KR101563985B1 - Organic electroluminescent display device and method of driving the same - Google Patents

Abstract

The present invention relates to an organic electroluminescence display, comprising: a load including an organic electroluminescence panel; And a power supply circuit for converting an input voltage to supply an output voltage to the load, wherein the power supply circuit comprises: an input terminal for receiving the input voltage; An output terminal for outputting the output voltage; A voltage conversion circuit that includes a power switching transistor and converts the input voltage to the output voltage; A PFM switching controller for outputting a PFM switching pulse; And a PWM switching control unit for selectively outputting a PWM switching pulse synchronized with the frequency of the PWM driving pulse and a PFWM switching pulse synchronized with the frequency of the PFM switching pulse and having a variable pulse width, wherein the PFM switching pulse and the PFWM switching pulse And the PWM switching pulse are supplied to the power switching transistor when the size of the load is low, middle, or high, respectively.

Description

[0001] The present invention relates to an organic electroluminescence display device and a driving method thereof,

The present invention relates to an organic light emitting display, and more particularly, to an organic light emitting display and a driving method thereof.

2. Description of the Related Art [0002] With the development of an information society, demands for a display device for displaying images have been increasing in various forms. Recently, a liquid crystal display (LCD), a plasma display panel (PDP) Various flat display devices such as an organic electroluminescent display device (OELD) have been utilized.

Among these flat panel display devices, organic light emitting display devices are self-luminous display devices having advantages of miniaturization, weight reduction, thinning, low power driving, and are widely used recently.

The organic light emitting display device is driven by receiving a necessary power from a DC-DC converter. Generally, the power supply voltage for driving the organic light emitting display device is higher than the input voltage input to the DC-DC converter. Therefore, the DC-DC converter is driven in the boost mode to boost the input voltage, and the boosted output voltage is supplied as the power supply.

1 is a schematic view of a conventional DC-DC converter.

As shown in the drawing, a conventional DC-DC converter 10 includes a switching control section 11, a power supply switching transistor TP, an inductor L, a diode D and a capacitor C .

The conventional DC-DC converter 10 having such a configuration can increase the input voltage Vin by adjusting on / off switching of the power supply switching transistor TP. That is, when the switching transistor TP is turned on, the current flowing from the input terminal is stored. Thereafter, when the switching transistor TP is turned off, the stored current is discharged through the diode D. [ As a result, the voltage Vout at the output terminal rises and the applied voltage Vout is boosted to a voltage higher than the input voltage Vin. The capacitor C stores the boosted output voltage Vout.

Such a conventional DC-DC converter 10 controls the output voltage Vout in a certain range. As a method of controlling the output voltage Vout to a constant range, there are a pulse width modulation (PWM) method and a pulse frequency modulation (PFM) method. Conventional DC-DC converter 10 is driven in one of these ways.

The PWM method changes the time for turning on the power supply switching transistor TP based on the difference between the feedback voltage divided by the output voltage Vout and the PWM reference voltage. In other words, when the PWM reference voltage is higher than the feedback voltage, the time when the voltage difference increases becomes longer, that is, the pulse width of the PWM switching pulse becomes longer. On the other hand, the frequency of the PWM switching pulse is constant. As described above, in the PWM method, the pulse width of the PWM switching pulse changes.

On the other hand, the PFM method changes the frequency of the PFM switching pulse that turns on the power supply switching transistor TP based on the difference between the feedback voltage obtained by dividing the output voltage Vout and the PFM reference voltage. In other words, when the PFM reference voltage is higher than the feedback voltage, the frequency of the PFM switching pulse becomes higher as the voltage difference increases. On the other hand, the duty ratio of the PFM switching pulse is constant. As described above, in the PFM method, the frequency of the PFM switching pulse changes.

The PWM method can be useful when the power consumption of the load is large, that is, when the load is heavy. However, there is a problem in that the power conversion efficiency is low when the power consumption is small, that is, the light load is low. That is, in the PWM method, even in the case of a low load, the PWM switching pulse is outputted and the power supply switching transistor TP performs the switching operation. Thus, in the case of a low load, the power loss due to the switching operation becomes large.

On the other hand, the PFM method can be usefully used for a low load. However, there is a problem that the voltage conversion efficiency is low for a high load. That is, in the PFM method, in the case of a high load, the frequency of the PFM switching pulse becomes high, and the power supply switching transistor TP performs switching operation at a high frequency. Accordingly, in the case of a high load, the power loss due to the switching operation becomes large.

As described above, the PWM method and the PFM method have advantages and disadvantages depending on the size of the load. However, the power consumption, i.e., the load, of the organic light emitting display device varies greatly depending on the type of displayed image. Therefore, the conventional DC-DC converter driven by one of the PWM system and the PFM system can not be driven with high efficiency when the size of the load changes greatly.

To improve this, a DC-DC converter is proposed, which utilizes the advantages of PFM and PWM schemes and selectively uses two schemes depending on the load size. Hereinafter, for convenience of explanation, such a DC-DC converter is referred to as a PFM / PWM DC-DC converter.

2 is a schematic diagram of a conventional PFM / PWM DC-DC converter.

Referring to FIG. 2, the conventional PFM / PWM DC-DC converter 20 is driven in the PFM mode when the load is small. In this case, the PFM switching pulse output from the PFM switching controller 21 is input to the power switching transistor TP. To this end, the selection switch SS connects the PFM switching control section 21 and the power switching transistor TP.

On the other hand, when the load is large, it is driven in the PWM mode. In such a case, the PWM switching pulse output from the PWM switching control section 22 is input to the power supply switching transistor TP. To this end, the selection switch SS connects the PWM switching control section 22 and the power switching transistor TP.

As described above, the conventional PFM / PWM DC-DC converter 20 can be selectively driven in the PFM mode and the PWM mode in accordance with the change in the load. Accordingly, it can be driven with high efficiency at low load and high load.

However, even in the case of selective driving in the PWM mode and the PFM mode as described above, it is still impossible to drive with a high efficiency with respect to the middle load between the high load and the low load. That is, in the case of driving in the PWM mode in the middle load, the power loss due to the switching operation is larger than when the load is high. In addition, even in the case of driving in the PFM mode at the middle portion, the power loss due to the switching operation is larger than that at the low portion.

Disclosure of the Invention Problems to be Solved by the Invention An object of the present invention is to provide an organic light emitting display device and a driving method thereof that can improve the efficiency of a DC-DC converter.

According to an aspect of the present invention, there is provided an organic light emitting display comprising: a load including an organic electroluminescence panel; And a power supply circuit for converting an input voltage to supply an output voltage to the load, wherein the power supply circuit comprises: an input terminal for receiving the input voltage; An output terminal for outputting the output voltage; A voltage conversion circuit that includes a power switching transistor and converts the input voltage to the output voltage; A PFM switching controller for outputting a PFM switching pulse; And a PWM switching control unit for selectively outputting a PWM switching pulse synchronized with the frequency of the PWM driving pulse and a PFWM switching pulse synchronized with the frequency of the PFM switching pulse and having a variable pulse width, wherein the PFM switching pulse and the PFWM switching pulse And the PWM switching pulse are supplied to the power switching transistor when the size of the load is low, middle, and high, respectively.

Here, the voltage conversion circuit may include: an inductor positioned between a node to which the power switching transistor is connected and the input terminal; A diode positioned between said node and said output terminal; And a capacitor connected in parallel to the output terminal.

Wherein the power supply circuit comprises: a PFM error amplifier that compares a feedback voltage to the output voltage with a PFM reference voltage and outputs the comparison result to the PFM switching controller; A PWM error amplifier for comparing the feedback voltage with a PWM reference voltage and outputting the comparison result to the PWM switching controller; A ramp wave generator for outputting a ramp wave synchronized with a frequency of an input pulse to the PWM switching control unit; A pulse generator for generating the PWM drive pulse; A first selector switch for selectively connecting the pulse generator and the PFM switching controller to the ramp generator; And a second selection switch for selectively connecting the PWM switching controller and the PFM switching controller to the power switching transistor.

The power supply circuit may further include a feedback circuit connected in parallel to the output terminal and detecting the feedback voltage divided by the output voltage.

In another aspect, the present invention provides a method comprising: generating a PFM switching pulse at a PFM switching controller; Generating a PWM switching pulse synchronized with the frequency of the PWM driving pulse in the PWM switching control section; Generating a PFWM switching pulse synchronized with a frequency of the PFM switching pulse and having a variable pulse width in a PWM switching control section; Switching the power switching transistor using the generated PFM switching pulse and the PFWM switching pulse and the PWM switching pulse when the size of the load is low, middle, and high, respectively; Converting an input voltage input to the power supply circuit to an output voltage through switching of the power supply switching transistor; And driving the organic electroluminescent panel of the load using the output voltage.

Here, the output voltage may be a voltage obtained by stepping up the input voltage.

Comparing the feedback voltage to the output voltage with a PFM reference voltage and outputting the comparison result to the PFM switching controller; Comparing the feedback voltage with a PWM reference voltage and outputting the comparison result to the PWM switching controller; Inputting a PFM switching pulse and a PWM driving pulse to the ramp generator at each of the heavy load and the high load; And outputting the ramp wave synchronized with the frequency of the pulse input to the ramp wave generator to the PWM switching controller.

The feedback voltage may be a voltage obtained by dividing the output voltage.

In the present invention, the DC-DC converter is driven in the PFM mode at the time of low load and in the PWM mode at the time of high load. This makes it possible to drive with high efficiency at low load and high load.

Moreover, in the middle of the day, it is driven in the PFWM mode. In the PFWM mode operation, the power switching transistor is switched by generating a PFWM switching pulse whose frequency can be changed in synchronization with the PFM switching pulse and whose pulse width can be varied. This makes it possible to reduce the power loss due to the switching operation as compared with the case of driving in the PWM mode, the PFM mode, or the PFM / PWM mode at the middle portion. Therefore, it is possible to drive with high efficiency even under a heavy load.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a view schematically showing an organic light emitting display according to an embodiment of the present invention, FIG. 4 is a diagram showing pixels of the organic light emitting display panel of FIG. 2, Fig. 6 is a diagram showing the control circuit of Fig. 5, and Fig. 7 is a diagram showing a comparator of the PWM switching control unit of Fig.

The organic light emitting display 100 according to the embodiment of the present invention includes an organic electroluminescent panel 200, a panel driving circuit 250, and a power supply circuit 300. Here, the organic electroluminescence panel 200 and the panel driving circuit 250 for driving the organic electroluminescence panel 200 correspond to a load LOAD on the side of the power supply circuit 300.

The organic electroluminescence panel 200 is a display panel for displaying an image. Referring to FIG. 5, a gate line GL extending in a row direction and a data line DL extending in a column direction intersect the organic electroluminescence panel 200 to define a pixel P. The pixels P are arranged in a matrix form in the organic electroluminescent panel 200. [

The pixel P configured in the organic electroluminescent panel 200 may include R (red), G (green), and B (blue) pixels. Each of the R, G, and B pixels P is input with corresponding R, G, and B image data. Here, neighboring R, G, and B pixels P constitute one image display unit.

The switching transistor Ts, the driving transistor Td, the organic light emitting diode D, and the storage capacitor C may be formed in each pixel P. [

The switching transistor Ts is connected to the corresponding gate wiring and data lines GL and DL. The gate terminal of the driving transistor Td is connected to the drain terminal of the switching transistor Ts. One electrode of the organic light emitting diode D may be connected to the drain terminal of the driving transistor Td. The other electrode of the organic light emitting diode D can receive the driving voltage VDD. The source terminal of the driving transistor Td may be grounded. The storage capacitor C may be connected between the gate terminal and the source terminal of the driving transistor Td. Such a structure of the pixel P is an example, and may be configured in various other structures.

The pixel P as described above is driven as follows.

And the gate lines GL are sequentially scanned on a frame-by-frame basis. During each scan period, a gate signal having a turn-on voltage is supplied to the gate line GL. On the other hand, a turn-off voltage is supplied to the gate line GL until the next frame is scanned. The turn-on voltage is applied during the scan period, so that the switching transistor Ts is turned on.

When the switching transistor Ts is turned on, the image data is applied to the data line DL in synchronization therewith. The image data thus applied passes through the switching transistor Ts of the pixel P and is applied to the driving transistor Td.

When image data is applied to the driving transistor Td, the driving transistor Td is turned on and a light emitting current flows through the driving transistor Td. Here, the value of the light emission current is adjusted according to the value of the applied image data. The light emitting current is applied to the organic light emitting diode D so that the organic light emitting diode D emits light of a luminance corresponding to the light emitting current. In other words, light of a luminance corresponding to the applied image data is emitted through the organic light emitting diode D. Accordingly, as the image data is adjusted, the luminance of the light emitted through the organic light emitting diode D is adjusted.

On the other hand, the image data applied to the driving transistor Td is stored in the storage capacitor C. Accordingly, the image data is stored in the storage capacitor C until the next scan of the pixel, and the organic light emitting diode D can emit light of a luminance corresponding to the image data until the next scan.

The driving voltage VDD for driving the organic light emitting diode D is supplied from the power supply circuit 300.

The panel driving circuit 250 includes various driving circuits for driving the organic electroluminescent panel 200. For example, a data driving circuit for outputting image data to the data line DL and a gate driving circuit for outputting a gate signal to the gate wiring GL. And a timing control circuit for controlling operations of the data driving circuit and the gate driving circuit. Such driving circuits are also operated by receiving power from the power supply circuit 300.

As the power supply circuit 300, a DC-DC converter can be used. For example, a boost type DC-DC converter that boosts the input voltage Vin may be used. In the following description, the power supply circuit 300 may be referred to as a DC-DC converter for convenience.

The DC-DC converter 300 according to the embodiment of the present invention can be used in a PFM mode, a PFWM mode, a PWM mode, or a PWM mode, for example, in each of a low load, a middle load, and a high load, Lt; / RTI > The DC-DC converter 300 driven in this manner will be described in more detail with reference to FIGS. 5 to 7. FIG.

The DC-DC converter 300 according to the embodiment of the present invention may include a voltage conversion circuit 310, a control circuit 320, and a feedback circuit 330.

The voltage conversion circuit 310 boosts the input voltage Vin input from the system 400 according to the switching operation and outputs the boosted output voltage Vout to the load LOAD. To this end, the voltage conversion circuit 310 includes an inductor L, a diode DP, a capacitor CP, and a power supply switching transistor TP. The inductor L may be connected between an input terminal and a node N to which the power supply switching transistor TP is connected. The diode DP may be connected between the node N and the output terminal. The capacitor CP may be connected in parallel to the output terminal.

When the power switching transistor TP is turned on, the current flowing from the input terminal is stored. Thereafter, when the power supply switching transistor TP is turned off, the current stored in the inductor L is discharged through the diode DP. As a result, the voltage Vout at the output terminal rises and the output voltage Vout is boosted to a voltage higher than the input voltage Vin. And the capacitor CP stores the boosted output voltage Vout. As described above, the voltage conversion circuit 310 boosts the input voltage Vin to generate the output voltage Vout through the switching operation of the power supply switching transistor TP.

The feedback circuit 330 is connected in parallel to the output terminal to detect the feedback voltage VF that divides the output voltage Vout. The feedback voltage VF thus detected is transmitted to the control circuit 320. [ The feedback circuit 330 may be composed of a voltage dividing resistor circuit including first and second resistors R1 and R2 connected in series. In such a case, the feedback voltage VF is detected through the node between the first and second resistors.

The control circuit 320 generates a switching pulse which is a switching signal for controlling on / off switching operation of the power supply switching transistor TP. Such a switching pulse is output in a different manner depending on the low load, the heavy load, and the high load. To this end, the control circuit 320 includes a PFM control unit 321, a PWM control unit 322, and first and second selection switches SS1 and SS2.

The PFM control unit 321 includes a PFM error amplifier OPF and a PFM switching control unit SWF.

The PFM error amplifier OPF receives the PFM reference voltage VFref and the feedback voltage VF and amplifies and outputs the voltage difference between these voltages. For example, the PFM reference voltage VFref and the feedback voltage VF may be input to the non-inverting terminal and the inverting terminal of the PFM error amplifier OPF, respectively.

The PFM switching control section SWF outputs the PFM switching pulse PF in response to the output from the PFM error amplifier OPF. That is, the frequency of the PFM switching pulse PF varies depending on the voltage difference between the PFM reference voltage VFref and the feedback voltage VF. For example, when the PFM reference voltage VFref is larger than the feedback voltage VF, as the voltage difference between the PFM reference voltage VFref and the feedback voltage VF increases, the frequency of the PFM switching pulse PF becomes higher do. On the other hand, when the PFM reference voltage VFref is equal to or smaller than the feedback voltage VF, the operation of the PFM switching control section SWF is stopped, so that the PFM switching pulse PF may not be output.

In the embodiment of the present invention, the PFM switching pulse PF is used under a low load and a heavy load. For example, at the time of the bottom load, the power supply switching transistor TP performs the switching operation by the output PFM switching pulse PF. On the other hand, under the middle load, the output PFM switching pulse PF is transmitted to the PWM controller 322, which will be described in more detail below.

The PWM control section 322 includes a PWM error amplifier OPW, a PWM switching control section SWW, a ramp wave generator 323 and a pulse wave generator 324.

The PWM error amplifier OPW receives the PWM reference voltage VWref and the feedback voltage VF and amplifies and outputs the voltage difference between these voltages. For example, the PWM reference voltage VWref and the feedback voltage VF may be input to the non-inverting terminal and the inverting terminal of the PWM error amplifier OPW, respectively.

The pulse generator 324 generates a PWM drive pulse having a fixed frequency. The PWM drive pulse corresponds to a reference signal for driving the DC-DC converter 300 in the PWM mode.

The ramp wave generator 323 generates a ramp wave in response to an input signal. Since the ramp wave has a serrate shape or a triangle shape, it may be called a sawtooth wave or a triangle wave.

In the embodiment of the present invention, the ramp wave generator 323 is selectively supplied with the PWM drive pulse and the PFM switching pulse PF according to the drive mode. For example, in the case of a heavy load, a PFM switching pulse PF is applied to drive the PFWM mode. In the case of a high load, a PWM drive pulse is applied for PWM mode driving. On the other hand, in the case of a low load, since the PFM mode is driven, a PFM switching pulse PF or a PWM driving pulse can be applied.

In order to selectively apply a signal to the ramp wave generator 322, the first selection switch SS1 may be used. For example, in the PFWM mode driving, the first selection switch SS1 connects the ramp wave generator 323 and the PFM control unit 321, so that the PFM switching pulse PF is input. At the time of the PWM mode operation, the first selection switch SS1 connects the ramp wave generator 323 and the pulse generator 324 to input the PWM drive pulse.

If the ramp wave generator 323 receives the PWM drive pulse, it generates a ramp wave synchronized with the PWM drive pulse. On the other hand, when the ramp wave generator 323 receives the PFM switching pulse PF, it generates a ramp wave synchronized with the PFM switching pulse PF. Here, since the PWM drive pulse has a fixed frequency, when a PWM drive pulse is applied, a ramp wave of a fixed frequency is generated. On the other hand, since the frequency of the PFM switching pulse PF may vary, when the PFM switching pulse PF is applied, the frequency of the ramp wave may also be changed according to the frequency change. As described above, the ramp wave generator 323 can generate other types of ramp waves in accordance with the drive mode.

The PWM switching control unit SWW compares the voltage output from the PWM error amplifier OPW with the ramp wave and outputs a switching pulse according to the comparison result. For example, the output voltage may be compared with the ramp wave to cause the power supply switching transistor TP to turn on in a region where the ramp wave is higher than the waveform of the output voltage. Through such waveform comparison, the PWM switching control unit SWW can change the pulse width of the output switching pulse. In this regard, the pulse width of the output switching pulse increases as the voltage difference between the PWM reference voltage VWref and the feedback voltage VF increases. Here, the increasing direction of the voltage difference is a direction in which the feedback voltage VF decreases with reference to the PWM reference voltage VWref.

The PWM switching control unit SWW performing the above operation includes a comparator (OPC). For example, the voltage output from the PWM error amplifier OPW and the ramp wave are respectively input to the inverting terminal and the non-inverting terminal of the comparator OPC, respectively. Thus, the comparator (OPC) compares the input voltages and outputs switching pulses.

On the other hand, as described above, since the ramp wave is changed according to the driving mode, the switching pulse outputted through the PWM switching control unit SWW also changes. For example, at the PWM mode driving, a ramp wave synchronized with the PWM drive pulse is input to the PWM switching control section SWW. As a result, as a switching pulse to be outputted, a PWM switching pulse PW is outputted whose frequency is fixed and pulse width can be changed.

On the other hand, at the PFWM mode driving, a ramp wave synchronized with the PFM switching pulse PF is input to the PWM switching control section SWW. As a result, a PFWM switching pulse PFW which can change both the frequency and the pulse width is output as the output switching pulse.

The second selection switch SS2 selectively switches the switching pulse output through the PFM control unit 321 and the PWM control unit 322 and transmits the switching pulse to the power switching transistor TP. For example, during the PFM mode driving, the second selection switch SS2 connects the PFM control unit 321 and the power switching transistor TP. Accordingly, the PFM switching pulse PF generated through the PFM mode driving is supplied to the power switching transistor TP, and the power switching transistor TP performs the switching operation in accordance with the PFM switching pulse PF.

On the other hand, when driving in the PFWM mode and the PWM mode, the second selection switch SS2 connects the PWM control section 321 and the power switching transistor TP. Here, in the PFWM mode driving, the PFWM switching pulse PFW generated through the driving of the PFWM mode is supplied to the power switching transistor TP so that the power switching transistor TP switches according to the PFWM switching pulse PFW . At the time of the PWM mode driving, the PWM switching pulse PW generated through the PWM mode driving is supplied to the power supply switching transistor TP so that the power supply switching transistor TP performs the switching operation according to the PWM switching pulse PW .

Hereinafter, a driving method of the DC-DC converter according to the embodiment of the present invention will be described.

First, in the case of a low load, the DC-DC converter 300 is driven in the PFM mode. To this end, the second selection switch SS2 is switched to connect the PFM switching control section SWF and the power switching transistor PT.

On the other hand, the first selection switch SS1 is switched to connect the pulse generator 324 and the ramp generator 323. Of course, the first selection switch SS1 may be switched to connect the PFM switching controller SWF and the ramp generator 323. Accordingly, the PFM switching pulse PF generated in the PFM switching controller SWF is input to the power supply switching transistor TP to control the switching operation.

Next, in the case of a high load, the DC-DC converter 300 is driven in the PWM mode. To this end, the second selection switch SS2 is switched to connect the PWM switching control section SWW and the power supply switching transistor TP.

On the other hand, the first selection switch SS1 is switched to connect the pulse generator 324 and the ramp generator 323. Thus, the PWM switching control section SWW generates the PWM switching pulse PW synchronized with the frequency of the PWM drive pulse. The PWM switching pulse PW thus generated is input to the power supply switching transistor TP to control the switching operation.

Next, in the case of the heavy load, the DC-DC converter 300 is driven in the PFWM mode. To this end, the second selection switch SS2 is switched to connect the PWM switching control section SWW and the power supply switching transistor TP.

On the other hand, the first selection switch SS1 is switched to connect the PFM switching control section SWF and the ramp waveform generation section 323. Thus, the PWM switching control section SWW generates the PFWM switching pulse PFW synchronized with the frequency of the PFM switching pulse. The PFWM switching pulse PFW thus generated is input to the power supply switching transistor TP to control the switching operation.

As described above, in the embodiment of the present invention, the DC-DC converter is driven in the PFM mode at the time of the low load and in the PWM mode at the time of the high load. This makes it possible to drive with high efficiency at low load and high load.

Moreover, in the middle of the day, it is driven in the PFWM mode. In the PFWM mode operation, the power switching transistor is switched by generating a PFWM switching pulse whose frequency can be changed in synchronization with the PFM switching pulse and whose pulse width can be varied. This makes it possible to reduce the power loss due to the switching operation, compared to the case of driving in the conventional PWM mode, PFM mode, or PFM / PWM mode at the middle portion. Therefore, it is possible to drive with high efficiency even under a heavy load.

It will be apparent to those skilled in the art that the terms low load, heavy load, and high load referred to in the embodiments of the present invention are relative concepts of load size rather than a fixed concept of load size.

The embodiment of the present invention described above is an example of the present invention, and variations are possible within the spirit of the present invention. Accordingly, the invention includes modifications of the invention within the scope of the appended claims and equivalents thereof.

FIG. 1 schematically shows a conventional DC-DC converter; FIG.

2 is a schematic view of a conventional PFM / PWM DC-DC converter;

3 is a view schematically showing an organic light emitting display according to an embodiment of the present invention.

4 is a view showing pixels of the organic electroluminescence panel of FIG. 2;

Fig. 5 shows the power supply circuit of Fig. 3; Fig.

Fig. 6 shows the control circuit of Fig. 5; Fig.

7 is a view showing a comparator of the PWM switching control unit of Fig. 6;

Description of the Related Art

321: PFM control unit 322: PWM control unit

323: ramp wave generator 324: pulse generator

OPF: PFM error amplifier OPW: PWM error amplifier

SWF: PWM switching control section SWW: PWM switching control section

SS1: first selection switch SS2: second selection switch

Claims (8)

A load including an organic electroluminescence panel; And a power supply circuit for converting an input voltage to supply an output voltage to the load, The power supply circuit includes: An input terminal for receiving the input voltage; An output terminal for outputting the output voltage; A voltage conversion circuit that includes a power switching transistor and converts the input voltage to the output voltage; A PFM switching controller for outputting a PFM switching pulse; And a PWM switching control unit for selectively outputting a PWM switching pulse synchronized with the frequency of the PWM driving pulse and a PFWM switching pulse synchronized with the frequency of the PFM switching pulse and having a variable pulse width, The PFM switching pulse, the PFWM switching pulse and the PWM switching pulse are supplied to the power switching transistor when the size of the load is low, middle, and high, respectively Organic electroluminescence display device. The method according to claim 1, Wherein the voltage conversion circuit comprises: An inductor located between a node to which the power switching transistor is connected and the input terminal; A diode positioned between said node and said output terminal; And a capacitor connected in parallel to the output terminal Organic electroluminescence display device. The method according to claim 1, The power supply circuit includes: A PFM error amplifier for comparing the feedback voltage to the output voltage with a PFM reference voltage and outputting the comparison result to the PFM switching controller; A PWM error amplifier for comparing the feedback voltage with a PWM reference voltage and outputting the comparison result to the PWM switching controller; A ramp wave generator for outputting a ramp wave synchronized with a frequency of an input pulse to the PWM switching control unit; A pulse generator for generating the PWM drive pulse; A first selection switch for selectively connecting the pulse generator and the PFM switching controller to the ramp generator; And a second selection switch for selectively connecting the PWM switching controller and the PFM switching controller to the power switching transistor Organic electroluminescence display device. The method of claim 3, The power supply circuit may further include a feedback circuit connected in parallel to the output terminal for detecting the feedback voltage divided by the output voltage Organic electroluminescence display device. Generating a PFM switching pulse at the PFM switching controller; Generating a PWM switching pulse synchronized with the frequency of the PWM driving pulse in the PWM switching control section; Generating a PFWM switching pulse synchronized with a frequency of the PFM switching pulse and having a variable pulse width in a PWM switching control section; Switching the power switching transistors using the generated PFM switching pulses, the PFWM switching pulses and the PWM switching pulses in the case where the size of the load is low, middle, and high, respectively; Converting an input voltage input to the power supply circuit to an output voltage through switching of the power supply switching transistor; Driving the organic electroluminescent panel of the load using the output voltage; Wherein the organic electroluminescent display device comprises a plurality of pixels. 6. The method of claim 5, Wherein the output voltage is a voltage obtained by stepping up the input voltage A method of driving an organic electroluminescent display device. 6. The method of claim 5, Wherein the step of generating the PFM switching pulse in the PFM switching controller includes comparing the feedback voltage with respect to the output voltage and the PFM reference voltage and outputting the comparison result to the PFM switching controller, Generating the PWM switching pulse at the high load at the PWM switching control unit and generating the PFWM switching pulse at the high load, Comparing the feedback voltage with a PWM reference voltage and outputting the comparison result to the PWM switching controller; Inputting the PFM switching pulse and the PWM driving pulse to the ramp wave generator and outputting the ramp wave synchronized with the frequency of the pulse inputted to the ramp wave generator to the PWM switching control unit in each of the heavy load and the high load, A method of driving an organic electroluminescent display device. 8. The method of claim 7, The feedback voltage is a voltage obtained by dividing the output voltage A method of driving an organic electroluminescent display device.

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