A small power-off delay circuit

Abstract

The present invention discloses a small power-off delay circuit, comprising: a voltage conversion circuit unit, an energy storage circuit, a voltage comparison unit, and a delay control unit. A transformer is used to reduce the voltage of high-voltage alternating current and isolate electromagnetic interference, and then a rectifier and filter circuit is used to convert the low-voltage alternating current into low-voltage direct current for subsequent power supply to the circuit. The circuit not only has a power-off delay function for inputting a wide voltage range of 20V to 400V AC, but also solves the problems of lack of electromagnetic interference isolation for the input signal and the large size and high heat generation of the rectifier and filter circuits. The functions of electromagnetic interference isolation of the input signal and circuit miniaturization are achieved. The difficulty of matching the circuit parameter design with the actual transformer conditions 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 drop delay circuit directly inputs 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 and filter circuit, a primary step-down circuit, a secondary step-down circuit, a power-off delay circuit, a relay drive circuit and a delay signal circuit.

[0004] The rectifier and filter circuits in existing power-off delay relays require high-voltage components, which are bulky and generate high heat. In addition, the input signal is not isolated from electromagnetic interference.

[0005] Therefore, how to improve the existing small-scale power-off delay circuit used for airborne applications 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 shortcomings of the existing technology, 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 the 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 invention process 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 and voltage reduction 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 input rectifier filter voltage regulator unit, and the other DC steamed wave is used as the positive end of the sampling voltage input voltage comparison unit.

[0012] The rectifier, filter and voltage stabilization unit outputs a reference voltage to the negative terminal of the voltage comparison unit, and outputs direct current to power the voltage comparison unit, the energy storage circuit and the delay control unit.

[0013] 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.

[0014] When the output voltage of the voltage conversion circuit unit suddenly disappears, the energy storage circuit outputs DC power to power the voltage comparison unit and the delay control unit. The voltage comparison 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.

[0015] The positive end of the voltage comparison unit inputs the sampling 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, and the voltage comparison unit outputs a delay start control signal to the delay control unit. When the sampling voltage is higher than the reference voltage after voltage division, the voltage comparison unit outputs a high voltage; when the sampling 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 the 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 regulator 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 regulator 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 end, and a capacitor C2 is connected in parallel between the common point of the resistor R1 and the resistor R2 and the ground end.

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

[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 delay 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 respectively connected to the VCC pin, B pin and A pin of the counter V8, and a Q pin of the counter V8 connected to the power-off control signal output terminal.

[0024] Beneficial effects: The present invention provides a small power-off delay circuit, comprising: 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 isolated from electromagnetic interference 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 for inputting a wide voltage AC power of 20V to 400V, but also solves the problems of no electromagnetic interference isolation for 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 matching the actual situation of the transformer with the circuit parameter design 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 component withstand voltage requirements and device size, achieving circuit miniaturization.

[0027] 2) Input wide voltage regulation, can withstand airborne 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 size of the device.

[0029] 4) The circuit is composed of analog components such as counters and resistors and capacitors, and has high circuit 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. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 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 and voltage reduction 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 input rectifier filter voltage regulator unit, and the other DC steamed wave is used as the positive end 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 DC power 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 the electricity through the capacitor, and outputs DC power to power 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 DC output for a period of time to power the voltage comparison unit and the delay control unit. The voltage comparison unit is powered by the 5V DC output of the rectifier, filter and 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 steamed wave divided voltage 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 and 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 delayed start control signal. When the delayed start control signal is a high voltage, the delay control unit is reset; when the delayed start control signal is a low voltage, the delay control unit starts counting, and when the count is full, the delay control unit outputs the 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 regulator 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 regulator 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. 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 end, and a capacitor C2 is connected in parallel between the common point of the resistor R1 and the resistor R2 and the ground end.

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

[0051] The sampling voltage is rectified and filtered by the diode V2 and the capacitor C1, and 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 diode V3 is connected to the positive input terminal of diode V5, and the capacitor C3 is connected to the negative output terminal of capacitor C4.

[0054] After the voltage conversion circuit unit outputs 5V DC, capacitors C3 and C4 begin charging. Diodes V3 and V5 prevent current from flowing through the capacitors during discharge, reducing power consumption. Resistors R3 and R4 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 via diode V4 at the first energy storage output voltage terminal. Capacitor C4 supplies power to the relay via diode V6 at 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 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.

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

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

[0058] When the AC power supply AC is operating normally, the comparator V7 is powered by both the 5V voltage and the first energy storage output voltage. When the AC power supply AC loses power and the voltage conversion circuit unit is insufficient to output 5V, 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 the remaining pins. When the sampled voltage is above the threshold, counter V8 is powered by a 5V voltage. When the sampled voltage is below the threshold, counter V8 is powered by the energy storage output voltage.

[0062] After the comparator outputs a low-level delay 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] Example 2:

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

[0065] A small power-off delay circuit is designed to generate an alarm when the effective value of an onboard AC power supply falls below a threshold for more than 200ms. When the onboard AC power supply is properly activated and the effective value exceeds the threshold, the energy storage circuit of the present invention begins charging and stops outputting signals. When the effective value of the AC power supply falls below the threshold for more than 200ms, a power-off control signal OUT is output.

[0066] The application scenario of a small power-off delay circuit works 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 of 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. When 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 decrease, which cannot meet the power supply needs of subsequent circuits.

[0069] Functional description of each state of the voltage comparator: The sampling voltage is input to the positive terminal of comparator V7, and the 2.5V reference voltage is input to the negative terminal of comparator V7. When the AC power supply AC is above the threshold, the peak value of the sampling voltage after the voltage divider R5 and R6 exceeds 2.5V, and the comparator outputs a high-level delayed start control signal. When the AC power supply AC is below the threshold, the peak value of the sampling voltage after the voltage divider R5 and R6 falls below 2.5V, and the comparator outputs a continuously low-level delayed start control signal.

[0070] Functional description of each state of the delay control unit: When the AC power supply AC is working 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 AC signals from electromagnetic interference. Circuit design reduces component withstand voltage requirements and device size, resulting in a miniaturized design with a circuit volume of less than 0.008m³.

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

[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 size of the device.

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

[0076] 5) Adjusting the resistance and capacitance can realize convenient debugging of the threshold and delay time, which is applicable to 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 principles 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: Voltage conversion circuit unit, energy storage circuit, voltage comparison unit and delay control unit; The voltage conversion circuit unit includes: an AC isolation step-down unit, a rectifier, filter 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 input to the rectifier, filter and voltage regulator 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 stabilization unit outputs a reference voltage to the negative terminal of the voltage comparison unit, and outputs direct current to power 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 power 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 DC power to supply power to the voltage comparison unit and the delay control unit; the voltage comparison 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; The positive terminal of the voltage comparison unit inputs the sampled voltage steamed wave divided voltage level output by the AC isolation step-down unit, and the negative terminal 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 the 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 regulator 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 regulator 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 between the resistors R1 and R2 is connected to the second voltage output terminal. A capacitor C2 is connected in parallel between the common point between the resistors R1 and 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 sequentially connected in series, and a common point between the resistor R3 and the capacitor C3 is connected to a first energy storage output voltage terminal via a diode V4. A diode V5, a resistor R4, a capacitor C4, and a ground terminal are sequentially connected in series, and a common point between the resistor R4 and the capacitor C4 is connected to a second energy storage output voltage terminal via 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. The 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 the positive input terminal of the comparator V7, a second voltage output terminal is connected to the negative input terminal of the comparator V7, a first voltage output terminal and a first energy storage output voltage terminal are both connected to the 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 the delayed start control signal terminal.

7. The 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. The 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 terminal connected to the MR pin of the counter V8, a first voltage output terminal and a second energy storage output voltage connected to the VCC pin, B pin and A pin of the counter V8 respectively, and a Q pin of the counter V8 connected to the power-off control signal output terminal.

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