The Problem :

MOSFETs are widely used in power circuits, but they can be damaged by overload currents if not protected. Overload typically happens when a connected device draws more current than expected, causing the MOSFET to heat up or even fail.

The Solution :

To prevent this, add current sensing resistors (low-ohm shunt resistors) in series with the load. Measure the voltage drop across the resistor, and use a comparator or microcontroller to detect overloads and shut off the MOSFET via its gate.

Practical Example :

Let’s say you’re controlling a 12V DC motor with a MOSFET.

Normally, it draws 1A.

But under a stall condition, it may draw 3A.

Using a 0.1Ω resistor, the voltage drop at 3A = V = I × R = 3A × 0.1Ω = 0.3V.

Feed this into a comparator to trigger overload protection if the voltage exceeds 0.2V.

Sample Calculation :

To choose the sense resistor for a 2A limit:

R = V / I = 0.2V / 2A = 0.1Ω

Power rating = I² × R = 2² × 0.1 = 0.4W, so use a 1W resistor for safety.

Product Suggestion :

Look for these:

MOSFET

Shunt Resistor

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