Stochastic frequency pulse modulation for LED control elements

Abstract

Control element (402) for a light-emitting diode (404), hereinafter referred to as LED, which has the following features: a control signal generator configured to generate a control signal (100) for controlling the LED (404), wherein the control signal (100) has several successive cycles and wherein each cycle (110) has an ON period (112) and an OFF period (114), wherein the control signal (100) in each cycle (110) has an ON value for a length of the ON period (112) of the cycle (110) and has an OFF value for a length of the OFF period (114) of the cycle (110), and a control unit (406) that is designed to: to control the control signal generator, to generate a current cycle (110) of the several successive cycles of the control signal such that the length of the ON period (112) of the current cycle (110) is based on a value of an ON variable (n i) (for the current cycle (110) and that the length of the AUS period (114) of the current cycle (110) is based on a value of an AUS variable (m i ) for the current cycle (110) the value of the EIN variable (n i ) for the current cycle (110) by setting a range of the ON variable (n i ) for the values ​​of the EIN variable (n i ) for the current cycle (110) based on a parameter that takes the values ​​of the EIN variable (n i ) for previous cycles of the multiple successive cycles of the control signal, and by selecting the value of the ON variable (n i ) for the current cycle (110) from the range of EIN variables (n i ) to determine, the value of the AUS variable (m i ) for the current cycle (110) by setting a range of the OFF variable (m i ) for the values ​​of the AUS variables (m i) for the current cycle (110) based on a parameter that defines the values ​​of the AUS variable (m i ) for previous cycles, and by selecting the value of the OFF variable (m i ) for the current cycle (110) from the range of AUS variables (m i ) to determine.

Description

Technical field of disclosure

[0001] The present disclosure relates to the field of electronic circuits and in particular to systems and methods for driving elements of light-emitting diodes (LEDs) that use modulation to generate drive signals for LEDs. background

[0002] LED drivers are components that generate drive signals for LEDs to provide power to them. A drive signal generated by an LED driver controls the electrical current through one or more LEDs, causing them to emit light (e.g., during periods when the drive signal is high) or not emit light (e.g., during periods when the drive signal is low). By varying the duration of the LEDs' emit and non-emitting periods, a technique known as "modulation," the LEDs can be dimmed as desired.

[0003] Designing an LED driver is not a trivial task because each application has different requirements regarding operational behavior, performance, cost, and size. Improvements in the provision of LED drivers are always desirable.

[0004] DE 10 2014 014 678 A1 relates to a device for generating a PWM output signal modulated using pulse-width modulation (PWM) with a spreading code for use in a DC power supply and / or a DC / DC converter for supplying LEDs with electrical energy in motor vehicles. The generation of the PWM output signal is based on n PWM spreading codes, where n is a positive integer and n > 1. The spreading codes are strung together in a spreading code sequence of m consecutive PWM spreading codes, with a spreading code length equal to the PWM period, where m is a positive integer and m ≥ 1, and a spreading code period.The generation of an optimized PWM spectrum of the PWM output signal comprises the following steps: generating a first PWM signal with a PWM period, a PWM period duration, and a duty cycle; generating one, in particular n - 1, further PWM signals by delaying the first PWM signal accordingly; and / or generating a delayed first PWM signal for each subsequent signal, where each i-th PWM signal generated in this way, with 1 < i ≤ n, is delayed by a temporal i-th offset relative to the first PWM signal, and where each of the n PWM signals represents one of the n PWM spreading codes. Finally, a k-th PWM signal is selected from the n PWM signals as the current PWM spreading code signal depending on a selection signal and converted into the PWM output signal.

[0005] DE 10 2009 026 612 A1 relates to a method for controlling at least one consumer, in particular at least one chain of several LEDs connected in series, by means of pulse-width modulated signals, in which clock pulses are generated after randomly varying period lengths by means of a random number generator, wherein in a first comparator a counter value generated by means of a counter is compared with a threshold value dependent on a random number and this first comparator generates an output signal when the threshold value is reached, wherein the sequence of the generated output signals determines the clock of at least one pulse-width modulated signal.The teaching further relates to a control circuit for controlling at least one consumer, in particular at least one chain of several LEDs connected in series, by means of pulse-width modulated signals with at least one counter coupled to at least one first comparator, wherein the first comparator compares the counter value with a threshold value and generates output signals whose sequence determines the clock of at least one pulse-width modulated signal, and with at least one random number generator for generating the threshold value, the output of which is coupled to an input of the first comparator.

[0006] WO 2009 / 013698 A1 relates to a control system for controlling the light output of a light-emitting unit comprising at least one light-emitting diode (LED) and configured to emit light of at least one color, wherein the control system comprises: a sensor unit configured to detect the light output of the light-emitting unit and to provide a corresponding feedback signal; and a control unit configured to control the light output of the light-emitting unit based on a comparison between the feedback signal and a corresponding reference signal representing a desired light output, in order to provide improved light output, wherein the control unit is further configured to: determine a random switching period; determine on-times for the LED(s) within the random switching period to provide the improved light output;and to control the switching on of the LED(s) according to the specified period and switching times. The teaching further relates to an LED light emission unit arrangement and a method for controlling the light output of an LED light emission unit.

[0007] US 2016 / 0157314 A1 relates to a controller for controlling a plurality of LED lighting strings, wherein the controller for each of the plurality of LED lighting strings comprises: a frequency modulator configured to modulate a base frequency to generate a time-varying modulated frequency, wherein the frequency modulator is configured to modulate the base frequency by a jitter superimposed on a regularly repeating structure that changes more slowly than the jitter, resulting in the modulated frequency; and a modulated PWM signal generator configured to generate a modulated PWM signal with the modulated frequency and a predetermined duty cycle; wherein the regularly repeating structures for the PWM signals are phase-shifted relative to each other. Associated drivers, LED lighting circuits, and methods are also disclosed.

[0008] It is an object of the invention to improve an LED driver, a system with an LED driver, and a method for operating an LED driver using pulse-width modulation. This object is achieved in each case by the subject matter of the independent claims. Advantageous embodiments and further developments are the subject matter of the dependent claims. Brief description of the drawings

[0009] To provide a more comprehensive understanding of the present disclosure and its features and advantages, reference is made to the following description in conjunction with the accompanying drawings, where the same reference numerals represent the same part; they show: Fig. 1 an exemplary timing diagram for a periodic control signal with a constant duty cycle D; Fig. 2 an exemplary timing diagram for a control signal implementing stochastic frequency pulse modulation according to some embodiments of the present disclosure; Fig. 3 a flowchart illustrating a method for generating a control signal for an LED using frequency pulse modulation according to some embodiments of the present disclosure, and Fig. 4 a schematic block diagram representing a system in which one or more LED control elements configured to implement stochastic frequency pulse modulation may be implemented according to some embodiments of the present disclosure. Description of exemplary embodiments of the disclosure Overview

[0010] The systems, methods, and devices of this disclosure each have several innovative aspects, none of which is responsible for all the desirable attributes disclosed herein. Details of one or more implementations of the subject matter described in this patent specification are set forth in the description below and the accompanying drawings.

[0011] For the purpose of describing stochastic frequency pulse modulation for LED drivers, as proposed here, it might be useful to first understand the phenomena involved in LED drivers. The following basic information can be considered a foundation upon which the present disclosure can be properly explained. Such information is offered for explanatory purposes only and should accordingly not be interpreted in any way as limiting the broad scope of the present disclosure and its possible applications.

[0012] A common modulation technique used by conventional LED drivers to dim LEDs is pulse width modulation (PWM). As the name suggests, PWM involves changing the pulse width of the drive signal to dim the LEDs as needed.

[0013] Embodiments of the present disclosures are based on the recognition that the use of PWM is associated with certain shortcomings that impair the operating behavior of LEDs and are therefore unacceptable in certain implementations. For example, PWM can be associated with visible flickering of the LEDs. To overcome this shortcoming (i.e., to avoid or at least reduce the visible flickering), the frequencies of the PWM drive signals must be at least 120 hertz (Hz) or even at least 300 Hz. In another example, PWM can be associated with audible noise because frequencies higher than 1 kilohertz (kHz) can be audible due to the controlling inductor acting as a loudspeaker.Other shortcomings of PWM include cutoff frequency components (the performance of the switching regulator depends on the width of the PWM pulse) and electromagnetic interference (EMI) generated by the PWM.

[0014] To improve upon one or more of the shortcomings described above, embodiments of the present disclosure provide systems and methods that enable LED drivers to generate drive signals by implementing a modulation technique referred to herein as "stochastic frequency pulse modulation" (SFPM). SFPM is based on randomly lengthening or shortening the duration (i.e., the length of a time period) that the drive signal is high or low, tracking the deviation of the total duration (i.e., over multiple cycles) that the drive signal is high or low from what it should be in order to provide an LED with a target average output prescribed by a target dimming level, and using the tracking to set range boundaries from which the length of the time periods in which the drive signal is high or low can be randomly selected.The name SFPM derives from the fact that in such a drive signal, pulses are modulated in such a way (hence "pulse modulation") that there is no single fixed frequency of pulses of the drive signal in successive cycles (hence "stochastic frequency"). Applying SFPM to generate a drive signal for an LED (hereafter, unless otherwise specified, reference to a single LED also applies to multiple LEDs, not just one) makes it possible to achieve a target average power output delivered to the LED in a manner that eliminates or at least reduces one or more of the shortcomings associated with other LED drive modulation techniques, such as visible flicker, audible noise, cutoff frequency components, and EMI.

[0015] In one aspect of the present disclosure, an exemplary LED driver configured to implement SFPM is described. The LED driver may include a drive signal generator configured to produce a drive signal for driving an LED. The drive signal has several successive cycles, each cycle having what are hereafter referred to as an "ON period" and an "OFF period," defined such that in each cycle the drive signal has an ON value (e.g., a high value, such as a value corresponding to digital logic 1) for the length of the ON period of the cycle, and the drive signal has an OFF value (e.g., a low value, such as a value corresponding to digital logic 0) for the length of the OFF period of the cycle.In order for such an LED driver to implement SFPM, the LED driver may further have a control unit configured to control the drive signal generator to generate different cycles i (each with a length T). i ), where i is a non-zero integer representing a given, e.g., current, cycle of the multiple successive cycles of the control signal. In particular, the control unit is configured to control the control signal generator to create a current cycle such that the length of the ON period of the current cycle is determined by a value of an ON variable (hereinafter referred to as n). i marked) is based on the current cycle and the length of the AUS period of the current cycle is based on a value of an AUS variable (hereinafter referred to as m). i(marked) for the current cycle. For this purpose, the control unit is configured to determine the value of the ON variable for the current cycle by setting a range for the values ​​of the ON variable for the current cycle (where this range is referred to here as a "range of ON variables") based on a parameter that specifies the values ​​of the ON variables for the previous cycles of the control signal. The control unit is then configured to select the value of the ON variable for the current cycle from the set range of ON variables.Similarly, the control unit is configured to determine the value of the OFF variable for the current cycle by setting a range for the values ​​of the OFF variable for the current cycle (here referred to as a "range of OFF variables") based on a parameter that specifies the values ​​of the OFF variables for previous cycles. The control unit is then configured to select the value of the OFF variable for the current cycle from the set range of the OFF variables.

[0016] As will be recognized by those skilled in the art, at least some aspects of the present disclosure, in particular at least some aspects of SFPM for LED drivers as described herein, can be embodied in various ways, e.g., as a method, a system, a computer program product, or a computer-readable storage medium. Accordingly, aspects of the present disclosure can take the form of an entire hardware implementation, an entire software implementation (including firmware, native software, microcode, etc.), or an embodiment combining software and hardware aspects, all of which may be generally referred to herein as a "circuit," "module," or "system." At least some functions described in this disclosure can be implemented as an algorithm executed by one or more hardware processing units, e.g.,The process is executed by one or more microprocessors of one or more computers. In various embodiments, different steps and sections of the steps of each of the methods described herein can be performed by different processing units. Furthermore, aspects of this disclosure can take the form of a computer program product embodied in one or more computer-readable media, preferably non-volatile, which contain computer-readable program code embodied, e.g., stored thereon. In various embodiments, such a computer program can, for example, be downloaded (updated) to existing devices and systems (e.g., to existing LED drivers and / or their control units, etc.) or stored thereon during the manufacture of these devices and systems.

[0017] The following detailed description presents various descriptions of specific embodiments. However, the innovations described here can be embodied in a variety of different ways, as defined and covered, for example, by the claims or selected examples. Reference is made in the following description to the drawings, where identical reference numerals denote identical or functionally similar elements. It is understood that elements shown in the drawings are not necessarily drawn to scale. Furthermore, it is understood that certain embodiments may have more elements than are shown in a drawing and / or a subset of the elements shown in a drawing. Finally, some embodiments may include a suitable combination of features from two or more drawings.

[0018] The description may use the phrases "in one embodiment" or "in embodiments," each referring to one or more embodiments of the same or different embodiments. Unless otherwise specified, the use of the ordinal adjectives "first," "second," and "third," etc., to describe an ordinary object merely indicates that different instances of the same object are being designated and is not intended to imply that the objects so described are in any given sequence in terms of time, space, hierarchy, or otherwise. Furthermore, for the purposes of this disclosure, the phrase "A and / or B" or the notation "A / B" means (A), (B), or (A and B), whereas the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C). As used here, the notation "A / B / C" means (A, B, and / or C).The term "between" is used when referring to measurement ranges, including the ends of the measurement ranges.

[0019] Various aspects of the illustrated embodiments are described using terms commonly employed by those skilled in the field to communicate the content of their work to other skilled workers in the field. For example, the term "random" in the context of randomly selecting a value from a range of values ​​(e.g., randomly selecting the length of the ON period or the length of the OFF period, or randomly selecting values ​​to change the lengths, as described here) refers, for example, to using a computer-implemented random number generator or an algorithm to generate a value such that a sequence of such values ​​would have properties that approximate the properties of sequences of random numbers.Since computer-based random number generators are almost always pseudorandom number generators, references to a "random" selection of values ​​include the pseudorandom selection of values.

[0020] In another example, the term "connected" means a direct electrical connection between the things being connected, without any intermediate devices or components, while the term "coupled" means either a direct electrical connection between the things being connected or an indirect connection through one or more passive or active intermediate devices or components. In yet another example, the term "circuit" means one or more passive and / or active components designed to work together to provide a desired function. Sometimes, in the present description, the terms "circuit" or "signal" may be omitted. If they are used, the terms "essentially," "approximately," "about," etc., may be used.can be used to refer generally to being within + / - 20% of a target value, e.g., within + / - 10% of a target value, based on a specific value as described here or as is known in the field.

[0021] Other features and advantages of the disclosure will be evident from the following description and claims. Explanation of an example SFPM

[0022] Fig. Figure 1 provides an exemplary timing diagram for a periodic control signal 100 with a constant duty cycle D. The control signal 100 has several consecutive cycles 110, four of which are designated as cycles 110-1 to 110-4 in Fig. Figure 1 shows that because the control signal 100 is a periodic signal, the length of each cycle is the same and can be denoted as a time period T. As also shown in Figure 1. Fig. As shown in Figure 1, each cycle 110 has an ON period 112 (i.e., a period in which the control signal 100 has a certain ON value, e.g., a high value, as in Figure 1). Fig. 1 is shown) and an OFF period 114 (i.e., a period in which the control signal 100 has a certain OFF value, e.g., a low value, as in Fig. (as shown in Figure 1). As used here, the term "duty cycle" (D) (alternatively called "power cycle") refers to the fraction of a period during which a signal or system is active. The duty cycle is generally expressed as a percentage or ratio. A period is the time it takes for a signal to complete one ON-OFF cycle. Because the drive signal 100 has a constant duty cycle D, the length of each ON period is 112T · D, while the length of each OFF period is 114T · (1 - D).

[0023] Fig. Figure 2 is an exemplary timing diagram for a control signal 200, which SFPM implements according to some embodiments of the present disclosure. Similar to the control signal 100, the control signal 200 has several consecutive cycles 210, four of which are designated as cycles 210-1 to 210-4 in Figure 2. Fig. Figure 2 shows that, unlike the control signal 100, the control signal 200 is not a periodic signal, which means that the lengths of the different cycles 210 generally do not have to be the same, and the length of each cycle 210 can be defined as a time period T. i It can be marked. As it is used here, the index “i” refers to a value for a specific cycle 210-i, where i is an integer greater than zero.

[0024] As in Fig. As shown in Figure 2, each cycle 210 has an ON period 212 (i.e., a period in which the control signal 200 has a certain ON value, e.g., a high value, as in Figure 2). Fig. 2 is shown) and an OFF period 214 (i.e., a period in which the control signal 200 has a certain OFF value, e.g., a low value, as in Fig. (as shown in Figure 2). In contrast to the control signal 100, the control signal 200 does not have a constant duty cycle D. Rather, the length of the ON period 212 for each cycle 210 can be determined by an ON variable n. i can be changed, while the length of the AUS period is determined by an AUS variable m. i can be changed. For example, in some embodiments, the length of the ON and OFF periods 212, 214 can be changed for different cycles 210 based on what they are for a target operating cycle D and for a periodic control signal with a period T (with the nominal values ​​D and T as defined by reference to Fig. 1 are described) would have been. This means that, instead of the length of the ON period being 212 T · D (as is the case for the ON period 112 in the control signal 100 of Fig. 1 was), the length of the ON period 212-i of a given cycle i of the control signal 200 by the ON variable n i can be changed, T • D · (1 + n i to be, as in Fig. Figure 2 shows that the length of the ON period is 212-1 T · D · (1 + n1), the length of the ON period is 212-2 T · D · (1 + n2), and so on. This means that instead of the length of the OFF period being 214 T · (1 - D) (as shown for the OFF period 114 in the control signal 100 of Fig. 1 was), the length of the OFF period 214-i of a given cycle i of the control signal 200 by the OFF variable m i may be changed, T · (1 - D) · (1 + m i to be, as in Fig. Figure 2 shows that the length of the AUS period is 214-1 T · (1 - D) · (1 + m1), the length of the AUS period is 214-2 T · (1 - D) · (1 + m2), and so on.

[0025] To have a control signal where the length of each ON period 212 and the length of each OFF period 214 (i.e., the lengths of periods 212 and 214 for each of the cycles 210) is determined by a respective variable (e.g., by the ON variable n). i and the AUS variable m iThe example of the control signal 200, which can be changed, is an example of applying SFPM to generate the control signal. To generate such a control signal, an LED driver can have at least one control signal generator configured to generate the control signal and further a control unit configured to control the length of the ON periods 212 and the OFF periods 214 for different cycles 210 of the control signal 200.

[0026] Fig. Figure 3 is a flowchart illustrating a method 300 for generating a drive signal for an LED using SFPM according to some embodiments of the present disclosure. The method can be implemented using any LED driver (e.g., an LED driver 402, which is Fig. 4) is implemented, which includes a control unit (e.g., a control unit 406, as shown in Fig. 4) exhibits or is coupled to them via communication technology. Although the procedure 300 refers to system components of the system that is in Fig. As shown in Figure 4, described is any system that is designed to perform operations of Procedure 300 in any order, within the scope of this disclosure.

[0027] As in Fig. As shown in Figure 3, the method 300 can begin with a process 302, which features the LED driver receiving nominal values ​​for the cycle period T and the duty cycle D. The values ​​of T and D can be such as those specified with reference to Fig. 1 are described, and they can be called “nominal” because they generally define how much power is supplied to the LED with a given drive signal having cycle period T and duty cycle D. In various embodiments, the LED driver can obtain the nominal values ​​of cycle period D and duty cycle D by storing them in a memory (e.g., a memory 410 located in Fig. 4) accesses these values ​​by setting them based on some design criteria (e.g., based on some information provided by a user, or based on some information about the operation of an LED system for which the control signal is generated), by receiving these values ​​from an external source (e.g., user input), etc.

[0028] Procedure 300 can then proceed with a process 304 in which the LED driver (e.g., the control unit of the LED driver) uses both the nominal values ​​of T and D obtained in process 302 and the values ​​of ON and OFF variables set in a process 310 (described below) to set the lengths of the ON period 212 and the OFF period 214 for the current cycle. For example, in process 304, the LED driver can set the length of the ON period 212-i of the current cycle i of the drive signal 200, T · D · (1 + n i ) to be, and can set the length of the OFF period 214-i of the current cycle i of the control signal 200, T · (1 - D) · (1 + m i to be, as in Fig. 2 is shown. Although it is not specifically in Fig. As shown in Figure 3, a control signal generator of the LED control element can then generate the current cycle 210 with the length of the ON period 212 and the OFF period 214, which are set in the process 304.

[0029] Method 300 can also include a process 306 in which the LED driver (e.g., the control unit of the LED driver) calculates a parameter that specifies the values ​​of the ON variable (n) for at least a subset or all of the preceding cycles of the drive signal 200, and a parameter that specifies the values ​​of the OFF variable (m) for at least a subset or all of the preceding cycles of the drive signal 200. In some embodiments, such parameters can be mean values.

[0030] Method 300 can then proceed with a process 308, which includes the LED driver (e.g., the control unit of the LED driver) setting ranges of the ON and OFF variables based on the parameters calculated in process 306. For example, in some embodiments, the range of the ON variable in process 306 can be set such that, after the value of the ON variable for the current cycle has been selected from the range of the ON variable, and the current cycle becomes one of the preceding cycles (i.e., when the current cycle is over and becomes the last cycle to be added to the preceding cycles), the parameter (e.g., the mean value) that specifies the values ​​of the ON variable for the preceding cycles satisfies one or more criteria of the ON parameter.In another example, in some embodiments of process 306, the range of the OFF variables can be set such that, after the value of the OFF variable for the current cycle has been selected from the range of the OFF variables and the current cycle becomes one of the preceding cycles, the parameter (e.g., the mean value) that specifies the values ​​of the OFF variables for the preceding cycles satisfies one or more criteria of the OFF parameter. What such criteria might be can depend on how exactly the parameters calculated in process 306 are defined (e.g., whether the parameter is a mean value) and on how the lengths of the ON and OFF periods 212, 214 are set based on the ON and OFF variables. For example, if the length of the ON period 212 is essentially equal to T · D · (1 + n) i ) is, where n iThe value of the EIN variable for the current cycle, and the parameter that specifies the values ​​of the EIN variables for previous cycles, is an average of the values ​​of the EIN variables for previous cycles, which has one or more criteria for the EIN parameter that the average of the values ​​of the EIN variables for previous cycles is approximately zero or lies within a certain acceptable tolerance window centered at zero. One such criterion means that the length of the EIN periods should on average be approximately T · D, which is the value of T · D · (1 + n i ) is when the mean of n i for several preceding cycles is 0. Likewise, if the length of the AUS period is essentially equal to T · (1 - D) · (1 + m i ) is, where m iThe value of the AUS variable for the current cycle, and the parameter that specifies the values ​​of the AUS variables for previous cycles, is an average of the values ​​of the AUS variables for previous cycles, which has one or more criteria for the AUS parameter that the average of the values ​​of the AUS variables for previous cycles is approximately zero or lies within a certain acceptable tolerance window centered at zero. One such criterion means that the length of the AUS periods should on average be approximately T · (1 - D), which is the value of T · (1 - D) · (1 + m i ) is when the mean of m i for several preceding cycles, the value is 0. On the other hand, if the length of the ON / OFF periods is defined differently, the criteria may be different. For example, if the length of the ON period is essentially equal to T · D · n, then... iis that one or more criteria of the EIN parameter show that the mean of the values ​​of the EIN variable for the preceding cycles is approximately one or lies within a certain acceptable tolerance window centered at one. Such a criterion means that the length of the EIN periods 212 should on average be approximately T · D, which is the value of T • D · n i is when the mean of n i for several preceding cycles 1. Likewise, if the length of the AUS period 214 is essentially equal to T · (1 - D) · m iis that one or more criteria of the AUS parameter show that the mean value of the AUS variable for the preceding cycles is approximately one or lies within a certain acceptable tolerance window centered at one. Such a criterion means that the length of the AUS periods should on average be approximately T · (1 - D), which is the value of T · (1 - D) · m i is when the mean of m i for several previous cycles 1.

[0031] Method 300 can then proceed with Process 310, which includes the LED driver (e.g., the LED driver control unit) selecting ON and OFF variables based on the ranges of the ON and OFF variables set in Process 308. For example, in some embodiments, Process 310 can include randomly selecting an ON variable value for the next cycle from the range of ON variables set in Process 308, and / or randomly selecting an OFF variable value for the next cycle from the range of OFF variables set in Process 308. The ON and OFF variables set in Process 310 can then be used in Process 304 for the next current cycle. Thus, processes 304-310 can be executed for each new current cycle of a control signal (e.g.the control signal 200), which is generated by the LED control element, is performed iteratively.

[0032] The implementation of SFPM, as described here, can be described as follows: y¯=1T(∫0DT(1+n)ymax⋅dt+1T∫DTnTm(1+m)ymin⋅dt) where y is the mean value of the control signal 200, y max The LIN value of the control signal is 200, y min The OFF value of the control signal 200 is , and D and T are as described above. If the procedure 300 can ensure that the mean of n and m is 0, then the mean of y should also be the expected mean.

[0033] Fig. Figure 4 provides a schematic block diagram representing a System 400 in which one or more LED drivers configured to implement an SFPM may be implemented according to some embodiments of the present disclosure. As shown in Fig. As shown in Figure 4, the system can include an LED driver 402, an LED 404, and a control unit 406. The LED driver 402 can be configured to apply SFPM to generate a drive signal to control the LED 404. The control unit 406 can control at least parts of the operation of the LED driver 402, in particular, aspects of the LED driver 402 that implement SFPM when generating drive signals for the LED 404. For example, the control unit 406 can perform operations described above with reference to Fig. 3 are described. For this purpose, the control unit 406 can have at least one processor 408 and one memory 410 and can have access to input parameters 412, which can have, for example, the nominal values ​​of T and D described above.

[0034] In some embodiments, the processor 408, e.g., a hardware processor 408, can be coupled to the memory 410 via a system bus. Therefore, the control unit 406 can store program code within the memory 410. The processor 408 can execute the program code accessed from the memory 410 via a system bus. From one perspective, the control unit 406 can be implemented as a computer capable of storing and / or executing program code. However, it should be acknowledged that the control unit 406 can be implemented in the form of any system comprising a processor and memory capable of performing the functions described within this disclosure.

[0035] In some embodiments, the processor 408 can execute software or an algorithm to perform the activities discussed in this patent, in particular activities associated with SFPM for LED drivers, e.g., according to method 300 described herein. The processor 408 can comprise any combination of hardware, software, or firmware-providing programmable logic, including, by non-limiting examples, a microprocessor, a digital signal processor (DSP), a free form factor gate array (FPGA), a programmable logic array (PLA), an integrated circuit (IC), an application-specific integrated circuit (ASIC), or a virtual machine processor.The processor 408 can be coupled to the memory 410 via communication technology, for example in a direct memory access (DMA) configuration, so that the processor 408 can read from or write to the memory 410.

[0036] In general, the memory 410 may comprise a suitable volatile or non-volatile memory technology, including double-rate random-access memory (DDR), synchronous RAM (SRAM), dynamic RAM (DRAM), flash memory, read-only memory (ROM), optical media, virtual memory areas, magnetic or tape storage, or any other suitable technology. Unless otherwise specified, the memory elements discussed herein should be understood as being contained within the broad term "memory." The information measured, processed, tracked, or sent to any of the components of the control unit 406 could be provided in a database, register, control list, cache, or memory structure, all of which could be obtained on a suitable timescale.Each such storage option can be included within the comprehensive term "memory" as used here. Likewise, the possible processing elements, modules, and machines described herein should be understood as being included within the comprehensive term "processor." Each of the elements shown in the present figures, e.g., the circuits / components shown in . Fig. As shown in Figure 4, it may also have suitable interfaces for receiving, sending and / or otherwise communicating data or information in a network environment, so that it can communicate, for example, with the control unit 406 or analog control units of other such elements.

[0037] In certain exemplary implementations, mechanisms for implementing SFPM for LED drivers, as outlined here, can be implemented by logic encoded in one or more physical media, which may include non-volatile media, such as embedded logic provided in an ASIC, in DSP instructions, software (possibly including object code and source code) to be executed by a processor or other similar machine, etc. In some of these cases, memory elements such as the 410 memory located in Fig. Figure 4 shows that memory stores data or information used for the operations described here. This includes memory elements that can store software, logic, code, or processor instructions that are executed to perform the activities described here. A processor can execute any type of instruction associated with data or information to accomplish the operations described here. For example, processors such as the 408 processor, which is shown in Figure 4, could... Fig. As shown in Figure 4, an element or item (e.g., data) is transformed from one state or thing into another state or thing. In another example, the activities outlined here can be implemented with fixed logic or programmable logic (e.g., software / computer instructions executed by a processor), and the elements identified here could be of the type of a programmable processor, programmable digital logic (e.g., an FPGA, a DSP, an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM)), or an ASIC comprising digital logic, software, code, electronic instructions, or a suitable combination thereof.

[0038] In some embodiments, the memory 410 can store an application. It should be noted that the control unit 406 can also store an operating system (not in Fig. (as shown in Figure 4) can execute the application stored in memory 410. The application stored in memory 410 can be executed by processor 408. In response to the execution of the application, control unit 406 can be configured to perform one or more operations or procedural steps described herein.

[0039] Although it is in Fig. Unless specifically shown in Figure 4, in some embodiments an input / output (I / O) device may be coupled to the System 400 and / or the Control Unit 406. Examples of input devices include, but are not limited to, a keyboard, a pointing device such as a mouse, or the like. Examples of output devices include, but are not limited to, a screen or display, a loudspeaker, or the like. In some embodiments, an output device coupled to the System 400 and / or the Control Unit 406 may be a type of screen display such as a plasma display, a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, an electroluminescent display (EL display), or another indicator such as a scale, a barometer, or an LED. In some implementations, the System may include a control element (not shown) for the output device.Input and / or output devices can be coupled to the System 400 and / or the Control Unit 406 either directly or through intermediary I / O control units. In one embodiment, the input and output devices can be implemented as a combined input / output device such as a touch-sensitive display, sometimes referred to as a "touch-sensitive screen display" or simply a "touchscreen." In such an embodiment, input to the device can be provided by moving a physical object, such as a stylus or a user's finger, on or near the touch-sensitive screen display.

[0040] Although it is not in Fig. As shown in Figure 4, a network adapter can optionally be connected to the System 400 and / or the Control Unit 406 to allow them to be connected to other systems, computer systems, remote network devices, and / or remote storage devices via intervening private or public networks. The network adapter can include a data receiver for receiving data sent by the systems, devices, and / or networks to the System 400 and / or the Control Unit 406, and a data transmitter for sending data from the System 400 and / or the Control Unit 406 to the systems, devices, and / or networks. Selected examples

[0041] The following examples provide various selected examples of the embodiments disclosed herein.

[0042] Example 1 provides an LED driver comprising a drive signal generator and a control unit. The drive signal generator is configured to generate a drive signal to control an LED (which could have multiple LEDs). The drive signal has several successive cycles, each cycle having an ON period and an OFF period. In each cycle, the drive signal has an ON value for the length of the ON period and an OFF value for the length of the OFF period. The control unit is configured to control the drive signal generator and execute a current cycle (for example, a cycle i with a length T). i , where i is an integer greater than zero) of the several successive cycles of the control signal such that the length of the ON period of the current cycle is on a value of an ON variable (n i) for the current cycle and that the length of the AUS period of the current cycle is based on a value of an AUS variable (m iThe control unit is further configured to determine the value of the ON variable for the current cycle by setting a range of ON variables based on a parameter that specifies the values ​​of the ON variables for previous cycles of the control signal, and by selecting the value of the ON variable for the current cycle from the range of ON variables. Additionally, the control unit is configured to determine the value of the OFF variable for the current cycle by setting a range of OFF variables based on a parameter that specifies the values ​​of the OFF variables for previous cycles, and by selecting the value of the OFF variable for the current cycle from the range of OFF variables.

[0043] Example 2 provides the LED control element according to Example 1, where the parameter specifying the values ​​of the ON variables for the previous cycles is an average of the values ​​of the ON variables for the previous cycles, and the parameter specifying the values ​​of the OFF variables for the previous cycles is an average of the values ​​of the OFF variables for the previous cycles.

[0044] Example 3 provides the LED control element according to Example 1 or 2, wherein setting the range of the ON variable based on the parameter specifying the values ​​of the ON variable for the previous cycles has the setting of the range of the ON variable such that, after the value of the ON variable for the current cycle has been selected from the range of the ON variable and the current cycle becomes one of the previous cycles (i.e. when the current cycle is over and becomes the last cycle to be added to the previous cycles), the parameter specifying the values ​​of the ON variable for the previous cycles satisfies one or more criteria of the ON parameter.

[0045] Example 4 provides the LED driver according to Example 3, wherein controlling the driver signal generator to create the current cycle such that the length of the ON period is based on the value of the ON variable for the current cycle, has the control of the driver signal generator to create the current cycle such that the length of the ON period is essentially equal to T · D · (1 + n i ) where T is a nominal period value (i.e., a period value applicable to all cycles of the control signal), D is a nominal duty cycle (D) (i.e., a duty cycle value applicable to all cycles of the control signal), and n iThe value of the ON variable for the current cycle. In such an LED driver, the parameter that specifies the values ​​of the ON variable for previous cycles is an average of the values ​​of the ON variable for the previous cycles, and one or more criteria of the ON parameter indicate that the average of the values ​​of the ON variable for the previous cycles lies within a tolerance window centered at zero.

[0046] Example 5 provides the LED driver according to Example 3, wherein controlling the driver signal generator to create the current cycle such that the length of the ON period is based on the value of the ON variable for the current cycle, and controlling the driver signal generator to create the current cycle such that the length of the ON period is essentially equal to T · D · n iis where T is a nominal period value (i.e., a period value applicable to all cycles of the control signal), D is a nominal duty cycle (D) (i.e., a duty cycle value applicable to all cycles of the control signal), and n i The value of the ON variable for the current cycle. In such an LED driver, the parameter that specifies the values ​​of the ON variable for previous cycles is an average of the values ​​of the ON variable for the previous cycles, and one or more criteria of the ON parameter indicate that the average of the values ​​of the ON variable for the previous cycles lies within a tolerance window centered at one.

[0047] Example 6 provides the LED control element according to one of the previous examples, wherein selecting the value of the ON variable for the current cycle from the range of the ON variables involves randomly selecting the value of the ON variable for the current cycle from the range of the ON variables.

[0048] Example 7 provides the LED control element according to one of the preceding examples, wherein setting the range of the OFF variables based on the parameter specifying the values ​​of the OFF variables for the preceding cycles has the setting of the range of the OFF variables such that, after the value of the OFF variable for the current cycle has been selected from the range of the OFF variables and the current cycle becomes one of the preceding cycles (i.e., when the current cycle is over and becomes the last cycle to be added to the preceding cycles), the parameter specifying the values ​​of the ON variables for the preceding cycles satisfies one or more criteria of the OFF parameter.

[0049] Example 8 provides the LED driver according to Example 7, wherein controlling the drive signal generator to create the current cycle such that the length of the OFF period is based on the value of the OFF variable for the current cycle, includes controlling the drive signal generator to create the current cycle such that the length of the OFF period is substantially equal to T · (1 - D) · (1 + m i ) where T is a nominal period value (i.e., a period value applicable to all cycles of the drive signal), D is a nominal duty cycle (D) (i.e., a duty cycle value applicable to all cycles of the drive signal), and m iThe value of the OFF variable for the current cycle. In such an LED driver, the parameter that specifies the values ​​of the OFF variable for previous cycles is an average of the values ​​of the OFF variable for the previous cycles, and one or more criteria of the OFF parameter indicate that the average of the values ​​of the OFF variable for the previous cycles lies within a tolerance window centered at zero.

[0050] Example 9 provides the LED driver according to Example 7, wherein controlling the driver signal generator to generate the current cycle such that the length of the OFF period is based on the value of the OFF variable for the current cycle, includes controlling the driver signal generator to generate the current cycle such that the length of the OFF period is substantially equal to T · (1 - D) · m iis where T is a nominal period value (i.e., a period value applicable to all cycles of the control signal), D is a nominal duty cycle (D) (i.e., a duty cycle value applicable to all cycles of the control signal), and m i The value of the OFF variable for the current cycle. In such an LED driver, the parameter that specifies the values ​​of the OFF variable for previous cycles is an average of the values ​​of the OFF variable for the previous cycles, and one or more criteria of the OFF parameter indicate that the average of the values ​​of the OFF variable for the previous cycles lies within a tolerance window centered at one.

[0051] Example 10 provides the LED control element according to one of the previous examples, wherein selecting the value of the OFF variable for the current cycle from the range of the OFF variables involves randomly selecting the value of the OFF variable for the current cycle from the range of the OFF variables.

[0052] Example 11 provides a system that includes a control unit configured to control an LED driver, generating a drive signal to control an LED, wherein the drive signal has several successive cycles, and wherein each cycle has an ON period and an OFF period. In each cycle, the drive signal has an ON value for the length of the ON period of the cycle and has an OFF value for the length of the OFF period of the cycle.The control unit has one or more circuits configured to randomly select, for each cycle of the multiple successive cycles, the length of the ON period of the cycle from a range of ON period lengths, wherein the range of ON period lengths for the cycle is based on the ON period lengths selected for previous cycles of the multiple successive cycles, and to randomly select the length of the OFF period of the cycle from a range of OFF period lengths, wherein the range of OFF period lengths for the cycle is based on the OFF period lengths selected for the previous cycles.

[0053] Example 12 provides the system according to Example 11, wherein the one or more circuits of the control unit are further configured to determine the range of ON-period lengths for the cycle such that, after the cycle becomes one of the preceding cycles (i.e., for subsequent cycles), an average of the ON-period lengths selected for preceding cycles lies within a tolerance window centered at T · D, where T is a nominal period value (i.e., a period value applicable to all cycles of the drive signal) and D is a nominal duty cycle (D) (i.e., a duty cycle value applicable to all cycles of the drive signal).

[0054] Example 13 provides the system according to Example 12, wherein the control unit further includes a memory configured to store data indicating the mean of the lengths of the ON period selected for the preceding cycles.

[0055] Example 14 provides the system according to Example 12 or 13, wherein the one or more circuits of the control unit are further configured to determine the range of lengths of the OFF period for the cycle such that, after the cycle becomes one of the preceding cycles, an average of the lengths of the OFF period selected for preceding cycles lies within a tolerance window centered at T · (1 - D).

[0056] Example 15 provides the system according to Example 14, wherein the control unit further includes a memory configured to store data indicating the mean of the lengths of the ON period selected for the preceding cycles.

[0057] Example 16 provides the system according to one of Examples 11-15, wherein the length of each cycle is a sum of the length of the ON period of the cycle and the length of the OFF period of the cycle, and wherein different cycles of the multiple successive cycles have different lengths.

[0058] Example 17 provides the system according to one of Examples 11-16, wherein the system includes the LED control element.

[0059] Example 18 provides the system according to one of Examples 11-17, where the system includes the LED.

[0060] Example 19 provides a method for operating an LED driver to generate a drive signal for controlling an LED, wherein the drive signal has several successive cycles and wherein each cycle has an ON period and an OFF period, wherein in each cycle the drive signal has an ON value for a length of the ON period of the cycle and an OFF value for a length of the OFF period of the cycle.The method involves randomly selecting the length of the ON period of a current cycle from a range of ON period lengths, wherein the range of ON period lengths for the cycle is based on the ON period lengths selected for previous cycles of the multiple successive cycles; randomly selecting the length of the OFF period of the current cycle from a range of OFF period lengths, wherein the range of OFF period lengths for the cycle is based on the OFF period lengths selected for the previous cycles; and causing the LED driver to generate the current cycle of the drive signal.

[0061] Example 20 provides the procedure according to Example 19, which further includes repeating steps of randomly selecting the length of the ON period of the current cycle, randomly selecting the length of the OFF period of the current cycle, and causing the LED driver to generate the current cycle for each cycle of the multiple successive cycles.

[0062] In various other examples, the method according to Example 19 or 20 may have features of the LED control element according to one of Examples 1-10 and / or the system according to one of Examples 11-18, or be implemented in them. Other implementation notes, modifications and applications

[0063] In the discussions of the above embodiments, components of a system such as LEDs, control units, and / or other components can readily be replaced, exchanged, or otherwise modified to accommodate specific circuit arrangements. Furthermore, it should be noted that the use of complementary electronic devices, hardware, software, etc., offers an equally viable option for implementing the teachings of this disclosure, which are associated with providing SFPM for LED drivers as described herein.

[0064] In an exemplary embodiment, a number of electrical circuits shown in the present drawings can be implemented on a board of an associated electronic device. The board can be a general-purpose printed circuit board (PCB) that holds various components of the electronic device's internal electronic system and also provides interconnects for other peripherals. More specifically, the board can provide the electrical connections through which the other components of the system can communicate electrically. Suitable processors (including DSPs, microprocessors, supporting chipsets, etc.), computer-readable non-volatile memory elements, etc., can be appropriately coupled to the board based on specific configuration needs, processing requirements, computer designs, etc.Other components, such as external storage, additional sensors, audio / video display control units, and peripheral devices, can be integrated into the disk as expansion cards, via cables, or directly into the disk itself. In various embodiments, the functionalities described herein can be implemented in emulation form, such as software or firmware, running within one or more configurable (e.g., programmable) elements arranged in a structure that supports these functions. The software or firmware providing the emulation can be provided on a non-volatile, computer-readable storage medium containing instructions to allow a processor to execute these functionalities.

[0065] In another exemplary embodiment, the electrical circuits of the present drawings can be implemented as independent modules (e.g., a device with associated components and circuit arrangement configured to perform a specific application or function) or as plug-in modules in application-specific hardware of electronic devices. It should be noted that certain embodiments of the present disclosure can readily be incorporated, either partially or entirely, into a system-on-a-chip (SOC) assembly. An SOC represents an integrated circuit (IC) that integrates components of a computer or other electronic system onto a single chip. It can include digital and analog functions, as well as mixed-signal and often high-frequency functions, all of which can be provided on a single chip substrate.Other embodiments may include multi-chip modules (MCMs) in which several separate ICs are located within a single electronic assembly and are configured to work closely together through the electronic assembly.

[0066] It is also absolutely essential to note that all specifications, dimensions, and ratios outlined here (e.g., the number and length of cycles or segments of cycles of a control signal, which are described in Fig. The number of steps shown in 2 represents the number of steps taken in Fig. The number of components shown in 3 indicates the number of components that are in Fig.The diagrams shown in Figure 4 are provided for illustrative and teaching purposes only. Such information may be substantially modified without departing from the spirit of the present disclosure. It should be acknowledged that the system can be assembled in any suitable manner. Along with similar design alternatives, the circuits, components, modules, and elements shown in the present drawings can be combined in various possible configurations, all of which are obviously within the broad scope of this patent specification. Exemplary embodiments have been described in the preceding description with reference to certain component arrangements. Various modifications and alterations may be made to such embodiments without departing from the scope of the present disclosure.The description and drawings should therefore be viewed in a descriptive rather than a restrictive sense.

[0067] According to one aspect, systems and methods are disclosed that enable LED drivers to generate drive signals by implementing a modulation technique referred to herein as "stochastic frequency pulse modulation" (SFPM). SFPM is based on randomly lengthening or shortening the duration of the drive signal that is high or low, tracking the deviation of the total duration (i.e., over multiple cycles) that the drive signal is high or low from what it should be in order to provide an LED with a target average power output prescribed by a target dimming level, and using the tracking to set range boundaries from which the length of the time periods in which the drive signal is high or low can be randomly selected.

Claims

[1] Control element (402) for a light-emitting diode (404), hereinafter referred to as LED, which has the following features: a control signal generator configured to generate a control signal (100) for controlling the LED (404), wherein the control signal (100) has several successive cycles and wherein each cycle (110) has an ON period (112) and an OFF period (114), wherein in each cycle (110) the control signal (100) has an ON value for a length of the ON period (112) of the cycle (110) and has an OFF value for a length of the OFF period (114) of the cycle (110), and a control unit (406) that is designed to: to control the control signal generator, to generate a current cycle (110) of the several successive cycles of the control signal such that the length of the ON period (112) of the current cycle (110) is based on a value of an ON variable (n i) (for the current cycle (110) and that the length of the AUS period (114) of the current cycle (110) is based on a value of an AUS variable (m i ) for the current cycle (110) the value of the EIN variable (n i ) for the current cycle (110) by setting a range of the ON variable (n i ) for the values ​​of the EIN variable (n i ) for the current cycle (110) based on a parameter that takes the values ​​of the EIN variable (n i ) for previous cycles of the multiple successive cycles of the control signal, and by selecting the value of the ON variable (n i ) for the current cycle (110) from the range of EIN variables (n i ) to determine, the value of the AUS variable (m i ) for the current cycle (110) by setting a range of the OFF variable (m i ) for the values ​​of the AUS variables (m i) for the current cycle (110) based on a parameter that defines the values ​​of the AUS variable (m i ) for previous cycles, and by selecting the value of the OFF variable (m i ) for the current cycle (110) from the range of AUS variables (m i ) to determine. [2] LED control element (402) according to claim 1, wherein: the parameter that determines the values ​​of the EIN variable (n i ) for the preceding cycles, an average of the values ​​of the EIN variable (n i ) for the preceding cycles is and the parameter that determines the values ​​of the AUS variable (m i ) for the preceding cycles, an average of the values ​​of the AUS variables (m i ) for the preceding cycles. [3] LED control element (402) according to one of the preceding claims, wherein the setting of the range of the ON variable (n i) based on the parameter that determines the values ​​of the EIN variable (n i ) for the preceding cycles, setting the range of the ON variable (n i ) such that, after the value of the EIN variable (n i ) for the current cycle (110) from the range of EIN variables (n i ) has been selected and the current cycle (110) becomes one of the previous cycles, the parameter that determines the values ​​of the EIN variable (n i ) for the preceding cycles, one or more criteria of the EIN parameter are met. [4] LED control element (402) according to any one of the preceding claims, wherein: controlling the control signal generator to generate the current cycle (110) such that the length of the ON period (112) is based on the value of the ON variable (n) i) for the current cycle (110) is based on the control of the control signal generator, to generate the current cycle (110) such that the length of the ON period (112) is essentially equal to T · D · (1 + n i ) where T is a target period value, D is a target work cycle, and n i the value of the EIN variable (n i ) for the current cycle (110) is, the parameter that determines the values ​​of the EIN variable (n i ) for the preceding cycles, an average of the values ​​of the EIN variable (n i ) for the preceding cycles is and that one or more criteria of the EIN parameter show that the mean of the values ​​of the EIN variables (n i ) for the preceding cycles lies within a tolerance window centered at zero. [5] LED control element (402) according to one of claims 1 to 3, wherein: controlling the control signal generator to generate the current cycle (110) such that the length of the ON period (112) is based on the value of the ON variable (n) i ) for the current cycle (110) is based on the control of the control signal generator, to generate the current cycle (110) such that the length of the ON period (112) is essentially equal to T · D · n i is, where T is a target period value, D is a target work cycle, and n i the value of the EIN variable (n i ) for the current cycle (110) is, the parameter that determines the values ​​of the EIN variable (n i ) for the preceding cycles, an average of the values ​​of the EIN variable (n i ) for the preceding cycles is and that one or more criteria of the EIN parameter show that the mean of the values ​​of the EIN variables (n i) for the preceding cycles lies within a tolerance window centered at one. [6] LED control element (402) according to one of the preceding claims, wherein the selection of the value of the ON variable (n i ) for the current cycle (110) from the range of EIN variables (n i ) the use of a random number generator or a pseudorandom number generator to determine the value of the EIN variable (n i ) for the current cycle (110) from the range of EIN variables (n i to select. [7] LED control element (402) according to one of the preceding claims, wherein the setting of the range of the OFF variable (m i ) based on the parameter that determines the values ​​of the AUS variable (m i ) for the preceding cycles, setting the range of the OFF variable (m i ) such that, after the value of the AUS variable (m i) for the current cycle (110) from the range of AUS variables (m i ) has been selected and the current cycle (110) becomes one of the previous cycles, the parameter that determines the values ​​of the EIN variable (n i ) for the previous cycles, one or more criteria of the AUS parameter are met. [8] LED control element (402) according to any one of the preceding claims, wherein: controlling the control signal generator to generate the current cycle (110) such that the length of the OFF period (114) is based on the value of the OFF variable (m i ) for the current cycle (110) is based on the control of the control signal generator, to generate the current cycle (110) such that the length of the OFF period (114) is essentially equal to T · (1 - D) · (1 + m i ) where T is a target period value, D is a target work cycle, and m i the value of the AUS variable (m i) for the current cycle (110) is, the parameter that determines the values ​​of the AUS variable (m i ) for the preceding cycles, an average of the values ​​of the AUS variables (m i ) for the preceding cycles is and that one or more criteria of the AUS parameter show that the mean of the values ​​of the AUS variables (m i ) for the preceding cycles lies within a tolerance window centered at zero. [9] LED control element (402) according to any one of claims 1 to 7, wherein: controlling the control signal generator to generate the current cycle (110) such that the length of the OFF period (114) is based on the value of the OFF variable (m i ) for the current cycle (110) is based on the control of the control signal generator, to generate the current cycle (110) such that the length of the OFF period (114) is essentially equal to T · (1 - D) · m iis, where T is a target period value, D is a target work cycle, and m i the value of the AUS variable (m i ) for the current cycle (110) is, the parameter that determines the values ​​of the AUS variable (m i ) for the preceding cycles, an average of the values ​​of the AUS variables (m i ) for the preceding cycles is and that one or more criteria of the AUS parameter show that the mean of the values ​​of the AUS variables (m i ) for the preceding cycles lies within a tolerance window centered at one. [10] LED control element (402) according to one of the preceding claims, wherein the selection of the value of the OFF variable (m i ) for the current cycle (110) from the range of AUS variables (m i ) the use of a random number generator or a pseudorandom number generator to determine the value of the AUS variable (m i) for the current cycle (110) from the range of AUS variables (m i to select. [11] System (400) comprising a control unit (406) configured to control a drive element (402) for a light-emitting diode (404), hereinafter referred to as LED, in order to generate a drive signal (100) for driving the LED (404), wherein the drive signal (100) has several successive cycles and wherein each cycle (110) has an ON period (112) and an OFF period (114), wherein in each cycle (110) the drive signal (100) has an ON value for a length of the ON period (112) of the cycle (110) and an OFF value for a length of the OFF period (114) of the cycle (110), wherein the control unit (406) comprises the following: one or more circuits designed to perform, for each cycle (110) of the several successive cycles: to use a random number generator or a pseudorandom number generator to select the length of the EIN period (112) of the cycle (110) from a range of lengths of EIN period (112), wherein the range of lengths of EIN period (112) for the cycle (110) is based on the lengths of EIN period (112) selected for previous cycles of the several successive cycles, to use a random number generator or a pseudorandom number generator to select the length of the AUS period (114) of the cycle (110) from a range of lengths of the AUS period (114), wherein the range of lengths of the AUS period (114) for the cycle (110) is based on the lengths of the AUS period (114) selected for the preceding cycles. [12] System (400) according to claim 11, wherein the one or more circuits of the control unit (406) are further configured to determine the range of lengths of the ON period (112) for the cycle (110) such that, after the cycle (110) becomes one of the preceding cycles, an average of the lengths of the ON period (112) selected for preceding cycles lies within a tolerance window centered at T · D, where T is a target period value and D is a target work cycle. [13] System (400) according to claim 11 or 12, wherein the control unit (406) further comprises a memory configured to store data indicating the mean of the lengths of the ON period (112) selected for the preceding cycles. [14] System (400) according to one of claims 11 to 13, wherein the one or more circuits of the control unit (406) are further configured to determine the range of lengths of the OFF period (114) for the cycle (110) such that, after the cycle (110) becomes one of the preceding cycles, an average of the lengths of the OFF period (114) selected for preceding cycles lies within a tolerance window centered at T · (1 - D). [15] System (400) according to any one of claims 11 to 14, wherein the control unit (406) further comprises a memory configured to store data indicating the mean of the lengths of the AUS period (114) selected for the preceding cycles. [16] System (400) according to any one of claims 11 to 15, wherein a length of each cycle (110) is a sum of the length of the ON period (112) of the cycle (110) and the length of the OFF period (114) of the cycle (110) and wherein different cycles of the several successive cycles have different lengths. [17] System (400) according to any one of claims 11 to 16, wherein the system (400) comprises the LED control element (402). [18] System (400) according to any one of claims 11 to 17, wherein the system (400) comprises the LED (404). [19] Method for operating a control element (402) for a light-emitting diode (404), hereinafter referred to as LED, to generate a control signal (100) for controlling the LED (404), wherein the control signal (100) has several successive cycles and wherein each cycle (110) has an ON period (112) and an OFF period (114), wherein in each cycle (110) the control signal (100) has an ON value for a length of the ON period (112) of the cycle (110) and has an OFF value for a length of the OFF period (114) of the cycle (110), wherein the method comprises: Selecting the length of the ON period (112) of a current cycle (110) of the multiple successive cycles from a range of ON period lengths (112), wherein the range of ON period lengths (112) for the cycle (110) is based on the ON period lengths (112) selected for previous cycles of the multiple successive cycles, Selecting the length of the AUS period (114) of the current cycle (110) from a range of lengths of the AUS period (114), wherein the range of lengths of the AUS period (114) for the cycle (110) is based on the lengths of the AUS period (114) selected for the previous cycles, and Causing the LED driver (402) to generate the current cycle (110) of the control signal. [20] The method of claim 19, further comprising the following repetition steps: Selecting the length of the ON period (112) of the current cycle (110), Selecting the length of the AUS period (114) of the current cycle (110) and Causing the LED driver (402) to generate the current cycle (110) for each cycle (110) of the multiple successive cycles.

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