Paul over at Dorkbotpdx writes:
I purchased a cheap USB power pack, thinking it would be ideal for powering small projects. But it automatically shuts off if the device isn’t drawing a lot of power, since it’s meant for charging cell phones.
Here’s a 2 transistor circuit I built this morning that keeps it on with very little battery drain by using brief pulses.
Interesting.
There would be a MOSFET which connects and disconnects the internal batteries from the USB port. I think I would have added a switch to force the MOSFET on.