Step-down power supply circuit and electronic device

Abstract

The application discloses a voltage reduction power supply circuit and electronic equipment, and belongs to the technical field of electronic circuits. The voltage reduction power supply circuit comprises a series RC circuit, a power-down circuit and a switch circuit. The series RC circuit comprises a first capacitor component and a first resistor component in series connection. The series RC circuit is connected to an input voltage, and outputs a voltage signal on the first capacitor component according to the input voltage. The power-down circuit is used for discharging the energy on the first capacitor component in response to the input voltage being less than a preset voltage. The switch circuit is connected to the input voltage. The switch circuit converts the input voltage into an output voltage in response to the voltage signal being greater than or equal to a preset value, and disconnects the output voltage in response to the voltage signal being less than the preset value. Therefore, the voltage reduction power supply circuit meets a timing constraint.

Description

Technical Field

[0001] This application belongs to the field of electronic circuit technology, and in particular relates to a step-down power supply circuit and electronic equipment. Background Technology

[0002] When a system includes functional chips with electrical isolation characteristics, the voltage build-up and shutdown timing of each power supply domain often fails to meet the coordinated operation requirements of the power supplies on both sides of the isolation barrier. For example, for isolation chips with primary and secondary power supply units, existing power supply architectures have timing mismatch risks in power management, mainly manifested in the following ways: during system power-up, the voltage ramp-up rate of the secondary power supply unit does not effectively lag behind that of the primary power supply unit; during system power-down, the voltage decay rate of the secondary power supply unit does not reliably lead that of the primary power supply unit. This power management defect will lead to systemic failures such as unexpected logic state flips, false triggering of protection mechanisms, or complete loss of normal function in the isolation chip. Currently, mainstream power management integrated circuits have not yet integrated an adaptive control mechanism that can simultaneously meet the aforementioned timing constraints and voltage accuracy requirements.

[0003] Therefore, the relevant step-down power supply circuit cannot meet the timing constraints. Utility Model Content

[0004] The purpose of this application is to provide a step-down power supply circuit and electronic device, which aims to solve the problem that related step-down power supply circuits cannot meet timing constraints.

[0005] This application provides a step-down power supply circuit, including:

[0006] A series RC circuit includes a first capacitor component and a first resistor component connected in series. The series RC circuit is used to receive an input voltage and output a voltage signal on the first capacitor component according to the input voltage.

[0007] A power-down circuit, connected to the series RC circuit, is used to discharge the energy on the first capacitor assembly when the input voltage is less than the preset voltage.

[0008] A switching circuit, connected to the power-off circuit and the series RC circuit, is used to receive the input voltage. When the voltage signal is greater than or equal to a preset value, the input voltage is converted into an output voltage. When the voltage signal is less than the preset value, the output voltage is disconnected.

[0009] In one embodiment, the power-down circuit includes a second transistor, a third transistor, a third resistor, a fourth resistor, and a fifth resistor;

[0010] The first end of the third resistor and the first end of the fifth resistor are connected and together form the input voltage input terminal of the power-off circuit, which is connected to the series RC circuit and the switching circuit to receive the input voltage;

[0011] The second end of the third resistor is connected to the base of the second transistor and the first end of the fourth resistor, and the collector of the second transistor is connected to the second end of the fifth resistor R5 and the base of the third transistor.

[0012] The collector of the third transistor forms the energy input terminal to be discharged in the power-down circuit, and is connected to the unidirectional conduction circuit, the series RC circuit and the switching circuit to access the energy on the first capacitor assembly and the energy on the second capacitor assembly.

[0013] The second terminal of the fourth resistor, the emitter of the second transistor, and the emitter of the third transistor are all connected to the power supply ground.

[0014] In one embodiment, the switching circuit includes a fourth transistor;

[0015] The collector of the fourth transistor forms the input terminal of the switching circuit, and is connected to the series RC circuit and the power-off circuit to receive the input voltage;

[0016] The base of the fourth transistor forms the control terminal of the switching circuit, and is connected to the feedback circuit, the series RC circuit and the power-off circuit to receive the voltage signal and the feedback voltage.

[0017] The emitter of the fourth transistor forms the output terminal of the switching circuit and is connected to the feedback circuit to output the output voltage.

[0018] In one embodiment, it further includes:

[0019] A feedback circuit, connected to the switching circuit, the power-off circuit, and the series RC circuit, is used to receive the output voltage and generate a corresponding feedback voltage.

[0020] The switching circuit is specifically used to connect the input voltage. When the voltage signal is greater than or equal to the preset value, the input voltage is converted into an output voltage according to the feedback voltage. When the voltage signal is less than the preset value, the output voltage is disconnected.

[0021] In one embodiment, the feedback circuit includes a first transistor, a Zener diode, a first resistor, and a second resistor;

[0022] The first end of the first resistor constitutes the input terminal of the feedback circuit and is connected to the switching circuit to receive the output voltage;

[0023] The second end of the first resistor is connected to the first end of the second resistor and the base of the first transistor;

[0024] The collector of the first transistor forms the output terminal of the feedback circuit, which is connected to the switching circuit, the series RC circuit and the power-down circuit to output the feedback voltage;

[0025] The emitter of the first transistor is connected to the negative terminal of the Zener diode, the positive terminal of the Zener diode is connected to the power supply ground, and the second terminal of the second resistor is connected to the power supply ground.

[0026] In one embodiment, it further includes:

[0027] A filter circuit, connected to the switching circuit, is used to filter the output voltage.

[0028] In one embodiment, the filter circuit includes a second capacitor assembly.

[0029] In one embodiment, the step-down power supply circuit further includes:

[0030] A unidirectional conduction circuit, connected to the switching circuit, the filtering circuit, the series RC circuit, and the power-off circuit, is used to conduct energy unidirectionally on the second capacitor assembly.

[0031] The power-down circuit is also used to discharge energy on the second capacitor assembly after unidirectional conduction when the input voltage is less than the preset voltage.

[0032] In one embodiment, the filter circuit includes a second resistor assembly and a second capacitor assembly connected in parallel.

[0033] This utility model embodiment also provides an electronic device, which includes the above-described step-down power supply circuit.

[0034] The beneficial effects of this utility model embodiment compared with the prior art are as follows: Since the series RC circuit includes a first capacitor component and a first resistor component connected in series, firstly, the series RC circuit is connected to the input voltage and outputs a voltage signal on the first capacitor component according to the input voltage; then, the switching circuit responds to the voltage signal being greater than or equal to a preset value and converts the input voltage into an output voltage; finally, the power-down circuit responds to the input voltage being less than a preset voltage and discharges the energy on the first capacitor component; when the energy on the first capacitor component is discharged to the point that the voltage signal is less than the preset value, the switching circuit responds to the voltage signal being less than the preset value and disconnects the output voltage; thus, during the system power-on phase, due to the delay effect of the series RC circuit, the voltage ramp-up rate of the secondary power supply unit effectively lags behind that of the primary power supply unit; during the system power-off phase, due to the timely discharge of energy on the first capacitor component by the power-down circuit, the voltage decay rate of the secondary power supply unit leads that of the primary power supply unit; thus, the buck power supply circuit meets the timing constraints and reduces the possibility of systemic failures such as unexpected logic state flips, false triggering of protection mechanisms, or complete loss of normal function of the isolation chip in the system. Attached Figure Description

[0035] To more clearly illustrate the technical utility model in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A schematic diagram of a step-down power supply circuit provided in an embodiment of this application;

[0037] Figure 2 This is a schematic diagram of another structure of a step-down power supply circuit provided in one embodiment of this application;

[0038] Figure 3 This is a schematic diagram of another structure of a step-down power supply circuit provided in one embodiment of this application;

[0039] Figure 4 This is a schematic diagram of another structure of a step-down power supply circuit provided in one embodiment of this application;

[0040] Figure 5 This is a partial example circuit schematic diagram of a step-down power supply circuit provided in an embodiment of this application. Detailed Implementation

[0041] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0042] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0043] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0045] Figure 1 A schematic diagram of a step-down power supply circuit according to a preferred embodiment of this application is shown. For ease of explanation, only the parts relevant to this embodiment are shown, and are described in detail below:

[0046] The aforementioned step-down power supply circuit includes a series RC circuit 10, a power-off circuit 20, and a switching circuit 30.

[0047] The series RC circuit 10 includes a first capacitor component 12 and a first resistor component 11 connected in series. The series RC circuit 10 is used to receive the input voltage and output the voltage signal on the first capacitor component 12 according to the input voltage.

[0048] The power-down circuit 20 is connected to the series RC circuit 10 and is used to discharge the energy on the first capacitor assembly 12 when the input voltage is less than the preset voltage.

[0049] The switching circuit 30 is connected to the power-off circuit 20 and the series RC circuit 10. It is used to connect the input voltage. When the voltage signal is greater than or equal to the preset value, the input voltage is converted into the output voltage. When the voltage signal is less than the preset value, the output voltage is disconnected.

[0050] It is understood that the switching circuit 30 may include a transistor or a field-effect transistor. In the series RC circuit 10, the first capacitor component 12 outputs a ramp voltage (voltage signal) when the input voltage is applied to the series RC circuit 10, thereby delaying the opening of the switching circuit 30; the first resistor component 11 serves as a current limiter.

[0051] In one embodiment, the power-down circuit 20 includes a voltage divider module and a switching module. The input voltage is divided by the voltage divider module and then connected to the control terminal of the switching module. When the input voltage is equal to the preset voltage, the switching module is turned on. Therefore, the preset voltage is related to the voltage division coefficient of the voltage divider module and the threshold voltage of the switching transistor in the switching module.

[0052] In one embodiment, the switching circuit 30 includes a switching transistor. It is understood that a voltage signal is connected to the control terminal of the switching transistor in the switching circuit 30, and the preset value is the threshold voltage of the switching transistor.

[0053] like Figure 2 As shown, the above-mentioned step-down power supply circuit also includes a feedback circuit 40.

[0054] The feedback circuit 40 is connected to the switching circuit 30, the power-off circuit 20, and the series RC circuit 10, and is used to input the output voltage and generate the corresponding feedback voltage.

[0055] The switching circuit 30 is specifically used to connect the input voltage. When the voltage signal is greater than or equal to the preset value, the input voltage is converted into the output voltage according to the feedback voltage. When the voltage signal is less than the preset value, the output voltage is disconnected.

[0056] It is understandable that the feedback circuit 40 is a negative feedback circuit, which maintains the stability of the output voltage.

[0057] The above technical solution maintains the stability of the output voltage and improves the stability of the buck power supply circuit.

[0058] like Figure 3 As shown, the above-mentioned step-down power supply circuit also includes a filter circuit 50.

[0059] The filter circuit 50 is connected to the switch circuit 30 and is used to filter the output voltage.

[0060] The above technical solutions further maintain the stability of the output voltage and improve the stability of the buck power supply circuit.

[0061] like Figure 4As shown, the filter circuit 50 includes a second capacitor assembly.

[0062] The above technical solution makes the implementation of the filter circuit 50 simple and reliable.

[0063] Please continue to refer to this. Figure 4 The step-down power supply circuit also includes a unidirectional conduction circuit 60.

[0064] The unidirectional conduction circuit 60 is connected to the switching circuit 30, the filter circuit 50, the series RC circuit 10, and the power-off circuit 20, and is used to conduct energy unidirectionally on the second capacitor assembly.

[0065] The power-down circuit 20 is also used to discharge energy on the second capacitor assembly after unidirectional conduction in response to an input voltage lower than a preset voltage.

[0066] Through the above technical solution, when the input voltage drops, the energy on the second capacitor component in the filter circuit 50 is discharged in time, so that the buck power supply circuit can disconnect the output voltage in time, thereby improving the reliability of the buck power supply circuit.

[0067] In one embodiment, the filter circuit 50 includes a second resistor assembly and the aforementioned second capacitor assembly connected in parallel.

[0068] Figure 5 The illustration shows a partial example circuit structure of a step-down power supply circuit provided by an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below:

[0069] The feedback circuit 40 includes a first transistor Q1, a Zener diode Z1, a first resistor R1, and a second resistor R2.

[0070] The first end of the first resistor R1 forms the input terminal of the feedback circuit 40 and is connected to the switching circuit 30 to receive the output voltage; the second end of the first resistor R1 is connected to the first end of the second resistor R2 and the base of the first transistor Q1; the collector of the first transistor Q1 forms the output terminal of the feedback circuit 40 and is connected to the switching circuit 30, the series RC circuit 10 and the power-down circuit 20 to output the feedback voltage; the emitter of the first transistor Q1 is connected to the negative terminal of the Zener diode Z1, the positive terminal of the Zener diode Z1 is connected to the power supply ground, and the second end of the second resistor R2 is connected to the power supply ground.

[0071] It is understandable that the first transistor Q1 acts as a variable resistor, meaning that the resistance between the drain and source of the first transistor Q1 is negatively correlated with the voltage at the base of the first transistor Q1; the voltage between the drain and source of the first transistor Q1 is negatively correlated with the voltage at the base of the first transistor Q1; the Zener diode Z1 acts as a reference voltage source; and the first resistor R1 and the second resistor R2 form a voltage divider circuit to divide the output voltage. Thus, the voltage at the control terminal of the switching circuit 30 is negatively correlated with the output voltage, achieving negative feedback of the output voltage.

[0072] The power-down circuit 20 includes a second transistor Q2, a third transistor Q3, a third resistor R3, a fourth resistor R4, and a fifth resistor R5.

[0073] The first end of the third resistor R3 and the first end of the fifth resistor R5 are connected and together form the input voltage input terminal of the power-down circuit 20, which is connected to the series RC circuit 10 and the switching circuit 30 to receive the input voltage; the second end of the third resistor R3 is connected to the base of the second transistor Q2 and the first end of the fourth resistor R4, and the collector of the second transistor Q2 is connected to the second end of the fifth resistor R5 and the base of the third transistor Q3; the collector of the third transistor Q3 forms the energy input terminal to be discharged in the power-down circuit 20, which is connected to the unidirectional conduction circuit 60, the series RC circuit 10 and the switching circuit 30 to receive the energy on the first capacitor assembly 12 and the energy on the second capacitor assembly; the second end of the fourth resistor R4, the emitter of the second transistor Q2 and the emitter of the third transistor Q3 are all connected to the power supply ground.

[0074] The third resistor R3 and the fourth resistor R4 form a voltage divider circuit to divide the input voltage and output the divided input voltage to the base of the second transistor Q2. Therefore, when the input voltage is less than the preset voltage, the second transistor Q2 is cut off and the third transistor Q3 is turned on. Thus, the third transistor Q3 can quickly discharge the energy on the first capacitor assembly 12 and the energy on the second capacitor assembly to the power supply ground.

[0075] The switching circuit 30 includes a fourth transistor Q4.

[0076] The collector of the fourth transistor Q4 forms the input terminal of the switching circuit 30, which is connected to the series RC circuit 10 and the power-down circuit 20 to receive the input voltage; the base of the fourth transistor Q4 forms the control terminal of the switching circuit 30, which is connected to the feedback circuit 40, the series RC circuit 10 and the power-down circuit 20 to receive the voltage signal and the feedback voltage; the emitter of the fourth transistor Q4 forms the output terminal of the switching circuit 30, which is connected to the feedback circuit 40 to output the output voltage.

[0077] The switching circuit 30 is simple and reliable.

[0078] The unidirectional conduction circuit 60 includes a diode D1, wherein the anode of the diode D1 forms the input terminal of the unidirectional conduction circuit 60 and is connected to the switching circuit 30, the feedback circuit 40 and the filter circuit 50 to receive energy from the second capacitor assembly; the cathode of the diode D1 forms the output terminal of the unidirectional conduction circuit 60 and is connected to the switching circuit 30, the feedback circuit 40 in series with the RC circuit 10 and the power-off circuit 20 to output energy from the second capacitor assembly.

[0079] The first resistor assembly 11 includes a sixth resistor R6, the first capacitor assembly 12 includes a first capacitor C1, the second resistor assembly includes a seventh resistor R7, and the second capacitor assembly includes a second capacitor C2 and a third capacitor C3 connected in parallel.

[0080] It is understood that all transistors in this application can be NPN transistors.

[0081] The following is based on the working principle. Figure 5 Further explanation is provided below:

[0082] When the system is powered on, the input voltage charges the first capacitor C1 through the sixth resistor R6. When the voltage across the first capacitor C1 is greater than the threshold voltage (preset value) of the first transistor Q1, the first transistor Q1 conducts, thus converting the input voltage connected to its drain into an output voltage. It should be noted that when the input voltage is greater than the preset voltage, the third resistor R3 and the fourth resistor R4 form a voltage divider circuit to divide the input voltage and output the divided input voltage to the base of the second transistor Q2, causing the second transistor Q2 to conduct and the third transistor Q3 to turn off. The first resistor R1 and the second resistor R2 form a voltage divider circuit to divide the output voltage. The first transistor Q1 acts as a variable resistor, meaning the resistance between the drain and source of the first transistor Q1 is negatively correlated with the voltage at its base. The Zener diode Z1 acts as a reference voltage source, so the voltage between the drain and source of the first transistor Q1 is negatively correlated with the voltage at its base. Therefore, the voltage at the control terminal of the switching circuit 30 is negatively correlated with the output voltage, achieving negative feedback regulation of the output voltage. The filter circuit 50, including the second capacitor C2, the third capacitor C3, and the seventh resistor R7, filters the output voltage.

[0083] When the system is powered off, the third resistor R3 and the fourth resistor R4 form a voltage divider circuit to divide the input voltage and output the divided input voltage to the base of the second transistor Q2. Therefore, when the input voltage is less than the preset voltage, the second transistor Q2 is cut off and the third transistor Q3 is turned on. Thus, the third transistor Q3 can quickly discharge the energy on the first capacitor assembly 12 and the energy on the second capacitor assembly to the power supply ground. When the energy on the first capacitor assembly 12 is discharged to the point where the voltage signal is less than the preset value, the first transistor Q1 responds to the voltage signal being less than the preset value and disconnects the output voltage. At the same time, since the third transistor Q3 is turned on, the energy on the second capacitor C2 and the energy on the third capacitor C3 are transferred to the drain of the third transistor Q3 through the diode D1. The third transistor Q3 discharges the energy on the second capacitor C2 and the energy on the third capacitor C3 to the power supply ground.

[0084] Thus, during the system power-on phase, due to the delay effect of the series RC circuit 10, the voltage ramp-up rate of the secondary power supply unit effectively lags behind that of the primary power supply unit; during the system power-off phase, due to the timely discharge of energy on the capacitor component by the power-down circuit 20, the voltage decay rate of the secondary power supply unit leads that of the primary power supply unit.

[0085] This utility model embodiment also provides an isolation amplifier, which includes an isolation amplifier chip and the above-described step-down power supply circuit.

[0086] For example, the isolation amplifier can be connected to a multi-output isolation switching power supply with consistent timing for each output. One output voltage of the isolation switching power supply is used to power the primary side of the isolation amplifier chip, while the voltage of the other output voltage is converted by the step-down power supply circuit described in this application to power the secondary side of the isolation amplifier.

[0087] This utility model embodiment also provides an electronic device, which includes the above-described step-down power supply circuit.

[0088] 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 this application.

[0089] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 this application, and should all be included within the protection scope of this application.

Claims

1. A step-down power supply circuit, characterized in that, include: A series RC circuit includes a first capacitor component and a first resistor component connected in series. The series RC circuit is used to receive an input voltage and output a voltage signal on the first capacitor component according to the input voltage. A power-down circuit, connected to the series RC circuit, is used to discharge the energy of the first capacitor component when the input voltage is less than a preset voltage; a switching circuit, connected to the power-down circuit and the series RC circuit, is used to connect the input voltage, convert the input voltage into an output voltage when the voltage signal is greater than or equal to a preset value, and disconnect the output voltage when the voltage signal is less than the preset value.

2. The step-down power supply circuit as described in claim 1, characterized in that, The power-off circuit includes a second transistor, a third transistor, a third resistor, a fourth resistor, and a fifth resistor; The first end of the third resistor and the first end of the fifth resistor are connected and together form the input voltage input terminal of the power-off circuit, which is connected to the series RC circuit and the switching circuit to receive the input voltage; The second end of the third resistor is connected to the base of the second transistor and the first end of the fourth resistor, and the collector of the second transistor is connected to the second end of the fifth resistor R5 and the base of the third transistor. The collector of the third transistor forms the energy input terminal to be discharged in the power-down circuit, and is connected to the unidirectional conduction circuit, the series RC circuit and the switching circuit to access the energy on the first capacitor assembly and the energy on the second capacitor assembly. The second terminal of the fourth resistor, the emitter of the second transistor, and the emitter of the third transistor are all connected to the power supply ground.

3. The step-down power supply circuit as described in claim 1, characterized in that, The switching circuit includes a fourth transistor; The collector of the fourth transistor forms the input terminal of the switching circuit, and is connected to the series RC circuit and the power-off circuit to receive the input voltage; The base of the fourth transistor forms the control terminal of the switching circuit, and is connected to the feedback circuit, the series RC circuit and the power-off circuit to receive the voltage signal and the feedback voltage. The emitter of the fourth transistor forms the output terminal of the switching circuit and is connected to the feedback circuit to output the output voltage.

4. The step-down power supply circuit as described in claim 1, characterized in that, Also includes: A feedback circuit, connected to the switching circuit, the power-off circuit, and the series RC circuit, is used to receive the output voltage and generate a corresponding feedback voltage. The switching circuit is specifically used to connect the input voltage. When the voltage signal is greater than or equal to the preset value, the input voltage is converted into an output voltage according to the feedback voltage. When the voltage signal is less than the preset value, the output voltage is disconnected.

5. The step-down power supply circuit as described in claim 4, characterized in that, The feedback circuit includes a first transistor, a Zener diode, a first resistor, and a second resistor; The first end of the first resistor constitutes the input terminal of the feedback circuit and is connected to the switching circuit to receive the output voltage; The second end of the first resistor is connected to the first end of the second resistor and the base of the first transistor; The collector of the first transistor forms the output terminal of the feedback circuit, which is connected to the switching circuit, the series RC circuit and the power-down circuit to output the feedback voltage; The emitter of the first transistor is connected to the negative terminal of the Zener diode, the positive terminal of the Zener diode is connected to the power supply ground, and the second terminal of the second resistor is connected to the power supply ground.

6. The step-down power supply circuit as described in claim 5, characterized in that, Also includes: A filter circuit, connected to the switching circuit, is used to filter the output voltage.

7. The step-down power supply circuit as described in claim 6, characterized in that, The filter circuit includes a second capacitor assembly.

8. The step-down power supply circuit as described in claim 7, characterized in that, The step-down power supply circuit also includes: A unidirectional conduction circuit, connected to the switching circuit, the filtering circuit, the series RC circuit, and the power-off circuit, is used to conduct energy unidirectionally on the second capacitor assembly. The power-down circuit is also used to discharge energy on the second capacitor assembly after unidirectional conduction when the input voltage is less than the preset voltage.

9. The step-down power supply circuit as described in claim 7, characterized in that, The filter circuit includes a second resistor assembly and a second capacitor assembly connected in parallel.

10. An electronic device, characterized in that, The electronic device includes a step-down power supply circuit as described in any one of claims 1 to 9.

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