Abstract:
Circuits to make a 3-way LED light bulb correctly interface to a standard 3-way light socket, producing three levels of light corresponding to the three settings of the socket. One of the circuits prevents color shift due to varying LED current.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/097,680, filed Sep. 17, 2008, which is incorporated herein by this reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to circuitry for a 3-way LED light bulb, and more particularly, to a circuit that interfaces with a standard 3-way light socket, and produces three levels of light corresponding to the three settings of the socket. 
       BACKGROUND OF THE INVENTION 
       [0003]    An LED (light-emitting diode) consists of a semiconductor junction, which emits light due to a current flowing through the junction. An LED light bulb is a device that contains one or more LEDs and potentially a drive circuit for the LEDs, which are both located inside a conventionally shaped container (or shell). Conventional LED light bulbs screw into a standard socket and receive AC power from the two power connections of the socket. 
         [0004]    However, 3-way sockets differ from standard sockets in that they have three power connections. The control of the socket is configured so that, in sequence, a first power configuration (i.e., a first pair) consisting of the base and one of the power connections, which is energized with AC power, a second power configuration (i.e., a second pair) consisting of the base and a second power connection which is energized, and a third power configuration, which includes the base and both connections (i.e., the first and the second power connections), which are energized. A conventional LED light bulb will be energized only in one of the configurations, and will not respond with different light levels to the different settings. 
         [0005]    It can be appreciated that one solution to this problem is to have separate driving circuits energized by each of the configurations (or pairs). It can be appreciated that the circuits can be designed to deliver different drive power to the LEDs, and to deliver the sum of these two drive powers when both are energized. However, in practice, this solution may be expensive, and very difficult to fit inside the bulb. 
       SUMMARY OF THE INVENTION 
       [0006]    This invention has the object of developing a circuit for an LED light bulb such that the above-described primary problem is effectively solved by providing an inexpensive circuit that drives the LEDs in the bulb at different power levels depending on the energization of the 3-way socket. In accordance with an exemplary embodiment, the invention includes at least two (or a pair of) rectifier bridges attached to a pair of AC input connections, either of which may power an AC/DC converter. Each pair of inputs also includes a set (or pair) of low-power bridges. In accordance with an exemplary embodiment, the low-power bridges can be used to detect which of the pairs of AC connections are powered. In accordance with an embodiment, detection is accomplished, for example, by a resistor and a capacitor acting as an integrator. If the first pair of AC connections is powered, the first detector signals the AC/DC converter to produce a first level of power into the LEDs. Similarly, if the second pair of AC connections is powered, the second detector signals the AC/DC converter to produce a second level of power into the LEDs. Finally, if both pairs of AC connections are powered, both detectors signal the AC/DC converter, causing it to produce the sum of the two power levels into the LEDs. 
         [0007]    In an alternative circuit, if the first pair of AC connections is powered, the first detector signals the AC/DC converter to produce current into a first string of LEDs. Similarly, if the second pair of AC connections is powered, the second detector signals the AC/DC converter to produce current into a second string of LEDs. Finally, if both pairs of AC connections are powered, both detectors signal the AC/DC converter, causing it to produce current into both strings (i.e., a plurality of LEDs in series) of LEDs. In accordance with an exemplary embodiment, this configuration can be desirable to avoid slight changes in color (or color spectrum) of the LEDs caused by running the LEDs at different currents. 
         [0008]    In accordance with an exemplary embodiment, the time constant of the integrator must be set appropriately for both circuits. In particular, the time constant of the integrator must be substantially longer than half a line cycle of the AC power. In a preferred embodiment, the time constant of the integrator is approximately 5 to 10 times as long as half a line cycle of the AC power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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 an embodiment of the invention and, together with the description, serve to explain the principles of the invention. 
           [0010]      FIG. 1  is a circuit schematic of a circuit that drives the LEDs in an LED bulb at different power levels depending on the energization of a 3-way socket. 
           [0011]      FIG. 2  is a circuit schematic of a circuit that selectively drives the LEDs in an LED bulb depending on the energization of a 3-way socket. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]    Reference will now be made in detail to the present preferred embodiments of the invention, an example of which is illustrated in the accompanying drawing. Wherever possible, the same reference numbers are used in the drawing and the description to refer to the same or like parts. 
         [0013]    According to the design characteristics, a detailed description of the preferred embodiments is given below. 
         [0014]      FIG. 1  is a schematic of a circuit  10  that drives at least one string of LEDs  110  (i.e., a plurality of LEDs  110  in series) in an LED bulb at different power levels depending on the energization of a 3-way socket (not shown). In accordance with a preferred embodiment, the circuit  10  includes a base  120  and a first ring  121  of the socket, which are connected to an AC power bridge (or bridge rectifier)  20 . The AC power bridge  20  is preferably a standard AC power bridge, which includes a first half  21  consisting of a first pair of diodes  31 ,  32 , and a second half  22  consisting of a second pair of diodes  33 ,  34 . In accordance with an exemplary embodiment the first and second pairs of diodes  31 ,  32 ,  33 ,  34  (i.e., the four (4) diodes) are configured in a standard full-wave rectification configuration. The output and ground of the bridge  20  are connected to a power system  130 , which drives the at least one LED  110 . 
         [0015]    In a preferred embodiment, the circuit  10  also includes a second ring  122  of the socket, which is connected to a bridge rectifier circuit  23 , which consists of a third pair (i.e., two) of diodes  35 ,  36 . In accordance with an exemplary embodiment, the second half  22  of the bridge rectifier  20  is the same as the first half  21  of the first bridge rectifier  20 . In operation, current being drawn from the second ring  122  is rectified by the first and third pairs of diodes  31 ,  32 ,  35 ,  36 , which acts as a complete bridge rectifier. The output of this bridge rectifier is used to power the power system  130 , in parallel with the output of the bridge rectifier  20 . 
         [0016]    In accordance with an exemplary embodiment, in order to determine which light level is desired, the first and second rings  121 ,  122  each have an independent detection circuit  40 ,  50  (i.e., a first detection circuit  40 , and a second detection circuit  50 ). In the first detection circuit  40 , an input connection in the form of AC power (AC 3 ) from the second ring  122  is half-wave rectified by diode  41 . This signal is integrated by an RC circuit consisting of a resistor  42  and a capacitor  44 . When AC power (AC 3 ) from the second ring  122  is energized, the voltage on the capacitor  44  rises to a level set approximately by the values of the resistor dividers  42 ,  43 . When AC power (AC 3 ) from the second ring  122  is not energized, the voltage on capacitor  44  falls to zero, as energy is bled out through the resistor  43 . The voltage on the capacitor  44  is thus indicative of the presence or absence of energization of AC power (AC 3 ) on the second ring  122 . In accordance with an exemplary embodiment, the functionality and structure of the second detection circuit  50  for energization detection of an input or input connection in the form of AC power (AC 2 ) on the first ring  121  is essentially identical to the first detection circuit  40 . 
         [0017]    In accordance with an exemplary embodiment, the voltage present on capacitors  44 ,  54  is used to determine the on or off state of transistors  60 ,  70 . The transistors  44 ,  54  are used in turn to determine the value of the current sense resistor used in a power switcher  130 , which sets the power level. In particular, if the AC power (AC 2 ) in the first ring  121  is energized, capacitor  53  will have a voltage on it. By suitable selection of resistors  52  and  53 , this voltage can be designed to be high enough to turn on transistor  70 . When transistor  70  is on, resistor  71  in series with transistor  70  is used as a current sensor by the power switching circuit  130 . The current sensor (resistor  71  in series with transistor  70 ) is used by the power switcher  130  to set the amount of current that flows through the at least one LED  110 . If AC power (AC 2 ) in the first ring  121  is not energized, the voltage on capacitor  54  will be zero, transistor  70  will be off, and the power switcher  130  will use the default resistor  80  to set the LED current. 
         [0018]    In the similar case wherein the AC power (AC 3 ) in the second ring  122  is energized, transistor  60  is turned on, and resistor  61  in series with transistor  60  is used as a current sensor by the power switching circuit  130 . If both AC power (AC 2 ) and (AC 3 ) from the first and second rings  121 ,  122  are energized, both capacitors  44  and  54  will be charged, both transistors  60  and  70  will be on, and the two current sense resistors  61  and  71  in series with their respective transistors  60  and  70  will be used as current sensors. 
         [0019]    Thus in this circuit  10 , three different light levels are available by suitably selecting the values of current sense resistors  61  and  71 . When AC power (AC 2 ) from the first ring  121  is energized, the current generated by the power switcher  130  will be set by resistor  71 . When AC power (AC 3 ) is energized, the current generated by power switcher  130  will be set by resistor  61 . When both the AC power (AC 2 ), (AC 3 ) from the first and second rings  121 ,  122  are energized, the current generated by power switcher  130  will be set by the parallel combination of resistors  61 ,  71 . In accordance with an exemplary embodiment, resistor  80  is preferentially selected to set a very low current through the at least one LED  110 , so that during the time it takes for the capacitors  44  and/or  54  to charge, no destructive switching occurs in the power switcher  130 . 
         [0020]      FIG. 2  is a schematic of a circuit  11  that drives at least two series or strings of LEDs  110 ,  111  (i.e., a first series and a second series of LEDs  110 ,  111 ) in an LED bulb with differing LEDs on or off depending on the energization of a 3-way socket. In accordance with an exemplary embodiment, each of the at least two strings of LEDs  110 ,  111  includes at least one LED  110 ,  111 . It can be appreciated that in accordance with an exemplary embodiment, each of the at least two strings of LEDs  110 ,  111  are comprised of a single LED  110 ,  111 . In accordance with a preferred embodiment, the base  120  and the first ring  121  of the socket are connected to an AC power bridge  20  (i.e., a standard AC power bridge or bridge rectifier), consisting of two halves  21 ,  22  (i.e., a first half  21  and a second half  22 ). The first half  21  consists of a first pair (i.e., two) diodes  31 ,  32 , and the second half  22  consists of a second pair (i.e., two) of diodes  33 ,  34 . The four diodes  31 ,  32 ,  33 ,  34  (i.e., the first and second pair of diodes) being configured in a standard full-wave rectification configuration. In accordance with an exemplary embodiment, the output and ground of the bridge  20  are connected to the power system  130 , which drives the at least one two strings of LEDs  110  and  111 . 
         [0021]    In this preferred embodiment, the second ring  122  of the socket is connected to a bridge rectifier circuit  23 , which consists of a third pair (i.e., two) diodes  35 ,  36 . In accordance with an exemplary embodiment, the second half  22  of the bridge rectifier  20  is the same as the first half  21  of the first bridge rectifier  20 . In operation, current being drawn from the second ring  122  is rectified by the first and third pair of diodes  31 ,  32 ,  35 ,  36 , which act as a complete bridge rectifier. The output from the bridge rectifier is used to power the power system  130 , in parallel with the output of the bridge rectifier  20 . 
         [0022]    In order to determine which light level is desired, the two rings  121 ,  122  have independent detection circuits  40 ,  50  (i.e., a first detection circuit and a second detection circuit). In the first detection circuit  40 , the AC power (AC 3 ) from second ring  122  is half-wave rectified by diode  41 . The signal from diode  41  is integrated by an RC circuit consisting of a resistor  42  and a capacitor  44 . When the AC power (AC 3 ) from the second ring  122  is energized, the voltage on the capacitor  44  rises to a level set approximately by the values of the resistor divider, which is comprised of resistors  42 ,  43 . When the AC power (AC 3 ) from the second ring  122  is not energized, the voltage on the capacitor  44  falls to zero, as energy is bled out through the resistor  43 . The voltage on the capacitor  44  is thus indicative of the presence or absence of energization of AC power (AC 3 ) on the second ring  122 . The second detection circuit  50  works identically for energization detection of the AC power (AC 2 ) on the first ring  121 . 
         [0023]    The voltage present on the capacitors  44 ,  54  is used to determine the on or off state of transistors  60 ,  70 , respectively. The transistors  60 ,  70  are used in turn to determine which of the string or series of LEDs  110 ,  111  are shunted, setting the light level of the bulb. In particular, if the AC power (AC 2 ) in the first ring  121  is energized, capacitor  53  will have a voltage on it. By suitable selection of resistors  52 ,  53 , the voltage can be designed to be high enough to turn on transistor  70 . When transistor  70  is on, shunting circuit  140  is off, permitting current to flow through the first series of LEDs  110 . When transistor  70  is off, shunting circuit  140  is on, which shunts current around the first series of LEDs  110 , keeping the first series of LEDs  110  in an unlit state or condition. 
         [0024]    In accordance with an exemplary embodiment, the circuit  11  also includes a first shunting circuit  140 , which consists of a transistor  141 , resistors  142 ,  144  and a diode  143 . When transistor  70  is off, the gate voltage on the transistor  141  is pulled up to its drain voltage by resistor  142 . If the voltage across the gate to source of transistor  141  exceeds the rating of the transistor, the gate to source voltage can be clamped by a zener diode (not shown). When transistor  70  is on, the gate voltage on transistor  141  is pulled down. In accordance with an exemplary embodiment, the diode  143  and the resistor  144  limit how negative the gate to source voltage of transistor  141  can go, which avoids exceeding the rating of transistor  141 . 
         [0025]    In the similar case wherein the AC power (AC 3 ) in the second ring  122  is energized, transistor  60  is turned on, and a second shunting circuit  150  is de-activated, permitting current to flow through second series LEDs  111 . The second shunting circuit  150  consists of a transistor  151 , resistors  152 ,  154  and a diode  153 . If both AC power (AC 2 ), (AC 3 ) in the first and second rings  121 ,  122  are energized, both the capacitors  44 ,  54  will be charged, both the transistors  60 ,  70  will be on, and both the shunt circuits  140 ,  150  will be de-activated, permitting current to flow through both the first series or string of LEDs  110  and the second series or string of LEDs  111 . 
         [0026]    Thus in this circuit, three different light levels are available by suitably selecting which of the shunt units or shunt circuits  140 ,  150  are de-activated. When AC power (AC 2 ) in the first ring  121  is energized, the current generated by the power switcher  130  flows through the second series or string of LEDs  111 . When AC power (AC 3 ) in the second ring  122  is energized, the current generated by the power switcher  130  flows through the first series or string of LEDs  110 . When AC power (AC 2 ), (AC 3 ) in both the first and second rings  121 ,  122  are energized, the current generated by power switcher  130  flows through both the first and second series or strings of LEDs  110 ,  111 . 
         [0027]    It will be apparent to those skilled in the art that various modifications and variation can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.