LED light-adjustment driver module, backlight module and liquid crystal display device

1. Field of the Invention

The present invention relates to the field of LED light-adjustment techniques, and in particular to an LED light-adjustment driver module, backlight module and liquid crystal display device.

2. The Related Arts

Due to the advantages of low energy-consumption, environmental friendliness and high efficiency, the LED backlight is widely adopted in many applications.

Because the luminance of the backlight must be adjusted, light-adjustment must be performed on LED. At present, the majority of the light-adjustment uses pulse width modulation (PWM) technique. Referring to FIG. 1 , FIG. 1 is a schematic view showing the structure of a known LED light-adjustment driver circuit. The LED light-adjustment driver circuit comprises a comparator A, a current source S and a capacitor C; one end of capacitor C being connected a first input end of the comparator A, and the other end being grounded. The current source S is connected to the first input end of the comparator A. A second input end of the comparator A inputs a threshold voltage V. The LED light-adjustment driver circuit will respond to PWM signal P. When PWM signal P is high, current source S outputs a current to charge capacitor C. When the voltage of capacitor C rises to exceed the threshold voltage V, the comparator A outputs high for adjusting the luminance of the LED backlight.

However, when the known LED light-adjustment driver circuit adjusts the luminance of the LED backlight, a flickering problem exists. In the condition that the duty cycle of the PWM signal P is small, when the LED backlight is lit for the second time, because a voltage exists on the capacitor C, the voltage is backlight, but will only last for a short time. Then, the current source S charges the capacitor C. Because the duty cycle of the PWM signal P is small, the charge time for the capacitor C is short. Therefore, the voltage on capacitor C will not reach the threshold voltage V. Only after the PWM signal P goes through a plurality of high levels, the voltage on capacitor C can exceed the threshold voltage V, and the comparator A can output high level to light LED backlight. During lighting the LED backlight, because the voltage on capacitor C takes longer time to reach the threshold voltage V, a flickering problem occurs, which affects the lighting quality.

The technical issue to be addressed by the present invention is to provide an LED light-adjustment driver module, backlight module and liquid crystal display device, to avoid the flickering problem.

The present invention provides an LED light-adjustment driver module, which comprises: a duty cycle detection unit, a current output unit, a comparator and a capacitor unit; the first input end of the comparator being connected to capacitor unit, the second input end of the comparator inputting a default threshold voltage; the current output unit being connected to the capacitor unit for charging the capacitor unit; the duty cycle detection unit being for receiving externally inputted PWM signal and detecting the duty cycle of the PWM signal; when the duty cycle detection unit detecting the duty cycle being less than a default threshold, the current output unit increasing the output current or the capacitor unit reducing the capacitance provided to reduce the time for the voltage of the capacitor unit to reach the threshold voltage.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the current output unit outputs a first current; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the current output unit outputs a second current; wherein the second current is smaller than the first current.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the capacitor unit provides a first capacitance; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the capacitor unit provides a second capacitance; wherein the first capacitance is smaller than the second capacitance.

According to a preferred embodiment of the present invention, the current output unit comprises a first control switch, a first current source and a second current source; the capacitor unit comprises a first capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted to the first control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted to the first control switch; the first control switch comprises a first end, a second end, a third end and a fourth end; the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end; the first current source is connected to the second end of the first control switch and outputs a first current; the second current source is connected to the third end of the first control switch and outputs a second current; one end of the first capacitor is connected to the fourth end of the first control switch and the first input end of the comparator; the other end of the first capacitor is grounded.

According to a preferred embodiment of the present invention, the current output unit comprises a third current source; the capacitor unit comprises a second control switch, a second capacitor and a third capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted the second control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted the second control switch; the second control switch comprises a first end, a second end, a third end and a fourth end; the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end; one end of the second capacitor is connected to the second end of the second control switch; the other end of the second capacitor is grounded; the second capacitor provides a first capacitance; one end of the third capacitor is connected to the third end of the second control switch; the other end of the third capacitor is grounded; the third capacitor provides a second capacitance; the third current source is connected to the fourth end of the second control switch and the first input end of the comparator.

According to a preferred embodiment of the present invention, the duty cycle detection unit, the current output unit and the comparator are packaged in a single package.

The present invention provides a backlight module, which comprises: an LED light and an LED light-adjustment driver module; the LED light-adjustment driver module further comprising: a duty cycle detection unit, a current output unit, a comparator and a capacitor unit; the first input end of the comparator being connected to capacitor unit, the second input end of the comparator inputting a default threshold voltage; the current output unit being connected to the capacitor unit for charging the capacitor unit; the duty cycle detection unit being for receiving externally inputted PWM signal and detecting the duty cycle of the PWM signal; when the duty cycle detection unit detecting the duty cycle being less than a default threshold, the current output unit increasing the output current or the capacitor unit reducing the capacitance provided to reduce the time for the voltage of the capacitor unit to reach the threshold voltage; the output end of the comparator outputting a high level or a low level to adjust the luminance of the LED light.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the current output unit outputs a first current; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the current output unit outputs a second current; wherein the second current is smaller than the first current.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the capacitor unit provides a first capacitance; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the capacitor unit provides a second capacitance; wherein the first capacitance is smaller than the second capacitance.

According to a preferred embodiment of the present invention, the current output unit comprises a first control switch, a first current source and a second current source; the capacitor unit comprises a first capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted to the first control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted to the first control switch; the first control switch comprises a first end, a second end, a third end and a fourth end, the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end; the first current source is connected to the second end of the first control switch and outputs a first current; the second current source is connected to the third end of the first control switch and outputs a second current; one end of the first capacitor is connected to the fourth end of the first control switch and the first input end of the comparator; the other end of the first capacitor is grounded.

According to a preferred embodiment of the present invention, the current output unit comprises a third current source; the capacitor unit comprises a second control switch, a second capacitor and a third capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted the second control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted the second control switch; the second control switch comprises a first end, a second end, a third end and a fourth end; the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end; one end of the second capacitor is connected to the second end of the second control switch; the other end of the second capacitor is grounded; the second capacitor provides a first capacitance; one end of the third capacitor is connected to the third end of the second control switch; the other end of the third capacitor is grounded: the third capacitor provides a second capacitance; the third current source is connected to the fourth end of the second control switch and the first input end of the comparator.

According to a preferred embodiment of the present invention, the duty cycle detection unit, the current output unit and the comparator are packaged in a single package.

The present invention provides a liquid crystal display device, which comprises: a backlight module; the backlight module comprising: an LED light and an LED light-adjustment driver module; the LED light-adjustment driver module further comprising: a duty cycle detection unit, a current output unit, a comparator and a capacitor unit; the first input end of the comparator being connected to capacitor unit, the second input end of the comparator inputting a default threshold voltage; the current output unit being connected to the capacitor unit for charging the capacitor unit; the duty cycle detection unit being for receiving externally inputted PWM signal and detecting the duty cycle of the PWM signal; when the duty cycle detection unit detecting the duty cycle being less than a default threshold, the current output unit increasing the output current or the capacitor unit reducing the capacitance provided to reduce the time for the voltage of the capacitor unit to reach the threshold voltage, the output end of the comparator outputting a high level or a low level to adjust the luminance of the LED light.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the current output unit outputs a first current; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the current output unit outputs a second current; wherein the second current is smaller than the first current.

According to a preferred embodiment of the present invention, when the duty cycle detection unit detects the duty cycle being less than the default threshold, the capacitor unit provides a first capacitance; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, the capacitor unit provides a second capacitance; wherein the first capacitance is smaller than the second capacitance.

According to a preferred embodiment of the present invention, the current output unit comprises a first control switch, a first current source and a second current source; the capacitor unit comprises a first capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted to the first control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted to the first control switch; the first control switch comprises a first end, a second end, a third end and a fourth end; the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end: the first current source is connected to the second end of the first control switch and outputs a first current; the second current source is connected to the third end of the first control switch and outputs a second current; one end of the first capacitor is connected to the fourth end of the first control switch and the first input end of the comparator; the other end of the first capacitor is grounded.

According to a preferred embodiment of the present invention, the current output unit comprises a third current source; the capacitor unit comprises a second control switch, a second capacitor and a third capacitor; wherein when the duty cycle detection unit detects the duty cycle being less than the default threshold, a first control signal is transmitted the second control switch; when the duty cycle detection unit detects the duty cycle being larger than the default threshold, a second control signal is transmitted the second control switch; the second control switch comprises a first end, a second end, a third end and a fourth end; the first end is connected to the duty cycle detection unit; when the first end receives the first control signal; the fourth end is connected to the second end; when the first end receives the second control signal; the fourth end is connected to the third end; one end of the second capacitor is connected to the second end of the second control switch; the other end of the second capacitor is grounded; the second capacitor provides a first capacitance; one end of the third capacitor is connected to the third end of the second control switch; the other end of the third capacitor is grounded; the third capacitor provides a second capacitance; the third current source is connected to the fourth end of the second control switch and the first input end of the comparator.

According to a preferred embodiment of the present invention, the duty cycle detection unit, the current output unit and the comparator are packaged in a single package.

In summary, through increasing the output current of the current output unit or reducing the capacitance provided by the capacitor unit, the LED light-adjustment driver module, backlight module and LCD of the present invention can increase the charging speed of the capacitor unit to reduce the time required for the voltage of the capacitor unit to reach the threshold voltage, avoid the flickering problem and improve the lighting quality.

To make the technical solution of the embodiments according to the present invention, a brief description of the drawings that are necessary for the illustration of the embodiments will be given as follows. Apparently, the drawings described below show only example embodiments of the present invention and for those having ordinary skills in the art, other drawings may be easily obtained from these drawings without paying any creative effort. In the drawings:

FIG. 1 is a schematic view showing the structure of a known LED light-adjustment driver circuit;

FIG. 2 is a schematic view showing the circuit of the first embodiment of an LED light-adjustment driver module according to the present invention:

FIG. 3 is a schematic view showing the circuit of the second embodiment of an LED Light-adjustment driver module according to the present invention; and

FIG. 4 is a schematic view showing the circuit of the third embodiment of an LED light-adjustment driver module according to the present invention.

The following provides a clear and complete description of the technical solution according to the present invention using the drawing and the embodiment. Apparently, the drawings described below show only example embodiments of the present invention, instead of all embodiments. For other embodiments based on the disclosed drawings and embodiments, and obtained by those having ordinary skills in the art without paying any creative effort are also within the scope of the present invention,

Referring to FIG. 2 , FIG. 2 is a schematic view showing the circuit of the first embodiment of an LED light-adjustment driver module according to the present invention. The LED light-adjustment driver module comprises a duty cycle detection unit M, a current output unit S 0 , a comparator B and a capacitor unit C 0 .

The first input end of the comparator B is connected to the capacitor unit C 0 , the second input end of the comparator B inputs a default threshold voltage VT; wherein the first input end is a positive input end, and the second input end is an inverting input end. Alternatively, the first input end is an inverting input end and the second input end is a positive input end.

The current output unit S 0 is connected to capacitor unit C 0 for charging the capacitor unit C 0 .

The duty cycle detection unit M is for receiving the externally inputted PWM signal P and detecting the duty cycle of the PWM signal P.

In the instant embodiment, the duty cycle detection unit M, the current output unit S 0 and the comparator B are all packaged in a single package.

When the duty cycle detection unit M detects the duty cycle is less than the default threshold, the current output unit S 0 increases the output current or the capacitor unit C 0 reduces the provided capacitance to reduce the time required for the voltage of the capacitor unit C 0 to reach the default threshold voltage VT. In other words, under the condition of maintaining the capacitance provided the capacitor unit C 0 , the current output unit S 0 must increase the outputted current; alternatively, under the condition of maintaining the outputted current from current output unit S 0 , the capacitor unit C 0 provides a smaller capacitance. In this manner, regardless of increasing the current or reducing the capacitance, the charging speed for the capacitor unit CO will increase so that the voltage of the capacitor unit C 0 can reach the default threshold voltage VT sooner. As such, the comparator B can compare faster to avoid flickering problem.

Referring to FIG. 3 , FIG. 3 is a schematic view showing the circuit of the second embodiment of an LED light-adjustment driver module according to the present invention. The LED light-adjustment driver module comprises a duty cycle detection unit M 1 , a current output unit S 20 , a comparator B 1 and a capacitor unit C 20 . The duty cycle detection unit M 1 and, the comparator B 1 of the instant embodiment have the same features as those in the first embodiment, and thus the description will not be repeated here.

In the instant embodiment, the capacitance provided by the capacitor unit C 20 remains unchanged, and the current output unit S 20 increase outputted current. When the duty cycle detection unit M 1 detects the duty cycle is less than the default threshold, the current output unit S 20 outputs a first current; the duty cycle detection unit M 1 detects the duty cycle is larger than the default threshold, the current output unit S 20 outputs a second current; wherein the second current is smaller than the first current.

Specifically, the current output unit 520 comprises a first control switch K 1 , a first current source S 1 and a second current source S 2 ; the capacitor unit C 20 comprises a first capacitor C 1 .

When duty cycle detection unit M 1 detects the duty cycle of the PWM signal P is less than a default threshold, a first control signal is transmitted to the first control switch K 1 ; when duty cycle detection unit M 1 detects the duty cycle of the PWM signal P is larger than a default threshold, a second control signal is transmitted to the first control switch K 1 .

The first control switch K 1 comprises a first end NC 1 , a second end NC 2 , a third end NC 3 and a fourth end NC 4 . The first end NC 1 is connected to the duty cycle detection unit M 1 . When the first end NC 1 receives the first control signal, the fourth end NC 4 is connected to the second end NC 2 ; and when the first end NC 1 receives the second control signal, the fourth end NC 4 is connected to third end NC 3 .

The first current source S 1 is connected to the second end NC 2 of the first control switch K 1 and outputs a first current; and the second current source S 2 is connected to the third end NC 3 of the first control switch K 1 and outputs a second current.

One end of the first capacitor C 1 is connected to the fourth end NC 4 of the first control switch K 1 and the first input end of the comparator B 1 ; and the other end of the first capacitor C 1 is grounded.

Therefore, the increasing outputted current by the current output unit S 0 only occurs when the duty cycle is less than a default threshold. It is known to those with ordinary skill in the field that when the output current increases, the voltage of the capacitor unit C 20 must start at 0 at the moment when the power switches on so that the entire LED light-adjustment driver module is in a near-short state and generates a huge peak current. This peak current is also called inrush current (or surge current). The inrush current is usually 20-1000 times of the normal operating current peak, and can bring much trouble to power supply manufacturer, especially when the application demands high reliability and safety. Therefore, industry defines restrict specification for the inrush current.

If the current output unit S 20 increases the current regardless that the duty cycle is less or larger than the default threshold, the inrush current will be generated, which is bad for the LED light-adjustment driver module. Therefore, in the instant embodiment, the current output unit S 20 generates a first current only when the duty cycle is less than the default threshold, and generates a second current only when the duty cycle is larger than the default threshold so that the inrush current can be avoided to improve the reliability and safety of the LED light-adjustment driver module.

Through disposing the first control switch K 1 the LED light-adjustment driver module of the present embodiment can switch between the first current source S 1 and the second current source S 2 to output different current according to the output of the duty cycle detection unit M 1 . When the duty cycle is less than the default threshold, the LED light-adjustment driver module provides a larger current to the first capacitor C 1 ; when the duty cycle is larger than the default threshold, the LED light-adjustment driver module can suppress the inrush current to improve operation reliability.

Referring to FIG. 4 , FIG. 4 is a schematic view showing the circuit of the third embodiment of an LED light-adjustment driver module according to the present invention. The LED light-adjustment driver module comprises a duty cycle detection unit M 2 , a current output unit S 30 , a comparator B 2 and a capacitor unit C 30 . The duty cycle detection unit M 2 and the comparator B 2 of the instant embodiment have the same features as those in the first embodiment, and thus the description will not be repeated here.

In the instant embodiment, the current outputted by the current output unit. S 30 remains unchanged, and the capacitor unit. C 30 reduces the provided capacitance. When the duty cycle detection unit M 2 detects the duty cycle is less than the default threshold, the capacitor unit C 30 provides a first capacitance; when the duty cycle detection unit M 2 detects the duty cycle is larger than the default, threshold, the capacitor unit C 30 provides a second capacitance; wherein the first capacitance is less than the second capacitance.

Specifically, the current output unit S 30 comprises a third current source S 3 , and the capacitor unit C 30 comprises a second control switch K 2 , a second capacitor C 2 and a third capacitor C 3 .

When duty cycle detection unit M 1 detects the duty cycle of the PWM signal P is less than a default threshold, a first control signal is transmitted to the second control switch K 2 ; when duty cycle detection unit M 1 detects the duty cycle of the PWM signal P is larger than a default threshold, a second control signal is transmitted to the second control switch K 2 .

The second control switch K 2 comprises a first end N 01 , a second end NO 2 , a third end NO 3 and a fourth end N 04 . The first end NO 1 is connected to the duty cycle detection unit M 2 . When the first end NO 1 receives the first control signal, the fourth end N 04 is connected to the second end NO 2 ; and when the first end NO 1 receives the second control signal, the fourth end N 04 is connected to third end NO 3 .

One end of the second capacitor C 2 is connected to the second end NO 2 of the second control switch K 2 , and the other end of the second capacitor C 2 is grounded. The second capacitor C 2 provides a first capacitance. One end of the third capacitor C 3 is connected to third end NO 3 of the second control switch K 2 , and the other end of the third capacitor C 3 is grounded. The third capacitor C 3 provides a second capacitance.

The third current source S 3 is connected to the fourth end NO 4 of the second control switch K 2 and the first input end of the comparator B 2 .

For the capacitor unit C 30 , the reduction of provided capacitance only occurs during the duty cycle less than the default threshold, and can avoid the occurring of inrush current. The specific realization is similar to the current output unit S 20 of the second embodiment. The description will not be repeated here.

Through disposing the second control switch K 2 , the LED light-adjustment driver module of the present embodiment can switch between the second capacitor C 2 and the third capacitor C 3 to provide different capacitance according to the output of the duty cycle detection unit M 2 . When the duty cycle is less than the default threshold, the LED light-adjustment driver module provides a smaller capacitance to the third current source S 3 ; when the duty cycle is larger than the default threshold, the LED light-adjustment driver module can suppress the inrush current to improve operation reliability.

The present invention further provides a backlight module. The backlight module comprises: an LED light and the LED light-adjustment driver module. The output end of the comparator outputting a high level or a low level to adjust the luminance of the LED light to achieve the object of light adjustment.

The present invention further provides a liquid crystal display device. The liquid crystal display device comprises the above backlight module. The remaining structure of the backlight module and the liquid crystal display device refer to the known technique, and the description will not be repeated here.

As such, the LED light-adjustment driver module, backlight module and LCD of the present invention can increase the charging speed of the capacitor unit to reduce the time required for the voltage of the capacitor unit to reach the threshold voltage, avoid the flickering problem and improve the lighting quality. In addition, through disposing the first control switch or the second control switch, the present invention can avoid the inrush current to improve the operation reliability.

Embodiments of the present invention have been described, but not intending to impose any unduly constraint to the appended claims. Any modification of equivalent structure or equivalent process made according to the disclosure and drawings of the present invention, or any application thereof, directly or indirectly, to other related fields of technique, is considered encompassed in the scope of protection defined by the clams of the present invention.