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3-16.
POWER SUPPLY CIRCUIT (GA, GB BOARDS)
3-16-1. AC Power Supply, Rectifier Circuit
Voltage selector located at the rear side of the unit should be
selected to the local line voltage (AC I 00/ I 20V or 220/240V).
In case of AC 100/120V selected by voltage selector, rectifier D21
capacitors C80 and C81 operate as a double multiple rectifier.
See Figure 17(a).
In case of AC 220/240V selected by voltage selector, rectifier D21
capacitors C80 and C81 operate as a full-wave rectifier.
See Figure 17(b).
02'
AC IN
Passes through D2ld
AC ~d
charges to CB!.
Passes through D2la
and charges to C80.
Figure 17/a)
)>-----'-~---
+
Figure 17/b}
3-16-2. Degauss Circuit
+
DC
DC
There are 2 posistors (PTHl,
PTH2) in the degaussing circuit.
One is used for AC 100/I20V operation, the other is for AC 220/
240V operation, these posistors are switched by voltage selector.
This degaussing circuit is turned ON and OFF by using Relay (RY
1)
automatically.
When power is turned ON, Automatic degaussing starts to work and
a few seconds later stops automatically.
Also Manual degaussing is available if necessary after a few minutes
power is turned on when posistor (PTHl or PTH2) gets cool down.
This manual degaussing is operated by a push of button (Degauss
Switch) at the left of the front panel.
When degaussing circuit starts to work, Ql 1 transistor turns on by
time constant circuit composed of resistors R88, 91 and capacitor
C74. Ql 1 drives Ql2 transistor. Relay (RYl) is driven by Ql2.
Time constant circuit keeps degaussing circuit to activate for several
seconds until degaussing is finished.
~--------~-
+
12V
Of.(,jAlJSS
COIL
"'
3-29
"'
•
PHIi
IC
74
l,
MANUAL
OE(,jAUSS SW
CONTROL
~
cm)
Figure 18
3-16-3.
Starter
Circuit
PANEL
Blocking oscillator composed of integrated circuit IC! and trans-
former T4 operates when power is turned on. DC voltage obtained
by diode D7 and capacitor C57 as a rectifier at the secondary
circuit of T4 is supplied to IC2 and IC3, when AC voltage is higher
than 50 - 70Y (voltage selector at I 00/ l 20Y position). Then power
supply regulator starts to work and +!SY line power supply is pro-
vided to IC2 and IC3 via diode D20, also voltage from T4 stops
providing power supply to IC2 and IC3 because blocking oscillator
is shut down by voltage generated at primary windings of SRT
(Switching Regulator Transformer).
3-16-4.
Switching Regulator Circuit
Block diagram is shown in Figure 19. This is half bridge type of
switching regulator in this model.
Following
Description
is the Theory
of Half-Bridge
Switching
Regulator.
DC voltage EJN rectified from AC voltage in AC power rectifier
section is divided by capacitor Cl and C2. Cl and C2 have almost
same value. Ql (contains 2 transistors) operates as a switch driven
by PWM modulated
pulse via T2 (Drive Transformer).
Switching
current flows through primary windings of Tl (SRT) by switching
transistor QI via T3 (Current Transformer).
Thus output voltages are generated at secondary windings of Tl.
Practical Circuit Used in this Model
There are 2 switching regulators in this power supply. One is for
low voltage power supply,
!
!
SY,
:!:
I SY and +5 V. The other is for
high voltage
-t.
I SOY power supply.
Low voltages are generated by IC2, Tl, T2, T3 and Ql.
High voltages are generated by IC3, T6, T7 and Q2
Refer to block diagram
Current Transformer T3 and T7 detects excess current in transistor
Q 1 and 02 for the protection of damage.
"
112E,•
'"
+
'
"
1/2[ ,.
"
SRT-1
n
CURRENT
TR.II.NS I
Figure 19
3-16-5. Over Voltage Protector
Daughter board GB is mounted in mcither board GA.
GB board works for over voltage protection.
When output voltage gets higher value than predetermined
value,
over voltage protector activates to prevent damage of unit.
BLOCK
DIAGRAM OF GA, GB BOARD
011 ,12
•+----------------11
OE GIi.USS
---
'
_
__,
_CONTRO.
"
SRT •
0 I ,
,o
D22, 26
+ 8v RECT
AC INPUT
<)-
VOLT.II.GE
J1*
SELECT SW
l.k1-
& --------~
AC IN
POWER
SWITCH
AC RECT
OC -AC
(~NvERT!R
DRIVE I
j
i
n
CURRENT
~--JI: (----'
I_~,;:;,
L
c,Rcu,r
--
3-30
SE(ONOARY
'"
CVP
SW
f-----------~-o<l-t-18V
f-----------.W~.A
-
1Sv
'
m
G
11(AC RECT,)
~
DC REG
+
150V
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