WO2024077528A1

WO2024077528A1 - GaN-BASED SWITCHED-MODE POWER SUPPLY WITH PLANAR TRANSFORMER

Info

Publication number: WO2024077528A1
Application number: PCT/CN2022/124952
Authority: WO
Inventors: Yanbo Zou; Fada Du; Yulin Chen; Chao Tang
Original assignee: Innoscience (Shenzhen) Semiconductor Co., Ltd.
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2024-04-18
Also published as: CN116076011A

Abstract

A switched mode power supply is provided. The power supply includes a flyback converter with a GaN-based power semiconductor transistor and a planar transformer. The planar transformer includes a magnetic core and primary and secondary planar coil windings. The magnetic core has an upper core and a lower core being configured to accept the primary and the secondary planar coil windings. The lower core has at least three projections including two peripheral projections and a central projection being surrounded by the primary and the secondary planar coil windings. The central projection and the two peripheral projections have a same height such that there is no air gap between the central projection of the lower core and the upper core when the two peripheral projections contact the upper core. The central projection being made of iron powder and the two peripheral projections being made of ferrite material.

Description

GaN-BASED SWITCHED-MODE POWER SUPPLY WITH PLANAR TRANSFORMER

Field of the Invention:

The present invention generally relates to GaN-based switched mode power supplies. More specifically, the present invention relates to GaN-based switched mode power supplies with planar transformers exhibiting improved electrical and magnetic properties.

Background of the Invention:

Switched mode power supplies are increasingly used in power converters from AC to DC and in electrical battery charging applications (mobile electronics, electric vehicles) . Switched mode power supplies switch between full-on and full-off states with minimal time spent in transitions, which reduces energy wastage. Switching may take place at high frequencies up to several MHz; as a result, smaller transformers and other components (e.g., capacitors, inductors) may be used, permitting the overall footprint of power supplies and power converters to be reduced.

One technique for reducing the size of the transformer in switched mode power supplies is through the use of a planar transformer. In planar transformers, transformer coils are typically deposited on substrates using printed circuit techniques. The coils are configured to surround magnetic core for raising the level of magnetic flux. For certain types of switched mode power supplies, gapped magnetic core is used to avoid saturation of inductance. However, the air gap may cause leakage magnetic flux lines which pass through the transformer coils such that eddy current loss is generated and system efficiency is reduced. Thus, there is a need in the art for improved GaN-based switched mode power supplies with improved planar transformers with improved magnetic and electrical characteristics.

Summary of the Invention:

In accordance with one aspect of the present disclosure, a switched mode power supply is provided. The power supply includes a flyback converter with a GaN-based power semiconductor transistor and a planar transformer. The planar transformer includes a magnetic core and primary and secondary planar coil windings. The magnetic core has an upper core and a lower core being configured to accept the primary and the secondary planar coil windings. The lower core has at least three projections including two peripheral projections and a central projection being surrounded by the primary and the secondary planar coil windings. The central projection and the two peripheral projections have a same height such that there is no air gap between the central projection of the lower core and the upper core when the two peripheral projections contact the upper core. The central projection being made of iron powder and the two peripheral projections being made of ferrite material.

By making the central projection of the magnetic core with iron powder, no air gap between the upper and lower cores is required to avoid saturation of inductance. Therefore, leakage magnetic flux lines is avoided and system efficiency is improved.

Brief Description of the Drawings:

FIG. 1 depicts a switched mode power supply with flyback converter according to an embodiment;

FIG. 2 is a cross-sectional side view of a planar transformer that may be used in the power supply of FIG. 1;

FIG. 3 is a perspective view of the planar transformer of FIG. 2;

FIG. 4 depicts a switched mode power supply with an active clamp flyback converter according to an embodiment.

Detailed Description

In the following description, preferred examples of the present disclosure will be set forth as embodiments which are to be regarded as illustrative rather than restrictive. Specific details may be omitted so as not to obscure the present disclosure; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

Turning to the drawings in detail, FIG. 1 is a switched mode power supply 10 according to an embodiment that includes a flyback converter configuration. Power supply 10 includes a GaN-based power semiconductor transistor 110 that is the main switch of the circuit. Transistor 110 is switched on and off at extremely high frequency, up to the megahertz range. When the GaN-based switching transistor 110 is in the “on” state, it conducts current; consequently, the voltage drop across transistor 110 is at its minimal value. In the “off” state, no current flows through transistor 110. This switching creates a high-frequency AC intermediary. The AC is rectified to produce the desired DC output when the switched mode power supply is used as an AC to DC converter. Alternatively, a DC input may be used and an output DC may be stepped up or stepped down.

The switched mode power supply of FIG. 1 has a flyback converter configuration. The flyback converter is a type of buck-boost converter that can produce an output voltage greater or less than the input voltage depending upon the duty cycle. The flyback converter configuration includes a clamper circuit for shifting an input voltage supplied to the transformer, The clamper circuit may include a clamp capacitor 137 having one end electrically connected to the input voltage supply; a resistor 138 connected in parallel to the clamp capacitor 137; and a clamp diode 135 having a cathode electrically connected to the other end of the clamp capacitor 137 and an anode electrically connected to the primary winding.

When the GaN-based switching transistor 110 is closed/off, a primary coil 190 (as shown in FIG. 2) of transformer 100 is directly connected to an input voltage source 107. The primary current and magnetic flux in the transformer increases. As a result, energy is stored in transformer 100. An induced voltage in the secondary coil 192 will be negative. Capacitor 120 supplies energy to the output load 130. When the GaN-based switching transistor is open/on, the primary current and magnetic flux drops. The secondary voltage is positive, and current flows from the transformer 100 and recharges capacitor 120.

In order to increase the efficiency of the switched mode power supply 10, the transformer of FIG. 2 is provided. In the transformer of FIG. 2, the magnetic flux lines are shaped by the configuration of the magnetic core portions, as discussed in further detail below. The magnetic flux lines avoid the primary and second coils in order to reduce the loss in the primary and second coils when the magnetic flux lines pass through the coil (as seen in FIG. 3A) . Transformer 100 includes a magnetic core that includes an upper core 150 and a lower core 160. The lower core includes three projections: two peripheral projections 170 and a central projection 180. the central projection and the two peripheral projections 170 have a same height such that there is no air gap between the central projection of the lower core 180 and the upper core when the two peripheral projections contact the upper core 172.

In some embodiments, the central projection 180 is made of iron powder and the two peripheral projections 170 are made of ferrite material.

Surrounding the central projection 180 are primary planar coils 190 and secondary planar coils 192. The

planar coils

190 and 192 may be metal lines (e.g., copper, nickel) deposited on a substate such as a printed circuit board 196 (as shown FIG. 3) or polymer substrate using printed circuit techniques. However, any technique may be used to create the

planar metal coils

190 and 192. In the configuration shown in FIG. 2, the primary coils 190 are surrounded on the upper and lower sides by secondary coils 192; other arrangements may also be used. Alternative arrangements include alternating primary and secondary coils, or a set of one or more primary coils positioned adjacent to a set of one or more secondary coils. Each

element

190 and 192 may be part of a set of side-by-side coils arranged in a planar spiral format, as seen more clearly in FIG. 3

FIG. 3 is a perspective view of the planar transformer of FIG. 2 with the primary coils 190 (not visible in FIG. 3) and secondary coils 192 disposed on substrates 196. Each of the coils is disposed in a spiral configuration surrounding the central projection 180 such that plural metal lines are in a coplanar configuration in each of the primary and secondary coil layers. Note that, depending on the selected number of windings, more or fewer layers of primary and secondary coils may be used in FIG. 3. Other optional layers (not shown) may provide shielding or insulation or other electrical components.

FIG. 4 is a switched mode power supply 20 including an active clamped flyback converter configuration according to another embodiment of the present invention. The power supply with active clamped flyback converter 20 differs from the power supply with a flyback converter 10 of FIG. 1 in that a switch 212 (that may be a GaN-based power semiconductor transistor) replaces the clamp diode 135. In the active clamped flyback converter of FIG. 4, energy from the leakage inductance of transformer 200 is reused and supplied to load 230. This increases the efficiency of the switched mode power supply 210. Capacitor 220 alternately stores energy from transformer 200 and supplies energy to output load 230 as in the embodiment of FIG. 1, above.

In the power supply with active clamped flyback converter of FIG. 4, the peak voltage across the main switch 215 (GaN-based transistor) may be reduced; as a result, the on-resistance and conduction loss may be reduced. There is also a reduction in electromagnetic interference in the circuit of FIG. 4.

INDUSTRIAL APPLICABILITY:

The switched mode power supplies of the present invention may be used in AC-DC converters, DC-DC converters, electronic device (e.g., mobile phone) battery chargers, and electronic vehicle battery chargers.

While the present disclosure has been described and illustrated with reference to specific embodiments thereof, these descriptions and illustrations are not limiting. It should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the present disclosure as defined by the appended claims. The illustrations may not necessarily be drawn to scale. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus due to manufacturing processes and tolerances. There may be other embodiments of the present disclosure which are not specifically illustrated. The specification and the drawings are to be regarded as illustrative rather than restrictive. Modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the present disclosure. All such modifications are intended to be within the scope of the claims appended hereto. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations.

As used herein, terms "approximately" , "basically" , "substantially" , and "about" are used for describing and explaining a small variation. When being used in combination with an event or circumstance, the term may refer to a case in which the event or circumstance occurs precisely, and a case in which the event or circumstance occurs approximately. As used herein with respect to a given value or range, the term "about" generally means in the range of ±10%, ±5%, ±1%, or ±0.5%of the given value or range. The range may be indicated herein as from one endpoint to another endpoint or between two endpoints. Unless otherwise specified, all the ranges disclosed in the present disclosure include endpoints. The term "substantially coplanar" may refer to two surfaces within a few micrometers (μm) positioned along the same plane, for example, within 10 μm, within 5 μm, within 1 μm, or within 0.5 μm located along the same plane. When reference is made to "substantially" the same numerical value or characteristic, the term may refer to a value within ±10%, ±5%, ±1%, or ±0.5%of the average of the values.

Claims

A switched-mode power supply comprising:

a flyback converter including:

a GaN-based power semiconductor transistor;

a planar transformer including a magnetic core and primary and secondary planar coil windings;

wherein:

the magnetic core includes an upper core and a lower core being configured to accept the primary and the secondary planar coil windings;

the lower core having at least three projections including two peripheral projections and a central projection being surrounded by the primary and the secondary planar coil windings;

the central projection and the two peripheral projections have a same height such that there is no air gap between the central projection of the lower core and the upper core when the two peripheral projections contact the upper core;

the central projection being made of iron powder and the two peripheral projections being made of ferrite material.
The switched-mode power supply of claim 1, wherein the primary and secondary planar coil windings are disposed on one or more planar substrates.
The switched-mode power supply of claim 2, wherein the one or more planar substrates include one or more printed circuit boards.
The switched-mode power supply of claim 1, wherein the primary planar coil windings are surrounded in upper and lower sides by secondary coil windings.
The switched-mode power supply of claim 1, wherein the flyback converter further includes a clamper circuit for shifting an input voltage supplied to the transformer.
The switched-mode power supply of claim 1, wherein the flyback converter further includes an output capacitor for storing power from the transformer in an off-state.
The switched-mode power supply of claim 1, wherein the flyback converter further includes a primary switch electrically coupled to the primary planar coil winding and being switched to allow or block a current flowing through the primary planar coil winding.
The switched-mode power supply of claim 1, wherein the flyback converter further includes a synchronous rectifier electrically coupled to the secondary planar coil winding and being switched to allow or block a current flowing through the secondary planar coil winding.
An electronic device charger including the switched-mode power supply of claim 1.
The electronic device charger of claim 9, wherein the primary and secondary planar coil windings are disposed on one or more planar substrates.
The electronic device charger of claim 10, wherein the one or more planar substrates include one or more printed circuit boards.
The electronic device charger of claim 9, wherein the primary planar coil windings are surrounded in upper and lower sides by secondary coil windings.
The electronic device charger of claim 9, wherein the flyback converter further includes a clamper circuit for shifting an input voltage supplied to the transformer.
The electronic device charger of claim 9, wherein the flyback converter further includes an output capacitor for storing power from the transformer in an off-state.
The electronic device charger of claim 9, wherein the flyback converter further includes a primary switch electrically coupled to the primary planar coil winding and being switched to allow or block a current flowing through the primary planar coil winding.
The electronic device charger of claim 9, wherein the flyback converter further includes a synchronous rectifier electrically coupled to the secondary planar coil winding and being switched to allow or block a current flowing through the secondary planar coil winding.
An AC-to-DC converter including the switched-mode power supply of claim 1.
The AC-to-DC converter of claim 17, wherein the primary and secondary planar coil windings are disposed on one or more planar substrates.
The AC-to-DC converter of claim 18, wherein the one or more planar substrates include one or more printed circuit boards.
The AC-to-DC converter of claim 17, wherein the primary planar coil windings are surrounded in upper and lower sides by secondary coil windings.
The AC-to-DC converter of claim 17, wherein the flyback converter further includes a clamper circuit for shifting an input voltage supplied to the transformer.
The AC-to-DC converter of claim 17, wherein the flyback converter further includes an output capacitor for storing power from the transformer in an off-state.
The AC-to-DC converter of claim 17, wherein the flyback converter further includes a primary switch electrically coupled to the primary planar coil winding and being switched to allow or block a current flowing through the primary planar coil winding.
The switched-mode power supply of claim 1, wherein the flyback converter further includes a synchronous rectifier electrically coupled to the secondary planar coil winding and being switched to allow or block a current flowing through the secondary planar coil winding.