KR100902548B1 - Led backlight unit and display device comprising the same - Google Patents

Abstract

An LED backlight unit and a display device are provided to improve white uniformity of an LED array as improving reliability and performance of goods. An LED backlight unit(110) comprises a power supply unit(120), an LED array(111), a pulse width modulation controller(116), an amplitude modulation controller, and a pulse width amplitude modulation controller. The power supply unit improves a power factor of AC input power by including a plurality of passive devices. The power supply unit comprises a power factor improvement unit and an AC/DC converter for converting AC voltage, outputted from the power factor improvement unit, into DC voltage. The LED array comprises a plurality of light emitting diodes provided with the converted DC voltage. The pulse width modulation controller generates a pulse width modulation signal where a duty ratio is determined according to brightness setting information for the LED array. The amplitude modulation controller generates an amplitude modulation signal where amplitude is determined according to at least one of temperature information of the LED array and color information of light emitted from the LED array. The pulse width amplitude modulation controller generates a control signal of a variable amplitude variable pulse width for controlling the amount of the light emitted from the LED array based on the amplitude of the amplitude modulation signal and the duty ratio of the pulse width modulation signal.

Description

LED backlight unit and display device including same {LED Backlight Unit and Display Device comprising the same}

The present invention provides a light emitting diode backlight unit (LED BLU), and more particularly, a light emitting diode backlight unit having a power supply unit including a power factor improving unit composed of passive elements and a display device using the light emitting diode backlight unit. It is about.

Recently, flat panel display devices have shown explosive growth. Flat panel display devices are widely used in mobile devices that require miniaturization and low power, as well as large digital TVs that require weight and thickness reduction. Among them, the LCD (Liquid Crystal Display) method is the most widely used among flat panel display methods because it can be applied to small devices and large devices.

The LCD display device requires a light source called a backlight unit (BLU) at the rear of the liquid crystal panel because the liquid crystal panel does not emit light by itself. The light generated from the backlight unit passes through the liquid crystal layer and the color filter to show the screen to the outside. Thus, the backlight unit has a significant effect on the performance of the LCD display device. For example, not only screen quality such as color reproducibility, maximum brightness, contrast ratio, white uniformity, color temperature, etc., but also weight, design, lifespan, power consumption, etc. of the display device may be significantly affected by the backlight unit.

Recently used LED backlight unit is composed of a large number of LEDs, and since the light emission is made by such LEDs, their performance is determined by how to drive each LED. The amount of light emitted by the LED can be said to be approximately proportional to the magnitude of the drive current passing through the active layer of the LED. LED drive is a method of supplying and controlling such drive current. Conventionally, the LED driving method can be largely divided into a constant voltage driving method and a constant current driving method.

The constant voltage driving method has a simple circuit configuration, but heat is generated when the LED emits light. The driving current passing through the LED active layer generally increases the forward voltage drop (Vf) of the LED when the temperature increases. Since there is a characteristic, a change in luminance may occur severely as the light emission time increases. On the other hand, in the constant current driving method, since the driving current is controlled to be constant even when the temperature changes, the amount of emitted light is also kept constant, thereby greatly reducing the luminance change. In this case, the expression that the driving current is constant means that the driving current is continuously variable over time but remains constant on average. In recent years, the constant current driving method is more widely used. If the light emission amount of the LED is not constant, the image quality is degraded, such as the screen is speckled, it is very important for the performance of the LCD display device to maintain a constant light emission amount of the LED backlight unit, and further to emit light according to the set conditions.

In particular, the LED backlight unit may further reduce power through a dimming dimming method or a local dimming method in which the entire area is divided into several areas to adjust illumination brightness of each part. In the multi-divided dimming method, each divided area may have different brightness due to differences in heat generation and time-dependent characteristics of LEDs, constant current driving devices, and other devices. This phenomenon causes color deviation and is a factor of deterioration of image quality and thus of overall product quality. Therefore, there is a need for an LED driving circuit that can effectively reduce color deviation in a multi-division LED backlight unit.

On the other hand, when power factor (PF) is generally poor, larger currents must flow at the same workload, so that individual devices consume more power and use larger capacity circuit elements, and power companies use larger capacity. You need to be equipped and produce more power. In order to reduce such social losses, countries have policies to increase the power factor of electrical appliances.

Because of the high speed switching within the LED backlight unit, the LED backlight unit is a very nonlinear load. Due to this nonlinearity, the input current of the LED backlight unit also has nonlinearity, which may adversely affect the power factor. In order to improve the power factor in the LED backlight unit, a conventional active power factor correction circuit having a good power factor improvement effect is mainly used. However, such an active power factor correction circuit is complicated to implement and manufactured because the power factor is close to 1 and the harmonic distortion ratio is small, but a control circuit is required and the components constituting the power factor correction circuit must be high. The cost rises.

LED devices themselves have a relatively long lifespan, but drive systems such as these active power factor correction circuits contain many active devices and are short-lived because such devices undergo rapid current voltage changes, reducing the overall product life. It becomes a factor. Therefore, there is a need for a power factor improvement circuit having a low manufacturing cost, a high efficiency, and a long lifetime.

The problem to be solved by the present invention is to include an LED backlight unit and the LED backlight unit having a power factor correction circuit composed of passive elements to improve the white uniformity of the LED array, and improve the reliability and performance of the product It is to provide a display device.

LED backlight unit according to the present invention for solving the above problems includes a power factor improving unit for improving the power factor of the AC input power, including a plurality of passive elements, and AC for converting the AC voltage output from the power factor improving unit into a DC voltage A power supply unit including a / DC converter; An LED array including a plurality of light emitting diodes receiving the converted direct current voltage; A variable amplitude variable pulse width controlling an amount of light emitted from the LED array based on at least one of brightness setting information of the LED array, color information of light emitted from the LED array, and temperature information of the LED array; A driving control unit generating a control signal of the driving unit; And a constant current driver configured to drive a current flowing in the LED array according to the control signal.

In addition, a display device according to the present invention for solving the above problems is a panel; A backlight unit partitioned into a plurality of partition blocks; And a multi-division dimming control unit for adjusting luminance of the plurality of divided blocks, wherein the backlight unit includes a power factor improving unit for improving a power factor of an AC input power including a plurality of passive elements, and an output from the power factor improving unit. A power supply unit including an AC / DC converter for converting an alternating voltage into a direct current voltage; A plurality of LED arrays provided with the converted DC voltages, each corresponding to the plurality of partition blocks, and each of which includes a plurality of light emitting diodes (LEDs); At least one of brightness setting information of the LED array corresponding to each of the plurality of dividing blocks and provided from the multi-dividing dimming controller, color information of light emitted from each LED array, and temperature information of each LED array; A plurality of driving controllers each generating a control signal of a variable amplitude variable pulse width for controlling the amount of light emitted from each of the LED arrays; And a plurality of constant current drivers respectively corresponding to the plurality of partition blocks and driving currents flowing through the respective LED arrays according to the respective control signals.

According to the present invention, the LED backlight unit and the display device including the same have a power supply unit including a power factor improving unit including a plurality of passive elements, thereby improving reliability and performance of a product at low cost. In detail, the power supply unit may configure a power factor improving unit having a high efficiency even at a small manufacturing cost by using a power factor improving unit composed of a plurality of passive elements, and the power factor is improved, thereby reducing the load current and reducing power loss. Can be.

In addition, the control of the variable amplitude variable pulse width for controlling the amount of light emitted from the LED array, based on at least one of the brightness setting information of the LED array, the color information of the light emitted from the LED array and the temperature information of the LED array. By generating a signal and driving a current flowing in the LED array according to the control signal, the LED light emission of each divided block can be kept constant in driving the LED backlight unit of the LCD display device at a constant current. As such, by using a multi-dimmable dimming control method by precisely adjusting the current flowing through the LED array corresponding to each divided block, the brightness is adjusted according to the divided block, but there is a difference according to the image, but a cold cathode fluorescent lamp (CCFL) It can save up to 40% more power than the method, and the effect is bigger for movies with many dark screens, and color reproducibility can be more than 110% when using RGB LED.

In addition, by precisely adjusting the current flowing through the LED array, it is possible to effectively reduce the color deviation between each partition block, and to improve the white uniformity of the LED array. In addition, a low pass filtering unit may be added to reduce the ripple of the current flowing in the LED backlight unit and to prolong the life of the LED.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. The same reference numerals are used for the same elements in the drawings, and duplicate descriptions of the same elements are omitted.

1 is a schematic block diagram showing an LCD display device according to an embodiment of the present invention.

Referring to FIG. 1, the LCD display apparatus 10 includes an LED backlight unit 110, a power supply unit 120, an image controller 130, a liquid crystal panel 140, and a multi-dimmable dimming controller 150. The display apparatus 10 displays an image to the outside by passing light generated by the LED backlight unit 110 through the liquid crystal panel 140. Here, although the LED backlight unit 110 and the power supply unit 120 are shown in different blocks for convenience of description, the power supply unit 120 supplies power suitable for the operation of the LED backlight unit 110. It may be regarded as being included in the LED backlight unit 110.

The power supply unit 120 receives an alternating current (AC) power voltage and converts it into a direct current (DC) power voltage, and converts the converted DC power voltage into an image control unit 130, a multi-dimmable dimming control unit 150, and Supply to LED array 111. Here, since the operating voltages of the image controller 130, the multi-dimmable dimming controller 150, and the LED array 111 may be different from each other, the power supply unit 120 may supply voltages of levels suitable for the respective operating voltages. . Therefore, the power supply unit 120 may be classified according to the output voltage.

In more detail, the power supply unit 120 includes a noise filter 121, a power factor improving unit 122, and an AC / DC converter 120.

The noise filter 121 attenuates the noise of the input AC power, thereby preventing the noise of the AC voltage (V _AC ) from flowing into the LCD display device 10, and at the same time, the noise generated from the LCD display device 10 is reduced. It can prevent the influence on the outside. In addition, when the power factor correcting unit 122 includes a valley-fill passive power factor control circuit, the power factor may be improved by inductance and capacitance values of the device included in the noise filter 121.

The power factor improving unit 122 includes a plurality of passive elements to improve the power factor of the voltage supplied from the noise filter 121. In one embodiment of the present invention, the power factor improving unit 122 may include a valley-fill passive power factor control circuit. The valley fill passive power factor control circuit will be described in detail with reference to FIG. 9 below. As such, the power factor improving unit 122 may achieve power factor close to 95% while simplifying the design by implementing only passive elements, and may improve product reliability.

The AC / DC converter 123 receives the AC power supply voltage output from the power factor improving unit 122 and converts the DC power supply voltage suitable for driving the LED array 111. In another embodiment of the present invention, when the structure of the power factor correcting unit 122 exhibits low harmonic distortion, the inductance and capacitance values may be adjusted by the noise filter 121.

The image controller 130 receives the image signal from the outside to control the liquid crystal panel 140 and supplies a control signal to the multi-dimmable dimming controller 150 to control the LED backlight unit 110 in a constant current driving manner.

The multi dimming controller 150 may directly provide the individual PWM data under the control of the image controller 120 to the driving controller 115 as luminance setting information. Here, as the number of divisions of the LED backlight unit 110 increases, a plurality of data wires between the dividing dimming controller 150 and the driving controller 115 may be required. To compensate for this, in one embodiment of the present invention, the LCD display device 10 further includes an encoder 151 connected to the multi-dimmable dimming control unit 150, and the driving control unit 115 further includes a decoder 119. can do. In detail, the encoder 151 encodes the individual PWM data provided from the dividing dimming controller 150 in a serial or parallel manner in accordance with a protocol determined by the image controller 120 to the driving controller 115. Transfer to the included decoder 119. In this case, the decoder 119 may decode the encoded result into individual PWM data, and transmit the decoded individual PWM data to the PWM controller 116.

The LCD display apparatus 10 may divide the LED backlight unit 110 into a plurality of dividing blocks according to a multidivision dimming scheme. Accordingly, the LED backlight unit 110 may include at least one LED array 111, at least one constant current driver 112, at least one temperature sensor 113, at least one color sensor 114, and at least one driving controller. 115. Specifically, when the LCD display device 10 divides the LED backlight unit 110 into N divided blocks, the LED backlight unit 110 includes N LED arrays 111, N constant current drivers 112, The N temperature sensors 113 and the N color sensors 114 may include N driving controllers 115. Here, N is an integer of 1 or more.

The drive controller 115 generates a drive control signal and generates a constant current according to the luminance setting information provided from the multi-dimmable dimming controller 150 and according to the detection information provided from the temperature sensor 113 and the color sensor 114. The driving unit 112 is provided. Here, the LED backlight unit 110 includes a temperature sensor 113 and a color sensor 114, but this is only an example, and in another embodiment of the present invention, the LED backlight unit 110 is the state of the LED It may further include other types of sensors that can be detected.

In more detail, the driving controller 115 may include a pulse width modulation (PWM) controller 116, an amplitude modulation (AM) controller 117, and a PWAM controller 118. Here, the PWM controller 116 generates a PWM control signal according to the luminance setting information provided from the multi-dimmable dimming controller 150. The AM control unit 117 generates an AM control signal according to the detection information provided from the temperature sensor 113 and the color sensor 114. The PWM control signal and the AM control signal are provided to the PWAM control unit 118. The PWAM control unit 118 generates the PWAM control signal as the drive control signal using the PWM control signal and the AM control signal, and generates the generated PWAM control signal. The constant current driver 112 is provided.

When there is an appropriate drive signal from the drive controller 115, the constant current driver 112 generates a forward current If that is a drive current and supplies it to the LED array 111. In this case, the forward current If may be finely adjusted according to the control of the driving controller 115, which will be described later.

The LED array 111 is a plurality of LED strings are connected in parallel with a plurality of LEDs in series, and emits light according to the forward current (If). For example, the plurality of LEDs may emit a color or white light expressed by combining primary colors of one of red, green, and blue, and three primary colors.

The temperature sensor 113 and the color sensor 114 detect the current state of the LED array 111 and feed back the detection information to the drive control unit 115. In detail, the color sensor 114 detects the light emitted from the LED array 111, whereby the luminance change of the LED array 111 may be detected. On the other hand, the temperature sensor 113 detects a temperature related to the LED array 111. For example, the temperature sensor 113 may directly contact the LED array 111 to measure the temperature of the LED array 111. As such, the color information and the temperature information detected by the temperature sensor 113 and the color sensor 114 are provided to the driving control unit 115, whereby the driving control unit 115 can locally control luminance with respect to the block. Can be.

Specifically, the driving controller 115 controls the PWAM of the variable amplitude variable pulse width type so that the constant current driver 112 may finely adjust the forward current If based on the luminance setting information, the detected color information, and the temperature information. A signal is generated and the generated PWAM control signal is provided to the constant current driver 112. For example, as a result of the detection of the temperature sensor 113, when the temperature of the LED array 111 rises, the magnitude of the forward current If increases and the luminance becomes higher than a desired level, so that the driving controller 115 determines the forward current If To generate a PWAM control signal for reducing the size of < RTI ID = 0.0 > On the other hand, if the brightness of the light emitted from the LED array 111 is lower than the set level as a result of the detection of the color sensor 114, the driving controller 115 increases the magnitude of the forward current If, the brightness of the light emitted Generate the PWAM control signal so that is the desired level.

The constant current driver 112 provides a constant current to the LED array 111 based on the PWAM control signal received from the drive controller 115. In detail, the constant current driver 112 may generate a constant current in a linear manner or a switching manner.

In another embodiment of the present invention, the constant current driver 112 may further include a low pass filter (not shown). PWAM signal is composed of many pulses, so there is a lot of ripple in the forward current (If), and such components generate heat at the chip junction in the LED package mounted on the LED array 11. Low Pass Filter 622 A filter for removing such a ripple component may be a passive RC filter composed of a resistor and a capacitor filter. The low pass filter may be inserted in front of the base of the driving transistor Q in which a relatively small current flows so as to minimize power consumption by itself.

2 is a circuit diagram schematically showing an LED backlight unit using a pulse width modulation (PWM) controlled constant current driving scheme.

Referring to FIG. 2, the LED backlight unit 200 includes an LED array 210, a constant current driver 220, and a PWM controller 230. Although not shown in FIG. 2, the LED backlight unit 200 may further include at least one of a color sensor and a temperature sensor.

The LED array 210 has a plurality of LED strings connected in series with a plurality of LEDs in parallel. The plurality of LEDs may emit, for example, one of primary colors of red, green, and blue, and a color or white light representing a combination of three primary colors. Since the LED backlight unit includes a large number of LEDs, the circuit of FIG. 2 may be repeatedly used when actually implementing the LED backlight unit. For example, the circuit of FIG. 2 may be used for each type of primary color and may be repeatedly used for each zone. Terminations (+ and −) of the LED backlight unit 200 may be connected to the power supply unit 120 of FIG. 1, specifically, to the AC / DC converter 123.

The constant current driver 220 includes an amplifier 221 having a gain A, a driving transistor Q, and a detection resistor Rs. Although the driving transistor Q is shown as one transistor in FIG. 2, a plurality of transistors may be connected in parallel to increase the size of the collector current. In addition, although the driving transistor Q has been described using an N-type BJT transistor as an example, the driving transistor Q may be implemented as a P-type BJT transistor disposed in front of the LED array 210, and may be appropriately implemented as an N-type and P-type MOS transistor. Can be.

The PWM controller 230 receives luminance setting information of the LED array 210 and information detected from at least one of a color sensor and a temperature sensor (not shown) to generate an appropriate PWM signal. In FIG. 2, a color sensor and a temperature sensor for providing color and temperature detection information are not illustrated, but one of ordinary skill in the art to which the present embodiment belongs may properly arrange the color sensor and the temperature sensor. In addition, although FIG. 2 illustrates a method of controlling a linear driving transistor using a PWM signal with respect to an LED backlight unit using a configuration for generating a constant current in a linear manner, an LED backlight unit having a configuration for generating a constant current in a switching manner. Similarly, a method of controlling a switching converter using a PWM signal may be adopted.

The operation of the LED backlight unit 200 of the PWM control constant current driving method is as follows. The supply voltage Vin is applied to the LED array 210, the driving transistor Q and the detection resistor Rs. When the supply voltage Vin is sufficiently high, the voltage Vf applied to the LED array 210 is each The LEDs can all be high enough to emit light. Since LEDs are inherently diodes, current must flow through their turn-over voltages in the forward direction, and they can emit light accordingly.

Since the currents flowing through the LED strings included in the LED array 210 are all connected to flow through the driving transistor Q, the average of the current flowing through the LED array 210 by controlling the base current of the driving transistor Q. The size can be adjusted effectively. When the base current of the driving transistor Q is controlled by the PWM signal, the flow of the forward current If supplied to the LED array 210 can be controlled, and as a result, the light emission amount of the LED array 210 can be controlled. The duty ratio of the PWM signal is determined according to the luminance setting information of the LED array 210 and the emission color of the LED array 210 or the temperature of the LED backlight unit 200 received from the temperature sensor or the color sensor. Adjust to get what you want.

First, for convenience of description, assuming that there is no PWM controller 230, the constant current driver 220 is a kind of voltage for flowing a constant forward current If to the driving transistor Q according to a constant reference voltage Vref. It is a current conversion circuit. The collector current, i.e., the forward current If, is determined according to the voltage and current of the base and the emitter of the driving transistor Q. The forward current If is combined with the base current and flows to the detection resistor Rs. The detection voltage Rs is applied to the detection resistor Rs, and the detection voltage Vs is applied to the amplifier 221. The difference between the detection voltage Vs and the reference voltage Vref is amplified by the gain A and applied to the base of the driving transistor Q again.

If the forward current If increases by some factor, the detection voltage Vs will increase as a result. Subsequently, the difference between the detection voltage Vs and the reference voltage Vref applied to the amplifier 221 is reduced, and the base-emitter voltage of the driving transistor Q is also reduced, resulting in a collector current, that is, a forward current If. To reduce. Conversely, if the forward current If decreases due to some factor, the detection voltage Vs decreases, and the base-emitter voltage of the driving transistor Q increases, resulting in an increase in the forward current If. Therefore, the maximum forward current can be adjusted by the detection resistor Rs, and in this way, the constant current driver 220 can allow a constant forward current If to flow.

Next, considering the PWM controller 230, the PWM signal provided from the PWM controller 230 is applied to the base of the driving transistor Q. The base voltage level of the driving transistor Q is determined by factors such as the voltage level of the PWM signal output from the PWM control unit 230, the output voltage level of the amplifier 221, the effective capacitance of the base of the driving transistor Q, and the like. Is substantially determined close to the voltage level of the PWM signal.

In the period where the PWM signal has the maximum level in one period, the base voltage of the driving transistor Q will reach the maximum level accordingly, and the base-emitter voltage of the driving transistor Q will also rise accordingly, and the driving transistor ( Q) is turned on, and as a result, the forward current If greatly increases. On the other hand, in the period where the PWM signal has the lowest level, the base voltage of the driving transistor Q will drop accordingly, and the base-emitter voltage of the driving transistor Q will also fall along, so that the driving transistor Q will turn. Off, and as a result, the forward current If decreases rapidly.

Therefore, the duty ratio of the forward current If is determined according to the duty ratio of the PWM signal, and accordingly, the average size of the forward current If can be adjusted, and the amount of light emitted from the LED array 210 is also transferred. I can regulate it. During the maximum level section and the minimum level section of the pulse, the forward current If may be maintained at a constant level by the amplifier 221 and the detection resistor Rs. That is, the waveform of the forward current If is shaped to be close to the square wave waveform of the PWM signal. That is, in the PWM controlled constant current driving method of FIG. 2, the amount of light emitted as the duty ratio of the section having the maximum level and the section having the lowest level of the PWM signal is adjusted.

3 is a circuit diagram illustrating an LED backlight unit using a pulse amplitude modulation (PAM) controlled constant current driving scheme.

Referring to FIG. 3, the LED backlight unit 300 includes an LED array 310, a constant current driver 320, and a PAM controller 330. Although not shown in FIG. 3, the LED backlight unit 300 may further include at least one of a color sensor and a temperature sensor. Since the LED array 310 may be substantially the same as the LED array 210 of FIG. 2, the description of the LED array 310 is omitted.

The constant current driver 320 may be contrasted with the constant current driver 220 of FIG. 2. In the case of the constant current driver 220 of FIG. 2, the forward current If is generated to linearly correspond to a PWM signal having a pulse shape in which the maximum level and the minimum level are fixed and the pulse duty ratio is varied. The constant current driver 320 of FIG. ), The forward current If is variable so that the maximum level is variable and the pulse duty ratio is configured to linearly correspond to the PAM signal having a fixed pulse shape. Thus, FIG. 3 also corresponds to a linear driving method.

The constant current driver 320 includes a driving transistor Q and a current limiting resistor Rs. Although the driving transistor Q is shown as one transistor in FIG. 3, a plurality of transistors may be connected in parallel to increase the collector current. In addition, although the driving transistor Q has been described using an N-type BJT transistor as an example, the driving transistor Q may be implemented as a P-type BJT transistor disposed in front of the LED array 310, and may be appropriately implemented as an N-type and P-type MOS transistor. Can be. The current limiting resistor Rs is connected between the emitter of the driving transistor Q and the negative power supply terminal of the supply voltage Vin, thereby adjusting the base-emitter voltage of the driving transistor Q, thereby driving the driving transistor. It is a kind of current peak limiting resistor that limits the collector current of (Q), that is, the forward current If.

The PAM controller 330 receives luminance setting information of the LED array 310 and information detected from at least one of a color sensor and a temperature sensor (not shown) to generate an appropriate amplitude modulated PAM signal. Other features of the PAM control unit 330 are similar to the PWM control unit 230 of FIG. 2 and will not be described.

The PAM signal generated by the PAM controller 330 is supplied to the constant current driver 320. The base voltage level of the driving transistor Q is determined to be substantially close to the voltage level of the PAM signal. In the period in which the PAM signal has the maximum amplitude in one period, the base voltage of the driving transistor Q will reach the maximum level accordingly, and the base-emitter voltage of the driving transistor Q is also determined accordingly, and the driving transistor ( Q) is turned on and the forward current If is also determined accordingly. On the other hand, during the period where the PAM signal has the lowest level, the base voltage of the driving transistor Q will drop accordingly, and the base-emitter voltage of the driving transistor Q will also drop along, so that the driving transistor Q is turned off. As a result, the forward current If decreases rapidly.

Therefore, the amplitude of the forward current If is determined according to the amplitude of the PAM signal, and thus, the average magnitude of the forward current If can be adjusted and the amount of light emitted from the LED array 310 can be adjusted. That is, in the PAM controlled constant current driving method of FIG. 3, the amount of light emitted is adjusted according to the level of the PAM signal.

Comparing the constant current driving schemes shown in FIGS. 2 and 3, the PWM control scheme in FIG. 2 is generally LED backlight in that precisely controlling the duty ratio is easier to implement than precisely controlling the magnitude of the voltage. The brightness of the unit can be precisely controlled very effectively as the duty ratio of the PWM control signal.

However, in the case of the multi-division LED backlight unit, for example, even if all the divided blocks are driven with a duty ratio of 1, the brightness or the color temperature is not uniform among the divided blocks, the relatively low brightness The split block can no longer be lightened by adjusting the duty ratio. Lowering the brightness of a relatively bright split block to make the brightness uniform will result in a decrease in overall brightness.

On the other hand, the PAM control method is not easy to implement precisely controlling the voltage level due to various reasons such as component change, temperature change, manufacturing defect, etc., but if you want to increase the brightness, simply increase the level of the PAM control signal. This allows more flexibility in increasing the level of forward current.

4 is a circuit diagram schematically illustrating an LED backlight unit using a PWAM controlled constant current driving method used in the LCD display device of FIG. 1, according to an exemplary embodiment.

Referring to FIG. 4, the LED backlight unit 400 includes an LED array 410, a constant current driver 420, and a PWAM driving controller 430. Although not shown in FIG. 4, the LED backlight unit 400 may further include a multi-dimmable dimming controller, and may further include at least one of a color sensor and a temperature sensor. In addition, the LED backlight unit 400 may further include a power supply. Since the LED array 410 may be substantially the same as the LED arrays 210 and 310 of FIGS. 2 and 3, description of the LED array 410 is omitted.

The constant current driver 420 includes an amplifier 421 having a gain A, a driving transistor Q, and a detection resistor Rs. Since the operation of the constant current driver 420 may be substantially the same as that of the constant current driver 220 of FIG. 2, a detailed description of the operation of the constant current driver 420 is omitted.

The PWAM driving controller 430 receives the detected information from at least one of brightness setting information, a color sensor, and a temperature sensor (not shown) for the LED array 410 to generate an appropriate PWAM control signal. Although not shown a color sensor and a temperature sensor to provide the color and temperature detection information to the PWAM drive control unit 430, those of ordinary skill in the art can appropriately arrange the color sensor and the temperature sensor will be. In addition, although FIG. 4 illustrates a method of controlling a linear driving transistor using a PWAM control signal with respect to the LED backlight unit adopting a configuration of generating a constant current in a linear manner, a configuration of generating a constant current in a switching scheme is illustrated. Similarly, the LED backlight unit may adopt a method of controlling the switching converter using a PWAM control signal.

FIG. 5A is a graph illustrating waveforms of a PWM signal used in the PWAM driving controller of FIG. 4, and FIG. 5B is a graph illustrating waveforms of an AM signal used in the PWAM driving controller of FIG. 4, and FIG. 5C is a graph of FIG. 4. It is a graph which illustrates the waveform of the PWAM control signal used by a PWAM drive control part.

Referring to FIG. 5A, the PWM signals are pulses having a duty ratio determined according to the overall brightness setting of the LED array. For example, in the period A, the luminance is set to about 0.5 for the duty ratio D, and in time, the duty ratio D is set to about 0.33 in the interval B, and then in the interval C, the duty ratio D is set. ) Is an example of setting 0.75.

Referring to FIG. 5B, the AM signal is to finely adjust the luminance of the partition block by reflecting local temperature or color detection information of the partition block. The AM signal, in section A, is a signal voltage such that, depending on the temperature of the LED array or the color detection feedback information, 50% of the maximum flowable current flows in the corresponding LED array, for example, the brightness that can actually be maximized. It is adjusted to the level (V1), and then to the signal voltage level (V2) to allow 40% of the maximum current to flow in the section B where the temperature is high over time. The example illustrates a situation where the signal voltage level V3 is adjusted to allow the% level to flow.

Although not shown in FIG. 5B, the AM signal may be adjusted to a signal voltage level of V3 or higher in order to allow 100% of the maximum flowable current to flow in the corresponding LED array according to the temperature or color detection feedback information of the corresponding LED array. . As described above, in one embodiment of the present invention, in order to compensate for the difficulty in finely adjusting the brightness of the LED array when only the PWM signal is used, the white uniformity of the LED array may be improved by adjusting the amplitude of the AM signal.

Referring to FIG. 5C, the PWAM control signal is based on the PWM signal and the AM signal, the pulse duty ratio of the PWAM control signal reflects the duty ratio of the PWM signal, and the pulse size of the PWAM control signal reflects the amplitude of the AM signal. Is generated as a variable amplitude variable pulse width signal. The PWAM control signal is a pulse whose duty ratio is set to 0.5 and the maximum voltage level is set to V1 in section A, the duty ratio is set to 0.33 and the maximum voltage level is set to V2 in section B, and in section C. The duty ratio may be set to 0.75 and the maximum voltage level may be a pulse adjusted to V3.

4, the PWAM driving controller 430 generates a PWM signal based on the luminance setting information for the LED array 410, and generates an AM signal based on information detected from at least one of the temperature sensor and the color sensor. The PWAM control signal is generated as shown in FIG. 5 based on the PWM signal and the AM signal. In some embodiments, the PWAM control signal may be generated directly without an intermediate step of generating the PWM signal and the AM signal.

In detail, the PWAM driving controller 430 includes a PWM controller 431, an AM controller 432, and a PWAM controller 433. The PWM controller 431 generates a PWM signal whose duty ratio is substantially determined according to the luminance set value of the LED array. The AM control unit 432 generates an AM signal whose amplitude level is substantially determined according to the fine adjustments related to the temperature and color detection feedback information of the corresponding partition block. The PWAM controller 433 receives the PWM signal and the AM signal and generates a PWAM signal based on these signals. The PWAM signal is a variable amplitude variable pulse width signal whose duty ratio is substantially determined by the duty ratio of the PWM signal and its maximum level is substantially determined by the amplitude of the AM signal.

The PWAM signal provided from the PWAM driving controller 430 is applied to the base of the driving transistor Q in the constant current driver 420. The base voltage level of the driving transistor Q is substantially determined to be close to the voltage level of the PWAM signal, which is the output of the PWAM driving controller 430. In the section in which the PWAM signal has the maximum level in one period, the base voltage of the driving transistor Q reaches the maximum level of the PWAM signal accordingly. The base-emitter voltage of the driving transistor Q also increases accordingly, and consequently the forward current If also increases significantly. On the other hand, in the period where the PWAM signal has the lowest level, the base voltage of the driving transistor Q will drop accordingly, and the base-emitter voltage of the driving transistor Q will also fall accordingly, so that the driving transistor Q will turn. Off, and as a result, the forward current If decreases rapidly.

Accordingly, the duty ratio of the forward current If is determined according to the duty ratio of the PWAM signal, and accordingly, an average size of the forward current If may be adjusted and an amount of light emitted from the LED array 410 may be adjusted. If the maximum level of the PWAM signal changes, the magnitude of the forward current If changes accordingly. Accordingly, the amount of light emitted from the LED array 410 may also be adjusted. That is, in the PWAM controlled constant current driving method of FIG. 5, the level of the overall light emission amount is adjusted as the maximum level of the PWAM signal, and the amount of the current light emission amount is fine as the duty ratio of the section having the maximum level of the PWAM signal and the section having the lowest level. Adjusted.

6 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to an embodiment of the present invention.

Referring to FIG. 6, the power supply unit 610, the multi-dimmable dimming control unit 620, the driving control unit 630, the constant current control unit 640, and the LED array 650 may be included in the LCD display device of FIG. 1. The specific function of each block is as described in FIG. In an embodiment of the present invention, the LED array 650 is an array of white LEDs, and one AC / DC converter 613 supplies a drive current If to the LED array 650.

The power supply unit 610 includes a noise filter 611, a power factor correction unit 612, and an AC / DC converter 613. Here, the power factor improving unit 612 may be implemented as a valley-fill passive power factor improving circuit including a plurality of passive elements, in which case the design is simple and the reliability is high. The AC / DC converter 613 receives an AC power supply voltage having a compensated power factor and converts it into a DC power supply voltage having a size suitable for driving the LED array 650. According to an exemplary embodiment, the noise filter 611 may adjust the inductance and capacitance values of the noise filter 611 when the structure of the power factor corrector 612 exhibits low harmonic distortion.

The drive controller 630 receives the dimming signal from the multi-dimmable dimming controller 620, generates a PWAM control signal, and provides the PWAM control signal to the constant current driver 640. The constant current driver 640 may drive the LED array 650 by controlling the magnitude of the current If provided from the AC / DC converter 613 according to the PWAM control signal.

7 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to another embodiment of the present invention.

Referring to FIG. 7, the power supply unit 710, the multi-division dimming control unit 720, the plurality of driving control units 730, 750, and 770, the plurality of constant current control units 735, 755, and 775 and the plurality of LED arrays. Reference numerals 740, 760, and 780 may be included in the LCD display device of FIG. 1. In this case, specific functions of the blocks are the same as those described with reference to FIG. 1. In an embodiment of the invention, the plurality of LED arrays may include a green LED array 740, a red LED array 760 and a blue LED array 780.

The power supply unit 710 includes a noise filter 711, a power factor correction unit 712, and a plurality of AC / DC converters 713, 714, and 715. Here, the first AC / DC converter 713 provides an appropriate operating voltage to the green LED array 740, the second AC / DC converter 714 provides an appropriate operating voltage to the red LED array 760, The third AC / DC converter 715 provides a suitable operating voltage for the blue LED array 780. According to an exemplary embodiment, when the structure of the power factor corrector 712 exhibits a low harmonic distortion, the noise filter 711 may adjust the inductance and capacitance values of the noise filter 711.

The first driving controller 730 receives the dimming signal from the multi-dimmable dimming controller 720, generates a PWAM control signal, and provides the PWAM control signal to the first constant current driver 735. The first constant current driver 735 may drive the green LED array 740 by controlling the magnitude of the current If provided from the first AC / DC converter 713 according to the PWAM control signal. The second driving controller 750 receives the dimming signal from the multi-dimmable dimming controller 720, generates a PWAM control signal, and provides the PWAM control signal to the second constant current driver 755. The second constant current driver 755 may drive the red LED array 760 by controlling the magnitude of the current If provided from the second AC / DC converter 714 according to the PWAM control signal. The third driving controller 770 receives the dimming signal from the multi-dimmable dimming controller 720, generates a PWAM control signal, and provides the PWAM control signal to the third constant current driver 775. The third constant current driver 775 may drive the blue LED array 780 by controlling the magnitude of the current If provided from the third AC / DC converter 715 according to the PWAM control signal.

In another embodiment of the present invention, the plurality of LED arrays 740, 760, 780 may comprise a white LED array. In this case, the first to third driving controllers 730, 750, and 770 respectively determine the magnitude of the current If provided from the first to third AC / DC converters 713, 714, and 715 according to the PWAM control signal. By controlling, the white LED array, the red LED array, the green LED array, or the blue LED array can be driven.

8 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to another embodiment of the present invention.

According to FIG. 8, the power supply unit 810, the multi-dividing dimming control unit 820, the plurality of driving control units 830, 850, 870, the plurality of constant current controllers 835, 855, 875, and the plurality of LED arrays ( 840, 860, and 880 may be included in the LCD display device of FIG. 1. In this case, specific functions of the blocks are the same as those described with reference to FIG. 1. In an embodiment of the invention, the plurality of LED arrays may include a green LED array 840, a red LED array 860 and a blue LED array 880.

The power supply unit 810 includes a plurality of noise filters 811, 814, 817, a plurality of power factor correction units 812, 815, 818, and a plurality of AC / DC converters 813, 816, 819. Here, the first noise filter 811, the first power factor improving unit 812, and the first AC / DC converter 813 are connected to the green LED array 840 to provide an appropriate operating voltage to the green LED array 840. do. Similarly, the second noise filter 814, the second power factor corrector 815, and the second AC / DC converter 816 are connected to the red LED array 860 to provide an appropriate operating voltage to the red LED array 860. do. The third noise filter 817, the third power factor improving unit 818, and the third AC / DC converter 819 are connected to the blue LED array 880 to provide an appropriate operating voltage to the blue LED array 880. According to an embodiment, one of the noise filters 811, 814, 817 is the noise filters 811, 814, 817 when the structure of the corresponding power factor correcting units 812, 815, 818 exhibits low harmonic distortion. You can adjust the inductance and capacitance values of.

The multidivision dimming control unit 820, the plurality of driving control units 830, 850, and 870, and the plurality of constant current control units 835, 855, and 875 include the multidivision dimming control unit 720 and the plurality of driving units shown in FIG. 7. Since the controllers 730, 750, and 770 are substantially similar to the plurality of constant current controllers 735, 755, and 775, a detailed description thereof will be omitted.

In another embodiment of the present invention, the plurality of LED arrays 840, 860, 880 may comprise a white LED array. In this case, the first to third driving controllers 830, 850, and 870 respectively determine the magnitude of the current If provided from the first to third AC / DC converters 813, 816, and 819 according to the PWAM control signal. By controlling, the white LED array, the red LED array, the green LED array, or the blue LED array can be driven.

In the case of FIG. 7, since the noise filter 711 and the power factor improving unit 712 are shared for the plurality of LED arrays, the overall circuit configuration may be simplified and the number of devices may be reduced, but the capacity of the devices constituting them is increased. In general, large capacity devices can be difficult to make the device as a whole thin because of their large size or height. In contrast, in the case of FIG. 8, noise filters 811, 814, and 817 and power factor improving units 812, 815, and 818 are provided for each of the plurality of LED arrays. Can be.

9 is a circuit diagram illustrating a specific implementation of a power supply unit in an LCD display device according to an embodiment of the present invention.

9, the power supply unit 900 includes an AC power supply 910, a noise filter 920, a rectifier 930, a valley fill passive power factor correction circuit 940, and an AC / DC converter 950. Here, the noise filter 920 corresponds to the noise filter 121 of FIG. 1, the rectifying unit 930 and the valley fill passive power factor improving circuit 940 correspond to the power factor improving unit 920 of FIG. The DC converter 950 may correspond to the AC / DC converter 123 of FIG. 1. In addition, the power supply unit 900 may correspond to the power supply unit illustrated in FIGS. 6 to 8.

The noise filter 920 is an LC circuit including the inductor Lf and the capacitor Cf, and attenuates the noise component of the input AC power source 910. The rectifier 930 is configured as a bridge diode to full-wave rectify the power attenuated by the noise component in the noise filter 920.

The valley fill passive power factor correction circuit 940 includes first and second capacitors C1 and C2 and first to third diodes D1, D2, and D3. One end of the first capacitor C1 is connected to the + output terminal of the rectifier 930, the + terminal of the first diode D1 is connected to the other end of the first capacitor C1, and The negative terminal is connected to the negative output terminal of the rectifier 930. The + terminal of the second diode D2 is connected to the + output terminal of the rectifier 930, and the − terminal of the second diode D2 is connected to one end of the second capacitor C2. The other end of the second capacitor C2 is connected to the − output terminal of the rectifier 930. The + terminal of the third diode D3 is connected to the − terminal of the second diode D2, and the − terminal of the third diode D3 is connected to the + terminal of the first diode D1.

In a steady state, in an interval where the input AC power voltage V _AC is less than or equal to 1/2 of the highest value, the voltage is increased by an electric charge precharged to the first and second capacitors C1 and C2. 950 is supplied. On the other hand, the first and second capacitors C1 and C2 are charged and the rectified voltage is directly supplied to the AC / DC converter 950 in a section in which the input AC power voltage V _AC is 1/2 or more of the highest value. . Accordingly, the valley fill passive power factor correction circuit 940 improves the power factor by continuously flowing current at 1/2 or more of the input voltage.

In addition to the display device, the LED backlight unit or the LED driving circuit according to an embodiment of the present invention may be widely used in a device for driving LEDs such as an LED signal lamp, an LED lighting device, an LED character display device, and the like. In addition, the power supply unit according to another embodiment of the present invention includes a valley fill passive power factor improvement circuit, the power supply unit to supply power to the LED signal light, LED lighting device, LED floodlight, LED signal remaining indicator device, to improve the power factor In addition, it can efficiently satisfy specifications such as power up time. Further, in another embodiment of the present invention, by applying a valley fill passive power factor improvement circuit and a PWAM constant current drive driver to the LED traffic light, LED flood light, LED traffic light remaining indicator device, etc. to improve the efficiency through power factor improvement, more precise I can make a color tone well.

As described above, although the present invention has been described by way of limited embodiments and drawings, the present invention is not limited to the above-described embodiments, which can be variously modified and modified by those skilled in the art to which the present invention pertains. Modifications are possible. Accordingly, the spirit of the invention should be understood only by the claims set forth below, and all equivalent or equivalent modifications will fall within the scope of the invention.

In addition, the system according to the present invention can be embodied as computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of the recording medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like, and also include a carrier wave (for example, transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

1 is a schematic block diagram showing an LCD display device according to an embodiment of the present invention.

2 is a circuit diagram schematically showing an LED backlight unit using a pulse width modulation (PWM) controlled constant current driving scheme.

3 is a circuit diagram schematically illustrating an LED backlight unit using a pulse amplitude modulation (PAM) controlled constant current driving scheme.

FIG. 4 is a circuit diagram schematically illustrating an LED backlight unit using a pulse width-amplitude modulation (PWAM) controlled constant current driving method used in the LCD display device of FIG. 1, according to an exemplary embodiment.

FIG. 5A is a graph illustrating waveforms of a PWM signal used in the PWAM driving controller of FIG. 4, and FIG. 5B is a graph illustrating waveforms of an AM signal used in the PWAM driving controller of FIG. 4, and FIG. 5C is a graph of FIG. 4. It is a graph which illustrates the waveform of the PWAM control signal used by a PWAM drive control part.

6 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to an embodiment of the present invention.

7 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to another embodiment of the present invention.

8 is a schematic block diagram illustrating a power supply unit, a multi-dimmable dimming control unit, and an LED backlight unit in an LCD display device according to another embodiment of the present invention.

9 is a circuit diagram illustrating a specific implementation of a power supply unit in an LCD display device according to an embodiment of the present invention.

Claims (11)

A power supply including a power factor improving unit for improving a power factor of an AC input power source including a plurality of passive elements, and an AC / DC converter for converting an AC voltage output from the power factor improving unit into a DC voltage; An LED array including a plurality of light emitting diodes (LEDs) receiving the converted DC voltages; A pulse width modulation controller configured to generate a pulse width modulated signal whose duty ratio is determined according to luminance setting information for the LED array; An amplitude modulation controller configured to generate an amplitude modulation signal whose amplitude is determined according to at least one of color information of light emitted from the LED array and temperature information of the LED array; A pulse width amplitude modulation controller configured to generate a control signal having a variable amplitude variable pulse width for controlling an amount of light emitted from the LED array based on the duty ratio of the pulse width modulated signal and the amplitude of the amplitude modulated signal; And And a constant current driver configured to drive a current flowing through the LED array according to the control signal. The method of claim 1, The power factor correcting unit includes a valley-fill passive power factor improving circuit. delete delete The method of claim 1, The brightness setting information is encoded in a serial or parallel manner and supplied to the pulse width modulation control unit, The LED backlight unit further comprises a decoder for decoding the encoded brightness setting information, and transmits the decoded result to the pulse width modulation control unit. The method according to claim 1 or 2, The constant current driver A driving transistor including a control terminal to which the control signal is applied and a first terminal connected to one end of the LED array; A resistor connected to a second terminal of the driving transistor and providing a feedback voltage level linearly corresponding to a current flowing in the LED array; And And an amplifier receiving the reference voltage level and the feedback voltage level, amplifying the difference, and outputting the difference to the control terminal of the driving transistor. Panels; A backlight unit partitioned into a plurality of partition blocks; And A dividing dimming control unit for adjusting luminance of the plurality of divided blocks; The backlight unit, A power supply including a power factor improving unit for improving a power factor of an AC input power source including a plurality of passive elements, and an AC / DC converter for converting an AC voltage output from the power factor improving unit into a DC voltage; A plurality of LED arrays provided with the converted DC voltages, each corresponding to the plurality of partition blocks, and each of which includes a plurality of light emitting diodes (LEDs); A plurality of pulse width modulation controllers respectively corresponding to the plurality of division blocks, each generating pulse width modulation signals whose duty ratio is determined according to luminance setting information of the plurality of LED arrays provided by the multi-dimmation dimming controller; field; Each of the amplitude modulation signals corresponding to each of the plurality of partition blocks and whose amplitude is determined according to at least one of color information of light emitted from each of the plurality of LED arrays and temperature information of each of the plurality of LED arrays, respectively. Generating a plurality of amplitude modulation controllers; A control signal of a variable amplitude variable pulse width corresponding to each of the plurality of partition blocks, and controlling an amount of light emitted from the LED array based on a duty ratio of the pulse width modulation signal and an amplitude of the amplitude modulation signal. A plurality of pulse width amplitude modulation controllers for generating the respective signals; And And a plurality of constant current drivers respectively corresponding to the plurality of partition blocks and driving currents flowing through the respective LED arrays according to the respective control signals. The method of claim 7, wherein The power factor improving unit includes a valley fill passive power factor improvement circuit. delete The method according to claim 7 or 8, Each of the plurality of constant current drivers A driving transistor including a control terminal to which the control signal is applied and a first terminal connected to one end of the LED array; A resistor connected to a second terminal of the driving transistor and providing a feedback voltage level linearly corresponding to a current flowing in the LED array; And And an amplifier receiving the reference voltage level and the feedback voltage level, amplifying the difference, and outputting the difference to the control terminal of the driving transistor. The method of claim 7, wherein An encoder for encoding luminance setting information of the LED array in a serial or parallel manner, The backlight unit may further include a decoder for decoding the encoded luminance setting information and transmitting the decoded result to the plurality of pulse width modulation controllers.

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