Pioneer PL-200 Service Manual page 18

o
Drive
Circuit
1.
The
signals
employed
in
the switching
of
Q2
-
Q7
in
Fig.
7-6 are generated
by
3
Hall elements,
and applied
to
terminals
a, b,
and
c
via
the
position
signal
formation circuit.
2.
"lhe
phase
of
these step waveform signals
is
displaced
by 120' from
each
other.
3.
When
the
step waveform signals
at
position I
in
Fig.
7-7a are applied
to
the
drive circuit
terminals a,
b,
and c, the potential at terminal
a
will
be lowered, resulting
in
Q2 being turned
on.
The potential at
terminal
b will
be
raised,
resulting
in
Q6
being turned
oh, but
the
potential
at
terminal
c will
remain
at
the
reference
level voltage (the bias
settings for
Q4 and Q7
have been designed
to
prevent
these
2
transistors
from
operating when
a
reference level voltage
is
applied).
4.
Vcc
will
thus be applied
across
the
Q2
-
coil
La
-
coil Le
-
(2)
-
Q6 route, thereby
pro-
ducing an S polarity
in
La,
and an
N
polarity
in
Ls.
5.
Once
the
magnetic
field
is generated, the rotor
will
commence
to
rotate. After the rotor
turns
through 15'
,
the
signals at
position II
in
Fig. 7-7b
will
be applied
to
terminals a, b, and c, thereby
resulting
in
a
change
in
the flow
routes
of
the
drive currents.
After the rotor turns
through
another
15',
the
signals
shown
at position
III
in
Fig.
7-?-c
will
be applied,
again
resulting in
changes
in
flow
routes
of
the drive
currents.
For every 15' that the rotor turns through,
the
flow
routes
for the
drive currents
will
change
as shown
in
Figs. 7-7d, 7-7e, and 7-'7f, finally
returning to the routes shown in Fig.
7
-7
a
again.
6.
A
control voltage
generated
by the
forward/
reverse
direction discriminator indicator circuit
is applied
to
the control input terminal, thereby
controlling the
flow of
current
in
the
coils.
1A
Fis.7-6