Switching power supply and method for use in a switching power supply

Abstract

This invention provides a switching power supply and a method for using it. The switching power supply provided by this invention is used to charge a device, and includes: a secondary-side synchronous rectifier chip configured to output a temperature protection request message when the chip's body temperature is detected to be higher than a first preset threshold; and a primary-side feedback chip configured to enter an automatic restart state in response to receiving the temperature protection request message. According to the above technical solution, the secondary-side synchronous rectifier chip can be used to detect its body temperature, and when an excessively high temperature is detected, it sends a temperature protection request message to the primary-side feedback chip, causing the primary-side feedback chip to enter an automatic restart state, preventing excessively high secondary-side temperatures that could lead to problems such as fuselage.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuits, and particularly relates to a switching power supply and a method for use in a switching power supply. Background Technology

[0002] In chargers or adapters, using synchronous rectification to control ultra-low on-resistance MOSFETs instead of diode rectification can effectively reduce losses caused by the high voltage drop across the output rectifier diodes, thereby improving the overall system efficiency. This is also a simple and low-cost way to improve energy efficiency.

[0003] However, the secondary-side synchronous rectifier chip of a traditional switching power supply cannot detect its own temperature. When the temperature is too high, it may cause damage to the secondary-side switching transistor or cause problems such as fuse. Summary of the Invention

[0004] This invention provides a switching power supply and a method for use in the switching power supply. The secondary-side synchronous rectifier chip can be used to detect its body temperature, and when the temperature is detected to be too high, a temperature protection request message is sent to the primary-side feedback chip, so that the primary-side feedback chip enters an automatic restart state, preventing problems such as damage to the secondary-side switching transistor or fuse occurrence due to excessive secondary-side temperature.

[0005] On one hand, embodiments of the present invention provide a switching power supply for charging a device to be charged, comprising: a secondary-side synchronous rectifier chip configured to output temperature protection request information when the body temperature of the secondary-side synchronous rectifier chip is detected to be higher than a first preset threshold; and a primary-side feedback chip configured to enter an automatic restart state in response to receiving the temperature protection request information.

[0006] On the other hand, embodiments of the present invention provide a method for charging a device to be charged in a switching power supply. The switching power supply includes a primary-side feedback chip and a secondary-side synchronous rectification chip. The method includes: when the secondary-side synchronous rectification chip detects that its body temperature is higher than a first preset threshold, it outputs a temperature protection request message; and in response to receiving the temperature protection request message, it causes the primary-side feedback chip to enter an automatic restart state.

[0007] The switching power supply and the method used in the switching power supply provided in this invention can use the secondary-side synchronous rectifier chip to detect its body temperature, and send a temperature protection request message to the primary-side feedback chip when the temperature is detected to be too high, so that the primary-side feedback chip can be automatically restarted, preventing problems such as damage to the secondary-side switching transistor or fuse occurrence due to excessive secondary-side temperature. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of the structure of a switching power supply provided in the first embodiment of the present invention is shown;

[0010] Figure 2 A schematic diagram of the structure of a switching power supply provided in the second embodiment of the present invention is shown;

[0011] Figure 3 A schematic diagram of the structure of a switching power supply provided in the third embodiment of the present invention is shown;

[0012] Figure 4 A schematic diagram of the structure of a switching power supply provided in the fourth embodiment of the present invention is shown;

[0013] Figure 5 The diagram shows the waveform of a corresponding signal in a switching power supply provided in an embodiment of the present invention;

[0014] Figure 6 A schematic diagram of the primary-side feedback chip provided in an embodiment of the present invention is shown;

[0015] Figure 7 A schematic diagram of the secondary-side synchronous rectifier chip provided in an embodiment of the present invention is shown;

[0016] Figure 8 The diagram shows waveforms of the temperature protection cycle and normal operation cycle provided in an embodiment of the present invention.

[0017] Figure 9 The code corresponding to the temperature protection coding cycle provided in the embodiments of the present invention is shown; and

[0018] Figure 10 A flowchart illustrating a method 1000 used in a switching power supply according to an embodiment of the present invention is shown. Detailed Implementation

[0019] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0020] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended 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 such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0021] Primary-side feedback (PSR) AC / DC control technology is a novel AC / DC control technology that has developed in the last 10 years. It directly achieves high-precision constant voltage output from the primary winding or primary auxiliary winding of the transformer through a sample-and-hold circuit; at the same time, it achieves high-precision constant current output through peak current control, without the need for TL431, optocouplers, secondary feedback, and detection devices. This greatly reduces the number of system components, saves board space, lowers the overall system cost, and improves system reliability. Therefore, it has broad application prospects in small and medium power markets where size is a critical factor, such as smartphone chargers, network adapters, and LED drivers.

[0022] With the mandatory implementation of power efficiency standards, such as the US DoE VI, EU CoC V5, and GB20943, higher requirements have been placed on the efficiency of chargers and adapters. In chargers or adapters, using synchronous rectification and controlling MOSFETs with ultra-low on-resistance instead of diode rectification can effectively reduce losses caused by the high voltage drop across the output rectifier diodes, thereby improving the overall system efficiency. This is currently a simple and low-cost way to improve energy efficiency.

[0023] However, in the prior art, due to the presence of the body diode of the synchronous rectification MOSFET, when the temperature of the synchronous rectification MOSFET exceeds the preset temperature, temperature protection cannot be achieved by shutting down the control circuit of synchronous rectification.

[0024] To address one or more of the aforementioned technical problems, the switching power supply provided in this embodiment of the invention, by setting an on-chip temperature detection circuit for the synchronous rectifier chip, can realize over-temperature detection of the synchronous rectifier switching transistor (e.g., MOSFET). When the body temperature of the secondary-side synchronous rectifier chip is detected to exceed the preset value of the Over Temperature Protection (OTP), the secondary-side synchronous rectifier chip can control different turn-off modes of the synchronous rectifier switching transistor based on the detected over-temperature signal, and send the OTP protection request information to the primary-side feedback chip, so that the primary-side control system is turned off, thereby preventing problems such as damage or fuse of the secondary-side switching transistor due to excessive temperature of the secondary-side synchronous rectifier chip. The above embodiment can be implemented without adding any components, which provides a simple and reliable implementation method.

[0025] The following describes the switching power supply provided in the embodiments of the present invention, for example, referring to... Figure 1 and Figure 2 , Figure 1 A schematic diagram of the structure of a switching power supply provided in the first embodiment of the present invention is shown, and... Figure 2 A schematic diagram of the structure of a switching power supply provided in the second embodiment of the present invention is shown.

[0026] Specifically, Figure 1 It is a primary-side feedback three-winding scheme with on-chip OTP function in the secondary-side synchronous rectifier chip. Figure 2 It is a primary-side feedback three-winding scheme with external OTP function for secondary-side synchronous rectifier chips.

[0027] like Figure 1 As shown, the switching power supply mainly includes: an EMI filter 110, a primary-side feedback chip 120, a transformer T1, a secondary-side synchronous rectifier chip 130, and a USB interface 140, etc. The primary-side feedback chip 120 may include a power switch Q1, and the secondary-side synchronous rectifier chip 130 may include a synchronous rectifier switch Q2, which has a body diode D1.

[0028] like Figure 2 As shown, the switching power supply mainly includes: an EMI filter 210, a primary-side feedback chip 220, a transformer T1, a secondary-side synchronous rectifier chip 230, and a USB interface 240, etc. The primary-side feedback chip 220 may include a power switch Q1, and the secondary-side synchronous rectifier chip 230 may include a synchronous rectifier switch Q2, which has a body diode D1.

[0029] It can be seen that, in Figure 1 and Figure 2In the embodiment shown, transformer T1 may include a primary winding Npri, a secondary winding Nsec, and an auxiliary winding Naux.

[0030] Figure 1 and Figure 2 The only difference between the two schemes shown is the implementation of the OTP function. For example, Figure 1 The secondary-side synchronous rectifier chip shown has on-chip OTP functionality, which saves the number of pins and temperature sensing resistors of the secondary-side synchronous rectifier chip, thereby saving system costs. Figure 2 The secondary-side synchronous rectifier chip shown has an external OTP function, which results in an increase of one pin in the number of pins of the secondary-side synchronous rectifier chip, such as... Figure 2 The RT pin shown can achieve OTP protection function by detecting the temperature through the temperature sensing resistor NTC. Figure 1 Compared to the structure shown, Figure 2 The advantage of the structure shown is that the NTC protector can be placed according to the actual PCB design requirements, and the protection accuracy is further improved. The disadvantage is that it adds a pin, a resistor and an NTC resistor.

[0031] In addition, refer to Figure 3 and Figure 4 , Figure 3 A schematic diagram of the structure of a switching power supply provided in the third embodiment of the present invention is shown, and... Figure 4 A schematic diagram of the structure of a switching power supply provided in the fourth embodiment of the present invention is shown.

[0032] Specifically, Figure 3 It is a primary-side feedback two-winding scheme with on-chip OTP function in the secondary-side synchronous rectifier chip. Figure 4 It is a primary-side feedback two-winding scheme with external OTP function of secondary-side synchronous rectifier chip.

[0033] like Figure 3 As shown, the switching power supply mainly includes: an EMI filter 310, a primary-side feedback chip 320, a transformer T1, a secondary-side synchronous rectifier chip 330, and a USB interface 340, etc. The primary-side feedback chip 320 may include a power switch Q1 (not shown in the figure), and the secondary-side synchronous rectifier chip 330 may include a synchronous rectifier switch Q2, which has a body diode D1.

[0034] like Figure 4As shown, the switching power supply mainly includes: an EMI filter 410, a primary-side feedback chip 420, a transformer T1, a secondary-side synchronous rectifier chip 430, and a USB interface 440, etc. The primary-side feedback chip 420 may include a switching transistor Q1 (not shown in the figure), and the secondary-side synchronous rectifier chip 430 may include a switching transistor Q2, which has a body diode D1.

[0035] It can be seen that, in Figure 3 and Figure 4 In the embodiment shown, transformer T1 may include a primary winding Npri and a secondary winding Nsec.

[0036] Similar to the combination above Figure 1 and Figure 2 What is introduced Figure 3 and Figure 4 The only difference between the two schemes shown is the implementation of the OTP function, which will not be elaborated here for the sake of simplicity.

[0037] For two-winding or three-winding schemes, the protection principles of on-chip OTP and external OTP are basically the same. To simplify the description, the most commonly used and cost-effective method will be used below. Figure 1 The following description uses a switching power supply as an example. As an example, the system architecture can employ a flyback converter; it is understood that this is provided only as an example and should not be construed as restrictive. Other converters utilizing transformer isolation can also be used.

[0038] The embodiments of the present invention provide Figure 1 and Figure 3 The secondary-side synchronous rectifier chip in the switching power supply shown has an on-chip temperature detection function. For example, when the ambient temperature of the secondary-side switch Q2 (e.g., MOSFET) or the secondary-side synchronous rectifier chip exceeds the OTP preset value, the secondary-side synchronous rectifier chip can control the delayed turn-off of the secondary-side switch Q2 and send a temperature protection request message to the primary-side feedback chip via the primary winding or primary auxiliary winding of the transformer and the CS pin of the primary-side feedback chip. The primary-side feedback chip can be configured to determine whether the temperature protection request message has been received, and when the temperature protection request message is detected, determine that the temperature of the secondary-side switch or the ambient temperature of the secondary-side synchronous rectifier chip is too high, so that the primary-side feedback chip enters an automatic restart state. This can protect the system from problems such as damage to the secondary-side switch or fuses due to excessive temperature of the secondary-side switch or the ambient temperature of the secondary-side synchronous rectifier chip.

[0039] To better understand the switching power supply provided in the embodiments of the present invention, the following will use... Figure 1 The normal operating principle of the system is introduced using the switching power supply shown as an example.

[0040] like Figure 1 As shown, the switching power supply mainly includes an EMI filter 110, a rectifier bridge BD, an input capacitor Cbulk, a primary-side feedback chip 120, a primary-side current sampling resistor Rs, a transformer T1 (including a primary-side winding Npri, a secondary-side winding Nsec, and an auxiliary winding Naux), a secondary-side synchronous rectifier chip 130, a USB interface 140, and an output capacitor Co, etc.

[0041] In some embodiments, the primary-side feedback chip 120 may include a power switch Q1, and the secondary-side synchronous rectification chip 130 may include a synchronous rectification switch Q2. The above is provided by way of example only and should not be construed as limiting; for example, in other embodiments, switches Q1 and Q2 may be separately packaged.

[0042] As an example, the primary-side feedback chip 120 can be configured to start working when the input characteristic signal representing the input voltage of the switching power supply is greater than a first preset threshold; the secondary-side synchronous rectifier chip 130 can be configured to start working when the output feedback signal representing the output voltage of the switching power supply is greater than a second preset threshold.

[0043] Specifically, as shown in the figure, when the AC voltage is input, it is filtered by the EMI filter 110. The filtered AC voltage is rectified into DC voltage by the rectifier bridge BD. Then, the input capacitor Cbulk is charged using the filtered and rectified voltage. The DC voltage is used to charge the capacitor Cd through the start-up resistor Rst. When the voltage on the capacitor Cd (i.e., the voltage at the VDD pin of the primary-side feedback chip 120) is higher than the undervoltage lockout (UVLO) voltage set by the primary-side feedback chip 120, the primary-side feedback chip 120 starts to work and outputs energy to the secondary side. The body diode D1 inside the secondary-side synchronous rectifier chip 130 is turned on, causing the output voltage Vo of the switching power supply to start to rise. When the output voltage Vo is higher than the UVLO voltage set by the secondary-side synchronous rectifier chip 130, the secondary-side synchronous rectifier chip 130 starts to work.

[0044] As an example, the normal operation process of the flyback switching power supply provided in this embodiment of the invention can be mainly divided into the following stages:

[0045] In the first stage, during the conduction time of the power switch Q1, energy is stored at the primary winding Npri of the transformer T1, while the secondary winding is powered by the output capacitor Co.

[0046] In the second stage, when the power switch Q1 changes from the on state to the off state, the synchronous rectifier switch Q2 is controlled to change from the off state to the on state. During the period when the synchronous rectifier switch Q2 is in the on state, the energy stored in the primary winding Npri of the transformer T1 is released to the secondary winding of the transformer T1 (this corresponds to the demagnetization time Tdemg) to provide energy for the load and charge the output capacitor Co. At this time, the voltage on the auxiliary winding Vaux of the transformer T1 can reflect the output voltage Vo (since the synchronous rectification conduction impedance is small, the voltage drop can be ignored here). The output feedback signal VFB (that is, the output feedback signal can characterize the output voltage Vo) after the voltage Vaux on the auxiliary winding Naux is divided by resistors R1 and R2 is used as the feedback control signal and input to the primary feedback chip 120 for control via the FB pin.

[0047] In the third stage, after the synchronous rectifier switch Q2 changes from the on state to the off state, the inductance Lmi of the primary winding Npr of the transformer T1 and the output capacitance Coss of the power switch Q1 resonate (corresponding to the resonance time Tring). Depending on the output load, the primary feedback chip 120 can control the power switch Q1 to change from the off state to the on state at different resonance valleys. The above three processes are repeated, and finally the desired output voltage and output current are provided to the device to be charged through the USB interface 140.

[0048] Combination Figure 1 and Figure 5 ,in Figure 5 The diagram shows a waveform of a corresponding signal in a switching power supply provided in an embodiment of the present invention.

[0049] In this circuit, waveform PSR gate represents the control signal of the primary-side feedback chip 120 used to control the on and off of power switch Q1; waveform PSR Ipk represents the current flowing through the primary winding (also called primary current); waveform PSR FB represents the output feedback signal used to characterize the output voltage; waveform SR Vdrain represents the voltage at the drain of synchronous rectifier switch Q2 in the secondary-side synchronous rectifier chip 130; waveform SR gate represents the control signal of the secondary-side synchronous rectifier chip 130 used to control the on and off of synchronous rectifier switch Q2; waveform SR Isk represents the current flowing through the secondary winding (also called secondary current); Tdemg corresponds to the demagnetization time; and Tring corresponds to the resonance time. The correspondence between the waveforms of each signal is as follows: Figure 5 As shown, for the sake of simplicity, further details will not be elaborated here.

[0050] In the switching power supply provided in this embodiment of the invention, the primary-side feedback chip can control the power switch Q1 to turn on and off, and the secondary-side synchronous rectification chip can control the synchronous rectification switch Q2 to turn on and off, with the two switches working interactively.

[0051] As an example, the secondary-side synchronous rectifier chip can be configured to output a temperature protection request message when the body temperature of the secondary-side synchronous rectifier chip is detected to be higher than a first preset threshold, and the primary-side feedback chip can be configured to enter an automatic restart state in response to receiving the temperature protection request message.

[0052] Specifically, the synchronous rectifier chip can have on-chip temperature detection. When the temperature of the synchronous rectifier switch Q2 or the temperature around the synchronous rectifier chip exceeds, for example, an OTP preset value, the synchronous rectifier switch Q2 can be delayed and turned off. A temperature protection request message is output and sent to the primary feedback chip through the primary main winding or primary auxiliary winding of transformer T1 and the CS pin of the primary feedback chip. When the primary feedback chip detects the temperature protection request message, it can determine that the temperature of the synchronous rectifier switch Q2 or the temperature around the synchronous rectifier chip is too high, causing the primary feedback chip to enter an automatic restart state. This protects the system from safety problems such as damage to the synchronous rectifier switch Q2 or fuses due to excessively high temperatures around the synchronous rectifier chip Q2 or the synchronous rectifier chip.

[0053] To better understand the working principle of the switching power supply provided in the embodiments of the present invention, specific examples are given below. Figure 1 The specific implementation of the primary-side feedback chip in the shown switching power supply is described. (Reference) Figure 6 , Figure 6 A schematic diagram of the primary-side feedback chip provided in an embodiment of the present invention is shown.

[0054] like Figure 6 As shown, the primary-side feedback chip 120 may include VDD pin, FB pin, GND pin, CS pin and Drain pin, etc., and may include UVLO and AVDD modules 1202, reference signal generation module 1204, protection module 1206, sampling module 1208, demagnetization detection module 1210, constant voltage control module 1212, current detection module 1214, OTP detection module 1216, constant current control module 1218, logic control module 1220 and gate drive module 1222, etc.

[0055] As an example, the first terminal of UVLO and AVDD module 1202 is connected to the VDD pin, the second terminal is connected to the first terminal of reference signal generation module 1204, and the third terminal can output a Power Good (PG) signal. The second terminal of reference signal generation module 1204 can output a reference voltage Vref. The first terminal of protection module 1206 is connected to the FB pin, and the second terminal of protection module 1206 is connected to the first terminal of logic control module 1220. The first terminal of sampling module 1208 is connected to the FB pin, and the second terminal of sampling module 1208 is connected to the first terminal of constant voltage control module 1212. The second terminal of constant voltage control module 1212 receives Vref_cv. The first terminal of demagnetization detection module 1210 is connected to the FB pin, and the second terminal of demagnetization detection module 1210 is connected to the first terminal of constant current control module 1218. The first terminal of current detection module 1214 is connected to the CS pin, and the second terminal of current detection module 1214 is connected to the third terminal of constant voltage control module 1212. The third terminal of current detection module 1214 is connected to the third terminal of constant current control module 1218. Two terminals: the fourth terminal of the current detection module 1214 is connected to the first terminal of the OTP detection module 1216; the second terminal of the OTP detection module 1216 is connected to the fourth terminal of the constant voltage control module 1212; the fifth terminal of the constant voltage control module 1212 is connected to the second terminal of the logic control module 1220; the third terminal of the constant current control module 1218 is connected to the third terminal of the logic control module 1220; the third and fourth terminals of the OTP detection module 1216 are respectively connected to the third terminal of the protection module 1206 and the fourth terminal of the logic control module 1220; the fifth terminal of the logic control module 1220 is connected to the first terminal of the gate drive module 1222; the second terminal of the gate drive module 1222 is connected to the first terminal of the power switch Q1 and the fifth terminal of the current detection module 1214; the second terminal of the power switch Q1 is connected to the Drain pin; and the third terminal of the power switch Q1 is connected to the CS pin.

[0056] As an example, the UVLO and AVDD modules 1202 can be configured to provide operating voltage and internal reference voltage Vref to the primary-side feedback chip 120. When the VDD voltage exceeds the UVLO voltage, the PG signal can be set to 1, enabling the various modules built into the primary-side feedback chip 120 to start working.

[0057] As an example, the reference signal generation module 1204 can be used to output a reference voltage Vref_cv to the constant voltage control module 1212.

[0058] As an example, the protection module 1206 can mainly consist of two parts. One part can be used for protection based on the output feedback signal representing the output voltage from the FB pin, such as open / short circuit protection of the voltage divider resistor, open circuit protection of the auxiliary winding, etc. The other part can be used for protection based on the OTP signal from the OTP detection module 1216. For example, when the OTP signal is valid, the protection module 1206 can control the primary-side feedback chip 120 to enter the automatic restart state, thereby protecting the system from serious problems such as damage to the synchronous rectifier switch or fuse due to excessive temperature of the synchronous rectifier switch or the temperature around the synchronous rectifier chip.

[0059] As an example, the demagnetization detection module 1210 can be configured to detect the demagnetization of the primary winding of the transformer based on the output feedback signal when the power switch Q1 is in the off state.

[0060] Specifically, the demagnetization detection module 1210 can be further configured to determine the demagnetization time Tdemg of the primary winding as the time between the rising edge of the output feedback signal rising above a certain preset value (e.g., 0.1V) and the falling edge of the output feedback signal falling below a certain preset value (e.g., 0.1V) when the power switch Q1 is in the off state. (See [link to relevant documentation]) Figure 5 ).

[0061] As an example, the sampling module 1208 can be configured to sample the platform voltage of the output feedback signal of the current cycle during the demagnetization time of the primary winding and hold it until the next cycle, and input the sampled voltage Vs to the constant voltage control module 1212.

[0062] As an example, the constant voltage control module 1212 can be configured to generate a first control signal for controlling the turn-on and turn-off of the power switch Q1 based on the sampled voltage Vs and the voltage signal Vcs characterizing the primary current.

[0063] Specifically, the constant voltage control module 1212 receives a sampled voltage Vs from the sampling module 1208 at its first terminal and a reference voltage Vref_cv (where the reference voltage Vref includes the reference voltage Vref_cv) at its second terminal. The constant voltage control module 1212 may have a built-in error amplifier EA for core operation. The sampled voltage Vs can be input to, for example, the negative input terminal of the error amplifier EA (the first terminal of the constant voltage control module 1212), and the reference voltage Vref_cv can be input to, for example, the positive input terminal of the error amplifier EA (the second terminal of the constant voltage control module 1212). The two voltages are then amplified to obtain the error signal UEA. The constant voltage control module 1212 may also have a built-in pulse width modulation (PWM) function. The Modulation (PWM) module is used to perform pulse width modulation on the error signal UEA and the voltage signal Vcs (Vcs = Ipk * Rsense) that characterizes the primary current Ipk, so as to control the conduction time of the power switch Q1 and make the output feedback signal VFB follow the reference voltage when the input Bulk voltage and load change.

[0064] As an example, the current detection module 1214 can be configured to detect the primary current Ipk, including positive current detection and negative current detection.

[0065] Specifically, when the power switch Q1 is turned on, the primary current Ipk is a positive current. This current flows through the input capacitor Cbulk, the primary winding Npri of the transformer, the power switch Q1, the current sensing resistor Rs, and to ground. The current sensing module 1214 can be configured to detect the magnitude and width of the positive current and send the detection results to the constant voltage control module 1212 and the constant current control module 1218.

[0066] As an example, the constant voltage control module 1212 can be configured to control the switching power supply to provide a constant voltage to the device to be charged based on the demagnetization condition and the forward current detection result, and the constant current control module 1218 can be configured to control the switching power supply to provide a constant current to the device to be charged based on the demagnetization condition and the forward current detection result.

[0067] Furthermore, after the demagnetization of the primary winding is completed, the primary current Ipk is a negative current. This current flows through ground, the current sensing resistor Rs, the parasitic capacitance of the power switch Q1, the primary winding Npri of the transformer, and the input capacitor Cbulk. The current sensing module 1214 can be configured to detect the magnitude and width of the negative current and send the detection result to the OTP detection module 1216.

[0068] As an example, the OTP detection module 1216 can be configured to receive demagnetization status and negative current detection results, determine whether the temperature of the synchronous rectifier switch Q2 or the temperature around the synchronous rectifier chip exceeds a preset value according to preset rules, and provide temperature protection request information to the protection module 1206 for protection if the temperature exceeds the preset value. The primary-side feedback chip 120 enters an automatic restart state, thereby protecting the system from serious problems such as damage to the synchronous rectifier switch Q2 or fuse due to excessively high temperature of the synchronous rectifier switch Q2 or the temperature around the synchronous rectifier chip.

[0069] As an example, the constant current control module 1218 can be configured to output a constant current in constant current mode based on a positive current detection signal. Specifically, the magnitude of the constant current can be adjusted by an external current sensing resistor Rsense.

[0070] As an example, the logic control module 1220 can be configured to perform logic analysis on each input signal and output logic control signals to the gate drive module 1222 to control the turn-on and turn-off of the power switch Q1.

[0071] As an example, the gate drive module 1222 can be configured to enable the signal to achieve totem output after logic control.

[0072] Specifically, the gate drive module 1222 can be configured to process signals from the logic control module 1220 to generate control signals for controlling the turn-on and turn-off of the power switch Q1. The second terminal of the power switch Q1 can be connected to the Drain pin, and the third terminal can be connected to the CS pin.

[0073] It should be noted that, in addition to being located inside the primary-side feedback chip as shown in the figure, the power switch Q1 can also be packaged independently, and this invention does not impose any restrictions on this.

[0074] To better understand the switching power supply provided in the embodiments of the present invention, the following detailed examples illustrate the specific implementation of the secondary-side synchronous rectifier chip in the switching power supply provided in the embodiments of the present invention. (Refer to...) Figure 7 , Figure 7 A schematic diagram of the secondary-side synchronous rectifier chip provided in an embodiment of the present invention is shown.

[0075] like Figure 7As shown, the secondary-side synchronous rectification chip 130 mainly includes a Vin pin, a VDD pin, a GND pin, and a Drain pin, and may include a synchronous rectification control module 1302, an LDO power supply module 1304, a reference module 1306, a UVLO 1308, a demagnetization detection module 1310, a dynamic response module 1312, a dummy load module 1314, an OTP detection module 1316, and a synchronous rectification switch Q2. The synchronous rectification control module 1302 may include an HV switch, a comparator 1318, a comparator 1320, a minimum on-time setting module 1322, an RS flip-flop 1324, a logic control module 1326, and a gate drive module 1328.

[0076] like Figure 7As shown, the first terminal of the demagnetization detection module 1310 can be connected to the Drain pin, the second terminal can be connected to the first terminal of the synchronous rectification control module 1302, the third terminal can be connected to the first terminal of the dynamic response module 1312, the second terminal of the dynamic response module 1312 can be connected to the Vin pin, the third terminal of the dynamic response module 1312 can be connected to the dummy load module 1314, the fourth terminal of the dynamic response module 1312 can be connected to the second terminal of the synchronous rectification control module 1302, the OTP detection module 1316 can be connected to the third terminal of the synchronous rectification control module 1302, the fourth terminal of the synchronous rectification control module 1302 can be connected to the gate of the switching transistor Q2, the drain of the switching transistor Q2 can be connected to the Drain pin, and the source can be grounded. The first terminal of the LDO power supply module 1304 can be connected to the VDD pin, the second terminal of the LDO power supply module 1304 can be connected to the Drain pin, and the third terminal of the LDO power supply module 1304 can be connected to the first terminal of the UVLO 1308. The second terminal of 1308 can output the PG signal. The fourth terminal of the LDO power supply module 1304 can be connected to the first terminal of the reference module 1306. The second terminal of the reference module 1306 can output the Vref signal. The fifth terminal of the LDO power supply module 1304 can be connected to the Vin pin and the second terminal of the dynamic response module 1312. The first terminal of comparator 1318 receives the Vdrain voltage (the voltage at the drain of the synchronous rectifier switch Q2), and the second terminal is grounded. The first terminal of comparator 1320 receives the Vdrain voltage, and the second terminal is grounded. The third terminal of comparator 1318... The minimum on-time control module 1322 is connected to the reset terminal of the RS flip-flop 1324. The third terminal of the comparator 1320 is connected to the set terminal of the RS flip-flop 1324. The output terminal of the RS flip-flop 1324 can be connected to the first terminal of the logic control module 1326. The second and third terminals of the logic control module 1326 can be connected to the second and third terminals of the synchronous rectification control module 1302, respectively. The fourth terminal of the logic control module 1326 can be connected to the first terminal of the gate drive module 1328. The second terminal of the gate drive module 1328 can be connected to the gate of Q2.

[0077] As an example, when the system starts up, both the VDD and Vin voltages are low, the body diode of the synchronous rectifier switch Q2 is turned on, and Vdrain is used to charge VDD, causing the VDD voltage to rise. The LDO power supply module 1304 can be configured to set the PG (power good) signal to 1 after detecting that the VDD voltage exceeds the UVLO voltage, so that the circuit inside the synchronous rectifier chip starts to work.

[0078] As an example, the synchronous rectification control module 1302 can be configured to demagnetize the secondary winding after the power switch Q1 is turned off to prevent the primary and secondary windings from being connected simultaneously. First, the body diode of the synchronous rectification switch Q2 is turned on. When the VD voltage is less than a certain level (e.g., VD < -300mV), the synchronous rectification switch Q2 is turned on. As the demagnetizing current gradually decreases, the VD voltage gradually increases. When the VD voltage is greater than a certain level (e.g., VD > -3.5mV or 0mV), the synchronous rectification switch Q2 is turned off. To prevent the demagnetizing resonance from affecting the VD voltage detection and causing the synchronous rectification switch Q2 to be prematurely turned off, a minimum synchronous rectification on-time can be set.

[0079] As an example, the demagnetization detection module 1310 can be configured to detect, for example, the demagnetization time of synchronous rectification, the demagnetization frequency, and the rising and falling edges of demagnetization, so that the detection results can be used to control the on and off of the synchronous rectification switch Q2, and the detected demagnetization frequency can be transmitted to the dynamic response module 1312.

[0080] As an example, the OTP detection module 1316 can provide temperature protection request information to the primary-side feedback chip when it is configured to delay the shutdown of the synchronous rectifier switch when the body temperature of the secondary-side synchronous rectifier chip is detected to be higher than a preset threshold, and to normally shut down the synchronous rectifier switch when the body temperature is lower than or equal to the preset threshold.

[0081] Specifically, the OTP detection module 1316 can be used as an on-chip OTP protection circuit. By detecting the temperature of the chip itself, it predicts the temperature around the synchronous rectifier chip or the temperature of the synchronous rectifier switch Q2. When the temperature is detected to be too high, it performs on-chip OTP protection detection and transmits the signal to the logic control module 1326. The logic control module 1326 then controls the gate drive module 1328 to delay the turn-off of the synchronous rectifier switch Q2. The OTP protection request information is transmitted to the primary-side feedback chip through transformer coupling for identification of OTP protection.

[0082] As an example, the dynamic response module 1312 can be configured to, when the switching power supply is in an unloaded state, increase the dummy load of the switching power supply if the demagnetizing frequency of the primary winding is less than a preset threshold and the output voltage of the switching power supply is greater than another preset threshold; and when the switching power supply is in a loaded state, if the output voltage of the switching power supply is less than another preset threshold, notify the primary feedback chip of the load change of the switching power supply after a preset period of time, so that the primary feedback chip increases the switching frequency of the first power switch and the current flowing through the primary winding.

[0083] Specifically, the dynamic response module 1312 can be configured to increase the load on the switching power supply to consume energy when the system output is suddenly unloaded, which causes the output voltage to rise and the operating frequency to decrease. When the demagnetizing frequency of the primary winding is detected to be less than a certain set threshold (e.g., the threshold is 5kHz) and the output voltage of the switching power supply exceeds a certain set threshold (e.g., the threshold is 5V and the output voltage is 5.8V). When the system is momentarily loaded, which causes the output voltage to drop momentarily, when the output voltage is detected to be lower than a certain fixed value (e.g., the threshold is 5V and the output voltage is 4.6V), the dynamic response module 1312 can provide information indicating the load change to the primary feedback chip through transformer coupling after a certain fixed time (e.g., 100us) to inform the primary feedback chip of the load change, increase the switching frequency of the primary power switch and the current flowing through the primary winding, thereby increasing the power and boosting the output voltage.

[0084] As an example, the dummy load module 1314 can be configured such that when the system output is momentarily unloaded, since the output voltage is controlled by the primary auxiliary winding, the output voltage response has a certain delay. After the unload, the output voltage of the switching power supply spikes. To prevent the output voltage from spiked too high, when the demagnetizing frequency is less than a certain set threshold (e.g., the threshold is 5kHz) and the output voltage exceeds a certain set threshold (e.g., the threshold is 5V and the output voltage is 5.8V), the dummy load of the chip can be increased to consume excess energy and reduce the output voltage.

[0085] It should be noted that, in addition to being located inside the secondary-side synchronous rectification chip as shown in the figure, the synchronous rectification switch Q2 can also be packaged independently, and this invention does not impose any restrictions on this.

[0086] It can be seen that, in Figure 7 In the secondary-side synchronous rectifier chip shown, when the temperature of the synchronous rectifier switch or the temperature around the synchronous rectifier chip exceeds a preset OTP threshold (for example, the OTP threshold can be divided into different levels through trimming inside the chip, where the trimming threshold can be set according to the actual PCB test value), the synchronous rectifier switch Q2 is turned off after a delay of 2µs or other fixed time. The OTP information is coupled to the CS pin of the primary-side auxiliary winding and the primary-side feedback chip through the transformer. The primary-side feedback chip can detect the OTP information according to preset rules, determine whether the temperature of the secondary-side synchronous rectifier switch or the temperature around the synchronous rectifier chip exceeds the preset OTP threshold, and when the temperature exceeds the preset OTP threshold, the primary-side feedback chip enters an automatic restart state.

[0087] To better understand the temperature protection detection principle provided in the embodiments of the present invention, the temperature protection detection logic is described below through specific examples. (Reference) Figure 8 , Figure 8 The diagram shows waveforms of the temperature protection cycle and normal operation cycle provided in the embodiments of the present invention.

[0088] In this context, waveform SR gate represents the control signal of the secondary-side synchronous rectifier chip 130 used to control the turn-on and turn-off of the synchronous rectifier switch Q2, waveform SR Vdrain represents the voltage at the drain of the synchronous rectifier switch Q2 in the secondary-side synchronous rectifier chip 130, waveform SR Isk represents the secondary-side current, waveform PSR gate represents the control signal of the primary-side feedback chip 120 used to control the turn-on and turn-off of the power switch Q1, waveform PSR FB represents the output feedback signal used to characterize the output voltage, waveform PSR Ipk represents the primary-side current, Tdemg corresponds to the demagnetization time, and Tring corresponds to the resonance time.

[0089] As shown in the figure, the main difference between the temperature protection cycle (corresponding to the time period t0 to t9, marked as 1) and the normal operation cycle (corresponding to the time period t9 to t13, marked as 0) is that during the temperature protection cycle, the synchronous rectifier switch Q2 is turned off with a certain delay (e.g., 2µs) (see reference). Figure 8 During the time period t2 to t3 (the dashed part of the SR gate waveform), after the secondary current Isk drops to zero, it continues to increase negatively to Isk1. At this time, the converter's output voltage reverse-excites the secondary winding Nsec to store energy, and the voltage on the auxiliary winding Naux continues to be clamped at Vaux = (V0 * Naux) / Nsec. After being divided by voltage divider resistors R1 and R2, the voltage Vaux on the auxiliary winding Naux maintains a voltage plateau at the FB pin. (Refer to...) Figure 8The PSR FB waveform is shown in the diagram. After the synchronous rectifier switch Q2 is turned off, the reverse excitation energy on the secondary side is transferred to the primary side. For example, the reverse excitation energy can be transferred to the primary side through the current sensing resistor Rs, the parasitic capacitance of the power switch Q1, the primary winding Npri, and the input capacitor Cbulk. The primary winding Npri is demagnetized in the reverse direction, resulting in energy recirculation. After demagnetization, the feedback energy charges the junction capacitance (denoted as Coss) of the power switch Q1 again, clamping the drain-source voltage of the power switch Q1 at Vbulk + N*Vo. When the flyback switching power supply operates in quasi-resonant (QR) mode and the primary current Ipk gradually increases to 0, the output feedback signal PSR FB oscillates to its lowest point. Under light load, it can maintain the original resonant period and continue to operate. Under heavy load, it allows the primary power switch Q1 to be turned on at zero voltage (ZVS).

[0090] from Figure 8 As can be seen, during the temperature protection cycle, due to the delayed turn-off of the synchronous rectifier switch Q2, the falling rate of the falling edge of the output feedback signal FB at the primary side during the temperature protection cycle (denoted as Tf1) is significantly faster than the falling rate of the falling edge of the output feedback signal FB during the normal operating cycle (denoted as Tf2). The voltage signal Vcs (Vcs = Ipk * Rsense, where Rsense is the sensing resistor and Ipk is the primary side current) characterizes the temperature protection cycle. Figure 6 The negative voltage of Is) is significantly different from the negative voltage of the voltage signal Vcs, which characterizes the primary current Ipk during normal operation.

[0091] Therefore, the falling edge of the output feedback signal FB and the negative voltage of the voltage signal Vcs representing the primary current Ipk can be used as the temperature protection identification conditions to form temperature protection cycle 1. During temperature protection cycle 1, after demagnetization ends, when the fall time Tf1 of the falling edge of the output feedback signal FB is less than a certain threshold (e.g., 200 ns), and the negative signal of the primary voltage Vcs representing the primary current is lower than a certain threshold (e.g., -200 mV) and remains below a certain threshold for a certain period of time (e.g., 150 ns), it can be determined that there is a temperature protection request information from the secondary synchronous rectifier chip, and temperature protection is required. In other words, the primary feedback chip can begin preparing for protection identification in subsequent cycles.

[0092] Furthermore, to avoid false detections, a combination of multiple temperature protection cycles and multiple normal cycles can be set as a single temperature protection coding cycle. Therefore, the entire temperature protection coding cycle can be set as a multi-bit flag to prepare for the implementation of temperature protection functionality on the primary side. For example, a temperature protection coding cycle can be set as a combination of multiple temperature protection cycles 1 and multiple normal operating cycles 0, and an end flag can be set after coding is completed.

[0093] As an example, the code corresponding to the temperature protection coding cycle can be set to 11010111, such as... Figure 9 As shown, Figure 9 The code corresponding to the temperature protection coding cycle provided in this embodiment of the invention is shown. Specifically, the temperature protection coding cycle can consist of 8 cycles. The first two cycles can be flag bits 11, the next four cycles can be 0101, which indicates that the secondary-side synchronous rectifier chip needs to perform over-temperature protection and requests the primary-side feedback chip to automatically restart. The last two cycles can be end flag bits 11. After the end flag bits end, the OTP detection module of the primary-side feedback chip can determine that the secondary-side synchronous rectifier chip has malfunctioned by performing the OTP detection function. To protect the secondary-side synchronous rectifier chip, the primary-side feedback chip needs to enter an automatic restart state to prevent damage to the synchronous rectifier switch or problems such as fuse failure due to excessive temperature of the secondary-side synchronous rectifier chip.

[0094] The encoding length provided in this embodiment of the invention is not limited to a certain number of bits. As described above, the encoding length can be set to 8 bits. However, when the request information from the secondary-side synchronous rectifier chip is relatively small, the encoding length can be reduced; when the request information from the secondary-side synchronous rectifier chip is relatively large, the encoding length can be increased. For the specific encoding logic principle, please refer to [link to relevant documentation]. Figure 8 Simply put, when an excessively high temperature is detected, the synchronous rectifier switch can be turned off with a delay. This will cause the falling edge of the output feedback signal to fall faster and the voltage signal Vcs representing the primary current to decrease. Therefore, the falling edge of the output feedback signal and the voltage signal Vcs representing the primary current can be used to characterize the encoding as 1.

[0095] As can be seen, by setting an on-chip temperature detection circuit, the synchronous rectifier chip can detect the temperature of the synchronous rectifier switch or the temperature of the environment around the synchronous rectifier chip. When the detected temperature exceeds the preset value of the over-temperature protection (OTP), the OTP protection request information can be transmitted to the primary side feedback chip by controlling the delayed turn-off of the synchronous rectifier switch Q2. The primary side control system then shuts down, preventing safety problems such as fuse failure caused by damage to the synchronous rectifier switch Q2 due to excessive secondary side temperature.

[0096] In summary, the isolated switching power supply, control circuit, and control method for transmitting information between the primary and secondary sides provided by the embodiments of the present invention can achieve temperature protection for the synchronous rectifier chip without increasing system components, preventing damage or melting caused by excessive ambient temperature of the secondary-side synchronous rectifier chip or temperature of the synchronous rectifier switching transistor. Furthermore, the switching power supply provided by the embodiments of the present invention can also transmit various types of information to improve the diversity of information transmission.

[0097] Furthermore, embodiments of the present invention also provide a method for use in the aforementioned switching power supply, see reference. Figure 10 , Figure 10 The following is a flowchart illustrating a method 1000 used in a switching power supply according to an embodiment of the present invention, which may include the following steps: S1010, when the secondary-side synchronous rectifier chip detects that the body temperature of the secondary-side synchronous rectifier chip is higher than a first preset threshold, outputting a temperature protection request message; and S1020, in response to receiving the temperature protection request message, causing the primary-side feedback chip to enter an automatic restart state.

[0098] As an example, the switching power supply also includes a transformer, and the primary-side feedback chip includes a first power switching transistor. The method 1000 may further include using the primary-side feedback chip to perform the following operations: when the first power switching transistor is in the off state, detecting the demagnetization of the primary winding of the transformer based on an output feedback signal characterizing the output voltage of the switching power supply; generating a first current detection signal when a negative current flowing through the primary winding is detected; determining, based on the demagnetization and the first current detection signal, that a temperature protection request information has been received; and entering an automatic restart state based on the temperature protection request information.

[0099] As an example, method 1000 may also include using a primary-side feedback chip to perform the following operations: generating a second current detection signal when a positive current flowing through the primary winding is detected; and controlling the switching power supply to provide a constant voltage and current to the device to be charged based on the demagnetization condition and the second current detection signal.

[0100] As an example, method 1000 may also include performing the following operations using the primary-side feedback chip: sampling the plateau voltage of the output feedback signal during the demagnetization time of the primary winding to obtain a sampled voltage; and generating a first control signal for controlling the on and off of the first power switch based on the sampled voltage and a voltage signal characterizing the current flowing through the primary winding.

[0101] As an example, the demagnetization of the primary winding is detected based on the output feedback signal, including: taking the time period between the output feedback signal rising above a second preset threshold and the output feedback signal falling below a second preset threshold as the demagnetization time of the primary winding.

[0102] As an example, based on the demagnetization status and the first current detection signal, it is determined that a temperature protection request message has been received, including: when the demagnetization of the primary winding is completed, and the fall time of the falling edge of the output feedback signal is less than a third preset threshold and the first current detection signal is less than a fourth preset threshold, it is determined that a temperature protection request message has been received.

[0103] As an example, the secondary-side synchronous rectifier chip includes a second power switch, and method 1000 may also include using the secondary-side synchronous rectifier chip to perform the following operations: after the first power switch is turned off, generating a second control signal for controlling the turn-on and turn-off of the second power switch based on the drain voltage of the second power switch.

[0104] As an example, method 1000 may also include performing the following operations using a secondary-side synchronous rectifier chip: providing temperature protection request information to the primary-side feedback chip by delaying the turn-off of the second power switch when the body temperature is detected to be higher than a first preset threshold and normally turning off the second power switch when the body temperature is lower than or equal to the first preset threshold.

[0105] As an example, based on the drain voltage of the second power switch, a second control signal is generated to control the turn-on and turn-off of the second power switch, including: controlling the second power switch to be in the turn-on state when the drain voltage of the second power switch is less than a fifth preset threshold; and controlling the second power switch to be in the turn-off state when the drain voltage of the second power switch is greater than a sixth preset threshold, wherein the fifth preset threshold is less than the sixth preset threshold.

[0106] As an example, method 1000 may also include performing the following operation using a secondary-side synchronous rectifier chip: setting the minimum on-time of the second power switch when the inductance of the primary winding and the junction capacitance of the second power switch resonate, so as to prevent the second power switch from being prematurely turned off.

[0107] As an example, method 1000 may also include performing the following operations using a secondary-side synchronous rectifier chip: when the switching power supply is in an unloaded state, if the demagnetizing frequency of the primary winding is less than a seventh preset threshold and the output voltage of the switching power supply is greater than an eighth preset threshold, then adding a dummy load to the switching power supply; and when the switching power supply is in a loaded state, if the output voltage of the switching power supply is less than a ninth preset threshold, then after a preset period of time, notifying the primary-side feedback chip of the load change of the switching power supply, causing the primary-side feedback chip to increase the switching frequency of the first power switch and the current flowing through the primary winding, wherein the eighth preset threshold is greater than the ninth preset threshold.

[0108] It is understood that the technical details of the switching power supply have been described in detail above. Therefore, for the sake of simplicity, some details of the method embodiments can be found in the above description of the switching power supply embodiments, and will not be repeated here.

[0109] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0110] The functional blocks shown in the above-described structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the required tasks. The programs or code segments can be stored in a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc.

[0111] It should also be noted that the exemplary embodiments mentioned in this invention describe methods or systems based on a series of steps or apparatus. However, this invention is not limited to the order of the steps described above; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0112] The above description is merely a specific embodiment of the present invention. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A switching power supply for charging a device to be charged, characterized in that, include: transformer; The secondary-side synchronous rectifier chip is configured to output a temperature protection request message when the body temperature of the secondary-side synchronous rectifier chip is detected to be higher than a first preset threshold. as well as The primary-side feedback chip, including a first power switch, is configured to detect the demagnetization of the primary winding of the transformer based on an output feedback signal characterizing the output voltage of the switching power supply when the first power switch is in the off state; generate a first current detection signal when a negative current flowing through the primary winding is detected; determine that the temperature protection request information has been received based on the demagnetization and the first current detection signal; and enter an automatic restart state based on the temperature protection request information.

2. The switching power supply according to claim 1, characterized in that, The primary-side feedback chip is further configured to: When a positive current flowing through the primary winding is detected, a second current detection signal is generated; as well as Based on the demagnetization status and the second current detection signal, the switching power supply is controlled to provide a constant voltage and current to the device to be charged.

3. The switching power supply according to claim 1 or 2, characterized in that, The primary-side feedback chip is further configured to: During the demagnetization time of the primary winding, the plateau voltage of the output feedback signal is sampled to obtain the sampled voltage; and Based on the sampled voltage and the voltage signal characterizing the current flowing through the primary winding, a first control signal is generated for controlling the on and off of the first power switch.

4. The switching power supply according to claim 1, characterized in that, The primary-side feedback chip is further configured to: The time period between when the output feedback signal rises above a second preset threshold and when the output feedback signal falls below a second preset threshold is taken as the demagnetization time of the primary winding.

5. The switching power supply according to claim 1, characterized in that, The primary-side feedback chip is further configured to: After the demagnetization of the primary winding is completed, when the fall time of the falling edge of the output feedback signal is less than a third preset threshold and the first current detection signal is less than a fourth preset threshold, it is determined that the temperature protection request information has been received.

6. The switching power supply according to claim 1, characterized in that, The secondary-side synchronous rectifier chip includes a second power switch, and the secondary-side synchronous rectifier chip is further configured as follows: After the first power switch is turned off, a second control signal is generated based on the drain voltage of the second power switch to control the turn-on and turn-off of the second power switch.

7. The switching power supply according to claim 6, characterized in that, The secondary-side synchronous rectifier chip is also configured to: The temperature protection request information is provided to the primary-side feedback chip by delaying the shutdown of the second power switch when the body temperature is detected to be higher than the first preset threshold and normally shutting down the second power switch when the body temperature is lower than or equal to the first preset threshold.

8. The switching power supply according to claim 6, characterized in that, The secondary-side synchronous rectifier chip is also configured to: When the drain voltage of the second power switch is less than a fifth preset threshold, the second power switch is controlled to be in the on state; and When the drain voltage of the second power switch is greater than the sixth preset threshold, the second power switch is controlled to be in the off state, wherein the fifth preset threshold is less than the sixth preset threshold.

9. The switching power supply according to claim 6, characterized in that, The secondary-side synchronous rectifier chip is also configured to: When the inductance of the primary winding and the junction capacitance of the second power switch resonate, the minimum on-time of the second power switch is set to prevent the second power switch from being prematurely turned off.

10. The switching power supply according to claim 1, characterized in that, The secondary-side synchronous rectifier chip is also configured to: When the switching power supply is in an unloaded state, if the demagnetizing frequency of the primary winding is less than a seventh preset threshold and the output voltage of the switching power supply is greater than an eighth preset threshold, then the dummy load of the switching power supply is increased. as well as When the switching power supply is in a loaded state, if the output voltage of the switching power supply is less than the ninth preset threshold, the primary-side feedback chip is notified of the load change of the switching power supply after a preset period of time, so that the primary-side feedback chip increases the switching frequency of the first power switch and the current flowing through the primary winding, wherein the eighth preset threshold is greater than the ninth preset threshold.

11. A method for charging a device to be charged in a switching power supply, characterized in that, The switching power supply includes a transformer, a primary-side feedback chip, and a secondary-side synchronous rectification chip. The primary-side feedback chip includes a first power switching transistor. The method includes: When the secondary-side synchronous rectifier chip detects that its body temperature exceeds a first preset threshold, it outputs a temperature protection request message; and The primary-side feedback chip performs the following operations: when the first power switch is in the off state, the demagnetization of the primary winding of the transformer is detected based on the output feedback signal characterizing the output voltage of the switching power supply; when a negative current flowing through the primary winding is detected, a first current detection signal is generated; based on the demagnetization and the first current detection signal, it is determined that the temperature protection request information has been received; and based on the temperature protection request information, the system enters an automatic restart state.

12. The method according to claim 11, characterized in that, The method also includes performing the following operations using the primary-side feedback chip: When a positive current flowing through the primary winding is detected, a second current detection signal is generated; as well as Based on the demagnetization status and the second current detection signal, the switching power supply is controlled to provide a constant voltage and current to the device to be charged.

13. The method according to claim 11 or 12, characterized in that, The method also includes performing the following operations using the primary-side feedback chip: During the demagnetization time of the primary winding, the plateau voltage of the output feedback signal is sampled to obtain the sampled voltage; as well as Based on the sampled voltage and the voltage signal characterizing the current flowing through the primary winding, a first control signal is generated for controlling the on and off of the first power switch.

14. The method according to claim 11, characterized in that, The demagnetization of the primary winding is detected based on the output feedback signal, including: The time period between when the output feedback signal rises above a second preset threshold and when the output feedback signal falls below a second preset threshold is taken as the demagnetization time of the primary winding.

15. The method according to claim 11, characterized in that, Based on the demagnetization status and the first current detection signal, it is determined that the temperature protection request information has been received, including: After the demagnetization of the primary winding is completed, when the fall time of the falling edge of the output feedback signal is less than a third preset threshold and the first current detection signal is less than a fourth preset threshold, it is determined that the temperature protection request information has been received.

16. The method according to claim 11, characterized in that, The secondary-side synchronous rectifier chip includes a second power switch, and the method further includes performing the following operations using the secondary-side synchronous rectifier chip: After the first power switch is turned off, a second control signal is generated based on the drain voltage of the second power switch to control the turn-on and turn-off of the second power switch.

17. The method according to claim 16, characterized in that, The method also includes performing the following operations using the secondary-side synchronous rectification chip: The temperature protection request information is provided to the primary-side feedback chip by delaying the shutdown of the second power switch when the body temperature is detected to be higher than the first preset threshold and normally shutting down the second power switch when the body temperature is lower than or equal to the first preset threshold.

18. The method according to claim 16, characterized in that, Based on the drain voltage of the second power switch, a second control signal is generated to control the on and off states of the second power switch, including: When the drain voltage of the second power switch is less than a fifth preset threshold, the second power switch is controlled to be in the on state; and When the drain voltage of the second power switch is greater than the sixth preset threshold, the second power switch is controlled to be in the off state, wherein the fifth preset threshold is less than the sixth preset threshold.

19. The method according to claim 16, characterized in that, The method also includes performing the following operations using the secondary-side synchronous rectification chip: When the inductance of the primary winding and the junction capacitance of the second power switch resonate, the minimum on-time of the second power switch is set to prevent the second power switch from being prematurely turned off.

20. The method according to claim 11, characterized in that, The method also includes performing the following operations using the secondary-side synchronous rectification chip: When the switching power supply is in an unloaded state, if the demagnetizing frequency of the primary winding is less than a seventh preset threshold and the output voltage of the switching power supply is greater than an eighth preset threshold, then the dummy load of the switching power supply is increased. as well as When the switching power supply is in a loaded state, if the output voltage of the switching power supply is less than the ninth preset threshold, the primary-side feedback chip is notified of the load change of the switching power supply after a preset period of time, so that the primary-side feedback chip increases the switching frequency of the first power switch and the current flowing through the primary winding, wherein the eighth preset threshold is greater than the ninth preset threshold.

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