A LED driving circuit and driving method for reducing harmonic distortion

Abstract

The present invention discloses an LED driving circuit and a driving method thereof for reducing harmonic distortion. The LED driving circuit comprises a phase detection module, a sine wave generating module, a constant current source module and an LED light string; the phase detection module is used for sampling a line voltage and then outputting a corresponding phase signal to the sine wave generating module; the sine wave generating module is used for outputting a corresponding voltage signal to the constant current source module according to the phase signal; the constant current source module is used for controlling a working current flowing through the LED light string according to the voltage signal; the sine wave generating module controls the constant current source module to adjust the output current, i.e., the working current flowing through the LED light string, so that the working current is a nearly sine wave with the same frequency and phase as the line voltage, thereby reducing harmonic distortion and eliminating the problem of light flickering of the LED light string.

Description

Technical Field

[0001] The present invention relates to the technical field of LEDs, and in particular to an LED driving circuit and a driving method thereof for reducing harmonic distortion. Background Art

[0002] In the traditional linear LED driving method, the current that drives the LED light string to emit light is a square wave signal synchronized with the rectification cycle. The step change of the current will introduce high-order harmonic distortion. Harmonic distortion refers to the frequency components other than the fundamental wave. The general voltage or current waveform can be understood as a superposition of many sine waves with different frequencies, phases, and amplitudes. The input voltage is a sine wave, so if the output current is a sine wave with the same frequency and phase as the input voltage, the harmonic distortion is 0, but the LED is a non-resistive load, so the current cannot change in phase with the input voltage. For example Figure 1a and Figure 1b As shown in the figure, the general linear LED driving method needs to use the AC voltage division signal as the reference voltage of the output current to achieve synchronous changes of the current and AC voltage in order to meet the specification of sub-harmonic distortion. In this way, there will be no step jump of the current, and no high-order harmonic distortion will be introduced. Figure 2a and Figure 2b As shown, since the reference voltage is obtained by dividing the line network voltage, when the line network voltage fluctuates, the reference voltage follows the line network fluctuation, and the output current also fluctuates accordingly, eventually causing the LED to flicker.

[0003] Therefore the prior art still needs to be improved and enhanced. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide an LED driving circuit and a driving method thereof for reducing harmonic distortion, which can ensure that the working current flowing through the LED lamp string is a near-sine wave with the same frequency and phase as the input voltage and does not fluctuate with the line voltage, thereby reducing harmonic distortion.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] An LED driving circuit for reducing harmonic distortion comprises a phase detection module, a sine wave generating module, a constant current source module and an LED light string; the phase detection module is used to sample the line voltage and then output a corresponding phase signal to the sine wave generating module, the sine wave generating module is used to output a corresponding voltage signal to the constant current source module according to the phase signal, and the constant current source module is used to control the working current flowing through the LED light string according to the voltage signal.

[0007] In the LED driving circuit for reducing harmonic distortion, the phase detection module includes a sampling unit and a phase signal output unit; the sampling unit is used to output a sampling signal to the phase signal output unit after sampling the line voltage divider; the phase signal output unit is used to output the phase signal to the sine wave generating module according to the sampling signal.

[0008] In the LED driving circuit for reducing harmonic distortion, the sine wave generating module includes a timer and a conversion unit; the timer is used to start timing when receiving the phase signal, and output timing information to the conversion unit every sampling period, and clear when the line voltage period is reached; the conversion unit selects a corresponding voltage signal according to the timing information and outputs it to the constant current source module.

[0009] In the LED driving circuit for reducing harmonic distortion, the conversion unit includes a voltage divider subunit and a multi-way selection subunit; the voltage divider subunit divides the reference voltage and outputs the corresponding voltage signal to the multi-way selection subunit through different taps, and the multi-way selection subunit outputs the voltage signal output by the corresponding tap of the voltage divider subunit to the constant current source module according to the timing information.

[0010] In the LED driving circuit for reducing harmonic distortion, the sine wave generating module also includes a sampling frequency adjusting unit, which is used to calculate the time interval between two outputs of the same phase signal by the phase detection module, and then calculate the sampling period according to the time interval and the number of samplings within the time interval, and output the sampling period to the timer.

[0011] In the LED driving circuit for reducing harmonic distortion, the sampling unit includes a first resistor and a second resistor, one end of the first resistor is connected to the line voltage input terminal, the other end of the first resistor and one end of the second resistor are both connected to the phase signal output unit, and the other end of the second resistor is grounded.

[0012] In the LED driving circuit for reducing harmonic distortion, the phase signal output unit includes a comparator, a non-phase input terminal of the comparator is connected to the other end of the first resistor and one end of the second resistor, an inverting input terminal of the comparator is grounded, and an output terminal of the comparator is connected to the sine wave generating module.

[0013] In the LED driving circuit for reducing harmonic distortion, the phase signal output unit includes an analog-to-digital converter, one end of the analog-to-digital converter is connected to the other end of the first resistor and one end of the second resistor, and the other end of the analog-to-digital converter is connected to the sine wave generating module.

[0014] A driving method for an LED driving circuit with reduced harmonic distortion as described above comprises the following steps:

[0015] The phase detection module samples the line voltage and outputs a corresponding phase signal to the sine wave generation module;

[0016] The sine wave generating module outputs a corresponding voltage signal to the constant current source module according to the phase signal;

[0017] The constant current source module controls the operating current flowing through the LED light string according to the voltage signal.

[0018] In the driving method of the LED driving circuit for reducing harmonic distortion, the step of the phase detection module sampling the line voltage and then outputting the corresponding phase signal to the sine wave generating module comprises:

[0019] The sampling unit samples the line voltage and then outputs a sampling signal to the phase signal output unit;

[0020] The phase signal output unit outputs the phase signal to the sine wave generating module according to the sampling signal.

[0021] Compared with the prior art, the present invention provides an LED driving circuit and a driving method thereof for reducing harmonic distortion. The LED driving circuit includes a phase detection module, a sine wave generating module, a constant current source module and an LED light string; the phase detection module is used to sample the line voltage and then output a corresponding phase signal to the sine wave generating module; the sine wave generating module is used to output a corresponding voltage signal to the constant current source module according to the phase signal; the constant current source module is used to control the working current flowing through the LED light string according to the voltage signal; the sine wave generating module controls the constant current source module to adjust the output current, i.e., the working current flowing through the LED light string, to ensure that the working current flowing through the LED light string is a nearly sine wave with the same frequency and phase as the line voltage, thereby reducing harmonic distortion and eliminating the problem of flickering of the LED light string. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1a and Figure 1b is an existing first LED driving circuit and a waveform diagram of its input voltage and output current;

[0023] Figure 2a and Figure 2b is an existing second LED driving circuit and a waveform diagram of its input voltage and output current;

[0024] Figure 3 A structural block diagram of an LED driving circuit for reducing harmonic distortion provided by the present invention;

[0025] Figure 4 A circuit schematic diagram of a phase detection module in a first embodiment of an LED driving circuit for reducing harmonic distortion provided by the present invention;

[0026] Figure 5 A circuit schematic diagram of a sine wave generating module of a first embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0027] Figure 6 A current principle diagram of a nonlinear digital-to-analog converter in an LED driving circuit for reducing harmonic distortion provided by the present invention;

[0028] Figure 7 The waveform diagram of the input AC power, line voltage and voltage signal and the timing diagram of θflag and timing information To in the first embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0029] Figure 8 A circuit schematic diagram of a phase detection module in a second embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0030] Fig. 9 A circuit schematic diagram of a sine wave generating module of a second embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0031] Fig.10 A circuit schematic diagram of a phase detection module in a third embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0032] Fig.11 A timing diagram of the line voltage cycle TAC in the LED driving circuit for reducing harmonic distortion provided by the present invention and a waveform diagram of the input alternating current and the line voltage;

[0033] Fig.12 A schematic diagram of a sampling frequency adjustment unit of a third embodiment of the LED driving circuit for reducing harmonic distortion provided by the present invention;

[0034] Fig.13 A flow chart of a driving method for an LED driving circuit for reducing harmonic distortion provided by the present invention;

[0035] Fig.14 This is a flow chart of step S100 in the driving method of the LED driving circuit for reducing harmonic distortion provided by the present invention. DETAILED DESCRIPTION

[0036] An LED driving circuit and driving method for reducing harmonic distortion provided by the present invention can ensure that the working current flowing through the LED light string is a near-sine wave with the same frequency and phase as the input voltage and does not fluctuate with the line voltage, thereby reducing harmonic distortion and preventing the LED light string from flickering.

[0037] In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] See also Figure 3 The LED driving circuit for reducing harmonic distortion provided by the present invention includes a rectifier module 100, a phase detection module 200, a sine wave generating module 300, a constant current source module 400 and an LED light string. The input end of the rectifier module 100 inputs alternating current Vac, the output end of the rectifier module 100 is connected to the input end of the LED light string and the phase detection module 200, the phase detection module 200 is connected to the sine wave generating module 300, the sine wave generating module 300 is connected to the constant current source module 400, and the output end of the LED light string is also connected to the constant current source module 400.

[0039] The present invention rectifies the input alternating current Vac through the rectifier module 100 and then outputs a line voltage Vrec to the phase detection module 200 and the LED light string; thereafter, the phase detection module 200 is used to sample the line voltage Vrec and then output a corresponding phase signal to the sine wave generating module 300, the sine wave generating module 300 is used to output a corresponding voltage signal Vref to the constant current source module 400 according to the phase signal, the constant current source module 400 is used to control the working current flowing through the LED light string according to the voltage signal Vref, and the output current, i.e., the working current flowing through the LED light string, is adjusted by controlling the constant current source module 400 through the sine wave generating module 300, so that the working current is a nearly sine wave with the same frequency and phase as the input line voltage, thereby reducing harmonic distortion and eliminating the problem of flickering of the LED light string.

[0040] For specific implementation, please refer to Figure 4The phase detection module 200 includes a sampling unit 210 and a phase signal output unit 220; the sampling unit 210 is used to output a sampling signal to the phase signal output unit 220 after dividing the line voltage Vrec for sampling; the phase signal output unit 220 is used to output the phase signal to the sine wave generation module 300 according to the sampling signal. After the sampling unit 210 divides the line voltage Vrec output by the rectifier module 100 for sampling, the phase signal output unit 220 outputs the phase signal θ according to the sampling signal, so as to adjust the working current flowing through the LED light string, control the waveform of the working current to be consistent with the waveform of the line voltage, thereby reducing harmonic distortion.

[0041] For further information, see Figure 5 The sine wave generating module 300 includes a timer 310 and a conversion unit 320; the timer 310 is used to start timing when receiving the phase signal, and output timing information to the conversion unit 320 every sampling period Ts, and is reset when the line voltage period Tac is reached; the conversion unit 320 selects the corresponding voltage signal Vref according to the timing information and outputs it to the constant current source module 400, and the sine wave generating module 300 is reset after the timing of a line voltage period Tac is completed, so as to adjust the timing starting point when the phase signal is received again, which can effectively avoid the accumulation of phase deviation of the output sine wave signal caused by the deviation of the timer 310 clock.

[0042] For further information, please refer to Figure 4 The sampling unit 210 includes a first resistor Rph1 and a second resistor Rph2, one end of the first resistor Rph1 is connected to the line voltage input end, the other end of the first resistor Rph1 and one end of the second resistor Rph2 are both connected to the phase output unit 220, and the other end of the second resistor Rph2 is grounded. The line voltage is divided and sampled by the first resistor Rph1 and the second resistor Rph2 to obtain the corresponding phase signal of the sampling signal.

[0043] For further information, please refer to Figure 3The constant current source module 400 includes an operational amplifier OP1, a MOS tube Q1 and a sampling resistor Rcs; the non-inverting input end of the operational amplifier OP1 is the control end of the constant current source module 400, which is connected to the sine wave generating module 300, the inverting input end of the operational amplifier OP1 is connected to the source of the MOS tube Q1 and one end of the sampling resistor Rcs, the output end of the operational amplifier OP1 is connected to the gate of the MOS tube Q1; the drain of the MOS tube Q1 is connected to the output end of the LED light string; the other end of the sampling resistor Rcs is grounded, and the constant current source module 400 controls the working current Iled flowing through the LED light string according to the voltage signal Vref output by the sine wave generating module 300, which is Vref / Rcs.

[0044] In the first embodiment of the present invention, the phase detection module 200 detects whether the phase signal of the line voltage Vrec currently output by the rectifier module 100 is a preset phase signal θ', and outputs a corresponding phase signal to the sine wave generating module 300 according to the detection result. For details, please continue to refer to Figure 4 The phase signal output unit 220 includes a comparator COMP, a non-inverting input terminal of the comparator COMP is connected to the other end of the first resistor Rph1 and one end of the second resistor Rph2, an inverting input terminal of the comparator COMP is grounded, and an output terminal of the comparator COMP is connected to the timer 310. The sampling signal obtained after the first resistor Rph1 and the second resistor Rph2 divide the line voltage and sample the line voltage is output to the comparator COMP, and the comparator COMP compares the sampling voltage with the comparison voltage Vrefp. When the sampling voltage is greater than the comparison voltage Vrefp, the θflag output by the comparator COMP is 1, which corresponds to the rising edge signal of θflag, indicating that the phase signal of the line voltage is θ=θ '(0<θ'<π / 2) is the preset phase signal. At this time, the sine wave generating module 300 receives the phase signal and generates a positive half-cycle sine wave signal with the same phase as the line voltage, that is, the voltage signal Vref=|A*sin(wt+θ)|, A is the signal amplitude, w is the Vac frequency, and t is the time; when the sampling voltage is less than the comparison voltage Vrefp, the θflag output by the comparator COMP is 0, which corresponds to the falling edge signal of θflag. The phase signal of the line voltage is θ=π-θ'. At this time, the sine wave generating module 300 keeps the output unchanged; wherein, the comparison voltage Vrefp=Rph2 / (Rph1+Rph2)*Vrec_max*sin(θ'), and Vrec_max is the peak voltage of the alternating current.

[0045] For further information, please refer to Figure 5 , in this embodiment, the conversion unit 320 corresponds to a non-linear digital-to-analog converter, that is, the sine wave generation module 300 in this embodiment is composed of the timer 310 and the non-linear digital-to-analog converter. At this time, the timer 310 counts time according to the line voltage period Tac. When the timer 310 receives the rising edge of θflag, it adjusts to the moment corresponding to the phase signal θ and starts counting, and outputs the timing information to the conversion unit 320 every sampling period Ts. The timing information can be obtained according to the timing value T of the timer 310 or directly be the timing value T of the timer 310; in this embodiment, the timing information is calculated according to the timing value T, and the corresponding timing information is To. Specifically, every sampling period Ts, the timing value T increases by 1. When the T value reaches Ns / 2, T returns to 0. If T < Ns / 4, then output To = T, otherwise, output To = Ns / 2 - T, that is

[0046]

[0047] To is output to the non-linear digital-to-analog converter, where Ns is the number of sampling times within one Vac sine wave period.

[0048] Furthermore, in this embodiment, the output of the digital-to-analog converter is designed with a range of 0 to Vref_dac, and the 1 / 4 sine wave ratio is divided into Ns / 4 sampling points, and the method of unequal ratio resistor voltage division is adopted; specifically, as Figure 6 shown, the conversion unit 320 includes a voltage division subunit 321 and a multiplexing subunit 322; the voltage division subunit 321 divides the reference voltage Vref_dac and outputs the corresponding voltage signal Vref to the multiplexing subunit 322 through different taps. The multiplexing subunit 322 outputs the voltage signal Vref output by the corresponding tap of the voltage division subunit 321 to the constant current source module 400 according to the timing information, so that the constant current source module 400 controls the working current flowing through the LED lamp string to be a nearly sine wave with the same frequency and phase as the input line voltage, thereby reducing harmonic distortion.

[0049] Furthermore, please continue to refer to Figure 6, the voltage divider subunit 321 includes a resistor string, one end of the resistor string is connected to the reference voltage Vref_dac input terminal, and the lower end of the resistor string is grounded; the resistor string is composed of a plurality of voltage divider resistors connected in series, and the lower end tap of each voltage divider resistor is respectively led out and connected to the multi-way selection subunit 322. In this embodiment, the voltage divider resistors of the resistor string are R1, R2, R3, ..., R31. Of course, in other embodiments, the number of voltage divider resistors can also be selected according to actual needs, and the present invention does not limit this; the present invention divides the reference voltage Vref_dac through a plurality of voltage divider resistors, and the lower end tap of each voltage divider resistor will output a voltage signal Vref of different amplitudes. The multi-way selection subunit 322 selects the voltage signal Vref output to the constant current source module 400 by controlling the conduction and closing of each tap, thereby controlling the current flowing through the LED light string.

[0050] Furthermore, the multi-way selection subunit 322 includes an encoder and a number of switches, such as Figure 6 K0 to K31 shown in , wherein one end of each switch in switches K0 to K30 is respectively connected to the lower end tap of the voltage-dividing resistors R1 to R30, the other end of each switch is connected to the constant current source module 400, and the control end of each switch is connected to the encoder; wherein one end of switch K31 is connected to the reference voltage Vref_dac input end, the other end of switch K31 is connected to the constant current source module 400, the control end of switch K31 is connected to the encoder, and the encoder is also connected to the timer 310. The switch can be implemented by relays, triodes, MOSFETs, transmission gates, etc. wherein the encoder encodes the timing information output from the timer 310 to select and control the conduction and closure of the corresponding switch, so as to output the corresponding voltage signal Vref to the constant current source module 400, thereby realizing the control of the working current flowing through the LED light string, ensuring that the waveform of the working current is consistent with the waveform of the line voltage, and the unique hot encoding is adopted in this embodiment, and the specific encoding process is the prior art, which will not be repeated here.

[0051] In this embodiment, an unequal ratio resistor voltage division method is adopted. For example, a 50Hz AC sine wave is sampled at 128 times the frequency, and θ' is preset to 2*2π / 128, then the corresponding timing information To is 2. Therefore, the timer 310 sets the timing information To to 2 at the rising edge of θflag, and starts timing again from 2. The output value of the timer 310 changes by one level every sampling period Ts=1 / (50Hz*128)=0.15625ms, such as Figure 7As shown, To changes alternately according to 2~31, 31~0~2, 2~31, 31~0~2, and the nonlinear digital-to-analog converter is divided into Ns / 4=32 sampling points, so the output of the nonlinear digital-to-analog converter has 32 levels, and the voltage signal of each level output is

[0052] Vref=V(n)=Vref_dac*sin(n / 31*π / 2)=Vref_dac*sin(n*π / 62),

[0053] n is an integer from 0 to 31, that is, the voltage signal Vref is a sine wave signal; wherein the resistance values ​​of the voltage dividing resistors R1 to R31 can be calculated accordingly:

[0054] R1=R*sin(π / 62)≈0.0506R

[0055] R2=R*[sin(2π / 62)-sin(π / 62)]≈0.0505R

[0056] R3=R*[sin(3π / 62)-sin(2π / 62)]≈0.0503R

[0057] R4=R*[sin(4π / 62)-sin(3π / 62)]≈0.0499R

[0058] …

[0059] R31=R*[sin(31π / 62)-sin(30π / 62)]≈0.0013R

[0060] R=R1+R2+…+R31, which shows that the voltage-dividing resistors R1~31 are not of equal proportion.

[0061] For further information, see Figure 8 In the second embodiment of the present invention, the phase signal output unit 220 includes an analog-to-digital converter, one end of the analog-to-digital converter is connected to the other end of the first resistor Rph1 and one end of the second resistor Rph2, and the other end of the analog-to-digital converter is connected to the sine wave generating module 300. In this embodiment, after the first resistor Rph1 and the second resistor Rph2 divide the line voltage, the analog-to-digital converter calculates the divided sampling signal, i.e., the sampling voltage Vin, through an inverse trigonometric function to obtain the current phase signal θ; specifically, by detecting the sampling voltages twice, it is determined whether the sine wave waveform of the line voltage is in a rising or falling interval. If it is in the rising interval, the corresponding phase signal is:

[0062] θ=arcsin(Vin / Vin_max),

[0063] If it is in the falling range, the corresponding phase signal is: θ = π-arcsin (Vin / Vin_max), where,

[0064] Vin=Vrec*Rph2 / (Rph1+Rph2)

[0065] Vin_max=Vrec_max*Rph2 / (Rph1+Rph2).

[0066] For further information, see Fig. 9 In this embodiment, the conversion unit 320 includes a digital-to-analog converter and a lookup table. The timer 310 counts according to the line voltage cycle Tac. In this embodiment, the timer 310 directly uses the timing value T as the timing information. When the phase signal θ value is received, the timer 310 is adjusted to the moment corresponding to the phase signal θ to start timing. Every time the line voltage cycle Tac is reached, the timer 310 is reset and the timing is restarted. The timer 310 directly outputs the timing value T to the lookup table, and the reference value corresponding to the timing value T is found through the lookup table and output to the digital-to-analog converter. The digital-to-analog converter converts the reference value into the voltage signal Vref and outputs it to the constant current source module 400. The constant current source module 400 controls the working current flowing through the LED light string according to the voltage signal Vref, so that the working current is a nearly sinusoidal wave with the same frequency and phase as the input voltage, thereby reducing harmonic distortion.

[0067] For further information, see Fig.10 In the third embodiment of the present invention, the sine wave generating module 300 further includes a sampling frequency adjusting unit 330, and the sampling frequency adjusting unit 330 is used to calculate the time interval between two outputs of the same phase signal by the phase detection module 200, and then calculate the sampling period Ts according to the time interval and the number of samplings within the time interval, and output the sampling period Ts to the timer 310; the sampling period Ts in the first embodiment and the second embodiment are both pre-set. In practical applications, in order to adapt to the line network frequency, the sampling period Ts can be calculated by the sampling frequency adjusting unit 330 in this embodiment, thereby enhancing the adaptability of the LED driving circuit; wherein the sampling frequency adjusting unit 330 can be applied to the sine wave generating module 300 in the first embodiment and the second embodiment.

[0068] Please note that Fig.11 and Fig.12, the time interval between the two outputs of the same phase signal by the phase detection module 200 in this embodiment refers to the time T1 between two rising edges of θflag in the first embodiment, and refers to the time T2 between two occurrences of the same phase signal θ value in the second embodiment, that is, the line voltage cycle Tac; specifically, the sampling frequency adjustment unit 330 counts the interval time through timer 0, and then calculates the sampling period Ts=Tac / Ns / 2 according to the interval time, that is, the line voltage cycle Tac and the sampling number Ns, and then the sampling frequency adjustment unit 330 outputs the calculated sampling period Ts to the timer 310 in the sine wave generation module 300, so that the sine wave generation module 300 subsequently outputs the voltage signal Vref to the constant current source module 400 to reduce harmonic distortion.

[0069] Based on the above LED drive circuit to reduce harmonic distortion, please refer to Fig.13 The present invention also provides a driving method for an LED driving circuit for reducing harmonic distortion, which specifically includes the following steps:

[0070] S100, the phase detection module samples the line voltage and outputs a corresponding phase signal to the sine wave generation module;

[0071] S200, the sine wave generating module outputs a corresponding voltage signal to the constant current source module according to the phase signal;

[0072] S300, the constant current source module controls the operating current flowing through the LED light string according to the voltage signal.

[0073] Furthermore, if Fig.14 As shown, step S100 includes:

[0074] S110, the sampling unit samples the line voltage and outputs a sampling signal to the phase signal output unit;

[0075] S120. The phase signal output unit outputs the phase signal to the sine wave generating module according to the sampling signal.

[0076] In summary, the present invention provides an LED driving circuit and a driving method thereof for reducing harmonic distortion. The LED driving circuit includes a phase detection module, a sine wave generating module, a constant current source module and an LED light string; the phase detection module is used to sample the line voltage and then output a corresponding phase signal to the sine wave generating module, the sine wave generating module is used to output a corresponding voltage signal to the constant current source module according to the phase signal, the constant current source module is used to control the working current flowing through the LED light string according to the voltage signal, and the sine wave generating module controls the constant current source module to adjust the output current, that is, the working current flowing through the LED light string, so that the working current flowing through the LED light string is a nearly sine wave with the same frequency and phase as the input line voltage, thereby reducing harmonic distortion and eliminating the problem of flickering of the LED light string.

[0077] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. An LED driving circuit for reducing harmonic distortion, characterized in that: It includes a phase detection module, a sine wave generation module, a constant current source module and an LED light string; the phase detection module is used to sample the line voltage and then output a corresponding phase signal to the sine wave generation module, the sine wave generation module is used to output a corresponding voltage signal to the constant current source module according to the phase signal, and the constant current source module is used to control the working current flowing through the LED light string according to the voltage signal; The sine wave generating module comprises a timer and a conversion unit; the timer is used to start timing when receiving the phase signal, and output timing information to the conversion unit every sampling period, and clear when the line voltage period is reached; the conversion unit selects a corresponding voltage signal according to the timing information and outputs it to the constant current source module; When the timer receives a rising edge, it adjusts to the moment corresponding to the phase signal to start timing, and outputs timing information to the conversion unit every other sampling period. The timing information is converted according to the timing value of the timer or is directly the timing value of the timer.

2. The LED driving circuit for reducing harmonic distortion according to claim 1, characterized in that: The phase detection module includes a sampling unit and a phase signal output unit; the sampling unit is used to sample the line voltage and then output a sampling signal to the phase signal output unit; the phase signal output unit is used to output the phase signal to the sine wave generation module according to the sampling signal.

3. The LED driving circuit for reducing harmonic distortion according to claim 1, characterized in that: The conversion unit includes a voltage divider subunit and a multi-way selection subunit; the voltage divider subunit divides the reference voltage and outputs the corresponding voltage signal to the multi-way selection subunit through different taps, and the multi-way selection subunit outputs the voltage signal output by the corresponding tap of the voltage divider subunit to the constant current source module according to the timing information.

4. The LED driving circuit for reducing harmonic distortion according to claim 1, characterized in that: The sine wave generating module also includes a sampling frequency adjusting unit, which is used to calculate the time interval between two outputs of the same phase signal by the phase detection module, and then calculate the sampling period according to the time interval and the number of samples within the time interval, and output the sampling period to the timer.

5. The LED driving circuit for reducing harmonic distortion according to claim 2, characterized in that: The sampling unit includes a first resistor and a second resistor, one end of the first resistor is connected to the line voltage input terminal, the other end of the first resistor and one end of the second resistor are both connected to the phase signal output unit, and the other end of the second resistor is grounded.

6. The LED driving circuit for reducing harmonic distortion according to claim 5, characterized in that: The phase signal output unit comprises a comparator, a non-phase input terminal of the comparator is connected to the other end of the first resistor and one end of the second resistor, an inverting input terminal of the comparator is grounded, and an output terminal of the comparator is connected to the sine wave generating module.

7. The LED driving circuit for reducing harmonic distortion according to claim 5, characterized in that: The phase signal output unit includes an analog-to-digital converter, one end of the analog-to-digital converter is connected to the other end of the first resistor and one end of the second resistor, and the other end of the analog-to-digital converter is connected to the sine wave generating module.

8. A driving method for an LED driving circuit with reduced harmonic distortion according to any one of claims 1 to 7, characterized in that: Includes steps: The phase detection module samples the line voltage and outputs a corresponding phase signal to the sine wave generation module; The sine wave generating module outputs a corresponding voltage signal to the constant current source module according to the phase signal; The constant current source module controls the operating current flowing through the LED light string according to the voltage signal.

9. The driving method of the LED driving circuit with reduced harmonic distortion according to claim 8, characterized in that: The step of the phase detection module sampling the line voltage and outputting the corresponding phase signal to the sine wave generation module comprises: The phase detection module comprises a sampling unit and a phase signal output unit, wherein the sampling unit samples the line voltage and then outputs a sampling signal to the phase signal output unit; The phase signal output unit outputs the phase signal to the sine wave generating module according to the sampling signal.

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