4 ms·

It was sort of magical when switched capacitors put all of this into a single IC. I've built a number of supplies over the years using a venerable 555 timer IC

It was sort of magical when switched capacitors put all of this into a single IC. I've built a number of supplies over the years using a venerable 555 timer IC driving one side of a 1:1 transformer at about 1MHz, then rectifying it on the other side and using a linear regulator to get the "negative" voltage I want. The real trick is to understand that ground is only a concept not an absolute :-)

dls2016 5y ago
Earth ground, signal ground, digital ground, virtual ground…
- eurasiantiger 5y ago
  Buffered ground.
exmadscientist 5y ago
My favorite way of generating a negative rail using more modern components, the inverting sync buck configuration, is especially maddening. The circuit's input, the positive voltage, is the regulator's VCC: so far, so good. The output, the negative voltage, is the regulator's VEE... which sounds fine until you remember these are single supply regulators and so that's their "ground". It's the regulator output that's the mind-bending one: it gets tied to ground! A switching node output, grounded, just does not look right. It actually makes a lot of sense once you draw it out. The startup is the truly confusing bit, but fortunately it's only unstable for your brain. These guys are actually pretty robust if you can find a part that withstands the full voltage stress (|Vin| + |Vout|), which isn't too hard these days. Highly recommended for a production-quality negative rail generator. Just don't try and do it with a regular buck; synchronous controllers only need apply.
- fbrozovic 5y ago
  Also works with non-synchronous buck converters, Maxim has an app note here with a schematic: https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3844.html https://www.maximintegrated.com/en/design/technical-document...
  - exmadscientist 5y ago
    Turns out you're right, I was working from app notes which were trying to sell sync bucks. (Not that that's hard to do, sync bucks are awesome.) I do think there are a few pathological startup cases that get easier when the output can sink current, but while those cases are easier to get into with bipolar rails, they still ought to be quite rare.
  - ChuckMcM 5y ago
    Just want to say both of these responses are awesome. Sent off a kicad file to OSHPark for a dual +/- 15V supply using the same circuit twice. Will see how it works out :-)

dls2016 5y ago

Earth ground, signal ground, digital ground, virtual ground…

eurasiantiger 5y ago
Buffered ground.

exmadscientist 5y ago

My favorite way of generating a negative rail using more modern components, the inverting sync buck configuration, is especially maddening. The circuit's input, the positive voltage, is the regulator's VCC: so far, so good. The output, the negative voltage, is the regulator's VEE... which sounds fine until you remember these are single supply regulators and so that's their "ground". It's the regulator output that's the mind-bending one: it gets tied to ground! A switching node output, grounded, just does not look right. It actually makes a lot of sense once you draw it out. The startup is the truly confusing bit, but fortunately it's only unstable for your brain. These guys are actually pretty robust if you can find a part that withstands the full voltage stress (|Vin| + |Vout|), which isn't too hard these days. Highly recommended for a production-quality negative rail generator. Just don't try and do it with a regular buck; synchronous controllers only need apply.

fbrozovic 5y ago
Also works with non-synchronous buck converters, Maxim has an app note here with a schematic: https://www.maximintegrated.com/en/design/technical-documents/app-notes/3/3844.html https://www.maximintegrated.com/en/design/technical-document...
- exmadscientist 5y ago
  Turns out you're right, I was working from app notes which were trying to sell sync bucks. (Not that that's hard to do, sync bucks are awesome.) I do think there are a few pathological startup cases that get easier when the output can sink current, but while those cases are easier to get into with bipolar rails, they still ought to be quite rare.
- ChuckMcM 5y ago
  Just want to say both of these responses are awesome. Sent off a kicad file to OSHPark for a dual +/- 15V supply using the same circuit twice. Will see how it works out :-)