Abstract:
A fan structure with externally connected circuit includes a frame body, a stator, a fan impeller and a circuit board. The stator and the fan impeller are disposed in the frame body. The circuit board is disposed on an outer face of the frame body in contact with ambient air. Therefore, the room for the circuit board is increased without increasing the thickness of the frame body. Moreover, the heat dissipation effect of the circuit board is enhanced.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to a fan structure with externally connected circuit, and more particularly to a fan structure in which the circuit board is disposed on an outer face of the frame body. 
         [0003]    2. Description of the Related Art 
         [0004]    A prior art discloses a cooling fan including a fan frame, a bearing system, a stator assembly and a rotor assembly. The rotor assembly is correspondingly disposed around the stator assembly. The rotor assembly and the stator assembly are both received in the fan frame. The fan frame includes a base section and a bearing cup upward protruding from a center of the base section of the fan frame. The top end of the bearing cup is an open end. The bearing cup is formed with a central receiving space. An annular groove is formed on inner circumference of the top end of the bearing cup in communication with the receiving space. The inner diameter of the section of the top end of the bearing cup that is formed with the annular groove is larger than the inner diameter of the other section of the bearing cup. The bottom face of the center of the base section of the fan frame is recessed to form a cylindrical receiving sink opposite to the receiving space of the bearing cup. The receiving sink is not in communication with the receiving space. The stator assembly is fitted around the bearing cup. A retainer ring is disposed on the shaft and fixed at the top end of the bearing cup. The stator assembly includes a circuit board and an armature composed of multiple stacked silicon steel sheets. A winding assembly is wound around the armature to produce alternate magnetic field. The winding assembly is electrically connected to the circuit board. Insulation plates are disposed on upper and lower sides of the armature to cover the same so as to avoid electrical contact between the armature and the winding assembly. 
         [0005]    The above conventional cooling fan has the following shortcomings: 
         [0006]    When the fan is driven to operate, the drive current will flow through the electronic components arranged on the circuit board. At this time, the electronic components will generate high heat. The circuit board is coaxially positioned under the armature and the space between the circuit board and the armature is limited so that the heat dissipation effect is poor. As a result, the lifetime of the electronic components arranged on the circuit board will be shortened. Moreover, the existent motor is generally designed with additional control function. Therefore, it is necessary to arrange additional components on the circuit board. In order to combine the drive function and the additional control function, it is necessary to integrate the original electronic components and the additional electronic control components onto the circuit board. However, the area of the circuit board for arrangement of the electronic components is limited to the maximum outer diameter of the motor. Therefore, it is hard to arrange the electronic components. 
         [0007]    To overcome the above problem, another prior art discloses a cooling fan including a frame body and a fan impeller. The frame body has an air inlet face, an air outlet face, an inner wall, an axial flow passage and a support section. The air inlet face and the air outlet face are respectively formed on two sides of the frame body. The inner wall defines the axial flow passage, which passes through the frame body. The fan impeller is disposed in the frame body. Multiple blades are annularly disposed on outer circumference of the fan impeller. The support section is formed on at least one part of the frame body. The support section includes a first sidewall, a second sidewall and a support space. The first sidewall is formed of at least one part of the inner wall. The second sidewall is spaced from the first sidewall. The support space is defined between the first and second sidewalls to support a drive circuit board. Accordingly, the heat dissipation effect of the drive circuit board is enhanced and the axial thickness of the stator is increased so as to increase the output torque of the motor and the air volume of the fan. 
         [0008]    However, the above conventional cooling fan has a shortcoming. That is, the support section is formed of a part of the frame body so that the thickness of the frame body is increased. In this case, it is difficult to arrange the fan in a limited space of a device. Moreover, the total weight of the fan is increased. 
       SUMMARY OF THE INVENTION 
       [0009]    It is therefore a primary object of the present invention to provide a fan structure with externally connected circuit, in which the circuit board is disposed on an outer face of the frame body in contact with ambient air. Therefore, the room for the circuit board is increased without increasing the thickness of the frame body. In this case, more electronic components can be arranged on the circuit board. Moreover, the heat dissipation effect of the circuit board is enhanced. 
         [0010]    To achieve the above and other objects, the fan structure with externally connected circuit of the present invention includes: a frame body having an air inlet end, an air outlet end, an inner wall, an outer wall, an axial flow passage and a seat section, the air inlet end and the air outlet end being respectively formed on two sides of the frame body, the axial flow passage being defined by the inner wall to pass through the frame body, the seat section being positioned in the axial flow passage and connected to the inner wall via multiple support sections; a stator disposed on the seat section; a fan impeller disposed on the seat section of the frame body corresponding to the stator, the fan impeller having multiple blades annularly arranged on an outer circumference of the fan impeller; and a circuit board disposed on the outer wall and electrically connected to the stator. The circuit board has a connection side snugly attached to a part of the surface of the outer wall or the entire surface of the outer wall and an outer side exposed to ambient environment. A solid body is formed between the inner wall and the outer wall. 
         [0011]    In comparison with the conventional technique, the circuit board is disposed on an outer face of the frame body in contact with ambient air. Therefore, the room for the circuit board is increased without increasing the thickness of the frame body. In this case, more electronic components can be arranged on the circuit board. Moreover, the heat dissipation effect of the circuit board is enhanced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The structure and the technical means adopted by the present invention to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a perspective exploded view of the present invention; 
           [0014]      FIG. 2  is a perspective assembled view of the present invention; 
           [0015]      FIG. 3  is a sectional assembled view of the present invention; and 
           [0016]      FIG. 4  is a perspective assembled view of another embodiment of the present invention, in which the circuit board is attached to the entire surface of the outer wall of the frame body. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Please refer to  FIGS. 1 ,  2  and  3 .  FIG. 1  is a perspective exploded view of the present invention.  FIG. 2  is a perspective assembled view of the present invention.  FIG. 3  is a sectional assembled view of the present invention. The axial-flow fan of the present invention includes a frame body  11 , which can be a square frame body or an annular frame body. The frame body has an axial flow passage  115 . When a fan impeller  13  rotates, airflow can flow through the axial flow passage  115 . 
         [0018]    The present invention includes a frame body  11 , a stator  12 , a fan impeller  13  and at least one circuit board  14 . In this embodiment, the frame body  11  is, but not limited to, an annular frame body. Alternatively, the frame body  11  can be a square frame body. The stator  12  and the fan impeller  13  are disposed in the frame body  11 . The fan impeller  13  has multiple blades  131  annularly arranged on an outer circumference of the fan impeller  13 . The blades  131  radially outward extend from the fan impeller  13 . The fan impeller  13  is rotatable relative to the stator  12 . Each blade  131  has an air inlet side  1311 , an air outlet side  1312  and an outer side  1313 . 
         [0019]    The frame body  11  has an air inlet end  111 , an air outlet end  112 , an inner wall  113 , an outer wall  114 , an axial flow passage  115  and a seat section  116 . The air inlet end  111  and the air outlet end  112  are respectively formed on two sides of the frame body  11 . The axial flow passage  115  is defined by the inner wall  113  to pass through the frame body  11 . The seat section  116  is positioned near the air outlet end  112 . Multiple support members  117  are connected between the outer circumference of the seat section  116  and the inner wall  113  to support and fix the seat section  116  in the axial flow passage  115 . A hollow bearing cup  1161  protrudes from the seat section  116 . A solid body is formed between the inner wall  113  and the outer wall  114 . 
         [0020]    The stator  12  includes a silicon steel sheet assembly composed of multiple stacked silicon steel sheets. The silicon steel sheet assembly is disposed between an insulation support assembly. A winding assembly is wound around the silicon steel sheet assembly and the insulation support assembly. The stator  12  is fitted around the bearing cup  1161  and disposed on the seat section  116 . 
         [0021]    The fan impeller  13  is disposed on the seat section  116  corresponding to the stator  12 . The air inlet sides  1311  of the blades  131  correspond to the air inlet end  111  of the frame body  11 , while the air outlet sides  1312  of the blades  131  correspond to the air outlet end  112 . The outer sides  1313  of the blades  131  correspond to the inner wall  113 . 
         [0022]    The circuit board  14  is disposed on the outer wall  114  and electrically connected to the stator  12 . In this embodiment, the circuit board  14  has a connection side  141  snugly attached to a part of the surface of the outer wall  114  and an outer side  142  exposed to ambient environment.  FIG. 4  shows another embodiment of the present invention, in which the circuit board  14  is snugly attached to the entire surface of the outer wall  114 . 
         [0023]    The circuit board  14  can be attached to the outer wall  114  by means of adhesion. 
         [0024]    Alternatively, a boss can be formed on the outer wall  114  and the circuit board  14  can be formed with a through hole corresponding to the boss for latching the circuit board  14  on the outer wall  114 . Still alternatively, a blind hole is formed on the outer wall  114  and a through hole is formed on the circuit board  14  corresponding to the blind hole. A screw member is passed through the through hole and screwed into the blind hole to lock the circuit board  14  on the outer wall  114 . 
         [0025]    When the fan impeller  13  is driven by the circuit board  14  to rotate, airflow is driven to go from the air inlet end  111  of the frame body  11  through the axial flow passage  115  to the air outlet end  112  and then flow out from the air outlet end  112 . The heat generated by the circuit board  14  is partially dissipated from the outer side  142  of the circuit board  14  to the ambient air and partially transferred to the outer wall  114  in contact with the ambient air and then dissipated from the outer wall  114  to the ambient air. The circuit board  14  is not limited to be positioned on the base seat as in the conventional device. Instead, the circuit board  14  is disposed on an outer face of the frame body  11  in contact with ambient air. Therefore, there is more room for placing the circuit board  14 . In this case, more electronic components with various functions can be arranged on the circuit board  14 . 
         [0026]    In conclusion, in the present invention, the circuit board  14  is directly disposed on the outer wall  114  of the frame body  11 . In comparison with the prior art, it is unnecessary for the frame body  11  to have additional receiving space for receiving the circuit board  14 . Therefore, neither the thickness nor the weight of the frame body  11  will be increased. 
         [0027]    The present invention has been described with the above embodiments thereof and it is understood that many changes and modifications in the above embodiments can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.