Let us assume we tried to salvage the existing design (I'll get a schematic up later - though it's pretty much the step-up application circuit with this extra part to it to bump up the duty cycle and a little bit of extra filtering on the output)
I would suggest not, but I'll cover that in more detail...
Would a 2200R series inductor or similar be of any use for the power supply?
Umm, probably. Looks to be a ferrite bobbin type. Winding losses are dominant on those, so make sure you get a low enough DCR to handle it (minus skin effect and all that).
What you really want is a step-up autoformer or transformer, like in my circuit. Then you don't need to worry about ridiculous duty cycles, fast pulses and huge losses. Examples are also in the '34063 datasheet.
Oh aye! Meant to ask, what's wrong with the MC34063 out of curiosity ? (might as well turn this into a learning experience!!!)
- It's old. OOoooollld. Not necessarily a bad thing, but that brings inevitable process and design limitations that modern parts don't have.
- The operating frequency is low.
- The control method sucks.
- Actually, they never even say what the control method *is*. There's that "current sense" block, but it's not peak current mode, it doesn't turn off a latch. It just kind of... pokes at the oscillator duty cycle. WTF?
- Regulation is typically (always?) hysteretic, so the output ripple is incessant, low frequency, chaotic and hard to filter.
- Because the frequency is low, you spend extra on caps and inductor(s). Doubly so if you need to filter down the ripple.
I was originally going to use a MAX1771; but once again was tempted by the lower price and the DIP package of the MC34063. I was also (perhaps naively) reassured by the number of nixie clocks using the MC34063 in it's PSU.
This lesson repeats time and time again:
Just because everyone is doing it, doesn't mean it's a smart thing to do.
Weekend projects are very frequently that sort of thing. Slap together a nixie clock, or Arduino-whatever, or a Tesla coil, or... Almost none of them have real consideration involved, they're just following what someone else did. But usually making "this looks close enough" compromises that degrade performance in poorly defined ways. It's still useful learning or "doing" experience, but don't mistake it for understanding.
As for modern/ish suggestions:
UC384x -- also bipolar, but somewhat faster (<500kHz), and designed to drive MOSFETs (high efficiency!); peak current mode control; Micrel makes a BiCMOS version MIC38C4x.
UCC3808 -- CMOS, made for push-pull applications, acts like a 3844 with both output phases brought out to driver pins.
Any of a number of integrated and external-switch controllers, from LT, ADI, TI and others. TPS54xxx series are generally good.
I tend not to remember a wide selection of "newer" parts unfortunately, but sticking to the brand names and following appnotes will generally go well.
All of these are more expensive, but inductors and capacitors are expensive, too. You save a lot of space by going to a higher frequency, and not having to dissipate half your converted power as heat!
Tim