Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-07-24
2002-06-18
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S063000, C345S904000
Reexamination Certificate
active
06407725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for detecting over current in a plasma display panel, and more particularly, to an apparatus for detecting lowering of at least first and second output voltages from a driving apparatus of a plasma display panel below a corresponding regular voltage due to over current in the plasma display panel and generating an output control signal to be transmitted to the driving apparatus.
2. Description of the Related Art
FIG. 1
shows an apparatus for detecting over current in a conventional plasma display panel. Referring to the drawing, a first output voltage Vo
1
input to a first input port
11
, the level of which is dropped by resistors R
101
, R
102
, R
103
and R
104
, is input to a negative input port (−) of a first comparator Co
1
. The first comparator Co
1
generates an output control signal in a high state indicating that there is an over current flow in a plasma display panel (not shown) when the input first output voltage Vo
1
is lower than a first reference voltage Vref
1
. Also, the first comparator Co
1
generates an output control signal in a low state indicating that there is a normal current flow in the plasma display panel when the input first output voltage Vo
1
is higher than or equal to the first reference voltage Vref
1
. The output control signal generated from the first comparator Co
1
is input to a driving apparatus (not shown) of the plasma display panel via a diode D
11
and a control output port SC. Devices D
13
, R
109
, ZD
11
, ZD
12
and ZD
13
connected in series between the first input port
11
and the control output port SC protect a circuit by allowing a first output voltage Vo
1
at an upper limit level only to be input when the first output voltage Vo
1
becomes abnormally high. Reference numeral G denotes a ground port.
Likewise, a second output voltage Vo
2
input to a second input port
12
, the level of which is dropped by resistors R
105
, R
105
, R
107
and R
108
, is input to a negative input port (−) of a second comparator Co
2
. The second comparator Co
2
generates an output control signal in a high state indicating that over current flows in the plasma display panel when the input second output voltage Vo
2
is lower than a second reference voltage Vref
2
. Also, the second comparator Co
2
generates an output control signal in a low state indicating that there is a normal current flow in the plasma display panel when the input second output voltage Vo
2
is higher than or equal to the second reference voltage Vref
2
. The output control signal generated from the second comparator Co
2
is input to the driving apparatus of the plasma display panel via a diode D
12
and the control output port SC. Devices D
14
, D
15
, ZD
15
, ZD
16
, ZD
17
, ZD
18
, R
110
and D
16
connected in series between the second input port
12
and the control output port SC protect the circuit by allowing a second output voltage Vo
2
at an upper limit level only to be input when the second output voltage Vo
2
becomes abnormally high.
The conventional over current detecting apparatus has the following problems as it uses the comparators with respect to each of the output voltages Vo
1
and Vo
2
.
First, as transmission delay time of each of the comparators Co
1
and Co
2
is relatively long, the over current flowing in the plasma display panel cannot be detected rapidly.
Second, as each of the output voltages Vo
1
and Vo
2
is compared separately, it is not suitable for a plasma display panel having various levels of driving voltages.
Third, as the reference voltages Vref
1
and Vref
2
of the comparators Co
1
and Co
2
must be accurately generated, the configuration of a circuit of the apparatus becomes relatively complicated.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an apparatus for rapidly detecting over current flowing in a plasma display panel with simple circuitry even when there are various levels of the driving voltage in the plasma display panel.
Accordingly, to achieve the above objective, there is provided an apparatus for detecting lowering of at least first and second output voltages from a driving apparatus of a plasma display panel than a corresponding regular voltage due to over current in the plasma display panel and generating an output control signal to be transmitted to the driving apparatus, which comprises a switching transistor having a collector to which a bias voltage of a positive polarity is applied, an emitter which is grounded, and a base, the switching transistor being operated according to the level of a voltage applied to the base and generating the output control signal through the collector, a voltage signal generating portion connected between the base of the switching transistor and a port of the first output voltage, and the base and a port of the second output voltage, respectively, for changing a bias voltage of the base as the first and second output voltages change, and a switching support portion connected between the emitter of the switching transistor and at least any one of the first and second output ports, for allowing a lowered voltage to be applied to the emitter when at least any one of the first and second output voltages is lower than a corresponding regular voltage, to thus prevent incorrect operation of the switching transistor.
The effects of the present invention are as follows.
First, as a switching transistor is used, the transmission delay time is relatively short so that over current flowing in the plasma display panel can be rapidly detected.
Second, as the output voltages for driving the plasma display panel are integrally monitored by the switching transistor, the over current detecting apparatus is suitable for a plasma display panel having various levels of a driving voltage.
Third, a reference voltage for comparison need not be generated as the switching transistor is used. Thus, the configuration of the apparatus becomes relatively simple.
Fourth, as incorrect operation of the switching transistor is prevented by the switching support portion, detecting over current can be performed more accurately.
REFERENCES:
patent: 4347509 (1982-08-01), Hardway et al.
patent: 5621623 (1997-04-01), Kuriyama et al.
patent: 5694030 (1997-12-01), Sato et al.
Hjerpe Richard
Leydig , Voit & Mayer, Ltd.
Nguyen Jennifer T.
Samsung SDI & Co., Ltd.
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