Switching power supply system and control circuit thereof

Abstract

A switching power supply system and a control circuit thereof are disclosed. The switching power supply system comprises a rectifying unit connected to an AC side power supply, and a supply capacitor for providing a supply voltage to the control circuit. The control circuit comprises: a supply path having one end connected to the rectifying unit and the other end connected to the supply capacitor; and a supply control module configured to control a state of the supply path based on a load feedback voltage of the switching power supply system and the supply voltage, so as to charge the supply capacitor by the supply path based on the rectifying unit.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more particularly to a switching power supply system and its control circuit. Background Technology

[0002] With switching power supplies becoming increasingly higher frequency and smaller, the structure of depletion-mode power transistors cascaded with low-voltage power switches is increasingly used in switching power supplies due to its advantages in cost and reliability. The control circuit of the switching power supply can achieve self-powering through this depletion-mode power transistor. Summary of the Invention

[0003] According to an embodiment of the present invention, the control circuit of a switching power supply system includes a rectifier unit connected to an AC power supply and a power supply capacitor for providing a power supply voltage to the control circuit. The control circuit includes a power supply path connected at one end to the rectifier unit and at the other end to the power supply capacitor; and a power supply control module configured to control the state of the power supply path based on the load feedback voltage and the power supply voltage of the switching power supply system, so that the power supply path charges the power supply capacitor based on the rectifier unit.

[0004] According to an embodiment of the present invention, a switching power supply system includes the control circuit described above, a rectifier unit connected to an AC power supply, and a power supply capacitor for providing a power supply voltage to the control circuit. Attached Figure Description

[0005] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein: Figure 1 A schematic block diagram of a switching power supply system in the prior art is shown.

[0006] Figure 2 A waveform diagram of a prior art switching power supply system under dynamic load is shown.

[0007] Figure 3 The diagram shows a waveform of a prior art switching power supply system under light load or no load.

[0008] Figure 4 A schematic block diagram of a switching power supply system according to an embodiment of the present invention is shown.

[0009] Figure 5 A partial schematic block diagram of a first example of a control circuit according to an embodiment of the present invention is shown.

[0010] Figure 6 A waveform diagram of a power supply path related signal is shown according to an embodiment of the present invention.

[0011] Figure 7Another waveform diagram of the power supply path related signal is shown according to an embodiment of the present invention.

[0012] Figure 8 A partial schematic block diagram of a second example of a control circuit according to an embodiment of the present invention is shown.

[0013] Figure 9 A partial schematic block diagram of a third example of a control circuit according to an embodiment of the present invention is shown. Detailed Implementation

[0014] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0015] Figure 1 A schematic block diagram of a prior art switching power supply system is shown. For example... Figure 1As shown, the switching power supply system 100 includes a rectifier bridge BD1 connected to the AC power supply, capacitors C1-C3, a transformer T1 and auxiliary winding L2, diode D1, a control circuit 101, and an optocoupler isolation and feedback control circuit 102. The control circuit 101 includes a depletion-mode power transistor M1, a power switching transistor M2, a startup module 110, a self-powered module 111, a PWM driver 112, and a drive module 113. When the switching power supply system 100 is connected to the AC power supply and powered on, M2 is off, the gate of M1 is close to 0V, and the source voltage of M1 rises, charging C3 through the startup module 110. The non-grounded terminal of C3 provides the supply voltage VCC to the control circuit 101. When VCC rises to the startup threshold of the control circuit 101, the charging path of the startup module 110 is disconnected, the control circuit 101 starts working, and controls M1 to conduct through the self-powered module 111 to charge C3. The time for C3 to be charged by the self-powered module 111 is called the self-powered time. The self-powered time is related to the PWM drive signal PWM_GATE output by the drive module 113. The self-powered time can occur during the pre-on period before the PWM_GATE's on-time (Ton) or during the PWM_GATE's off-time (Toff) period. During PWM_GATE's operation, M2, driven by PWM_GATE, alternately conducts with the self-powered module 111. The switching power supply system based on the depletion-mode power transistor M1 can eliminate the need for auxiliary winding power supply, simplifying transformer design and peripheral circuitry.

[0016] The self-powered mode implemented by the control circuit 101 via the self-powered module 111 exhibits different performance under different load conditions. When the output load is heavy, the PWM_GATE frequency is higher, resulting in higher system power and self-powered energy. The control circuit 101 consumes more power, while the self-powered module 111 consumes less power and has a smaller impact on system efficiency. However, the performance of the self-powered mode changes under non-heavy load conditions. Figure 2 This diagram illustrates the waveform of a prior art switching power supply system under dynamic load. Figure 3 The diagram illustrates waveforms of a prior art switching power supply system under light load or no-load conditions. Here, "dynamic" refers to the short-term switching of load between heavy load and non-heavy load. Figure 2 and Figure 3 As shown, when VFB drops to FB_Burst_L, PWM_GATE stops operating; when VFB rises to FB_Burst_H, PWM_GATE resumes operation. Figure 2 and Figure 3As shown, when the output load is under dynamic load, light load, or no load, the PWM_GATE stop time is longer due to the influence of the regulation loop, and the PWM_GATE envelope frequency is greatly reduced. At this time, the self-powering time of the self-powering module 111 is limited, meaning the charging time of C3 is limited. Since C3 continuously supplies power to the control circuit 101, its power is constantly consumed, and VCC will gradually decrease during the PWM_GATE stop phase. This continuous decrease in VCC poses a risk of unstable power supply. Once VCC becomes too low, it will lead to system restarts and other issues.

[0017] Some researchers have proposed increasing the supply current of the self-powered module 111 during its self-powered time to address this potential issue. However, the voltage on the transformer is already high, and further increasing the supply current would significantly increase the power consumption of the self-powered path, as well as its proportion of the total power consumption, resulting in a marked decrease in efficiency under light loads.

[0018] The control circuit of the switching power supply system according to an embodiment of the present invention includes a power supply path and a power supply control module. One end of the power supply path is connected to a rectifier unit connected to the AC power supply, and the other end is connected to a power supply capacitor. When the power supply control module controls the power supply path to be turned on, the rectifier unit and the power supply path will charge the power supply capacitor based on the AC power supply. This charging process does not involve other transistors in the switching power supply system, and charging can continue even when PWM_GATE is off, thus solving the potential problem of power supply failure when PWM_GATE is off. Moreover, since the voltage output by the rectifier unit does not involve subsequent circuits of the switching power supply system, the voltage value is relatively low, the power consumption of the power supply path is small, and its proportion in the total power consumption is small. The system efficiency under non-heavy load conditions will not be reduced due to the power consumption of the control circuit. This improves the system stability under non-heavy load and wide-range dynamic load conditions.

[0019] Figure 4 A schematic block diagram of a switching power supply system according to an embodiment of the present invention is shown. Figure 4 As shown, the switching power supply system 400 includes a rectifier bridge BD1 connected to the AC power supply AC, capacitors C1-C2, transformer T1 and auxiliary winding L2, diode D1, control circuit 401, and optocoupler isolation and feedback control circuit 402. It also includes a rectifier unit 403 connected to the AC power supply AC, and a power supply capacitor C3 for providing power supply voltage VCC to the control circuit 401.

[0020] like Figure 4As shown, the control circuit 401 includes a depletion-mode power transistor M1, a power switching transistor M2, a self-powered module 411, a PWM driver 412, and a drive module 413. It also includes a power supply path 420 with one end connected to the rectifier unit 403 and the other end connected to the power supply capacitor C3, and a power supply control module 430. The power supply control module 430 is configured to control the state of the power supply path 420 based on the load feedback voltage VFB and the supply voltage VCC of the switching power supply system, so as to charge the power supply capacitor C3 through the rectifier unit 403 and the power supply path 420.

[0021] like Figure 4 As shown, the rectifier unit 403 may include two diodes D01 and D02. The anodes of D01 and D02 are respectively connected to the power supply terminals of the AC side power supply AC. The cathodes of D01 and D02 are connected and serve as the output terminal HV of the rectifier unit 403. The rectifier unit 403 rectifies the input AC voltage AC and outputs a non-negative rectified output voltage Vline at the output terminal HV. The waveform of this rectified output voltage Vline is a dome wave. Besides... Figure 4 The rectifier unit 403 can also be implemented using other circuit structures, and the waveform of the rectified output voltage can also be of other shapes, which are not limited here.

[0022] like Figure 4 As shown, power supply path 420 is connected between rectifier unit 403 and power supply capacitor C3. The rectified output voltage Vline of rectifier unit 403 can charge power supply capacitor C3 through power supply path 420, causing the power supply voltage VCC to rise. Power supply control module 430 controls the state of power supply path 420 based on load feedback voltage VFB and power supply voltage VCC. Here, load feedback voltage VFB is the voltage at the output terminal FB of optocoupler isolation and feedback control circuit 402, which reflects the load status connected to switching power supply system 400. Typically, VFB decreases when the load decreases. When power supply control module 430 determines that charging capacitor C3 needs to be charged through power supply path 420 based on VFB and VCC, it controls power supply path 420 to charge power supply capacitor C3. During charging, a current flows from rectifier unit 403 to charging capacitor C3 through power supply path 420. The larger the current, the faster the charging speed (VCC rise speed).

[0023] Figure 5 A partial schematic block diagram of a first example 401A of a control circuit according to an embodiment of the present invention is shown. Figure 5 As shown, in some embodiments, the power supply path 420 may include a current source I_charge that generates the path current of the power supply path 420, and the power supply control module 430 may be further configured to adjust the path current by controlling the current source I_charge.

[0024] like Figure 5 As shown, to further enhance the control of the power supply path 420, the power supply path 420 may also include a state switch SW1 connected in series with the current source I_charge and controlling the power supply path 420 to be turned on or off. The corresponding power supply control module 430 can be further configured to control the state of the state switch SW1. When the power supply control module 430 controls the state switch SW1 to close, the power supply path 420 is turned on; when the power supply control module 430 controls the state switch SW1 to open, the power supply path 420 is turned off.

[0025] As shown in Figure 5, in some embodiments, the power supply path 420 may also include a depletion-type JFET MOS switch M0, with the first terminal of M0 connected to the rectifier unit 403, the second terminal connected to the current source I_charge, and the control terminal grounded.

[0026] like Figure 5 As shown, the power supply path 420 may also include a diode D0 for controlling unidirectional charging.

[0027] like Figure 4 As shown, under heavy load conditions, PWM_GATE is not stopped, the self-powered module 411 can normally supply power to C3, and the power consumption is relatively ideal. The power supply path 420 in this embodiment can be configured to provide supplementary power to C3 under non-heavy load conditions. In some embodiments, the power supply control module 430 can be further configured to: determine whether the comprehensive charging conditions are met; control the power supply path 420 to conduct when the comprehensive charging conditions are met, so as to charge the power supply capacitor C3 through the rectifier unit 403 and the power supply path 420; and control the power supply path 420 to disconnect when the comprehensive charging conditions are not met, so as to stop charging the power supply capacitor C3. The comprehensive charging conditions include that the load feedback voltage VFB is less than the preset feedback voltage FB_lightload, and the supply voltage VCC is less than the first supply voltage VCC_EN, and the rectified output voltage Vline of the rectifier unit 403 is within the preset charging range.

[0028] In the comprehensive charging conditions, the preset feedback voltage FB_lightload is the dividing line between heavy load and non-heavy load. When VFB is not less than FB_lightload, the current load is heavy load, and the existing self-powered module 411 can charge C3 without affecting system efficiency. When VFB is less than FB_lightload, the current load is non-heavy load, and the original self-powered module 411's charging method for C3 is difficult to support VCC. The power supply control module 430 prepares to control the power supply path 420 to charge the power supply capacitor C3.

[0029] In the comprehensive charging condition, the first power supply voltage VCC_EN is the boundary for whether the power supply capacitor C3 is allowed to be charged. When VCC is less than VCC_EN, it indicates that the current power supply capacitor C3 is allowed to be charged, and VCC is allowed to rise further.

[0030] In the comprehensive charging condition, the preset charging interval is used to limit whether the current Vline can charge the power supply capacitor C3. According to the working principle of the rectification unit 403, the rectified output voltage Vline fluctuates periodically with the change of the AC voltage, and the preset charging interval defines the time period in a cycle during which Vline can be used to charge C3, that is, C3 can only be charged when Vline is located in the preset interval.

[0031] When Vline charges the power supply capacitor C3, Vline changes with the AC voltage. Generally, a larger Vline corresponds to higher power consumption. In some embodiments, to reduce power consumption, during the change of Vline, the time period when the voltage value of Vline is small can be selected to charge the power supply capacitor C3, that is, the preset charging interval is set as the time period when the voltage value of Vline is small. This time period can have the following feature: the rectified output voltage Vline within the preset charging interval is less than the preset rectification voltage Vline_EN, where Vline_EN = k0 × Vline_max, k0 is a preset coefficient, 0<k0<1, and Vline_max is the peak value of the rectified output voltage Vline. It should be noted that this feature only describes the overall performance of Vline in the preset charging interval, and does not stipulate that "as long as Vline is less than Vline_EN, it is determined that Vline is located in the preset charging interval". For example, in some embodiments, since Vline fluctuates periodically with the change of the AC voltage, the preset charging interval can be set according to the change process of Vline as follows: when Vline drops to the first rectification voltage Vline_ON, it is determined that Vline enters the preset charging interval; when Vline rises to the second rectification voltage Vline_OFF, it is determined that Vline exits the preset charging interval. Vline_ON and Vline_OFF can be expressed respectively as: Vline_ON = k1 × Vline_max, 0≤k1≤k0, k1 is the first coefficient, Vline_OFF = k2 × Vline_max, 0≤k2≤k0, k2 is the second coefficient.

[0032] Here, both Vline_ON and Vline_OFF are not greater than Vline_EN, which conforms to the feature description that Vline in the preset charging interval is less than Vline_EN. There is no requirement on the magnitude relationship between the coefficient k1 and the coefficient k2.

[0033] In some embodiments, the power supply control module 430 can be further configured to: control the path current of the power supply path 420 when the comprehensive charging conditions are met, so that the path current is negatively correlated with the rectified output voltage Vline. Under the constraint that power consumption cannot be too high, the value of Vline cannot be too high. In this case, in order to improve the charging speed of C3, the path current can be increased when Vline is low and decreased when Vline is high.

[0034] Controlling the state of the power supply path 420 solely based on the overall charging conditions results in relatively lenient charging requirements. It is possible to further add a judgment on the urgency of the power supply demand of the control circuit 401A, serving as a trigger condition for determining whether the overall charging conditions are met, thereby avoiding unnecessary frequent charging actions of the power supply path 420.

[0035] like Figure 4 As shown, in control circuit 401, if the supply voltage VCC drops below the minimum supply threshold, control circuit 401 will not function properly. Before VCC drops to the minimum supply threshold, the closer VCC is to the minimum supply threshold, the more urgent the power supply demand of control circuit 401. Therefore, a second supply voltage VCC_ON, slightly higher than or equal to the minimum supply threshold, can be set as the trigger voltage in the trigger condition. When VCC drops to VCC_ON, it means that the power supply demand is relatively urgent, and the self-powered module 411 cannot support the power supply demand of control circuit 401. It can choose to control the power supply path 420 to charge C3. To deal with this emergency, the power supply control module 430 can first control the power supply path 420 to perform a large-current emergency charge on C3. When VCC rises to the third supply voltage VCC_OFF, the emergency is considered to be resolved, and the emergency charging operation ends. Then, it enters the loop of judging whether the comprehensive charging conditions are met and the corresponding small-current charging. Therefore, in some embodiments, the power supply control module 430 can be further configured to: before determining whether the comprehensive charging conditions are met, when the power supply voltage VCC drops to the second power supply voltage VCC_ON, control the power supply path 420 to be turned on and control the path current of the power supply path 420 to be the first charging current Icharge_H, so as to charge the power supply capacitor C3 through the rectifier unit 403 and the power supply path 420; and when the power supply voltage VCC rises to the third power supply voltage VCC_OFF, control the power supply path 420 to be turned off to stop charging the power supply capacitor C3, wherein the second power supply voltage VCC_ON is less than the third power supply voltage VCC_OFF, and the third power supply voltage VCC_OFF is less than the first power supply voltage VCC_EN.

[0036] Figure 6 A waveform diagram of a power supply path related signal is shown according to an embodiment of the present invention. Figure 6As shown, when controlling the power supply path 420 based on triggering conditions and comprehensive charging conditions, the following charging process can exist inside the control circuit 401: Monitor VFB, VCC, and Vline; When VFB drops below FB_lightload at time t1, the signal EN_FB changes from low to high. When VFB drops to FB_Burst_L at time t2, PWM_GATE stops, and the self-powered module 411 stops charging C3. When VCC drops to VCC_ON at time t3, the signal EN_VCC changes from low level to high level, the power supply path 420 charges C3, and the path current Icharge is set to Icharge_H. When VCC rises to VCC_OFF at time t4, power supply path 420 stops charging C3, and VCC starts to drop again. After EN_VCC becomes high at time t3, VCC is always less than VCC_EN. When Vline drops to Vline_ON at time t5, the signal EN_Vline changes from low level to high level. At this time, EN_FB, EN_VCC, and EN_Vline are all high level, and the corresponding comprehensive charging conditions are met, so power supply path 420 charges C3. When Vline rises to Vline_OFF at time t7, the signal EN_Vline changes from high level to low level, the overall charging condition is no longer met, and the power supply path 420 stops charging C3.

[0037] like Figure 6 As shown, during the time period t5-t7, the current Icharge of power supply path 420 is negatively correlated with Vline: during the time period t5-t6, Vline decreases from Vline_ON to 0, and the current Icharge gradually increases from Icharge_L to Icharge_M; during the time period t6-t7, Vline increases from 0 to Vline_OFF, and the current Icharge gradually decreases from Icharge_M to Icharge_L. Where Icharge_L < Icharge_M < Icharge_H. The current during the t5-t7 time period is usually small and will not reach the Icharge_H of the t3-t4 time period.

[0038] like Figure 6 As shown, the waveform of SW1 is used to indicate the state of the status switch SW1. When the power supply path 420 charges C3, the status switch SW1 is closed. Figure 6 The state is indicated by a high level. When the power supply path 420 stops charging C3, the state switch SW1 is open. Figure 6 The middle level is represented as low level.

[0039] Figure 6 In the example shown, Vline_ON < Vline_OFF < Vline_EN, which conforms to the characteristic description that Vline is less than Vline_EN within the preset charging range. Besides this example, Vline_ON and Vline_OFF can also be other valid values; there are no restrictions here.

[0040] like Figure 6 As shown, the time period t3-t4 represents the charging of C3 in an emergency, signifying the occurrence of the trigger condition. After time t4, the power supply path 420 is controlled to charge C3 based on whether the comprehensive charging conditions are met. Specifically, if EN_FB and EN_VCC remain high, power supply path 420 charges C3 when EN_Vline is high. By setting the high-level condition of EN_Vline to control the charging duration and current Icharge of power supply path 420 to C3, and repeating the charging action during the time period t5-t7, VCC can fluctuate between VCC_ON and VCC_EN, achieving the effect of supplying power with lower power consumption under light system load.

[0041] like Figure 6 As shown, at time t7, power supply path 420 stops charging C3. The judgment for the next charging cycle is usually still based on the comprehensive charging conditions. However, when it is determined based on VCC and VFB that power supply to power supply path 420 is no longer necessary, power supply control module 430 can completely exit the judgment and charging based on comprehensive charging conditions, which is equivalent to resetting signals EN_FB, EN_VCC, and EN_Vline to low level. Subsequently, when the trigger condition (VCC drops to VCC_ON) is met again, the charging will resume as before. Figure 6 The series of actions after time t3. Here, determining that the power supply of power supply path 420 is no longer necessary can be based on either VFB not being less than FB_lightload or VCC not being less than VCC_EN, or only VFB not being less than FB_lightload or only VCC not being less than VCC_EN.

[0042] In the switching power supply system according to an embodiment of the present invention, the variation of VFB is related to the magnitude of the load. For example... Figure 6As shown, as the load decreases, VFB decreases. When VFB drops to FB_Burst_L at time t2, PWM_GATE stops, and the self-powered module 411 stops charging C3. If the load increases (e.g., switching from no-load or light-load to heavy-load), VFB rises above FB_Burst_H, PWM_GATE stops and starts outputting pulses, and the self-powered module 411 resumes charging C3. Before VFB rises to FB_lightload, the power supply path 420 will still charge C3 when the overall charging conditions are met. Therefore, it is possible for both the power supply path 420 and the self-powered module 411 to operate simultaneously. Each power supply mode independently determines whether the corresponding charging conditions are met and executes the charging action.

[0043] In the switching power supply system according to an embodiment of the present invention, a rise in VCC may be related to the charging of the power supply path 420 or the charging of the self-powered module 411. Typically, the values ​​of VCC_EN, VCC_OFF, Vline_ON, Vline_OFF, and Icharge can be adjusted so that when the self-powered module 411 is not operating and the power supply path 420 repeats the charging operation during the t5-t7 time period, VCC fluctuates between VCC_ON and VCC_EN. With this set of values, if VCC rises to VCC_EN, it indicates that the self-powered module 411 has also started charging C3.

[0044] Therefore, the power supply to the power supply path 420 can be determined based on the changes in VFB or VCC. If it is no longer necessary, the signals EN_FB, EN_VCC, and EN_Vline can be initialized in preparation for the next emergency power supply requirement.

[0045] It is important to note that Figure 6 This is an example of a specific case of the charging process of the control circuit according to an embodiment of the present invention, and not a limitation. For example, the signal EN_VCC going high can occur at time t3, time t4, or sometime within the time period t3-t4. Furthermore, the definitions of the high and low levels of each waveform can be adjusted according to actual conditions; it can be specified that the high level of signals EN_FB, EN_VCC, and EN_Vline represents satisfying a corresponding interval, or that the low level of each signal represents satisfying a corresponding interval. Moreover, various preset values ​​such as VCC_EN, VCC_OFF, Vline_ON, Vline_OFF, Icharge_H, charge_L, and Icharge_M can be set according to the actual configuration of the switching power supply system and the control circuit.

[0046] like Figure 5As shown, in some embodiments, the control circuit 401A may further include: a first detection circuit 501 for receiving VFB, a second detection circuit 502 for receiving VCC, and a third detection circuit 503 for receiving Vline. The three detection circuits 501-503 are configured to compare the received voltage with an internally preset voltage and output a signal indicating the comparison result, for example... Figure 6 The signals EN_FB, EN_VCC, and EN_Vline appear in the process.

[0047] like Figure 5 As shown, in some embodiments, the control circuit 401A may further include voltage divider resistors R1 and R2. R1 and R2 are connected in series between the rectifier unit 403 and the ground terminal to divide the voltage of Vline, and the third detection circuit 503 is connected to the common node of R1 and R2 to receive the voltage division of Vline.

[0048] Regarding the third detection circuit 503, multiple reference voltages can be internally set for comparison with Vline. The power supply control module 430 receives multiple signals from the third detection circuit 503 indicating the corresponding comparison results. Based on the requirement that the current in the power supply path 520 during charging is negatively correlated with Vline, the module can determine the magnitude of the corresponding current.

[0049] In some embodiments, the charging operation of the power supply capacitor by the startup module when the control circuit is powered on in the prior art can also be implemented by the power supply path 420 of the present invention. In this case, the power supply control module 430 can be further configured to: control the power supply path 420 to be turned on when the control circuit 401 is powered on, so as to charge the power supply capacitor C3 through the rectifier unit 403 and the power supply path 420 until the power supply voltage VCC rises to the fourth power supply voltage Uvlo_off.

[0050] Figure 7 Another waveform diagram of the power supply path related signal is shown according to an embodiment of the present invention. For example... Figure 7 As shown, Istartup is the current in the power supply path 420 during the charging process of C3 when the control circuit 401 is powered on and started. VCC starts to rise from 0. When VCC rises to Uvlo_off, which is the start-up threshold of the control circuit 401, the power supply path 420 stops supplying power to C3. Besides Figure 7 In the example Istartup, which is a gradually decreasing current, Istartup can also be a constant value, or it can increase according to a certain pattern or have other changes. The specific current value and waveform can be selected according to the actual situation, and there are no restrictions here.

[0051] The charging action of C3 by the power supply path 420 during the power-on startup of the control circuit 401 can be controlled by... Figure 5 This is achieved through a medium current source I_charge and a status switch SW1. When the control circuit 401 is powered on, the power supply control module 430 controls the status switch SW1 to close and controls the current source I_charge to output. Figure 7 The path current Istartup is shown to charge C3 via power supply path 420.

[0052] Figure 8 A partial schematic block diagram of a second example 401B of a control circuit according to an embodiment of the present invention is shown. Figure 8 As shown, in some embodiments, the power supply path 420 may further include a start switch SW2 connected in parallel with the status switch SW1. The charging action of the power supply path 420 on C3 when the control circuit 401 is powered on can be achieved by the current source I_charge and the start switch SW2. When the control circuit 401 is powered on, the power supply control module 403 controls the start switch SW2 to close and controls the current source I_charge to output. Figure 7 The path current Istartup is shown to charge C3 via power supply path 420.

[0053] Figure 9 A partial schematic block diagram of a third example 401C of a control circuit according to an embodiment of the present invention is shown. Figure 9 As shown, in some embodiments, the power supply path 420 may further include a current source I_startup and a start switch SW2. The charging of C3 by the power supply path 420 when the control circuit 401 is powered on can be achieved by the current source I_startup and the start switch SW2. When the control circuit 401 is powered on, the power supply control module 403 controls the start switch SW2 to close and the control circuit current source I_startup to output power. Figure 7 The current path shown is I_startup. The current path formed by the current source I_startup and the start switch SW2 is independent of the current path formed by the current source I_charge and the status switch SW1.

[0054] like Figure 4 As shown, in some embodiments, the switching power supply system 400 may further include a preset capacitor CX connected in parallel with the rectifier unit 403 to ensure that the switching power supply system 400 meets high-power safety requirements. Figure 5As shown, the control circuit example 401A may further include: a power failure detection module 440, used to detect whether the AC power supply has failed via the rectified output voltage Vline of the rectifier unit 403; and a capacitor discharge module 450, connected to the power supply path 420, used to discharge a preset capacitor CX after the AC power supply fails. Here, the capacitor discharge module 450 can be connected to the second terminal of the depletion-type switching transistor M0, and the preset capacitor CX discharges through the path of M0 and the capacitor discharge module 450. The configuration of the power failure detection module 440 and the capacitor discharge module 450 ensures that the preset capacitor CX discharges rapidly when the AC power supply fails, improving the safety of the system.

[0055] like Figure 5 As shown, in some embodiments, the control circuit 401 may also include an undervoltage protection circuit 460 and an overvoltage protection circuit 470, which take protective measures, such as shutting down part or all of the control circuit 401, when undervoltage or overvoltage of Vline is detected.

[0056] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0057] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A control circuit for a switching power supply system, wherein, The switching power supply system includes a rectifier unit connected to the AC power supply and a power supply capacitor for providing power supply voltage to the control circuit. The control circuit includes: A power supply path connecting one end to the rectifier unit and the other end to the power supply capacitor; and The power supply control module is configured as follows: The load condition of the switching power supply system is determined based on the load feedback voltage of the switching power supply system. When the load condition is non-heavy load, the power supply path is controlled based on the supply voltage to charge the power supply capacitor using the rectifier unit; and When the load condition is heavy load, the power supply path is disconnected to stop the power supply path from charging the power supply capacitor. The control circuit also includes a first depletion-mode power transistor, a power switching transistor, and a self-powered module. The first end of the first depletion-mode power transistor is connected to the transformer of the switching power supply system, the second end is connected to the power switching transistor, and the control terminal is grounded. One end of the self-powered module is connected to the second end of the first depletion-mode power transistor, and the other end is connected to the power supply capacitor.

2. The control circuit according to claim 1, wherein, The power supply path includes a current source that generates the path current of the power supply path, and the power supply control module is configured to adjust the path current by controlling the current source.

3. The control circuit according to claim 2, wherein, The power supply path also includes a state switch connected in series with the current source and controlling the power supply path to be turned on or off, and the power supply control module is configured to control the state of the state switch.

4. The control circuit according to claim 2, wherein, The power supply path also includes a second depletion-mode power transistor, the first end of which is connected to the rectifier unit, the second end of which is connected to the current source, and the control terminal is grounded.

5. The control circuit according to claim 1, wherein, The power supply control module is configured as follows: Determine whether the comprehensive charging conditions are met, wherein the comprehensive charging conditions include the load feedback voltage being less than the preset feedback voltage, the supply voltage being less than the first supply voltage, and the rectified output voltage of the rectifier unit being within the preset charging range; When the comprehensive charging conditions are met, the power supply path is controlled to be turned on so that the power supply path charges the power supply capacitor based on the rectifier unit; as well as If the overall charging conditions are not met, the power supply path is disconnected to stop charging the power supply capacitor.

6. The control circuit according to claim 5, wherein, The power supply control module is configured as follows: When the comprehensive charging conditions are met, the current in the power supply path is also controlled so that the current in the path is negatively correlated with the rectified output voltage.

7. The control circuit according to claim 5, wherein, The rectified output voltage within the preset charging range is less than the preset rectified voltage.

8. The control circuit according to claim 5, wherein, The power supply control module is configured as follows: Before determining whether the comprehensive charging conditions are met... When the supply voltage drops to the second supply voltage, the power supply path is turned on and the current of the power supply path is controlled to be the first charging current, so that the power supply path charges the power supply capacitor based on the rectifier unit. When the power supply voltage rises to the third power supply voltage, the power supply path is controlled to be disconnected to stop charging the power supply capacitor, wherein the second power supply voltage is less than the third power supply voltage, and the third power supply voltage is less than the first power supply voltage.

9. The control circuit according to claim 1, wherein, The power supply control module is configured as follows: When the control circuit is powered on, the power supply path is turned on so that the power supply path charges the power supply capacitor based on the rectifier unit until the power supply voltage rises to the fourth power supply voltage.

10. The control circuit according to any one of claims 1 to 9, wherein, The switching power supply system further includes a preset capacitor connected in parallel with the rectifier unit, and the control circuit further includes: A power failure detection module is used to detect whether the AC power supply has failed by measuring the rectified output voltage of the rectifier unit; and A capacitor discharge module, connected to the power supply path, is used to discharge the preset capacitor after the AC power supply fails.

11. A switching power supply system, comprising a control circuit as described in any one of claims 1-10, a rectifier unit connected to an AC power supply, and a power supply capacitor for providing a power supply voltage to the control circuit.

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