SEPIC coupling capacitor?

[Martin Griffith]

I havent done much with sepic's, but going by AN1484
http://www.national.com/JS/searchDocument.do?textfield=an1484&x=35&y=8

Bottom of P3

"The SEPIC capacitor must be rated for a large RMS current
relative to the output power."

I don't think I've ever seen capacitor datasheets with RMS current
stated

Any suggestions?

martin

 

[Phil Allison]

"Martin Griffith"

I havent done much with sepic's, but going by AN1484
http://www.national.com/JS/searchDocument.do?textfield=an1484&x=35&y=8

Bottom of P3

"The SEPIC capacitor must be rated for a large RMS current
relative to the output power."

I don't think I've ever seen capacitor datasheets with RMS current
stated...

** Then WTF do you think " rms ripple current " refers to - eh ??

In some cases YOU will have to compute the rms rating from the published
worsts case ESR figures over the frequency spectrum involved.

Losta fun.



...... Phil

 

[legg]

I havent done much with sepic's, but going by AN1484
http://www.national.com/JS/searchDocument.do?textfield=an1484&x=35&y=8

Bottom of P3

"The SEPIC capacitor must be rated for a large RMS current
relative to the output power."

I don't think I've ever seen capacitor datasheets with RMS current
stated

Any suggestions?

RMS current is a regular rating of Al electrolytics and some film
parts dedicated for power applications. Keep looking. Chances are, if
it's not rated, you may be misapplying the part.

For film caps, dv/dt specs give peak current, indirectly. RMS has to
be figured out based on dissipation factor, part size and body
temperature limits. The old Philips apps are good with this, for their
polyester parts.

Similar procedures for ceramic are sometimes made quicker by
publication of associated ESR data.

RL

 

[Martin Griffith]

"Martin Griffith"


** Then WTF do you think " rms ripple current " refers to - eh ??

In some cases YOU will have to compute the rms rating from the published
worsts case ESR figures over the frequency spectrum involved.

Losta fun.



..... Phil

I thought I was missing out something from the app note, which should
have stated RMS ripple current.

martin

 

[Eeyore]

I havent done much with sepic's, but going by AN1484

Bottom of P3

"The SEPIC capacitor must be rated for a large RMS current
relative to the output power."

I don't think I've ever seen capacitor datasheets with RMS current
stated

Any suggestions?

Siemens (oops Epcos) polypropylenes. Is that the type you mean ?

Graham

 

[Martin Griffith]

Siemens (oops Epcos) polypropylenes. Is that the type you mean ?

Graham

I was looking at the AVX X7R datasheet, (from farnell), the app note
just said 10uF ceramic, P5 step 5.
Maybe I was expecting more clarity, like you normally get in Linear's
app notes

The LM3478 datsheet, is quite helpful.

OT, from your earlier thread
http://www.guardian.co.uk/commentisfree/2007/aug/13/fashion.comment


martin

 

[Hammy]

I was looking at the AVX X7R datasheet, (from farnell), the app note
just said 10uF ceramic, P5 step 5.
Maybe I was expecting more clarity, like you normally get in Linear's
app notes

The LM3478 datsheet, is quite helpful.

OT, from your earlier thread
http://www.guardian.co.uk/commentisfree/2007/aug/13/fashion.comment


martin

Hi Martin

en-genius (formerly Analogzone ) Has a pretty good series (5 parts) on
Sepic converter. You can find it here.

http://www.en-genius.net/site/zones/technoteZONE/technical_notes/col_100608

There is also a note from Vorpérian Here

http://www.switchingpowermagazine.com/downloads/Sepic Analysis.pdf

 

[Martin Griffith]

Hi Martin

en-genius (formerly Analogzone ) Has a pretty good series (5 parts) on
Sepic converter. You can find it here.

http://www.en-genius.net/site/zones/technoteZONE/technical_notes/col_100608

There is also a note from Vorpérian Here

http://www.switchingpowermagazine.com/downloads/Sepic Analysis.pdf

Thanks, quite useful

martin