The Problem :

Switch Mode Power Supplies (SMPS) are essential for converting AC to DC efficiently in electronic circuits. However, they are vulnerable to input voltage surges, which can damage sensitive components. A sudden power spike, caused by lightning or faulty wiring, can exceed the voltage tolerance of the SMPS, leading to failure.

The Solution :

The best way to protect your SMPS from surges is by adding an NTC thermistor at the input. When the device is first powered on, the thermistor limits the inrush current by offering high resistance. As it heats up, its resistance drops, allowing normal current flow.

Practical Example :

Imagine powering your home automation system with a 12V/5A SMPS. On switching it ON, a surge of current may damage the supply. By placing an NTC thermistor (e.g., 10D-9) in series with the input, you can limit the initial current.

Sample Calculation :

For a 12V/5A SMPS, an NTC thermistor with an initial resistance of 10 ohms limits the inrush current to:

Iinrush​=RV​=10Ω230V​=23A

As the thermistor heats up, the resistance drops to near zero, allowing normal current to flow.

Recommended Components :

Check out NTC thermistors and MOV surge protectors to protect your circuits from surges. Browse our range here:

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