TWI838862B - Constant current switching power supply system and control circuit and control method thereof - Google Patents

Abstract

A constant current switching power supply system and a control circuit and control method thereof are provided, wherein the constant current switching power supply system includes an inductor and a power switch, and the control circuit is configured to: generate a current sampling signal associated with the current detection signal based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal representing the inductor current flowing through the inductor; and generate a pulse width modulation signal based on the current sampling signal, a demagnetization detection signal representing the demagnetization condition of the inductor, and a reference voltage, wherein the current sampling signal is the current detection signal itself when the pulse width modulation signal is at a first logic level, and is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at a second logic level.

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.

A switching power supply, also known as an alternating current power supply or a switching converter, is a type of power supply. The function of a switching power supply is to convert a voltage level into the voltage or current required by the user through different forms of architecture (for example, fly-back architecture, buck architecture, or boost architecture, etc.).

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

According to a control method for a constant current switching power supply system according to an embodiment of the present invention, the constant current switching power supply system includes an inductor and a power switch, and the control method includes: based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal representing the inductor current flowing through the inductor, generating a current sampling signal associated with the current detection signal; and based on the current sampling signal, a demagnetization detection signal representing the demagnetization condition of the inductor, and a 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 is a sampling signal generated by sampling the current detection signal when the pulse width modulation signal is at a second logic level.

The constant current switching power supply system according to the embodiment of the present invention includes the above-mentioned control circuit.

100: Constant current switching power supply system

102: Low voltage dropout 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 capacitor

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, _{IL_Ton} , _{IL_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 the 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: Slope 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 the specific implementation of the present invention in conjunction with the drawings, wherein:

FIG1 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.

FIG2 shows a timing diagram of multiple signals of the constant current switching power supply system shown in FIG1.

FIG3 shows a circuit diagram of an example circuit implementation of the constant current control unit shown in FIG1.

FIG4 shows a timing diagram of multiple signals associated with the sampling control unit shown in FIG3.

FIG5 shows a circuit diagram of another example circuit implementation of the constant current control unit shown in FIG1.

FIG6 shows a timing diagram of multiple signals associated with the sampling control unit shown in FIG5.

FIG7 shows a circuit diagram of an example circuit implementation of the error amplifier shown in FIG5.

The features and exemplary embodiments of various aspects of the present invention are described in detail below. In the detailed description below, many specific details are set forth in order to provide a comprehensive understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the present invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary ambiguity of the present invention.

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

FIG1 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 FIG1 , the constant current switching power supply system 100 adopts a BUCK architecture, mainly including 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 U100, wherein: 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 outputs a gate drive signal Gate for driving the power switch Q1 to turn on and off based on a current detection signal (Current Sensor, CS) representing the inductor current IL (not shown in the figure) flowing through the inductor L1.

As shown in FIG1 , 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, wherein: the low dropout linear 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 a 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 108. 06 (it should be understood that the method for the demagnetization detection module 104 to detect the demagnetization condition of the inductor L1 is not limited to this. The demagnetization detection module 104 can also generate the demagnetization detection signal Dem based on the demagnetization detection related signal received from the outside via the chip pin); the constant current control module 106 generates a pulse width modulation signal (Pulse) for controlling the on and off of the power switch Q1 based on the reference voltage Vref, the demagnetization detection signal Dem, and the current detection signal CS. Width Modulation, PWM) and outputs the pulse width modulation signal PWM to the driver module 108; the driver module 108 generates a 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.

In the constant current switching power supply system 100 shown in FIG1 , the power switch Q1 is in the on state when the pulse width modulation signal PWM is at a logical high level, and is in the off state when the pulse width modulation signal PWM is at a logical low level; the reference voltage Vref is used to control the magnitude of 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 operate in a discontinuous conduction mode (DCM) or a 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 FIG1 , constant current control is mainly realized by utilizing the inductor current IL flowing through the inductor L1 to present a triangular waveform characteristic in a switching cycle of the power switch Q1. However, due to the adoption of a 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 peak voltage CS_peak of the current detection 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 obtained and the triangular area operation is performed based on the two to realize constant current control.

FIG2 shows a timing diagram of multiple signals in the constant current switching power supply system 100 shown in FIG1. As shown in FIG2, the inductor current IL flowing through the inductor L1 presents a waveform characteristic approximately in a triangular shape in a switching cycle of the power switch Q1 (i.e., the duration Ton of the gate drive signal Gate being a logical high level + the duration Toff of the gate drive signal Gate being a logical low level); and during the period when the power switch Q1 is in the off state (i.e., the duration Toff of the gate drive signal Gate being a logical 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 in 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>

Where, _{IL_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 inductor current IL is more severely distorted relative to the linear change.

Since the system output current Iout is the sum of the inductor current _{IL_Ton} flowing through the inductor L1 when the power switch Q1 is in the on state and the inductor current _{IL_Toff} flowing through the inductor L1 when the power switch Q1 is in the off state, there is a large deviation between the actual value and the design value of the system output current Iout when the system bus voltage VIN is low. 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, the system bus voltage VIN changes in the range of approximately 0V to 1.4 times the AC line voltage in one industrial frequency AC cycle. The change in the AC line voltage has a greater impact on the accuracy of the system output current Iout, that is, the line voltage regulation 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 regulation capability, is an issue that needs to be solved urgently.

In view of the above situation, a constant current control scheme according to the embodiment of the present invention is proposed, wherein the 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, so as 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.

As shown in Figure 2, 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, while during the duration Toff when the power switch Q1 is in the off state, the inductor current IL flowing through the inductor L1 and the demagnetization time of the inductor L1 are basically linearly related. Therefore, staged constant current control is an optimized constant current control solution, that is, when the power switch Q1 is in the on state, no current detection signal CS is distorted. The sampling process directly performs integration calculation based on the current detection signal CS, and adopts peak sampling combined with integration calculation when the power switch Q1 is in the off state, so that the main information of the inductor current IL in a complete switching cycle of the power switch Q1 is fully detected by the control chip U100 and participates in the calculation of the system output current Iout, so that the system output current Iout is more in line 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 FIG1. Specifically, the constant current control module 106 can be configured to: generate a current sampling signal CS_sample associated with the current detection signal CS based on the pulse width modulation signal PWM for controlling the on and off of the power switch Q1 and the current detection signal CS representing the inductor current IL flowing through the inductor L1; and generate a demagnetization detection signal De based on the current detection signal CS and the demagnetization condition of the inductor L1. m, and the reference voltage Vref, generate a pulse width modulation signal PWM, wherein the current sampling signal CS_sample is the current detection signal CS itself when the pulse width modulation signal PWM is at a first logic level (e.g., a logic high level), and is a sampling signal generated by sampling the current detection signal CS when the pulse width modulation signal PWM is at a second logic level (e.g., a logic low level).

In some embodiments, the constant current control module 106 can be further configured to generate a shutdown control signal PWM_off for controlling the power switch Q1 to change 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 can 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 can 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 Ramp based on the pulse width modulation signal PWM or the current detection signal CS; and generate a shutdown control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp.

FIG3 shows a circuit diagram of an example circuit implementation of the constant current control module 106 shown in FIG1. As shown in FIG3, the constant current control module 106 includes a sampling control unit U200, an error amplifier U201, a slope generating unit U202, a comparator U203, an RS flip-flop U204, and a capacitor C203, wherein: the sampling control unit U200 receives a current detection signal CS, generates a 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 inputs of the error amplifier U201 are connected to the output of the current sampling signal CS_sample. The input end receives the reference voltage Vref and the current sampling signal CS_sample respectively, generates an error amplified signal by amplifying the error between the current sampling signal CS_sample and the reference voltage Vref, and outputs the error amplified signal to the capacitor C203; the capacitor C203 generates an error compensation signal CMP by integrating the error amplified signal, and outputs the error compensation signal CMP to the comparator U203; the slope generation unit U202 receives the pulse width modulation signal PWM or current detection signal CS, generates a ramp signal Ramp based on the pulse width modulation signal PWM or the current detection signal CS, and outputs the ramp signal Ram to the comparator U203; the two input terminals of the comparator U203 receive the error compensation signal CMP and the ramp signal Ramp respectively, and generates a shutdown control signal PWM_off based on the error compensation signal CMP and the ramp signal Ramp, and outputs the shutdown control signal PWM_off to the RS flip-flop U204; the RS flip-flop U204 The two input terminals receive the shutdown control signal PWM_off and the demagnetization detection signal Dem respectively, generate a pulse width modulation signal PWM based on the shutdown control signal PWM_off and the demagnetization detection signal Dem, and output the pulse width modulation signal PWM to the driver module 1028, wherein the shutdown control signal PWM_off controls the pulse width modulation signal PWM to change from a logical high level to a logical low level, and the demagnetization detection signal Dem controls the pulse width modulation signal PWM to change from a logical low level to a logical high level.

Furthermore, as shown in FIG3 , the sampling control unit U200 includes switches K201, K202, K203 and capacitors C201, C202, wherein the capacitance of capacitors C201 and C202 is the same, the on and off of switches K201 and K203 are controlled by a pulse width modulation signal PWM, and the on and off of switch K202 is controlled by a switch control signal SW1. Here, switches K201 and K203 are in the on state when the pulse width modulation signal PWM is at a logical high level, and are in the off state when the pulse width modulation signal PWM is at a logical low level; switch K202 is in the on state when the switch control signal SW1 is at a logical high level, and is in the off state when the switch control signal SW1 is at a logical low level.

FIG4 shows a timing diagram of multiple signals related to the sampling control unit U200 shown in FIG3. As shown in FIG4, the rising edge of the switch control signal SW1 (the moment when the logical low level changes to the logical high level) is delayed by a preset time (t1~t2 in the figure) compared to the rising edge of the pulse width modulation signal PWM, and the falling edge of the switch control signal SW1 (the moment when the logical high level changes to the logical 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 When the signal PWM is at a logical high level, the complete current detection signal CS is input into the error amplifier U201 as the current sampling signal CS_sample, and when the pulse width modulation signal PWM is at a logical 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 into the error amplifier U201.

Specifically, as shown in Figures 3 and 4, when the pulse width modulation signal PWM is at a logical high level (t0~t1), switches K201 and K203 are in the on state, 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 The voltage at the end Vc201 = Vcs_sample = Vcs; in the peak sampling stage (t1~t2) when the pulse width modulation signal PWM is at a logical low level, switches K201, K202, and K203 are all in the off state, and the peak voltage CS_peak of the current detection signal CS is stored in the capacitor C201 and the input end of the error amplifier U201. The voltage across capacitor C202 is Vc202=0V, and the voltage across capacitor C201 is Vc201=Vcs_sample=Vcs_peak; in the peak value "divided by 2" operation phase (t2~t3) when the pulse width modulation signal PWM is at a logical low level, switches K201 and K203 are in the off state, and switch K202 is in the on state, and the value is stored in capacitor C20 The peak voltage CS_peak on 1 is adjusted by capacitor C202 through switch K202. Because the capacitance of capacitors C201 and C202 is equal, and the initial voltage of capacitor C202 is 0V, the peak voltage CS_peak can be "divided by 2" at this time, that is, Vc201=Vc202=Vcs_sample=Vcs_peak/2.

It can be seen that in the embodiment described in conjunction with FIG. 3 and FIG. 4 , the constant current control module 106 can be further configured as follows: when the pulse width modulation signal PWM is at a logical low level, the current sampling signal CS_sample is generated by sampling the peak voltage CS_peak of the current detection signal CS and performing a "divide by 2" operation on the sampling result; the error compensation signal CMP is generated by performing an error amplification on the current sampling signal CS_sample and the reference voltage Vref; and the shutdown control signal PWM_off is generated by comparing the error compensation signal CMP with the ramp signal Ramp.

FIG5 shows a circuit diagram of another example circuit implementation of the constant current control module 106 shown in FIG1. As shown in FIG5, the constant current control module 106 includes a sampling control unit U300, an error amplifier U301, a slope generating unit U302, a comparator U303, an RS flip-flop U304, and a capacitor C303, wherein the sampling control unit U300 processes the current detection signal CS in the same manner as the sampling control unit U200 when the pulse width modulation signal PWM is at a logical high level, but only samples the peak voltage CS_peak of the current detection signal CS without performing a "divide by 2" operation when the pulse width modulation signal PWM is at a logical low level, and the "divide by 2" operation of the peak voltage CS_peak is implemented by the error amplifier U301. In addition, the processing of the ramp generation unit U302, the comparator U303, the RS flip-flop U304, and the capacitor C303 is the same as the corresponding units shown in FIG4, so it is not repeated. FIG6 shows a timing diagram of multiple signals related to the sampling control unit U300 shown in FIG5.

FIG7 shows a circuit diagram of an example circuit implementation of the error amplifier U301 shown in FIG6. As shown in FIG7, the error amplifier U301 implements the "divide by 2" operation of the current sampling signal CS_sample through two resistors R502 and R503 of equal resistance, a switch K501, and a pulse width modulation signal PWM, and performs error amplification on the "divide by 2" operation result and the reference voltage Vref.

It can be seen that in the embodiment described in conjunction with FIG. 5 to FIG. 7, the constant current control module 106 can be further configured as follows: when the pulse width modulation signal PWM is at a logical low level, the current sampling signal CS_sample is generated by sampling the peak voltage CS_peak of the current detection signal CS; the error compensation signal CMP is generated by performing a "divide by 2" operation on the current sampling signal CS_sample and performing error amplification on the operation result and the reference voltage Vref; and the shutdown control signal PWM_off is generated by comparing the error compensation signal CMP with the ramp signal Ramp.

As described in conjunction with FIGS. 1 to 7 , the control method for the constant current switching power supply system 100 includes: generating a current sampling signal CS_sample associated with the current detection signal CS based on a pulse width modulation signal PWM for controlling the on and off of the power switch Q1 and a current detection signal CS representing the inductor current IL flowing through the inductor L1; and generating a current sampling signal CS_sample associated with the current detection signal CS 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 generate a pulse width modulation signal PWM, wherein the current sampling signal CS_sample is the current detection signal CS itself when the pulse width modulation signal PWM is at a first logic level, and is a sampling signal generated by sampling the current detection signal CS when the pulse width modulation signal PWM is at a second logic level.

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

In summary, according to the control circuit and control method for the constant current switching power supply system of the embodiment of the present invention, the 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, which can eliminate the error caused by the distortion of the inductor current IL flowing through the inductor L1 and improve the constant current control accuracy.

The present invention may be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithm described in a specific embodiment may be modified, and the system architecture does not deviate from the basic spirit of the present invention. Therefore, the present embodiments are considered to be exemplary rather than restrictive in all aspects, the scope of the present invention is defined by the attached claims rather than the above description, and all changes that fall within the meaning and scope of equivalents of the claims are therefore included in the scope of the present 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 the control signal

Q: RS trigger 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: Slope generation unit

U203: Comparator

U204: RS trigger

Vref: reference voltage

Claims (17)

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 to: based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal representing an 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 current detection signal representing the inductor current. The demagnetization detection signal of the demagnetization condition of the inductor and the reference voltage are used to generate the pulse width modulation signal, wherein the current sampling signal is the current detection signal itself when the pulse width modulation signal is at the first logic level, and when the pulse width modulation signal is at the second logic level, the peak voltage of the current detection signal is sampled and the sampling result is "divided by 2" to generate the current sampling signal. The control circuit as described in claim 1 is further configured to generate the current sampling signal by sampling the peak voltage of the current detection signal when the pulse width modulation signal is at the second logic level. The control circuit as described in claim 1 is further configured to generate a shutdown control signal for controlling the power switch to change from an on state to an off state based on the current sampling signal and the reference voltage. The control circuit as described in claim 3 is further configured to: 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 generate the shutdown control signal based on the error compensation signal and the ramp signal. The control circuit as described in claim 4 is further configured to generate the error compensation signal by performing error amplification on the current sampling signal and the reference voltage. The control circuit as described in claim 4 is further configured to: Generate the error compensation signal by performing a "divide 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 4 is further configured to generate the shutdown control signal by comparing the error compensation signal and the ramp signal. The control circuit as described in claim 1 is further configured to use the demagnetization detection signal 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: based on a pulse width modulation signal for controlling the on and off of the power switch and a current detection signal representing an inductor current flowing through the inductor, generating a current sampling signal associated with the current detection signal; and based on the current sampling signal, representing the inductor current The demagnetization detection signal of the demagnetization condition and the reference voltage are used to generate the pulse width modulation signal, wherein the current sampling signal is the current detection signal itself when the pulse width modulation signal is at the first logic level, and when the pulse width modulation signal is at the second logic level, the peak voltage of the current detection signal is sampled and the sampling result is "divided by 2" to generate the current sampling signal. The control method as described in claim 9, wherein the process of generating the current sampling signal includes: when the pulse width modulation signal is at the second logic level, generating the current sampling signal by sampling the peak voltage of the current detection signal. The control method as described in claim 9, wherein the process of generating the pulse width modulation signal includes: generating a shutdown control signal for controlling the power switch to change from an on state to an off state based on the current sampling signal and the reference voltage. The control method as claimed in claim 11, wherein the process of generating the shutdown control signal includes: generating an error compensation signal based on the current sampling signal and the reference voltage; generating a ramp signal based on the pulse width modulation signal or the current detection signal; and generating the shutdown control signal based on the error compensation signal and the ramp signal. A control method as described in claim 12, wherein the error compensation signal is generated by performing error amplification on the current sampling signal and the reference voltage. A control method as described in claim 12, wherein the error compensation signal is generated by performing a "divide by 2" operation on the current sampling signal and performing error amplification on the operation result and the reference voltage. A control method as described in claim 12, wherein the shutdown control signal is generated by comparing the error compensation signal and the ramp signal. As described in claim 9, the process of generating the pulse width modulation signal includes: using the demagnetization detection signal 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, comprising a control circuit as described in any one of claims 1 to 8.

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