Light load control method, control device and switching power supply

Abstract

The application discloses a light load control method, a control device and a switching power supply. The control method comprises the following steps: step one, detecting a load, and determining that the load is light load when the load is less than a preset light load value, and entering a discontinuous operation mode; step two, controlling the first and second switching tubes to be turned off; step three, controlling the first switching tube to be turned on, and controlling the first switching tube to be turned off for a first dead time when a first current integral quantity is equal to a first current integral reference value; step four, controlling the second switching tube to be turned on, and controlling the second switching tube to be turned off for a second dead time when a second current integral quantity is equal to a second current integral reference value; step five, controlling the first switching tube to be turned on, and controlling the first switching tube to be turned off for a third dead time when a third current integral quantity is equal to the second current integral reference value; step six, controlling the second switching tube to be turned on, and controlling the second switching tube to be turned off when a fourth current integral quantity is equal to a third current integral reference value; and repeating steps two to six. The application can realize miniaturization.

Description

TECHNICAL FIELD

[0001] The present application relates to a switching converter, in particular to a light load control method, a control device and a switching power supply. BACKGROUND

[0002] The efficiency of the switching power supply is an important component for electronic equipment to achieve low-carbon energy saving, and the industry has increasingly high requirements for the energy efficiency of the switching power supply. In more and more application scenarios, in addition to requiring high efficiency under heavy load, there are higher requirements for light load efficiency and no-load power consumption.

[0003] The resonant converter is widely used in high efficiency and small size occasions due to its easy realization of soft switching, and the current typical representative is LLC resonant converter.

[0004] The LLC resonant converter is shown in Figure 1 When the first switch Q1 is turned on, the secondary diode D1 is turned on and D2 is turned off, the transformer excitation inductance Lm is clamped by the output, and the inductor Lr and the capacitor Cr resonate. When the first switch Q1 is turned off, the resonant current Ir is positive, and in the dead time, the resonant current Ir discharges the junction capacitance of the second switch Q2 and charges the junction capacitance of the first switch Q1. When the junction capacitance voltage of the second switch Q2 drops to zero, the second switch Q2 is turned on, realizing soft opening of the second switch. When the second switch Q2 is turned on, the secondary diode D2 is turned on and D1 is turned off, the transformer excitation inductance Lm is clamped by the output, and the inductor Lr and the capacitor Cr resonate. When the second switch Q2 is turned off, the resonant current Ir is negative, and in the dead time, the resonant current Ir discharges the junction capacitance of the first switch Q1 and charges the junction capacitance of the second switch Q2. When the junction capacitance voltage of the first switch Q1 drops to zero, the first switch Q1 is turned on, realizing soft opening of the first switch.

[0005] The LLC resonant converter can work in continuous mode under heavy load, realizing high efficiency, but as the load decreases, the switching frequency will show an upward trend, on the one hand, leading to a decrease in light load efficiency, which cannot meet the full load high efficiency application scenario; on the other hand, it also limits the improvement of the design frequency of full load work, which is not conducive to the miniaturization of the power supply. SUMMARY

[0006] Therefore, the technical problem to be solved by the present application is to provide a light load control method, a control device and a switching power supply, which at least solves one of the technical problems existing in the prior art to some extent.

[0007] As a first aspect of the present application, the technical scheme of the embodiment of the light load control method provided is as follows:

[0008] A light load control method is applied to an LLC resonant converter, a primary side of the LLC resonant converter includes a first switch tube at a high end and a second switch tube at a low end, the first switch tube and the second switch tube constitute a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and turned off, wherein the light load control method comprises the following steps:

[0009] Step one, light load judgment and switching control step, detecting the load size of the LLC resonant converter, when the load is less than a light load preset value, judging that the LLC resonant converter is in light load, and switching the LLC resonant converter into a discontinuous operation mode;

[0010] Step two, pause phase control step, controlling the first switch tube and the second switch tube to be turned off, and the duration of this step is a pause time;

[0011] Step three, first switch tube first turn-on control step, controlling the first switch tube to be turned on, and integrating a resonant current to obtain a first current integral, when the first current integral is equal to a first current integral reference value, controlling the first switch tube to be turned off for a first dead time;

[0012] Step four, second switch tube first turn-on control step, controlling the second switch tube to be turned on, and integrating the resonant current to obtain a second current integral, when the second current integral is equal to a second current integral reference value, controlling the second switch tube to be turned off for a second dead time;

[0013] Step five, first switch tube second turn-on control step, controlling the first switch tube to be turned on, and integrating the resonant current to obtain a third current integral, when the third current integral is equal to the second current integral reference value, controlling the first switch tube to be turned off for a third dead time;

[0014] Step six, second switch tube second turn-on control step, controlling the second switch tube to be turned on, and integrating the resonant current to obtain a fourth current integral, when the fourth current integral is equal to a third current integral reference value, controlling the second switch tube to be turned off;

[0015] The steps two to six are repeated in turn.

[0016] Further, in the step six, the second switch tube is controlled to be turned off for a fourth dead time;

[0017] After the step six, there is further a step seven, first switch tube third turn-on control step, controlling the first switch tube to be turned on, and when the resonant current reaches a resonant current preset value, controlling the first switch tube to be turned off; and then the steps two to seven are repeated in turn.

[0018] Preferably, the output voltage error amplification signal or the signal related to the output voltage error amplification signal fed back to the primary side of the LLC resonant converter is used as the signal compared with the light load preset value in the step one.

[0019] Further, the resonant current direction integrated during the conduction of the first switch is the first current direction, and the resonant current direction integrated during the conduction of the second switch is the second current direction, and the first current direction is opposite to the second current direction.

[0020] Further, the corresponding current integration quantity needs to be cleared before the first switch is turned on again after being turned off and before the second switch is turned on again after being turned off.

[0021] Preferably, in the step two, the fixed stop time is achieved by setting the peak value of the voltage free resonance at the common connection point of the first switch and the second switch during the stop period as a fixed value; or the variable stop time is achieved by setting the peak number of the voltage free resonance at the common connection point of the first switch and the second switch during the stop period as a variable value which increases with the lightening of the load.

[0022] Further, the second current integration reference value is the output voltage error amplification signal value of the LLC resonant converter, the first current integration reference value is K1 times of the output voltage error amplification signal value of the LLC resonant converter, and the third current integration reference value is K2 times of the output voltage error amplification signal value of the LLC resonant converter, wherein K1 and K2 are respectively values in the range of 0.3-0.8.

[0023] Further, K1 is fixedly taken as 0.5, and K2 is fixedly taken as 0.4; or K1 is fixedly taken as 0.5, and K2 is a variable value which gradually increases with the lightening of the load; or K2 is fixedly taken as 0.4, and K1 is a variable value which gradually decreases with the lightening of the load.

[0024] Further, the resonant current preset value is zero.

[0025] As a second aspect of the present application, the embodiment technical scheme of the light load control device provided is as follows:

[0026] A light load control device applied to an LLC resonant converter, the primary side of the LLC resonant converter comprising a first switch at the high end and a second switch at the low end, the first switch and the second switch constituting a half-bridge circuit, and the first switch and the second switch being alternately turned on and turned off, wherein the light load control device comprises the following modules:

[0027] The light load judgment and switching control module is configured to detect a load size of the LLC resonant converter, judge that the LLC resonant converter is in a light load state when the load is smaller than a light load preset value, and switch the LLC resonant converter into a discontinuous operation mode.

[0028] The resonant current integration module is configured to integrate a resonant current during the conduction of the first switch tube to obtain a corresponding current integration quantity, and integrate the resonant current during the conduction of the second switch tube to obtain a corresponding current integration quantity.

[0029] The pause stage control module is configured to set a pause time, and the first switch tube and the second switch tube of the LLC resonant converter are both in an off state during the pause time.

[0030] The wave emission control module is configured to control wave emission in the following steps:

[0031] The pause state, in which no wave is emitted, lasts for the pause time;

[0032] The first wave emission to the first switch tube is controlled, the first switch tube is turned on, and a first current integration quantity is obtained by integrating the resonant current, and when the first current integration quantity is equal to a first current integration reference value, the wave emission to the first switch tube is stopped, and the first switch tube is turned off for a first dead time;

[0033] The first wave emission to the second switch tube is controlled, the second switch tube is turned on, and a second current integration quantity is obtained by integrating the resonant current, and when the second current integration quantity is equal to a second current integration reference value, the wave emission to the second switch tube is stopped, and the second switch tube is turned off for a second dead time;

[0034] The second wave emission to the first switch tube is controlled, the first switch tube is turned on, and a third current integration quantity is obtained by integrating the resonant current, and when the third current integration quantity is equal to the second current integration reference value, the wave emission to the first switch tube is stopped, and the first switch tube is turned off for a third dead time;

[0035] The second wave emission to the second switch tube is controlled, the second switch tube is turned on, and a fourth current integration quantity is obtained by integrating the resonant current, and when the fourth current integration quantity is equal to a third current integration reference value, the wave emission to the second switch tube is stopped, and the second switch tube is turned off;

[0036] All the steps are repeated in a cycle.

[0037] Further, the wave control module controls the second switch tube to be off for a fourth dead time in the step of controlling the second switch tube to emit waves for the second time; and after the step of controlling the second switch tube to emit waves for the second time, the method further comprises the steps of: controlling the first switch tube to emit waves for the third time, controlling the first switch tube to be on, stopping the first switch tube from emitting waves when the resonant current reaches a preset resonant current value, and controlling the first switch tube to be off; and then repeating all the steps in turn.

[0038] As a third aspect of the present application, the technical solutions of the embodiments of the switching power supply are as follows:

[0039] A switching power supply comprises an LLC resonant converter, a primary side of the LLC resonant converter comprising a first switch tube at a high end and a second switch tube at a low end, the first switch tube and the second switch tube forming a half-bridge circuit, and the first switch tube and the second switch tube being alternately turned on and turned off, wherein: the switching power supply further comprises the light load control device of any one of the second aspect.

[0040] The working principle of the present application will be analyzed in combination with specific embodiments, which will not be described here, and the beneficial effects of the present application are as follows:

[0041] (1) The embodiment of the present application, on the one hand, when the load is determined to be light, makes the converter enter the discontinuous mode, reduces the switching times of the switch tube, that is, reduces the equivalent switching frequency, and on the other hand, by setting the on and off time or threshold value of the switch tube in the discontinuous mode, the energy loss during the on and off of the switch is reduced, thereby effectively improving the light load efficiency of the power supply, and the overall energy consumption of the power supply is lower and the performance is better.

[0042] (2) The embodiment of the present application solves the problem that the frequency increase under light load leads to the limitation of the design frequency under full load, thereby making the LLC resonant converter have the advantages of frequency increase and miniaturization, and meeting the needs of high performance and small size application occasions. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a circuit diagram of the LLC resonant converter;

[0044] Figure 2 It is a circuit schematic diagram of the LLC resonant converter suitable for the present application;

[0045] Figure 3 It is Figure 2 a circuit schematic diagram of the control device of the LLC resonant converter;

[0046] Figure 4 It is an internal circuit schematic diagram of the resonant current integration module;

[0047] Figure 5 Light load control waveform diagram of the switching power supply of the third embodiment of the present application. DETAILED DESCRIPTION

[0048] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0049] In order to enable persons skilled in the art to better understand the scheme of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by persons skilled in the art without creative labor should belong to the scope of protection of the present application.

[0050] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so as to describe the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0051] It should be understood that, in the specification, claims and drawings, when it is described that a step is connected to another step, the step can be directly connected to the other step, or connected to the other step through a third step; when it is described that an element / unit is "connected" to another element / unit, the element / unit can be "directly connected" to the other element / unit, or "connected" to the other element / unit through a third element / unit.

[0052] In addition, the drawings of the present disclosure are only schematic and not necessarily to scale. Identical or similar components are denoted by the same reference signs throughout the drawings and a repeated description is omitted. Some of the block diagrams in the drawings are functional entities that do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented by software, or in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0053] Figure 2 A circuit schematic diagram of an LLC resonant converter suitable for the present application, please refer to Figure 2The LLC resonant converter comprises an input voltage port Vin, a first switch Q1 and a second switch Q2, a resonant capacitor Cr, a transformer T, a rectifier switch D1, a rectifier switch D2, an output filter capacitor Co, an output voltage port Vo, a resonant current sampling resistor Rcs, a primary side reference ground GND, a secondary side reference ground SGND, wherein the transformer T has a leakage inductance Lr, a magnetizing inductance Lm, and a primary-to-secondary winding ratio N. The first switch Q1 is located at the high end, the second switch Q2 is located at the low end, Vsw is the common connection point of the first switch Q1 and the second switch, GQ1 is the first switch control signal, GQ2 is the second switch control signal, and Vcs is the resonant current sampling signal.

[0054] It should be noted that, Figure 2 is only an example and should not limit the scope of protection of the present application. Those skilled in the art can design specific LLC resonant converter circuits as needed, for example: Figure 1 The half-bridge circuit in the above-mentioned example can be replaced by a full-bridge circuit (i.e., the LLC resonant converter comprises two half-bridge circuits, and this topology is still within the scope of protection of the present application); the resonant cavity in the above-mentioned example can be replaced by a resonant capacitor at the high end; and the secondary rectifier circuit in the above-mentioned example can be replaced by a diode half-wave rectifier, a diode full-bridge rectifier, or a synchronous rectifier full-wave rectifier, etc.

[0055] First embodiment

[0056] The present embodiment provides a light load control method applied to an LLC resonant converter. The primary side of the LLC resonant converter comprises a first switch at the high end and a second switch at the low end. The first switch and the second switch constitute a half-bridge circuit. The first switch and the second switch are alternately turned on and turned off. The light load control method comprises the following steps:

[0057] Step one, light load judgment and switching control step, detecting the load size of the LLC resonant converter, when the load is smaller than the light load preset value, judging that the LLC resonant converter is in light load, and switching the LLC resonant converter into a discontinuous operation mode;

[0058] Step two, pause phase control step, controlling the first switch and the second switch to be turned off. The duration of this step is the pause time;

[0059] Step three, first switch first turn-on control step, controlling the first switch to be turned on, and integrating the resonant current to obtain a first current integral quantity. When the first current integral quantity is equal to a first current integral reference value, the first switch is controlled to be turned off for a first dead time;

[0060] Step four, the first time the second switch tube is turned on control step, control the second switch tube is turned on, and the resonant current is integrated, the second current integral is obtained, when the second current integral is equal to the second current integral reference value, the second switch tube is turned off for the second dead time;

[0061] Step five, the second time the first switch tube is turned on control step, control the first switch tube is turned on, and the resonant current is integrated, the third current integral is obtained, when the third current integral is equal to the second current integral reference value, the first switch tube is turned off for the third dead time;

[0062] Step six, the second time the second switch tube is turned on control step, control the second switch tube is turned on, and the resonant current is integrated, the fourth current integral is obtained, when the fourth current integral is equal to the third current integral reference value, the second switch tube is turned off;

[0063] Step two to step six are repeated in turn.

[0064] The control method of the embodiment realizes that the LLC converter works in the discontinuous mode with low equivalent frequency and low resonant energy consumption at light load, solves the problem that the existing LLC converter works in the continuous mode at light load, the frequency is raised, the efficiency is low, and it is difficult to further miniaturize, so that the LLC converter has the advantages of high efficiency and miniaturization at full load, and can meet the application occasions with high performance and small size.

[0065] Further, in step six, the second switch tube is turned off for the fourth dead time; after step six, step seven, the third time the first switch tube is turned on control step, control the first switch tube is turned on, when the resonant current reaches the resonant current preset value, control the first switch tube is turned off; then step two to step seven are repeated in turn.

[0066] As a specific implementation, the output voltage error amplification signal fed back to the primary side of the LLC resonant converter, or the signal related to the output voltage error amplification signal, can be used as the signal compared with the light load preset value in step one.

[0067] It should be noted that the resonant current direction integrated during the first switch tube is turned on is the first current direction, and the resonant current direction integrated during the second switch tube is turned on is the second current direction, and the first current direction is opposite to the second current direction.

[0068] It should be noted that in specific implementation, the corresponding current integral needs to be cleared before the first switch tube is turned on again after being turned off, and before the second switch tube is turned on again after being turned off.

[0069] As a specific implementation, in step two, the fixed stop time can be achieved by setting the wave peak of the free resonance of the voltage at the common connection point of the first switch tube and the second switch tube during the stop period as a fixed value; or the variable stop time can be achieved by setting the wave peak of the free resonance of the voltage at the common connection point of the first switch tube and the second switch tube during the stop period as a variable value that increases as the load decreases.

[0070] As a specific implementation, the second current integral reference value is the error amplified signal value of the output voltage of the LLC resonant converter, the first current integral reference value is K1 times the error amplified signal value of the output voltage of the LLC resonant converter, and the third current integral reference value is K2 times the error amplified signal value of the output voltage of the LLC resonant converter, where K1 and K2 are values in the range of 0.3-0.8.

[0071] As a specific implementation, K1 is fixed at 0.5 and K2 is fixed at 0.4; or K1 is fixed at 0.5 and K2 is a variable value that gradually increases as the load decreases; or K2 is fixed at 0.4 and K1 is a variable value that gradually decreases as the load decreases.

[0072] As a specific implementation, the preset value of the resonant current is zero.

[0073] Second embodiment

[0074] The embodiment provides a light load control device applied to an LLC resonant converter. The primary side of the LLC resonant converter comprises a first switch tube located at a high end and a second switch tube located at a low end. The first switch tube and the second switch tube form a half-bridge circuit. The first switch tube and the second switch tube are alternately turned on and turned off. The light load control device comprises the following modules.

[0075] The light load judgment and switching control module is configured to detect the load size of the LLC resonant converter, judge that the LLC resonant converter is in light load when the load is smaller than a preset light load value, and switch the LLC resonant converter into a discontinuous working mode.

[0076] The resonant current integral module is configured to integrate the resonant current during the conduction period of the first switch tube to obtain a corresponding current integral quantity, and integrate the resonant current during the conduction period of the second switch tube to obtain a corresponding current integral quantity.

[0077] The stop phase control module is configured to set a stop time, and the first switch tube and the second switch tube of the LLC resonant converter are both in the turned-off state within the stop time.

[0078] The wave emission control module is configured to control wave emission according to the following steps.

[0079] The stop state, no wave emission, the duration of this state is the stop time.

[0080] The first switch tube is controlled to be turned on by the first time, and the first current integration quantity is obtained by integrating the resonant current. When the first current integration quantity is equal to the first current integration reference value, the first switch tube is controlled to be turned off for the first dead time.

[0081] The second switch tube is controlled to be turned on by the first time, and the second current integration quantity is obtained by integrating the resonant current. When the second current integration quantity is equal to the second current integration reference value, the second switch tube is controlled to be turned off for the second dead time.

[0082] The first switch tube is controlled to be turned on by the second time, and the third current integration quantity is obtained by integrating the resonant current. When the third current integration quantity is equal to the second current integration reference value, the first switch tube is controlled to be turned off for the third dead time.

[0083] The second switch tube is controlled to be turned on by the second time, and the fourth current integration quantity is obtained by integrating the resonant current. When the fourth current integration quantity is equal to the third current integration reference value, the second switch tube is controlled to be turned off.

[0084] All steps are repeated in turn in a cycle.

[0085] Further, the wave emission control module controls the second switch tube to be turned off for the fourth dead time in the step of emitting the wave to the second switch tube for the second time. After the step of emitting the wave to the second switch tube for the second time, the wave emission control module further comprises: emitting the wave to the first switch tube for the third time, controlling the first switch tube to be turned on, and stopping emitting the wave to the first switch tube when the resonant current reaches the resonant current preset value, and controlling the first switch tube to be turned off. Then, all steps are repeated in turn in a cycle.

[0086] Figure 3 For Figure 2 A circuit schematic diagram of a control device of an LLC resonant converter, which is used to make the LLC resonant converter work in a discontinuous mode under a light load condition. Please refer to Figure 3 The control device is provided with a light load judgment and switching control module U1, a resonant current integration module U2, a stop stage control module U3, a wave emission control module U4, and an output voltage error amplification circuit composed of an optical coupler and 431.

[0087] The input end IN of the light load judgment and switching control module U1 is connected with the output signal Vcomp of the output voltage error amplification circuit, and the output end OUT of the load judgment mode U1 outputs a light load mode enabling signal, which is connected to the input end IN1 of the stop stage control module U3 and the wave emission control module U4, respectively.

[0088] As a specific implementation method, the light load judgment and switching control module U1 uses the output voltage error amplification signal Vcomp as the load judgment condition. When Vcomp is less than the preset value, it judges light load and outputs the light load mode enable signal.

[0089] The input terminal IN3 of the resonant current integrator module U2 is connected to the resonant current sampling signal Vcs, and the output terminal OUT of the resonant current integrator module U2 is connected to the input terminal IN4 of the wave generation control module U4. The input terminals IN1 and IN2 of the resonant current integrator module U2 are connected to the output terminals OUT1 and OUT2 of the wave generation control module U4, respectively.

[0090] As one specific implementation method, the internal circuit of the resonant current integrator module U2 can adopt... Figure 4 The circuit shown is divided into two main parts, which respectively implement... Figure 2 The integral operation of the resonant current during the conduction of the first switch Q1 and the integral operation of the anti-phase resonant current during the conduction of the second switch Q2 are integrated, and the result of the integration is the voltage Vint on the capacitor C.

[0091] Specifically, the resonant current sampling signal Vcs is input to the input terminal of the voltage-controlled current source VCCS1. When the first switch Q1 is turned on, GQ1 is at a high level, controlling switch S1 to turn on. The current output by the voltage-controlled current source VCCS1, which is proportional to Vcs (K times), charges capacitor C, thereby realizing the integration of the resonant current during the period when the first switch Q1 is turned on. During the dead time from when the first switch Q1 is turned off to when the second switch Q2 is turned on, the reset signal Rset is at a high level, controlling switch S3 to turn on, and clearing the voltage of capacitor C to zero. When the second switch Q2 is turned on, GQ2 is at a high level, controlling switch S2 to turn on. The voltage-controlled current source VCCS2 outputs a current that is inversely proportional to Vcs (-K times) to charge capacitor C, thereby realizing the integration of the inverted resonant current during the conduction of the second switch Q2. During the dead time from the turn-off of the second switch Q2 to the turn-on of the first switch Q1, the reset signal Rset is at a high level, controlling switch S3 to turn on, clearing the voltage of capacitor C to zero.

[0092] The input terminal IN1 of the pause phase control module U3 is connected to the output terminal OUT of the light load judgment and switching control module U1. When the light load is judged, the pause phase control module is activated. The input terminal IN2 of the pause phase control module U3 is connected to the intermediate node Vsw of the half bridge. The output terminal OUT of the pause phase control module U3 is connected to the input terminal IN3 of the wave generation control module U4.

[0093] As a specific embodiment, the effect of setting a fixed idle time can be achieved by setting the number of wave peaks or wave troughs of the free resonance of the intermediate node Vsw voltage of the half-bridge during the idle period as a fixed value; or the effect of setting a variable idle time can be achieved by setting the number of wave peaks or wave troughs of the free resonance of the intermediate node Vsw voltage of the half-bridge during the idle period as a variable value that increases as the load decreases.

[0094] The input ends IN1, IN2, IN3, IN4 and IN5 of the wave generation control module U4 are connected with the output end OUT of the light load judgment and switching control module U1, the output end OUT of the idle stage control module U3, the output voltage error amplification signal Vcomp, the output end OUT of the resonant current integration module U2 and the resonant current sampling signal Vcs respectively, and the output ends OUT1 and OUT2 of the wave generation control module U4 output the first switch tube Q1 control signal and the second switch tube Q2 control signal respectively.

[0095] As a specific embodiment, the main operation steps of the wave generation control module U4 in a complete wave generation stage are as follows:

[0096] Step 1: At the end of the idle stage, the first switch tube Q1 is turned on and the second switch tube Q2 remains closed; preferably, at the end of the idle stage, the intermediate node voltage Vsw of the first switch tube Q1 and the second switch tube Q2 is at the free resonance wave peak, and the first switch tube is turned on at this time;

[0097] Step 2: When the first current integration Vint1 is equal to the first current integration reference value Vref1, the first switch tube Q1 is turned off; after the dead time ends, the second switch tube Q2 is turned on;

[0098] Step 3: When the second current integration Vint2 is equal to the second current integration reference value Vref2, the second switch tube Q2 is turned off; after the dead time ends, the first switch tube Q1 is turned on;

[0099] Step 4: When the first current integration Vint1 is equal to the second current integration reference value Vref2, the first switch tube Q1 is turned off; after the dead time ends, the second switch tube Q2 is turned on;

[0100] Step 5: When the second current integration Vint2 is equal to the third current integration reference value Vref3, the second switch tube Q2 is turned off; after the dead time ends, the first switch tube Q1 is turned on;

[0101] Step 6: When the resonant current is zero, the first switch tube Q1 is turned off and enters the idle stage.

[0102] Third embodiment

[0103] The embodiment provides a switching power supply, comprising an LLC resonant converter, a primary side of the LLC resonant converter comprising a first switch tube at a high end and a second switch tube at a low end, the first switch tube and the second switch tube forming a half-bridge circuit, and the first switch tube and the second switch tube being alternately turned on and turned off, wherein the switching power supply further comprises the light load control device in any one of the second embodiments.

[0104] In order to make the present application more easily understood, the following will be combined with Figure 3 The switching power supply of the embodiment is further described.

[0105] Figure 5 The switching power supply of the third embodiment of the present application is a light load control working waveform diagram, and the waveform diagram fixes the half-bridge midpoint voltage Vsw peak number to 2 in the pause stage. The light load working process of the switching power supply of the embodiment is described below in combination with the waveform diagram.

[0106] When the light load judgment and switching control module U1 detects that the output voltage error amplification signal Vcomp is lower than a preset value, it is judged that the light load, and the converter works in the light load mode. Specifically, the steady state working process is as follows:

[0107] At t1, the pause stage ends, at this time, the first switch tube Q1 and the second switch tube Q2 common connection point voltage Vsw is just resonated to the maximum value (i.e. at the resonant peak), the control signal GQ1 changes from low level to high level, and the first switch tube Q1 is turned on;

[0108] After the first switch tube Q1 is turned on, the current output by the voltage-controlled current source VCCS1 in proportion (K times) to Vcs charges the capacitor C, and generates the first current integral Vint1. At t2, the first current integral Vint1 is equal to the first current integral reference value Vref1, the control signal GQ1 changes from high level to low level, and the first switch tube Q1 is turned off;

[0109] The t2-t3 stage is the dead time from the first switch tube Q1 being turned off to the second switch tube Q2 being turned on, and the resonant current integral module U2 generates the Rest reset signal to quickly discharge the capacitor C capacitor and perform the integral zero operation;

[0110] At t3, the control signal GQ2 changes from low level to high level, the second switch tube Q2 is turned on, the current output by the voltage-controlled current source VCCS2 in inverse proportion (-K times) to Vcs charges the capacitor C, and generates the second current integral Vint2. At t4, the second current integral Vint2 is equal to the second current integral reference value Vref2, the control signal GQ2 changes from high level to low level, and the second switch tube Q2 is turned off;

[0111] The stage t4-t5 is the dead time from the turn-off of the second switch Q2 to the turn-on of the first switch Q1, and the reset signal Rest is generated by the resonant current integration module U2 to quickly discharge the capacitor C and perform the integration zero operation.

[0112] At the moment t5, the control signal GQ1 changes from low to high, the first switch Q1 is turned on, and the current proportional to Vcs (K times) output by the voltage-controlled current source VCCS1 charges the capacitor C to generate the first current integration Vint1. At the moment t6, the first current integration Vint1 is equal to the second current integration reference Vref2, the control signal GQ1 changes from high to low, and the first switch Q1 is turned off.

[0113] The stage t6-t7 is the dead time from the turn-off of the first switch Q1 to the turn-on of the second switch Q2, and the reset signal Rest is generated by the resonant current integration module U2 to quickly discharge the capacitor C and perform the integration zero operation.

[0114] At the moment t7, the control signal GQ2 changes from low to high, the second switch Q2 is turned on, and the current inversely proportional to Vcs (-K times) output by the voltage-controlled current source VCCS2 charges the capacitor C to generate the second current integration Vint2. At the moment t8, the second current integration Vint2 is equal to the third current integration reference Vref3, the control signal GQ2 changes from high to low, and the second switch Q2 is turned off.

[0115] The stage t7-t8 is the dead time from the turn-off of the second switch Q2 to the turn-on of the first switch Q1, and the reset signal Rest is generated by the resonant current integration module U2 to quickly discharge the capacitor C and perform the integration zero operation.

[0116] At the moment t9, the control signal GQ1 changes from low to high, the first switch Q1 is turned on, and the current proportional to Vcs (K times) output by the voltage-controlled current source VCCS1 charges the capacitor C to generate the first current integration Vint1. However, Vint1 is no longer used as the turn-off control condition of the first switch Q1. At the stage t9-t10, the resonant current Ir is detected. When the resonant current gradually approaches zero at the zero-crossing point (the moment t10), the control signal GQ1 changes from high to low, and the first switch Q1 is turned off.

[0117] The stage t10-t11 is a stop control stage, since the first switch tube Q1 and the second switch tube Q2 are both in the off state, the stage is composed of a resonance network of the excitation inductance Lm, the leakage inductance Lr, the resonance capacitor Cr and the junction capacitances of the first switch tube Q1 and the second switch tube Q2, the common connection point voltage Vsw of the first switch tube Q1 and the second switch tube Q2 presents a free resonance waveform, and the resonance peak detection or counting is performed from t10, and when the preset value 2 is reached, the stop control stage is entered into the next cycle.

[0118] Preferably, Figure 5 The first current integral reference value Vref1 is equal to 0.5Vcomp, the second current integral reference value Vref2 is equal to Vcomp, and the third current integral reference value Vref3 is equal to 0.4Vcomp. Through the processing of the first current integral reference value and the second current integral reference value in the wave emission stage, the output current Id in the wave emission control stage can be more balanced, the converter output voltage fluctuation is smaller, and the ripple is smaller.

[0119] Preferably, when the first switch tube Q1 and the second switch tube Q2 adopt devices with reverse recovery characteristics such as Si MOS tubes, the last first switch tube Q1 in the wave emission control stage is turned off at the time when the resonance current is zero, which can effectively avoid the reverse recovery loss of the first switch tube and reduce the free resonance energy loss in the stop stage.

[0120] Preferably, when the first switch tube Q1 and the second switch tube Q2 adopt new devices without reverse recovery such as GaN or SiC, the control drive of the last first switch tube in the wave emission control stage can be omitted.

[0121] The above is only the preferred embodiment of the present application, and it should be noted that the above preferred embodiment should not be regarded as a limitation of the present application, and for those skilled in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application, which will not be described in detail here, and the protection scope of the present application should be limited by the scope defined in the claims.

Claims

1. A light load control method applied to an LLC resonant converter, a primary side of the LLC resonant converter comprising a first switch tube located at a high end and a second switch tube located at a low end, the first switch tube and the second switch tube constituting a half-bridge circuit, and the first switch tube and the second switch tube being alternately turned on and turned off, characterized in that, The light load control method comprises the following steps: Step one, light load judgment and switching control step, detecting the load size of the LLC resonant converter, when the load is smaller than the light load preset value, judging that the LLC resonant converter is in light load, and switching the LLC resonant converter into discontinuous operation mode; Step two, pause stage control step, controlling the first switch tube and the second switch tube to be both off, and the duration of this step is the pause time; Step three, first time-on control step of the first switch tube, controlling the first switch tube to be on, and integrating the resonant current to obtain a first current integral, when the first current integral is equal to a first current integral reference value, controlling the first switch tube to be off for a first dead time; Step four, first time-on control step of the second switch tube, controlling the second switch tube to be on, and integrating the resonant current to obtain a second current integral, when the second current integral is equal to a second current integral reference value, controlling the second switch tube to be off for a second dead time; Step five, second time-on control step of the first switch tube, controlling the first switch tube to be on, and integrating the resonant current to obtain a third current integral, when the third current integral is equal to the second current integral reference value, controlling the first switch tube to be off for a third dead time; Step six, second time-on control step of the second switch tube, controlling the second switch tube to be on, and integrating the resonant current to obtain a fourth current integral, when the fourth current integral is equal to a third current integral reference value, controlling the second switch tube to be off; Steps two to six are repeated in turn.

2. The light load control method according to claim 1, wherein: In step six, the second switch tube is controlled to be off for a fourth dead time; After step six, step seven, third time-on control step of the first switch tube, is further included, in which the first switch tube is controlled to be on, and when the resonant current reaches a resonant current preset value, the first switch tube is controlled to be off, and then steps two to seven are repeated in turn.

3. The light load control method according to claim 1 or 2, characterized in that: An output voltage error amplification signal fed back to the primary side of the LLC resonant converter, or a signal related to the output voltage error amplification signal, is used as the signal compared with the light load preset value in step one.

4. The light load control method according to claim 1 or 2, wherein: The resonant current direction for integrating the resonant current during the on period of the first switch tube is a first current direction, and the resonant current direction for integrating the resonant current during the on period of the second switch tube is a second current direction, the first current direction being opposite to the second current direction.

5. The light load control method according to claim 1 or 2, wherein: Before the first switch tube is turned on again after being turned off, and before the second switch tube is turned on again after being turned off, the corresponding current integral needs to be cleared.

6. The light load control method according to claim 1 or 2, wherein: In step two, the fixed pause time is achieved by setting the wave peak of the free resonant voltage at the common connection point of the first switch tube and the second switch tube during the pause period as a fixed value, or the variable pause time is achieved by setting the wave peak of the free resonant voltage at the common connection point of the first switch tube and the second switch tube during the pause period as a variable value that increases with the decrease of the load.

7. The light load control method according to claim 1 or 2, wherein: The second current integral reference value is an output voltage error amplification signal value of the LLC resonant converter, the first current integral reference value is K1 times of the output voltage error amplification signal value of the LLC resonant converter, and the third current integral reference value is K2 times of the output voltage error amplification signal value of the LLC resonant converter, wherein K1 and K2 are values in the range of 0.3-0.

8.

8. The light load control method of claim 7, wherein: K1 is fixed at 0.5, and K2 is fixed at 0.4; or K1 is fixed at 0.5, and K2 is a variable value that gradually increases as the load decreases; or K2 is fixed at 0.4, and K1 is a variable value that gradually decreases as the load decreases.

9. The light load control method of claim 2, wherein: The preset value of the resonant current is zero.

10. A light load control device applied to an LLC resonant converter, a primary side of the LLC resonant converter comprising a first switch tube located at a high end and a second switch tube located at a low end, the first switch tube and the second switch tube constituting a half-bridge circuit, and the first switch tube and the second switch tube being alternately turned on and turned off, characterized in that, The light load control device comprises the following modules: A light load judgment and switching control module is configured to detect the load size of the LLC resonant converter, judge that the LLC resonant converter is in light load when the load is smaller than a preset light load value, and switch the LLC resonant converter into a discontinuous operation mode; A resonant current integral module is configured to integrate the resonant current during the conduction of the first switch tube and obtain a corresponding current integral quantity; integrate the resonant current during the conduction of the second switch tube and obtain a corresponding current integral quantity; A pause stage control module is configured to set a pause time, during which the first switch tube and the second switch tube of the LLC resonant converter are both in the off state; A wave emission control module is configured to control wave emission in the following steps: pause state, no wave emission, the duration of this state is the pause time; first wave emission to the first switch tube, control the conduction of the first switch tube, and the first current integral quantity obtained by integrating the resonant current, when the first current integral quantity is equal to the first current integral reference value, stop wave emission to the first switch tube, and control the first switch tube to be off for a first dead time; first wave emission to the second switch tube, control the conduction of the second switch tube, and the second current integral quantity obtained by integrating the resonant current, when the second current integral quantity is equal to the second current integral reference value, stop wave emission to the second switch tube, and control the second switch tube to be off for a second dead time; second wave emission to the first switch tube, control the conduction of the first switch tube, and the third current integral quantity obtained by integrating the resonant current, when the third current integral quantity is equal to the second current integral reference value, stop wave emission to the first switch tube, and control the first switch tube to be off for a third dead time; second wave emission to the second switch tube, control the conduction of the second switch tube, and the fourth current integral quantity obtained by integrating the resonant current, when the fourth current integral quantity is equal to the third current integral reference value, stop wave emission to the second switch tube, and control the second switch tube to be off; all steps are repeated in turn in a cycle.

11. The light load control device according to claim 10, wherein: The wave emitting control module controls the second switch tube to be off for a fourth dead time in the step of emitting the second wave to the second switch tube; and after the step of emitting the second wave to the second switch tube, the wave emitting control module further comprises the steps of emitting a third wave to the first switch tube, controlling the first switch tube to be on, stopping emitting the wave to the first switch tube when the resonant current reaches a preset resonant current value, and controlling the first switch tube to be off; and then repeating all the steps in turn.

12. A switching power supply comprising an LLC resonant converter, a primary side of the LLC resonant converter comprising a first switch tube located at a high end and a second switch tube located at a low end, the first switch tube and the second switch tube constituting a half-bridge circuit, the first switch tube and the second switch tube being alternately turned on and turned off, characterized in that: The switching power supply further comprises the light load control device according to any one of claims 10 to 11.

Images