Block Diagrams
Theory of Operation
2 - 50
0070-00-0420
Passport 5-Lead, 5L, LT, XG Service Manual
Detail
The reader should refer to the Line/Battery block diagram , sub-circuit diagrams, and
complete circuit schematics while reading the following operation descriptions.
FIGURE 2-19
Diode OR Circuit
Diode - “OR”
Immediately upon entering this module, the three voltage sources are fused. The 17V line
input is tied to fuse F1 which is rated for 2.5 A and is a slow-blow type fuse. Fuses F3 & F4
are 4 A fuses and are also slow-blow type fuses. The selected fuses are a common 5 X 20
mm size and are approved for both Domestic and International use.This block provides
power entry selection where the line voltage will always be selected before battery power is
selected. The “OR-ing” function is provided by diodes CR8-CR10. These Schottky diodes
are used because of their low forward drop. If the line voltage is available (+17V), CR8 will
forward conduct and CR9 and CR8 will be reversed biased. When line power is removed,
a smooth transition will be made to battery power through CR9 and CR10. The output from
the diode OR (system power) exits this module and returns through the main power switch.
When the system is off, diodes CR11 and CR12 allow a charging path from the battery
charger to each battery. Resistors R10 and R13 provide a path to ground, to bleed
accumulated charge from CR11 and CR12.
Vbattery
12V
Vline
17+-1V
Vbattery
12V
FPSW
CR8
CR9
CR10
2.5A
4A
4A
F1
F2
BA
T
CH
AR
G
ER
USD945
USD945
USD945
R13
100K
R10
100K
Содержание Passport 5-Lead
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