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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Designs of voltage/current controlled resistance
Date: Thu, 22 May 2025 23:30:27 +1000
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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