⚡ The Problem: Input Surges in SMPS Circuits

Switched-mode power supplies (SMPS) are highly efficient, but they’re sensitive to input voltage surges—especially when powering on or during grid fluctuations. These surges can stress components, reduce lifespan, or even cause catastrophic failure.

🛠️ The Solution: Input Surge Protection

The simplest way to handle this is by adding an NTC thermistor or a metal oxide varistor (MOV) at the AC input. The NTC limits inrush current by initially offering high resistance, while the MOV absorbs sudden high-voltage spikes. Combined, they create an effective surge barrier.

🔌 Practical Example: Home Automation PSU

Let’s say you’re building a home automation hub powered by a 230V AC SMPS. Each time the power resumes after an outage, a surge risks damaging the supply. Adding an NTC thermistor rated for 5A and an MOV of 275V helps absorb that spike and keep your circuit safe.

🧮 Sample Calculation: NTC Thermistor Resistance

If your SMPS draws 2A, a thermistor with a cold resistance of 5Ω limits inrush current:

• V = IR → 230V = 2A × R

• Initial inrush: I = 230V / 5Ω = 46A (short burst, then it drops)

This brief current is manageable and better than an unprotected spike!

🧰 Product Suggestions: Made in India Components

• 🔥 NTC Thermistor

• 💥 MOV Surge Protector

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