TW202404237A - Constant-current switching power supply system and control circuit and control method thereof - Google Patents

Abstract

The invention provides a constant-current switching power supply system and a control circuit and a control method thereof, the constant-current switching power supply system comprises an inductor and a power switch, and the control circuit is configured to control the power switch to be switched on and off based on a pulse width modulation signal used for controlling the power switch to be switched on and switched off and a current detection signal representing inductive current flowing through the inductor. Generating a current sampling signal associated with the current detection signal; a pulse width modulation signal is generated based on the current sampling signal, a demagnetization detection signal representing the demagnetization condition of the inductor and a reference voltage, the current sampling signal is the current detection signal itself when the current sampling signal is at a first logic level, and the current sampling signal is the current detection signal itself when the current sampling signal is at a second logic level. And when the pulse width modulation signal is at the second logic level, the pulse width modulation signal is a sampling signal generated by sampling the current detection signal.

Description

Constant current switching power supply system and its control circuit and control method

The present invention relates to the field of circuits, and more specifically to a constant current switching power supply system and its control circuit 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 circuit for a constant current switching power supply system according to an embodiment of the present invention, wherein the constant current switching power supply system includes an inductor and a power switch, and the control circuit is configured to: based on the control circuit used to control the turn-on and turn-off of the power switch. The pulse width modulation signal and the current detection signal representing the inductor current flowing through the inductor generate a current sampling signal associated with the current detection signal; and based on the current sampling signal, the demagnetization detection signal representing the demagnetization of the inductor, and the reference voltage, Generating a pulse width modulation signal, wherein the current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and the current detection signal is sampled when the pulse width modulation signal is at a second logic level generated sampled signal.

A control method for a constant current switching power supply system according to an embodiment of the present invention, wherein the constant current switching power supply system includes an inductor and a power switch. The control method includes: based on a pulse width used to control the turn-on and turn-off of the power switch. The modulation signal and the current detection signal representing the inductor current flowing through the inductor generate a current sampling signal associated with the current detection signal; and based on the current sampling signal, the demagnetization detection signal representing the demagnetization of the inductor, and the reference voltage, generate a pulse wide modulation signal, wherein the current sampling signal is at the first logic level when the pulse width modulation signal is is the current detection signal itself, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at the second logic level.

A constant current switching power supply system according to an embodiment of the present invention includes the above control circuit.

100:Constant current switching power supply system

102:Low dropout voltage regulator module

1028:Driver module

104: Demagnetization detection module

106:Constant current control module

108:Driver module

BD1: Rectifier

C1: input capacitor

C2: Output load capacitance

C201, C202, C203, C303: capacitor

CMP: error compensation signal

CS: current detection signal

CS_peak: peak voltage

CS_sample: current sampling signal

D1: Diode

Dem: demagnetization detection signal

Gate: Gate drive signal

HV:pin

IL,I _{L_Ton} ,I _{L_Toff} : inductor current

Iout: system output current

K201, K202, K203, K501: switch

L: inductance

L1: Inductor

PWM: pulse width modulation signal

PWM_off: turn off control signal

Q1: Power switch

R1: current detection resistor

R502, R503: Resistor

Ramp: ramp signal

SW1: switch control signal

Ton: duration

U100: Control chip

U200, U300: Sampling control unit

U201, U301: error amplifier

U202, U302: ramp generation unit

U203, U303: comparator

U204, U304: RS flip-flop

VIN: system bus voltage

Vout: system output voltage

Vref: reference voltage

The present invention can be better understood from the following description of specific embodiments of the invention in conjunction with the drawings, in which:

FIG. 1 shows an example circuit diagram of a constant current switching power supply system for light emitting diode (LED) lighting according to an embodiment of the present invention.

FIG. 2 shows a timing diagram of multiple signals of the constant current switching power supply system shown in FIG. 1 .

FIG. 3 shows a circuit diagram of an example circuit implementation of the constant current control unit shown in FIG. 1 .

FIG. 4 shows a timing diagram of a plurality of signals related to the sampling control unit shown in FIG. 3 .

FIG. 5 shows a circuit diagram of another example circuit implementation of the constant current control unit shown in FIG. 1 .

FIG. 6 shows a timing diagram of a plurality of signals related to the sampling control unit shown in FIG. 5 .

FIG. 7 shows a circuit diagram of an example circuit implementation of the error amplifier shown in FIG. 5 .

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 drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

In recent years, light-emitting diodes (LEDs) have been widely used in all aspects of social production and life due to their advantages such as long life, low cost, and small size compared to traditional incandescent lamps, halogen lamps, or fluorescent lamps and other lighting products. , the brightness of the LED itself is mainly controlled by the current flowing through the LED, so high-precision constant current control is designed for constant current switching power supply systems for LED lighting. key.

FIG. 1 shows an example circuit diagram of a constant current switching power supply system 100 for LED lighting according to an embodiment of the present invention. As shown in Figure 1, the constant current switching power supply system 100 adopts a BUCK architecture and mainly includes a rectifier BD1, input capacitor C1, diode D1, inductor L1, output load capacitor C2, power switch Q1, current detection resistor R1, and control Chip U100, in which: the system bus voltage VIN supplies power to the control chip U100 via the HV pin of the control chip U100; the control chip U100 is based on a current detection signal (Current Sensor) that represents the inductor current IL (not shown in the figure) flowing through the inductor L1 , CS), output the gate drive signal Gate used to drive the power switch Q1 on and off.

As shown in Figure 1, the control chip U100 includes a low dropout linear regulator (LDO) module 102, a demagnetization detection module 104, a constant current control module 106, and a driver module 108, where: low dropout The voltage regulator module 102 supplies power to the internal circuit of the control chip U100 based on the system bus voltage VIN; the demagnetization detection module 104 generates the demagnetization detection signal Dem of 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 106 (it should be understood that the way in which the demagnetization detection module 104 detects the demagnetization of the inductor L1 is not limited to this. The demagnetization detection module 104 can also be based on demagnetization detection related signals received from the outside via the chip pins. to generate the demagnetization detection signal Dem); the constant current control module 106 generates a pulse width modulation signal (Pulse Width Modulation, PWM) and outputs the pulse width modulation signal PWM to the driver module 108; the driver module 108 generates the gate drive signal Gate based on the pulse width modulation signal PWM and outputs the gate drive signal Gate to the power switch Q1 gate.

In the constant current switching power supply system 100 shown in Figure 1, the power switch Q1 is in the on state when the pulse width modulation signal PWM is at a logic high level, and is in an off state when the pulse width modulation signal PWM is at a logic low level; refer to The voltage Vref is used to control the system output current Iout of the constant current switching power supply system 100; the demagnetization detection signal Dem is used for system constant current control, and is also used to control the constant current switching power supply system 100 to work in the intermittent conduction mode. (Discontinuous Conduction Mode, DCM) or quasi-resonant (Quasi-Resonant, QR) mode; the current detection signal CS is used to implement closed-loop constant current control of the constant current switching power supply system 100. Here, the design value of the system output current Iout can be expressed by the following Equation 1:

In the constant current switching power supply system 100 shown in FIG. 1 , constant current control is mainly realized by utilizing the inductor current IL flowing through the inductor L1 to exhibit an approximately triangular waveform characteristic during a switching cycle of the power switch Q1 . However, due to the common ground BUCK architecture, the current detection resistor R1 cannot detect the inductor current IL flowing through the inductor L1 when the power switch Q1 is in the off state. Therefore, in the traditional constant current control scheme, the current detection resistor R1 The peak voltage CS_peak of the signal CS before the power switch Q1 changes from the on state to the off state and the demagnetization time of the inductor L1 are calculated based on the triangle area calculation to achieve constant current control.

FIG. 2 shows a timing diagram of multiple signals in the constant current switching power supply system 100 shown in FIG. 1 . As shown in Figure 2, the inductor current IL flowing through the inductor L1 is in one switching cycle of the power switch Q1 (that is, the duration Ton during which the gate drive signal Gate is at a logic high level + the duration during which the gate drive signal Gate is at a logic low level). Toff) exhibits approximately triangular waveform characteristics; and during the period when the power switch Q1 is in the off state (that is, during the duration Toff during which the gate drive signal Gate is at a logic low level), the current detection signal CS is 0V.

Since the system bus voltage VIN is not an ideal DC voltage but has power frequency fluctuations, the inductor current IL flowing through the inductor L1 does not increase linearly ideally during the duration Ton when the power switch Q1 is in the on state. Specifically, the inductor current IL flowing through the inductor L1 when the power switch Q1 is in the on state can be expressed by the following Equation 2:

I _{L_Ton} = L ×( Vin - Vout )× Ton <Equation 2>

Among them, I _{L_Ton} represents the inductor current flowing through the inductor L1 when the power switch Q1 is in the on state, Vin represents the system bus voltage VIN, Vout represents the system output voltage, and L represents the inductance of the inductor L1. It can be seen from Equation 2 that when the system bus voltage VIN is low and close to the system output voltage, the relative linear variation distortion of the inductor current IL becomes more severe.

Since the system output current Iout is the sum of the inductor current I _{L_Ton} flowing through the inductor L1 when the power switch Q1 is in the on state and the inductor current I _{L_Toff} flowing through the inductor L1 when the power switch Q1 is in the off state, when the system bus voltage VIN is lower In this case, there is a large deviation between the actual value of the system output current Iout and the design value. At the same time, the system output current Iout changes with the change of the system bus voltage VIN. In particular, when the power factor of the constant current switching power supply system 100 is high, the input bus voltage VIN changes in an M-wave shape, that is, within a power frequency AC cycle, the system bus voltage VIN ranges from approximately 0V to 1.4 times the AC line. The voltage changes within the range, and changes in the AC line voltage have a greater impact on the accuracy of the system output current Iout, that is, the line voltage adjustment capability of the constant current switching power supply system 100 is poor. Therefore, improving the constant current control accuracy of the constant current switching power supply system 100, especially the line voltage adjustment capability, is an issue that needs to be solved urgently.

In view of the above situation, a constant current control scheme according to an embodiment of the present invention is proposed, in which constant current control is performed in stages according to the on/off state of the power switch Q1 and the change of the inductor current IL flowing through the inductor L1, In order to eliminate the error caused by the distortion of the inductor current IL flowing through the inductor L1, and improve the constant current control accuracy.

It can be seen from Figure 2 that the distortion of the inductor current IL flowing through the inductor L1 mainly occurs during the duration Ton when the power switch Q1 is in the on state, and flows through the inductor L1 during the duration Toff when the power switch Q1 is in the off state. There is basically a linear relationship between the inductor current IL and the demagnetization time of the inductor L1. Therefore, constant current control in stages is an optimized constant current control scheme, that is, the current detection signal CS is not performed when the power switch Q1 is in the on state. The sampling process directly performs the integral operation based on the current detection signal CS, and uses peak sampling combined with the integral operation method when the power switch Q1 is in the off state, so that the main information of the inductor current IL is controlled within a complete switching cycle of the power switch Q1. Chip U100 completely detects and participates in the calculation of system output current Iout, making the system output current Iout more consistent with the ideal design equation 1 and almost does not change with the system bus voltage VIN.

The constant current control scheme according to the embodiment of the present invention is mainly implemented by the constant current control module 106 shown in FIG. 1 . Specifically, the constant current control module 106 may be configured to: based on the The pulse width modulation signal PWM that controls the turn-on and turn-off of the power switch Q1 and the current detection signal CS that represents the inductor current IL flowing through the inductor L1 are generated, and the current sampling signal CS_sample associated with the current detection signal CS is generated; and based on the current detection The signal CS, the demagnetization detection signal Dem of the demagnetization condition of the inductor L1, and the reference voltage Vref generate the pulse width modulation signal PWM, wherein the current sampling signal CS_sample is at the first logic level (for example, logic level) when the pulse width modulation signal PWM is when the pulse width modulation signal PWM is at a second logic level (eg, a logic low level), it is a sampling signal generated by sampling the current detection signal CS.

In some embodiments, the constant current control module 106 may be further configured to: generate a turn-off control signal PWM_off for controlling the power switch Q1 from the on state to the off state based on the current sampling signal CS_sample and the reference voltage Vref.

In some embodiments, the constant current control module 106 may be further configured to use the demagnetization detection signal Dem as a conduction control signal for controlling the power switch Q1 to change from the off state to the on state.

In some embodiments, the constant current control module 106 may be further configured to: generate an error compensation signal CMP based on the current sampling signal CS_sample and the reference voltage Vref; generate a ramp signal based on the pulse width modulation signal PWM or the current detection signal CS Ramp; and generating the off control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp.

FIG. 3 shows a circuit diagram of an example circuit implementation of the constant current control module 106 shown in FIG. 1 . As shown in Figure 3, the constant current control module 106 includes a sampling control unit U200, an error amplifier U201, a slope generation unit U202, a comparator U203, an RS flip-flop U204, and a capacitor C203, where the sampling control unit U200 receives current detection. The signal CS generates the current sampling signal CS_sample based on the current detection signal CS, and outputs the current sampling signal CS_sample to the error amplifier U201; the two input terminals of the error amplifier U201 receive the reference voltage Vref and the current sampling signal CS_sample respectively, and the current sampling signal is The error between CS_sample and the reference voltage Vref is amplified to generate an error amplification signal, and the error amplification signal is output to capacitor C203; capacitor C203 generates error compensation by integrating the error amplification signal. signal CMP, and outputs the error compensation signal CMP to the comparator U203; the ramp generation unit U202 receives the pulse width modulation signal PWM or the current detection signal CS, generates the ramp signal Ramp based on the pulse width modulation signal PWM or the current detection signal CS, and The ramp signal Ram is output to the comparator U203; the two input terminals of the comparator U203 receive the error compensation signal CMP and the ramp signal Ramp respectively, generate the turn-off control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp, and control the turn-off The signal PWM_off is output to the RS flip-flop U204; the two input terminals of the RS flip-flop U204 receive the turn-off control signal PWM_off and the demagnetization detection signal Dem respectively, and generate a pulse width modulation signal based on the turn-off control signal PWM_off and the demagnetization detection signal Dem. PWM, and output the pulse width modulation signal PWM to the driver module 1028, where the turn-off control signal PWM_off controls the pulse width modulation signal PWM to change from a logic high level to a logic low level, and the demagnetization detection signal Dem controls the pulse width modulation. Signal PWM changes from a logic low level to a logic high level.

Further, as shown in Figure 3, the sampling control unit U200 includes switches K201, K202, K203 and capacitors C201 and C202. The capacitors C201 and C202 have the same capacitance. The on and off of the switches K201 and K203 are controlled by pulse width modulation. It is controlled by variable signal PWM, and the on and off of switch K202 is controlled by switch control signal SW1. Here, switches K201 and K203 are in a conducting state when the pulse width modulation signal PWM is a logic high level, and are in an off state when the pulse width modulation signal PWM is a logic low level; switch K202 is in a conducting state when the switch control signal SW1 is a logic high level. state, it is in the off state when the switch control signal SW1 is logic low.

FIG. 4 shows a timing diagram of multiple signals related to the sampling control unit U200 shown in FIG. 3 . As shown in Figure 4, the rising edge of the switch control signal SW1 (the moment when the logic low level changes to the logic high level) is delayed by a preset time compared to the rising edge of the pulse width modulation signal PWM (t1~t2 in the figure) , the falling edge of the switch control signal SW1 (the moment when the logic high level changes to the logic low level) is consistent with the falling edge of the pulse width modulation signal PWM; through the sampling control circuit U200, the pulse width modulation signal PWM can be at the logic high level. Input the complete current detection signal CS as the current sampling signal CS_sample to the error amplifier U201, and When the wide modulation signal PWM is at a logic low level, the peak voltage CS_peak of the current detection signal CS is sampled and the current sampling signal CS_sample obtained by "dividing by 2" is input to the error amplifier U201.

Specifically, as shown in Figures 3 and 4, when the pulse width modulation signal PWM is at a logic high level (t0~t1), the switches K201 and K203 are in the on state, the switch K202 is in the off state, and the current detection signal CS is directly input To the input end of capacitor C201 and error amplifier U201, the voltage across capacitor C202 is Vc202=0V, and the voltage across capacitor C201 is Vc201=Vcs_sample=Vcs; in the peak sampling stage (t1~t2) when the pulse width modulation signal PWM is at a logic low level ), switches K201, K202, and K203 are all in the off state, the peak voltage CS_peak of the current detection signal CS is stored at the input end of the capacitor C201 and the error amplifier U201, the voltage across the capacitor C202 Vc202=0V, the voltage across the capacitor C201 Vc201=Vcs_sample=Vcs_peak; In the peak "divide by 2" operation stage (t2~t3) when the pulse width modulation signal PWM is at a logic low level, the switches K201 and K203 are in the off state, and the switch K202 is in the on state, which is stored in the capacitor The peak voltage CS_peak on C201 is adjusted by the capacitor C202 through the switch K202. Because the capacitance values of the capacitors C201 and C202 are equal, and the initial voltage of the capacitor C202 is 0V, the "division by 2" operation of the peak voltage CS_peak can be realized at this time. That is, Vc201=Vc202=Vcs_sample=Vcs_peak/2.

It can be seen that in the embodiment described in conjunction with FIGS. 3 and 4 , the constant current control module 106 can be further configured to: when the pulse width modulation signal PWM is at a logic low level, by adjusting the peak voltage of the current detection signal CS CS_peak is sampled and the sampling result is divided by 2 to generate the current sampling signal CS_sample; by error amplification of the current sampling signal CS_sample and the reference voltage Vref, the error compensation signal CMP is generated; and by amplifying the error compensation signal CMP and the slope The signal Ramp is compared to generate the off control signal PWM_off.

FIG. 5 shows a circuit diagram of another example circuit implementation of the constant current control module 106 shown in FIG. 1 . As shown in Figure 5, the constant current control module 106 includes a sampling control unit U300, an error amplifier U301, a slope generation unit U302, a comparator U303, an RS flip-flop U304, and and capacitor C303, wherein the sampling control unit U300 processes the current detection signal CS when the pulse width modulation signal PWM is a logic high level in the same manner as the sampling control unit U200, but only processes the current when the pulse width modulation signal PWM is a logic low level. The peak voltage CS_peak of the detection signal CS is sampled without performing a "dividing by 2" operation, and the "dividing by 2" operation of the peak voltage CS_peak is implemented by the error amplifier U301. In addition, the processing of the slope generating unit U302, the comparator U303, the RS flip-flop U304, and the capacitor C303 is the same as that of the corresponding units shown in Figure 4, and therefore will not be described again. FIG. 6 shows a timing diagram of multiple signals related to the sampling control unit U300 shown in FIG. 5 .

FIG. 7 shows a circuit diagram of an example circuit implementation of error amplifier U301 shown in FIG. 6 . As shown in Figure 7, the error amplifier U301 implements the "division by 2" operation on the current sampling signal CS_sample through two resistors R502 and R503 with equal resistance, the switch K501, and the pulse width modulation signal PWM, and " The operation result divided by 2" and the reference voltage Vref are used for error amplification.

It can be seen that in the embodiments described with reference to FIGS. 5 to 7 , the constant current control module 106 can be further configured to: when the pulse width modulation signal PWM is at a logic low level, by adjusting the peak voltage of the current detection signal CS CS_peak is sampled to generate the current sampling signal CS_sample; the current sampling signal CS_sample is divided by 2 and the error is amplified between the operation result and the reference voltage Vref to generate the error compensation signal CMP; and the error compensation signal CMP and the slope are The signal Ramp is compared to generate the off control signal PWM_off.

As described in conjunction with FIGS. 1 to 7 , the control method for the constant current switching power supply system 100 includes: based on the pulse width modulation signal PWM used to control the turn-on and turn-off of the power switch Q1 and the inductance representing the flow through the inductor L1 The current detection signal CS of the current IL generates a current sampling signal CS_sample associated with the current detection signal CS; and based on the current sampling signal CS_sample, the demagnetization detection signal Dem of the demagnetization condition of the inductor L1, and the reference voltage Vref, a pulse width modulation is generated signal PWM, where the current sampling signal CS_sample is the current detection signal CS itself when the pulse width modulation signal PWM is at the first logic level, and when the pulse width modulation signal When the PWM is at the second logic level, it is a sampling signal generated by sampling the current detection signal CS.

In addition, the specific details of the control method according to the embodiment of the present invention are similar to the corresponding content categories of the control chip U100 described in conjunction with FIGS. 1 to 7 , and will not be described again here.

To sum up, according to the control circuit and control method for a constant current switching power supply system according to the embodiment of the present invention, the constant current IL is performed in stages according to the on/off state of the power switch Q1 and the change of the inductor current IL flowing through the inductor L1. Current control can eliminate the error caused by the distortion of the inductor current IL flowing through the inductor L1 and improve the accuracy of constant current control.

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.

106:Constant current control module

C201, C202, C203: capacitor

CMP: error compensation signal

CS: current detection signal

CS_sample: current sampling signal

Dem: demagnetization detection signal

EA: Error Amplifier

K201, K202, K203: switch

PWM: pulse width modulation signal

PWM_off: turn off control signal

Q: RS flip-flop output terminal

Q1: Power switch

R: RS trigger Reset input terminal

Ramp: ramp signal

S: RS trigger Set input terminal

SW1: switch control signal

U200: Sampling control unit

U201: Error amplifier

U202: Ramp generation unit

U203: Comparator

U204:RS trigger

Vref: reference voltage

Claims (19)

A control circuit for a constant current switching power supply system, wherein the constant current switching power supply system includes an inductor and a power switch, and the control circuit is configured as: generating a current sampling signal associated with the current detection signal based on a pulse width modulation signal used to control the on and off of the power switch and a current detection signal representing an inductor current flowing through the inductor; and The pulse width modulation signal is generated based on the current sampling signal, the demagnetization detection signal characterizing the demagnetization condition of the inductor, and the reference voltage, where The current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is an analysis of the current detection signal when the pulse width modulation signal is at a second logic level. Sampled signal generated by sampling. The control circuit as described in claim 1 is further configured as: When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal. The control circuit as described in claim 1 is further configured as: When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal and performing a "division by 2" operation on the sampling result. The control circuit as described in claim 1 is further configured as: Based on the current sampling signal and the reference voltage, a shutdown control signal for controlling the power switch to change from an on state to an off state is generated. The control circuit as described in claim 4 is further configured as: Generate an error compensation signal based on the current sampling signal and the reference voltage; Generate a ramp signal based on the pulse width modulation signal or the current detection signal; and The shutdown control signal is generated based on the error compensation signal and the ramp signal. The control circuit as described in claim 5 is further configured as: The error compensation signal is generated by performing error amplification on the current sampling signal and the reference voltage. The control circuit as described in claim 5 is further configured as: The error compensation signal is generated by performing a "division by 2" operation on the current sampling signal and performing error amplification on the operation result and the reference voltage. The control circuit as described in claim 5 is further configured as: The shutdown control signal is generated by comparing the error compensation signal and the ramp signal. The control circuit as described in claim 1 is further configured as: The demagnetization detection signal is used as a conduction control signal for controlling the power switch to change from an off state to an on state. A control method for a constant current switching power supply system, wherein the constant current switching power supply system includes an inductor and a power switch, and the control method includes: generating a current sampling signal associated with the current detection signal based on a pulse width modulation signal used to control the on and off of the power switch and a current detection signal representing an inductor current flowing through the inductor; and The pulse width modulation signal is generated based on the current sampling signal, the demagnetization detection signal characterizing the demagnetization condition of the inductor, and the reference voltage, where The current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is an analysis of the current detection signal when the pulse width modulation signal is at a second logic level. Sampled signal generated by sampling. The control method according to claim 10, wherein the process of generating the current sampling signal includes: When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal. The control method according to claim 10, wherein the process of generating the current sampling signal includes: When the pulse width modulation signal is at the second logic level, the current sampling signal is generated by sampling the peak voltage of the current detection signal and performing a "dividing by 2" operation on the sampling result. The control method according to claim 10, wherein the process of generating the pulse width modulation signal includes: Based on the current sampling signal and the reference voltage, a shutdown control signal for controlling the power switch to change from an on state to an off state is generated. The control method according to claim 13, wherein the process of generating the shutdown control signal includes: Generate an error compensation signal based on the current sampling signal and the reference voltage; Generate a ramp signal based on the pulse width modulation signal or the current detection signal; and The shutdown control signal is generated based on the error compensation signal and the ramp signal. The control method according to claim 14, wherein the error compensation signal is generated by error amplification of the current sampling signal and the reference voltage. The control method according to claim 14, wherein the error compensation signal is generated by performing a "division by 2" operation on the current sampling signal and performing error amplification on the operation result and the reference voltage. The control method according to claim 14, wherein the shutdown control signal is generated by comparing the error compensation signal and the ramp signal. As for the control method described in claim 10, the process of generating the pulse width modulation signal includes: The demagnetization detection signal is used as a conduction control signal for controlling the power switch to change from an off state to an on state. A constant current switching power supply system includes the control circuit described in any one of claims 1 to 9.

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