Capacitor choice question

[[email protected]]

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

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

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.

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

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.

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.

 

[[email protected]]

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)

 

[Pooh Bear]

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.

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

 

[Phil Hobbs]

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)

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

Cheers,

Phil Hobbs

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

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)

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

 

[John Woodgate]

I read in sci.electronics.design that Pooh Bear

5W isn't much.

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

 

[Winfield Hill]

Phil Hobbs wrote...

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

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

 

[martin griffith]

Phil Hobbs wrote...

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

why?


martin

 

[John Woodgate]

I read in sci.electronics.design that Winfield Hill

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

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

 

[Phil Hobbs]

Phil Hobbs wrote...



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

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

 

[Winfield Hill]

Phil Hobbs wrote...

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.)

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.

 

[Pooh Bear]

I read in sci.electronics.design that Pooh Bear


100 A at 50 mV? (;-)

I anticipated that requirement was unlikely !

What current is associated with your 3 kW?

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

Graham

 

[Phil Hobbs]

Phil Hobbs wrote...



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.

Ah, gotcha. Air America on AM.

Cheers,

Phil Hobbs

 

[Ross Herbert]

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)

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.

 

[[email protected]]

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

 

[Jon]

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.

From this, you can calculate the resultant voltage that will appear

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