
The Problem :
MOSFETs are powerful and efficient switches, but when used with inductive loads (motors, solenoids, relays), they’re vulnerable to avalanche breakdown. This occurs when a sudden voltage spike—caused by inductive energy—exceeds the MOSFET’s drain-source breakdown voltage (V<sub>DSS</sub>), damaging the part.
The Solution :
Use a freewheeling diode (also called a flyback diode) across inductive loads. Alternatively, for high-speed switching, you can add a TVS diode across the MOSFET or select a MOSFET rated for avalanche energy. This protects your design from sudden spikes.
Real-World Example :
An engineer in Pune powering a small 12V DC fan via MOSFET noticed random failures. After switching to an avalanche-rated MOSFET and placing a 1N5822 diode across the fan, the issue was resolved and no further failures occurred.
Sample Calculation :
Let’s say:
Inductance = 100µH
Peak current = 2A
Inductive energy = ½ × L × I² = 0.5 × 100×10⁻⁶ × 4 = 0.2mJ
Ensure your MOSFET’s avalanche energy rating (E<sub>AS</sub>) exceeds this value.
Product Suggestion – Made in India
Try avalanche-rated MOSFETs ➜
Or use a TVS diode ➜
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Written by smartxbrains
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