Sony VPL-FX50 Manual page 66

(3) Timer Function
As a watchdog timer function is incorporated inside
the IC1000, no external oscillator is required. When
the current flowing to the chalk coil L1002 reaches
zero and the drive output becomes OFF for more than
620 µs, the timer automatically starts or restarts the
pre-converter.
(4) Internal over-voltage comparator
To prevent abnormal output voltages, the control
IC1000 is equipped with an over-voltage comparator.
This comparator turns ON at initial startup, when the
load changes suddenly, and when the output ripple
increases. The over-voltage comparator monitors the
peak output voltage of the converter, and turns OFF
the FET Q1008 immediately after the reference value
is exceeded.
The threshold value of the comparator is set to 1.08 V
in the control IC1000.
(5) External over-voltage comparator
In view that the internal over-voltage comparator does
not function because the control IC1000 performs
abnormal operations, an over-voltage protection circuit
composed of the shunt regulator IC1001 has been
equipped externally.
The voltage in between the two ends of R1049 moni-
tors the output voltage.
When this potential reaches 2.495 V(428 V as output
voltage), IC1001 is turned ON to operate the latch
circuit which is composed of Q1003, Q1004, etc., and
turn OFF the control IC1000.
(6) External Pre-drive Circuit
Although the control IC1000 is equipped with a totem
pole output stage, generation of a heat would be rather
strong due to the selection of a surface mount device,
when driving a FET of a large input capacity.
To suppress this heat, added the pre-drive circuit,
composed of Q1006 and Q1007, in the stage just prior
to the FET Q1008.
(7) Details of Parts
. L1000
Chalk coil to eliminate noise components in
the common mode
. D1002
Bridge Rectification Diode rectifying AC
voltage into both waveforms.
Adopted 800V Voltage tolerable taking account of
4-6
of voltage changes in the market.
. R1000
Resistor to limit a rush current at AC voltage input.
. RY1000
Relay to short-circuit a R1000 immediately after
AC voltage input.
. Q1008
Switching FET of the active filter that is performed
by PWM control of IC1000.
. L1002
Chalk coil for the active filter.
It accumulates energy when Q1008 is ON
and supplies a current to the later stage when ON.
. D1009
Rectifying Diode for the active filter.
Adopted fast recovery diode for high voltage
to lerance and high speed ON/OFF.
. C1013, C1016
Smoothing capacitor for the active filter that
rectifies the half wave after bridge rectification
during stand-by.
Supply DC voltage to the sub-converter in the
later stage. Recharge and discharge the step-up
converter when the active filter is working.
. IC1000
IC to control an operation of the active filter.
. R1037
Resistor to detect a current.
A current flowing to the active filter is input to
IC1000 by the potential in between the two ends
of this resistor.
VPL-FX50