Two 12v Battery Isolator Circuit with a LTC4412

designed by David A. Johnson, P.E.
Linear Expertise has announced a tidy small chip (LTC4412). It's been designed to be used together with an outside P-channel power FET, to form an ideal diode function with a low 0.05v voltage drop. The chip monitors the voltage on either side of the FET.
As long as the voltage on the drain side is greater than the source side, the FET is turned on. The tool controls the voltage at the gate of the FET to maintain a voltage drop of about 0.05 volts across the FET. When the current direction tries to reverse, the hobby circuit senses the voltage polarity change and turns off the transistor, blocking the current. This action mimics how an ideal diode would function. The circuit below shows how this tool can be used with a FET from International Rectifier, to form an ideal diode with a rating of twenty amps and a voltage up to 28v.
How are these devices used? Letâs suppose you owned a recreational vehicle (RV). When the RVs engine is running, you would like the engineâs alternator to charge both the engineâs battery and the battery used in the RV. But, when the engine is off you donât require the 12v RV lots to pull current from the engine battery. Likewise, you donât require to pull current from the RV battery when the engine is running. way to solve this issue is with the use of diodes. The alternator output of the engine is fed to the anode side of power diodes. diode routes current to the engineâs battery while the second diode routes current to the RV battery.
The diodes block any current path between the batteries. In a traditional circuit, high current diodes would be used. But, since there could be a sizeable current passing through the diodes, they must be mounted onto a immense heat sink, to be able to handle the power dissipated in the diodes. The circuit shown below is much more efficient. It shows this battery isolator using ideal diodes. With the parts shown, the electronic circuit ought to be able to handle 60 amps of current to each battery.
source: www.discovercircuits.com