Re: Curve Tracers

On Thu, 21 Nov 2024 23:35:13 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

On Thu, 21 Nov 2024 08:03:00 -0800, john larkin wrote:
>

On Thu, 21 Nov 2024 12:02:28 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
 

On Wed, 20 Nov 2024 16:37:39 -0800, john larkin wrote:
>

On Thu, 21 Nov 2024 00:00:10 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
 

On Wed, 20 Nov 2024 12:27:04 -0800, john larkin 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.

>
If you only want C/V curves, what's wrong with a plain 'scope and a
pulse generator?

 
How would you do that?

>
Ah! Well, I obviously mis-read your earlier statement. My bad, soz.
>

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.

>
It would only be a (slight) issue if I needed to share an image with a
third party. Aside from that, there's nothing I couldn't live with.
You're obviously requiring more than that, though.
>

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.

>
So you never need to wear a wrist/earth strap? That's a big plus. I
find them *so* restrictive and irritating when they (invariably) catch
on something.
>

Most mosfets drain avalanche, but the voltage is never specified,
in fact deliberately hidden. I have to measure that.  A good curve
tracer should measure that too.
 
Currents should go down to picoamps.
 
The fact that there aren't many curve tracers for sale suggests a
small market.

>
But a market, though small perhaps, there must be.

 
Sure. It would be a fun project.

>
And with thanks to Trump's tariffs, you might even make a few buxx out
of it, too.

 
Is there going to be tariffs on USB capacitance-measuring curve
tracers?

>
Not specifically, but I imagine Trump will want tariffs on Chinese
imports in general, which should give some breathing space profit-wise
to US manufacturers.
I have to say I do admire Trump's job creation ideas, which should
produce solid results, as opposed to old Joe's approach of destroying US
jobs, seemingly on purpose. I say old Joe's approach, but what I really
mean is the approach of the Globalists who tell him and his ilk what to
do.

 
We should stop paying the Chinese for the shipping costs of cheap junk,
for starters.

>
The US does that too?? Wow. I thought that was just a European thing.

The Chinese are a "disadvantaged country" per the International Postal
Union.

They will ship a cheap ebay thing here for free. It would cost me a
bundle to ship it back.