Hi Andy very interetsing details on your build. I have always been a but
uncertain about the headroom on Vdd and have never tried less than 4*supply,
but probably 5*supply would be safer and fairly easy to achieve. I wonder if
the higher swing was a function of your circuit Q?? I am pleased the Class E
acquitted itself well, it certainly seemed a good option for narrow-band
operation.
Have you looked at Johan's antiphase pair with a single L2 and C2 ? That
looked very interesting but I have not had the enthusiasm to go further. I
think Johan built a test unit and it worked well.
Alan
----- Original Message -----
From: "Andy Talbot" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 26, 2011 12:28 PM
Subject: LF: Litz Wire and Class E
> Hi Alan -
>
> I think that using thicker Litz would lead to too big a coil now I've
> mounted things on a chassis, so have air cooled the existing one instead.
> Its OK at teh moment, although I suspect summer temperatures would give a
> few problems. In retrospect, I suspect using teh L-match wasn't too
> sensible, and were I to make another one would now use a ferrite
transformer
>
> The downside to combining the tank L with the L-Match network is this
effect
> that minor changes to the coil lead to a quite fast increase in current
(and
> power out), even though efficiency doesn't degrade noticeably much. Its
a
> very forgiving design once the waveforms are correct to start with -
> UNLESS L drops too much. I blew the IRF452s on the original by idly
playing
> with the coil when operating, and reduced L too much without monitoring Vd
> waveform and current.
>
> My Vd peak is a bit higher than your spreadsheet suggests it should be -
> typically 220V from a 50V rail , but there are too many variables to
tweak,
> all giving different Pout vs Vdd when optimised, and all at similar
> efficiency to want to play much more in that area. With teh new IRFP360
> devices efficiency is now at the point where accurate determination is not
> possible, and I've so far measured values from 80% up to 105% - so yes,
> perpetual motion is possible :-) But the latter was before realising my
> Bird power attenuator is temperature dependent. Think it averages out
in
> the upper 80's
>
> Now I'm on the antenan and tweak the variometer minutely, I see current
goes
> up with a slightly inductive load and down when L is reduced for a
> capacitive load. Something that needs to be watched out for at max
power
> settings if rain / dry conditions are likely to detune the
> antenna. However, if I keep to a 50v rail all should stay inside safe
> zones - but have tested it at 60v (the max the PSU can deliver) and was
> getting > 700 Watts into the dummy load at one point.
>
> I did lose one new device - not from tuning overload, but because I was
> experimenting with turning RF drive on / off. One of the TC4420 driver
> chips wasn't happy at this and popped, throwing the entire load onto just
> the remaining one of the two parallel FETs - which promptly blew. So
now,
> CW idents are out (no bad thing), or at least when generated by toggling
RF
> in the source. Any on off keying must be done by switching power to the
> driver.
>
> Mind you, any duty cycle less than 100% can never be an efficient way to
> communicate. After all, average power just reduces! If I was really
> forced to use CW, it would be FSK so therefore probably DFCWi. (Unless a
> PA is thermal limited I suppose)
>
> Andy
>
>
>
> On 22 January 2011 18:16, Alan Melia <[email protected]> wrote:
>
> > Hi Andy I think I have some lengths from a Decca coil left that would be
> > long enough for you (If I can remember where I put them :-)) ) I
stripped
> > down a movable coil a number of year ago and spent a long time unwinding
> > it.
> > There were some nice long lengths but there were also a number of
shorter
> > ones....I will dig around.
> >
> > Alan
> > G3NYK
> >
> > ----- Original Message -----
> > From: "Andy Talbot" <[email protected]>
> > To: <[email protected]>
> > Sent: Saturday, January 22, 2011 5:14 PM
> > Subject: LF: Thick Litz wire needed, and more on class E PA development
> >
> >
> > > Is there still any of the really thick Litz wire from the old Decca
> > stations
> > > around? I'm after about 3 to 3.5 metres of whatever is available
that
> > is
> > > thicker than 3mm, and preferably nearer 3.5mm diameter. Enough to
make
> > a
> > > 9.3uH coil
> > >
> > > The Tank coil in the latest version of the class E PA under test is
now
> > the
> > > power-determining item. At 450 Watts output the heatsink with fan is
> > COLD
> > > - but the coil annoyingly smells of hot varnish.
> > > It is wound with the cotton covered Litz, about 2.5mm overall diameter
> > which
> > > itself is a big improvement over the plastic covered stuff I was using
> > for
> > > the breadboard. But, I have the surreal situation that as teh coil
gets
> > > hot, teh wire expands, inductance falls and due to the nature of the
> > > combined Tank + L-Match circuitry causes a resulting *increase* in
powser
> > > output - leadign to higher dissipation and you can guess what will
> > > eventually happen if left unchecked.
> > >
> > > One soluition will be to duct air from the fan through the coil, but
I'd
> > > feel happier if loses were lower to start with.
> > >
> > > At reduced Vdd it reaches stability running at 400 Watts without
getting
> > too
> > > hot and increasing itself spontaneously.
> > >
> > > Efficiency, by the way, variously measures at 86 - 94%. So I'll say
> > around
> > > 88%. Hard to believe, but I have been over everything and double
> > checks,
> > > and can't get teh value below 84% however much I try to push errors in
> > the
> > > worst direction.
> > >
> > > The FETs are now a pair of IRFP360, and the driver chip had to be
> > replaced
> > > - the poor ICL7667 just went bang and split itself open driving them.
> > The
> > > copper of the PCB tracks running under it became discoloured so it
must
> > have
> > > bene running very hot before dying Now using a pair of SMT TC4420
> > devices -
> > > one per FET - with additional copper heat dissipating fins on the
PCB.
> > > They've survived so far.
> > >
> > > Its been delivering 320 Watts for an hour now off a 37V rail, so at
that
> > > power level is certainly reliable; brief forays up to a 55V rail gave
> > > slightly over 700 Watts - and I could see current rising as I watched
due
> > to
> > > the coil expanding, so didn't hold it there for long, but does mean
the
> > PA
> > > as it stands could be used with AM/envelope modulation.
> > >
> > > The shack is getting quite warm now !
> > > A second chapter to the write-up will appear in due course
> > >
> > > Andy
> > > www.g4jnt.com
> > >
> >
> >
> >
>
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