I've read a bunch of negative complaints on the MC34063 basically saying that it is old and slow but apart from this post no one really mentions any good alternatives. (And can someone please explain the concepts of "internal", "external" and "offline" regarding switch mode regulators?)
Sadly, the average hobbyist completely shuts down from such an onslaught of "paradox of choice"...
And, hence you have so many hangers-on to 2N2222, and 2N3055, and MC34063, and...
No one really mentions alternatives, because
they're almost all good, and there are
thousands to choose from. A complete listing is impossible. Go peruse Digikey like the rest of us do!
Another good (if all too brief) listing is AoE3, Tables 9.5 and 9.6 (pp. 653-658).
As for type: regulators are internal switch: you might need to add a diode, but all the active circuitry is contained within.
Controllers are external switch: you must add transistors, and often, shunt resistors, bootstrap power (or external gate drivers, even) or other things.
Sometimes, the controller has enough poop to be useful in small applications (MC34063 and TL494 for example, which have uncommitted BJT type outputs in the 1A and 200mA range, respectively). In that case, the distinction is kind of here-or-there, but if it's usually found alone, it's probably more of a regulator (like MC34063), or if it's usually in the middle of a bunch of stuff (like TL494), it's probably more of a controller.
Offline types are made for mains operation. TL494 is not offline (it needs an aux supply to start up and run). UC3842 is offline (it has a wide operating voltage range, and internal UVLO circuitry so it can be charged slowly from a large-value resistor, then it kicks on and starts up). TOPSwitch devices are offline (in fact exclusively operating from an internal pass regulator, no aux winding needed).
Offline types may be regulator (TOPSwitch, etc.) or controller (UC3842, etc.) types; they are non-exclusive.
One of the reasons people seems to dislike the MC34063 is that it uses a lot of external components, and in particular a big inductor due to it's slow frequency. But the ones in T3sl4co1l's post doesn't really have less components the MC34063has 11, TPS54231 has 12, LM2675 has 5, LM5008 has 11. I guess they are smaller though.
So what are the more modern approach to switch mode power supplies? What do you use when you need a buck converter?
Sheer parts count misses size: most of those are chip resistors and/or capacitors. The externally compensated chips are more flexible, but if you're truly strapped on space, the internally compensated chips work just fine (but follow the appnote carefully: stray too far from recommended L and C, and the internal compensation will be wrong). They also operate at higher frequency, so the inductors and capacitors are much smaller. (Remember you need output AND input capacitors. Ripple goes both ways!)
There are further knock-on savings from reduced overall footprint, reduced power dissipation (higher efficiency), reduced ripple, and a lot of other features that aren't available on the old parts (or not without a lot of fiddling), like supply sequencing.
Tim