Capacitor choice question

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jwodin 20 years ago

Hi there, I'm looking for a DC blocking capacitor with C ~ 0.1uF (for impedance reasons) that will take fairly high AC power through it. At the upper end, I'm going to be pushing about 5W (at 10 MHz AC) of power through this cap, so I'd like it not to turn into a puff of smoke. Any suggestion as to the type? I figure that electrolytic is out, and that probably ceramic is fine, but I wanted to make sure. Oh, and I also need the cap to be leaded, since it fits into a PCB.

Thanks for any help!

Jesse Wodin

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jwodin 20 years ago

Wow, I guess I found what I needed. Cornell Dubilier makes "High frequency" mica caps (type CDV16). Specifically

CDV16FF102J03 1nF 2.2A max continuous current at 1MHz ($3.110 at NewarkInOne)

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Winfield Hill 20 years ago

I drop 7000V RMS at 1MHz across some of my capacitors. :>)

Thanks, - Win

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Phil Hobbs 20 years ago

Wow, that's 350V RMS at 1 MHz dropped across that poor capacitor.

Cheers,

Phil Hobbs

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Phil Hobbs 20 years ago

Admitting that on Usenet was a serious mistake... Expect a call from People for the Ethical Treatment of Capacitors.

(And I bet even *you* aren't twisted enough to do it at 2.2 A.)

Cheers,

Phil Hobbs

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Winfield Hill 20 years ago

It's somewhere between 5 and 8 amps, I don't remember right now. OK, I'll admit it, the cap was a glass vacuum tuning capacitor.

Thanks, - Win

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John Woodgate 20 years ago

I read in sci.electronics.design that snipped-for-privacy@gmail.com wrote (in ) about 'Capacitor choice question', on Fri, 30 Sep 2005:

What is the current? The power doesn't matter, the current does.

Well, yes, ceramic, but 99.99% certain not a general-purpose 0.1 uF multi-layer, even one with leads. You probably need the type of component that's used in transmitters.

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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Pooh Bear 20 years ago

5W isn't much. I'm looking at an application that shoves ~ 3kW through 0.47uF for comparison ! Check the impedance curves at 10MHz though.

Graham

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John Woodgate 20 years ago

I read in sci.electronics.design that snipped-for-privacy@gmail.com wrote (in ) about 'Capacitor choice question', on Fri, 30 Sep 2005:

Oh, well, if one 100 times smaller than you asked for is OK, enjoy!

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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John Woodgate 20 years ago

I read in sci.electronics.design that Pooh Bear wrote (in ) about 'Capacitor choice question', on Fri, 30 Sep 2005:

100 A at 50 mV? (;-) What current is associated with your 3 kW?

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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John Woodgate 20 years ago

I read in sci.electronics.design that Winfield Hill wrote (in ) about 'Capacitor choice question', on Fri, 30 Sep 2005:

You must have friends in the FCC! (;-)

Regards, John Woodgate, OOO - Own Opinions Only. If everything has been designed, a god designed evolution by natural selection. http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

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Phil Hobbs 20 years ago

Ah, gotcha. Air America on AM.

Cheers,

Phil Hobbs

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martin griffith 20 years ago

why?

martin

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Pooh Bear 20 years ago

I anticipated that requirement was unlikely !

About 20A ( @ 100kHz ) . It's a job for a polypropylene type. It gets warm.

Graham

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Ross Herbert 20 years ago

1nF is a lot less than the ~100nF you specified so you'll need 100 of 'em to get this value. At least they will handle the current better with so many in par'l.

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jwodin 20 years ago

yeah, i realized that I can live with 1nF, so that should be fine. Thanks for all the help, as usual on this board!

jesse

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Jon 20 years ago

Jesse, I'm a little confused by your requirement. An ideal capacitor will dissipate zero power, regardless of the current. Do you mean that you are delivering 5W of power to a load through the capacitor? In this case, you need to calculate the load current (Iload) that will flow.

across the capacitor. V = (Iload)/(2Pi*f*C). The power that will be dissipated by the capacitor depends in the equivalent series resistance (ESR) of the capacitor. P = (Iload)^2*ESR. You can get the ESR from the capacitor spec sheet. Or, you can calculate ESR from the Dissipation Factor (DF) if this parameter is specified. Regards, Jon

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Capacitor choice question

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