Hi cachehiker, thanks for the reply!
Interesting link, looks like a 'beefier' circuit to the method my original LC meter used. That is, using the inductor as part of an oscillator with a known capacitance, and measuring the frequency.
A meter I built, as stock:
Digital LC Meter Version 2 - VK3BHR
Original page for above meter:
**broken link removed**
Alas, like my own meter (but probably to a lesser extent) I fear it may suffer the same problem. For SMPS transformers/flybacks/coupled inductors, the second winding can change the resonance, or perhaps shift the frequency giving wildly inaccurate results. This is why I chose the rather inaccurate method of di/dt. It won't be much good for very low or very high inductance (say a range of only 4.7u to 47m) but it should also allow a rough estimate the 'saturation knee' given enough current. This can of course be performed with a basic circuit and oscilloscope, but as I mentioned in my first post... I'm tired of having to set up my scope, AND a bench 10A supply every time I just want to check something. A small, standalone, moderately accurate unit would be great.
I believe I have a good idea of the measurement process, providing a constant voltage across an inductor, and cutting off the supply once a certain current level is reached - which will be slowly incremented in stages from 50mA to 1A for inductance meansurement. And 0.5 to 8A for saturation.
My only problem seems to be using a capacitor (perhaps a super capacitor) to provide a
constant regulated voltage to the inductor. I've no doubt there will be some sag in the voltage, but to maximise accuracy, I'm using a low voltage of just 2V. This means that a sag in voltage becomes more siginficant when compared to an inductor voltage of say 12V. It also means Voltage drops across a current sense resistor and MOSFET switch must be minimised, or perhaps eliminated entirely by putting them inside the voltage regulation loop.
So, I have seen some app notes on using supercaps (or just 'large value' capacitors) for powering 'flash LEDs' in mobile phone cameras, using the supercap for a high current pulse - but these are constant current discharges. I require constant voltage disharge. So far I have a simple opamp-based linear regulator in LTspice, with a high current NPN darlington. A 12V 2200uF capacitor powers this, and it regulates down to 2V. Getting it to hold regulation when one suddenly draws up to 10A is tricky, but seems the cheapest and easiest way.
Any idea's on how fast transient voltage regulation is done at these currents? We're talking pulses of <500uS and with the input-output differential of a linear reguator being 12V to 2V the capacitor can discharge significantly before regulation is lost.