I am building a small solar system of 5 solar cells in series (each about 5V 500mA in full load, total 25V 500mA) and want to maximize efficiency in case one cell is shaded.

Traditionally there are used bypass schottky diodes like this:

enter image description here

But since each solar cell has only 5V volts at full load, most diodes will make significant decrease of voltage (about 0,4V).

I saw examples of battery short circuit protection using P MOSFET as diode like this: enter image description here

Is there any reason why I cant use this solution in solar cells aplication above? I have a lot of TPC8107 mosfets around. Voltage drop should be below 50 mV if I calculate right.

Only drawback I see the "mosfet diode" will stop working around treshold voltage (around 2V), but this is I think good. At 2V solar cell dont give any usable current at all.

What do you think? Is there any important drawback I missed?

I actually never seen a mosfet as diode connection in any applications yet and dont see any reason except the price...

  • 1
    \$\begingroup\$ For a P channel FET you want the source connected to the input so you can turn it on. It's the -Vgs that turns on the FET. \$\endgroup\$
    – Aaron
    Commented Nov 23, 2020 at 20:15
  • \$\begingroup\$ unlike a diode, wouldn't a FET conduct in reverse through it's intrinsic diode? \$\endgroup\$
    – dandavis
    Commented Nov 23, 2020 at 20:48
  • \$\begingroup\$ Check out active rectifier controller IC's. They are designed expressly for this purpose. \$\endgroup\$ Commented Nov 23, 2020 at 22:31


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