The Cyber-Spy.Com Usenet Archive Feeds Directly From The Open And Publicly Available Newsgroup Sci.Electronics.Design
This Group And Thousands Of Others Are Available On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic, Opinions Or Content Posted To This Or Any Other Newsgroup. This Web Archive Of The Newsgroup And Posts Are For Informational Purposes Only.
From: Mike Poulton
Newsgroups: sci.electronics.design
Subject: Re: Problems with MOSFET drivers
Date: 19 Nov 2002 02:51:52 GMT
Organization: MTP Technologies
Message-ID:
References: <21a524b0.0211160310.3cfbce8b@posting.google.com> <21a524b0.0211161739.4ac616b1@posting.google.com> <21a524b0.0211171752.9f6baa1@posting.google.com> <21a524b0.0211180005.7aac7c0d@posting.google.com>
NNTP-Posting-Host: pcp035640pcs.unl.edu
User-Agent: Xnews/L5
On 18 Nov 2002, "markp" said:
>> All of these schemes rely on the feedback winding giving an accurate
>> representation of what's happening in the secondary resonant circuit.
>> I'm not sure it does.
>
> With good inductive coupling from feedback to secondary it *has* to
> follow it, but it relies on good coupling.
Coupling is not good. The feedback winding is better coupled to the
primary than the secondary. This is an air-core transformer with
intentionally loose coupling.
>> The goings-on of the primary also influence it's
>> signal greatly. This makes it much more complicated to deduce what
>> the feedback means.
>
> Why? If there is good inductive coupling between the the windings the
> only perturbations will be due to things like leakage inductance.
There is extensive leakage inductance, and the coupling is not good.
The primary is in there, too.
>With
> adequate filtering the feedback winding will represent what is
> happening on the output voltage, it *has* to because it is coupled to
> the same flux as the output winding. If this were not true by the way
> your original system of driving the FETs from this is totally invalid.
It was invalid. It didn't work well at all.
> I'm proposing inserting a PLL into all this, which is actually a
> filter to remove such things as leakage inductance noise spikes that
> could end up causing wierd oscillations.
>
>> Measuring average current over a fraction of a second
>> is easy, and dI/dF near the resonant frequency is quite high. A tiny
>> bump of the frequency knob on the function generator drops the
>> current tremendously.
>
> OK, assuming a high Q on the output this would be true I guess.
If the Q's not high, it's not a Tesla coil. The bandwidth is very
narrow.
> Both halves of the primary are equally coupled to the secondary aren't
> they? If not, why not?
They not located in the exact same space, so they are not equally
coupled. Coupling is highly geometry-dependent here. The one closer to
the bottom will see a lower impedance than the one higher up. I suppose
you could use coax, with the shield as one half and the core as the
other.
--
Mike Poulton
MTP Technologies
Not only do I speak for my company, I AM my company!
Live free or die!
http://www.indefenseoffreedom.org/
Go Back To The Cyber-Spy.Com Usenet Web Archive Index Of The sci.electronics.design Newsgroup
|