Click here to go to our main page on curve tracer measurements
New for November 2024. A curve tracer is one of the best instruments for understanding nonlinear behavior of semiconductors. What the heck is a curve tracer? It's a voltage source hooked up to a selectable current-limiting resistor, for tracing voltage versus current curves, displayed on some type of screen. In the not-so-old days that screen was a cathode-ray tube. Secondary features include the ability sweep the voltage at some low frequency (a few hertz), and control an additional voltage or current source for tracing a family of curves of three-terminal devices.
In this modern age, a curve tracer can be replaced with some expensive "source measurement units" and software. But like playing a vinyl LP instead of digitized crap on an MP3 player, you are gonna miss a wonderful experience. You have some options for acquiring a curve tracer... look for a used Tektronics 576, buy a new Chinese copy of a Tek 576, or buy or build some current/voltage adapters and plug them into the X-Y terminals of an oscilloscope. There are many web pages and videos dedicated to creating a curve tracer from an oscilloscope, like this one.
Curve tracing without a curve tracer
What if you just need to make just one or two I-V curve measurements and you don't want to screw around all day figuring out how to build yourself a curve tracer from an oscilloscope? For example, what if you wanted to evaluate a diode to accurately see its voltage/current characteristic, rather than plugging it into a Fluke meter and get a good/bad indication.
To help you out, we produced a video of how to MacGyver your own curve tracer with a couple of digital volt meters, a resistor, some wires and of course an Excel spreadsheet for plotting the data. The device under test is a TVS diode. We don't have a page on TVSs, so here it is described on Wikipedia. TVS diodes should be considered as your first line of defense against power supply voltage transients when you are building a system that you plan on marketing.
There are many types of nonlinear behavior, In the video you will learn that for certain IV curves such as FETs you can get away with NOT using a current limiting resistor, but for diode breakdown curves you are going blow the device if you are not careful. You could step the current limit on a power supply through a set of values and plot the voltage across the diode at each current. We don't recommend putting a lot of faith in power supply current limiting, you are likely to spike the voltage before the limit sets in. Put your faith in an actual current limiting resistor, like all real curve tracers do!
Curve tracing without a curve tracer
Note to the Day Job: no fifty-ohm loads were harmed in this experiment! And if only our Chinese knock-off curve tracer was not MIA, it would not have been necessary to do this.
Note to readers... the above paragraph could be construed as the equivalent of a theatric performance breaking the "fourth wall"...
Useless information, opinion and advice
MacGyver was a TV show about sticking it to the The Man, with hefty doses of quickly-developed engineering solutions. Speaking of MacGyver, B. A. Baracas was just as good at hacking together a life-saving technical result on the A-Team. These shows overlapped for a few years in the 1980s, with McGyver on ABC and A-Team on NBC. Are these shows worthy of being cataloged by the Library of Congress? Of course not, but they don't suck any worse than many recent efforts. Angus MacGyver was played by Richard Dean Anderson and B. A. Baracus was played by Mr. T. It is a tough call judging who had the better haircut in 1985. Both actors are alive and well and are known for charity work. You would do well to follow their lead, take time out from being greedy and give something back.