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Author Topic: "RF and molecular bond breaking Kanzius style"  (Read 102624 times)

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As i wanted to follow the output section as mentioned in the PDF design as close as possible.
I can respect that.

Note that your winding has a very high pitch which creates large ratio of circumferential current to toroidal current.  This results in a large leakage inductance.
A winding that was wound like that with a Litz wire, would create the same circumferential current component and large leakage inductance, so this particular problem is not of the wire vs. tape variety but of a winding geometry.

Leakage inductance affects the Q negatively.
From the frequency sweep I can see that the Q is much better now, compared to the Q of your old build (more narrowband freq. response), but I attribute that difference to these new better capacitors.
   

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An inductor employing foil windings combines the very low dc resistance of a copper foil with the
low ac resistance of a Litz-wire winding. In particular, for high-current, high-ripple inductors, the shaped-foil winding can be the lowest-loss solution.

In other words for what we want here it is better than litz, at low frequencies and low power litz would probably be better :)

Regards

Mike 8)


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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."
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As a general rule, the most successful person in life is the person that has the best information.
   

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An inductor employing foil windings combines the very low dc resistance of a copper foil with the low ac resistance of a Litz-wire winding.
It does not "combine" it, it trades it off.

In particular, for high-current, high-ripple inductors, the shaped-foil winding can be the lowest-loss solution.
Yes, but not for high frequency inductors.  The 99% skin depth for copper at 13.5MHz is only 0.089mm so any copper located deeper than that does not participate in AC conduction and is utterly wasted.  However most of the copper in a Litz wire with 0.05mm strands will participate in AC conduction.

In other words for what we want here it is better than litz, at low frequencies and low power litz would probably be better :)
No, at low frequencies the skin depth increases so more of the copper participates in AC conduction.  At DC the entire copper participates.

For example, at 1kHz the 99% skin depth in copper is over 10mm, so almost an entire 0.1mm thick copper tape participates in the AC conduction, while at 13.5MHz only 35% of copper participates in AC conduction in such tape.
   

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@ Verpies

OK I'm still learning, I'm not a professional :)

regards

Mike 8)

But there still must be a reason for the professionals to use it :-\


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"All truth passes through three stages. First, it is ridiculed, second it is violently opposed, and third, it is accepted as self-evident."
Arthur Schopenhauer, Philosopher, 1788-1860

As a general rule, the most successful person in life is the person that has the best information.
   

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The copper strip i am using is 0.2mm thick and 1cm wide and i was meaning to silver plate it like in the PDF using this stuff:

http://www.homecareessentials.co.uk/acatalog/1Silver_Plating_Polish.html

It will increase conductivity for another 3% as i understand it, however not sure the above silver plating will be thick enough.


I can always use the litz wire (i got 10m) when efficiency stays low.
I also have 0.8m of 2mm diameter silvered copper wire which i can use.

But first of all, i would like to have a stable 100W output with this setup.


Regards Itsu
   

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But there still must be a reason for the professionals to use it :-\
There is a good reason to use tape windings at low frequencies.
Also, a thin tape works better at higher frequencies.  
There is also a technique that electrochemically deposits many layers of silver and a dielectric alternately and such sandwich collectively has a very high equivalent AC conductivity (admittance).

There is also the issue of the proximity effect which makes the admittance even worse than with the skin effect alone.
I can calculate the skin effect very precisely but I cannot do the same for the proximity effect, which is unfortunate because the proximity effect usually dominates the skin effect.
   

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IXRFD630 MOSFET driver also received and installed.

12.5V input voltage on this driver, direct connection between its output and the MOSFET gates as recommended by the datasheet.
Input signal is 13.5MHz 2.3V positive square wave 50% duty cycle, so i expected to see something like 12V square wave signal on its output
Instead its a 24V terrible shaped signal

Output into the dummy load seems ok 120W, however, the DC input / RF output relationship does not add up.

Anyway, its a start.

I have some 18V TVS which i could install across the gate/source, but i am not sure they can handle this output and/or the frequency
1.5KE18CA  

Screenshot shows:
yellow: input across the 50 Ohm input resistor attached to the input pin of the driver to ground
blue: signal on the gates of the MOSFET.

Video here:   https://www.youtube.com/watch?v=Mfucvo-C7Ms&feature=youtu.be

Regards Itsu

« Last Edit: 2015-09-19, 20:58:36 by Itsu »
   

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i expected to see something like 12V square wave signal on its output Instead its a 24V terrible shaped signal
If the amplitude of the gate signal varies together with the supply voltage applied to the drain, then you will know, that the extra gate voltage comes through the Miller capacitance between the drain and the gate.
Otherwise you have some parasitic inductance around the gate driver.
« Last Edit: 2015-09-20, 14:54:21 by verpies »
   

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Thanks verpies,

its almost inevitable to have some parasitic inductance as the minimum distance between a Vcc lug and the nearest ground lug is 1.6cm, while a decoupling cap is only 2mm, the rest are wires (inductance).

Regards Itsu
   

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Without a drain voltage on the MOSFET, i still have this badly shaped 26Vpp output signal on the drivers output lug and the MOSFET gates,
so to me this means that its not the miller capacitance that drives up that voltage.

I rearranged the drivers voltage (12V) return lead to be on the Vcc side and use very short wired caps (4 parallel on each Vcc lug)
to decouple the Vcc to this return/ground.

Caps used there are 4x 0.1uF parallel, 10uF tantalum and a 1nF wima.  This is on each Vcc lug

But even now i have a similar signal in the 26V pp range (13.5MHz).
Adding the 18V TVS across the gate/source of the MOSFET lowered this to about 22V pp, but still badly shaped.
So still struggling with this driver to get a decent signal out and into the MOSFET.


Regards Itsu
   

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Without a drain voltage on the MOSFET, i still have this badly shaped 26Vpp output signal on the drivers output lug and the MOSFET gates, so to me this means that its not the miller capacitance that drives up that voltage.
Yes, you eliminated that cause.


Could you have a scope grounding issue?
   

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I used my RF probe tip (you know the slip-on spring-like ground thingy) today, but the signals are still as bad.
I am almost sure it has to do with the decoupling of the 12V supply voltage (battery), so i will try some variations with some caps.
I see a distinct 42MHz signal ontop of the input signal (independent of the input frequency), so there seems to be a inductive loop somewhere.

Regards Itsu   
   

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i made some improvements on the MOSFET driver Vcc decoupling and added the 18V TVS on the gate again.
The input and gate signals are better now and the amp seems stable.
Next is to use the powerpack to supply 48/53V and a Dc2DC converter (48V to 12V@10A) to power from this also the driver.
Hopefully i will reach the 300W output so i can continue to the next step.

Video here: https://www.youtube.com/watch?v=wi4sbldNbf4&feature=youtu.be


edit: a quick test shows with the powerpack on (53.3V) it pulls 6A and shows 350W on the output meter, so its look enough.

Regards Itsu
« Last Edit: 2015-09-29, 20:17:01 by Itsu »
   

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Did you ever do any "water burning" with that 13.5MHz 350W output ?
   

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Nope,  no water burning attempted.

It was a great project, and i learned a lot, but the thing is not very stable.
Pumping 350W into a 50 Ohm dummy load is OK, but i don't see how to open the line and insert a tube of seawater in the stream without creating havoc on the final stage and thus blowing it.

I would need a much better variable impedance matching system (antenna tuner) between the Amp. and this tube insertion setup then the fixed matching setup i have now.

Perhaps when i run into some coils/caps i could build something and continue with it.


Itsu
   
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