Variable frequency component tester

[Sigmoid]

The oldschool octopus component tester is fed from the wall, and utilizes its 60/50Hz oscillation to generate the voltage swipe for tracing the UI curve of the component...
What I'm thinking about is using a function generator as the driver instead. This way I'm thinking I could test components for real-world characteristics at higher AC frequencies, audio freq and beyond, which would be really cool.

What I'm unsure about is if the 50 Ohm output of a function generator, coupled through an isolation transformer, can handle the voltage and current range needed to make meaningful readings... Has anyone done something like this before?

[PA4TIM]

Just connect an adjustable oscillator or your FG  to a power amplifier (an audio amp or make one with a power opamp)
Or use an oldschool generator. My old HP does 30Vrms in 600 Ohm, A GR bridge osciillator does 300V.

I do not know if a transformer between load and generator is a good idea. Does it not load your generator depending on the impedance of the load.(impedance transformation)

I made an octopus a few years agoo, after that a curve trace but since a few years I have a Tek 576 

[Sigmoid]

Thanks, yea using a transformer is a bad idea. I think I'll use some high speed op amps.

One for the driving signal, and one for each scope axis. What maximum peak-to-peak voltage and driving current should I aim for? I think most op amps go nonlinear around 10 mA.
Should I use some kind of transistor driver (like a darlington pair or mosfet) to avoid connecting the DUT directly to the op-amp output?

Also, I'd like to aim for a maximum frequency of 1MHz... that said, I've never built anything analog that operated above audio frequencies. Everything is going to be well below 1/100th wavelength, so I'm guessing all I'll need to watch out for is parasitic caps, but some pointers and hints would be welcome.

[PA4TIM]

There are opamps that can deliver a few hundered mA upto a few ampere.

Around 50-100 kHz skineffect will start to be no longer neglectable (depends how lineair it needs to be) and the same for paracitics. Upto 200-300 kHz it often only takes some proper (RF) building, (like enough and suitable decouple caps, traces or wire routing etc) but as frequency increases it becomes more needed and often it needs to use some form of compensation and/or R/L/C networks. (like small caps or trimmers over resistors, RF chokes etc)

And you need to be shure the opamps are stable in all circumstances.

[oldway]

Have a look here:
http://www.huntron.com/products/trackers.htm
NB: register and download the full 51 page version