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

Just about any audio amplifier and a sine wave generator will do the job.

What exactly is it that you want to achieve?

Reply to
dmm
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Correct (see my other post with the info). Just the thing for transparently filtering 100Hz ripple.

Bob

Reply to
Bob Parker

but

You haven't tried Googling 7815 datasheet?

I think you also need to revise basic power supply design, in particular, the manner in which regulators work, and the recommended filtering configuration on the input and output of the regulator.

As others have pointed out, it may well be that your AC power supply isn't supplying adequate voltage to prevent one or both of the regulators dropping out under load.

No, I don't appreciate that perspective, because it isn't the most obvious answer to what you've explained. The fact that you believe a regulator requires an input voltage within some percentage, either postive or negative, of the output voltage underpins where your thinking has gone wrong.

You're also convinced the issue is overvoltage, whereas looking at the whole system, it looks more like the AC transformer isn't putting out enough voltage. It could well be that another plug pack with a higer output voltage and suitable current rating would solve the problem, or it could be that the plugpack you have is a dud.

clipping

supply

Possibly, but there's a much more obvious answer that does a better job of explaining your problem.

better

Perhaps if you had stated from the start that your plugpack-powered preamp (I'm guessing) is exhibiting distortion and that you suspect a power supply issue, you might have gotten more rigorous and methodical advice. The next question would have been what are the regulators, what voltage is appearing at the input of each regulator, and are they getting hot.

That said, *nobody* deserves the kind of response and language that a certain person has used in this thread.

Also, if you are asking for help and advice, it's polite to observe accepted etiquette - that inlcudes refraining from top-posting particularly if asked not to.

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Reply to
Poxy

How could I not have realized that's what you meant? For everyone's edification, from

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....

Black Gate Electrolytic Capacitors

----------------------------------

There are very few audio parts that promise a guaranteed improvement when replacing practically any other part, but this is what the BLACK GATE? capacitors actually do. Exchanging any electrolytic capacitor anywhere in the circuit of a CD-player, amplifier or in the crossover of a speaker will greatly improve sound quality. BLACK GATE? are recognised worldwide as the best electrolytics capacitors money can buy.

Reply to
Bob Parker

BUT I DON'T want to eliminate the half wave rectifier!!! It is pre-existing inside the application.

I don't want to alter the application, at all and I would prefer not even to discuss it.

I would like to point out that my original question deliberately had NOTHING to do with the application. The easiest way to eliminate the unwanted discussion is to not provide information on the application.

So, WE are stuck with AC as an input to the application. I wanted to eliminate the AC/AC wall-wart transformer (which uses an Iron core transformer) and replace if with a Toroidal core transformer.

Do I need to justify this choice as well?

Reply to
Mark

Three things:

1) "7815" gives about 4 million hits on Goggle.

2) I asked for the help a little over 48 hours ago, and since that time I have had to suffer about 30 attacks, but NO HELP what-so-ever.

3) I have a family and one particular dependant who is bed ridden.

What did you expect from me?

Reply to
Mark

I haven't been paying close attention to this thread, but no item of audio (or any other mains-powered) equipment which is working properly is going to be affected by tiny mains voltage variations. If that's happening, then it's faulty and it should be looked at and repaired by someone who understands electronics. All this talk about toroidal transformers, voltage regulators and acoustically transparent capacitors seems irrelevant, or did I miss something by not reading everything? BTW: 'wall wart' is another Americanism creeping into the Australian vernacular. I suppose one day we'll have 117V 60Hz mains and beoome the

51st or 52nd or whatever it is state of the USA.
Reply to
Bob Parker

Oh be nice and go to bed Phil.

Reply to
Poxy

A Google on 7815 datasheet gets you the answer - very first result. Secondly, it isn't really about the specific attributes of the 7815 - as soon as you've had anything to do with power supplies, you get familiar with some very basic rules, one of which is that you need 2-3v extra at the input of a regulator for it to work - that applies to 7805s, 7812s etc.

That's because you didn't provide sufficient information from the start, and I don't mean to be rude, but what you initially suggested was absurd - it was. Really. It might have made sense to you given your background, but to anyone with experience in almost any field of electronics, regulated power supplies are such common and basic things that we pretty much all understand how they work, the issues that arise and how to deal with them.

What you said initially was the equivalent of saying: "How can I synthesise better fuel?" Then you say "I've purchased lots of really expensive fuel filters, which are black by the way - that hasn't helped, so I clealry need to re-sythesise my existing fuel to make it more consistent".

Everyone laughs at you. Particulalry when we discover how much those fuel filters cost.

Finally you say: "My engine is running badly, I think it's a fuel problem".

And if you were really being straight-up with us, you'd also say "Actually, I built the engine, it's running badly, does anyone want to buy some really good fuel filters?"

I'm honestly sorry to hear that one of your family is ill, and I'm also sorry that you've had to endure such unpleasant language and abuse, but it's Usenet, a base level of mocking and general derision comes with the protocol.

If you really want help, rather than seeking confirmation of your various theories, just tell us what the actualy device is, who designed and built it, what the voltage is at the input of the regulators is and what caps you have on each side of the regulator.

Oh, and maybe refrain from top-posting - it really does annoy people.

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Reply to
Poxy

"Bob Parker"

** Meeeeeeoooooowwwwww ........

........ Phil

Reply to
Phil Allison

That is the first thing that you've said in here that I actually agree with Phil.

Bob is a Pussy.

But you still didn't know that a voltage doubling rectifier CAN BE a variant of the simple half wave rectifier.

Nar, nar, nan-nar-nar!!!

Boy, this is fun isn't it.

Reply to
Mark
9 VAC, at a resonable cost.
Reply to
Mark

Well, he doesn't know his voltage doubling rectifier design. That point is proven.

Philthy could get out of it by claiming that he has made a simple mistake but I mean how likely is that event really? Huh???

Phil REALLY believes he is infallible and so would be incapable if making such an admission.

That is why he is the 'decider' of "what others should accept or believe" He has inferred as much, in this very forum, about a dozen times or so.

Reply to
Mark

You really don't get it, do you Mark? It's all over your head like a tent. I felt a bit sorry fot you and tried to steer you in the right direction, but you won't listen.

Bob (the one Phil's comment was aimed at - you think)

Reply to
Bob Parker

There is probably about a million ...no, no, a billion things I don't "get", but I've learnt not to worry about contingencies and just deal with matters as they happen.

I would need a microscope to find your compassion, mate. That is one of the defining characteristics of the 'Phil-o-phile'.

He has the hart of a Pussy.

Reply to
Mark

**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.
**Again. Proper selection of transformer will eliminate any problems.
**No, it is not what you originally indicated.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

**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
Reply to
Trevor Wilson

**YOU don't have to justify anything. YOU should be aware that, for low level audio applications, a toroidal transformer will be your worst choice. See what happens when you tell us what you are doing? You get sensible answers. Dump the toroidal and look for a decent 'R' core transformer. Additionally, I suggest you dump the 78XX & 79XX regulators and redesign with LM317/LM337 regulators. Much more significant than bothering with those silly Blackgate caps.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

No. At the input of a typical 15V regulator you need 17V or 18V as a minimum, and the maximum will typically be either around 30V-35V, or less if large load currents are being drawn such that the heat sink of the regulator gets so hot that the power dissipation of the regulator needs to be reduced by lowering the input voltage below 30V.

No, not if the "(nominally) 9 VAC" is actually anywhere near 9VAC, the peak value of the waveform is sqrt(2) (about 1.4 times) the RMS value, and 9VAC is conventionally used to refer to 9VRMS, unless otherwise stated.

It is not small enough to ignore.

It needs to be well ABOVE the nominal output OR IT WILL NOT WORK.

If you are using the regulators properly, then they will regulate. On a bad day, the output voltage might change by a millivolt or so, and nobody will notice. On a good day it will change even less and you will have great difficulty even measuring the change.

No, not if it is a regulator. Maybe you mean "transformer".

Should work just fine with 19.8V into a 15V regulator.

Ok, that's why you already have a regulator. If you are using it properly then you should not be having any problems.

All common regulators will accept inputs 40% above the output voltage. It is when the input voltage is NOT at least a couple of volts greater than the output voltage that you will have trouble.

I am not sure that you would make any improvement by changing the capacitors. It is possible that you have introduced problems due to the modifications. If you would explain what you have done then people would probably help you, but you indicated that you did not want to do that.

The problem seems to be that you started out by asserting as facts a few things that happen not to be correct, and then insulted anyone who tried to point out your errors. If you had started out with more humility and less conviction that you already knew everything on the subject of power supplies, then you would have received more helpful replies.

I suggest you learn what is inside a voltage regulator and how it works (from application notes on the National Semiconductor and On Semiconductor websites if you don't have any suitable books), learn what a half-wave rectifier and a full-wave bridge rectifier is, learn the relationship between the peak and RMS voltages of a sine wave, and next time when you're not sure about something, remember that you won't be attacked for not knowing something but you will be mocked and insulted viciously if you pretend to know things that you don't know and persist in asserting with confidence things that are incorrect rather than listening to correct (albeit not particularly polite) advice.

Chris

Reply to
Chris Jones

aaahhhh - the electrolytic equivalent of monster OFC cables ;-)

Reply to
budgie

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