Hello Marco,
I was unable to write a longer text for a few days (no desktop PC
available, just the smartphone and Teamviewer) so my answer is a bit
late. You've got a lot of advice since that time.
I'm just adding what came to my mind...
-I assume you already checked that the supply voltages stay constand in
any working point.
-The gate voltages are important. Also the duty cycle should be constant
and close to 50% for best operation.
In my H bridge PA for 137 kHz the gate voltage is +- 8V, quite a
rectangular waveform. Unfortunately i have no scope captures quickly
available.
-Try to lower the 4 Ohm resistor after the IDXX driver. It is there to
avoid oscillations after the switching slopes. Maybe 2 Ohm is enough.
-Even more important: Make sure the transformer is wound for a minimum
stray inductance because this will quickly lead to strong oscillations.
Wind all the 3 windings equally spread arround the whole core (ferrite,
e.g. N30, AL>2000nH). Wind them trifilar, not separated.
If there are still problems show us images of: The gate source voltage,
the gate drive transformer.
73, Stefan
Am 03.06.2017 16:44, schrieb [email protected]:
Hi Stefan,
and thank you :-) so you have too something to mumble while sending
VLF SMS ;-)
There is nothing really new.. I started from an avalable
chassis with on board a PS giving 180Vdc (1200W) and assembled the
Andy's half bridge 700W switching PA and before give it the full power
I'm checking with lower DC supply. Attached you see the schematic with
some change at the moment..
The output xfmr has 7T/19T, the coil of the guard circuit is not
connected (now is in serie with L2) and the resonating caps now are
5x1000pF in parallel.
The aim is finally with 180Vdc of supply have an output of 0,5÷1kW
but.... as you probably red in the previous messages, from 10 to 30Vdc
the PA runs, at low power of course (up to 15W), and complies the
calculations; with supply between 30 and 50 Vdc the output go down to a
couple of W.
I made several trials it the last days, changing the core of the xfmr,
the turn ratio, the kind of capacitators but nothing changes (or at
least the change are within a fraction of dB).
that's the sad history Stefan...
All thoughts and suggestions are welcome! (including go to fish ;-)) )
Marco
----Messaggio originale----
Da: [email protected]
Data: 3-giu-2017 16.19
A:<[email protected]>
Ogg: Re: R: Re: LF: Re: I: Fw: For today the FETs survived...
Hi Marco,
If you like, i can help you. Just need a schematic to see what you
want
to do. Targer power, voltage, etc...
73, Stefan
Am 03.06.2017 16:02, schrieb [email protected]:
Hi Alan, Andy, Chris,
I replaced the caps in the output LC with WIMA FKP1, the 2 caps wich
replaces the missing half of the bridge are still Cornell Dubillier
940C serie (rated at 9A @100kHz), so now all the caps are pulse rated
but...
I regret to admit it, nothing changed :-((
Power out increases from 10 to 30Vdc and at 40Vdc after a first pulse
the power slowly decreases till a couple of watts..
Just to check another thing: being the coil of the guard circuit
disconnected, I jointed the 2 coils together (they are wound on the
same support) increasing so the inductance of the L (25T more). Of
course I had to retune and now I need C in the range of 5000pF but
this
narrowed the 3dB bandwidth of the LC from abt 15kHz to abt 8kHz so is
the Q increased!
... I should visit Decathlon and look for a fishing rod!
your sincerely depressed IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 2-giu-2017 15.58
A:<[email protected]>
Ogg: Re: LF: Re: I: Fw: For today the FETs survived...
Hi Marco, I may well be wrong I was experimenting with 150W at 35V I
measured 12 to 15A through the capacitors (from memory) .......the
confirmation is that the change is permanent. I dont remember seeing
any
heating effects. Single ended Class E may be considerably different
to
H-bridge. The currents a lower power will be less, about 1.5A or so
(??) I
am not sure it that would produce damage, but you would certainly see
it as
the power increased.
Good Luck with it
Alan
G3NYK
----- Original Message -----
From:<[email protected]>
To:<[email protected]>
Sent: Friday, June 02, 2017 2:00 PM
Subject: R: LF: Re: I: Fw: For today the FETs survived...
Hi Alan,
and thanks for joining :-)
it's hard to believe at this stage that is correct to speak of "high
currents"..
The PA is an half bridge like
Andy's 700W but now I'm testing at low voltage: I see these problem
trepassing the 30Vdc supply level (and power is about 15W)..
Anyway will try with the "pulse rated caps" you suggested just in
case
my "low current" "low tension" ideas are wrong.
73 Marco
----Messaggio originale----
Da: [email protected]
Data: 2-giu-2017 14.36
A:<[email protected]>
Ogg: LF: Re: I: Fw: For today the FETs survived...
Hi Marco I dont know where you are putting the caps but I am assuming
they
are passing a high RF corrent. I found that the old style (valve)
high
voltage caps in my Class E test rig changed capacitance permanently
during
and after a run (capacitance reduced). I assumed that the current was
fusing
the foil connection to the lead-out wires. When using "pulse rated"
capacitors as used in SMPSUs I had no further capacitance change
problems.
The ones I have are RIFA PHE 428 2000v from RS Components. I think
Farnell
do a WIMA equivalent.
Best Wishes
Alan
G3NYK
----- Original Message -----
From:<[email protected]>
To:<[email protected]>
Sent: Friday, June 02, 2017 1:06 PM
Subject: R: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...
now my thoughts are even more confused....
Hi Andy, me again....
after a long night of meditation, I remembered I had a bounch of old
style mica capacitators 1000pF 1000V..
I put
9 of them in parallel to get the closer value to the 8800pF I had
before.
Of course the resonance moved a bit and now is on 134.5 kHz with 3dB
bandwidth of 9 kHz (Q=15 I know is a bit to high..) so carried out
some
tests on 134 kHz (of course on the dummyload) all without guard
circuit
1st test xfmr 7T/19T (Ae197mm² R50 mat T38): 2Wout @10Vdc; 6,5
Wout@20Vdc; 13,7Wout@30Vdc stable.. @40Vdc after a quick peak the
power
slowly goes down till below 1W!
2nd test I had still on hands the previous xfmr 5T/12T (Ae197mm² same
core as 1st test) so was worth to make a trial... same trend :-( for
Vdc> 30V after a first peak... it goes down.
I had another core available with different material (N30, Ae 154mm²
R58) so I prepared a new xfmr with this core 7T/14T:
1,4Wout@10Vdc; 4,6Wout@20Vdc; 9,2Wout@30Vdc .... at 40Vdc a short
burst
with almost 15Wout and then down down down... :-((((((
I noticed a difference in comparison to your project: you connected
the
+ and - rails to ground via 10nF and here I used 100nF caps could it
explain this behaviour?
73 Marco
----Messaggio originale----
Da: [email protected]
Data: 1-giu-2017 22.20
A:<[email protected]>
Ogg: R: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...
that was also my thought.. but they run at room temperature: the
resonance is obtained with 4 polyesther 2200 pF 2000 Vdc caps. the
classic boxes 25x15x5mm
Marco
----
Messaggio originale----
Da: [email protected]
Data: 1-giu-2017 22.03
A:<[email protected]>
Ogg: Re: Re: Re: LF: Re: I: Fw: For today the FETs survived...
If the conditions change as the PA is operating, it looks like
capacitors
heating up and changing its value. I can't think of any other
component
that will change with dissipation / heating. What type of capacitor
are
you using in the tank?
Andy
On 1 June 2017 at 19:59, [email protected]<[email protected]>
wrote:
anybody has good ideas for a replacement hobby?? fishing? growing
flowers?
Andy: the suggestion of try without the guard circuit revealed that
some effects in this area are present.
I left the guard coil in place (I'm a bit lazy...) and disconnected
simply the 2 wires from the rectifier bridge.
The output improve of about 4dB with Vdd from 10 to 30V, the output
is
stable up to 20Vdd, on 30V it show a peak of 16W, then the output
starts to decrease till a couple of watts :-( this happens also at
40
and 50V.
The resonance of the output LC (with the guard coil open) shifts
from
137 to 140 kHz and the bandwidth decreases from 20kHz to 10 kHz.
I need a long weekend of meditation...
73 Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 31-mag-2017 21.05
A:<[email protected]>
Ogg: R: Re: Re: LF: Re: I: Fw: For today the FETs survived...
Andy.. you are almost better than online help desks :-D
yes the guard circuit is on place but no current is flowing toward
the
PA, testing disconnetting it needs just to warm up the iron ;-)
the PS should
provide enough juice for 1200W input and the IRF460A are rated for
20A
@ 25°C (13A @ 100°C) so.. I admit it would like to give a try ;-)
I don't guess the core is saturating specially at this power level
where rms is only 22V, the core is 50mm OD and has 195,7 mm²Ae: if I
am
not totally wrong B should be< 0,03T @50V with 7 turns on the
primary
Will tru to disconnect the guard circuit just in case the squirrel
is
running in its cage ;-)
Thanks again for assistence
Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 31-mag-2017 20.39
A:<[email protected]>
Cc:<[email protected]>
Ogg: Re: Re: LF: Re: I: Fw: For today the FETs survived...
7:19 turns (assuming 50R output) means you have a load resistance
of
6.8
ohms which for 180V DC (81 V RSM fund sine) is nearly 1kW I don't
think
you really mean to go that extreme do you? 13 ohms is more
realistic.
As for the tank resonance changing as power increases, that is very
wrong.
I wonder if the transformer is saturating. Not sure of your core
Ae,
but
lets assume 200mm square, a core of about 16mm diameter.
V = 4.44.F.N.A.B Plugging in 137kHz 7 turns, 200 mm^2 and a Bmax
of
0.1
that suggests 85V RMS.
Which is exactlyly what you have. I suggest more primary turns .
Before
a transformer ratio of 1:2 was suggested, for Rload = 13 ohms
Is the guard circuit in place ? Don't forget, it has to be
customised
to
you exact currents and coil Q. Get teh PA operating to its proper
settings
foirst - that you can do at low voltage power, it scales perfectly.
Only
when it it working properly can you add and set up the guard
circuit.
When I did teh 700W PA, I had a complete workign (albeit unreliable)
unit
before even thinking of teh guard circuitry.
Andy
On 31 May 2017 at 18:50, [email protected]<[email protected]>
wrote:
Hi Andy... me again...
I was so curious to see what could happen thatI had a very quick
dinner and connected all, but...
now the output xfmr has 7T/19T here my
readings/calculations:
(see attached picture)
again the power increase from 10 to 30Vcc then from 30 to 50Vcc
after
an initial burst it start to fall down..
I checked also the resonance of the LC: till 30Vcc is tuned on 137
kHz
with a 3dB bandwidth of 20 kHz, when I move to 40 and 50Vcc the
"maximum" output shifts to 165 kHz...
mumble mumble
I tempted to have roasted FETs for dessert and see what happens at
180V!
Marco, IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 30-mag-2017 23.50
A:<[email protected]>
Cc:<[email protected]>
Ogg: Re: LF: Re: I: Fw: For today the FETs survived...
I've just looked again at the circuit diagram you sent - on there
the
values are different from your statement in the email. It shows
primary 5
turns, secondary 12 turns so a load resistance in the order of 9
ohms
which
is rather low if you are intending a Vdd of 180V - but closer to
the
ideal
Rl
The tank components have a reactance of 130 ohms which is too high
a
Q
is
used with that 9 ohms Rload, You should be aiming for a Q in the
region
of
6.
Even with the optimum load R of 13 ohms described last time for 500
Watts
from 180V rail the resulting Q of 10 is a bit too high - you will
end
up
with high voltage and critical tuning
Andy G4JNT
On 29 May 2017 at 19:07, Andy Talbot<[email protected]> wrote:
Yes.
As you'll see in my original write up, I originally forgot that
the
peak
of the fundamental sine component of a square wave is GREATER
than
the peak
by a factor of 4 / pi and initially my PA delivered a lot more
power
(1.6
times) than it was supposed to.
So if the square wave has a peak value of 1, its fundamental sine
component has a peak value of 4/pi or around 1.27. The RMS of
the
resulting sine is SQRT(2) less than this giving a Peak square to
RMS-
sine
ratio of 0.9.. If you specifye peak-peak of the square wave, a
further
factor of 2 applies, leading to the 0.45 ratio described before.
Incidentally, this same ratio appears in that equation for flux
in
a
magnetic code, V = 4.44.F.N.A.B
The magic number 4.44 is actually SQRT(2) * pi and comes
about
from
the same sort of sine to square transform.
Andy
On 29 May 2017 at 18:48, [email protected]<marcocadeddu@tin.
it>
wrote:
uhuh... a slightly silly misleading assumption... Vdc are the
same
of
Vrms before FETs make their work!
Thank you Andy for pointing out it!!
With this approach calculation changes a bit and probably with
the
right Xfmr the PA can give higher satisfaction :-)
Hopefully the FETs will survive and this time I'm ready to
burnout
the
antenna hi
Will keep you both updated, thank you once more Andy
73 Marco, IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 28-mag-2017 21.18
A: "[email protected]"<[email protected]>,
<[email protected]>
Cc:<[email protected]>
Ogg: LF: Re: I: Fw: For today the FETs survived...
First thing I noticed is that your turns ratio on the output
transformer
doesn't look right.
You quote "* ... with primary winding of 15 turns and secondary
of
12
turns...*"
180V DC in a half bridge is 180V peak-peak square wave.
The fundamental sine part of that is 4/pi * 180 = 229V pk-pk
so is 229V /[2.SQRT(2)] = 81V RMS
To a good approximation RMS(fund) from a half bridge is Vrms
(fund)
=
0.45VDC
For 500 Watts out, Rload = 81 ^ 2 / 500 = 13 ohms
So to match to 50 ohms you need a turns ratio of SQRT(50/13) =
1.9:
1 so
call it 2:1 Keeping 12 turns on the secondary means you need 6
turns
on
the primary
When operating at reduced voltage, the power out will vary
exactly
as
the
square of the voltage.
Recalculating from first principles for a 12V supply:
12V DC = 12V pk-pk = 12 / [2.SQRT(2)] * 4/pi = 5.4V RMS
(fundamental)
in 13 ohms should give 5.4^2/13 = 2.2 Watts
check using ratio of voltages, squared :
(12V/180V) ^ 2 * 500W = 2.2 Watts which is the same as above.
QED
Your 15:12 ratio result sin a load impedance of (15/12)^2 * 50 =
78
ohms
At 40V DC == 18V RMS(fund) that will give 18^2/78 = 4.1 watts
which
is
actually LESS that you are seeing - the 2* discrepancy is odd,
but
the
low
power is in the area of what you measured..
Andy G4JNT
On 28 May 2017 at 19:34, [email protected]<marcocadeddu@tin.
it>
wrote:
Hi Chris,
I tried to post this message on the reflector but apparently I
had
no
success..
As promised I keep you updated but as you can read in the
attachment the first trials were not enocouraging...
Andy, may I ask you to read my report? your interpretation and
suggestion are welcome!
73, Marco IK1HSS
-----Original message-----
From: "[email protected]" [email protected]
Date: Sun, 28 May 2017 17:01:33 +0200
To: [email protected]
Subject: For today the FETs survived...
Hi LF,
hope that also the toroids of Chris survived!
My FETs survived, but they are not working as expected :-(
Attached the report on my attempt to duplicate the half bridge
of
Andy..
Has anyone suggestions before I try to cook all connecting to
the
180Vdc supply?
Thank you
73 Marco IK1HSS
--
This message has been scanned by E.F.A. Project and is
believed
to
be
clean.
---------- Forwarded message ----------
From: "[email protected]"<[email protected]>
To:<[email protected]>
Cc:
Bcc:
Date: Sun, 28 May 2017 17:01:33 +0200 (CEST)
Subject: For today the FETs survived...
Hi LF,
hope that also the toroids of Chris survived!
My FETs survived, but they are not working as expected :-(
Attached the report on my attempt to duplicate the half bridge
of
Andy..
Has anyone suggestions before I try to cook all connecting to
the
180Vdc supply?
Thank you
73 Marco IK1HSS
--
This message has been scanned by E.F.A. Project and is
believed
to
be
clean.
|
