Re: Designs of voltage/current controlled resistance

On 22/05/2025 6:14 am, john larkin wrote:

On Wed, 21 May 2025 16:03:54 -0400, "Edward Rawde"
<invalid@invalid.invalid> wrote:
 

"John R Walliker" <jrwalliker@gmail.com> wrote in message news:100l974$2nno5$1@dont-email.me...

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
>

>
Thanks. Interesting device, and LTSpice models exist.
>

 Interesting, but that looks linear to maybe 20 millivolts.

We are talking about the linearity of the light-sensitive FET
https://www.onsemi.com/products/interfaces/high-performance-optocouplers/specific-function-optocouplers/h11f1m
which is shown in Figure 2 of the data sheet. Like all FETs the channel turns into a constant current diode when there's enough voltage drop across  it - here at more than about +/-100mV, but the range over which it is linear enough is going to depend on the application.
--
Bill Sloman, Sydney