I'm working on a group project, where for one part of the circuitry we have a "Royer Oscillator", which can be turned on/off via an N-channel MOSFET (IRFU4105ZPBF) at the input (whose gate is connected to an Arduino). The second part of the circuitry (not included in the image below), is essentially the filtering stage where we filter out desired frequencies.

The problem I'm having with this implementation is the MOSFET configuration (top left, disregard the diode), where the drain is connected to the supply, and the source is connected to the load (the rest of the circuit), however I'm not sure if this is the right configuration since when we build the circuit, it doesn't work (the MOSFET wouldn't turn on), and even the simulation has next to no current at the source, which leads me to think that it should be connected to ground, and the drain going from the Power Supply -> to the rest of the circuit?

Essentially my questions are:

  1. Why am I getting next to no current at the source?
  2. Is the MOSFET connected properly?
  3. Can I have the drain connected to the supply, then have it connected to the rest of the circuit?

The individual MOSFET works by itself in turning on an LED, with the source to ground, and the supply coming through a resistor -> LED -> drain.

Most MOSFET circuits I've come across have the source going to ground, with the load coming from the drain, though I have come across others with my configuration below, so I'm unsure which is the correct one? Royer Oscillator

  • \$\begingroup\$ How about telling us where the earth symbol reference (shown at the bottom of V4) connects to in relation to the rest of the partial circuit shown? I studies EE and not mind reading. Ideally you should be using a P channel unless you can drive the gate higher than the source. \$\endgroup\$
    – Andy aka
    Commented Jul 17, 2016 at 8:55
  • \$\begingroup\$ The ground is at the very bottom rail, it's kinda hidden behind the .tran and .lib writing. What would the advantage of P-channel be? \$\endgroup\$
    – deki
    Commented Jul 18, 2016 at 10:33

1 Answer 1


Move your V4 source from ground to source of top left transistor. If LTspice complains about it floating/takes forever to simulate, add a 1 Mohm resistor to ground.

  1. No gate-source voltage.
  2. No.
  3. Yes.

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