Asymmetric half-bridge flyback power converter and operation method thereof

Abstract

The invention provides an asymmetric half-bridge flyback power converter and an operation method thereof. The power converter comprises a transformer, a resonance circuit, a first switch, a second switch, a discharge switch, an energy storage capacitor and a controller. The resonance circuit is coupled between a node between the first switch and the second switch and the transformer, and the discharge switch is coupled between the node and the energy storage capacitor. When the power converter is operated in a discontinuous resonance mode, and the controller switches on the discharge switch before controlling the first switch to be switched on, so that the current flowing to the node is boosted through the energy storage of the energy storage capacitor.

Description

Technical Field

[0001] The present invention relates to a power converter and an operating method thereof, and more particularly to an asymmetric half-bridge flyback power converter and an operating method thereof. Background Art

[0002] In recent years, consumer electronics have seen increasing demands for adapter power and size. Switching power converters, with their high efficiency and compact size, have replaced linear regulators as the mainstream choice for consumer electronics. Asymmetric half-bridge flyback converters, in particular, offer the advantage of low input current ripple. Their built-in current ripple cancellation mechanism can further effectively reduce input current ripple. Therefore, they have become a more suitable circuit architecture for switching power converters.

[0003] Traditional asymmetric half-bridge flyback power converters typically use metal oxide semiconductors (MOSFETs) as the switching element for pulse width modulation (PWM). This is due to their fast switching speed and low loss characteristics. However, if the MOSFET's parasitic capacitance is not fully discharged when the switch is turned on, a voltage will appear between the MOSFET's drain and source. This voltage, combined with the current flowing through the MOSFET's source, will cause losses, known as MOSFET switching losses. As the demand for high efficiency in power converter technology continues to rise, minimizing MOSFET switching losses is imperative.

[0004] Therefore, how to design an asymmetric half-bridge flyback power converter to achieve zero voltage switching at any time point during the power conversion process to reduce the switching loss of the MOSFET is a major research topic of this application. Summary of the Invention

[0005] To address the aforementioned issues, the present application provides an asymmetric half-bridge flyback power converter to overcome the problems of the prior art. The asymmetric half-bridge flyback power converter of the present application includes a transformer, a resonant circuit, a switching circuit, a zero-voltage switching circuit, and a controller. The transformer includes a primary winding, a secondary winding, and an excitation inductor. The primary winding is coupled to the secondary winding, and the excitation inductor is connected in parallel with the primary winding. The resonant circuit is coupled to the primary winding, and the switching circuit includes a first switch and a second switch connected in series. The node between the first and second switches is coupled to the resonant circuit. The zero-voltage switching circuit is coupled to the node and includes a discharge switch, a diode, and an energy storage capacitor connected in series. The controller is coupled to the zero-voltage switching circuit and controls the first and second switches to turn on or off based on a feedback signal to generate an output voltage. When the output energy of the power converter is lower than a threshold, the controller turns on the discharge switch before turning on the first switch to increase the current flowing to the node by storing energy in the energy storage capacitor.

[0006] In one embodiment, when the output energy is an output voltage and the output voltage is lower than a voltage threshold, the controller turns on the discharge switch before controlling the first switch to turn on; when the output energy is an output current of the power converter and the output current is lower than a first current threshold, the controller turns on the discharge switch before controlling the first switch to turn on.

[0007] In one embodiment, the asymmetric half-bridge flyback power converter further includes an auxiliary winding and a voltage regulator circuit. The auxiliary winding is coupled to the primary winding, and the voltage regulator circuit is coupled to the auxiliary winding. The auxiliary winding generates a winding voltage by coupling to the primary winding, and the voltage regulator circuit supplies power to the controller based on the winding voltage.

[0008] In one embodiment, the energy storage capacitor is connected in parallel with the voltage stabilizing circuit to store the operating voltage provided by the voltage stabilizing circuit, and the controller operates by receiving the operating voltage.

[0009] In one embodiment, the first switch includes a first parasitic capacitor, and the capacitance of the first parasitic capacitor is smaller than the energy storage capacitance of the energy storage capacitor.

[0010] In one embodiment, when the first switch is on and the second switch is off, the excitation inductor stores an excitation current. When the excitation current is greater than or equal to a threshold value, the controller controls the first switch to be turned off, and the second parasitic capacitor of the second switch is discharged toward the node.

[0011] In one embodiment, when the first switch is off and the second switch is on, energy from the primary winding is transferred to the secondary winding and the auxiliary winding. When the first and second switches are off, and the magnetizing current has discharged to zero, the magnetizing inductance, the first parasitic capacitance, and the second parasitic capacitance resonate with a resonant period.

[0012] In one embodiment, the resonant period is related to the magnitude of the output current of the power converter.

[0013] In one embodiment, the resonant circuit includes a resonant capacitor, and when the discharge switch is turned on, the resonant capacitor charges the second parasitic capacitor, the energy storage capacitor, and the excitation inductor.

[0014] In one embodiment, when the current increases to a second current threshold, the controller controls the discharge switch to be turned off, and the second current threshold is associated with the time when the first parasitic capacitor is completely discharged.

[0015] In order to solve the above problems, the present application also provides an operating method of an asymmetric half-bridge flyback power converter to overcome the problems of the prior art. Therefore, the power converter of the present application includes a transformer, a resonant circuit, a first switch, a second switch, a discharge switch and an energy storage capacitor. The resonant circuit is coupled between the node between the first switch and the second switch and the transformer, and the discharge switch is coupled between the node and the energy storage capacitor. The operating method of the asymmetric half-bridge flyback power converter includes the following steps: (a) controlling the first switch and the second switch to be turned on or off according to the feedback signal to generate an output voltage. (b) determining whether the output energy of the power converter is lower than a threshold. (c) turning on the discharge switch before controlling the first switch to be turned on according to the output energy being lower than the threshold.

[0016] In one embodiment, when the output energy is an output voltage, the following steps are further included: (b1) determining whether the output voltage is lower than a voltage threshold; and (b2) turning on the discharge switch before turning on the first switch based on the output voltage being lower than the voltage threshold.

[0017] In one embodiment, when the output energy is the output current of the power converter, the following steps are further included: (b3) determining whether the output current is lower than a first current threshold; and (b4) turning on the discharge switch before turning on the first switch based on the output current being lower than the first current threshold.

[0018] In one embodiment, the operating method of the asymmetric half-bridge flyback power converter further includes the following steps: (c1) when the first switch is on and the second switch is off, the transformer's magnetizing inductor stores a magnetizing current. (c2) when the magnetizing current is greater than or equal to a threshold value, the first switch is controlled to turn off. (c3) the second parasitic capacitance of the second switch is discharged toward the node.

[0019] In one embodiment, the operating method of the asymmetric half-bridge flyback power converter further includes the following steps: (c4) when the first switch is off and the second switch is on, energy from the transformer is transferred to the secondary winding and the auxiliary winding of the power converter. (c5) when the first switch is off and the second switch is off, and the excitation current is discharged to zero, the excitation inductance, the first parasitic capacitance of the first switch, and the second parasitic capacitance generate a resonance having a resonant period. The resonant period is related to the magnitude of the output current of the power converter.

[0020] In one embodiment, the operating method of the asymmetric half-bridge flyback power converter further includes the following steps: (c6) when the discharge switch is turned on, the resonant capacitor of the resonant circuit charges the second parasitic capacitor, the energy storage capacitor, and the excitation inductor. (c7) when the current increases to a second current threshold, the discharge switch is controlled to turn off. The second current threshold is related to the time when the first parasitic capacitor is completely discharged.

[0021] The primary purpose and effectiveness of this application is to achieve zero-voltage switching (ZVS) even in discontinuous resonant mode. This is accomplished by connecting a discharge switch and a diode in series at the node between the first and second switches. The discharge switch is activated before the first switch is turned on, allowing the resonant circuit to reversely charge the magnetizing inductor, thereby increasing the reverse current flowing into the node between the first and second switches. This reverse current discharges the parasitic capacitance of the first switch, achieving ZVS.

[0022] In order to further understand the technology, method and effects of the present invention and achieve the intended purpose of the present invention, please refer to the following detailed description and drawings; in addition, the purpose, characteristics and features of the present invention can be understood more deeply and specifically; however, the drawings are provided for reference and description only and are not intended to limit the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A A circuit block diagram of the asymmetric half-bridge flyback power converter of the present application;

[0024] Figure 1B This is a waveform timing diagram of the asymmetric half-bridge flyback power converter of the present application operating in a continuous resonance mode;

[0025] Figure 2 This is a waveform timing diagram of the asymmetric half-bridge flyback power converter of the present application operating in a discontinuous resonance mode;

[0026] Figures 3A to 3G They are respectively current path diagrams of the asymmetric half-bridge flyback power converter of the present application operating in a discontinuous resonance mode; and

[0027] Figure 4This is a flow chart of the operating method of the asymmetric half-bridge flyback power converter of the present application.

[0028] Wherein, the reference numerals:

[0029] 100: Power Converter

[0030] 1: Power conversion circuit

[0031] 12: Switching circuit

[0032] S1: First switch

[0033] Cs1: first parasitic capacitance

[0034] S2: Second switch

[0035] Cs2: Second parasitic capacitance

[0036] SW:Node

[0037] 14: Resonant Circuit

[0038] Lr: resonant inductor

[0039] Cr: resonant capacitor

[0040] 16: Transformer

[0041] 162: Primary side winding

[0042] 164: Secondary side winding

[0043] Lm: magnetizing inductance

[0044] 18: Rectifier circuit

[0045] Co: output capacitance

[0046] Do: output diode

[0047] 2: Auxiliary power supply circuit

[0048] 22: Auxiliary winding

[0049] 24: Voltage stabilizing circuit

[0050] 3: Controller

[0051] 4: Zero voltage switching circuit

[0052] 42: Discharge switch

[0053] 44: diode

[0054] 46: Energy storage capacitor

[0055] 200: Load

[0056] Vdc: DC voltage

[0057] Vo: output voltage

[0058] Vaux: winding voltage

[0059] VCC: operating voltage

[0060] Sc: Control signal

[0061] Ilm: excitation current

[0062] Icr: resonant current

[0063] Isec: Secondary side current

[0064] Io: output current

[0065] Isw: current

[0066] -Ith: Second current threshold

[0067] t1~t8: time. DETAILED DESCRIPTION

[0068] The technical content and detailed description of the present invention are described below with reference to the accompanying drawings:

[0069] See also Figure 1A This is a circuit block diagram of an asymmetric half-bridge flyback power converter according to the present invention. An asymmetric half-bridge flyback power converter 100 (hereinafter referred to as power converter 100) receives a DC voltage Vdc and converts it into an output voltage Vo to power a load 200 coupled to the downstream side. Power converter 100 includes a power conversion circuit 1, an auxiliary power supply circuit 2, a controller 3, and a zero-voltage switching circuit 4. The power conversion circuit 1 includes a switching circuit 12, a resonant circuit 14, a transformer 16, and a rectifier circuit 18. Rectifier circuit 18 can be implemented in various ways; here, a configuration including an output capacitor Co and an output diode Do is used as an example. Switching circuit 12 receives a DC voltage Vdc and includes a first switch S1 and a second switch S2 connected in series. Transformer 16 includes a primary winding 162, a secondary winding 164, and a magnetizing inductor Lm. Primary winding 162 is coupled to secondary winding 164, and magnetizing inductor Lm is connected in parallel with primary winding 162. The magnetizing inductance Lm may be an equivalent inductance formed by the primary-side winding 162 , or an additional winding wound by the transformer 16 .

[0070] One end of the resonant circuit 14 is coupled to a node SW between the first switch S1 and the second switch S2, and the other end of the resonant circuit 14 is coupled to the primary winding 162. In one embodiment, the resonant circuit 14 may include a resonant inductor Lr and a resonant capacitor Cr. One end of the resonant inductor Lr is coupled to a node SW between the first switch S1 and the second switch S2, and the other end of the resonant inductor Lr is coupled to one end of the primary winding 162. One end of the resonant capacitor Cr is coupled to the second switch S2 and ground, and the other end of the resonant capacitor Cr is coupled to the other end of the primary winding 162. However, the present application is not limited to the above-described structure of the resonant circuit 14; any circuit structure that can enable the resonant circuit 14 to generate a resonant function is included within the scope of this embodiment. One end of the rectifier circuit 18 is coupled to the secondary winding 164, and the other end of the rectifier circuit 18 is coupled to the load 200 to provide an output voltage Vo to power the load 200.

[0071] The auxiliary power supply circuit 2 includes an auxiliary winding 22 and a voltage regulator circuit 24. The auxiliary winding 22 is coupled to the primary winding 162. One end of the voltage regulator circuit 24 is coupled to the auxiliary winding 22, and the other end of the voltage regulator circuit 24 is coupled to the controller 3. The auxiliary winding 22 generates a winding voltage Vaux by coupling to the primary winding 162. The voltage regulator circuit 24 provides an operating voltage VCC based on the winding voltage Vaux to power the controller 3. The zero-voltage switching circuit 4 is coupled to the node SW between the first switch S1 and the second switch S2. The zero-voltage switching circuit 4 includes a discharge switch 42, a diode 44, and a storage capacitor 46 connected in series. The controller 3 is coupled to the first switch S1 and the second switch S2 and provides a pulse-width modulation signal to control the first switch S1 and the second switch S2 to turn on or off, thereby controlling the power conversion circuit 1 to convert the DC voltage Vdc into the output voltage Vo. Furthermore, the controller 3 receives a feedback signal corresponding to the output voltage Vo and adjusts the pulse-width modulation signal based on the feedback signal to stabilize the output voltage Vo through the adjustment of the pulse-width modulation signal. The output capacitor Co stores the output voltage Vo to provide the output voltage Vo to power the load 200. It is worth noting that in one embodiment, the voltage regulator circuit 24 may be, for example but not limited to, a linear regulator, a clamping circuit, or other circuit capable of regulating the winding voltage Vaux. For example but not limited to, the simplest implementation of the voltage regulator circuit 24 may be a diode to reverse-bias and block negative voltages of the winding voltage Vaux.

[0072] On the other hand, the controller 3 is coupled to the discharge switch 42. When the output energy of the power converter 100 is lower than the threshold, and before the controller 3 controls the first switch S1 to turn on, it first provides a control signal Sc to turn on the discharge switch 42 to store energy in the energy storage capacitor 46, and increase the current flowing to the node SW through the energy storage of the energy storage capacitor 46. Among them, the energy storage capacitor 46 can be a capacitor with a larger capacitance value, and an electrolytic capacitor is a preferred embodiment. Specifically, the energy storage capacitor 46 is mainly used to increase the current flowing to the node SW by means of energy storage. Therefore, its capacitance needs to be larger to provide a better energy storage means. It is worth mentioning that in one embodiment, the controller 3 can be, for example but not limited to, a control chip such as a microcontroller (MCU) or a digital signal processor (DSP), but the controller 3 does not exclude that it can also be implemented by devices such as a control circuit and a logic circuit.

[0073] On the other hand, since the energy storage capacitor 46 is preferably implemented as an electrolytic capacitor, a capacitor with a larger capacitance value in the power converter 100 can be used as the energy storage capacitor 46 (for example, but not limited to, the input capacitor, the output capacitor, the capacitor of the power supply end of the controller 3, etc., and this embodiment uses the energy storage capacitor 46 coupled to the power supply end of the controller 3 as an illustrative example) to save additional capacitor configuration costs and improve the power density of the power converter 100. However, it is not ruled out that the energy storage capacitor 46 is configured as an independent one. In this embodiment, since the energy storage capacitor 46 is coupled to the power supply end of the controller 3, the energy storage capacitor 46 is connected in parallel with the voltage regulator circuit 24 to store the operating voltage VCC provided by the voltage regulator circuit 24, and the controller 3 receives the operating voltage VCC and operates.

[0074] See also Figure 1B This is a waveform timing diagram of the asymmetric half-bridge flyback power converter of the present application operating in the continuous resonance mode, and is also referred to in conjunction with Figure 1AWhen the power converter 100 operates in continuous resonance mode and the first switch S1 is turned on, the DC voltage Vdc charges the magnetizing inductor Lm of the transformer 16 and the resonant capacitor Cr of the resonant circuit 14. Consequently, the magnetizing current Ilm flowing through the magnetizing inductor Lm and the resonant current Icr flowing through the resonant capacitor Cr gradually increase. When the second switch S2 is turned on, energy is transferred from the resonant capacitor Cr on the primary side of the transformer 16 to the secondary side of the transformer 16. The waveform of the secondary-side current Isec resembles a half-sine wave current waveform of a resonant converter. Fluctuations in the output voltage and output current Io (collectively referred to herein as output energy) affect the on-time of the first switch S1. Under this operation, the magnetizing inductor Lm is clamped at nVo (i.e., n times the output voltage Vo) for demagnetization. As the output energy fluctuates, the demagnetization time also changes.

[0075] Generally speaking, because switching elements are not ideal, the first switch S1 includes a first parasitic capacitor Cs1, and the second switch S2 includes a second parasitic capacitor Cs2. When the power converter 100 operates in continuous resonant mode, after the magnetizing inductor Lm is discharged to 0A, the power converter 100 typically turns on the second switch S2 to reversely charge the magnetizing inductor Lm, causing its magnetizing current Ilm to reverse direction (i.e., the current direction flows toward the node SW). This reverse current is then used to discharge the first parasitic capacitor Cs1 of the first switch S1, thereby achieving zero voltage switching. This continuous resonant mode can achieve zero voltage switching even under full load and high voltage conditions.

[0076] However, when the output current Io or the output voltage Vo (i.e., the output energy) decreases, the peak current of the excitation current Ilm of the excitation inductor Lm also decreases, causing the operating frequency of the power converter 100 to be too high. Furthermore, the circulating energy in the resonant circuit 14 will also limit the overall efficiency of the power converter 100. Therefore, under low output energy conditions, the asymmetric half-bridge flyback power converter 100 typically operates in a discontinuous resonant mode with an excitation current Ilm (i.e., the controller 3 adjusts the operating mode to the discontinuous resonant mode). However, if the second switch S2 in the discontinuous resonant mode is turned off when the excitation inductor Lm discharges to 0 A, there will not be sufficient reverse excitation current Ilm in the discontinuous resonant mode, and zero voltage switching may not be achieved, resulting in additional switching losses.

[0077] Therefore, the primary purpose and effectiveness of this application is to achieve zero-voltage switching (ZVS) in discontinuous resonant mode. This is accomplished by connecting a discharge switch 42 and a diode 44 in series at the node SW between the first switch S1 and the second switch S2. By turning on the discharge switch 42 before turning on the first switch S1, the resonant circuit 14 reversely charges the magnetizing inductor, increasing the reverse current flowing into the node SW between the first and second switches S1 and S2. This reverse current then discharges the parasitic capacitance of the first switch S1, achieving ZVS.

[0078] Furthermore, since the asymmetric half-bridge flyback power converter 100 operates in a discontinuous resonant mode with a magnetizing current Ilm under low output energy conditions, the resonant circuit 14 must be used to reversely charge the magnetizing inductor to increase the current flowing in the reverse direction into the node SW between the first switch S1 and the second switch S2. Therefore, the controller 3 must detect the level of the output energy. The output energy can be the output voltage Vo. When the output energy is the output voltage Vo, and the output voltage Vo is lower than a voltage threshold (for example, but not limited to, a wide range of output voltage Vo with an upper limit of 48V, where the voltage threshold can be set at 12V), the controller 3 turns on the discharge switch 42 before controlling the first switch S1 to conduct, so as to reversely charge the magnetizing inductor using the resonant circuit 14 and increase the current flowing in the reverse direction into the node SW. Alternatively, the output energy can be the output current Io. When the output energy is the output current Io, and the output current Io is lower than a first current threshold (for example, but not limited to, the first current threshold may be set at 5A for a full-load output current Io of 20A), the controller 3 first turns on the discharge switch 42 before controlling the first switch S1 to turn on, so as to utilize the resonant circuit 14 to reversely charge the excitation inductor and thereby increase the current flowing in the reverse direction into the node SW.

[0079] See also Figure 2 This is a waveform timing diagram of the asymmetric half-bridge flyback power converter of the present application operating in a discontinuous resonance mode, and Figure 3A to Figure 3G They are respectively the current path diagrams of the asymmetric half-bridge flyback power converter of the present application operating in the discontinuous resonance mode, and are used in conjunction with Figure 1A-1B , and refer to it repeatedly Figures 2 to 3G At time t1~t2 (see Figure 3A ), the controller 3 controls the first switch S1 to conduct, and controls the second switch S2 and the discharge switch 42 to turn off, causing the output diode Do and the diode 44 to be reverse-biased and cut off. At this time, the DC voltage Vdc charges the excitation inductor Lm, and the excitation inductor Lm stores the excitation current Ilm. After the current value of the excitation current Ilm rises to or above the threshold value, the controller 3 controls the first switch S1 to turn off, entering the period t2-t3 (dead time). During the period t2-t3 (see also Figure 3B), controller 3 turns off first switch S1, second switch S2, and discharge switch 42, and reverse-bias ...

[0080] At time t3-t4 (see Figure 3C ), the controller 3 controls the second switch S2 to be turned on, and controls the first switch S1 and the discharge switch 42 to be turned off. At this time, the output diode Do is forward biased and turned on, and the diode 44 is reverse biased and turned off. In addition, the energy of the primary winding 162 is transferred to the secondary winding 164 and the auxiliary winding 22, so that the stored energy is provided to the output capacitor Co and the controller 3 to maintain the normal operation of the power converter 100. At time t4-t5 (see Figure 3D ), the controller controls the first switch S1, the second switch S2 and the discharge switch 42 to be turned off, so that the output diode Do and the diode 44 are reverse-biased and cut off, and the excitation current Ilm is released to 0A.

[0081] At time t5-t6 (see Figure 3E ), the controller 3 continuously controls the first switch S1, the second switch S2, and the discharge switch 42 to be off, and the output diode Do and the diode 44 are continuously reverse-biased and cut off. At this time, the excitation inductor Lm, the first parasitic capacitor Cs1, and the second parasitic capacitor Cs2 generate a resonance with a resonant period (i.e., current flows back and forth through the excitation inductor Lm, the first parasitic capacitor Cs1, and the second parasitic capacitor Cs2), and the resonant period is related to the magnitude of the output current Io of the power converter 100. Generally speaking, the larger the output current Io, the shorter the resonant period, and vice versa. After a sufficient number of resonant cycles and the resonant current Icr resonates to 0A, the controller 3 controls the discharge switch 42 to be turned on, entering time t6-t7.

[0082] At time t6-t7 (see Figure 3F), the controller 3 controls the discharge switch 42 to be turned on, so that the diode 44 is forward-biased and turned on. Similarly, the controller 3 continuously controls the first switch S1 and the second switch S2 to be continuously turned off, and the output diode Do is continuously reverse-biased and cut off. At this time, the resonant capacitor Cr charges the second parasitic capacitor Cs2 of the second switch S2, the energy storage capacitor 46 and the excitation inductor Lm at the same time. Since the capacitance of the energy storage capacitor 46 is much larger than the second parasitic capacitor Cs2 of the second switch S2. Therefore, most of the charging current will flow to the energy storage capacitor 46, so that the second parasitic capacitor Cs2 of the second switch S2 will not be fully charged immediately. Therefore, during the charging process, the excitation inductor Lm is charged with a sufficiently large reverse current, and the direction of this current is opposite to the direction of the excitation current Ilm and flows through the node SW to the second parasitic capacitor Cs2 to charge the second parasitic capacitor Cs2.

[0083] When the reverse current Isw reaches a sufficiently large value (i.e., the current Isw flowing to the node SW increases to the second current threshold -Ith), the controller controls the discharge switch 42 to be turned off, and enters the time t7-t8. At the time t7-t8 (see Figure 3G ), the controller 3 turns off the first switch S1, the second switch S2, and the discharge switch 42, and reverse-biassing the output diode Do and the diode 44. At this point, a current Isw, which is opposite to the excitation current Ilm, discharges the first parasitic capacitor Cs1 of the first switch S1, turning its junction diode forward, thereby achieving zero-voltage switching.

[0084] The above-mentioned "sufficiently large" means a current sufficient to completely charge the second parasitic capacitor Cs2 of the second switch S2 and to completely discharge the first parasitic capacitor Cs1 of the first switch S1. Therefore, the capacitance of the first parasitic capacitor Cs1 and the capacitance of the second parasitic capacitor Cs2 are preferably smaller than the energy storage capacitance of the energy storage capacitor 46, and the second current threshold -Ith is associated with the time required for the first parasitic capacitor Cs1 to be completely discharged. When the capacitance of the first parasitic capacitor Cs1 and the capacitance of the second parasitic capacitor Cs2 are larger, the second current threshold -Ith can be increased (meaning that its absolute value is higher), and vice versa. The formula is as follows:

[0085]

[0086] Wherein, −Ilm is a current setting value (ie, a second current threshold −Ith) that is opposite to the excitation current Ilm, and the setting value can be set by the controller 3 .

[0087] See also Figure 4 This is a flowchart of the method for operating the asymmetric half-bridge flyback power converter of the present invention. Figure 3GThe power converter 100 includes a transformer 16, a resonant circuit 14, a first switch S1, a second switch S2, a discharge switch 42, and an energy storage capacitor 46. The resonant circuit 14 is coupled between a node SW between the first switch S1 and the second switch S2 and the transformer 16. The discharge switch 42 is coupled between the node SW and the energy storage capacitor 46. The first switch S1, the second switch S2, and the discharge switch 42 are primarily operated by the controller 3. Furthermore, the operating method of the power converter includes controlling the first switch and the second switch to be turned on or off according to a feedback signal to generate an output voltage (S100). In a preferred embodiment, the controller 3 provides a pulse width modulation signal to control the first switch S1 and the second switch S2 to be turned on or off, thereby controlling the power conversion circuit 1 to convert the DC voltage Vdc into the output voltage Vo. Furthermore, the controller 3 receives a feedback signal corresponding to the output voltage Vo and adjusts the pulse width modulation signal according to the feedback signal to stabilize the voltage value of the output voltage Vo by adjusting the pulse width modulation signal.

[0088] Then, it is determined whether the output energy of the power converter is lower than the threshold (S120). Due to the fluctuations in the output voltage and the output current Io (collectively referred to as the output energy here), the demagnetization time will change when the output energy changes. Therefore, it is necessary to determine whether the power converter 100 is operating in the continuous resonant mode or the discontinuous resonant mode by determining whether the output energy is lower than the threshold, so as to provide corresponding operating steps according to the different modes. When the judgment result of step (S120) is yes, it means that the output energy is lower than the threshold and the power converter 100 is operating in the discontinuous resonant mode. Therefore, based on the output energy being lower than the threshold, the discharge switch is turned on before the first switch is turned on (S140). In this way, the resonant circuit 14 can be used to reversely charge the excitation inductor to increase the current flowing in the reverse direction into the node SW between the first switch S1 and the second switch S2, and this reverse current is used to discharge the parasitic capacitance of the first switch S1 to achieve the effect of zero voltage switching.

[0089] When the judgment result of step (S120) is no, it means that the output energy is higher than the threshold value and the power converter 100 operates in the continuous resonance mode. Therefore, the process returns to step (S100) for continuous judgment. It is worth mentioning that, in one embodiment, Figure 4 For operation steps not described in detail, please refer to Figure 1~ Figure 3G , which will not be described in detail here. In addition, in one embodiment of the present application, the control of the first switch S1, the second switch S2, and the discharge switch 42 is not limited to being controlled only by the controller 3. Any controller, control circuit (composed of passive electronic components), logic circuit (composed of logic components), and other devices that can perform the above operations should be included in the scope of this embodiment.

[0090] The above description is merely a preferred embodiment of the present application and should not limit the scope of implementation of the present application. That is, all equivalent changes and modifications made based on the present application should still fall within the scope of protection intended by the patent coverage of the present application. The present application may also have many other embodiments. Without departing from the spirit and essence of the present application, those skilled in the art should be able to make various corresponding changes and modifications based on the present application, and these corresponding changes and modifications should fall within the scope of protection of the claims attached to the present application.

Claims

1. An asymmetric half-bridge flyback power converter, characterized in that: include: A transformer comprising a primary winding, a secondary winding and an excitation inductor, wherein the primary winding is coupled to the secondary winding, and the excitation inductor is connected in parallel with the primary winding; a resonant circuit coupled to the primary side winding; a switch circuit comprising a first switch and a second switch connected in series, wherein a node between the first switch and the second switch is coupled to the resonant circuit; a zero voltage switching circuit coupled to the node and comprising a discharge switch, a diode, and an energy storage capacitor connected in series; and a controller coupled to the zero-voltage switching circuit, the controller controlling the first switch and the second switch to turn on or off according to a feedback signal to generate an output voltage; When an output energy of the power converter is lower than a threshold, the controller turns on the discharge switch before controlling the first switch to turn on, so as to increase a current flowing to the node through energy stored in the energy storage capacitor.

2. The asymmetric half-bridge flyback power converter according to claim 1, wherein: When the output energy is the output voltage and the output voltage is lower than a voltage threshold, the controller turns on the discharge switch before controlling the first switch to turn on; when the output energy is an output current of the power converter and the output current is lower than a first current threshold, the controller turns on the discharge switch before controlling the first switch to turn on.

3. The asymmetric half-bridge flyback power converter according to claim 1, wherein: Also includes: an auxiliary winding coupled to the primary winding; a voltage stabilizing circuit coupled to the auxiliary winding; and The auxiliary winding generates a winding voltage by coupling with the primary winding, and the voltage stabilizing circuit supplies power to the controller according to the winding voltage.

4. The asymmetric half-bridge flyback power converter according to claim 3, wherein: The energy storage capacitor is connected in parallel with the voltage stabilizing circuit to store an operating voltage provided by the voltage stabilizing circuit, and the controller operates by receiving the operating voltage.

5. The asymmetric half-bridge flyback power converter according to claim 4, wherein: The first switch includes a first parasitic capacitor, and a capacitance of the first parasitic capacitor is smaller than an energy storage capacitance of the energy storage capacitor.

6. The asymmetric half-bridge flyback power converter according to claim 5, wherein: When the first switch is turned on and the second switch is turned off, the excitation inductor stores an excitation current; When the current value of the excitation current is greater than or equal to a threshold value, the controller controls the first switch to be turned off, and a second parasitic capacitance of the second switch is discharged toward the node.

7. The asymmetric half-bridge flyback power converter according to claim 6, wherein: When the first switch is turned off and the second switch is turned on, the energy of the primary winding is transferred to the secondary winding and the auxiliary winding; When the first switch and the second switch are turned off and the excitation current is discharged to zero, the excitation inductor, the first parasitic capacitor and the second parasitic capacitor generate a resonance with a resonance period.

8. The asymmetric half-bridge flyback power converter according to claim 7, wherein: The resonance period is related to a magnitude of an output current of the power converter.

9. The asymmetric half-bridge flyback power converter according to claim 7, wherein: The resonant circuit includes a resonant capacitor, and when the discharge switch is turned on, the resonant capacitor charges the second parasitic capacitor, the energy storage capacitor, and the excitation inductor.

10. The asymmetric half-bridge flyback power converter according to claim 9, wherein: When the current increases to a second current threshold, the controller controls the discharge switch to be turned off, and the second current threshold is associated with a time when the first parasitic capacitor is completely discharged.

11. An operating method of an asymmetric half-bridge flyback power converter, characterized in that: The power converter includes a transformer, a resonant circuit, a first switch, a second switch, a discharge switch, and an energy storage capacitor. The resonant circuit is coupled between a node between the first switch and the second switch and the transformer, and the discharge switch is coupled between the node and the energy storage capacitor. The operating method includes the following steps: controlling the first switch and the second switch to be turned on or off according to a feedback signal to generate an output voltage; determining whether an output energy of the power converter is lower than a threshold; and According to the output energy being lower than the threshold, the discharge switch is turned on before the first switch is controlled to be turned on.

12. The operating method of the power converter according to claim 11, wherein: When the output energy is the output voltage, the following steps are further included: determining whether the output voltage is lower than a voltage threshold; and According to the output voltage being lower than the voltage threshold, the discharge switch is turned on before the first switch is controlled to be turned on.

13. The operating method of the power converter according to claim 11, wherein: When the output energy is an output current of the power converter, the method further includes the following steps: Determining whether the output current is lower than a first current threshold; and According to the output current being lower than the first current threshold, the discharge switch is turned on before the first switch is controlled to be turned on.

14. The operating method of the power converter according to claim 11, wherein: The following steps are also included: When the first switch is turned on and the second switch is turned off, an excitation inductor of the transformer stores an excitation current; When the current value of the excitation current is greater than or equal to a threshold value, controlling the first switch to be turned off; and A second parasitic capacitance of the second switch is discharged toward the node.

15. The operating method of the power converter according to claim 14, wherein: The following steps are also included: When the first switch is turned off and the second switch is turned on, the energy of the transformer is transferred to a secondary winding and an auxiliary winding of the power converter; and When the first switch is turned off and the second switch is turned off, and the excitation current is discharged to zero, the excitation inductor, a first parasitic capacitor of the first switch, and the second parasitic capacitor generate a resonance having a resonance period; The resonance period is related to the magnitude of an output current of the power converter.

16. The operating method of the power converter according to claim 15, wherein: The following steps are also included: When the discharge switch is turned on, a resonant capacitor of the resonant circuit charges the second parasitic capacitor, the energy storage capacitor and the excitation inductor; When the current increases to a second current threshold, controlling the discharge switch to turn off; and The second current threshold is associated with a time when the first parasitic capacitor is completely discharged.

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