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8.2.3.4 Outputs
The
secondary-winding
outputs of
th~
chopping
t
ransformer
are
all
full-wave
center-tapped
rectified.
Each
of
these
outputs
is filtered by
an
LC
low-pass fil-
ter.
The output
voltages are
listed
in
Table
8-2.
These
voltages are specified when
the
+5V output
is
adjusted
for
!l.2V
±
1 percent.
This
adjustment is located at R6
on Control
board A4. The
+ 33V
and
- 5V
outputs
are
protected against overvoltage by this
board's
zener
diodes,
VR1
and VR2.
The
+5V
output
is protected
against overvoltage
by a zener diode (VR3) on the
Battery Charger
board (A3). The
+
12V
and
-
12V
outputs are protected
against
overvoltage
by
a com
-
parator
(U7) on
the
Control
board,
which
shuts down
the power supply when
it
detects an
overvoltage.
Table
8-2.
Output Voltages
OutpuL
Voltage (Volts)
+:W
+5.2
±
1'',
-
w
-
5.2
±
s•·,
+ t2V
+
12.4
±
5 '',
-
12V
-
12.4
±
5'',
+:l:lV
+11
±
5',
+110V
+
110
±
5',
-
I
IOV
-
llO
± 5'',
8.2.4
SWITCHER BOARD
(A6)
8.2.4.1 General
The
Switcher
board
contains
the
main
switching
transistors
for the ac off-line and
low-voltage
de-
switching
converters.
The A6 board
also
contains
the
de -input filter, which
provides
filtered de to
the DC
BUS,
the
DC
CENTER
TAP,
and
the
'
a c/dc
relay.
A
schematic of t
he
Switcher board
is
shown at
the
end
of
this
section in Figure
8-10,
the
printed
wiring
board
assembly
and
parts list in
Figure 8-11,
and the
assembly
and
parts
list
in Figure
8-12.
8-4
8.2.4.2
AC/DC Relay
Relay K1 switches
either the
DC CENTER TAP
signal
to
the
de
primary
of
the chopping
transformer
for de
operation, or the
XFMR DC
DR signal
to
t
he
ac
primary
for ac
operation.
For de
operation,
the de input
is
applied to
voltage regulator
U1,
which
will energize
relay
K1
when the Control
board's
RELAY ON
input
line
goes
low. For
ac
operation,
the
RELAY
ON
line
is
either
floating
or pulled
high,
which
disables
regulator
Ul and
relay Kl. AC
operation
will always
override
de
operation.
8.2.4 .3 DC Switches
Field-effect
transistors
Q~
and
Q4
are the
dc -oper-
at ion
switches,
connected in a
push-pull
configura-
lion.
These transistors are
dri ven
by
comple me
n
t~
pulse-width-modulated
signals
(DC DRIVE
and
DC
DRIVE)
coming
from
the
Control board. The fre
-
quency
of
the
signals is
40
kHz, with
a
dead time
het ween
the
signals of
greater
than
0.5
JJSec.
The
cur-
rent
heing
switched
in
the
primary
of the
chopping
transformer is monitored
by
resistor
R20.
8.2.4.4
AC
Switches
Field -effect
transistors
Q
1 and
Q2
are the ac-oper-
at ion
switches,
connected
in
a
half-bridge
configura-
lion. AC
DRIVE
and
AC
DRIVE, the complementary,
pulse-width -modulated
signals coming
from the Con-
trol board
,
drive the
ac switches
via transformer Tl.
The
frequency
of the
drive
signal
is
40kHz, with a dead
time
of l{reater than
2
JJSec.
The
rectified
and
filtered
<H'
inpu
l.
V('+ and
V('-
,
is
further
filtered
by
LC
fil-
ters
L2,
C3, Cl2 and
L3,
C4,
Cl3.
This
signal
is con-
nected
to the ac
switches.
8.2.5
REAR PANEL
The rear panel
contains t
he
ac line
filter,
the de and
ac
input
fuse,
the
110/220
switch, and
the
external
de-
input
connector.
The
System
Motherboard
co ntains
the
line
transient
protectors,
neon bulbs
(NEl
and
NE:.!l
and
va ristors (V
RI and
VR2).
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