Small power-down delay circuit

Abstract

The invention discloses a small power-down time delay circuit which comprises a voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit and a time delay control unit. High-voltage alternating current is subjected to voltage reduction and electromagnetic interference isolation through the transformer, and then low-voltage alternating current is converted into low-voltage direct current through the rectification filter circuit for subsequent power supply of the circuit. The circuit not only has a power-down delay function of inputting 20V-400V wide-voltage alternating current, but also solves the problems that an input signal has no electromagnetic interference isolation, and a rectification filter circuit is large in size and high in heating. And the functions of input signal electromagnetic interference isolation and circuit miniaturization are realized. The difficulty that circuit parameter design needs to be matched with the actual condition of the transformer is overcome.

Description

Technical Field

[0001] The invention relates to a small power-off delay circuit, belonging to the technical field of airborne electrical appliances. Background Art

[0002] The traditional airborne voltage power-off delay circuit directly inputs the AC power into the rectifier and filter circuit, so the rectifier and filter circuit needs to use high-voltage components, resulting in a large circuit size and high heat generation.

[0003] The existing power-off delay relay includes a magnetic latching relay and a control circuit connected to a single coil of the magnetic latching relay. The control circuit includes: a rectifier filter circuit, a primary buck circuit, a secondary buck circuit, a power-off delay circuit, a relay drive circuit and a delay signal circuit.

[0004] The rectifier filter circuit in the existing power-off delay relay requires high-voltage components, which are large in size and generate high heat; and the input signal is not isolated from electromagnetic interference.

[0005] Therefore, how to improve the existing small-sized power-off delay circuit for airborne use is a technical problem that those skilled in the art urgently need to solve. Summary of the invention

[0006] Purpose: In order to overcome the deficiencies in the prior art, the present invention provides a small power-off delay circuit, which uses a transformer to first isolate the input AC power from electromagnetic interference and perform voltage reduction processing before inputting it into a rectifier and filter circuit. Therefore, the rectifier and filter circuit can select devices with a smaller withstand voltage value, thereby achieving the effect of electromagnetic interference isolation and miniaturization of the power-off delay circuit.

[0007] The present invention designs a small power-off delay circuit, and the complete process of the invention will be described in detail below.

[0008] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A small power-off delay circuit comprises a voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit and a delay control unit.

[0010] The voltage conversion circuit unit includes: an AC isolation step-down unit and a rectification, filtering and voltage stabilization unit.

[0011] The AC power supply inputs the AC isolation step-down unit, and outputs two DC steamed waves. One DC steamed wave is used as the power supply input rectification filtering and voltage stabilization unit, and the other DC steamed wave is used as the positive terminal of the sampling voltage input voltage comparison unit.

[0012] The rectifying, filtering and voltage stabilizing unit outputs a reference voltage to the negative terminal of the voltage comparison unit, and outputs direct current to supply power to the voltage comparison unit, the energy storage circuit and the delay control unit.

[0013] The energy storage circuit inputs direct current, stores electric quantity through capacitors, and outputs direct current to supply power to the voltage comparison unit and the delay control unit respectively.

[0014] When the output voltage of the voltage conversion circuit unit disappears suddenly, the energy storage circuit outputs direct current to supply power to the voltage comparison unit and the delay control unit. The voltage comparison unit is simultaneously powered by the direct current output by the rectifier filter voltage regulator unit and the direct current output by the energy storage circuit.

[0015] The positive end of the voltage comparison unit inputs the sampled voltage mandarin wave divided voltage level output by the AC isolation step-down unit, the negative end of the voltage comparison unit inputs the reference voltage output by the rectifier filter voltage regulator unit, and the voltage comparison unit outputs a delay start control signal to the delay control unit. When the sampled voltage is higher than the reference voltage after voltage division, the voltage comparison unit outputs a high voltage; when the sampled voltage is lower than the reference voltage after voltage division, the voltage comparison unit outputs a low voltage.

[0016] The delay control unit is powered by the DC power output by the rectifier, filter and voltage regulator unit and the DC power output by the energy storage circuit at the same time, and inputs the delay start control signal. When the delay start control signal is a high voltage, the delay control unit is reset; when the delay start control signal is a low voltage, the delay control unit starts counting, and when the count is full, the delay control unit outputs a power-off control signal OUT.

[0017] As a preferred solution, the voltage conversion circuit unit includes: a transformer T1, the output end of the transformer T1 is connected to the input end of the rectifier chip V1, the positive output end of the rectifier chip V1 is respectively connected to the sampling voltage end and the input pin IN of the voltage stabilizing chip N1, the negative output end of the rectifier chip V1 is respectively connected to the ground end and the input pin COM of the voltage stabilizing chip N1, the output end of the rectifier chip V1 is respectively connected to the first voltage output end and one end of the voltage divider circuit, the output end of the voltage divider circuit is connected to the second voltage output end, and the other end of the voltage divider circuit is connected to the ground.

[0018] As a preferred solution, it also includes: a diode V2 and a capacitor C1. The positive output end of the rectifier chip V1 is connected to the input pin IN of the voltage regulator chip N1 through the diode V2. The capacitor C1 is connected in parallel between the input pin IN of the voltage regulator chip N1 and the input pin COM of the voltage regulator chip N1.

[0019] As a preferred solution, it also includes: the voltage divider circuit includes a resistor R1 and a resistor R2 connected in series, the common point of the resistor R1 and the resistor R2 is connected to the second voltage output terminal, and a capacitor C2 is connected in parallel between the common point of the resistor R1 and the resistor R2 and the ground terminal.

[0020] As a preferred solution, the energy storage circuit includes: capacitor C3, capacitor C4, diode V3, resistor R3, capacitor C3 and ground terminal are connected in series in sequence, and the common point of resistor R3 and capacitor C3 is connected to the first energy storage output voltage terminal through diode V4; diode V5, resistor R4, capacitor C4 and ground terminal are connected in series in sequence, and the common point of resistor R4 and capacitor C4 is connected to the second energy storage output voltage terminal through diode V6; the positive input terminal of diode V3 and diode V5 are connected, and the capacitor C3 and negative output terminal of capacitor C4 are connected.

[0021] As a preferred embodiment, the voltage comparison unit includes: a comparator V7, a sampling voltage terminal connected in series with a resistor R5, a resistor R6 and a ground terminal, a common point of the resistor R5 and the resistor R6 is connected to the positive input terminal of the comparator V7, the second voltage output terminal is connected to the negative input terminal of the comparator V7, the first voltage output terminal and the first energy storage output voltage terminal are both connected to the positive power supply terminal of the comparator V7, the negative power supply terminal of the comparator V7 is connected to the ground terminal, and the output terminal of the comparator V7 is connected to the delayed start control signal terminal.

[0022] As a preferred solution, a capacitor C5 is connected in parallel between the resistor R6 and the ground terminal.

[0023] As a preferred solution, the delay control unit includes: a counter V8, a delayed start control signal terminal connected to the MR pin of the counter V8, a first voltage output terminal, and a second energy storage output voltage are respectively connected to the VCC pin, the B pin and the A pin of the counter V8, and the Q pin of the counter V8 is connected to the power-off control signal output terminal.

[0024] Beneficial effects: The present invention provides a small power-off delay circuit, including: a voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit, and a delay control unit. The high-voltage AC power is stepped down and electromagnetic interference is isolated by a transformer, and then the low-voltage AC power is converted into low-voltage DC power by a rectifier and filter circuit for subsequent power supply of the circuit. It not only has the power-off delay function of inputting 20V to 400V wide voltage AC power, but also solves the problems of no electromagnetic interference isolation of the input signal and large size and high heat generation of the rectifier and filter circuit. The functions of input signal electromagnetic interference isolation and circuit miniaturization are realized. The difficulty of circuit parameter design that must match the actual situation of the transformer is overcome.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) Airborne scenarios require equipment with electromagnetic interference isolation and miniaturized design. Transformers are used to isolate AC signals from electromagnetic interference; circuit design reduces device withstand voltage requirements, reduces device size, and achieves circuit miniaturization.

[0027] 2) Input wide voltage regulation, can withstand onboard surge voltage, and realize input 20V ~ 400V AC power failure delay function.

[0028] 3) The system is powered by a single AC power supply, and the DC voltage required by the circuit is output by the internal voltage conversion circuit unit. No additional DC power supply is required, reducing the volume occupied.

[0029] 4) The circuit is composed of analog components such as counters and resistors and capacitors, and has high operating reliability.

[0030] 5) Adjusting the resistance and capacitance can realize convenient debugging of the delay time, which can be applied to circuits with different delay requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the small power-off delay circuit of the present invention.

[0032] Figure 2 This is the schematic diagram of the voltage conversion circuit unit.

[0033] Figure 3 This is the schematic diagram of the energy storage circuit.

[0034] Figure 4 This is the schematic diagram of the voltage comparison unit.

[0035] Figure 5 This is the schematic diagram of the delay control unit. DETAILED DESCRIPTION

[0036] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0037] The present invention will be further described below in conjunction with specific embodiments.

[0038] Embodiment 1:

[0039] This embodiment introduces a small power-off delay circuit. Figure 1 As shown, it includes: a voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit and a delay control unit.

[0040] The voltage conversion circuit unit includes: an AC isolation step-down unit and a rectification, filtering and voltage stabilization unit.

[0041] The AC power supply inputs the AC isolation step-down unit, and outputs two DC steamed waves. One DC steamed wave is used as the power supply input rectification filtering and voltage stabilization unit, and the other DC steamed wave is used as the positive terminal of the sampling voltage input voltage comparison unit.

[0042] The rectifier, filter and voltage regulator unit outputs a 2.5V reference voltage to the negative terminal of the voltage comparison unit, and outputs a 5V direct current to power the voltage comparison unit, the energy storage circuit and the delay control unit.

[0043] The energy storage circuit inputs 5V DC power, stores electricity through capacitors, and outputs DC power to supply power to the voltage comparison unit and the delay control unit respectively.

[0044] When the output voltage of the voltage conversion circuit unit suddenly disappears, the energy storage circuit will maintain the DC output for a period of time to supply power to the voltage comparison unit and the delay control unit. The voltage comparison unit is powered by the 5V DC output of the rectifier filter voltage regulator unit and the DC output of the energy storage circuit.

[0045] The positive end of the voltage comparison unit inputs the sampling voltage mantou wave voltage division level output by the AC isolation step-down unit, and the negative end of the voltage comparison unit inputs the 2.5V reference voltage output by the rectifier filter voltage regulator unit. The voltage comparison unit outputs a delay start control signal to the delay control unit. When the sampling voltage is higher than the 2.5V reference voltage after voltage division, the voltage comparison unit outputs a high voltage; when the sampling voltage is lower than the 2.5V reference voltage after voltage division, the voltage comparison unit outputs a low voltage.

[0046] The delay control unit is powered by the 5V DC output by the rectifier, filter and voltage regulator unit and the DC output by the energy storage circuit at the same time, and inputs the delay start control signal. When the delay start control signal is a high voltage, the delay control unit is reset; when the delay start control signal is a low voltage, the delay control unit starts counting, and when the count is full, the delay control unit outputs a power-off control signal OUT.

[0047] Furthermore, the voltage conversion circuit unit, such as Figure 2 As shown, it includes: a transformer T1, the output end of the transformer T1 is connected to the input end of the rectifier chip V1, the positive output end of the rectifier chip V1 is respectively connected to the sampling voltage end and the input pin IN of the voltage stabilizing chip N1, the negative output end of the rectifier chip V1 is respectively connected to the ground end and the input pin COM of the voltage stabilizing chip N1, the output end of the rectifier chip V1 is respectively connected to the first voltage output end and one end of the voltage divider circuit, the output end of the voltage divider circuit is connected to the second voltage output end, and the other end of the voltage divider circuit is connected to the ground.

[0048] Furthermore, it also includes: a diode V2 and a capacitor C1, the positive output end of the rectifier chip V1 is connected to the input pin IN of the voltage regulator chip N1 through the diode V2, and the capacitor C1 is connected in parallel between the input pin IN of the voltage regulator chip N1 and the input pin COM of the voltage regulator chip N1.

[0049] Furthermore, it also includes: the voltage divider circuit includes a resistor R1 and a resistor R2 connected in series, the common point of the resistor R1 and the resistor R2 is connected to the second voltage output terminal, and a capacitor C2 is connected in parallel between the common point of the resistor R1 and the resistor R2 and the ground terminal.

[0050] The voltage conversion circuit unit is powered by a single AC power supply, and DC conversion and electromagnetic isolation are achieved through a customized transformer T1. After passing through the rectifier chip V1, the steamed bun wave is output as the sampling voltage.

[0051] The sampling voltage is rectified and filtered by the diode V2 and the capacitor C1, and voltage is stabilized by the voltage regulator chip N1. The first voltage output terminal outputs a 5V voltage for subsequent power supply of the circuit.

[0052] After the 5V voltage is divided by resistors R1 and R2 and filtered by capacitor C2, the second voltage output terminal outputs a stable 2.5V reference voltage for the secondary input of comparator V7.

[0053] Furthermore, the energy storage circuit, such as Figure 3 As shown, it includes: capacitor C3, capacitor C4, diode V3, resistor R3, capacitor C3 and ground terminal are connected in series in sequence, and the common point of resistor R3 and capacitor C3 is connected to the first energy storage output voltage terminal through diode V4; diode V5, resistor R4, capacitor C4 and ground terminal are connected in series in sequence, and the common point of resistor R4 and capacitor C4 is connected to the second energy storage output voltage terminal through diode V6; the positive input terminal of diode V3 and diode V5 is connected, and the capacitor C3 and the negative output terminal of capacitor C4 are connected.

[0054] After the voltage conversion circuit unit outputs 5V DC, capacitors C3 and C4 begin to charge. The role of diodes V3 and V5 is to prevent current from flowing when the capacitor is discharged, reducing power consumption. The role of resistors R3 and R4 is to reduce the capacitor charging current. When the AC power is lost, the 5V voltage disappears, and capacitor C3 supplies power to the delay control unit through the diode V4 via the first energy storage output voltage terminal; capacitor C4 supplies power to the relay through the diode V6 via the second energy storage output voltage terminal.

[0055] Furthermore, the voltage comparison unit, such as Figure 4As shown, it includes: a comparator V7, a sampling voltage terminal connected in series with a resistor R5, a resistor R6 and a ground terminal, a common point of the resistor R5 and the resistor R6 is connected to the positive input terminal of the comparator V7, the second voltage output terminal is connected to the negative input terminal of the comparator V7, the first voltage output terminal and the first energy storage output voltage terminal are both connected to the positive power supply of the comparator V7, the negative power supply of the comparator V7 is connected to the ground terminal, and the output terminal of the comparator V7 is connected to the delayed start control signal terminal.

[0056] Furthermore, a capacitor C5 is connected in parallel between the resistor R6 and the ground terminal.

[0057] The sampling voltage is input to the positive terminal of the comparator V7 after being divided and filtered by resistors R5, R6 and capacitor C5. The 2.5V reference voltage is input to the negative terminal of the comparator V7.

[0058] When the AC power supply AC is powered normally, the comparator V7 is powered by the 5V voltage and the first energy storage output voltage at the same time. When the AC power supply AC loses power and the voltage conversion circuit unit is insufficient to output the 5V voltage, the comparator V7 is powered by the first energy storage output voltage.

[0059] The positive terminal of the comparator inputs the sampling voltage wave output by the AC isolation and pressure reducing unit, and the negative terminal of the comparator inputs the 2.5V reference voltage output by the rectifier, filter and voltage regulator circuit. The comparator outputs a delay start control signal to the delay control unit. When the sampling voltage is higher than the 2.5V reference voltage, the voltage comparison unit outputs a high voltage; when the sampling voltage is lower than the 2.5V reference voltage, the voltage comparison unit outputs a low voltage.

[0060] Furthermore, the delay control unit is as follows: Figure 5 As shown, it includes: a counter V8, a delayed start control signal terminal connected to the MR pin of the counter V8, a first voltage output terminal, and a second energy storage output voltage are respectively connected to the VCC pin, the B pin and the A pin of the counter V8, and the Q pin of the counter V8 is connected to the power-off control signal output terminal.

[0061] The delay time and state of counter V8 are configured by connecting resistors R7, R8, capacitor C6 and other pins. When the sampling voltage is higher than the threshold, counter V8 is powered by 5V voltage. When the sampling voltage is lower than the threshold, counter V8 is powered by the energy storage output voltage.

[0062] After the comparator outputs a low-level delayed start control signal, the counter V8 starts working, and the Q pin first outputs a low level. After a set delay, the Q pin outputs a high-level power-off control signal OUT.

[0063] Embodiment 2:

[0064] This embodiment introduces the application scenario and working principle of a small power-off delay circuit.

[0065] An application scenario of a small power-off delay circuit is to alarm when the effective value of the onboard AC power supply is detected to be lower than the threshold value for more than 200ms. When the onboard AC power supply is started normally, the effective value of the AC power supply exceeds the threshold value, and the energy storage circuit in the present invention starts charging without outputting a signal. When the effective value of the AC power supply drops below the threshold value for more than 200ms, a power-off control signal OUT is output.

[0066] The application scenario of a small power-off delay circuit is as follows:

[0067] Functional description of each state of the energy storage circuit: When the AC power supply AC is working normally, the output voltage of the energy storage circuit is 5V, which together with the 5V DC output by the voltage conversion circuit unit supplies power to the subsequent circuits; when the AC power supply AC is lower than the threshold voltage, the output voltage of the energy storage circuit is 5V. Since the output voltage of the voltage conversion circuit unit is insufficient, the subsequent circuits are powered by the energy storage circuit alone. The output voltage of the energy storage circuit decreases over time, but can meet the power supply requirements of the subsequent circuits within 200ms.

[0068] Functional description of each state of the voltage conversion circuit unit: When the AC power supply AC is working normally, the peak value of the sampling voltage output by the voltage conversion circuit unit is higher than 2.5V after being divided by resistors R1 and R2, and the output 5V and 2.5V voltages are also normal, which can meet the power supply needs of subsequent circuits; when the AC power supply AC is lower than the threshold voltage, the peak value of the sampling voltage output by the voltage conversion circuit unit is lower than 2.5V after being divided by resistors R1 and R2, and the output 5V and 2.5V voltages will also be reduced, which cannot meet the power supply needs of subsequent circuits.

[0069] Functional description of each state of the voltage comparison unit: The sampling voltage is input to the positive terminal of the comparator V7, and the 2.5V reference voltage is input to the negative terminal of the comparator V7. When the AC power supply AC is higher than the threshold, the peak value of the sampling voltage after the voltage division by R5 and R6 is higher than 2.5V, and the comparator outputs a high-level delayed start control signal. When the AC power supply AC is lower than the threshold, the peak value of the sampling voltage after the voltage division by R5 and R6 is lower than 2.5V, and the comparator outputs a continuous low-level delayed start control signal.

[0070] Functional description of each state of the delay control unit: When the AC power supply AC works normally, the delay control unit does not work and continuously outputs a low level; when the AC power supply AC is lower than the threshold voltage, the delay control unit starts timing and outputs a high level after 200ms. During this period, if the AC power supply AC resumes normal operation, the delay control unit is reset and does not output a high level.

[0071] A small power-off delay circuit can realize the following functions:

[0072] 1) Airborne scenarios require equipment with electromagnetic interference isolation and miniaturized design. A transformer is used to isolate the AC signal from electromagnetic interference; the device withstand voltage requirement is reduced through circuit design, and the device volume is reduced, achieving a miniaturized design with a circuit volume of less than 0.008m³.

[0073] 2) Wide voltage regulation, can withstand airborne surge voltage, and realize input 20V~400V wide voltage AC power-off delay function.

[0074] 3) The system is powered by a single AC power supply, and the DC voltage required by the circuit is output by the internal voltage conversion circuit unit. No additional DC power supply is required, reducing the volume occupied.

[0075] 4) The circuit is composed of analog components such as counters and resistors and capacitors, and has high circuit reliability.

[0076] 5) By adjusting the resistance and capacitance, the threshold and delay time can be easily debugged, which is suitable for circuits with 30V~300V threshold and 0.01s~1000s delay requirements.

[0077] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A small power-off delay circuit, characterized in that: include: A voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit and a delay control unit; The voltage conversion circuit unit includes: an AC isolation step-down unit and a rectification, filtering and voltage stabilization unit; The AC power supply inputs the AC isolation step-down unit, and outputs two DC steamed waves, one DC steamed wave is used as the power supply input rectification filter voltage stabilization unit, and the other DC steamed wave is used as the positive terminal of the sampling voltage input voltage comparison unit; The rectifier, filter and voltage regulator unit outputs a reference voltage to the negative terminal of the voltage comparison unit, and outputs direct current to supply power to the voltage comparison unit, the energy storage circuit and the delay control unit; The energy storage circuit inputs direct current, stores electricity through the capacitor, and outputs direct current to supply power to the voltage comparison unit and the delay control unit respectively; When the output voltage of the voltage conversion circuit unit suddenly disappears, the energy storage circuit outputs direct current to supply power to the voltage comparison unit and the delay control unit; the voltage comparison unit is simultaneously supplied with power by the direct current output by the rectifier, filter and voltage regulator unit and the direct current output by the energy storage circuit; The positive end of the voltage comparison unit inputs the sampled voltage steamed wave divided voltage level output by the AC isolation step-down unit, the negative end of the voltage comparison unit inputs the reference voltage output by the rectifier filter voltage regulator unit, the voltage comparison unit outputs a delay start control signal to the delay control unit, when the sampled voltage is higher than the reference voltage after voltage division, the voltage comparison unit outputs a high voltage; when the sampled voltage is lower than the reference voltage after voltage division, the voltage comparison unit outputs a low voltage; The delay control unit is powered by the DC power output by the rectifier, filter and voltage regulator unit and the DC power output by the energy storage circuit at the same time, and inputs the delay start control signal. When the delay start control signal is a high voltage, the delay control unit is reset; when the delay start control signal is a low voltage, the delay control unit starts counting, and when the count is full, the delay control unit outputs a power-off control signal OUT.

2. A small power-off delay circuit according to claim 1, characterized in that: The voltage conversion circuit unit includes: a transformer T1, the output end of the transformer T1 is connected to the input end of the rectifier chip V1, the positive output end of the rectifier chip V1 is respectively connected to the sampling voltage end and the input pin IN of the voltage stabilizing chip N1, the negative output end of the rectifier chip V1 is respectively connected to the ground end and the input pin COM of the voltage stabilizing chip N1, the output end of the rectifier chip V1 is respectively connected to the first voltage output end and one end of the voltage divider circuit, the output end of the voltage divider circuit is connected to the second voltage output end, and the other end of the voltage divider circuit is connected to the ground.

3. A small power-off delay circuit according to claim 2, characterized in that: Also includes: Diode V2 and capacitor C1, the positive output end of the rectifier chip V1 is connected to the input pin IN of the voltage regulator chip N1 through the diode V2, and the capacitor C1 is connected in parallel between the input pin IN of the voltage regulator chip N1 and the input pin COM of the voltage regulator chip N1.

4. A small power-off delay circuit according to claim 2, characterized in that: Also includes: The voltage divider circuit includes a resistor R1 and a resistor R2 connected in series, a common point of the resistor R1 and the resistor R2 is connected to the second voltage output terminal, and a capacitor C2 is connected in parallel between the common point of the resistor R1 and the resistor R2 and the ground terminal.

5. The small power-off delay circuit according to claim 1, characterized in that: The energy storage circuit includes: a capacitor C3 and a capacitor C4. A diode V3, a resistor R3, a capacitor C3 and a ground terminal are connected in series in sequence, and a common point of the resistor R3 and the capacitor C3 is connected to a first energy storage output voltage terminal through a diode V4; a diode V5, a resistor R4, a capacitor C4 and a ground terminal are connected in series in sequence, and a common point of the resistor R4 and the capacitor C4 is connected to a second energy storage output voltage terminal through a diode V6; the diode V3 and the positive input terminal of the diode V5 are connected, and the capacitor C3 and the negative output terminal of the capacitor C4 are connected.

6. A small power-off delay circuit according to claim 1, characterized in that: The voltage comparison unit includes: a comparator V7, a sampling voltage terminal connected in series with a resistor R5, a resistor R6 and a ground terminal, a common point of the resistor R5 and the resistor R6 is connected to a positive input terminal of the comparator V7, the second voltage output terminal is connected to a negative input terminal of the comparator V7, the first voltage output terminal and the first energy storage output voltage terminal are both connected to a positive power supply terminal of the comparator V7, a negative power supply terminal of the comparator V7 is connected to the ground terminal, and an output terminal of the comparator V7 is connected to a delayed start control signal terminal.

7. A small power-off delay circuit according to claim 6, characterized in that: A capacitor C5 is connected in parallel between the resistor R6 and the ground terminal.

8. A small power-off delay circuit according to claim 1, characterized in that: The delay control unit includes: a counter V8, a delay start control signal end connected to the MR pin of the counter V8, a first voltage output end, and a second energy storage output voltage are respectively connected to the VCC pin, the B pin and the A pin of the counter V8, and the Q pin of the counter V8 is connected to the power-off control signal output end.

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