LC640.480.21-065 Operations Manual (OM610-00)
25
Temperature Sensors
The temperature sensors are located at opposite corners of the backlight module, just
outside the active area of the display. The output of the sensors are sent to the
microprocessor on the inverter module through a board-to-board connector.
Heater Operation and Over Heat Status Lines
There are two situations when the inverter controller will override the external control of
the backlight:
1. At cold temperatures, the backlight will not turn on until it is warmed up.
2. At high temperatures, the luminance will be reduced until the temperature drops to a
safe level.
Two digital status signals notify the user computer of these conditions. These CMOS-
level outputs sink up to 20 mA to accommodate an LED load.
Table 19. Heater Operation and Over Heat Status Line Parameters.
Parameter
Value
Units
Heater status (/HT, pin 39, J1)
0 = heating, +5 = normal
Vdc
Over heat status (/OHT, pin 40, J1)
0 = over heat, +5 = normal
Vdc
Backlight Heater
The backlight heater consists of nichrome wire wrapped around each lamp. The purpose
of the heater is to vaporize the mercury at low temperatures providing proper lamp
emission color and extending lamp life.
When the inverter is first powered up it checks the backlight cavity temperature. If the
temperature is below +10° C, the lamp heaters are turned on at 100% duty cycle and the
inverter is disabled for a specific time period as shown in Figure 15 on page 26. After the
time delay, the inverter is enabled and the heater duty cycle is set to the value shown in
Figure 16 on page 27. The heater continues to operate until the sensor temperature
r10° C. See Figure 17 on page 27 for actual display warm-up performance.
