⚠️ The Problem: Input Surges in SMPS Circuits

Switch Mode Power Supplies (SMPS) are efficient, but highly sensitive to voltage spikes or surges on the AC input. In India, unstable grid conditions and lightning strikes can easily damage components like bridge rectifiers and bulk capacitors, reducing lifespan or causing complete failure.

✅ The Solution: Add Input Surge Protection

To protect your SMPS from input surges, add a Metal Oxide Varistor (MOV) and an NTC Thermistor at the input. The MOV clamps high-voltage spikes, while the thermistor limits inrush current. This simple combo provides significant protection for both hobby and industrial designs.

🔧 Practical Example: Designing a 230V to 12V SMPS

Say you’re building a 12V power supply from 230V AC for a home automation controller. Add a 275V-rated MOV across the input line and a 5Ω NTC thermistor in series before the bridge rectifier. This guards against surge pulses during power-on or lightning-induced transients.

📐 Sample Calculation: MOV Selection

For a 230V AC input:

• Peak voltage = 230V × √2 ≈ 325V

• Choose MOV clamping voltage > 350V, e.g., S10K275 (275V RMS, ~710V max clamp).

🛍️ Product Suggestion

🔹 MOV Varistor

🔹 NTC Thermistor

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