Toshiba VT130G1 User Manual
Page 9
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A. Main Circuit
Section 3
HCT
OUT^
AC
TO
MOTOR
FIGURE 3^
Incoming 3 phase A.C. line voltage is rectified to a 650V D.C. bus by the
diodes in the full wave rectifier.
Input line fuses Drotect the main circuit from fault currents. (7.5 HP and above)
V\/hen the input is first energized, contactors MS1 working with resistor R1, pro
vide a slow charge to filtering capacitors Cl. A red LED (light emitting diode)
on the base drive board turns on to indicate voltage on the bus.
A Hall-Effect D.C. current transformer (HCT) monitors bus current for the
regulator board.
Output to the motor is obtained by switching the D.C. bus with the transistor
(GTR) inverter. G-TR control comes from the regulator board through the base
amplifiers.
Pulse width is decreased for lower RMS voltage and increased for higher
voltage. Lower frequencies have a greater number of pulses in one cycle. As
the frequency increases, the microprocessor selects the optimum number of
pulses per waveform.
Switching of the transistors is controlled by the regulator board.