Abstract:
An LED bulb uses an LED strip suspended between two lead frames of a stem as a light source to provide uniform illumination with wider angles. The lead frames of the stem provide an improved structural stability to the LED strip while maintaining a reliable electrical connection between the components of the stem and the LED strip. The utilization of both top-emitting and side-emitting LEDs on the LED strip further allows lights emitted in directions substantially parallel and perpendicular to the LED strip to cover a wide angle of illumination from the LED bulb.

Description:
FIELD OF THE INVENTION 
     The present invention is related to a light bulb and, more particularly, to a light-emitting diode (LED) bulb that may be used as a replacement light bulb. 
     BACKGROUND OF THE INVENTION 
     Conventional incandescent bulbs mostly include a conductive filament, such as a tungsten filament, supported by lead frames which are connected to an external power source via a bulb base to supply electricity to the filament. The filament is rendered incandescent by current flowing therethrough and thus generates light that radiates outward uniformly and extensively. The conventional incandescent bulb, though capable of a wide lighting angle, is disadvantageous because of its high power consumption, high temperature, and short lifetime. By contrast, a light-emitting diode (LED) bulb has a long lifetime, is power saving, produces no wastes that may cause pollution, and is therefore environmentally friendly. Hence, LED bulbs are gradually replacing the conventional incandescent bulbs and are regarded as the new generation lighting devices. However, the limited lighting angle and high production costs of LED bulbs have restricted their applicability in our daily lives. 
     U.S. Patent Application Publication No. 2005/0254264 discloses an LED bulb which includes a bent circuit board mounted with LEDs thereon, to provide more extensive and uniform illumination in a three-dimensional space by arranging each of the LEDs to have a light-emitting direction perpendicular to the bent circuit board. However, this LED bulb still has its drawbacks such as high production costs, difficult assembly, and a hard-to-control yield. In addition, a wide lighting angle is unattainable if fewer LEDs are used. Moreover, to expose heat radiating ribs, the circuit board cannot enclose the lateral sides and thus, there will be no LEDs at the lateral sides. Consequently, the LED bulb cannot provide effective lateral illumination. 
     On the other hand, while it is common practice to connect several through-hole LEDs together for multi-angle light emission, the slender pins typical of commercially available through-hole LEDs tend to cause lack of stability and reliability in the resultant mechanical structure. The multi-angle illumination is achieved by bending the pins of LEDs to different directions, and thus the overall structural stability of the finished product will be even lower. The connection between the pins of LEDs may also be problematic. For instance, short circuit and safety hazards may arise from improper arrangement or spacing between the pins when they are electrically conducted. 
     Taiwan Pat. No. M340562 provides a lighting device which includes top-emitting LEDs mounted on the central region of the top surface of a circuit board to provide illumination to the front side of the circuit board, side-emitting LEDs mounted on the peripheral region of the top surface to provide illumination to the lateral side of the circuit board, and driver circuitry for driving the LEDs is mounted on the bottom surface of the circuit board. Since all the LEDs are disposed on the top surface of the circuit board, they do not provide illumination to the backside of the circuit board. Furthermore, the LEDs and the driver circuitry for driving the LEDs are mounted on the opposite surfaces of the same circuit board, and thus gather heat within a small area. As a result, it is hard to provide effective heat dissipation for the circuit board and the elements mounted thereon, and overheating is likely to occur, thereby shortening the lifetime and impairing the reliability of the lighting device. 
     Therefore, it is desired an LED bulb which has a wide lighting angle and multiple light-emitting directions, can effectively dissipate heat so as to maintain the lifetime of the LEDs thereof, is reliable in terms of structure and design, and incurs low production costs. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an LED bulb having an increased lighting angle and light-emitting directions. 
     Another object of the present invention is to provide a highly reliable LED bulb. 
     Yet another object of the present invention is to provide a low cost LED bulb. 
     According to the present invention, an LED bulb includes a member joined to or utilized to combine a housing and a bulb base together, a stem having a first lead frame and a second lead frame extending from the stem into a cavity of the housing, and at least one LED strip suspended between the first and second lead frames. The first and second lead frames of the stem are electrically connected to the bulb base and the at least one LED strip, to provide power to the at least one LED strip. Each of the at least one LED strip includes a substrate mounted with top-emitting LEDs and side-emitting LEDs thereon. The top-emitting LEDs have a light-emitting direction substantially perpendicular to the mounting surface of the substrate that they are mounted thereon, and the side-emitting LEDs have a light-emitting direction substantially parallel to the mounting surface of the substrate that they are mounted thereon. 
     Preferably, the side-emitting LEDs are mounted on the peripheral region of the mounting surface of the substrate that they are mounted thereon, to provide lateral light and thereby increase the lighting angle of the LED bulb, resulting in wide and uniform illumination. In addition, by using the lead frames to support the at least one LED strip, the LED bulb may have higher reliability and less production costs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a sectional view taken along the longitudinal axis of the LED bulb according to a first embodiment of the present invention; 
         FIG. 2  is an exploded view of the LED bulb as shown in  FIG. 1 ; 
         FIG. 3  is an illustrative circuit diagram of the LED bulb as shown in  FIG. 1 ; 
         FIG. 4  shows an LED bulb according to a second embodiment of the present invention; 
         FIG. 5  is a perspective view of a LED strip of the present invention; 
         FIG. 6  is a side view of the LED strip as shown in  FIG. 5 ; 
         FIG. 7  shows a first embodiment of the LED strip of the present invention; and 
         FIG. 8  shows a second embodiment of the LED strip of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an LED bulb  100  according to an embodiment of the present invention;  FIGS. 2 and 3  show the exploded view and circuit diagram of the LED bulb  100  of the present invention. The LED bulb  100  includes a housing  110  and a bulb base  150  joined to or combined together by a member  140 . In this embodiment, the housing  110  has an end  114  inserting into a groove  144  of the member  140 , with a securing medium  170 , for example a glue, filled in the groove  144  to secure the housing  110  at the front side of the member  140 , and the bulb base  150  is secured at the rear side of the member  140 , for example, by means of snug fit or adhesive. As is well known, the bulb base  150  has two electrodes to be connected to an external power source  230 , and the housing  110  has a cavity  112  for containing a filament. A stem  130  has lead frames  131  and  132  extending from the front end  134  of the stem  130  into the cavity  112  of the housing  110 , and an LED strip  120  is suspended between the lead frames  131  and  132  and has electrodes  121  and  122  electrically connected to the lead frames  131  and  132  respectively. Preferably, the lead frame  131  of the stem  130  extends into the cavity  112  away from the lead frame  132  of the stem  130  at a distance greater than or equal to the length of the substrate  310  of the LED strip  120 . In this embodiment, the stem  130  supports the LED strip  120  in the cavity  112  of the housing  110  and supplies power to the LED strip  120  by the electrodes  121  and  122 . The housing  110  has an end opening  116  to allow the lead frames  131  and  132  to place into the cavity  112 . Through the rear end  136  of the stem  130 , the lead frames  131  and  132  are electrically connected to the electrodes of the bulb base  150  by wires  133  and  135  respectively, to deliver power from the external power source  230  through the bulb base  150  and the lead frames  131 ,  132  to the LED strip  120 . Preferably, a power control unit  160  is connected between the electrode  152  of the bulb base  150  and the wire  135 , to limit the voltage or power supplied to the LED strip  120 . In this embodiment, the stem  130  is secured to the member  140 , for example, by applying a securing medium  180 , such as glue, between the member  140  and the stem  130 , so that the member  140  may support the stem  130 . The member  140  has a front-side opening  142  to allow the stem  130  passing therethrough, and a beck-side opening  146  to allow the wires  133  and  135  passing therethrough. The bulb base  150  has a top opening  154  to allow the power control unit  160  and/or the wires  133  and  135  to pass through. 
     In an embodiment, the power control unit  160  includes a voltage step-down or clamp element, such as a resistor, to control the voltage or power supplied to the LED strip  120  within a predetermined range. It is understood that the power control unit  160  may be dispensed with in another embodiment, depending on the number and power demands of the LEDs mounted on the LED strip  120 . 
     In other embodiments, either or both of the housing  110  and the stem  130  are secured to the member  140  by gluing, thermal fusion, pressing, snug fit, or screw engagement. In some embodiments, the electrodes  121  and  122  of the LED strip  120  are electrically connected to the lead frames  131  and  132  of the stem  130  by soldering, gluing with an electrically conductive adhesive, hook engagement, or winding. 
     Preferably, each of the lead frames  131  and  132  has a slender shape, for example, in the form of electrically conductive metal wires or rods, so as to be easily adjusted in its dimension to pass through the end openings of different apertures and be received in the housings of various sizes. Preferably, the slender shape of the lead frames  131  and  132  has an upper width greater than a lower width thereof, and both the upper and lower widths are smaller than or equal to the width of the end opening  116  of the housing  110 . When current is supplied from the external power source  230  to the LED strip  120  through the bulb base  150 , the current flows into the LED strip  120  via the lead frame  131  and exits the LED strip  120  via the lead frame  132 , or, alternatively, flows into the LED strip  120  via the lead frame  132  and exits the LED strip  120  via the lead frame  131 . It is understood that the configurations of the lead frames  131  and  132  may be modified in variant embodiments of the present invention. For instance, the lead frames  131  and  132  may be curved or bent, solid or hollow. 
     More LED strips  120  may be used in different embodiments according to practical demands enhancing the applications of the LED bulb  100 . As shown in  FIG. 4  for another embodiment of the present invention, an LED bulb  200  includes two LED strips  120  and  120 ′ adjacent to each other and both electrically connected to the lead frames  131  and  132  by their electrodes  121 ,  122  and  121 ′,  122 ′. It is understood that, in a variant embodiment of the present invention, there may be more than two LED strips supported in the cavity  112  by the stem  130  so as to increase the brightness of an LED bulb. In this embodiment, the LED strips  120  and  120 ′ may be suspended between the lead frames  131  and  132  in a face-to-face manner or in a side-by-side manner. In an embodiment, the electrodes  121 ,  122 , and  121 ′,  122 ′ of the LED strips  120 ,  120 ′ are electrically connected to the lead frames  131 ,  132  of the stem  130  by soldering, gluing with an electrically conductive adhesive, hook engagement, or winding. 
       FIG. 5  is a perspective view of the LED strip  120 , and  FIG. 6  is a side-view of the LED strip  120  as shown in  FIG. 5 . The LED strip  120  includes top-emitting LEDs  320  and side-emitting LEDs  330  mounted on the substrate  310 . Each of the top-emitting LEDs  320  has a light-emitting direction perpendicular to the mounting surface of the substrate  310  that it is mounted on, and each of the side-emitting LEDs  330  has a light-emitting direction parallel to the mounting surface of the substrate  310  that it is mounted on. Preferably, the top-emitting LEDs  320  are mounted in the central regions of the opposite mounting surfaces of the substrate  310 , and the side-emitting LEDs  330  are mounted in the peripheral regions of the mounting surfaces in a manner surrounding the top-emitting LEDs  320  on the same mounting surfaces, so that the LED strip  120  may provide light emitted by the side-emitting LEDs  330  in multiple lateral directions  360 ,  361 ,  362 , and  363 , and light emitted by the top-emitting LEDs  320  in the forward direction  366  and the backward direction  364 . Consequently, the planar LED strip  120  is capable of multi-direction light emission and a wide lighting angle that contribute to extensive and uniform illumination. In this embodiment, the top-emitting LEDs  320  and the side-emitting LEDs  330  both include surface mounted LEDs. 
     Referring to  FIG. 5 , in an embodiment, the substrate  310  includes conductors  123  and  125  electrically connected to the electrodes  121  and  122  respectively, to provide power to the top-emitting LEDs  320  and the side-emitting LEDs  330  mounted on the substrate  310 . The conductors  123  and  125  include conductive pads, such as metal pads, through which current may flow from the electrode  121  or  122  to the top-emitting LEDs  320  and the side-emitting LEDs  330 . In an embodiment, the conductors  123  and  125  are coplanar to a mounting surface of the substrate  310 ; in another embodiment, the conductors  123  and  125  are on the opposite mounting surfaces of the substrate  310  respectively. The electrodes  121  and  122  may be electrically connected to the conductors  123  and  125  by welding, soldering, gluing with an electrically conductive adhesive, or hook engagement. Current may flow from the electrode  121  to the top-emitting LEDs  320  and the side-emitting LEDs  330  through the conductor  123  and exit the LED strip  120  through the conductor  125  and the electrode  122 , or, alternatively, from the electrode  122  to the top-emitting LEDs  320  and the side-emitting LEDs  330  through the conductor  125  and exit the LED strip  120  through the conductor  123  and the electrode  121 . Thus, the LED strip  120  is safe and reliable in terms of structure and design. 
     In an embodiment, as shown in  FIG. 7 , the substrate  310  includes a double-sided circuit board  410 , and the opposite mounting surfaces  412  and  414  thereof are mounted with some of the top-emitting LEDs  320  and some of the side-emitting LEDs  330  respectively. In an embodiment, the top-emitting LEDs  320  and the side-emitting LEDs  330  are divided into two groups, one group of the top-emitting LEDs  320  and the side-emitting LEDs  330  are mounted on the mounting surface  412 , and the other group of the top-emitting LEDs  320  and the side-emitting LEDs  330  are mounted on the other mounting surface  414 . The double-sided circuit board  410  may be a rigid printed circuit board or a flexible printed circuit board. In another embodiment, as shown in  FIG. 8 , the substrate  310  includes two single-sided circuit boards  420  and  430  attached to each other in a back-to-back manner. The top-emitting LEDs  320  and the side-emitting LEDs  330  are divided into two groups, one group of the top-emitting LEDs  320  and the side-emitting LEDs  330  are mounted on the mounting surface  422  of the single-sided circuit board  420 , and the other group of the top-emitting LEDs  320  and the side-emitting LEDs  330  are mounted on the mounting surface  434  of the single-sided circuit board  430 . The backside surface  424  of the single-sided circuit board  420  is attached to the backside surface  432  of the single-sided circuit board  430 . The single-sided circuit boards  420 ,  430  may be rigid printed circuit boards or flexible printed circuit boards. It is understood that, in another embodiment, all the top-emitting LEDs  320  may be mounted on the mounting surface  422  of the single-sided circuit board  420 , and all the side-emitting LEDs  330  may be mounted on the mounting surface  434  of the single-sided circuit board  430 . 
     Referring to  FIG. 5  again, by mounting the side-emitting LEDs  330  in the peripheral regions of the opposite mounting surfaces of the substrate  310 , the LED strip  120  can emit light in multiple lateral directions and thereby provide extensive and uniform illumination. Even if fewer LEDs are used for the LED strip  120 , a wide lighting angle is still achievable. Therefore, the dimension of the substrate  310  as well as the number of the top-emitting LEDs  320  and the side-emitting LEDs  330  can be adjusted according to practical demands, so that the LED strip  120  is flexibly applicable to bulbs of different sizes, such as bulbs with standard bulb bases E 10 , E 12 , E 14 , E 17 , E 26 , E 27 , B 15 , B 22 , and GU-10. Compared with the conventional LED bulbs using through-hole LEDs as the light source, the LED bulb according to the present invention using the LED strip  120  with surface mounted LEDs or chip-on-board LEDs as its light source has higher structural stability and enhanced safety in current control. As the surface mounted LEDs are available in both the top-emitting type and the side-emitting type, and have higher mounting speed, higher production yield, lower costs, and fewer components than the through-hole LEDs, the LED bulb according to the present invention features multiple light-emitting directions, high assembly speed, high production yield, low costs, and fewer components. Furthermore, if surface mounted LEDs, which are smaller than through-hole LEDs, are used for the LED strip  120 , the LED bulb according to the present invention can be made in a variety of dimensions while production costs are also effectively reduced. 
     Referring to  FIGS. 1 ,  3 , and  5 , the top-emitting LEDs  320  and the side-emitting LEDs  330  are divided into two lighting groups  210  and  220  that are parallel connected between the lead frames  131  and  132 . As shown in  FIG. 3 , where the external power source  230  is an alternating-current (AC) power source, the lighting group  210  establishes a first circuitry forward biased from the lead frame  131  to the lead frame  132 , and the lighting group  220  establishes a second circuitry forward biased from the lead frame  132  to the lead frame  131 . Thus, the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  210  are lit during the positive half cycle of the AC power source  230 , and the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  220  are lit during the negative half cycle of the AC power source  230 . As a result, the lighting groups  210 ,  220  will emit light alternately. In an embodiment, the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  210  are mounted on one mounting surface of the substrate  310 , and the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  220  are mounted on the opposite mounting surface of the substrate  310 , so that the LED strip  120  is capable of alternate light emission from its two mounting surfaces. In another embodiment, the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  210  are mounted on an upper portion of the substrate  310 , and the top-emitting LEDs  320  and the side-emitting LEDs  330  in the lighting group  220  are mounted on a lower portion of the substrate  310 , so that the LED strip  120  can emit light from its upper and lower portions by turns. Alternatively, the lighting group  210  includes all the top-emitting LEDs  320  mounted on the substrate  310 , and the lighting group  220  includes all the side-emitting LEDs  330  mounted on the substrate  310 . 
     Similarly, as shown in  FIGS. 3-5 , where the LED bulb  200  includes the LED strips  120  and  120 ′, the top-emitting LEDs  320  and the side-emitting LEDs  330  of the LED strips  120  and  120 ′ may be divided into the lighting groups  210  and  220 . In an embodiment, the lighting group  210  includes the top-emitting LEDs  320  and the side-emitting LEDs  330  mounted on the LED strip  120 , and the lighting group  220  includes the top-emitting LEDs  320  and the side-emitting LEDs  330  mounted on the LED strip  120 ′, thus allowing the LED strips  120  and  120 ′ to emit light by turns. In another embodiment, the lighting group  210  includes all the top-emitting LEDs  320  of the LED strips  120  and  120 ′, and the lighting group  220  includes all the side-emitting LEDs  330  of the LED strips  120  and  120 ′. 
     As shown in the above embodiments, the present invention uses a planar LED strip to achieve the object of increasing the lighting angle of an LED bulb. Compared with the arts using a three-dimensional array of LEDs to achieve the same object, the present invention advantageously employs fewer components, can be assembled more easily, has a higher production yield, and requires lower production costs. In addition, even if a small number of the LEDs fail during use, the LED bulb can still function normally, thus providing high economic benefits. 
     The lead frames disclosed herein not only support the LED strip, but also supply power from the external power source to the LED strip. Hence, the lead frames of the LED bulb according to the present invention can be formed as their counterparts in standard bulbs so as to be compatible with the shapes of existing glass bulbs and the Edison screw bulb bases. By grouping the LEDs into two opposite polarity directions to be driven by an AC power source directly or under the limitation of the power control unit, there will be no need of power converters, for example AC-to-DC converters, and consequently the reliability and component safety of the LED bulb are increased while the costs of the LED bulb are further reduced. 
     The foregoing description and disclosure only serve to demonstrate the principle and features of the present invention and are not intended to limit the scope of the present invention, which is defined by the appended claims. It is understood that all equivalent modifications, changes, and combination of the disclosed components should be encompassed by the appended claims. In addition, as the words “a”, “an”, and “one” used in the description and disclosure of the present invention and the appended claims connote “at least one”, changes in the number of the disclosed components should also fall within the scope of the present invention.