Panasonic PANAFAX DF-1100, Service Manual

Page: 233 / 333

System Description
6–37
ETXDN036E4C (220
ƞ
240V)
Input Filter Circuit
AC line voltage travels to the rectifying circuit through the line filter. The line filter eliminates RFI noise which
may otherwise pass to the AC line from the power supply unit. It also protects the power supply unit from
transient noise which may pass into the unit from the AC line.
Rectifying and Smoothing Circuit
As soon as power is applied to the Power Supply Unit, AC line voltage is rectified by D101 and is smoothed
by capacitor C107. The protection circuit at the time of startup is controlled by an IC (MC101) and resistors
R107, R108 and R109.
Inrush Current Protection Circuit
When the capacitor C107 is not charged by the AC input, an inrush current, or current surge, appears at the
input side. Power thermistor TH101 limits the inrush current.
Converter Circuit
A hybrid IC (MC101), in combination with transformer T1, form a switching power supply circuit using the
RCC (Ringing Choke Converter) system.
Ei
Eo
D203
P --- Primary Winding
S --- Secondary Winding
B --- Control Winding
T101
Q102
P
B
Control Circuit
S
+
Main Switching Circuit
In the above circuit, when the main switching transistor, Q102, is turned On, input voltage, Ei, is supplied
to the primary winding of transformer T101. However, no current will flow through diode D203 of the
secondary side, due to reverse polarity of the secondary winding causing no current flow within T1. But the
transformer charges with energy. When Q102 is turned Off, the supply voltage to the primary winding shuts
off and the windings of T101 change polarity, allowing D203 to conduct, releasing the energy accumulated
in T101 to the circuit. When the energy is discharged through D203, Q102 turns on, once again reversing
the polarity on T101 windings, creating a self–oscillation circuit.