STYLUS 800 Service Manual Operating Principles
The figure below shows a block diagram of the power supply circuit (C106
PSB/PSE).
This power
supply circuit employs the
RCC
(ringing choke converter) switching control system. The input AC
voltage supplied from the external AC source is first input to the filter circuit for higher harmonics
absorption. The AC voltage is then input to the rectification and smoothing circuit, converting it
into DC voltage. This DC voltage is input to the switching circuit for switching operation. Along
with the switching operation on the primary side, +35
VDC
is generated after passing through the
smoothing circuit. The +35
VDC
level is fed back to the primary switching circuit through the +35
V line voltage detection circuit and, thus, the +35
VDC
output level is stabilized. This +35
VDC
is
also input to the +5
VDC
generation circuit to generate a stable +5
VDC.
Primary-side
C7
QI
T1
~~
,.—.
Smoothing
Circuit
4
Main
Switching
I--Id
w-J----
k
Full-wave
Rectifier
Circuit
C21C
9
L1/C6
CIIR1
Filter
Circuit
L
1-
Pcl
!–
lC51/Q51/L51
Secondary-side
D5!YR53/C55
*“V”’
C51/C52
.—,
I
—
ZD52
+
ZD511R70/R711R72/Q52
+35V
—
Constant
Voltage Control
-
Crcult
. .
ZD53
-
-44+
+35VDC
u
+5V
Over-current
Protection
. .
AC Input
Figure 2-12. Power Supply Circuit Block Diagram
This circuit contains the protection circuits described below.
1)
2)
3)
4)
+5
VDC
line over voltage protection circuit
The output voltage level of +5 V line is monitored with a
Zener
diode
(ZD53)
and if the voltage
level exceeds predefined level (+7 V), the status is fed back to the primary switching circuit
through a
photocoupler
(PC1)
to stop the +35 V generation.
+5
VDC
line over current protection circuit
The output current is monitored with a detection resistor
(R53)
and fed back to the +5
VDC
generation switching control
IC
(IC51).
If the current level exceeds the limit, the control IC
shortens the ON
time
of the switching transistor
(Q51)
to decrease the output voltage level
(constant current operation).
+35
VDC
line over voltage protection circuit
The output level is monitored with a
Zener
diode
(ZD36).
If the voltage level exceeds the limit
level (+36 V), it activates a photocoupler
(PC1),
and this stops the primary switching circuit
operation.
+35
VDC
line constant voltage output control circuit
The output level of +35
VDC
line is monitored by a detection circuit that consists of a
Zener
diode
(ZD51),
a transistor
(Q52),
and resistors
(R70,
R71,
R72).
This circuit feeds back the
output voltage level status through a
photocoupler
to the primary switching circuit to control
the ON/OFF time
of
the switching transistor for constant output voltage control.
Rev. A
2-11