A start-up control method and start-up control device for a flyback converter

Abstract

The application discloses a starting control method and device of a flyback converter. The method comprises the following steps: in a first working mode, a first control signal controls a primary side switch unit to be off, and a second control signal controls an auxiliary switch unit to be off; in a second working mode, the first control signal controls the primary side switch unit to be soft-started, and the second control signal controls the auxiliary switch unit to be off; and in a third working mode, the first control signal controls the primary side switch unit to work, the second control signal controls the auxiliary switch unit to be soft-started, and the turn-on time of the auxiliary switch unit is increased from a first turn-on time to a second turn-on time according to the second control signal. The application controls the turn-on time sequence and the turn-on time of the primary side switch unit and the auxiliary switch unit, thereby effectively solving the problem of excessive stress of the auxiliary switch unit in the starting process, and further improving the working reliability of the flyback converter.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to a start-up control method and start-up control device for a flyback converter. Background Technology

[0002] Flyback converters are widely used in small and medium power switching power supplies due to their low cost and simple topology. To improve the efficiency of flyback converters, a common method is to achieve zero-voltage switching (ZVS) on the primary-side switching transistors. Figure 1 This is a flyback converter circuit in the prior art that designs the auxiliary winding rectifier unit as a controllable auxiliary switching unit, and requires separate control of the primary-side switching unit and the auxiliary switching unit.

[0003] like Figure 2 The existing flyback converter startup control strategy is as follows: During time period T1, both the primary-side switching unit and the auxiliary switching unit are turned off; at the end of time period T1 and the beginning of time period T2, since the output voltage has not been established at this time, the second control signal will turn off the auxiliary switching transistor to prevent the charge of the auxiliary energy storage capacitor from being released. At this time, the first control signal controls the primary-side switching unit to soft-start, and the output voltage gradually rises; at the end of time period T2 and the beginning of time period T3, the second control signal controls the auxiliary switching transistor to be turned on for a set time, which satisfies the requirement of achieving ZVS under steady state.

[0004] In practical research, it was found that in low-voltage, high-current converter output applications, such as 5V / 12A, the auxiliary winding cannot be fully coupled with the primary and secondary windings, and the start-up transient current often exceeds the steady-state current. This situation causes a continuous increase in the voltage on the auxiliary energy storage capacitor even when the auxiliary switching unit has not started working. Therefore, when the first time period ends and the second time period begins, such as... Figure 3 The diagram shows the detailed waveform at the beginning of time period T2. Because the voltage accumulated on the auxiliary energy storage capacitor during the first time period is sufficiently high, exceeding the voltage on the auxiliary energy storage capacitor during steady-state operation, the second control signal controls the clamping transistor to turn on according to the conduction time set for steady-state operation. This will cause an excessively large negative current to be generated during the first auxiliary switch's turn-on cycle. Figure 3 As shown in the t3 to t4 time period, this causes excessive stress on the start-up auxiliary switch unit. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a start-up control method and start-up control device for a flyback converter that can achieve zero-voltage switching on the primary side, so as to solve the problem of excessive stress on the auxiliary switching unit when the auxiliary switching unit starts working during the start-up process of the existing flyback converter, and further improve the working reliability of the flyback converter.

[0006] To solve the above-mentioned technical problems, the present invention proposes the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a start-up control method for a flyback converter, the flyback converter comprising: a primary-side input capacitor, a primary-side switching unit, a clamping unit, a primary-side winding, a secondary-side winding, a secondary-side rectifier unit, a secondary-side output capacitor, and an auxiliary switching unit, the start-up control method comprising the following steps:

[0008] In the first operating mode, the first control signal controls the primary-side switching unit to turn off, and the second control signal controls the auxiliary switching unit to turn off.

[0009] In the second operating mode, the first control signal controls the primary-side switching unit to soft start, and the second control signal controls the auxiliary switching unit to turn off;

[0010] In the third operating mode, the first control signal controls the primary side switching unit to operate, the second control signal controls the auxiliary switching unit to soft start, and according to the second control signal, the turn-on time of the auxiliary switching unit is increased from the first conduction time to the second conduction time, wherein the second conduction time is greater than the first conduction time.

[0011] The first control signal and the second control signal operate in the same switching cycle.

[0012] Furthermore, in the second operating mode, the first control signal controls the primary-side switching unit to soft-start, and the second control signal controls the auxiliary switching unit to turn off, further comprising:

[0013] The frequency of the first control signal remains unchanged, and the duty cycle of the first control signal is gradually increased to the preset duty cycle value.

[0014] Alternatively, the duty cycle of the first control signal remains unchanged, and the switching frequency of the first control signal is gradually increased to a preset value.

[0015] Alternatively, the duty cycle of the first control signal can be gradually increased to a preset duty cycle value, and the switching frequency of the first control signal can be gradually increased to a preset switching frequency value.

[0016] Furthermore, the step of increasing the on-time of the auxiliary switch unit from the first on-time to the second on-time according to the second control signal specifically involves:

[0017] The second control signal controls the turn-on time of the auxiliary switch unit to increase linearly from the first turn-on time to the second turn-on time;

[0018] Alternatively, the second control signal controls the turn-on time of the auxiliary switch unit to be adjusted to the first conduction time, and after a preset number of switching cycles, the turn-on time is linearly increased from the first conduction time to the second conduction time;

[0019] Alternatively, the second control signal controls the auxiliary switch unit to adjust the turn-on time to the first conduction time, and after a preset number of switching cycles, adjusts the turn-on time to the second conduction time.

[0020] Furthermore, in each switching cycle of the third operating mode, the second control signal controls the auxiliary switching unit to turn off after a preset conduction time, and after a set dead time, the first control signal controls the primary-side switching unit to turn on.

[0021] Furthermore, it also includes:

[0022] In the fourth operating mode, the second control signal controls the auxiliary switch unit to turn on for a first conduction time and then turn off. After a set dead time, the first control signal controls the primary-side switch unit to turn on with zero voltage.

[0023] Furthermore, it also includes:

[0024] In the fourth operating mode, the second control signal controls the turn-on time of the auxiliary switch unit to be adjusted according to the voltage difference between the two ends of the primary-side switch unit before it is turned on.

[0025] Furthermore, the second control signal controls the turn-on time of the auxiliary switching unit to be adjusted according to the voltage difference between the two ends of the primary-side switching unit before it is turned on, specifically as follows:

[0026] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is greater than the first voltage threshold, then the turn-on time of the auxiliary switching unit is increased in the next switching cycle.

[0027] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is equal to the first voltage threshold, then the turn-on time of the auxiliary switching unit remains unchanged in the next switching cycle.

[0028] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is less than a first voltage threshold, then the turn-on time of the auxiliary switching unit is reduced in the next switching cycle.

[0029] Furthermore, it also includes:

[0030] According to preset switching conditions, the flyback converter in the second working mode is controlled to enter the third working mode.

[0031] Furthermore, the step of controlling the flyback converter in the second operating mode to enter the third operating mode according to preset switching conditions specifically includes:

[0032] Once the output voltage of the flyback converter is determined to be greater than or equal to a set voltage threshold, the flyback converter enters the third operating mode.

[0033] or,

[0034] Once the operating time of the flyback converter in the second operating mode reaches the switching time, the flyback converter enters the third operating mode.

[0035] Secondly, embodiments of the present invention also provide a start-up control device for a flyback converter, the flyback converter comprising: a primary-side input capacitor, a primary-side switching unit, a clamping unit, a primary-side winding, a secondary-side winding, a secondary-side rectifier unit, a secondary-side output capacitor, and an auxiliary switching unit, the start-up control device comprising:

[0036] A first mode unit is configured to, in a first operating mode, control the primary-side switching unit to turn off with the first control signal and control the auxiliary switching unit to turn off with the second control signal.

[0037] The second mode unit is used in the second operating mode, where the first control signal controls the primary side switching unit to soft start, and the second control signal controls the auxiliary switching unit to turn off.

[0038] The third mode unit is used in the third working mode, where the first control signal controls the primary side switch unit to work, the second control signal controls the auxiliary switch unit to soft start, and the second control signal controls the turn-on time of the auxiliary switch unit to increase from the first conduction time to the second conduction time according to the second control signal, wherein the second conduction time is greater than the first conduction time.

[0039] The first control signal and the second control signal operate in the same switching cycle.

[0040] The beneficial effects of this invention are as follows:

[0041] The present invention discloses a start-up control method and start-up control device for a flyback converter. By controlling the turn-on sequence and turn-on time of the primary-side switching unit and the auxiliary switching unit in the flyback converter, it can not only effectively solve the problem of excessive stress in the auxiliary switching unit during the start-up process, but also further improve the working reliability of the flyback converter. Attached Figure Description

[0042] Figure 1This is a circuit diagram of an existing flyback converter in which the auxiliary winding-side rectifier tube is designed as a controllable switch.

[0043] Figure 2 The waveform diagram shows the operation of a current start-up control method for an auxiliary winding-side switching unit.

[0044] Figure 3 The waveform diagram for starting up an existing auxiliary winding-side switching unit is shown.

[0045] Figure 4 This is a flowchart of the start-up control method in this invention;

[0046] Figure 5 This is a control flowchart of a preferred embodiment of the present invention;

[0047] Figure 6 This is a waveform diagram of the circuit control operation according to a preferred embodiment of the present invention;

[0048] Figure 7 This is a control timing diagram of a preferred embodiment of the present invention;

[0049] Figure 8 This is a control timing diagram of a preferred embodiment of the present invention;

[0050] Figure 9 This is a control timing diagram of a preferred embodiment of the present invention;

[0051] Figure 10 This is a schematic diagram of experimental results from a preferred embodiment of the present invention;

[0052] Figure 11 This is a block diagram of the start-up control device in this invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0054] The circuit of the flyback converter used in this application is as follows: Figure 1 As shown, it specifically includes: primary side input capacitor, primary side switching unit, current sampling unit, clamping unit, primary side winding, secondary side winding, secondary side rectifier unit, secondary side output capacitor and auxiliary switching unit.

[0055] The first terminal of the primary-side capacitor is connected to the first terminal of the primary-side winding, and the second terminal of the primary-side capacitor is connected to reference ground; the second terminal of the primary-side winding is connected to the first terminal of the primary-side switching unit, the second terminal of the primary-side switching unit is connected to reference ground, and the third terminal of the primary-side switching unit receives a first control signal; the first terminal of the secondary-side winding is connected to the first terminal of the secondary-side rectifier unit, the second terminal of the secondary-side winding is connected to the first terminal of the secondary-side output capacitor, and the second terminal of the secondary-side rectifier unit is connected to the second terminal of the secondary-side output capacitor;

[0056] The clamping unit has a first end connected to the first end of the primary winding and a second end connected to the second end of the primary winding. The auxiliary power supply unit includes an auxiliary winding, an auxiliary switching unit, and an auxiliary energy storage capacitor. The first end of the auxiliary winding is connected to the first end of the auxiliary switching unit, the second end of the auxiliary winding is connected to the first end of the auxiliary energy storage capacitor, the second end of the auxiliary switching unit is connected to the second end of the auxiliary energy storage capacitor, and the third end of the auxiliary switching unit receives a second control signal.

[0057] The clamping unit can be an RCD clamping circuit or an active clamping circuit; the secondary-side rectifier unit can be a diode rectifier or a synchronous rectifier. When it is a synchronous rectifier, the secondary-side rectifier unit also has a third terminal, which receives a third control signal.

[0058] The inventive concept of this application is that during the startup process of a flyback converter, in the first time period, the first control signal and the second control signal respectively control the primary-side switching unit and the auxiliary switching unit to be turned off. When the first time period ends and the second time period begins, the first control signal controls the primary-side switching unit to be soft-started, while the second control signal controls the auxiliary switching unit to remain off. When the second time period ends and the third time period begins, the second control signal controls the auxiliary switching unit to be soft-started, and the conduction time of the auxiliary switching unit is gradually increased to the set turn-on time.

[0059] Typical embodiments embodying the features and advantages of this disclosure will be described in detail in the following description in conjunction with the accompanying drawings. It should be understood that this disclosure can have various variations in different embodiments, all of which do not depart from the scope of this disclosure, and the description and drawings herein are intended to illustrate these variations and not to limit this disclosure.

[0060] Furthermore, the accompanying drawings disclosed in this application are merely illustrative diagrams of various embodiments and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Since this invention involves numerous signal codes, etc., they are collectively described below:

[0061] Vds_Q1: Drain-source voltage of the primary-side power switch;

[0062] Vds_Q2: Drain-source voltage of the auxiliary switching transistor;

[0063] V_c: Voltage of auxiliary energy storage capacitor;

[0064] I_Lm: Primary side electromagnetic current;

[0065] T1: First working mode time period;

[0066] T2: Second working mode time period;

[0067] T3: Third work mode time period;

[0068] T3a: The first time period in the third work mode time period;

[0069] Ton_DRV2: On-time of the second control signal;

[0070] DRV1: First control signal, used to control the on / off state of primary-side switching unit Q1;

[0071] DRV2: Second control signal, used to control the on / off state of auxiliary switch unit Q2.

[0072] refer to Figure 4 This invention provides a start-up control method for a flyback converter, which specifically includes the following steps:

[0073] S101. In the first operating mode, the first control signal controls the primary-side switching unit to turn off, and the second control signal controls the auxiliary switching unit to turn off.

[0074] S102. In the second operating mode, the first control signal controls the primary-side switching unit to start softly, and the second control signal controls the auxiliary switching unit to turn off.

[0075] S103. In the third working mode, the first control signal controls the primary side switch unit to work, the second control signal controls the auxiliary switch unit to start softly, and according to the second control signal, the turn-on time of the auxiliary switch unit is increased from the first conduction time to the second conduction time, and the second conduction time is greater than the first conduction time.

[0076] The first control signal and the second control signal operate in the same switching cycle.

[0077] Specifically, Figure 5 A flowchart of one embodiment of the startup control method for a flyback converter according to the present invention is shown.

[0078] Initially, the flyback converter operates in the first operating mode, where the first control signal DRV1 controls the primary-side switching unit Q1 to turn off, and the second control signal DRV2 controls the auxiliary switching unit Q2 to also turn off.

[0079] Furthermore, after the first operating mode ends, the flyback converter enters the second operating mode. The first control signal DRV1 controls the primary-side switching unit Q1 to soft-start. At this time, the frequency or duty cycle of the primary-side switching unit Q1 is gradually increased, and the output voltage rises. However, at this time, the second control signal controls DRV2 to control the auxiliary switching unit Q2 to remain off.

[0080] Furthermore, when the output voltage increases to the set voltage threshold, or when the working time of the second working mode reaches the set switching time, the second working mode ends and enters the third working mode.

[0081] Furthermore, upon the end of the second operating mode, the flyback converter enters the third operating mode. The second control signal controls DRV2 to soft-start the auxiliary switching unit Q2, increasing the conduction time of the auxiliary switching unit Q2 to the final steady-state operating duration. The second control signal DRV2 and the first control signal DRV1 operate within the same switching cycle.

[0082] Specifically, Figure 6 The diagram shows the operating waveforms of a start-up control method for a flyback converter according to the present invention.

[0083] During time period T1, the flyback converter operates in the first operating mode. The first control signal DRV1 controls the primary-side switching unit Q1 to turn off, and the second control signal DRV2 controls the auxiliary switching unit Q2 to also turn off. At this time, the flyback converter has not started working.

[0084] When the T1 time period ends and the T2 working time period begins, the flyback converter enters the second working mode. The first control signal DRV1 controls the primary side switching unit Q1 to soft start. At this time, the frequency or duty cycle of the primary side switching unit Q1 is gradually increased, and the output voltage rises. However, at this time, the second control signal DRV2 controls the auxiliary switching unit Q2 to remain off.

[0085] The T2 working period ends when the output voltage increases to the set voltage threshold, or when the working time of the second working mode reaches the set switching time.

[0086] When the T2 operating period ends and the T3 operating period begins, the flyback converter enters the third operating mode. The second control signal controls DRV2 to soft-start the auxiliary switching unit Q2, increasing the on-time of the auxiliary switching unit Q2 from the first on-time to the second on-time. The second control signal DRV2 and the first control signal DRV1 operate within the same switching cycle, and their waveforms are shown below. Figure 2 Consistent.

[0087] Specifically, Figure 7 A timing diagram of the startup control method for a flyback converter according to the present invention is shown;

[0088] During the T3 time period, when the flyback converter enters the third operating mode, the second control signal controls the conduction time of the auxiliary switching unit to increase linearly from the first turn-on time to the second turn-on time.

[0089] Specifically, Figure 7 A timing diagram of the startup control method for a flyback converter according to the present invention is shown;

[0090] During time period T3, when the flyback converter enters the third operating mode, the second control signal controls the auxiliary switching unit to conduct for a first turn-on time within time period T3a. After time period T3a ends, the second control signal controls the auxiliary switching unit to linearly increase its conduction time from the first turn-on time to the second conduction time.

[0091] Specifically, in another embodiment, Figure 8 A timing diagram of the startup control method for a flyback converter according to the present invention is shown.

[0092] During time period T3, when the flyback converter enters the third operating mode, the second control signal controls the auxiliary switching unit to have a first turn-on time during time period T3a. After time period T3a ends, the second control signal controls the auxiliary switching unit to have a second turn-on time.

[0093] Specifically, Figure 10 The results shown are a comparison of actual debugging using the present invention and existing solutions. Using the solution of the present invention, the maximum stress of the auxiliary switching unit during startup is much smaller than that of the existing solution, effectively solving the problem of excessive stress in the auxiliary switching unit during startup. Furthermore, in practical applications, switching devices with a lower Vds_max withstand voltage can be selected, which greatly improves the compatibility of the devices.

[0094] Therefore, the control strategy of the present invention can effectively solve the problem of excessive voltage stress across the auxiliary switching unit Q2 at the start-up time of the flyback converter, and improve the safety and reliability of the flyback converter in transient operation.

[0095] In one embodiment, during each switching cycle of the third operating mode, the second control signal controls the auxiliary switching unit to turn off after a preset conduction time, and after a set dead time, the first control signal controls the primary-side switching unit to turn on.

[0096] In one embodiment, the method further includes: the flyback converter enters a fourth operating mode after the third operating mode ends;

[0097] In the fourth operating mode, the second control signal controls the auxiliary switch unit to turn on for a first conduction time and then turn it off. After a set dead time, the first control signal controls the primary-side switch unit to turn on with zero voltage.

[0098] Specifically, in another embodiment, when the flyback converter is in the fourth operating mode, the second control signal controls the turn-on time of the auxiliary switching unit to be adjusted according to the voltage difference between the two ends of the primary-side switching unit before it is turned on. The main function is to adaptively adjust the conduction time so that ZVS conduction can be achieved under all operating conditions, as follows:

[0099] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is greater than the first voltage threshold, then the turn-on time of the auxiliary switching unit is increased in the next switching cycle.

[0100] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is equal to the first voltage threshold, then the turn-on time of the auxiliary switching unit remains unchanged in the next switching cycle.

[0101] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is less than a first voltage threshold, then the turn-on time of the auxiliary switching unit is reduced in the next switching cycle.

[0102] In this embodiment, by using the fourth operating mode, the energy stored in this part is refracted to the primary side within a preset dead time to inject into the resonance process of the parasitic capacitance of the main power transistor and the primary side inductance, thereby further releasing the remaining energy on the parasitic capacitance and realizing zero-voltage conduction of the primary side power switch, effectively reducing switching losses.

[0103] refer to Figure 11This invention also provides a start-up control device for a flyback converter, the flyback converter comprising: a primary-side input capacitor, a primary-side switching unit, a clamping unit, a primary-side winding, a secondary-side winding, a secondary-side rectifier unit, a secondary-side output capacitor, and an auxiliary switching unit, characterized in that the start-up control device comprises:

[0104] A first mode unit is configured to, in a first operating mode, control the primary-side switching unit to turn off with the first control signal and control the auxiliary switching unit to turn off with the second control signal.

[0105] The second mode unit is used in the second operating mode, where the first control signal controls the primary side switching unit to soft start, and the second control signal controls the auxiliary switching unit to turn off.

[0106] The third mode unit is used in the third working mode, where the first control signal controls the primary side switch unit to work, the second control signal controls the auxiliary switch unit to soft start, and the second control signal controls the turn-on time of the auxiliary switch unit to increase from the first conduction time to the second conduction time according to the second control signal, wherein the second conduction time is greater than the first conduction time.

[0107] The first control signal and the second control signal operate in the same switching cycle.

[0108] Initially, the flyback converter operates in the first operating mode, where the first control signal DRV1 controls the primary-side switching unit Q1 to turn off, and the second control signal DRV2 controls the auxiliary switching unit Q2 to also turn off.

[0109] Furthermore, after the first operating mode ends, the flyback converter enters the second operating mode. The first control signal DRV1 controls the primary-side switching unit Q1 to soft-start. At this time, the frequency or duty cycle of the primary-side switching unit Q1 is gradually increased, and the output voltage rises. However, at this time, the second control signal controls DRV2 to control the auxiliary switching unit Q2 to remain off.

[0110] Furthermore, when the output voltage increases to the set voltage threshold, or when the working time of the second working mode reaches the set switching time, the second working mode ends and enters the third working mode.

[0111] Furthermore, upon the end of the second operating mode, the flyback converter enters the third operating mode. The second control signal controls DRV2 to soft-start the auxiliary switching unit Q2, increasing the conduction time of the auxiliary switching unit Q2 to the final steady-state operating duration. The second control signal DRV2 and the first control signal DRV1 operate within the same switching cycle.

[0112] Specifically, refer to Figure 6 During the T1 time period, the flyback converter operates in the first operating mode. The first control signal DRV1 controls the primary-side switching unit Q1 to turn off, and the second control signal DRV2 controls the auxiliary switching unit Q2 to also turn off. At this time, the flyback converter has not started working.

[0113] When the T1 time period ends and the T2 working time period begins, the flyback converter enters the second working mode. The first control signal DRV1 controls the primary side switching unit Q1 to soft start. At this time, the frequency or duty cycle of the primary side switching unit Q1 is gradually increased, and the output voltage rises. However, at this time, the second control signal DRV2 controls the auxiliary switching unit Q2 to remain off.

[0114] The T2 working period ends when the output voltage increases to the set voltage threshold, or when the working time of the second working mode reaches the set switching time.

[0115] When the T2 operating period ends and the T3 operating period begins, the flyback converter enters the third operating mode. The second control signal controls DRV2 to soft-start the auxiliary switching unit Q2, increasing the on-time of the auxiliary switching unit Q2 from the first on-time to the second on-time. The second control signal DRV2 and the first control signal DRV1 operate within the same switching cycle, and their waveforms are shown below. Figure 2 Consistent.

[0116] Specifically, refer to Figure 7 During the T3 time period, when the flyback converter enters the third operating mode, the second control signal controls the conduction time of the auxiliary switching unit to increase linearly from the first turn-on time to the second turn-on time.

[0117] During time period T3, when the flyback converter enters the third operating mode, the second control signal controls the auxiliary switching unit to conduct for a first turn-on time within time period T3a. After time period T3a ends, the second control signal controls the auxiliary switching unit to linearly increase its conduction time from the first turn-on time to the second conduction time.

[0118] Specifically, in another embodiment, reference is made to Figure 8 During time period T3, when the flyback converter enters the third operating mode, the second control signal controls the auxiliary switch unit to have a first turn-on time during time period T3a. After time period T3a ends, the second control signal controls the auxiliary switch unit to have a second turn-on time.

[0119] In one embodiment, during each switching cycle of the third operating mode, the second control signal controls the auxiliary switching unit to turn off after a preset conduction time, and after a set dead time, the first control signal controls the primary-side switching unit to turn on.

[0120] In one embodiment, the method further includes: the flyback converter enters a fourth operating mode after the third operating mode ends;

[0121] In the fourth operating mode, the second control signal controls the auxiliary switch unit to turn on for a first conduction time and then turn it off. After a set dead time, the first control signal controls the primary-side switch unit to turn on with zero voltage.

[0122] Specifically, in another embodiment, when the flyback converter is in the fourth operating mode, the second control signal controls the turn-on time of the auxiliary switching unit to be adjusted according to the voltage difference between the two ends of the primary-side switching unit before it is turned on, specifically as follows: if the voltage difference between the two ends of the primary-side switching unit before it is turned on is greater than a first voltage threshold, then the turn-on time of the auxiliary switching unit is increased in the next switching cycle.

[0123] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is equal to the first voltage threshold, then the turn-on time of the auxiliary switching unit remains unchanged in the next switching cycle.

[0124] If the voltage difference between the two ends of the primary-side switching unit before it is turned on is less than a first voltage threshold, then the turn-on time of the auxiliary switching unit is reduced in the next switching cycle.

[0125] In this embodiment, by using the fourth operating mode, the energy stored in this part is refracted to the primary side within a preset dead time to inject into the resonance process of the parasitic capacitance of the main power transistor and the primary side inductance, thereby further releasing the remaining energy on the parasitic capacitance and realizing zero-voltage conduction of the primary side power switch, effectively reducing switching losses.

[0126] It should be noted that for details not disclosed in the start-up control device of this embodiment, please refer to the details disclosed in the start-up control method of this embodiment, which will not be repeated here.

[0127] Although the invention has been described with reference to several exemplary embodiments, it should be understood that the terminology used is descriptive and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or nature of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A start-up control method for a flyback converter, the flyback converter comprising: The system comprises a primary-side input capacitor, a primary-side switching unit, a clamping unit, a primary-side winding, a secondary-side winding, a secondary-side rectifier unit, a secondary-side output capacitor, an auxiliary winding, and an auxiliary switching unit connected to the auxiliary winding. The start-up control method includes the following steps: In the first operating mode, the first control signal controls the primary-side switching unit to turn off, and the second control signal controls the auxiliary switching unit to turn off. In the second operating mode, the first control signal controls the primary-side switching unit to soft start, and the second control signal controls the auxiliary switching unit to turn off; In the third operating mode, the first control signal controls the primary side switching unit to operate, the second control signal controls the auxiliary switching unit to soft start, and according to the second control signal, the turn-on time of the auxiliary switching unit is increased from the first conduction time to the second conduction time, wherein the second conduction time is greater than the first conduction time. The first control signal and the second control signal operate in the same switching cycle.

2. The start-up control method as described in claim 1, characterized in that: In the second operating mode, the first control signal controls the primary-side switching unit to soft-start, and the second control signal controls the auxiliary switching unit to turn off, further comprising: The frequency of the first control signal remains unchanged, and the duty cycle of the first control signal is gradually increased to the preset duty cycle value. Alternatively, the duty cycle of the first control signal remains unchanged, and the switching frequency of the first control signal is gradually increased to a preset value. Alternatively, the duty cycle of the first control signal can be gradually increased to a preset duty cycle value, and the switching frequency of the first control signal can be gradually increased to a preset switching frequency value.

3. The start-up control method as described in claim 1, characterized in that: The specific steps of controlling the turn-on time of the auxiliary switch unit to increase from the first turn-on time to the second turn-on time according to the second control signal are as follows: The second control signal controls the turn-on time of the auxiliary switch unit to increase linearly from the first turn-on time to the second turn-on time; Alternatively, the second control signal controls the turn-on time of the auxiliary switch unit to be adjusted to the first conduction time, and after a preset number of switching cycles, the turn-on time is linearly increased from the first conduction time to the second conduction time; Alternatively, the second control signal controls the auxiliary switch unit to adjust the turn-on time to the first conduction time, and after a preset number of switching cycles, adjusts the turn-on time to the second conduction time.

4. The start-up control method as described in claim 1, characterized in that: In each switching cycle of the third operating mode, the second control signal controls the auxiliary switching unit to turn off after a preset conduction time, and after a set dead time, the first control signal controls the primary-side switching unit to turn on.

5. The start-up control method as described in claim 1, characterized in that: Also includes: In the fourth operating mode, the second control signal controls the auxiliary switch unit to turn on for a first conduction time and then turn off. After a set dead time, the first control signal controls the primary-side switch unit to turn on with zero voltage.

6. The start-up control method as described in claim 5, characterized in that: Also includes: In the fourth operating mode, the second control signal controls the turn-on time of the auxiliary switch unit to be adjusted according to the voltage difference between the two ends of the primary-side switch unit before it is turned on.

7. The start-up control method as described in claim 6, characterized in that: The second control signal controls the turn-on time of the auxiliary switching unit to be adjusted according to the voltage difference between the two ends of the primary-side switching unit before it is turned on, specifically as follows: If the voltage difference between the two ends of the primary-side switching unit before it is turned on is greater than the first voltage threshold, then the turn-on time of the auxiliary switching unit is increased in the next switching cycle. If the voltage difference between the two ends of the primary-side switching unit before it is turned on is equal to the first voltage threshold, then the turn-on time of the auxiliary switching unit remains unchanged in the next switching cycle. If the voltage difference between the two ends of the primary-side switching unit before it is turned on is less than a first voltage threshold, then the turn-on time of the auxiliary switching unit is reduced in the next switching cycle.

8. The start-up control method as described in claim 1, characterized in that: Also includes: According to preset switching conditions, the flyback converter in the second working mode is controlled to enter the third working mode.

9. The start-up control method as described in claim 8, characterized in that: The aforementioned control of the flyback converter, which is in the second operating mode, to enter the third operating mode according to preset switching conditions specifically includes: Once the output voltage of the flyback converter is determined to be greater than or equal to a set voltage threshold, the flyback converter enters the third operating mode. or, Once the operating time of the flyback converter in the second operating mode reaches the switching time, the flyback converter enters the third operating mode.

10. A start-up control device for a flyback converter, the flyback converter comprising: The device comprises a primary-side input capacitor, a primary-side switching unit, a clamping unit, a primary-side winding, a secondary-side winding, a secondary-side rectifier unit, a secondary-side output capacitor, an auxiliary winding, and an auxiliary switching unit connected to the auxiliary winding, characterized in that the start-up control device includes: The first mode unit is used in the first operating mode to control the primary side switch unit to turn off with a first control signal and the auxiliary switch unit to turn off with a second control signal. The second mode unit is used in the second operating mode, where the first control signal controls the primary side switching unit to soft start, and the second control signal controls the auxiliary switching unit to turn off. The third mode unit is used in the third working mode, where the first control signal controls the primary side switch unit to work, the second control signal controls the auxiliary switch unit to soft start, and the second control signal controls the turn-on time of the auxiliary switch unit to increase from the first conduction time to the second conduction time according to the second control signal, wherein the second conduction time is greater than the first conduction time. The first control signal and the second control signal operate in the same switching cycle.

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