Sharp A260 Service Manual - Page 41

[4] Circuit description of power supply PWB 1. Block diagram 3.15A/125V AC IN Noise Filter Circuit Rectifying Smoothing Circuit Switching Circuit Control Circuit UX-A260U FUSE 4A/32V +24V +5V Fig. 7 Photo Coupler 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 components 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 Subwinding. The over voltage protection is performed by operating the over current protection circuit through detection of Zener diode ZD4 and shortcircuiting of load. 2-5. +5V circuit DC voltage supplied by rectifying the output of transformer T1 with diode D8, C10. [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 SCE214V of the control board, and VO is output. 5ms øT 2µs Approx.3.3V 0V CISCLK VO 0.8V~2.9V (White original paper) Fig. 8 5 - 13