Single cell LIPO boost 12v 1.5A / lipo charger: Is my design good or not? - Page 1
Forum section: electronics / projects

author: dumle29
author_rank: Regular Contributor
timestamp: March 16, 2014, 02:01:14 am
content: SO, I have a portable monitor that takes a 12v input, and it's rated on the back for 1.2A (Never really manged to pull more than 500mA from it?) So I ventured in to the world of boost converters, and decided to try and build a LiPo boost converter, and have ended up with this:Schematic:Board:The board is exclusively top side, and passes OSHPark DRC (which I know is rater high end DRC) There's nothing on the bottom, other than ground. This is the first time I dick around with anything containing an inductor, and would like to hear if I've done anything completely wrong?Here's the.schand the.brdThanks a bunch

author: I_may_be_drunk_right_now
author_rank: Contributor
timestamp: March 16, 2014, 02:34:43 am
content: Can you really get 800mA from a USB port like that? Are you willing to wait an entire day to charge the battery?What is your estimated cost for this project?I recommend trawling eBay for modules and slapping them together. It's an utter waste of time to make a PCB, order parts and assemble them.For example:http://www.ebay.ca/itm/DC-DC-Auto-Boost-Buck-adjustable-step-down-Converter-Module-Solar-Voltage-G9-/161151788234?pt=LH_DefaultDomain_0&hash=item25856524ca3$. Three. Dollars. You can't even buy a large bag of chips for that. Could you even order just the passives for 3$? Wow.But if you insist, it looks like you covered the bases, it is vital to have a UVP or UVLO for LiPO discharge protection. I didn't even check your part values but it's better for the life of the battery to lock out on a higher voltage like 3.3 than 3.0, let's say.Also, do you plan on storing this device unused with the battery for long periods of time? You might want to put in a 3.8V storage charge option.A LiFePO might be a better idea in any case, they last somewhat longer.I have one of these monkeyshttp://www.ebay.ca/itm/iMAX-B6-Lipo-NiMh-Li-ion-Ni-Cd-RC-Battery-Balance-Digital-Charger-Discharger-/390741820031?pt=Radio_Control_Parts_Accessories&hash=item5afa07027fYou might want one just for charging that battery somewhat faster than a day. (PS not included)

author: dumle29
author_rank: Regular Contributor
timestamp: March 16, 2014, 03:28:35 am
content: argh danm you that's no funBut at that price I probably should just do thatSo a lipo charger, UV protection (I think I will cut off at 3v, as I've read many places that damage occurs under 2.5) and a boost.I will use these batteries:http://www.hobbyking.com/hobbyking/store/__18560__Turnigy_5000mAh_1S_20C_Lipoly_Single_Cell_.htmlOne or maybe two in parallel.Would I be able to use two of these in parallel to have 8A of discharge available? as I will need 6A at 3v to get 12v at 1.5A.I could make my own protection board, that also controls power redirection, so that when it's charging, it's power directly from the charging power source (thinking of powering it from a 12v source, with a buck module to go to the 1A lipo board I ordered. A little over 5Hour charge time is ok)

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 16, 2014, 03:40:35 am
content: Many tablets can pull as much as 2A from USB. You might want to add a potentiometer or something to select various currents between 500mA and 2A. If possible, setting the charge voltage to 4.1V instead of the usual 4.2V would help extend battery lifetime.I would add some resistors to restrict the output voltage range, if only to avoid accidentally damaging stuff.You can make R2 much larger, maybe 470k or bigger. While you're at it, you can add a switch between the UVLO and MOSFET, so it can be turned off without switching the entire current.If the battery doesn't already have a protection board in it (the one you linked doesn't), you would probably want to add a protection chip on the board.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2014, 04:13:49 am
content: Without looking at datasheets, I don't have much about the schematic, it's probably not too bad. As far as layout, stitch the ground plane (add vias), especially around the ground end of C6-C8. Also, D1 should be placed between Q3 and C6, to minimize loop inductance. (If this runs in CCM, some inductance may be helpful, in which case you'll need an R+C snubber across the diode, and perhaps a peak clamp (D + RC)from Q3 drain to ground. I'd also like to see the output connector not inline with the diode, because it'll pick up more switching noise there than after a few caps. But switching is all going on near C6 and such, so they'd kind of have to shuffle, so it goes in order: choke, transistor, caps, then output jack.Regarding EMC, it'll still need, like, a ferrite bead or better and some ceramic caps to take the edge off further, if it matters to keep noise down. This goes for both power inputs and output.Tim

author: dumle29
author_rank: Regular Contributor
timestamp: March 16, 2014, 04:27:41 am
content: I've decided, seing the price, that I will buy and piece together items from ebay, however I'm very very interested in DC/DC circuits, and really appreciate all the things I can learn about them here, based around what I've don (I find it easier to understand based around something I made)