Voltage controlled variable capacitor

[devonNash]

I'm looking for a voltage controlled variable capacitor which can work in the range of micro-farads.The varacator diodes which I found only works in the pico-farad range.Any suggestions.Thanks in advance.

 

[Diver300]

I am fairly sure that they don't exist.

What are you trying to do with the capacitors?

 

[MikeMl]

Motorized variable tuning capacitor? I have built an HF automatic antenna tuner which has motorized variable tuning capacitors and roller inductors. I also have a mil surplus Collins unit like that. The motors is part of a servo, so you could say they follow a voltage

 

[Mr RB]

I'm pretty sure I've seen an opamp circuit that acts like (simulates) a big electrolytic cap, you may be able to adapt that circuit so the capacitance is electrically controlled.

Please post the circuit if you find/build one, it may be handy.

 

[devonNash]

I am fairly sure that they don't exist.

What are you trying to do with the capacitors?

I want to create a LC circuit.The driving signal has wide range of frequencies.The capacitor has to be automatically adjusted (by microcontroller) so that LC resonance frequency matches the frequency of the driving signal hence the reactance of the LC is very small.Because I am trying to make an automated system, a voltage controlled cap is needed.

 

[canadaelk]

google "capacitance multiplier" and maybe "totem-pole gyrator filter" E