Lcd Inverter Module - 0670-00-0649 - Datascope Accutorr Plus Service Manual

2.2.8 LCD Inverter Module - 0670-00-0649

This describes the circuit that will provide the 90 VAC required for the LCD Module
back lite exitation.
DC to AC Inverter
The system +12V signal is fed into the module on J2-1. This signal is then fed to J1-1.
The inverter is powered by +12SW (12.5 volt nominal) from J1-2.
Once powered, the inverter is designed to provide the AC waveform required by the
backlight over the cabinet temperature range and +12V tolerance. The output AC wave-
form is 90 Vrms minimum voltage. The AC frequency is to be between 360Hz and
440Hz. C1 and C2 provide filtering of the inverter DC input.
Current Switch
The Q1 gate is connected to J2-3, ELOFF*. This control signal is pulled low by R1
which maintains Q1 in the off state if J2-3 is floating. Since Q1 passes the inverter
return current to the ground signal PGND on J2-2, Q1 must be on to enable the
inverter. The host can turn on Q1 and enable the T1 inverter by driving ELOFF* high.
D1 filters switching transients on +12SW when Q1 is turned on and off.
J2
POWER SUPPLY
CONNECTOR
Figure 2-9
LCD Inverter Module
Block Diagram
2-28
Revised 12/20/00
FILTER
GND
+12V
FILTER
ELOFF*
GND
GND
CONTROL
DC/AC
INVERTER
T1
GND
FET SWITCH
Accutorr Plus Service Manual
Chapter 2 - Theory of Operation
J1
ELPOWER
GND
LCD CONNECTOR