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Portable 12v LiPo supply. Bypassing the battery.

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dumle29:
Hey there. So I'm build a portable LiPo pack for a 12v supply. I have everything figured out except one thing.

I have built it up like so:

LiPo charge board -> battery -> battery protection board -> boost converter.

When I hook up the LiPo charger board to usb, I want to take the 5v and run that directly to the boost converter, bypassing the battery, and I therefor need some sort of circtuit to disconnect the battery.

I've drawn up this, and want to know if this would work. If it's stupid, and if theres any better way.

-Mikkel

Quick sketch:
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Eagle schematic:
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NiHaoMike:
Turn the MOSFET around to avoid a sneak path and use a Schottky diode to reduce the voltage drop. The MOSFET must also have a threshold voltage well below that of the minimum battery voltage.

dumle29:
If I turn the fet around, wouldn't the parasitic diode mean that the battery and thereby charger would be connected to the boost converter all the time?

dumle29:
actually thinking about it there would be a .8v reverse biasing the internal parsitic diode (battery at 4.2v) so I guess that should be fine, and yeah will go with a schottky

sleemanj:
https://www.eevblog.com/forum/projects/primary-(eg-usb)-and-auxillary-(eg-battery)-power-steering-ic/msg299942/#msg299942

Edit to add: the circuit I made in that thread didn't *quite* work, close but not close enough.  I was going to try using a logic IC to see if I could improve it, but havn't got around to it yet.

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