A control circuit and switching power supply

Abstract

The utility model provides a kind of control circuit and switching power supply, comprising: load detection module, load indicating signal is output based on the signal of representing switching power supply load state;Valley bottom opening detection module, valley bottom opening signal is output based on primary side switch tube drain voltage signal or auxiliary winding voltage division signal;Logic operation module, conducting signal is output based on load indicating signal and valley bottom opening signal;Switching frequency control module, enable signal is output based on switch period signal;Switching control module, switching control signal is output based on conducting signal, enable signal, current sampling signal and output feedback signal, and switching control signal controls the on-off of primary side switch tube.The control circuit of the utility model adopts valley bottom opening mode to optimize switching loss under heavy load working condition, adopts non-valley bottom opening mode to realize opening point position random under light load working condition, can improve power supply transmission performance under light load working condition, ensure that efficiency and temperature rise under heavy load are not affected.

Description

Technical Field

[0001] This utility model relates to the field of electronics, specifically, but not limited to, a control circuit and a switching power supply. Background Technology

[0002] Flyback power supplies, with their simple structure, low cost, and significant advantages such as electrical isolation, have been widely used in various low-to-medium power applications. Valley-turn-on control is a common and effective control strategy in flyback power supplies. Its core principle is to turn on the MOSFET when its drain voltage Vds oscillates below a specific value. This control strategy effectively reduces switching losses and significantly improves the power supply's efficiency.

[0003] like Figure 1 The flyback switching power supply shown employs valley-turn-on control. During the waveform changes under full load, medium load, and light load conditions, the primary-side MOSFET always turns on when the drain voltage Vds oscillates below a certain value, thus achieving the so-called valley-turn-on. Figure 2 As shown, the number of voltage oscillation valleys varies under different loads (first valley under heavy load, second valley under medium load, and sixth valley turn-on under light load), meaning the valley turn-on time varies with the load. It can also be seen that under light load, the fixed turn-on point leads to complex drain voltage Vds oscillations and easily deteriorated conduction. In practical applications, there are various methods to achieve valley turn-on control. A representative scheme is to delay the MOSFET turn-on for a period of time after detecting that the drain voltage Vds is less than a set threshold.

[0004] However, although valley turn-on control can optimize the efficiency of flyback switching power supplies, a fixed turn-on point can negatively impact the power supply's conduction performance: 1) Under full load, the power supply's conduction performance remains relatively ideal when using valley turn-on control. This is because under full load, bus voltage ripple causes the power supply's operating frequency to fluctuate within a certain range. This frequency fluctuation manifests in the frequency domain as energy being evenly distributed across the frequency band and its harmonics within that range, significantly reducing the noise peak measured at a single frequency point, thus ensuring that the power supply's conduction performance meets relevant standards. 2) Under light load, the system operating frequency tends to stabilize when using valley turn-on control. A fixed turn-on point will create periodic current change rate (di / dt) and voltage change rate (dv / dt), which in the frequency domain results in high-amplitude narrow pulses at the switching frequency and its harmonics, causing energy to concentrate highly and significantly deteriorating the power supply's conduction performance.

[0005] In summary, existing valley-to-peak control schemes, due to their fixed switching frequency under light loads, are prone to conduction exceeding limits and cannot meet the conduction performance requirements in practical applications.

[0006] In view of this, there is a need to provide a new structure or control method in order to solve at least some of the above problems. Utility Model Content

[0007] In response to at least one or more problems in the background art, this utility model proposes a control circuit and a switching power supply. The control circuit adopts a dual-mode control strategy, which uses load detection combined with valley detection to achieve valley-turn-on mode under heavy load and non-valley-turn-on mode under light load. This significantly improves the power supply conduction performance under light load conditions, while ensuring that efficiency and temperature rise are not affected under heavy load conditions.

[0008] According to one aspect of the present invention, a control circuit for a switching power supply includes:

[0009] The load detection module has an input terminal that receives a signal representing the load state of the switching power supply. The load detection module is used to output a load indication signal based on the signal representing the load state of the switching power supply. The load indication signal includes a first indication signal and a second indication signal, wherein the first indication signal represents that the load is heavy load and the second indication signal represents that the load is light load.

[0010] The valley bottom turn-on detection module is connected to the primary-side switch drain voltage signal or the auxiliary winding voltage divider signal at its input terminal. The valley bottom turn-on detection module is used to output a valley bottom turn-on signal based on the primary-side switch drain voltage signal or the auxiliary winding voltage divider signal.

[0011] The logic operation module has a first input terminal coupled to the output terminal of the load detection module and a second input terminal coupled to the output terminal of the valley opening detection module. The logic operation module is used to output a conduction signal based on the load indication signal and the valley opening signal.

[0012] The switching frequency control module has a switching cycle signal that represents the on / off state of the primary-side switch connected to its input terminal. The switching frequency control module is used to output an enable signal based on the duration of each switching cycle or the off-state duration.

[0013] The switching control module has a first input terminal coupled to the output terminal of the logic operation module, a second input terminal coupled to the output terminal of the switching frequency control module, a third input terminal connected to the primary-side inductor current sampling signal of the switching power supply, a fourth input terminal connected to the output feedback signal characterizing the output signal of the switching power supply, and an output terminal coupled to the control terminal of the primary-side switching transistor. The switching control module is used to output a switching control signal based on the conduction signal, the enable signal, the current sampling signal, and the output feedback signal. The switching control signal is used to control the primary-side switching transistor to be turned on or off.

[0014] Optionally, the load detection module includes:

[0015] The counting module has a first input terminal coupled to the valley opening detection module and a second input terminal connected to the switching cycle signal. The counting module is used to output a load indication signal based on the number of times the valley opening signal is received in each switching cycle. When the number of times is less than or equal to the built-in counting threshold, the load indication signal is a first indication signal. When the number of times is greater than the built-in counting threshold, the load indication signal is a second indication signal.

[0016] Optionally, the load detection module includes:

[0017] The first comparison circuit has a first input terminal connected to a loop compensation signal and a second input terminal connected to a load judgment threshold. The first comparison circuit is used to compare the loop compensation signal and the load judgment threshold and output a load indication signal. When the loop compensation signal is less than or equal to the load judgment threshold, the load indication signal is a first indication signal. When the loop compensation signal is greater than the load judgment threshold, the load indication signal is a second indication signal.

[0018] Optionally, the control circuit includes:

[0019] The compensation circuit has a first input terminal connected to the output feedback signal and a second input terminal connected to a reference reference signal. The compensation circuit is used to output a loop compensation signal based on the output feedback signal and the reference reference signal.

[0020] Optionally, the signals characterizing the load state of the switching power supply include valley turn-on signals, switching cycle signals, and loop compensation signals.

[0021] Optionally, the logic operation module includes an OR gate circuit, with a first input terminal coupled to the output terminal of the load detection module and a second input terminal coupled to the output terminal of the valley opening detection module. The OR gate circuit is used to output a conduction signal based on the load indication signal and the valley opening signal.

[0022] Optionally, the switch control module includes:

[0023] The AND gate circuit has a first input terminal coupled to the output terminal of the logic operation module and a second input terminal coupled to the output terminal of the switching frequency control module. The AND gate circuit is used to output a switch turn-on signal based on the conduction signal and the enable signal.

[0024] A current control circuit has a first input terminal connected to the current sampling signal and a second input terminal connected to the output feedback signal. The current control circuit is used to output a switch turn-off signal based on the current sampling signal and the output feedback signal.

[0025] An RS flip-flop has a set terminal coupled to the output of an AND gate circuit and a reset terminal coupled to the output of a current control circuit. The RS flip-flop is used to output a switching cycle signal based on the switch transistor turn-on signal and the switch transistor turn-off signal.

[0026] The driving circuit has its input terminal coupled to the output terminal of an RS flip-flop and its output terminal coupled to the control terminal of the primary-side switching transistor. The driving circuit is used to output a switching control signal based on the switching cycle signal.

[0027] Optionally, the current control circuit includes:

[0028] The compensation circuit has the output feedback signal connected to its first input terminal and the reference reference signal connected to its second input terminal. The compensation circuit is used to output a loop compensation signal based on the output feedback signal and the reference reference signal.

[0029] A current reference generation circuit is provided, with its input terminal coupled to the output terminal of the compensation circuit. The current reference generation circuit is used to output a cycle-by-cycle current protection reference signal based on the loop compensation signal.

[0030] The second comparison circuit has a first input terminal coupled to the output terminal of the current reference generation circuit, a second input terminal connected to the current sampling signal, and an output terminal coupled to the reset terminal of the RS flip-flop. The second comparison circuit is used to compare the cycle-by-cycle current protection reference signal and the current sampling signal and output a switch-off signal.

[0031] According to another aspect of the present invention, a switching power supply includes a primary-side switching transistor, a transformer, and any of the aforementioned control circuits, wherein the primary-side switching transistor is coupled to the primary winding of the transformer, and the output terminal of the control circuit is coupled to the control terminal of the primary-side switching transistor.

[0032] The control circuit proposed in this invention adopts a dual-mode control strategy. Under heavy load conditions, it adopts a valley-to-turn-on mode to optimize switching losses, and under light load conditions, it adopts a non-valley-to-turn-on mode to achieve random turn-on points. This can significantly improve the power conduction performance under light load conditions, while ensuring that efficiency and temperature rise are not affected under heavy load conditions. Attached Figure Description

[0033] 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:

[0034] Figure 1 A schematic diagram of an existing switching power supply employing valley-turn-on control is shown.

[0035] Figure 2 The diagram shows the operating waveforms of an existing switching power supply with valley turn-on control under different loads.

[0036] Figure 3 A block diagram of the control circuit structure of this utility model is shown.

[0037] Figure 4 A block diagram of the control circuit structure according to an embodiment of the present invention is shown.

[0038] Figure 5 The diagram shows the control circuit signal waveform of an embodiment of the present invention.

[0039] Figure 6 A block diagram of the control circuit structure of another embodiment of the present invention is shown.

[0040] Figure 7 The diagram shows the input and output signal waveforms of a valley opening detection module according to an embodiment of the present invention.

[0041] Figure 8 The diagram shows the input and output signal waveforms of the valley opening detection module according to another embodiment of the present invention.

[0042] Figure 9 The diagram shows the input and output signal waveforms of a switching frequency control module according to an embodiment of the present invention.

[0043] Figure 10 The diagram shows the input and output signal waveforms of the switching frequency control module according to another embodiment of the present invention. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] 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 function, such as connections through switches, signal amplification circuits, follower circuits, or other circuits or components. "Multiple" or "more" indicates two or more.

[0047] This utility model proposes a control circuit for a switching power supply, such as... Figure 3 As shown, the control circuit includes a load detection module 1, a valley-level turn-on detection module 2, a logic operation module 3, a switching frequency control module 4, and a switching control module 5, wherein:

[0048] The input terminal of the load detection module 1 is connected to a signal characterizing the load state of the switching power supply. The load detection module 1 outputs a load indication signal LLM based on the signal characterizing the load state of the switching power supply. The load indication signal LLM includes a first indication signal and a second indication signal, wherein the first indication signal indicates that the load is heavily loaded (represented by LLM = 0), and the second indication signal indicates that the load is lightly loaded (represented by LLM = 1). Depending on the specific application circuit, the first indication signal of the load indication signal LLM can also indicate that the load is lightly loaded, and the second indication signal can also indicate that the load is heavily loaded.

[0049] In one embodiment, such as Figure 4As shown, the load detection module 1 has a valley turn-on signal (Valley) and a switching cycle signal (PWM) at its input, and outputs a load indication signal (LLM) based on the Valley turn-on signal (Valley) and the switching cycle signal (PWM). In one specific embodiment, the load detection module 1 includes a counting module. The first input of the counting module is coupled to the valley turn-on detection module 2, and the second input is connected to the switching cycle signal (PWM). The counting module is used to output the load indication signal (LLM) based on the number of times the Valley turn-on signal (Valley) is counted in each switching cycle. When the number of counts is less than or equal to a built-in counting threshold N, the load indication signal (LLM) is a first indication signal; when the number of counts is greater than the built-in counting threshold N, the load indication signal (LLM) is a second indication signal. Specifically, the counting module is reset at the rising or falling edge of each switching cycle. After the reset, its output load indicator signal LLM is set to 0 (indicating that the load is heavy), and the valley turn-on signal is set to 1, thus increasing the count by 1. When the number of valley turn-on signals in one switching cycle exceeds its built-in counting threshold N, its output load indicator signal LLM is set to 1 (indicating that the load is light). Preferably, the built-in counting threshold N is 3, and the corresponding signal waveforms of the control circuit are as follows. Figure 5 As shown. In another specific embodiment, the load detection module 1 includes a valley pulse counter and a comparison unit. The first input terminal of the valley pulse counter is coupled to the valley turn-on detection module 2, and the second input terminal is connected to the switching cycle signal PWM. The valley pulse counter outputs a valley count value based on the valley turn-on signal (Valley) output by the valley turn-on detection module 2 and the switching cycle signal PWM. The first input terminal of the comparison unit is coupled to the output terminal of the valley pulse counter, and the second input terminal is connected to a counting threshold N. The comparison unit outputs a load indication signal LLM based on the valley count value and the counting threshold N. Specifically, when the switching cycle signal PWM arrives (including the rising edge, falling edge, and any position between the rising and falling edges of the switching cycle signal PWM), the valley pulse counter is reset (i.e., the valley count value is 0), and the load indication signal LLM is set to 0. When the valley turn-on signal Valley is set high once, the valley count value is incremented by 1. When the valley count value is less than or equal to the counting threshold N, the comparison unit outputs that the load indication signal LLM is still 0 (i.e., indicating that the load is heavy at this time); when the valley count value is greater than the counting threshold N, the comparison unit outputs that the load indication signal LLM is set to 1 (i.e., indicating that the load is light at this time).

[0050] In another embodiment, such as Figure 6As shown, the load detection module 1 receives a loop compensation signal Vcomp at its input and outputs a load indication signal LLM based on the loop compensation signal Vcomp. In this embodiment, the load detection module 1 includes a first comparison circuit. The first input of the first comparison circuit receives the loop compensation signal Vcomp, and the second input receives a load judgment threshold. The first comparison circuit compares the loop compensation signal Vcomp with the load judgment threshold and outputs the load indication signal LLM. Specifically, when the loop compensation signal Vcomp is less than or equal to the load judgment threshold, the load indication signal LLM is a first indication signal (indicating that the load is heavy); when the loop compensation signal Vcomp is greater than the load judgment threshold, the load indication signal LLM is a second indication signal (indicating that the load is light). In other circuit applications, when the loop compensation signal Vcomp is less than or equal to a preset load judgment threshold, the load indication signal can be the second indication signal; when the loop compensation signal Vcomp is greater than the preset load judgment threshold, the load indication signal can be the first indication signal. Specifically, the loop compensation signal Vcomp connected to the load detection module can be obtained from the compensation circuit. The first input terminal of the compensation circuit is connected to the output feedback signal VFB, and the second input terminal is connected to the reference signal Vref. The compensation circuit is used to output the loop compensation signal Vcomp based on the output feedback signal VFB and the reference signal Vref, and the loop compensation signal Vcomp can be output to the load detection module.

[0051] Furthermore, the signals characterizing the load state of the switching power supply input to the load detection module 1 can also be the power supply's output signals (including but not limited to output voltage signals, output current signals, etc.), control feedback related signals (including but not limited to feedback voltage signals, current sampling signals, etc.), switching cycle signals, etc. Based on the aforementioned signals and their related signals, the load detection module can output a load indication signal indicating whether the load is heavy or light for subsequent signal processing and switching control. Based on different input signals, the load detection module can have different internal signal processing elements to process or convert the input signals, ultimately still outputting a load indication signal.

[0052] The input terminal of the valley turn-on detection module 2 is connected to the drain voltage signal Vdrain of the primary-side switch Q or the auxiliary winding voltage divider signal Vdem. The valley turn-on detection module 2 outputs a valley turn-on signal Valley based on the drain voltage signal Vdrain or the auxiliary winding voltage divider signal Vdem of the primary-side switch Q. The valley turn-on signal Valley includes a high-level valley turn-on signal Valley and a low-level valley turn-on signal Valley.

[0053] In one embodiment, the valley turn-on detection module 2 outputs a valley turn-on signal Valley based on the drain voltage signal Vdrain of the primary-side switch Q. In a specific embodiment, the valley turn-on detection module 2 adopts a delayed turn-on operating mode. Specifically, when the drain voltage signal Vdrain oscillates to a level lower than the first valley turn-on threshold V1 and remains there for a first preset time T1, the valley turn-on detection module 2 outputs a single-pulse high-level valley turn-on signal Valley. The preset pulse width of the one-shot high-level valley turn-on signal Valley is T2. After the one-shot high-level valley turn-on signal Valley remains for a duration of T2, the valley turn-on detection module 2 outputs a low-level valley turn-on signal Valley. The waveforms of each signal are as follows: Figure 7 As shown. In another specific embodiment, the valley turn-on detection module 2 adopts an immediate turn-on working mode. Specifically, when the drain voltage signal Vdrain oscillates to a level lower than the second valley turn-on threshold V2, the valley turn-on detection module 2 directly outputs a high-level valley turn-on signal Valley. The high-level valley turn-on signal Valley continues until the drain voltage signal Vdrain oscillates to a level greater than or equal to the second valley turn-on threshold V2, at which point it becomes a low-level valley turn-on signal Valley. The waveforms of each signal are shown in the figure. Figure 8 As shown.

[0054] In another embodiment, the valley turn-on detection module 2 outputs a valley turn-on signal Valley based on the auxiliary winding voltage divider signal Vdem. The auxiliary winding voltage divider signal Vdem and the drain voltage signal Vdrain of the primary-side switch Q have a fixed phase and ratio relationship. Therefore, in this embodiment, the principle of the valley turn-on detection module 2 outputting a high-level or low-level valley turn-on signal Valley based on the auxiliary winding voltage divider signal Vdem is the same as the principle of outputting a high-level or low-level valley turn-on signal Valley based on the drain voltage signal Vdrain of the primary-side switch Q. The valley turn-on detection module 2 can adopt a delayed turn-on or immediate turn-on operating mode. In the delayed turn-on operating mode, after the auxiliary winding voltage divider signal Vdem oscillates to below a first turn-on threshold and is delayed for a first time, the valley turn-on detection module 2 outputs a single-pulse valley turn-on signal Valley. In the immediate activation mode, when the auxiliary winding voltage divider signal Vdem oscillates to below the second activation threshold, the valley activation detection module 2 outputs a high-level valley activation signal Valley, which continues until the auxiliary winding voltage divider signal Vdem oscillates to above or equal to the second activation threshold. Besides the aforementioned embodiments / implementations, other existing valley activation detection modules can also be directly applied to this control circuit to achieve the output of a valley activation signal.

[0055] The first input terminal of the logic operation module 3 is coupled to the output terminal of the load detection module, and the second input terminal is coupled to the output terminal of the valley turn-on detection module 2. The logic operation module 3 is used to output a conduction signal based on the load indication signal LLM and the valley turn-on signal Valley. In one embodiment, the logic operation module 3 can be an OR gate circuit. The first input terminal of the OR gate circuit is coupled to the output terminal of the load detection module 1, and the second input terminal of the OR gate circuit is coupled to the output terminal of the valley turn-on detection module 2. The OR gate circuit is used to output a conduction signal based on the load indication signal LLM and the valley turn-on signal Valley. Specifically, when the load indication signal LLM is a first indication signal (represented by LLM=0) and the valley turn-on signal Valley is high (represented by Valley=1), or when the load indication signal LLM is a second indication signal (represented by LLM=1), the logic operation module 3 outputs a high-level conduction signal. When the load indication signal LLM is the first indication signal (represented by LLM=0) and the valley turn-on signal Valley is low (represented by Valley=0), the logic operation module 3 outputs a low-level turn-on signal. In addition to the aforementioned embodiments / implementations, other existing logic operation modules with the same input and output signals can also be directly applied to this control circuit to achieve the output turn-on signal.

[0056] The input terminal of the switching frequency control module 4 is connected to the switching cycle signal PWM, which characterizes the on / off state of the primary-side switch. The switching frequency control module 4 outputs an enable signal Fs_en based on the duration of each switching cycle or the off-state duration. In one embodiment, specifically, when the duration of the current cycle of the switching cycle signal PWM reaches a first threshold T3, the switching frequency control module outputs a high-level enable signal Fs_en (represented by Fs_en = 1). This high-level enable signal Fs_en continues until the rising edge of the next switching cycle signal PWM arrives; that is, when the rising edge of the next switching cycle signal PWM arrives, the switching frequency control module 4 outputs a low-level enable signal Fs_en (represented by Fs_en = 0). The waveforms of each signal are as follows: Figure 9 As shown. In another embodiment, specifically, when the current cycle off-time of the switching period signal PWM reaches the second threshold T4, the switching frequency control module 4 outputs a high-level enable signal Fs_en (represented by Fs_en = 1). The high-level enable signal Fs_en continues until the rising edge of the next switching period signal PWM arrives, that is: when the rising edge of the next switching period signal PWM arrives, the switching frequency control module 4 outputs a low-level enable signal Fs_en (represented by Fs_en = 0). The waveforms of each signal are as follows. Figure 10 As shown. In addition to the aforementioned embodiments / implementations, other existing switching frequency control modules with the same input and output signals can also be directly applied to this control circuit to realize the output enable signal.

[0057] The first input terminal of the switch control module 5 is coupled to the output terminal of the logic operation module 3, the second input terminal is coupled to the output terminal of the switch frequency control module 4, the third input terminal is connected to the primary-side inductor current sampling signal Vcs of the switching power supply, the fourth input terminal is connected to the output feedback signal VFB representing the output signal of the switching power supply, and the output terminal is coupled to the control terminal of the primary-side switch Q. The switch control module 5 is used to output a switch control signal based on the conduction signal, the enable signal Fs_en, the current sampling signal Vcs, and the output feedback signal VFB. The switch control signal is used to control the primary-side switch Q to be turned on or off.

[0058] In one embodiment, such as Figure 3 As shown, the switch control module 5 includes an AND gate circuit 51, a current control circuit 52, an RS flip-flop 53, and a drive circuit 54. Specifically, the first input of the AND gate circuit 51 is coupled to the output of the logic operation module 3, and the second input is coupled to the output of the switch frequency control module 4. The AND gate circuit 51 is used to output a switch-on signal based on the conduction signal and the enable signal Fs_en. Specifically, when both the conduction signal and the enable signal Fs_en are high, the AND gate circuit 51 outputs a high-level switch-on signal; when either the conduction signal or the enable signal Fs_en is low, the AND gate circuit 51 outputs a low-level switch-on signal. The first input of the current control circuit 52 is connected to the current sampling signal Vcs, and the second input is connected to the output feedback signal VFB. The current control circuit 52 is used to output a switch-off signal based on the current sampling signal Vcs and the output feedback signal VFB. The set terminal of RS flip-flop 53 is coupled to the output terminal of AND gate circuit 51, and the reset terminal is coupled to the output terminal of current control circuit 52. RS flip-flop 53 is used to output a switching period signal (PWM) based on the switch transistor's turn-on signal and turn-off signal. The input terminal of drive circuit 54 is coupled to the output terminal of RS flip-flop 53, and the output terminal is coupled to the control terminal of primary-side switch transistor Q. Drive circuit 54 is used to output a switching control signal based on the switching period signal (PWM). In one specific embodiment, such as... Figure 3As shown, the current control circuit 52 includes a compensation circuit 521, a current reference generation circuit 522, and a second comparison circuit 523. The first input terminal of the compensation circuit 521 is connected to the output feedback signal VFB, and the second input terminal is connected to the reference signal Vref. The compensation circuit 521 outputs a loop compensation signal Vcomp based on the output feedback signal VFB and the reference signal Vref, enabling the switching power supply to have good stability. The loop compensation signal Vcomp can also be used to adjust the aforementioned first threshold T3 and second threshold T4. The input terminal of the current reference generation circuit 522 is coupled to the output terminal of the compensation circuit 521, and the current reference generation circuit 522 outputs a cycle-by-cycle current protection reference signal Vcs_ref based on the loop compensation signal Vcomp. The first input terminal of the second comparator circuit 523 is coupled to the output terminal of the current reference generation circuit 522, the second input terminal is connected to the current sampling signal Vcs, and the output terminal is coupled to the reset terminal of the RS flip-flop 53. The second comparator circuit 523 is used to compare the cycle-by-cycle current protection reference signal Vcs_ref and the current sampling signal Vcs to output a switch-off signal. Specifically, when the current sampling signal Vcs is greater than the cycle-by-cycle current protection reference signal Vcs_ref, the second comparator circuit 523 outputs a high-level switch-off signal, and the flip-flop 53 is reset; when the current sampling signal Vcs is less than or equal to the cycle-by-cycle current protection reference signal Vcs_ref, the second comparator circuit 523 outputs a low-level switch-off signal, and the flip-flop 53 is not reset. In addition to the aforementioned embodiments / implementations, other existing switch control modules with the same input and output signals can also be directly applied to this control circuit to realize the output enable signal.

[0059] The control circuit may also include an output feedback circuit. For example... Figure 3 As shown, the input terminal of the output feedback circuit is connected to the output voltage signal Vo of the switching power supply or the auxiliary winding voltage divider signal Vdem, and the output terminal is coupled to the input terminal of the compensation circuit. The output feedback circuit is used to output an output feedback signal VFB based on the output voltage signal Vo or the auxiliary winding voltage divider signal Vdem. Since the auxiliary winding voltage divider signal Vdem and the output voltage signal Vo maintain a proportional relationship during a portion of the switching cycle, the output feedback signal VFB, characterizing the output signal of the switching power supply, can be output by sampling and holding the auxiliary winding voltage divider signal Vdem at appropriate times.

[0060] With the control circuit structure of this scheme, when the load is heavy, the primary-side switch is turned on only when the drain voltage of the primary-side switch is detected to be at its lowest point and the enable signal is valid. When the load is light, the primary-side switch can be turned on as long as the enable signal is valid, without waiting for the drain voltage of the primary-side switch to reach its lowest point.

[0061] This control circuit controls whether the switching power supply operates in valley-turn-on mode based on the load state. First, a load detection module acquires a signal representing the load state to determine whether the load is heavy or light. When the load is heavy, the primary-side switch is turned on at the valley of its drain voltage oscillation after the switching cycle reaches a certain threshold (i.e., valley-turn-on mode). When the load is light, the primary-side switch is turned on immediately after the switching cycle reaches a certain threshold (i.e., non-valley-turn-on mode). This scheme employs a dual-mode control strategy: valley-turn-on mode under heavy load conditions to optimize switching losses, and non-valley-turn-on mode under light load conditions to achieve random turn-on point. This significantly improves power conduction performance under light load conditions while ensuring that efficiency and temperature rise are not affected under heavy load conditions.

[0062] The switching control process corresponding to the control circuit of this scheme is as follows:

[0063] S1. Obtain the drain voltage Vdrain of the primary-side switching transistor Q of the switching power supply or the auxiliary winding voltage Vdem that is proportional to it. When it is lower than the voltage threshold, output the valley turn-on signal Valley.

[0064] S2. Obtain the switching cycle signal PWM that represents the on / off state of the primary-side switching transistor of the switching power supply, obtain the duration of each switching cycle or the off-state duration, and output the enable signal Fs_en when it reaches the preset time threshold.

[0065] S3. Acquire the signal characterizing the load state of the switching power supply, determine the load state and output the load indication signal LLM;

[0066] S4. Select control logic based on the load indication signal LLM:

[0067] 1) When the load indication signal LLM indicates that the load is heavy, the primary-side switch Q is turned on when the enable signal Fs_en and the valley turn-on signal Valley are both active.

[0068] 2) When the load indication signal LLM indicates that the load is light, the primary-side switch Q is turned on immediately after the enable signal Fs_en becomes effective.

[0069] In one embodiment, the determination of the load status in S3 can be achieved through the following process:

[0070] Obtain the loop compensation signal Vcomp; compare the loop compensation signal Vcomp with a preset load judgment threshold: when the loop compensation signal Vcomp is less than or equal to the load judgment threshold, the load is determined to be heavy load; when the loop compensation signal Vcomp is greater than the load judgment threshold, the load is determined to be light load.

[0071] In another embodiment, the detection of the load state described in S3 can also be achieved through the following process:

[0072] The counting module is initialized in each switching cycle; the valley turn-on signal is counted within each switching cycle; when the count exceeds the counting threshold N, the load is determined to be lightly loaded, otherwise the load is heavy loaded, where N≥2. Preferably, N=3.

[0073] In one embodiment, the output of the valley opening signal in S1 can be achieved through the following process:

[0074] After detecting that the drain voltage of the primary-side switch Q drops to the first threshold V1, a single-pulse valley turn-on signal is output after a delay time T1.

[0075] In another embodiment, the output of the valley opening signal in S1 can also be achieved through the following process:

[0076] When the drain voltage of the primary-side switch is detected to be lower than the second threshold V2, a valley turn-on signal is immediately output. The valley turn-on signal continues until the drain voltage is greater than or equal to the second threshold V2.

[0077] This utility model also proposes a switching power supply, including a primary-side switching transistor, a transformer, and any of the aforementioned control circuits. The primary-side switching transistor is coupled to the primary winding of the transformer, and the output terminal of the control circuit is coupled to the control terminal of the primary-side switching transistor. In one embodiment, a flyback switching power supply includes a flyback MOSFET, a transformer, and the aforementioned control circuit. The drain of the flyback MOSFET is coupled to the primary winding of the transformer, the source is grounded through a resistor, and the gate is coupled to the output terminal of the control circuit. The flyback MOSFET is turned on or off based on a switching control signal output by the control circuit.

[0078] 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.

[0079] 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 control circuit for a switching power supply, characterized in that, include: The load detection module has an input terminal that receives a signal representing the load state of the switching power supply. The load detection module is used to output a load indication signal based on the signal representing the load state of the switching power supply. The load indication signal includes a first indication signal and a second indication signal, wherein the first indication signal represents that the load is heavy load and the second indication signal represents that the load is light load. The valley bottom turn-on detection module is connected to the primary-side switch drain voltage signal or the auxiliary winding voltage divider signal at its input terminal. The valley bottom turn-on detection module is used to output a valley bottom turn-on signal based on the primary-side switch drain voltage signal or the auxiliary winding voltage divider signal. The logic operation module has a first input terminal coupled to the output terminal of the load detection module and a second input terminal coupled to the output terminal of the valley opening detection module. The logic operation module is used to output a conduction signal based on the load indication signal and the valley opening signal. The switching frequency control module has a switching cycle signal that represents the on / off state of the primary-side switch connected to its input terminal. The switching frequency control module is used to output an enable signal based on the duration of each switching cycle or the off-state duration. The switching control module has a first input terminal coupled to the output terminal of the logic operation module, a second input terminal coupled to the output terminal of the switching frequency control module, a third input terminal connected to the primary-side inductor current sampling signal of the switching power supply, a fourth input terminal connected to the output feedback signal characterizing the output signal of the switching power supply, and an output terminal coupled to the control terminal of the primary-side switching transistor. The switching control module is used to output a switching control signal based on the conduction signal, the enable signal, the current sampling signal, and the output feedback signal. The switching control signal is used to control the primary-side switching transistor to be turned on or off.

2. The control circuit according to claim 1, characterized in that, The load detection module includes: The counting module has a first input terminal coupled to the valley opening detection module and a second input terminal connected to the switching cycle signal. The counting module is used to output a load indication signal based on the number of times the valley opening signal is received in each switching cycle. When the number of times is less than or equal to the built-in counting threshold, the load indication signal is a first indication signal. When the number of times is greater than the built-in counting threshold, the load indication signal is a second indication signal.

3. The control circuit according to claim 1, characterized in that, The load detection module includes: The first comparison circuit has a first input terminal connected to a loop compensation signal and a second input terminal connected to a load judgment threshold. The first comparison circuit is used to compare the loop compensation signal and the load judgment threshold and output a load indication signal. When the loop compensation signal is less than or equal to the load judgment threshold, the load indication signal is a first indication signal. When the loop compensation signal is greater than the load judgment threshold, the load indication signal is a second indication signal.

4. The control circuit according to claim 3, characterized in that, The control circuit includes: The compensation circuit has a first input terminal connected to the output feedback signal and a second input terminal connected to a reference reference signal. The compensation circuit is used to output a loop compensation signal based on the output feedback signal and the reference reference signal.

5. The control circuit according to claim 1, characterized in that, The signals characterizing the load state of the switching power supply include the valley turn-on signal, the switching cycle signal, and the loop compensation signal.

6. The control circuit according to claim 1, characterized in that, The logic operation module includes an OR gate circuit. The first input terminal is coupled to the output terminal of the load detection module, and the second input terminal is coupled to the output terminal of the valley opening detection module. The OR gate circuit is used to output a conduction signal based on the load indication signal and the valley opening signal.

7. The control circuit according to claim 1, characterized in that, The switch control module includes: The AND gate circuit has a first input terminal coupled to the output terminal of the logic operation module and a second input terminal coupled to the output terminal of the switching frequency control module. The AND gate circuit is used to output a switch turn-on signal based on the conduction signal and the enable signal. A current control circuit has a first input terminal connected to the current sampling signal and a second input terminal connected to the output feedback signal. The current control circuit is used to output a switch turn-off signal based on the current sampling signal and the output feedback signal. An RS flip-flop has a set terminal coupled to the output of an AND gate circuit and a reset terminal coupled to the output of a current control circuit. The RS flip-flop is used to output a switching cycle signal based on the switch transistor turn-on signal and the switch transistor turn-off signal. The driving circuit has its input terminal coupled to the output terminal of an RS flip-flop and its output terminal coupled to the control terminal of a primary-side switching transistor. The driving circuit is used to output a switching control signal based on the switching cycle signal.

8. The control circuit according to claim 7, characterized in that, The current control circuit includes: The compensation circuit has a first input terminal connected to the output feedback signal and a second input terminal connected to a reference signal. The compensation circuit is used to output a loop compensation signal based on the output feedback signal and the reference signal. A current reference generation circuit is provided, with its input terminal coupled to the output terminal of the compensation circuit. The current reference generation circuit is used to output a cycle-by-cycle current protection reference signal based on the loop compensation signal. The second comparison circuit has a first input terminal coupled to the output terminal of the current reference generation circuit, a second input terminal connected to the current sampling signal, and an output terminal coupled to the reset terminal of the RS flip-flop. The second comparison circuit is used to compare the cycle-by-cycle current protection reference signal and the current sampling signal and output a switch turn-off signal.

9. A switching power supply, characterized in that, It includes a primary-side switching transistor, a transformer, and a control circuit as described in any one of claims 1-8, wherein the primary-side switching transistor is coupled to the primary winding of the transformer, and the output terminal of the control circuit is coupled to the control terminal of the primary-side switching transistor.

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