CN101466186A - Driving method and driving device capable of adjusting brightness of high-power LED - Google Patents

Abstract

The invention provides a driving method and a device capable of adjusting the brightness of a high-power LED, wherein the method obtains the brightness data of the LED by receiving control information input from the outside, sets the current flowing through the LED by a current adjusting unit connected with a driving unit, and lights the LED to enable the brightness of the LED to reach a target value; or the current flowing through the LED is firstly set according to the method, the brightness of the LED is preliminarily adjusted, then the signal duty ratio of the PWM adjusting unit connected with the current adjusting unit in parallel is further set, and the brightness of the LED is further adjusted to finally reach the target value; and turning off the LED by setting the duty ratio of the PWM regulating unit signal to be 0%. By utilizing the technical scheme provided by the invention, the brightness of the LED can be dynamically adjusted in real time, the EMC (electromagnetic compatibility) performance of the device can be obviously improved, and the service life of the LED is prolonged.

Description

A driving method and a driving device capable of adjusting the brightness of a high-power LED

technical field

The invention relates to a high-power LED, in particular to a driving method and a driving device capable of adjusting the brightness of the high-power LED.

Background technique

In the prior art, PWM is usually used to adjust the brightness of LEDs. For low-power LEDs, the PWM dimming method is feasible because the driving current is not large and the driving voltage is not high. But for high-power LEDs, due to the large driving current (usually hundreds of milliamps), the high driving voltage (when multiple high-power LEDs are driven in series, the driving voltage often reaches tens of volts), which greatly limits the power of PWM. The highest frequency that the signal can reach, so the dimming effect of high-power LED dimming by PWM method is not very ideal, mainly in the two aspects that the gray level and gray refresh frequency are difficult to improve. In addition, the PWM method leads to the rapid on-off of the LED drive circuit current. In the case of high current and high voltage, it will form strong electromagnetic radiation to the surrounding environment and deteriorate the EMC (Electromagnetic Compatibility; Electromagnetic Compatibility) performance of the device or equipment. PWM causes the current flowing through the LED to fluctuate drastically from 0 to hundreds of milliamps in a very short period of time, which will also affect the working life of the LED.

Contents of the invention

In order to solve the above problems in the prior art, the present invention provides a high-power LED driving method combining real-time dynamic current regulation and PWM regulation, and provides a high-power LED driving device.

The present invention adopts following technical scheme:

Receive the control signal input from the outside, get the brightness data of the LED from it, get a corresponding value through software calculation or numerical table lookup, and output the value to a current adjustment unit connected to a drive unit to adjust the current flowing through the LED Value, so as to achieve the purpose of adjusting the brightness of the LED; or divide the corresponding value obtained by calculation or table lookup into two parts, one part is input into the current adjustment unit, and first adjust the current flowing through the LED to initially adjust the brightness of the LED, that is, " Coarse adjustment”, the other part is input to the PWM adjustment unit connected to the drive unit, and the duty cycle of its output signal is set to further adjust the brightness of the LED, that is, “fine adjustment”, and finally adjust the brightness of the LED to the target value; The LED is turned off by setting the duty ratio of the output signal of the PWM adjustment unit to 0%.

The current regulating unit includes a reference voltage generator, the output of the reference voltage generator is divided by a digital potentiometer to obtain a reference voltage, and the reference voltage is input to the negative phase input terminal of the comparator; the reference voltage The voltage can also be obtained by buffering and RC filtering the output signal of a PWM generator, and then input to the negative phase input terminal of the comparator.

The input signal of the current regulation unit also includes a sampling voltage, which is provided by a sampling resistor of the drive unit, and is input to the positive phase input of a comparator of the current regulation unit directly or after being buffered and amplified. terminal, the output of the comparator is connected to a logic circuit.

The logic circuit is connected with an oscillator;

The PWM adjustment unit and the current adjustment unit are controlled by a microcontroller.

A drive device capable of adjusting the brightness of a high-power LED, comprising a high-power LED drive unit, a PWM adjustment unit, a current adjustment unit and a microcontroller connected in sequence, the current adjustment unit and the PWM adjustment unit are connected in parallel to the micro between the controller and the drive unit.

The current regulation unit includes a digital potentiometer, a comparator, and a logic circuit connected in sequence, and the logic circuit is connected with an oscillator.

The drive unit includes an AND gate connected to the PWM adjustment unit and the current adjustment unit.

The drive unit includes a field effect transistor, one end of the field effect transistor is connected to the non-inverting input end of the comparator and the sampling resistor, the other end is connected to the LED and the Schottky diode, and the gate of the field effect transistor is connected to the AND gate .

The drive unit also includes a sampling resistor, an inductor, and a Schottky diode.

The technical scheme provided by the present invention has the following advantages:

(1) The current adjustment unit is used to dynamically adjust the high-power LED to adjust the brightness of the LED. When the brightness of the LED is not changed, the current flowing through the LED is constant. Compared with the existing PWM method of LED brightness adjustment technology, which greatly improves the gray level and gray refresh frequency of LED brightness adjustment (the gray refresh frequency of the technical solution provided by the present invention is equivalent to infinity), and can also improve the electromagnetic compatibility performance of the system and prolong the working life of LED ;

(2) The microcontroller is used to set the current parameters of the current regulation unit in real time, and the current value flowing through the LED can be adjusted at any time according to the external control signal;

(3) PWM technology is used as an auxiliary means of LED brightness adjustment. After the "rough adjustment" of the LED brightness through the current adjustment unit, the PWM adjustment unit connected in parallel can be used to further "fine-adjust" the LED brightness, so as to Get richer gray levels (when red, green and blue LEDs are used for light mixing and color mixing, the richer gray levels make the mixed colors more realistic). The LED can be set to be completely off by setting the PWM adjustment unit.

The technical solutions of the present invention will be explained in detail below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is a schematic flow chart of a driving method capable of adjusting the brightness of a high-power LED according to the present invention;

Fig. 2 is a schematic block diagram of a driving device capable of adjusting the brightness of a high-power LED according to the present invention;

Fig. 3 is a structural schematic diagram of a driving device capable of adjusting the brightness of a high-power LED according to the present invention.

In the figure, 10, microcontroller, 20, current regulation unit, 201, digital potentiometer, 202, comparator, 203, logic circuit, 204, oscillator, 205, reference voltage generator, 30, PWM regulation unit/PWM Generator, 40, drive unit, 401, AND gate, 402, field effect transistor, 403, Schottky diode, 404, inductor, 405, sampling resistor, 50, high-power LED.

Detailed ways

Referring to Fig. 1, the driving method capable of adjusting the brightness of a high-power LED provided by the present invention includes the following steps:

In step S1: the microcontroller receives an external control signal;

In step S2: the microcontroller judges the received control signal. Determine whether the external control signal is to completely turn off the LED or adjust the LED to a certain brightness, if it is necessary to completely turn off the LED, then perform step S6, and if it is necessary to adjust the LED to a certain brightness value, then perform step S3;

In step S6: the microcontroller sets the duty cycle of the PWM adjustment unit to 0%, completely turns off the LED drive unit, and the LED goes out, and completes a brightness adjustment process;

In step S3: the software in the microcontroller calculates according to the LED brightness target value in the received external control signal or performs a software value look-up table to obtain the data A to be written into the current regulation unit and the data to be written into the PWM regulation unit data B;

Next, in step S4: the microcontroller writes the data A into the current adjustment unit, and sets the current value flowing through the LED so that the brightness of the LED reaches or approaches the target value;

Next, in step S5: the microcontroller writes the data B into the PWM adjustment unit, sets the duty ratio of the PWM adjustment unit, and further "finely adjusts" the brightness of the LED to reach the target value. If it is not necessary to further "fine-tune" the LED brightness, here the duty cycle of the PWM adjustment unit is set to 100%. This completes a brightness adjustment process;

With reference to Fig. 2, according to the above method, the present invention provides a driving device capable of adjusting the brightness of a high-power LED, comprising a microcontroller 10, a current regulating unit 20, a PWM regulating unit 30, a driving unit 40, and a high-power LED 50 sequentially connected , the current regulation unit 20 and the PWM regulation unit 30 are connected in parallel between the microcontroller 10 and the driving unit 40 . The current regulation unit 20 is used to dynamically adjust the current value flowing through the LED 50 through the drive unit 40 to control the brightness of the LED, and the PWM control unit 30 is used to change the duty cycle of the output signal to change the LED 50 within a PWM period. The ratio of "on"/"off" to control the brightness of the LED. The microcontroller 10 is used to set the operating parameters of the current regulating unit 20 and the PWM regulating unit 30 at any time, so as to realize the real-time control of the brightness of the LED 50 by the driving device.

With further reference to FIG. 3 , the current regulating unit 20 includes a digital potentiometer 201, a comparator 202, a logic circuit 203, an oscillator 204, and a reference voltage generator 205 connected in sequence; the input terminal of the digital potentiometer 201 is directly connected to In microcontroller 10, terminals A and B are respectively connected to reference voltage generator 205 and ground (GND), and tap W is connected to the negative phase input terminal of comparator 202. The logic circuit 203 and the AND gate 401 in the drive unit 40 In other words, one input end of the AND gate is directly connected to the PWM adjustment unit 30, and the other input end is directly connected to the logic circuit 203 in the current adjustment unit 20; the output of the AND gate 401 is connected to N-channel field effect transistor 402, the S pole of the field effect transistor 402 is connected with the non-inverting input terminal of the comparator 202 and the sampling resistor 405, the D pole is connected with the inductor 404 and the Schottky diode 403, the G pole is connected with the output of the AND gate 401 connected. The other end of the inductor 404 is connected to the high-power LED 50.

The digital potentiometer 201 is used to divide the output voltage of the reference voltage generator 205 to obtain a reference voltage and input it into the comparator 202 . The comparator 202 is used to compare the reference voltage with the sampling voltage provided by the sampling resistor 405, and output different levels according to the comparison result. The logic circuit 203 will determine the on-off time ratio of the field-effect transistor 402 in one oscillation cycle according to the output signals of the comparator 202 and the oscillator 204, and its function is: when power-on reset, output a low-level signal " 0", at the rising edge of the signal output by the oscillator 204, its output is inverted as a high-level signal "1", and at the rising edge of the output signal of the comparator 202, its output is inverted as a low-level signal "0"; the logic The specific implementation method of the circuit is not difficult to realize by a person skilled in the field of electronic circuits, and will not be described in detail here. In addition, the functions of the comparator 202 and the logic circuit 203 can also be realized by an integrated circuit chip NE555. Under the premise of understanding the principle of the present invention and the working mechanism of the NE555, its specific implementation method is a medium-level technology in the field of electronic circuits. It is not difficult for personnel to realize, so it will not be repeated here. The oscillator 204 is used to generate an oscillating signal. The field effect transistor 402 is used to drive the LED 50.

Referring to FIG. 3 again, when the driving device capable of adjusting the brightness of high-power LEDs is working, the microcontroller 10 inputs control data to the digital potentiometer 201 and the PWM generator 30, for example, the output signal of the PWM generator 30 is set at this time. The empty ratio is 100%, and the level is continuously "1"; the digital potentiometer 201 is set to provide an appropriate reference voltage to the comparator 202; the logic circuit 203 outputs a low-level signal "0" at the end of the power-on reset, and the AND gate 401 outputs "0", the field effect transistor 402 is turned off, the sampling voltage provided by the sampling resistor 405 is 0, which is lower than the reference voltage at the negative phase terminal of the comparator 202, and the output of the comparator 202 is "0"; when the oscillator 204 outputs the signal When a rising edge arrives, the output of the trigger logic circuit 203 is reversed to "1", causing the output of the AND gate 401 to be "1". ground; due to the hysteresis characteristic of the inductance 404, the current in the loop will rise according to the integral curve, so that the sampling voltage at the upper end of the sampling resistor 405 also rises according to the integral curve, and the sampling voltage is directly (or amplified by buffering) input to the comparator 202 When the sampling voltage exceeds the reference voltage provided by the digital potentiometer 201 of the comparator 202, the output of the comparator 202 is turned from "0" to "1", and the rising edge of this level change makes the logic The output of the circuit 203 is turned from "1" to "0", the field effect transistor 402 is turned off, and the inductor 404 discharges through the Schottky diode 403 to provide a continuous current for the LED 50; after the field effect transistor 402 is turned off, the sampling resistor 405 The voltage drop at the upper end is 0, the output of the comparator 202 becomes "0", the logic circuit 203 waits for the arrival of the rising edge of the next signal generated by the oscillator 204, and then enters the next working cycle that repeats the above-mentioned actions;

Obviously, in the above technical solution, the average value of the current flowing through the LED is proportional to the time length between the rising edge of the output signal of the oscillator 204 and the rising edge of the output signal of the comparator 202, and this "time length" is determined by comparing The reference level of the comparator 202, the resistance value of the sampling resistor 405, and the inductance value of the inductor 404 are determined. When the resistance value of the sampling resistor 405 and the inductance value of the inductor 404 are fixed, it is completely determined by the reference level of the comparator 202. , so the microcontroller 10 can control the average current flowing through the LED 50 by controlling the reference level output by the digital potentiometer 201, and then control the brightness of the LED 50.

In addition, in this embodiment, a PWM adjustment unit 30 is also provided, and the PWM generator 30 jointly controls the on-off of the field effect transistor 402 through the output of the AND gate 401 and the logic circuit 203. Therefore, the microcontroller 10 can also be controlled by The duty cycle of the output signal of the PWM generator 30 is set to adjust the brightness of the LED. Different from the mechanism that the current regulation unit 20 adjusts the brightness of the LED by adjusting the current flowing through the LED circuit, the PWM regulation unit 30 controls the brightness of the LED by setting the ratio of the LED "on"/"off" duration within a PWM signal cycle. Obviously, the frequency of the PWM signal generated by the PWM adjustment unit 30 is much lower than the signal frequency of the oscillator 204, so that the current adjustment function can work normally. In this embodiment, the PWM mechanism is used as an auxiliary means for adjusting the brightness of the LED.

Because the current regulation mechanism usually cannot adjust the current in the loop to 0, so when the LED is set to be completely off, the PWM mechanism must be used. At this time, the signal duty cycle of the PWM generator 30 is set to 0 by the microcontroller 10 % is enough.

In the above embodiments, the reference voltage of the comparator 202 is provided by the tap W of the digital potentiometer 201 . Another optional solution is that the microcontroller 10 controls a PWM generator, and the PWM signal output by the PWM generator is buffered and the DC level obtained after RC filtering is used as the reference voltage of the comparator 202 .

From the above description of the embodiments of the present invention, it can be seen that the present invention provides two parallel mechanisms for controlling LED brightness: a real-time and dynamic current regulation mechanism that plays a major role and a PWM mechanism that plays an auxiliary role. The microcontroller can adopt appropriate software control strategies to use these two mechanisms to achieve the best effect on the brightness adjustment of high-power LEDs. A successful software control strategy is that the MCU receives an external control signal to obtain the target brightness value of the LED, which is used as the basis for setting the comparator reference voltage or PWM duty cycle. In addition to the need to adjust the LED to very low brightness, generally only the current regulation mechanism is used. When it is necessary to adjust the LED to a very low brightness, first use the current regulation mechanism to adjust the current to the minimum value (such as 2mA), and then use the PWM mechanism to further adjust the LED brightness to a lower level to obtain more gray levels. Because PWM is used in a small current state, it usually does not cause serious EMC (electromagnetic compatibility) problems.

Finally, it should be noted that the above embodiment is only used to illustrate a technical solution of the present invention, not to limit it. With reference to the detailed description of the above embodiments, those of ordinary skill in the art should be able to understand and implement them. At the same time, the technical solutions of the above embodiments can also be modified or replaced with equivalent functions, but if these modifications or replacements do not have significant technical progress , it means still not departing from the essence and scope of the present invention.

Claims (12)

1. A driving method capable of adjusting high-power LED brightness, characterized in that, the method comprises the following steps: Receive the control signal input from the outside, get the brightness data of the LED from it, and get a corresponding value through software calculation or software value look-up table, input the value to a current adjustment unit connected to a drive unit, and set the current flowing through the LED. The magnitude of the current, light the LED and make its brightness reach the target value; Or set the current flowing through the LED according to the above method to initially adjust the brightness of the LED, and then set the signal duty ratio of the PWM adjustment unit connected in parallel with the current adjustment unit to further adjust the brightness of the LED so that it finally reaches target value; The LED is turned off by setting the duty ratio of the signal of the PWM adjustment unit to 0%. 2. The driving method capable of adjusting the brightness of a high-power LED according to claim 1, wherein the current regulating unit comprises a reference voltage generator, and the output voltage of the reference voltage generator is divided by a digital potentiometer After obtaining a reference voltage, the reference voltage is connected to the input terminal of a comparator of the current adjustment unit, and another input signal of the comparator is provided by a sampling resistor connected in series in the LED loop, the comparator The output terminal is connected to the input terminal of a logic circuit. 3. The driving method capable of adjusting the brightness of a high-power LED according to claim 2, wherein the digital potentiometer is controlled by a microcontroller. 4. The driving method capable of adjusting the brightness of high-power LEDs according to claim 2, wherein the reference voltage input to the comparator is obtained after buffering and RC filter processing of the output signal of a PWM generator, the The PWM generator is controlled by a microcontroller. 5. The driving method capable of adjusting the brightness of a high-power LED according to claim 2, wherein an input end of the logic circuit is connected to an output end of an oscillator, and the output of the logic circuit is controlled by the oscillator output of the comparator and the output of the comparator are determined. 6. The driving method capable of adjusting the brightness of a high-power LED according to claim 1, wherein the PWM adjustment unit and the current adjustment unit are controlled by a microcontroller, and the outside world sends a signal to the microcontroller. Control signal to adjust LED brightness. 7. A driving device capable of adjusting the brightness of a high-power LED, comprising a sequentially connected LED drive unit, a current adjustment unit, a PWM adjustment unit and a microcontroller, wherein the current adjustment unit is connected in parallel with the PWM adjustment unit Connected between the microcontroller and the drive unit. 8 . The driving device capable of adjusting the brightness of high-power LED according to claim 7 , wherein the current regulating unit comprises a digital potentiometer, a comparator, and a logic circuit connected in sequence. 9. The driving device capable of adjusting the brightness of high-power LEDs according to claim 7, wherein the driving unit comprises an AND gate, and the two inputs of the AND gate are respectively connected to the PWM adjustment unit, and the current regulation unit connection. 10. The driving device capable of adjusting the brightness of high-power LED according to claim 9, characterized in that, the driving unit also includes a field effect transistor, one end of the field effect transistor is connected to the non-inverting input terminal of the comparator and a sampling The resistors are connected, the other end is connected to the LED loop, and the gate of the field effect transistor is connected to the AND gate. 11. The driving device capable of adjusting the brightness of a high-power LED according to claim 9, wherein the driving unit includes an inductor, and the inductor is connected with a field effect transistor and the LED. 12. The driving device capable of adjusting the brightness of a high-power LED according to claim 9, wherein the driving unit comprises a Schottky diode, the anode of the Schottky diode is connected to the inductor and the field effect transistor, and the cathode is connected to the field effect transistor. The power supply VCC is connected.

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