DC bias on an LCR

[Noody]

Hi,

I have noticed a "DC bias" feature on some LCR units. What is it for and when could I need this?

Many thanks.

[tszaboo]

Ceramic capacitors (for example) have a high DC voltage dependence. They can drop their capacitance by up to some 70-90% at their rated voltage. Dave has a video on it, watch it.

[rfeecs]

It can be used to measure voltage dependence of the capacitance of a diode.  A varactor for example.

[dacman]

The capacitance of a power supply filter could be checked at actual working voltage if within range.

[Smokey]

http://www.kemet.com/Lists/TechnicalArticles/Attachments/191/Why%2047%20uF%20capacitor%20drops%20to%2037%20uF-%2030%20uF-%20or%20lower.pdf

DC Bias discussion starts at page 8... but the whole thing is seriously interesting.

[Noody]

Thanks guys! I'll watch Dave's video now and will study-up on the rest afterwards.

It seems that the Applent AT2816 LCR that I was looking at getting, doesn't have a DC bias feature, yet some cheaper alternatives, do. I see why this is useful, so should I be considering the lack of DC biasing as a strong negative in getting the Applent? It's been 25 years since I last seriously played with electronics. I don't recall DC biasing being a feature back then.

[tszaboo]

Depends what you are going to use it for. For inductors and resistors, it does not make a lot difference. For capacitors, you can just select ceramics which are known to behave well, or have datasheet with the information available. For a capacitor, it is a go/no-go test anyway.