Chapter · Power and protection
Lithium cells
The only part on the bench that stores enough energy to hurt you, and the four chips people put in front of it.
- 07Inside a lithium cell8 minA lithium cell is the only part on your bench that stores enough energy to hurt you, and it has no way of telling you it has been damaged. Three numbers keep it safe, and one of them has no tolerance at all.
- 08Protected and unprotected cells7 minA protection board is two MOSFETs and a chip watching for four things that must never happen. It is not a charger, it is not a fuel gauge, and the most common thing it does is convince people their battery is dead.
- 09Charging with a TP40569 minThe TP4056 is the three-dollar red board everybody owns, and it is a complete lithium charger in a SOP-8 with one resistor to configure. That resistor is almost always the wrong value for the cell you have attached.
- 10Power path8 minPower path means the input feeds your board directly and the battery separately, instead of everything meeting at one node. It is the difference between a project that can be left plugged in and one that quietly destroys its own cell.
- 11Charging while it runs8 minThe IP5306 is an entire power bank in one eight-pin package — charger, boost converter, power path, fuel gauge and button. It also switches itself off after thirty-two seconds if your project is too quiet, which is how most IP5306 projects die.
Start at 07 and read down — the order is the order things get easier in. Or take the one with your part in it; every article stands on its own, and links back to whatever it needs.