Bootstrap voltage charging circuit applied to switching converter

Abstract

The utility model provides a bootstrap voltage charging circuit applied to a switching converter. The bootstrap voltage charging circuit comprises a bootstrap capacitor, a first switching tube, a first time delay circuit, a second time delay circuit and a logic judgment unit. The second end of the bootstrap capacitor is coupled with the switch node; the first end of the first switch tube receives a charging voltage signal, the second end of the first switch tube is coupled with the first end of the bootstrap capacitor, and the control end of the first switch tube receives a charging control signal; the first end of the bootstrap capacitor generates a bootstrap voltage signal; the first time delay circuit receives the switch control signal and outputs a first time delay signal; the second time delay circuit receives the switch control signal and outputs a second time delay signal; the logic judgment unit generates a charging control signal according to the first delay signal, the switch control signal and the second delay signal. According to the utility model, the diode is replaced by the switch tube with smaller conduction voltage drop, and by controlling the switch tube, the same effect as that of the diode can be achieved, and the problem of insufficient voltage can be avoided.

Description

Technical Field

[0001] The utility model relates to the technical field of switching power supplies, in particular to a bootstrap voltage charging circuit applied to a switching converter. Background Art

[0002] In the field of switching power supplies, the main switch tube driver usually uses a floating power rail control, that is, the BST_SW voltage domain, with a voltage difference of 5V, and is stabilized by an external capacitor. The switch node SW will switch to 0V or the input voltage VIN every time the chip switches, and the bootstrap voltage VBST will switch to 5V or VIN+5V voltage. Each switch of the main switch tube consumes the energy of the power rail, so a bootstrap voltage charging circuit needs to be designed in the chip to complete the charging. Common bootstrap voltage charging circuits are as follows: Figure 1 As shown, when the freewheeling switch tube M2 is turned on, the power supply voltage generated by the linear regulator charges the bootstrap capacitor CB through the diode DB; when the main switch tube M1 is turned on and the freewheeling switch tube M2 is turned off, the voltage at the switch node SW is the input voltage VIN. At this time, the voltage at the common node of the diode DB and the bootstrap capacitor CB, that is, the bootstrap voltage VBST, is raised to the voltage on the bootstrap capacitor CB superimposed on the input voltage VIN, thereby achieving the purpose of obtaining a voltage signal higher than the input voltage VIN in the step-down DC voltage conversion circuit. At this time, the bootstrap voltage VBST voltage is higher than the input voltage VIN, and the diode DB is reverse biased and turned off, preventing the energy on the bootstrap capacitor CB from flowing back to VIN, protecting the linear regulator from damage. The bootstrap voltage VBST will be sent to the drive circuit to drive the high-side switch M1 to turn on.

[0003] However, in the above bootstrap voltage charging circuit, a large conduction voltage drop will be generated when the diode DB is turned on. If VIN is low, the voltage of the bootstrap capacitor CB will be insufficient after charging, affecting system performance. At the same time, the diode DB usually needs to be placed separately in the chip layout, which has a large area, and some processes need to add a separate mask when using the diode DB, which increases the chip manufacturing cost. Utility Model Content

[0004] The utility model aims to solve at least one of the technical problems existing in the prior art.

[0005] To this end, the utility model provides a bootstrap voltage charging circuit applied to a switching converter.

[0006] The utility model provides a bootstrap voltage charging circuit applied to a switching converter. The switching converter includes a main switch tube, a freewheeling switch tube and a switch control signal. The common end of the main switch tube and the freewheeling switch tube is a switch node. The main switch tube is coupled between the voltage input end and the switch node, and the freewheeling switch tube is coupled between the switch node and a reference ground. The switch control signal is used to control the main switch tube and the freewheeling switch tube. The bootstrap voltage charging circuit at least includes a bootstrap capacitor, a first switch tube, a first delay circuit, a second delay circuit and a logic judgment unit.

[0007] The bootstrap capacitor has a first end and a second end, and the second end of the bootstrap capacitor is coupled to the switch node. The first switch tube has a first end, a second end and a control end, the first end of the first switch tube receives a charging voltage signal, the second end of the first switch tube is coupled to the first end of the bootstrap capacitor, and the control end of the first switch tube receives a charging control signal; the first end of the bootstrap capacitor generates a bootstrap voltage signal. The first delay circuit receives the switch control signal, and outputs a first delay signal after delaying the switch control signal for at least a first preset time length. The second delay circuit receives the switch control signal, and outputs a second delay signal after delaying the switch control signal for at least a second preset time length. The logic judgment unit receives the first delay signal, the switch control signal, and the second delay signal, and generates a charging control signal according to the first delay signal, the switch control signal, and the second delay signal; wherein the charging control signal controls the bootstrap capacitor to be charged after the first switch tube is turned on, the first delay signal is used to control the end time of charging the bootstrap capacitor, and the second delay signal is used to control the start time of charging the bootstrap capacitor.

[0008] In summary, due to the adoption of the above technical features, the beneficial effects of the utility model are:

[0009] The utility model replaces a diode with a large conduction voltage drop in a conventional bootstrap voltage charging circuit with a switch tube with a smaller conduction voltage drop. By controlling the on and off of the switch tube, it can play the same role as the diode and avoid the problem of insufficient voltage after the bootstrap capacitor CB is charged. The utility model controls the switch tube through a charging control signal, controls the charging time and charging duration of the bootstrap capacitor, and realizes efficient operation of the bootstrap voltage charging circuit.

[0010] Additional aspects and advantages of the present invention will become apparent in the following description or will be understood through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0012] Figure 1It is a circuit schematic diagram of an existing bootstrap voltage charging circuit;

[0013] Figure 2 It is a circuit schematic diagram of a bootstrap voltage charging circuit applied to a switching converter according to an embodiment of the utility model;

[0014] Figure 3 It is a circuit schematic diagram of a bootstrap voltage control circuit in a bootstrap voltage charging circuit applied to a switching converter according to an embodiment of the utility model;

[0015] Figure 4 It is a waveform diagram of some signals in a bootstrap voltage charging circuit applied to a switching converter according to an embodiment of the utility model;

[0016] Figure 5 The present invention is a circuit schematic diagram of a bootstrap voltage control circuit in a bootstrap voltage charging circuit applied to a switching converter according to another embodiment of the present invention.

[0017] in, Figures 1 to 5 The corresponding relationship between the reference numerals and the component names is as follows:

[0018] 1. Bootstrap voltage control circuit; 11. Logic judgment unit; 111. RS trigger; 12. Comparator. DETAILED DESCRIPTION

[0019] In order to more clearly understand the above-mentioned purpose, features and advantages of the utility model, the utility model is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0020] In the following description, many specific details are set forth to facilitate a full understanding of the utility model, but the utility model can also be implemented in other ways different from those described herein, and therefore, the protection scope of the utility model is not limited by the specific embodiments disclosed below. References to "one embodiment" or "an embodiment" throughout the specification mean that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the utility model. Therefore, the phrases "in one embodiment" or "in an embodiment" that appear throughout this specification do not necessarily all refer to the same embodiment. The verbs "include" and "have" are used as open restrictions in this article, which neither exclude nor require the presence of undescribed features. Unless otherwise expressly stated, the features recorded in the dependent claims can be freely combined with each other. The elements defined by "one" or "one" (i.e., singular form) throughout the document do not exclude the possibility of multiple elements. Further, the described features, structures or characteristics can be combined in any suitable manner in one or more embodiments. Unless otherwise specified, the terms "connect" or "couple" are used to specify electrical connections between circuit elements that can be direct or can be via one or more other elements. In contrast, when an element is said to be "directly connected to" or "directly coupled to" another element, there are no intervening elements. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. When referring to the voltage of a node or terminal, unless otherwise indicated, the voltage is considered to be the voltage between the node and a reference potential (usually ground).

[0021] Refer to the following Figures 2 to 5 The bootstrap voltage charging circuit applied to a switching converter according to some embodiments of the present invention is described.

[0022] like Figure 2 As shown, the first embodiment of the utility model proposes a bootstrap voltage charging circuit for a switching converter. Figure 2 In the illustrated embodiment, the switching converter is illustrated as mainly including a main switch tube M1, a freewheeling switch tube M2, an output inductor L and an output capacitor COUT, wherein a first end of the main switch tube M1 is coupled to a voltage input end, a second end of the main switch tube M1 is coupled to a first end of the freewheeling switch tube M2, a second end of the freewheeling switch tube M2 is coupled to a reference ground, a common end of the main switch tube M1 and the freewheeling switch tube M2 is defined as a switching node SW, a first end of the output inductor L is coupled to the switching node SW, a second end of the output inductor L is coupled to a first end of the output capacitor COUT, a second end of the output capacitor COUT is coupled to the reference ground, wherein a common end of the output inductor L and the output capacitor COUT is a voltage output end VOUT of the switching converter.

[0023] exist Figure 2In the illustrated embodiment, the bootstrap voltage charging circuit includes a bootstrap capacitor CB, a first switch tube M3 and a bootstrap voltage control circuit 1. The first end of the first switch tube M3 receives a charging voltage signal, the second end of the first switch tube M3 is coupled to the first end of the bootstrap capacitor CB, and the control end of the first switch tube M3 receives a charging control signal DRV3. The first end of the bootstrap capacitor CB generates a bootstrap voltage signal; the second end of the bootstrap capacitor CB is coupled to the switch node SW. In some embodiments, the charging voltage signal received by the first end of the first switch tube M3 can be provided by a linear regulator, the linear regulator has an input end and an output end, the input end of the linear regulator is coupled to the voltage input end and receives the input voltage signal, and the output end of the linear regulator generates a charging voltage signal and is coupled to the first end of the first switch tube M3. In a specific embodiment, the linear regulator can be composed of an error amplifier, a feedback circuit and a switch tube, so that it generates a charging voltage signal with a relatively fixed voltage value according to the input voltage signal VIN. It should be noted that the circuit structure of the above-mentioned linear regulator can be in a variety of ways, as long as the voltage regulation and voltage stabilization function can be achieved. The specific embodiments of the above-mentioned linear regulator are only illustrative and should not be regarded as limiting the present disclosure. Under some specific conditions, if the voltage level of the input voltage signal VIN can meet the requirement of directly charging the bootstrap capacitor CB, the input voltage signal may also be directly used as the charging voltage signal.

[0024] The bootstrap voltage control circuit 1 receives the switch control signal CTL, and generates a charging control signal DRV3 at least according to the switch control signal CTL. The charging control signal DRV3 is at least used to turn on the first switch tube M3 for a fixed duration when the main switch tube is turned off and the freewheeling switch tube is turned on. Specifically, the bootstrap voltage control circuit 1 determines the switch switching state of the switching converter according to the switch control signal CTL, and then selects a suitable time within the signal cycle to turn on the first switch tube M3 for a fixed duration to charge the bootstrap capacitor CB, and the first switch tube M3 is turned off for the rest of the time. In addition, the first switch tube M3 has a parasitic diode D0, the cathode of the parasitic diode D0 is coupled to the second end of the first switch tube M3, and the anode of the parasitic diode D0 is coupled to the first end of the first switch tube M3. The parasitic diode D0 prevents the energy of the bootstrap capacitor CB from being backflowed into the linear regulator when the first switch tube M3 is turned off.

[0025] In this way, when the first switch tube M3 is turned on, the bootstrap capacitor CB can be charged with a relatively small conduction voltage drop, thereby ensuring charging efficiency and system performance.

[0026] Among them, the switch control signal CTL can be any one of the main switch control signal HS and the freewheeling switch control signal LS. The main switch control signal HS is used to control the main switch tube M1, and the freewheeling switch control signal LS is used to control the freewheeling switch tube M2. The bootstrap voltage control circuit 1 can generate the charging control signal DRV3 according to the main switch control signal HS, and can also generate the charging control signal DRV3 according to the freewheeling switch control signal LS. In the following embodiments, the bootstrap voltage control circuit 1 generates the charging control signal DRV3 according to the main switch control signal HS as an example for description.

[0027] Preferably, the first switch tube M3 can be a MOS tube (metal semiconductor field effect tube) with a relatively small conduction voltage drop. Figure 2 In the illustrated embodiment, the first switch tube M3 is illustrated as a PMOS tube, wherein the first end of the first switch tube M3 is the drain of the PMOS tube, the second end of the first switch tube M3 is the source of the PMOS tube, and the control end of the first switch tube M3 is the gate of the PMOS tube. It is understandable that the first switch tube M3 can also select any other controllable switch device with a small conduction voltage drop, such as a junction field-effect transistor (Junction Field-effect Transistor, JFET), an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT) and a double diffusion metal oxide semiconductor (Double Diffusion Metal Oxide Semiconductor, DMOS) and the like.

[0028] exist Figure 2 In the illustrated embodiment, the switching converter further includes a driving circuit for receiving a bootstrap voltage signal VBST and a switch control signal CTL, thereby generating a main switch driving signal CRVH and a freewheeling switch driving signal CRVL to respectively drive the main switch tube M1 and the freewheeling switch tube M2 to be turned on and off.

[0029] In one embodiment, the bootstrap voltage control circuit 1 includes a first delay circuit, a second delay circuit and a logic judgment unit 11 .

[0030] like Figure 3As shown, the first delay circuit receives the main switch control signal HS, and outputs the first delay signal DL1 after delaying the switch control signal CTL for at least the first preset time length t1. The second delay circuit receives the main switch control signal HS, and outputs the second delay signal DL2 after delaying the main switch control signal HS for at least the second preset time length t2. The logic judgment unit 11 receives the first delay signal DL1, the main switch control signal HS and the second delay signal DL2, and generates a charging control signal DRV3 according to the first delay signal DL1, the main switch control signal HS and the second delay signal DL2. The charging control signal DRV3 controls the first switch tube M3 to be turned on and the bootstrap capacitor CB is charged.

[0031] In this embodiment, the first preset duration t1 is used to set the end time of the first switch tube M3 being turned on in each switching cycle, that is, the end time of charging the bootstrap capacitor CB. Usually, the turn-on duration of the first switch tube M3 is less than the first preset duration t1.

[0032] The second preset time length t2 is used to select a suitable time point within the first preset time length t1 to start charging the bootstrap capacitor CB, that is, to control the start time of turning on the first switch tube M3 through the second delay signal DL2, that is, to control the start time of charging the bootstrap capacitor CB. The second preset time length t2 should be greater than the turn-off time of the main switch tube M1 from turning on to turning off, so as to ensure that the main switch tube M1 has been completely turned off when the first switch tube M3 is turned on.

[0033] Continue reading Figure 3 In one embodiment, the logic judgment unit 11 includes: a pulse generating circuit, an RS trigger 111, and an OR gate R1.

[0034] The pulse generating circuit receives the second delayed signal DL2, and generates a narrow pulse signal B at the effective edge of the second delayed signal DL2. The effective edge of the second delayed signal DL2 may include a rising edge or a falling edge, which may be selected according to the specific embodiment. Similarly, the effective edge of other signals involved in the present disclosure may also be selected as a rising edge or a falling edge. For example, Figure 3 In the embodiment shown, the pulse generating circuit is a rising edge pulse generating circuit, and the logic judgment unit 11 further includes a first inverter F1 and a second inverter F2. The second delayed signal DL2 passes through the second inverter F2 and then inputs into the pulse generating circuit, and the first delayed signal DL1 passes through the first inverter F1 and then inputs into the OR gate R1.

[0035] The RS trigger 111 has a reset terminal, a set terminal and an output terminal. The reset terminal of the RS trigger 111 receives the narrow pulse signal B, the set terminal of the RS trigger 111 receives the main switch control signal HS, and the output terminal of the RS trigger 111 generates a shutdown confirmation signal C.

[0036] The OR gate R1 has a first end, a second end and an output end. The first end of the OR gate R1 receives the inverted signal A of the first delay signal DL1, the second end of the OR gate R1 receives the shutdown confirmation signal C, and the output end of the OR gate R1 generates a charging control signal DRV3. The duration of the effective state of the charging control signal DRV3 is the first preset duration t1 minus the second preset duration t2. The above is only a specific illustration of the logic judgment unit 11. According to the different effective logic states set by the main switch control signal HS, the first delay signal DL1 and the second delay signal DL2, and the different types of tubes selected, the logic judgment unit 11 can also select other forms of circuit structures to perform logic operations on the main switch control signal HS, the first delay signal DL1 and the second delay signal DL2.

[0037] Figure 4 Shows Figure 3 The waveforms of the signals in the bootstrap voltage charging circuit shown in the embodiment include the main switch control signal HS, the inverted signal A of the first delayed signal, the inverted signal DL2-inv of the second delayed signal, the narrow pulse signal B, the shutdown confirmation signal C, and the charging control signal DRV3. Among them, the first preset time length t1 is greater than the second preset time length t2; the pulse generating circuit generates a narrow pulse at the rising edge of the inverted signal DL2-inv of the second delayed signal, thereby generating a narrow pulse signal B. When the inverted signal A of the first delayed signal and the shutdown confirmation signal C are both at low levels, the charging control signal DRV3 is at a low level, because Figure 3 In the embodiment shown, the first switch tube M3 is a PMOS tube, so when the charging control signal DRV3 is at a low level, the first switch tube M3 is turned on. In each switching cycle, the effective time of the charging control signal DRV3, that is, the time for the bootstrap capacitor CB to be charged, is equal to the difference between the first preset time length t1 and the second preset time length t2.

[0038] Combine the following Figure 3 and Figure 4 In the illustrated embodiment, the working principle of the bootstrap voltage charging circuit is described as follows.

[0039] When the main switch control signal HS is high, the main switch tube M1 is turned on. At this time, the inverted signal A of the first delayed signal after the first preset time length t1 (for example, 500ns) is high, the narrow pulse signal B is low, the shutdown confirmation signal C generated at the output end of the RS trigger 111 is set high, the charging control signal DRV3 turns high, and the first switch tube M3 is turned off to prevent the energy of the bootstrap capacitor CB from flowing back to the voltage input end.

[0040] The main switch control signal HS turns low, the main switch tube M1 is turned off, and the switch node SW will turn low to 0V within a certain period of time (for example, 10ns). At the same time, after the main switch control signal HS turns low and passes through a delay of a second preset time length t2 (for example, 12ns), the pulse generating circuit sends a positive narrow pulse and sets the shutdown confirmation signal C to low. In addition, the inverted signal A of the first delayed signal is still low within the first preset time length after the main switch control signal HS turns low, so the charging control signal DRV3 is set low, the first switch tube M3 is turned on, and the bootstrap capacitor CB is charged.

[0041] After the main switch control signal HS turns low, the inverted signal A of the first delay signal turns high after a delay of the first preset time length t1, causing the charging control signal DRV3 to turn high, and the first switch tube M3 is turned off. The delay control of the first preset time length t1 is a protective control. After confirming that the first preset time length t1 is reached, the first switch tube M3 is turned off anyway. After the first switch tube M3 is turned off, if the switch node SW is still low, the charging voltage signal can continue to charge the bootstrap capacitor CB through the parasitic diode D0 of the first switch tube M3.

[0042] In some applications, for example, when the main switch tube M1 and the freewheeling switch tube M2 are not turned on, the voltage on the switch node SW may float up to the output voltage VOUT. At this time, VBST may be higher than the input voltage VIN. Once VBST is higher than the input voltage VIN, the bootstrap capacitor CB will discharge to the linear regulator through the first switch tube M3. Therefore, Figure 5 In the disclosed embodiment, the bootstrap voltage charging circuit also has a charging abnormality protection function.

[0043] Specifically, it can be realized by setting a charging abnormality protection unit in the bootstrap voltage control circuit 1. Among them, the charging abnormality protection unit has a first end, a second end, a third end and an output end, the first end of the charging abnormality protection unit is coupled to the first end of the first switch tube M3; the second end of the charging abnormality protection unit is coupled to the second end of the first switch tube M3; the third end of the charging abnormality protection unit receives the switch control signal CTL, and the charging abnormality protection unit starts working according to the logic state of the switch control signal CTL; the output end of the charging abnormality protection unit generates a reverse current monitoring signal PLS, and the reverse current monitoring signal PLS is used to indicate whether the voltage difference between the first end of the first switch tube M3 and the second end of the first switch tube M3 is positive or negative. The charging abnormality protection unit is used to determine the current flow direction according to the voltage difference between the first end of the first switch tube M3 and the second end of the first switch tube M3, that is, to generate a reverse current monitoring signal PLS that can use the change of the signal logic state to indicate that the current direction between the bootstrap capacitor CB and the voltage input end has changed.

[0044] The obtained reverse current monitoring signal PLS is sent to the logic judgment unit 11. The logic judgment unit 11 jointly generates a charging control signal DRV3 based on the first delay signal DL1, the switch control signal CTL, the second delay signal DL2, and the reverse current monitoring signal PLS. Among them, on the basis of the original control logic of the logic judgment unit 11, the reverse current monitoring signal PLS is also introduced to turn off the first switching transistor M3 when the voltage difference between the first end and the second end of the first switching transistor M3 is negative, that is, when the energy of the bootstrap capacitor CB is back-fed to the voltage input terminal.

[0045] In a specific embodiment, the charging anomaly protection unit includes a comparator 12. The comparator 12 has a first end, a second end, an enable end, and an output end. The first end of the comparator 12 is coupled to the first end of the first switching transistor M3 to receive VBST-sen, the second end of the comparator 12 is coupled to the first end of the bootstrap capacitor CB to receive VBST, the enable end of the comparator 12 receives the switch control signal CTL, and the output end of the comparator 12 generates the reverse current monitoring signal PLS.

[0046] In addition, in Figure 5 the shown embodiment, the set end of the RS flip-flop 111 receives both the switch control signal CTL and the reverse current monitoring signal PLS at the same time, and the output end of the RS flip-flop 111 generates a turn-off confirmation signal C. It can be understood that when the reverse current monitoring signal PLS is logically valid, that is, when the energy of the bootstrap capacitor CB is back-fed to the voltage input terminal. In this embodiment, the first delay signal DL1 and the reverse current monitoring signal PLS are jointly used to control the end time of the charging of the bootstrap capacitor CB. That is, after reaching the set charging time or when the energy back-feed situation of the bootstrap capacitor CB occurs, the first switching transistor M3 is turned off.

[0047] In Figure 5 the shown embodiment, after the main switch control signal HS goes low, the comparator 12 starts to work, compares the potential VBST-sen at the first end of the first switching transistor M3 with the potential VBST at the first end of the bootstrap capacitor CB. If it is detected that VBST-sen > VBST voltage, it proves that the current flows from the voltage input terminal to the bootstrap capacitor CB, which is a normal charging state. The reverse current monitoring signal PLS output by the comparator 12 is low, and the state of the RS flip-flop 111 is not changed, and the first switching transistor M3 remains open. If it is detected that VBST-sen < VBST voltage, it proves that the current flows from the bootstrap capacitor CB to the voltage input terminal, and the charging state is abnormal. The reverse current monitoring signal PLS quickly goes high, sets the turn-off confirmation signal C high, and turns off the first switching transistor M3 to ensure that the energy of the bootstrap capacitor CB will not be lost to the voltage input terminal.

[0048] In Figure 5 In the illustrated embodiment, even if the comparator 12 makes a misjudgment and fails to turn off the first switch tube M3, the first delay signal DL1 can ensure that the first switch tube M3 can be safely turned off after the first preset time t1, ensuring that the energy of the bootstrap capacitor CB will not flow back to the voltage input terminal.

[0049] In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0050] Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this utility model should be included in the protection scope of this utility model.

Claims

1. A bootstrap voltage charging circuit for a switching converter, the switching converter comprising a main switch tube, a freewheeling switch tube and a switch control signal, the common end of the main switch tube and the freewheeling switch tube being a switch node, the main switch tube being coupled between a voltage input terminal and the switch node, and the freewheeling switch tube being coupled between the switch node and a reference ground; The switch control signal is used to control the main switch tube and the freewheeling switch tube; it is characterized in that: The bootstrap voltage charging circuit comprises: A bootstrap capacitor having a first end and a second end, wherein the second end of the bootstrap capacitor is coupled to the switch node; A first switch tube has a first end, a second end and a control end, the first end of the first switch tube receives a charging voltage signal, the second end of the first switch tube is coupled to the first end of the bootstrap capacitor, and the control end of the first switch tube receives a charging control signal; the first end of the bootstrap capacitor generates a bootstrap voltage signal; A first delay circuit receives a switch control signal, delays the switch control signal for at least a first preset time length, and then outputs a first delay signal; A second delay circuit receives the switch control signal, delays the switch control signal for at least a second preset time length, and then outputs a second delay signal; A logic judgment unit receives a first delay signal, a switch control signal and a second delay signal, and generates the charging control signal according to the first delay signal, the switch control signal and the second delay signal; wherein the charging control signal controls the bootstrap capacitor to be charged after the first switch tube is turned on, the first delay signal is used to control the end time of the bootstrap capacitor charging, and the second delay signal is used to control the start time of the bootstrap capacitor charging.

2. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: The logic judgment unit comprises: A pulse generating circuit receives a second delayed signal, and generates a narrow pulse signal at the effective edge time of the second delayed signal; An RS trigger, having a reset terminal, a set terminal and an output terminal, wherein the reset terminal of the RS trigger receives a narrow pulse signal, the set terminal of the RS trigger receives at least a switch control signal, and the output terminal of the RS trigger generates a shutdown confirmation signal; wherein the shutdown confirmation signal switches a logic state at least at the effective edge moment of the narrow pulse signal and the effective edge moment of the switch control signal in each switching cycle; The OR gate has a first end, a second end and an output end. The first end of the OR gate receives a first delay signal, the second end of the OR gate receives a shutdown confirmation signal, and the output end of the OR gate generates a charging control signal.

3. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: Also includes: A charging abnormality protection unit, comprising a first end, a second end, a third end and an output end, wherein the first end of the charging abnormality protection unit is coupled to the first end of the first switch tube; the second end of the charging abnormality protection unit is coupled to the second end of the first switch tube; the third end of the charging abnormality protection unit receives a switch control signal, and the charging abnormality protection unit starts working according to the logic state of the switch control signal; the output end of the charging abnormality protection unit generates a reverse current monitoring signal, and the reverse current monitoring signal is used to indicate whether the voltage difference between the first end of the first switch tube and the second end of the first switch tube is positive or negative; The logic judgment unit also receives a reverse current monitoring signal, and generates a charging control signal according to the first delay signal, the switch control signal, the second delay signal and the reverse current monitoring signal; wherein, at least when the voltage difference between the first end of the first switch tube and the second end of the first switch tube is negative, the charging control signal turns off the first switch tube.

4. The bootstrap voltage charging circuit for a switching converter according to claim 3, characterized in that: The abnormal charging protection unit comprises: A comparator having a first end, a second end, an enable end and an output end, wherein the first end of the comparator is coupled to the first end of the first switch tube, the second end of the comparator is coupled to the first end of the bootstrap capacitor, the enable end of the comparator receives a switch control signal, and the output end of the comparator generates a reverse current monitoring signal.

5. The bootstrap voltage charging circuit for a switching converter according to claim 3, characterized in that: The logic judgment unit comprises: A pulse generating circuit receives a second delayed signal, and generates a narrow pulse signal at the effective edge time of the second delayed signal; An RS trigger, having a reset terminal, a set terminal and an output terminal, wherein the reset terminal of the RS trigger receives a narrow pulse signal, the set terminal of the RS trigger receives a switch control signal and a reverse current monitoring signal, and the output terminal of the RS trigger generates a shutdown confirmation signal; wherein the shutdown confirmation signal switches the logic state at least at the effective edge time of the narrow pulse signal, the effective edge time of the switch control signal and the reverse current monitoring signal logic valid in each switching cycle; The OR gate has a first end, a second end and an output end. The first end of the OR gate receives a first delay signal, the second end of the OR gate receives a shutdown confirmation signal, and the output end of the OR gate generates a charging control signal.

6. The bootstrap voltage charging circuit for a switching converter according to claim 3, characterized in that: The first preset duration is greater than the second preset duration; and The first delay signal and the reverse current monitoring signal are used together to control the end time of charging the bootstrap capacitor, wherein in each switching cycle, the bootstrap capacitor is charged for a time not greater than the difference between the first preset time length and the second preset time length.

7. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: The first switch tube has a parasitic diode, a cathode of the parasitic diode is coupled to the second end of the first switch tube, and an anode of the parasitic diode is coupled to the first end of the first switch tube.

8. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: The switch control signal includes a main switch control signal and a freewheeling switch control signal. The main switch control signal is used to control the main switch tube, and the freewheeling switch control signal is used to control the freewheeling switch tube. The main switch control signal and the freewheeling switch control signal are logically complementary.

9. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: Also includes: A linear regulator has an input end and an output end, wherein the input end of the linear regulator is coupled to the voltage input end and receives an input voltage signal, and the output end of the linear regulator generates a charging voltage signal and is coupled to the first end of the first switch tube; wherein the charging voltage signal is used to provide a fixed charging voltage.

10. The bootstrap voltage charging circuit for a switching converter according to claim 1, characterized in that: The first switch tube is a PMOS tube, wherein the first end of the first switch tube is the drain of the PMOS tube, the second end of the first switch tube is the source of the PMOS tube, and the control end of the first switch tube is the gate of the PMOS tube.

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