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-   -   Look at my schematics? Dual-transformer, dual-voltage power supply... Thy built one? (http://www.caraudioforum.com/showthread.php?t=183909)

geolemon 04-04-2004 12:22 PM

Look at my schematics? Dual-transformer, dual-voltage power supply... Thy built one?
 
Alright...

Since I've already [i]started[/i] building my power supply, I thought now would be a good time to nail down the details on the schematic for the darn thing.. :p

And of course, I found that I had some questions.
Fortunately, I have some nice, easy, simple schematics to display. :cool:

My first question was with regard to the connector that I'll need, to go [b]from[/b] my power supply, [b]to[/b] my amp rails.

I was initially thinking that I'd have essentially a common center tap from the transformer, one tap being +25vdc relative to it, and the other being -25vdc relative to it...

So I was picturing that I could use a 3-wire connector, like a computer power supply connector to go from the power supply to the amps.

But after I drew up the schematic, it seems that I do essentially have four points...
A 0vdc and 12vdc, after [b]each[/b] transformer secondary, after the rectifier and capacitors.

So I'm wondering if I should do two 2-wire connectors (or one 4-wire connector), rather than a 3-wire connector?

[URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_connectors.pdf]This schematic[/URL] shows what I mean.

The top schematic shows what I'm picturing for wiring to a 3 pin socket (to which I'd plug a 3-wire interconnect to an amp).
The bottom schematic shows being wired to two separate 2 pin sockets (I could obviously do a 4 pin socket too).

What do you think?
Would there be any issues in using a 3-wire interconnect, since I've got the rectifier and two caps between where that center tap splits, and where I'm proposing to "reconnect" it?

:confused:

geolemon 04-04-2004 12:31 PM

For the moment, I drew up the rest of these schematics being conservative, using multiple 2-pin sockets.

So next, I dove into how to manage actually building a [i]two transformer[/i] power supply. :cool:

What I want to do, is have multiple connectors on my chassis....
Some of them providing 25v, some of them providing 50v...
Affording me the ability to use either/or at any given time.

...Maybe running two small chip-amps on two of the 25v sockets, and a higher-voltage solid state amp on one of the 50v sockets to power a sub or something. ;)

You can see in [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_diodes.pdf]this next schematic[/URL], I've got two transformers, a rectifier, the capacitors...
And I've drawn in several sockets, and some diodes to isolate them all.

The sockets labeled J1-J4 are all 25v sockets.
The sockets J5-J6 are the 50v sockets.

As you can see, I put diodes everywhere. :p

So my question is...
Do I need all these diodes?

I'm wondering if I'd be better off simply having the two diodes on the wires that bridge the two transformers together, as pictured in [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_diodes_2.pdf]this schematic[/URL].

Or, is there enough isolation by virtue of having transformers, that I could get away with not having [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_no_diodes.pdf]any diodes at all?[/URL]

:confused: also...

geolemon 04-04-2004 12:34 PM

Also - maybe most fundamentally - and primarily displaying how little I've retained of school from nearly 10 years ago... :p

I'm curious about the ground.

Will this essentially simply go to the round prong on my 3-prong wall outlet?
Or do I want to tie my chassis into this somehow (rather difficult, since it's going to be essentially all plastic and stone! :p)?
Or something else altogether?

In advance - huge thanks for help! :cool:

geolemon 04-04-2004 12:40 PM

Oh, and this is of course related to [URL=http://www.betteraudio.com/geolemon/powersupply/]my power supply project[/URL].

And ignore all the part numbers and labels on the schematics..
I don't know what the specific part numbers actually are... I just mean to use them in the schematics as generic transformers, diodes, capacitors, etc. ;)

hieroglyphics 04-05-2004 04:10 AM

Grounding the chassis is only essential when it is made of a conductive material (ie. aluminum). If by chance you were sloppy with the wiring and there were some exposed wire touching the chassis, that wire will have a voltage relative to ground. If the chassis is not grounded and you touch it, YOU become the ground :D Current flows through you and geolemon turns to geotoast. Of course, if the chassis is not conductive, you haven't got much to worry about.... but to answer your original question, yes the ground in your schematics is connected to earth ground (round prong).
I believe that your ground will be giving you issues the way that it is wired. I think you'll want to go with the top arrangement that you've drawn [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_connectors.pdf]here[/URL] with a common ground for both + and - rails. Your ground point on J1 needs to be rewired though. The centre pin (ground) should be tied to the negative edge of the first bridge rectifier (D1 in schematic) and the positive edge of the second rectifier (D2). All you gotta do is connect the wire marked "1" from D2 to the centre pin of J1 and connect the wire marked "3" from D2 to the bottom pin of J1.
The drawing below that one may have issues with floating ground (ie. there may be a voltage between your two grounds--no good). This is easily fixed by connecting them together like the top schematic.
One more thing I gotta point out is that you're gonna need to wire the two transformers in series to obtain the 50V output. You've got them in parallel.
You got a wackload of diodes in there--shouldn't need em unless you want to lower DC voltage. You've shown them wired [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_diodes.pdf]here[/URL] where the supply would still work fine but there will be about 2 x 0.7V = 1.4V DC drop because of them. This CAN be to your advantage if the DC voltage is too high and you want to reduce it. A little trick for later.
I should mention that you won't be getting 25V and 50V DC output but rather multiply those values by sqrt(2) or 1.414. That will be your DC voltage.
I don't have much time so I'll finish up quick (should have time later today). Along with wiring the two transformers in series (the primaries), you'll also have to connect the negative secondary (wire "3" of D2 aka bottom pin of J4) to the next positive secondary (wire "1" of D3 aka top pin of J2). This will form your ground for the +- "50V" (times 1.414) supply.
Hope this helps. Keep up the work geo--you got the initiative, it'll pay off once you're bumpin your 'clones :bun: :bun: :bun:

geolemon 04-05-2004 04:45 AM

[QUOTE][i]Originally posted by hieroglyphics [/i]
[B]I believe that your ground will be giving you issues the way that it is wired. I think you'll want to go with the top arrangement that you've drawn [URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_connectors.pdf]here[/URL] with a common ground for both + and - rails. Your ground point on J1 needs to be rewired though. The centre pin (ground) should be tied to the negative edge of the first bridge rectifier (D1 in schematic) and the positive edge of the second rectifier (D2). All you gotta do is connect the wire marked "1" from D2 to the centre pin of J1 and connect the wire marked "3" from D2 to the bottom pin of J1.[/quote][/b]
Let me make sure I'm understanding...
Right now, I have it wired in that top picture so that you'd measure +12v from the center pin to the upper pin, and +12v from the center pin to the lower pin.

Rewiring it as you say, will essentially give me +12v from the center pin to the upper pin, and -12v from the center pin to the lower pin, correct?

[quote][b]
The drawing below that one may have issues with floating ground (ie. there may be a voltage between your two grounds--no good). This is easily fixed by connecting them together like the top schematic.[/b][/quote]This is actually good news, as I was hoping to use the IEC connectors, like your computer's power supply plug, your monitor's plug... those standard 3-prong interconnects.
Sounds like that'll work then! :cool:

[quote][b]One more thing I gotta point out is that you're gonna need to wire the two transformers in series to obtain the 50V output. You've got them in parallel.[/quote][/b]
Take a closer look...
Of course, it may not be correct the way I have it drawn)...
But I've got one secondary of the top transformer in series with one secondary of the bottom transformer.

The plugs marked J6 and J5 are my 50v (well, 70v, you know ;) ) plugs, the rest are 25v (35v).

If you trace the path from say, one pin of J5 around, and back to the other pin of J5, you'll see what I mean...
And you'll also maybe see one reason I chose to include diodes on plugs J1-J4...

For example, if something is plugged in to J2 or J4, that's suddenly in parallel with anything plugged into J6, correct?

[quote][b]...you'll also have to connect the negative secondary (wire "3" of D2 aka bottom pin of J4) to the next positive secondary (wire "1" of D3 aka top pin of J2). This will form your ground for the +- "50V" (times 1.414) supply.
Hope this helps. Keep up the work geo--you got the initiative, it'll pay off once you're bumpin your 'clones :bun: :bun: :bun: [/B][/QUOTE] Thanks, it helps quite a bit! :cool:

I'll draw up a new schematic at some time today or this evening, see if I can tie these in, and wire the "alternative" series wiring that I was thinking of before, see if that is more correct. ;)

thylantyr 04-05-2004 06:32 AM

Did you read this link I posted before ?

:cool:

[url]http://www.tnt-audio.com/clinica/ssps1_e.html[/url]

If you want to do a series/parallel with your power supply
then you can use a switch. I have a schematic somewhere. /lol

Note diode polarity and capacitor polarity. For negative rail,
the capacitor positive is connected to ground and the capacitor
negative is connected to -V rail because the ground reference
is more positive than the negative rail therefore the +terminal on
the capacitor needs to be connected to ground otherwise .. a
possible kaboom ...

Redraw the schematic and repost so any new discussion has
a clean reference to look at.

That link I posted, I noticed they don't have capacitor bleeder
resistors. Make sure you place a resistor across each rail to
bleed the capacitors when the power is off. The value of
resistor chosen determines how fast you want to bleed
but also it presents a load on the power supply that you may
not desire. In other words, a 1 ohm resistor would bleed the
capacitors fast but also place a huge burden on the power supply.
Ideally you want a high ohms resistor so it doesn't present a
big load on the power supply -- but at the same time you
want the resistor adequate enough for bleeding. Youc an
calculate the RC time constant and figure out what value
of resistor you want. If you want a 30 second disharge then
do some math to get you a resistor that fits that ball park
range of discharge. Then calculate the resistor wattage and
factor in a safety margin, perhaps 1.5x - 2x high than calculated. /hehe

Last, your amplifier is a load that will disharge the power supply
also, perhaps much faster than the bleeders. But since this is
a stand alone supply, insert the bleeders.

geolemon 04-05-2004 09:42 AM

Geez, CAF when down right when I was going to post this earlier: :rolleyes:

I didn't add any bleeder resistors yet...
I did check out that TNT link though, it's a good one.
I'll need to go through it a few more times, I think. ;)

But here's what I've revised my schematic to:

[URL=http://www.betteraudio.com/geolemon/powersupply/power_supply_2.pdf]new schematic[/URL]

I changed to 3 prong connectors...
And I changed how I am tapping for my 50v, this time essentially paralleling two secondaries on the same transformer... probably makes more sense that way. ;)

Does this seem more fundamentally correct?
Those ties that I've made to go to the center pin of each connector are what has me nervous. Look good?

Note that I also changed where my ground was attached...
I had it on the supply side of the transformer originally, that TNT link shows it on the load side.
I placed it electrically where it existed on that TNT site, but they show a single transformer, single voltage supply... essentially a ground on the same plane as the grounds for the 35v terminal plugs.

I'm concerned about the ground on the 70v terminal plug... or rather, lack of one.
Should there be one here?
I can't imagine it - it seems bad to essentially have this tie from the ground of the 35v terminal to the ground for the 75v terminal... since the ground for the 70v terminal is essentially the + for the lower 35v terminal (and the - for the upper 35v terminal). Sounds like short-circuit city...

But does that mean I'm operating ungrounded, if I'm running the 70v terminal?
:confused:

Well,hopefully I'm on the right track here...
I'm looking to get the schematic functionally correct, and then I'll add things like the switches, fuses, additional caps or RC circuits or bleeders... that'll be the next step. :cool:

thylantyr 04-05-2004 02:44 PM

Wasn't unable to post this earlier;

Connectors to use? Whatever you like that fits the current
requirement. For my PCB layout project I chose the Molex
Minifit Sr. connectors. High current contacts with beefy pins.

Like this;


Receptacle;
[url]http://www.molex.com/product/power/42816.pdf[/url]

Choose 2,3,4,5,6 pin.

Plug housing
[url]http://www.molex.com/product/power/42818.pdf[/url]

Header;
[url]http://www.molex.com/product/power/42819.pdf[/url]

Terminals
[url]http://www.molex.com/product/power/42817.pdf[/url]
[url]http://www.molex.com/product/power/42815.pdf[/url]


For PCB mount, I chose the header not plug housing.

These are nice connectors. Each pin is rated for 49A :bun:

I think Mouser.com had the best prices on these.
For my project I doubled up on the pins and used a
6 pin connector.

2 pins in parallel for +V
2 pins in parallel for gnd
2 pins in parallel for -V

Nothing beats redundency. The reason being is these connectors
are only rated for low insertions, 30-50 cycles. After that
contact resistance rises so adding the redundency is simple
and effective.

thechris 04-05-2004 05:17 PM

quick look - doesn't that create a diode-short condtion on the negitive swing? pretty sure. notice there is a path from T1 secondary top to T1 secondary center tap if T1 top < T1 center tap.

so you get a pretty nice sized current...
also, there are more diode-shorts like this. have you simulated this? i don't think the problem will show up in the output voltages, but the current supplied by the transformer will be very, very high. i find multiple short circuits.

why not use just 1 full-wave bridge per PSU? very easy, low losses, ect...

thechris 04-05-2004 05:27 PM

change 1uF to an appropriate value...

[url]http://www.siue.edu/~cstahl/psu.wmf[/url]

and yes, this is also a vector scalable graphics format...

thylantyr 04-05-2004 05:53 PM

Edit:

The new schematic looks good but as
thechris suggested, check the center tap connections. See the TNT link, they
don't connect the secondaries together
to form a center tap, instead they are isolated. (or see below).

Why use two bridges ?
[url]http://www.diyaudio.com/forums/showthread.php?threadid=6773&highlight=[/url]
[i]If you use one bridge with two secondaries and some
net DC current flows through the ground, there will be
a tendency toward saturation (and mechanical noise)
in the transformer if the two windings are not precisely
identical. Most of the time this is not a problem, but
when it is, two bridges prevents it.

Nelson Pass[/i]


In your schematic you are using 3
power connectors. If you wanted to
optimize this perhaps you could use
one power connector with a toggle
switch to supply standard voltage or 2x standard voltage. /hehe

Or do you plan to feed J1 to one
amplifier and J2 to another amplifier
so each channel has it's own PS with
J3 being the 'experimental' higher voltage rail ?

Or is it the other way around? J3 feeds
all the amplifiers and J1 and J2 are aux
power sources ?

Is J1 and J2 grounds connected together or do you plan for them
to be isolated ? If isolated, then label
the schematic -- perhaps GND1, GND2,
and for J3 ground, perhaps GND3.
Not important because you are wiring
it up and detailed documentation is
not really needed.

Using even more switches you could
create something more complex where
both transformers connect as either series or parallel. /hehe


some babble;

[url]http://home.pacbell.net/lordpk/temp/PS1.jpg[/url]

Figure 1 shows a generic bridge rectifier
with +70VDC and GND output. The center
tap of the tranformer is not used.

Figure 2 shows the same circuit except that the diodes and capacitor are rewired
for -70VDC and GND output. The center
tap of the transformer is not used.

Figure 3 shows another way to get -70VDC
and GND output using the same circuit
shown in Figure 1. Just change the 'labels'
on your connector. ie, connect your load
backwards. <-- hehe

Figure 4 is the same as Figure 1
(and Figure 5 is the same as Figure 2)
except it's using the center tap and NOT
the other leg of the transformer.
Essentially you are only using 1/2 of the
secondary. You can use this method if
you need 1/2 the voltage only.

Figure 6 shows how to create a 'bipolar'
power supply, two voltage rails, positive and negative in reference to
ground. You are essentially cutting the
70VDC in 1/2 so you get +35 and -35V
and ground. The voltage across the
+35v and -35v nodes net 70VDC.

Figure 7 is the exotic version of Figure 6
that DIY'er commonly use because it's cool :bun:

These are the simple methods for
power supply creation

If you wanted to take the examples
above further and wanted to make

a power supply to output either
+/- 35VDC or +/- 70VDC by just
toggling a switch, you can do something
like this;

[url]http://home.pacbell.net/lordpk/temp/PS2.jpg[/url]

It's a DPDT switch that either selects
the center tap or outside leg of the
transformer.

see the Nelson Pass grounding tips :bun:

[url]http://www.caraudioforum.com/showthread.php?s=&threadid=179245&perpage=15&pagenumber=2[/url]

[url]http://www.diyaudio.com/forums/showthread.php?threadid=28421&highlight=[/url]

thylantyr 04-05-2004 06:44 PM

re: the J1, J2, J3 grounds.

To clarify. The J1 and J2 grounds can
be connnected together but nothing more.

Or, J1 ground can be isolated from J2 ground - perhaps if you wanted to
supply power to two amplfiier modules
to prevent ground loops between the
two channels :bun:

Ground is just a reference in this case.
J3 has a ground reference just as you
drew it. But this ground reference is
not connected to the other grounds ..
otherwise ..kaboom.

A car battery +12v wire can be considered a ground reference for
some other circuit and you do nothing
to create this reference.

Suppose you had a 'black box' device
with a sticker on it that said;

Green wire: -12v input
Brown wire: gnd input

Car battery black terminal connects to
the -12v of the black box and the car
battery red terminal connects to gnd of the black box. /silly

It would be alot easier to change out
the sticker with something that makes
more sense;

Change the green wire to black.
Change the brown wire to red.
Change the label.

Red wire: +12v
Black wire: gnd.

now it makes sense


:p

Update your schematic with bleeders
and misc. capacitors, switches, etc.
Do you want to add an MOV to the input for giggles ? (MOV) = metal oxide
varistor, aka the dreaded surge protector. Any nasty power glithes,
electrical storms that could send a nasty glitch to the precious power amp?
/hehe The MOV looks like a small disc
capacitor and I think it's a cheap item.
Do a google for more info.

geolemon 04-06-2004 02:07 AM

[QUOTE][i]Originally posted by thechris [/i]
[B]change 1uF to an appropriate value...

[url]http://www.siue.edu/~cstahl/psu.wmf[/url]

and yes, this is also a vector scalable graphics format... [/B][/QUOTE] Link didn't work, site down?

geolemon 04-06-2004 02:23 AM

[QUOTE][i]Originally posted by thylantyr [/i]
[B]See the TNT link, they
don't connect the secondaries together
to form a center tap, instead they are isolated. (or see below).
[/b][/quote]I'll go through it again...
I didn't see that they had a schematic for series-wiring two transformers to combine voltages... I'll check again!

[quote][b]Why use two bridges ?[/b][/quote]:confused:
I'm using 2 bridges [i]per transformer[/i], right?

[quote][b]In your schematic you are using 3
power connectors. If you wanted to
optimize this perhaps you could use
one power connector with a toggle
switch to supply standard voltage or 2x standard voltage. /hehe

Or do you plan to feed J1 to one
amplifier and J2 to another amplifier
so each channel has it's own PS with
J3 being the 'experimental' higher voltage rail ?[/b][/quote]
Yes, I want to be able to have my power supply provide both 35v and 70v at the same time, if I ever had the need...
For example, two chip-amps using 35v rails, and a solid-state higher power small subwoofer amp using 70v rails.

[quote][b]
Or is it the other way around? J3 feeds
all the amplifiers and J1 and J2 are aux
power sources ?[/b][/quote]J1 and J2 will be to supply 35v, and J3 is to supply 70v.

[quote][b]Is J1 and J2 grounds connected together or do you plan for them
to be isolated ? If isolated, then label
the schematic -- perhaps GND1, GND2,
and for J3 ground, perhaps GND3.
Not important because you are wiring
it up and detailed documentation is
not really needed.[/b][/quote]
To be honest- I don't know how to isolate the grounds.
Diodes?
I was picturing them all as simply being tied to the round pin on my wall plug, not isolated.
But I'm certainly not locked into that, obviously, if that's wrong.

[quote][b]
Figure 6 shows how to create a 'bipolar'
power supply, two voltage rails, positive and negative in reference to
ground. You are essentially cutting the
70VDC in 1/2 so you get +35 and -35V
and ground. The voltage across the
+35v and -35v nodes net 70VDC.

Figure 7 is the exotic version of Figure 6
that DIY'er commonly use because it's cool :bun:
[/b][/quote]Figure 6 looks like what I am doing...
But that's only 1/2 of my PS.

I'll have two "figure 6's" please, each with the option of "figure 1'ing" so their output can be combined into a bigger "figure1/figure 6" super-size combo.
And I'll have a milkshake and fries with that. :D

The only catch is essentially how to do that ground then, for my J3 plug, is that what I'm understanding?
So that's where my earlier diode-craze fits in here? :p

Let me see if I can do up another schematic and guess the answer. :cool:


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