Patent Publication Number: US-2011068693-A1

Title: Lighting apparatus and the method for using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lighting apparatus and method for using the same, and more particularly to an apparatus that is powered by a regulated AC power or a DC power. 
     2. Description of the Related Art 
     Due to their low power consumption, high brightness, small volume and long life, light emitting diodes (LED) have become widely applied in the lighting field. Among a variety of LED applications, most are powered by a DC voltage regulated from a normal AC power, such as 110V, 60 Hz.  FIG. 1  shows a conventional power supply  10  which is composed of a DC-DC converter or a switched regulator. Referring to  FIG. 1 , the power supply  10  receives an AC power input first, and then filters noise through a bridge rectifier  12  and a capacitor C filter  to provide a non-regulated DC voltage as the input voltage V in  of the DC-DC converter  14 . The DC-DC converter  14  may be a forward converter for performing a voltage drop. The converter  14  includes a transformer  142 , diodes D 1  and D 2 , an inductor L and a capacitor C. The converter  14  further includes an isolator  144  for forwarding error signals V error  from the error amplifier  146  to the modulator  148 . 
     Due to the switching characteristic of the DC-DC converter, the above converter extracts current from the power source in a pulse-by-pulse manner, thus causing some drawbacks, such as a reduction of the power factor. To achieve the optimization of efficiency of the AC power, the input current extracted from the AC power would ideally be in the sine wave form and in phase with the AC power. Such so-called unity power factor is usually generated in a pure loading condition. However, the characteristic of the above DC-DC converter and generated pulse current extraction results in the power factor of the apparatus in  FIG. 1  being less than the unity power factor, and thus does not satisfy the demand of optimized power efficiency. In addition, the capacitor C filter  between the bridge rectifier  12  and the DC-DC converter  14  further weakens the power factor. 
     Taiwan Patent Number I220047 discloses an LED driving circuit, which can directly drive the LED in the positive cycle of the supply voltage without filtering capacitors.  FIG. 2  shows the structure of the LED driving circuit. Referring to  FIG. 2 , the driving circuit comprises a power supply V s , a bridge rectifier  22 , a current-oriented control circuit  24  composed of a plurality of current control units I 1 -I n , and a voltage detecting circuit  20  used to detect the voltage level of the power supply V s . When the AC voltage is determined by the voltage detecting circuit  20  to be greater than the threshold voltage of the diode D 1 , the current control unit I 1  is activated to turn on the LED D 1 . Next, when the AC voltage is determined by the voltage detecting circuit  20  to be greater than the threshold voltage of the diode D 1  and diode D 2 , the current control unit I 1  is off and another current control unit I 2  is activated to turn on the diodes D 1  and D 2 . Under such a structure, since the diodes D 1 -D n  are repeatedly turned on in different current paths, if a pulse width modulation is used to control the brightness, the design of the current-oriented control circuit  24  is complicated, and D 1 -D n  fail to have the same brightness level. 
     To achieve maximum efficiency of the AC power and to provide a uniform and adjustable light source, it is necessary to propose a lighting apparatus and method to meet the demand of the market. 
     SUMMARY OF THE INVENTION 
     The lighting apparatus in accordance with one embodiment of the present invention receives an AC power as its input power and comprises an LED array and a driving circuit. The LED array has a plurality of LED sets connected in parallel. The driving circuit includes a plurality of outputs corresponding to the LED sets, and each of the outputs has a predetermined value to control the brightness of the corresponding LED set. Each of the LED sets is turned on in sequence in accordance with the output of the driving circuit and the amplitude of the regulated AC power, and is turned off in accordance with the predetermined value. 
     The lighting apparatus in accordance with one embodiment of the present invention receives a DC power as its input power and comprises an LED array and a driving circuit. The LED array has a plurality of LED sets connected in parallel. The driving circuit includes a plurality of outputs corresponding to the LED sets to control the brightness of the corresponding LED set. Each of the LED sets is selectively turned on in accordance with the output of the driving circuit and is turned off in accordance with a predetermined value of the output of the driving circuit, and the LED sets are arranged in accordance with the number of LED components in the LED set in descending order or ascending order. 
     The present invention proposes a lighting method for turning on an LED array in sequence. The LED array receives an AC power as an input power, and has a plurality of LED sets connected in parallel. The method comprises the steps of: providing a first LED set with a first driving signal; turning on the first LED set in accordance with a first amplitude of the AC power; cutting off the current of the first LED set when the current of the first LED set reaches a first predetermined value; providing a second LED set with a second driving signal; turning on the second LED set in accordance with a second amplitude of the AC power; and cutting off the current of the second LED set when the current of the second LED set reaches a second predetermined value. The number of LED components in the first LED set is less than the number of LED components in the second LED set when the first amplitude is less than the second amplitude, while the number of LED components in the first LED set is greater than the number of LED components in the second LED set when the first amplitude is greater than the second amplitude. 
     The present invention proposes a lighting method for turning on an LED array in sequence. The LED array receives a DC power as an input power, and the LED array has a plurality of LED sets connected in parallel. The method comprises the steps of: turning on a first LED set in accordance with an enable signal; cutting off the current of the first LED set when the current of the first LED set reaches a first predetermined value; turning on a second LED set in accordance with a first timing signal; cutting off the current of the second LED set when the current of the second LED set reaches a second predetermined value; and turning on a third LED set in accordance with a second timing signal. The number of LED components connected in series in each of the first, second and third LED sets is in descending order or ascending order. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described according to the appended drawings in which: 
         FIG. 1  shows a conventional power supply which is composed of a DC-DC converter or a switched regulator; 
         FIG. 2  shows a structure of the LED driving circuit; 
         FIG. 3  shows a block diagram of the lighting apparatus incorporating a power supply device in accordance with one embodiment of the present invention; 
         FIG. 4  shows a flow chart of serially turning on an LED array in accordance with one embodiment of the present invention; 
         FIG. 5  shows the timing of a turn-on sequence; 
         FIG. 6  shows another structure of an LED array in accordance with one embodiment of the present invention; 
         FIG. 7  shows an arrangement of LED bars in an LED array in accordance with one embodiment of the present invention; 
         FIG. 8  shows another arrangement of LED bars in an LED array in accordance with one embodiment of the present invention; 
         FIG. 9  shows another structure in contrast to the structure in  FIG. 3 ; 
         FIG. 10  shows a turn-on timing of an LED array in accordance with the AC power; 
         FIG. 11  shows a structure diagram of a lighting apparatus in accordance with one embodiment of the present invention; and 
         FIG. 12  shows a flow chart of serially turning on the LED array in accordance with one embodiment of the present invention. 
     
    
    
     PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
       FIG. 3  shows a block diagram of the lighting apparatus  32  incorporating a power supply device  30  in accordance with one embodiment of the present invention. The lighting apparatus  32  receives an AC power V AC,reg  regulated by the power supply device  30  as the input power thereof. The power supply device  30  includes a rectifier  302  for receiving an AC power input. To supply a positive voltage of the lighting apparatus  32 , the rectifier  302  can be a full-wave rectifier or a half-wave rectifier. The power supply device  30  can also include a capacitor C 1  coupled to the rectifier  302  for filtering high-frequency noises of the AC power input. 
     Referring to  FIG. 3 , the lighting apparatus  32  includes an LED array  322  and a driving circuit  324 . In one embodiment, the LED array  322  is assembled in parallel with a plurality of LED bars  326 ,  328  and  330 , and each LED bar comprises a plurality of LED components connected in series. The driving circuit  324  includes a plurality of outputs OUT 0 , OUT 1 , . . . , OUT n , each corresponding to one LED bar, and used to control the brightness of the corresponding LED bar with a predetermined value. In one embodiment, the predetermined value is a fixed current value and a fixed turn-on duration. By changing the current and turn-on duration, the brightness of the LED bars can be efficiently adjusted. 
     Referring to  FIG. 3 , the power V DD  of the driving circuit  324  is derived from a divided voltage of the AC power V AC, reg  and a filter circuit. The divided voltage and filter circuit include resistors R 1 , R 2  and C 2 . Alternatively, the power V DD  of the driving circuit  324  is derived from a battery. In addition, each LED bar of the LED array  322  includes a resistor coupled to the AC power V AC, reg  and the driving circuit  324 . The resistor is used to protect the normal operation of the LED bar, such as over-current or under-current protection. In one embodiment, each LED bar of the LED array  322  includes a switch component coupled to the AC power V AC, reg  and the driving circuit  324 . The switch component is used to implement dimming control or to perform protection under an abnormal operation. 
       FIG. 4  shows a flow chart of serially turning on the LED array in accordance with one embodiment of the present invention, where the LED array receives a regulated AC power as an input power. In step S 40 , a first driving signal of a first LED set is provided. In step S 42 , the first LED set is turned on in accordance with the first amplitude of the AC power. In step S 44 , when the current of the first LED set reaches a first predetermined value, the current of the first LED set is cut off. In step S 46 , a second driving signal of a second LED set is provided. In step S 48 , the second LED set is turned on in accordance with the second amplitude of the AC power. In step S 49 , when the current of the second LED set reaches a second predetermined value, the current of the second LED set is cut off. It is noted that when the first amplitude is less than the second amplitude, the number of the LED components connected in series in the first LED set is less than the number of the LED components connected in series in the second LED set, while when the first amplitude is greater than the second amplitude, the number of the LED components connected in series in the first LED set is greater than the number of the LED components connected in series in the second LED set. 
     The following describes an operation of one embodiment of the present invention. First, a regulated AC power V AC, reg  is used to provide a power supply of the LED array  322 , while the AC power V AC, reg  can be a full-wave rectifier or a half-wave rectifier. Next, following the amplitude of the AC power V AC, reg  and the turn-on sequence of the outputs OUT 0 , OUT 1 , . . . , OUT n , the LED bars  326 ,  328  and  330  are turned on in sequence. 
       FIG. 5  shows the timing of a turn-on sequence. First, when t&lt;t 1 , the OUT 0  of the driving circuit  324  is activated, which represents that the first LED bar  326  is ready to be turned on. Next, when t=t 1 , the amplitude of the AC power V AC, reg  is greater than the voltage drop of the LED components in the LED bar  326  and the voltage drop between OUT 0  of the driving circuit  324  and Gnd, and therefore the LED components in the LED bar  326  are turned on. Subsequently, when the current of the first LED bar  326  reaches a predetermined value of OUT 0  that is, the current of the LED bar  326  reaches the fixed current and fixed turn-on duration, the current of the first LED bar  326  is cut off. Meanwhile, the OUT 1  of the driving circuit  324  is activated, which represents that the second LED bar  328  can be turned on. 
     When t=t 2 , the amplitude of the AC power V AC, reg  is greater than the voltage drop of the serially-connected LEDs in the second LED bar and the voltage drop between the OUT 1  of the driving circuit  324  and Gnd, and thus the second LED bar  328  is turned on and the LED components therein are turned on as well. When the current of the second LED bar  328  reaches a predetermined value of OUT 1 , the current of the second LED bar  328  is cut off. Similarly, when t=t 3  to t 6 , the LED array  322  is turned on or turned off in sequence in accordance with the amplitude of the AC power V AC, reg , the status of OUT 0  OUT 1 , . . . , OUT n  of the driving circuit  324  and the predetermined value. Due to the function of the internal current detecting mechanism of the driving circuit  324 , only a single LED bar or more are turned on each time, and thus the purpose of reducing entire power loss can be achieved. In addition, when the frequency of the input AC power is 60 Hz, each LED bar can be turned on in sequence 120 times per second. Because of the residual images in the human eye, the visual effect of the present invention is better than that of the conventional Cold Cathode Fluorescent Lamp (CCFL). 
     In addition, in one embodiment of the present invention, the driving circuit  324  includes a synchronous tracking unit  332 , which is used to track the amplitude and cycle of the AC power V AC, reg  for adjusting the turn-on sequence and operating frequency of the OUT 0 , OUT 1 , . . . , OUT n . In one embodiment, the synchronous tracking unit  332  detects the first and second turn-on status of the first LED bar  326  to synchronously track the cycle of the AC power V AC, reg  for adjusting the operating frequency outputted by the driving circuit  324  to be consistent with the AC power V AC, reg , and thus the turn-on sequence controlled by the driving circuit  324  is adjusted as well. 
       FIG. 6  shows another structure of an LED array in accordance with one embodiment of the present invention. In contrast to the LED array  322  in  FIG. 5 , in which the LED bars  326 ,  328  and  330  are arranged in accordance with the amplitude of the AC power V AC, reg , the LED columns in  FIG. 6  are cascaded in series by LED bars having the number of LED components from the least to the most, and the LED array is shaped like a rectangle. Alternatively, LED columns are cascaded in series by LED bars having the number of LED components from the most to the least. 
     Furthermore, in another embodiment, the LED columns in  FIG. 7  are cascaded in series by LED bars having the number of LED components from the least to the most, and the LED array is shaped like a triangle. Alternatively, the LED columns in  FIG. 8  are cascaded in series by LED bars having the number of LED components from the most to the least. 
       FIG. 9  shows another structure in contrast to the structure in  FIG. 3 , where an LED set  91  is assembled with a single LED bar, while an LED set  92  is assembled with two LED bars connected in parallel, each of which is assembled with three LED components. Namely, each LED set can be assembled with at least one LED bar connected in parallel, and the LED bar is assembled with at least one LED component connected in series. 
     In addition, the LED set in the LED array can be turned on not only in the fully positive voltage cycles of the AC power V AC, reg , but also in the partially positive voltage cycles of the AC power V AC, reg .  FIG. 10  shows a turn-on timing of an LED array  99  in accordance with the AC power V AC, reg . The turn-on range of each LED set of the LED array  99  is limited to the partially positive voltage cycle of the AC power V AC, reg . 
     The lighting apparatus  32  in  FIG. 3  receives a regulated AC power V AC, reg  from the power supply device  30  as an input power. However, the lighting apparatus  32  can also receive a DC power as its input power.  FIG. 11  shows another structure of lighting apparatus  100  in accordance with one embodiment of the present invention. The lighting apparatus  100  receives a DC power supply V ic  from a battery, from a linear regulator, or from a DC-DC converter as an input power. Referring to  FIG. 11 , the LED apparatus  100  includes an LED array  102  and a driving circuit  104 . The LED array  102  can be arranged like the structures shown in  FIG. 5  to  FIG. 8 . 
       FIG. 12  shows a flow chart of serially turning on the LED array in accordance with one embodiment of the present invention, where the LED array receives a DC power supply as its input power. In step S 110 , a first LED set is turned on in accordance with an enable signal. In step S 112 , when the current of the first LED set reaches a first predetermined value, the current of the first LED set is cut off. In step S 114 , a second LED set is turned on in accordance with a first timing signal. In step S 116 , when the current of the second LED set reaches a second predetermined value, the current of the second LED set is cut off. In step S 118 , a third LED set is turned on in accordance with a second timing signal. It is noted that the number of the LED components connected in series in the first, second and third LED sets is in descending order or ascending order. 
     The following describes the operations of the structure in  FIG. 11 . First, the LED array  102  receives a DC power V DC  as its input power. Next, the turn-on sequence of the LED bars  106 ,  107  and  108  of the LED array  102  is determined by the enable signal EN outputted by the driving circuit  104  and clock signals OUT 0 , OUT 1 , . . . , OUT n , not by the amplitude of the DC power V DC . When the current of the first LED bar reaches a predetermined value, e.g., a fixed current and a fixed turn-on duration, the current of the LED bar is cut off. 
     In the above embodiments, adjusting the brightness of the LED bars or LED sets in the LED array  102  is performed by changing the fixed current or changing the fixed turn-on duration. However, to further reduce the power loss of the lighting apparatus, when the LED array  102  is to be dimmed, the LED bars or LED sets maintain a fixed turn-on duration but only change the magnitude of the driving current, thereby achieving the purpose of dimming or mixing RGB colors. 
     The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.