Capacitance versus voltage for X7S caps?

Mar 24, 2010 69 Replies

No, I have in a follow-up post in this thread, that the graph ends at

50V but I need to know higher. Oscons don't get into that range much.

I need to replace an electrolytic that was used so far because it's too large and also prone to failure. Total 100uF/100V, although in a pinch we could scrape by with a 63V rating if we zener any larger excursions than 55V or so. High pulsed load, easily two amps. Hi-rel application meaning stress fracture is an issue with very large SMT footprints. I don't want to get up to 2220, better stay with 1812. Height restriction

2.5mm or just under 0.100".

Nominal voltage is 50V but we have to (ideally) allow excursions up to

70V because this is the only capacitance at the end of a cable that can easily be 250ft long in some situations.

If X7S really drops by around 50% as I have a hunch it will then we'll have to see if the remaing 50uF is going to be enough. X7R in 2220 would be better but we can't really fit that many, plus the stress fracture issue. So, the classic situation of being between a rock and a hard spot.

Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

All those I know, except some of the other pulsed loads to some extent. Simulated it, woiks :-)

Well, we had to press on and the layout is going to be done by tonight. Not much choice considering real estate and the possibility of stress fractures.

I've made a converter but not in the shape of a capacitor can, because it has to be as flat as a PCMCIA card.

Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

You need to know:

Permissible real estate and profile limits. Permissible capacitive droop under pulsed loading conditions. Source transient capability under the same pulsed loading. If unregulated - the source impedance after 250 feet. Repetition rate of pulsed load. RMS source ripple current at the conversion frequency. Permissible body surface demperature rise

For voltage dependancy of the TDK parts above 50V, click the 'display data' control button when viewing the 'zoom' window. The data is presented over the ratings in a plain text list. I guess the GUI guy had a hard time fitting a variable graph axis.

You can make a POL converter in the volume occupied by some 100uF 100V capacitors.......

RL

electrical=20

but

=20

No, but if i read the datasheets correctly it is less than the MLCs with=20 comparable volumetric charge density.

Klondike=20

=20

around=20

=20

spot.

=46rom the link i already provided it drops at least 60%. Please = continue.

electrical=20

but that=20

a graph=20

1/2 cubic inch refers to film caps. Ceramic has not needed that much=20 volume for 4.7 uF for 20 years.

How would freezing affect a polymer (solid) electrolyte? Height may be=20 the issue. Perhaps you could end using 50 2.2 uF caps instead.

this:

electrical=20

X7R but that=20

with a graph=20

is=20

of=20

would they

In a brand name, "Microsoft".

that

graph

That's what I don't know (yet). Unequal expansion in materials can cause seals to let go a bit, moisture gets in, and so on. Can't take a risk here and with the "responsiveness" of today's support lines I can't really wait. Layout is done now ;-)

BTW, it's been almost a week now and AVX hasn't bothered to answer at all. It used to be such a great company. Anyone knows what happened?

We might have to. Although 4.7uF X7S dropping to half capacitance would be essentially the same then, except they are a bit less expensive.

Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

is=20

of=20

=20

I suppose you could get some samples and play with temperature and = voltage.

IIRC they got bought up not too long ago.

Well, it's done and done. We are well beyond the point of no return by now :-)

Sad. That's when things often go downhill, and fast.

[...]
Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.

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