MOSFET Overload Protection Design Made Easy
🔧 The Problem: MOSFET Overload and Burnout
When a MOSFET handles more current than it’s rated for, it heats up rapidly and can fail catastrophically. This is a common issue in motor drivers, power supplies, and battery chargers—especially when there’s no built-in overload protection. For hobbyists and prototypers, this often results in damaged components and wasted time.
🛠️ The Solution: Add Overload Protection Circuits
The best way to prevent overload is by designing a simple current-limiting or sensing circuit. This can be done using a sense resistor in series with the MOSFET’s source pin. When the voltage across this resistor exceeds a certain level (indicating excessive current), it can trigger a shutdown or divert the gate drive using a comparator or microcontroller.
🏠 Practical Example: Motor Driver Setup
Imagine running a small 12V DC motor using an IRFZ44N MOSFET. If the motor stalls, the current can spike beyond 20A—well over the safe limits. A 0.1Ω shunt resistor placed in the source leg detects this spike, and an op-amp comparator cuts off the gate signal if the voltage exceeds 0.5V.
📐 Sample Calculation: Choosing the Sense Resistor
Using Ohm’s Law:
V = I × R → 0.5V = 5A × R → R = 0.1Ω
Power across resistor:
P = I² × R = 25 × 0.1 = 2.5W, so use a 3W resistor.
🛍️ Product Suggestion: MOSFETs & Shunt Resistors
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