EMC improved planar transformer

Abstract

The application discloses an EMC improved flat transformer, which is mainly composed of a bridge rectifier circuit, a magnetic core T1 and a control circuit, a main working OC winding, a VCC power supply winding and a SHIELD winding are arranged on the primary side of the magnetic core T1, and an NS output winding is arranged on the secondary side of the magnetic core T1; the positive pole of the output end of the bridge rectifier circuit is connected with the control circuit and the main working OC winding respectively, and the negative pole of the output end of the bridge rectifier circuit is connected with the control circuit, the VCC power supply winding and the SHIELD winding respectively. The application can effectively reduce the conduction and radiation interference of EMC signals when the flat transformer is used, and greatly reduce the thickness and production cycle of the flat transformer. Meanwhile, the application can effectively increase the layer number of the VCC power supply winding, and reduce the conduction interference and space radiation disturbance of the flat transformer to the power grid.

Description

Technical Field

[0001] The present invention relates to a planar transformer, in particular to an EMC improved planar transformer. Background Art

[0002] At present, with the rise of GaN (Gallium Nitride) in the consumer electronics industry, the supporting power supply products are also gradually miniaturized. The number of turns of traditional wire-wound transformers is getting smaller and smaller, and the PCB printed circuit board wire package will replace the wire package of the wire-wound transformer. With the continuous high-frequency development of products, the volume and number of turns of transformers are bound to decrease significantly, and the corresponding planar transformers will be widely adopted. Due to the long PCB manufacturing cycle of planar transformers, their own EMC (Electromagnetic Compatibility) issues are more complex and more difficult to handle than traditional wire-wound transformers. Therefore, the EMC issues of planar transformers greatly limit their application scope and fields, resulting in not only long manufacturing cycles, but also high costs and unstable performance. Summary of the Invention

[0003] In order to overcome the above shortcomings of the prior art, the present invention proposes an EMC improved planar transformer.

[0004] The present invention provides the following technical solution: An EMC improved planar transformer, which is mainly composed of a bridge rectifier circuit, a magnetic core T1 and a control circuit. A main working OC winding, a VCC power supply winding and a SHIELD winding are arranged on the primary side of the magnetic core T1, and an NS output winding is arranged on the secondary side of the magnetic core T1; the positive electrode of the output end of the bridge rectifier circuit is connected to the control circuit and the main working OC winding respectively, and the negative electrode thereof is connected to the control circuit, the VCC power supply winding and the SHIELD winding respectively.

[0005] Further, the VCC power supply winding and the SHIELD winding are wound in parallel with two wires, the dotted terminal of the VCC power supply winding is connected to the ground through the diode D1 and the parasitic capacitor C2 in sequence, and the non-dotted terminal of the VCC power supply winding is connected to the ground; the dotted terminal of the SHIELD winding is connected to the ground, and the non-dotted terminal thereof is suspended at the end.

[0006] The VCC power supply winding and the SHIELD winding are wound in parallel with two wires, the dotted terminal of the VCC power supply winding is connected to the ground through the diode D1 and the parasitic capacitor C2 in sequence, and the non-dotted terminal of the VCC power supply winding is connected to the ground; the non-dotted terminal of the SHIELD winding is connected to the ground, and the dotted terminal thereof is suspended at the end.

[0007] Meanwhile, in the present invention, the shielding signal between the main working OC winding and the SHIELD winding is directly guided to the ground; the VCC power supply winding and the SHIELD winding share one layer of the PCB board.

[0008] As one of the preferred embodiments of the present invention, the control circuit is composed of an integrated chip U1 of model DK065. Its HV pin is connected to both the positive terminal of the bridge rectifier circuit output and the starting point of the primary coil of the main working OC winding. Its SW pin is connected to the ending point of the primary coil of the main working OC winding. Its CS pin is grounded through resistor R1. Its VCC pin is connected to the connection point of diode D1 and parasitic capacitor C2.

[0009] As a second preferred embodiment of the present invention, the control circuit is composed of an integrated chip U2 and a MOS-N field-effect transistor or a Gan transistor. The HV pin of the integrated chip U2 is connected to both the positive terminal of the bridge rectifier output and the starting point of the primary coil of the main working OC winding. The ending point of the primary coil of the main working OC winding is connected to the drain of the MOS-N field-effect transistor or the Gan transistor. The gate of the MOS-N field-effect transistor or the Gan transistor is connected to the PWM pin of the integrated chip U2. The source of the MOS-N field-effect transistor or the Gan transistor is grounded through a resistor R1. The VCC pin of the integrated chip U2 is connected to the connection point of diode D1 and parasitic capacitance C2.

[0010] The integrated chip U2 is either an RM6665 integrated chip, an NCP1342 integrated chip, an MK2697G integrated chip, or an HL9550 integrated chip.

[0011] Compared with the prior art, the advantages and beneficial effects of this invention are:

[0012] 1. This invention can effectively reduce the conduction and radiation interference of EMC signals when using flat plate transformers, and can greatly reduce the thickness and production cycle of flat plate transformers.

[0013] 2. This invention can effectively increase the number of layers in the VCC power supply winding, and can reduce the interference of the flat plate transformer on the power grid conduction and spatial radiation disturbance. Attached Figure Description

[0014] Figure 1 A schematic diagram of the winding structure for shielding an existing flat-plate transformer;

[0015] Figure 2 for Figure 1 The equivalent circuit diagram of the design schematic shown;

[0016] Figure 3 for Figure 2 A schematic diagram of coupled signal transmission in the equivalent circuit shown;

[0017] Figure 4 This is a schematic diagram of the winding structure for the shielding design of the flat-plate transformer of the present invention;

[0018] Figure 5 for Figure 4 The schematic diagram of the first designed reflection architecture;

[0019] Figure 6 for Figure 4 A schematic diagram of another designed reflection architecture;

[0020] Figure 7 for Figure 4 A schematic diagram of coupled signal transmission in the equivalent circuit shown;

[0021] Figure 8 A schematic diagram illustrating the shielding and conduction effect of an existing flat-plate transformer;

[0022] Figure 9 This is a schematic diagram illustrating the shielding and conduction effect of the flat-plate transformer of the present invention. Detailed Implementation

[0023] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Those skilled in the art will appreciate that these descriptions are merely descriptive and exemplary and should not be construed as limiting the scope of protection of the present invention.

[0024] Example

[0025] like Figures 1-3 As shown, existing planar transformers use a conventional shielding design, characterized by better shielding effectiveness the closer the shielding circuit is to the grounding terminal. However, at the end of the shield, due to the inductance, a voltage exists at the shielding terminal, changing accordingly with the switching power supply's on and off states. This is equivalent to the primary winding coupling the signal to the shielding winding, and then from the shielding winding to the secondary winding. Further simplification is equivalent to the signal emitted by the primary winding of magnetic core T1 being directly coupled to its secondary NS winding, turning the secondary circuit into a large transmitting antenna, resulting in a very poor overall EMC performance.

[0026] The EMC-improved flat-plate transformer of this invention consists of a bridge rectifier circuit, a magnetic core T1, and a control circuit. The primary side of the magnetic core T1 has a main operating OC winding, a VCC power supply winding, and a SHIELD winding (also known as a "shielding winding"). The secondary side of the magnetic core T1 has an NS output winding.

[0027] This invention abandons the traditional shielding winding method and adopts a layout and setting of dual-wire parallel winding of VCC power supply winding and SHIELD winding, as shown in the design schematic diagram. Figure 4 As shown, its overall reflection architecture principle diagram is as follows: Figure 5As shown. The same-name terminal of the VCC power supply winding (i.e., the starting point of the VCC power supply winding) is grounded after passing through diode D1 and parasitic capacitor C2 in sequence, while the non-same-name terminal of the VCC power supply winding (i.e., the ending point of the VCC power supply winding) is grounded.

[0028] One of the most important creative aspects of this invention is that the same-name terminal (i.e., the starting point of the SHIELD winding) of the SHIELD winding is grounded, while its non-same-name terminal (i.e., the ending point of the SHIELD winding) is left floating at the end. In other words, the end point of the VCC power supply winding is the starting point of the SHIELD winding. Alternatively, as another implementation, the polarity of the SHIELD winding can be interchanged. That is, the non-same-name terminal (i.e., the starting point of the SHIELD winding) of the SHIELD winding is connected to the non-same-name terminal of the VCC power supply winding and grounded, while its same-name terminal (i.e., the ending point of the SHIELD winding) is left floating at the end. Its structure is as follows: Figure 6 As shown.

[0029] With the above structure, since the VCC power supply winding and the SHIELD winding are bi-wire parallel windings, each winding itself generates a coupling capacitor. Each winding has a grounding point at its respective start and end point, and the induced voltages are coupled to ground through the parasitic capacitance C2. In this structure, the coupling signal from the primary winding of magnetic T1 to the SHIELD winding will be guided to ground through the shielded coupling line, instead of flowing to the NS secondary winding. Its equivalent circuit is as follows: Figure 7 As shown.

[0030] Meanwhile, this invention combines the SHIELD winding and VCC winding, and the shielding and power supply design can be completed with only one PCB board, which can significantly reduce the cost of the planar transformer.

[0031] Actual testing showed that the shielding and conduction effects of this invention are as follows: Figure 9 As shown, the shielding conduction effect of a traditional planar transformer is as follows: Figure 8 As shown in the figure. Data comparison shows that the shielding conduction effect of the present invention can reduce the conduction effect by 10dB compared with the traditional shielding conduction effect, which is very significant.

[0032] To better realize this invention, as another important inventive point, the control circuit described in this invention can be implemented by the following two schemes. The first scheme is detailed in the appendix. Figure 5 As shown, the control circuit is composed of integrated chip U1, which is implemented using the DK065 chip. During connection, its HV pin is connected to both the positive terminal of the bridge rectifier circuit output and the starting point of the primary coil of the main working OC winding, its SW pin is connected to the end point of the primary coil of the main working OC winding, and its CS pin is grounded through resistor R1.

[0033] Meanwhile, capacitor C1 is connected in series between the positive and negative terminals of the bridge rectifier circuit output, with the negative terminal of the bridge rectifier circuit grounded. The N-terminus of diode D1 is connected to the VCC pin of integrated chip U1 to provide operating voltage for integrated chip U1.

[0034] The second scheme for the control circuit is as follows: Figure 6 As shown, it is composed of an integrated chip U2 and a MOS-N field-effect transistor or a Gan transistor. That is, in the second scheme, the control circuit can be composed of an integrated chip U2 and a MOS-N field-effect transistor, or it can be composed of an integrated chip U2 and a Gan transistor. MOS-N field-effect transistors and Gan transistors have the same function and role.

[0035] To ensure optimal performance, the integrated chip U2 can be implemented using RM6665, NCP1342, MK2697G, HL9550, DAP030H, SC3021, KP2206, SC3057, SW1106, INN3370, or UCC27782 integrated chips, all of which have similar or identical functions.

[0036] During connection, the HV pin of integrated chip U2 is simultaneously connected to the positive terminal of the bridge rectifier output and the starting point of the primary coil of the main working OC winding. The ending point of the primary coil of the main working OC winding is connected to the drain of a MOS-N field-effect transistor or a Gan transistor. The gate of the MOS-N field-effect transistor or a Gan transistor is connected to the PWM pin of integrated chip U2, and the source of the MOS-N field-effect transistor or a Gan transistor is grounded through resistor R1. The VCC pin of integrated chip U2 is connected to the junction of diode D1 and parasitic capacitance C2. Simultaneously, a Zener diode D3 is connected in series between the source and drain of the MOS-N field-effect transistor or a Gan transistor.

[0037] As described above, the present invention can be implemented well.

Claims

1. An improved EMC flat-plate transformer, mainly composed of a bridge rectifier circuit, a magnetic core T1, and a control circuit, characterized in that, The primary side of magnetic core T1 is provided with a main working OC winding, a VCC power supply winding, and a SHIELD winding, and the secondary side of magnetic core T1 is provided with an NS output winding. The positive terminal of the bridge rectifier circuit output is connected to the control circuit and the main working OC winding, respectively, and its negative terminal is connected to the control circuit, the VCC power supply winding, and the SHIELD winding, respectively. The VCC power supply winding and the SHIELD winding are double-wire parallel windings. The same-name terminal of the VCC power supply winding is grounded after passing through diode D1 and parasitic capacitor C2 in sequence, and the non-same-name terminal of the VCC power supply winding is grounded. The same-name terminal of the SHIELD winding is grounded, and its non-same-name terminal is left floating at the end; or the non-same-name terminal of the SHIELD winding is grounded, and its same-name terminal is left floating at the end. The shielding signal between the main working OC winding and the SHIELD winding is directly guided to the ground wire.

2. The EMC-improved flat-plate transformer according to claim 1, characterized in that, The VCC power supply winding and the SHIELD winding share the same PCB board.

3. The EMC-improved flat-plate transformer according to claim 1, characterized in that, The control circuit is composed of an integrated chip U1 with model number DK065. Its HV pin is connected to the positive terminal of the bridge rectifier circuit output and the starting point of the primary coil of the main working OC winding. Its SW pin is connected to the ending point of the primary coil of the main working OC winding. Its CS pin is grounded through resistor R1. Its VCC pin is connected to the connection point of diode D1 and parasitic capacitor C2.

4. The EMC-improved flat-plate transformer according to claim 1, characterized in that, The control circuit consists of an integrated chip U2 and a MOS-N field-effect transistor or a Gan transistor. The HV pin of the integrated chip U2 is connected to both the positive terminal of the bridge rectifier output and the starting point of the primary coil of the main working OC winding. The ending point of the primary coil of the main working OC winding is connected to the drain of the MOS-N field-effect transistor or the Gan transistor. The gate of the MOS-N field-effect transistor or the Gan transistor is connected to the PWM pin of the integrated chip U2. The source of the MOS-N field-effect transistor or the Gan transistor is grounded through a resistor R1. The VCC pin of the integrated chip U2 is connected to the junction of diode D1 and parasitic capacitance C2.

5. The EMC-improved flat-plate transformer according to claim 4, characterized in that, The integrated chip U2 is an RM6665 integrated chip, an NCP1342 integrated chip, an MK2697G integrated chip, or an HL9550 integrated chip.

Images