Pitfalls with ceramic SMD caps - diyAudio
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Old 17th July 2014, 09:51 PM   #1
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Default Pitfalls with ceramic SMD caps

This EEVBLOG youtube link: EEVblog #626 - Ceramic Capacitor Voltage Dependency - YouTube goes into detail on the pitfalls of class 2 cermaic caps - for example X5R / Y5V and so on, ***not NP0 or C0G**, or tantalum / elctrolytic.

Summary:
DC bias on a ceramic cap changes the value radically. A step change 0-5V square wave may yield the cap's value and correct time constant, but experimentation reveals that using a 4 - 5V square wave reduces a 10uF cap to 4.8uF, in the video. Also, AC voltage may increase the rated value, apparently.
This is important as you might be using these as reservoir caps, which are going to basically be decoupling a power rail and so this is exactly how they would be used.
I've seen many people say ceramic caps are a poor choice in audio applications, but here's a valid reason why, that I didn't find with a quick search on the forums
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Old 17th July 2014, 10:10 PM   #2
dmills is offline dmills  United Kingdom
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Also the class 2 dielectrics tend to be piezoelectric so can cause microphony when ysed as coupling caps into high Z inputs.

It is a complete non problem with C0G/NP0 of course.

Regards, Dan.
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Old 18th July 2014, 08:04 AM   #3
udok is offline udok  Austria
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Murata, TDK and Samsung specify this effect quite clearly on their website.
Especially with the high-valued and small sized parts it is common today that the nominal capacitor value is down to -90% (no typo!) at nominal DC voltage.
In addition temperature effects, AC effects and production tolerances must be added too.
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Old 18th July 2014, 08:55 AM   #4
DF96 is offline DF96  England
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Quote:
Originally Posted by TheGabbleDuck
I've seen many people say ceramic caps are a poor choice in audio applications, but here's a valid reason why, that I didn't find with a quick search on the forums
Some ceramic caps are a poor choice for some audio applications. That is quite well known. Some people can't distinguish between this and 'all ceramics must be avoided for audio'. NP0/C0G are fine for filters, while high-K ceramics may be fine when used carefully for local supply rail decoupling.
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Old 21st July 2014, 07:06 AM   #5
marce is offline marce  United Kingdom
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This is not exactly breaking news....these devices and their uses have been discussed in length on various threads. They have there uses, X7R's being one of the best choices for decoupling purposes especially digital and high speed analogue for the devices that go next to the pins.
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