High-frequency jitter-free LED control method, control circuit, driving circuit and lamp

Abstract

The invention provides a high-frequency jitter-free LED control method, a control circuit, a driving circuit and a lamp, which are used for solving the problem of light jitter caused by sudden change of brightness during PWM dimming due to slow and non-uniform decrease of an LED driving current in a PWM high-frequency state. Specifically, two sets of high-frequency PWM signals with the same frequency and opposite phases are provided, the first set of PWM signals are used for LED dimming, the second set of PWM signals are switching signals, and when the first set of PWM signals control the LED to be turned off, the second set of PWM signals are used for opening a low-impedance path between the positive electrode and the negative electrode of the LED and releasing current on the LED. According to the invention, it can be ensured that images captured by the camera have no stroboflash, and the shooting quality is improved.

Description

Technical Field

[0001] The present invention relates to the field of LED lamp driving circuits, and in particular to a high-frequency debouncing method and circuit. Background Art

[0002] Existing LED lighting systems often experience flickering during dimming, especially when using mobile phones and other devices for filming, affecting lighting quality and user experience. High-frequency PWM dimming is often used to reduce flicker. This is primarily due to its adaptability to human visual perception, its excellent compatibility with mobile phone camera shutter speeds, and its improved dimming accuracy. The specific reasons are as follows:

[0003] 1. Exceeding the human visual perception threshold: The human eye has a certain threshold for light flicker, approximately between 100Hz and 120Hz. When the PWM dimming frequency is much higher than the human eye's perception threshold, the LED switches on and off extremely frequently per unit time. The human eye cannot distinguish such rapid brightness changes, making the flicker almost imperceptible. Under this high-frequency dimming, the brightness of the light source perceived by the human eye is stable, effectively avoiding the problem of flicker caused by visual perception and providing a stable visual environment for mobile phone photography.

[0004] 2. Compatible with mobile phone camera shutter speeds: Most mobile phone camera shutter speeds range from 1 / 30 to 1 / 60 seconds, corresponding to a frequency of 30Hz to 60Hz. When the PWM dimming frequency is much higher than the mobile phone camera shutter speed, it means that the LED has completed multiple on-off switching in the extremely short time the camera shutter is open. The brightness changes are almost negligible during the camera capture process, thus eliminating flicker in the captured image and ensuring the stability of the captured image.

[0005] 3. Improved dimming accuracy and reduced brightness fluctuations: High-frequency PWM dimming allows for finer brightness adjustments. Due to its high frequency, more brightness adjustments can be made per unit time. Compared to low-frequency PWM dimming, high-frequency dimming can more precisely control the average brightness of the LED, resulting in smoother brightness changes. When adjusting brightness, high-frequency PWM dimming can achieve more delicate brightness transitions by fine-tuning the duty cycle, reducing brightness fluctuations caused by inaccurate dimming. This stable brightness output not only improves the screen display quality but also ensures consistent brightness of images captured by the phone's camera, further reducing the possibility of flicker and ensuring high-quality photography.

[0006] However, flickering can still occur at high PWM frequencies. The PWM signal directly controls the LED's current. When the PWM signal is high, the LED turns on and emits light. When the PWM signal transitions from high to low, the current does not immediately drop to 0mA, but instead slowly decreases through the LED's natural discharge. This slow current drop means the LED's brightness doesn't change instantaneously, but rather gradually. This gradual change appears as light jitter to the human eye. Especially when the PWM signal's duty cycle changes rapidly, the uneven current drop causes the LED's brightness to change suddenly, resulting in uneven visual perception, light jitter, and sudden changes in brightness. Summary of the Invention

[0007] In view of this, the present invention proposes a high-frequency jitter-free LED control method, control circuit, drive circuit and lamp, which are used to solve the light jitter problem caused by slow and uneven decrease of LED drive current under PWM high-frequency state, resulting in sudden change of brightness during PWM dimming.

[0008] On the one hand, the present application provides a control method for high-frequency continuous dimming without jitter, including providing two groups of high-frequency PWM signals with the same frequency and opposite phases. The first group of PWM signals is used for LED dimming, and the second group of PWM signals is a switching signal. When the first group of PWM signals controls the LED to turn off, the second group of PWM signals is used to open a low-impedance path between the positive and negative poles of the LED to release the current on the LED.

[0009] Furthermore, the PWM signal frequency is greater than the shooting frequency of the shooting device.

[0010] On the other hand, the present application provides a high-frequency continuous dimming and jitter-free control circuit, including an LDO voltage regulator circuit, an MCU control circuit, and a continuous dimming de-jitter circuit; the MCU control circuit is used to output two groups of high-frequency PWM signals with the same frequency and opposite phases, wherein the first group of PWM signals is used for LED dimming, and the second group of PWM signals is output to the continuous dimming de-jitter circuit; the continuous dimming de-jitter circuit is placed between the positive and negative poles of the LED, and when the first group of PWM signals turns off the LED, the second group of PWM signals controls the continuous dimming de-jitter circuit to form a low-impedance path between the positive and negative poles of the LED, releasing the current on the LED; the LDO voltage regulator circuit is used to provide power for the MCU control circuit.

[0011] Furthermore, the continuous dimming and debouncing circuit includes a two-stage switch, the first-stage switch is controlled by the second set of PWM signals, and the second-stage switch is controlled by the first-stage switch. After the second-stage switch is turned on, a low-impedance path is formed between the positive and negative poles of the LED.

[0012] Furthermore, the first-stage switch includes a transistor, a base voltage divider circuit and a collector power supply circuit; the collector of the transistor is connected to the positive electrode of the LED via the collector power supply circuit, the emitter of the transistor is connected to the negative electrode of the LED, the base voltage divider circuit is used to provide the base bias voltage of the transistor, and the collector power supply circuit is used to provide the DC bias voltage of the transistor.

[0013] Furthermore, the second-stage switch includes a high-power transistor, the gate of the high-power transistor is connected to the collector of the transistor in the first-stage switch, the source of the high-power transistor is connected to the positive electrode of the LED, and the drain of the high-power transistor is connected to the negative electrode of the LED.

[0014] Furthermore, the base voltage divider circuit includes two resistors, one resistor is connected between the base of the transistor and the second group of PWM signals; the other resistor is connected between the emitter of the transistor and the negative electrode of the LED; the collector power supply circuit includes a resistor, which is connected between the collector of the transistor and the positive electrode of the LED.

[0015] Furthermore, when the second set of PWM signals is at a high level, the transistors in the first stage switch are turned on, thereby controlling the high-power transistors in the second stage switch to be turned on, so that a short-circuit current is formed between the positive and negative electrodes of the LED.

[0016] Furthermore, the PWM signal frequency is greater than the shooting frequency of the shooting device.

[0017] Furthermore, the MCU control circuit is connected to the power supply via a key switch, and the three working modes of turning on the LED, turning off the LED, and adjusting the LED brightness are switched by pressing the key switch for a certain period of time.

[0018] On the other hand, the present application provides a high-frequency continuous dimming and jitter-free driving circuit, including an LED driving constant current circuit and the above-mentioned control circuit connected to the LED driving constant current circuit. The first group of PWM signals output by the control circuit is input into the LED driving constant current circuit as the LED high-frequency dimming control signal, and the second group of PWM signals output by the control circuit is used to eliminate the current on the LED when the LED is turned off.

[0019] On the other hand, the present application provides a high-frequency continuous dimming LED lamp without jitter, including an LED lamp and a driving circuit connected to the LED lamp.

[0020] The present invention can achieve at least the following technical effects:

[0021] 1. The PWM dimming frequency used in this invention is much higher than the human eye's perception threshold for light flicker, which can effectively reduce visually perceived flicker;

[0022] 2. The PWM frequency used in this invention is much higher than the shutter speed of the mobile phone camera, so that the camera can capture stable images at any shutter speed, avoid strobing, improve the shooting quality, and enhance the user experience;

[0023] 3. The high-frequency PWM used in the present invention allows for finer brightness adjustment;

[0024] 4. The present invention provides two sets of PWM signals with the same frequency and opposite phases. One is used to adjust the brightness of the LED, and the other is used to release the residual current on the LED when the LED is turned off, so that the rise / fall time (Rise / Fall Time) of the driving waveform is steep enough, solving the flicker problem caused by high-frequency signals.

[0025] 5. The present invention can ensure the actual light output modulation depth. When dimming deeply (such as 1% duty cycle), even if the proportion of on-off time is too low, it will not cause actual brightness unevenness.

[0026] 6. The control circuit provided by the present invention has a simple structure and a unique architecture, and is suitable for various existing LED drive circuits.

[0027] 7. The driving circuit provided by the present invention has a simple structure, is easy to use, and is applicable to various existing LED lamps.

[0028] 8. The LED lamp provided by the present invention has smoother brightness changes, which improves visual comfort. In particular, when using high-speed camera equipment, such as stage lighting, industrial inspection scenes, etc., flicker will not be captured. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of a high-frequency continuous dimming and jitter-free control circuit described in this application;

[0030] Figure 2 This is a schematic diagram of a high-frequency continuous dimming and jitter-free driving circuit described in this application;

[0031] Figure 3 A schematic diagram of the structure of an LDO voltage stabilization circuit provided in an embodiment of the present application;

[0032] Figure 4 A schematic diagram of the structure of an LED driving constant current circuit provided in an embodiment of the present application;

[0033] Figure 5 A schematic diagram of the structure of an MCU control circuit provided in an embodiment of the present application;

[0034] Figure 6 A schematic diagram of the structure of a continuous dimming and debouncing circuit provided in an embodiment of the present application;

[0035] Figure 7 A schematic diagram of the structure of a high-frequency continuous dimming and jitter-free driving circuit provided in an embodiment of the present application;

[0036] Figure 8 A driving output current waveform when the PWM signal is converted from a high level to a low level when there is no parallel low-impedance path at the output end of an LED driver provided by an embodiment of the present application;

[0037] Figure 9 This is a driving output current waveform when a low-impedance path is connected in parallel to an LED driving output terminal provided by an embodiment of the present application and a PWM signal is converted from a high level to a low level. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0039] According to the background technology, when the PWM signal is high, the LED is turned on and emits light. When the PWM signal is low, the LED is turned off and the current gradually decreases. The current decreases through the natural discharge process of the LED. Therefore, when the PWM signal switches from high to low, the current does not drop to 0mA immediately, but decreases slowly. The specific decrease process is as follows: Figure 8 As shown in the waveform in the rectangular box.

[0040] To this end, the present invention proposes a high-frequency continuous dimming control method without jitter, including providing two sets of high-frequency PWM signals with the same frequency and opposite phases. The first set of PWM signals (i.e., PWM1) is used for LED dimming, and the second set of PWM signals (i.e., PWM2) is a switching signal. When the first set of PWM signals controls the LED to turn off, the second set of PWM signals is used to open a low-impedance path between the positive and negative poles of the LED, releasing the current on the LED.

[0041] When the LED is turned off, the formation of residual current in it is complex. However, no matter what the reason is, as long as a low-impedance path between the positive and negative poles of the LED is opened, the residual current can be quickly released.

[0042] Furthermore, the timing of turning on the low-impedance path is also important because the current gradually decreases when the LED is off only when the PWM signal is low. This phenomenon does not occur when the PWM signal is high. Therefore, a pair of mutually exclusive signals is used as the LED turn-on control signal and the low-impedance path enable control signal to ensure that the low-impedance path is not enabled when the LED is on, and is enabled when the LED is off.

[0043] Combined with the background technology records, it can be seen that the human eye's perception threshold for light flicker is approximately between 100Hz and 120Hz; the shutter speed of most mobile phone cameras is between 1 / 30 second and 1 / 60 second, that is, 30Hz to 60Hz; other application scenarios may use higher frequency shooting speeds; for various situations, the PWM signal frequency is higher than the human eye's perception threshold and the camera's shutter speed. For example, if the PWM signal frequency is greater than 24KHZ, the human eye will hardly perceive the flicker and can adapt well to the shutter speed of the mobile phone camera, thereby achieving the purpose of visual jitter-free.

[0044] Based on the above control method, the present invention proposes a high-frequency continuous dimming and jitter-free control circuit. This control circuit can provide the two sets of high-frequency PWM signals described in the above method. Specifically, it includes an LDO voltage regulator circuit, an MCU control circuit, and a continuous dimming and jitter elimination circuit.

[0045] The LDO voltage regulator circuit is used to provide power to the MCU control circuit. Figure 3 The specific structural form shown is only one implementation method, in which the 24V voltage is converted into the 5V stable operating voltage required by the MCU control circuit. C3 is the input filter capacitor and C4 is the output filter capacitor.

[0046] A specific implementation form of the MCU control circuit is as follows Figure 5 As shown, it includes the chip JZ8PT2501. The following are the specific functions and pin descriptions.

[0047]

[0048]

[0049]

[0050] The following combination Figure 5 Further explanation of the working principle of the MCU control circuit:

[0051] 1. Connect pin 1 of the IC to the push button switch for light control. The other pin of the push button switch is connected to a 5V power supply. Pin 1 is set to a pull-down low level state. When the button is pressed, 5V voltage is supplied to pin 1 of the IC through the button. At this time, when the IC detects that pin 1 is at a high level, it internally determines that a button has been pressed. If the button is pressed for less than 0.5 seconds, it is a short press, which turns the light on and off. If the button is pressed for more than 0.6 seconds, it is a long press, which adjusts the brightness of the light.

[0052] 2. Long press for dimming function logic: the brightness adjustment range is 5-100% adjustable; at the lowest brightness, long press to increase the brightness; at the highest brightness, long press to decrease the brightness; when the brightness is in any intermediate state, long press the button to dim in the opposite direction of the last dimming direction.

[0053] 3. The output frequency of PWM1 and PWM2 signals of MCU is 32KHz, and the phases of the two sets of PWM signals PWM1 and PWM2 are opposite. When PWM1 is high, PWM2 is low, and when PWM1 is low, PWM2 is high.

[0054] 4. IC pin 6 is the PWM1 signal output port. This signal is used to control the LED drive circuit to achieve functions such as controlling the LED on / off / brightness adjustment.

[0055] 5. Pin 5 of IC is the PWM2 signal output port. This PWM signal output is connected to the continuous dimming de-jitter circuit to control the light jitter phenomenon caused by continuous dimming of the LED driver.

[0056] At this point, two PWM signals have been generated, and one implementation uses a 32kHz PWM signal frequency. Although 32kHz is well beyond the human eye's perceptible range (typically below 200Hz), the afterglow effect of the LED material can cause residual flicker. If the rise / fall times of the drive waveform are not steep enough, the actual light output modulation depth may be insufficient. Therefore, a continuous dimming debounce circuit is required to quickly release the current flowing through the LED when it is off.

[0057] Figure 6 It is an implementation of a continuous dimming and debounce circuit, specifically including two-stage switches, the first-stage switch is controlled by the second group of PWM signals (i.e. Figure 6The second-stage switch is controlled by the first-stage switch. When the second-stage switch is turned on, a low-impedance path is formed between the positive and negative electrodes of the LED, and the first-stage switch improves the driving capability of the PWM2 signal. The first-stage switch is composed of a transistor Q2, a base voltage divider circuit, and a collector power supply circuit. The base voltage divider circuit is composed of resistors R16 and R15. The PWM2 signal is input to the base of the transistor Q2 through resistor R16. The emitter of the transistor Q2 is connected to the negative electrode of the LED through resistor R15; the collector power supply circuit includes resistor R14, and the collector of the transistor Q2 is connected to the positive electrode of the LED through resistor R14; the second-stage switch includes a high-power transistor Q1. The source of the high-power transistor Q1 is connected to the positive electrode of the LED, the drain of the high-power transistor Q1 is connected to the negative electrode of the LED, and the gate of the high-power transistor Q1 is connected to the positive electrode of the LED. It is connected to the collector of transistor Q2; the high-power transistor Q1 is connected between the positive and negative poles of the LED. When the PWM1 signal output is low and the LED is turned off, the PWM2 signal is high. At this time, the transistor Q2 and the high-power transistor Q1 are quickly turned on, short-circuiting the positive and negative poles of the LED, so that the current can be quickly released through the high-power transistor Q1, allowing the LED to go out quickly; when the PWM1 signal output is high and the LED is turned on, the PWM2 signal is low. At this time, the transistor Q2 and the high-power transistor Q1 are quickly turned off, the low-impedance path between the positive and negative poles of the LED disappears, the current flows through the LED, and the LED emits light.

[0058] Based on the above control circuit, the present invention proposes a high-frequency continuous dimming and jitter-free driving circuit, such as Figure 7 As shown, it is used to drive an LED lamp. The driving circuit includes an LED driving constant current circuit and the above-mentioned control circuit connected to the LED driving constant current circuit. The LED driving constant current circuit ensures stable LED brightness by maintaining a constant current output, avoids damage caused by current fluctuations, and prolongs its service life. Figure 4 This is only one implementation of the LED driving constant current circuit, which is described in detail as follows:

[0059] The LED driver constant current circuit consists of LED driver chip U3, input capacitors C1 and C2, current detection resistors R1 and R2, decoupling capacitor C11, freewheeling diode D1, inductor L1, power supply resistor R5, and resistor R11. Among them, U3 is the core control component, integrating PWM and LD dimming interfaces, and is responsible for constant current drive, PWM dimming, and output current control. U3 uses PWM1 output by the control circuit as the control signal for high-frequency dimming. Input capacitors C1 and C2 are used to smooth the input voltage and reduce power supply noise and voltage fluctuations. Power supply resistor R5 and input capacitor C2 together form a power supply circuit to provide the IC with the required operating voltage. Current-limiting resistors R1 and R2 are used to limit the current flowing through the LED, maintaining a constant value for the LED current. Decoupling capacitors C11 and R11 form an RC network to eliminate noise signals when the freewheeling diode D1 is turned on and off, improving EMC. Freewheeling diode D1 provides a freewheeling path for the current in inductor L1 when the LED is turned off. Inductor L1 works with freewheeling diode D1 to reduce voltage and store energy, providing a smooth voltage for the LED.

[0060] The basic functions of LED driving constant current circuit include:

[0061] Power input: Power is input through the LED+ terminal to provide voltage for the entire circuit.

[0062] Current detection: The current detection circuit composed of R1 and R2 monitors the current flowing through the LED to ensure that the current is within a safe range.

[0063] Constant current control: The U3 chip adjusts the conduction state of the internal MOSFET according to the voltage drop of the current detection resistor to ensure that the LED light board is not affected by input voltage fluctuations and achieve constant current control.

[0064] PWM dimming: The PWM1 signal controls the PWM port of U3 and adjusts the on / off / brightness of the LED by changing the duty cycle.

[0065] Based on the above driving circuit, the present invention proposes a high-frequency continuous dimming LED lamp without jitter, which is composed of the above driving circuit and an LED lamp connected together.

[0066] Figure 8 This is the output waveform at the driver circuit end of the high-frequency, continuous dimming, jitter-free LED lamp described in the present invention. As can be seen, due to the fast response of high-power transistor Q1, the current can quickly drop to 0 mA when the PWM1 signal switches from a high level to a low level. This rapid current cutoff reduces the time it takes for the current to fall, making the LED brightness change more instantaneous.

Claims

1. A high-frequency continuous dimming control method without jitter, characterized by: It includes providing two sets of high-frequency PWM signals with the same frequency and opposite phases. The first set of PWM signals is used for LED dimming, and the second set of PWM signals is a switching signal. When the first set of PWM signals controls the LED to turn off, the second set of PWM signals is used to open a low-impedance path between the positive and negative poles of the LED, releasing the current on the LED.

2. The high-frequency continuous dimming control method without jitter according to claim 1, characterized in that: The PWM signal frequency is greater than the shooting frequency of the shooting device.

3. A high-frequency continuous dimming control circuit without jitter, characterized by: It includes an LDO voltage regulator circuit, an MCU control circuit, and a continuous dimming and debouncing circuit; the MCU control circuit is used to output two groups of high-frequency PWM signals with the same frequency and opposite phases, wherein the first group of PWM signals is used for LED dimming, and the second group of PWM signals is output to the continuous dimming and debouncing circuit; the continuous dimming and debouncing circuit is placed between the positive and negative poles of the LED. When the first group of PWM signals turns off the LED, the second group of PWM signals controls the continuous dimming and debouncing circuit to form a low-impedance path between the positive and negative poles of the LED, releasing the current on the LED; the LDO voltage regulator circuit is used to provide power for the MCU control circuit.

4. The high-frequency continuous dimming control circuit without jitter according to claim 3, characterized in that: The continuous dimming and debouncing circuit includes a two-stage switch, the first-stage switch is controlled by the second group of PWM signals, and the second-stage switch is controlled by the first-stage switch. After the second-stage switch is turned on, the low-impedance path is formed between the positive and negative poles of the LED.

5. The high-frequency continuous dimming control circuit without jitter according to claim 4, characterized in that: The first-stage switch includes a transistor, a base voltage divider circuit and a collector power supply circuit; the collector of the transistor is connected to the positive electrode of the LED via the collector power supply circuit, the emitter of the transistor is connected to the negative electrode of the LED, the base voltage divider circuit is used to provide the base bias voltage of the transistor, and the collector power supply circuit is used to provide the DC bias voltage of the transistor.

6. The high-frequency continuous dimming control circuit without jitter according to claim 4, characterized in that: The second-stage switch includes a high-power transistor, the gate of the high-power transistor is connected to the collector of the transistor in the first-stage switch, the source of the high-power transistor is connected to the positive electrode of the LED, and the drain of the high-power transistor is connected to the negative electrode of the LED.

7. The high-frequency continuous dimming control circuit without jitter according to any one of claims 5 to 6, characterized in that: The base voltage divider circuit includes two resistors, the first resistor is connected between the base of the transistor and the second group of PWM signals; the second resistor is connected between the emitter of the transistor and the cathode of the LED; the collector power supply circuit includes a third resistor, and the third resistor is connected between the collector of the transistor and the anode of the LED.

8. The high-frequency continuous dimming control circuit without jitter according to claim 7, characterized in that: When the second set of PWM signals is at a high level, the transistor in the first stage switch is turned on, thereby controlling the high-power transistor in the second stage switch to be turned on, so that a short-circuit current is formed between the positive and negative electrodes of the LED.

9. The high-frequency continuous dimming control circuit without jitter according to claim 8, characterized in that: The PWM signal frequency is greater than the shooting frequency of the shooting device.

10. A high-frequency continuous dimming and jitter-free driving circuit, characterized by: The device comprises an LED driving constant current circuit, and a control circuit according to any one of claims 3 to 9 connected to the LED driving constant current circuit, wherein the first group of PWM signals output by the control circuit is input into the LED driving constant current circuit as the LED high-frequency dimming control signal, and the second group of PWM signals output by the control circuit is used to eliminate the current flowing through the LED when the LED is turned off.

11. A high-frequency continuous dimming LED lamp without jitter, characterized by: It comprises an LED lamp and a driving circuit as described in right 10 connected to the LED lamp.

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