V300-I
THEORY OF OPERATION
PRECHARGE & PROTECTION CIRCUITS
The DC voltage from the Input Rectifier is applied to the
Driver Board to begin charging the Switch Board
capacitors at a slow rate. When the pre-charge level is
achieved, the input relays close, applying the full DC
voltage to the capacitors. Depending on the Code
Number of the machine, there will be either two or four
relays and they may or may not be mounted on the
Driver Board.
The Driver Board is also responsible for gating the
Field Effect Transistors (FETs) on the Switch Boards,
as directed by the pulse width modulated (PWM) signal
from the Control Board.
The Protection Board monitors the capacitors for prop-
er balance and voltage level. If an imbalance or over-
voltage condition is detected, the Protection Circuit will
de-energize the relays, removing the power from the
switch circuits. The machine output will also be dis-
abled.
Another function of the Protection Board is to detect
whether the input voltage is single phase or three
phase and pass that information to the Control Board.
The maximum output of the machine will be limited to
approximately 250 amps with single phase input and
360 amps with 3 phase input.
E-3 E-3
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FIGURE E-3 ---PRECHARGE & PROTECTION CIRCUITS
