A planar transformer in LLC resonant converter

Abstract

The present invention discloses a planar transformer in an LLC resonant converter, comprising a magnetic core, a primary printed board, and a secondary printed board, wherein the primary printed board and the secondary printed board are stacked, the magnetic core passes through the primary printed board and the secondary printed board, the primary printed board comprises a fixed-turn printed board and an adjustable printed board, the fixed-turn printed board has an input end and an output end, the adjustable printed board has an input end and multiple output ends, the input end of the fixed-turn printed board is electrically connected to an external circuit, the output end of the fixed-turn printed board is electrically connected to the input end of the adjustable printed board, the number of turns of the transformer can be adjusted by adjusting the output end of the adjustable printed board, and the number of turns can be adjusted according to the different external connection terminals through the windings arranged on the top board, the first middle board, the second middle board, and the bottom board in the adjustable printed board. The planar transformer in the LLC resonant converter provided by the present invention has the effect of variable number of turns.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to a planar transformer in an LLC resonant converter. Background Art

[0002] High power density, high efficiency and high performance indicators are the development trend of DC / DC converters. In DC / DC converters, transformers are usually used to achieve voltage conversion and electrical isolation between input and output. Traditional wire-wound transformers cannot adapt to the development trend of DC / DC converters due to their large size, many distributed parameters and low efficiency. Planar transformers are becoming more and more valued for their advantages of miniaturization, high efficiency and low loss under high frequency conditions.

[0003] The design of planar transformer mainly includes the selection of planar core materials and models, design of winding PCB printed circuit boards, arrangement, assembly and lead wire welding of primary and secondary winding PCB printed circuit boards, adjustment of parameters such as primary and secondary side excitation inductance and leakage inductance of transformer, and consideration of heat dissipation performance.

[0004] The existing planar transformers have the following two shortcomings: 1. Under high-frequency conditions, the parasitic inductance and capacitance between single-layer turns in the primary and secondary winding PCB printed circuit board in the LLC resonant converter, as well as the inter-layer parasitic inductance and capacitance between layers have a greater impact on the transformer; 2. In applications with different input voltages and output voltages, the turns ratio of the LLC resonant converter transformer changes with the input and output voltages, which causes the planar transformer to change with the turns ratio and also needs to be redesigned. The existing planar transformers. Summary of the invention

[0005] In view of the above problems, a planar transformer in an LLC resonant converter is provided to solve the problems existing in the prior art.

[0006] The specific technical solutions are as follows:

[0007] A planar transformer in an LLC resonant converter comprises a magnetic core, a primary printed board, and a secondary printed board. The primary printed board and the secondary printed board are stacked and arranged, and the magnetic core passes through the primary printed board and the secondary printed board. The primary printed board comprises a fixed-turn printed board and an adjustable printed board. The fixed-turn printed board has an input end and an output end, and the adjustable printed board has an input end and multiple output ends. The input end of the fixed-turn printed board is electrically connected to an external circuit, and the output end of the fixed-turn printed board is electrically connected to the input end of the adjustable printed board. The number of turns of the transformer can be adjusted by adjusting the output end of the adjustable printed board.

[0008] The planar transformer in the above-mentioned LLC resonant converter also has the following characteristics: the fixed-turn printed circuit board includes multiple board bodies and single-turn windings corresponding to the board bodies one by one; the board body is provided with multiple connection terminals, and the multiple connection terminals are evenly spaced from top to bottom on the left side of the board body; the board body is also spaced apart with multiple connection contacts; the multiple single-turn windings have different shapes; each single-turn winding is provided on a corresponding board body; one end of the single-turn winding is electrically connected to the corresponding connection terminal, and the other end of the single-turn winding is electrically connected to the corresponding connection contact; when multiple layers of the board bodies are stacked, the connection terminals on the board bodies of each layer are correspondingly connected, and the connection contacts on the board bodies of each layer are correspondingly connected, the single-turn windings on the multiple layers of the board bodies are connected in series.

[0009] The planar transformer in the above-mentioned LLC resonant converter also has the following characteristics: the single-turn winding includes an inner winding group and an outer winding group, the inner winding group is close to the magnetic core, and the outer winding group is far away from the magnetic core; when a plurality of the plates are stacked, the plates provided with the inner winding group and the plates provided with the outer winding group are stacked alternately.

[0010] The planar transformer in the LLC resonant converter has the following characteristics: the adjustable printed circuit board includes a top board, a first middle board, a second middle board and a bottom board; five connection terminals are evenly arranged on the left side of the top board, the first middle board, the second middle board and the bottom board; the five connection terminals are respectively a third terminal, a fourth terminal, a second terminal, an input terminal and a first terminal from top to bottom; and the top board, the first middle board, the second middle board and the bottom board are also spaced apart with a first contact, a second contact and a third contact;

[0011] A first single turn is provided on the top plate, one end of the first single turn is electrically connected to the third terminal, the other end of the first single turn is electrically connected to the fourth terminal, and one end of the first single turn close to the third terminal is also electrically connected to the first contact;

[0012] A second single turn is provided on the first intermediate plate, one end of the second single turn is electrically connected to the second terminal, and the other end of the second single turn is electrically connected to the first contact;

[0013] The second intermediate plate is provided with a third single turn, one end of the third single turn is electrically connected to the first terminal, one end of the third single turn is also electrically connected to the third contact, and the other end of the third single turn is electrically connected to the second contact;

[0014] A fourth single turn is provided on the bottom board, one end of the fourth single turn is electrically connected to the input terminal, and the other end of the fourth single turn is electrically connected to the third contact;

[0015] When the top board, the first middle board, the second middle board and the bottom board are stacked and connected in sequence, the connection terminals on different printed boards are connected correspondingly, and the connection contacts on different printed boards are connected correspondingly.

[0016] The planar transformer in the above-mentioned LLC resonant converter also has the following feature: the first single turn and the third single turn are close to the magnetic core distribution, and the second single turn and the fourth single turn are far away from the magnetic core distribution.

[0017] The planar transformer in the LLC resonant converter has the following characteristics: the secondary printed circuit board includes a top board and a bottom board, and the top board and the bottom board are both provided with three spaced external terminals, the three external terminals are respectively a first external terminal, a second external terminal and a third external terminal;

[0018] A first secondary winding is disposed on the top plate, one end of the first secondary winding is electrically connected to the second external terminal, and the other end of the first secondary winding is electrically connected to the third external terminal;

[0019] A second secondary winding is disposed on the bottom plate, one end of the second secondary winding is electrically connected to the first external terminal, and the other end of the second secondary winding is electrically connected to the second external terminal.

[0020] The planar transformer in the LLC resonant converter described above also has the feature that the first secondary winding and the second secondary winding cover the areas around the magnetic core holes of the top plate and the bottom plate respectively.

[0021] The planar transformer in the above LLC resonant converter also has the feature that the winding is arranged on the printed circuit board and then covered by an insulating material.

[0022] In summary, the beneficial effects of this scheme are:

[0023] In the planar transformer of the LLC resonant converter provided by the present invention, the number of turns can be adjusted according to the difference of the external connection terminals by means of the windings arranged on the top plate, the first middle plate, the second middle plate and the bottom plate in the adjustable printed circuit board. The planar transformer of the LLC resonant converter provided by the present invention has the effect of variable number of turns.

[0024] In the planar transformer in the LLC resonant converter provided by the present invention, a single-turn winding is arranged on each layer of the printed circuit board, and the single-turn winding is divided into an inner ring and an outer ring, and the inner winding group and the outer winding group are staggered, so that two insulating layers are present between two adjacent inner winding groups. The planar transformer in the LLC resonant converter provided by the present invention has the effect of reducing parasitic inductance and capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a front view structural schematic diagram of a fixed-turn printed circuit board of a planar transformer in an LLC resonant converter of the present invention;

[0026] Figure 2 It is a front view structural schematic diagram of the first layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention;

[0027] Figure 3 It is a front view structural schematic diagram of the second layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention;

[0028] Figure 4 It is a front view structural schematic diagram of the third layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention;

[0029] Figure 5 It is a front view structural schematic diagram of the fourth layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention;

[0030] Figure 6 It is a front view structural schematic diagram of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention;

[0031] Figure 7 It is a front view structural schematic diagram of an adjustable printed circuit board top plate of a planar transformer in an LLC resonant converter of the present invention;

[0032] Figure 8 It is a front view structural schematic diagram of a first intermediate plate of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention;

[0033] Fig. 9 It is a front view structural schematic diagram of a second intermediate plate of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention;

[0034] Fig.10 It is a front view structural schematic diagram of an adjustable printed circuit board bottom plate of a planar transformer in an LLC resonant converter of the present invention;

[0035] Fig.11 It is a front view structural schematic diagram of the secondary printed circuit board top plate of the planar transformer in the LLC resonant converter of the present invention;

[0036] Fig.12 It is a front view structural schematic diagram of the secondary printed circuit board bottom plate of the planar transformer in the LLC resonant converter of the present invention.

[0037] In the figure: 1, board body; 2, third connection terminal; 3, input connection terminal; 4, second connection terminal; 5, fourth connection terminal; 6, first connection terminal; 7, first turn; 8, second turn; 9, third turn; 10, fourth turn; 101a, top board; 101b, first middle board; 101c, second middle board; 101d, bottom board; 102, third terminal; 103, fourth terminal; 104, second terminal; 105, input terminal; 106, first terminal; 107, first single turn; 108, second single turn; 109, third single turn; 1010, fourth single turn; 110a, top board; 110b, bottom board; 111, first external terminal; 112, second external terminal; 113, third external terminal; 114a, first secondary winding; 114b, second secondary winding. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0040] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0041] Figure 1 FIG. 1 is a front view of the structure of a fixed-turn printed circuit board of a planar transformer in an LLC resonant converter of the present invention. Figure 2 FIG. 1 is a front view of the first layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention. Figure 3 FIG. 1 is a front view of the second layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention. Figure 4 FIG. 1 is a front view of the third layer of the fixed-turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention. Figure 5 FIG. 1 is a front view of the fourth layer of the fixed turn printed circuit board of the planar transformer in the LLC resonant converter of the present invention, according to Figure 1-Figure 5As shown, the planar transformer in the LLC resonant converter provided by this embodiment includes a magnetic core, a primary printed board, and a secondary printed board. The primary printed board and the secondary printed board are stacked, and the magnetic core passes through the primary printed board and the secondary printed board. The primary printed board includes a fixed-turn printed board and an adjustable printed board. The fixed-turn printed board has an input end and an output end, and the adjustable printed board has an input end and multiple output ends. The input end of the fixed-turn printed board is electrically connected to the external circuit, and the output end of the fixed-turn printed board is electrically connected to the input end of the adjustable printed board. The number of turns of the transformer can be adjusted by adjusting the output end of the adjustable printed board.

[0042] It should be noted that the planar transformer also includes a shielding printed circuit board. The stacking structure is as follows: a secondary printed circuit board, a shielding printed circuit board, a fixed-turn printed circuit board, an adjustable printed circuit board, a fixed-turn printed circuit board, a shielding printed circuit board, and a secondary printed circuit board. The boards are stacked in the above order, and the number of adjustable printed circuit boards can be increased as needed to achieve the effect of adjustable turns.

[0043] It should be noted that the magnetic core adopts ER planar magnetic core. For other magnetic cores such as EI, EE, etc., when designing the primary and secondary winding printed circuit boards, it is only necessary to change the circular hole in the middle of the PCB printed circuit board into the corresponding other magnetic core shapes.

[0044] In the above embodiment, the fixed-turn printed circuit board includes a plurality of board bodies 1 and single-turn windings corresponding to the board bodies 1 one by one, a plurality of connection terminals are arranged on the board body 1, and the plurality of connection terminals are evenly spaced from top to bottom on the left side of the board body 1, and a plurality of connection contacts are also spaced on the board body 1, and the shapes of the plurality of single-turn windings are different, and each single-turn winding is arranged on a corresponding board body 1, one end of the single-turn winding is electrically connected to the corresponding connection terminal, and the other end of the single-turn winding is electrically connected to the corresponding connection contact, and when the multi-layer board bodies 1 are stacked, the connection terminals on each layer of the board body 1 are correspondingly connected, and the connection contacts on each layer of the board body 1 are correspondingly connected, the single-turn windings on the multi-layer board bodies 1 are connected in series.

[0045] It should be noted that the single-turn winding is divided into a first turn 7, a second turn 8, a third turn 9 and a fourth turn 10, the connection terminals are divided into a third connection terminal 2, an input connection terminal 3, a second connection terminal 4, a fourth connection terminal 5 and a first connection terminal 6 from top to bottom, and the connection contacts are divided into a first fixed contact, a second fixed contact and a third fixed contact, wherein one end of the first turn 7 is electrically connected to the input connection terminal 3, and the other end of the first turn 7 is electrically connected to the first fixed contact;

[0046] One end of the second turn 8 is electrically connected to the first fixed contact, and the other end of the second turn 8 is electrically connected to the second fixed contact;

[0047] One end of the third turn 9 is electrically connected to the second fixed contact, and the other end of the third turn 9 is electrically connected to the third fixed contact;

[0048] One end of the fourth turn 10 is electrically connected to the third fixed contact, and the other end of the fourth turn 10 is electrically connected to the fourth connection terminal 5 .

[0049] In the above embodiment, the single-turn winding includes an inner winding group and an outer winding group, the inner winding group is close to the magnetic core, and the outer winding group is far away from the magnetic core. When multiple plates 1 are stacked, the plates 1 provided with the inner winding group and the plates 1 provided with the outer winding group are stacked alternately.

[0050] Figure 6 FIG. 1 is a front view of the structure of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention. Figure 7 FIG. 1 is a front view of the structure of the adjustable top plate 101a of the planar transformer of the LLC resonant converter of the present invention. Figure 8 FIG. 1 is a front view structural diagram of a first intermediate plate of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention, Fig. 9 FIG. 1 is a front view structural diagram of a second intermediate plate of an adjustable printed circuit board of a planar transformer in an LLC resonant converter of the present invention, Fig.10 FIG. 1 is a front view of the structure of the adjustable printed circuit board bottom plate of the planar transformer in the LLC resonant converter of the present invention, according to Figure 6-Figure 10 As shown, in the above embodiment, the adjustable printed circuit board includes a top plate 101a, a first middle plate 101b, a second middle plate 101c and a bottom plate 101d, and five connection terminals are evenly spaced on the left side of the top plate 101a, the first middle plate 101b, the second middle plate 101c and the bottom plate 101d. The five connection terminals are respectively a third terminal 102, a fourth terminal 103, a second terminal 104, an input terminal 105 and a first terminal 106 from top to bottom, and a first contact, a second contact and a third contact are also spaced on the top plate 101a, the first middle plate 101b, the second middle plate 101c and the bottom plate 101d;

[0051] A first single turn 107 is provided on the top plate 101a, one end of the first single turn 107 is electrically connected to the third terminal 102, the other end of the first single turn 107 is electrically connected to the fourth terminal 103, and one end of the first single turn 107 close to the third terminal 102 is also electrically connected to the first contact;

[0052] A second single turn 108 is disposed on the first intermediate plate 101 b , one end of the second single turn 108 is electrically connected to the second terminal 104 , and the other end of the second single turn 108 is electrically connected to the first contact point;

[0053] A third single turn 109 is disposed on the second intermediate plate 101c, one end of the third single turn 109 is electrically connected to the first terminal 106, one end of the third single turn 109 is also electrically connected to the third contact, and the other end of the third single turn 109 is electrically connected to the second contact;

[0054] A fourth single turn 1010 is provided on the bottom plate 101d, one end of the fourth single turn 1010 is electrically connected to the input terminal 105, and the other end of the fourth single turn 1010 is electrically connected to the third contact;

[0055] When the top board 101a, the first middle board 101b, the second middle board 101c and the bottom board 101d are sequentially stacked and connected, the connection terminals on different printed boards are correspondingly connected, and the connection contacts on different printed boards are correspondingly connected.

[0056] It should be noted that when the top plate 101a, the first middle plate 101b, the second middle plate 101c and the bottom plate 101d are stacked and connected in sequence, the multiple third terminals 102 are interconnected and conductive, the multiple fourth terminals 103 are interconnected and conductive, the multiple second terminals 104 are interconnected and conductive, the multiple input terminals 105 are interconnected and conductive, the multiple first terminals 106 are connected and conductive, the multiple first contacts are connected and conductive, the multiple second contacts are connected and conductive, and the multiple third contacts are connected and conductive.

[0057] In the above embodiment, the first single turn 107 and the third single turn 109 are distributed close to the magnetic core, and the second single turn 108 and the fourth single turn 1010 are distributed far from the magnetic core.

[0058] Fig.11 FIG. 1 is a front view of the structure of the secondary printed circuit board top plate 110a of the planar transformer in the LLC resonant converter of the present invention. Fig.12 FIG. 1 is a front view of the structure of the secondary printed circuit board bottom plate 110b of the planar transformer in the LLC resonant converter of the present invention. Fig.11 and Fig.12 As shown, in the above embodiment, the secondary printed circuit board includes a top plate 110a and a bottom plate 110b, and three spaced external terminals are arranged on the top plate 110a and the bottom plate 110b, and the three external terminals are respectively a first external terminal 111, a second external terminal 112 and a third external terminal 113;

[0059] A first secondary winding 114a is disposed on the top plate 110a, one end of the first secondary winding 114a is electrically connected to the second external terminal 112, and the other end of the first secondary winding 114a is electrically connected to the third external terminal 113;

[0060] A second secondary winding 114 b is disposed on the bottom plate 110 b . One end of the second secondary winding 114 b is electrically connected to the first external terminal 111 , and the other end of the second secondary winding 114 b is electrically connected to the second external terminal 112 .

[0061] In the above embodiment, the first secondary winding 114 a and the second secondary winding 114 b cover the areas around the magnetic core holes of the top plate 110 a and the bottom plate 110 b respectively.

[0062] In the above embodiment, the winding is arranged on the printed circuit board and then covered with insulating material.

[0063] Working principle: Through the design of the lead-out terminals of the multi-layer PCB printed board winding, a single planar transformer can achieve variable turns ratio through different connection methods of the lead-out terminals. Compared with the traditional transformer, the volume and weight of the transformer are reduced, the operating frequency is improved, and the design production cost and cycle are reduced. By staggering the windings on adjacent printed boards, the inter-turn parasitic inductance and capacitance problems between single-layer windings in the multi-layer PCB printed board, as well as the inter-layer parasitic inductance and capacitance problems of the windings between layers are greatly reduced.

[0064] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A planar transformer in an LLC resonant converter, comprising a magnetic core, a primary printed board, and a secondary printed board, wherein the primary printed board and the secondary printed board are stacked, and the magnetic core passes through the primary printed board and the secondary printed board, characterized in that: The primary printed board includes a fixed-turn printed board and an adjustable printed board. The fixed-turn printed board has an input end and an output end, and the adjustable printed board has an input end and multiple output ends. The input end of the fixed-turn printed board is electrically connected to an external circuit, and the output end of the fixed-turn printed board is electrically connected to the input end of the adjustable printed board. The number of turns of the transformer can be adjusted by adjusting the output end of the adjustable printed board.

2. The planar transformer in an LLC resonant converter according to claim 1, characterized in that: The fixed-turn printed circuit board comprises a plurality of board bodies (1) and single-turn windings corresponding to the board bodies (1) one by one. The board bodies (1) are provided with a plurality of connection terminals, and the plurality of connection terminals are evenly spaced from top to bottom on the left side of the board body (1). The board body (1) is also spaced and provided with a plurality of connection contacts. The plurality of single-turn windings have different shapes. Each of the single-turn windings is provided on a corresponding board body (1). One end of the single-turn winding is electrically connected to the corresponding connection terminal, and the other end of the single-turn winding is electrically connected to the corresponding connection contact. When multiple layers of the board bodies (1) are stacked and the connection terminals on each layer of the board bodies (1) are correspondingly connected and the connection contacts on each layer of the board bodies (1) are correspondingly connected, the single-turn windings on the multiple layers of the board bodies (1) are connected in series.

3. The planar transformer in the LLC resonant converter according to claim 2, characterized in that: The single-turn winding comprises an inner winding group and an outer winding group, wherein the inner winding group is close to the magnetic core and the outer winding group is far away from the magnetic core; when a plurality of the plate bodies (1) are stacked, the plate bodies (1) provided with the inner winding group and the plate bodies (1) provided with the outer winding group are stacked alternately.

4. The planar transformer in an LLC resonant converter according to claim 1, characterized in that: The adjustable printed circuit board comprises a top plate (101a), a first middle plate (101b), a second middle plate (101c) and a bottom plate (101d); five connection terminals are evenly spaced apart on the left sides of the top plate (101a), the first middle plate (101b), the second middle plate (101c) and the bottom plate (101d); the five connection terminals are respectively a third terminal (102), a fourth terminal (103), a second terminal (104), an input terminal (105) and a first terminal (106) from top to bottom; and a first contact point, a second contact point and a third contact point are also spaced apart on the top plate (101a), the first middle plate (101b), the second middle plate (101c) and the bottom plate (101d); A first single turn (107) is provided on the top layer board (101a), one end of the first single turn (107) is electrically connected to the third terminal (102), the other end of the first single turn (107) is electrically connected to the fourth terminal (103), and one end of the first single turn (107) close to the third terminal (102) is also electrically connected to the first contact point; A second single turn (108) is provided on the first intermediate plate (101b), one end of the second single turn (108) is electrically connected to the second terminal (104), and the other end of the second single turn (108) is electrically connected to the first contact point; The second intermediate plate (101c) is provided with a third single turn (109), one end of the third single turn (109) is electrically connected to the first terminal (106), one end of the third single turn (109) is also electrically connected to the third contact, and the other end of the third single turn (109) is electrically connected to the second contact; A fourth single turn (1010) is provided on the bottom plate (101d), one end of the fourth single turn (1010) is electrically connected to the input terminal (105), and the other end of the fourth single turn (1010) is electrically connected to the third contact point; When the top board (101a), the first middle board (101b), the second middle board (101c) and the bottom board (101d) are stacked and connected in sequence, the connection terminals on different printed boards are connected correspondingly, and the connection contacts on different printed boards are connected correspondingly.

5. The planar transformer in the LLC resonant converter according to claim 4, characterized in that: The first single turn (107) and the third single turn (109) are distributed close to the magnetic core, and the second single turn (108) and the fourth single turn (1010) are distributed far away from the magnetic core.

6. A planar transformer in an LLC resonant converter according to claims 2-5, characterized in that: The secondary printed circuit board comprises a top plate (110a) and a bottom plate (110b), and the top plate (110a) and the bottom plate (110b) are both provided with three external connection terminals which are spaced apart from each other, and the three external connection terminals are respectively a first external connection terminal (111), a second external connection terminal (112) and a third external connection terminal (113); A first secondary winding (114a) is disposed on the top plate (110a), one end of the first secondary winding (114a) is electrically connected to the second external terminal (112), and the other end of the first secondary winding (114a) is electrically connected to the third external terminal (113); A second secondary winding (114b) is disposed on the bottom plate (110b), one end of the second secondary winding (114b) is electrically connected to the first external terminal (111), and the other end of the second secondary winding (114b) is electrically connected to the second external terminal (112).

7. The planar transformer in the LLC resonant converter according to claim 6, characterized in that: The first secondary winding (114a) and the second secondary winding (114b) respectively cover the areas around the magnetic core holes of the top plate (110a) and the bottom plate (110b).

8. The planar transformer in the LLC resonant converter according to claim 7, characterized in that: After the winding is set on the printed circuit board, it is covered with insulating material.

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