Bipolar transistor with isolated gate
Kirill Gopenko
Group K-22 M
IGBT Cell
A cross-section of a typical IGBT
showing the internal connection of a
MOSFET and a bipolar device
The IGBT cell is constructed
similarly to the n-channel vertical
structure. A power MOSFET,
except that the n+ drain is
replaced by a p+ collector layer,
thus forming a vertical bipolar
PNP transient transistor. This
additional p+ region creates a
cascade connection of a PNP
bipolar transient transistor with a
surface n-channel.
2
What's new?
A. Nakagawa invented the
design concept of an IGBT
device without fixation in
1984. The invention is
characterized by a device
design that sets the
saturation current of the
device below the fixation
current, which triggers a
parasitic thyristor.
Static characteristic of IGBT
In this invention, for the first time, complete suppression of the parasitic
action of thyristors was realized, since the maximum collector current was
limited by the saturation current and never exceeded the fixation current
3
Practical implementation of the device
Successful attempts to suppress the fixation of a parasitic thyristor and
scaling of the nominal voltage of devices in GE allowed the introduction of
commercial devices in 1983.4
Once the lock-free
capability was achieved in
IGBTs, it was found that
IGBTs have a very reliable
and very large safe
working area.
Typical gate drive circuit for IGBT modules
It was demonstrated that the product of the operating current density and collector
5
voltage exceeds the theoretical limit of bipolar transistors 2 ∙ 10 𝑊/с𝑚2 and
5
achieved 5 ∙ 10 𝑊/с𝑚2
4
Commercial Customized IGBT Modules
1. Commercial customized IGBTs available have a rated current of 200-400 A and a
rated voltage of 1700 V. The rated voltage is predicted to be up to 2-3 kV. (The
rated voltage of IGBTs is higher than that of BJTs, due to the small current gain
of pnp BJT.)
2. For a 1 kV device, the operating voltage is 2-3 V at rated current.
3. The on and off time is less than 1 microsecond.
4. IGBTs are available in a module in which 4 to 6 separate IGBTs are connected in
parallel. Therefore, the current nominal values are in the range from 1000 to
1500 A.
5
IGBT Operation Process
The whole process of IGBT operation can be
represented by two stages: as soon as a
positive voltage is applied, a field-effect
transistor opens between the gate and the
source, that is, an n-channel is formed
between the source and the drain.
At the same time, charges begin to move
from the n region to the p region, which
entails the opening of a bipolar transistor, as
a result of which a current rushes from the
emitter to the collector.
Simplified equivalent IGBT scheme
The essence of his work is that a field-effect transistor controls a powerful bipolar. As
a result, switching of a powerful load becomes possible at low power, since the
control signal enters the gate of the field-effect transistor.
6
Modes of operation of the transistor
1. Inverse active mode. The amplifying properties in this mode are as bad as
possible, so transistors in this mode are used very rarely.
2. Saturation mode. The main charge carriers of the collector and emitter "run" to the
base, where they actively recombine with its main carriers. Due to the resulting
redundancy of charge carriers, the resistance of the base and p-n junctions decreases.
3. Cut-off mode. The current of the main charge carriers between the emitter and
the collector stops. Flows of non-primary charge carriers create only small and
uncontrolled thermal currents of transitions. Due to the poverty of the base and
transitions by charge carriers, their resistance increases greatly.
4. Barrier mode. In this mode, the base is directly or through a small resistance
closed with the collector. A resistor is included in the collector or emitter circuit,
which sets the current through the transistor. Thus, the equivalent of a diode circuit
with a series-connected resistance is obtained.
7
Features and applications of IGBT.
Distinctive qualities of IGBT:
• Voltage-controlled (like any field-effect transistor);
• Have low losses in the open state;
• They can work at a temperature of more than 100°C;
• They are capable of operating with a voltage of more than 1000
volts and capacities of more than 5 kilowatts.
Install these devices in uninterruptible power supplies and in high-voltage
networks. They can be found in the electronic circuits of washing machines,
sewing machines and dishwashers, inverter air conditioners, pumps, electronic
ignition systems of cars, power supply systems of server and telecommunication
equipment.
8
Thanks for your attention
9