Switch Mode Power Supplies (SMPS) are commonly used to power electronic circuits, but they can get damaged if overloaded. Over-power protection (OPP) prevents this by limiting the power drawn by the load, ensuring the SMPS operates within safe limits. Without OPP, excessive power can lead to overheating, damage, or even component failure.

The Problem : 

When an SMPS powers multiple devices or high-current motors, the total power consumed can exceed the SMPS limit. For example, if a 12V SMPS rated for 5A drives a load consuming 7A, the excess current can overheat and damage the SMPS. Many commercial SMPS units come with OPP, but for DIY projects, adding external protection is necessary.

The Solution :

To prevent overload, use a shunt resistor to measure current and a comparator to trigger a cutoff when the current exceeds the limit. A MOSFET can disconnect the load, protecting the SMPS from damage.

Practical Example : 

Consider an Arduino project where you control motors and sensors using a 12V, 5A SMPS. If the total load exceeds 5A due to motor surge currents, the OPP circuit detects this and disconnects the load, preventing SMPS failure.

Sample Calculation :

To calculate the shunt resistor value:

V=I×R

For a 5A current limit and a 0.5V threshold:

R=50.5​=0.1Ω

A 0.1Ω, 5W resistor is ideal for this setup.

The comparator senses the voltage drop across the resistor and cuts power when the limit is exceeded.

Recommended Products :

1. MOSFET IRF540N – Ideal for load cutoff.

2. 0.1Ω Shunt Resistor – Accurately senses current for overload protection.

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