Panasonic KX-B620 - Output System; Block Diagram

KX-B620 Series
KX-B520 Series
3. MAIN UNIT
3-1.
+24V
Output
System
3-1-1.
Description
of
Operation
1C3
is
the
single
output
regulator
for
24V
using
step-down
chopper
with
cut-off
function.
Figure
below
shows
the
block
diagram
of
IC3.
AC
voltage
is
supplied
from
pins
1
and
2
of
|C3,
full-wave
rectified
by
D3
is
stored
at
capacitor
C13.
When
the
charging
voltage
of
C13
exceeds
DC28V,
pin
12(cut-off
terminal)
of
IC3
becomes
high,
IC3
is
activated
and
DC+24V
is
sent
to
pin
2
of
IC3.
L11
and
L12
are
choke
coils,
and
R13
and
C21
are
for
switching
pulse
reduction.
BLOCK DIAGRAM
Vin
©
SW.OUT
Vin
©
@
SW.OUT
© F.WHEEL
lo SENSE 2
lo SENSE 1
sw. =I
@
®
@ vo SENSE
CONTROL ®
C3
CUT OFF
© GND
SUB
3-1-2.
Overvoltage
Protection
Circuit
OVP
Detects
the
output
voltage
of
1C3
at
pin
2
of
C3,
feedback,
and
sets
it
between
the
range
of
DC23.6V
to
DC24.4V.
When
the
output
voltage
exceeds
27V,
zener
diode
ZD1
(27V)
is
activated
to
restrict
the
voltage
to
27V.
3-1-3.
Over
Current
Protection
Circuit
+CLM
When
the
output
current
exceeds
DC10A,
the
voltage
generated
at
resistor
R12
between
pin
3
and
4
of
C3
is
detected
at
pin
4
of
1C3,
over
current
protection
is
activated
to
shut
down
the
output.