Sharp FO-475TH, UX-258TH Circuit description of power supply PWB, Circuit description of CIS unit

UX-258TH

FO-475TH

[4] Circuit description of power supply PWB

1. Block diagram F1

T1.25A/250V

AC IN

F2

T1.25A/250V

Noise

Filter

Circuit

Rectifying

Smoothing

Circuit

Switching

Circuit

(RCC system)

Regulater +5V Circuit

+24V F3

4A/72V

2-1. Noise filter circuit

The input noise filter section is composed of L and C, 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 C5 to supply DC voltage to the switching circuit section.

Power thermistor TH1 suppresses inrush current at power switch-on.

Photo Coupler

Fig. 7

The overcurrent protection is performed by bringing Q1 to OFF state through detection of voltage increase in the auxiliary winding of T1 by ZD2 and R9.

The overvoltage protection is performed by operating the overcurrent protection circuit through destruction of zener diode ZD4 and short- circuiting of load.

2-4. +5V circuit

Each DC voltage supplied by rectifying the output of transformer T1 with diode D8 is stabilized by 3-terminal regulator IC1.

2-3. Switching circuit

This circuit employs the self excited ringing choke convertor (RCC) sys- tem. In this system, the DC voltage supplied from the rectifying/smooth- ing section is converted into high frequency pulses by ON/OFF repeti- tion of MOS FET Q1.

Energy is charged in the primary winding of T1 during ON period of Q1, and discharged to the secondary winding during OFF period.

The output voltage is controlled by adjusting ON period of Q1 which changes charge time of C9 through operation of photo-coupler PC1 from +24V output.

2-5. VTH circuit

VTH output is supplied through the relay RY1. Relay RY1 is operated by VTH-ON signal.

[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.

2. Waveforms

The following clock is supplied from FC200 of the control board, and VO is output.

5ms

øT	Approx.5V
	0V
	2∝s
CISCLK
VO	2V(TYP)
	(White original paper)

Fig. 8

5 – 11