Transformerless Power Supply Calculator

This calculator is an online tool to quickly determine the capacitor value required for transformerless power supply circuit. A simple transformerless power supply with resistive load can be used if there is a need to connect to the AC mains a load designed for a voltage (Vout) much less than the mains voltage (Vin), for example, a soldering iron. In this circuit a capacitor (C) and resistive load (RL) are connected in series to AC mains.

transformerless power supply with resistive load

To calculate the capacitor value this tool uses the following equation:

C = (Pout / Vout) / (2πf√(Vin² - Vout²))

CAUTION! Polarized capacitors cannot be used in this circuit. A transformerless power supply has no galvanic isolation from the AC mains. Touching any part of it may cause electric shock!

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