A control method and device for a switching power supply, and a switching power supply

Abstract

The present invention discloses a control method, device, and switching power supply. The control method includes, during each operating cycle of the switching power supply: obtaining a first signal representing the magnitude of the switching power output; obtaining a second signal representing the peak of the resonant voltage across the drain and source of the main switching tube; comparing the first signal with a first set value; if the first signal is greater than or equal to the first set value, generating a third signal, operating in mode one, and not turning on the synchronous rectifier switch tube a second time; and if the first signal is less than the first set value, generating a fourth signal, operating in mode two, and turning on the synchronous rectifier switch tube a second time. The present invention enables the switching power supply to have high efficiency and low stress on power devices over the full voltage and full load range.

Description

Technical Field

[0001] The present invention relates to the field of switching power supplies, and more particularly to a control method and a control device for a switching power supply, and a switching power supply. Background Art

[0002] Traditional flyback converters offer advantages such as simple circuitry, low cost, high reliability, and excellent input-output isolation, making them widely used in low- and medium-power switching power supplies. However, their efficiency is limited, limiting their application in high-performance, high-power applications. One of the main reasons for this low efficiency is that the flyback transformer's leakage inductance accounts for 2%-5% of the magnetizing inductance. In applications with higher input-output isolation requirements, the leakage inductance contributes even more. During the on-time of the main switch, energy is simultaneously magnetized and stored in both the magnetizing and leakage inductances. However, during the demagnetization period of the magnetizing inductance, this leakage inductance energy cannot be transferred to the secondary side. Instead, a large voltage spike is generated between the drain and source of the main switch when it turns off. In severe cases, this voltage spike can cause the switch to breakdown. Furthermore, the leakage inductance energy is dissipated through resonance between the leakage inductance and the junction capacitance. Therefore, it is necessary to process this leakage inductance energy; otherwise, it will be directly dissipated as heat, significantly impacting efficiency and leading to more severe EMI issues.

[0003] Therefore, it's necessary to add a clamping circuit to handle the flyback converter's leakage inductance energy, suppress the main switch's turn-off voltage spike, and feed the leakage inductance energy back to the main power circuit to improve efficiency and reliability. Currently, existing clamping circuits include passive RCD clamping, passive LCD clamping, and active clamping. Passive RCD absorption solutions only clamp to reduce the voltage stress on the main switch but cannot feed back leakage inductance energy, thus failing to improve efficiency. Passive LCD clamping, on the other hand, is relatively complex and difficult to implement.

[0004] Figure 1 This is the schematic diagram of the existing high-side tube clamping circuit. This solution adds a clamping switch tube Q2 and turns on the clamping switch tube Q2 for a period of time before the main power switch tube Q1 turns on, thereby achieving zero-voltage turn-on of the main power switch tube Q1. The drain-source voltage spike of the main power switch tube Q1 is limited by the clamping capacitor C3. However, in order to store sufficient energy to achieve zero-voltage turn-on of the main power switch tube Q1, the clamping capacitor C3 requires a larger capacitance clamping capacitor C3 and a higher current rating clamping switch tube Q2. In addition, the clamping switch tube Q2 requires an independent bootstrap drive circuit or IC, which leads to high costs. Therefore, this solution is more suitable for use in high-power and high-frequency applications.

[0005] Figure 2a The schematic diagram of the existing secondary side clamping is shown below. Secondary side clamping refers to clamping the voltage across the drain and source of the primary side main switch tube by using the output voltage during the conduction period of the secondary side synchronous rectification switch tube. Figure 2b for Figure 2a The operating waveform of the existing secondary-side clamping circuit shows that this solution achieves zero-voltage turn-on of the main switch Q3 by controlling the secondary-side synchronous rectification switch Q4 to turn on again before the main switch Q3 turns on. However, the problem with this solution is that it can only achieve zero-voltage turn-on of the main switch Q3, and the leakage inductance energy cannot be recovered, resulting in limited efficiency improvement. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a control method, a control device and a switching power supply for a switching power supply, which can not only achieve zero-voltage turn-on of the main switch tube of the active clamp flyback converter, but also realize energy recovery of the primary side leakage inductance, thereby achieving the purpose of improving efficiency.

[0007] As a first aspect of the present invention, an embodiment of a method for controlling a switching power supply is provided as follows:

[0008] A control method for a switching power supply, wherein the switching power supply adopts an active clamp flyback converter topology and comprises: a primary-side controller configured to control the turning on and off of a main switch and a clamp switch in a primary-side circuit of the switching power supply; a secondary-side controller configured to control the turning on and off of a synchronous rectifier switch in a secondary-side circuit of the switching power supply; an isolated signal transmission module configured to transmit signals between the primary-side controller and the secondary-side controller; and control logic configured to execute the control method; the main switch, the clamp switch, and the synchronous rectifier switch are all turned off at the initial state of each operating cycle of the switching power supply; and the control method comprises, during each operating cycle of the switching power supply:

[0009] Acquire a first signal representing the output power of the switching power supply;

[0010] Acquire a second signal indicating that the resonant voltage across the drain and source of the main switch tube is at a peak;

[0011] Comparing the first signal with a first set value; if the first signal is greater than or equal to the first set value, generating a third signal; if the first signal is less than the first set value, generating a fourth signal;

[0012] The switching power supply is controlled to operate in different modes according to the result of comparing the first signal with a first set value:

[0013] Mode 1: If the third signal is generated, the main switch tube is controlled to be turned on for a first duration. After the first time interval, the synchronous rectifier switch tube is controlled to be turned on for a second duration. During the second time interval, when the second signal is obtained, the clamp switch tube is controlled to be turned on for a third duration. After the second time interval, the next working cycle begins.

[0014] In mode two, the fourth signal is generated, and the main switch tube is controlled to be turned on for the fourth time length in sequence. After the third time interval, the synchronous rectifier switch tube is controlled to be turned on for the fifth time length, and then the fourth time interval is entered. When the second signal is obtained, the clamp switch tube is controlled to be turned on for the sixth time length, and the synchronous rectifier switch tube is also controlled to be turned on for the seventh time length. The sixth time length is less than the seventh time length. After the seventh time length ends, the next working cycle is entered after the fifth time interval.

[0015] Furthermore, in each working cycle of the switching power supply, the first signal is also compared with the second set value, and the first set value is greater than the second set value;

[0016] If the second set value ≤ the first signal ≤ the first set value, the fourth signal is still generated, and the switching power supply still operates in the second mode;

[0017] If the first signal is less than the second set value, a fifth signal is generated. At this time, the switching power supply operates in mode three, which is:

[0018] The main switch tube is controlled to be turned on for an eighth time period, and enters the next working cycle after a sixth time interval.

[0019] Preferably, the third time duration or the sixth time duration is a natural resonance period of resonance between the output junction capacitance of the clamping switch tube and the excitation inductance of the switching power supply.

[0020] As a second aspect of the present invention, an embodiment of a control device for a switching power supply is provided as follows:

[0021] A control device for a switching power supply, wherein the switching power supply adopts an active clamp flyback converter topology, and the control device comprises:

[0022] A primary-side controller configured to control the on / off of a main switch tube and a clamp switch tube in a primary-side circuit of the switching power supply;

[0023] A secondary-side controller configured to control the on / off switching of a synchronous rectifier switch in the secondary-side circuit of the switching power supply;

[0024] an isolated signal transmission module, configured to transmit signals between the primary-side controller and the secondary-side controller;

[0025] The control logic is configured to cause the control device to perform the following actions in each working cycle of the switching power supply:

[0026] Controlling the main switch tube, the clamp switch tube and the synchronous rectification switch tube to be initially turned off;

[0027] Acquire a first signal representing the output power of the switching power supply;

[0028] Acquire a second signal indicating that the resonant voltage across the drain and source of the main switch tube is at a peak;

[0029] Comparing the first signal with a first set value; if the first signal is greater than or equal to the first set value, generating a third signal; if the first signal is less than the first set value, generating a fourth signal;

[0030] The switching power supply is controlled to operate in different modes according to the result of comparing the first signal with a first set value:

[0031] Mode 1: If the third signal is generated, the main switch tube is controlled to be turned on for a first duration. After the first time interval, the synchronous rectifier switch tube is controlled to be turned on for a second duration. During the second time interval, when the second signal is obtained, the clamp switch tube is controlled to be turned on for a third duration. After the second time interval, the next working cycle begins.

[0032] In mode two, the fourth signal is generated, and the main switch tube is controlled to be turned on for the fourth time length in sequence. After the third time interval, the synchronous rectifier switch tube is controlled to be turned on for the fifth time length, and then the fourth time interval is entered. When the second signal is obtained, the clamp switch tube is controlled to be turned on for the sixth time length, and the synchronous rectifier switch tube is also controlled to be turned on for the seventh time length. The sixth time length is less than the seventh time length. After the seventh time length ends, the next working cycle is entered after the fifth time interval.

[0033] Furthermore, the control logic is further configured to cause the control device to perform the following actions in each working cycle of the switching power supply:

[0034] Comparing the first signal with the second set value, where the first set value is greater than the second set value;

[0035] If the second set value ≤ the first signal ≤ the first set value, the fourth signal is still generated, and the switching power supply still operates in the second mode;

[0036] If the first signal is less than the second set value, a fifth signal is generated. At this time, the switching power supply operates in mode three, which is:

[0037] The main switch tube is controlled to be turned on for an eighth time period, and enters the next working cycle after a sixth time interval.

[0038] Preferably, the third time duration or the sixth time duration is a natural resonance period of resonance between the output junction capacitance of the clamping switch tube and the excitation inductance of the switching power supply.

[0039] Preferably, the second signal is obtained by detecting the Mth peak of the voltage across the drain and source of the main switch tube, where M is a natural number greater than or equal to 1; or the second signal is obtained by detecting the Nth valley of the voltage across the drain and source of the synchronous rectifier switch tube, where N is a natural number greater than or equal to 1.

[0040] Preferably, the secondary side controller obtains the result of comparing the first signal with the first set value, and transmits the result to the primary side controller through the isolated signal transmission module, so that the primary side controller detects the result of comparing the first signal with the first set value.

[0041] Preferably, the first signal is obtained by directly sampling the output load of the switching power supply through a sampling resistor, so that the secondary-side controller detects a result of comparing the first signal with a first set value.

[0042] Preferably, the primary side controller generates a driving signal to control the synchronous rectifier switch tube to turn on the second half of the second time period or to turn on the seventh time period, and then transmits it to the secondary side controller through the isolated signal transmission module. The second half of the second time period in which the synchronous rectifier switch tube is turned on refers to the part from the beginning of the third time period to the end of the second time period.

[0043] Preferably, the secondary-side controller generates a driving signal for controlling the clamp switch tube to be turned on for a third time period, and then transmits the driving signal to the primary-side controller through the isolated signal transmission module.

[0044] As a third aspect of the present invention, an embodiment of a switching power supply is provided as follows:

[0045] A switching power supply adopts an active clamp flyback converter topology and includes any one of the control devices described above.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. After the secondary-side demagnetization current passes through zero, the present invention turns on the clamping switch tube for a short period of time so that the energy recovered on the clamping capacitor is transferred to the secondary side in the form of a forward pulse. In order to prevent the energy transferred by the forward pulse from increasing loss on the secondary side due to the excessive peak current, the synchronous rectifier switch tube continues to turn on after detecting that the demagnetization current passes through zero when the load is heavy; when the load is light, the synchronous rectifier switch tube is immediately turned off after the demagnetization current passes through zero, but it will be turned on for the second time at the same time as the clamping switch tube. In this way, leakage inductance energy recovery is achieved through the clamping switch tube, and ZVS opening of the main switch tube is achieved through the synchronous rectifier switch tube, so that the efficiency of the switching power supply above the entire heavy load is improved, and the voltage stress problem of the single secondary-side clamped primary-side switch tube is solved.

[0048] 2. Control the converter to operate in the optimal mode according to different load conditions, so that the converter can maintain the highest efficiency under full input voltage and full load conditions.

[0049] 3. The secondary side clamping realizes ZVS and reuses the function of synchronous rectifier tube, saving development cost.

[0050] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained through the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is the schematic diagram of the existing upper tube clamp circuit;

[0052] Figure 2a This is the schematic diagram of the existing secondary side clamping circuit;

[0053] Figure 2b for Figure 2a Working waveform of existing secondary side clamping circuit;

[0054] Figure 3 This is a schematic diagram of a switching power supply according to a third embodiment of the present invention;

[0055] Figure 4 The present invention is aimed at Figure 3 The first waveform diagram provided by the switching power supply shown;

[0056] Figure 5 The present invention is aimed at Figure 3 The second waveform diagram provided by the switching power supply shown;

[0057] Figure 6 The present invention is aimed at Figure 3 The third waveform diagram provided by the switching power supply shown;

[0058] Figure 7 This is a schematic diagram of a switching power supply according to a fourth embodiment of the present invention;

[0059] Figure 8 The present invention is aimed at Figure 7 The first waveform diagram provided by the switching power supply shown;

[0060] Figure 9 The present invention is aimed at Figure 7 The second waveform diagram provided by the switching power supply shown. DETAILED DESCRIPTION

[0061] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0062] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0063] 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 described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes 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 devices.

[0064] 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.

[0065] In addition, the figures of this disclosure are merely schematic diagrams of the present disclosure and are not necessarily drawn to scale. Identical reference numbers in the figures denote identical or similar parts, and therefore repeated descriptions thereof will be omitted. Some of the blocks shown in the figures are functional entities that do not necessarily correspond to physically or logically separate entities. These functional entities may be implemented using software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontrollers.

[0066] First embodiment

[0067] This embodiment provides a control method for a switching power supply, wherein the switching power supply adopts an active clamp flyback converter topology, and the switching power supply includes: a primary-side controller configured to control the turning on and off of a main switch tube and a clamp switch tube in a primary-side circuit of the switching power supply; a secondary-side controller configured to control the turning on and off of a synchronous rectifier switch tube in a secondary-side circuit of the switching power supply; an isolated signal transmission module configured to transmit signals between the primary-side controller and the secondary-side controller; and control logic configured to execute the control method of this embodiment; the main switch tube, the clamp switch tube, and the synchronous rectifier switch tube are all turned off in the initial state of each working cycle of the switching power supply.

[0068] The control method of this embodiment includes, in each working cycle of the switching power supply:

[0069] Acquire a first signal representing the output power of the switching power supply;

[0070] Acquire a second signal indicating that the resonant voltage across the drain and source of the main switch tube is a peak;

[0071] Compare the first signal with the first set value; if the first signal is greater than or equal to the first set value, generate a third signal; if the first signal is less than the first set value, generate a fourth signal;

[0072] The switching power supply is controlled to operate in different modes according to the result of comparing the first signal with the first set value:

[0073] Mode 1: If the third signal is generated, the main switch tube is controlled to be turned on for a first time period. After the first time interval, the synchronous rectifier switch tube is controlled to be turned on for a second time period. During the second time period, when the second signal is obtained, the clamp switch tube is controlled to be turned on for a third time period. After the second time period, the next working cycle begins after the second time interval.

[0074] In mode two, the fourth signal is generated, and the main switch tube is controlled to be turned on for the fourth time period. After the third time interval, the synchronous rectifier switch tube is controlled to be turned on for the fifth time period, and then the fourth time interval is entered. When the second signal is obtained, the clamp switch tube is controlled to be turned on for the sixth time period, and the synchronous rectifier switch tube is also controlled to be turned on for the seventh time period. The sixth time period is less than the seventh time period. After the seventh time period ends, the next working cycle is entered after the fifth time interval.

[0075] Mode 1 corresponds to the switching power supply operating at a heavy full load, while Mode 2 corresponds to the switching power supply operating at a light load. These two modes differ from the control methods of the prior art in that, after the secondary-side demagnetization current crosses zero (i.e., when the second signal is obtained), this embodiment turns on the clamping switch for a short period of time, allowing the energy recovered from the clamping capacitor to be transferred to the secondary side in the form of a forward pulse. Furthermore, to prevent increased losses on the secondary side due to excessive peak current in the forward pulse transfer, the synchronous rectifier switch remains on after detecting the demagnetization current crossing zero under heavy full load conditions. Under light load conditions, the synchronous rectifier switch is immediately turned off after the demagnetization current crosses zero, but is turned on a second time simultaneously with the clamping switch. Consequently, this embodiment offers the advantage of both recovering leakage inductance energy through the clamping switch and achieving ZVS switching of the main switch through the synchronous rectifier switch. This improves the efficiency of the switching power supply above heavy load conditions and solves the voltage stress issue of a single secondary-side clamped primary switch.

[0076] In summary, the above two-mode switching control method of this embodiment improves the overall efficiency of the switching power supply, reduces the voltage stress of the power devices, and thus improves the reliability of the entire switching power supply.

[0077] Furthermore, the control method of this embodiment further compares the first signal with the second set value in each working cycle of the switching power supply, and the first set value is greater than the second set value;

[0078] If the second set value ≤ the first signal ≤ the first set value, the fourth signal is still generated, and the switching power supply still operates in mode 2;

[0079] If the first signal is less than the second set value, the fifth signal is generated. At this time, the switching power supply operates in mode three, which is:

[0080] The main switch tube is controlled to be turned on for an eighth time period, and then enters a next working cycle after a sixth time interval.

[0081] Among them, mode three corresponds to the situation when the switching power supply operates at extremely light load or no load. This mode is consistent with the control method of the prior art, and reduces losses by lowering the switching frequency, thereby minimizing no-load power consumption.

[0082] In summary, the three-mode switching control method of this embodiment not only meets the high efficiency of the entire system, but also improves the reliability of the system and can reduce the no-load power consumption of the system.

[0083] Preferably, the duration of the clamp switch tube being turned on, that is, the third duration or the sixth duration, is a natural resonance period of resonance between the output junction capacitance of the clamp switch tube and the excitation inductance of the switching power supply. The reason for this design is that the clamp switch tube is turned on and off when the resonant current passes through zero, which can further reduce the loss caused by the reverse recovery of the clamp switch tube and improve efficiency.

[0084] Second embodiment

[0085] This embodiment discloses a control device for a switching power supply. The switching power supply adopts an active clamp flyback converter topology. The control device of this embodiment includes:

[0086] The primary-side controller is configured to control the on / off of the main switch and the clamp switch in the primary-side circuit of the switching power supply;

[0087] A secondary-side controller is configured to control the on / off switching of a synchronous rectifier switch in a secondary-side circuit of the switching power supply;

[0088] an isolated signal transmission module, configured to transmit signals between the primary-side controller and the secondary-side controller;

[0089] The control logic is configured to enable the control device to execute various specific actions in any specific implementation of the control method of the first embodiment in each working cycle of the switching power supply.

[0090] The beneficial effects of the control device of this embodiment correspond to the specific implementation methods of the first embodiment and are not repeated here.

[0091] In addition, the control device of this embodiment also has the following detailed implementation methods:

[0092] The primary side controller generates a driving signal to control the synchronous rectifier switch tube to turn on the second half of the second time period or the seventh time period, and then transmits it to the secondary side controller through the isolated signal transmission module. The second half of the second time period in which the synchronous rectifier switch tube is turned on refers to the part from the beginning of the third time period to the end of the second time period.

[0093] The secondary side controller obtains a comparison result between the first signal and the first set value, and transmits the comparison result to the primary side controller through the isolated signal transmission module, thereby enabling the primary side controller to detect the comparison result between the first signal and the first set value.

[0094] The sampling resistor directly samples the output load of the switching power supply to obtain a first signal, thereby realizing that the secondary side controller detects a result of comparing the first signal with a first set value.

[0095] The secondary side controller generates a driving signal for controlling the clamp switch tube to be turned on for a third time period, and then transmits the driving signal to the primary side controller through the isolation signal transmission module.

[0096] The second signal is obtained by detecting the Mth peak of the voltage across the drain and source of the main switch tube, where M is a natural number greater than or equal to 1; or the second signal is obtained by detecting the Nth valley of the voltage across the drain and source of the synchronous rectifier switch tube, where N is a natural number greater than or equal to 1.

[0097] Third embodiment

[0098] This embodiment discloses a switching power supply. Figure 3 The switching power supply of this embodiment adopts an active clamp flyback converter topology, wherein the control device includes:

[0099] The primary-side controller U1 is configured to control the on / off of the main switch Q1 and the clamp switch Q2 in the primary-side circuit of the switching power supply;

[0100] The secondary side controller U3 is configured to control the on and off of the synchronous rectifier switch Q3 in the secondary side circuit of the switching power supply;

[0101] The isolated signal transmission module U2 is configured to transmit signals between the primary side controller U1 and the secondary side controller U3;

[0102] The control logic is configured to cause the control device to perform the specific actions in any specific implementation of the control method of the first embodiment in each working cycle of the switching power supply, Figure 3 Not drawn in.

[0103] The beneficial effects of the control device of this embodiment correspond to the specific implementation methods of the first embodiment and are not repeated here.

[0104] Figure 4 The present invention is aimed at Figure 3 The first waveform diagram provided by the switching power supply shown; Figure 5 The present invention is aimed at Figure 3 The second waveform diagram provided by the switching power supply shown; Figure 6 The present invention is aimed at Figure 3The third waveform diagram provided by the switching power supply is shown; SW1 is the driving signal of the main switch tube Q1, SW2 is the driving signal of the clamp switch tube Q2, SR is the driving signal of the synchronous rectifier switch tube Q3, VDS is the drain-source voltage of the main switch tube, Ilr is the leakage inductance current of the primary side transformer, and Ils is the demagnetization current of the secondary side transformer.

[0105] In addition, the control device of this embodiment also has the following detailed implementation methods:

[0106] The second signal is obtained by detecting the Mth peak of the voltage across the drain and source of the main switch tube Q1, where M is a natural number greater than or equal to 1; or the second signal is obtained by detecting the Nth valley of the voltage across the drain and source of the synchronous rectifier switch tube Q3, where N is a natural number greater than or equal to 1.

[0107] The secondary side controller U3 obtains the result of comparing the first signal with the first set value (ie Figure 3 FB in the FB), and transmits the result to the primary side controller U1 through the isolated signal transmission module U2, so as to realize the result of comparing the first signal with the first set value detected by the primary side controller U1.

[0108] The sampling resistor directly samples the output load of the switching power supply to obtain a first signal, thereby realizing that the secondary side controller U3 detects the result of comparing the first signal with a first set value.

[0109] The primary side controller U1 generates a driving signal to control the synchronous rectifier switch Q3 to turn on the second half of the second duration or the seventh duration (i.e. Figure 3 SR1), and then transmitted to the secondary side controller U3 through the isolated signal transmission module U2. The second half of the second duration of the synchronous rectifier switch Q3 is the part from the beginning of the third duration to the end of the second duration, corresponding to Figure 4 The driving signal of the synchronous rectifier switch Q3 between t2 and t4, the driving signal of the seventh period corresponds to Figure 5 The driving signal of the synchronous rectification switch Q3 between t3 and t5.

[0110] Figure 4 The waveform is for Figure 3 The key waveform of the switching power supply in the embodiment of the present invention is that the third signal is generated by comparing the first signal with the first set value, and the switching power supply operates in mode 1.

[0111] It should be noted that Figure 4The driving signal of the synchronous rectifier switch Q3 is disconnected in the middle. This is because the driving signal for the first half of the second duration of the synchronous rectifier switch Q3 and the driving signal for the second half of the second duration of the synchronous rectifier switch Q3 come from different sources. Therefore, the driving signal may be interrupted in the connection. It is also feasible to connect the first half and the second half together.

[0112] The following combination Figure 4 Waveform pair Figure 3 Analyze the working sequence of the switching power supply in:

[0113] Phase 1, t1-t2: After the main switch Q1 turns off, a period of dead time passes, namely, at time t1. At this point, the main switch Q1 is completely off, and the voltage across its drain and source reaches its maximum value. Under the control of controller U3, the secondary-side synchronous rectifier switch Q3 begins conducting to continue the secondary-side demagnetization current. At time t2, the secondary-side controller U3 detects that the demagnetization current has crossed zero and turns off the synchronous rectifier switch Q3. Simultaneously, the voltage across the drain and source of the main switch Q1 reaches an inflection point due to resonance between the magnetizing inductance and the output junction capacitance of the main switch Q1. The primary-side controller U1 detects this inflection point and immediately outputs the turn-on signal SW2 to control the clamp switch Q2 and the turn-on signal SR1 to control the secondary-side synchronous rectifier switch Q3.

[0114] Phase 2 t2~t3: This phase is the time when the clamp switch tube Q2 and the secondary side synchronous rectification switch tube Q3 are turned on at the same time. At this time, the clamp capacitor on the primary side transfers energy to the secondary side through the clamp switch tube Q2. At time t3, the clamp switch tube Q2 is turned off, and the secondary side synchronous rectification switch tube Q3 continues to be turned on.

[0115] Phase 3 t3~t4: After t3, since the secondary synchronous rectifier switch Q3 continues to be turned on, the output capacitor on the secondary side will reversely excite the secondary winding S1, thereby generating a negative current on the secondary side. The energy generated by the negative secondary current is stored in the secondary winding S1. At t4, the drive signal of the secondary synchronous rectifier switch Q3 is turned off, and the secondary winding S1 begins to transfer energy to the primary winding P1, while generating a negative current on the primary side.

[0116] Phase 4 t4~t5: The negative current generated on the primary side will draw the charge from the output junction capacitance of the main switch tube Q1, causing the voltage VDS across the drain and source of the main switch tube Q1 to drop rapidly to zero. At time t5, the primary side controller U1 controls the main switch tube Q1 to turn on, and the converter enters the next switching cycle.

[0117] Figure 5 The waveform is for Figure 3 The key waveform of the switching power supply in the embodiment of the present invention is that the first signal is compared with the first set value to generate the fourth signal, and the switching power supply operates in mode 2.

[0118] The following combination Figure 5 Waveform pair Figure 3 Analyze the working sequence of the switching power supply in:

[0119] Phase 1, t1-t2: After the main switch Q1 turns off, a period of dead time passes, namely at time t1. At this time, the main switch Q1 is completely off, and the voltage across the drain and source of the main switch Q1 reaches its maximum value. Under the control of controller U3, the secondary-side synchronous rectifier switch Q3 begins to conduct to continue the secondary-side demagnetization current. At time t2, the secondary-side controller U3 detects that the demagnetization current has crossed zero and turns off the synchronous rectifier switch Q3. At the same time, the voltage across the drain and source of the main switch Q1 resonates with the output junction capacitance of the main switch Q1 due to the magnetizing inductance.

[0120] Phase 2, t2-t3: The voltage across the drain and source of the main switch Q1 resonates due to the magnetizing inductance and the output junction capacitance of the main switch Q1. When the resonance reaches the peak, that is, at time t3, the primary-side controller detects the peak and immediately outputs the turn-on signal SW2 to control the clamp switch Q2 and the turn-on signal SR1 to control the secondary-side synchronous rectifier switch Q3.

[0121] Phase 3 t3~t4: This phase is the time when the clamp switch tube Q2 and the secondary side synchronous rectification switch tube Q3 are turned on at the same time. At this time, the clamp capacitor on the primary side transfers energy to the secondary side through the clamp switch tube Q2. At time t4, the clamp switch tube Q2 is turned off, and the secondary side synchronous rectification switch tube Q3 continues to be turned on.

[0122] Phase 4 t4-t5: After t4, the secondary synchronous rectifier switch Q3 continues to conduct. At this time, the output capacitor on the secondary side will reversely excite the secondary winding S1, thereby generating a negative current on the secondary side. The energy generated by the negative secondary current is stored in the secondary winding S1. At t5, the drive signal of the secondary synchronous rectifier switch Q3 is turned off, and the secondary winding S1 begins to transfer energy to the primary winding P1, while generating a negative current on the primary side.

[0123] Phase 5, t5-t6: The negative current generated on the primary side draws charge from the output junction capacitance of the main switch Q1, causing the drain-source voltage VDS of the main switch Q1 to drop rapidly to zero. At t6, the primary-side controller U1 turns on the main switch Q1, and the converter enters the next switching cycle.

[0124] Figure 6 The waveform is for Figure 3 The key waveform of the switching power supply in the embodiment of the present invention is when the switching power supply operates under extremely light load or no load conditions, that is, the fifth signal is generated by comparing the first signal with the first set value, and the switching power supply operates in mode three.

[0125] The following combination Figure 5 Waveform pair Figure 3 Analyze the working sequence of the switching power supply in:

[0126] from Figure 6 It can be seen that the main switch tube Q1 is turned on for the eighth time period and enters the next working cycle after the sixth time interval. In this mode, the primary side main switch tube Q1 is valley-turned on and cannot achieve ZVS. In addition, the secondary side synchronous rectification switch tube Q3 is also not turned on, and freewheeling is only carried out through the body diode of the synchronous rectification switch tube Q3.

[0127] Fourth embodiment

[0128] Figure 7 This is a schematic diagram of a switching power supply according to a fourth embodiment of the present invention; Figure 8 The present invention is aimed at Figure 7 The first waveform diagram provided by the switching power supply shown; Figure 9 The present invention is aimed at Figure 7 The second waveform diagram provided by the switching power supply shown.

[0129] The switching power supply of this embodiment differs from the first embodiment in that:

[0130] The secondary-side controller U3 generates a driving signal for controlling the clamp switch tube Q2 to be turned on for the third duration, and then transmits the driving signal to the primary-side controller U1 through the isolated signal transmission module U2.

[0131] In addition, through Figure 7 and Figure 8 It can be seen that the switching tube of the synchronous rectifier switch tube in this embodiment is directly generated by the secondary side controller U3, so the driving signal of the synchronous rectifier switch tube Q3 during the second turning-on period is not as Figure 4 It is also divided into the front half and the back half.

[0132] Figure 8 The waveform is for Figure 7 The key waveform of the switching power supply in the embodiment of the present invention is that the third signal is generated by comparing the first signal with the first set value, and the switching power supply operates in mode 1.

[0133] The following combination Figure 8 Waveform pair Figure 7 Analyze the working sequence of the switching power supply in:

[0134] Phase 1, t1-t2: After the main switch Q1 turns off, a period of dead time passes, namely at time t1. At this time, the main switch Q1 is completely off, and the voltage across the drain and source of the main switch Q1 reaches its maximum value. Under the control of controller U3, the secondary-side synchronous rectifier switch Q3 begins to conduct to continue the secondary-side demagnetization current. At time t2, the secondary-side controller U3 detects that the demagnetization current has crossed zero, and the synchronous rectifier switch continues to conduct. At this time, the secondary-side controller U3 immediately generates a control signal SW2, which is transmitted to the primary-side controller U1 via the capacitor isolation transmission module, controlling the clamp switch Q2 to turn on.

[0135] Phase 2 t2~t3: This phase is the time when the clamp switch tube Q2 and the secondary side synchronous rectification switch tube Q3 are turned on at the same time. At this time, the clamp capacitor on the primary side transfers energy to the secondary side through the clamp switch tube Q2. At time t3, the clamp switch tube Q2 is turned off, and the secondary side synchronous rectification switch tube Q3 continues to be turned on.

[0136] Phase 3 t3~t4: After t3, since the secondary synchronous rectifier switch Q3 continues to be turned on, the output capacitor on the secondary side will reversely excite the secondary winding S1, thereby generating a negative current on the secondary side. The energy generated by the negative secondary current is stored in the secondary winding S1. At t4, the drive signal of the secondary synchronous rectifier switch Q3 is turned off, and the secondary winding S1 begins to transfer energy to the primary winding P1, while generating a negative current on the primary side.

[0137] Phase 4 t4~t5: The negative current generated on the primary side will draw the charge from the output junction capacitance of the main switch tube Q1, causing the voltage VDS across the drain and source of the main switch tube Q1 to drop rapidly to zero. At time t5, the primary side controller U1 controls the main switch tube Q1 to turn on, and the converter enters the next switching cycle.

[0138] Figure 9 The waveform is for Figure 7 The key waveform of the switching power supply in the embodiment of the present invention is that the first signal is compared with the first set value to generate the fourth signal, and the switching power supply operates in mode 2.

[0139] The following combination Figure 9 Waveform pair Figure 7 Analyze the working sequence of the switching power supply in:

[0140] Phase 1, t1-t2: After the main switch Q1 turns off, a period of dead time passes, namely at time t1. At this time, the main switch Q1 is completely off, and the voltage across its drain and source reaches its maximum value. Under the control of controller U3, the secondary-side synchronous rectifier switch Q3 begins conducting to continue the secondary-side demagnetization current. At time t2, the secondary-side controller U3 detects that the demagnetization current has crossed zero and turns off the synchronous rectifier switch Q3. Simultaneously, the voltage across the drain and source of the main switch Q5 resonates with the output junction capacitance of the main switch Q5 due to the magnetizing inductance.

[0141] Phase 2, t2-t3: The voltage across the drain and source of the main switch Q5 resonates due to the magnetizing inductance and the output junction capacitance of the main switch Q5. When the resonance reaches the peak, the secondary-side synchronous rectifier switch Q3 is at the valley, that is, at time t3. The secondary-side controller U3 detects the valley and immediately outputs the turn-on signal SW2 to control the clamp switch Q2, and generates the turn-on signal SR to control the secondary-side synchronous rectifier switch Q3 again.

[0142] Phase 3 t3~t4: This phase is the time when the clamp switch tube Q2 and the secondary side synchronous rectification switch tube Q3 are turned on at the same time. At this time, the clamp capacitor on the primary side transfers energy to the secondary side through the clamp switch tube Q2. At time t4, the clamp switch tube Q2 is turned off, and the secondary side synchronous rectification switch tube Q3 continues to be turned on.

[0143] Phase 4 t4-t5: After t4, the secondary synchronous rectifier switch Q3 continues to conduct. At this time, the output capacitor on the secondary side will reversely excite the secondary winding S1, thereby generating a negative current on the secondary side. The energy generated by the negative secondary current is stored in the secondary winding S1. At t5, the drive signal of the secondary synchronous rectifier switch Q3 is turned off, and the secondary winding S1 begins to transfer energy to the primary winding P1, while generating a negative current on the primary side.

[0144] Phase 5, t5-t6: The negative current generated on the primary side draws charge from the output junction capacitance of the main switch Q1, causing the drain-source voltage VDS of the main switch Q1 to drop rapidly to zero. At t6, the primary-side controller U1 turns on the main switch Q1, and the converter enters the next switching cycle.

[0145] The key waveform of the switching power supply of the fourth embodiment operating under extremely light load or no load conditions (i.e., the fifth signal generated by comparing the first signal with the first set value, and the switching power supply operating in mode three) is the same as that of the third embodiment and will not be repeated here.

[0146] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention. Persons skilled in the art will appreciate that equivalent power supplies, improvements, and modifications may be made without departing from the spirit and scope of the present invention. These equivalent power supplies, improvements, and modifications should also be considered within the scope of protection of the present invention. Examples will not be used here for further elaboration. The scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A method for controlling a switching power supply, wherein the switching power supply adopts an active clamp flyback converter topology, and the switching power supply comprises: A primary-side controller configured to control the on / off of a main switch tube and a clamp switch tube in a primary-side circuit of the switching power supply; A secondary-side controller configured to control the on / off switching of a synchronous rectifier switch in the secondary-side circuit of the switching power supply; An isolated signal transmission module is configured to transmit signals between the primary-side controller and the secondary-side controller; a control logic is configured to execute the control method; the main switch tube, the clamp switch tube, and the synchronous rectifier switch tube are all turned off at the initial state of each working cycle of the switching power supply; and the control method includes, in each working cycle of the switching power supply: Acquire a first signal representing the output power of the switching power supply; Acquire a second signal indicating that the resonant voltage across the drain and source of the main switch tube is at a peak; Comparing the first signal with a first set value; if the first signal is greater than or equal to the first set value, generating a third signal; if the first signal is less than the first set value, generating a fourth signal; The switching power supply is controlled to operate in different modes according to the result of comparing the first signal with a first set value: Mode 1: If the third signal is generated, the main switch tube is controlled to be turned on for a first duration. After the first time interval, the synchronous rectifier switch tube is controlled to be turned on for a second duration. During the second time interval, when the second signal is obtained, the clamp switch tube is controlled to be turned on for a third duration. After the second time interval, the next working cycle begins. In mode two, the fourth signal is generated, and the main switch tube is controlled to be turned on for the fourth time length in sequence. After the third time interval, the synchronous rectifier switch tube is controlled to be turned on for the fifth time length, and then the fourth time interval is entered. When the second signal is obtained, the clamp switch tube is controlled to be turned on for the sixth time length, and the synchronous rectifier switch tube is also controlled to be turned on for the seventh time length. The sixth time length is less than the seventh time length. After the seventh time length ends, the next working cycle is entered after the fifth time interval.

2. The control method according to claim 1, characterized in that: In each working cycle of the switching power supply, the first signal is further compared with a second set value, and the first set value is greater than the second set value; If the second set value ≤ the first signal ≤ the first set value, the fourth signal is still generated, and the switching power supply still operates in the second mode; If the first signal is less than the second set value, a fifth signal is generated. At this time, the switching power supply operates in mode three, which is: The main switch tube is controlled to be turned on for an eighth time period, and enters the next working cycle after a sixth time interval.

3. The control method according to claim 1 or 2, characterized in that: The third time duration or the sixth time duration is a natural resonance period of resonance between the output junction capacitance of the clamping switch tube and the excitation inductance of the switching power supply.

4. A control device for a switching power supply, wherein the switching power supply adopts an active clamp flyback converter topology, characterized in that: The control device comprises: A primary-side controller configured to control the on / off of a main switch tube and a clamp switch tube in a primary-side circuit of the switching power supply; A secondary-side controller configured to control the on / off switching of a synchronous rectifier switch in the secondary-side circuit of the switching power supply; an isolated signal transmission module, configured to transmit signals between the primary-side controller and the secondary-side controller; The control logic is configured to cause the control device to perform the following actions in each working cycle of the switching power supply: Controlling the main switch tube, the clamp switch tube and the synchronous rectification switch tube to be initially turned off; Acquire a first signal representing the output power of the switching power supply; Acquire a second signal indicating that the resonant voltage across the drain and source of the main switch tube is at a peak; Comparing the first signal with a first set value; if the first signal is greater than or equal to the first set value, generating a third signal; if the first signal is less than the first set value, generating a fourth signal; The switching power supply is controlled to operate in different modes according to the result of comparing the first signal with a first set value: Mode 1: If the third signal is generated, the main switch tube is controlled to be turned on for a first duration. After the first time interval, the synchronous rectifier switch tube is controlled to be turned on for a second duration. During the second time interval, when the second signal is obtained, the clamp switch tube is controlled to be turned on for a third duration. After the second time interval, the next working cycle begins. In mode two, the fourth signal is generated, and the main switch tube is controlled to be turned on for the fourth time length in sequence. After the third time interval, the synchronous rectifier switch tube is controlled to be turned on for the fifth time length, and then the fourth time interval is entered. When the second signal is obtained, the clamp switch tube is controlled to be turned on for the sixth time length, and the synchronous rectifier switch tube is also controlled to be turned on for the seventh time length. The sixth time length is less than the seventh time length. After the seventh time length ends, the next working cycle is entered after the fifth time interval.

5. The control device according to claim 4, characterized in that: The control logic is further configured to cause the control device to perform the following actions in each working cycle of the switching power supply: Comparing the first signal with a second set value, where the first set value is greater than the second set value; If the second set value ≤ the first signal ≤ the first set value, the fourth signal is still generated, and the switching power supply still operates in the second mode; If the first signal is less than the second set value, a fifth signal is generated. At this time, the switching power supply operates in mode three, which is: The main switch tube is controlled to be turned on for an eighth time period, and enters the next working cycle after a sixth time interval.

6. The control device according to claim 4 or 5, characterized in that: The third time duration or the sixth time duration is a natural resonance period of resonance between the output junction capacitance of the clamping switch tube and the excitation inductance of the switching power supply.

7. The control device according to claim 4 or 5, characterized in that: The second signal is obtained by detecting the Mth peak of the voltage across the drain and source of the main switch tube, where M is a natural number greater than or equal to 1; or the second signal is obtained by detecting the Nth valley of the voltage across the drain and source of the synchronous rectifier switch tube, where N is a natural number greater than or equal to 1.

8. The control device according to claim 4 or 5, characterized in that: The secondary side controller obtains a comparison result between the first signal and the first set value, and transmits the comparison result to the primary side controller through the isolated signal transmission module, thereby enabling the primary side controller to detect the comparison result between the first signal and the first set value.

9. The control device according to claim 8, characterized in that: The first signal is obtained by directly sampling the output load of the switching power supply through the sampling resistor, so that the secondary-side controller detects the result of comparing the first signal with a first set value.

10. The control device according to claim 4 or 5, characterized in that: The primary side controller generates a driving signal to control the synchronous rectifier switch tube to turn on the second half of the second time period or to turn on the seventh time period, and then transmits it to the secondary side controller through the isolated signal transmission module. The second half of the second time period in which the synchronous rectifier switch tube is turned on refers to the part from the beginning of the third time period to the end of the second time period.

11. The control device according to claim 4 or 5, characterized in that: The secondary-side controller generates a driving signal for controlling the clamp switch tube to be turned on for a third time period, and then transmits the driving signal to the primary-side controller through the isolated signal transmission module.

12. A switching power supply, characterized in that: The switching power supply adopts an active clamp flyback converter topology, and the switching power supply includes the control device according to any one of claims 4 to 11.

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