Switching power supply and overcurrent protection circuit thereof

Abstract

The embodiment of the present application discloses a switching power supply and an overcurrent protection circuit thereof. The overcurrent protection circuit for the switching power supply provided by the embodiment of the present application is configured to generate an overcurrent protection duty cycle signal based on the size of an input voltage or an output voltage of the switching power supply, generate an overcurrent protection threshold voltage based on the overcurrent protection duty cycle signal, and generate a switching control signal for controlling a switching tube in the switching power supply to change from a conducting state to an off state based on the overcurrent protection threshold voltage and a sensing current representation signal representing an output current of the switching power supply.

Description

Technical Field

[0001] This invention generally belongs to the field of integrated circuits, and particularly relates to a switching power supply and its overcurrent protection circuit. Background Technology

[0002] After decades of development, current switching power supply technology has placed higher demands on charging efficiency and charging speed. Among these advancements, the multi-output voltage mode, which divides the output voltage into multiple segments, has been widely used in power adapters of different power ratings.

[0003] However, when such segmented multi-output switching power supplies are applied under wide input voltage conditions, the operating frequency of the switching power supply when overcurrent protection occurs under high voltage input can reach hundreds of kHz, while the operating frequency when overcurrent protection occurs under low voltage input is only tens of kHz. This results in a large difference in the operating mode and operating frequency of the wide input and wide output switching power supply when overcurrent protection occurs, which in turn leads to a large difference in the overcurrent protection operating point and increases the design difficulty of the overcurrent protection point. Summary of the Invention

[0004] In a first aspect, embodiments of the present invention provide an overcurrent protection circuit for a switching power supply, characterized in that the overcurrent protection circuit is configured to: generate an overcurrent protection duty cycle signal based on the magnitude of the input voltage or output voltage of the switching power supply; generate an overcurrent protection threshold voltage based on the overcurrent protection duty cycle signal; and generate a switching control signal for controlling the switching transistor in the switching power supply to change from an on state to an off state based on the overcurrent protection threshold voltage and a sensing current characterization signal characterizing the output current of the switching power supply.

[0005] In a second aspect, embodiments of the present invention provide a switching power supply, including the overcurrent protection circuit described in the first aspect.

[0006] Thirdly, the switching power supply described in the first and second aspects is one of the following: buck switching power supply, boost switching power supply, buck-boost switching power supply, flyback switching power supply, forward switching power supply, and asymmetric half-bridge switching power supply.

[0007] The switching power supply and its overcurrent protection circuit provided in this embodiment of the invention generate a corresponding overcurrent protection threshold voltage based on the magnitude of the input voltage or output voltage of the switching power supply, and generate a switching control signal for controlling the switching transistor in the switching power supply to change from the on state to the off state based on the overcurrent protection threshold voltage and the sensing current characterization signal characterizing the output current of the switching power supply, so as to prevent the difference of the overcurrent protection point when overcurrent protection occurs from being too large. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of a traditional flyback multi-mode switching power supply is shown.

[0010] Figure 2 It shows Figure 1 The diagram shows the operating frequency range of a flyback switching power supply when overcurrent protection occurs under wide input voltage conditions.

[0011] Figure 3 It shows Figure 1 The diagram shows a partial circuit structure of a switching power supply.

[0012] Figure 4 It shows Figure 3 The waveform diagram shown illustrates the correspondence between the corresponding signals of the overcurrent protection threshold generation control unit.

[0013] Figure 5 It shows Figure 1 The diagram shows the timing relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection in the logic-distinguished low-voltage segment.

[0014] Figure 6 It shows Figure 1 The timing diagram shown illustrates the relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection in the logic-distinguished high-voltage section.

[0015] Figure 7 A schematic diagram of the structure of a flyback switching power supply according to an embodiment of the present invention is shown;

[0016] Figure 8 It shows Figure 7 The diagram shows a schematic of the circuit in a switching power supply that generates an overcurrent protection threshold voltage based on the input voltage.

[0017] Figure 9 It shows Figure 7 The diagram shows the operating frequency range of a flyback switching power supply when overcurrent protection occurs under wide input voltage conditions.

[0018] Figure 10 It shows Figure 7The diagram shows the timing relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection under wide input voltage conditions.

[0019] Figure 11 It shows Figure 7 The diagram shows a schematic of the circuit in a switching power supply that generates an overcurrent protection threshold voltage based on the output voltage.

[0020] Figure 12 It shows Figure 7 The diagram shows the operating frequency range of a flyback switching power supply under wide output voltage conditions when overcurrent protection occurs; and

[0021] Figure 13 It shows Figure 7 The diagram shows the timing relationship between the overcurrent protection duty cycle signal OCP_duty and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection under wide output voltage conditions. Detailed Implementation

[0022] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0023] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0024] After decades of development, current switching power supply technology has placed higher demands on charging efficiency and charging speed. Among them, the multi-output voltage mode, which divides the output voltage into multiple segments, has been widely used in power adapters of different power ratings. With the increasing demand for miniaturization of power adapters and the large-scale application of low-loss devices such as gallium nitride (GaN) high-frequency switches, the transformer inductance used in the system is getting smaller and smaller, and the switching control frequency of the system can reach up to several hundred kHz.

[0025] When such a switching power supply with multiple segmented output voltages is applied to a switching power supply system with a wide range of AC input voltages, such as 90V to 264V, this may result in the system operating at frequencies as high as hundreds of kHz when overcurrent protection occurs under high-voltage input conditions, while under low-voltage input conditions, the system may operate in continuous conduction mode (CCM), at which point the system operating frequency is only tens of kHz. This leads to a significant difference in the operating mode and frequency of the wide-input, wide-output switching power supply system when overcurrent protection occurs, resulting in a huge difference in the overcurrent protection operating point under wide-input, wide-output voltage systems, which brings great difficulty to the system design of the overcurrent protection point of the switching power supply system.

[0026] To better understand the switching power supply and its overcurrent protection circuit provided in the embodiments of the present invention, the following first introduces the traditional switching power supply and its overcurrent protection circuit.

[0027] refer to Figure 1 , Figure 1 A schematic diagram of a traditional flyback multi-mode switching power supply is shown. Figure 1 The flyback switching power supply 100 shown can output multiple output voltages Vout1 to VoutN. The switching power supply 100 may include a frequency control unit 102, an input unit 104, a quasi-resonant valley detection unit 106, a switching transistor turn-on and turn-off control logic 108, a frequency selection control logic 110, a CCM clamping frequency control unit 112, a duty cycle controlled overcurrent protection circuit 114, a comparator 116, a comparator 118, a transformer 120, a segmented output voltage control unit 122, and an error amplifier feedback control unit 124, etc.

[0028] like Figure 1 As shown, the output voltage is controlled by the segmented output voltage control unit 122 located on the secondary side of the transformer, and then the output voltage is regulated by the error amplifier feedback control unit 124 to obtain the output voltage characterization signal FB, which characterizes the output voltage of the switching power supply.

[0029] refer to Figure 2 , Figure 2 It shows Figure 1 The diagram shows the operating frequency range of a flyback switching power supply when overcurrent protection occurs under wide input voltage conditions.

[0030] like Figure 2 As shown, disregarding the output voltage, when the input voltage of the switching power supply is a high voltage input, through... Figure 1 The frequency selection control logic 110 shown causes the switching power supply to operate on the second frequency curve controlled by the output voltage characterization signal FB. The switching power supply is in quasi-resonant operating mode most of the time. As the load increases, the output voltage characterization signal FB increases accordingly. For a period of time, the operating frequency of the switching power supply increases with the increase of the output voltage characterization signal FB. The frequency f2 is the maximum value of the upper clamping frequency of the second frequency curve. Next, as the load continues to increase, according to the quasi-resonant characteristics, the switching frequency of the switching power supply will gradually decrease after reaching the maximum value of the upper clamping frequency f2, and will eventually be clamped by the lower clamping frequency fmin2 of the CCM.

[0031] When the input voltage of the switching power supply is low voltage, through Figure 1 The frequency selection control logic 110 shown causes the switching power supply to operate on the first frequency curve controlled by the output voltage characterization signal FB, where frequency f1 is the maximum value of the quasi-resonant upper clamping frequency of the first frequency curve. As the load increases, the output voltage characterization signal FB increases accordingly. As the load continues to increase, according to the quasi-resonant characteristics, the switching frequency of the switching power supply will gradually decrease after rising to the maximum value of the quasi-resonant upper clamping frequency f1, and will eventually be clamped by the lower clamping frequency fmin2 of CCM.

[0032] like Figure 2 As shown, the input voltage is simply divided into high-voltage and low-voltage segments by input detection. When the input voltage logic of the switching power supply is classified as high-voltage and overcurrent protection is triggered, the switching power supply can operate in the following conditions: Figure 2 The shaded area near the maximum value f2 of the clamping frequency shown in the diagram represents the overcurrent protection condition when the input voltage logic classifies the switching power supply as a low-voltage input. In this case, the switching power supply can operate under conditions such as... Figure 2 The shaded area near the clamping frequency fmin2 shown in the CCM diagram.

[0033] Understandably, since switching power supplies operate in quasi-resonant mode most of the time, it is impossible to detect the actual switching frequency of the switching power supply as the output power changes. This makes it difficult to detect or count the actual switching duty cycle (PWM duty) of the switching control signal of the switching power supply. Therefore, in traditional switching power supplies, the overcurrent protection threshold voltage Vth_oc can usually only be generated based on the duty cycle generated at a certain fixed frequency.

[0034] refer to Figure 3 , Figure 3 It shows Figure 1 The diagram shows a partial circuit structure of a switching power supply. Figure 3 It shows Figure 1 The system includes a CCM lower clamp frequency control unit 112, a duty cycle controlled overcurrent protection circuit 114, and a comparator 116. The duty cycle controlled overcurrent protection circuit 114 may include a comparator 1142 and an overcurrent protection threshold generation control unit 1144.

[0035] exist Figure 3 In the illustrated embodiment, the CCM lower clamp frequency control unit 112 can generate a ramp voltage signal Osc_ramp based on the CCM lower clamp frequency fmin2. Comparator 1142 can generate an overcurrent protection duty cycle signal OCP_duty based on the ramp voltage signal Osc_ramp and the reference voltage signal Vref. The overcurrent protection threshold generation control unit 1144 can generate an overcurrent protection threshold voltage Vth_oc based on the overcurrent protection duty cycle signal OCP_duty. Comparator 116 can generate an OCP turn-off signal OCP_Trigger to control the switching transistor Q1 from the on state to the off state based on the overcurrent protection threshold voltage Vth_oc and the sensed current characterization signal Vcs (voltage across the current sensing resistor Rs), which characterizes the output current of the switching power supply. The switching transistor turn-on and turn-off control logic 108 (see...) Figure 1 The switching control signal PWM for controlling the switching transistor Q1 to change from the on state to the off state can be generated based on the OCP turn-off signal OCP_Trigger.

[0036] It can be seen that, in Figure 3 In the conventional switching power supply shown, the ramp voltage signal Osc_ramp can be generated based on the CCM clamping frequency fmin2. The overcurrent protection duty cycle signal OCP_duty can be generated based on the ramp voltage signal Osc_ramp and the reference voltage signal Vref. The overcurrent protection threshold voltage Vth_oc can be generated based on the overcurrent protection duty cycle signal OCP_duty. The overcurrent protection threshold voltage Vth_oc can be compared with the sensed current characterization signal Vcs to generate the OCP turn-off signal OCP_Trigger for controlling the switch Q1 to change from the on state to the off state.

[0037] Combination Figure 3 and Figure 4 , Figure 4 It shows Figure 3 The waveform diagram shown illustrates the correspondence between the corresponding signals of the overcurrent protection threshold generation control unit 1144.

[0038] like Figure 4 As shown, as the overcurrent protection duty cycle signal OCP_duty gradually increases (e.g., from 0 to OCP_duty1 and then to OCP_duty2), the overcurrent protection threshold voltage Vth_oc gradually increases (e.g., from V1 to V2 until reaching a maximum value V3 which remains constant).

[0039] like Figure 3 As shown, as the output load current gradually increases, comparator 116 can be configured to generate an OCP turn-off signal OCP_trigger to turn off switch Q1 when the sensed current characterization signal Vcs rises above the overcurrent protection threshold voltage Vth_oc. The purpose of this overcurrent protection to turn off switch Q1 is to avoid excessive current flowing through switch Q1, thereby preventing damage to switch Q1 and avoiding magnetic saturation of transformer T1.

[0040] refer to Figure 5 , Figure 5 It shows Figure 1 The diagram shows the timing relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection in the logic-distinguished low-voltage segment.

[0041] Combination Figure 2 It can be seen that the switching frequency of the flyback switching power supply when overcurrent protection occurs under low input voltage is in the region near the clamping frequency fmin2 under CCM. Therefore, in situations such as Figure 5 Under this low-voltage input condition, the difference between the duty cycle of the overcurrent protection duty cycle signal OCP_duty generated based on the CCM clamping frequency fmin2 and the duty cycle of the actual PWM signal of the switching power supply is small. At this time, the difference ΔVthoc between the overcurrent protection threshold voltage Vth_oc1 actually required by the switching power supply under low-voltage input and the overcurrent protection threshold voltage Vth_oc2 generated based on the overcurrent protection duty cycle signal OCP_duty is small.

[0042] refer to Figure 6 , Figure 6 It shows Figure 1 The diagram shows the timing relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply triggers overcurrent protection in the logic-distinguished high-voltage section.

[0043] In such Figure 6Under the high-voltage input condition shown, the operating frequency for overcurrent protection of the switching power supply is near the maximum clamping frequency f2 of the second frequency. However, the overcurrent protection threshold is generated by the clamping frequency fmin2 under CCM (Continuous Current Management). At this time, there is a significant difference between the duty cycle of the PWM (Pulse Width Control Signal) for the switching transistor Q1 and the duty cycle of the overcurrent protection duty cycle signal OCP_duty generated based on the clamping frequency fmin2 under CCM. This results in a much higher actual overcurrent protection threshold voltage Vth_oc1' required by the switching power supply under high voltage input than the overcurrent protection threshold voltage Vth_oc2' generated by the overcurrent protection duty cycle signal OCP_duty under the clamping frequency fmin2 under CCM, leading to a lower overcurrent protection threshold voltage generated by the switching power supply under high voltage input. This difference results in an excessively large difference between the current cut-off points when overcurrent protection occurs under high and low voltage input conditions, making it difficult to effectively protect devices in a wide-input switching power supply.

[0044] To address one or more of the problems in the prior art, embodiments of the present invention provide a switching power supply and its overcurrent protection circuit. The switching power supply and its overcurrent protection circuit provided by embodiments of the present invention will be described below.

[0045] When a switching power supply operates under wide input and output voltage conditions, the frequency at which overcurrent protection occurs varies significantly. This leads to a large difference between the required overcurrent protection threshold and the actual overcurrent protection threshold. To address the significant differences in operating frequency and duty cycle caused by wide input and output voltages, resulting in discrepancies in overcurrent protection points, the switching power supply and its overcurrent protection circuit provided in this invention adopt an adaptive duty cycle overcurrent protection control method that changes with the input or output voltage. This greatly reduces the differences in overcurrent protection points under wide input and output voltages and simplifies the design of overcurrent protection for switching power supplies with wide input and output voltages to a certain extent.

[0046] Figure 7 A schematic diagram of a flyback switching power supply according to an embodiment of the present invention is shown. Figure 7 As shown, Figure 1 and Figure 7 In the embodiments shown, the same components are referred to by the same reference numerals.

[0047] exist Figure 7The flyback switching power supply 700 shown may include an input unit 104, a quasi-resonant valley detection unit 106, a switching transistor turn-on and turn-off control logic 108, a ramp voltage signal generation unit 128 (including a frequency control unit 102 and a frequency selection control logic 110), a CCM down-clamp frequency control unit 112, a duty cycle controlled overcurrent protection circuit 114, a comparator 116, a comparator 118, a transformer 120, a segmented output voltage control unit 122, an error amplifier feedback control unit 124, and an input voltage detection and selection unit 126, etc., through comparison... Figure 1 and Figure 7 It can be seen that the main difference between the two is that... Figure 7 The switching power supply shown is compared to Figure 1 The switching power supply shown has added an input voltage detection and selection unit 126, which allows it to select the ramp voltage signal OSC_ramp corresponding to the frequency control unit 102 according to the voltage range of the input voltage, and then generate the overcurrent protection threshold voltage Vth_oc. Its detailed working principle will be introduced below.

[0048] Figure 8 It shows Figure 7 The diagram shows a schematic of a circuit in a switching power supply that generates an overcurrent protection threshold voltage based on the input voltage. For example, Figure 8 It shows Figure 7 The input voltage detection and selection unit 126, the ramp voltage signal generation unit 128, the duty cycle controlled overcurrent protection circuit 114, and the comparator 116 are included.

[0049] In some embodiments, the input voltage detection and selection unit 126 may include input voltage judgment logic 1262 and wide input multi-frequency switch gating logic 1264, and the duty cycle controlled overcurrent protection circuit 114 may include comparator 1142 and overcurrent protection threshold generation and control unit 1144.

[0050] Combination Figure 7 and Figure 8The Vin_detect signal output by the input unit 104 can be provided to the input voltage detection and selection unit 126. The input voltage judgment logic 1262 in the input voltage detection and selection unit 126 can be used to segment the input voltage to divide the input voltage Vin into N segments Vin1...VinN. Then, the segmented input voltages Vin1 to VinN are provided to the wide input multi-frequency switch gating logic 1264. The wide input multi-frequency switch gating logic 1264 can output switch gating signals Sel1 to SelN to the ramp voltage signal generation unit 128 to control the conduction and de-conduction of multiple switches Sw1 to SwN in the ramp voltage signal generation unit 128, thereby selecting different frequency control units from multiple frequency control units.

[0051] Specifically, the corresponding frequency control unit is selected from different frequency control units (e.g., the first frequency control unit to the Nth frequency control unit) by controlling the conduction of one of the multiple switches Sw1 to SwN. For example, the ramp voltage signals OSC_ramp1 to OSC_rampN generated by the first frequency control unit to the Nth frequency control unit are selected sequentially by controlling the conduction of the multiple switches Sw1 to SwN in turn.

[0052] For example, refer to Figure 8 When the input voltage is within the voltage range Vin1, the switch selection signal Sel1 is valid, and the remaining switch selection signals Sel2 to SelN are invalid. At this time, the switch selection signal Sel1 is used to control switch Sw1 to be in the on state and to control the remaining switches Sw2 to SwN to be in the off state. By controlling switch Sw1 to be in the on state and controlling the remaining switches Sw2 to SwN to be in the off state, the first frequency control unit is selected, so that the Osc_ramp signal is selected as the ramp voltage signal OSC_ramp1 generated by the first frequency control unit. Comparator 1142 can be used to select the ramp voltage selected by switch Sw1. The signal OSC_ramp1 is compared with the reference voltage signal Vref to generate an overcurrent protection duty cycle signal OCP_duty. The overcurrent protection duty cycle signal OCP_duty can be input to the overcurrent protection threshold generation control unit 1144 to generate an overcurrent protection threshold voltage Vth_oc related to the duty cycle. The overcurrent protection threshold voltage Vth_oc can be provided to the comparator 116. The comparator 116 can be used to compare the overcurrent protection threshold voltage Vth_oc with the sensed current characterization signal Vcs to generate an OCP turn-off signal OCP_Trigger for controlling the switch Q1 to change from the on state to the off state.

[0053] exist Figure 7In the switching power supply shown, the OCP turn-off signal OCP_Trigger and the Vcs turn-off signal Cs_trigger from comparator 118 are signals used to control the switching transistor Q1 from the on state to the off state, and the CCM lower clamp frequency fmin2 and the signal Tri_on from the frequency selection control logic 110 are signals used to control the switching transistor Q1 from the off state to the on state.

[0054] refer to Figure 9 , Figure 9 It shows Figure 7 The diagram shows the operating frequency range of a flyback switching power supply when overcurrent protection occurs under wide input voltage conditions.

[0055] like Figure 9 As shown, when the input voltage is within the first segment input voltage Vin1, the operating frequency of the switching power supply when overcurrent protection occurs is maintained near the upper clamping frequency signal f1 of the first frequency control curve. When the input voltage is within the Nth segment input voltage VinN, the operating frequency of the switching power supply when overcurrent protection occurs is maintained near the upper clamping frequency signal fn of the Nth frequency control curve.

[0056] For each input voltage segment, the switch corresponding to that segment voltage is controlled to be in the on state and the remaining switches are controlled to be in the off state, so as to select the corresponding frequency control unit to generate the ramp voltage signal osc_ramp, and the overcurrent protection duty cycle signal OCP_duty is generated based on the ramp voltage signal osc_ramp.

[0057] By determining the voltage range of the input voltage and generating a corresponding overcurrent protection duty cycle signal OCP_duty for each range, the difference between the actual duty cycle of the PWM signal required for overcurrent protection under each input voltage range and the actual duty cycle of the generated OCP_duty signal is very small. Figure 10 As shown.

[0058] refer to Figure 10 , Figure 10 It shows Figure 7 The diagram shows the timing relationship between the PWM signal, the overcurrent protection duty cycle signal OCP_duty, and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection under wide input voltage conditions.

[0059] from Figure 10As can be seen, for the first input voltage Vin1, the difference ΔVthoc1 between the overcurrent protection threshold voltage Vth_oc1 generated by the actual duty cycle of the PWM signal and the overcurrent protection threshold voltage Vth_oc2 generated by the duty cycle of the OCP_duty signal is very small, for example, ΔVthoc1 ≌ 0. Similarly, for the second to Nth input voltages Vin2 ∽ VinN, the difference ΔVthoc2..M between the actual required overcurrent protection threshold voltage Vth_oc1 and the actual generated overcurrent protection threshold voltage Vth_oc2 is very small, for example, ΔVthoc2..M ≌ 0.

[0060] In summary, by selecting different frequency control units to generate different overcurrent protection thresholds based on different input voltage ranges, the problem of the huge difference between the duty cycle of the PWM signal and the duty cycle of the OCP_duty signal generated by a single fixed clamping frequency in traditional switching power supplies under wide input voltage conditions is solved. This greatly reduces the huge difference in the overcurrent protection point when the input voltage of a switching power supply with a wide input voltage range changes significantly, and optimizes the overcurrent protection design to a certain extent.

[0061] As described above, one embodiment of the present invention provides a switching power supply that generates different overcurrent protection thresholds based on different voltage ranges of the input voltage, and another embodiment of the present invention provides a switching power supply that generates different overcurrent protection thresholds based on different voltage ranges of the output voltage.

[0062] refer to Figure 11 , Figure 11 It shows Figure 7 The diagram shows a schematic of the circuit in a switching power supply that generates an overcurrent protection threshold voltage based on the output voltage. Figure 8 The illustrated embodiments and Figure 11 The main difference between the embodiments shown is that Figure 8 The illustrated embodiment generates a corresponding overcurrent protection threshold based on the voltage range of the input voltage, while Figure 11 The embodiment shown generates a corresponding overcurrent protection threshold based on the voltage range of the output voltage.

[0063] exist Figure 11 In the illustrated embodiment, the circuit may include output voltage detection logic 130, multi-frequency switch gating logic 132, ramp voltage signal generation unit 128, duty cycle controlled overcurrent protection circuit 114, and comparator 116, etc.

[0064] In some embodiments, the duty cycle controlled overcurrent protection circuit 114 may include a comparator 1142 and an overcurrent protection threshold generation control unit 1144.

[0065] exist Figure 11 In the illustrated embodiment, the output signals Vout1 to VoutX from the switching power supply can be provided to the output voltage detection logic 130. The output voltage detection logic 130 can output selection signals Vout1_sel...VoutX_sel and provide the selection signals Vout1_sel...VoutX_sel to the multi-frequency switch gating logic 132. The multi-frequency switch gating logic 132 can output switch gating signals Sel1 to Selh to the ramp voltage signal generation unit 128 to control the on and off of multiple switches Sw1 to SwZ in the ramp voltage signal generation unit 128.

[0066] Specifically, a frequency control unit is selected from different frequency control units (e.g., the first to the Nth frequency control units) by controlling the conduction of one of the multiple switches Sw1 to SwZ. For example, the ramp voltage signals OSC_ramp1 to OSC_rampN generated by the first to the Nth frequency control units are sequentially selected by controlling the conduction of the multiple switches Sw1 to SwZ in turn.

[0067] Next, comparator 1142 can be used to compare the ramp voltage signal OSC_ramp generated by the frequency control unit with the reference voltage signal Vref to generate an overcurrent protection duty cycle signal OCP_duty. The overcurrent protection duty cycle signal OCP_duty can be input to the overcurrent protection threshold generation control unit 1144 to generate an overcurrent protection threshold voltage Vth_oc related to the duty cycle. The overcurrent protection threshold voltage Vth_oc (Vth_oc1...Vth_ocN) can be provided to comparator 116. Comparator 116 can be used to compare the overcurrent protection threshold voltage Vth_oc with the sensed current characterization signal Vcs to generate an OCP turn-off signal OCP_Trigger for controlling the switch Q1 to change from the on state to the off state.

[0068] refer to Figure 12 , Figure 12 It shows Figure 7 The diagram shows the operating frequency range of a flyback switching power supply when overcurrent protection occurs under wide output voltage conditions.

[0069] like Figure 12As shown, when the output voltage is within the voltage range Vout1, the operating frequency of the switching power supply when overcurrent protection occurs is maintained near the upper clamping frequency signal f1 of the first frequency curve. When the output voltage is within the voltage range VoutN, the operating frequency of the switching power supply when overcurrent protection occurs is maintained near the upper clamping frequency signal fn of the Nth frequency curve.

[0070] refer to Figure 13 , Figure 13 It shows Figure 7 The diagram shows the timing relationship between the overcurrent protection duty cycle signal OCP_duty and the overcurrent protection threshold voltage Vth_oc when the flyback switching power supply experiences overcurrent protection under wide output voltage conditions.

[0071] like Figure 13 As shown, the wide output voltage range of the switching power supply, Vout1...VoutX, is achieved through... Figure 7 The segmented output voltage control unit 122 shown provides power to the load in multiple segments, where Vout1>Vout2…>VoutX.

[0072] By using this adaptive overcurrent protection control method that selects different frequency control units based on the output voltage, the overcurrent protection threshold voltage Vth_oc can be gradually reduced as the output voltage decreases, ultimately achieving the wide output voltage power limit protection requirement of a wide output voltage system and preventing damage to the transformer saturation switch.

[0073] The wide input and wide output overcurrent protection scheme provided in this embodiment of the invention is applicable to switching power supplies with wide input and wide output operation. It should be understood that the above flyback switching power supply is only provided as an example and should not be interpreted as restrictive. Its power supply topology may also include buck switching power supply, boost switching power supply, buck-boost switching power supply, forward switching power supply, asymmetric half-bridge switching power supply, etc.

[0074] The switching power supply provided in this invention utilizes adaptive wide input and wide output duty cycle overcurrent protection technology. When overcurrent protection occurs under wide input and wide output voltage conditions, the switching power supply selects different overcurrent protection threshold voltages by choosing a frequency control unit. This reduces the large difference between the actual required overcurrent protection threshold and the actual overcurrent protection threshold caused by the large difference in the operating frequency of the overcurrent protection point under wide input and wide output conditions, thereby further optimizing the design of the switching power supply.

[0075] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0076] It should also be noted that the exemplary embodiments mentioned in this invention describe methods or systems based on a series of steps or apparatus. However, this invention is not limited to the order of the steps described above; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0077] The above description is merely a specific embodiment of the present invention. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. An overcurrent protection circuit for a switching power supply, characterized in that, The overcurrent protection circuit is configured as follows: Based on the voltage range of the input or output voltage of the switching power supply, an overcurrent protection duty cycle signal is generated; Based on the overcurrent protection duty cycle signal, an overcurrent protection threshold voltage is generated; as well as Based on the overcurrent protection threshold voltage and the sensing current characterization signal characterizing the output current of the switching power supply, a switching control signal is generated to control the switching transistor in the switching power supply to change from the on state to the off state, wherein the difference between the duty cycle of the overcurrent protection duty cycle signal and the duty cycle of the switching control signal is within a preset threshold.

2. The overcurrent protection circuit according to claim 1, characterized in that, The overcurrent protection circuit is further configured as follows: Based on the voltage range of the input or output voltage of the switching power supply, a corresponding ramp voltage signal is selected from the generated ramp voltage signals, wherein the ramp voltage signal is related to the operating frequency of the overcurrent protection point; and The selected ramp voltage signal is compared with the reference voltage signal to generate the overcurrent protection duty cycle signal.

3. The overcurrent protection circuit according to claim 2, characterized in that, The overcurrent protection circuit includes multiple frequency control units and multiple switches, wherein: If the input voltage or output voltage of the switching power supply is within a first voltage range, then the first switch among the plurality of switches is controlled to be in the ON state, and the remaining switches among the plurality of switches are controlled to be in the OFF state; and By controlling the first switch to be in the on state and controlling the remaining switches to be in the off state, the first frequency control unit among the plurality of frequency control units is selected, so as to select the first ramp voltage signal among the plurality of ramp voltage signals.

4. The overcurrent protection circuit according to claim 1, characterized in that, The overcurrent protection circuit is further configured as follows: The overcurrent protection threshold voltage is compared with the sensed current characterization signal to generate an overcurrent protection point turn-off signal. as well as The switch control signal is generated based on the overcurrent protection point turn-off signal.

5. The overcurrent protection circuit according to claim 1, characterized in that, The magnitude of the overcurrent protection threshold voltage decreases as the input voltage of the switching power supply increases.

6. The overcurrent protection circuit according to claim 1, characterized in that, The magnitude of the overcurrent protection threshold voltage decreases as the output voltage of the switching power supply decreases.

7. A switching power supply, characterized in that, Includes the overcurrent protection circuit as described in any one of claims 1 to 6.

8. The switching power supply as described in claim 7, characterized in that, The switching power supply is one of the following: buck switching power supply, boost switching power supply, buck-boost switching power supply.

9. The switching power supply according to claim 7, characterized in that, The switching power supply is one of the following: flyback switching power supply, forward switching power supply, or asymmetric half-bridge switching power supply.

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