Electric power circuit for driving display panel
An electric power circuit for driving a display panel, which supplies a plurality of gradation voltages to driver parts of the display panel, is provided. The electric power circuit has a fine-controlling circuit for fine-controlling the gradation voltage in response to a difference between the gradation voltage and a referential voltage, by which excess increase and decrease of the gradation voltage can be appropriately suppressed. Therefore, the electric power circuit can generates a stable gradation voltage.
1 . An electric power circuit for driving a display panel comprising:
a generation circuit for generating a plurality of reference voltages on corresponding reference voltage terminals thereof; and
a plurality of amplifiers for respectively amplifying said plurality of reference voltages so as to generate gradation voltages to gradation output terminals thereof,
wherein at least one of said amplifiers comprises:
a differential amplification circuit having a positive input terminal connected to said reference voltage terminal;
a buffer amp driven by an output of said differential amplification circuit, for generating said gradation voltage;
a feedback path by which said gradation voltage is fed back to a negative input terminal of said differential amplification circuit; and
a fine-controlling circuit for fine-controlling said gradation voltage.
2 . An electric power circuit for driving a display panel according to the claim 1 ,
wherein
said buffer amp is a first output transistor having a first conductivity type, a conductivity of said first output transistor being controlled by said output of said differential amplification circuit, and
said fine-controlling circuit comprises:
a second output transistor having a second conductivity type, for providing a bypass electric current, a conductivity of said output transistor being controlled by said output of said differential amplification circuit,
a switching element having on/off-states for relaying said bypass electric current to said gradation voltage output terminal in said on-state; and
a comparative part for turning on said switching element when a difference between said gradation voltage and said reference voltage is equal to or larger than a predetermined voltage.
3 . An electric power circuit for driving a display panel according to the claim 1 ,
wherein said fine-controlling circuit comprises:
a plurality of constant current source for respectively providing substantially constant bypass electric currents;
a plurality of switching elements, each having on/off-states, for respectively relaying said bypass electric currents to said gradation voltage output terminal in said on-states;
a comparative part for receiving said gradation voltage and said referential voltage so as to selectively turn on said switching elements in response to a difference between said gradation voltage and said reference voltage.
4 . An electric power circuit for driving a display panel according to the claim 2 ,
wherein said comparative part includes a hysteresis comparator having a negative input terminal connected to said referential voltage terminal via a first resistor, and a positive input terminal connected to said gradation voltage output terminal via a second resistor.
5 . An electric power circuit for driving a display panel according to the claim 3 ,
wherein said comparative part includes a hysteresis comparator having a negative input terminal connected to said referential voltage terminal via a first resistor, and a positive input terminal connected to said gradation voltage output terminal via a second resistor.