⚡ MOSFET as a Switch (Very Important for Embedded Systems)

🎯 Why This Matters

In embedded systems, MOSFETs are the bridge between tiny logic signals and real-world power.
If you control LEDs, motors, relays, solenoids, heaters, pumps, you are already in MOSFET territory.

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🤝 Why MOSFETs Are Perfect for Embedded Systems

📚 Core Idea

Microcontrollers (Arduino, ESP32, STM32, etc.) can output:

• 3.3 V or 5 V
• Only a few tens of milliamps

But real loads need:

• Amps of current
• Higher voltages (12 V, 24 V, more)

A MOSFET solves this mismatch effortlessly.

⚡ Key Advantage

• Gate needs voltage only
• Almost zero gate current
• MCU stays safe
• MOSFET handles the heavy power

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🔌 MCU → MOSFET → Load : The Embedded Power Chain

📚 How It Works

1. Microcontroller outputs 3.3 V / 5 V to the MOSFET gate
2. MOSFET fully turns ON
3. Large current flows through the load
4. MOSFET on-resistance is very small
5. Heat loss is minimal
6. MCU output goes LOW → MOSFET turns OFF instantly

🔬 Conceptual Flow

MCU GPIO → Gate → Drain → Load → Source → Ground

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🛠 Practical Example: Driving a Motor

📚 Real-World Scenario

• Arduino pin: 5 V, max 40 mA
• Motor: 12 V, 2 A

Direct connection? ❌ Impossible
MOSFET solution? ✅ Perfect

⚡ Result

• Arduino only provides gate voltage
• MOSFET handles 2 A motor current
• No stress on microcontroller

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🔍 Choosing the Right MOSFET (Critical!)

📚 Three Specs You MUST Check

1️⃣ Drain-Source Voltage

$$V_{DS(max)} > V_{supply}$$

Example:

• 12 V system → choose ≥ 20–30 V MOSFET

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2️⃣ Drain Current

$$I_{D(max)} \ge 2 \times I_{load}$$

Example:

• Load peaks at 5 A → choose ≥ 10 A MOSFET

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3️⃣ Gate Threshold Voltage

$$V_{GS(th)} < V_{MCU}$$

⚠️ Important:
Gate threshold is not full turn-on voltage.

For embedded systems, always choose:

• Logic-level MOSFET
• Fully ON at 3.3 V or 5 V

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🎚 Pulse Width Modulation (PWM)

📚 Why MOSFETs Enable PWM

MOSFETs can switch millions of times per second.

This allows PWM, where power is controlled by duty cycle.

$$Duty\ Cycle = \frac{T_{ON}}{T_{TOTAL}} \times 100\%$$

⚡ PWM Applications

• LEDs → brightness control
• Motors → speed control
• Heaters → temperature control
• Power supplies → regulation

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🔀 Common MOSFET Switching Configurations

📚 1️⃣ Low-Side Switching

• MOSFET between load and ground
• Simple
• Most common
• Ideal for beginners
• +V → Load → MOSFET → GND

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📚 2️⃣ High-Side Switching

• MOSFET between supply and load
• More complex
• Requires gate voltage above supply
• Needed for some safety-critical systems

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⚠️ Real-World Protection (Do NOT Skip)

🔥 Inductive Load Protection

Motors, relays, solenoids store energy.

When MOSFET turns OFF:

$$V = L \frac{di}{dt}$$

This creates huge voltage spikes.

✅ Always add a flyback (freewheeling) diode across the load.

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⚡ Gate Protection

MOSFET gates are ESD sensitive.

Best practices:

• Gate-to-GND resistor: 10 kΩ – 100 kΩ
• Optional gate series resistor: 100 Ω – 330 Ω
• Never leave gate floating

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🌡 Thermal Considerations

Even with low resistance:

$$P = I^2 \times R_{DS(on)}$$

High current = heat.

Solutions:

• Choose low $R_{DS(on)}$
• Add heatsink if needed
• Verify junction temperature

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🚀 The Embedded Engineer’s Takeaway

🚀 Key Takeaways

• MOSFETs turn logic signals into power control
• Ideal for MCU-based systems
• Efficient, fast, scalable
• Essential for PWM control
• Core skill for embedded engineers

Final Insight:
⚡ If microcontrollers are the brains, MOSFETs are the muscles of embedded systems.