Sharp AL-1000 Manual De Servicio página 89

Circuit descriptions
(1) Main section
a. Noise filter circuit
The noise filter circuit of the DC power is composed of
L and C as shown in the figure below. It reduces normal
mode noises and common mode noises which come
from and go to the AC line.
The normal mode noises are noises which are gener-
ated in the AC line or the output line and are attenuated
by C4B and C3. The common mode noises are noise
voltages generated between the AC line and GND, and
are attenuated by L1 and L2. The noise composition is
bypassed to GND through C4 and C5.
b. Rectifying/smoothing circuit
The AC voltage of 50(60)Hz is full-wave rectified by the
rectifying diode DB1 and smoothed by the smoothing
capacitor C6.
TH1 is the power thermistor which limits a rush current
flowing to C6.
C. Invertor circuit
The DC voltage from the rectifying/smoothing circuit is
supplied to the secondary side of transformer T1 by
switching operation of FET Q1.
For switching, the RCC (Ringing Choke Convertor) sys-
tem is employed.
FET Q1 is turned on by the starting resistors R20 and
R1 to generate a voltage between terminals 4 and 6 of
transformer T1 and between terminals 2 and 3 simulta-
neously. Then a voltage is applied to the gate of FET
Q1 to oscillate high frequency.
The actual line in the circuit diagram shows the current
to turn ON FET Q1, and the dotted line shows the cur-
rent loop through which the energy accumulated in the
transformer is discharged when FET Q1 is turned OFF.
d. Rectifying/smoothing circuit on the secondary side
The high frequency pulse generated by the invertor cir-
cuit is dropped by transformer T1, rectified by diodes
D51, D52, and D53, and smoothed by capacitors C51,
C52, C53, and C54.
12-18
AL-1000/1010
Voltage across Q1 drain and source (VDS)
Q1 drain current (ID)