Hi Chris,
Wow, i'm impressed. There seem to be really better FETs nowadays, and
they are quite cheap!
Here is another parametric search from RS UK:
https://uk.rs-online.com/web/c/semiconductors/discrete-semiconductors/mosfets/?sra=p&applied-dimensions=4294883714,4294346016,4294356649,4294340889,4294340829,4294325803,4294347334,4294346061,4294356694,4294271671,4293188740,4294351546,4294336395,4294356497,4294356498,4294340915,4294340906,4294281922,4294351533,4294351512,4291957692,4291958309,4293607141,4294356611,4294435318,4294354817,4293419583,4294356613,4294356492,4294340837,4294356630,4294352824,4294356609,4294352812,4294282675,4294356616,4294435880,4291780226,4294354815,4293630940,4294340845,4291786173,4294275706,4294336384,4294281953,4294356604,4294356639,4294356602,4294354822,4294342065,4293134062,4291957764,4291957715,4294340883,4294356691,4291780201,4293603750,4294340886,4294356614,4294336385,4294351481,4293168570,4291958370,4294340830,4294268551,4294304110,4294336423,4294285794,4293620944,4291957714,4294340885,4294356468,4294271862,4291957726,4293590123,4293417294,4294345236,4293370811,4293402921,4294301289,4294351473,4291958394,4291786168,4294385938,4293305664,4293417382,4294340859,4294356626,4291957724,4294310769,4294356466,4294354413,4291957712,4294301883,4294356705,4294271831,4294356594,4294271868,4294356465,4294336381,4294340836,4291957672,4293134064,4294309392,4293173443,4294356493,4294510397,4294510768,4294512045,4294486622,4294480672,4294510058,4294498013,4294482870,4294441480,4293141137,4294505790,4294512081,4294490971,4294503594,4294510198,4294480460,4294498014,4294509212,4294499631,4294508125,4294510055,4294509995,4294509984,4294501309,4294481304,4294500555,4294508082,4294510092&sort-by=P_breakPrice1&sort-order=asc&rpp=100
The cheapest one, on the top of the list (yes, buy a tube of 30! This
will reduce the actual parameter variations), the STW28N60M2 allows more
current, more voltage, less on-resistance and a lower input capacity.
And it is just the first out of the compilation i looked on.
If i would plan to build a new H bridge PA, then this would be a
candidate...
73, Stefan
Am 04.12.2018 15:44, schrieb DK7FC:
Hi Chris,
Am 02.12.2018 18:01, schrieb Chris Wilson:
Any chance of a few photos of the H Bridge amp construction please?
OK, here are some impressions ;-)
Outside:
http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/pa/20181204_151804.jpg
Filters:
http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/pa/20181204_151945.jpg
FETs mounted to heat sink:
http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/pa/20181204_152015.jpg
Gate transformer:
http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/pa/20181204_152050.jpg
Some PTT watchdog stuff:
http://www.iup.uni-heidelberg.de/schaefer_vlf/LF/pa/20181204_152158.jpg
I take it the BF862's in the optocoupler feeds act as current
limiters?
Yes. I had the idea just to reduce the dependency of the duty cycle
from the supply voltage level and shape of the driver a bit.
Any reason you didn't just use resistors instead? Or is it for
galvanic isolation?
Yes, galvanic isolation. One aspect is the safety (oh yes, i like
safety but only when it is useful to consider), the other aspect is
the prevention of EMC issues in the shack. This way, the PC or other
sensible signal generators is carefully decoupled from the power side.
The IXDD414CI appears obsolete, the IXDD614CI is
still current from none Chinese suppliers, should I use a 614?
Yes, there seems to be no difference except the name.
I got them from https://www.digikey.com/products/en?keywords=ixdd614ci
Any
thoughts on more modern FET's as the IRFP460A is also off the current
device listings from named suppliers :( Thanks!
Oh! At least here they are available:
https://www.reichelt.de/mosfet-n-ch-500v-20a-280w-to-247-irfp-460a-p118998.html?&trstct=pos_0
Thanks for the note. I should order a bunch of them as long as they
are available.
For LF, the normal IRFP460 worked reasonable too but at MF you already
notice a significant difference in upwarming due to higher switching
losses!
Try to get them from somewhere. It should be possible. Or search
another FET with similar parameters.
RS allows a good parametric search, e.g.
https://de.rs-online.com/web/c/halbleiter/diskrete-bauteile/mosfet/?sra=p&applied-dimensions=4294424079,4294424036,4294341069,4294374353,4294393595,4294386882,4294421462,4291196625,4294392327,4294407012,4293040733,4294389435,4294337998,4293043627,4291658865,4294421649,4292771966,4294416407,4294215551,4294324063,4294136743,4294325511,4292899339,4294220644,4294204641,4294326243,4294095386,4294303277,4294136519,4293253351,4294324990,4294124426,4294222002,4294136239,4294124482,4294325988,4294222053,4294324870,4294133462,4294137170,4294325552,4294325005,4294324039,4291653797,4294325177,4294325265,4294325021,4294325269,4294325291,4294325157,4294099290,4294136648,4293272063,4294136333,4291453942,4294098433,4294324788,4291658391,4294136487,4294330306,4294324584,4294325413,4294323450,4294136639,4294119632,4294132386,4291653453,4294325018,4294086943,4293245047,4294221031,4293048710,4294116300,4294126751,4291653865,4291453937,4294324581,4292940441,4293063774,4294200481,4294131612,4291653452,4294116869,4294332397,4294086951,4294126698,4292801591,4294136028,4294325168,4294226681,4294095381,4294325172,4294136903,4294323509,4294086948,4291653818,4294087757,4291658390,4294193644,4291653837,4294325565,4291653538,4294116716,4294136800,4294421967,4294422427,4294424078,4294137854,4294413678,4294136280,4294421650,4294127968,4294132407,4294420404,4294409034,4294419000,4294421459,4294421386,4294421369,4294410955,4294128048,4294410089,4294418957,4294421504,4293247874,4294419079,4294403642,4294419075,4294409642,4294416416,4294421582,4294397063,4294422422,4293250149,4294398715,4294421360
Can you upload screen shots of the
gate and drain waveforms you are now seeing for comparison, they are
kind of hard to envisage in words ;)
Unfortunately i did not document this very well in 2012. My camera and
also the scope didn't really make impressive photos during that time ;-)
I remember the curves were quite smooth and there was a transient
swing on the positive edge, maybe up to 140 % and then back to 100%.
This transient swing is smoothed with the gate resistor, on the cost
of a slightly lower rise time.
Regarding the 2 kW statement: You know this always depends on the
temperature of your heat sink and thus, the strength of the fan and
the ambient temperature in the shack. I never run it at 2 kW but
something near 1.5, during winter.
My fan is stepless regulated in speed (not like the annoying
on/off/on/off switched fans in most commercial power supplies), so the
speed gives a feedback about the heat sinkl temperature. In winter, at
high power, it was running quite relaxed mostly, even at WSPR-30! :-)
Hope this helps...
73, Stefan
|
