LED displays (TIL305, TIL308, etc.)

[Tony Duell]

> > Alternatively, consider using a transformer 'back to front'. Start of 
> > taking in mains and stepping it down to, say, 12V AC using a normal 
> > transformer in the conventional way. Yo ucan rectify/smooth/regulate that 
> > for your logic supply. But then take another 220V-12V trasnformer and 
> > connect the 12V winding to the secondary (12V) side of the first 
> > transformer. You'll get around 230V from the other (original primary) 
> > winding of that transformer. 
> 
> If you happen to have one handy in the USA, of course.  Although 
> "universal" 95-240v transformers can be found in the US, most of the 
> small ones (such as are found in wall warts) are 120vac primaries 
> only.

I am suprised. Over here, most mains transformers have 2 off 115V 
primary windings that you connect in series for 230V mains (Europe) and 
parallel for 115V mains (USA). I assumed (given that 115V-input 
transformers are not commonly needed over here) that such things were 
available worldwide.
 
> But if I had a 12vdc supply at sufficient current and needed to power 
> some nixies, I'd be sore tempted to work up a boost supply using any 
> of the currently available DC-DC converter ICs.  EDN/Electronic 

I really do find iron more reliable than silicon :-)

> Design is full of such circuits (e.g. using the Maxim MAX1771).  Much 
> more compact and not requiring much in the way of a DC filter 
> capacitor.
> 
> Where I'd draw the line is with any small signal application, such as 
> a receiver using tubes/valves.  Those converter ICs can really 
> generate a lot of RF noise.

Totally OT, but if you're trying to run one of those valved portable 
radios that used a 90V HT supply, it's worth noting that a 30V 
transformer (the ends of a 15-0-15 winding, for example), voltage 
doubled, gives about 84V. That's run all the radios I've tried, including 
an AM/FM (yes, a valved FM portable radio) Vidor set.

-tony