IDEALARC DC-600
E-3
THEORY OF OPERATION
FIGURE E.3 Output, Rectification, Control and Feedback
OUTPUT, RECTIFICATION,
CONTROL AND FEEDBACK
The neutrals of the Main Transformer secondary wind-
ings are connected together and the six starts are con-
nected to the six SCR assemblies to form a six phase
output. This six phase AC output from the Main
Transformer secondary is rectified and controlled
through the SCR bridge. Output current and voltage is
sensed at the shunt and output terminals. This feed-
back information is processed in the control board.
The control board compares the commands of the
Mode switch and the Output Control Potentiometer (or
Remote Control) with the feedback information and
sends the appropriate signal to the Firing Board.
The Firing Board is a three phase circuit. Each phase
provides two firing pulses, one for each of the two
Silicon Controlled Rectifiers (SCR) controlled by that
phase. The firing circuit supplies the proper amount of
energy to the gates of the power SCRs. When this
energy is applied, at the correct time, the SCR will turn
"ON". The amount of "ON" time versus "OFF" time
determines the output of the machine. See SCR
Operation.
The Pilot Relay signals the Firing Board circuit to sup-
ply gate pulses to the SCR Bridge. Closing of the Pilot
Relay ( a "dry" closure of leads #2 and #4) also brings
the Latching Resistor into the machine output circuit.
The Latching Resistor provides a pre-load for the SCR
Bridge.
A Choke is connected between the neutral connection
of the Main Transformer secondaries and the negative
output terminal. This large inductor stores energy and
provides filtering for the output of the DC-600.
TERMINAL
STRIP
CONTACTOR
TO
CONTROL
BOARD
REMOTE
CONTROL
MAIN
TRANSFORMER
CONTROL
TRANSFORMER
115 VAC
115 VAC
FAULT PROTECTION
PROTECTION
DEVICES &
CIRCUTS
CONTACTOR
HOLD-IN
(
)
FIRING BOARD
CONTROL
BOARD
PILOT
RELAY
F
E
E
D
B
A
C
K
F
E
E
D
B
A
C
K
OUTPUT
CONTROL
MODE
SWITCH
POSITIVE
TERMINAL
NEGATIVE
TERMINAL
LATCHING
RESISTOR
PILOT
RELAY
CHOKE
1
1
5
V
A
C
FAN
R
E
C
O
N
N
E
C
T
SCR BRIDGE
SHUNT
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
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