EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: olsenn on May 10, 2012, 05:05:09 pm
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Are there any discrete voltage/current controlled capacitors or inductors? A three terminal device in which the state of one pin affects the rate of change of voltage/current of the other two pins?
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A gyrator could perhaps work if this is more a signal processing than a power application.
Check e.g. http://mysite.du.edu/~etuttle/electron/elect66.htm (http://mysite.du.edu/~etuttle/electron/elect66.htm) to see if that could work for you. The gyrator circuit as such is not controllable by an external signal, but incorporating a variable gain amplifier this could maybe be accomplished.
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Are there any discrete voltage/current controlled capacitors or inductors? A three terminal device in which the state of one pin affects the rate of change of voltage/current of the other two pins?
While not a 3-terminal device, a varactor diode is a used as a voltage controlled capacitance (over a relatively small range of capacitance).
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Siliconix used to make something called a Voltage Controlled Resistor, it's basically a high RDS(on) JFET. These had a resistance curve that was fairly linear, I don't know if it was a result of any special manufacturing process or not.
These are old, and I don't think you can buy them anymore, and maybe there is something else available now to replace them. Also, you can probably do exactly the same thing now with any number of off the shelf FETs operating in the triode region.
Basically my thought is to control the series resistance before your capacitor or inductor to limit the current and slow the energy transfer. This is no problem at DC but you have to be extra careful with this at frequency, as you'll obviously be creating a filter at anything other than DC. So you'll have to decide what a suitable topology will be for your purpose.
If your currents aren't too high, you could also use digital resistors.
it certainly would be much better if you could control the overall internal resistances of the two terminal devices :)