mc34063 1A 3.7v up to 4.2v usb charger, is it possible? - Page 1
Forum section: electronics / projects

author: m.m.m
author_rank: Regular Contributor
timestamp: July 20, 2014, 04:41:32 pm
content: hello, I wanted to make an emergency 3.7 up to 4.2v (li-ion batt) usb phone charger, and my cell phone draws about 1A during charge, so I thought a classic mc34063 would be a good choice, what do you think? have anyone tried it? is this IC suitable for this application?P.S: unfortunately I don't have access to some minor ICs so I have to use classic ones (probably much harder)

author: mariush
author_rank: Super Contributor
timestamp: July 20, 2014, 04:49:02 pm
content: The efficiency of a mc34063 is bad, and it can only handle a peak switch current of 1.5a - that's reached if you output about 4.9v @ 500mACan't do 1A with it.If you put two li-ion in series to use the regulator in buck mode, you can get 0.75A out of it until you hit the 1.5A switch current limit.

author: m.m.m
author_rank: Regular Contributor
timestamp: July 20, 2014, 05:19:41 pm
content: thanks a lot mariush, so if this is not gonna make it, is there any other circuit doing the job using classic ICs? for example some use maxim max756, but it's not available here and I don't want to order it and wait for about 1 month for it to receive (and much much more expensive).

author: tom66
author_rank: Super Contributor
timestamp: July 20, 2014, 10:30:54 pm
content: You're better off playing with TI's WeBENCH and designing a power converter there.

author: dannyf
author_rank: Super Contributor
timestamp: July 21, 2014, 12:03:30 am
content: The datasheet is loaded with examples. Look in it if I were you.

author: m.m.m
author_rank: Regular Contributor
timestamp: July 23, 2014, 07:52:14 pm
content: so I guess the best is to try it on breadboard first. thank you everyone.

author: microbug
author_rank: Frequent Contributor
timestamp: July 23, 2014, 08:48:32 pm
content: I just punched 3.7V->4.2V @ 1A into my MC34063 calculator spreadsheet (soon to be posted). See attached PDF.

author: rob77
author_rank: Super Contributor
timestamp: July 23, 2014, 09:26:20 pm
content: Quote from: microbug on July 23, 2014, 08:48:32 pmover 2.6Amp througfh the switch... poor litle IC => glue down that 34063 - otherwise it'll fly away very sooni would suggest to look after a better solution than 34063 for 1Amp output (the external transistor for 34063 is hopeless)another point... what is the 3.7V source ? a single cell LiPo ? that might be well below 3.7V till drained completely (approx 3.0V or slightly below) - so the Ipk will be well above 2.6Amp under such a conditions...

author: Rick Law
author_rank: Super Contributor
timestamp: July 23, 2014, 10:33:00 pm
content: Here is where the cheap Chinese made boards took all the fun out of it.I too made an booster out of the MC34063 but merely as a learning project. I did it for a single 3.7 LiIon to output about 6.2V for driving a pair of 0.5W LED's in serial. I use the MC34063 and the inductor from an old phone car-charger, and use new parts for the other components. It works, and I put it aside.Lately, I decided to go back to see now that I am a little more knowledgeable, see if I can improve it. I know at least the inductor is not of the best value since it was sized for buck instead of boost.I decided to compare it with those $2 booster boards which I have from before. It works better (clean power) and more stability than the MC34063. Okay, I thought, now I have the base line, lets start getting some appropriate parts matching that of the datasheet and see if improve it any as step one.For the price of an inductor I can get more than two of those cheap $2 boards. Add in a couple of new capacitors, and at least a prototyping board... The $2 board is far better packaged than my prototyping board based final result. I was pleased I got my MC34063 booster working reasonably well, but not at all pleased that I can get one with a better layout and more compact for less than 1/2 what I spend on parts alone...I am working on a project that could use a booster (5v to 7v), I should probably choose the $2 board but I want to use my own. But I know that is a dumb choice because actually the $2 one gives me a cleaner signal and better load&line regulation... But I want to use my own...

author: LukeW
author_rank: Frequent Contributor
timestamp: July 23, 2014, 11:50:59 pm
content: The 34063's peak switch current is 1.5A. Let's assume the peak switch current is about 2x the output current... so the maximum current draw from the output is about 750mA, in the ballpark.Many cheap generic in-car smartphone USB chargers do use the 34063, but only to provide an output current within that range. (However, a 34063 can easily power a USB port with the 500mA supply that a standard, compliant device will expect. If an iPhone etc is used, the current-programming resistors on the USB lines should be set up for 500mA charge.)There is the ability to go higher by adding an external switching device to the 34063, the above just applies to using the chip with its internal switch.

author: void_error
author_rank: Frequent Contributor
timestamp: July 24, 2014, 10:26:11 pm
content: You can always add an external high current switching transistor to boost the MC34063's current. That could be one option.Take a look at this app notehttp://www.intusoft.com/onsemipdfs/AN920-D.pdf

author: Ribster
author_rank: Frequent Contributor
timestamp: July 29, 2014, 04:28:23 pm
content: The booster circuits from china use the XL6002 chip from XLSEMI.http://www.ksmcu.com/pdf/XL6002%20datasheet.pdfSince that one's lowest VIN is 4.5V, it's not suitable. Maybe it's cousin the XL6001?http://www.xlsemi.com/datasheet/XL6001%20datasheet.pdfAlthough VIN min 3.6V is quite pushing it..