MOSFETs are a favorite in power electronics due to their speed and efficiency. But switching them improperly—especially under load—can lead to voltage spikes, overheating, or total failure. That’s where safe switching circuits come in.

The Problem: Unprotected MOSFET Switching

When MOSFETs switch rapidly, especially in inductive loads like motors or relays, they can generate voltage transients. These spikes can damage the MOSFET gate or drain unless properly handled.

The Solution: Gate Resistors, Snubbers & Flyback Diodes

• Gate resistors (10–100Ω) slow down switching, reducing voltage stress.

• Snubber circuits absorb energy from inductive spikes.

• Flyback diodes protect against reverse voltage on inductive loads.

Practical Example: Controlling a 12V Relay

An engineer noticed the MOSFET in his relay driver circuit getting hot and failing.

Fix: Added a 100Ω gate resistor and a 1N5819 flyback diode across the relay coil. Problem solved, and circuit now runs cool and stable.

Sample Calculation: Gate Drive Resistor

For a gate charge (Qg) of 40nC and desired rise time of 200ns:

R = t / (Qg / V) = 200ns / (40nC / 10V) ≈ 50Ω

Product Suggestions (Made in India)

• MOSFETs – High-efficiency switching

• Flux Paste – Clean, strong solder joints

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