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fall times will incur more power loss in driver due
to increased Vcc and Qg. If that happens,
approach described in Fig. (10) can be
employed. Or possibility of using a 30 Amp
driver can be investigated by power calculation
as shown above. 8. High overall efficiency of gate drive is possible. 6.0
MOSFET/IGBT Almost all possible configurations of bi-directional
switches employing IGBTs and FREDs (Fast
Recovery Epitaxial Diodes) are shown in Fig.(15).
When connected in series with the IGBT, the FRED
gives reverse blocking capability to the bi-directional
switch. When connected inversely across the IGBT,
the FRED provides a path for the line current to flow
in the reverse direction. Both techniques prevent
reverse voltage application to the emitter of IGBT. GATE DRIVE FOR Many applications of MOSFETs and IGBTs
require an isolated Gate Drive Circuit. For
example in H-B ridge and 3 -Phase Bridge
inverters, the upper MOSFETs and IGBTs
require an isolated gate drive, because the
Source/Emitter of upper MOSFETs/IGBTs are
not at the ground potential. Similarly in matrix
converters, all bi-directional switches require
isolated gate drive circuits.
Basically there are two popular techniques
available to implement isolated gate drive.
Fig.15 shows a method to implement an isolated
gate drive, using Gate Drive Transformers.
There are several advantages in using the gate
1. If properly wound and built, they can give
2. Depending on the drive current and voltage
required, they give step-up or step-down
3. They are immune to dv/dt transients
4. They experience no propagation delays.
5. Using modern high permeability cores, tiny
Gate Drive Transformers are now available
that meet most stringent design specifications.
6. There is no need to have an isolated power
7. Large duty cycle range of pulse widths is
possible, say, from 1% to 99%. The two disadvantages are:
1. Gate drive transformers are not suitable for DC
and very low frequency signals.
2. It is difficult...
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- Winter '08