Panasonic UF-580 Service Manual page 218

DZEA000057
Input 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 Circuit
AC power is rectified by D100 and charges C103 to make high DC voltage, then supply power to
converter circuit.
Kick-on voltage for control IC (IC105) is supplied AC power through R134, R135 and R136.
Inrush current is limited by TH100.
Converter Circuit
A IC (IC105), in combination with transformer T100, form a switching power supply circuit using the RCC
(Ringing Choke Converter) system.
As soon as power is applied to the Power Supply Unit, AC line voltage is rectified by D100 and is
smoothed by capacitor C103. The protection circuit at the time of start-up is controlled by an IC (IC105)
and resistors R134, R135 and R136.
Ei
Q100
Main Switching Circuit
In the above circuit, when the main switching transistor, Q100, is turned On, input voltage, Ei, is supplied
to the primary winding of transformer T100. However, no current will flow through diode D102 of the
secondary side, due to reverse polarity of the secondary winding causing no current flow within T100.
But the transformer charges with energy. When Q100 is turned Off, the supply voltage to the primary
winding shuts off and the windings of T100 change polarity, allowing D102 to conduct, releasing the
energy accumulated in T100 to the circuit. When the energy is discharged through D102, Q100 turns on,
once again reversing the polarity on T100 windings, creating a self-oscillation circuit.
T100
P
B
Control Circuit
P --- Primary Winding
S --- Secondary Winding
B --- Control Winding
D102
Eo
+
S
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