Path: ...!eternal-september.org!feeder2.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: clamper
Date: Tue, 5 Nov 2024 00:48:17 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 34
Message-ID: <vgbq0h$16ogn$1@dont-email.me>
References: <oiniijh85snm49j4ook6s2db2vbdehndbn@4ax.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Tue, 05 Nov 2024 01:48:19 +0100 (CET)
Injection-Info: dont-email.me; posting-host="9d039dd2fb801fde7e54e92b9b2851cf";
	logging-data="1270295"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+bVLETjVpwMZg7NTJoZSdc"
User-Agent: NewsTap/5.5 (iPhone/iPod Touch)
Cancel-Lock: sha1:oM1V7aBt1wmDbTh3judBjLpDK9k=
	sha1:zvxvX8xzNCFmByP2bO+sx3arZJ0=
Bytes: 2169

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 

-- 
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics