manishanand14
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There's probably an error of reasoning involved because thicker dielectric will be already compensated by larger effective area. The ESR is however not located in the Al2O3 dielectricum itself rather than adjacent conductive layers. How it's thickness and conductivity varies with rated voltage depends.ESR goes up with higher voltage rated capacitors. Fortunately however a higher voltage capacitor is larger in size that more than offsets the increased power dissipation caused by the increased ESR.
One of the causes of ESR is the condition of the dialectric and a higher voltage capacitor has a thicker dialectric which causes the higher ESR.
There's probably an error of reasoning involved because thicker dielectric will be already compensated by larger effective area
ESR is not even a bit flat between 0 and 150 KHz..
Besides that, it is depending on the size of the cap. A big cap will reach it's SRF far before 1MHz,. And a low ESR 10V cap from brand X can have a much higer ESR as a 100V cap from brand Y. Low ESR is not defined. If the best cap you produce has a dreadfull ESR you are still alowed to call it a low ESR cap. I have seen chinese junk low ESR caps with a much higher ESR as standard caps from a brand like Panasonic.
I too designed some ESR meters, and measured hundereds of cap using GR (including the GR-1620) , ESI , Marconi and HP bridges , A IET DE-5000 and things like VNA's other impedance meters. I collect bad caps that I measure and mount on test pcbs to test meters. ESR is in the MOhms at DC, then drops fast until 1 to 5 KHz. Then it drops a bit lower to reach the lowest value around 50-100 kHz (for bigger can sooner as for smal smd caps, and thie lowest value is not at the SRF) The cause is the dielectroic loss and the increasing skin effect. The SRF is caused by the increasing ESL Bigger caps, longer legs cause more skin effect and ESL and lower SRF
It's not a matter of agreeing or not agreeing. One only need make a series of measurements to find out what the facts are.I do not complete agree with the flat ESR and lowest ESR at SRF.
Today using VNA's it is proven that ESR is not at a minimum on the SRF.
I have read several publications about that. I was looking for that because I found out using my VNA that the ESR was often lower before SRF (self resonant frequency, in case of caps sometimes called series resonant frequency). The reason they thought ESR was at minumum at SRF is because they used to measure caps using an impedance analysers that only measured |Z| and were not able to split this into R and jX.
Most VNAs are not able to measure at low frequencys. But with the very small smd caps and much higher frequencys today the VNA is used more often because many impedance meters are limmited to a few MHz. However the difference is very small and very hard to measure. A very small calibration mistake can shift the SRF to a complete other frequency. I use custom traces, de-embedding, OSLC calibration and custom made fixtures with calkits for these measurements. Very interesting things. I also measured on thinngs like skin effects, dielectrics behaviour and leakage, fringing fields (if that is the correct english term for edge effect) etc
About the flat ESR, it is not important, the graphs show it and people can see it. But for those who do not are experienced in reading analyser graphs and if we keep it correct, I have to add that you use a log scale. My experience is it is getting flat somewhere between 10-50kHz. On linear VNA plots the picture looks complete different but it is the same. The reason it looks flatter in your plot is because you use a log sweep. Make a linear sweep and you will see it better.
I'm not saying that the ESR curve is absolutely flat, but you said that it's "...not even a bit flat." You were, of course, referring to pjmelect's unfortunate choice of a frequency range that went all the way down to zero hertz. It's quite true that the curve is not even approximately flat over that range, but it is reasonably flat for some electrolytics if the sweep only goes down to 50 Hz. I show an example above where it is NOT even reasonably flat when the sweep starts at 50 Hz, and in the other post where it IS reasonably flat.
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