I am trying to design a solid state SPDT switch around a powerpath IC but the only circuits I have come up with use MOSFETs and their body diode shorts the charger and battery when both are present.

Is it possible at all to make the following solid state SPDT (current directions allowed are shown with arrows) with MOSFETs? In any case, how can I make this switch (using bipolar transistors I assume?)?

Ideally I would like to short something to select between the two positions, but I can take care of the design of the control (I hope no charge pump is necessary).

Note: the load current is 10A and the charge current is 2A. The voltage is ~15V.

enter image description here

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    \$\begingroup\$ I know, I doubt that people who can answer this are actually thrown off by the crude drawing of the switch but maybe I'm wrong. \$\endgroup\$
    – user42875
    Feb 4, 2022 at 1:15
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    \$\begingroup\$ @jsotola, OP's added an arrow now but you can tell with switches easily: the line between the 'contacts' goes into one, as if a hinge, and lays on the other. That was always clear in this drawing. The 90o arrangement is unusual but unambiguous. \$\endgroup\$
    – TonyM
    Feb 4, 2022 at 1:43
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    \$\begingroup\$ No such thing as a SPDT switch. More like multiple SPST switches connected with logic to make them behave together like SPDT. With MOSFETs you just put them back to back common source, and drive with floating gate. You will find those laying around. I've not heard of any BJT attempts...anti-parallel BJTs? Like how thyristors are used to imitate a triac or vise versa. The drive sounds trickier than with the MOSFET version. \$\endgroup\$
    – DKNguyen
    Feb 4, 2022 at 1:51
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    \$\begingroup\$ Thanks TonyM and DKNguyen. Glad that it's a real challenge and not me being stupid :) \$\endgroup\$
    – user42875
    Feb 4, 2022 at 2:12
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    \$\begingroup\$ If you search the manufacturer’s websites, you will find IC’s for this very purpose. They are called “load switches”or “power mux.” \$\endgroup\$
    – user69795
    Feb 4, 2022 at 3:01

1 Answer 1


If you insist on building it without Relays and want to do it the solid state way, you can use "Photovoltaic Isolators" and use them to open a pair of antiserial power-MOSFET. It will form a bidirectionally conducting and bidirectionally blocking power switch controlled from a small logic current of about 2 mA through D3.

If it wasn't clear: the photovoltaic isolators are integrated parts, available from multiple manufacturers under different names. They provide a ~9 VDC output signal with which you can drive MOSFET gates.


simulate this circuit – Schematic created using CircuitLab

Then add a second such unit for the second switch to form the second pole (as commented by DKNguyen).


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