Patent Publication Number: US-6710691-B2

Title: Transformer with an associated heat-dissipating plastic element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 91212596, filed Aug. 14, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a transformer. More particularly, the present invention relates to a transformer with an associated heat-dissipating plastic element. 
     2. Description of Related Art 
     Following the rapid progress in information technologies, various types of communication products and server structures with multiple functions are developed. Using the ever more popular mobile phone as an example, the transmission/reception of a mobile phone depends on a base station. In general, the base station is located at the top of a high-rise building and hence the broadcasting equipment in a base station is normally housed inside a wafer-proofed casing. In fact, the interior of a wafer-proofed casing can be regarded as a sealed space with little air current flowing inside. Obviously, the heat produced by various devices (all heat producing sources) inside the base station equipment is difficult to get out from the interior by air because air is a poor conductor of heat. Consequently, the best method of dissipating the heat generated by various devices inside the casing of a base station to the outside world is an important issue. 
     FIG. 1 is a perspective view of a conventional transformer structure. As shown in FIG. 1, a conventional transformer  100  includes a hollow main body  102 , a core  104  and a coil  106 . The core  104  is installed in the middle of the hollow main body  102  while the coil  106  wraps around the core  104 . 
     FIG. 2 is a cross-sectional view of a conventional transformer and the sealed space within the transformer. As shown in FIG. 2, a conventional transformer  100  normally mounts on top of a circuit board  108 . The circuit board  108  has an open cavity  110  for accommodating a first thermal pad  112 . In general, a second thermal pad  114  is also attached to the upper surface of the hollow main body  102 . Using a base station as an example, the transformer  100  is housed inside the sealed space of a casing  116 . The transformer  100  contacts the casing  116  through the first thermal pad  112  and the second thermal pad  114  to facilitate heat dissipation. 
     The main source of heat comes from the coil  106  inside the transformer  100 . Because convection circulation inside the sealed interior of the casing  116  is very poor, heat produced by the coil  106  can hardly be channeled away to the exterior. In other words, the heat generated by the coil  106  of the transformer  100  is mainly carried away through the contact with the core  104 . Through the core  104 , heat is conducted away via the hollow main body  102 , the first thermal pad  112  and the second thermal pad  114  to the casing  116 . 
     In a conventional transformer, contact area between the coil and the core is very limited. Hence, very little heat generated by the coil can be conducted to the core via the contact area for thermal dissipation. It is inevitable that a gap is existing between the coil and the core when copper wires are wrapped around the core to produce the coil, contact area between the coil and the core is diminished even further. Ultimately, the capacity for dissipating heat away from the transformer coil would further get worse for the transformer in a limited space. 
     Therefore, subject to the effect caused by the very limited contact area between the coil and the core, the coil may be overheated when the transformer is in operation. The low efficiency of thermal dissipation causes an accumulation of thermal into high temperature. This will also directly affect the lifetime and the performance for the transformer and its peripheral electronic devices. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a transformer with an associated heat-dissipating plastic element therein capable of dissipating heat away from a transformer coil faster. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a transformer with an associated heat-dissipating plastic element. The transformer includes a hollow main body, a core, a coil and a heat-dissipating plastic element. The core is installed inside the hollow main body while the coil wraps around the core. The heat-dissipating plastic element is also installed inside the hollow main body but encloses the core and the coil. In addition, the heat-dissipating plastic element has a heat transfer coefficient higher than air. 
     In this invention, the hollow main body and the core inside the transformer are formed as an integrative unit made from a material such as ferrous ceramics. In addition, the coil is coated with a layer of lacquer. 
     In this invention, the transformer may be mounted on a printed circuit board. The circuit board has an open cavity for installing a first thermal pad. The first thermal pad serves to conduct heat away from the hollow main body to the casing. To increase the heat-dissipating capacity of the transformer, a second thermal pad may be installed above the hollow main body for conducting heat away from the hollow main body to the casing via the second thermal pad. 
     In another embodiment of this invention, the heat-dissipating plastic element occupies the hollow main body and encloses the core and the coil entirely so that the plastic element is able to conduct heat directly from the first thermal pad and the second thermal pad to the casing. In this embodiment, the heat transfer coefficient of the heat-dissipating plastic is higher than the hollow main body. 
    
    
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 is a perspective view of a conventional transformer structure; 
     FIG. 2 is a cross-sectional view of a conventional transformer and the sealed pace within the transformer; 
     FIG. 3 is a perspective view of a transformer having a heat-dissipating plastic element according to a first embodiment of this invention; 
     FIG. 4 is a cross-sectional view of a transformer having a heat-dissipating plastic element inside the sealed space of the transformer according to the first embodiment of this invention; 
     FIG. 5 is a perspective view of a transformer having a heat-dissipating plastic element according to a second embodiment of this invention; and 
     FIG. 6 is a cross-sectional view of a transformer having a heat-dissipating plastic element inside the sealed space of the transformer according to the second embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     FIG. 3 is a perspective view of a transformer having a heat-dissipating plastic element according to a first embodiment of this invention. As shown in FIG. 3, the transformer  200  mainly includes a hollow main body  202 , a core  204 , an electric coil  206  and a block of heat-dissipating plastic  218 . The core  204  is installed inside the hollow main body  202  while the electric coil  206  wraps around the core  204 . The heat-dissipating plastic element  218  occupies the interior of the hollow main body  202  and encloses the core  204  and the electric coil  206 . In this embodiment, the hollow main body  202  and the core  204  are formed as an integrative unit using a material such as ferrous ceramics and the electric coil  206  is made from lacquer coated wires. Furthermore, the heat-dissipating plastic  218  has a heat transfer coefficient greater than air. 
     FIG. 4 is a cross-sectional view of a transformer having a heat-dissipating plastic element inside the sealed space of the transformer according to the first embodiment of this invention. As shown in FIG. 4, the transformer  200  is mounted on a circuit board  208 . The circuit board  208  has an open cavity  210 . The open cavity  210  is able to accommodate a first thermal pad  212 . In addition, a second thermal pad  214  is also attached to the roof of the transformer  200  or the upper surface of the hollow main body  202 . Using a base station as an example, the transformer  200  is set up inside the sealed space of a casing  216 . The transformer  200  is in contact with the casing  216  through the first thermal pad  212  and the second thermal pad  214 . Hence, heat is transferred to the casing  216  and channeled away from the transformer  200 . 
     The electric coil  206  inside the transformer  200  is the main source of heat. Since convection current inside the sealed space of the transformer  200  is minimal, the electric coil  206  can hardly transfer any heat away from the interior of the casing to the exterior by air. The heat generated by the coil  206  can be channeled away via two major routes. In the first route, the heat can be conducted away from the coil  206  to the core  204  through contact with the core  204 . Thereafter the heat is conducted away from the core  204  to the hollow main body  202 . In the second route, the heat generated by the coil  206  is passed to the core  204  and the hollow main body  202  via the heat-dissipating plastic element  218 . After transferring to the core  204  and the hollow main body  202 , the heat is transferred to the casing  216  through the first thermal pad  212  and the second thermal pad  214 . 
     In this embodiment, the heat transfer coefficient of the heat-dissipating plastic element  218  is much greater than air. Hence, the heat-dissipating plastic element  218  is very effective in transferring heat away to the core  204  and the hollow main body  202 . In other words, by using a block of heat-dissipating plastic  218  with a high heat transfer coefficient, the problem of cooling a sealed interior space with a heat-producing source is effectively solved. 
     FIG. 5 is a perspective view of a transformer having a heat-dissipating plastic element according to a second embodiment of this invention. As shown in FIG. 5, the transformer  300  includes a hollow main body  302 , a core  304 , an electric coil  306  and a heat-dissipating plastic element  318 . The core  304  is installed inside the hollow main body  302  while the coil  306  wraps around the core  304 . The heat-dissipating plastic element  318  encloses the entire hollow main body  302  including the core  304  and the coil  306  so that heat can be directly conducted to the exterior. In addition, the hollow main body  302  and the core  304  may be manufactured as an integrative unit using a material such as ferrous ceramics and the electric coil  306  is made from lacquer coated wires. Furthermore, the heat-dissipating plastic  318  has a heat transfer coefficient greater than the hollow main body  302 . This embodiment is very similar to the first embodiment except the extent of distribution of the heat-dissipating plastic element  318 . 
     FIG. 6 is a cross-sectional view of a transformer having a heat-dissipating plastic element inside the sealed space of the transformer according to the second embodiment of this invention. As shown in FIG. 6, the transformer  300  mounts on a circuit board  308 . The circuit board  308  has an open cavity  310 . The open cavity  310  is able to accommodate a first thermal pad  312 . In addition, a second thermal pad  314  is also attached to the roof of the transformer  300  or the upper surface of the hollow main body  302 . Using a base station as an example, the transformer  300  is set up inside the sealed space of a casing  316 . The transformer  300  is in contact with the casing  316  through the first thermal pad  312  and the second thermal pad  314 . Hence, heat is transferred to the casing  316  and channeled away from the transformer  300 . 
     The electric coil  306  inside the transformer  300  is the main source of heat. The heat generated by the coil  306  can be channeled away via three major routes. In the first route, the heat can be conducted away from the coil  306  to the core  304  through contact with the core  304 . Thereafter the heat is conducted away from the core  304  to the hollow main body  302  and then to the heat-dissipating plastic element  318 . In the second route, the heat generated by the coil  306  is passed to the core  304  and the hollow main body  302  via the heat-dissipating plastic element  318 . Thereafter, the heat is transferred to the heat-dissipating plastic element  318  outside the hollow main body  302 . In the third route, the heat generated by the coil  306  is transferred directly from the interior of the hollow main body  302  to the exterior of the hollow main body  302  through the heat-dissipating plastic element  318 . After transferring to the heat-dissipating plastic element  318  via the hollow main body  302 , the heat is conducted away to the casing  316  via the first thermal pad  312  and the second thermal pad  314 , thereby cooling the transformer  300 . 
     In this embodiment, the heat transfer coefficient of the heat-dissipating plastic element  318  is much greater than the hollow main body  302 . Hence, the heat-dissipating plastic element  318  is very effective in transferring heat away from the coil  306 . In a similar way, this embodiment resolves the problem of cooling a sealed interior space (without any convection current therein) with a heat-producing source is effectively solved. 
     In summary, the advantages of having a heat-dissipating plastic element inside the transformer include: 
     1. Using a heat-dissipating plastic with a thermal transfer coefficient greater than air, heat produced by the coil is rapidly channeled away to the hollow main body. Hence, the low heat-dissipating capacity in a conventional transformer due to a small contact area between the coil and the core is boosted. 
     2. This invention also uses a heat-dissipating plastic element with a thermal transfer coefficient higher than the hollow main body so that heat may pass directly from the transformer to the casing without going through any intervening thermal pads. This arrangement not only reduces production cost, but also has a positive effect on the cooling of the transformer. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.