CN101017730A - Transformer structure - Google Patents

Abstract

The present invention provides a transformer structure, comprising: a primary coil; a plurality of secondary circuit units, each of which includes a printed circuit board complex; the printed circuit board complex comprises at least one printed circuit board provided with a secondary side conductor coil; and at least one output rectifying circuit configured on the printed circuit board composite body, wherein the output rectifying circuit comprises an output filtering device and a rectifying device. The invention can effectively reduce the length of the alternating current lead and the loss of the transformer, thereby improving the efficiency of the whole circuit.

Description

Transformer structure

technical field

The invention relates to a transformer structure of a switch mode power supply, in particular to a high-power, high-frequency transformer structure (transformer design).

Background technique

Today, when the power supply is developing towards high power density, in order to achieve higher efficiency, in addition to the structure of the circuit itself, the reasonable selection of components and the optimization of circuit parameters, the mechanism, thermal design and reasonable printed circuit board (PCB: Printed Circuit Board) layout and other non-traditional electrical designs are becoming more and more important in the actual design of power supplies.

In power supply design, the high frequency caused by high power density makes the design of magnetic core components particularly important. In addition, the design of power transformers is also the key, which is even more important in high-power and high-frequency applications. For example, as shown in Figure 1, it is the overall structure of a traditional direct current/direct current (DC/DC) converter, wherein the secondary side of the transformer 1 includes a secondary winding of the transformer, an output rectifier 3 and an output filter 4 and other components, and the primary side of the transformer 1 includes the primary winding of the transformer and the primary switching element 2, the switching element 2 is connected to the input terminal 5, and the output filter 4 is connected to the load (load) 6. Increasing the frequency of circuit switching can effectively reduce the volume of magnetic core components, but high frequency has brought many problems to the winding design of transformers. The skin depth effect and proximity effect of the wire under high frequency operation will cause additional power loss between the transformer winding itself and the winding, especially in the case of high current output. In addition, for the output side structure of the traditional transformer, as shown in Figure 2, the winding of the transformer 1 is connected to the primary switching element 2 and the output rectifier 3 and filter 4, and the rectifier 3 and filter part 4 on the output side are installed in the On the printed circuit board PCB, in addition, Zp represents the parasitic impedance of the lead wire. Such a configuration leads to a large distance from the secondary side leads of the transformer 1 to the output rectifier and a long AC path. The switching loss of the switching device increases, which affects the reliability and efficiency of the circuit. Similarly, the output winding of the traditional high-power transformer 1 will also greatly increase the terminal loss due to the terminal effect.

Therefore, designing a better transformer winding structure and output side structure has become an important factor affecting the reliability and efficiency of the circuit. Therefore, based on the above-mentioned shortcomings of the prior art and many adverse effects of traditional transformers, the present invention provides a transformer structure that can effectively reduce the length of AC leads and the loss of the transformer so as to improve the efficiency of the overall circuit.

Contents of the invention

In view of the problem of excessive outgoing loss of the output winding of the transformer in the prior art, the present invention provides a transformer structure that can effectively reduce the length of the AC lead wire and the loss of the transformer, thereby improving the efficiency of the overall circuit.

The purpose of the present invention is to provide a transformer structure. The above-mentioned structure mainly utilizes the interleaved winding arrangement structure of the primary side and the secondary side, and the input and output ends of the secondary side winding are arranged roughly vertically, thus greatly reducing the It reduces the thermal resistance and the loss of the output end, prolongs the service life of the transformer and increases the output efficiency and stability of the transformer.

Another object of the present invention is to provide a transformer structure, which can utilize parallel connection of primary sides, parallel connection of secondary sides, or other combinations of different units to match the application of actual output power.

According to above object, the present invention provides a kind of transformer structure, comprises:

a primary coil;

A plurality of secondary circuit units, each of which includes a printed circuit board composite; the printed circuit board composite includes at least one printed circuit board configured with a secondary conductor coil; and at least one output rectifier circuit , configured on the printed circuit board complex, wherein the output rectification circuit includes an output filter device and a rectification device.

The filtering device and rectifying device are located between two printed circuit board assemblies.

The printed circuit board complex also includes a driving chip, which is arranged on the printed circuit board.

The primary and secondary sides can be replaced.

Moreover, the wire-in end and the wire-out end of the secondary conductor coil of the printed circuit board complex are roughly perpendicular to each other.

The transformer includes multiple primary coils.

The output rectification circuit also includes a rectification switch, and the operation frequency of the rectification switch is greater than 100Khz.

The transformer structure also includes at least two primary coils connected in parallel, and at least two secondary circuit units connected in parallel for output.

The transformer structure also includes at least two primary coils connected in series and at least two secondary circuit units connected in parallel for output; wherein at least one secondary circuit unit outputs independently.

Each primary coil and secondary circuit units are arranged in a staggered manner.

Multiple primary coils include multi-layer windings, and each layer of windings of a primary coil is alternately arranged with secondary circuit units.

The transformer structure also includes an insulating medium for isolating the primary side coil and the secondary side circuit unit.

The transformer structure further includes a mask layer disposed between the primary side coil and the first primary side of the secondary side circuit unit and the winding of the first secondary side printed circuit board. Each primary coil and secondary circuit units are arranged in a staggered manner.

The present invention also provides a high-frequency transformer, including:

One primary coil and multiple secondary coils;

an iron core;

Each transformer secondary coil is connected to at least one rectifying device;

A ripple reduction device including at least one capacitor is connected to the rectification device. The high-frequency transformer is characterized in that it has multiple rectification and filter circuit substrates, each rectification and filter circuit substrate has at least three conductor areas isolated from each other, and at least one secondary The two output ends of the side coil are respectively connected to the first conductor area and the second conductor area of the circuit substrate, and the ripple reducing device is connected to the third conductor area and outputs the regulated DC voltage to the load.

The invention has the beneficial effects of effectively reducing the length of the AC leads and the loss of the transformer, thereby improving the efficiency of the overall circuit.

Description of drawings

Figure 1 shows the overall structure diagram of a conventional direct current/direct current (DC/DC) transformer;

Figure 2 shows the structure of the primary and secondary sides of a traditional transformer;

Figure 3 shows a half-bridge LLC series resonant circuit;

Fig. 4 shows the transformer assembly structure diagram of the present invention;

5A and 5B show the magnetomotive force distribution in the vertical direction of the internal windings of the traditional sandwich winding transformer and the interleaved transformer of the present invention;

Fig. 6 A and Fig. 6 B show the equivalent thermal resistance model of conventional transformer and transformer of the present invention;

Fig. 7 A and Fig. 7 B show the equivalent circuit diagram of conventional transformer and the use integrated technology transformer of the present invention;

Fig. 8A and Fig. 8B show the specific structure diagram of the printed circuit board winding under the condition that the secondary side of the transformer is one turn;

Figure 9A and Figure 9B show the effect of different terminal forms of the transformer;

Figure 10 shows the structural diagram of the primary winding;

Figure 11 shows a schematic diagram of a unit composed of the primary and secondary sides when the secondary side of the transformer is multi-turn;

Figure 12 shows the positive and negative two-layer structure diagram of a printed circuit board winding on the secondary side;

Figure 13A and Figure 13B show the structural diagrams of the output rectifier before and after adding a heat sink in the case of multiple turns on the secondary side;

Figure 14 shows schematic diagrams of printed circuit board windings with different numbers of turns;

Figure 15 shows the structure diagram of the primary side using the printed circuit board winding;

Figure 16 shows the winding structure of the primary side using printed circuit board integration technology;

Figure 17 shows the structure in which the primary and secondary sides are all integrated on the same printed circuit board;

Figure 18 shows the structure of integrating two units at the same time using a printed circuit board;

Figure 19 shows a schematic structural view of more units integrated into a printed circuit board;

Figures 20A and 20B show schematic diagrams of possible primary and secondary winding forms for the transformer structure;

21A and 21B are schematic diagrams showing possible secondary side combinations of transformer structures;

Figure 22 shows the different topologies of the secondary side that the printed circuit board complex can use;

Figure 23A and Figure 23B show the structural schematic diagrams of the safety solutions of two primary and secondary sides;

Figure 24 shows another security solution;

Figure 25 shows a solution to electromagnetic interference by adding a mask layer.

Detailed ways

Embodiments of the present invention are described in detail as follows in conjunction with the accompanying drawings.

Please refer to the drawings, which are only for illustrating preferred embodiments of the present invention, and are not intended to limit the present invention. As shown in Figure 3, it is a structural diagram of the LLC series resonant circuit of the half bridge, which illustrates the output rectification unit (including the output filter capacitor) of the secondary side complex of the transformer. The transformer structure of the present invention can be applied to high-power transformers, and is not limited to high-power transformers, and can also be applied to transformers of other powers. Generally speaking, the inductor (Ls), capacitor (Cs) and the magnetizing inductance (Lm) of the transformer form an LLC resonant circuit. The two main switches S1 and S2 form a half-bridge structure, and the constant output voltage is realized by changing the switching frequency. The resonant circuit is connected between the midpoint of the half bridge and the ground, therefore, the resonant capacitor Cs also acts as a DC blocking capacitor. On the output side, the rectifier diodes D1 and D2 constitute a center-tapped rectifier circuit, and the rectifier diodes are directly connected to the output capacitor Co. In addition, Z1, Z2, Z3 represent the parasitic impedance of the leads. As an example, the LLC resonant circuit includes a 1.2kW LLC-SRC (Series Resonant Converter, series resonant inverter), the output current of this circuit can reach 100 amperes (A), and the operating frequency can reach MHz level, And the circuit structure requires that the output filter unit only includes the output filter capacitor Co. Therefore, the design of traditional transformers in such high-frequency and high-current occasions will not only produce the terminal loss and AC lead loss discussed earlier, but will also cause many defects such as thermal design problems and excessive transformer winding loss. . The transformer structure of the present invention is to integrate the output filter capacitor and the transformer winding to better solve the above-mentioned problems. The overall structure of the transformer is shown in FIG. 4 .

Please refer to Figure 4, where the primary side 4a of the transformer can be a single-core or multi-core wire, wound on the same plane according to a certain direction, which includes two layers of the same windings connected in series as the primary side of a unit. The secondary side 3c of the transformer adopts the winding of the printed circuit board (PCB), and the output rectification circuit of the secondary side including the filter capacitor and the rectifier are integrated on the printed circuit board. In other words, the secondary side 3c is the printed circuit board winding of the secondary side complex of the transformer, and the primary side 4a is a two-layer primary winding connected in series. The secondary side 3c is embedded in the primary side 4a to form a unit 5b of the entire transformer. The core groups 3a, 3b integrate a plurality of units 5b into a whole transformer. As an example, the output rectification circuit includes a rectification switch whose operating switching frequency is greater than 100Khz. For the design of the overall transformer, several such units 5b can be connected in parallel to form, and then the work of optimizing the entire transformer can be simplified as optimizing each parallel unit. Greater power requires more units 5b to be connected in parallel.

Next, please refer to FIG. 5A and FIG. 5B , which respectively show the magnetomotive force distribution in the vertical direction of the internal windings of the traditional sandwich winding transformer and the interleaved transformer of the present invention. Among them, 6a is the primary winding, 7 is the secondary winding, and 8 is the magnetic core. The magnetic field distribution inside the transformer can be obtained by the law of Ampere's loop, as shown in the curve in the figure, where the magnetomotive force (Magnetic Motive Force: MMF) It directly affects the loss on the transformer winding, in other words, the greater the magnetomotive force, the greater the winding loss inside the transformer. Fig. 5A is a traditional sandwich winding transformer and its magnetomotive force distribution, and Fig. 5B is a transformer with an interlaced structure and its magnetomotive force distribution according to the present invention. From the comparison of the two figures, it is known that the interleaved structure produces smaller transformer winding losses , that is, the copper loss is significantly reduced.

Please refer to Figure 6A and Figure 6B. From the perspective of thermal design, most of the heat generation sources of the transformer are the winding and the iron core. From the horizontal direction, the equivalent thermal resistance 9 of the traditional transformer winding is similar to that in series, as shown in the figure 6A, so the heat dissipation conditions of its internal windings are very bad, and there are large thermal problems; and the transformer of the present invention changes the winding arrangement, and its equivalent thermal resistance 9 is similar to parallel connection, as shown in Figure 6B, its All windings can dissipate heat directly to the outside of the transformer, thus significantly reducing thermal resistance and improving heat dissipation.

Please refer to FIG. 7A and FIG. 7B , the difference of the circuits before and after the secondary side integration is adopted. Traditional transformer, its equivalent circuit is as shown in Figure 7A, and it adopts traditional winding mode, and just carries out filtering at last; And the transformer of the present invention can be applicable to the transformer of high power, and it comprises several units (cell) 10 connected in parallel, each of which can effectively spread power. The transformer of the present invention adopts a structure in which the primary side is connected in parallel and the secondary side is connected in parallel, and the difference from the traditional one lies in the integration technology of the secondary side and the interleaved winding structure of the primary side and the secondary side. After the integration, the terminal structure of the secondary side of the transformer can be simplified, the terminal loss can be reduced, the length of the output AC (AC) path can be significantly reduced, and the influence of parasitic parameters on the circuit can be reduced. Furthermore, the original alternating current (AC) terminal of the transformer can be changed to a direct current (DC) terminal.

Please refer to FIG. 8A and FIG. 8B , which show the secondary side printed circuit board winding integration technology. The integration technology of the secondary side (that is, the secondary side of the transformer) is the core of the transformer design, and its detailed structure is shown in Fig. 8A and Fig. 8B. The printed circuit board is composed of upper and lower layers. FIG. 8A and FIG. 8B respectively show the structure of the upper layer (toplayer) and the lower layer (bottom layer), which are respectively connected to the output end and the input end. As an example, the secondary side of the transformer includes: an output filter capacitor 11 integrated on the front of the printed circuit board, a conductor coil 12 of the printed circuit board, a driver chip 13 and an output rectifier 15 . In addition, the front and back sides of the printed circuit board have through holes 14 for connecting the upper and lower two-layer windings of the secondary side. For the center-tapped transformer structure, the structure of the upper and lower layers of the printed circuit board is completely symmetrical. Synchronous rectification technology is usually used in low-voltage and high-current occasions. The printed circuit board winding on the secondary side of the transformer adopts synchronous rectification technology and integrates the driver chip while the output filter capacitor is integrated, and the output synchronous rectification transistor (MOSFET) . It can be seen from the figure that the output AC path is very short, which can effectively reduce the loss in high-frequency and high-current occasions.

Please refer to FIG. 9A and FIG. 9B , which respectively show the effects of different terminal forms of the transformer. The use of printed circuit board windings is beneficial to reduce terminal loss. Figure 9A shows the terminal structure of the secondary side of the traditional copper foil winding. Its disadvantage lies in the loss at the terminal 16. Since the input terminal and the output terminal of the secondary winding are arranged in parallel, the AC current ip on the primary side is generated. The magnetic field causes uneven distribution of the current is on the output side, resulting in a great loss. However, the present invention adopts the overlapped output terminal structure in FIG. 9B. Since the input terminal and the output terminal of the secondary side winding are roughly perpendicular, the magnetic fields generated by the primary and secondary AC currents can cancel each other out, and the loss can be greatly reduced. For ordinary copper foil windings, the terminals are relatively complicated, and it is even more complicated when multiple units are connected in parallel. However, the winding method of printed circuit boards can solve this problem relatively easily. In addition, the wire-in terminal and the wire-out terminal of the winding on the primary side of the primary side may also be arranged roughly vertically.

In addition, due to the good heat dissipation conditions of the copper foil on the printed circuit board winding, no additional heat sink is required for the output rectifier, so the volume can be effectively saved and the power density can be greatly improved. According to actual design results, the transformer structure of the present invention can save about 40% of the volume at the same power level, and it can be applied to high power density occasions.

Please refer to Figure 10, which shows the structure diagram of the primary winding. The winding on the primary side is made of single-core or multi-core wire 17, such as copper foil, which is wound in a certain direction. Each unit contains two layers of winding 17 and is connected in series at the connector 18, and installed separately. On both sides of the secondary printed circuit board winding, as shown in Figure 4. In addition, the connector 18 can also be located outside the primary winding, that is, lead it out as shown in FIG. 11 . As mentioned above, based on the secondary side using the printed circuit board winding complex secondary side output filter capacitor and output rectifier, and adopting a transformer structure in which several units are interleaved and connected in parallel, it is the transformer structure proposed by the present invention. In addition, it must be emphasized that the selection of the magnetic core of the transformer of the present invention is not limited to the type shown in the figure, and various other types of magnetic cores with different shapes can also be used.

Please refer to FIG. 11 , which shows a schematic diagram of a unit composed of primary and secondary sides when the secondary side of the transformer has multiple turns. For the lower output voltage, the winding takes one turn as mentioned above. When the winding has two turns, it can be formed by connecting two printed circuit boards in series, for example, the upper and lower layers of copper foil windings 19 are used to form the two-turn winding. Similarly, the output filter device 20 complex is on the printed circuit board. In this embodiment, the filter device 20 is a filter capacitor; the output rectifier device 21 is installed on both sides of the printed circuit board. In this embodiment, the output rectifier device 21 is Output rectifier. In other words, in this embodiment, two printed circuit boards are connected in series to form a printed circuit board complex, and one of the printed circuit boards does not have a complete filtering and rectifying device, or neither of the two boards has a complete filtering and rectifying device. As shown in Figure 11, when two printed circuit boards are stacked, the filter device 20 is provided on each board, but the rectifier device 21 can be shared by two boards; on the contrary, the filter device can also be shared, so it constitutes a complete filter rectification function Multiple circuit boards are the printed circuit board composite. In addition, the winding 22 of the primary side is similar to FIG. 4 , and the entire winding 22 and 19 form a unit. Among them, the printed circuit board winding structure 19, as shown in FIG. 12 , can be seen that it integrates the output filter capacitor, and considering the installation of the output rectifier tube nearby, the AC path is reduced. The upper and lower layers of copper foil are connected in series through the through hole 23 . The entire transformer structure can be obtained by connecting several units as shown in Figure 11 in parallel, as shown in Figure 13A. If the output rectifier needs a cooling fin, a cooling fin 24 can be added as shown in FIG. 13B. The cooling fin 24 can also be used as an output wire at the same time.

Similarly, the transformer structure of the present invention can also use more than two turns, such as 2 or N turns, which can be achieved by connecting the corresponding number of printed circuit board windings in parallel, as shown in FIG. 14 . Therefore, the transformer structure of the present invention is applicable to both multi-turn printed circuit board windings and situations requiring heat sinks. In addition, two units can also be integrated on one printed circuit board, as shown in Figure 18. The same applies to the case where more secondary side units are combined together on a printed circuit board, as shown in FIG. 19 .

Similar to the secondary side, the primary side can also be made by using printed circuit board windings or using a printed circuit board composite primary side switch circuit 25, which are shown in Fig. 15 and Fig. 16 respectively. In addition, similarly, the primary and secondary windings can be integrated on one printed circuit board, as shown in FIG. 17 .

The transformer of the present invention can be applied to the situation where the primary side voltage is higher than the secondary side voltage, or the situation where the secondary side voltage is higher than the primary side voltage. It only needs to exchange the windings of the primary side and the secondary side, and it also belongs to the transformer of the present invention. type. In addition, for the combination of windings, the transformer structure can be applied to the parallel connection of the primary side and the parallel connection of the secondary side, as shown in Figure 20B, and can also be applied to the structure of the primary side in series and the secondary side in parallel, as shown in Figure 20A . For the secondary side, different units can also be combined to obtain different output requirements, as shown in Figure 21B, or each channel can be used as an independent load output, as shown in Figure 21A.

The above-mentioned application is the transformer of the secondary side center-tapped half-wave rectifier circuit. The method of integrating the printed circuit board is also applicable to the output structure of any other structure, such as the full-bridge rectifier output circuit, the current multiplier rectifier circuit, etc., as shown in Figure 22 As shown, the output rectifier and filter complex can be placed on the winding printed circuit board in the same way. In addition, the output filter inductance shown in the figure can be an additional inductance or an inductance of a magnetic composite.

Because the primary side and the secondary side of the transformer of the present invention are closely connected together, compared with the traditional transformer, the safety regulation problem is more important. We can use an external insulating medium 26 to encapsulate the winding of the primary side to meet the safety insulation level requirements of the primary side and secondary side of the transformer, as shown in FIG. 23A . Or, apply insulating paint 27 on the winding of the printed circuit board or select three layers of insulated wires to also meet the requirements of safety regulations, as shown in FIG. 23B . Similarly, the winding of the secondary printed circuit board can also be wrapped with an insulating medium 28 to solve the safety problem, as shown in FIG. 24 .

In the design of power transformers, due to the large parasitic capacitance between transformer windings, in order to improve the isolation effect on high-frequency interference, a layer of masking layer 29, such as copper foil, can be added between transformer windings, and the masking layer Layer 29 is grounded (the length of the ground wire should be as short as possible, otherwise the attenuation of the interference will be deteriorated due to the impedance division of the ground wire). Please refer to FIG. 25 , which shows a typical single mask layer 29 added between the primary and secondary sides of the transformer to reduce electromagnetic interference.

In some applications, one layer of the multi-layer printed circuit board structure can also be used as a mask layer, so that no additional copper foil is required.

Therefore, compared with the terminal loss and heat dissipation problems of transformers in the prior art, it is difficult to meet strict requirements, the technical solution proposed by the present invention can meet the low terminal loss and heat dissipation requirements, and at the same time achieve high circuit reliability and efficiency .

The above-mentioned embodiments are only used to illustrate the present invention, but not to limit the present invention.

Claims (15)

1. a transformer device structure is characterized in that, comprising:

One primary coil;

A plurality of secondary circuits unit, each described secondary circuit unit comprises:

One printed circuit board (PCB) complex;

Described printed circuit board (PCB) complex comprises at least one printed circuit board (PCB) that disposes the secondary conductor coils; And

At least one output rectification circuit is disposed on the described printed circuit board (PCB) complex, and wherein this output rectification circuit comprises output filter and rectifying device.

2. transformer device structure as claimed in claim 1 is characterized in that described filter and rectifying device are between two printed circuit board (PCB) complexs.

3. transformer device structure as claimed in claim 1 is characterized in that, comprises a chip for driving on the described printed circuit board (PCB) complex.

4. transformer device structure as claimed in claim 1 is characterized in that, former limit, secondary can be replaced.

5. transformer device structure as claimed in claim 1 is characterized in that, the lead-in wire terminal of the secondary conductor coils of described printed circuit board (PCB) complex is rough vertical with leading-out terminal.

6. transformer device structure as claimed in claim 1 is characterized in that described output rectification circuit also comprises a rectifier switch, and this rectifier switch operating frequency is greater than 100Khz.

7. transformer device structure as claimed in claim 1 is characterized in that described transformer comprises a plurality of primary coils.

8. transformer device structure as claimed in claim 1 is characterized in that, also comprises at least two primary coil parallel connections, at least two secondary circuit unit outputs in parallel.

9. transformer device structure as claimed in claim 1 is characterized in that, also comprises at least two primary coil series connection, at least two secondary circuit unit outputs in parallel.

10. transformer device structure as claimed in claim 1 is characterized in that, at least one secondary circuit unit is independently exported.

11. transformer device structure as claimed in claim 7 is characterized in that, each primary coil and secondary circuit unit take alternating expression to arrange.

12. transformer device structure as claimed in claim 7 is characterized in that, a plurality of primary coils comprise the multilayer winding, and each layer winding of a primary coil and secondary circuit units alternately are arranged.

13. transformer device structure as claimed in claim 1 is characterized in that, also comprises a dielectric, isolates described primary coil and secondary circuit unit.

14. transformer device structure as claimed in claim 1 is characterized in that, also comprises a mask layer, is disposed between described primary coil and the secondary circuit unit.

15. a high frequency transformer is characterized in that, comprising:

A primary coil and a plurality of secondary coil;

An iron core;

Each transformer secondary coil is connected at least one rectifying device;

A minimizing ripple device that comprises at least one electric capacity is connected to described rectifying device;

Wherein, has polylith current rectifying and wave filtering circuit substrate, at least three conductor regions that have mutual isolation on each described current rectifying and wave filtering circuit substrate, two outputs of at least one secondary coil are connected respectively to first conductor region and second conductor region of circuit substrate, and the direct voltage that described minimizing ripple device is connected to after the 3rd conductor region and the output adjusting arrives load.

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