Flyback converter and start-up control method thereof

Abstract

The application discloses a flyback converter and a starting control method thereof. The flyback converter comprises a transformer, a power switch tube, a rectifier tube, a primary side control circuit, and a secondary side control circuit. The primary side control circuit generates a first control signal to control the transmission of starting energy to a secondary side part of the flyback converter after the flyback converter is powered on. The secondary side control circuit transmits a stop signal and a second control signal to the primary side control circuit in sequence after starting. The application can prevent the primary side switch signal from suddenly changing during the starting process, realize the smooth transition of primary side and secondary side control, and realize the smooth starting of the output voltage. The application has good output characteristics, a simple control method, better compatibility, and lower cost.

Description

Technical Field

[0001] This invention relates to the field of converter technology, and specifically to a flyback converter and its startup control method. Background Technology

[0002] With the rapid development of power electronics technology, the requirements for small size, high efficiency, and high reliability of switching converters are becoming increasingly stringent. Flyback converters, due to their simple topology, fewer components, and low cost, are widely used in the electronics industry, including switching power supplies. A flyback converter is an isolated power converter, commonly used for AC-to-DC and DC-to-DC conversion with current isolation between the input and one or more outputs. More precisely, a flyback converter is a boost / buck converter with inductor splitting, forming a transformer that multiplies the voltage ratio by the additional advantage of isolation. In conventional flyback converters, to improve efficiency, synchronous rectifiers are usually used instead of diode rectifiers on the secondary side. Therefore, a secondary-side control circuit is also required in the flyback converter to control the switching on and off of the synchronous rectifier.

[0003] A typical flyback converter consists of a primary power switch coupled to the primary winding of the transformer, and a synchronous rectifier coupled to the secondary winding. The input voltage is provided through the primary winding and the primary power switch. The primary drive voltage controls the on / off state of the primary power switch, conducting the primary current. The secondary switch and synchronous rectifier act as a complement during operation. The conduction cycles of the power switch and synchronous rectifier do not overlap; one switch is on while the other is off. The current flowing in the secondary winding of the transformer is called the secondary current, which charges the output capacitor and provides the output voltage.

[0004] To achieve higher system efficiency, existing flyback converters typically employ a secondary-side control circuit to simultaneously control the on / off state of both the primary-side power switches and the secondary-side synchronous rectifier. However, the secondary-side control circuit cannot be directly started upon initial power-up of the flyback converter. The primary-side control circuit must first operate the primary-side power switches for a period to transfer energy to the secondary side via the transformer, thus starting the secondary-side control circuit. Afterward, the secondary-side control circuit takes over control of the primary-side power switches. However, existing flyback converter startup schemes suffer from the following problems: 1. The output voltage startup cannot transition smoothly, exhibiting hook-back or overshoot issues. 2. Traditional primary-side control systems have a high risk of primary-secondary crosstalk, resulting in low system efficiency.

[0005] Therefore, it is necessary to provide improved technical solutions to overcome the above-mentioned technical problems existing in the prior art. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a flyback converter and its startup control method, which prevents abrupt changes in the primary-side switching signal during startup, achieving a smooth transition between primary and secondary-side control. It also enables smooth startup of the output voltage, exhibiting good output characteristics. The control method is simple, has better compatibility, and lower cost.

[0007] According to a first aspect of this disclosure, a flyback converter is provided, comprising:

[0008] A transformer consists of a primary winding and a secondary winding;

[0009] A power switching transistor is connected to the primary winding.

[0010] A rectifier diode is connected between the secondary winding and the output terminal of the flyback converter;

[0011] The primary-side control circuit starts after the flyback converter is powered on, and generates a first control signal after startup to control the transfer of startup energy to the secondary side of the flyback converter.

[0012] The secondary-side control circuit, after startup, sequentially transmits a stop signal and a second control signal to the primary-side control circuit.

[0013] Wherein, both the first control signal and the second control signal are used to trigger the on / off control of the power switch, and the stop signal is used to trigger the primary-side control circuit to stop generating the first control signal or to trigger the shielding of the first control signal from controlling the on / off control of the power switch.

[0014] Optionally, the secondary-side control circuit is configured to transmit the stop signal to the primary-side control circuit at a first moment after startup, and to transmit the second control signal to the primary-side control circuit after a first time delay starting from the first moment.

[0015] Optionally, the first moment is the moment when the output feedback signal reaches the first reference voltage, wherein the output feedback signal characterizes the output power of the flyback converter.

[0016] Optionally, the first moment is the moment when the power switch is simultaneously within a preset time period after it starts to conduct and the output feedback signal is greater than or equal to the first reference voltage, wherein the output feedback signal represents the output power of the flyback converter.

[0017] Optionally, the secondary control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first moment, the output unit comprising:

[0018] The first comparison unit receives the output feedback signal at its non-inverting input terminal and receives the first reference voltage at its inverting input terminal. The first comparison unit is configured to output a first trigger signal when the output feedback signal is greater than or equal to the first reference voltage.

[0019] A stop signal generating unit has its input terminal connected to the output terminal of the first comparison unit, and the stop signal generating unit is configured to generate the stop signal when the first trigger signal is received.

[0020] Optionally, the secondary control circuit includes an output unit configured to receive the output feedback signal and generate the stop signal at the first moment, the output unit comprising:

[0021] The second comparison unit receives the output feedback signal at its non-inverting input terminal and receives the first reference voltage at its inverting input terminal. The second comparison unit is configured to output a first comparison signal when the output feedback signal is greater than the first reference voltage.

[0022] The third comparison unit receives a second reference voltage at its non-inverting input terminal, receives the voltage difference between the two power terminals of the rectifier tube at its inverting input terminal, and outputs a second comparison signal at its output terminal.

[0023] The rising edge pulse generation unit receives the second comparison signal at its input terminal and generates a pulse on the rising edge of the second comparison signal to output a first pulse signal;

[0024] A first combinational logic circuit receives the first comparison signal and the first pulse signal, and the first combinational logic circuit is configured to output a first trigger signal when the first comparison signal and the first pulse signal are simultaneously detected to be valid for the first time.

[0025] A stop signal generating unit has its input terminal connected to the output terminal of the first combinational logic circuit, and the stop signal generating unit is configured to generate the stop signal when the first trigger signal is received.

[0026] Optionally, the output unit further includes:

[0027] The delay unit receives the first trigger signal at its input terminal. The delay unit is configured to start timing when the first trigger signal is received and to output a second trigger signal after the first time.

[0028] A first AND logic circuit has a first input terminal that receives the second control signal, and a second input terminal that is connected to the output terminal of the delay unit. The first AND logic circuit is configured to output the received second control signal after receiving the second trigger signal.

[0029] The OR logic circuit has a first input terminal connected to the output terminal of the first AND logic circuit, and a second input terminal connected to the output terminal of the stop signal generation unit. The OR logic circuit is configured to implement time-division multiplexing of the stop signal and the second control signal.

[0030] Optionally, the secondary-side control circuit further includes:

[0031] An output feedback signal generation circuit is configured to generate the output feedback signal based on the output voltage of the flyback converter.

[0032] The second control signal generation unit is configured to generate the second control signal based on the output feedback signal.

[0033] Optionally, the difference between the frequency and pulse width parameters of the second control signal and the frequency and pulse width parameters of the first control signal in at least the initial pulse period is less than a preset threshold.

[0034] Optionally, the primary-side control circuit includes:

[0035] The first control signal generation unit is configured to start generating the first control signal after the flyback converter is powered on, and to stop generating the first control signal according to the stop signal.

[0036] The drive unit is configured to transmit a first drive control signal to the control terminal of the power switch when it receives the first control signal or the second control signal, so as to realize the on / off control of the power switch.

[0037] According to a second aspect of this disclosure, a startup control method for a flyback converter is provided, applicable to the flyback converter described above, the startup control method comprising:

[0038] After the flyback converter is powered on, a first control signal is generated by the primary-side control circuit to control the transfer of start-up energy to the secondary side of the flyback converter.

[0039] After the secondary-side control circuit is started, it transmits a stop signal and a second control signal to the primary-side control circuit sequentially.

[0040] Wherein, both the first control signal and the second control signal are used to trigger the on / off control of the power switch, and the stop signal is used to trigger the primary-side control circuit to stop generating the first control signal or to trigger the shielding of the first control signal from controlling the on / off control of the power switch.

[0041] Optionally, the secondary-side control circuit sequentially transmits a stop signal and a second control signal to the primary-side control circuit, including:

[0042] The stop signal is transmitted to the primary control circuit at the first moment after the secondary control circuit is started, and the second control signal is transmitted to the primary control circuit after a first time delay starting from the first moment.

[0043] Optionally, the first moment is the moment when the output feedback signal of the flyback converter reaches the first reference voltage.

[0044] Optionally, the first moment is the moment when the power switch is simultaneously within a preset time period after it starts to conduct and the output feedback signal is greater than or equal to the first reference voltage, wherein the output feedback signal represents the output power of the flyback converter.

[0045] Optionally, the difference between the frequency and pulse width parameters of the second control signal and the frequency and pulse width parameters of the first control signal in at least the initial pulse period is less than a preset threshold.

[0046] Optionally, the difference between the first time and the period of the first control signal is less than a preset threshold.

[0047] The beneficial effects of the present invention include at least the following:

[0048] This invention, through its embodiment, sets the primary-side control circuit to start upon power-up of the flyback converter, outputting a first control signal to control the on / off state of the power switch, thereby providing startup energy to the secondary-side control circuit and the flyback converter's output. After the secondary-side control circuit receives startup energy and starts, it first triggers the primary-side control circuit to stop generating the first control signal, then transmits a second control signal to the primary-side control circuit to replace the first control signal and continue controlling the power switch's on / off state. This ensures a smooth transition from primary-side to secondary-side control. Furthermore, by setting the difference between the frequency and pulse width parameters of the second control signal in its initial pulse period and those of the first control signal to be less than a preset threshold (i.e., the second control signal has essentially the same frequency and pulse width as the first control signal in its initial pulse period), the drive signal for the primary-side power switch does not undergo abrupt changes during startup, achieving a smooth transition between primary and secondary-side control and a smooth startup of the output voltage, thus improving the output quality of the flyback converter.

[0049] It should be noted that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the present invention. Attached Figure Description

[0050] Figure 1A schematic diagram of the structure of a flyback converter provided according to an embodiment of the present invention is shown;

[0051] Figure 2 This diagram illustrates the structure of a primary-side control circuit according to an embodiment of the present invention.

[0052] Figure 3 A schematic diagram of the secondary control circuit provided according to an embodiment of the present invention is shown;

[0053] Figure 4 This diagram illustrates the structure of the output unit provided according to the first embodiment of the present invention;

[0054] Figure 5 This diagram illustrates the structure of the output unit provided according to a second embodiment of the present invention.

[0055] Figure 6 Showing according to Figure 4 The provided timing waveform diagram for the start-up control of the flyback converter;

[0056] Figure 7 This diagram illustrates a timing waveform for the startup control of a flyback converter according to an embodiment of the present invention.

[0057] Figure 8 This diagram illustrates another timing waveform for the startup control of a flyback converter according to an embodiment of the present invention.

[0058] Figure 9 Showing according to Figure 5 A timing waveform diagram of the start-up control of the provided flyback converter;

[0059] Figure 10 Showing according to Figure 5 Another timing waveform diagram of the start-up control of the provided flyback converter;

[0060] Figure 11 A flowchart illustrating the start-up control method for a flyback converter according to an embodiment of the present invention is shown. Detailed Implementation

[0061] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in various forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0062] refer to Figure 1 The flyback converter disclosed in this embodiment of the invention includes: a primary winding N P and secondary winding NS The transformer TR is connected to the primary winding N. P The voltage input circuit is connected to the secondary winding N. S The voltage output circuit, as well as the power switch Q1, primary side control circuit 5, rectifier Q2, secondary side control circuit 8, isolation device 6, and output feedback signal generation circuit 9.

[0063] The voltage input circuit is connected between the input terminal of the flyback converter and the primary winding Np, and includes a rectifier circuit 3 and an input capacitor C1. The rectifier circuit 3 can be connected to a power source via the first connection port 1, facilitating the supply of electrical energy to the flyback converter. This power source can be, but is not limited to, a power grid, generator, transformer, battery, solar panel, wind turbine, regenerative braking system, hydraulic or wind turbine, or any other device capable of supplying electrical energy to the flyback converter. The voltage input circuit may further include a filter circuit 2 connected between the rectifier circuit 3 and the first connection port 1, and a power factor correction circuit 4 connected between the rectifier circuit 3 and the input capacitor C1.

[0064] Furthermore, the voltage input circuit also includes the primary winding N of the transformer TR. P A resistor R1, a capacitor C2, and a diode D1 are placed between the same-named and different-named terminals. The resistor R1 and capacitor C2 are connected in parallel to the primary winding N. P The opposite terminal is between the cathode of diode D1 and the anode of diode D1, and the primary winding N is between the anode and the cathode of diode D1. P With the same terminals connected, resistor R1, capacitor C2, and diode D1 can absorb the primary winding N. P This reduces leakage inductance current, thereby improving transformer performance.

[0065] The voltage output circuit is connected to the secondary winding N. S Between the flyback converter and its output, there is an output capacitor Co, which can be connected to the load via a second connection port 7. The load receives electrical energy (e.g., voltage and current) converted by the flyback converter. In some instances, the electrical energy converted by the flyback converter passes through a filter before reaching the load. In some instances, the filter is a sub-component of the flyback converter, an external component of the flyback converter, and / or a sub-component of the load. In any case, the load can perform its function using filtered or unfiltered electrical energy from the flyback converter. Optionally, the load may include, but is not limited to, computing devices and related components, such as microprocessors, electrical components, circuits, laptop computers, desktop computers, tablet computers, mobile phones, batteries, speakers, lighting units, automotive / marine / aircraft / train related components, motors, transformers, or any other type of electrical equipment and / or circuits that receive voltage or current from the flyback converter.

[0066] Power switch Q1 and primary winding N P Connection. In one possible embodiment, the power switch Q1 is an NMOS field-effect transistor.

[0067] The primary-side control circuit 5 provides a first drive signal Vgs1 to the control terminal of the power switch Q1 to control the turn-on / turn-off of the power switch Q1. In this embodiment, the primary-side control circuit 5 is configured to start after the flyback converter is powered on, and after startup, it generates a first control signal Vgs1_P to control the transfer of startup energy to the secondary side of the flyback converter. The primary-side control circuit 5 further includes a first input terminal SYNC, a first output terminal DRV, and a ground terminal GND. The first input terminal SYNC of the primary-side control circuit 5 is connected to the isolation device 6 to receive the signal transmitted by the secondary-side control circuit 8; the first output terminal DRV of the primary-side control circuit 5 is connected to the control terminal of the power switch Q1 to output the first drive signal Vgs1 to the control terminal of the power switch Q1; the ground terminal GND of the primary-side control circuit 5 is connected to the reference ground.

[0068] For example, the flyback converter disclosed in this invention can operate using secondary-side control to achieve higher system efficiency. That is, after the secondary-side control circuit 8 is started, the control signal for turning on / off the primary-side power switch Q1 is provided by the secondary-side control circuit 8. At this time, the primary-side control circuit 5 can only act as a driver during the normal operation of the flyback converter, converting the second control signal transmitted from the secondary-side control circuit to drive the power switch Q1. This greatly reduces the complexity of the primary-side control circuit 5 and the system cost. Furthermore, in one possible embodiment, such as... Figure 2 As shown, the primary-side control circuit 5 includes a first control signal generation unit 51 and a driving unit 52.

[0069] The first control signal generation unit 51 is configured to start generating the first control signal Vgs_P after the flyback converter is powered on, and to stop generating the first control signal Vgs_P based on a stop signal. The drive unit 52 is configured to transmit the first drive signal Vgs1 to the control terminal of the power switch Q1 when it receives the first control signal Vgs_P or the second control signal PWM1, so as to realize the on / off control of the power switch Q1.

[0070] It is understandable that the power supply for the flyback converter is located on its primary side. Therefore, after the flyback converter is powered on, the primary-side control circuit 5 will be powered on and start first, while the secondary-side control circuit 8, located on the secondary side of the flyback converter, needs the primary side to transfer startup energy before it can start. The first control signal generation unit 51 set in the primary-side control circuit 5 is to generate a first control signal Vgs_P before the secondary-side control circuit 8 of the flyback converter starts to control the on / off state of the power switch Q1, thereby transferring energy from the primary side to the secondary side and starting the secondary-side control circuit 8. Furthermore, the first control signal Vgs_P is, for example, an open-loop pulse signal with a fixed frequency and pulse width (see reference). Figures 6-10 Let the frequency of the first control signal Vgs_P be 1 / Ts_p, so as to stabilize the initial energy transfer process of the flyback converter and facilitate control and management. The drive unit 52 is used to implement the drive function of the primary-side control circuit 5.

[0071] It should be noted that the first control signal generation unit 51 receives a stop signal from the first input terminal SYNC of the primary-side control circuit 5, and the drive unit 52 transmits the first drive signal Vgs1 from the first output terminal DRV of the primary-side control circuit 5 to the control terminal of the power switch Q1, and receives the second control signal PWM1 from the first input terminal SYNC of the primary-side control circuit 5. Figure 4 The dashed and solid lines with arrows are used only to indicate that the stop signal and the second control signal PWM1 received by the primary-side control circuit 5 are received in a time-division manner from its first input terminal SYNC. Both the first control signal Vgs1_P and the second control signal PWM1 are used to trigger the on / off control of the power switch Q1, while the stop signal is used to trigger the primary-side control circuit 5 to stop generating the first control signal Vgs1_P, or to trigger the shielding of the first control signal Vgs1_P from controlling the on / off operation of the power switch Q1.

[0072] Optionally, the isolation device 6 can be any of the following: an isolation transformer, an optocoupler, an isolation capacitor, and an isolation chip. The isolation device 6 enables signal transmission between the primary and secondary sides of the flyback converter.

[0073] The rectifier diode Q2 is connected between the secondary winding Ns and the voltage output circuit. Optionally, the rectifier diode Q2 can be connected to the secondary winding Ns. S The first terminal can be connected between the low-order output terminal of the flyback converter, i.e., the reference ground, or it can be connected to the secondary winding N. S The second terminal is connected to the high-order output terminal of the flyback converter; this invention does not limit this connection.

[0074] Optionally, the rectifier Q2 can be, for example, a freewheeling diode or a synchronous rectifier. When the rectifier Q2 is a synchronous rectifier, it can be, for example, an NMOS field-effect transistor. Furthermore, the flyback converter also includes a resistor R2 and a capacitor C3 connected in series between the drain and source of the synchronous rectifier Q2. The resistor R2 and capacitor C3 can absorb the stress of the MOS transistor and protect the synchronous rectifier Q2. It should be noted that the accompanying drawings and description in this application are merely illustrative examples of the technical solution of the present invention using a synchronous rectifier. Solutions using a freewheeling diode can be directly or unambiguously obtained based on the content of this document and should also be within the scope of protection of this invention.

[0075] The secondary-side control circuit 8 starts based on the startup energy and, after startup, transmits a stop signal and a second control signal PWM1 to the primary-side control circuit 5. Further, the secondary-side control circuit 8 is configured to transmit a stop signal to the primary-side control circuit 5 at the first moment after its startup, and to transmit the second control signal PWM1 to the primary-side control circuit 5 after a first time delay (denoted as Td) starting from the first moment.

[0076] The secondary-side control circuit 8 receives a first voltage (denoted as V1, which characterizes the potential difference between the first node a and the second node b in the flyback converter, and the first voltage V1 is directly proportional to the output voltage Vo of the flyback converter, i.e., V1*k=Vo, where k is a positive number) and a second voltage (denoted as V SW The second voltage V SW The second node (b) is used to characterize the potential difference between the third node c and the second node b in the flyback converter (at least one of the third node c and the second node b is connected to the rectifier Q2). It outputs a stop signal and a second control signal PWM1 to the isolation device 6, which then transmits the signal to the primary-side control circuit 5. It also outputs a third control signal (denoted as PWM2) to the control terminal of the synchronous rectifier Q2 to control the on / off state of the synchronous rectifier Q2. It is understood that the second node b is used to characterize the reference zero potential point of the secondary-side control circuit 8. For example, in some possible embodiments of the present invention, the second node b, i.e., the reference zero potential point of the secondary-side control circuit 8, is the same as the reference ground potential point of the secondary side of the flyback converter, and both are connected to the low-order output terminal of the flyback converter. In other possible embodiments of the present invention, the second node b, i.e., the reference zero potential point of the secondary-side control circuit 8, is not the same as the reference ground potential point of the secondary side of the flyback converter.

[0077] The secondary-side control circuit 8 further includes: a power supply terminal Vcc_s, a first input terminal SW, a second input terminal V1, a third input terminal SCS, a fourth input terminal COMP, a first output terminal GT, a second output terminal SYNC, and a ground terminal GND. The power supply terminal Vcc_s of the secondary-side control circuit 8 is connected to the second node b via a first capacitor Ci, and is used to provide a power supply voltage to the secondary-side control circuit 8 based on the startup energy transferred from the primary side of the flyback converter; the first input terminal SW of the secondary-side control circuit 8 is connected to the third node c to receive the second voltage V. SW The second input terminal V1 of the secondary control circuit 8 is connected to the first node a to receive the first voltage V1; the third input terminal SCS of the secondary control circuit 8 is connected via a preset proportional resistor (denoted as R in this embodiment). CS_S It is connected to the second node b to receive the proportional voltage (denoted as V). SCS ), and then based on the proportional voltage V SCS A voltage signal characterizing the excitation current information of the flyback converter is obtained; the fourth input terminal COMP of the secondary-side control circuit 8 is connected to the high-order output terminal of the output feedback signal generation circuit 9 to receive the output feedback signal Vcomp; the first output terminal GT of the secondary-side control circuit 8 is connected to the control terminal of the synchronous rectifier Q2 to output the third control signal PWM2 to the control terminal of the synchronous rectifier Q2; the second output terminal SYNC of the secondary-side control circuit 8 is connected to the isolation device 6 to realize signal transmission with the primary-side control circuit 5 of the flyback converter through the isolation device 6, for example, the stop signal and the second control signal PWM1 are transmitted to the primary-side control circuit 5 through the isolation device 6; the ground terminal GND of the secondary-side control circuit 8 is connected to the second node b.

[0078] refer to Figure 3 The secondary control circuit 8 further includes: a start-up unit 81, a second control signal generation unit 82, an output unit 83, a drive interlock unit 84, and a third control signal generation unit 85.

[0079] The startup unit 81 is configured to receive startup energy and generate the required supply voltage for the secondary control circuit 8 across the first capacitor Ci based on the received startup energy. For example, the startup unit 81 can employ two power supply units based on a first voltage V1 and a second voltage Vsw, respectively, in conjunction with a corresponding low dropout regulator (LDO) circuit to provide the required supply voltage to the secondary control circuit 8. This ensures that the secondary control circuit 8 has a suitable supply voltage value to support the corresponding application scenarios of the flyback converter under different voltage states of the flyback converter's output voltage Vo, thereby improving the working efficiency and compatibility of the flyback converter.

[0080] Optionally, in some possible embodiments of the present invention, the synchronous rectifier Q2 is connected to the low-order output terminal of the flyback converter. In this case, the first voltage V1 is the voltage at the first terminal of the secondary winding Ns, which is also the output voltage Vo of the flyback converter, and the second voltage V SW This refers to the voltage at the second terminal where the secondary winding Ns is connected to the synchronous rectifier 2. In some other possible embodiments of the present invention, the synchronous rectifier Q2 is connected to the low-level output terminal of the flyback converter. In this case, the first voltage V1 is the potential difference between the high-level output terminal of the flyback converter and the second node b, which is also the output voltage Vo of the flyback converter. The second voltage V SW This refers to the potential difference between the first end of the secondary winding Ns and the second node b, where the second node b has the same potential value as the reference ground potential point of the secondary side of the flyback converter. In some other possible embodiments of the invention, the transformer TR further includes an auxiliary winding, one end of which is connected to the second node b. Simultaneously, the synchronous rectifier Q2 is connected to the high-level output terminal of the flyback converter. In this case, the first voltage V1 is the voltage difference across the auxiliary winding, and the second voltage V... SW This is the potential difference between the high-level output terminal of the flyback converter and the second node b, where the second node b is the common connection node between the secondary winding Ns and the synchronous rectifier Q2.

[0081] In this embodiment, the output feedback signal generation circuit 9 is configured to generate an output feedback signal Vcomp based on the output voltage Vo of the flyback converter, thereby characterizing the output power of the flyback converter. It is understood that the circuit structure of the output feedback signal generation circuit 9 can employ existing conventional circuit structures, such as a combination of an error amplifier and compensation, to obtain the output feedback signal Vcomp; this invention does not limit this to any particular type.

[0082] Continue to refer to Figure 5 The second control signal generation unit 82 is configured to generate a control signal based on the output feedback signal Vcomp and the proportional voltage V. SCS The voltage signal representing the excitation current information of the flyback converter is used to generate the second control signal PWM1. The specific working principle and circuit structure of the second control signal generation unit 82 are not closely related to the technical problem to be solved in this application, and can be understood by referring to the prior art, so they will not be described in detail.

[0083] The third control signal generation unit 85 is configured to generate a third control signal PWM2 based on the two power terminal voltages, Vsw, of the synchronous rectifier Q2. This third control signal PWM2 is used to control the on / off state of the synchronous rectifier Q2. The specific working principle and circuit structure of the third control signal generation unit 85 are not closely related to the technical problem to be solved in this application and can be understood by referring to the prior art; therefore, they will not be described in detail.

[0084] The drive interlock unit 84 generates a secondary-side turn-off signal based on the second control signal PWM1. This signal triggers the turn-off control of the synchronous rectifier Q2. In this embodiment, the drive interlock unit 84 enables drive interlocking between the primary and secondary sides of the flyback converter, preventing the primary-side power switch Q1 and the secondary-side synchronous rectifier Q2 from turning on simultaneously. Furthermore, since the control signal for the power switch Q1 is also generated by the secondary-side control circuit 8, no additional isolation device is needed to receive the feedback signal from the primary side.

[0085] The output unit 83 receives the output feedback signal Vcomp and the second control signal PWM1. The output unit 83 is configured to determine a first time based on the output feedback signal Vcomp, generate a stop signal at the first time, and output the second control signal PWM1 after a first time delay Td from the first time.

[0086] like Figure 4 and Figure 5 As shown, the output unit 83 further includes: a first trigger signal generation unit, a stop signal generation unit 833, a delay unit 834, a first AND logic circuit 835, and an OR logic circuit 836. The first trigger signal generation unit is configured to determine a first moment based on the output feedback signal Vcomp and generate a first trigger signal at the first moment. The stop signal generation unit 833 is configured to generate a stop signal upon receiving the first trigger signal. In this embodiment, the stop signal is a single-pulse signal, such as... Figures 6-10 As shown. The input terminal of delay unit 834 receives a first trigger signal. Delay unit 834 is configured to start timing upon receiving the first trigger signal and output a second trigger signal after a first time Td. The first input terminal of first AND logic circuit 835 receives a second control signal PWM1. The second input terminal of first AND logic circuit 835 is connected to the output terminal of delay unit 834. First AND logic circuit 835 is configured to output the received second control signal PWM1 after receiving the second trigger signal. The first input terminal of OR logic circuit 836 is connected to the output terminal of first AND logic circuit 835, or the second input terminal of OR logic circuit 836 is connected to the output terminal of stop signal generation unit 833. OR logic circuit 836 is configured to implement time-division multiplexing of the stop signal and the second control signal PWM1.

[0087] In the first embodiment of the present invention, the aforementioned first moment is the moment when the output feedback signal Vcomp reaches the first reference voltage Vref1. In this embodiment, the reference... Figure 4The first trigger signal generation unit includes a first comparison unit 831. The non-inverting input of the first comparison unit 831 receives an output feedback signal Vcomp, and the inverting input receives a first reference voltage Vref1. The first comparison unit 831 is configured to output a first trigger signal when the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref1.

[0088] The following is combined with Figure 6 The startup process of the flyback converter in the first embodiment of the present invention will be described in detail below:

[0089] At time t0, the primary-side control circuit 5 of the flyback converter starts and begins to generate the first control signal Vgs1_P. The first control signal Vgs1_P begins to control the transfer of start-up energy to the secondary side of the flyback converter. That is, the start-up unit 81 in the secondary-side control circuit 8 begins to obtain start-up energy through the first input terminal SW and the second input terminal Vo in the secondary-side control circuit 8 and begins to increase the voltage of the power supply terminal in the secondary-side control circuit 8.

[0090] At time t1, the secondary control circuit 8 is enabled and begins soft start, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo begin to rise steadily.

[0091] During the time period t1 to t2, the secondary control circuit 8 gradually soft-starts, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo gradually and smoothly increase, thus realizing the smooth start of the output voltage Vo.

[0092] At time t2, the output feedback signal Vcomp reaches the first reference voltage Vref1, i.e., the aforementioned first time point is reached. At this time, the stop signal generation unit 833 in the secondary-side control circuit 8 begins to transmit a stop signal to the primary-side control circuit 5. The first control signal generation unit 51 in the primary-side control circuit 5 stops generating the first control signal Vgs1_P upon being triggered by the stop signal, and the delay unit 834 begins timing. The stop signal during the time period t2 to t3 is represented by a dashed line. In one embodiment, the first control signal generation unit 51 in the primary-side control circuit 5 can be configured to stop generating the first control signal Vgs1_P upon receiving the stop signal.

[0093] After the delay unit 834 times the first time Td, i.e., at time t3, the secondary-side control circuit 8 begins to transmit the second control signal PWM1 to the primary-side control circuit 5 normally. This second control signal PWM1 begins to replace the first control signal Vgs1_P to trigger the drive unit 52 to generate the first drive signal Vgs1, thereby continuing to control the on / off state of the power switch Q1 and realizing the energy transfer between the primary and secondary sides of the flyback converter. That is, from time t3, the flyback converter enters the secondary-side control mode.

[0094] In the second embodiment of the present invention, the aforementioned first moment is the moment when the conditions are simultaneously met for the first time that the power switch Q1 is turned on and the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref1. Preferably, the length of this preset time period is less than the pulse period T of the first control signal Vgs1_P. S_P And it is at least greater than one high-level validity period of the first control signal Vgs1_P and one high-level validity period of the first pulse signal Von2.

[0095] Optionally, in one possible implementation of this embodiment, the first moment is determined jointly by the voltage difference Vds2 between the two power terminals of rectifier Q2 and the output feedback signal Vcomp. (See reference) Figure 5 The first trigger signal generation unit includes a second comparison unit 837, a rising edge pulse generation unit 838, a third comparison unit 839, and a first combinational logic circuit. The non-inverting input of the second comparison unit 837 receives the output feedback signal Vcomp, and the inverting input receives the first reference voltage Vref1. This second comparison unit is configured to output a first comparison signal when the output feedback signal Vcomp is greater than the first reference voltage Vref1. The non-inverting input of the third comparison unit 839 receives the second reference voltage Vref2, and the inverting input receives the voltage difference Vds2 between the two power terminals of rectifier diode Q2. The output of the third comparison unit 839 outputs a second comparison signal. The input of the rising edge pulse generation unit 838 receives the second comparison signal and generates a pulse on the rising edge of the second comparison signal to output a first pulse signal Von2, such as... Figure 9 and Figure 10 As shown, the first combinational logic circuit receives a first comparison signal and a first pulse signal Von2, and is configured to output a first trigger signal when it first detects that the first comparison signal and the first pulse signal Von2 are both valid.

[0096] Exemplarily, the first combinational logic circuit further includes a second AND logic circuit 8311, a NOT logic circuit 8310, and an RS flip-flop 8312. The first input terminal of the second AND logic circuit 8311 is connected to the output terminal of the rising edge pulse generation unit 838, the second input terminal of the second AND logic circuit 8311 is connected to the output terminal of the third comparison unit 839, and the output terminal of the second AND logic circuit 8311 is connected to the set terminal of the RS flip-flop 8312. The input terminal of the NOT logic circuit 8310 is connected to the output terminal of the third comparison unit 839, and the output terminal of the NOT logic circuit 8310 is connected to the reset terminal of the RS flip-flop 8312. The output terminal of the RS flip-flop 8312 is connected to the input terminal of the stop signal generation unit 833 to transmit a first trigger signal to the stop signal generation unit 833 at a first moment. It should be understood that in other embodiments of the present invention, the first combinational logic circuit may also employ other conventional logic circuit combination structures, as long as the aforementioned corresponding functions can be achieved.

[0097] The following is combined with Figure 9 and Figure 10 The startup process of the flyback converter in this implementation scheme is described in detail below:

[0098] At time t0, the primary-side control circuit 5 of the flyback converter starts and begins to generate the first control signal Vgs1_P. The first control signal Vgs1_P begins to control the transfer of start-up energy to the secondary side of the flyback converter. That is, the start-up unit 81 in the secondary-side control circuit 8 begins to obtain start-up energy through the first input terminal SW and the second input terminal Vo in the secondary-side control circuit 8 and begins to increase the voltage of the power supply terminal in the secondary-side control circuit 8.

[0099] At time t1, the secondary control circuit 8 is enabled and begins soft start, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo begin to rise steadily.

[0100] During the time period t1 to t2, the secondary control circuit 8 gradually soft-starts, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo gradually and smoothly increase, thus realizing the smooth start of the output voltage Vo.

[0101] At time t2, the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref1, and the first pulse signal Von2 is also at a valid high level, i.e., the aforementioned first time point is reached. At this time, the stop signal generation unit 833 in the secondary-side control circuit 8 begins to transmit a stop signal to the primary-side control circuit 5. The first control signal generation unit 51 in the primary-side control circuit 5 stops generating the first control signal Vgs1_P upon being triggered by the stop signal, and the delay unit 834 begins timing. The stop signal during the time period t2 to t3 is represented by a dashed line. In one embodiment, the first control signal generation unit 51 in the primary-side control circuit 5 can be configured to stop generating the first control signal Vgs1_P upon receiving the stop signal.

[0102] After the delay unit 834 times the first time Td, i.e., at time t3, the secondary-side control circuit 8 begins to transmit the second control signal PWM1 to the primary-side control circuit 5 normally. This second control signal PWM1 begins to replace the first control signal Vgs1_P to trigger the drive unit 52 to generate the first drive signal Vgs1, thereby continuing to control the on / off state of the power switch Q1 and realizing the energy transfer between the primary and secondary sides of the flyback converter. That is, from time t3, the flyback converter enters the secondary-side control mode.

[0103] It should be noted that if the output feedback signal Vcomp reaches the first reference voltage Vref1 while the first pulse signal Von2 is at a low level, then time t2 is the moment when the first pulse signal Von2 first changes to a high level after the output feedback signal Vcomp reaches the first reference voltage Vref1. Figure 9 As shown; if the output feedback signal Vcomp reaches the first reference voltage Vref1 while the first pulse signal Von2 is at a high level, then time t2 is the time when the output feedback signal Vcomp reaches the first reference voltage Vref1, as follows. Figure 10 As shown.

[0104] In another possible implementation of this embodiment (the aforementioned second embodiment), the first moment is determined jointly by the on-state of the power switch Q1 and the output feedback signal Vcomp. It is understood that, in this implementation, the output unit 83 can adopt a circuit structure that is essentially the same as that in the first implementation of the aforementioned second embodiment, only requiring the following adjustment: Figure 5The circuit that generates the first pulse signal Von2 can be replaced with a corresponding circuit structure that detects the conduction state of the power switch Q1. For example, the conduction state of the power switch Q1 can be obtained by comparing the voltage difference between the two power terminals of the rectifier Q2 with a corresponding reference voltage, or by using an additional isolation device in the flyback converter to detect at least one of the following parameters: the control signal of the power switch Q1, the voltage difference between the two power terminals of the power switch Q1, and the current flowing through the power switch Q1. Specific circuit structures can be understood by referring to existing technologies and will not be detailed here.

[0105] The following is combined with Figure 7 and Figure 8 The startup process of the flyback converter in this implementation scheme is described in detail below:

[0106] At time t0, the primary-side control circuit 5 of the flyback converter starts and begins to generate the first control signal Vgs1_P. The first control signal Vgs1_P begins to control the transfer of start-up energy to the secondary side of the flyback converter. That is, the start-up unit 81 in the secondary-side control circuit 8 begins to obtain start-up energy through the first input terminal SW and the second input terminal Vo in the secondary-side control circuit 8 and begins to increase the voltage of the power supply terminal in the secondary-side control circuit 8.

[0107] At time t1, the secondary control circuit 8 is enabled and begins soft start, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo begin to rise steadily.

[0108] During the time period t1 to t2, the secondary control circuit 8 gradually soft-starts, that is, the output voltage Vo of the flyback converter and the output feedback signal Vcomp characterizing the output voltage Vo gradually and smoothly increase, thus realizing the smooth start of the output voltage Vo.

[0109] At time t2, the output feedback signal Vcomp is greater than or equal to the first reference voltage Vref1, and the first control signal vgs1_P is also at a valid high level, i.e., the aforementioned first time point is reached. At this time, the stop signal generation unit 833 in the secondary control circuit 8 begins to transmit a stop signal to the primary control circuit 5. The first control signal generation unit 51 in the primary control circuit 5 stops generating the first control signal Vgs1_P under the trigger of the stop signal, and the delay unit 834 starts timing. The stop signal during the time period from t2 to t3 is represented by dashed lines. To ensure the smoothness and continuity of the flyback converter during the switching of control modes between the primary and secondary sides, optionally, if time t2 occurs when the first control signal vgs1_P is at a low level, that is, when the first control signal generation unit 51 in the primary-side control circuit 5 receives the stop signal while the first control signal vgs1_P is at a low level, it can be configured to stop generating the first control signal Vgs1_P upon receiving the stop signal; if time t2 occurs when the first control signal vgs1_P is at a high level, that is, when the first control signal generation unit 51 in the primary-side control circuit 5 receives the stop signal while the first control signal vgs1_P is at a high level, it can be configured to stop generating the first control signal Vgs1_P only after the first control signal vgs1_P becomes low.

[0110] After the delay unit 834 times the first time Td, i.e., at time t3, the secondary-side control circuit 8 begins to transmit the second control signal PWM1 to the primary-side control circuit 5 normally. This second control signal PWM1 begins to replace the first control signal Vgs1_P to trigger the drive unit 52 to generate the first drive signal Vgs1, thereby continuing to control the on / off state of the power switch Q1 and realizing the energy transfer between the primary and secondary sides of the flyback converter. That is, from time t3, the flyback converter enters the secondary-side control mode.

[0111] It should be noted that if the output feedback signal Vcomp reaches the first reference voltage Vref1 while the first control signal vgs1_P is at a low level, then time t2 is the moment when the first control signal vgs1_P first changes to a high level after the output feedback signal Vcomp reaches the first reference voltage Vref1. Figure 7 As shown; if the output feedback signal Vcomp reaches the first reference voltage Vref1 while the first control signal vgs1_P is at a high level, then time t2 is the time when the output feedback signal Vcomp reaches the first reference voltage Vref1, as follows. Figure 8 As shown.

[0112] As can be seen from the above description, the output unit 83 disclosed in the first embodiment of the present invention has a simple circuit structure and low manufacturing cost. The output unit 83 disclosed in the second embodiment of the present invention ensures that during the switching of the primary and secondary control modes of the flyback converter, there will be no excessively long blank period in the control of the primary-side power switch Q1, i.e., the first drive signal Vgs1 will not experience pulse loss, which is beneficial to improving the smoothness and continuity of the control switching of the primary-side power switch Q1.

[0113] Furthermore, in this embodiment of the invention, the difference between the period of the first time Td and the period of the first control signal Vgs1_P is set to be less than a preset threshold, so as to further improve the stability and continuity of the flyback converter in the process of switching the control modes of the primary and secondary sides.

[0114] Furthermore, the present invention sets the frequency (i.e., 1 / Ts_s) and pulse width parameters of the second control signal PWM1 at least in the initial pulse period (corresponding to the time period t3 to t4) to be basically consistent with the frequency (i.e., 1 / Ts_p) and pulse width parameters of the first control signal Vgs1_P. That is, the difference between the frequency and pulse width parameters of the second control signal PWM1 at least in the initial pulse period (corresponding to the time period t3 to t4) and the frequency and pulse width parameters of the first control signal Vgs1_P is less than a preset threshold. This ensures that the drive signal of the primary-side power switch does not change abruptly during startup, achieving a smooth transition of primary and secondary-side control and a smooth startup of the output voltage, thereby improving the output quality of the flyback converter.

[0115] It should also be noted that, in the first embodiment of the present invention, although there is a pulse missing during the primary-side control circuit 5 outputting the first drive signal Vgs1 to the gate of the power switch Q1 during the primary-secondary side control switching process, i.e., during the period when the stop signal triggers the first control signal generation unit 51 to stop generating the first control signal Vgs1_P, the output capacitor Co is provided at the output terminal of the flyback converter, and the frequency of the first drive signal Vgs1 is very high, so it will not affect the stability and continuity of the output voltage Vo of the flyback converter.

[0116] Furthermore, the flyback converter disclosed in this invention also includes a current-limiting resistor R connected in series in the primary power circuit of the flyback converter. CS_P Furthermore, the primary-side control circuit 5 also includes a fifth input terminal PCS. The fifth input terminal PCS of the primary-side control circuit 5 is used to receive the current-limiting resistor R. CS_P The voltage across the two ends. The primary-side control circuit is used to turn off the power switch Q1 when the voltage across the current-limiting resistor exceeds a preset voltage threshold.

[0117] In this embodiment, the primary-side control circuit 5 acquires data from the current-limiting resistor R. CS_PThe voltage across the terminals is compared with a preset voltage threshold, and the current is limited by the current-limiting resistor R. CS_P When the voltage across the terminals exceeds a preset voltage threshold, the power switch Q1 is turned off. Thus, this embodiment can effectively suppress the current in the power circuit when the transformer's magnetizing inductance is abnormal, preventing abnormal increases in current and improving system stability and reliability. It should be noted that in this embodiment, the preset voltage threshold is a fixed value, used only to determine whether the current in the power circuit is abnormal, and the current-limiting resistor R... CS_P If the resistance value is small, for example, less than a preset threshold, the power is also low, meaning the current-limiting resistor R... CS_P The resistance value is much smaller than that of the sampling resistor connected in series in the primary power circuit of a traditional flyback converter. It cannot achieve peak current control of the flyback converter, nor will it occupy too much integrated circuit area. It can reduce the specifications and number of resistors in the system, and its impact on the efficiency and cost of the flyback converter system can be ignored.

[0118] Furthermore, the present invention also discloses a startup control method for a flyback converter, which can be applied to, for example... Figures 1 to 10 The flyback converter described in [reference]. Figure 11 The startup control method specifically includes performing the following steps:

[0119] In step S1, after the flyback converter is powered on, a first control signal is generated using the primary-side control circuit to control the transfer of startup energy to the secondary side of the flyback converter. In this embodiment, the specific operation method of step S1 can be understood by referring to the foregoing description of the primary-side control circuit 5 and the first control signal generation unit 51, and will not be repeated here.

[0120] In step S2, after the secondary-side control circuit is started, it transmits a stop signal and a second control signal to the primary-side control circuit sequentially. Both the first and second control signals are used to trigger the on / off control of the power switch Q1. The stop signal triggers the primary-side control circuit to stop generating the first control signal Vgs1_P, or it triggers the blocking of the first control signal Vgs1_P's on / off control of the power switch Q1. Simultaneously, the difference between the frequency and pulse width parameters of the second control signal and those of the first control signal, at least in the initial pulse period, is less than a preset threshold.

[0121] In this embodiment, step S2 further includes: transmitting a stop signal to the primary-side control circuit at the first instant after the secondary-side control circuit starts, and transmitting a second control signal to the primary-side control circuit after a first time delay starting from the first instant. The first instant is the moment when the output feedback signal of the flyback converter reaches the first reference voltage; or it is the moment when, for the first time, the output feedback signal is greater than or equal to the first reference voltage and simultaneously falls within a preset time period after the power switch starts conducting. Further, the specific operation method of step S2 can be understood by referring to the aforementioned description of the output unit 83, and will not be repeated here.

[0122] In summary, this embodiment of the invention, by configuring the primary-side control circuit to start upon power-up of the flyback converter, outputs a first control signal to control the on / off state of the power switch, thereby providing startup energy to the secondary-side control circuit and the flyback converter output. After the secondary-side control circuit receives startup energy and starts, it first triggers the primary-side control circuit to stop generating the first control signal, and then transmits a second control signal to the primary-side control circuit to replace the first control signal and continue controlling the power switch. This ensures a smooth transition from primary-side control to secondary-side control. Furthermore, by ensuring that the difference between the frequency and pulse width parameters of the second control signal in its initial pulse period and those of the first control signal is less than a preset threshold (i.e., the second control signal has essentially the same frequency and pulse width as the first control signal in its initial pulse period), the drive signal of the primary-side power switch will not undergo abrupt changes during startup, achieving a smooth transition between primary and secondary-side control and a smooth startup of the output voltage, thus improving the output quality of the flyback converter.

[0123] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A flyback converter, wherein, The application relates to a transformer, a power switch tube, a rectifier tube, a primary side control circuit, a secondary side control circuit, and a method for starting a flyback converter. The transformer comprises a primary winding and a secondary winding. The power switch tube is connected to the primary winding. The rectifier tube is connected between the secondary winding and an output terminal of the flyback converter. The primary side control circuit is started after the flyback converter is powered on, and generates a first control signal to control the delivery of starting energy to a secondary part of the flyback converter after being started. The secondary side control circuit delivers a stop signal and a second control signal to the primary side control circuit in sequence after being started, and the frequency and pulse width parameters of the second control signal in an initial pulse period are both less than the difference between the frequency and pulse width parameters of the first control signal by a preset threshold. The first control signal and the second control signal are both used to trigger the on-off control of the power switch tube, and the stop signal is used to trigger the primary side control circuit to stop generating the first control signal or to trigger the shielding of the first control signal from controlling the on-off of the power switch tube. The secondary side control circuit is configured to deliver the stop signal to the primary side control circuit at a first time after being started, and to deliver the second control signal to the primary side control circuit after delaying a first time from the first time. The primary side control circuit receives the stop signal and the second control signal by using the same pin.

2. The flyback converter of claim 1, wherein, The first time is the time when an output feedback signal reaches a first reference voltage, wherein the output feedback signal represents the output power of the flyback converter.

3. The flyback converter of claim 1, wherein, The first time is the time when the output feedback signal is greater than or equal to the first reference voltage and is within a preset time period after the power switch tube starts to conduct for the first time, wherein the output feedback signal represents the output power of the flyback converter.

4. The flyback converter of claim 2, wherein, The secondary side control circuit comprises an output unit configured to receive the output feedback signal and generate the stop signal at the first time, and the output unit comprises: A first comparison unit having a positive input end receiving the output feedback signal and a negative input end receiving the first reference voltage, and being configured to output a first trigger signal when the output feedback signal is greater than or equal to the first reference voltage. A stop signal generation unit having an input end connected to the output end of the first comparison unit and being configured to generate the stop signal when the first trigger signal is received.

5. The flyback converter of claim 3, wherein, The secondary side control circuit comprises an output unit configured to receive the output feedback signal and generate the stop signal at the first time, and the output unit comprises: A second comparison unit having a positive input end receiving the output feedback signal and a negative input end receiving the first reference voltage, and being configured to output a first comparison signal when the output feedback signal is greater than the first reference voltage. A third comparison unit having a positive input end receiving a second reference voltage and a negative input end receiving a voltage difference between two power ends of the rectifier tube, and an output end outputting a second comparison signal. The third comparison unit is configured to output the second comparison signal when the voltage difference between the two power ends of the rectifier tube is less than the second reference voltage. The rising edge pulse generation unit receives the second comparison signal at the input end and generates a pulse at the rising edge of the second comparison signal to output a first pulse signal; The first combination logic circuit receives the first comparison signal and the first pulse signal, and is configured to output a first trigger signal when the first comparison signal and the first pulse signal are detected to be in an active state at the same time for the first time. The stop signal generation unit is connected to the output end of the first combination logic circuit, and is configured to generate the stop signal when the first trigger signal is received.

6. The flyback converter of claim 4 or 5, wherein, The output unit further comprises: The delay unit receives the first trigger signal at the input end, and is configured to start timing when the first trigger signal is received, and output a second trigger signal after the first time; The first AND logic circuit receives the second control signal at the first input end, and is connected to the output end of the delay unit at the second input end, and is configured to output the received second control signal after the second trigger signal is received; The OR logic circuit is connected to the output end of the first AND logic circuit at the first input end, and is connected to the output end of the stop signal generation unit at the second input end, and is configured to realize time-sharing output of the stop signal and the second control signal.

7. The flyback converter of claim 2 or 3, wherein, The secondary side control circuit further comprises: The output feedback signal generation circuit is configured to generate the output feedback signal according to the output voltage of the flyback converter; The second control signal generation unit is configured to generate the second control signal according to the output feedback signal.

8. The flyback converter of claim 1, wherein, The primary side control circuit comprises: The first control signal generation unit is configured to start generating the first control signal after the flyback converter is powered on, and to stop generating the first control signal according to the stop signal; The driving unit is configured to transmit a first driving control signal to the control end of the power switch tube to realize on-off control of the power switch tube when the first control signal or the second control signal is received.

9. A start-up control method of a flyback converter, applied to the flyback converter according to any one of claims 1 to 8, wherein, The start control method comprises: After the flyback converter is powered on, the primary side control circuit generates a first control signal to control the transfer of start-up energy to the secondary side part of the flyback converter; After the secondary side control circuit starts, the secondary side control circuit successively transmits a stop signal and a second control signal to the primary side control circuit, Wherein, the first control signal and the second control signal are used to trigger the on-off control of the power switch tube, and the stop signal is used to trigger the primary side control circuit to stop generating the first control signal or to trigger the first control signal to mask the on-off control of the power switch tube.

10. The start-up control method according to claim 9, wherein The secondary side control circuit successively transmits a stop signal and a second control signal to the primary side control circuit comprises: The stop signal is transmitted to the primary side control circuit at a first time after the start of the secondary side control circuit, and the second control signal is transmitted to the primary side control circuit after a first time delay from the first time.

11. The start-up control method according to claim 10, wherein The first time is when the output feedback signal of the flyback converter reaches a first reference voltage.

12. The start-up control method according to claim 10, wherein The first time is when the output feedback signal is greater than or equal to a first reference voltage for the first time after the power switch tube starts to conduct within a preset time period.

13. The start-up control method according to claim 9, wherein The difference between the frequency and pulse width parameters of the second control signal in the initial pulse period and the frequency and pulse width parameters of the first control signal is less than a preset threshold.

14. The start-up control method according to claim 10, wherein The difference between the first time and the period of the first control signal is less than a preset threshold.

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