Light load control method, control device and switching power supply

Abstract

The invention discloses a light load control method, a control device and a switching power supply, and the control method comprises the steps: 1, detecting a load, judging that the load is a light load when the load is smaller than a light load preset value, and entering a discontinuous working mode; 2, controlling the first switch tube and the second switch tube to be switched off; 3, controlling the first switching tube to be switched on, and controlling the first switching tube to be switched off for first dead time when the first current integral quantity is equal to the first current integral reference value; 4, controlling a second switch tube to be switched on, and controlling the second switch tube to be switched off for second dead time when the second current integral quantity is equal to the second current integral reference value; 5, controlling the first switching tube to be switched on, and controlling the first switching tube to be switched off for third dead time when the third current integral quantity is equal to the second current integral reference value; 6, controlling a second switch tube to be switched on, and controlling the second switch tube to be switched off when the fourth current integral quantity is equal to the third current integral reference value; and repeating the steps 2-6. According to the invention, miniaturization can be realized.

Description

Technical Field

[0001] The invention relates to a switching converter, and in particular to a light load control method, a control device and a switching power supply. Background Art

[0002] The efficiency of switching power supplies is an important component for electronic equipment to achieve low-carbon energy conservation. The industry's requirements for the energy efficiency of switching power supplies are increasing. In more and more applications, in addition to requiring high efficiency under heavy loads, there are higher requirements for light load efficiency and no-load power consumption.

[0003] Resonant converters are widely used in high-efficiency, small-volume applications because of their ease of soft switching. The most typical representative is the LLC resonant converter.

[0004] LLC resonant converter Figure 1 As shown, when the first switch tube Q1 is turned on, the secondary diode D1 is turned on and D2 is turned off, the transformer excitation inductance Lm is output clamped, and the inductance Lr resonates with the capacitor Cr; when the first switch tube Q1 is turned off, the resonant current Ir is positive. During the dead time, the resonant current Ir discharges the junction capacitance of the second switch tube Q2 and charges the junction capacitance of the first switch tube Q1. When the junction capacitance voltage of the second switch tube Q2 drops to zero, the second switch tube Q2 is turned on to achieve soft opening of the second switch tube; when the second switch tube Q2 is turned on, the secondary diode D2 is turned on and D1 is turned off, the transformer excitation inductance Lm is output clamped, and the inductance Lr resonates with the capacitor Cr; when the second switch tube Q2 is turned off, the resonant current Ir is negative. During the dead time, the resonant current Ir discharges the junction capacitance of the first switch tube Q1 and charges the junction capacitance of the second switch tube Q2. When the junction capacitance voltage of the first switch tube Q1 drops to zero, the first switch tube Q1 is turned on to achieve soft opening of the first switch tube.

[0005] The LLC resonant converter can operate in continuous mode under heavy load and achieve higher efficiency. However, as the load decreases, its switching frequency will show an upward trend. On the one hand, it leads to a decrease in light load efficiency and cannot meet the full-load high-efficiency application scenario. On the other hand, it also limits the increase in the full-load operating design frequency, which is not conducive to the miniaturization of the power supply. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to propose a light load control method, a control device and a switching power supply, which at least solve one of the technical problems existing in the prior art to a certain extent.

[0007] As a first aspect of the present invention, the technical solution 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, wherein the 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, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and off, wherein the light load control method includes the following steps:

[0009] Step 1, a light load judgment and switching control step, detecting the load size of the LLC resonant converter, and when the load is less than a light load preset value, judging that the LLC resonant converter is light load, and switching the LLC resonant converter to enter a discontinuous working mode;

[0010] Step 2, a stop phase control step, controlling the first switch tube and the second switch tube to be turned off, and the duration of this step is the stop time;

[0011] Step 3, a first turn-on control step of the first switch tube, controlling the first switch tube to turn on, and integrating the resonant current to obtain a first current integral amount, and when the first current integral amount is equal to a first current integral reference value, controlling the first switch tube to turn off the first dead time;

[0012] Step 4, a first conduction control step of the second switch tube, controlling the second switch tube to conduct, and integrating the resonant current to obtain a second current integral amount, and when the second current integral amount is equal to a second current integral reference value, controlling the second switch tube to turn off the second dead time;

[0013] Step 5, a second conduction control step of the first switch tube, controlling the first switch tube to be turned on, and integrating the resonant current to obtain a third current integral amount, and when the third current integral amount 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 6, a second turn-on control step of the second switch tube, controlling the second switch tube to turn on, and integrating the resonant current to obtain a fourth current integral value, and when the fourth current integral value is equal to the third current integral reference value, controlling the second switch tube to turn off;

[0015] Repeat steps 2 to 6 in sequence.

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

[0017] After step six, the method further includes: step seven, a third conduction control step of the first switch tube, controlling the first switch tube to be turned on, and when the resonant current reaches a preset value of the resonant current, controlling the first switch tube to be turned off; and then repeating steps two to seven in sequence.

[0018] Preferably, the 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 to be compared with the light load preset value in step one.

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

[0020] Furthermore, after the first switch tube is turned off and before it is turned on again, and after the second switch tube is turned off and before it is turned on again, it is necessary to perform a clearing operation on the corresponding current integral amount.

[0021] Preferably, in step 2, a fixed pause time is achieved by setting the peak of the free resonance of the voltage at the common connection point between the first switch tube and the second switch tube during the pause period to a fixed value; or a variable pause time is achieved by setting the number of peaks of the free resonance of the voltage at the common connection point between the first switch tube and the second switch tube during the pause period to a variable value that increases as the load is reduced.

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

[0023] Furthermore, 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, which gradually increases as the load is reduced; or K2 is fixed at 0.4, and K1 is a variable value, which gradually decreases as the load is reduced.

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

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

[0026] A light load control device is applied to an LLC resonant converter, wherein the 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, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and off, wherein the light load control device includes the following modules:

[0027] A light load judgment and switching control module is configured to detect the load size of the LLC resonant converter, and when the load is less than a light load preset value, judge that the LLC resonant converter is light load, and switch the LLC resonant converter into a discontinuous working mode;

[0028] The resonant current integration module is configured to integrate the resonant current during the conduction period of the first switch tube to obtain a corresponding current integral amount; integrate the resonant current during the conduction period of the second switch tube to obtain a corresponding current integral amount;

[0029] A rest phase control module, configured to set a rest time, during which the first switch tube and the second switch tube of the LLC resonant converter are both in an off state;

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

[0031] The pause state is a state where no wave is emitted and the duration of this state is the pause time;

[0032] The first switch tube is waved for the first time to control the first switch tube to be turned on, and a first current integral amount is obtained by integrating the resonant current. When the first current integral amount is equal to a first current integral reference value, the first switch tube is stopped from being waved, and the first switch tube is controlled to be turned off for a first dead time;

[0033] The second switch tube is wave-generated for the first time to control the second switch tube to be turned on, and the second current integral amount is obtained by integrating the resonant current. When the second current integral amount is equal to the second current integral reference value, the wave-generated for the second switch tube is stopped, and the second switch tube is controlled to be turned off for the second dead time;

[0034] The first switch tube is wave-generated for the second time to control the first switch tube to be turned on, and a third current integral amount is obtained by integrating the resonant current. When the third current integral amount is equal to the second current integral reference value, the first switch tube is stopped from being wave-generated, and the first switch tube is controlled to be turned off for a third dead time;

[0035] The second switch tube is wave-generated for the second time to control the second switch tube to be turned on, and a fourth current integral amount is obtained by integrating the resonant current. When the fourth current integral amount is equal to the third current integral reference value, the wave-generated for the second switch tube is stopped, and the second switch tube is controlled to be turned off;

[0036] The cycle repeats all steps in sequence.

[0037] Furthermore, the wave generation control module controls the second switch tube to turn off the fourth dead time in the step of generating waves for the second switch tube for the second time; and after the step of generating waves for the second switch tube for the second time, it also includes: generating waves for the first switch tube for the third time, controlling the first switch tube to be turned on, and when the resonant current reaches a preset resonant current value, stopping generating waves for the first switch tube, and controlling the first switch tube to be turned off; and then repeating all steps in sequence.

[0038] As a third aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0039] A switching power supply includes an LLC resonant converter, wherein the primary side of the LLC resonant converter includes 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, and the first switch tube and the second switch tube are alternately turned on and off, wherein: the switching power supply also includes the light load control device described in any one of the second aspects above.

[0040] The working principle of the present invention will be analyzed in conjunction with specific embodiments, which will not be described in detail here. The beneficial effects of the present invention are as follows:

[0041] (1) The embodiments of the present invention, on the one hand, when the load is judged to be light load, make the converter enter the discontinuous mode, reduce the number of switching times of the switch tube, that is, reduce the equivalent switching frequency, and on the other hand, by setting the on and off time or threshold of the switch tube in the discontinuous mode, so that it changes with the load, reduce the energy loss during the switch on and off period, 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 embodiments of the present invention solve the problem that the frequency increase under light load leads to the limited frequency increase under full load design, so that the LLC resonant converter has the advantage of frequency increase and miniaturization, which can meet the needs of high-performance and small-volume applications. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0044] Figure 2 A circuit diagram of an LLC resonant converter applicable to the present invention;

[0045] Figure 3 for Figure 2 A circuit diagram of a control device of an LLC resonant converter;

[0046] Figure 4 This is a schematic diagram of the internal circuit of the resonant current integration module of the present invention;

[0047] Figure 5 FIG. 1 is a light load control operation waveform diagram of a switching power supply according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0048] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0049] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0050] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application are described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, the process, method, system, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

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

[0052] In addition, the drawings of the present disclosure are only schematic diagrams of the present disclosure and are not necessarily drawn to scale. The same symbols in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented using software, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontrollers.

[0053] Figure 2 A circuit diagram of an LLC resonant converter applicable to the present invention is shown in FIG. Figure 2The LLC resonant converter includes an input voltage port Vin, a first switch tube Q1 and a second switch tube 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, and a secondary side reference ground SGND, wherein the leakage inductance of the transformer T is Lr, the excitation inductance is Lm, and the turns ratio of the primary and secondary windings P1 and S1 is N. The first switch tube Q1 is located at the high end, the second switch tube Q2 is located at the low end, Vsw is the common connection point of the first switch tube Q1 and the second switch tube, GQ1 is the first switch tube control signal, GQ2 is the second switch tube control signal, and Vcs is the resonant current sampling signal.

[0054] It should be noted that Figure 2 This is just an example and should not limit the protection scope of the present invention. Those skilled in the art can design a specific LLC resonant converter circuit as needed. For example, Figure 1 The half-bridge circuit is changed into a full-bridge circuit (that is, the LLC resonant converter includes two half-bridge circuits, and this topology is still within the protection scope of the present invention); the resonant cavity is changed to place the resonant capacitor at the high end; the secondary side rectification circuit is changed into a diode half-wave rectification, a diode full-bridge rectification or a synchronous rectifier full-wave rectification, etc.

[0055] First embodiment

[0056] This embodiment provides a light load control method, which is applied to an LLC resonant converter. The 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 form a half-bridge circuit. The first switch tube and the second switch tube are alternately turned on and off. The light load control method includes the following steps:

[0057] Step 1, light load judgment and switching control step, detecting the load size of the LLC resonant converter, when the load is less than the light load preset value, judging that the LLC resonant converter is light load, and switching the LLC resonant converter to enter the discontinuous working mode;

[0058] Step 2, a stop phase control step, controlling the first switch tube and the second switch tube to be turned off, and the duration of this step is the stop time;

[0059] Step 3, a first turn-on control step of the first switch tube, controlling the first switch tube to turn on, and integrating the resonant current to obtain a first current integral amount, and when the first current integral amount is equal to the first current integral reference value, controlling the first switch tube to turn off the first dead time;

[0060] Step 4, a first conduction control step of the second switch tube, controlling the second switch tube to conduct, and integrating the resonant current to obtain a second current integral amount, and when the second current integral amount is equal to the second current integral reference value, controlling the second switch tube to turn off the second dead time;

[0061] Step 5, a second conduction control step of the first switch tube, controlling the first switch tube to conduct, and integrating the resonant current to obtain a third current integral amount, and when the third current integral amount is equal to the second current integral reference value, controlling the first switch tube to turn off the third dead time;

[0062] Step 6, a second conduction control step of the second switch tube, controlling the second switch tube to conduct, and integrating the resonant current to obtain a fourth current integral amount, and when the fourth current integral amount is equal to the third current integral reference value, controlling the second switch tube to turn off;

[0063] Repeat steps 2 to 6 in sequence.

[0064] The control method of this embodiment realizes the LLC converter to operate in a discontinuous mode with low equivalent frequency and low resonant energy consumption under light load by setting load judgment, rest stage control and wave generation stage control, wherein the wave generation stage control also includes resonant current integral control, thereby solving the problem that the existing LLC converter operates in a continuous mode under light load, resulting in lower efficiency and difficulty in further miniaturization due to increased frequency, so that the LLC converter has the advantages of high efficiency at full load and miniaturization, and can meet high-performance and small-volume applications.

[0065] Furthermore, in step six, the second switch tube is controlled to be turned off for the fourth dead time; after step six, it also includes: step seven, the first switch tube is turned on for the third time, the first switch tube is controlled to be turned on, and when the resonant current reaches the preset value of the resonant current, the first switch tube is controlled to be turned off; then steps two to seven are repeated in sequence.

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

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

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

[0069] As a specific implementation method, in step 2, a fixed pause time can be achieved by setting the peak value of the free resonance of the voltage at the common connection point of the first switch tube and the second switch tube during the pause period to a fixed value; or a variable pause time can be achieved by setting the number of peaks of the free resonance of the voltage at the common connection point of the first switch tube and the second switch tube during the pause period to a variable value that increases as the load is reduced.

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

[0071] As a specific factual method, 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, which gradually increases as the load is reduced; or K2 is fixed at 0.4, and K1 is a variable value, which gradually decreases as the load is reduced.

[0072] As a specific embodiment, the resonant current is preset to zero.

[0073] Second embodiment

[0074] This embodiment provides a light-load control device, which is applied to an LLC resonant converter. The 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 form a half-bridge circuit. The first switch tube and the second switch tube are alternately turned on and off. The light-load control device includes the following modules:

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

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

[0077] A rest phase control module is configured to set a rest time, during which the first switch tube and the second switch tube of the LLC resonant converter are both in an off state;

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

[0079] In the rest state, no wave is generated, and the duration of this state is the rest time;

[0080] The first switch tube is waved for the first time to control the first switch tube to be turned on, and the first current integral amount is obtained by integrating the resonant current. When the first current integral amount is equal to the first current integral reference value, the first switch tube is stopped from being waved, and the first switch tube is controlled to be turned off for the first dead time;

[0081] The second switch tube is waved for the first time to control the second switch tube to be turned on, and the second current integral is obtained by integrating the resonant current. When the second current integral is equal to the second current integral reference value, the second switch tube is stopped from being waved, and the second switch tube is controlled to be turned off for the second dead time;

[0082] The first switch tube is waved for the second time to control the first switch tube to be turned on, and a third current integral amount is obtained by integrating the resonant current. When the third current integral amount is equal to the second current integral reference value, the first switch tube is stopped from being waved, and the first switch tube is controlled to be turned off for a third dead time;

[0083] The second switch tube is wave-generated for the second time to control the second switch tube to be turned on, and a fourth current integral amount is obtained by integrating the resonant current. When the fourth current integral amount is equal to the third current integral reference value, the second switch tube is stopped from being wave-generated to control the second switch tube to be turned off;

[0084] The cycle repeats all steps in sequence.

[0085] Furthermore, the wave generation control module controls the second switch tube to turn off the fourth dead time in the step of generating the wave for the second switch tube for the second time; and after the step of generating the wave for the second switch tube for the second time, it also includes: generating the wave for the first switch tube for the third time, controlling the first switch tube to be turned on, and when the resonant current reaches a preset value of the resonant current, stopping generating the wave for the first switch tube, and controlling the first switch tube to be turned off; and then repeating all the steps in sequence.

[0086] Figure 3 for Figure 2 A circuit diagram of a control device for an LLC resonant converter, which is used to make the LLC resonant converter operate in discontinuous mode under light load conditions. 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 phase control module U3, a wave generation control module U4, and an output voltage error amplifier circuit composed of an optocoupler and 431.

[0087] The input terminal IN of the light load judgment and switching control module U1 is connected to the output signal Vcomp of the output voltage error amplifier circuit. The output terminal OUT of the load judgment mode U1 outputs a light load mode enable signal, which is respectively connected to the input terminal IN1 of the rest phase control module U3 and the wave control module U4.

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

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

[0090] As a specific implementation, the internal circuit of the resonant current integration module U2 can be Figure 4 The structure shown in the figure is divided into two parts, which are respectively implemented Figure 2 The integration operation of the resonant current during the conduction period of the first switch tube Q1 and the integration operation of the anti-phase resonant current during the conduction period of the second switch tube Q2, the integration result is the voltage Vint on the capacitor C.

[0091] Specifically, the resonant current sampling signal Vcs is input to the input end of the voltage-controlled current source VCCS1. When the first switch tube Q1 is turned on, GQ1 is at a high level, the control switch S1 is turned on, and the current output by the voltage-controlled current source VCCS1 is proportional to (K times) Vcs to charge the capacitor C, thereby realizing the integration of the resonant current during the conduction period of the first switch tube Q1; during the dead time from the turn-off of the first switch tube Q1 to the turn-on of the second switch tube Q2, the reset signal Rset is at a high level, the control switch S3 is turned on, and the voltage of the capacitor C is cleared. When the second switch tube Q2 is turned on, GQ2 is at a high level, the control switch S2 is turned on, and the current output by the voltage-controlled current source VCCS2 is inversely proportional to Vcs (-K times) to charge the capacitor C, thereby realizing the operation of integrating the inverted resonant current during the conduction period of the second switch tube Q2; during the dead time from the second switch tube Q2 being turned off to the first switch tube Q1 being turned on, the reset signal Rset is at a high level, the control switch S3 is turned on, and the voltage of the capacitor C is cleared.

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

[0093] As a specific implementation, the effect of setting a fixed pause time can be achieved by setting the number of peaks or troughs of the free resonance of the voltage at the middle node Vsw of the half-bridge during the pause period to a fixed value; or the effect of setting a variable pause time can be achieved by setting the number of peaks or troughs of the free resonance of the voltage at the middle node Vsw of the half-bridge during the pause period to a variable value that increases as the load is reduced.

[0094] The input terminals IN1, IN2, IN3, IN4, and IN5 of the wave generation control module U4 are respectively connected to the output terminal OUT of the light load judgment and switching control module U1, the output terminal OUT of the stop phase control module U3, the output voltage error amplification signal Vcomp, the output terminal OUT of the resonant current integration module U2, and the resonant current sampling signal Vcs. The output terminals 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 implementation, the main operation steps of the wave control module U4 in a complete wave stage are as follows:

[0096] Step 1: At the end of the pause phase, the first switch tube Q1 is turned on and the second switch tube Q2 remains turned off; preferably, at the end of the pause phase, the voltage Vsw at the common connection point between the first switch tube Q1 and the second switch tube Q2 is at the free resonance peak, and the first switch tube is turned on at this moment;

[0097] Step 2: When the first current integral amount Vint1 is equal to the first current integral 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 integral amount Vint2 is equal to the second current integral 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 integral value Vint1 is equal to the second current integral 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 integral value Vint2 is equal to the third current integral 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 passes through zero, the first switch tube Q1 is turned off and enters the rest phase.

[0102] Third embodiment

[0103] The present embodiment provides a switching power supply, including an LLC resonant converter, wherein the 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, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and off, wherein: the switching power supply also includes any one of the light load control devices in the second embodiment described above.

[0104] To make the present invention easier to understand, the following Figure 3 The switching power supply of this embodiment is further described.

[0105] Figure 5 This is a light load control working waveform diagram of the switching power supply of the third embodiment of the present invention. In the rest stage of the waveform diagram, the number of peaks of the half-bridge midpoint voltage Vsw is fixed to 2. The light load working process of the switching power supply of this embodiment is described below in conjunction 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 the preset value, it is judged as light load, and the converter works in light load mode. Specifically, the steady-state working process is as follows:

[0107] At time t1, the pause phase ends. At this time, the voltage Vsw at the common connection point between the first switch tube Q1 and the second switch tube Q2 resonates to the maximum value (i.e., the resonance peak), and the control signal GQ1 changes from a low level to a 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, which is proportional to Vcs (K times), charges the capacitor C, generating a first current integral amount Vint1. At time t2, the first current integral amount Vint1 is equal to the first current integral reference value Vref1, and the control signal GQ1 changes from a high level to a low level, and the first switch tube Q1 is turned off;

[0109] The stage t2 to t3 is the dead time from the first switch tube Q1 being turned off to the second switch tube Q2 being turned on. The resonant current integration module U2 will generate a Rest reset signal to quickly discharge the capacitor C and perform an integration clearing operation.

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

[0111] The stage t4 to t5 is the dead time from the second switch tube Q2 being turned off to the first switch tube Q1 being turned on. The resonant current integration module U2 will generate a Rest reset signal to quickly discharge the capacitor C and perform an integration clearing operation.

[0112] At time t5, the control signal GQ1 changes from a low level to a high level, the first switch tube Q1 is turned on, and the current output by the voltage-controlled current source VCCS1, which is proportional to Vcs (K times), charges the capacitor C, generating a first current integral amount Vint1. At time t6, the first current integral amount Vint1 is equal to the second current integral reference value Vref2, the control signal GQ1 changes from a high level to a low level, and the first switch tube Q1 is turned off;

[0113] The stage t6 to t7 is the dead time from the first switch tube Q1 being turned off to the second switch tube Q2 being turned on. The resonant current integration module U2 will generate a Rest reset signal to quickly discharge the capacitor C and perform an integration clearing operation.

[0114] At time t7, the control signal GQ2 changes from a low level to a high level, the second switch tube Q2 is turned on, and the current output by the voltage-controlled current source VCCS2, which is inversely proportional to Vcs (-K times), charges the capacitor C, generating a second current integral amount Vint2. At time t8, the second current integral amount Vint2 is equal to the third current integral reference value Vref3, the control signal GQ2 changes from a high level to a low level, and the second switch tube Q2 is turned off;

[0115] The stage t7-t8 is the dead time from the second switch tube Q2 being turned off to the first switch tube Q1 being turned on. The resonant current integration module U2 will generate a Rest reset signal to quickly discharge the capacitor C and perform an integration clearing operation.

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

[0117] The stage t10 to t11 is a stop control stage. Since the first switch tube Q1 and the second switch tube Q2 are both in the off state, in this stage, the transformer's excitation inductance Lm, leakage inductance Lr, resonant capacitor Cr and the junction capacitance of the first switch tube Q1 and the second switch tube Q2 form a resonant network. The voltage Vsw at the common connection point of the first switch tube Q1 and the second switch tube Q2 presents a free resonance waveform. The resonance peak detection or counting starts from t10. When the preset value 2 is reached, the control stage is stopped and the next cycle begins.

[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. By processing the first current integral reference value and the second current integral reference value in the wave generation stage, the output current Id can be more balanced in the wave generation control stage, and the converter output voltage fluctuation and ripple are smaller.

[0119] Preferably, when the first switch tube Q1 and the second switch tube Q2 use devices with reverse recovery characteristics such as Si MOS tubes, the last first switch tube Q1 in the wave control stage is turned off when the resonant 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 are new devices without reverse recovery such as GaN or SiC, the control drive of the last first switch tube in the wave control stage can be omitted.

[0121] The above are only preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limitations of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention. The embodiments will not be repeated here. The protection scope of the present invention should be based on the scope defined by the claims.

Claims

1. A light load control method, applied to an LLC resonant converter, wherein the primary side of the LLC resonant converter comprises a first switch tube at a high end and a second switch tube at a low end, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and off, characterized in that: The light load control method comprises the following steps: Step 1, a light load judgment and switching control step, detecting the load size of the LLC resonant converter, and when the load is less than a light load preset value, judging that the LLC resonant converter is light load, and switching the LLC resonant converter to enter a discontinuous working mode; Step 2, a stop phase control step, controlling the first switch tube and the second switch tube to be turned off, and the duration of this step is the stop time; Step 3, a first turn-on control step of the first switch tube, controlling the first switch tube to turn on, and integrating the resonant current to obtain a first current integral amount, and when the first current integral amount is equal to a first current integral reference value, controlling the first switch tube to turn off the first dead time; Step 4, a first conduction control step of the second switch tube, controlling the second switch tube to conduct, and integrating the resonant current to obtain a second current integral amount, and when the second current integral amount is equal to a second current integral reference value, controlling the second switch tube to turn off the second dead time; Step 5, a second conduction control step of the first switch tube, controlling the first switch tube to be turned on, and integrating the resonant current to obtain a third current integral amount, and when the third current integral amount is equal to the second current integral reference value, controlling the first switch tube to be turned off for a third dead time; Step 6, a second turn-on control step of the second switch tube, controlling the second switch tube to turn on, and integrating the resonant current to obtain a fourth current integral value, and when the fourth current integral value is equal to the third current integral reference value, controlling the second switch tube to turn off; Repeat steps 2 to 6 in sequence.

2. The light load control method according to claim 1, characterized in that: In the step six, the second switch tube is controlled to be turned off for a fourth dead time; After step six, the method further includes: step seven, a third conduction control step of the first switch tube, controlling the first switch tube to be turned on, and when the resonant current reaches a preset value of the resonant current, controlling the first switch tube to be turned off; and then repeating steps two to seven in sequence.

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

4. The light load control method according to claim 1 or 2, characterized in that: The direction of the resonant current integrated during the conduction period of the first switch tube is a first current direction, and the direction of the resonant current integrated during the conduction period of the second switch tube is a second current direction. The first current direction is opposite to the second current direction.

5. The light load control method according to claim 1 or 2, characterized in that: After the first switch tube is turned off and before it is turned on again, and after the second switch tube is turned off and before it is turned on again, it is necessary to perform a clearing operation on the corresponding current integral amount.

6. The light load control method according to claim 1 or 2, characterized in that: In the step 2, a fixed pause time is achieved by setting the peak of the free resonance of the voltage at the common connection point between the first switch tube and the second switch tube during the pause period to a fixed value; or a variable pause time is achieved by setting the number of peaks of the free resonance of the voltage at the common connection point between the first switch tube and the second switch tube during the pause period to a variable value that increases as the load is reduced.

7. The light load control method according to claim 1 or 2, characterized in that: The second current integral reference value is the output voltage error amplified signal value of the LLC resonant converter, the first current integral reference value is K1 times the output voltage error amplified signal value of the LLC resonant converter, and the third current integral reference value is K2 times the output voltage error amplified signal value of the LLC resonant converter, wherein K1 and K2 are values ​​in the range of 0.3 to 0.8 respectively.

8. The light load control method according to claim 7, characterized in that: The K1 is fixed at 0.5, and the K2 is fixed at 0.4; or K1 is fixed at 0.5, and K2 is a variable value, which gradually increases as the load is reduced; or K2 is fixed at 0.4, and K1 is a variable value, which gradually decreases as the load is reduced.

9. The light load control method according to claim 2, characterized in that: The preset value of the resonant current is zero.

10. A light load control device, applied to an LLC resonant converter, wherein the primary side of the LLC resonant converter comprises a first switch tube at a high end and a second switch tube at a low end, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and 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, and when the load is less than a light load preset value, judge that the LLC resonant converter is light load, and switch the LLC resonant converter into a discontinuous working mode; A resonant current integration module, configured to integrate the resonant current during the conduction period of the first switch tube to obtain a corresponding current integral amount; Integrate the resonant current during the conduction period of the second switch tube to obtain a corresponding current integral amount; A rest phase control module, configured to set a rest time, during which the first switch tube and the second switch tube of the LLC resonant converter are both in an off state; The wave control module is configured to control the wave according to the following steps: The pause state is a state where no wave is emitted and the duration of this state is the pause time; The first switch tube is waved for the first time to control the first switch tube to be turned on, and a first current integral amount is obtained by integrating the resonant current. When the first current integral amount is equal to a first current integral reference value, the first switch tube is stopped from being waved, and the first switch tube is controlled to be turned off for a first dead time; The second switch tube is wave-generated for the first time to control the second switch tube to be turned on, and the second current integral amount is obtained by integrating the resonant current. When the second current integral amount is equal to the second current integral reference value, the wave-generated for the second switch tube is stopped, and the second switch tube is controlled to be turned off for the second dead time; The first switch tube is wave-generated for the second time to control the first switch tube to be turned on, and a third current integral amount is obtained by integrating the resonant current. When the third current integral amount is equal to the second current integral reference value, the first switch tube is stopped from being wave-generated, and the first switch tube is controlled to be turned off for a third dead time; The second switch tube is wave-generated for the second time to control the second switch tube to be turned on, and a fourth current integral amount is obtained by integrating the resonant current. When the fourth current integral amount is equal to the third current integral reference value, the wave-generated for the second switch tube is stopped, and the second switch tube is controlled to be turned off; The cycle repeats all steps in sequence.

11. The light load control device according to claim 10, characterized in that: The wave generation control module controls the second switch tube to turn off the fourth dead time in the step of generating waves for the second switch tube for the second time; and after the step of generating waves for the second switch tube for the second time, it also includes: generating waves for the first switch tube for the third time, controlling the first switch tube to be turned on, and when the resonant current reaches a preset resonant current value, stopping generating waves for the first switch tube and controlling the first switch tube to be turned off; and then repeating all steps in sequence.

12. A switching power supply, comprising an LLC resonant converter, wherein the primary side of the LLC resonant converter comprises a first switch tube at a high end and a second switch tube at a low end, wherein the first switch tube and the second switch tube form a half-bridge circuit, and the first switch tube and the second switch tube are alternately turned on and 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