I've been trying to design a DIY light dimmer circuit but I'm pulling my hair over this particular problem I'm facing. Is there any way to control conduction of both MOSFETs in both cycles of input? I can control conduction for the positive cycle but for the negative cycle the gate is always at higher potential than source which results in continuous conduction for the negative cycle. Is there any way to achieve controlled conduction using 2 N-MOSFETs only? I can achieve the dimming effect using a PMOS with an NMOS but I see this configuration very often and I do not understand why it works for people. enter image description here

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    \$\begingroup\$ I don't see anything unusual in the plot. You may want to choose a different reference potential. \$\endgroup\$
    – greybeard
    Oct 19, 2023 at 6:22
  • \$\begingroup\$ Shouldn't the Applied input appear as complete sine wave and the voltage across the load for the negative cycle should resemble the voltage for the positive cycle? \$\endgroup\$
    – Salman
    Oct 19, 2023 at 6:26
  • \$\begingroup\$ Only if one side of this sine source was at reference potential. \$\endgroup\$
    – greybeard
    Oct 19, 2023 at 6:43
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    \$\begingroup\$ Odd, the waveforms are labeled V(vin), V(vload) but the schematic is not, so we have no idea what these nodes are \$\endgroup\$ Oct 19, 2023 at 9:29

1 Answer 1


You've connected GND/0 volts (via the triangle symbol) to a strange place for making any sense of this circuit. All your plots will be made relative to where this symbol connects. If you want to see the voltage across the load (R5) then connect the GND/0 volts symbol to the top node of R5.


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