KR20030004772A - power saving circuit in display element of current driving type - Google Patents

Abstract

PURPOSE: An energy saving circuit of a current driving display device is provided to reduce an overall driving current by utilizing an energy saving circuit. CONSTITUTION: An energy saving circuit of a current driving display device includes a data driving blocks for controlling an on/off of a constant current source, an electroluminescence(EL) panel for determining the status of emission in response to the voltage applied to the data driving blocks and the scan driving block, a data sink block for removing the charges trapped at an anode line of the EL and N number of electroluminescence driving blocks(201-20N) consisted of the scan driving block.

Description

Power saving circuit in display element of current driving type

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit of a display element, and more particularly, to a power saving circuit of a current driving type display element which obtains low power consumption by recovering wasted power using a power recovery circuit.

Recently, in the field of flat panel display, rapid progress has been made.

In particular, current-driven flat panel displays, which started to emerge as the leading liquid crystal displays (LCDs), have recently surpassed the Cathode Ray Tube (CRT), which has been the most used in the display field for decades. Many developments are being made such as (Visual Fluorescent Display), FED (Field Emission Display), LED (Light Emitting Diode), EL (Electroluminescence).

Such current-driven display devices are not only good in visibility and color, but also have a simple manufacturing process, thereby expanding their applications in many areas.

However, as the size of the display panel increases, the current driven display elements consume more current in the display and the driving circuit. In addition, the higher the resolution, the less time is required to drive the display due to the physical quantity of the display, which requires more current to achieve the desired brightness.

LCD, which is widely used in portable information devices, has disadvantages such as response time, viewing angle, and color, but is widely used because it has the advantage of low power consumption.

Of course, considering the use of LCD back light, the power consumption is not small, but in recent years there is a transflective or reflective type LCD that can be used with little back light. It is used.

Recently, the organic EL display panel has been attracting attention as a flat panel display panel with less space occupancy due to the enlargement of the display device.

In the organic EL display panel, a data line and a scan line cross each other in a matrix form, and a light emitting layer is formed on each pixel that crosses each other. That is, the organic EL display panel is a display device in which the light emission state is determined according to the voltages applied to the data line and the scan line.

The light emission of each pixel is sequentially selected from the first line to the last line of the scan line during one frame through the scan driver, and selectively inputs power to the data line through the data driver during the same frame to scan lines. The pixel which intersects and the data line emits light.

The current-emitting characteristics of such an organic EL display panel have little temperature dependence, but the current-voltage characteristics move toward higher voltage when the temperature is lowered. Therefore, when the organic EL element is voltage driven, it is difficult to obtain stable operation. Therefore, a constant current driving method is adopted for driving the organic EL element.

1 is a diagram showing an organic EL driving circuit according to the prior art.

Referring to FIG. 1, a data driver configured as a PMOS receives Vdd as a power source for applying a power supply voltage, controls on / off of a constant current source, and controls an amount of current flowing from the constant current source to the anode of the organic EL. . In addition, the data sink part composed of NOMS has a drain connected to the anode of the organic EL and a source connected to the ground. The data sink part removes charge trapped in the anode line of the organic EL.

Further, the drain of the scan driver composed of NMOS is connected to the cathode of the organic EL, and the source is connected to the ground. The driving of the data driver, the data sink unit, and the scan driver is controlled by a controller (not shown).

That is, when the data driver is turned on under the control of the controller, current flows into the anode of the organic EL to emit light of the organic EL panel.

The organic EL driven in this way has a lower power consumption than the CRT, no distortion of the edge portion, and can be ultra-thin. In addition, it is more robust than LCD, and its self-emission makes it possible to make a large screen because of its wide viewing angle and good response. In addition, the use temperature conditions are -40 ° ~ + 70 ° wide, and the emission color can be freely selected, there is an advantage that can be driven at a low voltage of less than 15V.

However, the biggest reason that LCDs having many disadvantageous characteristics are used more than organic EL displays having the above advantages in portable information devices and the like is that organic EL displays have a disadvantage in that they consume more power than LCDs.

In addition, as the use of portable information terminal devices increases, the consumption of power becomes a big problem, and the use of a display for driving a display using current serves as a proposed element.

However, although the power consumption of a display driven by a current is many times that of an LCD, this is not meaningful because it is simply a comparison of an LCD and a display driven by a current. That is, if the LCD includes a back light, the current driven display and the LCD do not show much difference.

In addition, if the power consumption of the display driven by using the current is lowered by half from the entire level, the total power consumption can be almost reduced to the level of the LCD.

Accordingly, an object of the present invention is to provide a power saving circuit of a current-driven display element that reduces power consumption of a display by providing a power recovery circuit in an organic EL driving circuit.

Another object of the present invention is to provide a power saving circuit of a current-driven display element that can reduce the power of the entire system by recovering and reusing the wasted power in the conventional organic EL driving circuit.

1 shows a driving circuit of an organic EL according to the prior art.

2 is a view showing a power saving circuit of a current driven display device according to the present invention;

3 is an operation waveform diagram of each part of FIG.

4 illustrates an example of using an inductor as the DC-DC converter of FIG. 2.

5 is a view showing an example using a charge pump as the DC-DC converter of FIG.

Explanation of symbols for main parts of the drawings

201 to 20N: organic EL driver 301: transformer

302: DC-DC conversion control unit 303: diode

304: power supply

In order to achieve the above object, a power saving circuit of a current-driven display device according to the present invention includes an organic EL driver comprising a data driver, a data sink, and an organic EL panel which emits light when the data driver is turned on in parallel. N (N is a natural number) are provided, and a DC-DC converter is connected to each data sink in the N organic EL drivers.

Preferably, when the data sink is turned on, the DC-DC converter is configured to receive an anode voltage of the corresponding organic EL panel through the turned on data sink and convert it to a higher DC voltage and output the same to the power supply.

Preferably, the DC-DC converter includes a transformer connected to one side of the data sink unit and a ground to induce a current flowing through the data sink unit to the secondary coil, and the transformer to control the transformer. Characterized in that the control unit for outputting a DC voltage proportional to the induced current on the secondary side of the power supply.

Preferably, the DC-DC converter is configured to connect an inductor between the data sink and the power supply, and when the data sink is turned on, receives the anode voltage of the corresponding organic EL panel and converts the anode voltage into a higher DC voltage.

Preferably, the DC-DC converter is configured to connect a charge pump between the data sink and the power supply, and when the data sink is turned on, receives the anode voltage of the corresponding organic EL panel and converts it to a higher DC voltage.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

A preferred embodiment of a power saving circuit of a current driven display device according to the present invention will be described with reference to the accompanying drawings.

2 is a view showing a power saving circuit of the current driven display device according to the present invention.

Referring to FIG. 2, a data driver controlling on / off of a constant current source, an organic EL panel in which a light emission state is determined according to voltages applied to the data driver and the scan driver, and a charge trapped in an anode line of the organic EL is eliminated. A main sink is provided with a data sink unit and N organic EL driver units 201 to 20N.

Here, the structure of each said organic EL drive part is the same as that of FIG. 1 mentioned above. The difference is that one of the N data sinks is commonly connected to the ground through the transformer 301. That is, the data driver is composed of PMOS, and the data sink and scan driver are composed of NMOS. At this time, each data driver of the organic EL driver 201 to 20N is supplied with Vdd as a power source for applying a power supply voltage, controls the on / off of the constant current source, and the current flows from the constant current source to the anode of the organic EL. To control the amount of.

The source of the NMOS of the data sink of each of the organic EL drivers 201 to 20N is connected to ground through the primary coil of the transformer 301, and the source of the scan driver is usually directly connected to ground.

In FIG. 2, for convenience of explanation, the portion where the drain of the NMOS of the data sink of the first organic EL driver 201 and the anode of the organic EL are connected is indicated by A, and the data sink of the Nth organic EL driver 20N is represented by A. FIG. The portion where the drain of the negative NMOS is connected to the anode of the organic EL is denoted by N, and the portion where the source of the NMOS of the N data sink portions and the primary coil of the transformer 301 are connected is denoted by B.

In addition, a DC-DC conversion control unit 302 is connected to a secondary coil of the transformer 301, that is, an output terminal for the control of the transformer 301, and a diode 303 at an output of the DC-DC conversion control unit 302. The power source 304 is connected to the through. The diode 303 is a reverse voltage prevention diode that prevents the voltage of the power supply unit 304 from being output to the DC-DC conversion control unit 302. The power supply unit 304 is a kind of battery, and the power supply voltage Vdd is input from the input voltage. Create and provide to that part. In addition, the output node portion of the transformer 301 is denoted by C, and the portion where the cathode of the diode 303 and the power supply unit 304 are connected is denoted by P.

At this time, the signals input to the data driver and data sink of the organic EL driver 201 to 20N are the same. Thus, the data driver and the data sink perform opposite operations. That is, when the data driver is turned on, the data sink is turned off. When the data driver is turned off, the data sink is turned on.

If the data driver is turned on, the constant current source is turned on to emit light of the organic EL panel. If the data driver is turned off, the voltage applied to the anode of the organic EL (eg, voltage at point A) is applied to the transformer 301 through the data sink. Output to the primary coil.

In the present invention, the transformer 301 and the DC-DC conversion control unit 302 are called DC-DC conversion units.

The operation of the power saving circuit of the current driven display device according to the present invention configured as described above will be described in detail with reference to the accompanying drawings.

FIG. 3 is a diagram showing an operation waveform of each part of FIG. 2, wherein Data1 to DataN of FIGS. 3A and 3B are examples of signals input to each data driver, and FIGS. Data1_B to DataN_B in d) are examples of signals input to each data sink unit.

For example, if the signal input to the data driver of the first organic EL driver 201 is low, the PMOS of the data driver is turned on, and a high voltage (ie, Vdd) is applied to the point A as shown in FIG. . That is, corresponding to the change of the Data1 to DataN signals, the waveforms of A to N in the anode line of the organic EL are also changed as shown in FIGS. 3E and 3F. At this time, in the anode line, the waveform changes with a slight response time. Then, the organic EL panel connected to the PMOS source of the data driver emits light.

Then, when the signal input to the data driver of the first organic EL driver 201 is changed from low to high, the PMOS of the data driver is turned off, while the NMOS of the data sink is turned on, the voltage at the point A is transmitted through the NMOS transformer 301. It is input to the primary coil of). At this time, since the resistance value of the transformer 301 is very small, the voltage at point B drops to almost the ground level as shown in FIG. Then, the voltage charged on the primary side of the transformer 301 is induced in the secondary coil in proportion to the turns ratio. That is, the current flowing to the primary side of the transformer 301 is transmitted to the secondary side, where as much current is transmitted to the secondary side as the ratio of the amount of current flowing to the primary side and the winding ratio of the transformer 301 is about 1: M. do.

In addition, the voltage at point B to which one of the NMOSs of the N data sink units is connected is increased in proportion to the number of the data sink units to be turned on. That is, the intensity of the current flowing to the primary coil of the transformer 301 changes in proportion to the voltage at point B, and the voltage varies in proportion to the intensity of the current. Due to this change in voltage, the voltage at point C to which the output portion of the transformer 301 is connected also increases. That is, the voltage at point C increases as shown in FIG. 3H in proportion to the voltage at point B and the turns ratio. As a result of this change, the voltage at the point P output through the DC-DC conversion controller 302 and the diode 303 is generated higher than the input voltage of the transformer 301 as shown in FIG.

Then, the voltage at the point P turns on the diode 303, and the power supply unit 304 generates a power supply voltage (eg, Vdd) required for each unit by using the voltage input through the diode 303. Supply to each part. That is, the power supply unit 304 may lower the power of the entire system by recovering and reusing the power consumed by the data sink as much as possible.

In this configuration, in order for the DC-DC converter using the transformer 301 to operate properly, the value of the input inductor of the transformer 301 connected to the NMOS of the data sink part must be very small. Otherwise, the response time of the NMOS N-sink's NMOS will be very slow, affecting the overall system operation. This is because the value of the inductor increases and the impedance value increases in proportion to it.

In addition, the resistance value of the input inductor of the transformer 301 should have some resistance value. This is because the DC-DC converter does not operate because the operating conditions of the DC-DC converter using the transformer 301 are not met if the amount of the input current does not exceed a predetermined level.

As such, when the data driver is turned off and the data sink is turned on, the voltage that falls to the ground through the data sink is fed back to the power supply using the DC-DC converter. That is, the power of the entire system is lowered by recovering and reusing the power consumed by the data sink as much as possible.

In this case, the transformer 301 is a preferred embodiment of the present invention, and an inductor or a charge pump may be used instead of the transformer.

4 illustrates an example of using an inductor in a power saving circuit of a current driven display device according to an exemplary embodiment of the present invention, in which one source of the data sink unit, that is, an NMOS source, is commonly connected to the inductor. That is, when any one or more data sinks of the N data sinks are turned on, anode voltages (voltages at points A through N) of the organic EL panel are charged to the coil 401 through the data sinks. At this time, when the switching element 402 is off, the voltage charged by the coil 401 is charged to the capacitance 404 through the diode 403. The voltage occupied by the capacitance 404 becomes higher than the voltage input to the coil 401, and the voltage is applied to the power supply unit 304 through the diode 303.

5 shows an example of using a charge pump in a power saving circuit of a current driven display device according to the present invention, in which the charge pump increases the input voltage to a voltage of a predetermined level.

That is, when any one or more data sinks of the N data sinks are turned on, the anode voltages (voltages at points A through N) of the organic EL panel are input to the diode 501 through the data sinks. Then, the diode 501 is turned on, the voltage is charged to the capacitance 504. At this time, the switching element 505 should be turned on. When the switching element 505 is turned off, the power source voltage Vcc of the switching element 505 and the voltage occupied by the capacitance 504 are added to turn on the diode 502. In this case, the switching device 507 operates in the opposite manner to the switching device 505. That is, the switching element 507 is turned off when the switching element 505 is turned on, and the switching element 507 is turned on when the switching element 505 is turned off.

Therefore, when the switching element 507 is turned on, the output voltage of the diode 502 is occupied by the capacitance 506. When the switching element 507 is turned off, the power source voltage Vcc of the switching element 507 and the voltage occupied by the capacitance 506 are added to turn on the diode 503. The output voltage C of the diode 503 is higher than the voltage B input to the diode 501, and the diode 303 is turned on by the output voltage C to be fed back to the power supply 304. Is applied.

As such, when the data sink is turned on, a large amount of current flows instantaneously through the input of the DC-DC converter (eg, a transformer). This instantaneous current creates a flow of charge at the output of the transformer, which creates a constant voltage at the output of the DC-DC converter by the operation of the DC-DC converter using the transformer. Applying this to the power supply of the whole system can lower the power of the entire system.

As described above, the power saving circuit of the current driving display device according to the present invention has the following effects by recovering the current consumed by the data sink and supplying it to the power supply.

First, there is an effect of lowering the total drive current by using a power recovery circuit.

Second, by recovering and reusing the current consumed by the data sink, the total power of the display device driven by the current can be reduced.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (6)

In the power-saving circuit of a current-driven display device, in which N (N is a natural number) organic EL driver units including a data driver, a data sink unit, and an organic EL panel emitting light when the data driver is turned on are provided in parallel, One of each data sink part in the N organic EL driver parts is connected to an anode of the corresponding organic EL panel, and the other is connected to a DC-DC converter part. The DC-DC converter, when the data sink is turned on, receives the anode voltage of the corresponding organic EL panel through the data sink turned on, converts the DC voltage into a higher DC voltage, and outputs the voltage to the power supply. Power saving circuit. The method of claim 1, wherein the DC-DC converter A transformer in which a primary coil is commonly connected between one of the data sink units and a ground, and a transformer for inducing a current flowing through the primary coil to a secondary coil; And a control unit which controls the transformer and outputs a DC voltage proportional to a current induced on the secondary side of the transformer to a power supply unit. The method of claim 1, wherein the power supply unit And a power supply circuit for receiving the output of the control unit and feeding back the driving power to each unit. The method of claim 1, And a reverse voltage preventing diode is connected between the DC-DC converter and the power supply. The method of claim 1, wherein the DC-DC converter An inductor is commonly connected between each of the data sinks and the power supply, and when the data sink is turned on, the anode voltage of the corresponding organic EL panel is input and converted into a higher DC voltage. . The method of claim 1, wherein the DC-DC converter A charge pump is commonly connected between the data sink and the power supply, and when the data sink is turned on, the anode voltage of the corresponding organic EL panel is input and converted into a higher DC voltage. Circuit.