Sony VPL-PX20 Service Manual page 72

6. External over-voltage protection circuit
In case the internal over-voltage comparator does not function when the control IC2100 performs
abnormal operations, an over-voltage protection circuit composed of the shunt regulator IC2105 has
been equipped externally. The output voltage is monitored by the voltages of the two ends of R2177.
When this potential reaches 2.495 (428V output voltage), IC2105 turns ON, to turn OFF the control
IC IC2100 operating the latch circuit composed of Q2106 and Q2102.
7. External pre-drive circuit
The control ICIC2100 is equipped with a totem pole output stage, but due to the selection of a surface
mounted device, strong heat is generated when a large input MOS-FET is driven. To suppress this
heat, the pre-drive circuit composed of Q2109 and Q2110 has been added in front of the MOS-FET
Q2100.
8. Details of parts
L2000 Choke coil for eliminating the noise components of the common mode.
D2100 Bridge rectification diode rectifying the AC voltage to both waveforms. Taking into
account the voltage changes in the market, the 800V voltage resistor was used.
R2101 Resistor limiting the bridge current when AC voltage is input.
D2101 Thyristor short-circuiting R2101 when the main converter is operating.
Q2100 MOS-FET for switching the active filter. Performs switching by the PWM control of
IC2100. Taking into account the heat generated by power loss, the current capacity
of 16A is driven in series.
L2100 Choke coil for the active filter. Accumulates energy when Q2100 is ON and supplies
current to the later stage when OFF.
D2108 Rectification diode for the active filter. A fast recovery diode is used for high
voltage tolerance and high speed ON/OFF.
C2112, C2113 Smoothing capacitor for the active filter. Rectifies the half waveform after bridge
rectification during standby. DC voltage is supplied to the sub-converter in the later
stage. Recharges and discharges the step-up converter when the active filter is
operating.
IC2100 Controls the operations of the active filter.
R2101 Current detection resistor. The current flowing to the active filter is input to IC2106
by the voltage of the two ends of this resistor.
3-12-4. Main Converter
1. ON/OFF Operations of the Main Converter
The main converter control IC is IC2101. During standby, Q2103 maintains the ON state. As the
IC2101/CONTROL pin is Low, the main converter does not operate. When the "High" signal is
received from the microprocessor at power ON of Pin 7 of CN2106, Q2103 goes OFF, and the main
converter starts operating.
VPL-PX20/PX30
3-19