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I have a project that runs off a 4S LIPO battery and I want to switch to 24V wall power when I plug in an DC wall adapter. I have two designs, an inexpensive one with discretes and one with an expensive LTC4412HV IC.

I simulated both and they seem to work fine. In terms of safety since the battery is a LIPO, is the discrete design okay? Is there anything I should add other than a fuse which I already have?

Edit: The reason I use a PFET instead of a schottky diode is because the diode consumes too much power and I want to maximize battery life.

circuit simulation

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  • \$\begingroup\$ Check PFETs polarity \$\endgroup\$ – Umar Jul 9 '15 at 17:32
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The discrete design exactly mirrors Microchip's AN1149, "Design A Load Sharing System Power Path Management with Microchip's Stand-Alone Li-Ion Battery Charger". The only difference is that your design does not include battery charging capability or multiple external inputs.

enter image description here

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You should be able to detect low battery voltage when wall adapter takes long time to come up. In the circuits, the MOSFETs are merely acting like a diode(body diode, later turns on automatically when the wall adapter goes off (body diode conducts first, Vgs becomes more negative, FET turns on). When wall adapter is present, the body diode of the FET is still protecting the battery. I do not see purpose of FETs there. (except low drop compared to normal diodes)

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