Positive And Negative Voltages from one transformer

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

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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

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 ) (---.| | | )|( |'-)-----|

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

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.

mike

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:

Tim

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

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

"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

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

Nice to feel your warmth Phil, welcome back! MikeK

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

"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

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

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@Hovnanian.com
------------------------------------------------------------------
Speed is n0 subsittute fo accurancy.

ONE FWB across xfmr, CT to GND will do it.

Thanks to all for the great suggestions!

Rich