Potential Controlled Variable Capacitor
I am looking for a kind of variable capacitor, which can
be controlled by voltage applied on it, and whose capacitance range can
1nF-20nF. I knew that varactor diode is controlled by voltage, but its
value range is 100-800pf, which is not I want.
The use of Diodes as capacitors is the only means I am aware of in current
use as voltage controlled capacitors. Still, the values you desire are
close enough in range to what you can get that a work around is available.
Wire 10 Varactor Diodes in parallel with each other, and you will accomplish
the same result. for a 500 pF Diode, ten of them equate to 5 nF. It is not
the simplest, cheapest, nor most compact means of accomplishing this goal,
but it is the only means that comes to mind. I will include the formulas for
adding capacitance just to post them in a logical place, though I am sure
with the question you are asking, you are already well aware.
Capacitors in series with each other. (end to end)
1/C1 + 1/C2 = 1/Ct (where Ct is the total achieved capacitance)
Capacitors in parallel with each other. (Side by Side)
C1 + C2 = Ct
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Update: June 2012