Curve Tracers

I’ve done C(V) measurements with a Labjack and a Boonton 72A. Works great.

Cheers

Phil Hobbs

I normally just use a Python script and a couple of DC supplies/DDS to generate the signals, and a DMM to capture.

Won't do dynamic measurements, steady state only.

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).

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.

Great choice, Phil! You can't go wrong with a boat anchor and what you have there is about the most modern CT it's possible to own which you can still repair for yourself if necessary. I doff my cap to you, sir.

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

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.

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.

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

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!

How would you do that?

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

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

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.

You can buy an AD5522, but it only does low voltages.

Reading the spec and studying the state diagrams was a great learning experience. No nightmares whatsoever.

I designed lots of GPIB = HPIB = IEEE-488 interfaces for existing and new equipment, first starting with TTL, then CMOS, then LSI chips, then MCU bit-banging, and finally using the NI (National Instruments) chips together with an MCU. Last design with GPIB was the PLPS2005

Arie

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

We like USB for small boxes. It's basically free on an RP2040. If it enumerates as a serial port, you don't even have to install drivers.

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.

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

I said "a bit" more modern! I like my plots on a PC screen not on an analog scope!

I haven't had to thankfully. I have a few pieces of HP-IB gear (Agilent E3631 bench supply, frequency counter, couple of bench multimeters) and they all connect to a Linux PC via a USB dongle, and I can use them in Python scripts with PyVisa:

All works very well considering. And there's a surplus dealer south of Boston where I can get nice ex-MIT Belkin cables at $10 a piece 8-)

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.

They didn't when he was last in power. He talks a lot, but isn't great on making things happen (except perhaps extra deaths from the US Covid-19 pandemic, but even there it was his inaction which was decisive).

Except that Biden didn't destroy any US jobs - in fact he created a lot of new ones.

And your "globalists" exist only in your diseased imagination.

That needs updating!

Same here. Function generator arrived today direct from China and I didn't have to pay a penny in sales tax for it. No duties whatsoever. Express postage was free, too. The treasuries of Europe must be losing untold tens of billions in taxes due to this. And yet everyone has to pay sales tax on domestically-produced goods! It's madness on steroids. They'll probably claim it would cost more to collect the tax than the revenue doing so would generate, but that's indefensible BS plain and simple.