CN113422505A - Voltage overshoot protection circuit, switching power supply chip and switching power supply system - Google Patents

Abstract

The invention provides a voltage overshoot protection circuit, a switching power supply chip and a switching power supply system, which are applied to the technical field of switching power supplies. The invention provides a voltage overshoot protection circuit for solving the voltage overshoot of the output terminal voltage of a switching power supply chip. Specifically, the output terminal voltage of the switching power supply chip is collected by the voltage overshoot control module, and when the output terminal voltage is higher than the first voltage threshold (the output terminal voltage overshoot), the constant current discharge control module is activated to pass the constant current discharge control module. The discharge circuit in the current discharge control module dissipates (discharges) the excess energy generated by the overshoot voltage in the form of heat, thereby reducing the output voltage and suppressing the voltage overshoot at the output of the switching power supply chip, and then The damage to the rear-stage unit is avoided, and the performance and reliability of the switching power supply chip are improved.

Description

Voltage overshoot protection circuit, switching power supply chip and switching power supply system

technical field

The invention relates to the technical field of switching circuits, in particular to a voltage overshoot protection circuit, a switching power supply chip and a switching power supply system.

Background technique

At present, in the DC-DC (direct current to direct current) power supply system, the load connected to the output end of the switching power supply chip sometimes has switching applications from heavy load to light load, such as the moment when the WIFI signal transmission ends, the solenoid valve drive stops. Moment wait. During the switching process of the load from heavy load to light load, when the load of the output terminal of the switching power supply is heavy, a large amount of energy is stored in the external inductor of the output terminal of the switching power supply chip, and this part The energy will eventually be stored in the output capacitor, which in turn causes the output capacitor voltage to rise (that is, the output voltage rises), that is, the output voltage of the switching power supply chip overshoots. In addition, the overshoot of the output terminal voltage of the switching power supply chip is a challenge to the withstand voltage of the post-stage components. Therefore, when the design is improper, the overshoot voltage of the output terminal of the switching power supply chip can easily cause damage to the post-stage unit.

Although, according to the principle of the switching power supply chip, during the switching process of the connected load from heavy load to light load, the switching power supply chip can be adjusted internally to alleviate the problem of voltage overshoot at the output terminal. However, since the adjustment of the switching power supply chip takes a certain amount of time, when the switching power supply chip detects that there is an overshoot at the output, the chip also needs several cycles to completely turn off the power tube. Therefore, during the internal adjustment process of the switching power supply chip , the power tube that controls whether the switching power supply chip is turned off or not is always in the switching state, which causes the output terminal voltage of the switching power supply chip to further rise and increase the overshoot.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a voltage overshoot protection circuit, a switching power supply chip and a switching power supply system, so as to suppress the occurrence of voltage overshoot at the output end of the switching power supply chip when the load of the switching power supply chip changes suddenly from heavy load to light load It can improve the performance and reliability of the switching power supply chip.

In the first aspect, in order to solve the above technical problems, the present invention proposes a voltage overshoot protection circuit, which is applied to the output voltage overshoot control of a switching power supply chip, and the switching power supply chip has a switching control for controlling whether the input voltage is output or not. A terminal SW, a first output voltage feedback pin FB and a second output voltage feedback pin FB1 for feeding back the change of the output voltage, and a power tube for adjusting the output voltage.

The voltage overshoot protection circuit may include: a power tube current acquisition module, connected to the output end of the power tube, for detecting the output current of the power tube before the output voltage of the switching power supply chip overshoots, and outputting a second voltage obtained by converting the output current into a voltage.

The voltage overshoot control module is connected to the second output voltage feedback pin FB1 and the constant current discharge control module, and is used for controlling the second output voltage feedback pin FB1 when the voltage of the second output voltage feedback pin FB1 is higher than the first voltage threshold The constant current discharge control module turns on the discharge working mode, and controls the constant current discharge control module to turn off the discharge working mode when the voltage of the second output voltage feedback pin FB1 is lower than the second voltage threshold.

The constant current discharge control module is connected to the power tube current acquisition module and the voltage overshoot control module, and is used for starting the discharge operation with the second voltage as the reference voltage and under the control of the voltage overshoot control module mode, and when the output voltage of the switching power supply chip overshoots, the excess energy generated by the overshoot voltage is discharged to reduce the output voltage.

Further, the power tube current collection module may include first to fourth resistors, a first operational amplifier, a second operational amplifier and a first diode, wherein both the first operational amplifier and the second operational amplifier may be Including non-inverting input, inverting input and output.

One end of the first resistor is connected to the source of the power tube and the input voltage, and the other end is connected to one end of the third resistor and the inverting input end of the first operational amplifier. The power tube The drain is connected to one end of the second resistor, the other end of the second resistor is connected to one end of the fourth resistor and the non-inverting input end of the first operational amplifier, the other end of the fourth resistor is connected connected to the reference ground; the other end of the third resistor is connected to the output end of the first operational amplifier and the non-inverting input end of the second operational amplifier, and the output end of the second operational amplifier is connected to the first operational amplifier The anode of a diode is connected, and the cathode of the first diode is connected to the inverting input terminal of the second operational amplifier and serves as the output terminal of the power tube current collection module, which is connected to the constant current discharge control module.

Further, the voltage overshoot control module may include an input end, an output end, eighth to eleventh resistors, a fourth operational amplifier and a NOT gate, wherein the fourth operational amplifier includes a non-inverting input end, an inverting input terminal and output terminal.

One end of the eighth resistor is connected to the second output voltage feedback pin FB1, and is used as the input end of the voltage overshoot control module to collect the output voltage of the switching power supply chip, and the other end is connected to the second output voltage feedback pin FB1. The ninth resistor is connected to the inverting input terminal of the fourth operational amplifier, and the other end of the ninth resistor is connected to the reference ground terminal; the non-inverting input terminal of the fourth operational amplifier is connected to one end of the tenth resistor and one end of the eleventh resistor is connected to the other end of the tenth resistor is connected to the preset reference voltage, and the other end of the eleventh resistor is connected to the output end of the fourth operational amplifier and the NOT gate The output terminal of the NOT gate is used as the output terminal of the voltage overshoot control module, and is connected to the constant current discharge control module to obtain the output voltage obtained by dividing the collected output voltage. The comparison result between the voltage of the second output voltage feedback pin FB1 and the first voltage threshold and/or the second voltage threshold controls whether the constant current discharge control module starts the discharge working mode.

Further, the constant current discharge control module may include fifth to seventh resistors, capacitors, a first MOS transistor, a second MOS transistor, a third operational amplifier and a sampling resistor, wherein the third operational amplifier includes a non-inverting input terminal, inverting input terminal and output terminal.

One end of the fifth resistor is connected to the output end of the power tube current collection module, and the other end is connected to the upper plate of the capacitor and the drain of the first MOS tube, and the source of the first MOS tube is connected The pole is connected to one end of the sixth resistor and the non-inverting input end of the third operational amplifier, the gate of the first MOS transistor is connected to the output end of the voltage overshoot control module, and the third operational amplifier The output terminal of the MOSFET is connected to the seventh resistor and the gate of the second MOS transistor, the drain of the second MOS transistor is connected to the output voltage of the switching power supply chip, and the source of the second MOS transistor pole with the stated

The inverting input end of the third operational amplifier is connected to one end of the sampling resistor, the other end of the sampling resistor, the other end of the seventh resistor, the other end of the sixth resistor and the capacitor are connected. The lower electrode plates are all connected to the reference ground terminal.

Further, each of the first to fourth operational amplifiers may further include a power supply terminal and a ground terminal; wherein, the power supply terminal of the first operational amplifier is connected to the input voltage, so that the first operational amplifier passes through all the The input voltage obtains power, and the power supply terminals of the second to fourth operational amplifiers are all connected to the power supply voltage inside the chip, so that the second to fourth operational amplifiers obtain power through the power supply voltage inside the chip; The first to fourth operational amplifiers are connected to the reference ground terminal through the ground terminal.

In the second aspect, based on the above-mentioned voltage overshoot protection circuit, the present invention also provides a switching power supply chip. Specifically, the switching power supply chip may include other components included in the voltage overshoot protection circuit in addition to the capacitor, the second MOS transistor, the sampling resistor, the eighth resistor, and the ninth resistor. All components.

Further, the capacitor, the second MOS transistor, the sampling resistor, the eighth resistor and the ninth resistor included in the voltage overshoot protection circuit can all be set in the switching power supply. outside of the chip, so that the user can configure the components arranged outside the switching power supply chip by himself, thereby improving the flexibility of the switching power supply chip.

Further, the inside of the switching power supply chip may also be provided with a transconductance amplifier, a voltage regulator module, a sawtooth wave generation module, a pulse modulation signal generation module, a power tube driving module and a frequency compensation module.

Wherein, the transconductance amplifier is used to amplify the error of the difference between the reference voltage and the voltage of the output voltage feedback pin.

The voltage regulator module is used to provide working voltage for each functional module included in the switching power supply chip.

The sawtooth wave generating module is used for forming a sawtooth wave signal.

The pulse modulation signal generating module is used for comparing the sawtooth wave signal with the output signal of the transconductance amplifier to form a pulse modulation signal.

The power tube drive module is used to convert the pulse modulation signal into a power tube drive signal, and drive the power tube through the power tube drive signal, so that the voltage of the output voltage feedback pin is the same as the reference. voltage is equal.

The frequency compensation module is used to perform frequency compensation on the output signal of the transconductance amplifier to stabilize the output voltage of the switching power supply chip.

Further, the voltage regulator module may further include a reference voltage unit, which is used to provide a required reference voltage for each functional module included in the switching power supply chip.

In a third aspect, based on the switching power supply chip as described above, the present invention also provides a switching power supply system, which may specifically include: the switching power supply chip as described above, and an input filter capacitor disposed outside the switching power supply chip , inductor, second diode, upper voltage divider resistor, lower voltage divider resistor, feedforward capacitor and output filter capacitor.

The positive pole of the input filter capacitor is connected to the input voltage of the switching power supply chip, and the negative pole of the input filter capacitor and the ground terminal of the switching power supply chip are both connected to the reference ground terminal.

One end of the inductor is connected to the switch control end of the switching power supply chip and the cathode of the second diode, and the other end is connected to one end of the upper voltage dividing resistor and the upper plate of the feedforward capacitor, The other end of the upper voltage dividing resistor is connected to one end of the lower voltage dividing resistor, the lower plate of the feedforward capacitor and the first output voltage feedback pin FB, and the other end of the lower voltage dividing resistor is connected. One end and the anode of the second diode are both connected to the reference ground.

The positive pole of the output filter capacitor is connected to the switch control terminal, and the negative pole of the output filter capacitor is connected to the reference ground terminal.

Further, the switching power supply chip also has a filter capacitor access pin for external connection of the capacitor, a second output terminal for external connection of the second MOS transistor, and a third output for external connection of the sampling resistor. end.

Wherein, the upper plate of the capacitor in the constant current discharge control module is connected to the filter capacitor access pin of the switching power supply chip, and the lower plate of the capacitor is connected to the reference ground.

The gate of the second MOS transistor is connected to the second output terminal of the switching power supply chip, and the source of the second MOS transistor and one end of the sampling resistor are both connected to the third output terminal of the switching power supply chip The drain of the second MOS transistor is connected to the inductor, one end of the upper voltage dividing resistor and the anode of the output filter capacitor, and the other end of the sampling resistor is connected to the reference ground.

One end of the eighth resistor is connected to the anode of the output filter capacitor, one end of the upper voltage dividing resistor and the other end of the inductor, and the other end is connected to one end of the ninth resistor and the switching power supply chip. The second output voltage feedback pin FB1 is connected, and the other end of the ninth resistor is connected to the reference ground.

Compared with the prior art, the present invention has the following beneficial effects:

The invention provides a voltage overshoot protection circuit for solving the voltage overshoot of the output terminal voltage of a switching power supply chip. Specifically, the output terminal voltage of the switching power supply chip is collected by the voltage overshoot control module, and when the output terminal voltage is higher than the first voltage threshold (the output terminal voltage overshoot), the constant current discharge control module is activated to pass the constant current discharge control module. The discharge circuit in the current discharge control module dissipates (discharges) the excess energy generated by the overshoot voltage in the form of heat, thereby reducing the output terminal voltage, suppressing the voltage overshoot at the output terminal of the switching power supply chip, thereby avoiding The damage to the rear stage unit is avoided, and the performance and reliability of the switching power supply chip are improved.

In addition, since some components in the voltage overshoot protection circuit provided by the present invention can be arranged outside the switching power supply chip, users can configure the components arranged outside the switching power supply chip according to actual needs, thereby improving the Design flexibility and stability of switching power supply chips.

Description of drawings

FIG. 1 is a schematic circuit diagram of a voltage overshoot protection circuit provided in an embodiment of the present invention.

FIG. 2 is a schematic circuit diagram of a switching power supply chip provided in an embodiment of the present invention.

FIG. 3 is a schematic circuit diagram of a switching power supply system provided in an embodiment of the present invention.

4a to 4d are waveform diagrams of key nodes of a switching power supply system using the voltage overshoot protection circuit of the present invention provided in an embodiment of the present invention and a switching power supply system not using the voltage overshoot protection circuit provided by the present invention. Output voltage comparison chart.

Among them, in the attached drawings,

10-Power tube current acquisition module; 20-Constant current discharge control module;

30-voltage overshoot control module; 40-voltage regulator module;

50-sawtooth wave generation module; 60-pulse modulation signal generation module;

70-power tube drive module; 80-frequency compensation module;

VIN-input voltage; V1-first voltage;

V2-the output terminal voltage of the second voltage/power tube current acquisition module 10;

M1-the first MOS tube; M2-the second MOS tube;

A-power tube; OP1-first operational amplifier;

OP2-second operational amplifier; OP3-first operational amplifier;

COMP1- the fourth operational amplifier; NOT1- NOT gate;

VREF/VREF1-reference voltage; GND-reference ground terminal;

100-switching power supply chip; R1~R11-first to eleventh resistors;

VO-output voltage; VH-first voltage threshold/upper threshold voltage;

VL-the second voltage threshold/lower threshold voltage; VDD-the power supply voltage inside the chip;

C1-capacitor; RCS-sampling resistor;

FB-the first output voltage feedback pin; SW-switch control terminal;

CT- filter capacitor access pin; MGATE- the second output terminal;

MCS-the third output terminal; CIN/C2-input filter capacitor;

COUT-output filter capacitor; D1-first diode;

D2-the second diode; L1-inductance;

OTA1-transconductance amplifier; RT-upper divider resistor;

RB-lower divider resistor; CFF-feedforward capacitor;

FB1-the second output voltage feedback pin FB1; RD-sampling resistance of power tube A;

-功率管A的输出电流；

-流过M2的电流。

- output current of power tube A;

- Current flowing through M2.

Detailed ways

In order to make the objects, advantages and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and are not drawn to scale, and are only used to facilitate and clearly assist the purpose of explaining the embodiments of the present invention. Furthermore, the structures shown in the drawings are often part of the actual structure. In particular, each drawing needs to show different emphases, and sometimes different scales are used.

As used herein, the singular forms "a," "an," and "the" include plural referents, the term "or" is generally employed in its sense including "and/or", and the term "a number" It is usually used in the sense including "at least one", the term "at least two" is usually used in the sense including "two or more", in addition, the terms "first", "the second" "Second" and "Third" are for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first", "second", "third" may expressly or implicitly include one or at least two of those features, "one end" and "the other end" and "proximal end" and "Distal" usually refers to two corresponding parts, which not only include end points, and the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection, or It can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication between the two elements or the interaction relationship between the two elements. In addition, as used in the present invention, the arrangement of one element on another element generally only means that there is a connection, coupling, cooperation or transmission relationship between the two elements, and the relationship between the two elements may be direct or indirect through intermediate elements connection, coupling, cooperation or transmission, and should not be construed as indicating or implying the spatial positional relationship between two elements, that is, one element can be in any position inside, outside, above, below or on one side of the other element, unless the content Also clearly stated. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

As mentioned in the background art, although, according to the principle of the switching power supply chip, during the switching process of the connected load from heavy load to light load, the switching power supply chip can be adjusted internally to alleviate the voltage overshoot at the output terminal. question. However, since the adjustment of the switching power supply chip takes a certain amount of time, when the switching power supply chip detects that there is an overshoot at the output, the chip also needs several cycles to completely turn off the power tube. Therefore, during the internal adjustment process of the switching power supply chip , the power tube that controls whether the switching power supply chip is turned off or not is always in the switching state, which causes the output terminal voltage of the switching power supply chip to further rise and increase the overshoot.

Therefore, in order to solve the above problems, the core idea of the present invention is to provide a voltage overshoot protection circuit, a switching power supply chip and a switching power supply system, so as to suppress the switching when the load of the switching power supply chip changes from heavy load to light load abruptly Voltage overshoot occurs at the output end of the power supply chip, thereby improving the performance and reliability of the switching power supply chip.

A voltage overshoot protection circuit, a switching power supply chip and a switching power supply system of the present invention will be described in further detail below. The present invention will be described in more detail below with reference to Fig. 1 to Fig. 4a to Fig. 4d, wherein preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art can modify the invention described herein and still implement the present invention Advantageous effects of the invention. Therefore, the following description should be construed as widely known to those skilled in the art and not as a limitation of the present invention.

Please refer to FIG. 1 , in conjunction with FIG. 2 , FIG. 1 is a schematic circuit diagram of a voltage overshoot protection circuit according to an embodiment of the present invention, and FIG. 2 is a circuit schematic diagram of a switching power supply chip including the voltage overshoot protection circuit described in FIG. 1 . Specifically, the voltage overshoot protection circuit provided in the embodiment of the present invention can be specifically applied to the output voltage overshoot control of a switching power supply chip (as shown in FIG. 2 ). The switching power supply chip has an input terminal VIN for connecting the input voltage, a switch control terminal SW for controlling whether the input voltage is output, an output voltage feedback pin FB for feeding back the change of the output voltage, and a The second output voltage feedback pin FB1 of the voltage FB of the output voltage feedback pin and the power transistor A used to adjust the output voltage. Specifically, the voltage overshoot protection circuit provided by the present invention may include: a power tube current collection module 10, a constant current discharge control module 20 and a voltage overshoot control module 30, wherein,

，并输出将所述输出电流

转换为电压后的第二电压V2。The power tube current acquisition module 10 is connected to the output end of the power tube A, so as to detect the output current of the power tube A before the output voltage of the switching power supply chip overshoots

, and the output will be the output current

The second voltage V2 after being converted into a voltage.

It should be noted that, in the voltage overshoot protection circuit shown in FIG. 1 , in order to facilitate understanding, the power tube A can be equivalent to its corresponding sampling resistance RD (the on-resistance of the power tube A), and in other In the embodiment, the power tube can also be equivalent to a resistor connected in series with the power tube.

Specifically, the power tube current collection module 10 may include first to fourth resistors R1 ˜ R4 , a first operational amplifier OP1 , a second operational amplifier OP2 and a first diode D1 , wherein the first operational amplifier Both OP1 and the second operational amplifier OP2 may include a non-inverting input terminal (+), an inverting input terminal (-) and an output terminal.

One end of the first resistor R1 is connected to the source of the power tube A (or one end of the corresponding sampling resistor RD) and the input voltage VIN, and the other end is connected to one end of the third resistor R3 and the input voltage VIN. The inverting input terminal (-) of the first operational amplifier OP1 is connected, the drain of the power transistor A is connected to one end of the second resistor R2, and the other end of the second resistor R2 is connected to the fourth One end of the resistor R4 is connected to the non-inverting input terminal (+) of the first operational amplifier OP1, the other end of the fourth resistor R4 is connected to the reference ground terminal GND; the other end of the third resistor R3 is connected to the first The output terminal of an operational amplifier OP1 is connected to the non-inverting input terminal (+) of the second operational amplifier OP2, the output terminal of the second operational amplifier OP2 is connected to the anode of the first diode D1, and the first operational amplifier OP2 is connected to the anode of the first diode D1. The cathode of a diode D1 is connected to the inverting input terminal (-) of the second operational amplifier OP2, and serves as the output terminal of the power tube current collection module 10, and is connected to the constant current discharge control module 20.

，以将该输出电流

的峰值电流对应的电压作为所述恒流放电控制模块20的泄放电流的基准电压，以使所述恒流放电控制模块20的泄放电流处于一个合理的值，并将所述泄放电流转换为第二电压V2，以通过所述功率管电流采集模块10提供的所述第二运算放大器OP2，将所述功率管A的输出电流

传递到恒流放电控制模块20。其中，所述第一电阻R1~第四电阻R4与所述第一运算放大器OP1组成差分放大器，由于所述第一运算放大器OP1的反相输入端（-）的输入电压较高，因此，为了保证该第一运算放大器OP1可以正常工作，则需要将所述第一运算放大器OP1的供电端与所述输入电压VIN连接，而其接地端与所述参考地端GND连接。In this embodiment, the power tube current acquisition module 10 is specifically configured to detect the output current of the power tube A before the voltage overshoot of the output terminal of the switching power supply chip

, to this output current

The voltage corresponding to the peak current of the constant current discharge control module 20 is used as the reference voltage of the discharge current of the constant current discharge control module 20, so that the discharge current of the constant current discharge control module 20 is at a reasonable value, and the discharge current is converted into a second voltage V2 to convert the output current of the power tube A through the second operational amplifier OP2 provided by the power tube current collection module 10

It is transmitted to the constant current discharge control module 20 . The first resistor R1 to the fourth resistor R4 and the first operational amplifier OP1 form a differential amplifier. Since the input voltage of the inverting input terminal (-) of the first operational amplifier OP1 is relatively high, in order to To ensure that the first operational amplifier OP1 can work normally, the power supply terminal of the first operational amplifier OP1 needs to be connected to the input voltage VIN, and the ground terminal of the first operational amplifier OP1 needs to be connected to the reference ground terminal GND.

Exemplarily, if the resistance values of the first resistor R1 to the fourth resistor R4 are all equal, that is, R1=R2=R3=R4, the output voltage V1 of the first operational amplifier OP1 can be expressed as the following formula:

为开关电源芯片内部连接的所述功率管A的输出电流，RD为所述功率管A对应的采样电阻。in,

is the output current of the power tube A connected inside the switching power supply chip, and RD is the sampling resistance corresponding to the power tube A.

传递到恒流放电控制模块20。In addition, the second operational amplifier OP2 and the first diode D1 form a voltage follower, and the fifth resistor R5 and the capacitor C1 in the constant current discharge control module 20 form a filter. Therefore, no matter whether the constant current discharge control module 20 is in the discharge operation mode or in the off discharge operation mode, due to the existence of the first diode D1, the capacitor C1 with the function of storing energy cannot be discharged through the second operational amplifier OP2, so the The voltage of the second voltage V2 is the peak voltage of the first voltage V1; and only when the constant current discharge control module 20 is ignored, the voltage value of the second voltage V2 of the output terminal voltage of the power tube current collection module 10 It is equal to the voltage value of the first voltage V1 (voltage following characteristic), that is, V2=V1, so as to realize the output current of the power tube A

It is transmitted to the constant current discharge control module 20 .

通常为脉冲信号，因此，所述第一电压V1与第二电压V2通常也为脉冲信号。并且，由于本发明实施例中的所述功率管电流采集模块10的输出端连接有所述第一二极管D1，因此，在所述恒流放电控制模块20处于放电工作模式时，其采集的是功率管A的最大电流。It can be understood that, since the power tube generally works on a certain duty cycle, the output current of the power tube A is

Usually it is a pulse signal, therefore, the first voltage V1 and the second voltage V2 are also usually a pulse signal. In addition, since the output end of the power tube current collection module 10 in the embodiment of the present invention is connected with the first diode D1, when the constant current discharge control module 20 is in the discharge operation mode, its collection is the maximum current of power tube A.

Further, the constant current discharge control module 20 is connected to the power tube current acquisition module 10 and the voltage overshoot control module 30, and is used for taking the second voltage V2 as the reference voltage and in the voltage overshoot control module Under the control of 30, the discharge working mode is turned on, and when the output voltage of the switching power supply chip overshoots, the excess energy generated by the overshoot voltage is discharged to reduce the output voltage VO.

Specifically, the constant current discharge control module 20 may include fifth to seventh resistors R5 to R7, a capacitor C1, a first MOS transistor M1, a second MOS transistor M2, a third operational amplifier OP3 and a sampling resistor RCS, wherein the The third operational amplifier OP3 may include a non-inverting input terminal (+), an inverting input terminal (-) and an output terminal.

One end of the fifth resistor R5 is connected to the output end of the power tube current collection module 10, and the other end is connected to the upper plate of the capacitor C1 and the drain of the first MOS transistor M1. The source of the MOS transistor M1 is connected to one end of the sixth resistor R6 and the non-inverting input terminal (+) of the third operational amplifier OP3, and the gate of the first MOS transistor M1 is connected to the voltage overshoot control module 30 is connected to the output terminal, the output terminal of the third operational amplifier OP3 is connected to the seventh resistor R7 and the gate of the second MOS transistor M2, and the drain of the second MOS transistor M2 is connected to the voltage The input terminal of the overshoot control module 30 (or understood as the output voltage of the switching power supply chip) is connected, and the source of the second MOS transistor M2 is connected to the inverting input terminal of the third operational amplifier OP3 (- ) and one end of the sampling resistor RCS, the other end of the sampling resistor RCS, the other end of the seventh resistor R7, the other end of the sixth resistor R6 and the lower plate of the capacitor C1 are all connected to The reference ground terminal is connected to GND.

In this embodiment, the fifth resistor R5 in the constant current discharge control module 10 and the capacitor C1 form a filter circuit, so when M1 is turned off, the second operational amplifier OP2 in the power tube current acquisition module 10 outputs The first diode D1 is connected in series at the end, so the capacitor C1 can only be charged through the resistor R5 without a discharge loop. In this way, although the voltage V2 is a pulse signal, the voltage V3 also rushes to the maximum value of the voltage V2 little by little. In addition, since the capacitor C1 has no discharge loop, even if the voltage V2 drops to 0V, the voltage across the capacitor C1 can be maintained for a long time. The second MOS transistor M2 and the sampling resistor RCS form a bleeder circuit, so as to control the turn-on and turn-off of the first MOS transistor M1 through the output terminal voltage V7 of the voltage overshoot control module 30, and through the turn-on of M1 and off control the on and off of the MOS transistor M2, so that when V7 is at a high voltage, M1 is controlled to be turned on. Since the resistance value of the sixth resistor R6 is set very large, it can be considered that the non-inverting input of the third operational amplifier OP3 The voltage V4 at the terminal (+) is the same as the voltage V3 at both ends of the capacitor C1, so that when the output voltage of the switching power supply chip overshoots, the excess energy generated by the overshoot voltage is dissipated at M2 in the form of heat, and then The purpose of reducing the output terminal voltage VO is achieved.

Specifically, when the voltage overshoot control module 30 detects that the voltage of V8 is greater than VH, it means that the output terminal voltage VO is overshooted. Since the voltage of V8 is greater than VH, V7 outputs a high level, and the high level of V7 controls the constant current discharge control module The first MOS tube M1 of 20 is turned on, M1 is turned on, and M2 is controlled to be turned on, that is, the constant current discharge control module 20 works in the discharge operation mode (through the second MOS tube M2 in the constant current discharge control module 20 to When the voltage overshoot control module 30 detects that the voltage of V8 is less than VL, it means that the voltage of the output terminal VO is normal. Since the voltage of V8 is less than VL, the output voltage of V7 is low. If V7 is low, the first MOS transistor M1 of the constant current discharge control module 20 is turned off, M1 is turned off, and M2 is controlled to be turned off, that is, the M2 of the constant current discharge control module 20 is no longer discharged.

In addition, when the voltage of V8 is lower than VL, V7 outputs a low level, and the low level of V7 controls the first MOS tube M1 of the constant current discharge control module 20 to be turned off, the sixth resistor R6 connects the non-inverting input terminal (+) of the third operational amplifier OP3. ) is grounded to prevent the non-inverting input terminal (+) of the third operational amplifier OP3 from floating and causing abnormality. When M1 is turned on, due to the existence of the sixth resistor R6, the voltage V3 of the capacitor C1 will gradually decrease, but in reality we only need the voltage V3 of the capacitor C1 to maintain a short period of time when M1 is turned on. The capacity requirement of C1 is not very high.

Furthermore, in the constant current discharge control module 20, the third operational amplifier OP3, the second MOS transistor M2, the sampling resistor RCS and the sixth resistor R6 form a linear constant current discharge loop, so the flow through the The current of M2 can be expressed as:

为0A；当M1导通时，流过M2的电流

约为之前时刻所述功率管的输出电流

的峰值。因此，本发明通过这部分电路，可以将输出电压VO过冲所产生的多余的电能消耗在所述第二MOS管M2上，从而保证开关电源系统中的输出电容基本不过冲，或者过冲的程度在一个可以接受的范围内，进而保证后级工作的稳定，并且，将M2外置，可以通过合理的计算，设置合适的散热条件，保证系统工作稳定，具体如何将M2外置，本发明将在如下附图3所示的开关电源系统对应的部分详细说明。It can be seen from the above formula that if the resistance value of the sampling resistor RCS is set to be equal to the resistance value of the equivalent resistance RD of the power tube A, then when M1 is turned off, the voltage of V4 is 0V, and the current flowing through M2

is 0A; when M1 is turned on, the current flowing through M2

about the output current of the power tube at the previous moment

Peak. Therefore, through this part of the circuit, the present invention can consume the excess electric energy generated by the overshoot of the output voltage VO on the second MOS transistor M2, thereby ensuring that the output capacitor in the switching power supply system is basically overshoot, or overshoot The degree of control is within an acceptable range, so as to ensure the stability of the post-stage operation. Moreover, if the M2 is externally installed, appropriate heat dissipation conditions can be set through reasonable calculations to ensure the stable operation of the system. Specifically, how to externally install the M2, the present invention It will be described in detail in the corresponding part of the switching power supply system shown in FIG. 3 below.

Wherein, since the second MOS transistor M2 needs to be externally installed, the function of the resistor R7 is to prevent the second MOS transistor M2 from being damaged due to excessive charge accumulation between the gate and the source GS of the second MOS transistor M2.

Further, the voltage overshoot control module 30 is connected to the second output voltage feedback pin FB1 and the constant current discharge control module 20, and is used when the voltage of the second output voltage feedback pin FB1 is higher than that of the second output voltage feedback pin FB1. When the first voltage threshold VH, the constant current discharge control module 20 is controlled to start the discharge working mode, and when the voltage of the second output voltage feedback pin FB1 is lower than the second voltage threshold VL, the constant current is controlled The discharge control module 20 turns off the discharge working mode.

Specifically, the voltage overshoot control module 30 may include an input end, an output end, eighth R8 to eleventh resistors R11, a fourth operational amplifier COMP1 and a NOT gate NOT1, wherein the fourth operational amplifier COMP1 includes a non-inverting Input (+), inverting input (-) and output.

One end of the eighth resistor R8 is connected to the second output voltage feedback pin FB1, and is used as the input end of the voltage overshoot control module 30 to collect the output voltage VO of the switching power supply chip, and the other end is connected to the output voltage VO of the switching power supply chip. The ninth resistor R9 is connected to the inverting input terminal (-) of the fourth operational amplifier COMP1, and the other end of the ninth resistor R9 is connected to the reference ground terminal GND; the fourth operational amplifier COMP1 The non-inverting input terminal (+) is connected to one end of the tenth resistor R10 and one end of the eleventh resistor R11, the other end of the tenth resistor R10 is connected to the preset reference voltage VREF1, and the eleventh resistor The other end of R11 is connected to the output end of the fourth operational amplifier COMP1 and the input end of the NOT gate NOT1. The output end of the NOT gate NOT1 serves as the output end of the voltage overshoot control module 30 and is connected to the The constant current discharge control module 20 is based on the voltage of the second output voltage feedback pin FB1 obtained by dividing the collected output voltage VO and the first voltage threshold VH and/or the second output voltage The comparison result of the voltage threshold VL controls whether the constant current discharge control module 20 starts the discharge working mode.

The fourth operational amplifier COMP1 further includes a power supply terminal and a ground terminal, and the power supply terminal of the fourth operational amplifier COMP1 is connected to the power supply voltage VDD inside the chip, so that the fourth operational amplifier COMP1 passes through the inside of the chip The power supply voltage VDD obtains power, and the fourth operational amplifier COMP1 is connected to the reference ground terminal GND through the ground terminal.

In the embodiment of the present invention, the eighth resistor R8 and the ninth resistor R9 are divided by resistors to collect the output voltage VO of the switching power supply chip, so that the divided voltage is V8. Specifically, the V8 It can be expressed by the following formula:

Among them, VO is the output voltage of the switching power supply system, and R8 and R9 are the resistance values of the resistors. It can be seen from the above formula that whether the output voltage VO of the switching power supply system is overshoot can be known by detecting the voltage value of the voltage V8, that is, if V8 is too high, it means that VO is too high.

Moreover, as shown in FIG. 1 , the tenth resistor R10 , the eleventh resistor R11 , the fourth operational amplifier COMP1 and the NOT gate NOT1 form a hysteresis comparator, wherein the fourth operational amplifier COMP1 can be Rail-to-rail output comparator, so the highest output voltage is VDD and the lowest output voltage is 0V, then, the upper threshold voltage VH (first voltage threshold) and lower threshold voltage VL (second voltage threshold) of the hysteresis comparator can be expressed as:

和

and

When the voltage V8 is greater than the upper threshold voltage VH (the first voltage threshold) of the hysteresis comparator, it means that the output voltage VO is too high. At this time, the output terminal voltage V7 of the NOT1 NOT1 outputs a high level; Back to the lower threshold voltage VL of the comparator (the second voltage threshold), it means that the output voltage VO is normal, then the output terminal voltage V7 of the NOT gate NOT1 outputs a low level; when the voltage V8 is between VL and VH, the NOT1 NOT1 The output terminal voltage V7 keeps the previous working state unchanged. The reason for using the hysteresis comparator here is to prevent the control circuit of M2 from oscillating when the second MOS transistor M2 is discharged, which affects the performance of the circuit.

In a voltage overshoot protection circuit to solve the voltage overshoot of the output terminal voltage of the switching power supply chip provided by the present invention, the voltage overshoot control module collects the output terminal voltage of the switching power supply chip, and the output terminal voltage is When the voltage is higher than the first voltage threshold (overshoot of the output terminal voltage), the constant current discharge control module is activated to convert the excess energy generated by the overshoot voltage into heat through the discharge loop in the constant current discharge control module Dissipated (discharged), thereby reducing the voltage at the output terminal, suppressing the voltage overshoot at the output terminal of the switching power supply chip, thereby avoiding damage to the subsequent unit, and improving the performance and reliability of the switching power supply chip.

Continuing to refer to FIG. 2 and in conjunction with FIG. 3 , based on the same inventive concept, the present invention further provides a switching power supply chip 100 , including the capacitor C1 , the second MOS transistor M2 , the sampling All other components included in the voltage overshoot protection circuit (as shown in FIG. 1 ) except the resistor RCS, the eighth resistor R8 and the ninth resistor R9.

In addition, the capacitor C1, the second MOS transistor M2, the sampling resistor RCS, the eighth resistor R8 and the ninth resistor R9 included in the voltage overshoot protection circuit are all arranged in the The outside of the switching power supply chip 100 enables the user to configure the components arranged outside the switching power supply chip 100 to improve the flexibility of the switching power supply chip.

In this embodiment, in order to improve the flexibility and stability of the switching power supply chip 100, and based on the fact that some components need to be manually operated, the inventor of the present invention proposes to design the voltage overshoot protection circuit in the circuit. Some components are arranged outside the switching power supply chip by adding the external pins of the switching power supply chip 100. Specifically, the present invention is to combine the capacitor C1, the second MOS transistor M2, the sampling resistor RCS, the The eighth resistor R8 and the ninth resistor R9 are disposed outside the switching power supply chip 100 . Therefore, the switching power supply chip 100 may also have a filter capacitor access pin CT for external connection of the capacitor C1, a second output terminal MGATE for external connection of the second MOS transistor M2, and an external connection for the sampling The third output terminal MCS of the resistor RCS.

Among them, since the second MOS transistor M2 needs to be externally installed, the function of the resistor R7 is to prevent the MOS transistor from being damaged due to excessive charge accumulation between the gate and the source GS of the M2.

Further, as shown in FIG. 2 , the switching power supply chip 100 may also be provided with a transconductance amplifier OTA1, a voltage regulator module 40, a sawtooth wave generation module 50, a pulse modulation signal generation module 60, and a power tube drive module 70. and a frequency compensation module 80 .

Wherein, the transconductance amplifier OTA1 is used to amplify the error of the difference between the reference voltage and the voltage of the output voltage feedback pin FB.

The voltage regulator module 40 is used to provide working voltage for each functional module included in the switching power supply chip.

The sawtooth wave generating module 50 is used for forming a sawtooth wave signal.

The pulse modulation signal generating module 60 is configured to compare the sawtooth wave signal with the output signal of the transconductance amplifier OTA1 to form a pulse modulation signal.

The power tube driving module 70 is used for converting the pulse modulation signal into a power tube driving signal, and driving the power tube A through the power tube driving signal, so that the voltage of the output voltage feedback pin FB is the same as that of the output voltage feedback pin FB. The reference voltages VREF are equal.

The frequency compensation module 80 is used to perform frequency compensation on the output signal of the transconductance amplifier, so as to stabilize the output voltage of the switching power supply chip, so as to obtain the purpose of stabilizing the output voltage.

Further, the voltage regulator module 40 further includes a reference voltage unit (not shown) for providing a required reference voltage for each functional module included in the switching power supply chip.

Since some components in the voltage overshoot protection circuit provided by the present invention can be arranged outside the switching power supply chip 100, the user can configure the components arranged outside the switching power supply chip according to actual needs, thereby improving the switching performance. Design flexibility and stability of the power chip 100 .

Also, referring to FIG. 3 , based on the same inventive concept, the present invention also provides a switching power supply system, and FIG. 3 is a schematic circuit diagram of the switching power supply system provided in an embodiment of the present invention. As shown in FIG. 3 , the switching power supply system provided by the present invention may include: a switching power supply chip 100 as shown in FIG. 2 , and an input filter capacitor CIN, an inductor L1 , a second two The pole tube D2, the upper voltage dividing resistor RT, the lower voltage dividing resistor RB, the feedforward capacitor CFF and the output filter capacitor COUT.

The positive pole of the input filter capacitor CIN is connected to the input voltage VIN of the switching power supply chip 100 , the negative pole of the input filter capacitor CIN and the ground terminal gnd of the switching power supply chip 100 are both connected to the reference ground terminal GND connect.

One end of the inductor L1 is connected to the switch control end SW of the switching power supply chip 100 and the cathode of the second diode D2, and the other end is connected to one end of the upper voltage dividing resistor RT and the feedforward capacitor CFF. The upper plate is connected to the upper plate, the other end of the upper voltage dividing resistor RT is connected to one end of the lower voltage dividing resistor RB, the lower plate of the feedforward capacitor CFF and the first output voltage feedback pin FB is connected, And the other end of the lower voltage dividing resistor RB and the anode of the second diode D2 are both connected to the reference ground GND.

The positive pole of the output filter capacitor COUT is connected to the switch control terminal SW, and the negative pole of the output filter capacitor COUT is connected to the reference ground terminal GND.

In addition, the connection between some components arranged outside the switching power supply chip 100 in the voltage overshoot protection circuit provided by the present invention and the switching power supply chip 100 may specifically be: The upper plate of the capacitor C1 is connected to the filter capacitor access pin CT of the switching power supply chip 100 , and the lower plate of the capacitor C1 is connected to the reference ground terminal GND.

The gate of the second MOS transistor M2 is connected to the second output terminal MGATE of the switching power supply chip 100 , and the source of the second MOS transistor M2 and one end of the sampling resistor RCS are both connected to the switching power supply chip. The third output terminal MCS of 100 is connected, the drain of the second MOS transistor M2 is connected to the inductor L1, one end of the equivalent resistance RT of the potentiometer and the anode of the output filter capacitor COUT, the sampling The other end of the resistor RCS is connected to the reference ground terminal GND.

One end of the eighth resistor R8 is connected to the anode of the output filter capacitor COUT, one end of the equivalent resistance RT of the potentiometer, and the other end of the inductor L1, and the other end of the eighth resistor R8 is connected to the One end of the ninth resistor R9 is connected to the second output voltage feedback pin FB1 of the switching power supply chip 100 , and the other end of the ninth resistor R9 is connected to the reference ground GND.

In this embodiment, RT/RB=R8/R9 of the potentiometer should be satisfied in actual use, so as to ensure that the FB voltage is consistent with the FB1 voltage during normal operation (the reason why the FB voltage and the FB1 voltage are not combined) It is that the divider resistor on the FB voltage often adds a feedforward capacitor CFF. When the output voltage VO changes drastically, the FB voltage is different from the FB1 voltage).

It should be noted that, in the switching power supply system provided by the present invention, both the input filter capacitor CIN and the output filter capacitor COUT may be one capacitor device or multiple capacitor devices connected in parallel. Exemplarily, as shown in FIG. 3 , the capacitor C2 is also an input filter capacitor.

Referring to FIG. 4a to FIG. 4d, FIG. 4a to FIG. 4d are the waveform diagrams of each key node of the switching power supply system using the voltage overshoot protection circuit of the present invention provided in an embodiment of the present invention and the voltage overshoot provided by the present invention is not used. The output voltage comparison diagram of the switching power supply system of the protection circuit. 4a, 4b and 4c are the waveform diagrams of each key node in the switching power supply system using the voltage overshoot protection circuit of the present invention when the output load fluctuates greatly, and FIG. 4d is the voltage overshoot without the use of the present invention. The output voltage waveform diagram of the switching power supply system of the protection circuit.

It can be seen from FIG. 4a that the overshoot of the output voltage VO of the switching power supply system using the voltage overshoot protection circuit of the present invention does not exceed 5.5V, which is very safe for the post-stage system. It can be seen from Figure 4b that the maximum value of the output current IO of the switching power supply system using the voltage overshoot protection circuit of the present invention is about 3A, and the minimum value is about 0A. During the process, the drop speed of the output current IO is very fast. Generally speaking, the faster the speed, the greater the test for the power supply. Figure 4c is a waveform diagram of the current flowing through the MOS tube M2. It can be seen from Figure 4c that when the system load current changes from heavy to light, the MOS tube M2 quickly flows a large current to provide a discharge loop for excess energy, thereby reducing the output. Voltage overshoot problem. As can be seen from Figure 4d, when the system load suddenly changes (the load conditions are the same), the system output voltage VO has a very obvious overshoot, and the overshoot voltage is close to 7V, which is a very big challenge for the subsequent loads. Obviously, when the switching power supply system using the voltage overshoot protection circuit of the present invention encounters a sudden change of load from heavy load to light load, the overshoot of the output terminal voltage is well suppressed.

To sum up, the present invention provides a voltage overshoot protection circuit for solving the voltage overshoot of the output terminal voltage of the switching power supply chip. Specifically, the output terminal voltage of the switching power supply chip is collected by the voltage overshoot control module, and when the output terminal voltage is higher than the first voltage threshold (the output terminal voltage overshoot), the constant current discharge control module is activated to pass the constant current discharge control module. The discharge circuit in the current discharge control module dissipates (discharges) the excess energy generated by the overshoot voltage in the form of heat, thereby reducing the output terminal voltage, suppressing the voltage overshoot at the output terminal of the switching power supply chip, thereby avoiding The damage to the rear stage unit is avoided, and the performance and reliability of the switching power supply chip are improved.

In addition, since some components in the voltage overshoot protection circuit provided by the present invention can be arranged outside the switching power supply chip, users can configure the components arranged outside the switching power supply chip according to actual needs, thereby improving the Design flexibility and stability of switching power supply chips.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," or "specific example," etc., means a specific feature, structure, material, or characteristic described in connection with the embodiment or example. Included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in one or more embodiments. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

The above are only preferred embodiments of the present invention, and do not have any limiting effect on the present invention. Any person skilled in the art, within the scope of not departing from the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, all belong to the technical solution of the present invention. content still falls within the protection scope of the present invention.

Claims (10)

1. A voltage overshoot protection circuit applied to output voltage overshoot control of a switching power supply chip, the switching power supply chip having a switch control terminal SW for controlling whether an input voltage is output, a first output voltage feedback pin FB and a second output voltage feedback pin FB1 for feeding back a change of the output voltage, and a power tube for regulating the output voltage, the voltage overshoot protection circuit comprising:

the power tube current acquisition module is connected with the output end of the power tube and used for detecting the output current of the power tube before the output voltage of the switching power supply chip is overshot and outputting a second voltage after the output current is converted into the voltage;

the voltage overshoot control module is connected with the second output voltage feedback pin FB1 and the constant current discharge control module, and is used for controlling the constant current discharge control module to start a discharge working mode when the voltage of the second output voltage feedback pin FB1 is higher than a first voltage threshold value, and controlling the constant current discharge control module to stop the discharge working mode when the voltage of the second output voltage feedback pin FB1 is lower than a second voltage threshold value;

and the constant current discharge control module is connected with the power tube current acquisition module and the voltage overshoot control module and is used for starting a discharge working mode by taking the second voltage as a reference voltage and under the control of the voltage overshoot control module, and discharging redundant energy generated by the overshoot voltage when the output voltage of the switching power supply chip overshoots so as to reduce the output voltage.

2. The voltage overshoot protection circuit of claim 1, wherein the power transistor current collection module comprises first through fourth resistors, a first operational amplifier, a second operational amplifier, and a first diode, wherein the first operational amplifier and the second operational amplifier each comprise a non-inverting input terminal, an inverting input terminal, and an output terminal;

one end of the first resistor is connected with the source electrode of the power tube and the input voltage, the other end of the first resistor is connected with one end of the third resistor and the inverting input end of the first operational amplifier, the drain electrode of the power tube is connected with one end of the second resistor, the other end of the second resistor is connected with one end of the fourth resistor and the non-inverting input end of the first operational amplifier, and the other end of the fourth resistor is connected with a reference ground end; the other end of the third resistor is connected with the output end of the first operational amplifier and the non-inverting input end of the second operational amplifier, the output end of the second operational amplifier is connected with the anode of the first diode, and the cathode of the first diode is connected with the inverting input end of the second operational amplifier and serves as the output end of the power tube current collection module to be connected with the constant current discharge control module.

3. The voltage overshoot protection circuit of claim 2, wherein the voltage overshoot control module comprises an input, an output, eighth to eleventh resistors, a fourth operational amplifier and a not gate, wherein the fourth operational amplifier comprises a non-inverting input, an inverting input and an output;

one end of the eighth resistor is connected to the second output voltage feedback pin FB1 and serves as an input end of the voltage overshoot control module to acquire the output voltage of the switching power supply chip, the other end of the eighth resistor is connected to the ninth resistor and an inverting input end of the fourth operational amplifier, and the other end of the ninth resistor is connected to the reference ground; the non-inverting input end of the fourth operational amplifier is connected with one end of the tenth resistor and one end of the eleventh resistor, the other end of the tenth resistor is connected with a preset reference voltage, the other end of the eleventh resistor is connected with the output end of the fourth operational amplifier and the input end of the not gate, the output end of the not gate is used as the output end of the voltage overshoot control module and is connected with the constant current discharge control module, and therefore whether the discharge working mode is started or not is controlled by the constant current discharge control module according to a comparison result of the voltage of the second output voltage feedback pin FB1, obtained by dividing the acquired output voltage, and the first voltage threshold and/or the second voltage threshold.

4. The voltage overshoot protection circuit according to claim 3, wherein the constant current discharge control module comprises fifth to seventh resistors, a capacitor, a first MOS transistor, a second MOS transistor, a third operational amplifier, and a sampling resistor, wherein the third operational amplifier comprises a non-inverting input terminal, an inverting input terminal, and an output terminal;

one end of the fifth resistor is connected with the output end of the power tube current acquisition module, the other end of the fifth resistor is connected with the upper polar plate of the capacitor and the drain electrode of the first MOS tube, the source electrode of the first MOS tube is connected with one end of the sixth resistor and the non-inverting input end of the third operational amplifier, the grid electrode of the first MOS tube is connected with the output end of the voltage overshoot control module, the output end of the third operational amplifier is connected with the seventh resistor and the grid electrode of the second MOS tube, the drain electrode of the second MOS tube is connected with the output voltage of the switching power supply chip, and the source electrode of the second MOS tube is connected with the inverting input end of the third operational amplifier and one end of the sampling resistor, the other end of the sampling resistor, the other end of the seventh resistor, the other end of the sixth resistor and the lower pole plate of the capacitor are all connected with the reference ground end.

5. The voltage overshoot protection circuit of claim 4, wherein the first through fourth operational amplifiers each further comprise a supply terminal and a ground terminal; the power supply end of the first operational amplifier is connected with the input voltage so that the first operational amplifier can obtain electric energy through the input voltage, and the power supply ends of the second to fourth operational amplifiers are connected to the power supply voltage inside the chip so that the second to fourth operational amplifiers can obtain electric energy through the power supply voltage inside the chip; the first to fourth operational amplifiers are connected to the reference ground terminal through the ground terminal.

6. A switching power supply chip, comprising all the other components of the voltage overshoot protection circuit according to claim 5 except for the capacitor, the second MOS transistor, the sampling resistor, the eighth resistor, and the ninth resistor.

7. The switching power supply chip according to claim 6, wherein the capacitor, the second MOS transistor, the sampling resistor, the eighth resistor, and the ninth resistor included in the voltage overshoot protection circuit are all disposed outside the switching power supply chip, so that a user can configure the components disposed outside the switching power supply chip by himself/herself, thereby improving flexibility of the switching power supply chip.

8. The switching power supply chip according to claim 7, wherein a transconductance amplifier, a voltage regulator module, a sawtooth wave generating module, a pulse modulation signal generating module, a power tube driving module and a frequency compensation module are further disposed inside the switching power supply chip,

the transconductance amplifier is used for carrying out error amplification on the difference between the reference voltage and the voltage of the output voltage feedback pin FB;

the voltage stabilizing module is used for providing working voltage for each functional module contained in the switching power supply chip;

the sawtooth wave generating module is used for forming a sawtooth wave signal;

the pulse modulation signal generation module is used for comparing the sawtooth wave signal with an output signal of the transconductance amplifier to form a pulse modulation signal;

the power tube driving module is used for converting the pulse modulation signal into a power tube driving signal and driving the power tube through the power tube driving signal so as to enable the voltage of the output voltage feedback pin FB to be equal to the reference voltage;

the frequency compensation module is used for performing frequency compensation on the output signal of the transconductance amplifier so as to stabilize the output voltage of the switching power supply chip.

9. A switching power supply system, comprising: the switching power supply chip according to any one of claims 6 to 8, and an input filter capacitor, an inductor, a second diode, an upper voltage-dividing resistor, a lower voltage-dividing resistor, a feed-forward capacitor, and an output filter capacitor, which are provided outside the switching power supply chip,

the anode of the input filter capacitor is connected with the input voltage of the switch power supply chip, and the cathode of the input filter capacitor and the grounding end of the switch power supply chip are both connected with the reference ground end;

one end of the inductor is connected with a switch control end of the switch power supply chip and a cathode of the second diode, the other end of the inductor is connected with one end of the upper divider resistor and an upper polar plate of the feedforward capacitor, the other end of the upper divider resistor is connected with one end of the lower divider resistor, a lower polar plate of the feedforward capacitor and the first output voltage feedback pin FB, and the other end of the lower divider resistor and an anode of the second diode are both connected with the reference ground end;

and the anode of the output filter capacitor is connected with the switch control end, and the cathode of the output filter capacitor is connected with the reference ground end.

10. The switching power supply system according to claim 9, wherein the switching power supply chip further has a filter capacitor access pin for externally connecting the capacitor, a second output terminal for externally connecting the second MOS transistor, and a third output terminal for externally connecting the sampling resistor, wherein,

the upper polar plate of the capacitor in the constant current discharge control module is connected with a filter capacitor access pin of the switching power supply chip, and the lower polar plate of the capacitor is connected with the reference ground end;

the grid electrode of the second MOS tube is connected with the second output end of the switching power supply chip, the source electrode of the second MOS tube and one end of the sampling resistor are both connected with the third output end of the switching power supply chip, the drain electrode of the second MOS tube is connected with the inductor, one end of the upper divider resistor and the anode of the output filter capacitor, and the other end of the sampling resistor is connected with the reference ground end;

one end of the eighth resistor is connected to the anode of the output filter capacitor, one end of the upper divider resistor and the other end of the inductor, the other end of the eighth resistor is connected to one end of the ninth resistor and the second output voltage feedback pin FB1 of the switching power supply chip, and the other end of the ninth resistor is connected to the reference ground.

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