Gate drivers

This drive loss ean beeome signifieant. A driver transistor ean be added to the pass transistor to inerease the effeetive gain of the pass unit and thus deerease the drive eurrent, or a power MOSFET ean be used as a pass unit that uses magnitudes less de drive eurrent than the bipolar power transistor. Unfortunately, the MOSFET requires up to 10 VDC to drive the gate. This ean drasti-eally inerease the dropout voltage. In the vast majority of linear regulator applieations, there is little differenee in operation between a buffered pass unit and a MOSFET insofar as effieieney is eoneerned. Bipolar transistors are mueh less expensive than power MOSFET and have less propensity to oseillate. 

Driving the IGBT is identical to the MOSFET. It has similar gate driving characteristics and a MOSFET driver IC works very well with an IGBT... 

The drive signal applied to the switching Fet is usually created by a driver stage sitting inside the IC, and therefore connected to the IC ground. But the actual behavior displayed by a Fet is not determined by the voltage applied on its Gate terminal with respect to our... 

In DC-DC converters, we can somewhat slow the turn-on of Fets if we insert a small resistor (10 to 20Q. typically) in series with the decoupling capacitor of their respective driver stages. For example, a small resistor can be placed in series with the bootstrap capacitor of the third-generation switcher family I used to cover. That helped with almost 10 to 20% of customers, but somehow this trick didn t find its way into the applications information section of their datasheet. If the Fets are external, we can try a small resistor in series with the Gate, but this affects both the turn-on and turnoff (with such low threshold voltages, a diode in parallel to the resistor will not do anything). 

So, if you can access the gates of the Fets, try putting in small resistors in series with them. If it is a switcher IC (with no access to the gates), try inserting a small resistor in series with the decoupling capacitor of the driver supply (usually a 0.1 pF capacitor attached to the Vdd pin and/or the bootstrap pin). Better still, pick an IC with less aggressive drive to start with. Because otherwise it will commit suicide sooner or later. 

For then she bore a son, of many shifts, blandly cunning, a robber, a cattle driver, a bringer of dreams, a watcher by night, a thief at the gates, one who was soon to show forth wonderful deeds among the deathless gods.. . ... 

Figure 7.36 Diagram of a single photon counting apparatus for time-resolved spectroscopy. L, pulsed light source S, sample P, photodiode F, filter or monochromator D, photomultiplier R, voltage ramp driver G, gate Cj, C comparators M, multichannel analyser...

As Bugayev gave the nod to the driver, and they rolled off towards the gate, she tried to put that out of her mind and settle back to at least look as if she were enjoying the ride. Trix cast her eyes outside, watching the guards, barriers and crowds slip past her window and tried to think of herself as someone important to the Colonel s investigation as opposed to a suspect. 

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