6300
accomplished by taking the output
of
the
VCO
and counting
it
down with the Sector
Pll
Countdown Counter.
The
specific countdown value is programmed by the Countdown
Programming Array and the output of the counter is converted to a square
wave
by the
Sector Countdown Divider Flip-Flop. The outputs
of
the Sector Countdown Divider
Flip-Flop
are
compared with the Phase
lock
Flip-Flop output by the Phase Comparator.
The
output of the Phase Comparator is suitably filtered and applied to a
Sum-And-Difference Amplifier which generates the control voltage
for
servoing the
frequency of the
VCO.
This causes the output
of
the
VCO
to become phase-locked to the
phase lock pulses obtained from the phase-locked ring.
The
output of the
VCO
may be taken directly or the frequency may
be
divided by a factor
of
2 by the
VCO
Divider Flip-Flop and applied to the Sectoring Selection Programming Array
for purposes
of
selecting the specific electronic sectoring configuration. This
high-frequency oscillator signal is then frequency divided by the
Sector Countdown
Counter for the particular platter. The exact value
of
a count used for the division is
determined by the respective Electronic
Sector Programming Array. The count is
synchronized to a specific platter by the associated synchronizer in conjunction with the
index pulse derived for use with that particular platter. The pulse train output from the
particular sector countdown counter has a repetition rate corresponding to the number
of
desired sectors
as
programmed by the respective Electronics Sector Programming Array.
This pulse train is synchronized with the respective index pulse.
When electronic sectoring is selected by the Sectoring Selection Programming Array, this
pulse train is fed directly to the respective pulse former.
4.8
MOTOR
CONTROL
A functional element
of
disk rotational speed control is provided by the Motor Control
circuitry.
The
current switching necessary to control drive current for the drive motor is
provided
by
this subsystem. Additionally, provisions are made to accommodate drive
motor operation at different line voltages in
this
subsystem.
The
disk drive motor is a permanent split-phase induction motor with multiple windings to
accommodate the two classes
of
line voltage operation. A permanent split
induc~ion
motor requires the use of a capacitor
or
other type of phase shifting arrangement
connected
in
series with the start winding (or windings). This is done to provide a current
in
that winding, phase shifted with respect
to
the main winding, such that the net
magnetic field produced by the windings is a pseudo rotating magnetic field.
In
the
D3000
Disk Drive, motor capacitors mounted on the power supply chassis are connected to
provide the phase
shift
of
current in the start windings with respect to the main winding.
For
11
Ov
operation, main winding number 1 is connected in parallel with main winding
number 2
and
Is operated directly from the line voltage. Current through the winding is
switched
on
and
off
by a triac on the Motor Control PCBA. For
220v
operation, main
winding number 1 is connected in series with main winding number 2 and the series
combination
of
these windings is operated directly from the line voltage.
The
current is
switched
on
and
off
by the triac on the Motor Control PCBA. The motor capacitors
are
parallel-connected for 110v operation and series-connected
for
220v
operation.
Therefore, the effective arrangement for
110v operation is that the parallel combination of
the motor capacitors is connected in series with the parallel combination
of
start winding
number 1 and start winding number
2.
This parallel series network is operated directly
from the line voltage and is not switched by the triac. For
220v
operation, the series
4-30
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