I got those answers, when I was young, and failed and failed and failed. Often it's only a very small step between a brilliant working circuit and a failing one. Assume for instance you would have chosen BLM15AG100SN1 instead of BLM15AG102SN1, then this would make a difference as big as the universe!




In electronics on many issues semi-right truths have well established, which are learned by each new generation of engineers. When then one fine day new regulations to deal with EMC became legally sanctioned, like CE standards in 1996, then the whole world of electronics had to overthink their design rules and heavy mistakes were suddenly found to be designed in many many applications. What a surprise.
So, I think it's really needed to overthink what we do each day. Why ferrite beads are necessary? What are they good for? For instance.
One big mistake which can often be found is the paralleling of caps to enhance the decoupling performance over an extended range of frequencies. This is only a good idea, when one of the two provides a rather high equivalent series resistance, means when one of them is a tantal or aluminium electrolytic. With two very low impedant caps heaviest resonances occur in a certain very narrow range of frequencies, with the consequence of increasing the tendency of instability and oscillation.
But even today in datasheets of video amplifiers and HF OPamps the recommendation can be found to parallel two or more ceramics at the supply pins. The best way to decouple such amps is to use one of the new ceramic high caps. Take one in the µF range sitting in 0805 package and you will get a resonance free ultra low impedance from lowest to highest frequencies. Add a proper ferrite bead and a small resistance to avoid series resonance of the LC filter and you will never have any problems.


Many of them visit this or other fora, believe me. Many of them never posting, but reading and learning...

Kai