I am trying to charge a lipo cell for a project, but I do not have a charger or charger IC. I heard that you can charge a cell with a lab bench power supply set to 4.2v, but I do not have access to one. My question is: Is it possible to charge a cell with just a 4.2v supply and a resistor (to limit current)? The cell i'm trying to charge has a protection circuit.
This is my proposed circuit:
+4.2v --------/\/\/\/---------- BAT +
100 ohm
GND ------------------------- BAT -
While your proposed charging circuit might work (making sure you selected that resistor correctly to prevent excessive current), it will likely reduce the life of the battery. Usually battery chargers supply more than the battery operating voltage when charging to speed up charging and controls the current to prevent "toasting" the battery. So your method will probably take longer to recharge and may not recharge fully.
So, srnet has provided the best choice, but if you can live with the reduced battery life, you could hobble along with your circuit. If you do use your circuit, make sure you don't exceed 4.2 volts or you may have a fire on your hands.