Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-06-28
2004-03-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S060000
Reexamination Certificate
active
06710550
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of Korean Application No. 2002-3386, filed Jan. 21, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to plasma display apparatuses, and more particularly, to a plasma display apparatus having an over-current protection circuit that protects a switching device from an over-current generated during an abnormal driving of a driving circuit of a discharge sustaining electrode and a method of protecting over-current thereof.
2. Description of the Related Art
A plasma display panel (PDP) is a display apparatus using a discharge of gas. The PDP is generally classified into a direct current (DC) type that applies a facing discharge, and an alternating current (AC) type that applies a surface discharge, depending upon its driving type. The AC type PDP has attracted more attention because it has a lower power consumption and a longer lifetime in comparison with the DC type.
The PDP using the AC driving type applies an alternating current (AC) voltage between electrodes insulated with a dielectric layer, and performs a discharge every half-cycle of the AC voltage, which is used to display a picture mainly in a sub-field method. In the sub-field method, since the power consumption used for a charge and the discharge of the PDP panel during the sustain of the discharge is very large, a circuit is used to collect reactive power in a driving device of the PDP.
As illustrated in
FIG. 2
, a circuit to drive the discharge sustaining electrode generally includes a unit driving cell of a discharge sustaining electrode connected to a Y-electrode (hereinafter referred to as ‘Y-electrode unit driving cell’) and a unit driving cell of a common electrode connected in common to a plurality of X-electrodes (hereinafter referred to as ‘X-electrode unit driving cell’). The Y-electrode and the X-electrode perform a surface discharge with supplied sustain pulses generated in the X-electrode unit driving cell and the Y-electrode unit driving cell as sustaining electrode pairs. By this, brightness of the picture displayed on a screen is sustained. Here, a panel capacitor
41
indicates equivalently electrostatic capacity formed between the Y-electrode and the X-electrode in the panel.
Referring to
FIG. 2
, the Y-electrode unit driving cell includes a capacitor
43
a
to collect energy, first and third switches
35
a
,
37
a
connected in parallel with the energy collecting capacitor
43
a
, second and fourth switches
31
a
,
33
a
connected in series between a voltage supply source Vcc
1
and a ground, and a coil
39
a
connected between a first node n
1
and a second node n
2
. The X-electrode unit driving cell is positioned symmetrically relative to the Y-electrode unit driving cell through the panel capacitor
41
.
To the branch point of the first node n
1
and the second switch
31
a
are connected a reset resistance
45
, a reset capacitor
47
and a reset switch
48
to reset a voltage of the panel capacitor
41
. If the reset switch
48
is turned on, the voltages charged in the panel capacitor
41
, the X-electrode unit driving cell, and the Y-electrode unit driving cell become uniform.
An operation of the discharge sustaining electrode driving circuit will be described below with reference to
FIGS. 3A
to
3
E. The second switch
31
a
and a switch
49
to connect to the panel capacitor
41
(hereinafter, “panel capacitor connecting switch”) are turned on during the reset, and the electric current then flows. If the panel capacitor connecting switch
49
is turned off during the flow of the electric current, the reset switch
48
is turned on. Thus, a bypass current is formed by the reset capacitor
47
and the reset switch
48
. At this time, the electric current flowing in the panel capacitor
41
constitutes a reset pulse.
If the panel capacitor connecting switch
49
and the third switch
37
a
are turned on after the circuit is in the reset state and the current charged in the panel capacitor
41
is discharged, electric charge is transmitted to the energy collecting capacitor
43
a
and charging is performed. The first switch
35
a
and the panel capacitor connecting switch
49
are turned on during a voltage rising time t
0
of the discharge sustaining pulse. An electric current due to the energy charged in the energy collecting capacitor
43
a
is transmitted to the panel capacitor
41
, through the first switch
35
a
, the coil
39
a
and the panel capacitor connecting switch
49
. On an end of the voltage rising time t
0
of the discharge sustaining pulse, the second switch
31
a
and the panel capacitor connecting switch
49
are turned on, thereby allowing the discharge sustaining pulse to remain in a “high” state t
1
. On an end terminal point of the discharge sustaining pulse in the t
1
, the third switch
37
a
and the panel capacitor connecting switch
49
are turned on, the voltage of the discharge sustaining pulse reduces to a “low” state. The electric current due to the energy charged in the panel capacitor
41
is stored in the energy collecting capacitor
43
a
through the panel capacitor connecting switch
49
and the third switch
37
a
, and the discharge sustaining pulse is in the “suspension” state. On an end point of a falling time t
2
of the discharge sustaining pulse, the fourth switch
33
a
and the panel capacitor connecting switch
49
are turned on and the panel capacitor
41
is completely discharged, so the discharge sustaining pulse remains in the “low” state t
3
. The discharge is sustained through a repetition of the above-described processes.
If a sub-field ends, each switch
31
a
,
33
a
,
35
a
,
37
a
,
48
,
49
is turned on or off so as to return back to the “reset” state to maintain the discharge sustaining pulse, and the discharge process is progressed, thereby allowing a plasma display panel to emit light. Also, like the Y-electrode unit driving cell, the X-electrode unit driving cell operates alternately with the Y-electrode unit driving cell through the above-described processes.
However, if any of the switches
31
a
,
33
a
,
35
a
,
37
a
,
48
,
49
are abnormally turned on at the same time during the process of applying an on/off control signal to each of the switches
31
a
,
33
a
,
35
a
,
37
a
,
48
,
49
while a conventional discharge sustaining electrode driving circuit has been driven, over-current flows into the switches
31
a
,
33
a
,
35
a
,
37
a
,
48
,
49
by which they may be damaged.
SUMMARY OF THE INVENTION
The present invention has been made keeping in mind the above-described and other shortcomings, and an object of the present invention is to provide a plasma display apparatus having an over-current protection circuit that protects a switching device from the over-current generated during an abnormal driving of the driving circuit of discharge sustaining electrode.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
This and other objects of the present invention may be achieved by providing a plasma display panel apparatus according to an embodiment of the invention that includes a pair of discharge sustaining electrodes, a panel capacitor to supply charged voltage alternately to each electrode of the pair of discharge sustaining electrodes, at least one discharge switching device to perform a discharge, the switching device being turned on when the panel capacitor is discharged to thereby pass through discharged current of the panel capacitor, a current sensing part to sense the current passing through the discharge switching device, and an over-current controlling part to turn off the discharge switching device when the current sensed in the current sensing part is at or higher than a predetermined reference value.
According to an asp
A Minh D
Sughrue & Mion, PLLC
Wong Don
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