Thursday, February 25, 2016

Why use different size capacitor for bypassing

This video shows how the test was done and gives some explanation.

Youtube video about capacitor self resonance

The question was asked "why use those small capacitors to bypass the power supply when those 100 micro farads are there?".
I used  a dip meter as demonstrated in the video to determined the self resonance of several capacitor. I used them with the leads full length and short. Here are the results of the test.
A straight piece or wire will have inductance. The leads resonant with the capacitance and if you go above the resonant frequency the signal sees an inductor instead of a capacitor. This is why you will sometimes hear the old sage advice "keep your leads short.". Here is another problem which is will be hard to find and explain without some understanding of the lead inductance.

We are all probably guilt of this but when you have unexplainable parasitic it is one thing to look for. Inductance is directly related to the amp turns of the circuit so double the current and double the inductance. 

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