Table of Contents
Advertisement
ad oe Ae
5.1.7 Phono Motor Circuit
The phono motor of this player uses magnetism along
the outside edge of the drive magnet to determine its rpm
value. (Formerly, a separate magnet was needed in addition
to the drive magnet.)
This motor uses a PA2017 as its control drive IC and a
crystal oscillator circuit in the oscillator circuit unit. Also,
since this motor
is brushless and coreless, the position of
the rotor magnet is detected by two Hall elements HA and
HB, which
make the motor turn by switching the current
to the drive coil electronically. When voltage is applied to
the whole
elements
HA and HB, a voltage differential
is
created in the output interval by the magnetic field of the
approaching rotor. The Hall elements HA and HB are also
attached 90° electrically out of phase so their output sig-
nals have a 90° phase difference. (See Fig. 5-13)
After the output voltage from the Hall elements have
been amplified by the PA2017
Hall amplifier,
it enters a
position
signal
composite
circuit
(See
Fig. 5-15).
The
output from the position signal composite circuit is then
input into the respective drive amplifiers. The coil current
at this time is as shown is figure 5-13 coils
A and B. This
current produces a magnetic field in the drive coil, and the
polarity of the coil and the polarity of the rotor attract and
repel each other causing the motor to start turning.
When the motor starts turning, the signal (approximately
0.5mV
p-p) produced
by a frequency generator (FG) in
the mtor rotation unit, is amplified to about 0.3V p-p by
Pin 22 HAt
Pin 21 HA—
Pin 20 HB+
Pin 19 HB—
Coil A
Pin 1 waveform
seen with pin 2
as reference
Coil B
Pin 23 waveform
seen with pin 24
as reference
Fig. 5-13 Hall Elements and Coil Terminal Waveforms
13
an FG amplifier (5, Q6) and is input into the FG ampli-
fier (input pin 17) inside PA2017.
Possible frequencies at
this point are 55.55 Hz for 33 rpm and 75 Hz for 45 rpm.
The
signal
then
undergoes
waveform
shaping
in the
Schmitt transistor, and is then input into the reset circuit,
the sample and hold circuit and finally the timing circuit
for a timing pulse for the phase comparison circuit. In the
PDO0008, the crystal generated 6.144MHz frequency is divi-
ded into 1.5kHz (a division of 1/4096) by the frequency
divider circuit. This signal is further divided by a dividing
ratio selection circuit to 55.55Hz for 33 rpm (a division of
1/27) and to 75 Hz for 45 rpm (a division of 1/20). These
pulses are output to PDOOO8
pin 15. This reference pulse
from
PD0008
and the signal from
the timing circuit of
PA2017
undergo
phase comparison
in the phase compa-
rison circuit. Output pulses can then be made in reference
to the phase difference. Because these pulses speed up the
charging time constants
of their output sections,
P —
V
conversion
takes
place.
Also,
F —
V conversion
takes
place in those sections of the sample and hold circuit and
the reset circuit when
there is no output
pulse from the
phase comparison
circuit. As a result, voltage which
has
undergone P — V and F — V conversion is output to pin 8.
This output is then amplified by the buffer amplifier and
input into the V — | conversion circuit. The V — | con-
version circuit controls the current that flows into the drive
circuit based on the difference between the output of the
buffer amplifier and the referance voltage (1/2VCC2).
Drive circuit current
Steady rotation
operation point
ie)
-<-__—_
+
Voltage between pin 10 and pin 11
Crystal!
Oscillator circuit
Hail amplifier +
Position signal
composite circuit
'Sample and
hold circuit
Toall
blocks
regulator
circuit
indicator
circuit
1/2 VCC,
circuit
¢))
vec
a
r
Bo
|
i
(8)
(2)
i
2
G 33/3: H (OPEN)
4h
ib
G START:
H (OPEN)
pk
STOP
Fig. 5-15 Phono motor circuit
(Approximately 0.3V p-p)
3.7V
en Cl
oh
hat
2.3V
ZV
OV
0.86 msec
"i
2.1V
Pin 14
ans |
|
1.4v
TAV
Pin 13
| zs
| J
| e
Ov
'
'
'
t
4
i
4
1
'
t
3.6V
Pin 6
Ov
Pin 10).
3.6V
Fig. 5-16 Phono Motor Circuit Waveforms
14
Advertisement
Table of Contents
