A control circuit for a resonant circuit and a control method thereof

Abstract

A control circuit for a resonant circuit is disclosed. By accurately estimating the resonant current flowing through the resonant circuit near the turn-on time of the pull-up switch, the conduction time of the pull-down switch in the resonant circuit is adjusted. This ensures that after the pull-down switch is turned off, the energy stored in the inductor in the resonant circuit is sufficient to make the voltage at the switch terminal, i.e., the voltage at the connection point between the upper and lower switches and the pull-down switch, reach the input voltage. This makes the voltage difference across the pull-up switch zero when it is turned on, thus realizing the soft-switching of the pull-up switch.

Description

Technical Field

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

[0002] In traditional low-power AC / DC conversion applications, flyback topology switching converters, or 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. In other words, to provide the same power while reducing the overall size of the flyback converter, the switching frequency needs to be increased. But for hard-switching flyback converters, increasing the switching frequency means increasing switching losses. This obviously limits the application of flyback converters in high-power power supplies.

[0003] Soft-switching technology refers to 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, thereby reducing switching losses. To enable soft switching in flyback converters and reduce switching losses, 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, causing the primary-side switch to operate in resonant mode, thus achieving soft switching on the primary side. Summary of the Invention

[0004] This invention provides a zero-voltage switching control circuit. By accurately estimating the resonant current of the resonant circuit near the turn-on time of the pull-up switch, the conduction time of the pull-down switch is adjusted so that when the pull-up switch is turned on, the voltage at the switch terminal reaches the input voltage value, making the voltage difference across the pull-up switch zero, thereby realizing the soft-switching of the pull-up switch.

[0005] According to an embodiment of the present invention, a control circuit for a resonant circuit is proposed, comprising: a resonant current detection circuit, receiving a resonant current, a first current reference, and a second current reference, and outputting a current detection signal based on the resonant current, the first current reference, and the second current reference; a current adjustment circuit, receiving the current detection signal and an energy storage current reference, and outputting a conduction duration control signal based on the current detection signal and the energy storage current reference; and a conduction duration control circuit, receiving the conduction duration control signal and an initial value of the conduction duration signal, and outputting a conduction duration signal based on the conduction duration control signal and the initial value of the conduction duration signal for controlling the pull-down switch of the resonant circuit.

[0006] According to an embodiment of the present invention, a resonant circuit is also provided, including the aforementioned control circuit, and further comprising: a pull-up switch transistor coupled between the input voltage and the switch terminal, receiving a pull-up control signal, and turning on or off under the control of the pull-up control signal; and a pull-down switch transistor coupled between the switch terminal and the primary ground, receiving a pull-down control signal, and turning on or off under the control of the pull-down control signal.

[0007] In one embodiment, the resonant circuit further includes a transformer, comprising a primary winding and a secondary winding; and a resonant capacitor, connected in series with the primary winding between the switch terminal and the primary ground.

[0008] According to an embodiment of the present invention, a control method for a resonant circuit is also proposed. The resonant circuit includes a transformer, a resonant capacitor connected in series with the primary winding of the transformer, and a pull-up switch and a pull-down switch connected in series between the input voltage and the primary ground. The control method includes: outputting a current detection signal based on the resonant current flowing through the resonant capacitor of the resonant circuit, a first current reference, and a second current reference; outputting a conduction duration control signal based on the current detection signal and the energy storage current reference; and controlling the conduction duration of the pull-down switch of the resonant circuit based on the conduction duration control signal and the initial value of the conduction duration signal. Attached Figure Description

[0009] To better understand this invention, it will be described in detail with reference to the following figures:

[0010] Figure 1 This is a schematic diagram of the existing asymmetric half-bridge flyback converter 10.

[0011] Figures 2A-2F A schematic diagram of the operation process of the asymmetric half-bridge flyback converter 10 is shown.

[0012] Figure 3 This is a schematic diagram of the signal waveforms of an asymmetric half-bridge flyback converter under the control of the control circuit of an asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0013] Figure 4 This is a schematic diagram of the circuit structure of the control circuit 40 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0014] Figure 5 This is a schematic diagram of the circuit structure of a resonant current detection circuit 50 according to an embodiment of the present invention;

[0015] Figure 6 This is a waveform diagram of a portion of the signal from the resonant current detection circuit 50 according to an embodiment of the present invention;

[0016] Figure 7 This is a schematic diagram of the circuit structure of the control circuit 70 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0017] Figure 8 This is a schematic diagram of the circuit structure of the control circuit 80 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0018] Figure 9 This is a schematic diagram of the circuit structure of the control circuit 90 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0019] Figure 10 This is a flowchart illustrating a control method 100 for a resonant circuit according to an embodiment of the present invention. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] Figure 1 This is a schematic diagram of the circuit structure of an existing asymmetric half-bridge flyback converter 10. (See attached diagram.) Figure 1 As shown, the asymmetric half-bridge flyback converter 10 includes: a pull-up switch QH and a pull-down switch QL connected in series between the input voltage Vin and the primary ground PGND; a transformer T1 including a primary winding Np and a secondary winding Ns; 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 and not an actual inductor. In some applications, a separate resonant inductor may be added 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 both a diode and a controllable switching transistor. Furthermore, the secondary-side switch Ds can be coupled between the secondary-side winding Ns and the secondary-side ground SGND. The pull-up switch QH and pull-down switch QL of the flyback converter 10 alternately switch on and off, transferring energy from the primary side to the secondary side, forming an output voltage Vout across the output capacitor Co, and supplying power to the load Ro.

[0023] Figures 2A-2F This is a schematic diagram of the working process of the asymmetric half-bridge flyback converter 10. Figure 3 The diagram shows the waveforms of various signals of the asymmetric half-bridge flyback converter under the control of the control circuit of the asymmetric half-bridge flyback converter according to an embodiment of the present invention. In the diagram, Ir is the resonant current flowing through the resonant capacitor Cr, 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 Vsw, 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.

[0024] The following is Figure 1 Taking the asymmetric half-bridge flyback converter 10 shown as an example, combined with... Figures 2A-2F and Figure 3 This paper will elaborate on the operation of the control circuit of the asymmetric half-bridge flyback converter according to an embodiment of the present invention.

[0025] exist Figure 2AIn the circuit, the pull-down switch QL is in the off state, and the pull-up switch QH switches from the on state to the off state. When the pull-up switch QH is off, due to the freewheeling function of the primary winding Np, the direction of the resonant current Ir remains unchanged, but its value begins to decrease. At this time, the secondary diode Ds turns on, the current Is begins to increase, and energy is transferred from the primary side to the secondary side, that is, the energy stored in the resonant inductor Ir is transferred to the output capacitor Co. This resonant current Ir will pull down the connection point voltage Vsw of the pull-up switch QH and the pull-down switch QL, corresponding to... Figure 3 The duration t1-t2 in the middle.

[0026] After the resonant current Ir pulls the connection point voltage Vsw of the pull-up switch QH and the pull-down switch QL down to zero, if the pull-down switch QL is not conducting, then the resonant current Ir will conduct the parasitic body diode DL of the pull-down switch QL. Figure 2B As shown, and corresponding to Figure 3 The duration is t2-t3. During this time, the body diode DL, resonant inductor Lr, primary winding Np, and resonant capacitor Cr form a circuit, and the resonant current Ir continues to decrease. The voltage across the primary winding Np is VNp = -VCr, where VCr is the voltage across the resonant capacitor.

[0027] exist Figure 2C In the middle, the pull-up switch QH remains off, and the pull-down switch QL is on, corresponding to... Figure 3 The duration is t3-t4. At this time, the secondary winding Ns induces a voltage in the primary winding Np, and the voltage across the secondary winding VNs≈-(N2 / N1)×VNp=(N2 / N1)×VCr.

[0028] It should be understood that after the pull-up switch QH is turned off, the pull-down switch QL can be turned on immediately after the voltage Vsw at the switch terminal drops to zero. That is, the pull-down switch QL turns on at zero voltage. In other words, the working process of time t2-t3 may not necessarily exist.

[0029] At time t4, the resonant current Ir drops to zero. During the time interval t4-t5, the resonant capacitor Cr begins to discharge, the resonant current Ir reverses direction, and simultaneously supplies power to the secondary side, as shown below. Figure 2D As shown.

[0030] exist Figure 2E In the middle, the pull-up switch QH remains off, while the pull-down switch QL changes from on to off, corresponding to... Figure 3 The duration is t5-t6. After the negative resonant current Ir pulls the switching terminal voltage Vsw up to the input voltage Vin, if the pull-up switch QH is not conducting, the resonant current Ir will conduct the body diode DH of the pull-up switch QH. The secondary diode Ds is reverse-biased and cut off. The output capacitor Co supplies power to the load Ro.

[0031] exist Figure 2FIn the middle, the pull-up switch QH is turned on, and the pull-down switch QL remains off, corresponding to... Figure 3 The duration is t6-t7. The resonant current Ir gradually increases from a negative value to zero and then increases in the positive direction. The input voltage Vin charges the primary winding Np and the resonant capacitor Cr.

[0032] At time t7, the pull-up switch QH is turned off, and a new switching cycle begins.

[0033] It should be understood that the switches of the asymmetric half-bridge flyback converter 10 are periodically turned on and off. Therefore, a switching cycle can begin with the turn-on of the pull-up switch QH and end before it turns on again, or it can begin with the turn-on of the pull-down switch QH and end before it turns on again, or it can begin at any switching state and end before that switching state reappears. Figure 3 As shown, a switching cycle can be from time t0 to time t6, or from time t1 to time t7, and so on.

[0034] from Figure 3 As can be seen, at time t0, when the pull-up switch QH is turned on, the switching voltage Vsw at the switching terminal SW does not reach the input voltage Vin. That is, when the pull-up switch QH is turned on, the voltage difference Vin - Vsw across it is greater than 0, therefore switching losses still occur when QH is turned on. The main reason why the switching voltage Vsw cannot reach the input voltage Vin is that before time t0, i.e., before the pull-up switch QH is turned on, the resonant current Ir, while flowing through the body diode DH, simultaneously charges the parasitic drain-source capacitance of the pull-down switch QL, thus raising the voltage Vsw at the switching terminal SW to the level of the input voltage Vin. If the absolute value of the negative resonant current Ir is too small, it is insufficient to raise the switching voltage Vsw to the input voltage Vin. This results in the voltage difference Vin - Vsw > 0 at the moment the pull-up switch QH is turned on.

[0035] Figure 4 This is a schematic diagram of the circuit structure of an asymmetric half-bridge flyback converter control circuit 40 according to an embodiment of the present invention. Figure 4As shown, the control circuit 40 includes: a resonant current detection circuit 401, which receives a resonant current Ir, a first current reference I1, and a second current reference I2, and outputs a current detection signal Is based on the resonant current Ir, the first current reference I1, and the second current reference I2; a current adjustment circuit 402, which receives the current detection signal Is and the energy storage current reference Iref, and outputs a conduction duration control signal Tcon based on the current detection signal Is and the energy storage current reference Iref; and a conduction duration control circuit 403, which receives the conduction duration control signal Tcon and the initial value of the conduction duration signal QLON_pre, and outputs a conduction duration signal QLON based on the conduction duration control signal Tcon and the initial value of the conduction duration signal QLON_pre. The conduction duration signal QLON controls the conduction duration of the pull-down switch QL. In other words, the control circuit 40 records the conduction duration of the pull-down switch QL in the previous switching cycle. After adjustment by the conduction duration control signal Tcon, it generates a conduction duration signal QLON to control the conduction duration of the pull-down switch QL in the next adjacent switching cycle, thereby controlling the value of the negative resonant current Ir to a level sufficient to make the switching voltage Vsw rise to the input voltage Vin before the pull-up switch QH is turned on.

[0036] The current detection signal Is corresponds to Figure 3 The resonant current Ir near time t6. The energy storage current reference Iref corresponds to the target current value of the resonant current Ir at the corresponding time. Figure 4 In the circuit, when the current detection signal Is is less than the energy storage current reference Iref, the current adjustment circuit 402 outputs a conduction duration control signal Tcon to adjust the conduction duration of the pull-down switch QL. In one embodiment, the initial value of the conduction duration signal QLON_pre is provided by a register; that is, the control circuit 40 includes a register for storing a signal characterizing the conduction duration of the pull-down switch in the current switching cycle, thereby calculating the conduction duration of the pull-down switch in the next switching cycle. In one embodiment, the value of the conduction duration signal QLON is the result of calculating the initial value of the conduction duration signal QLON_pre and the value of the conduction duration control signal Tcon.

[0037] In one embodiment, when the resonant current Ir rises to its peak value, the pull-up switch QH is turned off, and then the pull-down switch QL is turned on. The on-time of QL is determined by the value of the on-time signal QLON. In one embodiment, the initial value of the on-time signal QLON is determined by the peak value of the resonant current Ir and the excitation current Im on the primary side of transformer T1 (e.g., ...). Figure 3The slope (as shown) is calculated, and after the circuit is running, the conduction duration signal of the next switching cycle is updated by adjusting the conduction duration control signal Tcon based on the conduction duration signal of the current switching cycle. The excitation current Im can be calculated based on the peak value of the resonant current Ir, the primary and 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.

[0038] Figure 5 This is a schematic diagram of the circuit structure of a resonant current detection circuit 50 according to an embodiment of the present invention. The resonant current detection circuit 50 can be used for... Figure 4 The control circuit 40 shown is an example. Figure 5 As shown, the resonant current detection circuit 50 includes: a first comparison circuit 501, which receives the resonant current Ir and compares it with a first current reference I1, and outputs a first comparison signal CP1 based on the comparison result; a second comparison circuit 502, which receives the resonant current Ir and compares it with a second current reference I2, and outputs a second comparison signal CP2 based on the comparison result; a first timing circuit 503, which receives a timing start signal ST and a first comparison signal CP1, and outputs a first timing signal TC1; a second timing circuit 504, which receives the timing start signal ST and a second comparison signal CP2, and outputs a second timing signal TC2; and a calculation circuit 505, which receives the first current reference I1, the second current reference I2, the first timing signal TC1 and the second timing signal TC2, and outputs a current detection signal Is based on the first current reference I1, the second current reference I2, the first timing signal TC1 and the second timing signal TC2.

[0039] The first current reference I1 and the second current reference I2 can be two separate current reference signals, or they can be generated based on the same current reference signal, such as different voltage divisions of the same current reference. In one embodiment, the value of the second current reference I2 is twice the value of the first current reference I1. In other embodiments, the first current reference I1 and the second current reference I2 can also have other proportional relationships.

[0040] Figure 6 This is a schematic diagram of the waveforms of a portion of the signals from a resonant current detection circuit 50 according to an embodiment of the present invention. Figure 3 and 6As shown, after the pull-up switch QL is turned on, the resonant current Ir begins to rise. When it rises to the first current reference I1, the first comparison signal CP1 jumps from the first level (low level) to the second level (high level). When the resonant current Ir rises to the second current reference I2, the second comparison signal CP2 jumps from the first level (low level) to the second level (high level). The first timing circuit 503 receives the timing start signal ST and the first comparison signal CP1. At the timing start time represented by the timing start signal ST, for example, when the pull-up switch QH is turned on, the first timing circuit 503 starts timing, and when the first comparison signal CP1 flips, that is, when it jumps from the first level to the second level, the timing ends, and the first timing signal TC1 is output. Therefore, the first timing signal TC1 represents the following: Figure 6 The duration shown is from the timing start time represented by the timing start signal ST to the flipping time of the first comparison signal CP1. The second timing circuit 504 receives the timing start signal ST and the second comparison signal CP2. At the timing start time represented by the timing start signal ST, for example, the time when the pull-up switch QH is turned on, the second timing circuit 504 starts timing and ends timing when the second comparison signal CP2 flips, i.e., when it jumps from the first level to the second level, outputting the second timing signal TC2. Therefore, the second timing signal TC2 represents the duration from the timing start time represented by the timing start signal ST to the flipping time of the first comparison signal CP1. Figure 6 The duration shown is from the timing start time represented by the timing start signal ST to the flip time of the second comparison signal CP2. Figure 6 As shown, we can obtain the following formula:

[0041]

[0042] When the second current reference I2 is equal to twice the value of the first current reference I1, formula (1) can be written as:

[0043]

[0044] The calculations of formulas (1) and (2) can be performed by the calculation circuit 505. The calculation circuit 505 can generate digital circuits using digital description languages ​​such as Verilog and VHDL to realize the above calculation functions. In other embodiments, the calculation process in formulas (1) or (2) can also be realized by a capacitor charging and discharging circuit to obtain the current detection signal Is.

[0045] In one embodiment, the timing start signal ST can be the pull-up control signal GH of the pull-up switch QH. In other embodiments, the timing start signal ST can be the signal after a certain delay of the pull-up switch QH, or a signal representing the time point between the turn-off of the pull-down switch QL and the turn-on of the pull-up switch QH, or other signals that can represent the time points before and after the turn-on of the pull-up switch QH. It should be understood that the theoretical basis for the above formula (1) is that after the pull-up switch QH is turned on, the resonant current Ir rises linearly within a certain time range from near the turn-on time of the pull-up switch QH. From near the turn-on time of the pull-up switch QH to the turn-off time of the pull-up switch QH, the waveform of the resonant current Ir is approximately a sine curve. Based on the approximately linear characteristic of the middle segment of the waveform from the valley to the peak of the sine curve, the present invention estimates the current using a linear method. Those skilled in the art can select the values ​​of the first current reference I1 and the second current reference I2 based on the approximately linear characteristic of the sine curve from the valley to the peak and the specific parameters of the application. In some embodiments, the value of the first current reference I1 is 300mA, and the value of the second current reference I2 is 600mA.

[0046] It should be understood that Figure 6 The signal levels and logical relationships between the signals are only used to illustrate the principles of the invention. In practical applications, the signal levels and relationships can vary depending on the application requirements. Essentially, within the linearly increasing duration of the resonant current Ir, two different time periods are counted starting from the on-time of the pull-up switch QH, and the current detection Is is calculated according to formulas (1) and (2). Therefore, in addition to the pull-up control signal GH, other signals representing the on-time of the pull-up switch QH can also be used in the embodiments of this invention. Furthermore, as long as the resonant current Ir is within the linearly increasing duration, counting two different time periods starting from any point to calculate the value of the resonant current Ir at that point is within the protection scope of this invention, and the signal representing that point can be used to control the start of timing for the first and second timing circuits.

[0047] Figure 7 This is a schematic diagram of the control circuit 70 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention. Figure 7As shown, the control circuit 70 includes: a resonant current detection circuit 401, which receives the resonant current Ir, a first current reference I1, and a second current reference I2, and outputs a current detection signal Is based on the first current reference I1, the second current reference I2, and the resonant current Ir; a current adjustment circuit 702, which receives the current detection signal Is and a first energy storage current reference Iref1, and outputs a duration adjustment signal Tadj based on the current detection signal Is and the first energy storage current reference Iref1; and a conduction duration control circuit 703, which receives the duration adjustment signal Tadj and an initial value of the conduction duration signal QLON_pre, and outputs a conduction duration signal QLON based on the duration adjustment signal Tadj and the initial value of the conduction duration signal QLON_pre. The conduction duration signal QLON is used to control the conduction duration of the pull-down switch QL. Figure 7 In this embodiment, the first energy storage current reference Iref1 corresponds to Figure 4 In the embodiment, the energy storage current reference Iref, and the duration adjustment signal Tadj, correspond to... Figure 4 The on-time control signal Tcon in the embodiment.

[0048] exist Figure 7In this embodiment, the current adjustment circuit 702 includes: an energy storage comparison circuit 7021, which receives a current detection signal Is and a first energy storage current reference Iref1, and outputs a current comparison signal Icp based on the comparison result of the two; and a duration adjustment circuit 7022, which receives the current comparison signal Icp and an enable signal EN, and outputs a duration adjustment signal Tadj based on the current comparison signal Icp and the enable signal EN. When the current detection signal Is is greater than the first energy storage current reference Iref1, the current comparison signal Icp output by the energy storage comparison circuit 7021 changes from low to high. The duration adjustment circuit 7022 receives the current comparison signal Icp, and when it changes from low to high, the duration adjustment signal Tadj is set to a preset value and superimposed on the initial value of the conduction duration signal QLON_pre, thereby outputting an increased conduction duration signal QLON, which is used to control the conduction duration of the pull-down switch QL, that is, the conduction duration of the pull-down switch QL in the current switching cycle is increased compared to the previous switching cycle. In one embodiment, the preset value of the duration adjustment signal Tadj can be set via a register. In some embodiments, the preset value of the duration adjustment signal Tadj can also be adjusted via an external component. In some embodiments, the preset value of the duration adjustment signal Tadj can also be set or adjusted via a communication interface. The enable signal EN, within each switching cycle, resets or enables the duration adjustment circuit 7022 as needed, without affecting the on-time timing of the pull-down switch QL. Therefore, the enable signal EN can be a pull-down control signal GL, a pull-up control signal GH, or other signals that reflect the switching cycle. In one embodiment, when the duration adjustment circuit 7022 is reset, the value of the duration adjustment signal Tadj is zero. In other embodiments, when the duration adjustment circuit 7022 is reset, the value of the duration adjustment signal Tadj can be a non-zero initial value.

[0049] exist Figure 7 In this embodiment, the conduction duration control circuit 703 is an adder circuit that superimposes the initial value of the conduction duration signal QLON_pre of the pull-down switch QL with the duration adjustment signal Tadj to generate the conduction duration signal QLON of the pull-down switch QL.

[0050] Figure 8 This is a schematic diagram of the control circuit 80 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention. Figure 8As shown, the control circuit 80 includes: a resonant current detection circuit 401, which receives the resonant current Ir, a first current reference I1, and a second current reference I2, and outputs a current detection signal Is based on the resonant current Ir, the first current reference I1, and the second current reference I2; a current adjustment circuit 802, which receives the current detection signal Is, a first energy storage current reference Iref1, and a second energy storage current reference Iref2, and outputs a duration adjustment signal Tadj and a duration adjustment signal Treg based on the current detection signal Is, the first energy storage current reference Iref1, and the second energy storage current reference Iref2; and a conduction duration control circuit 803, which receives the duration adjustment signal Tadj, the duration adjustment signal Treg, and the initial value of the conduction duration signal QLON_pre, and outputs a conduction duration signal QLON based on the duration adjustment signal Tadj, the duration adjustment signal Treg, and the initial value of the conduction duration signal QLON_pre. The conduction duration signal QLON is used to control the conduction duration of the pull-down switch QL. Figure 8 In this embodiment, the first energy storage current reference Iref1 and the second energy storage current reference Iref2 correspond to Figure 4 In the embodiment, the energy storage current reference Iref, the duration adjustment signal Tadj, and the duration adjustment signal Treg correspond to... Figure 4 The on-time control signal Tcon in the embodiment.

[0051] exist Figure 8In this embodiment, the current adjustment circuit 802 includes: an energy storage comparison circuit 7021, which receives a current detection signal Is and a first energy storage current reference Iref1, and outputs a current comparison signal Icp based on the comparison result of the two; a duration adjustment circuit 7022, which receives the current comparison signal Icp and an enable signal EN, and outputs a duration adjustment signal Tadj based on the current comparison signal Icp and the enable signal EN; and an error amplifier circuit 8021, which receives the current detection signal Is and a second energy storage current reference Iref2, and outputs a duration adjustment signal Treg based on the error between the current detection signal Is and the second energy storage current reference Iref2. That is, when the current detection signal Is is detected to be greater than the first energy storage current reference Iref1, the current comparison signal Icp output by the energy storage comparison circuit 7021 changes from low to high. The duration adjustment circuit 7022 receives the current comparison signal Icp. When Icp changes from low to high, the duration adjustment circuit 7022 outputs a signal Tadj representing the duration, which is superimposed on the initial value of the conduction duration signal QLON_pre to output an increased conduction duration signal QLON, used to control the conduction duration of the pull-down switch QL, i.e., the conduction duration of the pull-down switch QL increases. The enable signal EN resets or enables the duration adjustment circuit 7022 in each switching cycle. The error amplifier circuit 8021 receives the current detection signal Is and the second energy storage current reference Iref2. The smaller the current detection signal Is, the larger the duration adjustment signal Treg output by the error amplifier circuit 8021. The initial value of the conduction duration signal QLON_pre is added to the duration adjustment signal Tadj, and then the duration adjustment signal Treg is subtracted to obtain the conduction duration signal QLON, used to control the conduction duration of the pull-down switch QL. That is, in Figure 8 In this embodiment, QLON = QLON_pre + Tadj - Treg. When the current detection signal Is is too small, the duration adjustment signal Treg reduces the conduction time of the pull-down switch QL, thereby maintaining the conduction time of the pull-down switch QL within a certain range to prevent the increase in the loss of the pull-up switch QH from reducing the circuit efficiency.

[0052] exist Figure 8 In this embodiment, the conduction duration control circuit 803 is an addition and subtraction circuit that superimposes the initial value of the conduction duration signal QLON_pre with the duration adjustment signal Tadj and subtracts the duration adjustment signal Treg from it to generate the conduction duration signal QLON of the pull-down switch QL.

[0053] In one embodiment, the value of the second energy storage current reference Iref2 is less than the value of the first energy storage current reference Iref1. Those skilled in the art can set the values ​​of the first energy storage current reference Iref1 and the second energy storage current reference Iref2 according to application requirements.

[0054] Figure 9 This is a schematic diagram of the control circuit 90 of an asymmetric half-bridge flyback converter according to an embodiment of the present invention. Figure 9 As shown, the control circuit 90 includes: a resonant current detection circuit 401, which receives the resonant current Ir, a first current reference I1, and a second current reference I2, and outputs a current detection signal Is based on the resonant current Ir, the first current reference I1, and the second current reference I2; a current adjustment circuit 902, which receives the current detection signal Is and the second energy storage current reference Iref2, and outputs a duration adjustment signal Treg based on the current detection signal Is and the second energy storage current reference Iref2; and a conduction duration control circuit 903, which receives the duration adjustment signal Treg and the initial value of the conduction duration signal QLON_pre, and outputs a conduction duration signal QLON based on the duration adjustment signal Treg and the initial value of the conduction duration signal QLON_pre. The conduction duration signal QLON is used to control the conduction duration of the pull-down switch QL. Figure 9 In this embodiment, the second energy storage current reference Iref2 corresponds to Figure 4 In the embodiment, the energy storage current reference Iref, and the duration adjustment signal Treg, correspond to Figure 4 The on-time control signal Tcon in the embodiment.

[0055] exist Figure 9 In this embodiment, the current adjustment circuit 902 includes an error amplifier circuit 8021, which receives a current detection signal Is and a second energy storage current reference Iref2, and outputs a duration adjustment signal Treg based on the error between the current detection signal Is and the second energy storage current reference Iref2. The error amplifier circuit 8021 receives the current detection signal Is and the second energy storage current reference Iref2; the smaller the current detection signal Is, the larger the duration adjustment signal Treg output by the error amplifier circuit 8021. The initial value of the conduction duration signal QLON_pre is subtracted from the duration adjustment signal Treg to obtain the conduction duration signal QLON, which is used to control the conduction duration of the pull-down switch QL. That is, in... Figure 9 In this embodiment, QLON = QLON_pre-Treg. When the current detection signal Is is too small, the duration adjustment signal Treg reduces the conduction time of the pull-down switch QL, thereby maintaining the conduction time of the pull-down switch QL within a certain range to prevent the increase in the loss of the pull-up switch QH from reducing the circuit efficiency.

[0056] exist Figure 9 In this embodiment, the conduction duration control circuit 903 is a subtraction circuit that subtracts the duration adjustment signal Treg from the initial value of the conduction duration signal QLON_pre to generate the conduction duration signal QLON of the pull-down switch QL.

[0057] Figure 10 This is a flowchart illustrating a control method 100 for a resonant circuit according to an embodiment of the present invention. The resonant circuit includes, for example: Figure 1 The asymmetric half-bridge flyback converter 10 is shown. For example... Figure 10 As shown, the control method 100 includes: step 101, outputting a current detection signal based on the resonant current flowing through the resonant capacitor of the resonant circuit, a first current reference, and a second current reference; step 102, outputting a conduction duration control signal based on the current detection signal and the energy storage current reference; and step 103, controlling the conduction duration of the pull-down switch of the resonant circuit based on the conduction duration control signal and the initial value of the conduction duration signal.

[0058] In one embodiment, the initial value of the conduction duration signal is the conduction duration signal of the pull-down switch in the previous switching cycle. In other embodiments, the initial value of the conduction duration signal can also be a fixed conduction duration signal preset by the circuit. The conduction duration control signal and the initial value of the conduction duration signal are calculated to obtain the conduction duration signal, which is used to control the pull-down control signal of the pull-down switch, thereby controlling the conduction duration of the pull-down switch.

[0059] In one embodiment, step 101 includes: outputting a first comparison signal based on a first current reference and a current detection signal; outputting a second comparison signal based on a second current reference and a current detection signal; outputting a first timing signal based on the first comparison signal and a timing start signal; outputting a second timing signal based on the second comparison signal and the timing start signal; and outputting a current detection signal based on the first current reference, the second current reference, the first timing signal, and the second timing signal. The timing start signal represents the turn-on time of the pull-up switch transistor in the resonant circuit or any time near the turn-on time.

[0060] In one embodiment, step 102 includes: outputting a current comparison signal based on a comparison result between a current detection signal and a first energy storage current reference; and outputting a duration adjustment signal as a conduction duration control signal based on the current comparison signal and an enable signal. Wherein, when the current detection signal is greater than the first energy storage current reference, the duration adjustment signal is set to a preset value; the enable signal resets the duration adjustment signal in each switching cycle; the energy storage current reference includes the first energy storage current reference.

[0061] Correspondingly, step 103 includes: superimposing the initial value of the conduction duration signal and the duration adjustment signal, and outputting the conduction duration signal to control the conduction duration of the pull-down switch of the resonant circuit.

[0062] In one embodiment, step 102 includes: outputting a current comparison signal based on the comparison result of the current detection signal and the first energy storage current reference; outputting a duration adjustment signal based on the current comparison signal and an enable signal; and outputting a duration adjustment signal based on the error amplification signal of the current detection signal and the second energy storage current reference. Wherein, when the current detection signal is greater than the first energy storage current reference, the duration adjustment signal is set to a preset value; the enable signal resets the duration adjustment signal in each switching cycle; the energy storage current reference includes the first energy storage current reference and the second energy storage current reference, and the conduction duration control signal includes the duration adjustment signal and the duration adjustment signal.

[0063] In one embodiment, the second energy storage current reference is less than the first energy storage current reference.

[0064] Correspondingly, step 103 includes: superimposing the initial value of the conduction duration signal and the duration adjustment signal, and subtracting the duration adjustment signal from the superposition result to output the conduction duration signal to control the conduction duration of the pull-down switch of the resonant circuit.

[0065] In one embodiment, step 102 includes: outputting a duration adjustment signal as a conduction duration control signal based on the current detection signal and the error amplification signal of the second energy storage current reference; wherein, the enable signal resets the duration adjustment signal in each switching cycle; and the energy storage current reference includes the second energy storage current reference.

[0066] Correspondingly, step 103 includes: subtracting the duration adjustment signal from the initial value of the conduction duration signal to output a conduction duration signal to control the conduction duration of the pull-down switch of the resonant circuit.

[0067] In one embodiment, the value of the duration adjustment signal increases as the current detection signal decreases.

[0068] It should be understood that the circuits and operating processes described in this invention are for illustrative purposes only. Any circuit that can implement the functions and operating processes of the circuits in this invention does not depart from the spirit or essence of this invention.

[0069] The above embodiments use an asymmetric half-bridge flyback converter as an example to illustrate the control circuit and control method of the present invention for controlling the resonant current to achieve zero-voltage switching of the resonant switch. It should be understood that the control circuit and control method of the present invention can also be applied to other resonant circuits besides the asymmetric half-bridge flyback converter, such as LLC resonant circuits, LCC resonant circuits, etc. In these resonant circuits, the control circuit and control method of the present invention can be used to estimate the resonant circuit near the turn-on time of the pull-up switch, thereby adjusting the conduction time of the pull-down switch and achieving zero-voltage switching of the pull-up switch.

[0070] 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, comprising: The resonant current detection circuit receives the resonant current, a first current reference, and a second current reference. Based on the resonant current, the first current reference, and the second current reference, it outputs a current detection signal, which is the value of the resonant current at the moment when the pull-up switch of the resonant circuit is turned on. The current adjustment circuit receives the current detection signal and the energy storage current reference, and outputs a conduction duration control signal based on the current detection signal and the energy storage current reference, so that the conduction duration of the pull-down switch of the resonant circuit changes with the comparison result or error between the current detection signal and the energy storage current reference. as well as The conduction duration control circuit receives the conduction duration control signal and the initial value of the conduction duration signal, and outputs the conduction duration signal based on the conduction duration control signal and the initial value of the conduction duration signal to control the pull-down switch of the resonant circuit.

2. The control circuit as described in claim 1, wherein the resonant current detection circuit comprises: The first comparison circuit receives the resonant current, compares the resonant current with the first current reference, and outputs a first comparison signal based on the comparison result. The second comparison circuit receives the resonant current, compares the resonant current with the second current reference, and outputs a second comparison signal based on the comparison result. The first timing circuit receives the timing start signal and the first comparison signal, and outputs the first timing signal; The second timing circuit receives the timing start signal and the second comparison signal, and outputs the second timing signal. as well as The computing circuit receives a first current reference, a second current reference, a first timing signal, and a second timing signal, and outputs a current detection signal based on the first current reference, the second current reference, the first timing signal, and the second timing signal.

3. The control circuit as described in claim 1, wherein the current adjustment circuit comprises: The energy storage comparison circuit receives the current detection signal and the first energy storage current reference, and outputs a current comparison signal based on the comparison result of the two. as well as The duration adjustment circuit receives a current comparison signal and an enable signal, and outputs a duration adjustment signal as a conduction duration control signal based on the current comparison signal and the enable signal. The enable signal is reset for a duration that is adjusted during each switching cycle. The energy storage current reference includes the first energy storage current reference.

4. The control circuit as described in claim 3, wherein, The conduction duration control circuit includes an adder circuit, which superimposes the initial value of the conduction duration signal with the duration adjustment signal and outputs a conduction duration signal to control the conduction duration of the pull-down switch.

5. The control circuit as claimed in claim 1, wherein the current adjustment circuit comprises: The energy storage comparison circuit receives the current detection signal and the first energy storage current reference, and outputs a current comparison signal based on the comparison result of the two. The duration adjustment circuit receives a current comparison signal and an enable signal, and outputs a duration adjustment signal based on the current comparison signal and the enable signal. as well as An error amplifier circuit receives a current detection signal and a second energy storage current reference, and outputs a duration adjustment signal based on the error between the current detection signal and the second energy storage current reference. The enable signal is reset for a duration that is adjusted during each switching cycle. The conduction duration control signal includes a duration adjustment signal and a duration regulation signal; The energy storage current reference includes the first energy storage current reference and the second energy storage current reference.

6. The control circuit as described in claim 5, wherein the first energy storage current reference is greater than the second energy storage current reference.

7. The control circuit as described in claim 5, wherein the conduction duration control circuit includes an addition / subtraction circuit, wherein the addition / subtraction circuit superimposes the initial value of the conduction duration signal with the duration adjustment signal and subtracts the duration adjustment signal, thereby outputting a conduction duration signal to control the conduction duration of the pull-down switch.

8. The control circuit of claim 1, wherein the current adjustment circuit comprises: An error amplifier circuit receives a current detection signal and a second energy storage current reference, and outputs a duration adjustment signal as a conduction duration control signal based on the error between the current detection signal and the second energy storage current reference. The energy storage current reference includes the second energy storage current reference.

9. The control circuit of claim 8, wherein the conduction duration control circuit comprises: The subtraction circuit subtracts the duration adjustment signal from the initial value of the pull-down switch transistor's on-time signal to generate an on-time signal to control the on-time of the pull-down switch transistor.

10. A resonant circuit, comprising the control circuit as described in any one of claims 1 to 9, further comprising: A pull-up switch is coupled between the input voltage and the switching terminal, receives a pull-up control signal, and is turned on or off under the control of the pull-up control signal. as well as The pull-down switch is coupled between the switch terminal and the primary ground, receives the pull-down control signal, and turns on or off under the control of the pull-down control signal.

11. The resonant circuit of claim 10, further comprising: A transformer consists of a primary winding and a secondary winding; as well as The resonant capacitor is connected in series with the primary winding between the switch terminal and the primary ground.

12. The resonant circuit of claim 11, further comprising: The secondary switch is coupled between the secondary winding and the output voltage.

13. The resonant circuit of claim 11, further comprising: The secondary switch is coupled between the secondary winding and the secondary ground.

14. A control method for a resonant circuit, the resonant circuit comprising a transformer, a resonant capacitor connected in series with the primary winding of the transformer, and a pull-up switch and a pull-down switch connected in series between an input voltage and primary ground, the control method comprising: The current detection signal is based on the resonant current flowing through the resonant capacitor of the resonant circuit, the first current reference, and the second current reference. The current detection signal represents the value of the resonant current at the moment corresponding to the timing start signal. Based on the current detection signal and the energy storage current reference, the on-time control signal is output so that the on-time of the pull-down switch of the resonant circuit changes with the comparison result or error between the current detection signal and the energy storage current reference. as well as The conduction duration of the pull-down switch in the resonant circuit is controlled based on the conduction duration control signal and the initial value of the conduction duration signal.

15. The control method of claim 14, wherein the resonant current based on the resonant capacitor flowing through the resonant circuit, the first current reference, and the second current reference output current detection signal include: The first comparison signal is output based on the first current reference and the resonant current; A second comparison signal is output based on the second current reference and the resonant current; The first timing signal is output based on the first comparison signal and the timing start signal; A second timing signal is output based on the second comparison signal and the timing start signal; as well as The current detection signal is output based on the first current reference, the second current reference, the first timing signal, and the second timing signal.

16. The control method of claim 14, wherein the timing start signal includes a signal characterizing the turn-on time of the pull-up switch.

17. The control method as described in claim 14, wherein, The timing start signal includes a signal representing the turn-on time of the pull-up switch transistor after a delay.

18. The control method as described in claim 14, wherein, The timing start signal includes a signal representing the time before the pull-up switch is turned on.

19. The control method of claim 14, wherein the control signal for the on-time output based on the current detection signal and the energy storage current reference includes: Based on the comparison result between the current detection signal and the first energy storage current reference, a current comparison signal is output; as well as Based on the current comparison signal and the enable signal, the output duration adjustment signal is used as the conduction duration control signal; Wherein, when the current detection signal is greater than the first energy storage current reference, the duration adjustment signal is set to a preset value, and the energy storage current reference includes the first energy storage current reference; The enable signal is a reset duration adjustment signal in each switching cycle.

20. The control method of claim 19, wherein the conduction duration of the pull-down switch transistor in the resonant circuit controlled based on the conduction duration control signal and the initial value of the conduction duration signal includes: The initial value of the conduction duration signal and the duration adjustment signal are superimposed to output the conduction duration signal to control the conduction duration of the pull-down switch of the resonant circuit.

21. The control method of claim 14, wherein the control signal for the on-time output based on the current detection signal and the energy storage current reference includes: Based on the comparison result between the current detection signal and the first energy storage current reference, a current comparison signal is output; Based on the current comparison signal and the enable signal, the duration adjustment signal is output; as well as Based on the error amplification signal of the current detection signal and the second energy storage current reference, the output duration adjustment signal is generated. When the current detection signal is greater than the first energy storage current reference, the duration adjustment signal is set to a preset value. The enable signal is a reset duration adjustment signal in each switching cycle; The conduction duration control signal includes a duration adjustment signal and a duration regulation signal, and the energy storage current reference includes a first energy storage current reference and a second energy storage current reference.

22. The control method of claim 21, wherein the conduction duration of the pull-down switch transistor in the resonant circuit controlled based on the conduction duration control signal and the initial value of the conduction duration signal includes: The initial value of the conduction duration signal and the duration adjustment signal are superimposed, and the duration adjustment signal is subtracted from the superposition result to output the conduction duration signal to control the conduction duration of the pull-down switch of the resonant circuit.

23. The control method of claim 21, wherein the first energy storage current reference is greater than the second energy storage current reference.

24. The control method of claim 14, wherein the control signal for the on-time output based on the current detection signal and the energy storage current reference includes: Based on the error amplification signal of the current detection signal and the second energy storage current reference, the output duration adjustment signal is used as the conduction duration control signal; The energy storage current reference includes the second energy storage current reference.

25. The control method of claim 24, wherein the conduction duration of the pull-down switch transistor in the resonant circuit controlled based on the conduction duration control signal and the initial value of the conduction duration signal includes: The initial value of the conduction duration signal is subtracted from the duration adjustment signal to output the conduction duration signal, which controls the pull-down switch of the resonant circuit.

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