Portable 12V bipolar powersupply, best approach? - Page 1
Forum section: electronics / projects

author: PeterFW
author_rank: Frequent Contributor
timestamp: July 19, 2018, 08:15:41 pm
content: Hello!I would like to make a small analog synth portable, i need around 500mA and a positive and negative 12V rail, ideally regulated.The load can be split up between modules, so i could use multiple regulators for that.My current idea is to use a few charge pump inverters on a 3S or 4S lithium back with a balancer and charger, but that might be a bit costly.The simplest idea would be to just chuck a few D-Cells at the problem, all in series with a center tap, maybe some regulation on that.Two lead gel batteries would be a solution too, but they are a bit heavy, but then again, the D cells would be too.

author: Buriedcode
author_rank: Super Contributor
timestamp: July 19, 2018, 08:39:01 pm
content: Generally, there are a few ways of creating a bipolar power supply from batteries:1. Split the pack: half the batteries fro positive, half for negative. Charge them all in series. This is the simplest - as you've already pointed out.2. Using charge pumps to create the negative rail (or if the positive rail requires significantly less current) the positive. Although they can work for >100mA, for higher currents it becomes more economical (both in terms of cost, size, weight and even efficiency) to ..3. Use an inverting switcher for the negative rail - followed by a linear reg if you require low noise.3a. Use a boost converter with a coupled inductor to generate both the positive and negative rail - has the advantage the input can be <12V at the cost of higher input current.4. Off-the-shelve DC-DC module that has dual outputs. Probably more expensive, tend not to be that efficient, run a lower frequencies, and aren't regulated but... easiest!500mA sounds like a lot to me, but I know all-analogue synths can have many many opamps. Using a single LiPo cell, with +/-12V @ 500mA is 12W out of the switcher, say 15W input @ 3.7V means a constant 4A draw. So I would use at least two cells. In terms of weight, you're right that the LiPo's would be best.I'd say, work on everything else first to get a more specific idea of current requirements. Could be you could get away with 200mA on each rail. Also you might draw significantly more current from positive than negative (which would help the charge pump idea).

author: Mazo
author_rank: Regular Contributor
timestamp: July 23, 2018, 11:42:08 am
content: Here is a solution(or atleast I can't see a inherent problem with it).The idea is to switch the 2 mosfets in such way to have alternating cycles of boost and inverting converter.I would implement it in D(B)CM(easier to get symmetrical power delivery to the + and - rails) with bidirectional current sense on the inductor(probably the trickiest part but not that hard)+some glue logic.Regulation of the rails can be achieved with hysteretic gating of the pulses or peak current control(probably requires different thresholds for the boost and invert cycles as the rails aren't gonna be 100% symmetrical and the unmonitored rail can runaway-pulse skipping circuit may be a solution).As it's for audio stuff you would probably want to take the "pure" PWM path or you will have low frequency components in the ripple(linear postregulator may be your friend).Never built such a circuit nor I have bothered to simulate one so take my words with a grain of salt.