Opinion needed: 12V ± supply, low power, <100mA

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Boredom is really boring. There's a project I've been thinking about for decades. To accomplish it, one of the things I'll need is a dual rail supply, 12V pos and 12V neg. I know this will work, but the opinion I'm looking for is "Build" or "Buy"? If "Buy" - what? Is there something or some other method that is better?

I'm drastically old school so I'm sure there are better ways to accomplish this part of the task. The rest of it is going to be a couple op-amps being driven by an audio signal. Though I haven't given much thought to that part of the circuit just yet, in the end this will power a small laser pointer module, just like the stuff you can buy in the cat toy isle of a pet store. Power requirement is likely going to be <100mA.

[edit] incorrect drawing removed and replaced. See post #6 [end edit]
 
Last edited:

crutschow

Joined Mar 14, 2008
27,438
The easiest is just to buy a couple of wall-worts.
Since their outputs are isolated, you can connect the outputs to provide a plus and minus supply.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
The easiest is just to buy a couple of wall-worts.
Since their outputs are isolated, you can connect the outputs to provide a plus and minus supply.
That's going to be drastically larger than is needed. I DO have several 12V warts around, and they may be useful for testing, but in the end I want a relatively small project. Don't have dimensions yet but I'm thinking around 4 by 5 by 1 1/2 inch box. It may end up being a little larger, but two 12V warts would already be way overkill.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Thanks SamR. Already have transformers and almost all components. I would need to buy the 7912 though. So I remain open to the idea of buying something as opposed to building. But as I opened, I'm bored of being bored. So I want to do something with my time other than just sit around, drink beer and watch football. I'm already suffering enough from the Covid Spread.
 

bertus

Joined Apr 5, 2008
21,451
Hello,

The common needs also to be connected to the CT of the transformer:
tonyr dual power corr.png
I would take some larger caps in stead of the 10 μF caps, 470 μF would likely work better.

Bertus
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Looking through my stockpile, off hand I've found four "Zetter Magnetics AH20012" transformers. My design does not absolutely require 12V, I could probably design around 6V. So just one of these will (should) suffice. If not, two of them wired in parallel.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
These transformers, rectified and filtered without regulation won't provide more than 8.9VDC filtered.

See! Already making improvements.
 

SamR

Joined Mar 19, 2019
3,453
That little PSU kit is rated for 5-40VDC @ at least 1.5A so the limiting factor is what XFMR you feed it from. with my 28-0-28 2000mA XFMR it goes to 20.92V unloaded. So... I would build for at least+/-15V.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
SamR this project is going to be a dedicated project. Won't be used anywhere else. And so far I don't have to buy anything. I have all the components for my project; in including the laser pointer modules.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,077
Can use any filter cap I want. Can go up to 1500µF. Even higher I believe. I don't think ripple will be an issue since the amp is going to be firing either a FET or the laser directly. I think, though, probably a 2N7000. But I haven't thought the design through that far yet.
 
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