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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: Curve Tracers
Date: Wed, 20 Nov 2024 22:26:05 -0000 (UTC)
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john larkin <jl@glen--canyon.com> wrote:
> On Wed, 20 Nov 2024 18:00:34 -0000 (UTC), Cursitor Doom
> <cd999666@notformail.com> wrote:
> 
>> On Wed, 20 Nov 2024 07:40:08 -0800, john larkin wrote:
>> 
>>> On Wed, 20 Nov 2024 11:32:32 -0000 (UTC), Cursitor Doom
>>> <cd999666@notformail.com> wrote:
>>> 
>>>> Gentlemen,
>>>> 
>>>> Curve tracers reveal useful info about the dynamic characteristics of
>>>> semiconductors and make designing for same much more predictable and
>>>> dependable than relying on spice models and simulation alone. But
>>>> they're typically rare beasts and expensive to come by and boat anchor
>>>> varieties are seriously heavy and bulky.
>>>> I think therefore that a curve tracer would make an excellent project,
>>>> using the X&Y inputs of a scope as the display. Has anyone here
>>>> attempted this? I'd be interested to know what the main challenges are
>>>> likely to be.
>>>> 
>>>> -CD
>>> 
>>> I've considered it. It would be much more valuable if it traced
>>> capacitances too.
>> 
>> A VNA is best for that. I've been using my big HP one this afternoon to 
>> label some random bunches of caps and inductors whose values I couldn't 
>> read. Trouble is, there doesn't seem to be much agreement on what 
>> frequency to test these devices at. I've heard 100khz, 1Mhz, 10Mhz and 
>> 100Mhz mentioned from different sources. I'm pretty sure the 100Mhz 
>> testing is for RF specified devices only, though. From what I've seen, 
>> there's no reliable alternative to testing each batch for oneself, because 
>> (certainly with ancient NOS leaded (as in non-SMD) stock) you have no idea 
>> what frequency the factory tested them at and different manufacturers in 
>> different countries at different times used different methods!
> 
> What I want is C-V curves. I guess a VNA can do that with a some bias
> tees and various power supplies.
> 
> 
> 
>> 
>>> The display should be on a computer and the data archived.
>> 
>> For people such as yourself, certainly. For me as a hobbyist, a CRT is 
>> fine.
> 
> You have to read the analog screen and write down numbers. Or take a
> picture.
> 
> 
>> 
>>> I often just set up a breadboard and test parts. Last week I blew out
>>> some power mosfet gates. Some have internal zeners; this one doesn't.
>> 
>> I can kill a MOSFET at 50' just by looking at it (certainly in winter). In 
>> fact I shock myself from all the static I build up and it ain't funny. 
>> Having dry skin is great for when I touch HV by accident (happens quite a 
>> lot) but the flip side is I accumulate and hold static charge like no one 
>> else I know.
> 
> Some fets have protective gate zeners. They typically clamp at +-40
> volts.
> 
> Here in San Francisco, we never get static zapped. High humidity.
> 

I’ve done C(V) measurements with a Labjack and a Boonton 72A. Works great. 

Cheers 

Phil Hobbs 


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