Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-08-06
2001-08-14
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S211000
Reexamination Certificate
active
06275208
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a DC/DC voltage converter with multiple output voltages (hereinafter, it is called as multiple output DC/DC voltage converter) mainly applied to an active matrix-type liquid crystal display (LCD). More particularly, this invention relates to the multiple output DC/DC voltage converter combining a choke method with a fly-back method using a transformer and the LCD using thereof.
(b) Description of the Related Art
The DC/DC voltage converter converting DC supply voltage to a predetermined DC voltage having a different magnitude from the DC supply voltage is broadly used to a portable electronic equipment. Accordingly, this DC/DC voltage converter requires high efficiency, compactness and low price. Furthermore, since the portable electronic equipment commonly requires a plurality of DC supply voltages, the DC/DC voltage converter requires a plurality of output DC voltages.
FIG. 1
shows a pixel structure in the LCD.
As shown in
FIG. 1
, the pixel of the LCD comprises a pixel electrode formed in an area where a gate line crosses a data line, a common electrode facing the pixel electrode and a switch which is connected to the gate line, the data line and the pixel electrode, and is turned on/off responsive to a gate voltage applied through the gate line. The switch is made up of a thin film transistor (TFT). According to on/off state of the TFT, the switch applies or cut off a data supply voltage to the pixel electrode.
FIG. 2
shows waveforms of voltages applied to the pixel in FIG.
1
.
In
FIG. 2
, the gate voltages have a gate on voltage Von for turning on the TFT and a gate off voltage Voff for turning off the TFT, and are applied to the gate line in
FIG. 1. A
common electrode voltage has a reverse phase with a data voltage. The common electrode voltage is applied to the common electrode and the data voltage is applied to the data line.
The common electrode voltage and the data voltage consume a significant amount of energy and require accurate voltages, and therefore, the common electrode voltage and the data voltage are provided from a main power supply. The gate on voltage Von and the gate off voltage Voff needs a small amount of energy, and therefore the gate on voltage Von and the gate off voltage Voff are provided from auxiliary power supplies.
In order to generate the voltages needed in driving the LCD, voltage generators using the choke method or the fly-back method are generally used.
FIG. 3
shows a voltage generator of the choke method.
As shown in
FIG. 3
, in the voltage generator of the choke method, a transistor Q
1
periodically turns on or off responsive to a switching signal SW from switch control circuit
31
. Consequently, it happens the current of an inductor L
1
to change. The changing current causes a DC input voltage Vin to change into an AC(alternate current) voltage. The changed AC voltage is rectified by a diode D
1
and a capacitor C
1
. At this time, the magnitude of a voltage charged in the capacitor C
1
, that is, an output voltage Vout depends on an on/off duty ratio of transistor Q
1
. The output voltage has a good efficiency. However, the voltage generator of the choke method produces only one output voltage. Therefore, there is a problem that the voltage generators are needed as many as DC voltages needed in an LCD for the purpose of applying to the LCD.
FIG. 4
shows a voltage generator of the fly-back method using the transformer.
As shown in
FIG. 4
, the voltage generator of the fly-back method has a transistor Q
2
connected to a primary coil T
1
of the transformer and pairs of diode-capacitors D
2
, C
2
: D
3
, C
3
: D
4
, C
4
each connected to a plurality of secondary coils of the transformer T
2
, T
3
, T
4
.
In the voltage generator described in
FIG. 4
, the transistor Q
2
periodically turns on or off responsive to a switching signal SW from a switch control circuit
41
and consequently it causes the current flowing through the primary coil T
1
to change. The current change causes magnetic field to change and the change of magnetic field induces a voltage to the secondary coils T
2
, T
3
, T
4
respectively. Accordingly, voltages induced in the secondary coils T
2
, T
3
, T
4
are rectified to constant voltages by pairs of diode-capacitors and magnitude of the voltages charged in each capacitor C
2
, C
3
, C
4
are determined by winding numbers of the primary and secondary coils. The voltages charged in the each capacitor C
2
, C
3
, C
4
are used as the gate on voltage Von, the data supply voltage VDD and the gate off voltage Voff which are provided to the LCD module.
However, since the voltage generator of the fly-back method has a feature that the magnetic energy from the primary coil transfers to the secondary coil via magnetic core, there is a problem that it basically has a low efficiency and a big size of the transformer. Specifically, in case that the main power supply is generated using the voltage generator of the fly-back method, the size of the transformer becomes bigger.
SUMMARY OF THE INVENTION
An object of the invention is to minimize the related impediments described above. Another object of the invention is to the voltage generator which can obtain multiple output voltages as well as the main power supply with high efficiency, combining the choke method with the fly-back method.
The LCD in accordance with the present invention comprises a LCD panel, a gate driver, a source driver, a gray voltage generator and a multiple output DC/DC voltage converter.
The LCD panel has a plurality of the pixels arranged in a matrix type and the each pixel is formed in the area where is defined by a plurality of the gate lines and a plurality of the data lines crossing the gate lines. The gate driver is connected to the LCD panel via a plurality of the gate lines and scans the pixels of the LCD by a row. The source driver is connected to the LCD panel via a plurality of the data lines, and receives the gray voltage and a video signal to select the gray voltage corresponding to the video signal, and then applies the selected gray voltage to the LCD panel as the data supply voltage.
The multiple output DC/DC voltage converter generates a main supply voltage and at least two more auxiliary supply voltages. The main supply voltage is used as the data supply voltage which requires a significant amount of the power in the LCD and the auxiliary supply voltages are used as the gate on voltage and the gate off voltage. The data supply voltage is provided to the gray voltage generator and used in generating the gray voltage. The gate on voltage and the gate off voltage are provided to the gate driver.
The multiple output DC/DC voltage converter comprises a transformer having a primary coil applied with the input DC voltage and at least two more secondary coils, a switch which repeatedly turns on or off responsive to the switching signal to change the current of the primary coil, a plurality of diodes connected to the each winding of the transformer and rectifying the voltage generated in the each coil and a plurality of capacitors connected to the each diode, charging the rectified voltage and generating constant voltage.
In accordance with the present invention, the main supply voltage uses the constant voltage obtained from the primary coil of the transformer, the auxiliary supply voltage uses at least the two more constant voltages from the secondary coils of the transformer, and accordingly, the multiple output voltages are supplied to the LCD.
Further, the multiple output DC/DC voltage converter in accordance with the present invention generates the main supply voltage with high efficiency directly obtained from the primary coil, and, together with the auxiliary supply voltages obtained from the secondary coils. the main supply voltage with the high efficiency is supplied. That is, the DC/DC voltage converter provides the multiple output voltages and the main supply voltage with the high efficiency simultaneously.
REFERENCES:
patent: 35716
Myers Bigel & Sibley & Sajovec
Piziali Jeff
Samsung Electronics Co,. Ltd.
Shalwala Bipin
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