Product Reference
2–39
LCD Bias Supply Option
The LCD Bias supply option is a small circuit bo ard th at suppl ies Vee p owe r to an LCD di spl ay.
The board converts the +5V from the Little Board/486e CPU to the Vee voltage (between 15V –
35V) required by many LCD panels. This voltage is ava ilable on fl at p anel con nector J3.
LCD displays are sensitive to the sequence order and timing that power supply and control signals
are applied to the display during power up and removed during power down cycles. LCD
manufactures warn OEMs that violating the sequence and timing specifications of these signals
can damage the display or reduce its service life. The LCD Bias supply option, in conjunction with
control signals from the Little Board/486e video controller automatically sequences the appropriate
signals to meet the requirements of virtually any LCD display
The Ampro LCD Bias Supply option mounts parallel to the Little Board/486e CPU connected to the
board via a 12-pin connector, J4. Secure the board to the Litt le Board/48 6e CPU us ing a .6 inch
standoff. Table 2–32 shows the connector pinou t for J 4, wi th a d escr iption o f ea ch sig nal. So me
signals also appear on flat panel connec tor J 3.
Table 2–32. LCD Bias Supply Option Connector ( J4)
J4 Pin J3 Pin Description
1 Ground
2 +5V to the Vee Supply Option Board
4 Ground
6 38 Enable Vee
TTL control signal driver by the VGA controller chip
8 Ground
11 46 Vee output, to panel
12 47 Contrast adjustment
Analog control signal
Selecting Vee PolarityMost LCD displays require a Vee supply of between 15v – 35V. Some panels need a negative
supply, and some a positive supply. The LCD Bias Supply Option provides a jumper for selecting
the Vee output polarity. To select the polarity for the panel being used, set the jumper on W1 on
the LCD Bias Supply board, not on the Little Board/ 486e C PU, as shown in F igure 2 –-9.