LED temperature detection method and system for distinguishing environment temperature and dissipation temperature rise

Abstract

The invention discloses an LED temperature detection method and system capable of distinguishing ambient temperature and dissipative temperature rise, and the method comprises the steps: carrying out the five stages of turn-off, detection (before), driving, detection (after) and turn-off in sequence through precise time sequence control in a complete PWM drive period based on the voltage-temperature characteristics of a PN junction of an LED; the problem that in the prior art, the LED environment temperature and the working temperature rise of the LED can not be obtained at the same time with low cost and high reliability on the premise that high-temperature electric leakage interference is avoided is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic technology, specifically to a temperature detection method and system based on the electrical characteristics of LEDs. It is particularly suitable for scenarios that require distinguishing between ambient temperature and chip operating temperature rise and intelligent thermal management, such as automotive interior lighting and high-reliability display backlighting. Background Technology

[0002] Due to the physical properties of LED semiconductors and the characteristics of phosphors, the operating status of LEDs, especially the luminous performance and reliability of automotive interior lights, is severely affected by the chip junction temperature. When the junction temperature shifts, the LED's color coordinates will drift, causing a change in the perceived color of the emitted light. If the junction temperature remains close to or exceeds its operating tolerance temperature for an extended period, it will significantly accelerate light decay and shorten the LED's lifespan. Therefore, during LED operation, real-time and accurate acquisition of the ambient temperature and the heat rise dissipated by the LED itself is crucial for achieving proactive and intelligent thermal management. Only by simultaneously mastering these two independent temperature parameters can a microcontroller (MCU) not only compensate for color differences but also adjust the driving strategy or heat dissipation measures at the source, thereby fundamentally optimizing energy efficiency and extending lifespan while ensuring color consistency.

[0003] It is well known to those skilled in the art that, under constant low-current driving, the forward voltage drop of a diode's PN junction exhibits an approximately linear negative correlation with its junction temperature. Based on this "forward voltage method," indirectly detecting the LED junction temperature has become the mainstream technical approach in the industry. However, this approach faces two major challenges in practical engineering: firstly, the feasibility of the measurement implementation, i.e., how to safely and reliably obtain its PN junction voltage without interfering with the LED's normal light-emitting function (without introducing visible flicker or dim light); secondly, the reliability contradiction at high temperatures. Specifically, on the one hand, LEDs are low-turn-on current devices, and a forward current as low as 2uA is sufficient to produce a dim light perceptible to the naked eye; on the other hand, when automotive-grade drive switching chips operate at junction temperatures as high as 150°C, their off-state leakage current can reach the range of 1uA to hundreds of uA. The combination of these two factors makes it extremely easy for the switch's off-state leakage current to flow through the LED under high-temperature conditions, causing it to exhibit abnormal dim light, constant light, or flickering at unexpected times. Furthermore, the exponential nature of the IV characteristic of LEDs means that minute power supply noise can be amplified into significant current fluctuations, further exacerbating the risk of unstable light output under high-temperature conditions. Therefore, overcoming high-temperature leakage interference is an unavoidable prerequisite for achieving accurate online temperature measurement.

[0004] To address the above challenges, existing technologies have proposed several solutions, but all of them have significant drawbacks: The first approach, as shown in patent application CN2017103041810 (published November 13, 2018), attempts to indirectly sense temperature by embedding an additional temperature-sensing diode, which is mounted on an aluminum substrate along with the LED chip. While this method has a simple structure, it introduces additional sensor costs and packaging complexity. More importantly, there is a significant thermal resistance between the external diode and the LED chip junction, resulting in slow measurement response and limited accuracy. Furthermore, the measured temperature is only a mixed temperature of a local area of ​​the substrate, failing to effectively distinguish and output the independent ambient temperature and LED operating dissipation temperature rise, thus limiting the accuracy of thermal management.

[0005] The second approach, as shown in patent document CN202010885829X (published November 24, 2020), employs two independent constant current sources and switches, inserting a small current during the LED's off-state interval to detect the PN junction voltage. While this approach attempts to achieve integrated measurement, it suffers from a fundamental contradiction: the semiconductor switches, which isolate the measurement path from the driving path, inherently exhibit leakage characteristics at high temperatures, which conflict with the requirement for interference-free measurement during the off-state period. This fails to eliminate the aforementioned problem of abnormal LED illumination caused by high-temperature leakage, severely impacting the reliability and accuracy of the measurement. Furthermore, this approach only performs voltage sampling once per operating cycle, obtaining only a single summative temperature value. It also cannot separate ambient temperature from operating dissipation temperature rise, forcing the MCU to passively compensate for brightness or color by changing the driving current and duty cycle through table lookups, unable to identify the root cause of the temperature rise and implement fundamental optimization.

[0006] In summary, existing technologies either have deficiencies in measurement dimensions (unable to distinguish between ambient temperature and temperature rise) or inherent flaws in reliability (unable to overcome high-temperature leakage), making it difficult to meet the stringent requirements of high-reliability, high-precision, and multi-dimensional online monitoring of LED temperature in high-end application scenarios such as automotive. Summary of the Invention

[0007] The purpose of this invention is to provide an LED temperature detection method and system that distinguishes between ambient temperature and dissipated temperature rise, thereby solving the problem that existing technologies cannot simultaneously obtain the LED's ambient temperature and its own operating temperature rise in a low-cost and highly reliable manner while avoiding high-temperature leakage interference. The method is based on the LED's own PN junction voltage-temperature characteristics. Within a complete PWM drive cycle, through precise timing control, it sequentially executes five stages: "light-off - detection (before) - drive - detection (after) - light-off". Specifically, before and after the LED is driven to emit light, the system inserts two brief small current detection windows, respectively, to accurately acquire the LED's PN junction voltage through an operational amplifier and an analog-to-digital converter. Simultaneously, by designing a dedicated light-off branch including parallel resistors and switches, it ensures that the voltage at the first node is reliably clamped below its conduction threshold during non-drive and non-detection periods, thereby completely blocking abnormal dim light or flickering that may be caused by high-temperature leakage of the chip. Based on the two voltage values ​​collected before and after the drive, the microcontroller can calculate the independent ambient temperature and operating heat dissipation, providing core data for implementing precise and proactive thermal management, and ultimately achieving the goal of ensuring LED color consistency, working life and overall system reliability.

[0008] According to one aspect of the present invention, an LED temperature detection method for distinguishing between ambient temperature and dissipated temperature rise is provided, comprising: application to a system including an LED, a constant current source, an operational amplifier, a sampling unit, a first switch, a second switch, a parallel resistor, and a microcontroller, the method comprising sequentially executing the following timing control within one PWM drive cycle: During the first lamp-off period, the second switch is controlled to close, so that the parallel resistor is connected in parallel with the LED, and the constant current source is controlled to output the first detection current through the parallel resistor, clamping the voltage at the first node below its conduction threshold. During the first detection period, the second switch is controlled to open and the first switch is controlled to close so that the first voltage across the LED is read by the operational amplifier. After sampling by the sampling unit, the first voltage value is obtained. The first voltage value represents the junction temperature when the LED is not working. During the driving period, the first switch is controlled to open, and the constant current source is controlled to output driving current to drive the LED to emit light normally; During the second detection period, the constant current source is controlled to switch to output the second detection current, and the first switch is controlled to close so that the second voltage across the LED is read through the operational amplifier. After sampling by the sampling unit, the second voltage value is obtained. The second voltage value represents the total temperature after the LED has been working. During the second light-off period, the first switch is opened and the second switch is closed, causing the detection current to flow through the parallel resistor, and the LED is turned off. The microcontroller calculates the ambient temperature and the operating temperature rise of the LED based on the first voltage value and the second voltage value.

[0009] As a further technical solution, the resistance value of the parallel resistor is configured according to the magnitude of the detected current and the estimated high-temperature leakage current, so that during the first and second lamp-off periods, the voltage drop at the first node is limited to between 0.1V and 1V. This voltage drop value is lower than the LED's conduction threshold, thereby preventing abnormal light emission or flickering caused by the high-temperature leakage current flowing through the LED.

[0010] As a further technical solution, the duration of both the first detection period and the second detection period is less than 20 microseconds.

[0011] As a further technical solution, the values ​​of the first detection current and the second detection current range from 100 microamps to 1 milliamp.

[0012] As a further technical solution, the first detection period occurs before the LED is driven to emit light, and the second detection period immediately follows the end of the driving period; the MCU calculates the operating dissipation temperature rise of the LED by comparing the first voltage value and the second voltage value.

[0013] According to one aspect of the present invention, an LED temperature detection system for distinguishing between ambient temperature and dissipated temperature rise is provided, comprising: An LED has its anode connected to a power source and its cathode connected to the first node. The PWM driver module is used to generate PWM signals to drive LEDs. A constant current source, the output of which is connected to the first node, and can be controlled to switch between the drive current level and the detection current level; The parallel branch includes a second switch connected in series and a parallel resistor connected in parallel between the anode and cathode of the LED. The cathode of the LED, one end of the constant current source, and one end of the parallel branch are all connected to the first node. The voltage detection branch includes a first switch and an operational amplifier connected in series. The input terminal of the operational amplifier is connected to the anode of the LED and the first node, respectively, for detecting the voltage drop across the LED. The sampling unit is connected to the output terminal of the operational amplifier; The microcontroller is electrically connected to the PWM drive module, constant current source, first switch, second switch, and sampling unit; The timing control module, in response to the edge of the PWM signal, generates multiple control signals with specific delay relationships to precisely control the gear switching of the constant current source, the on / off state of the first and second switches, and the sampling time of the sampling unit.

[0014] As a further technical solution, the timing control module includes multiple independent configurable delay units, which are used to generate delay signals to control the operation of the constant current source, the first switch, the second switch and the sampling unit.

[0015] As a further technical solution, the resistance value of the parallel resistor satisfies the following relationship: during the first or second lamp-off period, when the constant current source outputs the detection current and the second switch is closed, the voltage at the first node is clamped by the parallel resistor within a predetermined voltage range below the LED conduction threshold, so as to ensure that all current flows through the parallel resistor and no current flows through the LED.

[0016] As a further technical solution, the constant current source, the first switch, the second switch, the operational amplifier, and the sampling unit are integrated into a single automotive-grade chip.

[0017] As a further technical solution, the system includes multiple detection channels with the same structure for simultaneously detecting the temperature of multiple LEDs, and the driving period of each channel is controlled by a PWM signal with a phase offset.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention eliminates the need for an external temperature sensor, utilizing the LED's own PN junction as the temperature sensing element. By reusing existing resources in the driving circuit, such as the constant current source, operational amplifier, ADC, and MCU, it achieves direct temperature detection of the LED chip without increasing additional hardware costs. This greatly simplifies the system structure, reduces material and packaging costs, and is particularly suitable for cost-sensitive large-scale applications.

[0019] 2. This invention introduces a dedicated lamp-off branch consisting of a parallel resistor and a controlled switch, and effectively connects it during the lamp-off period to actively clamp the voltage at the first node below its conduction threshold. This design, in principle, completely blocks the path of the turn-off leakage current generated by the driver chip at high temperatures (e.g., 150°C) through the LED, thereby completely eliminating the abnormal dim, constant, or flickering LED phenomena caused by this, meeting the extreme requirements of stability and reliability for automotive-grade applications.

[0020] 3. This invention sets two independent detection points within a single PWM cycle: before and after the drive, capturing voltage signals representing the pure ambient temperature and the total temperature including the operating temperature rise, respectively. This enables the MCU to accurately calculate these two independent key parameters—ambient temperature and operating dissipation temperature rise—for the first time while operating online, thus distinguishing the root cause of the temperature rise.

[0021] 4. The low-current (e.g., 100uA-1mA) and short-duration (e.g., <20us) detection pulses used in this invention have minimal impact on the normal brightness of the LED. This slight impact can be easily compensated for by the algorithm, truly achieving non-intrusive measurement. Simultaneously, precise timing control and signal chain design ensure the sampling stability and accuracy of the PN junction voltage, laying a reliable data foundation for subsequent temperature calculations.

[0022] 5. The core circuit of this invention, including a constant current source, switches, operational amplifiers, and an ADC, can be highly integrated into a single automotive-grade driver chip, forming an intelligent single-chip solution. This system architecture is easily expandable to synchronous or time-sharing detection of multiple LEDs, and through load balancing strategies such as phase-shifting drive, it maintains stable overall system power supply, further ensuring measurement accuracy.

[0023] In summary, this invention achieves synergistic optimization in terms of cost, reliability, information dimensions, measurement quality, and integration, providing a complete solution for addressing the challenges of high-precision online thermal management and lifespan assurance for LEDs, especially automotive LEDs. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the circuit principle of an LED temperature detection system that distinguishes between ambient temperature and dissipated temperature rise, provided in an embodiment of the present invention.

[0026] Figure 2 This is a timing diagram within a single working cycle provided in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical features of the various embodiments or individual embodiments provided by the present invention can be arbitrarily combined to form new technical solutions. Such combinations are not bound by the order of steps and / or structural composition patterns, but must be 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 a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0028] This invention provides an LED temperature detection method that distinguishes between ambient temperature and dissipated temperature rise, including: an application to a system comprising an LED, a constant current source, an operational amplifier, a sampling unit, a first switch, a second switch, a parallel resistor, and a microcontroller.

[0029] Please see Figure 1 The provided system circuit schematic diagram. The system mainly includes: an LED as the light-emitting element, an adjustable normally open constant current source Is, an operational amplifier OP, an analog-to-digital converter (ADC) as the sampling unit, a first switch K1, a second switch K2, a parallel resistor R1, a microcontroller MCU, and a timing control module composed of multiple delay units (delay1~delay4). The anode of the LED is connected to the power supply Vbat, and its cathode is connected to the constant current source Is. One end of the constant current source Is is connected to the cathode of the LED and can switch between a driving current range (e.g., 5mA-60mA) and a detection current range (e.g., 100uA-1mA) under the control signal issued by the MCU through the timing control module.

[0030] Specifically, the system includes a parallel branch and a voltage detection branch. The parallel branch consists of a second switch K2 connected in series and a parallel resistor R1, connected in parallel between the anode and cathode of the LED. The cathode of the LED, one end of the constant current source, and one end of the parallel branch are all connected to the first node A (i.e., the cathode of the LED). Its core function is to provide a low-impedance shunt path during the lamp-off period. The voltage detection branch consists of a first switch K1 connected in series and an operational amplifier OP. The non-inverting input of the operational amplifier OP is connected to the anode of the LED, and its inverting input is connected to the cathode of the LED, thereby enabling high-precision detection of the voltage drop across the LED (i.e., the forward voltage Vf of the PN junction). The output of the operational amplifier OP is connected to the input of the ADC. The operation of the entire system is triggered by the edge of the PWM drive signal, which generates control signals with precise timing relationships through four independent delay modules (delay1~delay4) to control ADC sampling, K1 switching, Is level switching, and K2 switching, respectively.

[0031] The specific functions of each module in the system are explained below: 1. Light-emitting unit and driving module: including the vehicle-mounted light-emitting diode (LED) as the load and its PWM driving signal source.

[0032] 2. Parallel Branch: Its core function is to connect R1 in parallel across the LED by closing K2 during the system's designated LED off period. This provides a low-impedance path to ground for the detection current and any potential chip leakage current, thereby clamping the voltage at the first node below the LED's conduction threshold. This ensures the LED is completely extinguished and eliminates the risk of dim light or flickering caused by high-temperature leakage. The closing and opening of switch K2 is triggered by a control signal generated after the PWM signal edge is processed by an independent delay module (delay4).

[0033] 3. Voltage Detection Branch: During the system's designated detection period, OP is connected to the measurement circuit by closing K1. Its input terminals are connected to the anode and cathode of the LED, respectively, for high-precision detection and amplification of the forward voltage drop of the LED's PN junction. The closing and opening of switch K1 is triggered by the PWM signal edge after being processed by another independent delay module (delay2).

[0034] 4. Analog-to-Digital Converter (ADC): Its function is to sample the analog voltage signal output by the OP at precise times and convert it into a digital quantity to be transmitted to the MCU. The sampling trigger time of the ADC is precisely controlled by the control signal generated after the edge of the PWM signal is processed by the delay module (delay1).

[0035] 5. Adjustable range normally open constant current source: This constant current source can switch between a drive current range (e.g., 5mA-60mA) and a detection current range (e.g., 100uA-1mA), used for normal LED illumination drive and PN junction voltage measurement excitation, respectively. The control signal for range switching is triggered by the edge of the PWM signal after processing by the delay module (delay3).

[0036] 6. Timing Control Module: The system includes multiple independent configurable delay modules (delay1~delay4), each using the edges (rising and / or falling edges) of the PWM signal as the initial trigger reference. Each module can generate different and precise delays to produce the timing signals controlling the operation of the ADC, K1, Is, and K2. The delay values ​​for the rising and falling edges of the PWM signal can be configured independently to meet complex multi-stage timing requirements.

[0037] Combination Figure 2 The timing diagram of a single PWM duty cycle shown illustrates the specific workflow of the method described in this embodiment. A complete duty cycle consists of five stages: the first lamp-off period (T0), the first detection period (T1), the driving period (T2), the second detection period (T3), and the second lamp-off period (T4). Generally, the entire duty cycle is approximately 10ms to 1ms.

[0038] During the first lamp-off period (T0): the PWM drive signal is low. The timing control module causes the constant current source Is to output the first detection current and controls the second switch K2 to close, while the first switch K1 is open. At this time, the flow path of the detection current and any potential chip leakage current is: constant current source Is → closed K2 → parallel resistor R1 → power supply Vbat. By carefully designing the resistance value of the parallel resistor R1, the voltage drop generated on the LED cathode is precisely clamped between 0.1V and 1V. Since the voltage drop corresponding to the LED's 1uA forward conduction current is greater than 1V, the detection current flows entirely through the parallel resistor, and no current flows through the LED, resulting in a reliable extinguished state. This design completely eliminates the possibility of the LED dimly lighting during the extinguishing period due to high-temperature leakage.

[0039] For example, if the detection current is known to be 200uA, the high-temperature leakage current at the pin is 200uA, the LED's on-state current is 1uA, and the voltage drop is 1.4V, with the LED and R1 connected in parallel, to ensure that the voltage drop is not too close to 1.4V due to noise interference and thus does not cause it to light up, we can assume the terminal voltage is 1V. Then, Iled = 0uA, Ir = 1V / 400uA = 2.5kΩ. Therefore, a parallel resistor <2.5kΩ is selected, which allows the resistor to divert all the current, leaving no current to the LED and ensuring that the LED does not light up. At this time, the ADC is not sampling, and since the on-state voltage drop for the LED to light up is >1.4V, the LED is in an off state.

[0040] During the first detection period (T1): the PWM drive signal changes from low to high (rising edge), triggering timing control. The system maintains the constant current source Is outputting the detection current and controls the second switch K2 to open, leaving only the LED. At this time, since there are no other branches, the detection current flows entirely through the LED. Subsequently, after a delay of t2_h by the delay2 module, the first switch K1 is closed, and the operational amplifier OP is connected to the circuit to read the voltage across the LED. After another delay of t1_h by the delay1 module (t1_h>t2_h to ensure stable op-amp output), the ADC is triggered to sample and obtain the first voltage value (Vf1). Since the LED is in a cooling state during the T0 period, Vf1 directly represents the ambient temperature of the LED. Because the LED is flowing with a detection current of 100uA~1mA, the LED has a relatively weak brightness. However, since the detection period is generally less than 20us, it accounts for a small proportion of the entire period greater than 1ms, so its impact on the PWM control of the LED brightness is small, and the slight impact can be compensated for by the algorithm.

[0041] During the driving period (T2): the PWM drive signal remains high. The system controls the first switch K1 to open to isolate the detection circuit, and simultaneously controls the constant current source Is to switch to the drive current level (e.g., 30mA) to drive the LED to light normally. During this period, K2 remains open, leaving only the LED connected. Since there are no other branches, the drive current flows entirely through the LED. Meanwhile, the ADC does not sample during this period. In this embodiment of the invention, the drive current is generally 5mA~60mA, which can be set according to the LED's electrical characteristics. At the end of the T2 period, the PWM signal will be pulled low beforehand by the delay3 module at a time t3_l, in preparation for subsequent measurements.

[0042] During the second detection period (T3): the PWM signal has gone low (falling edge). The system controls the constant current source Is to quickly switch back to the second detection current, and closes K1 after a delay t2_l generated by delay2, connecting the op-amp to read the voltage; after a delay t1_l generated by delay1 (>t2_l), the OP output is stable, triggering the ADC to sample and send it to the MCU to obtain the second voltage value (Vf2). At this time, the LED has just finished working, and its junction temperature has risen. Therefore, Vf2 represents the total temperature including the ambient temperature rise and its own operating dissipation temperature rise.

[0043] During the second lamp-off period (T4): This stage operates on the same principle as the T0 period. The system disconnects K1 and closes K2, causing the detection current to be shunted by R1 again, ensuring that the LED is completely extinguished at the end of the cycle, preparing for the next cycle.

[0044] Data processing: After the MCU obtains Vf1 and Vf2, it can calculate the ambient temperature and the final temperature based on the pre-calibrated voltage-temperature coefficient (K coefficient) of the LED under the detection current. The difference between the two is the operating dissipation temperature rise.

[0045] Based on the foregoing embodiments, this embodiment further explains the selection of the parallel resistor R1. The resistance value of R1 needs to be designed based on the magnitude of the detection current and the estimated high-temperature leakage current of the chip. The core principle is to ensure that during periods T0 and T4, even if leakage current exists, the voltage of the LED cathode is firmly clamped below the LED conduction threshold. For example, if the detection current Is_det = 200uA, the estimated high-temperature leakage current I_leak = 200uA, and the target clamping voltage V_clamp = 1V, then the required resistance R ≤ V_clamp / (Is_det + I_leak) = 1V / 400uA = 2.5kΩ. Choosing a nominal resistor smaller than this value (such as 2.2kΩ) ensures that all current is shunted by the resistor, the LED current is zero, and thus the risk of flicker is absolutely avoided from a physical perspective.

[0046] Based on any of the foregoing embodiments, preferably, this embodiment describes high-reliability integration. The constant current source Is, the first switch K1, the second switch K2, the operational amplifier OP, the ADC, and even the timing control logic (delay module) can be integrated and manufactured into a single automotive-grade chip conforming to standards such as AEC-Q100. This chip connects to external LEDs, parallel resistors R1, and the MCU through a few pins, greatly improving the system's reliability and consistency while reducing its size, making it particularly suitable for applications in space-constrained and harsh automotive environments.

[0047] Based on any of the foregoing embodiments, preferably, this embodiment describes system expansion. The system architecture can be reused for the detection of multiple LEDs. The system can include multiple identical detection channels, and the MCU can time-division multiplex the same set of core detection resources (such as OP, ADC) to sequentially measure the temperature of multiple LEDs, or it can be achieved by integrating a multiplexer. In addition, an important optimization is that during the driving period (T2), the MCU can control the phases of the PWM drive signals of each LED to be staggered. This staggered driving strategy avoids the drastic change in the total power supply current caused by all LEDs turning on or off simultaneously, reduces the impact on the power supply network, stabilizes the system operating point, and thus indirectly ensures the consistency of voltage measurement accuracy of each channel.

[0048] In summary, this invention, through the synergistic application of four core technologies—single constant current source range switching, parallel resistor shunt lamp extinguishing, dual-time-point voltage sampling, and precise timing control—simultaneously solves two major industry challenges in online temperature measurement—reliability (no leakage flicker) and information integrity (distinguishing between ambient temperature and temperature rise)—while maintaining low cost. Key points are specifically reflected in: 1. This invention employs a switchable constant current source, combined with a parallel resistor branch controlled by a switch, along with an operational amplifier, analog-to-digital converter, and programmable delay module, to construct a highly efficient multiplexed detection system. All actions of this system are triggered by the edge of the PWM drive signal. Multiple independently configurable delay modules generate precise and coordinated control timing, thereby achieving cyclic control of the LED path through five states within a single PWM working cycle: no current (light off), low current detection, high current drive, low current detection, and no current (light off). This architecture achieves a perfect integration of drive and detection functions with minimal hardware cost.

[0049] 2. To overcome the limitation of existing technologies that can only obtain a single summative temperature, this invention makes a key design in timing: within the same PWM cycle, two brief small current detection windows are inserted before the LED emits light and after the driving ends. By collecting the first voltage value before driving (corresponding to ambient temperature) and the second voltage value after driving (corresponding to summative temperature), the microcontroller can directly calculate the pure LED operating temperature rise using the difference between the two. This dual-time-point sampling method is the core of achieving accurate differentiation between ambient temperature and operating temperature rise.

[0050] 3. Addressing the technical problem of abnormally dim LED brightness caused by leakage current in power devices under automotive-grade high-temperature environments, this invention proposes an active hardware solution. During periods when the LED needs to be off, the system controls a switch to connect a small-value precision parallel resistor across the LED. This resistor, along with the constant current source and any potential leakage current, forms a path, actively clamping the LED cathode potential to a predetermined voltage (e.g., 0.1V-1V) far below its conduction threshold. This design physically ensures that even with leakage current in the hundreds of microamps, the voltage across the LED cannot reach the conduction condition, thus fundamentally eliminating any flickering or dim brightness caused by high-temperature leakage, guaranteeing the purity of the measurement and the absolute reliability of the system.

[0051] Any aspects not elaborated above are common knowledge in the field. Those skilled in the art can make adaptive adjustments to the current value, resistance value, delay parameters, and integration method without departing from the concept of this invention, and all such modifications should be included within the scope of protection of this invention.

[0052] The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and accompanying drawings of this invention are intended to cover a non-exclusive inclusion, such as a process, method, system, product, or apparatus that includes a series of steps or units, not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting LED temperature that distinguishes between ambient temperature and dissipated temperature rise, characterized in that, include: Applied to a system including LEDs, constant current sources, operational amplifiers, sampling units, first switches, second switches, parallel resistors, and a microcontroller, the method includes sequentially executing the following timing control within one PWM drive cycle: During the first lamp-off period, the second switch is controlled to close, so that the parallel resistor is connected in parallel with the LED, and the constant current source is controlled to output the first detection current through the parallel resistor, clamping the voltage at the first node below its conduction threshold. During the first detection period, the second switch is controlled to open and the first switch is controlled to close so that the first voltage across the LED is read by the operational amplifier. After sampling by the sampling unit, the first voltage value is obtained. The first voltage value represents the junction temperature when the LED is not working. During the driving period, the first switch is controlled to open, and the constant current source is controlled to output driving current to drive the LED to emit light normally; During the second detection period, the constant current source is controlled to switch to output the second detection current, and the first switch is controlled to close so that the second voltage across the LED is read through the operational amplifier. After sampling by the sampling unit, the second voltage value is obtained. The second voltage value represents the total temperature after the LED has been working. During the second light-off period, the first switch is opened and the second switch is closed, causing the detection current to flow through the parallel resistor, and the LED is turned off. The microcontroller calculates the ambient temperature and the operating temperature rise of the LED based on the first voltage value and the second voltage value.

2. The LED temperature detection method for distinguishing between ambient temperature and dissipated temperature rise according to claim 1, characterized in that, The resistance value of the parallel resistor is configured according to the magnitude of the detected current and the estimated high-temperature leakage current, so that during the first and second lamp-off periods, the voltage drop at the first node is limited to between 0.1V and 1V. This voltage drop value is lower than the LED's conduction threshold, thereby preventing abnormal light emission or flickering caused by the high-temperature leakage current flowing through the LED.

3. The LED temperature detection method for distinguishing between ambient temperature and dissipated temperature rise according to claim 1, characterized in that, The duration of both the first detection period and the second detection period is less than 20 microseconds.

4. The LED temperature detection method for distinguishing between ambient temperature and dissipated temperature rise according to claim 1, characterized in that, The values ​​of the first detection current and the second detection current range from 100 microamps to 1 milliamp.

5. The LED temperature detection method for distinguishing between ambient temperature and dissipated temperature rise according to claim 1, characterized in that, The first detection period occurs before the LED is driven to emit light, and the second detection period immediately follows the end of the driving period. The MCU calculates the operating temperature rise of the LED by comparing the first voltage value and the second voltage value.

6. An LED temperature detection system that distinguishes between ambient temperature and dissipated temperature rise, characterized in that, include: An LED has its anode connected to a power source and its cathode connected to the first node. The PWM driver module is used to generate PWM signals to drive LEDs. A constant current source, the output of which is connected to the first node, and can be controlled to switch between the drive current level and the detection current level; The parallel branch includes a second switch connected in series and a parallel resistor connected in parallel between the anode and cathode of the LED. The cathode of the LED, one end of the constant current source, and one end of the parallel branch are all connected to the first node. The voltage detection branch includes a first switch and an operational amplifier connected in series. The input terminal of the operational amplifier is connected to the anode of the LED and the first node, respectively, for detecting the voltage drop across the LED. The sampling unit is connected to the output terminal of the operational amplifier; The microcontroller is electrically connected to the PWM drive module, constant current source, first switch, second switch, and sampling unit; The timing control module, in response to the edge of the PWM signal, generates multiple control signals with specific delay relationships to precisely control the gear switching of the constant current source, the on / off state of the first and second switches, and the sampling time of the sampling unit.

7. The LED temperature detection system for distinguishing between ambient temperature and dissipated temperature rise according to claim 6, characterized in that, The timing control module includes multiple independent configurable delay units, which are used to generate delay signals to control the operation of the constant current source, the first switch, the second switch, and the sampling unit.

8. The LED temperature detection system for distinguishing between ambient temperature and dissipated temperature rise according to claim 6, characterized in that, The resistance values ​​of the parallel resistor satisfy the following relationship: during the first or second lamp-off period, when the constant current source outputs the detection current and the second switch is closed, the voltage at the first node is clamped by the parallel resistor within a predetermined voltage range below the LED conduction threshold, so as to ensure that all current flows through the parallel resistor and no current flows through the LED.

9. The LED temperature detection system for distinguishing between ambient temperature and dissipated temperature rise according to claim 6, characterized in that, The constant current source, first switch, second switch, operational amplifier, and sampling unit are integrated into a single automotive-grade chip.

10. An LED temperature detection system for distinguishing between ambient temperature and dissipated temperature rise according to claim 6, characterized in that, The system includes multiple identical detection channels for simultaneously detecting the temperature of multiple LEDs, and the driving time of each channel is controlled by a phase-staggered PWM signal.

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