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= Drive Circuit
1.
The HA and HB Hall elements (6 magnetized
pole pieces fixed to the circumference
of the
motor)
are
attached
electrically
90°
out of
phase
with
each
other.
These
elements
are
used
to sense
the rotational
position
of the
motor.
The position sensing signal produced
by the
Hall
elements
are each
output
to the block
diagram
position
signal
synthesizing
circuit,
and their waveforms
are shaped as shown in
Fig. 4-12.
The
staircase
waves
are each
input into the
block
diagram
4-phase
drive
circuit, and
as
shown in Fig. 4-12, LA and LB alternate back
and forth in a 90° duty cycle (voltage) to turn
the motor.
LA and LB amplitude is in proportion to the
output of the absolute value amp.
90°}
90°!
90°
HA
Solhe
ie
+
Fig. 4-12
Drive circuit waveforms
=
Reverse Rotation Sensing Circuit
a
The motor
used in the PL-L800
is the dual-
direction drive circuit type, and if manually
forced in the reverse direction, it will continue
to apply a forward
torque in an attempt to
restore forward rotation as long as it does not
exceed specified rotation speed.
However,
when reverse rotation exceeds 45 or
33 1/3 rpm,
the rotation
direction indicator
circuit detects this as an overrun in the forward
direction
and
applies
reverse
torque
in
an
attempt to bring it to specified rotation speed.
Reverse
torque applied to the platter already
rotating
in reverse
will
further
increase
the
speed and the turntable will run out of control.
The reverse rotation guard circuit prevents the
platter from running out of control.
The
equivalent circuit of the reverse rotation
sensing circuit consists of a D type flip-flop
(D input output at Q by CK triggering).
PL-L8SOo
Dtype
FF
Absolute value amp
Both
directions
Single
direction
Fig. 4-13
Reverse rotation sensor equivalent circuit
Motor
current control
Control current
Reverse
torque
Forward direction mode
——_—_—_—————e
eek aik
Triggering edge
aot
ek Leh.
Qa
——<—____}-_
Both directions operating
L
Fig. 4-14 Forward direction mode
Control current
Forward
torque
Reverse torque
Reverse direction mode
—_———_—___»
rm eee
got el tel
oH
One side directions operating
L
Fig. 4-15
Reverse direction mode
17
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