Here the pair of n channel and pchannel mosfets acts

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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 during turn-off. 3.2 ACHIEVING GALVANIC ISOLATION BY USING OPTO-COUPLERS TO DRIVE UPPER MOSFET/IGBT For driving high side MOSFET/IGBT in any topology, opto-couplers can be used with following advantages: 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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