Source: https://mokxi.com/mosfet-simulator Simulator # A MOSFET simulator: a 2N7000 switching an LED Mokxi is a free online MOSFET simulator that runs in your browser, with nothing to install and no account needed. A 2N7000 N-channel MOSFET as a low-side switch: an LED and its 220 ohm resistor on the drain, the source on ground, and a slide switch putting the gate on 5 V or on ground. No gate resistor, no microcontroller, nothing in between. Start building free or compare a MOSFET with a BJT - 455 parts on the bench - 43 boards running now - 1.00x real time, on every board Hold the button Click the slide switch to put the gate on 5 V and light the LED. Click anything else to open it in the editor. ## What you can do here In the circuit above, or in the editor it opens. - Switch an LED with a MOSFET’s gate and nothing else - Read the drain current under the part as it runs - Swap the 2N7000 for an IRLZ44N or an IRF540N - Try a P-channel BS250 or IRF9540N as a high-side switch - Drive the gate from an Arduino pin instead of a switch - Export the circuit as an ngspice deck ## What the running circuit shows A gate that takes a voltage, not a current. A MOSFET’s gate is a plate behind an insulator, so it takes no steady current: put a voltage on it above the threshold and the channel between drain and source turns on. That is why there is no gate resistor here, where a bipolar transistor would need one on its base. The switch is wired across both rails so the gate is always held at one or the other; a floating gate is the one thing a MOSFET circuit must not have. In the engine, with the gate on ground nothing flows. With the gate on 5 V the drain current under the part reads about 14.8 mA, the LED lights, and the drain sits about 30 mV above ground: fully on, the 2N7000’s channel is about 2 ohms. Swap in an IRLZ44N, whose TO-220 legs read gate, drain, source so its three jumpers move with it, and the drain falls under 1 mV for the same current; an IRF540N leaves about 2.4 mV. ## How the MOSFET is modeled A SPICE level 1 model, with each part’s own card. Each MOSFET is a level 1 model solved with the rest of the circuit, with its threshold, transconductance and capacitances from its own model card: the 2N7000’s threshold is about 1.8 V, the logic-level IRLZ44N’s 1.5 V and the IRF540N’s 3 V. Below the threshold the channel is off; above it the current rises with the square of the overdrive until the channel is fully on and the load sets the current. What it leaves out: the parts do not heat up, so a MOSFET carrying amps with too little gate voltage will not fail here the way a real one would. The analog circuit exports as an ngspice deck for anything the canvas does not show. MOSFET or BJT? The NPN transistor switch simulator A transistor as a switch The relay simulator ## Questions Is it free? Yes. The circuit on this page, every part in it and the editor it opens in are on the free plan, with no card. Do I need an account? No. The circuit runs the moment the page does, and the editor opens without one. A free account is only for saving a project to the cloud and sharing it by link. Do I need a gate resistor? Not to limit a steady current, because the gate takes none. Real designs often add a small one to soften the edges when a pin switches a big MOSFET fast, and a pull-down so the gate never floats. Can an Arduino pin drive a MOSFET? Yes, for a logic-level part. The IRLZ44N’s threshold is about 1.5 V, well under a pin’s 5 V, and the small 2N7000 on this page works from a pin too, for loads like this LED. What is the difference between N-channel and P-channel? An N-channel MOSFET sits between the load and ground and turns on when its gate is above its source; a P-channel one sits between the supply and the load and turns on when its gate is pulled below its source. Both kinds are in the parts bin. ## More simulators Each one opens on a circuit that is already running. 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Nothing to install, and no account needed. Start building free Open the editor