Sony PVM-9L2 Service Manual page 39

5-2.
G
Board
The power supply block of
this
board
consists
of the
following
two
switching regulators.
1
.
The power
regulator for
improving
power
factor to
conform
to the
power
supply
harmonics
regula-
tion.
2.
The power
regulator for the
main power
supply
that
supplies the
necessary voltages
to
the signal
system
circuit
and
to the deflection
and
high voltage
circuits.
Power
factor
improvement
block
The power
factor
improvement block
uses the active filter
IC module
(IC666) of
the
current-critical
type
boost-chopper
system
to
conform
to
the
power
supply
harmonics
regulation.
The power
factor
improvement
block consists
of IC666,
T602, C630,
C615
and
the related parts.
IC666
is
the
module IC
containing control IC,
switching
FET, boost diode
and
input/output voltage
detector inside the
module.
The
basic operation of the
power
factor
improvement block
is
described below.
When
the
VCC
power
is
supplied,
it
turns
on
FET
so
that
a current
starts
flowing in the
primary winding of
T602 and FET. This
current increases
with the slope of
Vin (RMS)/L. Here,
L
is
the inductance value of the
primary winding
of T602.
The
FET
current
is
monitored
by
the
source current detecting
resistor
connected
between
pin-4
and pin-7 of
IC666.
When
the detected voltage increases
and
reaches the
set
value determined
by
the
multiplier located inside the control IC, the
FET
is
turned
off.
Then
a current that
decreases
with
the slop
of
(Vd
-
Vin (RMS))/L
flows
in
the
boost
diode.
When
this
current
becomes
zero,
the
FET
is
turned on.
By
the circuit
operation as described above, the current-critical
operation
is
realized.
(Vd:
Voltage across
C615,
Vin: Input
power
voltage)
The
above-described
single
cycle of the
circuit
operation
is
repeated
aU
the time.
\Vhen
this circuit
operation
is
observed during a half-cycle
period of a
commercial
power
frequency, the control
IC
controls
the
ON/OFF
timing of the
FET
so
that the
peak
value of the
choke
current resembles to the sine
wave-
form
of the input
power
voltage.
As
the result
of
this
control
by the control IC, the input voltage
waveform
resembles to the
input current
waveform
so
that
the
power
factor
is
improved.
As
the result of this control,
the voltage
Vd
across
C615
becomes higher than
the
peak
value of the input
power
voltage,
and
is
set to
about 380
V
regardless of the
input
power
voltage.
Power
regulator for
the
main power supply
The
circuit
system of
this
power
regulator
is
the separate-excitation
type current
composite resonant
system
that realizes
high efficiency
and low
noise.
The main power
supply block
consists of:
IC603,
IC690, T604, C644,
C623
and
the
secondary
rectifier circuit
of
T604.
IC603
is
the multi-chip
module
in
which
the four chip parts
of control block,
FET
drive block,
switching
FET
block
(high side)
and
switching
FET
block (low
side)
are
coimected together inside the
IC
by
the
bonding
wires.
Circuit
operation of
this
regulator
is
as
follows.
The
two
FET
switches, the
two
capacitors
C644 and
C623, and the transformer
T604 form
a half bridge
rectifier
circuit for
the input voltage
Vd
where
die
secondary
circuit
of
the
transformer
T604
has the
full
wave
rectifier circuit
with center
tap.
IC603 receives the control signal
from IC609
that
performs
the constant voltage control of the
+13
V
line
via the isolator
PH601. This
control signal
changes the oscillating
frequency
and
realizes
the constant
voltage
power
regulation.
5-2
PVM-9L2