I used these in the past along with some IRFZ44N http://www.irf.com/product-info/datasheets/data/irf4905.pdf
Regards, Alex On 8/1/2010 8:27 PM, Jon Elson wrote: > Kirk Wallace wrote: > >> Is this the high side bootstrap that creates the high side FET gate >> control voltage? >> > No, not really. That may be where John Kasunich got the name to call it > the "bootstrap" > parameter of the driver (I didn't supply that name to him). These servo > amps do have such a bootstrap > scheme to supply the high side bias. But, what this one pulse each > direction thing does is to reset the shutdown latches in the IR2113S FET > driver chips. I would have been fine without such a latch, but it is a > feature of the chip, I can't change it. When the positioning loop > starts up, EMC may decide the motor needs to move in one direction to > null the error, and if the amp hasn't seen at least one tiny pulse in > the opposite direction, it won't produce any output. > >> This has always seemed to create more trouble than it >> is worth. Why not have another supply with the proper voltage and not >> have to deal with the bootstrap? Or use N and P FET's? I know the >> bootstrap method may save a portion of the parts cost, but for the >> product quantities for the CNC market, it doesn't seem worth it. I may >> be showing my ignorance here. >> >> > I really don't see it as a problem. It does mean you can't go to 100.0% > duty cycle, somewhere around 95% is a good limit. > I did put a high-side supply on my first generation servo amp. It > required winding a custom transformer, and having a power > driver circuit for it. The reason is this is not just a fixed voltage a > little above the motor supply voltage, it is a FLOATING supply that > tracks the source terminal of the high-side FET. So, this whole power > supply swings the entire range of the motor supply in 200 ns or so, > every time the transistors switch. And, you need TWO of them, one for > each high side transistor. The capacitive coupling between the drive > winding and the output windings causes problems with blowing out the > driver chip, so isolation of the windings is needed. A TOTAL pain! So, > that's why these bootstrap circuits are so popular, they work and are > elegantly simple. > > Using P-channel FETS would work, and avoid the loating supplies, > but..... I use 40 milli-Ohm transistors in my drives. Try to find a > 200 V 40 mOhm P-channel FET. > They don't exist. > > Jon > > ------------------------------------------------------------------------------ > The Palm PDK Hot Apps Program offers developers who use the > Plug-In Development Kit to bring their C/C++ apps to Palm for a share > of $1 Million in cash or HP Products. Visit us here for more details: > http://p.sf.net/sfu/dev2dev-palm > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
