Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-06-28
2004-07-27
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C345S060000
Reexamination Certificate
active
06768270
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plasma display panel technology; and, more particularly, to an energy recovery unit of a sustain driver in an AC-type plasma display panel.
DESCRIPTION OF RELATED ART
A plasma display panel(PDP) is a device for displaying a picture and it has been known as a gas discharge display device. Discharge gases, such as Kr and Xe, are filled up between upper and lower panels of the plasma display panel, and an ultraviolet ray generated through the gas discharge exciting red, green and yellow fluorescents, which are formed at least one of the upper and lower panels thereby to generate visible lights.
The PDP is classified into a DC type and an AC type. In the DC type PDP, electrodes for applying voltage to the panel is exposed directly to the discharge gas so that a current directly flows between electrodes in order to form the plasma. Therefore, it is advantageous that the structure is relatively simple. On the other hand, it has disadvantage that the external resistor has to be placed to limit the current. In the AC type PDP, the electrodes are covered with the dielectric substances so that the electrodes are not exposed directly to the discharge gas in order to flow a displacement current. The AC type PDP has longer life span, compared with the DC type PDP, because the electrodes of the AC type PDP can be protected from an ion impact by covering the electrodes with the dielectric substances to limit the current naturally. The AC type PDP can be classified into an opposite discharge type and a surface discharge type. The opposite discharge type has the disadvantage that the life span is shortened by the degradation of the fluorescent substances owing to the ion impact. In the surface discharge type, on the other hand, the discharge is generated near the front panel opposite to the fluorescent substances in order to minimize the degradation of the fluorescent substances, therefore, the surface discharge type is adopted to most of the PDP manufacturing processes.
In the AC type PDP, the high voltage has to be applied continuously and alternately between the sustain electrodes (X electrode and Y electrode) in the discharge cell during the operation of the PDP. Therefore, the dielectric substances are spread over the sustain electrodes so that a panel capacitor exists between X electrode and Y electrode.
In order to alternatively apply the positive and negative high voltage between the sustain electrodes during the operation of the PDP, the charge and discharge operations of the panel capacitor has to be performed. However, the power is consumed considerably by the panel capacitor during the charge and discharge operations, and the power loss problem of a panel drive circuit is generated because the capacitance of the panel capacitor is increased in proportion to the size of the panel.
In order to solve the power loss problems in the panel drive circuit, an energy recovery unit is adopted to the conventional panel drive circuit. In the energy recovery unit, an inductor for forming a LC resonance circuit with the panel capacitor is used to recover the energy loss during the discharge of the panel capacitor. The energy is stored in the inductor through the recovery, and the stored energy is used during the next charge operation of the panel capacitor to reduce the power loss.
A conventional circuit structure of a Weber-type sustain driver in the PDP having an energy recovery unit is shown in FIG.
1
.
Referring to
FIG. 1
, a sustain driver, in the PDP having the energy recovery unit, includes a first and second sustain drivers
100
and
200
which are connected across a panel capacitor Cp.
The first sustain driver
100
includes a driving unit
12
and an energy recovery unit
10
. The driving unit
12
drives the panel capacitor Cp to a sustain voltage Vsus or the ground voltage. The energy recovery unit
10
recoveries the energy loss caused during the discharge operation of the panel capacitor Cp and provides the recovered energy to the panel capacitor Cp during the next charge operation.
The first and second sustain drivers
100
and
200
have symmetrical configuration across the panel capacitor Cp. During the charge and discharge operations, the voltage Vp of the panel capacitor Cp is swung to positive and negative voltage by the first and second sustain drivers
100
and
200
operating alternatively with each other. Therefore, the detailed diagram of the second sustain driver
200
is not shown in
FIG. 1
, because the second sustain driver
200
has the same structure with the first sustain driver
100
.
The driving unit
12
of the first sustain driver
100
includes a first switch S
1
and a second switch S
2
. The first switch is connected to a power source supplying the sustain voltage Vsus and the panel capacitor Cp and transfers the sustain voltage to the panel capacitor. The second switch S
2
is connected the ground and the panel capacitor Cp and transfers the ground voltage to the panel capacitor.
The first energy recovery unit
10
in the first sustain driver
100
includes an inductor Lr, an external capacitor Ce, third and fourth switches S
3
and S
4
, and first and second diodes D
1
and D
2
.
The inductor Lr is connected to the panel capacitor Cp for operating the panel capacitor Cp with a half resonance. The external Capacitor Ce stores the energy recovered by the resonance operation of the inductor Lr and the panel capacitor Cp. The third and fourth switches S
3
and S
4
, coupling in parallel, are connected to the external capacitor Ce for switching an energy recovery path. The first and second diodes D
1
and D
2
, coupled in parallel and to reversal direction with each other, are respectively connected to the third and fourth switches S
3
and S
4
. The inductor Lr is connected to the first and second diodes D
1
and D
2
in order to prevent a reverse of resonance current IL.
Each switch S
1
, S
2
, S
3
and S
4
can be formed with a metal oxide semiconductor field effect transistor (MOSFET), a reversal and parallel connected diode or an insulate gate bipolar transistor (IGBT).
A resonance frequency (f
0
) of a L-C series resonance circuit can be described as formula 1:
f
0
=½ (
LC
)
1/2
. [Formula 1]
A resonance cycle (T) can be described as formula 2:
T
=2 (
LC
)
1/2
. [Formula 2]
A resonance current has a period of 2 (LC)
1/2
, and the maximum resonance current is generated in a condition of a half resonance, &pgr; (LC)
1/2
.
FIG. 2
shows waveforms of the sustain driver having the energy recovery unit shown in FIG.
1
. In
FIG. 2
, a waveform of the voltage Vp of the panel capacitor Cp, a waveform of the resonance current IL, and each waveform Vg(S
1
), Vg(S
2
), Vg(S
3
) and Vg(S
4
) of switch S
1
, S
2
, S
3
and S
4
, are shown.
Referring to
FIG. 2
, the first sustain driver
100
is operated by setting four periods T1 to T4 as one cycle. The energy of Vsus/2, recovered from the panel capacitor Cp in the previous cycle, is stored in the external capacitor Ce of the first energy recovery unit
10
.
An initial condition reflects the operation of the second sustain driver
200
. In the period of T0, the second switch S
2
in the driving unit
12
of the first sustain driver
100
is turned on and a pull-down switch (not shown) in a driving unit of the second sustain driver
200
is turned on to form a closed-loop. At this time, the voltage Vp of the panel capacitor Cp is the ground voltage 0V and the resonance current IL does not flows.
In the first period of T1, a current path is formed between the external capacitor Ce and the panel capacitor Cp by turning on the switch S
3
. At this time, the resonance current IL is formed by the resonance operation of the inductor Lr and the panel capacitor Cp so that the voltage Vp of the panel capacitor Cp increases up to the sustain voltage Vsus.
In the second period of T2, the voltage Vp of the panel capacitor Cp is sustained to the sustain voltage Vsus by turning on the switch S
1
. The swit
Blakely & Sokoloff, Taylor & Zafman
Ultra Plasma Display Corporation
Vu Jimmy T
Wong Don
LandOfFree
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