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.
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.
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?
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.
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.
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.