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Old 19th November 2011, 11:01 AM   #18091
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Variation of capacitance with frequency for several cap types. MKN is polyethylene, and this makes biggest troubles regarding step response. It is impossible to make proper step response compensation with this cap, as the response is both over and under compensated.
Is that plot capacitance or imaginary part of impedance?
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Old 19th November 2011, 11:08 AM   #18092
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No, it's not. MKN is generally PEN, a type of polyester. Polyethylene is rarely used as a dielectric (despite superb dielectric properties) because of its low melting point.
EPCOS data sheet says PEN = polyethelene napthalate
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Old 19th November 2011, 11:21 AM   #18093
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Exactly. It's a polyester, it's not polyethylene.
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Old 19th November 2011, 11:22 AM   #18094
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Is that plot capacitance or imaginary part of impedance?
Axis shows delta C/C. So effective capacitance varies by 8% at 1 MHz.
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Old 19th November 2011, 11:32 AM   #18095
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Is that plot capacitance or imaginary part of impedance?
deltaC/C (cap. dev./cap)
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Old 19th November 2011, 11:35 AM   #18096
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Axis shows delta C/C. So effective capacitance varies by 8% at 1 MHz.
Yes, and this makes pretty bad step response.

We had a trick, in High Voltage dividers. For 1 : 200 divider, make it from a chain of 200 equivalent cells (R//C or R//R-C). Then the parasites and non linearities divide at 1 : 200 as well.
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Old 19th November 2011, 11:37 AM   #18097
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No, it's not. MKN is generally PEN, a type of polyester. Polyethylene is rarely used as a dielectric (despite superb dielectric properties) because of its low melting point.
You are wrong. MKN is polyethylene naphthalate. MKT is polyethylene terephtalate = polyester. I have already told you that you know almost everything, but just almost.
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Old 19th November 2011, 11:46 AM   #18098
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deltaC/C (cap. dev./cap)
I will have to research mechanisms for C rising with frequency.
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Old 19th November 2011, 11:54 AM   #18099
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The Siemens/EPCOS doc is at

http://www.epcos.com/web/generator/W...nformation.pdf

(page 13)
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Old 19th November 2011, 11:59 AM   #18100
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You are wrong. MKN is polyethylene naphthalate. MKT is polyethylene terephtalate = polyester. I have already told you that you know almost everything, but just almost.
Polymers I know reasonably well. Polyethylene terephthalate (PET) is a polyester. Polyethylene naphthalate (PEN) is a polyester as well. There are lots of polyesters- anything with a structure of -R1-CO-O-R2- is a polyester. PEN and PET have different Rs, but the same polyester structure.

Polyethylene is a polyolefin, a completely different polymer family. No carbonyls, no oxygens, no aryls, just (CH2)x.
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