Epson Stylus Photo 720, Service Manual

Page: 43 / 154

EPSON Stylus Photo 720 / EPSON Stylus Photo EX3 Revision A
Operating Principles Electrical Circuit Operating Principles 43
Figure 2-12. C301PSB/PSE Board Block Diagram
The C301PSB/PSE board has the various control circuits to stop voltage output if a
malfunction occurs on the power supply board or the main board while the printer
mechanism is on duty. Following explains each control and protection circuit.
o
+42V line constant voltage control circuit:
The output level of +42V line is monitored by a detection circuit composed of the
seven Zener diodes. When the output voltage becomes less than 35V, this circuit
prevents the voltage from dropping by driving the primary circuit switching FET.
o
+5V line constant voltage control circuit:
The output level of the +5VDC line voltage is monitored by the regulator IC51. If
abnormal voltage is detected, the information is fed back to the internal
comparator.
o
+42VDC line over voltage protection circuit:
The output voltage line is monitored by two Zener diodes. If the output level of the
voltage level of +42VDC line e48V, this circuit halts the operation of the
switching FET and prevents high voltage from applied to the secondary side.
o
+5V line over voltage/ line over current protection circuit:
This protection circuit is in the same line as the +42V over voltage protection
circuit is located. The output voltage level of the +5V line is monitored by a Zener
diode. This circuit shuts down the +5V line forcefully when the voltage level
e9V.
o
+42VDC line over current protection circuit:
The output voltage is monitored by two transistors. When the output voltage is
dropped abnormally, this circuit regards this as short circuit and halts the operation
of the primary switching FET via photocoupler to prevent over current from
flowing.
F 1
C 1 1
L 1
D B 1
T R A N S ( T 1 )
O v e r C u r r e n t
P r o t e c t i o n
F i l t e r C i r c i u t
F u l l W a v e
R e c t i f i e r c i r c u i t
S m o o t h i n g
C i r c u i t
M a i n S w i t c h i n g
C i r c u i t
Q 1
A b n o r m a l
F e e d b a c k c i r c u i t
Q 2 , Q 3 , Q 3 1
P h o t o
C o u p l e r
P C 1
D 5 1
A C I n p u t
S m o o t h i n g
C i r c u i t
C 5 1
+ 4 2 V D C L i n e
C o n s t a n t C o n t r o l
Z D 8 1 - 8 6 , Z D 5 1
P o w e r D r o p
D e l a y C i r c u i t
C 8 4 , Q 8 4
+ 4 2 V D C L i n e
O v e r V o l t a g e
L i m i t a t i o n
Z D 5 2 , 8 6
+ 5 V R e g u l a t o r
I C 5 1
+ 4 2 V D C
+ 5 V D C
+ 5 V D C L i n e
O v e r V o l t a g e
L i m i t a t i o n
P S C S i g n a l
f r o m M a i n b o a r d
Z D 5 3
+ 4 2 V D C L i n D r o p
L i m i t a t i o n C i r c u i t
Z D 9 0