Lincoln Electric SVM149-A service manual Insulated Gate Bipolar Transistor Igbt Operation

E-8 THEORY OF OPERATION E-8

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INSULATED GATE BIPOLAR TRANSISTOR (IGBT) OPERATION

An IGBT is a type of transistor. IGBTs are semicon- ductors 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 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.

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FIGURE E.5 – IGBT

POSITIVE

VOLTAGE

APPLIED

	GATE		GATE
SOURCE		SOURCE
n +	n +	n +	n +
p	BODY REGION	p	BODY REGION
n -	DRAIN DRIFT REGION	n -	DRAIN DRIFT REGION
n +	BUFFER LAYER	n +	BUFFER LAYER
p +	INJECTING LAYER	p +	INJECTING LAYER
DRAIN		DRAIN
A. PASSIVE		B. ACTIVE

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