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12. CIRCUIT DESCRIPTIONS
12.1
SIMPLE SIGNAL PATH
The
PL-8F
motor
drive circuit consists of the
control IC PA2007,
reference phase generator IC
PD1007, motor drive IC PA2008, and IC TD62503P
functioning
to
produce
the various
operational
switch signals.
The
signal picked
up
from
the speed sensor
section is amplified
by the FG amp, then convert-
ed to the speed sensor
signal voltage (DC) by the
F/V converter.
Reference phase voltage is obtained by extract-
ing the reference phase from PD1007 pin 15, pass-
ing it through
the
1/2 divider, then sending it
through the P/V converter to be used as reference
phase voltage (DC).
The speed sensor
signal voltage and reference
phase
voltage
are
each passed through
a buffer
amp
and
resistance
and
combined
(compared).
The resulting voltage is taken from the IC PA2008
pin 6 and input into the absolute value amp, and
is used to control the 4-phase drive circuit motor
rotation voltage, maintaining the motor at a fixed
speed.
12.2
SPEED SENSOR SECTION
1.
The
speed
sensor
board consists of a single
printed circuit.
2.
Above
this, rotates a rotor with 200 magnet-
ized poles on its lower face.
Output varies
in accordance with the rotational speed of the
rotor.
3.
The output (frequency) from the speed sensor
board is 55.5Hz for 33 1/3 rpm and 75Hz for
45 rpm.
4.
The
output
signal is sent to PA2007
as a
balanced input.
12.3
FG AMP
In order to square the waveform
of the signal
obtained
from the speed sensor section (output:
0.5 — 2.0 mV rms) prior to inputting it into the
F/V converter,
it is amplified 69dB across a band
width of 20 to 160Hz.
12.4 F/V CONVERTER
1.
Since the rotational speed is detected at a fixed
frequency,
the frequency
must
be converted
to a voltage (DC).
This function is performed
by the F/V converter.
2. Previously
(in PA2004)
this was done by a
2-frequency F/V converter, however, increasing
control gain of PA2007 allows a signal-frequen-
cy F/V to be used.
3.
F/V converter gain does not change even with
rpm changes.
4.
Switching reference frequency is shown in Fig.
12-1.
When the switch is OFF, speed is set to 33 1/3
rpm, and when the switch is ON, the variable
resistor
used
by
33
1/3
rpm
is connected
parallel to the 45 rpm variable resistor.
The
resulting
total
impedance
establishes
rotat-
ional speed.
Thus, each time 33 1/3 rpm is
adjusted, 45 rpm must also be adjusted.
This
arrangement
prevents
any
rotational
instabi-
lity that might result from both switches being
temporarily OFF when speed changes are made
by switching from 33 1/8 — 45 rpm.
5.
Co,
Ct, Rt, and
Rfv are each
connected
to
ground, but the grounding point is very close
to that of PA2007.
Also, Rt is a 0.01
uF
ceramic
capacitor
for noise
and
oscillation
removal,
and
it is grounded
in close
prox-
imity to PA2007 too.
-——_¢——__-O
Rt
45 rp.mZ
z 33 1/3 r.p.m
ie
sw\,
7
™7™
Fig. 12-1 Switching reference frequency
12.5
REFERENCE
PHASE
GENERATOR
IC
PD1007
1.
When
power is turned ON, the X'tal oscillator
block
generates
a 6.144 MHz
signal by using
the externally connected crystal oscillator.
2. This is reduced to 1.5kHz by divider circuit 1
(1/4096),
then this divided signal is input to
divider circuit 2.
3. The 1.5kHz
signal input to divider circuit 2 is
further divided 1/27 for 33 1/3 rpm operation,
and 1/20 for 45 rpm, then transmitted from
pin 15 to PA2007 pin 7.
33 1/3 rpm: 55.5Hz
45 rpm: 75Hz
33
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