A disappearing regulator circuit, silicon carbide driver and switching power supply system

Abstract

The application discloses a disappearing adjusting circuit, a silicon carbide driver and a switching power supply system, comprising a demagnetization detection circuit, which is used for outputting a demagnetization detection signal when a feedback voltage output by an auxiliary winding of a transformer is detected; a constant current adjusting circuit, which is used for adjusting a preset error threshold voltage according to a deviation between a primary side peak voltage collected and a constant current threshold voltage, and outputting the adjusted error threshold voltage when the demagnetization detection signal is received; and a PWM driving circuit, which is used for outputting an enable control signal to control a power switch tube to be turned on when a real-time detection voltage signal is less than the error threshold voltage. Through a closed-loop adjusting mode of the constant current adjusting circuit, the primary side peak voltage is compared with the constant current threshold voltage, and the error threshold voltage is corrected according to a comparison result, so that the switching power supply system is in a dynamic balance state after repeated correction of a plurality of switching periods, thereby effectively offsetting an influence of an input end offset voltage, and realizing high-precision constant current output.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a vanishing tone circuit, a silicon carbide driver, and a switching power supply system. Background Technology

[0002] Switching power supplies, as the core power supply devices for various electronic devices and industrial systems, are widely used in new energy, automotive electronics, and industrial automation. With the large-scale application of silicon carbide drivers in switching power supplies, ensuring constant current output control in the discontinuous constant current operating mode is a key aspect of ensuring stable operation of the drive circuit and reliable switching of power devices.

[0003] In existing constant current control schemes, constant current amplifiers are used for constant current control output. However, due to objective factors such as manufacturing process, there will inevitably be an input offset voltage at the input terminal of the constant current amplifier. This offset voltage will be superimposed on the constant current control process of the constant current amplifier, thereby interfering with the output current. Its constant current accuracy is greatly affected, making it difficult to meet the application requirements of high-precision constant current output. Summary of the Invention

[0004] The main purpose of this application is to provide a vanishing offset circuit, a silicon carbide driver, and a switching power supply system, which aims to solve the technical problem that the input of existing constant current amplifiers has an offset voltage, which has a significant impact on the accuracy of constant current.

[0005] To achieve the above objectives, this application proposes a fade-out modulation circuit for use in a switching power supply system, the switching power supply system including a transformer and a power switching transistor connected to the transformer, the fade-out modulation circuit including: A demagnetization detection circuit, wherein the input terminal of the demagnetization detection circuit is connected to the output terminal of the auxiliary winding of the transformer, and the demagnetization detection circuit is used to output a demagnetization detection signal when it detects the feedback voltage output by the auxiliary winding of the transformer; A constant current regulating circuit is provided, wherein the regulating terminal of the constant current regulating circuit is connected to the first output terminal of the demagnetization detection circuit, the first input terminal of the constant current regulating circuit is connected to a real-time detection voltage signal used to characterize the instantaneous value of the primary current, and the peak voltage of the primary current instantaneous value is collected. The second input terminal of the constant current regulating circuit is connected to a constant current threshold voltage. When the demagnetization detection signal is received, the constant current regulating circuit adjusts the preset error threshold voltage according to the deviation between the collected peak voltage of the primary current and the constant current threshold voltage, and outputs the adjusted error threshold voltage. A PWM driving circuit is provided, wherein the first input terminal of the PWM driving circuit is connected to the output terminal of the constant current regulation circuit, the second input terminal of the PWM driving circuit is connected to the real-time detected voltage signal, and the output terminal of the PWM driving circuit is connected to the controlled terminal of the power switching transistor. The PWM drive circuit is used to output an enable control signal to control the power switch to turn on when the real-time detected voltage signal is less than the error threshold voltage.

[0006] By adopting the above technical solution and using the closed-loop regulation method of the constant current regulation circuit, in the initial stage of regulation, the offset voltage at the input terminal will cause the primary current to deviate from the actual value. The constant current regulation circuit compares it with the constant current threshold voltage and corrects the error threshold voltage according to the comparison result. After repeated corrections over multiple switching cycles, the switching power supply system is in a dynamic equilibrium state, and the output current remains constant, thereby effectively offsetting the influence of the input offset voltage and achieving high-precision constant current output.

[0007] The constant current regulation circuit, as described above, comprises: The frequency divider module has its input terminal connected to the first output terminal of the demagnetization detection circuit. The first output terminal of the frequency divider module outputs a first frequency divider signal, and the second output terminal of the frequency divider module outputs a second frequency divider signal that is inverted from the first frequency divider signal. When the rising edge of the demagnetization detection signal is received, the first frequency divider signal is inverted. The adjustment channel selection module has a first channel selection terminal connected to the first output terminal of the frequency divider module, a second channel selection terminal connected to the second output terminal of the frequency divider module, a first input terminal connected to the primary-side peak voltage, a second input terminal connected to the constant current threshold voltage, a first channel output terminal connected to the first input terminal of the PWM drive circuit, and a second channel output terminal connected to the first input terminal of the PWM drive circuit. When the first frequency division signal is a high-level pulse, the path between the first channel selection terminal and the first channel output terminal of the adjustment channel selection module is connected. When the second frequency division signal is a high-level pulse, the path between the second channel selection terminal and the second channel output terminal of the adjustment channel selection module is turned on.

[0008] The constant current regulation circuit further includes, as described above, the disappearance modulation circuit. A peak sampling module, wherein the first input terminal of the peak sampling module is connected to the real-time detected voltage signal, the second input terminal of the peak sampling module is connected to the output terminal of the PWM drive circuit, and the output terminal of the peak sampling module is connected to the first input terminal of the adjustment channel selection module; The peak sampling module is used to acquire the peak value of the instantaneous primary current before the falling edge of the enable control signal arrives, and output the peak voltage of the primary current to the first input terminal of the adjustment channel selection module.

[0009] The vanishing tone circuit described above, wherein the adjustment channel selection module includes: The first channel unit has its selection terminal connected to the first output terminal of the frequency divider module, its first input terminal connected to the primary-side peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit. The second channel unit has its selection terminal connected to the second output terminal of the frequency divider module, its first input terminal connected to the primary peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit.

[0010] As described above, the demagnetization detection circuit is further configured to output a valley detection signal at its second output terminal when the feedback voltage value output by the auxiliary winding of the transformer is within a preset valley voltage range and the duration is longer than a preset duration.

[0011] The vanishing tone circuit described above, wherein the PWM drive circuit includes: The comparison module has its first input terminal connected to the output terminal of the constant current regulation circuit, and its second input terminal connected to the real-time detected voltage signal. The comparison module is used to output a low-level pulse signal when the real-time detected voltage value is less than the error threshold voltage. The trigger module has its first input terminal connected to the output terminal of the comparison module and its second input terminal connected to the second input terminal of the demagnetization detection circuit. The trigger module is used to output a drive signal when it receives the low-level pulse signal and the valley detection signal. The driving module has its input terminal connected to the output terminal of the trigger module and its output terminal connected to the controlled terminal of the power switch. When the driving module receives the driving signal, it outputs an enable control signal to control the power switch to turn on.

[0012] As described above, the demagnetization detection circuit is also used to output an equivalent compensation current at its third output terminal that is proportional to the feedback voltage output by the auxiliary winding of the transformer when the power switch is turned off. The third output terminal of the demagnetization detection circuit is connected to the real-time detection voltage signal, which is used to superimpose the equivalent compensation current onto the real-time detection voltage signal to compensate for the detection deviation caused by the power switch turn-off delay due to the input voltage change.

[0013] The vanishing tone circuit described above further includes: The power supply circuit has its input terminal connected to the power supply. The power supply circuit is used to output the constant current threshold voltage when the power supply voltage is greater than the power-on start-up threshold voltage of the switching power supply system.

[0014] In addition, to achieve the above objectives, this application also proposes a silicon carbide driver, which includes the vanishing tone circuit described above.

[0015] In addition, to achieve the above objectives, this application also proposes a switching power supply system, which includes the silicon carbide driver described above.

[0016] Compared with the prior art, the disappearance modulation circuit, silicon carbide driver and switching power supply system proposed in this application have the following advantages: 1. The offset voltage proposed in this application, through the closed-loop regulation method of the constant current regulation circuit, causes the primary current to deviate from the actual value during the initial stage of regulation due to the offset voltage at the input terminal. The constant current regulation circuit compares this value with the constant current threshold voltage and corrects the error threshold voltage based on the comparison result. After repeated corrections over multiple switching cycles, the switching power supply system is brought into a dynamic equilibrium state, and the output current remains constant, thereby effectively offsetting the influence of the offset voltage at the input terminal and achieving high-precision constant current output. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a block diagram of the disappearing modulation circuit of this application; Figure 2 This is another structural block diagram of the disappearing modulation circuit of this application; Figure 3 This is a block diagram of the constant current regulation circuit of this application; Figure 4 This is a block diagram of the PWM drive circuit of this application; Figure 5 This is the circuit schematic diagram of the disappearing tone circuit in this application; Figure 6 This is a partial circuit diagram of the constant current regulation circuit in this application; Figure 7 This is the circuit schematic of the peak sampling module of this application; Figure 8 This is the internal circuit schematic diagram of the current converter in this application; Figure 9 This is the circuit schematic diagram of the disappearing modulation circuit applied to a PSR switching power supply system in this application; Figure 10 This is the circuit schematic diagram of the disappearing modulation circuit applied to an SSR switching power supply system in this application; Figure 11 This is a timing waveform diagram of the disappearing modulation circuit of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0022] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0023] In existing constant current control schemes, constant current amplifiers are used for constant current control output. However, due to objective factors such as manufacturing process, there will inevitably be an input offset voltage at the input terminal of the constant current amplifier. This offset voltage will be superimposed on the constant current control process of the constant current amplifier, thereby interfering with the output current. Its constant current accuracy is greatly affected, making it difficult to meet the application requirements of high-precision constant current output.

[0024] To solve the above problem, please refer to Figure 1 and Figure 5 As shown in the embodiment of this specification, a disappearing tone circuit 200 is proposed and applied in a switching power supply system. The switching power supply system includes a transformer and a power switching transistor connected to the transformer. The disappearing tone circuit 200 includes: A demagnetization detection circuit 210 is provided, the input terminal of which is connected to the output terminal of the auxiliary winding of the transformer. The demagnetization detection circuit 210 is used to output a demagnetization detection signal when it detects the feedback voltage output by the auxiliary winding of the transformer. A constant current adjustment circuit 220 is provided. The adjustment terminal of the constant current adjustment circuit 220 is connected to the first output terminal of the demagnetization detection circuit 210. The first input terminal of the constant current adjustment circuit 220 is connected to a real-time detection voltage signal used to characterize the instantaneous value of the primary current, and the peak voltage of the primary current is collected. The second input terminal of the constant current adjustment circuit 220 is connected to a constant current threshold voltage. When the demagnetization detection signal is received, the constant current adjustment circuit 220 adjusts the preset error threshold voltage according to the deviation between the collected peak voltage of the primary current and the constant current threshold voltage, and outputs the adjusted error threshold voltage. The PWM driving circuit 230 has a first input terminal connected to the output terminal of the constant current regulation circuit 220, a second input terminal connected to a real-time detection voltage signal used to characterize the instantaneous value of the primary current, and an output terminal connected to the controlled terminal of the power switch. The PWM drive circuit 230 is used to output an enable control signal to control the power switch to turn on when the real-time detected voltage signal is less than the error threshold voltage.

[0025] It should be noted that the fade-out circuit 200 provided in this application can be applied to a switching power supply system, which can be... Figure 9 The primary-side feedback switching power supply system (PSR) shown is or Figure 10The diagram shows a secondary-side feedback switching power supply system (SSR). The basic circuit structures of the two switching power supply systems are the same; the only difference is that the primary-side feedback switching power supply system obtains the output voltage feedback signal directly from the transformer auxiliary winding, without requiring an optocoupler or voltage reference chip. The secondary-side feedback switching power supply system obtains the output voltage feedback signal directly from the output terminal and transmits it to the chip via optocoupler isolation.

[0026] This application describes a primary-side feedback switching power supply system as an example. This system includes at least a transformer TX1 and a power switching transistor M1. The transformer TX1 includes a primary winding. Secondary winding and auxiliary winding The auxiliary winding One end of the auxiliary winding is grounded. The other end is connected to the input terminal of the disappearance modulation circuit 200 via a voltage divider resistor R5. The drain of the power switch M1 is connected to the primary winding. The power switch M1 is connected such that its source is grounded via a current sensing resistor R4, and its gate is driven and controlled by the vanishing modulation circuit 100.

[0027] It is important to note that when the switching power supply system operates in discontinuous mode, the discontinuity modulation circuit 100 controls the on / off state of the power switch M1 to control the transformer TX1 to transfer the input energy to the output terminal of the secondary winding, ultimately achieving constant current operation. During the operation of the switching power supply system, the auxiliary winding... The feedback voltage reflects the operating state of the output of the switching power supply system. When the power switch M1 is turned on, the transformer TX1 is in a magnetized state, and the auxiliary winding... The feedback voltage is 0 and cannot be used to reflect output voltage information; when the power switch M1 is turned off, the transformer TX1 is in a demagnetized state, and the auxiliary winding... The feedback voltage is a positive voltage.

[0028] It should also be noted that in the discontinuous operation mode of the switching power supply system, the transformer TX1 undergoes three stages in each switching cycle: magnetization, demagnetization, and dead zone. The demagnetization stage is the only time period during which the transformer TX1 transfers energy to the secondary side. That is, after the power switch M1 is turned off, the energy stored in the magnetic core is released to the load through the secondary winding. During this period, the auxiliary winding induces a positive feedback voltage proportional to the output voltage. The constant current regulation function of the disappearance modulation circuit 200 in this application will be explained below in conjunction with the three stages experienced by the transformer TX1 in each switching cycle under discontinuous operation mode.

[0029] When the switching power supply system is in the magnetization stage, the power switch M1 is turned on. At this time, the system input voltage is applied to the primary winding of transformer TX1, and the magnetic core of transformer TX1 begins to store energy. Simultaneously, the primary current of transformer T1 also rises linearly from 0. At this time, the real-time detection voltage used to characterize the instantaneous value of the primary current also rises accordingly. When the real-time detection voltage signal received at the second input terminal of the PWM drive circuit 230 is greater than or equal to the error threshold voltage at the first input terminal (i.e., ... When the power switch M1 is turned off, the output enable cut-off signal is activated, and the power switch M1 is turned off. At this time, the switching power supply system will enter the demagnetization stage from the magnetization stage. After entering the demagnetization stage, the magnetic core of transformer TX1 begins to release the stored energy to the secondary winding. The auxiliary winding induces a feedback voltage proportional to the output voltage. When the demagnetization detection circuit 210 receives the feedback voltage, its first output terminal outputs a demagnetization detection signal to the adjustment terminal of the constant current regulation circuit 220. At this time, the constant current regulation circuit 220 collects the primary peak voltage of the instantaneous primary current in the current switching cycle (i.e., ), and compare it with the constant current threshold voltage (i.e. The system compares the peak detection voltage and the constant current threshold voltage, and adjusts the preset error threshold voltage based on the current difference between them. The adjusted error threshold voltage is then used as the error threshold voltage for the next switching cycle. Specifically, if the current difference is greater than 0, the adjustment amount is increased based on the preset error threshold voltage to raise its value; if the current difference is less than 0, the adjustment amount is decreased based on the preset error threshold voltage to decrease its value; if the current difference is equal to 0, the preset error threshold voltage remains unchanged.

[0030] It should be noted that the preset error voltage threshold can be set based on historical experience or based on measured estimates; the increased or decreased adjustment amount can be set to the same value, or the increased adjustment amount can be greater than the decreased adjustment amount, or the increased adjustment amount can be less than the decreased adjustment amount. This manual does not specify the specific setting value of the adjustment amount.

[0031] As the demagnetization phase continues, the primary current of transformer T1 will gradually decrease. When the real-time detection voltage signal received at the second input terminal of the PWM drive circuit 230 is less than the error threshold voltage at the first input terminal, an enable control signal is output to control the power switch M1 to prepare to conduct. At this time, the switching power supply system will enter the dead zone phase from the demagnetization phase. When the valley detection signal output by the demagnetization detection circuit 210 is received, the switching cycle ends, and the power switch M1 is controlled to conduct, entering the next switching cycle. At the same time, the error threshold voltage adjusted in the previous switching cycle is used as the basis for judging the current switching cycle.

[0032] The constant current regulation circuit 220 described above forms a negative feedback control loop for adjusting the error threshold voltage. The level of the error threshold voltage directly determines the conduction time of the power switch M1 in each switching cycle. Specifically, the higher the error threshold voltage, the longer the conduction time of the power switch M1, and the more energy the transformer transfers; conversely, the lower the error threshold voltage, the shorter the conduction time of the power switch M1, and the less energy the transformer transfers. Specifically, when the output current is too high, the real-time detection voltage signal representing the instantaneous value of the primary current is too high, corresponding to a higher discharge charge. This reduces the net charge on the integrating capacitor, lowers the error threshold voltage, and the PWM drive circuit 230 advances the turn-off time of the power switch M1, shortening the conduction time, reducing the energy transferred by the transformer, and causing the output current to drop. Conversely, when the output current is too low, the error threshold voltage rises, the conduction time lengthens, and the output current rises. After several switching cycles of negative feedback regulation, the system reaches a dynamic equilibrium state, where the amount of charge added to the integrating capacitor in each switching cycle is exactly equal to the amount of charge released. In this balanced state, the output current is stabilized at a constant value determined by the error threshold voltage, unaffected by the input offset voltage, as well as by parameters such as input voltage, switching frequency, and transformer inductance. Figure 11 The timing waveforms of the above negative feedback regulation process are shown. Figure 11 It can be seen that when the peak value of the primary current... When it is too high, the error threshold voltage Automatic reduction causes the power switch M1 to turn off earlier, shortening the conduction time; when the peak primary current is low At that time, the error threshold voltage The automatic rise extends the conduction time, and after multiple cycles of negative feedback adjustment, the system eventually enters a steady state, maintaining a constant output current. This characteristic ensures that the present invention can achieve high-precision constant current output under different input voltages and different load conditions.

[0033] Due to manufacturing processes and other objective factors, constant current amplifiers inevitably have an offset voltage at their input. This offset voltage is superimposed on the primary-side current sensing voltage at the amplifier's input, causing sampling errors in both the primary-side voltage and the peak voltage, thus affecting the constant current output accuracy of the switching power supply system. Therefore, this embodiment employs a closed-loop adjustment method using a constant current regulation circuit. In the initial adjustment phase, the input offset voltage causes the primary-side current sampling to deviate from the actual value. The constant current regulation circuit compares this deviation with the constant current threshold voltage and corrects the error threshold voltage based on the comparison result. After repeated corrections over multiple switching cycles, the switching power supply system reaches a dynamic equilibrium state, maintaining a constant output current. This effectively counteracts the impact of the input offset voltage, achieving high-precision constant current output.

[0034] In one embodiment, please refer to Figure 2 As shown, the vanishing tone circuit 200 further includes: The power supply circuit 240 has its input terminal connected to the power supply. The power supply circuit 240 is used to output the constant current threshold voltage when the power supply voltage is greater than the power-on start-up threshold voltage of the switching power supply system.

[0035] In this embodiment, the power supply circuit 240 includes a power management chip. The power input terminal of the power management chip is connected to the power supply VDD. When the power supply VDD is greater than the power-on threshold voltage of the switching power supply system, the power management chip outputs the constant current threshold voltage at its first output terminal, the VB voltage at its second output terminal, the EN voltage at its third output terminal, and the 5V voltage at its fourth output terminal.

[0036] In this embodiment, the power management chip only starts working when the power supply VDD is greater than the system's power-on threshold voltage. This is to ensure that the switching power supply system operates stably after power-on before outputting the power supply voltage required by internal circuit modules such as the constant current threshold voltage. This prevents the constant current regulation circuit 220 from adjusting the error threshold voltage in the early stage of power-on due to the instability of the reference reference, which would prolong the adjustment cycle of the error threshold voltage and make it difficult to ensure that the switching power supply system can quickly establish dynamic balance and guarantee high-precision constant current output.

[0037] It should be noted that the VB voltage output by the power management chip is used to provide a bias voltage for the constant current regulation circuit 220, enabling the constant current regulation circuit 220 to operate stably; the EN voltage output by the power management chip provides an enable signal for the PWM drive circuit 230, which is used to ensure that the PWM drive circuit 230 only operates when the system is powered on and running stably, preventing the power switch M1 from abnormally conducting when the supply voltage is unstable; the 5V voltage output by the power management chip provides power to the internal low-voltage circuit module.

[0038] In one embodiment, please refer to Figure 3 As shown, the constant current regulation circuit 220 includes: The frequency divider module 221 has its input terminal connected to the first output terminal of the demagnetization detection circuit 210. The first output terminal of the frequency divider module 221 outputs a first frequency divider signal, and the second output terminal of the frequency divider module 221 outputs a second frequency divider signal that is inverted from the first frequency divider signal. When the rising edge of the demagnetization detection signal is received, the first frequency divider signal is inverted. The adjustment channel selection module 222 has a first channel selection terminal connected to the first output terminal of the frequency divider module 221, a second channel selection terminal connected to the second output terminal of the frequency divider module 221, a first input terminal connected to the primary-side peak voltage, a second input terminal connected to the constant current threshold voltage, a first channel output terminal connected to the first input terminal of the PWM drive circuit 230, and a second channel output terminal connected to the first input terminal of the PWM drive circuit 230. When the first frequency division signal is a high-level pulse, the path between the first channel selection terminal and the first channel output terminal of the adjustment channel selection module 222 is turned on. When the second frequency division signal is a high-level pulse, the path between the second channel selection terminal and the second channel output terminal of the adjustment channel selection module 222 is turned on.

[0039] It should be noted that the frequency divider module 221 is implemented using a frequency divider. The input terminal of the frequency divider is connected to the first output terminal of the demagnetization detection circuit 210. The first output terminal of the frequency divider outputs a first frequency divider signal, and the second output terminal of the frequency divider outputs a second frequency divider signal that is inversely related to the first frequency divider signal. When the rising edge of the demagnetization detection signal is received, the first frequency divider signal is reversed.

[0040] In this embodiment, combined with Figure 11 As shown in the timing diagram, the frequency divider divides the received demagnetization detection signal ( The frequency division is the first frequency division signal, which is half the frequency of the demagnetization detection signal and is in opposite phase to it. ) and the second frequency division signal ( Upon receiving the rising edge of each demagnetization detection signal, the first and second frequency division signals are inverted, thereby alternately controlling the first and second adjustment channels of the adjustment channel selection module 222 to be turned on in a complete adjustment cycle consisting of two switching cycles. The following explanation uses a complete adjustment cycle as an example.

[0041] In the first switching cycle, when the frequency divider receives the demagnetization detection signal, it divides it into a first frequency divider signal and a second frequency divider signal. The first frequency divider signal is a high-level pulse, and the second frequency divider signal is a low-level pulse. At this time, the first channel selection terminal of the adjustment channel selection module 222 receives the first frequency divider signal with a high-level pulse, and the path between the first channel selection terminal and the first channel output terminal is turned on. At this time, the first adjustment channel compares the primary peak voltage of the primary instantaneous current in the current switching cycle with the constant current threshold voltage. Based on the current difference between the peak detection voltage and the constant current threshold voltage, the preset error threshold voltage is adjusted, and the adjusted error threshold voltage is transmitted from the first channel output terminal to the first input terminal of the PWM drive circuit 230 as the error threshold voltage for the next switching cycle.

[0042] After the first switching cycle ends, when the second switching cycle begins, and the frequency divider receives the demagnetization detection signal again, it divides the signal into a first frequency divider signal and a second frequency divider signal, and inverts them. The first frequency divider signal is a low-level pulse, and the second frequency divider signal is a high-level pulse. At this time, the first channel selection terminal of the adjustment channel selection module 222 receives the first frequency divider signal with a low-level pulse, and the first adjustment channel is turned off. The second channel selection terminal receives the second frequency divider signal with a high-level pulse, and the path between the second channel selection terminal and the second channel output terminal is turned on. At this time, the second adjustment channel compares the primary peak voltage of the instantaneous primary current in the current switching cycle with the constant current threshold voltage. Based on the current difference between the peak detection voltage and the constant current threshold voltage, the preset error threshold voltage is adjusted, and the adjusted error threshold voltage is transmitted from the second channel output terminal to the first input terminal of the PWM drive circuit 230 as the error threshold voltage for the next switching cycle.

[0043] In the above manner, during each complete adjustment cycle, the first and second adjustment channels of the adjustment channel selection module will alternately correct the error threshold voltage. After several cycles of iterative accumulation of the error threshold voltage, the offset voltage at the input of the constant current adjustment circuit is offset on average, and the error threshold voltage eventually converges to the steady-state value corresponding to the accurate constant current output. This keeps the switching power supply system in a dynamic equilibrium state, and the output current remains constant, thereby effectively offsetting the influence of the input offset voltage and achieving high-precision constant current output.

[0044] In one embodiment, please refer to Figure 3 As shown, the channel selection module 222 includes: The first channel unit 2221 has its selection terminal connected to the first output terminal of the frequency divider module 221, its first input terminal connected to the primary side peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit 230. The second channel unit 2222 has its selection terminal connected to the second output terminal of the frequency divider module 221, its first input terminal connected to the primary side peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit 230.

[0045] In this embodiment, refer to Figure 6 As shown, the first channel unit 2221 includes a first current converter 31, a first switch K2, a second switch K2A, a third switch K3, a fourth switch K3A, a fifth switch K4, and a sixth switch K5. The controlled terminal of the first switch K2 is connected to the first output terminal of the frequency divider module 221 (i.e., The first terminal of the first switch K2 is connected to the constant current threshold voltage, and the second terminal of the first switch K2 is connected to the first inverting input terminal (i.e., VN1 terminal) of the first current converter 31. The second terminal of the first switch K2 is also connected to the first terminal of the second switch K2A. The second terminal of the second switch K2A is grounded, and the controlled terminal of the second switch K2A is connected to the second output terminal (i.e., VN1 terminal) of the frequency divider module 221. (End) connection; The controlled terminal of the third switch K3 is connected to the first output terminal of the frequency divider module 221. The first terminal of the third switch K3 is connected to the primary side peak voltage. The second terminal of the third switch K3 is connected to the first positive input terminal (i.e., VP1 terminal) of the first current converter 31. The second terminal of the third switch K3 is also connected to the first terminal of the fourth switch K3A. The second terminal of the fourth switch K3A is grounded. The controlled terminal of the fourth switch K3A is connected to the second output terminal of the frequency divider module 221. The second positive input terminal (i.e., VP terminal) of the first current converter 31 is connected to the error threshold voltage, the second inverting input terminal (i.e., VN terminal) of the first current converter 31 is connected to the first terminal of the fifth switch K4, the second terminal of the fifth switch K4 is connected to the first terminal of the sixth switch K5, the controlled terminal of the fifth switch K4 is connected to the second output terminal of the frequency divider module 221, and the output terminal of the first current converter 31 is connected to the first terminal of the sixth switch K5. The controlled terminal of the sixth switch K5 is connected to the first output terminal of the frequency divider module 221, the second terminal of the sixth switch K5 is connected to the first input terminal of the PWM drive circuit 230, and a grounding capacitor C21 is connected between the second terminal of the sixth switch K5 and the first input terminal of the PWM drive circuit 230.

[0046] When the first frequency division signal When it is a high-level pulse, the second frequency division signal When the pulse is low, the first switch K2, the third switch K3, and the sixth switch K5 are turned on, while the second switch K2A, the fourth switch K3A, and the fifth switch K4 are turned off. At this time, because the fifth switch K4 is turned off, the second positive input terminal (i.e., the VP terminal) of the first current converter 31 receives the error threshold voltage. The current is biased to the second inverting input terminal (i.e., VN terminal), so the current deviation between the second positive input terminal and the second inverting input terminal is 0. Since the first switch K2 and the third switch K3 are turned on, the first positive input terminal (i.e., VP1 terminal) of the first current converter 31 receives a constant current threshold voltage. The second inverting input terminal (i.e., VN1 terminal) of the first current converter 31 receives the primary side peak voltage. Assume there is an offset voltage between the positive and negative input terminals of the first current converter 31. Under the action of the first current converter 31, the superimposed offset voltage is calculated. back, and primary peak voltage Current difference between The error threshold voltage is adjusted by charging and discharging capacitor C21 through the current difference between the two. Specifically, if the current difference between the two... If the current difference is zero, then capacitor C21 is charged, causing the error threshold voltage to rise; conversely, if the current difference is zero, then the error threshold voltage is not adjusted.

[0047] In this embodiment, refer to Figure 6As shown, the second channel selection unit 2222 includes a second current converter 32, a seventh switch K6, an eighth switch K6A, a ninth switch K7, a tenth switch K7A, an eleventh switch K8, and a twelfth switch K9. The controlled terminal of the seventh switch K6 is connected to the second output terminal of the frequency divider module 221. The first terminal of the seventh switch K6 is connected to the primary side peak voltage. The second terminal of the seventh switch K6 is connected to the first inverting input terminal (i.e., VN1 terminal) of the second current converter 32. The second terminal of the seventh switch K6 is also connected to the first terminal of the eighth switch K6A. The second terminal of the eighth switch K6A is grounded. The controlled terminal of the eighth switch K6A is connected to the first output terminal of the frequency divider module 221. The controlled terminal of the ninth switch K7 is connected to the second output terminal of the frequency divider module 221. The first terminal of the ninth switch K7 is connected to the constant current threshold voltage. The second terminal of the ninth switch K7 is connected to the first positive input terminal (i.e., VP1 terminal) of the second current converter 32. The second output terminal of the ninth switch K7 is also connected to the first terminal of the tenth switch K7A. The second terminal of the tenth switch K7A is grounded. The controlled terminal of the tenth switch K7A is connected to the first output terminal of the frequency divider module 221. The second positive input terminal (i.e., VP terminal) of the second current converter 32 is connected to the error threshold voltage, the second inverting input terminal (i.e., VN terminal) of the second current converter 32 is connected to the first terminal of the eleventh switch K8, the second terminal of the eleventh switch K8 is connected to the first terminal of the twelfth switch K9, the controlled terminal of the eleventh switch K8 is connected to the first output terminal of the frequency divider module 221, and the output terminal of the second current converter 32 is connected to the first terminal of the twelfth switch K9. The controlled terminal of the twelfth switch K9 is connected to the second output terminal of the frequency divider module 221, the second terminal of the twelfth switch K9 is connected to the first input terminal of the PWM drive circuit 230, and a grounding capacitor C21 is connected between the second terminal of the twelfth switch K9 and the first input terminal of the PWM drive circuit 230.

[0048] When the first frequency division signal When it is a low-level pulse, the second frequency division signal When the pulse is high, switches K6 (seventh), K7 (ninth), and K9 (twelfth) are turned on, while switches K6A (eighth), K7A (tenth), and K8 (eleventh) are turned off. At this time, because switch K8 is off, the second positive input terminal (VP terminal) of the second current converter 32 receives the error threshold voltage. The current is biased to the second inverting input terminal (i.e., VN terminal), so the current deviation between the second positive input terminal and the second inverting input terminal is 0. Since the seventh switch K6, the ninth switch K7 and the twelfth switch K9 are turned on, the first positive input terminal (i.e., VP1 terminal) of the second current converter 32 receives a constant current threshold voltage. The first inverting input terminal (i.e., VN1 terminal) of the second current converter 32 receives the primary side peak voltage. Assume there is an offset voltage between the positive and negative input terminals of the second current converter 32. Under the action of the second current converter 32, the superimposed offset voltage is calculated. back, and primary peak voltage Current difference between The error threshold voltage is adjusted by charging and discharging capacitor C21 through the current difference between the two. Specifically, if the current difference between the two... If the current difference is zero, then capacitor C21 is charged, causing the error threshold voltage to rise; conversely, if the current difference is zero, then the error threshold voltage is not adjusted.

[0049] It should be noted that in the process of adjusting the error threshold voltage to achieve the final high-precision constant current output, the following steps are taken: Figure 11 As shown, the first frequency division signal A high-level pulse, the second frequency division signal The following explanation uses a low-level pulse as an example.

[0050] First frequency division signal When it is a high-level pulse, we have: ; Therefore: ; in, This refers to the demagnetization duty cycle.

[0051] Based on the formula for calculating the output current: ; in, This represents the turns ratio of the primary and secondary sides of the transformer.

[0052] We can obtain: .

[0053] Therefore, it can be concluded that when the system reaches dynamic stability, the output current is locked at a fixed value determined by the turns ratio of the primary and secondary sides of the transformer by the current sensing resistor.

[0054] It should also be noted that the internal circuit structures of the first current converter 31 and the second current converter 32 are completely identical, as detailed in the reference [reference needed]. Figure 8 As shown. This embodiment uses the internal circuit structure of the first current converter 31 as an example to illustrate the principle and process of eliminating input offset voltage.

[0055] in, Figure 8 In the diagram, current sources I5A and I5B, and I5C and I5D are each a pair of current sources, with current values ​​of... Current sources I6A, I6B and I6C, I6D are all pairs of NMOS current sources, with current values ​​of M10, M11, M12, and M13 are PMOS input switches, respectively connected to the second positive input terminal VP, the second negative input terminal VN, the first positive input terminal VP1, and the first negative input terminal VN1; resistors RA and RB are current bridge arm resistors; M40 / M40A and M41 / M41A are a pair of PMOS current mirrors; M20 / M20A and M200 / M200A are a pair of NMOS current mirrors, M21 / M21A and M210 / M210A are a pair of NMOS current mirrors, M30 / M30A and M300 / M300A are a pair of NMOS current mirrors, and M31 / M31A and M310 / M310A are a pair of NMOS current mirrors.

[0056] The aforementioned current mirror and current source are used to respond to the signals at the positive and negative input terminals of the first current converter 31, at the output terminal (i.e. The output current is determined by the second positive input terminal VP. The second positive input terminal VP is used to receive the error threshold voltage. The input transistors M10 / M11, current sources I5A / I5B, bridge arm resistor RA, current mirrors M20 / M20A and M200 / M200A, and current mirrors M21 / M21A and M210 / M210A follow their values ​​and are placed at the second inverting input terminal VN; the first positive input terminal VP1 is used to receive... The first inverting input terminal VN1 is used to receive... The current is adjusted by input transistors M12 / M13, current sources I5C / I5D, bridge arm resistor RB, current mirrors M30 / M30A and M300 / M300A, and current mirrors M31 / M31A and M310 / M310A. The adjustment formula is as follows: ; It is placed at the output terminal, and C21 is charged and discharged under the action of switch K5 / K9.

[0057] Here it is assumed For two pairs of input switching transistors of the same type and size under the same manufacturing conditions, the offset voltage exists. If so, then there exists the same offset voltage between VP and VN, and between VP1 and VN1. .

[0058] Therefore: ; After transformation, we have: ; ; ; .

[0059] After multiple switching cycles of iterative accumulation, the offset voltage between the input switching transistors is eliminated, and the error threshold voltage eventually converges to the steady-state value corresponding to the precise constant current output. This puts the switching power supply system in a dynamic equilibrium state, keeping the output current constant, thus effectively offsetting the influence of the input offset voltage and achieving high-precision constant current output.

[0060] In one embodiment, please refer to Figure 3 As shown, the constant current regulation circuit 220 further includes: Peak sampling module 223, the first input terminal of peak sampling module 223 is connected to the real-time detected voltage signal, the second input terminal of peak sampling module 223 is connected to the output terminal of PWM drive circuit 230, and the output terminal of peak sampling module 223 is connected to the first input terminal of adjustment channel selection module 222; The peak sampling module 223 is used to acquire the peak value of the instantaneous primary current before the falling edge of the enable control signal arrives, and output the peak voltage of the primary current to the first input terminal of the adjustment channel selection module 222.

[0061] In this embodiment, refer to Figure 7 As shown, the peak sampling module 223 includes a sampling pulse generator 30, an inverter 34, a capacitor C21A, a thirteenth switch K10, a fourteenth switch K10A, and a fifteenth switch K10B. The output terminal of the PWM drive circuit 230 is connected to the input terminal of the sampling pulse generator 30, and the output terminal of the sampling pulse generator 30 is connected to the controlled terminal of the thirteenth switch K10. The first terminal of the thirteenth switch K10 is connected to the real-time detection voltage signal, the second terminal of the thirteenth switch K10 is connected to the first terminal of the fourteenth switch K10A, the second terminal of the fourteenth switch K10A outputs the primary-side peak voltage, and the capacitor C21A is also connected between the second terminal of the fourteenth switch K10A and ground. The first output terminal of the demagnetization detection circuit 210 is connected to the input terminal of the inverter 34, the first output terminal of the inverter 34 is connected to the controlled terminal of the fourteenth switch K10A, the second output terminal of the inverter 34 is connected to the controlled terminal of the fifteenth switch K10B, the first terminal of the fifteenth switch K10B is connected to the second terminal of the fourteenth switch K10A, and the fifteenth switch K10B is grounded.

[0062] During the magnetization phase, when the input terminal of the sampling pulse generator 30 receives the enable control signal output by the PWM drive circuit 230, it generates a narrow pulse signal SH to the controlled terminal of the thirteenth switch K10, controlling the thirteenth switch K10 to conduct, thereby enabling the enable control signal... Before the falling edge arrives, the peak value of the instantaneous primary current is sampled, and the capacitor C21A is charged to clamp it across the two ends of the capacitor C21A. At the same time, since the inverter 34 is connected to the first output terminal of the demagnetization detection circuit 210, the fourteenth switch K10A is turned on and the fifteenth switch K10B is turned off when entering the demagnetization stage. At this time, the capacitor C21A is discharged, and the previously captured primary peak voltage is stably output to the first input terminal of the adjustment channel selection module 222.

[0063] In one embodiment, the demagnetization detection circuit 210 is further configured to output a valley detection signal at its second output terminal when it detects that the feedback voltage value output by the auxiliary winding of the transformer is within a preset valley voltage range and the duration is longer than a preset duration.

[0064] In this embodiment, after the demagnetization stage ends and the energy of the secondary winding of transformer TX1 is completely released, the feedback voltage on the auxiliary winding enters a free resonance state under the combined action of the transformer's magnetizing inductance and the circuit's parasitic capacitance, and the feedback voltage on the auxiliary winding is at the instant the demagnetization ends. have The negative voltage ringing (set to a preset valley voltage range) lasts for approximately one-quarter of the transformer's ringing cycle (set to a preset duration). Therefore, after demagnetization, if the demagnetization detection circuit 210 detects that the feedback voltage on the auxiliary winding is within the preset valley voltage range and lasts for a duration longer than the preset duration, it outputs a valley detection signal, controls the PWM drive circuit 230 to output a drive signal, and drives the power switch M1 to turn on, thereby minimizing the conduction loss of the power switch M1.

[0065] In one embodiment, the demagnetization detection circuit 210 is further configured to output an equivalent compensation current at its third output terminal that is proportional to the feedback voltage output by the auxiliary winding of the transformer when the power switch M1 is turned off. The third output terminal of the demagnetization detection circuit 210 is connected to the real-time detection voltage signal, and is used to superimpose the equivalent compensation current onto the real-time detection voltage signal to compensate for the detection deviation caused by the turn-off delay of the power switch M1 due to the input voltage change.

[0066] Because there is an inherent turn-off delay time due to the signal transmission delay of the circuit, from the time the power switch M1 receives the enable / disable signal from the PWM drive circuit 230 until it is completely turned off, during this turn-off delay time, the power switch M1 is still in the conducting state, and the primary current continues to rise at a slope proportional to the input voltage, causing the output constant current value to be too high as the input voltage increases. To address this in this embodiment, before connecting the real-time detection voltage signal representing the instantaneous value of the primary current, equivalent compensation is performed on the input voltage. The equivalent compensation calculation formula is as follows: ; in, The equivalent compensation current is 0 when the power switch M1 is turned on; As a fixed coefficient, R5 is a voltage divider resistor. Figure 9 or Figure 10 As shown, Let be the input voltage. Therefore, it can be known that when the equivalent compensation current... Flow through resistor Generate compensation voltage: Therefore: .

[0067] In one embodiment, reference is made to Figure 4 As shown, the PWM drive circuit 230 includes: Comparison module 231, the first input terminal of the comparison module 231 is connected to the output terminal of the constant current regulation circuit 220, the second input terminal of the comparison module 231 is connected to the real-time detected voltage signal, the comparison module 231 is used to output a low-level pulse signal when the real-time voltage detection value is less than the error threshold voltage; The trigger module 232 has its first input terminal connected to the output terminal of the comparison module 231, and its second input terminal connected to the second input terminal of the demagnetization detection circuit 210. The trigger module 232 is used to output a drive signal when it receives the low-level pulse signal and the valley detection signal. The driving module 233 has its input terminal connected to the output terminal of the trigger module 232 and its output terminal connected to the controlled terminal of the power switch M1. The driving module 231 is used to output an enable control signal when it receives the driving signal, thereby controlling the power switch M1 to turn on.

[0068] In this embodiment, the comparison module 231 includes a comparator 12, the trigger module 232 includes an RS trigger 14, and the drive module 233 includes a drive chip 20.

[0069] In this embodiment, the comparison module 231 compares the real-time detection voltage signal at the first input terminal with the error threshold voltage at the second input terminal. When the real-time detection voltage signal is greater than or equal to the error threshold voltage, it outputs a high-level pulse signal. When the trigger module 232 receives the high-level pulse signal, it outputs a low-level turn-off signal. After the drive module 233 receives the low-level turn-off signal, it outputs an enable cut-off signal to control the power switch M1 to stop working and end the conduction cycle of the power switch M1 in the current switching cycle. When the real-time detected voltage signal is less than the error threshold voltage signal, a low-level pulse signal is output. When the trigger module 232 receives the low-level pulse signal and the valley detection signal, it outputs a high-level drive signal. When the drive module 233 receives the high-level drive signal, it outputs an enable control signal to control the power switch M1 to turn on, thus starting the next switching cycle of the power switch M1.

[0070] This specification also provides a silicon carbide driver 100, which includes the vanishing tone circuit 200 as described above.

[0071] It is worth noting that since the silicon carbide driver 100 in this specification is based on the above-mentioned vanishing tone circuit 200, the embodiments of the silicon carbide driver 100 proposed in this specification include all the technical solutions of all embodiments of the above-mentioned vanishing tone circuit 200, and the technical effects achieved are exactly the same, so they will not be repeated here.

[0072] Please refer to Figure 9 and Figure 10 As shown in the embodiments of this specification, a switching power supply system is also provided, wherein the switching power supply system 10 includes the silicon carbide driver 100 as described above.

[0073] It should be noted that the switching power supply system proposed in this embodiment can be a primary-side feedback controlled switching power supply system 10 (i.e., a PSR switching power supply system), or a secondary-side feedback controlled switching power supply system 10A (i.e., an SSR switching power supply system), or of course, other types of switching power supply systems. This embodiment does not limit the specific type of switching power supply system.

[0074] It is worth noting that since the switching power supply system in this specification is based on the silicon carbide driver 100 described above, the embodiments of the switching power supply system proposed in this specification include all the technical solutions of all embodiments of the silicon carbide driver 100 and the vanishing tone circuit 200, and the technical effects achieved are exactly the same, so they will not be repeated here.

[0075] Those skilled in the art should understand that the above-described embodiments are specific to the content and do not imply that the specific implementation of this application is limited to these descriptions. Furthermore, due to differences in industry naming conventions, the application is not limited to the above names or English names. Any methods or structures similar to or identical to those of this application, or any technical deductions or substitutions made based on the concept of this application, should be considered within the scope of protection of this application.

Claims

1. A vanishing tone circuit, characterized in that, The circuit is applied in a switching power supply system, the switching power supply system including a transformer and a power switching transistor connected to the transformer, and the disappearing modulation circuit includes: A demagnetization detection circuit, wherein the input terminal of the demagnetization detection circuit is connected to the output terminal of the auxiliary winding of the transformer, and the demagnetization detection circuit is used to output a demagnetization detection signal when it detects the feedback voltage output by the auxiliary winding of the transformer; A constant current regulating circuit is provided, wherein the regulating terminal of the constant current regulating circuit is connected to the first output terminal of the demagnetization detection circuit, the first input terminal of the constant current regulating circuit is connected to a real-time detection voltage signal used to characterize the instantaneous value of the primary current, and the peak voltage of the primary current instantaneous value is collected. The second input terminal of the constant current regulating circuit is connected to a constant current threshold voltage. When the demagnetization detection signal is received, the constant current regulating circuit adjusts the preset error threshold voltage according to the deviation between the collected peak voltage of the primary current and the constant current threshold voltage, and outputs the adjusted error threshold voltage. A PWM driving circuit is provided, wherein the first input terminal of the PWM driving circuit is connected to the output terminal of the constant current regulation circuit, the second input terminal of the PWM driving circuit is connected to the real-time detected voltage signal, and the output terminal of the PWM driving circuit is connected to the controlled terminal of the power switching transistor. The PWM drive circuit is used to output an enable control signal to control the power switch to turn on when the real-time detected voltage signal is less than the error threshold voltage.

2. The vanishing tone circuit according to claim 1, characterized in that, The constant current regulation circuit includes: The frequency divider module has its input terminal connected to the first output terminal of the demagnetization detection circuit. The first output terminal of the frequency divider module outputs a first frequency divider signal, and the second output terminal of the frequency divider module outputs a second frequency divider signal that is inverted from the first frequency divider signal. When the rising edge of the demagnetization detection signal is received, the first frequency divider signal is inverted. The adjustment channel selection module has a first channel selection terminal connected to the first output terminal of the frequency divider module, a second channel selection terminal connected to the second output terminal of the frequency divider module, a first input terminal connected to the primary-side peak voltage, a second input terminal connected to the constant current threshold voltage, a first channel output terminal connected to the first input terminal of the PWM drive circuit, and a second channel output terminal connected to the first input terminal of the PWM drive circuit. When the first frequency division signal is a high-level pulse, the path between the first channel selection terminal and the first channel output terminal of the adjustment channel selection module is connected. When the second frequency division signal is a high-level pulse, the path between the second channel selection terminal and the second channel output terminal of the adjustment channel selection module is turned on.

3. The vanishing tone circuit according to claim 2, characterized in that, The constant current regulation circuit further includes: A peak sampling module, wherein the first input terminal of the peak sampling module is connected to the real-time detected voltage signal, the second input terminal of the peak sampling module is connected to the output terminal of the PWM drive circuit, and the output terminal of the peak sampling module is connected to the first input terminal of the adjustment channel selection module; The peak sampling module is used to acquire the peak value of the instantaneous primary current before the falling edge of the enable control signal arrives, and output the peak voltage of the primary current to the first input terminal of the adjustment channel selection module.

4. The vanishing tone circuit according to claim 2, characterized in that, The adjustment channel selection module includes: The first channel unit has its selection terminal connected to the first output terminal of the frequency divider module, its first input terminal connected to the primary-side peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit. The second channel unit has its selection terminal connected to the second output terminal of the frequency divider module, its first input terminal connected to the primary peak voltage, its second input terminal connected to the constant current threshold voltage, and its output terminal connected to the first input terminal of the PWM drive circuit.

5. The vanishing tone circuit according to claim 1, characterized in that, The demagnetization detection circuit is also used to detect when the feedback voltage value output by the auxiliary winding of the transformer is within a preset valley voltage range and the duration is longer than a preset duration, and then outputs a valley detection signal at its second output terminal.

6. The vanishing tone circuit according to claim 5, characterized in that, The PWM drive circuit includes: The comparison module has its first input terminal connected to the output terminal of the constant current regulation circuit, and its second input terminal connected to the real-time detected voltage signal. The comparison module is used to output a low-level pulse signal when the real-time detected voltage value is less than the error threshold voltage. The trigger module has its first input terminal connected to the output terminal of the comparison module and its second input terminal connected to the second input terminal of the demagnetization detection circuit. The trigger module is used to output a drive signal when it receives the low-level pulse signal and the valley detection signal. The driving module has its input terminal connected to the output terminal of the trigger module and its output terminal connected to the controlled terminal of the power switch. When the driving module receives the driving signal, it outputs an enable control signal to control the power switch to turn on.

7. The vanishing tone circuit according to claim 1, characterized in that, The demagnetization detection circuit is also used to output an equivalent compensation current at its third output terminal that is proportional to the feedback voltage output by the auxiliary winding of the transformer when the power switch is turned off. The third output terminal of the demagnetization detection circuit is connected to the real-time detection voltage signal, which is used to superimpose the equivalent compensation current onto the real-time detection voltage signal to compensate for the detection deviation caused by the power switch turn-off delay due to the input voltage change.

8. The vanishing tone circuit according to claim 1, characterized in that, The vanishing tone circuit also includes: The power supply circuit has its input terminal connected to the power supply. The power supply circuit is used to output the constant current threshold voltage when the power supply voltage is greater than the power-on start-up threshold voltage of the switching power supply system.

9. A silicon carbide driver, characterized in that, The silicon carbide driver includes the vanishing tone circuit as described in any one of claims 1 to 8.

10. A switching power supply system, characterized in that, The switching power supply system includes the silicon carbide driver as described in claim 9.

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