Basic Operations Of Sub-Converter - Sony VPL-PX20 Service Manual

2. Basic operations of the main converter
The main converter is composed of the self-excited forward converter operating on the DC voltage
received from the active filter.
The switching and control are performed by IC2101. The oscillating frequency is fixed to about 100
kHz by the internal oscillator for PWM control.
. Transformer secondary operations
i 1
T1
V in
Q1
When Q1 (built-in FET of IC2101 in this case) turns ON, the output voltage of the active filter is
supplied to the primary line T1 of the transformer. At the same time, voltage is induced according to
the number of coils in the secondary coiled line T2.
As the secondary side rectification diode D1 is biased in the normal direction, the current i2 is
supplied. This current flows along the path for recharging the smoothing capacitor C1 in the order of
D1, L1, and C1. The inductance L1 at this time is accumulated with PL energy.
Next, when Q1 goes OFF, no voltage Vin is transmitted from the primary side. Based on the PL
energy accumulated when Q1 is ON, reverse power is generated in the L1 inductor. The current i3
from the L1 inductor flows from L1 to C1, and then to D2, and while Q1 is OFF according to the PL
energy above.

3-12-5. Basic Operations of Sub-Converter

Composed of the RCC (Ringing Choke Converter) which can operate by the DC voltage obtained by
completely rectifying the AC voltage or the output voltage of the active filter. This switching and control
are performed by IC2102. The oscillating frequency is fixed at about 100 kHz by the internal oscillator
for PWM control. During standby, voltage is supplied to the GC board generating the SUB5V for the
microprocessor, and the VCC of the control ICs are also supplied when the main converter and active
filter are operating (POWER ON).
When DC voltage is supplied between Pins 5 and 7 of the transformer T2101, a voltage corresponding to
the number of coils is induced between Pins 8 and 9 of the transformer. IC2102 controls PWM so that the
CONTROL terminal is always 5.7 V (TYP).
3-20
i 2
D1
T2
D2
Fig. 5 Principle of Operations of Main Converter
L1
17.5V
+
AUDIO+B
C1
A6V
i 3
-7V
VPL-PX20/PX30