|
DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
Hobby Circuits'
Category List
The contents &
graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server |
 |
|
|
|
|
|
|
More
Battery Chargers
Opto-Isolators |
|
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. |
|
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. |
|
|
Click on Drawing Below to view PDF version of Schematic |
|
 |
|
|
More
Battery Chargers
Opto-Isolators
Hobby Circuits'
Category List
eMail David A.
Johnson, P.E. about this circuit |
