Positive And Negative Voltages from one transformer

Tue Aug 31, 2010 10:14 pm   

I have a circuit requiring two equal voltages, one positive and one
negative. Is there a proven way to obtain these voltages from one
transformer?

Perhaps two bridge rectifiers sharing the secondary center tap and a
common ground?

Thanks

Rich

Tue Aug 31, 2010 10:14 pm   

"rich" <rsoennichsen_at_gmail.com> wrote in message
news:90295ac2-676a-4cd1-851d-ed09ed41151a_at_i4g2000prf.googlegroups.com...

One bridge rectifier. Center tap to ground. Positive bridge terminal is your
positive supply and the negative terminal is your negative supply. Both are
referenced to ground.

tm



--- news://freenews.netfront.net/ - complaints: news_at_netfront.net ---

Tue Aug 31, 2010 10:14 pm   

Hi Rich,

Several
The simplest doesn't need a center tap. Use two simple diodes one for
the positive and the other for the negative supply.


Then you are able to use full wave rectifying like "tm" wrote..
Marte

Tue Aug 31, 2010 10:14 pm   

On 08/31/2010 12:14 PM, rich wrote:

There are several proven ways.

The easiest, if you have a center-tapped transformer of the right
voltage uses _one_ bridge rectifier (or four diodes):



.------->|------o------o--------o V++
-. ,----o | |
)|( | .----->|------' |
Vac ) (---.| | |
)|( |'-)-----|<------. |
-' '---)--o | |
| '-----|<----o-o------)--------o V--
| | |
| | |
| --- ---
=== --- ---
GND | |
| |
=== ===
GND GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tue Aug 31, 2010 10:14 pm   

rich wrote:

Try a search on the web using the words "dual polarity DC regulated power
supply schematic". There are several variations on the basic circuit.
Before switching power supplies came along, this is just how it
was always or almost always done ... at least it was in the 1950s-1970s
consumer audio products that I've taken apart.

IIRC, The Art of Electronics (Horowitz and Hill) has a discussion on
ripple voltage that may be helpful as well.

Jay Ts

Tue Aug 31, 2010 10:26 pm   

Tim Wescott wrote:



I tried the AACircuit program in Linux. It works well under Wine.
Being able to rotate the components by right clicking the mouse is a
nice feature. Thank you, Andy.


http://www.tech-chat.de/download.html



mike

Tue Aug 31, 2010 10:48 pm   

"Marte Schwarz" <marte.schwarz_at_gmx.de> wrote in message
news:8e554nF7ccU1_at_mid.uni-berlin.de...

Unfortunately, each output is half wave rectified (though the total is
full wave). This requires big caps and results in low power factor, since
you're getting double the output voltage after all.

Analogy between four principle rectifier types:
http://webpages.charter.net/dawill/tmoranwms/Circuits_2008/Rectifier_Tutorial.gif

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Tue Aug 31, 2010 10:54 pm   

Tim Williams wrote:

Each output is full-wave centre-tapped. That doesn't hurt the ripple or
power factor, but does reduce the transformer utilization if the loads
are unbalanced.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

Tue Aug 31, 2010 10:59 pm   

"Tim Williams is a Hee Hawing Ass"



** Filter electros need to be double the value for the same ripple voltage.

This is not usually any problem at all.

The asinine comment about "low power factor " is utter BOLLOCKS.



.... Phil

Tue Aug 31, 2010 11:09 pm   

On 08/31/2010 02:26 PM, m II wrote:

I'm using it under Wine, also. It has it's drawbacks, but for quick
schematics to go into USENET posts or comments in a program or HDL file
it's aces.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tue Aug 31, 2010 11:15 pm   

"Phil Allison" <phil_a_at_tpg.com.au> wrote in message
news:i5ju0c$o7m$1_at_news-01.bur.connect.com.au...

MikeK

Tue Aug 31, 2010 11:19 pm   

"Phil Allison" <phil_a_at_tpg.com.au> wrote in message
news:i5ju0c$o7m$1_at_news-01.bur.connect.com.au...

Out of random curiosity, Phil, have you in fact measured the power factor
of any typical devices?

I'll show you my numbers if you show me yours.

Tim

P.S. "Bloody hell" to you too ;-)

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Tue Aug 31, 2010 11:25 pm   

"Tim Williams is a Stupid Lying Ass."


** A " random curiosity " is what YOU are - pal.

Just another genetically defective usenet troll.




** You have NO idea what the term even means.

FOAD you ridiculous asshole.




.... Phil

Wed Sep 01, 2010 12:40 am   

"Paul Hovnanian P.E." <Paul_at_Hovnanian.com> wrote in message
news:4C7D94ED.E8BBD94B_at_Hovnanian.com...

I often put that in kinda-sorta implicitly. Just a divider to make the
op-amps bias right. If I need it in a lot of places (like a proper
ground), I might use a funny ground symbol (like a hollow triangle) to
differentiate it from power ground.

If I have a spare op-amp section, or need the current range, I've been
known to buffer the divider. A couple ohms between output and bypass caps
(+V to GND to -V) stiffens things up nicely without instability.

If the ground isn't drawing power, it's usually possible to arrange it so
a voltage divider is "good enough", e.g., using 1k's in the divider, and
at the load, use 100k feedback resistors instead of 1 or 10k.



Heh...let's see:

"Speec is no sbustitute for accurance"
Probably typed ~100 WPM. Pretty awful, but not entirely correct either.
I'm so used to backspacing that trying to avoid it slows me down. :)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

Wed Sep 01, 2010 12:49 am   

rich wrote:

How much current will you be drawing from the common supply? There's a
little trick you can use with an op-amp as a follower from a resistor
divider that will produce a mid-point reference.

--
Paul Hovnanian mailto:Paul_at_Hovnanian.com
------------------------------------------------------------------
Speed is n0 subsittute fo accurancy.