The Problem: MOSFET Overheating

MOSFETs are the backbone of modern power electronics—used in everything from motor drivers to SMPS circuits. However, they generate heat during switching and conduction. Without protection, excessive heat can damage or destroy the MOSFET, especially in compact or enclosed designs. This is a major risk in robotics, IoT, and power supply projects.

The Solution: Thermal Shutdown Circuit

To protect your MOSFET from overheating, you can implement a thermal shutdown design. This uses a thermistor (a temperature-sensitive resistor) connected to a comparator or microcontroller. When the temperature exceeds a safe limit (e.g., 80°C), the circuit disables the gate signal—safely shutting down the system until it cools down.

Practical Example: DIY Motor Driver

Imagine you’re building a 12V DC motor controller for a smart fan. After running for 15 minutes, the MOSFET’s case temperature crosses 85°C—way too hot! With a thermistor placed near the MOSFET, you can cut off the gate drive when the temperature exceeds 80°C, protecting the circuit and extending the MOSFET’s life.

Sample Calculation: Setting the Threshold

Using a 10kΩ NTC thermistor with a voltage divider and comparator:

• At 25°C: Thermistor ≈ 10kΩ

• At 80°C: Thermistor ≈ 1.4kΩ

Choose resistor values so the voltage at the divider drops below the comparator threshold at 80°C. This triggers the shutdown.

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