CN213547894U

CN213547894U - LED lighting circuit and time-sharing dimming circuit based on PWM

Info

Publication number: CN213547894U
Application number: CN202022931191.7U
Authority: CN
Inventors: 朱晓晖; 季逊然
Original assignee: Swit Electronics Co Ltd
Current assignee: Swit Electronics Co Ltd
Priority date: 2020-12-07
Filing date: 2020-12-07
Publication date: 2021-06-25
Anticipated expiration: 2030-12-07

Abstract

The utility model discloses a LED lighting circuit based on PWM, including power, control circuit, LED light emitting component, its characterized in that: the LED constant current source is connected with the LED luminous element in parallel, the power supply is connected with a constant current source, the constant current source supplies power to the LED luminous element and the non-luminous load element, and when the constant current source is in a current rising or falling stage, the control circuit controls the LED luminous element to be disconnected in a loop and the non-luminous load element to be connected in a loop; when the current of the constant current source is in a stable state, the control circuit controls the non-luminous load element loop to be switched off, and the LED luminous element loop is switched on. The utility model discloses still include a timesharing dimming control circuit based on PWM, the utility model discloses can solve the luminance of light source among the prior art and the problem that the colour degree of accuracy can not reach the user demand.

Description

LED lighting circuit and time-sharing dimming circuit based on PWM

Technical Field

The utility model belongs to movie & TV trade lighting field, more specifically say, relate to a LED lighting circuit, timesharing dimmer circuit based on PWM.

Background

The existing color lighting device utilizes the light of three primary colors of red, green and blue (RGB) to mix in different proportions and output different colors. In order to solve the problems of obvious color cast, low color rendering index, and color temperature adjusting range and accuracy of white light mixed by RGB three-color lamp beads, one path of white light W or two paths of high and low color temperature white light W are added on the basis of RGB three colors to form an RGBW mode and an RGBWW mode, or an amber mode A, namely an RGBA mode is added. The white light illuminating device realizes color temperature adjustment by mixing two paths of high and low color temperature white light W, namely a WW mode. Regardless of which mode is used, the problem of driving the lamp beads needs to be solved, at present, in lighting equipment in the video industry, the most common driving method is to adopt a plurality of paths of constant current sources to respectively drive and control the lamp beads with different colors after the input of a main power supply, and utilize PWM signals with different duty ratios to control the on-off of a lamp bead string, so as to complete the light mixing of the lamp beads and realize the color adjustment. The method is simple to implement, but in order to avoid the power overload of the power supply when the multiple paths of lamp bead strings work simultaneously, the sum of the maximum powers when the multiple paths of lamp bead strings work independently is taken as the total power supply during the common design, which causes the actual power of the lighting equipment during the work to be not the nominal power, and taking the RGB mode as an example, the actual power of the lighting equipment during the work is only one third of the nominal power.

In order to solve the above problem, the utility model discloses a utility model patent application with application number 201110272764.2 discloses a LED lamp color adjustment driver passes through time division multiplexing control module, cut apart the light source module control signal that three color corresponds in time, make them at any one moment, have one at most to be in the high level, power output module is at most all the way output drive voltage or electric current, the light source module that the drive corresponds is luminous, the electric energy that provides power converter distributes different branch roads in different time quantums in proper order like this and uses. The embodiment provides a scheme for controlling the on-off of the light source modules by using a constant current driver and three switches, which explains that the light source modules can be mixed into different colors and brightness states by adjusting the high level time of the control signals of the light source modules, and explains that the high levels of the control signals of the light source modules are uniformly spaced in the control time T, so that the stability of the output power of the power converter can be further maintained.

However, in practical application, the switching tube has response time, that is, in an actual highlight state, one path of lamp bead string is turned off and another path of lamp bead string is turned on, and a delay exists between the two paths of lamp bead strings, and the load of the constant current driver is discontinuous in the delay time. In the semi-bright state, in order to keep the stability of the output power of the power converter, the high levels of the control signals are uniformly spaced, and the load of the constant current driver is also discontinuous. The discontinuous load can cause abnormal leakage of inductance energy in the constant current driver circuit, thereby causing abnormal circuit operation, such as the light source module can have a situation of flickering or abnormal brightness, and even circuit devices can be damaged. In addition, because a single constant current source driver always outputs constant current, in order to keep the stability of the output power of the power converter, the interval time between the high levels of all control signals cannot be adjusted at will, so that the brightness adjusting range of the scheme is limited.

Due to the discontinuous load, when the period of the multi-path PWM time-sharing dimming is in the millisecond level, the factors can be ignored, but in the film and television industry, the problem of discontinuous load can not be ignored when the shooting effect of a professional camera is not flickering, and the PWM period is required to be in the tens of microseconds level or less. Moreover, the film and television industry requires that the brightness of the lighting equipment can be smoothly adjusted in a wide range, and the technical scheme in the prior art has a limited brightness adjustment range and cannot meet the requirement of the film and television industry on the adjustment of the brightness of the light.

Disclosure of Invention

1. Problems to be solved

Because the discontinuous problem that leads to luminance, the colour of light to reach the user demand of load among the prior art movie & TV illumination field, the utility model provides a LED lighting circuit, timesharing dimming method and system based on PWM, furtherly, the utility model discloses can also solve the not steady problem inadequately of movie & TV lighting system's luminance in the regulation of wide range.

2. Technical scheme

In order to solve the above problem, the utility model discloses the technical scheme who adopts as follows: the LED lighting circuit based on the PWM comprises a power supply, a control circuit, an LED light-emitting element and a non-light-emitting load element, wherein the non-light-emitting load element is connected with the LED light-emitting element in parallel; when the current of the constant current source is in a stable state, the control circuit controls the non-luminous load element loop to be disconnected and the LED luminous element loop to be connected. According to the technical scheme, the non-luminous load element is controlled to be switched on in a current rising or falling stage of the constant current source so as to consume circuit energy in a non-constant current stage, so that the condition that the current acts on the luminous element in the section to enable the display and adjustment of the brightness and the color of the lighting equipment to be free from the control of a PWM (pulse width modulation) signal and further influence the adjustment of the brightness and the color of the lighting equipment is avoided; and in the current stabilization stage, the light-emitting element is controlled to be switched on, so that the brightness and the color of the light can be adjusted more accurately by a user.

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

Further, the number of the non-light emitting load elements is 2, one of which is turned on at a current rising stage of the constant current source, and the other of which is turned on at a current falling stage of the constant current source. By adopting the technical scheme, the rising time and the falling time of the current are respectively controllable, the design freedom degree is higher, and meanwhile, the rising time and the falling time of the current are shorter, and the heat loss is lower.

The utility model also provides a timesharing dimming control circuit based on PWM, including being used for the main power supply for whole circuit power supply, still include: the constant current source is used for providing driving current for the LED light-emitting elements; the control module is used for controlling the on-off of the switch circuit; the switch circuit is used for controlling the connection between the constant current source and the LED light-emitting element to be switched on and off; the constant current source, the switch circuit and the LED light-emitting element are connected in series, the switch circuit comprises at least two paths of switches, each path of switch is connected with one path of LED light-emitting element, and the control module outputs a PWM control signal to control the on-off of the switch circuit; when the LED light-emitting elements are switched, the control module controls the PWM waveforms corresponding to the two LED light-emitting elements to be partially overlapped. In the technical scheme, the PWM waveforms corresponding to the two LED light-emitting elements are partially overlapped under the control of the control module, so that the load continuity of the circuit is realized at the moment of switching the two LED light-emitting elements, and the problem that the brightness and color stability of a light source cannot meet the requirements of a user when the brightness and color of light are adjusted by the user in the prior art is solved.

Furthermore, 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 are partially overlapped. At the moment of switching the two paths of LED light-emitting elements, the PWM signal corresponding to the rear path of LED light-emitting element is always controlled to output a high level, and then the PWM signal corresponding to the front path of LED light-emitting element is controlled to output a low level, so that the load continuity of the circuit is realized at the moment of switching the two paths of LED light-emitting elements, and the problem that the brightness and color stability of a light source cannot meet the requirements of a user when the user adjusts the brightness and color of light in the prior art is solved. Further, the constant current source is plural. Among this technical scheme, set up the constant current source of a plurality of grades, the electric current is the biggest constant current source of ampere level generally speaking, and the constant current source that sets up ampere level is in order to satisfy the demand of lighting system hi-lite, and sets up the constant current source of more grades of lower is in order to satisfy the demand of lighting system smooth transition, thereby makes the utility model discloses can satisfy the user to the requirement of the hi-lite of light, can adjust luminance and color very smoothly again when the user carries out the regulation of luminance and color.

Furthermore, the control module controls the on-off of the switch circuits, and the constant current sources are called in a time-sharing manner in a single period to adjust the driving current of the LED light-emitting element;

or the control module controls the on-off of a plurality of switch circuits so as to select constant current sources with different currents to drive the LED light-emitting elements.

In the two technical solutions, in order to implement smooth adjustment of brightness, the control module may control to implement time-sharing call of the plurality of constant current sources in a single period, or may select different constant current sources to drive the LED light emitting element when different brightness needs to be output.

Furthermore, the number of the constant current sources is two, wherein one constant current source is an ampere constant current source, and the other constant current source is a milliamp constant current source. According to the technical scheme, only two constant current sources can be adopted, and when the light is in a low-brightness stage, only milliampere constant current sources work; when the light is in a high brightness or normal brightness stage, the ampere-level constant current source and the milliampere-level constant current source work simultaneously, and the two constant current sources can meet the requirements of users on smooth adjustment of high brightness and have a simpler control circuit and lower cost.

Further, the control module comprises a user control module and a driving module, the user control module is used for receiving a user instruction, converting the user instruction into a time point of high-low level conversion of the PWM signal and sending the time point to the driving module, the driving module comprises a register and a PWM generator, the register is connected with the PWM generator, the register receives the time point of high-low level conversion of the PWM signal sent by the control module and stores the time point, then transmits the time point to the PWM generator, and the PWM generator generates and outputs PWM signals for respectively controlling the constant current source and the switch circuit.

The LED constant current source is characterized by further comprising a non-luminous load element, wherein the non-luminous load element is connected with the LED luminous element in parallel, and the control module controls the LED luminous element to be switched off and the non-luminous load element to be switched on at the current rising or falling stage of the constant current source; when the current of the constant current source is stable, the control module controls the non-luminous load element loop to be disconnected and the LED luminous element loop to be connected. The technical scheme includes that the non-luminous load element works in the current rising or falling stage, namely in the current unstable stage, only the non-luminous load element is switched on but the LED luminous element is not switched on, and when a circuit is stable, the control module outputs PWM signals to control on-off switching of the LED luminous elements, so that the problem that the brightness and color adjustment caused by current change is not accurate is solved.

The utility model also provides a timesharing dimming control method based on PWM for foretell timesharing dimming control circuit based on PWM, control method includes: when the LED light-emitting elements are switched, the control module controls the PWM waveforms corresponding to the two LED light-emitting elements to be partially overlapped when the two LED light-emitting elements are switched. The PWM waveforms corresponding to the two LED light-emitting elements are partially overlapped to enable the circuit load to be kept stable all the time, so that the problem that the brightness and the color stability of a light source cannot meet the requirements of users in the prior art due to the fact that the circuit load is discontinuous in the prior art is solved.

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. In the technical scheme, when two paths of LED light-emitting elements are switched, the LED light-emitting element on the next path is always turned on first, and then the LED light-emitting element on the previous path is turned off, so that the problem that the brightness and the color stability of a light source cannot meet the requirements of a user in the prior art due to discontinuous circuit load in the prior art is solved.

Further, the control method further includes:

s1, the control module receives and converts the user input instruction into a PWM duty ratio;

s2, sending the PWM duty ratio signal to a register in the control module, and sending the received PWM duty ratio signal to a PWM generator by the register to generate the PWM signal;

s3, the control module outputs PWM signals to control the switching of the LED light-emitting element and the constant current source respectively;

alternatively, the first and second electrodes may be,

s1', the control module receives and converts the user input instruction into PWM duty ratio;

s2 ', converting the PWM duty ratio of the corresponding LED light emitting element in step S1' to a time point corresponding to the high-low level conversion of the PWM signal;

s3 ', the time point corresponding to each LED luminous element in the step S2' is sent to a register in the control module, and the register sends the stored time point to the PWM generator to generate a PWM signal;

s4', the control module outputs PWM signals to control the switching of the LED luminous element and the constant current source respectively.

The control module receives an instruction input by a user and converts the instruction into a PWM duty ratio to obtain a PWM signal, wherein one scheme is that a PWM generator is used for directly generating the PWM signal, the other scheme is that the PWM duty ratio is converted into a time point corresponding to high-low level conversion of the PWM signal, each time point is stored and then is sent to the PWM generator, and the PWM generator generates the PWM signal according to the time point corresponding to the high-low level conversion.

Furthermore, in the current rising and falling stages of the constant current source, the control module controls the LED light-emitting element loop to be switched off and the non-light-emitting load element loop to be switched on; when the current is stable, the control module controls the non-luminous load element loop to be disconnected and the LED luminous element loop to be closed.

3. Advantageous effects

Compared with the prior art, the beneficial effects of the utility model are that:

(1) the utility model discloses can solve in the multichannel PWM timesharing dimmer circuit because the discontinuous problem of load leads to the luminance of light, the problem that the colour can not reach user's demand, adopt the utility model discloses a lighting equipment's colour stability and degree of accuracy are higher, can realize richer, more accurate color;

(2) the utility model discloses can solve the limited problem of luminance control range in single constant current source drive PWM timesharing dimmer circuit, make luminance wide region level and smooth regulation, do not have the sudden change problem.

Drawings

FIG. 1 is a schematic block diagram of the system of the present invention;

FIG. 2 is a simplified schematic block diagram of FIG. 1 (a plurality of lamp beads are simplified into a string);

FIG. 3 is a timing diagram of FIG. 2;

FIG. 4 is a timing diagram of FIG. 1;

FIG. 5 is a schematic block diagram of the system in RGBW mode;

fig. 6 is an equivalent circuit diagram of the present invention in the RGBW mode;

FIG. 7 is a timing diagram of the present invention at a certain maximum brightness of orange;

FIG. 8 is a timing diagram of the brightness of the present invention at 30% of a certain orange color;

fig. 9 is a schematic block diagram of a system according to embodiment 2 of the present invention;

fig. 10 is an equivalent circuit diagram of embodiment 2 of the present invention;

fig. 11 is a schematic block diagram of embodiment 3 of the present invention;

FIG. 12 is a simplified functional block diagram of the load of FIG. 11;

FIG. 13 is a timing diagram illustrating time-sharing scheduling of multiple power supplies in a single cycle of the present invention;

fig. 14 is a timing diagram of the present invention when a certain level of power is used alone at different brightness levels;

fig. 15 is a timing diagram of a multi-stage power supply generated during the continuous brightness adjustment process of the present invention;

fig. 16 is a timing chart according to embodiment 3 of the present invention;

fig. 17 is a schematic block diagram of a system according to embodiment 4 of the present invention;

FIG. 18 is the timing diagram of FIG. 17;

fig. 19 is a schematic block diagram of a control module according to the present invention;

FIG. 20 is a flowchart illustrating the processing of the user control module according to the present invention;

fig. 21 is a schematic diagram of the PWM duty cycle conversion to time point according to the present invention;

FIG. 22 is a schematic diagram of the synchronizer according to the present invention;

fig. 23 is a second schematic block diagram of a control module according to the present invention;

fig. 24 is a third schematic block diagram of a control module (a user control module is integrated in a driving module) according to the present invention;

in the figure: 1: a main power supply; 2: a first constant current source; 3: a control module; 4: a second constant current source; 5: a multi-stage regulation circuit; 6: a user control module; 7: a drive module; 8: a register; 9: a synchronizer; 10: a PWM generator; 11: and a power supply conversion module.

Detailed Description

The present invention is further described below with reference to specific embodiments in which the LED light emitting elements are strings of light beads.

Example 1

The multi-channel PWM time-sharing dimming system shown in fig. 1 includes a main power supply 1, a first constant current source 2, a control module 3, a switch circuit K, K1, K2, K3 … … Kn, a non-light-emitting load element LD, also called a dummy load LD, which is represented by the dummy load LD in the drawings in the specification, and a lamp string CH1, CH2, CH3 … … CHn. The main power supply 1 can be an external power supply input of AC or DC, and it should be noted that, because the LED lamp beads are nonlinear elements, when the LED lamp beads are turned on, the voltage slightly increases, the current will obviously increase, and the LED lamp beads are easy to overcurrent, so that the first constant current source 2 is needed, and after the input of the main power supply 1, the input of the main power supply 1 passes through the first constant current source 2, and the AC-DC or DC-DC conversion forms a constant current output to drive the multi-street lamp bead string to emit light. The number of the lamp bead strings CH1, CH2, CH3 … … CHn is determined by the dimming mode selected by the system, which may be RGB, RGBW, RGBWW, RGBA, WW, etc. For example, if the RGBW pattern is selected, the number of the 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-luminous load element LD is generally selected from non-luminous energy dissipation devices such as resistors, and is turned on at the rising and falling stages of the constant current source current to consume the circuit energy at the non-constant current stage, so as to prevent the two stages from acting on the lamp bead string to influence the brightness and color of the lighting device. Because the current of the constant current source is in a changing state in the rising and falling stages, if the lamp bead string is conducted in the two stages, the brightness and the color of the lighting equipment are not controlled by the PWM signal, and the brightness and the color are not accurate enough for the field of movie and television lighting, so that the lamp bead string is prevented from being connected in the two stages as much as possible. The quantity of the switch circuits K1, K2 and K3 … … Kn corresponds to the quantity of the lamp bead strings, namely, one switch circuit controls one lamp bead string to realize time-sharing control of the lamp bead strings. And the other switching circuit K is used for controlling the on-off of the non-luminous load element LD. In a specific implementation, the switch circuits K, K1, K2, and K3 … … Kn may be implemented by MOSFETs, IGBTs, triodes, GaN fets, or high-speed relays, the control module 3 is configured to output the enable signal EN and PWMK, PWMK1 … … PWMKn signal, the enable signal EN is the enable signal of the first constant current source 2, the PWMK, PWMK1 … … PWMKn signal is used to control the on/off of the switch circuits K, K1, K2, and K3 … … Kn, and the control module 3 is configured to supply power from the main power source through AC-DC or DC-DC (not shown in the figure). The control module 3 can be realized by logic control chips such as MCU, CPLD, FPGA or DSP.

For convenience of describing the role of the non-light emitting load element LD, we simplify the lamp bead strings CH1, CH2, CH3 … … CHn of fig. 1 to the lamp bead string CH of fig. 2 at the time of description. The shutter speed of the video camera in the film and television industry is generally in the microsecond level, different frame rates may be selected during shooting, and for the case that the frame rate is higher or the shutter speed is more extreme, in order to meet the requirement that the light does not flicker during shooting in the film and television industry, the setting of the period time T, which is the sum of the total time of all the lamp bead strings CH1, CH2 and CH3 … … CHn after one on and one off plus the on time of the non-light-emitting load element LD and the off time of the constant current source, must meet the requirement. In this embodiment, the period time T may be selected to be 50us, and in a specific implementation, the length of the period time T may be determined according to a specific shutter speed of the camera and a specific frame rate of shooting, but the period time T must be smaller than the shutter speed, so that the light adjustment can meet the high requirement of the video industry. In order to ensure that the load of the first constant current source 2 is continuous in the non-maximum brightness condition of the lighting device, the first constant current source 2 needs to be turned off after all the lamp bead strings CH1, CH2 and CH3 … … CHn are sequentially turned on. As shown in fig. 2 and fig. 3, during a period time T (which can also be called a period 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 existence of an inductance in the circuit of the first constant current source 2, the output current cannot change suddenly, that is, the current cannot instantaneously go from 0 to 1, or from 1 to 0, there are rising and falling phases, in which the output current of the first constant current source 2 changes constantly, and the change of the output current causes the user to be inaccurate when performing brightness adjustment, thereby also causing the displayed color to be inaccurate. The switching on and off of the string of beads CH therefore requires avoiding these two phases. In order to normally discharge the inductive energy of the first constant current source 2 in these two stages, an additional non-light-emitting energy consuming device is required to serve as a temporary load, i.e. the non-light-emitting load element LD of the present invention. The choice of non-light emitting load element is typically a non-light emitting device that consumes power, typically a resistor. In two stages of the rise and the fall of the current of the constant current source, the control module 3 outputs a PWMK signal to control the switch circuit K to be switched on and turn on the non-luminous load element LD, and at the moment, only the non-luminous load element LD works in the circuit. After the current is stably output in a constant current mode, the PWMK signal controls the switch circuit K to be switched off, the non-luminous load element LD is switched off, the PWMKch signal is output to control the switch circuit Kch to be switched on, the lamp bead string CH is switched on, and the first constant current source 2 is kept outputting in a continuous constant current mode in the adjusting process of the lamp bead string CH.

Because non-luminous load element LD and lamp pearl cluster CH realize the break-make through switch circuit K and Kch, and switch circuit has a switching speed's problem, in order to avoid causing the influence for lighting equipment because of switch circuit's switching speed, the utility model discloses a control module 3 outputs PWMK signal high level when time length t1 in advance, comes control switch circuit K switch-on, and time length output PWMK signal low level when time delay t1, control switch circuit K disconnection, as shown in fig. 3. During the off phase of the first constant current source 2 at the single cycle time T, the time period T3 does not necessarily exist since the first constant current source 2 has been turned off by the enable signal EN output by the control module 3. the duration of t1 and t3 is generally determined according to the characteristics of the control switch circuits K and Kch. For example, if the switching circuits K and Kch are implemented by MOSFET AON7534 with a theoretical on-time of 8.8ns and an off-time of 22.3ns, then the time durations of t1 and t3 may be set to 30 ns. The utility model discloses an above-mentioned method can solve because of the circuit load that the periodic rising decline problem of switch response time and constant current source leads to is discontinuous to luminance, the colour of the light that leads to are unstable, can not reach the problem of user's demand.

In the dimming system shown in fig. 1, assuming that the required color of the lamp light needs to light the lamp bead strings CH1, CH2, and CH3 … … CHn within the period time T for the time duration D1, D2, and D3 … … Dn, respectively, the timing diagram of the whole system is as shown in fig. 4. At the moment of switching between the non-luminous load element LD and the lamp bead string CH1, the control module 3 controls to partially overlap the PWM waveforms corresponding to the two paths of LED light-emitting elements, so as to realize continuous load of the circuit at the moment of switching between the two paths of LED light-emitting elements, in this embodiment, the control module 3 outputs a PWMK1 signal high level ahead of time t1 before outputting a PWMK signal low level, controls the switch circuit K1 to be switched on, and lights the lamp bead string CH 1; and after the time length of t1, the PWMK signal low level is output, and the switching circuit K is controlled to be switched off. At the moment of switching between the lamp bead string CH1 and the lamp bead string CH2, the control module 3 outputs a PWMK2 signal high level in advance of t1 before outputting a PWMK1 signal low level, controls the switch circuit K2 to be switched on, and lights the lamp bead string CH 2; after the time length of t1, the PWMK1 signal low level is output, the switching circuit K1 is controlled to be disconnected, and the lamp bead string CH1 is closed. Analogize in proper order, in the twinkling of an eye that two way lamp pearl cluster switched, control module 3 is the PWM signal output high level that a preceding control back street lamp pearl cluster corresponds always, and the PWM signal output low level that a preceding street lamp pearl cluster corresponds is controlled again (the utility model discloses the preceding all the way that says indicates that the street lamp pearl cluster of lighting before two way lamp pearl cluster switch, the later all the way that indicates that the street lamp pearl cluster of lighting after two way lamp pearl cluster switch). The purpose of doing so is to make the circuit load continuous in the moment of two way lamp pearl cluster switch, and the constant current source can output current I continuously, stabilizes the luminance and the colour of lamp pearl cluster. Therefore, the brightness is adjusted through the sum of the duty ratios of the lamp bead strings, and the color is adjusted through the proportion of the duty ratios of the lamp bead strings, namely the adjustment of the color and the brightness can be realized by changing the time length of D1, D2 and D3 … … Dn.

Control module 3 control PWM signal adopt positive logic to the high level is effective, control constant current source 2 drive lamp pearl cluster CH is luminous, during concrete implementation, also can adopt negative logic, use the low level as effective, perhaps adopt the mixed mode of positive negative logic.

The color and brightness adjustment of the dimming system will be described below by taking an RGBW mode as an example, as shown in fig. 5, the total power supply 1 is input by DC48V, the first constant current source 2 is a typical DC-DC BUCK circuit, and outputs a constant current value 5A, the circuit switching frequency is 1MHz, the circuit is equivalent to that shown in fig. 6, Vin is 48V, the inductance L of the first constant current source 2 is 10uH, the output is 4 groups of 14 lamp bead strings, the non-light-emitting load element LD is a resistor Rld, the typical voltage value Vout of the reference lamp bead string is 3V × 14V 42V (different voltage values of the lamp beads in different colors are selected, and the typical voltage value is substituted into a calculation) and the current value (5A), and the equivalent resistance value is 8.4 Ω. Since the oscillation of the DC-DC BUCK circuit itself exists, actually, the time of the rising phase 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 phase is calculated as the time taken for the current to fall from 100% to 10%. In the current rise phase of the first constant current source 2

The current I (A) and the time t (us) are related to

After the control module 3 outputs the enable signal EN to control the first constant current source 2 to be opened, the time tp for the current to rise from 0% to 90% is about 1.84 us. In the current falling phase of the first constant current source 2

The relationship between current I (A) and time t (us) is I ═ 5 × e^-0.84tAfter the control module 3 outputs the enable signal EN to control the first constant current source 2 to be turned off, the current is from 100% to the lower partThe time td taken to fall to 10% is about 2.74 us. The dimming system cycle time T is 50us, then we can set the total on-time 45us of the string of beads to 100% brightness implementation, the remaining 5us being the non-light emitting load element LD and the off-time. The sum of the on-times of all the strings of beads does not exceed 45 us. As described above, the coincidence time t1 of two adjacent channels (including the non-light-emitting load element LD) being simultaneously turned on is set to 30ns, which accounts for 0.0067% of 45us, and is negligible when calculating the duty ratio. Within a single period time T, the total duration of the on-state of all the lamp bead strings determines the total brightness of the light source, and the duration proportion of the lamp bead strings with different colors determines the color of the light source. As shown in fig. 7 and 8, achieving a certain orange color requires a duty ratio of red R and green G of 3: 2, then the orange maximum brightness is achieved by turning on the red string of light beads R27us and the green string of light beads G18us in a single cycle. The orange 30% brightness is realized by turning on the red light bead string R8.41us and the green light bead string G5.4us in a single period. As shown in fig. 8, under the condition that the brightness is not maximum, the required lamp bead strings are sequentially lighted, the first constant current source 2 is continuously output in the adjusting process, and after the lamp bead strings are sequentially lighted, the first constant current source 2 is timely turned off through the enable signal EN, so that the problem that the load of the first constant current source 2 is discontinuous is avoided, and the stability and the accuracy of color display are ensured.

Example 2

The calculation formula of the change rate of the inductance current is delta I/delta t-delta U/L. In any DC-DC or AC-DC power supply topological model, the delta U of the current rising and falling intervals are different, the current rising or falling time is longer by using only one non-luminous load element, and the power loss of the non-luminous load element is also larger. The use of two non-luminous load elements is therefore a more optimal design, as shown in fig. 9. The circuit equivalent diagram is shown in fig. 10, in the current rising stage, Δ I/Δ t ═ Δ U/L ≈ Vin-I × Rld1)/L, so that the smaller the Rld1, the faster the current rising, and the Rld1 can adopt a small-value resistor of m Ω level; in the current reduction stage, Δ I/Δ t ≈ Δ U/L ≈ I × Rld2/L, so the larger the Rld2, the faster the current reduction, and the Rld2 can adopt Vout/I in normal operation. In the same embodiment 1, the total power supply 1 is a DC48V input, the first constant current source 2 is a typical DC-DC BUCK circuit, the output constant current value is 5A, the circuit switching frequency is 1MHz, Vin is 48V, the inductance L of the first constant current source 2 is 10uH, the output is 4 groups of 14 lamp bead strings, and the two non-light emitting load elements are Rld1 and Rld2, respectively, where Rld1 is a power resistor of 1m Ω (approximately equal to a short circuit when being turned on), and Rld2 is a power resistor of 10 Ω; where Δ I is a variation of the inductor current, Δ t is a variation of time, Δ U is a variation of the inductor voltage, L is an inductance value of the inductor, I is the inductor current, Rld1 is a resistance value of the non-light-emitting load element LD1, Rld2 is a resistance value of the non-light-emitting load element LD2, Vin is a dc input voltage of the total power supply, and Vout is an output voltage of the system load circuit.

Compared with one non-light-emitting load element in embodiment 1, the two non-light-emitting load elements in the present embodiment have several advantages as follows:

(1) the rising time and the falling time of the current are respectively controllable, and the design freedom degree is higher.

(2) The current rise and fall time is shorter, the first period of time is that the current rises from 0 percent to 90 percent

The second stage current I (A) and time t (us) have a relationship of I ═ 5e^-tThe calculated time period for the current to drop from 100% to 10% was 2.3 us.

(3) The heat loss is lower.

In embodiment 1, the heat loss power of the non-light emitting load element is estimated by the formula:

the two non-light-emitting load elements of the present embodiment have negligible loss of the Rld1 in the current rising stage and mainly have loss of the Rld2 in the current falling stage, so the heat loss power of the non-light-emitting load elements in the embodiment 2 is estimated as:

example 2 has lower heat loss than example 1.

Example 3

The brightness adjustment of the

embodiments

1 and 2 is adjusted by the sum of the duty cycle duration of the PWM signal of each street lamp bead string output by the control module 3, and the brightness adjustment range is limited. The most direct method for adjusting brightness is to reduce the current flowing through the lamp bead, so in order to improve the dimming accuracy of the lighting system and smoothly adjust the brightness, it is necessary to improve the current source therein.

As shown in fig. 11, the main power supply 1 may be An external power supply input of AC or DC, after the main power supply 1 is input, different constant current sources a1 and a2 … … An are selected through the switching circuits S1 and S2 … … Sn, and AC-DC or DC-DC conversion is performed to form a multi-stage constant current output, so as to drive the multi-street lamp bead string to emit light. The constant current sources a1 and a2 … … An output different current values I1 and I2 … … In, for example, 5A, 1A, 0.2A, 0.04A … … or 4A, 0.4A, 0.04A … …, and In short, the current values output by the constant current sources a1 and a2 … … An may be arranged In An equal ratio or may be configured In other ways to achieve a transition from An ampere level to a milliampere level, so as to simultaneously satisfy the high luminance of the lighting system and the smooth transition of the light adjustment In the field of video lighting. On one hand, the control module 3 outputs PWMS1 and PWMS2 … … PWMSn signals to control the on-off of the switch circuits S1 and S2 … … Sn, so that the constant current source is controlled; meanwhile, the PWMK1 and PWMK2 … … PWMKn signals are output to control the on-off of the switching circuits K1 and K2 … … Kn, so that the on-off of the lamp bead strings CH1 and CH2 … … CHn is controlled, namely the embodiment controls the change of the color and the brightness of the lamp light by adjusting two groups of PWM signals. The switch circuits S1 and S2 … … Sn may be implemented by MOSFETs, IGBTs, triodes, GaN field effect transistors, or high-speed relays.

For convenience of describing control of the control module 3 on the multi-stage constant current source, the multi-path lamp bead string and the non-luminous load element in fig. 11 are simplified into a lamp bead string CH as shown in fig. 12, and the constant current source and the switch circuit are assumed to be in an ideal state, that is, there is no problem of rising and falling stages of current or switch delay and the like. The multi-stage constant current source has two working modes, one mode is to call the multi-stage power source in a time-sharing manner in a single period T, the time sequence is shown in fig. 13, the control module 3 controls the on-off of the switching circuits S1 and S2 … … Sn through PWMS1 and PWMS2 … … PWMSn signals, and calls the constant current sources a1 and a2 … … An in a time-sharing manner in the single period T, namely, calls different constant current sources in different time periods to control the duty ratio of PWMS1 and PWMS2 … … PWMSn in the single period T, so that the driving current of the lamp bead string CH can be adjusted, and the brightness can be smoothly adjusted. The other is to use a certain level of power supply at different brightness levels, the timing sequence is shown in fig. 14, the control module 3 controls the on-off of the switch circuits S1 and S2 … … Sn through PWMS1 and PWMS2 … … PWMSn signals, and different constant current sources are selected to drive the lamp string CH at different brightness levels, so as to realize smooth brightness adjustment. Fig. 15 shows a timing chart generated during the continuous adjustment of the brightness.

As shown in fig. 11, assuming that the multi-stage constant current source PWM time-sharing dimming system operates in a manner that the multi-stage constant current source selects different constant current source drives according to the different brightness, the PWM ratio of the light color requires that the lighting bead strings CH1, CH2, and CH3 … … CHn are D1, D2, and D3 … … Dn durations respectively in the period T, and the brightness of the color is smoothly adjusted from the brightest to the darkest, so the timing diagram of the entire system is as shown in fig. 16 (PWMs 1 and PWMs2 … … PWMSn are omitted).

Example 4

This embodiment is a special form of embodiment 3, that is, in embodiment 3, there are a plurality of constant current sources, and this embodiment employs two constant current sources. As shown in fig. 17, the main power supply 1 is divided into two paths after being input, one path is converted into a direct current power supply through the power conversion module 11 as AC-DC or DC-DC, and then is equivalent to the second constant current source 4 through the resistor, so as to output a constant current i; the other path outputs a constant current I after passing through the first constant current source 2 as in embodiment 1. 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 drive the lamp string CH1, CH2 … … CHn and the non-light emitting load element LD in parallel. The first constant current source 2 is used in the high current stage of the lighting equipment, and the current I is generally in ampere level; the second constant current source 4 is used in the low current phase of the lighting device, and the current i is typically several tens of mA, i.e. 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 the

embodiments

3 and 4 is the same as that of the embodiment 1, and the control module 3 always controls the PWM signal corresponding to the next lamp bead string to output the high level in advance and then controls the PWM signal corresponding to the previous lamp bead string to output the low level.

Fig. 18 shows a timing chart in which the enable signal EN controls the first constant current source 2 to be turned on, and the lamp lighting device operates in a normal brightness stage, which is similar to the timing chart shown in fig. 4 of embodiment 1. When the enable signal EN controls the first constant current source 2 to be turned off, only the second constant current source 4 works, the driving current i of the lamp string is only milliampere level, the lighting equipment works in a low-brightness stage, the energy output by the second constant current source 4 is relatively low, and for the power conversion module 11, the load resistor and the control module 3 work continuously all the time, and at this time, the PWMK1 and PWMK2 … … PWMKn signals do not need to output high level in advance.

Both embodiment 1 and embodiment 2, embodiment 3 and embodiment 4 involve the PWM signal timing problem. The PWM signal is generated by the control module 3. As shown in fig. 19, 23 and 24, the control module 3 includes a user control module 6 and a drive module 7. The driving module 7 internally includes a register 8, a synchronizer 9, and a PWM generator 10. The user control module 6 and the driving module 7 transmit signals through the SPI interface. The user control module 6 is responsible for converting the result of the user operation into the PWM duty ratio and sending the PWM duty ratio to the driving module 7, as shown in the flowchart of the user control module 6 shown in fig. 20, S1: the user operation, the user adjusts the required light hue, brightness and color temperature by adjusting the HSI parameter of the light illumination device, and the user control module 6 converts the HSI parameter into the value of each street lamp bead string corresponding to the dimming mode, such as RGBWW or RGB value; s2: converting the numerical value into a PWM duty ratio, and converting the numerical value of each lamp bead string into a corresponding PWM duty ratio; the above-mentioned S1 and S2 are prior art and will not be described again; s3: converting the PWM duty ratio of the corresponding lamp bead string into a time point corresponding to the high and low levels of the PWM signal; s4: and sending the time point obtained in the step S3 to the register 8 of the driving module 7 for storage. In step S3, the PWM duty ratio needs to be converted to the time corresponding to the PWM high-low level conversion, and the time points marked by the simplified timing chart of embodiment 1, i.e. fig. 3, are shown in fig. 21. In fig. 21, 8 time points of the 3-way PWM signal are referred to, which are Reg1, Reg2, Reg3, Reg4, Reg5, Reg6, Reg7 and Reg8 in sequence, since the non-light-emitting load element LD is turned on first, the PWMK signal is output at the first time high level, the time point of Reg1 may be set to 0, that is, the PWMK signal needs to be changed from the low level to the high level at the time point of 0, the first constant current source 2 is turned on after t1 time, the enable signal EN is output at the high level, and the time point of Reg2 is 0+ t1, that is, the enable signal EN needs to be changed from the low level to the high level at the time point of 0+ t 1. 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, which are determined by the circuit of the first constant current source 2, the time point of Reg4 is tp +2t1, that is, the PWMK signal needs to be changed from high level to low level at the time point of tp +2t1, assuming that the rise time is tp and the fall time is td depending on the voltage and current of the inductor. The first constant current source 2 can turn on the lamp bead CH after being stably output, the high level of the PWMch signal is output, the time point of Reg3 is Reg4-t1, namely the PWMch signal needs to be changed from the low level to the high level at the time point of tp + t 1. The high time of PWMch is calculated by the PWM duty cycle, assuming D, the time point of Reg6 is Reg3+ D, i.e. the PWMch signal needs to change from high to low at tp + t1+ D. The time point of Reg7 is equal to Reg6, that is, the enable signal EN needs to be changed from high level to low level at the tp + t1+ D time point. The time point of Reg5 is Reg7-t1, namely the PWMK signal needs to be changed from low level to high level at the tp + D time point. The time point of Reg8 is Reg7+ td + t1, that is, the PWMK signal needs to be changed from high level to low level at the time point tp + D + td +2t 1.

After obtaining the corresponding time point of the PWM signal, the user control module 6 sends the time point to the register 8. The register 8 sends the time point to the synchronizer 9, and then the synchronizer 9 sends the time point to the PWM generator 10, and the PWM generator 10 generates a PWM signal according to the time point received by the register 8. Of course, the duty ratio generated by step S2 of the user control module 6 may be sent to the register 8, and the PWM generator 10 may generate the PWM signal. However, the PWM signal changes only with the change of the duty ratio, and once the circuit parameter changes, the driving module 7 cannot be applied, and the portability is poor. If the PWM signal is generated at a time point, the PWM signal changes with the change of the time point, and either a user or a manufacturer can change the PWM signal according to the change of the circuit parameter, for example, an accurate mode with shorter time t1 is provided for the user or the debugging selection in the factory. For example, the parameters of the first constant current source 2 or the second constant current source 4 are changed, and only the values of the time periods tp and td need to be changed, so that the driving module 7 can adapt to different circuit parameters. The synchronizer 9 functions as shown in fig. 22, assuming that the user adjusts the HSI of the lighting device at the time point F indicated by the arrow, according to the normal procedure, the time point C of PWMK1 should be adjusted at the time point F, because the time point of E is related to C, the time point of E should be adjusted synchronously, and multiple PWM waveforms need to be adjusted synchronously in sequence, but in practice, because the PWM signal time points are generated sequentially and sent to the register 8 in series, the control module 3 cannot adjust multiple PWM waveforms simultaneously. The adjusted PWM signal time point needs to be buffered in the register 8, and then sent to the PWM generator 10 through the synchronizer 9 after the single period T is finished, and then the adjusted PWM signal is generated in the next period T.

Of course, the synchronizer 9 is not necessarily present in practical implementation, and as shown in fig. 23, the function of the synchronizer 9 can be realized in the PWM generator 10 in practical use. In addition, as long as the resource of the driver module 7 is enough, the function of the user control module 6 can also be implemented in the driver module 7, that is, the user control module 6 can be arranged in the driver module 7, as shown in fig. 24.

By adopting the technical scheme of the utility model, the single constant current source is controlled in one period, when the brightness is adjusted by using the sum of duty ratios, each PWM signal is continuously output, the constant current source is continuously output in the adjusting process, and the constant current source is turned off after the adjustment is finished; at the moment of switching any two street lamp bead strings by multi-path PWM time-sharing dimming, the street lamp bead string needing to be switched on is firstly switched on, and then the previous street lamp bead string is switched off, so that the time delay existing in normal switching is eliminated, and the continuity of the total current of the system is ensured.

Claims

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

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

3. The PWM based LED lighting circuit according to claim 1 or 2, wherein: the number of the non-light-emitting load elements is 2, one of which is turned on at a current rise stage of the constant current source, and the other of which is turned on at a current fall stage of the constant current source.

4. A time-sharing dimming circuit based on PWM comprises a main power supply for supplying power to the whole circuit, and is characterized in that: further comprising: at least two LED light-emitting elements are arranged,

the constant current source is used for providing driving current for the LED light-emitting element;

the control module is used for controlling the on-off of the switch circuit;

the switch circuit is used for controlling the connection between the constant current source and the LED light-emitting element to be switched on and off;

the constant current source, the switch circuit and the LED light-emitting element are connected in series, the switch circuit comprises 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-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 be partially overlapped.

5. The PWM-based time sharing dimming circuit of 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 are partially overlapped.

6. The PWM-based time sharing dimming circuit of claim 4, wherein: the constant current source is a plurality of.

7. The PWM-based time sharing dimming circuit of claim 6, wherein: the control module controls the on-off of the switch circuits, and the constant current sources are called in a time-sharing manner in a single period to adjust the driving current of the LED light-emitting element;

8. The PWM-based time sharing dimming circuit of claim 4, wherein: the number of the constant current sources is two, wherein one constant current source is an ampere constant current source, and the other constant current source is a milliampere constant current source.

9. A PWM-based time sharing dimming circuit according to any of claims 4-8, wherein: the control module comprises a user control module and a driving module, the user control module is used for receiving a user instruction, converting the user instruction into a time point of high-low level conversion of a PWM signal and sending the time point to the driving module, the driving module comprises a register and a PWM generator, the register is connected with the PWM generator, the register receives the time point of high-low level conversion of the PWM signal sent by the control module and stores the time point, then the time point is transmitted to the PWM generator, and the PWM generator generates and outputs the PWM signal for respectively controlling the constant current source and the switch circuit.

10. A PWM-based time sharing dimming circuit according to any of claims 4-8, wherein: the LED constant current source is characterized by further comprising a non-luminous load element, wherein the non-luminous load element is connected with the LED luminous element in parallel, and the control module controls the LED luminous element loop to be switched off and the non-luminous load element loop to be switched on at the current rising or falling stage of the constant current source; when the current of the constant current source is stable, the control module controls the non-luminous load element loop to be disconnected and the LED luminous element loop to be connected.