CN118017842A - System and method for operating an asymmetric half-bridge flyback power converter - Google Patents

Abstract

The invention discloses a method of operating a circuit. In one aspect, the disclosed method includes providing a power converter circuit having a transformer with a primary winding and a secondary winding, a first switch and a second switch coupled to the primary winding, a third switch coupled to the secondary winding, and a controller coupled to the first switch and the second switch. The disclosed method further includes sensing the turn-on of the third switch and responsively transmitting a turn-on signal to the controller; and responsive to receiving the turn-on signal, turning on the second switch using the controller. In another aspect, the disclosed method further includes sensing the turning off of the third switch and responsively transmitting a turn-off signal to the controller using an isolation module; and responsive to receiving the shutdown signal, shutting down the second switch using the controller. In yet another aspect, the controller is used to turn off the second switch after a delay time.

Description

System and method for operating an asymmetric half-bridge flyback power converter

Cross Reference to Related Applications

The present application claims priority from chinese patent application number 202211406902.6 (attorney docket number 096868-1356915-007500 CNP) filed on 10/11/2022, entitled "Control Method For ASYMMETRIC HALF-Bridge Flyback Converter," 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, the present embodiments relate to systems and methods for controlling and operating asymmetric half-bridge flyback power converters.

Background

Electronic devices (such as computers, servers, televisions, etc.) employ one or more power conversion circuits to convert one form of electrical energy to another. Some power conversion 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 may also be smaller and lighter than linear power supplies due to the smaller size and weight of the transformer.

Disclosure of Invention

In some embodiments, a method of controlling a circuit is disclosed. The method includes providing a power converter circuit having: a transformer comprising a primary winding extending between the first terminal and the second terminal, and further comprising a secondary winding extending between the third terminal and the first output 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 second terminal, and the second drain terminal coupled to the power source; a third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third source terminal coupled to the third terminal, and the third drain terminal coupled to the second output terminal. The method also includes providing a controller coupled to the first gate terminal and the second gate terminal; sensing the turn-on of the third switch, transmitting a turn-on signal to the controller; and responsive to receiving the turn-on signal, turning on the second switch using the controller.

In some embodiments, the method further comprises sensing the turning off of the third switch and responsively transmitting a turn-off signal to the controller; and responsive to receiving the shutdown signal, shutting down the second switch using the controller.

In some embodiments, the turning off the second switch occurs after a delay time T _delay.

In some embodiments, the time delay T _delay corresponds to the drain-source voltage V _{ds_on} of the first switch.

In some embodiments, the controller includes a shutdown management module, wherein the shutdown management module stores N threshold voltages V _{TH_1}、V_{TH_2}..and V _{TH_N} having different magnitudes, wherein V _{TH_1}＜V_{TH_2}＜...＜V_{TH_N}, and wherein the N threshold voltages correspond to N different delay times T _{delay_1}、T_{delay_2}..and T _{delay_N}, wherein T _{delay_1}＜T_{delay_2}＜...＜T_{delay_N}.

In some embodiments, the turn-off management module detects the drain-source voltage _{ds_on} of the first switch when the first switch was turned on in a previous period.

In some embodiments, the magnitudes of the drain-source voltage V _{ds_on} and the N different threshold voltages of the first switch are compared to select the delay time T _delay from a lookup table containing T _{delay_1}、T_{delay_2}.

In some embodiments, the second switch has a maximum on-time T _{on_max}, and wherein the turn-off management module immediately turns off the second switch when the on-time of the second switch exceeds the maximum on-time T _{on_max}.

In some embodiments, if the shutdown signal is not received by the shutdown management module within a specific time interval T _sp, the shutdown management module controls the second switch to temporarily enter a special control mode, and wherein the second switch will immediately exit the special control mode when the shutdown management module again receives the shutdown signal.

In some embodiments, the shutdown management module determines a demagnetization time when the second switch is in the special control mode, and controls the shutdown of the second switch corresponding to the demagnetization time.

In some embodiments, the transmitting the turn-on signal to the controller is performed using an isolation module.

In some embodiments, the isolation module includes optocoupler isolation or magnetic isolation and/or capacitive isolation.

In some embodiments, the power converter circuit further includes a capacitor coupled between the second terminal and the second source terminal.

In some embodiments, a method of controlling a circuit is disclosed. The method includes providing a power converter circuit having: a transformer comprising a primary winding extending between the first terminal and the second terminal, and further comprising a secondary winding extending between the third terminal and the first output 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 second terminal, and the second drain terminal coupled to the power source; a third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third source terminal coupled to the third terminal, and the third drain terminal coupled to the second output terminal. The method also includes providing a controller coupled to the first gate terminal and the second gate terminal; and in response to sensing the turning off of the first switch, turning on the second switch using the controller.

In some embodiments, a circuit is disclosed. The circuit comprises: a transformer having a primary winding extending between the first terminal and the second terminal, and further comprising a secondary winding extending between the third terminal and the first output 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 second terminal, and the second drain terminal coupled to the power source; a third switch having a third gate terminal, a third source terminal, and a third drain terminal, the third source terminal coupled to the third terminal, and the third drain terminal coupled to the second output terminal; and a controller coupled to the first gate terminal and the second gate terminal; wherein the controller is arranged to receive an on signal corresponding to the on of the third switch, and wherein the controller is further arranged to switch on the second switch in response to receiving the on signal.

In some embodiments, the controller is further arranged to receive a turn-off signal corresponding to the turn-off of the third switch, and wherein the controller is arranged to turn off the second switch in response to receiving the turn-off signal.

In some embodiments, the circuit further comprises an isolation module arranged to transmit a signal from the secondary side to the primary side of the transformer.

In some embodiments, the isolation module includes optocoupler isolation or magnetic isolation and/or capacitive isolation.

In some embodiments, the circuit further includes a capacitor coupled between the second terminal and the second source terminal.

In some embodiments, the controller is further arranged to turn off the second switch after a delay time T _delay.

Drawings

FIG. 1 illustrates a schematic diagram of an asymmetric half-bridge flyback converter with a controller, according to certain embodiments;

FIG. 2 illustrates a method of operating an asymmetric half-bridge flyback converter using the controller of FIG. 1, according to some embodiments;

FIG. 3 illustrates a method of operating an asymmetric half-bridge flyback converter using the controller of FIG. 1, according to some embodiments;

FIG. 4 illustrates a method of operating an asymmetric half-bridge flyback converter using the controller of FIG. 1, according to certain embodiments;

FIG. 5 illustrates a method of operating an asymmetric half-bridge flyback converter using the controller of FIG. 1, according to some embodiments;

FIG. 6 illustrates a method of operating an asymmetric half-bridge flyback converter using the controller of FIG. 1, according to certain embodiments;

Fig. 7 illustrates a flow chart of a method 700 for controlling auxiliary switches in an asymmetric half-bridge flyback converter, according to some embodiments; and

Fig. 8A-8D illustrate simulation results of a method of operating an asymmetric half-bridge flyback converter 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 control and methods of operation for operating an asymmetric half-bridge flyback power converter in which an off signal of a main switch may be used to control the turning on of an auxiliary switch. In some embodiments, the secondary side synchronous rectifier switch on signal may be used to control the on of auxiliary switches in an asymmetric half-bridge flyback power converter. The control and operating methods disclosed herein may enable Zero Voltage Switching (ZVS) of the primary switch and Zero Current Switching (ZCS) of the secondary side synchronous rectifier switch under all operating conditions, including light load conditions, thereby improving the performance of the asymmetric half-bridge flyback converter. In this way, the efficiency of the asymmetric half-bridge flyback converter may be improved and the electromagnetic interference (EMI) performance of the power converter may be improved, enabling high frequency operation when using gallium nitride (GaN) based switches.

In some embodiments, the on signal of the synchronous rectifier switch may be used to generate the on signal of the auxiliary switch. After generating the on signal of the synchronous rectifier switch tube, the on signal of the synchronous rectifier switch can be transmitted to the primary side through the isolation module to generate the on signal of the auxiliary switch. In various embodiments, the turn-off signal of the synchronous rectifier switch may be used to generate a first turn-off signal for turning off the auxiliary switch. After generating the turn-off signal of the synchronous rectifier switch, the turn-off signal may be transmitted to the primary side through the isolation module. In some implementations, the primary side shutdown management module may receive the first shutdown signal and increase a delay time before closing the auxiliary switch. The delay time may be based on a drain-source voltage of the main switch, wherein an off timing of the auxiliary switch may be adjusted based on the drain-source voltage of the main switch sensed in a previous period. 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 an asymmetric half-bridge flyback converter 100 with a controller according to certain embodiments. As shown in fig. 1, an asymmetric half-bridge flyback converter with a controller 100 may include a main switch 102, an auxiliary switch 104, a synchronous rectifier switch 112, a resonant capacitor 106, an excitation inductance 110, and a leakage inductance 108 of a transformer 114. The main switch 102 and the auxiliary switch 104 are located on the primary side, while the synchronous rectifier switch 112 is located on the secondary side. The excitation inductance 110 and the resonance capacitor 106 may store energy when the main switch 102 is on and the auxiliary switch 104 and the synchronous rectifier switch 112 are off. When the main switch is turned off and the auxiliary switch is turned on, the energy stored in the transformer can be released to the secondary side.

When the main switch 102 is turned off, the auxiliary switch 104 and the synchronous rectifier switch 112 are turned on, the excitation inductance 110 may be clamped by the output voltage, the leakage inductance 108 and the resonance capacitor 106 may resonate, and the resonance period is Tr. In this way, the main switch 102 may operate with zero voltage switching on (ZVS), so the asymmetric half-bridge flyback converter may reduce switching losses of the main switch 102 and improve EMI performance thereof.

As shown in fig. 1, the controller 120 is coupled to the main switch 102 and the auxiliary switch 104. The controller may be arranged to transmit control signals to the main switch 102 and the auxiliary switch 104 in order to control their on and off. In some embodiments, the controller 120 may include a Pulse Width Modulation (PWM) controller circuit. In various embodiments, the controller 120 may include a shutdown management module circuit. In certain embodiments, the controller 120 may include drive circuitry for the main switch 102 and the auxiliary switch 104. In some embodiments, the main switch 102 and the auxiliary switch 104 may be silicon-based MOS transistors. In various embodiments, the main switch 102 and the auxiliary switch 104 may be gallium nitride (GaN) based HEMTs. In some embodiments, the main switch 102 and the auxiliary switch 104 may be silicon carbide based MOS transistors. In various embodiments, the main switch 102 and the auxiliary switch 104 may be bipolar transistors. In some embodiments, the synchronous rectifier switch may be a silicon-based MOS transistor, a GaN-based transistor, a silicon carbide-based transistor, or a bipolar transistor. The asymmetric half-bridge flyback converter 100 with a controller may also include an isolation module 124. In some embodiments, the isolation module may be optocoupler isolation, magnetic isolation, and/or capacitive isolation, among others. The isolation module 124 may be arranged to transmit signals from the secondary side to the primary side. In various embodiments, the isolation module may be arranged to transmit and receive signals from the secondary side to the primary side.

In the current approach, a primary side control mode is used to control an asymmetric half-bridge flyback converter. In these methods, when the main switch 102 is turned off, the turning on of the auxiliary switch 104 may be controlled by an off signal of the main switch 102. Synchronous rectifier switch 112 can only achieve zero current switching off (ZCS) under certain operating conditions, but not all operating conditions. This may lead to reduced electromagnetic interference (EMI) performance and reduced efficiency of the asymmetric half-bridge flyback converter.

In some embodiments, an asymmetric half-bridge flyback converter with a shutdown management module may operate with greater efficiency and reduced EMI. In various embodiments, efficient control of the turning on and off of the auxiliary switch 104 may enable ZCS of the synchronous rectifier switch 112 under all operating conditions, thereby significantly improving the performance of the asymmetric half-bridge flyback converter. In some embodiments, the transformer 114 and resonant capacitor 106 may store energy when the main switch 102 is on and the auxiliary switch 104 is off. When the main switch 102 is turned off and the auxiliary switch 104 is turned on, the energy stored in the transformer 114 and the resonant capacitor 106 is discharged into the secondary circuit.

Fig. 2 illustrates a method of operating an asymmetric half-bridge flyback converter according to certain embodiments. In the illustrated method, an asymmetric half-bridge flyback converter may be operated so that the auxiliary switch may be precisely controlled to turn on and off. In the illustrated embodiment, the off signal to turn off the main switch 102 may cause the auxiliary switch 104 to turn on. The Pulse Width Modulation (PWM) module 202 may send an off signal to the main switch 102. After the main switch 102 is turned off, an on signal for the auxiliary switch may be generated after a delay period (step 204). The on signal of the auxiliary switch may cause the auxiliary switch 104 to turn on (step 206).

Fig. 3 illustrates a method of operating an asymmetric half-bridge flyback converter according to some embodiments. In the illustrated embodiment, a Pulse Width Modulation (PWM) module 302 may send an on signal to the synchronous rectifier switch 112. When the synchronous rectifier switch 112 is on, a signal may be captured indicating that the synchronous rectifier switch has been on, and then an on signal for the auxiliary switch 104 is generated (step 304). The on signal of the auxiliary switch may be transmitted to the primary side of the asymmetric half-bridge flyback converter through the isolation module (step 306). The isolation module may be optocoupler isolation, magnetic isolation, capacitive isolation, etc. Subsequently, the auxiliary switch may be turned on (step 308).

Fig. 4 illustrates a method of operating an asymmetric half-bridge flyback converter according to certain embodiments. In the illustrated embodiment, a Pulse Width Modulation (PWM) module 402 may send an off signal to the synchronous rectifier switch 112. The off signal of the synchronous rectifier switch 112 may be used to generate a first off signal of the auxiliary switch (step 404). The first off signal of the auxiliary switch may be transmitted to a turn-off management module (408) of the primary side through the isolation module (step 406).

Fig. 5 illustrates a method of operating an asymmetric half-bridge flyback converter according to some embodiments. When the shutdown management module 504 receives the first shutdown signal, the shutdown management module 504 may turn off the auxiliary switch after increasing the delay time T _delay. T _delay corresponds to the drain-source voltage V _{ds_on} when the main switch 102 is on. The delay time T _delay may be used to adjust the off-time of the auxiliary switch 104 to ensure that the main switch 102 operates with zero voltage on or valley voltage on. The shutdown management module 504 may sense the drain-source voltage V _{ds_on} when the main switch 102 is turned on to obtain a voltage signal VD reflecting the magnitude of V _{ds_on} (step 502). The drain-source voltage V _{ds_on} may be sensed directly or by an indirect method. The shutdown management module may use the voltage difference between VD and the corresponding threshold voltage V _TH to select the corresponding delay time T _delay.

In the illustrated embodiment, N different magnitudes of threshold voltages V _{TH_1}、V_{TH_2} and V _{TH_N} may be stored in the shutdown management module 504 (e.g., in a lookup table), where V _{TH_1}＜V_{TH_2}＜...＜V_{TH_N}, and the N threshold voltages correspond to N different delay times T _{delay_1}、T_{delay_2} and T _{delay_N}, where T _{delay_1}＜T_{delay_2}＜...＜T_{delay_N}. In some implementations, the shutdown management module 504 may be included in the controller 120. Upon receiving the first shutdown signal, the shutdown management module 504 may select a corresponding delay time T _delay according to the voltage signal VD (VD is sensed in a previous switching cycle). When VD is V _{TH_1} or less, the shutdown management module 504 may turn off the auxiliary switch 104 after the delay time T _{delay_1} after receiving the first shutdown signal. When V _{TH_1}＜VD≤V_{TH_2}, after receiving the first shutdown signal, shutdown management module 504 may shutdown auxiliary switch 104 after delay time T _{delay_2}. When V _{TH_N-1}＜VD≤V_{TH_N}, after receiving the first shutdown signal, shutdown management module 504 may shutdown auxiliary switch 104 after delay time T _{delay_N-1}. When VD > V _{TH_N}, after receiving the first shutdown signal, the shutdown management module 504 may shutdown the auxiliary switch 104 after a delay time T _{delay_N}. In the illustrated embodiment, the auxiliary switch 104 may have a maximum on-time of T _{on_max}. When the on-time T _on of the auxiliary switch exceeds the maximum on-time T _{on_max}, i.e., T _on＞T_{on_max}, the off-management module 504 may override and turn off the auxiliary switch 104.

Fig. 6 illustrates a method of operating an asymmetric half-bridge flyback converter according to certain embodiments. Under operating conditions where the shutdown management module 504 does not receive the first shutdown signal, the shutdown management module may detect when the first shutdown signal 602 has disappeared. In fig. 6, t _miss is the vanishing time of the first turn-off signal. Under the condition that the first turn-off signal disappears to be smaller than T _sp, i.e., T _miss＜T_sp, the auxiliary switch 104 is declared to be in the normal operation mode. T _sp is a predefined period of time. In some embodiments, the value of T _sp may be 1.2 to 1.5 times the demagnetization time T _dmag, although other values of T _sp may be used.

The turn-off signal of the synchronous rectifier switch 112 may control the turn-off of the auxiliary switch to ensure that the synchronous rectifier switch 112 may operate under ZCS. During the period when the first off signal is disappeared, if the disappearing time exceeds T _sp, i.e., T _miss＞T_sp, the off management module may cause the auxiliary switch 104 to enter the special control mode during the temporary period. In addition, when the shutdown management module 504 receives the first shutdown signal again, the auxiliary switch 104 may immediately exit the special control mode. When the auxiliary switch enters the special control mode, the shutdown management module 504 may calculate a demagnetization time t _dmag of the transformer 114, determine a shutdown time of the auxiliary switch, and turn the auxiliary switch off.

Fig. 7 illustrates a flow chart of a method 700 for controlling auxiliary switches in an asymmetric half-bridge flyback converter, according to some embodiments. In step 702, the method 700 includes receiving an off signal of the main switch 102 or an on signal of the synchronous rectifier switch 112. After a predetermined delay time, the auxiliary switch 104 may be turned on in step 704. In step 706, the method includes determining whether the auxiliary switch on time T _on is less than T _{on_max}. If T _on is less than T _{on_max}, then in step 708, the method determines if an off signal for the synchronous rectifier switch is received. If so, in step 710, a first off signal of the auxiliary switch is generated and transmitted to the primary side through the isolation module. In step 712, the method determines whether the shutdown management module received a first shutdown signal. If so, in step 714, the voltage signal VD is compared with N threshold voltages in the lookup table, and a delay time T _{delay_N} corresponding to the corresponding threshold voltage in the lookup table is selected. In step 716, after the time T _{delay_N} elapses, the shutdown management module turns off the auxiliary switch.

If the time T _on is not less than T _{on_max} in step 706, then the shutdown management module may override to turn off the auxiliary switch in step 730. If the shutdown management module does not receive the first shutdown signal in step 712, then in step 720T _miss is compared to T _sp to determine if T _miss is less than T _sp. If T _miss is less than T _sp, then in step 718, the synchronous rectifier switch off signal may generate an auxiliary switch off signal. If the time exceeds T _sp, i.e., T _miss＞T_sp, during which the first shutdown signal is lost (step 722), the shutdown management module may cause the auxiliary switch 104 to enter a special control mode for a temporary period of time (step 728). In addition, when the shutdown management module 504 again receives the first shutdown signal, the auxiliary switch 104 may exit the special control mode (step 726). When the auxiliary switch enters the special control mode, the shutdown management module 504 may calculate a demagnetization time t _dmag of the transformer, determine a shutdown time of the auxiliary switch, and control the auxiliary switch to be turned off (step 724). It should be understood that the method 700 is illustrative and that variations and modifications are possible. Steps described as sequential may be executed in parallel, order of steps may be varied, and steps may be modified, combined, added, or omitted.

Fig. 8A-8D illustrate simulation results of a method of operating an asymmetric half-bridge flyback converter according to some embodiments. Fig. 8A to 8D show simulation waveforms of an asymmetric half-bridge flyback converter with different output loads. As can be seen from fig. 8A-8D, when the main switch 102 is off, embodiments of the present disclosure may detect the occurrence of this event and may cause the auxiliary switch 104 to be on. In some embodiments, when the synchronous rectifier switch 112 is turned on, the occurrence of this event may be detected and the auxiliary switch 104 may be turned on. When the synchronous rectifier switch 112 is off, the occurrence of this event is detected and a first off signal of the auxiliary switch is generated and the auxiliary switch 104 is turned off. The disclosed embodiments may ensure that synchronous rectifier switch 112 achieves zero current switching off (ZCS) at 100% load (fig. 8A), 75% load (fig. 8B), 50% load (fig. 8C), and 25% load (fig. 8D), thereby improving the efficiency and EMI performance of an asymmetric half-bridge flyback converter.

In some embodiments, the combination of circuits and methods disclosed herein may be used to operate an asymmetric half-bridge flyback converter. Although the circuits and methods are described and illustrated herein with respect to several specific configuration methods of controlling and operating an asymmetric half-bridge flyback converter, the disclosed embodiments are also applicable to methods of controlling and operating other power converter topologies, such as, but not limited to, half-bridge flyback 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, as used herein, the term "one or more" 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 method of controlling a circuit, the method comprising:

Providing a power converter circuit, the power converter 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;

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 second terminal, and the second drain terminal coupled to the power source;

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

Providing a controller coupled to the first gate terminal and the second gate terminal;

sensing the turn-on of the third switch and responsively transmitting a turn-on signal to the controller; and

The second switch is turned on using the controller in response to receiving the turn-on signal.

2. The method of claim 1, further comprising:

sensing the turning off of the third switch and responsively transmitting a turning off signal to the controller; and

In response to receiving the shutdown signal, the second switch is turned off using the controller.

3. The method of claim 2, wherein the turning off the second switch occurs after a delay time T _delay.

4. A method according to claim 3, wherein the time delay T _delay corresponds to the drain-source voltage V _{ds_on} of the first switch.

5. The method of claim 4, wherein the controller comprises a shutdown management module, and wherein the shutdown management module stores N threshold voltages V _{TH_1}、V_{TH_2}..and V _{TH_N} having different magnitudes, V _{TH_1}＜V_{TH_2}＜...＜V_{TH_N}, and wherein the N threshold voltages correspond to N different delay times T _{delay_1}、T_{delay_2}..and T _{delay_N}, wherein T _{delay_1}＜T_{delay_2}＜...＜T_{delay_N}.

6. The method of claim 5, wherein the turn-off management module detects the drain-source voltage _{ds_on} of the first switch when the first switch was turned on in a previous cycle.

7. The method of claim 6, wherein the drain-source voltage V _{ds_on} of the first switch and the magnitudes of the N different threshold voltages are compared to select the delay time T _delay from a lookup table containing T _{delay_1}、T_{delay_2}.

8. The method of claim 7, wherein the second switch has a maximum on-time T _{on_max}, and wherein the turn-off management module immediately turns off the second switch when the on-time of the second switch exceeds the maximum on-time T _{on_max}.

9. The method of claim 8, wherein if the shutdown signal is not received by the shutdown management module within a particular time interval T _sp, the shutdown management module controls the second switch to temporarily enter a special control mode, and wherein the second switch will immediately exit the special control mode when the shutdown management module again receives the shutdown signal.

10. The method of claim 9, wherein the shutdown management module determines a demagnetization time when the second switch is in the special control mode and controls the shutdown of the second switch corresponding to the demagnetization time.

11. The method of claim 1, wherein the transmitting the turn-on signal to the controller is performed using an isolation module.

12. The method of claim 11, wherein the isolation module comprises optocoupler isolation or magnetic isolation and/or capacitive isolation.

13. The method of claim 1, wherein the power converter circuit further comprises a capacitor coupled between the second terminal and the second source terminal.

14. A method of controlling a circuit, the method comprising:

Providing a power converter circuit, the power converter 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;

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 second terminal, and the second drain terminal coupled to the power source;

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

Providing a controller coupled to the first gate terminal and the second gate terminal; and

The second switch is turned on using the controller in response to sensing the turning off of the first switch.

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;

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 second terminal, and the second drain terminal coupled to the power source;

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

A controller coupled to the first gate terminal and the second gate terminal;

wherein the controller is arranged to receive an on signal corresponding to the on of the third switch, and wherein the controller is further arranged to switch on the second switch in response to receiving the on signal.

16. The circuit of claim 15, wherein the controller is further arranged to receive a turn-off signal corresponding to a turn-off of the third switch, and wherein the controller is arranged to turn off the second switch in response to receiving the turn-off signal.

17. The circuit of claim 15, further comprising an isolation module arranged to transmit a signal from a secondary side to a primary side of the transformer.

18. The circuit of claim 17, wherein the isolation module comprises optocoupler isolation or magnetic isolation and/or capacitive isolation.

19. The circuit of claim 15, further comprising a capacitor coupled between the second terminal and the second source terminal.

20. The circuit of claim 16, wherein the controller is further arranged to turn off the second switch after a delay time T _delay.