A dimming circuit and dimming system

Abstract

This application provides a dimming circuit and a dimming system. The dimming circuit includes: a power supply module for providing power to an LED string, and a switching transistor that controls the current flowing through the LED string according to a dimming signal; a detection module for detecting the circuit parameters of the switching transistor and generating a control signal; and a control module for receiving the control signal and adjusting the transmission state of the dimming signal. By introducing the detection module and the control module, a complete protection mechanism of detection, decision-making, and execution is constructed. It can continuously detect the circuit parameters of the switching transistor and directly control the operating state of the switching transistor based on these circuit parameters. This allows the circuit to no longer rely solely on back-end overcurrent or overvoltage protection, but to directly intervene in the health status of the core power device, the switching transistor, achieving a fundamental shift from passively responding to the consequences of faults to actively preventing device damage.

Description

Technical Field

[0001] This application relates to the field of electronic circuit technology, and more specifically, to a dimming circuit and dimming system. Background Technology

[0002] In the field of LED driver applications, in order to achieve LED brightness adjustment (such as the gradual brightening and dimming function of car headlights), a switching transistor connected in series with the LED string is usually set in the driver circuit, and the switching transistor is controlled by the pulse width modulation (PWM) signal to precisely control the average current flowing through the LED string.

[0003] However, existing dimming circuits have a significant reliability flaw: when the LED string experiences an unexpected output short circuit, the circuit lacks a fast and effective protection mechanism. In a short-circuit state, the system maintains a huge current output, and the switching devices responsible for current control will be subjected to electrical and thermal stresses far exceeding their rated capabilities. This continuous overstress state will rapidly lead to overheating and permanent damage to the switching devices, ultimately causing the entire dimming circuit to fail. Utility Model Content

[0004] In view of this, the purpose of this application is to provide a dimming circuit and dimming system to overcome the problems in the prior art.

[0005] In a first aspect, embodiments of this application provide a dimming circuit for receiving a dimming signal to adjust the brightness of an LED string, including a power supply module for providing power to the LED string, and a switching transistor for controlling the current flowing through the LED string according to the dimming signal. The dimming circuit further includes: The detection module is used to detect circuit parameters and generate control signals; wherein the control signals include a shutdown signal or an operating signal. A control module is used to receive control signals and adjust the transmission state of the dimming signals; If the detection module generates a working signal, the control module allows the transmission of the dimming signal to control the switching transistor to be in the on state; if the detection module generates the off signal, the control module blocks the transmission of the dimming signal to control the switching transistor to be in the off state. In the off state, the control module continues to receive control signals after waiting for a preset time.

[0006] In some technical solutions of this application, the aforementioned power module is used to provide electrical energy at a given voltage. The detection module is connected to a preset first position of the switching transistor and is used to detect the circuit parameters of the first position of the switching transistor. Alternatively, the power module can be used to provide electrical energy at various voltages; The detection module is connected to a preset second position of the switching transistor and is used to detect the circuit parameters of the second position of the switching transistor; wherein the first position and the second position are different positions.

[0007] In some technical solutions of this application, the above-mentioned detection module includes: a voltage divider circuit and a voltage comparison circuit; The voltage divider circuit is used to divide the electrical energy supplied to the power module according to the voltage division ratio to obtain the second voltage of the switching transistor; wherein the voltage division ratio changes with the voltage of the electrical energy. The voltage comparison circuit is used to compare the second voltage at the second position with the second reference voltage, and generate a shutdown signal when the second voltage is lower than the second reference voltage, and generate an operating signal when the second voltage is higher than the second reference voltage.

[0008] In some technical solutions of this application, the aforementioned switching transistor includes a PMOS transistor; The detection module is connected to the source of the PMOS transistor and is used to detect a first voltage between the source and drain of the PMOS transistor; when the first voltage is lower than a first threshold range, a turn-off signal is generated; when the first voltage rises to the first threshold range, a turn-on signal is generated.

[0009] In some technical solutions of this application, the aforementioned switching transistor includes a PMOS transistor; The detection module is connected to the drain of the PMOS transistor and is used to detect the second voltage between the drain of the PMOS transistor and ground when the dimming signal is high; generate a turn-off signal when the second voltage is lower than a second threshold range; and generate a working signal when the second voltage rises to the second threshold range.

[0010] In some technical solutions of this application, the above-mentioned detection module includes: a fixed threshold circuit and a voltage comparison circuit; The fixed threshold circuit is used to generate a fixed first reference voltage; The voltage comparison circuit is used to compare a first voltage at a first position with a first reference voltage, and generate a shutdown signal when the first voltage is lower than the first reference voltage, and generate an operating signal when the first voltage is higher than the first reference voltage.

[0011] In some technical solutions of this application, the fixed threshold circuit includes a current-limiting resistor and a Zener diode; the voltage comparison circuit includes a comparator.

[0012] In some technical solutions of this application, the above-mentioned logic control circuit includes a logic AND gate, the voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor; the voltage comparison circuit includes a comparator.

[0013] In some technical solutions of this application, the control module includes a third NMOS transistor, a fourth NMOS transistor, and a delay unit.

[0014] Secondly, embodiments of this application provide a dimming system, including the dimming circuit and control chip described above; the control chip is used to output a control signal, which is used to adjust the brightness of the LED string.

[0015] The technical solutions provided by the embodiments of this application may include the following beneficial effects: This application provides a dimming circuit for receiving dimming signals to control the brightness adjustment of an LED string. The dimming circuit includes: a power supply module for providing power to the LED string; a switching transistor connected to the current path formed by the power supply module and the LED string, for receiving the dimming signal, controlling the current flowing through the LED string, and thus adjusting the brightness; a detection module connected to a preset position of the switching transistor for detecting the circuit parameters of the switching transistor and generating a control signal; wherein the control signal includes an off signal or an on signal; and a control module for adjusting the operating state of the switching transistor by controlling the transmission state of the dimming signal. If the detection module generates an on signal, the control module allows the transmission of the dimming signal to control the switching transistor to be in an on state; if the detection module generates an off signal, the control module blocks the transmission of the dimming signal to control the switching transistor to be in an off state; the control module allows the transmission of the dimming signal after waiting for a preset time; if the detection module still generates an off signal, the control module blocks the transmission of the dimming signal and waits again.

[0016] This application establishes a complete protection mechanism encompassing detection, decision-making, and execution by introducing detection and control modules. It continuously monitors the circuit parameters of the switching transistor and directly controls its operating state based on these parameters. This allows the circuit to move beyond relying solely on downstream overcurrent or overvoltage protection, enabling direct intervention in the health of the core power device—the switching transistor—achieving a fundamental shift from passively responding to fault consequences to proactively preventing device damage.

[0017] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of a dimming circuit provided in an embodiment of this application is shown; Figure 2 This paper shows a schematic diagram of a PMOS driving circuit under MTQ6111 provided in an embodiment of this application; Figure 3 This illustration shows a fixed threshold circuit and a voltage comparison circuit provided in an embodiment of this application; Figure 4 This illustration shows a voltage divider circuit and a voltage comparator circuit provided in an embodiment of this application; Figure 5 This paper presents a schematic diagram of an output current waveform without using a dimming circuit, provided in an embodiment of this application. Figure 6 This illustration shows a schematic diagram of an output current waveform using a dimming circuit, as provided in an embodiment of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the accompanying drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0021] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0022] It should be noted that the term "comprising" will be used in the embodiments of this application to indicate the presence of the features declared thereafter, but does not exclude the addition of other features.

[0023] In the field of LED driver applications, in order to achieve LED brightness adjustment (such as the gradual brightening and dimming function of car headlights), a switching transistor connected in series with the LED string is usually set in the driver circuit, and the switching transistor is controlled by the pulse width modulation (PWM) signal to precisely control the average current flowing through the LED string.

[0024] However, existing dimming circuits have a significant reliability flaw: when the LED string experiences an unexpected output short circuit, the circuit lacks a fast and effective protection mechanism. In a short-circuit state, the system maintains a huge current output, and the switching devices responsible for current control will be subjected to electrical and thermal stresses far exceeding their rated capabilities. This continuous overstress state will rapidly lead to overheating and permanent damage to the switching devices, ultimately causing the entire dimming circuit to fail.

[0025] Based on this, embodiments of this application provide a dimming circuit and a dimming system. Some implementation methods of this application are described in detail below. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] like Figure 1 As shown in the illustration, this application provides a dimming circuit, including: an LED string for brightness adjustment; a switching transistor for controlling the current flowing through the LED string; a power supply module for providing electrical energy; a detection module connected to a preset position of the switching transistor for detecting the circuit parameters of the switching transistor and generating a control signal; wherein the control signal includes an off signal or an on signal; a control module for adjusting the operating state of the switching transistor by controlling the transmission state of the dimming signal; wherein if the detection module generates an on signal, the control module allows the transmission of the dimming signal to control the switching transistor to be in an on state; if the detection module generates an off signal, the control module blocks the transmission of the dimming signal to control the switching transistor to be in an off state; the control module allows the transmission of the dimming signal after waiting for a preset time; if the detection module still generates an off signal, the control module blocks the transmission of the dimming signal and waits again.

[0027] The output of the power module is connected to the input of the switching transistor, and the output of the switching transistor is connected to the positive terminal of the LED string. The negative terminal of the LED string is grounded, thus forming a complete circuit. The detection module's detection terminal is connected across a specific position of the switching transistor to detect its circuit parameters. The control module's control output terminal is directly connected to the control terminal of the switching transistor, forming an independent protection control loop. This connection architecture allows the protection module to detect the power path status in real time and, when necessary, override the normal PWM dimming signal to directly control the switching transistor's on / off state, thereby achieving intelligent protection of the system.

[0028] Here, an LED string refers to a load consisting of multiple light-emitting diodes (LEDs) or at least one LED, whose brightness can be varied by adjusting the average current. For example, a single LED is used in automotive lighting, while multiple LEDs are used in LCD backlight systems. In both of these applications, the brightness of the LED string is adjusted via an external dimming signal, such as a PWM control signal. This PWM signal is generated by an independent dimming controller and directly controls the on / off state of the switching transistors, thereby regulating the average current flowing through the LED string.

[0029] The switching transistor here is connected in series in the current path of the LED string, and its on or off state directly determines the current flowing through the LED string. This device is preferably a metal-oxide-semiconductor field-effect transistor (MOSFET), but depending on the circuit topology, a PMOS (for high-side drive) or NMOS (for low-side drive) can be selected, or a bipolar junction transistor (BJT) or other semiconductor switching devices can also be used. It is worth emphasizing that the switching transistor is under dual control: under normal operation, it is controlled by the PWM dimming signal, and under fault conditions, it is forcibly controlled by the protection module.

[0030] The power module here refers to the unit that provides electrical energy to the entire system, which converts the input voltage into a target voltage suitable for the operation of the LED string. This module can be a switching power supply (such as SEPIC, Buck, Boost, etc. topologies) or a linear power supply.

[0031] The detection module here collects circuit parameters of the switching transistor in real time (electrical parameters that directly or indirectly reflect whether the switching transistor is in the normal operating range or the dangerous fault range, including but not limited to: the voltage and current of the switching transistor itself, or the voltage and current of circuit nodes connected in series or parallel with the switching transistor). Based on the collected circuit parameters, it generates control signals, including turn-off signals and turn-on signals. The generated control signals are then sent to the control module, which executes corresponding control actions based on the received control signals. The control module's control actions include adjusting the operating state of the switching transistor by controlling the transmission state of the dimming signal. Controlling the transmission state of the dimming signal includes shielding the transmission of the dimming signal and allowing the transmission of the dimming signal.

[0032] Specifically, when the circuit starts working, if the detection module generates a working signal, it indicates that the circuit parameters of the switching transistor are within the normal range and no faults such as short circuits are detected. At this time, the control module executes normal control logic: allowing the dimming signal to be transmitted to the control terminal of the switching transistor, while controlling the switching transistor to be in the on state, so that the switching transistor can respond to the dimming signal to perform normal conduction and shutdown operations, thereby achieving precise adjustment of the brightness of the LED string. Conversely, when the detection module detects abnormal circuit parameters and generates a shutdown signal, the control module will immediately execute protective control logic. This protective logic specifically involves: shielding the transmission of the dimming signal, that is, cutting off the control path of the dimming signal to the switching transistor, thereby controlling the switching transistor to be in the off state, forcibly cutting off the current flowing through the LED string. Through this protection mechanism, it is ensured that the switching transistor will not be damaged due to continuous high current or high power consumption. Subsequently, a preset waiting time begins (for example, 36 milliseconds, this waiting time ensures that the shut-off switching transistor has enough time to dissipate heat and reduce its junction temperature to within a safe range). After the waiting time ends, the control module enters the automatic restart attempt phase. In this phase, the control module will allow the dimming signal to be transmitted again. When dimming signal transmission is permitted, the switching transistor and its circuit may still be in an abnormal state or may have returned to normal. The control module distinguishes between these two situations by querying the output signal of the detection module in real time and executes the corresponding control strategy: if the detection module outputs a shutdown signal, it indicates that the fault still exists, and the control module immediately re-shields the dimming signal, thereby controlling the switching transistor to turn off and starting a new round of waiting timer; if the detection module outputs a normal operation signal, it indicates that the fault has disappeared, and the control module maintains the state of allowing dimming signal transmission, so that the system fully recovers to normal operation. This mechanism enables the system to automatically and intelligently switch between the "protection-attempt-protection" cycle mode and the normal operation mode, ensuring safety protection under fault conditions and achieving automatic recovery after fault elimination.

[0033] In one optional embodiment, the switching transistor in this application embodiment can be an NMOS, PMOS, or a bipolar transistor. When the specific type of the switching transistor is different, the specific circuit structure and connection position of the detection module and the control module need to be adjusted accordingly.

[0034] Specifically, when a PMOS transistor is selected as the switching transistor: the detection module is used to detect the source-drain voltage V. SD Or detect the voltage V between the drain and ground. D The control module's control signal output is connected to the dimming controller that generates the dimming signal or to the path where the dimming signal is transmitted to the PMOS gate, and employs an active pull-up turn-off mechanism. When a fault is detected, the gate potential is pulled up to the source potential, causing the gate-source voltage V to... GS The value is zero, thus achieving rapid turn-off of the PMOS. This control logic perfectly matches the negative gate-source voltage conduction characteristic of the PMOS, ensuring the reliability and effectiveness of the protection.

[0035] When an NMOS transistor is selected as the switching transistor: the detection point of the detection module is set between the drain and source of the NMOS transistor to detect the drain-source voltage V. SD The control signal of the control module is connected to the gate of the NMOS transistor, employing an active pull-down turn-off mechanism. In a fault state, the gate potential is pulled down to the source potential (V0). GS Achieving reliable turn-off (=0V) corresponds to the forward bias conduction characteristics of NMOS.

[0036] When a bipolar junction transistor (BJT) is selected as the switching transistor: the control signal module detects the collector-emitter voltage V. CE To assess the device status, the control module applies control signals to the base of the transistor, employing a current-limited turn-off mechanism. In the event of a fault, rapid turn-off is achieved by cutting off or significantly reducing the base drive current, utilizing the current control characteristics of the BJT.

[0037] On the other hand, the specific circuit structure of the detection module and control module of this application will be optimized according to the different output voltages of the power supply module to ensure that effective protection functions can be provided in various application scenarios.

[0038] For fixed output voltage adaptation: When the power module provides a single fixed output voltage, a fixed threshold protection strategy is employed. In this configuration, the built-in reference voltage source of the detection module generates a fixed protection threshold that matches the power supply output voltage. For example, in an automotive high beam application driving multiple LEDs in series, the power module outputs a fixed 36V voltage, and the detection module accordingly sets a fixed voltage protection threshold (e.g., 5.6V) to achieve precise matching with the system voltage characteristics.

[0039] Specifically, the detection module includes a fixed threshold circuit and a voltage comparison circuit; the fixed threshold circuit is used to generate a fixed first reference voltage; the voltage comparison circuit is used to compare the first voltage at the first position with the first reference voltage, and generate a shutdown signal when the first voltage is lower than the first reference voltage; and generate a working signal when the first voltage is higher than the first reference voltage.

[0040] For the adjustable output voltage adaptation scheme: when the power module has multiple output voltage capabilities, the detection module enables the protection threshold to automatically adjust according to changes in the power output voltage. Specifically, the detection module includes: a logic control circuit for shielding or enabling signal generation by the voltage comparison circuit; a voltage divider circuit for dividing the power supplied to the power module according to a voltage division ratio to obtain the second voltage of the switching transistor; wherein the voltage division ratio changes with the voltage of the power supply; and a voltage comparison circuit for comparing the second voltage at a second position with a second reference voltage, generating a shutdown signal when the second voltage is lower than the second reference voltage, and generating an operating signal when the second voltage is higher than the second reference voltage.

[0041] In order to adapt to the different voltages provided by the power module, the detection position of the detection module also needs to be changed accordingly: when the power module provides one voltage of electrical energy, the circuit parameters of the switching transistor at the first position are detected; when the power module provides multiple different voltages of electrical energy, the circuit parameters of the switching transistor at the second position are detected; wherein, the first position and the second position are different positions of the switching transistor.

[0042] The following section uses PMOS under the SEPIC architecture as an example to explain in detail the detection module and control in the embodiments of this application, such as... Figure 2 The diagram shows the PMOS driver circuit under the MTQ6111. When the LED string is short-circuited, the fault behavior is as follows: the voltage at the drain terminal of M2 is 0. At this time, V D =0V,V G =I LIMT *R DS_ON V SD =V TH +V G .

[0043] The conduction condition of M2 is: V SG >V TH V G =I LIMT *R DS_ON =0.2Ma * 200Ω = 0.04V, V TH =2.5V; VSD =V TH +V G =2.5V + 0.04V = 2.54V.

[0044] The LED current is 1A, and the power dissipation of the PMOS is: P PMOS = V SD *I OUT =2.54 * 1A = 2.5W. The thermal resistance of the TO-252 package is R. ja =80℃ / W, ambient temperature T a =25℃, then the junction temperature T of the PMOS is J =T a +P PMOS *R ja =25 + 2.54 * 80 = 228.2. The AEC-Q102 PMOS operates within a junction temperature range of -40 to 150℃. Excessive junction temperature can lead to overheating and damage to the PMOS.

[0045] To prevent damage to the PMOS, embodiments of this application include a detection module and a control module. For example... Figure 3 As shown, the protection module includes a detection module and a control module. The detection module includes a fixed threshold circuit and a voltage comparison circuit. Specifically, the fixed threshold circuit consists of a current-limiting resistor R. LMIT It consists of a Zener diode Z2 and a comparator EA1, with a current-limiting resistor R. LMIT Connected in series with Zener diode Z2, R LMITZ2 is connected to the source of the PMOS switch, and Z2 is connected between the drain of the PMOS switch and ground. A fixed reference threshold (first reference voltage) is generated at the inverting input of comparator EA1. The core of the voltage comparison circuit, EA1, compares the first voltage between the source and drain of the PMOS switch with the first reference voltage in real time. The control module includes NMOS transistors M3 and M4, and a timer (delay circuit). The drain of M3 is directly connected to the gate of the PMOS switch, and the source is grounded. The gate of M3 is controlled by the output of comparator EA1. When M3 is turned on, it quickly pulls the gate voltage of the PMOS transistor down to ground, thereby directly forcibly turning off the power switch. The drain of M4 is connected to the gate control node of the signal channel switch (M2), and the source of M4 is grounded. The gate of M4 is also controlled by the combination logic of the output signal of the detection module and the output signal of the timer. When M4 is turned on, it pulls the gate of M2 down, thereby forcibly turning off M2 to shield the transmission path of the PWM dimming signal. Timer: Its start input is connected to the output of EA1, and its output is connected to the control logic circuit of the gate of M4. When a fault is detected, the timer is triggered and starts counting; after a preset delay time (e.g., 36ms) is reached, the timer outputs a reset signal.

[0046] The specific setting is when the source-drain voltage V of the PMOS switch is... SD When the voltage drops below 3.8V, the LED string is considered short-circuited, and the following protection procedure is executed: Voltage comparator EA1 detects V... SD Once the condition of <3.8V is met, its output immediately jumps to a high level. This high-level signal turns on M3, which in turn turns off MOSFET M2. At this time, the gate-source voltage of the PMOS is pulled up to 0V by the internal pull-up circuit, causing the PMOS to turn off immediately, thereby cutting off the output current path and preventing the PMOS from continuously bearing high power loss. Simultaneously with the high-level output of EA1, the timer is triggered and starts counting. After a 36ms delay, the timer outputs a high-level signal, which turns on MOSFET M4, which in turn turns off M3. At this time, M2 is again controlled by the PWM signal, the system enters a restart state, and the PMOS resumes normal operation.

[0047] By introducing this detection and control module, the power consumption of the PMOS under short-circuit conditions is significantly reduced. Specific calculations show that under a 1A operating current, the power consumption of the PMOS without protection is P. PMOS1 =2.54V×1A=2.5W; After adding protection, due to the intermittent working mode (5ms on / 36ms off), the actual average power consumption is reduced to P PMOS2=2.5W×5 / (5+36)=0.3W.

[0048] Thermodynamic analysis further verified the protection effect: TO-252 packaging (thermal resistance R) was used. ja =80℃ / W, ambient temperature T a At 25℃, the PMOS junction temperature in the unprotected state reaches as high as T. J1 =25 + 2.54 × 80 = 228.2℃, far exceeding the safe operating range; while after adding protection, the junction temperature drops to T J2 =25 + 0.3 × 70 = 49℃, fully meeting the device's safe operating requirements. This effectively solves the problem of PMOS overheating and damage caused by LED string short circuits in the SEPIC architecture. The output current waveform without the detection and control modules is as follows: Figure 5 As shown, the output current waveform using the detection module and control module is as follows: Figure 6 As shown.

[0049] like Figure 4 As shown, the detection module includes a voltage divider circuit and a voltage comparator circuit. The voltage divider circuit consists of resistors R1 and R2 connected in series between the drain of the PMOS switch and ground. It measures the drain voltage V... D The voltage is divided to obtain the detection voltage; the core comparator EA1 of the voltage comparison circuit connects its inverting input to the voltage divider node to receive the detection voltage, while its non-inverting input is connected to a fixed reference voltage V. REF The control module includes NMOS transistors M3 and M4, and a timer. The drain of M3 is directly connected to the gate of the PMOS transistor, and its source is grounded. The gate of M3 is controlled by the output of comparator EA1. When M3 is turned on, it rapidly pulls the gate voltage of the PMOS transistor down to ground, thus directly forcibly turning off the power switch. The drain of M4 is connected to the gate control node of the signal channel switch (M2), and its source is grounded. The gate of M4 is also controlled by the combination logic of the output signal of the detection module and the output signal of the timer. When M4 is turned on, it pulls the gate of M2 down, thus forcibly turning off M2 and shielding the transmission path of the PWM dimming signal. The timer's start input is connected to the output of EA1, and its output is connected to the control logic circuit of the gate of M4. When a fault is detected, the timer is triggered and starts counting; after a preset delay time (e.g., 36ms), the timer outputs a reset signal.

[0050] The resistance values ​​of the voltage divider resistors R1 and R2 are flexibly selected according to system requirements. When Vout changes, the resistance values ​​of R1 and R2 are adjusted, thereby adjusting the voltage division ratio. The protection threshold is reconfigured to adapt the dimming circuit to the new operating voltage.

[0051] The fixed threshold protection scheme's detection mechanism is based on the PMOS source-drain voltage V. SD Furthermore, the protection threshold is a fixed value (e.g., 3.8V), while the normal operating voltage of a single LED is typically only around 3V, lower than this fixed threshold. This will cause the system to mistakenly identify a short circuit and trigger protection upon power-on or normal operation, making it unsuitable for applications involving single LEDs. In contrast, the voltage divider detection scheme has a better protection threshold for drain voltage V. D Flexible voltage division and the use of a lower reference voltage (e.g., 1V) allow the protection threshold to be precisely adapted to the low operating voltage characteristics of a single LED by adjusting the voltage division ratio. When the detection module includes a fixed threshold circuit and a voltage comparison circuit, it is used to detect LED strings composed of multiple LEDs. When the detection module includes a voltage divider circuit and a voltage comparison circuit, it is used to detect LED strings composed of at least one LED.

[0052] Furthermore, for the voltage divider scheme, the protection module also includes a shielding circuit (not shown in the figure, but can be implemented using a logic AND gate). The shielding circuit monitors the level of the PWM dimming signal and automatically shields V when the PWM signal is low (dimming off). D The detection function effectively avoids false protection triggering due to output voltage drop during normal dimming, greatly improving system stability. During operation, the protection module is enabled when the PWM signal is high. If V... D When the voltage drops abnormally, and the detected voltage after voltage division by R1 and R2 falls below the 1V reference threshold, the voltage comparator EA1 outputs a high level, triggering subsequent protection actions. The entire protection process, through reasonable parameter configuration and an intelligent detection shielding mechanism, achieves reliable protection for the PMOS while ensuring stable system operation under various working conditions. In practical implementation, the shielding circuit can use logic gate circuits.

[0053] This application realizes intelligent and adaptive protection for LED driving systems, effectively improving the system's survivability and long-term reliability under various abnormal operating conditions, while taking into account the flexibility and cost-effectiveness of the design, and has high practical value and market competitiveness.

[0054] In another aspect, this application embodiment also provides a dimming system, including the dimming circuit and control chip described in the above embodiments. The control chip is preferably a dedicated LED driver chip (such as MTQ6111, TPS92692, etc.), which has the following functional characteristics: integrated PWM signal generator to generate precise dimming control signals; provides constant current driving capability to ensure stable operation of the LED string; includes necessary logic control circuits and a reference voltage source; and optionally integrates some or all of the functional circuits in the protection module. The PWM output terminal of the control chip is connected to the control electrode of the switching transistor in the dimming circuit, forming a normal dimming control path. Simultaneously, the control chip and the dimming circuit are interconnected through detection signal lines, status feedback lines, etc., to achieve information interaction and collaborative control. In normal dimming mode, the PWM signal output by the control chip directly drives the switching transistor to turn on and off, precisely controlling the average current of the LED string by adjusting the signal duty cycle, thereby achieving stepless brightness adjustment from 0% to 100%. When the dimming circuit detects an abnormal state, its protection module will exceed the normal PWM control signal and forcibly set the switching transistor to the off state. Simultaneously, the dimming circuit can send a fault status signal to the control chip, which then adjusts its output strategy or records fault information accordingly. During the delay period of the protection action, the control chip can choose to maintain or pause the PWM signal output. Once the dimming circuit completes its delay period and resets, the system automatically resumes normal operation, and the control chip continues to output the PWM dimming signal.

[0055] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In addition, the terms "first", "second", "third", etc. are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0056] Finally, it should be noted that the above-described embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the scope of the technology disclosed in this application; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application. All should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A dimming circuit, characterized in that, The dimming circuit is used to receive dimming signals to adjust the brightness of LED strings, including a power supply module for providing power to the LED strings, and a switching transistor for controlling the current flowing through the LED strings according to the dimming signal. The dimming circuit also includes: The detection module is used to detect circuit parameters and generate control signals; wherein the control signals include a shutdown signal or an operating signal. A control module is used to receive control signals and adjust the transmission state of the dimming signals; If the detection module generates a working signal, the control module allows the transmission of the dimming signal to control the switching transistor to be in the on state; if the detection module generates the off signal, the control module blocks the transmission of the dimming signal to control the switching transistor to be in the off state. In the off state, the control module continues to receive control signals after waiting for a preset time.

2. The dimming circuit according to claim 1, characterized in that, The power module is used to provide electrical energy at a given voltage. The detection module is connected to a preset first position of the switching transistor and is used to detect the circuit parameters of the first position of the switching transistor. Alternatively, the power module can be used to provide electrical energy at various voltages; The detection module is connected to a preset second position of the switching transistor and is used to detect the circuit parameters of the second position of the switching transistor; wherein the first position and the second position are different positions.

3. The dimming circuit according to claim 2, characterized in that, The detection module includes: a fixed threshold circuit and a voltage comparison circuit; The fixed threshold circuit is used to generate a fixed first reference voltage; The voltage comparison circuit is used to compare a first voltage at a first position with a first reference voltage, and generate a shutdown signal when the first voltage is lower than the first reference voltage, and generate an operating signal when the first voltage is higher than the first reference voltage.

4. The dimming circuit of claim 2, wherein, The detection module includes: a voltage divider circuit and a voltage comparison circuit; The voltage divider circuit is used to divide the electrical energy supplied to the power module according to the voltage division ratio to obtain the second voltage of the switching transistor; wherein the voltage division ratio changes with the voltage of the electrical energy. The voltage comparison circuit is used to compare the second voltage at the second position with the second reference voltage, and generate a shutdown signal when the second voltage is lower than the second reference voltage, and generate an operating signal when the second voltage is higher than the second reference voltage.

5. The dimming circuit of claim 3, wherein, The switching transistor includes a PMOS transistor; The detection module is connected to the source of the PMOS transistor and is used to detect a first voltage between the source and drain of the PMOS transistor; when the first voltage is lower than a first threshold range, a turn-off signal is generated; when the first voltage rises to the first threshold range, a turn-on signal is generated.

6. The dimming circuit of claim 4, wherein, The switching transistor includes a PMOS transistor; The detection module is connected to the drain of the PMOS transistor and is used to detect the second voltage between the drain of the PMOS transistor and ground when the dimming signal is high; generate a turn-off signal when the second voltage is lower than a second threshold range; and generate a working signal when the second voltage rises to the second threshold range.

7. The dimming circuit of claim 5, wherein, The fixed threshold circuit includes a current-limiting resistor and a Zener diode; the voltage comparison circuit includes a comparator.

8. The dimming circuit of claim 6, wherein, The voltage divider circuit includes a first voltage divider resistor and a second voltage divider resistor; the voltage comparison circuit includes a comparator.

9. The dimming circuit of claim 5 or 6, wherein, The control module includes a third NMOS transistor, a fourth NMOS transistor, and a delay unit.

10. A dimming system characterized by, include: The dimming circuit and control chip as described in any one of claims 1 to 9; The control chip is used to output a dimming signal, which is used to adjust the brightness of the LED string.

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