EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: bitwelder on December 23, 2012, 10:27:23 pm
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This is something that I haven't thought about it before: whether non-polarized capacitors have an orientation and so whether there is a difference in how to place them on a PCB.
http://e2e.ti.com/blogs_/b/thesignal/archive/2012/12/10/pcb-layout-tricks-striped-capacitors-and-more.aspx (http://e2e.ti.com/blogs_/b/thesignal/archive/2012/12/10/pcb-layout-tricks-striped-capacitors-and-more.aspx)
(via a recent hackaday post)
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jep. that is very well known ( or it should be ) . Wound and stacked film caps have an indicator stripe to tell you where the 'shell' sits ( the outer plate ). that is the plate that should be connected to the low impedance point of the circuit.
lets say you got R-C chain for an oscillator and one terminal is ground. The capacitor shell should be ground so the cap shoud be installed with the stripe connected to ground. this in effect acts as a shield.
when i was doing ADSL this was important. you needed to know where the transmitter and receiver node was. swapping the electrodes of the cap sometimes gave as much as 15dB attenuation of the TX into the RX ( which is what you want)
important stuff to know. The same is true for electrlytics. the metal can is tied to the negative pole through the electolyte... so it acts as a shield.