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THEORY OF OPERATION
E-5 E-5
RANGER 305D
FIGURE E.5 – WELD POWER & CONTROL
Weld Power and Control
Weld Power:
Approximately 90VDC power, as described earlier
under the heading “Generating Power”, is supplied to
the IGBTʼs, (See IGBT Operation) and to the control cir-
cuitry in the power module, as well as the weld control
PC board.
The IGBTʼs control the weld output by switching the
weld power on and off using a 20 Khz PWM (Pulse
Width Modulation) signal from the control PC board.
This PWM signal varies the ratio of on and off time,
thereby controlling the power passing through to the
welding arc. (See Pulse Width Modulation)
The DC power that is being controlled by the IGBTʼs is
now applied to the choke. The choke is a heavy con-
ductor wound around an iron core. This device stores
power and tends to resist any change to current flow.
During the IGBT off cycle, the choke begins to dis-
charge through a freewheeling diode, on the power
module. This diode provides the necessary current
path, allowing the choke to use its stored power to
maintain a smooth flow of current to the welding arc
during the IGBTʼs off times. (See Chopper
Technology Fundamentals)
Weld Control and Feedback:
The operator provides input to the weld control circuitry
by means of the output control and arc control poten-
tiometers, and the mode switch. These operator inputs
are used by the microprocessor, together with pre-pro-
grammed internal parameters, current feedback from
the shunt, and voltage feedback from the output studs,
to control the IGBTʼs via the PWM signal discussed ear-
lier.
ROTOR
ENGINE
PROTECTION
CIRCUIT
ENGINE
PROTECTION
LIGHT
RUN
STOP
SWITCH
GLOW
PLUG
BUTTON
12V.
BATTERY
STARTER
ENGINE
ENGINE
SENSORS
GLOW
PLUGS
ENGINE
ALTERNATOR
START
BUTTON
IDLE
SOLENOID
PULL
COIL
HOLD
COIL
FUEL
PUMP
FUEL
SOLENIOD
PULL COIL
PULL COIL
PC BOARD
CHARGING
SYSTEM LIGHT
(CODE 10926 ONLY)
WELD
WINDING
STATOR
EXCITER
WINDING
120/240 VAC
AUX.WINDING
42VAC
WINDING
240
VAC
CURRENT
SENSOR
14
PIN
120
vac
FLASHING
RECEPTACLES
HOLD COIL
6
PIN
AMPHENALS
OUTPUT
CONTROL
ARC
CONTROL
MODE
SWITCH
WELDING
TERMINAL
SWITCH
IDLE
SWITCH
AMP
DISPLAY
VOLT
DISPLAY
WELD CONTROL
P.C. BOARD
POWER
MODULE
IGBTs
SHUNT
+
CHOKE
-