Measuring inductor saturation (inductance at a DC bias) and capacitance at a DC bias

In power electronics, it is essential to make sure that the inductance of a choke will not decrease too much due to core saturation at the working current. There are basically two possibilities how to measure it - "statically" by using a usual LCR meter but providing DC current bias to the inductor, or "dynamically" by measuring the dI(t)/dt curve after connecting the inductor to a hard voltage source and checking its (non)linearity. The former method is simpler so I choose it first.
It is possible by the same device to measure the dependence of capacitance on DC bias voltage, which is rather large for capacitors with high-permittivity dielectrics.

The measurement tool is almost trivial, consisting essentially of a large capacitor separating the LCR meter from the DC-biased component under test, and a large inductor which blocks the AC test signal from the LCR meter flowing into the lab power supply used to provide the DC current/voltage bias. However, it is handy to have a tool built for this, to prevent accidental damage of an expensive LCR meter by voltage spikes when connecting a charged capacitor/disconnecting DC bias from an inductor connected to LCR. So I made one, where the LCR meter is actually connected only when a button is pressed, otherwise a resistor is connected instead. As the inductor used a toroidal mains power transformer, with switchable primary/secondary if higher blocking inductance or higher bias current is needed.

The schematics is dcbias.pdf, I built it without a PCB just connection the components together in a box and to plug-in banana sockets on its panel.

For the time-dependent method I have another project: inductor saturation tester.

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