CN111491412A - Light-emitting diode driving method for local dimming - Google Patents

Abstract

The present invention discloses a light emitting diode driving method for local dimming, comprising the following steps: (a) generating a plurality of pulse width modulation signals, wherein the rising edges/falling edges of the working cycles of the plurality of pulse width modulation signals appear at different time points; (b) a plurality of fixed current sources output a plurality of light emitting diode currents correspondingly according to the plurality of pulse width modulation signals; and (c) the plurality of light emitting diode currents flow through a plurality of light emitting diode strings respectively, so that the plurality of light emitting diode strings respectively present corresponding brightness.

Description

Light-emitting diode driving method applied to local dimming

technical field

The present invention is related to light emitting diodes, and more particularly, to a driving method of light emitting diodes applied to local dimming.

Background technique

Please refer to FIG. 1 . FIG. 1 is a schematic diagram of a general LED local dimming system 1 . As shown in FIG. 1 , in the LED local dimming system 1 , the LED current controller 12 generates n pulse width modulation signals PWM1 - PWMn to a current sink circuit 14 . The current sink circuit 14 includes n fixed current sources 141 to 14n, which respectively change the duty cycle of the output light-emitting diode currents ILED1 to ILEDn according to the duty cycle of the n pulse width modulation signals PWM1 to PWMn, and the n light-emitting diode strings LED1-LEDn will emit different brightness according to the light-emitting diode currents ILED1-ILEDn flowing thereon, and finally the sum of all light-emitting diode currents ILED1-ILEDn LED current ILED_SUM becomes the current load on the light-emitting diode voltage VLED and is controlled by the power supply circuit 10 power supply, as shown in Figure 2.

However, as shown in FIG. 3 , if the n PWM signals PWM1 ˜ PWMn have different duty cycles, the n LED currents ILED1 ˜ILEDn output by the n fixed current sources 141 ˜ 14n also have corresponding Different duty cycles, but traditionally, the rising edges of the duty cycles of the n light-emitting diode currents ILED1-ILEDn all appear at the same time point (for example, time T1), which makes the total light-emitting diode current ILED_SUM at the time of T1 rises instantaneously and cannot be powered by the power supply circuit 10 , resulting in a significant voltage drop of the light-emitting diode voltage VLED, which seriously affects the brightness performance of the light-emitting diode and needs to be improved.

In addition, as shown in FIG. 4, if the n pulse width modulation signals PWM1-PWMn have the same duty cycle, the n light-emitting diode currents ILED1-ILEDn output by the n fixed current sources 141-14n also have corresponding The same duty cycle, but traditionally, the rising edges of the duty cycles of the n light-emitting diode currents ILED1-ILEDn all appear at the same time point (for example, time T1) and the n light-emitting diode currents ILED1-ILEDn The falling edge of the duty cycle will all appear at the same time point (eg time T2), which will cause the total light-emitting diode current ILED_SUM to rise instantaneously at time T1 and drop instantaneously at time T2, and cannot be powered by the power supply circuit 10, As a result, the voltage VLED of the light emitting diode will have a large voltage drop and a voltage rise, which seriously affects the brightness performance of the light emitting diode, and needs to be improved urgently.

SUMMARY OF THE INVENTION

In view of this, the present invention proposes a light-emitting diode driving method applied to local dimming, so as to effectively solve the above-mentioned problems encountered in the prior art.

A specific embodiment according to the present invention is a method for driving a light emitting diode applied to local dimming. In this embodiment, the LED driving method includes the following steps: (a) generating a plurality of PWM signals, wherein the rising/falling edges of the duty cycles of the plurality of PWM signals appear at different time points (b) a plurality of fixed current sources respectively output a plurality of light-emitting diode currents according to the plurality of PWM signals; and (c) the plurality of light-emitting diode currents respectively flow through a plurality of light-emitting diode strings, so that the plurality of light-emitting diode currents The plurality of light emitting diode strings respectively exhibit corresponding brightness.

In one embodiment, the rising edges/falling edges of the duty cycles of the plurality of LED currents also occur at different time points corresponding to the rising edges/falling edges of the duty cycles of the plurality of PWM signals.

In one embodiment, the LED driving method further includes the following steps: providing a LED voltage through a power circuit to generate a total LED current, wherein the total LED current is the plurality of LEDs flowing through the plurality of LED strings respectively. The sum of the currents of the LEDs.

In one embodiment, if the rising edges of the duty cycle of a first PWM signal and a second PWM signal among the plurality of PWM signals occur at a first time and a first time, respectively For two times, the rising edges of the duty cycle of a corresponding first LED current and a second LED current among the plurality of LED currents also appear at the first time and the second time, respectively.

In one embodiment, the sum of the first LED current and the second LED current is the summed LED current, and the summed LED current presents a ramp-up shape at the first time and the second time.

In one embodiment, the power supply circuit provides an LED voltage to generate a total LED current, and the LED voltage exhibits a linear ramp down at the first time and the second time.

In one embodiment, if the falling edges of the duty cycles of a first PWM signal and a second PWM signal among the plurality of PWM signals occur at a third time and a first time, respectively For four times, the falling edges of the duty cycles of a corresponding first LED current and a second LED current among the plurality of LED currents also appear at the third time and the fourth time, respectively.

In one embodiment, the sum of the first LED current and the second LED current is the summed LED current, and the summed LED current exhibits a gradually decreasing step shape at the third time and the fourth time.

In one embodiment, the power circuit provides an LED voltage to generate a total LED current, and the LED voltage exhibits a linear ramp at the third time and the fourth time.

In one embodiment, the plurality of PWM signals have different duty cycles and the plurality of LED currents also have different duty cycles correspondingly.

In one embodiment, the plurality of PWM signals have the same duty cycle and the plurality of LED currents also have the same duty cycle correspondingly.

In one embodiment, the light-emitting diode driving method further includes the following steps: respectively providing different delay times to the plurality of PWM signals, so as to cause the rising edge/falling edge of the duty cycle of the plurality of PWM signals appeared at different points in time.

Compared with the prior art, according to the LED driving method for local dimming of the present invention, the rising edge/falling edge of the duty cycle of a plurality of PWM signals generated by the LED current controller occurs respectively at the At different time points, correspondingly, the rising edge/falling edge of the duty cycle of the multiple LED currents output by the multiple fixed current sources also appear at different time points, so as to avoid the summation of the multiple LED currents. The current suddenly swells or sags. Therefore, the LED voltage provided by the power supply circuit of the present invention does not have the phenomenon of voltage sag or voltage swell in the prior art, so that the LED can maintain normal brightness. Performance.

The advantages and spirit of the present invention can be further understood from the following detailed description of the invention and the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of a general light-emitting diode local dimming system.

FIG. 2 is a timing diagram showing the corresponding duty cycle of the PWM signal and the duty cycle of the LED current.

FIG. 3 shows that when the PWM signal has different duty cycles, the conventional rising edges of the duty cycles of each LED current appear at the same time point, resulting in an instantaneous increase in the total LED current and a large LED voltage. Timing diagram for amplitude dips.

FIG. 4 shows that when the PWM signal has the same duty cycle, the conventional rising edges of the duty cycles of each LED current appear at the same time point and the falling edges all appear at another same time point, resulting in a summation of the LED currents. The timing diagram of the instantaneous swell and the instantaneous sag of the current, and the large sag and the large swell of the voltage of the light-emitting diode.

FIG. 5 is a flowchart illustrating a method for driving an LED for local dimming according to a preferred embodiment of the present invention.

6 shows that when the PWM signal has different duty cycles, the rising edges and falling edges of the duty cycles of the LED currents of the present invention appear at different time points respectively, so that the summation The light-emitting diode current ramps up and down slowly, and can effectively slow down the large-scale slump and large-scale swell of the light-emitting diode voltage.

7 shows that when the PWM signals have the same duty cycle, the rising edges of the duty cycles of the LED currents of the present invention appear at different time points and the falling edges also appear at different time points, so that the summation The light-emitting diode current ramps up and down slowly, and can effectively slow down the large-scale slump and large-scale swell of the light-emitting diode voltage.

Description of main component symbols:

Steps S10～S14

1 LED local dimming system

10 Power circuit

12 LED current controller

14 Current sink circuit

141～14n fixed current source

LED1～LEDn 1st light emitting diode string～nth light emitting diode string

PWM1～PWMn 1st PWM signal～nth PWM signal

ILED1～ILEDn 1st LED current～nth LED current

ILED_SUM Sum LED current

VLED Light Emitting Diode Voltage

t1～t16 Time 1～Time 16

T period

D1～D8 delay time

Detailed ways

Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Elements/members using the same or similar numbers in the drawings and the embodiments are intended to represent the same or similar parts.

A specific embodiment according to the present invention is a method for driving a light emitting diode applied to local dimming. In this embodiment, the LED driving method can be applied to a general LED local dimming system 1 as shown in FIG. 1 , that is, the LED local dimming system 1 may include a power supply circuit 10 , an LED current control The device 12, a current sink circuit 14 and a plurality of light emitting diode strings LED1-LEDn, but not limited thereto.

Please refer to FIG. 5 . FIG. 5 is a flowchart illustrating a method for driving an LED for local dimming in this embodiment. As shown in FIG. 5, the LED driving method may include the following steps:

Step S10 : generating a plurality of pulse width modulation signals (eg, PWM1 to PWMn in FIG. 1 ), wherein the rising edge/falling edge of the working cycle of the plurality of pulse width modulation signals occurs at different time points;

Step S12 : a plurality of fixed current sources (eg, 141 to 14n in FIG. 1 ) respectively output a plurality of light-emitting diode currents (eg, ILED1 to ILEDn in FIG. 1 ) according to the plurality of PWM signals; and

Step S14: The plurality of LED currents respectively flow through the plurality of LED strings (eg, LED1 ˜ LEDn in FIG. 1 ), so that the plurality of LED strings respectively exhibit corresponding brightness.

In practical applications, the plurality of PWM signals (eg, PWM1 ˜ PWMn in FIG. 1 ) may have the same or different duty cycles. When the plurality of PWM signals have different duty cycles, the plurality of fixed current sources (eg, 141˜14n in FIG. 1 ) respectively output the plurality of light-emitting diodes according to the plurality of PWM signals The currents (eg, ILED1 ˜ILEDn in FIG. 1 ) also have different duty cycles; conversely, when the multiple PWM signals (eg, PWM1 ˜ PWMn in FIG. 1 ) have the same duty cycle, the Each light-emitting diode current (eg, ILED1 ˜ILEDn in FIG. 1 ) also has the same duty cycle correspondingly.

It should be noted that, since the rising edge/falling edge of the duty cycle of the plurality of PWM signals (eg, PWM1 to PWMn in FIG. 1 ) of the present invention needs to appear at different time points and cannot appear at the same time point, Therefore, the plurality of fixed current sources (for example, 141 to 14n in FIG. 1 ) respectively output the duty cycles of the plurality of LED currents (for example, ILED1 to ILEDn in FIG. 1 ) according to the plurality of PWM signals. The rising/falling edges of , also appear at different time points and cannot appear at the same time point.

For example, if the first PWM signal (eg PWM1 in FIG. 1 ) and the second PWM signal (eg PWM1 to PWMn in FIG. 1 ) and The rising edges of the duty cycle of PWM2 in FIG. 1 appear at different time points (eg, the first time and the second time) respectively. As shown in FIG. The rising edges of the duty cycles of the first light-emitting diode current ILED1 and the second light-emitting diode current ILED2 also occur at different time points (ie, the first time t1 and the second time t2 ). Similarly, if the falling edges of the duty cycles of the first PWM signal (such as PWM1 in FIG. 1 ) and the second PWM signal (such as PWM2 in FIG. 1 ) appear at different time points (such as the first three times and a fourth time), the falling edges of the duty cycles of the first LED current ILED1 and the second LED current ILED2 also appear at different time points (ie, the third time and the fourth time).

In addition, the LED driving method of the present invention can also provide a LED voltage (eg, VLED in FIG. 1 ) through a power supply circuit (eg, 10 in FIG. 1 ) to generate a total LED current (eg, ILED_SUM in FIG. 1 ), where The total LED current is the sum of the multiple LED currents (eg, ILED1 ˜ILED8 ) flowing through the multiple LED strings (eg, LED1 ˜ LED8 ) respectively, but not limited thereto.

Referring to the above example, as shown in FIG. 6 , since the rising edges of the duty cycles of the first light-emitting diode current ILED1 and the second light-emitting diode current ILED2 of the present invention occur at different time points (ie, the first time t1 and the second time, respectively) t2), and the total LED current ILED_SUM is the sum of the first LED current ILED1 and the second LED current ILED2. The third light emitting diode current ILED3 to the eighth light emitting diode current ILED8 can also be deduced in the same way, which will not be described in detail here. Therefore, the total light-emitting diode current ILED_SUM of the present invention exhibits a gradual rise from the first time t1 to the eighth time t8, and does not rise instantaneously at the first time t1 as in the prior art. As for the power supply circuit 10 to provide The voltage VLED of the light-emitting diodes shows a linear and gradual decrease from the first time t1 to the eighth time t8, and the phenomenon of voltage sharp drop as in the prior art will not occur.

Similarly, since the falling edges of the duty cycles of the first light-emitting diode current ILED1 and the second light-emitting diode current ILED2 of the present invention occur at different time points (ie, the fifteenth time t15 and the sixteenth time t16 ), and the sum of The light emitting diode current ILED_SUM is the sum of the first light emitting diode current ILED1 and the second light emitting diode current ILED2. The third light emitting diode current ILED3 to the eighth light emitting diode current ILED8 can also be deduced in the same way, which will not be described in detail here. Therefore, the total light-emitting diode current ILED_SUM of the present invention will show a gradual drop from the ninth time t9 to the sixteenth time t16, and will not drop instantaneously as in the prior art; as for the light-emitting diode voltage provided by the power circuit 10 The VLED exhibits a linear ramp from the ninth time t9 to the sixteenth time t16 , without the phenomenon of a large voltage surge as in the prior art.

In another embodiment, as shown in FIG. 7 , when the plurality of PWM signals (eg, PWM1 - PWM8 ) have the same duty cycle, the rising edges of the duty cycles of the plurality of light-emitting diode currents ILED1 - ILED8 are respectively Occurs at different time points (ie, the first time t1 to the eighth time t8 ), so that the total light-emitting diode current ILED_SUM rises slowly, which can effectively slow down the large voltage drop phenomenon of the light-emitting diode voltage VLED.

Similarly, the falling edges of the duty cycles of the plurality of light-emitting diode currents ILED1-ILED8 also appear at different time points (ie, the first time t1-eighth time t8), so that the total light-emitting diode current ILED_SUM decreases slowly. It can effectively slow down the large voltage rise phenomenon of the light emitting diode voltage VLED.

In addition, as shown in FIG. 7 , the LED driving method of the present invention may further provide different delay times (eg D1 to D8 ) for the plurality of PWM signals (eg PWM1 to PWM8 ), so as to ensure the The rising edges of the duty cycles of a plurality of PWM signals (eg, PWM1 to PWM8) will appear at different time points (ie, the first time t1 to the eighth time t8) and will not appear at the same time point, thereby ensuring that the The rising edges of the duty cycles of the plurality of LED currents ILED1-ILED8 also appear at different time points (ie, t1-t8) and not at the same time point, so that the total LED current ILED_SUM increases slowly , and can effectively slow down the phenomenon that the voltage of the light-emitting diode VLED drops sharply.

Similarly, the delay times D1-D8 can also ensure that the falling edges of the duty cycles of the plurality of PWM signals (eg, PWM1-PWM8) will appear at different time points (ie, the ninth time t9 to the sixteenth time t16). ) will not appear at the same time point, thereby ensuring that the falling edges of the duty cycles of the plurality of light-emitting diode currents ILED1-ILED8 will also appear at different time points (that is, the ninth time t9 to the sixteenth time t16). ) does not appear at the same time point, so that the total light-emitting diode current ILED_SUM decreases slowly, which can effectively slow down the large-scale surge of the light-emitting diode voltage VLED.

Compared with the prior art, according to the LED driving method for local dimming of the present invention, the rising edge/falling edge of the duty cycle of a plurality of PWM signals generated by the LED current controller occurs respectively at the At different time points, correspondingly, the rising edge/falling edge of the duty cycle of the multiple LED currents output by the multiple fixed current sources also appear at different time points, so as to avoid the summation of the multiple LED currents. The current suddenly swells or sags. Therefore, the voltage of the light-emitting diode provided by the power supply circuit of the present invention will not have the phenomenon of voltage sag or voltage swell in the prior art, so that the light-emitting diode can maintain normal brightness. Performance.

Claims (12)

1. A light-emitting diode driving method applied to local dimming, characterized in that, comprising the following steps: (a) generating a plurality of PWM signals, wherein the rising edge/falling edge of the working cycle of the plurality of PWM signals occurs at different time points; (b) a plurality of fixed current sources respectively output a plurality of LED currents according to the plurality of PWM signals; and (c) The plurality of light-emitting diode currents flow through the plurality of light-emitting diode strings respectively, so that the plurality of light-emitting diode strings respectively exhibit corresponding brightness. 2 . The LED driving method for local dimming according to claim 1 , wherein the rising edge/falling edge of the duty cycle of the LED currents corresponds to the pulse width modulation signal. 3 . The rising/falling edge of the duty cycle also occurs at different points in time. 3. The light-emitting diode driving method applied to local dimming according to claim 1, further comprising the following steps: A LED voltage is supplied through a power circuit to generate a sum LED current, wherein the sum LED current is the sum of the LED currents flowing through the LED strings respectively. 4 . The light-emitting diode driving method for local dimming according to claim 1 , wherein if a first PWM signal and a second PWM signal among the plurality of PWM signals are used, 4 . The rising edge of the duty cycle of the variable signal occurs at a first time and a second time respectively, and the corresponding one of the plurality of LED currents and the rising edge of the duty cycle of a second LED current The edges also appear at the first time and the second time, respectively. 5 . The LED driving method for local dimming according to claim 4 , wherein the sum of the first LED current and the second LED current is a total LED current, and the sum emits light. 6 . The diode current presents a ramp-up step shape at the first time and the second time. 6. The LED driving method for local dimming as claimed in claim 5, wherein a power supply circuit provides a LED voltage to generate the total LED current, and the LED voltage is at the first time And the second time shows a linear decline. 7 . The light-emitting diode driving method for local dimming according to claim 1 , wherein if a first PWM signal and a second PWM signal among the plurality of PWM signals are used, 8 . The falling edge of the duty cycle of the variable signal occurs at a third time and a fourth time, respectively, and the corresponding one of the plurality of LED currents and a corresponding drop of the duty cycle of a second LED current. The edges also appear at the third time and the fourth time, respectively. 8 . The LED driving method for local dimming according to claim 7 , wherein the sum of the first LED current and the second LED current is a total LED current, and the sum is emitting light. 9 . The diode current exhibits a step shape with a gradual decrease at the third time and the fourth time. 9 . The LED driving method for local dimming as claimed in claim 8 , wherein a power supply circuit provides a LED voltage to generate the total LED current, and the LED voltage is at the third time. 10 . And the fourth time showed a linear slow rise. 10 . The light-emitting diode driving method of claim 1 , wherein the plurality of PWM signals have different duty cycles and the plurality of light-emitting diode currents also have different correspondingly. 11 . Working period. 11 . The light-emitting diode driving method for local dimming according to claim 1 , wherein the plurality of PWM signals have the same duty cycle and the plurality of light-emitting diode currents also have the same correspondingly. 12 . Working period. 12. The light-emitting diode driving method for local dimming according to claim 1, further comprising the following steps: Different delay times are respectively provided for the plurality of PWM signals, so that the rising edges/falling edges of the duty cycles of the plurality of PWM signals appear at different time points.

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