Flyback-based OTP circuit

Abstract

A switching power supply overheat protection circuit, control circuit, and overheat protection method, which relate to the field of power adapters and are used to achieve an accurate overheat protection function. In response to the problem that it is not easy to implement an external overheat protection function in some current scenarios, an overheat protection circuit is provided. By installing a temperature detection circuit between conventional pins, external temperature detection is introduced. During the on period of the power switch, a voltage clamp is further used to realize the formation of a potential difference across both terminals of the temperature detection circuit. Since the temperature of the switching power supply is judged through the change in the current flowing through the temperature detection circuit, it is possible to realize an external overheat protection function for the switching power supply. In addition, since the temperature detection circuit has unidirectional conductivity from the control terminal to the sampling terminal during the on time and off time of the operating power switch, the overheat protection function is realized on the premise of not affecting the realization of the conventional function, and it better meets the needs in the actual application aspect of the switching power supply.

Description

Technical Field

[0001] This application relates to the field of power adapters, and particularly to an overheat protection circuit, a control circuit, and an overheat protection method for a switching power supply.

Background Art

[0002] In current power application scenarios, as an energy supply device, the power supply is prone to heat generation. If the temperature is too high, there will be risks such as spontaneous combustion and explosion, which may cause unexpected losses. Currently, power adapters usually have a built-in overheat protection function, but the built-in overheat protection function generally has poor accuracy and cannot meet the requirements in some specific application scenarios. In such cases, it is necessary to use an external NTC (Negative Temperature Coefficient, referring to the thermistor phenomenon and materials with a negative temperature coefficient) resistor to achieve precise overheat protection. Otherwise, there is a risk that the power supply overheats and the equipment explodes.

[0003] In the SSR Flyback structure (Flyback: Flyback Converter; SSR: Secondary Side Regulator), since it was urgent to achieve overheat protection for the primary side Pulse Width Modulation (PWM) controller through an external NTC resistor, it was necessary to provide a pin for connecting the NTC resistor to the PWM controller to realize the overheat protection function. As shown in Figure 1, in a system based on the SSR Flyback structure, in addition to the conventional VCC, DEMG, GND, Comp, SENSE, and GATE terminals, the PWM controller requires an additional pin (RT) outside the specified ones to detect the change in the resistance value of the NTC resistor (R_NTC) and achieve external overheat protection. Among them, the DEMG terminal is a port for the PWM controller to sample the demagnetization signal of the switching power supply, and the GATE terminal is a control terminal for controlling the on / off of the power switch (M120) of the switching power supply.

[0004] However, in the case of a 6-pin (PIN) package (SOT23-6), there is no spare pin for connecting the NTC resistor to implement the NTC overheat protection function, and since each of the conventional pins already realizes its own function, randomly connecting the NTC resistor may affect the realization of the conventional functions.

[0005] Therefore, currently, those skilled in the art are in urgent need of an overheat protection circuit to solve the problem that it is not easy to implement the overheat protection function in the current SSR Flyback structure. SUMMARY OF THE INVENTION

[0006] An object of the present application is to provide an overheat protection circuit, a control circuit, and an overheat protection method for a switching power supply, and to solve the problem that it is not easy to implement the overheat protection function in the current SSR Flyback structure.

[0007] To solve the above technical problem, the present application provides an overheat protection circuit applied to a switching power supply having a power switch. The overheat protection circuit includes: a control circuit coupled to the power switch and configured to control the on and off of the power switch via a control terminal, the control circuit having a sampling terminal for sampling a demagnetization signal of the switching power supply; a temperature detection circuit coupled between the control terminal and the sampling terminal; During the on period of the power switch, the control circuit clamps the voltages of the control terminal and the sampling terminal to form a potential difference, and overheat-protects the switching power supply according to the change in the current flowing through the temperature detection circuit. During the off period of the power switch, the current direction of the temperature detection circuit is characterized by one-way conduction from the control terminal to the sampling terminal.

[0008] Preferably, the temperature detection circuit includes an overheat protection resistor and a diode, and is serially coupled between the control terminal and the sampling terminal. The current flowing direction is from the first terminal after serial connection to the second terminal after serial connection. The first terminal after serial connection is connected to the control terminal, and the second terminal after serial connection is connected to the sampling terminal.

[0009] Preferably, the control circuit includes a clamp circuit, a current mirror, a comparator, and a pull-down transistor. The input terminal of the clamp circuit is connected to the positive power supply, and the output terminal of the clamp circuit is connected to the input terminal of the current mirror, and is used to clamp at a fixed voltage value greater than 0 where the high level of the control terminal is set. The first output terminal of the current mirror is grounded through the pull-down transistor and is connected to the control terminal, and the second output terminal of the current mirror is connected to the input terminal of the comparator. The comparator is used to output a corresponding overheat protection signal according to the magnitude relationship between the current value input to the current mirror and a predetermined threshold value.

[0010] Preferably, the predetermined threshold value is positively correlated with the voltage value of the positive power supply.

[0011] Preferably, the comparator is a current comparator. Correspondingly, the second output terminal of the current mirror is connected to the first input terminal of the current comparator, the predetermined threshold value is a reference current value, and is input to the second input terminal of the current comparator.

[0012] Preferably, the comparator is a voltage comparator. Correspondingly, the control circuit further includes a current-voltage converter. The second output terminal of the current mirror is connected to the first input terminal of the voltage comparator through the current-voltage converter, the predetermined threshold value is a reference voltage value, and is input to the second input terminal of the voltage comparator.

[0013] Preferably, the control circuit further includes a first voltage divider and a voltage-current converter. Correspondingly, the output terminal of the clamp circuit is further connected to the input terminal of the voltage-current converter via a first voltage divider, and the output terminal of the voltage-current converter is connected to the second input terminal of the current comparator and is used to provide a reference current value.

[0014] Preferably, the control circuit further includes a second voltage divider. Correspondingly, the output terminal of the clamp circuit is further connected to the second input terminal of the voltage comparator via a second voltage divider and is used to provide a reference voltage value.

[0015] Preferably, it further includes a switch for controlling whether the temperature detection circuit operates.

[0016] Preferably, the switch is a first switch installed between the clamp circuit and the current mirror.

[0017] Preferably, the switch is a second switch installed between the second output terminal of the current mirror and the pull-down transistor and the control terminal.

[0018] Preferably, the temperature detection circuit further includes a resistor connected in series in the temperature detection circuit.

[0019] In order to solve the above technical problems, the present application provides a control circuit for a switching power supply having a power switch. A control terminal coupled to the power switch for controlling the on and off of the power switch. A sampling terminal for sampling the demagnetization signal of the switching power supply. A temperature detection circuit coupled between the control terminal and the sampling terminal and having a one-way conduction in the current direction from the control terminal to the sampling terminal. A clamp circuit for clamping the voltages of the control terminal and the sampling terminal during the on period of the power switch to form a potential difference. A comparison circuit that compares the magnitude relationship between the current flowing through the temperature detection circuit and a predetermined threshold value and outputs a thermal protection signal that serves as a basis for triggering a thermal protection operation is included.

[0020] Preferably, the comparison circuit includes a current mirror, a comparator, and a pull-down transistor. The input terminal of the clamp circuit is connected to the positive power supply, and the output terminal of the clamp circuit is connected to the input terminal of the current mirror. The first output terminal of the current mirror is grounded through a pull-down transistor and connected to the control terminal, and the second output terminal of the current mirror is connected to the input terminal of the comparator. The comparator is used to output a corresponding thermal protection signal according to the magnitude relationship between the current value input to the current mirror and a predetermined threshold value.

[0021] Preferably, the predetermined threshold value has a positive correlation with the voltage value of the positive power supply.

[0022] Preferably, the comparator is a current comparator. Correspondingly, the second output terminal of the current mirror is connected to the first input terminal of the current comparator, the predetermined threshold value is a reference current value, and is input to the second input terminal of the current comparator.

[0023] Preferably, the comparator is a voltage comparator. Correspondingly, the comparison circuit further includes a current-voltage converter. The second output terminal of the current mirror is connected to the first input terminal of the voltage comparator through a current-voltage converter, the predetermined threshold value is a reference voltage value, and is input to the second input terminal of the voltage comparator.

[0024] Preferably, the comparison circuit further includes a first voltage divider and a voltage-current converter. Correspondingly, the output terminal of the clamp circuit is further connected to the input terminal of the voltage-current converter through the first voltage divider, and the output terminal of the voltage-current converter is connected to the second input terminal of the current comparator and is used to provide a reference current value.

[0025] Preferably, the comparison circuit further includes a second voltage divider, Correspondingly, the output terminal of the clamp circuit is further connected to the second input terminal of the voltage comparator via the second voltage divider and is used to provide a reference voltage value.

[0026] Preferably, it further includes a switch for controlling whether the temperature detection circuit operates.

[0027] Preferably, the switch is a first switch installed between the clamp circuit and the current mirror.

[0028] Preferably, the switch is a second switch installed between the second output terminal of the current mirror and the pull-down transistor and the control terminal.

[0029] In order to solve the above technical problems, in the present application, there is further provided a temperature protection method for a switching power supply applied in a switching power supply having a power switch, During the on period of the power switch, clamping the control terminal voltage of the control circuit of the switching power supply to a first set value and clamping the sampling terminal voltage of the control circuit to a second set value, where the first set value is greater than the second set value, collecting the current change in the temperature detection circuit coupled between the control terminal and the sampling terminal, and determining the current ambient temperature of the switching power supply so that the switching power supply is overheat protected, The magnitude of the current flowing through the temperature detection circuit changes with the temperature change, and the current direction during the on period and off period of the power switch is unidirectional conduction from the control terminal to the sampling terminal.

[0030] Preferably, further, including blocking the voltage output of the control terminal within a partial time period of the on period of the power switch.

[0031] Preferably, further, During the on-period of the power switch, it includes turning on the voltage output of the control terminal at a predetermined periodic interval.

[0032] The overheat protection circuit provided by the present application introduces the collection of the ambient temperature of the switching power supply by coupling a temperature detection circuit between the control terminal and the sampling terminal of the control circuit in a switching power supply system having a power switch. Specifically, by clamping the output voltages of the control terminal and the sampling terminal during the on-period of the power switch, a potential difference is formed across the temperature detection circuit, and further, the ambient temperature of the current switching power supply is determined based on the change in the magnitude of the current flowing through the temperature detection circuit, enabling overheat protection. In addition, the temperature detection circuit of the present application further has a one-way conductivity. When the power switch tube is in the off-period, due to the turn-off of the power switch tube, the control terminal voltage is lowered. If the control terminal is directly connected to the sampling terminal, it may cause a problem of lowering the sampling terminal voltage, which affects the realization of the original function of the switching power supply control circuit. However, the temperature detection circuit with one-way conductivity used in the present application can effectively solve this problem, avoiding the reverse flow of current from the sampling terminal to the control terminal (with the positive current direction as the current flow direction) during the off-period of the power switch, without affecting the realization of the normal function of the switching power supply, multiplexing the existing pins of the control circuit, and achieving the purpose of introducing the overheat protection function. That is, without changing the conventional 6PIN package of the switching power supply control circuit, accurate overheat protection can still be realized by an external NTC resistor, better satisfying the requirements in the application aspect of the actual power adapter.

[0033] The control circuit and overheat protection method of the switching power supply provided by the present application correspond to the above overheat protection circuit, and the effects are as described above.

[0034] To more clearly explain the embodiments of the present application, the following briefly introduces the attached drawings that need to be used in the embodiments. As is obvious, the attached drawings in the following description are only some embodiments of the present application. For those skilled in the art, on the premise of not performing creative labor operations, further, other attached drawings can be obtained based on these drawings.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Modes for Carrying Out the Invention

[0036] In the following, in connection with the drawings in the embodiments of the present application, the technical means in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments of the present application, all other embodiments obtained on the premise that those skilled in the art do not perform creative labor all belong to the protection scope of the present application.

[0037] The core of the present application is to provide an overheat protection circuit.

[0038] In order for those skilled in the art to better understand the aspects of the present application, the present application will be described in more detail below in connection with the accompanying drawings and specific embodiments.

[0039] In the current application of power adapters, the power system constructed based on the SSR Flyback structure is as shown in Figure 1. In order to achieve accurate overheat protection, usually an external NTC resistor and a PWM controller are connected so that the PWM controller can detect the change in the resistance value of the NTC resistor to realize the monitoring of the system temperature, and further the overheat protection function must be realized.

[0040] Considering that the design of the switching power supply system based on the SSR Flyback structure shown in Figure 1 is relatively mature, each conventional pin of the PWM controller has its own function. In order not to affect the realization of the conventional function, currently, usually, a separate pin is used to connect to the NTC resistor to detect the change in the resistance value. As shown in Figure 1, the pin that needs to be added is the RT terminal. That is, in the realization of the conventional external NTC overheat protection mode shown in Figure 1, only the extra pin RT terminal drawn from the PWM controller and the circuit part of the NTC resistor connected to the RT terminal are the circuit parts added to realize the overheat protection function, and the other parts are all the conventional circuit parts for the system to realize its function, so they will not be described in detail here in this embodiment.

[0041] However, in some specific application scenarios, the requirements for the number of pins of the PWM controller are relatively strict. For example, when the PWM controller is under a 6PIN package (SOT23-6), at this time, all the conventional 6 pins have realized their respective functions, and there is no free pin available for detecting the resistance value of the external NTC resistor. Therefore, it is not easy to implement the overheat protection function.

[0042] Therefore, to solve the above problems, in the present application, as shown in FIG. 2, an overheat protection circuit is provided. A control circuit that is coupled to the power switch (M120) and controls the on and off of the power switch through a control terminal (that is, the GATE terminal of the PWM controller). (It can be a PWM controller that plays a control role in a conventional switching power supply), and the control circuit has a sampling terminal (that is, the DEMG terminal of the PWM controller) for sampling the demagnetization signal of the switching power supply. A temperature detection circuit coupled between the control terminal and the sampling terminal. According to the requirements generally used to realize the overheat protection function at present, the temperature detection circuit should at least include, as shown in FIG. 2, an overheat protection resistor (that is, an NTC resistor). Its resistance value changes with the temperature change. After a potential difference is applied across the overheat protection resistor, the ambient temperature of the current switching power supply can be determined according to the change in the current flowing through the overheat protection resistor. The temperature detection circuit includes the above. During the on period of the power switch, the control circuit clamps the voltages of the control terminal and the sampling terminal to form a potential difference, and implements overheat protection for the switching power supply according to the change in the current flowing through the temperature detection circuit. During the off period of the power switch, the current direction of the temperature detection circuit is unidirectional conduction from the control terminal to the sampling terminal (assuming the current direction with a positive value as the current flowing direction).

[0043] What needs to be explained here is that for the above temperature detection circuit, the temperature detection function can be realized by the overheat protection resistor. However, for the one-way conductivity of the temperature detection circuit, in a possible embodiment, as shown in FIG. 2, it can be realized by a diode. Specifically, the above temperature detection circuit includes an overheat protection resistor R_NTC and a diode D105. The overheat protection resistor R_NTC and the diode D105 are serially coupled between the control terminal and the sampling terminal. The current flowing direction is from the first terminal after serial connection to the second terminal after serial connection. The first terminal after serial connection is connected to the control terminal, and the second terminal after serial connection is connected to the sampling terminal.

[0044] What needs to be explained here is that this embodiment does not limit the serial connection order of the overheat protection resistor R_NTC and the diode D105. The overheat protection resistor R_NTC can be serially connected to the positive electrode of the diode D105, or can also be serially connected to the negative electrode of the diode D105. FIG. 2 is only one possible embodiment. Even if the positions of the overheat protection resistor R_NTC and the diode D105 described in FIG. 2 are interchanged (the connection correspondence relationship between the positive and negative electrodes of the diode D105 and the two ports of the PWM controller cannot be changed, and the positive electrode of the diode D105 must be correspondingly connected to the GATE terminal), the same function can be realized.

[0045] Here, the PWM controller, which is the control circuit in the switching power supply, also includes a clamp circuit 11, a current mirror 12, a comparator, and a pull-down transistor M1, as shown in FIGS. 3 and 4.

[0046] The input terminal of the clamp circuit 11 is connected to the power supply positive electrode VCC, and the output terminal of the clamp circuit 11 is connected to the input terminal of the current mirror 12 and is used to clamp the high level of the GATE terminal to a fixed voltage value VGATE_H greater than 0. The first output terminal of the current mirror 12 is grounded via the pull-down transistor M1 and connected to the GATE terminal. The second output terminal of the current mirror 12 is connected to the input terminal of the comparator. The comparator is used to output a corresponding overheat protection signal according to the magnitude relationship between the current value input to the current mirror 12 and a predetermined threshold value.

[0047] What should be explained here is that the devices included in the above control circuit and their connection relationships are circuit parts newly added on the basis of the conventional control circuit (PWM controller) to realize the overheat protection function. That is, in the control circuit of the present application, not only the clamp circuit 11, the current mirror 12, the comparator and the pull-down transistor M1 are included, but also the circuit configuration that the conventional control circuit should have to realize its own function is included.

[0048] That is, in order to realize the overheat protection function of the external NTC resistor, the improvement made to the original power supply system with a power switch can be divided into two parts. One part is the improvement outside the control circuit. Specifically, as shown in FIG. 2, an overheat protection resistor R_NTC and a diode D105 are installed between the DEMG terminal and the GATE terminal. The positive electrode of the diode D105 is connected corresponding to the GATE terminal, thereby avoiding the DEMG terminal from pulling down the voltage of the GATE terminal. The other part is the improvement inside the control circuit. Specifically, as shown in FIGS. 3 and 4, by installing the clamp circuit 11, the current mirror 12, the comparator and the pull-down transistor M1, the PWM control chip realizes the detection of the change in the resistance value of the overheat protection resistor R_NTC, obtains the information of the current temperature of the system, and judges whether an overheat phenomenon has occurred, whether it is necessary to execute a protection operation, etc. The above improvements are all newly added improvement points based on the original circuit without the external NTC overheat protection function system, and there is no need for the present application to modify or delete the original circuit part of the system.

[0049] Also, regarding the two-path output of the current mirror 12, the first-path output corresponding to the first output terminal connected to the GATE terminal of the current mirror 12 is the current signal actually flowing through the overheat protection resistor R_NTC, and the second-path output connected to the comparator of the current mirror 12 is another current signal proportional to the current signal of the NTC. The proportional relationship m1:m2 can be determined according to actual requirements. However, in actual applications, generally, in order to adapt to the control requirements and reduce power consumption, outputs with ratios such as m1:m2 = 1:10 or m1:m2 = 1:100 are selected.

[0050] What should be explained here is that the circuit configurations shown in FIGS. 3 and 4 are only embodiments when the comparators are the current comparator 131 and the voltage comparator 132 respectively. When a device with a comparison function other than the current comparator 131 and the voltage comparator 132 is adopted for the comparator, and when the inputs and outputs of the comparator are determined, how to adaptively adjust the circuit configuration is easy for those skilled in the art to realize, so it is not described in detail in this embodiment. For example, since the input signal recognizable by the voltage comparator 132 must be a voltage signal, and the signal output by the current mirror 12 is a current signal, as shown in FIG. 4, a current-voltage converter for converting the current signal output by the current mirror 12 into a voltage signal and inputting it into the voltage comparator 132 is further required.

[0051] At the same time, when the comparator is the current comparator 131, the circuit part added in the control circuit to realize overheat protection is as shown in FIG. 3. The second output terminal of the current mirror 12 is connected to the first input terminal of the current comparator 131, and the predetermined threshold value is the reference current value Iref, which is input to the second input terminal of the current comparator 131.

[0052] When the comparator is the voltage comparator 132, the circuit part added in the control circuit to achieve overheat protection is as shown in FIG. 4. The control circuit further includes a current-voltage converter 141. The second output terminal of the current mirror 12 is connected to the first input terminal of the voltage comparator 132 through the current-voltage converter 141. The predetermined threshold value is the reference voltage value Vref, which is input to the second input terminal of the voltage comparator 132.

[0053] Furthermore, in order to clearly explain the operating principle of the overheat protection circuit provided in the present application, the following will be described in conjunction with the signal waveform diagram of FIG. 5.

[0054] Regarding the conventional 6PIN package PWM controller, its PIN DEMG terminal has a negative clamping function. That is, when the PWM controller is overloaded (during the TON period or when the power switch of the switching power supply is on), the output voltage of the DEMG terminal is negative and is clamped at the set fixed value Vclamp. The fixed value Vclamp is adjustable, and in actual applications, generally Vclamp is set to 0 or a voltage value close to 0. Therefore, the output voltage of the DEMG terminal is as shown in FIG. 5. During the TON period, the output voltage value of the DEMG segment is 0.

[0055] Also, as can be seen from the above circuit configuration, the overheat protection resistor R_NTC is serially connected between the DEMG terminal and the GATE terminal. That is, when there is a potential difference between the output voltages of the DEMG terminal and the GATE terminal, if there is a potential difference across the overheat protection resistor R_NTC, a current will flow through the overheat protection resistor R_NTC, and the current value can be detected to determine the current temperature. The current signal to be monitored is as shown in the following expression.

[0056] I_NTC=(VGATE - VDEMG) / R_NTC Where, I_NTC is the current value of the current signal flowing through the overheat protection resistor R_NTC, VGATE is the output voltage of the GATE terminal, VDEMG is the output voltage of the DEMG terminal, and R_NTC in the formula specifically refers to the resistance value of the NTC resistor.

[0057] As can be seen from the above and FIG. 5, during the TON period, due to the negative direction clamp function of the DEMG terminal, its output voltage is clamped to a fixed value (generally 0). Furthermore, as can be seen from the overheat protection circuit provided in the present application, the output of the GATE terminal is similarly clamped to another fixed voltage value VGATE_H greater than 0 by the clamp circuit 11. Therefore, as shown in FIG. 5, VGATE and VDEMG in the above current signal display formula are determined, and only one variable R_NTC remains. The display formula of the above current signal is as follows.

[0058] I_ON_OTP = (VGATE_H - Vclamp) / R_NTC Where, I_ON_OTP is the current value flowing through the overheat protection resistor R_NTC during the TON period, VGATE_H is a fixed voltage value greater than 0, and Vclamp is a fixed voltage value equal to or close to 0.

[0059] The comparator can determine the current system temperature by detecting the current signal during the TON period and judge whether overheating has occurred. The judgment of whether overheating has occurred is related to the above predetermined threshold value, and further realizes overheat protection.

[0060] Also, what should be described here is that the embodiment of the predetermined threshold value is related to the selection of the comparator. When the comparator is the voltage comparator 132, the voltage comparator 132 outputs a corresponding signal by comparing the magnitudes of the voltage values input to the two input terminals. At this time, the realization of the predetermined threshold value should be a voltage input with one path of the voltage value fixed, which can be realized by the reference voltage provided by the reference voltage source, and the reference voltage value is the predetermined threshold value. Similarly, the same is true when the comparator is the current comparator 131. The predetermined threshold value can be realized by the reference current provided by the reference current source. When the comparator is realized by selecting a more complex device, for example, when a processor with a certain data processing ability is selected, the predetermined threshold value can also be the data stored in the processor in advance. When the processor collects a current signal (which can be converted from a current signal to a digital signal by a collection circuit), it compares with the predetermined threshold value to determine whether overheating has occurred in the current system and outputs a corresponding overheating protection signal.

[0061] Furthermore, since the overheat protection circuit provided in the present application realizes overheat protection by detecting the change in current caused by the change in the resistance value of the overheat protection resistor R_NTC during the TON period, the DEMG terminal utilizes the characteristic that it is originally clamped in the negative direction during the TON period, and also limits the current conduction direction by the one-way conductivity of the diode D105. When the power switch is off, when the voltage of the GATE terminal becomes low and further becomes a negative value, the reverse DEMG voltage is prevented from being pulled down, and the influence of the connection between the DEMG terminal and the GATE terminal is removed, so that the multiplexing of pins is realized without affecting the realization of functions such as the original line voltage sampling (Line Compensation) and output voltage (Vout OVP / UVP) sampling.

[0062] The overheat protection circuit provided by this application realizes the detection of the overheat protection resistance R_NTC current by multiplexing the pins of a conventional PWM controller. By detecting the current during the TON period, on the one hand, in line with the installation of the clamp circuit 11, the change in current is related only to the change in the NTC resistance value, satisfying the detection requirements for realizing the overheat protection function. On the other hand, in line with the installation of the diode D105, the current between the GATE terminal and the DEMG terminal is made to conduct in one direction, avoiding the situation where the GATE terminal pulls down the voltage of the DEMG terminal during the off period of the power switch, and better satisfying the need to realize the overheat protection of the external NTC of the power adapter without adversely affecting the realization of the conventional functions of the multiplexed pins.

[0063] Furthermore, in the application of an actual power adapter, in some systems, the power supply positive electrode (VCC) voltage in actual application is not always constant. When in a light load state or within a certain output voltage range, the VCC voltage is relatively low. Also, as in the display formula of the above monitoring current signal, if VCC < VGATE_H, the change in the current value of I_ON_OTP is small, and the monitored I_ON_OTP is not accurate, and an accurate overheat protection function cannot be realized.

[0064] Therefore, to solve the above problems, a more suitable embodiment is provided in this example, and the predetermined threshold is positively correlated with the power supply positive electrode voltage value.

[0065] By changing the predetermined threshold along with the change in the power supply positive electrode voltage, when the system is in a light load or the VCC voltage drops, the comparator similarly compares the current signal I_ON_OTP to be monitored currently according to the decreased predetermined threshold, determines whether an overheat phenomenon has occurred, and can realize accurate overheat protection.

[0066] Specifically, regarding how to realize the positive correlation between the predetermined threshold and the power supply positive electrode voltage value, in connection with the example where the above comparators are respectively the current comparator 131 and the voltage comparator 132, this example will be further explained.

[0067] As shown in FIG. 6, it corresponds to the case where the comparator is the current comparator 131. At this time, the output of another path separately drawn from the clamp circuit 11 is grounded and voltage-divided through the first voltage divider 151. The voltage division output by the first voltage divider 151 is converted into a current signal by the voltage-current converter 142 and then input into the second input terminal of the current comparator 131, and compared with the current signal I_ON_OTP as a reference value to determine whether an overheating phenomenon has occurred.

[0068] When the comparator is the voltage comparator 132, to realize the positive correlation between the predetermined threshold value and the power supply positive voltage, as shown in FIG. 7, the output of the clamp circuit 11 of another path is similarly drawn out and voltage-divided by the second voltage divider 152. Since the comparator is the voltage comparator 132, the distributed voltage is directly input into the second input terminal of the voltage comparator 132 and participates in the determination and control of overheat protection as the reference voltage.

[0069] It should be noted here that in this embodiment, it is not limited whether the first input terminal and the second input terminal of the comparator described in the above embodiment correspond to the positive-phase input terminal or the inverted-phase input terminal of the voltage comparator 132 or the current comparator 131. As can be seen from the operating principles of the voltage comparator 132 and the current comparator 131, when a change appears in the magnitude relationship of the input signals of the positive-phase input terminal and the inverted-phase input terminal of the comparator, the output of the comparator will invert. Therefore, the correspondence relationship between the first input terminal and the second input terminal with respect to the positive-phase input terminal and the inverted-phase input terminal shall be determined by the signal control logic for performing overheat protection according to the output signal of the comparator.

[0070] A preferred aspect provided by this embodiment is that by making the predetermined threshold value of the comparator have a positive correlation with the power supply positive voltage, the relative change of both input terminals of the comparator is realized. When the current value of the detected overheat protection resistor R_NTC decreases due to the decrease of the power supply voltage, the predetermined threshold value as the comparison reference can also be adaptively reduced accordingly. Therefore, the influence on the overheat protection judgment due to the change of the system power supply voltage is reduced, the accuracy of the overheat judgment is improved, and more accurate overheat protection is realized.

[0071] As can be seen from the above, the embodiment provided by the above embodiment can realize the external NTC overheat protection under the conventional 6PIN package, multiplex the conventional pins, and at the same time have no impact on the realization of its function. Further, in actual implementation, those skilled in the art usually desire that the above overheat protection circuit does not additionally consume excessive additional power for the system. Based on this, in this embodiment, a further preferred embodiment is provided, and the above overheat protection circuit further includes a switch for controlling whether the temperature detection circuit operates or not.

[0072] In this embodiment, by installing the switch on the main circuit of the temperature detection circuit or at any one location during the supply of the terminal voltage for the temperature detection circuit to provide a potential difference, the control of circuit on / off is realized. When the switch is off, the current flowing through the overheat protection resistor R_NTC is not detected, and the overall power consumption is reduced. However, this embodiment does not limit the quantity of the switch and the installation position in the overheat protection circuit. In the above embodiment, the circuit configuration and operating principle of the overheat protection circuit have already been clearly described. Those skilled in the art can, based on this, install the switch to control whether the entire circuit operates or not. However, regarding the installation position of the switch, in this embodiment, it is preferably installed specifically on the high-level side of the potential difference supply, that is, the output control of the control terminal voltage, and several possible embodiments are provided.

[0073] 1. As shown in FIGS. 8 and 9, the switch can be the first switch K1 installed between the clamp circuit 11 and the current mirror 12. FIG. 8 corresponds to the case where the comparator is the current comparator 131, and FIG. 9 corresponds to the case where the comparator is the voltage comparator 132.

[0074] As can be easily understood, the detection of the resistance value change of the above-mentioned overheat protection resistor R_NTC realizes the potential difference across the overheat protection resistor R_NTC by outputting a high voltage at the GATE terminal location and a zero voltage to the DEMG, generates a current, detects the current value, and determines whether an overheat phenomenon has occurred. Therefore, as shown in FIG. 8, when the first switch K1 is off, no voltage is input to the current mirror 12, which corresponds to cutting off the path where the overheat protection resistor R_NTC is located, that is, cutting off the I_ON_OTP current, and the power consumption of the system is reduced.

[0075] As shown in FIGS. 10 and 11, the switch can be the second switch K2 installed between the second output terminal of the current mirror 12, the pull-down transistor M1, and the GATE terminal. FIG. 10 corresponds to the case where the comparator is the current comparator 131, and FIG. 11 corresponds to the case where the comparator is the voltage comparator 132.

[0076] Similar to the above-mentioned first switch K1, the second switch K2 can also play a role in cutting off the I_ON_OTP current. When the detection of the I_ON_OTP current is not required, the circuit can be cut off to reduce the power consumption of the system.

[0077] It should be noted here that the above-mentioned first switch K1 and second switch K2 only distinguish the installation positions of two different switches, and do not mean that they distinguish and limit the types and specifications of the switches in the selection of the switches. At the same time, the installation positions of the two types of switches described for the above-mentioned first switch K1 and second switch K2 are only two possible embodiments, and do not represent that there are only these two types of embodiments. Also, there is no limit on the installation quantity of the above-mentioned switches, and multiple switches can be redundantly installed at different or the same positions. For example, the above-mentioned first switch K1 and second switch K2 can be installed simultaneously to ensure the power consumption reduction effect, and there is no limitation on this in this embodiment.

[0078] Regarding the on / off control of the above switch, as can be seen from the above embodiments, in the present application, in order to determine the change in the resistance value of the overheat protection resistor R_NTC by detecting the current flowing through it when the system is in the TON period, there is no need to detect the current at times other than the TON period, and the switch can be turned off to reduce power consumption.

[0079] Furthermore, it is not necessary to constantly detect the current signal I_ON_OTP throughout the TON period. The current signal I_ON_OTP can be continuously detected according to the detection accuracy, and the switch is turned off after the comparator reaches a certain number of comparison times, ensuring the accurate realization of the overheat protection function. At the same time, the power consumption of the system can be further reduced so that the power consumption generated additionally by the overheat protection circuit can be ignored for the entire power adapter system. Also, the control of turning off the switch within the above TON period can be done in the second half of the TON period. It is also possible to adopt a method of detecting the current signal I_ON_OTP by periodically turning on the switch within the TON period and turning it off for the remaining time. In this embodiment, it is not restricted.

[0080] The preferred embodiment provided by this example is to control whether the entire overheat protection circuit operates by installing a switch, and when it is not necessary, cut off the overheat protection circuit to avoid unnecessary losses brought by its operation to the system. Furthermore, the premise for realizing the overheat protection function is the detection of the change in the resistance value of the overheat protection resistor R_NTC. Since the above detection process occurs during the TON period of the system, the overheat protection circuit can be cut off through the switch during the non-TON period. Even during the TON period, according to requirements such as the actual protection accuracy, the overheat protection circuit can be selectively cut off at a certain time or within a certain period, or the overheat protection circuit can be turned on according to a predetermined periodic interval, so as to further reduce power consumption. Finally, it is possible to achieve the effect that the power consumption brought by the overheat protection circuit can be ignored for the entire power adapter system. At the same time, in this example, a preferred embodiment of the above switch installation is further provided. Specifically, by controlling whether the current signal I_ON_OTP of the GATE terminal is cut off, it is possible to control whether the entire circuit operates. Regarding the installation of the switch, redundant multiple switches can also be installed at the same or different positions to achieve a more stable control effect and better ensure the reduction of the power consumption of the system.

[0081] Also, regarding the realization of the overheat protection function, it is necessary to determine the corresponding temperature protection point. The setting of the temperature protection point is comprehensively determined according to factors such as the parameters of the overheat protection resistor R_NTC and the ratio m1:m2 of the output of the current mirror 12 to a predetermined threshold value. The predetermined threshold value is usually realized by a reference source. Considering that it is installed inside the PWM controller together with the current mirror 12, relatively speaking, it is not easy to adjust. Furthermore, the overheat protection resistor R_NTC is installed outside the PWM control chip and is externally connected. However, it is also not easy to adjust the temperature protection point by the overheat protection resistor R_NTC. Therefore, in this example, a preferred embodiment for this is provided. As shown in FIG. 2, the overheat protection circuit further includes a resistor R122 serially connected in the circuit where the overheat protection resistor R_NTC and the diode D105 are located.

[0082] The resistor added in this embodiment is a resistor for adjusting the temperature protection point. According to the requirements of different temperature protection points, resistors with different resistance values are serially connected into the circuit where the overheat protection resistor R_NTC and the diode D105 are located. This type of temperature protection point adjustment method can be more easily implemented compared to the method of adjusting the internal circuit and devices of the PWM controller chip or adjusting the overheat protection resistor R_NTC, and the cost can also be more easily controlled, which better meets the needs of the actual application scenario.

[0083] In the above embodiment, the overheat protection circuit is described in detail. However, in this application, embodiments corresponding to the control circuit of the switching power supply are further provided. As described in the above embodiment of the overheat protection circuit, the main improvement made by the switching power supply control circuit provided in this embodiment can be divided into internal and external parts. The basis for dividing the internal and external parts is whether it is integrated in the control circuit existing in the form of a chip or the like. Specifically, the above control circuit includes a control terminal (i.e., the above GATE terminal) coupled to the power switch to control the on and off of the power switch, and a sampling terminal (i.e., the above DEMG terminal) for sampling the demagnetization signal of the switching power supply, and a temperature detection circuit coupled between the control terminal and the sampling terminal and having a one-way conduction in the current direction from the control terminal to the sampling terminal, and a clamp circuit for clamping the voltages of the control terminal and the sampling terminal during the on period of the power switch to form a potential difference, and a comparison circuit for comparing the magnitude relationship between the current flowing through the temperature detection circuit and a predetermined threshold value and outputting an overheat protection signal serving as the basis for triggering the overheat protection operation.

[0084] Among them, the control terminal and the sampling terminal are pins of a control circuit integrated in the form of a chip or the like (for example, a PWM controller), and are connected to other circuit parts in the switching power supply to be used for realizing the basic functions of the control circuit. For example, as shown in FIG. 2, the control terminal is used to control the on / off of the power switch M120 coupled thereto, and the sampling terminal is used to sample the demagnetization signal of the switching power supply. The above control terminal, sampling terminal, and temperature detection circuit are all improvements outside the control circuit chip, and can be regarded as part of the control circuit in the same way, and are realized in the form of an external circuit. For the above clamp circuit and comparison circuit, they are circuits integrated in the control circuit chip.

[0085] It should be explained here that the PWM controller used in the switching power supply as in the above embodiment, as the above control circuit, its sampling terminal itself has a clamp function. When the PWM controller is in an overload state or the power switch of the switching power supply is in the on period, the sampling terminal has a negative direction clamp function. In actual applications, generally, the sampling terminal voltage is clamped to 0V or a voltage value close to 0V. Also, since there is a potential difference between the above sampling terminal and the control terminal, the overheat protection requirement must be satisfied, and in the specified current flowing direction, it is necessary to avoid preventing the realization of the original function of the control circuit. Generally, the output of the control terminal voltage is set to a high level, and the current flowing direction of the temperature detection circuit is from the control terminal to the sampling terminal.

[0086] Since other embodiments of the control circuit part of the switching power supply provided by this embodiment correspond to the embodiments of the above overheat protection circuit part, for the embodiments of the control circuit part, the description of the embodiments of the above overheat protection circuit part shall be referred to, and will not be elaborated here again.

[0087] The control circuit of the switching power supply provided by this embodiment multiplexes the conventional control terminal and sampling terminal of the pin, and connects a temperature detection circuit therebetween. The temperature detection circuit can be realized by an external NTC resistor according to the actual overheat protection requirement. When the ambient temperature around the switching power supply changes, the resistance value of the NTC resistor also changes accordingly. Further, the output voltage during the power switch-on period of the control terminal and the sampling terminal is clamped by a clamp circuit. To ensure that the power switch is on, the voltage of the control terminal is clamped to a high level. Since the sampling terminal of a conventional control circuit, such as a PWM controller, generally also has a negative-direction clamping function when the power switch is on, a potential difference is formed between the two terminals, and current flows through the temperature detection circuit. By comparing the magnitude relationship between the current flowing through the temperature detection circuit and a predetermined threshold value by a comparison circuit, the overheat protection function can be realized. The overheat protection function realized by this embodiment realizes the introduction of an external NTC overheat protection function on the premise of not adding new pins. Moreover, the overheat protection function operates during the on period of the power switch of the switching power supply. Further, due to the one-way conductivity of the temperature detection circuit, the occurrence of current backflow during the off period of the power switch (defining the flowing direction of the current with a positive value as the current direction and avoiding the backflow of current from the sampling terminal to the control terminal) is avoided, and the interference with the realization of the original function of the sampling terminal is also avoided. In summary, the control circuit provided by this embodiment can realize the introduction of an external NTC overheat protection function by multiplexing the conventional pins on the premise of not interfering with the realization of the original function of the control circuit, and better satisfies the requirements in the actual application scenario.

[0088] Except for the above overheat protection circuit and the control circuit of the switching power supply having corresponding features, in this application, further, an overheat protection method for the switching power supply is provided. During the on period of the power switch, clamp the voltage of the control terminal of the control circuit of the switching power supply to a first set value, and clamp the voltage of the sampling terminal of the control circuit to a second set value, where the first set value is greater than the second set value. Collecting the current change in the temperature detection circuit coupled between the control terminal and the sampling terminal to determine the current ambient temperature of the switching power supply so that the switching power supply is overheat protected, The magnitude of the current flowing through the temperature detection circuit changes with temperature changes, and the current direction during the on-period and off-period of the power switch is unidirectional conduction from the control terminal to the sampling terminal.

[0089] Regarding the hardware implementation of the above method, specifically, reference can be made to the above embodiments of the overheat protection circuit part (the embodiments of the control circuit part and the overheat protection circuit part have the same or corresponding technical features), and for this embodiment, it will not be elaborated here again.

[0090] However, this embodiment further provides a preferred embodiment related to the above overheat protection method. Specifically, in a preferred embodiment, the above method further includes During a part of the on-period of the power switch, blocking the voltage output of the control terminal.

[0091] In another preferred embodiment, the above method further includes During the on-period of the power switch, turning on the voltage output of the control terminal at a predetermined periodic interval.

[0092] Regarding the overheat protection control of the above two preferred embodiments, the purpose is to reduce the unnecessary losses caused by the overheat protection circuit. As can be seen from the embodiments of the above circuit part, the overheat protection function is realized during the TON period, that is, during the on-period of the power switch of the switching power supply. However, according to the differences in actual application requirements, it is not necessary to always perform temperature detection throughout the entire TON time for overheat protection. Therefore, the on / off of the above overheat protection function is realized by a switch for controlling whether the temperature detection circuit operates, which is disclosed in the embodiments of the circuit part. Specifically, the purpose of energy saving is realized by controlling whether a high-level voltage is output at the control terminal.

[0093] The overheat protection method for the switching power supply provided by this embodiment utilizes the sampling terminal and the control terminal of the conventional pins of the switching power supply control circuit to clamp its output voltage when the power switch is on. On the one hand, a potential difference is formed for use by the temperature detection circuit, and on the other hand, it does not affect the realization of the normal functions of the control circuit. Also, the above temperature detection circuit has a one-way conductivity, and even when the power switch is in the off state, no reverse current occurs, and it is avoided that the control terminal voltage pulls down the sampling terminal voltage, and the realization of its normal function is also avoided. Summing up the above, the overheat protection method provided by this embodiment can realize an external NTC overheat protection function by using the existing pins on the premise of not affecting the realization of the functions of the existing control circuit, and better meets the need to protect the actual switching power supply circuit. Also, this embodiment further provides several preferred embodiments, and reduces energy consumption by controlling the high-level voltage supply of the overheat protection function (that is, the voltage output of the control terminal).

[0094] The above is a detailed introduction to the overheat protection circuit, control circuit and overheat protection method for the switching power supply provided by this application. Each embodiment in the specification is described in an incremental manner, and what each embodiment focuses on explaining is the difference from other embodiments. For the same or similar parts between each embodiment, only cross-reference is needed. Regarding the device disclosed in the embodiment, in order to correspond to the method disclosed in the embodiment, it is described relatively simply, and for the relevant parts, only refer to the description of the method part. It should be pointed out here that those skilled in the art can make some improvements and modifications to this application on the premise of not departing from the principle of this application, and these improvements and modifications are also included in the protection scope of the claims of this application.

[0095] It should be further noted that, in this specification, terms related to relationships such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such substantial relationship or order between those entities or operations. Further, the term "comprising", "including" or any other variation thereof is meant to cover non-exclusive inclusion, such that a process, method, article or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed or elements inherent to this kind of process, method, article or apparatus. Further, in the absence of more limitations, an element limited by the phrase "comprising..." does not exclude the presence of further identical elements in the process, method, article, or apparatus that includes the said element.

Claims

1. In a thermal protection circuit applied in a switching power supply having a power switch, a control circuit coupled to the power switch for controlling on and off of the power switch via a control terminal, the control circuit having a sampling terminal for sampling a demagnetization signal of the switching power supply; and a temperature detection circuit coupled between the control terminal and the sampling terminal, during an on period of the power switch, the control circuit clamps voltages of the control terminal and the sampling terminal to form a potential difference, and protects the switching power supply from overheating according to a change in a current flowing through the temperature detection circuit; during an off period of the power switch, a current direction of the temperature detection circuit is unidirectionally conductive from the control terminal to the sampling terminal. A thermal protection circuit characterized by this.

2. The temperature detection circuit includes a thermal protection resistor and a diode, and is serially coupled between the control terminal and the sampling terminal, a current flowing direction is from a first terminal after serial connection to a second terminal after serial connection, the first terminal after serial connection is connected to the control terminal, and the second terminal after serial connection is connected to the sampling terminal. The thermal protection circuit according to Claim 1, characterized by this.

3. The control circuit includes a clamp circuit, a current mirror, a comparator, and a pull-down transistor, an input terminal of the clamp circuit is connected to a positive power supply, and an output terminal of the clamp circuit is connected to an input terminal of the current mirror and is used for clamping to a location of a fixed voltage value greater than 0 where a high level of the control terminal is set, The first output terminal of the current mirror is grounded via the pull-down transistor and is connected to the control terminal. The second output terminal of the current mirror is connected to the input terminal of the comparator. The comparator is used to output a corresponding overheat protection signal according to the magnitude relationship between the current value input to the current mirror and a predetermined threshold value. The overheat protection circuit according to claim 1 or 2, characterized in that.

4. The overheat protection circuit according to claim 3, characterized in that the predetermined threshold value has a positive correlation with the voltage value of the positive power supply terminal.

5. The comparator is a current comparator, Correspondingly, the second output terminal of the current mirror is connected to the first input terminal of the current comparator. The predetermined threshold value is a reference current value and is input to the second input terminal of the current comparator. The overheat protection circuit according to claim 4, characterized in that.

6. The comparator is a voltage comparator, Correspondingly, the control circuit further includes a current-voltage converter, The second output terminal of the current mirror is connected to the first input terminal of the voltage comparator via the current-voltage converter. The predetermined threshold value is a reference voltage value and is input to the second input terminal of the voltage comparator. The overheat protection circuit according to claim 4, characterized in that.

7. The control circuit further includes a first voltage divider and a current-voltage converter, Correspondingly, the output terminal of the clamp circuit is further connected to the input terminal of the current-voltage converter via the first voltage divider. The output terminal of the current-voltage converter is connected to the second input terminal of the current comparator and is used to provide the reference current value. The overheat protection circuit according to claim 5, characterized in that.

8. The control circuit further includes a second voltage divider, Correspondingly, the output terminal of the clamping circuit is further connected to the second input terminal of the voltage comparator via the second voltage divider and is used to provide the reference voltage value. The overheat protection circuit according to claim 6.

9. The overheat protection circuit according to claim 3, further comprising a switch for controlling whether the temperature detection circuit operates.

10. The overheat protection circuit according to claim 9, wherein the switch is a first switch installed between the clamping circuit and the current mirror.

11. The overheat protection circuit according to claim 9, wherein the switch is a second switch installed between the second output terminal of the current mirror and the pull-down transistor and the control terminal.

12. The overheat protection circuit according to claim 2, wherein the temperature detection circuit further includes a resistor connected in series in the temperature detection circuit.

13. In a control circuit of a switching power supply having a power switch, A control terminal coupled to the power switch for controlling on and off of the power switch, A sampling terminal for sampling a demagnetization signal of the switching power supply, A temperature detection circuit coupled between the control terminal and the sampling terminal and having a one-way conduction in a current direction from the control terminal to the sampling terminal, A clamping circuit for clamping the voltages of the control terminal and the sampling terminal during the on period of the power switch to form a potential difference, A comparison circuit for comparing the magnitude relationship between the current flowing through the temperature detection circuit and a predetermined threshold value and outputting an overheat protection signal serving as a basis for triggering an overheat protection operation. A control circuit of a switching power supply, characterized by including.

14. The comparison circuit includes a current mirror, a comparator, and a pull-down transistor, The input terminal of the clamp circuit is connected to the positive power supply, and the output terminal of the clamp circuit is connected to the input terminal of the current mirror, The first output terminal of the current mirror is grounded through the pull-down transistor and is connected to the control terminal, and the second output terminal of the current mirror is connected to the input terminal of the comparator, The comparator is used to output a corresponding overheat protection signal according to the magnitude relationship between the current value input to the current mirror and a predetermined threshold value. The control circuit according to claim 13, characterized in that.

15. The control circuit according to claim 14, characterized in that the predetermined threshold value is positively correlated with the voltage value of the positive power supply.

16. The comparator is a current comparator, Correspondingly, the second output terminal of the current mirror is connected to the first input terminal of the current comparator, the predetermined threshold value is a reference current value, and is input to the second input terminal of the current comparator. The control circuit according to claim 15, characterized in that.

17. The comparator is a voltage comparator, Correspondingly, the comparison circuit further includes a current-voltage converter, The second output terminal of the current mirror is connected to the first input terminal of the voltage comparator through the current-voltage converter, the predetermined threshold value is a reference voltage value, and is input to the second input terminal of the voltage comparator. The control circuit according to claim 15, characterized in that.

18. The comparison circuit further includes a first voltage divider and a voltage-current converter, Correspondingly, the output terminal of the clamp circuit is further connected to the input terminal of the voltage-current converter through the first voltage divider, and the output terminal of the voltage-current converter is connected to the second input terminal of the current comparator and is used to provide the reference current value. The control circuit according to claim 16, characterized in that.

19. The comparison circuit further includes a second voltage divider, Correspondingly, an output terminal of the clamp circuit is further connected to a second input terminal of the voltage comparator via the second voltage divider and is used to provide the reference voltage value. The control circuit according to claim 17, characterized in that.

20. The control circuit according to claim 14, further comprising a switch for controlling whether the temperature detection circuit operates.

21. The control circuit according to claim 20, wherein the switch is a first switch installed between the clamp circuit and the current mirror.

22. The control circuit according to claim 20, wherein the switch is a second switch installed between a second output terminal of the current mirror and the pull-down transistor and the control terminal.

23. In a temperature protection method of a switching power supply applied in a switching power supply having a power switch, During the on period of the power switch, clamping the control terminal voltage of the control circuit of the switching power supply to a first set value and clamping the sampling terminal voltage of the control circuit to a second set value, wherein the first set value is greater than the second set value; Determining the current environmental temperature of the switching power supply so that the switching power supply is overheat protected by collecting a change in current in a temperature detection circuit coupled between the control terminal and the sampling terminal. A temperature protection method of a switching power supply, characterized in that the magnitude of the current flowing through the temperature detection circuit changes with temperature changes, and the current direction during the on period and the off period of the power switch is unidirectional conduction from the control terminal to the sampling terminal.

24. Further including cutting off the voltage output of the control terminal during a partial period of the on-period of the power switch The temperature protection method according to claim 23, characterized in that

25. Further including turning on the voltage output of the control terminal at a predetermined periodic interval during the on-period of the power switch The temperature protection method according to claim 24, characterized in that

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