TWI711249B - Output overvoltage sensing system and sensing method - Google Patents

Abstract

The invention provides an output overvoltage sensing system and sensing method. The output overvoltage sensing system includes a control chip and a resistor located outside the control chip and coupled with the control chip. The control chip includes a current source, a control capacitor, a comparator, and an overvoltage sensing circuit. The current size of the current source is set by the externally coupled resistance of the control chip. The control capacitor is discharged and cleared after the control chip drive is turned on for a period of time, and is charged by the current source of the control chip during the demagnetization time of the output inductor after the control chip drive is turned off. The comparator compares the voltage across the control capacitor with the peak voltage of the current switching cycle on the sampling resistor. The overvoltage sensing circuit responds to a demagnetization end signal indicating that the inductance is completely demagnetized after the control chip is driven off, and determines whether an overvoltage state is sensed based on the comparison result of the comparator.

Description

Output overvoltage sensing system and sensing method

The present invention generally relates to the field of wafers, and more specifically, to an output overvoltage sensing system and sensing method.

The output over-voltage protection can prevent the system from being damaged when the output voltage is too high when the system is abnormal. Output voltage sensing then becomes the key to output overvoltage protection. Traditionally, voltage sensing is generally achieved by directly sensing the output voltage of the system or by sensing the voltage across the output inductor in the system. However, under certain system application conditions, it is impossible to directly sense the output voltage of the system or the voltage across the output inductor in the system, and it is often necessary to add additional components to assist in implementing voltage sensing.

According to an aspect of the present invention, there is provided an output overvoltage sensing system, including a control chip and a resistor, the resistor being located outside the control chip and coupled with the control chip. The control chip includes a current source, a control capacitor, a comparator, and an overvoltage sensing circuit. The current size of the current source is set by the externally coupled resistance of the control chip. The control capacitor is discharged and cleared after a period of delay after the drive of the control chip is turned on, and is charged by the current source of the control chip during the demagnetization time of the output inductor after the drive of the control chip is turned off. The comparator controls the voltage across the control capacitor and the sampling resistor. Compare the peak voltage of the current switching cycle on the above; and the overvoltage sensing circuit responds to the demagnetization end signal indicating that the inductance is completely demagnetized after the control chip is driven off, and determines whether the overvoltage state is sensed based on the comparison result of the comparator .

According to another aspect of the present invention, there is provided an output overvoltage sensing method, including: collecting the voltage across a control capacitor in a control chip, wherein the control capacitor is discharged and cleared after a delay in driving the control chip on for a period of time, and the control chip Output inductance after chip drive is turned off During the demagnetization time, the current source of the control chip is charged by the current source of the control chip. The current size of the current source of the control chip is set by the resistor externally coupled to the control chip; the peak voltage of the current switching cycle on the sampling resistor is collected; the voltage across the control capacitor is compared with The peak voltage is compared; and in response to a demagnetization end signal indicating that the output inductor is completely demagnetized after the control chip is driven off, it is determined whether an overvoltage state is sensed based on the comparison result of the comparator.

According to the output overvoltage sensing system and sensing method of the present invention, it is convenient to realize voltage sensing and thereby realize the output overvoltage protection function when the reference ground of the control chip cannot directly sense the output voltage or the voltage across the output inductor, and No additional auxiliary circuit is needed, so it can help reduce the system volume and thereby reduce the cost.

1, 3, 4‧‧‧Frame

3013, 4016‧‧‧Comparator

2, 303‧‧‧Load

3014, 4017‧‧‧Overvoltage sensing circuit

13‧‧‧Current Sensing Module

4011‧‧‧Converter

14‧‧‧Demagnetization Sensing Module

FB‧‧‧Signal

16‧‧‧Drive

I _L ‧‧‧Output inductor current

301, 401‧‧‧control chip

I _SET ‧‧‧Current

3011、4012‧‧‧Current source

S ₁ 、S ₁ 4013‧‧‧First switch

3012, C 4014‧‧‧Control capacitor

S ₂ 、S ₂ 4015‧‧‧Second switch

C‧‧‧Control the capacitance of the capacitor

S701-S705, S801-S808‧‧‧Step

I _{CS_PEAK ‧‧‧The} current flowing through the sampling resistor

T‧‧‧Time

L‧‧‧Inductance value of output inductor

T _DMG ‧‧‧Demagnetization time

R _CS ‧‧‧Resistance value of sampling resistor

T _{ON_DELAY ‧‧‧Delay} time

V _C ‧‧‧Control the voltage across the capacitor

V _DD ‧‧‧Power supply voltage

V _{CS_PEAK ‧‧‧Peak} voltage of sampling resistor

V _OUT ‧‧‧Output voltage

302, RSET, RSET 402‧‧‧Resistor

11‧‧‧Undervoltage protection (UVLO) module

12‧‧‧Constant current (CC)/constant voltage (CV) adjustment module

15‧‧‧Pulse width modulation (PWM) control module

17‧‧‧Over Voltage Protection (OVP) Module

GATE‧‧‧The signal that controls the turn-on and turn-off of the chip drive

OVP‧‧‧Sensing result signal of over-voltage sensing circuit

The present invention can be better understood from the following description of the specific embodiments of the present invention in conjunction with the drawings, in which: Figure 1 shows a schematic diagram of an exemplary system for output voltage sensing through an optocoupler; Figure 2 A schematic diagram of an exemplary system for output voltage sensing through an auxiliary winding is shown; Figure 3 shows a schematic block diagram of an output overvoltage sensing system according to an embodiment of the present invention; A schematic circuit diagram of an output overvoltage sensing system according to an embodiment of the present invention; Figure 5 shows a schematic diagram of a control waveform of an output overvoltage sensing system according to an embodiment of the present invention when an overvoltage state is sensed; sixth The figure shows a schematic diagram showing a control waveform of an output overvoltage sensing system according to an embodiment of the present invention when the overvoltage state is not sensed.

Figure 7 shows a flowchart of an output overvoltage sensing method according to an embodiment of the present invention.

Fig. 8 shows a flowchart of a specific example of a method for output overvoltage sensing according to an embodiment of the present invention.

The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, many specific details are proposed in order to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by showing examples of the present invention. The present invention is by no means limited to any specific configuration proposed below, but covers any modification, replacement 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 technologies are not shown in order to avoid unnecessary obscurity of the present invention.

Figure 1 shows a schematic diagram of an exemplary system for output voltage sensing through an optocoupler. As described in Figure 1, this exemplary system uses high-voltage alternating current (AC, Alternate Current) to supply power to the control system, thereby providing power to the load. More specifically, the input high-voltage AC is applied to the two input ends of a rectifier bridge composed of four diodes, and then rectified by the rectifier bridge and then filtered by a filter capacitor, and then the entire system is controlled by the control chip indicated by the dashed box 1 Load 2 provides power.

As shown in Figure 1, the control chip includes UVLO (Under Voltage Lock Out) module 11, constant-current (CC, Constant-current)/constant-voltage (CV, Constant-voltage) adjustment module 12, and current The sensing module 13, the demagnetization sensing module 14, the Pulse Width Modulation (PWM, Pulse Width Modulation) control module 15, the driver 16, and the Over Voltage Protection (OVP) module 17.

The under-voltage protection (UVLO) module) 11 senses whether the power supply voltage V _DD is lower than the under-voltage protection threshold, and when the power supply voltage V _{DD is} lower than the under-voltage protection threshold, the control chip is in a protection state. The constant current (CC)/constant voltage (CV) adjustment module 12 realizes the adjustment of the CC and CV modes according to the load condition. The pulse width modulation (PWM) control module 15 performs pulse width modulation on the voltage waveform. The driver 16 drives the switching transistor to be turned on or off through the signal GATE. The current sensor (CS, Current Sensor) module 13 senses the current flowing through the sampling resistor through the sampling signal CS. The demagnetization sensing module 14 senses the time when the output inductor is completely demagnetized after the switching transistor is turned off (that is, the control chip is driven to turn off). The overvoltage protection (OVP) module 17 senses whether the output voltage is higher than the output overvoltage protection threshold through the signal FB, and activates the overvoltage protection when the sensed voltage is higher than the output overvoltage protection threshold.

As described in Figure 1, the exemplary system uses optocoupler elements and related circuits (shown in dashed boxes 3 and 4 in the figure) to assist in voltage sensing.

Figure 2 shows a schematic diagram of an exemplary system for output voltage sensing through an auxiliary winding. The components and functions in Figure 2 that are the same as those in Figure 1 will not be repeated here. The difference is that in Figure 2, auxiliary windings are added to the left of the output inductor, and output voltage sensing is realized by these windings.

However, in the exemplary systems shown in FIG. 1 and FIG. 2, the control chip needs to add additional auxiliary circuits to assist in realizing output voltage sensing, which increases the volume of the system and further increases the cost.

According to the embodiment of the present invention, a new type of output overvoltage sensing technology is provided. This new type of output overvoltage sensing technology can be easily implemented when the reference ground of the control chip cannot directly sense the output voltage or the voltage across the output inductor Voltage sensing and then realize the output overvoltage protection function without additional auxiliary circuit, so it can help reduce the system volume and thereby reduce the cost.

Figure 3 shows a schematic block diagram of an output overvoltage sensing system according to an embodiment of the present invention. Please note that in order not to obscure the present invention, Figure 3 only illustrates the parts that are helpful for understanding the present invention. In fact, the system may also include other components, such as demagnetization sensing modules, current sensing modules, Drivers, switching transistors, sampling resistors, output inductors, etc., and these other components have the same functions and operations as shown in Figures 1 and 2.

As shown in Figure 3, the system includes a control chip 301 and a resistor 302 located outside the control chip and coupled with the control chip. The control chip 301 controls the power supply to the load 303.

The control chip 301 includes a current source 3011, a control capacitor 3012, a comparator 3013, and an overvoltage sensing circuit 3014.

The magnitude of the current of the current source 3011 is set by the resistor 302 externally coupled to the control chip 301.

The control capacitor 3012 is discharged and cleared after the control chip 301 is driven and turned on for a period of time, and the demagnetization time of the output inductor is charged by the current source 3011 of the control chip 301 after the control chip 301 is driven and turned off.

The comparator 3013 compares the voltage across the control capacitor 3012 with the peak voltage of the current switching cycle on the sampling resistor.

The overvoltage sensing circuit 3014 responds to a demagnetization end signal indicating that the inductance is completely demagnetized after the control chip 301 is turned off, and determines whether an overvoltage state is sensed based on the comparison result of the comparator 3013.

In some embodiments, in response to the comparison result of the comparator 3013 at the end of the demagnetization indicating that the voltage across the control capacitor 3012 is lower than the peak voltage of the current switching cycle on the sampling resistor, the overvoltage sensing circuit 3014 senses the overvoltage state . In response to the comparison result of the comparator 3013 at the end of the demagnetization indicating that the voltage across the control capacitor 3012 is higher than the peak voltage of the current switching cycle on the sampling resistor, the overvoltage sensing circuit 3014 does not sense the overvoltage state.

In some embodiments, the control chip 301 further includes a first switch S ₁ and a second switch S _{2. The} first switch S _{1 is} connected across the control capacitor 3012, and the second switch S _{2 is} connected in series with the control capacitor 3012 and the current between the source 3011, and wherein, when the control wafer 301 drives the opening of the second switch S ₂ is turned off, after a delay, the first switch S ₁ is opened, the driving and shutdown of the output inductor 301 of the control chip During the demagnetization, the first switch S ₁ is turned off, and the second switch S ₂ is turned on.

Figure 4 shows a schematic diagram of a sensing circuit of an output overvoltage sensing system according to an embodiment of the present invention.

As shown in FIG. 4, the system includes a control chip 401 (shown as a dashed frame) and a resistor R _SET 402 located outside the control chip 401 and coupled with the control chip 401. The chip power supply voltage is loaded into the control chip 401, and is converted into a current source current I _SET via the converter 4011 under the setting of the resistance R _SET 402 as the internal current applied to the control chip 401.

The control chip also includes a current source 4012, a first switch S ₁ 4013, a control capacitor C 4014, a second switch S ₂ 4015, a comparator 4016, and an overvoltage sensing circuit 4017.

The current source 4012 provides the internal current I _SET for the control chip 401.

The first switch S ₁ 4013 is connected across the control capacitor C 4014 and is turned on in response to a delay of T _{ON_DELAY} of the control chip driving on, and is turned off in response to the control chip driving being turned off.

The control capacitor C 4014 is discharged and cleared after the control chip 401 is driven on and delayed for a period of time T _{ON_DELAY} , and is charged by the internal current I _{SET of the} control chip 401 during the demagnetization time (T _DMG ) of the output inductor after the control chip is driven off.

The second switch S ₂ 4015 is connected in series between the control capacitor C 4014 and the current source 4012, and is turned on in response to the driving of the control chip 401 being turned off, and is turned off in response to the control chip sensing that the demagnetization of the output inductor ends (demagnetization) After the end, the control chip can enter the next switching cycle, and then enter a new loop).

The comparator 4016 compares the voltage across the control capacitor C 4014 with the peak voltage (V _{CS_PEAK} ) of the current switching cycle on the sampling resistor.

The overvoltage sensing circuit 4017 responds to a demagnetization end signal (DMG, Demagnetization) indicating that the inductance is completely demagnetized after the control chip 401 is turned off, and determines whether an overvoltage state is sensed based on the comparison result of the comparator 4016. In some embodiments, the comparison result of the comparator 4016 after the end of demagnetization indicates that the voltage across the control capacitor C 4014 is lower than the peak voltage of the current switching period on the sampling resistor, the overvoltage sensing circuit 4017 senses the overvoltage state , And the overvoltage protection is activated. After the demagnetization is over, the comparison result of the comparator 4016 indicates that the voltage across the control capacitor C 4014 is higher than the peak voltage of the current switching cycle on the sampling resistor, the overvoltage sensing circuit 4017 does not sense the overvoltage state, and the control chip works as usual .

Figure 5 shows a schematic diagram of the control waveform of an output overvoltage sensing system when an overvoltage state is sensed according to an embodiment of the present invention; Figure 6 shows an implementation according to the present invention A schematic diagram of outputting the control waveform when the overvoltage sensing system does not sense the overvoltage state of the embodiment.

As shown in Figure 5 and Figure 6, the figures both illustrate the four physical quantities (ie GATE, I _L , V _C , OVP) over time T, where GATE represents the turn-on and control chip drive Turn-off signal, _IL represents the output inductor current, V _C represents the voltage across the control capacitor, and OVP represents the sensing result signal of the overvoltage sensing circuit. In Figures 5 and 6, as an example, only two switching periods are shown. Those skilled in the art can understand that these waveform curves may include more or fewer switching periods.

First, referring to Figure 5, in the GATE curve, the high level represents the turn-on time of the control chip drive, and the low level represents the turn-off time of the control chip drive. As shown in the figure, it can be seen that the control chip is _turned on first in each switching cycle, and after a period of time (shown by the dotted line in the figure), it enters T _{ON_DELAY} (during this time, the first switch S _{1 is turned} on). Please note that the second switch S ₂ is turned off during the entire turn-on time of the control chip drive. Then, the control chip is turned off, and the output inductor enters the demagnetization time T _DMG (during this time, the second switch S _{2 is} turned on, and the first switch S _{1 is} turned off).

Next is the output inductor current _IL curve. It can be seen that during the turn-on time of the control chip (that is, the GATE signal is at a high level), the output inductor current gradually increases from zero. After the control chip is driven off, the output inductor current During the demagnetization time (that is, the GATE signal is at a low level), the output inductor current gradually decreases to zero. When the control chip drive is turned off (that is, when the GATE signal transitions from a high level to a low level), the output inductor current reaches the peak value I _{L_PEAK} .

Next is the voltage V _C curve across the control capacitor. It can be seen that after the control chip drive is _turned on for a period of time (this time corresponds to the delay from the control chip drive on to the T _{ON_DELAY} in the GATE signal curve) Time), the voltage across the control capacitor drops to zero, that is, clears and resets. After that, during the demagnetization time T _DMG of the output inductor after the control chip is driven off, the control capacitor is gradually increased due to the internal current I _{SET of the} control chip being charged. In the figure, the peak voltage across the control capacitor is less than the peak voltage V _{CS_PEAK of the} sampling resistor.

Next is the OVP curve of the sensing result signal of the overvoltage sensing circuit. It can be seen from it that during the driving on time of the control chip and before the voltage V _C across the control capacitor is reset and cleared, the sensing of the overvoltage sensing circuit The measurement result signal OVP is at a high level, so the overvoltage state is sensed, and the overvoltage protection is activated.

The difference between Figure 6 and Figure 5 is the voltage V _C across the control capacitor and the OVP curve of the sensing result signal of the overvoltage sensing circuit. Because the peak voltage across the control capacitor in each switching cycle is greater than the peak voltage V _{CS_PEAK of the} sampling resistor. Therefore, the overvoltage condition is not sensed during these two switching cycles.

According to the output overvoltage sensing system of the present invention, it is convenient to realize voltage sensing and then realize the output overvoltage protection function when the reference ground of the control chip cannot directly sense the output voltage or the voltage across the output inductor, without additional auxiliary The circuit can therefore help reduce the size of the system and thereby reduce costs.

Figure 7 shows a flowchart of an output overvoltage sensing method according to an embodiment of the present invention. As shown in Figure 7, the output overvoltage protection method includes steps S701-S705.

In step S701, the voltage across the control capacitor in the control chip is collected, where the control capacitor is discharged and cleared after a period of delay when the control chip is driven on, and the demagnetization time of the output inductor is determined by the current of the control chip after the control chip is driven off. Source charging, where the current size of the current source of the control chip is set by a resistor externally coupled to the control chip.

In step S702, the peak voltage of the current switching cycle on the sampling resistor is obtained.

In step S703, the voltage across the control capacitor is compared with the peak voltage.

In step S704 and step S705, in response to a demagnetization end signal indicating that the output inductor is completely demagnetized after the control chip is driven off, it is determined whether an overvoltage state is sensed based on the comparison result. In some embodiments, when the comparison result of the comparator indicates that the voltage across the control capacitor is lower than the peak voltage of the current switching cycle on the current sampling resistor, the overvoltage state is sensed; the comparison result of the comparator indicates that the two When the voltage at the terminal is higher than the peak voltage of the current switching cycle on the current sampling resistor, the overvoltage state is not sensed and the control chip works as usual.

In some embodiments, the on-off time of the control chip is determined by the state of the system and the demagnetization time of the output inductor. Specifically, the control chip may further include a first switch and a second switch, the first switch is connected across the control capacitor, and the second switch is connected in series between the control capacitor and the current source, and wherein the driving of the control chip is turned on When the second switch is turned off, after a delay, the first switch is turned on, and when the output inductor is demagnetized after the control chip is driven off, the first switch is turned off and the second switch is turned on.

Fig. 8 shows a flowchart of a specific example of a method for output overvoltage sensing according to an embodiment of the present invention. As shown in Figure 8, the output overvoltage sensing method of this example includes steps S801-S808.

In step S801, the current I _SET of the current source of the control chip is set by controlling the resistor R _SET externally coupled to the chip. The current I _{SET is} used as the internal current applied to the control chip.

In step S802, during the demagnetization time of the output inductor of the control chip, the current I _SET of the current source charges the control capacitor in the control chip.

In step S803, the voltage across the control capacitor is collected.

In step S804, the peak voltage of the current switching cycle on the sampling resistor is obtained.

In step S805, the voltage across the control capacitor is compared with the peak voltage.

In step S806 and step S807, in response to a demagnetization end signal indicating that the output inductor is completely demagnetized after the control chip is driven off, it is determined whether an overvoltage state is sensed based on the comparison result. In some embodiments, when the comparison result of the comparator indicates that the voltage across the control capacitor is lower than the peak voltage of the current switching cycle on the current sampling resistor, the overvoltage state is sensed; the comparison result of the comparator indicates that the two When the voltage at the terminal is higher than the peak voltage of the current switching cycle on the current sampling resistor, the overvoltage state is not sensed and the control chip works as usual.

In step S808, after the control chip drive is turned on for a period of time delay, the control capacitor is discharged and cleared.

According to the output overvoltage sensing method of the above embodiment, it is convenient to control The chip's reference ground cannot directly sense the output voltage or the voltage across the output inductor to achieve voltage sensing and then realize the output over-voltage protection function without additional auxiliary circuits, so it can help reduce the size of the system and thereby reduce the cost .

The technical principle of implementing output overvoltage protection of the present invention is given below. As mentioned above, the conditions for controlling the chip to enter the overvoltage protection are:

In addition, the output inductor transfers the energy of the inductor to the output capacitor during the demagnetization phase, and the calculation formula is: V _OUT . T _DMG = L. I _{CS_PEAK} (2)

Through the above two calculation formulas, it can be concluded that the conditions for the V _OUT voltage to enter the protection are:

Where V _C represents the voltage across the control capacitor, C is the capacitance value of the control capacitor, I _SET is the internal current of the control chip, T _DMG is the demagnetization time of the output inductor after the control chip is driven off, and V _{CS_PEAK} is the peak voltage of the sampling resistor , I _{CS_PEAK} represents the current flowing through the sampling resistor, R _CS represents the resistance value of the sampling resistor, L is the inductance value of the output inductor, and V _OUT represents the output voltage. The capacitance value C of the control capacitor is a fixed value, and the inductance value L of the output inductor and the resistance value R _{CS of the} sampling resistor are also fixed values under the same system.

Therefore, only by adjusting the resistance of the R _SET resistor to change the I _SET current, the output overvoltage protection threshold of the output voltage can be set. Therefore, when it is inconvenient to directly sense the output voltage or the voltage across the output inductor, the overvoltage state is sensed by sensing the voltage across the control capacitor and comparing it with the peak voltage of the current switching cycle of the sampling resistor , And then decide whether to activate the overvoltage protection.

Please note that “one embodiment”, “another embodiment”, and “another embodiment” are mentioned above. However, it should be understood that the features mentioned in each embodiment are not necessarily only applicable Used in this embodiment, but may be used in other embodiments. Features in one embodiment may be applied to another embodiment, or may be included in another embodiment.

The ordinal numbers such as "first" and "second" are mentioned above. However, it should be understood that these expressions are only for the convenience of narrative and reference, and there is no sequence relationship between the defined objects.

The present invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in the specific embodiment can be modified, and the system architecture does not deviate from the basic spirit of the present invention. Therefore, the current embodiments are regarded as illustrative rather than restrictive in all aspects, and the scope of the present invention is defined by the scope of the attached patent application rather than the above description, and the meaning and equivalents falling within the scope of the patent application All changes within the scope of things are thus included in the scope of the present invention.

301‧‧‧control chip

302‧‧‧Resistor

303‧‧‧Load

3011‧‧‧Current source

3012‧‧‧Control capacitor

3013‧‧‧Comparator

3014‧‧‧Overvoltage sensing circuit

Claims (8)

An output overvoltage sensing system, comprising: a control chip, a resistor, located outside the control chip and coupled with the control chip; characterized in that, the control chip includes a current source, a control capacitor, a comparator, an overvoltage sensor The measuring circuit, wherein the magnitude of the current of the current source is set by the resistor externally coupled to the control chip, wherein the control capacitor is discharged and cleared after the control chip is turned on for a period of time. The output inductor is charged by the current source of the control chip during the demagnetization time after the control chip is driven off, wherein the comparator compares the voltage across the control capacitor with the peak voltage of the current switching cycle on the sampling resistor; In addition, the overvoltage sensing circuit responds to a demagnetization end signal indicating that the output inductor is completely demagnetized after the control chip is driven off, and determines whether an overvoltage state is sensed based on the comparison result of the comparator. The output overvoltage sensing system according to item 1 of the scope of patent application, wherein, when the comparison result of the comparator indicates that the voltage across the control capacitor is lower than the peak voltage of the current switching cycle on the sampling resistor , The overvoltage sensing circuit senses an overvoltage state. The output overvoltage sensing system according to item 1 of the scope of patent application, wherein, when the comparison result of the comparator indicates that the voltage across the control capacitor is higher than the peak voltage of the current switching cycle on the sampling resistor , The overvoltage sensing circuit does not sense an overvoltage state. According to the output overvoltage sensing system described in item 1 of the scope of patent application, the control chip further includes a first switch and a second switch, the first switch is connected across the control capacitor, and the first switch Two switches are connected in series between the control capacitor and the current source, and wherein, when the control chip is turned on, the second switch is turned off. After a delay of the period of time, the first switch is turned off. Turn on, and after the control chip is driven off, the When the output inductor is demagnetized, the first switch is turned off and the second switch is turned on. An output overvoltage sensing method, including collecting the voltage across a control capacitor in a control chip, characterized in that the control capacitor is discharged and cleared after the control chip is turned on for a period of time, and the control chip is driven The output inductor is charged by the current source of the control chip during the demagnetization time after the switch is turned off, wherein the current of the current source of the control chip is set by the resistor externally coupled to the control chip; the current switching period on the sampling resistor is collected Comparing the voltage across the control capacitor with the peak voltage; and responding to the demagnetization end signal indicating that the output inductor is completely demagnetized after the control chip is driven off, based on the comparison result of the comparison To determine whether an overvoltage condition is sensed. The output overvoltage sensing method according to item 5 of the scope of patent application, wherein, when the comparison result of the comparison indicates that the voltage across the control capacitor is lower than the peak voltage of the current switching cycle on the sampling resistor, An overvoltage condition is sensed. The output overvoltage sensing method according to item 5 of the scope of patent application, wherein when the comparison result of the comparison indicates that the voltage across the control capacitor is higher than the peak voltage of the current switching cycle on the sampling resistor, The overvoltage condition is not sensed. The output overvoltage sensing method according to item 5 of the scope of patent application, wherein the control chip further includes a first switch and a second switch, the first switch is connected across the control capacitor, and The second switch is connected in series between the control capacitor and the current source, and wherein, when the control chip is driven to turn on, the second switch is turned off. After a delay of the period of time, the first The switch is turned on, and when the output inductor is demagnetized after the control chip is turned off, the first switch is turned off and the second switch is turned on.

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