Abstract:
The present invention discloses a light emitting device control method for adjusting the brightness of the light emitting device by an AC signal, comprising: receiving a signal having a turn ON angle and converting the signal to a DC signal; obtaining an average of the DC signal level, the average being a function of the turn ON angle; determining a reference voltage of a current source circuit according to the average of the DC signal level; and controlling a current flow through the light emitting device by the current source circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Provisional U.S. Patent Application No. 61/192,610, filed Sep. 18, 2008. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a light emitting device controller circuit with dimming function adjustable by AC signal, wherein the light emitting device is, e.g., an LED (Light Emitting Diode). 
       DESCRIPTION OF RELATED ART 
       [0003]    U.S. Pat. No. 7,358,679 discloses an LED bulb as shown in  FIG. 1 . Its benefit is that it can be readily applied to the light bulb socket designed for CCFL (Cold Cathode Fluorescent Lamp) which has already been provided in a building, without changing the previously built infrastructure for the light bulb socket. However in terms of brightness control, the traditional control mechanism for CCFL can not be applied to the LED bulb disclosed in U.S. Pat. No. 7,358,679. Referring to  FIG. 2 , a traditional method for controlling the brightness of a CCFL is to adjust the turn ON angle of an AC input by a TRIAC (Tri-electro AC) switch device. As shown in the figure, an AC signal  201  is converted to a TRIAC signal  209  with a turn ON angle α which is adjustable. However, in LED application, the brightness of an LED can not be directly controlled by an AC signal; in the circuit of the U.S. Pat. No. 7,358,679 shown in  FIG. 1 , a rectifier  11  converts an AC signal to a DC signal, and the DC signal passes through a low pass filter (LPF)  12  and a DC converter  13  so that it becomes a signal acceptable by the LED circuit  15 . It is only after the AC signal is converted to a DC signal acceptable by the LED circuit  15  that the brightness can be adjusted by an adjustment circuit  14  in  FIG. 1 . In other words, in the circuit shown in U.S. Pat. No. 7,358,679, a user can not adjust the brightness of the LED bulb by adjusting an AC input, but must adjust the brightness of the LED bulb by controlling the adjustment circuit  14 . In practical application, this means that when an AC switch and the LED bulb are located at two different locations (the former on a wall and the latter on a ceiling, for example), one must provide a wiring connecting the adjustment circuit  14  to the location where the AC switch is, which is apparently inconvenient. 
         [0004]    U.S. Pat. No. 7,358,679 further discloses several application circuits, in which the DC converter is either a boost or a buck converter. However, such boost or buck converter has disadvantages in dealing with signals converted from an AC input. 
       SUMMARY OF THE INVENTION 
       [0005]    An objective of the present invention is to provide a light emitting device controller circuit with dimming function adjustable by AC signal. 
         [0006]    Another objective of the present invention is to provide an LED bulb with dimming function adjustable by AC signal. 
         [0007]    Yet another objective of the present invention is to provide a method for adjusting the brightness of a light emitting device by AC signal. 
         [0008]    According to the present invention, brightness can be adjusted at the AC input end directly. It is not required to convert the AC input signal to a DC signal, and to adjust the DC signal by an additional adjustment circuit. 
         [0009]    In order to achieve the foregoing objective, the present invention provides a light emitting device controller circuit with dimming function adjustable by AC signal, comprising a controller which controls an operation of at least one power transistor to convert an input voltage to an output voltage to be supplied to a light emitting device, characterized in that the controller comprises a dimming circuit for controlling a current flow through the light emitting device, the dimming circuit comprising: a signal conversion circuit receiving a signal having a turn ON angle and converting the signal to a DC signal; an average circuit obtaining an average of the DC signal level, the average being a function of the turn ON angle; and a current control circuit for controlling a current flow through the light emitting device according to the average of the DC signal level. 
         [0010]    In another aspect, the present invention provides a light emitting device controller circuit with dimming function adjustable by AC signal, comprising a controller which controls an operation of at least one power transistor to convert an input voltage to an output voltage to be supplied to a light emitting device, characterized in that the controller comprises a dimming circuit for controlling a current flow through the light emitting device, the dimming circuit comprising: a signal conversion circuit receiving a signal having a turn ON angle and converting the signal to a DC signal, the DC signal having a duty which is a function of the turn ON angle; a duty to voltage conversion circuit converting the duty of the DC signal to a voltage; and a current control circuit for controlling a current flow through the light emitting device according to the voltage converted from the duty of the DC signal. 
         [0011]    In another aspect, the present invention provides an LED bulb with dimming function adjustable by AC signal, comprising: a rectifier receiving an AC voltage and rectifying the AC voltage to generate a rectified voltage; a DC converter providing an output voltage according to the rectified voltage; and an LED circuit coupled to the output voltage, wherein the DC converter includes a dimming circuit for controlling a current flow through the light emitting device, the dimming circuit comprising: a signal conversion circuit receiving a signal having a turn ON angle and converting the signal to a DC signal; an average circuit obtaining an average of the DC signal level, the average being a function of the turn ON angle; and a current control circuit for controlling a current flow through the light emitting device according to the average of the DC signal level. 
         [0012]    In another aspect, the present invention provides an LED bulb with dimming function adjustable by AC signal, comprising: a rectifier receiving an AC voltage and rectifying the AC voltage to generate a rectified voltage; a DC converter providing an output voltage according to the rectified voltage; and an LED circuit coupled to the output voltage, wherein the DC converter includes a dimming circuit for controlling a current flow through the light emitting device, the dimming circuit comprising: a signal conversion circuit receiving a signal having a turn ON angle and converting the signal to a DC signal, the DC signal having a duty which is a function of the turn ON angle; a duty to voltage conversion circuit converting the duty of the DC signal to a voltage; and a current control circuit for controlling a current flow through the light emitting device according to the voltage converted from the duty of the DC signal. 
         [0013]    In another aspect, the present invention provides a light emitting device control method for adjusting the brightness of the light emitting device by an AC signal, comprising: receiving a signal having a turn ON angle and converting the signal to a DC signal; obtaining an average of the DC signal level, the average being a function of the turn ON angle; determining a reference voltage of a current source circuit according to the average of the DC signal level; and controlling a current flow through the light emitting device by the current source circuit. 
         [0014]    In another aspect, the present invention provides a light emitting device control method for adjusting the brightness of the light emitting device by an AC signal, comprising: receiving a signal having a turn ON angle and converting the signal to a DC signal, the DC signal having a duty which is a function of the turn ON angle; generating a voltage according to the duty of the DC signal; determining a reference voltage of a current source circuit according to the voltage generated according to the duty of the DC signal; and controlling a current flow through the light emitting device by the current source circuit. 
         [0015]    The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below, with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic circuit diagram showing the internal circuit of an LED bulb according to prior art. 
           [0017]      FIG. 2  shows how an AC signal is converted to a TRIAC signal having a turn ON angle. 
           [0018]      FIG. 3  shows an LED bulb according to the present invention. 
           [0019]      FIG. 4  shows an embodiment of the present invention. 
           [0020]      FIGS. 5A-5C  show three embodiments of the DC converter  33  and the LED circuit  35 , respectively. 
           [0021]      FIG. 5D  shows that the DC converter  33  may be a synchronous boost converter. 
           [0022]      FIGS. 6A-6C  show three possible waveforms of the input voltage VIN, respectively. 
           [0023]      FIG. 7  shows an embodiment of the dimming circuit  330 . 
           [0024]      FIG. 8  shows a more detailed embodiment of the dimming circuit  330 . 
           [0025]      FIG. 9A  shows two possible waveforms of the input voltage VIN, VIN 1  and VIN 2 . 
           [0026]      FIG. 9B  shows the signal waveform at the node A after the input voltage VIN has been processed by the operational amplifier OP 1 . 
           [0027]      FIGS. 9C-9F  show other possible waveforms generated by the signal conversion circuit  3301 . 
           [0028]      FIG. 10  shows another embodiment of the dimming circuit  330 . 
           [0029]      FIGS. 11 and 12  show that the signal having a turn ON angle can be obtained directly from the AC signal. 
           [0030]      FIG. 13  shows an embodiment of the transformer  28 . 
           [0031]      FIGS. 14 and 15  show embodiments wherein the transformer  28 , the bridge rectifier  31  and the low pass filter  32  are replaced by an AC-DC converter  29 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]      FIG. 3  shows the basic concept of the present invention, wherein the DC converter  33  receives a signal having a brightness adjustment function resulting from an AC source, i.e., the brightness is determined by the AC signal, in contrast to the prior art shown in  FIG. 1  wherein the brightness is determined by an adjustment circuit  14 . Furthermore, the present invention has a simpler circuit than the prior art. 
         [0033]    Referring to  FIG. 4 , in one embodiment, an AC power is (but does not necessarily have to be) processed by a TRIAC device  26  outside of the light bulb, and transformed by a transformer  28 ; the transformed voltage is rectified by a bridge rectifier  31  inside the light bulb. Certainly, it can be embodied in such a way that the transformer  28 , or even the TRIAC device  26 , is included inside the light bulb. If an AC switch and the LED bulb is located at two different locations (the former on a wall and the latter on a ceiling, for example), the TRIAC device  26  can be located at a location near the AC switch so that it is convenient to adjust the brightness. The bridge rectifier  31  can be a full bridge rectifier or a half bridge rectifier. The rectified voltage passes through a low pass filter  32  and is then inputted to a DC converter  33 . The low pass filter  32  for example can be circuit including a diode and a capacitor connected in series. In this invention, since the bridge rectifier  31  already includes diodes, the low pass filter  32  can include only a capacitor, without a diode. An example of the bridge rectifier  31  and the low pass filter  32  is disclosed in FIG. 5 of U.S. provisional application No. 61/192,610. 
         [0034]    The DC converter  33  receives an input voltage Vi and converts it to an output voltage Vo. In one embodiment, as shown in  FIG. 4 , the LED circuit  35  is coupled between the input voltage Vi and the output voltage Vo, not between the output voltage Vo and ground. The reason for this is because there may not be a fixed relationship between the voltage required by the LED circuit  35  and the input voltage Vi. For example, depending on the power or brightness requirement of a product, the number of LEDs in the LED circuit  35  may be different. Thus, the voltage required by the LED circuit  35  may be higher or lower than the input voltage Vi. If the LED circuit  35  is coupled between the output voltage Vo and ground, then the LED circuit  35  operates according to the output voltage Vo, and in this case if the DC converter  33  is a boost converter, it can not handle the situation where Vo&lt;Vi; if the DC converter  33  is a buck converter, it can not handle the situation where Vo&gt;Vi. In the embodiment shown in the figure, the LED circuit  35  operates by the voltage (Vo−Vi), which can be higher or lower than Vi, but the DC converter  33  can handle both cases [(Vo−Vi)&lt;Vi and (Vo−Vi)&gt;Vi] by a boost structure. In other words, by coupling the LED circuit  35  between the output voltage Vo and the input voltage Vi, a boost converter can achieves both buck and boost conversion effects. But of course, one can couple the LED circuit  35  between the output voltage Vo and ground, and uses one of the arrangements as shown in  FIGS. 5A-5C , i.e., the DC converter  33  may be a boost converter, a buck converter or a buck-boost converter according to the relationship between the operational voltage of the LED circuit  35  and the input voltage Vi. All such modifications should belong to the scope of the present invention. 
         [0035]    The DC converter  33  shown in  FIG. 4  is an asynchronous boost converter which comprises a controller  331 , a power transistor  332 , an inductor L and a diode  333 . The controller  331  controls the operation of the power transistor  332 , with the assistance from the inductor L and the diode  333 , to convert the input voltage Vi to the output voltage Vo. However as shown in  FIG. 5D , the diode  333  can be replaced by a power transistor  334  such that the DC converter  33  becomes a synchronous boost converter; certainly, this should also belong to the scope of the present invention. In addition, the controller  331  can be an integrated circuit by itself, or can be integrated with other devices such as with the power transistor  332 , or with the power transistors  332  and  334 . The resistor Rcs shown in the figure is for detecting the LED current for feedback control. 
         [0036]    One important feature of the present invention is that the controller  331  includes a dimming circuit  330 . The dimming circuit  330  is capable of receiving a signal having a turn ON angle (such as the shark fin signal VIN shown in  FIG. 4 ) and adjusting the brightness according to the turn ON angle. The dimming circuit  330  can receive signals in the forms other than that shown in  FIG. 4 . For example, please refer to  FIGS. 6A-6C ; when an AC power is processed by the TRIAC device  26  and rectified by a full bridge rectifier  31 , the resultant signal is as shown in  FIG. 6A ; when the AC power is processed by the TRIAC device  26  and rectified by a half bridge rectifier  31 , the resultant signal is as shown in  FIG. 6B ; when the AC power is not processed by the TRIAC device  26  and is rectified by a half bridge rectifier  31 , the resultant signal is as shown in  FIG. 6C . The dimming circuit  330  can receive any of the above signal forms and adjust the LED brightness according to the turn ON angle α. In other words, a user can determine the LED brightness at the AC input end by adjusting the turn ON angle α of an AC input signal. In practical application, the AC switch and the LED bulb can be located at two different locations, and a device for adjusting the turn ON angle α can be located near the AC switch, so that it is convenient to adjust the brightness. 
         [0037]      FIG. 7  shows an embodiment of the dimming circuit  330  which includes a signal conversion circuit  3301 , a duty to voltage conversion circuit  3302 , and a current control circuit  3303 . The function of the signal conversion circuit  3301  is to obtain information relating to the turn ON angle of the input signal VIN; it receives the input signal VIN having the turn ON angle and converts it to a DC signal relating to the turn ON angle. In this embodiment, the duty of the DC signal is a function of the turn ON angle. The duty to voltage conversion circuit  3302  converts the duty of the DC signal to a voltage. The current control circuit  3303  controls a current flow through the LED according to the voltage converted from the duty, to determine the brightness of the LEDs. 
         [0038]    Referring to  FIG. 8  in conjunction with  FIGS. 9A and 9B , a more detailed circuit embodiment of the dimming circuit  330  is illustrated. For simplicity and convenience, let us assume that the AC power is first processed by the TRIAC device  26  and rectified by a full bridge rectifier  31 , and the operational amplifier in the dimming circuit  330  operates by an operational voltage 1.2V; however, certainly the operational voltage can be any number. As shown in the figure, the operational amplifier OP 1  receives an input signal VIN, which for example is a shark fin signal as shown in  FIG. 6A , but as shown in  FIG. 9A , due to different AC power specifications (such as 110V or 220V specification) or other reasons (such as different transformation ratio by different transformers  28 ), the input signal VIN may be of different levels as shown by VIN 1  and VIN 2 . It will be understood from the following description that one advantage of the present invention is that different AC levels do not affect the dimming function. 
         [0039]    The operational amplifier OP 1  receives the input signal VIN and generates a square wave signal as shown in  FIG. 9B , at its output (node A). The amplitude of the square wave signal is equal to the operational voltage of the operational amplifier OP 1 , and the duty ratio D % of the square wave signal is equal to the turn ON angle α of the input signal VIN divided by its period T, i.e., D %=α/T. A resistor R 330  and a capacitor C 330  form an RC (Resistor-Capacitor) circuit  3302  which converts the duty to a voltage. A DC voltage having a level of 1.2V*D % is generated at the node B. A current source circuit  3303  constructed by an operational amplifier OP 2 , a bipolar transistor BJT and a resistor R uses the voltage 1.2V*D % as a reference voltage such that the current flow through the LEDs is proportional to (1.2V*D %)/R. In other words, a user can adjust the brightness of the LEDs at the AC input end by adjusting the turn ON angle α. The transistor BJT shown in the figure is a bipolar transistor, but it can be replaced by a MOS transistor. And, depending on the capacitance of the capacitor C 330 , when the controller  331  is an integrated circuit, the capacitor C 330  can be an external device outside of the integrated circuit, or integrated into the integrated circuit. 
         [0040]    In comparison with prior art, besides the advantage that the brightness can be directly adjusted at the AC input end, the present invention is also advantageous in that its circuit is simpler. The present invention does not require the complicated adjustment circuit  14 ; it only requires adding an operational amplifier OP 1  and an RC circuit  3302  to the controller  331  (the current source circuit  3303  is also required in the prior art, so this part of the circuit is not an increased overhead). Furthermore, because the LED brightness is only relevant to the duty ratio D % (i.e., only relevant to the turn ON angle α of the input signal VIN) but not relevant to the original AC voltage level, the same controller  331  can be applied to different AC power environments; an unstable AC power source does not affect the LED brightness, so the flashing problem due to power instability is also solved. Thus, the present invention is apparently superior to the prior art. 
         [0041]    The embodiment shown in  FIG. 8  and  FIGS. 9A-9B  is not the only way to embody the present invention. In the spirit of the present invention, the input signal VIN having the turn ON angle α does not have to be converted to a square wave; it suffices as long as the converted DC signal is a function of the turn ON angle α. For example, the signal conversion circuit  3301  can convert the input signal VIN to any forms shown in  FIGS. 9C-9F , or many other forms. When the converted DC signal does not have a clearly identifiable duty (such as the waveform shown in  FIG. 9F ), as shown in  FIG. 10 , an average circuit  3304  can be employed to obtain an average signal level of the DC signal. In this way, the brightness of the LEDs can be controlled according to the turn ON angle α as well. The average circuit  3304  for example can be an RC circuit. 
         [0042]    Note that what is shown in  FIG. 4  is not the only way to obtain the signal VIN. The input signal VIN having the turn ON angle α does not have to come from the bridge rectifier  31 ; it can be directly obtained from an AC signal. For example, as shown in  FIG. 11 , after the AC signal is processed by the TRIAC device  26 , the signal can be converted to the input signal VIN by photo coupling. Or, as shown in  FIG. 12 , it can be arranged so that in voltage transformation by the transformer  28 , the power and the dimming signal are separated to two signals. To this end, the transformer  28  can include a structure as shown in  FIG. 13 , wherein the upper windings obtain the dimming signal and generate the signal VIN, while the lower windings obtain the power and generate the input voltage Vi. In this case the upper windings can have a smaller number of turns. Moreover, because the present invention allows to obtain the signal having the turn ON angle directly from an AC signal, the transformer  28 , the bridge rectifier  31  and the low pass filter  32  can be replaced by an AC-DC converter  29 , as shown in  FIGS. 14 and 15 . 
         [0043]    The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, the present invention can be applied to any light emitting device whose brightness can be adjusted by controlling a current flow therethrough, not limited to LEDs. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.