ViewSonic VA550 Service Manual - Page 33

ViewSonic VA550 - LCD Display - TFT Manual

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ViewSonic Corporation THEORY OF CIRCUIT OPERATION Service Manual VA550 POWER SYSTEM L32 8410102 012 4700 25V IC18 1RF7304 C24 470u .12V :\ / C 08 R78 1K (1206) - 17 G1 D S2 D2 L02 'SV' x6x1x2nyn 0112 22u 16V R92 47K G2 D 01/8 22K 330u 16V R 9 00 R94 C 14 82I< 102 V 4 I? VCC 090 PO C30 7' 4013 P0Vv2 WO3 018 N.0 038 00 5601 993 OK 41 6 0011 100P 949 4.710 011 3906 C146 ▪ R148 1210017 479 33 16V DIP R97 10K 990 ZDO3 22K 5-2 4.7K 10R99 R96 2216 067 220 1206) 3904 Q 2 R90 - 220 (1206) R39 35 1206) IC21 1007 1 019 L33 5V 0133 15054 160u1i 0 .1u R107 , 4.71 YY C124 16 ZDO4 5003 Zit+ IT 0132 zui. 3904 R114 D17 700 6V N4148 10 IC1- 2 C04049U1316, /C12 470u 2V 18V CE.O.UEINI 0038 1012 102 15 004049013,1 I .1u IC19 C136 40 0.5 304 L34 0128 (1206) 6091-1 C C110 3330 16V 05V 7,9 014 3904 IC20 --OM- L1.4339 R115 - c 21 ,c R104 43K 0122 N.0 OtR N4/48 4 0 0103 C135 470), • 10V -4 D20 105" 150F4 IC12 C04049UMM IC12 004049601V IC12 CO4049UBM 10K tC2 51./1339 13 0134 470u 16V 015 11,4148 R124 22 R112 43K O 2V R10A6A 22)11 I a yr C120 9.14 (023 10 7411014 1 o 78o 5V 0111 10K VLCO 0 5.6 1020 14 C2 This product uses an external power dapter to provide the DC +12 volts. In order to greatly reduce the power consumption during power saving, the circuit in Fig. 1 is used not only to convert the 12 V to 5 V, but also to control the 5V `s ON/OFF status. IC30 (4013) is a D-Flip-Flop CMOS and IC18 is a P-channel MOSFET. When Vgs < 0.7 V, IC18 turns on. As shown in the circuit diagram, when 12 V DC current enters W09, it creates a pulse through C115 and presets the Flip-Flop. When Q (IC30, pin 1) is high, IC18 disables 12 V and the system is in OFF status. When the power switch is pressed, pin3 of IC30 creates a pulse to force Q to a low level. Pin 7 & 8 conducts enabling 12 V and the system is in ON status. There are two regulators that convert the 12 V to 5 V. They are +5Vx and Vlcd. The comparator of IC20 will make the output of two regulators as a feed back to compare with the reference voltage. The compared result controls the IC19 ON/OFF time to achieve the voltage regulation effects. ZD04 creates the reference voltage. Q13, Q14, and MC14049 are basically used to speed up the MOSFET ON/OFF switching time in order to reduce IC19 power consumption. This product is also equipped with an over-voltage protection circuit. When voltage at NO9 is over 15 Volts, Q12 will turn on to making pin 6 of IC30 high and IC18 off. The +5V and VLCD sources provide most of the required power for the VA550 and LCD panel. When the system enters the power saving stage, the above two power sources will turn off through pin 3 of IC25. The + 5 V source provides power to the CPU and SYNC processor, so it must be isolated from other power sources. When in power saving mode, pin 3 of IC25 will be set to low causing +5 V and VLCD to be off. CONFIDENTIAL - DO NOT COPY Page 31

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ViewSonic
Corporation
Service
Manual
VA550
THEORY
OF
CIRCUIT
OPERATION
POWER
SYSTEM
PO
P0Vv2
012
IC18
L32
4700
1RF7304
8410102
25V
C
R78
08
1K
-
17
(1206)
L02
'SV'
x6x1x2nyn
0112
22u
R92
16V
47K
C24
.12V
470u
:\
/
G1
D
S2
D2
G2
D
22K
R
9
35
IC21
019
L33
5V
0133
R39
1206)
10
07
1
15054
160u1i
0
.1u
01/8
330u
16V
00
C
14
102
V
R94
82I<
4
I?
038
00
VCC
090
C30
7'
4013
41
6
00
11
100P
WO3
018
N.0
5601
993
OK
949
4.710
011
3906
C146
▪
R96
R148
479
33
2216
1210017
16V
DIP
067
R97
10K
990
220
ZDO3
22K
1206)
R90
5-2
4.7K
3904
-
220
-
Q
2
(1206)
R99
10
3904
R114
D17
R107
C124
4.71
,
16
YY
ZDO4
+
Zit
5003
IT
102
40
0.5
0132
0
700
zui.
6V
N4148
IC1-
2
10
C04049U1316,
/C12
CE.O.UEINI
1012
00
38
15
004049013,1
I
.1u
IC19
C136
C110
3330
16V
7,
9
0128
05V
015
11,4148
R124
22
(023
10
7411014
1
C
(1206)
014
3904
OtR
IC20
--OM-
N4/48
L1.4339
R115
-
c
21
,c
R104
43K
4
0
304
L34
470u
2V
18V
78
o
o
5V
0111
10K
VLCO
0
5.6
6091
-
1
C135
470)
,
•
10V
-4
D20
105"
150F4
IC12
C04049UMM
IC12
004049601V
IC12
CO4049UBM
0103
10K
0122
N.0
R112
43K
O
tC2
51./1339
13
0134
470u
16V
R10A6A
22)11
yr
C
120
9.14
I
a
2V
1020
14
C2
This
product
uses
an
external
power
dapter
to
provide
the
DC
+12
volts.
In
order
to
greatly
reduce
the
power
consumption
during
power
saving,
the
circuit
in
Fig.
1
is
used
not
only
to
convert
the
12
V
to
5
V,
but
also
to
control
the
5V
`s
ON/OFF
status.
IC30
(4013)
is
a
D
-Flip
-Flop
CMOS
and
IC18
is
a
P
-channel
MOSFET.
When
Vgs
<
0.7
V,
IC18
turns
on.
As
shown
in
the
circuit
diagram,
when
12
V
DC
current
enters
W09,
it
creates
a
pulse
through
C115
and
presets
the
Flip
-Flop.
When
Q
(IC30,
pin
1)
is
high,
IC18
disables
12
V
and
the
system
is
in
OFF
status.
When
the
power
switch
is
pressed,
pin3
of
IC30
creates
a
pulse
to
force
Q
to
a
low
level.
Pin
7
&
8
conducts
enabling
12
V
and
the
system
is
in
ON
status.
There
are
two
regulators
that
convert
the
12
V
to
5
V.
They
are
+5Vx
and
Vlcd.
The
comparator
of
IC20
will
make
the
output
of
two
regulators
as
a
feed
back
to
compare
with
the
reference
voltage.
The
compared
result
controls
the
IC19
ON/OFF
time
to
achieve
the
voltage
regulation
effects.
ZD04
creates
the
reference
voltage.
Q13, Q14,
and
MC14049
are
basically
used
to
speed
up
the
MOSFET
ON/OFF
switching
time
in
order
to
reduce
IC19
power
consumption.
This
product
is
also
equipped
with
an
over
-voltage
protection
circuit.
When
voltage
at
NO9
is
over
15
Volts,
Q12
will
turn
on
to
making
pin
6
of
IC30
high
and
IC18
off.
The
+5V
and
VLCD
sources
provide
most
of
the
required
power
for
the
VA550
and
LCD
panel.
When
the
system
enters
the
power
saving
stage,
the
above
two
power
sources
will
turn
off
through
pin
3
of
IC25.
The
+
5
V
source
provides
power
to
the
CPU
and
SYNC
processor,
so
it
must
be
isolated
from
other
power
sources.
When
in
power
saving
mode,
pin
3
of
IC25
will
be
set
to
low
causing
+5
V
and
VLCD
to
be
off.
CONFIDENTIAL
—
DO
NOT
COPY
Page
31