Re: Designs of voltage/current controlled resistance

On 21/05/2025 17:26, Edward Rawde wrote:

"RodionGork" <rodiongork@github.com> wrote in message news:d469c760bbcd14a1f148c0e1b29653f7@www.novabbs.com...

Hi Friends!
>
What approaches exist of creating voltage or current-controlled
resistance?

 Usually opto devices or FETs.
It has been recently demonstrated here that there are other approaches but it depends on what you're trying to achieve.

To be more specific, have a look at the H11F1 which is an LED
coupled with a bidirectional light sensitive FET.  This has been
around for many decades but is still available.
John

 

>
There is no some specific schematic in which I want it to be plugged in,
but I'm designing a few gadgets related to electronic musical
instruments - and sometimes I want such resistance for volume control
while at other times to be used in certain frequency generator to
control the frequency itself.
>
I vaguely remember there is JFET but care is needed to fit signal into
its small-voltage "ohmic" region and provide suitable bias to the gate.
>
Also at least for some schematics opto-couple with resistor in the
output part seems viable (though I'm not sure about linearity - on the
other hands linearity is not often needed).
>
Next there are motor-driven potentiometers but in my context it looks
ridiculous.
>
Also I vaguely remember tube triode has curious voltage-current
characteristic which probably means it could be utilized in a way
similar to JFET (though it is a bit exotic).
>
And then there are complex and composite devices, digital resistors etc,
but I prefer to work out some more "plain" solutions as they are in part
for educational purposes (e.g. to be constructed by school pupils).

 If it's for school students I'd have them play with one of these and a variable light source in a closed box.
 https://www.google.com/search?q=ORP12&udm=2
 

>
May I be missing some fine schematic with a handful BJT or something
like this?

 Depends on exactly what you want to achieve.
 

>
thank you in advance,
sincerely yours,
Rodion
>
-- to email me substitute github with gmail please