Backlight LED driving circuit, driving chip and driving system

Abstract

This application provides a backlight LED driving circuit, driving chip, and driving system. The circuit includes a demagnetization detection module, a sampling detection module, a PWM dimming module, an error amplification module, a valley locking module, and a logic driving module. The demagnetization detection module receives the drain resonant voltage signal of the power switch in the peripheral circuit as a demagnetization feedback signal and generates a valley detection signal at the valley of the drain resonant voltage signal. The sampling detection module receives the sampled voltage and outputs a detection voltage. The PWM dimming module outputs a reference voltage based on the PWM dimming signal. The error amplification module outputs an error voltage based on the detection voltage and the reference voltage. The valley locking module determines the number of locked valleys based on the error voltage and counts the current number of valleys based on the valley detection signal. If the current number of valleys equals the number of locked valleys, it outputs a conduction control signal. The logic driving module outputs a driving signal based on the conduction control signal to control the power switch to conduct.

Description

Technical Field

[0001] This application belongs to the field of LED driver technology, and in particular relates to a backlight LED driver circuit, driver chip and driver system. Background Technology

[0002] Currently, quasi-resonant control is widely used in LED (Light-Emitting Diode) backlight driving. This method achieves soft-switching by detecting the resonant trough of the drain voltage of the power switching transistor, thus reducing switching losses and electromagnetic interference. However, in traditional quasi-resonant drive circuits, the operating frequency tends to fluctuate significantly with the output current during PWM (Pulse Width Modulation) dimming and load changes. Especially under light load or deep dimming conditions, the switching frequency is prone to frequent jumps and abnormal increases, leading to decreased system stability, significant inductor current fluctuations, and consequently, noticeable LED flickering, affecting dimming uniformity and display quality. Summary of the Invention

[0003] This application provides a backlight LED driving circuit, driving chip, and driving system, which can solve the problem that in existing systems, under light load or deep dimming conditions, the switching frequency is prone to frequent jumps and abnormal increases, resulting in decreased system stability, significant fluctuations in inductor current, and consequently, noticeable flickering of the LED, affecting dimming uniformity and display effect.

[0004] In a first aspect, embodiments of this application provide a backlight LED driving circuit applied to a driver chip. The backlight LED driving circuit includes a demagnetization detection module, a sampling detection module, a PWM dimming module, an error amplification module, a valley locking module, and a logic driving module. The error amplification module is electrically connected to the sampling detection module, the PWM dimming module, and the valley locking module, respectively. The valley locking module is electrically connected to the demagnetization detection module and the logic driving module, respectively. The demagnetization detection module, the sampling detection module, and the logic driving module are all used for electrical connection to peripheral circuits.

[0005] The demagnetization detection module receives the drain resonant voltage signal of the power switch in the peripheral circuit as a demagnetization feedback signal and generates a trough detection signal at the trough of the drain resonant voltage signal. The sampling detection module receives the sampled voltage and outputs the detection voltage. The PWM dimming module outputs a reference voltage based on the PWM dimming signal. The error amplification module outputs an error voltage based on the detection voltage and the reference voltage. The trough locking module determines the number of locked troughs based on the error voltage and counts the current number of troughs based on the trough detection signal. If the current number of troughs equals the number of locked troughs, the trough locking module outputs a conduction control signal. The logic driving module outputs a driving signal based on the conduction control signal to control the power switch to conduct.

[0006] In one possible implementation of the first aspect, the valley locking module is further configured to increment the locked valley number by 1 when the current valley number is greater than the locked valley number, and decrement the locked valley number by 1 when the current valley number is less than the locked valley number.

[0007] In one possible implementation of the first aspect, the valley locking module is further configured to increase the number of locked valleys when the operating frequency of the driving chip is greater than a preset upper frequency threshold, and to decrease the number of locked valleys when the operating frequency of the driving chip is less than a preset lower frequency threshold.

[0008] In one possible implementation of the first aspect, the number of locked troughs is negatively correlated with the error voltage, and the lower the error voltage, the larger the number of locked troughs.

[0009] In one possible implementation of the first aspect, when the enable of the PWM dimming signal is turned off, the logic drive module stops outputting the drive signal, thereby turning off the power switch.

[0010] In one possible implementation of the first aspect, the error amplification module includes an error amplifier, a first input terminal of the error amplifier being electrically connected to the sampling detection module, a second input terminal of the error amplifier being electrically connected to the PWM dimming module, and an output terminal of the error amplifier being electrically connected to the valley locking module.

[0011] In one possible implementation of the first aspect, the logic driving module includes a logic unit and a driving unit, the logic unit being electrically connected to the valley locking module and the driving unit respectively, and the driving unit being used to be electrically connected to the gate of the power switch.

[0012] The logic unit is used to output a logic signal to the driving unit according to the conduction control signal, and the driving unit is used to output the driving signal according to the logic signal.

[0013] Secondly, embodiments of this application provide a driver chip, including the backlight LED driver circuit described in any one of the first aspects.

[0014] Thirdly, embodiments of this application provide a driving system, including peripheral circuits and the driving chip described in the second aspect, wherein the driving chip is electrically connected to the peripheral circuits.

[0015] In one possible implementation of the third aspect, the peripheral circuit includes an inductor, a first diode, an output capacitor, an LED, a power switch, a sampling resistor, a first capacitor, a first resistor, and a second resistor. The cathode of the first diode, the first terminal of the output capacitor, and the anode of the LED are all electrically connected to the power supply. The anode of the first diode is electrically connected to the first terminal of the inductor, the drain of the power switch, and the first terminal of the first capacitor, respectively. The second terminal of the inductor is electrically connected to the second terminal of the output capacitor and the cathode of the LED, respectively. The first terminal of the first resistor is electrically connected to the second terminal of the first capacitor. The second terminal of the first resistor is electrically connected to the first terminal of the second resistor. The first terminal of the sampling resistor is electrically connected to the source of the power switch. The second terminals of the sampling resistor and the second terminals of the second resistor are both grounded. The gate of the power switch, the source of the power switch, and the second terminal of the first resistor are all electrically connected to the driver chip.

[0016] The beneficial effects of the embodiments in this application compared with the prior art are:

[0017] The backlight LED driving circuit provided in this application includes a demagnetization detection module, a sampling detection module, a PWM dimming module, an error amplification module, a valley locking module, and a logic driving module. The demagnetization detection module receives the drain resonant voltage signal of the power switch in the peripheral circuit as a demagnetization feedback signal and generates a valley detection signal at the valley of the drain resonant voltage signal. The sampling detection module receives the sampled voltage and outputs a detection voltage. The PWM dimming module outputs a reference voltage based on the PWM dimming signal. The error amplification module outputs an error voltage based on the detection voltage and the reference voltage. The valley locking module determines the number of locked valleys based on the error voltage and counts the current number of valleys based on the valley detection signal. If the current number of valleys equals the number of locked valleys, the valley locking module outputs a conduction control signal. The logic driving module outputs a driving signal based on the conduction control signal to control the power switch to conduct. Therefore, the backlight LED driving circuit of this application adds a valley locking module and introduces valley locking technology. The power switch is only allowed to turn on when the current valley number is consistent with the locked valley number. This can effectively constrain the switching cycle and stabilize the operating frequency, avoid frequency drift and current fluctuation during PWM dimming and load changes, and ensure constant LED current and smooth dimming without flicker. At the same time, it makes the power switch always turn on at the resonant valley, realize quasi-resonant soft switching, reduce switching losses and electromagnetic interference, and significantly improve system stability, dimming quality and working efficiency.

[0018] It is understood that the beneficial effects of the second and third aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art 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.

[0020] Figure 1 This is a circuit diagram of the peripheral circuit;

[0021] Figure 2 This is a schematic block diagram of a backlight LED driving circuit provided in one embodiment of this application;

[0022] Figure 3 This is a flowchart of valley detection provided in an embodiment of this application;

[0023] Figure 4 This is a schematic diagram illustrating the variation of the number of troughs with error voltage according to an embodiment of this application;

[0024] Figure 5This is a circuit connection diagram of a backlight LED driving circuit provided in an embodiment of this application;

[0025] Figure 6 This is a timing diagram of quasi-resonant control provided in an embodiment of this application.

[0026] In the figure, 10 is the backlight LED driving circuit; 101 is the demagnetization detection module; 102 is the sampling detection module; 103 is the PWM dimming module; 104 is the error amplification module; 105 is the valley locking module; 106 is the logic driving module; 1061 is the logic unit; and 1062 is the driving unit. Detailed Implementation

[0027] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0028] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0029] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0030] As used in this application specification and the appended claims, the term "if" may be interpreted, depending on the context, as "when," "once," "in response to determination," or "in response to detection." Similarly, the phrase "if determined" or "if [the described condition or event] is detected" may be interpreted, depending on the context, as "once determined," "in response to determination," "once [the described condition or event] is detected," or "in response to detection of [the described condition or event]."

[0031] Furthermore, in the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0033] Currently, quasi-resonant control is widely used in LED backlight driving. This method achieves soft switching by detecting the resonant trough of the drain voltage of the power switch, thereby reducing switching losses and electromagnetic interference. However, in traditional quasi-resonant drive circuits, the operating frequency tends to fluctuate significantly with the output current during PWM dimming and load changes. Especially under light load or deep dimming conditions, the switching frequency is prone to frequent jumps and abnormal increases, leading to decreased system stability, significant inductor current fluctuations, and consequently, noticeable LED flickering, affecting dimming uniformity and display quality.

[0034] To address the aforementioned issues, the backlight LED driving circuit provided in this application includes a demagnetization detection module, a sampling detection module, a PWM dimming module, an error amplification module, a valley locking module, and a logic driving module. The demagnetization detection module receives the drain resonant voltage signal of the power switch in the peripheral circuit as a demagnetization feedback signal and generates a valley detection signal at the valley of the drain resonant voltage signal. The sampling detection module receives the sampled voltage and outputs a detection voltage. The PWM dimming module outputs a reference voltage based on the PWM dimming signal. The error amplification module outputs an error voltage based on the detection voltage and the reference voltage. The valley locking module determines the number of locked valleys based on the error voltage and counts the current number of valleys based on the valley detection signal. If the current number of valleys equals the number of locked valleys, the valley locking module outputs a conduction control signal. The logic driving module outputs a driving signal based on the conduction control signal to control the power switch to conduct. Therefore, the backlight LED driving circuit of this application adds a valley locking module and introduces valley locking technology. The power switch is only allowed to turn on when the current valley number is consistent with the locked valley number. This can effectively constrain the switching cycle and stabilize the operating frequency, avoid frequency drift and current fluctuation during PWM dimming and load changes, and ensure constant LED current and smooth dimming without flicker. At the same time, it makes the power switch always turn on at the resonant valley, realize quasi-resonant soft switching, reduce switching losses and electromagnetic interference, and significantly improve system stability, dimming quality and working efficiency.

[0035] To illustrate the technical solution described in this application, specific embodiments are provided below.

[0036] Figure 1 A circuit diagram of peripheral circuit 20 is shown. Peripheral circuit 20 includes inductor L, first diode D1, output capacitor CLoad, LED, power switch Q1 (NMOS transistor), sampling resistor RCS, first capacitor C1, first resistor R1, and second resistor R2. The cathode of first diode D1, the first terminal of output capacitor CLoad, and the anode of LED are all electrically connected to the power supply VDD. The anode of first diode D1 is electrically connected to the first terminal of inductor L, the drain of power switch Q1, and the first terminal of first capacitor C1. The second terminal of inductor L is electrically connected to the second terminal of output capacitor CLoad and the cathode of LED. The first terminal of first resistor R1 is electrically connected to the second terminal of first capacitor C1. The second terminal of first resistor R1 is electrically connected to the first terminal of second resistor R2. The first terminal of sampling resistor RCS is electrically connected to the source of power switch Q1. The second terminal of sampling resistor RCS and the second terminal of second resistor R2 are both grounded. The gate of power switch Q1, the source of power switch Q1, and the second terminal of first resistor R1 are all electrically connected to the driver chip.

[0037] Figure 2 A schematic block diagram of a backlight LED driving circuit 10 according to an embodiment of this application is shown. See also Figure 2 As shown, the backlight LED driving circuit 10 is applied to the driving chip. The backlight LED driving circuit 10 includes a demagnetization detection module 101, a sampling detection module 102, a PWM dimming module 103, an error amplification module 104, a valley locking module 105, and a logic driving module 106. The error amplification module 104 is electrically connected to the sampling detection module 102, the PWM dimming module 103, and the valley locking module 105, respectively. The valley locking module 105 is electrically connected to the demagnetization detection module 101 and the logic driving module 106, respectively. The demagnetization detection module 101 is electrically connected to the second terminal of the first resistor R1 and the first terminal of the second resistor R2, respectively. The sampling detection module 102 is electrically connected to the source of the power switch Q1 and the first terminal of the sampling resistor RCS, respectively. The logic driving module 106 is electrically connected to the gate of the power switch Q1.

[0038] Specifically, in the peripheral circuit 20, the first diode D1 is used to prevent reverse current flow, the inductor L is used for energy storage and transfer, the output capacitor CLoad is used to stabilize the output voltage, the LED is the load light-emitting device, the power switch Q1 is used to control the on / off switching of energy transmission, the sampling resistor RCS is used to convert the output current into a sampling voltage, and the first capacitor C1, the first resistor R1, and the second resistor R2 form a voltage divider and filter network to divide and filter the resonant voltage of the drain of the power switch Q1 to provide a safe and stable demagnetization feedback signal. The demagnetization detection module 101 of this application obtains the resonant voltage signal of the drain of the power switch Q1 as a demagnetization feedback signal by connecting the common terminal of the first resistor R1 and the second resistor R2, and generates a trough detection signal at the trough of the drain resonant voltage signal. When the inductor L completes demagnetization, the ZVS pin drops to a low level, at which point the driver chip knows that the current of the inductor L has reached zero. The sampling detection module 102 obtains the sampling voltage by connecting the source of the power switch Q1 and the sampling resistor RCS to realize the real-time detection and feedback of the LED output current and outputs the detection voltage VCS. The PWM dimming module 103 outputs a reference voltage Ref based on the PWM dimming signal. The error amplification module 104 outputs an error voltage EA_OUT based on the detected voltage VCS and the reference voltage Ref. The valley locking module 105 determines the number of locked valleys based on the error voltage EA_OUT, and counts the current number of valleys based on the valley detection signal. If the current number of valleys equals the number of locked valleys, the valley locking module 105 outputs a conduction control signal. The logic drive module 106 is connected to the gate of the power switch Q1 and is used to output a drive signal based on the conduction control signal to control the conduction of the power switch Q1. Therefore, the backlight LED driver circuit 10 of this application adds a valley locking module 105, which introduces valley locking technology. The power switch Q1 is only allowed to turn on when the current valley number is consistent with the locked valley number. This can effectively constrain the switching cycle and stabilize the operating frequency, avoid frequency drift and current fluctuation when PWM dimming and load changes, and ensure constant LED current and smooth dimming without flicker. At the same time, it makes the power switch Q1 always turn on at the resonant valley, realize quasi-resonant soft switching, reduce switching losses and electromagnetic interference, and significantly improve system stability, dimming quality and working efficiency.

[0039] It should be noted that in LED dimming applications, as the load current I_LED decreases, the operating frequency of the driver chip increases significantly, leading to increased switching losses and reduced system efficiency. Some existing technologies suppress the frequency rise by setting a frequency upper limit that decreases with decreasing load, but such solutions cannot guarantee that the power switch Q1 is always turned on at the resonant trough, which can easily cause drastic fluctuations and oscillations in the switching frequency, resulting in unstable LED current and noticeable flickering during dimming.

[0040] To address this, this application proposes a quasi-resonant dimming control circuit and method based on valley-locking technology. After the inductor L completes demagnetization, the parasitic capacitance of the power switch Q1 forms a resonant circuit with the inductor L, generating a resonant voltage at the switch drain. The system initiates a new switching cycle at the trough of this resonant voltage, significantly reducing switching losses and electromagnetic interference. Since the resonant period formed by the inductor L and the parasitic capacitance is much shorter than the switching period, the system can operate stably in the critical conduction mode, eliminating the need for complex control calculations and simplifying the control logic.

[0041] Building upon this foundation, this application introduces a trough-locking mechanism to effectively suppress frequency drift and oscillation, ensuring that the power switch Q1 always operates stably at the resonant trough position. This maintains a constant LED output current during dimming, thereby eliminating flicker and improving system efficiency. Furthermore, this application's control scheme requires no modification to the traditional peripheral circuit 20 or the addition of extra components. Trough-locking and frequency stabilization are achieved solely through the chip's internal digital logic and control algorithm, without significantly increasing chip area, circuit size, or control complexity. While maintaining the original system cost and layout compatibility, it comprehensively improves dimming smoothness, system efficiency, and operational stability.

[0042] The valley detection process inside the valley locking module 105 is as follows: Figure 3 As shown, after the system starts working, it first determines the range of valley counts based on the error voltage EA_OUT, then detects the current valley count (increments the current valley count by 1 whenever a valley of the drain resonant voltage is detected). The current valley count is then compared with the target count. If the current valley count is less than the target count, the valley count is incremented by 1, and the detection and counting of the next valley is repeated. If the current valley count is greater than the target count, the valley count is decremented by 1, and the detection and counting process continues. If the current valley count equals the target count, the current valley count is locked. Then, the valley detection signal is counted. If the valley detection count equals the locked valley count, a turn-on control signal is output to control the power switch Q1 to turn on. If the valley detection count does not equal the locked valley count, the valley detection signal is counted until the valley detection count equals the locked valley count, thus completing this switching cycle and entering the next valley detection and counting loop. Specifically, by comparing the current number of valleys with the locked number of valleys in real time: when the current number of valleys is greater than the locked number of valleys, the locked number of valleys is incremented by 1; when the current number of valleys is less than the locked number of valleys, the locked number of valleys is decremented by 1. Through the above dynamic adjustment, the system gradually converges and finally determines the minimum number of locked valleys that satisfies the stable operation of the system.

[0043] Figure 4This diagram illustrates the relationship between the number of troughs and the error voltage EA_OUT. Here, Inc represents the upper frequency threshold for increasing the number of troughs, Dec represents the lower frequency threshold for decreasing the number of troughs, Inc_max is the maximum number of troughs that can be increased, Inc_min is the minimum number of troughs that can be increased, Dec_max is the maximum number of troughs that can be decreased, and Dec_min is the minimum number of troughs that can be decreased. By setting these threshold ranges, the number of troughs and the operating frequency can be limited within a reasonable range, avoiding excessively high or low frequencies. This ensures stable operation of the system under different error voltages EA_OUT and load conditions, achieving smooth frequency adjustment and preventing dimming flicker.

[0044] Figure 5 A circuit diagram of the backlight LED driving circuit 10 is shown. Figure 5 It can be seen that the error amplification module 104 includes an error amplifier EA. The first input terminal of the error amplifier EA is electrically connected to the sampling and detection module 102, the second input terminal of the error amplifier EA is electrically connected to the PWM dimming module 103, and the output terminal of the error amplifier EA is electrically connected to the valley locking module 105.

[0045] Specifically, the positive input of error amplifier EA receives the reference voltage Ref, and the inverting input receives the detection voltage VCS. When the PWM dimming duty cycle decreases (the load becomes lighter), the reference voltage Ref of error amplifier EA decreases accordingly, shortening the demagnetization time of inductor L and increasing the system operating frequency. Therefore, it can be deduced that the error voltage EA_OUT output by error amplifier EA is negatively correlated with the number of lock-in troughs. The lower the error voltage EA_OUT, the lower the reference voltage Ref, and the larger the corresponding number of lock-in troughs. By adjusting the number of troughs, stable control of the operating frequency is achieved, ensuring stable current and flicker-free operation during LED dimming.

[0046] In addition, the logic drive module 106 includes a logic unit 1061 and a drive unit 1062. The logic unit 1061 is connected to the valley locking module 105 and is used to receive and process the turn-on control signal to generate an internal logic control signal. The drive unit 1062 is connected to the logic unit 1061 and the gate of the power switch Q1 and is used to convert the weak logic signal output by the logic unit 1061 into a gate drive signal with sufficient drive capability, thereby reliably controlling the turn-on and turn-off of the power switch Q1 and realizing precise control of the resonant switching cycle.

[0047] It should be noted that as the system's operating frequency gradually increases to Figure 4When the Inc threshold curve is shown, the controller reduces the operating frequency by increasing the number of troughs. After increasing the number of troughs, the chip's operating frequency will fluctuate between the Inc and Dec threshold curves. If the operating frequency is again higher than the Inc threshold, the number of troughs is further increased. If the PWM signal duty cycle is increased, the load increases accordingly, and the operating frequency decreases. When the operating frequency is lower than the Dec threshold, the operating frequency is increased by reducing the number of troughs. Once the number of troughs is determined, it is latched by a latch, and the number of troughs turned on is precisely controlled according to the latched state in each switching cycle. To ensure the stability of the number of troughs when the power supply voltage fluctuates and to avoid frequent jumps in the number of troughs at switching points, sufficient margin needs to be set between the Inc and Dec curves. At the same time, the system dynamically adjusts the allowable upper and lower limits of the number of troughs according to the error voltage EA_OUT.

[0048] It should be noted that, Figure 5 The ZVS detection circuit in the demagnetization detection module 101, the CS detection circuit in the sampling detection module 102, the PWM dimming circuit in the PWM dimming module 103, the logic unit 1061, and the drive unit 1062 are all existing mature technologies and will not be described in detail here. Furthermore, the valley locking module 105 typically includes a controller, a counter, a comparator, and a latch. The controller determines the number of valleys to be locked based on the error voltage, the counter counts based on the valley detection signal, the comparator compares the current valley number with the locked valley number, and the latch latches and stabilizes the determined valley number to achieve valley counting, comparison, and quantity locking functions.

[0049] It should be noted that, by Figure 5 As can be seen, each module in the backlight LED driving circuit 10 of this application is set inside the driver chip. ZVS, CS, PWM, and GATE are all used as signal receiving pins / signal output pins of the driver chip. Among them, the ZVS pin is used to receive the demagnetization feedback signal, the CS pin is used to receive the sampling voltage, the PWM pin is used to input the external PWM dimming signal, and the GATE pin is used to output the gate drive signal to control the external power switch. Each pin is connected to the corresponding peripheral circuit and module to realize the input, output and interactive control of signals.

[0050] Figure 6The quasi-resonant control timing diagram is shown. During dimming, the chip receives the PWM dimming signal, and the controller determines the number of pre-locked valleys (e.g., 3) based on the current dimming reference voltage Ref. The demagnetization feedback signal, i.e., the ZVS signal, generates a valley detection signal each time it experiences a resonant zero-crossing. After continuously detecting the set number of valley signals, the system generates a turn-on control signal to control the gate of the power switch Q1 to turn it on. During the PWM enable period, the number of valleys is kept locked, ensuring a stable and consistent switching cycle, thereby guaranteeing a constant LED load current I_LED and preventing flickering caused by current fluctuations. When the PWM enable signal is invalid, the logic drive module 106 stops outputting drive signals, and the power switch Q1 is forcibly turned off, at which point the load current I_LED drops to zero. Finally, by coordinating the control of the PWM enable signal and the PWM duty cycle, stable PWM dimming control of the LED load current I_LED is achieved.

[0051] This application also discloses a driver chip, including the backlight LED driver circuit 10 described above. By adopting the backlight LED driver circuit 10, the driver chip can stably operate at a frequency within a wide load and PWM dimming range, ensuring that the power switch is always turned on at the resonant trough, suppressing frequency drift and oscillation, maintaining a constant LED output current, avoiding dimming flicker, reducing switching losses and electromagnetic interference, and without modifying the peripheral circuit or significantly increasing the chip complexity, effectively improving system efficiency, stability and dimming quality.

[0052] This application also discloses a driving system, including peripheral circuit 20 and the aforementioned driving chip, wherein the driving chip is electrically connected to the peripheral circuit 20. The driving system using the aforementioned driving chip can achieve stable trough locking and frequency control during wide load and PWM dimming processes, ensuring constant LED output current, smooth dimming without flicker, and simultaneously achieving quasi-resonant soft-switching operation, reducing switching losses and electromagnetic interference. It possesses advantages such as simple structure, strong compatibility, high system efficiency, and stable and reliable operation.

[0053] Since the processing and functions implemented by the driver chip and driver system in this embodiment are basically the same as the embodiments, principles and examples of the aforementioned backlight LED driver circuit, any details not covered in this embodiment can be found in the relevant descriptions in the aforementioned embodiments, and will not be repeated here.

[0054] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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 of the technical features. Such modifications 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, and should all be included within the protection scope of this application.

Claims

1. A backlight LED driving circuit, characterized in that, The backlight LED driving circuit, applied to a driver chip, includes a demagnetization detection module, a sampling detection module, a PWM dimming module, an error amplification module, a valley locking module, and a logic driving module. The error amplification module is electrically connected to the sampling detection module, the PWM dimming module, and the valley locking module, respectively. The valley locking module is electrically connected to the demagnetization detection module and the logic driving module, respectively. The demagnetization detection module, the sampling detection module, and the logic driving module are all used for electrical connection to peripheral circuits. The demagnetization detection module receives the drain resonant voltage signal of the power switch in the peripheral circuit as a demagnetization feedback signal and generates a trough detection signal at the trough of the drain resonant voltage signal. The sampling detection module receives the sampled voltage and outputs the detection voltage. The PWM dimming module outputs a reference voltage based on the PWM dimming signal. The error amplification module outputs an error voltage based on the detection voltage and the reference voltage. The trough locking module determines the number of locked troughs based on the error voltage and counts the current number of troughs based on the trough detection signal. If the current number of troughs equals the number of locked troughs, the trough locking module outputs a conduction control signal. The logic driving module outputs a driving signal based on the conduction control signal to control the power switch to conduct. The valley locking module is also used to increment the locked valley number by 1 when the current valley number is greater than the locked valley number, and to decrement the locked valley number by 1 when the current valley number is less than the locked valley number; The valley locking module is also used to increase the number of locked valleys when the operating frequency of the driver chip is greater than the preset upper frequency threshold, and to decrease the number of locked valleys when the operating frequency of the driver chip is less than the preset lower frequency threshold.

2. The backlight LED driving circuit according to claim 1, characterized in that, The number of locked troughs is negatively correlated with the error voltage; the lower the error voltage, the larger the number of locked troughs.

3. The backlight LED driving circuit according to claim 1, characterized in that, When the enable of the PWM dimming signal is turned off, the logic drive module stops outputting the drive signal, thereby turning off the power switch.

4. The backlight LED driving circuit according to claim 1, characterized in that, The error amplification module includes an error amplifier. The first input terminal of the error amplifier is electrically connected to the sampling and detection module, the second input terminal of the error amplifier is electrically connected to the PWM dimming module, and the output terminal of the error amplifier is electrically connected to the valley locking module.

5. The backlight LED driving circuit according to claim 1, characterized in that, The logic driving module includes a logic unit and a driving unit. The logic unit is electrically connected to the valley locking module and the driving unit, respectively. The driving unit is used to be electrically connected to the gate of the power switch. The logic unit is used to output a logic signal to the driving unit according to the conduction control signal, and the driving unit is used to output the driving signal according to the logic signal.

6. A driver chip, characterized in that, Includes the backlight LED driving circuit as described in any one of claims 1-5.

7. A drive system, characterized in that, It includes peripheral circuitry and the driver chip as described in claim 6, wherein the driver chip is electrically connected to the peripheral circuitry.

8. The drive system according to claim 7, characterized in that, The peripheral circuit includes an inductor, a first diode, an output capacitor, an LED, a power switch, a sampling resistor, a first capacitor, a first resistor, and a second resistor. The cathode of the first diode, the first terminal of the output capacitor, and the anode of the LED are all electrically connected to the power supply. The anode of the first diode is electrically connected to the first terminal of the inductor, the drain of the power switch, and the first terminal of the first capacitor, respectively. The second terminal of the inductor is electrically connected to the second terminal of the output capacitor and the cathode of the LED, respectively. The first terminal of the first resistor is electrically connected to the second terminal of the first capacitor, and the second terminal of the first resistor is electrically connected to the first terminal of the second resistor. The first terminal of the sampling resistor is electrically connected to the source of the power switch. The second terminals of the sampling resistor and the second terminals of the second resistor are both grounded. The gate of the power switch, the source of the power switch, and the second terminal of the first resistor are all electrically connected to the driver chip.

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