I am in search of SMALL polypropylene capacitors---a tall order, I suppose. I need 25 volt 4.7 uF, 10 uF, 22 uF caps with lengths UNDER 20mm, and hopefully lead spacing of no more than 10mm. I can't find any....maybe they don't exist. Anyone found these??
Polypropylene capacitors tend to be large. The size is set by, among others things, the permittivity and voltage breakdown field. Hence there is little scope for a manufacturer to do much better than anyone else. If you want small high value caps then you need electrolytics or possibly ceramic.
25V polypropylene capacitors? Good luck. Minimum voltage rating is around 400V, and therefore the sizes will be big. If you need film caps with small sizes you must use polyester.
So, how much worse do you think polyester is than polypropylene as a capacitor dielectric? MUCH worse----somewhat worse-----a tiny bit worse---- none?
A tiny bit worse. In most situations no practical difference. The only place where polypropylene would have a small advantage over polyester is a coupling capacitor which also acts as the main LF rolloff point in the system and has a significant signal voltage. This means loudspeaker passive crossovers, and some coupling caps towards the back end of some amplifiers.
You can search for :
22u/63V: WIMA MKS4C052206D00KSSD
with 27.5mm rasterbut you can use 2 of 10u/30V in parallel for a 5mm raster
4.7u/30V: WIMA MKS2B044701K00KSSD
10u/30V: WIMA MKS2B051001N00JO00
with 5mm raster
and 10u/30V: WIMA MKS2B051001N00JO00
with 5mm raster
22u/63V: WIMA MKS4C052206D00KSSD
with 27.5mm raster
Yeah, the 10uF/30V: WIMA MKS2B051001N00JO00 is the best I have found. It's polyester rather than polypropylene, but its size (7.2 mm x 11mm) makes it the best choice so far.
I have used in some of my amplifiers wima cap (like these) on signal route.
On two amplifiers I have only plastic on signal, more of 10U in parallel when higher capacity is needed.
Works very nice.
On two amplifiers I have only plastic on signal, more of 10U in parallel when higher capacity is needed.
Works very nice.
Mouser's search engine allows you to sort by pin spacing (PCM). Lowest voltage rating for PP is 63V for Vishay's
Before setting your heart on polypro you might want to read Scott Wurcer and Sam Groner's article in Linear Audio #12 - "Quadrature Bridge Measures Harmonic Distortion in Capacitors" -- a quote from the abstract: ...These show that parts with ceramic C0G dielectric have more consistent, and generally speaking lower distortion than polyester, polypropylene or polystyrene film capacitors.
Before setting your heart on polypro you might want to read Scott Wurcer and Sam Groner's article in Linear Audio #12 - "Quadrature Bridge Measures Harmonic Distortion in Capacitors" -- a quote from the abstract: ...These show that parts with ceramic C0G dielectric have more consistent, and generally speaking lower distortion than polyester, polypropylene or polystyrene film capacitors.
calculate what capacitor value you need to get the required LF response. Then decide whether this cap will set the LF rolloff. If yes, choose a good dielectric such as polypropylene and accept the resultant cap size. If no, use 10x the cap value and use almost any dielectric (including electrolytic). That is all engineering can tell you. If you want mystic recipes, then I can't help.
Meanwhile, 5 years later, the problem is still faced by designers. There is an excellent article in the TI Analog Design Journal of 2020 Q3, entitled "Selecting capacitors to minimize distortion" by Zak Kaye. There are some interesting graphs that mitigate the bad name MLCC have in some parts of the Audio field. Well worth a read.
PDF is here.
There is another TI article about distortion in general, but points out the difference between two dielectrics. A 3.9nF 50V ceramic cap is in the feedback chain of an opamp with 3.5VBrms output.
The measure distortion was :
X7R dielectric : -68dB
NP0/C0G dielectric : -135dB
That PDF is here.
PDF is here.
There is another TI article about distortion in general, but points out the difference between two dielectrics. A 3.9nF 50V ceramic cap is in the feedback chain of an opamp with 3.5VBrms output.
The measure distortion was :
X7R dielectric : -68dB
NP0/C0G dielectric : -135dB
That PDF is here.
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Those are large values of capacitance for a film cap, so they must be large. I have a lot of small PP caps with values from 1nF to 470nF.
25V is a common rating for MLCC caps, but not for film caps.
Capacitor volume should scale with capacitance and with voltage squared.
I've got a handfull of CBB "Polypropylene" capacitors coming from AliExpress. I'll check them out and report back. Yes, all polypropylene caps are big I'm afraid.
I looked further into the MLCC thoughts. The only ceramic caps with a fairly linear C against V graph are the C0G/NP0 dielectrics, but the biggest I could find easily were 470nF. I can't see how any of the high capacity Barium based dielectrics can give low distortion when the capacitance drops by as much as 80% at rated voltage.
BB - the small voltage Wima caps. I haven't seen them yet, are they small values or anything in the 1uF to 10uF range?. Thanks.
I looked further into the MLCC thoughts. The only ceramic caps with a fairly linear C against V graph are the C0G/NP0 dielectrics, but the biggest I could find easily were 470nF. I can't see how any of the high capacity Barium based dielectrics can give low distortion when the capacitance drops by as much as 80% at rated voltage.
BB - the small voltage Wima caps. I haven't seen them yet, are they small values or anything in the 1uF to 10uF range?. Thanks.
A low-voltage film caps usually have larger distortion (than "typical" >=250-400 VDC rated ones).
I don't see a reason to use large sized PP film caps if there is a possibility to use much smaller NP0/C0G caps with the same outcome.
I use PP film (or other film type) caps only in old or high-voltage designs (up to 0.1-0.2 uF).
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