A control method of a switching power supply and a switching power supply

Abstract

The embodiment of the application discloses a control method and a switching power supply. The control method comprises the following steps: after the high-voltage starting of the switching power supply, and when the switching time interval of the second switch tube is equal to or smaller than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switch tube; when the voltage waveform of the second connection point does not realize zero voltage switching, the secondary side control module adjusts the off current of the second switch tube until the voltage waveform of the first connection point between the primary side winding and the first switch tube is just zero; when the voltage waveform of the first connection point is just zero, the primary side control module controls the first switch tube to be turned on, so as to realize the zero voltage opening of the primary side. The embodiment reduces the switching loss of the switching power supply, and improves the EMI characteristics of the switching power supply.

Description

Technical Field

[0001] This invention relates to the field of power supply technology, and in particular to a control method for a switching power supply and a switching power supply. Background Technology

[0002] In the power supply field, isolated switching power supplies play a crucial role. As the most common type of isolated switching power supply, flyback AC-DC isolated switching power supplies are widely used in the power supply processes of electronic devices such as mobile phones, tablets, and home appliances.

[0003] In existing technologies, typical flyback AC-DC isolated switching power supplies suffer from high primary switching losses, low efficiency, and significant electromagnetic interference (EMI), thus limiting the increase in switching frequency and hindering the miniaturization of the switching power supply. Based on this, active clamp flyback designs capable of zero-voltage switching have emerged. However, compared to typical flyback AC-DC isolated switching power supplies, actively clamped flyback AC-DC isolated switching power supplies require additional control stages and corresponding hardware circuit structures, resulting in a more complex power supply structure and higher hardware costs and power control complexity. Summary of the Invention

[0004] This invention provides a control method and a switching power supply for reducing switching losses and improving EMI characteristics of the switching power supply.

[0005] In a first aspect, embodiments of the present invention provide a control method for a switching power supply, the switching power supply including a primary side winding, a secondary side winding, a primary side control module, a secondary side control module, a first switching transistor connected to the primary side winding, and a second switching transistor connected to the secondary side winding;

[0006] The control method includes:

[0007] After the switching power supply is started at high voltage, and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switching transistor.

[0008] When the voltage waveform at the second connection point does not achieve zero voltage switching, the secondary side control module adjusts the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary side winding and the first switching transistor just returns to zero.

[0009] When the voltage waveform at the first connection point returns to zero, the primary side control module controls the first switch to turn on, thereby achieving zero-voltage turn-on of the primary side.

[0010] Optionally, the switching power supply further includes an auxiliary winding and a first voltage divider circuit, wherein the first voltage divider circuit is connected between the auxiliary winding and the voltage detection terminal of the primary side control module;

[0011] When the voltage waveform at the first connection point is exactly zero, the primary-side control module controls the first switch to turn on to achieve zero-voltage turn-on of the primary side. This includes: when the primary-side control module detects that the voltage waveform at the first connection point is exactly zero through the first voltage divider circuit, the primary-side control module controls the first switch to turn on to achieve zero-voltage turn-on of the primary side.

[0012] Optionally, the switching power supply further includes an optocoupler and a second voltage divider circuit. The optocoupler is connected between the current drive port and the optocoupler output port of the secondary side control module, and the second voltage divider circuit is connected between the secondary side winding and the output voltage detection terminal of the secondary side control module.

[0013] The method further includes:

[0014] When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module obtains the output voltage of the switching power supply through the second voltage divider circuit and generates an optocoupler drive signal.

[0015] The optocoupler generates a current feedback signal based on the optocoupler drive signal;

[0016] The primary side control module adjusts the peak current of the first switching transistor according to the current feedback signal, thereby achieving stable loop control of the output voltage of the switching power supply.

[0017] Optionally, it also includes:

[0018] When the load at the output of the switching power supply changes and the switching current of the first switching transistor is less than the second preset value, the primary-side control module controls the switching current of the first switching transistor to remain at the second preset value and changes the frequency of the drive signal of the first switching transistor to adjust the output voltage of the switching power supply.

[0019] Optionally, it also includes:

[0020] When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module adjusts the second switching transistor again to bring the voltage waveform at the first connection point back to zero.

[0021] Optionally, the switching power supply further includes an absorption circuit, which is connected in parallel across the primary winding; the absorption circuit includes a fifth resistor and a first capacitor connected in series.

[0022] Secondly, embodiments of the present invention also provide a switching power supply, including a primary side winding, a secondary side winding, a primary side control module, a secondary side control module, a first switching transistor connected to the primary side winding, and a second switching transistor connected to the secondary side winding.

[0023] The primary winding is used to store energy when the first switch is turned on;

[0024] The secondary winding is used to generate an output voltage when the second switch is turned on;

[0025] The first switch is used to turn on or off according to the drive signal generated by the primary side control module;

[0026] The second switch is used to turn on or off according to the drive signal generated by the secondary side control module;

[0027] The primary side control module is used to control the first switch to turn on when the voltage waveform at the first connection point is exactly zero; it is also used to adjust the peak current of the first switch according to the current feedback signal; it is also used to control the switching current of the first switch to remain at the second preset value and change the frequency of the drive signal of the first switch when the load at the output of the switching power supply changes and the switching current of the first switch is less than the second preset value.

[0028] The secondary-side control module is used to acquire the voltage waveform at the second connection point between the secondary winding and the second switching transistor after the high-voltage start-up of the switching power supply and when the switching time interval of the second switching transistor is equal to or less than a first preset value; it is also used to adjust the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary winding and the first switching transistor returns to zero when the voltage waveform at the second connection point has not achieved zero voltage switching; it is also used to acquire the output voltage of the switching power supply through a second voltage divider circuit and generate an optocoupler drive signal when the output load of the switching power supply changes; and it is also used to adjust the second switching transistor again to make the voltage waveform at the first connection point return to zero when the output load of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value.

[0029] Optionally, it also includes an auxiliary winding and a first voltage divider circuit, the first voltage divider circuit including a first resistor and a second resistor;

[0030] The auxiliary winding is used to provide power to the primary side control module;

[0031] The first voltage divider circuit is used to generate a first voltage divider signal so that the primary side control module can obtain the voltage waveform of the first connection point.

[0032] Optionally, it also includes an optocoupler and a second voltage divider circuit, the second voltage divider circuit including a third resistor and a fourth resistor;

[0033] The optocoupler is used to generate a current feedback signal based on the optocoupler drive signal;

[0034] The second voltage divider circuit is used to generate a second voltage divider signal so that the secondary-side control module can obtain the output voltage of the switching power supply.

[0035] Optionally, it also includes an absorption circuit, which includes a fifth resistor and a first capacitor connected in series.

[0036] This invention provides a control method and a switching power supply for a switching power supply. The method includes: after the switching power supply is started at high voltage, and when the switching time interval of the second switching transistor is equal to or less than a first preset value, a secondary-side control module acquires the voltage waveform of the second connection point between the secondary winding and the second switching transistor; when the voltage waveform of the second connection point does not achieve zero-voltage switching, the secondary-side control module adjusts the cutoff current of the second switching transistor until the voltage waveform of the first connection point between the primary winding and the first switching transistor is exactly zero; when the voltage waveform of the first connection point is exactly zero, the primary-side control module controls the first switching transistor to conduct, so as to achieve zero-voltage start-up of the primary side.

[0037] Compared to existing typical flyback AC-DC isolated switching power supplies, the embodiments of the present invention do not add additional control links or circuit structures, thus not increasing the circuit cost or control complexity of the switching power supply. Furthermore, typical flyback AC-DC isolated switching power supplies cannot achieve zero-voltage switching (ZVS). The embodiments of the present invention use a secondary-side control module to acquire the voltage waveform at the second connection point and adjust the cutoff current of the second switching transistor; the primary-side control module controls the first switching transistor to conduct when the voltage waveform at the first connection point is exactly zero, ultimately achieving ZVS in the switching power supply. This not only reduces the switching losses of the switching power supply but also improves its EMI characteristics.

[0038] Compared with existing active clamped flyback AC-DC isolated switching power supplies, the embodiments of the present invention do not require additional control links and corresponding hardware circuit structures, thus the circuit structure is simple, easy to control, and has a low cost. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of a switching power supply provided in an embodiment of the present invention;

[0040] Figure 2 This is a flowchart of a control method for a switching power supply provided in an embodiment of the present invention;

[0041] Figure 3 This is a flowchart of another control method for a switching power supply provided in an embodiment of the present invention;

[0042] Figure 4 This is a flowchart of another control method for a switching power supply provided in an embodiment of the present invention;

[0043] Figure 5 This is a waveform diagram of a switching power supply provided in an embodiment of the present invention. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0045] Figure 1 This is a schematic diagram of a switching power supply provided in an embodiment of the present invention. Figure 2 This is a flowchart of a control method for a switching power supply provided in an embodiment of the present invention. This embodiment is applicable to power supply scenarios for any device with a typical flyback AC-DC isolated switching power supply structure. The method can be, but is not limited to, executed by the switching power supply in this embodiment as the execution subject, which can be implemented in software and / or hardware. The switching power supply includes a primary winding X1, a secondary winding X2, a primary control module K1, a secondary control module K2, a first switching transistor M1 connected to the primary winding X1, a second switching transistor M2 connected to the secondary winding X2, a first connection point A between the primary winding X1 and the first switching transistor M1, and a second connection point B between the secondary winding X2 and the second switching transistor M2. Figure 2 As shown, the method specifically includes the following steps:

[0046] Step 110: After the switching power supply is started at high voltage, and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switching transistor.

[0047] The high-voltage startup method of the switching power supply can be to obtain power from the bus voltage through the existing high-voltage startup circuit of the switching power supply. The setting method of the first preset value can be the initial setting of the switching power supply or it can be set by the user. The switching time interval of the second switching transistor M2 refers to the time interval between the turn-off and turn-on of the second switching transistor M2.

[0048] Understandably, after the switching power supply starts at high voltage, it will adaptively change its output voltage according to the changes in the output load. If the switching time interval of the second switching transistor M2 is equal to or less than the first preset value, it indicates that the current load impedance is too low, the current flowing through the load is large, and the switching power supply is operating under heavy load. Therefore, the switching time interval of the second switching transistor M2 being equal to or less than the first preset value means that the switching power supply is under heavy load.

[0049] Step 120: When the voltage waveform at the second connection point does not achieve zero voltage switching, the secondary side control module adjusts the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary side winding and the first switching transistor just returns to zero.

[0050] The cutoff current of the second switching transistor refers to its turn-off current. The adjustment process of the cutoff current of the second switching transistor M2 can be an increase, a decrease, an initial increase followed by a decrease, an initial decrease followed by an increase, or any kind of repeated oscillation adjustment process. The adjustment process of the cutoff current of the second switching transistor M2 can be adapted to the specific settings and parameter selection of the switching power supply; this embodiment of the invention does not impose any limitations on this.

[0051] Step 130: When the voltage waveform at the first connection point is exactly zero, the primary side control module controls the first switch to turn on, so as to achieve zero-voltage turn-on of the primary side.

[0052] In this embodiment, since the switching power supply has a typical flyback AC-DC isolated switching power supply structure, the first switching transistor M1 and the second switching transistor M2 cannot be turned on at the same time.

[0053] For example, see Figure 1 It is understandable that the turn-off process of the first switching transistor is as follows:

[0054] The primary-side control module K1 acquires the feedback signal from the optocoupler P to generate a voltage reference value corresponding to the peak current of the first switch M1 at its source. When the voltage value at the source of the first switch M1 reaches the voltage reference value, the primary-side control module K1 controls the first switch M1 to turn off.

[0055] This invention provides a control method and a switching power supply for a switching power supply. The method includes: after the switching power supply is started at high voltage, and when the switching time interval of the second switching transistor is equal to or less than a first preset value, a secondary-side control module acquires the voltage waveform of the second connection point between the secondary winding and the second switching transistor; when the voltage waveform of the second connection point does not achieve zero-voltage switching, the secondary-side control module adjusts the cutoff current of the second switching transistor until the voltage waveform of the first connection point between the primary winding and the first switching transistor is exactly zero; when the voltage waveform of the first connection point is exactly zero, the primary-side control module controls the first switching transistor to conduct, so as to achieve zero-voltage start-up of the primary side.

[0056] Compared to existing typical flyback AC-DC isolated switching power supplies, the embodiments of the present invention do not add additional control links or circuit structures, thus not increasing the circuit cost or control complexity of the switching power supply. Furthermore, typical flyback AC-DC isolated switching power supplies cannot achieve zero-voltage switching (ZVS). The embodiments of the present invention configure a secondary-side control module K2 to acquire the voltage waveform at the second connection point B and adjust the cutoff current of the second switching transistor M2; the primary-side control module K1 controls the first switching transistor M1 to conduct when the voltage waveform at the first connection point A is exactly zero, ultimately achieving ZVS in the switching power supply. This not only reduces the switching losses of the switching power supply but also improves its EMI characteristics.

[0057] Compared with existing active clamped flyback AC-DC isolated switching power supplies, the embodiments of the present invention do not require additional control links and corresponding hardware circuit structures, thus the circuit structure is simple, easy to control, and has a low cost.

[0058] Figure 3 This is a flowchart of another control method for a switching power supply provided by an embodiment of the present invention. Optionally, based on the above scheme, the switching power supply further includes an auxiliary winding X3 and a first voltage divider circuit E1, wherein the first voltage divider circuit E1 is connected between the auxiliary winding X3 and the voltage detection terminal of the primary-side control module K1.

[0059] When the voltage waveform at the first connection point is exactly zero, the primary-side control module controls the first switch to turn on, thereby achieving zero-voltage turn-on of the primary side. This includes: when the primary-side control module detects that the voltage waveform at the first connection point is exactly zero through the first voltage divider circuit, the primary-side control module controls the first switch to turn on, thereby achieving zero-voltage turn-on of the primary side.

[0060] Optionally, the switching power supply also includes an optocoupler P and a second voltage divider circuit E2. The optocoupler P is connected between the current drive port and the optocoupler output port of the secondary side control module K2, and the second voltage divider circuit E2 is connected between the secondary side winding X2 and the output voltage detection terminal of the secondary side control module K2.

[0061] Control methods for switching power supplies also include:

[0062] When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module obtains the output voltage of the switching power supply through the second voltage divider circuit and generates an optocoupler drive signal.

[0063] The optocoupler generates a current feedback signal based on the optocoupler drive signal.

[0064] The primary control module adjusts the peak current of the first switching transistor based on the current feedback signal, thereby achieving stable loop control of the output voltage of the switching power supply.

[0065] like Figure 3 As shown, the method specifically includes the following steps:

[0066] Step 210: After the switching power supply is started at high voltage, and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switching transistor.

[0067] Step 220: When the voltage waveform at the second connection point does not achieve zero voltage switching, the secondary side control module adjusts the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary side winding and the first switching transistor just returns to zero.

[0068] Step 230: When the primary side control module detects that the voltage waveform at the first connection point is exactly zero through the first voltage divider circuit, the primary side control module controls the first switch to turn on, so as to realize the zero-voltage start-up of the primary side.

[0069] In a typical flyback AC-DC isolated switching power supply circuit structure, since the voltage detection terminal of the primary side control module K1 is not directly connected to the first connection point A, the primary side control module K1 cannot directly obtain the voltage waveform of the first connection point A.

[0070] Based on this, a typical flyback AC-DC isolated switching power supply sets up an auxiliary winding X3 and a first voltage divider circuit E1. By connecting the first voltage divider circuit E1 between the auxiliary winding X3 and the voltage detection terminal of the primary side control module K1, the voltage waveform of the first connection point A can be indirectly obtained.

[0071] For example, in other embodiments, when the primary side control module K1 detects that the voltage waveform of the first connection point A is close to zero through the first voltage divider circuit E1, the primary side control module K1 controls the first switch M1 to turn on, so as to realize the zero voltage turn-on of the primary side.

[0072] Step 240: When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module obtains the output voltage of the switching power supply through the second voltage divider circuit and generates an optocoupler drive signal.

[0073] It is understood that the optocoupler driving signal can be any current signal, and the specific current magnitude of the optocoupler driving signal is related to the specific model and structural parameters of the optocoupler P. This embodiment of the invention does not impose any restrictions on this.

[0074] Step 250: The optocoupler generates a current feedback signal based on the optocoupler drive signal.

[0075] It is understood that the current feedback signal can be any current signal, and the specific value of the current feedback signal is related to the specific model and structural parameters of the optocoupler P. This embodiment of the invention does not impose any restrictions on this.

[0076] Step 260: The primary side control module adjusts the peak current of the first switching transistor according to the current feedback signal, thereby realizing stable loop control of the output voltage of the switching power supply.

[0077] It can be understood that when the load at the output of the switching power supply changes and the switching time interval of the second switching transistor M2 is equal to or less than the first preset value, it means that the switching power supply is in a heavy-load state and the load at its output has changed. In this case, the secondary-side control module K2 needs to control the primary-side control module K1 to change the output voltage of the switching power supply, thereby achieving controllable adjustment of the output voltage.

[0078] Based on this, firstly, the secondary-side control module K2 directly calculates the output voltage of the switching power supply through the second voltage divider circuit E2 connected between the secondary-side winding X2 and the output voltage detection terminal of the secondary-side control module K2, and generates a corresponding optocoupler drive signal to drive the optocoupler P. Secondly, the optocoupler P generates a current feedback signal based on the optocoupler drive signal. Finally, the primary-side control module K1 can adjust the peak current of the first switching transistor M1 by adjusting the conduction time of the first switching transistor M1 based on the current feedback signal, thereby achieving stable loop control of the output voltage of the switching power supply.

[0079] Building upon the ZVS (Zero Voltage Regulator) implementation in the above embodiments, this embodiment enables stable loop control of the switching power supply's output voltage even when the power supply is under heavy load and the output load changes. Compared to existing technologies, this embodiment reduces switching losses and improves EMI characteristics of the switching power supply without increasing additional circuit costs or control complexity.

[0080] Figure 4 This is a flowchart of another control method for a switching power supply provided by an embodiment of the present invention. Optionally, based on the above scheme, the switching power supply further includes an absorption circuit Q, which is connected in parallel across the primary winding X1; the absorption circuit Q includes a fifth resistor R5 and a first capacitor C1 connected in series.

[0081] Optionally, the control method further includes:

[0082] When the load at the output of the switching power supply changes and the switching current of the first switching transistor is less than the second preset value, the primary side control module controls the switching current of the first switching transistor to remain at the second preset value and changes the frequency of the drive signal of the first switching transistor to adjust the output voltage of the switching power supply.

[0083] Optionally, the control method further includes:

[0084] When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module adjusts the second switching transistor again to bring the voltage waveform at the first connection point back to zero.

[0085] like Figure 4 As shown, the control method specifically includes the following steps:

[0086] Step 310: After the switching power supply is started at high voltage, and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switching transistor.

[0087] Step 320: When the voltage waveform at the second connection point does not achieve zero voltage switching, the secondary side control module adjusts the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary side winding and the first switching transistor just returns to zero.

[0088] Step 330: When the primary side control module detects that the voltage waveform at the first connection point is exactly zero through the first voltage divider circuit, the primary side control module controls the first switch to turn on, so as to realize the zero-voltage start-up of the primary side.

[0089] Step 340: When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module obtains the output voltage of the switching power supply through the second voltage divider circuit and generates an optocoupler drive signal.

[0090] Step 350: The optocoupler generates a current feedback signal based on the optocoupler drive signal.

[0091] Step 360: The primary side control module adjusts the peak current of the first switching transistor according to the current feedback signal, thereby realizing stable loop control of the output voltage of the switching power supply.

[0092] Step 370: When the load at the output of the switching power supply changes and the switching current of the first switching transistor is less than the second preset value, the primary side control module controls the switching current of the first switching transistor to remain at the second preset value and changes the frequency of the drive signal of the first switching transistor to adjust the output voltage of the switching power supply.

[0093] The second preset value can be set either as the initial setting of the power supply or as a user-defined setting.

[0094] It is understandable that a change in the output load of the switching power supply, and the fact that the switching current of the first switching transistor M1 is less than the second preset value, means that the switching power supply has switched from a heavy-load state to a light-load state due to the change in output load. Based on this, when the switching power supply switches to a light-load state, the primary-side control module K1 controls the switching current of the first switching transistor M1 to maintain it at the second preset value, and adjusts the output voltage of the switching power supply by changing the drive signal frequency of the first switching transistor M1 according to the signal fed back from the optocoupler P. In other words, the efficiency of the switching power supply is optimized through frequency regulation.

[0095] For example, step 370 can be implemented in the following ways:

[0096] When the load at the output of the switching power supply changes and the switching current of the first switching transistor M1 is less than the second preset value, the primary-side control module K1 controls the switching current of the first switching transistor M1 to remain near the second preset value based on an appropriate anti-jitter threshold, thereby keeping the peak current and source reference voltage of the first switching transistor M1 in a steady state. Then, the primary-side control module K1 adaptively changes the time interval for the first switching transistor M1 to turn on based on the feedback signal from the optocoupler P at this time, adjusting the output voltage of the switching power supply in a frequency regulation manner.

[0097] Step 380: When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module adjusts the second switching transistor again to bring the voltage waveform at the first connection point back to zero.

[0098] The phrase "the output load of the switching power supply changes, and the switching time interval of the second switching transistor M2 is equal to or less than the first preset value" means that due to the change in the output load, the switching time interval of the second switching transistor M2 changes from being greater than the first preset value to being equal to or less than the first preset value, and the switching power supply changes from a light-load state to a heavy-load state. It is understandable that at this time, the secondary-side control module K2 needs to repeat steps 310 to 320 to readjust the voltage waveform at the first connection point A back to zero.

[0099] In summary, based on the above embodiments that achieve ZVS (Zero-Voltage Switching) under heavy load conditions and maintain a steady-state output voltage, this embodiment can optimize the efficiency of the switching power supply under light load conditions by adjusting the frequency when the switching power supply transitions from a heavy load state to a light load state. Furthermore, when the switching power supply transitions from a light load state to a heavy load state, this embodiment can readjust the voltage waveform at the first connection point A to zero, achieving ZVS again. Compared with existing technologies, the technical solution of this embodiment, without increasing additional circuit costs or control complexity, can achieve real-time switching between light load frequency adjustment and heavy load ZVS modes based on changes in the output load of the switching power supply. This not only reduces switching losses but also improves the EMI characteristics of the switching power supply.

[0100] See also Figure 1 The switching power supply includes a primary winding X1, a secondary winding X2, a primary control module K1, a secondary control module K2, a first switching transistor M1 connected to the primary winding X1, a second switching transistor M2 connected to the secondary winding X2, a first connection point A between the primary winding X1 and the first switching transistor M1, and a second connection point B between the secondary winding X2 and the second switching transistor M2.

[0101] The primary winding X1 is used to store energy when the first switch M1 is turned on.

[0102] The secondary winding X2 is used to generate the output voltage when the second switch M2 is turned on.

[0103] The first switch M1 is used to turn on or off according to the drive signal generated by the primary side control module K1.

[0104] The second switch M2 is used to turn on or off according to the drive signal generated by the secondary side control module K2.

[0105] The primary side control module K1 is used to control the first switch M1 to turn on when the voltage waveform at the first connection point A is exactly zero; it is also used to adjust the peak current of the first switch M1 according to the current feedback signal; it is also used to control the switching current of the first switch M1 to remain at the second preset value and change the frequency of the drive signal of the first switch M1 when the load at the output of the switching power supply changes and the switching current of the first switch M1 is less than the second preset value.

[0106] The secondary-side control module K2 is used to acquire the voltage waveform at the second connection point B between the secondary winding X2 and the second switching transistor M2 after the high-voltage start-up of the switching power supply and when the switching time interval of the second switching transistor M2 is equal to or less than the first preset value; it is also used to adjust the cutoff current of the second switching transistor M2 until the voltage waveform at the first connection point A between the primary winding X1 and the first switching transistor M1 is exactly zero when the voltage waveform at the second connection point B has not achieved zero voltage switching; it is also used to acquire the output voltage of the switching power supply through the second voltage divider circuit E2 and generate an optocoupler drive signal when the output load of the switching power supply changes; it is also used to adjust the second switching transistor M2 again to make the voltage waveform at the first connection point A return to zero when the output load of the switching power supply changes and the switching time interval of the second switching transistor M2 is equal to or less than the first preset value.

[0107] The first connection point A is used to provide the voltage waveform at the connection terminal between the first switching transistor M1 and the primary winding X1.

[0108] The second connection point B is used to provide the voltage waveform at the connection terminal between the second switching transistor M2 and the secondary winding X2.

[0109] In this embodiment, the first switch M1 and the second switch M2 may be, but are not limited to, metal-oxide-semiconductor field-effect transistors (MOSFETs). It is understood that the specific type and structural parameters of the first switch M1 and the second switch M2 are related to the desired power supply effect, and this embodiment of the invention does not impose any limitations on this.

[0110] It is known that the primary side control module K1 can also be used to control the first switch M1 to turn on when the voltage waveform at the first connection point A is close to zero.

[0111] Understandably, the secondary-side control module K2 is also used to adjust the second switching transistor M2 again to bring the voltage waveform at the first connection point A back to zero when the load at the output of the switching power supply changes and the switching time interval of the second switching transistor M2 changes from being greater than the first preset value to being equal to or less than the first preset value.

[0112] Optionally, the switching power supply also includes an auxiliary winding X3 and a first voltage divider circuit E1, wherein the first voltage divider circuit E1 includes a first resistor R1 and a second resistor R2.

[0113] The auxiliary winding X3 is used to provide power to the primary side control module K1.

[0114] The first voltage divider circuit E1 is used to generate the first voltage divider signal so that the primary side control module K1 can obtain the voltage waveform of the first connection point A.

[0115] Optionally, the switching power supply also includes an optocoupler P and a second voltage divider circuit E2, the second voltage divider circuit E2 including a third resistor R3 and a fourth resistor R4.

[0116] The optocoupler P is used to generate a current feedback signal based on the optocoupler drive signal.

[0117] The second voltage divider circuit E2 is used to generate the second voltage divider signal so that the secondary side control module K2 can obtain the output voltage of the switching power supply.

[0118] Optionally, the switching power supply also includes a snubber circuit Q, which includes a fifth resistor R5 and a first capacitor C1 connected in series.

[0119] It is understood that, compared to the clamping and absorption circuits composed of resistors, capacitors and diodes widely used in the prior art, the absorption circuit Q provided in this embodiment of the invention can achieve a simpler clamping and absorption function, further reduce the hardware cost of the switching power supply, optimize the switching loss of the system, and improve the electromagnetic interference characteristics of the switching power supply.

[0120] It should be noted that the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 can be any type of resistor. The types and specific parameters of the above resistors can be adaptively adjusted according to the power supply effect to be achieved by the switching power supply, and this embodiment of the invention does not impose any restrictions on this. For example, all of the above resistors can be surface mount resistors.

[0121] It should also be noted that the first capacitor C1 can be any type of capacitor. The type and specific parameters of this capacitor can be adaptively adjusted according to the power supply effect to be achieved by the switching power supply, and this embodiment of the invention does not impose any restrictions on this. For example, the first capacitor C1 can be a mica capacitor.

[0122] Furthermore, the circuit component connection relationships of the switching power supply based on a typical flyback AC-DC isolated switching power supply topology provided in this embodiment of the invention are as follows: Figure 1 As shown, it will not be elaborated further here.

[0123] See also Figure 1 The working process of a switching power supply is as follows:

[0124] First, after the switching power supply starts at high voltage, and when the switching time interval of the second switching transistor M2 is equal to or less than a first preset value, the secondary-side control module K2 acquires the voltage waveform at the second connection point B. Second, when the voltage waveform at the second connection point B does not achieve zero-voltage switching, the secondary-side control module K2 adjusts the cutoff current of the second switching transistor M2 until the voltage waveform at the first connection point A between the primary winding X1 and the first switching transistor M1 returns to zero. Third, when the voltage waveform at the first connection point A returns to zero, the primary-side control module K1 controls the first switching transistor M1 to conduct, achieving zero-voltage turn-on of the primary side. Fourth, the primary-side control module K1 acquires the feedback signal from the optocoupler P to generate a voltage reference value corresponding to the peak current of the first switching transistor M1's source. When the voltage value at the source of the first switching transistor M1 reaches the voltage reference value, the primary-side control module K1 controls the first switching transistor M1 to turn off. Furthermore, when the load at the output of the switching power supply changes, and the switching time interval of the second switching transistor M2 is equal to or less than the first preset value, the secondary-side control module K2 obtains the output voltage of the switching power supply through the second voltage divider circuit E2 and generates an optocoupler drive signal. Next, the optocoupler P generates a current feedback signal based on the optocoupler drive signal. Then, the primary-side control module K1 adjusts the peak current of the first switching transistor M1 based on the current feedback signal, thereby achieving stable loop control of the switching power supply's output voltage. Again, when the load at the output of the switching power supply changes, and the switching current of the first switching transistor M1 is less than the second preset value, the primary-side control module K1 controls the switching current of the first switching transistor M1 to remain at the second preset value and changes the frequency of the drive signal of the first switching transistor M1 to adjust the output voltage of the switching power supply. Finally, when the load at the output of the switching power supply changes, and the switching time interval of the second switching transistor M2 is equal to or less than the first preset value, the secondary-side control module K2 adjusts the second switching transistor M2 again to bring the voltage waveform at the first connection point A back to zero.

[0125] It should be noted that the secondary side control module K2 in this embodiment of the invention can integrate a typical 431 reference module internally, or can use an external 431 reference module to compare the output voltage of the switching power supply with the module reference voltage provided by the 431 reference module, thereby generating an optocoupler drive signal.

[0126] Figure 5 This is a waveform diagram of a switching power supply provided in an embodiment of the present invention. Refer to the above-described working process of the switching power supply and... Figure 5 It can be seen that when the voltage V at the first connection point A... A When the waveform just returns to zero, the voltage V at the second connection point B is... B The waveform just returned to high, and the voltage V at the third connection point Z... Z The waveform just returns to low. Furthermore, when the second switch M2 is turned off, the switching current I of the second switch M2... S Reaching the cutoff current I S_min This invention enables zero-voltage switching (ZVS) of the power supply under heavy load conditions. While maintaining a steady-state output voltage, when the power supply transitions from a heavy load to a light load state, this embodiment optimizes the power supply efficiency under light load conditions through frequency adjustment. Furthermore, when the power supply transitions from a light load to a heavy load state, this embodiment can readjust the voltage waveform at the first connection point to zero, thus achieving ZVS for the power supply.

[0127] Compared with the prior art, the technical solution of this embodiment can realize real-time switching between light load frequency regulation mode and heavy load ZVS mode according to the load change of the output terminal of the switching power supply without increasing the additional circuit cost and control complexity. This not only reduces the switching loss of the switching power supply, but also improves the EMI characteristics of the switching power supply.

[0128] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A control method for a switching power supply, characterized in that, The switching power supply includes a primary side winding, a secondary side winding, a primary side control module, a secondary side control module, a first switching transistor connected to the primary side winding, and a second switching transistor connected to the secondary side winding. The control method includes: After the switching power supply is started at high voltage, and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module acquires the voltage waveform of the second connection point between the secondary side winding and the second switching transistor. When the voltage waveform at the second connection point does not achieve zero voltage switching, the secondary side control module adjusts the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary side winding and the first switching transistor just returns to zero. When the voltage waveform at the first connection point is exactly zero, the primary side control module controls the first switch to turn on, so as to achieve zero-voltage turn-on of the primary side. The switching power supply also includes an auxiliary winding and a first voltage divider circuit, wherein the first voltage divider circuit is connected between the auxiliary winding and the voltage detection terminal of the primary side control module; When the voltage waveform at the first connection point is exactly zero, the primary side control module controls the first switch to turn on to achieve zero-voltage turn-on of the primary side, including: when the primary side control module detects that the voltage waveform at the first connection point is exactly zero through the first voltage divider circuit, the primary side control module controls the first switch to turn on to achieve zero-voltage turn-on of the primary side. The first voltage divider circuit is used to obtain the voltage waveform at the first connection point; The switching time interval of the second switching transistor being equal to or less than the first preset value indicates that the switching power supply is in a heavy-load state.

2. The method according to claim 1, characterized in that, The switching power supply also includes an optocoupler and a second voltage divider circuit. The optocoupler is connected between the current drive port and the optocoupler output port of the secondary side control module, and the second voltage divider circuit is connected between the secondary side winding and the output voltage detection terminal of the secondary side control module. The method further includes: When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module obtains the output voltage of the switching power supply through the second voltage divider circuit and generates an optocoupler drive signal. The optocoupler generates a current feedback signal based on the optocoupler drive signal; The primary side control module adjusts the peak current of the first switching transistor according to the current feedback signal, thereby achieving stable loop control of the output voltage of the switching power supply.

3. The method according to claim 2, characterized in that, Also includes: When the load at the output of the switching power supply changes and the switching current of the first switching transistor is less than the second preset value, the primary side control module controls the switching current of the first switching transistor to remain at the second preset value and changes the frequency of the drive signal of the first switching transistor to adjust the output voltage of the switching power supply. The fact that the switching current of the first switching transistor is less than the second preset value means that the switching power supply changes from the heavy load state to the light load state due to a change in the output load.

4. The method according to claim 3, characterized in that, Also includes: When the load at the output of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value, the secondary side control module adjusts the second switching transistor again to bring the voltage waveform at the first connection point back to zero.

5. The method according to claim 4, characterized in that, The switching power supply also includes an absorption circuit, which is connected in parallel across the two ends of the primary winding; the absorption circuit includes a fifth resistor and a first capacitor connected in series.

6. A switching power supply, characterized in that, It includes a primary side winding, a secondary side winding, a primary side control module, a secondary side control module, a first switching transistor connected to the primary side winding, and a second switching transistor connected to the secondary side winding; The primary winding is used to store energy when the first switch is turned on; The secondary winding is used to generate an output voltage when the second switch is turned on; The first switch is used to turn on or off according to the drive signal generated by the primary side control module; The second switch is used to turn on or off according to the drive signal generated by the secondary side control module; The primary side control module is used to control the first switch to turn on when the voltage waveform at the first connection point is exactly zero; it is also used to adjust the peak current of the first switch according to the current feedback signal; it is also used to control the switching current of the first switch to remain at the second preset value and change the frequency of the drive signal of the first switch when the load at the output terminal of the switching power supply changes and the switching current of the first switch is less than the second preset value. The secondary-side control module is used to acquire the voltage waveform at the second connection point between the secondary winding and the second switching transistor after the high-voltage start-up of the switching power supply and when the switching time interval of the second switching transistor is equal to or less than a first preset value; it is also used to adjust the cutoff current of the second switching transistor until the voltage waveform at the first connection point between the primary winding and the first switching transistor returns to zero when the voltage waveform at the second connection point has not achieved zero voltage switching; it is also used to acquire the output voltage of the switching power supply through a second voltage divider circuit and generate an optocoupler drive signal when the output load of the switching power supply changes; and it is also used to adjust the second switching transistor again to make the voltage waveform at the first connection point return to zero when the output load of the switching power supply changes and the switching time interval of the second switching transistor is equal to or less than the first preset value. It also includes an auxiliary winding and a first voltage divider circuit, wherein the first voltage divider circuit includes a first resistor and a second resistor; The auxiliary winding is used to provide power to the primary side control module; The first voltage divider circuit is used to generate a first voltage divider signal so that the primary side control module can obtain the voltage waveform of the first connection point.

7. The switching power supply according to claim 6, characterized in that, It also includes an optocoupler and a second voltage divider circuit, the second voltage divider circuit including a third resistor and a fourth resistor; The optocoupler is used to generate a current feedback signal based on the optocoupler drive signal; The second voltage divider circuit is used to generate a second voltage divider signal so that the secondary-side control module can obtain the output voltage of the switching power supply.

8. The switching power supply according to claim 7, characterized in that, It also includes an absorption circuit, which comprises a fifth resistor and a first capacitor connected in series.

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