drive%20mosfet

There are two ways of doing this just by connecting a

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Unformatted text preview: ronment for implementing soft turn-off. There are two ways of doing this. Just by connecting a resistor of appropriate value from Gate to source/emitter, the CGS gets discharged through this resistor and, depending on the value of the connected resistor, soft turn-off of any duration can be achieved. Another way, as shown in the Fig. (2), is to use a signal MOSFET Q1 to pull down the Gate, when short circuit is detected. The resistor in series with this signal MOSFET determines the time duration of this soft turn-off. Soft turn-off helps protect IGBT/MOSFET from any voltage transients generated due to L*dIC/dt (or L*dID/ dt) that could otherwise bring about avalanche breakdown. The PC board layout and Bill of Materials for this circuit are shown in Fig. (3). For an IGBT, Desat detection (Desat = Desaturation of forward voltage drop) is a method used for short circuit/overload protection. When short circuit/overload occurs, the forward voltage drop of the IGBT (V CE) rises to disproportionately high values. One must ignore the initial turn-on rise in VCE, when output from Driver has still not risen to high enough value. Nevertheless, when V CE rises to a level of, say, 7 Volts, in presence of sufficient Gate Drive voltage, it means the collector current IC has risen to a disproportionately high value, signalling overload. When a voltage level higher than 6.5 Volts is detected, Gate signal can be softly turned off, resulting into soft turn-off of the IGBT. Fig. (12) shows how Desat feature can be wired into a total Driver Circuit, using also other features, such as Opto-isolation and –ve turn-off bias. 3. HIGH SIDE DRIVING TECHNIQUES 3.1 EMPLOYING CHARGE-PUMP BOOTSTRAP METHODS AND For driving the upper MOSFET/IGBT in a phase leg employed in a bridge topology, a buck converter or a 2-transitor forward converter, low side drivers cannot be used directly. This is because the source/emitter of upper MOSFET/IGBT is not sitting at ground potential. Fig. (5) shows how a charge pump creates a higher Vcc to be used for the...
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This note was uploaded on 01/15/2014 for the course ECE 624 taught by Professor Staff during the Winter '08 term at Ohio State.

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