Patent Publication Number: US-2023155509-A1

Title: Switching module

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to China Patent Application No. 202111370610.7, filed on Nov. 18, 2021, the entire contents of which are incorporated herein by reference for all purposes. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a switching module, and more particularly to a switching module for reducing the mutual inductance between a power loop and a control loop. 
     BACKGROUND OF THE INVENTION 
     Generally, a switching module of a power electronic system operates at a high frequency to achieve high power density. However, the high operating frequency may increase the switching loss, and thus reduce the efficiency of the switching module. Consequently, when the switching module operates at the high frequency, it is necessary to increase the switching speed of the switching module in order to reduce the switching loss. However, when the switching module operates at the higher switching speed, a serious electromagnetic interference (EMI) problem occurs. 
     Especially, in case that the switching module has a high power density structure, the power loop is relatively close to the control loop. When the current in the power loop changes, the induced magnetic field also changes around the power loop. As the induced magnetic field passes through the control loop, a corresponding induced voltage is generated in the control loop. Consequently, the electromagnetic interference of the mutual inductance between the power loop and the control loop is formed, which affects the switching operation of the switching module. 
     In the conventional switching module, a plurality of power loops are located beside each other, and a plurality of control loops are located beside each other. In other words, no control loop is arranged between every two adjacent power loops, and no power loop is arranged between every two adjacent control loops. Consequently, the induced magnetic fields generated by the power loops pass through the control loops in the same direction. Under this circumstance, the electromagnetic interference of the mutual inductance between the power loops and the control loops is largely increased. If the electromagnetic interference of the mutual inductance is too large, the interference voltage at a control terminal of the switching module may exceed the safe range. Under this circumstance, the reliability of the switching module is reduced, and the switching module is even unable to work normally. 
     Therefore, there is a need of providing an improved switching module in order to overcome the drawbacks of the conventional technologies. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a switching module for reducing the mutual inductance between a power loop and a control loop. 
     In accordance with an aspect of the present disclosure, a switching module is provided. The switching module includes at least one substrate, at least one switching element, at least one control loop, a first power part and a second power part. The at least one switching element is disposed on the at least one substrate. The at least one control loop is connected with the corresponding switching element. The first power part is connected with the corresponding switching element. The second power part is connected with the corresponding switching element. A direction of a first current flowing through the first power part and a direction of a second current flowing through the second power part are identical. A projection of the first power part on a reference plane and a projection of the second power part on the reference plane are located at two opposite sides of a projection of the control loop on the reference plane. 
     The above contents of the present disclosure will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic view illustrating the structure of a switching module according to a first embodiment of the present disclosure; 
         FIG.  2    is a schematic side view illustrating a portion of the switching module as shown in  FIG.  1    and taken along the section A-A′; 
         FIG.  3    schematically illustrates the magnetic flux cancellation principle for the switching module as shown in  FIG.  1   ; 
         FIG.  4    is a schematic view illustrating the structure of a switching module according to a second embodiment of the present disclosure; 
         FIG.  5 A  is a schematic view illustrating the structure of a switching module according to a third embodiment of the present disclosure; 
         FIG.  5 B  is a schematic circuit diagram of the switching module as shown in  FIG.  5 A ; 
         FIG.  6    is a schematic view illustrating the structure of a switching module according to a fourth embodiment of the present disclosure; 
         FIG.  7    is a schematic view illustrating the structure of a switching module according to a fifth embodiment of the present disclosure; 
         FIG.  8    is a schematic view illustrating the structure of a switching module according to a sixth embodiment of the present disclosure; 
         FIG.  9    is a schematic view illustrating the structure of a switching module according to a seventh embodiment of the present disclosure; 
         FIG.  10    is a schematic view illustrating the structure of a switching module according to the eighth embodiment of the present disclosure; 
         FIG.  11    is a schematic view illustrating the structure of a switching module according to a ninth embodiment of the present disclosure; 
         FIG.  12    schematically illustrates a first example of the relationship between the first control part, the second control part and the control loop of the switching module as shown in  FIG.  1   ; 
         FIG.  13    schematically illustrates a second example of the relationship between the first control part, the second control part and the control loop of the switching module as shown in  FIG.  1   ; and 
         FIG.  14    is a schematic view illustrating the structure of a switching module according to a tenth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this disclosure are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Please refer to  FIGS.  1 ,  2  and  3   .  FIG.  1    is a schematic view illustrating the structure of a switching module according to a first embodiment of the present disclosure.  FIG.  2    is a schematic side view illustrating a portion of the switching module as shown in  FIG.  1    and taken along the section A-A′.  FIG.  3    schematically illustrates the magnetic flux cancellation principle for the switching module as shown in  FIG.  1   . 
     In an embodiment, the switching module  1  is disposed on a main circuit board (not shown) and electrically connected with the main circuit board. The switching module  1  includes a substrate  2 , a switching element  3 , a first control part  4 , a second control part  5 , a first power part  6  and a second power part  7 . 
     In an embodiment, the switching element  3  is a vertical-type device. Preferably but not exclusively, the switching element  3  is an insulated gate bipolar transistor (IGBT), a bipolar junction transistor (BJT), a metal-oxide-semiconductor field-effect transistor (MOSFET), a junction field effect transistor (JFET) or a gallium nitride high electron mobility transistor (GaN-HEMT). 
     As shown in  FIG.  2   , the switching element  3  is welded on the substrate  2  through a connecting material  11 . The switching element  3  includes a first control terminal  31 , a second control terminal, a first power terminal and a second power terminal  33 . The first control terminal  31 , the second control terminal and the first power terminal are disposed on a first surface  34  of the switching element  3 . Since the second control terminal and the first power terminal are located at the same region of the switching element  3 , the second control terminal and the first power terminal are also referred as a common conductive terminal  32 . The second power terminal  33  is disposed on a second surface  35  of the switching element  3 . The second power terminal  33  is connected with the substrate  2  through the connecting material  11 . 
     In some embodiments, in case that the switching element  3  is an insulated gate bipolar transistor (IGBT), the first control terminal  31  is served as a gate terminal of the switching element  3 , the common conductive terminal  32  (i.e., the second control terminal and the first power terminal) is served as an emitter of the switching element  3 , and the second power terminal  33  is served as a collector of the switching element  3 . In some other embodiments, in case that the switching element  3  is a bipolar junction transistor (BJT), the first control terminal  31  is served as a base of the switching element  3 , the common conductive terminal  32  (i.e., the second control terminal and the first power terminal) is served as an emitter of the switching element  3 , and the second power terminal  33  is served as a collector of the switching element  3 . In some other embodiments, in case that the switching element  3  is a metal-oxide-semiconductor field-effect transistor (MOSFET), a junction field effect transistor (JFET) or a gallium nitride high electron mobility transistor (GaN-HEMT), the first control terminal  31  is served as a gate terminal of the switching element  3 , the common conductive terminal  32  (i.e., the second control terminal and the first power terminal) is served as a source terminal of the switching element  3 , and the second power terminal  33  is served as a drain terminal of the switching element  3 . 
     Please refer to  FIG.  1    again. The first control part  4  is connected with the first control terminal  31  of the switching element  3 . The first control part  4  includes a first control pin  41  and a first control conductor  42 . The first control pin  41  is disposed on the main circuit board. The first control conductor  42  is connected between the first control pin  41  and the first control terminal  31  of the switching element  3 . The second control part  5  is connected with the second control terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . The second control part  5  includes a second control pin  51  and a second control conductor  52 . The second control pin  51  is disposed on the main circuit board. The second control conductor  52  is connected between the second control pin  51  and the second control terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . Moreover, a control loop of the switching module  1  is defined by the second control terminal (i.e., the common conductive terminal  32 ), the second control conductor  52 , the second control pin  51 , the main circuit board, the first control pin  41 , the first control conductor  42  and the first control terminal  31  collaboratively. 
     The first power part  6  is connected with the first power terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . The first power part  6  includes a first power pin  61  and a first power conductor  62 . The first power pin  61  is disposed on the main circuit board. The first power conductor  62  is connected between the first power pin  61  and the first power terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . A first current flows through the first power part  6 . The second power part  7  is connected with the first power terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . The second power part  7  includes a second power pin  71  and a second power conductor  72 . The second power pin  71  is disposed on the main circuit board. The second power conductor  72  is connected between the second power pin  71  and the first power terminal (i.e., the common conductive terminal  32 ) of the switching element  3 . A second current flows through the second power part  7 . 
     It is noted that the switching element  3  corresponding to the first power part  6  and the switching element  3  corresponding to the second power part  7  may be the identical or different switching elements  3 . In other words, the first power part  6  and the second power part  7  may be connected with the same switching element  3  or respectively connected with two different switching elements  3 . In this embodiment, the direction of the first current flowing through the first power part  6  and the direction of the second current flowing through the second power part  7  are identical. That is, the first current flows from the first power terminal (i.e., the common conductive terminal  32 ) to the first power pin  61  of the first power part  6  and the second current flows from the first power terminal (i.e., the common conductive terminal  32 ) to the second power pin  71  of the second power part  7 , or the first current flows from the first power pin  61  of the first power part  6  to the first power terminal (i.e., the common conductive terminal  32 ) and the second current flows from the second power pin  71  of the second power part  7  to the first power terminal (i.e., the common conductive terminal  32 ). It is noted that numerous modifications and alterations may be made while retaining the teachings of the disclosure. For example, in another embodiment, the first power part  6  and the second power part  7  are connected with the second power terminal  33  of the corresponding switching element  3 . However, the direction of the first current flowing through the first power part  6  and the direction of the second current flowing through the second power part  7  are identical. 
     In this embodiment, the first power part  6 , the first control part  4 , the second control part  5  and the second power part  7  are arranged sequentially. The projection of the first power part  6  on a reference plane and a projection of the second power part  7  on the same reference plane are located at two sides of a projection of the control loop of the switching module  1  (i.e., the control loop defined by the first control part  4  and the second control part  5 ) on the reference plane. Preferably, the reference plane is coplanar with the substrate  2 . In an embodiment, the length of the first power part  6  is equal to the length of the second power part  7 . Consequently, the current value of the first current flowing through the first power part  6  and the current value of the second current flowing through the second power part  7  are equal. Under this circumstance, the current value here refers to the amplitude of the corresponding current or the effective value of the corresponding current. 
     In  FIG.  3   , the projections of the first power part  6 , the second power part  7  and the control loop on the reference plane are shown. The point A and the point B as shown in  FIG.  3    denote two ends of the projection of the first control part  4  on the reference plane, respectively. The point C and the point D as shown in  FIG.  3    denote two ends of the projection of the second control part  5  on the reference plane, respectively. Moreover, the line P 1  denotes the first current flowing through the first power part  6 , and the line P 2  denotes the second current flowing through the second power part  7 . In the embodiment, the point B and the point D are connected with each other through the main circuit board. 
     Consequently, the rectangular region defined by the points A, B, C and D represents the projection of the control loop on the reference plane. The line O-O′ represents the center line of the control loop on the reference plane. That is, the center line O-O′ passes through the midpoint of a line segment connecting the point A and the point C, and the midpoint of a line segment connecting the point B and the point D. The projection of the first power part  6  on the reference plane and the projection of the second power part  7  on the reference plane are located at two sides of the projection of the control loop on the reference plane, respectively. For example, the first current P 1  flowing through the first power part  6  and the second current P 2  flowing through the second power part  7  are symmetrical the two sides of the projection of the control loop on the reference plane. Preferably but not exclusively, the distance between the projection of the first power part  6  on the reference plane and the center line O-O′ is equal to the distance between the projection of the second power part  7  on the reference plane and the center line O-O′. For example, it can be set that the smallest distance between the projection of the first power part  6  on the reference plane and the center line O-O′ is 1 mm, and the smallest distance between the projection of the second power part  7  on the reference plane and the center line O-O′ is 1 mm. The first current P 1  flowing through the first power part  6  produces a total magnetic flux Φ 1  through the control loop. The second current P 2  flowing through the second power part  7  produces a total magnetic flux Φ 2  through the control loop. Since the direction of the first current P 1  and the direction of the second current P 2  are identical, the magnitude of the magnetic flux Φ 1  and the magnitude of the magnetic flux Φ 2  are equal, but the direction of the magnetic flux Φ 1  and the direction of the magnetic flux Φ 2  are opposite. In other words, the direction of the magnetic flux induced by the first current P 1  through the control loop is perpendicular to the paper surface and inward, and the direction of the magnetic flux induced by the second current P 2  through the control loop is perpendicular to the paper surface and outward. The magnetic flux Φ 1  and the magnetic flux Φ 2  are cancelled out. Consequently, the overall mutual inductance between the first power part  6 , the second power part  7  and the control loop is largely reduced. 
     As mentioned above, the direction of the first current P 1  flowing through the first power part  6  and the direction of the second current P 2  flowing through the second power part  7  are identical. In addition, the projection of the first power part  6  on the reference plane and the projection of the second power part  7  on the same reference plane are located at two sides of the projection of the control loop of the switching module  1  on the reference plane. In comparison with the conventional switching module, the mutual inductance between the power loop and the control loop in the switching module  1  of the present disclosure is reduced. Consequently, the safety performance of the switching module  1  is enhanced. 
     As mentioned above, the direction of the first current P 1  and the direction of the second current P 2  are identical. That is, the direction of the first current P 1  and the direction of the second current P 2  are in parallel with each other. It is noted that the direction of the first current P 1  and the direction of the second current P 2  are not restricted to be in parallel with each other. For example, in some embodiments, there is an angle between the direction of the first current P 1  and the direction of the second current P 2 . The angle is smaller than 90 degrees. Particularly, after the first power part  6  and the second power part  7  are projected to a reference plane, the angle between first current P 1  and the second current P 2  is 0 degree or an acute angle. The reference plane is a plane coplanar with the substrate  2  or a plane that is perpendicular to the substrate  2  and passes through the center line O-O′. 
     In some embodiments, the direction of the first current P 1  and the direction of the second current P 2  are identical, but the first power part  6  and the second power part  7  are not completely symmetric with respect to the control loop or the magnitude of the first current P 1  and the magnitude of the second current P 2  are different. Since the direction of the magnetic flux Φ 1  corresponding to the first current P 1  and the direction of the magnetic flux Φ 2  corresponding to the second current P 2  are opposite, the magnetic flux Φ 1  and the magnetic flux Φ 2  are cancelled out. Consequently, the overall mutual inductance between the first power part  6 , the second power part  7  and the control loop is largely reduced. 
     In some embodiments, the direction of the first current P 1  flowing through the first power part  6  and the direction of the second current P 2  flowing through the second power part  7  are in parallel with each other or tilted respective to each other. As long as the magnetic flux Φ 1  corresponding to the first current P 1  and the magnetic flux Φ 2  corresponding to the second current P 2  can be cancelled out and the mutual inductance is reduced, the installation positions of the first power part  6  and the second power part  7  are not restricted. 
     Please refer to  FIG.  4   .  FIG.  4    is a schematic view illustrating the structure of a switching module according to a second embodiment of the present disclosure. The structures and functions of the components of the switching module  1   a  which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. In comparison with the switching module  1 , the switching module  1   a  of this embodiment further includes a fourth power part  9 . The first power part  6  and the second power part  7  of the switching module  1   a  are connected with the second power terminal  33  of the corresponding switching element  3  through the substrate  2 . The fourth power part  9  is connected with the common conductive terminal  32  of the corresponding switching element  3 . The fourth power part  9  includes a fourth power pin  91  and the fourth power conductor  92 . The fourth power pin  91  is disposed on the main circuit board. The fourth power conductor  92  is connected between the fourth power pin  91  and the common conductive terminal  32  of the corresponding switching element  3 . 
     In this embodiment, the projection of the substrate  2  on the reference plane is a square with four sides. The projections of the first power part  6  and the second power part  7  are located at the same side with respect to the projection of the substrate  2 . The projection of the fourth power part  9  and the projection of the first power part  6  (or the second power part  7 ) are located at different sides of the projection of the substrate  2 . For example, the projections of the first power part  6  and the second power part  7  are located at a first side of the projection of the substrate  2 , and the projection of the fourth power part  9  is located at a second side of the projection of the substrate  2 . In an embodiment, the first side and the second side of the projection of the substrate  2  are opposite to each other. In another embodiment, the first side and the second side of the projection of the substrate  2  are adjacent to each other. 
     Please refer to  FIGS.  5 A and  5 B .  FIG.  5 A  is a schematic view illustrating the structure of a switching module according to a third embodiment of the present disclosure.  FIG.  5 B  is a schematic circuit diagram of the switching module as shown in  FIG.  5 A . The structures and functions of the components of the switching module  1   b  which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. The switching element  3  of the switching module  1  as shown in  FIG.  1    has a vertical-type structure. In this embodiment, the switching element  3  of the switching module  1   b  is a planar switching element. That is, the second power terminal  33 , the first control terminal  31  and the common conductive terminal  32  are disposed on the first surface  34  of the switching element  3 . The first power part  6  and the second power part  7  are connected with the common conductive terminal  32 . The fourth power part  9  is connected with the second power terminal  33 . 
       FIG.  6    is a schematic view illustrating the structure of a switching module according to a fourth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   c  which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. In this embodiment, the switching module  1   c  includes two switching elements (i.e., a first switching element  3   a  and a second switching element  3   b ), two first control parts  4 , two second control parts  5 , a first power parts  6  and a second power part  7 . The first switching element  3   a  and the second switching element  3   b  are connected with each other in parallel. One of the two first control parts  4  is connected with the first control terminal  31  of the first switching element  3   a . The other of the two first control parts  4  is connected with the first control terminal  31  of the second switching element  3   b . One of the two second control parts  5  is connected with the common conductive terminal  32  of the first switching element  3   a . The other of the second control parts  5  is connected with the common conductive terminal  32  of the second switching element  3   b.    
     The first power part  6  is connected with the common conductive terminal  32  of the first switching element  3   a . The second power part  7  is connected with the common conductive terminal  32  of the second switching element  3   b . In this embodiment, the first power part  6 , the second control part  5  connected with the first switching element  3   a , the first control part  4  connected with the first switching element  3   a , the first control part  4  connected with the second switching element  3   b , the second control part  5  connected with the second switching element  3   b  and the second power part  7  are arranged sequentially. 
     In this embodiment, a first control loop of the switching module  1   c  is defined by the common conductive terminal  32  of the first switching element  3   a , the corresponding second control conductor  52 , the second control pin  51 , the main circuit board, the first control pin  41 , the corresponding first control conductor  42  and the first control terminal  31  of the first switching element  3   a  collaboratively. In addition, a second control loop of the switching module  1   c  is defined by the common conductive terminal  32  of the second switching element  3   b , the corresponding second control conductor  52 , the corresponding second control pin  51 , the main circuit board, the first control pin  41 , the first control conductor  42  and the first control terminal  31  of the second switching element  3   b  collaboratively. In this embodiment, the direction of the first current flowing through the first power part  6  and the direction of the second current flowing through the second power part  7  are identical. That is, the first current flows from the common conductive terminal  32  to the first power pin  61  of the first power part  6  and the second current flows from the common conductive terminal  32  to the second power pin  71  of the second power part  7 , or the first current flows from the first power pin  61  of the first power part  6  to the common conductive terminal  32  and the second current flows from the second power pin  71  of the second power part  7  to the common conductive terminal  32 . The magnetic flux through the first control loop and the second control loop induced by the first current flowing through the first power part  6  and the magnetic flux through the first control loop and the second control loop induced by the second current flowing through the second power part  7  are cancelled out. Consequently, the overall mutual inductance between the first power part  6 , the second power part  7  and the first control loop and/or the second control loop is largely reduced. In this way, the reliability of the switching elements  1   c  is increased. 
       FIG.  7    is a schematic view illustrating the structure of a switching module according to a fifth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   d  which are identical to those of the fourth embodiment as shown in  FIG.  6    are not redundantly described herein. In comparison with the switching module  1   c  of  FIG.  6   , the switching module  1   d  includes three switching elements (i.e., a first switching element  3   a , a second switching element  3   b  and a third switching element  3   c ), three first control parts  4 , three second control parts  5 , a first power parts  6  and a second power part  7 . The third switching element  3   c  is arranged between the first switching element  3   a  and the second switching element  3   b . The first switching element  3   a , the second switching element  3   b  and the third switching element  3   c  are connected with each other in parallel. The additional first control part  4  is connected with the first control terminal  31  of the third switching element  3   c . The additional second control part  5  is connected with the common conductive terminal  32  of the third switching element  3   c.    
     In this embodiment, the switching module  1   d  further includes a third power part  8 . The third power part  8  is connected with the common conductive terminal  32  of the third switching element  3   c . The third power part  8  includes a third power pin  81  and the third power conductor  82 . The third power pin  81  is disposed on the main circuit board. The third power conductor  82  is connected between the third power pin  81  and the common conductive terminal  32  of the third switching element  3   c . A third current flows through the third power part  8 . The direction of the third current, the direction of the first current flowing through the first power part  6  and the direction of the second current flowing through the second power part  7  are identical. In this embodiment, the first power part  6 , the second control part  5  connected with the first switching element  3   a , the first control part  4  connected with the first switching element  3   a , the third power part  8 , the second control part  5  connected with the third switching element  3   c , the first control part  4  connected with the third switching element  3   c , the first control part  4  connected with the second switching element  3   b , the second control part  5  connected with the second switching element  3   b  and the second power part  7  are arranged sequentially. It is noted that the position of the third power part  8  is not restricted. For example, in another embodiment, the first power part  6 , the second control part  5  connected with the first switching element  3   a , the first control part  4  connected with the first switching element  3   a , the second control part  5  connected with the third switching element  3   c , the first control part  4  connected with the third switching element  3   c , the third power part  8 , the first control part  4  connected with the second switching element  3   b , the second control part  5  connected with the second switching element  3   b  and the second power part  7  are arranged sequentially. 
     In this embodiment, the direction of the first current flowing through the first power part  6 , the direction of the second current flowing through the second power part  7  and the direction of the third current flowing through the third power part  8  are identical. Consequently, the mutual inductance between the first power part  6 , the second power part  7  and the control loops is largely reduced, and the mutual inductance between the second power part  7 , the third power part  8  and the control loops is largely reduced. Since the interference of the high-frequency control signal is avoided, the reliability of the switching elements  1   d  is increased. 
       FIG.  8    is a schematic view illustrating the structure of a switching module according to a sixth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   e  which are identical to those of the fifth embodiment as shown in  FIG.  7    are not redundantly described herein. In comparison with the switching module  1   d  of  FIG.  7   , the switching module  1   e  further includes a third connecting conductor  103 . The third connecting conductor  103  is connected between the first control terminal  31  of the second switching element  3   b  and the first control terminal  31  of the third switching element  3   c . Consequently, one first control part  4  is shared by the second switching element  3   b  and the third switching element  3   c  of the switching module  1   e . Since the first control part  4  connected with the third switching element  3   c  is shared by the second switching element  3   b  and the third switching element  3   c , the first control part  4  connected with the second switching element  3   b  as shown in  FIG.  7    is omitted in the switching module  1   e  of this embodiment. It is noted that numerous modifications and alterations may be made while retaining the teachings of the disclosure. For example, in another embodiment, one second control part  5  is shared by the second switching element  3   b  and the third switching element  3   c  of the switching module  1   e . In addition, a connecting conductor is connected between the common conductive terminal  32  of the second switching element  3   b  and the common conductive terminal  32  of the third switching element  3   c . In some other embodiments, the number of switching elements sharing the same control part is not restricted to two. That is, the number of switching elements sharing the same control part may be increased according to the practical requirements. 
       FIG.  9    is a schematic view illustrating the structure of a switching module according to a seventh embodiment of the present disclosure. The structures and functions of the components of the switching module if which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. In comparison with the switching module  1  as shown in  FIG.  1   , the switching module if further includes a diode  10 , a first connecting conductor  101  and a second connecting conductor  102 . The diode  10  is disposed on the substrate  2 . The first connecting conductor  101  is connected between a terminal of the diode  10  and the common conductor terminal  32  of the switching element  3 . In addition, the first connecting conductor  101  is connected with the first power conductor  62  of the first power part  6 . The second connecting conductor  102  is connected between the same terminal of the diode  10  and the common conductor terminal  32  of the switching element  3 . In addition, the second connecting conductor  102  is connected with the second power conductor  72  of the second power part  7 . Similarly, the projections of the first connecting conductor  101  and the second connecting conductor  102  on the reference plane are symmetrically located at two opposite sides of the projections of two control parts  4  and  5  on the reference plane. Consequently, the mutual inductance between the two connecting conductors  101 ,  102  and the control loop is as small as possible. 
       FIG.  10    is a schematic view illustrating the structure of a switching module according to the eighth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   g  which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. In comparison with the switching module  1  as shown in  FIG.  1   , the switching module  1   g  includes two substrates, two switching elements, two first control parts  4   a ,  4   b , two second control parts  5   a ,  5   b , a first power part  6  and a second power part  7 . The two substrates include a first substrate  2   a  and a second substrate  2   b . The two switching elements include a first switching element  3   a  and a second switching element  3   b.    
     The first switching element  3   a  is disposed on the first substrate  2   a . The second switching element  3   b  is disposed on the second substrate  2   b . The first control part  4   a  is connected with the first control terminal  31  of the first switching element  3   a . The first control part  4   b  is connected with the first control terminal  31  of the second switching element  3   b . The second control part  5   a  is connected with the common conductive terminal  32  of the first switching element  3   a . The second control part  5   b  is connected with the common conductive terminal  32  of the second switching element  3   b.    
     The first power part  6  is connected with the common conductive terminal  32  of the second switching element  3   b . The second power part  7  is connected with the common conductive terminal  32  of the second switching element  3   b . In this embodiment, the first control part  4   a  and the second control part  5   a  are located at a first side of the second substrate  2   b . In addition, the first control part  4   a  and the second control part  5   a  are arranged between the first substrate  2   a  and the second substrate  2   b . The first power part  6 , the first control part  4   b , the second control part  5   b  and the second power part  7  are located at a second side of the second substrate  2   b . The first side and the second side of the second substrate  2   b  are opposite to each other. In this embodiment, the first power part  6 , the first control part  4   b , the second control part  5   b  and the second power part  7  are arranged sequentially. 
     In this embodiment, the switching module  1   g  further includes a first connecting conductor  101  and a second connecting conductor  102 . The first connecting conductor  101  is connected between the common conductive terminal  32  of the first switching element  3   a  and the second substrate  2   b . The second connecting conductor  102  is connected between the common conductive terminal  32  of the first switching element  3   a  and the second substrate  2   b . Consequently, the first switching element  3   a  and the second switching element  3   b  are connected with each other in series. 
     Preferably, the first connecting conductor  101  and the second connecting conductor  102  are located at two opposite sides with respect to the first control part  4   a  and the second control part  5   a . That is, the projections of the first connecting conductor  101  and the second connecting conductor  102  on the reference plane are located at the two opposite sides of the projections of the two control parts  4   a  and  5   a  on the reference plane, respectively. Consequently, the mutual inductance is reduced. In an embodiment, the length of the first connecting conductor  101  and the length of the second connecting conductor  102  are equal. Consequently, the magnitude of the current flowing through the first connecting conductor  101  and the magnitude of the current flowing through the second connecting conductor  102  are equal. Since the first connecting conductor  101  and the second connecting conductor  102  are symmetric with respect to the control loop, the effect of cancelling out the magnetic fluxes is further improved. Consequently, the mutual inductance is further reduced. 
       FIG.  11    is a schematic view illustrating the structure of a switching module according to a ninth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   h  which are identical to those of the eighth embodiment as shown in  FIG.  10    are not redundantly described herein. In comparison with the switching module  1   g  as shown in  FIG.  10   , the positions of the first switching element  3   a , the first control part  4   a  and the second control part  5   a  of the switching module  1   g  are different. The first control part  4   a  and the second control part  5   a  are located at a third side of the second substrate  2   b . In addition, the first control part  4   a  and the second control part  5   a  are arranged between the first substrate  2   a  and the second substrate  2   b . The first power part  6 , the first control part  4   b , the second control part  5   b  and the second power part are located at the second side of the second substrate  2   b . The first side and the second side of the second substrate  2   b  are opposite to each other. In addition, the third side of the second substrate  2   b  is arranged between the first side and the second side of the second substrate  2   b.    
       FIG.  12    schematically illustrates a first example of the relationship between the first control part, the second control part and the control loop of the switching module as shown in  FIG.  1   . As mentioned above, the center line O-O′ of the control loop is defined by the first control part  4  and the second control part  5 . As shown in  FIG.  12   , the center line O-O′ of the control loop passes through the center of the first control terminal  31  of the switching element  3  and a center of a line segment connecting the center of the first control pin  41  of the first control part  4  and the center of the second control pin  51  of the second control part  5 . The smallest distance between the projection of the first power pin  61  of the first power part  6  on the reference plane and the center line O-O′ of the control loop is defined as a first distance X 1 . The smallest distance between the projection of the second power pin  71  of the second power part  7  on the reference plane and the center line O-O′ of the control loop is defined as a second distance X 2 . In some embodiments, the minimum of the first distance X 1  is 1 mm, and the minimum of the second distance X 2  is 1 mm. 
     In case that the magnitude of the first current flowing through the first power part  6  and the magnitude of the second current flowing through the second power part  7  are equal, it is necessary to assure that the first power part  6  and the second power part  7  are symmetric with respect to the control loop of the first control part  4  and the second control part  5 . If the first power part  6  and the second power part  7  are symmetric with respect to the control loop, the magnetic flux corresponding to the first current flowing through the first power part  6  and the magnetic flux corresponding to the second current flowing through the second power part  7  can be effectively cancelled out. Whether the first power part  6  and the second power part  7  are symmetric with respect to the control loop can be determined according to the asymmetry percentage of the first power part  6  and the second power part  7  with respect to the center line O-O′ of the control loop. 
     The asymmetry percentage of the first power part  6  and the second power part  7  with respect to the center line O-O′ of the control loop is defined as the absolute value of the difference between the first distance X 1  and the second distance X 2  divided by the smaller one of the first distance X 1  and the second distance X 2 . For example, if the first distance X 1  is smaller than the second distance X 2 , the asymmetry percentage is expressed as (X 2 −X 1 )/X 1 . Whereas, if the second distance X 2  is smaller than the first distance X 1 , the asymmetry percentage is expressed as (X 1 −X 2 )/X 2 . 
     A smaller asymmetry percentage indicates a better symmetry of the projection areas of the first power part  6  and the second power part  7  (on the reference plane) with respect to the center line O-O′ of the control loop. A larger asymmetry percentage indicates a worse symmetry of the projections of the first power part  6  and the second power part  7  (on the reference plane) with respect to the center line O-O′ of the control loop. 
     As mentioned above, if the magnetic flux corresponding to the first current P 1  flowing through the first power part  6  and the magnetic flux corresponding to the second current P 2  flowing through the second power part  7  are cancelled out, the mutual inductance between the first power part  6  (and the second power part  7 ) and the control loop is reduced. For achieving this purpose, the asymmetry percentage of the first power part  6  and the second power part  7  with respect to the center line O-O′ of the control loop needs to be smaller than or equal to a predetermined asymmetry percentage (e.g., 60%, 40% or 20%). In case that the asymmetry percentage is 0%, the projections of the first power part  6  and the second power part  7  on the reference plane are completely symmetric with respect to the center line O-O′ of the control loop. When the asymmetry percentage is smaller than 40%, the mutual inductance between the first power part  6  (and the second power part  7 ) and the control loop is reduced and the switching speed of the switching module  1  is increased by 50%, basing on case of 100% asymmetry percentage. In case that the asymmetry percentage is further reduced, the switching speed of the switching module  1  is further increased. 
     Please refer to  FIGS.  1 ,  12  and  13   .  FIG.  13    schematically illustrates a second example of the relationship between the first control part, the second control part and the control loop of the switching module as shown in  FIG.  1   . In this embodiment, the magnitude of the first current P 1  flowing through first power part  6  and the magnitude of the second current P 2  flowing through the second power part  7  are different. By adjusting the first distance X 1  and the second distance X 2 , the magnetic flux corresponding to the first current P 1  flowing through the first power part  6  and the magnetic flux corresponding to the second current P 2  flowing through the second power part  7  can be cancelled out. In case that the magnitude of the first current P 1  flowing through first power part  6  is greater than the magnitude of the second current P 2  flowing through the second power part  7 , the first distance X 1  is set to be greater than the second distance X 2 . Consequently, the magnetic flux corresponding to the first current P 1  flowing through the first power part  6  and the magnetic flux corresponding to the second current P 2  flowing through the second power part  7  can be cancelled out. Whereas, in case that the magnitude of the first current P 1  flowing through first power part  6  is lower than the magnitude of the second current P 2  flowing through the second power part  7 , the first distance X 1  is set to be smaller than the second distance X 2 . Consequently, the magnetic flux corresponding to the first current P 1  flowing through the first power part  6  and the magnetic flux corresponding to the second current P 2  flowing through the second power part  7  can also be cancelled out. In an embodiment, the minimum of the first distance X 1  is 1 mm, and the minimum of the second distance X 2  is 1 mm. 
       FIG.  14    is a schematic view illustrating the structure of a switching module according to a tenth embodiment of the present disclosure. The structures and functions of the components of the switching module  1   i  which are identical to those of the first embodiment as shown in  FIG.  1    are not redundantly described herein. In comparison with the switching module  1 , the switching module  1   i  of this embodiment further includes a third power part  8 . The third power part  8 , the first power part  6  and the second power part  7  are connected with the common conductive terminal  32  of the corresponding switching elements  3 . The third power part  8  includes a third power pin  81  and a third power conductor  82 . The third power pin  81  is disposed on the main circuit board. The third power conductor  82  is connected between the third power pin  81  and the common conductor terminal  32  of the corresponding switching element  3 . Moreover, a third current flows through the third power part  8 . The direction of the first current, the direction of the second current and the direction of the third current are identical. 
     In an embodiment, the first current, the second current and the third current flow from the common conductive terminal  32  of the switching module  1   i  to the corresponding power pins. In this embodiment, the second power part  7  and the third power part  8  are located at the same side with respect to the control loop, and the second power part  7  and the first power part  6  are located at opposite sides with respect to the control loop. Consequently, the direction of the magnetic flux through the control loop corresponding to the second current flowing through the second power part  7  and the direction of the magnetic flux through the control loop corresponding to the third current flowing through the third power part  8  are identical, and the direction of the magnetic flux through the control loop corresponding to the second current flowing through the second power part  7  and the direction of the magnetic flux through the control loop corresponding to the first current flowing through the first power part  6  are opposite. 
     Similarly, the smallest distance between the projection of the first power pin  61  on the reference plane and the center line O-O′ of the control loop is defined as a first distance X 1 . Similarly, the smallest distance between the projection of the second power pin  71  on the reference plane and the center line O-O′ of the control loop is defined as a second distance X 2 . In addition, the smallest distance between the projection of the third power pin  81  on the reference plane and the center line O-O′ of the control loop is defined as a third distance. For balancing the magnetic fluxes at the two opposite sides of the control loop, it is preferred that the first distance X 1  is equal to the second distance X 2 . Since the third distance is much longer than the first distance X 1  and the second distance X 2 , the magnetic flux corresponding to the third current flowing through the third power part  8  has small influence on the control loop. Consequently, the purpose of cancelling out the magnetic fluxes can be achieved. 
     It is noted that numerous modifications and alterations may be made while retaining the teachings of the disclosure. For example, in another embodiment, the switching module includes a plurality of third power parts  8 . The plurality of third power parts  8  are located at the same side of the control loop. Alternatively, some of the third power parts  8  are located at a first side of the control loop, and the others of the third power parts  8  are located at a second side of the control loop. For controlling the mutual inductance of the first and second power loops and the control loop and increasing the switching speed of the switching module by 50%, the number of the third power parts  8  at the first side of the control loop and the number of the third power parts  8  at a second side of the control loop should be specially designed. For example, the sum of the numbers of the first power part  6  and the third power part  8  located at one side of the control loop is defined as the first number, and the sum of the numbers of the second power part  7  and the third power part  8  located at the other side of the control loop is defined as the second number. The absolute value of the difference between the first number and the second number is smaller than or equal to 3. 
     From the above description, the direction of the first current flowing through the first power part and the direction of the second current flowing through the second power part are identical. In addition, the projection of the first power part on the reference plane and the projection of the second power part on the reference plane are located at two sides of the control loop of the switching module. Consequently, the mutual inductance of the control loop is reduced, and the safety performance of the switching module is enhanced. 
     While the disclosure has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.