Sharp UX-A255U, Руководство по обслуживанию

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UX-A255U
[4] Circuit description of power supply PWB
1. Block diagram
[5] Circuit description of CIS unit
1. CIS
Cis is an image sensor which puts the original paper in close contact
with the full-size sensor for scanning, being a monochromatic type
with the pixel number of 1,728 dots and the main scanning density of
8 dots/mm.
It is composed of sensor, rod lens, LED light source, light-conductive
plate, control circuit and so on, and the reading line and focus are
previously adjusted as the unit.
Due to the full-size sensor, the focus distance is so short that the set
is changed from the light weight type to the compact type.
Fig. 8
Fig. 7
5ms
2
µ
s
0V
0.8V~2.9V
(White original paper)
Approx.3.3V
øT
CISCLK
VO
5 – 13
2. Waveforms
The following clock is supplied from SCE214V of the control board,
and VO is output.
Noise
Filter
Circuit
Rectifying
Smoothing
Circuit
Switching
Circuit
VREG
(+5V)
+24V
AC IN
Photo Coupler
2.5A/125V
FUSE
4A/32V
Control
Circuit
2-1. Noise filter circuit
The input noise filter section is composed of L1 and C1, which reduces
normal mode noise from the AC line and common mode noise to the AC
line.
2-2. Rectifying/smoothing circuit
The AC input voltage is rectified by diode D1, 2, 3, 4 and smoothed by
capacitor C2 to supply DC voltage to the switching circuit section.
2-3. Switching circuit
This circuit includes MOS FET Q1 and the gate drive circuit, and com-
ponents around Q1.
In this circuit, the DC voltage supplied from the rectifying/smoothing
section is converted into high Frequency pulses by ON/OFF repetition
of Q1.
2-4. Control circuit
This circuit controls output voltage of +24V by adjusting ON period of
Q1, looking at signal from photo coupler PC1.
In this operation PC1 takes charge of important part.
The over current protection is performed by bringing Q1 to OFF state
through detection of voltage of T1 Subwiding.
The over voltage protection is performed by operating the over current
protection circuit through detection of Zener diode ZD4 and short-
circuiting of load.
2-5. VREG(+5V) circuit
DC voltage supplied by rectifying the output of transformer T1 with di-
ode D8, C10.