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Matthew Smith  
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 More options Feb 9 2010, 6:16 pm
From: Matthew Smith <m...@smiffytech.com>
Date: Wed, 10 Feb 2010 09:46:34 +1030
Local: Tues, Feb 9 2010 6:16 pm
Subject: Re: [NEONIXIE-L] Transformers

Mike/David, many thanks for your replies.

Quoth Mike Harrison at 2010-02-09 21:13...
...

> You may get some regulation issues if different parts of
> the winding have different loadings. For low-power apps
> it probably works - it's not normally done on conventional
> step-down flybacks as the optimum thickness of wire will
> be different for different windings.

OK, might try that.  I don't think that regulation will be a real issue
with the various supplies for the dekatrons.  Logic will be on a
separate supply anyway.

Quoth David Forbes at 2010-02-10 02:12...
...

> The start end labeling assumes winding all windings in the same
> direction. Why would you wind in two different directions?

I really was just asking that out of curiosity - wanted to know if my
understanding of phasing was correct or not.  Haven't done anything like
that since college and that was over 20 years of dead braincells ago.

> Yes, you can have as many secondaries as you like. I put five
> secondaries on my scope clock transformer. Only one of them will be
> tightly regulated, but that is not a problem for "digital" loads such
> as Dekatrons.

Ties in with what I understood from Application Note 19.  Feedback for
regulation comes off the most critical secondary, other secondaries get
something approximating to the relevant turns ratio.

> Kapton tape is a fine gap maker. The formula for gap assumes only the
> center leg has a gap ground into it, so if you use tape, make your
> gap half as thick as the calculations say. But I've found that the
> gap size is not at all critical. Having it at all is critical.

Ah, that's good!  Gapping sounded too much like a Black Art.  "A bit of
tape is good enough" sounds like one less variable with which to be
concerned.

> I'd stick with 12V if I were you. I made a bunch of flyback supplies
> with mains input, but I wouldn't do it again.

I think I will.  I'm not unduly worried about working with 240V - it's
240V coming from a 15A breaker that tends to worry me.  Plenty of time
for something to catch fire before the breaker finally trips.  The
LT1171 has onboard current limiting - it should never pull more than the
rated current.  Pop in a fuse between there and the DC supply and the
risk of conflagration should be minimised.

Now all I need to do is to build a turns counter so I can actually start
to wind the damn things.  Sadly, I have no dead tape recorders to
pillage so I might turn the problem on its head and rotate the bobbin
with a stepper motor.

Cheers

M

--
Matthew Smith
Smiffytech - Technology Consulting & Web Application Development
Business:      http://www.smiffytech.com/
Blog/personal: http://www.smiffysplace.com/
LinkedIn:      http://www.linkedin.com/in/smiffy
Skype:         msmiffy
Twitter:       @smiffy


 
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