Planar transformer with main winding and auxiliary winding multiplexing coil
By introducing a tap design on the primary winding, part of the primary winding can be reused as an auxiliary winding, which solves the problems of large space occupation and complex manufacturing of traditional planar transformers, optimizes PCB space and improves performance, and is suitable for high-efficiency and miniaturized power supply applications.
Patent Information
- Application Number
- CN202520284210.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-21
- Publication Date
- 2026-01-27
- Estimated Expiration
- 2035-02-21
AI Technical Summary
Traditional planar transformers, with their independent winding design, occupy a large PCB space, are complex to manufacture, and increase parasitic inductance and capacitance, thus limiting miniaturization and performance improvement.
A tap design is introduced on the primary winding to reuse part of the primary winding as an auxiliary winding, realizing the functional integration of the main winding and the auxiliary winding. The series connection and disconnection of the winding are controlled by the power transistor, simplifying the peripheral circuit and optimizing the PCB space utilization.
It optimizes PCB space utilization, reduces manufacturing complexity and cost, improves winding resource utilization and transformer performance, and enhances electrical stability and high-frequency performance.
Smart Images
Figure CN223842734U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of electronic power, and in particular to a planar transformer with a main winding, auxiliary winding, and multiplexed coil. Background Technology
[0002] Planar transformers are widely used in high-frequency switching power supplies and power conversion devices due to their compact structure, high power density, and low losses. However, traditional planar transformers typically employ an independent design for the main and auxiliary windings, with each winding positioned on a different layer of a printed circuit board (PCB). While this design meets functional requirements, it has significant technical drawbacks. First, the independent winding design occupies a large amount of PCB space, limiting the miniaturization potential of the power supply unit. Second, because the main and auxiliary windings require multiple vias and complex connections for electrical connection, this design not only increases manufacturing difficulty but also easily introduces large parasitic inductance and capacitance, affecting the transformer's high-frequency performance. Furthermore, this design increases the number of PCB layers and manufacturing complexity, indirectly driving up production costs. More importantly, traditional auxiliary winding designs are often only used to extract low-power signals, failing to fully utilize winding resources, resulting in low inductance utilization and limiting the overall performance improvement of the transformer. Utility Model Content
[0003] The purpose of this invention is to provide a planar transformer with a main winding and auxiliary winding multiplexed coil. By introducing a tap design on the primary winding, part of the primary winding is reused as an auxiliary winding, thereby integrating the functions of the main winding and the auxiliary winding. This design optimizes PCB space utilization, eliminates the need for separate wiring for the auxiliary winding, reduces PCB area and layer requirements, and provides greater space flexibility for miniaturized power supply devices.
[0004] To achieve the above objectives, this utility model provides a planar transformer with a main winding and an auxiliary winding multiplexed coil. The planar transformer includes a primary winding and a secondary winding. The primary winding has a first end, a second end, a first tap, and a second tap.
[0005] The second tap draws a portion of the primary winding, so that the coil between the second tap and the second end forms an auxiliary winding; a power transistor is connected in series between the first tap and the second tap, wherein the first tap is connected to the drain of the power transistor, and the second tap is connected to the source of the power transistor.
[0006] Preferably, the primary winding is constructed on a four-layer printed circuit board (PCB);
[0007] In this process, on the top layer of the four-layer PCB, starting from the first tap, a first number of turns m are wound along the first direction, then connected to the inner first layer through the first via, and connected to the innermost side of the primary winding through the first connecting copper foil on the first layer. The winding then returns to the top layer through the second via, and continues to wind a second number of turns n along the first direction to the first end. On the bottom layer of the four-layer PCB, starting from the second end, a third number of turns p are wound along the first direction, then connected to the inner second layer through the third via, and connected to the outermost side of the primary winding through the second connecting copper foil on the second layer. The winding then returns to the bottom layer through the fourth via, and continues to wind a fourth number of turns q along the first direction to the second tap.
[0008] More preferably, the first number of turns m, the second number of turns n, the third number of turns p, and the fourth number of turns q are all positive numbers.
[0009] Preferably, the secondary winding is constructed on the inner first layer and inner second layer of a four-layer PCB. Starting from the first end of the secondary winding, after winding a fifth number of turns h along the first direction, it is connected to the inner second layer through a fifth via, and then continues to wind a sixth number of turns i along the first direction to the second end of the secondary winding.
[0010] More preferably, the fifth number of turns h and the sixth number of turns i are both positive numbers.
[0011] Preferably, the power transistor is connected to an external control circuit;
[0012] When the power transistor is in the on state, the first tap and the second tap are connected in series through the power transistor, and the connection between the first end and the second end constitutes the primary winding.
[0013] When the power transistor is in the off state, the first tap and the second tap are not connected, and the coil between the second tap and the second end constitutes the auxiliary winding.
[0014] This utility model provides a planar transformer with a main winding and auxiliary winding multiplexed coil. By introducing a tap design on the primary winding, a portion of the primary winding is reused as an auxiliary winding, thereby integrating the functions of the main winding and auxiliary winding. This design optimizes PCB space utilization, eliminating the need for separate wiring for the auxiliary winding, reducing PCB area and layer requirements, and providing greater space flexibility for miniaturized power supply devices. Simultaneously, the multiplexing design simplifies peripheral circuitry, reduces manufacturing complexity, and effectively reduces the impact of parasitic parameters on high-frequency performance. Furthermore, the reduced design requirement for independent windings simplifies the manufacturing process, resulting in a decrease in the number of PCB layers and production costs. Functionally, this solution uses dynamic control of the power transistors to flexibly switch the operating mode of the primary winding, enabling the auxiliary winding to efficiently participate in energy transfer and signal extraction, thereby improving the utilization rate of winding resources and the overall performance of the transformer. This innovative design not only improves the electrical performance and stability of the transformer but also provides a new solution for efficient and miniaturized power supply applications. Attached Figure Description
[0015] Figure 1 A copper foil routing diagram on the top plate of a planar transformer with a main winding and auxiliary winding multiplexed coil provided for an embodiment of this utility model;
[0016] Figure 2 A copper foil routing diagram on the internal first layer plate of a planar transformer with a main winding, auxiliary winding, and multiplexed coil provided for an embodiment of this utility model;
[0017] Figure 3 A copper foil routing diagram on the internal second layer plate of a planar transformer with a main winding and auxiliary winding multiplexed coil provided for an embodiment of this utility model;
[0018] Figure 4 A copper foil routing diagram on the bottom plate of a planar transformer with a main winding, auxiliary winding, and multiplexed coil provided for an embodiment of this utility model.
[0019] Figure 5 This invention provides a specific application of a planar transformer with a main winding and an auxiliary winding multiplexed coil in a power module. Detailed Implementation
[0020] The technical solution of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments.
[0021] This utility model embodiment provides a planar transformer with a main winding and auxiliary winding multiplexed coil, including a primary winding and a secondary winding. The primary winding has a first end, a second end, a first tap, and a second tap. The second tap draws a portion of the primary winding, so that the coil between the second tap and the second end constitutes an auxiliary winding. A power transistor is connected in series between the first tap and the second tap, wherein the first tap is connected to the drain of the power transistor, and the second tap is connected to the source of the power transistor.
[0022] The power transistor is connected to an external control circuit. When the power transistor is in the on state, the first tap and the second tap are connected in series through the power transistor, and the first end and the second end are connected to form a primary winding. When the power transistor is in the off state, the first tap and the second tap are not connected, and the coil between the second tap and the second end forms an auxiliary winding.
[0023] Figure 1-4 The figures show the copper foil traces of the four-layer board of the planar transformer PCB provided in this embodiment.
[0024] The primary winding (AD) is constructed on a four-layer printed circuit board (PCB); such as Figure 1 As shown, on the top layer of a four-layer PCB, starting from the first tap B, a first number of turns m (m = 0.5 in this example) are wound along the first direction (clockwise in the figure), and connected to the first via (position B'). Figure 2 The inner first layer board shown connects to the innermost side of the primary winding via the first connecting copper foil on the first layer board (the metal connection from B' to A' in the diagram), and then connects back to the top layer board via the second via (position A'), continuing to wind a second number of turns n (n = 5.5 in this example) along the first direction to the first end A; on the bottom layer board of the four-layer PCB, as Figure 4 As shown, starting from the second end D, along the first direction (clockwise direction, and...) Figure 4 After winding the third number of turns p (in this example, p = 5.5) in the opposite direction (see directly in the middle), it is connected to the inner second layer plate through the third via (position D'). It is then connected to the outermost winding of the primary winding through the second connecting copper foil on the second layer plate (the metal connection from D' to C' in the figure), and then connected back to the bottom plate through the fourth via (position C'). The fourth number of turns q (in this example, q = 0.5) is then wound in the first direction to the second tap C.
[0025] Note here: Figure 4 The copper foil in the middle is printed on the opposite side of the first three layers, and the description above still refers to the direction in which the copper foil faces upward in the first three layers.
[0026] The first number of turns m, the second number of turns n, the third number of turns p, and the fourth number of turns q are all positive numbers. In this example, m + n = p + q, but this is not used to limit the protection scope of this scheme to only be implemented in the above manner. The specific winding direction, number of turns, etc., can be designed by those skilled in the art according to the application scenario and design constraints of the technical solution.
[0027] In this application, the first tap B is connected to the drain of the power transistor, and the second tap C is connected to the source of the power transistor. Therefore, when the power transistor is turned on, coils AB and CD are connected in series through the power transistor to form the primary winding.
[0028] The secondary winding is constructed on the inner first layer of a four-layer PCB. Figure 2 ) and the inner second layer ( Figure 3 Starting from the first end F of the secondary winding, the fifth number of turns h (h=1 in this example) is wound along the first direction (clockwise). Then, it is connected to the second inner plate through the fifth via (E' in the figure). The sixth number of turns i (i=1 in this example) is wound along the first direction (clockwise) to the second end E of the secondary winding.
[0029] Similarly, the fifth number of turns h and the sixth number of turns i are both positive numbers. In this example, h = i, but this is not used to limit the protection scope of this scheme to only be implemented in the above manner. The specific winding direction, number of turns, etc., can be designed by those skilled in the art according to the application scenario and design constraints of the technical solution.
[0030] After the power transistor is turned off, coils AB and CD are no longer connected in series. Coil CD acts as an auxiliary winding. In specific power module applications, the auxiliary winding is powered by the secondary winding based on the output voltage Vout via flyback. The voltage across the auxiliary winding is: Vout×(p+q) / (h+i), meaning the voltage of the auxiliary winding is proportional to the voltage of the secondary winding.
[0031] Figure 5 This invention provides a specific application of a planar transformer with a main winding and auxiliary winding multiplexed coil in a power module. U1 is a primary main control chip with a built-in power transistor, and T1 is the planar transformer provided in the above embodiment, which is connected to the power transistor built into U1 as described above.
[0032] When the power transistor is turned on, parallel capacitors C5 and C6 filter out high-frequency interference signals at the input. The controller in the primary main control chip U1 generates a pulse width modulation (PWM) signal to control the switching state of the power transistor. That is, by adjusting the duty cycle, the voltage pulse width applied to the primary winding is precisely controlled, thereby transferring the energy input to the secondary side through the planar transformer T1. The secondary rectifier U2, output filter capacitor C14, resistor R15, and parallel output filter circuit C15-C23 rectify the AC current of the secondary winding of the planar transformer T1 into DC current and filter it at the output to ensure the stability of the output voltage.
[0033] The output voltage Vout is divided by sampling resistors R20 and R21 and sent to operational amplifier U4 for error amplification. It is compared with the built-in reference voltage to generate an error signal, which is then filtered by an RC filter circuit composed of C4 and R8 to suppress high-frequency noise. The error signal output by operational amplifier U4 is transmitted to the feedback signal input terminal (FB) of the primary main control chip U1 through optocoupler U3, thereby dynamically adjusting the PWM duty cycle of the power transistor to achieve feedback control.
[0034] After the power transistor is turned off, the secondary rectifier U2 and D6 are turned on, and the voltage across the auxiliary winding is proportional to the output voltage, thus supplying power to the primary main control chip through this circuit.
[0035] The above is merely an example of a specific circuit application of a planar transformer with a main winding and auxiliary winding multiplexed coil provided in this embodiment. Those skilled in the art will understand that the planar transformer of this embodiment can be used in other application scenarios, not limited to the specific circuit described above.
[0036] This utility model provides a planar transformer with a main winding and auxiliary winding multiplexed coil. By introducing a tap design on the primary winding, a portion of the primary winding is reused as an auxiliary winding, thereby integrating the functions of the main winding and auxiliary winding. This design optimizes PCB space utilization, eliminating the need for separate wiring for the auxiliary winding, reducing PCB area and layer requirements, and providing greater space flexibility for miniaturized power supply devices. Simultaneously, the multiplexing design simplifies peripheral circuitry, reduces manufacturing complexity, and effectively reduces the impact of parasitic parameters on high-frequency performance. Furthermore, the reduced design requirement for independent windings simplifies the manufacturing process, resulting in a decrease in the number of PCB layers and production costs. Functionally, this solution uses dynamic control of the power transistors to flexibly switch the operating mode of the primary winding, enabling the auxiliary winding to efficiently participate in energy transfer and signal extraction, thereby improving the utilization rate of winding resources and the overall performance of the transformer. This innovative design not only improves the electrical performance and stability of the transformer but also provides a new solution for efficient and miniaturized power supply applications.
[0037] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above description is only a specific embodiment of this utility model and is not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.
Claims
1. A planar transformer with a main winding and auxiliary winding multiplexed coil, characterized in that, The planar transformer includes a primary winding and a secondary winding, wherein the primary winding has a first end, a second end, a first tap, and a second tap; The second tap draws a portion of the primary winding, so that the coil between the second tap and the second end forms an auxiliary winding; a power transistor is connected in series between the first tap and the second tap, wherein the first tap is connected to the drain of the power transistor, and the second tap is connected to the source of the power transistor.
2. The planar transformer with a main winding and auxiliary winding multiplexed coil according to claim 1, characterized in that, The primary winding is constructed on a four-layer printed circuit board (PCB). In this process, on the top layer of the four-layer PCB, starting from the first tap, a first number of turns m are wound along the first direction, then connected to the inner first layer through the first via, and connected to the innermost side of the primary winding through the first connecting copper foil on the first layer. The winding then returns to the top layer through the second via, and continues to wind a second number of turns n along the first direction to the first end. On the bottom layer of the four-layer PCB, starting from the second end, a third number of turns p are wound along the first direction, then connected to the inner second layer through the third via, and connected to the outermost side of the primary winding through the second connecting copper foil on the second layer. The winding then returns to the bottom layer through the fourth via, and continues to wind a fourth number of turns q along the first direction to the second tap.
3. The planar transformer with a main winding and auxiliary winding multiplexed coil according to claim 2, characterized in that, The first number of turns m, the second number of turns n, the third number of turns p, and the fourth number of turns q are all positive numbers.
4. The planar transformer with a main winding and auxiliary winding multiplexed coil according to claim 1, characterized in that, The secondary winding is constructed on the inner first layer and inner second layer of the four-layer PCB. Starting from the first end of the secondary winding, after winding a fifth number of turns h along the first direction, it is connected to the inner second layer through the fifth via, and continues to wind a sixth number of turns i along the first direction to the second end of the secondary winding.
5. The planar transformer with a main winding and auxiliary winding multiplexed coil according to claim 4, characterized in that, The fifth number of turns h and the sixth number of turns i are both positive numbers.
6. The planar transformer with a main winding and auxiliary winding multiplexed coil according to claim 1, characterized in that, The power transistor is connected to an external control circuit. When the power transistor is in the on state, the first tap and the second tap are connected in series through the power transistor, and the connection between the first end and the second end constitutes the primary winding. When the power transistor is in the off state, the first tap and the second tap are not connected, and the coil between the second tap and the second end constitutes the auxiliary winding.