Hello all!
I'm designing a circuit for my gf as a second xmas gift, and don't worry her first gift was a $200 purse, so don't think I'm cranking out cheesy gifts. ... Anyways on topic, I'm designing a circuit which will charge a 9v Lithum battery using 5v. Now the reason why I wont use 12v, is that I want the user to be able just to plug this charger into their computer's USB port or connect it to a cell phone charger with a USB port. Now a number of things pop into mind designing this.
My Idea:
Simply write a charger code for my favorite PIC the 12F675, which will control a NPN that has a input of 5v and the output will have a diode to keep the current from going backwards. The problem with this is that there isn't enough juice to make the battery go back to 9v. So I must use a MAXIM IC to turn the 5v into 10v. Then use the ADC pin on the pic to read the voltage on the battery to see if it's fully charged or not.
Is this a good way of accomplishing this? So I avoid over charging, tickle charging, and etc? Or... Should I just buy a IC that does it all, but will have to use the MAXIM IC to boost the voltage?
I'm designing a circuit for my gf as a second xmas gift, and don't worry her first gift was a $200 purse, so don't think I'm cranking out cheesy gifts. ... Anyways on topic, I'm designing a circuit which will charge a 9v Lithum battery using 5v. Now the reason why I wont use 12v, is that I want the user to be able just to plug this charger into their computer's USB port or connect it to a cell phone charger with a USB port. Now a number of things pop into mind designing this.
My Idea:
Simply write a charger code for my favorite PIC the 12F675, which will control a NPN that has a input of 5v and the output will have a diode to keep the current from going backwards. The problem with this is that there isn't enough juice to make the battery go back to 9v. So I must use a MAXIM IC to turn the 5v into 10v. Then use the ADC pin on the pic to read the voltage on the battery to see if it's fully charged or not.
Is this a good way of accomplishing this? So I avoid over charging, tickle charging, and etc? Or... Should I just buy a IC that does it all, but will have to use the MAXIM IC to boost the voltage?