Electrical – Is LTSPICE really flawed


It really seems as if Ltspice is indeed flawed, not only did I catch op-amp input terminals taking milliamps of current, but now nmos fets take huge amounts of current into the gate.

Previous post had no mosfets:
LTSpice Has bizzare results for high input impedance devices

Try for yourself.



Gate Current:

Gate Current


Another mosfet with low gate charge


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Gate Current:

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Best Answer

What you're seeing is perfectly fine - your FET has a huge gate charge and charging that at 400Hz does take some current. The waveform is distorted because dQ/dU of the FET is not constant. (That is, depending on the gate voltage, the capacitance of the gate changes.)

Q_gate = 405nC (from datasheet)
f = 800Hz (gate being charged two times per full cycle)

405nC * 800Hz = 324µA

That's exactly what you're seeing in the simulation.