From: email@example.com (Andre)
Subject: Re: hi-capacity voltage controlled capacitor?
Date: 13 Oct 2002 12:00:41 -0700
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 13 Oct 2002 19:00:41 GMT
firstname.lastname@example.org (N. Thornton) wrote in message news:...
> email@example.com (transformer) wrote in message news:<firstname.lastname@example.org>...
> > The truth is that I have built such a device but do not know if it is
> > a useful invention.I see that there are no such devices present. Could
> > anybody comment on its usage. The invented device varies between 2uF -
> > 100nF and has bad linearity.
> > Thanks
> I don't think you're the first, as is usually the case. Most ideas
> fall at some hurdle.
> One can take a 1930s style paper capacitor, wind it loosely instead of
> tight, and just vary the pressure on the resulting paper stack. Voila,
> one variable cap.
> Or make a wet electrolytic and vary the liquid level.
How about paralleling standard varicaps ? They go to 10pF IIRC, so
1000 in parallel = 10 nF .
Just a (fairly pointless) idea . Imagine troubleshooting something
like that ! :)
Alternative idea . How about using a standard device but reverse
biased ? Something like a large area transistor.
How about a MOSFET ? Those have a pretty large gate capacitance,
especially the old style devices . For example, the 2SK2038 has a gate
capacitance of 4 nF according to my RS meter , with drain and source
One way it measures 1 Mohm , the other it measures open .
> I don't know of any example of such a thing being used.
> Whatever haps with your idea, if you can have one you can have
> another, and another... and at some time you'll get a goodie
> hopefully. Thats how it worked for me.
> Regards, NT
> > > > Dear All,
> > > > I need a voltage controlled capacitor for the nF-uF range. I know the
> > > > varactor diodes but they are in the pF range. Is there such a device
> > > > present or am I dreaming?