Ga Board; Main Converter - Sony VPL-PX20 Service Manual

3-12-3. GA Board

1. Structure
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Active Filter
The active filter improves the power factor of the AC voltage after bridge rectification, and at the
same time, serves as a step-up converter and supplies DC358V± 10V to the lamp power supply in the
later stage, sub converter, and main converter. However, when the maximum AC voltage exceeds the
output voltage of the active filter, the power factor will not be improved correctly.
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Inrush Current Limit Circuit
When the AC voltage is supplied with the electric load of the smoothing capacitors C2112 and C2113
fully discharged, the inrush current flows to the capacitor, and as a result, damage the fuse in the
input stage. To prevent this, immediately after inputting the AC voltage, the inrush current is limited
by R2101. After the operations of the standby converter start, the thyristor D2102 turns ON and
short-circuits the two edges of R2101. (The VPL-X600 series and VPL-SC50 series turn ON the
thyristor after the operations of the main converter start.)
•
Sub converter
The DC voltage obtained by completely rectifying the AC voltage or the output voltage of the active
filter is stepped-down to the GC board input voltage and the VCC for the active filter control IC.
These operations are controlled by IC2102.
. VCC (18.5V± 0.5V)
. GC board input voltage (9.0V± 2.0V)
( ) shows the potential of the connector.
•

Main converter

The output voltage of the active filter is stepped-down to the following signal circuits and AUDIO
circuit. These operations are controlled by IC2101.
However, when no load, the voltage is clamped to about 17.8V by the diode.
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Power protector
Normally, when the main converter is operating, GA/Q2107 turn ON, and the microprocessor port of
the Y board is kept "Low". When the output voltage lines and GND line of the main converter are
short-circuited, GA/Q2107 goes OFF, and the microprocessor port of the Y board is set to "High".
Furthermore, the microprocessor sets the POWER ON signal to "Low", and stops the operations of
the main converter. (At this time, both the TEMP and LAMP LEDs of the control panel light up.)
2. Operations of the Active Filter
•
ON/OFF operations
The active filter starts operations at the same time as the main converter in the later stage. At standby,
Q2106 maintains Pin 8 of IC2100 at "Low", and the active filter does not operate. When the "High"
signal is received from the microprocessor of the Y board, Pin 7 of CN2106 becomes "High", Q2106
goes OFF, Q2104 turns ON, and Q2105 also turns ON. As a result, VCC is supplied to IC2100 and
IC2100 starts operating.
3-16
VPL-PX20/PX30