Abstract:
Disclosed is a light-emitting device configured in such a manner that all light-emitting elements always emit light irrespective of the magnitude of an input voltage when the magnitude of the voltage is higher than the minimum light-emitting voltage, and that the light-emitting elements are connected to each other in parallel when the magnitude of the voltage is small, and connected to each other in series when the magnitude of the voltage is large.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2014-0087561, filed on Jul. 11, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to a lighting device and, more particularly, to a lighting device capable of changing a serial/parallel connection structure of light-emitting elements based on an input voltage. 
         [0004]    2. Description of the Related Art 
         [0005]    A light-emitting diode (LED) refers a type of semiconductor element capable of implementing light of various colors by forming a light-emitting source using a PN diode of a compound semiconductor. The LED has a long life, a small size, and a small weight, and can be driven using a low voltage. In addition, the LED is durable against impact and vibration, does not require preheating or complicated driving, and is mountable on a substrate or a lead frame in various forms before packaging. As such, the LED may be modularized for various purposes and applied to a backlight unit or a variety of lighting devices. 
         [0006]    A plurality of LEDs may be used to provide an independent lighting device. In this case, the LEDs may be connected to each other in series or in parallel. In this case, commercial power may be converted into alternating current (AC) power and the AC power may be provided to the LEDs to always turn on all LEDs. 
         [0007]    When the AC power is provided and used as described above, an AC rectifier is necessary. However, the AC power may be directly applied to the LEDs without using the AC rectifier. In this case, the LEDs may be connected to each other in series, and on/off states of the LEDs may be changed based on the magnitude of a variable input voltage. As the on/off states are repeated, flicker of light occurs, usability of each LED is reduced, and thus light output efficiency is reduced. 
       SUMMARY 
       [0008]    The present invention provides a light-emitting diode (LED) lighting device capable of increasing usability of LEDs and improving light output efficiency when alternating current (AC) power is directly applied to the LEDS. 
         [0009]    According to an aspect of the present invention, there is provided a lighting device including a light-emitting unit including a current input node, a current output node, a current bypass output node, and a first light-emitting group for emitting light due to a current input to the current input node, a second light-emitting group connected to receive a current output from the current output node, and a flicker controller provided between the current input node and the current bypass output node to turn off the first and second light-emitting groups when a voltage input to the current input node is equal to or lower than a predetermined voltage, wherein the current output node is configured to selectively output a whole or a part of a current input through the current input node, and wherein the current bypass output node is configured to output a remaining part of the current input through the current input node when the current output node outputs only the part of the current. 
         [0010]    When the lighting device operates in a steady state, the current bypass output node may be configured to output the remaining part of the current input through the current input node when the current output node outputs the part of the current, and the part of the current may have a value greater than 0. 
         [0011]    The remaining part of the current may be at least a part or a whole of a current flowing through the first light-emitting group. 
         [0012]    The second light-emitting group may belong to another light-emitting unit including another current input node, another current output node, another current bypass output node, and the second light-emitting group for emitting light due to a current input to the other current input node, and the current bypass output node included in the light-emitting unit may be configured to be connected to the other current bypass output node included in the other light-emitting unit. 
         [0013]    Distribution switches may be separately connected between the first light-emitting group and the current output node and between the second light-emitting group and the other current output node, and the flicker controller may turn off the distribution switches to turn off the first and second light-emitting groups using a comparator or a Zener diode connected to the current input node when the voltage input to the current input node is equal to or lower than a predetermined voltage. 
         [0014]    The current output node may be configured to output the part of the current when the voltage input to the current input node has a first potential, and to output the whole of the current when the voltage input to the current input node has a second potential higher than the first potential. 
         [0015]    According to another aspect of the present invention, there is provided a light-emitting device including a plurality of light-emitting groups electrically connected to each other to be numbered in a direction from an upper stream to a lower stream, and receiving power from a power supply for supplying power having a variable potential, a first bypass unit, a second bypass unit, and a flicker controller for turning off the light-emitting groups when a voltage input from the power supply is equal to or lower than a predetermined voltage, wherein each of the light-emitting groups includes one or more light-emitting elements, wherein the first bypass unit is configured to electrically connect an upper stream node of a first light-emitting group which is arbitrary-numbered, to an upper stream node of a second light-emitting group which is arbitrary-numbered and provided at a lower stream of the first light-emitting group, in an interruptive manner, and wherein the second bypass unit is configured to electrically connect a lower stream node of the first light-emitting group to a lower stream node of the second light-emitting group or a lower stream node of a third light-emitting group which is arbitrary-numbered and provided at a lower stream of the second light-emitting group, in an interruptive manner. 
         [0016]    The first bypass unit may be configured to serve as a constant current source when the first bypass unit connects the upper stream node of the first light-emitting group to the upper stream node of the second light-emitting group. 
         [0017]    The second bypass unit may be configured to flow a current therethrough when a current flows through the first bypass unit, and not to flow a current therethrough when a current does not flow through the first bypass unit. 
         [0018]    According to another aspect of the present invention, there is provided an alternating current (AC) power light-emitting diode (LED) lighting device including a plurality of light-emitting groups linearly and electrically connected to each other to be numbered from an uppermost stream to a lower stream, a first circuit unit for connecting connection nodes between the light-emitting groups to a ground, a second circuit unit for bypass-connecting the connection nodes to each other, and a flicker controller for turning off the light-emitting groups when a voltage input to a light-emitting group of the uppermost stream is equal to or lower than a predetermined voltage, wherein the light-emitting groups are configured to be switched from a parallel connection state to a serial connection state sequentially from the light-emitting group of the uppermost stream to a light-emitting group of the lowermost stream during a potential of supplied AC power is increased, and wherein each of the light-emitting groups includes one or more LED elements. 
         [0019]    The light-emitting groups may be configured to be switched from a serial connection state to a parallel connection state sequentially from the light-emitting group of the lowermost stream to the light-emitting group of the uppermost stream during the potential of supplied AC power is reduced. 
         [0020]    According to another aspect of the present invention, there is provided a lighting device including a light-emitting unit including a first light-emitting group, a first bypass unit, a second bypass unit, and a current input node commonly connected to an input node of the first light-emitting group and an input node of the first bypass unit to supply a current to the first light-emitting group and the first bypass unit, a second light-emitting group connected to the light-emitting unit to receive a current output from an output node of the first light-emitting group in a first circuit state and to receive a current output from an output node of the first bypass unit in a second circuit state, and a flicker controller connected to the current input node to turn off the first and second light-emitting groups when a voltage input to the current input node is equal to or lower than a predetermined voltage, wherein the first bypass unit is configured to be interrupted not to flow a current therethrough, and the second bypass unit is configured to be interrupted not to flow therethrough the current output from the first light-emitting group, in the first circuit state, and wherein the first bypass unit is configured to flow a current therethrough, and the second bypass unit is configured flow therethrough at least a part of the current output from the first light-emitting group, in the second circuit state. 
         [0021]    The second bypass unit may be configured to connect an output node thereof to a current output node of the second light-emitting group. 
         [0022]    The second light-emitting group may be included in another light-emitting unit having a configuration equal to the configuration of the light-emitting unit. 
         [0023]    The first circuit state may indicate a first time period, and the second circuit state may indicate a second time period different from the first time period. 
         [0024]    The first circuit state may indicate a state having a first input voltage level, the second circuit state may indicate a state having a second input voltage level, and the first input voltage level may be higher than the second input voltage level. 
         [0025]    According to another aspect of the present invention, there is provided a lighting device including two light-emitting units connected to each other in parallel at a first voltage higher than a turn-on voltage, and a flicker controller for turning off the two light-emitting group when a voltage input to an upper stream node of the two light-emitting units is equal to or lower than a predetermined voltage, wherein the two light-emitting units are switched to a serial connection state at a second voltage higher than the first voltage, and wherein the two light-emitting units are always turned on at a voltage higher than the turn-on voltage. 
         [0026]    The two light-emitting units may include light-emitting diodes (LEDs), and the turn-on voltage may be a forward voltage of any one of the two light-emitting units. 
         [0027]    A current flowing into the two light-emitting units may have a higher value at the second voltage compared to the first voltage. 
         [0028]    According to another aspect of the present invention, there is provided a lighting device including N light-emitting groups linearly connected to each other (N is a natural number equal to or greater than 2), one or more first switching units for bypass-connecting input and output nodes of 1 st  to (N−1) th  light-emitting groups to each other, one or more second switching units for connecting output nodes of the 1 st  to (N−1) th  light-emitting groups to a ground, and a flicker controller provided between the input node and the second switching unit of the (N−1) th  light-emitting group to turn off the N light-emitting groups when a voltage input to the input node is equal to or lower than a predetermined voltage, wherein a first connection node for connecting the output node and the first switching unit of each of the 1 st  to (N−1) th  light-emitting groups to each other is provided at a lower steam of a second connection node for connecting the output node and the second switching unit of each of the 1 st  to (N−1) th  light-emitting groups to each other, wherein a backflow preventer for preventing current flow to an upstream is provided between the first and second connection point, and wherein the first and second switching units of the light-emitting groups are sequentially turned on or off and thus the light-emitting groups are connected to each other in parallel and/or in series based on a magnitude of a supplied voltage. 
         [0029]    In this case, each of the light-emitting groups may include one or more light-emitting elements connected to each other in series and/or in parallel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0031]      FIGS. 1A and 1B  are diagrams showing a light-emitting diode (LED) lighting circuit and the operation principle thereof, according to an embodiment of the present invention; 
           [0032]      FIG. 2  is a diagram showing an example of an LED lighting circuit according to another embodiment of the present invention; 
           [0033]      FIGS. 3A and 3B  are diagrams showing on/off states of switches included in the LED lighting circuit of  FIG. 2 , based on an input voltage; 
           [0034]      FIGS. 4A to 4E  are diagrams showing circuit structures of the LED lighting circuit in a plurality of time periods; 
           [0035]      FIGS. 5A to 5E  are diagrams showing equivalent circuits approximated from the circuits illustrated in  FIGS. 4A to 4E , respectively; 
           [0036]      FIG. 6A  is a diagram showing the structure of a light-emitting device according to an embodiment of the present invention; 
           [0037]      FIG. 6B  is a diagram showing a power supply, a light-emitting group, a first bypass unit, a second bypass unit, and a light-emitting element illustrated in  FIG. 6A ; 
           [0038]      FIG. 7  is a diagram showing the structure of an LED lighting device according to another embodiment of the present invention; 
           [0039]      FIG. 8  is a diagram showing the structure of an LED lighting device according to another embodiment of the present invention; 
           [0040]      FIG. 9  is a diagram showing the structure of an LED lighting device according to another embodiment of the present invention; 
           [0041]      FIGS. 10A to 10C  are diagrams showing an example of a light-emitting unit included in an LED lighting circuit, according to an embodiment of the present invention; 
           [0042]      FIG. 11  is a diagram showing an LED lighting circuit including a flicker controller, according to an embodiment of the present invention; 
           [0043]      FIG. 12  is a diagram showing an example of a flicker controller applied to an LED lighting circuit according to embodiments of the present invention; 
           [0044]      FIG. 13  is a diagram showing another example of a flicker controller applied to an LED lighting circuit according to embodiments of the present invention; 
           [0045]      FIG. 14  is a diagram showing an LED lighting circuit including a flicker controller, according to another embodiment of the present invention; and 
           [0046]      FIG. 15  shows graphs illustrating an alternating current (AC) input waveform and an output waveform of a triac dimmer. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Hereinafter, the present invention will be described in detail by explaining embodiments of the invention with reference to the attached drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. The terminology used herein is for the purpose of describing particular embodiments and is not intended to limit the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
         [0048]      FIGS. 1A and 1B  are diagrams showing a light-emitting diode (LED) lighting circuit  1  and the operation principle thereof, according to an embodiment of the present invention. 
         [0049]    In the LED lighting circuit  1  illustrated in  FIG. 1A , a plurality of light-emitting groups CH 1  and CH 2  are connected to each other. The light-emitting groups CH 1  and CH 2  may be switched between a serial connection state and a parallel connection state, and this connection state switching may be performed by controlling on/off states of a distribution switch CS 1  and a bypass switch BS 1 . The on/off states of the distribution switch CS 1  and the bypass switch BS 1  may be automatically controlling based on the magnitude of an input voltage Vi. 
         [0050]    In  FIG. 1A , the bypass switch BS 1  and the distribution switch CS 1  may be configured as transistors. Examples of the transistor include a bipolar transistor (BT), a field effect transistor (FET), and an insulated gate bipolar transistor (IGBT), but are not limited thereto. 
         [0051]    When the bypass switch BS 1  operates in an unsaturated zone, the magnitude of a current Ip 1  flowing through the bypass switch BS 1  may be determined based on a ratio of the value of a bias voltage Vp 1  to the value of a resistor R 1 . That is, one current source may be configured using the bypass switch BS 1 , the current Ip 1 , and the bias voltage Vp 1 . Unlike this, when the bypass switch BS 1  operates in a saturated zone, the bypass switch BS 1  may serve similarly to a resistor. 
         [0052]    In addition, when the distribution switch CS 1  operates in an unsaturated zone, the magnitude of a current I 1  flowing through the distribution switch CS 1  may be determined based on a ratio of the value of a bias voltage V 1  to the value of a resistor Rs. That is, one current source may be configured using the distribution switch CS 1 , the current I 1 , and the bias voltage V 1 . Unlike this, when the distribution switch CS 1  operates in a saturated zone, the distribution switch CS 1  may serve similarly to a resistor. 
         [0053]      FIG. 1B  show voltage and current characteristics based on time at nodes and elements of the LED lighting circuit  1  illustrated in  FIG. 1A . 
         [0054]    For convenience of explanation, the following description assumes that both the light-emitting groups CH 1  and CH 2  have a forward voltage of Vf. The following description also assumes that the maximum values of currents capable of flowing through the bypass switch BS 1 , the distribution switch CS 1 , and a distribution switch CS 2  are designed as I BS1 , I CS1 , and I CS2 , respectively. 
         [0055]    When an input voltage Vn 1  is between 0 and Vf, no current flows through the LED lighting circuit  1 . 
         [0056]    When the input voltage Vn 1  is between Vf and 2 Vf, the bypass switch BS 1  and the distribution switch CS 1  may operate in an unsaturated zone and thus serve as current sources, and the distribution switch CS 2  may operate in a saturated zone. In this case, a current having a magnitude of I BS1  may flow through the bypass switch BS 1  and the distribution switch CS 2 . In this case, the magnitude of a current flowing through the distribution switch CS 1  may have a value obtained by subtracting the value I BS1  of the current flowing through the distribution switch CS 2 , from I CS1 . A current ID 1  flowing through the light-emitting group CH 1  has the same value as the current flowing through the distribution switch CS 1  (i.e., I CS1 −I BS1 ), and a current ID 2  flowing through the light-emitting group CH 2  has the same value as the current flowing though the distribution switch CS 2  (i.e., I BS1 ). In this case, since the input voltage Vn 1  is not sufficiently high, no current flows through a diode D 1 . 
         [0057]    When the input voltage Vn 1  is equal to or higher than 2 Vf, a current can flow through the diode D 1 . In this case, an additional current flows through the diode D 1  into the resistor R 1  and thus the bypass switch BS 1  is switched to an off state. The distribution switch CS 2  operates in an unsaturated zone, and the distribution switch CS 1  may be switched to an off state. In this case, a current having a magnitude of I CS2  may flow through the distribution switch CS 2 . The current ID 1  flowing through the light-emitting group CH 1  has the same value as the current flowing through the distribution switch CS 2  (i.e., I CS2 ). 
         [0058]      FIG. 2  is a diagram showing an example of an LED lighting circuit  1  according to another embodiment of the present invention. 
         [0059]    The LED lighting circuit  1  illustrated in  FIG. 2  is extended and modified from the LED lighting circuit  1  illustrated in  FIG. 1A . 
         [0060]    In the LED lighting circuit  1  of  FIG. 2 , a plurality of light-emitting groups CH 1  to CH 5  are connected to each other. The light-emitting groups CH 1  to CH 5  may be switched between a serial connection state and a parallel connection state, and this connection state switching may be performed by controlling on/off states of distribution switches CS 1  to CS 5  and bypass switches BS 1  to BS 4 . The on/off states of the distribution switches CS 1  to CS 5  and the bypass switches BS 1  to BS 4  may be automatically controlling based on the magnitude of an input voltage Vi. 
         [0061]    In detail, a lighting device including this LED lighting circuit  1  may include the light-emitting groups CH 1  to CH 5  linearly connected to each other, the bypass switches BS 1  to BS 4  (or first switching units) for bypass-connecting input and output nodes of the light-emitting groups CH 1  to CH 4  to each other, respectively, and the distribution switches CS 1  to CS 5  (or second switching units) for connecting output nodes of the light-emitting groups CH 1  to CH 5  to the ground, respectively. Here, first connection nodes for connecting the output nodes of the light-emitting groups CH 1  to CH 4  to the bypass switches BS 1  to BS 4  (or the first switching units) may be provided at a lower stream of second connection nodes for connecting the output nodes of the light-emitting groups CH 1  to CH 5  to the distribution switches CS 1  to CS 5  (or the second switching units), backflow preventers D 1  to D 4  may be provided between the first and the second connection nodes, and the bypass switches BS 1  to BS 4  (or the first switching units) and the distribution switches CS 1  to CS 5  (or the second switching units) of the light-emitting groups CH 1  to CH 5  may be sequentially turned on or off based on the magnitude of a supplied voltage to connect the light-emitting groups CH 1  to CH 5  to each other in parallel and/or in series. 
         [0062]    In this case, each of the light-emitting groups CH 1  to CH 5  may include one or more light-emitting elements connected to each other in series and/or in parallel. 
         [0063]      FIGS. 3A and 3B  are diagrams showing on/off states of the switches BS 1  to BS 4  and CS 1  to CS 5  included in the LED lighting circuit  1  of  FIG. 2 , based on the input voltage Vi. 
         [0064]    A plot line  143  of  FIG. 3A  shows the magnitude of the input voltage Vi based on time. The input voltage Vi may be given as a triangle wave as shown in  FIG. 3A , or given as any other wave such as a circle wave or a sawtooth wave. 
         [0065]    The magnitude of the input voltage Vi may be divided into a plurality of voltage periods LI 0  to LI 5 , and each of the voltage periods LI 0  to LI 5  may correspond to a plurality of time periods P 0  to P 5 . The lengths and positions of the time periods P 0  to P 5  on a time axis t may be determined based on a predetermined forward voltage value of the light-emitting groups CH 1  to CH 5  illustrated in  FIG. 2 . 
         [0066]    In the time periods P 0  to P 5  shown in  FIG. 3A , the LED lighting circuit  1  according to an embodiment of the present invention may operate in a steady state. However, the LED lighting circuit  1  may operate in a transient state for switching states thereof between every two of the time periods P 0  to P 5 . The following description is focused on the steady state for convenience of explanation. 
         [0067]    Rows of  FIG. 3B  indicate the time periods P 0  to P 5 , and columns thereof indicate on/off states of the bypass switches BS 1  to BS 4  and the distribution switches CS 1  to CS 5  in the time periods P 0  to P 5 . This on/off switching may be automatically performed by the LED lighting circuit  1  illustrated in  FIG. 2 . 
         [0068]    The operation principle of the LED lighting circuit  1  illustrated in  FIG. 2  is now described with reference to  FIGS. 2 to 5E . 
         [0069]      FIGS. 4A to 4E  are diagrams showing circuit structures of the LED lighting circuit  1  in the time periods P 1  to P 5 , respectively. Particularly,  FIG. 4A  illustrates the circuit structure of the LED lighting circuit  1  in the time period P 0  as well as the time period P 1 . 
         [0070]    In the time period P 0 , since the magnitude of the input voltage Vi is not sufficiently high, none of the light-emitting groups CH 1  to CH 5  may be turned on. 
         [0071]    In the time period P 1 , since the bypass switches BS 1  to BS 4  and the distribution switches CS 1  to CS 5  are all turned on, the LED lighting circuit  1  illustrated in  FIG. 2  has the circuit structure illustrated in  FIG. 4A . In this case, the bypass switch BS 1  and the distribution switch CS 1  among the turned-on switches may operate in an unsaturated zone and thus serve as current sources. The other switches among the turned-on switches may operate in a saturated zone. In this case, since a voltage of an anode of each of the backflow preventers D 1  to D 4  is higher than a voltage of a cathode thereof, two ends thereof may be regarded as being open. Accordingly, the circuit illustrated in  FIG. 4A  may be expressed as an equivalent circuit illustrated in  FIG. 5A . 
         [0072]    In the time period P 2 , since the bypass switches BS 2  to BS 4  and the distribution switches CS 2  to CS 5  are all turned on and the bypass switch BS 1  and the distribution switch CS 1  are both turned off, the LED lighting circuit  1  illustrated in  FIG. 2  has the circuit structure illustrated in  FIG. 4B . In this case, the bypass switch BS 2  and the distribution switch CS 2  among the turned-on switches may operate in an unsaturated zone and thus serve as current sources. The other switches among the turned-on switches may operate in a saturated zone. In this case, since a voltage of the anode of each of the backflow preventers D 2  to D 4  is higher than a voltage of the cathode thereof, two ends thereof may be regarded as being open. Accordingly, the circuit illustrated in  FIG. 4B  may be expressed as an equivalent circuit illustrated in  FIG. 5B . 
         [0073]    In the time period P 3 , since the bypass switches BS 3  and BS 4  and the distribution switches CS 3  to CS 5  are all turned on and the bypass switches BS 1  and BS 2  and the distribution switches CS 1  and CS 2  are all turned off, the LED lighting circuit  1  illustrated in  FIG. 2  has the circuit structure illustrated in  FIG. 4C . In this case, the bypass switch BS 3  and the distribution switch CS 3  among the turned-on switches may operate in an unsaturated zone and thus serve as current sources. The other switches among the turned-on switches may operate in a saturated zone. In this case, since a voltage of the anode of each of the backflow preventers D 3  and D 4  is higher than a voltage of the cathode thereof, two ends thereof may be regarded as being open. Accordingly, the circuit illustrated in  FIG. 4C  may be expressed as an equivalent circuit illustrated in  FIG. 5C . 
         [0074]    In the time period P 4 , since the bypass switch BS 4  and the distribution switches CS 4  and CS 5  are all turned on and the bypass switches BS 1  to BS 3  and the distribution switches CS 1  to CS 3  are all turned off, the LED lighting circuit  1  illustrated in  FIG. 2  has the circuit structure illustrated in  FIG. 4D . In this case, the bypass switch BS 4  and the distribution switch CS 4  among the turned-on switches may operate in an unsaturated zone and thus serve as current sources. The other switch among the turned-on switches may operate in a saturated zone. In this case, since a voltage of the anode of the backflow preventer D 4  is higher than a voltage of the cathode thereof, two ends thereof may be regarded as being open. Accordingly, the circuit illustrated in  FIG. 4D  may be expressed as an equivalent circuit illustrated in  FIG. 5D . 
         [0075]    In the time period P 5 , since the distribution switch CS 5  is turned on and the bypass switches BS 1  to BS 4  and the distribution switches CS 1  to CS 4  are all turned off, the LED lighting circuit  1  illustrated in  FIG. 2  has the circuit structure illustrated in  FIG. 4E . In this case, the distribution switch CS 5  may operate in an unsaturated zone and thus serve as a current source. The circuit illustrated in  FIG. 4E  may be expressed as an equivalent circuit illustrated in  FIG. 5E . 
         [0076]    As described above, the circuits illustrated in  FIGS. 5A to 5E  may be understood as equivalent circuits approximated from the circuits illustrated in  FIGS. 4A to 4E , respectively. 
         [0077]    The equivalent circuits illustrated in  FIGS. 5A to 5E  show that the circuit structure of the LED lighting circuit  1  illustrated in  FIG. 2  is changed based on the magnitude of the input voltage Vi. 
         [0078]    In  FIG. 5A  showing the time period P 1 , the light-emitting groups CH 1  to CH 5  are connected to each other in parallel. 
         [0079]    In  FIG. 5B  showing the time period P 2 , the light-emitting groups CH 2  to CH 5  are connected to each other in parallel, and the light-emitting group CH 1  is connected thereto in series. 
         [0080]    In  FIG. 5C  showing the time period P 3 , the light-emitting groups CH 3  to CH 5  are connected to each other in parallel, and the light-emitting groups CH 1  and CH 2  are connected thereto in series. 
         [0081]    In  FIG. 5D  showing the time period P 4 , the light-emitting groups CH 4  and CH 5  are connected to each other in parallel, and the light-emitting groups CH 1  to CH 3  are connected thereto in series. 
         [0082]    In  FIG. 5E  showing the time period P 5 , the light-emitting groups CH 1  to CH 5  are connected to each in series. 
         [0083]    In the circuits of  FIGS. 5A to 5E , a sum of currents input to and output from the LED lighting circuit  1  in the time periods P 1  to P 5  may be defined as Itt 1 , Itt 2 , Itt 3 , Itt 4 , and Itt 5 , respectively. In this case, the LED lighting circuit  1  may be designed to satisfy Itt 5 &gt;Itt 4 &gt;Itt 3 &gt;Itt 2 &gt;Itt 1 . Using the above design, since the sum of supplied currents is increased as the magnitude of the input voltage Vi is increased, a power factor of the LED lighting circuit  1  may be improved. 
         [0084]    An embodiment of the design satisfying Itt 5 &gt;Itt 4 &gt;Itt 3 &gt;Itt 2 &gt;Itt 1  is now described with reference to  FIGS. 5A to 5E . 
         [0085]    In  FIG. 5A , the distribution switch CS 1  operates in an unsaturated zone, and the value of I 1  is adjusted in such a manner that the value of I 1 +I 2 +I 3 +I 4 +I 5  is the same as the maximum current value I CS1  allowed by the distribution switch CS 1 . In this case, a ratio of I 1  to a sum of I 2 +I 3 +I 4 +I 5  may be determined based on the maximum current value I BS1  provided when the bypass switch BS 1  operates as a current source. Accordingly, Itt 1 =I CS1  is satisfied. 
         [0086]    In  FIG. 5B , the distribution switch CS 2  operates in an unsaturated zone, and the value of I 2  is adjusted in such a manner that the value of I 2 +I 3 +I 4 +I 5  is the same as the maximum current value I CS2  allowed by the distribution switch CS 2 . In this case, a ratio of I 2  to a sum of I 3 +I 4 +I 5  may be determined based on the maximum current value I BS2  provided when the bypass switch BS 2  operates as a current source. Accordingly, Itt 2 =I CS2  is satisfied. 
         [0087]    In  FIG. 5C , the distribution switch CS 3  operates in an unsaturated zone, and the value of I 3  is adjusted in such a manner that the value of I 3 +I 4 +I 5  is the same as the maximum current value I CS3  allowed by the distribution switch CS 3 . In this case, a ratio of I 3  to a sum of I 4 +I 5  may be determined based on the maximum current value I BS3  provided when the bypass switch BS 3  operates as a current source. Accordingly, Itt 3 =I CS3  is satisfied. 
         [0088]    In  FIG. 5D , the distribution switch CS 4  operates in an unsaturated zone, and the value of I 4  is adjusted in such a manner that the value of I 4 +I 5  is the same as the maximum current value I CS4  allowed by the distribution switch CS 4 . In this case, a ratio of I 4  to I 5  may be determined based on the maximum current value I BS4  provided when the bypass switch BS 4  operates as a current source. Accordingly, Itt 4 =I CS4  is satisfied. 
         [0089]    In  FIG. 5E , the distribution switch CS 5  operates in an unsaturated zone. Accordingly, Itt 5 =I CS5  is satisfied. 
         [0090]    To make relative brightness levels of the light-emitting groups CH 1  to CH 5  as uniform as possible at a predetermined timing, the maximum current values providable when the switches CS 1  to CS 5  and BS 1  to BS 4  serve as current sources may be optimized. 
         [0091]      FIG. 6A  is a diagram showing the structure of a light-emitting device  100  according to an embodiment of the present invention. 
         [0092]    In  FIG. 6A , the light-emitting device  100  may be the above-described LED lighting circuit  1 . 
         [0093]    The light-emitting device  100  may include a power supply  10  for supplying power having a variable potential, and a plurality of light-emitting groups  20 . 
         [0094]    In this case, each of the light-emitting groups  20  includes one or more light-emitting elements. The light-emitting groups  20  are electrically connected to each other to be numbered in a direction from an upper stream to a lower stream, and are configured to receive power supplied from the power supply  10 . Here, the ‘upper stream’ may refer to a direction closer to a current output node of the power supply  10 , and the ‘lower stream’ may refer to a direction farther away from the current output node of the power supply  10 . 
         [0095]    The light-emitting device  100  may further include a first bypass unit  30  for electrically connecting an upper stream node of a first light-emitting group  20 ,  21  which is arbitrary-numbered, to an upper stream node of a second light-emitting group  20 ,  22  which is arbitrary-numbered and provided at a lower stream of the first light-emitting group  20 ,  21 , in an interruptive manner. Here, the ‘upper stream node’ may refer to a node closer to the power supply  10  between nodes provided to each light-emitting group (i.e., a current input node), and a ‘lower stream node’ may refer to a node farther away from the power supply  10  between nodes provided to each light-emitting group (i.e., a current output node). Here, the ‘interruptive manner’ mean that a current flowing channel can be formed or interrupted between two nodes provided by the first bypass unit  30 . 
         [0096]    The light-emitting device  100  may further include a second bypass unit  40  for electrically connecting a lower stream node of the first light-emitting group  20 ,  21  to a lower stream node of the second light-emitting group  20 ,  22  or a lower stream node of a third light-emitting group  20 ,  23  which is arbitrary-numbered and provided at a lower stream of the second light-emitting group  20 ,  22 , in an interruptive manner. Here, the ‘interruptive manner’ mean that a current flowing channel can be formed or interrupted between two nodes provided by the second bypass unit  40 . 
         [0097]      FIG. 6B  is a diagram showing the power supply  10 , the light-emitting group  20 , the first bypass unit  30 , the second bypass unit  40 , and the light-emitting element  901  illustrated in  FIG. 6A .  FIG. 6B  also shows specific implementation examples of the light-emitting group  20 , the first bypass unit  30 , and the second bypass unit  40 . These implementation examples are applied to the LED lighting circuit  1  of  FIG. 2 . In this case, a circuit between two nodes T 1  and T 2  provided by the first bypass unit  30  may be interrupted by a bypass switch  903  BS. Another node T 3  may be selectively provided to the first bypass unit  30  according to an embodiment. A circuit between two nodes T 1  and T 2  provided by the second bypass unit  40  may be interrupted by a distribution switch  902  CS. 
         [0098]    In the following embodiments of the present invention, the power supply  10  may also be called a ‘rectifier’. 
         [0099]    The light-emitting group  20  may also be called a ‘light-emitting channel’ or an ‘LED light-emitting group’. 
         [0100]    The first bypass unit  30  may also be called a ‘jump circuit unit’, a ‘bypass line’, or a ‘first circuit unit’. 
         [0101]    The second bypass unit  40  may also be called a ‘distribution circuit unit’ or a ‘second circuit unit’. 
         [0102]    The light-emitting element  901  may also be called an ‘LED cell’ or an ‘LED element’. 
         [0103]    The bypass switch  903  may also be called a ‘jump switch’. 
         [0104]      FIG. 7  is a diagram showing the structure of an LED lighting device  200  according to another embodiment of the present invention. 
         [0105]    The LED lighting device  200  may receive alternating current (AC) power  90  as operation power. 
         [0106]    The LED lighting device  200  includes one or more LED cells  901 , and may include N light-emitting channels  20  linearly connected to each other (N is a natural number equal to or greater than 2). 
         [0107]    The LED lighting device  200  may further include a rectifier  10  electrically connected to an initial node of the light-emitting channels  20  to rectify the AC power  90  to be supplied to a last node of the light-emitting channels  20 . Here, the initial node may refer to a light-emitting channel provided closest to a current output node of the rectifier  10  among the light-emitting channels  20 , and the last node may refer to a light-emitting channel provided farthest away therefrom. 
         [0108]    The LED lighting device  200  may further include a plurality of distribution circuit units  40  each extending from a connection node between two light-emitting channels  20 , connected to the ground, and including a distribution switch  902  for interrupting a current flowing through a connection path thereof. 
         [0109]    The LED lighting device  200  may further include a jump circuit unit  30  extending from an input node of an M th  light-emitting channel  20 ,  211  among the light-emitting channels  20 , connected to an input node of an (M+1) th  light-emitting channel  20 ,  212 , and including a jump switch  903  for interrupting a current flowing through a connection path thereof (M is a natural number equal to or greater than 1 and equal to or less than N−1). 
         [0110]    The LED lighting device  200  may further include a backflow preventer  904  provided on a line between a connection node between the M th  light-emitting channel  20 ,  211  and the (M+1) th  light-emitting channel  20 ,  212 , and the input node of the (M+1) th  light-emitting channel  20 ,  212  to prevent a current flowing through the jump circuit unit  30  to the input node of the (M+1) th  light-emitting channel  20 ,  212  from flowing back toward the rectifier  10 . 
         [0111]      FIG. 7  also shows an implementation example of the backflow preventer  904 . The backflow preventer  904  may be implemented as a diode D or a transistor. Examples of the transistor are as described above. This implementation example is applied to the LED lighting circuit  1  illustrated in  FIG. 2 . The backflow preventer  904  may be implemented as a transistor other than a diode D. In this case, an on/off state of the transistor may be controlled based on the time periods P 0  to P 5  shown in  FIG. 3 . 
         [0112]    The jump circuit unit  30 , the light-emitting channels  20 , and the distribution circuit units  40  illustrated in  FIG. 7  may be implemented to have the same structures as the first bypass unit  30 , the light-emitting groups  20 , and the second bypass unit  40  illustrated in  FIG. 6A , respectively. 
         [0113]      FIG. 8  is a diagram showing the structure of an LED lighting device  300  according to another embodiment of the present invention. 
         [0114]    The LED lighting device  300  may have a structure in which a plurality of LED light-emitting groups  20  each including one or more LED elements  901  are sequentially connected to each other. 
         [0115]    The LED lighting device  300  may include a power supply  10  for supplying AC power to an LED light-emitting group  20 ,  203  provided at one end of the LED light-emitting groups  20 . 
         [0116]    The LED lighting device  300  may further include a bypass line  30  for interconnecting input and output nodes of a first LED light-emitting group  20 ,  204  corresponding to at least one of the LED light-emitting groups  20 . 
         [0117]    The LED lighting device  300  may further include a bypass switch  903  provided on the bypass line  30  to close the bypass line  30  when the potential of the power supplied by the power supply  10  is not higher than the potential of power capable of turning on an LED light-emitting group  20 ,  205  next to the first LED light-emitting group  20 ,  204 . 
         [0118]    The bypass line  30 , the LED light-emitting groups  20 , and distribution circuit units  40  illustrated in  FIG. 8  may be implemented to have the same structures as the first bypass unit  30 , the light-emitting groups  20 , and the second bypass unit  40  illustrated in  FIG. 6A , respectively. In this case, since the above-described backflow preventer  904  is provided between a current output node of the bypass line  30  and a current output node of the first LED light-emitting group  20 ,  204 , a current output from the current output node of the bypass line  30  may be prevented from flowing toward the first LED light-emitting group  20 ,  204 . 
         [0119]      FIG. 9  is a diagram showing the structure of an LED lighting device  400  according to another embodiment of the present invention. 
         [0120]    The LED lighting device  400  may receive AC power  10  as operation power. 
         [0121]    The LED lighting device  400  may include a plurality of light-emitting groups  20 . In this case, each of the light-emitting groups  20  may include one or more LED elements  901 , and the light-emitting groups  20  may be linearly and electrically connected to each other to be numbered from the uppermost stream to the lowermost stream. Here, the ‘uppermost stream’ refers to the closest location to a current output node of the power supply  10 , and the ‘lowermost stream’ refers to the farthest location therefrom. 
         [0122]    The LED lighting device  400  may further include first circuit units  30  for bypassing connection nodes between the light-emitting groups  20 . 
         [0123]    The LED lighting device  400  may further include second circuit units  40  for connecting the connection nodes to the ground in such a manner that AC power is supplied to a lower stream light-emitting group earlier than an upper stream light-emitting group among the light-emitting groups  20  while the potential of the supplied AC power  10  is being increased. 
         [0124]    In this case, a backflow preventer may be prevented between a current output node of an arbitrary light-emitting group  20  and a current output node of the first circuit unit  30  configured to bypass a current capable of flowing through the arbitrary light-emitting groups  20 . In this case, a current output from the current output node of the first circuit unit  30  may not pass through the backflow preventer. 
         [0125]      FIGS. 10A to 10C  are diagrams showing an example of a light-emitting unit  2  included in an LED lighting circuit, according to an embodiment of the present invention. 
         [0126]      FIG. 10A  is a block diagram of the light-emitting unit  2  according to an embodiment of the present invention. The light-emitting unit  2  may have three input and output nodes, e.g., a current input node TI, a current output node TO 1 , and a current bypass output node TO 2 . 
         [0127]    The light-emitting unit  2  may include a first bypass unit  30 , a light-emitting group  20 , and a second bypass unit  40 . The light-emitting unit  2  may selectively include a backflow preventer  904 . 
         [0128]    When two nodes of the first bypass unit  30  are connected to each other (i.e., when a current flows through the first bypass unit  30 ), two nodes of the second bypass unit  40  may be connected to each other (i.e., a current may flow through the second bypass unit  40 ). When the two nodes of the first bypass unit  30  are open (i.e., when no current flows through the first bypass unit  30 ), the two nodes of the second bypass unit  40  may also be open (i.e., no current may flow through the second bypass unit  40 ). 
         [0129]    Accordingly, when the two nodes of the first bypass unit  30  are connected to each other, a part of a current input through the current input node TI may be input to the light-emitting group  20  and the other part thereof may be bypassed along a path provided by the first bypass unit  30 . At least a part or the whole of a current output from an output node of the light-emitting group  20  may not be output to the current output node TO 1  but may be bypassed through the second bypass unit  40  and output to the current bypass output node TO 2 . The current passing through the path provided by the first bypass unit  30  may be output to the current output node TO 1 . 
         [0130]    Unlike this, when the two nodes of the first bypass unit  30  are open, the current input through the current input node TI is completely input to the light-emitting group  20 . The current output from the output node of the light-emitting group  20  may be completely output to the current output node TO 1 . 
         [0131]    A resistor may be connected to the current bypass output node TO 2 . The resistor may be, for example, the resistor Rs of  FIG. 2 . The value of a current flowing through a distribution switch CS of  FIG. 10B  may be determined based on the value of the resistor and the value of a voltage V input to the distribution switch CS. 
         [0132]      FIG. 10B  shows an implementation example of the light-emitting unit  2  illustrated in  FIG. 10A . The implementation example of the light-emitting unit  2  according to  FIG. 10B  is applied to the LED lighting circuit  1  of  FIG. 2 . 
         [0133]      FIG. 10C  illustrates an LED lighting circuit  600  achieved by interconnecting the light-emitting units  2  illustrated in  FIG. 10A , according to an embodiment of the present invention. 
         [0134]    The LED lighting circuit  600  may include one or more light-emitting units  2  each including the light-emitting group  20 , the current input node TI, the current output node TO 1 , and the current bypass output node TO 2 . 
         [0135]    In this case, the current output node TO 1  is configured to selectively output the whole or a part of a current input through the current input node TI. The current bypass output node TO 2  is configured to output the other part of the current when the current output node TO 1  outputs the part of the current. In this case, the other part of the current may be a current flowing through the light-emitting group  20 . 
         [0136]    The current output node TO 1  of the light-emitting unit  2  may be connected to another light-emitting group  20 . In this case, the other light-emitting group  20  may or may not be included in another light-emitting unit  2 . 
         [0137]    The current bypass output node TO 2  of the light-emitting unit  2  may be connected to a current output node of another light-emitting group  20 . In this case, the other light-emitting group  20  may or may not be included in another light-emitting unit  2 . 
         [0138]    Meanwhile, an LED lighting device driven using AC power may adjust a brightness level thereof using a triac dimmer. However, when the triac dimmer is used, if a voltage applied to an LED is reduced at a low brightness level, jittering of an output waveform of the triac dimmer may be delivered to the LED and thus the LED may flicker. 
         [0139]    Referring to  FIG. 15 , in the case of the output waveform of the triac dimmer (see (b) of  FIG. 15 ), jitters in phase may occur at low dimming and thus flicker of light may be caused. (a) of  FIG. 15  shows an AC input waveform. 
         [0140]    A description is now given of a dimming control LED lighting circuit included in an LED lighting circuit according to the previous embodiment to prevent flicker of light when a triac dimmer is applied to the LED lighting circuit. 
         [0141]      FIG. 11  is a diagram showing an LED lighting circuit  1  including a flicker controller  60 , according to an embodiment of the present invention. The LED lighting circuit  1  according to the current embodiment further includes the flicker controller  60  compared to the LED lighting circuit  1  of  FIG. 1A , and thus a repeated description between the two embodiments is not provided here. 
         [0142]    Referring to  FIG. 11 , the flicker controller  60  may be connected to an input node n 1  through which power or a current is input, to control flicker of the light-emitting groups CH 1  and CH 2 . For example, the flicker controller  60  may be connected between the input node n 1  and a current bypass output node. On-off states of the distribution switches CS 1  and CS 2  may be controlled based on bias voltages V 1  and V 2  applied through gates thereof. For example, these bias voltages V 1  and V 2  may be set by dividing a reference voltage Vref. 
         [0143]    The flicker controller  60  may prevent flicker of the light-emitting groups CH 1  and CH 2  by controlling the bias voltages V 1  and V 2  applied to the distribution switches CS 1  and CS 2 , in association with input power Vi. For example, the bias voltages V 1  and V 2  may be set by dividing the reference voltage Vref using resistors CR 1  and CR 2  connected to each other in series. The flicker controller  60  may be connected to the input voltage Vi and may be configured to set the reference voltage Vref to 0 and thus to turn off the light-emitting groups CH 1  and CH 2  when the input voltage Vi is equal to or lower than a predetermined voltage which causes flicker of light. 
         [0144]    In addition to the lighting device of  FIG. 1A , the flicker controller  60  may also be included in the lighting circuits or lighting devices of  FIGS. 2 to 10C  to control bias voltages. 
         [0145]      FIG. 12  is a diagram showing an example of a flicker controller  60   a  applied to an LED lighting circuit according to embodiments of the present invention. For example, the flicker controller  60   a  may be at least a part of the flicker controller  60  illustrated in  FIG. 11 . 
         [0146]    Referring to  FIGS. 11 and 12 , the flicker controller  60   a  may adjust the reference voltage Vref based on the input voltage Vi using a comparator CP 1 . In detail, the input voltage Vi may be connected to a resistor R 22 , and the resistor R 22  may be connected through a node n 20  to a resistor R 21  in series. As such, the potential of the node n 20  may be determined based on the values of the two resistors R 21  and R 22 , and has a value of Vi*R 21 /(R 21 +R 22 ) in the circuit of  FIG. 12 . 
         [0147]    A minus (−) node of the comparator CP 1  may be connected to the node n 20 , and a plus (+) node thereof may be connected to a threshold voltage Vth. An output node of the comparator CP 1  is connected to a gate of a transistor ST 11 , and one end of the transistor ST 11  is connected through a resistor R 23  to a voltage Va and another end thereof is grounded. The reference voltage Vref is connected to a node n 21  provided between the one end of the transistor ST 11  and the resistor R 23 . 
         [0148]    According to the above description, when the input voltage Vi is lower than a comparative voltage, i.e., Vth*(1+R 22 /R 21 ), output of the comparator CP 1  is in an high state and thus the reference voltage Vref is 0V. In this case, both the bias voltages V 1  and V 2  have a value of 0V and thus the light-emitting groups CH 1  and CH 2  are both turned off. Otherwise, when the input voltage Vi is higher than the comparative voltage, the output of the comparator CP 1  in a low state and thus the reference voltage Vref has a value of Va. In this case, one or both of the light-emitting groups CH 1  and CH 2  are turned on based on the magnitude of Va. 
         [0149]    Using this flicker controller  60   a,  when the input voltage Vi is equal to or lower than the comparative voltage, both the light-emitting groups CH 1  and CH 2  may be turned off and thus the LED may not flicker. 
         [0150]      FIG. 13  is a diagram showing another example of a flicker controller  60   b  applied to an LED lighting circuit according to embodiments of the present invention. For example, the flicker controller  60   b  may be at least a part of the flicker controller  60  illustrated in  FIG. 11 . 
         [0151]    Referring to  FIGS. 11 and 13 , the flicker controller  60   b  may adjust the reference voltage Vref based on the input voltage Vi using a Zener diode ZD. In detail, two resistors R 31  and R 32  are connected to each other in series by intervening a node n 30  therebetween, and the input power Vi is connected through the resistor R 32 . One end of the Zener diode ZD is connected to the node n 30 , another end thereof is connected to a gate of a transistor ST 31 , and the Zener diode ZD is provided in such a manner that a direction from the one end to the other end is reversed. A voltage Vcc is connected through a resistor R 34  to one end of the transistor ST 31 , and another end of the transistor ST 31  is grounded. A node n 31  between the resistor R 34  and the one end of the transistor ST 31  is connected to a gate of a transistor ST 32 . A voltage Va is connected through a resistor R 33  to one end of the transistor ST 32 , and another end of the transistor ST 32  is grounded. The reference voltage Vref is connected to a node n 32  between the resistor R 33  and the transistor ST 32 . 
         [0152]    According to the above description, when the input voltage Vi is lower than a comparative voltage, i.e., Vth*(1+R 32 /R 31 ), the transistor ST 31  is turned off and thus the potential of the node n 31  is Vcc. As such, the transistor ST 32  is turned on and thus the reference voltage Vref is 0V. In this case, both the bias voltages V 1  and V 2  have a value of 0V and thus the light-emitting groups CH 1  and CH 2  are both turned off. Otherwise, when the input voltage Vi is higher than the comparative voltage, the transistor ST 31  is turned on, 0V is applied to the gate of the transistor ST 32 , the transistor ST 32  is turned off, and thus the reference voltage Vref has a value of Va. In this case, one or both of the light-emitting groups CH 1  and CH 2  are turned on based on the magnitude of Va. 
         [0153]    Using this flicker controller  60   b,  when the input voltage Vi is equal to or lower than the comparative voltage, both the light-emitting groups CH 1  and CH 2  may be turned off and thus the LED may not flicker. 
         [0154]    The above-described LED lighting device is configured in such a manner that AC power is rectified using a bridge diode, that the numbers of parallel- and serial-connected LED groups are automatically adjusted based on a voltage level of the rectified ripple voltage, and that a total current applied to the LED group is increased based on voltage levels. As such, a power factor and efficiency may be simultaneously improved. Furthermore, flicker of light which is caused when the light is dimmed may be prevented by adding a flicker controller. 
         [0155]      FIG. 14  is a diagram showing an LED lighting circuit including a flicker controller  60 , according to another embodiment of the present invention. The LED lighting circuit of  FIG. 14  is similar to the LED lighting circuit  1  of  FIG. 11  except that no bypass circuit is included and the number of light-emitting groups is increased to n, and thus a repeated description between the two embodiments is not provided here. 
         [0156]    Referring to  FIG. 14 , n light-emitting groups CH 1  to CHn are connected to each other in series, and an input voltage Vi may be applied through a current input node n 10  to the light-emitting group CH 1  of the uppermost stream. Connection nodes between the light-emitting groups CH 1  to CHn may be connected through distribution switches CS 1  to CSn to a current bypass output node n 20 , and the current bypass output node n 20  may be connected through the resistor Rs to the ground. 
         [0157]    Bias voltages V 1  to Vn may be applied to gates of the distribution switches CS 1  to CSn, and these bias voltages V 1  to Vn may be set by dividing a reference voltage Vref. For example, the reference voltage Vref may be divided using resistors CR 1  to CRn, and the bias voltages V 1  to Vn may be connected to nodes between the resistors CR 1  to CRn. 
         [0158]    The flicker controller  60  may be connected between the current input node n 10  and the current bypass output node n 20 , for example, between the current input node n 10  and the reference voltage Vref. For a description of the flicker controller  60 , reference can be made to the descriptions of the flicker controllers  60   a  and  60   b  of  FIGS. 12 and 13 . 
         [0159]    Using this flicker controller  60 , when the input voltage Vi is equal to or lower than a comparative voltage, the light-emitting groups CH 1  to CHn may be all turned off, and thus flicker of light which is caused when an LED is turned on may be prevented. 
         [0160]    The above-described flicker controller of the dimming control LED lighting circuit may also be applied to the lighting circuit or the lighting device of  FIGS. 1 to 10 , and may be used in a variety of lighting circuits for controlling an LED using a bias voltage. 
         [0161]    According to the present invention, a light-emitting diode (LED) lighting device capable of increasing usability of LEDs and improving light output efficiency when alternating current (AC) power is directly applied to the LEDS may be provided. 
         [0162]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.