TW201909541A - Switching power supply chip and switching power supply circuit including the same - Google Patents

Abstract

The invention discloses a switching power supply chip and a switching power supply circuit comprising the same. The switching power supply chip comprises a controller and a power switch; the controller comprises a high-voltage diode, a first resistor and a second resistor, a first comparator and a second comparator, a first switching tube and a second switching tube, and a control signal generation module; in the starting process of the switching power supply chip, a linear voltage received by a linear voltage detection pin from the external supplies a starting current for the switching power supply chip through the first resistor and the high-voltage diode; in the working process of the switching power supply chip, the first comparator, by making comparison between a linear voltage sampling value of a connecting node between the first resistor and the second resistor, and a first reference voltage, generates a linear voltage overvoltage detection signal; the second comparator, by making comparison between a linear voltage sampling value and a second reference voltage, generates a linear voltage undervoltage detection signal; and the control signal generation module generates signals for controlling the power switches to be switched on and switched off based on the linear voltage overvoltage detection signal and the linear voltage undervoltage detection signal.

Description

   Switching power supply chip and switching power supply circuit including the same   

The present invention relates to the field of circuits, and more particularly, to a switching power supply chip and a switching power supply circuit including the same.

The switching power supply circuit uses the control circuit to control the electronic switching devices (such as transistors, field-effect transistors, thyristors, etc.) to be continuously turned on and off to pulse-adjust the input voltage to achieve AC. -A direct current (AC / DC) or direct current (DC / DC) voltage conversion circuit.

FIG. 1 is a schematic diagram showing an example system structure of a conventional switching power supply circuit. In the following, the switching power supply circuit shown in FIG. 1 is taken as an example to explain the high-voltage startup and line voltage sensing principles of the switching power supply chip.

As shown in Figure 1, Vline is the line voltage obtained after the rectifier bridge rectifies the input voltage from the AC (AC) power supply; Cbulk is the filter capacitor; between the primary winding, the secondary winding, and the auxiliary winding of the three-winding transformer The turns ratio is Np: Ns: Na; U1 is the switching power supply chip, including the controller and the bipolar transistor S1; Cp is the chip power supply capacitor; D1 is the power supply diode; Rst is the high-voltage startup resistance; Rup is the wire Voltage-dividing resistor, Rdn is the voltage-dividing resistor under line voltage.

When the AC power is turned on (ie, during the startup process of the switching power supply chip U1), the line voltage Vline provides the startup current to the switching power supply chip U1 via the high-voltage startup resistor Rst. Specifically, the line voltage Vline charges the chip power supply capacitor Cp via the high-voltage startup resistor Rst; when the voltage on the chip power supply capacitor Cp, that is, the voltage at the power supply pin (ie, VCC pin) of the switching power supply chip U1 is greater than that of the switching power supply chip U1 When the under voltage latch (UVLO) turns on the threshold voltage, the switching power supply chip U1 starts, and the controller controls the bipolar transistor S1 to be turned on and off with a certain switching frequency and duty cycle.

After the switching power supply chip U1 is started (ie, during the operation of the switching power supply chip U1), the auxiliary winding Na of the transformer supplies power to the switching power supply chip U1 via the power supply diode D1 and the VCC pin of the switching power supply chip U1; the controller passes The line voltage sensing pin (ie, the RT pin) of the switching power supply chip U1 senses the divided voltage of the line voltage Vline, and inputs the divided voltage of the line voltage Vline to an internal comparator to compare with a predetermined reference voltage, thereby realizing input Overvoltage and undervoltage protection.

In the system structure shown in FIG. 1, the switching power supply chip U1 is increased due to the use of a high-voltage startup circuit (that is, the high-voltage startup resistor Rst) and a line voltage sensing circuit (that is, the line voltage divider resistors Rup, Rdn). The number of peripheral devices increases the system cost of the switching power supply circuit. In addition, the high-voltage startup circuit and the line voltage sensing circuit generate large power consumption, which reduces the system efficiency of the switching power supply circuit.

In view of one or more of the problems described above, the present invention provides a switching power supply chip and a switching power supply circuit including the same.

A switching power supply chip according to an embodiment of the present invention includes a controller and a power switch. The controller includes a high-voltage diode, a first resistor and a second resistor, a first comparator and a second comparator, and a first power MOS field effect power. The crystal and the second power MOS field effect transistor, and a control signal generating module, wherein the first resistor, the second resistor, and the first power MOS field effect transistor are connected to a line voltage sensing pin and a ground of a switching power supply chip. The first resistor and the high-voltage diode are connected between the line voltage sensing pin and the power supply pin of the switching power supply chip; the connection node between the first resistor and the second resistor is via a second power MOS field effect transistor Connected to the input terminal of the first comparator and the input terminal of the second comparator; during the startup process of the switching power supply chip, the first power MOS field effect transistor, the second power MOS field effect transistor, and the power switch are in In the off state, the line voltage received from the outside by the line voltage sensing pin provides the startup current for the switching power supply chip via the first resistor and the high voltage diode; during the working process of the switching power supply chip, the first The force MOS field effect transistor and the second power MOS field effect transistor are both in an on state. The first comparator compares the sampled line voltage at the connection node between the first resistor and the second resistor with the first reference voltage. Generate a line voltage overvoltage sensing signal. The second comparator generates a line voltage undervoltage sensing signal by comparing the line voltage sampling value with a second reference voltage. The control signal generation module is based on the line voltage overvoltage sensing signal and the line voltage undervoltage. Pressure sensing signal to generate a signal to control the power switch on and off.

In the switching power supply chip according to the embodiment of the present invention, the first resistor simultaneously functions as a line voltage dividing resistor and a high-voltage starting resistor, and forms a line voltage sensing circuit with the second resistor to implement the line voltage sensing function, and its own composition High voltage start circuit to achieve high voltage start function.

A switching power supply circuit according to an embodiment of the present invention includes the above-mentioned switching power supply chip. In a switching power supply circuit using a switching power supply chip according to an embodiment of the present invention, the number of peripheral components of the switching power supply chip is reduced, thereby reducing the system cost of the switching power supply circuit; in addition, since the first resistor simultaneously functions as a high-voltage startup resistor and The voltage dividing resistor on the line voltage saves the power consumption of the traditional line voltage sensing circuit and improves the system efficiency of the switching power supply circuit.

Vline‧‧‧line voltage

S1‧‧‧Bipolar Transistor

AC‧‧‧AC Power

U1, U2‧‧‧ switching power chip

Rst‧‧‧High-voltage starting resistance

M1, M2‧‧‧MOS switches

Rup‧‧‧line voltage resistance

PG‧‧‧ Power-on completion signal

Rdn‧‧‧ Voltage Divider at Line Voltage

AVDD‧‧‧Low-voltage power signal

RT‧‧‧line voltage sensing pin

comp1, comp2‧‧‧ comparator

Cbulk‧‧‧filter capacitor

Cp‧‧‧Chip Power Capacitor

VCC‧‧‧Power supply pin

Line_det‧‧‧Line voltage sampling value

GND‧‧‧ ground pin

202‧‧‧Controller

Na‧‧‧ auxiliary winding

204‧‧‧Power Switch

Np‧‧‧ primary winding

D1‧‧‧ Power Diode

Ns‧‧‧secondary winding

D3‧‧‧High-voltage startup diode

UVLO‧‧‧Under Voltage Latch

2 ^ m1xTclk‧‧‧Duration

clk‧‧‧ clock signal

D‧‧‧Trigger input

D2‧‧‧ Output Rectifier Diode

Q‧‧‧Trigger output

R1‧‧‧Feedback voltage-dividing resistor

QN‧‧‧ flip-flop inverting output

R2‧‧‧Feedback resistor

Cout‧‧‧ output filter capacitor

CS‧‧‧Primary current sensing pin

Vout‧‧‧Output voltage

FB‧‧‧Feedback pin

Rout‧‧‧Load

Rcs‧‧‧Primary current sensing resistor

OR‧‧‧OR

C‧‧‧Trigger Clock Input

Set terminal of S‧‧‧RS latch

INV‧‧‧Reverse

Latch‧‧‧RS Latch

dff‧‧‧D trigger

Vref_OVP, Vref_BO‧‧‧Reference voltage

Line_OVP_det, Line_OVP‧‧‧ Line voltage overvoltage sensing signal

Brown_out_det, Brown_out‧‧‧ Line voltage undervoltage sensing signal

Line_off_st‧‧‧Line voltage abnormality detection signal (when starting)

Line_off‧‧‧line voltage abnormal sensing signal (during normal operation)

Line_OVP_rst‧‧‧ Line voltage overvoltage sensing reset signal

The present invention can be better understood from the following description of specific embodiments of the present invention with reference to the accompanying drawings, in which: FIG. 1 shows a schematic diagram of an example system structure of a conventional switching power supply circuit; and FIG. 2 shows a diagram according to the present invention. A schematic diagram of an exemplary circuit structure of a switching power supply chip and its peripheral components according to an embodiment of the invention; FIG. 3 is a schematic diagram of an exemplary system structure of a switching power supply circuit including the switching power supply chip and its peripheral components shown in FIG. 2; FIG. 4 shows waveform diagrams of a plurality of voltage signals in the switching power supply chip shown in FIG. 2; FIG. 5 shows a schematic diagram of an example implementation circuit of the switching power supply chip shown in FIG. 2.

Features and exemplary embodiments of various aspects of the invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is merely for providing a better understanding of the present invention by showing examples of the present invention. The invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

In view of one or more problems associated with the switching power supply circuit described in FIG. 1, a switching power supply chip with a high-voltage startup circuit and a line voltage sensing circuit integrated therein is provided.

FIG. 2 is a schematic diagram showing an example circuit structure of a switching power supply chip and its peripheral components according to an embodiment of the present invention. As shown in FIG. 2, the switching power supply chip U2 includes a controller 202 and a power switch 204. The controller 202 includes a high-voltage diode D3, a high-voltage starting resistor Rst, a line voltage dividing resistor Rdn, and MOS switches M1 and M2 (wherein, M2 can be a high-voltage MOS switch), comparators comp1 and comp2, and a control signal generation module.

In the embodiment shown in FIG. 2, the high-voltage starting resistor Rs, the line voltage dividing resistor Rdn, and the MOS switch M1 are connected to the line voltage sensing pin (ie, the RT pin) and the ground pin (ie, the RT pin) of the switching power supply chip U2. , GND pin); the high-voltage startup resistor Rs and the high-voltage diode D3 are connected between the RT pin and the power supply pin (ie, the VCC pin) of the switching power supply chip U2; the high-voltage startup resistor Rst and the line voltage dividing resistor Rdn The connection node between them is connected to the positive-phase input terminal of the comparator comp1 and the negative-phase input terminal of the comparator comp2 via the MOS switch M2.

In the embodiment shown in FIG. 2, the gate input of the MOS switch M1 is a chip power-on completion (PG) signal of the switching power supply chip U2, and the initial state of the PG signal is a logic low level; the gate of the MOS switch M2 The input is the low-voltage power AVDD signal inside the switching power supply chip U2, and the initial state of the AVDD signal is a logic low level. That is, when the switching power supply chip U2 has not been started or is in the process of startup, the MOS switches M1 and M2 are in an off state.

FIG. 3 is a schematic diagram showing an example system structure of a switching power supply circuit including the switching power supply chip and its peripheral components shown in FIG. 2. Taking the switching power supply circuit shown in FIG. 3 as an example, the high-voltage startup and line voltage sensing principles of the switching power supply chip U2 shown in FIG. 2 are described in detail below.

When the AC power is turned on (ie, during the startup of the switching power supply chip U2), the PG signal is at a logic low level and the MOS switch M1 is in an off state; the AVDD signal is at a logic low level and the MOS switch M2 is in an off state; The line voltage Vline provides a startup current to the switching power supply chip U2 via a high-voltage startup resistor Rst and a high-voltage diode D3. Specifically, the line voltage Vline charges the chip power supply capacitor Cp connected to the VCC pin of the switching power supply chip U2 via the high voltage startup resistor Rst and the high voltage diode D3; the voltage on the chip power supply capacitor Cp, that is, the VCC of the switching power supply chip U2 When the voltage at the pin is greater than the UVLO turn-on threshold voltage of the switching power supply chip U2, the switching power supply chip U2 starts.

After the switching power supply chip U2 is started (that is, power-on is completed), the PG signal changes from a logic low level to a logic high level, and the MOS switch M1 changes from an off state to an on state; the AVDD signal changes from a logic low level to a logic high Yes, the MOS switch M2 changes from the off state to the on state. During the operation of the switching power supply chip U2, the high-voltage startup resistor Rst and the line voltage dividing resistor Rdn form a line voltage dividing voltage sensing circuit, and divide the line voltage Vline to obtain a line voltage sampling value Line_det (the line voltage sampling value is less than The voltage at the VCC pin of the switching power supply chip U2); the comparator comp1 compares the line voltage sampling value Line_det with the reference voltage Vref_OVP to generate a line voltage overvoltage sensing signal Line_OVP_det; the comparator comp2 compares the line voltage sampling value Line_det with the reference voltage Vref_BO is compared to generate a line voltage undervoltage sensing signal Brown_out_det; the control signal generating module generates a signal for controlling the power switch 204 to be turned on and off based on the line voltage overvoltage sensing signal Line_OVP_det and the line voltage undervoltage sensing signal Brown_out_de.

FIG. 4 shows waveform diagrams of the line voltage Vline, the voltage at the VCC pin, the AVDD signal, the PG signal, and the line voltage sampling value Line_det in the switching power supply chip shown in FIG. 2.

As can be seen from the above description, in the switching power supply chip U2, the high-voltage startup resistor Rst and the line voltage dividing resistor Rdn constitute a line voltage sensing circuit to implement the line voltage sensing function, and the high-voltage startup resistor Rst itself constitutes a high-voltage startup circuit. To achieve the high-voltage start function. Therefore, in the switching power supply circuit using the switching power supply chip U2, since the switching power supply chip U2 has integrated the high-voltage start resistance Rst and the line voltage dividing resistor Rdn, the number of peripheral components of the switching power supply chip U2 is reduced, thereby reducing System cost of the switching power supply circuit; In addition, because the high-voltage startup resistor Rst is used not only for the high-voltage startup function but also for the line voltage sensing function, the power consumption of the conventional line voltage sensing circuit is saved, and the system of the switching power supply circuit is improved effectiveness.

In the embodiment described with reference to FIGS. 2 and 3, when the line voltage sampling value Line_det is greater than the reference voltage Vref_OVP, the line voltage overvoltage sensing signal Line_OVP_det changes from a logic low level to a logic high level, indicating that the power supply input voltage is too high. High, the line voltage overvoltage sensing signal Line_OVP_det will forcibly turn off the power switch 204, thereby protecting the switching power supply circuit from damage; when the line voltage sampling value Line_det is less than the reference voltage Vref_BO, the line voltage undervoltage sensing signal Brown_out_det starts from a logic low The quasi-high level indicates that the input voltage of the power supply is too low, and the brown-out detection signal Brown_out_det of the line voltage will forcibly turn off the power switch 204, thereby protecting the switching power supply circuit from damage; when the line voltage sampling value Line_det is between two reference voltages, Between Vref_OVP and Vref_BO, the line voltage overvoltage sensing signal Line_OVP_det and the line voltage undervoltage sensing signal Brown_out_det are both logic low levels, indicating that the power supply input voltage is within the required range, and the switching power supply circuit works normally.

FIG. 5 is a schematic diagram showing an example implementation circuit of the switching power supply chip shown in FIG. 2. In the implementation circuit shown in FIG. 5, the line voltage overvoltage sensing signal Line_OVP_det and the line voltage are within a predetermined number of pulse width modulation (PWM) cycles after the switching power supply chip U2 is powered on (ie, started). The logic or result of the undervoltage sensing signal Brown_out_det is used directly to control the power switch 204 to be turned on and off. That is, the control signal generating module performs a logical OR operation on the line voltage overvoltage sensing signal Line_OVP_det and the line voltage undervoltage sensing signal Brown_out_det to generate a signal for controlling the power switch 204 to be turned on and off. At this time, if the line voltage Vline is not within the required range, the power switch 204 is immediately turned off.

In the implementation circuit shown in Figure 5, if the input line voltage is within the required range, for example, the Line_off_st signal is invalidated after about 3 PWM cycles (for example, the Line_off_st signal is masked), and then based on the line voltage The over-voltage sensing signal Line_OVP_det and the line-voltage under-voltage sensing signal Brown_out_det are Line_off signals obtained by more complicated processing to control the power switch 204 to be turned on and off.

In the implementation circuit shown in Figure 5, the period of the clock signal clk is Tclk. For the input line voltage overvoltage, when the comparator comp1 senses that the line voltage sampling value Line_det is greater than the reference voltage Vref_OVP, the comparator comp1 outputs The line voltage overvoltage sensing signal Line_OVP_det changes from a logic low level to a logic high level, and the Line_OVP_rst signal changes from a logic low level to a logic high level. A counter composed of (m2 + 1) D flip-flops is enabled. After (2 ^ m2) After the delay of xTclk, the Line_OVP signal changes from a logic low level to a logic high level, triggering the input overvoltage protection function; because the line voltage Vline fluctuates, in order to make the line voltage overvoltage sensing result more accurate, The pressure sensing function adds a peak sensing function. Within the delay of (2 ^ m2) xTclk, if the line voltage overvoltage sensing signal Line_OVP_det is at a logic low level for a duration longer than (2 ^ m1) xTclk (generally Vline period) 1 ~ 2 times and m1 <m2), then the Line_OVP_rst signal will change from a logic high level to a logic low level, and the Line_OVP signal will remain at a logic low level without triggering the input overvoltage protection function; for the input In the case of voltage undervoltage, when the comparator comp2 senses that the line voltage sampling value Line_det is less than the reference voltage Vref_BO, the line voltage undervoltage sensing signal Brown_out_det changes from a logic low level to a logic high level, from (n + 1) D The counter constituted by the flip-flop is enabled. After a delay of (2 ^ n) xTclk, the Brown_out signal becomes a logic high level, triggering the input under-voltage protection function.

That is, the control signal generating module shown in FIG. 2 may include a first delay circuit (for example, a counter composed of (m2 + 1) D flip-flops) and a second delay circuit (for example, (n + 1) Counter consisting of D flip-flops), wherein: the first delay circuit is connected to the output terminal of the comparator comp1, and is used to delay the line voltage overvoltage sensing signal Line_OVP_det by the first time (for example, (2 ^ m2) xTclk); The second delay circuit is connected to the output terminal of the comparator comp2, and is configured to delay the line voltage undervoltage sensing signal Brown_out_det by a second time (for example, (2 ^ n) xTclk). After a predetermined number of pulse width modulation cycles are completed after the switching power supply chip U2 is powered on, the control signal generation module passes the delayed line voltage overvoltage sensing signal (for example, Line_OVP) and the delayed line voltage undervoltage sensing. The measurement signal (for example, Brown_out) performs a logical OR operation to generate a signal for controlling the power switch 204 to be turned on and off.

In addition, in order to make the line voltage overvoltage sensing result more accurate, the control signal generating module shown in FIG. 2 may further include a peak sensing circuit. The peak sensing circuit is connected to the output of the comparator comp1 and the first delay. Between circuits for generating a line voltage peak sensing signal (for example, Line_OVP_rst) by sensing whether the duration of the line voltage overvoltage sensing signal Line_OVP_det is at a logic low level exceeds a third time (for example, (2 ^ m1) xTclk) The first delay circuit delays the line voltage peak sensing signal for a first time, and the control signal generating module performs a logical OR operation on the delayed line voltage peak sensing signal and the delayed line voltage undervoltage sensing signal to A signal is generated to control the power switch 204 to be turned on and off.

Here, the peak sensing circuit includes an inverter, a third delay circuit (for example, a counter composed of (m1 + 1) D flip-flops), and an RS latch, where the inverter is connected to the output of the comparator comp1 Between the terminal and the input of the third delay circuit, the two inputs of the RS latch are respectively connected to the output of the comparator comp1 and the output of the third delay circuit, and the output of the RS latch is connected to the first delay The input of the circuit is connected.

It should be understood that the present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. Therefore, the current embodiment is considered in all aspects as exemplary rather than limiting, the scope of the present invention is defined by the scope of the attached patent application rather than the above description, and the meanings and equivalents falling within the scope of the patent application All changes within the scope of the substance are thus included in the scope of the present invention.

Claims (10)

    A switching power supply chip includes a controller and a power switch. The controller includes a high-voltage diode, a first resistor and a second resistor, a first comparator and a second comparator, a first power MOS field effect transistor, and a first resistor. Two power MOS field effect transistors and a control signal generating module, wherein: the first resistor, the second resistor, and a line voltage of the first power MOS field effect transistor connected to the switching power supply chip; Between the sensing pin and the ground pin; the first resistor and the high voltage diode are connected between the line voltage sensing pin and the power supply pin of the switching power supply chip; the first resistor and the second The connection node between the resistors is connected to the input terminal of the first comparator and the input terminal of the second comparator via the second power MOS field effect transistor; during the startup process of the switching power supply chip, The first power MOS field effect transistor, the second power MOS field effect transistor, and the power switch are all in an off state, and a line voltage received from the outside by the line voltage sensing pin passes through the line voltage. First resistance and said high voltage The polar body provides a starting current for the switching power supply chip; during the operation of the switching power supply chip, the first power MOS field effect transistor and the second power MOS field effect transistor are both in an on state, The first comparator generates a line voltage overvoltage sensing signal by comparing a line voltage sampling value at a connection node between the first resistor and the second resistor with a first reference voltage, and the second comparator A line voltage undervoltage sensing signal is generated by comparing the line voltage sampling value and a second reference voltage, and the control signal generating module is based on the line voltage overvoltage sensing signal and the line voltage undervoltage sensing signal to A signal is generated to control the power switch to be turned on and off.         The switching power supply chip according to item 1 of the scope of patent application, wherein the control signal generating module performs a logical OR operation on the line voltage overvoltage sensing signal and the line voltage undervoltage sensing signal to A signal is generated to control the power switch to be turned on and off.         The switching power supply chip according to item 1 or 2 of the scope of patent application, wherein the control signal generating module includes: a first delay circuit connected to an output terminal of the first comparator for connecting the line The voltage overvoltage sensing signal is delayed for a first time; a second delay circuit is connected to the output terminal of the second comparator, and is configured to delay the line voltage undervoltage sensing signal for a second time, wherein the control signal The generating module performs a logical OR operation on the delayed line voltage overvoltage sensing signal and the delayed line voltage undervoltage sensing signal to generate a signal for controlling the power switch to be turned on and off.         The switching power supply chip according to item 3 of the scope of patent application, wherein the control signal generating module further includes: a peak sensing circuit connected between the output end of the first comparator and the first delay circuit. For generating a line voltage peak sensing signal by sensing whether the duration of the line voltage overvoltage sensing signal being at a logic low level exceeds a third time, wherein the first delay circuit senses the line voltage peak The measured signal is delayed for a first time, and the control signal generating module generates and controls the power switch by performing a logical OR operation on the delayed line voltage peak sensing signal and the delayed line voltage undervoltage sensing signal. On and off signals.         The switching power supply chip according to item 4 of the scope of patent application, wherein the peak sensing circuit includes an inverter, a third delay circuit, and an RS latch, wherein the inverter is connected to the first Between an output terminal of a comparator and an input terminal of the third delay circuit, two input terminals of the RS latch are respectively connected to an output terminal of the first comparator and an output of the third delay circuit. And the output terminal of the RS latch is connected to the input terminal of the first delay circuit.         The switching power supply chip according to item 5 of the patent application scope, wherein the first delay circuit includes a first number of D flip-flops, the second delay circuit includes a second number of D flip-flops, and the third The delay circuit includes a third number of D flip-flops, wherein the third number is smaller than the first number.         The switching power supply chip according to item 1 of the patent application scope, wherein the gate input of the first power MOS field effect transistor is a power-on completion signal of the chip, and the gate of the second power MOS field effect transistor is The input is a low-voltage power supply inside the switching power supply chip.         The switching power supply chip according to item 1 of the scope of patent application, wherein a connection node between the first resistor and the second resistor is connected to the first comparison via the second power MOS field effect transistor. A non-inverting input terminal of the comparator and an inverting input terminal of the second comparator.         The switching power supply chip according to item 1 of the scope of patent application, wherein the first power MOS field effect transistor is a MOS tube, and the second power MOS field effect transistor is a high voltage MOS tube.         A switching power supply circuit includes the switching power supply chip according to any one of claims 1 to 9.