CN111511071B - PWM signal correction method and LED lighting device - Google Patents
PWM signal correction method and LED lighting device Download PDFInfo
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- CN111511071B CN111511071B CN201910098409.4A CN201910098409A CN111511071B CN 111511071 B CN111511071 B CN 111511071B CN 201910098409 A CN201910098409 A CN 201910098409A CN 111511071 B CN111511071 B CN 111511071B
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Abstract
The invention relates to a PWM signal correction method and an LED lighting device. The PWM signal correction method is used for an LED lighting device comprising n paths of PWM driving loops, and comprises the following steps: measuring to obtain the ith pathCurrent I at maximum output current in PWM drive loopimaxAnd current I at current minimumiminWherein i is 1,2, … n; determining the corresponding current IimaxPWM value of (1), denoted as PWMimaxDetermining the corresponding current IiminPWM value of (1), denoted as PWMimin(ii) a Determining dimming whole-course time T and PWM duty ratio refreshing time T; according to the PWMimax、PWMiminT, t calculating a PWM adjustment step PWMistep; according to the PWMimax、PWMimin、PWMistep corrects the PWM signal input into the ith PWM driving circuit. According to the invention, the PWM output signals of each PWM driving loop are synchronously adjusted according to the maximum value and the minimum value of PWM in each PWM driving loop, and uniform synchronous control dimming of each loop can be realized.
Description
Technical Field
The present invention relates to a lighting device, and more particularly, to a PWM signal correction method and an LED lighting device using the same.
Background
The Light Emitting Diode (LED) has the advantages of energy conservation and environmental protection as an illumination light source, and is widely applied. LED dimming devices can be employed in LED lighting systems to provide desired brightness at different times, at different locations, and according to the particular needs of the user. The LED dimming device not only can reduce energy consumption, but also can provide a comfortable lighting environment.
PWM (Pulse Width Modulation) dimming is one of the most commonly used LED dimming methods, and PWM dimming arbitrarily changes the on-time of an LED by changing the duty ratio of high and low levels, thereby increasing the number of steps for adjusting the brightness. However, with the increasing of the LED driving schemes, the PWM dimming precision and the dimming interval requirement can be changed according to the different driving IC chips, and if only one set of MCU control program is used for PWM dimming control, the dimming process will jump, and especially the jump is more obvious in low brightness.
The three-way LED driving circuit for LED lighting device shown in fig. 1 has a non-uniform driving current output waveform for each driving loop when the PWM value is changed to adjust from 0.1% to 100% to dim the LED load as the time T increases. As for the first driving loop, when the duty ratio of the PWM signal from the MCU is increased from 0.1% to 25%, as shown by the current waveform L1 in fig. 1, the luminance (i.e., I-current ratio) of the LED load in the first driving loop has already changed from 5% to 100%, and the luminance of the LED load remains substantially unchanged regardless of how the PWM signal duty ratio is adjusted upward after 25%, so the overall change time of the luminance adjustment of the lighting device is relatively short. For the second driving loop, when the duty ratio of the PWM signal is increased from 0.1% to 50%, as shown by the current waveform L2 in fig. 1, the brightness of the LED load in the second driving loop changes from 5% to 100%, when the duty ratio of the PWM signal is adjusted upward after 50%, the brightness of the LED load is maintained substantially unchanged, and when the duty ratio of the PWM signal is in a low PWM value interval from 0.1% to a certain threshold value, the I current ratio is not output, and when the PWM signal reaches the threshold value, the I current ratio is suddenly started from 5%, and the brightness change of the LED load is not synchronized with the change of the PWM signal. The third driving circuit is similar to the second driving circuit, except that the minimum brightness of the I-current ratio is different in the adjustable threshold interval (low threshold starting point and upper limit point) of the PWM signal. When the duty ratio of the PWM signal is increased from 0.1% to 75% in the third driving loop, as shown by the current waveform L3 in fig. 1, the brightness of the LED load is changed from 8% to 100%, and the brightness of the LED load is maintained substantially unchanged even when the PWM signal is adjusted upward from 75% to 100%.
In order to obtain the ideal dimming curve shown in fig. 1 (as shown in a current waveform curve L4 in fig. 1, the ideal dimming effect of a designer is that when a PWM duty cycle signal is changed, an I current ratio is also changed uniformly and time is substantially synchronized), so as to avoid discomfort caused by uneven dimming of the dimming curve, for this reason, the designer needs to adjust the lighting circuits, but this approach has low design efficiency, and if a lighting device involves dimming and color mixing of multiple LED circuits, it is necessary to perform special adjustment on each circuit at the same time to ensure that smooth dimming of loads in the multiple LED circuits can be achieved, and the program universality is poor.
Disclosure of Invention
The invention aims to provide a PWM signal correction method with a smoother and softer dimming effect and an LED lighting device, so as to solve the defects in the prior art.
The invention provides a PWM signal correction method, which is used in an LED lighting device comprising n paths of PWM driving loops, wherein n is an integer and is more than or equal to 1, and the method comprises the following steps: s1, measuring the current I when the output current in the ith PWM driving loop is maximumimaxAnd current I at current minimumiminWherein i is 1,2, … n; s2, determining the current IimaxPWM value of (1), denoted as PWMimaxDetermining the corresponding current IiminPWM value of (1), denoted as PWMimin(ii) a S3, determining dimming whole time T and PWM duty ratio refreshing time T; s4, according to the PWMimax、PWMiminT, t calculating a PWM adjustment step PWMistep; s5, according to the PWMimax、PWMimin、PWMistep corrects the PWM signal input into the ith PWM driving circuit.
Further, in step S4, a PWM adjustment step PWM is calculated using a linear equation or a correction curve equationistep。
Further, PWMistep＝(PWMimax-PWMimin)/N，N＝T/t。
Further, the steps S1, S2 are completed in the learning correction mode.
Further, in step S1, detecting a current value in the ith PWM driving loop in real time, determining that the output current of the ith PWM driving loop reaches a maximum value after detecting that the current in the ith PWM driving loop does not increase in the forward direction and the continuous change of the current value does not exceed a preset first threshold value for a plurality of times, and taking an average value of a plurality of PWM values during the plurality of times of measurement as a PWMimax。
Further, the first threshold value is 100% ± 5% of the maximum current value.
Further, in step S1, the current value output by the ith PWM driving loop is detected in real time, the current value detected each time is compared with the current value detected last time, and when the current amplitude is detected to be maximum, the PWM value corresponding to the current value detected last time is taken as the PWMimin。
Further, T is a prescribed value selected from the range of 1 to 3 seconds, and T is a value obtained by dividing said T by a prescribed accuracy value.
The invention provides an LED lighting device which is characterized by comprising a control unit, n PWM driving loops and n current detection circuits, wherein n is an integer and is not less than 1, the n current detection circuits are used for detecting the current values output by the n PWM driving loops in real time, and the control unit measures the current I when the ith PWM driving loop outputs the maximum current value according to the current value detected by the current detection circuits in real timeimaxAnd current I at current minimumiminDetermining the corresponding current IimaxAnd is recorded as PWMimaxDetermining the corresponding current IiminAnd is recorded as PWMiminDetermining the whole dimming time T and the PWM duty ratio refreshing time T, and according to the PWMimax、PWMiminT, t calculating a PWM adjustment step PWMistep and according to said PWMimax、PWMimin、PWMistep corrects the PWM signal input into the ith PWM driving circuit, wherein i is 1,2 and … n.
Further, the control unit calculates PWM regulating step length PWM by adopting a linear equation or a correction curve equationistep。
Further, PWMistep＝(PWMnmaxPWMimax-PWMimin)/N，N＝T/t。
Further, the LED lighting device comprises a learning correction mode, and the control unit obtains I in the learning correction modeimax、Iimin，PWMimaxAnd PWMimin。
Furthermore, the LED lighting device further comprises an instruction receiving circuit, wherein the instruction receiving circuit receives a control instruction for entering the self-learning correction mode, which is input by a user, and enters the learning correction mode.
Further, the instruction receiving circuit is selected from one of a remote controller, a Bluetooth module, a touch device comprising touch keys and a wireless transmission module.
Further, the control unit is a main control MCU.
Further, in the learning correction mode, a 16-bit precision timer is used for generating a PWM (pulse width modulation) adjusting step length used by a user when the user adjusts light upwards/downwards through the instruction receiving circuit each time.
Further, when the control unit detects that the output current of the ith PWM driving circuit is not increased in the forward direction for multiple times and the continuous change of the current value does not exceed a preset first threshold value, the control unit judges that the output current of the ith PWM driving circuit reaches the maximum value, and takes the average value of multiple PWM values during multiple measurements as the PWM valueimax。
Further, the first threshold value is 100% ± 5% of the maximum current value.
Further, the control unit compares the current value detected each time with the current value detected last time, and when the maximum current reduction amplitude is detected, the PWM value corresponding to the current value detected last time is taken as the PWMimin。
Further, T is a prescribed value selected from the range of 1 to 3 seconds, and T is a value obtained by dividing said T by a prescribed accuracy value.
Furthermore, the ith PWM driving circuit is composed of a driving IC chip and an LED load circuit, and is configured to receive the PWM signal output by the control unit to perform dimming driving.
Further, in the learning correction mode, each time a user performs upward/downward dimming through the instruction receiving circuit, the PWM adjustment step size is 0.1%.
Another aspect of the present invention provides an LED lighting device, which executes the PWM signal correction method to generate a corrected PWM signal.
According to the technical scheme of the invention, the maximum value and the minimum value of PWM of each PWM driving loop are obtained, the PWM duty ratio regulating step length is calculated by utilizing the maximum value and the minimum value of the PWM, and the PWM output signal of each PWM driving loop is regulated according to the parameters, so that the uniform synchronous control of each loop can be realized.
Drawings
FIG. 1 is a graph of dimming curves for a prior art LED lighting device;
FIG. 2 is a schematic diagram of a circuit configuration of an LED lighting device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an instruction receiving circuit according to an embodiment of the present invention;
FIG. 4 is a flow chart of entering a modified learning mode according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of PWM duty cycle in self-learning correction mode according to an embodiment of the present invention;
FIG. 6 is a flow chart of a method for step size correction for n PWM drive loops in an LED lighting device;
FIG. 7 is a schematic diagram of PWM duty cycle adjustment for n PWM drive loops in an LED lighting device;
fig. 8 is a schematic diagram showing a specific example of PWM duty adjustment of a PWM drive circuit in the LED lighting device.
Detailed Description
The invention uses the control unit to generate PWM signals with different duty ratios, thereby realizing the adjustment of the output light of the LED lighting device. The control unit may be built up from separate elements or may be implemented by a microcontroller (MCU control circuit). In a preferred embodiment of the present invention, the control unit is an MCU main processing module.
Fig. 2 is a schematic circuit diagram of an LED lighting device according to an embodiment of the present invention.
As shown in fig. 2, the LED lighting device includes an MCU main processing module 1, an instruction receiving circuit 2, and at least one PWM driving circuit, wherein for each PWM driving circuit, the LED lighting device is provided with a corresponding current detection circuit.
The instruction receiving circuit 2 is configured to receive a control instruction input by a user, such as a PWM dimming level instruction, an instruction to enter a self-learning correction mode, and the like. The instruction receiving circuit can be a remote controller, a Bluetooth module, or a related loop including a touch key and the like and capable of giving instructions, a wireless transmission module and the like. The at least one PWM drive backEach PWM driving loop in the circuit is composed of a driving IC chip and an LED load loop and is used for receiving the PWM signal output by the MCU main processing module 1 to carry out dimming driving. And the current detection circuit is used for detecting the current in the PWM driving circuit in real time and recording and storing the detection result in a ROM (read only memory) in the MCU main processing module 1. The MCU main processing module 1 analyzes the instruction receiving signal received by the instruction receiving circuit 2, compares the current sampled by the current detection circuit, and identifies the maximum value of the current in each PWM driving loop and the PWM threshold value PWM when the current is stablemaxAnd PWM threshold value PWM when current is minimum and stableminAnd through algorithm processing, outputting the corrected PWM data, so that the output of a plurality of paths of PWM driving loops in the LED lighting device can be kept synchronous.
In the present embodiment, the LED lighting device includes a first PWM driving loop 3 and a second PWM driving loop 4. Correspondingly, the LED lighting device includes a first current detection circuit 5 for detecting the current in the first PWM driving circuit 3 in real time and a second current detection circuit 6 for detecting the current in the second PWM driving circuit 4 in real time.
Fig. 3 is a schematic diagram of a command receiving circuit according to an embodiment of the present invention, which is a remote controller. The remote controller can be any existing remote controller, and only the remote controller comprises at least three input parts, such as three keys. As shown in fig. 3, the remote controller includes a learning mode key 7, an up dimming key 8, and a down dimming key 9. The user enters a self-learning correction mode instruction by using the learning mode key 7, and the up dimming key 8 and the down dimming key 9 perform operations of up dimming (up) and down dimming (down), respectively. The up and down dimming keys can be operated by single pressing or continuous pressing, the PWM span of each step, i.e. the duty cycle change step length, is fixed and can be generated by a 16bit precision timer, in a preferred embodiment, the PWM duty cycle change step length is 0.1% when the up dimming key or the down dimming key is pressed once, and the precision and the span can be modified and defined, and can be set according to different application occasions. Meanwhile, the dimming duration time T can be set according to different application occasions.
A user sends a learning mode entering instruction to the instruction receiving circuit 2 by using the learning mode key 7, the instruction receiving circuit 2 sends the learning mode entering instruction to the MCU main processing module 1, and the MCU main processing module 1 controls the LED lighting device to enter a self-learning correction mode. The PWM driving loops 3 and 4 receive PWM signals sent by the MCU main processing module, dimming driving is carried out according to the PWM signals, meanwhile, the MCU main processing module 1 starts a current acquisition function, PWM real-time data and acquired current data are analyzed and processed, a first current detection circuit 5 carries out real-time detection on current in the first PWM driving loop 3, a second current detection circuit 6 carries out real-time detection on current in the second PWM driving loop 4, and therefore the maximum value of current of each driving loop is obtained, and PWM threshold PWM when the current of each driving loop is stable is achievedmaxPWM threshold value PWM when value and current are minimum and stableminThe value is obtained. And restarting after learning is finished, and prompting a user to finish learning, acquiring data and calculating through light flicker.
FIG. 4 is a flow chart of a modified learning mode, the method comprising the steps of:
step S401: starting;
step S402: and judging whether the LED lighting device enters a self-learning correction mode or not. If the MCU main processing module 1 receives a learning mode entering instruction sent by a user by pressing a learning mode key on a remote controller, the MCU main processing module 1 controls the LED lighting device to enter a self-learning correction mode and enter a step S403, otherwise, the MCU main processing module enters a step S409 and still maintains a normal mode;
step S403: starting AD current detection, and then entering step S404;
step S404: judging whether a user presses an upward dimming key on the remote controller, if so, entering a step S405, otherwise, entering a step S410;
step S405: the PWM duty is increased by a predetermined step size, and the process proceeds to step S406;
step S406: starting a current acquisition function, detecting the current in the first PWM driving loop 3 in real time by the first current detection circuit 5, detecting the current in the second PWM driving loop 4 in real time by the second current detection circuit 6, transmitting the ratio of the current value detected by each current detection circuit to the rated maximum output current, namely the current ratio, to the MCU main processing module 1, storing the current ratio of each time point and the corresponding PWM value in an internal ROM by the MCU main processing module 1 in real time, and then entering the step S407;
step S407: the MCU main processing module 1 analyzes and processes the PWM real-time data and the acquired current ratio data, judges whether each PWM driving loop is in a stable current ratio maximum state, if so, enters a step S408, otherwise, returns to the step S404;
step S408: the MCU main processing module 1 is provided with ImaxIdentifying the mark, recording the corresponding PWM value when each path of PWM driving loop is in the maximum current ratio and the stable state, and recording as PWMmaxA value;
step S409: the LED lighting device is in a normal mode;
step S410: judging whether the user presses a downward dimming key on the remote controller, if so, entering step S411, otherwise, entering step S418;
step S411: the PWM duty is decreased by a predetermined step size, and the process proceeds to step S412;
step S412: starting a current acquisition function, detecting the current in the first PWM driving loop 3 in real time by the first current detection circuit 5, detecting the current in the second PWM driving loop 4 in real time by the second current detection circuit 6, transmitting the ratio of the detected current value to the rated maximum output current, namely the current ratio, to the MCU main processing module 1, storing the current ratio and the corresponding PWM value of each time point in the internal ROM by the MCU main processing module 1 in real time, and then entering the step S413;
step S413: the MCU main processing module 1 analyzes and processes the PWM real-time data and the acquired current ratio data, judges whether each PWM driving loop is in a state of minimum and stable current ratio, if so, enters a step S414, otherwise, returns to the step S404;
step S414: the MCU main processing module 1 is provided with IminIdentifying the mark, recording the corresponding PWM value when each PWM driving loop is in the stable current ratio minimum state, and recording as PWMminA value;
step S415: to ImaxAnd IminThe identification bits are judged whether all are 1, namely, the PWM of each PWM driving loop is judgedmaxValue, PWMminWhether the values are recorded with the effect is finished, if yes, the step S416 is carried out, and if not, the step S404 is carried out;
step S416: prompting the user to learn and obtain data through light flicker, and completing calculation;
step S417: restarting the LED lighting device;
step S418: and (6) ending.
Fig. 5 is a waveform diagram illustrating a current ratio in the self-learning correction mode. In fig. 5, the second vertical axis on the right side is the current ratio, and the first vertical axis on the left side is labeled as the real-time PWM value corresponding to the current ratio waveform for convenience.
As shown in fig. 5, as the user continuously presses the up dimming button, the PWM value correspondingly increases, but since the increasing trend of the brightness (i.e. I current ratio) of the LED load is not completely consistent with the increasing trend of the PWM value (the variation curve of the PWM value is not shown in fig. 5), when the current ratio output from the PWM driving circuit reaches the maximum value, even if the up dimming button is pressed again, that is, the PWM value is increased (i.e. the DE stage shown in fig. 5), the current ratio value does not continuously increase any more, and the PWM value corresponding to the current ratio at this time is defined as the PWM valuemaxThe value is obtained. However, due to the existence of discrete errors, when the current ratio is detected to be the maximum value of the current ratio, the deviation of the set current ratio meets a certain error range, and then the corresponding PWM value is regarded as being at the maximum value, and the PWM driving loop can be confirmed to be in a stable maximum state of the current ratio by continuously fluctuating for a plurality of times in the error range, namely, the PWM value at the moment can be determined to be the PWM valuemaxThe value is obtained. For example, when it is detected that the current ratio in the PWM driving loop is not continuously increased in the forward direction for a plurality of timesIf the current ratio value is large and the continuous change of the current ratio value does not exceed a certain preset first threshold value, the current ratio value can be considered to reach the maximum value, and the average value of the corresponding PWM values in the last measurement is taken as the PWMmaxThe value is obtained. In a preferred embodiment, the first threshold may be 100% ± 5% of the maximum current value.
Similarly, as the user continuously presses the down dimming button in the on state, the PWM value is correspondingly decreased, and similarly, since the decrease trend of the brightness of the LED load is not completely synchronized with the decrease trend of the PWM value, various situations may occur in the low current stage. As shown in fig. 5, between the line segment AB points, even if the up dimming button is pressed or the down dimming button is pressed, since the MCU main processing module outputs the PWM value at this time, the current ratio is not changed, and the I current ratio is not output, that is, the LED lighting device is in the off state. In the curve BC segment, for example, when the upward dimming button is pressed, the I current ratio suddenly starts to light the LED lighting device with the increase of the PWM value output, and the curve is jagged and not smooth, so the current ratio at the point C (i.e., the current ratio before the point where the current detection has the maximum decrease amplitude) can be selected as the minimum current ratio, and the corresponding PWM threshold value at the time of stabilization can be used as the PWM threshold value at the time of PWMminAnd (6) recording the value. More specifically, it may be preferable that, for example, a current ratio detected after each downward dimming key is pressed is compared with a current ratio detected last time, and when the current ratio is detected to have a maximum amplitude, a PWM value corresponding to the current ratio detected last time is taken as the PWMmin。
Fig. 6 is a flowchart of a method for PWM step correction adjustment of n PWM driving circuits in an LED lighting device, the method comprising the steps of:
s601: obtaining PWM of each PWM driving loop through learning modemaxAnd PWMminRecorded as PWM, respectivelyimaxAnd PWMimin；
S602: setting dimming whole-course time T and PWM duty ratio refreshing time T, wherein the whole-course time T can be selected and set to be proper time within 1-3 seconds, preferably 2 seconds according to the environment, the specific condition of the lighting device and the adaptive effect experiment of human eyes. T is primarily determined by selectively dividing the full time T into, for example, 1/1000, according to the required accuracy of the PWM variation, and in the present embodiment, T may preferably be 2 ms when the full time T is 2 seconds.
S603: calculating PWM regulating step PWMstep of each PWM driving circuit and recording as PWMistep, said PWMistep＝(PWMimax-PWMimin) N, wherein N is T/T, and N is the number of PWM duty ratio refreshing sections; those skilled in the art will appreciate that although a linear relationship is used for the calculation, a correction curve or other optimized curve equation may be used for the calculation.
S604: the MCU main processing module 1 is used for processing the PWMiAnd step adjusts the PWM signals of each PWM driving circuit, respectively generates corresponding PWM control signals and sends the PWM control signals to each PWM driving circuit.
Fig. 7 is a schematic diagram of PWM duty cycle adjustment for n PWM driving loops in an LED lighting device according to an embodiment of the present invention.
The LED lighting device in this embodiment includes two PWM driving circuits, and the MCU main processing module 1 respectively drives the dimming operations of the two PWM driving circuits by sending a uniform PWM dimming signal to the two PWM driving circuits. In fig. 7, the horizontal axis is time, the first vertical axis on the left side is a PWM dimming signal value output by the MCU main processing module 1, and the second vertical axis on the right side is a current ratio output by each PWM driving circuit, where the current ratio is a ratio of a current value actually output by the PWM driving circuit to a rated maximum output current.
As shown in fig. 7, a line segment O is a signal curve of the PWM dimming signal sent by the MCU main processing module 1 when the PWM value is changed to adjust from 0.1% to 100% to dim the LED load as the dimming full time T increases, a curve Q1 is a graph of the current ratio output by the first PWM driving loop, and a curve P1 is a graph of the current ratio output by the second PWM driving loop, as can be seen from fig. 7, at this time, the outputs of the two PWM driving loops are not synchronized with the PWM dimming signal. Due to such output, the two paths cannot be output as originally assumed in design for a certain period of time, and such variations vary depending on the selection of the driver ICs.
In order to solve the above problem, according to the present invention, the LED lighting device first enters into a self-learning mode, and aims to obtain a maximum PWM duty ratio and a minimum PWM duty ratio corresponding to a maximum current ratio and a minimum current ratio. According to the detection result of the current detection circuit, when the output in the first PWM driving circuit is at the maximum value of the current ratio and the minimum value of the current ratio, the PWM duty ratios respectively corresponding to the output in the first PWM driving circuit are PWM1maxAnd PWM1minAnd recording the PWM duty ratios of the output current ratio maximum value and the output current ratio minimum value in the second PWM driving circuit as PWM2maxAnd PWM2minAnd recorded, in this embodiment, PWM1minAnd PWM2minAre all equal to PWMmin. And then, the previous PWM output signal is adjusted according to the parameters, the adjustment range and the accuracy are still in the initial basic setting, and only the interval of PWM output is adjusted according to the detection result.
The calculated PWM regulating step length is as follows: step-size-adjusting PWM of first PWM driving circuit1step＝(PWM1max–PWM1min) N, where N is T/T, in this embodiment, T still continues to use the previous dimming whole time T, and T is the PWM duty cycle refresh time; step-size-adjusting PWM of second PWM driving circuit2step＝(PWM2max–PWM2min)/N。
Adjusting PWM output signals of each PWM driving circuit according to the calculation result, wherein the maximum value of the PWM duty ratio of each PWM output signal is PWMimaxMinimum value being PWMiminThe PWM duty ratio refreshing time is t, and the PWM duty ratio regulating step length is PWMistep。
As shown in FIG. 7, the line segment O1 is in accordance with PWM1step PWM duty ratio regulating step length, and PWM value input into first PWM driving circuit is regulated from PWM1minRegulating to PWM1maxIn this case, the signal curve of the PWM dimming signal, the curve Q2 is the current ratio graph of the output of the first PWM driving loop corresponding to the curve, and the segment O2 is according to the PWM2step PWM duty cycleAdjusting step size to output PWM value of the second PWM driving loop from PWM2minRegulating to PWM2maxIn the meantime, a signal curve of the PWM dimming signal, curve P2, is a graph of the current ratio output by the second PWM driving loop corresponding to the signal curve, and as can be seen from fig. 7, the current ratios of the two PWM driving loops both change synchronously with the input PWM value, and are uniform and smooth, and the synchronous change of the outputs of the two PWM driving loops is also realized.
A specific example is substituted below to specifically describe one of the PWM driving circuits.
For ease of notation, the subscript i labels that distinguish between different PWM drive loops are omitted below.
In this example, when the full time T is 2 seconds, the PWM duty refresh time T is 2 milliseconds, and N is T/T is 2000/2 is 1000, that is, the PWM slave PWMminTo PWMmaxDividing into 1000 sections; PWM through self-learning mode detectionmin＝7％，PWM max75%, the PWM duty cycle adjustment step PWMstep is (PWM)max-PWMmin) And/1000 is 0.068. The signal curve of the PWM dimming signal and the current ratio curve of the PWM driving circuit are shown in fig. 8, and are not described herein again.
According to the technical scheme of the invention, through a self-learning mode, PWM values, namely PWM values, which correspond to PWM driving loops when the output current ratio reaches the maximum or the minimum respectively, are obtained and recordedmaxValue sum PWMminValue and using the PWMmaxValue sum PWMminAnd calculating the PWM duty ratio adjusting step length, and adjusting the PWM output signal of each PWM driving loop according to the parameters, so that smooth and uniform synchronous control of each loop can be realized.
In the present embodiment, the PWM signal correction method according to the present invention is described using a current ratio, that is, a ratio of a real-time current value output from the PWM drive circuit to a rated maximum output current. Those skilled in the art will appreciate that the present invention may be implemented as well by detecting the absolute maximum or minimum of the real-time current value output by the PWM drive loop and determining the PWM value corresponding to the absolute maximum and minimum.
It should be understood by those skilled in the art that the present embodiment has been described with respect to the first PWM driving circuit 3 and the second PWM driving circuit 4, but it is possible to implement the present invention and obtain the corresponding technical effects in the case of only one PWM driving circuit. And will not be repeated herein.
In addition, it will be appreciated by those of ordinary skill in the art that in the embodiments described above, numerous technical details are set forth in order to provide a better understanding of the present application. However, the technical solutions claimed in the claims of the present application can be basically implemented without these technical details and various changes and modifications based on the above-described embodiments. Accordingly, in actual practice, various changes in form and detail may be made to the above-described embodiments without departing from the spirit and scope of the invention.
Claims (23)
1. A PWM signal correction method is used in an LED lighting device comprising n paths of PWM driving loops, wherein n is an integer and is more than or equal to 1, and the method comprises the following steps:
s1, measuring current Iimax when the current is output to the ith PWM driving circuit at the maximum value and current Iimin when the current is output to the ith PWM driving circuit at the minimum value, wherein i is 1,2 and … n;
s2, determining a PWM value corresponding to the current Iimax, which is recorded as PWMimax, and determining a PWM value corresponding to the current Iimin, which is recorded as PWMimin;
s3, determining dimming whole time T and PWM duty ratio refreshing time T;
s4, calculating a PWM adjusting step length PWMistep according to the PWMimax, the PWMimin, the T and the T;
and S5, correcting the PWM signal input into the ith PWM driving circuit according to the PWMimax, the PWMimin and the PWMistep.
2. The PWM signal modification method according to claim 1,
in step S4, a PWM adjustment step pwmisstep is calculated using a linear equation or a correction curve equation.
3. The PWM signal modification method according to claim 1 or 2,
PWMistep＝(PWMimax-PWMimin)/N，N＝T/t。
4. the PWM signal modification method according to claim 1 or 2,
the steps S1, S2 are completed in the learning correction mode.
5. The PWM signal modification method according to claim 1 or 2,
in step S1, detecting a current value in the ith PWM driving loop in real time, determining that the output current of the ith PWM driving loop reaches the maximum value after detecting that the current in the ith PWM driving loop does not increase in the forward direction and the continuous change of the current value does not exceed a preset first threshold value many times, and taking an average value of a plurality of PWM values during the measurement many times as PWMimax.
6. The PWM signal modification method according to claim 5,
the first threshold is 100% ± 5% of the maximum current value.
7. The PWM signal modification method according to claim 1 or 2,
in step S1, the current value output by the i-th PWM driving circuit is detected in real time, the current value detected each time is compared with the current value detected last time, and when the maximum current drop amplitude is detected, the PWM value corresponding to the current value detected last time is pwmmin.
8. The PWM signal modification method according to claim 1 or 2,
t is a defined value selected between 1 and 3 seconds, and T is the value obtained by dividing said T by a defined precision value.
9. An LED lighting device is characterized in that,
comprises a control unit, n PWM driving loops and n current detection circuits, wherein n is an integer and is more than or equal to 1,
the n current detection circuits are used for detecting the current values output by the n PWM driving circuits in real time,
the control unit measures current Iimax when the ith PWM driving circuit outputs the maximum current value and current Iimin when the current is the minimum value according to the current value detected by the current detection circuit in real time, determines a PWM value corresponding to the current Iimax and records the PWM value as PWMimax, determines a PWM value corresponding to the current Iimin and records the PWM value as PWMimin, determines dimming whole-time T and PWM duty ratio refreshing time T, calculates PWM adjusting step length PWMistep according to the PWMimax, PWMimin, T and T, and corrects a PWM signal input into the ith PWM driving circuit according to the PWMimax, PWMimin and PWMistep, wherein i is 1,2 and … n.
10. The LED lighting device of claim 9,
and the control unit calculates the PWM adjusting step length PWMistep by adopting a linear equation or a correction curve equation.
11. The LED lighting device according to claim 9 or 10,
PWMistep＝(PWMnmaxPWMimax-PWMimin)/N，N＝T/t。
12. the LED lighting device according to claim 9 or 10,
the LED lighting device comprises a learning correction mode, and the control unit obtains Iimax, Iimin, PWMimax and PWMimin in the learning correction mode.
13. The LED lighting device according to claim 9 or 10,
the LED lighting device further comprises an instruction receiving circuit, wherein the instruction receiving circuit receives a control instruction for entering the self-learning correction mode input by a user and enters the learning correction mode.
14. The LED lighting device of claim 13,
the instruction receiving circuit is selected from one of a remote controller, a Bluetooth module, a touch device comprising touch keys and a wireless transmission module.
15. The LED lighting device according to claim 9 or 10,
the control unit is a main control MCU.
16. The LED lighting device of claim 13,
in the learning correction mode, a 16-bit precision timer is used for generating a PWM (pulse width modulation) adjusting step length used when a user adjusts light upwards/downwards through the instruction receiving circuit each time.
17. The LED lighting device according to claim 9 or 10,
and when the control unit detects that the output current of the ith PWM driving circuit is not increased in the positive direction for multiple times and the continuous change of the current value does not exceed a preset first threshold value, judging that the output current of the ith PWM driving circuit reaches the maximum value, and taking the average value of the multiple PWM values during multiple times of measurement as PWMimax.
18. The LED lighting device of claim 17,
the first threshold is 100% ± 5% of the maximum current value.
19. The LED lighting device according to claim 9 or 10,
and the control unit compares the current value detected each time with the current value detected last time, and when the maximum current reduction amplitude is detected, the PWM value corresponding to the current value detected last time is taken as PWMimin.
20. The LED lighting device according to claim 9 or 10,
t is a defined value selected between 1 and 3 seconds, and T is the value obtained by dividing said T by a defined precision value.
21. The LED lighting device according to claim 9 or 10,
the ith PWM driving loop is composed of a driving IC chip and an LED load loop and is used for receiving the PWM signal output by the control unit to carry out dimming driving.
22. The LED lighting device of claim 16,
in the learning correction mode, each time a user performs upward/downward dimming through the instruction receiving circuit, the PWM adjustment step size is 0.1%.
23. An LED lighting device, performing the PWM signal modification method according to any one of claims 1 to 8, and generating a modified PWM signal.
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