Insulated Gate Bipolar Transistor (Igbt) Operation; Pulse Width Modulation - Lincoln Electric POWER WAVE S500 Service Manual

E-9
FIGURE E.8 - INSULATED GATE BIPOLAR TRANSISTOR (IGBT) OPERATION
SOURCE
n +
p
n -
n +
p +
DRAIN
A. PASSIVE
INSULATED GATE BIPOLAR TRAN-
SISTOR (IGBT) OPERATION
An IGBT is a type of transistor. IGBTs are semiconduc-
tors 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 rel-
ative to the source) and therefore, no current flow. The
drain terminal of the IGBT may be connected to a volt-
age 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 con-
nected to the drain terminal will allow the IGBT to con-
duct and supply current to circuit components coupled
to the source. Current will flow through the conducting
IGBT to downstream components as long as the posi-
tive gate signal is present. This is similar to turning ON
a light switch.
THEORY OF OPERATION
GATE
n +
BODY REGION
DRAIN DRIFT REGION
BUFFER LAYER
INJECTING LAYER
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
POWER WAVE
SOURCE
n + n +
p
n -
n +
p +
DRAIN
B. ACTIVE

PULSE WIDTH MODULATION

The term PULSE WIDTH MODULATION (PWM) is
used to describe how much time is devoted to conduc-
tion. Changing the pulse width is known as MODULA-
TION. Pulse Width Modulation is the varying of the
pulse width over the allowed range of a cycle to affect
the output of the machine.
® S500
E-9
POSITIVE
VOLTAGE
APPLIED
GATE
BODY REGION
DRAIN DRIFT REGION
BUFFER LAYER
INJECTING LAYER