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Rc
Ayden SR
ARRAN
GS
RR
JL-F50
3. Block Diagram
1)
Reverse
electromo-
tive force
signal
Reference voltage
Comparison
Speed adjustment
voltage
Starting platter revolution (refer to Schematic Diagram
on page 23)
When the speed select knob is set to '33', switch S6 is
closed
(ON).
For 45 rpm, switch S6 is opened. When
the switch S6 is ON, the emitter of X13 is connected to
the earth wire through the resisters for coarse and fine
speed adjustment.
The base of X13 is under a reference
voltage of about 2V and the collector of X13 takes an
earth level, causing the base of X12 to take an earth level
at the same time.
Drive circuit
Switching circuit
Active filter and
DC amplifier
Fig. 1
Switching
|
signal
DC 18V
power supply
6) If current
flows through the base of X12, the platter
rotation is accelerated.
If no base current flows, the rom
of the platter tends to decrease.
The collector potential
of X13
is determined
by its base potential and emitter
resistance.
When
the X13
collector
potential
drops by
more than 0.6V from the reference +18V, current flows
to the base of X12, starting accelaration of the platter
rotation.
7)
An inverse voltage ripple remains in the X12 transistor
collector. This ripple, in nearly 2.2V sine wave form, is
2) This makes conductive,
raising the emitter potential of
added to the direct current.
X11 to make X10 conductive.
8) The Hall element switching output is amplified by X5 —
3) The conducting X10 causes X9 to become conductive.
X8
transistors
to
permit
switching
of
X1
—
X4
In this condition, the emitters of X5, 6 and X7, 8 are
transistors. The collector voltage of transistors X1 — X4
connected to the positive line, allowing the maximum
which drives the motor is approximately 6.5Vp-p.
current to flow.
9) To ensure that the same amount of current flows to X1,
4) Therefore,
the output
of the Hall elements
inside the
2 and X3, 4 voltage across R45 is fed back to XTO.
This
motor
is amplified
to
the
maximum
degree,
and
prevents variations due to the components used.
transistors X1, 2 and X3, 4 connected in series to the
*
Speed adjustment
ee
pee oe
by this output,
starting the
The
rpm of the platter can be changed
by varying the
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collector current
of X13, which
is varied
by changing
its
electromotive
voltage
induced
in the drive coil of the
motor
also
increases
gradually
and,
after
being
rectified by D1~D4 is stored by C5 and R14.
ce ae
emitter resistance.
The rpm drops with
reduced current.
Therefore,
lower
speeds
are
obtained
using
higher
resistances and vice versa.
*
Power supply
The reference voltage of 18V is generated
by a transistor
2SD325(E
or D), and
a Zener diode.
The
non-adjusted
output voltage is about 0..V lower than the voltage of the
Zener diode.
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