LED displays (TIL305, TIL308, etc.)

Tony Duell ard at p850ug1.demon.co.uk
Fri Oct 3 15:29:17 CDT 2008


> But all wall-wart supplies that I've seen here (which is about the 
> only easy way to obtain small power transformers) have a single 

Ah... The wall-warts we have over here generally have a single primary 
winding too. But I don;t consider those to be particularly useful 
transformers.

I generally buy 'loose' transformers from RS or Farnell. Although at 
least one of those companies sells 230V-only transfoemrs in some sizes, 
they certainly also sell the dual-primary ones I mentioned.

> 120vac primary.  It might be that the cost of the extra copper 
> required for 220vac operation justifies a separate product run for 
> North America and Japan. (Somewhat OT is that Japanese mains power is 
> spec-ed somewhere around 100vac.  Expats who brought their US-rated 

Indeed. I've worked on many devices, particularly HP, which have 4 
voltage selector settings -- 110V, 120V, 220 and 240V. There were 
typically 2 types of transformer used - -one had 2 primaries tapped 
0-100-120V, the other had 1 primarly like that and a second primary of 
120V (no tap). The settings worked as follows : 

100V --For the first type, the 2 100V sections of the windings in 
parallel. For the second type, mains to the 100V sectionm, then this 
acted as an autotransformer providing 120V to the other winding which was 
connected in parallel with it

120V -- the 2 120V windings in parallel

220V -- A 120V winidng in series with a 100V one

240V -- The 2 120V windings in series.

The HP THinkjet printers used the latter type, with a mains input module 
that contained the IEC connector, mains filter, fuse holder and a set of 
5 contacts operated by a rotatable drum for the voltage selection. For 
some reason the exact operation of this is not in the Thinkjet service 
manual (even though all the rest of the schematic, PCB layouts, theory, 
etc are).

The 9836 I've been talking about in another thread was the former type. 
Why, I don;t know, the votlage regulator PCB in that machine (the only 
thing run off the single secondary winding on the transformer) is happy 
with inputs from avout 18V up to 32V at least. So a simple 115/230V 
selector should have been fine.

> appliances (such as a refrigerator) were often disappointed by the 
> short motor life when run on Japanese power).

I am suprised that motors objected to too low a voltage. Wasn't there a 
frequency difference too -- I thought that some of Japan was 50Hz. That 
might have been more of a problem

> 
> > 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.
> 
> Given that many battery-powered sets used a 45vdc "B" battery, I 
> would agree with you.  

Over here, a few sets used 67.5V HT batteries, but most used 90V. Older 
sets (with a 2V 'wet cell' accumulator for the LT (A battery)) used 120V 
or 150V I think.

I'd seen 45V batteries listed, but I assumed (incorrectly, I guess) that 
they were normally used in pairs to give 90V. I've never seen a radio 
that used them, I do have one device, totally off-topic, that should use one.

-tony



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