waveform. Conversely, in reverse phase control, the load current is turned ON when the zero-crossing is detected and turned OFF sometime before the next zero-crossing is detected. 
     Because the PWM pulse is controlled by the microcomputer  110 - 1  with such a high degree of granularity while simultaneously monitoring the load current, the dimmer circuit may be employed in forward phase for certain optimized ELV, CFL and LED devices. The microcontroller transmits the PWM signal at a very low duty cycle until the I SNS AMP OUT signal (from the load current detector  112 ) indicates that there is a load current being drawn. If the fixture is an incandescent one, the load current in this region is substantially linear with respect to the PWM duty cycle. If the fixture is an LED fixture, the load current will not be present until the duty cycle has been increased to a certain threshold. Stated differently, the present invention employs a control loop that optimizes the PWM duty cycle for any given lighting load. Moreover, the microcomputer  110 - 1  may adjust the PWM signal to operate in forward phase or reverse phase by operation of the software. Again, as those skilled in the art will appreciate, forward phase control is appropriate for conventional incandescent lighting, magnetic low voltage (MLV) lighting fixtures, conventional fluorescent lighting fixtures employing electronic ballasts (EFL), and halogen lighting. Reverse phase control is generally appropriate for electronic low voltage (ELV) lighting. Bulbs designed as higher efficiency 120V incandescent replacements, including LED bulbs and compact florescent lights (CFL) typically perform better with forward phase control. 
     In one embodiment of the present invention, thermal sensors (Ts)  52  and  54  measure the heat being generated by the MOSFETs to obtain an estimate of power consumption. Thus, the sensor  52  is positioned proximate the transistors  30 - 3 ,  30 - 4  to obtain a measurement of the heat being generated thereby. The second sensor  54  is disposed in a region of the device that experiences the ambient temperature of the device  10 . The microcomputer  110 - 1  is programmed to calculate the temperature difference to determine the amount of thermal energy generated by the transistors  30 - 3 ,  30 - 4 . As those skilled in the art will appreciate, there is a relationship (I 2 R) between the dissipated heat and the power. 
     (Again, with respect to  FIGS. 10A-10C , the AC signal may be provided via the HOT/LOAD terminal and the dimmed signal by way of the SWITCH POLE terminal, or vice-versa, depending on which switch position the device  10  occupies in the three-way arrangement). Finally, note that wire-loop  50 - 1  is connected between transistor  30 - 4  and the SWITCH POLE terminal. The wire loop passes through the current sensor toroid  50  depicted in  FIG. 8 . 
     Referring to  FIG. 7 , a detailed circuit diagram of the switch relay circuit  40  in accordance with an embodiment of the present invention is disclosed. Again, the latching relay  40 - 1  may be configured to support both SPST applications as well as single pole double throw (SPDT) applications. In the SPDT application the relay  40 - 1  is moved between a first switch position that connects T 1  and SWITCH POLE, and a second switch position that connects T 2  with SWITCH POLE. The relay command signals RC 1  and RC  2  are logic level signals that control transistors  40 - 3  and  40 - 2 , respectively. If the latching relay is in the first switch position, the microcontroller  110 - 1  will provide a pulse via the relay command signal RC 2  to cause the switch  40 - 1  to toggle into the second switch position. Conversely, if the latching relay is in the second switch position, the microcontroller  110 - 1  will provide a pulse via relay command signal RC 1  to cause the relay  40 - 1  to toggle back into the first switch position. 
     Referring to  FIG. 8 , a diagrammatic depiction of the load sensor  50  in accordance with the present invention is disclosed. The current sensor  50  may be implemented as a toroid. As noted above, a wire loop connected to the SWITCH POLE terminal is disposed through the center of the toroid to create a transformer circuit. The wire loop  50 - 1  carries the load current and functions as the transformer primary. 
     Referring to  FIG. 9 , a detailed circuit diagram of a load sensor detector circuit  112  in accordance with the present invention is disclosed. In this embodiment the detector  112  is configured as a threshold detector  112 - 1  that compares the I SNS signal from sensor  50  described above, with a predetermined threshold value. In this particular embodiment, the detector  112 - 1  provides a logic signal to the microcomputer  110 - 1 . In one embodiment, if the load current is greater than about 10 mA, the detector  112 - 1  is configured to provide a logic one (+5V) signal. If the load current is below the threshold a logic zero (0 V) is provided. Those skilled in the art will appreciate that the threshold level is adjustable and depends on the level of sensitivity desired and the type of load. In this embodiment, the microcomputer  110 - 1  is signaled by I SNS AMP OUT when a minimal amount of current is being drawn by the load. 
     As embodied herein and depicted in  FIGS. 10A-10C , diagrammatic depictions of a three-way switch arrangement in accordance with the present invention are disclosed.  FIG. 10A  shows a typical three-way switch arrangement wherein the line voltage (i.e. 120 VAC) is connected to the pole of a first SPDT switch S 1  and the load is connected to the pole of a second SPDT switch S 2 . In this diagram, the load L is ON by virtue of the switch positions of S 1  and S 2 . Toggling either S 1  or S 2  into a second switch position will turn the load OFF. The present invention may replace either one of the switches S 1  and S 2 . 
       FIG. 10B  shows device  10  of the present invention being connected to switch S 1  in  FIG. 10A . Thus, the hot AC line signal is directed into the dimmer/latching switch  30 / 40  via the T 1  terminal, and further directed into the regulator  20 - 1  via diode  200  and the zero-cross detector  20 - 2  via diode  204 . The dimmed power is provided to the load via the HOT/LOAD terminal. If the device  10  is switched such that AC power is provided via the T 2  terminal, the diode arrangement ( 201 , 205 ) ensures that AC power is directed to the regulator and the zero-cross detector. 
       FIG. 10C  shows device  10  of the present invention being connected to switch S 2  in  FIG. 10A . In this configuration, the AC hot is directed into the dimmer/relay circuits  30 / 40  via the relay pole line; dimmed power is provided to the load via terminal T 1 . Because of the diode circuit described previously, AC hot is provided to the regulator  20 - 1  via diode  202  and to ZC Detector  20 - 2  via diode  206 . 
     As embodied herein and depicted in  FIG. 11 , a block diagram of the AC power circuitry in accordance with another embodiment of the present invention is disclosed. This embodiment is identical to the one depicted in  FIG. 2A  with the exception that there is no neutral terminal or ground terminal available for circuit reference. Thus, this device  10  may be employed in a retrofit/remodeling project wherein the existing device box does not include a neutral conductor. 
     Referring to  FIG. 12 , a detailed circuit diagram of the power supply depicted in  FIG. 11  is disclosed. Because there is no neutral connection, two less diodes are required. The zero-cross detection circuit  20 - 2  is essentially the same as the one depicted in  FIG. 5 . The linear regulator circuit produces a virtual ground node approximately 24V below the Hot/Load terminal. D 203  is biased with R 200  and R 201  to produce 24V, and Q 200  provides current amplification and improved load regulation compared with a zener regulator acting alone. U 200  further regulates the 24V down to 5V for use by the dimmer control circuitry. R 202 -R 205  provide current limiting in the event of a short circuit on 24V or 5V. 
     Referring to  FIG. 13 , a detailed circuit diagram of the dimmer circuit  30  depicted in  FIG. 11  is disclosed. As before, the microcomputer  110 - 1  controls the dimmer circuit  30  by way of the PWM signal. The PWM signal is at logic levels (+5V, GND) and controls the operation of transistor  30 - 1 . When transistor  30 - 11  is turned ON at a predetermined point in the AC half cycle, an appropriate amount of current is provided to the triac  30 - 10  to turn it ON such that dimmed power is provided to the load. L 300 , R 300 , and C 300  implement RFI filtering to minimize electromagnetic interference into nearby electronic equipment. 
     Referring to  FIG. 14 , a detailed circuit diagram of the switch relay depicted in  FIG. 11  is disclosed. This circuit is identical to the one depicted in  FIG. 7 . Thus, no further description is required with the exception that the transistors  40 - 2  and  40 - 3  are connected to the HOT/LOAD terminal instead of the rectified HVDC signal ( FIG. 7 ). As stated previously, the circuit&#39;s ground reference is 24V below the Hot/Load terminal; therefore this configuration provides 24V for driving the relay coil. 
     As embodied herein and depicted in  FIGS. 15A-15B , diagrammatic depictions of another three-way switch arrangement in accordance with the present invention are disclosed. These diagrams illustrate that the embodiment of  FIG. 11  may replace either switch S 1  or switch S 2  in  FIG. 10A . This capability is enabled by the diode arrangement  200 - 203  and the analysis is similar to the one provided in conjunction with  FIGS. 10A-10C . 
     As embodied herein and depicted in  FIG. 16 , a flow chart diagram illustrating a software auto-calibration sequence  1600  in accordance with the present invention is disclosed. In step  1602  the device is energized and in step  1604  the microcontroller sets the duty cycle of the PWM pulse at an initial value that may be thought of as an idling value. In step  1606 , the microcomputer  110 - 1  waits a predetermined time to determine if the load current is detected. In steps  1608 - 1612 , the PWM pulse width is increased until either the load current is detected or a maximum width value is exceeded. If the maximum width value is exceeded, the microcontroller  110 - 1  assumes that the load is turned OFF by the companion switch (S 1  or S 2 ) and goes back to the initial PWM setting in step  1604 . The cycle is repeated until the load current is detected in step  1614 . The microcontroller  110 - 1 , of course, knows the PWM value when load current is detected. 
     Load current detection is achieved when the threshold detector  112 - 1  finds that the I SNS signal from sensor  50  reliably exceeds the threshold. In one embodiment, I SNS is sampled 1000 times over a second. If at least 800 of the samples do not indicate load presence, the lamp is either off or flickering, and the PWM width is widened for an approximately 10 VRMS step increase in voltage to the lamp. This process of checking threshold detector and widening the PWM step keeps repeating until the lamp is either reliably on, meaning at least 800 samples indicating load presence, or until the maximum width is exceeded. The hunting stops at about 70 VRMS. 
     As has been described, the automatic calibration process can be accomplished in a matter of seconds. In one embodiment the calibration is initiated when an upstream breaker is opened momentarily and then closed to restore the voltage on the dimmer&#39;s power supply. In another embodiment, the automatic calibration takes place when a button on the dimmer is actuated by the user. In another approach, the automatic calibration takes place each time a switch is toggled to apply power to the load. 
     The ultimate voltage at which the lamp is reliably on is indicative of the type of load in use. For example, if the absolute value of the load current is low, it may indicate that the load is an LED lamp. As another example, how many of the samples are progressively indicating load presence from one step to the next may indicate the type of load. 
     The present invention may also determine if the device is a capacitive load device if, when set in a forward phase mode it detects current spikes. Conversely, if the device is pre-set to operate in reverse phase there will be current spikes if an inductive load is used. 
     The present invention may also determine the type of load on the basis of whether or not there is an inrush current when the load is turned on. The inrush characteristic can be compared against curves held in memory, e.g. the characteristic curve for a tungsten filament load. Unlike traditional incandescent bulbs, modern high-efficiency bulbs such as CFLs and LEDs do not turn on smoothly as their terminal voltage is increased from zero volts. Rather, these bulbs turn on abruptly at a turn-on voltage that is a function of the bulb design. For example, one manufacturer&#39;s LED bulb may turn on at 40Vrms, while another manufacturer&#39;s LED bulb may turn on at 60Vrms. Additionally, if the bulb voltage is maintained at approximately the turn-on voltage, bulb flashing may occur. 
     When high-efficiency bulbs are used in conjunction with Light Dimmers, it is desirable that the dimmer&#39;s output voltage never drops below a stable turn-on voltage for the bulb being used. Dimmers designed for use with these high-efficiency bulbs are typically calibrated at the factory to accomplish this requirement; that is, a specific low-end voltage is programmed into each dimmer based on the load type that the dimmer is designed to operate with. Dimmers that are intended to be used with varying load types can be developed using multiple strategies, such as: Calibrate the minimum dimmer output voltage during manufacturing to a level so high that all bulbs will turn on with no flashing at this minimum voltage—the downside of this approach is that the resulting dimming range will be unacceptably narrow for many load types. Design a feature into the dimmer that allows the end user to calibrate the dimmer after installation—the downside of this approach is that it burdens the user with extra work at installation. Also, this approach may result in unacceptable dimmer operation if the user fails to perform the calibration properly. 
     A calibration algorithm can be embedded into the light dimmer so that the dimmer automatically calibrates itself for the load being used. This auto-calibration can occur when power is first applied to the dimmer after installation. To implement this, the dimmer estimates the power being delivered to the load as the dimmer automatically increments up its output voltage. When a sudden increase in load power is sensed, the dimmer determines that its output voltage is now at or near the load&#39;s turn-on voltage, and calibrates itself accordingly. 
     The following pages illustrate one possible implementation that utilizes a current sensor to estimate load power, and a microcontroller to perform the calibration and control the dimming. This implementation is suitable for use in either single pole or 3-way switch installations. 
     As embodied herein and depicted in  FIG. 17  is a flow chart diagram illustrating a software main program in accordance with the present invention is disclosed. After initialization and calibration, the microcomputer  110 - 1  reads and records the user input from, e.g., the button inputs described herein. If an ON/OFF command is issued by the user, the microcomputer  110 - 1  directs the relay circuit  40  accordingly. After determining if a load current is present, the computer  110 - 1  adjusts the PWM dimmer setting in accordance with user commands and updates the display LEDs accordingly. This process is performed continually thereafter. 
     As embodied herein and depicted in  FIG. 18  is a flow chart diagram illustrating a software zero cross interrupt routine  1800  in accordance with the present invention is disclosed. In step  1804 , the microcomputer  110 - 1  determines whether device  10  should operate in forward phase control (FPC) or in reverse phase control (RPC) using any one of the methods described herein. In the forward phase, the load current is switched ON a predetermined time after the zero-crossing of the AC half-cycle and turned OFF at the next zero-crossing of the AC waveform. Conversely, in reverse phase control, the load current is turned ON immediately after the zero-crossing is detected and turned OFF at a predetermined time before the next zero-crossing is detected. The predetermined time intervals described above can be implemented by scheduling a software load timer interrupt. 
     As embodied herein and depicted in  FIG. 19  is a flow chart diagram illustrating a software load timer interrupt routine in accordance with the present invention is disclosed. As an extension to discussion on  FIG. 18  above, the load timer interrupt turns the load current off when operating in reverse phase, and turns the load current on when operating in forward phase. 
     As embodied herein and depicted in  FIG. 20 , a front isometric view of a power control device  10  in accordance with an embodiment of the present invention is disclosed. Device  10  includes a switch cover  204  disposed on heat sink assembly  202 . The power handling PCB  10 - 1  is disposed under the heat sink  202  and within the back body member  200 .  FIG. 21  is a rear isometric view of the power control device depicted in  FIG. 20  and shows the back body member  200  and the heat sink  202 . 
     Referring to  FIG. 22 , a rear isometric view of the heat sink assembly of the power control device depicted in  FIG. 20  is disclosed. The separator member  202 - 2  is connected to the front of the heat sink  202  and the pins of the MOSFETs  30 - 3 ,  30 - 4  and the interface circuit  10 - 3  extend through the separator  202 - 2  such that they may be coupled to the PCB  10 - 1 . 
     In  FIG. 23 , a rear isometric view of the heat sink assembly is shown with the power handling printed circuit board  10 - 1  added. In this view, the sensor  50 , the sensor wire  50 - 1 , the relay  40  and various other components are shown as being disposed on the power handling PCB  10 - 1 . Note that ground clip spring  202 - 1  is attached to the rear side of the heat sink  202 . The spring clip is configured to engage a front portion of a frame assembly (not shown in this view). Reference is made to U.S. patent Ser. No. 13/680,675, which is incorporated herein by reference as though fully set forth in its entirety, for a more detailed explanation of A MODULAR ELECTRICAL WIRING DEVICE SYSTEM and the associated framing system. 
     Referring to  FIG. 24 , a front isometric view of  FIG. 20  is disclosed with the aesthetic cover  204  removed. Thus, the switch actuator  204 - 2  is shown with a central aperture that accommodates the locator LED  130 - 5 . Note also that the dimmer cover assembly  206  is seated within a portion of the switch actuator  204 - 2 .  FIG. 25  is a front isometric view of  FIG. 20  with the aesthetic actuator cover  204  and the dimmer cover  206  removed such that the dimmer control switches  120 - 2 ,  120 - 3  are accessible. Snap elements  202 - 3  are formed in the separator  202 - 2  and are use to engage the dimmer cover  206  and secure it to the assembly. Snap elements  202 - 3  are also pivot points to allow dimmer cover  206  to rotate in order to actuate dimmer control switches  120 - 2 , 120 - 3 . 
     Referring to  FIG. 26 , a front isometric view of the heat sink assembly disposed within the back body member  200  is shown. Note that the logic PCB  10 - 2  is mounted to the front side of the heat sink  202 . The microcomputer  110 - 1  is mounted on the PCB  10 - 2 . The switches  120 - 1 ,  120 - 2  and  120 - 3 , as well as LED indicators  130 - 2 , are mounted on the PCB  10 - 2 . 
     Referring to  FIG. 27 , a front isometric view of the device with the heat sink  202  removed, revealing separator member  202 - 2 . The MOSFETS  30 - 3  and  30 - 4  are electrically connected to the PCB  10 - 1  and are shown as extending through the openings in the separator  202 - 2 . The snap elements  202 - 3  are clearly shown in this view, and as noted above, accommodate snap-in elements formed in the dimmer cover  205  (not shown). The separator  202 - 2  also includes trunions  202 - 4  at either end. The trunions  202 - 4  accommodate the snap-openings  204 - 12  in the functional actuator  204 - 2  (See  FIG. 29 ). Trunions  202 - 4  allow the functional actuator  204 - 2  to rotate to allow engagement of switch  120 - 1 . Finally, the separator  202 - 2  includes a spring arm  202 - 5  that is configured to bias the functional actuator  204 - 2  upwardly. 
     Referring to  FIG. 28 , an exploded view of the power control device depicted in  FIG. 20  is disclosed. The device  10  includes an aesthetic cover  204  that includes an LED lens  204 - 1  disposed in a central portion thereof. In an embodiment of the invention, lens  204 - 1  is a thin section of cover  204 . The aesthetic cover further includes an opening  204 - 6  that accommodates the dimmer switch cover  206 . The dimmer switch cover  206  includes a light pipe structure  206 - 1  that is held in place within the dimmer cover  206  by an alignment mask  206 - 2 . The dimmer cover  206 , the light pipe  206 - 1  and the alignment mask  206 - 2  are configured to be disposed within opening  204 - 5  formed in one side of the functional switch actuator  204 - 2 . The functional switch actuator  204 - 2  includes a central opening  204 - 3 . The logic PCB  10 - 2  is shown over top of the front side of the heat sink  202 . The two MOSFETs  30 - 3  and  30 - 4  are coupled to the bottom of heat sink  202  by insulator members  30 - 3 ,  30 - 40 , respectively. Of course, the MOSFETs  30 - 3  and  30 - 4  are electrically connected to the power handling PCB  10 - 1  via openings in the separator  202 - 2 . The entire assembly is disposed within back body member  200 . See  FIGS. 24-27 . 
     Referring to  FIG. 29 , a bottom isometric view of the functional actuator  202 - 2  is disclosed. The central portion of the functional switch  204 - 2  includes a central opening  204 - 3  that may accommodate an LED. At one side of the functional switch  204 - 2  there are snap-in elements ( 204 - 10 ,  204 - 11 ) that are configured to mate with the snap-elements  202 - 6  formed in the separator (See  FIG. 27 ) Snap-in elements ( 204 - 10 ,  204 - 11 ) are bearing surfaces for springs  202 - 6  and also to limit the spring-biased rotation. Recessed surface  204 - 13  engages the switch  120 - 1  when cosmetic actuator  204  is depressed, opposing the spring biased rotation. At the opposite side, there are trunion mounts  204 - 12  that accommodate the trunions  202 - 4  formed in the separator  202 - 2 . The trunions allow the functional switch  204 - 2  when switch  120 - 1  is manually actuated. The tray portion  204 - 5  which accommodates the dimmer cover assembly  206  includes light isolation openings  204 - 6  for the light pipe element  206 - 1 . 
     In reference to  FIGS. 30-31 , detailed isometric views of the dimmer actuator cover  206  depicted in  FIG. 20  are disclosed.  FIG. 30  shows the underside of the dimmer cover  206 . An alignment mask  206 - 2  is disposed overtop the light pipe structure  206 - 1  to prevent undesired light leakage from the light pipe. The down button light pipe  206 - 5 , the up button light pipe  206 - 6  and the LED bar graph light pipes  206 - 7  are shown extending through the mask portion  206 - 2 . In  FIG. 31 , the mask portion  206 - 2  is removed such that the light pipe structure  206 - 1  can be clearly seen within the dimmer cover  206 . 
     Referring to  FIG. 32 , a cross-sectional view of the power control device  10  depicted in  FIG. 20  is disclosed. This view shows the aesthetic cover  204  disposed over the functional switch  204 - 2  and other elements underneath, such as the logic PCB  10 - 2 , separator  202 - 2  and the power handling PCB  10 - 1 . Aesthetic cover  204  is configured to be removable by the user as is dimmer cover  206 . 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. 
     The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. 
     All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed. 
     No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.