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N(r pm)
Phase-locked area
F-V
output
Vo
discrimination
threshold
— f (Hz)
Fig. 4-8 F/V converter output
Fig. 4-9 Phase-locked discrimination theoretical circuit
= Stop Discriminator Circuit
1.
Depressing
the
START/STOP
button
of the
PL-L800
transmits
a stop signal generating a
reverse
torque
and
applying
a brake
to the
motor.
Motor rotation stops almost immedi-
ately.
2.
The
stop
discriminator
circuit
functions
to
detect low or high rotation speed through the
charge/discharge
status
of
capacitors
and
resistors
connected
to
IC
PA2007
pin
10
(To/STOP),
and
when
rotation
drops below
a certain
speed, motor
torque is dropped to
zero.
<A theoretical circuit diagram is shown
in Fig, 4-10.
3.
After
that, the platter turns
a small amount
pasoo?
Stop discriminator
circuit
a
due to inertia, then stops.
R/S
FF
Normally
mon-conducting
PA2008
O——_
—
ref H
Phase-locked area
LOCK
LED
No-load operating point
= Absolute Value Amp and Rotation Direction
Indicator Circuit
The signal at the 6 pin (control input) is com-
pared with the signal at the 5 pin (reference
voltage) and the difference in voltage is used
to
generate
current
in the
motor
winding.
The
input/output
characteristics
are
shown
in Fig. 4-11.
The control input is higher than the reference
voltage
(Vref 5V) when
the rotation
of the
platter is higher than specified speed.
When
this occurs,
the absolute value amp
sends an
indication
(instruction) to the rotation direct-
ion indicator circuit to generate reverse torque
in order to drop the speed of the motor.
The control input is lower than the reference
voltage
(Vref 5V) when
the rotation
of the
platter is lower
than specified speed.
When
this occurs,
the absolute value amp
sends an
indication
(instruction) to the rotation direct-
ion indicator circuit to generate forward torque
in order to increase the speed of the motor.
control current
Reverse torque region
Forward torque region
No-load operating
point
0
( Vref —Vin )
Fig. 4-11
Input/output characteristics
Comparator
reference
voltage
/
Lev
GNO
PA2008
Absolute value amp
4-phase drive circuit
Fig. 4-10
Stop discriminator theoretical circuit
16
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