Best DC/DC board to convert 13.8V to a steady 12V  - Page 1
Forum section: electronics / beginners

author: Mule
author_rank: Contributor
timestamp: May 04, 2017, 08:02:05 am
content: Hello,Can someone point me in the direction for the best DC/DC board to convert 13.8V from a LiPo battery to a steady 12V output.Obviously, the 13.8V will vary as it is coming from a battery, but a steady 12V output is what is needed.I have tried the XL6009 DC-DC board but it is a step up board and doesn't have the range to meet 12V.Any help much appreciated.

author: Kilrah
author_rank: Unknown
timestamp: May 04, 2017, 08:08:19 am
content: What load? 10mA or 10A?...What battery, your voltage suggests 4s but maybe you mean 12.6V/3s and it would be a whole different thing.For 3S you definitely need a step up/down since battery will go <12V. For 4S no, but then the solution has to handle 16.8V.

author: X
author_rank: Regular Contributor
timestamp: May 04, 2017, 08:26:56 am
content: Depending on the current draw, you may be better off with a low-dropout regulator (eg. LM1085IT-12) for this as the power loss as a result of the voltage drop will essensially be 13%, but if you are not taking much current then that's the loss you'll get with a typical DC/DC buck converter.Some loads such as motors and even some equipment like decent routers/modems/switches can actually handle the extra 1.8V too, so if your load can cope with it, then it is a good idea to omit the LDO or DC/DC converter.

author: Mule
author_rank: Contributor
timestamp: May 04, 2017, 08:56:30 am
content: The battery is 4S, my apologies on the voltage being wrong. And there will be ~100mA of current.

author: 2N3055
author_rank: Super Contributor
timestamp: May 04, 2017, 10:32:55 am
content: SD-50A-12 from Meanwell 9-18V input, constant 12V(11-13,2V adjustable) /4A out.there is also 25W/ 2A version.

author: rob77
author_rank: Super Contributor
timestamp: May 04, 2017, 11:09:51 am
content: ok so we have 12.8 - 16.8V input range and 100mA load. that's 4V drop @ 100mA worst case, so 400mW power dissipation... 0.8V drop is the lowest drop required...LM1117 costs few cents, 16.8V input would be on the edge but 400mW diussipation not a problem.. 1.2V drop + 12V out will give us 13.2V which is more than the desired 12.8 , but close enough (at least you will not overly discharge the pack).worst case efficiency with lm1117 would be approx 70% - that's on par with a simple buck converter.EDIT:and forgot to mention - nothing gives you more steady voltage than a battery followed by linear regulator.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2017, 12:47:05 am
content: For 100mA with that drop I would also probably just use a linear regulator, the dissipation will be fairly low. A buck regulator would work too, there are some small inexpensive parts but even a lowly 7812 will do the job just fine. All it needs is a capacitor across the input and output.

author: mariush
author_rank: Super Contributor
timestamp: May 06, 2017, 01:12:43 am
content: Pick a ldo with a very low voltage dropout ... here's a few hundred of them:https://www.digikey.com/short/3nbb88For example ADP7118 from Analog Devices , 0.2v drop at 200mA :https://www.digikey.com/product-detail/en/analog-devices-inc/ADP7118AUJZ-R7/ADP7118AUJZ-R7CT-ND/6568645Or a cheaper LDK320M, same deal :https://www.digikey.com/product-detail/en/stmicroelectronics/LDK320M-R/497-16565-1-ND/6072608

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2017, 04:13:13 pm
content: For a 4 cell LiPo it probably doesn't even need to have a super low dropout, you should never drain one of those packs below about 3.4V per cell anyway so that leaves around 1.2V of overhead. Of course having a lower dropout never hurts and does give you some wiggle room if you accidentally drain the battery too far.