A current limiting protection method, circuit and switching power supply

Abstract

This invention discloses a current-limiting protection method, circuit, and switching power supply. The current-limiting protection method includes the following steps: converting a current signal representing the input power of the switching power supply into a first voltage signal, and simultaneously converting a voltage signal representing the input voltage of the switching power supply into a second voltage signal; then superimposing the first voltage signal and the second voltage signal to generate a third voltage signal, wherein when the voltage signal representing the input voltage of the switching power supply reaches a second preset value, the third voltage signal no longer changes with the increase of the second voltage signal; comparing the third voltage signal with the first preset value, and generating a current-limiting protection trigger signal when the third voltage signal is greater than or equal to the first preset value. The switching power supply using this invention can significantly improve the consistency of the current-limiting protection point, which is beneficial for reducing device stress and improving the reliability of the switching power supply.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of switching power supply, in particular to a current limiting protection method, circuit and switching power supply. BACKGROUND

[0002] Switching power supply is widely used as power supply device of many electronic products and device systems, etc. In addition to its performance meeting the requirements of power supply products, its own protection measures are also very important. For example, when the output end of the switching power supply exceeds the rated load or is short-circuited, it will cause damage to the switching power supply, so that the electronic products and device systems, etc. on the output side cannot work normally, and even cause electric shock and fire of the operator.

[0003] In view of the above-mentioned abnormalities, when designing the switching power supply, current limiting protection design should be carried out. The rationality and effectiveness of the protection design means that the reliability of the switching power supply can be higher. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide a current limiting protection method, circuit and switching power supply, so that the deficiencies of the prior art can be overcome, and the consistency of the overcurrent protection ratio can be significantly improved. The discovery and analysis of the prior art will be described in detail in the subsequent specification.

[0005] As a first aspect of the present application, the following embodiments are provided:

[0006] A current limiting protection method applied to a switching power supply, comprising the following steps:

[0007] Converting a current signal representing the input power size of the switching power supply into a first voltage signal, and converting a voltage signal representing the input voltage size of the switching power supply into a second voltage signal, then superimposing the first voltage signal and the second voltage signal to generate a third voltage signal, wherein when the voltage signal representing the input voltage size of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal by clamping the second voltage signal, and the second set value represents that the input voltage of the switching power supply is the maximum value of the feedforward compensation voltage range;

[0008] Comparing the third voltage signal with a first set value, and when the third voltage signal is greater than or equal to the first set value, generating a current limiting protection trigger signal.

[0009] As a second aspect of the present application, the following embodiments are provided:

[0010] A current limiting protection circuit applied to a switching power supply, comprising:

[0011] An input state monitoring circuit is configured to convert a current signal representing the input power of the switching power supply into a first voltage signal, convert a voltage signal representing the input voltage of the switching power supply into a second voltage signal, and then superimpose the first voltage signal and the second voltage signal to generate a third voltage signal. When the voltage signal representing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal by clamping the second voltage signal, and the second set value represents the maximum value of the input voltage of the switching power supply in the feed-forward compensation voltage range.

[0012] A comparison circuit is configured to compare the third voltage signal and a first set value, and generate a current-limiting protection trigger signal when the third voltage signal is greater than or equal to the first set value.

[0013] As a specific embodiment of the input state monitoring circuit, it includes a resistor R1, a resistor R2H, a resistor R2L, and a clamping circuit. One end of the resistor R1 is configured to input the current signal representing the input power of the switching power supply. One end of the resistor R2H is configured to input the input voltage of the switching power supply. The other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit. The other end of the resistor R1 and the other end of the resistor R2L are connected together to output the third voltage signal. The other end of the clamping circuit is configured to be grounded.

[0014] As a specific embodiment of the clamping circuit, it includes a zener diode. The anode of the zener diode is the other end of the clamping circuit, and the cathode of the zener diode is one end of the clamping circuit.

[0015] As a specific embodiment of the comparison circuit, it includes a comparator. The same-phase input end of the comparator is configured to input the first set value. The opposite-phase input end of the comparator is configured to input the third voltage signal. The output end of the comparator is configured to output the current-limiting protection trigger signal.

[0016] A current-limiting protection circuit applied to a switching power supply includes:

[0017] The input state monitoring circuit comprises resistors R1, R2H, R2L and a clamping circuit, one end of the resistor R1 is used for inputting a current signal representing the input power of the switching power supply, one end of the resistor R2H is used for inputting a voltage signal representing the input voltage of the switching power supply, the other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit, the other end of the resistor R1 and the other end of the resistor R2L are connected together to output a third voltage signal, the other end of the clamping circuit is used for grounding, and the clamping circuit is used for limiting the voltage between the two ends of the resistor R2L to a fixed value.

[0018] The comparison circuit comprises a comparator, the non-inverting input end of the comparator is inputted with a first set value, the inverting input end of the comparator is inputted with the third voltage signal, and the output end of the comparator outputs the current-limiting protection trigger signal.

[0019] The current-limiting protection circuit is applied to a switching power supply and comprises:

[0020] The input state monitoring circuit comprises resistors R1, R2H, R2L and a clamping circuit, one end of the resistor R1 is used for inputting a current signal representing the input power of the switching power supply, one end of the resistor R2H is used for inputting a voltage signal representing the input voltage of the switching power supply, the other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit, the other end of the resistor R1 and the other end of the resistor R2L are connected together to output a third voltage signal, the other end of the clamping circuit is used for grounding, and the clamping circuit is used for limiting the voltage between the two ends of the resistor R2L to a fixed value.

[0021] The comparison circuit comprises a comparator, the non-inverting input end of the comparator is inputted with a first set value, the inverting input end of the comparator is inputted with the third voltage signal, and the output end of the comparator outputs the current-limiting protection trigger signal.

[0022] As a third aspect of the present application, the following embodiments are provided:

[0023] A switching power supply, comprising: a first conversion circuit comprising a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first inductor and a first sampling resistor, one end of the first switch tube being a positive input end of the first conversion circuit and a positive input end of the switching power supply, the other end of the first switch tube being connected to one end of the second switch tube and one end of the first inductor, the other end of the second switch tube and one end of the sampling resistor being connected together as a negative input end of the first conversion circuit and a negative input end of the switching power supply, the other end of the first inductor and one end of the third switch tube being connected together and then connected to one end of the fourth switch tube, the other end of the fourth switch tube being a positive output end of the first conversion circuit and a positive output end of the switching power supply, the other end of the third switch tube and the other end of the sampling resistor being connected together as an output end of the first conversion circuit and a negative output end of the switching power supply.

[0024] and the current limiting protection circuit of any one of the above.

[0025] Further, the switching power supply further comprises:

[0026] a second conversion circuit, a positive input end of the second conversion circuit being connected to a positive output end of the first conversion circuit, a positive output end of the second conversion circuit being a positive output end of the switching power supply, a negative input end of the second conversion circuit being connected to a negative output end of the first conversion circuit, a negative output end of the second conversion circuit being a negative output end of the switching power supply, or a positive input end of the second conversion circuit being a positive input end of the switching power supply, a negative input end of the second conversion circuit being a negative input end of the switching power supply, a positive output end of the second conversion circuit being connected to a positive input end of the first conversion circuit, and a negative output end of the second conversion circuit being connected to a negative input end of the first conversion circuit.

[0027] A switching power supply, comprising:

[0028] a first conversion circuit comprising a first switch tube, a second switch tube, a third switch tube, a first inductor and a first sampling resistor, one end of the first switch tube being a positive input end of the first conversion circuit and a positive input end of the switching power supply, the other end of the first switch tube being connected to one end of the second switch tube and one end of the first inductor, the other end of the second switch tube and one end of the sampling resistor being connected together as a negative input end of the first conversion circuit and a negative input end of the switching power supply, the other end of the first inductor and one end of the third switch tube being connected together as a positive output end of the first conversion circuit, and the other end of the third switch tube and the other end of the sampling resistor being connected together as a negative output end of the first conversion circuit.

[0029] The second conversion circuit has its positive input terminal connected to the positive output terminal of the first conversion circuit, and its positive output terminal is the positive output terminal of the switching power supply. The negative input terminal of the second conversion circuit is connected to the negative output terminal of the first conversion circuit, and its negative output terminal is the negative output terminal of the switching power supply.

[0030] And the current limiting protection circuit described in any of the second aspects above.

[0031] The advantages of this invention compared to the prior art are at least as follows:

[0032] The current limiting protection method provided by this invention converts the voltage signal characterizing the input voltage of the switching power supply into a second voltage signal, and then superimposes the first voltage signal and the second voltage signal to generate a third voltage signal. This allows the current limiting protection method to perform input voltage feedforward compensation. Furthermore, when the voltage signal characterizing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal. This ensures that the second voltage signal does not exhibit a larger feedforward compensation value when the switching power supply is in the high-voltage input segment, thus preventing the switching power supply from limiting its rated power output or even causing it to have no rated power output under such circumstances.

[0033] The current limiting protection circuit provided by this invention converts the voltage signal characterizing the input voltage of the switching power supply into a second voltage signal, and then superimposes the first voltage signal and the second voltage signal to generate a third voltage signal. This enables the current limiting protection circuit to have an input voltage feedforward compensation function. Furthermore, when the voltage signal characterizing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal. This ensures that the second voltage signal will not have a larger feedforward compensation value when the switching power supply is in the high-voltage input segment, so that in this case, the rated power output of the switching power supply will not be limited or even cause the switching power supply to have no rated power output.

[0034] The switching power supply provided by this invention, due to the application of the current limiting protection circuit provided by this invention, can significantly improve the consistency of the overcurrent protection ratio, and does not affect the output power of the high-voltage input section, which is beneficial to improving the reliability of the power supply product.

[0035] Other advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0036] Figure 1 The schematic diagram of the dual-resistor sampling principle for a four-transistor Buck-Boost + push-pull two-stage converter topology;

[0037] Figure 2The schematic diagram of a single-resistor sampling principle for a four-transistor Buck-Boost + push-pull two-stage converter topology;

[0038] Figure 3 Based on Figure 2 Peak inductor current curve in practical application of two-stage transformation topology products;

[0039] Figure 4 This is a schematic diagram of a conventional current limiting protection circuit.

[0040] Figure 5 for Figure 4 The current limiting protection circuit is based on Figure 2 Overcurrent protection curves for the application;

[0041] Figure 6 This is a schematic diagram of a current-limiting protection circuit with voltage feedforward compensation function.

[0042] Figure 7 for Figure 6 The current limiting protection circuit is based on Figure 2 The current limiting protection curve of the application;

[0043] Figure 8 A flowchart of the current limiting protection method provided in the first embodiment of the present invention;

[0044] Figure 9 A schematic diagram of the current limiting protection circuit provided in the second embodiment of the present invention;

[0045] Figure 10 A circuit diagram of a current limiting protection circuit provided in an embodiment of the present invention;

[0046] Figure 11 Another circuit diagram of the current limiting protection circuit provided in the embodiment of the present invention;

[0047] Figure 12 A circuit diagram of a switching power supply provided in the third embodiment of the present invention;

[0048] Figure 13 Another circuit diagram of a switching power supply provided in the third embodiment of the present invention;

[0049] Figure 14 for Figure 13 Current limiting protection curve of switching power supply;

[0050] Figure 15 Another circuit diagram of a switching power supply provided in the third embodiment of the present invention;

[0051] Figure 16 for Figure 15 The current limiting protection curve of the switching power supply. Detailed Implementation

[0052] Figure 1 The schematic diagram for a dual-resistor sampling circuit in a four-transistor Buck-Boost + push-pull two-stage converter topology is shown below. Figure 1 In the application of a two-stage converter using a four-transistor Buck-Boost converter and a push-pull circuit, the front-stage four-transistor Buck-Boost converter is used to implement VBus voltage regulation control, while the rear-stage push-pull circuit is used to achieve output isolation conversion. To achieve current detection and protection for the front-stage Buck-Boost converter, the industry commonly employs a dual-resistor sampling scheme, such as... Figure 1 Resistors Rcs1 and Rcs2 are shown. When the cascaded converter circuit operates in Buck mode, the freewheeling transistor Q4 is typically in a shoot-through state, and the power output is characterized by sampling resistor Rcs2. When the cascaded converter circuit operates in Boost mode, the switching transistor Q1 is typically in a shoot-through state, and the power input is characterized by sampling resistor Rcs1, thereby achieving overcurrent and short-circuit protection for the system. In medium to high power applications, the dual-resistor sampling scheme suffers from problems such as numerous sampling components, high sampling losses, and complex differential sampling circuits, resulting in a large PCB footprint, increased power supply cost, and increased design complexity.

[0053] Figure 2 The schematic diagram for a single-resistor sampling circuit in a four-transistor Buck-Boost + push-pull two-stage converter topology is shown below. Figure 2 Through the Figure 1 The dual-resistor sampling scheme shown is simplified and optimized to propose a single-resistor Rcs sampling scheme. As shown in the schematic diagram, the current sampling resistor Rcs is connected in series with the preceding Buck-Boost power inductor L. Therefore, the voltage signal across resistor Rcs represents the current signal of inductor L. By detecting the voltage signal across Rcs, output overcurrent and short-circuit protection can be achieved.

[0054] The inventors of this application noted that, based on Figure 2 In practical applications of the circuit shown, when the input voltage range is wide and the output power is high, the peak inductor current differs significantly between low-voltage and high-voltage inputs. This results in extremely poor consistency of the power supply overcurrent protection point, greatly reducing product reliability. For example, in a power supply with an input voltage of 9-36V and an output of 12V, the peak inductor current Ipk=35A at 9V input, Ipk=19A at 24V input, and Ipk=24A at 36V input. Figure 3 The curve exhibits an inverse parabolic shape, which greatly increases the number of overcurrent protection points when high voltage is input, causing excessive stress on the device and ultimately leading to power supply damage.

[0055] It should be noted that the overcurrent protection point is the ratio between the output current when the power supply overcurrent protection is triggered and the rated output current of the power supply, also known as the overcurrent protection ratio.

[0056] Please refer to Figure 4 ,against Figure 2 The problems encountered in the application of the cascaded converter circuit shown are addressed by adopting the following approach: Figure 4 The industry-standard current-limiting protection circuit shown implements overcurrent and short-circuit protection. The protection curve is as follows: Figure 5 As shown, the overcurrent protection ratio is 1.14 to 2 times, while the overcurrent protection ratio of switching power supplies for medium and high power applications is usually between 1.1 and 1.4 times, which is more appropriate. The current limiting protection circuit needs further optimization.

[0057] Please refer to Figure 6 ,against Figure 2 The problems encountered in the application of the cascaded converter circuit shown are addressed by adopting the following approach: Figure 6 The circuit shown is a widely used current-limiting protection circuit with voltage feedforward compensation. Its output overcurrent protection curve is as follows: Figure 7 As shown, the overcurrent protection ratio is 1.02 to 1.26 times, with a significant improvement in the maximum overcurrent protection ratio. Meanwhile, it is observed that in the high-voltage input section, excessive voltage feedforward compensation limits the output power or even prevents the output of rated power.

[0058] In summary, based on Figure 2 In the application of the cascaded converter circuit shown, regardless of whether a conventional current limiting protection circuit or a current limiting protection circuit with voltage feedforward compensation is used, there will be a contradiction between an excessively high overcurrent protection ratio or a limited rated output power. It is difficult to achieve good consistency in the overcurrent protection ratio, which reduces power supply reliability, limits the selection of components, and hinders efficiency optimization.

[0059] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0060] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0061] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or unit circuits is not necessarily limited to those steps or unit circuits explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0062] It should be understood that in the specification, claims, and drawings, when a step is described as continuing into another step, the step may continue directly into that other step or be continued into that other step via a third step; when an element is described as being "connected" to another element, the element may be "directly connected" to that other element or be "connected" to that other element via a third element.

[0063] First Embodiment

[0064] Figure 8 The flowchart of the current limiting protection method provided in the first embodiment of the present invention includes, but is not limited to, the following steps S101 to S102:

[0065] S101: The current signal representing the input power of the switching power supply is converted into a first voltage signal, and the voltage signal representing the input voltage of the switching power supply is converted into a second voltage signal. Then, the first voltage signal and the second voltage signal are superimposed to generate a third voltage signal. When the voltage signal representing the input voltage of the switching power supply reaches a second set value, the third voltage signal is clamped so that it no longer changes with the increase of the second voltage signal. The second set value represents the maximum value of the feedforward compensation voltage range of the input voltage of the switching power supply.

[0066] The current signal, which characterizes the input power of the switching power supply, is converted into a first voltage signal. This can be obtained by direct current sampling or indirect current sampling, or by further conditioning.

[0067] The voltage signal characterizing the input voltage of the switching power supply is converted into a second voltage signal, which can be obtained by directly or indirectly sampling the input voltage, or by further conditioning.

[0068] The superposition of the first voltage signal and the second voltage signal can be achieved by connecting a resistor network in parallel according to the superposition theorem, or by using an operational amplifier adder circuit, etc.

[0069] The second set value is related to the voltage feedforward compensation range that the switching power supply needs to be designed for. The voltage range from which the input voltage gradually increases from a low voltage until the second set value is triggered is the voltage feedforward compensation range. Once the input voltage exceeds this range, the voltage feedforward compensation value does not change with further increases in input voltage, exhibiting the characteristic of segmented voltage feedforward compensation. Obtaining the second set value is common knowledge to those skilled in the art. For example, as shown in the second embodiment below, it is generated using a series resistor and a Zener diode circuit. By adjusting the resistance values ​​of the two voltage divider resistors and the Zener diode's voltage regulation value, different second set values ​​can be set, thereby adjusting the voltage feedforward compensation range of the power supply. It is understood that the magnitude of the second set value can be configured according to actual conditions, and this embodiment of the invention does not impose limitations.

[0070] S102: Compare the third voltage signal with the first set value. When the third voltage signal is greater than or equal to the first set value, generate a current limiting protection trigger signal.

[0071] The first set value is related to the overcurrent protection ratio that the switching power supply needs to be designed for. Obtaining the first set value is common knowledge to those skilled in the art. For example, it can be obtained by dividing a stable voltage source using two voltage-dividing resistors. Different first set values ​​can be obtained by adjusting the resistance ratio of the two voltage-dividing resistors. It is understood that the method for obtaining the first set value and its magnitude can be configured according to actual conditions, and the embodiments of the present invention do not limit it.

[0072] The generation of the current limiting protection trigger signal indicates that an overcurrent or short-circuit event has occurred in the switching power supply. This signal is output to the corresponding controller, microcontroller (MCU), digital signal processing unit (DSP), or other hardware or software device with logic processing execution functions. These hardware or software devices then instruct the relevant devices to perform the current limiting protection action. It is understood that the type of hardware or software device used to perform the current limiting protection action can be selected according to the actual situation, and this embodiment of the invention does not limit it.

[0073] The current limiting protection method in this embodiment converts the voltage signal characterizing the input voltage of the switching power supply into a second voltage signal, and then superimposes the first voltage signal and the second voltage signal to generate a third voltage signal. This allows the current limiting protection method to perform input voltage feedforward compensation. Furthermore, when the voltage signal characterizing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal. This ensures that the second voltage signal does not exhibit a larger feedforward compensation value when the switching power supply is in the high-voltage input segment. Therefore, in this case, the rated power output of the switching power supply is not limited, and the switching power supply may even have no rated power output.

[0074] It should be noted that although the inventive concept of the current limiting protection method in this application originated from the technical problems discovered during the research on the aforementioned "four-tube Buck-Boost + push-pull two-stage transform topology", the current limiting protection method proposed in this application has strong versatility. The application scenarios of the aforementioned "four-tube Buck-Boost + push-pull two-stage transform topology" do not constitute a limitation on the protection scope of the current limiting protection method provided by this invention. After understanding the inventive concept of the current limiting protection method in this application, those skilled in the art can reasonably predict, expand, and experimentally verify the applicable scenarios based on their knowledge.

[0075] Second Embodiment

[0076] Figure 9 The schematic diagram of the current limiting protection circuit provided in the second embodiment of the present invention includes:

[0077] The input status monitoring circuit is used to convert the current signal Ics, which represents the magnitude of the input power of the switching power supply, into a first voltage signal, and simultaneously convert the voltage signal Vin', which represents the magnitude of the input voltage of the switching power supply, into a second voltage signal. Then, the first voltage signal and the second voltage signal are superimposed to generate a third voltage signal. When the voltage signal Vin', which represents the magnitude of the input voltage of the switching power supply, reaches a second set value, the third voltage signal is clamped so that it no longer changes with the increase of the second voltage signal. The second set value represents the maximum value of the feedforward compensation voltage range of the input voltage of the switching power supply.

[0078] The comparison circuit is used to compare the third voltage signal with the first set value. When the third signal is greater than or equal to the first set value, a current limiting protection trigger signal ERR is generated.

[0079] Figure 10 This is a circuit diagram of the current limiting protection circuit provided in an embodiment of the present invention. Figure 11 For another circuit diagram of the current limiting protection circuit provided in this embodiment of the invention, please refer to... Figure 10 , Figure 11 :

[0080] in, Figure 10 The input status monitoring circuit includes resistors R1, R2H, R2L and a clamping circuit. One end of resistor R1 is used to input a current signal that characterizes the input power of the switching power supply. One end of resistor R2H is used to input the input voltage of the switching power supply. The other end of resistor R2H is connected to one end of resistor R2L and one end of the clamping circuit. The other ends of resistor R1 and R2L are connected together to output a third voltage signal. The other end of the clamping circuit is used for grounding.

[0081] See Figure 11The clamping circuit includes a Zener diode D1, with the anode of Zener diode D1 being the other end of the clamping circuit and the cathode of Zener diode D1 being one end of the clamping circuit.

[0082] Figure 10 The clamping circuit in this embodiment can also be implemented in other ways. For example, the clamping circuit in this embodiment can be built using a TL431 circuit, as long as the voltage across the resistor R2L can be limited to a fixed value. The specific circuit to be used can be selected according to the actual situation, and this embodiment of the invention does not limit it.

[0083] It is understandable that the voltage signal characterizing the magnitude of the input voltage of a switching power supply can be directly represented as the input voltage Vin of the switching power supply. Figure 10 and Figure 11 The voltage signal input at one end of the resistor R2H, which represents the magnitude of the input voltage of the switching power supply, is the input voltage Vin of the switching power supply. It should be noted that this embodiment does not limit how the voltage signal representing the magnitude of the input voltage of the switching power supply is obtained.

[0084] in, Figure 11 and Figure 11 The comparison circuit includes comparator U1, with a first set value input at the non-inverting input terminal, a third voltage signal input at the inverting input terminal, and a current limiting protection trigger signal ERR output at the comparator output terminal.

[0085] by Figure 12 Taking this example, the specific working process of this embodiment is described as follows:

[0086] As the input voltage Vin of the switching power supply gradually increases from the low voltage Vin.min, the second voltage signal generated after Vin passes through the feedforward resistors R2H and R2L is applied to the inverting input of comparator U1. The resulting feedforward voltage compensation value increases proportionally with Vin. The formula for calculating the feedforward voltage compensation value ΔV1 is as follows:

[0087] ΔV1=Vin*R1 / (R2H+R2L+R1)

[0088] Where R1 is the resistance value of resistor R1, R2H is the value of resistor R2H, and R2L is the value of resistor R2L.

[0089] Furthermore, as the input voltage Vin continues to increase to the high voltage Vin.max, Vin is divided by the feedforward resistors R2H and R2L. The voltage division value of resistor R2L is clamped by the Zener diode D1. The clamping voltage at this time is denoted as Vclamp, and the input voltage at this time is denoted as Vin.nom. From this point onward, the feedforward voltage compensation value no longer increases with the input voltage Vin but remains constant. The feedforward voltage compensation value remains at ΔV2, and the formula for calculating ΔV2 is as follows:

[0090] ΔV2=Vclmp*R1 / (R2L+R1)

[0091] The above analysis of the working process shows that this embodiment ensures that the second voltage signal corresponds to a switching power supply that does not have a larger feedforward compensation value in the high voltage input section, thereby effectively avoiding the limitation of rated power output due to a larger feedforward compensation value in the high voltage input section.

[0092] The voltage feedforward compensation signal is the second voltage signal, the clamping voltage Vclamp is the second set value, and the input voltage Vin.nom is the segment point of the voltage feedforward segment compensation.

[0093] against Figure 13 By setting different parameters for resistor R2H, resistor R2L, or Zener diode D1, the power input voltage Vin.nom and the feedforward voltage compensation values ​​ΔV1 and ΔV2 can be flexibly set.

[0094] Analysis of the above working process shows that the current limiting protection circuit provided by the present invention converts the voltage signal characterizing the input voltage of the switching power supply into a second voltage signal, and then superimposes the first voltage signal and the second voltage signal to generate a third voltage signal. This enables the current limiting protection circuit to have an input voltage feedforward compensation function. Furthermore, when the voltage signal characterizing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal. This ensures that the second voltage signal will not have a larger feedforward compensation value when the switching power supply is in the high voltage input segment. Therefore, under such circumstances, the rated power output of the switching power supply will not be limited or even cause the switching power supply to have no rated power output.

[0095] It should be noted that although the inventive concept of the current limiting protection circuit in this application originated from the technical problems discovered during the research on the aforementioned "four-transistor Buck-Boost + push-pull two-stage converter topology", the current limiting protection circuit proposed in this application has strong versatility. The application scenarios of the aforementioned "four-transistor Buck-Boost + push-pull two-stage converter topology" do not constitute a limitation on the protection scope of the current limiting protection circuit provided by this invention. After understanding the working process of the current limiting protection circuit in this application, those skilled in the art can reasonably predict, expand, and experimentally verify the application scenarios based on their knowledge, and are not limited to the application embodiments described in the following specification.

[0096] Third Embodiment

[0097] Figure 15 A circuit diagram of a switching power supply provided in the third embodiment of the present invention; Figure 12 and Figure 10 These are alternative circuit diagrams of a switching power supply provided in the third embodiment of the present invention.

[0098] See Figure 11 The switching power supply includes:

[0099] The first conversion circuit includes a first switch Q1, a second switch Q2, a third switch Q3, a fourth switch Q4, a first inductor L, and a first sampling resistor Rcs. One end of the first switch Q1 is the positive input terminal of the first conversion circuit and the positive input terminal Vin of the switching power supply. The other end of the first switch Q1 is connected to one end of the second switch Q2 and one end of the first inductor L. The other end of the second switch Q2 is connected to one end of the sampling resistor Rcs as the negative input terminal of the first conversion circuit and the negative input terminal GND of the switching power supply. The other end of the first inductor L is connected to one end of the third switch Q3 and one end of the fourth switch Q4. The other end of the third switch Q3 is connected to the other end of the sampling resistor Rcs as the output terminal of the first conversion circuit and the negative output terminal of the switching power supply. The other end of the fourth switch Q4 is the positive output terminal of the first conversion circuit and the positive output terminal of the switching power supply.

[0100] And any specific implementation circuit of the current limiting protection circuit in the second embodiment.

[0101] The other end of the sampling resistor Rcs outputs a current signal Ics that characterizes the input power of the switching power supply. Figure 12 and Figure 13 The current limiting protection circuit has the current signal Ics input to one end of resistor R1.

[0102] The current limiting protection trigger signal ERR indicates that an overcurrent or short circuit event has occurred in the switching power supply. This signal is output to the corresponding controller, microcontroller (MCU), digital signal processing (DSP), or other hardware or software devices with logic processing execution functions, which instruct the switching power supply to perform current limiting protection.

[0103] Figure 12 The switching power supply provided by this invention utilizes the current limiting protection circuit, which significantly improves the consistency of the overcurrent protection ratio and does not limit the rated output power under high voltage input. It provides reliable current limiting protection while meeting the requirements of a wider input voltage range.

[0104] See Figure 13 The switching power supply among them is relatively Figure 14 The difference also includes:

[0105] The second conversion circuit has its positive input terminal connected to the positive output terminal of the first conversion circuit (this connection point is denoted as Vbus). The positive output terminal of the second conversion circuit is the positive output terminal of the switching power supply. The negative input terminal of the second conversion circuit is connected to the negative output terminal of the first conversion circuit. The negative output terminal of the second conversion circuit is the negative output terminal of the switching power supply.

[0106] The second conversion circuit can be a push-pull converter, a half-bridge converter, a full-bridge converter, a forward converter, an interleaved forward converter, etc., depending on the specific topology used. Figure 13 The embodiments shown are not intended to be limiting.

[0107] Figure 14 for Figure 13 The current limiting protection curve of the switching power supply shown is from... Figure 13 It can be seen that, Figure 15 The switching power supply shown has a very high overcurrent protection ratio consistency, and still has an overcurrent capability of 1.16 times in the high-voltage input voltage range, which meets the rated power output and dynamic load requirements of the power supply.

[0108] It should be noted that, Figure 13 The first conversion circuit in the circuit is a four-transistor Buck-Boost converter. By regulating the voltage of its intermediate bus VBus, the voltage regulation of the switching power supply output Vout can be achieved. The first conversion circuit is called the voltage-mode output conversion circuit. Since the first conversion circuit and the second conversion circuit are decoupled, their positions can be interchanged. That is, the positive input terminal of the second conversion circuit is the positive input terminal of the switching power supply, the negative input terminal of the second conversion circuit is the negative input terminal of the switching power supply, the positive output terminal of the second conversion circuit is connected to the positive input terminal of the first conversion circuit, and the negative output terminal of the second conversion circuit is connected to the negative input terminal of the first conversion circuit.

[0109] See Figure 16 The switching power supply in this system mainly operates in current-fed mode, and its switching power supply is relatively... Figure 15 The difference is:

[0110] The first conversion circuit omits the fourth switch Q4 and connects the other end of the first inductor L and one end of the third switch Q3 together as the positive output terminal of the first conversion circuit.

[0111] The positive input terminal of the second conversion circuit is connected to the positive output terminal of the first conversion circuit, the positive output terminal of the second conversion circuit is the positive output terminal of the switching power supply, the negative input terminal of the second conversion circuit is connected to the negative output terminal of the first conversion circuit, and the negative output terminal of the second conversion circuit is the negative output terminal of the switching power supply.

[0112] The second conversion circuit is either a push-pull conversion circuit or a full-bridge conversion circuit.

[0113] It should be noted that when the second conversion circuit is a push-pull conversion circuit, the third switch Q3 in the first conversion circuit can replace the common timing of the primary-side MOS in the second conversion circuit, which greatly reduces the conduction loss of the second conversion circuit. In miniaturized design applications, the third switch Q3 can be omitted without affecting the normal operation of the circuit.

[0114] In addition, when the second circuit is a full-bridge converter circuit, the third switch Q3 in the first converter circuit can be omitted without affecting the normal operation of the circuit.

[0115] Figure 16 for Figure 15 The cascaded switching power supply current limiting protection curve shown is from... ​ It can be seen that, ​ The switching power supply shown has a very high overcurrent protection ratio consistency, still having an overcurrent capability of 1.21 times in the high-voltage input range, meeting the rated power output and dynamic load requirements of the power supply in wide input voltage applications.

[0116] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A current limit protection method applied to a switching power supply, characterized in that, The method comprises the following steps: Converting a current signal representing the input power of the switching power supply into a first voltage signal, and converting a voltage signal representing the input voltage of the switching power supply into a second voltage signal, then superimposing the first voltage signal and the second voltage signal to generate a third voltage signal, wherein when the voltage signal representing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal by clamping the second voltage signal, and the second set value represents the maximum value of the input voltage of the switching power supply in the feedforward compensation voltage range; Comparing the third voltage signal with a first set value, and generating a current-limiting protection trigger signal when the third voltage signal is greater than or equal to the first set value.

2. A current limit protection circuit applied to a switching power supply, characterized in that, The method comprises: An input state monitoring circuit for converting a current signal representing the input power of the switching power supply into a first voltage signal, and converting a voltage signal representing the input voltage of the switching power supply into a second voltage signal, then superimposing the first voltage signal and the second voltage signal to generate a third voltage signal, wherein when the voltage signal representing the input voltage of the switching power supply reaches a second set value, the third voltage signal no longer changes with the increase of the second voltage signal by clamping the second voltage signal, and the second set value represents the maximum value of the input voltage of the switching power supply in the feedforward compensation voltage range; A comparison circuit for comparing the third voltage signal with a first set value, and generating a current-limiting protection trigger signal when the third voltage signal is greater than or equal to the first set value.

3. The current limit protection circuit of claim 2, wherein: The input state monitoring circuit comprises a resistor R1, a resistor R2H, a resistor R2L and a clamping circuit, one end of the resistor R1 is used for inputting the current signal representing the input power of the switching power supply, one end of the resistor R2H is used for inputting the input voltage of the switching power supply, the other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit, the other end of the resistor R1 and the other end of the resistor R2L are connected together to output the third voltage signal, and the other end of the clamping circuit is used for grounding.

4. The current limit protection circuit of claim 3, wherein: The clamping circuit comprises a zener diode, the anode of the zener diode is the other end of the clamping circuit, and the cathode of the zener diode is one end of the clamping circuit.

5. The current limit protection circuit of claim 2, wherein: The comparison circuit comprises a comparator, the same-phase input end of the comparator inputs the first set value, the opposite-phase input end of the comparator inputs the third voltage signal, and the output end of the comparator outputs the current-limiting protection trigger signal.

6. A current limit protection circuit applied to a switching power supply, characterized in that, The method comprises: The input state monitoring circuit comprises resistors R1, R2H, R2L and a clamping circuit, one end of the resistor R1 is used for inputting a current signal representing the input power of the switching power supply, one end of the resistor R2H is used for inputting a voltage signal representing the input voltage of the switching power supply, the other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit, the other end of the resistor R1 and the other end of the resistor R2L are connected together to output a third voltage signal, the other end of the clamping circuit is used for grounding, and the clamping circuit is used for limiting the voltage between the two ends of the resistor R2L to a fixed value. The comparison circuit comprises a comparator, the non-inverting input end of the comparator is inputted with a first set value, the inverting input end of the comparator is inputted with the third voltage signal, and the output end of the comparator outputs the current limiting protection trigger signal.

7. A current limit protection circuit applied to a switching power supply, characterized in that, The input state monitoring circuit comprises resistors R1, R2H, R2L and a clamping circuit, one end of the resistor R1 is used for inputting a current signal representing the input power of the switching power supply, one end of the resistor R2H is used for inputting a voltage signal representing the input voltage of the switching power supply, the other end of the resistor R2H is connected to one end of the resistor R2L and one end of the clamping circuit, the other end of the resistor R1 and the other end of the resistor R2L are connected together to output a third voltage signal, the other end of the clamping circuit is used for grounding, and the clamping circuit is used for limiting the voltage between the two ends of the resistor R2L to a fixed value. The comparison circuit comprises a comparator, the non-inverting input end of the comparator is inputted with a first set value, the inverting input end of the comparator is inputted with the third voltage signal, and the output end of the comparator outputs the current limiting protection trigger signal. The first conversion circuit comprises first, second, third and fourth switch tubes, a first inductor and a first sampling resistor, one end of the first switch tube is the positive input end of the first conversion circuit and the positive input end of the switching power supply, the other end of the first switch tube is connected to one end of the second switch tube and one end of the first inductor, the other end of the second switch tube and one end of the sampling resistor are connected together to serve as the negative input end of the first conversion circuit and the negative input end of the switching power supply, the other end of the first inductor and one end of the third switch tube are connected together and then connected to one end of the fourth switch tube, the other end of the fourth switch tube is the positive output end of the first conversion circuit and the positive output end of the switching power supply, and the other end of the third switch tube and the other end of the sampling resistor are connected together to serve as the output end of the first conversion circuit and the negative output end of the switching power supply.

8. A switching power supply, characterized by comprising: The current limiting protection circuit of any one of claims 2 to 7. The second conversion circuit is further included, the positive input end of the second conversion circuit is connected to the positive output end of the first conversion circuit, the positive output end of the second conversion circuit is the positive output end of the switching power supply, the negative input end of the second conversion circuit is connected to the negative output end of the first conversion circuit, and the negative output end of the second conversion circuit is the negative output end of the switching power supply. ​ 9. The switching power supply of claim 8, wherein ​ ​ Or the positive input end of the second conversion circuit is the positive input end of the switching power supply, the negative input end of the second conversion circuit is the negative input end of the switching power supply, the positive output end of the second conversion circuit is connected to the positive input end of the first conversion circuit, and the negative output end of the second conversion circuit is connected to the negative input end of the first conversion circuit.

10. A switching power supply, characterized by comprising: Comprise: The first conversion circuit comprises a first switch tube, a second switch tube, a third switch tube, a first inductor and a first sampling resistor, one end of the first switch tube is the positive input end of the first conversion circuit and the positive input end of the switching power supply, the other end of the first switch tube is connected to one end of the second switch tube and one end of the first inductor, the other end of the second switch tube and one end of the sampling resistor are connected together as the negative input end of the first conversion circuit and the negative input end of the switching power supply, the other end of the first inductor and one end of the third switch tube are connected together as the positive output end of the first conversion circuit, and the other end of the third switch tube and the other end of the sampling resistor are connected together as the negative output end of the first conversion circuit; The second conversion circuit, the positive input end of the second conversion circuit is connected to the positive output end of the first conversion circuit, the positive output end of the second conversion circuit is the positive output end of the switching power supply, the negative input end of the second conversion circuit is connected to the negative output end of the first conversion circuit, and the negative output end of the second conversion circuit is the negative output end of the switching power supply; And the current limiting protection circuit of any one of claims 2 to 7.

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