noob capacitor question

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Buellboy

New Member

• Dec 13, 2010

• #1

Hi all, please excuse the noobie question, but I've searched high and low for a definitive answer and have found very little. So the question is...
Can a plastic box type cap be substituted with a ceramic cap of the same value? It probably depends somewhat on the circuit, so lets say for a control board on a dc to ac inverter.

 

audioguru

Well-Known Member

Most Helpful Member

• Dec 13, 2010

• #2

A ceramic capacitor is excellent at high frequencies. A DC to AC inverter might operate at high frequencies. But a ceramic capacitor has a wide range for its value (its tolerance) and its value changes with temperature change so it makes an inaccurate frequency in an oscillator.

A metalized plastic film capacitor is in a plastic box or is an Oriental "green cap" in an epoxy drop shape and is very good for audio and can have a tight tolerance for an accurate oscillator frequency.

 

killivolt

Well-Known Member

• Dec 14, 2010

• #3

I like the example.

But which ones are we talking about.

 

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audioguru

Well-Known Member

Most Helpful Member

• Dec 14, 2010

• #4

Almost all audio coupling capacitors are PET metalized polyester film type.
I haven't seen paper or polystyrene capacitors for about 35 years.

 

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Buellboy

New Member

• Dec 14, 2010

• #5

This is for a board that controls the gates on a MOSFET inverter. dc to ac. I'm guessing that it would be pretty high frequency. So the ceramic caps are good with high freq but not precise enough? Ok. So are the box type and epoxy drop interchangeable? Having trouble finding the value I need in a box type.

 

Last edited: Dec 14, 2010

audioguru

Well-Known Member

Most Helpful Member

• Dec 14, 2010

• #6

I buy EPCOS metalized film boxed capacitors usually in 5% tolerance and nearly any value that is made.

 

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Buellboy

New Member

• Dec 14, 2010

• #7

Where do you order from?

 

killivolt

Well-Known Member

• Dec 14, 2010

• #8

audioguru said:

I buy EPCOS metalized film boxed capacitors usually in 5% tolerance and nearly any value that is made.

Click to expand...

I've seen these used before; when I work with a Military Contractor. The circuit boards were very robust.

 

audioguru

Well-Known Member

Most Helpful Member

• Dec 14, 2010

• #9

I like the small European Epcos ones instead of the larger Oriental "green caps".