Auxiliary power supply circuit, auxiliary power supply and photovoltaic grid-connected inverter

Abstract

This invention provides an auxiliary power supply circuit, an auxiliary power supply, and a photovoltaic grid-connected inverter. The circuit includes a power chip, a flyback transformer, and an undervoltage shutdown circuit. The first secondary side of the flyback transformer supplies power to the power chip. The primary side of the flyback transformer responds to the control signal from the power chip, causing the auxiliary power supply to start according to the startup voltage. The undervoltage shutdown circuit is powered by the first secondary side. A voltage-stabilizing capacitor module and an output buffer resistor are provided between the first secondary side and the power supply port. The output power of the first secondary side increases as the resistance of the output buffer resistor decreases. The output buffer resistor is a positive temperature coefficient thermistor. By setting the output buffer resistor on the first secondary side as a thermistor, its resistance decreases as the temperature decreases, thereby increasing the output power on the first secondary side. This prevents the leakage current of the undervoltage shutdown circuit from affecting the power chip on the first secondary side, ensuring that the power chip can control the auxiliary power supply to start under normal startup voltage.

Description

Technical Field

[0001] This invention belongs to the field of switching power supply technology, and particularly relates to an auxiliary power supply circuit, an auxiliary power supply, and a photovoltaic grid-connected inverter. Background Technology

[0002] The auxiliary power supply (hereinafter referred to as auxiliary power supply) of a household string photovoltaic grid-connected inverter is generally required to have a wide voltage and temperature operating range. Therefore, the auxiliary power supply is generally selected as a single-tube flyback power supply with an operating voltage range of 80 to 600Vdc.

[0003] In existing technologies, flyback power supplies typically place the power supply chip and undervoltage shutdown circuit on the same secondary side for power supply. However, in low-temperature environments, the auxiliary power supply often fails to start normally. To find the cause of this failure, the system ambient temperature was increased. The higher the temperature, the lower the power supply's startup voltage, confirming that temperature is indeed the cause of the auxiliary power supply's startup failure. However, heating the system in a low-temperature environment is impractical to solve the startup problem. Therefore, the cause of the increased startup voltage at low temperatures was further analyzed. Capacitors degrade at low temperatures. Increasing the value of the voltage regulator capacitor did not significantly change the startup voltage at low temperatures. Removing the main power-consuming component of the undervoltage shutdown circuit resulted in a slight increase in the startup voltage at the same temperature, proving that the actual cause of the auxiliary power supply's startup failure was leakage current. The comparator in the undervoltage shutdown circuit generates a large leakage current, affecting the supply voltage of the power supply chip on the same secondary side, causing the auxiliary power supply to fail to start normally under normal startup voltage. Summary of the Invention

[0004] In view of this, the present invention provides an auxiliary power supply circuit, an auxiliary power supply, and a photovoltaic grid-connected inverter, aiming to solve the problem that the auxiliary power supply in the prior art cannot start normally.

[0005] A first aspect of the present invention provides an auxiliary power supply circuit, including: a power chip, a flyback transformer, and an undervoltage shutdown circuit;

[0006] The primary side of the flyback transformer supplies power to the power chip through the power supply port of the power chip; the primary side of the flyback transformer responds to the control signal of the output port of the power chip, causing the auxiliary power supply to start according to the corresponding start-up voltage.

[0007] The undervoltage shutdown circuit is powered by the first secondary side of the flyback transformer; the undervoltage shutdown circuit is used to instruct the power chip to shut off the auxiliary power supply when the starting voltage of the primary side of the flyback transformer is less than the voltage of the undervoltage protection shutdown point.

[0008] A voltage regulator capacitor module and an output buffer resistor are installed between the primary secondary side of the flyback transformer and the power supply port of the power chip; the voltage regulator capacitor module is located between the output buffer resistor and the power supply port of the power chip; the output power of the primary secondary side of the flyback transformer increases as the resistance of the output buffer resistor decreases; the output buffer resistor is a thermistor with a positive temperature coefficient.

[0009] In some possible implementations, the output buffer resistors include a first output buffer resistor, a second output buffer resistor, and a third output buffer resistor connected in parallel;

[0010] The first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all located on the first secondary side of the flyback transformer.

[0011] In some possible implementations, one or more of the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are thermistors with positive temperature coefficients.

[0012] In some possible implementations, the resistance of the first output buffer resistor is smaller than that of the second and third output buffer resistors; the first output buffer resistor is a nonlinear thermistor with a positive temperature coefficient; and the temperature coefficient of the first output buffer resistor increases as the temperature decreases.

[0013] In some possible implementations, the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all linear thermistors with positive temperature coefficients.

[0014] The resistance value of the first output buffer resistor is a preset multiple of the resistance value of the second output buffer resistor;

[0015] The resistance value of the second output buffer resistor is a preset multiple of the resistance value of the third output buffer resistor.

[0016] In some possible implementations, a current-limiting resistor is placed between the primary side of the flyback transformer and the feedback port of the power supply chip; the overcurrent protection point of the flyback transformer increases as the current-limiting resistor decreases.

[0017] A transistor is provided on the primary side of the flyback transformer; the power chip uses the transistor to enable the first secondary side of the flyback transformer to output the supply voltage required for the power chip to operate.

[0018] The current-limiting resistor is connected to the transistor; the output power of the first secondary side of the flyback transformer increases as the resistance of the current-limiting resistor decreases.

[0019] In some possible implementations, the current-limiting resistors include a first current-limiting resistor and a second current-limiting resistor connected in parallel.

[0020] In some possible implementations, both the first current-limiting resistor and the second current-limiting resistor are thermistors with positive temperature coefficients.

[0021] A second aspect of the present invention provides an auxiliary power supply, including: the auxiliary power supply circuit as described in the first aspect above.

[0022] A third aspect of the present invention provides a photovoltaic grid-connected inverter, comprising: an auxiliary power supply as described in the second aspect above.

[0023] The auxiliary power supply circuit, auxiliary power supply, and photovoltaic grid-connected inverter provided in this invention embodiment include: a power supply chip, a flyback transformer, and an undervoltage shutdown circuit; the first secondary side of the flyback transformer supplies power to the power supply chip through the power supply port of the power supply chip; the primary side of the flyback transformer responds to the control signal of the output port of the power supply chip, causing the auxiliary power supply to start according to the corresponding start-up voltage; the undervoltage shutdown circuit is supplied by the first secondary side of the flyback transformer; the undervoltage shutdown circuit is used to instruct the power supply chip to shut down the auxiliary power supply when the start-up voltage of the primary side of the flyback transformer is less than the voltage of the undervoltage protection shutdown point; a voltage stabilizing capacitor module and an output buffer resistor are provided between the first secondary side of the flyback transformer and the power supply port of the power supply chip; the voltage stabilizing capacitor module is located between the output buffer resistor and the power supply port of the power supply chip; the output power of the first secondary side of the flyback transformer increases as the resistance value of the output buffer resistor decreases; the output buffer resistor is a positive temperature coefficient thermistor. By setting the output buffer resistor on the first secondary side as a thermistor, the resistance decreases as the temperature decreases, thereby increasing the output power on the first secondary side. This avoids the leakage current of the undervoltage shutdown circuit from affecting the power chip on the first secondary side, ensuring that the power chip can control the auxiliary power supply to start under normal startup voltage. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the auxiliary power supply circuit provided in an embodiment of the present invention;

[0026] Figure 2 This is a schematic diagram of the auxiliary power supply circuit provided in an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the undervoltage shutdown circuit provided in an embodiment of the present invention. Detailed Implementation

[0028] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0029] Overcurrent protection circuits typically include a comparator to compare the output voltage of the auxiliary power supply with the voltage at the undervoltage protection cutoff point, thereby achieving overcurrent protection for the auxiliary power supply. However, in low-temperature environments, the leakage current of the comparator in the overcurrent protection circuit will increase compared to normal temperature conditions. Since the power supply chips of the overcurrent protection circuit and the auxiliary power supply are powered by the same secondary side of the flyback transformer, the leakage current will increase the equivalent load on that secondary side, causing the load power supply to fail to start under normal starting voltage and requiring a higher starting voltage.

[0030] Figure 1 This is a schematic diagram of the auxiliary power supply circuit provided in an embodiment of the present invention. Figure 1 As shown, in some embodiments, the auxiliary power supply circuit includes: a power chip 11, a flyback transformer 12, and an undervoltage shutdown circuit 13.

[0031] The first secondary side of the flyback transformer 12 supplies power to the power chip 11 through the power supply port of the power chip 11; the primary side of the flyback transformer 12 responds to the control signal of the output port of the power chip 11, causing the auxiliary power supply to start according to the corresponding start-up voltage; the undervoltage shutdown circuit 13 is powered by the first secondary side of the flyback transformer 12; the undervoltage shutdown circuit 13 is used to instruct the power chip 11 to shut down the auxiliary power supply when the start-up voltage of the primary side of the flyback transformer 12 is less than the voltage of the undervoltage protection shutdown point; a voltage stabilizing capacitor module and an output buffer resistor are provided between the first secondary side of the flyback transformer 12 and the power supply port of the power chip; the voltage stabilizing capacitor module is located between the output buffer resistor and the power supply port of the power chip; the output power of the first secondary side of the flyback transformer 12 increases as the resistance value of the output buffer resistor decreases; the output buffer resistor is a positive temperature coefficient thermistor.

[0032] In this embodiment of the invention, the power chip 11 has multiple ports, specifically including a power supply port VCC, a compensation port COM, a feedback port, an output port OUT, a reference value output port Vref, and a ground port. The flyback transformer 12 includes a primary side and multiple secondary sides; the power supply port of the power chip 11 and the power supply port of the undervoltage shutdown circuit 13 are connected to the same secondary side, i.e., the first secondary side. The voltage regulator capacitor module is used to enable the first secondary side to output a stable DC voltage to the output port OUT.

[0033] The power chip 11 is located at one end of the primary side of the flyback transformer 12, and the other end of the primary side of the flyback transformer 12 is connected to the bus. When the auxiliary power supply needs to be started, the bus provides a starting voltage to the other end of the primary side of the flyback transformer 12, and then the first secondary side supplies power to the power supply port of the power chip 11, thereby causing the output port of the power chip 11 to output a control signal to adjust the voltage of the primary side of the flyback transformer 12, thereby completing the start-up of the auxiliary power supply.

[0034] The undervoltage shutdown circuit 13 collects the start-up voltage of the primary side of the flyback transformer 12 and compares it with the voltage of the undervoltage protection shutdown point output by the reference value output port of the power chip 11 to realize the undervoltage protection of the auxiliary power supply.

[0035] In low-temperature environments, the undervoltage shutdown circuit 13 will generate a large leakage current. Since the undervoltage shutdown circuit is powered by the first secondary side, it will cause the equivalent load of the first secondary side to increase, causing the power chip 11, which is also connected to the first secondary side, to be de-energized, resulting in the auxiliary power supply being unable to start under normal startup voltage.

[0036] In this embodiment of the invention, by setting the output buffer resistor on the first secondary side as a thermistor, the resistance value decreases as the temperature decreases, thereby increasing the output power on the first secondary side. This avoids the leakage current of the undervoltage shutdown circuit from affecting the power chip on the first secondary side, ensuring that the power chip can control the auxiliary power supply to start under normal startup voltage.

[0037] The number of output buffer resistors can be one or more, and is not limited here. In some embodiments, the output buffer resistors include a first output buffer resistor, a second output buffer resistor, and a third output buffer resistor connected in parallel; the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all disposed on the first secondary side of the flyback transformer 12.

[0038] In some embodiments, one or more of the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are thermistors with positive temperature coefficients.

[0039] In this embodiment of the invention, if the output buffer resistor is composed of multiple resistors connected in series and / or in parallel, one or more of them can be set as a thermistor with a positive temperature coefficient, that is, the resistance decreases as the temperature decreases, thereby increasing the output power of the first secondary side.

[0040] In some embodiments, the resistance of the first output buffer resistor is less than that of the second and third output buffer resistors; the first output buffer resistor is a nonlinear thermistor with a positive temperature coefficient; the temperature coefficient of the first output buffer resistor increases as the temperature decreases.

[0041] In this embodiment of the invention, since the parallel resistors are most affected by the resistor with the smallest value, the first output buffer resistor with the smallest resistance can be set as a nonlinear thermistor with a positive temperature coefficient. Since the leakage current of different comparators is also different, the appropriate temperature coefficient can be selected according to the model / leakage current of the comparator in the undervoltage shutdown circuit 13, thereby achieving synchronous adjustment of the resistance value with the leakage current.

[0042] In some embodiments, the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all linear thermistors with positive temperature coefficients; the resistance value of the first output buffer resistor is a preset multiple of the resistance value of the second output buffer resistor; the resistance value of the second output buffer resistor is a preset multiple of the resistance value of the third output buffer resistor.

[0043] In this embodiment of the invention, the temperature coefficients of the three output buffer resistors can be the same or different, and are not limited thereto. The preset multiplier can be any value; setting their resistance values ​​sequentially according to the preset multiplier allows for flexible adjustment of the overall resistance. Assuming the temperature coefficients of the first, second, and third output buffer resistors are all k, and their resistances at room temperature are 1Ω, 10Ω, and 100Ω respectively (equivalent resistance 1 / 1.11Ω), when the temperature changes by t, the change in equivalent resistance is 1 / [(1 / (1+kt))+(1 / (10+kt))+(1 / (100+kt))]Ω. That is, the changes in the three resistors with temperature change correspond to the units, tenths, and hundredths of the equivalent resistance, respectively. Therefore, by selecting the resistance values ​​of the three resistors at room temperature, i.e., selecting different preset multipliers, the degree of change in equivalent resistance with temperature can be flexibly controlled, thereby effectively adjusting the output power of the first secondary side.

[0044] In some embodiments, the number of parallel output buffer resistors, as well as the temperature coefficient and room temperature resistance of each output buffer resistor, can be flexibly set according to the actual situation of the undervoltage shutdown circuit, thereby realizing the adaptive adjustment of the equivalent resistance of all output buffer resistors and enabling the first secondary side to output the corresponding power.

[0045] In some embodiments, a current-limiting resistor is provided between the primary side of the flyback transformer 12 and the feedback port of the power chip 11; the overcurrent protection point of the flyback transformer 12 increases as the current-limiting resistor decreases; a transistor is provided on the primary side of the flyback transformer 12; the power chip 11 outputs the supply voltage required for the operation of the power chip through the transistor on the first secondary side of the flyback transformer 12; the current-limiting resistor is connected to the transistor; the output power of the first secondary side of the flyback transformer 12 increases as the resistance value of the current-limiting resistor decreases.

[0046] The above method of adjusting the output buffer resistor increases the output power of the first secondary side by adjusting the equivalent load at the output terminal. However, increasing the output power of the first secondary side can also be achieved in other ways.

[0047] In this embodiment of the invention, a current-limiting resistor is connected to one of the feedback ports of the power chip 11. The power chip 11 inputs the control signal output from the output port to the gate of the transistor, causing the transistor to conduct according to the corresponding duty cycle, thereby enabling the primary side of the flyback transformer to operate under different voltages. Since the current-limiting resistor is also connected to the transistor, the resistance value of the current-limiting resistor will affect the duty cycle of the transistor. Therefore, reducing the resistance value of the current-limiting resistor can increase the power of the primary side, thereby increasing the output power of the first secondary side and ensuring the normal startup of the auxiliary power supply. However, adjusting the current-limiting resistor will raise the overcurrent protection point, making it impossible to perform overcurrent protection in time, thus affecting the safe operation of the auxiliary power supply.

[0048] In some embodiments, the current-limiting resistor includes a first current-limiting resistor and a second current-limiting resistor connected in parallel.

[0049] In some embodiments, both the first current-limiting resistor and the second current-limiting resistor are thermistors with positive temperature coefficients.

[0050] In this embodiment of the invention, the number of current-limiting resistors can be one or more, and their temperature coefficients can be adjusted according to the actual situation. The adjustment method can be similar to the adjustment method of the output buffer resistor described above, and will not be described again here.

[0051] The present invention is illustrated below by way of an implementation example, but is not intended to be limiting. Figure 2 This is a schematic diagram of the auxiliary power supply circuit provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the undervoltage shutdown circuit provided in an embodiment of the present invention. Figure 2 and Figure 3 As shown, in this embodiment, the power supply chip 11 includes a power supply port VCC, a compensation port COM, a feedback port Vfb, a feedback port Is, an output port OUT, a reference value output port Vref, a ground port GND, and an operating frequency design port RC. The flyback transformer 12 includes multiple coils, where coils labeled 18 and 20 correspond to the primary winding, and the others are secondary windings. Coils labeled 23 and 24 are the first secondary winding. R294, R295, and R264 in dashed box A are output buffer resistors, and R331 and R319 in dashed box B are current-limiting resistors. The power supply port VCC is powered by the VCC_+15V node on the first secondary winding, and the output port OUT is connected to the gate of the transistor on the primary winding of the flyback transformer 12.

[0052] When the auxiliary power supply needs to be started, the bus BUS provides a starting voltage to the other end of the primary side of the flyback transformer 12. Then, the VCC_+15V node on the first secondary side reaches the corresponding voltage, which powers the power chip 11 and starts it up. This causes the output port OUT to output a control signal, which controls the transistor to output a signal with the corresponding duty cycle to adjust the voltage on the primary side of the flyback transformer 12, thereby completing the start-up of the auxiliary power supply.

[0053] The undervoltage shutdown circuit 13 collects the voltage of the primary side HV node and the bus grounding point voltage (representing the bus BUS), compares it with the voltage of the undervoltage protection shutdown point output by the reference value output port Vref of the power chip 11, and sends the comparison result to the compensation port COM to realize the undervoltage protection of the auxiliary power supply.

[0054] Figure 3 The undervoltage shutdown circuit is an 8-port comparator, where ports 2, 3, 5, and 6 are input ports, ports 1 and 7 are output ports, and ports 4 and 8 are power supply ports. In low-temperature environments, the undervoltage shutdown circuit 13 generates a large leakage current. Since the undervoltage shutdown circuit is powered by the VCC_+15V_S node on the first secondary side, the increased leakage current causes the voltage at the VCC_+15V_S node to drop, effectively increasing the equivalent load on the first secondary side. At this point, the potential of VCC_+15V_S is lower than that of VCC_+15V, causing diode D29 to cut off, thus causing the VCC power supply port to lose its connection, preventing the auxiliary power supply from starting at the normal startup voltage.

[0055] By reducing the resistance value in dashed box A or dashed box B, the output power on the first auxiliary side can be increased, thereby raising the potential of the VCC_+15V_S node, preventing diode D29 from being cut off, and ensuring that the power chip can control the auxiliary power supply to start under normal startup voltage.

[0056] In summary, the beneficial effects of the present invention are as follows: by setting the output buffer resistor on the first secondary side as a thermistor, or by adjusting the current limiting resistor on the primary side, the output power on the first secondary side can be increased, thereby avoiding the leakage current of the undervoltage shutdown circuit from affecting the power chip on the first secondary side, and ensuring that the power chip can control the auxiliary power supply to start under normal startup voltage.

[0057] This invention provides an auxiliary power supply, which is a single-transistor flyback power supply. The auxiliary power supply includes the auxiliary power supply circuit as described in any of the above embodiments. In addition, the auxiliary power supply may also include devices / circuits for rectification, voltage regulation, protection, heat dissipation, etc.

[0058] The present invention also provides a photovoltaic grid-connected inverter, including the auxiliary power supply as described in the above embodiment, such as a photovoltaic inverter of the SPI5-40k model of a residential string photovoltaic grid-connected inverter.

[0059] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0060] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0061] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0062] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0063] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0064] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. An auxiliary power supply circuit, characterized in that, include: Power supply chip, flyback transformer, and undervoltage shutdown circuit; The first secondary side of the flyback transformer supplies power to the power chip through the power supply port of the power chip; The primary side of the flyback transformer responds to the control signal at the output port of the power chip, causing the auxiliary power supply to start according to the corresponding startup voltage. The undervoltage shutdown circuit is powered by the first secondary side of the flyback transformer; The undervoltage shutdown circuit is used to instruct the power chip to shut off the auxiliary power supply when the starting voltage of the primary side of the flyback transformer is less than the voltage of the undervoltage protection shutdown point. A voltage-stabilizing capacitor module and an output buffer resistor are provided between the first secondary side of the flyback transformer and the power supply port of the power chip; the voltage-stabilizing capacitor module is located between the output buffer resistor and the power supply port of the power chip; the output power of the first secondary side of the flyback transformer increases as the resistance value of the output buffer resistor decreases; the output buffer resistor is a thermistor with a positive temperature coefficient.

2. The auxiliary power supply circuit according to claim 1, characterized in that, The output buffer resistors include a first output buffer resistor, a second output buffer resistor, and a third output buffer resistor connected in parallel. The first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all located on the first secondary side of the flyback transformer.

3. The auxiliary power supply circuit according to claim 2, characterized in that, One or more of the first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are thermistors with positive temperature coefficients.

4. The auxiliary power supply circuit according to claim 3, characterized in that, The resistance of the first output buffer resistor is less than that of the second and third output buffer resistors; the first output buffer resistor is a nonlinear thermistor with a positive temperature coefficient; the temperature coefficient of the first output buffer resistor increases as the temperature decreases.

5. The auxiliary power supply circuit according to claim 3, characterized in that, The first output buffer resistor, the second output buffer resistor, and the third output buffer resistor are all linear thermistors with positive temperature coefficients. The resistance value of the first output buffer resistor is a preset multiple of the resistance value of the second output buffer resistor; The resistance value of the second output buffer resistor is a preset multiple of the resistance value of the third output buffer resistor.

6. The auxiliary power supply circuit according to claim 1, characterized in that, A current-limiting resistor is provided between the primary side of the flyback transformer and the overcurrent protection port of the power chip; the overcurrent protection point of the flyback transformer increases as the current-limiting resistor decreases. The primary side of the flyback transformer is equipped with a transistor; the power chip uses the transistor to enable the first secondary side of the flyback transformer to output the power supply voltage required for the operation of the power chip. The current-limiting resistor is connected to the transistor; the output power of the first secondary side of the flyback transformer increases as the resistance of the current-limiting resistor decreases.

7. The auxiliary power supply circuit according to claim 6, characterized in that, The current-limiting resistors include a first current-limiting resistor and a second current-limiting resistor connected in parallel.

8. The auxiliary power supply circuit according to claim 7, characterized in that, Both the first current-limiting resistor and the second current-limiting resistor are thermistors with positive temperature coefficients.

9. An auxiliary power supply, characterized in that, include: The auxiliary power supply circuit as described in any one of claims 1-8 above.

10. A photovoltaic grid-connected inverter, characterized in that, include: The auxiliary power supply as described in claim 9 above.

Images