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I have a need for a push pull circuit which can drive a line to either +12V, -12V or leave the line floating. The circuit needs to be able to source and sink 2 amperes to and from the line.

A 5V microcontroller is to control 2 transistors which should control the 2 mosfets

enter image description here

The general idea is that R3 keeps Q2 off by pulling the gate of Q1 to the source so that Vgs = 0V. Liikewise, R6 should pull the gate of Q1 to the source so that Q2 is also off in idle state.

Will this circuit work like I hope it will work?

EDIT: I completely forgot about the forward diode effect of the MOSFETs. As such I shorted the +12V to -12V directly.

I have no real need for a galvanic isolation. It was merely the best thing I could come up with. I believe I can replace them by conventional transistors

EDIT2: I replaced the optocouplers by a pair of transistors. And I fixed the symbols for the mosfets.

I think with this schematic that the P channel MOSFET will work but I am not 100% sure about the N channel. If Q4 is on, the Vgs of Q1 will be aprox. 12V + (5V - 0.7V) = 16.3V. This N channel mosfet is a P65NF06 and can handle a Vgs of 20V.

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    \$\begingroup\$ Do you need galvanic isolation, or is this just the best way you've found to do this? \$\endgroup\$
    – The Photon
    Jan 1, 2021 at 22:44
  • \$\begingroup\$ Optos tend to be slow. So, this (modified to avoid Vgs limitations) had better be for on/off control, not PWM. \$\endgroup\$
    – user16324
    Jan 1, 2021 at 22:57
  • \$\begingroup\$ Blast! I totally forgot about the diode functionality of mosfet. Real silly as you can clearly see them in the sechamatic I have indeed no need for galvanic isolation.It was merely the best I came up with. \$\endgroup\$
    – bask185
    Jan 2, 2021 at 8:44

2 Answers 2

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enter image description here

You have your MOSFETs placed incorrectly; it should be a P channel at the top and an N channel lower down. There may be other problems but this one sprung out as obvious.

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No, it won't.

The N-channel FET has Vgs maximum of +/- 8V, it will be exceeded and it is almost sure to get damaged after applying 24V potential difference.

The P-channel FET has Vgs maximum of +/- 20V, it will be exceeded and it might get damaged too.

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  • \$\begingroup\$ If only electronics would just work the way we imagine it does, things would be so much easier. \$\endgroup\$
    – jonk
    Jan 2, 2021 at 4:40

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