There is no point reaching for a calculator that cannot show its working. This one starts from source-drain current (id), drain-source voltage (vds), gate-source voltage (vgs), threshold voltage (vt), area, capacitance per unit area, electron mobility (μn), length (l), resistance, time in seconds, voltage in volts and width (w) and reports source-drain current (id), electron mobility (µn) and check i saturation, so you can see how each answer follows from the numbers you entered.
What Is the MOSFET Calculator?
This mosfet calculator is for the kind of problem where you know the physical quantities but not the number you need. It turns source-drain current (id), drain-source voltage (vds), gate-source voltage (vgs), threshold voltage (vt), area, capacitance per unit area, electron mobility (μn), length (l), resistance, time in seconds, voltage in volts and width (w) into source-drain current (id), electron mobility (µn) and check i saturation.
Physics calculations go wrong in predictable ways, usually through mixing units or dropping a digit. Work through the result one step at a time and check that the figures are the size you would expect at each stage.
How the MOSFET Physics Works
The relationship is applied step by step, and each step is a standard piece of physics rather than a single opaque formula. That means you can check the intermediate values against what the theory predicts, which is usually faster than checking only the final answer.
Keep every value in the same unit system throughout the calculation. Mixing metres and feet part way through is the single most common reason a correct formula gives a wrong answer.
Units, Assumptions and the Limits of the Model
The calculation assumes ideal conditions: no air resistance, no heat loss, and dimensions that do not change while you work. Those assumptions are reasonable for most classroom and engineering estimates, and unreasonable for anything more precise.
Where a value is a rate, it has to be quoted for the same period as everything else. A per-hour figure cannot be combined with a per-day figure without converting one of them first.
A Worked Example
Working through an example, with source-drain current (id) set to 10, drain-source voltage (vds) set to 5, gate-source voltage (vgs) set to 2, the calculator returns electron mobility (µn) of 2, and k parameter of 0.25, and check i cut off of 1. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out source-drain current (id)?
Enter source-drain current (id), drain-source voltage (vds), gate-source voltage (vgs), threshold voltage (vt), area, capacitance per unit area, electron mobility (μn), length (l), resistance, time in seconds, voltage in volts and width (w). The calculator then works through the relationship and reports source-drain current (id), electron mobility (µn) and check i saturation.
What does the mosfet actually calculate?
It takes source-drain current (id), drain-source voltage (vds), gate-source voltage (vgs), threshold voltage (vt), area, capacitance per unit area, electron mobility (μn), length (l), resistance, time in seconds, voltage in volts and width (w) and converts them into source-drain current (id), electron mobility (µn) and check i saturation using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter source-drain current (id)?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Do I have to fill in every field?
Only the fields a particular result depends on. If you leave one blank, the results that need it simply show a note instead of a number, and everything else still works.
Can I use this for a quick estimate as well as a precise answer?
Yes. The calculator is built for quick checks, so round your inputs to a sensible number of significant figures and the result will be just as useful. If you need more precision, keep the same method and add digits to the inputs rather than adjusting the method itself.