CN118199367A - Power converter with synchronous rectifier circuit powered by auxiliary winding - Google Patents

Abstract

The invention discloses a circuit. The circuit comprises: a transformer having a primary winding extending between a first terminal and a second terminal, and a secondary winding extending between a third terminal and a first output terminal, and an auxiliary winding extending between a fourth terminal and the third terminal; a first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to the second terminal, and the first source terminal coupled to a power source; a second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to a second output terminal, the secondary winding having a winding direction opposite to a winding direction of the primary winding, and the auxiliary winding having a winding direction identical to the winding direction of the primary winding.

Description

Power converter with synchronous rectifier circuit powered by auxiliary winding

Cross Reference to Related Applications

The present application claims priority to U.S. patent application number 63/486,938, entitled "Synchronous Rectifier Circuit Powered by Auxiliary Windings", filed 24 at 2023, 12, and chinese patent application number 202211600509.0, entitled "Synchronous Rectifier Circuit Powered by Auxiliary Windings", filed 12 at 2022, and chinese patent application number 202211598349.0, entitled "Synchronous Rectifier Circuit Powered By Power Windings", filed 12 at 2022, and priority to U.S. patent application number 18/531,619, entitled "Power Converters Having Synchronous Rectifier Circuits Powered By Auxiliary Windings", filed 6 at 2023, 12, the contents of which are incorporated herein by reference in their entirety for all purposes.

Technical Field

The described embodiments relate generally to power converters, and more particularly, to power converters having synchronous rectifier circuits powered by auxiliary windings.

Background

Electronic devices (such as computers, servers, televisions, etc.) employ one or more power converter circuits to convert one form of electrical energy to another. Some power converter circuits use a switching power supply, such as a flyback converter. The switching power supply may efficiently convert power from the power supply to a load. The switching power supply may have a relatively high power conversion efficiency compared to other types of power converters. Switching power supplies can also be substantially smaller and lighter than linear power supplies due to the smaller size and weight of the transformer.

Disclosure of Invention

In some embodiments, a circuit is disclosed. The circuit comprises: a transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal, and further comprising an auxiliary winding extending between a fourth terminal and the third terminal; a first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to the second terminal, and the first source terminal coupled to a power source; and a second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to the second output terminal; wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

In some embodiments, the circuit further comprises a diode having an anode and a cathode, wherein the cathode is coupled to the fourth terminal. In some embodiments, the circuit further includes a controller circuit coupled to the anode, the third terminal, the second gate terminal, and the second drain terminal. In some embodiments, the controller circuit is arranged to control the voltage at the second gate terminal such that the second switch is off when the first switch is on and the second switch is on when the first switch is off. In some embodiments, the circuit further comprises a load coupled between the first output terminal and the second output terminal. In some embodiments, the circuit further comprises a capacitor coupled between the first output terminal and the second output terminal. In some embodiments, the first switch is a gallium nitride (GaN) based transistor.

In some embodiments, a circuit is disclosed. The circuit comprises: a transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal, and further comprising an auxiliary winding extending between a fourth terminal and the third terminal; a first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to the second terminal, and the first source terminal coupled to a power source; a second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to the second output terminal; and a third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third drain terminal coupled to the second terminal, and the second source terminal coupled to a first node of a first capacitor, a second node of the first capacitor coupled to the first terminal; wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

In some embodiments, a circuit is disclosed. The circuit comprises: a transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal, and further comprising an auxiliary winding extending between a fourth terminal and the third terminal; a first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to a first node of a capacitor, and the first source terminal coupled to a power source, a second node of the capacitor coupled to the second terminal; a second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to the second output terminal; a first winding coupled between the first terminal and the power supply; and a third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third drain terminal coupled to the first winding, and the second source terminal coupled to the first drain terminal; wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

Drawings

FIG. 1 illustrates a schematic diagram of a power converter having a synchronous rectifier circuit powered by an auxiliary winding, according to some embodiments;

FIG. 2 illustrates a schematic diagram of a synchronous rectified flyback converter with an auxiliary winding that acts as a forward converter to power a synchronous rectifier controller, according to some embodiments;

FIG. 3 illustrates a schematic diagram of a flyback converter with a synchronous converter with active clamp, according to some embodiments; and

Fig. 4 shows a schematic diagram of an asymmetric half-bridge converter with a synchronous rectifier circuit powered by an auxiliary winding, according to some embodiments.

Detailed Description

The circuits, devices, and related techniques disclosed herein relate generally to power converters. More particularly, the circuits, devices, and related techniques disclosed herein relate to power converter circuits having synchronous rectification circuits powered by auxiliary windings, where the auxiliary windings may power synchronous rectification controllers. In some embodiments, power for the synchronous rectification controller may be generated by a forward mode, which may effectively reduce fluctuations in the supply voltage and reduce the number of turns of the auxiliary winding. In various embodiments, a power converter circuit includes a primary winding, a secondary winding, an auxiliary winding, a synchronous rectifier switch, and a synchronous rectifier switch controller.

In some embodiments, the secondary winding has a winding direction opposite to a winding direction of the primary winding, and the auxiliary winding has the same winding direction as the winding direction of the primary winding. In various embodiments, the power converter circuit further comprises a primary side main switch. In some embodiments, the main switch and/or the synchronous rectifier switch may be gallium nitride (GaN) based transistors, silicon carbide (SiC) based transistors, or silicon based transistors. Various inventive embodiments are described herein, including methods, processes, systems, devices, and the like.

Several exemplary embodiments will now be described with respect to the accompanying drawings which form a part hereof. The following description merely provides embodiments and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the embodiments will provide those skilled in the art with an enabling description for implementing one or more embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosure. In the following description, for purposes of explanation, specific details are set forth in order to provide a thorough understanding of certain inventive embodiments. It may be evident, however, that the various embodiments may be practiced without these specific details. The drawings and description are not intended to be limiting. The word "example" or "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "example" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1 shows a schematic diagram of a power converter 100 having a synchronous rectification circuit powered by an auxiliary winding, according to some embodiments. The power converter 100 may include a transformer 148 having a primary winding 112, a secondary winding 116, and an auxiliary winding 118. The auxiliary winding 118 may be forward coupled with the primary winding 112 and may be counter-coupled with the secondary winding 116. The primary winding 112 may be counter-coupled to the secondary winding 116. The primary winding 112 may be coupled to the input power source 110 and may also be coupled to a main switch 114. The main switch may be coupled to the input power 110. A first terminal of the auxiliary winding 118 may be coupled to an anode of a diode 120. The cathode of the diode 120 may be coupled to a Synchronous Rectifier Controller (SRC) 130 at node 122. A second terminal of the auxiliary winding 118 may be coupled to a Synchronous Rectifier (SR) switch 134.

In some embodiments, SR switch 134 may be a transistor having a source terminal 135, a gate terminal 137, and a drain terminal 133. In various embodiments, the SR switch 134 may be a gallium nitride (GaN) -based, or silicon (Si) -based, or silicon carbide (SiC) -based transistor. A second terminal of the auxiliary winding 118 may also be coupled to an SRC 130 at node 124. The gate terminal 137 may be coupled to the SRC 130 at a node 132. The SRC 130 may be arranged to provide a gate drive signal to the SR switch 134 at node 132, wherein the SRC 130 may control the voltage at the gate terminal 137. The drain terminal 133 may be coupled to the SRC 130 at the node 126. The drain terminal 133 may also be connected to an output terminal 141. The output terminal 141 may be coupled to the load 128. A first terminal of the secondary winding 116 may be coupled to the source terminal 135 and a second terminal of the secondary winding 116 may be coupled to the load 128. The secondary winding 116 may be counter-coupled to the auxiliary winding 118.

The power converter 100 with synchronous rectifier circuit powered by the auxiliary winding may operate as a flyback converter. When the main switch 114 is closed, the output of the auxiliary winding 118 may be positive and the diode 120 may be forward biased, producing a positive voltage Vcc at node 122. During the period when the main switch 114 is closed, the magnets of the primary winding 112 may be charged. The SR switch 134 may remain open during this period. When the main switch 114 is open, the output of the auxiliary winding 118 may become negative, thereby reverse biasing the diode 120. The voltage at the secondary winding 116 may become positive and the SR switch 134 may be turned on. Secondary winding 116 may also be coupled to an output terminal 141.

Fig. 2 shows a schematic diagram of a synchronous rectified flyback converter 200 with an auxiliary winding that acts as a forward converter to power a Synchronous Rectifier Controller (SRC) according to some embodiments. The power converter 200 may include a transformer 248 having a primary winding 214, a secondary winding 222, and an auxiliary winding 220. The auxiliary winding 220 may be forward coupled with the primary winding 214 and may be counter-coupled with the secondary winding 222. The primary winding 214 may be counter-coupled to the secondary winding 222. The primary winding 214 may be coupled to the input power source 210 (Vin) and may also be coupled to a main switch 218. The primary winding 214 may also be coupled to an input capacitor 212, wherein the input capacitor 212 may be coupled in parallel to the input power source 210. The main switch 218 may be coupled to the input power source 210. A first terminal of auxiliary winding 220 may be coupled to an anode of diode 224. The cathode of the diode 224 may be coupled to a Synchronous Rectifier Controller (SRC) 230 at a node 226. A second terminal of the auxiliary winding 220 may be coupled to a Synchronous Rectifier (SR) switch 234.

In some embodiments, the SR switch 234 may be a transistor having a source terminal 235, a gate terminal 237, and a drain terminal 233. In various embodiments, SR switch 234 may be a gallium nitride (GaN) based, or silicon (Si) based, or silicon carbide (SiC) based transistor. A second terminal of auxiliary winding 220 may also be coupled to SRC 230 at node 228. The gate terminal 237 may be coupled to the SRC 230 at node 232. The SRC 230 may be arranged to provide a gate drive signal to the SR switch 234 at node 232, wherein the SRC 230 may control the voltage at the gate terminal 237. Drain terminal 233 may be coupled to SRC 230 at node 240. The drain terminal 233 may also be connected to the output terminal 241. The output terminal 241 may be coupled to the load 238. A first terminal of the secondary winding 222 may be coupled to the source terminal 235 and a second terminal of the secondary winding 222 may be coupled to the load 238. The secondary winding 222 may be counter-coupled to the auxiliary winding 220. Capacitor 236 may be coupled in parallel with load 238.

The power converter 200 may operate as a combination of a forward converter and a flyback converter. During the first period, when the main switch 218 is closed, the magnetization and leakage inductance of the primary winding 214 may be charged. The voltage of auxiliary winding 220 may be positive, forward biasing diode 224 and driving node 226 as Vcc (the power supply for SRC 230). The SR switch 234 may be turned off during the first time period. During the second period, when the main switch 218 is open, the voltage of the auxiliary winding 220 may become negative, thereby reverse biasing the diode 224. The SR switch 234 may be turned on, thereby connecting the secondary winding 222 to the output terminal 241.

In the example of power converter 200, primary winding 214 may have 14 turns, secondary winding 222 may have 2 windings, and auxiliary winding 220 may have 1 winding. The output voltage of the secondary winding 222 is 2/14 vin. The voltage at the auxiliary winding 220 is 1/14 vin. The gain of the secondary winding may be higher than the winding ratio due to the magnetic discharge of the primary winding. The primary winding 214 may have a plurality of windings Np, the secondary winding 222 may have a plurality of windings Ns, and the auxiliary winding 220 may have a plurality of windings Na. The output of the auxiliary winding may be the ratio of Na winding to Np winding. The disclosed embodiments are advantageous in that gain can be minimized with one winding aid for use as a forward converter. Due to the lower gain, variations in the input voltage may result in lower voltage deviations at node 226 that power Vcc to SRC 230.

The power converter 200 shown in fig. 2 may use a flyback converter. In an example, the variation range of the input voltage V _in may be 127V to 373V, and the variation range of the output voltage V _o at the output terminal 241 may be 3.3V to 20V. The number of turns np=14 of the primary winding, and the number of turns ns=2 of the secondary winding. In the illustrated example, only one turn of auxiliary winding Na (na=1) may be used, so that sufficient power may be provided to SRC 230. When the main switch 218 is closed, the SR switch 234 is open. Since auxiliary winding 220 is positively coupled with primary winding 214, diode 224 may be forward biased and auxiliary winding 220 may supply node 226 (Vcc) that powers SRC 230. When the main switch 218 is off, the SR switch 234 is on and the diode 224 may be reverse biased. Auxiliary winding 220 may supply power to SRC 230 using a forward converter. According to the formula: vcc=na/Np Vin, and the power supply voltage Vcc varies in the range of 9V to 26V. It can be seen that the maximum power supply voltage is only 2.9 times the minimum power supply voltage, and that the fluctuation of the power supply voltage Vcc is greatly reduced. In addition, the number of turns of the auxiliary winding 220 is reduced to 1 turn, and the minimum power supply voltage is increased to 9V, thereby improving the operation performance of the power converter 200.

Fig. 3 shows a schematic diagram of a flyback converter 300 with a synchronous converter with active clamp, according to some embodiments. Flyback converter 300 may include a transformer 348 having a primary winding 316, a secondary winding 322, and an auxiliary winding 324. The auxiliary winding 324 may be forward coupled with the primary winding 316 and may be counter-coupled with the secondary winding 322. The primary winding 316 may be counter-coupled to the secondary winding 322. The primary winding 316 may be coupled to an input power source 310 (Vin) and may also be coupled to a main switch 320. The clamp capacitor 314 may be coupled in series with the switch 318, wherein the clamp capacitor 314 and the switch 318 may be coupled in parallel with the primary winding 316. The primary winding 316 may also be coupled to an input capacitor 312, wherein the input capacitor 312 may be coupled in parallel to the input power source 210. The main switch 320 may be coupled to the input power source 310. A first terminal of auxiliary winding 324 may be coupled to an anode of diode 328. The cathode of diode 328 may be coupled to a Synchronous Rectifier Controller (SRC) 332 at node 326. A second terminal of the auxiliary winding 324 may be coupled to a Synchronous Rectifier (SR) switch 336.

In some embodiments, the SR switch 336 may be a transistor having a source terminal 335, a gate terminal 337, and a drain terminal 333. In various embodiments, switch SR336 may be a gallium nitride (GaN) based, or silicon (Si) based, or silicon carbide (SiC) based transistor. A second terminal of the auxiliary winding 324 may also be coupled to an SRC 332 at node 330. The gate terminal 337 may be coupled to the SRC 332 at node 334. The SRC 332 may be arranged to provide a gate drive signal to the SR switch 336 at node 334, wherein the SRC 230 may control the voltage at the gate terminal 337. The drain terminal 333 may be coupled to the SRC 230 at node 342. The drain terminal 333 is also connectable to the output terminal 341. The output terminal 341 may be coupled to the load 340. A first terminal of the secondary winding 322 may be coupled to the source terminal 335 and a second terminal of the secondary winding 322 may be coupled to the load 340. The secondary winding 322 may be counter-coupled to the auxiliary winding 220. The capacitor 338 may be coupled in parallel with the load 340.

The circuit of fig. 3 may operate as a flyback converter with a synchronous rectifier at the output. During the first period, the cycle begins with the closing of the main switch 320, which may cause current to flow through the primary winding 316 and charge the magnetization and leakage inductance. The current flowing through the primary winding 316 may produce a positive output in the auxiliary winding 324, causing the diode 328 to be forward biased to power the node 326 that is the Vcc input of the SRC 332. During the first period, the SR switch 336 may be open. During the second period of time, voltage stress may occur on the main switch 320 when the main switch 320 is open. To relieve this voltage stress, switch 318 may be closed to absorb leakage energy dissipated from primary winding 316. The energy stored in the magnetization of the primary winding 316 may be transferred to the output of the secondary winding 322. The SR switch 336 may be turned on and the voltage of the secondary winding 322 may be applied to the output terminal 341 across the load 340.

Fig. 4 shows a schematic diagram of an asymmetric half-bridge converter 400 with synchronous rectifier circuits powered by auxiliary windings, according to some embodiments. The converter 400 may include a transformer 448 having a primary winding 420, a secondary winding 424, and an auxiliary winding 426. Auxiliary winding 426 may be forward coupled with primary winding 420 and may be counter-coupled with secondary winding 424. The primary winding 420 may be counter-coupled to the secondary winding 424. The primary winding 420 may be coupled to an input power source 410 (Vin) and may also be coupled to a capacitor 422. Capacitor 422 may be coupled to a switching node 429. The primary winding 420 may also be coupled in series to an inductor 418. An inductor 418 may be coupled to the high side switch 414 and also to the input power source 410. The high side switch 414 may be coupled to the low side switch 416 at a switch node 429. The input capacitor 412 may be coupled in parallel to the input power source 210. The high side switch 414 may be coupled to the input power source 410 and the low side switch 416 may be coupled to the input power source 410. A first terminal of auxiliary winding 426 may be coupled to an anode of diode 428. The cathode of the diode 428 may be coupled to a Synchronous Rectifier Controller (SRC) 434 at node 430. A second terminal of the auxiliary winding 426 may be coupled to a Synchronous Rectifier (SR) switch 436.

In some embodiments, the SR switch 436 may be a transistor having a source terminal 435, a gate terminal 437, and a drain terminal 433. In various embodiments, the SR switch 436 may be a gallium nitride (GaN) based, or silicon (Si) based, or silicon carbide (SiC) based transistor. A second terminal of the auxiliary winding 426 may also be coupled to an SRC 434 at node 432. The gate terminal 437 may be coupled to the SRC 434 at node 438. The SRC 434 may be arranged to provide a gate drive signal to the SR switch 436 at node 438, wherein the SRC 434 may control the voltage at the gate terminal 437. The drain terminal 433 may be coupled to the SRC 434 at a node 440. The drain terminal 433 may also be connected to the output terminal 441. The output terminal 441 may be coupled to a load 444. A first terminal of the secondary winding 424 may be coupled to the source terminal 435 and a second terminal of the secondary winding 424 may be coupled to the load 444. Secondary winding 424 may be counter-coupled to auxiliary winding 426. Capacitor 442 may be coupled in parallel with load 444.

In some implementations, the circuit of fig. 4 may operate as an asymmetric half-bridge. During a first period, when the low-side switch 416 is closed and the high-side switch 414 is open, the input power source 410 may drive a resonant circuit formed by the inductor 418, the primary winding 420, and the capacitor 422. The current through the primary winding 420 may generate a positive voltage on the auxiliary winding 426. Diode 428 may be forward biased and supply voltage Vcc at node 430 to SRC 434. During a first period, the SR switch 436 is open. During the second period, the low side switch 416 is open and the high side switch 414 is closed so that the energy stored in the primary winding 420 may be transferred into the secondary winding 424. Current is circulated through the resonant circuit formed by 418, 420 and 422 so that the voltage of auxiliary winding 426 becomes negative, thereby reverse biasing diode 428. During the second period, the SR switch 436 may be turned on such that the voltage across the secondary winding 424 drives the voltage at the output terminal 441 (across the load 444). The resonant circuit consisting of 418, 420 and 422 may be arranged to operate in three main modes: below resonance, at resonance, or above resonance mode. These modes may be used for zero voltage switching and relieve voltage stress on the high side switch 414 and the low side switch 416.

In some embodiments, the combination of the circuits and methods disclosed herein may be used in a power converter circuit having a synchronous rectifier circuit powered by an auxiliary winding. Although the circuits and methods are described and illustrated herein with respect to several specific configurations of power converters, embodiments of the present disclosure are applicable to other power converter topologies, such as, but not limited to, PFC converters and LLC converters.

In the foregoing specification, embodiments of the disclosure have been described with reference to numerous specific details that may vary from implementation to implementation. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. The sole and exclusive indicator of the scope of the disclosure, and what is intended by the applicants to be the scope of the disclosure, is the literal and equivalent scope of the claims that issue from this disclosure, in the specific form in which such claims issue, including any subsequent correction. The particular details of the particular embodiments may be combined in any suitable manner without departing from the spirit and scope of the embodiments of the present disclosure.

Furthermore, spatially relative terms (such as "bottom" or "top" and the like) may be used to describe one element and/or feature's relationship to another element and/or feature, for example, as illustrated. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and/or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "bottom" surfaces would then be oriented "over" other elements or features. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

As used herein, the terms "and," "or," and/or "may include a variety of meanings that are also intended to depend, at least in part, on the context in which the terms are used. Typically, or if used with an association list (such as A, B or C), is intended to mean A, B and C (used herein in an inclusive sense) and A, B or C (used herein in an exclusive sense). Furthermore, the terms "one or more" as used herein may be used to describe any feature, structure, or characteristic in the singular or may be used to describe some combination of features, structures, or characteristics. It should be noted, however, that this is merely an illustrative example and claimed subject matter is not limited to this example. Furthermore, the term "at least one" if used in association with a list (such as A, B or C) may be interpreted to mean any combination of A, B and/or C, such as A, B, C, AB, AC, BC, AA, AAB, ABC, AABBCCC, etc.

Reference throughout this specification to "one example," "an example," "certain examples," or "example implementations" means that a particular feature, structure, or characteristic described in connection with the feature and/or example may be included in at least one feature and/or example of claimed subject matter. Thus, the appearances of the phrases "in one example," "an example," "in some examples," "in some implementations," or other similar phrases in various places throughout this specification are not necessarily all referring to the same feature, example, and/or limitation. Furthermore, the particular features, structures, or characteristics may be combined in one or more examples and/or features.

In the previous detailed description, numerous specific details have been set forth to provide a thorough understanding of the claimed subject matter. However, it will be understood by those skilled in the art that the claimed subject matter may be practiced without these specific details. In other instances, methods and apparatuses known by those of ordinary skill have not been described in detail so as not to obscure claimed subject matter. It is intended, therefore, that the claimed subject matter not be limited to the particular examples disclosed, but that such claimed subject matter may also include all aspects falling within the scope of the appended claims, and equivalents thereof.

Claims (20)

1. A circuit, the circuit comprising:

A transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal; and further comprising an auxiliary winding extending between a fourth terminal and the third terminal;

A first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to the second terminal, and the first source terminal coupled to a power source; and

A second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to a second output terminal;

Wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

2. The circuit of claim 1, further comprising a diode having an anode and a cathode, wherein the cathode is coupled to the fourth terminal.

3. The circuit of claim 2, further comprising a controller circuit coupled to the anode, the third terminal, the second gate terminal, and the second drain terminal.

4. A circuit according to claim 3, wherein the controller circuit is arranged to control the voltage at the second gate terminal such that when the first switch is on, the second switch is off and when the first switch is off, the second switch is on.

5. The circuit of claim 4, further comprising a load coupled between the first output terminal and the second output terminal.

6. The circuit of claim 5, further comprising a capacitor coupled between the first output terminal and the second output terminal.

7. The circuit of claim 1, wherein the first switch is a gallium nitride (GaN) based transistor.

8. A circuit, the circuit comprising:

A transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal; and further comprising an auxiliary winding extending between a fourth terminal and the third terminal;

A first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to the second terminal, and the first source terminal coupled to a power source;

A second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to a second output terminal; and

A third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third drain terminal coupled to the second terminal, and the second source terminal coupled to a first node of a first capacitor, a second node of the first capacitor coupled to the first terminal;

Wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

9. The circuit of claim 8, further comprising a diode having an anode and a cathode, wherein the cathode is coupled to the fourth terminal.

10. The circuit of claim 9, further comprising a controller circuit coupled to the anode, the third terminal, the second gate terminal, and the second drain terminal.

11. The circuit of claim 10, wherein the controller circuit is arranged to control the voltage at the second gate terminal such that the second switch is off when the first switch is on and the second switch is on when the first switch is off.

12. The circuit of claim 8, further comprising a load coupled between the first output terminal and the second output terminal.

13. The circuit of claim 12, further comprising a second capacitor coupled between the first output terminal and the second output terminal.

14. The circuit of claim 8, wherein the first switch is a gallium nitride (GaN) based transistor.

15. A circuit, the circuit comprising:

A transformer comprising a primary winding extending between a first terminal and a second terminal, and further comprising a secondary winding extending between a third terminal and a first output terminal;

and further comprising an auxiliary winding extending between a fourth terminal and the third terminal;

a first switch having a first gate terminal, a first source terminal, and a first drain terminal, the first drain terminal coupled to a first node of a capacitor, and the first source terminal coupled to a power source, a second node of the capacitor coupled to the second terminal;

A second switch having a second gate terminal, a second source terminal, and a second drain terminal, the second source terminal coupled to the third terminal, and the second drain terminal coupled to a second output terminal;

A first winding coupled between the first terminal and the power supply; and

A third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third drain terminal coupled to the first winding, and the second source terminal coupled to the first drain terminal;

Wherein the secondary winding has a winding direction opposite to a winding direction of the primary winding, and wherein the auxiliary winding has the same winding direction as the winding direction of the primary winding.

16. The circuit of claim 15, further comprising a diode having an anode and a cathode, wherein the cathode is coupled to the fourth terminal.

17. The circuit of claim 16, further comprising a controller circuit coupled to the anode, the third terminal, the second gate terminal, and the second drain terminal.

18. The circuit of claim 17, wherein the controller circuit is arranged to control the voltage at the second gate terminal such that the second switch is off when the first switch is on and the second switch is on when the first switch is off.

19. The circuit of claim 15, further comprising a load coupled between the first output terminal and the second output terminal.

20. The circuit of claim 15, wherein the first switch is a gallium nitride (GaN) based transistor.