Need a USB LiPo Charge Circuit

erco

Looking for a simple USB Li-Po or Li-Ion charger to build into various projects. Every product under the sun has a 3.7V LiPo built in and recharges off a USB cable: those Spycams, hamburger speakers, etc. Surely there's a tiny surface mount board that does this for a buck. Yep, a buck.

Anybody can do it with a $15 charging circuit. But that's a different thread for those rich guys.

A buck. Less is OK, too.

Don't make me reverse engineer something off a hamburger speaker, 'cuz I'll do it!

ratronic

erco maybe something like this ?

CuriousOne

LM3658 - from Linear tech.
MCP73833 - from Microchip

and a lot of others.

erco

Yup... all good for function, but where's the dollar solution?

Ebay China has everything but this.

tonyp12

$2 shipped OK?
I think it have Charger IC in the plug of cable, but not sure.
http://www.ebay.com/itm/Lipo-Battery-USB-Charging-Charger-Cable-6020-1-6025-1-/260581913847?pt=US_Radio_Control_Control_Line&hash=item3cabe474f7

Here is the 99cent you wanted and if you order 10, the total comes to $1.20 each
http://www.ebay.com/itm/USB-Charging-Charger-Cable-for-V-Max-6020-6020-1-6020i-6023-1-6025-1-6025i-6030-/271079390310?pt=Radio_Control_Parts_Accessories&hash=item3f1d973c66

CuriousOne

Since both linear and microchip offer free samples....

LoopyByteloose

Here you go, use a 2N2222 and a zener diode to limit voltage to 3.8 volts and the 2N2222 is rated over 500ma... so that should work for under $1 USD. Of course, you are excluding low voltage shut out, current regulation, and so on.

You might be able to combine that with a constant current circuit (in the same link) to limit the rate of charge, or just a current limiting resistor.

I have used their constant current circuit to charge small NiCad with a wall wart with great success. Why use an IC when a transistor can do the job?

http://www.satcure-focus.com/tutor/page5.htm

Gadgetman

I wouldn't bet on those eBay cables.

Most probably the RC choppers they're built for has the charger built-in, and the cable is just that; a cable with a special plug at the end.

erco

Interesting thought about the cables. My little Hubsan quadrotor has a USB charging cable with an LED which goes out after charging. That's such a tiny thing that a gram or two makes a difference, so it would make sense to leave the weight of charger "smarts" on the ground to minimize the flying weight. Will have a closer look at that cable tonight.

Great thoughts, Loopy. That's the kind of thinking I'm looking for.

tonyp12

>and the cable is just that; a cable with a special plug at the end.

I think there is a 4.2v zener to stop charging

But something with a Maxim's enumerating charge IC or TI bq24190 would be best.
If you are OK with 100mA from a usb host port,http://www.mouser.com/ds/2/405/slus821c-128404.pdf

erco

Thanks, tonyp12. Maybe that simple circuit is all that's inside the cheap little Ebay chargers, like this one for $1.56!

http://www.ebay.com/itm/Rechargeable-Battery-Auto-AC-100-240V-wall-Home-charger-For-18650-AA-AAA-/190875754319?pt=Battery_Chargers&hash=item2c7114df4f#ht_969wt_917

LoopyByteloose

I never seem to build much or code much... but I do read quite a bit ;-)

I just thought I might mention that many of the newer R/C electric ESC motor controllers have the low voltage cut off to protect the Lipo from excessive discharge. So if that is the context, the charger doesn't need to check voltage before charging.

The 3.7 Lipo cell is an attractive solution for driving the Propeller without a voltage regulator.. just use a diode to knock the 3.7 down to 3.1 and go. But this should have a low voltage detector of some sort. ... a comparator with a zener reference or an ADC setup.

Duane Degn

The Parallax charger if based on a $1.02 chip. (Less if you get 10 or more.) (CuriousOne mentioned this chip too.)

These are $0.67 each.

Both of these chips require a few passives.

I'm sure erco already knows, but a fully charged single cell LiPo can have a voltage of over 4.2V.

LoopyByteloose

A fully charged Lipo may be 4.2volts, but if you are going to DIY this ... 3.8 or 3.9 volts is a wiser target for cutoff.
The threshold for dramatic failure may be 4.25 volts.

The built-in thermister cut-off circuit is very prudent if you are going all the way to 4.2 volts.

erco

Ask and ye shall receive... from Ebay China! It's $1.12, not a buck, but dang close. Give it a month or two.

http://www.ebay.com/itm/New-1PCS-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-WST-/300948038687?pt=Battery_Chargers&hash=item4611e6a41f#ht_4902wt_1136

Now it only says "lithium" battery and full charge voltage 4.2V, but doesn't specify Li-Po or Li-Ion. 4.2V max sounds like Li-Ion to me. What say ye, my venerable Forumistas?

Duane Degn

This with the boost regulator should take care of a lot of battery powered projects.

Darn it. Time to stock up on more parts.

Thank you VIP.

erco

Duane, just send me your lunch money for the next month and I'll order you a bunch of cool stuff. Minus my 10% commission, natch.

Hmmm.

Twins. College fund. Better make that 20%.

And please be sure to update your "stuff erco made me buy" page.

PS: It sure is nice to be posting again with impunity without having to worry about breaking 10,000!

tonyp12

>but doesn't specify Li-Po or Li-Ion.
1A USB-Compliant Li-Ion/Polymer Charger IC for Portable Applications
http://www.tpmicro.com/goods.php?id=47

wass

Here's a cheap board that uses the tp4056 chip.

http://dx.com/p/tp4056-1a-li-ion-battery-charging-module-blue-4v-8v-215797

Twice the price as Erco's ebay find, but at least you know what you're getting.

erco

Reply from seller, re Li-Po vs Li-Ion:

Hi, dear, I have checked, this is charge for Lithium polymer! Thanks!

Not the most technically sounding spec, but it's more to go on than the Ebay description "for Lithium battery".

So there you are, my dears.