System for driving a cold-cathode fluorescent lamp connected to a piezoelectric transformer
AssigneeTaiheiyo Cement Corporation
InventorsTakeshi Fujimura, Katsuyuki Ishikawa, Masaaki Toyama
Life of this patent
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Abstract
In a piezoelectric transformer control circuit for driving a load (2) connected to a piezoelectric transformer (1), an oscillation signal as a basis of driving of the piezoelectric transformer (1) is oscillated, and the piezoelectric transformer (1) is driven by a driving circuit (4) on the basis of the oscillation signal. A pulse power supply circuit (5) for supplying a pulse voltage to the driving circuit (4) intermittently drives the driving circuit (4) by pulse-modulating the pulse voltage to be supplied to the driving circuit (4).
Claims34
A piezoelectric transformer control circuit for driving a cold-cathode fluorescent lamp connected to a piezoelectric transformer, the control circuit comprising:
- oscillation means for generating an oscillation signal in accordance with a control voltage;
- driving means for driving said piezoelectric transformer by an AC voltage generated in accordance with the oscillation signal from said oscillation means;
- load current detecting means for detecting a current flowing in the cold-cathode fluorescent lamp connected to an output terminal of said piezoelectric transformer;
- sample-and-hold means for sampling and holding the output from said load current detecting means in accordance with a predetermined control signal;
- load current error output means for comparing an output from said sample-and-hold means with a predetermined value and outputting the control voltage in accordance with a result of the comparison;
- and
- intermittent oscillating means for intermittently driving said driving means by pulse-modulating a pulse signal, for intermittently driving said piezoelectric transformer, to be supplied to said driving means,
- wherein said sample-and-hold means outputs, to said load current error output means, a held voltage corresponding to the output from said load current detecting means during oscillation period of said intermittent oscillating means when said intermittent oscillating means does not oscillate, and
- said intermittent oscillating means can adjust a duty ratio of the pulse signal to be generated.
A piezoelectric transformer control method, for driving a cold-cathode fluoresent lamp connected to a piezoelectric transformer, of generating an oscillation signal in accordance with a control voltage and pulse-modulated signal and intermittently driving the piezoelectric transformer by an AC voltage generated in accordance with the oscillation signal, comprising the steps of:
- detecting a current flowing in the cold-cathode fluoresent lamp connected to an output terminal of said piezoelectric transformer and controlling an oscillation frequency of the oscillation signal by controlling the control voltage such that the current flowing is held substantially constant;
- sampling-and-holding a voltage signal corresponding to the current flowing in accordance with a predetermined control signal;
- and
- outputting a held voltage corresponding to the voltage signal during oscillation period of the pulse-modulated signal when the pulse-modulated signal is not oscillated,
- wherein brightness of the cold-cathode fluoresent lamp can be changed by adjusting a duty ratio of the pulse-modulated signal.
Dependencies are inferred from the claim text.