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Unformatted text preview: on to a
copper pad on a printed circuit board for better
heat dissipation. It is possible then to use these
high current drivers for very high frequency
switching application, driving high current
Fig. (1) shows a basic low side driver
configuration. C1 is used as a bypass capacitor
placed very close to pin No. 1 and 8 of the driver
IC. Fig. (9) shows a method to separately control
the turn on and turn off times of MOSFET/IGBT.
Turn-on time can be adjusted by Rgon, while the
turn-off time can be varied by R . Schotkky
diodes facilitate this, by virtue of their very low
forward voltage drop and low trr. The 18V,
400mW Zener diodes protect the Gate-Emitter
junction of the IGBT. A careful layout of the
PCB, making shortest possible length between
output pin and IGBT Gate, while providing
generous copper surface for a ground plane, helps achieve fast turn-on and turn-off times without
creating oscillation in the Drain/Collector current.
Fig. (9) shows another arrangement and includes a
method for faster turn-off using a PNP transistor
placed very close to the MOSFET Gate and Source.
It is a good practice to tie the ENABLE pin of drivers
to Vcc through a 10K resistor. This ensures that the
driver always remains in its ENABLED mode except
when driven low due to a FAULT signal. Again, this
FAULT signal puts these two drivers into their
TRISTATE output mode.
Fig. (10) shows a method to boost output from driver
IC to a much higher level for driving very high power
IGBT module. Here the turn-on and turn-off times
can be varied by choosing different values of
resistors: Rgon and Rgoff. To provide –ve bias of 5
Volts, the IGBT emitter is grounded to the common
of +15V and –5V power supply, which feeds +15V
and –5 v to the IXD_408. Notice that the incoming
signals must also be level shifted.
Fig. (12) shows a high current driver IC driving one
IGBT of a Converter Brake Inverter (CBI) module.
Here all protection features are incorporated. For
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- Winter '08