Patent Publication Number: US-2016234909-A1

Title: Led lamp

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. application Ser. No. 14/717,341 filed on May 20, 2015, which is a continuation of U.S. application Ser. No. 13/886,002 filed on May 2, 2013, which is a continuation-in-part of U.S. application Ser. No. 13/708,267 filed on Dec. 7, 2012, which is a continuation of U.S. application Ser. No. 12/473,098 filed on May 27, 2009. This application also claims the benefit of U.S. application Ser. No. 13/886,002, filed on May 2, 2013, U.S. application Ser. No. 13/708,267 filed on Dec. 7, 2012, U.S. application Ser. No. 12/473,098 filed on May 27, 2009, Korean Patent Application No. 10-2008-0101413 filed on Oct. 16, 2008, No. 10-2008-0109048 filed on Nov. 4, 2008, No. 10-2008-0123444 filed on Dec. 5, 2008, and No. 10-2009-0018268 filed on Mar. 4, 2009 in the Korean Intellectual Property Office, the disclosures of which are expressly incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light-emitting diode (LED) lamp, and more particularly, to an LED lamp which is suitable for use, instead of a typical fluorescent lamp, with a fluorescent lamp ballast. 
     2. Description of the Related Art 
     Due to the improvement of the optical efficiency of light-emitting diodes (LEDs), which has been previously used as low-power indicator lights, the range of application of LEDs has gradually widened. LEDs, unlike other light sources, do not contain mercury and are thus deemed as environment-friendly light sources. Therefore, LEDs have recently come into the limelight as next-generation light sources for mobile terminals, liquid crystal display (LCD) TVs, or automobiles. Accordingly, incandescent lamps or fluorescent lamps, which have been used as major light sources for the past hundred years, are rapidly being replaced by LEDs. 
     LED lamps can directly replace incandescent lamps such as E26 base lamps. However, in order to replace existing fluorescent lamps with LED lamps, it is necessary to change lamp fixtures or to additionally install a power supply exclusive for LED lamps. Thus, LED lamps have not yet been widely distributed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light-emitting diode (LED) fluorescent lamp which is suitable for use, instead of a typical fluorescent lamp, in an existing fluorescent lamp fixture without any requirement for installation of an additional fluorescent lamp ballast exclusively for the LED lamp or modification of internal wiring of the fixture. 
     According to an aspect of the present invention, there is provided a light-emitting diode (LED) lamp comprising a plurality of external connection; an LED array including a plurality of LEDs in series; one or more circuit breakers (e.g., fuse) connected between the LED array and the external connection pins; and one or more capacitors connected in series between the LED array and the external connection pins, wherein the one or more capacitors varying an impedance of the electronic lamp ballast connected to the LED lamp through the external connection pins. 
     According to an aspect of the present invention, the one or more circuit breakers include at least one of, a first circuit breaker having a first end connected to a first connection pin and a second end connected to an anode terminal of the LED array; and a second circuit breaker having a first end connected to a second connection pin and a second end connected to a cathode terminal of the LED array. 
     According to another aspect of the present invention, the one or more circuit breakers include at least one of, a first circuit breaker having a first end, which is connected to a first connection pin, and a second end; and a second circuit breaker having a first end, which is connected to a second connection pin, and a second end, and the one or more capacitors include at least one of, a first capacitor having a first end connected to the second end of the first circuit breaker and a second end connected to an anode terminal of the LED array; and a second capacitor having a first end connected to the second end of the second circuit breaker and a second end connected to a cathode terminal of the LED array. 
     According to another aspect of the present invention, the one or more circuit breakers include at least one of, a first circuit breaker having a first end, which is connected to a first connection pin, and a second end; and a second circuit breaker having a first end, which is connected to a second connection pin, and a second end, the one or more capacitors include at least one of, a first capacitor having a first end which is connected to the second end of the first circuit breaker, and a second end; and a second capacitor having a first end which is connected to the second end of the second circuit breaker, and a second end, and the LED lamp further includes at least one of, a first diode having an anode connected to the second end of the first capacitor and a cathode connected to an anode terminal of the LED array; and a second diode having a cathode connected to the second end of the second capacitor and an anode connected to a cathode terminal of the LED array. 
     According to another aspect of the present invention, the one or more circuit breakers include at least one of, a first circuit breaker having a first end which is connected to a first connection pin, and a second end; and a second circuit breaker having a first end which is connected to a second connection pin, and a second end; a third circuit breaker having a first end which is connected to a third connection pin, and a second end; and a fourth circuit breaker having a first end which is connected to a fourth connection pin, and a second end, the one or more capacitors include at least one of, a first capacitor having a first end which is connected to the second end of the first circuit breaker, and a second end; and a second capacitor having a first end and which is connected to the second end of the second circuit breaker, a second end; a third capacitor having a first end connected to the second end of the third circuit breaker and a second end connected to the anode of the first diode; and a fourth capacitor having a first end connected to the second end of the fourth circuit breaker and a second end connected to the cathode of the first diode, and the LED lamp further includes at least one of, a first diode having an anode connected to the second end of the first capacitor and a cathode connected to an anode terminal of the LED array; and a second diode having a cathode connected to the second end of the second capacitor and an anode connected to a cathode terminal of the LED array. 
     According to another aspect of the present invention, the LED lamp further comprises at least one of, a third diode connected in parallel to the first capacitor; a fourth diode connected in parallel to the second capacitor; a fifth diode connected in parallel to the third capacitor; and 
     a sixth diode connected in parallel to the fourth capacitor. 
     According to another aspect of the present invention, the LED lamp further comprises at least one of, a first resistor connected in parallel to the third capacitor; a second resistor connected in parallel to the fourth capacitor; a third resistor connected in parallel to the fifth capacitor; and a fourth resistor connected in parallel to the sixth capacitor. 
     According to another aspect of the present invention, the LED lamp further comprises at least one of, a seventh diode having an anode connected to the anode of the fourth diode and a cathode connected to the anode of the third diode; an eighth diode having an anode connected to the cathode of the fourth diode and a cathode connected to the cathode of the third diode; a ninth diode having an anode connected to the cathode of the sixth diode and a cathode connected to the cathode of the fifth diode; and a tenth diode having an anode connected to the anode of the sixth diode and a cathode connected to the anode of the fifth diode. 
     According to another aspect of the present invention, the LED lamp further comprises at least one of, a seventh diode having an anode connected to the cathode of the fourth diode and a cathode connected to the cathode of the first diode; and an eighth diode having an anode connected to the anode of the second diode and a cathode connected to the cathode of the fifth diode. 
     According to another aspect of the present invention, the circuit breaker can be a fuse; the electronic fluorescent lamp ballast can be a half-bridge-type fluorescent lamp ballast; and the LED lamp comprises a plurality of LED arrays connected in parallel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a circuit diagram of a light-emitting diode (LED) fluorescent lamp according to a first exemplary embodiment of the present invention; 
         FIG. 2  illustrates a circuit diagram of an LED array shown in  FIG. 1 ; 
         FIG. 3  illustrates a circuit diagram of an LED lamp according to a second exemplary embodiment of the present invention; 
         FIG. 4  illustrates a circuit diagram of an LED lamp according to a third exemplary embodiment of the present invention; 
         FIG. 5  illustrates a circuit diagram of an LED lamp according to a fourth exemplary embodiment of the present invention; 
         FIG. 6  illustrates a circuit diagram of an LED lamp according to a fifth exemplary embodiment of the present invention; 
         FIG. 7  illustrates a circuit diagram of an LED lamp according to a sixth exemplary embodiment of the present invention; 
         FIG. 8  illustrates a circuit diagram of an LED lamp according to a seventh exemplary embodiment of the present invention; 
         FIG. 9  illustrates a circuit diagram of an LED lamp according to an eighth exemplary embodiment of the present invention; 
         FIG. 10  illustrates a circuit diagram of an LED lamp according to a ninth exemplary embodiment of the present invention; 
         FIG. 11  illustrates a circuit diagram of an LED lamp according to a tenth exemplary embodiment of the present invention; 
         FIG. 12  illustrates a circuit diagram of a half-bridge-type electronic fluorescent lamp ballast to which the LED lamp of the fourth exemplary embodiment is applied; 
         FIG. 13  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp of the fourth exemplary embodiment is applied; 
         FIG. 14  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp of the sixth exemplary embodiment is applied; 
         FIG. 15  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp to which the LED lamp of the seventh exemplary embodiment is applied; 
         FIG. 16  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp of the ninth exemplary embodiment of the present invention is applied; 
         FIG. 17  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp of the tenth exemplary embodiment of the present invention is applied; 
         FIG. 18  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp of the fourth exemplary embodiment is applied; 
         FIG. 19  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp of the sixth exemplary embodiment is applied; 
         FIG. 20  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp of the seventh exemplary embodiment is applied; 
         FIG. 21  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp of the tenth exemplary embodiment is applied; 
         FIG. 22  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp of the fourth exemplary embodiment is applied; 
         FIG. 23  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp of the sixth exemplary embodiment is applied; 
         FIG. 24  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp of the seventh exemplary embodiment is applied; 
         FIG. 25  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp of the tenth exemplary embodiment is applied; 
         FIG. 26  illustrates a circuit diagram of a rapid start-type magnetic fluorescent lamp ballast to which the LED lamp of the fourth exemplary embodiment is applied; 
         FIG. 27  illustrates a circuit diagram of a rapid start-type magnetic fluorescent lamp ballast to which the LED lamp of the sixth exemplary embodiment is applied; 
         FIG. 28  illustrates a circuit diagram of a rapid start-type magnetic fluorescent lamp ballast to which the LED lamp of the seventh exemplary embodiment is applied; 
         FIG. 29  illustrates a circuit diagram of an iron-core rapid start-type fluorescent lamp ballast to which the LED lamp of the ninth exemplary embodiment is applied; and 
         FIG. 30  illustrates a circuit diagram of an iron-core rapid start type fluorescent lamp ballast to which the LED lamp of the tenth exemplary embodiment is applied; 
         FIG. 31  illustrates a circuit diagram of an LED lamp according to a eleventh exemplary embodiment of the present invention, in which circuit breakers are applied in the sixth exemplary embodiment to protect the circuit; 
         FIG. 32  illustrates a circuit diagram of an LED lamp according to a twelfth exemplary embodiment of the present invention, in which circuit breakers are applied in the seventh exemplary embodiment to protect the circuit; 
         FIG. 33  illustrates a circuit diagram of an LED lamp according to a thirteenth exemplary embodiment of the present invention, in which circuit breakers are applied in the eighth exemplary embodiment to protect the circuit. 
         FIG. 34  illustrates a circuit diagram of an LED lamp according to a fourteenth exemplary embodiment of the present invention, in which circuit breakers are applied in the ninth exemplary embodiment to protect the circuit; 
         FIG. 35  illustrates a circuit diagram of an LED lamp according to a fifteenth exemplary embodiment of the present invention, in which circuit breakers are applied in the tenth exemplary embodiment to protect the circuit; 
         FIG. 36  illustrates an exploded perspective view of an LED lamp according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will hereinafter be described in detail with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. 
     Basic circuitries of electronic fluorescent lamp ballasts can generally be classified into a half bridge-type, an instant start-type and a program start-type. A conventional iron-core based magnetic ballasts can be classified into a starter type and a rapid start type. LED lamps according to exemplary embodiments of the present invention can be applied to almost all types of fluorescent lamp ballasts. The structures of the LED lamps according to the exemplary embodiments of the present invention and the operations of various types of fluorescent lamp ballasts to which the LED lamps according to exemplary embodiments of the present invention are applied will hereinafter be described in detail. 
       FIG. 1  illustrates a circuit diagram of an LED lamp  110  according to a first exemplary embodiment of the present invention. Referring to  FIG. 1 , the LED lamp  110  may include an LED array  10 , a plurality of capacitors C 11  through C 14 , and a plurality of external connection pins, i.e., first  111  through fourth  114 . The LED lamp  110  may use only two of the first through fourth connection pins  111  through  114 . The LED lamp  110  may include two or more LED arrays  10  connected in parallel to each other. The structure of the LED lamp  110  may be directly applied to LED lamps according to other exemplary embodiments of the present invention. 
     The LED array  10  may include a plurality of LEDs (not shown) connected in series, an anode terminal  10   a  and a cathode terminal  10   b . The capacitor C 11  may be connected between the anode terminal  10   a  and the first connection pin  111 , and the capacitor C 12  may be connected between the cathode terminal  10   b  and the second connection pin  112 . The capacitor C 13  may be connected between the anode terminal  10   a  and the third connection pin  113 , and the capacitor C 14  may be connected between the cathode terminal  10   a  and the fourth connection pin  114 . 
     The capacitors C 11  through C 14  may be connected to a half-bridge type of electronic ballast circuit via the first through fourth connection pins  111  through  114  and may thus control the operating frequency of the series resonant circuit which is composed of internal inductor and capacitor of the ballast. Due to the variation of the operating frequency of the ballast, the impedance of the inductor inside the ballast can be controlled and, as a result, the amount of current of LED lamp  110  can also be controlled. Thus, the basic structure of LED lamp  110  may be applied to almost all types of fluorescent lamp ballasts. 
       FIG. 2  illustrates a circuit diagram of the LED array  10  shown in  FIG. 1 . Referring to  FIG. 2( a ) , the LED array  10  may include a plurality of LEDs D 1  through Dn connected in series. 
     In order to protect the LEDs D 1  through Dn, the LED array  10  may also include a plurality of zener diodes Z 1  through Zn connected in parallel to the LEDs D 1  through Dn, respectively, in an opposite direction to the direction in which the LEDs D 1  through Dn are aligned, as shown in  FIG. 2( b ) . Referring to  FIG. 2( b ) , if the applied voltage at  10   a  is positive with respect to  10   b , a current may flow through the LEDs D 1  through Dn. On the other hand, during a negative period of the input AC voltage, a current may flow through the zener diodes Z 1  through Zn. The flow of a current through the zener diodes Z 1  through Zn may become an ineffective loss. Therefore, in order to prevent the flow of a reverse current through the zener diodes Z 1  through Zn and thus to improve efficiency, various modifications may be made to the first exemplary embodiment, and this will hereinafter be described in detail. 
       FIG. 3  illustrates a circuit diagram of an LED lamp  120  according to a second exemplary embodiment of the present invention. The second exemplary embodiment is the same as the first exemplary embodiment except that the LED lamp  120  includes two diodes D 21  and D 22  connected in series to either end of an LED array  12 . The LED lamp  120  may include only one of the diodes D 21  and D 22 . The diodes D 21  and D 22  may allow a current to flow in the LED array  12  only in a forward direction. Therefore, even if the LED array  12  includes a plurality of zener  10  diodes (not shown) connected in parallel to LEDs, it is possible to prevent power loss that may be caused by a current flown through the zener diodes during a negative period of an input AC voltage. 
       FIG. 4  illustrates a circuit diagram of an LED lamp  130  according to a third exemplary embodiment of the present invention. Referring to  FIG. 4 , the LED lamp  130  may include an LED array  13 , first through fourth connection pins  131  through  134 , a plurality of capacitors C 31  through C 34  connected to the first through fourth connection pins  131  through  134 , respectively, and a plurality of diodes D 33  through D 36  connected in parallel to the capacitors C 31  through C 34 , respectively. If the output terminals of a series-resonant type of electronic ballast is connected to the connection pin pairs ( 131  and  133 ) and ( 132  and  134 ) and a series-resonance sustain capacitor inside the electronic ballast is connected between the first and second connection pins  131  and  132  or between the third and fourth connection pins  133  and  134  as shown in  FIG. 12 , the flow of a current in the LED array  13  may be controlled by the diodes D 33  through D 36  according to the polarity of an input voltage provided by the electronic ballast. For example, if a positive voltage is applied to the third connection pin  133  when the connection pin  134  is set as a reference point and the series-resonance sustain capacitor is connected between the first and second connection pins  131  and  132 , the capacitor C 33  may become short-circuited by the diode D 35 , the diodes D 33  and D 34  may become open, and the capacitor C 34  may become short-circuited by the diode D 36 . In this case, the initial resonant capacitance of the electronic ballast may be equal to the total capacitance of the capacitor C 31 , the series-resonance sustain capacitor C 1  and the capacitor C 32  in series and the resonant frequency of the ballast may be changed by the variation of the resonant capacitance. In addition, if a negative voltage is applied to the third connection pin  133 , the capacitor C 32  may become short-circuited by the diode D 34 , and the capacitor C 31  may be short-circuited by the diode D 33 . In this case, the total capacitance of the electronic ballast may be equal to the total capacitance of the capacitor C 34 , the series-resonance sustain capacitor C 1  and the capacitor C 33  in series. 
       FIG. 5  illustrates a circuit diagram of an LED lamp  140  according to a fourth exemplary embodiment of the present invention. The fourth exemplary embodiment is the same as the third exemplary embodiment except that the LED lamp  140  also includes a plurality of diodes D 47  through D 50 . Thus, the LED lamp may be able to stably operate keeping the characteristics of symmetric operation regardless of variations in the phase of a voltage applied thereto by a fluorescent lamp ballast. 
       FIG. 6  illustrates a circuit diagram of an LED lamp  150  according to a fifth exemplary embodiment of the present invention. Referring to  FIG. 6 , the LED lamp  150  may include an LED array  15 , first through fourth connection pins  151  through  154 , a plurality of capacitors C 51  through C 54  connected to the first through fourth connection pins  151  through  154 , respectively, a plurality of diodes D 53  through D 56  connected in parallel to the capacitors C 51  through C 54 , respectively, and a plurality of resistors R 51  through R 54  connected in parallel to the capacitors C 51  through C 54 , respectively, for applying a current for an initial trigger operation of the ballast. 
       FIG. 7  illustrates a circuit diagram of an LED lamp  160  according to a sixth exemplary embodiment of the present invention. Referring to  FIG. 7 , the LED lamp  160  may include an LED array  16 , first through fourth connection pins  161  through  164 , a plurality of capacitors C 61  through C 64  connected to the first through fourth connection pins  161  through  164 , respectively, and a plurality of diodes D 63  through D 66  connected in series to the capacitors C 61  through C 64 , respectively. The diodes D 63  through D 66  and a plurality of diodes D 67  through D 70  may allow the LED lamp  160  to stably operate keeping the characteristics of symmetric operation regardless of the phase of an AC voltage applied by a fluorescent lamp ballast. 
       FIG. 8  illustrates a circuit diagram of an LED lamp  170  according to a seventh exemplary embodiment of the present invention. Referring to  FIG. 8 , the anode of a diode D 73  may be connected to a first connection pin  171 , and the cathode of the diode D 73  may be connected to the anode of a diode D 71 . The anode of a diode D 74  may be connected to a second connection pin  172 , and the cathode of the diode D 74  may be connected to the cathode of a diode D 72 . The anode of a diode D 75  may be connected to a third connection pin  173 , and the cathode of the diode D 75  may be connected to the anode of the diode D 71 . The anode of a diode D 76  may be connected to a fourth connection pin  174 , and the cathode of the diode D 76  may be connected to the cathode of the diode D 72 . The anode of the diode D 77  may be commonly connected to the cathode of the diode D 72  and second ends of capacitors C 72  and C 74 , and the cathode of the diode D 77  may be connected to an anode terminal  17   a  of an LED array  17 . 
     The anode of the diode D 78  may be connected to a cathode terminal  17   b  of the LED array  17 , and the cathode of the diode D 78  may be commonly connected to the anode of the diode D 71  and second ends of capacitors C 71  and C 73 . 
     The diodes D 77  and D 78  may allow the LED lamp  170  to stably operate keeping the characteristics of symmetric operation regardless of variations in the phase of a voltage applied to the first through fourth connection pins  171  through  174  by a fluorescent lamp ballast. 
       FIG. 9  illustrates a circuit diagram of an LED lamp  180  according to an eighth exemplary embodiment of the present invention. The eighth exemplary embodiment is the same as the seventh exemplary embodiment except for the reverse direction of diodes D 83  through D 86  which are connected in parallel to a plurality of capacitors C 81  through C 84 , respectively. 
       FIG. 10  illustrates a circuit diagram of an LED lamp  190  according to a ninth exemplary embodiment of the present invention. Referring to  FIG. 10 , the LED lamp  190  may include first through fourth connection pins  191  through  194 , a plurality of capacitors C 91  through C 94  connected to the first through fourth connection pins  191  through  194 , respectively, and a plurality of diodes D 93  through D 96  connected in series to the capacitors C 91  through C 94 , respectively. The LED lamp  190  may also include a diode D 97  having an anode connected to a second end of an LED array  19  and a cathode connected to the anode of the diode D 93  and a diode D 98  having an anode connected to the cathode of the diode D 94  and a cathode connected to a first end of the LED array  19 . 
     The diodes D 93  through D 98  may allow the LED lamp  190  to operate in various types of fluorescent lamp ballasts regardless of the phase of an AC voltage. 
       FIG. 11  illustrates a circuit diagram of an LED lamp  200  according to a tenth exemplary embodiment of the present invention. The LED lamp  200  is almost the same as the LED lamp  190  shown in  FIG. 10  except that it also includes diodes D 109  and D 110 . More specifically, referring to  FIG. 11 , the anode of the diode D 109  may be connected to the cathode of a diode D 106 , and the cathode of the diode D 109  may be connected to a first end of an LED array  20 . The anode of the diode D 110  may be connected to a second end of the LED array  20 , and the cathode of the diode D 110  may be connected to the anode of the diode D 105 . The diodes D 109  and D 110  may allow the LED lamp  200  to operate symmetrically in response to a voltage applied thereto by an external voltage source. 
     The basic structures of the LED lamps  110  through  200  of the first through tenth exemplary embodiments can be applied to nearly most types of fluorescent lamp ballasts. The operations of various types of fluorescent lamp ballasts will hereinafter be described in detail, taking the LED lamps  140 ,  160 ,  170 ,  190  and  200  of the fourth, sixth, seventh, ninth and tenth exemplary embodiments as an example. 
       FIG. 12  illustrates a circuit diagram of a half-bridge-type of fluorescent lamp ballast to which the LED lamp  140  of the fourth exemplary embodiment is applied. 
     In a half-bridge type of electronic fluorescent lamp ballast, a series-resonant circuit including an inductor and a capacitor may be connected to a switching output node of a half-bridge inverter composed of a semiconductor switching device. The half-bridge type of electronic ballast may initially ignite a fluorescent lamp using a series-resonance voltage applied to either end of the resonant capacitor. Once the fluorescent lamp is discharged, the main current flown in the fluorescent lamp will be controlled by the impedance of an inductor of the series-resonant circuit. Referring to  FIG. 12 , the resonant frequency of a series-resonant circuit and the operating frequency of switching devices Q 61  and Q 62  may be synchronized with each other by a current transformer To. Power consumption Ps may be defined by Equation (1): 
         Ps ≃IsVs   (1)
 
     where, Vs indicates a direct current (DC) input voltage and Is indicates an average current applied to an inverter. 
     A load current may be the same as the average current Is. Thus, if C 0 &gt;&gt;C 1 , C 0 &gt;&gt;C 41 ˜C 44 , and if we let the total capacitance of the LED lamp ( 140 ) with the capacitor C 1  inside the ballast to Ca then the average current Is may be defined using Equations (2) through (4): 
     
       
         
           
             
               
                 
                   
                     Is 
                     ≃ 
                     
                       
                         fCQ 
                         0 
                       
                        
                       Vs 
                     
                   
                   ; 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     C 
                     = 
                     
                       
                         
                           2 
                            
                           
                               
                           
                            
                           
                             C 
                             0 
                           
                            
                           
                             C 
                             a 
                           
                         
                         
                           
                             C 
                             a 
                           
                           + 
                           
                             2 
                              
                             
                                 
                             
                              
                             
                               C 
                               0 
                             
                           
                         
                       
                       ≃ 
                       
                         C 
                         a 
                       
                     
                   
                   ; 
                   and 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     Q 
                     0 
                   
                   = 
                   
                     
                       1 
                       
                         R 
                         0 
                       
                     
                      
                     
                       
                         
                           L 
                           0 
                         
                          
                         
                           / 
                         
                          
                         C 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     where, f indicates the operating frequency of the switching devices Q 61  and Q 62  and Ro indicates the internal resistance of the LED lamp  140  when the LED lamp  140  is operating at a resonant frequency. 
     An operating frequency f of an inverter may be defined by Equations (5): 
     
       
         
           
             
               
                 
                   
                     f 
                     = 
                     
                       
                         ω 
                         
                           2 
                            
                           
                               
                           
                            
                           π 
                         
                       
                       = 
                       
                         
                           
                             ω 
                             0 
                           
                           
                             2 
                              
                             
                                 
                             
                              
                             π 
                           
                         
                          
                         
                           
                             1 
                             - 
                             
                               1 
                                
                               
                                 / 
                               
                                
                               4 
                                
                               
                                   
                               
                                
                               
                                 Q 
                                 0 
                                 2 
                               
                             
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       ω 
                       0 
                     
                     = 
                     
                       1 
                        
                       
                         / 
                       
                        
                       
                         
                           
                             
                               L 
                               0 
                             
                              
                             C 
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Therefore, the average current Is may be calculated using Equations (2) and (5), as indicated by Equation (6): 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           I 
                           S 
                         
                         ≃ 
                           
                          
                         
                           
                             1 
                             
                               2 
                                
                               
                                   
                               
                                
                               π 
                             
                           
                            
                           
                             ω 
                             0 
                           
                            
                           
                             CQ 
                             0 
                           
                            
                           
                             V 
                             s 
                           
                            
                           
                             
                               1 
                               - 
                               
                                 1 
                                  
                                 
                                   / 
                                 
                                  
                                 4 
                                  
                                 
                                     
                                 
                                  
                                 
                                   Q 
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           ≃ 
                             
                            
                           
                             
                               
                                 
                                   Q 
                                   0 
                                 
                                  
                                 
                                   V 
                                   S 
                                 
                               
                               
                                 2 
                                  
                                 
                                     
                                 
                                  
                                 π 
                                  
                                 
                                     
                                 
                                  
                                 Z 
                               
                             
                              
                             
                               
                                 1 
                                 - 
                                 
                                   1 
                                    
                                   
                                     / 
                                   
                                    
                                   4 
                                    
                                   
                                       
                                   
                                    
                                   
                                     Q 
                                     2 
                                   
                                 
                               
                             
                           
                         
                         ; 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where Z indicates impedance. The impedance Z may be defined by Equation (7): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       
                         ω 
                         0 
                       
                        
                       
                         L 
                         0 
                       
                     
                     = 
                     
                       
                         1 
                         
                           
                             ω 
                             0 
                           
                            
                           C 
                         
                       
                       = 
                       
                         
                           
                             
                               L 
                               0 
                             
                              
                             
                               / 
                             
                              
                             C 
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     If C 0 &gt;&gt;C 1 , the operating frequency f may be determined by the total capacitance Ca. Therefore, once the LED lamp  140  is connected to a half-bridge type of electronic ballast, the half-bridge inveller may operate as follows. Referring to  FIG. 12 , at initial resonance stage, if the switching device Q 61  is turned on and thus the voltage Vs is applied to a node A, a resonance current may flow, sequentially passing through Lo, D 45 , C 41 , C 1 , C 42 , D 46 , and 2Co. On the other hand, if the switching device Q 62  is turned on, the voltage at the node A may become a ground voltage, and the resonance current may flow along an opposite path to the path of the resonant current, 2Co, C 44 , D 44 , C 1 , D 43 , C 43  and Lo. 
     To guarantee the general usage of the LED lamp  140 , the basic structure of LED lamp  140  must be symmetrical. Thus, the first through fourth connection pins  141  through  144  of the LED lamp  140  must not have any polarity. Therefore, at series-resonant condition, if C 41 =C 42 =C 43 =C 44 =C 2 , the total capacitance Ca may be defined by Equation (8): 
     
       
         
           
             
               
                 
                   
                     C 
                     a 
                   
                   = 
                   
                     
                       
                         
                           C 
                           1 
                         
                          
                         
                           C 
                           2 
                         
                       
                       
                         
                           2 
                            
                           
                               
                           
                            
                           
                             C 
                             1 
                           
                         
                         + 
                         
                           C 
                           2 
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     Therefore, if C 2 &gt;&gt;C 1 , Ca≈C 2 /2 and the impedance Z may increase. Accordingly, a current flown in the LED lamp  140  may decrease, and thus, it is possible to properly control the current flown in the LED lamp  140 . Thus, it is possible to install the LED lamp  140  in a half-bridge type of electronic fluorescent lamp ballast without the need to re-wiring the fluorescent lamp fixture. 
       FIG. 13  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  140  of the fourth exemplary embodiment is applied. Referring to  FIG. 13 , due to a self-oscillation operation of a circuit including transformers T 1  and T 2  and a capacitor C, switching devices Q 71  and Q 72  may be able to continue a switching operation. The transformer T 2  may be connected between a switching node A and a node B by a primary winding T 2 - 1 . The instant start-type of electronic fluorescent lamp ballast may initially discharge the fluorescent lamp using a high voltage induced to a secondary winding T 2 - 2  of the transformer T 2 . Once the fluorescent lamp is discharged, the instant start-type of electronic ballast may control the stabilization current with the use of a capacitor C 1 , which is connected in series to a lamp load. 
     The operation of the instant start-type of electronic ballast operating with LED lamp  140  will hereinafter be described in further detail. The transformer T 2  may resonate with the self-oscillation frequency and may thus induce a high AC voltage to the secondary winding T 2 - 2 . If the voltage at the node C is positive with respect to the voltage at the node D, a current may flow, sequentially passing through the node C, the capacitor C, the diode D 43 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 44  and the node D. On the other hand, if the voltage at the node C is negative with respect to the voltage at the node D, a current may flow, sequentially passing through the node D, the diode D 48 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 47 , the capacitor C 1  and the node C. Alternatively, a current may flow, sequentially passing through the node D, the capacitor C 42 , the diode D 47 , the capacitor c, and the node C or the node D, the diode D 48 , the capacitor C 41 , the capacitor C 1 , and the node C depending upon the total number of LEDs. 
     Therefore, the main current flown in the LED array  14  may be controlled by the value of the impedance of the capacitor C 1 , that is, 1/jΩC 1  of the instant start-type ballast and the total number of series-connected LEDs of LED array  14 . 
       FIG. 14  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  160  of the sixth exemplary embodiment is applied. Referring to  FIG. 14 , when the instant start-type electronic fluorescent lamp ballast is connected to the first and second connection pins  161  and  162  of the LED lamp  160 , a transformer T 2  may resonate with self-oscillation frequency and may thus induce a high AC voltage to a secondary winding T 2 - 2 . If the voltage at the node C is positive with respect to the voltage at the node D, a current may flow, sequentially passing through the node C, the capacitor C 1 , the capacitor C 61 , the diode D 63 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 64 , the capacitor C 62  and the node D with a phase being shifted by π/2 by the capacitance of the capacitors C 61  through C 64 . 
     On the other hand, if the voltage at the node C is negative with respect to the voltage at the node D, a current may flow, sequentially passing through the node D, the capacitor C 62 , the diode D 68 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 67 , the capacitor C 61 , the capacitor C  1  and the node C with a phase being shifted by π/2 by the capacitance of the capacitors C 61  through C 64 . 
     Therefore, the main current flown in the LED array  16  may be controlled by the total composite impedance of the series-connected capacitors C, C 61  and C 62 . Therefore, it is possible to control a current flown in an LED array load by varying the capacitances of the capacitors C 61  and C 62  in the LED lamp  160 . 
     If we let C 61 =C 62 =C 2 , the composite impedance Z may be defined by Equation (9): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       
                         - 
                         j 
                       
                        
                       
                         1 
                         
                           ω 
                            
                           
                               
                           
                            
                           
                             C 
                             1 
                           
                         
                       
                     
                     - 
                     
                       j 
                        
                       
                         
                           2 
                           
                             ω 
                              
                             
                                 
                             
                              
                             
                               C 
                               2 
                             
                           
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The third and fourth connection pins  163  and  164  of the LED lamp  160  may be provided in order to make the LED lamp  160  operate symmetrically not having any polarity. The operation of an instant start-type electronic fluorescent lamp ballast when the ballast is connected to the third and fourth connection pins  163  and  164  may be basically the same as the operation when the ballast is connected to the first and second connection pins  161  and  162 . 
       FIG. 15  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  170  of the seventh exemplary embodiment is applied. Referring to  FIG. 15 , switching devices Q 71  and Q 72  continue a switching operation by the self-oscillation operation of the circuit composed of transformers T 1 , T 2  and a capacitor C. Primary winding T 2 - 1  of the transformer T 2  is connected between the switching point A and the center point of the series-connected capacitors Co and a high AC voltage may be induced at the secondary winding T 2 - 2 . If the voltage at the node C is positive with respect to the voltage at the node D, a current may flow, sequentially passing through the node C, the capacitor C 1 , the diode D 73 , the diode D 71 , the LED array  17 , the diode D 72 , the capacitor C 72  and the node D. On the other hand, if the voltage at the node C is negative with respect to the voltage at the node D, a current may flow, sequentially passing through the node D, the diode D 74 , the diode D 77 , the LED array  17 , the diode D 78 , the capacitor C 71 , the capacitor C 1  and the node C. 
     The operation of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  180  shown in  FIG. 9  is applied is almost the same as the operation of the instant start-type electronic fluorescent lamp ballast shown in  FIG. 15 . More specifically, in the instant start-type electronic fluorescent lamp ballast having the LED lamp  180 , if a positive voltage is applied to the first connection pin  181  of the LED lamp  180  and a negative voltage is applied to the second connection pin  182  of the LED lamp, i.e., if the voltage at a node C is positive with respect to the voltage at a node D, a current may flow, sequentially passing through the node C, the capacitor C 1 , the capacitor C 81 , the diode D 81 , the LED array  18 , the diode D 82 , the diode D 84  and the node D. On the other hand, if a negative voltage is applied to the first connection pin  181  and a positive voltage is applied to the second connection pin  182 , i.e., if the voltage at the node C is negative with respect to the voltage at the node D, a current may flow, sequentially passing through the node D, the capacitor C 82 , the diode D 87 , the LED array  18 , the diode D 88 , the diode D 83 , the capacitor C 1  and the node C. 
     In short, the operation of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  180  of the eighth exemplary embodiment is applied is almost the same as the operation of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  170  of the seventh exemplary embodiment is applied, except for the path of a current. 
       FIG. 16  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  190  of the ninth exemplary embodiment of the present invention is applied, and  FIG. 17  illustrates a circuit diagram of an instant start-type electronic fluorescent lamp ballast to which the LED lamp  200  of the tenth exemplary embodiment of the present invention is applied. 
     Referring to  FIG. 16 , when the output wires of the electronic fluorescent lamp ballast are connected to the first and second connection pins  191  and  192 , a transformer T 2  may resonate with self-oscillation frequency and may thus induce a high AC voltage to a secondary winding T 2 - 2 . If the voltage at the node C is positive with respect to the voltage at the node D, a current may flow, sequentially passing through the node C, the capacitor C 1 , the capacitor C 91 , the diode D 93 , the diode D 91 , the LED array  19 , the diode D 92 , the diode D 94 , the capacitor C 92  and the node D, with a phase being shifted by π/2 by the capacitances of the capacitors C 91  through C 94 . On the other hand, if the voltage at the node C is negative with respect to the voltage at a node D, a current may flow, sequentially passing through the node D, the capacitor C 92 , the diode D 98 , the LED array  19 , the diode D 97 , the capacitor C 91 , the capacitor C 1 , and the node C, with a phase being shifted by π/2 by the capacitances of the capacitors C 91  through C 94 . 
     Referring to  FIG. 17 , the third and fourth connection pins  203  and  204  may be provided in order for the LED lamp  200  to operate symmetrically. The operation of the electronic fluorescent lamp ballast shown in  FIG. 17  is almost the same as the operation of the electronic fluorescent lamp ballast shown in  FIG. 16 . 
       FIG. 18  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp  140  of the fourth exemplary embodiment is applied. Referring to  FIG. 18 , a series resonant circuit including an inductor T 3  and a capacitor C 1  may be connected between switching node A, switching point of switching devices Q 81  and Q 82 , and ground point, and the LED lamp  140  may be connected to both ends of the capacitor C 1 . Originally, the secondary windings of inductor T 3 - a  and T 3 - b  are intended for preheating the filament of fluorescent lamp in order to maximize the lifetime of the fluorescent lamp by minimizing the dissipation of the oxide components coated on the filament of the fluorescent lamp. But when this soft start-type of electronic ballast drives the LED lamp, these secondary windings should not influence an abnormal effect upon the normal operation of the LED lamp  180 . 
     If the operating frequency f of the switching devices Q 81  and Q 82  is synchronized with the resonant frequency which is composed of inductance L 1  of the inductor T 3  and the capacitance C 1  and if we suppose CO&gt;&gt;C 1 , the operating frequency f may be defined by Equation (10): 
         f= 1/2π√{square root over ( L   1   C   1 )}  (10).
 
     A high AC voltage with the operating frequency f may be induced to both ends of the capacitor C 1 . Since the secondary windings T 3 - a  and T 3 - b  are coupled to the inductor T 3 , during a positive period of the AC voltage induced to T 3 - a , a preheating current may flow, sequentially passing through a capacitor Ca, the diode D 43  and the capacitor C 43 . On the other hand, during a negative period of the AC voltage, a preheating current may flow, sequentially passing through the diode D 45 , the capacitor C 41  and the capacitor Ca. Similarly during a positive period of the AC voltage induced to T 3 - b , a preheating current may flow, sequentially passing through the capacitor C 44 , the diode D 44  and the capacitor Cb. On the other hand, during a negative period of the AC voltage, a preheating current may flow, sequentially passing through the capacitor Cb, the capacitor C 42  and the diode D 46 . If we let C 41 =C 42 =C 43 =C 44 =C 2 , the total capacitance C that controls the preheating current flown in the secondary winding T 3 - a  or T 3 - b  may be defined by Equation (11): 
     
       
         
           
             
               
                 
                   C 
                   = 
                   
                     
                       
                         
                           C 
                           a 
                         
                          
                         
                           C 
                           2 
                         
                       
                       
                         
                           C 
                           a 
                         
                         + 
                         
                           C 
                           2 
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     Since Ca&gt;&gt;C 2  the current flown in the secondary windings T 3 - a  or T 3 - b  may be determined by capacitance C 2 , which is equal to the value of capacitor C 41  through C 44 . Since the capacitance C 2  is only as small as several thousands of pico-farads and the voltage induced to the secondary windings T 3 - a  or T 3 - b  are only as low as several volts, the current flown through the secondary windings T 3 - a  or T 3 - b  may be ignored by the diodes D 43  through D 46 . 
     If the resonant voltage induced at the node B is positive with respect to the voltage at the node C, a current may flow in the LED lamp  140 , sequentially passing through the node B, the diode D 45 , the diode D 41 , the LED array  14 , the diode D 42 , and the diode D 46 . On the other hand, if the voltage at the node B is negative with respect to the voltage at the node C, a current may flow in the LED lamp  140 , sequentially passing through the node C, the diode D 49 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 50  and the node B. 
     The main current flown in the LED array  14  may be controlled by varying the number of series connected LEDs. 
       FIG. 19  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp  160  of the sixth exemplary embodiment is applied. Referring to  FIG. 19 , an operating frequency f may be the same as that described above with reference to FIG.  18 , and an AC voltage with the operating frequency f may be induced to both ends of a capacitor C 1 . During the operation of the soft start-type electronic fluorescent lamp ballast with LED lamp instead of conventional fluorescent lamp, since the voltage induced to a secondary winding T 3 - a , which is coupled to an inductor T 3  and is designed for pre-heating the filaments of fluorescent lamp, is only as low as below 10 V, the voltage at the secondary winding T 3 - a  may be blocked by the diodes D 63  and D 65 , and thus, a preheating current for fluorescent lamp filament may not be able to flow through the secondary winding T 3 - a . Likewise, the voltage at the secondary winding T 3 - b  for preheating the fluorescent lamp filament may be blocked by the diodes D 64  and D 66 , and thus, a preheating current for fluorescent lamp filament may not be able to flow through the winding T 3 - b . Therefore, power loss that may be caused by the secondary winding T 3 - a  and T 3 - b  may be ignored and as a result, the current for filament preheating generated by the secondary windings T 3 - a  and T 3 - b  may be ignored. 
     If we ignore the secondary windings T 3 - a  and T 3 - b , when the voltage at the node B is positive with respect to the voltage at the node C, a current may flow, sequentially passing through the node B, the capacitor C 63 , the diode D 65 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 66 , the capacitor C 64  and the node C. On the other hand, if the voltage at the node B is negative with respect to the voltage at the node C, a current may flow, sequentially passing through the node C, the capacitor C 64 , the diode D 69 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 70 , the capacitor C 63  and the node B. Therefore, if we let C 61 =C 62 =C 63 =C 64 =C 2 , the composite impedance of the soft start-type electronic fluorescent lamp ballast may become 2/jωC 2 . Thus, the main current flown in the LED array  16  may be controlled by varying the capacitance C 2  of the capacitors C 61  through C 64 . 
       FIG. 20  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp  170  of the seventh exemplary embodiment is applied. The basic operation of the soft start-type electronic ballast shown in  FIG. 20  is almost the same as the operation of the soft start-type electronic ballast shown in  FIG. 19 . 
     Referring to  FIG. 20 , a current flown into the LED array  17  by secondary windings T 3 - a  and T 3 - b  for pre-heating the fluorescent lamp filaments may be low enough to be ignored. If we ignore the secondary windings T 3 - a  and T 3 - b , when the voltage at the node B is positive with respect to the voltage at the node C, a current may flow, sequentially passing through the node B, the diode D 75 , the diode D 71 , the LED array  17 , the diode D 72 , the capacitor C 74  and the node C. On the other hand, if the voltage at the node B is negative with respect to the voltage at the node C, a current may flow, sequentially passing through the node C, the diode D 76 , the diode D 77 , the LED array  17 , the diode D 78 , the capacitor C 73  and the node B. Therefore, if we let C 71 =C 72 =C 73 =C 74 =C 2 , the total composite impedance of the soft start-type electronic fluorescent lamp ballast may become 1/jωC 2 . Thus, the main current flown in the LED array  17  may also be controlled by varying the capacitance C 2  and the total number of LEDs. 
       FIG. 21  illustrates a circuit diagram of a soft start-type electronic fluorescent lamp ballast to which the LED lamp  200  of the tenth exemplary embodiment is applied. Referring to  FIG. 21 , a current flown into the LED array  20  by secondary windings T 3 - a  and T 3 - b  for pre-heating filaments may be low enough to be ignored. If we ignore the secondary windings T 3 - a  and T 3 - b , when the voltage at the node B is positive with respect to the voltage at the node C, a current may flow, sequentially passing through the node B, the capacitor C 103 , the diode D 105 , the diode D 101 , the LED array  20 , the diode D 102 , the diode D 106 , the capacitor C 104  and the node C, with a phase being shifted by π/2 by the capacitance of the capacitors C 101  through C 104 . 
     On the other hand, if the voltage at the node B is negative with respect to the voltage at the node C, a current may flow, sequentially passing through the node C, the capacitor C 104 , the diode D 109 , the LED array  20 , the diode D 110 , the capacitor C 103  and the node B, with a phase being shifted by π/2 by the capacitance of the capacitors C 101  through C 104 . Therefore, if we let C 101 =C 102 =C 103 =C 104 =C 2 , the total composite impedance of the soft start-type electronic fluorescent lamp ballast may become 2/jωC 2  and the main current flown in the LED array  20  may be controlled by varying the capacitance C 2  of capacitors C 101  through C 104 . 
       FIG. 22  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp  140  of the fourth exemplary embodiment is applied. Referring to  FIG. 22 , when we drive the LED lamp instead of conventional fluorescent lamp, a starter lamp (S)  300  may be considered to be open, and thus, during a positive period of an input AC voltage, a current may flow, sequentially passing through an inductor L, the diode D 45 , the diode D 41 , the LED array  14 , the diode D 42  and the diode D 46 . In this case, the main current flown in the LED lamp  140  may be controlled by the impedance of the inductor L, i.e., jωL and the total number of LEDs. 
     On the other hand, during a negative period of the input AC input voltage, a current may flow, sequentially passing through the diode D 49 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 50  and the inductor L. In this case, the current flown in the LED lamp  140  may be a pulsating current having twice as high a frequency (100/120 Hz) as the frequency f (50/60 Hz) of the commercial electric power source. Therefore, it is possible to considerably reduce the probability of occurrence of flickering, which may be caused by driving the LED lamp  140  at the frequency f of the commercial electric power source. 
       FIG. 23  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp  160  of the sixth exemplary embodiment is applied. Referring to  FIG. 23 , when we drive the LED lamp instead of conventional fluorescent lamp, a starter lamp (S)  300  may be considered to be open, and thus, during a positive period of an input AC input voltage, a current may flow, sequentially passing through the capacitor C 63 , the diode D 65 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 66 , and the capacitor C 64 , with a phase being shifted by π/2 by the capacitance of the capacitors C 61  through C 64 . 
     On the other hand, during a negative period of the input AC input voltage, a current may flow, sequentially passing through the capacitor C 64 , the diode D 69 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 70 , and the capacitor C 63  with a phase being shifted by it/2 by the capacitance of the capacitors C 61  through C 64 . 
     If we let C 61 =C 62 =C 63 =C 64 =C 2 , total composite impedance Z that controls the main current flown in the LED lamp  160  may be defined by Equation (12): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       jω 
                        
                       
                           
                       
                        
                       L 
                     
                     - 
                     
                       j 
                        
                       
                         2 
                         
                           ω 
                            
                           
                               
                           
                            
                           
                             C 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     where L indicates the inductance of an inductor L. 
     The current flown in the LED lamp  160  may be a pulsating current having twice as high a frequency (100/120 Hz) as the frequency f (50/60 Hz) of the commercial electric power source. Therefore, it is possible to considerably reduce the probability of occurrence of flickering, which may be caused by driving the LED lamp  140  at the frequency f. 
       FIG. 24  illustrates a circuit diagram of a starter lamp-based magnetic fluorescent lamp ballast to which the LED lamp  170  of the seventh exemplary embodiment is applied. Referring to  FIG. 24 , during a positive period of an input AC input voltage, a current may flow, sequentially passing through the diode D 75 , the diode D 71 , the LED array  17 , the diode D 72  and the capacitor C 74 . On the other hand, during a negative period of the input AC input voltage, a current may flow, sequentially passing through the diode D 76 , the diode D 77 , the LED array  17 , the diode D 78  and the capacitor C 73 . 
     If we let C 71 =C 72 =C 73 =C 74 =C 2 , total composite impedance Z that controls the main current flown in the LED lamp  170  may be defined by Equation (13): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       jω 
                        
                       
                           
                       
                        
                       L 
                     
                     - 
                     
                       j 
                        
                       
                         1 
                         
                           ω 
                            
                           
                               
                           
                            
                           
                             C 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     where L indicates the inductance of an inductor. 
       FIG. 25  illustrates a circuit diagram of a starter lamp-type magnetic fluorescent lamp ballast to which the LED lamp  200  of the tenth exemplary embodiment is applied. Referring to  FIG. 25 , when we drive the LED lamp instead of conventional fluorescent lamp, a starter lamp (S)  300  may be considered to be open and thus during a positive period of the input AC input voltage, a current may flow, sequentially passing through the capacitor C 103 , the diode D 105 , the diode D 101 , the LED array  20 , the diode D 102 , the diode D 106 , and the capacitor C 104 , with a phase being shifted by π/2 by the capacitance of the capacitors C 101  through C 104 . 
     On the other hand, during a negative period of the AC input voltage, a current may flow, sequentially passing through the capacitor C 104 , the diode D 109 , the LED array  20 , the diode D 110 , the capacitor C 103 , with a phase being shifted by π/2 by the capacitance of the capacitors C 101  through C 104 . If we let C 101 =C 102 =C 103 =C 104 =C 2 , total composite impedance Z that controls the main current flown in the LED lamp  200  may also be defined by equation (12). 
       FIG. 26  illustrates a circuit diagram of a magnetic rapid start-type fluorescent lamp ballast to which the LED lamp  140  of the fourth exemplary embodiment is applied. Referring to  FIG. 26 , if we define the voltages for preheating the filaments of fluorescent lamp induced to the secondary windings n 1  and n 2  as V n1  and V n2 , respectively, during a positive period of the voltage V n1 , that is, when the voltage applied to the node C is positive with respect to the node A, the capacitor C 41  may be short-circuited by the diode D 43 , and thus, the load of the secondary winding n 1  may become equal to the capacitance of the capacitor C 42 , and during a negative period of the voltage V n1 , the capacitor C 43  may be short-circuited by the diode D 45 , and thus, the load of the secondary winding n 1  may become equal to the capacitance of the capacitor C 41 . 
     Likewise, during a positive period of the voltage V n2 , that is, when the voltage applied to the node B is positive with respect to the node D, the load of the winding n 2  may become equal to the capacitance of the capacitor C 44 , and during a negative period of the voltage V n2 , that is, when the voltage applied to the node D is positive with respect to node B, the load of the winding n 2  may become equal to the capacitance of the capacitor C 42 . 
     To keep the symmetric characteristics of fluorescent lamp, the first through fourth connection pins  141  through  144  of the LED lamp  140  should not have any polarity. For this purpose, the capacitors C 41  through C 44  should be designed to have the same capacitance value. If we let this value as C 2 , since the capacitance C 2  is only as low as several thousands of pico-farads, the composite impedance, i.e., 1/jωC 2  may become very high at the frequency of 50-60 Hz. Therefore, the preheating current of the secondary windings n 1  and n 2  may be ignored. 
     An output voltage Vo applied to node A and node B may be defined by Equation (14): 
     
       
         
           
             
               
                 
                   Vo 
                   = 
                   
                     
                       
                         
                           n 
                            
                           
                               
                           
                            
                           3 
                         
                         + 
                         
                           n 
                            
                           
                               
                           
                            
                           4 
                         
                       
                       
                         n 
                          
                         
                             
                         
                          
                         4 
                       
                     
                      
                     Vi 
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     where Vi indicates the input voltage from the commercial electric power source. 
     When the voltage at the node A is positive with respect to the voltage at the node B, a current may flow in the LED lamp  140 , sequentially passing through the node C, the diode D 43 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 44  and the node D. On the other hand, if the voltage at the node C is negative with respect to the voltage at the node D, a current may flow in the LED lamp  140 , sequentially passing through the node D, the diode D 48 , the diode D 41 , the LED array  14 , the diode D 42 , the diode D 47  and the node C. The main current flown in the LED array  14  may be controlled by the impedance of the leakage inductance of the ballast jcoL 1  and the total number of series connected LEDs. 
     In case of magnetic rapid start-type fluorescent lamp ballast, like in the starter lamp-based magnetic fluorescent lamp ballast shown in  FIG. 25 , the main current flown in the LED lamp  140  may be a pulsating current having twice as high a frequency (100/120 Hz) as the frequency f (50/60 Hz) of the commercial electric power source. Therefore, it is possible to considerably reduce the probability of occurrence of flickering, which may be caused by driving the LED lamp  140  at the frequency f of commercial electric power source. 
       FIG. 27  illustrates a circuit diagram of a magnetic rapid start-type fluorescent lamp ballast to which the LED lamp  160  of the sixth exemplary embodiment is applied. Referring to  FIG. 27 , if the voltage at the node A is positive with respect to the voltage at the node B, a current may flow, sequentially passing through the node C, the capacitor C 61 , the diode D 63 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 64 , the capacitor C 62 , and the node D, with a phase being shifted by π/2 by the capacitance of the capacitors C 61  through C 64 . 
     On the other hand, if the voltage at the node A is negative with respect to the voltage at the node B, a current may flow, sequentially passing through the node D, the capacitor C 62 , the diode D 68 , the diode D 61 , the LED array  16 , the diode D 62 , the diode D 67 , the capacitor C 61 , and the node C, with a phase being shifted by π/2 by the capacitance of the capacitors C 61  through C 64 . 
     If we let C 61 =C 62 =C 63 =C 64 =C 2 , total composite impedance Z that controls the main current flown in the LED lamp  160  may be defined by Equation (15): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       jω 
                        
                       
                           
                       
                        
                       
                         L 
                         1 
                       
                     
                     - 
                     
                       j 
                        
                       
                         2 
                         
                           ω 
                            
                           
                               
                           
                            
                           
                             C 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     where L 1  indicates leakage inductance of the ballast. 
       FIG. 28  illustrates a circuit diagram of a magnetic rapid start-type fluorescent lamp ballast to which the LED lamp  170  of the seventh exemplary embodiment is applied. Referring to  FIG. 28 , if the voltage at the node A is positive with respect to the voltage at the node B, a current may flow, sequentially passing through the node C, the diode D 73 , the diode D 71 , the LED array  17 , the diode D 72 , the capacitor C 72 , and the node D. On the other hand, if the voltage at the node A is negative with respect to the voltage at the node B, a current may flow, sequentially passing through the node D, the diode D 74 , the diode D 77 , the LED array  17 , the diode D 78 , the capacitor C 71 , and the node C. 
     If we let C 71 =C 72 =C 73 =C 74 =C 2 , total composite impedance Z that controls the main current flown in the LED lamp  170  may be defined by Equation (16): 
     
       
         
           
             
               
                 
                   Z 
                   = 
                   
                     
                       jω 
                        
                       
                           
                       
                        
                       
                         L 
                         1 
                       
                     
                     - 
                     
                       j 
                        
                       
                         1 
                         
                           ω 
                            
                           
                               
                           
                            
                           
                             C 
                             2 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
     where L 1  indicates leakage inductance of the ballast. 
     In this case, the current flown through the LED lamp  170  may be a pulsating current having twice as high a frequency (100/120 Hz) as the frequency f (50/60 Hz) of the commercial electric power source. 
       FIG. 29  illustrates a circuit diagram of an iron core rapid start-type fluorescent lamp ballast to which the LED lamp  190  of the ninth exemplary embodiment is applied, and  FIG. 30  illustrates a circuit diagram of an iron core rapid start-type fluorescent lamp ballast to which the LED lamp  200  of the tenth exemplary embodiment is applied. 
     Referring to  FIG. 29 , if the voltage at the node A is positive with respect to the voltage at the node B, a current may flow, sequentially passing through the node C, the capacitor C 91 , the diode D 93 , the diode D 91 , the LED array  19 , the diode D 92 , the diode D 94 , the capacitor C 92 , and the node D, with a phase being shifted by π/2 by the capacitance of the capacitors C 91  through C 94 . 
     On the other hand, if the voltage at the node A is negative with respect to the voltage at the node B, a current may flow, sequentially passing through the node D, the capacitor C 92 , the diode D 98 , the LED array  19 , the diode D 97 , the capacitor C 91  and the node C, with a phase being shifted by π/2 by the capacitance of the capacitors C 91  through C 94 . 
     The operation of the magnetic rapid start-type fluorescent lamp ballast shown in  FIG. 30  is almost the same as the operation of the magnetic rapid start-type fluorescent lamp ballast shown in  FIG. 29  except that two diodes D 109  and D 110  are added to keep the symmetric characteristics of LED lamp  200 . 
     Generally, the instant start-type electronic fluorescent lamp ballast applies an initial voltage to a lamp that is many times greater than the lamps normal operating voltage. Thus, if there are loose contact between in the external connection pins and sockets, the sockets of the LED lamp or components of the LED lamp may be burned out by the spike voltage from the ballast. So, circuit breakers, e.g., fuses, fusible resistor or delay, can be connected in main current circuits of the LED lamp to protect the circuit from the surge voltage in this embodiment. Hereinafter, such exemplary embodiments will be described. 
       FIG. 31  illustrates a circuit diagram of an LED lamp  210  according to an eleventh exemplary embodiment of the present invention, in which circuit breakers are added in the sixth exemplary embodiment to protect the circuit diagram from high voltage or spike components from the ballast. 
     Referring to  FIG. 31 , the LED lamp  210  may include an LED array  16 , first through fourth connection pins  161  through  164 , a plurality of fuses F 61  through F 64  connected to the first through fourth connection pins  161  through  164 , respectively, a plurality of capacitors C 61  through C 64  connected to the first through fourth fuses F 61  through F 64 , respectively, and a plurality of diodes D 63  through D 66  connected in series to the capacitors C 61  through C 64 , respectively. The anode of a diode D 61  is connected to the cathodes of diodes D 63  and D 65  and the cathode of a diode D 62  is connected to anodes of diodes D 64  and D 66 , and the diodes D 63  through D 66  and a plurality of diodes D 67  through D 70  may allow the LED lamp  210  to stably operate keeping the characteristics of symmetric operation regardless of the phase of an AC voltage applied by a fluorescent lamp ballast. 
     Here, an exemplary embodiment, the circuit breakers may be a fuse, and another exemplary embodiment, the circuit breakers may be a thermal fuse. There may be a fire hazard due to a surge current flowing into the LED lamp induced by a spark which may occur between the connection pins  161  through  164  and a lighting fixture. Thus, as in this exemplary embodiment, the fuses or the thermal fuses can be inserted between the connection pins  161  through  164  and the LED array  26  to break the circuit from the connection pins  161  through  164  to the LED array  26  so as not to allow the surge current to flow into the LED array when the surge current is generated by the spark, whereby the fire hazard can be prevented. 
       FIG. 32  illustrates a circuit diagram of an LED lamp  220  according to a twelfth exemplary embodiment of the present invention, in which circuit breakers are added in the seventh exemplary embodiment to protect the circuit diagram from high voltage or spike components from the ballast. 
     Referring to  FIG. 32 , a terminal of a fuse F 71  can be connected to a first connection pin  171  and another terminal of the fuse is connected to the anode of a diode D 73 , and the cathode of the diode D 73  can be connected to the anode of a diode D 71 . A capacitor C 71  is connected in parallel with the diode D 73 . A terminal of a fuse F 72  can be connected to a second connection pin  172  and another terminal of the fuse is connected to the anode of a diode D 74 , and the cathode of the diode D 74  may be connected to the anode of a diode D 72 . A capacitor C 72  is connected in parallel with the diode D 74 . A terminal of a fuse F 73  can be connected to a third connection pin  173  and another terminal of the fuse is connected to the anode of a diode D 75 , and the cathode of the diode D 75  may be connected to the anode of a diode D 71 . A capacitor C 73  is connected in parallel with the diode D 75 . A terminal of a fuse F 74  can be connected to a fourth connection pin  174  and another terminal of the fuse is connected to the anode of a diode D 76 , and the cathode of the diode D 76  may be connected to the anode of a diode D 72 . A capacitor C 74  is connected in parallel with the diode D 76 . The anode of the diode D 77  may be commonly connected to the cathode of the diode D 72  and ends of capacitors C 72  and C 74 , and the cathode of the diode D 77  may be connected to an anode terminal  17   a  of an LED array  17 . The anode of the diode D 78  may be connected to a cathode terminal  17   b  of the LED array  17 , and the cathode of the diode D 78  may be commonly connected to the anode of the diode D 71  and ends of capacitors C 71  and C 73 . 
     The diodes D 77  and D 78  may allow the LED lamp  220  to stably operate keeping the characteristics of symmetric operation regardless of variations in the phase of a voltage applied to the first through fourth connection pins  171  through  174  by a fluorescent lamp ballast. 
       FIG. 33  illustrates a circuit diagram of an LED lamp  230  according to an thirteenth exemplary embodiment of the present invention, in which circuit breakers are added in the eighth exemplary embodiment to protect the circuit diagram from high voltage or spike components from the ballast. 
     The thirteenth exemplary embodiment is the same as the eight exemplary embodiment except for the reverse direction of diodes D 83  through D 86  which are connected in parallel to a plurality of capacitors C 81  through C 84 , respectively. 
       FIG. 34  illustrates a circuit diagram of an LED lamp  240  according to a fourteenth exemplary embodiment of the present invention. 
     Referring to  FIG. 34 , the LED lamp  240  may include first through fourth connection pins  191  through  194 , a plurality of fuses F 91  through F 94  connected to the first through fourth connection pins  191  through  194 , a plurality of capacitors C 91  through C 94  connected in series to the first through fourth fuses F 91  through F 94 , respectively, a plurality of diodes D 93  through D 96  connected in series to the capacitors C 91  through C 94 , respectively, and a diode D 91  connected to the cathodes of diodes D 93  and D 95  and a diode D 92  connected to the anodes of diodes D 94  and D 96 . 
     The LED lamp  240  may also include a diode D 97  having an anode connected to a second end of an LED array  19  and a cathode connected to the anode of the diode D 93  and a diode D 98  having an anode connected to the cathode of the diode D 94  and a cathode connected to a first end of the LED array  19 . 
       FIG. 35  illustrates a circuit diagram of an LED lamp  250  according to a fifteenth exemplary embodiment of the present invention. The LED lamp  250  is almost the same as the LED lamp  250  shown in  FIG. 34  except that it also includes diodes D 109  and D 110 . More specifically, referring to  FIG. 35 , the anode of the diode D 109  may be connected to the cathode of a diode D 106 , and the cathode of the diode D 109  may be connected to a first end of an LED array  20 . The anode of the diode D 110  may be connected to a second end of the LED array  20 , and the cathode of the diode D 110  may be connected to the anode of the diode D 105 . The diodes D 109  and D 110  may allow the LED lamp  250  to operate symmetrically in response to a voltage applied thereto by an external voltage source. 
       FIG. 36  illustrates an exploded perspective view of an LED lamp according to an exemplary embodiment of the present invention. With reference to  FIG. 36 , a position in which a circuit breaker, one of components included in the LED lamp according to the exemplary embodiment of the present invention, is disposed will be described in more detail. 
     The LED lamp according to this exemplary embodiment of the present invention comprises the LED array disposed inside a lamp housing and end caps coupled to both ends of the lamp housing. In  FIG. 36 , only one end cap  361  is shown as being coupled to an end of the lamp housing, but another end cap (not shown) can be coupled to the other end of the lamp housing. The end caps can have external connection pins (a and b) to get an electrical power from an external power source. Also, the external connection pins (a and b) can be electrically connected with the LED array  16 . 
     In an embodiment, as illustrated in  FIG. 36 , a first printed circuit board (PCB)  362  can be provided in an inner side of the end cap  361  or an end portion of the lamp housing  364 , on which the thermal fuse  363  can be mounted. By this way, when a spark occurs between the external connection pins (a and b) and the lighting fixture, the thermal fuse  363  is configured to break the circuit to prevent the surge current from flowing into the LED array  16 , thereby preventing a fire hazard. As in this embodiment, by placing the thermal fuse  363  in the inner side of the end cap  361 , the damage to the LED lamp which may be caused by the spark can be minimized. Also, it is advantageous that simply the thermal fuse  363  can be replaced instead of replacing whole LED lamp, even when the damage is caused. 
     Further, capacitors and/or diodes in addition to the thermal fuse  363  can be arranged between the external connection pins (a and b) and the LED array  16 . The capacitors are configured to adjust the impedance to match with the electronic fluorescent lamp ballast connected to the LED lamp, and the diodes are configured to control the direction of the current supplied to the LED lamp through both ends thereof, so that the LED lamp can work even under the AC power source. A second PCB  366  can be provided for mounting the capacitors and the diodes. 
     The first PCB  362  and the second PCB  366  can be provided with conductive traces for electrical connection between the components, such as the capacitor and the diodes. Also, the second PCB can be used for mounting various components, for example, the components used in the circuits illustrated in  FIGS. 31 through 35 . 
     The basic structures of the LED lamps  210  through  250  of the eleventh through fifteenth exemplary embodiments can be applied to almost all types of fluorescent lamp ballasts. 
     The LED lamps according to exemplary embodiments of the present invention can be readily installed and used with various types of electronic fluorescent lamp ballast. The LED lamp according to the present invention is not restricted to the exemplary embodiments set forth herein. Therefore, variations and combinations of the exemplary embodiments set forth herein may fall within the scope of the present invention. 
     As described above, the LED lamp according to the present invention can be readily installed and used with various types of fluorescent lamp ballasts without the requirement of the installation of an additional fluorescent lamp ballasts or the change of internal wiring of the fixture. Therefore, the LED lamp according to the present invention can replace an existing fluorescent lamp very efficiently at low cost. 
     While the present invention has been particularly 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.