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®@ Drive Circuit
1. The signals employed in the switching of Q2 ~
Q7 in Fig.23 are generated by 3 Hall elements,
and
applied
to terminals
a, b, and c via the
position signal formation circuit.
2. The
phase
of these
step waveform
signals is
displaced by 120° from each other.
3. When
the step waveform
signals at position I
in Fig. 24-a 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
on,
but the
(Q) ()
0)
(Vi,
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. Vec will thus be applied across the Q2 — coil
La — coil Lg — (2) — Q6 route, thereby pro-
ducing an S polarity in La, and an N polarity
in Lg.
5. Once the magnetic filed is generated, the rotor
will commence
to rotate. After the rotor turns
through 20°, the signals at position II in Fig. 24-b
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 20°, the signals shown at position III
in Fig. 24-c will be applied, again resulting in
changes
in flow routes of the drive currents.
For every 20° that the rotor turns through, the
flow routes for the drive currents will change
as
shown
in
Figs.24-d, 24-e, and 24-f, finally
returning to the routes shown in Fig.19-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.
oO
Fig. 23
45
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