Heathkit SB-401 - POWER SUPPLY

Page 136
720 VOC
250 MA
FULL LOAD
Figure 6-15
250 vDC
100 MA
FULL LOAD
-170 VOC
NO LOAD
POWER
SUPPLY
(Figure
6-15)
Four silicon diodes are used to rectify the AC
voltage
developed
across
the
high
voltage
sec-
ondary
winding
(red
and
red-yellow
leads)
of
the
power
transformer,
These
diodes,
D5
through
D8,
are
connected
in
a
full-wave
voltage-doubler
circuit,
The
diodes
are
connected
so
that
during
one-
half
of
the
AC
cycle,
capacitor
C78
becomes
charged;
and
during
the
next
one-half
of
the
AC
cycle,
capacitor
C79
is
charged,
resistors
R44
and
R45
provide
a
discharge
path
for
these
capacitors,
The
capacitors
are
charged
individ-
Gag neatTuxit:
240 VAC WIRING
BLK-RED
2 AMPERE
SLOW-BLOW
FUSE
Leen eee eee eee oes
BLK-RED
4 AMPERE
SLOW-BLOW
FUSE
ON-OFF
(ON FUNCTION
O “switcH)
ACCESSORY
SOCKET
VIEWED FROM
CHASSIS REAR
* 120 VAC PRIMARY WIRING
ually
but
discharge
in
series
to
produce
a
DC
voltage
equal
to
approximately
twice
the
applied
peak
AC
voltage,
Because
of
the
large
capac-
itance
of
C78
and
C79,
the
output
of
the
voltage
doubler
has
low
ripple
and
excellent
dynamic
regulation,
The
low
voltage
secondary
winding
(brown-
yellow
and
blue
leads)
applies
95
volts
AC
(rms)
to
a
half-wave
voltage-doubler
circuit,
consist-
ing
of
diodes
D3
and
D4,
capacitors
C81,
C77A
and
C77B,
and
the
filter
choke,
The
use
of
a
high
capacitance
input
pi-filter
network
provides
a
well
filtered
DC
output
with
a
low
percentage
of
ripple.