Isolated, regulated, toroidal step down transformer AC power supply design. - Page 4

Yeah, someone else suggested the UPS. I think they can be purchased quite
cheaply on EBay. I have no idea how others do it or if they suffer the same
problems.

We live in the far N/E Victoria, just near the NSW boarder and it is the
most notoriously unreliable power supply in the state. I've been told (by
TXU) that we suffer more lighting strikes here than any other part of the
state. We suffer black outs on a weekly basis, occasionally see brownouts
and get voltage over supply almost daily.

"Mark"




** Might as well just post your address and phone number as tell us that.

 How  *are* things in beautiful Merbein tonight  - really jumpin like usual
?

 ROTFL  !!!




.....  Phil

Does anyone else understand this? I don't. Merbein???

which removes the need for any tight regulation of the 9VAC.



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.)

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.

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?

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

the

My guess? They're "acoustically transparent" and cost a bomb.

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

Bob

*Black Gate. I don't know how I can live with myself.

    How could I not have realized that's what you meant?
    For everyone's edification, from
http://www.hificollective.co.uk/components/black_gate_caps.html ....


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.

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

**Not really. Monster Cables are designed to possess attractive cosmetics,
with no real regard for any tangible performance criteria. Blackgate caps,
OTOH, DO have some measurably significant parameters. HOWEVER, none of those
parameters is significant for power supply filtering. IOW: There are better
caps available, at lower cost for filtering. Mind you: After purchasing some
of those Dick Smith 'Joe Master' branded monstrosities once (and ONLY once)
I can readily understand why some purchasers would spend the Bucks for a cap
which is quite well made and performs respectably enough (Blackgate).

yeah, I second that. I wont buy a cap if I cant get a datasheet for it.
one 10uF cap with 27 Ohms ESR was enough for me. Of course now, thanks
to Bob, I can measure that in a jiffy :)

Cheers
Terry

Thanks Terry. Now I'm thinking about how to make a meter which shows
musicality in capacitors. Maybe do a frequency sweep to see how it
performs at the bass vs midrange vs treble ends of the spectrum? ;-)

Bob

perhaps you could have a web-enabled instrument. If it can find a
datsheet, it gives it a low score, and vice-versa.

Hey, who makes your kits in USA? I want to recommend it to one of my
customers there.

Cheers
Terry

    Yeah, sounds good to me!
    Now that DSE's stopped making kits, about the only place anyone can
get an ESR meter one is from John's Jukes in Vancouver, Canada.
    Website: http://www.flippers.com
    HTH

Bob

There seems to be a trend to put clear cases on everything these days... Maybe
if you can shine a light through it you can measure its 'transparency'?