LED driving device, driving circuit and driving method thereof

Abstract

The present invention discloses an LED driving device, a driving circuit and a driving method thereof. The LED driving circuit comprises a reference voltage output module, a control signal output module, a plurality of driving modules and a switch module corresponding thereto. The reference voltage output module outputs a corresponding reference voltage to each driving module according to a dimming signal. Each driving module drives a corresponding light string to light up or turn off in sequence according to a line voltage and a corresponding reference voltage. The control signal output module compares the dimming signal with a preset signal of each switch module respectively, and outputs a corresponding control signal to each switch module according to the comparison result, thereby controlling each driving module to turn on or off. The preset signal of each switch module decreases according to the turn-on sequence of each driving module, and the preset signal of the switch module is greater than the offset voltage signal of the driving module connected thereto, thereby avoiding the problem that some light strings are lit while some light strings are not lit when the brightness is lowered.

Description

Technical Field

[0001] The present invention relates to the field of LED technology, and in particular to an LED driving device, a driving circuit and a driving method thereof. Background Art

[0002] See also Figure 1 , LED dimming is achieved by changing the output of the reference voltage generation circuit by changing the dimming signal, and then controlling the output of the op amp to adjust the current flowing through the light string. In the multi-segment linear constant current dimming drive solution, the reference voltage generation circuit generates and outputs multiple reference voltages according to the dimming signal, and then controls the output of the corresponding op amp to adjust the current flowing through the corresponding light string. In the process of lowering the LED brightness, when the dimming signal is lowered to a level that is not enough to turn on the MOS tubes under all the light strings, because the offset voltages of the op amps are inconsistent, some MOS tubes cannot be turned off in the predetermined order, causing some LED lamp beads to be on and some LED lamp beads to be off.

[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 device, a driving circuit and a driving method thereof, which solve the problem that in the process of lowering the brightness of the light string, the MOS tubes connected in series with the light string cannot be turned off in a predetermined order, causing some light strings to light up and some light strings not to light up.

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

[0006] An LED driving circuit comprises a reference voltage output module, a control signal output module, a plurality of driving modules and switch modules corresponding to the driving modules; the reference voltage output module divides the dimming signal and outputs the corresponding reference voltage to each of the driving modules through different taps, and each of the driving modules drives the corresponding light string to light up or turn off in sequence according to the line voltage and the corresponding reference voltage; the control signal output module compares the dimming signal with the preset signal of each of the switch modules respectively, and outputs the corresponding control signal to each of the switch modules through different taps according to the comparison result; each of the switch modules controls each of the driving modules to turn on or off according to the corresponding control signal; wherein the preset signal of each of the switch modules decreases according to the turn-on sequence of each of the driving modules, and the preset signal of the switch module is greater than the offset voltage signal of the driving module connected to the switch module.

[0007] In the LED driving circuit, the control signal output module includes a plurality of comparators, the inverting input end of each comparator is connected to the dimming signal input end, the non-inverting input end of each comparator is connected to the preset signal input end, and the output end of each comparator is connected to each switch module.

[0008] In the LED driving circuit, the switch module includes a switch tube, a first end of the switch tube is connected to the driving module, a second end of the switch tube is grounded, and a control end of the switch tube is connected to the control signal output module.

[0009] In the LED driving circuit, the control signal output module includes an analog-to-digital converter and a plurality of comparators; the input end of the analog-to-digital converter is connected to the dimming signal input end, the output end of the analog-to-digital converter is respectively connected to the inverting input end of each of the comparators, the non-inverting input end of each of the comparators is respectively connected to the preset signal input end, and the output end of each of the comparators is respectively connected to each of the switch modules.

[0010] The LED driving circuit further includes a digital-to-analog conversion module, which performs digital-to-analog conversion on the dimming signal and outputs the resultant signal to the reference voltage output module.

[0011] In the LED driving circuit, the control signal output module includes a duty cycle calculation unit and a plurality of comparators; the input end of the duty cycle calculation unit is connected to the dimming signal input end, the output end of the duty cycle calculation unit is respectively connected to the inverting input end of each of the comparators, the non-inverting input end of each of the comparators is respectively connected to the preset signal input end, and the output end of each of the comparators is respectively connected to each of the switch modules.

[0012] In the LED driving circuit, the reference voltage output module includes a resistor string, which is composed of a plurality of voltage-dividing resistors connected in series. The upper end of the resistor string is connected to the dimming signal input terminal, the lower end of the resistor string is grounded, and the upper end tap of each voltage-dividing resistor is respectively led out and connected to each of the driving modules.

[0013] In the LED driving circuit, the driving module includes an operational amplifier and a MOS tube, the non-inverting input terminal of the operational amplifier is connected to the reference voltage output module, the inverting input terminal of the operational amplifier is grounded, the output terminal of the operational amplifier is connected to the gate of the MOS tube and the first end of the switch tube, the drain of the MOS tube is connected to the output terminal of the light string, and the source of the MOS tube is grounded.

[0014] A driving method based on the LED driving circuit as described above comprises the following steps:

[0015] The reference voltage output module divides the dimming signal and outputs corresponding reference voltages to each of the driving modules through different taps;

[0016] Each of the driving modules drives the corresponding light string to light up or turn off in sequence according to the line voltage and the corresponding reference voltage;

[0017] The control signal output module compares the dimming signal with the preset signals of each of the switch modules respectively, and outputs corresponding control signals to each of the switch modules through different taps according to the comparison results;

[0018] Each of the switch modules controls each of the drive modules to turn on or off according to a corresponding control signal; wherein, the preset signal of each of the switch modules decreases according to the turn-on sequence of each of the drive modules, and the preset signal of the switch module is greater than the offset voltage signal of the drive module connected to the switch module.

[0019] An LED driving device comprises the LED driving circuit as described above.

[0020] Compared with the prior art, the present invention provides an LED driving device, a driving circuit and a driving method thereof. The LED driving circuit includes a reference voltage output module, a control signal output module, a plurality of driving modules and a switch module corresponding thereto. The reference voltage output module outputs a corresponding reference voltage to each driving module according to a dimming signal. Each driving module drives a corresponding light string to light up or turn off in sequence according to a line voltage and a corresponding reference voltage. The control signal output module compares the dimming signal with a preset signal of each switch module respectively, and outputs a corresponding control signal to each switch module according to the comparison result, thereby controlling each driving module to turn on or off. The preset signal of each switch module decreases according to the turn-on sequence of each driving module, and the preset signal of the switch module is greater than the offset voltage signal of the driving module connected thereto, thereby avoiding the problem that some light strings are lit while some are not when the brightness is lowered. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a circuit schematic diagram of an existing LED driving circuit;

[0022] Figure 2 A structural block diagram of the LED driving circuit provided by the present invention;

[0023] Figure 3 A circuit schematic diagram of a first embodiment of the LED driving circuit provided by the present invention;

[0024] Figure 4 A relationship diagram of line voltage, dimming signal and lamp string current when three stages of lighting are performed in the LED driving circuit provided by the present invention;

[0025] Figure 5 A relationship diagram of line voltage, dimming signal and lamp string current when two sections are lit in the LED driving circuit provided by the present invention;

[0026] Figure 6 A relationship diagram of line voltage, dimming signal and lamp string current when a section of the LED driving circuit provided by the present invention is lit;

[0027] Figure 7 A circuit schematic diagram of a second embodiment of the LED driving circuit provided by the present invention;

[0028] Figure 8 A circuit schematic diagram of a third embodiment of the LED driving circuit provided by the present invention;

[0029] Fig. 9 The present invention provides a flow chart of a driving method for an LED driving circuit. DETAILED DESCRIPTION

[0030] In view of the deficiencies in the prior art, the object of the present invention is to provide an LED driving device, a driving circuit and a driving method thereof, which solve the problem that in the process of lowering the brightness of the light string, the MOS tubes connected in series with the light string cannot be turned off in a predetermined order, causing some light strings to light up and some light strings not to light up.

[0031] 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.

[0032] Please also read Figure 2 The LED driving circuit provided by the present invention is connected to a plurality of light strings including at least one LED lamp. The LED driving circuit comprises a rectifier module 100, a reference voltage output module 200, a control signal output module 300, a plurality of driving modules 400 and a switch module 500 corresponding to the driving module 400. The input end of the rectifier module 100 is connected to an alternating current power source AC, the output end of the rectifier module 100 is connected to the input end of the first light string, a plurality of the light strings are connected in series, and the output end of each light string is connected to a driving module 400, and each driving module 400 is also connected to a corresponding switch module 500; the input end of the reference voltage output module 200 is connected to a dimming signal input end, the output end of the reference voltage output module 200 is connected to each of the driving modules 400, the input end of the control signal output module 300 is connected to a dimming signal input end, and the output end of the control signal output module 300 is connected to the switch module 500.

[0033] The rectifier module 100 in the present invention rectifies the alternating current and outputs a line voltage to the light string to power the light string. The reference voltage output module 200 divides the dimming signal Vref and outputs a corresponding reference voltage to each of the driving modules 400 through different taps. Each of the driving modules 400 drives the corresponding light string to light up or turn off in sequence according to the line voltage and the corresponding reference voltage. The control signal output module 300 compares the dimming signal Vref with the preset signal of each of the switch modules 500, and outputs a corresponding control signal to each of the switch modules 500 through different taps according to the comparison result. Specifically, when the dimming signal Vref is less than the preset signal, the control signal output module 300 outputs a control signal to control the switch module 50 0 is turned on; each of the switch modules 500 controls each of the drive modules 400 to be turned on or off according to the corresponding control signal. During the dimming process of the light string, when the reference voltage is less than the offset voltage of the drive module 400, the drive module 400 will be disconnected and the corresponding light string will be extinguished. In order to avoid the influence of the offset voltage of each drive module 400 and ensure that each drive module 400 can be disconnected in a preset order, the preset signal of each of the switch modules 500 decreases according to the turn-on order of each drive module 400, and the preset signal of the switch module 500 is greater than the offset voltage signal of the drive module 400 connected to the switch module 500, thereby effectively avoiding the problem of some light strings being lit while some light strings are not lit in the process of lowering the brightness of the light string.

[0034] Please also refer to Figure 3 In the following embodiments, the working principle of the LED driving circuit is explained by a three-segment linear dimming drive. The corresponding driving modules and switch modules are three, namely, the first driving module 401, the second driving module 402 and the third driving module 403 and the first switch module 501, the second switch module 502 and the third switch module 503. In other embodiments, they can be adjusted as needed. The present invention adds a switch module under each driving module, and the switch module is uniformly managed by the control signal output module 300. When the brightness of the light string is lowered, the driving module can be effectively controlled to stop driving in a preset order, thereby avoiding the problem that some light strings are lit and some are not.

[0035] In a specific implementation, the reference voltage output module 200 includes a resistor string, which is composed of a plurality of voltage-dividing resistors connected in series. The upper end of the resistor string is connected to the dimming signal input end, and the lower end of the resistor string is grounded. The upper end tap of each voltage-dividing resistor is respectively led out and connected to each of the driving modules. The reference voltage output module 200 provides a corresponding reference voltage for each of the driving modules, so that the driving module can drive the corresponding light string to light up.

[0036] In this embodiment, the resistor string includes three voltage-dividing resistors, namely, a first resistor Ra1, a second resistor Ra2, and a third resistor Ra3. The upper end tap of the first resistor Ra1 is connected to the first driving module 401, the upper end tap of the second resistor Ra2 is connected to the second driving module 402, and the upper end tap of the third resistor Ra3 is connected to the third driving module 403. According to the voltage-dividing effect of the first resistor Ra1, the second resistor Ra2, and the third resistor Ra3, the first driving module 401, the second driving module 402, and the third driving module 403 are provided with a first reference voltage Vref1, a second reference voltage Vref2, and a third reference voltage Vref3, respectively, so that the first driving module 401, the second driving module 402, and the third driving module 403 drive the corresponding light string to light up, wherein,

[0037] Vref1=(Ra1*Vref) / (Ra1+Ra2+Ra3);

[0038] Vref2=((Ra1+Ra2)*Vref) / (Ra1+Ra2+Ra3);

[0039] Vref3 = Vref.

[0040] For further information, please refer to Figure 3In the first embodiment of the present invention, the preset signal of the switch module is the preset threshold voltage of the switch module, the offset voltage signal of the driving module is an analog voltage value, referred to as the offset voltage, the control signal output module 300 includes a plurality of comparators, the inverting input end of each comparator is connected to the dimming signal input end, the non-inverting input end of each comparator is respectively connected to the preset threshold voltage input end, and the output end of each comparator is respectively connected to each switch module. When each comparator compares that the dimming signal Vref is less than the preset threshold voltage of each switch module, the corresponding control signal is output to the switch module to control the corresponding switch module to be turned on, so that the corresponding driving module is turned off. In order to ensure that each driving module can be turned off according to a preset sequence and eliminate the influence of the offset voltage of the driving module, the preset threshold voltage of each switch module is decreased according to the turn-on sequence of each driving module, and the preset threshold voltage of the switch module is greater than the offset voltage of the driving module connected to the switch module, thereby avoiding the problem that some light strings are lit and some light strings are not lit when the brightness of the light string is lowered.

[0041] Specifically, the control signal output module 300 in this embodiment includes three comparators, namely a first comparator COMP1, a second comparator COMP2 and a third comparator COMP3. The first comparator COMP1, the second comparator COMP2 and the third comparator COMP3 respectively compare the dimming signal Vref with a preset threshold voltage Vth1 of the first switch module 501, a preset threshold voltage Vth2 of the second switch module 502 and a preset threshold voltage Vth3 of the third switch module 503. When the dimming signal Vref is less than the corresponding preset threshold voltage, the three comparators respectively provide control signals Vctr1, Vctr2 and Vctr3 to the first switch module 501, the second switch module 502 and the third switch module 503 to control each switch module to be turned on.

[0042] Among them, when the dimming signal Vref changes, the first reference voltage Vref1, the second reference voltage Vref2 and the third reference voltage Vref3 change, the current flowing through the light string changes accordingly, and the brightness of the light string also changes accordingly. As the line voltage rises, the first driving module 401, the second driving module 402 and the third driving module 403 are turned on in sequence, and the corresponding light strings have current flowing through them in sequence, and the light strings are lit in sequence; as the line voltage drops, the third driving module 403, the second driving module 402 and the first driving module 401 are disconnected in sequence, and no current flows through the light strings in sequence, and the light strings are extinguished in sequence. At this time, the relationship between the dimming signal, the line voltage and the light string current in the LED driving circuit is as follows: Figure 4As shown. When the reference voltage of each of the driving modules is less than the offset voltage of the driving module, the driving module is disconnected, and no current flows through the light string. In order to consider the performance of power efficiency, harmonics and light efficiency, the optimal solution is to disconnect the first driving module 401 first as the dimming signal Vref decreases. At this time, the light string corresponding to the first driving module is connected in series with the light string corresponding to the second driving module and is controlled by the second driving module; when the dimming signal Vref continues to decrease, the second driving module 402 is disconnected again. At this time, the light string corresponding to the first driving module is connected in series with the light string corresponding to the second driving module and the light string corresponding to the third driving module and is controlled by the third driving module; finally, when the dimming signal Vref decreases to the point where the light string current is insufficient to light up the light string normally, the third driving module 403 is disconnected, no current flows through all the light strings, and the light strings are extinguished. To achieve this disconnection sequence, the relationship (Vref3-Voffset3)>(Vref2-Voffset2)>(Vref1-Voffset1) needs to be satisfied, wherein Voffset1, Voffset2 and Voffset3 correspond to the offset voltages of the first driving module 401, the second driving module 402 and the third driving module 403, and the offset voltages may be positive or negative. When the offset voltages are different and the relationship (Vref3-Voffset3)>(Vref2-Voffset2)>(Vref1-Voffset1) cannot be satisfied, the disconnection sequence of the first driving module 401, the second driving module 402 and the third driving module 403 may be disordered, causing some light strings to be on while others to be off.

[0043] When the dimming signal Vref is reduced to the point where only two of the first driving module 401, the second driving module 402 and the third driving module 403 can be turned on, it is preferred to turn on the second driving module 402 and the third driving module 403 and disconnect the first driving module 401. At this time, the light string is merged from three sections into two sections and is lit. At this time, the relationship between the dimming signal, the line voltage and the light string current in the LED driving circuit is as follows: Figure 5 As shown. If the offset voltages of the various drive modules are different, different results may be caused by turning on the second drive module 402 and the first drive module 401 and disconnecting the third drive module 403 or turning on the third drive module 403 and the first drive module 401 and disconnecting the second drive module 402. Turning on the second drive module 402 and the first drive module 401 and disconnecting the third drive module 403 causes the light string connected in series to the third drive module 403 to be in an off state, while the light string connected in series to the first drive module 401 and the second drive module 402 to be in an on state, that is, there is a problem that some light strings are on and some are not.

[0044] When the dimming signal Vref is reduced to the point where only one of the first driving module 401, the second driving module 402 and the third driving module 403 can be turned on, the third driving module 403 is turned on first, and the first driving module 401 and the second driving module 402 are turned off. At this time, the light string is combined from three sections into one whole section and is lit. At this time, the relationship between the dimming signal, the line voltage and the light string current in the LED driving circuit is as follows: Figure 6 As shown. If the offset voltages of the various drive modules are different, different results may be caused by turning on the second drive module 402, disconnecting the first drive module 401 and the third drive module 403, or turning on the first drive module 401, disconnecting the second drive module 402 and the third drive module 403. Turning on the second drive module 402, disconnecting the first drive module 401 and the third drive module 403, causes the light string connected in series to the third drive module 403 to be in an off state, and the light string connected in series to the first drive module 401 and the second drive module 402 to be in an on state; turning on the first drive module 401, disconnecting the second drive module 402 and the third drive module 403, causes the light string connected in series to the second drive module 402 and the third drive module 403 to be in an off state, and the light string connected in series to the first drive module 401 to be in an on state. In both cases, some light strings will light up while others will not. Therefore, in order to eliminate the influence caused by the different offset voltages of the driving modules and to satisfy the disconnection sequence of the first driving module 401, the second driving module 402 and the third driving module 403, the settings of the preset threshold voltages Vth1, Vth2 and Vth3 should satisfy the following conditions:

[0045] Vth1>Vth2>Vth3;

[0046] Vth3>Voffset3;

[0047] Vth2>Voffset2;

[0048] Vth1>Voffset1.

[0049] Further, the switch module includes a switch tube, a first end of the switch tube is connected to the driving module, a second end of the switch tube is grounded, a control end of the switch tube is connected to the control signal output module 300, and a switch tube is connected to the ground in each driving module. By evaluating the magnitude of the offset voltage of each driving module, a threshold voltage of each switch tube is set, and when the offset voltage has no effect, one or more of the switch tubes are turned on in advance to disconnect one or more of the driving modules accordingly, thereby eliminating the effect caused by the offset voltage; wherein, the switch tubes K1, K2 and K3 correspond to the switch tubes of the first switch module 501, the second switch module 502 and the third switch module 503 respectively.

[0050] Further, the driving module includes an operational amplifier and a MOS tube, the non-inverting input end of the operational amplifier is connected to the reference voltage output module 200, the inverting input end of the operational amplifier is grounded, the output end of the operational amplifier is connected to the gate of the MOS tube and the first end of the switch tube, the drain of the MOS tube is connected to the output end of the light string, and the source of the MOS tube is grounded. The structure of each of the driving modules is the same, including an operational amplifier and a MOS tube. The offset voltage corresponding to each driving module is the offset voltage of the operational amplifier. The operational amplifier controls the conduction and disconnection of the MOS tube according to the magnitude of the reference voltage and the offset voltage. In order to avoid the influence of the offset voltage during the process of lowering the brightness of the light string, a switch tube is connected between the gate of the MOS tube and the ground, and then the MOS tube is controlled to be disconnected according to the control signal output module 300 through the switch tube, so that each MOS tube can be disconnected according to a preset sequence. Among them, the MOS tubes Q1, Q2 and Q3 correspond to the MOS tubes in the first driving module 401, the second driving module 402 and the third driving module 403 respectively, and the conduction and disconnection of the first driving module 401, the second driving module 402 and the third driving module 403 are the conduction and disconnection of the MOS tubes Q1, Q2 and Q3.

[0051] Furthermore, the LED driving circuit also includes a constant current resistor Rcs, one end of the constant current resistor Rcs is connected to the source of each of the MOS tubes, and the other end of the constant current resistor Rcs is grounded, and the current flowing through the light string is set by the constant current resistor Rcs.

[0052] In the second embodiment of the present invention, please refer to Figure 7, the control signal output module 300 includes an analog-to-digital converter ADC and a plurality of comparators; the input end of the analog-to-digital converter ADC is connected to the dimming signal input end, and the output end of the analog-to-digital converter ADC is respectively connected to the inverting input end of each of the comparators. In this embodiment, the preset signal of the switch module is the preset threshold value of the switch module, and the offset voltage signal of the driving module is a data value. Furthermore, the in-phase input end of each of the comparators is respectively connected to the preset threshold value input end, and the output end of each of the comparators is respectively connected to each of the switch modules. The analog-to-digital converter ADC samples the dimming signal Vref and outputs a group of dimming data values ​​to the comparator. The comparator compares the group of dimming data with the preset threshold value 1, threshold value 2 and threshold value 3 and then outputs control signals Vctr1, Vctr2 and Vctr3 to respectively control the conduction or disconnection of the switch tubes K1, K2 and K3 and thus control the disconnection or conduction of each driving module. In this embodiment, when the dimming data is greater than the preset threshold value, the corresponding control signal is output to disconnect the corresponding switch module, turn on the drive module, and the corresponding light string has current flowing through it, and the light string is lit; when the dimming data is less than the preset threshold value, the corresponding control signal is output to turn on the corresponding switch module, turn off the drive module, and the corresponding light string has no current flowing through it, and the light string is extinguished. The preset threshold value 1, threshold value 2, and threshold value 3 satisfy the following relationship:

[0053] Threshold 1>threshold 2>threshold 3;

[0054] Threshold value 3>data value 3;

[0055] Threshold value 2>data value 2;

[0056] Threshold value 1>data value 1.

[0057] Among them, data value 3 is the data value obtained after the analog-to-digital converter samples the offset voltage Voffset3, data value 2 is the data value obtained after the analog-to-digital converter samples the offset voltage Voffset2, and data value 1 is the data value obtained after the analog-to-digital converter samples the offset voltage Voffset1; the size of the preset threshold value determines when to disconnect or turn on the switch module, thereby controlling the MOS tubes Q1, Q2 and Q3 under the light string, thereby eliminating the influence caused by the offset voltage of the operational amplifier in each driving module, and realizing the control of each MOS tube to disconnect in a preset order, avoiding the problem of some light strings being lit and some light strings not being lit when the brightness of the light string is lowered.

[0058] In the third embodiment of the present invention, please refer to Figure 8, the LED driving circuit also includes a digital-to-analog conversion module 600, which converts the digital dimming signal into an analog dimming signal and then outputs it to the reference voltage output module 200. When the digital dimming signal is a PWM dimming signal, the duty cycle of the PWM dimming signal is proportional to the magnitude of the current flowing through the light string. One of the PWM dimming signals is input to the digital-to-analog conversion module 600, which converts the digital PWM dimming signal into an analog dimming signal; the other PWM dimming signal is input to the control signal output module 300, which controls the conduction or disconnection of each of the MOS tubes according to the PWM dimming signal, thereby realizing the orderly disconnection of each MOS tube; in this embodiment, the digital-to-analog conversion module 600 includes a digital-to-analog converter.

[0059] Furthermore, the control signal output module 300 in this embodiment includes a duty cycle calculation unit 310 and a plurality of comparators; the input end of the duty cycle calculation unit 310 is connected to the dimming signal input end, and the output end of the duty cycle calculation unit 310 is respectively connected to the inverting input end of each of the comparators. Similarly, the preset signal of the switch module in this embodiment is the preset threshold value of the switch module, and the offset voltage signal of the driving module is a data value. Furthermore, the non-inverting input end of each of the comparators is respectively connected to the preset threshold voltage input end. The output end of each comparator is connected to the control end of each switch tube, and the duty cycle calculation unit 310 counts the high and low level widths of the PWM signal, calculates the duty cycle value of the PWM signal through the width values ​​of the high and low levels of the PWM signal, and obtains the dimming data value. The comparator compares the dimming data value with the preset threshold value 1, threshold value 2 and threshold value 3, and then outputs control signals Vctr1, Vctr2 and Vctr3 to control the conduction or disconnection of the switch tubes K1, K2 and K3, and then controls the disconnection or conduction of each driving module. In this embodiment, when the dimming data value is greater than the preset threshold value, the corresponding control signal is output to disconnect the corresponding switch module, the driving module is turned on, the corresponding light string has current flowing through, and the light string is lit; when the dimming data is less than the preset threshold value, the corresponding control signal is output to turn on the corresponding switch module, the driving module is turned off, and the corresponding light string has no current flowing through, and the light string is extinguished; the duty cycle calculation unit in this embodiment can be a counter.

[0060] Correspondingly, the preset threshold value 1, threshold value 2 and threshold value 3 in this embodiment satisfy the following relationship:

[0061] Threshold 1>threshold 2>threshold 3;

[0062] Threshold value 3>data value 6;

[0063] Threshold value 2>data value 5;

[0064] Threshold value 1>data value 4.

[0065] Among them, data value 6 is the data value corresponding to the PWM signal duty cycle value when Voffset3 is equal to Vref3; data value 5 is the data value corresponding to the PWM signal duty cycle value when Voffset2 is equal to Vref2; data value 4 is the data value corresponding to the PWM signal duty cycle value when Voffset1 is equal to Vref1; the preset threshold value determines when to disconnect and open the corresponding switch module, thereby controlling the MOS tubes Q1, Q2 and Q3 under the light string, and then controlling each MOS tube to be disconnected according to a preset order, effectively avoiding the problem of some light strings being lit while some light strings are not lit in the process of lowering the brightness of the light string.

[0066] The present invention also provides a driving method of an LED driving circuit. Fig. 9 , the driving method of the LED driving circuit comprises the following steps:

[0067] S100, the reference voltage output module divides the dimming signal and outputs corresponding reference voltages to each of the driving modules through different taps;

[0068] S200, the reference voltage output module divides the dimming signal and outputs corresponding reference voltages to each of the driving modules through different taps;

[0069] S300, the control signal output module compares the dimming signal with the preset signals of each of the switch modules respectively, and outputs corresponding control signals to each of the switch modules through different taps according to the comparison results;

[0070] S400, each of the switch modules controls each of the drive modules to open or disconnect according to the corresponding control signal; wherein, the preset signal of each of the switch modules decreases according to the conduction sequence of each of the drive modules, and the preset signal of the switch module is greater than the offset voltage signal of the drive module connected to the switch module.

[0071] Based on the above-mentioned LED driving circuit, the present invention also provides a LED driving device accordingly. Since the LED driving circuit has been described in detail above, it will not be described again here.

[0072] In summary, the present invention provides an LED driving device, a driving circuit and a driving method thereof. The LED driving circuit includes a reference voltage output module, a control signal output module, a plurality of driving modules and a switch module corresponding thereto. The reference voltage output module outputs a corresponding reference voltage to each driving module according to a dimming signal. Each driving module drives a corresponding light string to light up or turn off in sequence according to a line voltage and a corresponding reference voltage. The control signal output module compares the dimming signal with a preset signal of each switch module respectively, and outputs a corresponding control signal to each switch module according to the comparison result, thereby controlling each driving module to turn on or off. The preset signal of each switch module decreases according to the turn-on sequence of each driving module, and the preset signal of the switch module is greater than the offset voltage signal of the driving module connected thereto, thereby avoiding the problem that some light strings are lit while some light strings are not lit when the brightness is lowered.

[0073] 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, characterized in that: It includes a reference voltage output module, a control signal output module, a plurality of driving modules and a switch module corresponding to the driving module; the reference voltage output module divides the dimming signal and outputs the corresponding reference voltage to each driving module through different taps, and each driving module drives the corresponding light string to light up or turn off in sequence according to the line voltage and the corresponding reference voltage; the control signal output module compares the dimming signal with the preset signal of each switch module respectively, and outputs the corresponding control signal to each switch module through different taps according to the comparison result; each switch module controls each driving module to turn on or off according to the corresponding control signal; wherein the preset signal of each switch module decreases according to the turn-on sequence of each driving module, and the preset signal of the switch module is greater than the offset voltage signal of the driving module connected to the switch module; It also includes a digital-to-analog conversion module, which converts the digital dimming signal into an analog dimming signal and outputs it to the reference voltage output module; the digital dimming signal is a PWM dimming signal, and the duty cycle of the PWM dimming signal is proportional to the magnitude of the current flowing through the light string; one PWM dimming signal is input to the digital-to-analog conversion module, and the digital-to-analog conversion module converts the digital PWM dimming signal into an analog dimming signal; the other PWM dimming signal is input to the control signal output module, and the control signal output module controls the conduction or disconnection of each MOS tube according to the PWM dimming signal, thereby realizing the orderly disconnection of each MOS tube.

2. The LED driving circuit according to claim 1, characterized in that: The control signal output module includes a plurality of comparators, the inverting input end of each comparator is connected to the dimming signal input end, the non-inverting input end of each comparator is connected to the preset signal input end, and the output end of each comparator is connected to each switch module.

3. The LED driving circuit according to claim 1, characterized in that: The switch module comprises a switch tube, a first end of the switch tube is connected to the driving module, a second end of the switch tube is grounded, and a control end of the switch tube is connected to the control signal output module.

4. The LED driving circuit according to claim 1, characterized in that: The control signal output module includes an analog-to-digital converter and a plurality of comparators; the input end of the analog-to-digital converter is connected to the dimming signal input end, the output end of the analog-to-digital converter is respectively connected to the inverting input end of each of the comparators, the non-inverting input end of each of the comparators is respectively connected to the preset signal input end, and the output end of each of the comparators is respectively connected to each of the switch modules.

5. The LED driving circuit according to claim 1, characterized in that: The control signal output module includes a duty cycle calculation unit and a plurality of comparators; the input end of the duty cycle calculation unit is connected to the dimming signal input end, the output end of the duty cycle calculation unit is respectively connected to the inverting input end of each of the comparators, the non-inverting input end of each of the comparators is respectively connected to the preset signal input end, and the output end of each of the comparators is respectively connected to each of the switch modules.

6. The LED driving circuit according to claim 1, characterized in that: The reference voltage output module includes a resistor string, which is composed of a plurality of voltage-dividing resistors connected in series. The upper end of the resistor string is connected to the dimming signal input terminal, the lower end of the resistor string is grounded, and the upper end tap of each voltage-dividing resistor is respectively led out and connected to each of the driving modules.

7. The LED driving circuit according to claim 3, characterized in that: The driving module includes an operational amplifier and a MOS tube, the non-inverting input terminal of the operational amplifier is connected to the reference voltage output module, the inverting input terminal of the operational amplifier is grounded, the output terminal of the operational amplifier is connected to the gate of the MOS tube and the first end of the switch tube, the drain of the MOS tube is connected to the output terminal of the light string, and the source of the MOS tube is grounded.

8. A driving method based on the LED driving circuit according to any one of claims 1 to 7, characterized in that: The steps include: The reference voltage output module divides the dimming signal and outputs corresponding reference voltages to each of the driving modules through different taps; Each of the driving modules drives the corresponding light string to light up or turn off in sequence according to the line voltage and the corresponding reference voltage; The control signal output module compares the dimming signal with the preset signals of each of the switch modules respectively, and outputs corresponding control signals to each of the switch modules through different taps according to the comparison results; Each of the switch modules controls each of the drive modules to turn on or off according to a corresponding control signal; wherein, the preset signal of each of the switch modules decreases according to the turn-on sequence of each of the drive modules, and the preset signal of the switch module is greater than the offset voltage signal of the drive module connected to the switch module.

9. An LED driving device, characterized in that: It comprises the LED driving circuit as claimed in any one of claims 1 to 7.

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