Driving apparatus of discharge tube lamp

Details Driving apparatus of discharge tube lamp Driving apparatus of discharge tube lamp

2002-05-07

2003-07-22

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Plural load device regulation

C315S291000, C315S278000, C315S224000, C315S318000, C315S325000

Reexamination Certificate

active

06597130

ABSTRACT:

This present invention claims the benefit of Korean Patent Application No. P2001-63206 filed in Korea on Oct. 13, 2001 and of Korean Patent Application No. P2001-66631 filed in Korea on Oct. 29, 2001, which are both hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a driving apparatus of a discharge tube lamp, and more particularly, to a driving apparatus of a discharge tube lamp that is capable of, when using a plurality of discharge tubes, controlling each of the electric currents supplied to each of the plurality of discharge tubes even though a ground level is used commonly, thereby reducing the brightness deviation.
2. Discussion of the Related Art
In recent years, there has been a general trend to broaden the scope of the applications of liquid crystal displays (LCDs) by improving characteristics such as, for example, the weight and size of LCDs and the power consumption required to drive LCDs. As a result of these improvements, LCDs are now used in such applications as office automation equipment and audio/video equipment. LCDs control the amount of a transmitted light beam in accordance with a video signal applied to a plurality of control switches that are arranged in a matrix.
Because LCDs are not a self light-emitting display devices, they require light sources such as back lights. A cold cathode fluorescent tube (CCFL) is used as a light source in the back light. A CCFL is a light source tube that utilizes cold emission, which is an electron emission caused by a strong electric field applied to the surface of a cathode cold emission has the advantages of low heat emission, high brightness, long life and full color. CCFLs can be classified into light guide systems, direct illumination systems and reflection plate systems. A proper light source tube is used in accordance with the need of the particular LCD.
A CCFL uses an inverter circuit to obtain a high voltage power in a direct current power of a low voltage.
Referring to
FIGS. 1 and 2
, a conventional driving apparatus includes a voltage source Vin. A first CCFL
100
, a second CCFL
110
and a third CCFL
120
emit light by an AC signal. A first resonance type inverter circuit
20
, a second resonance type inverter circuit
30
and a third resonance type inverter circuit
40
are each mounted between the voltage source Vin and the first to third CCFLs
100
,
110
and
120
for supplying the AC signal to the first to third CCFLs
100
,
110
and
120
. A first wire transformer T
1
, a second wire transformer T
2
and a third wire transformer T
3
each boost the voltage supplied from the voltage source Vin and supply the boosted AC signal to the first to third CCFLs
100
,
110
and
120
. A voltage detector
50
is commonly connected to the first to third CCFLs
100
,
110
and
120
and connected to the first to third resonance type inverter circuits
20
,
30
and
40
for detecting the voltage commonly supplied to the first to third CCFLs
100
,
110
and
120
.
One terminal of each of the first to third CCFLs
100
,
110
and
120
is connected to the first to third wire transformer T
1
, T
2
and T
3
, respectively. The other terminal of each of the first to third CCFLs
100
,
110
and
120
is commonly connected to the voltage detector
50
. Each of the first to third CCFLs
100
,
110
and
120
receives the boosted AC signals from the first to third wire transformers T
1
, T
2
and T
3
to emit light.
Each of the first to third wire transformers T
1
, T
2
and T
3
consists of a primary coil L
1
, a secondary coil L
2
and an auxiliary coil L
3
. Each of the primary coil L
1
and the auxiliary coil L
3
is connected to a radio frequency oscillation circuit
25
. One terminal of the secondary coil L
2
is connected to one terminal of each of the first to third CCFLs
100
,
110
and
120
through a first capacitor C
1
, and another terminal of the secondary coil is connected to a ground voltage source GND.
In the description that follows, only the first resonance type inverter circuit
20
is described because each of the first to third resonance type inverter circuits
20
,
30
and
40
has the same circuit configuration.
The first resonance type inverter circuit
20
includes a radio frequency oscillation circuit
25
connected to the primary coil L
1
of the first wire transformer T
1
. A first transistor Q
1
is connected between the radio frequency oscillation circuit
25
and the voltage source Vin for switching the voltage from the voltage source Vin to the radio frequency oscillation circuit
25
. A pulse width modulation (PWM) controller
24
supplies control signals to the first transistor Q
1
. A power switch
26
is connected between the PWM controller
24
and the voltage source Vin. A brightness controller
22
supplies a brightness control signal to the PWM controller
24
in accordance with the detected voltage signal FB supplied from the voltage detector
50
.
The radio frequency oscillation circuit
25
includes a second transistor Q
2
and a third transistor Q
3
having the ground voltage source GND in between and connected to the primary coil L
1
of the first wire transformer T
1
. A second capacitor C
2
is arranged parallel to the primary coil L
1
.
The collector terminals of the second transistor Q
2
and the third transistor Q
3
are respectively connected to both sides of the primary coil L
1
of the first wire transformer T
1
. The emitter terminals of the second and third transistors Q
2
and Q
3
are commonly connected to the ground voltage source GND. The middle point of the primary coil L
1
is connected to the base terminals of the second and third transistors Q
2
and Q
3
through a first resistance RI and a second resistance R
2
, and is connected to both sides of the auxiliary coil L
3
.
The second and third transistors Q
2
and Q
3
are alternately switched to store at the second capacitor C
2
the voltage supplied through the first transistor Q
1
.
Referring to
FIG. 3
, the voltage detector
50
includes a third resistance R
3
and a variable resistance RB serially connected between the ground voltage source GND and a first node N
1
that is commonly connected to the first to third CCFLs
100
,
110
and
120
. A second diode D
2
is arranged between the first node N
1
and the ground voltage source GND. A third diode D
3
is arranged between the first node N
1
and the brightness controller
22
.
The third resistance R
3
and the variable resistance RB detects by their own resistance values the voltage supplied to the first to third CCFLs
100
,
110
and
120
to have the detected voltage signal on the first node N
1
. The detected voltage signal FB on the first node N
1
is supplied to the brightness controller
22
through the third diode D
3
. The second diode D
2
shuts out the impulse of a negative potential to sustain the lowest potential of the detected voltage signal FB at zero potential.
The voltage detector
50
is commonly connected to the first to third CCFLs
100
,
110
and
120
, and detects an AC high voltage commonly supplied to the first to third CCFLs
100
,
110
and
120
.
The brightness controller
22
generates a brightness control signal by using a brightness duty ratio signal B-duty or a reference brightness signal B-dc supplied from the outside and the detected voltage signal FB supplied from the voltage detector
50
, and supplies the brightness control signal to the PWM controller
24
. The brightness duty ratio signal B-duty and the reference brightness signal B-dc may be supplied by a system engineer or a user.
PWM controller
24
receives the brightness control signal from the brightness controller
22
and supplies a PWM control signal to the base terminal of the first transistor Q
1
when the power switch is turned on. The PWM control signal controls the switching cycle of the first transistor Q
1
in accordance with the brightness control signal, thereby controlling the voltage supplied to the first wire transformer T
1
.
The first transistor Q
1
is turned o

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