U.S. patent application number 09/884487 was filed with the patent office on 2001-11-22 for multiple output dc/dc voltage converters.
Invention is credited to Park, Jin-Ho.
Application Number | 20010043181 09/884487 |
Document ID | / |
Family ID | 19517123 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043181 |
Kind Code |
A1 |
Park, Jin-Ho |
November 22, 2001 |
Multiple output DC/DC voltage converters
Abstract
The multiple output DC/DC voltage converter is needed to
generate voltages used in LCD. 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.
Inventors: |
Park, Jin-Ho; (Kyungki-do,
KR) |
Correspondence
Address: |
MYERS BIGEL SIBLEY & SAJOVEC
PO BOX 37428
RALEIGH
NC
27627
US
|
Family ID: |
19517123 |
Appl. No.: |
09/884487 |
Filed: |
June 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09884487 |
Jun 18, 2001 |
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09130005 |
Aug 6, 1998 |
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6275208 |
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Current U.S.
Class: |
345/87 |
Current CPC
Class: |
G09G 3/3696 20130101;
G09G 2330/023 20130101; H02M 3/155 20130101; H02M 1/009 20210501;
G09G 2330/024 20130101 |
Class at
Publication: |
345/87 |
International
Class: |
G09G 003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 1997 |
KR |
97-37918 |
Claims
What is claimed is:
1. A liquid crystal display comprising: a liquid crystal display
panel which has a plurality of pixels arranged in a matrix type in
areas determined by a plurality of gate lines and a plurality of
data lines crossing the gate lines.; a gate driver which applies a
gate on voltage to one of the gate lines sequentially thereby
scanning the pixels in the liquid crystal display panel by a row; a
source driver which receives a plurality of gray voltages and a
video signal and selects the gray voltage corresponding to the
video signal and applies the selected gray voltage to the data
lines of the liquid crystal display panel; a gray voltage generator
which generates a plurality of the gray voltages from data supply
voltage and provides the gray voltages to the source driver; and a
multiple output DC/DC converter which induces a transformer,
receives a DC input voltage and generates main supply voltage from
a primary coil of the transformer and at least two more auxiliary
supply voltages from a secondary coils of the transformer wherein,
the main supply voltage is used as the data supply voltage, the
auxiliary supply voltages are used as the gate on voltage and a
gate off voltage.
2. The liquid crystal display according to claim 1, wherein the
multiple output DC/DC voltage converter comprises: the transformer
which includes a primary coil having one terminal applied with the
DC input voltage and at least two more secondary coils; a switch
which is connected to the primary coil of the transformer, turns
on/off responsive to a switching signal and consequently causes the
current of the primary coil to change; a plurality of diodes which
are connected to the primary coil and the secondary coils
respectively and rectify voltages generated in the each coil; and a
plurality of capacitors which are connected to the each diode, are
charged by the rectified voltage to generate constant voltages.
3. The liquid crystal display according to claim 2, wherein the
constant voltage generated from the capacitor connected to the
primary coil is output as the data supply voltage and the constant
voltages generated from the each capacitor connected to at least
two more the secondary coils are output as the gate on voltage and
the gate off voltage.
4. The liquid crystal display according to claim 3, wherein the
magnitude of the constant voltage generated from the capacitor
connected to the primary coil is determined by on/off duty ratio of
the switch and the magnitude of the constant voltages generated
from the capacitors connected to the secondary coils are determined
by the winding number of the secondary coils.
5. The liquid crystal display according to claim 2, wherein the
multiple output DC/DC voltage converter further comprises a switch
control circuit for generating the switch signal.
6. The liquid crystal display according to claim 1, wherein the
multiple output DC/DC voltage converter comprises: an inductor
having one terminal applied with the DC input voltage; a
transformer which has a primary coil connected in parallel to the
inductor and at least two more secondary coils; a switch which is
connected to the other terminal of the inductor, turns on/off
responsive to a switch signal and consequentially causes the
current of the primary coil to change; a plurality of diodes which
are connected to the inductor and the secondary coils, respectively
and rectify voltages generated in the inductor and the secondary
coils; and a plurality of capacitors which are connected to the
each diode, are charged by the rectified voltages to generate
constant voltages.
7. The liquid crystal display according to claim 6, wherein the
constant voltage generated from the capacitor connected to the
primary coil is output as the data supply voltage and the constant
voltages generated from the each capacitor connected to at least
two more the secondary coils are output as the gate on voltage and
the gate off voltage.
8. The liquid crystal display according to claim 7, wherein the
magnitude of the constant voltage generated from the capacitor
connected to the primary coil is determined by on/off duty ratio of
the switch and the magnitude of the constant voltages generated
from the capacitors connected to the secondary coils are determined
by the winding number of the secondary coils.
9. The liquid crystal display according to claim 6, wherein the
multiple output DC/DC voltage converter further comprises a switch
control circuit for generating the switch signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] FIG. 1 shows a pixel structure in the LCD.
[0006] 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.
[0007] FIG. 2 shows waveforms of voltages applied to the pixel in
FIG. 1.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] FIG. 3 shows a voltage generator of the choke method.
[0012] As shown in FIG. 3, in the voltage generator of the choke
method, a transistor Q1 periodically turns on or off responsive to
a switching signal SW from switch control circuit 31. Consequently,
it happens the current of an inductor L1 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 D1 and a capacitor C1. At this time, the magnitude of a
voltage charged in the capacitor C1, that is, an output voltage
Vout depends on an on/off duty ratio of transistor Q1. 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.
[0013] FIG. 4 shows a voltage generator of the fly-back method
using the transformer.
[0014] As shown in FIG. 4, the voltage generator of the fly-back
method has a transistor Q2 connected to a primary coil T1 of the
transformer and pairs of diode-capacitors D2, C2 D:3, C3: D4, C4
each connected to a plurality of secondary coils of the transformer
T2, T3, T4.
[0015] In the voltage generator described in FIG. 4, the transistor
Q2 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 T1 to change. The current
change causes magnetic field to change and the change of magnetic
field induces a voltage to the secondary coils T2, T3, T4
respectively. Accordingly, voltages induced in the secondary coils
T2, T3, T4 are rectified to constant voltages by pairs of
diode-capacitors and magnitude of the voltages charged in each
capacitor C2, C3, C4 are determined by winding numbers of the
primary and secondary coils. The voltages charged in the each
capacitor C2, C3, C4 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.
[0016] 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
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] These and other features and advantages of the present
invention may be better and more completely understood by studying
the following detailed description of the presently preferred
embodiments together with the appended drawings, of which:
[0025] FIG. 1 roughly shows a structure of a pixel in an LCD.
[0026] FIG. 2 shows waveforms of voltages applied to the pixel
described in FIG. 1.
[0027] FIG. 3 shows a conventional voltage generator of a choke
method using an inductor FIG. 4 shows a conventional voltage
generator of a fly-back method using a transformer.
[0028] FIG. 5 is a block diagram of the LCD in accordance with a
first embodiment of the present invention.
[0029] FIG. 6 is a detailed circuit diagram of a multiple output
DC/DC voltage converter in FIG. 5.
[0030] FIG. 7 is a detailed circuit diagram of a multiple output
DC/DC voltage converter in accordance with a second embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Hereinafter, the accompanying drawings, which are
incorporated in and constitute a part of the specification,
illustrate an embodiment of the invention, and, together with the
description, serve to explain the principles of the invention:
[0032] FIG. 5 is a block diagram of the LCD in accordance with a
first embodiment of the present invention.
[0033] FIG. 6 is a detailed circuit diagram of a multiple output
DC/DC voltage converter in FIG. 5.
[0034] FIG. 7 is a detailed circuit diagram of a multiple output
DC/DC voltage converter in accordance with a second embodiment of
the present invention.
[0035] First, with reference to FIG. 5 and FIG. 6, the LCD in
accordance with the first embodiment of the present invention is
described.
[0036] As shown in FIG. 5, the LCD in accordance with the first
embodiment of the present invention comprises an LCD panel 1, a
gate driver 2, a source driver 3, a gray voltage generator 4 and a
multiple output DC/DC voltage converter 5.
[0037] The LCD panel 1 has a plurality of pixels arranged in the
matrix type and the each pixel has a structure described in FIG. 1.
The gate driver 2 is connected to the LCD panel 1 via a plurality
of the gate lines and scans the pixels of the LCD panel 1 by the
row. The scanning is achieved by applying the gate on voltage Von
to the each gate line sequentially. When the gate on voltage Von is
applied to one of the gate lines, the gate off voltage Voff is
applied to the rest of the gate lines. Herein, the gate on voltage
Von and the gate off voltage Voff are provided from the multiple
output DC/DC voltage converter 5.
[0038] The source driver 3 is connected to the LCD panel 1 via a
plurality of the data lines, receives the video signal RGB and the
gray voltage, selects the gray voltage corresponding to the video
signal, and applies the selected gray voltage serving as the data
voltage, to a plurality of the data lines of the LCD panel 1. The
gray voltage generator 4 generates a plurality of the gray voltages
using the data supply voltage VDD supplied from the multiple output
DC/DC voltage converter 5 and provides a plurality of the gray
voltages to the source driver 3. The multiple output DC/DC voltage
converter generates the data supply voltage VDD, the gate on
voltage Von and the gate off voltage Voff from the input voltage
Vin and the switching signal SW.
[0039] FIG. 6 shows a first embodiment of the multiple output DC/DC
voltage converter 5 in FIG. 5.
[0040] As shown in FIG. 6, the DC/DC voltage converter 5 includes a
transformer having a primary coil T61 and two secondary coils T62,
T63. The input voltage Vin is applied to one terminal of the
primary coil T61 of the transformer and the other terminal of the
primary coil T61 is connected the transistor Q61 turning on/off
responsive to the switching signal SW from the switch control
circuit 51. Anode of a diode D63 is connected between the
transistor Q61 and the primary coil T61 of the transformer, a
capacitor C63 is connected between cathode of the diode D63 and the
ground. A node voltage between the diode D63 and the capacitor C63
serves as the data supply voltage VDD.
[0041] A midpoint of the two secondary coils T62, T63 are grounded,
the diode D61 and the capacitor C61 are coupled to the secondary
coil T62, and the diode D62 and the capacitor C62 are coupled to
the secondary coil T63. At this time, in order to pass minus
current, the diode D62 is reverse-directional.
[0042] More specifically, the transistor Q61 periodically turns on
or off according to the switching signal SW. This switching
operation causes the current flowing through the primary coil T61
of the transformer to change. Accordingly, the AC voltage is
generated from the DC input voltage Vin. This AC voltage is
rectified by the diode D63, charged in the capacitor C63, and
accordingly the constant voltage is obtained thereby. At this time,
the magnitude of the voltage charged in the capacitor C63 is
determined by the on/off duty ratio of the transistor Q61.
[0043] Meanwhile, in the primary coil T61 of the transformer, it
happens to change the current according to the switching operation
of the transistor Q61, and consequently it happens to change
magnetic flux. This change of the magnetic flux causes to flow
currents through the secondary coils T62, T63 by
electronic-magnetic induction. These currents are converted into
the constant voltages by the diode-capacitor pairs connected to the
each secondary coil T62, T63. That is, as illustrated above, the
each current induced to the second winding T62 and T63 is rectified
by the diode D61 and D62 and then charged in the capacitor C61 and
C62, and therefore the constant voltages are obtained respectively.
At this time, the magnitude and polarity of the voltage charged in
the each capacitor C61, C62 are determined by the winding number
and the winding direction of the secondary coils T62, T63. Among
the above voltages, the constant voltage generated by
electromagnetic induction of the transformer has the low driving
ability of current and power accuracy and therefore, in the first
embodiment of the present invention, the voltages charged the
capacitor C61, C62 are used as the gate on voltage and the gate off
voltage. That is, since the gate on voltage Von and the gate off
voltage Voff may be supplied by auxiliary supply voltages requiring
the low power, the constant voltage with low efficiency is used.
Further, the data supply voltage VDD requiring the high power
utilizes the constant voltage directly generated from the primary
coil T61 of the transformer without the electronic-magnetic
induction.
[0044] As mentioned before, the first embodiment of the present
invention provides a circuit which generates one main supply
voltage VDD and two auxiliary supply voltages Von, Voff needed in
driving the LCD, by combining the choke method with the high
efficiency and the fly-back method having merits of providing the
multiple output voltages and compactness. Herein, in the first
embodiment of the present invention, the transformer has the two
secondary coils, but if needed, the number of the secondary coil
can be expanded.
[0045] FIG. 7 shows a second embodiment of the multiple output
DC/DC voltage converter 5 in FIG. 5.
[0046] The second embodiment of the present invention has a feature
that the size of the transformer in the multiple output DC/DC
voltage converter is reduced.
[0047] More specifically, in the first embodiment, the main supply
voltage generated from the primary coil T61 of the transformer
provides high power and consequently a thick winding should be
used. Accordingly, the size of the transformer becomes bigger. In
the second embodiment, an inductor is parallelly connected to a
primary coil of a transformer, and the inductor plays the same role
as the primary coil in the first embodiment. That is, the inductor
supplies a significant amount of the power, therefore, the primary
coil can be thin and accordingly the size of the transformer can be
reduced.
[0048] As shown in FIG. 7, the multiple output DC/DC voltage
converter 5' in accordance with the second embodiment of the
present invention includes an inductor L71 having one terminal
applied with the DC input voltage Vin, and the other terminal
connected to a transistor Q71 turning on/off responsive to the
switching signal SW from the switch control circuit 51, and a
transformer having a primary coil T71 connected to the inductor L71
in parallel and two secondary coils T72, T73. A diode D73 and a
capacitor C73 are connected to the inductor L71 in pair and the
each pair of the diode-capacitor D71, C71:D72, C72 is connected to
the secondary coils T72, T73 of the transformer, same as the
multiple output DC/DC voltage converter in accordance with the
first embodiment.
[0049] In the DC/DC voltage converter 5' in accordance with the
second embodiment, the voltage charged in the capacitor C73
connected to the inductor L71 is provided as the main supply
voltage, the data supply voltage VDD, the voltage charged in the
capacitor C71 connected to the one secondary coil T72 of the
transformer serves as the auxiliary supply voltage, the gate on
voltage Von, and the voltage charged in the capacitor C72 connected
to the other secondary coil T73 serves as the auxiliary supply
voltage, the gate off voltage Voff.
[0050] Herein, the main supply voltage is obtained by the combined
inductance made up of the inductor L71 and the primary coil T71 of
the transformer and therefore the main supply voltage has high
efficiency and high output. Further, the auxiliary supply voltage
is produced from at least two more secondary coils and therefore
the auxiliary supply voltage can supply the multiple output
voltage. Herein, the primary coil T71 is connected to the inductor
L71 in parallel and consequently, in order to get the inductance as
same as that of the first embodiment, smaller winding can be used,
and accordingly the size of the transformer can be reduced.
[0051] Except for the illustration above, the rest mechanism for
generating voltages is equal to mechanism of the DC/DC voltage
converter with the multiple output voltage 5' in accordance with
the first embodiment referring to FIG. 6.
[0052] As illustrated above, the LCD in accordance with the present
invention includes the multiple output DC/DC voltage converter
producing the main supply voltage according to the choke method and
the auxiliary supply voltages according to the fly-back method.
Therefore, the LCD provides high efficient multiple output voltages
needed in driving the LCD. Furthermore, since the multiple output
DC/DC voltage converter in accordance with the present invention
reduces the size of the transformer and consequently, it can be
made more compact than the voltage converter adopting the
conventional fly-back method. Therefore, it is preferred that the
multiple output DC/DC voltage converter is used the portable
electronic equipment like the LCD.
[0053] In this disclosure, there is shown and described only the
preferred embodiments of the invention, but, as aforementioned, it
is to be understood that the invention is capable of use in various
other combinations and environments and is capable of changes or
modification within the scope of the inventive concepts as
expressed herein.
* * * * *