Patent Publication Number: US-2010109569-A1

Title: Transformer with adjustable leakage inductance and driving device using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of co-pending application Ser. No. 11/616,865, filed Dec. 28, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to transformers, and particularly to a transformer with an adjustable leakage inductance. 
     2. Description of Related Art 
     In an electronic device, one or more transformers are used for converting a received power signal to an appropriate signal to ensure the electronic device to work normally. Generally, each transformer has leakage inductance more or less due to a primary winding not fully coupling to the secondary winding. Therefore, on one hand, it is needed to decrease the leakage inductance to save energy to increase conversion efficiency of the transformer. On the other hand, the leakage inductance can be used to meet resonance requirements. Thus, how to balance the need for saving energy and obtain suitable leakage inductance of the transformer to meet electromagnetic requirements to gain a good resonance is an important point. 
       FIG. 8  shows a cross sectional view of a conventional transformer  100 . The conventional transformer  100  includes a bobbin  10 , a first winding  11 , a second winding  12 , an insulating tape  13 , and a core assembly (not shown). The core assembly is inserted into a hollow portion  10   a  of the bobbin  10 . The first winding  11  is wound around the bobbin  10 . The second winding  12  is wound outside of the first winding  11 , which is insulated from the first winding  11  with the insulating tape  13 . Therefore, the first winding  11  and the second winding  12  form a layered structure, which provides a good coupling ratio but little leakage inductance. 
     A cross sectional view of another conventional transformer  200  is shown in  FIG. 9 . The transformer  200  includes a bobbin  20 , a first winding  21 , a second winding  22 , a plurality of isolating walls  24 , and a core assembly (not shown). A hollow portion  20   a  of the bobbin  20  is provided to receive the core assembly. The bobbin  20  is divided into a primary side region b 1 , a secondary side region b 2 , and an empty coiling region b 3  formed by two isolating walls  24 . In addition, the secondary side region b 2  is divided into a plurality of coiling regions by the isolating walls  24 . The first winding  21  is wound around the primary side region b 1 , and the second winding  22  is wound around the secondary side region b 2 . Therefore, the first winding  21  and the second winding  22  form a side-by-side structure, which provides greater leakage inductance but a poor coupling ratio. 
     Therefore, the conventional transformer  100  has less leakage inductance, but does not achieve a very good resonance response, and the conventional transformer  200  has a greater leakage inductance, but lower efficiency. In addition, the leakage inductances of the transformer  100  and  200  are fixed, so no fine-tuning can be accomplished to suit needs. One solution for changing the leakage inductance is changing the coiling structure, which is inconvenient. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a transformer with an adjustable leakage inductance, which includes a first bobbin, a first winding, and a second winding. The first bobbin includes a first region and a second region. The second winding includes a first coil portion and a second coil portion. One of the first winding and the first coil portion of the second winding is wound around the first region of the first bobbin, and the other of the first winding and the first coil portion of the second winding is wound outside of the one wound around the first region of the first bobbin. The second coil portion of the second winding is wound around the second region of the first bobbin. 
     Another aspect of the present invention provides a driving device for driving a light source module comprising a plurality of light sources. The driving device includes a converter circuit, a driving switch circuit, a transformer circuit, and a PWM controller. The converter circuit converts a received power signal to a direct current signal. The driving switch circuit is connected to the converter circuit, for converting the direct current signal to an alternating current signal. The transformer circuit is connected between the driving switch circuit and the light source module, for converting the alternating current signal to an appropriate alternating current signal, and includes a transformer with an adjustable leakage inductance. The transformer includes a first bobbin, a first winding, and a second winding. The first bobbin includes a first region and a second region. The second winding includes a first coil portion and a second coil portion. One of the first winding and the first coil portion of the second winding is wound around the first region of the first bobbin, and the other of the first winding and the first coil portion of the second winding is wound outside of the one wound around the first region of the first bobbin. The second coil portion of the second winding is wound around the second region of the first bobbin. The PWM controller is connected to the driving switch circuit, for controlling the alternating current signal output from the driving switch. 
     Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a driving device in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a block diagram of a driving device in accordance with another exemplary embodiment of the present invention; 
         FIG. 3   a  is an isometric, disassembled view of a transformer with an adjustable leakage inductance in accordance with a first embodiment of the present invention; 
         FIG. 3   b  is a cross-sectional view along a line Vb-Vb of  FIG. 3   a;    
         FIG. 4   a  is an isometric, disassembled view of a transformer with an adjustable leakage inductance in accordance with a second embodiment of the present invention; 
         FIG. 4   b  is a cross-sectional view along line VIb-VIb of  FIG. 4   a;    
         FIG. 4   c  is a cross-sectional view along line VIb-VIb of  FIG. 4   a;    
         FIG. 4   d  is a partially enlarged view along VId of  FIG. 4   a;    
         FIG. 5   a  is an isometric, disassembled view of a transformer with an adjustable leakage inductance in accordance with a third embodiment of the present invention; 
         FIG. 5   b  is a cross-sectional view along line VIIb-VIIb of  FIG. 5   a;    
         FIG. 6   a  is an isometric, disassembled view of a transformer with an adjustable leakage inductance in accordance with a fourth embodiment of the present invention; 
         FIG. 6   b  is a cross-sectional view along line VIIIb-VIIIb of  FIG. 6   a;    
         FIGS. 7   a ,  7   b , and  7   c  are elevational views of a core assembly of transformer with an adjustable leakage inductance in accordance with the present invention; 
         FIG. 8  is a cross-sectional view of a conventional transformer; and 
         FIG. 9  is a cross-sectional view of another conventional transformer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a block diagram of a driving device in accordance with an exemplary embodiment of the present invention. The driving device for driving a light source module  33  includes a converter circuit  30 , a driving switch circuit  31 , a transformer circuit  32 , a feedback circuit  34 , and a PWM controller  35 . The light source module  33  includes a plurality of light sources. 
     The converter circuit  30  converts a received power signal to a direct current (DC) signal. The driving switch circuit  31  is connected to the converter circuit  30 , and is used for converting the DC signal to an alternating current (AC) signal. The transformer circuit  32  is connected between the driving switch circuit  31  and the light source module  33 , for converting the AC signal to an appropriate AC signal to drive the light source module  33 . In the exemplary embodiment, the AC signal output from the driving switch circuit  31  is a rectangular-wave signal, and the AC signal output from the transformer circuit  32  is a sine-wave signal. The feedback circuit  34  is connected between the light source module  33  and the PWM controller  35 , for feeding back current flowing through the light source module  33  to the PWM controller  35 . The PWM controller  35  is connected between the feedback circuit  34  and the driving switch circuit  31 , for controlling the AC signal output from the driving switch circuit  31 . 
       FIG. 2  shows a block diagram of a driving device in accordance with another exemplary embodiment of the present invention. The driving device shown in  FIG. 2  is substantially the same as that of  FIG. 1 , except that the feedback circuit  44  is connected between the transformer circuit  42  and the PWM controller  45 , for feeding back current flowing through the light source module  43  to the PWM controller  45 . The transformer circuits  32  and  42  shown in  FIG. 1  and  FIG. 2  include a transformer with an adjustable leakage inductance. 
       FIG. 3   a  shows an isometric, disassembled view of a transformer  50  with an adjustable leakage inductance in accordance with a first embodiment of the present invention, and  FIG. 3   b  shows a cross-section view along a line Vb-Vb of  FIG. 3   a . The transformer  50  includes a bobbin  525 , a first winding  521 , a second winding  522 , and a core assembly  527 . In the exemplary embodiment, the second winding  522  includes a first coil portion  522   a  and a second coil portion  522   b . The bobbin  525  has a plurality of isolating walls  524 , which is divided into a first region B 1  and a second region B 2  by one isolating wall  524   a . The first region B 1  is used for winding the first winding and the first coil portion  522   a  of the second winding  522  around it, and the second region B 2  is used for winding the second coil portion  522   b  of the second winding  522  around it. 
     In the exemplary embodiment, the bobbin  525  has a hollow portion  525   a , a first base  525   b , and a second base  525   c . The first base  525   b  is near the first region B 1  of the bobbin  525 , and the second base  525   c  is near the second region B 2  of the bobbin  525 . In addition, a plurality of pins  529  are respectively disposed at the first base  525   b  and the second base  525   c , for electrically connecting the transformer  50  to a circuit board (not shown). In the exemplary embodiment, the isolating wall  524   b  is at the same side as the first base  525   b , and the isolating wall  524   c  is at the same side as the second base  525   c . Thicknesses of the isolating wall  524   b  and the isolating wall  524   c  are larger than that of the isolating wall  524   a , which enhance a rigidity of the transformer  50 . Similarly, a thickness of the isolating wall  524   a  is also larger than that of the other isolating walls  524  (except the isolating wall  524   b  and the isolating wall  524   c ), which can enhance voltage tolerances of the transformer  50 . 
     The core assembly  527  includes a first core  527   a  and a second core  527   b . The first core  527   a  and the second core  527   b  are inserted into the hollow portion  525   a  of the bobbin  525 , for forming magnetic loops. In the exemplary embodiment, the core assembly  527  includes two E-shaped cores made of highly conductive magnetic materials. 
     Referring to  FIG. 3   b , the first coil portion  522   a  of the second winding  522  is wound outside the first wind  521  and both are wound around the first region B 1  of the bobbin  525 . In the exemplary embodiment, the first winding  521  and the first coil portion  522   a  of the second winding  522  are insulated with an insulating layer  523  therebetween. In this embodiment, the insulating layer  523  is an insulating tape. The second coil portion  522   b  of the second winding  522  is wound around the second region B 2 . In alternative exemplary embodiments, the first winding  521  can be wound outside the first coil portion  522   a  of the second winding  522 . That is, one of the first winding  521  and the first coil portion  522   a  of the second winding  522  is wound around the first region B 1  of the first bobbin  525 , and the other of the first winding  521  and the first coil portion  522   a  of the second winding  522  is wound outside of the one wound around the first region B 1  of the first bobbin  525 . 
     The transformer  50  further includes at least a pair of margin tapes  528  wound around the insulating layer  523 . In the exemplary embodiment, the margin tapes  528  are also insulating tapes. Due to the margin tapes  528 , a length of a coiling region of the first coil portion  522   a  is shorter than that of the first winding  521 . In this way, the voltage tolerance of the transformer  525  is increased. The second region B 2  of the bobbin  525  is divided into a plurality of coiling regions by the isolating walls  524 . Thus, arcing does not occur when high voltages are present on the second coil portion  522   b  of the second winding  522 , and a voltage tolerance capability of the second coil portion  522   b  of the second winding  522  is increased. 
     In the exemplary embodiment, the second coil portion  522   b  of the second winding  522  and the first winding  521  are disposed in a side-by-side structure, the first coil portion  522   a  of the second winding  522  and the first winding  521  are disposed in a layered structure. That is, the transformer  50  comprises the side-by-side structure and the layered structure. In the side-by-side structure, the magnetic field of the first winding  521  is not fully coupled to the second coil portion  522   b  of the second winding  522 . Thus, a larger leakage inductance is generated, for example: 10 mH. While in the layered structure, the magnetic field of first winding  521  is fully coupled to the first coil portion  522   a  of the second winding  522 . Thus, a smaller leakage inductance is generated, for example: 2 mH. Consequently, the leakage inductance of the transformer  50  in accordance with the present invention is between 2 mH and 10 mH. 
     In the exemplary embodiment, the number of coils of the first coil portion  522   a  and the second coil portion  522   b  of the second winding  522  is adjustable, thus, the leakage inductance of the transformer  50  is also adjustable. 
     When the number of coils of the first winding  521  is fixed, and the total number of coils of the first coil portion  522   a  and the second coil portion  522   b  of the second winding  522  are also fixed, if the number of coils of the second coil portion  522   b  of the second winding  522  is greater than that of the first coil portion  522   a  of the second winding  522 , the leakage inductances of the side-by-side structure and the layered structure are increased. Thus, the leakage inductance of the transformer  50  is also increased. Coils may be left off the first coil portion  522   a  of the second winding  522  to obtain a conventional side-by-side structure only. 
     Contrarily, if the number of coils of the second coil portion  522   b  of the second winding  522  is less than that of the first coil portion  522   a , the leakage inductances of the side-by-side structure and the layered structure are decreased. Thus, the leakage inductance of the transformer  50  is also decreased. Coils may be left off the second coil portion  522   b  to obtain a conventional layered structure. 
     In the exemplary embodiment, the first winding  521  wound around the first region B 1  of the bobbin  525  is a primary winding, which is connected to the driving switch circuit  31  or  41  shown in  FIG. 3  or  FIG. 4 . The second winding  522  is a secondary winding, which is connected to the light source module  33  or  43  as shown in  FIG. 3  or  FIG. 4 . In addition, the number of coils of the first winding  521  is less than that of the second winding  522 . When a voltage is provided to the first winding  521 , a magnetic field produced by current flowing through the first winding  521  cuts the second winding  522 . Thus, a high voltage is generated on the second winding  522 . The leakage inductance and a leakage capacitor (not shown) of the transformer  50  form a resonance circuit, converting the high voltage to the appropriate AC signal to drive the light sources. 
       FIG. 4   a  shows an isometric, disassembled view of a transformer  60  with an adjustable leakage inductance in accordance with a second embodiment of the present invention. The transformer  60  has a similar structure to that of the transformer  50  shown in  FIG. 4   a , except that the transformer  60  includes a first bobbin  625  and at least one second bobbin  626 . The second bobbin  626  is movable along an axis of the first bobbin  625 , for adjusting the leakage inductance of the transformer  60 . 
       FIG. 4   b  and  FIG. 4   c  show a cross-sectional view along line VIb-VIb of  FIG. 4   a . In the exemplary embodiment, the transformer  60  shown in  FIG. 4   b  has a larger leakage inductance than as it is shown in  FIG. 4   c . The structures of  FIG. 4   b  and  FIG. 4   c  are substantially the same as that of  FIG. 3   b , except for the addition of the at least one second bobbin and that the first region B 1  of the first bobbin  625  is only partially covered by the first winding  621 . Further, a length of the second bobbin  626  is less than that of the first region B 1  of the first bobbin  625 . Consequently, the second bobbin  626  is moveable along the axis of the first bobbin  625 , for adjusting the leakage inductance of the transformer  60 . 
     In the exemplary embodiment, when the second bobbin  626  is near to the isolating wall  624   a  as shown in  FIG. 4   b , the magnetic field of the first winding  621  is not fully coupled to the first coil portion  622   a  of the second bobbin  626 . That is, the magnetic field in a region ‘d’ of the first winding  621  is not coupled to the first coil portion  622   a  of the second bobbin  626 , which forms a leakage magnetic flux, and generates a leakage inductance. In addition, when there is little or no gap between the second bobbin  626  and the isolating wall  624   a , the coupling ratio is low, and the leakage inductance of the transformer  60  is high. 
     Contrarily, when the second bobbin  626  is far from the isolating wall  624   a  as shown in  FIG. 4   c , the magnetic field of the first winding  621  is fully coupled to the first coil portion  622   a  of the second bobbin  626 . In addition, a gap exists between the second bobbin  626  and the isolating wall  624   a , thus the coupling ratio is high, and the leakage inductance of the transformer  60  is low. 
     Consequently, even though the number of coils of the first winding  621  and the second winding  622  of the transformer  60  are fixed, the coupling ratio between the first coil portion  622   a  of the second winding  622  and the first winding  621  is adjustable via adjusting the position of the second bobbin  626  along the axis of the first bobbin  625 , thereby adjusting the leakage inductance of the transformer  60 . 
       FIG. 4   d  shows a partially enlarged view along VId of  FIG. 4   a . In the exemplary embodiment, there are two second bobbins  626  ( FIG. 4   d  shows one second bobbin  626 ), arranged in parallel at opposite sides of the first region (not shown) of the first bobbin  625 , for winding of the first coil portion  622   a  of the second winding  622  therearound. 
       FIG. 5   a  shows an isometric, disassembled view of a transformer  70  with an adjustable leakage inductance in accordance with a third embodiment of the present invention, and  FIG. 5   b  shows a cross-sectional view along line VIIb-VIIb of  FIG. 5   a . The transformer  70  has a similar structure to that of the transformer  50  as shown in  FIG. 3   a , except that the transformer  70  includes a pair of second bobbins  726  with a plurality of coiling regions, for increasing voltage tolerances of the first coil portion  722   a  of the second winding  722  to avoid arcing. 
       FIG. 6   a  shows an isometric, disassembled view of a transformer  80  with an adjustable leakage inductance in accordance with a fourth embodiment of the present invention, and  FIG. 6   b  shows a cross-sectional view along line VIIIb-VIIIb of  FIG. 6   a . The transformer  80  has a similar structure to that of the transformer  60  of  FIG. 4   b , except that the second bobbin  826  of  FIG. 8   a  includes a plurality of coiling regions, for increasing voltage tolerances of the first coil portion  822   a  of the second winding  822  to avoid arcing. The second bobbin  826  is also movable along the axis of the first bobbin  825 , for adjusting the leakage inductance of the transformer  80 . 
     Similarly, in the exemplary embodiment, leakage inductance of the transformer  80  is adjusted through positioning of the movable second bobbin  826 . 
       FIG. 7   a  shows an elevational view of a core assembly as used for core assemblies  527 ,  627 ,  727 , and  827  of transformers  50 ,  60 ,  70 , and  80  in accordance with the present invention. The core assembly, in accordance with the present invention, can be EE shaped  927   a . In alternative exemplary embodiments, the core assembly can be UU shaped  927   b  or UI shaped  927   c  as depicted  FIGS. 7   b  and  7   c  or other shapes as determined by need. 
     While various embodiments and methods of the present invention have been described above, it should be understood that they have been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalent.