Bipolar voltages out of non center tapped transformer

[puretube]

information lost...

[gez]

!!!

[R.G.]

Yep, that's pretty much how to do it; The same approach was shown in the article "Power Supplies Basics" at GEO, http://geofex.com/Article_Folders/Power-supplies/powersup.htm.

[puretube]

gez: I was sure you knew the "Delon"-circuit... ?  

oh, yes, b.t.w.: it`s a doubler, too;
if you take the "-12V" as the new ground,
the "0V" becomes the new +12V,
and the "+12V" becomes the new +24V.

(if both halves are used rather symmetrically,
i.e. similar current consumption on both voltages...).

[R.G.]

Nota bene: some circuits are sensitive to power supplies coming up asymetrically. I ran into this with some op amps. They latch up if one side of a bipolar supply comes up before the other. That is one thing that this circuit does.

You may have to do some kind of circuit to let both sides come up to voltage, then switch it into the opamp power to keep this from happening. The "Good - and Cheap - Polarity Protection" circuit at GEO does this if you derive a signal externally to drive the "on" line of the NPN.

[StephenGiles]

Very good indeed - I can see a lot of uses for that. Any more thoughts on the filter thing?
Stephen

[Gringo]

Thanks a lot!!  

[Zero the hero]

Remember the heatsinks for 78xx and 79xx: when particulary stressed these chip could become very hot (my fingers know it very well...).
Will this circuit work with dc instead of using an ac transformer?

[puretube]

Yep, that's pretty much how to do it; The same approach was shown in the article "Power Supplies Basics" at GEO, http://geofex.com/Article_Folders/Power-supplies/powersup.htm.

sigh... if I woulda known that, I woulda posted a link...  

[puretube]

...
Will this circuit work with dc instead of using an ac transformer?

NO

(unless you chop the DC beforehand - there are circuits for that, too...)

[mikeb]

Yep, that's pretty much how to do it; The same approach was shown in the article "Power Supplies Basics" at GEO, http://geofex.com/Article_Folders/Power-supplies/powersup.htm.

sigh... if I woulda known that, I woulda posted a link...  

That's crazy talk ... RGs image doesn't contain enough info for most DIYers here to actually make something, whereas yours does!  :wink:

Oh, and.....
http://sound.westhost.com/project05.htm
(used pretty much as is for the infinitphase bipolar power supply)

Mike

[puretube]

... Any more thoughts on the filter thing?
Stephen

Not yet - the PC the printers are hooked to (the one that had a sneaking death of one of the 1 year old RAMs during the last 3months....),
had a wire broken on monday:

the manufacturer of the processor-fan obviously had used a very sharp tool to strip the wires - one of them broke straight at where the isolation ended close to the solder-joint (which itself was excellent!).

The processor was not amused...

(and I don`t like to stare at the monitor to analyze circuits...)

So my thoughts have been distracted...

[puretube]

mikeb: tnx - if I woulda known that one, I woulda...    

(that one`s even more explicit)

[Paul Perry (Frostwave)]

Nota bene: some circuits are sensitive to power supplies coming up asymetrically.

As usual, RG is right...and if anyone ever gets around to doing DSP stuff, with separate logic & analog rails etc, there is sometimes a problem if an analog signal to the chip gets there before the chips power rail comes up. Because, when they say "input to analog signal pin must not exceed power input voltage" and power input voltage is still around only a couple of volts,... the chip is gone.. Like every lesson,. learned that the hard way :oops:

[puretube]

the TL07x series work latch-up free...

doesn`t every 9V battery circuit with the well-known resistor-divider-with-cap-to-ground-from-the-Vbias start up assymmetrically?
(that electrolytic got to charge up slowly thru the "northern" resistor - at first instance, it`s a dead short to ground, while the pos. voltage is already at its point...?).

[RedHouse]

Not the 78xx latching, it's the OpAmps downstream to consider.

[puretube]

TL07x are opamps (e.g.: TL072 ...)

[R.G.]

the TL07x series work latch-up free...

doesn`t every 9V battery circuit with the well-known resistor-divider-with-cap-to-ground-from-the-Vbias start up assymmetrically?

Op amps vary a lot in how tolerant they are. Some are downright picky about power sequencing, some are not. The TL0xxx series are pretty tolerant. I ran into serious issues with some Burr-Brown opamps with the half wave doubler power supply not long ago. They latched into non-operation (although, thankfully, not destructive) about half the time.

Additionall, most of the time, the specification "latchup free" means that the opamps are free of latchup under certain conditions, notably exceeding the common mode input range, which used to latch up first-generation opamps.

It's not something to worry about, just something to know. If it turns out to be a problem, you can use a circuit somthing like my cheap and good polarity protection - one PNP in the positive rail, one NPN in the negative rail, and derive the turn-on signal from something like a zener to turn on both sides simultaneously after there is some voltage on both sides.