Dual Polarity Power Supply

Been a while since I lurked around here.

Anyway, been going through projects I have built or will build and have noticed I am lacking in power supplies, need them for existing and future projects, so I've decided to sort them out first instead of my typical backwards approach.

Now essentialy linear plugpacks have been banned here in Australia, switchmode is the only choice for DC, however AC plugpacks are still needed for various devices, security panels, reticulation etc. so have side stepped the ban despite them essentialy being the same minus any later rectification/regulation.

Anyway my plan is to build some linear power supplies in small cases with external AC supplies, due to size, cost, safety etc. over all out mains powered ones.

Now one build will require +12v and +5v DC, 12v for an amp and 5v for mucking around with a microcontroller.

However I need +-5v for an IC I want to tinker with, a volume control.

Having looked around I am not sure of the best course of action to get a dual polarity supply. Datasheet for the IC in question states a maximum current draw of 25mA.

Would the easiest/simplest way be to have another regulator on the +12v to drop it down to +10v then a vitual ground circuit to give me +-5v ?

Options like center tapped transformer are more or less out of the question unless completely unavoidable.

AMBs sigma 25 page shows the option of two of them bridged, but that it requires 2 secondarires/transformer, just out of curiousity what is the reason that they cannot both be connected to a single secondary ?

Sorry if it's a bit of a dumb question, just not knowledgeable enough to know off the top of my head which approach to pursue.

Quote:

Originally Posted by nikongod 

Run it off of a center tapped transformer.

 

Regulate "dirty" DC down to +/-12V Regulate that down to +/-5V

 

The -12V rail opens up tons of options for other amps.

 

A power supply based on virtual grounds requires lots of care in use. Much better to keep ground at the same potential as the wall plug. 

Mmmm... well I was concerned that especially with some virtual ground schematics I've seen there is mention of serious consequences if the ground was not connected or if one rail draws more than the other.

If the virtual ground circuit is specifically for this one IC though and not a general purpose supply could it be fairly simple and trouble free to implement ?

I definitely do want and need a +/- 15v in future however quite a few projects that I've built already need a single +12v and was hoping to incorporate this in the same case (if all goes to plan) and was hoping it was nice, easy, simple and stable to just regulate it down a little further and go virtual ground.

Although seems like it may be much more work.

Quote:

Originally Posted by geetar7 

 

What is your reason for this?

Well mainly added size and weight, so will need a larger case, then the added cost and component count, lastly also the extra safety measures for mains.

To me centre tapped transformer my first and most obvious choice but at this stage for just 1 IC that draws a measly 25mA it seems like a lot of work for little gain.

That is why I was considering a virtual ground off just a single +12v DC supply if it's easy enough to implement.

Quote:

Originally Posted by geetar7 

I have to agree with nikongod.  Center-tapped transformer is a very natural way to build a bi-polar power supply.  Yes, there are other alternatives, but center-tapped x-former is the most straightforward.  There are a plethora of transformers to choose from at places like mouser.com or digikey.com.

 

Not sure, but the secondary has a current limit, and 2 may be too much of a load.

Well I've seen several other designs that are the same, 2 secondaries with single rail power supplies bridged together, either seperate transformers or dual secondaries on the one transformer.

Well I didn't think it would be current limit as what's to stop you just using a higher VA transformer ?

Quote:

Originally Posted by wakibaki 

You can build a dual-rail supply without a centre-tapped tx, i.e. using a single secondary tx with half-wave rectification.

 

Look here:- http://www.head-fi.org/t/572822/headphone-amp-dc-supply. The second and third diagrams are for single secondary tx, the tx isn't shown, just the 2 pin inlet from an AC/AC wallwart.

 

w  

Ewwww... half wave.

I actually want it to try out a PGA2311, which I see you are using in your 5532 project, well the 2310. Getting a bit OT but what are your thoughts on it and how is this power supply of yours ?

I'm thinking I may just breadboard a few options up, see how they compare and then decide.

At the moment the options I've found (or been helpfully suggested) seem to be (in no order of preference):

• Centre tapped transformer
• Dual secondaries with bridged single rail power supplies
• Single Secondary with half wave rectification
• Single Secondary with full wave voltage doubler
• Charge Pump/Voltage Converter - 555 timer based or LT1054, TC1044 etc.
• Virtual Ground

edit: Thanks everyone so far