KR100895390B1 - Multi-color backlight control circuit and multi-color backlight control method - Google Patents

Abstract

The present invention relates to a multi-color backlight control circuit,

A plurality of pins electrically connected to the plurality of LED strings having different LED colors; And a voltage supply circuit for receiving an input voltage and supplying a single output voltage to the plurality of LED strings having the different LED colors.

In addition, the present invention relates to a multi-color backlight control method comprising the step of supplying a single output voltage to a plurality of LED strings having different LED colors.

Multicolor, Backlight, Control Circuit, LED, String

Description

MULTI-COLOR BACKLIGHT CONTROL CIRCUIT AND MULTI-COLOR BACKLIGHT CONTROL METHOD}

The present invention relates to a multicolor backlight control circuit and a multicolor backlight control method.

In liquid crystal displays (hereinafter referred to as "LCDs"), the backlight control circuit is designed to control the light emitting diodes (hereinafter referred to as "LEDs") that are irradiated to the back side of the LCD and allow the user to observe images from the front side of the LCD screen. To help.

According to the state of the art, there are two backlight LED structures, one using a single color white LED and another using red, green and blue LEDs. The latter is described herein as "multicolor backlight" and the control circuit of "multicolor backlight" is described as "multicolor backlight control circuit".

Monocolor white LED backlights are used in fine control circuits, and "white" light is not generated with true white light; In fact, it is a synthesized light having a light that is not excellent by stimulating a fluorescent powder by a blue LED. On the other hand, white light obtained by mixing light from R, G, and B LEDs has good quality light. However, regardless of whether the white backlight is obtained from white LEDs or R, G, B LEDs, light must pass through the color filter within the LCD. Any part of the light that does not match the color of the filter is filtered out. In other words, energy loss occurs and the photo energy is not optimally used.

A so-called "color sequential technique" is proposed to solve the above problem. In the color sequential technique, the color filters are not used because the R, G, and B LEDs emit light to match pixels of the same color in the LCD. This technique saves power but requires more complex control circuits. The multicolor backlight control circuit applied to this color sequential technique is very important and very necessary.

More specifically, the operating voltages of the R, G, and B LEDs are different. In general, the white LED has an operating voltage of 3.2V-3.8V, the red LED has an operating voltage of 1.9V-2.6V, the green LED has an operating voltage of 2.9V-3.7V, and the blue LED has 3.0V- It has an operating voltage of 3.8V. A large number of LEDs are required in series in the LCD backlight, and the voltages supplied to strings of LEDs of different colors are very different and are practically above 15V. As shown in Fig. 1, the conventional structure is a backlight control circuit 10R for supplying three different voltages Vout (R), Vout (G), and Vout (B) to control the brightness and power efficiency of each of R, G, and B, respectively. , 10G and 10B. The three backlight control circuits can be integrated into one circuit chip, but it is still necessary to repeat the three voltage supply circuits and the corresponding feedback control circuit.

The structure according to the prior art is not the optimal structure strictly. Therefore, it is desirable to provide a more efficient multicolor backlight control circuit that is made with simpler hardware structure and lower cost.

It is an object of the present invention to provide a multicolor backlight control circuit having a simpler hardware structure.

Another object of the present invention is to provide a multi-color backlight control method.

In order to achieve the above object, the multi-color backlight control circuit according to the present invention comprises: a plurality of pins electrically connected to a plurality of LED strings having different LED colors; And a voltage supply circuit for receiving an input voltage and supplying a single output voltage to the plurality of LED strings having the different LED colors.

The term "supplying a single output voltage" means "supplying one output voltage at a given time point". The supply voltage may change at different times according to feedback detection.

According to the present invention, the total number of LEDs with each color is equal to the number of other colors, or the irradiation time period for which the LEDs with different colors emit light is different from that of other colors through the LEDs having different or different colors. The amount of current is different.

In addition, the backlight control circuit according to the present invention includes a plurality of pins electrically connected to the plurality of LED strings; And a voltage supply circuit for receiving an input voltage and supplying a single output voltage to the plurality of LED strings, wherein the number of LEDs in at least two LED strings is different.

The above-described backlight control circuit may be a single color or a multi-color backlight control circuit.

According to the present invention, the multi-color backlight control method includes supplying a single output voltage to a plurality of LED strings having different LED colors.

The term "supplying a single output voltage" means "supplying one output voltage at a given time point". The supply voltage may change at different times according to feedback detection.

As described above, according to the multicolor backlight control circuit and the multicolor backlight control method according to the present invention, a plurality of LEDs having different colors can be controlled using a single multicolor backlight control circuit without providing a plurality of voltage supply circuits. Its structure is also economical because it can be produced simply and at low cost.

Hereinafter, the most preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. . Other objects, features, and operational advantages, including the object, operation, and effect of the present invention will become more apparent from the description of the preferred embodiment.

As shown in Fig. 2, the present invention provides a single output voltage Vout, and the output voltage requires a single multicolor backlight control circuit 100. The multi-color backlight control circuit 100 has a plurality of pins to be connected to the LED string having a different color. Three pins are shown for each color (R1-R3, G1-G3 and B1-B3) and the actual number of pins is not the same as the number shown. The output voltage Vout is slightly greater than or equal to the lowest common multiple operating voltage of the R, G, and B LEDs. Relatively, the number of LEDs in R, G, and B LEDs is different. So each LED string needs a similar voltage, ie all LED strings can be connected and operated under the same supply voltage Vout. As shown, the number of LEDs in the R, G, B LED strings is shown as 5, 4, and 3, respectively. Each symbolically represents a different number of LEDs; The actual number should be determined according to the requirements. In one embodiment, the number of red LEDs is 15 and the number of green LEDs and the number of blue LEDs are both 10; The output voltage Vout is 36V. If the operating voltages of the green and blue LEDs are similar and the differences between each LED are minute, they can be ignored. If the output voltage is slightly higher than the voltage required by the LED string, it does not matter as long as the danger level is not exceeded. Although the power utilization efficiency is slightly lower, the LEDs operate normally.

It is required to adjust the LED brightness because the number of LEDs having R, G, B LED strings in the structure of Fig. 2 is different. According to a preferred embodiment of the present invention, the number of LEDs having each color may be provided similar to the number of the same or different colors by adjusting the number of strings of each color. For example, assuming that the number of red LEDs is 15 in each string, the number of green LEDs and the number of blue LEDs is 10 in each string, the number of strings of the R, G, and B LEDs will be 2, 3, and 3, respectively. The total number of LEDs in each color is equal to 30.

As the number of strings changes, the total number of R, G, and B LEDs can be kept different while the irradiation cycle time of the LEDs is adjusted to compensate for the number difference. For example, assuming that the ratio between R, G, and B LEDs is 3: 2: 2, the irradiation time period can be relatively 2: 3: 3, and the decorative effect of each color is the same or similar. . Referring to FIG. 3, the irradiation time periods of the R, G, and B LEDs are T1, T2, and T3, respectively, with a ratio of 2: 3: 3. The periods of T1, T2 and T3 can be provided to the counter 16 and three pulse generators 17, 18 and 19, the counter 16 being pulsed in accordance with the clock signal to generate pulses T1, T2 and T3. Trigger generators 17, 18 and 19. The clock signal may be obtained from an external circuit up to a clock generator in the multicolor backlight control circuit 100 (as from the LCD controller) or in the multicolor backlight control circuit 100. Also, in some cases, after each color's LED emits light for one revolution, all LEDs are turned off and shaded to eliminate visible residual effects. In this case a fourth pulse generator (not shown) or more pulse generators are provided to generate the shaded state and the counter 16 triggers the pulse generators 17, 18, 19 and the fourth pulse generator sequentially.

In order to control the irradiation time according to another embodiment, the present invention controls the amount of current through LEDs having different colors, so that LEDs having different colors provide the same or similar brightness, wherein the total number of R, G, and B LEDs is used. Is a different state. 4 shows a simple structure for the LED string for each color. In an embodiment of the multi-color backlight control circuit 100, current sources CS1-CS3 are provided to control the current sources through LED strings having different LED colors, respectively. The sample-and-hold circuits S / H 31-33 sample and hold voltages of the corresponding nodes, respectively. The S / H circuits 31-33 are respectively controlled by signals 31-33. 5 shows the structure of the S / H circuit 31 in detail. When the signal S1 closes the switch SW, the S / H circuit 31 samples the voltage at the corresponding node NA1 and switches ( When SW is opened, the voltage is stored at capacitor C1.

Referring to FIG. 4, the minimum voltage selection circuit 21 selects the lowest voltage from the outputs 111-113 of the S / H circuits 31-33, compares the reference voltage with the lowest voltage, and compares the error amplifier circuit 13 with the lowest voltage. Transmit the selected voltage. The control signal 15 is generated by the comparison and the control signal 15 is sent to the voltage supply circuit 11 to generate a target output voltage Vout. The purpose of selecting the lowest voltage is to ensure that the output voltage Vout meets the requirements of all LED paths and the current source on all LED paths generally operates. For example, the voltage supply circuit 11 may be a boost converter, a buck converter, a buck-boost converter, a flyback converter or the like.

On the other hand, a transient voltage protection circuit can be provided to protect the multicolor backlight control circuit to prevent the output voltage Vout from increasing indefinitely. The transient voltage protection circuit is made in a conventional single color white LED backlight control circuit, and further description thereof will be omitted.

6 shows a detailed structure of the current sources CS1-CS3. As shown in the figure, except for the basic current source structure, the current sources CS1-CS3 are additionally controlled to correspond to the enable signals EN1-EN3. The current sources CS1-CS3 only operate when the enable signals EN1-EN3 turn on the corresponding switches. The enable signals EN1-EN3 have a waveform to enable as shown in FIG. 7, and sequentially enable the current sources CS1-CS3 so that LEDs having the corresponding colors emit light alternately. The figure shows the relationship between the enable signals EN1-EN3 and the signals S1-S3 in the S / H circuits 31-33; After the enable signals EN1-EN3 enable the corresponding current sources CS1-CS3, the signals S1-S3 trigger the S / H circuit that stores the voltage at that node.

Each current source CS1-CS3 controls LED paths with different colors and different amounts of current pass through LED strings with different colors and balance the brightness of the LEDs. The current amount of the current source CS1-CS3 is,

(1) by setting the reference voltage VR1, VR2 and VR3,

(2) setting resistors RS1, RS2 and RS3 or

(3) by always (1) and (2),

 Can be set.

An approach for setting the LED brightness may use any of the three described above.

The structure of the current source is not limited to that shown in FIG. For example, bipolar transistors can be fabricated. The enable signal may be applied in other ways and may be optional from that shown in FIG. The sampling nodes of the S / H circuits 31 to 33 are not limited to NA 1 -NA 3 and may instead be NB 1 -NB 3. All the above contents are included in the technical idea of the present invention.

Looking at the multi-color backlight control circuit 100 of FIG. 4, if there is an error in the LED path such that very low current or current does not pass through the path (when the pins are incorrectly connected, grounded or the LED in the path opens the path). Burned), the voltage supply circuit 11 keeps increasing the output voltage Vout. In order to avoid such a problem, the circuit 100 may be configured as an under current detection circuit (UCD) 41-43. The lower current detection circuit (UCD) 41-43 may be connected between the S / H circuit 31-33 and the minimum voltage selection circuit 21 or the S / H circuit 31-33 as shown in the drawing. It may be provided at a position between the current sources CS1-CS3. When no cases such as "no current" or "very low current" occur, the lower current detection circuits UCD 41-43 have a minimum voltage selection circuit 21 for receiving the signals 111-113. . When one or more of the LED paths are no current or very low current, the lower current detection circuits (UCD) 41-43 block the corresponding signals 111-113 so that a signal can be input to the minimum voltage selection circuit 21. And the output voltage Vout is not kept increasing.

FIG. 10 illustrates a lower current detection circuit UCD 41. The above concept may be more easily understood with reference to FIG. In the LED path 101, the current condition i ₁₀₁ is converted into a voltage signal and compared with a predetermined reference voltage Vuc. The comparison result is indicated by the signal S41 controlling the switch SW41 and when the "no current" or "very low current" case occurs in the path 101, the switch SW41 is opened (of course, the comparator CP41 according to the design of the switch SW41). Output can be switched). Fig. 10 shows another embodiment, in which the switch does not need to be provided in the path 111, and the expected effect (excludes a signal from the input of the micro voltage selection circuit 21) can be obtained.

There are various methods for converting a current condition into a voltage signal in the LED path 101 and there may be two examples. Referring to Fig. 11, if the current source CS1 is made of an NMOSFET, the drain of the transistor can be extracted and the voltage signal can be sent to the lower current detection circuit UCD 41 which is compared with a predetermined reference voltage Vuc. Alternatively, as shown in FIG. 12, the current voltage signal of the transistor may be extracted and sent to the lower current detection circuit UCD 41 which is compared with the reference voltage Vuc. Depending on the position relative to the extraction voltage, the value of the reference voltage Vuc should be set to suitably detect whether a "no current" or "very low current" condition occurs in the path 101.

In addition, the same effect is achieved by detecting the voltage at one or more nodes within the exterior of the outer LED path of the multicolor backlight control circuit 100, but is not preferred because additional pins are required. However, such changes are also included in the technical idea of the present invention.

The absence of the signals 111-113 under the condition that the lower current detection circuit UCD is provided makes it possible to become a valid input to the minimum voltage selection circuit 21 in the circuit initialization step. Thus no current flows on all LED paths. So the voltage supply circuit 11 is not initialized to provide power. Various approaches are described in the following examples in order to prevent the malfunction of the machine described above.

First, in the circuit initialization step, the lower current detection circuit (UCD) 41-43 may be shielded according to a signal such as a signal related to a circuit initialization, a reset signal or a power source of a soft start signal, and the lower current detection circuit (UCD) 41-43 does not send signals S41-S43 or signals S41-S43 are sent within a period of start period from the start of circuit initialization. This period typically occurs after a circuit initialization step (such as the end signal of the soft start signal) by counting a certain period of time by a counter or by monitoring whether the output voltage Vout exceeds a predetermined value (made by a comparator). It is blocked by the signal. 13 shows another method in which the start period shielding circuit 23 shields the signals S41-S43 of the lower current detection circuit UCD during the above-described method or start period period and restores the functions of the signals S41-S43 after the start period period ends. Generating shielding signal 24 according to one of the methods is shown. The logic AND gate is just an embodiment and the shielding function can be achieved by other suitable methods. In addition, the shielding signal 24 does not need to shield all of the signals S41-S43, but only one or some of them may be shielded instead.

Referring to Fig. 14, the malfunction can be selectively solved by providing a start period circuit. In a specific embodiment, the minimum voltage selection circuit 21 includes an additional input for receiving an output from the start period circuit 28. The purpose of the start period circuit 28 is to provide a minimum voltage selection circuit 21 with a valid input 110, wherein all values of the other inputs 111-113 are cut off. The valid input is compared with the reference voltage Vref in the error amplifier circuit 13 generating the valid signal 15 and the voltage supply circuit 11 is started to supply power. Therefore, when all other inputs 111-113 are cut off, the start period circuit 28 must be able to generate a voltage signal lower than the reference voltage Vref and the error amplifier circuit 13 generates a signal 15. However, there is no lasting effect when the overall circuit operates normally.

There are various ways to perform the above-described operation. For example, the signal 110 may be generated from the divided voltage of the output voltage Vout. Alternatively, the signal 110 may have a short period of 0 [V] at the time of initializing the circuit and at the time of switching to a high voltage level.

4, 9, and 14, the S / H circuits 31-33 are used to store the corresponding voltage, and the minimum voltage selection circuit 21 compares the reference voltage Vref with the corresponding voltage to obtain the lowest output ( 111-113). The method described above is not the only method used in the present invention. Fig. 15 shows another embodiment, in which the multiplexer circuit MUX, 50 selects one of the nodes NA1-NA3 according to the enable signals EN1-EN3, and the voltage at the node selected for the valley detection circuit 60. Provided by typing The valley detection circuit 60 is capable of maintaining the lowest voltage within a period and the output of the valley detection circuit 60 represents the lowest voltage in the nodes NA1-NA3 and is provided for the purpose of selecting the lowest voltage. On the other hand, it is preferable that a lower current detection circuit (UCD) 40 is provided for stability; The lower current detection circuit UCD 40 may be provided on the right side of the MUX 50 or the left side of the MUX 50 as shown. The minimum voltage selection circuit 21 selects the lowest voltage between multiple parallel inputs within a given time point, and the valley detection circuit 60 selects the lowest voltage between multiple serial inputs within a time period.

Fig. 16 shows the specific structure of the valley detection circuit 60, where a small current source (current source providing a small amount of current, 62) gradually charges the capacitor 64. As shown in Figs. When the voltage 64 applied to the capacitor is greater than the input voltage IN, the capacitor 64 is discharged through the differential amplifier 66 until the voltage of the capacitor 64 drops to the input voltage IN. Therefore, the output voltage maintains the lowest input voltage.

For reference, the specific embodiments of the present invention are only presented by selecting the most preferred embodiments to help those skilled in the art from the various possible examples, and the technical spirit of the present invention is not necessarily limited or limited only by the embodiments. In addition, various changes, additions, and changes are possible within the scope of the technical idea of the present invention, as well as other equivalent embodiments.

For example, the present invention is not limited to the backlight control circuits for R, G, and B LEDs, but can be applied to the multi-color backlight control circuits having other colors such as white LED backlight control circuits, red, yellow, and cyan. In another example, a circuit that does not affect the basic meaning of the signal, such as a delay circuit, is provided between the two illustrated devices, each directly connected in the above specific embodiment. As in additional embodiments, so-called "backlit" control circuits can be applied to control not only backlights for LCDs but also other light emitting devices.

All changes and changes in the present invention are within the scope of the spirit of the invention described in the claims and should be interpreted as the same category.

Figure 1 shows a control circuit design according to the prior art,

FIG. 2 is a structural diagram showing a preferred embodiment of the present invention showing supplying voltage to LED strings having different colors by a single multi-color backlight control circuit.

Figure 3 shows a preferred embodiment of the present invention, showing that LEDs having different colors emit light during different time periods,

4 shows a detailed structure of a multicolor backlight control circuit according to the present invention;

5 shows an embodiment of a sample-and-hold circuit,

6 shows an embodiment of a current source circuit,

Fig. 7 shows the waveform relationship between enable signals EN1-EN3 and signals S1-S3,

8 shows another embodiment of a current source circuit,

9 shows a detailed structure of a multi-color backlight control circuit as another embodiment according to the present invention;

10 shows the lower current detection circuit UCD.

11 and 12 show how two circuits are connected to other circuits as examples of the lower current detection circuit.

13 shows an embodiment of a start period shielding circuit;

14 shows how the start period is achieved by the start period shielding circuit;

Figure 15 shows another embodiment of the present invention,

Fig. 16 shows an embodiment of the valley detection circuit.

Claims (43)

In the multi-color backlight control circuit, A plurality of pins electrically connected to the plurality of LED strings having different LED colors; A voltage supply circuit for receiving an input voltage and supplying a single output voltage to a plurality of LED strings having different LED colors; A first circuit for extracting a voltage from the plurality of LED strings having different LED colors and selecting the lowest of the voltages; And Including an error amplifier for comparing a reference voltage with an output of the first circuit and outputting a signal for controlling the voltage supply circuit. Wherein said first circuit comprises a plurality of sample-and-hold circuits to maintain said extracted voltage and wherein the number of LEDs in at least two LED strings having different colors is different. delete The method of claim 1, LEDs having different colors emit light sequentially. The method of claim 3, Multi-color backlight control circuit, characterized in that the irradiation time period is different from at least two LED strings having different colors as LEDs of different colors emit light. The method of claim 4, wherein And a counter and a plurality of pulse generators, wherein the pulse generators generate pulses according to a counter output that controls each irradiation time period as LEDs having different colors emit light. delete delete delete delete delete delete delete The method of claim 1, And said first circuit comprises a minimum voltage detection circuit for selecting a lowest voltage from an input of said first circuit. In the multi-color backlight control circuit, A plurality of pins electrically connected to the plurality of LED strings having different LED colors; A voltage supply circuit for receiving an input voltage and supplying a single output voltage to a plurality of LED strings having different LED colors; A first circuit for extracting a voltage from the plurality of LED strings having different LED colors and selecting the lowest of the voltages; And Including an error amplifier for comparing a reference voltage with an output of the first circuit and outputting a signal for controlling the voltage supply circuit. The first circuit includes a valley detection circuit for detecting and maintaining a lowest voltage within a time period, wherein the number of LEDs in at least two LED strings having different colors is different. Color backlight control circuit. The method of claim 14, And the first circuit comprises a multiplexer circuit for selecting one of the extracted voltages and inputting the voltage to the valley detection circuit. The method of claim 14, The first circuit includes a lower current detection circuit for blocking a voltage lower than the third reference voltage from the extracted voltage. In the backlight control circuit, A plurality of pins electrically connected to the plurality of LED strings; A voltage supply circuit for receiving an input voltage and supplying a single output voltage to the plurality of LED strings; A first circuit for extracting a voltage from a plurality of LED strings and selecting a lowest voltage of the voltages; And And an error amplifier for comparing a reference voltage with an output of the first circuit and outputting a signal to control the voltage supply circuit. And said first circuit comprises a plurality of sample-and-hold circuits to maintain said extracted voltage, wherein the number of LEDs in at least two LED strings is different. delete delete delete delete delete delete The method of claim 17, And the first circuit comprises a minimum voltage detection circuit for selecting the lowest voltage from the input of the first circuit. In the backlight control circuit, A plurality of pins electrically connected to the plurality of LED strings; A voltage supply circuit for receiving an input voltage and supplying a single output voltage to the plurality of LED strings; A first circuit for extracting a voltage from a plurality of LED strings and selecting a lowest voltage of the voltages; And And an error amplifier for comparing a reference voltage with an output of the first circuit and outputting a signal to control the voltage supply circuit. And said first circuit comprises a valley detection circuit for detecting and maintaining a lowest voltage within a time period. The method of claim 25, The first circuit includes a multiplexer circuit for selecting one of the extracted voltages and inputting the voltage to the valley detection circuit. The method of claim 25, And the first circuit comprises a lower current detection circuit for blocking a voltage lower than the third reference voltage from the extracted voltage. In the multi-color backlight control method, Supplying a single output voltage to a plurality of LED strings having different LED colors; Extracting a voltage from the plurality of LED strings having different LED colors; Sampling and holding the extracted voltage; Selecting a lowest voltage among the extracted voltages; And And controlling an output voltage according to the selected lowest voltage. The method of claim 28, Providing a different number of LEDs in at least two plurality of LED strings having different LED colors. delete The method of claim 28, LEDs having different colors emit light sequentially. The method of claim 31, wherein The method of controlling a multi-color backlight, wherein the irradiation time period is different from at least two LED strings having different colors as LEDs having different colors emit light. delete delete delete delete The method of claim 28, The selecting of the lowest voltage is a step of selecting the lowest voltage among the voltages extracted at the same time. delete The method of claim 28, And blocking a voltage lower than a reference voltage from the extracted voltage. The method of claim 14, LEDs having different colors emit light sequentially. The method of claim 40, Wherein the irradiation time period is different from at least two LED strings having different colors as the LEDs having different colors emit light. The method of claim 41, wherein And a counter and a plurality of pulse generators, wherein the pulse generators generate pulses according to a counter output that controls each irradiation time period as LEDs having different colors emit light. In the multi-color backlight control method, Supplying a single output voltage to a plurality of LED strings having different LED colors; Extracting a voltage from the plurality of LED strings having different LED colors; Sampling and holding the extracted voltage; Selecting a lowest voltage among the extracted voltages; And Controlling an output voltage according to the selected lowest voltage; Including but not limited to: The selecting of the lowest voltage is a step of selecting the lowest voltage among the voltages extracted in one period.

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