Re: Curve Tracers

On Fri, 22 Nov 2024 00:37:37 +0000, chrisq <devzero@nospam.com> wrote:

On 11/20/24 11:32, Cursitor Doom 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

>
It's not too difficult to build a low power ct. We built one
in school decades ago, using a diode pump and clock, to generate
the stair step base drive. IIrc, we used half wave rectified
ac for the collector sweep.
>
Not so easy to build an accurate system, especially for testing
power devices, which typically need high voltage and current.
Here, an old Fairchild 6200B, none working from Ebay, gets
regular use, both go / no go and for matching devices. That dates
back to the late 1960s, and uses a four stage binary counter,
with 1,2,4,8 resistor network d to a, to generate the stairstep.
A small variac drives the collector sweep.
>
Chris

Ignoring thermals, a transistor data point can be taken in not many
microseconds. So a charged cap could furnish lots of amps.

A  c-v curve would be taken at zero current. So a curve tracer could
be tiny.