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DiscoverCircuits.com -- Hobby Corner
"Hobby Circuits for
your Hobby Projects"
Last Updated on:
06/19/2009 03:02:36 PM
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Two 12v Battery Isolator Circuit with
a LTC4412
designed by David A. Johnson, P.E. |
| Linear Technology has just
announced a neat little chip (LTC4412). It has been designed to be used in conjunction
with an external P-channel power FET, to form an ideal diode function with a very 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
device 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 device can be used with a FET from International Rectifier, to form an ideal
diode with a rating of 20 amps and a voltage up to 28v. |
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| How are these
devices used? Let’s suppose you owned a recreational vehicle (RV). When the RVs
engine is running, you would like the engine’s alternator to charge both the engine’s
battery and the battery used in the RV. But, when the engine is off you don’t want
the 12v RV loads to pull current from the engine battery. Likewise, you don’t want
to pull current from the RV battery when the engine is running. One way to solve
this problem is with the use of two diodes. The alternator output of the engine is
fed to the anode side of two power diodes. One diode routes current to the
engine’s battery while the second diode routes current to the RV battery. The
diodes block any current path between the two batteries. In a conventional
circuit, two high current diodes would be used. But, since there could be a
sizeable current passing through the diodes, they have to be mounted onto a large 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 two ideal diodes.
With the components shown, the electronic circuit should be able to handle 60 amps of
current to each battery. |
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Click on Schematic below to view PDF version of this
Circuit |
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