Re: Curve Tracers

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.