On Monday 26 October 2020 20:33:40 Jon Elson wrote: > On 10/26/2020 06:48 PM, Gene Heskett wrote: > > But the switching losses in the olimex board, even at only > > a 1 kilohertz pwm are killers, getting it hot enough to > > burn a finger in just 2 or 3 seconds. So, I need a d2a to > > drive one of the 150 watt class D audio boards after > > shorting the inputs hi-pass filters caps. And I have the > > feeling that even as sweet as the SpinX1 is for knocking > > around a vfd, that it won't be fast enough for this, so > > I'll need a real d2a that I can shove fresh data thru at > > servo-thread speeds. Looking for likely suspects I might > > be able to drive from the 7i76D sserial extension bus. > > Suggestions? > > I'm guessing the thing was designed for 50 Hz PWM or > thereabouts. That might actually be OK for a spindle motor. > Clearly NOT OK for a positioning servo. > Jon, Its a car seat positioner driver, claims very low milliohm on r's. $13 on fleabay. Looks promising, but write checks it can't cover even with a 1 kilohertz pwm. Rated up to 10 kilohertz. Either that or the first one is fubared. I bought two, and its not hard to change. I'll measure the rise and fall times being delivered to it tomorrow too on the chance the Sainsmart bob is slow. Manual claims up to 10 Mbits/S at any output. For driving switches, thats bordering on cook it slow. 10ns rise and fall would be a heck of a lot better. Designed for car seats, in cmos circuits, rated on time delay is 100 to 300us, off time is 85 to 255us.
And change of direction is 600 to 1800us. In polite language, that explains it all. For starters, there is no measureable lag coming out of the 7i76 for a direction reversal. So with our drive, this thing probably has 150us of shoot thru time for any dir signal change. I could probably design an interfacing circuit that would fix that, but IMNSHO that is the semi designers job. And STM failed, miserably. Thats not a problem in this particular circuit, but that geological rise and fall times for the pwm are a killer, even at 1 kilohertz. At 50 hz, maybe. At 10KHz, nearly instant overtemp shut down at 170C. Sigh... Thanks Jon. > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
