#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:
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.