The Problem : High-Current Switching Challenges

When switching high currents (like 5A or more) using a MOSFET, many beginners face issues like overheating, voltage drop, or even MOSFET failure. This happens due to incorrect gate drive voltage, poor heat sinking, or choosing the wrong MOSFET not rated for continuous high current.

The Solution : Use Properly Rated MOSFETs and Gate Drive

To fix this, choose a low R_DS(on) N-channel MOSFET with a continuous current rating higher than your load. Also, ensure the gate is driven fully (usually 10V for many MOSFETs) to turn it on completely and avoid partial conduction (which causes heating). Add a heatsink or thermal pad where needed.

Practical Example : Driving a 12V DC Motor

Let’s say you’re switching a 12V, 8A motor. You use an IRFZ44N, which handles up to 49A (with proper cooling) and has low R_DS(on). Drive the gate with 10V using a microcontroller + gate driver, and your switch will be cool and efficient.

Sample Calculation : Power Dissipation

If R_DS(on) = 0.03Ω and current = 8A:

P = I² × R = 8² × 0.03 = 1.92W — enough to require a heatsink!

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