KR101143880B1 - Led driving circuit for generating driving voltage with wide range - Google Patents

Abstract

PURPOSE: A light emitting diode of a driving circuit is provided to improve accuracy of control by controlling upper limit voltage and lower limit voltage according to a normal level state or an overflow state. CONSTITUTION: A driving voltage offer block(BKGDR) comprises a booster converter(110) and a pulse width modulator(120). The booster converter boosts and levels input voltage(VIN). The pulse width modulator modulates pulse width of a pulse signal(VMI) offered from the booster converter and creates a boost control signal(VMU). A control voltage generation block(BKVCON) offers shifting data(SDAT) and control reference voltage(VRCON). The control voltage generation block comprises a feedback monitoring part(210), a data shifter(220) and DAC(Digital-to-Analog Converter)(230).

Description

LED driving circuit for generating a driving voltage to extend the level range {LED driving circuit for generating driving voltage with wide range}

The present invention relates to a light emitting diode driving circuit, and more particularly, to a light emitting diode driving circuit for generating a driving voltage for driving a light emitting diode (LED) used as a light source of a backlight unit of a display panel.

Typically, a display device such as a liquid crystal display device has a display panel having a plurality of pixels arranged in a matrix, and the plurality of pixel cells display an intended image by adjusting the transmission amount of light supplied from the backlight unit. do.

In this case, as a light source for supplying light to the display panel, LEDs are often used. LED is eco-friendly, high-speed response is effective for video signal stream, impulsive driving, excellent color reproducibility, and can arbitrarily change brightness, color temperature, etc. The display panel has suitable advantages of miniaturization, thinness, and light weight. In this case, the plurality of LEDs are used in the form of LED strings connected in series, and the LEDs emit light by the driving voltage provided from the LED driving circuit. In terms of image quality and reliability, it is important to precisely adjust the driving voltage.

1 is a view showing a conventional LED driving circuit. The LED driving circuit of FIG. 1 provides a driving voltage VDR to a light emitting block BKLU including a plurality of LEDs. In this case, the plurality of LEDs are formed of a plurality of LED strings ST1 to STn, and are emitted by a driving voltage VDR provided to a head end.

The LED driving circuit of FIG. 1 includes a driving voltage providing block BKGDR, a feedback monitoring unit 10, a data shifter 20, a DAC 30, and a boundary voltage generator 40.

The feedback monitoring unit 10 monitors whether the voltage at the tail end of the LED strings ST1 to STn falls below a predetermined level, and generates monitoring feedback data FDAT accordingly. The data shifter 20 generates the shifting data SDAT by up counting the monitoring feedback data FDAT. The DAC 30 converts the shifting data SDAT of the digital component into a control reference voltage VRCON of the analog component.

The driving voltage providing block BKGDR provides the driving voltage VDR according to the input voltage VIN. The driving voltage VDR is adjusted to an appropriate level by the control reference voltage VRCON.

Here, the control reference voltage VRCON has a level within the range of the upper limit voltage VTOP and the lower limit voltage VBOT provided by the boundary voltage generator 40. At this time, in order to precisely control the driving voltage VDR, it is required to limit the difference between the upper limit voltage VTOP and the lower limit voltage VBOT to a predetermined magnitude.

By the way, in the conventional LED drive circuit, the upper limit voltage VTOP and the lower limit voltage VBOT are at a fixed level. Accordingly, since the level of the control reference voltage VRCON may be limited to a certain range, the level of the driving voltage VDR is also limited to a certain range. In this case, the range of the level of the driving voltage VDR provided in the conventional LED driving circuit may not include a voltage of a desired level.

Therefore, in the conventional LED driving circuit, too much current is generated in the LED strings ST1 to STn, so that reliability is reduced, or too little current is generated so that an image of an intended brightness cannot be displayed. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a light emitting diode driving circuit which generates a driving voltage in which a range of levels is expanded while maintaining precision of control.

One aspect of the present invention for achieving the above technical problem relates to a light emitting diode driving circuit for providing a driving voltage to the head end of each of a plurality of LED strings. The LED driving circuit of the present invention includes a driving voltage providing block for providing the driving voltage, wherein the level of the driving voltage is adjusted according to the level of a control reference voltage; A control voltage generation block for providing shifting data and the control reference voltage, wherein the shifting data has a data value that depends on a voltage at a tail end of at least one of the LED strings, wherein the control reference voltage is the at least one LED. The control voltage generation block having a level dependent on the voltage at the tail end of the string, the control voltage generation block having a level within a range corresponding to the level of the upper and lower boundary voltages received; And a threshold voltage providing block for providing the upper limit voltage and the lower limit voltage, wherein the levels of the upper limit voltage and the lower limit voltage are updated in response to the shifting data reaching a limit data value.

According to the LED driving circuit of the present invention, a driving voltage is generated in which a range of levels is expanded while maintaining control precision.

A brief description of each drawing used in the present invention is provided.
1 is a view showing a conventional LED driving circuit.
2 is a view showing a light emitting diode driving circuit according to an embodiment of the present invention.
3 is a diagram illustrating the boundary voltage providing block of FIG. 2 in detail.
4 is a diagram illustrating an example of an operation of the LED driving circuit of FIG. 2.

For a better understanding of the present invention and its operational advantages, and the objects attained by the practice of the present invention, reference should be made to the accompanying drawings, which illustrate preferred embodiments of the invention, and the accompanying drawings. In understanding each of the figures, it should be noted that like parts are denoted by the same reference numerals whenever possible. Incidentally, detailed descriptions of well-known functions and configurations that are determined to unnecessarily obscure the subject matter of the present invention are omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a view showing a light emitting diode driving circuit according to an embodiment of the present invention. The LED driving circuit of FIG. 2 provides the driving voltage VDR to the LED strings ST1 to STn constituting the light emitting block BKLU.

Each of the plurality of LED strings ST1 to STn includes LEDs connected in series and arranged in parallel with each other. In addition, the plurality of LED strings ST1 to STn emit light by the driving voltage VDR which is commonly provided to the respective head ends.

In this specification, the terms 'headend' and 'tailend' are used. In this case, the 'head end' refers to an anode terminal of the first LED to which the driving voltage VDR is applied in each LED string, and the 'tail end' refers to the cathode of the last first LED in each LED string. ) Means terminal.

Referring to FIG. 2, the LED driving circuit of the present invention includes a driving voltage providing block BKGDR, a control voltage generating block BKVCON, and a boundary voltage providing block BKGBD.

The driving voltage providing block BKGDR receives an input voltage VIN and a control reference voltage VRCON and provides the driving voltage VDR.

Specifically, the driving voltage providing block BKGDR includes a booster converter 110 and a pulse width modulator 120. The booster converter 110 boosts and flattens the input voltage VIN to provide the driving voltage VDR. In this case, the degree of boosting is controlled by the boost control signal VMU provided from the pulse width modulator 120.

The pulse width modulator 120 generates the boost control signal VMU by modulating the pulse width of the pulse signal VMI provided from the booster converter 110. In this case, the modulated pulse width is determined by comparing the control reference voltage VRCON and the boost feedback voltage VFST. The boost feedback voltage VFST is a voltage divided from the driving voltage VDR.

By the driving voltage providing block BKGDR as described above, the driving voltage VDR has a level corresponding to the level of the input voltage VIN, but is controlled by the control reference voltage VRCON.

2, the control voltage generation block BKVCON provides shifting data SDAT and the control reference voltage VRCON. In this case, the shifting data SDAT has a data value depending on a voltage of a tail end of at least one LED string.

The control reference voltage VRCON has a level that depends on the voltage of the tail end of at least one of the LED strings, and corresponds to the level of the received upper limit voltage VTOP and the level of the lower limit voltage VBOT. It has a level within the range.

In the present exemplary embodiment, the shifting data SDAT and the control reference voltage VRCON are applied to the lowest level voltage among the voltages VSC1 to VSCn of the tail ends of the LED strings ST1 to STn. It has a dependent data value.

The control voltage generation block BKVCON includes a feedback monitoring unit 210, a data shifter 220, and a DAC 230.

The feedback monitoring unit 210 monitors the voltages VSC1 to VSCn of the tail ends of the LED strings ST1 to STn to generate monitoring feedback data FDAT of a digital component. In this case, the monitoring feedback data FDAT has a data value corresponding to the voltage of the lowest level among the voltages VSC1 to VSCn of the tail ends of the LED strings ST1 to STn.

The feedback monitoring unit 210 includes a feedback monitor 211 and an ADC 213. The feedback monitor 211 monitors the voltages VSC1 to VSCn of the tail ends of the LED strings ST1 to STn to generate a monitoring signal VFMN of an analog component. In this case, the monitoring signal VFMN has a voltage level corresponding to the voltage of the lowest level among the voltages VSC1 to VSCn of the tail ends of the LED strings ST1 to STn.

The ADC 213 converts the monitoring signal VFMN of the analog component into the monitoring feedback data FDAT of the digital component and outputs the converted feedback signal.

The data shifter 220 generates the shifting data SDAT by shifting the monitoring feedback data FDAT in response to a clock of an externally provided updater signal XDATE.

The data shifter 220 resets the shifting data SDAT to an initial data value in response to the data initialization signal XST. In this case, the data initialization signal XST transitions in response to the data value of the shifting data SDAT reaching the limit data value.

The DAC 230 receives the upper limit voltage VTOP and the lower limit voltage VBOT, and converts the shifting data SDAT of a digital component to generate the control reference voltage VRCON of an analog component. In this case, the control reference voltage VRCON has a level corresponding to the shifting data SDAT, but a level within a range corresponding to the level of the upper limit voltage VTOP received and the level of the lower limit voltage VBOT. Have

2, the boundary voltage providing block BKGBD provides the upper limit voltage VTOP and the lower limit voltage VBOT. In this case, the levels of the upper limit voltage VTOP and the lower limit voltage VBOT are updated in response to the shifting data SDAT reaching a limit data value.

Here, the limit data value means that the level of the control reference voltage VRCON corresponds to one of the upper limit voltage VTOP and the lower limit voltage VBOT.

FIG. 3 is a diagram illustrating in detail the boundary voltage providing block BKGBD of FIG. 2. Referring to FIG. 3, the threshold voltage providing block BKGBD includes a threshold voltage generator 310, a lower limit selector 330, an upper limit selector 350, and an overflow checker 270.

The boundary voltage generator 310 generates first to third boundary voltages VBD1 to VBD3 having an ordered level. In the present embodiment, the level increases in the order of the first boundary voltage VBD1, the second boundary voltage VBD2, and the third boundary voltage VBD3.

The lower limit selector 330 provides any one selected from the first boundary voltage VBD1 and the second boundary voltage VBD2 to the lower limit voltage VBOT according to the overflow signal XOV.

 The upper limit selector 350 provides any one selected from the second boundary voltage VBD2 and the third boundary voltage VBD3 to the upper limit voltage VBOT according to the overflow signal XOV. .

The overflow checking unit 370 generates the overflow signal XOV that is activated in response to the data value of the shifting data SDAT reaching the limit data value. In addition, the overflow checking unit 370 generates the data initialization signal XST that is shifted in response to the data value of the shifting data SDAT reaching the limit data value.

4 is a diagram illustrating an example of an operation of the LED driving circuit of FIG. 2. In the present specification, when the LED driving circuit of FIG. 2 implements an appropriate level of the driving voltage VDR, it is described as an up counting method of gradually increasing the level of the driving voltage VDR.

In this case, the limit data value corresponds to the level of the upper limit voltage VTOP of the control reference voltage VRCON. The limit data value means a maximum data value that the shifting data SDAT may have. If the shifting data SDAT is 8-bit data, the limit data value is '255'. The initial data value is '0'.

First, the LED driving circuit of the present invention is operated in the 'normal level state (STATE1)' which is a state before the shifting data SDAT reaches the limit data value.

In the normal level state STAT1, the overflow signal XOV is "L". In this case, the lower limit selector 330 provides the first boundary voltage VBD1 as the lower limit voltage VBOT, and the upper limit selector 350 provides the second boundary voltage VBD2 as the upper limit voltage ( VTOP).

Accordingly, in the normal level state STAT1, the first threshold voltage VBD1 is the lower limit voltage VBOT and the second threshold voltage VBD2 is the upper limit voltage VTOP. In accordance with the shifting data SDAT, the level of the control reference voltage VRCON gradually increases.

In the normal level state STAT1, when the level of the control reference voltage VRCON does not reach the target voltage level VTAG, the overflow state STATE2 is entered.

 That is, when the shifting data SDAT reaches the limit data value, the LED driving circuit of the present invention proceeds in the 'overflow state' STATE2. In this case, the data initialization signal XST is generated as a pulse in response to the data value of the shifting data SDAT reaching the limit data value, and the overflow signal XOV transitions to " H ".

In this case, the lower limit selector 330 provides the second threshold voltage VBD2 as the lower limit voltage VBOT, and the upper limit selector 350 provides the third threshold voltage VBD3 to the upper limit voltage ( VTOP).

Therefore, in the overflow state (STATE2), the second boundary voltage VBD2 is the lower limit voltage VBOT and the third boundary voltage VBD3 is the upper limit voltage VTOP. According to the shifting data SDAT, the level of the control reference voltage VRCON gradually rises to reach the target voltage level VTAG.

In the LED driving circuit of the present invention, the difference between the first boundary voltage VBD1 and the second boundary voltage VBD2 is equal to the difference between the second boundary voltage VBD2 and the third boundary voltage VBD3. When designed identically, in the normal level state STAT1 and the overflow state STATE2, the precision of the control for the driving voltage VDR is kept the same as before.

In the LED driving circuit of the present invention, the upper limit voltage VTOP and the lower limit voltage VBOT are adjusted according to whether the steady state STAT1 or the overflow state STATE2 is used. Accordingly, the range of levels that the control reference voltage VRCON may have is expanded.

Therefore, according to the LED driving circuit of the present invention, the range of the level that the driving voltage VDR can have is expanded.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom.

For example, in the present specification, an up-counting LED driving circuit for gradually increasing the level of the driving voltage VDR in implementing an appropriate level of the driving voltage VDR is illustrated and described as an embodiment. do. However, the technical idea of the present invention may be realized by a down counting LED driving circuit that gradually lowers the level of the driving voltage VDR in implementing an appropriate level of the driving voltage VDR. It is obvious to those skilled in the art.

Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (5)

A light emitting diode driving circuit for providing a driving voltage to a head end of each of a plurality of LED strings,
A driving voltage providing block for providing the driving voltage, wherein the level of the driving voltage is adjusted according to a level of a control reference voltage;
A control voltage generation block for providing shifting data and the control reference voltage, wherein the shifting data has a data value that depends on a voltage at a tail end of at least one of the LED strings, wherein the control reference voltage is the at least one LED. The control voltage generation block having a level dependent on the voltage at the tail end of the string, the control voltage generation block having a level within a range corresponding to the level of the upper and lower boundary voltages received; And
A threshold voltage providing block for providing the upper limit voltage and the lower limit voltage, wherein the level of the upper limit voltage and the lower limit voltage includes the threshold voltage providing block that is updated in response to the shifting data reaching a limit data value A light emitting diode drive circuit.
The method of claim 1, wherein the control voltage generation block is
A feedback monitoring unit for monitoring the voltage at the tail end of the at least one LED string to generate monitoring feedback data of the digital component, the monitoring feedback data corresponding to the voltage at the tail end of the at least one LED string being monitored; The feedback monitoring unit having a data value;
A data shifter configured to generate the shifting data by down-up the monitoring feedback data, wherein the shifting data is reset to an initial data value in response to the data value of the shifting data reaching the limit data value; And
And a DAC which receives the upper limit voltage and the lower limit voltage and converts the shifting data of a digital component to generate the control reference voltage of an analog component.
The method of claim 2, wherein the feedback monitoring unit
A feedback monitoring unit for monitoring a voltage at a tail end of the at least one LED string to generate a monitoring signal of an analog component, wherein the monitoring signal has a voltage level corresponding to a voltage at a tail end of the at least one LED string; A feedback monitor having a; And
And an ADC for converting the monitoring signal into the monitoring feedback data.
The method of claim 1, wherein the threshold voltage providing block
A threshold voltage generator configured to generate first to third threshold voltages having an ordered level;
A lower limit selector for providing any one selected from the first boundary voltage and the second boundary voltage as the lower limit voltage in accordance with an overflow signal;
An upper limit selector for providing, as the upper limit voltage, any one selected from the second boundary voltage and the third boundary voltage according to the overflow signal; And
And an overflow confirmation unit for generating the overflow signal to be transited in response to the shift of the shift data value to the limit data value.
The method of claim 1, wherein the shifting data is
And a data value dependent on a voltage of a lowest level among voltages of tail ends of the plurality of LED strings.

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