Patent Publication Number: US-8970116-B2

Title: Photo controller, a photo controller assembly and a process of controlling non-unity power factor devices

Description:
FIELD OF THE INVENTION 
     The present invention is directed to photo controllers and photo controller assemblies, and more specifically to photo controllers for controlling non-unity power factor devices. 
     BACKGROUND OF THE INVENTION 
     Incandescent lamps are unity power factor devices where the current is proportional to instantaneous line voltage, and line current is always present, except at zero cross points. The zero cross points are the points on the voltage wave where the line voltage is zero. Solid state relays, such as AC thyristor switches, are useful for controlling large AC power flows with milliampere-scale control circuits. AC thyristors can be used with incandescent lamps because there is always enough current to keep the switches from turning off except at the zero cross over of the line voltage. A trigger pulse of current applied shortly after the zero cross over will turn the thyristor on again for powering incandescent lamps. 
     Newer high-efficiency lamps, such as compact fluorescent and LED lamps, consume electricity differently from traditional incandescent lamps, drawing their currents in short erratic bursts (non-linear loading) rather than smoothly (linear loading). Most non-incandescent lamps include an electronic ballast which uses an alternating current to direct current converter circuit which interrupts the current through its switching action. These types of circuits normally only conduct the line current for a brief time within the instantaneous line voltage maximum and minimum peaks. Non-linear loads change the shape of the current waveform from a sine wave to some other distorted form, creating harmonic currents in addition to the original (fundamental frequency) AC current. These harmonic waveforms are a distortion of the current waveform, and change the phase relationship between the voltage and the current. Thus, as non-incandescent lamps can have their voltage and current waveforms out of phase, they are difficult to control using AC thyristor switches. 
     For most non-incandescent lamps, the distortion of the current waveform causes there to be no line current available shortly after the zero cross over of the line voltage, resulting in the AC thyristor not activating. One solution is to design a delay of the trigger pulse until current is present for a specific non-incandescent lamp waveform. While the trigger pulse can be controlled to delay until a point where current is present in the harmonic waveform, different non-incandescent lamps can have different phase angle relationships between the voltage and the current, where they start conducting current, thus necessitating a variety of trigger delay points. 
     Non-incandescent lamps can be controlled by photosensitive devices, such as photodiodes, phototransistors, and photodarlington light sensors. However, light given off by the controlled lamp can be reflected off nearby objects, causing the lamp to oscillate on and off. Compact fluorescent and LED lamps, unlike incandescent lamps, emit very little light in the infrared spectrum. Sunlight, conversely, contains a large amount of infrared light. Photosensitive devices with an infrared filter are useful to conduct only the infrared wavelength light. 
     A photo controller, a photo controller assembly, and a process for controlling a non-unity power factor device not suffering from one or more of the above drawbacks would be desirable in the art. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an exemplary embodiment, a photo controller includes a housing and a circuit board positioned within the housing. The circuit board includes a photosensor, an electronic controller and a thyristor secured to the circuit board. The electronic controller is configured to produce a series of trigger pulses for activating the thyristor, and the thyristor is configured to control power switching of a non-unity power factor lamp. 
     In another exemplary embodiment, a photo controller assembly includes a fixture socket, a non-unity power factor lamp, and a photo controller configured to releasably engage the fixture socket and the non-unity power factor lamp. The photo controller includes a housing and a circuit board positioned within the housing. The circuit board includes a photosensor, an electronic controller and a thyristor secured to the circuit board. The electronic controller is configured to produce a series of trigger pulses for activating the thyristor, and the thyristor is configured to control power switching of the non-unity power factor lamp. 
     In another exemplary embodiment, a process for controlling a non-unity power factor lamp includes providing a photo controller including an AC thyristor, producing a repeating series of trigger pulses sent to the AC thyristor upon a signal dropping below a setpoint. 
     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of an exemplary photo controller assembly according to an embodiment of the present invention. 
         FIG. 2  is a plan view of a schematic layout of a circuit board in an exemplary photo controller assembly according to an embodiment of the present invention. 
         FIG. 3  is a wiring schematic layout of an exemplary photo controller assembly according to an embodiment of the present invention. 
         FIG. 4  is a schematic layout of an exemplary photo controller assembly according to an embodiment of the present invention. 
         FIG. 5  is a flow chart illustrating an exemplary process of controlling non-unity power factor devices based on the light level according to an embodiment of the present invention. 
         FIG. 6  is a graph illustrating exemplary voltage and current waveforms for a compact fluorescent lamp according to an embodiment of the present invention. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Provided is an exemplary photo controller, a photo controller assembly, and a process for controlling non-unity power factor devices. Embodiments of the present disclosure permit a photo controller to include a light sensor which responds to the level of infrared light and does not respond to visible light, permits use of an AC thyristor as a switching device for non-unity power factor lamps, permits triggering of the AC thyristor by multiple pulses of limited duration during each half line cycle of voltage, permits a greater variety of non-unity power factor lamps to be connected, and combinations thereof. 
     Referring to  FIG. 1 , in one embodiment, an exemplary photo controller assembly  100  includes a fixture socket  102  in electrical communication with a lamp  104 , and a photo controller  106  configured to releasably engage the fixture socket  102  and the lamp  104 . In one embodiment, the lamp  104  is a device that converts electrical energy to light and may have a non unity power factor (with distorted current waveform), such as compact fluorescent or LED light bulbs, for example. In one embodiment, the photo controller  106  is configured for indoor or outdoor applications and has a compact design that easily engages most table lamp or outdoor post lantern type fixtures. 
     The photo controller  106  includes a housing  108 , and the housing  108  is any suitable housing structure capable of structural and electrical connection to the lamp  104  and the fixture socket  102 . In one embodiment, the housing  108  is fabricated of polymeric or other durable material, such as polycarbonate (PC) or polypropylene (PP), or combinations thereof. The housing  108  is any suitable geometry, for example, cylindrical, cuboid, frustoconical, or combinations thereof. 
     The housing  108  includes a light transmitting port  112 , a lamp socket  114  and a lamp adaptor  116 . The light transmitting port  112  allows sunlight or ambient light to enter the housing  108  for control of lamp  104 . The lamp socket  114  is configured for making an electrical and structural connection to a base of the lamp  104 , the base being a threaded Edison screw base, for example. The lamp adaptor  116  is configured for making an electrical and structural connection to the fixture socket  102 , the lamp adaptor  116  being a threaded Edison screw base, for example. The fixture socket  102  is electrically connected to an AC power source (not shown). 
     The housing  108  substantially encloses a circuit board  110  (see  FIG. 2 ), and protects it from exposure to the environment. Referring to  FIG. 2 , in one embodiment, the circuit board  110  includes a photosensor  118 , an electronic controller  120  and an AC thyristor  122  secured to the circuit board  110 . The circuit board  110  includes any suitable electronic components  111 , such as diodes (D 1 -D 2 ), capacitors (C 1 -C 4 ) and resistors (R 1 -R 4 ), for example, used to provide a DC power supply to the photosensor  118  and to the electronic controller  120 , and to filter and regulate the trigger pulse sent to the AC thyristor  122 . The circuit board  110  electronic components take the AC voltage of a power line (not shown) and convert it to a DC voltage which is used to power the electronic controller  120  and the photosensor  118 . 
     In one embodiment, the photosensor  118  is a light sensor, such as a photodiode, phototransistor, or photodarlington, for example, that is sensitive to infrared light. In one embodiment, the photosensor  118  is a phototransistor rated for maximum collector emitter breakdown voltage of 30V, maximum collector current of 4.8 mA, maximum dark current of 100 nA, a viewing angle of 20 degrees, and maximum power of 100 mW. In one embodiment, the photosensor  118  includes a visible light blocking filter or coating  119  that makes it only sensitive to light of a predetermined wavelength. In one embodiment, the predetermined wavelength is an “infrared” or “IR” wavelength within the range of about 700 nanometers to about 1 millimeter, in the range of IR-A, IR-B or IR-C, or combinations thereof. The terms “near infrared” or “IR-A” refer to energy having a wavelength within the range of about 700 nanometers to about 1400 nanometers. The term “IR-B” refers to energy having a wavelength within the range of about 1400 nanometers to about 3000 nanometers. The terms “far infrared” or “IR-C” refer to energy having a wavelength within the range of about 3000 nanometers to about 1 millimeter. In another embodiment, the light of a predetermined wavelength is in the range of IR-A, or about 940 nanometers. The filter or coating blocks visible light and permits light of the predetermined wavelength to pass through. The coating is implemented by adding visible light absorbing pigments to the encapsulation of a photodiode, phototransistor, or photodarlington, for example. In one embodiment, the coating pigments or ink are applied to the encapsulation by printing methods such as dipping, spraying, inkjet, silk screen, impression, rubber stamping, brushing, or penning, for example. 
     In one embodiment, the AC thyristor  122  is configured to control power switching of the lamp  104 . In one embodiment, the lamp  104  is a non-unity power factor lamp, for example. The AC thyristor  122  is an electronic power switch which conducts current in either direction when it is triggered by applying a small current of either polarity between the gate and one of the two main terminals. An AC thyristor is also formally known as a bidirectional triode thyristor or bilateral triode thyristor. The conduction operation of the AC thyristor  122  makes the device useful for controlling large AC power flows with milliampere-scale control circuits. Once the AC thyristor  122  is triggered, it continues to conduct current until the level drops below a certain threshold value, or holding current, such as occurs at the end of a half-cycle of AC mains power, at which point the AC thyristor  122  turns off. For most non-incandescent lamps, the distortion of the current waveform causes there to be no line current available shortly after the zero cross over of the line voltage (see  FIG. 6 ), which causes deactivation of the AC thyristor. Application of repetitive trigger pulses overcomes the lack of current and reactivates the AC thyristor. Different non-incandescent lamps can have different phase angle relationships between the voltage and the current, resulting in various points where they start conducting current. To address this, a series of repetitive trigger pulses are applied to activate the AC thyristor  122 . 
     In one embodiment, the AC thyristor  122  does not require extra circuitry to prevent premature or false triggering. The AC thyristor  122  is rated for off state voltage of 600V, maximum hold and gate trigger current of 35 mA, non repetitive surge peak on-state current of 60 A at 50 Hz and 63 A at 60 Hz, maximum on state current of 6 A, and maximum gate trigger voltage of 1.3V. 
     The electronic controller  120  is an electronic circuit or microcontroller, for example, that receives the analog electrical signal produced by the photosensor  118 , and responds by determining whether it is day or night, or determining if a predetermined setpoint for activation of the lamp has been reached. If the photosensor  118  determines that it is night, the electronic controller  120  will provide a series of trigger pulses to the AC thyristor  122  to cause the AC thyristor  122  to switch on the lamp  104 . In one embodiment, an activation period is the period of time when the lamp  104  should be powered as determined by the electronic controller. The trigger pulses are applied continuously during the activation period. In one embodiment, microcontrollers, which offer more flexibility than traditional analog controllers, are used with the AC thyristor  122  for control of lamps by producing a series of trigger pulses applied repetitively during the activation period to activate the AC thyristor switch  122  at the moment the resulting lamp current is non-zero. In order for the electronic controller  120  to work with all non-incandescent lamp types, it continuously produces short duration trigger pulses during the activation period. 
     In one embodiment, the electronic controller  120  is an 8 bit flash microcontroller with processor rated for 4 MHz operating speed, four input/output pins, program memory of 384B (256×12) flash, RAM size of 16×8, supply voltage of 2V to 5.5V, operating temperature of minus 40° C. to 85° C., and includes an internal oscillator, power-on reset and watchdog timer. In one embodiment, trigger pulses are applied by the electronic controller  120  to the AC thyristor switch  122  trigger terminal every 100 microseconds during the activation period when the electronic controller  120  determines that the light level signal is below the predetermined set point for activation. The trigger pulses are applied continuously by the electronic controller  120  during the activation period, and the trigger pulses are not applied in synchronism with the line voltage. 
     In one embodiment, the photo controller  106  ( FIG. 1 ) produces a repeating series of short duration trigger pulses, thereby permitting the photo controller  106  to operate multiple types of non-incandescent lamps with different current waveforms. For example, the photo controller  106  operates all types of incandescent and non-incandescent lamps such as compact-fluorescent or LED types. 
     In one embodiment, the electronic controller  120  provides a trigger pulse repetition rate within the range of about 90 to about 100 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse repetition rate within the range of about 100 to about 110 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse repetition rate within the range of about 100 to about 105 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse repetition rate within the range of about 95 to about 100 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse repetition rate of about 100 microseconds. In further embodiment, the electronic controller  120  provides a trigger pulse repetition rate within the range of about 90 to about 110 microseconds. The repeating series of trigger pulses allow a pulse to be applied at a point where current is likely to be present in the current waveforms of the various types of lamps. 
     In one embodiment, the electronic controller  120  provides a trigger pulse duration within the range of about 2 to about 3 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse duration within the range of about 3 to about 4 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse duration within the range of about 2.5 to about 3 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse duration within the range of about 3 to about 3.5 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse duration of about 3 microseconds. In another embodiment, the electronic controller  120  provides a trigger pulse duration within the range of about 2 to about 4 microseconds. Applying a repeating series of short duration trigger pulses assure the triggering of the AC thyristor  122  at the correct point where current is likely to be present in the current waveform while using substantially less energy than in other applications where a continuous DC trigger is used. 
     Referring to  FIG. 3 , in one embodiment, a wiring diagram includes suitable electronic components, such as diodes, capacitors and resistors, electrically communicating to provide a DC power supply to the photosensor  118  and to the electronic controller  120 , and to filter and regulate the DC power supply. The photosensor  118  electrically communicates the level of light detected to the electronic controller  120 , which responds with a series of trigger pulses electrically communicated to the AC thyristor  122 . The AC thyristor  122  electrically communicates control power switching of the load or the lamp  104 . 
       FIG. 4  shows a schematic layout of the photo controller assembly  100  including the operation of the system according to one embodiment. Filtering of sunlight permits detection of infrared light levels by the photosensor  118 . The photosensor  118  signals the light levels to the electronic controller  120 , providing a series of trigger pulses to the AC thyristor  122 , and switching the lamp  104 . The circuit board  110  electronic components take the AC voltage of a power line (not shown) and convert it to a DC voltage which is used to power the electronic controller  120  and the photosensor  118 . The photosensor  118  receives power from a DC power supply  123  that receives power from an AC power supply  117  through AC-DC converter arrangement  121 . 
     Referring to  FIG. 5 , in one embodiment, a process  200  of controlling non-unity power factor devices includes monitoring or otherwise determining (step  202 ), the levels of infrared light, for example, proximate the photosensor  118 , converting the monitored or determined level of light into a light level signal (step  204 ), and comparing the light level signal (step  206 ), for example, to a predetermined setpoint. If the light level is not below the predetermined setpoint, the trigger pulses are not generated (step  208 ). If the light level is below the predetermined setpoint, the trigger pulses are generated and sent to the AC thyristor (step  210 ). The control power is then switched at the lamp (step  212 ) using the AC thyristor. This process is repeated to appropriately control the activation of the lamp according to the level of light available at the photo controller. 
       FIG. 6  shows a graph of voltage and current waveforms for a compact fluorescent lamp according to an embodiment. The graph illustrates the phase relationship between the voltage and current waveforms, and the harmonic distortion of the current waveform. The two waveforms are shown overlaying each other to better illustrate the locations of the zero current segments that occur before and after the voltage zero crossing points. The example current spikes shown can have different time durations and different phase relationships for different types of non-unity power factor devices. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.