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EP-4272232-B1 - A TRANSFORMER

EP4272232B1EP 4272232 B1EP4272232 B1EP 4272232B1EP-4272232-B1

Inventors

  • ZHANG, HUI
  • XIONG, Zhian
  • HU, GUOFU

Dates

Publication Date
20260506
Application Date
20211224

Claims (12)

  1. A transformer comprising a winding structure, wherein the winding structure comprises: a first, primary side, coil (40) having first and second ends, the first coil (40) being a part of a primary side circuit; a second, secondary side, coil (50) having first and second ends, the second coil (50) being a part of a secondary side circuit; a first wire (60); and a second wire (70), the first wire (60) and the second wire (70) are different from the first coil (40) and the second coil (50); wherein a first end of the first wire (60) is connected to the primary side wherein the first end of the first wire (60) is electrically connected to a cold point of the primary side circuit, wherein at least one of the first wire and the second wire is insulated by an insulating coating, wherein the first and second wires are alongside and adjacent each other, thereby to define a capacitance (C Y ) between them, and are wound into the coil structure of the transformer, wherein a cold point is a point that is decoupled from a high frequency dv/dt, thereby the capacitance (C Y ) forming a Y-capacitor across the primary side and the secondary side for suppressing EMI, wherein the first and second wires (60,70) extend within a space between the first and second coils and wherein the first coil is wound around an axis (30) at a radially inner portion of the transformer, the second coil is wound around the axis at a radially outer portion of the transformer, and the first and second wires are wound at a radially middle portion between the radially inner and the outer portions, characterized in that a first end of the second wire (70) is connected to the secondary side wherein the first end of the second wire (70) is electrically connected to a cold point of the secondary side circuit.
  2. The transformer of claim, wherein: the first end of the first wire (60) is electrically coupled to a ground of the primary side circuit, or the first end of the first wire (60) is electrically coupled to a high voltage end of the primary side circuit; and the first end of the second wire (70) is electrically coupled to a ground of the secondary side circuit, or the first end of the second wire (70) is electrically coupled to a high voltage end of the secondary side circuit.
  3. The transformer of claim 2, wherein the high voltage end of the primary side circuit is connected to an input voltage, and high voltage end of the secondary side circuit is connected to a load.
  4. The transformer of claim 1 or 2, wherein a second end of the first wire (60) is electrically floating and a second end of the second wire (70) is electrically floating, without being connected to any point in the primary side circuit and secondary side circuit.
  5. The transformer of any one of claims 1 to 4, wherein: the first end (42) of the first coil (40) is a low voltage end relative to a second end (44) of the first coil (40) and is adapted to be connected to a current flow-in terminal of a switch (80); the second end (44) of the first coil is adapted to receive an input voltage; the first wire (60) comprising a connection terminal, at its first end, adapted to be coupled to a current flow-out terminal of the switch (80); the first end (52) of the second coil (50) is a low voltage end relative to the second end (54) of the second coil (50) and is adapted to be connected to a negative terminal of a load (82); and the second end (54) of the second coil (50) is adapted to be connected to a positive terminal of the load (82).
  6. The transformer of claim 5, wherein the transformer is adapted to be used in an isolated power converter comprising a primary side and a secondary side, wherein: the first (40) coil and the first wire (60) are adapted to be placed in the primary side; and the second coil (50) and the second wire (70) are adapted to be placed in the secondary side.
  7. The transformer of claim 5 or 6, wherein the first end of the first coil (40) is electrically coupled to the current flow-out terminal of the switch (80) via a sensing resistor (Rsense).
  8. The transformer of any one of claims 1 to 7, wherein the said at least one of the first wire (60) and the second wire (70) is triple insulated.
  9. The transformer of any one of claims 1 to 8, wherein the length and diameter of the first wire (60) and the second wire (70) are adapted to form an effective area of the anode and cathode of an effective capacitor corresponding to the capacitance, a distance between the first wire and the second wire is adapted to form the effective space between the anode and cathode of the effective capacitor, and the insulating coating has a dielectric constant thereby providing the dielectric in the space.
  10. The transformer of any one of claims 1 to 9, wherein the capacitance is in the range 1pF to 1nF.
  11. A LED lighting driver comprising: an output for coupling to an LED lighting load; and a switched mode flyback converter for delivering energy to the output and to the LED lighting load, wherein the flyback converter comprises the transformer of any one of claims 1 to 13, functioning as a flyback transformer, wherein the second coil is connected to the output.
  12. A LED lighting device comprising: a LED lighting load; and the LED lighting driver of claim 11, wherein the output of the LED lighting driver is connected to the LED lighting load.

Description

FIELD OF THE INVENTION This invention relates to transformers, for example flyback transformers used in LED lighting drivers. BACKGROUND OF THE INVENTION Solid state lighting units, and in particular LED-based (retrofit) lamps, are used more and more in home buildings and offices. Besides their high efficiency they also attract consumers due to new design features, different color temperatures, dimming ability etc. To fit LED lighting to existing mains lighting fixtures, each LED light unit makes use of a converter circuit, for converting the AC mains into a DC drive signal, and also for reducing the voltage level. The converter circuit typically comprises a rectifier and a switched mode power converter. There are various possible designs of switched mode power converter. A low-cost switched mode power converter is a single stage converter, such as a buck converter or a buck-boost converter. In both cases, there is a main inductor which controls the delivery of energy to the load. A main power switch controls the supply of energy from the input to the main inductor. For isolation/safety requirement, isolated converters such as flyback converters are also used, which have a transformer with a primary winding connected to the input and the main power switch, and a secondary winding connected to the load. Energy is converted from the primary winding to the secondary winding via an electro-magnetic-electro conversion. US2020357571A1 discloses a transformer structure wherein the primary coil, the secondary coil, and multiple auxiliary coils are wound into the transformer structure. Tolerating electromagnetic interference (EMI) is generally challenging. It is known to add a dedicated and discrete capacitor such as a Y-capacitor between the two grounds of both the primary side and the secondary side to suppress the EMI, but the discrete capacitor takes up area on the PCB. There is therefore a need for an improved solution to provide the Y-capacitor in a space-saving manner. SUMMARY OF THE INVENTION The invention is defined by the claims. It is a concept of the invention to provide a transformer comprising a winding structure which forms a primary side coil and a secondary side coil. Additionally incorporated into this winding structure are first and second wires. The first wire is electrically coupled to a primary side circuit including the first coil and the second wire is electrically coupled to a secondary side circuit including the second coil, and the first wire and the second wire define a capacitance between them. This capacitance has a value which may be controlled by design, and it functions as a controllable parasitic capacitance of the transformer. This capacitance may for example be used for EMI suppression. According to examples in accordance with an aspect of the invention, there is provided a transformer comprising a winding structure, wherein the winding structure comprises: a first, primary side, coil having first and second ends, the first coil being a part of a primary side circuit;a second, secondary side, coil having first and second ends, the second coil being a part of a secondary side circuit;a first wire; anda second wire, the first wire and the second wire are different from the first coil and the second coil; anda first end of the first wire is connected to the primary side wherein the first end of the first wire is electrically connected to a cold point of the primary side circuit and a first end of the second wire is connected to the secondary side wherein the first end of the second wire is electrically connected to a cold point of the secondary side circuit;wherein at least one of the first wire and the second wire is insulated by an insulating coating,wherein the first and second wires are alongside and adjacent each other, thereby to define a capacitance between them, and are wound into the coil structure of the transformer. This transformer makes use of additional conducting wires (in addition to the primary and secondary coils) to define a capacitance. They are however part of the structure of the transformer, and thus integrated into the structure of the transformer. One end of the additional first wire is electrically connected to a primary side circuit (including the primary coil) and one end of the second wire is electrically connected to a secondary side circuit (including the secondary coil), so that they form a parasitic capacitance between the primary and secondary sides. This parasitic capacitance is thus more accurately defined, and it may be used to function as a Y-capacitor for providing EMI suppression. Thus, a dedicated discrete Y-capacitor can be provided and the PCB size can be reduced. The transformer is for example used in a LED driver and the capacitor is used to provide EMI suppression between the primary and secondary sides of transformer. The first and second wires are for example wound using a bifilar method. The two wires in this way are implemented as add