Re: clamper

On Tue, 5 Nov 2024 00:48:17 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

john larkin <jl@glen--canyon.com> wrote:

I want a small cheap voltage clamper device. I'd like under 2 volts
drop at 1 mA, but minimal current at a few hundred millivolts.
 
I tried two small diodes in series, but that's terrible. Better is a
logic-level mosfet with gate connected to drain. It clamps nicely at
1.5 volts or so but conducts picoamps at a few hundred mV, over 1000:1
better than the diodes.
 
This will go between the force and sense leads of a 4-wire temperature
sensor thing so it automatically works in 2-wire or 4-wire mode.
 
The alternative is to use two SSRs and let the user explicitely
declare 2-w or 4-w mode.
 
 
 

>
A red LED.  I’ve measured some which leaked less than 50 fA at 20 C, from
-5 to +0.5 V.
>
I used them as switches for a pyroelectric array, with bias current
supplied by illuminating them faintly under processor control.
>
They were cheap CML parts in early transfer- molded board (TMB) SMT
packages, and are now discontinued.
>
Cheers
>
Phil Hobbs

That's an idea. Maybe use the two LEDs inside a dual optocoupler. They
are always in the dark.