Mindray Passport 5-Lead, Service Manual

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Passport 5-Lead, 5L, LT, XG Service Manual 0070-00-0420 2 - 49
Theory of Operation Block Diagrams
2.2.5 Line Battery Board
Overview
The Line/Battery module provides four different power functions.
• Selects “raw” DC power from either an external regulated line supply of 17V, or from two
sealed 12V lead acid batteries. The order of selection is A) 17V external power, B) Two
12V batteries, C) One 12V battery.
• Gen15V @ 250 mA, -15V @ 250 mA, and +5V @ 1.5A.
• Allows the charging of lead acid batteries to occur.
• Monitors “raw” DC battery power and turns off system when battery voltage drops below
10.5V.
• Provides the battery voltages, the charging voltages and the ex17V for the Battery
Charging LED function on the VGA/EL Panel Board. The Battery Charging LED function
compares the battery voltage to the charging voltage. When the batteries are charging,
no matter what position the power-on switch is in, the green LED is lit.
Once the batteries discharge to a level of approximately 11 volts (for more than 20
seconds), the unit is automatically shut OFF with enough hysteresis that the main power
switch must be cycled to re-initiate a turn-ON. The hysteresis is necessary because when the
system load is removed from the battery, the terminal voltage of the battery will float back up
to the voltage of a charged battery. After the cutoff circuit is activated, a load greater than
100K (@ 12 volts) remains on the battery to avoid excessive discharge and therefore
sulfation of the battery. The low battery cutoff comparator controls a small oscillator that
generates an isolated voltage. This voltage is capacitively coupled via a full wave
rectification circuit. This “floating” supply controls the gate of a very low ON resistance
power FET. This FET controls power to the switching supplies to generate system voltages.
FIGURE 2-18 Line/Battery Block Diagram
0449 / 0626 BOARD BLOCK DIAGRAM
J53
FPSW
SW BULK IN
BULK
+17
BAT CHG A
BAT CHG B
CR11
CR9
+17
BAT CHG A
BAT CHG B
Battery A
Battery B
Battery A
Battery B
GND
J52
J51
SWITCH
D
iod
e -
O
R
OSC/
CHG
PUMP
Q3
20 SEC DELAY
LOW
VOLTAGE
SHUT
DOWN
P
o
wer
M
o
dul
e
UNIPOINT
GND
-15V
+15V
+5V
SW BULK OUT
J54
J55
COMPARATOR OUT
SWITCH ON/OFF
OSCILLATOR
SWITCH DRIVE
SW BULK IN
C7
U1
U2B
CV1