Hi,
Like a parrot, I'll repeat ad infinitum: Read a lot, research the subject, that's the best start, then you (or I) will understand some things, but not others, but be able to formulate more specific and therefore practical forum questions.
You seem to know Vout and Iout. You may also have decided whether your SMPS will be mains- or battery-powered. These two points, "A" and "Z" will be a good guide as to what to study to have an idea of what "B" to "Y" may need to be.
I suggest a way to begin designing the power supply is comtemplating whether the circuit being powered by the SMPS is analog or digital, will it function erratically with switching noise, etc? Will it therefore need for the SMPS to be followed by an LDO and/or appropriate filtering?
Another staring point is asking oneself: Do I trust my ability and knowledge to safely implement a non-isolated PS, or should I leave that kind of project for a future occasion when I feel certain I will not a) hurt myself and others, and less importantly b) keep destroying components with ill-designed circuits?
Looking at different SMPS topologies - and only you can do that, laziness or expecting others to fill in your learning gaps in a quickie answer isn't learning, my friend - will give insight into what you, at first, think will be the best-fit solution, never hurts to understand which are harder to provide compensation for if you're a beginner.
To summarise, my limited knowledge suggests: check topologies, choose one, do the calculations, simulate, if all goes well, prototype or make the finished PS, otherwise, back to the top of the design stage flow diagram
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Hi again,
Another first step question is: What's "better" - designing the whole thing myself, or getting some fantastic $0.70 multi-purpose SMPS IC that solves maybe 50 - 80% of the design procedure?
Along with: Have I thought the battery thing through yet...Maybe a 1.5V AA battery won't power this design, and a car battery won't make for a portable device, is there something inbetween that will be adequate, or must I accept that I need to plug this thing into a wall, or adjust my current requirements?
IC manufacturers have a host of design tools and reference designs that should be useful. Here are links to SMPS/PSU design tools, if you're interested in looking at them, and there are many others...
WeBench "Power supply design at your fingertips!"
Power Supply WebDesigner "A suite of tools for designing and optimising your power supply design"
eDesignSuite "easy-to-use comprehensive software suite"
PowerEsim "Free SMPS Switching Power Supply / Transformer Design Software"
Design Simulation and Device Models "a variety of custom design simulation tools and device models to allow even novice designers to quickly and easily evaluate circuits using high performance switching regulators, amplifiers, data converters, filters and more"
I'm not pretending any of these tools make anything easier, some may be hard to figure out and use effectively, but there are a whole range of free tools which theoretically simplify the design stage, and usually lead to the appropriate choice of IC, saving hours of cross-comparison work.