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8.2.1
HALL EFFECT TRANSDUCER
This magnetic transducer is located within the spindle hub. It senses spindle po-
sition and provides dynamic feedback proportional to motor speed. Two com-
plete square waves are generated for each revolution. This positional information
is supplied to both the speed reference circuits and motor driver control transis-
tors. To prevent both phases of the motor from being selected simultaneously,
transistor 2A inverts the Hall input to coil A.
8.2.2
SPEED REFERENCE CIRCUIT
Using the charge time of C5 as a standard, comparator lA, pin 2, will output
a low pulse indicative of speed error. The charge time of CS is set at the factory
by adjusting R2 to 3,600 RPM nominal.
8.2.3
PULSE SHAPER
This circuit smooths out the incoming error pulses for ease of integration.
8.2.4
INTEGRATOR
Speed error information is integrated and transformed into usable levels by IC
lA (pin 7) whose output determines the current flow per revolution through each
motor' phase.
8.2.5
CURRENT LIMIT
Transistor Q6 senses the current level drawn during motor start-up and limits
it to 3.S Amps by controlling the "on time" of 2A (pins 3, 12).
8.2.6
MICROPROCESSOR: MOTOR ON
This signal is maintained low by the microprocessor as long as the index sensor
indicates motor spin-up within a specified periode If the motor does not rotate
the signal is set high and motor current is removed. This circuit prevents damage
to the PCB and motor if, for sorne reason, rotation cannot occur.
8.2.7
MOTOR DRIVERS
Current is supplied to both motor phases by IC 3A. Hall information is used
to supply current to the correct phase, while the integrator error information
controls the current level.
8.2.8
DYNAMIC BRAKE
At power on C12 is charged up. When power is interrupted, C12 becomes the
source keeping QI, Q2 and Q3 on. At this time, transistor Q3 shorts both motor
phases to ground allowing motor generated EMF to bring the spindle to a stop.
32
ST212 PRODUCT MANUAL/Rev. B
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