CN110120747B

CN110120747B - Power supply controller capable of providing open circuit protection and related control method

Info

Publication number: CN110120747B
Application number: CN201810117724.2A
Authority: CN
Inventors: 周冠贤; 杨丰诚
Original assignee: Leadtrend Technology Corp
Current assignee: Leadtrend Technology Corp
Priority date: 2018-02-06
Filing date: 2018-02-06
Publication date: 2020-08-18
Anticipated expiration: 2038-02-06
Also published as: CN110120747A

Abstract

A power supply controller capable of providing open circuit protection and a related control method are suitable for a power supply. The transformer of the power supply includes a primary side winding, an auxiliary winding, and a secondary side winding. The power supply controller controls the power switch. The ground terminal of the auxiliary winding is connected to the input ground. The driving end of the power supply controller provides a driving signal to the power switch. The PWM signal generator generates a PWM signal to determine a driving signal. The pwm signal defines the on-time and the on-off time. The feedback terminal is connected to the floating terminal of the auxiliary winding through a resistor. The voltage change detector is connected with the feedback end. During the turn-on time, the voltage change detector detects the auxiliary winding voltage of the floating terminal. During the turn-on time, if the voltage variation of the auxiliary winding meets the first preset condition, the voltage variation detector stops providing the pulse width modulation signal, and keeps the power switch closed, thereby providing protection when the ground terminal and the input ground are open-circuited.

Description

Power supply controller capable of providing open circuit protection and related control method

Technical Field

The present invention relates to an open circuit protection for a power supply, and more particularly, to a power controller and a related control method for timely protecting a circuit of a power supply when the circuit is open.

Background

Power supplies are almost indispensable in consumer electronics. Almost every electronic product requires a power supply to convert the commercial power into the voltage or current required by the core circuit of the electronic product. Also, since the power supply is very close to people's daily life, many countries require regulations to configure many protection mechanisms to protect the power supply from fire or harm to human body when facing abnormal operation or abnormal environment.

Short/open testing of each component on a printed circuit board is one of the standard operating procedures that modern power supplies must pass. For example, the short circuit test condition of a resistor on the printed circuit board is that both ends of the resistor are abnormally short-circuited, and the resistance value of the resistor becomes 0. The open circuit test condition of the resistor is that one of the two ends of the resistor is not welded well, so that the resistor is not electrically connected to the position of the circuit board.

An open circuit in the ground path of an auxiliary winding in a power supply may lead to runaway results. A primary-side feedback control (PSR) switching power supply controls the output voltage on the secondary side by detecting the auxiliary winding voltage of an auxiliary winding on the primary side. However, when the ground path of the auxiliary winding is broken to become open, the voltage waveform of the auxiliary winding voltage is distorted, providing an error message to the control loop, which may cause the output voltage to drift and damage the circuit connected to the output voltage and powered by the power supply.

Therefore, when the ground path of the auxiliary winding is opened, the power supply should be shut down in time to stop the voltage conversion.

Disclosure of Invention

The embodiment of the invention provides a power supply controller which is suitable for a power supply. The power supply includes a transformer having a primary winding, an auxiliary winding, and a secondary winding. The power controller controls a power switch which is connected in series with the primary side winding between an input voltage and an input ground. The auxiliary winding has a ground terminal for connection to the input ground and a floating terminal. The power controller includes: the circuit comprises a driving end, a pulse width modulation signal generator, a feedback end and a voltage change detector. The driving end provides a driving signal to the power switch. The PWM signal generator generates a PWM signal that determines the driving signal. The PWM signal defines an ON time and an ON/OFF time. The feedback terminal is connected to the floating terminal through a resistor. The voltage change detector is connected to the feedback terminal. During the turn-on time, the voltage change detector detects an auxiliary winding voltage on the floating terminal. During the turn-on time, if a change in the auxiliary winding voltage meets a first predetermined condition, the voltage change detector provides an open-circuit protection signal to the pwm signal generator to stop providing the pwm signal, keeping the power switch off, thereby providing protection when there is an open circuit between the ground terminal and the input ground.

Embodiments of the present invention provide a control method for providing protection when an open circuit exists between a ground terminal of an auxiliary winding and an input ground. The control method is suitable for a power controller in a power supply. The power supply includes a transformer having a primary winding, the auxiliary winding, and a secondary winding. The power controller controls a power switch which is connected in series with the primary side winding between an input voltage and the input ground. The auxiliary winding has the ground terminal and a floating terminal. The ground terminal is used for connecting to the input ground, and the floating terminal is connected to a feedback end of the power supply controller through a resistor. The secondary side winding is used for generating an output voltage and an output ground, and the control method comprises the following steps: providing a driving signal to the power switch; providing a pulse width modulation signal which determines the driving signal, wherein the pulse width modulation signal is defined with an opening time and a switching time; detecting an auxiliary winding voltage on the floating terminal through the feedback terminal; identifying whether a change of the auxiliary winding voltage meets a first preset condition within the turn-on time; and providing an open circuit protection signal to stop providing the PWM signal and keep the power switch closed if the variation meets the first preset condition within the turn-on time, thereby providing protection when the ground terminal and the input ground are open circuit.

Drawings

Fig. 1 shows a power supply implemented according to the present invention.

FIG. 2 shows the driving signal S in FIG. 1_DRVAuxiliary winding voltage V at normal time_AUXAnd possibly an auxiliary winding voltage V during an open circuit test_AUX。

Fig. 3 shows a power supply controller implemented in accordance with the present invention.

Fig. 4 shows some of the signal waveforms of fig. 3 during an open circuit test.

FIG. 5 shows a PWM signal S_PWMCurrent detection voltage V_CSAnd the LEB signal S_LEB。

Fig. 6 shows some signal waveforms of fig. 3 in normal operation.

[ notation ] to show

10 power supply

12 bridge rectifier

13 load

14 power supply controller

20 voltage change detector

21 sampler

22. 26 current mirror

24 clamping circuit

25 counter

27 SR flip-flop

29 reverse Smith trigger

30 PWM signal generator

32 driver

34 LEB time generator

AUX auxiliary winding

BMP bump

CS Current detection terminal

DA diode

DRV drive end

Difference of DV voltage

FA floating terminal

FB feedback terminal

GA ground terminal

GND input ground

GND-O output ground

I_FBFeedback current

I_PRMCurrent of winding

I_SHRecording current

N1, N2 NMOS transistor

P1, P2, P3, P4 PMOS transistors

PRM primary side winding

PX symbol

RA, RB resistance

RCS current detection resistor

S_AGPOSignal

S_CLKClock signal

S_DRVDrive signal

SEC Secondary winding

S_LEBLEB signal

S_PROOpen circuit protection signal

S_PWMPWM signal

SW power switch

t1_DETPoint in time

t_FOUNDPoint in time

TF transformer

T_LEBRising edge mask time

T_OFFClosing time

T_ONTime of opening

V_ACAC commercial power

V_AUXVoltage of auxiliary winding

V_BASEReference voltage

V_CCOperating supply voltage

V_CSCurrent detection voltage

VCC power supply terminal

V_FBFeedback voltage

V_INInput voltage

V_LIMLimiting voltage

V_OUTOutput voltage

Detailed Description

In this specification, there are some common symbols representing components having the same or similar structures, functions, principles, and being understood by those skilled in the art based on the teachings of this specification. For the sake of brevity of the description, elements having the same reference numerals will not be repeated.

Fig. 1 shows a power supply 10 implemented according to the present invention, wherein the symbol PX represents a position where the ground path open of the auxiliary winding AUX occurs. The power supply 10 has a power controller 14, which in one embodiment may be a packaged integrated circuit having a plurality of pins. As shown in fig. 1, the pins may be a power supply terminal VCC, a driving terminal DRV, a current detection terminal CS, a feedback terminal FB, and the like.

The bridge rectifier 12 converts the AC commercial power V_ACRectifying to provide an input voltage V_INAnd input ground GND. The transformer TF includes a primary winding PRM, a secondary winding SEC, and an auxiliary winding AUX. As shown in FIG. 1, a primary winding PRM, a power switch SW, and a current detection resistor RCS are connected in series to an input voltage V_INAnd the input ground GND. The power controller 14 supplies a drive signal S from the drive terminal DRV_DRVThe switch SW is used for switching the power switch SW, so that the voltage across the primary winding PRM varies. The secondary winding SEC thus generates an induced alternating voltage which, after rectification, provides the output voltage V_OUTAnd an output ground GND-O for powering the load 13.

The auxiliary winding AUX has a ground terminal GA and a floating terminal FA. In normal operation, the ground terminal GA is directly connected to the input ground GND. In the ground path open test (hereinafter, referred to as open test) of the auxiliary winding AUX, the ground terminal GA is not short-circuited to the input ground GND as required in the design, and the symbol PX indicates a position where the ground path open of the auxiliary winding AUX occurs.

With auxiliary winding voltage V at floating terminal FA_AUXWhich after rectification by a diode DA may provide the operating supply voltage V of the supply controller 14_CC. The resistors RA and RB are connected in series between the floating terminal FA and the input ground GND. The feedback terminal FB of the power controller 14 serves as a connection point between the resistors RA and RB. The feedback terminal FB of the power controller 14 has a feedback voltage V_FB. FeedbackCurrent I_FBThe power controller 14 is flown from the feedback terminal FB of the power controller 14.

In FIG. 2, the auxiliary winding voltage V at the time of open circuit test_AUXApparent auxiliary winding voltage V following normal_AUXDifferent. FIG. 2 shows the auxiliary winding voltage V during the open circuit test_AUXAn example of being twisted. For true open circuit test, the auxiliary winding voltage V_AUXThe degree of distortion is determined by the actual electronic components and the parasitic electrical coefficients (resistance, capacitance, inductance).

Drive signal S_DRVIs a pulse-width modulation (PWM) signal, based on another PWM signal S_PWMGenerating, a defined on-time T_ONAnd closing time T_OFF. At a turn-on time T_ONWhen the power switch SW is on; at off time T_OFFAt this time, the power switch SW is turned off. The power controller 14 may implement primary-side feedback control (PSR) at a time point t1 shown in fig. 2_DETDetecting the auxiliary winding voltage V by means of resistors RA and RB_AUXIndirectly detecting the output voltage V on the secondary side_OUT. FIG. 2 shows, at time point t1, the open circuit test_DETDetected auxiliary winding voltage V_AUXWill be significantly lower than the auxiliary winding voltage V detected at normal times_AUX. Thus, during an open circuit test, the power controller 14 may misunderstand the output voltage V if no immediate protection is provided to shut down the power conversion_OUTLower, erroneously increasing the conversion energy to pull up the output voltage V_OUT. Excessive output voltage V_OUTThe load 13 may be damaged.

Fig. 3 shows a power controller 14 according to the present invention, which includes a voltage variation detector 20 and a PWM signal generator 30.

The PWM signal generator 30 generates a PWM signal according to the feedback voltage V_FBAnd electricityFlow detection voltage V_CSTo generate a PWM signal S_PWM. PWM signal S_PWMAs an input, the driver 32 provides an appropriate ground voltage level as the drive signal S_DRVTo drive the power switch SW. PWM signal S_PWMAnd a drive signal S_DRVHaving substantially the same logic value, the turn-on time T can be defined_ONAnd closing time T_OFF。

The voltage change detector 20 is connected to the feedback terminal FB. At a turn-on time T_ONIn the voltage variation detector 20, the auxiliary winding voltage V on the floating terminal FA is detected by a resistor RA_AUX. At a turn-on time T_ONIf the auxiliary winding voltage V_AUXThe voltage change detector 20 can provide the open-circuit protection signal S when a change of the voltage change detector meets a predetermined condition_PROTo the PWM signal generator 30. The PWM signal generator 30 thus stops supplying the PWM signal S_PWM. Open circuit protection signal S_PROCan make PWM signal S_PWMRemains at logic 0, keeping the power switch SW off, thus providing protection when there is an open circuit between the ground terminal GA and the input ground GND.

Please refer to FIG. 4, which shows some signal waveforms in FIG. 3 during the open circuit test.

Following the driving signal S_DRVSwitching power switch SW, auxiliary winding voltage V_AUXWith consequent changes. At a turn-on time T_ONIn the inner, the voltage change detector 20 shields (LEB) at a rising edge for a time T_LEBAt the end, the auxiliary winding voltage V is detected_AUXWhich at that time is the reference voltage V_BASE. Thereafter, at the turn-on time T_ONWhen the auxiliary winding voltage V_AUXAnd a reference voltage V_BASEWhen the voltage difference DV between the two signals reaches a predetermined difference, the open-circuit protection signal S can be provided_PRO. LEB time T_LEBWill be explained later on. By LEB time T_LEBEnd of time auxiliary winding voltage V_AUXAs a reference voltage V_BASEThe present invention is not limited thereto, but is only an example for convenience of description. Embodiments of the present invention may employ an on-time T_ONAt any time inIntermediate auxiliary winding voltage V_AUXAs a reference voltage V_BASE。

Please refer to fig. 3. The voltage variation detector 20 includes a clamping circuit 24, a current mirror 22, a current mirror 26, an inverted smith trigger 29, an SR flip-flop 27, and a counter 25, which are connected as shown in fig. 3.

The clamping circuit 24 is configured to provide a feedback current I_FBAt the turn-on time T_ONFor converting the feedback voltage V on the feedback terminal FB_FBAbout clamped to no less than 0 volts. Feedback current I_FBGreater than 0A and about-V_AUX/R_AWherein R is_AWhich is the resistance value of resistor RA in fig. 1. As shown in fig. 4, the feedback current I_FBIs approximately equal to the auxiliary winding voltage V_AUXA waveform portion of less than 0V.

The current mirror 22 is used to copy the feedback current I_FB. The ratio of the currents flowing through the PMOS transistors P1, P2, P3 may be about 1: 1: 1.

the current mirror 26 includes NMOS transistors N1, N2 and the sampler 21. The sampler 21 is controlled by the LEB signal S_LEBWhich defines the LEB time T_LEBFollowing opening time T_ONStarting at about the same time, but not recommended to be longer than the turn-on time T_ONAs shown in fig. 4. At LEB time T_LEBIn the case where the NMOS transistor N1 is connected to the gate of N2, the ratio of the currents flowing through the NMOS transistors N1 and N2 may be about 1: 0.8. thus, as shown in FIG. 4, at LEB time T_LEBIn the memory, a recording current I generated by an NMOS transistor N2_SHEqual to 0.8 times the feedback current I_FB. At LEB time T_LEBAfter the end, the sampler 21 maintains the gate voltage of the NMOS transistor N2 equal to the LEB time T_LEBEnd-of-time sampling of the feedback current I_FB. Thus, at LEB time T_LEBAfter that, the current I is recorded_SHCan represent the LEB time T_LEBEnd of time feedback current I_FBApproximately equal to the LEB time T_LEBEnd of time feedback current I_FB0.8 times as much as in fig. 4.

Reverse Smith trigger 29 acts as a current comparator. LEB time T_LEBThen, the time T is turned on_ONIf the current I is fed back_FBReduced to less than the recording current I_SHThe reverse Smith trigger 29 may cause the signal S_AGPOIs a logical 1.

PMOS transistor P4 for the reverse Smith trigger 29 to turn off at time T_OFFThe output of the clock remains at logic 0.

Signal S_AGPOAnd the LEB signal S_LEBControls the SR flip-flop 27 to provide the clock signal S_CLKWhich is received by a clock input of the counter 25. In FIG. 4, from the on time T_ONAt the beginning, to a point of time t_FOUNDBefore, feedback current I_FBAre all greater than the recording current I_SHThus signal S_AGPOAnd a clock signal S_CLKAre all logical 0's. At a point in time t_FOUNDFeedback current I_FBStart below the recording current I_SHThus, signal S_AGPOAnd a clock signal S_CLKTogether become a logical 1. From the circuit analysis, it can be known that at the turn-on time T_ONIf the voltage difference DV is greater than or equal to-0.2V_BASESignal S_AGPOWill change from a logical 0 to a logical 1.

The voltage difference DV is more than-0.2V_BASEDetermining whether to provide open circuit protection is merely a design choice and is not intended to limit the present invention. For example, in other embodiments, the voltage difference DV greater than 0.1V can be used to determine whether to provide open circuit protection.

In one embodiment, each turn-off time T_OFFAnd LEB time T_LEBInternal, signal S_AGPOIs forced to a logical 0.

In one embodiment, the clock signal S_CLKAt each LEB time T_LEBInitially, it is set to a logical 0 by the SR flip-flop 27.

Therefore, if each turn-on time T_ONInner, auxiliary winding voltage V_AUXAre so great that the voltage difference DV is equal to or greater than-0.2V_BASEThen the counter 25 is incremented by 1, as isAs shown in fig. 4.

In FIG. 4, at a time point t_PROTECTTime of day clock signal S_CLKWhen the counter 25 reaches 4, the open circuit protection signal S_PROIs enabled, so that the PWM signal generator 30 will generate the PWM signal S_PWMAnd remains at logic 0, keeping the power switch SW off, stopping power conversion. Thus providing protection when there is an open circuit between the ground terminal GA and the input ground GND. The count up to 4 times is merely an example and is not intended to limit the present invention. In other embodiments, the open protection may be triggered when the count value is any other number.

FIG. 5 shows a PWM signal S_PWMCurrent detection voltage V_CSAnd the LEB signal S_LEB. Please refer to fig. 5 and fig. 3. In one embodiment, the PWM signal generator 30 controls the current detection voltage V_CSPeak value of (a). Current detection voltage V_CSCan represent the winding current I flowing through the primary side winding PRM_PRM. When the current detects the voltage V_CSOver a limit voltage V_LIMAt this time, the PWM signal generator 30 ends the turn-on time T_ONAnd starts to close for a time T_OFFThus determining the current detection voltage V_CSPeak value of (a). Limiting the voltage V_LIMCan be related to the output voltage V_OUT. For example, when the output voltage V is_OUTWhen the voltage is lower than a rated voltage, the PWM signal generator 30 makes the limit voltage V_LIMIncreasing, current detecting voltage V_CSThus increasing the peak value of (d), the output voltage V after it can be pulled up_OUT. Therefore, the PWM signal generator 30 depends on the limit voltage V_LIMAnd a current detection voltage V_CSRegulating output voltage V_OUT. From one perspective, PWM signal generator 30 provides a signal path CPath, which in turn is an output voltage V_OUTLimit voltage V_LIMThen to the current detection voltage V_CSPeak value of (a).

The signal path CPath at LEB time T_LEBIs interrupted. The LEB time generator 34 is driven by the PWM signal S_PWMTriggered by the rising edge of (c) to generate the LEB signal S_LEBFor defining the LEB time T_LEBWhich is the on-time T_ONA predetermined time after the start, as shown in fig. 5. At a turn-on time T_ONIn the current detection voltage V due to the inductive effect of the primary winding PRM_CSIdeally should increase linearly with time. However, as illustrated in FIG. 5, at LEB time T_LEBIn the current detection voltage V due to the instantaneous short-circuit discharge at both ends of the channel of the switch SW_CSThe waveform of (c) may have a convex BMP. The raised BMP may influence the signal path CPath on the output voltage V_OUTAnd (4) controlling. In one embodiment, at LEB time T_LEBIn, the PWM signal generator 30 does not detect the voltage V according to the current_CSWith limited voltage V_LIMTo control the current detection voltage V_CSAnd regulating the output voltage V_OUT. In other words, at LEB time T_LEBThe bulge BMP can be ignored and the signal path CPath is interrupted.

In one embodiment, sampler 21 is at LEB time T_LEBEnd-of-time sampling of the feedback current I_FBThereby recording the reference voltage V_BASEHowever, the present invention is not limited thereto. In other embodiments, sampler 21 may be on for a time T_ONSampling the feedback current I at any time_FBAnd a recording reference voltage V_BASE。

Fig. 6 shows some signal waveforms of fig. 3 in normal operation.

As shown in fig. 6, the auxiliary winding voltage V_AUXAt a turn-on time T_ONAnd is approximately a fixed value without change. Thus, the LEB time T_LEBReference voltage at end V_BASEAlso about that fixed value. At a turn-on time T_ONInner, auxiliary winding voltage V_AUXAnd a reference voltage V_BASEThe difference between them, is about 0V, so open circuit protection is not triggered.

Please refer to fig. 6 and fig. 3. At a turn-on time T_ONInternal, recording current I_SHFeedback current I approximately equal to 0.8_FBSo as not to be larger than the feedback current I_FB. Thus, the signal S_AGPOAnd clockSignal S_CLKIs always maintained at logic 0 and the count value recorded by the counter 25 stays at 0 and does not trigger open circuit protection.

As can be seen from the above circuit analysis, when the ground path of the power supply 10 shown in fig. 1 is open at the position marked by PX, the power controller 14 can immediately keep the power switch SW off, stop the power conversion, and provide open-circuit protection.

The above-mentioned embodiments are only preferred embodiments of the present invention, and all equivalent changes and modifications made by the claims of the present invention should be covered by the scope of the present invention.

Claims

1. A power controller for a power supply, the power supply comprising a transformer including a primary side winding, an auxiliary winding, and a secondary side winding, the power controller controlling a power switch connected in series with the primary side winding between an input voltage and an input ground, the auxiliary winding having a ground terminal for connection to the input ground and a floating terminal for generating an output voltage and an output ground, the power controller comprising:

a driving end for providing a driving signal to the power switch;

a PWM signal generator for generating a PWM signal that determines the driving signal, the PWM signal defining an on-time and an on-off time;

a feedback terminal connected to the floating terminal through a resistor; and

a voltage variation detector connected to the feedback terminal for detecting the auxiliary winding voltage at the floating terminal during the turn-on time, wherein the voltage variation detector provides an open-circuit protection signal to the PWM signal generator to stop providing the PWM signal and keep the power switch off if the variation of the auxiliary winding voltage meets a first predetermined condition during the turn-on time, thereby providing protection when an open circuit is formed between the ground terminal and the input ground,

in the turn-on time, the voltage difference between the auxiliary winding voltage and the reference voltage reaches a predetermined difference, and the voltage change detector provides the open-circuit protection signal.

2. The power supply controller of claim 1, wherein the voltage variation detector comprises:

the clamping circuit provides a feedback current and is used for clamping the feedback voltage on the feedback end to be not lower than a preset voltage approximately during the starting time;

a sampler for sampling the feedback current at a predetermined time point within the turn-on time to correspondingly generate a recording current representing the feedback current at the predetermined time point; and

and the comparator provides the open-circuit protection signal to stop providing the driving signal and keep the power switch closed when the feedback current and the recording current accord with a second preset condition within the opening time after the preset time point.

3. The power controller as claimed in claim 2, wherein the predetermined time point is an end of a rising edge blanking time, the power controller receives a current detection voltage representing a winding current flowing through the primary side winding and the power switch, and the power controller does not regulate the output voltage according to the current detection voltage during the rising edge blanking time.

4. The power supply controller of claim 2, wherein the voltage change detector further comprises:

and the counter provides the open-circuit protection signal when the second preset condition is met for a preset number of times so as to stop providing the driving signal and keep the power switch closed.

5. A control method for providing open circuit protection, said method providing protection when an auxiliary winding is open circuited between a ground terminal and an input ground, said control method being adapted to a power supply controller in a power supply, said power supply comprising a transformer comprising a primary side winding, said auxiliary winding, and a secondary side winding, said power supply controller controlling a power switch connected in series with said primary side winding between an input voltage and said input ground, said auxiliary winding having said ground terminal and a floating terminal, said ground terminal being adapted to be connected to said input ground, said floating terminal being connected to a feedback terminal of said power supply controller through a resistor, said secondary side winding being adapted to generate an output voltage and an output ground, said control method comprising:

providing a driving signal to the power switch;

providing a pulse width modulation signal which determines the driving signal, wherein the pulse width modulation signal is defined with an opening time and a switching time;

detecting the auxiliary winding voltage on the floating terminal through the feedback terminal;

identifying whether the change of the auxiliary winding voltage meets a first preset condition within the starting time; and

providing an open circuit protection signal to stop providing the PWM signal and keep the power switch off if the variation meets the first predetermined condition during the turn-on time, thereby providing protection when the ground terminal and the input ground are open circuit,

the control method comprises the following steps:

detecting whether the voltage difference between the auxiliary winding voltage and the reference voltage reaches a preset difference within the starting time after the preset time point;

when the voltage difference reaches the predetermined difference, the open-circuit protection signal is provided to keep the power switch off, thereby providing protection when the ground terminal and the input ground are open-circuit.

6. The control method according to claim 5, comprising:

providing a feedback current for clamping the feedback voltage at the feedback end to be not lower than a preset voltage during the turn-on time;

sampling the feedback current at a predetermined time point within the turn-on time to correspondingly generate a recording current representing the feedback current at the predetermined time point; and

after the preset time point and within the starting time, identifying whether the feedback current and the recording current accord with a second preset condition or not; and

when the feedback current and the recording current meet the second preset condition, the open-circuit protection signal is provided to stop providing the driving signal and keep the power switch closed.

7. The control method as claimed in claim 6, wherein the predetermined time point is the end of the rising edge masking time, the control method comprises:

receiving a current detection voltage representing a winding current flowing through the primary side winding and the power switch;

regulating the output voltage according to the current detection voltage; and

the output voltage is not regulated according to the current detection voltage in the rising edge shielding time.

8. The control method of claim 6, comprising:

calculating the times that the feedback current and the recording current meet the second preset condition;

when the times reach the preset times, the open circuit protection signal is provided to stop providing the driving signal and keep the power switch closed.