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Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
Destroyer of mosfets wrote ...
The warter would probably detune the coil (unless your driver can compensate)
You can't compensate for a detuned secondary period. Primary current feedback ensures that your primary's ~fres and your switching speed always match. Not whether your secondary is in tune. Not that it would it matters unless you're running fin or dan's coils: if the secondary became untuned then to keep the system in tune then you would have to physically alter the ~fres of the primary to match it.
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
Looking good but Eon/Eoff values are for hard switching.
In perfect DRSSTC world you are not swithing any current so you only have to worry about conduction losses. Also switching delays are for hard swithing. (current rise/fall times)
I have tested these IGBTS up to 2kApk @ 60kHz in my test setup.. no problems at all with phase lead driver.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Kizmo wrote ...
Looking good but Eon/Eoff values are for hard switching.
In perfect DRSSTC world you are not swithing any current so you only have to worry about conduction losses. Also switching delays are for hard swithing. (current rise/fall times)
I have tested these IGBTS up to 2kApk @ 60kHz in my test setup.. no problems at all with phase lead driver.
Yeah I know its all data for hard switching, but its the numbers we have at hand :)
Conduction losses are as Terry Fritz also put it, highly neglect able with the very low duty cycles, by using the hard switching math, most IGBTs would run into MHz if only looking at the frequency limitation by temperature rise.
Are soft switching data normally available from the manufacturers?
Registered Member #599
Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624
There is still simple thermal limit. Even with "just" conduction losses.
Have a look at IGBT die temp rise during single burst.. push hard enough and poor die just does not have time to dissapate all heat through its substrate.
EDIT:
Of course this does not limit switching speed. In (properly timed, phase lead) soft switghing applications even big IGBTs can operate at surprisingly high frequencies.
In brick world there is of course one limit that is like a brick wall (pun not intended..). Larger igbts have several dies in parallel and their busbars can have 50-100nH worth of inductance which is usually NOT equally spread along all paralled dies. Same thing with gate leads. Both of those combined will have large effect on how fast you can actually switch and still maintain current sharing and keep ringing down.
With properly set phase lead driver (Wards UD2.0 or Prediktor) there is no reason why dirty old CM300 could not operate past 100kHz without any issues at all.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
zzz_julian_zzz wrote ...
What's with the UDv2.0 PLC/Predictor? can someone post a schematic of this? or if any like way circuits? Thanks
Steve gave me this link a while ago. its one of the non-released schematics, so don't go asking him to troubleshoot it for you if you have any problems.
those switching tables look fine. if i remember correctly i got some of the same times when i did the math a long time ago. just repeating that soft switching speeds are a bit faster.
people seem to be able to push cm300's to just under 100khz, so maybe the resonant switching formula should be: Fresmax= (1/((Ton+Toff)*10))*1.6 that would correspond to some real data. look at how fast people switch these in their projects, and it looks reasonably accurate.
it also matches your thermal data. so we've got a new rule:Fresmax= (1/((Ton+Toff)*10))*1.6 unless the thermal data shows otherwise
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
There are a few different kinds of "CM300", for instance the CM300DY-12F (?) uses Powerex's 600V F-series dice. These are much faster than the usual 1200V H-series, and I've seen it used in tabletop coils in the 200kHz region.
I'm a little wary of the practice of using the transient thermal impedance. It's OK to use it to calculate junction temperature rise during the burst, but that is just a ripple on top of a slower rise.
When the coil is run repetitively for a long time, the die temperature will be determined by the average power dissipation (switching plus conduction) and the steady-state thermal resistance.
You should maybe add the temperature ripple to this to find the actual peak die temperature, but it's probably only a few degrees because the transient thermal impedance is so low, unless you are really pushing the device to destruction.
Steve Ward and Jimmy Hynes used PSpice to do full transient thermal simulations, with an electrical analogue of the thermal circuit.
As Kizmo points out above, package inductance in bricks is a serious problem because it causes the switching losses to be shared unevenly between dice, and no amount of spreadsheets will help you quantify that. Zero current switching of course is a great help.
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igbt speed
