Low Voltage Smart Plug Power Supply Tips

🔌 The Problem: Powering Smart Plugs Safely at Low Voltage
Smart plugs need compact, low voltage power supplies to operate safely from 230V AC. Without proper design, they can overheat, fail, or drain excess power—not ideal for small, energy-efficient devices.
🛠️ The Solution: Use a Capacitive Dropper or Compact SMPS
For low-power smart plugs (e.g., 0.5W to 1W), a capacitive dropper circuit is cost-effective and space-saving. For higher power or safer isolation, a miniature SMPS module is preferred. Both options step down 230V AC to a usable DC level like 3.3V or 5V for microcontrollers.
🧪 Practical Example: Wi-Fi Smart Plug
Imagine a DIY smart plug using an ESP8266. It needs 3.3V @ ~250mA. Using a 5V SMPS module with an LDO or buck converter works well.
🧮 Sample Calculation: Capacitive Dropper Sizing
If your circuit needs 20mA:
Current = V × 2πfC
Rearranged: C = I / (2πfV)
C = 0.02 / (2×3.14×50×230) ≈ 0.28µF
Use a 400V X-rated capacitor for safety.
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