How to power an op-amp from a single cell lithium polymer battery? - Page 1
Forum section: electronics / beginners

author: ErnstHot
author_rank: Newbie
timestamp: January 18, 2012, 02:33:31 pm
content: Hi,I’m trying to design a portable headphone amp that will fit on the back of my MP3 player, because it isn’t really up to the task of driving my AKG K240 MKII phones.I’ve found thisChu Moycircuit which I’d like to use, but I can’t quite figure out a way to power it from a single cell lithium polymer battery.So basically what I’m looking for is a circuit or device that doesn’t take up a lot of space and will give me something like -3V / 0V / +3V from the battery. Also it shouldn’t release the magic smoke when I charge the batteryAlso feel free to point out any gotchas or problems, I’m not very experienced with electronics...EDIT:Here'sthe datasheet for the op-amp.Regards, Thorsten

author: vtl
author_rank: Regular Contributor
timestamp: January 18, 2012, 03:19:31 pm
content: If its a must to use a single cell then you'll need to use a DC-DC boost converter to get it up to your desired voltage. Just search for one of those boost ICs and you will jsut follow the datasheet's application circuit. The boost converter will require an inductor and capacitor to work properly. Will need to be greater than 6V since you don't have rail to rail opamps.Then you need to figure out your rails. What you can do is a voltage divider to half your battery voltage and use an opamp to buffer it so its low impedance. So now you have a 6,3 and GND rails but you can simply relabel them to your +3V,0V and -3V rails since the potential difference between the rails are the same. I've attached the example circuit. Make sure you pick an opamp that can sink enough current for you.If you can, you should just try and use two cells in series so you don't have to build a boost converter.

author: ErnstHot
author_rank: Newbie
timestamp: January 18, 2012, 03:45:15 pm
content: Thanks for your reply,I'd prefer to use two batteries in series since there's probably going to be room enough in the case, but as far as I know that complicates charging and isn't generally advisable with LiPo batteries unless you know what you're doing - which I don'tSo I guess my best bet so far is to use a DC-DC boost converter to get at least 6V followed by a buffered voltage divider.Regards, Thorsten

author: Balaur
author_rank: Unknown
timestamp: January 18, 2012, 06:34:40 pm
content: I've just completed such a project. However, I didn't bothered with the hipsterish CMoy headphone amplifier.My implementations uses a TDA1308 (recovered from a desktop PC CDROM) in an inverted, half-VDD-polarized configuration, straight from the datasheet.Power is supplied by a single slim LiPo battery charged by a MAX1555 equivalent that I have both recovered from a car Bluetooth unit.In addition to the audio/power circuitry I also added three buttons with some resistors that implement the Main/Vol+/Vol- commands for my new Xperia Ray.Cheers,Dan

author: slashguitar
author_rank: Contributor
timestamp: January 19, 2012, 07:10:43 am
content: You should take a look herehttp://tangentsoft.net/elec/vgrounds.htmlThere are quite a few virtual ground and headphone amplifier designs and they are very well explained

author: ErnstHot
author_rank: Newbie
timestamp: January 19, 2012, 12:13:32 pm
content: Quote from: slashguitar on January 19, 2012, 07:10:43 amThank you, that's very helpful!Regards, Thorsten