Shielded power transformer

Abstract

Disclosed are shielded power transformers and power converters using these transformers. In some embodiments, the shielded power transformer includes a magnetic core, a primary winding, a first secondary winding, and a second secondary winding. The transformer includes a first shield winding having the same voltage potential direction as the primary winding and connected in series with the primary winding to carry the current flowing through the primary winding. The transformer also includes a second shield winding having a voltage potential direction opposite to the primary winding and connected from the primary ground to a floating terminal. The first secondary winding, the second secondary winding, the first shield winding, and the second shield winding can each have approximately the same number of turns.

Description

Background Art

[0001] Power transformers use electromagnetic coupling to transfer energy from one coil to another. The ratio of the windings between the primary and secondary coils, also known as the "turns ratio," sets the relationship between the voltage and current for the coils. In practice, transformers can have some undesirable effects, such as the generation of electromagnetic interference, and energy losses due to eddy currents and other effects. Summary of the invention

[0002] In some embodiments, the transformer includes a shield that reduces electromagnetic interference (EMI) by generating a lower level of noise. The shield can have two segments arranged on opposite sides of the primary coil. For example, as an extension of the primary coil that carries the current of the primary coil, the first shield segment can be connected in series with the primary coil. This allows the winding of the first shield segment to act as both a shield and a part of the primary coil, wherein the winding of the first shield segment contributes to the total number of turns of the primary coil. The second shield segment can be arranged so that one terminal is connected to the primary ground and the other terminal is floating. The transformer can have two secondary coils, and the first shield segment and the second shield segment can each have a number of turns that is approximately equal to the number of turns of the secondary coil.

[0003] Transformers can be used in various types of power converters. For example, transformers can be used in AC-DC power adapters or DC-DC power adapters. In some embodiments, an AC / DC power adapter for consumer electronics may include an isolated DC-DC converter circuit that includes a high-frequency transformer as discussed in this document. The high-frequency transformer provides galvanic isolation and can provide high-efficiency power transmission.

[0004] Due to the large inter-winding capacitance between the primary and secondary windings, which makes high-frequency transformers the main conduction path for conducted common-mode noise, conventional transformers often generate a large amount of common-mode noise. To meet common-mode noise requirements, two stages of EMI filters may be required, which increases the size and cost of the power adapter. The transformer can include a shield to reduce noise, but typical shields reduce the electrical efficiency of the transformer, for example due to eddy currents in the shield windings.

[0005] Compared to conventional transformers, the transformer designs discussed in this document can reduce common mode noise while providing higher efficiency than typical shielded transformers. For example, connecting the first shield segment in series with the primary coil avoids eddy current losses that would otherwise be generated in the first shield segment. In addition, since the windings of the first shield segment contribute to the total number of turns of the primary coil, the primary coil can be reduced by a corresponding number of turns, allowing the transformer to be smaller than a typical shielded transformer and have lower winding losses. The benefit of lower noise can allow the use of smaller EMI filters, and in some cases, only one EMI filter can be used on the primary side.

[0006] In some embodiments, a shielded transformer includes: a magnetic core; a primary winding; a first secondary winding and a second secondary winding, the first secondary winding and the second secondary winding having approximately equal numbers of turns; and an electromagnetic shield, including: a first shield winding having the same voltage potential direction as the primary winding and being connected in series with the primary winding to carry current flowing through the primary winding, wherein the first shield winding has a number of turns approximately equal to the number of turns of each of the secondary windings, and wherein the first shield winding is located between the primary winding and the first secondary winding; and a second shield winding having a voltage potential direction opposite to the primary winding and being connected from the primary ground to a floating terminal, wherein the second shield winding has a number of turns approximately equal to the number of turns of each of the secondary windings, and wherein the first shield winding is located between the primary winding and the second secondary winding.

[0007] Some embodiments may include one or more of the following features. For example, in some embodiments, the first shield winding is evenly arranged along the interface between the primary winding and the first secondary winding; and wherein the second shield winding is evenly arranged along the interface between the primary winding and the second secondary winding.

[0008] In some embodiments, the secondary winding and the shield winding have turns within 5% of each other.

[0009] In some embodiments, a shielded power transformer includes a winding of wire around a ferrite core.

[0010] In some embodiments, the wire windings are concentrically arranged around the central portion of the ferrite core in the following order from the inner winding outward: one of the secondary windings, one of the shield windings, the primary winding, another of the shield windings, and another of the secondary windings.

[0011] In some embodiments, a shielded power transformer is implemented using planar magnetics with windings implemented using traces on stacked substrate layers.

[0012] In some embodiments, the stacked substrate layers are arranged along the axis in the following order from top to bottom: one of the secondary windings, one of the shield windings, the primary winding, another one of the shield windings, and another one of the secondary windings.

[0013] In some embodiments, the first shield winding and the second shield winding each have a terminal connected to a primary ground.

[0014] In some embodiments, the shielded power transformer includes four secondary windings, each secondary winding having a substantially equal number of turns. The shielded power transformer includes a wire winding around a core. The wire winding is arranged concentrically around the core in the following order from the inner winding outward: the first of the four secondary windings, the second of the four secondary windings, one of the shield windings, the primary winding, the other of the shield windings, the third of the four secondary windings, and the fourth of the four secondary windings. The first of the four secondary windings or the second of the four secondary windings is one of the first secondary winding or the second secondary winding, and the third of the four secondary windings or the fourth of the four secondary windings is the other of the first secondary winding or the second secondary winding.

[0015] In some embodiments, the shielded power transformer includes a third secondary winding and a fourth secondary winding, wherein the first secondary winding, the second secondary winding, the third secondary winding, and the fourth secondary winding each have a substantially equal number of turns; wherein the shielded power transformer includes a planar magnetic element in the case where the windings are arranged as a substantially planar coil; wherein the substantially planar coil is stacked along the axis in the following order from top to bottom: the first of the four secondary windings, the second of the four secondary windings, one of the shield windings, the primary winding, the other of the shield windings, the third of the four secondary windings, and the fourth of the four secondary windings. The first of the four secondary windings or the second of the four secondary windings is one of the first secondary winding or the second secondary winding, and the third of the four secondary windings or the fourth of the four secondary windings is the other of the first secondary winding or the second secondary winding.

[0016] In some embodiments, a first one of the four secondary windings and a second one of the four secondary windings have opposite voltage potential directions; and a third one of the four secondary windings and a fourth one of the four secondary windings have opposite voltage potential directions.

[0017] In some embodiments, a shielded power transformer has four secondary windings, each secondary winding having an approximately equal number of windings; a first group of two of the secondary windings arranged with the primary winding and the shield winding between them are configured so that the first group of two of the secondary windings (i) have the same voltage potential direction and (ii) are connected in series to act as a single effective secondary coil; a second group of two of the secondary windings arranged with the primary winding and the shield winding between them are configured so that the second group of two of the secondary windings (i) have the same voltage potential direction and (ii) are connected in series to act as a single effective secondary coil; the secondary windings in the first group are different from the secondary windings in the second group; and the voltage potential direction of the secondary windings for the first group is opposite to the voltage potential direction of the secondary windings for the second group.

[0018] In some embodiments, a shielded power transformer is configured to use a first shield winding as part of a primary winding such that use of the transformer reduces the voltage supplied to the primary winding when the effective turns ratio between the primary side of the shielded power transformer and one of the secondary windings is the ratio between (i) the sum of the number of turns of the primary winding and the first shield winding and (ii) the number of turns of one of the secondary windings.

[0019] In some embodiments, the first shielding member winding is arranged in the same structure as the first secondary winding, so that basically equal voltage potentials are induced in the first shielding member winding and the first secondary winding; and the second shielding member winding is arranged in the same structure as the first secondary winding, so that basically equal voltage potentials are induced in the second shielding member winding and the second secondary winding.

[0020] In some embodiments, the electromagnetic shield is arranged such that no common mode currents exist between the electromagnetic shield windings and the corresponding secondary windings.

[0021] In some embodiments, the shielded power transformer is configured to induce common-mode current from the primary winding to the electromagnetic shield and cause the common-mode current to flow back to the primary ground, so that the common-mode current circulates only in the primary side and no common-mode current passes between the primary winding and the secondary winding.

[0022] Other embodiments include an AC-DC power adapter including a shielded power transformer.The AC-DC power adapter may include a switch coupled to the secondary winding, the switch configured to operate as part of a synchronous rectifier.

[0023] Other embodiments include a DC-DC converter including a shielded power transformer.The DC-DC converter may include a switch coupled to the secondary winding, the switch configured to operate as part of a synchronous rectifier.

[0024] Other embodiments include a method of converting alternating current from one voltage to another using a shielded electronic transformer.

[0025] Other embodiments include a method of converting alternating current power to direct current power using an AC-DC power adapter.

[0026] Other embodiments include a method of converting a first DC voltage to a second, different DC voltage using a DC-DC converter.

[0027] The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a block diagram illustrating an example of an AC-DC power adapter using a shielded transformer;

[0030] Figure 2 is a block diagram illustrating an example of a DC-DC conversion circuit using a shielded transformer;

[0031] Figure 3A and 3B is used for Figure 2 A cross-sectional view of an example of a shielded transformer for a circuit;

[0032] Figure 4 is a block diagram illustrating an example of a DC-DC conversion circuit using a shielded transformer; and

[0033] Figure 5A and 5B is used for Figure 4 A cross-sectional view of an example of a shielded transformer for a circuit.

[0034] Throughout the various drawings, like reference numbers and designations indicate like elements. DETAILED DESCRIPTION

[0035] Figure 11 is a block diagram illustrating an example of an AC-DC power adapter 100 using a shielded transformer 150. The example uses the transformer 150 as part of a high-efficiency DC-DC conversion circuit. Other adapter designs can use the shielded transformer in other ways, such as directly stepping down an alternating current (AC) input to a low voltage AC. The adapter 100 can be a stand-alone adapter, or can be integrated into a device powered by the adapter 100. In some embodiments, the power adapter 100 is a universal serial bus (USB) Type-C adapter that can be capable of providing an output ranging from approximately 3V to approximately 20V.

[0036] Figure 1 The adapter 100 in the embodiment includes an EMI filter 120, a primary-side rectifying circuit 130, a primary-side signal generating circuit 140, a shielded transformer 150, and a secondary-side rectifying circuit 160. The adapter 100 receives power from an AC power source 110 (such as an electrical outlet). The adapter 100 provides DC power to a load 170.

[0037] In further detail, the AC input is provided to an EMI filter 120 that can at least partially suppress conducted EMI from the power supply. This may involve various passive components, such as capacitors and / or inductors that can be arranged to reduce common mode noise and / or differential mode noise. For example, the inductive portion of the filter can act as a low frequency pass-through device for AC line signals while blocking higher frequencies. In order to suppress common mode noise, inductors and capacitors placed in series with each AC power line can be grounded from both power lines. One or more capacitors connected from one AC power line to another can reduce differential mode noise.

[0038] The output of EMI filter 120 is provided to a primary side rectification circuit 130, which can use any of a variety of types of rectifiers (e.g., a switching rectifier, a diode bridge rectifier, a center-tapped transformer rectifier, etc.) The rectification circuit 130 can optionally include further filtering or voltage regulation circuitry.

[0039] The primary-side signal generating circuit 140, the transformer 150 and the secondary-side rectifying circuit 160 form a DC-DC conversion circuit, and Figure 2 and Figure 4An example is shown in FIG. The primary side signal generating circuit 140 includes, for example, a switching component to generate a switching signal from the output of the rectifier circuit 130 and the tank circuit. For example, pulse frequency modulation (PFM) can be used to generate this switching signal. In the case where the frequency is adjustable to change the output of the converter, this will provide a fixed 50% duty cycle for the primary side signal generating circuit 140. The switching signal can be provided to a tank circuit, such as an LLC tank, which filters the switching signal before the filtered signal is provided to the transformer 150, which typically reduces the voltage from the primary side to the secondary side. Then, the output at the secondary side of the transformer 150 is rectified by the secondary side rectifier circuit 160, which can use a switching rectifier, a diode bridge rectifier, or other rectifier circuit to generate a DC output. Although not shown, the DC output can be optionally further processed, for example, with a filter, a switching converter, a voltage regulator, etc. The DC output (as optionally further processed) is then provided to a DC load 170, which may be any of various types of electronic devices (eg, a phone, a laptop computer, an appliance, an entertainment device, etc.).

[0040] In some embodiments, as with others discussed below, Figure 1 The DC-DC conversion circuit of the present invention operates at a relatively high frequency. For example, although a frequency of about 150kHz is typical, the frequency of the DC-DC conversion circuit is instead approximately 200kHz, 250kHz, 300kHz, 400kHz or higher, and the primary side signal generating circuit 140, the transformer 150 and the secondary side rectifier circuit 160 are designed for higher frequencies.

[0041] Figure 2 2 is a block diagram illustrating an example of a DC-DC conversion circuit 200 using a shielded transformer 250. The circuit 200 includes a primary-side signal generating circuit 240, a shielded transformer 250, and a secondary-side rectifying circuit 260, which show Figure 1 Implementation of the corresponding elements 140, 150 and 160.

[0042] The primary side signal generating circuit 240 receives the AC input from the EMI filter. The two transistors are controlled using PFM to generate a switching output with a duty cycle of 50%. Capacitor C1, series inductor L1 and parallel inductor L2 form an LLC tank circuit that smoothes the switching output from the transistor. The output of the primary side signal generating circuit 240 is provided to the primary side of the shielded transformer 250, for example at the node connecting inductors L1 and L2.

[0043] The shielded transformer 250 has a primary side P, a shield X, and a secondary side S. In the illustrated example, the primary side P includes a single primary coil having two terminals P′ and P″, one at each end. Terminal P′ is connected to receive the output of the primary side signal generating circuit 240 . Terminal P″ is connected to the shield X via connection 252 .

[0044] The shield X has two segments: a first shield segment X1 and a second shield segment X2. The two shield segments X1, X2 each have a terminal connected to a primary ground illustrated as a connection at terminal Y. For example, the primary ground can be the same ground reference used by the primary side signal generating circuit 240. The other ends of the shield segments X1, X2 are connected differently.

[0045] The first shield segment X1 has the same voltage potential direction as the primary coil P. The first shield segment X1 has a terminal X' connected to a terminal P" of the primary coil P (e.g., through connection 252). As a result, the current flowing through the primary coil P also flows through the first shield segment X1. This allows the first shield segment X1 to function both as a part of the primary coil P and as a shield. In particular, the first shield segment X1 is used for both high-frequency shielding and power transmission. This arrangement allows the transformer 250 to reduce power losses compared to an arrangement in which both shield segments have floating or free ends.

[0046] The second shield segment X2 has a terminal X", which is left floating, e.g., not connected. The second shield segment X2 has a voltage potential direction opposite to that of the primary coil P. The difference in voltage potential direction can be achieved by winding the second shield segment X2 in a direction opposite to that of the primary coil. Alternatively, in some embodiments, the effect can be achieved by winding the second shield segment X2 in the same direction as the primary coil P, but by reversing the connection of the second shield segment X2 so that the polarity or voltage potential direction is also reversed. The high change in voltage over time (dv / dt) at the primary side P will induce a common mode current from the primary coil P to the shield, and then the common mode current will flow back to the primary ground through the node Y. The common mode current circulates only in the primary side P, and there is no common mode current between the primary side P and the secondary side S.

[0047] The secondary side S of the transformer 250 has two secondary segments (or coils) S1 and S2. These secondary segments are arranged so that they conduct in opposite directions. For example, the two secondary segments S1 and S2 are connected so that each secondary segment has a common terminal connected at a node Z, which is set to the output to the load 270. When the current flows into the node Z from the segment S1, it will flow out of the node Z through the segment S2. However, in use, since the secondary side rectifier circuit 260 only allows one path at any given time, the current only flows through one of the secondary segments S1 and S2 at a time. As shown, the secondary side rectifier circuit 260 includes a transistor, which acts as a synchronous switching rectifier controlled synchronously with the transistor of the primary side signal generating circuit 240. By alternately opening one of the switches, the output alternates between the secondary segments S1 and S2, thereby providing a rectified output from the different polarities of the secondary segments S1 and S2 relative to the load 270.

[0048] The secondary windings S1, S2 have approximately equal numbers of turns. Typically, approximately equal numbers of turns or substantially equal numbers of turns indicate that the turns are within 10% of each other. Of course, the tolerances can be much tighter, such as within 5%, or within 2.5%, or within 1%, within one turn of each other, or even exactly matched in turns.

[0049] Each of the shield segments X1, X2 has a number of turns that is approximately equal to each other and equal to the number of turns of the secondary segments S1, S2. Therefore, the number of turns of the shield segment X1 can be within 10% of the number of turns of the secondary segment S1, and the number of turns of the shield segment X2 can be within 10% of the number of turns of the secondary segment S2. Of course, the tolerance can be much tighter, such as within 5%, or within 2.5%, or within 1%, within one turn of each other, or even exactly matched in number of turns. It is beneficial for the shield segments X1, X2 and the secondary segments S1, S2 to have approximately the same number of turns, so that the same voltage potential will exist on the shield segments as on the secondary segments S1, S2. As a result, there is no common mode current between the shield segments X1, X2 and the secondary segments S1, S2.

[0050] As discussed further below, shield segments X1, X2 can be placed on opposite sides of the primary coil P such that one shield segment is located between the primary coil P and each of the secondary coils S1, S2. Each shield segment can be evenly distributed along the border between the primary coil P and the nearest secondary coil.

[0051] Figure 3A Can be used as Figure 2250 is a cross-sectional view of an example of a shielded transformer 300. The figure shows an implementation of a wire-wound transformer having a coil wrapped concentrically around a ferrite core 310, and optionally also around a bobbin 312. The various layers can be separated by insulating material, such as one or more layers of insulating tape 314 that provide several thousand volts of isolation.

[0052] The innermost winding represents the first secondary segment S1. The next winding shows the first shield segment X1, which is electrically connected in series with the primary winding P wrapped around the first shield segment X1. The same current flowing through the primary winding P also flows through the first shield segment X1. Then, the second shield segment X2 is wrapped around the primary winding P. As explained above, the second shield segment X2 does not carry current from the primary winding P. Instead, as Figure 2 As shown, the second shield segment X2 has a terminal Y connected to the primary ground and another terminal X'' that is left floating. The second secondary segment S2 is then wrapped around the second shield segment X2.

[0053] The shield segments X1, X2 can be wire windings of similar wire gauge and material as the primary P winding or the secondary S1, S2 windings. Alternatively, the shield segments X1, X2 can be formed of wires of different gauge or type or another conductor (e.g., solid wire, stranded wire, conductive foil, traces on a PCB layer, etc.).

[0054] In this example, each of the secondary segments S1, S2 has the same number of turns, and the shield segments X1, X2 have the same number of turns as the secondary segments S1, S2. The turns of the shield segment X1 act as part of the primary winding, so the total turns ratio between the primary winding P and each of the secondary windings S1, S2 is 3:1. Of course, the transformer 300 can be implemented with any appropriate turns ratio required by the application in which it will be used.

[0055] Figure 3B Can be used as Figure 2 250 is a cross-sectional view of another example of a shielded transformer 350. The transformer 350 is implemented using a planar magnetic device, for example, using traces on a printed circuit board (PCB) layer or multiple PCBs. In this illustration, components 370a-370f represent different PCB layers or PCB components. Each component 370a-370f can include multiple layers of a substrate or even multiple discrete substrate components to carry the coils represented. Similarly, the various components 370a-370f can be combined into a single substrate to carry the coils shown.

[0056] The transformer 350 has a core 360, such as a ferrite material, and has coils carried on a generally flat substrate element 3701-370f, such as a PCB layer. From top to bottom, element 370a carries a coil for a secondary segment S1, and element 370b carries a coil for a shield segment X1, which is connected to receive current through a primary coil P. Elements 370c and 370d carry the primary coil P. Element 370e carries a shield segment X2, which is connected to the primary ground and has a floating end. Element 370f carries a second secondary segment S2.

[0057] exist Figure 3B , cross-sectional elements of the coils are provided as a simple indication of the relative number of turns for the coils. Of course, the actual number of turns used for each coil will vary depending on the application in which the transformer 350 will be used. In this example, the shield segments X1, X2 have the same number of turns, and the number of turns matches the number of turns of the secondary segments S1, S2. The total turns ratio between the primary coil P and each individual secondary segment S1, S2 is 5:1. The two primary layers each show two turns, and the shield segment X1 contributes another turn to the primary, for a total of 5 turns in the illustration, while the secondary segments S1, S2 are each shown with one turn.

[0058] Figure 4 4 is a block diagram illustrating an example of a DC-DC conversion circuit 400 using a shielded transformer 450. The circuit 400 has the features discussed above for the circuit 200, wherein the primary side signal generation circuit 440, the shielded transformer 450, and the secondary side rectification circuit 460 have the features discussed above for the circuit 200. Figure 2 The structure and operation of the components 240, 250 and 260 of FIG. However, as discussed below, the transformer 450 has a different arrangement of secondary segments compared to the transformer 250.

[0059] exist Figure 4 In the example, there are four sub-segments S1, S2, S3 and S4, instead of Figure 2 Two are shown. The secondary segments S1, S2, S3 and S4 and the shield segments X1 and X2 can each have approximately the same number of turns. As discussed above, approximately equal turns or substantially equal turns indicates that the turns are within 10% of each other. Of course, the tolerances can be much tighter, such as within 5%, or within 2.5%, or within 1%, within one turn of each other, or even exactly matched in turns.

[0060] Secondary segments S1 and S3 have the same voltage potential direction relative to load 470 and are connected in series to act as one secondary coil. Similarly, secondary segments S2 and S4 have the same voltage potential direction relative to load 470 and are connected in series to act as another secondary coil. The two effective secondary coils, such as S1+S3 and S2+S4, have voltage potential directions opposite to each other. In other words, the alternating current from the primary coil can induce current in opposite directions in the two effective secondary coils. The difference in voltage potential direction can be achieved by changing the winding direction. For example, both secondary segments S1 and S3 can be wound in a first direction, while both secondary segments S2 and S4 can be wound in a second, opposite direction. Alternatively, in some embodiments, each of the secondary segments S1-S4 can be wound in the same direction, but the connection of one pair (e.g., S1 and S3) can be opposite to the connection of the other pair (e.g., S2 and S4), so that the polarity or voltage potential direction is also reversed.

[0061] As an example, the secondary segments S1-S4 may all be wound in the same direction, and each segment S1-S4 may have a top terminal (e.g., Figure 5A at the top winding) and the bottom terminal (e.g. at Figure 5A Given the same winding direction, the top terminal can be made of Figure 4 The black circle polarity indicator indicates the terminals. Node Z can be connected to the top terminal of secondary segment S2 and the bottom terminal of secondary segment S1. Secondary segment S3 is then connected, wherein its bottom terminal is connected to the top terminal of secondary segment S1 and its top terminal is connected to one of the transistors of the secondary side rectification circuit 460. S4 is then connected, wherein its top terminal is connected to the bottom terminal of secondary segment S1 and its bottom terminal is connected to another transistor of the secondary side rectification circuit 460.

[0062] like Figure 5A and 5B As shown, each effective secondary coil consists of coils physically arranged on opposite sides of the primary coil P. For example, the secondary segments S1 and S2 are placed on one side of the primary coil P, with the shield segment X1 between these segments S1, S2 and the primary coil P. The secondary segments S3 and S4 are placed on the other side of the primary coil P, with the shield segment X2 between these segments S3, S4 and the primary coil P.

[0063] Figure 5A and 5B is used for Figure 4 A cross-sectional view of an example of a shielded transformer for a circuit.

[0064] Figure 5AAn embodiment of a wire wound transformer 500 is shown having a coil wrapped concentrically around a ferrite core 510 and optionally also around a bobbin 512. In transformer 500, the inner windings are secondary segments S2 and S1, which are as shown in FIG. Figure 4 Similarly, the outer windings are secondary segments S3 and S4, which are also parts of different secondary coils. The turns ratio between the primary coil and each secondary coil (e.g., the combination of S1+S3 and the combination of S2+S4) is 11:4 or 2.75:1. Other features of transformer 500 are as follows: Figure 3A The transformer 300 is described.

[0065] Figure 5B An embodiment using a planar magnetic device is shown, where elements 570a-570h represent different layers or substrate elements of the conductors carrying the various coils. Secondary coils S1+S3 and secondary coils S2+S4 each include a segment below the primary coil P and a segment above the primary coil P. In this example, the turns ratio between the primary coil and each secondary coil (e.g., the combination of S1+S3 and the combination of S2+S4) is 5:2 or 2.5:1. Other features of transformer 550 such as for Figure 3B The transformer 350 is described.

[0066] Although this specification contains many details, these details should not be interpreted as limitations on the scope of the invention or what may be claimed, but rather as descriptions of features specific to a particular embodiment of the invention. Certain features described in this specification in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments individually or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed, in some cases one or more features in the claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or a variation of the sub-combination.

[0067] Similarly, although operations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that such operations be performed in the particular order shown or in a continuous order, or that all illustrated operations be performed, to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments.

[0068] Thus, certain embodiments of the invention have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results.

Claims

1. A shielded power transformer, comprising: Magnetic core; Primary winding; a first secondary winding and a second secondary winding, the first secondary winding and the second secondary winding having substantially equal numbers of turns; and An electromagnetic shielding component, the electromagnetic shielding component comprising: a first shield winding having the same voltage potential direction as the primary winding and connected in series with the primary winding to carry current flowing through the primary winding, wherein: The first terminal of the first shield winding is connected to the primary winding, The second terminal of the first shield winding is connected to the primary ground and the first terminal of the second shield winding, the first shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The first shield winding is located between the primary winding and the first secondary winding; and The second shield winding, having a voltage potential direction opposite to the primary winding, has the first terminal connected to the primary ground and a second terminal as a floating terminal, wherein: the second shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The second shield winding is located between the primary winding and the second secondary winding.

2. The shielded power transformer according to claim 1, wherein: The first shield winding is evenly arranged along an interface between the primary winding and the first secondary winding; and Wherein, the second shielding member winding is evenly arranged along the interface between the primary winding and the second secondary winding.

3. The shielded power transformer according to claim 1, wherein: The secondary winding and the shield winding have a number of turns within 5% of each other.

4. The shielded power transformer according to claim 1, wherein: The first shield winding and the second shield winding each have a terminal connected to a primary ground.

5. The shielded power transformer according to claim 1, wherein: The shielded power transformer includes a winding of wire around a ferrite core.

6. The shielded power transformer according to claim 1, wherein: In the case where the windings are implemented using traces on stacked substrate layers, the shielded power transformer is implemented using planar magnetics.

7. The shielded power transformer according to claim 6, wherein: The stacked substrate layers are arranged from top to bottom along the axis in the following order: one of the secondary windings, one of the shield windings, the primary winding, another one of the shield windings, and another one of the secondary windings.

8. The shielded power transformer according to claim 1, wherein: The shielded power transformer comprises four secondary windings, each of the secondary windings having a substantially equal number of turns; Wherein, the shielded power transformer comprises a conductor winding around a core; The wire windings are arranged concentrically around the core in the following order from the inner winding outward: The first of the four secondary windings, The second of the four secondary windings, one of the shield windings, The primary winding, another of the shield windings, the third of the four secondary windings, and The fourth of the four secondary windings, wherein the first of the four secondary windings or the second of the four secondary windings is one of the first secondary winding or the second secondary winding; and The third of the four secondary windings or the fourth of the four secondary windings is the other of the first secondary winding or the second secondary winding.

9. The shielded power transformer according to claim 1, wherein: The shielded power transformer comprises four secondary windings, the four secondary windings comprising the first secondary winding, the second secondary winding, the third secondary winding and the fourth secondary winding, wherein the first secondary winding, the second secondary winding, the third secondary winding and the fourth secondary winding each have a substantially equal number of turns; wherein, in the case where the windings are arranged as substantially planar coils, the shielded power transformer comprises planar magnetic elements; The substantially planar coils are stacked along the axis in the following order from top to bottom: The first of the four secondary windings, The second of the four secondary windings, one of the shield windings, The primary winding, another of the shield windings, the third of the four secondary windings, and The fourth of the four secondary windings, wherein the first of the four secondary windings or the second of the four secondary windings is one of the first secondary winding or the second secondary winding; and The third of the four secondary windings or the fourth of the four secondary windings is the other of the first secondary winding or the second secondary winding.

10. The shielded power transformer according to claim 8, wherein: The first of the four secondary windings and the second of the four secondary windings have opposite voltage potential directions; and Wherein, the third of the four secondary windings and the fourth of the four secondary windings have opposite voltage potential directions.

11. The shielded power transformer according to claim 1, wherein: The shielded power transformer has four secondary windings, each of the secondary windings having a substantially equal number of windings; wherein a first group of two of the secondary windings between which the primary winding and the shield winding are arranged are configured such that the first group of two of the secondary windings (i) have the same voltage potential direction and (ii) are connected in series to act as a single effective secondary coil; and wherein a second set of two of the secondary windings between which the primary winding and the shield winding are arranged are configured such that the second set of two of the secondary windings (i) have the same voltage potential direction and (ii) are connected in series to act as a single effective secondary coil; wherein the secondary windings in the first group are different from the secondary windings in the second group; and The voltage potential direction of the secondary windings for the first group is opposite to the voltage potential direction of the secondary windings for the second group.

12. The shielded power transformer according to claim 1, wherein: The shielded power transformer is configured to use the first shield winding as part of the primary winding so that the use of the transformer reduces the voltage supplied to the primary winding when the effective turns ratio between the primary side of the shielded power transformer and one of the secondary windings is the ratio between (i) the sum of the number of turns of the primary winding and the first shield winding and (ii) the number of turns of one of the secondary windings.

13. The shielded power transformer according to claim 1, wherein: The first shield winding is arranged in the same configuration as the first secondary winding, and Wherein, the second shielding member winding is arranged in the same structure as the first secondary winding.

14. The shielded power transformer according to claim 1, wherein: The electromagnetic shield is arranged such that no common mode currents exist between the electromagnetic shield windings and corresponding secondary windings.

15. The shielded power transformer according to claim 1, wherein: The shielded power transformer is configured to induce common mode current from the primary winding to the electromagnetic shield and cause the common mode current to flow back to the primary ground, so that the common mode current circulates only in the primary side and no common mode current passes between the primary winding and the secondary winding.

16. A shielded power transformer, comprising: Magnetic core; Primary winding; a first secondary winding and a second secondary winding, the first secondary winding and the second secondary winding having substantially equal numbers of turns; and An electromagnetic shielding component, the electromagnetic shielding component comprising: a first shield winding having the same voltage potential direction as the primary winding and connected in series with the primary winding to carry current flowing through the primary winding, wherein: the first shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The first shield winding is located between the primary winding and the first secondary winding; and a second shield winding having a voltage potential direction opposite to the primary winding and connected from the primary ground to the floating terminal, wherein: the second shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The second shield winding is located between the primary winding and the second secondary winding; The shielded power transformer comprises a wire winding around a ferrite core, and the wire winding is arranged concentrically around a central portion of the ferrite core from an inner winding outward in the following order: one of the secondary windings, one of the shield windings, The primary winding, another of the shield windings, and the other of the secondary windings.

17. A power adapter, comprising: A shielded power transformer, wherein the shielded power transformer comprises: a magnetic core, a primary winding, a first secondary winding, a second secondary winding and an electromagnetic shielding member, wherein the first secondary winding and the second secondary winding have substantially the same number of turns, and wherein the electromagnetic shielding member comprises: a first shield winding having the same voltage potential direction as the primary winding and connected in series with the primary winding to carry current flowing through the primary winding, wherein: The first terminal of the first shield winding is connected to the primary winding, The second terminal of the first shield winding is connected to the primary ground and the first terminal of the second shield winding, the first shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The first shield winding is located between the primary winding and the first secondary winding; and The second shield winding, having a voltage potential direction opposite to the primary winding, has the first terminal connected to the primary ground and a second terminal as a floating terminal, wherein: the second shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The first shield winding is located between the primary winding and the second secondary winding.

18. The power adapter of claim 17, comprising a switch coupled to the secondary winding, the switch configured to operate as part of a synchronous rectifier.

19. A method for converting alternating current from one voltage to another voltage, comprising: receiving power at a primary-side signal generating circuit configured to generate a switching signal; The switching signal is provided to a primary winding of a shielded power transformer, wherein the shielded power transformer comprises: a magnetic core, the primary winding, a first secondary winding, a second secondary winding, and an electromagnetic shield, wherein the first secondary winding and the second secondary winding have substantially equal numbers of turns, and wherein the electromagnetic shield comprises: a first shield winding having the same voltage potential direction as the primary winding and connected in series with the primary winding to carry current flowing through the primary winding, wherein: The first terminal of the first shield winding is connected to the primary winding, The second terminal of the first shield winding is connected to the primary ground and the first terminal of the second shield winding, the first shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and The first shield winding is located between the primary winding and the first secondary winding; and The second shield winding, having a voltage potential direction opposite to the primary winding, has the first terminal connected to the primary ground and a second terminal as a floating terminal, wherein: the second shield winding having a number of turns substantially equal to the number of turns of each of the secondary windings, and the second shield winding being located between the primary winding and the second secondary winding; and An output from at least one of the secondary windings is provided to a rectifier to generate a DC voltage.

Images