Split supply from single DC wallwart? (virtual ground?)

[eyAyXGhF]

Hey all,
After previously using an AC-AC wallwart to rectify and generate a split power supply (https://www.electro-tech-online.com...tion-within-north-america.128491/#post1069783) I'm looking for something that won't have issues with mains voltage variation or location.

I need to generate internally +/- 14V or 15V. I'm noticing that there are several 28VDC switching supplies on the market that are pretty cheap and work from 90 VAC to 264 VAC. This also solves my problem of trying to find AC-AC wallwarts for different locales.

I've read a bit about "virtual ground" circuits, and I'm wondering if something like that would be possible to turn a 28VDC supply into +/- 14V internally? I'll be drawing approximately 250mA per rail.

 

[ChrisP58]

First create your virtual ground voltage point with a resistor divider using two matched, equal value resistors. Second, make it low impedance by buffering that voltage with a unity gain op-amp.

You may need an op-amp with a >250mA output capability, but only if the 'ground' point will see unbalanced currents that high.

 

[ronv]

If your circuits will run on 14 volt supplies why did tou have a problem with your original supply?

What does the supply run?

 

[eyAyXGhF]

If your circuits will run on 14 volt supplies why did tou have a problem with your original supply?

What does the supply run?

Hi Ronv, thanks for the reply. The circuit worked to give me +/-15V with the ac-ac adapter I picked (12VAC - 1000mA) under the expected load (approx 150mA per rail). But only because I naively expected the mains power to remain at 122.5VAC for the entire continent

Reducing the supply output to +/-14V was a temporary fix to give some more headroom. I'm also wondering if maybe instead of redesigning the wheel here, I can just grab an appropriate higher voltage ac-ac adapter?

 

[ronv]

The higher voltage adapter is by far the best.

https://www.electro-tech-online.com...tion-within-north-america.128491/#post1069974

What keeps you from running at say +/- 12 volts?

 

[eyAyXGhF]

The higher voltage adapter is by far the best.

https://www.electro-tech-online.com...tion-within-north-america.128491/#post1069974

What keeps you from running at say +/- 12 volts?

Only that I already know my circuit works properly at +/-15V. However, in the next few days I'm going to go through it all and see if I can convert it to +/- 12V exactly as you recommend.

Mike

 

[audioguru]

First create your virtual ground voltage point with a resistor divider using two matched, equal value resistors. Second, make it low impedance by buffering that voltage with a unity gain op-amp.

You may need an op-amp with a >250mA output capability, but only if the 'ground' point will see unbalanced currents that high.

If the virtual ground is only used to bias opamps that have an extremely low bias current then the buffer opamp is not needed.

 

[Nigel Goodwin]

Only that I already know my circuit works properly at +/-15V. However, in the next few days I'm going to go through it all and see if I can convert it to +/- 12V exactly as you recommend.

It's still pretty dodgy using a 12V transformer to feed 12V regulated rails, particularly so when only using half wave rectification.

 

[ronv]

Yes, Probably be a good idea to make sure what the distribution is on your transformers. Could be they don't all supply 18.5 volts at 250 ma.

 

[lucy2012]

hi,are you only intereted with the AC AC converter?how about the dc dc /ac dc converter?