Ceramic capacitors for higher voltage switchers

Gents,

Anyone know what sort of ripple the FK22 series from TDK can take, say a
0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
variable up to almost 100V, with some gusto (>50 watts). Can't use
electrolytics because of a harsh environment.

http://www.tdk.co.jp/tefe02/e4942_fk.pdf

Stacked SMTs are great but boutiquish and expensive. Anything
>0.47uF/>100V in thru-hole seems outlandishly pricey.

--
Regards, Joerg

http://www.analogconsultants.com/

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"Joerg" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Anyone know what sort of ripple the FK22 series from TDK can take, say a
> 0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
> variable up to almost 100V, with some gusto (>50 watts). Can't use
> electrolytics because of a harsh environment.

Well, take a guess at power dissipation and find the damping factor (X7R is
what, 1.5% or something?). If you're running hot, low power is probably a
good idea, like 1/8W or something. And use lots of copper (ha, like you
ever have the space).

> http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>
> Stacked SMTs are great but boutiquish and expensive.

So stack them horizontally instead? :-)

Or if you're cramped for horizontal space, maybe you could make a capacitor
daughterboard so they're stacked horizontally, on a vertical board...

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Tim Williams wrote:
> "Joerg" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Anyone know what sort of ripple the FK22 series from TDK can take, say a
>> 0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
>> variable up to almost 100V, with some gusto (>50 watts). Can't use
>> electrolytics because of a harsh environment.
>
> Well, take a guess at power dissipation and find the damping factor (X7R is
> what, 1.5% or something?). If you're running hot, low power is probably a
> good idea, like 1/8W or something. And use lots of copper (ha, like you
> ever have the space).
>

I wish they were physically a tad larger.


>> http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>>
>> Stacked SMTs are great but boutiquish and expensive.
>
> So stack them horizontally instead? :-)
>
> Or if you're cramped for horizontal space, maybe you could make a capacitor
> daughterboard so they're stacked horizontally, on a vertical board...
>

The client won't like that :-)

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

Robert Baer wrote:
> Tim Williams wrote:
>> "Joerg" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed)...
>>> Anyone know what sort of ripple the FK22 series from TDK can take,
>>> say a 0.47uF/250V? I need some ceramics as output caps of a SEPIC
>>> that is variable up to almost 100V, with some gusto (>50 watts).
>>> Can't use electrolytics because of a harsh environment.
>>
>> Well, take a guess at power dissipation and find the damping factor
>> (X7R is what, 1.5% or something?). If you're running hot, low power
>> is probably a good idea, like 1/8W or something. And use lots of
>> copper (ha, like you ever have the space).
>>
>>> http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>>>
>>> Stacked SMTs are great but boutiquish and expensive.
>>
>> So stack them horizontally instead? :-)
>>
>> Or if you're cramped for horizontal space, maybe you could make a
>> capacitor daughterboard so they're stacked horizontally, on a vertical
>> board...
>>
>> Tim
>>
> Just solder the caps in so they are on edge (vertical); one may be
> able to use 4 in parallel this way and use the same PCB board space.


Can't do that, it must remain machine-solderable.

--
Regards, Joerg

http://www.analogconsultants.com/

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On Sat, 06 Mar 2010 01:55:35 -0800, Robert Baer <(E-Mail Removed)>
wrote:

> Can't use
>>> electrolytics because of a harsh environment.
>>

Use hermetically sealed military versions then.

The difference in performance is worth the difference in price.

On Sat, 06 Mar 2010 01:55:35 -0800, Robert Baer <(E-Mail Removed)>
wrote:

>>
> Just solder the caps in so they are on edge (vertical); one may be
>able to use 4 in parallel this way and use the same PCB board space.


Pretty much very labor intensive assembly work. Not very good for any
automated process, so not good for anything that has intentions of large
volume production.

For short run, hand assembly though, no problem.

Vertical daughter cards are the way we did it in the HV lab.

50 Watts is a lot of loading for a ceramic cap bank to manage the
ripple of.

Archimedes' Lever wrote:
> On Sat, 06 Mar 2010 01:55:35 -0800, Robert Baer <(E-Mail Removed)>
> wrote:
>
>> Can't use
>>>> electrolytics because of a harsh environment.
>
> Use hermetically sealed military versions then.
>
> The difference in performance is worth the difference in price.


I know, and I do that. But it's often not easy to find some for higher
voltages with low enough ESR _and_ being available without huge leadtimes.

--
Regards, Joerg

http://www.analogconsultants.com/

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mook johnson wrote:
> "Joerg" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Gents,
>>
>> Anyone know what sort of ripple the FK22 series from TDK can take, say a
>> 0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
>> variable up to almost 100V, with some gusto (>50 watts). Can't use
>> electrolytics because of a harsh environment.
>>
>> http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>>
>> Stacked SMTs are great but boutiquish and expensive. Anything
>>> 0.47uF/>100V in thru-hole seems outlandishly pricey.
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
>
>
>
> Haven't used these particular caps but I have run some X7R 250V surfamce
> mount 2220 caps at 1A p-p ripple current at 10Khz. No
> noticable heating at all.
>
> A also run a 500V 2225 .47uF caps on the output of a 150V rail that can put
> out 75W (300Khz ripple) with no noticable heating.
>

I can't use these large SMT sizes in this case because of thermal stress
issues, cracks, and all that.


> You really have to hog some current on the ceramics to heat them up.
>
> That said I did have some x7r .1uF cap with teh yellow epoxy turn red when a
> 5A audio amp IC started oscillating into it. It was in an RC damper on the
> output. Scratched my head for a while trying to figure out why that cap
> got hot. I had thought before that ceramic caps were nearly ideal.
>

That's one reason why I asked. I've managed to turn capacitor ceramic
into bubbly green glass. But that was several MHz and several amps
through just one. The usual, had only one, did a quick experiment, "Come
on, hang on another 10 secs" ... *PHOOMP*

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

(E-Mail Removed) wrote:
> On Mar 5, 4:18 pm, Joerg <inva...@invalid.invalid> wrote:
>> Gents,
>>
>> Anyone know what sort of ripple the FK22 series from TDK can take, say a
>> 0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
>> variable up to almost 100V, with some gusto (>50 watts). Can't use
>> electrolytics because of a harsh environment.
>>
>> http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>>
>> Stacked SMTs are great but boutiquish and expensive. Anything
>> >0.47uF/>100V in thru-hole seems outlandishly pricey.
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
>
> Rock | Joerg | Hard Place
> ;-)


The designs that get chucked over onto my desk are nearly always like
that :-)

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

On Fri, 05 Mar 2010 16:18:52 -0800, Joerg <(E-Mail Removed)>
wrote:

>Gents,
>
>Anyone know what sort of ripple the FK22 series from TDK can take, say a
>0.47uF/250V? I need some ceramics as output caps of a SEPIC that is
>variable up to almost 100V, with some gusto (>50 watts). Can't use
>electrolytics because of a harsh environment.
>
>http://www.tdk.co.jp/tefe02/e4942_fk.pdf
>
>Stacked SMTs are great but boutiquish and expensive. Anything
> >0.47uF/>100V in thru-hole seems outlandishly pricey.

You can get capacitor characteristics from TDK.

http://www.tdk.co.jp/ccv/index.asp

The resistance, reactance and voltage/temperature dependencies are
illustrated graphically.

A 0.1uF 100V X7R part in 1206/3216 body size, 3216X7R2A104M, exhibits
an internal series resistance of 30mOhms, over the range of common
power conversion frequencies.

RL