A cold cathode tube driving device using a piezoelectric transformer in which
an
output voltage varies depending on a frequency of an input voltage, as a booster
transformer for driving a cold cathode tube, includes: a frequency dividing means
which generates a driving pulse of an average frequency corresponding to frequency
data outputted from a frequency setting means at a distribution cycle which is
a driving pulse N cyclic period; a controller which controls a control cycle so
as to perform the same driving for predetermined number of times A (A2)
at the average frequency; and a burst pulse generating means which generates a
pulse having a duty width in accordance with a dimming level externally applied
thereto and having a frequency outputted from the controller.
A control cycle is A times (natural number) the distribution cycle and the driving
is performed A times at the same average frequency, whereby a digital driving system
using the frequency distribution of the driving pulse is achieved. Consequently,
a space for the driving circuit can be saved and cost can be reduced. Further,
a frequency distribution system is adopted, thereby obtaining frequency resolution
required for satisfactory dimming performance and lighting performance. Moreover,
a burst dimming system is adopted, thereby suppressing brightness flicker seen
in a tube current control system. Additionally, there is no electric power loss
seen in a system in which a power source is turned on or off and further a shield
circuit is unnecessary because of a system in which the driving pulse is turned
on or off. In particular, the control cycle is A times the distribution cycle and
the burst dimming is performed in which the driving is executed A times at the
same average frequency, whereby the brightness flicker can be prevented by controlling
the tube current to be constant with high dimming resolution assured.
