Backlight control device for liquid crystal display

A backlight control device for a liquid crystal display that is a transmissive type or a transreflective type liquid crystal display equipped with an LED as a backlight, comprising:

• an LED driving circuit that is connected to a power supply circuit and drives the LED;
• a first current control device that detects brightness around the liquid crystal display and controls a driving current of the LED according to the detection;
• and
• a second current control device that, for compensating for temperature dependency of luminescent brightness of the LED, controls a driving current of the LED according to temperature characteristic of the luminescent brightness,
• wherein the first current control device is equipped with a first control reference voltage generation circuit that generates a first control reference voltage according to brightness around the liquid crystal display, and an error amplifier circuit that generates a signal representing a difference between a detection voltage generated according to the drive current of the LED and the control reference voltage generated by the first control reference voltage generation circuit, and
• the power supply circuit varies an output voltage thereof according to an output of the error amplifier circuit.

A backlight control device for a liquid crystal display that is a transmissive type or a transreflective type liquid crystal display equipped with an LED as a backlight, comprising:

• an LED driving circuit that is connected to a power supply circuit and drives the LED;
• a control reference voltage generation circuit that is responsive to brightness around the liquid crystal display, and for compensating for temperature dependency of luminescent brightness of the LED, generates a control reference voltage according to temperature characteristic of the luminescent brightness;
• an error amplifier circuit that generates a signal representing a difference between a detection voltage generated according to a drive current of the LED and the control reference voltage generated by the control reference voltage generation circuit;
• and
• a voltage-current conversion circuit that converts the control reference voltage to a predetermined current,
• wherein the power supply circuit varies an output voltage thereof according to an output of the error amplifier circuit, and
• the LED driving circuit drives the LED by a driving current according to the predetermined current that is converted by the voltage-current conversion circuit.

A backlight control device for a liquid crystal display that is a transmissive type or a transreflective type liquid crystal display equipped with LEDs as a backlight, comprising:

• a plurality of LED driving circuits that are connected to a power supply circuit and drive the corresponding respective plurality of LEDs;
• a control reference voltage generation circuit that is responsive to brightness around the liquid crystal display, and for compensating for temperature dependency of luminescent brightness of each of the LEDs, generates a control reference voltage according to temperature characteristic of the luminescent brightness;
• a control reference voltage level conversion circuit that converts the control reference voltage generated by the control reference voltage generation circuit to a lower level voltage and outputs the same;
• an error amplifier circuit that generates a signal representing a difference between each detection voltage generated according to each drive current of each of the LEDs of the respective LED driving circuits;
• and
• a plurality of current control circuits that each converts the control reference voltage converted by the control reference voltage level conversion circuit to a predetermined current, and controls the drive current of each of the LEDs of the respective LED driving circuits to assume the predetermined current, wherein
• the power supply circuit varies an output voltage thereof according to an output of the error amplifier circuit.

A backlight control device for a liquid crystal display, comprising:

• a light emitting diode (LED) driving circuit that is connected to a power supply circuit and drives the LED;
• and
• means for detecting brightness around the liquid crystal display and controlling a driving current for the LED according to the detected brightness,
• wherein the means for detecting is equipped with a control reference voltage generation circuit that generates a control reference voltage according to the brightness around the liquid crystal display, and an error amplifier circuit that generates a signal representing a difference between a detection voltage according to the driving current for the LED and the control reference voltage generated by the control reference voltage generation circuit, and the power supply circuit varies an output voltage thereof according to an output of the error amplifier circuit.