Hi,

You all have a nice 2020

Yesterday I connected the 6x 10uF 50V WIMA to get an impression of the leakage current and DZA of these capacitors.

The large WIMA 100uF 63V MKS4 had become almost immeasurable, so low was the voltage across the 10K series resistor.

It was close to the drift, input leakage and noise of the reference and the measuring instrument used.

This 100V 63V WIMA MKS-4 capacitor could well be used in my LM399 reference circuit,

the leakage is very low and the DA can be used for a reference that is in a oven because of the heating time to get stable.

But it is much too big for my oven.

Great, let's go back to the 6x 10:00 WIMA in the 50V version...

It's always good to put your components to an extra test.

I have already used these capacitors in several filters and had no problems with that.

But with the filter application of this LM399 reference design, many more properties of the capacitor are important.

Of course I looked in the datasheet of this type of WIMA MKS2 and hoped that the insulation value would be better than mentioned in the datasheet.

And I think this is also the case but I use six capacitors in parallel, that doesn't really help.

And when I think of what forum user "maat" explained, that the leakage current of this type of capacitor is quite temperature sensitive, it is better not to use this type of capacitor in this project.

But then what?

Back to my old filter which I also used in other voltage references including my main LAB 10V reference which is also in an 42C oven.

That is a bootstrap electrolitic capacitor filter, placed here in the latest version of the schematic.

So now we are going to perform the next test with 330uF capacitors.

There are already a few types here, which I have already bought for low leakage applications in this kind of filters.

So now we are going to perform the next test with 330uF capacitors.

There are already a few types here, which I have already bought for low leakage applications in this kind of filters.

For the first test, I attached two 470uF 35V Nichion and two 470 Nichion 16V to my 10V reference PCB in a "real" professional way!

This test is with new capacitors, no formatting in place.

And here I am formatting 13 capacitors at 15.5V.

I'll leave this on for about 36 hours.

I still use my series HP and Harrison power supplies for general testing in the LAB.

Here I use the Harrison 6823A for the capacitor test, on this power supply I also mounted a BNC so it's easier to connect it to one of my function generators.

The test with these capacitors on the 10V reference is now on for 0.5 hours and the leakage current is already lower than with the 6x WIMA 10uF 50V capacitors!

And that is with completely new capacitors without having formatted them on 15V first.

I now measure 18uV over the 10K resistor and the 6x 10uF was 45uV after 12 hours.

Looking good for the first test...

Kind regards,

Bram

PS

I forgot to add the Spice simulation of the low pass filter.

Does anyone know how I can get the graph in LTSpice so that there are more lines so that it is easy to read?

I don't use spice much so I don't have much experience with it yet.