I'm at the stage of learning about switched-mode power supplies that I'm focused on understanding the role of input capacitance. Just for background, I'm working with a buck topology for this exploration, and haven't spent any real quality time with other topologies yet, although I've read about them.
I've been building up a buck converter (nominally 10V input to 3V/300mA out) from first principles, starting with the switch (P-Channel MOSFET) dumping into a load resistor. The idea is to add components one (or sometimes it has to be two) at a time and understand the waveforms and contributions of specific components, and fix any problems before moving on. So far it's been a terrific learning experience. It turns out there's a lot that can go wrong even with one or two new components :)
Even at this early precursor stage, I soon learned the importance of input capacitance. The SRC waveform looked like this:
and thus began my learning about input capacitance, and importantly the fact that my power supply and leads contribute inductance, which gives rise to these spikes.
It turned up several questions, I'll ask others in separate posts, but along the way it occurred to me that the equivalent inductance at the input, combined with the input capacitance I added, looks an awful lot like an LC low-pass filter. Sometime after that, I read a blog comment where the author used the phrase: "... would benefit from adding resistance to the input filter ... to reduce the Q of the filter ...". Since there was no PFC or more sophisticated line reflection filter on the schematic, it caused me to wonder whether he conceived the input as a filter where the input capacitor was the C in LC.
Up until then, I'd been thinking of the input capacitor in the time domain only.
So my question is: "Does it ever make sense to think of the input capacitor (and perhaps other components) of an SMPS as part of an LC low-pass filter for the purposes of analysis?"