Function And Operation Of The Control Circuit; Control Circuit (Block Diagram); Function Of Each Block - Hitachi SP 18VA Technical Data And Service Manual

8. FUNCTION AND OPERATION OF THE CONTROL CIRCUIT

8-1. Control Circuit (Block Diagram)

AC power source
Load current detecting circuit

8-2. Function of Each Block

(1) Rotation speed detector:
Generates a frequency signal proportionate to the actual rotation speed of the motor. A magnetic sensor in the
controller monitors changes in the magnetic flux from a magnet, and generates a frequency signal.
(2) F-V converter:
Converts the frequency signal produced by the rotation speed detector into DC voltage.
(3) Standard voltage circuit:
Generates a standard voltage which determines the no-load rotation speed of the motor and serves as a
reference in maintaining constant rotation speed even when there are fluctuations in the load.
(4) Ramp generator:
Generates the voltage which determines the acceleration of the motor. The soft start function when the motor
is turned on is achieved through a gradual increase of the voltage generated by this circuit. When fully
charged, the voltage of the ramp generator becomes equal to the standard voltage (above).
(5) Differential amplifier:
Compares the voltage from the ramp generator voltages received from the F-V converter (which is
proportionate to the actual motor rotation speed), and amplifies the result.
This circuit functions as follows to maintain a constant rotation speed:
Switch
Standard voltage
circuit
Variable resistor
Ramp generator
Soft start and constant speed control circuit
Motor rotation speed decreases (or increases)
(or increases) output voltage of the F-V converter decreases (or increases)
output voltage of the differential amplifier increases (or decreases).
Motor
Rotation speed
detector
F-V converter
Differential
amplifier
Load current control circuit
--- 7 ---
Triac
Phase control circuit
frequency signal decreases