Drive device and drive method for a cold cathode fluorescent lamp

A drive device for one or a plurality of series-connected cold cathode fluorescent lamps having an electrical terminal at both ends, comprising:

• a piezoelectric transformer having a pair of primary electrodes and first and second secondary electrodes, said piezoelectric transformer converting a primary ac input from the primary electrodes by a piezoelectric effect to a secondary ac output, outputting a secondary output in a first phase from the first secondary electrode and outputting a secondary output of a second phase opposite the first phase from the second secondary electrode, and enabling connection of the electrical terminals at both ends of the cold cathode fluorescent lamp between the first secondary electrode and the second secondary electrode;
• a variable oscillation circuit for oscillating the primary ac input at a specified frequency;
• a drive arrangement for applying the primary ac input to the primary electrodes;
• and
• a brightness control circuit for controlling cold cathode fluorescent lamp brightness by detecting an ac voltage of the secondary ac output applied to the end electrical terminals of the cold cathode fluorescent lamp such that,
• when the detected ac voltage of the secondary ac output is greater than a specific voltage, the primary ac input frequency approaches the resonance frequency of the piezoelectric transformer by the variable oscillation circuit, and
• when the detected ac voltage of the secondary ac output is less than the specific voltage, the primary ac input frequency recedes from the resonance frequency of the piezoelectric transformer by the variable oscillation circuit.

A drive device for one or a plurality of series-connected cold cathode fluorescent lamps having an electrical terminal at both ends, comprising:

• a piezoelectric transformer having a pair of primary electrodes and first and second secondary electrodes, said piezoelectric transformer converting a primary ac input from the primary electrodes by a piezoelectric effect to a secondary ac output, outputting a secondary output in a first phase from the first secondary electrode and outputting a secondary output of a second phase opposite the first phase from the second secondary electrode, and enabling connection of the electrical terminals at both ends of the cold cathode fluorescent lamp between the first secondary electrode and the second secondary electrode;
• a drive arrangement for applying the primary ac input to the primary electrodes;
• and
• a brightness control circuit for controlling cold cathode fluorescent lamp brightness by detecting an ac voltage of the secondary ac output such that,
• when the detected ac voltage of the secondary ac output is greater than a specific voltage, the drive arrangement reduces the ac voltage of the primary ac input to reduce the lamp brightness, and
• when the detected ac voltage of the secondary ac output is less than a specific voltage, the drive arrangement increases the ac voltage of the primary ac input to increase the lamp brightness.

A drive method for one or a plurality of series-connected cold cathode fluorescent lamps having an electrical terminal at both ends, comprising:

• applying a primary ac input from a drive arrangement to primary electrodes of a piezoelectric transformer,
• the piezoelectric transformer having a pair of primary electrodes and first and second secondary electrodes, converting the primary ac input from the primary electrodes by a piezoelectric effect to a secondary ac output, outputting a secondary output in a first phase from the first secondary electrode and outputting a secondary output in a second phase opposite the first phase from the second secondary electrode;
• striking the cold cathode fluorescent lamp connected with both end electrical terminals thereof connected between the first and the second secondary electrodes by applying the first phase secondary ac output to one of the electrical terminals, and applying the second phase second ac output to the other electrical terminal;
• detecting a phase difference between the secondary ac output and primary ac input by means of a brightness control circuit for controlling cold cathode fluorescent lamp brightness;
• controlling the drive arrangement to reduce primary ac input power to the primary electrodes of the piezoelectric transformer when the detected phase difference is greater than a specified phase difference;
• and
• controlling the drive arrangement to increase primary ac input power to the primary electrodes of the piezoelectric transformer when the detected phase difference is less than a specified phase difference.

A drive method for one or a plurality of series-connected cold cathode fluorescent lamps having an electrical terminal at both ends, comprising:

• applying a primary ac input oscillated by a variable oscillation circuit from a drive arrangement to primary electrodes of a piezoelectric transformer,
• the piezoelectric transformer having a pair of primary electrodes and first and second secondary electrodes, the piezoelectric transformer converting the primary ac input from the primary electrodes by a piezoelectric effect to a secondary ac output, outputting a secondary output in a first phase from the first secondary electrode and outputting a secondary output in a second phase opposite the first phase from the second secondary electrode;
• striking the cold cathode fluorescent lamp connected with both end electrical terminals thereof connected between the first and second secondary electrodes by applying the first phase secondary ac output to one of the electrical terminals, and applying the second phase second ac output to the other electrical terminal;
• detecting an ac voltage of the secondary ac output applied to the end electrical terminals of the cold cathode fluorescent lamp by means of a brightness control circuit for controlling cold cathode fluorescent lamp brightness;
• controlling the drive arrangement to reduce the ac voltage of the primary ac input when the detected ac voltage of the secondary ac output is greater than a specified voltage;
• controlling the drive arrangement to increase the ac voltage of the primary ac input when the detected ac voltage of the secondary ac output is less than a specified voltage;
• and
• making the detected ac voltage of the secondary ac output equal to the specified voltage.

A drive method for one or a plurality of series-connected cold cathode fluorescent lamps having an electrical terminal at both ends, comprising:

• applying a primary ac input oscillated by a variable oscillation circuit from a drive arrangement to primary electrodes of a piezoelectric transformer,
• the piezoelectric transformer having a pair of primary electrodes and first and second secondary electrodes, converting the primary ac input from the primary electrodes by a piezoelectric effect to a secondary ac output, outputting a secondary output in a first phase from the first secondary electrode and outputting a secondary output in a second phase opposite the first phase from the second secondary electrode;
• striking the cold cathode fluorescent lamp connected with both end electrical terminals thereof connected between the first and the second secondary electrodes by applying the first phase secondary ac output to one of the electrical terminals, and applying the second phase second ac output to the other electrical terminal;
• detecting an ac voltage of the secondary ac output applied to the end electrical terminals of the cold cathode fluorescent lamp by means of a brightness control circuit for controlling cold cathode fluorescent lamp brightness;
• controlling the variable oscillation circuit so that the primary ac input frequency approaches the resonance frequency of the piezoelectric transformer when the detected ac voltage of the secondary ac output is greater than a specific voltage;
• controlling the variable oscillation circuit so that the primary ac input frequency recedes from the resonance frequency of the piezoelectric transformer when the detected ac voltage of the secondary ac output is less than the specific voltage;
• and
• making the detected ac voltage of the secondary ac output and the specific voltage equal.