TWI831398B - Switching power supply system and control chip and control method thereof - Google Patents

Abstract

A switching power supply system and its control chip and control method are provided. The switching power supply system includes an inductor and a power switch, and the control chip is configured to: based on a dimming control signal for adjusting the brightness of the light-emitting diode, a current detection signal for characterizing the inductor current flowing through the inductor, A reference voltage that generates a turn-off control signal for controlling the power switch to change from the on-state to the off-state; based on the dimming control signal, the current detection signal, the demagnetization detection signal used to characterize the demagnetization of the inductor, and the second reference voltage to generate a conduction control signal for controlling the power switch from an off state to an on state; and based on the off control signal and the conduction control signal, generate a pulse width modulation signal for controlling the on and off of the power switch, The first reference voltage is used to control the system output current of the switching power supply system, and the second reference voltage is used to control the duration during which the power switch is in an off state.

Description

Switching power supply system and control chip and control method thereof

The present invention relates to the field of circuits, and more specifically to a switching power supply system and its control chip and control method.

Switching power supply, also known as switching power supply and switching converter, is a type of power supply. The function of the switching power supply is to convert a level of voltage to the user's desired voltage through different architectures (for example, fly-back architecture, buck architecture, or boost architecture, etc.) required voltage or current.

A control chip for a switching power supply system according to an embodiment of the present invention, wherein the switching power supply system includes an inductor and a power switch, and the control chip is configured to: based on a dimming control signal for adjusting the brightness of a light-emitting diode, A current detection signal used to characterize the inductor current flowing through the inductor and a first reference voltage are used to generate a shutdown control signal used to control the power switch from an on state to an off state; based on the dimming control signal and current detection signal, a demagnetization detection signal used to characterize the demagnetization condition of the inductor, and a second reference voltage to generate a conduction control signal for controlling the power switch from an off state to an on state; and based on the off control signal and the conduction control signal, Generate a pulse width modulation signal for controlling the on and off of the power switch, where the first reference voltage is used to control the system output current of the switching power supply system, and the second reference voltage is used to control the power switch to be in an off state duration.

A control method for a switching power supply system according to an embodiment of the present invention, wherein the switching power supply system includes an inductor and a power switch, the control method includes: based on a dimming control signal for adjusting the brightness of a light-emitting diode, for A current detection signal representing the inductor current flowing through the inductor and a first reference voltage are generated to control the power switch from a conductive state to a A shutdown control signal in the shutdown state; based on the dimming control signal, the current detection signal, the demagnetization detection signal used to characterize the demagnetization of the inductor, and the second reference voltage, it is generated to control the power switch from the shutdown state to the conduction state. state conduction control signal; and based on the turn-off control signal and the conduction control signal, generate a pulse width modulation signal for controlling the turn-on and turn-off of the power switch, wherein the first reference voltage is used to control the system output of the switching power supply system The magnitude of the current and the second reference voltage are used to control the duration the power switch is in the off state.

A switching power supply system according to an embodiment of the present invention includes the above-mentioned control chip.

100:Switching power supply system

102:Control chip

1022: Low dropout voltage regulator module

1024: Demagnetization detection module

1026:Constant current control module

1028:Driver module

202: Dimming signal processing unit

204: Sampling unit

206: Error amplifier

208:Detection unit

210: Comparator

212: Clamp unit

214: Delayed signal generation unit

2144: Compensation signal processing circuit

2146: Comparator

216:Digital unit

2162: Voltage-current conversion circuit

BD1: Rectifier

C1: input capacitor

C2: Output load capacitance

C201, C202, C501: capacitor

CMP: Compensation control signal

CS: current detection signal

CS_sen: current amplified signal

CS_smp: current sampling signal

D1: Diode

DCM: discontinuous conduction mode

Delay: time delay signal

Dem: demagnetization detection signal

DIM: dimming control signal

Gate: gate drive signal

HV:pin

Idim: dimming reference current

IL: inductor current

Iout: system output current

K201, K501, K502: switch

L1: Inductor

M303, M304, M305, M306: current mirror

PWM: pulse width modulation signal

PWM_off: turn off control signal

PWM_on: conduction control signal

Q1: Power switch

R1: current detection resistor

R301, R302, R303, R501: Resistors

Ramp: ramp control signal

Td: delay time

Tdem: The duration during which the inductor L1 is in the demagnetization state

Toff: the duration of power switch Q1 in the off state

Ton: the duration that the power switch Q1 is in the on state

U301, U302, U501: Amplifier

U502: Inverter

V1, V2, Vref: reference voltage

Vchop: chopped reference voltage

Vd: delay control signal

Vdim: dimming reference voltage

VIN: line voltage

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the drawings, in which: Figure 1 shows an example circuit diagram of a switching power supply system for dimmable LED lighting according to an embodiment of the present invention.

FIG. 2 shows an example circuit diagram of the constant current control module shown in FIG. 1 .

FIG. 3 shows an example circuit diagram of the compensation signal processing circuit shown in FIG. 2 .

FIG. 4 shows the operating waveform diagrams of multiple signals in the constant current control module shown in FIG. 2 .

FIG. 5 shows an example circuit diagram of the dimming signal processing unit shown in FIG. 2 .

FIG. 6 shows an example circuit diagram of the digital unit shown in FIG. 2 .

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modifications, substitutions and improvements of elements, components and algorithms without departing from the spirit of the invention. In the diagram and the description below In the description, well-known structures and techniques are not shown in order to avoid unnecessary obscurity of the present invention.

In recent years, Light Emitting Diodes (LEDs) have been widely used in social production due to their long life, low cost, and small size compared to traditional incandescent lamps, halogen lamps, or fluorescent lamps and other lighting products. All aspects of life. The brightness of the LED itself is mainly controlled by the current flowing through the LED. The brightness of the LED can be adjusted by adjusting the current flowing through the LED.

In a switching power supply system for LED lighting, flickering is easily caused by controlling the current flowing through the LED in pulse width modulation (PWM) chopper mode to adjust the brightness of the LED. In order to prevent stroboscopic occurrence, the brightness of the LED is generally adjusted by adjusting the current flowing through the LED in a continuously changing analogy. However, in the case of realizing LED low-brightness lighting, when the brightness of the LED is deeply adjusted by analogy, there are situations where the detected signal is weak and difficult to detect, and the control chip in the switching power supply system for LED lighting The input offset voltage of the internal circuit will cause the problem of insufficient adjustment depth of the LED brightness.

In view of the above problems, a switching power supply system and its control chip and control method according to embodiments of the present invention are proposed, which can realize deep adjustment of the brightness of LEDs through analogy.

FIG. 1 shows an example circuit diagram of a switching power supply system 100 for dimmable LED lighting according to an embodiment of the present invention. As shown in Figure 1, the switching power supply system 100 adopts a BUCK architecture and includes a rectifier BD1, an input capacitor C1, a diode D1, an inductor L1, an output load capacitor C2, a power switch Q1, a current detection resistor R1, and a control chip 102 , where: the line voltage VIN supplies power to the control chip 102 via the HV pin of the control chip 102; the control chip 102 is based on the dimming control signal DIM used to adjust the brightness of the LED and the inductor current IL that represents the flow through the inductor L1 (not shown in the figure) (shown), the current detection signal CS outputs the gate driving signal Gate used to drive the power switch Q1 to turn on and off.

As shown in Figure 1, the control chip 102 includes a low dropout regulator (LDO) module 1022, a demagnetization detection module 1024, a constant current control module 1026, and a driver module 1028, where: the low dropout regulator Voltage module 1022 is controlled based on line voltage VIN The internal circuit of the chip 102 is powered; the demagnetization detection module 1024 generates a demagnetization detection signal Dem representing the demagnetization condition of the inductor L1 based on the gate drive signal Gate and outputs the demagnetization detection signal Dem to the constant current control module 1026 (it should be understood that Yes, the way in which the demagnetization detection module 1024 detects the demagnetization of the inductor L1 is not limited to this. The demagnetization detection module 1024 can also generate a demagnetization detection signal Dem) based on the demagnetization detection related signal received from the outside via the chip pin; constant current control Based on the reference voltage Vref, the demagnetization detection signal Dem, and the current detection signal CS, the module 1026 generates a pulse width modulation signal PWM for controlling the on and off of the power switch Q1 and outputs the pulse width modulation signal PWM to the driver module. Group 1028; the driver module 1028 generates the gate drive signal Gate based on the pulse width modulation signal PWM and outputs the gate drive signal Gate to the gate of the power switch Q1. Here, the dimming control signal DIM can be a DC voltage signal or a pulse width modulation pulse signal, which is used to control the size of the system output current Iout (ie, the current flowing through the LED); the demagnetization detection signal Dem participates in the system constant current control and dimming control; the current detection signal CS is used to implement closed-loop constant current control of the switching power supply system 100 .

In the switching power supply system 100 shown in FIG. 1 , system constant current control and dimming control are mainly implemented through the constant current control module 1026 . FIG. 2 shows an example circuit diagram of the constant current control module 1026 shown in FIG. 1 . As shown in Figure 2, the constant current control module 1026 is configured to: based on the dimming control signal DIM, the current detection signal CS, and the reference voltage Vref, generate a switch for controlling the power switch Q1 to change from the on state to the off state. Off control signal PWM_off; based on the dimming control signal DIM, current detection signal CS, demagnetization detection signal Dem, and reference voltage V1, the conduction control signal PWM_on for controlling the power switch Q1 to change from the off state to the on state is generated (in the figure (not shown); and based on the off control signal PWM_off and the on control signal PWM_on, generate a pulse width modulation signal PWM for controlling the on and off of the power switch Q1, wherein the reference voltage Vref is used to control the switching power supply system 100 The size of the system output current Iout, the reference voltage V1 is used to control the duration of the power switch Q1 in the off state.

As shown in Figure 2, in some embodiments, the constant current control module 1026 includes a dimming signal processing unit 202, a sampling unit 204, an error amplifier 206, a capacitor C201, a detection unit 208, a comparator 210, and a clamp unit 212. , delayed signal generating unit 214, and digital unit 216, and the input signals of the constant current control module 1026 include the dimming control signal DIM, the current detection signal CS, the demagnetization detection signal Dem, and the reference voltages Vref, V1, and V2, where: the dimming signal processing unit 202 is based on dimming The control signal DIM and the reference voltage Vref generate the dimming reference voltage Vdim; the sampling unit 204 and the detection unit 208 respectively generate the current sampling signal CS_smp and the current amplification signal CS_sen based on the current detection signal CS; both the error amplifier 206 and the capacitor C201 are based on the modulation signal. The optical reference voltage Vdim and the current sampling signal CS_smp generate a compensation control signal CMP; the clamping unit unit 212 generates a clamping unit control signal (not shown in the figure) based on the compensation control signal CMP and the reference voltage V2, where the reference voltage V2 The lower clamping element is used to compensate the control signal CMP; the comparator 210 generates the off control signal PWM_off based on the clamping element control signal and the current amplification signal CS_sen; the delay signal generation unit 214 is based on the dimming reference voltage Vdim and the compensation control signal CMP. , demagnetization detection signal Dem, and reference voltage V1 to generate the time delay signal Delay; the digital unit 216 generates the conduction control signal PWM_on based on the demagnetization detection signal Dem and the time delay signal Delay, and generates a pulse based on the conduction control signal PWM_on and the off control signal PWM_off. Wide modulation signal PWM.

In the control chip 102 for the switching power supply system 100, by using the reference voltage V1 to control the duration of the power switch Q1 in the off state, it is possible to avoid the impact on the brightness of the LED due to the input offset voltage of the internal circuit of the control chip 102 The problem of insufficient adjustment depth, and by using the reference voltage V2 to clamp the compensation control signal CMP, can avoid the situation where the detected signal is weak and difficult to detect when deeply adjusting the brightness of the LED by analogy. .

As shown in FIG. 2 , in some embodiments, the dimming signal processing unit 202 operates on the dimming control signal DIM and the reference voltage Vref to generate the dimming reference voltage Vdim and outputs the dimming reference voltage Vdim to the error amplifier 206 used to control the size of the system output current Iout; the sampling unit 204 generates the current sampling signal CS_smp by sampling the current detection signal CS and outputs the current sampling signal CS_smp to the error amplifier 206; the error amplifier 206 generates the current sampling signal CS_smp by sampling the dimming reference voltage Vdim and The current sampling signal CS_smp performs error amplification to generate an error representation signal (not shown in the figure); the capacitor C201 integrates the error representation signal, The compensation control signal CMP is generated and output to the clamping unit unit 212; the clamping unit unit 212 clamps the compensation control signal CMP to generate a clamping unit control signal and outputs the clamping unit control signal. to the comparator 210. When the compensation control signal CMP is less than the reference voltage V2, the compensation control signal CMP is clamped at the V2 level; the detection unit 208 detects and amplifies the current detection signal CS to generate the current amplification signal CS_sen and The current amplification signal is output to the comparator 210; the comparator 210 compares the clamp element control signal and the current amplification signal CS_sen to generate the off control signal PWM_off and output the off control signal PWM_off to the digital unit 216. Here, it should be noted that when the compensation control signal CMP is not less than the reference voltage V2, the clamping element control signal is the compensation control signal CMP itself.

As shown in Figure 2, in some embodiments, the delay signal generation unit 214 includes a voltage-current conversion circuit 2142, a compensation signal processing circuit 2144, a switch K201, a comparator 2146, and a capacitor C202, wherein: the voltage-current conversion circuit 2142 Based on the dimming reference voltage Vdim, the dimming reference current Idim is generated; the capacitor C202 and the switch K201 generate the slope control signal Ramp based on the demagnetization detection signal Dem and the dimming reference current Idim; the compensation signal processing circuit 2144 is based on the compensation control signal CMP and The reference voltage V1 generates a delay control signal Vd; the comparator 2146 generates a time delay signal Delay based on the ramp control signal Ramp and the delay control signal Vd. For example, the voltage-to-current conversion circuit 2142 generates the dimming reference current Idim by performing voltage-to-current conversion on the dimming reference voltage Vdim; the capacitor C202 is coupled to the switch K201, and the turning on and off of the switch K201 is affected by the demagnetization detection signal Dem. Control of the inverted signal (that is, the switch K201 controls the charging of the capacitor C202 by the dimming reference current Idim based on the demagnetization detection signal Dem); when the demagnetization detection signal Dem is a logic low level, the switch K201 is turned on, and the dimming reference current Idim is incorrect. Capacitor C202 is charged, and the voltage on capacitor C202, that is, the voltage of slope control signal Ramp is 0V; when the demagnetization detection signal Dem is a logic high level, switch K201 is turned off, and the dimming reference current Idim charges capacitor C202, and the voltage on capacitor C202 voltage, that is, the voltage of the ramp control signal Ramp is greater than 0V; the compensation signal processing circuit 2144 generates the delay control signal Vd by operating on the voltage of the compensation control signal CMP and the reference voltage V1; The comparator 2146 generates the time delay signal Delay by comparing the ramp control signal Ramp and the delay control signal Vd.

In the constant current control module 1026 shown in Figure 2, the level of the dimming reference voltage Vdim corresponds to the size of the system output current Iout, that is, when the dimming reference voltage Vdim is high, the system output current Iout is large; when the dimming reference voltage Vdim is high, the system output current Iout is large; When the reference voltage Vdim is low, the system output current Iout is small. The compensation control signal CMP is the output signal of the error amplifier 206, and the voltage change of the compensation control signal CMP is in the same direction as the change direction of the dimming reference voltage Vdim. When the dimming reference voltage Vdim becomes high, the voltage of the compensation control signal CMP becomes high. When the dimming reference voltage Vdim becomes low, the voltage of the compensation control signal CMP becomes low.

The working process of the constant current control module 1026 shown in Figure 2 is divided into three stages as the dimming reference voltage Vdim (or compensation control signal CMP) changes: When the system output current Iout is large, the compensation control signal CMP The voltage is greater than the reference voltage V1, the switching power supply system 100 operates in a quasi-resonant (QR) mode, and the dimming control signal DIM adjusts the system output current Iout by controlling the peak current flowing through the inductor L1. In the switching power supply system 100 shown in FIG. 1, the current detection signal CS is used to represent the inductor current IL flowing through the inductor L1. The peak voltage of the current detection signal CS corresponds to the peak current flowing through the inductor L1, and the current detection signal CS The peak voltage of CS is controlled by the compensation control signal CMP. The time delay signal Delay is generated by comparing the voltage on the capacitor C202, that is, the ramp control signal Ramp and the delay control signal Vd. Because the voltage of the compensation control signal CMP is greater than the reference voltage V1, the delay control signal Vd generated by the compensation signal processing circuit 2144 is 0V. , so the delay time of the time delay signal Delay is also 0, which makes the switching power supply system 100 work in the QR mode.

When the system output current Iout is small, the voltage of the compensation control signal CMP is greater than the reference voltage V2 and less than the reference voltage V1, the switching power supply system 100 works in the Discontinuous Conduction Mode (DCM), and the dimming control signal DIM passes through the control The peak current flowing through the inductor L1 and the time delay signal Delay adjust the system output current Iout. In the constant current control module 1026 shown in Figure 2, the operation control of the compensation signal processing circuit 2144 satisfies Equation 1: V _d =k×(V ₁ -V _CMP ) <Equation 1>

Among them, k is the fixed coefficient of the design. Figure 3 shows an example circuit diagram of the compensation signal processing circuit 2144 shown in Figure 2, in which the resistance values of resistors R301 and R302 are fixed ratios (R301=R302 is set in Figure 3), and the mirror current ratios of current mirrors M303 and M304 are is 1, the mirror current ratio of current mirrors M305 and M306 is also 1, so the voltage of the delayed control signal Vd can be obtained by Equation 2:

Among them, R303/R301 corresponds to k in Equation 1 and is a fixed value.

That is, the compensation signal processing circuit 2144 generates the delay control signal Vd by scaling the difference between the voltage of the compensation control signal CMP and the reference voltage V1.

When the system output current Iout is smaller, the voltage of the compensation control signal CMP is equal to the reference voltage V2, and the switching power supply system 100 works in the discontinuous conduction mode (DCM). At this time, the compensation control signal CMP is clamped at V2 by the clamping unit 212 The system output current Iout cannot be adjusted on the level. The purpose of setting the minimum voltage of the compensation control signal CMP is to control the minimum peak current flowing through the inductor L1 during the dimming process to ensure that the control-related detection signals can be detected. At this stage, the voltage of the delay control signal Vd is also fixed at k*V2, but as the dimming reference voltage Vdim becomes lower, the dimming reference current Idim generated by the voltage-current conversion circuit 2142 based on the dimming reference voltage Vdim becomes smaller. , as shown in Equation 3:

Among them, Rdim is the equivalent resistance value of the voltage-current conversion circuit 2142 used to convert the dimming reference voltage Vdim into the dimming reference current Idim. The delay time Td corresponding to the time delay signal Delay increases with the dimming reference voltage Vdim. Decrease and increase, so that a deeper degree of dimming control can be achieved (that is, the brightness of the LED can be adjusted to a deeper degree). Figure 4 shows the working waveform diagrams of multiple signals in the constant current control module 1026 shown in Figure 2, where Ton Indicates the duration when the power switch Q1 is in the on state, Toff indicates the duration when the power switch Q1 is in the off state, Tdem indicates the duration in which the inductor L1 is in the demagnetization state, and Td indicates the moment when the power switch Q1 changes from the off state to the on state. Delay time relative to the time when inductor L1 ends demagnetization.

In the switching power supply system 100 shown in Figure 1, the dimming control signal DIM can be either an analog voltage signal or a PWM pulse signal. For deep dimming applications, the dimming control signal DIM is usually a PWM pulse signal, which is convenient for use The control chip in the switching power supply system of dimmable LED lighting is precisely controlled.

FIG. 5 shows an example circuit diagram of the dimming signal processing unit 202 shown in FIG. 2 . As shown in Figure 5, the dimming signal processing unit 202 includes an amplifier U501, switches K501 and K502, a resistor R501, a capacitor C501, and an inverter U502. The forward input end of the amplifier U501 is connected to the reference voltage Vref, and the amplifier U501 The negative input end and output end are connected to form a buffer structure. The output end of amplifier U501 is connected to switch K501. One end of switch K501 is connected to the output end of amplifier U501, and the other end is connected to switch K502 and resistor R501. The control signal of switch K501 is Dimming control signal DIM. When the dimming control signal DIM is a logic high level, the switch K501 is in the on state. When the dimming control signal DIM is a logic low level, the switch K501 is in an off state. One end of the switch K502 is connected to the switch K501 and The resistor R501 is connected, and one end is connected to the ground; the control signal of the switch K502 is the output signal after the inverter U502 inverts the dimming control signal DIM. When the dimming control signal DIM is a logic low level, the switch K502 is in the on state. , when the dimming control signal DIM is at a logic high level, the switch K502 is in the off state; the switches K501 and K502 are alternately turned on within a pulse period of the dimming control signal DIM; one end of the resistor R501 is connected to the switches K501 and K502, and the other end is connected to the capacitor C501 and dimming reference voltage Vdim; one end of capacitor C501 is connected to resistor R501 and dimming reference voltage Vdim, and one end is connected to ground. In the dimming signal processing unit 202, the reference voltage Vref is chopped by using the dimming control signal DIM and its inverted logic signal to control the on and off of the switches K501 and K502 to generate the chopped reference voltage Vchop; by using The low-pass filter formed by resistor R501 and capacitor C501 filters the chopped reference voltage Vchop to generate the dimming reference voltage Vdim. In other words, the dimming signal processing unit 202 generates the dimming reference voltage Vdim by multiplying the duty cycle of the dimming control signal DIM and the reference voltage Vref, as shown in Equation 4: V _dim =Duty×V _ref < Equation 4>

FIG. 6 shows an example circuit diagram of digital unit 216 shown in FIG. 2 . As shown in FIG. 6 , the digital unit 216 can output the pulse width modulation signal PWM based on the off control signal PWM_off, the demagnetization detection signal Dem, and the time delay signal Delay, so that the constant current control module 1026 shown in FIG. 2 can operate as shown in FIG. The timing logic shown in 4 is controlled.

The control chip and control method for the switching power supply system according to the embodiment of the present invention are not limited to the switching power supply system using the BUCK architecture. For switching power supply systems using other architectures, such as fly-back, BOOST, BUCK-BOOST, etc. The same applies, you just need to adjust the current detection signal CS and the control of the constant current control module accordingly.

The present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. For example, algorithms described in specific embodiments may be modified without departing from the basic spirit of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and the meanings and equivalents falling within the claims. All changes within the scope are therefore included in the scope of the invention.

100:Switching power supply system

1026:Constant current control module

202: Dimming signal processing unit

204: Sampling unit

206: Error amplifier

208:Detection unit

210: Comparator

212: Clamp unit

214: Delayed signal generation unit

2142: Voltage-current conversion circuit

2144: Compensation signal processing

2146: Comparator

216:Digital unit

C201, C202: capacitor

CMP: Compensation control signal

CS: current detection signal

CS_sen: current amplified signal

CS_smp: current sampling signal

Delay: time delay signal

Dem: demagnetization detection signal

DIM: dimming control signal

Idim: dimming reference current

K201: switch

PWM: pulse width modulation

PWM_off: turn off control signal

Ramp: ramp control signal

V1, V2: voltage

Vd: delay control signal

Vdim: dimming reference voltage

Vref: shutdown to reference voltage

Claims (21)

A control chip for a switching power supply system, wherein the switching power supply system includes an inductor and a power switch, the control chip is configured to: based on a dimming control signal for adjusting the brightness of a light-emitting diode, for characterizing The current detection signal of the inductor current flowing through the inductor and the first reference voltage generate a shutdown control signal for controlling the power switch to change from the on state to the off state; based on the dimming control signal, the The current detection signal, the demagnetization detection signal used to characterize the demagnetization condition of the inductor, and the second reference voltage are used to generate a conduction control signal for controlling the power switch to change from an off state to an on state; and based on the The turn-off control signal and the turn-on control signal generate a pulse width modulation signal used to control the turn-on and turn-off of the power switch, wherein the first reference voltage is used to control the system output current of the switching power supply system. The second reference voltage is used to control the duration during which the power switch is in the off state. The control chip according to claim 1, further configured to: generate a dimming reference voltage based on the dimming control signal and the first reference voltage; generate a current sampling signal and current amplification based on the current detection signal signal; based on the dimming reference voltage and the current sampling signal, a compensation control signal is generated; based on the compensation control signal and a third reference voltage, a clamping element control signal is generated, wherein the third reference voltage is used the lower clamping element of the compensation control signal; and generating the turn-off control signal based on the clamping element control signal and the current amplification signal. The control chip of claim 2 is further configured to generate the dimming reference voltage by multiplying the duty cycle of the dimming control signal by the first reference voltage. The control chip according to claim 2 is further configured to: generate the current sampling signal by sampling the current detection signal; By performing error amplification on the current sampling signal and the dimming reference voltage, an error representation signal is generated; by integrating the error amplification signal, the compensation control signal is generated; by using the third reference voltage to The compensation control signal is applied to the clamping element to generate the clamping element control signal. The control chip according to claim 2, further configured to: generate the current amplification signal by detecting and amplifying the current detection signal; and compare the current amplification signal with the clamping element control signal. , generating the shutdown control signal. The control chip according to claim 2, further configured to: generate a dimming reference current based on the dimming reference voltage; generate a slope control signal based on the demagnetization detection signal and the dimming reference current; The compensation control signal and the second reference voltage generate a delay control signal; a time delay signal is generated based on the ramp control signal and the delay control signal; and a time delay signal is generated based on the time delay signal and the demagnetization detection signal. The conduction control signal. The control chip of claim 6 is further configured to generate the dimming reference current by performing voltage-current conversion on the dimming reference voltage. The control chip of claim 6 is further configured to generate the ramp control signal by controlling the dimming reference current to charge a capacitor based on the demagnetization detection signal. The control chip of claim 6 is further configured to generate the delay control signal by scaling the difference between the voltage of the compensation control signal and the second reference voltage. The control chip according to claim 6 is further configured to generate the conduction control signal by comparing the time delay signal and the demagnetization detection signal. A control method for a switching power supply system, wherein the switching power supply The source system includes an inductor and a power switch, and the control method includes: based on a dimming control signal for adjusting the brightness of a light-emitting diode, a current detection signal for characterizing an inductor current flowing through the inductor, and a first reference voltage to generate a shutdown control signal for controlling the power switch to change from an on state to an off state; based on the dimming control signal, the current detection signal, and demagnetization detection used to characterize the demagnetization of the inductor. signal, and a second reference voltage, generating a conduction control signal for controlling the power switch from an off state to an on state; and based on the off control signal and the conduction control signal, generating a conduction control signal for controlling the power switch. The pulse width modulation signal of on and off, wherein the first reference voltage is used to control the system output current of the switching power supply system, and the second reference voltage is used to control the power switch to be off. The duration of the state. The control method according to claim 11, wherein the process of generating the shutdown control signal includes: generating a dimming reference voltage based on the dimming control signal and the first reference voltage; based on the current detection signal , generate a current sampling signal and a current amplification signal; generate a compensation control signal based on the dimming reference voltage and the current sampling signal; generate a clamping element control signal based on the compensation control signal and the third reference voltage, where, The third reference voltage is used for a lower clamping element of the compensation control signal; and the turn-off control signal is generated based on the clamping element control signal and the current amplification signal. The control method of claim 12, wherein the dimming reference voltage is generated by multiplying the duty cycle of the dimming control signal and the first reference voltage. The control method according to claim 12, wherein the process of generating the shutdown control signal further includes: generating the current sampling signal by sampling the current detection signal; and generating the current sampling signal by summing the current sampling signal and the current sampling signal. The dimming reference voltage is used to amplify the error and generate an error representation signal; The compensation control signal is generated by integrating the error amplification signal; the clamping control signal is generated by clamping the compensation control signal using the third reference voltage. The control method according to claim 12, wherein the process of generating the shutdown control signal further includes: generating the current amplification signal by detecting and amplifying the current detection signal; and generating the current amplification signal by summing the current amplification signal and The clamping element control signals are compared to generate the shutdown control signal. The control method according to claim 12, wherein the process of generating the conduction control signal includes: generating a dimming reference current based on the dimming reference voltage; based on the demagnetization detection signal and the dimming reference current, Generate a ramp control signal; generate a delay control signal based on the compensation control signal and the second reference voltage; generate a time delay signal based on the ramp control signal and the delay control signal; based on the time delay signal and the The demagnetization detection signal is used to generate the conduction control signal. The control method according to claim 16, wherein the dimming reference current is generated by performing voltage-current conversion on the dimming reference voltage. The control method of claim 16, wherein the ramp control signal is generated by controlling the dimming reference current to charge a capacitor based on the demagnetization detection signal. The control method of claim 16, wherein the delay control signal is generated by scaling a difference between the voltage of the compensation control signal and the second reference voltage. The control method according to claim 16, wherein the conduction control signal is generated by comparing the time delay signal and the demagnetization detection signal. A switching power supply system, including the control chip described in any one of claims 1 to 10.

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