Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
1999-07-22
2001-01-16
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169400, C315S169200
Reexamination Certificate
active
06175192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an energy recovering technique, and more particularly to energy recovering apparatus and method that are capable of reducing a power consumed during sustaining discharge.
2. Description of the Related Art
A plasma display panel(PDP) is a device for displaying a picture by utilizing a gas discharge. The PDP provides a large-scale screen as well as an improved image quality owing to the recent development. The PDP is largely classified into a direct current(DC) driving system performing an opposite discharge and an alternating current(AC) driving system performing a surface discharge in accordance with its driving strategy. The AC driving system has been highlighted because it has a lower power consumption and a longer life time than the DC driving system. The PDP of AC driving system is intervened with a dielectric to apply an AC voltage and performs a discharge every its half period. The AC driving system is classified into a sub-frame system and a sub-field system. When 256 gray scales are expressed, the sub-field system makes a time division of one frame into 8 sub-fields. Each sub-field is time-divided into a reset interval for initializing the entire screen, an address interval for writing a data while scanning the entire screen in a line-sequence manner and a sustaining interval for sustaining a luminous state of cells into which the data is written. A time is assigned such that the reset interval and the address interval of each sub-field are same at each sub-field while the sustaining interval increases at a ratio of 2
n
(n=0, 1, 2, 3, 4, 5, 6 or 7) depending on a relative ration of the brightness. The gray scales proportional to the corresponding sustaining interval is implemented at each sub-field and the gray scales implemented at each sub-field are combined, thereby expressing 256 gray scales from one frame.
The sub-field system has a problem in that a power consumption is large at the time of charging or discharging the PDP in the sustaining interval. In the PDP of AC driving system, its driving circuitry includes an energy recovering circuit for recovering a voltage discharged from the panel again to charge the panel.
Referring to
FIG. 1
, there is an energy recovering apparatus that includes a scanning/sustaining electrode unit driving cell
10
, hereinafter referred to as “Y electrode unit driving cell”, connected to a Y electrode
1
, and a common electrode unit driving cell
20
, hereinafter referred to as “Z electrode unit driving cell”, connected to a Z electrode
2
. The Y electrode
1
and the Z electrode
2
are connected to a panel capacitor Cp. The panel capacitor Cp equivalently represents an electrostatic capacity formed between the Y electrode
1
and the Z electrode
2
. The Y electrode
1
and the Z electrode
2
are discharged by a sustaining pulse applied to the Y electrode unit driving cell
10
and the Z electrode unit driving cell
20
. The Y electrode unit driving cell
10
includes an external capacitor Cex
1
connected to a ground terminal GND, first and third switches S
1
and S
3
connected, in parallel, to the external capacitor Cex
1
, second and fourth switches S
2
and S
4
connected, in series, between a sustaining voltage supply Vs and the ground terminal GND, and an inductor L
1
connected between a first node n
1
and a second node n
2
. The Z electrode unit driving cell
20
has the same configuration as the Y electrode unit driving cell
10
and is connected to the panel capacitor Cp in such a manner to be symmetrical to the Y electrode unit driving cell
10
. Specifically, the Z electrode unit driving cell
20
includes an external capacitor Cex
2
connected to a ground terminal GND, fifth and seventh switches S
5
and S
7
connected, in parallel, to the external capacitor Cex
2
, sixth and eighth switches S
6
and S
8
connected, in series, between a sustaining voltage supply Vs and the ground terminal GND, and an inductor L
2
connected between a third node n
3
and a fourth node n
4
. Diodes D
1
, D
2
, D
3
and D
4
connected to the first node n
1
and the fourth node n
4
are responsible for limiting a backward current.
The operation of the energy recovering apparatus will be explained on a basis of the Y electrode unit driving cell
10
with reference to FIG.
2
. When the panel capacitor Cp is charged and discharged several times by the sustaining pulse, a voltage is charged in the external capacitors Cex
1
and Cex
2
. In a t
1
interval, the first switch S
1
is closed. Then, a voltage charged in the external capacitor Cex
1
is applied, via the first switch S
1
and the inductor L
1
, to the inductor L
1
. Since the inductor L
1
constructs a serial LC resonance circuit along with the panel capacitor Cp, the panel capacitor Cp begins to be discharged by a LC resonance waveform. At this time, the eighth switch S
8
of the Z electrode unit driving cell
20
has been closed. In a t
2
interval, the second switch S
2
is closed at a resonant point of the LC resonance waveform. Then, since the sustaining voltage Vs is applied to the panel capacitor Cp, the panel capacitor Cp maintains a sustaining voltage level. A discharge is caused between the Y electrode
1
and the Z electrode
2
in a time interval when the panel capacitor Cp maintains a sustaining voltage level. In a t
3
interval, the second switch S
2
is opened and the third switch S
3
is closed and thus the panel capacitor Cp begins to be discharged. At this time, a voltage charged in the panel capacitor Cp is applied, via the inductor L
1
and the third switch S
3
, to the external capacitor Cex
1
to charge the external capacitor Cex
1
. Next, the fourth switch S
4
is closed. Then, a voltage of the panel capacitor Cp drops into a ground voltage. The Z electrode unit driving cell
20
charges and discharges a panel capacitor Cp alternately with the Y electrode unit driving cell
10
.
As a result, the energy recovering apparatus recovers a voltage discharged from the panel capacitor Cp by utilizing the external capacitors Cex
1
and Cex
2
and applies it to the panel capacitor Cp, thereby reducing an inordinate power consumption during the sustaining discharge. Since an efficiency and the brightness of the PDP are basically influenced by a current, they has a limit as long as the panel capacitor Cp is charged by means of voltage sources such as external capacitors Cex
1
and Cex
2
.
On the other hand, in the sub-frame driving system, an addressing interval of the entire screen is distributed partially every period of a sustaining pulse to continue the sustaining process without an interruption. In the sub-frame system, when it is intended to express the 256 gray scales, the entire screen is divided into 8 time regions T, T/
2
, T/
4
, T/
8
, T/
16
, T/
32
, T/
64
and T/
128
in the horizontal direction and a discharge weighting value is assigned to each time region in similarity to the sub-field system. Accordingly, at an optional time, 8 screen blocks with a different brightness level, that is, in a different sub-field state exist in the entire screen. 8 scanning lines selected in one sustaining pulse period repeats a process moved downward by one scanning line each time the sustaining pulse period is changed. In such a sub-frame driving system, the sustaining pulse includes a level of more than three steps such that it has a reference level of a writing pulse and a reference level of an erasing pulse every period. Since the energy recovering apparatus as shown in
FIG. 1
is connected in cascade as many as the number of step so as to generate a sustaining pulse having a level of more than three steps, the configuration of the driving circuitry becomes complicated.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an energy recovering apparatus and method of multi-step type that is capable of reducing a power consumption during sustaining discharge.
Further object of the present invention is to provide an energy recovering apparatus
Dinh Trinh Vo
Fleshner & Kim LLP
LG Electronics Inc.
Wong Don
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