I have a circuit that uses two CR2032 coin cells for power. Using two batteries allows me to replace one battery at a time without loosing power to the circuit. I use diodes to protect against reversed battery polarity during installation.
This works fine except for the losses of the diodes. I want the circuit to run one to two years on the two coin cells. The forward voltage of the diodes significantly shortens the life of the batteries. This is because occasional high peak currents and the forward voltage drop of the diodes make the end of life voltage of the batteries effectivley about 2.7 volts (instead of the normal 2.0 volts).
I would like to replace the Schottky diodes with "ideal" diodes using MOS-FET's. The obvious solution using two MOS-FETs does not work because when one battery is replaced, the other battery in still in place. The battery that is in place turns on the MOS-FET even when the new battery is reversed.
One final complication is that the reverse battery circuit must not draw any significant current itself. If it draws more than a couple of microamps it will shorten the life of the batteries a lot.
Here are the circuits:
Thanks in advance for any insights into this problem.
This works fine except for the losses of the diodes. I want the circuit to run one to two years on the two coin cells. The forward voltage of the diodes significantly shortens the life of the batteries. This is because occasional high peak currents and the forward voltage drop of the diodes make the end of life voltage of the batteries effectivley about 2.7 volts (instead of the normal 2.0 volts).
I would like to replace the Schottky diodes with "ideal" diodes using MOS-FET's. The obvious solution using two MOS-FETs does not work because when one battery is replaced, the other battery in still in place. The battery that is in place turns on the MOS-FET even when the new battery is reversed.
One final complication is that the reverse battery circuit must not draw any significant current itself. If it draws more than a couple of microamps it will shorten the life of the batteries a lot.
Here are the circuits:
Thanks in advance for any insights into this problem.