Abstract:
A circuit includes an input and an output, and an electronic light generator drive portion that is coupled to the input and drives the output. In one configuration, the circuit includes a further portion that is coupled to the input and that tunes a resonance at the input to a first frequency, the further portion having an additional portion with a resonance that is tuned to a second frequency different from the first frequency, and that effects damping of the first frequency at the input. In a different configuration, the drive portion includes an electronic switch coupled to the output of the circuit, and a further portion coupled to the input and having a phase tracking portion, the phase tracking portion tracking a phase of a signal at the input and producing a control signal that is used to control the electronic switch.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to devices that emit electromagnetic radiation and, more particularly, to devices that use light emitting diodes or other semiconductor parts to produce electromagnetic radiation. 
       BACKGROUND 
       [0002]    Over the past century, a variety of different types of lightbulbs have been developed, including incandescent lightbulbs and fluorescent lights. The incandescent bulb is currently the most common type of bulb. In an incandescent bulb, electric current is passed through a metal filament disposed in a vacuum, causing the filament to glow and emit light. The impedance or load characteristic of a standard incandescent bulb is basically resistive in nature. 
         [0003]    Recently, bulbs have been developed that produce illumination in a different manner, in particular through the use of light emitting diodes (LEDs). Pre-existing LED lightbulbs have been generally adequate for their intended purposes, but they have not been satisfactory in all respects. As one aspect of this, LED lightbulbs include a driver circuit for the LEDs. These driver circuits are peak charging from the line voltage, and are typically not power factor correcting circuits. LED driver circuits that are not power factor correcting typically have a conduction angle of 30-40 degrees. They exhibit a negative impedance characteristic, rather than a resistive characteristic comparable to that of a standard incandescent bulb. 
         [0004]    Dimmers are widely sold today for use with standard incandescent lightbulbs, or in other words bulbs that have a resistive characteristic. Most such dimmers include a triac that produces an output signal, and the output signal is applied to the lightbulb. These dimmers work well with standard incandescent bulbs. However, LED lightbulbs have not worked satisfactorily with these dimmers. More specifically, when used with an LED lightbulb having a negative impedance characteristic (rather than a resistive characteristic), the load applied to the triac is not always sufficient to keep the triac in conduction. Thus, when the triac is supposed to stay on, it will instead tend to oscillate on and off. Further, triacs typically have a resonant frequency, and this resonance can foster the undesired oscillation. 
         [0005]    It would be possible to design a dimmer that is not subject to this triac problem. However, for an LED lightbulb to be commercially viable, it is highly desirable that the LED lightbulb be compatible with existing electrical circuits (including those with phase dimmers), so that the LED lightbulb can be readily substituted almost anywhere that a comparable incandescent bulb is used. Electrically, one very simple solution would be to provide a large resistor in the bulb that loads the triac, thereby keeping the triac in conduction, while simultaneously damping its resonance. But as a practical matter, such a resistor would have a physical size that would be too large to be conveniently packaged within the form factor of a typical lightbulb. Further, such a resistor would dissipate a significant amount of power, causing it to be inefficient, and thus relatively expensive to operate. Moreover, the large power dissipation of the resistor would result in the emission of a significant amount of heat. It would be difficult to extract this much heat from the base of a lightbulb. Thus other components (such as integrated circuits) would be heated to temperatures beyond their specifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  is a block diagram of a light generating apparatus that embodies aspects of the invention, and that includes a power source, a phase dimmer, a socket, and a lightbulb, the lightbulb generating light using light emitting diodes. 
           [0008]      FIG. 2  is a graph showing a typical output signal from the phase dimmer of  FIG. 1 . 
           [0009]      FIG. 3  is a fragmentary sectional side view showing a base portion of the lightbulb of  FIG. 1 . 
           [0010]      FIG. 4  is a schematic circuit diagram showing the circuitry of a control circuit that is part of the lightbulb of  FIG. 1 . 
           [0011]      FIG. 5  is a timing diagram that shows several different waveforms relating to the control circuit of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  is a block diagram of a light generating apparatus  10  that includes a power source  12 , a phase dimmer  14 , a socket  16  and a lightbulb  18 . In the illustrated embodiment, the power source  12  generates standard household power of 120V at 60 Hz. However, the power source could alternatively generate power at some other voltage and/or frequency. 
         [0013]    The phase dimmer  14  is a commercially-available device, and is configured to replace a standard wall-mounted light switch. The phase dimmer  14  has a not-illustrated control knob that is supported for linear sliding movement or for rotational movement. When the knob is manually moved in one direction, the dimmer  14  causes a progressive increase in the amount of light produced by the lightbulb  18 . When the knob is manually moved in the opposite direction, the dimmer  14  causes a progressive decrease in the amount of light produced by the lightbulb  18 . Since the circuitry within the dimmer  14  is conventional, it is not shown and described in detail here. For purposes of the present disclosure, it is sufficient to understand that the circuitry in the phase dimmer  14  includes a triac  26 , and the triac produces the output signal of the phase dimmer. 
         [0014]      FIG. 2  is a graph showing a typical output signal from the triac  26  in the phase dimmer  14 . More specifically, the broken line  31  represents the 120V, 60 Hz sine wave input that the dimmer receives from the power source  12 . Reference numeral  32  designates the output signal of the phase dimmer  14 , as produced by the triac  26 . Each pulse of the output signal  32  has a width  36 . As the not-illustrated control knob of the phase dimmer  14  is manually moved, the triac  26  varies the width  36  of the pulses in the output signal  32 . In particular, when the control knob is manually moved in a direction that calls for more light, the pulse width  36  is increased. Conversely, when the control knob is manually moved in a direction that calls for less light, the pulse width  36  is decreased. 
         [0015]      FIG. 2  identifies a switching voltage VS. When the pulse width  36  decreases, the switching voltage VS increases. Conversely, when the pulse width  36  increases, the switching voltage VS decreases. Reference numeral  37  designates one-half of the period of the output signal  32 . The ratio of one pulse width  36  to the half-period  37  is the duty cycle of the output signal  32 . When the phase dimmer  14  is fully on, the duty cycle is typically about 65%, and the switching voltage VS has its lowest value, which is greater than 65V. 
         [0016]    Referring again to  FIG. 1 , the socket  16  is a commercially-available socket of a type found in most lamps and light fixtures, and is configured to receive the threaded base of a standard lightbulb. More specifically, the socket  16  is configured to receive a lightbulb base that conforms to an industry standard known as an E26 or E27-type base, or more commonly a medium “Edison” base. Alternatively, however, the socket  16  could have any of a variety of other configurations, including but not limited to configurations that are compatible with bulb bases commonly known as a candelabra base, a mogul base, or a bayonet base. The socket  16  includes a cup-shaped metal shell  41  with internal threads. A metal button  42  is centrally supported on an inner end wall of the shell  41  by a part  43  that is made of an insulating material  43 . The insulating material  43  electrically isolates the button  42  from the shell  41 . The shell  41  and the button  42  serve as respective electrical contacts. The shell  41  and button  42  are each electrically coupled to the output of the phase dimmer  14 , and in particular are coupled to respective different terminals of the triac  26 . 
         [0017]    The lightbulb  18  includes a housing  51 , and the housing  51  has a transparent portion  52  and a base  56 . The transparent portion  52  is made from a material that is transparent to radiation produced by the lightbulb  18 . For example, the transparent portion  52  can be made of glass or plastic. The base  56  is a medium Edison base, but could alternatively have any of a variety of other configurations, including but not limited to those known as a candelabra base, a mogul base, or a bayonet base. The base  56  is made of metal and has exterior threads, and serves as an electrical contact. A metal button  57  is supported on and electrically insulated from the base  56  by an annulus  58  of an electrically insulating material. The button  57  serves as a further electrical contact. The base  56  can be removably screwed into the socket  16 , until the buttons  42  and  57  physically engage each other and are thus in electrical contact. 
         [0018]    A control circuit  71  is disposed within the base  56 , and has two input leads or wires  72  and  73  that respectively electrically couple it to the base  56  and the button  57 . A light emitting diode (LED)  76  is supported within the lightbulb  18  by a not-illustrated support structure. The LED  76  is electrically coupled to the output of the control circuit  71  by two leads or wires  77  and  78 . The lightbulb  18  actually includes a plurality of the LEDs  76  that are all coupled to the output of the control circuit  71 . However, for simplicity and clarity, and since  FIG. 1  is a block diagram,  FIG. 1  shows only one of the LEDs  76 . 
         [0019]      FIG. 3  is a fragmentary sectional side view showing the base portion of the lightbulb  18  of  FIG. 1 . A flexible circuit board  86  is shaped to form an approximately cylindrical sleeve or ring, and is disposed within the base  56 . The electrical components of the control circuit  71  of  FIG. 1  are mounted on the circuit board  86 . Reference numeral  87  designates one of the electrical components of the control circuit  71 . The components of the control circuit  71  are electrically coupled by not-illustrated traces or runs within the flexible circuit board  86 . The circuit board  86  is held in place within the base  56  by a potting compound or overmolding material  88  of a known type. 
         [0020]    As discussed earlier, existing phase dimmers such as that shown at  14  in  FIG. 1  are designed to work satisfactorily with standard incandescent bulbs, but have not worked satisfactorily with pre-existing LED lightbulbs. This is because the load that an LED lightbulb applies to the triac  26  ( FIG. 1 ) is not always sufficient to keep the triac in conduction. Thus, when the triac is supposed to stay on, it will instead tend to oscillate on and off. The triac  26  has a resonant frequency, and this resonance can foster the undesired oscillation. 
         [0021]    An LED lightbulb is more commercially viable if it can be readily substituted for virtually any comparable incandescent bulb. Therefore, since many incandescent bulbs are installed in circuits that include a phase dimmer of the type show at  14  in  FIG. 1 , it would be beneficial to have an LED lightbulb that operates satisfactorily and efficiently with a phase dimmer. With reference to the lightbulb  18  in  FIG. 1 , the control circuit  71  has aspects that permit it to operate satisfactorily with a phase dimmer such as that shown at  14  in  FIG. 1 . 
         [0022]    In more detail,  FIG. 4  is a schematic circuit diagram showing the actual circuitry of the control circuit  71  of  FIG. 1 . The control circuit  71  has two input terminals  101  and  102 , and two output terminals  103  and  104 . The control circuit has an input section  106  that is coupled to the input terminals  101  and  102 , and has an electronic light generator drive section  107  that is coupled between the input section  106  and the output terminals  103  and  104 . An auxiliary section  108  is coupled to the input section  106  and to the drive section  107 . The drive section  107  includes a rectifying and filtering section  111 , an output section  112 , a control section  113 , and a switching section  114 . The auxiliary section  108  includes a phase tracking section  121 . Selected portions of the input section  106  and the auxiliary section  108  together form a preload and damping section  123 . 
         [0023]    Turning now to specific circuit components, a capacitor  151  has its ends respectively coupled to the input terminals  101  and  102 . Two inductors  152  and  153  each have one end coupled to a respective one of the input terminals  101  and  102 , and each have a further end that is coupled to a respective end of a resistor  154 . 
         [0024]    A diode bridge  156  has two input terminals that are coupled to respective ends of the resistor  154 . A resistor  157  and two capacitors  158  and  159  are coupled in parallel with each other between two output terminals of the diode bridge  156 , and one of the output terminals of the diode bridge  156  is coupled to ground. A diode  162  and a coil  163  are coupled in series with each other between the output terminals  103  and  104 , with the cathode of the diode coupled to the output terminal  103  and also to an output terminal of the diode bridge  156 . A transistor  171  has its drain coupled to the anode of diode  162 , and a resistor  172  is coupled between ground and the source of transistor  171 . 
         [0025]    An integrated circuit  174  is a commercially available part, and in particular can be obtained from Supertex, Inc. of Sunnyvale, Calif. as part number HV9910LG. Since the integrated circuit  174  is a known component, it is discussed here only briefly, and its internal circuitry is not illustrated and explained in detail. The integrated circuit  174  has an input VIN that is coupled to the cathode of the diode  162 . The integrated circuit  174  receives operating power through the input VIN. A current sensing input CS is coupled to the source of transistor  171 . A ground pin GND is coupled to ground. A gate control output GATE is coupled to the gate of transistor  171 . 
         [0026]    The integrated circuit  174  has an oscillator control input RT that is coupled to ground through a resistor  176 . The value of the resistor  176  sets the frequency of an internal oscillator within the integrated circuit  174 . In the disclosed embodiment, the internal oscillator produces a signal with a frequency of 100 KHz. A pulse width modulation control input (PWMD) is coupled to the phase tracking circuit  121 , as discussed in more detail later. Two pins LD and VDD are each coupled to one end of a capacitor  177 , and the other end of capacitor  177  is coupled to ground. 
         [0027]    The auxiliary circuit  108  includes a diode bridge  181  with two input terminals that are each coupled to a respective end of the resistor  154 . The diode bridge  181  also has two output terminals, one of which is coupled to ground. A resistor  183  and a capacitor  184  are each coupled between the output terminals of the diode bridge  181 , in parallel with each other. The phase tracking section  121  includes a resistor  187  and two Zener diodes  188  and  189  that are all coupled in series with each other between the outputs of the diode bridge  181 . The resistor  187  is disposed between the two Zener diodes, the anode of diode  189  is coupled to ground, and the anode of diode  188  is coupled to the resistor  187 . The cathode of diode  189  is coupled to the control input PWMD of the integrated circuit  174 . 
         [0028]    The following is a brief synopsis of the operation of the circuit  71  of  FIG. 4 . The signal  32  ( FIG. 2 ) from the phase dimmer  14  ( FIG. 1 ) is applied to the input terminals  101  and  102  of the control circuit  71 . The input section  106  of the control circuit  71  carries out some filtering and protection, and then the signal  32  is rectified and filtered by the rectifying and filtering section  111 . The output of the section  111  provides operating power to the integrated circuit  174 , and to the output circuit  112 . As noted earlier, the resistor  176  has a value that causes an internal oscillator in the integrated circuit  174  to oscillate at a frequency of approximately 100 KHz. Depending on the state of the control input PWMD, the integrated circuit  174  either applies the 100 KHz signal to the gate of transistor  171 , or else disables the gate of transistor  171 . 
         [0029]    The diode bridge  181  takes the filtered signal from the input circuit  106 , and rectifies it.  FIG. 5  is a timing diagram that shows several different waveforms relating to the control circuit  71 . The diode bridge  181  attempts to output a rectified signal that looks like waveform A in  FIG. 5 . However, the Zener diodes  188  and  189  in the phase tracking section  121  clamp the magnitude of this output signal at 65V, as discussed later. Consequently, the peaks of the pulses are clipped, and the signal at the output of the diode bridge  181  actually is the square wave signal shown at B in  FIG. 5 , which has a peak magnitude of 65 volts. 
         [0030]    As discussed earlier, it has been problematic to use pre-existing LED lightbulbs with a phase dimmer such as that shown at  14  in  FIG. 1 . In particular, the load applied to the triac  26  is not always sufficient to keep the triac in conduction, and the triac therefore oscillates on and off when it is supposed to stay on. This oscillation is compounded by the fact that triacs have a resonant frequency. This resonance can tend to encourage the triac to engage in the undesired oscillation at the resonant frequency. The particular resonant frequency will, of course, vary somewhat from part to part and from manufacturer to manufacturer. 
         [0031]    In  FIG. 4 , the capacitor  151  tunes the resonant frequency of the triac to a selected frequency, in order to make it easier to damp the resonance of the triac. The preload and damping section  123  is designed to resonate at a resonant frequency different from and significantly lower than the tuned resonant frequency of the triac, for example a resonant frequency that is at least a decade lower. This frequency differential ensures that the preload and damping section  123  will damp the resonance of the triac, rather than resonating with it. The resistor  184  also serves to keep the triac under a preload that is sufficient to keep the triac from going out of conduction. Consequently, the triac stays on when it is supposed to be on, rather than oscillating on and off. 
         [0032]    Turning now to the phase tracking circuit  189 , and as mentioned above, the diode bridge  181  attempts to output a signal that would theoretically have the waveform shown at A in  FIG. 5 . When the magnitude of this signal is less than 65V, or in other words at any time between pulses, the Zener diodes  188  and  189  are nonconducting, and thus the cathode of the diode  189  is at 0V. Accordingly, the potential of 0V at the cathode of diode  189  is applied to the control input PWMD of the integrated circuit  174 . Conversely, when a pulse occurs, the magnitude of the signal A ( FIG. 5 ) would theoretically exceed 65V. But as soon as it reaches 65V, the Zener diodes  188  and  189  reach their breakdown voltages and begin conducting, thereby clamping the output of the diode bridge  181  at a potential of 65V, so as to yield the waveform B of  FIG. 5 . 
         [0033]    As mentioned earlier, the switching voltage VS ( FIG. 2 ) for the traic  26  is always greater than 65V, regardless of the current duty cycle of the triac  26 . Consequently, by configuring the phase tracking section  121  so that a voltage of 65V causes the Zener diodes to experience breakdown, the phase tracking section  121  will always track the full width of each of the pulses from the triac. Stated differently, when the triac is operating at its maximum duty cycle of about 65%, where the pulse width  36  is at its maximum, the switching voltage VS of the triac will be greater than 65V, and thus the phase tracking section will accurately detect both the rising and falling edges of each pulse from the triac. 
         [0034]    The value of the resistor  187  is selected so that, when the cathode of diode  188  is at 65V, the cathode of diode  189  will be at 10V. Thus, a potential of 10V is applied to the control input PWMD of the integrated circuit  174 . The waveform C in  FIG. 5  is the control signal that is produced at the cathode of diode  189 , and that is applied to the control input PWMD of the integrated circuit  174 . 
         [0035]    When the signal at control input PWMD is 0V, the integrated circuit  174  disables its output GATE, so that the potential there is 0V. On the other hand, when the signal at control input PWMD is 10 volts, the integrated circuit  174  supplies a 100 KHz signal to its GATE output. The waveform D in  FIG. 5  is a diagrammatic representation of the signal that is produced by the integrated circuit  174  at its output GATE. Although the high frequency pulses at the GATE output occur at a frequency of 100 KHz, for clarity they are diagrammatically shown in waveform D of  FIG. 5  with a pulse width and period that correspond to a lower frequency. The signal from the GATE output of the integrated circuit  174  is applied to the gate of the transistor  171 . In response to a 100 KHz pulse burst at its gate, the transistor  171  causes the output circuit  112  to apply a 100 KHz pulse burst to the LED  76  ( FIG. 1 ). 
         [0036]    The preload and damping section  123 , in addition to providing preload and damping functions, also provides some high frequency filtering that keeps the 100 KHz switching frequency used for the transistor  171  and the LED  76  from leaking back through the input terminals  101  and  102  to the phase dimmer  14  and power source  12 . The cutoff frequency for this high frequency filter is the resonant frequency of the preload and damping section  123 . 
         [0037]    The control circuit  71  in the lightbulb  18  permits the LED lightbulb  18  to be substituted for an equivalent incandescent bulb and to operate properly, regardless of whether or not a phase dimmer is present. If there is a phase dimmer, its triac  26  will operate properly without resonant oscillation, and the LED  76  will dim properly through a wide range of brightness as the control knob of the dimmer is manually adjusted. On the other hand, if there is no dimmer, the lightbulb  18  will still operate entirely properly. 
         [0038]    The preload and damping section  123  is efficient, in that it uses a nominal amount of electricity, and thus operates at a low cost. Also, since the preload and damping section is efficient, it does not emit large amounts of heat that would be difficult to dissipate from within a lightbulb, and that could thus overheat electrical components within the lightbulb. Moreover, the components in the preload and damping section  123  are relatively small in physical size, thereby permitting the entire control circuit  71  to be implemented in a sufficiently small and compact space so that it can be disposed substantially entirely within a medium Edison base, for example in the manner discussed above in association with  FIG. 3 . 
         [0039]    In a variation of the circuit shown in  FIG. 4 , it would be possible to modify the phase tracking section  121  to add a not-illustrated sensor that influences the voltage potential between resistor  187  and diode  189 , as a function of a selected condition. The sensor could be any of a wide variety of sensors that monitor various different conditions. For example, the sensor could be a photocell that monitors the amount of ambient light, or a temperature sensor that monitors the ambient temperature. 
         [0040]    Although a selected embodiment has been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.