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Automatic changeover switch using IC LTC4412


The circuit diagram shown here is of a automatic changeover switch using IC LTC4412 from Linear Technologies. This circuit will be used for the automated switchover of a load between a battery and a wall adapter.LTC4412 controls an external P-channel MOSFET to make a close to ideal diode perform for power switch over and load sharing. This makes the LT4412 a perfect replacement for power supply Oring diodes. a good range of MOSFETs will be driven using the IC and this offers of excellent options like reverse battery protection, manual control input, MOSFET gate protection clamp etc.

The diode D1 prevents the reverse flow of current to the wall adapter when there's no mains supplyr. Capacitor C1 is that the output filter capacitor. Pin 4 of the IC is called the status output. When wall adapter input is gift the standing output pin are going to be high and this will be used to enable another auxiliary P-channel MOSFET (not shown within the circuit diagram.

Notes.

  • Assemble the circuit on a good quality PCB.
  • The wall adapter input can be anything between 3 to 28V DC.
  • The battery voltage can be anything between 2.5V to 28V.
  • Do not connect loads that consume more than 2A.
  • Maximum continuous drain current of Q1 (FDN306P) is 2.5A.
  • D1 (1N5819 is a 1A Schottky diode.
  • Q1 (FDN306P) is a P-channel MOSFET.