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I try to design a circuit, where a LiPo is switched by a PMOS over a mechanical switch. Further, the USB Voltage can also occur and the LiPo should be decoupled. My first attempt looks like this, and it seems to work:

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Now, the diode D2 is bad practise, because of the power dissipation, but I don't know how to get rid of it, since the Body Diode of M1 will directly couple the USB voltage into the battery. Has anyone a suggestion?

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I would use back-to-back P channel MOSFETs. The two body diodes will be opposite so they will never conduct, and you get the benefit of the Low on-resistance of the MOSFET. See this electronics stackexchange answer for details: Switch 5V with back voltage protection

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  • \$\begingroup\$ This looks good on a first sight, but there comes a problem when the switch is on and VUSB is applied. The PMOS will directly conduct the current through into the battery, which will be overloaded. I'm currently looking for a feedback path, to constantly turn off the FETs when VUSB is applied, but cannot find any at the moment... \$\endgroup\$ Nov 15, 2020 at 17:55

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