Low noise method and apparatus for driving electroluminescent panels
AssigneeSupertex, Inc.
InventorsScott Lynch, Jimes Lei, Roshanak Aflatouni
Life of this patent
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Abstract
A low noise method and apparatus for driving electroluminescent (EL) panels provides reduction in EL panel noise, and in the preferred embodiment, voltage compensation as the EL panel ages. The output of a high voltage power supply is applied to the EL panel through a circuit having an optimized time-constant, producing a waveform that reduces EL panel vibration. Additionally, if the time constant is derived in part from the capacitance of the EL panel, the time constant may be chosen such that aging of the EL panel maintains the time constant in the proper range to maintain noise reduction over the life of the panel and compensate for brightness reduction due to aging of the EL panel.
Claims22
A circuit for supplying a drive voltage to an electroluminescent (EL) panel, comprising:
- an output for connection to said EL panel;
- a high voltage power supply connection;
- an output circuit coupled to said output and further coupled to said high voltage power supply connection for alternating a voltage of said high voltage power supply connection at said output;
- a waveform generator connection coupled to said output circuit for providing a drive waveform for alternating said output;
- and
- a waveshaping circuit coupled to said output circuit for shaping a voltage at said output in a first-order exponential shape, wherein a ratio of a full period of said drive waveform to a time constant of said exponential shape is within the range of 3 to 8.
A circuit for supplying a drive voltage to an electroluminescent (EL) panel, comprising:
- an output for connection to said EL panel;
- a high voltage power supply connection;
- an output circuit coupled to said output and further coupled to said high voltage power supply connection for alternating a voltage of said high voltage power supply connection at said output;
- a waveform generator connection coupled to said output circuit for providing a drive waveform for alternating said output;
- and
- means for increasing a voltage at said output in conformity with aging of said EL panel wherein said means increases said voltage in conformity with a reduction of a capacitance of said EL panel.
A circuit for supplying a drive voltage to an electroluminescent (EL) panel, comprising:
- an output for connection to said EL panel;
- a high voltage power supply connection;
- an output circuit coupled to said output and further coupled to said high voltage power supply connection for alternating a voltage of said high voltage power supply connection at said output;
- a waveform generator connection coupled to said output circuit for providing a drive waveform for alternating said output;
- and
- a voltage-reducing circuit coupled to said output circuit for reducing a voltage at said output in conformity with a capacitance of said EL panel, whereby a reduction in capacitance of said EL panel due to aging of said EL panel causes an increase in voltage at said output, whereby a loss of brightness of said EL panel due to aging of said EL panel is reduced or eliminated.
A method for driving an electroluminescent (EL) panel, comprising:
- alternating a supply voltage at a repetitive period to produce an alternating high voltage;
- shaping said alternating supply voltage to produce a first-order exponential shape, wherein a ratio of said period to a time constant of said exponential shape is within the range of 3 to 8;
- and
- supplying a resulting shaped alternating high voltage to said EL panel, whereby audible noise from said EL panel is reduced by said shaping.
A method for driving an electroluminescent (EL) panel, comprising:
- alternating a supply voltage at a frequency to produce an alternating high voltage;
- reducing said alternating high voltage by a predertermined reduction;
- supplying a resulting reduced alternating high voltage to said EL panel, whereby brightness of said EL panel is initially reduced;
- and
- subsequent to aging of said EL panel, decreasing of said EL panel.
Dependencies are inferred from the claim text.