CN101738784A - Light emitting diode array of liquid crystal display, driving system thereof and liquid crystal display - Google Patents

Abstract

The invention provides a light emitting diode array of a liquid crystal display, and also provides a driving system of the light emitting diode of the liquid crystal display and the liquid crystal display. The light emitting diode array comprises a plurality of first light emitting diodes controlled by pulse width modulation signals and a plurality of second light emitting diodes powered by direct current constant current, and the display brightness of the liquid crystal display is uniformly adjusted by the staggered arrangement of the first light emitting diodes and the second light emitting diodes. The staggered array provided by the invention can simplify the design of the backlight drive of the light emitting diode and can reduce the cost of the drive IC.

Description

Light-emitting diode array of liquid crystal display, its driving system and liquid crystal display

technical field

The invention relates to a light-emitting diode array, in particular to a light-emitting diode array of a liquid crystal display.

Background technique

Cold cathode fluorescent lamp (cold cathode fluorescent lamp, CCFL) has traditionally been used as the light source for the backlight of liquid crystal display (liquid crystal display, LCD). Cold cathode fluorescent tubes may cause environmental pollution due to the use of mercury gas. Similarly. CCFLs have a low response rate and low color reproducibility, and are not sufficient to reduce the weight and size of LCD panels. Furthermore, high start-up and operating voltages are required, and the light source of the LCD backlight is the most power-consuming part of the system. Therefore, under the condition of increasingly strict power constraints, cold-cathode fluorescent tubes have gradually been replaced by light-emitting diodes (LEDs) at present. Light Emitting Diode, LED) replaced.

Compared to CCFLs, LEDs are environment-friendly and can respond quickly in nanoseconds, making them more efficient in video signal flow. In addition, the LEDs can be pulsed to reproduce colors at 100% or more, and the brightness and color temperature can be changed arbitrarily by adjusting the amount of light of the red, green, and blue LEDs. LEDs also have the advantage of resulting in lighter weight and smaller LCD panels. Therefore, light emitting diodes are actively employed as backlight sources for liquid crystal display panels.

Light-emitting diodes are current-driven devices whose brightness is proportional to the forward current. There are two ways to control the forward current.

The first method is to use the LED V-I curve, generally using a voltage source and a rectifier resistor, to determine the voltage required to provide the LED to generate the desired forward current. But this method has some disadvantages, for example: any change in the forward voltage of the light-emitting diode will cause a change in the current of the light-emitting diode.

Assuming that the fixed voltage is 3.6V and the current is 20mA, when the voltage changes to 4.0V, the specific voltage change caused by temperature or manufacturing changes will cause a large change of 30% in the current. Therefore, when there is a large change in the forward voltage, it will lead to a greater change in the forward current. In addition, the voltage drop and power consumption will also waste power and reduce the service life of the LED.

The second method is to use a fixed current to drive the LED. The fixed current cancels out the change in current caused by the change in forward voltage, thus producing a fixed brightness of the LED. Utilizing a fixed current only requires adjusting the voltage across the current sense resistor, not the output voltage of the power supply. The power supply voltage and the value of the current sense resistor determine the LED current. When driving multiple LEDs, a fixed current can be achieved in each LED simply by connecting them in series.

In addition, many LCD display backlight applications require brightness adjustment. In this part, two dimming methods can be used, namely analog or pulse width modulation (Pulse Width Modulation, PWM) method. Using analog dimming, as everyone is familiar with, increases the current by 50% on the LED, so that the brightness can be increased by 50%. But this method has disadvantages, that is, there will be a color shift of the LED, and an analog control signal is required. Therefore, this mode is generally not used very much.

Pulse Width Modulation is relatively common at present, and it is the best way to adjust the brightness of light-emitting diodes. The use of pulse width modulation has become popular with the increase of digital control logic circuits. Pulse Width Modulation provides a simple method for digital control logic to create analog-equivalent functions.

Please refer to FIG. 1 , which is a simple circuit for controlling the brightness of an LED through pulse width modulation and the corresponding pulse width modulation waveform. When the switch of the circuit is turned on (on), the waveform of the pulse width modulation is in the on position, and when the switch of the circuit is turned off (off), the waveform of the pulse width modulation is in the off position.

If the length of time the switch is in the "on" position is shortened, the LED will dim. In the example of FIG. 1, the light emitting diodes are shown to be on 50% of the time and off 50% of the time. Using a repetitive signal to control the light-emitting diode may be cut into several segments because of the cycle. Using a single cycle, it is completed within one cycle, from "off" to "on" and back to "off". The signal can be further characterized in terms of the signal period, that is, the ratio of the "on" time divided by the period. A long signal period will brighten the LED, and a short signal period will dim the LED.

The key to using PWM to adjust the brightness is that in order to ensure that the user's eyes cannot see the pulse phenomenon of PWM, generally speaking, the frequency of the PWM signal must be higher than 100 Hz.

As mentioned above, many publications have proposed to control the brightness of the light emitting diodes in the backlight module by pulse width modulation technology, so as to improve the efficiency of the backlight and maintain the uniformity of the brightness of the backlight. In addition, it can reduce the temperature of the backlight module and reduce energy loss, as shown in US Patent US 20070091057 and EU Patent EP 1780701.

In addition, Chinese patent CN 11013559 discloses a light emitting diode brightness control circuit, the main feature of which is to individually control the light emitting diodes of at least one pair of backlight modules through pulse width modulation, and the brightness of the remaining light emitting diodes will not be affected during the control.

However, adjusting the brightness through pulse width modulation requires a pulse width modulation driving circuit (PWMIC) to drive. When the number of light emitting diodes increases, the number of pulse width modulation driving circuits also increases, thus increasing the manufacturing cost and making the backlight of the light emitting diodes Driver design is becoming more complex.

Contents of the invention

In view of the above-mentioned background of the invention, in order to meet the needs of certain interests in the industry, the present invention provides a light-emitting diode (Light Emitting Diode, LED) array of a liquid crystal display (liquid crystal display, LCD) that can be used to solve the problems of the above-mentioned traditional liquid crystal display. goals that can be achieved.

An object of the present invention is to provide a light-emitting diode array of a liquid crystal display, which includes a plurality of first light-emitting diodes controlled by a pulse width modulation (Pulse Width Modulation, PWM) signal and a plurality of second light-emitting diodes powered by a constant current of direct current. Diodes, wherein at least one first light-emitting diode constitutes a dimming module to adjust the brightness of the liquid crystal display. And at least one second light emitting diode constitutes a constant light module to provide a constant light source for the liquid crystal display, and the dimming module and the constant light module are arranged alternately.

Another object of the present invention is to provide a light-emitting diode driving system of a liquid crystal display, which includes a multi-channel (channel) dimming area, a multi-channel constant light area, a plurality of pulse width modulation driving circuits (PWM IC) and a constant current power supply device . Each of the aforementioned dimming areas includes multiple series-connected light-adjusting modules, and each constant-light area includes multiple series-connected constant-light modules, wherein the multiple light-adjusting modules and the multiple constant-light modules are alternately arranged. Each of the above pulse width modulation drive circuits outputs pulse width modulation signals to part of the multi-channel dimming area to adjust the brightness of the first light emitting diode, and the constant current power supply device outputs a stable current to the constant light area to make the second light emitting diode The brightness of the diode is constant.

Another object of the present invention is to provide a liquid crystal display, which includes a liquid crystal display module and the above-mentioned light-emitting diode drive system, wherein the pulse width modulation drive circuit adjusts the brightness of the first light-emitting diode according to a brightness control signal to uniformly adjust The display brightness of the LCD module.

The staggered array proposed by the invention can simplify the design of the LED backlight drive and reduce the cost of the drive IC.

Description of drawings

1 is a schematic diagram of a pulse width modulation circuit and its pulse width modulation waveform;

Figure 2A, Figure 2B and Figure 2C are structural schematic diagrams of the staggered arrangement of dimming modules and constant light modules;

Fig. 3 is the light-emitting diode driving system of the liquid crystal display;

4A and 4B are LED driving circuits; and

FIG. 5 is a schematic diagram of a liquid crystal display.

The reference numerals in the above-mentioned accompanying drawings are explained as follows:

11 LED strings 12 Pulse width modulation drivers

13 switches 100 LCD display

110 LED drive system 120 dimming zones

130 constant light area 140 dimming module

142 first light-emitting diodes 150 constant light modules

152 second light-emitting diodes 160 pulse width modulation drive circuit

170 constant current power supply unit 180 liquid crystal display module

190 brightness control signal D diode

L inductor Vin DC current source

Rs Voltage Sense Resistor S Switch

Detailed ways

The aspect of the present invention discussed here is a light-emitting diode array of a liquid crystal display. In order to provide a thorough understanding of the present invention, detailed steps and components thereof will be set forth in the following description. Obviously, the practice of the invention is not limited to specific details familiar to those skilled in the art of LED arrays for liquid crystal displays. On the other hand, well-known components or steps have not been described in detail so as not to unnecessarily limit the invention. Preferred embodiments of the present invention will be described in detail as follows, however, in addition to these detailed descriptions, the present invention can also be widely implemented in other embodiments, and the scope of the present invention is not limited, it is based on the appended claims .

Based on the premise that the liquid crystal display (liquid crystal display, LCD) can be uniformly dimmed while maintaining the basic brightness, the present invention proposes a light emitting diode (Light Emitting Diode, LED) array of the liquid crystal display 100, as shown in FIG. 2A. The above-mentioned light emitting diode array includes one or more first light emitting diodes 142 controlled by a pulse width modulation (Pulse Width Modulation, PWM) signal and one or more second light emitting diodes 152 powered by a constant current of direct current, wherein at least one of the first light emitting diodes A light emitting diode 142 constitutes a dimming module 140 , and at least one second light emitting diode 152 constitutes a constant light module 150 .

In order to adjust the brightness of the liquid crystal display evenly, the above-mentioned dimming modules 140 and constant light modules 150 can be arranged in a staggered manner, as shown in FIG. 2A , FIG. 2B and FIG. 2C . FIG. 2A shows a plurality of dimming modules 140 and a plurality of constant light modules 150 arranged horizontally and vertically at intervals, wherein a constant light module 150 is arranged between every two dimming modules 140 .

FIG. 2B shows that a plurality of dimming modules 140 and a plurality of constant light modules 150 are also arranged horizontally and vertically at intervals, that is, in the horizontal direction, the arrangement of the dimming modules 140 and the constant light modules 150 is as shown in FIG. 2A . However, in the vertical direction in FIG. 2B , the separation distance between the dimming module 140 and the constant light module 150 is larger than the horizontal separation distance. In a preferred embodiment of the present invention, the distance between the dimming module 140 and the constant light module 150 is twice the horizontal distance.

FIG. 2C shows that a plurality of dimming modules 140 and a plurality of constant light modules 150 are arranged at intervals in an oblique direction, that is, a constant light module 150 is disposed between every two dimming modules 140 in an oblique direction. Furthermore, according to different dimming purposes, the present invention may further include other types of staggered LED arrays, which are not limited to the above illustrations. However, the staggered array proposed by the present invention can simplify the design of the LED backlight driver and reduce the cost of the driver IC.

The above light-emitting diode array also includes one or more pulse width modulation driving circuits (PWM IC) 160, wherein each pulse width modulation driving circuit 160 outputs a pulse width modulation signal to one or more than one (channel) dimming areas 120, and Each dimming zone 120 includes one or more dimming modules 140 connected in series. When a LED in the dimming module 140 in the same string fails, the design of the present invention can blur the local bright band.

In addition to each dimming module 140 and constant light module 150 including a first light emitting diode 142 and a second light emitting diode 152 as shown in FIG. 2A, each dimming module 140 can further include a plurality of first LED 142. The same is true for each constant light module 150 , which may further include a plurality of second light emitting diodes 152 connected in series. In another preferred embodiment of the present invention, the above-mentioned dimming module 140 may include two first light emitting diodes 142 , and the constant light module 150 includes two second light emitting diodes 152 , as shown in FIG. 2C .

Referring to FIG. 3 , the present invention also proposes a light-emitting diode driving system 110 of a liquid crystal display 100, which includes a multi-channel (channel) dimming area 120, a multi-channel constant light area 130, a plurality of pulse width modulation driving circuits 160 and a certain channel. Current power supply device 170.

Each dimming zone 120 includes a plurality of dimming modules 140 connected in series, and each dimming module 140 includes at least one first light-emitting diode 142, wherein each pulse width modulation driving circuit 160 outputs a pulse width modulation signal to some of the multiple The dimming area 120 is used to adjust the brightness of the first LED 142 .

Each constant light area 130 includes a plurality of constant light modules 150 connected in series, and each constant light module 150 includes at least one second light emitting diode 152, wherein the constant current power supply device 170 outputs a stable current to a plurality of constant light areas 130 to make the second light emitting diode 152 The brightness of diode 152 is constant. Furthermore, the plurality of dimming modules 140 and the plurality of constant light modules 150 can be arranged in a staggered manner to meet different dimming purposes.

As mentioned above, if a plurality of light-emitting diodes connected in series are used in the backlight module of a liquid crystal display, a driving circuit is required to provide a constant current for the light-emitting diodes. More specifically, when the user adjusts the brightness and color calibration temperature or compensates the temperature, a dimming circuit for adjusting the brightness is required. DC power converters usually use a pulse width modulation mechanism to control the conduction element. This technology will change the load cycle, that is, the ratio of the transistor on time to the off time, and cooperate with the power storage capacity of the inductor to make the output voltage within a limited range. The input voltage and load current ranges are kept constant. As shown in FIG. 4A and FIG. 4B , they show a known LED driving circuit.

First, FIG. 4A is an example circuit diagram of a conventional LED driving circuit of a buck DC-DC converter. As shown in Figure 4A, a traditional step-down DC-to-DC converter is used in the LED driving circuit. The inductor L and the LED are connected in series at the positive terminal of the DC current source Vin, and the diode D is connected to the inductor L and the LED Series 11 are connected in parallel. In addition, the switch 13 and the voltage detection resistor Rs are connected in series between the connection node between the LED series 11 and the diode D and the negative end of the DC current source Vin. The voltage value detected by the voltage detection resistor Rs is input to the pulse width modulation driver 12, and the on/off duty ratio of the switch 13 is adjusted according to the detected voltage value. As shown in FIG. 4A, the switch 13 can be a Metal Oxide Semiconductor Field-Effect Transistor (MOSFET for short). When a switching pulse is applied to the gate voltage of the MOSFET, the MOSFET can be used as a switch.

When the switch 13 is "on", the current supplied from the DC current source Vin is delivered to the LED string via the inductor L. At this time, energy is accumulated in the inductor L. When the switch 13 is “off”, power is supplied to the LED string 11 through the energy accumulated in the inductor L. The pulse width modulation driver 12 adjusts the on/off duty cycle of the switch 13 according to the voltage detection resistor Rs to adjust the power supplied to the LED string 11 .

FIG. 4B is a circuit diagram of an example of a conventional LED driving circuit of a boost DC-DC converter. As shown in FIG. 4B, a known boosted DC-to-DC converter is used in the LED driving circuit, the inductor L and the diode D are connected in series at the positive terminal of the DC current source Vin, and the capacitor C and the LED series 11 are connected in parallel with each other. Between the diode and the negative terminal of the DC current source Vin. The switch 13 and the voltage detection resistor Rs are connected in series between the connection node of the inductor L and the diode D and the negative terminal of the DC power supply Vin. The voltage value detected by the voltage detection resistor Rs is input to the pulse width modulation driver 12 , and the on/off duty cycle of the switch 13 is adjusted according to the detected voltage value. As shown in FIG. 4B , the switch 13 can be a MOSFET, and the MOSFET can be used as a switch by adjusting its gate voltage.

When the switch 13 is "on", the current supplied from the DC current source Vin flows through the inductor L and the switch S, and energy is stored in the inductor L. When the switch 13 is “closed”, the total sum of the energy accumulated in the DC current source Vin and the inductor L is transmitted to the LED string 11 through the diode D. Here, the voltage is smoothed by a smoothing capacitor C and sent to the LED string 11, and its voltage value is greater than or equal to the input voltage Vin.

In such an LED drive circuit, the resistance value of the voltage detection resistor Rs is adjusted to modify the voltage value detected from the voltage detection resistor Rs, thereby adjusting the on/off duty ratio of the switch 13, thereby controlling the LED brightness.

U.S. Patent US 20080002102 proposes a light-emitting diode drive system for backlight modules, which uses the AC-DC converter (AC-DC converter) in the switch mode power supply (Switch Mode Power Supply, SMPS) of the power conversion feedback loop to convert the external The alternating current is converted into direct current, and the DC-DC converter in the SMPS is used to convert the direct current to a predetermined value, thereby driving the light-emitting diode series in the backlight module.

In addition, Japanese patent JP 2007013183 proposes a LED drive circuit driven by a constant current control method, the main technology of which is to compare the preset internal reference voltage with the voltage detection resistor using a comparator included in the pulse width modulation controller. The measured voltage is used to measure the duty ratio (duty ratio) by the controller included in the pulse width modulation controller according to the comparison result, and then output a switching pulse (switch pulse) to the MOSFET accordingly.

Referring to FIG. 5 , the present invention also proposes a liquid crystal display 100 , which includes an LED driving system 110 and a liquid crystal display module 180 . The LED driving system 110 includes the multi-channel dimming area 120 , the multi-channel constant light area 130 , a plurality of pulse width modulation driving circuits 160 and a constant current power supply device 170 as described above.

When the pulse width modulation driving circuit 160 receives a brightness control signal 190 (for example, when the user wants to adjust the brightness of the liquid crystal display, the liquid crystal display will generate a brightness control signal to the pulse width modulation driving circuit), the pulse width modulation driving circuit The 160 outputs a pulse width modulation signal to a part of the multi-channel dimming area 120 according to the brightness control signal 190 to adjust the brightness of the first LED 142 .

When the pulse width modulation driving circuit 160 adjusts the brightness of the first LED 142 , the constant current power supply device 170 still outputs current stably to the multiple constant light regions 130 , so the second LED 152 still provides constant brightness. Therefore, the ratio of the number of the first LEDs 142 to the second LEDs 152 can determine the minimum brightness of the liquid crystal display 100 during dimming.

For example, when the quantity ratio of the first light emitting diode 142 and the second light emitting diode 152 is 1:1, and the first light emitting diode 142 is adjusted to the darkest through the pulse width modulation driving circuit 160 (that is, the first light emitting diode 142 is turned off) , only the second light emitting diode 152 continues to emit light, so the minimum brightness of the liquid crystal display 100 at this time is 50%.

In addition, since the display brightness of the liquid crystal display module 180 is provided by the first light emitting diode 142 and the second light emitting diode 152, the above-mentioned dimming module 140 and constant light module 150 can be arranged in a staggered manner to evenly adjust the liquid crystal display module 180 display brightness.

Generally speaking, the backlight of the liquid crystal display using the above-mentioned light emitting diodes includes an edge-type backlight and a direct-type backlight according to the position of the light source. In the former, the light source is designed as a strip and arranged on the side of a light guide plate to irradiate light onto the LCD panel. In the latter, the size of the surface light source is substantially equal to that of the liquid crystal display panel, and is disposed under the liquid crystal display panel to directly irradiate light onto the liquid crystal display panel. However, the light emitting diode array proposed by the present invention is quite suitable for direct-lit liquid crystal displays.

Obviously, according to the description in the above embodiments, the present invention may have many modifications and differences. It is therefore to be understood, within the scope of the appended claims, that the invention may be practiced broadly in other embodiments than the foregoing detailed description. The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the claims of the present invention; all other equivalent changes or modifications that do not deviate from the disclosed spirit of the present invention should be included in the appended claims In the range.

Claims (10)

1. A light-emitting diode array of a liquid crystal display, comprising: One or more first light-emitting diodes controlled by a pulse width modulation signal, at least one first light-emitting diode constitutes a dimming module to adjust the brightness of the liquid crystal display; and One or more second light-emitting diodes powered by a constant current of direct current, at least one second light-emitting diode constitutes a constant light module to provide a constant light source for the liquid crystal display, and the dimming module and the constant light module are arranged alternately. 2. The light-emitting diode array of a liquid crystal display according to claim 1, further comprising a plurality of pulse width modulation driving circuits, wherein each pulse width modulation driving circuit outputs a pulse width modulation signal to one or more than one dimming area, and each A dimming zone includes one or more dimming modules connected in series. 3. The light-emitting diode array of a liquid crystal display according to claim 1, wherein the staggered arrangement of the dimming modules and the constant light modules can be arranged at intervals, wherein a constant light module is disposed between every two dimming modules. 4. A light-emitting diode driving system for a direct-type liquid crystal display, comprising: One or more dimming areas, each dimming area includes a plurality of series-connected dimming modules, and each dimming module includes at least one first light-emitting diode; A plurality of pulse width modulation driving circuits, wherein each pulse width modulation driving circuit outputs a pulse width modulation signal to a part of one or more dimming areas to adjust the brightness of the first light-emitting diode; One or more constant light areas, each constant light area includes one or more constant light modules connected in series, and each constant light module includes at least one second light emitting diode, wherein the plurality of dimming modules and the plurality of constant light modules are arranged alternately; as well as The constant current power supply device outputs a stable current to the constant light area to make the brightness of the second light emitting diode constant. 5. The light-emitting diode driving system of a direct-type liquid crystal display according to claim 4, wherein the staggered arrangement of the above-mentioned dimming modules and the constant light modules can be arranged at intervals, wherein a constant light module is arranged between every two dimming modules . 6. The light-emitting diode driving system of a direct-type liquid crystal display according to claim 4, wherein the above-mentioned dimming module is composed of a plurality of first light-emitting diodes connected in series. 7. A direct-type backlit liquid crystal display, comprising: a liquid crystal display module; and A light emitting diode drive system, comprising: One or more dimming areas, each dimming area includes one or more series-connected dimming modules, and each dimming module includes at least one first light-emitting diode; One or more pulse width modulation driving circuits, each pulse width modulation driving circuit outputs a pulse width modulation signal to a part of the multi-channel dimming area according to a brightness control signal, so as to adjust the brightness of the first light-emitting diode; One or more constant light areas, the one or more constant light areas and the one or more dimming areas are arranged alternately, wherein each constant light area contains one or more constant light modules connected in series, and each constant light module contains at least one first two light emitting diodes; and A constant current power supply device, which outputs a stable current to the constant light area, so that the brightness of the second light emitting diode is constant; Wherein the dimming module and the constant light module are alternately arranged to evenly adjust the display brightness of the liquid crystal display module. 8 . The direct-lit liquid crystal display according to claim 7 , wherein the staggered arrangement of the above-mentioned dimming modules and the constant light modules can be arranged at intervals, wherein a constant light module is arranged between every two dimming modules. 9. The direct-lit liquid crystal display according to claim 7, wherein the above-mentioned dimming module is formed by a plurality of first light-emitting diodes connected in series. 10. The direct-lit liquid crystal display according to claim 7, wherein the constant light module is formed by a plurality of second light-emitting diodes connected in series.

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