Example of the use of IGBT gate drivers with optocouplers in an inverter
system (common power supply for all bottom IGBTdrivers)
In many cases an isolated power supply is required for the IGBT driver. Consequently,
this isolated power supply is regarded as part of the IGBT driver. The power supply is
typically provided by aDC/DC converter or bootstrap circuit.
Other tasks of the IGBT driver may also be implemented by logic functions such as
dead-timegeneration,minimum pulse suppressionor "safe stop".
In the following sections the various aspects of all functions will be discussed in detail
and - where appropriate - application hints aregiven.
6.2 Signal transmission
As discussed in the introduction, IGBTs require isolated control signals, which are the
turn-on, turn-off and, if existing, the feedback signals. The isolation of the signal
transmission path of these control signals can be made by means of a galvanic
separation or a non-galvanic separatio
. The galvanic separation is further divided into
a separationbased on inductive, optical, and very rarely capacitivedevices.
Normally for low and medium power applications with IGBT blocking voltages of up to
= 1.2kV level shifter IC and optocoupler driver IC are used for signal separation,
while at high power applications or with blocking voltages greater than 1.2kV inductive
and optical transmitters areused.
In addition to the design, the IGBT drivers also differ in the number of channels
provided. Thereare IGBTdriverswith signal separation to control one, two or six IGBTs.
Another distinguishing feature is the way the implemented separation of the upper and
A galvanic separation provides a separationof twoelectrical conductive objects, i.e. no charge carriers from one
electrical circuit can move to the other electrical circuit since no conductive connection between the two exists.
Only by using specific coupling devices such as transformers, can signals and energy be exchanged between the