LCR tester with DC bias.

[schmitt trigger]

've been wanting to investigate the actual capacitance of class-II MLCC, operating  with the actual workingbias. And yes I know that MLCC manufacturers publish typical data.

Conceptually, the idea is simple: connect a LCR meter to the cap under test while adding in parallel a variable DC power supply.

But even a dimwit like myself knows that this would be a VERY STUPID IDEA. At best, the supply will add a parallel impedance which will load the reading. At worst, the LCR will let out the magic smoke.


What I have struggled to figure out, is how would one isolate the LCR from the supply and viceversa. I am aware that some higher end LCR meters incorporate a DC bias option.

Any ideas how that could be done?

Edit: I also have posted this same question in another forum.

[magic]

For measuring junction capacitances of semiconductors I came up with this: isolate the meter from DC bias using a second capacitor with much lower impedance (higher value) in series, isolate the bias source using a resistor with much higher impedance (resistance).

Maybe this could work for MLCCs too, using an electrolytic to AC couple the cap under test.

[gamalot]

Some LCRs come with a built-in bias voltage source and some don't. When your LCR doesn't have it built-in, or its voltage range is too low for your application, you can consider an external voltage source.

You can consider buying an external voltage source adapter, or DIY a similar device to meet your needs.

Reading the Keysight Impedance Measurement Handbook will help.

https://www.keysight.com/au/en/assets/7018-06840/application-notes/5950-3000.pdf

[mawyatt]

If one is able to DIY, here's some threads one might find useful

https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/

https://www.eevblog.com/forum/projects/ceramic-capacitor-behavior/

https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/

https://www.eevblog.com/forum/projects/lcr-lab-grade-parameter-plotting-fixture/

We've measured everything (with this DC Bias Fixture and Techniques) from various ceramic types, to Electrolytics, to Tantalums, to Polymers, to Mylar, Polypropylene, Polystyrene, to Mica, to Diodes, to Zeners and so on. We can report this adapter and technique works quite well indeed

BTW we are considering creating a Special Version to venture above the typical 100KHz limitations of most LCR Meters, as well as into extremely high Capacitance (>1mF) devices, if interested let us know

Best,

[schmitt trigger]

I understand now, the protection diodes are the piece of the puzzle that was missing in my brain.

Thanks!