Theory Of Circuit Operation - ViewSonic VG150m-1 Service Manual

4-4 Theory of Circuit Operation

VG150m/mb is a multi-frequency and multi-mode color TFT LCD monitor. It supports different
resolutions including XGA, SVGA, VGA and other various high resolution up to 1024x768 for IBM, PC
compatibles, Power PC and Macintosh. VG150m uses a TFT LCD panel with a 0.297mm pixel pitch,
provides 16.7 millions color images.
As the previous block diagram illustrates, VG150m uses a highly integrated solution (U1: Mascot V)
that combines a high performance ADC with an advanced image process controller. Using advanced
image scaling algorithms, Mascot V has intelligently adaptive sub-algorithms that will automatically
optimize the display quality for different images – the text is sharper and the graphics is smoother.
Furthermore, each TFT LCD monitor uses the 24LC02 (U14) chip to provide DDC1/2B
Analog Plug&Play, the DDC data format is EDID v1.3.
Digital process and control system allows users to control OSD menu values to change monitor
settings. The follow sections are major part discussions of the TFT LCD display control board.
POWER SYSTEM
This product uses an external power adapter to provide DC+12V. It is the source of other voltages +5VX,
3.3VX, and VLCD.
The voltage of +5VX is produced by regulator LM2596-5V (U5) and external components that can realize DC
to DC conversion from +12V to +5V. For some chips (MPU, ADC) that are sensitive to any voltage variance,
we need LDO 1084-3.3V (U11) to produce a stable voltage 3.3VX.
There is still an important consideration about power consumption. We must greatly reduce the power
consumption even up to 90% in power saving mode. So we need to switch off the power that needn't exist
when the system enters to this mode. We use the P-channel MOSFET TRLML6402 (Q1) to control the on/off
state of the panel's power VLCD.
See FIG1-1.
ViewSonic Corporation
FIG1-1
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