One way I've seen an electronically variable inductor designed is to put a
DC control current through an extra winding. The control current moves the
operating point up or down on the B-H curve and thus changes the inductance.

This technique has advantage of being fast and inexpensive, but may not give
you the control range you need. It may also cause change Q with L, which may
or may not be a problem for your application. You also may need to
experiment to find an appropriate core material.

Of course the DC control voltage must be fed through an isolating choke, or
else it will look like a shorted turn to the 1-25 KHz signal.  If you are
using a toroid inductor, you can wind the magnetizing control winding on the
outside of the toroid, so that it is isolated from the internal signal.
Sort of like this:  (((o))) where the o is the toroid core with the windings
made in the normal fashion where the flux is constrained within the core,
and the ((())) represents a control winding made around the outside of the
core.


Jack


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vasile Surducan
Sent: Wednesday, August 13, 2003 7:42 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: my chalenge: 2KVrms sinusoidal in 1...25KHz range


I need to generate 2KVrms into a small capacitive load (below 1nF).
So far I have good results with a resonant output, voltage to current
converter. The problem I have is that I need a precise way to control
the generator output inductivity (other than changing the coil wires
numbers or the air gap in the ferrite core) to cover the whole frequency
range. Do you know other methodes to get such high voltage in the
frequency range required ?


top 10 wishes,
Vasile
http://surducan.netfirms.com


On Wed, 13 Aug 2003, Wouter van Ooijen wrote:

> > However, even though I have inserted the guards into my
> > header files as above, I am still getting multiple
> > definition errors relating to globals that are defined
> > within those header files.
>
> Global what's? Variables? A variable in a .h file should in most cases
> be declared external, and only appearing in one .c file as not external.
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
> consultancy, development, PICmicro products
>
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