Dual rail supply from a battery - Page 1
Forum section: electronics / projects

author: mojoe
author_rank: Frequent Contributor
timestamp: August 14, 2021, 08:22:19 am
content: Can two of those inexpensive boost converter boards you find on Amazon for a few dollars be used to create a +/- 12 VDC output, using a single 18650 cell? I know that this is possible for a single rail output, but I don't know if those boost boards can be connected for dual rail use. I haven't purchased any yet.The obvious way to create a dual rail, battery powered supply would be to use two 12 V batteries, but that increases size, cost, and charging complexity.Also, can anyone recommend a particular boost board that has low noise and ripple? The purpose is to power some op amps for use from 10 Hz to 1 MHz.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 14, 2021, 08:59:57 am
content: Getting + and minus 12 V gets a bis more complicated. Most (if not all) of the ready made modules are for a positive voltage. There is not principle proble in creating a negative higher voltage, but it is not as common - it may look more like a flyback converter, just without the insulation.An alternative would be forward DCDC converters - there may be ready made modules to do 3.3 V to isolated +-12 V. 5 V to +-12 V is very common. These may need some extra filtering though.A first point to question is if one really needs +-12 V. Many modern OPs work with only 5 V. It still depends on the purpose of the circuit.

author: Ian.M
author_rank: Super Contributor
timestamp: August 14, 2021, 09:12:47 am
content: You are probably confusing things with using abuckconverter module to get a negative output. If you are starting from a beefy higher voltage supply (e.g. a 19V ex-laptop PSU), you can certainly use two identical buck modules to get +/-12V. Seehttps://www.eevblog.com/forum/projects/dual-power-supply-from-two-buck-converters-(lm2596)/N.B. not all buck modules are suitable for inverting use - check the controller chip's datasheet for inverting application circuit(s).Getting a negative voltage from a non-isolated boost module is *MUCH* harder to do, and getting it to regulate that negative voltage is usually impractical. The obvious 'easy' option of simply stringing an inverting buck module on the output of your boost module is unlikely to work as most buck modules draw a very high startup current if wired an an inverting configuration.However dual (positive and negative) output boost modules can be found on Amazon, so I wouldn't waste my time trying to come up with a two module combo to do the job. If your system's analog bandwidth extends to 1MHz, ideally you'd want to pick a module with a switching frequency >1MHz. The switching frequency isn't always in the listings so you may have to review the controller chip's datasheet.

author: mojoe
author_rank: Frequent Contributor
timestamp: August 14, 2021, 10:10:03 am
content: Just before reading your reply, I found a dual rail boost module on Amazon:https://www.amazon.com/dp/B07PDQ6R3C/This one has a switching frequency of 400kHz.

author: mojoe
author_rank: Frequent Contributor
timestamp: August 14, 2021, 10:14:10 am
content: This chip has a lower input voltage, and a higher switching frequency (1.2 MHz). Now to see if I can find a ready made board.https://www.ti.com/lit/ds/symlink/tps61093.pdf

author: Ian.M
author_rank: Super Contributor
timestamp: August 14, 2021, 11:09:55 am
content: That 400KHz one may not meet your needs as its min. input voltage is 3.3V. You need one that will run right down to 3.0V to use the full capacity of the LiPO cell. OTOH if you were willing to use a 2S LiPO battery, giving it min. 6.0V in it should work well enough. That would be a better option anyway if you require significant current from the +/-12V outputs, as it would reduce I2R losses by a factor of four.If all you can find is 400KHz ones, and you don't need extremely accurate rail voltages, it may be worth considering active filtering using capacitance multipliers to lop off the ripple peaks. Dave did a video:https://www.eevblog.com/forum/blog/eevblog-1116-the-capacitance-multiplier/

author: Terry Bites
author_rank: Super Contributor
timestamp: August 14, 2021, 01:53:51 pm
content: https://www.digikey.co.uk/en/products/filter/dc-dc-converters/922?s=N4IgjCBcpgLA7BaIDGUBmBDANgZwKYA0IA9lANrgBMAHAMz0jFh0AMY8AbE%2BHVa63g8WdAKw0AnMLoJONabFqtpnDsuZjObafDoSIG%2BKxpDDrOnRUTO68IgkOe-Kpyqm79CZebx4sVrDCXAxSPqKsEqJBsGBgUT5sckFgbsoAusQADgAuUCAAytkATgCWAHYA5iAAvsRUVLFQoGiQWHhEpBQgVCAZIDl5AJJl2fgV%2BEU1td1dACYoALTzvdVAAClean layout, good filtering and shielding will make all the difference. An isolated converter separates the battery from your circuit ground. It will be simpler to filter out the crap.seehttps://recom-power.com/en/rec-n-very-low-noise-filter-for-isolated-dc!sdc-converters-46.html?0

author: tooki
author_rank: Super Contributor
timestamp: August 14, 2021, 03:12:15 pm
content: Quote from: mojoe on August 14, 2021, 08:22:19 amDo you actually need ±12V, or would ±5V do? (For op-amps, that’s usually enough.)If so, I can recommend theTI TPS65133, which generates ±5V at 250mA each from a single LIon. 1.7MHz switching frequency.