Unformatted text preview: driver IC for the Upper
MOSFET/IGBT. Here the pair of N
-Channel and PChannel MOSFETs acts as switches, alternately
connecting incoming supply voltage to output
through capacitors and Schottky diodes, isolating it
and almost doubling it. Switching frequency in
several hundred Kilohertz is used and, therefore, low
ripple isolated output voltage is available as DC
Supply for the Driver of Upper MOSFET/IGBT. Fig.
(7) illustrates how one IXD_404 can be used as
charge pump, delivering 350 mA, and one IXD_408 IXAN0009 as a Driver giving +/- 8 Amps, in conjunction with
IXBD4410 and IXBD4411, for driving a phase
leg of two IXFX50N50 MOSFETs. Fig. (8) shows
how a charge pump delivering as much as 500
mA can be constructed using one IXD_404; and
by utilizing one IXD_414, one can boost the
output from IXBD4410 and IXBD4411 to +/14Amps for driving Size 9 high power MOSFETs
and IGBTs or even MOSFET/IGBT module.
Another method is the Bootstrap Technique as
shown in Fig. (6). The basic bootstrap building
elements are the level shift circuit, bootstrap
diode DB, level shift transistor Q1, bootstrap
capacitor CB and IXD_408 or IXD_414. The
bootstrap capacitor, IXD_408/IXD_414 driver
and the gate resistor are the floating, sourcereferenced parts of the bootstrap arrangement.
The disadvantages of this technique are longer
turn-on and turn-off delays and 100% duty cycle
is not possible. Additionally the driver has to
overcome the load impedance and negative
voltage present at the source of the device
3.2 ACHIEVING GALVANIC ISOLATION BY
USING OPTO-COUPLERS TO DRIVE UPPER
For driving high side MOSFET/IGBT in any
topology, opto-couplers can be used with
1. They can be used to give a very high isolation
voltage; 2500 to 5000 Volts of isolation is
achievable by use of properly certified optocouplers.
2. Signals from DC to several MHz can be
handled by opto-couplers.
3. They can be easily interfaced to
Microcomputers, DSPs or other controller ICs
or any PWM IC.
One disadvantage is that the opto-coup...
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- Winter '08
- power supply, driver, gate drive, driver IC, MOSFET/IGBT