Akai VS-X9EGN

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8-3. OUTPUT REGULATION
The output voltage regulator serves to hold Vout, the
voltage output of coil Ls of transformer T1, at a steady
level.
Since
the
voltage
across
diode
D6
is
held
steadily
at
5V
the
TR4
base
voltage
will
be
held
at
about
5.7V.
As
voltage
Vout
climbs
up,
the
TR4
base
voltage
will
R8
R8+R9
collector
current,
IC,
will
be
increased,
and
the
photo-
coupler
PH-1
current
also
will
similarly
be
increased.
The
PH!
collector
current
will
therefore
be
increased
as
well,
and
ultimately,
the
TR2
emitter
current
will
similarly be increased.
For
the
above
reason,
current
“ib”
which
flows
from
coil
Ls
into
the
TR1
base
will
be
reduced
by
the
shunt-
ing
effect
of
TR2,
and
the
TRI
collector
current
as
well
the
voltage
across
coil
Ls
will
also
be
reduced.
As
Vout
drops
down,
a
reverse
phenomenon
to
the
above
takes
place,
where
the
TR2
emitter
current
is
reduced
to
increase
the
TR1
base
current.
See
Fig.
8-10.
>
also
rise.
(vb
=
Vout
)
In
consequence,
the
TR4
The
negative
voltage
similarly
generated
by
utilizing
the
pulses
that
have
been
generated
at
the
turning
off
of
TRI
will
also
vary
in
level
in
accordance
with
the
TR1
collector
current,
and
contributes
to
the
voltage
regula-
tion.
See
Fig.
8-11.
Capacitors
C4
and
C20
connected
together
in
series
have
been
arranged
as
a
safety
measure
in
case
one
of
them
happens
to
break
down
and
get
shorted.
C7
at
220
uF
prevents
an
inrush
current
to
TR]
at
the
switch-on
of
AC
power,
and
serves
soft
start-up
pur-
poses.
When
testing
the
power
supply
circuit,
be
sure
to
connect
a
dummy
resistor
on
at
the
Reg
6V
Out
ter-
minal,
and
under
no
circumstances
should
it
be
tested
at
no
load.
(Dummy
Resistor:
202,
2W)
The
circuit
generated
frequency
ranges:
from 20kHz (for a heavy load or at a low AC voltage)
to 200kHz (for a light load or at a high AC voltage)
The primary and secondary circuit grounds have been
isolated from each other, so that due caution will be
required especially when testing the primary circuit.
Fig. 8-10
Tl