A capacitor under-voltage and power-off detection circuit

Abstract

The present application provides a capacitance undervoltage and power-off detection circuit, including: a capacitor C1 connected to an external power supply, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage dividing circuit, a triode Q1, and a resistor R2. During the charging stage of the capacitor C1, the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit form a discharge loop, the optocoupler U1 conducts and pulls the output out to the ground, and the output out is at a low level; in the stable state, the capacitor C1 is in an undervoltage state, the voltage at the voltage dividing point of the voltage dividing circuit is less than the turn-on voltage threshold of the triode Q1, the triode Q1 is turned off, and the output out is at a high level; when the capacitor C1 loses power, when the voltage difference across the light-emitting diode in the optocoupler U2 changes from negative to positive and this positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2, the light-emitting diode in the optocoupler U2 conducts, the triode in the optocoupler U2 conducts, the triode Q2 conducts, the triode Q2 pulls the base of the triode Q1 to the ground, the triode Q1 is turned off, and the output out is at a high level.

Description

Technical Field

[0001] The present invention relates to the technical field of power supplies, and more specifically, to a capacitor under-voltage and power-off detection circuit. Background Art

[0002] During normal operation, when the power supply such as a battery or a filtering capacitor has under-voltage or power-off, it belongs to an abnormal state. At this time, an under-voltage and power-off detection circuit is required to output an action signal to an action unit in time to take measures such as power-off or switching to a backup power supply. Some products need to detect the power-off of the capacitor voltage at the load end. For example, for the power supply of some color-changing bulb lights, the brightness of the bulb lights is switched by detecting the change of the capacitor voltage at the output end of the bulb light power supply when the switch is turned on. When the user turns on the switch of the bulb light once, the output capacitor of the bulb light power supply module has a process of rising and then power-off. After the internal control chip of the bulb light collects the power-off signal, it performs brightness switching control. This type of solution requires detecting the power-off of the output capacitor at the load end.

[0003] Currently, the simplest solution for capacitor voltage detection is to use a voltage-dividing resistor for sampling, set the under-voltage threshold according to actual needs, compare the collected voltage with the under-voltage threshold, and output the comparison value to the action unit after conversion. The defect of this solution is that during the process of the capacitor charging from 0V to the rated value, there must be a process of under-voltage first, and the voltage-dividing resistor sampling cannot identify this normal under-voltage process at the initial stage of charging. In addition, by comparing the voltage sampling value with the threshold, it can only indirectly judge whether the capacitor is powered off. The resistance value of the voltage-dividing resistor needs to be calculated according to the rated voltage of the capacitor and the power-off threshold. When the rated voltage changes, the resistance value needs to be recalculated. There is also a more costly solution for capacitor voltage detection, which uses a single-chip microcomputer to collect the capacitor voltage, stores it, performs internal logical operations, and then outputs it to the action unit. The specific process will not be elaborated here. This type of solution has a high cost. The single-chip microcomputer often has multiple tasks and performs sampling in a polling manner. The detection time is limited by the sampling period, algorithm, and calculation frequency of the single-chip microcomputer. There are many related accessory components, the component cost is high, and the single-chip microcomputer is vulnerable to electromagnetic interference, which may cause the single-chip microcomputer to crash in a strong magnetic field working environment.

[0004] In view of this, the present invention provides a capacitor under-voltage and power-off detection circuit, which can distinguish the under-voltage at the initial stage of charging from the under-voltage in the stable state of the capacitor voltage. Only when the under-voltage occurs in the stable state of the capacitor voltage, the detection circuit will output an action signal to the action unit. The detection circuit can also detect the power-off process of the capacitor, and does not use a single-chip microcomputer, with low cost and no electromagnetic interference. Summary of the Invention

[0005] The object of the present invention is to provide a capacitor undervoltage and power-off detection circuit, which can distinguish the undervoltage during the charging period and the undervoltage in the capacitor voltage stable state. Only when the undervoltage occurs when the capacitor voltage is stable, the detection circuit will output an action signal (high level) to the action unit. And this circuit can directly detect the power-off process and does not use a single-chip microcomputer, with low cost and immunity to electromagnetic interference.

[0006] The capacitor undervoltage and power-off detection circuit of the present application: 1. It can distinguish the undervoltage during the charging period and the undervoltage in the capacitor voltage stable state. During the charging period of C1, the optocoupler U1 is turned on and the output out is pulled down to the ground. The optocoupler U2 is not turned on, and the state of the triode Q1 has no influence on the state of the output out. Therefore, regardless of whether the voltage of the detected capacitor C1 is less than the set undervoltage threshold, the output out is always at a low level. 2. The undervoltage threshold in the capacitor voltage stable state can be independently adjusted. When the detected capacitor C1 is in a stable state and the voltage is less than the set undervoltage threshold, the output out is at a high level, and the circuit outputs a working signal to the working unit. 3. The threshold of the capacitor power-off change amount in the present application is related to the voltage drop of the diode connected in series in the circuit. Therefore, the same circuit parameters can be compatible with different capacitor voltage ratings. Without modifying the circuit, this circuit can adapt to different rated voltages. 4. The present application does not use a single-chip microcomputer, has strong resistance to electromagnetic interference, and the switching action time is limited by the action time of the triode and the conversion time of the optocoupler. Since the switching time of the triode is relatively fast, it can be basically ignored, and the action time is basically only limited by the conversion time of the optocoupler, with a fast response speed. 5. The undervoltage threshold of the capacitor voltage and the power-off detection point of the present invention are separately and independently set, so it is more flexible. 6. This circuit can monitor the trend of the capacitor voltage change, not just the instantaneous value of the capacitor voltage.

[0007] A capacitor under-voltage and power-off detection circuit, comprising: a capacitor C1 connected to an external power supply, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage dividing circuit, a triode Q1, and a resistor R2. The capacitor C1 is connected to the charging circuit. The light-emitting diodes in the optocoupler U1 and the optocoupler U2 are connected to the capacitor C1 and the charging circuit, and the light-emitting diode in the optocoupler U1 is forward-connected, and the light-emitting diode in the optocoupler U2 is reverse-connected. The output end of the optocoupler U1 is connected to the ground and the output out of the capacitor under-voltage and power-off detection circuit. The output end of the optocoupler U2 is connected to the input end of the triode Q2. The output end of the triode Q2 is connected to the input end of the triode Q1. The output end of the triode Q1 is connected to the output out. The voltage dividing circuit is connected in parallel with the capacitor C1 and is connected to the input end of the triode Q1. One end of the resistor R2 is connected to the reference voltage Vref, and the other end is connected to the output out. The optocoupler U1 is used for, during the charging stage of the capacitor C1, the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit form a discharge loop, the optocoupler U1 conducts and pulls down the output out (output port) to the ground (GND), and the output out is at a low level. The voltage dividing circuit is used for, in the stable state, when the capacitor C1 is in an under-voltage state, the voltage at the voltage dividing point of the voltage dividing circuit is less than the turn-on voltage threshold of the triode Q1, the triode Q1 is turned off, and the output out is at a high level. The optocoupler U2 is used for, when the capacitor C1 loses power (the voltage drops rapidly), when the voltage difference across the light-emitting diode in the optocoupler U2 changes from a negative value to a positive value, and this positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2, the light-emitting diode in the optocoupler U2 conducts, the triode in the optocoupler U2 conducts, the triode Q2 conducts, the triode Q2 pulls down the base of the triode Q1 to the ground, the triode Q1 is turned off, and the output out is at a high level.

[0008] In some embodiments, the positive electrode of the capacitor C1 is connected to the positive electrode of the external power supply, the negative electrode of the capacitor C1 is connected to the negative electrode of the external power supply and grounded (GND). The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, the negative electrode of the light-emitting diode in the optocoupler U1 is connected to the charging circuit. When the light-emitting diode in the optocoupler U1 emits light, the triode in the optocoupler U1 conducts. The collector of the triode in the optocoupler U1 is connected to the output out, and the emitter of the triode in the optocoupler U1 is grounded. The negative electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, the positive electrode of the light-emitting diode in the optocoupler U2 is connected to the charging circuit. When the light-emitting diode in the optocoupler U2 emits light, the triode in the optocoupler U2 conducts. The collector of the triode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the emitter of the triode in the optocoupler U2 is connected to the input end (base) of the triode Q2.

[0009] Further, the triode Q1 is a MOS transistor. The collector of the triode Q2 is connected to the gate of the triode Q1. The emitter of the triode Q2 is grounded. The drain of the triode Q1 is connected to the output out, and the source of the triode Q1 is grounded.

[0010] Further, the collector of the transistor inside the optocoupler U2 is connected to the resistor R1 and then to the positive electrode of the capacitor C1. The resistor R1 is used to limit the current passing through the base of the triode Q2.

[0011] In some embodiments, the voltage dividing circuit is composed of the resistor R3 and the resistor R6 connected in series. One end of the resistor R3 is connected to the positive electrode of the capacitor C1, and the other end is connected to the resistor R6. The other end of the resistor R6 is grounded. The gate of the triode Q1 is connected to the voltage dividing point between the resistor R3 and the resistor R6.

[0012] Further, the resistance values of the resistor R3 and the resistor R6 are set according to the undervoltage threshold of the capacitor C1 and the turn-on voltage of the triode Q1, so that when the voltage of the capacitor C1 is higher than the undervoltage threshold, the triode Q1 conducts; when the voltage of the capacitor C1 is lower than the undervoltage threshold, the triode Q1 turns off, and the output out is at a high level.

[0013] Further, the resistor R6 is connected in parallel with the capacitor C4. The positive electrode of the capacitor C4 is connected to the voltage dividing point between the resistor R3 and the resistor R6, and the negative electrode of the capacitor C4 is grounded. The capacitor C4 is used for filtering.

[0014] In some embodiments, the charging circuit is a charging circuit composed of one branch or a charging circuit composed of two branches. Preferably, the charging circuit is a charging circuit composed of two branches.

[0015] Further, when the charging circuit is composed of two branches, these two branches are the first charging branch and the second charging branch respectively. The first charging branch is composed of the diode D1 and the capacitor C2 connected in series and is connected in parallel with the capacitor C1. Among them, the diode D1 is connected reversely and is connected in parallel with the light-emitting diode inside the optocoupler U1. The negative electrode of the diode D1 is connected to the positive electrode of the capacitor C1, and the positive electrode is connected to the positive electrode of the capacitor C2. The negative electrode of the capacitor C2 is grounded. The positive electrode of the light-emitting diode inside the optocoupler U1 is connected to the positive electrode of the capacitor C1, and the negative electrode is connected to the positive electrode of the capacitor C2. The second charging branch is composed of the diode D2 and the capacitor C3 connected in series and is connected in parallel with the capacitor C1. The positive electrode of the diode D2 is connected to the positive electrode of the capacitor C1, and the negative electrode is connected to the positive electrode of the capacitor C3. The negative electrode of the capacitor C3 is grounded. The positive electrode of the light-emitting diode inside the optocoupler U2 is connected to the positive electrode of the capacitor C3, and the negative electrode is connected to the positive electrode of the capacitor C1.

[0016] Further, the detection circuit further includes a resistor R4 and a resistor R5. One end of the resistor R4 is connected to the positive electrode of the light-emitting diode in the optocoupler U2, and the other end is connected to the positive electrode of the capacitor C3. The resistor R5 is connected in parallel with the capacitor C3. One end of the resistor R5 is connected to the positive electrode of the capacitor C3, and the other end is grounded. The resistor R4 is used to adjust the discharge speed of the discharge loop when a discharge loop is formed by the capacitor C1, the light-emitting diode in the optocoupler U2, the resistor R4, and the capacitor C3.

[0017] In some special applications, the voltage of the capacitor C1 is not continuously constant and may slowly increase or decrease. In these applications, such slow fluctuations are allowed. A slow decrease in the voltage of C1 should not trigger an action signal, and only a rapid decrease will trigger an action signal. The function of the resistor R5 is to adjust the sensitivity to the change in the voltage of CI. The specific process is as follows: when the voltage of C1 slowly decreases, since R5 continuously discharges C3, the voltage on the capacitor C3 follows the voltage of the capacitor C1 and decreases. During this process, the voltage difference between C1 and C3 is not sufficient to turn on the diode of the optocoupler U2, and no action signal will be triggered. By adjusting the resistance value of R5, the detection sensitivity to the power-off speed of C1 can be adjusted. The larger the resistance value of R5, the more sensitive the detection of the power-off of C1. R5 can also be not connected. In this case, the detection of the power-off of C1 is the most sensitive, and R5 participates in the discharge initialization of the capacitor C3 after the circuit is powered off.

[0018] Further, the capacitor C3 is an electrolytic capacitor with a capacitance value greater than or equal to 10 μF.

[0019] Further, during the entire charging stage of capacitor C1, whether in the initial stage or the later stage, the voltage of capacitor C1 is greater than that of capacitor C2. Capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 form a discharge loop. Capacitor C1 charges capacitor C2 through the light-emitting diode in optocoupler U1. The voltage of capacitor C2 is smaller than the voltage of capacitor C1 by the voltage drop of the light-emitting diode in optocoupler U1. The light-emitting diode in optocoupler U1 conducts, and the light emitted by the light-emitting diode in optocoupler U1 causes the triode in optocoupler U1 to conduct, pulling the output out to ground (GND), and the output out is at a low level. During the charging stage of capacitor C1, capacitor C3 in the second charging branch also charges. Capacitor C1 charges capacitor C3 through diode D2. The voltage of capacitor C3 is smaller than the voltage of capacitor C1 by the voltage drop of diode D2. And whether during the charging stage or the stable state of capacitor C1, the voltage of capacitor C1 is greater than that of capacitor C3. Since the light-emitting diode in optocoupler U2 is connected reversely, the voltage difference of the light-emitting diode in optocoupler U2 is negative (reverse bias), and the light-emitting diode in optocoupler U2 does not conduct, and the triode in optocoupler U2 is turned off. At the initial stage of the charging of capacitor C1, the gate voltage of triode Q1 is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off; at the later stage of the charging of capacitor C1, the voltage after voltage division by the voltage division circuit of the voltage of capacitor C1 is greater than the turn-on voltage threshold of triode Q1, and triode Q1 conducts. However, during the charging stage, whether triode Q1 is turned off or on, the effect of triode Q1 on the output out is less than the effect of the triode in optocoupler U1 conducting and pulling the output out to ground. The state of triode Q1 has no effect on the state of the output out during the charging stage. Therefore, during the charging stage of capacitor C1, the output out of the detection circuit is at a low level and does not output an action signal.

[0020] In the stable state of capacitor C1 or when the fluctuation is less than the voltage drop of the light-emitting diode in optocoupler U1, if capacitor C1 is in a set undervoltage state, capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 do not form a discharge loop, optocoupler U1 does not conduct, the voltage difference of the light-emitting diode in optocoupler U2 is still negative, and optocoupler U2 does not conduct; the voltage at the voltage division point of resistor R3 and resistor R6 in the voltage division circuit is less than the turn-on voltage threshold of triode Q1, triode Q1 is turned off, and the output out is at a high level (the output out is the output after the reference voltage Vref passes through resistor R2).

[0021] When the voltage of capacitor C1 drops rapidly, capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 do not form a discharge loop, and optocoupler U1 is not turned on; since there are diode D2 and the light-emitting diode in optocoupler U1 between capacitor C1 and capacitor C3, the voltage of capacitor C3 will not drop immediately with capacitor C1. As the voltage of capacitor C1 continues to drop, the voltage difference across the light-emitting diode in optocoupler U2 changes from negative to positive. When the voltage difference is greater than the turn-on voltage of the light-emitting diode in optocoupler U2 (the voltage of capacitor C1 is less than the voltage of capacitor C3 minus the turn-on voltage of the light-emitting diode in optocoupler U2), the light-emitting diode in optocoupler U2 is turned on. At this time, capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C3 form a discharge loop, the triode in optocoupler U2 is turned on, the base of triode Q2 is set high, the collector and emitter of triode Q2 are turned on, the gate of triode Q1 is pulled down to the ground, and the output out is at a high level. The power-down threshold of the detection circuit is the value obtained by subtracting the voltage drop of diode D2 and the turn-on voltage of the light-emitting diode in optocoupler U2 from the stable-state voltage of capacitor C1.

[0022] Further, when the charging circuit consists of one branch, the charging circuit consists of capacitor C5 or consists of capacitor C5 and diode D3. Preferably, the charging circuit consists of capacitor C5 and diode D3; when the charging circuit consists of capacitor C5 and diode D3, diode D3 is connected in series with capacitor C5, the positive pole of the light-emitting diode in optocoupler U1 is connected to the positive pole of capacitor C1, the negative pole is connected to the positive pole of diode D3, the negative pole of diode D3 is connected to the positive pole of capacitor C5, and the negative pole of capacitor C5 is grounded. The positive pole of the light-emitting diode in optocoupler U2 is connected to the positive pole of capacitor C5, and the negative pole is connected to the positive pole of capacitor C1; when the charging circuit consists of capacitor C5, the positive pole of the light-emitting diode in optocoupler U1 is connected to the positive pole of capacitor C1, the negative pole is connected to the positive pole of capacitor C5, the negative pole of capacitor C5 is grounded, and the positive pole of the light-emitting diode in optocoupler U2 is connected to the positive pole of capacitor C5, and the negative pole is connected to the positive pole of capacitor C1.

[0023] Further, the positive pole of the light-emitting diode in optocoupler U2 is connected to resistor R4 and then to the positive pole of capacitor C5. Capacitor C5 is connected in parallel with resistor R5. One end of resistor R5 is connected to the positive pole of capacitor C5, and the other end is grounded. Resistor R4 is used to adjust the discharge speed of the discharge loop when capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C5 form a discharge loop.

[0024] Further, during the entire charging stage of capacitor C1, regardless of whether it is the initial stage or the later stage, the voltage of capacitor C1 is greater than the voltage of capacitor C5. Capacitor C1, the light-emitting diode in optocoupler U1, diode D3, and capacitor C5 form a discharge loop, or capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C5 form a discharge loop. Capacitor C1 charges capacitor C5 through the light-emitting diode in optocoupler U1 and diode D3 or through the light-emitting diode in optocoupler U1. The voltage of capacitor C5 is smaller than the voltage drop of the light-emitting diode in optocoupler U1 and the voltage drop of diode D3, or smaller than the voltage drop of the light-emitting diode in optocoupler U1. The light-emitting diode in optocoupler U1 conducts, and the light-emitting diode in optocoupler U1 emits light, causing the triode in optocoupler U1 to conduct, pulling the output out to ground (GND), and the output out is at a low level. During the charging stage of capacitor C1, whether it is during the charging stage or the stable state of capacitor C1, the voltage of capacitor C1 is greater than the voltage of capacitor C5. Since the light-emitting diode in optocoupler U2 is reversely connected, the voltage difference of the light-emitting diode in optocoupler U2 is negative (reverse bias), and the light-emitting diode in optocoupler U2 does not conduct, and the triode in optocoupler U2 is turned off. At the initial stage of the charging of capacitor C1, the gate voltage of triode Q1 is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off; at the later stage of the charging of capacitor C1, the voltage after the voltage division of capacitor C1 by the voltage division circuit is greater than the turn-on voltage threshold of triode Q1, and triode Q1 conducts. However, during the charging stage, regardless of whether triode Q1 is turned off or on, the effect of triode Q1 on the output out is less than the effect of the triode in optocoupler U1 conducting and pulling the output out to ground. The state of triode Q1 during the charging stage has no effect on the state of the output out. Therefore, during the charging stage of capacitor C1, the output out of the detection circuit is at a low level and does not output an action signal.

[0025] In the stable state of capacitor C1 or when the fluctuation is less than the voltage drop of the light-emitting diode in optocoupler U1, if capacitor C1 is in a set undervoltage state, capacitor C5 stops charging and no discharge loop is formed, optocoupler U1 does not conduct, the voltage difference of the light-emitting diode in optocoupler U2 is still negative, and optocoupler U2 does not conduct; the voltage at the voltage division point of resistor R3 and resistor R6 of the voltage division circuit is less than the turn-on voltage threshold of triode Q1, triode Q1 is turned off, and the output out is at a high level (the output out is the output after the reference voltage Vref passes through resistor R2).

[0026] When the voltage of capacitor C1 drops rapidly, capacitor C5 stops charging and optocoupler U1 is not turned on. Since there is diode D3 and the light-emitting diode in optocoupler U1, or only the light-emitting diode in optocoupler U1, between capacitor C1 and capacitor C5, the voltage of capacitor C5 does not drop immediately with capacitor C1. As the voltage of capacitor C1 continues to drop, the voltage difference across the light-emitting diode in optocoupler U2 changes from negative to positive. When the positive voltage difference is greater than the turn-on voltage of the light-emitting diode in optocoupler U2, the light-emitting diode in optocoupler U2 turns on. At this time, capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C5 form a discharge loop, the triode in optocoupler U2 turns on, the base of triode Q2 is set high, the collector and emitter of triode Q2 are turned on, the gate of triode Q1 is pulled down to ground, and the output out is at a high level. The power-down threshold of the detection circuit is the value obtained by subtracting the voltage drop of diode D3 and the turn-on voltages of the light-emitting diodes in optocouplers U1 and U2 from the stable-state voltage value of capacitor C1, or the power-down threshold of the detection circuit is the value obtained by subtracting the turn-on voltages of the light-emitting diodes in optocouplers U1 and U2 from the stable-state voltage value of capacitor C1.

[0027] In some embodiments, the capacitor to be detected in the present application can be a battery or other capacitive devices, characterized in that the device functions as energy storage, the voltage value cannot change suddenly, and the voltage change is smooth.

[0028] Furthermore, the capacitor to be detected in the present application can be a power source such as a battery or a filter capacitor connected after rectification, or a load capacitor.

[0029] Furthermore, the circuit output in the present application does not have to be fixed to a high level corresponding to undervoltage and power-down. According to the actual circuit requirements, through a simple level conversion circuit, the output can be converted to different logics. The forms of the level conversion circuit are diverse, and this patent does not elaborate on the level conversion circuit.

[0030] Furthermore, the present application does not limit the reference voltage Vref, and Vref is determined according to the actual requirements of the output.

[0031] Furthermore, the diode used to set the power-down threshold in the present application can be replaced by a series circuit of multiple diodes. The effect of connecting multiple diodes in series is to increase the voltage difference threshold for power-down detection, and the type and model of the diodes are not limited. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Combined with the following attached Figure 1 When reading, the above and other features of the content of the present application will be more fully described. It can be understood that these drawings only depict several embodiments of the content of the present application, and therefore should not be considered as limiting the scope of the content of the present application. By using the drawings, the content of the present application will be described more clearly and in detail.

[0033] Figure 1 This is the circuit diagram of the capacitor undervoltage and power-off detection circuit for Embodiment 1 of the present application.

[0034] Figure 2 This is the circuit diagram of the capacitor undervoltage and power-off detection circuit for Embodiment 2 of the present application.

[0035] Figure 3 This is the circuit diagram of the capacitor undervoltage and power-off detection circuit for Embodiment 3 of the present application.

[0036] Figure 4 This is the waveform diagram of the output port varying with the capacitor voltage when the capacitor C1 of the present application is powered off.

[0037] Figure 5 This is the waveform diagram of the output port varying with the capacitor voltage when the capacitor C1 of the present application is charging.

[0038] Figure 6 This is the waveform diagram of the output port when the voltage of the capacitor C1 of the present application does not reach the static undervoltage threshold. Detailed implementation manners

[0039] The following embodiments are described to assist in understanding the present application. The embodiments are not and should not in any way be construed as limiting the protection scope of the present application.

[0040] In the following description, those skilled in the art will recognize that throughout this discussion, components may be described as separate functional units (which may include sub-units), but those skilled in the art will recognize that various components or portions thereof may be divided into separate components or integrated together (including being integrated within a single system or component).

[0041] At the same time, the connections between components or systems are not intended to be limited to direct connections. Instead, the data between these components may be modified, reformatted, or otherwise changed by intermediate components. Additionally, additional or fewer connections may be used. It should also be noted that the terms "coupled", "connected", or "input" "fixed" should be understood to include direct connections, indirect connections or fixings through one or more intermediate media. The terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0042] Embodiment 1:

[0043] A capacitor undervoltage and power-off detection circuit, such as Figure 1 , 4As shown in FIG. -6, it includes: a capacitor C1 connected to an external power supply, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage dividing circuit, a triode Q1, and a resistor R2. The capacitor C1 is connected to the charging circuit. The light-emitting diodes in the optocoupler U1 and the optocoupler U2 are connected to the capacitor C1 and the charging circuit. And the light-emitting diode in the optocoupler U1 is connected in the forward direction, and the light-emitting diode in the optocoupler U2 is connected in the reverse direction. The output end of the optocoupler U1 is connected to the ground and the output out of the capacitor undervoltage and power-off detection circuit. The output end of the optocoupler U2 is connected to the input end of the triode Q2. The output end of the triode Q2 is connected to the input end of the triode Q1. The output end of the triode Q1 is connected to the output out. The voltage dividing circuit is connected in parallel with the capacitor C1 and is connected to the input end of the triode Q1. One end of the resistor R2 is connected to the reference voltage Vref, and the other end is connected to the output out. The optocoupler U1 is used to form a discharge loop of the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit during the charging stage of the capacitor C1. The optocoupler U1 is turned on to pull the output out to the ground (GND), and the output out is at a low level. The voltage dividing circuit is used to make the voltage at the voltage dividing point less than the turn-on voltage threshold of the triode Q1 when the capacitor C1 is in an undervoltage state in the stable state, and the triode Q1 is turned off, and the output out is at a high level. The optocoupler U2 is used to turn on the light-emitting diode in the optocoupler U2 and the triode in the optocoupler U2 when the voltage difference across the light-emitting diode in the optocoupler U2 changes from a negative value to a positive value and the positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2 when the capacitor C1 loses power (the voltage drops rapidly). The triode Q2 is turned on, and the triode Q2 pulls the base of the triode Q1 to the ground, and the triode Q1 is turned off, and the output out is at a high level.

[0044] The positive electrode of the capacitor C1 is connected to the positive electrode of the external power supply, and the negative electrode of the capacitor C1 is connected to the negative electrode of the external power supply and grounded (GND). The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, and the negative electrode of the light-emitting diode in the optocoupler U1 is connected to the charging circuit. When the light-emitting diode in the optocoupler U1 emits light, the triode in the optocoupler U1 conducts. The collector of the triode in the optocoupler U1 is connected to the output out, and the emitter of the triode in the optocoupler U1 is grounded; the negative electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the positive electrode of the light-emitting diode in the optocoupler U2 is connected to the charging circuit. When the light-emitting diode in the optocoupler U2 emits light, the triode in the optocoupler U2 conducts. The collector of the triode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the emitter of the triode in the optocoupler U2 is connected to the input terminal (base) of the triode Q2. The triode Q1 is a MOS tube. The collector of the triode Q2 is connected to the gate of the triode Q1, the emitter of the triode Q2 is grounded, the drain of the triode Q1 is connected to the output out, and the source of the triode Q1 is grounded. The collector of the triode in the optocoupler U2 is connected to the resistor R1 and then to the positive electrode of the capacitor C1. The resistor R1 is used to limit the current passing through the base of the triode Q2. The voltage-dividing circuit is composed of the resistor R3 and the resistor R6 connected in series. One end of the resistor R3 is connected to the positive electrode of the capacitor C1, the other end is connected to the resistor R6, and the other end of the resistor R6 is grounded. The gate of the triode Q1 is connected to the voltage-dividing point between the resistor R3 and the resistor R6. The resistance values of the resistor R3 and the resistor R6 are set according to the undervoltage threshold of the capacitor C1 and the turn-on voltage of the triode Q1, so that when the voltage of the capacitor C1 is higher than the undervoltage threshold, the triode Q1 conducts; when the voltage of the capacitor C1 is less than the undervoltage threshold, the triode Q1 turns off, and the output out is at a high level. The resistor R6 is connected in parallel with the capacitor C4. The positive electrode of the capacitor C4 is connected to the voltage-dividing point between the resistor R3 and the resistor R6, and the negative electrode of the capacitor C4 is grounded. The capacitor C4 is used for filtering.

[0045] The charging circuit consists of two branches, namely the first charging branch and the second charging branch. The first charging branch is composed of a diode D1 and a capacitor C2 connected in series and is connected in parallel with a capacitor C1. Among them, the diode D1 is reversely connected and is connected in parallel with the light-emitting diode in the optocoupler U1. The negative electrode of the diode D1 is connected to the positive electrode of the capacitor C1, and the positive electrode is connected to the positive electrode of the capacitor C2. The negative electrode of the capacitor C2 is grounded. The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, and the negative electrode is connected to the positive electrode of the capacitor C2. The second charging branch is composed of a diode D2 and a capacitor C3 connected in series and is connected in parallel with the capacitor C1. The positive electrode of the diode D2 is connected to the positive electrode of the capacitor C1, and the negative electrode is connected to the positive electrode of the capacitor C3. The negative electrode of the capacitor C3 is grounded. The positive electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C3, and the negative electrode is connected to the positive electrode of the capacitor C1. The detection circuit further includes a resistor R4 and a resistor R5. One end of the resistor R4 is connected to the positive electrode of the light-emitting diode in the optocoupler U2, and the other end is connected to the positive electrode of the capacitor C3. The resistor R5 is connected in parallel with the capacitor C3. One end of the resistor R5 is connected to the positive electrode of the capacitor C3, and the other end is grounded. The resistor R4 is used to adjust the discharge speed of the discharge loop when a discharge loop is formed by the capacitor C1, the light-emitting diode in the optocoupler U2, the resistor R4, and the capacitor C3. In some special applications, the voltage of the capacitor C1 is not constantly unchanged. It may slowly increase or decrease. In these applications, this slow fluctuation is allowed. The slow decrease of the C1 voltage should not trigger an action signal. Only a rapid decrease will trigger an action signal. The function of the resistor R5 is to adjust the sensitivity to the change of the CI voltage. The specific process is that when the voltage of C1 slowly decreases, since R5 continuously discharges C3, the voltage on the capacitor C3 follows the voltage of the capacitor C1 and decreases. During this process, the voltage difference between C1 and C3 is not enough to turn on the diode of the optocoupler U2 and does not trigger an action signal. By adjusting the resistance value of R5, the detection sensitivity to the power-off speed of C1 can be adjusted. The larger the resistance value of R5, the more sensitive the detection of the power-off of C1. R5 can also be not connected. At this time, the detection of the power-off of C1 is the most sensitive, and R5 participates in the discharge initialization of the capacitor C3 after the circuit is powered off.

[0046] During the entire charging stage of capacitor C1, whether in the initial stage or the later stage, the voltage of capacitor C1 is greater than that of capacitor C2. Capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 form a discharge loop. Capacitor C1 charges capacitor C2 through the light-emitting diode in optocoupler U1. The voltage of capacitor C2 is smaller than the voltage of capacitor C1 by the voltage drop of the light-emitting diode in optocoupler U1. The light-emitting diode in optocoupler U1 conducts, and the light emitted by the light-emitting diode in optocoupler U1 causes the triode in optocoupler U1 to conduct, pulling the output out down to ground (GND), and the output out is at a low level. During the charging stage of capacitor C1, capacitor C3 in the second charging branch also charges. Capacitor C1 charges capacitor C3 through diode D2. The voltage of capacitor C3 is smaller than the voltage of capacitor C1 by the voltage drop of diode D2. Whether in the charging stage or the stable state of capacitor C1, the voltage of capacitor C1 is greater than that of capacitor C3. Since the light-emitting diode in optocoupler U2 is reverse-connected, the voltage difference of the light-emitting diode in optocoupler U2 is negative (reverse-biased), and the light-emitting diode in optocoupler U2 does not conduct, and the triode in optocoupler U2 is turned off. At the initial stage of the charging of capacitor C1, the gate voltage of triode Q1 is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off; at the later stage of the charging of capacitor C1, the voltage after voltage division by the voltage division circuit of the voltage of capacitor C1 is greater than the turn-on voltage threshold of triode Q1, and triode Q1 conducts. However, during the charging stage, whether triode Q1 is turned off or on, the effect of triode Q1 on the output out is less than the effect of the triode in optocoupler U1 conducting and pulling the output out down to ground. The state of triode Q1 has no effect on the state of the output out during the charging stage. Therefore, during the charging stage of capacitor C1, the output out of the detection circuit is at a low level and does not output an action signal. In the stable state of capacitor C1 or when the fluctuation is less than the voltage drop of the light-emitting diode in optocoupler U1, if capacitor C1 is in a set undervoltage state, capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 do not form a discharge loop, optocoupler U1 does not conduct, the voltage difference of the light-emitting diode in optocoupler U2 is still negative, and optocoupler U2 does not conduct; the voltage at the voltage division point of resistor R3 and resistor R6 in the voltage division circuit is less than the turn-on voltage threshold of triode Q1, triode Q1 is turned off, and the output out is at a high level (the output out is the output after the reference voltage Vref passes through resistor R2).When the voltage of capacitor C1 drops rapidly, capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C2 do not form a discharge loop, and optocoupler U1 is not turned on; since there are diode D2 and the light-emitting diode in optocoupler U1 between capacitor C1 and capacitor C3, the voltage of capacitor C3 will not drop immediately with capacitor C1. As the voltage of capacitor C1 continues to drop, the voltage difference across the light-emitting diode in optocoupler U2 changes from negative to positive. When the voltage difference is greater than the turn-on voltage of the light-emitting diode in optocoupler U2 (the voltage of capacitor C1 is less than the voltage of capacitor C3 minus the turn-on voltage of the light-emitting diode in optocoupler U2), the light-emitting diode in optocoupler U2 is turned on. At this time, capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C3 form a discharge loop, the triode in optocoupler U2 is turned on, the base of triode Q2 is set high, the collector and emitter of triode Q2 are turned on, the gate of triode Q1 is pulled down to ground, and the output out is at a high level. The power-down threshold of the detection circuit is the value obtained by subtracting the voltage drop of diode D2 and the turn-on voltage of the light-emitting diode in optocoupler U2 from the stable-state voltage of capacitor C1. The waveform diagram of the output terminal changing with the voltage value of capacitor C1 during the charging stage of capacitor C1 is as follows. Figure 5 shown. The waveform diagram of the output port when the voltage of capacitor C1 does not reach the static undervoltage threshold is as follows Figure 6 shown. The waveform diagram of the output port changing with the capacitor voltage when capacitor C1 loses power is as follows Figure 4 shown.

[0047] The capacitor to be detected in this application can be a battery or other capacitive devices. The characteristic is that the device plays a role in energy storage, the voltage value cannot change suddenly, and the voltage change is smooth. The capacitor to be detected in this application can be a power source such as a battery or a filter capacitor connected after rectification, or a load capacitor. The circuit output in this application does not have to be fixed at a high level corresponding to undervoltage and power-down. According to the actual circuit requirements, through a simple level conversion circuit, the output can be converted into different logics. The form of the level conversion circuit is diverse, and this patent will not elaborate on the level conversion circuit. This application does not limit the reference voltage Vref, and Vref is determined according to the actual needs of the output. The diode used to set the power-down threshold in this application can be replaced by a series circuit of multiple diodes. The effect of multiple diodes in series is that the voltage difference threshold for power-down detection is increased, and the type and model of the diode are not restricted.

[0048] Embodiment 2:

[0049] A capacitor undervoltage and power-down detection circuit, as shown in Figure 2 and Figures 4 - 6As shown in the figure, it includes: a capacitor C1 connected to an external power supply, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage division circuit, a triode Q1, and a resistor R2. The capacitor C1 is connected to the charging circuit. The light-emitting diodes in the optocoupler U1 and the optocoupler U2 are connected to the capacitor C1 and the charging circuit, and the light-emitting diode in the optocoupler U1 is forward-connected, and the light-emitting diode in the optocoupler U2 is reverse-connected. The output end of the optocoupler U1 is connected to the ground and the output out of the capacitor undervoltage and power-off detection circuit. The output end of the optocoupler U2 is connected to the input end of the triode Q2. The output end of the triode Q2 is connected to the input end of the triode Q1. The output end of the triode Q1 is connected to the output out. The voltage division circuit is connected in parallel with the capacitor C1 and is connected to the input end of the triode Q1. One end of the resistor R2 is connected to the reference voltage Vref, and the other end is connected to the output out. The optocoupler U1 is used to form a discharge loop with the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit during the charging stage of the capacitor C1. The optocoupler U1 conducts and pulls the output out to the ground (GND), and the output out is at a low level. The voltage division circuit is used to make the voltage at the voltage division point of the voltage division circuit less than the turn-on voltage threshold of the triode Q1 when the capacitor C1 is in an undervoltage state in the stable state, and the triode Q1 is turned off, and the output out is at a high level. The optocoupler U2 is used to make the light-emitting diode in the optocoupler U2 conduct and the triode in the optocoupler U2 conduct when the voltage difference across the light-emitting diode in the optocoupler U2 changes from a negative value to a positive value and the positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2 when the capacitor C1 loses power (the voltage drops rapidly). The triode Q2 conducts, and the triode Q2 pulls the base of the triode Q1 to the ground, and the triode Q1 is turned off, and the output out is at a high level.

[0050] The positive electrode of the capacitor C1 is connected to the positive electrode of the external power supply, and the negative electrode of the capacitor C1 is connected to the negative electrode of the external power supply and grounded (GND). The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, and the negative electrode of the light-emitting diode in the optocoupler U1 is connected to the charging circuit. When the light-emitting diode in the optocoupler U1 emits light, the triode in the optocoupler U1 conducts. The collector of the triode in the optocoupler U1 is connected to the output out, and the emitter of the triode in the optocoupler U1 is grounded. The negative electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the positive electrode of the light-emitting diode in the optocoupler U2 is connected to the charging circuit. When the light-emitting diode in the optocoupler U2 emits light, the triode in the optocoupler U2 conducts. The collector of the triode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the emitter of the triode in the optocoupler U2 is connected to the input terminal (base) of the triode Q2. The triode Q1 is a MOS transistor. The collector of the triode Q2 is connected to the gate of the triode Q1, the emitter of the triode Q2 is grounded, the drain of the triode Q1 is connected to the output out, and the source of the triode Q1 is grounded. The collector of the triode in the optocoupler U2 is connected to the resistor R1 and then to the positive electrode of the capacitor C1. The resistor R1 is used to limit the current passing through the base of the triode Q2. The voltage-dividing circuit is composed of the resistor R3 and the resistor R6 connected in series. One end of the resistor R3 is connected to the positive electrode of the capacitor C1, the other end is connected to the resistor R6, and the other end of the resistor R6 is grounded. The gate of the triode Q1 is connected to the voltage-dividing point between the resistor R3 and the resistor R6. The resistance values of the resistor R3 and the resistor R6 are set according to the undervoltage threshold of the capacitor C1 and the turn-on voltage of the triode Q1, so that when the voltage of the capacitor C1 is higher than the undervoltage threshold, the triode Q1 conducts; when the voltage of the capacitor C1 is less than the undervoltage threshold, the triode Q1 turns off and the output out is at a high level. The resistor R6 is connected in parallel with the capacitor C4. The positive electrode of the capacitor C4 is connected to the voltage-dividing point between the resistor R3 and the resistor R6, and the negative electrode of the capacitor C4 is grounded. The capacitor C4 is used for filtering.

[0051] The charging circuit consists of a capacitor C5 and a diode D3. The diode D3 is connected in series with the capacitor C5. The positive pole of the light-emitting diode inside the optocoupler U1 is connected to the positive pole of the capacitor C1, and the negative pole is connected to the positive pole of the diode D3. The negative pole of the diode D3 is connected to the positive pole of the capacitor C5, and the negative pole of the capacitor C5 is grounded. The positive pole of the light-emitting diode inside the optocoupler U2 is connected to the positive pole of the capacitor C5, and the negative pole is connected to the positive pole of the capacitor C1. The positive pole of the light-emitting diode inside the optocoupler U2 is connected to the resistor R4 and then to the positive pole of the capacitor C5. The capacitor C5 is connected in parallel with the resistor R5. One end of the resistor R5 is connected to the positive pole of the capacitor C5, and the other end is grounded. The resistor R4 is used to adjust the discharge speed of the discharge loop when a discharge loop is formed by the capacitor C1, the light-emitting diode inside the optocoupler U2, the resistor R4, and the capacitor C5. In some special applications, the voltage of the capacitor C1 is not continuously constant and may slowly increase or decrease. In these applications, such slow fluctuations are allowed. A slow decrease in the voltage of C1 should not trigger an action signal, and only a rapid decrease will trigger an action signal. The function of the resistor R5 is to adjust the sensitivity to changes in the voltage of CI. The specific process is that when the voltage of C1 slowly decreases, since R5 continuously discharges C3, the voltage on the capacitor C3 follows the voltage of the capacitor C1 and decreases. During this process, the voltage difference between C1 and C3 is not sufficient to turn on the diode of the optocoupler U2, and no action signal will be triggered. By adjusting the resistance value of R5, the detection sensitivity to the power-off speed of C1 can be adjusted. The larger the resistance value of R5, the more sensitive the detection of the power-off of C1. R5 can also be not connected. At this time, the detection of the power-off of C1 is the most sensitive, and R5 participates in the discharge initialization of the capacitor C3 after the circuit is powered off.

[0052] During the entire charging stage of capacitor C1, whether in the initial stage or the later stage, the voltage of capacitor C1 is greater than that of capacitor C5. Capacitor C1, the light-emitting diode in optocoupler U1, diode D3, and capacitor C5 form a discharge loop. Capacitor C1 charges capacitor C5 through the light-emitting diode in optocoupler U1 and diode D3. The voltage of capacitor C5 is smaller than the voltage of capacitor C1 by the voltage drop of the light-emitting diode in optocoupler U1 and the voltage drop of diode D3. The light-emitting diode in optocoupler U1 conducts, and the light emitted by the light-emitting diode in optocoupler U1 causes the triode in optocoupler U1 to conduct, pulling the output out to ground (GND), and the output out is at a low level. During the charging stage of capacitor C1, whether in the charging stage or the stable state of capacitor C1, the voltage of capacitor C1 is greater than that of capacitor C5. Since the light-emitting diode in optocoupler U2 is reversely connected, the voltage difference of the light-emitting diode in optocoupler U2 is negative (reverse bias), and the light-emitting diode in optocoupler U2 does not conduct, and the triode in optocoupler U2 is turned off. In the initial stage of charging capacitor C1, the gate voltage of triode Q1 is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off; in the later stage of charging capacitor C1, the voltage after voltage division by the voltage division circuit of the voltage of capacitor C1 is greater than the turn-on voltage threshold of triode Q1, and triode Q1 conducts. However, during the charging stage, whether triode Q1 is turned off or on, the effect of triode Q1 on the output out is less than the effect of the triode in optocoupler U1 conducting and pulling the output out to ground. The state of triode Q1 has no effect on the state of the output out during the charging stage. Therefore, during the charging stage of capacitor C1, the output out of the detection circuit is at a low level and does not output an action signal. In the stable state of capacitor C1 or when the fluctuation is less than the voltage drop of the light-emitting diode in optocoupler U1, if capacitor C1 is in a set undervoltage state, capacitor C5 stops charging and no discharge loop is formed, optocoupler U1 does not conduct, the voltage difference of the light-emitting diode in optocoupler U2 is still negative, and optocoupler U2 does not conduct; the voltage at the voltage division point of resistor R3 and resistor R6 in the voltage division circuit is less than the turn-on voltage threshold of triode Q1, triode Q1 is turned off, and the output out is at a high level (the output out is the output after the reference voltage Vref passes through resistor R2).When the voltage of capacitor C1 drops rapidly, capacitor C5 stops charging and optocoupler U1 is not conducting. Since there are diode D3 and the light-emitting diode in optocoupler U1 between capacitor C1 and capacitor C5, the voltage of capacitor C5 does not drop immediately with capacitor C1. As the voltage of capacitor C1 continues to drop, the voltage difference across the light-emitting diode in optocoupler U2 changes from negative to positive. When the positive voltage difference is greater than the conduction voltage of the light-emitting diode in optocoupler U2, the light-emitting diode in optocoupler U2 conducts. At this time, capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C5 form a discharge loop, the triode in optocoupler U2 conducts, the base of triode Q2 is set high, the collector and emitter of triode Q2 conduct, the gate of triode Q1 is pulled down to ground, and the output out is at a high level. The power-down threshold of the detection circuit is the value obtained by subtracting the voltage drop of diode D3 and the conduction voltages of the light-emitting diodes in optocouplers U1 and U2 from the stable-state voltage value of capacitor C1. The waveform diagram of the output terminal changing with the voltage value of capacitor C1 during the charging stage of capacitor C1 is as follows. Figure 5 shown. The waveform diagram of the output port when the voltage of capacitor C1 does not reach the static undervoltage threshold is as follows Figure 6 shown. The waveform diagram of the output port changing with the capacitor voltage when capacitor C1 loses power is as follows Figure 4 shown.

[0053] The capacitor to be detected in this application can be a battery or other capacitive devices. The characteristic is that the device functions as energy storage, the voltage value cannot change abruptly, and the voltage change is smooth. The capacitor to be detected in this application can be a power source such as a battery or a filter capacitor connected after rectification, or a load capacitor. The output of the circuit in this application does not necessarily have to be fixed at a high level corresponding to undervoltage and power-down. According to the actual circuit requirements, through a simple level conversion circuit, the output can be converted into different logics. The forms of the level conversion circuit are diverse, and this patent does not elaborate on the level conversion circuit. This application does not limit the reference voltage Vref, and Vref is determined according to the actual needs of the output. The diode used to set the power-down threshold in this application can be replaced by a series circuit of multiple diodes. The effect of multiple diodes in series is to increase the voltage difference threshold for power-down detection, and the type and model of the diodes are not restricted.

[0054] Embodiment 3:

[0055] A capacitor undervoltage and power-down detection circuit, as shown in Figures 3 - 6As shown in the figure, it includes: a capacitor C1 connected to an external power supply, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage dividing circuit, a triode Q1, and a resistor R2. The capacitor C1 is connected to the charging circuit. The light-emitting diodes in the optocoupler U1 and the optocoupler U2 are connected to the capacitor C1 and the charging circuit. And the light-emitting diode in the optocoupler U1 is connected in the forward direction, and the light-emitting diode in the optocoupler U2 is connected in the reverse direction. The output terminal of the optocoupler U1 is connected to the ground and the output out of the capacitor undervoltage and power-off detection circuit. The output terminal of the optocoupler U2 is connected to the input terminal of the triode Q2. The output terminal of the triode Q2 is connected to the input terminal of the triode Q1. The output terminal of the triode Q1 is connected to the output out. The voltage dividing circuit is connected in parallel with the capacitor C1 and is connected to the input terminal of the triode Q1. One end of the resistor R2 is connected to the reference voltage Vref, and the other end is connected to the output out. The optocoupler U1 is used for, during the charging stage of the capacitor C1, the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit form a discharge loop, the optocoupler U1 conducts and pulls the output out down to the ground (GND), and the output out is at a low level. The voltage dividing circuit is used for, in the stable state, the capacitor C1 is in the undervoltage state, the voltage at the voltage dividing point of the voltage dividing circuit is less than the turn-on voltage threshold of the triode Q1, the triode Q1 is turned off, and the output out is at a high level. The optocoupler U2 is used for, when the capacitor C1 loses power (the voltage drops rapidly), when the voltage difference across the light-emitting diode in the optocoupler U2 changes from a negative value to a positive value, and this positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2, the light-emitting diode in the optocoupler U2 conducts, the triode in the optocoupler U2 conducts, the triode Q2 conducts, the triode Q2 pulls the base of the triode Q1 down to the ground, the triode Q1 is turned off, and the output out is at a high level.

[0056] The positive electrode of the capacitor C1 is connected to the positive electrode of the external power supply, and the negative electrode of the capacitor C1 is connected to the negative electrode of the external power supply and grounded (GND). The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, and the negative electrode of the light-emitting diode in the optocoupler U1 is connected to the charging circuit. When the light-emitting diode in the optocoupler U1 emits light, the triode in the optocoupler U1 conducts. The collector of the triode in the optocoupler U1 is connected to the output out, and the emitter of the triode in the optocoupler U1 is grounded; the negative electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the positive electrode of the light-emitting diode in the optocoupler U2 is connected to the charging circuit. When the light-emitting diode in the optocoupler U2 emits light, the triode in the optocoupler U2 conducts. The collector of the triode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the emitter of the triode in the optocoupler U2 is connected to the input terminal (base) of the triode Q2. The triode Q1 is a MOS transistor. The collector of the triode Q2 is connected to the gate of the triode Q1, the emitter of the triode Q2 is grounded, the drain of the triode Q1 is connected to the output out, and the source of the triode Q1 is grounded. The collector of the triode in the optocoupler U2 is connected to the resistor R1 and then to the positive electrode of the capacitor C1. The resistor R1 is used to limit the current passing through the base of the triode Q2. The voltage-dividing circuit is composed of the resistor R3 and the resistor R6 connected in series. One end of the resistor R3 is connected to the positive electrode of the capacitor C1, the other end is connected to the resistor R6, and the other end of the resistor R6 is grounded. The gate of the triode Q1 is connected to the voltage-dividing point between the resistor R3 and the resistor R6. The resistance values of the resistor R3 and the resistor R6 are set according to the undervoltage threshold of the capacitor C1 and the turn-on voltage of the triode Q1, so that when the voltage of the capacitor C1 is higher than the undervoltage threshold, the triode Q1 conducts; when the voltage of the capacitor C1 is less than the undervoltage threshold, the triode Q1 turns off and the output out is at a high level. The resistor R6 is connected in parallel with the capacitor C4. The positive electrode of the capacitor C4 is connected to the voltage-dividing point between the resistor R3 and the resistor R6, and the negative electrode of the capacitor C4 is grounded. The capacitor C4 is used for filtering.

[0057] The charging circuit consists of capacitor C5. The positive pole of the light-emitting diode in optocoupler U1 is connected to the positive pole of capacitor C1, and the negative pole is connected to the positive pole of capacitor C5. The negative pole of capacitor C5 is grounded. The positive pole of the light-emitting diode in optocoupler U2 is connected to the positive pole of capacitor C5, and the negative pole is connected to the positive pole of capacitor C1. The positive pole of the light-emitting diode in optocoupler U2 is connected to resistor R4 and then to the positive pole of capacitor C5. Capacitor C5 is connected in parallel with resistor R5. One end of resistor R5 is connected to the positive pole of capacitor C5, and the other end is grounded. Resistor R4 is used to adjust the discharge speed of the discharge loop formed by capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C5 when they form a discharge loop. In some special applications, the voltage of capacitor C1 is not constantly unchanged and may slowly increase or decrease. In these applications, such slow fluctuations are allowed. A slow decrease in the voltage of C1 should not trigger an action signal, and only a rapid decrease will trigger an action signal. The role of resistor R5 is to adjust the sensitivity to changes in the voltage of CI. The specific process is that when the voltage of C1 slowly decreases, since R5 continuously discharges C3, the voltage on capacitor C3 follows the voltage of capacitor C1 and decreases. During this process, the voltage difference between C1 and C3 is not sufficient to turn on the diode of optocoupler U2 and does not trigger an action signal. By adjusting the resistance value of R5, the detection sensitivity to the power-off speed of C1 can be adjusted. The larger the resistance value of R5, the more sensitive the detection of the power-off of C1. R5 can also be not connected. At this time, the detection of the power-off of C1 is the most sensitive, and R5 participates in the discharge initialization of capacitor C3 after the circuit is powered off.

[0058] During the entire charging stage of capacitor C1, whether in the initial or later stage, capacitor C1, the light-emitting diode in optocoupler U1, and capacitor C5 form a discharge loop. Capacitor C1 charges capacitor C5 through the light-emitting diode in optocoupler U1. The voltage of capacitor C5 is smaller than the voltage of capacitor C1 by the voltage drop of the light-emitting diode in optocoupler U1. The light-emitting diode in optocoupler U1 conducts, and the light emitted by the light-emitting diode in optocoupler U1 causes the triode in optocoupler U1 to conduct, pulling the output out to ground (GND), and the output out is at a low level. During the charging stage of capacitor C1, whether in the charging stage or the stable state of capacitor C1, the voltage of capacitor C1 is greater than the voltage of capacitor C5. Since the light-emitting diode in optocoupler U2 is reversely connected, the voltage difference of the light-emitting diode in optocoupler U2 is negative (reverse bias), and the light-emitting diode in optocoupler U2 does not conduct, and the triode in optocoupler U2 is turned off. At the initial stage of the charging of capacitor C1, the gate voltage of triode Q1 is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off; at the later stage of the charging of capacitor C1, the voltage after the voltage division of the voltage of capacitor C1 by the voltage division circuit is greater than the turn-on voltage threshold of triode Q1, and triode Q1 conducts. However, during the charging stage, whether triode Q1 is turned off or on, the effect of triode Q1 on the output out is less than the effect of the triode in optocoupler U1 conducting and pulling the output out to ground. The state of triode Q1 has no effect on the state of the output out during the charging stage. Therefore, during the charging stage of capacitor C1, the output out of the detection circuit is at a low level and does not output an action signal. In the stable state of capacitor C1 or when the fluctuation is less than the voltage drop of the light-emitting diode in optocoupler U1, if capacitor C1 is in a set undervoltage state, capacitor C5 stops charging and no discharge loop is formed, optocoupler U1 does not conduct, the voltage difference of the light-emitting diode in optocoupler U2 is still negative, and optocoupler U2 does not conduct; the voltage at the voltage division point of resistor R3 and resistor R6 in the voltage division circuit is less than the turn-on voltage threshold of triode Q1, and triode Q1 is turned off, and the output out is at a high level (the output out is the output after the reference voltage Vref passes through resistor R2). When the voltage of capacitor C1 drops rapidly, capacitor C5 stops charging and optocoupler U1 does not conduct; because there is a light-emitting diode in optocoupler U1 between capacitor C1 and capacitor C5, the voltage of capacitor C5 does not drop immediately with capacitor C1. As the voltage of capacitor C1 continues to drop, the voltage difference across the light-emitting diode in optocoupler U2 changes from negative to positive. When the positive voltage difference is greater than the turn-on voltage of the light-emitting diode in optocoupler U2, the light-emitting diode in optocoupler U2 conducts. At this time, capacitor C1, the light-emitting diode in optocoupler U2, resistor R4, and capacitor C5 form a discharge loop, the triode in optocoupler U2 conducts, the base of triode Q2 is set high, the collector and emitter of triode Q2 conduct, the gate of triode Q1 is pulled to ground, and the output out is at a high level.The power-down threshold of the detection circuit is the value obtained by subtracting the conduction voltages of the light-emitting diodes in optocoupler U1 and optocoupler U2 from the stable-state voltage value of capacitor C1. The waveform diagram of the output terminal changing with the voltage value of capacitor C1 during the charging stage of capacitor C1 is as follows. Figure 5 shown. The waveform diagram of the output port when the voltage of capacitor C1 has not reached the static undervoltage threshold is as follows Figure 6 shown. The waveform diagram of the output port changing with the capacitor voltage when capacitor C1 powers down is as follows Figure 4 shown.

[0059] The detected capacitor in this application can be a battery or other capacitive devices. The feature is that the device functions as energy storage, the voltage value cannot change suddenly, and the voltage change is smooth. The detected capacitor in this application can be a power source such as a battery or a filter capacitor connected after rectification, or it can also be a load capacitor. The circuit output in this application does not have to be fixed to the high level corresponding to undervoltage and power-down. According to the actual circuit requirements, through a simple level conversion circuit, the output can be converted into different logics. The forms of the level conversion circuit are diverse, and this patent will not elaborate on the level conversion circuit. This application does not limit the reference voltage Vref, and Vref is determined according to the actual needs of the output. The diode used to set the power-down threshold in this application can be replaced by a series circuit of multiple diodes. The effect of connecting multiple diodes in series is that the voltage difference threshold for power-down detection is increased, and the type and model of the diodes are not restricted.

[0060] Although this application has disclosed multiple aspects and embodiments, other aspects and embodiments will be obvious to those skilled in the art. Without departing from the concept of this application, several deformations and improvements can still be made, and these all fall within the protection scope of this application. The multiple aspects and embodiments disclosed in this application are only used for illustration, and they are not intended to limit this application. The actual protection scope of this application is subject to the claims.

Claims

1. A capacitor under-voltage and power-off detection circuit, characterized in that, Including: A capacitor C1, a charging circuit, an optocoupler U1, an optocoupler U2, a triode Q2, a voltage dividing circuit, a triode Q1, and a resistor R2 connected to an external power supply. The capacitor C1 is connected to the charging circuit. The light-emitting diodes in the optocoupler U1 and the optocoupler U2 are connected to the capacitor C1 and the charging circuit. And the light-emitting diode in the optocoupler U1 is forward-connected, and the light-emitting diode in the optocoupler U2 is reverse-connected. The output end of the optocoupler U1 is connected to the ground and the output out of the capacitor under-voltage and power-off detection circuit. The output end of the optocoupler U2 is connected to the input end of the triode Q2. The output end of the triode Q2 is connected to the input end of the triode Q1. The output end of the triode Q1 is connected to the output out. The voltage dividing circuit is connected in parallel with the capacitor C1 and is connected to the input end of the triode Q1. One end of the resistor R2 is connected to the reference voltage Vref, and the other end is connected to the output out. The optocoupler U1 is used for, during the charging stage of the capacitor C1, the capacitor C1, the light-emitting diode in the optocoupler U1, and the charging circuit form a discharge loop, the optocoupler U1 conducts and pulls the output out to the ground, and the output out is at a low level. The voltage dividing circuit is used for, in the stable state, the capacitor C1 is in an under-voltage state, the voltage at the voltage dividing point of the voltage dividing circuit is less than the turn-on voltage threshold of the triode Q1, the triode Q1 is turned off, and the output out is at a high level. The optocoupler U2 is used for, when the capacitor C1 loses power, when the voltage difference across the light-emitting diode in the optocoupler U2 changes from a negative value to a positive value, and this positive voltage difference is greater than the turn-on voltage of the light-emitting diode in the optocoupler U2, the light-emitting diode in the optocoupler U2 conducts, the triode in the optocoupler U2 conducts, the triode Q2 conducts, the triode Q2 pulls the base of the triode Q1 to the ground, the triode Q1 is turned off, and the output out is at a high level. The positive electrode of the capacitor C1 is connected to the positive electrode of the external power supply, the negative electrode of the capacitor C1 is connected to the negative electrode of the external power supply and grounded. The positive electrode of the light-emitting diode in the optocoupler U1 is connected to the positive electrode of the capacitor C1, the negative electrode of the light-emitting diode in the optocoupler U1 is connected to the charging circuit. When the light-emitting diode in the optocoupler U1 emits light, the triode in the optocoupler U1 conducts. The collector of the triode in the optocoupler U1 is connected to the output out, and the emitter of the triode in the optocoupler U1 is grounded. The negative electrode of the light-emitting diode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, the positive electrode of the light-emitting diode in the optocoupler U2 is connected to the charging circuit. When the light-emitting diode in the optocoupler U2 emits light, the triode in the optocoupler U2 conducts. The collector of the triode in the optocoupler U2 is connected to the positive electrode of the capacitor C1, and the emitter of the triode in the optocoupler U2 is connected to the input end of the triode Q2. The triode Q1 is a MOS transistor. The collector of the triode Q2 is connected to the gate of the triode Q1, the emitter of the triode Q2 is grounded, the drain of the triode Q1 is connected to the output out, and the source of the triode Q1 is grounded;The collector of the triode in the optocoupler U2 is connected to the resistor R1 and then to the positive electrode of the capacitor C1. The resistor R1 is used to limit the current passing through the base of the triode Q2. The voltage-dividing circuit is composed of the resistor R3 and the resistor R6 connected in series. One end of the resistor R3 is connected to the positive electrode of the capacitor C1, the other end is connected to the resistor R6, and the other end of the resistor R6 is grounded. The gate of the triode Q1 is connected to the voltage-dividing point between the resistor R3 and the resistor R6.; 2. The capacitor under-voltage and power-off detection circuit according to claim 1, wherein The resistance values of the resistor R3 and the resistor R6 are set according to the undervoltage threshold of the capacitor C1 and the turn-on voltage of the triode Q1, so that when the voltage of the capacitor C1 is higher than the undervoltage threshold, the triode Q1 conducts; when the voltage of the capacitor C1 is lower than the undervoltage threshold, the triode Q1 turns off and the output out is at a high level.

3. The capacitor under-voltage and power-off detection circuit according to claim 1, wherein The charging circuit is a charging circuit composed of one branch or a charging circuit composed of two branches.

4. The capacitor under-voltage and power-off detection circuit according to claim 3, wherein, When the charging circuit is composed of two branches, these two branches are the first charging branch and the second charging branch respectively. The first charging branch is composed of a diode D1 and a capacitor C2 connected in series and is connected in parallel with the capacitor C1. Among them, the diode D1 is reversely connected and is connected in parallel with the light-emitting diode in the optocoupler U1. The negative pole of the diode D1 is connected to the positive pole of the capacitor C1, and the positive pole is connected to the positive pole of the capacitor C2. The negative pole of the capacitor C2 is grounded. The positive pole of the light-emitting diode in the optocoupler U1 is connected to the positive pole of the capacitor C1, and the negative pole is connected to the positive pole of the capacitor C2; the second charging branch is composed of a diode D2 and a capacitor C3 connected in series and is connected in parallel with the capacitor C1. The positive pole of the diode D2 is connected to the positive pole of the capacitor C1, and the negative pole is connected to the positive pole of the capacitor C3. The negative pole of the capacitor C3 is grounded. The positive pole of the light-emitting diode in the optocoupler U2 is connected to the positive pole of the capacitor C3, and the negative pole is connected to the positive pole of the capacitor C1.

5. The capacitor under-voltage and power-off detection circuit according to claim 4, wherein The detection circuit further includes a resistor R4 and a resistor R5. One end of the resistor R4 is connected to the positive pole of the light-emitting diode in the optocoupler U2, and the other end is connected to the positive pole of the capacitor C3. The resistor R5 is connected in parallel with the capacitor C3. One end of the resistor R5 is connected to the positive pole of the capacitor C3, and the other end is grounded. The resistor R4 is used to adjust the discharge speed of the discharge loop when a discharge loop is formed by the capacitor C1, the light-emitting diode in the optocoupler U2, the resistor R4 and the capacitor C3.

6. The capacitor undervoltage and power-off detection circuit according to claim 3, wherein When the charging circuit is composed of one branch, the charging circuit is composed of a capacitor C5 and a diode D3. The diode D3 is connected in series with the capacitor C5. The positive pole of the light-emitting diode in the optocoupler U1 is connected to the positive pole of the capacitor C1, and the negative pole is connected to the positive pole of the diode D3. The negative pole of the diode D3 is connected to the positive pole of the capacitor C5, and the negative pole of the capacitor C5 is grounded. The positive pole of the light-emitting diode in the optocoupler U2 is connected to the positive pole of the capacitor C5, and the negative pole is connected to the positive pole of the capacitor C1.

7. The capacitor under-voltage and power-off detection circuit according to claim 6, wherein The positive pole of the light-emitting diode in the optocoupler U2 is connected to the resistor R4 and then connected to the positive pole of the capacitor C5. The capacitor C5 is connected in parallel with the resistor R5. One end of the resistor R5 is connected to the positive pole of the capacitor C5, and the other end is grounded. The resistor R4 is used to adjust the discharge speed of the discharge loop when a discharge loop is formed by the capacitor C1, the light-emitting diode in the optocoupler U2, the resistor R4 and the capacitor C5.

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