12Vdc -> +-12Vdc - Electronic Circuits Projects Diagrams Free

bh00 · 10th August 2007, 04:13 PM

Hi,

Another issue, is the easiest way to convert a +12Vdc input to both +12Vdc and -12Vdc to power some op-amps and video switchers. The issue is, I will also need to power some 7805/7905 regulators off those supplies for PICs and some opamps at the lower voltage. I need to be able to source quite a bit of current therefore and the usual devices I come across will only provide 100mA or so at maximum which isn't enough. Any circuits out there to generate this for me reliably with at least 200mA of current on the -12Vdc rail?

Cheers

Hero999 · 10th August 2007, 10:30 PM

A 555 timer can give you a negitive voltage at the expense of some voltage drop.

Use shotky diodes to minimise the voltage drop.

Most op-amp circuits can be converted to run from a single supply though so it normally isn't a problem.

Blatman Bond · 11th August 2007, 02:02 AM

A battery mirror.
555 charge-pump is OK. Just buffer it to reach 200mA.

speakerguy79 · 11th August 2007, 03:05 AM

What's a battery mirror?

BTW, the expensive way to do this is to go to astrodyne.com and get a DC/DC converter.They make 'em from 1.5 watts up to waaaay more than you need. I used a 10 watt 5V-> +/-15V unit on a project a while back. $35 or so IIRC. PCB mount.

ETA: since you already have twelve, all you need is something like this:

http://rocky.digikey.com/scripts/Pro...6&M=PT78NR112V

400ma enough?

Hero999 · 11th August 2007, 10:29 AM

Quote:

Originally Posted by Blatman Bond

A battery mirror.
555 charge-pump is OK. Just buffer it to reach 200mA.

A 555 can output 200mA you know.

I presume a battery mirror just mirrors the voltage, i.e. it produces an equal negitive supply to the imput positive supply.

There are also IC that will do this, check out the MAXIM and Linear websites.

If you're using a wallwart, then go for one with an AC output, it's easy to build a rectifier that outputs both a positive and negitive voltage.

mvs sarma · 11th August 2007, 05:15 PM

Hi BH00 ,
try using a old device MC34063 ( an 8 pin device)
datasheet at www.alldatasheet.com

they offer you the design and pcb layout -- it can probably be housed in a square inch space.

Sarma

speakerguy79 · 11th August 2007, 05:20 PM

An AC power pack (wall wart) with a voltage doubler on it would be a good way to get this if you have AC available. Only problem with those is you need bigger filter caps and you'll have larger ripple currents when doing a +/- supply because you only get halfwave rectified current for each polarity.

http://sound.westhost.com/project05.htm

Hero999 · 11th August 2007, 06:25 PM

Ripple wouldn't be a problem for op-amps as the negitive feed-back should eliminate its effects.

Blatman Bond · 12th August 2007, 01:31 AM

Quote:

Originally Posted by Hero999

A 555 can output 200mA you know.

200mA at 2.5V output voltage drop.
Isn't the topology will decrease the current output?

bh00 · 12th August 2007, 09:33 PM

With a DC-DC converter IC, such as the NMA1209SC, can you connect the Vin ground to the output common, or is this not good as it greats issues with grounding or whatever?

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10th August 2007, 04:13 PM	(permalink)
bh00	12Vdc -> +-12Vdc Hi, Another issue, is the easiest way to convert a +12Vdc input to both +12Vdc and -12Vdc to power some op-amps and video switchers. The issue is, I will also need to power some 7805/7905 regulators off those supplies for PICs and some opamps at the lower voltage. I need to be able to source quite a bit of current therefore and the usual devices I come across will only provide 100mA or so at maximum which isn't enough. Any circuits out there to generate this for me reliably with at least 200mA of current on the -12Vdc rail? Cheers

10th August 2007, 10:30 PM	(permalink)
Hero999	A 555 timer can give you a negitive voltage at the expense of some voltage drop. Use shotky diodes to minimise the voltage drop. Most op-amp circuits can be converted to run from a single supply though so it normally isn't a problem. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

11th August 2007, 02:02 AM	(permalink)
Blatman Bond	A battery mirror. 555 charge-pump is OK. Just buffer it to reach 200mA.

11th August 2007, 03:05 AM	(permalink)
speakerguy79	What's a battery mirror? BTW, the expensive way to do this is to go to astrodyne.com and get a DC/DC converter.They make 'em from 1.5 watts up to waaaay more than you need. I used a 10 watt 5V-> +/-15V unit on a project a while back. $35 or so IIRC. PCB mount. ETA: since you already have twelve, all you need is something like this: http://rocky.digikey.com/scripts/Pro...6&M=PT78NR112V 400ma enough? Last edited by speakerguy79; 11th August 2007 at 03:09 AM.

11th August 2007, 05:15 PM	(permalink)
mvs sarma	Hi BH00 , try using a old device MC34063 ( an 8 pin device) datasheet at www.alldatasheet.com they offer you the design and pcb layout -- it can probably be housed in a square inch space. Sarma

11th August 2007, 05:20 PM	(permalink)
speakerguy79	An AC power pack (wall wart) with a voltage doubler on it would be a good way to get this if you have AC available. Only problem with those is you need bigger filter caps and you'll have larger ripple currents when doing a +/- supply because you only get halfwave rectified current for each polarity. http://sound.westhost.com/project05.htm

11th August 2007, 06:25 PM	(permalink)
Hero999	Ripple wouldn't be a problem for op-amps as the negitive feed-back should eliminate its effects. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

12th August 2007, 09:33 PM	(permalink)
bh00	With a DC-DC converter IC, such as the NMA1209SC, can you connect the Vin ground to the output common, or is this not good as it greats issues with grounding or whatever?