I assume the 2110 is similar to the eg 2111 from Motorola. I also assume that you understand the way the drive voltage is generated for the high side driver. The boot capacitor between Vb (driver IC's hi side driver supply input) and Vs (hi side FET source) is charged from Vcc when the bottom FET is on and drives the hi side FET when it is its turn to be on. As a consequence it is ESSENTIAL that the low side FET be driven at some stage prior to the hi side FET - to allow the boot capacitor to charge, and then that the lower side FET be occasionally (at least) be turned on to keep the boot capacitor charged. In some designs there are conditions where the lower driver would not be on for long periods (shouldn't apply in your application). If this happens it is necessary to arrange for the lower driver to be turned on occasionally to ensure the boot capacitor stays charged. Sizing of the bootstrap capacitor and associated components depends on the FET drive requirements and frequency. If the available charge is inadequate (capacitor too small, too much drive current required (may be being bled to hi-side source by drive cct?)) etc then the FET may turn off early. You really don't want this to happen :-). Too small a capacitor and it dies. A very large cap may have charge up problems when the lower FET is on (depending on other cct constraints). - A good way to cheat is to use a 9volt transistor radio battery (PP3?) for the high side boot strap supply while you are experimenting. Also start off seeing if the driver is working by using something other than a FET gate (FETS aren't cheap and have to be driven right or else :-)).An oscilloscope hepls a lot (floating input!). Run on vv reduced voltage while playing. - Harris have lots of application sheets on their site - some may be useful. See www.semi.harris.com/families/an.htm - If this is a one off you risk re-inventing the wheel. Power electronics in this sort of application takes a certain amount of black magic (read hard won knowledge). Ha ve you met the SA828 PWM IC - its probably ideal for your application as a PWM source. Its made by MITEL (info is on web but I haven't got their URL here.) ---------- > From: Walter Markiw > To: PICLIST@MITVMA.MIT.EDU > Subject: help with high side mosfet > Date: Wednesday, 8 July 1998 13:11 > > I'm trying to drive the high side mosfets of a six mosfet inverter project > I'm building,driven by a 16c74.The problem is that to drive the high side > transistors > I have put 310V (source) + 15 V on the gate to get it in full conduction. > I tried IR2110,a driver from International Rectifier,but for some reason I > can't > get it to work right. > Could any of you please help me out with this?,send me some schematics on how > to drive those mosfets,or on how to connect the IR2110 right?.(I tried following > the instructions in the IR page,but there must be something I'm doing wrong) > The mosfets should keep in full conduction during 320 microseconds at the most. > I intend to sinthesize a 30 hz 310V (peak) PWM wave,which would replace a > 50Hz 540V(peak) sine wave to power a three fase induction motor.