Overvoltage protection circuit and vehicle

Abstract

The embodiment of the invention discloses an overvoltage protection circuit and a vehicle, and relates to the technical field of vehicle lamp driving, the overvoltage protection circuit comprises an input end, a voltage division module, a switch module and a driving module, and the input end is used for being electrically connected with a power supply; the first end of the voltage dividing module is electrically connected with the input end, and the second end of the voltage dividing module outputs detection voltage; the first end of the switch module is grounded, and the controlled end of the switch module is electrically connected with the second end of the voltage dividing module; the controlled end of the driving module is electrically connected with the second end of the switch module, and the driving module is used for driving a vehicle lamp to be turned on; when the voltage of the input end is greater than or equal to a first threshold value, the switch module is switched off, and the driving module stops; when the voltage of the input end is smaller than or equal to a second threshold value, the switch module is switched on, the driving module is started, and the first threshold value is larger than the second threshold value.

Description

Technical Field

[0001] This application relates to the field of vehicle lighting drive technology, and in particular to an overvoltage protection circuit and a vehicle. Background Technology

[0002] The headlight driver module is used to turn on the headlights. To protect the headlight driver module, an overvoltage protection circuit is usually included. When the battery voltage exceeds a certain threshold, the headlight driver module is shut down; when the battery voltage returns to below that threshold, the headlight driver module restarts.

[0003] However, battery voltage can fluctuate. When the battery voltage fluctuates around a threshold, it can cause the headlight drive module to start and stop frequently, resulting in flickering headlights and affecting illumination. Summary of the Invention

[0004] This application provides an overvoltage protection circuit and a vehicle, which can solve the technical problem of frequent start-stop of the vehicle light drive module.

[0005] In a first aspect, embodiments of this application provide an overvoltage protection circuit, which includes an input terminal, a voltage divider module, a switch module, and a drive module. The input terminal is used to be electrically connected to a power supply. The first terminal of the voltage divider module is electrically connected to the input terminal, and the second terminal of the voltage divider module outputs a detection voltage. The first terminal of the switch module is grounded, and the controlled terminal of the switch module is electrically connected to the second terminal of the voltage divider module. The controlled terminal of the drive module is electrically connected to the second terminal of the switch module, and the drive module is used to drive the vehicle lights to illuminate. When the voltage at the input terminal is greater than or equal to a first threshold, the switch module is turned off, and the drive module stops. When the voltage at the input terminal is less than or equal to a second threshold, the switch module is turned on, and the drive module starts. The first threshold is greater than the second threshold.

[0006] Based on the above embodiments, this application introduces a hysteresis voltage window to ensure that once the vehicle is shut down due to overvoltage, the power supply voltage must drop to a sufficiently low and safe level before restarting. This avoids repeated jumps at the critical point, thus maintaining stable and continuous vehicle lighting. Especially during vehicle acceleration, deceleration, or power fluctuations caused by poor battery condition, there is no uncomfortable flickering, improving the visual comfort and safety for the driver and other road users. Furthermore, it avoids frequent switching between on and off states for the LED driver circuit and its components, such as power switches, inductors, and capacitors. Such switching generates thermal and electrical stress, which can reduce component lifespan over time. Stable switching behavior also protects the LED light source itself, preventing performance degradation or premature failure caused by frequent inrush currents.

[0007] Furthermore, this application eliminates the need for a microcontroller (MCU) and its peripheral circuits such as ADC, power supply, and programming interface, significantly reducing material costs and PCB area. The circuit structure is compact, consisting only of basic discrete components or simple ICs, eliminating the need for writing, debugging, and maintaining embedded software, thus shortening the development cycle. It also reduces the risks associated with MCU-related software failures, crashes, and electromagnetic compatibility issues, making the protection function more robust, hardware-based, and reliable.

[0008] The hysteresis characteristic itself constitutes a noise margin, effectively filtering out transient glitches or spikes in the power line and preventing false triggering of overvoltage protection. This makes it particularly suitable for automotive electrical systems operating in complex electromagnetic environments. It perfectly matches the significant voltage fluctuations of automotive batteries during engine start-up and heavy load start-stop (such as air conditioning and power steering), ensuring stable operation of the headlights under these conditions. This overvoltage protection circuit can be easily added to the front end of existing LED driver circuits as a standalone pre-amplifier protection unit.

[0009] In some exemplary embodiments, when the voltage at the input terminal increases from the second threshold and is less than the first threshold, the voltage division coefficient of the voltage divider module is the first voltage division coefficient; when the voltage at the input terminal is greater than or equal to the first threshold, the voltage division coefficient of the voltage divider module is the second voltage division coefficient; when the voltage at the input terminal decreases from the first threshold and is greater than the second threshold, the voltage division coefficient of the voltage divider module is the second voltage division coefficient; when the voltage at the input terminal is less than or equal to the second threshold, the voltage division coefficient of the voltage divider module is the first voltage division coefficient, wherein the first voltage division coefficient is less than the second voltage division coefficient.

[0010] Based on the above embodiments, by precisely designing the first and second voltage divider coefficients, the overvoltage cutoff point and undervoltage recovery point can be set independently and accurately, ensuring that the width and position of the hysteresis window fully meet the design requirements. The wide hysteresis voltage window, spanning several volts, provides the system with strong noise immunity; conventional ripple, switching noise, or transient interference on the power line cannot cross this window, thus eliminating false triggering and critical oscillations—something fixed threshold circuits cannot match.

[0011] Furthermore, the entire "detection-judgment-action-state retention" process is completed entirely by hardware logic, forming a simple mechanical memory. Compared to MCU polling or ordinary comparator plus latch solutions, it is simpler, faster, and more reliable. The dynamic voltage divider mechanism makes the circuit more adaptable to the parameter tolerances of components, such as resistor accuracy. With proper design, even if the components have slight deviations, the existence of the hysteresis window and the realization of the function can be guaranteed. The wide hysteresis window avoids frequent switching on and off at fault boundaries, such as unstable high voltages, reducing thermal shock and electrical stress on the power devices of the downstream LED driver, and extending the life of the entire lamp.

[0012] In some exemplary embodiments, the voltage divider module includes: A first resistor, the first end of which serves as the first terminal of the voltage divider module and is electrically connected to the input terminal; The second resistor is connected to the first terminal of the first resistor as the second terminal of the voltage divider module, and the second terminal of the second resistor is grounded. A first switch, wherein a first end of the first switch is electrically connected to a first end of the first resistor, and a second end of the first switch is electrically connected to a second end of the first resistor; The second switch has its controlled terminal electrically connected to the first terminal of the first resistor, its first terminal electrically connected to the controlled terminal of the first switch, and its second terminal grounded. When the voltage at the input terminal is greater than or equal to the first threshold, the second switch is turned on, the first switch is turned on, the first resistor is short-circuited by the first switch, and the voltage division coefficient of the voltage divider module increases; when the voltage at the input terminal is less than or equal to the second threshold, the second switch is turned off, the first switch is turned off, and the voltage divider module restores its voltage division coefficient.

[0013] Based on the above embodiments, by connecting or short-circuiting the first resistor with the first switch, the voltage division coefficient changes, thereby generating a clear hysteresis voltage window with strong anti-interference capability. The second switch triggers the first switch, and the conduction of the first switch maintains the conduction condition of the second switch, forming positive feedback, which makes the state switching instantaneous and the state stable. This is more direct and reliable than solutions relying on RC delay. Only two resistors and two switching devices are required, without any integrated circuits, resulting in lower material costs and PCB area. The wide hysteresis window makes it adaptable to harsh operating conditions such as wide voltage fluctuations and load drops in automotive batteries (12V / 24V systems).

[0014] In some exemplary embodiments, the first switch includes a transistor, the emitter of the transistor being electrically connected to the first terminal of the first switch as a first terminal of the first resistor, the collector of the transistor being electrically connected to the second terminal of the first switch as a second terminal of the first resistor, and the base of the transistor being electrically connected to the first terminal of the first resistor as a controlled terminal of the second switch. The second switch includes a first MOSFET, the drain of the first MOSFET is electrically connected to the first terminal of the first resistor as the controlled terminal of the second switch, the source of the first MOSFET is grounded as the second terminal of the second switch, and the gate of the first MOSFET is electrically connected to the controlled terminal of the first switch as the first terminal of the second switch.

[0015] Based on the above embodiments, the transistor operates in saturated switching mode, and its CE saturation voltage drop is low. When it is used to short-circuit the first resistor R1, it introduces almost no additional voltage drop, ensuring that the voltage division coefficient changes significantly under protection conditions, thereby generating the widest possible hysteresis voltage window and achieving theoretically optimal anti-interference capability.

[0016] The first MOSFET is a voltage-controlled device with extremely low gate drive current and very fast switching speed, enabling rapid response to overvoltage signals. The transistor also switches quickly between deep saturation and cutoff. The combination of these two characteristics results in an extremely short response time for the entire protection circuit. The high input impedance of the first MOSFET makes its load effect on the preceding voltage divider network almost negligible, allowing the voltage at the divider point to be set very precisely without being pulled low by the first MOSFET, thus improving threshold accuracy. Simultaneously, when the first MOSFET is turned on, it effectively pulls the base of the transistor to ground, providing a strong turn-off drive for the transistor.

[0017] The first MOSFET serves as both a detector and a trigger, while the transistor acts as a power actuator. This clear functional division reduces mutual interference and improves circuit stability.

[0018] The ultra-low voltage drop when the transistor is saturated ensures that the voltage at the detection point can be pulled to an extremely high level. This provides a very stable guarantee for maintaining the conduction state of the first MOSFET, making the circuit's latch-up effect robust and its anti-interference capability strong under protection conditions. Both transistors and MOSFETs are general-purpose, inexpensive semiconductor devices with wide supply channels and low cost.

[0019] In some exemplary embodiments, the voltage divider module further includes: The third resistor has its first end electrically connected to the emitter of the transistor, and the second resistor has its second end electrically connected to the collector of the transistor. A first capacitor, the positive terminal of which is electrically connected to the first end of the third resistor, and the negative terminal of which is electrically connected to the second end of the third resistor; The fourth resistor has its first end electrically connected to the first end of the third resistor, and its second end electrically connected to the drain of the first MOS transistor. The fifth resistor has its first end electrically connected to the drain of the first MOS transistor, and its second end electrically connected to the base of the transistor.

[0020] Based on the above embodiment, the third resistor and the first capacitor constitute an emitter decoupling and delay network. The third resistor is connected in series with the emitter of the transistor, introducing local current negative feedback, while the first capacitor is connected in parallel across the third resistor. When the transistor attempts to turn on, the emitter current generates a voltage drop across the third resistor, slowing down the establishment speed of the base-emitter voltage and thus suppressing the instantaneous turn-on current of the transistor. The first capacitor provides a low-impedance path for transient current, assisting in this smooth process, optimizing the switching dynamic characteristics of the transistor, and preventing current surges.

[0021] The fourth resistor provides a defined pull-up path and isolation, connected between the input terminal and the drain of the first MOSFET (i.e., the detection point). When the first MOSFET is off, it provides a defined pull-up path to the drain, ensuring the potential at that point remains stable at a high level and avoiding the uncertainty noise introduced by the floating state. As an impedance between the detection point and the power supply, the fourth resistor, together with the second resistor, precisely sets the initial voltage division factor. Simultaneously, when the first MOSFET is on, it limits the current flowing from the power supply to the drain of the first MOSFET.

[0022] The fifth resistor is used for gate current limiting and drive regulation. It is connected in series between the drain of the first MOSFET and the base of the transistor to prevent excessive current from flowing into the base of the transistor at the moment the first MOSFET turns on, thus protecting both the transistor and the first MOSFET. The fifth resistor, along with the input impedance of the transistor, determines the driving capability of the first MOSFET on the transistor, thereby affecting the speed of state switching and the accuracy of the hysteresis voltage. These are key parameters for adjusting the dynamic performance of the circuit.

[0023] The RC network formed by the third resistor and the first capacitor, along with the impedance of the entire voltage divider network, constitutes a low-pass filter that effectively attenuates high-frequency switching noise, EMI interference, and instantaneous voltage spikes on the power line. This ensures that only continuous and genuine overvoltage events trigger the protection, completely eliminating malfunctions caused by noise. At the critical point of state switching, the circuit may experience high-frequency oscillations due to parasitic parameters. The third and fifth resistors, among others, increase damping, effectively suppressing this potential instability and ensuring a clean and crisp state transition. The buffering effect of the third resistor and the first capacitor smooths the turn-on and turn-off process of the transistor. This significantly reduces the current stress and switching losses experienced by the transistor and the first MOSFET during switching, and also reduces the resulting electromagnetic radiation (EMI). For protection circuits that need to frequently respond to power fluctuations, this directly improves the reliability of long-term operation.

[0024] The beta value of the transistor and the threshold voltage of the first MOSFET can vary between different batches and temperatures. The negative feedback effect of the third resistor can stabilize the conduction behavior of the transistor, while the carefully selected values ​​of the fourth and fifth resistors can relax the requirements for specific parameters of the first MOSFET and the transistor, thus improving the consistency of circuit performance during mass production.

[0025] By adjusting the fifth resistor and other resistors, the gain of the positive feedback loop can be controlled, thereby keeping the state switching speed within a reasonable range that is fast enough to provide protection but not too abrupt to avoid overshoot and oscillation. The fourth resistor ensures that the drain level of the first MOSFET is clearly defined in the off-state, avoiding threshold drift caused by ambiguous input impedance. This makes the circuit's turn-on and turn-off thresholds more stable and predictable. By adjusting the values ​​of the third resistor and the first capacitor, the switching speed and EMI performance can be optimized; the protection point can be precisely set by fine-tuning the ratio of the fourth, first, and second resistors; and the width of the hysteresis voltage can be fine-tuned by changing the fifth resistor.

[0026] In some exemplary embodiments, the voltage divider module further includes a first Zener diode, the anode of which is electrically connected to a first terminal of the first resistor, and the cathode of which is electrically connected to the input terminal.

[0027] Based on the above embodiment, the first Zener diode is connected in reverse between the input terminal and the upper end of the first resistor. When the input voltage rises above the sum of the Zener diode's voltage regulation value and its forward voltage drop, the first Zener diode enters the breakdown regulation region. When the first Zener diode breaks down, the voltage at its positive terminal is clamped, and the offset of the positive voltage relative to the input voltage remains fixed regardless of input voltage fluctuations.

[0028] The driving condition of the controlled terminal of the first switch is no longer directly related to the absolute value of the fluctuating input voltage, but is related to the clamping voltage. This makes the input voltage threshold that triggers the first switch to turn on mainly determined by the stable clamping voltage, rather than by the resistance ratio or transistor that is susceptible to temperature and process influence.

[0029] By selecting diodes with different voltage regulation values, the same circuit framework can be easily adapted to different system voltage platforms, such as 12V automotive systems and 24V truck systems, or different protection margins can be set, resulting in high design flexibility.

[0030] The resistance value changes with temperature, causing a change in the voltage division ratio. The temperature characteristics of the first Zener diode are known and stable, and a temperature-compensated Zener diode can be selected to obtain better temperature stability. This ensures that the protection circuit's operating threshold hardly drifts within the automotive-grade temperature range of -40°C to +125°C, maintaining consistent and reliable performance.

[0031] The breakdown characteristic of a Zener diode has a relatively sharp inflection point, which provides a steeper and cleaner drive signal for driving the first switch. This makes the state switching of the entire protection circuit faster and more decisive, reducing hesitation or instability near the critical point. The Zener diode itself has a certain absorption and clamping effect on transient high-voltage pulses at the input, providing additional protection for the preceding circuitry.

[0032] In some exemplary embodiments, the switching module includes a second MOS transistor, the drain of the second MOS transistor being electrically connected to the controlled terminal of the driving module as the second terminal of the switching module, the source of the second MOS transistor being grounded as the first terminal of the switching module, and the gate of the second MOS transistor being electrically connected to the second terminal of the voltage divider module as the controlled terminal of the switching module.

[0033] Based on the above embodiments, the gate of the MOSFET is insulated, and its DC input impedance is high. The detection voltage output by the voltage divider module is almost not loaded by the gate of the second MOSFET. Due to the absence of a load effect, the turn-off and turn-on thresholds set by the voltage divider resistors can maintain high accuracy and stability. The MOSFET is a voltage-controlled device; its switching speed is controlled by the charging and discharging of its gate charge. This results in extremely rapid overvoltage protection response, minimizing the time that subsequent drive circuits are exposed to abnormally high voltages.

[0034] When the second MOSFET is turned on, the on-resistance between its source and drain can be reduced to the milliohm level. Under normal conditions when the lamp is on, the additional voltage drop and power loss introduced by the second MOSFET in the grounding or enable circuit of the drive module are almost negligible, resulting in high system efficiency.

[0035] Driving the second MOSFET only requires charging and discharging the gate capacitor, and does not consume current in steady state. This allows the voltage divider module in the front stage to be implemented with a resistor of higher resistance value, thereby significantly reducing the static power consumption of the entire protection circuit itself. This is an important advantage for constantly powered vehicle lighting systems.

[0036] The enable (EN) pin of the driver module has a standard logic interface that is active high or active low. The MOSFET, as an open-drain output, can perfectly drive this type of pin directly without the need for additional level conversion or buffer circuits, thus simplifying system design.

[0037] In some exemplary embodiments, the switch module further includes: The second capacitor has its positive terminal electrically connected to the gate of the second MOS transistor, and its negative terminal grounded. The second Zener diode has its anode grounded and its cathode electrically connected to the gate of the second MOSFET.

[0038] Based on the above embodiment, the second capacitor is connected in parallel between the gate of the second MOSFET and ground, forming a low-pass filter network with the internal resistance of the gate drive source. This network absorbs and filters out high-frequency noise, voltage glitches, and switching transient interference conducted from the voltage divider module to the gate. Any brief voltage fluctuations are smoothed out by the second capacitor, ensuring that only continuous and effective level changes can alter the switching state of the second MOSFET, thereby suppressing malfunctions.

[0039] The negative terminal of the second Zener diode is connected to the gate of the second MOSFET, and the positive terminal is grounded, forming a reverse parallel clamping circuit. When the gate voltage rises and exceeds the Zener diode's regulation value, the second Zener diode will immediately break down and conduct, clamping the gate voltage at the level of the diode's voltage drop, thus reliably protecting the second MOSFET from overvoltage breakdown.

[0040] Automotive electrical systems are filled with broadband electromagnetic noise generated by relays, motors, ignition coils, etc. The second capacitor effectively bypasses this high-frequency noise, preventing it from being misinterpreted as a valid control signal by the gate of the second MOSFET, ensuring that the protection action is triggered only by genuine DC overvoltage. In the critical region where the input voltage approaches the protection threshold, the circuit may be sensitive to minor disturbances. The damping effect provided by the second capacitor can eliminate potential parasitic oscillations, resulting in clean and crisp state switching. The automotive environment contains high-voltage, high-energy transient pulses such as load drops. The second Zener diode provides a safe discharge path for these potentially fatal high voltages that may couple to the gate, directly preventing damage to the second MOSFET due to gate overvoltage.

[0041] During production and maintenance, static electricity from people or tools can directly impact circuit ports. The second Zener diode, as an integrated ESD protection device, significantly improves the circuit's ESD protection level, increasing production yield and product durability. With the clamping protection of the second Zener diode, the preceding voltage divider module (or positive feedback loop) no longer needs to worry about excessively high output voltage, resulting in fewer design constraints. The capacitance value of the second capacitor can be used as a design parameter to fine-tune the switching speed of the second MOSFET. Increasing the second capacitor slows down the switching edge, which helps reduce EMI radiation; decreasing the second capacitor speeds up the response.

[0042] The addition of the second capacitor and the second Zener diode makes the circuit performance less sensitive to the minute batch differences in the gate threshold voltage (Vth) of the second MOSFET and the minute parasitic parameter changes caused by the PCB layout, thus improving the consistency of product performance during mass production.

[0043] In some exemplary embodiments, the switch module further includes: The sixth resistor has its first end electrically connected to the controlled end of the drive module and its second end grounded. The third capacitor has its positive terminal electrically connected to the controlled terminal of the drive module, and its negative terminal grounded.

[0044] Based on the above embodiments, the sixth resistor, acting as a pull-down resistor with a defined resistance value, pulls the controlled terminal of the drive module to a clear and stable low level when the switching module is off. This eliminates the floating state of the node, prevents level uncertainty caused by noise coupling, and ensures that the drive module is in a defined off state. At the instant the switching module is turned on, it limits the current flowing from the controlled terminal of the drive module to ground, acting as a buffer. The pull-down effect of the sixth resistor ensures that the enable terminal of the drive module is at a clear logic low when the protection circuit is not activated, avoiding level drift caused by PCB leakage, parasitic parameters, etc., making the system behavior predictable.

[0045] The third capacitor and the sixth resistor are connected in parallel to form a first-order low-pass filter (RC filter). This filter absorbs and bypasses high-frequency interference, glitches, and ringing coupled from the switching module or power line to the drive enable pin, preventing them from falsely triggering the internal logic of the drive module. The RC time constant ensures that the voltage change at the controlled terminal is not instantaneous but rather changes gradually with an exponential curve. This softens the switching edge, providing the drive module with a soft-start or soft-stop signal, helping to suppress the resulting voltage overshoot and current surge. The enable pin of the drive module is typically sensitive to noise. The filter formed by the sixth resistor and the third capacitor thoroughly filters out conducted and coupled noise on the control path, ensuring that only true, stable level signals from the protection circuit can change the state of the drive module. Steep switching edges can stress the internal circuitry of the drive module. The gradually changing control signal introduced by the third capacitor makes the start-up and shutdown process of the drive module smoother, reducing the switching stress on the internal logic and power stage, and helping to improve the lifespan and reliability of the drive module itself.

[0046] The rapid start-up or shutdown of the drive module can cause disturbances on the power network due to its own current changes. A softened control edge can slow down the rate of current change, thereby reducing interference to the input power supply and improving the overall electromagnetic compatibility of the system. The RC time constant can be precisely adjusted by selecting the values ​​of the sixth resistor and the third capacitor. A stronger anti-interference capability can be achieved by increasing the time constant; a faster protection response can be achieved by decreasing the time constant. Different drive modules may have different internal structures, logic levels, and input characteristics for their enable pins. This RC network provides certain interface adaptation and drive capability adjustment functions, enhancing the versatility and compatibility of this protection circuit.

[0047] Secondly, embodiments of this application provide a vehicle that includes an overvoltage protection circuit.

[0048] Based on the above embodiments, the vehicle's electrical system, especially the battery power supply system, is prone to voltage fluctuations, such as engine start-stop and heavy load switching. The overvoltage protection with hysteresis function provided in this application can ensure that the vehicle lights, such as headlights, daytime running lights, and taillights, provide stable and flicker-free illumination under complex operating conditions, thereby improving driving safety at night or in adverse weather conditions. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a block diagram of an overvoltage protection circuit in one embodiment of this application; Figure 2 This is a block diagram of an overvoltage protection circuit in another embodiment of this application; Figure 3 This is a circuit diagram of an overvoltage protection circuit in another embodiment of this application.

[0051] Explanation of reference numerals in the attached diagram: 100, Overvoltage protection circuit; 110, Input terminal; 120, Voltage divider module; 121, First switch; 122, Second switch; 130, Switch module; 140, Driver module; R1, First resistor; R2, Second resistor; R3, Third resistor; R4, Fourth resistor; R5, Fifth resistor; R6, Sixth resistor; Q1, Transistor; Q2, First MOSFET; Q3, Second MOSFET; C1, First capacitor; C2, Second capacitor; C3, Third capacitor; ZD1, First Zener diode; ZD2, Second Zener diode. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0053] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0054] Furthermore, the use of terms such as "first," "second," etc., in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0055] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0056] Furthermore, the technical solutions of the various embodiments of this application can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this application.

[0057] Overvoltage protection circuits are commonly used in LED driver circuits. When the battery voltage exceeds the overvoltage protection point, the LED driver circuit shuts down, and the LED lights up again when the battery voltage returns to normal. However, the overvoltage protection point lacks hysteresis. If the battery voltage fluctuates around the overvoltage protection point, the LED driver circuit will restart frequently, causing the LED to flicker and affecting the lighting effect of the lamp.

[0058] To address this issue, this application designs a protection circuit that enables hysteresis protection for overvoltage protection even without MCU control, thereby preventing the light from flickering.

[0059] like Figure 1 As shown, the first aspect of this application provides an overvoltage protection circuit 100, which includes an input terminal 110, a voltage divider module 120, a switch module 130, and a drive module 140.

[0060] Input terminal 110 is used for electrical connection to a power supply, such as a vehicle battery. The first terminal of voltage divider module 120 is electrically connected to input terminal 110, and the second terminal of voltage divider module 120 outputs a detection voltage. The first terminal of switch module 130 is grounded, and the controlled terminal of switch module 130 is electrically connected to the second terminal of voltage divider module 120. The controlled terminal of drive module 140 is electrically connected to the second terminal of switch module 130, and drive module 140 is used to drive the vehicle lights to illuminate.

[0061] When the voltage at input terminal 110 is greater than or equal to the first threshold, the switch module 130 is turned off and the drive module 140 stops; when the voltage at input terminal 110 is less than or equal to the second threshold, the switch module 130 is turned on and the drive module 140 starts, and the first threshold is greater than the second threshold.

[0062] This application introduces a hysteresis voltage window to ensure that once the vehicle is shut down due to overvoltage, the power supply voltage must drop to a sufficiently low and safe level before restarting. This avoids repeated jumps at the critical point, thus maintaining stable and continuous headlight illumination. Especially during vehicle acceleration, deceleration, or power fluctuations caused by poor battery condition, it prevents uncomfortable flickering, improving visual comfort and safety for the driver and other road users. Furthermore, it avoids frequent switching between on and off states for the LED driver circuit and its components, such as power switches, inductors, and capacitors. Such switching generates thermal and electrical stress, which can reduce component lifespan over time. Stable switching behavior also protects the LED light source itself, preventing performance degradation or premature failure caused by frequent inrush currents.

[0063] Furthermore, this application eliminates the need for a microcontroller (MCU) and its peripheral circuits such as ADC, power supply, and programming interface, significantly reducing material costs and PCB area. The circuit structure is compact, consisting only of basic discrete components or simple ICs, eliminating the need for writing, debugging, and maintaining embedded software, thus shortening the development cycle. It also reduces the risks associated with MCU-related software failures, crashes, and electromagnetic compatibility issues, making the protection function more robust, hardware-based, and reliable.

[0064] Hysteresis inherently provides a natural noise margin, effectively filtering out transient glitches or spikes in the power line and preventing false triggering of overvoltage protection. This makes it particularly suitable for automotive electrical systems operating in complex electromagnetic environments. It perfectly matches the significant voltage fluctuations of automotive batteries during engine start-up and heavy load start-stop (such as air conditioning and power steering), ensuring stable operation of the headlights under these conditions. This overvoltage protection circuit 100 can be easily added as a standalone pre-stage protection unit to the front end of existing LED driver circuits.

[0065] In some embodiments, when the voltage at input terminal 110 increases from a second threshold and is less than a first threshold, the voltage division coefficient of voltage divider module 120 is the first voltage division coefficient. When the voltage at input terminal 110 is greater than or equal to the first threshold, the voltage division coefficient of voltage divider module 120 is the second voltage division coefficient. When the voltage at input terminal 110 decreases from the first threshold and is greater than the second threshold, the voltage division coefficient of voltage divider module 120 is the second voltage division coefficient. When the voltage at input terminal 110 is less than or equal to the second threshold, the voltage division coefficient of voltage divider module 120 is the first voltage division coefficient, and the first voltage division coefficient is less than the second voltage division coefficient.

[0066] The first resistor R1 and the second resistor R2 form a basic voltage divider network. The first switch 121 is connected in parallel across the first resistor R1, and the second switch 122 controls the state of the first switch 121. When the input voltage rises to the first threshold, the second switch 122 turns on, and then the first switch 121 also turns on, short-circuiting the first resistor R1 and increasing the voltage division factor. Conversely, when the voltage drops to the second threshold, both the first switch 121 and the second switch 122 turn off, and the voltage division factor returns to its original state. In other words, the voltage division factor of the voltage divider module 120 is not a fixed value; the ratio of the detected voltage to the input voltage is not a fixed value but automatically switches according to the current state of the circuit.

[0067] By precisely designing the first and second voltage divider coefficients, the overvoltage cutoff point and undervoltage recovery point can be set independently and accurately, ensuring that the width and position of the hysteresis window fully meet design requirements. The wide hysteresis voltage window, spanning several volts, provides the system with strong noise immunity; conventional ripple, switching noise, or transient interference on the power line cannot cross this window, thus eliminating false triggering and critical oscillations—a feature unmatched by fixed threshold circuits.

[0068] Furthermore, the entire detection-judgment-action-state retention process is completed entirely by hardware logic, forming a simple mechanical memory. Compared to MCU polling or ordinary comparator plus latch solutions, this is simpler, faster, and more reliable. The dynamic voltage divider mechanism allows the circuit to better adapt to the parameter tolerances of components, such as resistor accuracy. With proper design, even slight component deviations can ensure the existence of the hysteresis window and the realization of the function. The wide hysteresis window avoids frequent switching on and off at fault boundaries, such as unstable high voltages, reducing thermal shock and electrical stress on the power devices of the downstream LED driver, and extending the life of the entire lamp.

[0069] like Figure 2 As shown, in some embodiments, the voltage divider module 120 includes a first resistor R1, a second resistor R2, a first switch 121, and a second switch 122.

[0070] The first end of the first resistor R1 is electrically connected to the input terminal 110 as the first end of the voltage divider module 120. The second end of the first resistor R1 is electrically connected to the first end of the second resistor R2 as the second end of the voltage divider module 120. The second end of the second resistor R2 is grounded. The first end of the first switch 121 is electrically connected to the first end of the first resistor R1. The second end of the first switch 121 is also electrically connected to the second end of the first resistor R1. The controlled end of the second switch 122 is electrically connected to the first end of the first resistor R1. The first end of the second switch 122 is electrically connected to the controlled end of the first switch 121. The second end of the second switch 122 is grounded. The first switch 121 can be a discrete device such as a transistor Q1, a MOSFET, or a Zener diode. The second switch 122 can also be a discrete device such as a transistor Q1, a MOSFET, or a Zener diode.

[0071] When the voltage at input terminal 110 is greater than or equal to the first threshold, the second switch 122 is turned on, the first switch 121 is turned on, the first resistor R1 is short-circuited by the first switch 121, and the voltage division coefficient of the voltage divider module 120 increases; when the voltage at input terminal 110 is less than or equal to the second threshold, the second switch 122 is turned off, the first switch 121 is turned off, and the voltage divider module 120 restores its voltage division coefficient.

[0072] The circuit dynamically changes the voltage division ratio by short-circuiting the first resistor R1 through the first switch 121, while the second switch 122 controls the occurrence of this short-circuit behavior, forming a positive feedback or locking mechanism with memory function.

[0073] When the voltage at input terminal 110 is less than the first threshold, the second switch 122 is turned off, as the input voltage is insufficient to turn the second switch 122 on. Since the second switch 122 is off, the controlled terminal of the first switch 121 has no effective drive, and therefore the first switch 121 is also turned off. At this time, the voltage divider coefficient is relatively small, and the voltage divider network consists of a complete first resistor R1 and a second resistor R2 connected in series. A relatively high voltage is required at the detection point to reach the turn-off threshold.

[0074] When the voltage at input terminal 110 is greater than or equal to the first threshold, an overvoltage trigger lockout state is activated. At this time, the second switch 122 is turned on, providing drive current or voltage to the first switch 121, causing it to quickly saturate and turn on. Simultaneously, the first resistor R1 is short-circuited, and the voltage divider network is effectively composed only of the second resistor R2. The voltage divider coefficient increases, and even if the input voltage drops slightly, the voltage at the monitoring point remains high, and the circuit remains locked in the off state. Only when the input voltage drops to a lower second threshold will the second switch 122 de-conduct.

[0075] At this point, the second switch 122 is turned off. After the second switch 122 is turned off, the first switch 121 loses its drive and is also turned off. The first resistor R1 is reconnected to the voltage divider network, and the circuit returns to its initial state, waiting for the next overvoltage trigger.

[0076] By connecting or short-circuiting the first resistor R1 through the first switch 121, the voltage division coefficient changes, thus generating a clear hysteresis voltage window with strong anti-interference capability. The second switch 122 triggers the first switch 121, and the conduction of the first switch 121 maintains the conduction condition of the second switch 122, forming positive feedback. This ensures that the state switching is completed instantly and the state is stable, which is more direct and reliable than solutions relying on RC delay. Only two resistors and two switching devices are required, without any integrated circuits, resulting in lower material costs and PCB area. The wide hysteresis window makes it suitable for harsh operating conditions such as wide voltage fluctuations and load drops in automotive batteries (12V / 24V systems).

[0077] like Figure 3 As shown, in some embodiments, the first switch 121 includes a transistor Q1, the emitter of the transistor Q1 is electrically connected to the first terminal of the first switch 121 as the first terminal, the collector of the transistor Q1 is electrically connected to the second terminal of the first switch 121 as the second terminal, and the base of the transistor Q1 is electrically connected to the first terminal of the first resistor R1 as the controlled terminal of the second switch 122.

[0078] The second switch 122 includes a first MOSFET Q2. The drain of the first MOSFET Q2 is electrically connected to the first terminal of the first resistor R1 as the controlled terminal of the second switch 122. The source of the first MOSFET Q2 is grounded as the second terminal of the second switch 122. The gate of the first MOSFET Q2 is electrically connected to the controlled terminal of the first switch 121 as the first terminal of the second switch 122.

[0079] When the input voltage is lower than its turn-on threshold, the first MOSFET Q2 is turned off. Since the first MOSFET Q2 is off, the base of transistor Q1 is pulled high, but at this time the base-emitter voltage is insufficient to turn on transistor Q1. Transistor Q1 is turned off, and the first resistor R1 is fully connected to the voltage divider network.

[0080] When the input voltage increases to the point where the detection voltage reaches and exceeds the gate threshold voltage of the first MOSFET Q2, Q2 quickly turns on, and its drain potential is pulled down to near ground. The conduction of Q2 pulls down the base potential of transistor Q1, causing Q1 to receive a forward bias and become deeply saturated. When Q1 is saturated, its collector-emitter saturation voltage drop is very small, typically 0.1-0.3V, equivalent to a near-ideal switch short-circuiting the first resistor R1. At this point, the voltage divider ratio increases sharply, positive feedback is formed, Q2 remains on, and the conduction of Q2 maintains the conduction of Q1, stabilizing the circuit in the off state.

[0081] When the input voltage drops low enough, the first MOSFET Q2 will turn off even if the voltage divider factor increases. After the first MOSFET Q2 turns off, the base potential of transistor Q1 is pulled up, and transistor Q1 exits saturation and turns off. When the first resistor R1 is reconnected, transistor Q1 turns off, the voltage divider network returns to normal, and the circuit resets.

[0082] Transistor Q1 operates in saturation switching mode, and its CE saturation voltage drop is low. When it is used to short-circuit the first resistor R1, it introduces almost no additional voltage drop, ensuring that the voltage division coefficient changes significantly in the protection state, thereby generating the widest possible hysteresis voltage window and achieving theoretically optimal anti-interference capability.

[0083] The first MOSFET Q2 is a voltage-controlled device with extremely low gate drive current and very fast switching speed, enabling it to respond quickly to overvoltage signals. Transistor Q1 also switches rapidly between deep saturation and cutoff. The combination of these two transistors results in an extremely short response time for the entire protection circuit. The high input impedance of the first MOSFET Q2 makes its load effect on the preceding voltage divider network almost negligible, allowing the voltage at the divider point to be set very precisely without being pulled low by the connection of the first MOSFET Q2, thus improving threshold accuracy. Simultaneously, when the first MOSFET Q2 is turned on, it effectively pulls the base of transistor Q1 low to ground, providing a strong turn-off drive for transistor Q1.

[0084] The first MOSFET Q2 serves as both a detector and a trigger, while the transistor Q1 functions as a power actuator. This clear functional division reduces mutual interference and improves circuit stability.

[0085] The ultra-low voltage drop of transistor Q1 during saturation ensures that the voltage at the detection point can be pulled to an extremely high level. This provides a very stable guarantee for maintaining the conduction state of the first MOSFET Q2, making the circuit's latch-up effect robust and its anti-interference capability strong. Both transistor Q1 and the MOSFET are general-purpose, inexpensive semiconductor devices with wide supply channels and low cost.

[0086] like Figure 3 As shown, in some embodiments, the voltage divider module 120 further includes a third resistor R3, a first capacitor C1, a fourth resistor R4, and a fifth resistor R5.

[0087] The first terminal of the third resistor R3 is electrically connected to the emitter of transistor Q1, and the second terminal of the second resistor R2 is electrically connected to the collector of transistor Q1. The positive terminal of the first capacitor C1 is electrically connected to the first terminal of the third resistor R3, and the negative terminal of the first capacitor C1 is electrically connected to the second terminal of the third resistor R3. The first terminal of the fourth resistor R4 is electrically connected to the first terminal of the third resistor R3, and the second terminal of the fourth resistor R4 is electrically connected to the drain of the first MOSFET Q2. The first terminal of the fifth resistor R5 is electrically connected to the drain of the first MOSFET Q2, and the second terminal of the fifth resistor R5 is electrically connected to the base of transistor Q1.

[0088] The third resistor R3 and the first capacitor C1 form an emitter decoupling and delay network. The third resistor R3 is connected in series with the emitter of transistor Q1, introducing local current negative feedback. The first capacitor C1 is connected in parallel across the third resistor R3. When transistor Q1 attempts to turn on, the emitter current generates a voltage drop across the third resistor R3, slowing down the establishment speed of the base-emitter voltage of transistor Q1, thereby suppressing the instantaneous turn-on current of transistor Q1. The first capacitor C1 provides a low-impedance path for transient current, assisting in this smooth process, optimizing the switching dynamic characteristics of transistor Q1, and preventing current surges.

[0089] The fourth resistor R4 provides a defined pull-up path and isolation. It is connected between input terminal 110 and the drain of the first MOSFET Q2 (i.e., the detection point). When the first MOSFET Q2 is off, it provides a defined pull-up path to its drain, ensuring the potential at that point remains stable at a high level and avoiding the uncertainty noise introduced by the floating state. As the impedance between the detection point and the power supply, the fourth resistor R4, together with the second resistor R2, precisely sets the initial voltage division factor. Simultaneously, when the first MOSFET Q2 is on, it limits the current flowing from the power supply into the drain of the first MOSFET Q2.

[0090] The fifth resistor, R5, is used for gate current limiting and drive regulation. It is connected in series between the drain of the first MOSFET Q2 and the base of the transistor Q1 to prevent excessive current from flowing into the base of transistor Q1 when Q2 is turned on, thus protecting both transistors Q1 and Q2. The fifth resistor, R5, and the input impedance of transistor Q1 together determine the driving capability of the first MOSFET Q2 on transistor Q1, thereby affecting the speed of state switching and the accuracy of the hysteresis voltage. These are key parameters for adjusting the dynamic performance of the circuit.

[0091] The RC network formed by the third resistor R3 and the first capacitor C1, along with the impedance of the entire voltage divider network, constitutes a low-pass filter that effectively attenuates high-frequency switching noise, EMI interference, and instantaneous voltage spikes on the power line. This ensures that only continuous and genuine overvoltage events trigger the protection, completely eliminating malfunctions caused by noise. At the critical point of state switching, the circuit may experience high-frequency oscillations due to parasitic parameters. Resistors such as the third resistor R3 and the fifth resistor R5 increase damping, effectively suppressing this potential instability and ensuring a clean and crisp state switching. The buffering effect of the third resistor R3 and the first capacitor C1 makes the turn-on and turn-off process of transistor Q1 smoother. This significantly reduces the current stress and switching losses experienced by transistor Q1 and the first MOSFET Q2 during switching, and also reduces the resulting electromagnetic radiation (EMI). For protection circuits that need to frequently respond to power fluctuations, this directly improves the reliability of long-term operation.

[0092] The β value of transistor Q1 and the threshold voltage of the first MOSFET Q2 can vary in different batches and temperatures. The negative feedback effect of the third resistor R3 can stabilize the conduction behavior of transistor Q1, while the carefully selected values ​​of the fourth resistor R4 and the fifth resistor R5 can relax the requirements for specific parameters of the first MOSFET Q2 and transistor Q1, improving the consistency of circuit performance during mass production.

[0093] By adjusting resistors such as the fifth resistor R5, the gain of the positive feedback loop can be controlled, thereby keeping the state switching speed within a reasonable range that is fast enough to provide protection but not too abrupt to avoid overshoot and oscillation. The fourth resistor R4 ensures a clear voltage level at the drain of the first MOSFET Q2 in the off-state, avoiding threshold drift caused by ambiguous input impedance 110. This makes the circuit's turn-on and turn-off thresholds more stable and predictable. Switching speed and EMI performance can be optimized by adjusting the values ​​of the third resistor R3 and the first capacitor C1. The protection point can be precisely set by fine-tuning the ratio of the fourth resistor R4, the first resistor R1, and the second resistor R2. The width of the hysteresis voltage can be fine-tuned by changing the fifth resistor R5.

[0094] like Figure 3 As shown, in some embodiments, the voltage divider module 120 further includes a first Zener diode ZD1, the anode of the first Zener diode ZD1 being electrically connected to the first terminal of the first resistor R1, and the cathode of the first Zener diode ZD1 being electrically connected to the input terminal 110.

[0095] The first Zener diode ZD1 is connected in reverse between the input terminal 110 and the upper end of the first resistor R1. When the voltage rise at the input terminal 110 exceeds the sum of the Zener voltage of the first Zener diode ZD1 and its forward voltage drop, the first Zener diode ZD1 enters the breakdown Zener region. The first Zener diode ZD1 breaks down, and the voltage at its positive terminal is clamped, maintaining a fixed offset relative to the input voltage regardless of input voltage fluctuations.

[0096] The driving condition of the controlled terminal of the first switch 121 is no longer directly related to the absolute value of the fluctuating input voltage, but is related to the clamping voltage. This makes the input voltage threshold that triggers the first switch 121 to turn on mainly determined by the stable clamping voltage, rather than by the resistance ratio or transistor that is susceptible to temperature and process influence.

[0097] By selecting diodes with different voltage regulation values, the same circuit framework can be easily adapted to different system voltage platforms, such as 12V automotive systems and 24V truck systems, or different protection margins can be set, resulting in high design flexibility.

[0098] The resistance value changes with temperature, causing a change in the voltage division ratio. The temperature characteristics of the first Zener diode ZD1 are known and stable, and a temperature-compensated Zener diode can be selected to obtain better temperature stability. This ensures that the protection circuit's operating threshold hardly drifts within the automotive-grade temperature range of -40°C to +125°C, maintaining consistent and reliable performance.

[0099] The Zener diode's breakdown characteristic has a relatively sharp inflection point, which provides a steeper and cleaner drive signal for driving the first switch 121. This makes the state switching of the entire protection circuit faster and more decisive, reducing hesitation or instability near the critical point. The Zener diode itself has a certain absorption and clamping effect on transient high-voltage pulses at the input terminal 110, providing additional protection for the preceding circuitry.

[0100] like Figure 3 As shown, in some embodiments, the switching module 130 includes a second MOSFET Q3. The drain of the second MOSFET Q3 is electrically connected to the controlled terminal of the driving module 140 as the second terminal of the switching module 130. The source of the second MOSFET Q3 is grounded as the first terminal of the switching module 130. The gate of the second MOSFET Q3 is electrically connected to the second terminal of the voltage divider module 120 as the controlled terminal of the switching module 130.

[0101] The gate of the MOSFET is insulated, resulting in high DC input impedance. The detection voltage output by the voltage divider module 120 is almost unloaded by the gate of the second MOSFET Q3. Due to the absence of a load effect, the turn-off and turn-on thresholds set by the voltage divider resistors maintain high accuracy and stability. As a voltage-controlled device, the charging and discharging of the gate charge controls its switching speed, making overvoltage protection extremely rapid and minimizing the time that subsequent drive circuits are exposed to abnormally high voltages.

[0102] When the second MOSFET Q3 is turned on, the on-resistance between its source and drain can be reduced to the milliohm level. Under normal conditions when the lamp is on, the additional voltage drop and power loss introduced by the second MOSFET Q3 in the grounding or enable circuit of the driver module 140 are almost negligible, resulting in high system efficiency.

[0103] Driving the second MOSFET Q3 only requires charging and discharging the gate capacitor, and does not consume current in steady state. This allows the voltage divider module 120 in the front stage to be implemented with a resistor of higher resistance value, thereby significantly reducing the static power consumption of the entire protection circuit itself. This is an important advantage for a vehicle lighting system that is constantly powered.

[0104] The enable (EN) pin of the driver module 140 has a standard logic interface that is active high or active low. The MOSFET, as an open-drain output, can perfectly drive this type of pin directly without the need for additional level conversion or buffer circuits, thus simplifying system design.

[0105] like Figure 3 As shown, in some embodiments, the switching module 130 further includes a second capacitor C2 and a second Zener diode ZD2.

[0106] The positive terminal of the second capacitor C2 is electrically connected to the gate of the second MOSFET Q3, and the negative terminal of the second capacitor C2 is grounded. The positive terminal of the second Zener diode ZD2 is grounded, and the negative terminal of the second Zener diode ZD2 is electrically connected to the gate of the second MOSFET Q3.

[0107] The second capacitor C2 is connected in parallel between the gate of the second MOSFET Q3 and ground. Combined with the internal resistance of the gate drive source, it forms a low-pass filter network that absorbs and filters out high-frequency noise, voltage glitches, and switching transient interference conducted from the voltage divider module 120 to the gate. Any brief voltage fluctuations are smoothed out by the second capacitor C2, ensuring that only continuous and effective level changes can alter the switching state of the second MOSFET Q3, thereby suppressing malfunctions.

[0108] The cathode of the second Zener diode ZD2 is connected to the gate of the second MOSFET Q3, and the anode is grounded, forming a reverse parallel clamping circuit. When the gate voltage rises and exceeds the Zener diode ZD2's regulation value, the second Zener diode ZD2 will immediately break down and conduct, clamping the gate voltage at the level of an additional diode voltage drop, thus reliably protecting the second MOSFET Q3 from overvoltage breakdown.

[0109] The automotive electrical system is filled with broadband electromagnetic noise generated by relays, motors, ignition coils, etc. The second capacitor C2 effectively bypasses this high-frequency noise, preventing it from being misinterpreted as a valid control signal by the gate of the second MOSFET Q3, ensuring that the protection action is triggered only by genuine DC overvoltage. In the critical region where the input voltage approaches the protection threshold, the circuit may be sensitive to minor disturbances. The damping effect provided by the second capacitor C2 can eliminate potential parasitic oscillations, resulting in clean and crisp state switching. The automotive environment contains high-voltage, high-energy transient pulses such as load drops. The second Zener diode ZD2 provides a safe discharge path for these potentially fatal high voltages that could couple to the gate, directly preventing damage to the second MOSFET Q3 due to gate overvoltage.

[0110] During production and maintenance, static electricity from the human body or tools may directly impact circuit ports. The second Zener diode ZD2, as an integrated ESD protection device, significantly improves the circuit's ESD protection level, increasing production yield and product durability. With the clamping protection of the second Zener diode ZD2, the pre-stage voltage divider module 120 (or positive feedback loop) no longer needs to worry about excessively high output voltage, resulting in fewer design constraints. The capacitance value of the second capacitor C2 can be used as a design parameter to fine-tune the switching speed of the second MOSFET Q3. Increasing the capacitance of C2 slows down the switching edge, which helps reduce EMI radiation; decreasing the capacitance of C2 speeds up the response.

[0111] The addition of the second capacitor C2 and the second Zener diode ZD2 makes the circuit performance less sensitive to the slight batch differences in the gate threshold voltage of the second MOSFET Q3 and the slight parasitic parameter changes caused by the PCB layout, thus improving the consistency of product performance during mass production.

[0112] like Figure 3 As shown, in some embodiments, the switch module 130 further includes a sixth resistor R6 and a third capacitor C3. The first end of the sixth resistor R6 is electrically connected to the controlled end of the drive module 140, and the second end of the sixth resistor R6 is grounded. The positive terminal of the third capacitor C3 is electrically connected to the controlled end of the drive module 140, and the negative terminal of the third capacitor C3 is grounded.

[0113] The sixth resistor, R6, acts as a pull-down resistor with a defined resistance value. When the switch module 130 is turned off, R6 clearly and stably pulls the controlled terminal of the drive module 140 to a low level, eliminating the floating state of this node and preventing level uncertainty caused by noise coupling, thus ensuring that the drive module 140 is in a defined off state. At the instant the switch module 130 is turned on, it limits the current flowing from the controlled terminal of the drive module 140 to ground, acting as a buffer. The pull-down effect of the sixth resistor R6 ensures that when the protection circuit is not activated, the enable terminal of the drive module 140 is in a defined logic low, avoiding level drift caused by PCB leakage, parasitic parameters, etc., making the system behavior predictable.

[0114] The third capacitor C3 and the sixth resistor R6 are connected in parallel to form a first-order low-pass filter (RC filter). This filter absorbs and bypasses high-frequency interference, glitches, and ringing coupled from the switching module 130 or the power line to the drive enable pin, preventing them from falsely triggering the internal logic of the drive module 140. The RC time constant ensures that the voltage change at the controlled terminal does not jump instantaneously, but rather changes gradually with an exponential curve. This softens the switching edge, providing the drive module 140 with a soft-start or soft-stop signal, which helps suppress the resulting voltage overshoot and current surge. The enable pin of the drive module 140 is typically sensitive to noise. The filter formed by the sixth resistor R6 and the third capacitor C3 can completely filter out conducted noise and coupled noise on the control path, ensuring that only a true, stable level signal from the protection circuit can change the state of the drive module 140. The steeper switching edge may cause stress to the internal circuitry of the drive module 140. The gradually changing control signal introduced by the third capacitor C3 makes the turn-on and turn-off process of the drive module 140 smoother, reduces the switching stress on the internal logic and power stage, and helps to improve the service life and reliability of the drive module 140 itself.

[0115] The rapid turn-on or turn-off of the drive module 140 can cause disturbances on the power network due to its own current changes. A softened control edge can slow down the rate of current change, thereby reducing interference to the input power supply and improving the overall electromagnetic compatibility of the system. The RC time constant can be precisely adjusted by selecting the values ​​of the sixth resistor R6 and the third capacitor C3. A stronger anti-interference capability can be achieved by increasing the time constant; a faster protection response can be achieved by decreasing the time constant. Different drive modules 140 may have different internal structures, logic levels, and input characteristics for their enable pins. This RC network provides certain interface adaptation and drive capability adjustment functions, enhancing the versatility and compatibility of this protection circuit.

[0116] A second aspect of this application provides a vehicle, which includes an overvoltage protection circuit 100.

[0117] The vehicle's electrical system, especially the battery power supply system, is prone to voltage fluctuations, such as engine start-stop and heavy load switching. The overvoltage protection with hysteresis function provided in this application ensures that the vehicle lights, such as headlights, daytime running lights, and taillights, provide stable and flicker-free illumination under complex operating conditions, thereby improving driving safety at night or in inclement weather.

[0118] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural transformations made based on the concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. An overvoltage protection circuit, characterized by, The utility model relates to a kind of vehicle lamp driving circuit, including: Input, for with power supply electric connection; Voltage division module, the first end of voltage division module is electrically connected with the input, the second end of voltage division module outputs detection voltage; Switching module, the first end of switching module is grounded, the controlled end of switching module is electrically connected with the second end of voltage division module; Drive module, the controlled end of drive module is electrically connected with the second end of switching module, and drive module is used to drive car light to light up; Wherein, the voltage of the input is greater than or equal to the first threshold value, the switching module is turned off, and the drive module stops; The voltage of the input is less than or equal to the second threshold value, the switching module is turned on, the drive module is started, and the first threshold value is greater than the second threshold value.

2. The overvoltage protection circuit of claim 1, wherein, When the voltage of the input is increased from the second threshold value and less than the first threshold value, the voltage division coefficient of the voltage division module is the first voltage division coefficient;When the voltage of the input is greater than or equal to the first threshold value, the voltage division coefficient of the voltage division module is the second voltage division coefficient;When the voltage of the input is reduced from the first threshold value and greater than the second threshold value, the voltage division coefficient of the voltage division module is the second voltage division coefficient;When the voltage of the input is less than or equal to the second threshold value, the voltage division coefficient of the voltage division module is the first voltage division coefficient, and the first voltage division coefficient is less than the second voltage division coefficient.

3. The overvoltage protection circuit of claim 1, wherein, The voltage division module includes: First resistor, the first end of first resistor is electrically connected with the input as the first end of voltage division module; Second resistor, the second end of first resistor is electrically connected with the second resistor as the second end of voltage division module, and the second end of second resistor is grounded; First switch, the first end of first switch is electrically connected with the first end of first resistor, and the second end of first switch is electrically connected with the second end of first resistor; Second switch, the controlled end of second switch is electrically connected with the first end of first resistor, the first end of second switch is electrically connected with the controlled end of first switch, and the second end of second switch is grounded; Wherein, the voltage of the input is greater than or equal to the first threshold value, the second switch is turned on, the first switch is turned on, the first resistor is short-circuited by the first switch, and the voltage division coefficient of the voltage division module increases;The voltage of the input is less than or equal to the second threshold value, the second switch is turned off, the first switch is turned off, and the voltage division coefficient of the voltage division module is restored.

4. The overvoltage protection circuit of claim 3, wherein, The first switch includes a triode, the emitter of the triode is electrically connected with the first end of the first resistor as the first end of the first switch, the collector of the triode is electrically connected with the second end of the first resistor as the second end of the first switch, and the base of the triode is electrically connected with the first end of the first resistor as the controlled end of the second switch. The second switch comprises a first MOS tube, a drain of the first MOS tube is electrically connected with the first end of the first resistor as a controlled end of the second switch, a source of the first MOS tube is grounded as a second end of the second switch, and a gate of the first MOS tube is electrically connected with the controlled end of the first switch as a first end of the second switch.

5. The overvoltage protection circuit of claim 4, wherein, The voltage dividing module further comprises: a third resistor, a first end of the third resistor is electrically connected with the emitter of the triode, and a second end of the second resistor is electrically connected with the collector of the triode; a first capacitor, a positive pole of the first capacitor is electrically connected with the first end of the third resistor, and a negative pole of the first capacitor is electrically connected with a second end of the third resistor; a fourth resistor, a first end of the fourth resistor is electrically connected with the first end of the third resistor, and a second end of the fourth resistor is electrically connected with the drain of the first MOS tube; a fifth resistor, a first end of the fifth resistor is electrically connected with the drain of the first MOS tube, and a second end of the fifth resistor is electrically connected with the base of the triode.

6. The overvoltage protection circuit of claim 3, wherein, The voltage dividing module further comprises a first zener diode, a positive pole of the first zener diode is electrically connected with the first end of the first resistor, and a negative pole of the first zener diode is electrically connected with the input end.

7. The overvoltage protection circuit of claim 1, wherein, The switch module comprises a second MOS tube, a drain of the second MOS tube is electrically connected with the controlled end of the driving module as a second end of the switch module, a source of the second MOS tube is grounded as a first end of the switch module, and a gate of the second MOS tube is electrically connected with the controlled end of the switch module as a second end of the voltage dividing module.

8. The overvoltage protection circuit of claim 7, wherein, The switch module further comprises: a second capacitor, a positive pole of the second capacitor is electrically connected with the gate of the second MOS tube, and a negative pole of the second capacitor is grounded; a second zener diode, a positive pole of the second zener diode is grounded, and a negative pole of the second zener diode is electrically connected with the gate of the second MOS tube.

9. The overvoltage protection circuit of claim 1, wherein, The switch module further comprises: a sixth resistor, a first end of the sixth resistor is electrically connected with the controlled end of the driving module, and a second end of the sixth resistor is grounded; a third capacitor, a positive pole of the third capacitor is electrically connected with the controlled end of the driving module, and a negative pole of the third capacitor is grounded.

10. A vehicle characterized by comprising: An overvoltage protection circuit comprising the overvoltage protection circuit according to any one of claims 1-9.

Images