Sorvall TC6, Руководство по обслуживанию

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System Descriptions SORVALL

Centrifuges
3-4
a. Theory of Operation
The drive is built with Motorola's MC33035 and a support chip
MC33039.
The MC33035 is a 24-pin linear integrated circuit (I.C.) that operates
as the control center for the brushless dc motor control system. The
main functions of MC33035 are to decode the signals from the
Hall-effect sensors and generate logic for electronically commutating
the motor. The commutation logic is internally delivered to the six
output drivers consisting of three open collector NPN transistors
that drive the upper legs of the bridge and three totem pole drivers
that control the devices. The open collector outputs can sink 50 mA.
With some additional circuitry this allows control of either N-channel
MOSFETs for higher power applications or P-channel MOSFETs if a
simple interface is desired. Since the three lower totem pole outputs
can source and sink 10 mA, they can drive power MOSFETs directly.
b. Fault Management
The MC33035 can detect and manage several types of faults. A
common method of overcurrent detection is to tie the sources of the
lower three transistors together and return them to the negative
supply rail through a current sense resistor. The sense voltage,
which is proportional to load current, is delivered into a comparator
on board the MC33035. The comparator then delivers an RS flip-flop,
which ensures that the output drivers will turn off the power
transistors for the remainder of the oscillator cycle if an overcurrent
condition is detected. Without the internal flip-flop, the overcurrent
protection loop would rapidly cycle on and off about the
comparator's threshold, causing excessive power transistor heating.
In addition to overcurrent management, the MC33035 provides
undervoltage lockouts that terminate the drive to the output tran-
sistors if any of three conditions occur:
• insufficient voltage to operate the I.C.;
• insufficient voltage to drive the power MOSFET gates; or
• output drivers turn the power transistors off when the MC33035
does not sustain its on-board 6.25 V reference.
An invalid set of Hall-effect signals or excessive temperature will
also cause shutdown.
Whenever any fault condition exists, an NPN transistor capable of
sinking 16 mA pulls the Fault Output pin low.