Re: Curve Tracer

On Wed, 05 Feb 2025 08:18:49 -0800, john larkin <JL@gct.com> wrote:

On Wed, 05 Feb 2025 15:33:11 +0000, Cursitor Doom <cd@notformail.com>
wrote:
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On Wed, 5 Feb 2025 08:27:01 -0000 (UTC), Ian
<${send-direct-email-to-news1021-at-jusme-dot-com-if-you-must}@jusme.com>
wrote:
>

On 2025-02-04, john larkin <jl@glen--canyon.com> wrote:

On Tue, 04 Feb 2025 23:03:34 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

On Tue, 04 Feb 2025 10:19:40 -0800, john larkin <jl@glen--canyon.com>
wrote:
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On Tue, 04 Feb 2025 16:51:22 +0000, Cursitor Doom <cd@notformail.com>
wrote:
>

Gentlemen,
>
I've decided a nice project would be to build a curve tracer which
would (because I'm a vintage nut) use a CRT display of an
oscilloscope. From time to time I have these Big Ideas and it could
conceivably become the latest in a long line of my unfinished
projects.
>
Which curves would be essential to include for a decent, functional
design? I know what the obvious ones are; just wondering if there are
any more obscure ones which would be advantageous to plot. Finally,
are there any additions one could make to a classic curve tracer's
functionality which were omitted from the early designs (modulation
feature at 1Mhz,100Mhz or whatever) for example?
>
CD.

>
I'd like to see pulsed avalanche behavior of mosfets, preferably to
destruction.
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C-V curves would be great too.
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Stuff that's not on the data sheet.
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The thing about an analog CRT scope is that it isn't quantitative and
forgets instantly. A digital scope would fix that. A curve tracer
should be able to trigger the scope and do short single-shot events.

>
DSOs have their own disadvantages for this sort of thing.
These people make this little thing with a CT function, but it needs a
computer screen and is only capable of applying up to 10V! The stupid
fucks have only used a single AAA battery for its power source. Can
you believe that? I suspect there'll be a revised model along in due
course which has a far better voltage range.
>
https://www.peakelec.co.uk/acatalog/dca75-dca-pro-semiconductor-analyser.html

>
Given a digital scope, most measurements can be done in a millisecond
or less, so a curve tracer can have some tiny power supplies and a few
big caps.
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People don't use bipolar transistors much any more, so one could
emphasize tracing mosfets and GaN fets and SiC parts.
>
When I need to characterize a part, I hack up a setup with power
supplies and pulse generators and stuff.  We have a Tek scope with 4
isolated channels, which is handy snooping drain currents and such.
>

>
(crossing threads... )
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I've sometimes wondered if a gadget could be made that analyses a component
and spits out a spice model for it.
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Maybe if fed with multiple samples of the same component it could average
out the parameters.

>
That is actually a really interesting idea if it could be implemented.
However it goes beyond my pay grade so I'll have to defer to those
more knowledgeable about generating models for an answer to that.
>
John, that was the other aspect I meant to say could use updating:
instead of having rows of switches and level controls, would it not be
better to let a Pi or an Arduino do all the heavy lifting. The
programming for such a straightforward task to automate things would
be pretty elementary and make the use of the device so much faster.
>
Oh - one other feature: a 'subtract' function to analyze a batch of
'identical' devices to quickly select matched-pairs. Again that would
require some computerization.

>
Fun, but hardly anyone needs matched pairs these days, with cheap
opamps having microvolt offsets and nanovolt drift.

I had power output devices for RF and/or audio in mind, John. Also, in
my particular interest of vintage equipment repair, one frequently
encounters double transistors: two BJTs in a single package which are
matched and thermally bonded by their mutual encapsulation. These are
unobtainium nowadays,, so subbing in two discrete devices with the
same characteristics bonded together is the only viable alternative.