Patent Publication Number: US-9848472-B1

Title: LED device with energy compensation

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an LED device and, more particularly, to an LED device with energy compensation. 
     2. Description of Related Art 
     Typically, an LED device is provided with a plurality of LEDs that are driven by an LED driver for illumination. The linear LED driver is known as one of the most popular LED drivers for sequentially driving the LEDs. With the linear LED driver, the waveform of the total consumed energy (or total consumed current) of the LED device is close to a sinusoid, so as to match the shape and phase of an AC power (voltage) provided from a power source, thereby achieving a high power factor (PF) value.  FIG. 1(A)  is a schematic diagram illustrating the structure of a prior linear LED device  100 . As shown in  FIG. 1(A) , the prior linear LED device  100  includes a plurality of LEDs  101  to  104  and a linear LED driver  105 .  FIG. 1(B)  is a schematic diagram illustrating the waveform of the total consumed energy, as denoted by energy_total, of the prior linear LED device  100  in operation. As shown in  FIG. 1(B) , the LED driver  105  sequentially turns on or off the LEDs  101  to  104 , and the waveform of the total consumed current of the prior linear LED device  100  is close to a sinusoid. 
     However, such a prior linear LED device  100  is likely to generate a flicking phenomenon, which indicates that the difference between the peak and valley of the consumed powers is huge, resulting in the flicking phenomenon when the prior linear LED device  100  is in operation. 
     In general, the flicking index indicates the flicking phenomenon. When the flicking index is high, the flicking phenomenon is significant. The flicking index can be presented as the following formula:
 
flicking index=area1/(area1+area2);
 
     wherein, area1 means an area surrounded by the consumed power value higher than an average value, and area1 means an area surrounded by the consumed power lower than the average value. 
     Although there are several schemes proposed to solve the flicking problem, for example, controlling the waveform of the total consumed energy of the LED device to be close to a constant waveform or a DC-like waveform, these schemes are not satisfactory and may cause a low PF value due to the waveform of the consumed current provided from the power source not being a sinusoid-like waveform. 
     Therefore, there is a need to provide an improved LED device for achieving a high PF value and decreasing the flicking. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an LED device with energy compensation, which comprises: a first LED driving circuit including a first LED driver and a plurality of first LED groups controlled by the first LED driver, wherein each of the first LED groups includes at least one LED; a second LED driving circuit including a second LED driver and a plurality of second LED groups controlled by the second LED driver, wherein the second LED driving circuit is connected in parallel with the first LED driving circuit, and each of the second LED groups includes at least one LED; and a capacitor having a first terminal coupled to the second LED driving circuit, wherein a power source is coupled to the first LED driving circuit, the second LED driving circuit, and the first terminal of the capacitor for applying an AC power to the first terminal of the capacitor. Thus, the capacitor and the second LED driving circuit can influence the waveform of the total consumed current of the LED device so as to minimize the difference between the peak and valley of the consumed power, and enable the phase of the waveform of the total consumed current to be consistent with that of the AC power provided from the power source. 
     In an embodiment, when PF value is equal or close to 1, the AC power is an voltage with a waveform including an increasing period corresponding to the phase of 0 to 90 degrees, and a decreasing period corresponding to the phase of 90 to 180 degrees. 
     Preferably, in the increasing period, the capacitor receives the energy from the power source, so that the current flowing through the first LED groups is influenced. 
     Preferably, in the decreasing period, the second. LED driver draws energy form the capacitor so as to provide a compensation current, and a part of the total consumed current of the LED device is increased due to an influence from the compensation current. 
     In an embodiment, the power source is coupled to a first terminal of the capacitor via a front LED, and a waveform of the capacitor current is influenced by the front LED. 
     In an embodiment, the compensation current has a phase inconsistent with that of the AC power source. 
     In an embodiment, a waveform of the total consumed current has a phase consistent with that of the AC power source. 
     In an embodiment, a number of the first LED groups is m, and a number of the second LED groups is n, wherein m and n are positive integer greater than one, and the 1st to m-th first LED groups correspond to 1st to m-th first driving energy thresholds, and the 1st to n-th second LED groups correspond to 1st to n-th second driving energy thresholds, and the 1st to m-thirst driving energy thresholds are monotonic, the 1st to n-th second driving energy thresholds are monotonic. 
     Preferably, the n-th second driving energy threshold is lower than the m-th first driving energy threshold. 
     In an embodiment, the first LED driver includes a plurality of amplifiers with a number corresponding to that of the first LED groups, and the second LED driver includes a plurality of amplifiers with a number corresponding to that of the second LED groups. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a schematic diagram illustrating the structure of a prior LED device; 
         FIG. 1(B)  is a schematic diagram illustrating the total consumed energy of the prior LED device in operation; 
         FIG. 2(A)  is a circuit diagram illustrating an LED device with energy compensation according to an embodiment of the invention; 
         FIG. 2(B)  is another circuit diagram illustrating an LED device with energy compensation according to an embodiment of the invention; 
         FIG. 2(C)  is still another circuit diagram illustrating an LED device with energy compensation according to an embodiment of the invention; 
         FIG. 3  is a schematic diagram illustrating the waveforms of the capacitor current, the driving current and the compensation current of the LED device in operation; 
         FIG. 4(A)  is a schematic diagram illustrating the waveform of the total consumed energy of the LED device according to an embodiment of the invention, in comparison with that of the prior LED device; 
         FIG. 4(B)  is another schematic diagram illustrating the waveform of the total consumed energy of the LED device according to an embodiment of the invention; and 
         FIG. 5  is a schematic diagram illustrating the detailed structures of the first LED driving circuit and the second LED driving circuit according to an embodiment in the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It is noted that, the term “coupled” hereinafter used in the invention may be representative of “directly connected” or “indirectly connected”. 
       FIG. 2(A)  is a circuit diagram illustrating an LED device with energy compensation  10  according to an embodiment of the invention. The LED device with energy compensation  10  includes a first LED driving circuit  20 , a second LED driving circuit  30 , and a capacitor  40 . 
     The first LED driving circuit  20  includes a first LED driver  21  and a plurality of first LED groups L 1  to Lm, where m is a positive integer greater than one, and the first LED groups L 1  to Lm are driven by the first LED driver  21  for being turned on, and each of the first LED groups L 1  to Lm includes at least one LED. The second LED driving circuit  30  includes a second LED driver  31  and a plurality of second LED groups E 1  to En, where n is a positive integer greater than one, and the second LED groups E 1  to En are driven by the second LED driver  31  for being turned on, and each of the second LED groups E 1  to En includes at least one LED. The number of the first LED groups L 1  to Lm can be different from that of the second LED groups E 1  to En. Besides, the first LED driving circuit  20  is preferably connected in parallel with the second LED driving circuit  30 . The capacitor  40  has a first terminal  41  and a second terminal  42 . The first terminal  41  of the capacitor  40  is coupled to a first terminal  33  of the second LED driving circuit  30 , and the second terminal  42  of the capacitor  40  is coupled to a first terminal  23  of the first LED driving circuit  20  according to this embodiment. However, in other embodiments, the second terminal  42  of the capacitor  40  is coupled to a second terminal  34  of the second LED driving circuit  30  or is coupled to ground. 
     The first terminal  41  of the capacitor  40  is coupled to a power source  50  for receiving energy. For example, the power source  50  applies an AC power to the first terminal  41 , so that the capacitor  40  can store the energy, such as an AC current, from the power source  50 . In an embodiment, the first terminal  41  of the capacitor  40  is coupled to the power source  50  via a front LED group E 0  including at least one LED, and the front LED group E 0  can influence the waveform of a capacitor current (ic) flowing through the capacitor  40 . Besides, the power source  50  is also coupled to a first terminal  23  of the first LED driving circuit  20 , so that the first LED driving circuit  20  receives energy from the power source  50 , and the first LED driver  21  enables a driving current (i 1 ) to flow through the first LED groups L 1  to Lm for driving the first LED groups L 1  to Lm. In other words, when the LED device  10  is in operation, the energy consumed by the capacitor  40  and the first LED driving circuit  20  is provided from the power source  50 . It is noted that, in an embodiment, although the power source  50  is also coupled to the first terminal  33  of the second LED driving circuit  30  via the front LED group E 0  and the first terminal  41  of the capacitor  40 , the energy consumed by the second LED driving circuit  30  in operation is provided from the capacitor  40 . It is noted that if the value of the capacitor current (ic) is increased, the value of the driving current (i 1 ) may be drop. 
     In this embodiment, the first LED driving circuit  20  further includes a sensing resistor group  22  having a terminal connected to ground and a node  24  coupled to the second terminal  42  of the capacitor  40 . Alternatively, as shown in  FIG. 2(B) , the second LED driving circuit  30  further includes a sensing resistor group  32  having a terminal connected to ground and a node  34  coupled to the second terminal  42  of the capacitor  40 . Besides, as shown in  FIG. 2(A)  or  FIG. 2(B) , the sensing resistor group  22  or  32  preferably includes, but not limited to, two resistors connected in series, and the second terminal  42  of the capacitor  40  is coupled to the node between the two resistors of the resistor group  22  or  32 . 
       FIG. 2(C)  is still another circuit diagram illustrating the LED device with energy compensation  10  according to an embodiment of the invention. Comparing  FIG. 2(C)  with  FIG. 2(A) or 2(B) , the first terminal of the capacitor  40  is still coupled to the power source  50  via the front LED E 0  in  FIG. 2(C) , but the second terminal of the capacitor  40  is coupled to ground. 
     With reference to  FIG. 2(A) to 2(C) , the first LED driving circuit  20  sends its feedback value (fb) to the second LED driving circuit  30 , the second driver  31  can be enabled or disabled according to the feedback value (fb). It is said that, when the driving circuit (i 1 ) receiving energy from the power source  50  is decreased, the second driver  31  can be enabled and the compensation circuit (i 2 ) can be provided, so that the difference between the peak and valley of the consumed power can be reduced. 
     Besides, in an embodiment, each of the first LED groups L 1  to Lm includes a plurality of LEDs connected in series with each other, connected in parallel with each other, or connected in a combination of serial connection and parallel connection. Similarly, in an embodiment, each of the second LED groups E 1  to En includes a plurality of LEDs connected in series with each other, connected in parallel with each other, or connected in a combination of serial connection and parallel connection. 
     About the first LED groups L 1  to Lm, the first LED groups L 1  to Lm is preferably but not limited to be connected in series with each other. Similarly, the second LED groups E 1  to En of the second LED driving circuit  30  is preferably but not limited to be connected in series with each other, i.e., the 1st first LED group L 1  is preferably connected in series with the 2nd first LED group L 2 . 
     In an embodiment, the first LED driver  21  is preferably but not limited to be a linear LED driver including a plurality of amplifiers with a number corresponding to the number of the first LED groups L 1  to Lm. The second LED driver  31  is preferably but not limited to be a linear LED driver including a plurality of amplifiers with a number corresponding to the number of the second LED groups E 1  to En. In other embodiments, the first LED driver  21  and the second LED driver  31  are not the linear LED driver, so that the time-variable reference voltages, such as sine waves, can be applied to the first LED driver  21  or the second LED driver  31 . 
     In addition, the AC power (voltage) provided from the power source  50  has a waveform including an increasing period corresponding to the phase of 0 to 90 degrees of the AC power, and a decreasing period corresponding to the phase of 90 to 180 degrees of the AC power. To achieve a high PF value, the waveform of the total consumed current should be close to that of the AC power. In an embodiment, in the increasing period, the capacitor current (ic) flowing through the capacitor  40  influences part of the total consumed current of the LED device  10 . In an embodiment, in the decreasing period, the second LED driver  31  receives energy from the capacitor  40  to provide a compensation current (i 2 ) flowing through the second LED groups E 1  to En, and the compensation current (i 2 ) influences part of the total consumed current of the LED device  10 . 
       FIG. 3  is a schematic diagram illustrating the waveforms of the capacitor current (ic), the driving current (i 1 ) and the compensation current (i 2 ) when the LED device  10  is in operation. In this embodiment, the number of the first LED groups L 1  to Lm of the first LED driving circuit  20  is four, and the number of the second LED groups E 1  to En of the second LED driving circuit  30  is four, which are specified herein for illustrative purpose only. With reference to  FIGS. 2(A)  to  3 , in the increasing period (the phase of 0 to 90 degrees), the energy outputted from the power source  50  is increased from low to high, the capacitor current (ic) flows through the capacitor  40  to charge the capacitor  40 , the driving current (i 1 ) is provided to the first LED groups L 1  to L 4  under the control of the LED driver  21 . 
     In the beginning of the increasing period, for example at the phase of about 22.5 degrees, the capacitor current (ic) has a very high value, the magnitude of the driving current (i 1 ) is low, thus the first LED groups L 1  to L 4  are off. When the AC power from the AC source  50  gradually reaches to its peak at the phase of 90 degrees, the capacitor current (ic) is gradually decreased, the driving current (i 1 ) is gradually increased, and the first LED groups L 1  to L 4  are sequentially driven by the first LED driver  21 . For example, at the phase of about 45 degrees, as the capacitor current (ic) drops, the LED driver  21  turns on the driving current (i 1 ) flowing through the 1st first LED group L 1  to maintain the total consumed current being equal to a first threshold, and the 1st groups L 1  is turned on for illumination. At the phase of about 60 degrees, the driving current (i 1 ) is increased to maintain the total consumed current being equal to a second threshold, and the 1 st and 2nd first LED groups L 1  and L 2  are on for illumination. Similarly, at the phase of about 70 degrees, the driving current (i 1 ) is increased to maintain the total consumed current being equal to a third threshold, the 1st, 2nd and 3rd first LED groups L 1  to L 3  are on for illumination. At the phase of about 90 degrees, the capacitor current (ic) is decreased to become zero, and the driving current (i 1 ) is increased to become a maximum value, all first LED groups L 1  to L 4  are on for illumination. 
     With reference to  FIG. 2(A)  to  3  again, in the decreasing period (the phase of 90 to 180 degrees), the energy outputted from the power source  50  is decreased from high to low, and the driving current (i 1 ) is gradually decreased, such that the first LED groups L 4  to L 1  are sequentially turned off so as to stop illuminating. In the decreasing period, when the driving current (i 1 ) is lower than a predetermined value (ip), which is, for example, an average current value of the driving current (i 1 ), the second LED driving circuit  30  starts to draw energy from the pre-charged capacitor  40 , so as to generate a compensation current (i 2 ) to drive the second LED groups E 1  to E 4 , thereby keeping the total consumed current (or total consumed energy) of the LED device  10  to be in a specific range. 
     As shown in  FIG. 3 , at the phase of about 90 to 1.10 degrees, the magnitude of the driving current (i 1 ) is still high, the first LED groups L 1  to L 4  are kept in illumination, and the second LED driving circuit  30  is disabled. At the phase of about 110 degrees, the energy outputted from the power source  50  is decreased and fails to illuminate all first LED groups L 1  to L 4 , so that the 4th first LED group L 4  is off and the 1st to 3rd first LED groups L 1  to L 3  are still on. Besides, due to the magnitude of the driving current (i 1 ) is still higher than the predetermined value (ip), the second LED driving circuit  30  is still disabled. At the phase of about 130 degrees, the energy outputted from the power source  50  is lower and fails to illuminate the 1st to 3rd first LED groups L 1  to L 3 , so that the 3rd first LED group L 3  is off and the 1st to 2nd first LED groups L 1  to L 2  are still on. Due to the magnitude of the driving current (i 1 ) is still higher than the predetermined value (ip) in this moment, the second. LED driving circuit  30  is still disabled. At the phase of about 140 degrees, the energy outputted from the power source  50  is lower and fails to illuminate the 1st to 2nd first LED group L 1  to L 2 , so that the 2nd first LED group L 2  is off and the 1st first LED group L 1  are still on. In this moment, the driving current (a) is lower than the predetermined value (ip), the second LED driving circuit  30  starts to draw energy from the pre-charged capacitor  40  and drive the second LED groups E 1  to E 4 , so as to increase the total illumination. Thus, the flicking of the LED device  10  can be alleviated. 
     It the embodiment, the compensation current (i 2 ) has a phase inconsistent with that of the power source  50 . And a waveform of the total consumed current of the LED device  10  has a phase consistent with that of the power source  50 . 
     Although in this embodiment, the second LED driving circuit  30  is operated in the decreasing period and is still operated in next increasing period until the capacitor is charged by the power source  50 , but in other embodiment, the LED driving circuit  30  is operated only in the decreasing period. 
     Besides, the number of the LEDs of the front LED group E 0  can influence the waveform of the capacitor current (ic). For example, if there are more LEDs connected in series with each other in the front LED group E 0 , the value of the capacitor current (ic) can be higher when it is turned on. 
       FIG. 4(A)  is a schematic diagram illustrating the waveform of the total consumed energy of the LED device  10  according to an embodiment of the invention, in comparison with that of the prior LED device. Referring to  FIGS. 1 to 4 , in the increasing period and the decreasing period, with the capacitor  40  and the second LED driving circuit  30 , the variation of the waveform of the total consumed energy in accordance with the present invention is relatively smooth, and thus the flicking problem can be minimized. Besides, the waveform of the total consumed current of the invention is still close to a sinusoid, so as to keep a high PF value. 
       FIG. 4(B)  is another schematic diagram illustrating the waveform of the total consumed energy of the LED device  10  according to an embodiment of the invention. Comparing with the prior art in  FIG. 1(B) , the valley value of the total consumed energy of the LED device  10  in  FIG. 4(B)  is filled, and the peak value of that is lower and narrow. Due to the valley value is increased and the peak value is decreased, although the average value of the total consumed energy in  FIG. 4(B)  is close to that in  FIG. 1(B) , but the area1 is reduced and the area1 is increased in  FIG. 4(B) , so that the flicking index in  FIG. 4(B)  is significantly lower than that in  FIG. 1(B) . Thus, the invention can reduce the flicking problem and keep a high PF value. 
       FIG. 5  is a schematic diagram illustrating detailed circuit structures of the first LED driving circuit  20  and the second LED driving circuit  30  according to an embodiment of the invention. In this embodiment, the number of the first LED groups L 1  to Lm is four, and the number of the second LED groups E 1  to En is four. It is noted that these circuit structures of the first LED driving circuit  20  and the second. LED driving circuit  30  are specified herein for exemplary purpose. In actual application, each of the LED driving circuit  20  and the second LED driving circuit  30  can be any kind of linear LED driving circuit. 
     With reference to  FIGS. 1(A)  to  5 , the circuit structure of the first LED driving circuit  20  is similar to the prior linear LED device  100 . The first LED driver  21  includes a plurality of first amplifiers op 1  to op 4  with a number corresponding to that of the first LED groups L 1  to L 4 . Each of the first amplifiers op 1  to op 4  has a positive input terminal, a negative input terminal and an output terminal. The output terminals of the first amplifiers op 1  to op 4  are respectively coupled to first switches s 1  to s 4  for controlling the first LED groups L 1  to L 4  to be turned on or off to regulate the current to the target values. In this embodiment, the first LED groups L 1  to L 4  are coupled in series on a first path p 1 , and one terminal of each of the first switches s 1  to s 4  is coupled to the first path p 1 . 
     In an embodiment, only one of the first amplifiers op 1  to op 4  can be operated each time, i.e. when the 1st first amplifier op 1  is operated, the 2nd to 4th first amplifiers op 2  to op 4  cannot be operated. Besides, the operation sequence of the first amplifiers op 1  to op 4  is from the 1st first amplifier op 1  to the 4th first amplifier op 4 . It is said that, in the beginning, the 1st first amplifier op 1  is operated, the 2nd to 4th first amplifiers op 2  to op 4  are not operated, only the 1st first switch s 1  is turned on, the driving current (i 1 ) flows through the 1st first LED group L 1  and the 1st first switch s 1 . Then, when the 2nd first amplifier op 2  is operated, the 1st first amplifier op 1  and the 3rd to 4th first amplifiers op 3  to op 4  are not operated, only the 2nd first switch s 2  is turned on, the driving current (i 1 ) flows through the 1st first LED group L 1 , the 2nd first LED group L 2  and the 2nd first switch s 2 . Then, when the 3nd first amplifier op 3  is operated, the 1st to 2nd first amplifiers op 1  to op 2  and 4th first amplifiers op 4  are not operated, only the 3nd first switch s 3  is turned on, the driving current (i 1 ) flows through the 1st first LED group L 1 , the 2nd first LED group L 2 , the 3rd first LED group L 3  and the 3nd first switch s 3 . Then, when the 4th first amplifier op 4  is operated, the 1st to 3rd first amplifiers op 1  to op 3  are not operated, only the 4th first switch s 4  is turned on, the driving current (i 1 ) flows through the 1st first LED group L 1 , the 2nd first LED group L 2 , the 3rd first LED group L 3 , the 4th first LED group L 4  and the 4th first switch s 4 . 
     Besides, the first driving energy thresholds ref 1  to ref 4  corresponding to the first LED groups L 1  to L 4  are inputted to the positive input terminals of the corresponding first amplifiers opt to op 4 , respectively. For example, a 1st first driving energy threshold ref 1  corresponding to the driving current (i 1 ) only flowing through theist first LED group L 1  (which is related to a predetermined value of the driving current (i 1 ) when the 1st first switch s 1  is turned on, the 1st first LED group L 1  is on, and the 2nd to 4th first LED groups L 2  to L 4  are off) is inputted to the positive input terminal of the first amplifier op 1 . Similarly, a 2nd first driving energy threshold ref 2  corresponding to the driving current flowing through the 1st and 2nd first LED groups L 1  and L 2  (which is related to a predetermined value of the driving current (i 1 ) when the 2nd first switch s 2  is turned on, the 1st to 2nd first LED groups L 1  to L 2  are on, and the 3rd to 4th first LED groups L 3  to L 4  are off) is inputted to the positive input terminal of the first amplifier opt. Similarly, a 3rd first driving energy threshold ref 3  corresponding to the driving current (i 1 ) flowing through the 1st to 3rd first LED groups L 1  to L 3  (which is related to a predetermined value of the driving current (i 1 ) when the 3rd first switch s 3  is turned on, the 1st to 3rd first LED groups L 1  to L 3  are on, and the 4th first LED group L 4  is off) is inputted to the positive input terminal of the first amplifier op 3 . Similarly, a 4th first driving energy threshold ref 4  corresponding to the driving current flowing through the 1st to 4th first LED groups L 1  to L 4  (which is related to a predetermined value of the driving current (i 1 ) when the 4th first switch s 4  is turned on, and the 1st to 4th first LED groups L 1  to IA are on) is inputted to the positive input terminal of the first amplifier op 4 . In an embodiment, the negative input terminals of the first amplifiers op 1  to op 4  are coupled to a second path p 2 , and the another terminal of each of the first switches s 1  to s 4  is coupled to the second path p 2 , while the second path p 2  is coupled to ground (gnd) via a sensing resistor (rs). 
     The second LED driver  31  includes a plurality of second amplifiers op 1 ′ to op 4 ′ with a number corresponding to that of the second LED groups E 1  to E 4 . Each of the second amplifiers opt′ to op 4 ′ has a positive input terminal, a negative input terminal and an output terminal. Besides, the output terminals of the second amplifiers op 1  to op 4 ′ are respectively coupled to second switches s 1 ′ to s 4 ′ for regulating the second LED groups E 1  to E 4 . In this embodiment, the second LED groups E 1  to E 4  are coupled in series on a first path p 1  and one terminal of each of the second switches s 1  to s 4 ′ is coupled to the first path p 1 ′. 
     In an embodiment, only one of the second amplifiers op 1 ′ to op 4 ′ can be operated each time, i.e. when the 1st second amplifier op 1 ′ is operated, the 2nd to 4th second amplifiers op 2 ′ to op 4 ′ cannot be operated. Besides, the operation sequence of the second amplifiers op 1 ′ to op 4 ′ is from the 4th second amplifier op 4 ′ to the 1st second amplifier op 1 ′. It is said that, when the second LED driver  31  starts to be operated, the 4th second amplifier op 4 ′ is operated first, the 3rd to 1st second amplifiers op 3 ′ to op 1 ′ are not operated, only the 4th second switch s 4 ′ is turned on, and the compensation current (i 2 ) flows through the 1st to 4th second LED groups E 1  to E 4  and the 4th second switch s 4 ′. When the 3rd second amplifier op 3 ′ is operated, the 4th second amplifier op 4 ′ and the 2nd to 1st second amplifiers op 2 ′ to op 1 ′ are not operated, only the 3rd second switch s 3 ′ is turned on, the compensation current (i 2 ) flows through the 1st second LED group E 1 , the 2nd second. LED group E 2 , the 3rd second LED group E 3  and the 3rd second switch s 3 ′. And when the 2nd second amplifier op 2 ′ is operated, the 4th and 3rd second amplifiers op 4 ′ to op 3 ′ and the 1st second amplifier op 1 ′ are not operated, only the 2nd second switch s 2 ′ is turned on, the compensation current (i 2 ) flows through the 1st second LED group E 1 , the 2nd second LED group E 2  and the 2nd second switch s 2 ′. Then, when the 1st second amplifier op 1 ′ is operated, the 4th to 2nd second amplifiers op 4 ′ to op 2 ′ are not operated, only the 1st second switch s 1 ′ is turned on, the compensation current (i 2 ) flows through the 1st second LED group E 1  and the 1st second switch s 1 ′. 
     Besides, the second driving energy thresholds ref 1 ′ to ref 4 ′ corresponding to the second LED groups E 1  to E 4  are respectively inputted to the positive input terminals of the corresponding second amplifiers op 1 ′ to op 4 ′. For example, a 1st second driving energy threshold ref 1  corresponding to the compensation current (i 2 ) flowing through only the 1st second LED group E 1  (which is related to a predetermined value of the compensation current (i 2 ) when the 1st second switch s 1 ′ is turned on, the 1st second LED group E 1  is on, and the 2nd to 4th second LED groups E 2  to E 4  are off) is inputted to the positive input terminal of the second amplifier op 1 ′. Similarly, the 2nd second driving energy threshold ref 2 ′ corresponding to the compensation current (i 2 ) flowing through the 1st to 2nd second LED groups E 1  to E 2  (which is related to a predetermined value of the compensation current (i 2 ) when the 2nd second switch s 2 ′ is turned on, the 1st to 2nd second LED groups E 1  to E 2  are on, and the 3rd to 4th second LED groups E 3  to E 4  are off) is inputted to the positive input terminal of the second amplifier op 2 ′. Similarly, the 3rd second driving energy threshold ref 3 ′ corresponding to the compensation current (i 2 ) flowing through the 1st to 3rd second LED groups E 1  to E 3  (which is related to a predetermined value of the compensation current (i 2 ) when the 3rd second switch s 3 ′ is turned on, the 1st to 3rd second LED groups E 1  to E 3  are on, and the 4th second LED group E 4  is off) is inputted to the positive input terminal of the second amplifier op 3 ′. Similarly, the 4th second driving energy threshold ref 4 ′ corresponding to the compensation current (i 2 ) flowing through the 1st to 4th second LED groups E 1  to E 4  (which is related to a predetermined value of the compensation current (i 2 ) when the 4th second switch s 4 ′ is turned on, and the 1st to 4th second LED groups E 1  to E 4  are on) is inputted to the positive input terminal of the second amplifier op 4 ′. In an embodiment, the negative input terminals of the second amplifiers op 1 ′ to op 4 ′ are coupled to the second path p 2  of the first LED driving circuit  20  via resistors r 1 ′ to r 4 ′, respectively, and are further coupled to a second path p 2 ′ via resistors r 5 ′ to r 8 ′, respectively, while another terminals of the second switches s 1 ′ to s 4 ′ are coupled to the second path p 2 ′, and the second path p 2 ′ is coupled to ground via a sensing resistor rs′. 
     In an embodiment, the first LED driver  21  and the second LED driver  31  are operated in cooperation with a logic circuit, which is used to determine whether to enable the second amplifiers op 1  to op 4 ′ (the sequence is from the 4th second amplifier op 4 ′ to the 1st second amplifier op 1 ′) of the second LED driver  31  to maintain the total consumed energy of the LED device  10  for minimizing the flicking problem. 
     In an embodiment, the amplifiers op 1  to op 4 ′ of the second LED driver  31  are operated in a monotonic manner; e.g., the currents (i 2 ) when the all second LED groups E 1  to E 4  are on to the currents (i 2 ) when only the 1st second LED group E 1  is on must be sequentially increased or decreased. 
     Besides, it is noted that when a number of the first LED groups L 1  to Lm is m, the m-th first driving energy threshold refm is related to a predetermined value of the driving current (i 1 ) when the m-th first switch sm is turned on, and the 1st m-th first groups L 1  to Lm are on. And when a number of the second LED groups E 1  to En is n, the n-th second driving energy threshold refn′ is related to a predetermined value of the compensation current (i 2 ) when the n-th second switch sn′ is turned on, and the 1st to n-th second LED groups E 1  to En are on. 
     In an embodiment, if a number of the first LED groups L 1  to Lm is m, and a number of the second LED groups E 1  to En is n, the n-th second driving energy threshold refn′ is lower than the m-th first driving energy threshold refm. For example, if m and n both are four, then ref 4 ′&lt;ref 4 . 
     In an embodiment, if n both are four, the values of the driving energy thresholds should be monotonic. i.e., the second driving energy thresholds ref 1 ′ to ref 4 ′ satisfy the relation of ref 1 ′≧ref 2 ′≧ref 3 ′≧ref 4 ′ or ref 4 ′≧ref 3 ′≧ref 2 ′≧ref 1 ′. In another embodiments, the second driving energy thresholds ref 1 ′ to ref 4 ′ satisfy the regulation of ref 1 ′&gt;ref 2 ′&gt;ref 3 ′&gt;ref 4 ′ or ref 4 ′&gt;ref 3 ′&gt;ref 2 ′&gt;ref 1 ′. 
     Thus, the invention provides an LED device with energy compensation, which makes use of the capacitor  40  and the second LED driving circuit  30  to compensate for both the waveform of the total consumed current and the total consumed energy of the LED device  10 , so as to solve the flicking problem and still achieving a high PF value. 
     Although the present invention has been explained in relation to its preferred embodiments, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.