Re: voltage controlled resistor


<cary.niza@xxxxxxxxx> wrote in message
news:1179337427.875745.286540@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Does anyone know of an IC chip or discrete component intended to be
used as a variable resistor whose resistance value may be controlled
by varying its voltage input/signal
It really does depend massively, on the linearity you require, whether you
need to handle voltages that are unipolar or bipolar, and the actual
current levels involved.
The simple FET, is the commonest solution.
For AC, a pair wired as a 'bilateral switch', is the normal solution (the
4066, contains a small pair of FETs that can be used this way).
Historically, the Cds photo cell, was also sometimes used.
If noise is not a problem, for higher powers, simple PWM control of a
on/off switch is probably a 'better' solution.
Generally, most solutions go 'non linear' at some point. You can achieve
much wider control ranges, using something like the IL300 opto (or it's HP
equivalent). The 'point' about this type of opto, is that two of the sense
elements, are integrated into the single package, allowing accurate
feedback control of the resistance achieved.
For pure AC, the 'ecstatically wound choke', can be used, where a DC
voltage fed through one winding, moves the choke into saturation.
The number of possible solutions, is 'myriad', and a bit more data on what
is required, might help in making a better suggestion.

Best Wishes


.

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