I am not compelled to explain anything more than what I already have and what I have explained is more than sufficient for my purpose.
This isn't rocket science. A minimal design AC source can be achieved with only ONE component but the output is then at the mercy of the vagaries of the input voltage.
A better design might involve transformation to a nominal VAC (+/- x%) , then rectification and regulation to a nominal DC (+/- y%
**You don't have to explain anything. You won't get any help, either. **Correct.
**Except that it is ridiculously complex and unnecessary. If you would explain what you are trying to do, then we can help you. **I suggest you Google the following: 'Top poster'.
-- Trevor Wilson www.rageaudio.com.au
You are assuming that I had a perfect 9 VAC sine wave input to my application. If I'd had what I wanted, I wouldn't need to ask the question.
What I DO have is an very imperfect NOMINAL 240 VAC, domestic supply, like everybody else. (actually more imperfect than most, as we live in remote rural area with many idiosyncrasies in the supply).
I can step down the domestic supply to (nominally) 9 VAC, but it suffers exactly the same problems as the domestic supply. i.e. the output of the transformer isn't 9 VAC and isn't a perfect sine wave.
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.
To take exception to the style of postings is such an enormously trivial and childish position to take that I hardly feel deprived of your advice.
You may consider yourself excused of offering and advice.
It's irrelevant, actually.
240 VAC in (nominal) , 9 VAC out (+/- 1%), about 2 amps (but you can make it 10 amps or 1 amp, I don't care), toroidal transformer.I've already given you sufficient information on the type of circuit it supplies.
You cruel bastard!!
YOU are the idiot asking for help here! If you cant give more info, I doubt you will get more help.
The way I understand it, the regulation that already occurs within the application can only operate within a tolerance of the regulating IC's nominal input voltage. The application is using 15 Volt DC regulators (output), after the bridge rectifier, and can only operate (+/- x%) of 15 volts DC input.
The rectification of (nominally) 9 VAC I understood to result in 18 VDC (ignoring any small voltage drop across the diodes). So even when the input voltage is nominal, the input voltage to the regulating IC's is only within 20% of their nominal output.
Now what happens if the domestic supply voltage is not nominal?
If the domestic supply comes in at 264 VAC (+10%), the existing linear regulator now supplies 9.9 VAC to the application, the bridge rectifier doubles that to 19.8 VAC. The input voltage to the regulating IC's is now only within 40% of their nominal output!
I monitor the domestic supply and regularly see voltages coming into our house outside the range of +/- 10%.
One solution, of course, would be to redesign the power supply within the application's case, including upgrading the regulating IC's input voltage tolerance to at least 40% of its output, if such an IC can be found!
However space within the applications case would not allow for a toroidal transformer, which I consider to be the optimum solution for a number of reasons that I don't need to explain here (or maybe they will insist that I do that as well?!!), and I have already invested considerable effort (and a small amount of money) in upgrading the capacitors within the existing application's power supply and really don't want to loose out on the already considerable improvements I have made therein.
Quite frankly, I am astounded and reviled that such a simple request has generated such a vile reaction from this group. I can only assume that it is because they, like me, were unable to Goggle a suitable design. So as to maintain their allusion of expertise and so they hide their inability to self-design a suitable solution, with insults!
I wonder what would happen if I took a simular request for such a simple thing to another newsgroup, say 'us.electronics', and pointed out to them that 'aus.electronics' does not have a single contributor who can satisfy the request. I wonder what they would say. "Too difficult", do you think?
**** Is that right? I would have thought it closer to 12.7v (minus the forward drop of the diodes), and from one 12Vdc supply how are you going to achieve +/- 15V. Of course you could use half wave rectification for +/-12Vdc but if you want to achieve a very stable supply?????
So even when the input
**** Nope....and an input 20% below the desired output wont work will it? Assuming (because you wont tell) you are talking about 7815 / 7915 regulators or similar you'd want a good few volts above the output if you want any sort of regulation.So your presumption may be that asking for help at 'aus.electronics' is an idiotic thing to do? Can't really disagree with you there.
I am all too aware of the inherent perils involved in asking for help on any newsgroup inhabited by the likes of Phil and his 'Phil-o-philes'.
That reason alone is enough to make me cautious of providing any more information than I need to. My perception of Phil is that the more information you give him to analize (sic), the deeper your own exposure to his vile hatred of (just about) everybody on the planet.
Well, according to the schematic it is +/- 15VDC after regulation. And I believe it.
Yes, I believe it is half wave rectification. Something above +/- 15VDC, after rectification of the 9VAC. The schematic does not say, probably it is assumed knowledge.
I have already employed high ripple current Backgate capacitors after the regulators, and in coupling the Op-amps, and at quite a few other points throughout the power supply. Worked a treat in improving the sound.
Yes they are 7815 / 7915 regulators. I remember reading the spec for them (not that I can find it now).
The case is simply stuffed full of large caps throughout the power supply and analogue section, and it would simple break my hart to have to pull them out and start over again (to eliminate the half wave rectification)
Which is why I made my objective the replacement of the 9VAC wall wart power supply.
Too much to ask?
15
A common 7815 regulator will put out a stable 15v for input voltages between
17.5v and 30v. That's plenty of headroom for any overvoltage situation on the mains side.It certainly would be reassuring to know that I have more head room than I remember.
Show me your spec please. I remember reading something less (much less), but I haven't got it in front of me.
I am sure that you can appreciate that since I am replacing a wall-wart power supply with a toroidal step down transformer, the cost of an additional IC regulator is rather trivial when compared to the cost of the rest of the project.
It may turn out that the particular IC's that I have in place don't regulate to a 30 VDC input, either by design or circumstance.
The application certainly occasionally behaves erratically (on/off clipping of output) and I know that this behaviour coincides with over voltage supply problems. I monitor the domestic supply using software which queries and records data from an UPS. So there is no doubt about the cause. 100% correlation.
If the cost of certainty (solving the problem by putting in a bigger, better IC regulator) is about 10 bucks (and, apparently, putting up with a few arse-clowns because I was foolish enough to ask for help @ 'aus.electronics') then I can go the extra distance, I guess.
Why ? If it works don't fix it.
If you need dual rails, thats the usual way to do it. Half wave rectifier from a centre tapped transformer + linear regs.
Nice and cheap.
Alex
Ummm, can someone enlighten me as to what a Backgate capacitor is...? I did the obligatory Google searching but didn't find anything very informative.
Bob
Not exactly. There are precious few (if any) three-terminal regulators that won't handle a 30V or 40V input for 15V out. Your configuration is far more likely to suffer from UNDER-voltage out of the rectifier arrangement.
No, three-terminal regs don't work that way. Get a datasheet for a 7815 or 7915 and have a good read of the input voltage range. Let's see, 7815 ...
Dropout voltage (typical): 2.0V Vin (max): 35V
So a 7815 will regulate as long as the input voltage doesn't exceed 35V or drop below 17V on the troughs of the input waveform.
It may be small but it isn't insignificant. And I don't like your rectification theory either.
The Vin-Vout capability of (again, 3-terminal) regs is a spec figure you'll find on the data sheet, often termed drop-out voltage. See above. It's *not* a percentage thing. If your input drops (even on transients) to 2V above your 15V output, or less, you will lose regulation. 20% of 15V is 3V which - if your rectifier is really providing 18V DC - is barely enough, and ripple at any sort of load will kill you.
I think you mean transformer
I don't like your rectifier model, but let's ignore that for the moment.
They should be happier. Warmer, but happier. Realise also that the output of your rectifier system will show significant ripple as load current increases, and those dips threaten the very regulation those regulators are trying to provide.
Your concept of how regulators work is more than a worry. And IMNSHO it unperpins all your problems.
Read the data sheet, and understand what a 3-terminal reg does.
Throwing bulk cap around will obviously improve (aka mask) the regulation situation. But it is masking the symptoms, not fixing the cause.
You mentioned in another post that this is accompanying a move from a 9VAC wall-wart to a hopefully better transformer.
What I sincerely suggest you do is (in order):
(a) Get the data sheets for the regulators that you are using. If they aren't
7815/7915 then I feel compelled to ask why not.(b) Measure (even with a DMM) the input voltage to the regulator(s) and convince yourself that you have enough headroom to operate properly. Better still if you check the ripple with a CRO too. Even better, get a CRO and watch the waveform applied to the input of the regulators, and load/unload teh system so that the ripple can be quantified.
(c) Check whether the regs are running hot to touch.
(d) Try a 12VAC wall wart, unless the DCin to the regs is already 23V or more.
Quite frankly, I am astounded that you seemed to think that these problems are best solved by shooting for an (affordable) transformer offering 1% line regulation. If that were the best solution, such transformers would abound, and Google would have turned up a mutitude of solutions for you. Rather, the solution to such requirements have been de rigeur for decades, earning the tag classical.
Your request was further obfuscated - and the task of steering you towards a sound and achievable/affordable solution - by giving more of your planned solution than the description of the application and the problem.
No, they'd wonder why you were searching for an electronic sledgehammer.
Whether you choose to follow my, or anyone else's, suggestions is up to you. But among the flaming, you have been given more than enough leads to achieve a sensible outcome.
And please don't top-post
-- >"rebel" wrote in message >news:9cfj03lh21i2v84iq298n08u61ththollf@4ax.com... >> On Tue, 27 Mar 2007 22:59:44 +1000, "Mark" >> >> wrote: >> >>>Yes, I really do need 9 VAC for my application. >>> >>>Within the application, the 9 VAC is rectified, filtered, regulated (to >>>+15 >>>VDC and -15 VDC) and then filtered again. >> >> which removes the need for any tight regulation of the 9VAC. >> >>>So the input needs to be regulated to within about (+ or -) 1% 9 VAC. >> >> Nah, THAT's bullshit. (Hint: Just think for a moment what effect an >> increase or >> decrease of 0.5V in your AC 9V will have on the REGULATED DC rails.) > >
Maybe if you bothered looking at the datasheets for the devices you are using. Usual first step before using a device is read the datasheet or manual.
For a 7815
input range is 17.5V to 30V DC. Need minimum of 17.5 to get regulated 15V output.
Using a simple AC circuit + bridge rectifier or diodes + linear reg is a lot cheaper and simpler than mucking around with AC regulation.
May not be the most energy efficient circuit but is simple and easy to fault find. Also a less noise than any switchmode or boost/buck converter circuit.
Alex
the
My guess? They're "acoustically transparent" and cost a bomb.
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