Switching power supply

Abstract

The invention discloses a switching power supply, and aims to generate a small current to charge an output capacitor by controlling the working state of a bus protection switch in a short circuit detection stage, so as to judge whether a short circuit occurs by detecting whether an output voltage can rise to a preset value or not. According to the short circuit detection method, bus detection resistance and differential sampling are not needed, the design difficulty of chip pins and chips can be reduced, secondly, in the soft start stage, the power-on time is prolonged, the peak value of the charging current of the output capacitor is reduced, the voltage of the output capacitor is made to rise slowly, the rising slope of the output voltage is reduced, and therefore the output voltage is improved. Therefore, the output voltage reaches the level equal to the input voltage, loss in the soft start process is reduced, the system efficiency is improved, and the safety is high.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and more specifically to a switching power supply and a short circuit detection method thereof. Background Art

[0002] As a non-isolated boost circuit, the boost circuit is simple in structure and low in cost, and is used by many engineers in various boosting situations that do not require isolation. However, the voltage change of the boost converter at the moment of power-on will generate a large current, and excessive current can easily damage electronic devices.

[0003] Therefore, how to solve the technical problem in the related technology that the large current generated by the instantaneous voltage change when the boost converter is powered on can easily cause damage to electronic devices has become a technical problem that technical personnel in this field urgently need to solve. In addition, during the power-on stage, if the output end is short-circuited to the ground, or the non-grounded end of the main power tube is short-circuited to the ground, a large current is generated on the input bus, causing damage to the electronic devices.

[0004] In an existing solution, Figure 1 As shown, the boost switching power supply includes a bus detection resistor R ISENSE , bus switch Q1, boost converter and output capacitor C OUT Short circuit detection depends on the acquisition bus detection resistor R ISENCE The voltage drop at both ends is used for judgment, and the control circuit needs to set two dedicated high-side sampling PIN pins to implement high-side sampling to obtain the bus detection resistor R ISENCE When the output voltage is short-circuited to ground or the switch node of switch Q2 in the boost converter is short-circuited to ground, a large current will be generated on the input bus, causing the bus detection resistor R ISENCE The voltage drop across the two ends exceeds a certain threshold, which triggers the short-circuit protection and turns off the bus switch Q1 on the bus. However, this method not only requires an additional detection PIN pin, but also the bus detection resistor R ISENCE There is power consumption, resulting in low system efficiency. Summary of the invention

[0005] In view of this, the present invention provides a switching power supply and a short circuit detection and soft start method thereof, in order to reduce the pins of the chip and improve the efficiency and safety of the system.

[0006] The present invention provides a switching power supply, characterized by comprising:

[0007] A boost converter for converting an input voltage to generate an output voltage;

[0008] a bus protection switch connected between the input terminal of the switching power supply and the boost converter, and shutting down in response to a short circuit fault of the switching power supply; and

[0009] A first diode, a cathode of which is coupled to a common node of the bus protection switch and the boost converter, and an anode of which is coupled to a ground terminal;

[0010] The bus protection switch, the first diode and the inductor in the boost converter form a buck converter, and the buck converter is used to work in the startup phase, receiving the input voltage and converting it into the output voltage at the output end of the switching power supply.

[0011] Preferably, it also includes: a control circuit, which controls the buck converter to work within a first time interval of the startup phase so that the output voltage rises slowly, and within the first time interval, determines whether the system has a short circuit fault by detecting whether the feedback signal of the output voltage is lower than a first threshold.

[0012] Preferably, the control circuit is configured to determine that the system has a short-circuit fault when it is detected that the feedback signal of the output voltage is lower than the first threshold value; and to determine that the system does not have a short-circuit fault when it is detected that the feedback signal of the output voltage can rise to the first threshold value.

[0013] Preferably, the control circuit is configured to soft-start the switching power supply in a subsequent second time interval when it is detected that the feedback signal of the output voltage can rise to the first threshold value in a first time interval of the startup phase.

[0014] Preferably, the control circuit is configured to disconnect the bus protection switch or stop the control circuit from working when it is detected that the feedback signal of the output voltage is lower than the first threshold value during the first time interval of the startup phase or the normal working phase, and to enter the startup phase again after a predetermined delay.

[0015] Preferably, during the second time interval, the buck converter controls the output voltage to soft-start the switching power supply, so that the output voltage continues to rise until it is close to the input voltage.

[0016] Preferably, the buck converter has a first duty cycle range in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and the value in the second duty cycle range is greater than the value in the first duty cycle range.

[0017] Preferably, the buck converter has a predetermined first duty cycle in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and the value in the second duty cycle range is greater than the value of the first duty cycle.

[0018] Preferably, the buck converter has a duty cycle that is increasing and within the second duty cycle range during a second time interval of the startup phase, and a maximum value within the second duty cycle range is 1.

[0019] Preferably, the bus protection switch is a P-channel field effect transistor, a source of which is connected to the input terminal of the switching power supply, and a drain of which is coupled to the boost converter.

[0020] Preferably, no sampling circuit for short-circuit protection is provided between the input end of the switching power supply and the boost converter.

[0021] Preferably, during the second time interval, the working state of the bus protection switch is controlled to achieve soft start of the switching power supply by reducing the rate of change of the inductor current of the inductor in the boost converter.

[0022] Preferably, the buck converter has a fixed third duty cycle in a second time interval of the startup phase, and the third duty cycle is within the range of the second duty cycle.

[0023] The present invention aims to generate a small current to charge the output capacitor by controlling the working state of the bus protection switch during the short circuit detection phase, so as to detect whether the output voltage can rise to a predetermined value and then determine whether a short circuit occurs. The short circuit detection method of the present invention does not require a bus detection resistor or differential sampling, and can reduce chip pins and chip design difficulty. Secondly, by extending the power-on time during the soft start phase, reducing the peak value of the output capacitor charging current, allowing the output capacitor voltage to rise slowly, and reducing the rising slope of the output voltage, so that the output voltage reaches a level equal to the input voltage, so as to reduce the loss during the soft start process, improve system efficiency, and have high safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0025] Figure 1 A schematic diagram of a switching power supply in the prior art;

[0026] Figure 2 is a schematic diagram of a switching power supply according to a first embodiment of the present invention;

[0027] Figure 3 The working waveform diagram of the switching power supply of the first embodiment of the present invention;

[0028] Figure 4 It is a partial schematic diagram of a driving voltage generating circuit of a bus switch in a switching power supply according to a first embodiment of the present invention;

[0029] Figure 5 It is a partial working waveform diagram of the driving voltage generating circuit of the bus switch in the switching power supply of the first embodiment of the present invention;

[0030] Figure 6 FIG. 1 is a schematic diagram of a switching power supply according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention is described below based on embodiments, but the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. It is possible for a person skilled in the art to fully understand the present invention without the description of these details. In order to avoid confusing the essence of the present invention, known methods, processes, flows, components and circuits are not described in detail.

[0032] In addition, persons of ordinary skill in the art will appreciate that the drawings provided herein are for illustration purposes and are not necessarily drawn to scale.

[0033] At the same time, it should be understood that in the following description, "circuit" refers to a conductive loop composed of at least one element or subcircuit through electrical connection or electromagnetic connection. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected between" two nodes, it can be directly coupled or connected to another element or there can be an intermediate element, and the connection between the elements can be physical, logical, or a combination thereof. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0034] Unless the context clearly requires otherwise, throughout the specification and claims, the words "include", "comprising" and similar words should be interpreted in an inclusive sense rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to".

[0035] In the description of the present invention, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0036] Figure 2 FIG. 1 is a schematic diagram of a switching power supply according to a first embodiment of the present invention. Figure 2 As shown, the switching power supply 20 of this embodiment includes a boost converter 21 , a bus protection switch Q1 and a control circuit 22 .

[0037] The boost converter 21 is used to boost the DC input voltage V IN The voltage is converted to generate an output voltage V OUT In this embodiment, the boost converter 21 includes an inductor L coupled to the input end, a main power tube Q2 coupled to the inductor L, a diode D1 coupled to both the inductor L and the main power tube Q2, and an output capacitor C connected to the output end. OUT , with the output capacitor C OUT The output voltage V is generated at both ends of OUT .

[0038] The bus protection switch Q1 is connected between the input end of the switching power supply 20 and the boost converter 21. Specifically, the first power end of the bus protection switch Q1 is connected to the input end of the switching power supply 20, and the second power end is connected to one end of the inductor L in the boost converter 21. The bus protection switch Q1 is turned off in response to a short-circuit fault in the system, that is, it is turned off when the short-circuit detection signal output by the control circuit 22 is valid. For example, when the output end of the switching power supply 20 is short-circuited to the ground, or when the non-grounded end of the main power tube Q2 is short-circuited to the ground, the short-circuit detection signal is valid to prevent a large current from being generated on the input bus, resulting in damage to the electronic device.

[0039] The switching power supply 20 further includes a first diode D PL , whose cathode is coupled to the common node of the bus protection switch Q1 and the boost converter 21, and whose anode is coupled to the ground. PL The inductor L in the boost converter 21 can form a buck converter. The control circuit 22 controls the buck converter to work so that the inductor current of the boost converter 21 is within the preset current range within the first time interval of the startup phase, so that the output voltage V OUT The output voltage V OUT With the input voltage V IN near.

[0040] Preferably, the bus protection switch Q1 is a P-channel field effect transistor, whose source is connected to the input end of the switching power supply 20, the drain is connected to one end of the inductor L in the boost converter 21, and the control end receives the control signal VQ1 output by the control circuit 22. When the control signal VQ1 is lower than the value of the input voltage Vin and exceeds the conduction threshold of the bus protection switch Q1, the bus protection switch Q1 will be fully turned on.

[0041] In the present invention, the control circuit 22 is configured to perform short-circuit detection on the switching power supply 20 in the first time interval of the startup phase, and when performing short-circuit detection, the working state of the bus protection switch Q1 is controlled so that the inductor current of the boost converter 21 is within a preset current range. In the first time interval, the output voltage V OUT Is the feedback signal FB lower than the first threshold V TH1 To generate a short circuit detection signal V S .

[0042] Furthermore, when short circuit detection is performed, the working state of the control bus protection switch Q1 is controlled so that the inductor current of the boost converter 21 is within a preset current range, and the preset current range is relatively small and smaller than the inductor current value when the boost converter 21 is working normally. The smaller inductor current has a significant impact on the output capacitor C OUT If the output terminal is not short-circuited to ground, and the non-grounded end of the main power tube Q2 is not short-circuited to ground, the output capacitor C OUT The output voltage V OUT will slowly rise and reach the first threshold V TH1 If the output terminal is short-circuited to ground, or the non-grounded end of the main power tube Q2 is short-circuited to ground, the output capacitor C OUT The output voltage V OUT Will be close to zero voltage and will not rise to reach the first threshold V TH1 Based on this, the control circuit 22 is further configured to detect the output voltage V OUT The feedback signal FB is lower than the first threshold V TH1 When a short circuit occurs, it is judged to exist and a valid short circuit detection signal V is output. S ; When the output voltage V OUT The feedback signal FB can rise to the first threshold value V TH1 When it is judged that there is no short circuit, an invalid short circuit detection signal V is output. S .

[0043] In the embodiment of the present invention, Figure 2 As shown, the output voltage V OUT The feedback signal FB is connected to the non-inverting input terminal of a comparator, and the first threshold V TH1Connected to the inverting input of the comparator, when the output voltage V OUT The feedback signal FB is lower than the first threshold V TH1 When the comparator outputs a low level short circuit detection signal V S , so here, the effective short-circuit detection signal V S is configured as a low level; conversely, the invalid short-circuit detection signal V S Of course, it can be understood that in other embodiments, the effective short circuit detection signal V S It can also be configured as a high level without invalidating the short-circuit detection signal V S It is configured as a low level, and the present invention does not limit the level of the valid signal and the invalid signal.

[0044] Furthermore, the control signal VQ1 of the bus protection switch Q1 is based on the short-circuit detection signal V S and PWM signal SD. Specifically, when the short-circuit detection signal V S When the short circuit detection signal V S When it is at an invalid level, that is, when it is determined that there is no short circuit, the control signal VQ1 is configured to be consistent with the PWM signal SD of the bus protection switch Q1 in the startup phase. It should be noted that the PWM signal SD of the bus protection switch Q1 in the startup phase is consistent with the curve of the predetermined duty cycle D of the bus protection switch Q1.

[0045] Based on the above short-circuit detection principle, there is no need to set a sampling circuit (such as a short-circuit protection circuit) between the input end of the switching power supply 20 and the boost converter 21 in the embodiment of the present invention. Figure 1 The bus detection resistor R ISENCE ). When there is a small current to the output capacitor, the output voltage C OUT During charging, if the output terminal is short-circuited to ground or the switch node of the main power tube Q2 in the boost converter 21 is short-circuited to ground, the output voltage V OUT It will not be able to rise to the preset value, thereby triggering the short-circuit protection and turning off the bus protection switch Q1 on the bus.

[0046] The control circuit 22 is further configured to detect the output voltage V OUT The feedback signal FB is lower than the first threshold V TH1 When a short circuit occurs, the bus protection switch Q1 is disconnected or the control circuit 22 stops working, and the startup phase is entered again after a predetermined delay time.

[0047] On the contrary, if the control circuit 22 detects that the feedback signal of the output voltage can rise to the first threshold value within the first time interval of the startup phase, that is, it is determined that there is no short circuit, the switching power supply 20 is soft-started within the next second time interval, so that the output voltage V OUT With the input voltage V IN near.

[0048] In the present invention, the control circuit 22 is configured to perform a soft start on the switching power supply 20 during the second time interval of the startup phase, and during the soft start, the working state of the bus protection switch Q1 is controlled so that the output voltage V OUT Continue to rise to the input voltage V IN In the soft start phase, the control circuit 22 adjusts the output voltage by adjusting the duty cycle of the control signal VQ1 of the bus protection switch Q1. The present invention aims to achieve soft start of the switching power supply by reducing the rate of change of the inductor current flowing through the inductor in the boost converter, that is, prolonging the time for the inductor current to reach the peak value, or reducing the peak amplitude of the inductor current.

[0049] In the present invention, the purpose of soft start is to prevent the inductor current flowing through the inductor in the boost converter from having a large peak value during the process of turning on the bus protection switch Q1, and the output voltage from substantially exceeding the input voltage V IN In one embodiment, the buck converter has a first duty cycle range in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and the value in the second duty cycle range is greater than the value in the first duty cycle range.

[0050] In another embodiment, the buck converter has a predetermined first duty cycle in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and the value in the second duty cycle range is greater than the value of the first duty cycle, wherein the first duty cycle is a fixed value.

[0051] Optionally, the buck converter has a duty cycle that is increasing and within a second duty cycle range during a second time interval of the startup phase.

[0052] Optionally, the buck converter has a fixed third duty cycle in a second time interval of the startup phase, and the third duty cycle is within the second duty cycle range.

[0053] In this embodiment, the switching power supply 20 enters the normal working stage after the start-up stage. The control signal VQ2 controls the main power tube Q2 to be turned on and off periodically. The boost converter 21 IN Converts the voltage to generate an output voltage V OUT.

[0054] refer to Figure 3 , which is a working waveform diagram of the switching power supply of the first embodiment of the present invention, Figure 2 and Figure 3 , to illustrate the working process of the switching power supply 20 during the entire startup phase. Wherein, D is the duty cycle of the buck converter during the startup phase, SD is the PWM signal corresponding to the duty cycle D, and I IN is the current flowing through the bus protection switch Q1, and the bus protection switch Q1 is a P-channel field effect transistor.

[0055] In t 0 At this moment, the system is powered on, and the input voltage V IN The bus protection switch Q1 and the main power tube Q2 in the boost converter 21 are both in the off state, the duty cycle D is 0, and the PWM signal SD is close to the input voltage V IN , input current I IN is 0;

[0056] t 1 ~t 2 The first time interval T1 of the startup phase is also called the short circuit detection interval. 1 At this moment, the control circuit 22 starts to work, and the bus protection switch Q1 and the first diode D PL The buck converter formed by the inductor L in the boost converter 21 starts to work. In this embodiment, the buck converter works at a fixed first duty cycle in the first time interval of the startup phase. Since the first duty cycle is relatively small (for example, around 5%), the inductor current flowing through the boost converter 21 is within a preset current range for short-circuit detection. During the short-circuit detection, the above-mentioned short-circuit detection method is used for judgment. If it is judged that there is no short-circuit within this interval, the output voltage V OUT If it rises slowly, the operation continues in the second time interval T2; if it is determined that a short circuit exists, the operation of this stage is repeated after a predetermined delay.

[0057] Again, refer to the attached Figure 3 , which also shows the input current I in the switching power supply without soft start setting IN ' and the output voltage V OUT 'The waveform during the startup process. Figure 3 As shown, in the scheme without soft start, if at t 2 If the bus protection switch Q1 is fully turned on at a certain moment after the moment, a large current spike will be formed on the inductor L. This current spike is too large to easily damage electronic devices, and a large inductor voltage will be formed at both ends of the inductor L. This inductor voltage is proportional to the input voltage V INThe sum forms the output voltage V OUT ', which will cause the output voltage V OUT 'Too high.

[0058] It should be noted that, in other implementations, during this stage, the buck converter may also operate within the first duty cycle range, that is, the buck converter may operate at a fixed duty cycle or at a variable duty cycle, and the present invention does not limit this. As long as the inductor current flowing through the boost converter 21 is within the preset current range, the output voltage V OUT Just rise slowly.

[0059] t 2 ~t 3 stage, at t 2 At this moment, the second time interval T2 of the startup phase, namely the soft start phase, begins. In this embodiment, from t 2 Starting from the moment, the duty cycle D gradually increases, and the duration of the effective level (here is a low level) of the PWM signal SD that changes accordingly also increases with each switching cycle, and the input current I IN First it rises and then falls. When the output voltage V OUT Continue to rise slowly to the input voltage V IN When approaching, the input current I IN After the current drops to zero, it remains unchanged. 3 At this moment, the second time interval of the startup phase ends, the switching power supply enters the normal working phase, the bus protection switch Q1 is controlled to be fully turned on, and the boost converter 21 starts to work. In this soft start phase, since the duty cycle D of the buck converter gradually increases, the output capacitor C OUT The peak value of the charging current, the output voltage V OUT The slow rise time prolongs the power-on time, thereby reducing the power consumption during the soft-start phase.

[0060] Figure 4 It is a partial schematic diagram of a driving voltage generating circuit of a bus switch in a switching power supply according to a first embodiment of the present invention; Figure 5 FIG. 1 is a partial working waveform diagram of the driving voltage generating circuit of the bus switch in the switching power supply according to the first embodiment of the present invention. Figure 4 Schematically shows the circuit structure of the circuit for generating the PWM signal SD. The circuit can be divided into a driving voltage circuit 41 and a driving timing circuit 42.

[0061] In a preferred embodiment, the driving voltage circuit 41 includes a voltage source V1, a transistor M1, a current source I1, resistors R1, R3 and R2. The transistor M1 is connected in series with the current source I1 and then connected in parallel with the voltage source V1. The first power terminal of the transistor M1 and the positive electrode of the voltage source V1 are both connected to the input voltage VIN The resistor R1 is connected between the first power terminal and the control terminal of the transistor M1, the resistors R2 and R3 are connected in series and then connected in parallel between the two power terminals of the transistor M1, and a PWM signal SD is generated at a common node of the resistors R2 and R3.

[0062] The driving timing circuit 42 includes a comparator U1 and a transistor M2. The comparator U1 has a non-inverting input terminal receiving a duty cycle signal representing a change curve of the duty cycle D, an inverting input terminal receiving a ramp signal Vramp, and an output terminal outputting a comparison signal connected to a control terminal of the transistor M2. One power terminal of the transistor M2 is connected to the control terminal of the transistor M1, and the other power terminal is grounded.

[0063] It can be understood that the driving voltage circuit of the bus switch also includes a logic circuit, which is used to detect the short circuit according to the short circuit detection signal V S The PWM signal SD generates a control signal VQ1 of the bus protection switch Q1. Specifically, when the short-circuit detection signal V S When the short-circuit detection signal V S When the control signal VQ1 is at an invalid level, the control signal VQ1 is configured to be consistent with the PWM signal SD of the bus protection switch Q1 in the startup phase. In the normal working phase, the PWM signal SD remains at an effective level, and the short-circuit detection signal V S is an invalid level, and the control signal VQ1 controls the bus protection switch Q1 to be fully turned on.

[0064] Combine the following Figure 4 and Figure 5 The working principle of the circuit generating the PWM signal SD is explained as follows: when the duty cycle D is higher than the ramp signal Vramp, the comparison result output by the comparator U1 is high level, so that the transistor M2 is turned on, the control terminal of the transistor M1 is pulled low, the transistor M1 is turned off, and the current source I1 flows through the resistor R2. IN A voltage drop of R2*I1 is generated between the SD output terminal, so that the PWM signal SD can be higher than the input voltage V IN The bus protection switch Q1 is above the turn-on threshold, thereby making the bus protection switch Q1 fully turned on; when the duty cycle D is lower than the ramp signal Vramp, the comparison result output by the comparator U1 is a low level, making the transistor M2 disconnected, and the control end of the transistor M1 is pulled up to the input voltage V by the resistor R1. IN , transistor M1 is turned on, and the SD output terminal is connected to the input voltage V IN The transistor M1 is short-circuited, thereby disconnecting the bus protection switch Q1.

[0065] It should be noted that this embodiment is explained by taking the example that in the first time interval of the startup phase, the duty cycle D of the bus protection switch Q1 is a fixed first duty cycle to work, and in the second time interval, the duty cycle D of the bus protection switch Q1 is increased within the second duty cycle range to work, and the present invention is not limited to this. For example, an increasing duty cycle can also be used in the first time interval, or a fixed duty cycle can be used in the second time interval, and the bus protection switch Q1 can even be completely turned on in the second time interval. The present invention also does not limit the circuit structure of the circuit generating the PWM signal SD, as long as the PWM signal SD can be consistent with the change trend or curve of the predetermined duty cycle D.

[0066] It can be seen that the present invention aims to generate a small current to charge the output capacitor by controlling the working state of the bus protection switch during the short circuit detection stage, so as to detect whether the output voltage can rise to a predetermined value and then determine whether a short circuit occurs. The short circuit detection method of the present invention does not require a bus detection resistor or differential sampling, and can reduce chip pins and chip design difficulty. Secondly, by extending the power-on time during the soft start stage, reducing the peak value of the output capacitor charging current, allowing the output capacitor voltage to rise slowly, and reducing the rising slope of the output voltage, so that the output voltage reaches a level equal to the input voltage, so as to reduce the loss during the soft start process, improve system efficiency, and have high safety.

[0067] Figure 6 FIG. 1 is a schematic diagram of a switching power supply according to a second embodiment of the present invention. The difference between the second embodiment and the first embodiment is that the first diode D PL The two ends of the input capacitor C are connected in parallel IN The short circuit detection method of the present invention can also be compatible with the existence of the capacitor to a certain extent, but the difference in the working principle is that in the scheme of this embodiment, during the short circuit detection phase, the bus protection switch Q1 and the first diode D PL The inductor L cannot form a buck converter, but the bus protection switch Q1 works at a smaller duty cycle D and can still output energy to the output end, thereby detecting whether the output voltage can rise to a predetermined value and then determining whether a short circuit occurs. The disadvantage of this method compared to the switching power supply of the first embodiment is that since its input current is not limited by the inductor L, it will be larger.

[0068] It should be noted that, in this embodiment, the input capacitor C IN The capacitance value has little effect on short-circuit detection; if the input capacitor C IN If the capacitance is small, for example, at the nF level, it will have little effect on the soft start process after short circuit detection. However, if the input capacitor C IN The capacitance is close to uF level. In the soft start phase, the bus protection switch Q1 and the first diode DPL The buck converter composed of inductor L will not work properly and can only be replaced by hard start.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A switching power supply, characterized in that: include: A boost converter for converting an input voltage to generate an output voltage; A bus protection switch connected between the input terminal of the switching power supply and the boost converter, and shutting down in response to a short circuit fault of the switching power supply; as well as A first diode, a cathode of which is coupled to a common node of the bus protection switch and the boost converter, and an anode of which is coupled to a ground terminal; The bus protection switch, the first diode and the inductor in the boost converter form a buck converter, and the buck converter is used to work in the startup phase, receiving the input voltage and converting it into the output voltage at the output end of the switching power supply.

2. The switching power supply according to claim 1, characterized in that: Also includes: The control circuit controls the buck converter to work in a first time interval of the startup phase so that the output voltage rises slowly. In the first time interval, whether the system has a short circuit fault is determined by detecting whether a feedback signal of the output voltage is lower than a first threshold.

3. The switching power supply according to claim 2, characterized in that: The control circuit is configured to determine that the system has a short circuit fault when it is detected that the feedback signal of the output voltage is lower than the first threshold value; and to determine that the system does not have a short circuit fault when it is detected that the feedback signal of the output voltage can rise to the first threshold value.

4. The switching power supply according to claim 2, characterized in that: The control circuit is configured to soft-start the switching power supply in a subsequent second time interval when it is detected that the feedback signal of the output voltage can rise to the first threshold value in a first time interval of the startup phase.

5. The switching power supply according to claim 2, characterized in that: The control circuit is configured to disconnect the bus protection switch or stop the control circuit from working when it is detected that the feedback signal of the output voltage is lower than the first threshold value during the first time interval of the startup phase or the normal working phase, and to enter the startup phase again after a predetermined delay.

6. The switching power supply according to claim 4, characterized in that: During the second time interval, the buck converter controls the output voltage to soft-start the switching power supply, so that the output voltage continues to rise until it is close to the input voltage.

7. The switching power supply according to claim 4, characterized in that: The buck converter has a first duty cycle range in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and the value in the second duty cycle range is greater than the value in the first duty cycle range.

8. The switching power supply according to claim 4, characterized in that: The buck converter has a predetermined first duty cycle in a first time interval of the startup phase, and has a second duty cycle range in a second time interval of the startup phase, and a value in the second duty cycle range is greater than a value of the first duty cycle.

9. The switching power supply according to claim 7 or 8, characterized in that: The buck converter has a duty cycle that is increasing and within the second duty cycle range during a second time interval of the startup phase, and a maximum value within the second duty cycle range is 1.

10. The switching power supply according to claim 1, characterized in that: The bus protection switch is a P-channel field effect transistor, a source of which is connected to the input end of the switching power supply, and a drain of which is coupled to the boost converter.

11. The switching power supply according to claim 1, characterized in that: No sampling circuit for short-circuit protection is provided between the input end of the switching power supply and the boost converter.

12. The switching power supply according to claim 4, characterized in that: In the second time interval, the working state of the bus protection switch is controlled to achieve soft start of the switching power supply by reducing the change rate of the inductor current of the inductor in the boost converter.

13. The switching power supply according to claim 7, characterized in that: The buck converter has a fixed third duty cycle in a second time interval of the startup phase, and the third duty cycle is within the range of the second duty cycle.

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