Adaptive Frequency Modulation Method for Boost Circuit Used in LED Driving

Abstract

The present invention discloses an adaptive frequency modulation method for a boost circuit used in LED driving, which includes: obtaining the turn-on duration T of the PWM signal on and the duty cycle D, and simultaneously obtaining the output control voltage V pk+ and the output voltage V at the load end out ; calculating the load current I using an estimation formula load . Sending the estimated load current I load to a low-pass filter to obtain the filtered load current I load_filt ; determining the control frequency f of the PWM signal based on the filtered load current I load_filt and the preset minimum PWM frequency f min according to a preset frequency-load curve pwm .

Description

Technical Field

[0001] The present invention relates to the technical field of image display, and particularly to an adaptive frequency modulation method for a boost circuit used for LED driving. Background Art

[0002] In LED driving applications, a boost circuit is often used to boost the input voltage to the target operating voltage. The overall losses of the boost circuit include switching losses and conduction losses. For the same load, if the input and output voltages remain unchanged, the higher the switching frequency of the boost circuit, the higher the switching losses but the lower the conduction losses.

[0003] As Figure 1 shown, when the PWM signal input to the MOS transistor gate switches between high and low duty cycles D, in the steady state, the current I ind in the inductor fluctuates in a triangular wave form between I pk+ and I pk- , and the finally output voltage V out is The main losses of this circuit include two parts: the switching losses of the MOS transistor and the conduction losses of the inductor and the diode. The former is positively correlated with the PWM frequency, and the latter is negatively correlated with the PWM frequency. The reasons are as follows: the higher the PWM frequency, the faster the switching speed of the MOS transistor, and the greater the generated switching losses. On the other hand, if the input and output voltages and the load remain unchanged, the average values of I pk+ and I pk- , that is remain unchanged. Increasing the PWM frequency will reduce I pk+ and increase I pk- . At this time, the result of integrating the square of the current becomes smaller, so the conduction losses of the inductor are reduced. Usually, when the load is large, the current is large, and the system losses are mainly conduction losses, and the PWM frequency needs to be increased; when the load is small, the proportion of conduction losses decreases, and the proportion of switching losses increases accordingly, and the PWM frequency needs to be reduced. In practical applications, how to estimate the load weight and adjust the switching frequency of the boost circuit according to the load is an important issue for improving efficiency.

[0004] The load in LED driving applications is of the constant current type. In the boost circuit of a constant current type load, the duty cycle of the switching signal (PWM signal) is usually achieved by controlling the peak value of the inductor current. This control method cannot directly obtain the magnitude of the load current. Therefore, in traditional practices, the frequency of the PWM signal is usually adjusted only depending on the peak value of the inductor current.

[0005] As Figure 2 shown, to improve the efficiency, the PWM frequency of the boost circuit needs to be dynamically adjusted according to the load change. In LED driving applications, the load is of the constant current type. Therefore, how to estimate the load current I loadAdjusting the PWM frequency accordingly is an important issue for optimizing efficiency. However, due to the limitations of the control method, the load current I load cannot be directly obtained. Figure 2 In the traditional control method given, the PWM is periodically set high at a fixed frequency, the MOS transistor is turned on, and the inductor current increases linearly; when it is known through the sampling resistor R sns that the inductor current increases to a certain threshold I pk+ after that, the comparator flips. At this time, the PWM is set low, the MOS transistor is turned off, and the inductor current decreases linearly. Here, V out The control logic dynamically adjusts I out by comparing the actual value V ref of the output voltage and the target value V pk+ . When V out is lower than V ref , it indicates that the load is heavy. At this time, by increasing I pk+ to extend the on-time of the PWM, thereby raising V out . Conversely, when V out is higher than V ref , the system reduces V pk+ by decreasing I out . This control method can only obtain the magnitude of I pk+ through the output voltage V sns of the digital-to-analog converter (DAC) and the sampling resistor R pk+ , but cannot obtain the load current I load . Since there is a certain positive correlation between I pk+ and I load , traditional LED driver applications will control the PWM frequency according to I pk+ . However, when the PWM frequency changes, I pk+ will also change. Therefore, the method of adjusting the PWM frequency according to I pk+ is prone to trigger oscillations, and a large hysteresis window needs to be superimposed on I pk+ in the application to prevent oscillations. The superimposition of the hysteresis window on the other hand affects the control accuracy of frequency modulation, thus hindering the improvement of efficiency. Another frequency modulation strategy is achieved by collecting the load current I load . Since I load is independent of the PWM frequency, oscillations will not be triggered when adjusting the PWM frequency according to the collected I load . However, this strategy requires an additional current collection circuit, increasing the hardware design cost.

[0006] It can be seen that there is a need for a new boost circuit adaptive frequency modulation method applicable to LED driver circuits in the prior art. Compared with the traditional method, the method proposed by the present invention has the advantages of high adjustment accuracy, no oscillation, and flexible control. Summary of the Invention

[0007] The technical object to be achieved by the present invention is to provide a boost circuit adaptive frequency modulation method applicable to an LED driving circuit. This method obtains the load current through estimation, thus eliminating the hardware circuit for current acquisition. Next, a flexible and configurable frequency modulation curve is used to dynamically adjust the PWM frequency according to the load current.

[0008] Based on the above technical object, the present invention provides an adaptive frequency modulation method for a boost circuit used for LED driving. The boost circuit at least includes: an inductor element, a MOS transistor switch element, a sampling resistor, a digital-to-analog converter DAC, a comparator, and a digital logic control module; the digital logic control module includes a PWM signal generation module, a frequency modulation operation module, and an output voltage control module;

[0009] The method includes:

[0010] S100, obtaining the on-duration T on and duty cycle D of the PWM signal, and simultaneously obtaining the output control voltage V pk+ and the output voltage V at the load end out ;

[0011] S101, calculating the load current I load . According to the physical quantities obtained in step S100, calculate the load current I load , and the estimation formula is where L is the inductance, R sns is the resistance value of the sampling resistor, and μ is the power loss factor;

[0012] S102, sending the estimated load current I load into a low-pass filter to obtain the filtered load current I load_filt ;

[0013] S103, based on the filtered load current I load_filt and the preset minimum PWM frequency f min , determine the control frequency f of the PWM signal based on the preset frequency-load curve pwm .

[0014] In one embodiment, the frequency-load curve satisfies: according to the coordinate point and the coordinate point I max , f max ) two points determine a coordinate broken line associating the intermediate variable f pwm1 and the filtered load current I load_filt ; and when when, f pwm1 takes the value of When when, the intermediate variable fpwm1 and the relationship with the filtered load current I load_filt is constrained by the line segment formed by the coordinate points and the coordinate point (I max , f max ); where, I max is the maximum current that the comparator can collect, which is equal to the full-scale voltage V ref_DAC of the DAC divided by the sampling resistor R sns ; f max is the highest PWM frequency supported by the system; f min is the lowest PWM frequency supported by the system, and N is the reciprocal of the ratio of the load current associated when the system frequency is reduced to to I max .

[0015] In one embodiment, determining the control frequency f of the PWM signal based on the filtered load current I load_filt and the preset minimum PWM frequency f min , based on the preset frequency-load curve, further includes: comparing the intermediate variable f pwm with f pwm1 , and the control frequency f of the final PWM signal min is the larger value between the intermediate variable f pwm and the preset minimum PWM frequency f pwm1 and the preset minimum PWM frequency f min .

[0016] Other features and advantages of the present invention will be described in the subsequent specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0018] Figure 1 is a schematic diagram of the relationship between the PWM signal and the inductor current in the LED driving boost circuit in the prior art;

[0019] Figure 2 is a schematic diagram of the LED driving constant current type load boost circuit in the prior art;

[0020] Figure 3 is a schematic diagram of the LED driving adaptive frequency modulation boost circuit of the present invention;

[0021] Figure 4It is a schematic flowchart of the adaptive frequency modulation boost control method for LED driving according to the present invention;

[0022] Figure 5 It is a curve graph of the frequency-load current relationship according to the present invention. Specific embodiments

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] It should be understood that when an element or layer is referred to as "on", "adjacent to", "connected to" or "coupled to" another element or layer, it can be directly on, adjacent to, connected or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as "directly on", "directly adjacent to", "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Thus, a first element, component, region, layer or part discussed below may be denoted as a second element, component, region, layer or part without departing from the teachings of the present invention. And when discussing a second element, component, region, layer or part, it does not imply that the present invention necessarily has a first element, component, region, layer or part.

[0025] Spatial relationship terms such as "under", "below", "lower", "beneath", "above", "upper", etc. are used herein for convenience of description to describe the relationship of one element or feature shown in the figures with other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figures is flipped, then an element or feature described as "under" or "beneath" or "below" other elements or features will be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "below" can include both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are to be interpreted accordingly.

[0026] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present invention. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the associated listed items.

[0027] Example 1

[0028] As Figures 3-4 shown, the boost circuit with the adaptive frequency modulation function of LED driving in the embodiment at least includes: an inductive element, a MOS transistor switching element, a sampling resistor, a digital-to-analog converter DAC, a comparator, and a digital logic control module. The digital logic control module includes a PWM signal generation module, a frequency modulation operation module, and an output voltage control module.

[0029] In this embodiment, the frequency modulation operation module generates a frequency signal for controlling the PWM signal according to a preset adaptive frequency modulation control method and outputs it to the PWM signal generation module for generating a corresponding PWM control signal.

[0030] In this embodiment, the output voltage control module generates an output control voltage V ref based on the reference voltage V out and the output voltage V pk+ at the load end, and inputs the output control voltage V pk+ into the digital-to-analog converter DAC to generate the control signal required by the PWM signal generation module.

[0031] The control method of the boost circuit with the adaptive frequency modulation function of LED driving in this embodiment includes:

[0032] S100, obtaining the on-time T on and duty cycle D of the PWM signal, and at the same time obtaining the output control voltage V pk+ and the output voltage V out at the load end. In this embodiment, on the one hand, the frequency modulation logic module obtains the high-level duration T on and duty cycle D information of the PWM signal from the PWM generation logic; on the other hand, it obtains the voltage V out output by the DAC and the output voltage V pk+ at the load end from the V out control logic.

[0033] S101, calculating the load current I using the estimation formulaload Calculate the load current I based on the physical quantity obtained in step 1 load , and the estimation formula is where L is the inductance, R sns is the resistance value of the sampling resistor, and μ is the power loss factor. The specific principle of the load current estimation formula of the present invention is as follows: First, the output power P out can be expressed as V out *I load , and the input power P in can be expressed as 0.5*V in *(I pk+ +I pk- ). Considering the conduction loss and switching loss, let μ be the power loss factor, then P out =P in / μ. Therefore, the load current I out 、V in 、I pk+ and I pk- can be used to estimate the load current I load . Under steady state, V in can be calculated according to the output voltage V out and the PWM duty cycle D; I pk- can be obtained according to I pk+ , the inductor L and the conduction time T on of the PWM. After sorting, the above-mentioned estimation formula of the load current I load can be obtained.

[0034] S102, send the estimated load current I load to a low-pass filter to obtain the filtered load current I load_filt ; in this embodiment, the low-pass filter adopts a common IIR digital implementation architecture, that is, I load_filt[n] =eta*I load +(1-eta)*I load_filt[n-1] , where n represents the result of the nth update of I load_filt , and eta ranges from 0 to 1 and is used to control the bandwidth of the low-pass filter. When eta is smaller, the filtering bandwidth is narrower and the low-pass filtering effect is more obvious.

[0035] S103, based on the filtered load current I load_filt and the preset minimum PWM frequency f min , determine the control frequency f pwm of the PWM signal based on the preset frequency-load curve. As Figure 5 shown, the generation method of the frequency-load curve is as follows: First, according to the coordinate points and the coordinate points (I max , f max)Two points generate an associated intermediate variable f pwm1 and the filtered load current I load_filt of the broken line. When when, f pwm1 is When I load_filt ≥ when, I load_filt and f pwm1 The relationship is and (I max , f max ) The line segment formed by two points. Next, the intermediate variable f pwm1 is compared with f min . Finally, the control frequency f pwm of the PWM signal is pwm1 and f min The larger of the two. Among them, I max is the maximum current that the comparator can collect, equal to the full-scale voltage V ref_DAC divided by the sampling resistor R sns ; f max is the highest PWM frequency supported by the system; f min is the lowest PWM frequency supported by the system, and N is the system frequency reduced to when the associated load current and I max The reciprocal of the ratio. In the entire curve, f max , f min and N can all be flexibly configured according to the actual system application.

[0036] The present invention can be any possible system, method and / or computer program product at the integrated technology detail level. The computer program product may include a computer-readable storage medium (or multiple media) having computer-readable program instructions thereon for causing a processor to execute aspects of the present invention.

[0037] A computer-readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer-readable storage medium can be, by way of example and not limitation, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of computer-readable storage media includes the following: a portable computer floppy disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punched card or raised structure in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer-readable storage medium, as used herein, shall not be construed to be a transitory signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0038] The computer-readable program instructions described herein can be downloaded to a respective computing / processing device from a computer-readable storage medium or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium within the respective computing / processing device.

[0039] The computer-readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state-setting data, configuration data for integrated circuits, or source code or object code written in any combination of one or more programming languages and procedural programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer, or entirely on the remote computer or server. In the latter case, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may have a connection to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, an electronic circuit, including, for example, a programmable logic circuit, a field-programmable gate array (FPGA), or a programmable logic array (PLA), may execute the computer-readable program instructions by utilizing the state information of the computer-readable program instructions to personalize the electronic circuit, thereby performing aspects of the present invention.

[0040] Aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer-readable program instructions.

[0041] These computer-readable program instructions can be provided to a processor of a computer, or to other programmable data processing apparatus, to produce a machine, such that the instructions executed via the processor of the computer or other programmable data processing apparatus create means for implementing the functions / acts specified in the flowchart and / or block Figure 1 diagram. These computer-readable program instructions may also be stored in a computer-readable storage medium that can direct a computer, a programmable data processing apparatus, and / or other devices to function in a particular manner, such that the computer-readable storage medium in which the instructions are stored comprises a manufacture, the manufacture including instructions for implementing aspects of the functions / acts specified in the flowchart and / or block diagram.

[0042] The computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other devices to produce a computer-implemented process, such that the instructions executed on the computer, other programmable apparatus, or other devices implement the functions / acts specified in the flowchart and / or block diagram.

[0043] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, segment, or portion of instructions that includes one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, in fact, two consecutive blocks shown may be completed as one step, and depending on the functions involved, may be executed concurrently, substantially concurrently, in a partially or fully time-overlapped manner, or sometimes may be executed in the reverse order. It will also be noted that each block of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, can be implemented by a system based on dedicated hardware that performs the specified functions or actions or a combination of dedicated hardware and computer instructions.

[0044] Embodiments of the present application are described with reference to the flowcharts and / or block diagrams of methods, apparatuses (devices), and computer program products according to embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, and combinations of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate a means for implementing the specified function in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0045] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including an instruction means that implements the specified function in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0046] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the specified function in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

Claims

1. An adaptive frequency modulation method for a boost circuit for LED driving, the boost circuit comprising at least: Inductor components, MOS switch components, sampling resistors, digital-to-analog converters DAC, comparators and digital logic control modules; The digital logic control module includes a PWM signal generation module, a frequency modulation operation module and an output voltage control module; The method comprises: S100, obtain the on time T of the PWM signal on and duty cycle D, and obtain the output control voltage V pk+ And the load end output voltage V out ; S101, calculate the load current I using the estimation formula load ; According to the physical quantity obtained in step S100, calculate the load current I load , the estimation formula is Where L is the inductance, R sns is the sampling resistor value, μ is the power loss factor; S102, the estimated load current I load Send it to the low-pass filter to get the filtered load current I load_filt ; S103, based on the filtered load current I load_filt And the preset minimum PWM frequency f min , based on the preset frequency load curve, determine the control frequency f of the PWM signal pwm .

2. The adaptive frequency modulation method according to claim 1, characterized in that: The frequency load curve is satisfied by: and coordinate point (I max ,f max ) Two points determine an associated intermediate variable f pwm1 and the filtered load current I load_filt The coordinate line of When f pwm1 The value is when When the intermediate variable f pwm1 and the filtered load current I load_filt The relationship between the coordinate points and coordinate point (I max ,f max ) is a line segment constraint consisting of two points; where I max is the maximum current that the comparator can collect, which is equal to the full-scale voltage V of the DAC ref_DAC Divide by the sampling resistance R sns ;f max is the highest PWM frequency supported by the system; f min is the lowest PWM frequency supported by the system, and N is the frequency that the system reduces to The load current associated with I max The inverse of the ratio.

3. The adaptive frequency modulation method according to claim 2, characterized in that: According to the filtered load current I load_filt And the preset minimum PWM frequency f min , based on the preset frequency load curve, the control frequency f of the PWM signal is determined pwm Further comprising: converting the intermediate variable f pwm1 Same as f min By comparison, the final PWM signal control frequency f pwm is the intermediate variable f pwm1 and the preset minimum PWM frequency f min The larger one.

4. A computer-readable storage medium having computer instructions stored thereon, wherein: When the computer instruction is executed by a processor, the steps of the method according to any one of claims 1 to 3 are implemented.

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