Driving duty ratio soft start circuit and switching power supply

Abstract

The invention provides a driving duty ratio soft start circuit and a switching power supply. The soft start circuit comprises a falling edge pulse module, a falling edge trigger module, a triangular wave module, an external soft start module and a main control chip. The falling edge pulse module controls the first controllable switch to be switched on when the falling edge pulse module is at the falling edge of the first driving pulse signal. And the falling edge triggering module triggers the output pin of the main control chip under the condition that the first controllable switch is switched on. And the triangular wave module outputs triangular wave voltage under the condition that the output pin of the main control chip is triggered. And the external soft start module outputs a linearly rising soft start voltage under the condition that the power supply of the main control chip is normal. The main control chip compares the triangular wave voltage with the soft start voltage and outputs a second driving pulse signal through an output pin of the main control chip according to a comparison result, soft start of the driving duty ratio of a BOOST topology freewheeling tube is achieved through the second driving pulse signal, and product damage caused by frequent startup and shutdown of the BOOST topology under no-load and capacitive load conditions is avoided.

Description

Technical Field

[0001] The present invention relates to the field of circuit technology, and in particular to a driving duty cycle soft-start circuit and a switching power supply. Background Art

[0002] With the widespread adoption of portable electronic products in communications, computers, and consumer electronics, the demand for power management chips continues to rise. DC-DC switching power supplies are widely used due to their advantages, such as a wide input voltage range, high output current, low quiescent current, and wide output load range. The BOOST structure, a key switching power supply topology, has been widely adopted in various switching power supply chips with the widespread use of low-voltage power supplies such as lithium batteries. During the power-up process of a BOOST topology, the output voltage rises from zero to its maximum value. Due to negative feedback, the duty cycle of the PWM (pulse-width modulation) control signal of the switching transistor starts at its maximum value and gradually decreases until the circuit stabilizes. The presence of the output filter capacitor in the circuit easily generates inrush current when the capacitor is charged. During this time, the current flowing through the switching transistor can reach very high levels, potentially damaging the circuit system. To prevent large inrush currents during startup and damage to the circuit system, current limiting is required. This requires incorporating a soft-start circuit into the switching power supply chip. A soft-start circuit controls the duty cycle of the PWM pulse waveform from its minimum value to the value required for normal operation as the power supply input voltage rises, thereby gradually changing the output voltage and ensuring a smooth output voltage waveform without overshoot. Because the duty cycle gradually changes from its minimum value, the switch tube will not be continuously turned on for an extended period of time, thus avoiding the generation of inrush current and ensuring the reliability of the circuit system.

[0003] To reduce losses and improve efficiency, boost topologies typically use NMOS transistors for freewheeling in high-power switching power supplies. This reduces the conduction losses of the boost topology's freewheeling transistor and improves overall product efficiency. However, the drive signal for the freewheeling NMOS transistor complements the drive signal for the switching transistor. Existing soft-start circuits can cause serious backflow problems when the boost topology's output is unloaded (even unloaded with a capacitive load) or when the input is frequently cycled. Summary of the Invention

[0004] The present invention provides a driving duty cycle soft-start circuit and a switching power supply, which realize the soft start of the driving duty cycle of a BOOST topology freewheeling tube through a second driving pulse signal, thereby avoiding damage to the BOOST topology product caused by frequent switching under no-load and capacity load conditions.

[0005] The present invention provides a drive duty cycle soft-start circuit, comprising: a falling edge pulse module, configured to control a first controllable switch to be turned on at the falling edge of a first drive pulse signal; the first drive pulse signal being a signal for driving a BOOST topology switch tube; the drive duty cycle of the first drive pulse signal increasing cycle by cycle during a startup process; a falling edge trigger module, the input end of the falling edge trigger module being electrically connected to the output end of the falling edge pulse module, the output end of the falling edge trigger module being electrically connected to a main control chip, and configured to trigger an output pin of the main control chip when the first controllable switch is turned on; a triangular wave module, electrically connected to the main control chip, configured to output a triangular wave voltage when the output pin of the main control chip is triggered; an external soft-start module, electrically connected to the main control chip, configured to output a linearly increasing soft-start voltage when the main chip is powered normally; the main control chip, configured to compare the triangular wave voltage with the soft-start voltage and output a second drive pulse signal through the output pin of the main control chip according to the comparison result; the second drive pulse signal being a signal for driving a BOOST topology freewheeling tube; and the drive duty cycle of the second drive pulse signal increasing cycle by cycle during a startup process.

[0006] According to a driving duty cycle soft-start circuit provided by the present invention, the first controllable switch is a first transistor; the falling edge pulse module includes a first resistor, a second resistor, a third resistor, a first capacitor and the first transistor; the first end of the first resistor serves as the input end of the falling edge pulse module, the second end of the first resistor is electrically connected to the first end of the first capacitor, the second end of the first capacitor is electrically connected to the first end of the second resistor and the base of the first transistor respectively, the second end of the second resistor is electrically connected to the emitter of the first transistor and the positive power supply end, the common end where the collector of the first transistor and the first end of the third resistor are connected serves as the output end of the falling edge pulse module, and the second end of the third resistor is grounded.

[0007] According to a driving duty cycle soft-start circuit provided by the present invention, the falling edge trigger module includes a fourth resistor and a second controllable switch; the first end of the fourth resistor is electrically connected to the second end of the second resistor and the common end connected to the emitter of the first transistor and the power supply pin of the main control chip, the control end of the second controllable switch serves as the input end of the falling edge trigger module, the common end connected to the second end of the fourth resistor and the first end of the second controllable switch serves as the output end of the falling edge trigger module, and the second end of the second controllable switch is electrically connected to the second end of the third resistor; the second controllable switch is configured to be turned on when the first transistor is turned on.

[0008] According to a driving duty cycle soft-start circuit provided by the present invention, the second controllable switch is an NMOS tube; the gate of the NMOS tube serves as the control end of the second controllable switch, the drain of the NMOS tube serves as the first end of the second controllable switch, and the source of the NMOS tube serves as the second end of the second controllable switch.

[0009] According to a driving duty cycle soft-start circuit provided by the present invention, the second controllable switch is a second triode; the base of the second triode serves as the control end of the second controllable switch, the collector of the second triode serves as the first end of the second controllable switch, and the emitter of the second triode serves as the second end of the second controllable switch.

[0010] According to a drive duty cycle soft-start circuit provided by the present invention, the triangular wave module includes a fifth resistor and a second capacitor; the first end of the fifth resistor is electrically connected to the second end of the second resistor, the emitter of the first transistor, the first end of the fourth resistor and the power supply pin of the main control chip, respectively; the second end of the fifth resistor is electrically connected to the first end of the second capacitor, the threshold pin of the main control chip and the discharge pin of the main control chip, respectively; the second end of the second capacitor is electrically connected to the ground.

[0011] According to a driving duty cycle soft-start circuit provided by the present invention, the external soft-start module includes a third capacitor; the first end of the third capacitor is electrically connected to the control pin of the main control chip, and the second end of the third capacitor and the common end connected to the second capacitor are grounded.

[0012] According to a driving duty cycle soft-start circuit provided by the present invention, the main control chip includes: a ground pin, the ground pin is grounded; a trigger pin, the trigger pin is electrically connected to the output end of the falling edge trigger module, and is used to obtain a low level when the second controllable switch is turned on; an output pin, which is used to meet the output high level condition when the trigger pin is low; a discharge pin, which is electrically connected to the threshold pin of the main control chip, and is used to control the voltage of the threshold pin when the output pin meets the output high level condition; the threshold pin is used to obtain the triangular wave voltage after the triangular wave module is charged; a control pin is used to obtain the soft-start voltage after the external soft-start module is charged; the output pin is also used to, when the voltage of the threshold pin is lower than the voltage of the control pin, the second drive pulse signal is high level; when the voltage of the threshold pin is higher than the voltage of the control pin, the second drive pulse signal is low level; the discharge pin is also used to pull down the voltage of the threshold pin to a preset voltage value when the output pin outputs a low level.

[0013] According to a drive duty cycle soft-start circuit provided by the present invention, the main control chip also includes a reset pin; the reset pin is used to receive a third drive pulse signal, and when the duty cycle of the second drive pulse signal is greater than the duty cycle of the third drive pulse signal, the second drive pulse signal is reset to a low level; the third drive pulse signal and the first drive pulse signal are complementary signals.

[0014] The present invention also provides a switching power supply, characterized in that it includes the above-mentioned driving duty cycle soft-start circuit and a BOOST topology circuit; the freewheeling tube in the BOOST topology circuit is driven by the driving duty cycle soft-start circuit.

[0015] The present invention provides a driving duty cycle soft-start circuit and a switching power supply, wherein the soft-start circuit includes a falling edge pulse module, a falling edge trigger module, a triangular wave module, an external soft-start module and a main control chip. The falling edge pulse module controls the first controllable switch to be turned on at the falling edge of the first driving pulse signal. When the first controllable switch is turned on, the falling edge trigger module triggers the output pin of the main control chip. When the output pin of the main control chip is triggered, the triangular wave module outputs a triangular wave voltage. When the power supply of the main control chip is normal, the external soft-start module outputs a linearly rising soft-start voltage. The main control chip compares the triangular wave voltage and the soft-start voltage, and outputs a second driving pulse signal through the output pin of the main control chip according to the comparison result. The present invention realizes the soft start of the driving duty cycle of the BOOST topology freewheeling tube through the second driving pulse signal, thereby avoiding damage to the BOOST topology product due to frequent switching on and off under no-load and full-load conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 It is a structural schematic diagram of a driving duty cycle soft start circuit provided by the present invention.

[0018] Figure 2 It is a structural schematic diagram of another driving duty cycle soft start circuit provided by the present invention.

[0019] Figure 3 It is a schematic diagram of the BOOST topology soft start process provided by the present invention.

[0020] Figure 4 It is a structural schematic diagram of a switching power supply provided by the present invention. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0022] To reduce losses and improve efficiency in high-power switching power supplies, boost topologies typically use NMOS transistors for freewheeling. This reduces the conduction losses of the boost transistor and improves overall product efficiency. The freewheeling NMOS transistor is typically driven by a drive signal complementary to the switch transistor's drive signal, provided by the main control IC. This drive design is beneficial for the boost topology's startup process, allowing energy to accumulate slowly and the output voltage to build up slowly, resulting in a smooth output voltage waveform with no overshoot. However, with this drive design, when the BOOST output is unloaded or unloaded with a capacitive load, the input is shut down. Since the BOOST output consumes almost no energy, the BOOST's VOUT remains > VIN. At this time, the input is started again. Since VOUT > VIN, and the switch tube (Q11) has a soft start when the BOOST starts, its drive (G1) duty cycle is very small, while the freewheeling tube drive (G2) complements the switch tube drive. The freewheeling tube (Q22) has a particularly large drive duty cycle, which will cause a large amount of VOUT energy to flow through the freewheeling tube in a short period of time to excite the inductor (L11), that is, backflow occurs, causing the freewheeling tube to be damaged by overcurrent, and then the switch tube to be damaged, ultimately leading to product damage.

[0023] Please refer to Figure 1 , Figure 1 This is a structural diagram of a drive duty cycle soft-start circuit provided by the present invention.

[0024] In order to solve the technical problems existing in the prior art, the present invention provides a drive duty cycle soft-start circuit, comprising: a falling edge pulse module, configured to control a first controllable switch to be turned on at the falling edge of a first drive pulse signal; the first drive pulse signal is a signal for driving a BOOST topology switch tube; the drive duty cycle of the first drive pulse signal increases cycle by cycle during the startup process; a falling edge trigger module, wherein the input end of the falling edge trigger module is electrically connected to the output end of the falling edge pulse module, and the output end of the falling edge trigger module is electrically connected to a main control chip, and is configured to trigger an output pin of the main control chip when the first controllable switch is turned on; a triangular wave module, electrically connected to the main control chip, configured to output a triangular wave voltage when the output pin of the main chip is triggered; an external soft-start module, electrically connected to the main control chip, configured to output a linearly increasing soft-start voltage when the main chip is powered normally; the main control chip, configured to compare the triangular wave voltage with the soft-start voltage and output a second drive pulse signal through the output pin of the main chip according to the comparison result; the second drive pulse signal is a signal for driving a BOOST topology freewheeling tube; and the drive duty cycle of the second drive pulse signal increases cycle by cycle during the startup process.

[0025] The present invention provides a driving duty cycle soft-start circuit, including a falling edge pulse module, a falling edge trigger module, a triangle wave module, an external soft-start module, and a main control chip. The falling edge pulse module includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, and a first transistor Q1. The falling edge trigger module includes a fourth resistor R4 and a second controllable switch Q2. The triangle wave module includes a fifth resistor R5 and a second capacitor C2. The external soft-start module includes a third capacitor C3. The main control chip includes a ground pin GND, a trigger pin , output pin OUT, reset pin , control pin CTRL, threshold pin THRESHOLD, discharge pin DISCHARGE and power supply pin VDD.

[0026] When the falling edge of the first drive pulse signal (G1) arrives, the charging and discharging of the first resistor R1 and the first capacitor C1 creates a negative voltage (Vbe) of a certain pulse width between the be terminals of the first transistor Q1, thereby turning on the first transistor Q1. The width of this pulse signal can be controlled by adjusting the values ​​of the first resistor R1 and the first capacitor C1.

[0027] When the first transistor Q1 is turned on, the reference voltage REF turns on the second controllable switch Q2 through the first transistor Q1. When the second controllable switch Q2 is turned on, the trigger pin of the main control chip U1 The voltage of the main control chip U1 is pulled down, so that the trigger pin Get a low level with a certain pulse width. When the trigger pin of the main control chip U1 When the voltage is pulled low, the output pin OUT of the main control chip U1 is allowed to output a high level (the output pin of the main control chip is triggered). The discharge pin DISCHARGE of the main control chip U1 is released, no longer pulling down the voltage of the threshold pin THRESHOLD. At the same time, the threshold pin THRESHOLD of the main control chip U1, at the reference voltage REF, is charged through the fifth resistor R5 and the second capacitor C2, and the voltage begins to rise in a triangular wave. The control pin CTRL of the main control chip U1, at the reference voltage REF (when the main control chip is powered normally), is charged through the capacitor C3, and the voltage begins to rise linearly, forming the soft-start voltage.

[0028] The main control chip U1 can be a 555 chip. The output pin of the 555 chip outputs the second drive pulse signal G21 based on the comparison between the triangular wave voltage and the soft-start voltage. When the triangular wave voltage is less than the soft-start voltage, the output pin outputs a high level; when the triangular wave voltage is greater than the soft-start voltage, the output pin outputs a low level. Because the soft-start voltage increases linearly while the triangular wave voltage changes periodically, the duty cycle of the second drive pulse signal increases cycle by cycle during the startup process until the soft-start voltage stabilizes.

[0029] Of course, when the main control chip is selected as a chip of other types, the output pin of the main control chip is triggered, which can be understood as the output pin of the main control chip is allowed to output a low level, corresponding to the release of the discharge pin, and the triangular wave module outputs a triangular wave voltage. The present invention does not make any special limitations here.

[0030] In a drive duty cycle soft-start circuit of the present invention, the drive duty cycles of the first drive pulse signal G1 and the second drive pulse signal G21 increase from small to large cycle by cycle during each startup process, thereby solving the above-mentioned problems of "BOOST topology output no-load (even no-load with capacitive load) and frequent switching on and off of the input end causing product damage", greatly improving the reliability of the product. The invention has good effect and high application value.

[0031] As a preferred embodiment, the first controllable switch is a first transistor; the falling edge pulse module includes a first resistor, a second resistor, a third resistor, a first capacitor and a first transistor; the first end of the first resistor serves as the input end of the falling edge pulse module, the second end of the first resistor is electrically connected to the first end of the first capacitor, the second end of the first capacitor is electrically connected to the first end of the second resistor and the base of the first transistor respectively, the second end of the second resistor is electrically connected to the emitter of the first transistor and the positive power supply end, the common end where the collector of the first transistor and the first end of the third resistor are connected serves as the output end of the falling edge pulse module, and the second end of the third resistor is grounded.

[0032] In this embodiment, the falling edge pulse module includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1 and a first transistor Q1. The first resistor R1 is used to limit the current flowing into the first capacitor C1 to prevent excessive current from damaging the capacitor. The second resistor R2 and the first capacitor C1 together form an RC charge and discharge circuit for generating a pulse signal. The third resistor R3 is used to limit the collector current of the first transistor Q1 to protect the transistor. The first capacitor C1 is used to store charge and generate a pulse signal. The first transistor Q1 acts as a controllable switch and is turned on at the falling edge of the first drive pulse signal G1.

[0033] As a preferred embodiment, the falling edge trigger module includes a fourth resistor and a second controllable switch; the first end of the fourth resistor is electrically connected to the second end of the second resistor and the common end connected to the emitter of the first transistor and the power supply pin of the main control chip, the control end of the second controllable switch serves as the input end of the falling edge trigger module, the common end connected to the second end of the fourth resistor and the first end of the second controllable switch serves as the output end of the falling edge trigger module, and the second end of the second controllable switch is electrically connected to the second end of the third resistor; the second controllable switch is used to be turned on when the first transistor is turned on.

[0034] As a preferred embodiment, the second controllable switch is an NMOS tube; the gate of the NMOS tube serves as the control end of the second controllable switch, the drain of the NMOS tube serves as the first end of the second controllable switch, and the source of the NMOS tube serves as the second end of the second controllable switch.

[0035] Please refer to Figure 2 , Figure 2 A schematic structural diagram of another drive duty cycle soft-start circuit provided by the present invention.

[0036] As a preferred embodiment, the second controllable switch is a second triode; the base of the second triode serves as the control end of the second controllable switch, the collector of the second triode serves as the first end of the second controllable switch, and the emitter of the second triode serves as the second end of the second controllable switch.

[0037] In this embodiment, the falling-edge trigger module includes a fourth resistor R4 and a second controllable switch Q2. The second controllable switch can be an NMOS transistor or a second transistor. The fourth resistor R4 is used to limit the current flowing into the control terminal of the second controllable switch Q2 to prevent excessive current from damaging the switch. The second controllable switch Q2 acts as a controllable switch, turning on when the first transistor (Q1) is on (Vgs>Vgsth), thereby triggering the output pin of the main control chip.

[0038] NMOS transistors typically have a low on-resistance (Rds(on)), which helps reduce power consumption when conducting and improve circuit efficiency. NMOS transistors also have a fast switching speed, enabling them to quickly respond to the first transistor's turn-on signal, ensuring the timeliness and accuracy of the trigger signal.

[0039] As a preferred embodiment, the triangular wave module includes a fifth resistor and a second capacitor; the first end of the fifth resistor is electrically connected to the second end of the second resistor, the emitter of the first transistor, the first end of the fourth resistor and the power supply pin of the main control chip, respectively; the second end of the fifth resistor is electrically connected to the first end of the second capacitor, the threshold pin of the main control chip and the discharge pin of the main control chip, respectively, and the second end of the second capacitor is grounded.

[0040] In this embodiment, the triangular wave module includes a fifth resistor R5 and a second capacitor C2. The fifth resistor R5 is used to limit the current flowing into the main control chip to prevent excessive current from damaging the chip. The second capacitor C2 is used to form an RC charge-discharge circuit with the fifth resistor R5 to generate a triangular wave voltage. The period and amplitude of the triangular wave can be controlled by adjusting the values ​​of the fifth resistor R5 and the second capacitor C2. Using standard resistor and capacitor components, the circuit structure is simple and reliable.

[0041] As a preferred embodiment, the external soft start module includes a third capacitor; a first end of the third capacitor is electrically connected to the control pin of the main control chip, and a second end of the third capacitor and a common end connected to the second capacitor are grounded.

[0042] In this embodiment, the capacitance of the third capacitor C3 determines the duration of the soft start.

[0043] As a preferred embodiment, the main control chip includes: a ground pin, the ground pin is grounded; a trigger pin, the trigger pin is electrically connected to the output end of the falling edge trigger module, and is used to obtain a low level when the second controllable switch is turned on; an output pin, which is used to meet the output high level condition when the trigger pin is low; a discharge pin, which is electrically connected to the threshold pin of the main control chip, and is used to control the voltage of the threshold pin when the output pin meets the output high level condition; the threshold pin, which is used to obtain a triangular wave voltage after the triangular wave module is charged; the control pin, which is used to obtain a soft start voltage after the external soft start module is charged; the output pin, which is also used to, when the voltage of the threshold pin is lower than the voltage of the control pin, the second drive pulse signal is high level; when the voltage of the threshold pin is higher than the voltage of the control pin, the second drive pulse signal is low level; the discharge pin is also used to pull the voltage of the threshold pin down to a preset voltage value when the output pin outputs a low level.

[0044] Please refer to Figure 3 , Figure 3This is a schematic diagram of the BOOST topology soft start process provided by the present invention.

[0045] In this embodiment, when the voltage (triangular wave voltage) of the threshold pin THRESHOLD of the main control chip U1 is lower than the voltage (soft-start voltage) of the control pin CTRL, the output pin OUT of the main control chip U1 outputs a high level. When the voltage (triangular wave voltage) of the threshold pin THRESHOLD of the main control chip U1 is higher than the voltage (soft-start voltage) of the control pin CTRL, the output pin OUT of the main control chip U1 outputs a low level. Simultaneously, the discharge pin DISCHARGE of the main control chip U1 is enabled to pull down the voltage of the threshold pin THRESHOLD, so that the voltage of the threshold pin THRESHOLD starts to rise from 0V in each cycle.

[0046] It should be explained that the voltage control of the threshold pin by the discharge pin includes pulling down the voltage of the threshold pin or not pulling down the voltage of the threshold pin.

[0047] When the next falling edge of the first drive pulse signal G1 arrives, the above process is repeated, and the voltage of the control pin CTRL continues to rise and finally stabilizes at a voltage of 0.667*REF, thereby achieving a cycle-by-cycle increase in the duty cycle of the second drive pulse signal G21 output from the output pin OUT during the soft start process. The second drive pulse signal G21 is a signal that drives the BOOST topology freewheeling tube.

[0048] As a preferred embodiment, the main control chip also includes a reset pin; the reset pin is used to receive the third drive pulse signal, and when the duty cycle of the second drive pulse signal is greater than the duty cycle of the third drive pulse signal, the second drive pulse signal is reset to a low level; the third drive pulse signal and the first drive pulse signal are complementary signals.

[0049] In this embodiment, the reset pin of the main control chip U1 The purpose of receiving the third drive pulse signal G2 is to use the low level of the third drive pulse signal G2 to reset the main control chip U1, forcing the second drive pulse signal G21 to output a low level. This function serves as a safety net, limiting the maximum on-time of the second drive pulse signal G21 to not exceed that of the third drive pulse signal G2, preventing the switch tube and the freewheeling tube from being connected together. By properly utilizing the pin functions of the 555 chip, a soft start of the BOOST freewheeling tube drive duty cycle is achieved.

[0050] The main control chip U1 can be LMC555 chip or RS555XK chip.

[0051] The switching power supply provided by the present invention is described below. The switching power supply described below and the driving duty cycle soft-start circuit described above can be referred to each other.

[0052] The present invention also provides a switching power supply, characterized in that it includes the above-mentioned driving duty cycle soft-start circuit and a BOOST topology circuit; the freewheeling tube in the BOOST topology circuit is driven by the driving duty cycle soft-start circuit.

[0053] Please refer to Figure 4 , Figure 4 This is a structural diagram of a switching power supply provided by the present invention.

[0054] In this embodiment, the switching power supply includes a drive duty cycle soft-start circuit and a boost topology circuit. The boost topology circuit includes a first topology capacitor C11, a topology inductor L11, a switch Q11, a freewheeling diode Q22, and a second topology capacitor C22. The common terminal of the first topology capacitor C11 and the first end of the topology inductor L11, which are connected, serves as the input voltage (VIN). The second end of the topology inductor L11 is electrically connected to the drain of the switch Q11 and the source of the freewheeling diode Q22, respectively. The common terminal of the drain of the freewheeling diode Q22 and the first end of the second topology capacitor C22, which are connected, serves as the output voltage (VOUT). The common terminal of the second end of the first topology capacitor C11, the source of the switch Q11, and the second end of the second topology capacitor C22 is grounded. The gate of the switch Q11 is electrically connected to a first pin of the boost control chip U2, receiving a first drive pulse signal G1. The gate of the freewheeling diode is electrically connected to an output pin OUT of the main control chip U1, receiving a second drive pulse signal G21. The second pin of the BOOST control chip U2 and the reset pin of the main control chip U1 Electrically connected to input the third driving pulse signal G2.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A driving duty cycle soft start circuit, characterized in that: include: A falling edge pulse module, used to control the first controllable switch to be turned on at the falling edge of the first driving pulse signal; The first driving pulse signal is a signal for driving a BOOST topology switch tube; The driving duty cycle of the first driving pulse signal increases cycle by cycle during the startup process; a falling edge trigger module, wherein the input end of the falling edge trigger module is electrically connected to the output end of the falling edge pulse module, and the output end of the falling edge trigger module is electrically connected to the main control chip, and is used to trigger the output pin of the main control chip when the first controllable switch is turned on; a triangular wave module, electrically connected to the main control chip, and configured to output a triangular wave voltage when an output pin of the main control chip is triggered; An external soft-start module is electrically connected to the main control chip and is used to output a linearly rising soft-start voltage when the main control chip is powered normally; A main control chip, configured to compare the triangular wave voltage with the soft-start voltage, and output a second drive pulse signal through an output pin of the main control chip according to the comparison result; The second driving pulse signal is a signal for driving a BOOST topology freewheeling tube; The driving duty cycle of the second driving pulse signal increases cycle by cycle during the startup process.

2. The driving duty cycle soft start circuit according to claim 1, characterized in that: The first controllable switch is a first transistor; the falling edge pulse module includes a first resistor, a second resistor, a third resistor, a first capacitor and the first transistor; The first end of the first resistor serves as the input end of the falling edge pulse module, the second end of the first resistor is electrically connected to the first end of the first capacitor, the second end of the first capacitor is electrically connected to the first end of the second resistor and the base of the first transistor respectively, the second end of the second resistor is electrically connected to the emitter of the first transistor and the positive power supply end, the common end connected to the collector of the first transistor and the first end of the third resistor serves as the output end of the falling edge pulse module, and the second end of the third resistor is grounded.

3. The driving duty cycle soft start circuit according to claim 2, characterized in that: The falling edge trigger module includes a fourth resistor and a second controllable switch; The first end of the fourth resistor is electrically connected to the second end of the second resistor, the emitter of the first transistor, and a common end connected to the power supply pin of the main control chip; the control end of the second controllable switch serves as the input end of the falling edge trigger module; the common end connected to the second end of the fourth resistor and the first end of the second controllable switch serves as the output end of the falling edge trigger module; and the second end of the second controllable switch is electrically connected to the second end of the third resistor; The second controllable switch is configured to be turned on when the first transistor is turned on.

4. The driving duty cycle soft start circuit according to claim 3, characterized in that: The second controllable switch is an NMOS tube; the gate of the NMOS tube serves as the control end of the second controllable switch, the drain of the NMOS tube serves as the first end of the second controllable switch, and the source of the NMOS tube serves as the second end of the second controllable switch.

5. The driving duty cycle soft start circuit according to claim 3, characterized in that: The second controllable switch is a second triode; the base of the second triode serves as the control end of the second controllable switch, the collector of the second triode serves as the first end of the second controllable switch, and the emitter of the second triode serves as the second end of the second controllable switch.

6. The driving duty cycle soft start circuit according to claim 3, characterized in that: The triangular wave module includes a fifth resistor and a second capacitor; The first end of the fifth resistor is electrically connected to the second end of the second resistor, the emitter of the first transistor, the first end of the fourth resistor and the power supply pin of the main control chip, respectively; the second end of the fifth resistor is electrically connected to the first end of the second capacitor, the threshold pin of the main control chip and the discharge pin of the main control chip, respectively; the second end of the second capacitor is electrically connected to the ground.

7. The driving duty cycle soft start circuit according to claim 6, characterized in that: The external soft start module includes a third capacitor; The first end of the third capacitor is electrically connected to the control pin of the main control chip, and the common end connected to the second end of the third capacitor and the second capacitor is grounded.

8. The driving duty cycle soft start circuit according to any one of claims 3 to 7, characterized in that: The main control chip includes: A ground pin, wherein the ground pin is grounded; a trigger pin, the trigger pin being electrically connected to the output end of the falling edge trigger module and being configured to obtain a low level when the second controllable switch is turned on; An output pin, used to satisfy a high level output condition when the trigger pin is at a low level; A discharge pin, electrically connected to a threshold pin of the main control chip, and configured to control the voltage of the threshold pin when the output pin meets an output high level condition; The threshold pin is used to obtain the triangular wave voltage after the triangular wave module is charged; A control pin, used to obtain the soft-start voltage after the external soft-start module is charged; The output pin is further configured to, when the voltage of the threshold pin is lower than the voltage of the control pin, enable the second drive pulse signal to be at a high level; and when the voltage of the threshold pin is higher than the voltage of the control pin, enable the second drive pulse signal to be at a low level; The discharge pin is further configured to pull down the voltage of the threshold pin to a preset voltage value when the output pin outputs a low level.

9. The driving duty cycle soft start circuit according to claim 8, characterized in that: The main control chip further includes a reset pin; the reset pin is used to receive the third drive pulse signal, and reset the second drive pulse signal to a low level when the duty cycle of the second drive pulse signal is greater than the duty cycle of the third drive pulse signal; The third driving pulse signal and the first driving pulse signal are complementary signals.

10. A switching power supply, characterized in that: The drive duty cycle soft start circuit according to any one of claims 1 to 9 further comprises a BOOST topology circuit; The freewheeling tube in the BOOST topology circuit is driven by the driving duty cycle soft start circuit.

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