The MOSFET: big DC loads, no click

A silent switch for 2 amps? That's a MOSFET 🔇⚡ (the lesson we promised after the relay!)

1️⃣ INSIDE: the gate is a metal plate sitting on a super-thin layer of glass (oxide). Put 5 V on the gate and it pulls electrons right under the glass. They make a channel between Source and Drain, and current flows. Take the 5 V away and the channel disappears.

2️⃣ ALMOST NO GATE CURRENT: the gate is insulated, so the Arduino pin only gives a tiny blip to charge it. Uno D9 → 220 Ω → gate, plus a 10 kΩ pull-down from gate to GND so it stays OFF when the pin floats (reset, upload).

3️⃣ THE LOAD: 12 V LED strip, 2 A (24 W). Strip − to the Drain, Source to GND, Arduino GND joined. An IRLZ44N has only ~0.025 Ω when ON → 2² × 0.025 = 0.1 W of heat. Cool, no heatsink, no click. It can even PWM-dim the strip.

4️⃣ PICK A LOGIC-LEVEL ONE: IRLZ44N is fully ON at 5 V. A standard one like IRF540N is rated at 10 V on the gate, so at 5 V it is only half ON and gets hot.

Relay = click, AC or DC. Transistor = small loads. MOSFET = amps of DC, silent and fast. (Motors / coils still need a flyback diode.)