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A simple power bank - keep alive module. As the name is already suggesting, this module keeps power banks from auto turn off, when the load current is too low.
The power banks usually monitor the current drawn from the usb, in order to find out if the connected mobile phone is charged, and if it is, turn off the output. This feature is good for usual purposes, or DIY circuits which draw a current above 100 milliamps; but not for tiny circuits with a supply current lower than 100mA.
This simple 555 based circuit, is an astable multivibrator with a period of ~5 seconds and a duty cycle of just 2%. So every 5 seconds, it turns on and connects a 100mA load accross powerbank for just 100ms. So the average power consumption of the module itself is quite low.
A schottky diode and a buffer cap, provide uninterrupted supply for the actual load.