Does brand matter at film capacitors

[Miyuki]

Hi folks,

Does brand matter at film capacitors ? And if, how much ?
Especially when used at high ripple current or is it similar story to electrolytic ?

[Kleinstein]

It depends on the required properties of the film cap.
The main advantage of some big brands can be more trust in there specs and less chance to get a really poor series which might need a recall or such. However the type of film capacitor can make a big difference. So the first thing is to get the right type (dielectric and construction (metalized or metal foil)) - the brand might matter when you need extreme properties, like very low loss.  I would not expect the differences to be as large as with electrolytic caps. The construction is usually easier and also small companies can make good film caps - there is way less magic included and also less aging.

With high ripple current, there usually is also a chance for dielectric losses to become significant, not just the ripple current.

[T3sl4co1l]

Well... how cheap do you want to go?

All the usual brands, at the big distributors, are good.  Regarding current, they are what they are.

Obviously, if you're shopping on eBay or Ali, you're on your own.

If you need current handling, then if they don't specify in the datasheet, it's probably no good.

One exception, Orange Drops (Vishay Sprague 715P) are surprisingly good at current, for not being specified.  It's unfortunate that they have steel leads.

X2 caps are mostly terrible, for example Vishay BC ones (which part number / family, I forget) are good for maybe 50mA in typical values.

Snubber caps often are rated for peak current but not RMS.  For these, you can estimate RMS current as: Irms = dV/dt(pk) * C / 20, or Ipk / 20.  This is a crude assumption and real parts vary higher or lower than this.  Example, CDE 935s are rated for a lot of peak but little RMS capacity, particularly at high frequencies.

The loss of current capacity, at high frequencies, can be considerable.  It's a skin effect phenomenon.  Lots of small pieces is better than one large piece.  At some point, ceramic also takes over from film caps, which stinks for commodity parts because C0G chip caps are so expensive (but then, so are industrial transmitter caps -- you're stuck on that, unfortunately).

Tim

[Miyuki]

Just cheapest one from local distributor, no need to risk eBay/Ali

They will be paralleled with electrolytic but much closer to semiconductors as they have no so big heat life issue when proper voltage is chosen