Abstract:
An LED lamp for lighting purpose includes a lamp base, a heat sink, a plurality of LED modules and a blower. The lamp base encloses an inner space and defines a plurality of vents therein. The vents communicate the inner space with a surrounding atmosphere. The heat sink comprises a cylinder at a centre thereof. The cylinder has a through hole therein, which communicates with the inner space and vents of the lamp base and cooperates therewith to form an air passage. The LED modules are attached to a periphery of the heat sink. The blower generates an airflow circulating through the air passage to thereby dissipate heat generated by the LED modules.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an LED lamp, and particularly to an LED lamp having a heat dissipation structure for dissipating heat from LEDs thereof. 
         [0003]    2. Description of Related Art 
         [0004]    An LED lamp is a type of solid state lighting that utilizes light-emitting diodes (LEDs) as a source of illumination. An LED is a device for transferring electricity to light by using a theory that, if a current is made to flow in a forward direction in a junction comprising two different semiconductors, electrons and cavities are coupled at the junction region to generate a light beam. The LED has an advantage in that it is resistant to shock, and has an almost eternal lifetime under a specific condition; thus, the LED lamp is intended to be a cost-effective yet high quality replacement for incandescent and fluorescent lamps. 
         [0005]    An LED lamp generally requires a plurality of LEDs, and most of the LEDs are driven at the same time, which results in a quick rise in temperature of the LED lamp. Since generally the LED lamp does not have a heat dissipation device with a good heat dissipating efficiency, operation of the LED lamp has a problem of instability because of the rapid increase of heat. Consequently, the light from the LED lamp often flickers, which degrades the quality of the illumination. Furthermore, the LED lamp is used in a high heat state for a long time and the life time thereof is consequently shortened. 
         [0006]    What is needed, therefore, is an LED lamp which has a heat dissipation structure with a great heat-dissipation capability. 
       SUMMARY OF THE INVENTION 
       [0007]    An LED lamp for lighting purpose includes a lamp base, a heat sink, a plurality of LED modules and a blower. The lamp base defines a plurality of vents therein. The heat sink comprises a cylinder at a centre thereof. The cylinder has a through hole therein, which communicates with an inner space and the vents of the lamp base and cooperates with the inner space and vents to form an air passage. The LED modules are attached to a periphery of the heat sink. The blower generates an airflow circulating through the air passage thereby to dissipate heat generated by the LED modules. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiment. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0009]      FIG. 1  is an isometric, assembled view of an LED lamp in accordance with a first preferred embodiment of the present invention; 
           [0010]      FIG. 2  is an exploded view of  FIG. 1 ; 
           [0011]      FIG. 3  is an enlarged view of a heat sink of the LED lamp of  FIG. 1 ; 
           [0012]      FIG. 4  is a cross-sectional view taken along line IV-IV of  FIG. 1 ; and 
           [0013]      FIG. 5  is an isometric, assembled view of an LED lamp in accordance with another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIGS. 1-2 , an LED lamp in accordance with a preferred embodiment of the present invention comprises a lamp base  10 , a heat sink  20  coupled to the lamp base  10 , a plurality of LED modules  30  thermally attached to a periphery of the heat sink  20  and a blower  40  ( FIG. 4 ) mounted in the lamp base  10 . 
         [0015]    The lamp base  10  comprises a lamp holder  12 , a first cover  14  connecting with the lamp holder  12  and a second cover  16  facing to and engaging with the first cover  12 . The lamp holder  12  is provided with screw threads formed on a periphery thereof and has a standard configuration for fitting in a standard lamp socket. The first cover  14  comprises an annular joining portion  140  coupled with the lamp holder  12  and a first bowl-shaped body  142  extending upwardly from an upper edge of the joining portion  140 . The first bowl-shaped body  142  has a caliber increasing gradually from a bottom to a top thereof. Three fixing orifices  1420  are evenly defined in an upper rim of the first bowl-shaped body  142 . The three fixing orifices  1420  extend vertically through the first bowl-shaped body  142  for allowing screws (not shown) to extend therethrough to screw into the second cover  16 , thereby fastening the first and second covers  14 ,  16  together. 
         [0016]    The second cover  16  comprises an annular engaging portion  160  at a top thereof and a second bowl-shaped body  162  extending downwardly form a lower edge of the engaging portion  160 . The engaging portion  160  has a diameter smaller than that of the joining portion  140  of the first cover  14  and forms screw threads  1600  in an inner wall thereof for engaging with the heat sink  20 . Three through orifices  1602  are evenly and radially defined in the engaging portion  160 . An upper portion of the second bowl-shaped body  162  has a caliber increasing gradually from a top to a bottom thereof and defines a plurality of leading orifices  164  therein for allowing lead wires (not shown) to extend therethrough to electrically connect the LED modules  30  with a rectifier circuit (not shown) and an electronic ballast (not shown) received in the lamp base  10 . A lower portion of the bowl-shaped body  162 , which has a constant caliber is substantially tube-shaped and symmetrically defines a plurality of vents  166 . The vents  166  are provided for allowing ambient air to flow into an inner space enclosed by the first and second covers  14 ,  16  and circulate through the LED lamp. Three engaging orifices (not shown) corresponding to the fixing orifices  1420  of the first cover  14  are symmetrically defined in the second bowl-shaped body  162  and adjacent to a lower rim of the second bowl-shaped body  162 . The three engaging orifices are used for engaging with the screws extending through the fixing orifices  1420  of the first cover  14  to couple the first cover  14  and the second cover  16  together. The first and second covers  14 ,  16  cooperatively form an enclosure with a space therein. The rectifier circuit and electronic ballast (not shown) for the LED modules  30  can be accommodated at a bottom of the enclosure namely a bottom of the first cover  12 . 
         [0017]    As shown in  FIG. 3 , the heat sink  20  is integrally formed of a material with good heat conductivity such as aluminum or copper. In the preferred embodiment, the heat sink  20  is formed by aluminum extrusion. The heat sink  20  has an elongated cylinder  22  at a center thereof. The cylinder  22  defines a through hole (not labeled) therein. The cylinder  22  has a plurality of first fins  24  extending inwardly from an inner wall thereof into the through hole. The first fins  24  are centrosymmetric relative to a central axis of the cylinder  22  and each have a thickness decreasing inwardly. The heat sink  20  has a plurality of conducting arms  26  extending outwardly from an outer wall of the cylinder  22 . The conducting arms  26  are identical to each other and centrosymmetric relative to the central axis of the cylinder  22 . The number of the conducting arms  26  is consistent with that of the LED modules  30  and can be different in different embodiments. In this embodiment, the numbers of the conducting arms  26  and the LED modules  30  are both six. A plurality pairs of second fins  260  are formed on two opposite lateral sides of the conducting arms  26 . Each pair of the second fins  260  extend oppositely and perpendicularly from two lateral sides of each of the conducting arms  26  and are symmetrical to each other relative to the corresponding conducting arm  26 . The second fins  260  at a lateral side of each of the conducting arms  26  increase in length outwardly from the cylinder  22  to a distal end of the corresponding conducting arm  26 . Each distal end of the conducting arms  26  terminates at an inner face of an outmost second fin  260 . An outer face of each outmost second fin  260  is flat and used for thermally contacting with one of the LED modules  30 . In addition, to facilitate airflow in the through hole of the cylinder  22 , a ratio of a length to a diameter of the cylinder  22  is in a range from 5:1 to 10:1. In this embodiment of the present invention, the length to diameter ratio of the cylinder  22  is 10:1. 
         [0018]    An annular fixing part  28  extends downwardly and vertically from a bottom edge of the cylinder  22  and forms screw thread (not labeled) thereon for screwing into the engaging portion  160  of the second cover  16  to mount the heat sink  20  on the lamp base  10 . The fixing part  28  symmetrically defines three through orifices  280  therein corresponding to the through orifices  1602  of the engaging portion  160  of the second cover  16 . The heat sink  20  and the lamp base  10  can be locked together by three bolts (not shown) inserting into the corresponding through orifices  1602 ,  280  when the fixing part  28  of the heat sink  20  is received in the engaging portion  160  of the second cover  16 . 
         [0019]    Also referring to  FIG. 2 , the LED modules  30  each comprise an elongated printed circuit board  32  with a size slightly smaller than that of the outmost second fin  260  of the heat sink  20 . A plurality of LED components  34  are mounted in a line on each of the printed circuit boards  32  along a length thereof. 
         [0020]    As shown in  FIG. 4 , the blower  40  is mounted in an upper portion of the second cover  16  and totally occupies an inlet from the inner space enclosed by the lamp base  10  to the through hole of the cylinder  22 . The blower  40  can be constructed by different airflow generating apparatuses such a piezoelectric blower or an electrical motor-driven blower. Furthermore, a direction sensor is provided in the LED lamp to detect a direction in which the LED lamp is placed so as to control the blower  40  to generate an upward airflow consistent with natural ventilation inside the LED lamp. The sensor can be mounted in either the through hole of the heat sink  20  or the lamp base  10 . 
         [0021]    In assembly of the LED lamp, the blower  40  is secured to the upper portion of second cover  16  by adhering or screwing. The screws extend through the fixing orifices  1420  of the first cover  14  of the lamp base  10  to screw into the second cover  16  of the lamp base  10 , whereby the first and second covers  14 ,  16  are thus assembled together. The heat sink  20  is mounted to the second cover  16  of the lamp base  10  by screwing the fixing part  28  at the bottom of the heat sink  20  downwardly into the engaging portion  160  of the second cover  16 , thus heat sink  20  and the lamp base  10  are connected together. The through hole of the cylinder  22  communicates with the lamp base  10  and further communicates with ambient air through the vents  166  of the second cover  16 . The LED modules  30  are respectively attached to the outer faces of the outermost second fins  260  of the heat sink  20  in a thermal conductive relationship. 
         [0022]    A preferred embodiment of the LED lamp having a heat dissipating structure according to the present invention has thus been described; however, it should be understood that the present invention is not limited to above. For example, an alternative embodiment is shown in  FIG. 5 , in which a blower  50  is mounted on a top of the heat sink  20  for blowing airflow into or drawing airflow from the through hole of the cylinder  22  of the heat sink  20 . The blower  50  comprises a frame (not labeled) fitting on the top of the heat sink  20  and totally covers the top of the heat sink  20 . 
         [0023]    In use of the LED lamp, the space enclosed by the first and second cover  14 ,  16  and the through hole in the cylinder  22  of the heat sink  20  communicate with each other and cooperate to form an air passage in the LED lamp. Ambient air can flow into the air passage in the LED lamp through the vents  166  of the first cover  14  of the LED base  10  and exit the air passage from the top of the cylinder  22  of the heat sink  20 ; thus, an air circulation can be formed between an inside and an outside of the LED lamp. Alternatively, ambient air also can enter into the air passage through the top of the cylinder  22  and exit therefrom via the vents  166 . An air circulation air circulates between the air passage in the LED lamp and ambient outside around the LED lamp is thus formed. Such an air circulation is greatly promoted by the blower  40 ,  50 . When the LED modules  30  are activated, heat generated by the LED components  34  is adsorbed by the outmost second fins  260  of the heat sink  20  and then evenly distributed to the whole heat sink  20  via the conducting arms  26  of the heat sink  20 . The heat of the heat sink  20  is finally removed by airflow circulating though the air passage. 
         [0024]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention