KR20140055087A - Dc-dc converter and organic light emitting display device using the same - Google Patents

Abstract

The present invention relates to a DC-DC converter and an organic light emitting display device using the same. A DC-DC converter according to an embodiment of the present invention includes a switching module which outputs a first voltage by converting an input voltage by turning on and off pulse width modulation (PWM) signals each corresponding to multiple switches; a converting module having a control module which controls switching operation of the switching module by generating the PWM signals; and a sensing unit which detects a drive current supplied to the load where the first voltage is provided. The control module is composed to adaptively control a frequency of the PWM signals based on the detected results of the sensing unit. According to the present invention, a DC-DC converter and an organic light emitting display device are provided which have an optimum efficiency by operating adaptively based on the loading conditions.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a DC-DC converter and an organic light emitting diode (OLED)

The present invention relates to a DC-DC converter and an organic light emitting display device using the DC-DC converter. More particularly, the present invention relates to a DC-DC converter having an optimal efficiency by operating adaptively according to load conditions and an organic light emitting display .

Among flat panel display devices, an organic light emitting display uses an organic light emitting diode (OLED), which generates light by the combination of electrons and holes, to display an image. The organic light emitting diode includes an anode electrode, a cathode electrode, and a light emitting layer positioned between the anode electrode and the cathode electrode. When an electric current flows from the anode electrode toward the cathode electrode, the organic light emitting diode emits light to express color. In the organic electroluminescent display device, the light emission luminance is determined according to the amount of current flowing in the organic light emitting diode of each pixel. Therefore, a high luminance image requires a larger driving current than a low luminance image. That is, the driving current required for driving the pixels of the organic light emitting display device is variable depending on the displayed image. Therefore, the DC-DC converter for driving the pixels of the organic light emitting display must be designed to have a high efficiency over the entire range of the driving current in order to reduce power consumption. However, since the conventional DC-DC converter is fixed at a frequency at which the DC-DC conversion can be normally performed under the maximum load condition, the efficiency becomes lower as the load is lowered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a DC-DC converter having an optimum efficiency by operating adaptively according to a load condition and an organic light emitting display using the DC-DC converter.

According to an aspect of the present invention, there is provided a DC-DC converter including a plurality of switches, each of which is turned on and off in response to a corresponding pulse width modulation (PWM) And a control module for controlling the switching operation of the switching module by generating the PWM signal and a sensing unit for sensing a driving current supplied to the load to which the first voltage is supplied, The control module is configured to adaptively control the frequency of the PWM signal according to a detection result of the sensing unit.

According to another aspect of the present invention, there is provided an organic light emitting display including a display panel having a plurality of pixels and displaying a gray level according to the brightness of the organic light emitting diodes of the pixels, A timing controller for providing a scan signal and a data signal for causing the organic light emitting diode to emit light to the display panel and a first voltage and a second voltage for supplying a current to the organic light emitting diode And a DC-DC converter provided to the display panel. The DC-DC converter includes a first converting module for receiving the input voltage to generate the first voltage, a second converting module for receiving the input voltage to generate the second voltage, And a sensing unit for sensing the driving current. Wherein each of the first and second converting modules includes a switching module for converting an input voltage and outputting the second voltage while being turned on and off in response to a corresponding pulse width modulation (PWM) signal, And a control module for generating a signal and controlling a switching operation of the switching module. At least one of the control modules of the first and second converting modules is configured to adaptively control the frequency of the PWM signal according to the detection result of the sensing unit.

As described above, according to the present invention, it is possible to provide a DC-DC converter having an optimum efficiency by operating adaptively according to a load condition, and an organic light emitting display using the DC-DC converter.

1 shows a DC-DC converter according to an embodiment of the present invention.
Fig. 2 shows an embodiment of the DC-DC converter shown in Fig.
Fig. 3 shows another embodiment of the DC-DC converter shown in Fig.
FIG. 4 shows an embodiment of the PWM signal generator shown in FIG. 2 and FIG.
5 illustrates an organic light emitting display according to an embodiment of the present invention.
6 illustrates an organic light emitting display according to another embodiment of the present invention.
7 illustrates an organic light emitting display according to another embodiment of the present invention.

The details of other embodiments are included in the detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. In the following description, it is assumed that a part is connected to another part, But also includes a case in which other elements are electrically connected to each other in the middle thereof. In the drawings, parts not relating to the present invention are omitted for clarity of description, and like parts are denoted by the same reference numerals throughout the specification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to embodiments of the present invention and drawings for explaining the present invention.

1 shows a DC-DC converter according to an embodiment of the present invention.

Referring to FIG. 1, the DC-DC converter 100 includes a converting module 120 and a sensing unit 140.

The converting unit 120 receives the input voltage VIN to generate a first voltage V1 and the sensing unit 140 provides the first voltage V1 to the load, Lt; RTI _ID = 0.0 > I _D < / RTI >

The converting module 120 is a type of switching regulator that performs pulse width modulation (PWM) driving and operates by varying the switching frequency according to the sensing result of the sensing unit 140. [

The converting module 120 includes a switching module 122 and a control module 124.

The switching module 122 converts an input voltage VIN applied from the outside into a first voltage V1 while being turned on and off in response to a corresponding pulse width modulation (PWM) signal.

The control module 124 is configured to control the switching operation of the switching module 122 by generating the PWM signal and adaptively control the frequency of the PWM signal according to the detection result of the sensing unit 140.

In the DC-DC converter 100, since the driving current I _D is small when the load is relatively small, the switching loss is large according to the parasitic capacitance of the switch. When the load is relatively large, the driving current I _D becomes large, The conduction loss due to the turn-on resistance is large. The switching loss is proportional to the switching frequency, that is, the frequency of the PWM signal that controls the on / off of the switch. Accordingly, the control module 124 of the DC-DC converter 100 adaptively adjusts the frequency of the PWM signal according to the driving current I _D to minimize the switching loss. Specifically, when the drive current I _D increases, the frequency of the PWM signal increases, and when the drive current I _D decreases, the frequency of the PWM signal decreases. At this time, the PWM driving of the converting module may be performed in a CCM (Continuous Conduction Mode) or a combination of CCM and DCM (Discontinuous Conduction Mode). As a result, the switching module 122 of the DC-DC converter 100 minimizes the switching loss in performing the voltage conversion, so that it can have optimal efficiency despite various load conditions.

The DC-DC converter 100 may generate the first voltage V1 by stepping up or down the input voltage VIN and may also generate the first voltage V1 by inverting the polarity of the input voltage VIN have. The driving current I _D of the load connected to the output terminal of the DC-DC converter 100 is variable. For example, the first voltage V1 may be a voltage ELVDD applied to the anode side of the organic light emitting diode OLED of each pixel of the organic light emitting display device or applied to the cathode side of the organic light emitting diode OLED Voltage (ELVSS).

Fig. 2 shows an embodiment of the DC-DC converter shown in Fig.

Referring to FIG. 2, the switching module 222 includes a first switch MP1, an inductor L, and a second switch MN1.

The first switch MP1 is located between an input node ND_I to which the input voltage VIN is input and the first node ND1 to form or cut off a current path. The inductor L is positioned between the first node ND1 and the ground, and generates an electromotive force according to an increase or decrease of an input current according to an input voltage VIN. The second switch MN1 is located between the first node ND1 and the second node ND2 to form or cut off a current path.

The first switch MP1 allows an input current to be transmitted to or disconnected from the inductor L so that an electromotive force is generated in the inductor L. The second switch MN1 transmits or blocks the reverse electromotive force formed in the inductor L while the input current is cut off. The first switch MP1 and the second switch MN1 are alternately turned on and off to generate and output the first voltage V1.

The sensing unit 240 includes a third switch MN2 and a sense voltage output unit 242. [

The third switch MN2 is located between the second node ND2 and the output node ND_O to form or cut off a current path. The sense voltage output unit 242 is connected to both ends of the third switch MN2 and outputs a sense voltage Vsense corresponding to the drive current. If a separate resistor is added to detect the driving current, a loss due to the additional resistance is additionally generated. Therefore, it is preferable to sense the driving current by using the turn-on resistance of the third switch MN2 in terms of minimizing the loss. The third switch MN2 is turned off when the DC-DC converter 200 is shut down, thereby blocking the leakage current path formed between the input node ND_I and the output node ND_O. The third switch MN2 is turned on and off in response to the control signal CON and turned on at the time of normal operation and turned off at the time of the short-time.

The control module 224 includes a PWM signal generator 224_4 and a switch driver 224_2.

The PWM signal generator 224_4 generates the PWM signal having a frequency determined according to the sense voltage Vsense and provides the PWM signal to the switch driver 224_2. Increases the frequency of the PWM signal when the sense voltage Vsense increases and reduces the frequency of the PWM signal when the sense voltage Vsense decreases.

The switch driver 224_2 receives the PWM signal and controls the first and second switches MP1 and MN1. The switch driving unit 224_2 can adjust the PWM signal for controlling the first switch MP1 and the PWM signal for controlling the second switch MN1 to be opposite to each other. In this case, the first switch MP1 and the second switch MN1 alternately turn on and off. The switch driver 224_2 may generate a control signal CON for controlling the third switch MN2.

DC-DC converter 200 may be an inverting buck-boost converter that inverts the polarity of input voltage VIN to produce a first voltage V1. The first switch MP1 may be implemented as a PMOS transistor, the second switch MN1 and the third switch MN2 may be implemented as NMOS transistors.

The DC-DC converter 200 generates the first voltage V1 by inverting the input voltage VIN through a switching operation in which the first switch MP1 and the second switch MN1 are alternately turned on and off, Output. More specifically, when the first switch MP1 is turned on and the second switch MN1 is turned off, the input voltage VIN is applied to the first node ND1, and thus the inductor L And the inductor L accumulates a predetermined amount of energy. Next, when the first switch MP1 is turned off and the second switch MN1 is turned on, the energy charged in the inductor L is reversed to the opposite ends of the inductor L The first voltage V1 having a polarity different from the input voltage VIN is output to the output node ND_O in the form of an electromotive force.

The DC-DC converter 200 includes a first capacitor C1 and a second capacitor C2 located between an input node ND_I (ND_I) and a ground and an output node ND_O (ND_O) . When the DC-DC converter 200 is implemented as a semiconductor chip, the inductor L, the first capacitor C1, and the second capacitor C2 of the switching module 222 may be implemented outside the chip have.

Fig. 3 shows another embodiment of the DC-DC converter shown in Fig.

Referring to FIG. 3, the switching module 322 includes an inductor L, a first switch MN1, and a second switch MP1.

The inductor L is located between the input node ND_I and the first node ND1 for receiving the input voltage VIN. The inductor L generates an electromotive force according to an increase or decrease of an input current according to an input voltage VIN.

The first switch MN1 is located between the first node ND1 and the ground to form or cut off a current path. The first switch MN1 allows an input current to be transmitted to or disconnected from the inductor L so that an electromotive force is generated in the inductor L.

The second switch MP1 is located between the first node ND1 and the second node ND2 to form or cut off a current path. The second switch (MP1) transmits or cuts off the flow of the input current transmitted through the inductor (L).

The first switch MN1 and the second switch MP1 are alternately turned on and off to generate and output the first voltage V1.

The sensing section includes a third switch (MP2) and a sense voltage output section (342).

The third switch MP2 is located between the second node ND2 and the output node ND_O to form or cut off a current path. The sensing voltage output unit 342 is connected to both ends of the third switch MP2 and outputs a sensing voltage Vsense corresponding to the driving current. In the case where a separate resistor is added to detect the driving current, a loss due to the additional resistance is additionally generated. Therefore, sensing the driving current by using the turn-on resistance of the third switch MP2 is preferable in terms of minimizing the loss. The third switch MP2 is turned off when the DC-DC converter is shut down, thereby blocking the leakage current path formed between the input node ND_I and the output node ND_O. The third switch MP2 is turned on and off in response to the control signal CON and is turned on in a normal operation and turned off in a short-time.

The control module 324 includes a PWM signal generator 324_4 and a switch driver 324_2.

The PWM signal generator 324_4 generates a PWM signal having a frequency determined according to the sense voltage Vsense and provides the generated PWM signal to the switch driver 324_2. The PWM signal generating unit 324_4 increases the frequency of the PWM signal when the sensing voltage Vsense increases and reduces the frequency of the PWM signal when the sensing voltage Vsense decreases.

The switch driver 324_2 receives the PWM signal and controls the first and second switches MN1 and MP1. The switch driver 324_2 may adjust the PWM signal for controlling the first switch MN1 and the PWM signal for controlling the second switch MP1 to be opposite to each other. In this case, the first switch MN1 and the second switch MP1 are alternately turned on and off. The switch driver 324_2 may generate a control signal CON for controlling the third switch MP2.

The DC-DC converter 300 may be a boost converter that boosts the input voltage VIN to generate the first voltage V1. The first switch MN1 may be implemented as a PMOS transistor, the second switch MP1 and the third switch MP2 may be implemented as PMOS transistors.

The DC-DC converter 300 boosts the input voltage VIN through a switching operation in which the first switch MN1 and the second switch MP1 are alternately turned on and off to generate and output the first voltage V1, do. More specifically, when the first switch MN1 is turned on and the second switch MP1 is turned off, the first node ND1 is grounded, and accordingly, the current flowing in the inductor L gradually decreases And the inductor L accumulates a predetermined energy. Next, when the first switch MN1 is turned off and the second switch MP1 is turned on, the input voltage VIN and the energy charged in the inductor L are transmitted together to the output node ND_O , A first voltage V1 higher than the input voltage VIN is output to the output node ND_O.

The DC-DC converter 300 includes a first capacitor C1 and an output node ND_O (ND_O) located between an input node ND_I (ND_I) and a ground and a second capacitor C2 located between the ground and the ground . When the DC-DC converter 300 is implemented as a semiconductor chip, the inductor L, the first capacitor C1, and the second capacitor C2 of the switching module 322 can be implemented outside the chip have.

FIG. 4 shows an embodiment of the PWM signal generator shown in FIG. 2 and FIG.

4, the PWM signal generating unit 224_4 of FIG. 2 or the PWM signal generating unit 324_4 of FIG. 3 includes a frequency selecting unit 420, a sawtooth wave generating unit 440, and a square wave generating unit 460 do.

The frequency selector 420 compares the sense voltage Vsense with at least one reference voltage Vref1 to Vrefm and generates frequency selection signals OCD1 to OCDm according to the comparison result. The frequency selector 420 includes m comparators Comp1 to Compm for comparing the sense voltage Vsense with m reference voltages Vref1 to Vrefm. Each of the comparators Comp1 to Compm outputs a high signal when the sensing voltage Vsense is equal to or greater than the reference voltage Vrefm and outputs a low signal when the sensing voltage Vsense is lower than the reference voltage Vrefm.

The sawtooth wave generator 440 generates a sawtooth wave having a corresponding frequency in response to the frequency selection signal OCDm. To this end, the sawtooth wave generator 440 includes a lamp oscillator.

Hereinafter, the specific operation of the frequency selecting unit 420 and the sawtooth wave generating unit 440 when the switching frequency can be set to one of four frequencies will be described. To this end, the frequency selector 420 includes three comparators Comp1, Comp2, and Comp3, and can compare the sense voltage Vsense with the three reference voltages Vref1, Vref2, and Vref3. First, when the sensing voltage Vsense is smaller than the first reference voltage Vref1, the second reference voltage Vref2, and the third reference voltage Vref3, the frequency selector 420 selects one of the first to third frequencies And outputs all of the selection signals OCD1, OCD2, and OCD3 as a low signal. The sawtooth wave generator 440 generates a sawtooth wave having a first frequency (e.g., 80 KHz) in response to the first through third frequency selection signals OCD1, OCD2 and OCD3. Next, when the first reference voltage Vref1, the sensing voltage Vsense, the second reference voltage Vref2, and the third reference voltage Vref3 are in a relationship, the frequency selector 420 selects the first frequency selection signal (OCD1) as a high signal, and outputs both the second and third frequency selection signals (OCCD2, OCD3) as a low signal. The sawtooth wave generator 440 generates a sawtooth wave having a second frequency (e.g., 300 KHz) in response to the first to third frequency selection signals OCD1, OCD2 and OCD3. Next, when the first reference voltage Vref1, the second reference voltage Vref2, the sense voltage Vsense, and the third reference voltage Vref3 are in a relationship, the frequency selector 420 selects the first and second The frequency selection signals OCD1 and OCCD2 are output as a high signal and the third frequency selection signal OCD3 is output as a low signal. The sawtooth wave generator 440 may generate a sawtooth wave having a third frequency (e.g., 900 KHz) in response to the first through third frequency selection signals OCD1, OCD2, and OCD3. Finally, when the first reference voltage Vref1, the second reference voltage Vref2, the third reference voltage Vref3, and the sense voltage Vsense are in a relationship, the frequency selector 420 selects one of the first to third And outputs the frequency selection signals OCD1, OCD2 and OCD3 as a high signal. The sawtooth wave generator 440 generates a sawtooth wave having a fourth frequency (e.g., 1.5 MHz) in response to the first to third frequency selection signals OCD1, OCD2 and OCD3.

The square wave generator 460 converts the sawtooth wave into a PWM signal using offset information of the feedback voltage Vf divided by the first voltage V1 and the set voltage VREF. The square wave generator 460 includes a voltage divider 462 for dividing the first voltage V1 to generate a feedback voltage Vf and a voltage divider 462 for dividing the difference between the feedback voltage Vf and the set voltage VREF An amplifier Amp for amplifying and outputting the sawtooth wave, and a comparator Comp for comparing the sawtooth wave and the output of the amplifier to output the PWM signal. The pulse width of the PWM signal is determined according to the output of the amplifier Amp. The amplifier Amp monitors the level of the feedback voltage Vf so that the first voltage V1 remains constant despite the variation of the driving current I _D. When the level of the first voltage V1 is lowered due to the rapid increase of the driving current I _D , the pulse width of the PWM signal is increased.

The PWM signal generating unit 224_4 in FIG. 2 or the PWM signal generating unit 324_4 in FIG. 3 may further include a reference voltage setting unit 480 for setting the plurality of reference voltages Vrefm.

The reference voltage setting unit 480 provides reference voltages Vref1 to Vrefm for comparison with the sense voltage Vsense. The switching frequency set according to the load condition can be changed by adjusting the reference voltages Vref1 to Vrefm.

5 shows an organic light emitting display device 500 according to an embodiment of the present invention.

5, an organic light emitting display 500 includes a display panel 520, a timing controller 540, and a DC-DC converter 560.

The display panel 520 includes a plurality of pixels (not shown), and the gradation is displayed according to the degree of light emission of the organic light emitting diodes of the pixels.

The timing controller 540 provides the display panel 520 with a scan signal and a data signal for causing the organic light emitting diodes of the respective pixels to emit light. The display panel 520 displays an image in response to the scan signal and the data signal.

The DC-DC converter 560 receives the input voltage VIN and generates a first voltage V1 and a second voltage V2 for supplying current to the organic light emitting diodes of the respective pixels, ). The first voltage V1 is a voltage ELVDD applied to the anode side of the organic light emitting diode of each pixel and the second voltage V2 is applied to the cathode side of the organic light emitting diode Voltage (ELVSS).

The DC-DC converter 560 includes a first converting module 562, a second converting module 564, and a sensing unit 566.

The first converting module 562 receives the input voltage VIN and generates the first voltage V1. The first converting module 562 may be a boost converter that boosts the input voltage VIN to generate the first voltage V1. The first voltage V1 may be a positive voltage.

The second converting module 564 receives the input voltage VIN and generates the second voltage V2. The second converting module 564 may be an inverting buck-boost converter that generates the second voltage V2 that is opposite to the polarity of the input voltage VIN. The input voltage VIN may be a positive voltage and the second voltage V2 may be a negative voltage.

The sensing unit 566 senses a driving current I _D supplied to the display panel 520. Specifically, the sensing unit 566 is located between an output node of the first converting module 562 and a first output node for providing the first voltage V1 to the display panel 520, (I _D ), and outputs the sense voltage (Vsense).

The second converting module 564 includes a switching module 564_4 and a control module 564_2.

The switching module 564_4 converts the input voltage VIN while outputting the second voltage V2 while being turned on and off in response to a corresponding pulse width modulation (PWM) signal.

The control module 564_2 generates the PWM signal to control the switching operation of the switching module 564_4. The control module 564_2 is configured to adaptively control the frequency of the PWM signal according to the detection result of the sensing unit 566. [ The frequency of the PWM signal is controlled so that the voltage conversion can be normally performed while minimizing the switching loss under the sensed load condition.

The frequency of the PWM signal may be set differently from the frequency of the scan signal applied to the display panel 520 and the harmonics thereof. A flicker may be generated when coupling between the switching frequency for generating the second voltage V2 and the scan frequency of the display panel 520 occurs and the control module 564_2 outputs the frequency of the scan signal and the harmonics thereof And the frequency of the PWM signal is varied according to the load. For example, since the scan frequency of WXGA and HD is 78KHz, the lowest switching frequency is set to 80KHz at no load, and the switching frequency is increased as the load is increased, but the harmonic of the scan frequency is avoided.

The second converting module 564 may take the configuration of the converting module 220 shown in FIG. The sensing unit 566 may have the configuration of the sensing unit 566 shown in FIG.

The first converting module 562 may take the configuration of the converting module 320 shown in FIG. Unlike the second converting module 564, the first converting module 562 does not operate by adaptively changing the frequency of the PWM signal according to the detection result of the sensing unit 566.

6 illustrates an organic light emitting display according to another embodiment of the present invention.

6, an organic light emitting display 600 includes a display panel 620, a timing controller 640, and a DC-DC converter 660.

5 in that the sensing portion 666 of the DC-DC converter 660 is positioned at the output terminal of the second converting module 664 to sense the driving current I _D. The first converting module 662 may take the configuration of the converting module 320 shown in FIG. 3 and the second converting module 664 may take the configuration of the converting module 220 shown in FIG. The sensing unit 666 may have the configuration of the sensing unit 240 shown in FIG.

5 and FIG. 6, the first conversion module 562 and the second conversion module 662 detect the sensing result Vsense of the sensing units 566 and 666, The second converting module 564 and the second converting module 664 may be modified to operate independently of the sensing result Vsense of the sensing units 566 and 666 . In this case, the first converting module 562, 662 may take the configuration of the converting module 320 shown in FIG. 3, and the second converting module 564, 664 may be a conversion module 220).

7 illustrates an organic light emitting display according to another embodiment of the present invention.

7, an organic light emitting display 700 includes a display panel 720, a timing controller 740, and a DC-DC converter 760.

5 differs from the embodiment of FIG. 5 in that both of the first converting module 762 and the second converting module 764 of the DC-DC converter 700 generate PWM signals The frequency of which is controlled in a manner adaptive. The first converting module 762 may take the configuration of the converting module 320 shown in FIG. The second converting module 764 may take the configuration of the converting module 220 shown in FIG. The sensing unit 766 may take the configuration of the sensing unit 340 shown in FIG.

7, the sensing unit 766 of the DC-DC converter 760 is located at the output terminal of the second converting module 764 and is driven The current I _D can be realized. In this case, the sensing unit 766 may have the configuration of the sensing unit 240 shown in FIG.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments described above are therefore to be considered in all respects only as illustrative and not restrictive. The scope of the present invention should be construed as including all changes or modifications derived from the meaning and scope of the claims and their equivalents.

100, 200, 300: DC-DC converter 120, 220, 320: converting module
140, 240, 340: sensing unit 122, 222, 322: switching module
124, 224, 324: control module 224_2, 324_2: switch driver
224_4, 324_4: a PWM signal generation unit 242, 342: a sense voltage output unit
420: frequency selecting unit 440: sawtooth wave generating unit
460: square wave generating unit 480: reference voltage setting unit

Claims (21)

A switching module for converting an input voltage and outputting a first voltage while a plurality of switches are turned on and off in response to a corresponding pulse width modulation (PWM) signal, respectively; And a control module for generating the PWM signal to control the switching operation of the switching module. And
And a sensing unit sensing a driving current supplied to a load supplied with the first voltage,
The control module
Wherein the control unit is configured to adaptively control the frequency of the PWM signal according to the detection result of the sensing unit. The method according to claim 1,
The switching module
A first switch positioned between an input node to which the input voltage is input and a first node to form or cut off a current path; An inductor located between the first node and ground; And a second switch located between the first node and the second node to form or cut off a current path,
The sensing unit
A third switch located between the second node and the output node; And a sense voltage generator connected to both ends of the third switch for outputting a sense voltage corresponding to the drive current,
The control module
A PWM signal generator for generating the PWM signal having a frequency determined according to the sensing voltage; And a switch driver for controlling the first to third switches. The apparatus as claimed in claim 2, wherein the PWM signal generating unit
A frequency selector for comparing the sensing voltage with a plurality of reference voltages and generating a frequency selection signal according to the comparison result;
A sawtooth wave generating unit for generating a sawtooth wave having a corresponding frequency in response to the frequency selection signal; And
And a square wave generator for converting the sawtooth wave into the PWM signal using offset information of a feedback voltage and a set voltage obtained by dividing the first voltage. The apparatus of claim 3, wherein the square wave generator
A voltage divider for dividing the first voltage to generate a feedback voltage;
An amplifier for amplifying and outputting a difference between the feedback voltage and the set voltage; And
And a comparator for comparing the sawtooth wave with the output of the amplifier and outputting the PWM signal. The method of claim 3,
And a reference voltage setting unit for setting the plurality of reference voltages. 6. The method of claim 5,
Wherein the first switch is a PMOS transistor, and the second and third switches are NMOS transistors. The method according to claim 1,
The switching module
An inductor positioned between an input node to which the input voltage is applied and a first node; A first switch positioned between the first node and ground to form or cut off a current path; And a second switch located between the first node and the second node to form or cut off a current path,
The sensing unit
A third switch located between the second node and the output node; And a sense voltage generator connected to both ends of the third switch for outputting a sense voltage corresponding to the drive current,
The control module
A PWM signal generator for generating the PWM signal having a frequency determined according to the sensing voltage; And a switch driver for controlling the first to third switches. 8. The apparatus of claim 7, wherein the PWM signal generator
A frequency selector for comparing the sensing voltage with a plurality of reference voltages and generating a frequency selection signal according to the comparison result;
A sawtooth wave generating unit for generating a sawtooth wave having a corresponding frequency in response to the frequency selection signal; And
And a square wave generator for converting the sawtooth wave into the PWM signal using offset information of a feedback voltage and a set voltage obtained by dividing the first voltage. 9. The apparatus of claim 8, wherein the square wave generator
A voltage divider for dividing the first voltage to generate a feedback voltage;
An amplifier for amplifying and outputting a difference between the feedback voltage and the set voltage; And
And a comparator for comparing the sawtooth wave with the output of the amplifier and outputting the PWM signal. 9. The method of claim 8,
And a reference voltage setting unit for setting the plurality of reference voltages. 11. The method of claim 10,
Wherein the first switch is an NMOS transistor, and the second and third switches are PMOS transistors. A display device comprising: a display panel having a plurality of pixels, wherein the display panel displays gradations according to the brightness of the organic light emitting diodes of the pixels;
A timing controller for providing a scan signal and a data signal for causing the organic light emitting diodes of each pixel to emit light to the display panel; And
And a DC-DC converter for generating a first voltage and a second voltage for supplying the input voltage to the organic light emitting diode and supplying the current to the display panel,
The DC-DC converter
A first converting module receiving the input voltage to generate the first voltage; A second converting module receiving the input voltage to generate the second voltage; And a sensing unit sensing a driving current supplied to the display panel,
Each of the first and second converting modules
A switching module for converting an input voltage and outputting the second voltage while the plurality of switches are turned on and off in response to a corresponding pulse width modulation (PWM) signal; And a control module for generating the PWM signal to control a switching operation of the switching module,
At least one of the control modules of the first and second converting modules
Wherein the control unit controls the frequency of the PWM signal according to the sensing result of the sensing unit. 13. The method of claim 12,
The switching module of the second converting module
A first switch located between the input node and the first node to form or cut off a current path; An inductor located between the first node and ground; And a second switch located between the first node and the second node to form or cut off a current path,
The control module of the second converting module
A PWM signal generating unit for generating the PWM signal having a frequency determined according to a sensing result of the sensing unit; And a switch driver for controlling the first and second switches. 14. The apparatus of claim 13, wherein the sensing unit
Wherein the organic light emitting display is positioned between an output node of the first converting module and a first output node for providing the first voltage to the display panel to sense the driving current. 15. The apparatus of claim 14, wherein the sensing unit
A third switch located between the output node of the first converting module and the first output node; And a sensing voltage generator connected to both ends of the third switch to output a sensing voltage corresponding to the driving current. 16. The apparatus of claim 15, wherein the PWM signal generator
A frequency selector for comparing the sensing voltage with a plurality of reference voltages and generating a frequency selection signal according to the comparison result;
A sawtooth wave generating unit for generating a sawtooth wave having a corresponding frequency in response to the frequency selection signal; And
And a square wave generator for converting the sawtooth wave into the PWM signal using offset information of a feedback voltage and a set voltage divided by the output voltage. 14. The apparatus of claim 13, wherein the sensing unit
Wherein the organic electroluminescent display is positioned between the second node and a second output node for providing the second voltage to the display panel, and senses the driving current. 13. The method of claim 12,
The switching module of the first converting module
A first inductor located between the input node and a first node; A first switch positioned between the first node and ground to form or cut off a current path; And a second switch located between the first node and the second node to form or cut off a current path,
The control module of the first converting module
A first PWM signal generating unit for generating a first PWM signal having a frequency determined according to a sensing result of the sensing unit; And a first switch driver for controlling the first and second switches,
The switching module of the second converting module
A third switch located between the input node and the third node to form or cut off a current path; A second inductor located between the third node and ground; And a fourth switch located between the third node and the fourth node to form or cut off a current path,
The control module of the second converting module
A second PWM signal generating unit for generating a second PWM signal having a frequency determined according to the sensing result of the sensing unit; And a second switch driver for controlling the third and fourth switches. 19. The apparatus of claim 18, wherein the sensing unit
Wherein the organic electroluminescent display is positioned between the second node and a first output node for providing the first voltage to the display panel, and senses the driving current. 20. The apparatus of claim 19, wherein the sensing unit
A third switch located between the second node and the first output node; And a sensing voltage generator connected to both ends of the third switch to output a sensing voltage corresponding to the driving current. 21. The method of claim 20,
Each of the first and second PWM signal generating units
A frequency selector for comparing the sensing voltage with a plurality of reference voltages and generating a frequency selection signal according to the comparison result;
A sawtooth wave generating unit for generating a sawtooth wave having a corresponding frequency in response to the frequency selection signal; And
And a square wave generator for converting the sawtooth wave into the first PWM signal or the second PWM signal using offset information of a feedback voltage and a set voltage divided by the output voltage.

Images