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OVERLOAD PROTECTION
CITOTIG 315DC & 415DC are electrically
protected from producing higher than normal
output currents. An electronic protection circuit
limits the current to within the capabilities of the
machine.
THERMAL PROTECTION
There is one thermal device located on the output
diodes heat-sink; it protects the machine from
excessive operating temperature.
Excessive temperature may be caused by a lack
of cooling air or by operating the machine beyond
the duty cycle and output rating. If excessive
operating temperature should occur, the Thermal
LED indicator on the control board, will turn ON
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INSULATED GATE BIPOLAR
TRANSISTOR (IGBT)
OPERATION
An IGBT is a type of transistor. IGBTs are
semiconductors well suited for high frequency
switching and high current applications.
Drawing A shows an IGBT in a passive mode.
There is no gate signal, zero volts relative to the
source, and therefore, no current flow. The drain
terminal of the IGBT may be connected to a
voltage supply; but since there is no conduction
the circuit will not supply current to components
connected to the source. The circuit is turned off
IGBT
and the thermostat will prevent output current.
The thermal protection devices are self-resetting
once the machine cools sufficiently. If the
shutdown was caused by excessive output or duty
cycle and the fan is operating normally, the power
switch may be left on and the reset should occur
within about 8 minutes period. If the fan is not
turning or the air intake louvers are obstructed,
the input power must be removed and the fan
problem or air obstruction must be corrected.
PROTECTIVE CIRCUITS
Protective circuits are designed into the 315DC
and 415DC to sense trouble and shut down the
machine before damage occurs to the machine's
internal components.
like a light switch in the OFF position.
Drawing B shows the IGBT in an active mode.
When the gate signal, a positive DC voltage
relative to the source, is applied to the gate
terminal of the IGBT, it is capable of conducting
current. A voltage supply connected to the drain
terminal will allow the IGBT to conduct and supply
current to circuit components coupled to the
source. Current will flow through the conducting
IGBT to downstream components as long as the
positive gate signal is present. This is similar to
turning ON a light switch.
27
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