On Sunday 28 September 2008, Jon Elson wrote: >Gene Heskett wrote: >> If it wasn't for the poor PIV ratings of the schotky's(sp?), that would be >> ideal, but I don't know of any power schotky's good for that sort of >> reverse voltage. > >There are insanely fast turn-off diodes on the market. By trying out a >few in a circuit already proven to provide a torture test, it was easy >to find a part that also had a VERY fast turn-on. I didn't need >anything super-fast, but it had to pick up 20 A in under 100 ns. > >> The std power si diodes slow turnoff can be a huge problem child also. In >> an old GE UHF transmitter, we had 6 stacks of 48 each 20a, 400piv si >> diodes in DO-5 cases that were used in the 3 phase beam supply. Load was >> about 6 amps per klystron at 20kv. Because of the slow turnoff, the 3 >> phase power was welded phase to phase 180 times a second for about 30 >> u-secs a blip. We had short lamp life all over the place cuz we had 2+kv >> spikes sitting on the 120 volt lines at the duplexes on the wall. We >> considered replacing them with schotky's, till we totaled up the materials >> cost's, which at the time would have come to about 20k$. Eventually >> lightning got the 375kw sola transformer between us and the powerline and >> I had to bypass it. That reduced the powerline impedance and dropped >> those spikes to 75 volts. It also got rid of the rectifier noise in the >> video it had had since it went on the air, so that was another set of >> jumpers, 4 pieces of 750mcm/phase, 12 total, that never got pulled back >> out. Almost any full power UHF broadcaster is going to be the power >> companies biggest customer. :) > >Well, there's no way you can use standard rectifiers in a switching >power supply, which any PWM servo drive is. These fast turn-off diodes >may cause some EMI, but at least they don't have to be "re-charged" much >after conducting. This is a big deal in 100 KHz+ power supplies. > >Another big power co. load is electric refrigeration. Many buildings >(or building complexes) have a 500 Hp electric turbine chiller >(basically same as a home A/C except the compressor is a turbine instead >of reciprocating). Newer ones run 6000 - 10,000 RPM with a VFD, too. I >was shown an older one at work and there was a phone on the thing, next >to the starting control panel. It had some early soft-start system. >Next to the phone was a list of power plant engineers that had to be >called, in order, one half hour before motor start. It had lots of >exclamation points about doing this exactly right or the university >would get a HUGE bill for not giving them adequate waning of starting a >big load. > >>> As you turn the >>> DC supply voltage up, the output rise/fall times can become quite a bit >>> shorter than the gate drive rise/fall times. I had expected with the >>> Miller effect, etc. that the output rise/fall times would be somewhat >>> slewrate limited, but not so, the slew rate speeds UP. >> >> The driver output probably gets stiffer faster than the FET's with the >> increased supply voltage. FET's also will sweep out the majority carriers >> faster at higher voltages, but I'd think miller effect is there, just >> being swamped by nitros burning drivers. > >The gate drive waveform has a distinct flat step when the transistor >starts to turn on or off, as the Miller effect takes control of the >gate. You can use this to tell what the gate threshold of the >transistor is. > I've seen that, and suspected that is what is was, thanks. New z axis pix up on my web page. <http://gene.homelinux.net:85/gene/emc/z-axis-drive.jpg>
click on it once to get 1/1 pixels so you can read the text notes. >Jon > >------------------------------------------------------------------------- >This SF.Net email is sponsored by the Moblin Your Move Developer's challenge >Build the coolest Linux based applications with Moblin SDK & win great > prizes Grand prize is a trip for two to an Open Source event anywhere in > the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ >_______________________________________________ >Emc-users mailing list >[email protected] >https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Perfect day for scrubbing the floor and other exciting things. ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
