Switching control circuit and flyback switching power supply

Abstract

This invention discloses a switching control circuit and a flyback switching power supply. The switching control circuit includes a detection circuit, a mode control circuit, and a drive circuit. The input terminal of the detection circuit is coupled to the drain of the main switching transistor to obtain a first acquisition signal characterizing the drain voltage of the main switching transistor. The input terminal of the mode control circuit is coupled to the output terminal of the detection circuit. The mode control circuit includes a first comparator circuit, the first input terminal of which is coupled to a first reference signal terminal, the second input terminal of which is coupled to the output terminal of the detection circuit, and the output terminal of the first comparator circuit outputs a mode control signal. The input terminal of the drive circuit is coupled to the output terminal of the mode control circuit, and the output terminal of the drive circuit is coupled to the main switching transistor. The drive circuit is used to generate a drive control signal. The switching control circuit and flyback switching power supply disclosed in this invention effectively improve the stability of the flyback switching power supply system and simultaneously improve system efficiency.

Description

Technical Field

[0001] This utility model belongs to the field of power electronics, and relates to a switch control technology, particularly a switch control circuit and a flyback switching power supply. Background Technology

[0002] Switching power supplies are widely used due to their advantages such as high efficiency and energy saving, small size and light weight, stable output, multiple protection functions, and wide input voltage range. These advantages enable switching power supplies to perform well in various application scenarios and meet the power requirements of modern electronic devices.

[0003] In low-to-medium power switching power supply applications requiring electrical isolation between input and output, the flyback switching power supply is the most commonly used topology. A simplified circuit diagram of a flyback switching power supply is shown below. Figure 1 As shown, a flyback switching power supply includes a primary circuit, a secondary circuit, and a transformer. Simplicity, reliability, low cost, and ease of implementation are the most prominent advantages of flyback switching power supplies. (The last sentence appears to be incomplete and possibly refers to a different topic.) Figure 2 In one technical solution, taking the intermittent mode working state as an example, and combining it with... Figure 3 When the drive control signal is at Ton (e.g., high level), the main switch Q1 is turned on, the voltage across its drain and source is close to 0V, the secondary diode D7 is reverse-biased and cut off, the primary voltage of the transformer is Vin, the transformer magnetizing inductor stores energy, and the primary current increases linearly. When the drive control signal is at Toff (e.g., low level), the main switch Q1 is turned off, the secondary diode D7 is turned on, the voltage across the secondary side of the transformer is Vo+VF, and the voltage across the drain and source of the main switch Q1 is Vin+Nps*(Vo+VF), where Nps is the turns ratio of the transformer winding. The transformer magnetizing inductor releases its capacity to the load, and the secondary current decreases linearly. When the secondary current drops to zero, the secondary diode is cut off, and the drain voltage of the main switch Q1 decreases under the resonance effect of the primary magnetizing inductor and the output junction capacitance. During this process, if the system operates in fixed frequency mode, the next switching cycle is started by the frequency signal. If it operates in quasi-resonant mode, the chip will start the next switching cycle at the valley position before the oscillator signal arrives. Quasi-resonant control can reduce the voltage at which the flyback main power device turns on, reduce turn-on losses, and improve system efficiency.

[0004] In view of this, a new structure is needed to solve at least some of the above problems. Utility Model Content

[0005] In view of one or more problems in the prior art, this utility model proposes a switching control circuit and a flyback switching power supply.

[0006] According to one aspect of this utility model, a switch control circuit is disclosed. The switch control circuit is used to control the main switching transistor of a flyback switching power supply. The switch control circuit includes:

[0007] The detection circuit has an input terminal coupled to the drain of the main switch transistor to obtain a first acquisition signal characterizing the drain voltage of the main switch transistor. The detection circuit includes a sampling circuit, the input terminal of which is coupled to the first acquisition signal terminal. The sampling circuit is used to sample and generate a detection signal based on the first acquisition signal.

[0008] A mode control circuit, whose input terminal is coupled to the output terminal of a detection circuit, includes a first comparator circuit. The first input terminal of the first comparator circuit is coupled to a first reference signal terminal to obtain a first reference signal. The second input terminal of the first comparator circuit is coupled to the output terminal of the detection circuit to obtain a detection signal. The output terminal of the first comparator circuit outputs a mode control signal to control the operating mode of the flyback switching power supply.

[0009] The driver circuit has its input terminal coupled to the output terminal of the mode control circuit, and its output terminal is used to couple to the main switch transistor to generate a drive control signal to control the main switch transistor.

[0010] In one embodiment, the input terminal of the sampling circuit is also coupled to the drive control signal terminal to obtain the drive control signal.

[0011] In one embodiment, the sampling circuit includes a first timing circuit coupled to a drive control signal terminal, and the first timing circuit is used to start timing when the drive control signal changes to a second level.

[0012] In one embodiment, the input of the sampling circuit is also coupled to a freewheeling detection circuit.

[0013] In one embodiment, the switching control circuit includes a frequency control circuit, the input of which is coupled to the output of the mode control circuit. The frequency control circuit is used to control the switching frequency of the main switching transistor according to the operating mode of the flyback switching power supply.

[0014] In one embodiment, the mode control circuit further includes:

[0015] The averaging circuit, whose input is coupled to the drain of the main switching transistor, is used to generate an average signal characterizing the bus voltage based on the drain voltage of the main switching transistor; and

[0016] The third comparison circuit has its first input terminal coupled to a detection circuit to obtain a first acquisition signal, its second input terminal coupled to the output terminal of an averaging circuit, and its output terminal outputting a zero-crossing detection signal.

[0017] In one embodiment, the mode control circuit further includes:

[0018] A sample-and-hold circuit, whose inputs are respectively coupled to a detection circuit to acquire a first acquisition signal and a drive control signal, is used to sample the first acquisition signal to generate a sample-and-hold signal after the drive control signal changes to a second level; and

[0019] The fourth comparator circuit has its first input terminal coupled to the output terminal of the sample-and-hold circuit, its second input terminal coupled to the detection circuit to obtain the first acquisition signal, and its output terminal outputting a zero-crossing detection signal.

[0020] In one embodiment, the input terminal of the mode control circuit is coupled to an auxiliary winding, and the mode control circuit obtains a zero-crossing detection signal through the auxiliary winding.

[0021] In one embodiment, the switch control circuit is a chip, and the main switch transistor is either built into or external to the switch control circuit.

[0022] According to another aspect of the present invention, a flyback switching power supply is disclosed, the flyback switching power supply including a primary side circuit, a secondary side circuit and a transformer, the primary side circuit including a switching control circuit as described in any of the above claims, the switching control circuit being used to generate a drive control signal to control the main switching transistor.

[0023] This invention discloses a switch control circuit and a flyback switching power supply. The switch control circuit controls the main switching transistor of the flyback switching power supply. The switch control circuit includes a detection circuit, a mode control circuit, and a drive circuit. The input terminal of the detection circuit is coupled to the drain of the main switching transistor to obtain a first acquisition signal characterizing the drain voltage of the main switching transistor. The detection circuit includes a sampling circuit, the input terminal of which is coupled to the first acquisition signal terminal. The sampling circuit is used to sample and generate a detection signal based on the first acquisition signal. The input terminal of the mode control circuit is coupled to the output terminal of the detection circuit. The mode control circuit includes a first comparator circuit, the first input terminal of which is coupled to a first reference signal terminal to obtain a first reference signal. The second input terminal of the first comparator circuit is coupled to the output terminal of the detection circuit to obtain a detection signal. The output terminal of the first comparator circuit outputs a mode control signal to control the operating mode of the flyback switching power supply. The input terminal of the drive circuit is coupled to the output terminal of the mode control circuit. The output terminal of the drive circuit is coupled to the main switching transistor. The drive circuit is used to generate a drive control signal to control the main switching transistor. The present invention proposes a switching control circuit and a flyback switching power supply, which effectively improves the stability of the flyback switching power supply system and enhances the system efficiency. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the present invention and, together with the description, serve to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 A schematic diagram of the circuit structure of a prior art flyback switching power supply is shown.

[0026] Figure 2 A schematic diagram of the circuit structure of another prior art flyback switching power supply is shown;

[0027] Figure 3 This diagram illustrates the signal waveform of another prior art flyback switching power supply.

[0028] Figure 4 A schematic diagram of the circuit structure of a switch control circuit according to an embodiment of the present invention is shown;

[0029] Figure 5 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0030] Figure 6 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0031] Figure 7 A schematic diagram of the circuit structure of a switch control circuit according to an embodiment of the present invention is shown;

[0032] Figure 8 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0033] Figure 9 A schematic diagram of the signal waveform of a flyback switching power supply according to an embodiment of the present invention. Detailed Implementation

[0034] To further understand this utility model, preferred embodiments of this utility model are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this utility model, and not for limiting the scope of the claims of this utility model.

[0035] The description in this section pertains to only a few typical embodiments, and this utility model is not limited to the scope of the embodiments described. Combinations of different embodiments, substitution of some technical features in different embodiments, and substitution of the same or similar prior art with some technical features in the embodiments are also within the scope of the description and protection of this utility model.

[0036] The terms "coupled" or "connected" in this specification include both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a connection through an electrically conductive medium like a conductor, which may contain parasitic inductance or capacitance. It can also be a connection through intermediate circuits or components described in the embodiments of this specification. Indirect connections may also include connections through other active or passive devices that achieve the same or similar functions, such as connections through switches, signal amplification circuits, follower circuits, or other circuits or components. "Multiple" or "more" indicates two or more. Furthermore, in this invention, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship or order between these technical features.

[0037] One embodiment of this utility model discloses a switch control circuit, which is used to control the main switch transistor Q1 of a flyback switching power supply. For example... Figure 4As shown, the switching control circuit includes a detection circuit 10, a mode control circuit 20, and a drive circuit 30. The input terminal of the detection circuit 10 is coupled to the drain of the main switching transistor Q1. The detection circuit 10 acquires a first acquisition signal characterizing the drain voltage Vdrain of the main switching transistor Q1 and generates a detection signal based on the first acquisition signal. In one embodiment, the first acquisition signal is equal to the drain voltage Vdrain of the main switching transistor Q1. In another embodiment, the first acquisition signal is proportional to or positively correlated with the drain voltage Vdrain of the main switching transistor Q1. In one embodiment, the detection circuit includes a sampling circuit, the input terminal of which is coupled to the first acquisition signal terminal. The sampling circuit generates a detection signal based on the first acquisition signal. The input terminal of the mode control circuit 20 is coupled to the output terminal of the detection circuit 10. The mode control circuit 20 compares the detection signal and a first reference signal and generates a mode control signal based on the comparison result to control the operating mode of the flyback switching power supply. In one embodiment, the mode control circuit includes a first comparator circuit. The first input terminal of the first comparator circuit is coupled to a first reference signal terminal to obtain a first reference signal. The second input terminal of the first comparator circuit is coupled to the output terminal of a detection circuit to obtain a detection signal. The first comparator circuit compares the first reference signal and the detection signal and outputs a mode control signal to control the operating mode of the flyback switching power supply. The operating modes of the flyback switching power supply include quasi-resonant mode and continuous mode. When the detection signal is greater than the first reference signal, the mode control circuit controls the flyback switching power supply to be in quasi-resonant mode. When the detection signal is less than the first reference signal, the mode control circuit controls the flyback switching power supply to be in continuous mode. The input terminal of the drive circuit 30 is coupled to the output terminal of the mode control circuit 20. The output terminal of the drive circuit 30 is used to couple to the control terminal of the main switch Q1. The drive circuit 30 is used to generate a drive control signal PWM to control the switching state of the main switch. The switching state of the main switch includes an on state and an off state.

[0038] like Figure 5As shown, one embodiment of this utility model discloses a switch control circuit, which includes a detection circuit 11, a mode control circuit 21, and a drive circuit 31. The detection circuit 11 includes a voltage divider circuit and a sampling circuit (not shown in the figure). The voltage divider circuit includes a first resistor R1 and a second resistor R2. The first end of the first resistor R1 is coupled to the drain of the main switch transistor Q1. The first end of the second resistor R2 is coupled to the second end of the first resistor R1, and the second end of the second resistor R2 is coupled to ground. The input terminal of the sampling circuit is coupled to the first end of the second resistor R2 and the drive control signal terminal to obtain the drive control signal. The sampling circuit samples the first acquisition signal at a preset time after the drive control signal PWM changes to the second level to generate a detection signal. In another embodiment, the sampling circuit includes a first timing circuit, which is coupled to the drive control signal terminal. The first timing circuit is used to start timing when the drive control signal changes to the second level. The sampling circuit samples the first acquisition signal at a preset time after the drive control signal changes to the second level to generate a detection signal.

[0039] In one embodiment, the first acquired signal is the voltage across the first terminal of the second resistor R2. In another embodiment, the detection circuit includes a voltage divider circuit and a sampling circuit. The voltage divider circuit includes a first resistor and a second resistor. The first terminal of the first resistor is coupled to the drain of the main switch transistor. The first terminal of the second resistor is coupled to the second terminal of the first resistor, and the second terminal of the second resistor is coupled to ground. The input terminal of the sampling circuit is coupled to the first terminal of the second resistor and the freewheeling detection circuit to acquire a freewheeling detection signal. The freewheeling detection signal characterizes whether the system is in the secondary-side freewheeling phase. The sampling circuit is used to sample the first acquired signal during the secondary-side freewheeling phase to generate a detection signal.

[0040] In one embodiment, such as Figure 5 As shown, the mode control circuit 21 includes a first comparator circuit 211. The first input terminal of the first comparator circuit 211 is coupled to a first reference signal terminal to obtain a first reference signal Vref1. The second input terminal of the first comparator circuit 211 is coupled to the output terminal of a detection circuit to obtain a detection signal. The output terminal of the first comparator circuit 211 is coupled to the input terminal of the drive circuit 31. When the detection signal is less than the first reference signal Vref1, the switching control circuit switches the flyback switching power supply from its operating mode to continuous mode, thereby improving the system efficiency under low-voltage input.

[0041] In another embodiment, such as Figure 6As shown, the switch control circuit includes a detection circuit 12, a mode control circuit 22, and a drive circuit 32. The switch control circuit provides a first reference signal Vref1 and a second reference signal Vref2, where the first reference signal Vref1 is greater than the second reference signal Vref2. The mode control circuit 22 includes a first comparison circuit 221 and a second comparison circuit 222. The first input terminal of the first comparison circuit 221 is coupled to the first reference signal terminal to obtain the first reference signal Vref1. The second input terminal of the first comparison circuit 221 is coupled to the output terminal of the detection circuit 12, and the output terminal of the first comparison circuit 221 is coupled to the input terminal of the drive circuit 32. The output terminal of the comparison circuit 221 outputs a first comparison result. The first input terminal of the second comparison circuit 222 is coupled to the second reference signal terminal to obtain the second reference signal Vref2. The second input terminal of the second comparison circuit 222 is coupled to the output terminal of the detection circuit 12, and the output terminal of the second comparison circuit 222 is coupled to the input terminal of the drive circuit. The output terminal of the second comparison circuit 222 outputs a second comparison result. The drive circuit 32 generates a drive control signal PWM based on the first and second comparison results. When the detected signal is less than the first reference signal Vref1, the switching control circuit does not need to switch the operating mode of the flyback switching power supply. When the detected signal is less than the second reference signal Vref2, the switching control circuit switches the operating mode of the flyback switching power supply to continuous mode.

[0042] like Figure 7 As shown, in one embodiment, the switch control circuit includes a detection circuit 13, a mode control circuit 23, and a drive circuit (not shown in the figure). In one embodiment, Figure 7 The mode control circuit 23 can be used to detect valleys and obtain valley signals. The mode control circuit 23 includes a first comparator circuit 231, an averaging circuit, and a third comparator circuit 233. The input of the averaging circuit is coupled to the drain of the main switching transistor, and the averaging circuit generates an average signal characterizing the bus voltage based on the drain voltage of the main switching transistor. The first input of the third comparator circuit 233 is coupled to the detection circuit 13 to obtain a first acquisition signal, the second input of the third comparator circuit 233 is coupled to the output of the averaging circuit, and the output of the third comparator circuit 233 outputs a zero-crossing detection signal ZCD. When the detection signal is greater than the first reference signal, the mode control circuit enables the third comparator circuit, thus the third comparator circuit operates.

[0043] In one embodiment, the averaging circuit includes a filter circuit, the input of which is coupled to the drain of the main switching transistor Q1. The filter circuit includes a third resistor R3, a fourth resistor R4, and a first capacitor C1. The first terminal of the third resistor R3 is coupled to the drain of the main switching transistor Q1. The first terminal of the fourth resistor R4 is coupled to the second terminal of the third resistor R3, and the second terminal of the fourth resistor R4 is coupled to ground. The first terminal of the first capacitor C1 is coupled to the first terminal of the fourth resistor R4, and the second terminal of the first capacitor C1 is coupled to ground. In another embodiment, as... Figure 7 As shown, the filter circuit includes a third resistor R3, a fourth resistor R4, a first capacitor C1, and a follower 232. The first input terminal of the follower 232 is coupled to the first terminal of the first capacitor C1, the second input terminal of the follower 232 is coupled to the output terminal of the follower 232, and the output terminal of the follower 232 is coupled to the second input terminal of the third comparator circuit 233.

[0044] In another embodiment, the averaging circuit includes a signal processing circuit for averaging the drain voltage of the main switching transistor and generating an average signal. In one embodiment, the average signal is equal to the average value of the drain voltage of the main switching transistor. In another embodiment, the average signal is proportional to or positively correlated with the average value of the drain voltage of the main switching transistor.

[0045] like Figure 8 As shown, in one embodiment, Figure 8 The mode control circuit 24 can be used to implement valley detection to obtain a valley signal. In one embodiment, the mode control circuit 24 includes a sample-and-hold circuit and a fourth comparator circuit. The input of the sample-and-hold circuit is coupled to the detection circuit to obtain a first acquisition signal. The sample-and-hold circuit is used to sample the first acquisition signal to generate a sample-and-hold signal after the drive control signal changes to the second level. The first input of the fourth comparator circuit is coupled to the output of the sample-and-hold circuit, the second input of the fourth comparator circuit is coupled to the detection circuit to obtain the first acquisition signal, and the output of the fourth comparator circuit outputs a zero-crossing detection signal ZCD. During one switching cycle, in the secondary freewheeling phase when the drive control signal PWM is in the off state, the drain voltage Vdrain is equal to Vbus + N*Vo. By sampling and holding the drain voltage Vdrain obtained in the secondary freewheeling phase and comparing it with the real-time sampled drain voltage Vdrain, when the drain voltage Vdrain is lower than the sample-and-hold signal, the system freewheeling ends and resonance begins. By sampling the zero-crossing detection ZCD at this time and after a delay of 1 / 2 of the resonance period, quasi-resonant valley turn-on can be achieved, thereby realizing the quasi-resonant turn-on of the main switch.

[0046] In another embodiment, the input of the mode control circuit is coupled to an auxiliary winding, and the mode control circuit can obtain a zero-crossing detection signal through the auxiliary winding.

[0047] In one embodiment of this utility model, combined with Figure 9 The drain voltage Vdrain is the drain terminal voltage of the main switch transistor. It is obtained by voltage detection of the drain of the main switch transistor. The drain voltage of the main switch transistor is 0V during the Ton phase (when the main switch transistor is on), and decreases during the Toff phase (when the main switch transistor is off), specifically during the secondary-side freewheeling phase (i.e., the freewheeling phase of the secondary diode). Figure 9 During the time interval T0 to T2, the drain voltage is Vbus + N*Vo. After the secondary freewheeling ends, the drain voltage begins to resonate and oscillate, with the center value of the oscillation being Vbus. Here, Vbus is the bus voltage, N is the transformer turns ratio, and Vo is the output voltage of the flyback converter. Figure 9 As shown, in one embodiment, the drive control signal PWM is in the off state at time T0, and the drain voltage Vdrain rises. A detection signal is acquired during the time period from T0 to T2, and compared with a first reference signal. When the detection signal is greater than the first reference signal, the switching control circuit controls the flyback switching power supply to be in quasi-resonant mode, achieving cycle-by-cycle state control. When the detection signal is less than the first reference signal (or, in other embodiments, less than a second reference signal), the switching control circuit controls the flyback switching power supply to be in continuous mode, achieving cycle-by-cycle state control. In one embodiment, as... Figure 9 As shown, the voltage Vzcd is the zero-crossing detection signal. Within one switching cycle, the zero-crossing detection signal can be obtained by comparing the drain voltage Vdrain and the bus voltage Vbus. Based on the obtained resonant period Treing, quasi-resonant valley-level turn-on can be achieved.

[0048] This utility model discloses a flyback switching power supply in one embodiment. The flyback switching power supply includes a primary-side circuit, a secondary-side circuit, and a transformer. The primary-side circuit includes a switching control circuit as described in any of the preceding embodiments. The switching control circuit generates a drive control signal to control the switching state of the main switching transistor. The switching control circuit includes a detection circuit, a mode control circuit, and a drive circuit. In one embodiment, the switching control circuit further includes a frequency control circuit, the input of which is coupled to the output of the mode control circuit. The frequency control circuit controls the switching frequency of the main switching transistor according to the operating mode of the flyback switching power supply. In continuous mode, the switching control circuit controls the switching state of the main switching transistor at a preset frequency. In quasi-resonant mode, the switching control circuit controls the switching state of the main switching transistor according to a set frequency range and the mode control signal. In one embodiment, in quasi-resonant mode, the switching control circuit controls the operating frequency of the main switching transistor within a set frequency range and controls the turn-on of the main switching transistor according to a zero-crossing detection signal. In one embodiment, the switching control circuit is a chip, and the main switching transistor is built into the switching control circuit. In another embodiment, the switching control circuit is a chip, and the main switching transistor is externally located in the switching control circuit.

[0049] An embodiment of this utility model also discloses a switch control method for controlling a switch control circuit, the switch control method comprising:

[0050] Step S01: Acquire a first acquisition signal characterizing the drain voltage of the main switch transistor, and generate a detection signal based on the first acquisition signal;

[0051] Step S02: Compare the detection signal and the first reference signal and generate a mode control signal to control the operating mode of the flyback switching power supply; when the detection signal is greater than the first reference signal, control the flyback switching power supply to be in quasi-resonant mode; when the detection signal is less than the first reference signal, control the flyback switching power supply to be in continuous mode for at least part of the time; and

[0052] Step S03: Generate a drive control signal based on the mode control signal to control the main switch transistor.

[0053] In one embodiment, the switching control circuit includes a detection circuit, a mode control circuit, and a drive circuit. The detection circuit acquires a first acquisition signal characterizing the drain voltage of the main switch transistor and samples and generates a detection signal based on the first acquisition signal. The mode control circuit compares the detection signal with a first reference signal and generates a mode control signal to control the operating mode of the flyback switching power supply. When the detection signal is greater than the first reference signal, the mode control circuit controls the flyback switching power supply to be in a quasi-resonant mode. When the detection signal is less than the first reference signal, the mode control circuit controls the flyback switching power supply to be in a continuous mode for at least a portion of the time. The drive circuit generates a drive control signal based on the mode control signal to control the switching state of the main switch transistor.

[0054] In another embodiment, the step of acquiring a first acquisition signal characterizing the drain voltage of the main switch and generating a detection signal based on the first acquisition signal includes: sampling the first acquisition signal at a preset time after the drive control signal changes to a second level to generate the detection signal.

[0055] In another embodiment, the step of acquiring a first acquisition signal characterizing the drain voltage of the main switch and generating a detection signal based on the first acquisition signal includes: sampling the first acquisition signal during the secondary freewheeling phase to generate the detection signal.

[0056] In one embodiment, in continuous mode, the switching control circuit controls the switching state of the main switch transistor at a preset frequency; and / or in quasi-resonant mode, the switching control circuit controls the switching state of the main switch transistor at a set frequency range and mode control signal.

[0057] Based on the switching control circuit and flyback switching power supply proposed in this invention, the flyback switching power supply can operate in quasi-resonant mode when the input voltage is high, and in continuous mode when the input voltage is low. The system is suitable for continuous mode (CCM mode) when the input voltage is low, as CCM mode is beneficial for improving efficiency at low input voltage. If operating in quasi-resonant mode, the chip will start the next switching cycle at the valley position before the oscillator signal arrives. Quasi-resonant control can reduce the voltage at which the flyback main power device turns on, reducing turn-on losses and improving system efficiency at high input voltage. Therefore, valley detection is also required at high input voltage. Simultaneously, rapid switching between continuous mode and quasi-resonant mode is necessary to avoid damage to system components caused by abnormal operating conditions. This invention enables rapid switching between continuous mode and quasi-resonant mode, while also implementing valley detection, effectively solving the problems existing in the prior art. Especially for semiconductors like gallium nitride (GaN) which exhibit dynamic resistance issues, flyback switching power supplies cannot enter continuous mode under high-voltage input and must operate in quasi-resonant mode. Furthermore, to improve system efficiency, the flyback switching power supply can be controlled to operate in continuous mode under low-voltage input. Therefore, this invention enables rapid switching control of the flyback switching power supply's operating mode when the input voltage changes or when sudden input changes occur due to lightning surges. This solves the detection delay problems inherent in common solutions that rely on input voltage or bus voltage detection for switching, effectively improving the stability of the flyback switching power supply system, reducing turn-on losses, and increasing system efficiency.

[0058] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting input" and "inverting input" in the logic control involved in the specification or drawings can be interchanged or changed, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic control.

[0059] The description and application of this utility model herein are illustrative and not intended to limit the scope of the utility model to the above embodiments. The effects or advantages described in the specification may not be apparent in actual experimental examples due to uncertainties in specific conditions or parameters or other factors, and such descriptions are not intended to limit the scope of the utility model. Variations and modifications to the embodiments disclosed herein are possible, and various substitutions and equivalent components of the embodiments are well known to those skilled in the art. It should be clear to those skilled in the art that this utility model can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts without departing from the spirit or essential characteristics of the utility model. Other variations and modifications can be made to the embodiments disclosed herein without departing from the scope and spirit of the utility model.

Claims

1. A switching control circuit for controlling the main switching transistor of a flyback switching power supply, characterized in that, The switch control circuit includes: The detection circuit has an input terminal coupled to the drain of the main switch transistor to obtain a first acquisition signal characterizing the drain voltage of the main switch transistor. The detection circuit includes a sampling circuit, the input terminal of which is coupled to the first acquisition signal terminal. The sampling circuit is used to sample and generate a detection signal based on the first acquisition signal. A mode control circuit, whose input terminal is coupled to the output terminal of a detection circuit, includes a first comparator circuit. The first input terminal of the first comparator circuit is coupled to a first reference signal terminal to obtain a first reference signal. The second input terminal of the first comparator circuit is coupled to the output terminal of the detection circuit to obtain a detection signal. The output terminal of the first comparator circuit outputs a mode control signal to control the operating mode of the flyback switching power supply. The driver circuit has its input terminal coupled to the output terminal of the mode control circuit, and its output terminal is used to couple to the main switch transistor to generate a drive control signal to control the main switch transistor.

2. The switch control circuit as described in claim 1, characterized in that, The input of the sampling circuit is also coupled to the drive control signal terminal to obtain the drive control signal.

3. The switch control circuit as described in claim 2, characterized in that, The sampling circuit includes a first timing circuit, which is coupled to the drive control signal terminal. The first timing circuit is used to start timing when the drive control signal changes to the second level.

4. The switch control circuit as described in claim 1, characterized in that, The input of the sampling circuit is also coupled to the freewheeling current detection circuit.

5. The switch control circuit as described in claim 1, characterized in that, The switching control circuit includes a frequency control circuit. The input of the frequency control circuit is coupled to the output of the mode control circuit. The frequency control circuit is used to control the switching frequency of the main switching transistor according to the operating mode of the flyback switching power supply.

6. The switch control circuit as described in claim 1, characterized in that, The mode control circuit further includes: The averaging circuit, whose input is coupled to the drain of the main switching transistor, is used to generate an average signal characterizing the bus voltage based on the drain voltage of the main switching transistor; and The third comparison circuit has its first input terminal coupled to a detection circuit to obtain a first acquisition signal, its second input terminal coupled to the output terminal of an averaging circuit, and its output terminal outputting a zero-crossing detection signal.

7. The switch control circuit as described in claim 1, characterized in that, The mode control circuit further includes: A sample-and-hold circuit, whose inputs are respectively coupled to a detection circuit to acquire a first acquisition signal and a drive control signal, is used to sample the first acquisition signal to generate a sample-and-hold signal after the drive control signal changes to a second level; and The fourth comparator circuit has its first input terminal coupled to the output terminal of the sample-and-hold circuit, its second input terminal coupled to the detection circuit to obtain the first acquisition signal, and its output terminal outputting a zero-crossing detection signal.

8. The switch control circuit as described in claim 1, characterized in that, The input terminal of the mode control circuit is coupled to the auxiliary winding, and the mode control circuit obtains the zero-crossing detection signal through the auxiliary winding.

9. The switch control circuit as described in claim 1, characterized in that, The switching control circuit is a chip, and the main switching transistor is either built into or external to the switching control circuit.

10. A flyback switching power supply, characterized in that, The flyback switching power supply includes a primary circuit, a secondary circuit, and a transformer. The primary circuit includes the switching control circuit according to any one of claims 1-9, which is used to generate a drive control signal to control the main switching transistor.

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