# N-MOSFET (2N7000)
## What is MOSFET
MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a voltage-controlled switching device that controls current with voltage.
## Pin Description
2N7000 N-MOSFET has 3 pins:
- **S (Source)**: Usually connected to GND
- **G (Gate)**: Control pin, input voltage signal
- **D (Drain)**: Output pin, connect to load
## Working Principle
- **Gate Voltage (VGS)**: Controls MOSFET conduction
- **Threshold Voltage (Vth)**: 2N7000 about 2V - 4V
- **VGS > Vth**: MOSFET conducts, resistance between drain and source is very small
- **VGS < Vth**: MOSFET blocks, resistance between drain and source is very large
## Operating Modes
- **Cutoff Region**: Gate voltage below threshold, MOSFET does not conduct
- **Linear Region**: Gate voltage slightly above threshold, for amplification
- **Saturation Region**: Gate voltage high enough, fully conducts, used as switch
### MOSFET Features
- **Voltage Control**: Almost no control current consumption (different from transistor)
- **Fast Switching Speed**: Suitable for PWM control and high-frequency applications
- **Low On-Resistance**: Low power consumption, high efficiency
- **Static Sensitive**: Gate is sensitive to static electricity, handle with care
## Connection Method
### MOSFET Switch Circuit (Direct Visual Effect)
### Connection Instructions (Switch Application)
According to the diagram above, connection order is:
```
VCC (5V) → Switch → Gate (G)
VCC (5V) → LED → 220Ω Resistor → Drain (D)
Source (S) → GND
```
**Working Principle**:
- **Switch Closed** (gate connected to VCC): MOSFET conducts, resistance between drain and source is very small, LED lights up
- **Switch Open** (gate floating or connected to GND): MOSFET blocks, resistance between drain and source is very large, LED turns off
- MOSFET is voltage controlled, almost no control current consumption
**Effect**: By controlling gate voltage through switch, can control LED on/off, visually see MOSFET's switching effect
### Advantages
- **Voltage Control**: Almost no control current consumption (different from transistor)
- **Fast Switching Speed**: Suitable for PWM control
- **Low On-Resistance**: Low power consumption
## Arduino Example Code
### Basic Example: MOSFET Controls LED
```cpp
const int gatePin = 9; // Pin connected to gate
void setup() {
pinMode(gatePin, OUTPUT);
}
void loop() {
digitalWrite(gatePin, HIGH); // MOSFET conducts, LED lights up
delay(1000);
digitalWrite(gatePin, LOW); // MOSFET blocks, LED turns off
delay(1000);
}
```
### Connection Method
- **Arduino Pin 9** → **Gate (G)**
- **Gate (G)** → Pull-down Resistor (10KΩ) → **GND** (optional)
- **Drain (D)** → LED → 220Ω Resistor → **VCC (5V)**
- **Source (S)** → **GND**
### Code Explanation
- MOSFET used as switch, gate voltage controls drain current
- Gate can be directly connected to Arduino pin (no current limiting resistor needed)
- Recommend adding pull-down resistor (10KΩ) to prevent false triggering
### Advanced Example: PWM Control (Dimming/Speed Control)
```cpp
const int gatePin = 9; // PWM pin
void setup() {
pinMode(gatePin, OUTPUT);
}
void loop() {
// Gradually brighten
for (int brightness = 0; brightness <= 255; brightness++) {
analogWrite(gatePin, brightness);
delay(10);
}
// Gradually dim
for (int brightness = 255; brightness >= 0; brightness--) {
analogWrite(gatePin, brightness);
delay(10);
}
}
```
**Explanation**: MOSFET is very suitable for PWM control, can be used for LED dimming, motor speed control, etc.
## Common Questions and Answers
### Q1: MOSFET Not Working?
- Check if gate voltage is sufficient (2N7000 needs 2V - 4V)
- Check if pin connections are correct (G, D, S)
- Check if drain load is connected
- Confirm it's N-MOSFET (not P-MOSFET)
### Q2: Why Gate Doesn't Need Current Limiting Resistor?
- MOSFET is voltage controlled, gate almost consumes no current
- Gate input impedance is very high, can be directly connected
- But recommend adding pull-down resistor to prevent false triggering
### Q3: What's the Difference Between MOSFET and Transistor?
- **MOSFET**: Voltage controlled, almost no control current needed, suitable for high current
- **Transistor**: Current controlled, needs base current, simple control
- MOSFET more suitable for PWM control and high current applications
## Safety Precautions
⚠️ **Important Notes**:
- Gate is sensitive to static electricity, pay attention to ESD protection
- Gate can be left floating, but recommend adding pull-down resistor (10KΩ) to prevent false triggering
- Cannot exceed maximum drain current (2N7000 is 200mA)
- Pay attention to heat dissipation, high current applications need heat sink
## Practical Applications
MOSFETs are commonly used for switch control, PWM dimming, motor speed control, high current driving, etc. In Arduino projects, commonly used to control LEDs, motors, relays, and other loads, especially suitable for applications requiring PWM control and high current.
