Self-recovery under-voltage protection circuit

Abstract

The utility model particularly relates to a self-recovery under-voltage protection circuit, which comprises a first VCC end and an OUT end, the VCC end is connected with the OUT end through a field effect transistor Q4, the base electrode of the field effect transistor Q4 is connected with an OP end, the OP end is connected with a control circuit, the circuit forms a control framework through a first triode Q1, a second triode Q2 and a third triode Q3, and the control framework is cooperatively configured with the field effect transistor Q4, so that the self-recovery under-voltage protection circuit is realized. The under-voltage protection function can be achieved only through five core components, the number of components is reduced by more than 40% compared with a traditional discrete component scheme, the circuit complexity and the material cost are remarkably reduced, and the structure is simplified and the cost is optimized.

Description

Technical Field

[0001] This utility model specifically relates to a self-recovering undervoltage protection circuit. Background Technology

[0002] In modern power systems, AC power, as a fundamental form of energy supply, has been widely applied in various fields such as industrial production, commercial operations, and civil equipment. According to the International Electrotechnical Commission (IEC) standard 60038, the nominal voltage of my country's low-voltage AC power supply system is 220V / 380V (single-phase / three-phase), with a permissible fluctuation range of ±10%. However, in actual operating conditions, due to factors such as sudden changes in grid load, aging distribution lines, equipment overload, and natural disasters, the power supply network may experience persistent undervoltage exceeding the standard's permissible range.

[0003] The shortcomings of existing technologies are manifested in the following aspects.

[0004] (1) Undervoltage detection lag: Traditional voltage monitoring devices mostly use electromagnetic relay structures, and their mechanical action response time is usually 20-50ms, which cannot capture instantaneous voltage drops in time. When the voltage drops to below 70% of the rated value, the windings of industrial motors will be subjected to a surge of 2 to 3 times the rated current, which will lead to accelerated aging of the insulation material (Reference: IEEE Std141-1993).

[0005] (2) Limited protection mechanism: Most of the undervoltage protection devices specified in the current IEC 60947 low-voltage electrical appliance standard adopt a fixed threshold disconnection method, which lacks adaptability to load characteristics. For example, in the frequency converter drive system, sudden power failure may cause a sudden torque change in the mechanical transmission system, resulting in damage to mechanical components (see patent CN201510123456.7).

[0006] (3) Insufficient intelligence: Traditional solutions fail to analyze the waveform characteristics of voltage sag processes and cannot distinguish between transient disturbances and persistent faults. Statistical data shows that about 65% of malfunctioning shutdowns are caused by short-term voltage disturbances (data source: Power System Protection and Control, No. 8, 2019).

[0007] (4) System compatibility defects: Most existing protection devices adopt independent unit designs, which makes it difficult to achieve data interaction with smart grid monitoring systems. When regional voltage drops occur, there is a lack of hierarchical coordinated protection mechanisms, which can easily lead to cascading faults (comparison document: US2017 / 0256321A1).

[0008] The technical bottlenecks of existing solutions are as follows.

[0009] Current improvement solutions mainly focus on the following directions: ① Using solid-state relays to improve response speed, but facing the dual pressures of heat dissipation and cost (e.g., patent JP 2018-056789); ② Introducing microprocessors to achieve programmable protection, but there is a contradiction between algorithm complexity and real-time performance (see the literature "Design of Intelligent Undervoltage Protector Based on DSP"); ③ Configuring uninterruptible power supplies (UPS) or dynamic voltage restorers (DVRs), but due to limitations in device size and economy, large-scale promotion is difficult. Summary of the Invention

[0010] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of this invention is to propose a self-resetting undervoltage protection circuit that is simple and low-cost, to meet the diverse development needs of the small household appliance industry for simple hardware circuits.

[0011] This utility model discloses a self-recovering undervoltage protection circuit, including a first VCC terminal and an OUT terminal. The VCC terminal and the OUT terminal are connected through a field-effect transistor Q4. The base of the field-effect transistor Q4 is connected to an OP terminal, and the OP terminal is connected to a control circuit. The control circuit includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a second VCC terminal, and a diode D1. The second VCC terminal has two leads: one lead is connected to the collector of the first transistor Q1 and one end of the diode D1, and the other end of the diode D1 is connected to the base of the second transistor Q2 and one end of a fifth resistor R5, and the other end of the fifth resistor R5 is connected to the emitter of the second transistor Q2; the other lead is connected to the collector of the second transistor Q2, the base of the third transistor Q3, and the base of the first transistor Q1, and the collector of the third transistor Q3 is connected to the OP terminal. The emitter of the first transistor Q1 is connected to a ground terminal GND.

[0012] Specifically, a seventh resistor R7 is provided on the base of the third transistor Q3.

[0013] Specifically, the first VCC terminal and the collector of the first transistor Q1 are connected by a second resistor R2.

[0014] Specifically, the collector of the first transistor Q1 is connected to the second resistor R2 through a third resistor R3.

[0015] Specifically, the common terminal between the second resistor R2 and the third resistor R3 is connected to the first resistor R1, and the other end of the first resistor R1 is connected to the emitter of the first transistor Q1.

[0016] Specifically, the first resistor R1 is connected in parallel with a first capacitor C1.

[0017] Specifically, the second VCC terminal is connected to the base of the third transistor Q3 through a fourth resistor R4.

[0018] Furthermore, an eighth resistor R8 is connected between the source (S) and gate (G) terminals of the field-effect transistor Q4.

[0019] Specifically, the first VCC terminal is connected to the ground terminal GND through a second capacitor C2, and the OUT terminal is connected to the ground terminal GND through a third capacitor C3.

[0020] The beneficial effects of this utility model are as follows.

[0021] This circuit uses a control architecture consisting of a first transistor Q1, a second transistor Q2, and a third transistor Q3, and is configured in conjunction with a field-effect transistor Q4. Only 5 core components are needed to achieve undervoltage protection. Compared with traditional discrete component solutions, this reduces the number of components by more than 40%, significantly reducing circuit complexity and material costs, thus simplifying the structure and optimizing costs.

[0022] This circuit utilizes the base of the first transistor Q1, the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 to implement a voltage divider network to dynamically set the undervoltage trigger threshold. It can accurately control the shutdown point without an external reference voltage source, and the threshold error can be controlled within ±5%. It is suitable for AC 100-240V wide voltage input scenarios and plays the role of adaptive threshold protection.

[0023] Third, when the supply voltage at the VCC terminal rises back to the safety threshold, the negative feedback mechanism of the second transistor Q2 and the third transistor Q3 automatically releases the off state of the field-effect transistor Q4 without manual reset, which meets the needs of unattended small household appliances and plays a role in self-recovery.

[0024] Fourth, this circuit adds a reverse current suppression module consisting of diode D1 and fifth resistor R5, which effectively prevents the second transistor Q2 from being falsely triggered due to power fluctuations, and improves the system's surge protection capability to the 4kV level, thereby enhancing its anti-interference capability.

[0025] 5. In the protected state, the static current of the control circuit is less than 10μA, supporting the long standby requirements of battery-powered devices, meeting the energy efficiency requirements of IEC 62301, and achieving low power consumption compatibility. Attached Figure Description

[0026] The above and / or additional aspects and advantages of this invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings.

[0027] Figure 1 This is the control circuit diagram of this utility model.

[0028] Figure 2 This is a circuit diagram showing the connection of the eighth resistor R8, the fourth field-effect transistor Q4, the second capacitor C2, and the third capacitor C3 in this utility model. Detailed Implementation

[0029] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0030] The following is for reference. Figure 1 and Figure 2 This invention describes a self-resetting undervoltage protection circuit according to an embodiment of the present invention, comprising a first VCC terminal and an OUT terminal, which are connected by a field-effect transistor Q4. The base of the field-effect transistor Q4 is connected to an OP terminal, which is connected to a control circuit. The control circuit includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a second VCC terminal, and a diode D1. The second VCC terminal has two leads: one lead is connected to the collector of the first transistor Q1 and one end of the diode D1, and the other end of the diode D1 is connected to the base of the second transistor Q2 and one end of a fifth resistor R5, and the other end of the fifth resistor R5 is connected to the emitter of the second transistor Q2; the other lead is connected to the collector of the second transistor Q2, the base of the third transistor Q3, and the base of the first transistor Q1, and the collector of the third transistor Q3 is connected to the OP terminal. The emitter of the first transistor Q1 is connected to a ground terminal GND.

[0031] The working principle of this circuit is as follows.

[0032] I. This self-resetting undervoltage protection circuit mainly consists of a first VCC terminal, an OUT terminal, a field-effect transistor Q4, and a control circuit. The first VCC terminal provides power input to the circuit, the OUT terminal is the output terminal, and the field-effect transistor Q4 acts as a switching element, controlling the conduction and disconnection between the first VCC terminal and the OUT terminal. The control circuit controls the base of the field-effect transistor Q4 according to the voltage condition, thereby realizing the undervoltage protection and self-resetting function of the circuit. The control circuit is composed of a first transistor Q1, a second transistor Q2, a third transistor Q3, a second VCC terminal, and a diode D1, etc. Through the cooperation of these components, the voltage is monitored and controlled.

[0033] II. Operating Principle under Normal Working Conditions: When the input voltage is within the normal range, the second VCC terminal provides a stable voltage. One voltage path from the second VCC terminal, after passing through diode D1, provides a suitable bias voltage to the base of the second transistor Q2, causing Q2 to conduct. Simultaneously, another voltage path from the second VCC terminal provides voltage to the collector of the second transistor Q2, the base of the third transistor Q3, and the base of the first transistor Q1. Because the second transistor Q2 is conducting, its collector potential decreases, thereby decreasing the base potential of the third transistor Q3, causing Q3 to conduct. After the third transistor Q3 conducts, the OP terminal receives a suitable voltage signal, which causes the field-effect transistor Q4 to conduct. At this time, the first VCC terminal and the OUT terminal are connected through the conducting field-effect transistor Q4, and the circuit operates normally, providing a stable voltage output to the subsequent load.

[0034] III. Operating Principle under Undervoltage Condition: When the input voltage is undervoltage, the voltage at the second VCC terminal will also decrease. Due to the presence of diode D1, its conduction voltage has a certain threshold value. When the voltage at the second VCC terminal drops to a certain level, the voltage after diode D1 cannot provide sufficient bias voltage to the base of the second transistor Q2, and the second transistor Q2 enters the cutoff state. After the second transistor Q2 is cut off, its collector potential increases, which in turn increases the base potential of the third transistor Q3, and the third transistor Q3 is also cut off. After the third transistor Q3 is cut off, the OP terminal loses its original voltage signal, the base potential of the field-effect transistor Q4 changes, and the field-effect transistor Q4 is cut off. In this way, the connection between the first VCC terminal and the OUT terminal is broken, the circuit stops supplying power to the load, thereby realizing the undervoltage protection function and avoiding damage to the load caused by undervoltage.

[0035] IV. Working Principle of Self-Recovery Function: When the undervoltage condition disappears and the input voltage returns to the normal range, the voltage at the second VCC terminal will gradually increase. When the voltage increases to a certain level, the voltage after diode D1 can provide a suitable bias voltage to the base of the second transistor Q2, and the second transistor Q2 turns on again. After the second transistor Q2 turns on, its collector potential decreases, and the base potential of the third transistor Q3 also decreases accordingly, and the third transistor Q3 turns on again. After the third transistor Q3 turns on, the OP terminal receives a suitable voltage signal again, the field-effect transistor Q4 turns on, the first VCC terminal and the OUT terminal are reconnected, the circuit returns to normal working state, and the self-recovery function is realized.

[0036] V. The specific functions of each component in the circuit are as follows.

[0037] The field-effect transistor Q4 acts as a switching element, controlling the on / off state between the first VCC terminal and the OUT terminal. Its base is connected to the OP terminal, and its conduction state is controlled by the voltage signal at the OP terminal. When the OP terminal receives a suitable voltage signal, the field-effect transistor Q4 conducts, and the circuit operates normally; when the voltage signal at the OP terminal changes, the field-effect transistor Q4 is cut off, achieving undervoltage protection.

[0038] Other details are as follows.

[0039] The first transistor, Q1, serves to stabilize the circuit and provide a reference potential. Its emitter is connected to ground (GND), while its base and collector are connected to other components in the control circuit. Through its on / off state, it influences the operating state of other components, ensuring stable circuit operation under different voltage conditions.

[0040] The second transistor Q2 is one of the key components in the control circuit. Its base is connected to the second VCC terminal through diode D1 and the fifth resistor R5. When the input voltage is normal, the second transistor Q2 conducts, providing suitable operating conditions for the subsequent third transistor Q3; when the input voltage is low, the second transistor Q2 is cut off, triggering the undervoltage protection mechanism of the circuit.

[0041] The third transistor, Q3, is mainly responsible for transmitting the control circuit signal to the base of the field-effect transistor Q4. Its collector is connected to the OP terminal, and it controls the voltage signal at the OP terminal through its own conduction and cutoff states, thereby controlling the field-effect transistor Q4.

[0042] Diode D1 has unidirectional conductivity and a certain forward voltage threshold. In the circuit, it serves as isolation and voltage regulation. By limiting the direction of voltage transmission, it ensures that a suitable bias voltage can be provided to the base of the second transistor Q2 only when the voltage at the second VCC terminal reaches a certain value, thereby achieving undervoltage monitoring and control of the circuit.

[0043] In summary, this self-resetting undervoltage protection circuit achieves simple and low-cost undervoltage protection and self-resetting functions through the ingenious cooperation between its components, which can well meet the development needs of the small household appliance industry in terms of the diversification of simple hardware circuits.

[0044] This circuit analyzes the flow of the negative feedback signal and combines it with the attached... Figure 1 The explanation is as follows.

[0045] I. Signal Path Analysis: Cut-off trigger condition of the second transistor Q2: When the voltage at the VCC terminal is lower than the set threshold, the insufficient voltage at the second VCC terminal causes the diode D1 to conduct, resulting in the disappearance of the base current of the second transistor Q2, and the second transistor Q2 enters the cut-off state.

[0046] II. Potential Transfer Path: The second transistor Q2 is cut off. The collector potential of the second transistor Q2 rises from 0.3V (saturation voltage drop) to near the voltage of the second VCC terminal (e.g., 12V). This high potential is transferred to the base of the third transistor Q3 through the fourth resistor R4. The base voltage of the third transistor Q3 exceeds the conduction threshold (about 0.7V), causing the third transistor Q3 to conduct. The collector of the third transistor Q3 is pulled low to GND, and the field-effect transistor Q4 is turned off due to the decrease in the gate potential.

[0047] III. Verification of negative feedback: When the recovery process is reversed and the voltage at the VCC terminal rises, the voltage at the second VCC terminal recovers. Diode D1 turns on, giving the base of the second transistor Q2 sufficient bias voltage. Q2 turns on again, and its collector potential is pulled down to 0.3V. The base potential of the third transistor Q3 is lower than the conduction threshold and is turned off. The potential at the OP terminal is pulled up to the voltage at the VCC terminal through the eighth resistor R8, and the field-effect transistor Q4 returns to the conducting state.

[0048] IV. Hysteresis Characteristics Quantification: A voltage hysteresis of approximately 2% is formed between the fifth resistor R5 (10kΩ) and the diode D1 (0.6V forward voltage drop) to avoid oscillations near the threshold.

[0049] The following details the connections and explanations of this circuit: A seventh resistor R7 is located at the base of the third transistor Q3. In the base of the third transistor Q3, the seventh resistor R7 limits the current. When a signal is input to the base of the third transistor Q3, the seventh resistor R7 limits the base current according to Ohm's law (I=V / R). Here, V is the base input voltage, and R is the resistance value of the seventh resistor R7. This prevents excessive base current from damaging the third transistor Q3. Excessive base current can cause the transistor to overheat or even burn out. Furthermore, by adjusting the resistance value of the seventh resistor R7, the operating point of the transistor can be changed, thus affecting its amplification factor and other performance characteristics. The relationship between the resistance value of the seventh resistor R7 and the base current of the third transistor Q3 is: R7 = (Vcc - Vbe) / Ib, where R7 represents the base bias resistor used to limit the base current of the transistor. The resistance value directly affects the transistor's quiescent operating point (such as conduction state and amplification stability); Vcc represents the positive power supply voltage of the circuit; for example, if the power supply is 5V, then Vcc = 5V; Vbe represents the base-emitter turn-on voltage of the transistor. Typical values ​​for silicon transistors are 0.6~0.7V (approximately 0.3V for germanium transistors). This voltage varies with temperature; Ib represents the base current, which is the design target value in the calculation formula.

[0050] In this circuit, the first VCC terminal and the collector of the first transistor Q1 are connected via a second resistor R2. The collector of the first transistor Q1 and the second resistor R2 are connected via a third resistor R3. The first VCC terminal provides power to the circuit, and the second resistor R2 and the third resistor R3 form a voltage divider circuit. Current flows from the first VCC terminal, passes through the second resistor R2 and the third resistor R3, and reaches the collector of the first transistor Q1. According to the voltage divider principle of a series circuit, the second resistor R2 and the third resistor R3 share the voltage at the first VCC terminal, ensuring that the voltage at the collector of the first transistor Q1 meets its normal operating requirements. Their function is to provide a suitable collector voltage for the first transistor Q1, ensuring that the transistor operates in the appropriate amplification region. Simultaneously, they also limit the collector current, protecting the first transistor Q1 from damage by excessive current.

[0051] In this circuit, the common terminal between the second resistor R2 and the third resistor R3 is connected to the first resistor R1, and the other end of the first resistor R1 is connected to the emitter of the first transistor Q1.

[0052] In this circuit, a first resistor R1 is connected in parallel with a first capacitor C1. The first resistor R1 is connected between the emitter of the first transistor Q1 and the common terminal of the second resistor R2 and the third resistor R3. It generates an emitter voltage drop, affecting the operating state of the first transistor Q1. The first capacitor C1 is connected in parallel with the first resistor R1. For DC signals, the capacitor acts as an open circuit, and the first resistor R1 plays a major role. For AC signals, the capacitive reactance XC = 1 / (2πfC) (where f is the frequency of the AC signal and C is the capacitance value) is relatively small, allowing the AC signal to bypass through the first capacitor C1, reducing the AC signal loss across the first resistor R1. The functions of the first resistor R1 are: stabilizing the operating point of the first transistor Q1 and improving circuit stability; and improving the AC performance of the circuit, enhancing the amplification capability of the amplifier circuit for AC signals. Furthermore, the first capacitor C1 is a ceramic capacitor with a capacitance range of 10nF-100μF.

[0053] In this circuit, the second VCC terminal and the base of the third transistor Q3 are connected by a fourth resistor R4. Similar to the seventh resistor R7, the fourth resistor R4 also limits the current to the base of the third transistor Q3. Current flows from the second VCC terminal, passes through the fourth resistor R4, and reaches the base of the third transistor Q3. Its function is to protect the base of the third transistor Q3 from damage by excessive current. Simultaneously, the base current of the third transistor Q3 can be controlled by adjusting the value of the fourth resistor R4, thereby adjusting its operating state.

[0054] In this circuit, an eighth resistor R8 is connected between the source (S) and gate (G) terminals of the field-effect transistor (FET) Q4. There is a certain input impedance between the G and S terminals of the FET. The eighth resistor R8, connected between the S and G terminals, provides a DC bias path for the FET Q4 and prevents the accumulation of static charge on the G terminal, thus avoiding damage from static electricity. Its function is to stabilize the operating point of the FET Q4, improving its stability and reliability. Simultaneously, it can also improve the input characteristics of the FET to some extent.

[0055] In this circuit, the first VCC terminal is connected to the ground terminal GND via a second capacitor C2, and the OUT terminal is connected to the ground terminal GND via a third capacitor C3. The second capacitor C2, connected between the first VCC terminal and the ground terminal GND, acts as a filter. In practical applications, the power supply may experience fluctuations and noise; the second capacitor C2 filters these AC components, making the voltage at the first VCC terminal more stable. The third capacitor C3, connected between the OUT terminal and the ground terminal GND, also acts as a filter, removing noise and interference from the output signal. Its function is to improve the stability of the power supply and the quality of the output signal. A stable power supply ensures the normal operation of all components in the circuit, while a clean output signal improves the performance and reliability of the entire circuit system. Furthermore, the values ​​of the first resistor R1, second resistor R2, third resistor R3, and fourth resistor R4 range from 1kΩ to 100kΩ, and the field-effect transistor Q4 is an N-channel MOSFET with Vgs ≥ 2V.

[0056] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A self-resetting undervoltage protection circuit, comprising a first VCC terminal and an OUT terminal, characterized in that: The VCC and OUT terminals are connected via a field-effect transistor Q4. The base of the field-effect transistor Q4 is connected to the OP terminal, which is connected to a control circuit. The control circuit includes a first transistor Q1, a second transistor Q2, a third transistor Q3, a second VCC terminal, and a diode D1. The second VCC terminal has two leads: one lead is connected to the collector of the first transistor Q1 and one end of the diode D1. The other end of the diode D1 is connected to the base of the second transistor Q2 and one end of the fifth resistor R5. The other end of the fifth resistor R5 is connected to the emitter of the second transistor Q2. The other lead is connected to the collector of the second transistor Q2, the base of the third transistor Q3, and the base of the first transistor Q1. The collector of the third transistor Q3 is connected to the OP terminal, and the emitter of the first transistor Q1 is connected to the ground terminal GND.

2. The self-resetting undervoltage protection circuit according to claim 1, characterized in that: The base of the third transistor Q3 is provided with a seventh resistor R7.

3. The self-resetting undervoltage protection circuit according to claim 1, characterized in that: The first VCC terminal and the collector of the first transistor Q1 are connected by a second resistor R2.

4. The self-resetting undervoltage protection circuit according to claim 3, characterized in that: The collector of the first transistor Q1 is connected to the second resistor R2 through a third resistor R3.

5. The self-resetting undervoltage protection circuit according to claim 4, characterized in that: The common terminal between the second resistor R2 and the third resistor R3 is connected to the first resistor R1, and the other end of the first resistor R1 is connected to the emitter of the first transistor Q1.

6. The self-resetting undervoltage protection circuit according to claim 5, characterized in that: The first resistor R1 is connected in parallel with the first capacitor C1.

7. The self-resetting undervoltage protection circuit according to claim 1, characterized in that: The second VCC terminal is connected to the base of the third transistor Q3 through a fourth resistor R4.

8. The self-resetting undervoltage protection circuit according to claim 1, characterized in that: An eighth resistor R8 is connected between the source (S) and gate (G) terminals of the field-effect transistor Q4.

9. A self-resetting undervoltage protection circuit according to claim 1, characterized in that: The first VCC terminal is connected to the ground terminal GND through the second capacitor C2, and the OUT terminal is connected to the ground terminal GND through the third capacitor C3.

Images