Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
2002-06-12
2004-11-23
Chang, Kent (Department: 2673)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C363S020000, C327S143000, C345S213000
Reexamination Certificate
active
06822646
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Korean Application No. 2001-64910, filed Oct. 20, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to a display apparatus, and more particularly, to a display apparatus having a power supply capable of lowering power consumption effectively in a power saving mode.
2. Description of the Related Art
Generally, in a display apparatus, a power supply supplies electric power to components such as a deflection circuit, a high voltage circuit, etc., respectively. Recently, technology related to an SMPS (Switched Mode Power Supply) has been rapidly developing. An SMPS is small, light and effective compared to a linear power supply.
A conventional SMPS
150
, as shown in
FIG. 5
, comprises a power supplying part
101
, a transformer (
105
,
105
a
,
105
b
,
106
and
106
a
), a feedback voltage sensing part
109
sensing a voltage applied to a secondary coil
106
, and a power driving part
110
supplying a square wave AC (Alternating Current) voltage to a primary coil
105
on the basis of a synchronous signal applied from a video card (not shown).
Referring to
FIG. 5
, an operation of the SMPS
150
is described hereinbelow. First, commercial AC power of 110V or 220V is supplied to the SMPS
150
by the power supplying part
101
. The commercial AC power is converted into a DC (Direct Current) voltage “B+” through a rectifier
102
and a capacitor
102
a
. The DC voltage “B+” generates a starting current based on a starting resistor
103
, so as to operate the power driving part
110
. As the power driving part
110
is operated, a PWM (Pulse Width Modulation) control signal S
1
is applied to the primary coil
105
. The PWM control signal S
1
is generated from a power driver (to be described later) provided inside the power driving part
110
. Further, the PWM control signal S
1
generates an AC voltage in the primary coil
105
, and therefore an AC voltage is induced in the secondary coils
106
and
106
a
and supplied to driving circuits (not shown) inside a display apparatus. The induced AC voltage of the secondary coil
106
a
goes through a diode
112
and is stabilized by a regulator
113
, thus being applied to a control part
114
.
Referring to
FIG. 6
, the power driving part
110
includes a free-run frequency generator
131
generating a synchronous signal by itself in a power saving mode in which the synchronous signal is not received from a video card (not shown) The power driving part
110
also includes a selecting part
132
selecting one of the synchronous signal received from the video card (not shown) in normal mode, and the synchronous signal received from the free-run frequency generator
131
in the power saving mode. In addition, the power driving part
110
includes a power driver
135
outputting the PWM control signal S
1
in response to the synchronous signal, a power transistor
138
which is switched on/off according to the PWM control signal S
1
outputted from the power driver
135
, and a feedback voltage regulating part
134
transmitting a voltage-regulating signal S
2
to the power driver
135
. The duty ratio of the voltage-regulating signal S
2
is regulated by comparing a feedback voltage with an output voltage of the power transistor
138
The drain of the power transistor
138
is coupled to drive, and the source of the power transistor
138
is coupled to resistor
139
.
Referring again to
FIG. 5
, in the power saving mode, the control part
114
cuts off the output of the secondary coil
106
supplied to each driving circuit by switching off a load connection switch
115
, thus lowering power consumption. Accordingly, as the output of the secondary coil
106
is cut off from the other components, the load thereof is decreased and the feedback voltage is reduced. On the basis of the reduced feedback voltage, the feedback voltage regulating part
134
of the power driving part
110
transmits the voltage-regulating signal S
2
to the power driver
135
. Then, the power driver
135
transmits the PWM control signal S
1
to the power transistor
138
in response to the synchronous signal generated from the free-run frequency generator
131
. According to the PWM control signal S
1
, the power transistor
138
is switched on/off, and thus an AC voltage is supplied to the primary coil
105
. At this time, the control part
114
and the power driving part
110
consume 0.2 Watt and 1 Watt or more, respectively, of power. Furthermore, because power consumption due to a leakage current at the starting resistor
103
is added to the above power consumption, total power consumption is at least 2 Watts or more.
Thus, in order to lower the power consumption in the power saving mode, lowering the power consumption of the power driving part
110
is effective because the power consumption of the power driving part
110
is relatively higher than that of the control part
114
. As a method for lowering the power consumption of the power driving part
110
in the power saving mode, there is proposed a method of lowering the frequency of the free-run frequency generator
131
and increasing the resistance of the starting resistor
103
.
However, if the frequency of the free-run frequency generator
131
is lowered, the transformer makes a noise. Further, if the resistance of the starting resistor
103
is increased, the starting current is decreased and the minimum on-duty of the PWM control signal for driving the transformer is not secured. Accordingly, the output voltage of the transformer is unstable, thus making the operations of the power driving part
110
and the control part
114
unstable.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made keeping in mind the above-described shortcomings and user's need.
An aspect of the present invention is to provide a display apparatus having a power supply minimizing power consumption at a power saving mode by operating a power driving part with a synthetic synchronous signal, securing stable operations of a control part and the power driving part.
This and other aspects of the present invention are accomplished by a display apparatus of the present invention. The display apparatus of the present invention inlcudes a power supply comprising a commercial AC power supplying part, a transformer having a primary coil and a secondary coil and supplying an AC voltage to driving circuits, and a feedback voltage sensing part sensing a load of the secondary coil. The power supply of the display apparatus of the present invention also comprises a power mode information part providing information for determining a normal mode or a power saving mode according to an input of a synchronous signal; a power driving part including a power driver generating a power regulating signal according to a synchronous signal on the basis of a feedback voltage sensed by the feedback voltage sensing part in the normal mode, and an idle power driver generating a power saving voltage on the basis of a synchronous signal which is made by synthesizing different frequency signals in the power saving mode; an idle switching part turning on/off the idle power driver; and a control part cutting off the feedback voltage applied to the power driver and controlling the idle switching part so as to operate the idle power driver in the power saving mode.
The power driving part includes a power transistor connected to the primary coil, and the idle power driver includes a plurality of sawtooth generators respectively generating sawtooth signals with several tens of hertz (Hz) and several tens of kilohertz (KHz), a plurality of comparators processing the sawtooth signals and outputting square wave signals having different pulse widths, and an AND gate logically synthesizing the square wave signals outputted from the comparators and supplying the synthetic square wave signal to the power transi
Chang Kent
Staas & Halsey , LLP
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