Mode switching method, control device and switching power supply

Abstract

The invention discloses a mode switching method, a control device and a switching power supply, and the control method comprises the steps: controlling an LLC resonant converter to be continuously switched from a heavy-load intermittent working mode to a light-load intermittent working mode, and comprises the steps: obtaining a mode switching control quantity representing the size of a load, and recognizing a mode switching synchronization signal; when the mode switching control quantity is smaller than a light load preset value and a mode switching synchronizing signal is recognized, a first switching tube is turned on, a reference value of the heavy load continuous working mode voltage loop control quantity is enlarged by K times to obtain a first reference quantity, and when the real-time voltage loop control quantity is equal to the first reference quantity, the first switching tube is turned off; after the first dead time, conducting a second switch tube, multiplying the first reference quantity by a coefficient a to obtain a second reference quantity, and when the real-time voltage loop control quantity is equal to the second reference quantity, switching off the second switch tube; and after the second dead time, the first switch tube is switched on, and when the resonance current tends to the preset value, the first switch tube is switched off, and switching is completed. According to the invention, the mode switching stability can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching converter design, in particular to a mode switching method, a control device and a switching power supply. BACKGROUND

[0002] The industry has increasingly high requirements for the energy efficiency of switching power supplies. In more and more application occasions, in addition to requiring high efficiency under heavy load, there are higher requirements for efficiency under light load and power consumption under no load.

[0003] Resonant converters are widely used in high-efficiency and small-size occasions due to their easy implementation of soft switching. The current typical representative is the LLC resonant converter.

[0004] The LLC resonant converter is shown in FIG. 1, and its working principle is as follows: when the first switch Q1 is turned on, the secondary diode D1 is turned on and the diode D2 is turned off, the transformer excitation inductor 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 the diode D1 is turned off, the transformer excitation inductor 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. Figure 1

[0005] Figure 1 The conventional control method of the switching converter includes: (1) control method under heavy load continuous working mode: the first switch and the second switch work with complementary driving and wave emission, and the reference value of the control quantity is the set reference quantity Vref; (2) switching method from heavy load continuous working mode to light load discontinuous working mode: when the mode switching control quantity is less than the light load preset value, and the first mode switching synchronization signal is recognized, the light load discontinuous working mode is switched in; (3) control method under light load discontinuous working mode: the first switch and the second switch work with a group of pulse combination driving and state period cycle emission with a pause time; (4) switching method from light load discontinuous working mode to heavy load continuous working mode: when the mode switching control quantity is greater than the heavy load preset value, and the second mode switching synchronization signal is recognized, the heavy load continuous working mode is switched in.

[0006] ​LLC resonant converter can work in continuous mode under heavy load, and achieve high efficiency. As the load decreases, in order to achieve high efficiency at light load, the applicant has filed a patent application No. 202510151109.3 on February 11, 2025, entitled "Light load control method, control device and switching power supply", which proposes a light load control method for LLC resonant converter. Although the light load control method can improve the light load efficiency, the mode switching is not different from the mode switching in the conventional control method, and the specific timing of mode switching is not mentioned, such as using the alternating edge of a certain signal as the mode switching synchronization signal or randomly switching. In addition, how to ensure smooth mode switching and avoid mode repeated switching to cause the switching power supply to be unstable is not mentioned.

[0007] It should be noted that the Chinese patent application No. 202510151109.3 has not been published yet. In order to help understand the present application, it is introduced in this application. This patent cannot be used as prior art to evaluate the creativity of the present application. SUMMARY

[0008] Therefore, the technical problem to be solved by the present application is to provide a mode switching method, control device and switching power supply to solve the stability problem in the mode switching process of LLC resonant converter.

[0009] The inventive concept of the present application is that when it is detected that the load of the LLC resonant converter is less than the light load preset value, it is determined that the LLC resonant converter is in light load, and the LLC resonant converter is switched into discontinuous operation mode. When it is detected that the load of the LLC resonant converter is greater than the heavy load preset value, it is determined that the LLC resonant converter is in heavy load, and the LLC resonant converter is switched into continuous operation mode. The representative quantity of light and heavy load is Vcomp or a parameter directly or indirectly represented by Vcomp, which determines when to switch into discontinuous operation mode and when to switch back to continuous operation mode. Before and after the switching of the operation mode, the continuity of the mode switching control quantity should be ensured to prevent the switching power supply from being unstable due to repeated switching of the mode under the same or similar load.

[0010] As a first aspect of the present application, the technical solutions of the embodiments of the provided mode switching method are as follows:

[0011] A mode switching method for controlling LLC resonant converter to switch from heavy load continuous operation mode to light load discontinuous operation mode, the LLC resonant converter at least includes a bridge arm, the bridge arm includes a first switch tube located at the high end and a second switch tube located at the low end; wherein the control LLC resonant converter to switch from heavy load continuous operation mode to light load discontinuous operation mode includes the following steps:

[0012] Step one, obtaining a mode switching control quantity representing the load size of the LLC resonant converter, and identifying a first mode switching synchronization signal;

[0013] Step two, when the mode switching control quantity is less than a light load preset value, and the first mode switching synchronization signal is identified, controlling the first switch to be turned on for the first time, and expanding the reference value of the voltage loop control quantity set in the steady state heavy load continuous working mode by K times to obtain a first reference quantity, when the real-time obtained voltage loop control quantity is equal to the first reference quantity, controlling the first switch to be turned off for a first dead time;

[0014] Step three, after the first dead time, controlling the second switch to be turned on, and multiplying the first reference quantity by a coefficient a to obtain a second reference quantity, when the real-time obtained voltage loop control quantity is equal to the second reference quantity, controlling the second switch to be turned off for a second dead time;

[0015] Step four, after the second dead time, controlling the first switch to be turned on for the second time, when the resonant current tends to a resonant current preset value, controlling the first switch to be turned off, and the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode, and enters the light load discontinuous working mode.

[0016] Preferably, the first mode switching synchronization signal is a falling edge of the second switch being turned off, at this time in the step two, when the mode switching control quantity is less than the light load preset value, and the first mode switching synchronization signal is identified, a dead time is needed before the first switch is controlled to be turned on for the first time;

[0017] Or the first mode switching synchronization signal is a rising edge of the first switch being turned on, at this time in the step two, when the mode switching control quantity is less than the light load preset value, and the first mode switching synchronization signal is identified, the first switch is immediately controlled to be turned on for the first time.

[0018] Further, the coefficient K is obtained by the following formula:

[0019]

[0020] Wherein, TL is the length of the entire cycle of the light load discontinuous working mode, and TLC is the length of the time of transferring energy to the secondary side in the light load discontinuous working mode.

[0021] Preferably, the coefficient a is a configurable value, and the value range is 0.2-0.8.

[0022] Preferably, the resonant current preset value in the step three is zero.

[0023] Further, the mode switching method is also used for controlling the LLC resonant converter to switch from the light load discontinuous working mode to the heavy load continuous working mode, and the step of controlling the LLC resonant converter to switch from the light load discontinuous working mode to the heavy load continuous working mode comprises the following steps:

[0024] Step five, acquiring a mode switching control quantity representing the load size of the LLC resonant converter, and identifying a second mode switching synchronization signal;

[0025] Step six, when the mode switching control quantity is greater than a heavy load preset value and the second mode switching synchronization signal is identified, the LLC resonant converter completes the switching from the light load discontinuous working mode to the heavy load continuous working mode and enters the heavy load continuous working mode.

[0026] Preferably, the step two is provided with a first mode switching filtering time, when the mode switching control quantity is continuously less than the light load preset value within the first mode switching filtering time and the first mode switching synchronization signal is identified, the first switch is controlled to be turned on for the first time;

[0027] The step six is provided with a second mode switching filtering time, when the mode switching control quantity is continuously greater than the heavy load preset value within the second mode switching filtering time and the second mode switching synchronization signal is identified, the switching power supply is controlled to enter the heavy load continuous working mode.

[0028] Further, when the mode switching control quantity reaches a first preset value, the first mode switching filtering time for switching from the heavy load continuous working mode to the light load discontinuous working mode is invalid; when the mode switching control quantity reaches a second preset value, the second mode switching filtering time for switching from the light load discontinuous working mode to the heavy load continuous working mode is invalid; the first preset value is less than the light load preset value; and the second preset value is greater than the heavy load preset value.

[0029] As a second aspect of the present application, the embodiment technical solutions of the provided mode switching device are as follows:

[0030] A mode switching device is used for controlling an LLC resonant converter to switch from a heavy load continuous working mode to a light load discontinuous working mode, the LLC resonant converter at least comprises a bridge arm, the bridge arm comprises a first switch at a high end and a second switch at a low end; wherein the mode switching device comprises:

[0031] A first acquisition and identification unit is configured to acquire a mode switching control quantity representing the load size of the LLC resonant converter, and identify a first mode switching synchronization signal;

[0032] The first control unit is configured to control the first switch tube to be turned on for the first time when the mode switching control amount is less than the light load preset value and the first mode switching synchronization signal is identified, and to expand the reference value of the voltage loop control amount set in the heavy load continuous working mode in the steady state by K times to obtain a first reference amount, and to control the first switch tube to be turned off for the first dead time when the real-time acquired voltage loop control amount is equal to the first reference amount.

[0033] The second control unit is configured to control the second switch tube to be turned on after the first dead time, and to multiply the first reference amount by a coefficient a to obtain a second reference amount, and to control the second switch tube to be turned off for the second dead time when the real-time acquired voltage loop control amount is equal to the second reference amount.

[0034] The third control unit is configured to control the first switch tube to be turned on for the second time after the second dead time, and to control the first switch tube to be turned off when the resonant current tends to a resonant current preset value, so that the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode and enters the light load discontinuous working mode.

[0035] As a third aspect of the present application, the embodiment of the switching power supply provided is as follows:

[0036] The switching power supply comprises an LLC resonant converter, and the LLC resonant converter comprises a first switch tube and a second switch tube, wherein the switching power supply further comprises the mode switching device of the second aspect.

[0037] In the mode switching from the heavy load continuous working mode to the light load discontinuous working mode, if the mode switching control quantity is less than the light load preset value, the LLC resonant converter is switched from the heavy load continuous working mode to the light load discontinuous working mode immediately, without considering the mode switching synchronization signal or processing the voltage loop control quantity for controlling the switch tube, because in the light load discontinuous working mode, the total number of the total output power reducing, the output voltage reducing, the mode switching control quantity of the LLC resonant converter will be larger after the LLC resonant converter is switched from the heavy load continuous working mode to the light load discontinuous working mode, the LLC resonant converter will be switched back to the heavy load continuous working mode immediately, thereby causing the switching power supply to be unstable due to repeated switching under the same or similar load, therefore, in the embodiment of the present application, after detecting that the mode switching control quantity is less than the light load preset value and identifying the set first mode switching synchronization signal, the light load discontinuous standby time will not be entered immediately, but three continuous pulses will be transmitted, specifically, the first switch tube is controlled to be turned on for the first time, the voltage loop control quantity for controlling the first switch tube to be turned off is expanded by K times, so that the time for the first switch tube to be turned on is increased, then the second switch tube is controlled to be turned on, and the voltage loop control quantity for controlling the second switch tube to be turned off is multiplied by the coefficient a on the basis of the voltage loop control quantity for controlling the first switch tube to be turned off which is expanded by K times, finally, the first switch tube is controlled to be turned on for the second time, and when the resonant current tends to the resonant current preset value, the first switch is turned off, and the light load discontinuous standby time is entered, through the combination of the three pulses, the following three beneficial effects are brought about:

[0038] (1) the energy transmitted by each pulse in the light load discontinuous mode can be increased, the total input power of the LLC resonant converter is constant, thereby ensuring that the mode switching control quantity is constant, the mode switching is smooth, and the switching power supply is effectively prevented from being unstable due to repeated switching under the same or similar load;

[0039] (2) the voltage of the resonant capacitor in the standby time in the light load discontinuous working mode can be kept at about half of the current input voltage, so that the resonant capacitor voltage corresponding to each pulse in the pulse transmission time is balanced, thereby balancing the output current of the converter, and realizing that the output voltage fluctuation of the converter is smaller and the ripple is smaller;

[0040] (3) when the first switch tube is turned on for the second time and the resonant current tends to the resonant current preset value, the switch tube is turned off, when the resonant current preset value is zero, the parasitic diode connected in parallel with the switch tube has no current flowing therethrough, and there is no reverse recovery time, thereby reducing the current oscillation in the standby time in the light load discontinuous working mode, reducing the overall loss, and improving the efficiency of the converter. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A circuit diagram of an LLC resonant converter;

[0042] Figure 2 A circuit schematic diagram of an LLC resonant converter applicable to the present application;

[0043] Figure 3 A working waveform diagram of a light load discontinuous working mode provided for Chinese patent application 202510151109.3;

[0044] Figure 4 A first control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a heavy load working mode to a light load working mode;

[0045] Figure 5 A second control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a heavy load working mode to a light load working mode;

[0046] Figure 6 A third control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a heavy load working mode to a light load working mode;

[0047] Figure 7 A first control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a light load working mode to a heavy load working mode;

[0048] Figure 8 A second control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a light load working mode to a heavy load working mode;

[0049] Figure 9 A third control working waveform diagram when the switching power supply in the third embodiment of the present application switches from a light load working mode to a heavy load working mode;

[0050] Figure 10 A circuit schematic diagram of a negative feedback sampling. DETAILED DESCRIPTION

[0051] 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.

[0052] In order to enable persons skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not 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.

[0053] It should be noted that the terms "first", "second", and the like in the description and in the claims of the present application and in the above-described drawings are intended to distinguish similar objects and not necessarily to describe a particular sequential or chronological order. It is to be understood that the use of the terms so used herein is merely intended to distinguish the comparable objects and the embodiments of the present application described herein can be adapted in suitable cases without departing from the scope of the present application. Moreover, the terms "comprising" and "having" and any variations thereof are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or apparatus including a list of steps or units not necessarily limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to such processes, methods, products, or apparatuses.

[0054] It should be understood that, in the description, claims, and drawings of the present application, 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.

[0055] 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 thus repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities, which 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 network and / or processor devices and / or microcontroller devices.

[0056] Figure 2 A circuit schematic diagram of an LLC resonant converter applicable to the present application is shown in FIG. 1. Figure 2 The LLC resonant converter includes 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, and a secondary side reference ground SGND. The transformer T has a leakage inductance Lr, a magnetizing inductance Lm, and a primary winding P1 and a secondary winding S1 with a turns ratio N. The first switch Q1 is connected at a high side, and the second switch Q2 is connected at a low side. Vsw is a common connection point of the first switch Q1 and the second switch Q2. GQ1 is a first switch control signal, GQ2 is a second switch control signal, and Vcs is a resonant current sampling signal.

[0057] It should be noted that, Figure 2Only an example, should not limit the scope of protection of the present application, those skilled in the art can design a specific LLC resonant converter circuit according to the needs, for example: can be changed to full-bridge circuit in the half-bridge circuit (i.e. LLC resonant converter includes two half-bridge circuit, this topology is still within the scope of the present application); the resonant cavity in the change to the resonant capacitor at the high end; the secondary rectifier circuit in the change to diode half-wave rectification, diode full-bridge rectifier or synchronous rectifier full-wave rectification, etc. Figure 1

[0058] In addition, the innovation of the present application is in the mode switching, the control strategy of heavy load continuous working mode and light load discontinuous working mode is not required in the present application, and those skilled in the art can select according to the needs.

[0059] First embodiment

[0060] The embodiment provided is a mode switching method for controlling Figure 2 The LLC resonant converter shown in the figure from heavy load continuous working mode to light load discontinuous working mode, the embodiment controls the LLC resonant converter from heavy load continuous working mode to light load discontinuous working mode, including the following steps:

[0061] Step one, obtain the mode switching control quantity representing the load size of the LLC resonant converter, and identify the first mode switching synchronization signal;

[0062] Step two, when the mode switching control quantity is less than the light load preset value, and the first mode switching synchronization signal is identified, control the first switch tube to conduct for the first time, and enlarge the reference value of the voltage loop control quantity set in the steady state heavy load continuous working mode by K times to obtain the first reference quantity, when the real-time obtained voltage loop control quantity is equal to the first reference quantity, control the first switch tube to be off for the first dead time;

[0063] Step three, after the first dead time, control the second switch tube to conduct, and multiply the first reference quantity by the coefficient a to obtain the second reference quantity, when the real-time obtained voltage loop control quantity is equal to the second reference quantity, control the second switch tube to be off for the second dead time;

[0064] Step four, after the second dead time, control the first switch tube to conduct for the second time, when the resonant current tends to the resonant current preset value, control the first switch tube to be off, the LLC resonant converter completes the switching from heavy load continuous working mode to light load discontinuous working mode, and enters light load discontinuous working mode.

[0065] The method for obtaining the mode switching control quantity Vcomp representing the load size of the LLC resonant converter includes but is not limited to the following ways:

[0066] ​The output voltage of the LLC resonant converter is divided and sampled by negative feedback, and then compared with the reference voltage through an error amplifier to obtain the mode switching control quantity Vcomp. An external compensation network needs to be added to the output end of the error amplifier to adjust the gain and phase of the loop to prevent the LLC resonant converter system from being unstable.

[0067] The output voltage of the LLC resonant converter is divided and sampled by negative feedback, and then compared with the reference voltage through an error amplifier to obtain the mode switching control quantity Vcomp. An external compensation network needs to be added to the output end of the error amplifier to adjust the gain and phase of the loop to prevent the LLC resonant converter system from being unstable.

[0068] The method for obtaining the voltage loop control quantity in real time includes but is not limited to the following ways:

[0069] The voltage across the resonant capacitor Cr is sampled through a resistor-capacitor device or directly sampled.

[0070] The resonant current is integrated during the conduction period of the corresponding switch tube to obtain the current integral quantity.

[0071] In this embodiment, when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is recognized, the light load discontinuous pause time will not be entered immediately, but three continuous pulses will be sent. The beneficial effects brought by the combination of the three pulses are as follows: the energy transmitted by a single pulse in the light load discontinuous mode is increased, the total input power of the LLC resonant converter is constant, the mode switching control quantity is constant, the mode switching is smooth, and the instability of the switching power supply caused by repeated switching under the same or similar load is effectively avoided; the voltage of the resonant capacitor during the pause time in the light load discontinuous working mode is kept at about half of the current input voltage, so that the resonant capacitor voltage corresponding to each pulse during the wave transmission time is balanced, the output current of the converter is balanced, the output voltage fluctuation of the converter is smaller, and the ripple is smaller; the first switch tube is turned on for the second time and turned off when the resonant current tends to the resonant current preset value, and when the resonant current preset value is zero, the parasitic diode in parallel with the switch tube has no current flowing through it, and the reverse recovery time is reduced, the current oscillation during the pause time in the light load discontinuous working mode is reduced, the overall loss is reduced, and the efficiency of the converter is improved.

[0072] In some examples, the first mode switching synchronization signal is a falling edge of the second switch or a rising edge of the first switch, so as to ensure the integrity of the heavy load continuous working mode and avoid the voltage and current stress caused by the incomplete pulse due to the random switching of the working mode during the current pulse emission. If the first mode switching synchronization signal is a falling edge of the second switch, when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is recognized in step two, the first switch needs to be controlled to be turned on for the first time after a dead time. If the first mode switching synchronization signal is a rising edge of the first switch, when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is recognized in step two, the first switch is immediately controlled to be turned on for the first time.

[0073] In some examples, the coefficient K is obtained by the following formula:

[0074]

[0075] wherein TL is the length of the entire cycle of the light load discontinuous working mode, and TLC is the length of the time of transferring energy to the secondary side in the light load discontinuous working mode.

[0076] In order to explain how the above K value is calculated, the working waveform diagram of the light load discontinuous working mode provided in Chinese patent application 202510151109.3 is cited here for explanation, please refer to Figure 3 wherein the first switch and the second switch are controlled by a group of cyclically emitted pulses with a pause time, each group of pulses controls the first switch to be switched three times and the second switch to be switched twice, wherein: the abscissa is time, and the ordinate is GQ1, which is the drive of the first switch Q1, GQ2, which is the drive of the second switch Q2, Vsw, which is the voltage of the common connection point of the first switch and the second switch, Vint, which is the integral value of the resonant current Ir (which can be used as the voltage loop control quantity of the present application), Vref1, which is the reference value of Vint when the first switch is controlled to be turned off for the first time, Vref2, which is the reference value of Vint when the first switch is controlled to be turned off for the second time, Vref3, which is the reference value of Vint when the first switch is controlled to be turned off for the third time, Ir, which is the resonant current, Id, which is the current value flowing through the secondary side diode D1 / D2, TL, which is the length of the entire cycle of the light load discontinuous working mode, TLC, which is the length of the time of transferring energy to the secondary side in the light load discontinuous working mode, and the coefficient K is calculated by the formula K=TL / TLC.

[0077] In some examples, the coefficient a is a configurable value, and the value range is 0.2-0.8.

[0078] In some examples, the coefficient a is set to 0.5.

[0079] In some examples, the resonant current preset value in step three is zero.

[0080] In some examples, the mode switching method is also used to control the LLC resonant converter to switch from the light load discontinuous working mode to the heavy load continuous working mode, comprising the following steps:

[0081] Step five, obtaining a mode switching control quantity representing the load size of the LLC resonant converter, and identifying a second mode switching synchronization signal;

[0082] Step six, when the mode switching control quantity is greater than a heavy load preset value, and the second mode switching synchronization signal is identified, entering the heavy load continuous working mode.

[0083] The mode switching control quantity can determine the power size transmitted to the output end in the current pulse period. Since there is no pause time in the heavy load continuous working mode as in the light load discontinuous working mode, when the working mode is switched from the light load discontinuous working mode to the heavy load continuous working mode, energy is continuously delivered to the output end of the LLC resonant converter, the total energy delivery period increases, and the output voltage increases. Therefore, the voltage loop control quantity needs to be reduced to reduce the energy transmitted in a single period, so as to ensure the constancy of the overall energy and stabilize the output. The mode switching control quantity is constant, and the voltage loop control quantity in the heavy load continuous working mode is reduced due to the negative feedback sampling working principle of the switching power supply. Therefore, the control method for controlling the LLC resonant converter to switch from the light load discontinuous working mode to the heavy load continuous working mode directly enters the heavy load continuous working mode after the second mode switching synchronization signal is identified, which can effectively avoid the instability of the switching power supply caused by repeated switching under the same or similar load.

[0084] In some examples, in the light load discontinuous working mode, the second switch and the first switch are alternately turned on between two pause times, and a dead time of simultaneous turn-off is arranged between the two. The driving of the second switch is combined by m pulses, and the driving of the first switch is combined by n pulses. m is a natural number greater than 1, n is a natural number greater than 2, the second mode switching signal is the falling edge of the Xth pulse of the second switch or the rising edge of the Yth pulse of the first switch, X can be any value in 1 to m-1, and Y can be any value in 2 to n-1.

[0085] When the second mode switching signal is the falling edge of the Xth pulse of the second switch, a dead time is needed before entering the heavy load continuous working mode in step six, that is, when the mode switching control quantity is greater than the heavy load preset value and the second mode switching synchronization signal is identified, the first switch is turned on after a dead time, and then the first switch and the second switch work with complementary driving, and the reference value of the control quantity is the set reference quantity.

[0086] When the second mode switching signal is the rising edge of the Yth pulse of the first switch tube, the heavy load continuous working mode is entered immediately at step six, that is, when the mode switching control quantity is greater than the heavy load preset value and the second mode switching synchronization signal is recognized, the first switch tube is turned on, and then the first switch tube and the second switch tube work in complementary driving and wave emission, and the reference value of the control quantity is the set reference value.

[0087] In some examples, a first mode switching filtering time is set in step two, when the mode switching control quantity is less than the light load preset value for the first mode switching filtering time, and the first mode switching synchronization signal is recognized, the first switch tube is controlled to be turned on for the first time; a second mode switching filtering time is set in step six, when the mode switching control quantity is greater than the heavy load preset value for the second mode switching filtering time, and the second mode switching synchronization signal is recognized, the switching power supply is controlled to enter the heavy load continuous working mode. The first mode switching filtering time and the second mode switching filtering time are both 0; or are the same value except 0; or are different values. The purpose of setting the first mode switching filtering time and the second mode switching filtering time is to avoid mode mis-switching caused by interference of the mode switching control quantity, and to cause the switching power supply to be unstable.

[0088] In some examples, when the mode switching control quantity reaches the first preset value, the first mode switching filtering time for switching from the heavy load continuous working mode to the light load discontinuous working mode is invalid; when the mode switching control quantity reaches the second preset value, the second mode switching filtering time for switching from the light load discontinuous working mode to the heavy load continuous working mode is invalid; the first preset value is less than the light load preset value; and the second preset value is greater than the heavy load preset value. According to the corresponding preset value, the corresponding mode switching filtering time is invalid, and the purpose is to quickly switch the working mode in a large dynamic state, so as to ensure a small over-undershoot.

[0089] Second embodiment

[0090] The embodiment provided is a mode switching device for controlling an LLC resonant converter to switch from a heavy load continuous working mode to a light load discontinuous working mode. The LLC resonant converter at least includes a bridge arm, which includes a first switch tube at a high end and a second switch tube at a low end. The mode switching device includes:

[0091] A first acquisition and recognition unit is configured to acquire a mode switching control quantity representing a load size of the LLC resonant converter, and to recognize a first mode switching synchronization signal.

[0092] The first control unit is configured to control the first switch tube to be turned on for the first time when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is identified, and to expand the reference value of the voltage loop control quantity set in the steady state heavy load continuous working mode by K times to obtain a first reference quantity, and to control the first switch tube to be turned off for a first dead time when the real-time obtained voltage loop control quantity is equal to the first reference quantity.

[0093] The second control unit is configured to control the second switch tube to be turned on after the first dead time, and to multiply the first reference quantity by a coefficient a to obtain a second reference quantity, and to control the second switch tube to be turned off for a second dead time when the real-time obtained voltage loop control quantity is equal to the second reference quantity.

[0094] The third control unit is configured to control the first switch tube to be turned on for the second time after the second dead time, and to control the first switch tube to be turned off when the resonant current tends to the resonant current preset value, so that the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode and enters the light load discontinuous working mode.

[0095] The technical means adopted by the control device of the embodiment corresponds to the control method of the first embodiment, has the same beneficial effects, and thus is not described herein. In addition, the technical means exemplarily provided in each step of the control method of the first embodiment or the further improved means can be extended to the embodiment, and the embodiment is not described one by one.

[0096] Third embodiment

[0097] The embodiment provides a switching power supply, which comprises an LLC resonant converter, and the LLC resonant converter comprises a first switch tube and a second switch tube.

[0098] Figure 4 The first control waveform diagram for the switching power supply in the third embodiment of the present application when switching from the heavy load working mode to the light load working mode, the switching power supply adopts the topology of the LLC resonant converter, and at least comprises a bridge arm, the bridge arm comprises the first switch tube at the high end and the second switch tube at the low end. Please refer to Figure 4 The waveform diagram, wherein Vcomp is a mode switching control quantity representing the load size of the LLC resonant converter, Vcomp1 is a light load preset value, MODE is a first mode switching synchronization signal, Vint is a voltage loop control quantity, Vref1 is a reference value of Vint when the first switch tube is controlled to be turned off for the first time, Vref2 is a reference value of Vint when the first switch tube is controlled to be turned off for the second time, and Ir is a resonant current. Figure 4 The control method for switching from the heavy load continuous working mode to the light load discontinuous working mode comprises the following steps:

[0099] Step 101, obtaining a mode switching control quantity Vcomp representing the load size of the LLC resonant converter, and identifying a first mode switching synchronization signal MODE;

[0100] Step 102, detecting at time t1 that the mode switching control quantity is less than a light load preset value Vcomp1. Here, the rising edge of the first switch is used as an example of the first mode switching synchronization signal. Therefore, during the period from t1 to t5, the working mode of the switching power supply is still the heavy load continuous working mode, and the first mode switching synchronization signal is high (representing that the switching power supply is in the heavy load continuous working mode). At time t5, which is the first time the rising edge of the first switch tube drive GQ1 is encountered, the first mode switching synchronization signal MODE becomes low. At this time, the condition that the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is identified is met.

[0101] Step 103, controlling the first switch tube to conduct for the first time at time t5, and expanding the reference value Vref of the voltage loop control quantity set in the heavy load continuous working mode before switching by K times to obtain a first reference quantity Vref1. The voltage loop control quantity can be the voltage VCr across the resonant capacitor Cr or the integral value Vint of the resonant current Ir. Here, the integral value Vint of the resonant current Ir is taken as an example. When the current integral voltage loop control quantity is equal to the first reference quantity Vref1 at time t6, the first switch tube is controlled to be turned off for a first dead time.

[0102] Step S104, at time t7 after the first dead time, the second switch tube is controlled to be turned on, and the first reference quantity is multiplied by a coefficient a to obtain a second reference quantity Vref2. When the integral value Vint of the resonant current Ir of the current integral voltage loop control quantity is equal to the second reference quantity Vref2 at time t8, the second switch tube is controlled to be turned off for a second dead time.

[0103] Step S105, at time t9 after the second dead time, the first switch tube is controlled to conduct for the second time. When the resonant current tends to a resonant current preset value at time t10, the first switch tube is controlled to be turned off, and the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode and enters the light load discontinuous working mode.

[0104] The steps 103 and 104 can not only increase the energy of single pulse transmission in the light load discontinuous mode, keep the total input power of the LLC resonant converter constant, and keep the mode switching control constant, so that the mode switching is smooth and the switching power supply is effectively prevented from being unstable due to repeated switching under the same or similar load, but also keep the voltage of the resonant capacitor at about half of the current input voltage during the pause time in the light load discontinuous mode, so that the resonant capacitor voltage corresponding to each pulse during the wave generation time is balanced, the output current of the converter is balanced, and the output voltage fluctuation of the converter is smaller and the ripple is smaller.

[0105] In the step 104, the first switch tube is turned on for the second time and is turned off when the resonant current tends to the resonant current preset value, so that the parasitic diode connected in parallel with the switch tube has no current flowing therethrough and no reverse recovery time, the current oscillation during the pause time in the light load discontinuous mode is reduced, the overall loss is reduced, and the efficiency of the converter is improved.

[0106] It should be noted that the specific control strategy of the light load discontinuous mode is not limited in the present application, and the person skilled in the art can select it according to the needs.

[0107] Figure 5 For the second control waveform diagram of the switching power supply in the third embodiment of the present application when switching from the heavy load working mode to the light load working mode, please refer to Figure 5 , which is different from Figure 4 in that the mode switching delay time T (i.e. the first mode switching filtering time) is arranged therein. Here, T is taken as an example of a specific amount of time. When the mode switching control is less than the light load preset value Vcomp1 at t1, the delay time T is set from t1 to t2. At t1', the rising edge of the first switch tube drive GQ1, the working mode does not change. At t6, the first time when the rising edge of the first switch tube drive GQ1 is encountered after T, the control process after t5 in Figure 4 is started to be executed. The purpose of arranging the first mode switching filtering time in this control strategy is to avoid mode mis-cutting caused by the interference of the mode switching control, and to cause the switching power supply to be unstable.

[0108] Figure 6 For the third control waveform diagram of the switching power supply in the third embodiment of the present application when switching from the heavy load working mode to the light load working mode, please refer to Figure 6 , which is different from Figure 5 in that although the mode switching delay time T is arranged therein, the time T is not reached, but the mode switching control reaches the first preset value PL, the mode switching delay time T is invalid, and thereafter, when the first time when the rising edge of the first switch tube drive GQ1 is encountered, the control process after t5 in Figure 4The control process after t5. Specifically, the mode switching control quantity reaches less than the light load preset value Vcomp1 at t1, t1-t7 is the set delay time T, but the mode switching control quantity reaches the first preset value PL at t4, so at t6, the first time the first switch tube drive GQ1 rising edge is encountered after t4, the control process of Figure 4 The control process after t5. The purpose of setting the first mode switching filter time to be invalid in this control strategy is that the mode error caused by the mode switching control quantity interference signal can be filtered out, and the load is already small but still in the heavy load working mode, which avoids causing a large overshoot.

[0109] Figure 7 The first control waveform diagram for the switching power supply in the third embodiment of the present application when switching from the light load working mode to the heavy load working mode. The switching power supply uses the LLC resonant converter topology, and at least includes one bridge arm, which includes the first switch tube at the high end and the second switch tube at the low end. Please refer to Figure 7 The waveform diagram, where MODE is the second mode switching synchronization signal, and the other code meanings are consistent with Figure 4 to Figure 6 . Figure 7 The control method for switching from the light load discontinuous working mode to the heavy load continuous working mode includes the following steps:

[0110] Step S201, the mode switching control quantity is greater than the heavy load preset value Vcomp2 at t1, where the first switch 2 rising edge of each pulse group is used as an example as the second mode switching synchronization signal, so during t1-t5, the working mode of the switching power supply is still the light load discontinuous working mode, and the second mode switching synchronization signal is low (representing the light load discontinuous working mode). At t5, the second mode switching synchronization signal MODE becomes high, which meets the condition that the mode switching control quantity is greater than the heavy load preset value, and the second mode switching synchronization signal is recognized;

[0111] Step S202, at t5, control according to the control method in the heavy load continuous mode, control the first switch tube to be on, and the reference quantity of the voltage loop control quantity is the voltage loop control quantity reference value set in the heavy load continuous working mode. When the voltage loop control quantity Figure 7 The integral value Vint of the resonant current Ir) is equal to the reference quantity at t6, control the first switch tube to be off;

[0112] Step S203, control according to the control method in heavy load continuous mode, after dead time, control the second switch tube to turn on at t7, the second switch tube and the first switch tube work with complementary drive, the reference of the control quantity is the reference value of the voltage loop control quantity set in heavy load continuous mode, when the voltage loop control quantity is equal to the reference at t8, control the second switch tube to turn off.

[0113] The switching power supply mode has been analyzed from the light load discontinuous mode to the heavy load continuous mode. Since there is no pause time in the heavy load continuous mode as in the light load discontinuous mode, energy is continuously transferred to the LLC resonant converter output end, the total energy transmission period increases, the voltage loop control quantity is reduced, the energy transmitted in a single period is reduced, the overall energy is constant, the output is stable, the mode switching control quantity is constant, the control loop itself can effectively avoid the switching power supply instability caused by repeated switching under the same or close load, and therefore it is not necessary to adjust the mode switching control quantity by increasing the pulse as when switching from the heavy load continuous mode to the light load discontinuous mode, so as to keep the mode switching control quantity constant.

[0114] Figure 8 For the second control waveform diagram of the switching power supply in the third embodiment of the present application when switching from the light load mode to the heavy load mode, please refer to Figure 8 The waveform diagram also sets a mode switching delay time T (i.e. the second mode switching filter time), which is taken as an example of a specific time amount. At t1, the mode switching control quantity is detected to be greater than the heavy load preset value Vcomp2, t1-t3 is the set delay time T, and the second mode switching synchronization signal is taken as an example of the rising edge of the second first switch, at t2, the working mode does not change, and at t4, the first time the rising edge of the second first switch drive GQ1 is encountered after t3, the control process after t5 in Figure 7 is started.

[0115] Figure 9 For the third control waveform diagram of the switching power supply in the third embodiment of the present application when switching from the light load mode to the heavy load mode, please refer to Figure 9 Although the mode switching delay time T is set, the time T does not reach, but the mode switching control quantity reaches the second preset value PH, the mode switching delay time T is invalid, and thereafter, when the first switch drive GQ1 rising edge is encountered for the first time, the control process after t5 in Figure 7The control process after the moment t5. Specifically, the mode switching control quantity is greater than the heavy load preset value Vcomp2 at the moment t1, t1-t5 is the set delay time T, but the mode switching control quantity reaches the second preset value PH at the moment t3, so at the moment t4 when the first second switch tube drive GQ1 rising edge is first encountered after the moment t3, the control process of Figure 7 The control process after the moment t5.

[0116] It should be noted that the mode switching control quantity Vcomp of the application needs to be obtained by first sampling the output voltage of the LLC resonant converter, so the mode switching control quantity Vcomp is opposite to the change of the output voltage. Figure 10 The schematic diagram of the negative feedback sampling circuit, when the load (output current) of the switching power supply becomes lighter, since the input power is constant, the lighter load will cause the output voltage to rise, and the sampling voltage of the REF point of the controllable precision voltage regulator TL1 will also rise, causing the conduction of TL1 (i.e. the conduction current from the cathode to the anode) to increase, since the current through the resistor R2 is clamped to a fixed value by the fixed voltage drop across the light-coupled primary side LED, and there is essentially no current flowing through the filter capacitor C1, according to Kirchhoff's current law, the current flowing through the light-coupled primary side LED increases, the current received by the light-sensitive triode on the secondary side of the light-coupled increases, the voltage across the pull-up resistor R inside the main control module U1 increases, thereby the voltage at the collector of the light-sensitive triode decreases, and the mode switching control quantity Vcomp generated by the analog or digital loop also decreases, the reduced Vcomp controls the loop to reduce the input power, thereby reducing the output voltage and maintaining the constant output voltage through feedback; similarly, when the load of the switching power supply becomes heavier, the output voltage will decrease, the current flowing through the light-coupled primary side LED will decrease, the current received by the light-sensitive triode on the secondary side of the light-coupled will decrease, the voltage across the pull-up resistor R inside the main control module U1 will decrease, thereby the voltage at the collector of the light-sensitive triode increases, and the mode switching control quantity Vcomp generated by the analog or digital loop also increases, the increased Vcomp controls the loop to increase the input power, thereby increasing the output voltage and maintaining the constant output voltage through feedback.

[0117] The above is only the preferred embodiment of the application, it should be noted that the above preferred embodiment should not be regarded as a limitation of the application, for those skilled in the art, without departing from the spirit and scope of the application, a number of improvements and refinements can also be made, which should also be regarded as the protection scope of the application, hereinafter, the protection scope of the application should be limited by the scope defined by the claims.

Claims

1. A mode switching method for controlling an LLC resonant converter to switch from a heavy load continuous operation mode to a light load discontinuous operation mode, the LLC resonant converter comprising at least one bridge arm, the bridge arm comprising a first switch tube at a high side and a second switch tube at a low side; characterized in that, The control method comprises the following steps of: Step 1: obtaining a mode switching control quantity representing the load size of the LLC resonant converter, and identifying a first mode switching synchronization signal; Step 2: when the mode switching control quantity is less than a light load preset value and the first mode switching synchronization signal is identified, controlling the first switch tube to be turned on for the first time, and expanding the reference value of the voltage loop control quantity set in the heavy load continuous working mode by K times to obtain a first reference quantity, when the real-time obtained voltage loop control quantity is equal to the first reference quantity, controlling the first switch tube to be turned off for a first dead time; Step 3: after the first dead time, controlling the second switch tube to be turned on, and multiplying the first reference quantity by a coefficient a to obtain a second reference quantity, when the real-time obtained voltage loop control quantity is equal to the second reference quantity, controlling the second switch tube to be turned off for a second dead time; Step 4: after the second dead time, controlling the first switch tube to be turned on for the second time, when the resonant current tends to a resonant current preset value, controlling the first switch tube to be turned off, and the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode and enters the light load discontinuous working mode.

2. The mode switching method according to claim 1, wherein: the first mode switching synchronization signal is a falling edge of the second switch tube, and at this time, in the step 2, when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is identified, a dead time is needed before the first switch tube is controlled to be turned on for the first time; or the first mode switching synchronization signal is a rising edge of the first switch tube, and at this time, in the step 2, when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is identified, the first switch tube is immediately controlled to be turned on for the first time.

3. The mode switching method of claim 1, wherein: The coefficient K is obtained by the following formula: wherein, TL is the length of the whole period of the light load discontinuous working mode, and TLC is the length of the time of transferring energy to the secondary side in the light load discontinuous working mode.

4. The mode switching method of claim 1, wherein: The coefficient a is a configurable value, and the value range is 0.2-0.

8.

5. The mode switching method of claim 1, wherein: The resonant current preset value in the step 3 is zero.

6. The mode switching method of claim 1, wherein: The mode switching method is also used for controlling the LLC resonant converter to switch from the light load discontinuous working mode to the heavy load continuous working mode, and the control method comprises the following steps of: Step 5: obtaining a mode switching control quantity representing the load size of the LLC resonant converter, and identifying a second mode switching synchronization signal; Step 6: when the mode switching control quantity is greater than a heavy load preset value and the second mode switching synchronization signal is identified, the LLC resonant converter completes the switching from the light load discontinuous working mode to the heavy load continuous working mode and enters the heavy load continuous working mode.

7. The mode switching method according to claim 6, wherein: The step two is provided with a first mode switching filter time, when the mode switching control quantity is less than the light load preset value in the first mode switching filter time, and the first mode switching synchronization signal is recognized, the first switch tube is controlled to be turned on for the first time. The step six is provided with a second mode switching filter time, when the mode switching control quantity is greater than the heavy load preset value in the second mode switching filter time, and the second mode switching synchronization signal is recognized, the switch power supply is controlled to enter the heavy load continuous working mode.

8. The mode switching method of claim 7, wherein: When the mode switching control quantity reaches the first preset value, the first mode switching filter time of the mode switching from the heavy load continuous working mode to the light load discontinuous working mode is invalid; when the mode switching control quantity reaches the second preset value, the second mode switching filter time of the mode switching from the light load discontinuous working mode to the heavy load continuous working mode is invalid; the first preset value is less than the light load preset value; the second preset value is greater than the heavy load preset value.

9. A mode switching device for controlling an LLC resonant converter to switch from a heavy load continuous mode to a light load discontinuous mode, the LLC resonant converter comprising at least one bridge arm, the bridge arm comprising a first switch tube at a high side and a second switch tube at a low side; characterized in that, The mode switching device comprises: A first acquisition and recognition unit is configured to acquire a mode switching control quantity representing a load size of the LLC resonant converter, and recognize a first mode switching synchronization signal; A first control unit is configured to control the first switch tube to be turned on for the first time when the mode switching control quantity is less than the light load preset value and the first mode switching synchronization signal is recognized, and expand a reference value of a voltage loop control quantity set in the heavy load continuous working mode in a steady state by K times to obtain a first reference quantity, and control the first switch tube to be turned off for a first dead time when a real-time acquired voltage loop control quantity is equal to the first reference quantity; A second control unit is configured to control the second switch tube to be turned on after the first dead time, multiply the first reference quantity by a coefficient a to obtain a second reference quantity, and control the second switch tube to be turned off for a second dead time when a real-time acquired voltage loop control quantity is equal to the second reference quantity; A third control unit is configured to control the first switch tube to be turned on for the second time after the second dead time, and control the first switch tube to be turned off when the resonant current tends to a resonant current preset value, so that the LLC resonant converter completes the switching from the heavy load continuous working mode to the light load discontinuous working mode and enters the light load discontinuous working mode.

10. A switching power supply comprising an LLC resonant converter, the LLC resonant converter comprising a first switch and a second switch, characterized in that: The switch power supply further comprises the mode switching device of claim 9.

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