Hello Everyone!! 
Well I'm working on a project that uses a single Li-poly battery for it's power. But unfortunately, I could only find a Li-poly cell that has no protection circuity on board that would fit my needs (Here).
So, I need to design an under voltage protection circuit. I don't need any over voltage protection, as I'm just going to charge them up with something like this. First, I thought that I could just find a chip to do the protection, but I couldn't find any that would just do under voltage protection. I also need the protection circuit to drop hardly any voltage at all, because of 3.3 volts power supply requirements of the rest of my circuit.
After doing a whole lot of thinking, I decided to try something like this:
So the way I would think this would work would be: power comes into the LDO regulator from the Li-poly battery at Vcc. Then the MOSFET pulls the Enable pin high, which then turns on the regulator. But then when the battery drops to about 3.45V the MOSFET stops conducting and R14 pulls the Enable pin low, turning off the regulator and the rest of the circuit (at 3.45 volts the regulator is almost to the point where it won't work anymore due to it's 0.13V drop out voltage).
Now the problem is, I have no idea how to select the MOSFET, or even if it's around the right way! I wonder if someone could point me in the right direction as to selecting it? Or even if this design is plausible!
Thanks very much Everyone!!!
Dan
Well I'm working on a project that uses a single Li-poly battery for it's power. But unfortunately, I could only find a Li-poly cell that has no protection circuity on board that would fit my needs (Here).
So, I need to design an under voltage protection circuit. I don't need any over voltage protection, as I'm just going to charge them up with something like this. First, I thought that I could just find a chip to do the protection, but I couldn't find any that would just do under voltage protection. I also need the protection circuit to drop hardly any voltage at all, because of 3.3 volts power supply requirements of the rest of my circuit.
After doing a whole lot of thinking, I decided to try something like this:
So the way I would think this would work would be: power comes into the LDO regulator from the Li-poly battery at Vcc. Then the MOSFET pulls the Enable pin high, which then turns on the regulator. But then when the battery drops to about 3.45V the MOSFET stops conducting and R14 pulls the Enable pin low, turning off the regulator and the rest of the circuit (at 3.45 volts the regulator is almost to the point where it won't work anymore due to it's 0.13V drop out voltage).
Now the problem is, I have no idea how to select the MOSFET, or even if it's around the right way!
I wonder if someone could point me in the right direction as to selecting it? Or even if this design is plausible! Thanks very much Everyone!!!
Dan
