It's not like the 0.1uF will act faster or anything.
I've seen posts here that talk about the low component count of the MAX7219 only needing 2 capacitors, and I've always used it with a 0.1uF cap across the power supply, so I wondered why they said it needs 2. I finally looked at the schematic that keeps getting linked and it has a 10uF and 0.1uF cap in parallel across the power supply.What is the purpose of doing it that way? I understand that the 0.1uF is intended to smooth short, sharp voltage spikes and using a 10uF is intended to smooth out ripples over the longer term, but won't the 10uF also deal with the spikes if used alone? It's not like the 0.1uF will act faster or anything. Thanks.
In theory any cap bypass cap has less and less capacitance reactance (AC resistance) to ground (which is good , acts like a high pass filter to ground) as the frequency of the noise or spike increases.
Quote from: retrolefty on Aug 30, 2012, 04:51 pmIn theory any cap bypass cap has less and less capacitance reactance (AC resistance) to ground (which is good , acts like a high pass filter to ground) as the frequency of the noise or spike increases. There's a lot of information in there, thank you. So first off, if there are several chips, I would just put the single 0.1uF near each chip's power pins as I normally do now, and not worry about the 10uF near each chip, that's something to think of as part of the power supply circuit as needed. For a commercial switching power supply, would the electrolytic near it make a difference ?Switching voltage regulators can be tricky finicky things to build from scratch and referencing the datasheet and application notes for the switching IC is always recommended. On finished switching regulator modules one can generally assume I would think that the basic requirements for the regulator are already mounted on the module and just using .1ufd caps at the ICs in your project should be all that is required? Second it's not simply the values that are important but the chemistry, so am I right that if I were to use a 10uF ceramic SMD cap right next to the 0.1uF ceramic cap near the power pin, it would have no more benefit beyond the 0.1uF cap alone?No, that is too general and encompassing a statement I think. You have to state the desired frequency bandwidth of the noise you are trying to effectively bypass to ground, larger cap sizes will almost always be more effective at lower frequencies. Recall the formula for capacitance reactance to see the effective AC resistance of two different cap sizes. Lower resistance to ground is always the desired property of a good bypass cap.Lefty
A question off the original if I can intrude into the thread.When two or more caps are in parallel are the not added? such as C = (10 ?F) + (20 ?F) = 30 (?F)