Re: Curve Tracers

On Wed, 20 Nov 2024 14:57:10 -0800, Dave Platt wrote:

In article <vhkhcg$2ip8$2@dont-email.me>,
Cursitor Doom  <cd999666@notformail.com> wrote:
 

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.

 
One of the challenges is the tradeoff between power and safety.  If you
design the tracer to be very-safe for small-signal devices (limited
voltage and current delivery ranges) then it won't be suitable for
tracing power semiconductors.  Make it beefy enough for big parts, and
one slight misadjustment of a switch will turn a small-signal
semiconductor into cheap or expensive vapor.
 
It's a multi-variable optimization problem (voltage and current range
and limiting, tracing speed, cost, and operator skill) and I suspect
there's nothing like a single right answer.  Ya pays yer money and ya
chooses yer limitations (or amount of shrapnel).
 
https://www.eevblog.com/forum/testgear/fooln-around-with-dso-awg/
 
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The SDG 2042X mentioned in the first article, and its faster cousins can
be controlled via SCPI.  It has voltage and current output capability
good enough to test small-signal transistors on its own,
and you can hook it to an external two-channel power amplifier and gain
stage to test heftier parts.
 
A lot of inexpensive digital-storage oscilloscopes also support SCPI
control.  So, you could automate a lot of the setup and testing, and
even capture the DSO screen image (or upload the two-channel data
traces, and re-plot them on your computer).
 
Many people feel that older analog scopes work better in X/Y mode than
any of the DSOs do, thanks to the persistence of the phosphors and the
continuous nature of the "data capture".
 
I haven't built one of these myself, as I have an old Heathkit
plugs-into-your-scope unit, and a 7CT1N plugin for a Tek 'scope
mainframe.

Interesting point. I've a couple of NOS analog storage CRTs that would be
absolutely ideal for this application as they naturally are able to
provide much longer persistence than a regular analog CRT. Thanks for the
suggestion!