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Should electrolytic or polypropylene capacitor be used in buck converter?

It's obvious that for same capacitance value electrolytic is way much cheaper, and its higher ESR produces a ESR zero at lower frequency which is beneficial to design of controller since type II compensator can be used. However since my design works at 55kHz, I'm just not sure if electrolytic is a good performer at such high frequency, or if I should go for a polypropylene one.

Besides, polypropylene has lower ESR, so does that mean it can handle much larger ripple current since the power dissipation is lower? Is there limitation on max ripple current that polypropylene cap can accept, since I couldn't find this parameter in most datasheets?

Thanks for any advice.

Reply to
w2kwong
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It's obvious that for same capacitance value electrolytic is way much

** Their impedance is at or near minimum value over a broader range - if that is what you mean.
** For series self resonance at 55kHz, you need a capacitor of about 330 uF to 470 uF.

Counts out film types entirely.

** No doubt, a 470 uF polypropylene could handle very large ripple currents.
** You are way off the mark.

Polypropylenes are not at all suited to a buck converter, while electros are near ideal.

..... Phil

Reply to
Phil Allison

Hello,

Generally spoken the ratio Ripple current / capacitor value is bigger for polypropylene then electrolytic.

You can find good info on ripple current and life time considerations for electrolytic capacitors on (for example)

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or
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A good source for info on foil capacitors is

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Or
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The technical info shows allowable AC voltage for value/size/voltage combinations. From that you can calculate the ripple current based on frequency and capacitance value. For many applications, (cheaper) polyester can also be used.

Hope this will help you a bit.

Best regards,

Wim PA3DJS

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Reply to
Wimpie

It is usually better to think about how many cubic inches of capacitor you need for the ripple current you have and not the microfarads. With electrolytic you may want to add a ceramic or two to take the sharp edges off the current. The losses in the electrolytics tends to rise at higher frequencies.

Chances are electrolytic will win on the cubic inches question. If you get up nearer a MHz, the plastic film capacitors will start nudging them out. Ceramics start to win in about the same area.

Reply to
MooseFET

Actually, what he meant is that its higher ESR produces an ESR zero at lower frequency.

John

Reply to
John Larkin

"John Larkin "Phil Allison"

** LOL ......

JL doing his favourite party trick - a featherless parrot impersonation.

" Polly wanna crackpot " ????

....... Phil

Reply to
Phil Allison

"MooseFET"

** Moooooooosseee droppings are very smelly ...

...... Phil

Reply to
Phil Allison

We weren't talking about personalities, or parrots. We were talking about capacitors. My point was that what he said is obviously what he meant.

John

Reply to
John Larkin

"John Larkin"

** But you acted just like a parrot and have the personality of one.
** No such things is obvious since the meaning of the OP's words is quite ambiguous.

The OP posted a whole load of drivel.

Same as your idiot post.

........ Phil

Reply to
Phil Allison

Now I know which capacitor I should go for. Thanks anyone who gave me constructive advices.

Reply to
w2kwong

Actually, I have a parrot, and we have very little in common.

In what way?

Seemed coherent to me.

Gosh, you *are* a sweetheart.

John

Reply to
John Larkin

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