Panasonic KX-B620 - Main Unit

KX-B620 Series
KX-B520 Series
2-6
Lamp
Drive
Circuit
1) Function
Lamp
drive
circuit
is
on
the
power
supply
board.
Control
signals
for
Lamp
drive
circuit
are
supplied
from
CPU.
Lamp
driver
lights
the
fluorescent
lamp
at
high
frequency
to
prevent
flickering.
It
also
preheats
the
filament
just
before
turning
it
on
to
reduce
blackening.
(increase
its
life)
2)
Circuit
Operation
CPU
makes
two
signals,
LAMPPRE
and
LAMPTON.
Timing
is
shown
below.
LAMPPRE
LAMPTON
Approx 2.5 sec.
Fig. 24 Timing Chart
Transistor
Q4
in
the
Lamp
Driver
turns
on
by
the
LAMPPRE
signal,
so
preheat
current
flows
through
the
Lamp
filaments.
Then
self
oscillating
circuit
composed
of
Q1,
Q2,
T1,
C23
and
L4,
start
oscillating
at
about
47
kHz
by
the
LAMPTON
signal.
It
supplies
AC110V,
47
kHz
power
source
to
the
Lamp,
so
the
Lamp
turns
on.
CONTROL BOARD
MAIN UNIT
Fig. 25 Circuit Diagram
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