KR20150005758A - Led driving apparatus capable of adjusting switching duty ratio for multi-channel led application - Google Patents

Abstract

A light emitting diode (LED) driving apparatus capable of adjusting a switching duty ratio according to the present invention can comprise: a first delay loop which receives a pulse train of a reference pulse width modulation (PWM) signal, generates a rough delay signal which is formed by roughly delaying the reference PWM signal by one period of a pulse, and activates a rough delay fixing signal when a phase difference between the rough delay signal and the reference PWM signal decreases to be smaller than or equal to a predetermined value; a second delay loop which generates a second delay signal by finely delaying a phase of the rough delay signal, when the rough delay fixing signal is activated; a duplication delay line which delays a phase of the reference PWM signal while maintaining phase delay characteristics of the first delay loop and the second delay loop and outputs a duplication delay signal; and a comparator which receives a voltage difference signal between a detection voltage by a driving current for one of a plurality of LED strings having different equivalent resistances and a predetermined reference voltage, and the duplication delay signal, and outputs a switching signal. The switching signal can have a duty rate for equalizing magnitudes of average currents for each of the LED strings according to a magnitude of a voltage difference signal between a detection voltage by the driving current of the one of the LED strings with different equivalent resistances and a predetermined reference voltage.

Description

TECHNICAL FIELD [0001] The present invention relates to a switching duty ratio adjustable LED driving device for a multi-channel LED device,

The present invention relates to an LED driving apparatus, and more particularly, to a switching duty ratio function of an LED driving apparatus.

Recently, a variety of lighting devices or image devices using LED (Light Emitting Diode) have appeared and are being welcomed in the market. Such devices include devices such as LED backlights or backlight of LCD (Liquid Crystal Display) TVs that can be directly connected to a commercial AC power source.

These LED devices drive an LED string in which a plurality of LEDs are connected in series. In some cases, one LED device may include multiple channels of LED strings. The electrical characteristics of the LED elements that make up the LED string of each channel may vary slightly depending on the operating environment or time and thus the equivalent resistance of each LED string may be different and as a result, The amount of current may also vary. In applications where brightness uniformity is important, such as LED backlighting, it is desirable to control the amount of current flowing through each LED string to be the same, since the amount of current actually determines the brightness.

Therefore, the multi-channel LED driving apparatus for driving such a multi-channel LED string controls a driving current by a pulse amplitude modulation (PAM) method or a pulse width modulation (PWM) method in order to maintain the same current amount for each channel. In the PAM scheme, the duty ratio of the current pulses supplied to each channel is fixed, and the current amount of each channel is kept the same by adjusting the magnitude of the current pulse. On the other hand, The amplitude of the current pulse is fixed, and the duty ratio of the current pulse is adjusted to maintain the same amount of current in each channel.

Furthermore, the LED driving device needs to control the amount of current for each channel for dimming, which is a function of dynamically adjusting the luminance. For example, the finer the dimming stage of the LED backlight, the greater the ability to express the darkness gradation on a large screen can be greatly improved. However, in the conventional PWM method, it is difficult to precisely control the duty ratio, that is, the ratio of the pulse width in the pulse period, and as a result, it is difficult to finely dim the LED strings.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a switching duty ratio adjustable LED driver for a multi-channel LED device.

A switching duty ratio adjustable LED driving device according to an aspect of the present invention includes:

And a control unit for receiving the pulse train of the reference PWM signal and generating a coarse delay signal in which the reference PWM signal is approximately delayed by one period of the pulse and when the phase difference between the coarse delay signal and the reference PWM signal is reduced to a predetermined value or less, A first delay loop for activating a fixed signal;

A second delay loop for generating a second delay signal having a precise phase delay based on the coarse delay signal while the coarse delay locked signal is activated;

A replica delay line for outputting a replica delay signal by phase-delaying the reference PWM signal while maintaining the phase delay characteristics of the first delay loop and the second delay loop as they are; And

And a comparator for receiving a voltage difference signal between a detection voltage and a predetermined reference voltage due to the driving current of any one of the plurality of LED strings having different equivalent resistances and outputting the switching signal by receiving the duplication delay signal, ,

Wherein the switching signal is generated based on a magnitude of a voltage difference signal between a detection voltage by a driving current of any one of a plurality of LED strings having different equivalent resistances and a predetermined reference voltage, Are all equal to each other.

According to one embodiment, the first delay loop

A first phase detector for outputting a first up signal or a first down signal according to a phase difference obtained by comparing a phase of the reference PWM signal with a phase of a first delay signal; And

And generates the first delay signal by advancing or delaying the phase based on the reference PWM signal according to the first up signal or the first down signal, And a first voltage control delay line for outputting the coarse delay signal of the first voltage control delay line.

According to one embodiment, the coarse delay locked signal may be activated through a majority voting technique.

According to one embodiment, the second delay loop

A second voltage control delay line receiving the coarse delay signal and outputting the second delay signal according to a bias output;

A second phase detector receiving the reference PWM signal and the second delay signal and outputting a second up signal or a second down signal according to a phase difference;

A charge pump for generating a control current according to the second up signal or the second down signal;

A loop filter for outputting a control voltage according to the control current; And

And a bias generator for generating the bias output according to the control voltage and the voltage difference signal and outputting the generated bias output to the second voltage control delay line.

A multi-channel LED device according to another aspect of the present invention includes:

A voltage difference signal between the detected voltage due to the driving current of each LED string and a predetermined reference voltage, which is connected in series to each of the LED strings connected to each other so as to have a different equivalent resistance and is commonly applied with a common driving voltage, A plurality of voltage difference detecting portions for detecting the voltage difference; And

Generates switching signals capable of adjusting the duty ratios of the driving currents so that the average currents of the LED strings are all equal to each other based on the voltage difference signals detected by the voltage difference detection units and the reference PWM signal, And a switching duty ratio adjustable LED driver,

Wherein the switching signals have respective rising and falling time points that are earlier or later than a rising time point of a pulse of the reference PWM signal and a falling time point of a pulse of the reference PWM signal, respectively, according to a magnitude of a voltage difference signal of the voltage difference detecting unit May be generated based on the pulse.

According to one embodiment,

If the voltage difference signal of the LED string is larger than a predetermined threshold value, the PWM signal is generated based on a pulse having a falling time point delayed from the reference PWM signal,

If the voltage difference signal of the LED string is smaller than a predetermined threshold value, it may be generated based on a pulse having a falling time point earlier than the reference PWM signal.

According to one embodiment, the switching duty ratio adjustable LED driver includes a plurality of PWM controls,

Each of the PWM control units includes:

And a control unit for receiving the pulse train of the reference PWM signal and generating a coarse delay signal in which the reference PWM signal is approximately delayed by one period of the pulse and when the phase difference between the coarse delay signal and the reference PWM signal is reduced to a predetermined value or less, A first delay loop for activating a fixed signal;

A second delay loop for generating a second delay signal having a precise phase delay based on the coarse delay signal while the coarse delay locked signal is activated;

A replica delay line for outputting a replica delay signal by phase-delaying the reference PWM signal while maintaining the phase delay characteristics of the first delay loop and the second delay loop as they are; And

And a comparator for receiving a voltage difference signal between a detection voltage and a predetermined reference voltage by a driving current of any one of the plurality of LED strings having different equivalent resistances and outputting the switching signal by receiving the replication delay signal .

According to one embodiment, the first delay loop

A first phase detector for outputting a first up signal or a first down signal according to a phase difference obtained by comparing a phase of the reference PWM signal with a phase of a first delay signal; And

And generates the first delay signal by advancing or delaying the phase based on the reference PWM signal according to the first up signal or the first down signal, And a first voltage control delay line for outputting the coarse delay signal of the first voltage control delay line.

According to one embodiment, the coarse delay locked signal may be activated through a majority voting technique.

According to one embodiment, the second delay loop

A second voltage control delay line receiving the coarse delay signal and outputting the second delay signal according to a bias output;

A second phase detector receiving the reference PWM signal and the second delay signal and outputting a second up signal or a second down signal according to a phase difference;

A charge pump for generating a control current according to the second up signal or the second down signal;

A loop filter for outputting a control voltage according to the control current; And

And a bias generator for generating the bias output according to the control voltage and the voltage difference signal and outputting the generated bias output to the second voltage control delay line.

According to an embodiment, further comprising a common drive voltage selector for generating a voltage selection signal for selectively outputting the common drive voltage according to a desired level,

The DC-DC converter may output a common driving voltage according to the voltage selection signal.

According to the switching duty ratio adjustable LED driving apparatus for a multi-channel LED device of the present invention, even if the equivalent resistances of the LED strings of the respective channels are different from each other, and furthermore, So that a desired luminance can be uniformly obtained.

1 is a block diagram schematically illustrating a switching duty ratio adjustable LED driver for a multi-channel LED device in accordance with an embodiment of the present invention.
2 is a block diagram illustrating a PWM control unit in a switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an exemplary embodiment of the present invention.
3 is a waveform diagram for explaining the operation of the first delay loop of the PWM control unit among the switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an embodiment of the present invention.
4 is a waveform diagram for explaining the operation of the second delay loop of the PWM control unit among the switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an embodiment of the present invention.
FIG. 5 is a graph showing the relationship between the driving currents and the driving currents of the LED strings according to the embodiment of the present invention. FIG. 8 is a waveform diagram illustrating that the duty ratios are eventually different according to the flow.

For the embodiments of the invention disclosed herein, specific structural and functional descriptions are set forth for the purpose of describing an embodiment of the invention only, and it is to be understood that the embodiments of the invention may be practiced in various forms, The present invention should not be construed as limited to the embodiments described in Figs.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

1 is a block diagram schematically illustrating a switching duty ratio adjustable LED driver for a multi-channel LED device in accordance with an embodiment of the present invention.

1, the multi-channel LED device 1 includes a switching duty ratio adjustable LED driver 10, a DC-DC converter 20, a reference PWM generator 30, LED strings 41, 42, ..., 43, power transistors 51, 52, ..., 53, and voltage difference detectors 61, 62, ...,

First, a DC-DC converter 20 generates and applies a common driving voltage V_MASTER to all the LED strings 41, 42, ..., 43.

Each of the LED strings 41, 42, ..., 43 has a plurality of LEDs connected in series so that the size of the driving currents I_LED1, I_LED2, ..., I_LEDn and the flowing time, Emits light with a proportional brightness.

The series-connected LEDs may have different equivalent resistances depending on the process temperature, temperature, cumulative operation time, and the like. The driving currents I_LED1, I_LED2, ..., I_LEDn flowing in the LED strings 41, 42, ..., 43 may be different from each other, , The amount of light emitted from the LED strings 41, 42, ..., 43 may not be uniform.

Each of the drive currents I_LED1, I_LED2, ..., and I_LEDn includes switching signals SW1, SW2, ..., SWn input to the gate terminals of the power transistors 51, 52, 43, and 43 in accordance with the duty ratio of the LED strings 41, 42, ..., 43 intermittently.

The voltage difference detectors 61, 62, ..., 63 are connected in series to the LED strings 41, 42, ..., 43 so that the driving currents I_LED1, I_LED2, ..., I_LEDn (V_ERR1, V_ERR2, ..., V_ERRn) between the detection voltage by the reference voltage detecting unit (not shown) and the predetermined reference voltage.

For example, if the voltage difference signal V_ERR1 detected with respect to any LED string 41 is lower than the reference voltage, this means that the magnitude of the driving current I_LED1 is smaller than the reference value.

The switching duty ratio adjustable LED driver 10 includes n PWM controllers 11, 12, ..., 13. V_ERRn, V_ERR2, ..., V_ERRn detected by the voltage difference detectors 61, 62, ..., 63. The PWM control units 11, 12, Based on the reference PWM signals in the reference PWM generation unit 30, the average currents of the LED strings 41, 42, ..., and 43 having different equivalent resistances are all equalized SW2, ..., SWn capable of adjusting the duty ratios of the currents I_LED1, I_LED2, ..., I_LEDn, respectively.

.., V_ERRn (V_ERR1, V_ERR2, ..., V_ERRn) of the voltage difference detectors 61, 62, ..., 63 are supplied to the PWM control units 11, 12, ) Of the reference PWM signal and a falling time point that is earlier or later than the falling point of the pulse of the reference PWM signal to generate the switching signal having the duty ratio adjusted (SW1, SW2, ..., SWn).

For example, if the voltage difference signal V_ERR1 detected for any LED string 41 is greater than a predetermined threshold, this means that the magnitude of the drive current I_LED1 is relatively smaller than the reference, The switching signal SW1 having the pulse whose falling time is delayed, that is, the duty ratio is larger than the PWM signal is generated. Since the duty ratio of the switching signal SW1 is increased, the LED string 41 terminates the light emission later than the reference, and a smaller drive current I_LED1 during the light emission period, that is, during the active period of the pulse, It is possible to show luminance close to the reference as a whole.

Conversely, if the voltage difference signal V_ERR1 detected with respect to any LED string 41 shows a positive value higher than the reference voltage, this means that the magnitude of the driving current I_LED1 is larger than the reference, A switching signal SW1 having a pulse whose falling time point is drawn, that is, the duty ratio is smaller than the signal is generated. The LED string 41 terminates the light emission earlier than the reference because the duty ratio of the switching signal SW1 is smaller, but more driving current I_LED1 during the light emitting period, i.e., the active period of the pulse, It is possible to show luminance close to the reference as a whole.

On the other hand, the multi-channel LED device 1 may further include a common driving voltage selector 70. The common drive voltage selector 70 selectively outputs a common drive voltage V_MASTER of a desired level according to the tendency of the voltage difference signals V_ERR1, V_ERR2, ..., V_ERRn, or for adjustment of the overall luminance, Can be generated.

The DC-DC converter 20 can generate the common drive voltage V_MASTER from the external power supply DC voltage based on the voltage selection signal.

For example, by controlling the switching frequency in accordance with the voltage selection signal, the switched-capacitor converter type DC-DC converter 20 can consequently output a common driving voltage V_MASTER of a desired level.

2 to 4 to refer to the configuration and operation of the PWM control units 11, 12 and 13 in more detail.

2 is a block diagram illustrating a PWM control unit in a switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an exemplary embodiment of the present invention.

2, the PWM control unit 11 may include a first delay loop 111, a second delay loop 112, a replication delay line 113, and a comparator 114.

The first delay loop 111 receives the pulse train of the reference PWM signal and outputs a coarse delay signal which coarsely delays the reference PWM signal by one period of the pulse.

Here, the expression of roughly delaying the signal may delay the original signal with a predetermined target delay phase to obtain a signal having the same waveform and delayed phase only, but the phase of the delayed signal may be delayed or less delayed than the target delay phase Which implies imprecision. This implicit inaccuracy is inevitable because there is a limit to the speed or accuracy of the phase detector that compares the phase of the original signal with the delayed signal in the delay loop and therefore the expression "approximately" Note that this is not an expression that makes the configuration obscure.

Also, since the degree of such inaccuracy is non-deterministic and may be larger than a predetermined threshold value, it converges within a threshold value over time, and furthermore, this inaccuracy is compensated by using an additional delay loop, It does not matter.

On the other hand, the expression "roughly delay" of the first delay loop 111 may be understood as a difference in resolution of the relative delay phase relative to the second delay loop 112, .

The first delay loop 111 compares the phase of the reference PWM signal PWM_REF with the phase of the first delay signal PWM_CD and outputs the first up signal UP1 or the first down signal DN1 A first phase detector PD1 for outputting a coarse delay lock signal LOCK when the phase difference decreases to a predetermined value or less and a second phase detector PD2 for outputting a first up signal UP1 or a first down signal The first delay signal PWM_CD is generated by advancing or delaying the phase based on the reference PWM signal PWM_REF according to the approximate delay locked signal DN1, And a first voltage-controlled delay line (VCDL1) for outputting a delay signal PWM_AFTER_COARSE.

According to the embodiment, if it is determined that the coarse delay locked signal LOCK is greater than a half of the predetermined number of comparison judgments for comparing the phase difference to the predetermined threshold value through the majority voting technique, that is, the phase difference is smaller than the predetermined threshold value, If it is determined that the phase difference is smaller than the predetermined threshold value three or more times during the fifth comparison determination, it can be activated.

3 is a waveform diagram for explaining the operation of the first delay loop of the PWM control unit among the switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an embodiment of the present invention.

Referring to FIG. 3, the operation starts immediately after the reset signal RST is applied.

The reference PWM signal PWM_REF is a pulse signal having a period of 20 占 퐏 and a duty ratio of 0.5. When the reference PWM signal PWM_REF is applied to the first phase detector PD1 of the first delay loop 111, the first delay loop 111 generates a first rising edge And the reference PWM signal PWM_REF to the next rising edge.

When the scanning is completed while the successive rising edges are detected, the first pulse of the first delay signal PWM_CD is generated in the first voltage control delay line (VCDL1).

The first delay signal PWM_CD is applied to the first phase detector PD1 together with the reference PWM signal PWM_REF. The first phase detector PD1 compares the rising edge of the reference PWM signal PWM_REF with the rising edge of the first delay signal PWM_CD to compare the rising edge of the first delay signal PWM_CD with the rising edge of the first delay signal PWM_CD, And outputs a first down signal DN1 that is activated by the lead phase of the up signal UP1 and the first delay signal PWM_CD.

In FIG. 3, the first delay signal PWM_CD is generated by being delayed by 3 占 퐏 in the first delay period. However, the phase difference is significantly narrowed in the second delay period, and the phase difference is corrected to be slightly ahead in the third to the fifth delay period. In the fifth delay period, the phase difference is reduced to a predetermined value or less, whereby the coarse delay locked signal LOCK is activated, and the coarse delayed signal PWM_AFTER_COARSE with the phase difference reduced is output.

Thus, a coarse delay signal PWM_AFTER_COARSE having a phase substantially coinciding with the reference PWM signal PWM_REF within a predetermined error range is generated.

2, a second delay signal PWM_OUT that follows the phase of the reference PWM signal PWM_REF relatively accurately based on the coarse delay signal PWM_AFTER_COARSE as the coarse delay locked signal LOCK is activated is output The operation of the second delay loop 112 is started.

The second voltage control delay line VCDL2 of the second delay loop 112 receives the coarse delay signal PWM_AFTER_COARSE and outputs the second delay signal PWM_OUT in accordance with the bias output BG_OUT.

The second phase detector PD2 receives the reference PWM signal PWM_REF and the second delay signal PWM_OUT and outputs the second up signal UP2 or the second down signal DN2 according to the phase difference.

The charge pump CP generates the control current I_LF according to the second up signal UP2 and the second down signal DN2 and outputs the control current I_LF to the loop filter LF according to the control current I_LF. And outputs the control voltage V_CNT.

The bias generator generates a bias output BG_OUT according to the control voltage V_CNT and the voltage difference signal V_ERR1 and outputs the bias output BG_OUT to the second voltage control delay line VCDL2.

4 is a waveform diagram for explaining the operation of the second delay loop of the PWM control unit among the switching duty ratio adjustable LED driving apparatus for a multi-channel LED device according to an embodiment of the present invention.

4, a second delay signal PWM_OUT whose delay is precisely controlled based on the coarse delay signal PWM_AFTER_COARSE is output from the second voltage control delay line VCDL2 while the coarse delay locked signal LOCK is activated do.

The second phase detector PD2 generates the second up signal UP2 and the second down signal DN2 in accordance with the phase difference between the second delay signal PWM_OUT and the reference PWM signal PWM_REF. The second down signal DN2 is continuously generated while the phase of the second delay signal PWM_OUT is slightly ahead and the magnitude of the control voltage V_CNT and the bias output BG_OUT rise step by step. The second up signal UP2 and the second down signal DN2 are not generated either because the second delay signal PWM_OUT is compared with the reference PWM signal PWM_REF Which means that the phase difference is less than the operation clock.

2, the replica delay line 113 receives the reference PWM signal PWM_REF and outputs the same phase delay as the phase delay of the first delay loop 111 and the second delay loop 112, 1 replica delay line (Replica VCDL) 113a and a second duplication delay line 113b to generate a duplication delay signal PWM_RE.

The comparator 114 receives the copy delay signal PWM_RE and the voltage difference signal V_ERRn and outputs a switching signal SWn.

FIG. 5 is a graph showing the relationship between the driving currents and the driving currents of the LED strings according to the embodiment of the present invention. FIG. 8 is a waveform diagram illustrating that the duty ratios are eventually different according to the flow.

Referring to FIG. 5, the duty ratio of the reference PWM signal is 50%. The equivalent resistance of the first LED string is equal to the nominal resistance value of the reference, the equivalent resistance of the second LED string is less than the nominal resistance value, and the equivalent resistance of the third LED string is greater than the nominal resistance value.

As a result, the duty ratio of the driving current I_LED1 of the first LED string is maintained at 50%, and the driving current I_LED2 of the second LED string is larger than the current magnitude and the duty ratio gradually decreases with time. On the other hand, the driving current I_LED3 of the third LED string is smaller in magnitude than the current magnitude and the duty ratio gradually increases over time.

The magnitudes of the driving currents of the three LED strings increase or decrease with the equivalent resistance, but the duty ratio becomes smaller or larger accordingly, so that the average current becomes equal and the brightness becomes the same.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the following claims, and all of the equivalent or equivalent variations will fall within the scope of the present invention.

1 Multi-channel LED device
10 Switching duty ratio adjustable LED drive
11, 12, 13 PWM control unit
111 first delay loop 112 second delay loop
113 Replication Delay Lines 114 Comparator
20 DC-DC converter 30 Reference PWM generation unit
41, 42, 43 LED strings
51, 52, 53 Power transistors
61, 62, 63 voltage difference detectors
70 common drive voltage selection unit

Claims (11)

And a control unit for receiving the pulse train of the reference PWM signal and generating a coarse delay signal in which the reference PWM signal is approximately delayed by one period of the pulse and when the phase difference between the coarse delay signal and the reference PWM signal is reduced to a predetermined value or less, A first delay loop for activating a fixed signal;
A second delay loop for generating a second delay signal having a precise phase delay based on the coarse delay signal while the coarse delay locked signal is activated;
A replica delay line for outputting a replica delay signal by phase-delaying the reference PWM signal while maintaining the phase delay characteristics of the first delay loop and the second delay loop as they are; And
And a comparator for receiving a voltage difference signal between a detection voltage and a predetermined reference voltage due to the driving current of any one of the plurality of LED strings having different equivalent resistances and outputting the switching signal by receiving the duplication delay signal, ,
Wherein the switching signal is generated based on a magnitude of a voltage difference signal between a detection voltage by a driving current of any one of a plurality of LED strings having different equivalent resistances and a predetermined reference voltage, And a duty ratio of the switching duty ratio adjustable LED driving device. The method of claim 1, wherein the first delay loop
A first phase detector for outputting a first up signal or a first down signal according to a phase difference obtained by comparing a phase of the reference PWM signal with a phase of a first delay signal; And
And generates the first delay signal by advancing or delaying the phase based on the reference PWM signal according to the first up signal or the first down signal, And a first voltage control delay line for outputting the coarse delay signal of the switching duty ratio adjuster. 2. The apparatus of claim 1, wherein the coarse delay locked signal is activated through a majority vote technique. The method of claim 1, wherein the second delay loop
A second voltage control delay line receiving the coarse delay signal and outputting the second delay signal according to a bias output;
A second phase detector receiving the reference PWM signal and the second delay signal and outputting a second up signal or a second down signal according to a phase difference;
A charge pump for generating a control current according to the second up signal or the second down signal;
A loop filter for outputting a control voltage according to the control current; And
And a bias generator for generating the bias output according to the control voltage and the voltage difference signal and outputting the bias output to the second voltage control delay line. A voltage difference signal between the detected voltage due to the drive current of each LED string and a predetermined reference voltage is detected in series with each of the LED strings connected to each other so as to have different equivalent resistances and to be commonly applied with a common drive voltage A plurality of voltage difference detecting units; And
Generates switching signals capable of adjusting the duty ratios of the driving currents so that the average currents of the LED strings are all equal to each other based on the voltage difference signals detected by the voltage difference detection units and the reference PWM signal, And a switching duty ratio adjustable LED driver,
Wherein the switching signals have respective rising and falling time points that are earlier or later than a rising time point of a pulse of the reference PWM signal and a falling time point of a pulse of the reference PWM signal, respectively, according to a magnitude of a voltage difference signal of the voltage difference detecting unit Channel LEDs. ≪ Desc / Clms Page number 13 > The method of claim 5,
If the voltage difference signal of the LED string is larger than a predetermined threshold value, the PWM signal is generated based on a pulse having a falling time point delayed from the reference PWM signal,
Channel LED device is generated based on a pulse having a falling time point earlier than the reference PWM signal if the voltage difference signal of the LED string is smaller than a predetermined threshold value. 6. The LED driving apparatus according to claim 5, wherein the switching duty ratio adjustable LED driving apparatus includes a plurality of PWM control units,
Each of the PWM control units includes:
And a control unit for receiving the pulse train of the reference PWM signal and generating a coarse delay signal in which the reference PWM signal is approximately delayed by one period of the pulse and when the phase difference between the coarse delay signal and the reference PWM signal is reduced to a predetermined value or less, A first delay loop for activating a fixed signal;
A second delay loop for generating a second delay signal having a precise phase delay based on the coarse delay signal while the coarse delay locked signal is activated;
A replica delay line for outputting a replica delay signal by phase-delaying the reference PWM signal while maintaining the phase delay characteristics of the first delay loop and the second delay loop as they are; And
A comparator for receiving a voltage difference signal between a detection voltage and a predetermined reference voltage by a driving current of any one of a plurality of LED strings having different equivalent resistances and a switching signal receiving the copying delay signal, Channel LED device. The method of claim 7, wherein the first delay loop
A first phase detector for outputting a first up signal or a first down signal according to a phase difference obtained by comparing a phase of the reference PWM signal with a phase of a first delay signal; And
And generates the first delay signal by advancing or delaying the phase based on the reference PWM signal according to the first up signal or the first down signal, And a first voltage control delay line for outputting the coarse delay signal of the first voltage control delay line. 8. The multi-channel LED device of claim 7, wherein the coarse delay locked signal is activated through a majority voting technique. The method of claim 7, wherein the second delay loop
A second voltage control delay line receiving the coarse delay signal and outputting the second delay signal according to a bias output;
A second phase detector receiving the reference PWM signal and the second delay signal and outputting a second up signal or a second down signal according to a phase difference;
A charge pump for generating a control current according to the second up signal or the second down signal;
A loop filter for outputting a control voltage according to the control current; And
And a bias generator for generating the bias output according to the control voltage and the voltage difference signal and outputting the bias output to the second voltage control delay line. 6. The display device according to claim 5, further comprising a common drive voltage selector for generating a voltage selection signal for selectively outputting the common drive voltage according to a desired level,
And the DC-DC converter outputs a common driving voltage according to the voltage selection signal.

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