Panasonic TC-L42D30

37
TC-L42D30 LED Backlight Power Circuit
The LED Drive circuit receives 24V from the SMPS. IC8000 provides the
Backlight_On command to turn on the LED drive circuit. This command enters the P-
Board via pin 13 of connector P2 and travels to the LD board to turn on the LED drive
circuit. The backlight control signal, PWM, is delivered to the LED drive circuit via pin
1 of connector P4 to control the brightness of the LEDs. The PWM signal is
dependent on user settings and picture content. An artificial intelligence circuit,
located inside IC8000, is used to manipulate the PWM signal for picture quality and
reduced power consumption. IC9500 and 9600 are boost regulators. Using the PWM
signal, they control the amount of voltage and current applied to the upper and lower
backlight LEDs of the panel.
To avoid catastrophic failures, when the LED backlight control circuit is defective, the
BACKLIGHT_SOS command is output to IC8000 to trigger the shutdown of the TV.
The power LED blinks one time.
This circuit diagram on the previous page is an example of the type of LED drive circuit that
exists inside the LCD panel