Free Article of the Week! USB Pseudo Battery

In one respect all batteries are identical: sooner or later they die on you! Even rechargeable types are not immune from this problem, as they always need charging again. This makes indoor use inconvenient of devices designed only for portable use, with no provision for connecting an AC adapter. All the same, wherever you find electronic gadgets, a solution is not far away. A pseudo-battery with a USB connection provides permanent power.

Original publication: Elektor magazine September 2015, page 102.

Author: Danny Winkler.

Free download expires: Friday 20 September 2019.

Elektor PCB available: yes, low stock. Extra boards available by 23 September 2019, please check article page

Please Note: Four years since its original publication, the referred article may contain components, software elements and/or linked urls that require updating to the present moment.

In one respect all batteries are identical: sooner or later they die on you! Even rechargeable types are not immune from this problem, as they always need charging again. This makes indoor use inconvenient of devices designed only for portable use, with no provision for connecting an AC adapter. All the same, wherever you find electronic gadgets a solution is not far away. A pseudo-battery with a USB connection provides permanent power.

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Go to the article page and download a pdf copy of the magazine article. Downloading is free until Friday 20 September, 2019

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Discussion (2 comments)

Charles V Britton 5 years ago

I am having trouble thinking of a device that uses one single AAA cell. This could be adapted to providing either 3 or 4.5 volts for replacing a collection of 2 or 3 cells.

Since the + and - terminals are not 'floating' it won't work to stack these pseudo-cells to increase the voltage.

I do intend to wire up some replacement pseudo-batteries to use these usb supplies to replace dry cell collections.

Thanks for the reminder.

0 Comment(s)

Michael Tempsch 5 years ago

@Charles V Britton For a 3V replacement just change the voltage setting resistors to get 3V (see the datasheet for the needed formulas). Attach by wires to the 2 "end" battery terminals, or insert the board in one slot using the springy terminals, and short the other slot.

For 4.5V you probably also want a little higher input voltage than 5V, as the difference of 0.5V is likely below the dropout voltage of the 317.
~6-7V should do...
Or substitute the regulator for a low dropout one that can do 0.5V or less drop. Adjust surrounding components to fit the regulator in question, of course.

Also note that exact 1.5 / 3 / 4.5V isnt normally neededneed a battery powered device as fresh alkalines start at a little bit higher than 1.5, and most devices (might be exceptions out there) are designed to run on batteries down to 1 - 1.1V per cell (where they're effectively empty).
For instance, any 3 cell AA/AAA item I've tested has run fine on a single LiIon (4.2 down to ~3V)