Fork me on GitHub

Project Notes

#066 Digital Logic Switch - N-Channel Enhancement FET

Using a small-signal n-channel MOSFET as a switch, with turn-off delay.

Here’s a quick video of the circuit in action:

Notes

N-Channel Enhancement FETs are easy to use as a digital switch:

ON when gate-source voltage is much greater than threshold voltage (into saturation region)
OFF when gate-source voltage is below threshold voltage (0.8-3V for 2N7000)

This circuit demonstrates the basic switch, with the addition of a turn-off delay.

The turn-off delay is implemented with a simple RC circuit: the R1=220kΩ C1=10μF pair having a time constant of 2.2 seconds.

Construction

The Breadboard

The Schematic

The Build

Credits and References

LEAP#106 SwitchPFET - same circuit but using p-channel MOSFET
LEAP#286 SwitchPowerNFET - low-side power switching variation to this circuit
2N7000 datasheet
MOSFET as a Switch

About LEAP#66 MOSFET

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..

To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.