Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2002-01-09
2003-03-18
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S20000A, C315S2090SC
Reexamination Certificate
active
06534928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for driving a cold cathode flat fluorescent lamp (CCFFL) and, more particularly, to a method for driving a CCFFL that enables the luminance uniformity of the CCFFL to be substantially constant while the CCFFL is adjusted for a desired luminance. Specifically, the method improves the luminance uniformity of the CCFFL when it is dim.
2. Description of the Related Art
The cold cathode flat fluorescent lamp (CCFFL) is used as a back-light source for an LCD display device or an LCD projector, or as a light source for a vehicle. The general construction of a CCFFL
100
is shown in
FIG. 1
, which is provided with a luminous surface
101
, and a pair of electrodes
102
and
103
. A conventional driving apparatus for the CCFFL
100
is composed of a power supply
104
, a pulse generator
105
, and an inverter driver
107
, as shown in FIG.
2
. In the conventional driving apparatus for the CCFFL
100
, a conventional driving method for the CCFFL
100
comprises the steps of generating a pulse signal
106
by the pulse generator
105
of
FIG. 2
, applying the pulse signal
106
to the inverter driver
107
, and generating a control signal by the inverter driver
107
to drive the CCFFL
100
to light up. In general, the control signal generated by the inverter driver
107
is a pulse signal or an alternating signal.
In addition, if it is necessary to adjust the luminance of the CCFFL
100
, a pulse width P
W
of the pulse signal
106
of
FIG. 3
is adjusted so as to alter the luminance of the CCFFL
100
. Furthermore, a pulse period P
T
of the pulse signal
106
is set to be less than the time of visual persistence for human beings, so that the power consumption of the CCFFL
100
with the same luminance is reduced.
Thus, using the conventional driving method for the CCFFL
100
, it is possible to alter the luminance of the CCFFL
100
and reduce the power consumption thereof by adjusting the pulse width P
W
and the pulse period P
T
of the pulse signal
106
, respectively. However, due to the characteristic of the CCFFL
100
, that is, when the pulse width P
W
is lowered to alter the luminance of the CCFFL
100
, the luminance at electrodes
102
and
103
are brighter than the luminance at the central region of the luminous surface
101
, such that a non-uniformity of luminance in the CCFFL
100
occurs. In addition, since the pulse width P
W
is lowered compared to the same pulse period P
T
, the effective pulse period becomes longer, that is, it is equal to, or longer than, the time of visual persistence for human beings, thereby unstable luminance of the CCFFL
100
occurs.
Therefore, it is difficult to have a desired luminance uniformity while the CCFFL is adjusted for a desired reduced luminance using the conventional driving method for the CCFFL.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for driving the cold cathode flat fluorescent lamp (CCFFL) for enabling the luminance uniformity of the CCFFL to be substantially constant while the CCFFL is adjusted for a desired luminance.
It is another object of the invention to provide a method for driving the CCFFL suitable for improving the luminance uniformity of the CCFFL when it is dim.
It is still another object of the invention to provide a method for driving the CCFFL suitable for reducing the power consumption thereof and preventing the luminance of the CCFFL from being unstable.
According to an aspect of the invention, there is provided the method for driving the CCFFL comprising the following steps: generating a pulse-combined signal, wherein the pulse-combined signal has a plurality of pulse signals, and each of the plurality of pulse signals has a pulse width and a pulse period; applying the pulse-combined signal to the inverter driver circuit, wherein the inverter driver circuit has a pair of output terminals, which are electrically connected to a pair of input terminals on the CCFFL so as to input a control signal to the CCFFL to light it up; adjusting the pulse width and the pulse period so that the CCFFL is at a first luminance while a first luminance uniformity thereof is maximum; setting the pulse width and the pulse period such that the CCFFL is at the first luminance and have the first luminance uniformity; and generating the pulse-combined signal having a turn-off time that allows the CCFFL to be at a second luminance and to have a second luminance uniformity; wherein the second luminance uniformity is substantially equal to the first luminance uniformity.
It is preferred that the step of generating the pulse-combined signal having the turn-off time comprises using a sinusoid-wave signal, a square-wave signal, or a triangle-shaped wave signal, and performing a modulating operation.
It is advantageous that the method for driving the CCFFL further comprises a step of generating the pulse-combined signal having a turn-on time that allows the CCFFL to be at a third luminance and to have a third luminance uniformity; wherein the third luminance uniformity is substantially equal to the first luminance uniformity.
It is preferred that the step of generating the pulse-combined signal having the turn-on time comprises using a sinusoid-wave signal, a square-wave signal, or a triangle-shaped wave signal, and performing a modulating operation.
It is preferred that the third luminance is the desired luminance of the CCFFL.
It is preferred that the third luminance is the first luminance of the CCFFL.
It is preferred that the first luminance is the maximum luminance of the CCFFL.
It is preferred that the second luminance is the desired luminance of the CCFFL.
Other objects and advantages of the present invention will become apparent from the detailed description to follow taken in conjunction with the appended claim.
REFERENCES:
patent: 6239558 (2001-05-01), Fujimura et al.
Li Hsien Jen
Yu Chih Jung
Bacon & Thomas PLLC
Delta Optoelectronics, Inc.
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