A control circuit and control method for a resonant circuit

Abstract

Disclosed is a control circuit of a resonant circuit. When the output power of the resonant circuit is low, the primary side inductance of the transformer of the resonant circuit stores maximum energy to charge the switching terminal of the resonant circuit, i.e. to charge the connection point of the pull-up switch tube and the pull-down switch tube, so as to ensure that the voltage of the switching terminal reaches the maximum value when the pull-up switch tube is turned on, and realize low-loss opening of the pull-up switch tube. When the output power of the resonant circuit is high, the on duration of the pull-down switch tube is adaptively adjusted to ensure that the voltage of the switching terminal reaches the input voltage value when the pull-up switch tube is turned on, and realize zero-voltage opening of the pull-up switch tube. The present application adopts a flexible control method to make the switches of the resonant circuit realize zero-voltage opening as much as possible, thereby achieving the purpose of reducing the opening loss.

Description

Technical Field

[0001] Embodiments of the present invention relate to switching power supplies, and more specifically, to a resonant circuit. Background Technology

[0002] In traditional low-power AC / DC conversion applications, flyback converters are widely used due to their simple structure, fewer required components, and low cost. However, traditional flyback converters typically operate in hard-switching mode, meaning that the voltage difference across the switch and / or the current flowing through the switch are not zero during turn-off and turn-on, resulting in switching losses. The higher the switching frequency of the flyback converter, the greater its switching losses. However, to meet the trend of miniaturization, lightweighting, and modularization of switching converters, the operating frequency of switching converters is gradually increasing. For hard-switching flyback converters, an increase in switching frequency means an increase in switching losses. This obviously limits the application of flyback converters in high-power power supplies.

[0003] Soft-switching technology refers to reducing switching losses by making the voltage difference across the switch zero (zero-voltage switching) or the current flowing through the switch zero (zero-current switching) at the moment of switching on and off. To enable soft switching and reduce switching losses in flyback converters, improved flyback converter topologies have been proposed based on the resonance principle, including active clamp flyback converters and asymmetric half-bridge flyback converters. The asymmetric half-bridge flyback converter combines a flyback converter with an LLC resonant circuit. On the primary side of the flyback converter, an LLC topology is used, allowing the primary circuit to operate in resonant mode. Furthermore, by controlling the current phase and amplitude appropriately, soft switching is achieved on the primary side. Summary of the Invention

[0004] This invention provides a control circuit that, when the output power of the resonant circuit is low, promptly turns off the pull-down switch, allowing the inductance of the primary winding of the transformer in the resonant circuit to store maximum energy to charge the switching terminals of the resonant circuit, i.e., to charge the connection point between the pull-up and pull-down switches. This ensures that the voltage at the switching terminals reaches its maximum value when the pull-up switch is turned on, achieving low-loss turn-on of the pull-up switch. When the output power of the resonant circuit is high, the conduction time of the pull-down switch is adaptively adjusted to ensure that the voltage at the switching terminals reaches the input voltage value when the pull-up switch is turned on, achieving zero-voltage turn-on of the pull-up switch. This invention, by employing different control methods in different modes, enables the resonant circuit to achieve zero-voltage turn-on as much as possible, thereby reducing turn-on losses.

[0005] According to an embodiment of the present invention, a control circuit for a resonant circuit is proposed. The resonant circuit includes a pull-up switch and a pull-down switch. The control circuit includes a pull-down switch control circuit that outputs a pull-down control signal. Before the pull-up switch is turned on, the pull-down control signal has a first pulse corresponding to the on-time of the pull-down switch. The end time of the first pulse corresponds to the moment when the resonant capacitor voltage of the resonant circuit crosses zero from positive to negative.

[0006] In one embodiment, the pull-down switch control circuit further receives a pre-charge duration signal. When the output voltage of the resonant circuit is less than the output voltage threshold and the power feedback signal is less than the power threshold, the first pulse ends when any of the following conditions are met: (1) the pre-charge duration signal indicates the end of the pre-charge conduction duration of the pull-down switch; (2) the resonant capacitor voltage crosses zero from positive to negative.

[0007] According to an embodiment of the present invention, a control circuit for a resonant circuit is proposed. The resonant circuit includes a pull-up switch and a pull-down switch. The control circuit includes a pull-down switch control circuit, which receives a conduction duration signal and outputs a pull-down control signal to control the on / off state of the pull-down switch. The pull-down switch is turned off when any of the following conditions are met: (1) the conduction duration signal indicates the end of the conduction duration of the pull-down switch; (2) the voltage of the resonant capacitor of the resonant circuit crosses zero from positive to negative.

[0008] In one embodiment, the resonant capacitor voltage is obtained by detecting the zero-crossing signal provided by the auxiliary winding of the transformer in the resonant circuit, based on the time when the voltage crosses from positive to negative zero.

[0009] According to an embodiment of the present invention, a resonant circuit is provided, including the aforementioned control circuit, and further including: a pull-up switch; and a pull-down switch, which is connected in series with the pull-up switch between the input voltage and the primary ground.

[0010] According to an embodiment of the present invention, a control method for a resonant circuit is proposed. The resonant circuit includes a pull-up switch and a pull-down switch. The control method includes: in each switching cycle: turning on the pull-down switch; turning off the pull-down switch when the pre-charge conduction time of the pull-down switch ends or the voltage of the resonant capacitor of the resonant circuit crosses zero from positive to negative; turning on the pull-up switch; turning off the pull-up switch when the value of the resonant current reaches a preset peak value; turning on the pull-down switch; and turning off the pull-down switch when the transformer of the resonant circuit demagnetizes or when the resonant cycle ends.

[0011] According to an embodiment of the present invention, a control method for a resonant circuit is proposed. The resonant circuit includes a pull-up switch and a pull-down switch. The control method includes: in each switching cycle: turning on the pull-up switch; turning off the pull-up switch when the value of the resonant current reaches a preset peak value; turning on the pull-down switch; and turning off the pull-down switch when either a preset on-time ends or the resonant capacitor voltage crosses zero from positive to negative is met. Attached Figure Description

[0012] To better understand this invention, it will be described in detail with reference to the following figures:

[0013] Figure 1 This is a schematic diagram of the existing resonant circuit 10.

[0014] Figure 2 A schematic diagram of the circuit structure of an existing resonant circuit 20 with another configuration is shown.

[0015] Figure 3 A schematic diagram of the circuit structure of a control circuit 30 according to an embodiment of the present invention is shown;

[0016] Figure 4 The diagram shows a signal waveform of a resonant circuit 10 according to an embodiment of the present invention when it is controlled by a control circuit 30 to operate in pulse skipping mode and when the output voltage is low.

[0017] Figure 5 The diagram shows a signal waveform of a resonant circuit 10 according to an embodiment of the present invention, which is controlled by a control circuit 30 to operate in pulse skipping mode and has a high output voltage.

[0018] Figure 6 The diagram shows a signal waveform of a resonant circuit 10 according to an embodiment of the present invention, which is controlled by a control circuit 30 to operate in a continuous conduction mode.

[0019] Figure 7 A schematic diagram of the circuit structure of a control circuit 70 according to an embodiment of the present invention is shown;

[0020] Figure 8 This is a flowchart illustrating a control method 80 for a resonant circuit operating in pulse-jump mode and with a low output voltage, according to an embodiment of the present invention.

[0021] Figure 9 This is a flowchart illustrating a control method 90 for a resonant circuit operating in continuous conduction mode according to an embodiment of the present invention. Detailed Implementation

[0022] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0023] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "in an embodiment," "in an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. The same reference numerals indicate the same elements. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Figure 1 This is a schematic diagram of the existing resonant circuit 10. (For example...) Figure 1 As shown, the resonant circuit 10 has an asymmetric half-bridge flyback topology, including: a pull-up switch QH and a pull-down switch QL connected in series between the input terminal IN and the primary ground PGND; a transformer T1 having a primary winding Np, a secondary winding Ns, and an auxiliary winding Nt; a resonant capacitor Cr connected in series with the primary winding Np between the switching terminal SW and the primary ground PGND; a secondary switch Ds connected in series with the secondary winding Ns; and an output capacitor Co. Figure 1 In this diagram, the resonant inductor Lr is the leakage inductance of the primary winding Np; it is merely an equivalent schematic device and not an actual inductor. In some applications, a separate inductor can be added as the resonant inductor, depending on the application requirements. Figure 1 In this context, the secondary-side switch Ds is also referred to as a secondary-side diode. It should be understood that the secondary-side switch Ds can include either a diode or a controllable switching transistor. Furthermore, in some applications, the secondary-side switch Ds can be coupled between the secondary-side winding Ns and the secondary-side ground SGND.

[0025] exist Figure 1In the resonant circuit 10, the pull-up switch QH and pull-down switch QL alternately turn on and off, transferring energy from the primary side to the secondary side. This forms the output voltage Vout across the output capacitor Co and supplies power to the load Ro. Specifically, when the pull-up switch QH is on and the pull-down switch QL is off, the inductance of the primary winding Np and the resonant capacitor Cr store energy, and the output capacitor Co supplies power to the load Ro. When the pull-up switch QH is off and the pull-down switch QL is on, the energy stored in the inductance of the primary winding Np and the resonant capacitor Cr is transferred to the secondary winding Ns. The secondary winding Ns charges the output capacitor Co and supplies power to the load Ro.

[0026] Figure 2 A schematic diagram of the circuit structure of an existing resonant circuit 20 with another configuration is shown. Figure 1 Compared to the resonant circuit 10 shown, in the resonant circuit 20, the resonant capacitor Cr is connected in series with the primary winding Np between the input terminal IN and the switch terminal SW. After being connected in series with the primary winding Np, the resonant capacitor Cr is connected in parallel with the pull-up switch QH.

[0027] exist Figure 1 and Figure 2 In this circuit, pull-up switch QH and pull-down switch QL form a half-bridge circuit coupled between input terminal IN and primary ground PGND. Input terminal IN receives the input voltage Vin. The input voltage Vin is a DC voltage, which can be obtained by rectifying an AC voltage. Ir is the resonant current flowing through resonant capacitor Cr, which is assumed in this paper as follows... Figure 1 The direction of the resonant current Ir shown is positive. Vsw is the voltage at the connection point (i.e., the switching terminal SW) of the pull-up switch QH and the pull-down switch QL, i.e., the switching voltage. GH is the pull-up control signal of the pull-up switch QH, and GL is the pull-down control signal of the pull-down switch QL. Figure 1 and Figure 2 In the circuit, the pull-up switch QH and pull-down switch QL are implemented using MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). It should be understood that the control circuit of this embodiment is also applicable to resonant circuits using other types of switching transistors.

[0028] The pull-up switch QH, pull-down switch QL, and other components in the circuit all have parasitic capacitances. If there is a voltage across the switches, when the pull-up switch QH or pull-down switch QL transitions from the off state to the on state, the parasitic capacitances of the switches and other components are charged or discharged, resulting in turn-on losses. This invention aims to enable the switches to turn on with zero voltage, or as close to zero voltage as possible, thereby reducing turn-on losses. The control circuit of this invention can be used for... Figure 1 and Figure 2The resonant circuit can also be used in other resonant circuits, such as LLC circuits, LCC circuits, etc.

[0029] Figure 3 A schematic diagram of the circuit structure of a control circuit 30 according to an embodiment of the present invention is shown. Figure 3 As shown, the control circuit 30 includes an output power detection circuit 301, an output voltage detection circuit 302, a switching voltage detection circuit 303, a zero-crossing detection circuit 304, a demagnetization detection circuit 305, a pull-down switch control circuit 306, a pull-up switch control circuit 307, and a duration control circuit 308.

[0030] In this embodiment of the invention, the control circuit 30 controls the resonant circuit to operate in continuous conduction mode (CCM) and pulse skip mode (PSM) according to different circuit operating conditions.

[0031] Figure 4 The diagram illustrates the signal waveforms of a resonant circuit 10 according to an embodiment of the present invention, when controlled by a control circuit 30 to operate in pulse-skipping mode. The following is in conjunction with... Figure 1 , Figure 3 and Figure 4 This section explains the working principle of the control circuit 30 and the operation of the resonant circuit 10 when the output voltage Vout is low in the pulse jump mode.

[0032] exist Figure 3 In this embodiment, the output power detection circuit 301 receives a power feedback signal Vfb characterizing the output power of the resonant circuit 10, compares the power feedback signal Vfb with a power threshold Vpth, and outputs a power judgment signal M1 based on the comparison result. In some embodiments of the present invention, when the power feedback signal Vfb is less than the power threshold Vpth, the control circuit 30 controls the resonant circuit 10 to operate in a pulse skipping mode. Otherwise, the resonant circuit 10 operates in a continuous conduction mode.

[0033] exist Figure 3 In the process, the output voltage detection circuit 302 detects the output voltage Vout of the resonant circuit 10, compares the output voltage Vout with the output voltage threshold Voth, and outputs the output voltage judgment signal M2 based on the comparison result.

[0034] Figure 4 The diagram shows the signal waveforms of the resonant circuit 10 when it is operating in pulse skipping mode and the output voltage Vout is low, i.e., the output voltage Vout is less than the output voltage threshold Voth and the power feedback signal Vfb is less than the power threshold Vpth.

[0035] The switching voltage detection circuit 303 detects the value of the switching voltage Vsw, compares the value of the switching voltage Vsw with the switching voltage threshold Vsth, and outputs a conduction control signal Con based on the comparison result. In one embodiment, the value of the switching voltage threshold Vsth is zero. Figure 4 As shown, at time t1, the value of the switching voltage Vsw drops to zero. The turn-on control signal Con affects the pull-down control signal GL through the pull-down switch control circuit 306, thereby controlling the turn-on of the pull-down switch QL. Turning on the pull-down switch QL when the value of the switching voltage Vsw drops to zero achieves zero-voltage turn-on of the pull-down switch QL, thus reducing turn-on losses. In some embodiments, the value of the switching voltage threshold Vsth can be slightly greater than zero or slightly less than zero, i.e., close to zero.

[0036] The zero-crossing detection circuit 304 outputs a turn-off control signal Coff based on the zero-crossing detection signal Vzcd.

[0037] During the conduction of the pull-down switch QL, the zero-crossing detection signal Vzcd being zero indicates the moment when the energy stored in the primary winding Np reaches its maximum. After turning off the pull-down switch QL when the energy stored in the primary winding Np reaches its maximum value, the energy stored in the primary winding Np is transferred to the parasitic capacitance of the switch terminal SW. This allows the switching voltage Vsw to reach its maximum value under the current operating conditions, thereby minimizing the turn-on loss of the pull-up switch QH when it is subsequently turned on.

[0038] exist Figure 1 and Figure 2 In the resonant circuit shown, the zero-crossing detection signal Vzcd is the voltage provided by the auxiliary winding Nt, which can be obtained through the auxiliary winding Nt. Figure 1 In the middle, during the conduction period of the pull-down switch QL, when the voltage Vcr on the resonant capacitor Cr drops to zero, that is... Figure 4 At time t2, the resonant current Ir reaches its minimum value (negative maximum value). Although the pre-charge duration signal TonL1 has not yet ended, the zero-crossing detection signal Vzcd has already dropped to zero. This is because the current in the secondary winding Ns is zero, and the auxiliary winding Nt induces a voltage in the primary winding Np. The voltage in the primary winding Np is equal to the voltage Vcr on the negative resonant capacitor Cr, i.e., -Vcr. In other words, at... Figure 4 In the above, the zero-crossing detection signal Vzcd corresponds to the moment when the voltage Vcr on the resonant capacitor Cr is zero, which is the moment when the resonant capacitor Ir reaches its reverse maximum value, and also the moment when the energy stored in the primary winding Np reaches its maximum value.

[0039] It should be understood that, Figure 2Although the power circuit connection structures are different, the zero-crossing detection signal Vzcd also corresponds to the moment when the voltage Vcr on the resonant capacitor Cr is zero, the moment when the resonant capacitor Ir reaches its reverse maximum value, and the moment when the energy stored in the primary winding Np reaches its maximum value.

[0040] In summary, when the zero-crossing detection signal Vzcd is zero, it represents the moment when the primary winding Np energy storage reaches its maximum.

[0041] The zero-crossing detection circuit 304 compares the zero-crossing detection signal Vzcd with the zero-crossing threshold Vzth (which has a value of zero or close to zero). When the zero-crossing detection signal Vzcd drops to the zero-crossing threshold Vzth, it outputs a turn-off control signal Coff to control the pull-down switch QL to turn off. The pull-down switch control circuit 306 receives the turn-off control signal Coff and the pre-charge duration signal TonL1, and outputs a pull-down control signal GL based on the turn-off control signal Coff and the pre-charge duration signal TonL1 to control the turn-off of the pull-down switch QL. Figure 4 At time t2, the zero-crossing detection signal Vzcd crosses zero, the pull-down control signal GL goes low, and the pull-down switch QL is turned off.

[0042] The pre-charge duration signal TonL1 presets the pre-charge conduction duration TD1 of the pull-down switch QL. In some embodiments of the present invention, the pull-down switch QL starts conducting at time t1, and after the pre-charge conduction duration TD1 characterized by the pre-charge duration signal TonL1, the pull-down control signal GL turns off the pull-down switch QL. However, when the zero-crossing point of the zero-crossing detection signal Vzcd arrives within the pre-charge conduction duration TD1 of the pull-down switch QL, the pull-down switch QL turns off before the zero-crossing point of the zero-crossing detection signal Vzcd, without waiting for the pre-charge conduction duration TD1 to end. Figure 4 As shown. That is, when the precharge conduction time TD1, represented by the precharge duration signal TonL1, ends, or the zero-crossing detection signal Vzcd crosses zero, the pull-down switch QL is turned off when either condition is met.

[0043] In some embodiments of the present invention, the precharge duration signal TonL1 may be stored in a memory unit such as a register.

[0044] In some embodiments of the present invention, the precharge duration signal TonL1 can be set by the user, or preset or changed by the upper-level system. For example, the control circuit may have a data interface, through which the user or the upper-level system can set or change the value of the precharge duration signal TonL1.

[0045] It should be understood that, besides using the auxiliary winding Nt to detect the moment when the resonant capacitor voltage Vcr is zero, other methods can also be used to obtain the moment when the resonant capacitor voltage Vcr is zero in other embodiments. For example, in one embodiment, the moment when the resonant capacitor voltage Vcr is zero can be roughly obtained by the resonant period Tm. The resonant period Tm can be calculated based on the inductance of the primary winding Np (the sum of Lr and Lm) and the value of the resonant capacitor Cr, that is: When the pull-down switch QL's on-time reaches 1 / 4 of the resonant period Tm, it roughly corresponds to the moment when the voltage Vcr across the resonant capacitor Cr is zero. In practical applications, since it is impossible to accurately obtain the inductance of the primary winding Np and the values ​​of the resonant capacitor Cr, this method yields an approximate time when the energy stored in the primary winding Np reaches its maximum.

[0046] exist Figure 4 In the process, after a dead time, at time t3, the pull-up switch QH is turned on. In one embodiment, the turning on of the pull-up switch QH can be determined according to the slew rate of the switching voltage Vsw. For example, the pull-up switch control circuit 307 can output a pull-up control signal GH to turn on the pull-up switch QH when it detects that the slew rate of the switching voltage Vsw has decreased to zero or a certain value. Any existing circuit for detecting voltage slew rate can be used in this invention to achieve the purpose of detecting the slew rate of the switching voltage Vsw.

[0047] exist Figure 4 At time t4, the pull-up switch control circuit 307 detects that the resonant current Ir has reached a preset peak value Ipk, and outputs a pull-up control signal GH to turn off the pull-up switch QH. Those skilled in the art can set the preset peak value Ipk according to the parameters and application requirements of the specific application.

[0048] exist Figure 4 At time t5, the switching voltage Vsw drops to zero again, and the turn-on control signal Con pulls up the pull-down control signal GL through the pull-down switch control circuit 306, turning on the pull-down switch QL again.

[0049] The demagnetization detection circuit 305 detects the demagnetization time of transformer T1, that is, the excitation current Im of transformer T1. Figure 4 The dashed line in the topmost waveform (which descends with a fixed slope to the trough, partially coinciding with the solid line) reaches zero at the moment of demagnetization, and the demagnetization signal Dem is output to characterize the demagnetization moment of transformer T1. The demagnetization detection circuit 305 can be implemented using existing demagnetization detection circuits. For example, the demagnetization signal Dem can be output by detecting the peak value of the resonant current Ir and the slope of the excitation current Im estimated based on specific application parameters.

[0050] The pull-down switch control circuit 306 receives the demagnetization signal Dem. The demagnetization signal Dem characterizes the demagnetization moment of transformer T1, i.e. Figure 4 At time t6, the output pull-down control signal GL turns off the pull-down switch QL.

[0051] In one embodiment, the pull-down switch control circuit 306 further receives the resonant period Tr. The resonant period can be calculated based on the values ​​of the resonant inductance Lr and the resonant capacitance Cr, i.e.: When the resonant period Tr ends before the demagnetization time, the pull-down switch GL is turned off at the end of the resonant period Tr. That is, when either the resonant period Tr ends or the demagnetization time of transformer T1 arrives, the pull-down control signal GL controls the pull-down switch QL to turn off.

[0052] exist Figure 4 At time t7, the switching voltage Vsw drops to zero again, the pull-down switch QL turns on again, and a new switching cycle begins. Time t1 to time t7 is one switching cycle in which the control circuit 30 controls the resonant circuit 10 to operate in pulse-jump mode.

[0053] In summary, under pulse-jump mode and when the output voltage Vout is low, the pull-down switch QL is turned on twice within a single switching cycle of the resonant circuit 10, i.e., the pull-down control signal GL includes a first pulse (t1~t2) and a second pulse (t5~t6). The first pulse is also called the pre-charge pulse. When the pull-down switch QL is turned on by the pre-charge pulse of the pull-down control signal GL, the inductance of the primary winding Np stores energy. When the first pulse ends and the pull-down switch QL is turned off, the energy stored in the inductance of the primary winding Np is transferred to the switch terminal SW, charging the switch terminal SW and raising the voltage of the switch voltage Vsw to the input voltage Vin or as close as possible to the input voltage Vin, so as to realize the zero-voltage turn-on of the pull-up switch QH. The first pulse ends when any of the following conditions are met: (1) the pre-charge duration signal TonL1 characterizes the end of the pre-charge conduction duration TD1 of the pull-down switch; (2) the zero-crossing detection signal Vzcd crosses zero from positive to negative. After the pull-up switch QH is turned off and a certain dead time has elapsed, the second pulse turns on the pull-down switch QL after the switching voltage Vsw drops to zero again. The second pulse ends when any of the following conditions are met: (1) the resonant period Tr of the resonant circuit ends; (2) the transformer T1 of the resonant circuit demagnetizes.

[0054] Figure 5The following diagram illustrates the signal waveforms of a resonant circuit 10 according to an embodiment of the present invention when it operates in pulse-skipping mode and the output voltage Vout is high, i.e., the output voltage Vout is greater than the output voltage threshold Voth and the power feedback signal Vfb is less than the power threshold Vpth. (The following is in conjunction with...) Figure 1 , Figure 3 and Figure 5 This section describes the operation of control circuit 30 in pulse skipping mode when the output voltage Vout is high.

[0055] At time t9, the switching rate of the switching voltage Vsw drops to zero, the pull-up switch QH turns on, and the resonant current Ir rises. At time t10, the resonant current Ir rises to a preset peak value Ipk, and the pull-up switch control circuit 307 outputs a pull-up control signal GH to turn off the pull-up switch QH. After a dead time, at time t11, the value of the switching voltage Vsw drops to zero, and the turn-on control signal Con influences the pull-down control signal GL through the pull-down switch control circuit 306, thereby controlling the turn-on of the pull-down switch QL, achieving zero-voltage turn-on of the pull-down switch QL to reduce turn-on losses. From time t11, the preset on-time TD2 of the pull-down switch QL begins, and this preset on-time TD2 is determined by the on-time signal TonL2. In some embodiments of the present invention, at time t12, when the preset on-time TD2 of the pull-down switch QL ends, the pull-down switch QL turns off. When the switching cycle ends and the switching rate of the switching voltage Vsw decreases to zero again, the pull-up switch QH turns on again, and the next switching cycle begins.

[0056] from Figure 5 As can be seen from the data, at time t9, when the pull-up switch QH is turned on, the switching voltage Vsw at the switch terminal SW does not reach the value of the input voltage Vin. That is, when the pull-up switch QH is turned on, the voltage difference Vin-Vsw > 0, therefore, turn-on losses still occur when the pull-up switch QH is turned on. However, since the voltage difference between Vin and Vsw is sufficiently small at this time, the turn-on losses generated when the pull-up switch QH is turned on are relatively small. Compared with the method of pre-charging the inductance of the primary winding Np by first turning on the pull-down switch QL, the losses are close to or even smaller, so there is no need to first turn on the pull-down switch QL for pre-charging.

[0057] Figure 6 The diagram illustrates the signal waveforms of the resonant circuit 10 according to an embodiment of the present invention when it operates in continuous conduction mode, i.e., when the power feedback signal Vfb is greater than the power threshold Vpth. The following is in conjunction with... Figure 1 , Figure 3 and Figure 6This section explains the working principle of control circuit 30 in continuous conduction mode and the working principle of duration control circuit 308.

[0058] like Figure 6 As shown, at time t13, the value of the switching voltage Vsw drops to zero. The turn-on control signal Con affects the pull-down control signal GL through the pull-down switch control circuit 306, thereby controlling the turn-on of the pull-down switch QL, realizing zero-voltage turn-on of the pull-down switch QL, and reducing turn-on losses.

[0059] Starting from time t13, after a preset on-time TD2 determined by the on-time signal TonL2, at time t14, the pull-down switch control circuit 306 outputs a pull-down control signal GL to control the pull-down switch QL to turn off. In some embodiments, when the zero-crossing detection signal Vzcd crosses zero earlier than the end of the preset on-time TD2, the pull-down control signal GL controls the pull-down switch QL to turn off at the zero-crossing moment of the zero-crossing detection signal Vzcd.

[0060] At time t15, the pull-up switch QH is turned on, and the resonant current Ir rises. At time t16, the resonant current Ir rises to the preset peak value Ipk, and the pull-up switch control circuit 307 outputs a pull-up control signal GH to turn off the pull-up switch QH. After a dead time, at time t17, the switching voltage Vsw returns to zero, the pull-down switch QL turns on again, and the next switching cycle begins.

[0061] from Figure 6 As can be seen from the data, at time t15, when the pull-up switch QH is turned on, the switching voltage Vsw at the switch terminal SW does not reach the value of the input voltage Vin. In other words, when the pull-up switch QH is turned on, the voltage difference Vin-Vsw across its terminals is greater than 0, therefore, turn-on losses still occur when the pull-up switch QH is turned on.

[0062] In this embodiment of the invention, the duration control circuit 308 adjusts the conduction duration signal TonL2 in the next switching cycle by detecting the resonant current Ir near the conduction time of the pull-up switch QH in the current switching cycle.

[0063] The duration control circuit 308 includes a current adjustment circuit 308A and a duration adjustment circuit 308B. The current adjustment circuit 308A receives a current detection signal Is and an energy storage current reference Iref, and outputs a duration adjustment signal Tcon based on the difference between the current detection signal Is and the energy storage current reference Iref. The duration adjustment circuit 308B receives the duration adjustment signal Tcon and an initial duration signal Toni, and outputs an on-time duration signal TonL2 based on the duration adjustment signal Tcon and the initial duration signal Toni.

[0064] In this embodiment of the invention, the current detection signal Is corresponds to Figure 6 The resonant current Ir is located near the turn-on moment of the pull-up switch QH. The energy storage current reference Iref corresponds to the target current value of the resonant current Ir at the corresponding moment. When the absolute value of the current detection signal Is is less than the absolute value of the energy storage current reference Iref, the current adjustment circuit 308A will output a duration adjustment signal Tcon to adjust the conduction duration of the pull-down switch QL. The specific working principle is as follows: Figure 6 As shown, at time t15, the absolute value of the resonant current Ir, i.e., the absolute value of the current detection signal Is, is less than the absolute value of the energy storage current reference Iref. The current adjustment circuit 308A outputs a duration adjustment signal Tcon to the duration adjustment circuit 308B. The duration adjustment circuit 308B, based on the initial duration signal Toni (characterizing the on-time of the pull-down switch QL in the current switching cycle) and the duration adjustment signal Tcon, outputs an adjusted on-time signal TonL2, thereby extending the preset on-time TD2 of the pull-down switch QL in the next switching cycle. Figure 6 As shown, the duration t17~t18 is longer than the duration t13~t14. After the preset on-time TD2 of the pull-down switch QL is extended, the inductance of the primary winding Np will store more energy when QL is turned off. After the pull-down switch QL is turned off, during the duration t18~t19, the energy of the inductance of the primary winding Np charges the switch terminal SW, raising the switching voltage Vsw to the input voltage Vin, thereby achieving zero-voltage turn-on of the pull-up switch QH. In one embodiment, when the absolute value of the current detection signal Is is greater than the absolute value of the energy storage current reference Iref, the duration adjustment signal Tcon adjusts the on-time signal TonL2 to correspondingly reduce the on-time of the pull-down switch QL in the next switching cycle.

[0065] In one embodiment, the value of the initial duration signal Toni is provided by a register. Specifically, the control circuit 30 includes a register for storing a signal characterizing the on-time of the pull-down switch QL in the current switching cycle, thereby calculating the on-time of the pull-down switch QL in the next switching cycle. The value of the on-time signal TonL2 is the result of calculating the value of the initial duration signal Toni and the value of the duration adjustment signal Tcon.

[0066] In one embodiment, the original value of the conduction duration signal TonL2 is obtained by considering the peak value of the resonant current Ir and the excitation current Im of the primary side of transformer T1 (e.g., Figure 3The slope is calculated from the curve shown. After the circuit is running, the conduction duration signal TonL2 for the next switching cycle is updated by adjusting the duration signal Tcon based on the conduction duration of the current switching cycle (characterized by the initial duration signal Toni). The excitation current Im can be calculated based on the peak value of the resonant current Ir, the primary-secondary turns ratio of the transformer T1, and the secondary winding voltage, which is well known to those skilled in the art and will not be described in detail here.

[0067] In one embodiment, the value of the conduction duration signal TonL2 is fixed and can be set according to the specific application needs and parameters of the circuit.

[0068] In one embodiment, the current detection signal Is can be obtained by detecting the value of the resonant current Ir at or before the pull-up switch QH is turned on, or it can be obtained by other existing calculation methods. The value of the energy storage current reference Iref can be set according to the circuit parameters and requirements of the specific application.

[0069] In this embodiment of the invention, the control circuit 30 can be implemented using digital circuitry, and the pull-up switch control circuit 307 and the pull-down switch control circuit 306 can be implemented using state machines. For example, hardware description languages ​​such as Verilog and VHDL can be used to describe the aforementioned circuit functions, thereby automatically generating the digital circuit. It should be understood that... Figure 3 The circuit modules shown in the embodiments are used to understand the principles of the present invention and do not represent the actual circuit of the present invention.

[0070] Figure 7 A schematic diagram of the circuit structure of a control circuit 70 according to an embodiment of the present invention is shown. Figure 7 As shown, the control circuit 70 includes an output power detection circuit 301, an output voltage detection circuit 302, a switching voltage detection circuit 703, a zero-crossing detection circuit 304, a demagnetization detection circuit 305, a pull-down switch control circuit 306, a pull-up switch control circuit 707, and a duration control circuit 308.

[0071] and Figure 3 Compared to the illustrated embodiment, in Figure 7 In this circuit, the switching voltage detection circuit 703 detects the slew rate of the switching voltage Vsw. When the slew rate of the switching voltage Vsw increases from a negative value to zero, the switching voltage detection circuit 703 outputs a turn-on control signal Con, which in turn affects the pull-down control signal GL through the pull-down switch control circuit 306, thereby controlling the pull-down switch QL to turn on.

[0072] and Figure 3 Compared to the illustrated embodiment, in Figure 7In this circuit, the pull-up switch control circuit 707 controls the conduction of the pull-up switch QH based on the zero-crossing detection signal Vzcd. For example, after detecting the zero-crossing moment of the zero-crossing detection signal Vzcd, the pull-up switch QH can be turned on after a certain delay. The pull-up switch control circuit 707 turns off the pull-up switch QH in the same way as the pull-up switch control circuit 307, that is, by detecting the peak value of the resonant current Ir to control the turn-off of the pull-up switch QH, which will not be elaborated here.

[0073] exist Figure 7 In this embodiment, the working principle of the other circuits of the control circuit 70 is the same as that of the control circuit 30, and will not be described in detail here.

[0074] It should be understood that the switch voltage detection circuits 303 and 703 are optional, and similarly, the pull-up switch control circuits 307 and 707 are also optional. Those skilled in the art can arbitrarily select suitable switch voltage detection circuits and pull-up switch control circuits for combination and application, guided by the embodiments of the present invention. Furthermore, it should be understood that other suitable control methods can also be applied to the embodiments of the present invention.

[0075] In this embodiment of the invention, to prevent false triggering caused by oscillation, when the pull-up switch QH or the pull-down switch QL is turned on based on the switching rate, a precondition can be added. For example, the time interval between the current turn-on of the pull-up switch QH and the previous turn-on of the pull-up switch QH must meet a certain interval duration condition, such as a preset switching cycle duration. Similarly, the time interval between the start of the current pre-charge turn-on duration and the start of the previous pre-charge turn-on duration of the pull-down switch QL must meet a certain interval duration condition, such as a preset switching cycle duration. It should be understood that there are many ways to prevent false triggering caused by oscillation, and other types of false triggering prevention mechanisms can also be used in this embodiment of the invention. For example, in... Figure 4 In the process, when the pull-down switch QL turns on at time t5 based on the switching voltage Vsw, the prerequisite of detecting the falling edge of the pull-up switch QH can also be added.

[0076] Figure 8 This is a flowchart illustrating a control method 80 for a resonant circuit operating in pulse-skipping mode and with a low output voltage, according to an embodiment of the present invention. The resonant circuit includes, as shown in... Figure 1 and 2 The resonant circuit shown is an asymmetric half-bridge flyback topology, and also includes other resonant circuits such as LLC resonant circuits and LCC resonant circuits.

[0077] In this embodiment of the invention, when the output power of the resonant circuit is lower than a power threshold, the resonant circuit operates in pulse-skipping mode. The power threshold can be set according to the specific application. The control method 80 illustrates the operation process of the resonant circuit 10 in pulse-skipping mode and with a low output voltage Vout within one switching cycle. In one embodiment, a low output voltage Vout means that the output voltage Vout is less than a certain output voltage threshold. Figure 8 As shown, the control method 80 includes the following steps in each switching cycle: step 801, turning on the pull-down switch; step 802, turning off the pull-down switch when the pre-charge conduction time of the pull-down switch ends or the resonant capacitor voltage crosses zero from positive to negative; step 803, turning on the pull-up switch; step 804, turning off the pull-up switch when the value of the resonant current reaches a preset peak value; step 805, turning on the pull-down switch; and step 806, turning off the pull-down switch when the transformer of the resonant circuit demagnetizes.

[0078] The zero-crossing detection signal characterizes the point at which the resonant capacitor voltage crosses from positive to negative. In one embodiment, the zero-crossing detection signal is obtained through the auxiliary winding of the transformer in the resonant circuit.

[0079] In one embodiment, the pull-down switch turns on when the switching voltage drops to a switching voltage threshold. The switching voltage is the voltage at the junction of the pull-up and pull-down switches. In one embodiment, the switching voltage threshold is zero or approximately zero.

[0080] In one embodiment, the pull-down switch is turned on based on the slew rate of the switching voltage. For example, the pull-down switch turns on when the slew rate of the switching voltage increases from a negative value to zero.

[0081] In one embodiment, the switching of the pull-down switch based on the switching voltage conversion rate further includes the prerequisite that the time interval between the switching of the pull-down switch at the start of the current pre-charge conduction duration and the switching of the pull-down switch at the start of the previous pre-charge conduction duration meets a certain interval duration condition, such as a preset switching cycle duration. Corresponding to Figure 4 That is to say, the interval between time t1 and time t7 is greater than or equal to a certain interval.

[0082] In one embodiment, the pull-up switch is turned on when the switching voltage switching rate decreases from a positive value to zero.

[0083] In one embodiment, the pull-up switch being turned on when the switching voltage conversion rate decreases from a positive value to zero also includes the following prerequisite: the time interval between the current turn-on of the pull-up switch and the previous turn-on of the pull-up switch meets a certain interval duration condition, such as a preset switching cycle duration.

[0084] In one embodiment, the pull-up switch turns on when the switching voltage increases to its maximum value. For example, the pull-up switch can turn on when the switching voltage increases to the same level as the input voltage of the resonant circuit. It should be understood that under certain operating conditions, the switching voltage may not necessarily rise to the value of the input voltage; in such cases, the pull-up switch can turn on when the switching voltage rises to its maximum achievable value.

[0085] In one embodiment, step 806 is replaced by step 807, which includes turning off the pull-down switch when either the transformer in the resonant circuit demagnetizes or the resonant period of the resonant circuit ends. The resonant period is the resonant period of the resonant inductor and the resonant capacitor of the resonant circuit.

[0086] Figure 9 This is a flowchart illustrating a control method 90 for a resonant circuit operating in continuous conduction mode according to an embodiment of the present invention. The resonant circuit includes, for example: Figure 1 and 2 The resonant circuit shown is an asymmetric half-bridge flyback topology, and also includes other resonant circuits such as LLC resonant circuits and LCC resonant circuits.

[0087] In this embodiment of the invention, when the output power of the resonant circuit is greater than a power threshold, the resonant circuit operates in continuous conduction mode. The control method 90 illustrates the operation of the resonant circuit 10 in continuous conduction mode within one switching cycle. For example... Figure 9 As shown, the control method 90 includes the following steps in each switching cycle: step 901, turning on the pull-up switch; step 902, turning off the pull-up switch when the value of the resonant current reaches a preset peak value; step 903, turning on the pull-down switch; and step 904, turning off the pull-down switch when the resonant capacitor voltage crosses zero from positive to negative or when the preset conduction time ends.

[0088] In one embodiment, the pull-up switch turns on when the switching voltage slew rate decreases from a positive value to zero. The switching voltage is the voltage at the connection point of the pull-up and pull-down switches.

[0089] In one embodiment, the pull-up switch being turned on when the switching voltage conversion rate decreases from a positive value to zero also includes the following prerequisite: the time interval between the current turn-on of the pull-up switch and the previous turn-on of the pull-up switch meets a certain interval duration condition, such as a preset switching cycle duration.

[0090] In one embodiment, the pull-up switch is turned on when the switching voltage is at its highest. For example, the pull-up switch can be turned on when the switching voltage increases to the same level as the input voltage of the resonant circuit. It should be understood that under certain operating conditions, the switching voltage may not necessarily rise to the value of the input voltage. In such cases, the pull-up switch can be turned on when the switching voltage rises to its maximum achievable value.

[0091] In one embodiment, the pull-down switch is turned on when the switching voltage conversion rate increases from a negative value to zero.

[0092] In one embodiment, the condition that the pull-down switch turns on when the switching voltage conversion rate increases from negative to zero also includes the following prerequisite: the time interval between the current turn-on of the pull-down switch and the previous turn-on of the pull-down switch meets a certain interval duration condition.

[0093] In one embodiment, the pull-down switch turns on when the switching voltage drops to a switching voltage threshold. The value of the switching voltage threshold is equal to or approximately zero.

[0094] In one embodiment, the preset conduction duration is fixed and can be set according to the specific application and parameters of the circuit.

[0095] In one embodiment, the preset conduction duration is adjusted based on the conduction duration of the pull-down switch in the previous switching cycle and the current value of the resonant current at the moment the pull-up switch is turned on.

[0096] In one embodiment, when the absolute value of the resonant current at the moment the pull-up switch is turned on in the previous switching cycle is less than the absolute value of the energy storage current reference, the conduction duration of the pull-down switch in the previous switching cycle is extended and used as the preset conduction duration of the pull-down switch in the current switching cycle. When the absolute value of the resonant current at the moment the pull-up switch is turned on in the previous switching cycle is greater than the absolute value of the energy storage current reference, the conduction duration of the pull-down switch in the previous switching cycle is shortened and used as the preset conduction duration of the current switching cycle.

[0097] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A control circuit for a resonant circuit, the resonant circuit comprising a pull-up switch and a pull-down switch, the control circuit comprising: The pull-up switch control circuit outputs a pull-up control signal to turn off the pull-up switch when the resonant current of the resonant circuit reaches a preset peak value. The pull-down switch control circuit outputs a pull-down control signal. Before the pull-up switch is turned on, the pull-down control signal has a first pulse, which corresponds to the conduction duration of the pull-down switch. The end time of the first pulse corresponds to the moment when the resonant capacitor voltage of the resonant circuit crosses zero from positive to negative. as well as The zero-crossing detection circuit compares the zero-crossing detection signal provided by the transformer auxiliary winding of the resonant circuit with the zero-crossing threshold, and provides the moment when the voltage on the resonant capacitor crosses zero from positive to negative based on the comparison result.

2. The control circuit of the resonant circuit as described in claim 1 further includes: The switching voltage detection circuit, based on the comparison result of the switching voltage at the connection point of the pull-up switch and the pull-down switch in the resonant circuit with the switching voltage threshold, outputs a conduction control signal to control the conduction of the pull-down switch.

3. The control circuit of the resonant circuit as described in claim 1 further includes: The switching voltage detection circuit outputs a conduction control signal to control the conduction of the pull-down switch based on the switching voltage conversion rate at the connection point of the pull-up and pull-down switches in the resonant circuit.

4. The control circuit of the resonant circuit as described in claim 1 further includes: The pull-up switch control circuit outputs a pull-up control signal to turn on the pull-up switch based on the switching voltage conversion rate at the connection point between the pull-up and pull-down switches.

5. The control circuit of the resonant circuit as described in claim 1 further includes: The pull-up switch control circuit detects the zero-crossing detection signal provided by the transformer auxiliary winding of the resonant circuit. After the zero-crossing detection signal crosses zero, and after a delay, it outputs a pull-up control signal to turn on the pull-up switch.

6. The control circuit of the resonant circuit as described in claim 1, after the pull-up switch is turned off, the pull-down control signal has a second pulse corresponding to the conduction duration of the pull-down switch, and the second pulse ends when any of the following conditions are met: (1) the resonant period of the resonant circuit ends, and the resonant period is the resonant period of the resonant inductor and the resonant capacitor; (2) the transformer of the resonant circuit is demagnetized.

7. The control circuit of the resonant circuit as described in claim 1 further includes a duration control circuit, the duration control circuit comprising: The current adjustment circuit receives the current detection signal and the energy storage current reference, and outputs a duration adjustment signal based on the current detection signal and the energy storage current reference. as well as The duration adjustment circuit receives the duration adjustment signal and updates the conduction duration signal based on the duration adjustment signal; The current detection signal represents the resonant current near the turn-on moment of the pull-up switch.

8. A resonant circuit, comprising the control circuit as described in any one of claims 1-7, further comprising: Pull-up switch transistor; as well as The pull-down switch is connected in series with the pull-up switch between the input terminal and the primary ground.

9. The resonant circuit as described in claim 8, further comprising: A transformer has a primary winding, a secondary winding, and an auxiliary winding; as well as The resonant capacitor is connected in series with the primary winding between the connection point of the pull-up switch and the pull-down switch and the primary ground.

10. The resonant circuit of claim 8, further comprising: A transformer has a primary winding, a secondary winding, and an auxiliary winding; as well as A resonant capacitor is connected in series with the primary winding and coupled between the input terminal and the connection point of the pull-up switch and the pull-down switch.

11. A control method for a resonant circuit, the resonant circuit comprising a pull-up switch and a pull-down switch, the control method comprising: Within each switching cycle: Turn on the pull-down switch transistor; The pull-down switch is turned off when the pre-charge conduction time of the pull-down switch ends or when the voltage of the resonant capacitor of the resonant circuit crosses zero from positive to negative. Turn on the pull-up switch transistor; The pull-up switch is turned off when the resonant current reaches a preset peak value. Turn on the pull-down switch transistor; as well as When the transformer in the resonant circuit demagnetizes or at the end of the resonant period, the pull-down switch is turned off. The resonant period is the resonant period of the resonant capacitor and the resonant inductor of the resonant circuit.

12. The control method of claim 11, wherein the pull-up switch is turned on when the switching voltage switching rate decreases to zero, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

13. The control method of claim 11, wherein the pull-down switch is turned on when the switching voltage switching rate increases to zero, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

14. The control method of claim 11, wherein the pull-down switch is turned on when the switching voltage drops to a switching voltage threshold, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

15. The control method as described in claim 11, wherein, The zero-crossing moment of the resonant capacitor voltage from positive to negative is obtained by detecting the zero-crossing moment of the zero-crossing detection signal, which is provided by the auxiliary winding of the transformer of the resonant circuit.

16. A control method for a resonant circuit, the resonant circuit comprising a pull-up switch and a pull-down switch, the control method comprising: Within each switching cycle: Turn on the pull-up switch transistor; The pull-up switch is turned off when the resonant current reaches a preset peak value. Turn on the pull-down switch transistor; The zero-crossing detection signal provided by the transformer auxiliary winding of the resonant circuit is compared with the zero-crossing threshold to detect the moment when the voltage on the resonant capacitor of the resonant circuit crosses zero from positive to negative. as well as When the voltage of the resonant capacitor crosses zero from positive to negative, the pull-down switch is turned off.

17. The control method as described in claim 16, wherein, When the absolute value of the resonant current at the moment the pull-up switch is turned on in the previous switching cycle is less than the absolute value of the energy storage current reference, the conduction time of the pull-down switch in the previous switching cycle is extended and used as the conduction time of the pull-down switch in the current switching cycle.

18. The control method as described in claim 16, wherein, When the absolute value of the resonant current at the moment the pull-up switch is turned on in the previous switching cycle is greater than the absolute value of the energy storage current reference, the conduction time of the pull-down switch in the previous switching cycle is shortened and used as the conduction time of the current switching cycle.

19. The control method of claim 16, wherein the pull-down switch is turned on when the switching voltage drops to a switching voltage threshold, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

20. The control method of claim 16, wherein the pull-down switch is turned on when the switching voltage slew rate rises to zero, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

21. The control method of claim 16, wherein the pull-up switch is turned on when the switching voltage switching rate drops to zero, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

22. The control method as described in claim 16, wherein the pull-up switch is turned on when the switching voltage is at its highest, and the switching voltage is the voltage at the connection point of the pull-up switch and the pull-down switch.

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