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Re: Isolated, regulated, toroidal step down transformer AC power supply design.


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Surely you had the lid off when you went all "recap" on it?

If the only power coming into the device is from the output of a 9V AC
plugpack, it is quite safe to poke about inside while it's on, but you need
to be careful not to short-circuit anything with your meter probes.

As I've mentioned before, you need to check the incoming AC voltage, the DC
voltage at the input of each regulator relative to its ground pin, and the
output of each regulator. You should check the pinouts of the regulators
from their respective datasheets.

While I realise the problem only presents itself occasionally, getting
steady-state measurements will give us some idea of how the power supply is
likely to behave as the supply voltage varies.





Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Oh, very droll.  I meant I haven't had the lid off SINCE it was suggested
that I take the measurements. Not YET, anyway.

I finished recapping it around 12 months ago.

The AC/AC transformer measures 11.2 VAC when unloaded.

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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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How about you take the damn lid off NOW and measure the voltage WHEN
LOADED too?

Having done that you might as well measure the voltages at the input
and output of the regulators, like countless others have suggested.

Oh, and while you are about it, measure the voltages when FULLY LOADED
as well. Perhaps the load does not vary, but then how the hell would I
know, because you insist that nobody needs to know what the gismo is.


Andy Wood
snipped-for-privacy@trap.ozemail.com.au

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Can't do it NOW, Andy. I'll get around to it.

I am a little apprehensive about poking around inside live electrical
equipment. Sorry to disappoint you so.

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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



"Poxy"

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**  Must be what fools do in panic after the Genie escapes from the bottle.




.......  Phil




Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Why not switch mode?

Rudolf

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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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**Because the clown who posted the original request has not revealed why he
needs 9VAC. An SMPS is the worst way to generate AC in low draw
applications.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Good boy, Trevor. At least you grasped that much. An SMPS is not an option
or I would have simply purchased one.

The reason WHY I need 9 VAC is because the application needs it and for
reasons that I have already explained.

I may post a schematic of the applications rectification, regulation and
filtering circuit, but I don't think this is necessary.

Most people can understand a statement like "240 VAC in, 9 VAC out",
regulated to a fine tolerance (Say 1%)  and isolated from the toroidal step
down transformer.

Back to Goggle now, like a good little boy.


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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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**ANY pre-regulation should always be done at DC. AC regulation is
expensive, insane and unnecessary. With modern regulators, pre-regulation is
not likely to be required.

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**Again. Proper selection of transformer will eliminate any problems.

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**No, it is not what you originally indicated.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


The subject of  the OP was "Isolated, regulated, toroidal step down
transformer AC power supply design."

So I actually didn't indicate what 'it' was that was being replaced. Good on
you for making that observation.

Brevity and relevance play a part in the formulation of my subjects for
obvious reasons. Limited character space being one of them.

I did indicate what I wanted to replace 'it' with, in the subject matter of
the OP.

So OK, why don't you help me select the 'self regulating' transformer that
will eliminate all my over voltage problems. 240 VAC in (nominal), 9 VAC
out. Fused at about 2 amps at the input. (it isn't critical.)

Tell me what else you need to know and I'll decide what I tell you, or not.

Regarding your speculation that "with modern regulators, pre-regulation is
not likely to be required.":

"Not Likely" is a very soft qualification in the face of the observed
behaviour of the applications performance during times of over supply. A
100% correlation suggests that it is VERY LIKELY. Statistically significant,
in other words.

What isn't clear is why my Regs (assuming it is my Regs) misbehave. I have
already conceded that the most cost effective action for me to take would be
to replace the 7815/7915 pair with a new pair that DOES have the 30V spec.
and see what happens.

But I may have to replace all other Regs in the applications power supply,
for the same reason, before I get to the bottom of it. I don't have the
necessary test equipment or the expertise to pre-determine which Regs are at
fault.

Apparently AC regulation is a difficult task. TXU certainly do it VERY
BADLY.


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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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**Obtain a signal generator, capable of delivering a stable 50Hz sine wave.
Operate it into a small (say) 50 Watt power amp. Drive the power amp into a
suitable power transformer. That'll work.

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**Bullshit. The only time pre-regulation will be required, is for
under-Voltage events. That is easy enough to deal with.

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**How (precisely) do they "misbehave"?

 I have
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**HUH? ALL 78XX/79XX regulators are specc'd virtually identically. Except
for a couple of low power variants, all have a 35 Volt maximum Vin limit.
Allhave a 2-2.5 Volt 'drop-out' Voltage. IOW: You should have AT LEAST 18
Volts DC at the regulator input terminal. There is a gotcha here too. You
need to measure the ripple too, as any ripple which has peaks falling below
the 2 - 2.5 Volt limit will impress that ripple on the output. IOW: Measure
the ripple to the input of the regulators.

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**Then you are screwed. You need to perform measurements to determine where
the problem is. I'll betcha it ain't the regulators. Regulators are VERY
reliable. And they all perform pretty much the same, if the have the same
designation.

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**And a stupid idea.

 TXU certainly do it VERY
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**TXU?

We're all bored with your top-posting now.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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well, you atleast know the whole story, there's a chance that someone
elee here has encountered a situation like yours and fixed it in a
totally different way.  If you want to keep secrets that's your problem.

We'll all just have to assume it's to power the irrigation controller
for your attic hydroponics setup, os some monitoring device for a meth
lab in your garage :)

FWIW  the 50W subwoofer amplifier sounds like a good approach if you need
regulated AC, maybe you can get one with a damaged speaker cheap on ebay.

for the signal generator maybe a Wein-bridge oscilator, or DDS.

Bye.
   Jasen

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Yeah, OK that's really creative thinking.

I think the UPS solution may be cheaper and easyier. Looking into it.
Thanks.


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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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**BTW: Depending on your application (which you foolishly have declined to
tell us) a toroidal transformer may well be the WORST choice imaginable.
Toroidal transformers are certainly trendy and have a low radiated flux, but
they lose out to EI transformers in most other areas, including regulation
and line noise rejection. For the best line noise rejection, an 'R' core
transformer is best.

But you won't tell us what you are trying to do, so we really can't help
you.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Ok, thanks for that. .It's probably bad advice, but thanks for trying.

Yep, Toroidal transformers are trendy ..because they are very  popular!

That there are better transformer types (maybe 'Air Core', *groan*)  I don't
doubt for one moment, but I assume that there is good reason for the
Toroidal transformer's popularity and it is likely to be cost/effectiveness.

(p.s. Weren't you the guy who WANTED to be excused from giving me 'advice'?
I excused you. Did you change you mind?)



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Re: Isolated, regulated, toroidal step down transformer AC power supply design.



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**My advice, bad? Not bloody likely.

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**Duh.

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**There are APPROPRIATE transformers for each application. Air core
transformers are not seen outside of RF work.

 I don't
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**Sure. Toroidals have a low radiated hum feild, are (nowadays) cheap to buy
and they're reasonably efficient. However, their downsides make them the
LEAST suitable choice for YOUR specific needs. An EI transformer would be
better, whilst an 'R' core would be better again. It's horses for courses.
You seem to be making a selection based on the simple criteria of: "Oh, it's
what everyone else does." BIG mistake.

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**I'm certainly toying with that idea. You appear to be spectacularly
stupid. You have assiduously avoided parting with details of your
application and have refused all attempts at offers of good advice.

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**I don't care what YOU did.


--
Trevor Wilson
www.rageaudio.com.au



--

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


Yeah, I can accept that.

Ok, I'll look into it. I hope they are not too expensive.

(well now I feel like one of youse guys)


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Re: Isolated, regulated, toroidal step down transformer AC power supply design.


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How do people with city power run this device?

Have you tried using an online UPS, or active line conditioner, that has
sine-wave output, (this won't be cheap) and then connect the ordinary
powersupply.

Bye.
   Jasen

Re: Isolated, regulated, toroidal step down transformer AC power supply design.


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    He wants everyone to keep playing his infantile guessing game so he
can remain the centre of attention.
    How many commercially manufactured mains-powered electronic devices
are critically sensitive to normal mains voltage variations, requiring
precise regulation of the input voltage? About none that I know of. Even
UPSs have to see a pretty big variation before they cut in.
    He's had this problem since he went through this audiophile thing,
ripped out most of the electrolytic caps and replaced them with
audiophile ones. Remember his comment about us being too dull to ask him
if he'd made any bad solder joints?
    He's made a pig's breakfast of what was a normally functioning CD
player or whatever it is, and now wants some loony solution to mask a
fault *he* caused.
    And no Mark, we're not going to keep trying to guess what it is. My
suspicion is that the reason you don't want to tell is because it's some
audiophile thing you know Phil will laugh his head off about, and you're
scared of Phil from your experience in the aus.hi-fi newsgroup.
    Here endeth today's sermon.... :-)






Re: Isolated, regulated, toroidal step down transformer AC power supply design.


On Sat, 31 Mar 2007 14:28:02 +1000, Bob Parker

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Bingo! - That explains his weird posts perfectly.

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ITYM: 'audiophool', not 'audiophile'. ;^)

--
   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
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