PWM-Based LED Lighting Circuit, Time-Sharing Dimming Circuit and Control Method

Abstract

The present invention discloses a PWM-based LED lighting circuit, which includes a power supply, a control circuit, and an LED lighting element. It is characterized in that: it further includes a non-light-emitting load element, and the non-light-emitting load element is connected in parallel with the LED lighting element. The power supply is connected to a constant current source, and the constant current source supplies power to the LED lighting element and the non-light-emitting load element. When the constant current source is in the current rising or falling stage, the control circuit controls the LED lighting element loop to be disconnected and the non-light-emitting load element loop to be connected; when the current of the constant current source is in a stable state, the control circuit controls the non-light-emitting load element loop to be disconnected and the LED lighting element loop to be connected. The present invention also includes a PWM-based time-sharing dimming control circuit and a control method. The present invention can solve the problem that the brightness and color accuracy of the light source in the prior art cannot meet the user's requirements.

Description

Technical Field

[0001] The present invention belongs to the field of lighting in the film and television industry. More specifically, it relates to an LED lighting circuit, a time-sharing dimming circuit, and a control method based on PWM. Background Art

[0002] Current color lighting devices use light of the three primary colors of red, green, and blue (RGB) to mix in different proportions to output different colors. To improve the problems of obvious color deviation of the white light mixed by RGB three-color lamp beads, low color rendering index, and the range and accuracy of color temperature adjustment, a white light W is added to the RGB three colors or two white lights W with high and low color temperatures are added, forming RGBW, RGBWW modes, or an amber A is added, that is, the RGBA mode. And the white light lighting device realizes color temperature adjustment by mixing two white lights W with high and low color temperatures, that is, the WW mode. No matter which mode is used, the problem of lamp bead driving needs to be solved. Currently, in the lighting devices in the film and television industry, the most common driving method is to use multiple constant current sources to drive and control lamp beads of different colors respectively after the total power supply is input, and use PWM signals with different duty cycles to control the on and off of the lamp bead strings, complete the mixing of the lamp beads, and realize color adjustment. This method is simple to implement, but to avoid power overload of the power supply when multiple lamp bead strings work simultaneously, the total power supply is usually designed as the sum of the maximum powers of multiple lamp bead strings when they work alone, which will result in the actual power of the lighting device not reaching the nominal power during operation. Taking the RGB mode as an example, the actual power of the lighting device during operation is only one-third of the nominal power.

[0003] To solve the above problems, the patent application with the application number 201110272764.2 discloses an LED lamp color adjustment driver. Through a time-division multiplexing control module, the control signals of the light source modules corresponding to the three colors are divided in time, so that at any moment, at most one of them is at a high level, and the power output module outputs driving voltage or current at most in one path to drive the corresponding light source module to emit light. In this way, the electric energy provided by the power converter is sequentially allocated to different branches for use in different time periods. In the embodiment, a scheme of using a constant current driver and three switches to control the on and off of the light source module is provided, which shows that different colors and brightness states can be mixed by adjusting the high-level time of the light source module control signal, and it is also shown that within the control time T, the high levels of the control signals of each light source module are evenly spaced, which can further maintain the stability of the power output of the power converter.

[0004] However, in practical applications, since the switching transistor has a response time, that is, when one string of LED beads is turned off and another string of LED beads is turned on in the actual high-brightness state, there is a delay between them. During this delay time, the load of the constant-current driver is discontinuous. In the half-brightness state, in order to maintain the smoothness of the output power of the power converter, the high-level intervals of each control signal are evenly spaced, and the load of the constant-current driver is also discontinuous. The discontinuous load will cause abnormal discharge of the inductance energy in the constant-current driver circuit, resulting in abnormal circuit operation. For example, the light source module may flicker or have abnormal brightness, or even damage to circuit components. In addition, since a single constant-current source driver always outputs a constant current, in order to maintain the smoothness of the output power of the power converter, the interval time between the high levels of each control signal cannot be adjusted arbitrarily, resulting in a limited brightness adjustment range for this solution.

[0005] Due to the discontinuous load, when the period of multi-channel PWM time-sharing dimming is in the millisecond level, the above factors can be ignored. However, in the film and television industry, in order to ensure that the filming effect of professional cameras has no picture flicker, it is required that the PWM period be in the level of dozens of microseconds or less. Then, the problem of discontinuous load cannot be ignored. Moreover, the film and television industry requires that the brightness of lighting equipment can be smoothly adjusted within a wide range, while the brightness adjustment range of this technical solution in the prior art is limited and cannot meet the requirements for lighting brightness adjustment in the film and television industry. Summary of the Invention

[0006] 1. Problems to be Solved

[0007] Aiming at the problem in the prior art that in the field of film and television lighting, due to the discontinuous load, the brightness and color of the light cannot meet the user's requirements, the present invention provides a PWM-based LED lighting circuit, a time-sharing dimming method and a system. Further, the present invention can also solve the problem that the brightness adjustment of the film and television lighting system is not smooth enough within a wide range.

[0008] 2. Technical Solutions

[0009] To solve the above problems, the technical solution adopted by the present invention is as follows: A PWM-based LED lighting circuit includes a power supply, a control circuit, and an LED lighting element, and further includes a non-light-emitting load element. The non-light-emitting load element is connected in parallel with the LED lighting element. The power supply is connected to a constant current source, and the constant current source supplies power to the LED lighting element and the non-light-emitting load element. When the constant current source is in the current rising or falling stage, the control circuit controls the LED lighting element circuit to be disconnected and the non-light-emitting load element circuit to be connected; when the current of the constant current source is in a stable state, the control circuit controls the non-light-emitting load element circuit to be disconnected and the LED lighting element circuit to be connected. In this technical solution, by controlling the non-light-emitting load element to be connected during the current rising or falling stage of the constant current source to consume the circuit energy in the non-constant current stage, it is avoided that the brightness and color display and adjustment of the lighting device are not controlled by the PWM signal under the action of this section of current, thereby affecting the brightness and color adjustment of the lighting device; during the current stable stage, the lighting element is controlled to be connected again, so that the user can more accurately adjust the brightness and color of the light.

[0010] Further, the non-light-emitting load element is a resistor.

[0011] Further, there are two non-light-emitting load elements, one of which is connected during the current rising stage of the constant current source, and the other is connected during the current falling stage of the constant current source. Adopting this technical solution makes the current rising and falling times controllable respectively, with a higher design freedom. At the same time, the current rising and falling times are shorter and the heat loss is lower.

[0012] The present invention also provides a PWM-based time-sharing dimming control circuit, which includes a main power supply for supplying power to the entire circuit, and further includes: at least two LED lighting elements, a constant current source for providing driving current for the LED lighting elements; a control module for controlling the on and off of the switching circuit; a switching circuit for controlling the on and off of the connection between the constant current source and the LED lighting elements; the constant current source, the switching circuit, and the LED lighting elements are connected in series. The switching circuit includes at least two paths of switches, and each path of switch is connected to one path of LED lighting element. The control module outputs a PWM control signal to control the on and off of the switching circuit; when the LED lighting elements are switched, the control module controls the PWM waveforms corresponding to the two paths of LED lighting elements to partially overlap. In this technical solution, through the control of the control module, the PWM waveforms corresponding to the two paths of LED lighting elements partially overlap, so as to achieve continuous load of the circuit at the moment of switching between the two paths of LED lighting elements, and solve the problem that the stability of the brightness and color of the light source cannot meet the user's requirements when the user adjusts the brightness and color of the light in the prior art.

[0013] Further, the control module controls the PWM signal corresponding to the rear LED light-emitting element to output a high level, and then controls the PWM signal corresponding to the front LED light-emitting element to output a low level, so that the PWM waveforms corresponding to the two LED light-emitting elements partially overlap. At the moment when the two LED light-emitting elements switch, the PWM signal corresponding to the rear LED light-emitting element is always controlled to output a high level, and then the PWM signal corresponding to the front LED light-emitting element is controlled to output a low level, so that the load of the circuit is continuous at the moment when the two LED light-emitting elements switch, so as to solve the problem that the brightness and color stability of the light source do not meet the user's needs when the user adjusts the brightness and color of the light in the prior art. Further, the constant current source is multiple. In this technical solution, multiple levels of constant current sources are set. Generally speaking, the ampere-level constant current source has the largest current. The ampere-level constant current source is set to meet the high brightness requirements of the lighting system, and the lower and more levels of constant current sources are set to meet the smooth transition requirements of the lighting system, so that the present invention can not only meet the user's requirements for high brightness of the light, but also can adjust the brightness and color very smoothly when the user adjusts the brightness and color.

[0014] Furthermore, the control module controls the on and off of multiple switch circuits, and time-divisionally calls multiple constant current sources in a single cycle to achieve regulation of the driving current of the LED light-emitting element;

[0015] Alternatively, the control module controls the on and off of multiple switch circuits to select constant current sources with different currents to drive the LED light-emitting elements.

[0016] In the above two technical solutions, in order to achieve smooth brightness adjustment, the control module can control the time-sharing call of multiple constant current sources in a single cycle, and can also select different constant current sources to drive LED light-emitting elements when different brightness outputs are required.

[0017] Furthermore, there are two constant current sources, one of which is an ampere-level constant current source and the other is a milliampere-level constant current source. This technical solution can use only two constant current sources. When the light is in the low brightness stage, only the milliampere-level constant current source works; when the light is in the high brightness or normal brightness stage, the ampere-level constant current source and the milliampere-level constant current source work at the same time. The use of two constant current sources can meet the user's needs for high brightness and smooth brightness adjustment while having a simpler control circuit and lower cost.

[0018] Further, the control module includes a user control module and a driving module. The user control module is configured to receive a user instruction, convert it into the time points of the high and low level conversions of a PWM signal, and send them to the driving module. The driving module includes a register and a PWM generator. The register is connected to the PWM generator. The register receives and stores the time points of the high and low level conversions of the PWM signal sent by the control module, and then transmits them to the PWM generator. The PWM generator generates and outputs PWM signals for respectively controlling the constant current source and the switching circuit.

[0019] Further, a non-light-emitting load element is further included. The non-light-emitting load element is connected in parallel with the LED light-emitting element. During the current rising or falling stage of the constant current source, the control module controls the LED light-emitting element loop to be disconnected and the non-light-emitting load element loop to be connected. When the current of the constant current source is stable, the control module controls the non-light-emitting load element loop to be disconnected and the LED light-emitting element loop to be connected. The purpose of setting the non-light-emitting load element is to solve the problem that during the on, off, or switching of the constant current source, there are current rising or falling stages. During these two stages, the current is changing. If the LED light-emitting element is connected during the current change stage, it will cause inaccurate brightness adjustment by the user, and thus also result in a lack of color accuracy. In the technical solution of the present invention, the non-light-emitting load element works during the current rising or falling stage, that is, during the stage when the current is unstable. Only the non-light-emitting load element is connected and the LED light-emitting element is not connected. When the circuit is stable, the control module outputs a PWM signal to control the on and off switching of each LED light-emitting element, thereby solving the problem of inaccurate brightness and color adjustment caused by current changes.

[0020] The present invention also provides a time-sharing dimming control method based on PWM for the above-mentioned time-sharing dimming control circuit based on PWM. The control method includes: when the LED light-emitting elements are switched, when two-way LED light-emitting elements are switched, the control module controls the PWM waveforms corresponding to the two-way LED light-emitting elements to partially overlap. The partial overlap of the PWM waveforms corresponding to the two-way LED light-emitting elements enables the circuit load to always remain stable, thereby solving the problem in the prior art that the circuit load is discontinuous, resulting in the brightness and color stability of the light source in the prior art not meeting the user's requirements.

[0021] Further, the control module controls the PWM signal corresponding to the latter LED light-emitting element to output a high level, and then controls the PWM signal corresponding to the former LED light-emitting element to output a low level. In the technical solution of the present invention, when switching between two-way LED light-emitting elements, the latter LED light-emitting element is always turned on first, and then the previous LED light-emitting element is turned off, thereby solving the problem in the prior art that the circuit load is discontinuous, resulting in the brightness and color stability of the light source in the prior art not meeting the user's requirements.

[0022] Further, the control method further includes:

[0023] S1. The control module receives and converts the user input instruction into a PWM duty cycle;

[0024] S2. The PWM duty cycle signal is sent to a register in the control module, and the register sends the received PWM duty cycle signal to a PWM generator to generate a PWM signal;

[0025] S3. The control module outputs the PWM signal to control the switching of the LED light-emitting element and the constant current source respectively;

[0026] Or,

[0027] S1'. The control module receives and converts the user input instruction into a PWM duty cycle;

[0028] S2'. Convert the PWM duty cycle corresponding to the LED light-emitting element in step S1' into the time points corresponding to the high and low level conversions of the PWM signal;

[0029] S3'. The time points corresponding to each LED light-emitting element in step S2' are sent to a register in the control module, and the register sends the stored time points to a PWM generator to generate a PWM signal;

[0030] S4'. The control module outputs the PWM signal to control the switching of the LED light-emitting element and the constant current source respectively.

[0031] There are two schemes for the control module to obtain a PWM signal after converting the user input instruction into a PWM duty cycle. One is to directly generate a PWM signal using a PWM generator, and the other is to convert the PWM duty cycle into the time points corresponding to the high and low level conversions of the PWM signal, store each time point, and then send it to the PWM generator. The PWM generator generates a PWM signal according to the time points corresponding to the high and low level conversions. Compared with the previous technical scheme, the latter technical scheme occupies less chip logic resources, has high portability, and can change the PWM signal accordingly according to the changes of the constant current source and the switching circuit, which is more flexible.

[0032] Further, during the current rising and falling stages of the constant current source, the control module controls the LED light-emitting element loop to be disconnected and the non-light-emitting load element loop to be connected; when the current is stable, the control module controls the non-light-emitting load element loop to be disconnected and the LED light-emitting element loop to be closed.

[0033] 3. Beneficial Effects

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] (1) The present invention can solve the problem that in a multi-channel PWM time-sharing dimming circuit, due to the discontinuous load, the brightness and color of the light cannot meet the user's requirements. The color stability and accuracy of the lighting device using the present invention are higher, and richer and more accurate colors can be achieved;

[0036] (2) The present invention can solve the problem of limited brightness adjustment range in a single constant current source-driven PWM time-sharing dimming circuit, enabling smooth adjustment of the brightness over a wide range without sudden changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the system principle block diagram of the present invention;

[0038] Figure 2 is Figure 1 the simplified principle block diagram of (simplifying multiple strings of lamp beads into one string);

[0039] Figure 3 is Figure 2 the timing diagram of ;

[0040] Figure 4 is Figure 1 the timing diagram of ;

[0041] Figure 5 the system principle block diagram of the present invention in RGBW mode;

[0042] Figure 6 is the equivalent circuit diagram of the present invention in RGBW mode;

[0043] Figure 7 is the timing diagram of the present invention at a certain maximum brightness of orange;

[0044] Figure 8 is the timing diagram of the present invention at 30% brightness of a certain orange;

[0045] Figure 9 is the system principle block diagram of Embodiment 2 of the present invention;

[0046] Figure 10 is the equivalent circuit diagram of Embodiment 2 of the present invention;

[0047] Figure 11 is the principle block diagram of Embodiment 3 of the present invention;

[0048] Figure 12 is Figure 11 the simplified principle block diagram of the load of ;

[0049] Figure 13 is the timing diagram of the present invention for time-sharing call of multiple-level power sources within a single cycle;

[0050] Figure 14It is the timing diagram of using a certain level of power supply alone under different brightness levels of the present invention;

[0051] Figure 15 It is the multi-level power supply timing diagram generated during the continuous brightness adjustment process of the present invention;

[0052] Figure 16 It is the timing diagram of Embodiment 3 of the present invention;

[0053] Figure 17 It is the system principle block diagram of Embodiment 4 of the present invention;

[0054] Figure 18 It is Figure 17 the timing diagram of;

[0055] Figure 19 It is one of the principle block diagrams of the control module in the present invention;

[0056] Figure 20 It is the processing flow chart of the user control module in the present invention;

[0057] Figure 21 It is the principle schematic diagram of converting the PWM duty cycle into a time point in the present invention;

[0058] Figure 22 It is the function schematic diagram of the synchronizer in the present invention;

[0059] Figure 23 It is the second principle block diagram of the control module in the present invention;

[0060] Figure 24 It is the third principle block diagram of the control module in the present invention (the user control module is integrated in the drive module);

[0061] In the figure: 1: main power supply; 2: first constant current source; 3: control module; 4: second constant current source; 5: multi-level adjustment circuit; 6: user control module; 7: drive module; 8: register; 9: synchronizer; 10: PWM generator; 11: power conversion module. Specific Embodiments

[0062] The present invention will be further described below in conjunction with specific embodiments. In the following embodiments, the LED light-emitting element is a string of lamp beads.

[0063] Embodiment 1

[0064] As Figure 1The shown multi-channel PWM time-sharing dimming system includes a main power supply 1, a first constant current source 2, a control module 3, switching circuits K, K1, K2, K3... Kn, a non-light-emitting load element LD, also known as a dummy load LD, which is represented by the dummy load LD in the attached drawings of the specification, and lamp bead strings CH1, CH2, CH3... CHn. The main power supply 1 can be an external power supply input of AC or DC. It should be noted that since LED lamp beads are non-linear elements, when conducting, a slight increase in voltage will cause a significant increase in current, making it easy to overcurrent. Therefore, the first constant current source 2 is required. After the main power supply 1 is input, it passes through the first constant current source 2, and AC-DC or DC-DC conversion forms a constant current output to drive multiple lamp bead strings to emit light. The number of lamp bead strings CH1, CH2, CH3... CHn is determined by the dimming mode selected by the system, and can be modes such as RGB, RGBW, RGBWW, RGBA, WW, etc. For example, if the RGBW mode is selected, the number of lamp bead strings is 4. In this embodiment, CH1 is a red lamp bead string, CH2 is a green lamp bead string, CH3 is a blue lamp bead string, and CH4 is a white lamp bead string. The non-light-emitting load element LD generally selects non-light-emitting energy-consuming devices such as resistors. The non-light-emitting load element LD is turned on during the rising and falling stages of the constant current source current, and is used to consume the circuit energy during the non-constant current stage, avoiding the impact of these two stages on the lamp bead strings and affecting the brightness and color of the lighting device. Since the current is in a changing state during the rising and falling stages of the constant current source, if the lamp bead strings are turned on during these two stages, the display and adjustment of the brightness and color of the lighting device will not be controlled by the PWM signal. For the field of film and television lighting, the brightness and color will not be accurate enough. Therefore, it is necessary to avoid connecting the lamp bead strings during these two stages as much as possible. The number of switching circuits K1, K2, K3... Kn corresponds to the number of lamp bead strings, that is, one switching circuit controls one lamp bead string to achieve time-sharing control of the lamp bead strings. Another switching circuit K is used to control the on and off of the non-light-emitting load element LD. Specifically, in implementation, the switching circuits K, K1, K2, K3... Kn can be implemented by MOSFETs, IGBTs, triodes, GaN field effect transistors, or high-speed relays, etc. The control module 3 is used to output an enable signal EN and PWMK, PWMK1... PWMKn signals. The enable signal EN is the enable signal of the first constant current source 2, and the PWMK, PWMK1... PWMKn signals are used to control the on and off of the switching circuits K, K1, K2, K3... Kn. The power supply of the control module 3 is realized by the main power supply through AC-DC or DC-DC (not shown in the figure). The control module 3 can be implemented by a logical control chip such as an MCU, CPLD, FPGA, or DSP.

[0065] To facilitate the description of the role of the non-light-emitting load element LD, when describing, we will Figure 1 the lamp bead strings CH1, CH2, CH3... CHn be simplified to Figure 2The lamp bead string CH. The shutter speed of cameras and video cameras in the film and television industry is generally at the microsecond level, and different frame rates may be selected during shooting. For cases with higher frame rates or more extreme shutter speeds, in order to meet the requirement of no light flicker during filming in the film and television industry, the setting of the cycle time T must meet the requirements. The cycle time T refers to the total time for all lamp bead strings CH1, CH2, CH3... CHn to go through one on and off cycle plus the on time of the non-light-emitting load element LD and the off time of the constant current source. In this embodiment, the cycle time T can be selected as 50 us. During specific implementation, the length of the cycle time T can be determined according to the specific shutter speed of the camera and the frame rate of shooting, but the cycle time T must be less than the shutter speed to enable the adjustment of the light to meet the high requirements of the film and television industry. To ensure the continuity of the load of the first constant current source 2 when the lighting device is not at the maximum brightness, the first constant current source 2 needs to be turned off after all the lamp bead strings CH1, CH2, CH3... CHn are sequentially lit. As Figure 2 , Figure 3 shown, within the cycle time T (which can also be said to be cycle T), the control module 3 outputs an enable signal EN to control the first constant current source 2 to output a current I. Due to the presence of an inductor in the first constant current source 2 circuit, the output current cannot change suddenly, that is, the current cannot instantaneously change from 0 to 1 or from 1 to 0. It has rising and falling stages, and during these two stages, the output current of the first constant current source 2 is constantly changing. The change in the output current will cause inaccurate brightness adjustment by the user, and thus also lead to inaccurate displayed colors. Therefore, the on and off of the lamp bead string CH needs to avoid these two stages. To enable the normal discharge of the inductor energy of the first constant current source 2 during these two stages, an additional non-light-emitting energy-consuming device is required to act as a temporary load, which is the non-light-emitting load element LD mentioned in the present invention. The non-light-emitting load element is generally a non-light-emitting energy-consuming device, such as a resistor commonly. During the rising and falling stages of the current of the constant current source, the control module 3 outputs a PWMK signal to control the switch circuit K to turn on, turning on the non-light-emitting load element LD. At this time, only the non-light-emitting load element LD is working in the circuit. After the current is stably output at a constant current, the PWMK signal controls the switch circuit K to turn off, turning off the non-light-emitting load element LD, and outputs a PWMKch signal to control the switch circuit Kch to turn on, turning on the lamp bead string CH, and maintaining the continuous constant current output of the first constant current source 2 during the adjustment of the lamp bead string CH.

[0066] Since the non-light-emitting load element LD and the lamp bead string CH are turned on and off through the switch circuits K and Kch, and there is a switching speed problem with the switch circuits. To avoid the impact of the switching speed of the switch circuits on the lighting device, the present invention uses the control module 3 to output a high level of the PWMK signal in advance for a duration of t1 to control the switch circuit K to turn on, and delays the output of a low level of the PWMK signal for a duration of t1 to control the switch circuit K to turn off. AsFigure 3 As shown. During the off-stage of the first constant current source 2 in a single cycle time T, since the first constant current source 2 has been turned off by the enable signal EN output by the control module 3, the time period t3 is not necessarily present. The durations of t1 and t3 are generally determined according to the characteristics of the control switch circuits K and Kch. For example, if the switch circuits K and Kch are implemented by MOSFET AON7534, whose theoretical turn-on time is 8.8 ns and turn-off time is 22.3 ns, then the durations of t1 and t3 can be set to 30 ns. The above method adopted by the present invention can solve the problem of discontinuous circuit load caused by the switch response time and the periodic rise and fall of the constant current source, resulting in unstable brightness and color of the light, which cannot meet the user's requirements.

[0067] As Figure 1 shown in the dimming system, assuming that the required lighting colors need to light up the lamp bead strings CH1, CH2, CH3... CHn for durations of D1, D2, D3... Dn respectively within the cycle time T, then the timing diagram of the entire system is as Figure 4 shown. At the moment of switching between the non-light-emitting load element LD and the lamp bead string CH1, the control module 3 controls the PWM waveforms corresponding to the two LED light-emitting elements to partially overlap, so as to achieve continuous circuit load at the moment of switching between the two LED light-emitting elements. The method adopted in this embodiment is that the control module 3 outputs a high level of the PWMK1 signal with a time advance of t1 duration before outputting a low level of the PWMK signal, controls the switch circuit K1 to turn on, and lights up the lamp bead string CH1; after a duration of t1, it outputs a low level of the PWMK signal and controls the switch circuit K to turn off. At the moment of switching between the lamp bead string CH1 and the lamp bead string CH2, the control module 3 outputs a high level of the PWMK2 signal with a time advance of t1 duration before outputting a low level of the PWMK1 signal, controls the switch circuit K2 to turn on, and lights up the lamp bead string CH2; after a duration of t1, it outputs a low level of the PWMK1 signal and controls the switch circuit K1 to turn off, turning off the lamp bead string CH1. And so on. At the moment of switching between two lamp bead strings, the control module 3 always first controls the PWM signal corresponding to the latter lamp bead string to output a high level, and then controls the PWM signal corresponding to the former lamp bead string to output a low level (in the present invention, the former lamp bead string refers to the lamp bead string that was lit before the switching between the two lamp bead strings, and the latter lamp bead string refers to the lamp bead string that will be lit after the switching between the two lamp bead strings). The purpose of doing this is to make the circuit load continuous at the moment of switching between two lamp bead strings, so that the constant current source can continuously output current I and stabilize the brightness and color of the lamp bead string. Thus, the brightness is adjusted by the sum of the duty cycles of the lamp bead strings, and the color is adjusted by the ratio of the duty cycles of each lamp bead string, that is, by changing the durations of D1, D2, D3... Dn, the adjustment of color and brightness can be achieved.

[0068] The control module 3 of the present invention controls the PWM signal to adopt positive logic, with high level being valid, and controls the constant current source 2 to drive the lamp string CH to emit light. Specifically in implementation, negative logic can also be adopted, with low level being valid, or a mixed mode of positive and negative logic can be adopted.

[0069] The color and brightness adjustment of the dimming system will be described below taking the RGBW mode as an example. As Figure 5 shown, the main power supply 1 is a DC48V input. The first constant current source 2 is a typical DC-DC BUCK circuit, with an output constant current value of 5A, a circuit switching frequency of 1MHz, and the circuit is equivalent to Figure 6 shown, Vin = 48V, the inductor L of the first constant current source 2 is 10uH, and the output is 4 groups of 14-strand lamp strings. The non-light-emitting load element LD is a resistor Rld. The typical voltage value of the reference lamp string is Vout = 3V × 14 = 42V (the voltage values of the lamp beads of different colors are different, and the typical voltage value of 3V is selected for calculation) and the current value (5A), and the equivalent resistance value is 8.4Ω. Due to the oscillation of the DC-DC BUCK circuit itself, actually, the time of the rising stage of the first constant current source 2 is calculated as the time taken for the current to rise from 0% to 90%, and the time of the falling stage is calculated as the time taken for the current to fall from 100% to 10%. During the current rising stage of the first constant current source 2 the relationship between the current I (A) and the time t (us) is After the control module 3 outputs the enable signal EN to control the first constant current source 2 to turn on, the time tp taken for the current to rise from 0% to 90% is approximately 1.84us. During the current falling stage of the first constant current source 2 the relationship between the current I (A) and the time t (us) is I = 5 × e -0.84t , after the control module 3 outputs the enable signal EN to control the first constant current source 2 to turn off, the time td taken for the current to fall from 100% to 10% is approximately 2.74us. The dimming system cycle time T is 50us. Then we can set the total on-time of the lamp string to 45us as the implementation method of 100% brightness, and the remaining 5us is for the non-light-emitting load element LD and the off-time. The total on-time of all lamp strings does not exceed 45us. As described above, the overlapping time t1 when two adjacent channels (including the non-light-emitting load element LD) are turned on simultaneously is set to 30ns, accounting for 0.0067% of 45us, which can be ignored when calculating the duty cycle. Within a single cycle time T, the total duration of all lamp strings being on determines the total brightness of the light source, and the duration ratio of different color lamp strings determines the color of the light source. As Figure 7 and Figure 8As shown, to achieve a certain orange color, the duty cycle ratio of red light R to green light G is 3:2. Then, the way to achieve the maximum brightness of this orange color is to turn on the red light bead string R for 27 us and the green light bead string G for 18 us within a single cycle. The way to achieve 30% brightness of this orange color is to turn on the red light bead string R for 8.41 us and the green light bead string G for 5.4 us within a single cycle. As Figure 8 shown, when the brightness is not the maximum, the required bead strings are still lit sequentially. During the adjustment process, the first constant current source 2 continuously outputs. After the bead strings are lit sequentially, the first constant current source 2 is timely turned off through the enable signal EN, avoiding the problem of discontinuous load of the first constant current source 2 and ensuring the stability and accuracy of color display.

[0070] Embodiment 2

[0071] Since the calculation formula for the rate of change of inductor current is ΔI / Δt = ΔU / L. In any DC-DC or AC-DC power topology model, ΔU in the current rising and falling intervals is different. Using only one non-light-emitting load element will result in a longer current rising or falling time, and the power loss of the non-light-emitting load element will also be larger. Therefore, using two non-light-emitting load elements is a more optimized design, as Figure 9 shown. The circuit equivalent diagram is Figure 10 . During the current rising stage, ΔI / Δt = ΔU / L ≈ (Vin - I×Rld1) / L. Therefore, the smaller Rld1 is, the faster the current rises, and Rld1 can take a small-value resistor of the mΩ level; during the current falling stage, ΔI / Δt = ΔU / L ≈ I×Rld2 / L. Therefore, the larger Rld2 is, the faster the current falls, and Rld2 can take Vout / I during normal operation. Similar to Embodiment 1, the total power supply 1 is a DC 48V input, the first constant current source 2 is a typical DC-DC BUCK circuit, with a constant current output value of 5A, a circuit switching frequency of 1 MHz, Vin = 48V, the inductor L of the first constant current source 2 = 10 uH, and the output is 4 groups of 14-strand bead strings. The two non-light-emitting load elements are Rld1 and Rld2 respectively. Among them, Rld1 is a 1 mΩ power resistor (approximately equal to a short circuit when turned on), and Rld2 is a 10 Ω power resistor; where, ΔI is the change in inductor current, Δt is the change in time, ΔU is the change in inductor voltage, L is the inductance value of the inductor, I is the inductor current, Rld1 is the resistance value of the non-light-emitting load element LD1, Rld2 is the resistance value of the non-light-emitting load element LD2, Vin is the DC input voltage of the total power supply, and Vout is the output voltage of the system load circuit.

[0072] Compared with the one non-light-emitting load element in Embodiment 1, the two non-light-emitting load elements in this embodiment have the following several

[0073] advantages:

[0074] (1) The current rise and fall times are controllable respectively, providing a higher degree of design freedom.

[0075] (2) The current rise and fall times are shorter. The time for the first-stage current to rise from 0% to 90% For the second-stage current I (A) and time t (μs), the relationship is I = 5e -t , and the calculated time for the current to fall from 100% to 10% is 2.3 μs.

[0076] (3) Lower heat loss.

[0077] In Embodiment 1, the formula for estimating the heat loss power of the non-light-emitting load element is:

[0078] For the two non-light-emitting load elements in this embodiment, the Rld1 during the current rise stage has negligible loss, and the main loss is in Rld2 during the current fall stage. Therefore, the estimated heat loss power of the non-light-emitting load element in Embodiment 2 is: Compared with Embodiment 1, Embodiment 2 has lower heat loss.

[0079] Embodiment 3

[0080] For the brightness adjustment in Embodiments 1 and 2, it is achieved by controlling the total duty cycle duration of the PWM signals output by the control module 3 for each street lamp bead string. However, the range of this brightness adjustment is still limited. The most direct way to adjust the brightness is to reduce the current flowing through the lamp beads. Therefore, in order to improve the dimming accuracy of the lighting system and be able to smoothly adjust the brightness, it is necessary to improve the current source therein.

[0081] Such as Figure 11As shown, the total power supply 1 can be an external power supply input of AC or DC. After the total power supply 1 is input, different constant current sources A1, A2...An are selected through the switch circuits S1, S2...Sn, and AC-DC or DC-DC conversion forms a multi-level constant current output to drive multiple lamp beads to emit light. The constant current sources A1, A2...An output different current values ​​I1, I2...In, such as 5A, 1A, 0.2A, 0.04A...or 4A, 0.4A, 0.04A...etc. In short, the current values ​​output by the constant current sources A1, A2...An can be arranged in geometric ratios or in other ways to achieve the transition from ampere level to milliampere level. The purpose of such a setting is to simultaneously meet the problems of high brightness and smooth transition of light adjustment of the lighting system in the field of film and television lighting. More specifically, the constant current source with a current value of ampere level is to meet the demand of high brightness of the lighting system, and the constant current source with a current value of milliampere level is to meet the demand of smooth transition of the lighting system, so that the present invention has both high brightness and can adjust the brightness very smoothly. On the one hand, the control module 3 outputs PWMS1, PWMS2...PWMSn signals to control the on and off of the switch circuits S1, S2...Sn, thereby realizing the control of the constant current source; and at the same time, it also outputs PWMK1, PWMK2...PWMKn signals to control the on and off of the switch circuits K1, K2...Kn, thereby controlling the on and off of the lamp beads CH1, CH2...CHn, that is, this embodiment controls the change of light color and brightness by adjusting two groups of PWM signals. The switch circuits S1, S2...Sn can be realized by MOSFET, IGBT, triode, GaN field effect tube or high-speed relay.

[0082] In order to facilitate the description of the control module 3 to the multi-stage constant current source control, Figure 11 The multi-channel lamp string and non-luminous load components are simplified as follows Figure 12 The lamp string CH shown in the figure is assumed to be in an ideal state for the constant current source and the switch circuit, that is, there are no current rise and fall phases or switch delays. There are two working modes for the multi-stage constant current source. One is to call the multi-stage power supply in a single cycle T in a time-sharing manner. The timing is as follows: Figure 13 As shown, the control module 3 controls the on and off of the switch circuits S1, S2...Sn through the PWMS1, PWMS2...PWMSn signals, and realizes the time-sharing call of the constant current sources A1, A2...An in a single cycle T. The so-called time-sharing call in a single cycle T means that in a single cycle T, by calling different constant current sources in different time periods to control the duty ratio of PWMS1, PWMS2...PWMSn, the driving current of the lamp string CH can be adjusted, thereby realizing smooth adjustment of the brightness. The other is to use a certain level of power supply alone at different brightness levels, and the timing is as follows Figure 14As shown, the control module 3 controls the on / off of the switch circuits S1, S2... Sn through the PWMS1, PWMS2... PWMSn signals, and selects different constant current sources to drive the lamp bead strings CH at different brightness levels to achieve smooth brightness adjustment. For example, Figure 15 Shown is the timing diagram generated during the continuous brightness adjustment process.

[0083] For example, Figure 11 In the multi-level constant current source PWM time-sharing dimming system shown, assuming that the multi-level constant current source operates in the above-mentioned manner of selecting different constant current sources at different brightness levels, the PWM ratio of the light color needs to light the lamp bead strings CH1, CH2, CH3... CHn for D1, D2, D3... Dn durations respectively within the period T, and smoothly adjust the brightness of this color from the brightest to the darkest. Then the timing diagram of the entire system is as Figure 16 Shown (omitting PWMS1, PWMS2... PWMSn) timing diagram.

[0084] Embodiment 4

[0085] This embodiment is a special form of Embodiment 3, that is, in Embodiment 3, there are multiple constant current sources, and this embodiment uses two constant current sources. For example, Figure 17 As shown, after the total power supply 1 is input, it is divided into two paths. One path passes through the power conversion module 11 to perform AC-DC or DC-DC conversion into a DC power supply, and then through a resistor. This part can be equivalent to the second constant current source 4, which outputs a constant current i; the other path is the same as in Embodiment 1, and outputs a constant current I after passing through the first constant current source 2. The power conversion module 11 also needs to supply power to the control module 3. The second constant current source 4 and the first constant current source 2 are connected in parallel to drive the lamp bead strings CH1, CH2... CHn and the non-light-emitting load element LD. The first constant current source 2 is used for the high-current stage of the lighting device, and the current I is generally at the ampere level; the second constant current source 4 is used for the low-current stage of the lighting device, and the current i is generally several tens of mA, that is, at the milliampere level. It should be noted that when the control module 3 controls the switching between the two lamp bead strings, the high-current stage of Embodiment 3 and Embodiment 4 is the same as that of Embodiment 1. The control module 3 always first controls the PWM signal corresponding to the latter lamp bead string to output a high level, and then controls the PWM signal corresponding to the former lamp bead string to output a low level.

[0086] The timing diagram is as Figure 18 Shown. When the enable signal EN controls the first constant current source 2 to turn on, the lighting device operates in the normal brightness stage, and the timing is the same as that of Embodiment 1 Figure 4Similar. When the enable signal EN controls the first constant current source 2 to turn off, only the second constant current source 4 works. The driving current i of the lamp string is only in the mA level, and the lighting device works in the low brightness stage. The energy output by the second constant current source 4 itself is relatively low. Moreover, for the power conversion module 11, its load resistance and the control module 3 keep working continuously. At this time, the PWMK1, PWMK2... PWMKn signals do not need to output a high level in advance.

[0087] Whether it is Embodiment 1 or Embodiment 2, Embodiment 3 and Embodiment 4, they all involve the issue of PWM signal timing. The PWM signal is generated by the control module 3. As Figure 19 、 Figure 23 and Figure 24 shown, the control module 3 consists of a user control module 6 and a driving module 7. The driving module 7 internally includes a register 8, a synchronizer 9 and a PWM generator 10. Signals are transmitted between the user control module 6 and the driving module 7 through the SPI interface. The user control module 6 is responsible for converting the result of the user operation into the PWM duty cycle and sending it to the driving module 7. As shown in the flowchart of the user control module 6 in Figure 20 : S1: User operation. The user adjusts the required light tone, brightness and color temperature by adjusting the HSI parameters of the lighting device. The user control module 6 will convert the HSI parameters into the values of each lamp string corresponding to the dimming mode, such as RGBWW or RGB values; S2: Value to PWM duty cycle. Convert the values of each lamp string into the corresponding PWM duty cycle; S1 and S2 above are prior arts and will not be elaborated; S3: PWM duty cycle to time point, that is, convert the PWM duty cycle of the corresponding lamp string into the time points corresponding to the high and low levels of the PWM signal; S4: Transmission. Send the time points obtained in S3 to the register 8 of the driving module 7 for storage. In step S3, it is necessary to convert the PWM duty cycle into the time points corresponding to the high and low level changes of the PWM. Taking the simplified timing diagram of Embodiment 1, that is Figure 3 as an example, the marked time points are as shown in Figure 21 : In Figure 21Among them, 8 time points of 3 PWM signals are involved, namely Reg1, Reg2, Reg3, Reg4, Reg5, Reg6, Reg7, and Reg8. Since the non-light-emitting load element LD is turned on first, the PWMK signal outputs a high level at the first time. Then the time point of Reg1 can be set to 0, that is, at the 0 time point, the PWMK signal needs to change from a low level to a high level. After t1 time, the first constant current source 2 is turned on, and the enable signal EN outputs a high level. Then the time point of Reg2 is 0 + t1, that is, at the 0 + t1 time point, the enable signal EN needs to change from a low level to a high level. Since the duration of the non-light-emitting load element LD is related to the current rise and fall time of the first constant current source 2, and the current rise and fall time is determined by the circuit of the first constant current source 2, depending on the voltage and current magnitude of the inductor. Assuming the rise time is tp and the fall time is td, then the time point of Reg4 is tp + 2t1, that is, at the tp + 2t1 time point, the PWMK signal needs to change from a high level to a low level. After the first constant current source 2 outputs stably, the lamp bead CH can be turned on, and the PWMch signal outputs a high level. The time point of Reg3 is Reg4 - t1, that is, at the tp + t1 time point, the PWMch signal needs to change from a low level to a high level. The high level time of PWMch is calculated by the PWM duty cycle. Assuming it is D, then the time point of Reg6 is Reg3 + D, that is, at the tp + t1 + D time point, the PWMch signal needs to change from a high level to a low level. The time point of Reg7 is equal to Reg6, that is, at the tp + t1 + D time point, the enable signal EN needs to change from a high level to a low level. The time point of Reg5 is Reg7 - t1, that is, at the tp + D time point, the PWMK signal needs to change from a low level to a high level. The time point of Reg8 is Reg7 + td + t1, that is, at the tp + D + td + 2t1 time point, the PWMK signal needs to change from a high level to a low level.

[0088] After obtaining the time points corresponding to the PWM signals, the user control module 6 sends the time points to the register 8. The register 8 sends the time points to the synchronizer 9, and then the synchronizer 9 sends them to the PWM generator 10. The PWM generator 10 generates PWM signals according to the time points received by the register 8. Of course, the duty cycle can also be generated by step S2 of the user control module 6 and sent to the register 8, and then the PWM generator 10 generates PWM signals. However, the PWM signal only changes with the duty cycle. Once the circuit parameters change, the driving module 7 is no longer applicable, and the portability is poor. When generating PWM signals through time points, the PWM signals change with the time points. Both users and manufacturers can change the PWM signals according to the changes in circuit parameters. For example, a precise mode with a shorter duration t1 can be provided for users or in-factory debugging. For example, if the parameters of the first constant current source 2 or the second constant current source 4 change, only the values of the durations tp and td need to be changed, and the driving module 7 can adapt to different circuit parameters. The function of the synchronizer 9 is as Figure 22 shown. Suppose the user adjusts the HSI of the lighting device at the time point F shown by the arrow. According to the normal procedure, the time point C of PWMK1 should be adjusted at the time point F. Since the time point of E is related to that of C, the time point of E should be adjusted synchronously. Consequently, multiple PWM waveforms need to be adjusted synchronously. However, in actual situations, since the time points of the PWM signals are generated sequentially and serially sent to the register 8, the control module 3 cannot adjust multiple PWM waveforms simultaneously. It is necessary to first cache the adjusted time points of the PWM signals in the register 8, and then, through the synchronizer 9, send the time points to the PWM generator 10 after a single cycle T ends, and generate the adjusted PWM signals in the next cycle T.

[0089] Of course, in specific implementation, the synchronizer 9 is not necessarily present. As Figure 23 shown, in actual use, the function of the synchronizer 9 can be implemented in the PWM generator 10. Additionally, as long as the resources of the driving module 7 are sufficient, the function of the user control module 6 can also be implemented in the driving module 7, that is, the user control module 6 can be set in the driving module 7, as Figure 24 shown.

[0090] Adopting the technical solution of the present invention, within one cycle, the enabling control of a single constant current source is achieved. When adjusting the brightness by using the sum of the duty cycles, each PWM signal continuously outputs, and the constant current source continuously outputs during the adjustment process and is turned off after the adjustment is completed; at the moment of switching between any two strings of LED beads during the multi-channel PWM time-division dimming, first turn on the string of LED beads that needs to be connected, and then turn off the previous string of LED beads to eliminate the delay existing in normal switching and ensure the continuity of the total current of the system.

Claims

1. A PWM-based LED lighting circuit, comprising a power supply, a control circuit, and an LED lighting element, characterized in that: It also includes a non-luminous load element, which is connected in parallel with the LED light-emitting element. The power supply is connected to a constant current source, which supplies power to the LED light-emitting element and the non-luminous load element. When the constant current source is in a current rising or falling stage, the control circuit controls the LED light-emitting element circuit to be disconnected and the non-luminous load element circuit to be connected; when the current of the constant current source is in a stable state, the control circuit controls the non-luminous load element circuit to be disconnected and the LED light-emitting element circuit to be connected.

2. The PWM-based LED lighting circuit according to claim 1, wherein: The non-luminous load element is a resistor.

3. The PWM-based LED lighting circuit according to claim 1 or 2, characterized in that: There are two non-luminous load elements, one of which is turned on during the current rising stage of the constant current source, and the other is turned on during the current falling stage of the constant current source.

4. A PWM-based time-sharing dimming control circuit, comprising a main power supply for supplying power to the entire circuit, characterized in that: Also includes: At least two LED light-emitting elements, A constant current source, used to provide driving current for the LED light-emitting element; A control module, used for controlling the on and off of the switch circuit; A switch circuit, used to control the on / off connection between the constant current source and the LED light emitting element; The constant current source, the switch circuit and the LED light-emitting element are connected in series, the switch circuit includes at least two switches, each switch controls one LED light-emitting element, and the control module outputs a PWM control signal to control the on and off of the switch circuit; when the two LED light-emitting elements are switched, the control module controls the PWM waveforms corresponding to the two LED light-emitting elements to overlap partially; It also includes a non-luminous load element, which is connected in parallel with the LED light-emitting element. During the current rising or falling stage of the constant current source, the control module controls the LED light-emitting element circuit to be disconnected and the non-luminous load element circuit to be connected; when the current of the constant current source is stable, the control module controls the non-luminous load element circuit to be disconnected and the LED light-emitting element circuit to be connected.

5. The PWM-based time-sharing dimming control circuit according to claim 4, wherein: The control module controls the PWM signal corresponding to the rear LED light emitting element to output a high level, and then controls the PWM signal corresponding to the front LED light emitting element to output a low level, so that the PWM waveforms corresponding to the two LED light emitting elements partially overlap.

6. The PWM-based time-sharing dimming control circuit according to claim 4, wherein: There are multiple constant current sources.

7. The PWM-based time-sharing dimming control circuit according to claim 6, wherein: The control module controls the on and off of multiple switch circuits, and calls multiple constant current sources in a single cycle in a time-sharing manner to achieve regulation of the driving current of the LED light-emitting element; Alternatively, the control module controls the on and off of multiple switch circuits to select constant current sources with different currents to drive the LED light-emitting elements.

8. The PWM-based time-sharing dimming control circuit according to claim 4, wherein: There are two constant current sources, one of which is an ampere-level constant current source, and the other is a milliampere-level constant current source.

9. The PWM-based time-sharing dimming control circuit according to any one of claims 4-8, characterized in that: The control module includes a user control module and a driving module. The user control module is used to receive user instructions and convert them into the time points of high and low level conversion of PWM signals and send them to the driving module. The driving module includes a register and a PWM generator. The register is connected to the PWM generator. The register receives the time points of high and low level conversion of the PWM signal sent by the control module and saves them, and then transmits them to the PWM generator. The PWM generator generates and outputs PWM signals that control the constant current source and the switch circuit respectively.

10. A PWM-based time-sharing dimming control method, characterized in that: For the PWM-based time-sharing dimming control circuit according to any one of claims 4-9, the control method includes: when switching between two LED light-emitting elements, the control module controls the PWM waveforms corresponding to the two LED light-emitting elements to partially overlap.

11. The PWM-based time-sharing dimming control method according to claim 10, wherein: The control module controls the PWM signal corresponding to the latter LED light-emitting element to output a high level, and then controls the PWM signal corresponding to the former LED light-emitting element to output a low level.

12. The PWM-based time-sharing dimming control method according to claim 10, wherein: The control method further includes: S1. The control module receives and converts the user input instruction into a PWM duty cycle; S2. The PWM duty cycle signal is sent to the register in the control module, and the register sends the received PWM duty cycle signal to the PWM generator to generate a PWM signal; S3. The control module outputs the PWM signal to control the LED light-emitting element and the constant current source respectively; Or, S1'. The control module receives and converts the user input instruction into a PWM duty cycle; S2'. Convert the PWM duty cycle of the corresponding LED light-emitting element in step S1' into the time points corresponding to the high and low level conversions of the PWM signal; S3'. The time points corresponding to each LED light-emitting element in step S2' are sent to the register in the control module, and the register sends the stored time points to the PWM generator to generate a PWM signal; S4'. The control module outputs the PWM signal to control the switching of the LED light-emitting element and the constant current source respectively.

13. The PWM-based time-sharing dimming control method according to claim 10, 11 or 12, characterized in that: During the current rising and falling stages of the constant current source, the control module controls the LED light-emitting element circuit to be disconnected and the non-light-emitting load element circuit to be connected; when the current is stable, the control module controls the non-light-emitting load element circuit to be disconnected and the LED light-emitting element circuit to be closed.

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