Smart Power Bank Keep-Alive

Ever wanted to power a project from a USB power bank, only to have it keep shutting itself off because the current draw was too low? This project aims to fix that with these handy and slightly over-engineered USB modules containing a microcontroller, op-amp, MOSFET and a few other bits to create a pulsed adjustable constant current sink, as well as supporting USB 3 pass-through!

A quick hack to keep power banks alive is to use something like a 150R resistor across the power output to draw an extra 33mA, but some power banks might need as much as 100mA to stay on, requiring a 50R 1W power resistor. Usually, power banks don’t need to have current continuously flowing to stay on, where a 2 second pulse every 15 seconds might be enough to keep it alive. This pulsing technique drastically improves the battery life of the power bank, perfect for powering a small project for a few weeks. Some unbranded power banks were tested to find their required current draw and shutdown timeouts:

Power bank # Keep-alive current Timeout
1 100mA 10 seconds
2 30mA 16 seconds
3 10mA 18 seconds

The smarts of this device is an ATtiny10 which controls the on and off cycling of the constant current sink (pulse duration and interval is adjustable via firmware). The current is adjustable via a small trim potentiometer from 0mA to 140mA and the supply voltage can be anywhere from 1.8V to 5.5V.

These power bank keep-alive modules are available to buy from my Tindie store! Or they can be ordered directly from me, send an email to shop AT

Designs and firmware are on my GitHub

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