Control method and control circuit of switching power supply and power conversion system applying control circuit

Abstract

The embodiment of the invention discloses a switching power supply control method, a switching power supply control circuit and a conversion system using the switching power supply control circuit. The minimum conduction time of the main power tube and / or the synchronous rectifier tube is controlled according to the voltage state of a time period when the voltage between the two power poles of the synchronous rectifier tube or the main power tube starts to oscillate, so that the minimum conduction time is dynamically adjusted in real time according to the state of the load, and different load applications are met. According to the method, the control circuit is simple, and the reliability and flexibility of system application are improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and more particularly to a control method and a control circuit for a switching power supply and a conversion system using the same. Background Art

[0002] In existing switching power supplies, due to the influence of parasitic parameters such as leakage inductance, the drain-source voltage of the synchronous rectifier in the early stage of freewheeling fluctuates. This can easily cause the controller to mistakenly determine that the synchronous rectifier has crossed the shutdown threshold and shut down the synchronous rectifier. To prevent the synchronous rectifier from shutting down prematurely, the existing technology typically sets a fixed minimum on-time after the synchronous rectifier is turned on to shield the positive zero-crossing oscillation of the drain-source voltage in the early stage of turn-on. The advantage of this approach is that the control circuit is relatively simple. The disadvantage is that when operating in a light load or no-load state, when the system circuit's minimum on-time remains the same as the minimum on-time under heavy load, it will cause the primary or secondary side switch to shut down too late, affecting the reliability of the system operation and reducing its applicability. Summary of the Invention

[0003] In view of this, the present invention proposes a control method for a switching circuit, a control circuit, and a conversion system using the same, to solve the problem caused by the constant minimum on-time in the prior art.

[0004] In a first aspect, an embodiment of the present invention provides a method for controlling a switching power supply, wherein, in a current switching cycle, when at least one of a main power transistor and a synchronous rectifier transistor is in an off state, detecting a voltage state during at least a portion of a time period from when the voltage between two power poles of the synchronous rectifier transistor or the main power transistor begins to oscillate when both the main power transistor and the synchronous rectifier transistor are in the off state;

[0005] According to the voltage state, the minimum on-time of the main power tube and / or the synchronous rectifier tube is controlled in the next switching cycle.

[0006] Preferably, when the voltage state indicates that the load is lightly loaded, in the next switching cycle, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced;

[0007] When the voltage state indicates that the load is heavy, in the next switching cycle, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained.

[0008] Preferably, the voltage status includes whether the duration of at least part of the time period reaches a preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value.

[0009] Preferably, when the synchronous rectifier is in the off state, a first time is generated by detecting the length of time from the first time the voltage between the two power poles of the synchronous rectifier reaches a preset voltage to the moment when the synchronous rectifier starts to turn on in the next switching cycle, and the first time is compared with the first preset time to control the minimum on-time.

[0010] Preferably, the preset voltage is greater than or equal to a turn-off threshold of the synchronous rectifier.

[0011] Preferably, when the main power tube is in the off state, a second time is generated by detecting the time length between the main power tube off moment and the main power tube start-on moment in the next switching cycle, and the second time is compared with a second preset time to control the minimum on-time.

[0012] Preferably, when the first time is greater than or equal to the first preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the first time is less than the first preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

[0013] Preferably, when the second time is greater than or equal to the second preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the second time is less than the second preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

[0014] Preferably, when the first time reaches the first preset time, an enable signal with a valid level is generated, wherein when a step signal representing the main power tube or the synchronous rectifier tube switching from the on state to the off state is received, the enable signal begins to switch to an invalid level.

[0015] Preferably, when the second time reaches the second preset time, an enable signal with a valid level is generated, wherein when a step signal representing the main power tube or the synchronous rectifier tube switching from the on state to the off state is received, the enable signal begins to switch to an invalid level.

[0016] Preferably, when the enable signal is at an effective level at the start of the next switching cycle of the main power tube or the synchronous rectifier tube, the minimum on-time of the next switching cycle of the corresponding switch tube is reduced.

[0017] Preferably, a first count value is generated by detecting the number of oscillation cycles of the voltage between two power poles of the main power tube or the synchronous rectifier tube, and the first count value is compared with a preset value to control the minimum on-time.

[0018] Preferably, the number of oscillation cycles is determined by comparing the voltage between two power poles of the synchronous rectifier with the output voltage of the switching power supply.

[0019] Preferably, the number of oscillation cycles is determined by comparing the voltage between two power poles of the main power tube with the input voltage of the switching power supply.

[0020] Preferably, when the first count value is greater than or equal to the preset value, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the first count value is less than the preset value, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

[0021] In a second aspect, an embodiment of the present invention further provides a control circuit of a switching power supply, wherein the detection module detects, during a current switching cycle, when at least one of a main power tube and a synchronous rectifier tube is in an off state, a voltage state during at least a portion of a time period from the moment when the voltage between two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the off state;

[0022] The regulating module controls the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle according to the voltage state.

[0023] Preferably, when the detection module detects that the voltage state indicates that the load is lightly loaded, the regulation module reduces the duration of the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle;

[0024] When the detection module detects that the voltage state indicates that the load is heavy, the regulation module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

[0025] Preferably, the voltage status includes whether the duration of at least part of the time period reaches a preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value.

[0026] Preferably, when the synchronous rectifier is in the off state, the detection module generates a first time by detecting the length of time between the first time the voltage between the two power poles of the synchronous rectifier reaches the preset voltage and the moment when the synchronous rectifier starts to turn on in the next switching cycle, and compares the first time with the first preset time to control the minimum on-time.

[0027] Preferably, the detection module generates a second time by detecting the time length between the main power tube shutoff moment and the main power tube start-on moment in the next switching cycle, and compares the second time with a second preset time to control the minimum on-time.

[0028] Preferably, when the first time is greater than or equal to the first preset time, the regulating module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle; when the first time is less than the preset time, the regulating module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

[0029] Preferably, when the second time is greater than or equal to the second preset time, the regulating module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle; when the second time is less than the second preset time, the regulating module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

[0030] Preferably, the detection module generates a first count value by detecting the number of oscillation cycles of the voltage between two power poles of the main power tube or the synchronous rectifier tube, and compares the first count value with a preset value to determine the voltage state.

[0031] Preferably, the detection module determines the number of the oscillation cycles by comparing the voltage between the two power poles of the synchronous rectifier with the output voltage of the switching power supply.

[0032] Preferably, the detection module determines the number of the oscillation cycles by comparing the voltage between the two power poles of the main power tube with the input voltage of the switching power supply.

[0033] Preferably, when the first count value is greater than or equal to the preset value, in the next switching cycle, the regulation module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube; when the first count value is less than the preset value, in the next switching cycle, the regulation module increases and / or maintains the minimum on-time of the main power tube or the synchronous rectifier tube.

[0034] Preferably, the comparison module is used to compare the voltage between the two power poles of the synchronous rectifier with a preset voltage and output a comparison signal;

[0035] The judgment module receives the comparison signal and is used to judge whether the time length of at least part of the time period reaches a preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value.

[0036] Preferably, the judgment module is used to judge whether the time length between the voltage between the two power poles of the synchronous rectifier tube reaches the preset voltage for the first time and the moment when the synchronous rectifier tube starts to turn on in the next switching cycle reaches the first preset time, and output a detection signal.

[0037] Preferably, the preset voltage is greater than or equal to a turn-off threshold of the synchronous rectifier.

[0038] Preferably, the detection module further comprises: an enable signal generating module, which receives the detection signal and generates an enable signal for indicating whether to shorten the minimum on-time.

[0039] Preferably, the judgment module includes: a shielding module, used to shield the oscillation level in the comparison signal and output a shielding signal; a delay unit, used to delay the transition edge of the shielding signal that jumps to the valid level for a first preset time and output the detection signal.

[0040] Preferably, the shielding module comprises an RS trigger, wherein a set terminal receives the comparison signal, a reset terminal receives a driving signal for controlling the state of the synchronous rectifier, and an output terminal outputs the shielding signal.

[0041] Preferably, the enable signal generating module includes a D flip-flop, wherein the data input terminal of the D flip-flop receives a high level, and the clock input terminal receives the detection signal. When the clear input terminal receives a step signal representing that the main power tube or the synchronous rectifier tube changes from the on state to the off state, the enable signal output by the D flip-flop begins to switch to an invalid level.

[0042] Preferably, when the enable signal detected by the regulating module is at a valid level at the start of conduction of the power tube or the synchronous rectifier tube in the next cycle, the minimum conduction time of the corresponding switch tube in the next cycle is reduced.

[0043] Preferably, the judgment module includes: a monostable trigger, when detecting a transition edge in which the comparison signal jumps to a valid level, the judgment module outputs a pulse of a fixed duration;

[0044] The pulse counting comparison module is coupled to the output end of the monostable trigger, counts the number of pulses in the received signal, and outputs a detection signal with a valid level when the number of pulses is greater than or equal to a preset value.

[0045] Preferably, the preset voltage is the output voltage of the switching circuit.

[0046] Preferably, the judgment module further includes: an AND gate, receiving the comparison signal and the output signal of the monostable trigger, and outputting a signal to the pulse counting comparison module.

[0047] In a third aspect, an embodiment of the present invention further provides a power conversion system, including a main power tube, a synchronous rectifier tube and the above-mentioned switching power supply control circuit.

[0048] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0049] When at least one of the main power tube and the synchronous rectifier tube is in the disconnected state, the voltage state of at least a portion of the time period when the voltage between the two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the disconnected state is detected to distinguish the state of the system load (heavy load or light load), so as to dynamically and in real time adjust the minimum on-time of the main power tube and the synchronous rectifier tube in the next switching cycle to meet different load applications. This method has a simple control circuit and improves the reliability and flexibility of system application. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0051] Figure 1 is a circuit diagram of a power conversion system according to an embodiment of the present invention;

[0052] Figure 2 A schematic block diagram of a control circuit according to an embodiment of the present invention;

[0053] Figure 3 This is a first schematic circuit diagram of a detection module according to an embodiment of the present invention;

[0054] Figure 4 This is a first working waveform diagram of the detection module according to an embodiment of the present invention;

[0055] Figure 5 A second schematic circuit diagram of a detection module according to an embodiment of the present invention;

[0056] Figure 6 This is a second working waveform diagram of the detection module according to an embodiment of the present invention;

[0057] Figure 7 Schematic diagram of a control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The present invention is described below based on the following embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, certain specific details are described in detail. Those skilled in the art can fully understand the present invention without these details. To avoid obscuring the essence of the present invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0059] Furthermore, persons of ordinary skill in the art will appreciate that the figures provided herein are for illustration purposes only and are not necessarily drawn to scale.

[0060] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit connected electrically or electromagnetically. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected" between two nodes, it can be directly coupled or connected to the other element or there can be intermediate elements. The connection between the elements can be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there are no intermediate elements between the two.

[0061] An embodiment of the present invention provides a power conversion system. Figure 1 A circuit diagram of a power conversion system according to an embodiment of the present invention includes a flyback converter, a primary control circuit, and a synchronous rectifier control circuit. In this embodiment, the flyback converter includes a transformer T1, a primary main power tube Q1, and a synchronous rectifier QS1. The transformer T1 includes a primary winding L M In the prior art, a fixed minimum on-time T is set after the main power tube and the synchronous rectifier tube are turned on. ON_MIN When the switching power supply is lightly loaded, the fixed minimum on-time T ON_MIN This causes the main power tube or synchronous rectifier tube to be shut down too late, affecting the reliability of the system.

[0062] An embodiment of the present invention proposes a control circuit for a switching power supply, comprising a detection module 1 and a regulation module 2. During a current switching cycle, when the main power tube and / or the synchronous rectifier are both in an off state, the detection module 1 detects a voltage state for at least a portion of a time period, including the moment when the voltage between the two power poles of the synchronous rectifier or the main power tube begins to oscillate when both the main power tube and the synchronous rectifier are in an off state; the regulation module 2 controls the minimum on-time of the main power tube and / or the synchronous rectifier in the next switching cycle based on the voltage state. The voltage state can represent the load state of the switching power supply; the voltage state includes whether the length of at least a portion of the time period reaches a preset time, or whether the number of voltage oscillation cycles within at least a portion of the time period reaches a preset value. When the detection module detects that the voltage state indicates that the load is lightly loaded, the regulation module reduces the duration of the minimum on-time of the main power tube or the synchronous rectifier tube in the next switching cycle. When the detection module detects that the voltage state indicates that the load is heavily loaded, the regulation module increases or maintains the duration of the minimum on-time of the main power tube or the synchronous rectifier tube in the next switching cycle. Specifically, when the duration of at least part of the time period reaches a preset time, or the number of voltage oscillation cycles within at least part of the time period reaches a preset value, the voltage state indicates that the load is lightly loaded; otherwise, the load is heavily loaded.

[0063] As an example, the detection module generates a first time by detecting the length of time between the first time the voltage between the two power poles of a synchronous rectifier exceeds a preset voltage and the moment the synchronous rectifier begins conducting in the next switching cycle, and compares the first time with the first preset time to control the minimum on-time; the preset voltage is greater than or equal to the turn-off threshold of the synchronous rectifier. The detection module generates a second time by detecting the length of time between the voltage between the two power poles of the main power tube and the moment the main power tube begins conducting in the next switching cycle, and compares the second time with the second preset time to control the minimum on-time. When the first time is greater than or equal to the first preset time, or the second time is greater than or equal to the second preset time, it indicates a light load, and the regulation module reduces the minimum on-time of the main power tube or synchronous rectifier in the next switching cycle. When the first time is less than the first preset time, or the second time is less than the second preset time, it indicates a heavy load, and the regulation module increases or maintains the minimum on-time of the main power tube or synchronous rectifier in the next switching cycle.

[0064] Specifically, if Figure 2The figure is a schematic block diagram of the control circuit of the switching power supply according to the embodiment of the present invention. The control circuit includes a detection module 1 and a regulation module 2. In this embodiment, the voltage between the two power poles of the synchronous rectifier is the drain-source voltage V DS The detection module 1 includes a comparison module 11 and a judgment module 12, wherein the comparison module 11 is used to compare the drain-source voltage V DS With the preset voltage V TH Compare and output comparison signal V CMP ; Judgment module, receiving comparison signal V CMP , receiving the comparison signal, and determining whether the length of at least part of the time period reaches a first preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value, and outputting a detection signal V DET Specifically, Figure 2 As shown, the detection module 1 further includes an enable signal generating module 13, whose input end is connected to the output end of the judgment module 12 and receives the detection signal V DET , generates an enable signal V for indicating whether to adjust the minimum on-time Minton_EN , and is input to the regulating module 2 as an input signal, so that the regulating module 2 is enabled according to the enable signal V Minton_EN The minimum on-time of the synchronous rectifier tube and / or the main power tube is controlled.

[0065] It should be noted that, in this embodiment, the main power tube and the synchronous rectifier tube are MOS tubes as an example, and the drain-source voltage V DS Taking the comparison with the preset voltage as an example for explanation, at this time, the preset voltage is greater than or equal to the turn-off threshold of the synchronous rectifier. In other embodiments, the switch tube may also be a bipolar junction transistor (BJT), or an insulated gate bipolar transistor (IGBT) and other types, which are not limited here. During the current switching cycle, when the main power tube and the synchronous rectifier are both in the off state, the voltage between the two power poles of the main power tube or the synchronous rectifier oscillates. The oscillation starts from the moment when the synchronous rectifier is disconnected when the main power tube is in the off state. When the drain-source voltage of the synchronous rectifier reaches the preset voltage, the voltage between the two power poles of the synchronous rectifier starts to oscillate. In other examples, during the current switching cycle, when the main power tube and the synchronous rectifier are both in the off state, when the drain-source voltage of the main power tube reaches another preset voltage, the voltage between the two power poles of the main power tube starts to oscillate.

[0066] As an example, the judgment module is used to judge whether the time length between the voltage between the two power poles of the synchronous rectifier reaches the preset voltage for the first time and the time when the synchronous rectifier starts to turn on in the next switching cycle reaches the first preset time, and outputs a detection signal. The judgment module includes a shielding module and a delay unit. The shielding module is used to shield the oscillation level in the comparison signal and output a shielding signal; the delay unit is used to delay the transition edge of the shielding signal that jumps to the valid level for the first preset time and output the detection signal. Specifically, the shielding module is used to detect the drain-source voltage V DS The oscillation level in the comparison signal after reaching the preset voltage for the first time is masked.

[0067] Specifically, if Figure 3 As shown in FIG. 1 , a circuit diagram of a specific embodiment of the detection module is shown. In this embodiment, the drain-source voltage V of the synchronous rectifier is detected. DS The oscillation time of is taken as an example. The positive input terminal of the comparison module 21 is connected to the drain-source voltage V DS , the reverse input terminal is connected to the preset voltage V TH , wherein the preset voltage V TH The shielding module 22 includes an RS trigger 221, wherein the set terminal S of the RS trigger 221 receives the comparison signal V CMP The reset terminal R receives the driving signal SR_PWM for controlling or characterizing the working state of the synchronous rectifier tube, and the output terminal Q outputs the shielding signal V A The input terminal of the delay unit 222 is connected to the output terminal Q of the RS trigger 221, which is used to shield the signal V A The rising edge is delayed for the first preset time t REF , thereby outputting the detection signal V DET The enable signal generation module includes a D flip-flop 23, wherein the data input terminal D of the D flip-flop 23 receives a high level, and the clock input terminal CLK receives a detection signal V DET The clear input terminal CLR receives a step signal representing the state of the synchronous rectifier tube. When the step signal representing that the synchronous rectifier tube is disconnected is received, the enable signal V output by the D flip-flop Minton_EN is reset to an invalid level; that is, when receiving a step level indicating that the synchronous rectifier is from the on state to the off state, the enable signal V output by the D trigger is Minton_ENSpecifically, as an example, in this embodiment, the step signal received by the clear input terminal CLR, indicating that the synchronous rectifier is switched from the on state to the off state, is the minimum off-time signal SR_Mintoff of the synchronous rectifier. The rising edge of the minimum off-time signal SR_Mintoff is aligned with the turn-off moment of the synchronous rectifier. During the period when the minimum off-time signal SR_Mintoff is at the valid level, the synchronous rectifier is not allowed to turn on.

[0068] Specifically, if Figure 4 The above is a waveform diagram of a specific embodiment of the detection module. Figure 3 The working process of the detection module is described. In this embodiment, the effective level is a high level as an example.

[0069] At time t0, the drain-source voltage of the synchronous rectifier is V DS drops to the preset voltage V TH (At this time, the preset voltage is greater than the turn-off threshold of the synchronous rectifier tube), the comparison signal V CMP The output starts at a low level. At t0+Δt1, the drain-source voltage V DS The turn-on threshold is less than the preset voltage V TH ( Figure 3 (Δt1 is not shown in the figure, Δt1 is small, so that t0 and t0+Δt1 are approximately overlapped), the driving signal SR_PWM that controls the working state of the synchronous rectifier jumps from a low level to a high level, and the synchronous rectifier starts to conduct. At t0+Δt1, the set terminal S of the RS trigger 221 receives the comparison signal V CMP is low level, the reset terminal R receives the driving signal SR_PWM which is high level, and the output terminal Q of the RS trigger 221 outputs the shielding signal V A At this time, the data input terminal D of the D flip-flop 23 receives the high level VDD, and the clock input terminal CLK receives the detection signal V DET is low level, the clear input CLR maintains the original low level, and the enable signal V Minton_EN Maintain the original level. At this time, the regulation module detects the enable signal V Minton_EN When the synchronous rectifier tube starts to turn on at a time t0+Δt1 that is at an effective level, the minimum on-time of the switch tube in the current cycle is reduced.

[0070] At the moment t1-Δt2, the drain-source voltage V DSWhen the voltage rises to the turn-off threshold of the synchronous rectifier, the driving signal SR_PWM that controls the working state of the synchronous rectifier jumps from a high level to a low level, and the synchronous rectifier begins to turn off. At this time, the minimum turn-off time signal SR_Mintoff that represents the minimum turn-off time of the synchronous rectifier begins to output a high level; the data input terminal D of the D flip-flop 23 receives the high level VDD, and the clock input terminal CLK receives the detection signal V DET Maintaining a low level, the clear terminal CLR receives the minimum off time signal SR_Mintoff and jumps to a high level, and the enable signal V Minton_EN is reset to a low level. At time t1, the drain-source voltage V DS Rising to the preset voltage V TH , where the preset voltage V TH is greater than the shutdown threshold, the comparison signal V CMP The output starts to be high level. At this time, the set terminal S of the RS trigger 221 receives the comparison signal V CMP is high level, the reset terminal R receives SR_PWM as low level, so the shielding signal V of its output terminal Q A At time t1 to t4, the comparison signal V CMP There will be a jump, the reset terminal R remains at a low level, so the shielding signal V of its output terminal Q A It will remain at a high level at time t1, thereby shielding the comparison signal V CMP The oscillation level between time t1 and time t4.

[0071] At time t2, the minimum off-time ends and the minimum off-time signal SR_Mintoff jumps to a low level.

[0072] At time t3, where t3 = t1 + t REF , t REF is the first preset time, shielding signal V A The rising edge delay time reaches the first preset time t REF , detection signal V DET The data input terminal D of the D flip-flop 23 receives the high level VDD, and the clock input terminal CLK receives the detection signal V DET The rising edge of the clear terminal CLR receives the minimum off time signal SR_Mintoff and continues to maintain a low level, and the enable signal V output by the D flip-flop 23 Minton_EN Starts to jump to high level, that is, output enable signal V Minton_ENRising edge. t0~t4 is a switching cycle of the synchronous rectifier. The waveform at t4 is the same as that at t0, and the waveform at t5 is the same as that at t1, which will not be described here. Minton_EN When the synchronous rectifier starts to be turned on at an effective level, the minimum on-time of the current on-time period is reduced.

[0073] It should be noted that, in this embodiment, the clear terminal CLR of the D flip-flop 23 receives the minimum off-time signal SR_Mintoff as an example for explanation. In other examples, the step signal received by the clear terminal CLR of the D flip-flop 23 includes a step level from the on state to the off state, and the duration of the level representing the off state in the step signal is less than the first preset time, which meets the requirements. The specific signal input to the clear terminal CLR of the D flip-flop 23 is not limited here.

[0074] In addition, in the above embodiments, the drain-source voltage V DS The time length from the first time when the voltage is greater than the preset voltage to the time when the synchronous rectifier starts to conduct in the next switching cycle generates a first time, which is greater than the first preset time t REF , an example is given in which a valid enable signal is detected at the turn-on moment of the next cycle of the synchronous rectifier. When the synchronous rectifier is turned off, the first time is less than the first preset time t REF When the delay unit detects that the first time is less than the first preset time t REF In order to prevent timing disorder, you can not A The rising edge of the enable signal V Minton_EN Maintaining a low level, the minimum on-time of the synchronous rectifier tube is not changed, and the original minimum on-time remains unchanged.

[0075] In this embodiment, when the first time is greater than or equal to the first preset time t REF When the first time is less than the first preset time t REF , it indicates that the switching power supply is working in the heavy load working mode, at which time the minimum on-time of the synchronous rectifier tube is kept unchanged; in other examples, when the first time is less than the first preset time t REF or the minimum on-time of the synchronous rectifier tube can be reduced or increased to different degrees according to the first time length being in different time intervals.

[0076] It should be noted that in the above example, the first time is generated by measuring the time between the first time the voltage between the two power terminals of the synchronous rectifier exceeds the preset voltage and the moment the synchronous rectifier begins conducting in the next switching cycle. The first time is compared with the first preset time to control the minimum on-time. In another example, a second time can be generated by detecting the time between the moment the main power transistor is turned off and the moment the main power transistor begins conducting in the next switching cycle. The second time is compared with the second preset time to control the minimum on-time. When the second time is greater than or equal to the second preset time, the minimum on-time of the main power transistor or synchronous rectifier is reduced in the next switching cycle; when the second time is less than the second preset time, the minimum on-time of the main power transistor or synchronous rectifier is increased or maintained in the next switching cycle. As an example, when the second time reaches the second preset time, the detection module generates an enable signal with an active level. When the regulation module receives a step signal indicating that the main power transistor or synchronous rectifier has transitioned from an on state to an off state, the enable signal begins to be cleared to an inactive level.

[0077] As another example, the detection module generates a first count value by detecting the number of voltage oscillation cycles between the two power poles of the synchronous rectifier or the main power tube within a time period including the moment when the voltage between the two power poles of the synchronous rectifier or the main power tube begins to oscillate when both the main power tube and the synchronous rectifier are in the off state. The first count value is compared with a preset value to control the minimum on-time. When the first count value is greater than or equal to the preset value, the regulation module reduces the minimum on-time of the main power tube or the synchronous rectifier in the next switching cycle; when the first count value is less than the preset value, the regulation module increases or maintains the minimum on-time of the main power tube or the synchronous rectifier in the next switching cycle. Specifically, when it is detected that the synchronous rectifier is switched to the off state, the number of oscillation cycles can be determined by comparing the voltage between the two power poles of the synchronous rectifier with the output voltage of the switching power supply, or when it is detected that the main power tube is switched to the off state, the voltage between the two power poles of the main power tube is compared with the input voltage of the switching power supply. Therefore, the load state can be judged by detecting whether the number of voltage oscillation cycles in at least a part of the time period when the voltage between the two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the disconnected state reaches a preset value, thereby controlling the minimum conduction time of the main power tube and / or the rectifier tube.

[0078] Specifically, the judgment module includes a monostable trigger, wherein when the monostable trigger detects the transition edge of the comparison signal to the valid level, it outputs a pulse signal of a fixed duration; the enable signal generation module includes a pulse counting comparison module, which is coupled to the output end of the monostable trigger, counts the number of pulses in the received signal, and compares the number of pulses with a preset value, and outputs an enable signal with a valid level when the number of pulses is greater than or equal to the preset value. In another example, the judgment module also includes an AND gate, which receives the comparison signal and the output signal of the monostable trigger, and outputs a detection signal to the pulse counting comparison module. The AND gate is used to perform a logical AND operation on the comparison signal and the output signal of the monostable trigger. When the comparison signal and the output signal of the monostable trigger are both high levels, the AND gate outputs a high level in the detection signal, thereby preventing external interference from triggering the monostable trigger to output an interfering pulse signal.

[0079] Specifically, if Figure 5 FIG. 1 is a circuit diagram of another embodiment of the detection module. In this embodiment, the preset voltage is the output voltage V OUT .like Figure 5 As shown, the positive input terminal of the comparison module 31 is connected to the drain-source voltage V DS The preset voltage connected to the reverse input terminal is the output voltage of the switching power supply V OUT , by increasing the drain-source voltage of the synchronous rectifier V DS The output voltage of the switching power supply V OUT Compare and output comparison signal V CMP The judgment module 32 includes a monostable trigger 321 and an AND gate 322. The monostable trigger 321 is based on the comparison signal V CMP Output trigger signal V B , each time the comparison signal V is detected CMP When the rising edge of , a pulse signal with a fixed duration is output. AND gate 322 receives the comparison signal V CMP and the output of the monostable trigger is the trigger signal V B , used to perform logical operations on the received signal and output the detection signal V DET The enable signal generating module includes a pulse counting comparison module 33, which receives the detection signal V DET The number of pulses in a switching tube cycle is counted. When the number of pulses is greater than or equal to the preset value, an enable signal V with a valid level is output. Minton_EN . Enable signal V Minton_EN As an input signal to the regulation module, so that according to the enable signal V Minton_EN The minimum on-time of the main power tube and / or synchronous rectifier tube in the next cycle is controlled.

[0080] like Figure 6 As shown in FIG. 1 , another embodiment of the working waveform of the detection module is shown. Figure 5 The working process of the detection module is described. In this embodiment, the effective level is high level as an example. At time t0, the drain-source voltage V DS Rising to the switching power supply output voltage V OUT , the comparison module 31 outputs the comparison signal V CMP The monostable trigger 321 detects the rising edge of the comparison signal V CMP When the rising edge of , a pulse signal of fixed duration is output. Time t1, time t2, time t3, time t4 and time t6 are the same as time t0, and the comparison module 31 outputs the comparison signal V CMP The monostable trigger 321 detects the rising edge of the comparison signal V CMP The rising edge of the detection signal V DET The pulse counting and comparison module 33 outputs a pulse signal of a fixed duration. DET The trigger signal V in one switching tube cycle B The number of pulses in the drain-source voltage V is counted. At time t5, when the number of pulses is greater than or equal to the preset value, in this embodiment, the number of pulses is equal to the drain-source voltage V DS The number of oscillation cycles corresponds to the preset value of 5. When the trigger signal V B When the number of pulses in the enable signal reaches the preset value, the enable signal V Minton_EN Switches to high level. At t7, the synchronous rectifier starts to conduct, and the enable signal V detected by the regulation module Minton_EN When the synchronous rectifier starts to conduct at a high level, the minimum conduction time during the current conduction period of the synchronous rectifier is reduced. At time t8, the synchronous rectifier is disconnected, and the enable signal V Minton_EN is reset to a low level, and at the same time, the pulse counting comparison module 33 detects the signal V DET The number of pulses in the PWM is restarted from 0.

[0081] It should be noted that, in this embodiment, when the drain-source voltage V DS When the number of oscillation cycles reaches the preset value, the switching power supply is defaulted to operate in light load mode, thereby reducing the minimum on-time of the synchronous rectifier tube; when the drain-source voltage V DS When the number of oscillation cycles is less than the preset value, the switching power supply is defaulted to operate in the heavy load mode, at which time the minimum on-time of the synchronous rectifier tube is kept unchanged; in other examples, when the drain-source voltage V DSWhen the number of oscillation cycles is less than the preset value, the minimum on-time of the synchronous rectifier can be increased; or the drain-source voltage V DS The number of oscillation cycles is in different value intervals, and the minimum on-time of the synchronous rectifier tube is reduced or increased to different degrees.

[0082] In the above embodiments, the oscillation waveform of the voltage of the secondary-side synchronous rectifier of the flyback converter is used as an example for description. In other examples, the oscillation waveform of the primary-side main power tube of the flyback converter may also be detected, and the number of oscillation cycles may be determined by comparing the voltage between the two power poles of the main power tube with the input voltage of the switching power supply. In addition, the switching power supply may also be an LLC resonant circuit or a Buck circuit. As long as the switching power supply operates in a DCM (Discontinuous Conduction Mode) operating mode, when the switch is switched, the voltage oscillation caused by parasitic parameters or inductance or capacitance in the circuit is caused, and the length of time when both the main power tube and the synchronous rectifier are in the off state can represent the load state of the switching power supply, any circuit or switching tube is applicable to the present invention, and the specific circuit or switching tube is not limited here.

[0083] like Figure 7 As shown, the present invention also discloses a method for controlling a switching power supply, comprising the following steps:

[0084] S01: in a current switching cycle, when at least one of the main power tube and the synchronous rectifier tube is in an off state, detecting a voltage state during at least a portion of a time period from when the voltage between two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the off state;

[0085] S02: According to the voltage state, in the next switching cycle, the minimum on-time of the main power tube and / or the synchronous rectifier tube is controlled.

[0086] When the voltage state indicates that the load is light, the minimum on-time of the main power tube and / or the synchronous rectifier is reduced in the next switching cycle; when the voltage state indicates that the load is heavy, the minimum on-time of the main power tube and / or the synchronous rectifier is increased or maintained in the next switching cycle. The voltage state includes whether the length of at least part of the time period reaches a preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value. In another example, when the length of at least part of the time period is less than the preset time, the minimum on-time of the switch is increased. At other times, the minimum on-time can be reduced or increased to varying degrees according to the length of at least part of the time period.

[0087] As an example, when the synchronous rectifier is in the off state, a first time is generated by detecting the length of time between the voltage between the two power terminals of the synchronous rectifier and the time when the synchronous rectifier begins conducting in the next switching cycle. The first time is compared with the first preset time to control the minimum on-time. The preset voltage is greater than or equal to the turn-off threshold of the synchronous rectifier. Alternatively, a second time is generated by detecting the length of time between the turn-off of the main power transistor and the time when the main power transistor begins conducting in the next switching cycle. The second time is compared with the second preset time to control the minimum on-time. When the first time is greater than or equal to the first preset time, or the second time is greater than or equal to the second preset time, the minimum on-time of the main power transistor and / or the synchronous rectifier is reduced in the next switching cycle. When the first time is less than the first preset time, or the second time is less than the second preset time, the minimum on-time of the main power transistor and / or the synchronous rectifier is increased or maintained in the next switching cycle. As an example, when the first time reaches the first preset time, or when the second time reaches the second preset time, an enable signal having an effective level is generated, wherein when a step signal indicating that the main power tube or the synchronous rectifier tube switches from an on state to an off state is received, the enable signal begins to be cleared to an inactive level. When the enable signal is at an effective level at the start of the next switching cycle of the main power tube or the synchronous rectifier tube, the minimum on-time of the next switching cycle of the main power tube or the synchronous rectifier tube is reduced.

[0088] As another example, when both the main power transistor and the synchronous rectifier are in the off state, a first count value is generated by detecting the number of oscillation cycles of the voltage between the two power poles of the main power transistor or the synchronous rectifier. The first count value is then compared with a preset value to control the minimum on-time. Specifically, as an example, the number of oscillation cycles can be determined by comparing the voltage between the two power poles of the synchronous rectifier with the output voltage of the switching power supply. The first count value is incremented by 1 each time the voltage between the two power poles of the synchronous rectifier rises or falls to the output voltage of the switching power supply. Alternatively, the number of oscillation cycles is determined by comparing the voltage between the two power poles of the main power transistor with the input voltage of the switching power supply. When the first count value is greater than or equal to the preset value, the minimum on-time of the main power transistor or the synchronous rectifier is reduced in the next switching cycle. When the first count value is less than the preset value, the minimum on-time of the main power transistor or the synchronous rectifier is increased or maintained in the next switching cycle.

[0089] In summary, the present invention discloses a control method and circuit for a switching power supply. During a current switching cycle, when at least one of a main power transistor and a synchronous rectifier is in the off state, the method detects a voltage state for at least a portion of the time period from the moment the voltage between the two power poles of the synchronous rectifier or the main power transistor begins to oscillate when both the main power transistor and the synchronous rectifier are in the off state. Based on this voltage state, the method controls the minimum on-time of the main power transistor and / or the synchronous rectifier in the next switching cycle. This voltage state can characterize the load state of the switching power supply. This allows the minimum on-time of the switching transistor to be dynamically adjusted in real time based on the load state to meet different load applications. This method simplifies the control circuit while improving the reliability and flexibility of system applications.

[0090] Although the embodiments or implementations are described and explained separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that they can be replaced and integrated between the embodiments or implementations. If the content is not clearly recorded in one of the embodiments or implementations, reference can be made to another recorded embodiment.

[0091] While embodiments of the present invention have been described above, these embodiments do not exhaustively describe all details and do not limit the invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the above description. These embodiments are selected and described in detail in this specification in order to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better utilize the present invention and its modifications. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for controlling a switching power supply, characterized in that: The following steps are involved: In the current switching cycle, when at least one of the main power tube and the synchronous rectifier tube is in the off state, detecting a voltage state of at least a portion of a time period from the moment when the voltage between the two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the off state; According to the voltage state, the minimum on-time of the main power tube and / or the synchronous rectifier tube is controlled in the next switching cycle.

2. The control method according to claim 1, wherein: When the voltage state indicates that the load is lightly loaded, in the next switching cycle, reducing the minimum on-time of the main power tube and / or the synchronous rectifier tube; When the voltage state indicates that the load is heavy, in the next switching cycle, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained.

3. The control method according to claim 1, wherein: The voltage status includes whether the duration of at least a portion of the time period reaches a preset time, or whether the number of voltage oscillation cycles within at least a portion of the time period reaches a preset value.

4. The control method according to claim 1, wherein: When the synchronous rectifier is in the off state, a first time is generated by detecting the length of time from the first time the voltage between the two power poles of the synchronous rectifier reaches a preset voltage to the moment when the synchronous rectifier starts to turn on in the next switching cycle. The first time is compared with the first preset time to control the minimum on-time.

5. The control method according to claim 4, characterized in that: The preset voltage is greater than or equal to a turn-off threshold of the synchronous rectifier.

6. The control method according to claim 1, wherein: When the main power tube is in the off state, a second time is generated by detecting the time length between the main power tube off moment and the main power tube start-on moment in the next switching cycle, and the second time is compared with a second preset time to control the minimum on-time.

7. The control method according to claim 4, characterized in that: When the first time is greater than or equal to the first preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the first time is less than the first preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

8. The control method according to claim 6, wherein: When the second time is greater than or equal to the second preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the second time is less than the second preset time, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

9. The control method according to claim 4, characterized in that: When the first time reaches the first preset time, an enable signal with a valid level is generated, wherein when a step signal representing the main power tube or the synchronous rectifier tube switching from the on state to the off state is received, the enable signal begins to switch to an invalid level.

10. The control method according to claim 6, characterized in that: When the second time reaches the second preset time, an enable signal with a valid level is generated, wherein when a step signal representing the main power tube or the synchronous rectifier tube switching from the on state to the off state is received, the enable signal begins to switch to an invalid level.

11. The control method according to claim 9 or 10, characterized in that: When the enable signal is at a valid level at the start of the next switching cycle of the main power tube or the synchronous rectifier tube, the minimum on-time of the next switching cycle of the corresponding switch tube is reduced.

12. The control method according to claim 1, wherein: A first count value is generated by detecting the number of oscillation cycles of the voltage between the two power poles of the main power tube or the synchronous rectifier tube, and the first count value is compared with a preset value to control the minimum on-time.

13. The control method according to claim 12, characterized in that: The number of the oscillation cycles is determined by comparing the voltage between the two power poles of the synchronous rectifier with the output voltage of the switching power supply.

14. The control method according to claim 12, wherein: The number of the oscillation cycles is determined by comparing the voltage between the two power poles of the main power tube with the input voltage of the switching power supply.

15. The control method according to claim 12, characterized in that: When the first count value is greater than or equal to the preset value, the minimum on-time of the main power tube and / or the synchronous rectifier tube is reduced in the next switching cycle; when the first count value is less than the preset value, the minimum on-time of the main power tube and / or the synchronous rectifier tube is increased or maintained in the next switching cycle.

16. A control circuit of a switching power supply, characterized in that: include: a detection module, configured to detect, during a current switching cycle, when at least one of the main power tube and the synchronous rectifier tube is in an off state, a voltage state during at least a portion of a time period from the moment when the voltage between two power poles of the synchronous rectifier tube or the main power tube starts to oscillate when both the main power tube and the synchronous rectifier tube are in the off state; The regulating module controls the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle according to the voltage state.

17. The control circuit according to claim 16, wherein: When the detection module detects that the voltage state indicates that the load is light, the regulation module reduces the duration of the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle; When the detection module detects that the voltage state indicates that the load is heavy, the regulation module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

18. The control circuit according to claim 16, wherein: The voltage status includes whether the duration of at least a portion of the time period reaches a preset time, or whether the number of voltage oscillation cycles within at least a portion of the time period reaches a preset value.

19. The control circuit according to claim 16, wherein: When the synchronous rectifier is in the off state, the detection module generates a first time by detecting the length of time between the first time the voltage between the two power poles of the synchronous rectifier reaches the preset voltage and the moment when the synchronous rectifier starts to turn on in the next switching cycle, and compares the first time with the first preset time to control the minimum on-time.

20. The control circuit according to claim 16, wherein: The detection module generates a second time by detecting the time length between the main power tube turning off and the main power tube starting to turn on in the next switching cycle, and compares the second time with a second preset time to control the minimum on-time.

21. The control circuit according to claim 19, wherein: When the first time is greater than or equal to the first preset time, the regulating module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle; when the first time is less than the preset time, the regulating module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

22. The control circuit according to claim 20, wherein: When the second time is greater than or equal to the second preset time, the regulating module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle; when the second time is less than the second preset time, the regulating module increases or maintains the minimum on-time of the main power tube and / or the synchronous rectifier tube in the next switching cycle.

23. The control circuit according to claim 16, wherein: The detection module generates a first count value by detecting the number of oscillation cycles of the voltage between two power poles of the main power tube or the synchronous rectifier tube, and compares the first count value with a preset value to determine the voltage state.

24. The control circuit according to claim 23, wherein: The detection module determines the number of the oscillation cycles by comparing the voltage between the two power poles of the synchronous rectifier with the output voltage of the switching power supply.

25. The control circuit according to claim 23, wherein: The detection module determines the number of the oscillation cycles by comparing the voltage between the two power poles of the main power tube with the input voltage of the switching power supply.

26. The control circuit according to claim 23, wherein: When the first count value is greater than or equal to the preset value, in the next switching cycle, the regulation module reduces the minimum on-time of the main power tube and / or the synchronous rectifier tube; when the first count value is less than the preset value, in the next switching cycle, the regulation module increases and / or maintains the minimum on-time of the main power tube or the synchronous rectifier tube.

27. The control circuit according to claim 16, wherein: The detection module includes: a comparison module, configured to compare the voltage between the two power electrodes of the synchronous rectifier with a preset voltage and output a comparison signal; The judgment module receives the comparison signal and is used to judge whether the time length of at least part of the time period reaches a preset time, or whether the number of voltage oscillation cycles in at least part of the time period reaches a preset value.

28. The control circuit according to claim 27, characterized in that: The judgment module is used to judge whether the time length between the voltage between the two power poles of the synchronous rectifier tube reaches the preset voltage for the first time and the moment when the synchronous rectifier tube starts to turn on in the next switching cycle reaches the first preset time, and output a detection signal.

29. The control circuit according to claim 27, wherein: The preset voltage is greater than or equal to a turn-off threshold of the synchronous rectifier.

30. The control circuit according to claim 27, wherein: The detection module also includes: The enable signal generating module receives the detection signal and generates an enable signal for indicating whether to shorten the minimum on-time.

31. The control circuit according to claim 28, wherein: The judgment module includes: a shielding module, configured to shield the oscillation level in the comparison signal and output a shielding signal; The delay unit is used to delay the transition edge of the shielding signal that jumps to the valid level for a first preset time and output the detection signal.

32. The control circuit according to claim 31, wherein: The shielding module includes an RS trigger, wherein a set end receives the comparison signal, a reset end receives a driving signal for controlling the state of the synchronous rectifier, and an output end outputs the shielding signal.

33. The control circuit according to claim 30, wherein: The enable signal generating module includes a D flip-flop, wherein the data input terminal of the D flip-flop receives a high level, and the clock input terminal receives the detection signal. When the clear input terminal receives a step signal indicating that the main power tube or the synchronous rectifier tube is switched from the on state to the off state, the enable signal output by the D flip-flop begins to switch to an invalid level.

34. The control circuit according to claim 30, wherein: When the enable signal detected by the regulating module is at a valid level at the start of conduction of the power tube or the synchronous rectifier tube in the next cycle, the minimum conduction time of the corresponding switch tube in the next cycle is reduced.

35. The control circuit according to claim 27, wherein: The judgment module includes: a monostable trigger, wherein when a transition edge of the comparison signal changing to a valid level is detected, the judgment module outputs a pulse of a fixed duration; The pulse counting comparison module is coupled to the output end of the monostable trigger, counts the number of pulses in the received signal, and outputs a detection signal with a valid level when the number of pulses is greater than or equal to a preset value.

36. The control circuit according to claim 27, wherein: The preset voltage is the output voltage of the switching circuit.

37. The control circuit according to claim 35, characterized in that The judgment module also includes: An AND gate receives the comparison signal and the output signal of the monostable trigger, and outputs a signal to the pulse counting comparison module.

38. A power conversion system, characterized in that: include: A main power tube, a synchronous rectifier tube and a control circuit of a switching power supply according to any one of claims 16 to 37.

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