component. As the individual switches usually have a lower blocking voltage rating than
the DC-bus voltage, the T
switch is destroyed. However, if T
is turned off first, the
short circuit current continues to flow through D
. The voltage is halved and T
cannowbe turned off safely.
This turning off scenario is important when using U
monitoring in IGBT gate drives
which, as already described,must not turn off the inner IGBTs before the outer IGBTs. If
a fault is detected, the supervising control must be notified so that it can activate the
turn-off sequence. If this is not possible, Active Clamping can protect the IGBTs from
over-voltage so that the inner switchmay be turnedoff before theouter switch.
6.12 Selecting adriver byperformanceand cost
Selecting the right gate drive is related to thewhole inverter design. Level shifter IC and
optocoupler solutions are usually single source solutions, and it is the same with driver
boards. With few exceptions, they are mostly also only single source solutions. On the
other hand, the development of a reliable gate driver solution including control and
protection functions is no small thing and usually takesmany years.
Reliability, availability and of course the electrical properties such as coupling
capability are the most important criteria. Optocouplers are well
established in many cost-sensitive applications, as are level shifters in the 600V class.
Pulse transformers, which have advantages compared to optocouplers because of their
superior electrical properties, are also gettingmore popular. Thanks to the fact that this
technology is becoming more affordable. The integration of control and protection
functions in IC and ASIC is the answer to ever more stringent quality requirements. The
integration of drive circuits in IC makes gate drives more reliable because there are
fewer components. Hence there are fewer solder junctions and the device as awhole is
As well as costs, reliability and functionality, another important point in the choice of the
correct gate drive is procurement. Obtaining components and assemblies is becoming a
key topic. Highly integrated solutions offer advantages, as the number of separate
components can be reducedby up to 95%.
Below is an overview – by no means comprehensive – of selected manufacturers of
IGBTdrivers and couplers for drivers.