PAGE 065 OF 150 · DRIVING WITH SWITCHES & TRANSISTORS
MOSFET as an LED Switch
A logic-level MOSFET is controlled by gate voltage.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Why use a MOSFET
A MOSFET is controlled by voltage on its gate and takes almost no steady gate current. It also has very low on-resistance, so it stays cool when switching strips and power LEDs.
Choosing
- Pick a logic-level N-channel type if driving from 3.3 V or 5 V, such as the IRLZ44N or a small 2N7000 for light loads.
- Check the gate threshold and that Rds(on) is low at your gate voltage.
Wiring
Source to ground, load between supply and drain, gate to the signal. Add a 10 kilohm resistor from gate to ground so it stays off when the signal floats, and an optional 100 ohm series gate resistor.
REMEMBER
A transistor lets a tiny signal control a much larger LED current.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
Explore LED clocks, stopwatches and electronics at cosycom.com.