Abstract:
An LED bulb is described, comprising LEDs within a shell and a driver circuit to operate the LEDs at a plurality of brightness levels. The driver circuit comprises first and second inputs to receive AC, a neutral input, a converter circuit, first and second rectifier circuits, a detector circuit, and a processing circuit. The first rectifier circuit is connected to the first and neutral inputs and rectifies the AC received. The second rectifier circuit is connected to the second and neutral inputs and rectifies the AC received. The detector circuit is connected to the first and second rectifier circuits. The processing circuit has a first and a second processor input, and is connected to the detector circuit. The processing circuit produces a chop signal with a duty cycle based on whether the first or second input is hot. The converter circuit powers the LEDs based on the chop signal.

Description:
BACKGROUND 
       [0001]    1. Field 
         [0002]    The present disclosure relates generally to microprocessor-based drivers for light emitting diode (LED) bulbs, and more specifically to microprocessor-based drivers for LED bulbs that enable the LED bulb to emit light at different levels of brightness. 
         [0003]    2. Description of Related Art 
         [0004]    Conventional incandescent light bulbs that have three lighting levels (“three-way light bulbs”) include two filaments; in the minimum illumination setting a low wattage filament is energized, in the medium illumination setting a medium wattage filament is energized, in the high illumination setting both filaments are energized. The illumination setting is selected by energizing a first input connected to the low wattage filament, energizing a second input connected to the medium filament, or energizing both the first and second inputs. 
         [0005]    The conventional incandescent three-way light bulb has three electrical contacts, hot 1 , hot 2 , and neutral. A switch, contained in the lamp base, connects terminal hot 1  to mains power (e.g., a 120 VAC 60 Hz signal in the United States) in the low power case, connects hot 2  to mains power in the medium power case, and connects both hot 1  and hot 2  to mains power in the high power case. Terminal hot 1  is connected to the low wattage filament and terminal hot 2  is connected to the medium wattage filament. Thus, either or both filaments may be selected to provide three levels of illumination. 
         [0006]    One method for reproducing the same functionality of the incandescent three-way light bulb in an LED bulb is to have two sets of LEDs with each set having its own driver connected to a different hot input. However, this requires having two driver circuits, which increases costs and increases space requirements that are limited when implementing LED bulbs in typical form factors of standard light bulbs. Therefore, it is desirable to connect multiple hot inputs to a single driver circuit. However, this requires the driver circuit to sense which of two terminals are energized and set the supply current of the LEDs accordingly. This could be done by inserting a component in series with each input and sensing the voltage drop across this series component. While this technique may work in principle, it would introduce power losses in the series component. Additionally, this technique requires many additional parts to amplify and detect the voltage. These parts increase the cost of the LED bulb, and are therefore undesirable. 
       BRIEF SUMMARY 
       [0007]    A light emitting diode (LED) bulb is described. The LED bulb comprises a shell, a plurality of LEDs within the shell, and a driver circuit. The driver circuit is configured to operate the plurality of LEDs at a plurality of brightness levels. The driver circuit comprises a first input configured to receive alternating current (AC), a second input configured to receive AC, a neutral input, a converter circuit connected to the plurality of LEDs, a first rectifier circuit, a second rectifier circuit, one or more detector circuits, and a signal processing circuit. The first rectifier circuit is connected to the first input and the neutral input. The first rectifier circuit is configured to rectify the AC received at the first input into direct current (DC). The second rectifier circuit is connected to the second input and the neutral input. The second rectifier circuit is configured to rectify the AC received at the second input into DC. The one or more detector circuits are connected to the first rectifier circuit and the second rectifier circuit. The signal processing circuit has a first processor input and a second processor input. The signal processing circuit is connected to the one or more detector circuits. The signal processing circuit is configured to produce a chop signal with a duty cycle. The duty cycle is based on whether the first input is hot and whether the second input is hot. The converter circuit powers the plurality of LEDs at a driving current. The driving current is based on the chop signal. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1  depicts an exemplary LED bulb that may be used with the exemplary LED driver circuit for brightness control. 
           [0009]      FIG. 2  depicts a block schematic of an exemplary LED driver circuit for brightness control. 
           [0010]      FIG. 3A  depicts an exemplary graph of the output of an SMPS power converter in an exemplary LED driver circuit. 
           [0011]      FIG. 3B  depicts an exemplary graph of Vchop in an exemplary LED driver circuit. 
           [0012]      FIG. 3C  depicts an exemplary graph of the output of an AND gate in an exemplary LED driver circuit. 
           [0013]      FIG. 4  depicts an exemplary circuit topology for an LED driver circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following description is presented to enable a person of ordinary skill in the art to make and use the various embodiments. Descriptions of specific devices, techniques, and applications are provided only as examples. Various modifications to the examples described herein will be readily apparent to those of ordinary skill in the art, and the general principles defined herein may be applied to other examples and applications without departing from the spirit and scope of the various embodiments. Thus, the various embodiments are not intended to be limited to the examples described herein and shown, but are to be accorded the scope consistent with the claims. 
         [0015]    An exemplary LED driver circuit that can drive one or more LEDs at three different brightness levels by driving the LEDs at three different currents is described below. The driver circuit uses a microcontroller to sense the input line voltages from a three-way switch. This reduces the number of required parts. Accordingly, the driver circuit is suitable for use in an LED bulb. 
         [0016]      FIG. 1  depicts an exemplary LED bulb  100 . The LED bulb maybe liquid-filled. LED bulb  100  includes a base  110  and a shell  101  encasing the various components of LED bulb  100 . The shell  101  is attached to the base  110  forming an enclosed volume. An array of LEDs  103  are mounted to support structures  107  and are disposed within the enclosed volume. The enclosed volume may be filled with a thermally conductive liquid  111 . 
         [0017]    For convenience, all examples provided in the present disclosure describe and show LED bulb  100  being a standard A-type form factor bulb. However, as mentioned above, it should be appreciated that the present disclosure may be applied to LED bulbs having any shape, such as a tubular bulb, globe-shaped bulb, or the like. 
         [0018]    Shell  101  may be made from any transparent or translucent material such as plastic, glass, polycarbonate, or the like. The shell  101  may be clear or frosted to disperse light produced by the LEDs. Shell  101  has a geometric center and an apex located at the top of the LED bulb  100  as it is drawn in  FIG. 1 . 
         [0019]    As noted above, light bulbs typically conform to a standard form factor, which allows bulb interchangeability between different lighting fixtures and appliances. Accordingly, in the present exemplary embodiment, LED bulb  100  includes connector base  115  for connecting the bulb to a lighting fixture. In one example, connector base  115  may be a conventional light bulb base having threads  117  for insertion into a conventional light socket. However, as noted above, it should be appreciated that connector base  115  may be any type of connector for mounting LED bulb  100  or coupling to a power source. For example, connector base may provide mounting via a screw-in base, a dual-prong connector, a standard two- or three-prong wall outlet plug, bayonet base, Edison Screw base, single pin base, multiple pin base, recessed base, flanged base, grooved base, side base, or the like. 
         [0020]    In some embodiments, LED bulb  100  may use 6 W or more of electrical power to produce light equivalent to a 40 W incandescent bulb. In some embodiments, LED bulb  100  may use 18 W or more to produce light equivalent to or greater than a 75 W incandescent bulb. Depending on the efficiency of the LED bulb  100 , between 4 W and 16 W of heat energy may be produced when the LED bulb  100  is illuminated. 
         [0021]    The LED bulb  100  includes several components for dissipating the heat generated by LEDs  103 . For example, as shown in  FIG. 1 , LED bulb  100  includes one or more support structures  107  for holding LEDs  103 . Support structures  107  may be made of any thermally conductive material, such as aluminum, copper, brass, magnesium, zinc, or the like. In some embodiments, the support structures are made of a composite laminate material. Since support structures  107  are formed of a thermally conductive material, heat generated by LEDs  103  may be conductively transferred to support structures  107  and passed to other component of the LED bulb  100  and the surrounding environment. Thus, support structures  107  may act as a heat-sink or heat-spreader for LEDs  103 . 
         [0022]    Support structures  107  are attached to bulb base  110  allowing the heat generated by LEDs  103  to be conducted to other portions of LED bulb  100 . Support structures  107  and bulb base  110  may be formed as one piece or multiple pieces. The bulb base  110  may also be made of a thermally conductive material and attached to support structures  107  so that heat generated by LED  103  is conducted into the bulb base  110  in an efficient manner. Bulb base  110  is also attached to shell  101 . Bulb base  110  can also thermally conduct with shell  101 . 
         [0023]    Bulb base  110  also includes one or more components that provide the structural features for mounting bulb shell  101  and support structure  107 . Components of the bulb base  110  include, for example, sealing gaskets, flanges, rings, adaptors, or the like. Bulb base  110  also includes a connector base  115  for connecting the bulb to a power source or lighting fixture. Bulb base  110  can also include one or more die-cast parts. 
         [0024]    LED bulb  100  may be filled with thermally conductive liquid  111  for transferring heat generated by LEDs  103  to shell  101 . The thermally conductive liquid  111  fills the enclosed volume defined between shell  101  and bulb base  110 , allowing the thermally conductive liquid  111  to thermally conduct with both the shell  101  and the bulb base  110 . In some embodiments, thermally conductive liquid  111  is in direct contact with LEDs  103 . 
         [0025]    Thermally conductive liquid  111  may be any thermally conductive liquid, mineral oil, silicone oil, glycols (PAGs), fluorocarbons, or other material capable of flowing. It may be desirable to have the liquid chosen be a non-corrosive dielectric. Selecting such a liquid can reduce the likelihood that the liquid will cause electrical shorts and reduce damage done to the components of LED bulb  100 . 
         [0026]    LED bulb  100  may include a mechanism to allow for thermal expansion of thermally conductive liquid  111  contained in the LED bulb  100 . In the present exemplary embodiment, the mechanism is a bladder  120 . The outside surface of the bladder  120  is in contact with the thermally conductive liquid  111 . 
         [0027]    The LED bulb  100  further contains the driver circuit. Connector base  115  may include two hot contacts and a neutral contact. In exemplary LED bulb  100 , the driver circuit may be driver circuit  200  discussed below with respect to  FIG. 2  and is substantially contained within connector base  115 . In this context, substantially contained means that the majority of the driver circuit is within connector base  115 , but portions of driver circuit components may be protruding from connector base  115 . For example, portions of the driver circuit may protrude above connector base  115  into bulb base  110  or shell  101 . Similarly, the driver circuit may be substantially contained within bulb base  110 . 
         [0028]    The driver circuit may be integrated onto a single printed circuit board, which fits within the LED bulb  100 . In one case, the driver circuit is integrated on a single printed circuit board and fits substantially within the bulb base or connector base of the LED bulb  100 . 
         [0029]      FIG. 2  depicts a block schematic of an exemplary LED driver circuit  200  for brightness control. Driver circuit  200  may be used in an LED bulb to power one or more LEDs  228 . Driver circuit  200  takes as input an input line voltage (e.g., 120 VAC, 60 Hz in the U.S.) from a three-way switch connected to input  202 , which includes hot input  202   a , hot input  202   b , and neutral input  202   c . At output  226 , driver circuit  200  outputs a current suitable for powering the one or more LEDs  228 . The three-way switch will energize hot input  202   a  only, hot input  202   b  only, or both hot inputs  202   a  and  202   b  at the same time. The one or more LEDs  228  will not be illuminated when the three-way switch does not energize any of hot inputs  202   a  and  202   b.    
         [0030]    As will be described in more detail below, driver circuit  200  includes rectifier circuits  204  and  206 , detector circuits  208  and  210 , signal processing circuit  212 , diodes  214 , SMPS power converter circuit  216 , AND gate  218 , FET switch  220 , and converter circuit  222 . Not all elements of driver circuit  200  are required. For example, some or all of the diodes  214  may be omitted. 
         [0031]    The rectifier circuits  204  and  206  are configured to convert the alternating currents (AC) from the hot inputs  202   a  and  202   b  into direct currents (DC). For example, the rectifier circuits  204  and  206  may each be a full-wave bridge rectifier circuit. Alternatively, a single rectifier circuit may be configured to convert the AC from the hot inputs  202   a  and  202   b  into DC. When hot input  202   a  is energized, the rectifier circuit  204  outputs a continuous stream of half-sine waves, which are detected by detector circuit  208 . Similarly, when hot input  202   b  is energized, the rectifier circuit  206  outputs a continuous stream of half-sine waves, which are detected by detector circuit  210 . 
         [0032]    The detector circuits  208  and  210  detect the state of the input lines as being above or below a threshold. In this example, detector circuits  208  and  210  are voltage level detector circuits that detect whether the voltage at their input is above or below a determined threshold voltage value. The detector circuits  208  and  210  output a high voltage signal when their inputs are above the determined threshold and output a low voltage signal when their outputs are below the determined threshold. The high voltage signal is relatively higher voltage than the low voltage signal. In one example, detector circuits  208  and  210  may each include a voltage splitter and a clamp. The voltage splitter portion of each detector circuit  208  and  210  reduces the voltage to a level useable by the signal processing circuit  212 . The clamp portion of each detector circuit serves to fix the signal to a determined DC value, such as for a high voltage signal or a low voltage signal. Additionally, the detector circuits  208  and  210  may optionally include a comparator for providing a further level of accuracy. 
         [0033]    The outputs of the detector circuits  208  and  210  are output to signal processing circuit  212 . For example, the signal processing circuit may be a microprocessor, a state machine, a customized integrated circuit, or other logic circuit. The signal processing circuit  212  processes the input signals received from the detector circuits  208  and  210  to determine whether only hot input  202   a , only hot input  202   b , or both hot inputs  202   a  and  202   b  at the same time are energized. The signal processing circuit  212  may have two inputs, called a first processor input and a second processor input. For each of the first processor input and the second processor input, the signal processing circuit  212  determines whether a received processor signal at the processor input is active (on) or inactive (off). For each of the first processor input and the second processor input, the received signal is time-integrated to protect against noisy conditions. A processor signal into the signal processing circuit  212  is determined to be active by the signal processing circuit  212  when the ratio between the duration of a high voltage signal and the duration of a low voltage signal is above an active threshold value. Similarly, a processor signal into the signal processing circuit  212  is determined to be inactive by the signal processing circuit  212  when the ratio between the duration of a high voltage signal and the duration of a low voltage signal is below the active threshold. The status of the processor signal at each processor input is indicative of the status of a corresponding hot input. For example, when the processor signal at the first processor input is active, it indicates that hot input  202   a  is energized. When the processor signal at the second processor input is active, it indicates that hot input  202   b  is energized. 
         [0034]    Various methods may be employed by the signal processing circuit  212  to determine the status of a processor signal. For example, a processor signal at a processor input may be determined to be active by the signal processing circuit  212  when the duration of a continuous high voltage signal exceeds a determined time. In another example, a processor signal at a processor input may be determined to be active by the signal processing circuit  212  when the duration of a continuous low voltage signal is less than a determined time. In another example, a processor signal at a processor input may be determined to be inactive by the signal processing circuit  212  when the duration of a continuous low voltage signal exceeds a determined time. In yet another example, a processor signal at a processor input may be determined to be inactive by the signal processing circuit  212  when the duration of a continuous high voltage signal is less than a determined time. Based on one or more of these durations at each processor input, the signal processing circuit  212  determines whether each of the hot inputs  202   a  and  202   b  are energized. 
         [0035]    The signal processing circuit  212  is configured performing time integration on the processor signals at a processor input of the signal processing circuit  212 . Time integration helps avoid incorrect results due to noisy conditions. It is advantageous to perform the time integration over two or more cycles before the signal processing circuit  212  makes a determination about the state of the hot inputs  202   a  and  202   b.    
         [0036]    Based on the determination of the states of the hot inputs  202   a  and  202   b , the signal processing circuit  212  outputs a chopped signal, named Vchop. For example: when only hot input  202   a  is energized, the duty cycle of the output signal of the signal processing circuit  212 , Vchop, is set to 25% (low illumination of LEDs); when only hot input  202   b  is energized, the duty cycle of the output signal of the signal processing circuit  212 , Vchop, is set to 50% (medium illumination of LEDs); when both hot inputs  202   a  and  202   b  are both energized, the duty cycle of the output signal of the signal processing circuit  212 , Vchop, is set to 100% (high illumination of LEDs). 
         [0037]    The signal processing circuit  212  sets the duty cycle of Vchop by performing pulse width modulation (PWM). Thus, at a high level, the signal processing circuit  212  selects between various duty cycles based on whether only hot input  202   a , only hot input  202   b , or both hot inputs  202   a  and  202   b  at the same time are energized. Accordingly, the signal output by the signal processing circuit  212  is pulse width modulated with a duty cycle based on the inputs  202   a  and  202   b . As discussed above, this pulse width modulated signal produced by the signal processing circuit  212  is called Vchop. 
         [0038]    It is advantageous for Vchop to have a PWM switching frequency that is at least 10 times higher than the frequency of the combined output at diode connection  224 . Assuming, for example, an input line frequency of 60 Hz at the hot inputs  202   a  and  202   b , the combined output at diode connection  224  is a 120 Hz half sine wave. This 120 Hz signal is produced at diode connection  224  by combining the outputs of the bridge rectifier circuits  204  and  206 . Thus, the minimum Vchop PWM switching frequency is 10 times higher than 120 Hz, which is 1.2 kHz. It is beneficial for Vchop to have a PWM switching frequency that is at least 10 times the frequency of the combined hot inputs  202   a  and  202   b  in order to reduce visible flickering in the illumination of the one or more LEDs  228 . Similarly, the maximum Vchop PWM switching frequency is one-tenth the frequency of the signal produced by the SMPS power converter circuit  216 . For example, assuming a frequency of 120 kHz for the signal produced by the SMPS power converter circuit  216 , the maximum Vchop PWM frequency is 12 kHz. 
         [0039]    The combined output at diode connection  224  is fed into the SMPS power converter circuit  216 . The SMPS power converter circuit  216  performs a second PWM. For example, the SMPS power converter circuit  216  may perform PWM at a frequency of between 65 kHz and 120 kHz. This output of the SMPS power converter circuit  216  is used to drive current to the one or more LEDs  228 . 
         [0040]    The two pulse width modulated signals, Vchop and the output of the SMPS power converter circuit  216 , are input into AND gate  218 . The AND gate  218  combines the two signals as illustrated in  FIG. 3 . The output of the AND gate  218  controls FET switch  220 . The FET switch  220  is connected to converter circuit  222 . The converter circuit  222  may be a step-down DC to DC converter that converts the combined output at diode connection  224  into a voltage configured to drive the LEDs  228 . In this example, converter circuit  222  is a buck-mode topology. Alternatively, the converter circuit  222  may be a flyback topology or other similar converter. 
         [0041]    While  FIG. 2  depicts a particular configuration of blocks, it should be understood that the blocks may be configured differently or some blocks may be omitted without deviating from embodiments of the present invention. 
         [0042]    To further improve performance, the PWM switching frequency of Vchop can be dithered or varied. Dithering or varying the PWM switching frequency of Vchop improves power factor effects and total harmonic distortion effects by spreading the noise over a frequency range. For example, the PWM switching frequency of Vchop can be varied from 1 kHz to 3 kHz. In another example, the PWM switching frequency can be dithered to a range of frequencies, such as by switching among various PWM switching frequencies. The circuit may be configured to switch among the various PWM switching frequencies after a set number of periods. 
         [0043]      FIG. 3  depicts graphs showing exemplary outputs at the output of the SMPS power converter circuit  216 , at Vchop, and at the output of AND gate  218 . For example, the SMPS output is a signal with a frequency of 100 kHz, as illustrated in  FIG. 3A , and Vchop is a signal with a PWM switching frequency of 2 kHz, as illustrated in  FIG. 3B . 
         [0044]    For Vchop in  FIG. 3B , the duty cycle is the percent of time that Vchop is ON as a fraction of the total period of the signal. In this example, the duration that Vchop is ON is the same as the duration for which Vchop is OFF. Thus, Vchop has a duty cycle of 50% and is said to be chopped at 50%. This case, where the duty cycle of Vchop is 50%, may exemplify the circumstance when only hot input  202   b  is energized. When Vchop and the output of the SMPS power converter circuit  216  are combined at the output of the AND gate  218 , as illustrated in  FIG. 3C , the result is a signal used for driving the one or more LEDs  228  with a medium intensity illumination. Similarly, a Vchop signal with a duty cycle of 25% would result in a signal that is ON for 25% of the signal period, and may exemplify the circumstance when only hot input  202   a  is energized. 
         [0045]      FIG. 4  illustrates an exemplary circuit topology  400  for an LED driver circuit. One of ordinary skill in the art will readily appreciate that different values of components may be used, that some components can be removed, some components can be added, and that some components may be re-arranged while maintaining a functional driver circuit. 
         [0046]    Line  402  is a hot 1  input, line  404  is a hot 2  input, and line  406  is a neutral input. Components  408  and  410  are resistors. Components  412  and  414  are capacitors. Components  416  and  418  are rectifiers, which convert AC to DC. Components  420  and  422  are capacitors. Component  424  is a microchip, such as a PIC10F320. Components  426 ,  428 ,  432  are resistors. Component  430  is a capacitor. Components  434  and  436  are diodes. Components  438 ,  440 ,  442 , and  444  are resistors. Components  446  and  448  are diodes. Component  450  is a resistor. Components  452  and  454  are inductors. Components  456  and  458  are capacitors. Component  460  is diode. Components  462 ,  464 ,  466 ,  468 ,  470 ,  472 ,  474 ,  476 ,  478 , and  480  are resistors. Components  482 ,  484 ,  486 , and  488  are capacitors. Components  490  and  492  are diodes. Component  494  is a resistor. Components  496  and  498  are transistors. Component  500  is an LED driver chip that outputs a pulse width modulated signal. Component  502  is an inductor. Component  504  is a capacitor. Component  506  is a diode. Outputs  508  may be connected to one or more LEDs to power the LEDs in one of three states: low, medium, and high illumination. 
         [0047]    Although a feature may appear to be described in connection with a particular embodiment, one skilled in the art would recognize that various features of the described embodiments may be combined. Moreover, aspects described in connection with an embodiment may stand alone.