LED dimming circuit, device and dimming method thereof

Abstract

The present invention discloses an LED dimming circuit, a device and a dimming method thereof. The LED dimming circuit comprises a control module, a digital-to-analog conversion module, an LED light string and a constant current source module, wherein the constant current source module comprises a first sampling resistor and / or a second sampling resistor; after the control module compares the dimming data with a first preset value, the constant current source module is controlled to select the first sampling resistor or the second sampling resistor according to the comparison result, and the first brightness data or the second brightness data is selected to be output to the digital-to-analog conversion module; the digital-to-analog conversion module outputs a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; the constant current source module controls the working current flowing through the LED light string according to the dimming signal; the present invention can effectively reduce the influence of the offset voltage of the operational amplifier on the dimming depth.

Description

Technical Field

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

[0002] There are usually two dimming methods for LED lamps. One is to use PWM dimming method, which adjusts the brightness of LED lamp string by controlling the on and off time ratio of LED lamp string. The advantage of using this method is that the circuit structure is simple and the brightness of LED lamp string can be adjusted to a very low level. However, because it keeps turning on and off the current of LED lamp string, the sudden change of lamp string current leads to serious conduction radiation problem. The other is to use DIM dimming method, which controls the size of DIM dimming voltage and then changes the current of LED lamp string to achieve brightness change. The advantage of using this method is that there is no conduction radiation problem, but it uses constant current source to achieve current regulation of LED lamp string. The minimum current of LED lamp string is limited by the offset voltage of operational amplifier in constant current source. When the dimming voltage is equal to or less than the offset voltage, the current of LED lamp string is not controlled by the dimming voltage. And because the offset voltage of operational amplifier of each LED driver chip is biased, the current of LED lamp string using this dimming method cannot be adjusted too small, the brightness cannot be adjusted too low, the dimming depth is poor, and the offset voltage difference of operational amplifier between chips leads to poor consistency between LED lamps when the brightness is reduced.

[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, an object of the present invention is to provide an LED dimming circuit, device and dimming method thereof, which can effectively solve the problem of dimming depth difference in the existing dimming methods.

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

[0006] An LED dimming circuit comprises a control module, a digital-to-analog conversion module, an LED light string and a constant current source module, wherein the constant current source module comprises a first sampling resistor and / or a second sampling resistor; the control module is used to compare input dimming data with a first preset value, and then control the constant current source module to select the first sampling resistor or the second sampling resistor according to the comparison result, and select to output the first brightness data or the second brightness data to the digital-to-analog conversion module; the digital-to-analog conversion module is used to output a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; the constant current source module is used to control the working current flowing through the LED light string according to the dimming signal.

[0007] In the LED dimming circuit, the control module is specifically used to compare that when the dimming data is greater than or equal to the first preset value, output a first control signal to the constant current source module to control it to select the first sampling resistor, and select to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module; when the dimming data is less than the first preset value, output a second control signal to the constant current source module to control it to select the second sampling resistor, and after multiplying the dimming data by the second preset value, select to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module; the resistance value of the second sampling resistor = the resistance value of the first sampling resistor * the second preset value.

[0008] In the LED dimming circuit, the constant current source module also includes a selection unit and a constant current source unit; the selection unit selects the first sampling resistor according to the first control signal, and selects the second sampling resistor according to the second control signal; the constant current source unit controls the working current flowing through the LED light string according to the dimming signal.

[0009] In the LED dimming circuit, the selection unit includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and an inverter; the constant current source unit includes a first operational amplifier, a first MOS tube, and a second MOS tube;

[0010] One end of the first switch and one end of the second switch are both connected to the inverting input end of the first operational amplifier, the control end of the first switch is connected to the control module, and the other end of the first switch is connected to the source of the first MOS tube and one end of the first sampling resistor; the control end of the second switch, the control end of the fourth switch and the control end of the fifth switch are all connected to the output end of the inverter, and the other end of the second switch is connected to the source of the second MOS tube and one end of the second sampling resistor; the other end of the first sampling resistor and the other end of the second sampling resistor are both grounded; one end of the third switch and one end of the fourth switch are both connected to the output end of the first operational amplifier, the other end of the third switch and one end of the fifth switch are both connected to the gate of the first MOS tube, the other end of the fourth switch and one end of the sixth switch are both connected to the gate of the second MOS tube, the other end of the fifth switch and the other end of the sixth switch are both grounded, and the control end of the third switch and the control end of the sixth switch are both connected to the control module; the positive input end of the first operational amplifier is connected to the digital-to-analog conversion module; the drain of the first MOS tube and the drain of the second MOS tube are both connected to the negative pole of the LED light string, and the input end of the inverter is connected to the control module.

[0011] In the LED dimming circuit, the selection unit includes a seventh switch, an eighth switch and an inverter; the constant current source unit includes a second operational amplifier and a third MOS tube; the control end of the seventh switch and the input end of the inverter are connected to the control module, one end of the seventh switch and one end of the eighth switch are connected to the inverting input end of the second operational amplifier and the source of the third MOS tube, the other end of the seventh switch is grounded through the first sampling resistor, the other end of the eighth switch is grounded through the second sampling resistor, the drain of the third MOS tube is connected to the negative electrode of the LED light string, the positive input end of the second operational amplifier is connected to the digital-to-analog conversion module, the output end of the second operational amplifier is connected to the gate of the third MOS tube, and the output end of the inverter is connected to the control end of the eighth switch.

[0012] In the LED dimming circuit, the selection unit includes a ninth switch, a tenth switch and an inverter; the constant current source unit includes a third operational amplifier, a fourth operational amplifier, a fourth MOS tube and a fifth MOS tube; the positive phase input terminal of the third operational amplifier and the positive phase input terminal of the fourth operational amplifier are connected to the digital-to-analog conversion module, one end of the ninth switch and the output terminal of the third operational amplifier are both connected to the gate of the fourth MOS tube, and the inverting input terminal of the third operational amplifier and the source of the fourth MOS tube are connected to ground through the first sampling resistor; the control terminal of the ninth switch is connected to the output terminal of the inverter, and the control terminal of the tenth switch and the input terminal of the inverter are both connected to the control module; one end of the tenth switch and the output terminal of the fourth operational amplifier are both connected to the gate of the fifth MOS tube, the other end of the tenth switch is grounded, the inverting input terminal of the fourth operational amplifier and the source of the fifth MOS tube are both grounded through the second sampling resistor, and the drain of the fourth MOS tube and the drain of the fifth MOS tube are both connected to the negative electrode of the LED light string.

[0013] In the LED dimming circuit, the digital-to-analog conversion module includes a voltage divider unit, a decoding unit and a multi-way selection unit; the voltage divider unit divides the reference voltage and outputs the dimming signal of the corresponding amplitude to the multi-way selection unit through different taps; the decoding unit controls the multi-way selection unit according to the first brightness data or the second brightness data to output the dimming signal output by the corresponding tap of the voltage divider unit to the constant current source module.

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

[0015] After the control module compares the input dimming data with the first preset value, the constant current source module is controlled to select the first sampling resistor or the second sampling resistor according to the comparison result, and the first brightness data or the second brightness data is output to the digital-to-analog conversion module;

[0016] The digital-to-analog conversion module outputs a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data;

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

[0018] In the dimming method of the LED dimming circuit, after the control module compares the input dimming data with the first preset value, the steps of controlling the constant current source module to select the first sampling resistor or the second sampling resistor according to the comparison result, and selecting to output the first brightness data or the second brightness data to the digital-to-analog conversion module include:

[0019] The control module compares and finds that when the dimming data is greater than or equal to the first preset value, it outputs a first control signal to the constant current source module to control it to select the first sampling resistor, and selects to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module; when the dimming data is less than the first preset value, it outputs a second control signal to the constant current source module to control it to select the second sampling resistor, and after multiplying the dimming data by the second preset value, it selects to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module.

[0020] An LED dimming device comprises a shell, a PCB board is arranged in the shell, and the LED dimming circuit as described above is arranged on the PCB board.

[0021] Compared with the prior art, the LED dimming circuit, device and dimming method provided by the present invention, the LED dimming circuit includes a control module, a digital-to-analog conversion module, an LED light string and a constant current source module, the constant current source module includes a first sampling resistor and / or a second sampling resistor; the control module is used to compare the input dimming data with the first preset value, and control the constant current source module to select the first sampling resistor or the second sampling resistor according to the comparison result, and select to output the first brightness data or the second brightness data to the digital-to-analog conversion module; the digital-to-analog conversion module is used to output the corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; the constant current source module is used to control the working current flowing through the LED light string according to the dimming signal; the present invention can effectively solve the problem of dimming depth difference in the existing dimming method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A structural block diagram of the LED dimming circuit provided by the present invention;

[0023] Figure 2 A circuit schematic diagram of a constant current source module in the first embodiment of the LED dimming circuit provided by the present invention;

[0024] Figure 3 A circuit schematic diagram of a control module in an LED dimming circuit provided by the present invention;

[0025] Figure 4 The circuit schematic diagram of the digital-to-analog conversion module in the LED dimming circuit provided by the present invention

[0026] Figure 5 A timing diagram of a first preset value, dimming data, a dimming signal, a control signal and a sampling resistor of the LED dimming circuit provided by the present invention;

[0027] Figure 6 A circuit schematic diagram of a constant current source module in a second embodiment of an LED dimming circuit provided by the present invention;

[0028] Figure 7 A circuit schematic diagram of a constant current source module in a third embodiment of an LED dimming circuit provided by the present invention;

[0029] Figure 8 A flowchart of the steps of the driving method of the LED dimming circuit provided by the present invention. DETAILED DESCRIPTION

[0030] An LED dimming circuit, device and dimming method provided by the present invention can effectively solve the problem of dimming depth difference in existing dimming methods.

[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 1 and Figure 2 The LED dimming circuit provided by the present invention includes a control module 100, a digital-to-analog conversion module 200, an LED light string 300 and a constant current source module 400. The control module 100 is connected to the dimming data input terminal, the digital-to-analog conversion module 200 and the constant current source module 400. The digital-to-analog conversion module 200 is also connected to the constant current source module 400. The constant current source module 400 is also connected to the negative pole of the LED light string 300. The positive pole of the LED light string 300 is connected to the power input terminal.

[0033] Among them, the constant current source module 400 includes a first sampling resistor Rcs1 and / or a second sampling resistor Rcs2; the control module 100 is used to compare the input dimming data with the first preset value, and control the constant current source module 400 to select the first sampling resistor Rcs1 and / or the second sampling resistor Rcs2 according to the comparison result, and select to output the first brightness data or the second brightness data to the digital-to-analog conversion module 200; the digital-to-analog conversion module 200 is used to output the corresponding dimming signal to the constant current source module 400 according to the first brightness data or the second brightness data; the constant current source module 400 controls the working current flowing through the LED light string 300 according to the dimming signal. The present invention compares the dimming data with a first preset value, and according to the size of the dimming data, selects to output different brightness data and a sampling resistor corresponding to the brightness data, and then outputs a dimming signal corresponding to the brightness data to adjust the working current of the LED light string 300, thereby ensuring that the corresponding relationship between the dimming data and the working current of the LED light string 300 remains unchanged, and effectively avoiding the influence of the offset voltage of the constant current source module 400 on the dimming depth; the dimming data can be data received by a wireless receiver, data obtained by counting PWM dimming signals, data received through a data bus, and data obtained by ADC (Analog-to-Digital converter) sampling, etc.

[0034] Further, the control module 100 is specifically used to compare and find out that when the dimming data is greater than or equal to the first preset value, output a first control signal to the constant current source module 400 to control it to select the first sampling resistor Rcs1, and select to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module 200; when the dimming data is less than the first preset value, output a second control signal to the constant current source module 400 to control it to select the second sampling resistor Rcs2, and after multiplying the dimming data by the second preset value, select to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module 200; wherein the resistance value of the second sampling resistor Rcs2 = the resistance value of the first sampling resistor Rcs1 * the second preset value, and after comparing the size of the dimming data, the control module 100 controls the resistance value of the sampling resistor in the constant current source module 400 accordingly, so that the corresponding relationship between the working current adjusted by the constant current source module 400 according to the dimming signal and the dimming data remains unchanged.

[0035] For specific implementation, please refer to Figure 3The control module 100 of the present invention includes a comparator 110, a multiplier 130 and a selector 120, wherein the non-phase input terminal of the comparator 110 is connected to the dimming data input terminal, the inverting input terminal of the comparator 110 is connected to the first preset value input terminal, and the output terminal of the comparator 110 is connected to the selector 120 and the constant current source module 400; the input terminal of the multiplier 130 is connected to the dimming data input terminal and the second preset value input terminal, the output terminal of the multiplier 130 is connected to the selector 120, and the selector 120 is also connected to the digital-to-analog conversion module 200.

[0036] Among them, the comparator 110 is used to compare and output a first control signal to the constant current source module 400 when the dimming data is greater than or equal to the first preset value, and output a second control signal to the constant current source module 400 when the dimming data is less than the first preset value; the multiplier 130 is used to multiply the dimming data by the second preset value and output it to the selector 120; the selector 120 is used to select and output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module 200 when the dimming data is greater than or equal to the first preset value, and select and output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module 200 when the dimming data is less than the first preset value.

[0037] The offset voltage of the constant current source module 400 refers to the offset voltage of the corresponding operational amplifier in the constant current source module 400. The first preset value is a pre-set comparison reference value, which is determined by the offset voltage of the corresponding operational amplifier in the constant current module. When the dimming data becomes smaller, the dimming signal becomes smaller accordingly. When the dimming signal is close to or less than the offset voltage of the operational amplifier, the output of the operational amplifier is not controlled, and the working current flowing through the LED light string 300 is not controlled, then the LED light string 300 flickers, and the dimming depth (the working current of the LED light string 300 cannot be adjusted to a very low level) is affected by the offset voltage of the operational amplifier. The dimming signal corresponding to the first preset value should be greater than the offset voltage of the operational amplifier. When the dimming data is less than the first preset value, the dimming signal and the resistance of the sampling resistor in the constant current source module 400 are amplified in the same proportion, that is, the dimming data and the resistance of the sampling resistor are simultaneously amplified by the multiple set by the second preset value. That is, when the dimming data is less than the first preset value, the control module 100 controls the constant current source module 400 to select the second sampling resistor Rcs2, and selects the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module 200. Under the condition of ensuring that the corresponding relationship between the dimming data and the current of the LED light string 300 remains unchanged, the dimming signal is amplified by a multiple of the second preset value that is much greater than the offset voltage of the operational amplifier, the output of the operational amplifier is controllable, the current of the LED light string 300 can be adjusted to a smaller value, and the brightness of the LED light string 300 is adjusted to a lower value.

[0038] In this embodiment, the first control signal is a high-level control signal, and the second control signal is a low-level control signal; after receiving the dimming data, the comparator 110 compares it with the first preset value. When the dimming data is greater than or equal to the first preset value, the comparator 110 outputs a high-level control signal to the constant current source module 400, so that the constant current source module 400 selects the first sampling resistor Rcs1, and outputs the dimming data as brightness data, that is, outputs the first brightness data to the digital-to-analog conversion module 200; when the dimming data is less than the first preset value, the comparator 110 outputs a low-level control signal to the constant current source module 400. The control signal is sent to the constant current source module 400, so that the constant current source module 400 selects the first sampling resistor Rcs1, and outputs the dimming data * the second preset value as the brightness data, that is, outputs the second brightness data to the digital-to-analog conversion module 200, and the size of the dimming signal output by the digital-to-analog conversion module 200 is determined according to the brightness data. Therefore, while ensuring that the corresponding relationship between the dimming data and the working current of the LED light string 300 remains unchanged, the dimming signal is amplified according to the increase of the brightness data, thereby reducing the influence of the offset voltage on the dimming depth.

[0039] For further information, please refer to Figure 2The constant current source module 400 also includes a selection unit 410 and a constant current source unit 420, the selection unit 410 is connected to the output end of the comparator 110, the constant current source unit 420 is connected to the digital-to-analog conversion module 200, one end of the first sampling resistor Rcs1 and one end of the second sampling resistor Rcs2 are both connected to the selection unit 410 and the constant current source unit 420, and the other end of the first sampling resistor Rcs1 and the other end of the second sampling resistor Rcs2 are both grounded.

[0040] The selection unit 410 selects the first sampling resistor Rcs1 according to the first control signal, and selects the second sampling resistor Rcs2 according to the second control signal; the constant current source unit 420 controls the working current flowing through the LED light string 300 according to the dimming signal, and the selection unit 410 selects the first sampling resistor Rcs1 or the second sampling resistor Rcs2 to connect to the circuit according to the control signal output by the comparator 110; when the dimming data is greater than or equal to the first preset value, the comparator 110 outputs the first control signal to the selection unit 410, and the selection unit 410 selects the first sampling resistor Rcs1 to connect, and the corresponding digital-to-analog converter The conversion module 200 also outputs a dimming signal to the constant current source unit 420 based on the first brightness data; when the dimming data is less than the first preset value, the comparator 110 outputs a second control signal to the selection unit 410, and the selection unit 410 selects the second sampling resistor Rcs2 to be connected, and the corresponding digital-to-analog conversion module 200 also outputs a dimming signal to the constant current source unit 420 based on the second brightness data, thereby realizing that the control module 100 controls the sampling resistors of different resistance values ​​selected in the constant current source module 400, and obtains the dimming signal corresponding to the brightness data, so as to ensure that the corresponding relationship between the dimming data and the working current of the LED light string 300 remains unchanged.

[0041] For further information, please refer to Figure 2In the first embodiment of the present invention, the selection unit 410 includes a first switch Key1, a second switch Key2, a third switch Key3, a fourth switch Key4, a fifth switch Key5, a sixth switch Key6, and an inverter INV; the constant current source unit 420 includes a first operational amplifier OP1, a first MOS transistor Q1, and a second MOS transistor Q2; one end of the first switch Key1 and one end of the second switch Key2 are both connected to the inverting input end of the first operational amplifier OP1, the control end of the first switch Key1 is connected to the output end of the comparator 110, and the other end of the first switch Key1 is connected to the source of the first MOS transistor Q1 and one end of the first sampling resistor Rcs1; the control end of the second switch Key2, the control end of the fourth switch Key4, and the control end of the fifth switch Key5 are all connected to the output end of the inverter INV, and the other end of the second switch Key2 is connected to the source of the second MOS transistor Q2 and one end of the second sampling resistor Rcs2; the other end of the first sampling resistor Rcs1 and the other end of the second sampling resistor Rcs2 are both grounded; one end of the third switch Key3 and the fourth switch Key4 are connected to the output end of the inverter INV, and the other end of the second switch Key2 is connected to the source of the second MOS transistor Q2 and one end of the second sampling resistor Rcs2; the other end of the first sampling resistor Rcs1 and the other end of the second sampling resistor Rcs2 are both grounded; One end of each of the third switch Key3 and the fifth switch Key5 is connected to the output end of the first operational amplifier OP1, the other end of each of the third switch Key3 and the one end of each of the fifth switch Key5 are connected to the gate of the first MOS transistor Q1, the other end of each of the fourth switch Key4 and the one end of each of the sixth switch Key6 are connected to the gate of the second MOS transistor Q2, the other end of each of the fifth switch Key5 and the other end of each of the sixth switch Key6 are grounded, the control end of each of the third switch Key3 and the control end of each of the sixth switch Key6 are connected to the output end of the comparator 110; the first operational amplifier OP1 The positive input end is connected to the digital-to-analog conversion module 200; the drain of the first MOS tube Q1 and the drain of the second MOS tube Q2 are both connected to the negative electrode of the LED light string 300, the input end of the inverter INV is connected to the output end of the comparator 110, and the positive electrode of the LED light string 300 is connected to the power input end, wherein the power input end Vin+ and the power output end Vin- are connected to the positive end and negative end of the AC voltage after rectification by the rectifier bridge, and can also be the output of a switching power supply or other DC power supply. Therefore, the grounding of each component discussed in the present invention corresponds to connecting the power output end Vin-.

[0042] In this embodiment, please refer to Figure 3When the comparator 110 outputs a high-level control signal, the first switch Key1, the third switch Key3 and the sixth switch Key6 are turned on, the second switch Key2, the fourth switch Key4 and the fifth switch Key5 are turned off, and the first sampling resistor Rcs1 is connected to the circuit, so that the constant current source module 400 is composed of the first operational amplifier OP1, the first MOS tube Q1 and the first sampling resistor Rcs1 to adjust the working current flowing through the LED light string 300; when the comparator 110 outputs a low-level control signal, the first switch Key1, the third switch Key3 and the sixth switch Key6 are turned off, the second switch Key2, the fourth switch Key4 and the fifth switch Key5 are turned on, and the second sampling resistor Rcs2 is connected to the circuit, so that the constant current source module 400 is composed of the first operational amplifier OP1, the second MOS tube Q2 and the second sampling resistor Rcs2 to control the working current flowing through the LED light string 300, wherein the first switch Key1 to the sixth switch Key6 are MOS switches.

[0043] When the comparator 110 outputs a high-level control signal, the sampling resistor in the constant current source module 400 is the first sampling resistor Rcs1, the dimming signal output by the digital-to-analog conversion module 200 corresponds to the dimming data, and the working current flowing through the LED light string 300 = dimming signal / Rcs1; when the comparator 110 outputs a low-level control signal, the sampling resistor in the constant current source module 400 is the second sampling resistor Rcs2, and the dimming signal output by the digital-to-analog conversion module 200 corresponds to the dimming data. The dimming data*the second preset value, the dimming signal is amplified by the second preset value, Rcs2=Rcs1*the second preset value, the working current flowing through the LED light string 300=dimming signal / Rcs2, wherein Rcs2 is the resistance value of the second sampling resistor Rcs2, and Rcs1 is the resistance value of the first sampling resistor Rcs1; thus, while ensuring that the corresponding relationship between the dimming data and the working current of the LED light string 300 remains unchanged, the dimming signal voltage is amplified, thereby reducing the influence of the offset voltage of the operational amplifier on the dimming depth.

[0044] For further information, see Figure 4The digital-to-analog conversion module 200 includes a voltage divider unit 210, a decoding unit 220 and a multi-way selection unit 230; the voltage divider unit 210 divides the reference voltage and outputs the dimming signal of the corresponding amplitude to the multi-way selection unit 230 through different taps; the decoding unit 220 controls the multi-way selection unit 230 to output the dimming signal output by the corresponding tap of the voltage divider unit 210 to the constant current source module 400 according to the first brightness data or the second brightness data, and provides the dimming signal to the constant current source module 400 through the digital-to-analog conversion module 200, thereby realizing the adjustment of the working current.

[0045] Specifically, the voltage divider unit 210 includes a resistor string, which is composed of a plurality of voltage divider resistors connected in series. The specific number of voltage divider resistors can be selected according to the actual dimming requirements, and the present invention does not limit this. The upper end of the resistor string is connected to the reference voltage output terminal Vref, and the lower end of the resistor string is grounded; in this embodiment, the number of the voltage divider resistors is 1024, namely R0, R1, R2, ..., R1021, R1022 and R1023, and the resistance value of each resistor is equal; the multi-way selection unit 230 includes a plurality of control switches corresponding to the number of the voltage divider resistors, such as Figure 4 Among K0 to K1023, one end of each control switch is connected to the lower tap of a voltage divider resistor, the other end of each control switch is connected to the constant current source module 400, and the control end of each control switch is connected to the decoding unit 220. The control switch can be implemented by a relay, a transistor, a MOSFET, a transmission gate, etc.

[0046] After receiving the first brightness data or the second brightness data output by the selector 130, the decoding unit 220 controls the corresponding control switch to be turned on or off, and then selects the corresponding dimming signal to be output to the constant current source unit 420. The control end of the control switch is turned on when the control end is at a high level, and is turned off when the control end is at a low level. The decoding unit 220 uses one-hot encoding to convert the received first brightness data and the second brightness data into one-hot codes (S0-S1023) and then select the corresponding control switches, and then select the dimming signal corresponding to the resistor string to be output to the constant current source unit 420. In this embodiment, the brightness data bit width is 10 bits. After one-hot encoding, 1024 control signals, namely one-hot codes S0-S1023, are output, and only one control signal is high at the same time.

[0047] Please also refer to Figure 5In this embodiment, the first preset value and the second preset value are both 32. Of course, the first preset value and the second preset value may also be different. The dimming data bit width is 10 bits, 1024 levels of dimming, and the reference voltage Vref is 3.3V. When the dimming data changes from large to small and is not less than the first preset value, the comparator 110 outputs a high-level control signal, the constant current source module 400 selects the sampling resistor to have a resistance value of R, the voltage of the dimming signal corresponding to each level of the digital-to-analog conversion module 200 = (3.3V*dimming data) / 1024, the working current flowing through the LED light string 300 = (3.3V*dimming data) / (1024*R); when the dimming data is equal to the preset value 1, the dimming signal can be calculated to be 103mV, and the operational amplifier in the constant current source module 400 has an offset voltage generally below tens of millivolts after calibration; when the dimming data becomes smaller again, the dimming signal will be close to the offset voltage, causing the LED light to flicker, so by setting the first preset value near the dimming signal of 103mV, when the dimming data is less than the preset value, the dimming signal will be adjusted to the offset voltage. When the first preset value is set, the comparator 110 outputs a low-level control signal, the constant current source module 400 correspondingly selects the sampling resistor to have a resistance of R*32, the corresponding dimming signal voltage for each level = (3.3V*dimming data*32) / 1024, the working current flowing through the LED light string 300 = (3.3V*dimming data*32) / (1024*32*R), which is consistent with the light string current calculation method when the comparator 110 outputs a high-level control signal, that is, the sampling resistor and the dimming data are both amplified by 32 times set by the second preset value. While ensuring that the corresponding relationship between the dimming data and the working current of the LED light string 300 remains unchanged, the dimming signal is amplified, reducing the influence of the offset voltage of the operational amplifier on the dimming depth, thereby solving the problem of dimming depth difference in the existing dimming method.

[0048] For further information, see Figure 6In the second embodiment of the present invention, the selection unit 410 includes a seventh switch Key7, an eighth switch Key8 and an inverter INV; the constant current source unit 420 includes a second operational amplifier OP2 and a third MOS tube Q3; the control end of the seventh switch Key7 and the input end of the inverter INV are connected to the control module 100, one end of the seventh switch Key7 and one end of the eighth switch Key8 are connected to the inverting input end of the second operational amplifier OP2 and the source of the third MOS tube Q3, the other end of the seventh switch Key7 is grounded through the first sampling resistor Rcs1, the other end of the eighth switch Key8 is grounded through the second sampling resistor Rcs2, the drain of the third MOS tube Q3 is connected to the negative electrode of the LED light string 300, the positive input end of the second operational amplifier OP2 is connected to the digital-to-analog conversion module 200, the output end of the second operational amplifier OP2 is connected to the gate of the third MOS tube Q3, and the output end of the inverter INV is connected to the control end of the eighth switch Key8.

[0049] In this embodiment, when the comparator 110 outputs a high-level control signal, the seventh switch Key7 is turned on, the eighth switch Key8 is turned off, and the first sampling resistor Rcs1 is connected to the circuit, so that the constant current source module 400 is composed of the second operational amplifier OP2, the third MOS tube Q3 and the first sampling resistor Rcs1, the dimming signal corresponds to the dimming data, and the working current flowing through the LED light string 300 = dimming signal / Rcs1; when the comparator 110 outputs a low-level control signal, the seventh switch Key7 is turned off, the eighth switch Key8 is turned on, and the second sampling resistor Rcs2 is connected to the circuit, so that the constant current source module 400 is composed of the second operational amplifier OP2, the third MOS tube Q3 and the second sampling resistor Rcs2, the dimming signal output by the digital-to-analog conversion module 200 corresponds to the dimming data*the second preset value, the dimming signal is amplified by the second preset value, Rcs2=Rcs1*the second preset value, and the working current flowing through the LED light string 300 = the dimming signal / Rcs2.

[0050] Of course, the eighth switch Key8 may not be used in this embodiment, and the same result can be obtained. That is, the constant current source module can select the first sampling resistor Rcs1 and the second sampling resistor Rcs2. Specifically, when a high-level control signal is received, the seventh switch Key7 is turned on, the first sampling resistor Rcs1 and the second sampling resistor Rcs2 are connected in parallel, and the resistance after parallel connection = Rcs2 / second preset value; when a low-level control signal is received, the seventh switch Key7 is disconnected, and the second sampling resistor Rcs2 is connected to the circuit; compared with the constant current source module 400 in the first embodiment, the constant current source module 400 in this embodiment has four fewer switches and one MOS tube connected, and has a simple structure and relatively low implementation cost.

[0051] For further information, see Figure 7 In the third embodiment of the present invention, the selection unit 410 includes a ninth switch Key9, a tenth switch Key10 and an inverter INV; the constant current source unit 420 includes a third operational amplifier OP3, a fourth operational amplifier OP4, a fourth MOS tube Q4 and a fifth MOS tube Q5; the positive phase input terminal of the third operational amplifier OP3 and the positive phase input terminal of the fourth operational amplifier OP4 are connected to the digital-to-analog conversion module 200, one end of the ninth switch Key9 and the output terminal of the third operational amplifier OP3 are both connected to the gate of the fourth MOS tube Q4, and the inverting input terminal of the third operational amplifier OP3 and the source of the fourth MOS tube Q4 are connected through the first sampling The resistor Rcs1 is grounded; the control end of the ninth switch Key9 is connected to the output end of the inverter INV, and the control end of the tenth switch Key10 and the input end of the inverter INV are both connected to the output end of the comparator 110; one end of the tenth switch Key10 and the output end of the fourth operational amplifier OP4 are both connected to the gate of the fifth MOS tube Q5, and the other end of the tenth switch Key10 is grounded, the inverting input end of the fourth operational amplifier OP4 and the source of the fifth MOS tube Q5 are both grounded through the second sampling resistor Rcs2, and the drain of the fourth MOS tube Q4 and the drain of the fifth MOS tube Q5 are both connected to the negative electrode of the LED light string 300.

[0052] In this embodiment, when the comparator 110 outputs a high-level control signal, the ninth switch Key9 is disconnected, the tenth switch Key10 is turned on, the gate of the fifth MOS tube Q5 is connected to the ground through the tenth switch Key10, the fifth MOS tube Q5 is not turned on, and the first sampling resistor Rcs1 is connected to the circuit, so that the constant current source module 400 is composed of the third operational amplifier OP3, the fourth MOS tube Q4 and the first sampling resistor Rcs1. The dimming signal corresponds to the dimming data, and the working current flowing through the LED light string 300 = dimming signal / Rcs1; when the comparator 110 outputs a low-level control signal, The ninth switch Key9 is turned on, the tenth switch Key10 is turned off, the gate of the fourth MOS tube Q4 is connected to the ground through the ninth switch Key9, the fourth MOS tube Q4 is not turned on, the second sampling resistor Rcs2 is connected to the circuit, so that the constant current source module 400 is composed of the fourth operational amplifier OP4, the fifth MOS tube Q5 and the second sampling resistor Rcs2, the dimming signal output by the digital-to-analog conversion module 200 corresponds to the dimming data*the second preset value, the dimming signal is amplified by the second preset value, Rcs2=Rcs1*the second preset value, and the working current flowing through the LED light string 300=dimming signal / Rcs2.

[0053] Based on the above LED dimming circuit, please refer to Figure 8 The present invention also provides a dimming method of an LED dimming circuit, which specifically includes the following steps:

[0054] S100, after comparing the input dimming data with the first preset value, the control module controls the constant current source module to select the first sampling resistor and / or the second sampling resistor according to the comparison result, and selects to output the first brightness data or the second brightness data to the digital-to-analog conversion module;

[0055] S200, the digital-to-analog conversion module is used to output a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data;

[0056] S300, the constant current source module is used to control the operating current flowing through the LED light string according to the dimming signal.

[0057] Further, step S100 specifically includes: when the control module compares and finds that the dimming data is greater than or equal to the first preset value, the control module outputs a first control signal to the constant current source module to control it to select the first sampling resistor, and selects to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module; when the dimming data is less than the first preset value, the control module outputs a second control signal to the constant current source module to control it to select the second sampling resistor, and after multiplying the dimming data by the second preset value, selects to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module.

[0058] Based on the above-mentioned LED dimming circuit, the present invention also provides a corresponding LED dimming device, including a shell, a PCB board is arranged in the shell, and the PCB board is provided with the above-mentioned LED dimming circuit. Since the LED dimming circuit is described in detail above, it will not be repeated here.

[0059] In summary, the LED dimming circuit, device and dimming method provided by the present invention, the LED dimming circuit includes a control module, a digital-to-analog conversion module, an LED light string and a constant current source module, the constant current source module includes a first sampling resistor or a second sampling resistor; the control module is used to compare the input dimming data with the first preset value, and control the constant current source module to select the first sampling resistor and / or the second sampling resistor according to the comparison result, and select to output the first brightness data or the second brightness data to the digital-to-analog conversion module; the digital-to-analog conversion module is used to output the corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; the constant current source module is used to control the working current flowing through the LED light string according to the dimming signal; the present invention can effectively solve the problem of dimming depth difference in the existing dimming method.

[0060] 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 dimming circuit, characterized in that: It includes a control module, a digital-to-analog conversion module, an LED light string and a constant current source module, wherein the constant current source module includes a first sampling resistor and / or a second sampling resistor; the control module is used to compare the input dimming data with a first preset value, and control the constant current source module to select the first sampling resistor or the second sampling resistor according to the comparison result, and select to output the first brightness data or the second brightness data to the digital-to-analog conversion module; The digital-to-analog conversion module is used to output a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; the constant current source module is used to control the working current flowing through the LED light string according to the dimming signal; The control module is specifically used to compare and find out that when the dimming data is greater than or equal to the first preset value, output a first control signal to the constant current source module to control it to select the first sampling resistor, and select to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module; when the dimming data is less than the first preset value, output a second control signal to the constant current source module to control it to select the second sampling resistor, and after multiplying the dimming data by the second preset value, select to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module; the resistance value of the second sampling resistor = the resistance value of the first sampling resistor * the second preset value; after comparing the size of the dimming data, the control module controls the resistance value of the sampling resistor in the constant current source module accordingly, so that the corresponding relationship between the working current adjusted by the constant current source module according to the dimming signal and the dimming data remains unchanged; The constant current source module also includes a selection unit and a constant current source unit; the selection unit selects the first sampling resistor according to the first control signal, and selects the second sampling resistor according to the second control signal; the constant current source unit controls the working current flowing through the LED light string according to the dimming signal.

2. The LED dimming circuit according to claim 1, characterized in that: The selection unit includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, a sixth switch, and an inverter; the constant current source unit includes a first operational amplifier, a first MOS tube and a second MOS tube; One end of the first switch and one end of the second switch are both connected to the inverting input end of the first operational amplifier, the control end of the first switch is connected to the control module, and the other end of the first switch is connected to the source of the first MOS tube and one end of the first sampling resistor; the control end of the second switch, the control end of the fourth switch and the control end of the fifth switch are all connected to the output end of the inverter, and the other end of the second switch is connected to the source of the second MOS tube and one end of the second sampling resistor; the other end of the first sampling resistor and the other end of the second sampling resistor are both grounded; one end of the third switch and one end of the fourth switch are both connected to the output end of the first operational amplifier, the other end of the third switch and one end of the fifth switch are both connected to the gate of the first MOS tube, the other end of the fourth switch and one end of the sixth switch are both connected to the gate of the second MOS tube, the other end of the fifth switch and the other end of the sixth switch are both grounded, and the control end of the third switch and the control end of the sixth switch are both connected to the control module; the positive input end of the first operational amplifier is connected to the digital-to-analog conversion module; the drain of the first MOS tube and the drain of the second MOS tube are both connected to the negative pole of the LED light string, and the input end of the inverter is connected to the control module.

3. The LED dimming circuit according to claim 1, characterized in that: The selection unit includes a seventh switch, an eighth switch and an inverter; the constant current source unit includes a second operational amplifier and a third MOS tube; the control end of the seventh switch and the input end of the inverter are connected to the control module, one end of the seventh switch and one end of the eighth switch are connected to the inverting input end of the second operational amplifier and the source of the third MOS tube, the other end of the seventh switch is grounded through the first sampling resistor, the other end of the eighth switch is grounded through the second sampling resistor, the drain of the third MOS tube is connected to the negative electrode of the LED light string, the positive input end of the second operational amplifier is connected to the digital-to-analog conversion module, the output end of the second operational amplifier is connected to the gate of the third MOS tube, and the output end of the inverter is connected to the control end of the eighth switch.

4. The LED dimming circuit according to claim 1, characterized in that: The selection unit includes a ninth switch, a tenth switch and an inverter; the constant current source unit includes a third operational amplifier, a fourth operational amplifier, a fourth MOS tube and a fifth MOS tube; the non-inverting input end of the third operational amplifier and the non-inverting input end of the fourth operational amplifier are connected to the digital-to-analog conversion module, one end of the ninth switch and the output end of the third operational amplifier are both connected to the gate of the fourth MOS tube, and the inverting input end of the third operational amplifier and the source of the fourth MOS tube are connected to the ground through the first sampling resistor; the control end of the ninth switch is connected to the output end of the inverter, and the control end of the tenth switch and the input end of the inverter are both connected to the control module; One end of the tenth switch and the output end of the fourth operational amplifier are both connected to the gate of the fifth MOS tube, the other end of the tenth switch is grounded, the inverting input end of the fourth operational amplifier and the source of the fifth MOS tube are both grounded through the second sampling resistor, and the drain of the fourth MOS tube and the drain of the fifth MOS tube are both connected to the negative electrode of the LED light string.

5. The LED dimming circuit according to claim 1, characterized in that: The digital-to-analog conversion module includes a voltage dividing unit, a decoding unit and a multi-channel selection unit; the voltage dividing unit divides the reference voltage and outputs the dimming signal of the corresponding amplitude to the multi-channel selection unit through different taps; The decoding unit controls the multi-way selection unit to output the dimming signal output by the corresponding tap of the voltage divider unit to the constant current source module according to the first brightness data or the second brightness data.

6. A dimming method based on the LED dimming circuit according to any one of claims 1 to 5, characterized in that: The steps include: After the control module compares the input dimming data with the first preset value, the constant current source module is controlled to select the first sampling resistor and / or the second sampling resistor according to the comparison result, and the first brightness data or the second brightness data is output to the digital-to-analog conversion module; The digital-to-analog conversion module outputs a corresponding dimming signal to the constant current source module according to the first brightness data or the second brightness data; The constant current source module controls the operating current flowing through the LED light string according to the dimming signal.

7. The dimming method of the LED dimming circuit according to claim 6, wherein after the control module compares the input dimming data with the first preset value, the step of controlling the constant current source module to select the first sampling resistor or the second sampling resistor according to the comparison result, and selecting to output the first brightness data or the second brightness data to the digital-to-analog conversion module comprises: The control module compares and finds that when the dimming data is greater than or equal to the first preset value, it outputs a first control signal to the constant current source module to control it to select the first sampling resistor, and selects to output the first brightness data corresponding to the dimming data to the digital-to-analog conversion module; when the dimming data is less than the first preset value, it outputs a second control signal to the constant current source module to control it to select the second sampling resistor, and after multiplying the dimming data by the second preset value, it selects to output the second brightness data corresponding to the dimming data multiplied by the second preset value to the digital-to-analog conversion module.

8. An LED dimming device, comprising a housing, wherein a PCB board is arranged in the housing, characterized in that: The PCB board is provided with the LED dimming circuit as described in any one of claims 1-5.

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