Abstract:
An apparatus includes circuitry that responds to application to its input of an alternating current input signal by producing at its output an output signal suitable for driving an electronic light generating element. The circuitry includes a regulating section that has a magnetic switch and that causes a current flowing through the output to be maintained substantially at a selected value. A different aspect relates to a method for operating circuitry having an input, an output and a magnetic switch. The method includes causing the circuitry to respond to application to its input of an alternating current input signal by producing at its output an output signal suitable for driving an electronic light generating element, where the magnetic switch is used in regulating a current flowing through the output so as to maintain the current substantially at a selected value.

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. 
         [0003]    Recently, bulbs have been developed that produce illumination in a different manner, in particular through the use of light emitting diodes (LEDs). An LED lightbulb typically includes a power supply circuit that drives the LEDs. The power supply circuit is typically configured to regulate the amount of current flowing through the LEDs, to keep it substantially uniform over time, so that the level of illumination produced by the LEDs remains substantially uniform over time. Various techniques have previously been used to achieve this current regulation. While these existing regulation techniques have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. 
         [0004]    As one aspect of this, pre-existing current regulation circuits often have the effect of producing a phase difference between the voltage and current, which in turn means the power supply circuit needs to make a power correction. This can phase difference can occur, for example, where a large capacitance is used to facilitate the current regulation. The use of a relatively large capacitance, along with the additional circuitry needed to effect power correction, has the effect of increasing the overall physical size of the power supply circuit. This in turn makes it difficult or impossible to package the power supply circuit within the form factor of a standard incandescent bulb. Also, pre-existing regulation techniques can produce a voltage stress within semiconductor parts. This voltage stress can in turn produce a thermal stress that shortens the effective lifetime of the semiconductor parts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    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: 
           [0006]      FIG. 1  is a block diagram of a light generating apparatus having a lightbulb that embodies aspects of the invention, and having a conventional power source that is shown diagrammatically in broken lines. 
           [0007]      FIG. 2  is a schematic circuit diagram showing a control circuit that is part of the lightbulb of  FIG. 1 . 
           [0008]      FIG. 3  is a timing diagram that shows several related waveforms within the circuit of  FIG. 2 . 
           [0009]      FIG. 4  is a timing diagram showing two additional waveforms within the circuit of  FIG. 2 . 
           [0010]      FIG. 5  is a timing diagram that shows, in a time-expanded scale, two pulses from one of the waveforms in  FIG. 3 , and that includes a diagrammatic representation of when a coil in the circuit of  FIG. 2  is respectively in high and low impedance states. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is a block diagram of a light generating apparatus  10  that has a lightbulb  14  embodying aspects of the invention, and that has a conventional power source  12  shown diagrammatically in broken lines. The power source  12  generates standard household power of 120V at 60 Hz. However, the power source  12  could alternatively generate power at some other voltage and/or frequency. 
         [0012]    The lightbulb  14  includes a housing  21 , and the housing  21  has a transparent portion  22  and a base  24 . The transparent portion  22  is made from a material that is transparent to radiation produced by the lightbulb  14 . For example, the transparent portion  22  can be made of glass or plastic. The base  56  is a type of base that conforms to an industry standard known as an E26 or E27 type base, commonly referred to as a medium “Edison” base. Alternatively, however, the base  24  could 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. 
         [0013]    The base  24  is made of medal, has exterior threads, and serves as an electrical contact. An annulus  27  is supported on the base  24 , and is made from an electrically insulating material. A metal button  26  is supported in the center of the annulus  27 . The button  26  is electrically insulated from the base  24  by the annulus  27 , and serves as a further electrical contact. The base  24  can be removably screwed into a conventional and not-illustrated socket of a lamp or light fixture, until the contacts  24  and  26  of the lightbulb  14  engage not-illustrated electrical contacts of the socket. In this manner, the contacts  24  and  26  become electrically coupled to opposite sides of the power source  12 , as indicated diagrammatically in  FIG. 1  by broken lines extending from the power source  12  to the lightbulb  14 . 
         [0014]    A control circuit  31  is disposed within the base  24 , and has two input leads or wires  32  and  33  that respectively electrically couple it to the base  24  and the button  26 . Thus, power from the power source  12  is supplied to an input of the control circuit  31 . A light-emitting diode (LED)  34  is supported within the lightbulb  14  by not-illustrated support structure. The LED  34  is electrically coupled to an output of the control circuit  31  by two leads or wires  36  and  37 . As a practical matter, the lightbulb  14  actually includes a plurality of the LEDs  34  that are all coupled to the output of the control circuit  31 . However, for simplicity and clarity, and since  FIG. 1  is a block diagram,  FIG. 1  shows only one of the LEDs  34 . 
         [0015]      FIG. 2  is a schematic circuit diagram showing the actual circuitry within the control circuit  31  of  FIG. 1 . More specifically, with reference to  FIG. 2 , the input of the control circuit  31  is defined by two input terminals  51  and  52 , and the output is defined by two output terminals  53  and  54 . The control circuit  31  has an input section  56 , and the input section  56  has a fuse  57  and a capacitor  58  that are coupled in series with each other between the input terminals  51  and  52 . A common mode coil  59  includes two coils  61  and  62 . The coils  61  and  62  each have one end coupled to a respective end of the capacitor  58 , and a further end coupled to a respective end of a metal oxide varistor (MOV)  63 . 
         [0016]    The control circuit  31  includes a diode bridge  66  that has two input terminals coupled to respective ends of the MOV  63 , and that has two output terminals. One output terminal of the diode bridge  66  is coupled to ground, and the other output terminal provides a voltage +HV to other portions of the circuit  31 . A capacitor  67  has each of its ends coupled to a respective output terminal of the diode bridge  66 . 
         [0017]      FIG. 3  is a timing diagram that shows several related waveforms within the circuit  31 . In  FIG. 3 , waveform W 1  is an input signal or waveform that is present at the input terminals  51  and  52  of the circuit  31 . In the disclosed embodiment, the waveform W 1  is the 120V, 60 Hz sine wave produced by the power source  12  ( FIG. 1 ). The input section  56  carries out some filtering and protection, and then the waveform W 1  is rectified and further filtered by the diode bridge  66  and the capacitor  67 . Waveform W 2  in  FIG. 3  represents the voltage that is present between the output terminals of the diode bridge  66 , or in other words the voltage across the capacitor  67 . This is the same as the voltage +HV in  FIG. 2 . 
         [0018]    The circuit  31  includes a chopping section  71  that has two field effect transistors (FETs)  72  and  73 , and a resistor  74 . The transistors  72  and  73  and the resistor  74  are all coupled in series with each other between the output terminals of the diode bridge  66 . The transistor  73  is disposed between the transistor  72  and the resistor  74 , with its drain coupled to the source of transistor  72 , and its source coupled to one end of the resistor  74 . The transistors  72  and  73  serve as electronic switches, as discussed later. 
         [0019]    The circuit  31  includes a switching control section  81 , and the switching control section  81  includes an integrated circuit device  82 . The integrated circuit device  82  is a component that is commercially available as part number IR2161 from International Rectifier Corporation of El Segundo, Calif. The switching control section  81  further includes a resistor  86 , a diode  87  and a capacitor  88  that are coupled in series with each between the output terminals of the diode bridge  66 . The capacitor  88  has one end coupled to ground, and its other end coupled to the cathode of diode  87 . The diode  87  is disposed between the resistor  86  and the capacitor  88 . A further capacitor  89  is coupled in parallel with the capacitor  88 . A resistor  91  and a capacitor  92  are coupled in series with each other across the resistor  86 , the anode of diode  87  being coupled to one end of capacitor  92 . A Zener diode  93  has its anode coupled to ground, and has its cathode coupled to the anode of diode  87 . An operating voltage VCC for the integrated circuit device  82  is produced at the cathode of diode  87 . The cathode of diode  87  is coupled to a VCC pin of the device  82 . 
         [0020]    The device  82  has a further pin COM that is coupled to ground. Two capacitors  96  and  97  each have one end coupled to ground, and the other end coupled to a respective one of two pins CSD and CS of the device  82 . The pin CS is also coupled through a resistor  98  to a circuit node  103  disposed between the transistor  73  and the resistor  74 . A diode  101  has its anode coupled to the cathode of diode  87 , and its cathode coupled to a pin VB on the device  82 . A capacitor  102  has one end coupled to the cathode of diode  102 , and its other end coupled to a pin VS of the device  82 . The pin VS of device  82  is also coupled to the circuit node  103  between transistors  72  and  73 . The device  82  has an output pin HO that is coupled through a resistor  106  to the gate of transistor  72 , and has a further output pin LO that is coupled through a resistor  107  to the gate of transistor  73 . 
         [0021]      FIG. 4  is a timing diagram showing the two waveforms that are respectively produced at the output pins HO and LO of the device  82 . As evident from  FIG. 4 , these waveforms are logical inverses of each other, and each is a square-wave signal with a duty cycle of approximately 50%. That is, the width  111  of each pulse is approximately 50% of the period  112  of the signal. In the disclosed embodiment, the signals at output pins HO and LO each have a frequency of approximately 100 KHz. However, these signals could alternatively have some other frequency, so long as it is substantially higher than the frequency of the power source  12  ( FIG. 1 ), or in other words the frequency of the waveform W 1  ( FIG. 3 ). 
         [0022]    As explained above, the two waveforms shown in  FIG. 4  are each applied to the gate of a respective one of the transistors  72  and  73 . Consequently, referring again to  FIG. 2 , the transistors  72 .and  73  are alternately actuated with a 50% duty cycle, thereby chopping the rectified waveform W 2  ( FIG. 3 ) from the output of-the diode bridge  66 . In  FIG. 3 , waveform W 3  is a diagrammatic representation of the chopped signal present at the circuit node  103  ( FIG. 2 ) between transistors  72  and  73 . The chopped waveform W 3  at circuit node  103 , has a frequency of 100 KHz. But for clarity, the waveform W 3  is shown diagrammatically in  FIG. 3  with a pulse width and a period that correspond to a lower frequency. 
         [0023]    Referring again to  FIG. 2 , the control circuit  31  includes a magnetic amplifier  121  that operates as a form of magnetic switch. The magnetic amplifier  121  includes a coil  122  and a core  123 . The core  123  can switch between two different magnetic states, with a degree of hysterisis. In particular, current flowing in one direction through the coil  122  can switch the core  123  to one state, and current flowing in the opposite direction through the coil  122  can switch the core  123  to its other state. When the core  123  is respectively in its two different magnetic states, the coil  122  respectively exhibits a high impedance and a low impedance to current flow. In other words, when the core  123  is in one state, the coil  122  exhibits a high impedance that permits only a small current flow through the coil  122 . In contrast, when the core  123  is in its other state, the coil  122  exhibits a low impedance that permits a significantly larger current flow through the coil  122 . A sufficient current flow through the coil  122  from left to right in  FIG. 2  can switch the core  123  from a magnetic state in which the coil  122  exhibits a high impedance to a magnetic state in which the coil  122  exhibits a low impedance. Similarly, a sufficient current flow through the coil  122  from right to left in  FIG. 2  can switch the core  123  from a magnetic state in which the coil  122  exhibits a low impedance to a magnetic state in which the coil  122  exhibits a high impedance. 
         [0024]    The circuit  131  includes a smoothing and averaging section  131 . The section  131  includes a diode  133  and a storage coil  134 , the storage coil  134  having a magnetic core associated therewith. The diode  133  has its anode coupled to an output side of the magnetic amplifier  121 , and the coil  134  is coupled between the cathode of diode  133  and the output terminal  53 . The section  131  also includes a further diode  137  and a capacitor  138 . The diode  137  has its cathode coupled to the cathode of diode  133 , and its anode coupled to ground. The capacitor  138  has one end coupled to the output terminal  53 , and its other end coupled to ground. A resistor  141  has one end coupled to the output terminal  54 , and its other end coupled to ground. 
         [0025]    The control circuit  31  includes an integrating section  146 , which in turn includes a shunt regulator  147 . The anode of the shunt regulator  147  is coupled to ground, and the cathode is coupled through a resistor  148  to the supply voltage VCC. A control terminal of the shunt regulator  147  is coupled to the output terminal  54 . The integrating section  146  also includes a capacitor  151 , a resistor  152 , and a capacitor  153 . The capacitor  151  has one end coupled to the cathode of shunt regulator  147 , and its other end coupled to the output terminal  54 . The resistor  152  and the capacitor  153  are coupled in series with each other between the cathode of shunt regulator  147  and the output terminal  54 , with one end of resistor  152  coupled to the cathode of the shunt regulator  147 . A diode  156  has its anode coupled to the cathode of shunt regulator  147 , and its cathode coupled to the anode of diode  133 , and thus to the output side of the magnetic amplifier  121 . 
         [0026]    As discussed earlier, the waveform at circuit node  103  between transistors  72  and  73  is the chopped waveform shown at W 3  in  FIG. 3 .  FIG. 5  is a timing diagram that shows two of the pulses of the waveform W 3 , in a time-expanded scale. Below the waveform W 3  in  FIG. 5  is a diagrammatic representation of when the coil  122  is respectively in its in its high impedance and low impedance states. As discussed earlier, the coil  122  is respectively in its high and low impedance state when the core  123  is respectively in two different magnetic states. 
         [0027]    For the sake of convenience, the discussion that follows will begin at a point in time T 1  ( FIG. 5 ), which is between two of the pulses in waveform W 3 . At time T 1 , the coil  122  is in its high impedance state. Thereafter, a leading edge of a pulse of the waveform W 3  occurs at a time T 2 . However, since the coil  122  is in its high impedance state, it will initially restrict the amount of current that can flow from the circuit node  103  through the coil  122  to the diode  133 . During the time interval  201 , energy from the first part of the pulse will counteract energy that is stored in a magnetic field around the coil  122 , causing the magnetic field to decrease until it is gone, and then causing an increase in a magnetic field of opposite polarity. In due course, the hysterisis of the core  123  will be overcome, and the core  123  will change magnetic state at time T 3 , which has the effect of switching the coil  122  from its high impedance state to its low impedance state. 
         [0028]    Then, for the remainder of the pulse, or in other words during time interval  203 , a larger amount of current can readily flow from the circuit node  103  through the coil  122 , the diode  133  and the coil  134  to the output terminals  53  and  54 . In other words, during the time interval  203 , energy from the pulse is supplied to and flows through the LED  34  ( FIG. 1 ) that is coupled to the output terminals  53  and  54 . When the pulse ends at time T 4 , the current flow induced by the pulse comes to an end. In particular, at time T 4 , the pulse ends because the transistor  72  is turned off, and the transistor  73  is turned on. 
         [0029]    A small reset current flow then commences from the integrating section  146  through the diode  156 , the coil  122 , the transistor  73 , and the resistor  74 . This reset current flow progressively removes the energy that, during time interval  203 , was stored in a magnetic field around the coil  122 . In particular, during time interval  206 , this magnetic field is decreased until it is gone, and then a magnetic field of opposite polarity is created and progressively increases. In due course, the hysterisis of the core  123  will be overcome, and the core  123  will change magnetic state at time T 5 , which has the effect of switching the coil  122  from its low impedance state to its high impedance state. 
         [0030]    During time interval  203 , as discussed above, energy from a pulse of the waveform W 3  is supplied to the outputs  53  and  54  of circuit  31 , and thus to the LED  34 . By increasing or decreasing the length of time interval  203 , it is possible to vary the cumulative amount of current or energy from the pulse that is supplied to the LED  34 . In order to effect such an increase or decrease of the time interval  203 , the time interval  201  is varied. In particular, the pulse has a fixed length, so as the time interval  201  is increased, the time interval  203  is necessarily decreased, and as the time interval  201  is decreased, the time interval  203  is necessarily increased. 
         [0031]    As discussed above, the time interval  201  represents the amount of time that is required to extract energy from and eliminate a magnetic field around the coil  122 , and then replace it with another magnetic field of opposite polarity, until the new magnetic field is sufficiently strong to overcome the hysterisis of the core  123  so that core  123  changes magnetic state at the time T 3 . The length of the time interval  201  is thus based in part of the amount of energy that must be removed from the pre-existing magnetic field around the coil  122 . The amount of energy in this pre-existing magnetic field is a function of the amount of energy or current that the integrating section  146  supplied to the coil  122  during the time interval  208  between a trailing edge of a preceding pulse at time T 0 , and the leading edge of the illustrated pulse at time T 2 . 
         [0032]    The current at the output terminals  53  and  54 , or in other words the current flowing through the LED  34 , also flows through the resistor  141 . As the magnitude of this current increases and decreases, the voltage across resistor  141  respectively increases and decreases, which in turn increases and decreases the voltage between the anode and control terminal of the shunt regulator  147 , thereby influencing the integration performed by the integrating section  146 . That is, the integration carried out by the integrating section  146  is a function of the amount of current that flows through the LED  34 . As the amount of current flowing through LED  34  increases, the voltage across resistor  141  increases, and the integration performed by the integrating section  146  will be affected so as to increase the current flowing through the coil  122  during the time interval  208  between pulses of the waveform W 3 , which in turn increases the amount of energy stored in the magnetic field around the coil  132 . As the amount of energy in this magnetic field increases, the amount of time required to later remove that energy also increases, thereby resulting in an increase in the time interval  201 , and a corresponding decrease in the time interval  203 . The decrease in time interval  203  causes a decrease in the overall amount current that is supplied to the LED  34  from the next pulse of waveform W 3 . 
         [0033]    Conversely, if the current flowing through the LED  34  decreases, the voltage across resistor  141  decreases, the integrating section  146  decreases the amount of reset current flowing through the coil  122  during the time interval  208  between pulses, thereby reducing the amount of energy stored in the magnetic field around coil  122 . As the amount of energy stored in this magnetic field decreases, the amount of time required to later remove the energy decreases, thereby decreasing the time interval  201 . The decrease in time interval  201  inherently increases the time interval  203 , so that more overall energy or current is supplied to LED  34  from the next pulse of waveform W 3 . In this manner, the current flowing through the LED  34  is regulated so as to keep it relatively uniform over time. Waveform W 4  in  FIG. 3  represents the voltage at output terminal  53 . 
         [0034]    With reference to waveform W 3  in  FIG. 3 , it will be noted that the amplitude of the pulses of this waveform progressively increase and decrease over time. It will be recognized that pulses with smaller magnitudes contain less overall energy than pulses with larger magnitudes. Consequently, if the time interval  203  had the same duration for two pulses of different magnitude, the amount of energy supplied to the LED  34  would be greater for the larger pulse than for the smaller pulse. However, since the circuit  31  monitors the amount of current actually flowing through the LED  34 , and varies the length of time interval  203  so as to maintain the current through LED  34  at a uniform level, the circuit  31  automatically compensates for the varying magnitude of the pulses as it regulates the current flow through LED  34 . 
         [0035]    Due in part to the use of a magnetic amplifier, the disclosed circuit achieves current regulation for an LED without the need for a large capacitor, and without modulating the 120V input signal. Consequently, the circuit does not cause a phase difference between the voltage and current, which in turn means the circuit does not need to make a power correction. Further, in the absence of a large components, and components to effect a power correction, the disclosed power supply circuit is relatively simple, and also relatively compact in overall physical size. The circuit is therefore relatively inexpensive, and can also be packaged within the form factor of a standard incandescent bulb. In particular, as mentioned earlier, the power supply circuit can be placed entirely or almost entirely within a standard Edison lightbulb base. Moreover, the voltage obtained at the node between the two switching transistors is about half of what it otherwise would be, thereby avoiding a voltage stress within semiconductor parts, which in turn avoids thermal stress that can shorten the effective lifetime of semiconductor parts. 
         [0036]    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.